Sediment-Hosted Mineral Deposits (IAS Special Publication 11)

. 39

c(

-

T iesiao Fm. ,.

.

...

.

Pillow shaped manganese ore

Graded bedding Lamina ted manganese Black shale Sandstone

Fig. 5. Stratigraphic column

showing manganese ore bearing succession, Datangpo, Guizhou.

Manganese deposits, Datangpo Formation

45

tated. Subsequently, this layer with fine cross-cutting veinlets would have been enveloped by another manganese-rich layer. Rhodochrosite exhibits a micronodular colloidal precipitation texture (Figs 9-11), with fibrous quartz and granular barite filling fractures and pores. This may be indicative of hydrothermal precipitation. 2

250

Laminated ore facies

Finely laminated manganese shales form the lower grade ore of the Datangpo deposits. Graded laminae also occur, individual laminae being less than 5 mm in thickness (Fig. 12). ABE and ABC Bouma se­ quences are observed. The laminae consist of car­ bonaceous black shale, suspended sediments with dark brown organic material, and manganese car­ bonate which shows a micropelleted fabric (Wang, 1988), and also contains algal microspheroids, acritarchs (both replaced by rhodochrosite) and possibly radiolaria (Fig. 13). Laminated ore facies, averaging 15-20 wt% manganese, occurs at the bottom and in the upper parts of the succession.

500m

Fig. 6. Map showing relationship between the thickness of

manganese ore deposits and grade of ore. (From Wang, 1985. )

into black shales. Internally, the pillow-shaped bodies appear to be made of nodular structures showing concentric layering (Fig. 8). Each layer is 10 mm or less in thickness, and is cut by fine veinlets of fibrous or granular barite and quartz. The veinlets are generally less than 2 mm in width. They tend to be concentrated in individual layers and usually terminate at layer boundaries. The veinlets show a wedge-like morphology, tapering toward the in­ terior. They seldom cut across several sets of layers. Veinlets also occur along the boundary between adjacent layers. It is suggested that following the formation of a single manganese-rich layer, shrinkage fissures were formed in which the veinlet minerals were precipi-

Discussion of palaeoenvironment

The manganese ore beds and their host black shales are both highly enriched in organic matter. They contain 2·68 and 2·02 wt% total organic carbon (TOC), respectively (Wang & Wang, 1985). The bitumen contains 6·78-20·78 wt% saturated hydro­ carbons and 2·54-8·66 wt% aromatic hydrocarbons (Wang & Wang, 1985). These are probably derived from the thermal breakdown of planktonic algae and protists. The o34S values for pyrite samples in the laminated ore range from 42·9-57·3%o (Wang & Wang, 1985), more than two times the value for present day seawater sulphate. These values are very high for sulphides generated by bacterial reduction of early seawater sulphide, and may be the result of restricted circulation in an anoxic environment. Hoefs (1987) has pointed out that the H2S produced at a later

!Om

Fig. 7. Sketch section showing

features of manganese ore bodies, Datangpo, Guizhou (by Wang, 1985).

15

25

35

45

55

65m

Fig. 8. Concentric layers with cross­

cutting veinlets of barite in nodular manganese ore, Datangpo Formation, Minle, Hunan.

Fig. 9. Rhodochrosite showing colloidal precipitation

texture in nodular manganese ore, Datangpo Formation, Minle, Hunan.

Fig. 10. Fibrous quartz filling pore space within dark

rhodochrosite, Datangpo Formation, Minle, Hunan.

Fig. 11. Granular barite filling pore space within dark

rhodochrosite, Datangpo Formation, Minle, Hunan.

stage exhibits heavier b34S values, and heavy sul­ phate may be found in the final stage of bacterial activity in a closed-system environment. The pre­ cipitation and diagenesis of the manganese deposits were both in a closed-system environment, and the sulphur may have been supplied by hot brine at the seafloor (Wang & Wang, 1985). The organic-rich black shales appear to be related to the development of an extensional basin, as indi­ cated by the sharp lateral thickness changes. Only small amounts of terrigenous clastic material entered the basin. The preservation of abundant organic matter and high b34S values indicate a reducing environment with anoxic conditions at the sediment-water interface. Numerous microfossils have been discovered 111

Manganese deposits, Datangpo Formation

47

Datangpo Formation was the product of deposition in deep-water conditions below the storm wave base. Abundant planktonic microorganisms presumably accumulated from suspension. Low density turbidity currents may account for the occurrence of graded bedding. The deeper-water facies of the Datangpo Forma­ tion occurs intercalated between two units of glacial origin and shallow-water setting. Such a situation could have resulted from a major phase of ice melting and consequent sea-level rise. The resulting transgression would have established relatively deep water conditions over the basin. Origin of manganese mineralization

Fig. 12. Graded laminae in manganese-rich black shale,

Datangpo Formation, Datangpo, Guizhou.

the manganese ore by Wang (1988), who compares the microfossils to the Precambrian Barney Creek HYC Shale from the McArthur Basin and the Urquhart Shale from Mount Isa, Queensland. These microfossils indicate a reducing environment in the deep water beneath the photic zone. The finely laminated lithology, the occurrence of grading, and the absence of coarse terrigenous clas­ tics and wave-formed structures suggest that the

Fig. 13. Graded laminae comprising radiolaria (white), rhodochrosite (dark), and micropellets (grey), Datangpo Formation, Datangpo, Guizhou.

The manganese mineralization of the Datangpo Formation is in our opinion syndiagenetic and the product of hydrothermal activity as opposed to a supergene origin. Paucity of detailed geochemical work precludes a conclusive answer. Evidence for a hydrothermal origin is as follows: 1 The concentric layered nodular structures within the pillow-shaped ore bodies indicate progressive precipitation of manganese around a central nucleus. Concentration of veinlets in individual layers sug­ gests cooling of the manganese-rich layers to create tensional fractures and a break in precipitation. 2 The colloform texture of rhodochrosite suggests colloidal precipitation from hydrothermal solutions. Seven homogenization temperature measurements

X. Xu, H. Huang and B. Liu

48 NW

melt waters

,

glacial

sediment transport

SW

Fig. 14. Model for manganese deposition in the Datangpo Formation.

from quartz fluid inclusions in the manganese ore give an average fluid palaeotemperature of 194°C (uncorrected), which is in accordance with a hydro­ thermal origin. 3 The high-grade pillow-shaped ore bodies occur in the centre of the ore-bearing structure, and are surrounded by lower-grade deposits which decrease in manganese content toward the margins. This bull's eye pattern may indicate the presence of an ancient vent, possibly fault-related, in the central area. 4 The occurrence of intercalated tuff beds in the manganese ore and host black shale succession indi­ cates contemporaneous mineralization. The occurrence of black shales containing abun­ dant organic microfossil remains associated with the manganese mineralization is striking. The role of microorganisms in the deposition of manganese is as yet uncertain. It could be that biogeochemical pre­ cipitation may have been a significant factor in the concentration of manganese.

MODEL FOR MINERALIZATION

Early Sinian glaciers of pre-Datangpo Formation times debouched into the sea from the northwest

(Fig. 14). At the close of this episode of glaciation, a major phase of ice melting would have brought about a sea-level rise. The resulting transgression would have established a relatively deep marine environment in the basin. Deglaciation may have caused stratification of the seawater column, with a lower layer of normal seawater and an upper freshwater layer derived from ice melting. A consequence of sea-level rise and stratification of the seawater column would have been to restrict circulation in the basin which would lead to oxygen-depleted or anoxic conditions being established in bottom waters. As a result, preser­ vation of abundant organic matter would be possible. Microorganisms may have played an important role in manganese precipitation. Extensional faulting would have allowed rapid subsidence of the basin and development of variable submarine topography. This would also have allowed the development of a restric;ted circulation and anoxic conditions. Submarine hot spring activity related to hydrothermal exhalation vents was prob­ ably concentrated in the vicinity of such extensional fractures. Deposition of high-grade manganese ore occurred at these sites and lower-grade ores ac­ cumulated marginally to them. Minor manganese

Manganese deposits, Datangpo Formation precipitation may have occurred due to supergene concentration.

ACKNOWLEDGEMENTS

Y. Wang and L. Wang are thanked for their support and for supplying information. S. Gupta made use­ ful suggestions and corrected the English version of the manuscript.

REFERENCES

GUANGXI BUREAU OF GEOLOGY AND MINERAL RESOURCES (1985) Regional Geology of Guangxi Province. People's Republic of China, Ministry of Geology and Mineral

49

Resources, Geological Memoirs, Series 1, No. 3. Geo­ logical Publishing House, Beijing (in Chinese). GUIZHOU BUREAU OF GEOLOGY AND MINERAL RESOURCES (1987) Regional Geology of Guizhou Province. People's Republic of China, Ministry of Geology and Mineral Resources, Geological Memoirs, Series 1, No. 7. Geo­ logical Publishing House, Beijing (in Chinese). HOEFS, J. (1987) Stable Isotope Geochemistry. Springer, Berlin. HUANG, J., REN, J., JIANG, C. , ZHANG, Z. & QIN, D. (1980) Geotectonics and Development of China, pp. 35-37. Science Publishing House, Beijing (in Chinese). WANG, F. (1988) Precambrian Algal Fossils from South­ western

China,

and

their

Geological

Significance,

pp. 229-231. Chongqing Publishing House (in Chinese). WANG, Y. & WANG, L. (1985) The Stratigraphy, Sedimen­ tary Environment and Manganese-Forming Process of

People's Publishing House of Guizhou, Guiyang (in Chinese).

the Datangpo Formation in Eastern Guizhou.

Spec. Pubis int. Ass. Sediment. (1990) 11, 51-56

Manganese enrichment in a Triassic aulacogen graben in the Lijiang Basin, Yunnan Province, China H . LIU Southwest Research Institute of Metallurgy and Geology, Erxianqiao, Chengdu, China

ABSTRACT The Lijiang Basin developed during the Norian stage of the late Triassic on the western passive continental margin of the Yangtze plate adjacent to the Tethys plate. A small aulacogen striking approximately east-west developed in the southwest part of this basin east of the Jinshajiang fault and the boundary of the plate near Jianchuan. The Runanshao fault forms a depression along the centre of the aulacogen. Tholeiitic olivine basalt and volcaniclastic rock in the middle and lower part of the Songgui Formation (Norian stage) are interbedded or intercalated in olistostromes of middle Triassic limestone, which are characteristic of the early stage of development of the aulacogen. During this stage, manganese ore bodies at the base of the volcanic rocks were formed by volcanic exhalation, sedimentary and diagenetic processes.

INTRODUCTION

basin. Thick Triassic strata were deposited east of the fault but very little Triassic strata occur to the west. Geophysical data indicate that the Xiaojinhe fault is a deep structure and formed the boundary of a passive continental margin during the Norian stage. A eugeosyncline developed between the Jianchuan and Xiaojinhe faults. Triassic strata in the active tectonic unit of the Tethys plate were extensively metamorphosed. Basement movement at the passive continental margin located east of this fault involved elevation and subsidence during the middle-late Triassic. Permian basalt was extruded from the sea­ floor along the Lijiang fault through the centre of the basin. The southwest end of the Lijiang fault joins the Jinshajiang fault near Jianchuan. A small aulacogen developed east of the junction of the Lijiang and Jinshajiang faults near Jianchuan in the Lijiang Basin and its depocentre strikes east­ west along the Runanshao fault (Fig. 1).

An axial trough basin striking northeast-southwest in the Lijiang area of western Yunnan Province developed on the basement rocks of the western passive continental margin of the Yangtze plate adjacent to the Tethys plate, from the early Permian to the late Triassic. The high-grade Heqing man­ ganese deposit occurs in the southwest part of the basin in the Lower Songgui Formation of Upper Triassic age (Liu Hongjun, 1987).

BASIN ANALYSIS Palaeotectonic background

The Kang-Dian axis located in the eastern part of the region (Fig. 1) was uplifted to form a land mass as early as pre-middle-Devonian and became the main source of sediments in the Lijiang Basin. The eastern border of the basin was controlled by the Chenghnai fault on the western border of this old land mass. Much ultrabasic and basic lava was extruded along this fault during the Hercynian. The Jianchuan fault situated on the eastern side of the Shigu Rise controlled the western border of the Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

Lijiang Basin sediments

The main sediments of the Lijiang Basin belong to the Songgui Formation of the Norian stage and are 51

H. Liu

52 TETHYS PLATE

1oo·

101"

@

Ling rang

27"

Runanshao fault. Pillow structures occur in the basalt and slump, scour planes and graded bedding features occur in the sandstone unit. This sequence of sedi­ ments becomes progressively finer grained upwards and is transitional to the coal-bearing shallowing­ upward beds of delta-front facies. The sandstone facies are interpreted as a delta-front collapse turbidite fan (Rupke, 1985). Basic facies zoning and manganese geochemistry

FS

0

10

20km

�

Fig. 1. Norian palaeotectonic map in Lijiang, western Yunnan Province. PtlKn, Proterozoic Kunyang Group; AnDsn, Shigu Group (pre-Devonian); Fl, Jinshajiang fault; F2, Xiaojinhe fault; F3, Lijiang fault; F4, Chenghai fault; F5, Junying fault; F6, Runanshao fault.

composed of five units. The lithological character­ istics of these beds are as follows: 1 thick black mudstone and pillow basalt at the base of the aulacogen; 2 greyish-white sandstone; 3 black mudstone in the lowest part of the aulacogen intercalated with basic and ultrabasic volcanic rock and olistostromes; 4 greyish-white sandstone; 5 coal-bearing grey-black silt-mudstone. Two shallowing-upward sequences can be iden.t­ ified which range from black mudstone, through turbiditic sandstone to coal-bearing mudstones, representing two transgressive- regressive cycles. Units 1 and 2 make up the first cycle, and units 3, 4 and 5 the second. Macroscopic features studied in the field and grain­ size analyses show that units 2 and 4 developed from large scale turbidity currents. A variety of flute casts occur at the base of the sandstone beds, and Bouma sequences are developed in facies in the centre of the basin. It should be noted that in the aulacogen the thickness of the lower sandstone unit 2 exceeds that of neighbouring units by a factor of 3-5. The thickest part, up to 480 m, is close to the contemporaneous

An obvious lithofacies zoning exists from east to west in the basin from near the old Kang-Dian land area to the Tethys Sea, including foreshore to near­ shore, intershelf, extra shelf and basin-centre facies (Fig. 2). A submarine rise was located in the middle of the shelf. A suite of pelitic sediments dominated by black mudstone was deposited in the southern basin. The pelitic seafloor sediments provided a favourable environment for perfect preservation of the fossil organisms. The predominant fossils are bivalves and Ammonoidea. There is an abundance of terrigenous clastic sediment in the open shelf environment in the northern part of the basin. Bivalves and other fossils are commonly found on the bedding surfaces of calcareous siltstone or micritic limestone. Great varieties of fossils and biodetritus were distributed in a disorderly fashion nearshore and transported to the submarine rise. The geochemjstry of the sedimentary microfacies is indicated by the content of trace elements and by their petrography. The content of manganese in the main rock types of the area is shown in Table 1. The manganese content is relatively high in the siltstone and decreases with the coarsening of the grain size of the rocks, with the exception of the mudstones and limestones. The content of manganese is lower in the shallow-water zone than in the deeper-water zone, and lower in other parts of the basin than in the aulacogen. Manganese was concentrated in banded sediments in the black mudstones of the Table 1. Manganese contents in rock types of the Songgui Formation, Lijiang Sample (n) Conglomerate Sandstone Siltstone Mudstone Limestone

3 88 11 41 11

Average Mn (ppm) 557 808 1650 998 994

Manganese enrichment, Lijiang Basin

53

E:23 1 C::::::l

m2 .

Fig. 2. Lithofacies palaeogeographic map of Lijiang, western Yunnan, early Songgui time proximal turbidite; (Norian). intermediate turbidite; distal turbidite; 1, sand-mud association; 2, mud-sand association; 3, sand­ lime association; 4, mud-lime­ siliceous association; 5, aulacogen sequence; 6, subaqueous depression; 7, shallow-water shelf; 8, confined shelf (deeper); 9, direction of sediment transport; 10, basic volcanics; 11, isopach (metres).

CD

(D

@

I® I s [i[)6 I® 17 I® Ia m9 Ivvvllo t-'"''-� II

aulacogen graben during early stages of the devel­ opment of the fault trough. It appears that there was a lower rate of deposition of manganese in the deeper water and that the aulacogen provided a favourable environment for manganese deposition. Co: Ni, Sr: Ba and B: Ga ratios vary with the changing abundance of manganese in the mudstone (Fig. 3). Manganese abundance and Co: Ni ratios (0·82) are highest in the aulacogen and decrease to 0·18, the lowest, towards the shelf and coast. The Sr: Ba ratios trend in the same way as the Co : Ni ratios. On the contrary, the average values of the B: Ga ratios vary from 0·85 to 1·66 in the aulacogen to 14·70, the highest, in the submarine rise zone. Manganese, cobalt, strontium and gallium are rela­ tively concentrated in the aulacogen. Basin evolution

The main tectonic activity in the passive continental margin which forms the basement of the Lijiang Basin was gradual elevation during the Norian stage. Because movements of the Tethys plate affected

this area the crustal structure was somewhat un­ stable. Extension (pull-apart) of the crust along the Xiaojinhe fault at different stages and the formation of the Runanshao fault caused the seafloor to sink considerably between two stages of uplift (Liu, 1985). Turbidite sediments were deposited twice during the sinking and elevation of the seabed, giving rise to two shallowing-upward sequences in the Songgui Formation in the Lijiang Basin. During the early Norian stage rapid extension (pull-apart) of the crust along the Runanshao fault, the fault depression of the aulacogen, controlled the formation of the delta-front collapse turbidite fan. This fault was also a vent for the submarine eruption of basalt magma that came from the deep crust or upper mantle. The olistostromes filling the centre of the fault depression consist of middle Triassic lime­ stone from the rising wall of the aulacogen graben. Deposition of black mudstone extended over the whole aulacogen basin following the eruption of submarine basalt. The sea retreated from this area in late Norian times and folding took place in the western part of

H. Liu

54

0 1 02

'
�3 t±lEJ4 I

I

""/:.� .: / · /'

.

o

.

a

.

.

.

c.section point

the region. The southern part of the region became a piedmont plain. The Runanshao fault converted from an extensional (pull-apart) to a compressional structure. The primary aulacogen was covered by a nappe outlier which is several kilometres wide and about 15 km long, and composed of the middle Triassic Baiya Formation. MANGANESE MINERALIZATION Ore-bearing formations

Manganese ore bodies occur only at the base of the succession of basic volcanic and siliceous carbonate rocks in the aulacogen. The olistolith shows dis­ orderly deposition with slump folding and irregularly shaped blocks. Some of the olistolith blocks occur within the ore bodies (Fig. 4). Black mudstones at the base of the ore bodies formed in deep water with

. :·,

. . ·· .

16 Km

�-�-�

. ..

.

I ·. . /.· .

. ....

.....

I.

Fig. 3. Manganese concentration data and geochemical ratios in Songgui Formation, Lijiang, Yunnan. 1, Mn <100 ppm; 2, Mn 500-750 ppm; 3, Mn 750-1000 ppm; 4, Mn >1000 ppm; 5, Co : Ni ratio; 6, Sr: Ba ratio; 7, B: Ga ratio.

low rates of deposition. Their manganese content is relatively high but not high enough to form com­ mercial ore bodies. The shapes of ore bodies in this area differ from those in typical marine sedimentary manganese deposits. The thickness of known ore bodies varies greatly and their length is five to eight times greater than their width. Their form is often concealed as shown by the No. 1 ore body in Xiaotianjin where the length of the outcrop is less than 100 m but it extends westward (along strike) for about 800 m. The prospective value of many ore bodies is greatly enhanced when their extension along strike is recognized. Ore texture and composition

There are differences between the manganese ore bodies at the base of the succession of volcanic rock

Mallgal!ese enrichme11t, Lijia11g 8asi11

55

r

jt,r r I 4

Fig. 4. Geologic section, line 45, Hoqing manganese deposit. 1, feldspathic quartz sandstone; 2, limestone olistolith; 3, mudstone; 4, olivine basalt; 5, pyroclastic rock; 6, manganese ore body.

and those in the siliceous carbonate formation. Oxidized manganese and iron-manganese charac­ terizes the former type but the latter type consists mainly of manganese carbonate. The secondary ore consists of oxide and mixed oxide and carbonate minerals. The central parts of the ore bodies consist of manganese carbonate which is surrounded by manganese oxide that extends into the surrounding rocks. The principal ore minerals are pyrolusite, psilomelane and rhodochrosite. Secondary minerals are manganite and braunite, magnetite and other minerals. Ore textures are allotriomorphic to hypidiomorphic granular and microscopic granular. Structures of the manganese carbonate ore include sub-blocky to blocky, perthitic, striped and colloidal forms. Structures in the manganese oxide ore are mainly sub-blocky, brecciated and concentric col­ loidal forms. The trace element content is similar in the two types of ore. The zinc content is evidently related to the content of manganese (average zinc in ore 3000-10 000 ppm). The content of cobalt, boron, molybdenum and copper in the ore is three to tens of times higher than that in the wall rocks at the top and bottom of the section. The content of cobalt in the ore at the base of the volcanic pile is up to 100150 ppm, and the Co: Ni ratio is as high as 3·39. The high ratio of B: Ga (average 42·58) is characteristic of the ore at the base of the siliceous carbonate rock. No alteration has been found in the upper and lower wall rocks and no minerals bearing zinc,

§2�5 c--::-:13 � s o

sam

lead, molybdenum, etc. have been found although fluid inclusion thermometry studies of individual ore samples show temperatures of up to 20SOC. Assessment of metallogenetic factors

The main controlling factors in the Heqing deposits are the processes of formation and their palaeo­ geographic context. Some of the ore bodies are overlain by volcanic rock that was extruded during the development of the graben. Other ore bodies are associated with siliceous carbonate rocks that were produced by the volcanic eruptions. There is no doubt that somehow volcanism was a part of the metallogenetic process, which is also indicated by the composition of the ore given above. However, the position of the known manganese ore bodies in this area is lower in the stratigraphic succession than the volcanic rocks, suggesting that the formation of the manganese ore ended during the eruption of the magma. This implies that the metals (manganese, iron) were carried directly from depth through the vent. They were then involved in new geological processes of sedimentation and diagenesis on the seafloor. It is reported that submarine volcanoes erupting iron and manganese have been identified in the region of the Galapagos rift zone (Lisitsyn, 1985), which would support this model. The deep-water pelitic environment that existed in the centre of the fault depression would have been favourable for the concentration and deposition of manganese. The amount of terrigenous clastic

H. Liu

56

sea level

Runansao Fault

turbiditic sandstone .r 3

s�2

material entering this basin centre as a diluent of the manganese minerals was small. Metallogenetic model

Volcanic exhalations brought the metallic elements for the ore into the water during the graben stage of aulacogen development. The metals were deposited in the low-lying parts or in depressions on the seafloor. Much middle Triassic limestone was deposited in the low-lying areas of the seafloor as olistoliths after the deposition of manganese (Fig. 5). The topography of the low-lying seabed or depressions controlled the shape of the ore lenses or facies, and the shapes of the depressions were con­ trolled by the Runanshao fault with an east-west strike (or axial) direction. The relatively high oxygen fugacity near the vent was favourable for the formation of oxidized manganese and iron- manganese ores. The zinc did not form as a sulphide mineral, which suggests that the environment was free of sulphur. Reducing environments in the topographic depressions far away from the vents and the alkalinity of the sea­ water in which the siliceous carbonate rocks formed were favourable for the formation of the manganese

Fig. 5. Schematic diagram showing manganese entering basin along extensional fault through seafloor, and deposition of manganese ore body.

carbonate ore. The lava did not extend to the de­ pressions distant from the vents and high-grade manganese ore was formed entirely during the diagenetic stage. The tenor of the ore far away from the volcanic vents is 10-15% higher than that near the volcanic vents.

ACKNOWLEDGEMENTS

I am grateful to G. Gross for criticism and correction of an earlier version of the manuscript, and to E. Mulqueeny for redrawing some of the figures.

REFERENCES

LISITSYN, A. P. (1985) Geochemistry of manganese in the oceans. Int. Ceo!. Rev. 27, 979-983. LIU, H. (1987) The Heqing manganese deposit, West Yunnan: Its sedimentary-diagenetic environment and metallogenic model. Geology and Prospecting 23, 1-7. L1u, Z. (1985) Plate Tectonics, pp. 106-113. Sichuan Scientific and Technical Pub!. Soc., Chongying, China. RuPKE, N.A. (1985) Abyssal clastic seas. In: Sedimentary Environments and Facies, Vol. 467 (Eel. by H.G. Reading; Trans. Chinese by Zhou Minjian), pp. 502-517. Scientific Pubis Soc., Beijing, China.

Spec. Pubis int. Ass. Sediment.

(1990) 11, 57-72

Processes of formation of iron-manganese oxyhydroxides in the Atlantis-11 and Thetis Deeps of the Red Sea G . Y U. B UT UZ O VA*, V. A. D R IT S *, A. A . M O R O Z O V ' and A . I. G O R S C H K O V r

*Geological Institute of the USSR Academy of Science, 7 Pyzhevsky per., 109017 Moscow, USSR; 'Institute of Oceanography of the USSR Academy of Science, 23 Krasikova Street, 117218 Moscow, USSR; and *Institute of Ore Geology and Mineralogy of the.USSR Academy of Science, 35 Staromonetny per., 109017 Moscow, USSR

ABSTRACT

A complex of iron-manganese oxyhydroxide mineral phases is recognized in ore deposits of the Atlantis-II and Thetis Deeps in the Red Sea. In the ore material of the Atlantis-II Deep goethite and hematite predominate among the ferruginous phases; the manganese phases are mainly represented by todorokite and manganite. In the Thetis Deep the iron ore material contains a predominant magnetite­ lepidocrocite association, and the manganese component is mainly represented by asbolanes. The bulk of the iron - manganese oxyhydroxides in the ore material of the Red Sea is formed by oxidation of Fe 2+ and Mn 2+ supplied to near bottom water by hot brines. The processes of transformation of amorphous hydrated particles into individual crystalline phases depend on physico-chemical conditions in the mineral-forming medium, i.e. on the relative concentrations of manganese, iron and oxygen, and pH value, as well as on the catalytic and adsorption activity of the amorphous hydrated particles. Stratified brines in the Atlantis-II Deep determine different physico-chemical conditions. The process of forma­ tion of todorokite mainly takes place in the u pper part of the brines, where in an alkaline environment with high oxygen content hydrated thixotropic macrostructures of nMn02·mH20 are formed. These particles can adsorb cations, leading to the formation of minerals with losse tunnel structures. Favourable conditions for manganite formation are found in the lower part of the brines with oxygen deficiency, large amounts of manganese and low pH. Under these conditions the amorphous manganese hydroxides are less hydrated and contain no adsorbed cations besides manganese. The bulk of goethite and hematite is also formed in the lower part of the brines or in the sediments during diagenesis. Ferrihydrite, present in the u pper parts of the sediment section, is formed through microbiological processes in the layer of the b'rines transitional to seawater. In the Thetis Deep there is no bottom water stratification. In the bottom water there, the manganese content is considerably lower than that in the brines in the Atlantis-II Deep. Under such conditions, the Mn0 2 gel coagulates slowly and this leads to the formation of asbolanes with layer structures. The main factor affecting the magnetite and lepidocrocite formation is the kinetics of crystallization of the amorphous phase which in turn depends on the iron : oxygen ratio. Due to an active supply of hydrothermal iron magnetite is formed, while lepidocrocite crystallizes when the hydrothermal activity diminishes.

INTRODUCTION

The geothermal system of the Red Sea rift zone is an object of intensive interest for researchers from many countries through the prospect of industrial exploitation and mining of ore deposits in that area. Besides the economic value, this area is extreme­ ly important scientifically as a unique natural lab·· Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

oratory for the study of the mechanisms of different phases of ore formation. A large part of the ores in the Red Sea basin is composed of iron-manganese oxyhydroxides. The physico-chemical conditions of the medium control their mineralogy, structural and crystallochemical 57

G. Yu. But uzova et a/.

58

characteristics, paragenetic assoCiatiOns and re­ ciprocal transformations. In this light the iron­ manganese oxyhydroxides may be regarded as im­ portant environmental indicators. Although the Red Sea sediments are well studied, the mineralogy of iron-manganese oxyhydroxides is usually described in general terms, and the con­ ditions of formation of iron-manganese ore accu­ mulations and the mineral phases composing them are almost unknown (Bischoff, 19 69; Backer & Richter, 1973; Bignell et a/. , 197 6). An extremely high dispersion of ore material, the low structural regularity of minerals and the polycomponent character of samples are all serious obstacles to the study of fine crystallochemical peculiarities of the different phases and their diagnosis. The traditional X-ray diffraction methods are almost ineffective if applied to such objects. The present paper gives results of detailed studies of iron-manganese oxyhydroxides in the ore material of sediments in two rift zone basins of the Red Sea, the Atlantis-II and Thetis Deeps. The major purpose of the study is an accurate diagnosis of mineral phases and the deciphering of the major mineral-forming mechanisms. Besides the traditional chemical, X-ray diffraction and CAMEBAX-micro­ probe analyses, we also applied methods of scanning and transmission electron microscopy which in­ cluded micro-diffraction of electrons and local energy dispersive analysis of individual micro­ particles. The research was prompted primarily by the high ore-bearing capacity of sediments in these basins and by essential differences in the morphology between the basins. These differences justify the description of each basin separately.

silicate (AM) zone. Twenty samples were selected for detailed mineralogical analysis from the different lithological-facial zones, except the lowest DOP zone which was not reached by our cores. In this section of the Atlantis-II Deep the major ore element in weight proportion is iron whose content in individual interlayers reaches 60% and on average is about 33%. The colour of iron ore inter­ layers and sequences is red-yellow, russet-ochre and sealing-wax red; the Ept values in them are in the range +170 to +250 mY. The manganese con­ centration varies from 0·1 to 2·7 %, while four­ valent manganese compounds are entirely absent. The element is partly present as manganosiderites irregularly dispersed throughout the sedimentary layer. The manganese-rich ore interlayers are dis­ tributed locally in the Atlantis-11 Deep, occupying a distinct position both in vertical section and in hori­ zontal distribution. In the sedimentary column they are found in the CO zone; on the area of the seafloor they are confined to the relatively high parts and the sides of the basin. In the studied sections the manganese-rich interlayers occur in the intervals 3350-3500 mm at site 1905(5) and 4830-5000 mm at site 1905(4). The thickness of the manganese ore interlayers, according to our data and information in the litera­ ture, is 150-400 mm (Bischoff, 1969; Butuzova, 1984a) and the content of manganese is 30-45% and that of iron is 6-11%. The interlayers are clearly identified in the section by their almost black to dark red-brown colour, their typical 'oily' consistency and sharp boundaries with the sur­ rounding muds. The sediments have high maximum oxidation-reduction potential values for the ore oozes of the Red Sea (Ept +500 to +600 mY). =

THE ATLANTIS-II DEEP

Iron oxyhydroxides Sample descriptions and mineral compositions

The study of the mineral composition of iron­ manganese oxyhydroxides was carried out on the basis of data from two typical sections. One of them is site 1905 (4) with coordinates 21°22·8'N , 38°05·3'W and thickness 5750 mm; the other is site 1905(5) with coordinates 21°20·5'N, 38°06·1'W and thickness 5800 mm. Backer & Richter (1973) distinguish five zones in the section (from bottom upwards): detrital oxide­ pyritic (DOP), lower sulphide (SUt ) , central oxide (CO), upper sulphide (SU2) and the amorphous-

The ferrous phases of the ore material are, on the whole, weakly crystallized with a large amount of amorphous matter. Among the crystalline phases goethite (cx- FeOOH) and hematite (Fe203) pre­ dominate in iron ore horizons, small quantities of ferrihydrite (5Fe203 ·9H20) are present in the upper parts of the section. In the manganese ore inter­ layers the major iron minerals are lepidocrocite (y­ FeOOH) and ferrihydrite. 1 Goethite forms platey microcrystals elongated along the 'b' axis (Fig. 1a), or aggregates of finely dispersed particles with 30-50 A diameter (Fig. lb).

Iron-manganese oxyhydroxides, the Red Sea

59

Fig. 1. Morphology of goethite and hematite particles (Atlantis-11 Deep) . (a) Elongate platey crystals of goethite; (b) aggregate of finely d ispersed goethite particles; (c) aggregate of finely flaked hematite; (d) monocrystal of hematite. Scale bars (a)-(c) 0·5 >UTI, (d) 4 !J.ITI.

The structural order of the mineral increases with greater depth. 2 Hematite is also present in two morphologically different forms, i.e. as dense finely flaked aggregates with goethite crystals (Fig. lc) and as flat 0·02-0·04 mm hexahedrons 2-4 f.tm thick (Fig. ld). We have also found hematite in the sediments in the south­ western part of the Atlantis-II Deep in the immediate

vicinity of hydrothermal vents where hematite forms lens-like patches and clearly delineated interlayers. 3 Ferrihydrite in iron-manganese ore deposits occurs as mineral aggregates with bacterial form (Fig. 2a). 4 Lepidocrocite occurs as elongated plates of less than 1 �lm size, which develop from a spherical jelly-like matrix (Fig. 2b). Individual samples of

60

G. Yu. But uzova et a/.

Fig. 2. Morphology of particles and microdiffraction

pattern of ferrihydrite and lepidocrocite (Atlantis-I I Deep). (a) Aggregate o f particles o f bacterial ferrihydrite; (b) globular aggregates of spicular crystals of lepidocrocite; (c) aggregate of particles of bacterial lepidocrocite. Each scale bar 0·5 �-tm.

lepidocrocite, like ferrihydrite, have bacterial forms of aggregates of mineral particles (Fig. 2c). This lepidocrocite variety has a lower structural ordering and is normally found together with ferrihydrite.

Manganese and iron-manganese oxyhydrox ides Three major components are distinguished in the manganese-rich interlayers: the basic finely dispersed mass, solid kidney-shaped micronodules and various concretions of complicated morpho­ logical type. The three components differ not only in texture and morphology, but their mineral compo­ sition is essentially different; they also have differ­ ently crystallized minerals and some geochemical peculiarities.

1

The major mass of ore material is composed of 2-6 �m globules shaped like rosette lepispheres with characteristic elongate crystals up to 2-4 �m long at the edges (Figs 3a, b). Electron micrographs show platey crystals sometimes forming twinned crystals (Fig. 3c). The mineralogy of the major mass is represented mainly by todorokite whose presence is characterized on diffractograms by reflections with d spacings of 9·58, 4·78, 2 4 0 and 2·20 A. We emphasize here that the same set of reflections characterizes at least four other mineral varieties of manganese hydroxides which are structurally dif­ ferent from todorokite (Chukhrov et a/., 1987). Therefore a reliable diagnosis of todorokite was carried out by combining the X-ray and micro­ diffraction methods. The analysis of electron diffrac·

,

Iron-manganese oxyhydroxides, the Red Sea

..

...

I

I

61

+

j '

' 1

' I

I '

I

'

I

..

t '

8

Fig. 3. Electron micrographs and electron diffraction

pattern of todorokite from the major mass of manganese ore horizon (Atlantis- II Deep, site 1905(5), horizon 48305000 mm). (a), {b) Globular todorokite particle; (c) triple cluster of todorokite; {d) electron diffraction pattern of the triple cluster of todorokite with a = 9·75 A; (e) electron diffraction pattern of todorokite with a = 24-4 A. Scale bars (a) 10 f.lm, {b) 2 f.tm, (c) 0·5 [lm .

62

G. Yu. But uzova et a/.

tion patterns, obtained from the studied samples, has shown that manganese ore horizons contain three todorokite modifications with parameter a of 9·75 (Fig. 3d), 19·5 and 24·4 A (Fig. 3e). This is associated with the different size of channels in the tunnel structure of microcrystals of minerals. The most common is todorokite with parameter a of 9 ·75 A. Short columnar microcrystals 0 ·1-0·15 �lm in size were revealed in the mass in association with todorokite. Their electron diffraction patterns cor­ respond to the characteristics of goethite (cx­ FeOOH) and groutite (cx-MnOOH) which are isostructural. The particles contain comparable amounts of manganese and iron. These data seemed to indicate the presence of isomorphic substitutions of Mn3+ and Fe3+ in the structure of the compounds or the growth of goethite and groutite at the sub­ microscopic level. H owever, a subsequent detailed X-ray absorption spectroscopic study has shown that this phase consists of Fe3+ and Mn4+ domains co­ existing within a uniform hexagonal packing. The cation distribution in Fe3+ domains is similar to that in goethite, while the Mn4+ cations in manganese domains are distributed layerwise as in phyllo­ manganates. This phase is to be called manganese goethite (Manceau et a!., 19 9 0). Individual samples of the basic mass of ore ma­ terial, besides todorokite and manganese goethite, have traces of buserite-II, a laminated 10 A man­ ganese oxide, the Mn4+ octahedron layers of which have chains of vacant octahedrons: below and above these octahedrons are located Mn3 + , Mn2+ , Ca2+ and other cations coordinated by H 20 molecules (Chukhrov et a/., 1984). A study of 10 samples by microprobe revealed considerable chemical inhomogeneity of the finely dispersed material. The manganese content varies from 55 to 93%, with an irregularly distributed admixture of iron (0·14-11·6% ), silicon (0 ·36% ), calcium (0·3-1·7%) and magnesium ( 1-1·16% ). Among trace elements the most com­ mon are zinc (0·02-1·5%) and lead (0·05 -0·5% ). The silicon, magnesium, calcium and some iron in the major ore mass are probably associated with insignificant and irregularly distributed admixtures of the host sediment, with small amounts of au­ thigenic smectites and the presence of cations in the adsorbed complex of manganese hydroxides. An essential admixture of iron is found in manganese goethite, lepidocrocite and ferrihydrite. 2 Kidney-shaped microconcretions are black and

shiny, 0 ·2-0·5 mm in size, seldom up to 1 mm. They are quite varied morphologically, occurring in rounded, oval, and dumb-bell forms, commonly with pancake 'growths' attached to the principal surface (Fig. 4a). The inner parts of microcon­ cretions are composed of randomly oriented crystals (2-5 �lm) of elongate platey shape (Fig. 4b). The microconcretions are composed of well-crystallized manganite. No other cations other than manganese are present in the manganite particles. 3 Morphologically complex concretions and crusts are normally dark-grey, dull, friable and slaggy. Their size does not exceed 1 mm, the shape is extremely variable (branched, dendritic, angular: Fig. 4c), and their surface is rough and bumpy. Their mineral and chemical composition is inter­ mediate between the first two types. The dominant minerals are todorokite and manganite. Some of the samples show small admixtures of manganese goethite. The set of associated microelements is the same as in the basic mass, but their content is generally less.

General descr iption of the phys ico-chemical env ironment The Atlantis-II Deep is the best-studied part of the Red Sea rift area. A number of papers describe the major structural features, the general mineralogical-geochemical characteristics of the sediments and physico-chemical parameters of brines filling the Atlantis-11 Deep (Degens & Ross, 19 69; Backer & Richter, 197 3; H ackett & Bischoff, 197 3; Butuzova, 1984a,b). The area of the Atlantis-II Deep is 7 0 km2; it is filled with dense, highly mineralized thermal brines about 17 0 m thick with distinct vertical stratification. The lower and thickest layer has a temperature of 62 -65°C, salinity up to 320 %o, is completely devoid of oxygen, and pH values in it reach 5·5-5 ·6. Above this layer, a change in all parameters of the water mass occurs at a definite boundary, i.e. the tempera­ ture falls to 51 °C, salinity is reduced to 153 %o, the pH value is 5·9, and oxygen is present in small amounts (0·05-0·06 mg/1). This layer is about 30 m thick, and above an intermediate horizon of about the same thickness is a layer of normal seawater (Degens & Ross, 1969). Data available in the literature on the structure of the brine layers and their physico-chemical charac­ teristics were used to work out a scheme for the formation of a complex of mineral phases (Fig. 5). A

Iron-manganese oxyhydroxides, the Red Sea

63

Fig. 4. Morphology of solid aggregates in the major mass

of manganese ore material and diffraction pattern of manganite (the Atlantis-II Deep, site 1905(5), horizon 4830-5000 mm). (a) Microconcretion of mangani te; (b) platey crystals of manganite composing the microconcretions; (c) aggregate of polycomponent composition ( todorokite, manganite, manganese goethite). Scale bars (a) 400 �-tm, (b) 1 �-tm, (c) 200 �tm.

rather informative addition to the scheme is a set of data on iron and manganese distribution throughout the brine layers, from the contact with bottom sediments to the boundary with seawater (from Brewer & Spencer, 1969) (Fig. 6). The mechanism of formation of iron oxyhydroxides

Figure 6 clearly shows that a sharp change in iron content in the brine layer occurs at the boundary between the lower layer (A) and the overlying hor­ izon (B). This change in properties is caused by an overall transition of the dissolved iron into solid' phases in the zone where oxygen appears. A direct confirmation of the formation of a major mass of iron hydroxides at the boundary between two layers in the brines is a perceptible rise in the amount of

rusty-brown suspended material in this area which is completely amorphous (Hartmann, 1979). Holm et a!. (1982), however, have established the presence of the mineral phase �-FeOOH (akaganeite) in the suspended material. Most workers believe that the presence of chlorine (or fluorine) anions in solution is a necessary condition for the formation of the phase �-FeOOH, in addition to an acid or neutral environment, as realized in the Atlantis-ll Deep. Akaganeite is as yet the only crystallized phase of 3 Fe +, found in small amounts in suspension in the brines of the Atlantis-II Deep. However, neither previous research nor our studies have found this mineral in the sediments. Taking into account the metastable character of the phase FeOOH, we as­ sume a rapid transformation of akaganeite into more stable crystalline phases (goethite, hematite).

-- J

64

_!:I � �------

_P

-1-

[O,]>IMn2•1. pH>7.t < 500C Mn>+ + V20

IC

II

Mn2+

102] < 1Mn2•]: pH- 6 1- so·c B

__ ____

[O,] = O pH- 5

1- 6s·c

A

l

G. Yu. Butuzova et al.

-;;�� -dp�;d- c;,-,- ;;::��W�O�E�- ; � � =�� matter

Corg

20H--+Mn0 ·H20 2+ 2

�

m r h

:x:e�!�)�o� :a�------F -

0JSSOCI3tiOO H2Mn03-+2H+ + Mno}----::lll - IMnOj· (nMn02·mH20)]2H+ Hydration polymerization

l/zO., + 2H,O -----. MnO , ·H, Q + 2H+

+

-

-

�,r I I

�n_'"_'-+

Mn2+

-

-

Polymerization

-

t

� ��1.:_���'---�-

Fe(II)

!

Mn2+ Mn0]�2Mn0(0H) -- nMnO(OH)·mH20

y

o

- -- -

Amorphous hydrox1de Fe(III)

_______

-----

,.

�

t---H-

,_ -_- _ _-_ _ _-_ _-_ ----,

I

•1.

nMnO,·mH,O Manganite

I

.I

I

2

�4

Fig. 5. The scheme of iron-manganese mineral formation in the Atlantis-IT Deep. A, B, C- layers of brines (A- lower,

B- upper, C - transitional to seawater); I- upper zone of active oxidation; II - lower zone of slower oxidation. ( 1) Amorphous phase of suspension; (2) mineral phases; (3) sedimentation and mineral formation (coagulation, dehydration, crystallization); (4) migration in brine; (5) transformation of solid phases of the suspension and sediment; (6) area of manganese ore deposits.

Another possible cause of the absence of akaganeite in the sediments might be its destruction due to loss of chlorine from the sediment in the process of elutriation of samples by water to remove easily soluble salts. Disintegration of akaganeite after chlorine removal has been confirmed experimentally (Chukhrov et al., 1975a). The ore layer of the Atlantis-ll Deep has two major mineral associations of iron oxyhydroxides: the goethite-hematite association, typical of iron ore deposits of all lithological-facies zones, and the ferrihydrite-lepidocrocite association, confined to manganese-rich interlayers. Small amounts of ferrihydrite were also found in the iron ore sedi­ ments, mostly in the upper horizons of the sections. Since the major mass of oxidized iron appears at the boundary between two layers (Figs 5, 6, A and B), the amorphous hydroxides formed at this place

may be the origin for the bulk of the goethite and hematite in the ore material. 1 Goethite is formed over a wide range of con­ ditions, but experiments to synthesize ferrous phases show that high concentrations of Fe2+ in the brine at low oxygen content and rather low pH values stimu­ late goethite formation (Chukhrov et al., 1975b). The environment in the region of formation of the major mass of iron hydroxides fully complies with these conditions. The regular increase in the struc­ tural ordering of goethite from top to bottom of the ore section confirms the formation of its larger part by crystallization of the amorphous phase. Another means of goethite formation is related to a trans­ formation from lepidocrocite; the absence of lepido­ crocite in ferrous ore deposits could be due to its transition into goethite at higher temperatures. 2 Hematite, in contrast to goethite, is formed as a

Iron-manganese oxyhydrox ides, the Red Sea

depth

�

30 50

70

90 100

ma

m

ho

65 20

�0

60

ao

100

:J;

1920

1960

2000

2040

2080

Fig. 6. Distribution of iron and

manganese in the layer of brines in the Atlantis-II Deep ( after Brewer & Spencer, 1969). (A) Lower layer of brines; ( B ) upper layer of brines; (C) layer transitional to seawater; (D) seawater.

2120

2160 2180

result of the crystallization of amorphous hydroxides at higher temperatures. Accordingly, the maximum amounts of well-crystallized hematite, in the form of hexahedrons, are confined to regions in the immedi­ ate vicinity of hydrothermal vents. In the studied sections the total hematite content is notably higher in sediments at site 1905(5), which is nearer to the vents, than in the core from site 1905(4). The presence of finely flaked aggregates, which form another morphological variety of hematite in the sediments of both sections, is probably caused by the transformation of ferrihydrite into hematite. It is important to note that ferrihydrite in ferrous ore deposits remains only in the upper parts of the sections, which may imply that the major part of the mineral was transformed into hematite in the course of aging of the sediment. 3 Ferrihydrite is found both in ferrous ore deposits and in manganese-rich interlayers. It contains par­ ticles with bacterial form which may testify to the active role of microbiological processes in the for­ mation of this mineral. The C layer of the brines, which is transitional to seawater, is the most favour­ able environment for active microbiological oxida­ tion-reduction reworking of the ferruginous suspension. This layer is the gradient zone with a perceptible change in density and an increase m oxygen content (Fig. 5). Consequently, the conditions of formation of

Fe

Mn

amorphous iron hydroxides, which are transformed on the one hand into goethite and hematite, and on the other hand into ferrihydrite, are spatially separ­ ated. The sources of iron are also different: in the first case amorphous hydroxides are produced by 2 oxidation of Fe + which is supplied by hydrothermal waters; while in the second case they are a result of the transformation of ferruginous suspension from seawater (Fig. 5). 4 Lepidocrocite includes particles with bacterial form which develop from a biogenic matrix by the same processes and under the same conditions as ferrihydrite. The abiogenic lepidocrocite is probably 2 formed as a result of Fe + oxidation in the boundary zone of brines between layers A and B. The extensive production of hydrated forms of Mn02 and the presence of amorphous Si02 in manganese ore interlayers apparently stimulate the preservation in the sediment of metastable hydroxide phases of iron, i.e. ferrihydrite and lepidocrocite. Mechanism of formation of manganese oxyhydroxides

The behaviour of hydrothermal manganese in the brine layer of the Atlantis-11 Deep is essentially different from that of iron. Due to the higher oxi­ dation potential of manganese the transition of 2 hydrothermal Mn + from solution to the solid phase

66

G. Yu. But uzova et a/.

2 Mn + takes place in the brine layer into which the seawater oxygen penetrates. The process of massive manganese oxidation is shown in Fig. 6 as a sharp change in manganese content in the C zone tran­ sitional to the normal seawater. According to the data of Hartmann ( 1979), it is in this zone that a notable amount of brown suspended material appears composed of amorphous manganese hydroxides. The particles of hydrated manganese dioxide, sinking into the brine layer and reaching the lower A layer completely devoid of oxygen, are reduced by 2 the dissolved Fe +, and manganese again passes into solution. This process obstructs precipitation of ox­ ide forms of manganese in brines and provides high concentrations of the element in the solution (80-90 mg/1), which is about 20 000 times as great as the average manganese content in seawater. The natural consequence of these processes is the almost complete absence of manganese oxyhydroxides in the sediments in extensive areas of the Atlantis-11 Deep. The local presence in the sedimentary layer of manganese ore interlayers, confined by sharp lithological contacts with the surrounding muds, is evidence of the change of physico-chemical conditions in the near-bottom water. This change occurs against the background of a quiescent hydrological setting with intensive mixing of water masses. The most probable cause for the change of con­ ditions in the near-bottom water would have been the lowering of the level of brines which in turn was connected with a lower or temporarily discontinued hydrothermal activity during the period of forma­ tion of manganese ore horizons. A number of lithological-geochemical peculiarities of deposits in the CO zone testify to this possibility, including an appreciable admixture of the biogenic-terrigenous component to the ore material, and a low content of sulphides including diagenetic sulphides. Confine­ ment of manganese ore horizons to the relatively high parts of the sea floor is also evidence because these parts are in the upper layer B when the level of brines is lowered (Fig. 5). It is in this region that conditions are created to allow the possibility of massive precipitation and preservation of manganese hydroxide compounds in sediments, these con­ ditions being an increase in the oxygen content, a 2 sudden fall in Fe + concentration and temperature, and a rise in pH. In discussing the possible mechanisms of the for­ mation of manganese hydroxide compounds, it is 2 important to consider the nature of Mn + oxidation

processes and certain properties of the compounds formed during these processes. 2 The act of Mn + oxidation by oxygen in solution results in the appearance of Mn4+ in the form of a hydrated dioxide according to the reaction: 2 Mn + + 1/202 + 20H- __,. Mn02·HzO At a molecular level the hydrolized products of 2 the initial Mn + oxidation are coordinated hydrated polymeric aggregates. Their coagulation produces hydrated microstructures with adsorptive activity capable of dehydration and intraphase oxidation­ reduction transformations by the scheme: 2 Mn + + Mn4+ � 2Mn3+ The development and direction of certain trans­ formations of the amorphous phase and the formation of individual compounds are determined 2 mostly by the conditions of Mn + interaction with 2 dissolved oxygen and by the ratios of Mn + : 02 concentration, pH value, and adsorptive and cata­ lytical activity of the newly formed surface of hy­ drated Mn02. In the environment of the Atlantis-11 Deep, the stratification of the water layer provides differen­ tiation in the physico-chemical conditions of the medium where mineral formation takes place; these conditions control the polymineral composition of ore material. Formation of todorokite and manganese goethite of the major mass

2 Figure 5 shows two Mn + oxidation zones with a number of essentially different parameters. Zone I of active oxidation generally coincides with layer C of the brines, which is transitional to seawater and has a high content of dissolved oxygen, an alkaline environment, and relatively low tem­ peratures ( <50°C). The underlying zone I I is oxygen deficient, has higher temperatures, and lower pH values ( �6). The massive oxidation of divalent manganese occurs in zone I where a hydrated man­ ganese dioxide (Mn02·nH20) is formed. An alkaline (or close to neutral) medium stimulates dissociation of the amphoteric oxide Mn02·nH20: Mn02·nH20

__,.

H2 Mn03

__,.

Mnol- + 2H+

2 The Mn03 - anions formed in the process are capable of being abundantly hydrated to form thixo­ tropic macrostructures of hydrated Mn02 (nMn02·mH20). Against the background of high

Iron-manganese oxyhydrox ides, the Red Sea salinity, the amorphous hydroxide acts as a cation­ exchanger irreversibly fixing dissolved and partially hydrolized cations of different metals, including Mn2+, which in the case of superfluous oxygen results in the oxidation of this cation, thus additionally increasing the mass of individual particles. The in­ crease of the mass of particles due to coagulation, combined with the oxidation mechanism and parallel dehydration, results in a loss of sedimentary stability of particles and their sinking into the underlying zone II (Fig. 5). Under these conditions, the capacity of particles to adsorb the cations of metals is drastically reduced because of the lower adsorptive activity in general (more acid environment) and competitive adsorption of Mn2+ cations. The oxygen deficit restricts oxi­ dation of adsorbed Mn2+ and, consequently, the appearance of new adsorption centres. As a result, the change in the composition of particles ceases, and the major means of their transformation be­ come dehydration and increasing density, paving the way to subsequent crystallization and precipitation. The crystallization of the amorphous phase is caused to a great extent by the presence of large hydrated cations in adsorptively saturated complexes. Due to steric restrictions, the presence of adsorbed cations obstructs crystallization of the amorphous phase and the formation of structures with dense packing of atoms, but stimulates the formation of minerals with relatively friable anion complexes. Therefore, the overall low degree of structural ordering of the basic mass of manganese ore material and the extensive development in its composition of weakly crystallized todorokite with a loose tunnel structure seem to be the natural consequences of the transformation processes of amorphous hydroxides formed in zone I of active oxidation. The iron-manganese phase identified as man­ ganese goethite and found in small amounts in the major mass of ore material in association with todorokite is probably the final product of the trans­ formation of thixotropic mixed macrostructures of amorphous iron and manganese hydroxides. Formation of manganite microconcretions

The presence of monominerallic manganite in sedi­ ments is evidence for specific conditions for Mn2+ oxidation in the water layer, which provide for the formation of the amorphous phase with no other cations except manganese. Zone II entirely complies with these conditions and is characterized by an

67

excessive amount of Mn2+ ions, an oxygen deficit, rather low pH values (about 6), and higher tempera­ ture (about 50°C) (Fig. 5). As noted earlier, oxidation of the Mn2+ ion by the oxygen molecule results in the formation of hydrated manganese dioxide (Mn0 ·nH 0). Within the struc­ 2 2 ture of manganite the manganese cations are tri­ valent. One of the possible ways of Mn3+ formation is the interaction of Mn0 ·nH 0 with Mn2+ cations, 2 2 as a result of which an intraphase oxidation­ reduction process takes place. This interaction can be realized with the decrease in adsorptive activity of the surface of particles of hydrated Mn0 in the 2 setting with excessive Mn2+, resulting in rapid trans­ formation of the adsorbed form into the compound Mn2+Mn4+0 and its subsequent oxidation­ 3 reduction transformation Mn2+ + Mn4+ --? 2Mn3+. Despite the lack of precise experimental data, we assume that this process is restricted to a specific interval of pH values, because in weakly alkaline conditions hydration of the Mn2+ ion and of adsorp­ tion centres of Mn0 stimulates stabilization of the 2 adsorptive Mn2+ form in the Mn0 ·nH 0 phase. In 2 2 acid media the trivalent manganese disproportion­ ation takes place. In contrast to highly hydrated complexes formed in zone I, the amorphous hydroxides formed in zone II are considerably less hydrated and practically lack adsorbed cations, which ensures their transformation into an energetically favourable compact packing typical of manganite.

Formation of morphologically composite nodules

Mutual precipitation of dehydrating gel particles of todorokite and manganite composition (lesser amounts of the latter) should be accompanied by the appearance of mechanically mixed phases whose final composition is probably determined only in the sedimentary layer. In this case the most probable process is the fixing of dissolved Mn2+ from inter­ stitial waters by the sorbently unsaturated areas of Mn0 . Moreover, the achievement of the ratio 2 Mn2+ : Mn4+ 1 : 1 allows the fragments of manga­ nite structure to form concurrently with todorokite crystallization. Other processes related to the re­ grouping of structural blocks of Mn0 and the 2 intraphase oxidation-reduction interactions are also possible. In general, the absence of a notable accumulation of manganese in the zone of its active oxidation is =

G. Yu. But uzova et a/.

68

evidence for its removal from this zone by precipit­ ation of manganese hydroxides. THE THETIS DEEP Description of samples and their mineral composition

The mineralogy of oxide phases was studied in 13 samples from a core 510 em long taken from site 224 with coordinates 22°47 ·2'N and 37°35 ·5'E. Studies conducted earlier on this section have

10

i

Fe,% 30

established the structure of the ore layer and its general mineralogical features (Backer & Schoell, 19 7 2; Bignell et al., 197 6; Shanks, 1983; Butuzova, 1 985; Missack, 1988). Two basic varieties of deposits were found to regularly alternate in the sediments (Fig. 7). One of them (sequences II and IV) is represented mostly by ferrous ore material with iron content reaching 32-56%, manganese 0·35-0·47 %, and manganese oxyhydroxides absent. The admix­ ture of biogenic-terrigenous components is ex­ tremely small (CaC03 <1 %). These sediments have

50

.50

100

350

Il

Fig. 7. Distribution of chemical elements in sediment section, site 224, Thetis Deep.

Iron-manganese oxyhydroxides, the Red Sea the highest copper and sulphur concentrations in the sediment column. The other variety of sediments (sequences I, III, V) has a high content of normal sedimentary material (CaC03 20-40%) and a mixed iron-manganese composition of ore material. The iron and manganese contents are similar (average Mn- 16 ·3%; Fe-18·2%). The iron oxyhydroxides magnetite and lepido­ crocite are the most typical minerals among the crystallized phases of the ore material. 1 Magnetite is found only in ferrous ore sediments (Fig. 7, sequences II, IV) in the form of well-faceted crystals several micrometres in size, as finely dis­ persed powdery material, and in collomorphic clots. The magnetite-rich interlayers are identified in the section by their sooty black colour. 2 Lepidocrocite forms small, platey crystals irregu­ larly distributed throughout the section. The maximum amounts of the mineral are confined to the upper part of the section (sequence I) where it is almost the only iron oxide phase. The lepidocrocite content decreases down the section. 3 Goethite and hematite are observed in individual samples, mostly at the bottom of the core. Manga­ nese oxyhydroxides occur in the ore material of sequences I, III, and V, predominantly in the form of minerals with lattice structure. 4 Asbolanes are the most common minerals particu­ larly in the upper parts of the section (sequence 1).

69

Asbolanes are mixed-layer phases (Chukhrov et a/., 1983). In the sediments they form aggregates of flaky particles (Fig. Sa). Their composition includes aluminium, magnesium and calcium, in addition to manganese. The structure of the minerals is built up by octahedral layers of two types. In one of them the major cation is Mn4+ and in the other it is MnH in combination with aluminium, magnesium and calcium. The quantity and the degree of structural ordering of asbolanes regularly increase from the top of the section downwards. 5 An asbolane-like stratified X-phase was observed by us for the first time. It was found only in the uppermost of the studied horizons (200-250 mm) where it dominates the composition of the manganese ore material; the asbolanes described above are noted in small admixtures. The X-phase particles are platey in shape, and they are domi­ nated by manganese cations. The electron diffraction pattern of the X-phase (Fig. 8b) is a superposition of three hexagonal nets of reflections which differ in their distances from the centre of the electron diffraction pattern. The triads of reflections nearest to the centre have interplane 2·49, 2·60 and 2·7 2 A, whereas the distances d triads of reflections farthest from the centre are characterized by d values equal to 1·44, 1·50 and 1·57 A. Three hexagonal nets of reflections on the electron diffraction pattern of the X-phase can be =

Fig. 8. Characteristics of manganese oxyhydroxides from sediment recovered at site 224, Thetis Deep . (a) Aggregate of flaked asbolane particles (horizon 2250-2350 mm), scale bar 0·5 fun; (b) electron diffraction pattern of X-phasc particles.

70

G. Yu. But uzova et a!.

related to the three hexagonal sublattices of the mineral, the basal parameters of which are a= 2·88, 3·00 and 3 ·40 A, respectively. The values of par­ ameter 'a' are different because the three types of layers contain mostly cations Mn4+, Mn3+ and Mn2+, respectively. 6 Manganese goethite, as in the Atlantis-II Deep, is observed in the form of tabular crystals locally form­ ing almost monominerallic microaccumulations. The manganese minerals are distributed regularly in the Thetis Deep. Thus, the X-phase is observed only in the uppermost of the studied horizons; the asbolanes with low structural ordering dominate in the sediments of sequence I approximately to a depth of 1 m; and in the lower-lying deposits the degree of structural ordering of asbolanes increases but their quantities are definitely subordinate, and manganese goethite becomes the dominant manga­ nese phase. General characteristics of the physico-chemical setting

The region of the Thetis Deep is one of the few areas of the Red Sea rift which combines high hydrothermal activity with an absence of strongly mineralized near-bottom brines. At the present time, the sediments are overlain with water which is only 0·8°C and 0·4% salinity higher than normal seawater. A slight rise in salinity of interstitial waters in some parts of the sediment column suggests periodic but insignificant changes in the mineralization of near-bottom waters in the past. Variations in the chemico-mineralogical character­ istics of the sediment section at site 224 reflect periodic changes in the intensity of the hydrothermal source. The iron ore horizons II and IV correspond to stages when the near-bottom water received large quantities of Fe2+ and Mn2+ as constituents of thermal brines whose mixing with oxygenated sea­ water caused oxidation of the reduced forms. Active oxygen consumption under conditions of high Fe2+ concentrations resulted in rapid exhaus­ tion of oxygen and in the temporary filling of the basin with oxygen-free waters rich in Mn2+ and Fe2+. In this setting, the complete absence of manganese oxide compounds in the ore material of sequences II and IV is expected. During periods of lower hydrothermal activity, the sedimentary se­ quences (I, III, V) were highly enriched in biogenic­ terrigenous material and contained mixed iron­ manganese ore material. At these times the water

mass parameters in the basin gradually equilibrated with the seawater parameters. In this way conditions were created for oxidation of Fe2+ remaining in the solution and of Mn2+ accumulated there. The mutual precipitation of iron-manganese hydroxide forms in approximately equal proportions indicates rather low Fe2+ concentrations insufficient for appreciable reduction (in weakly alkaline con­ ditions) of hydrated Mn02 formed in the upper more aerated water layers. Mechanism of formation of iron oxyhydroxides

Experimental research has established that in neutral or weakly alkaline solutions the oxidation of Fe2+ results in the formation of lepidocrocite or magne­ tite. It is suggested that the transformation of the amorphous material into another mineral phase is mainly controlled by kinetic factors. Rapid oxidation stimulates crystallization of lepidocrocite; slow oxi­ dation favours magnetite formation (Murray, 1 9 7 9). 1 Magnetite is formed in the periods of maximum hydrothermal activity when the Fe2+ concentration is much higher than the oxygen concentration, allowing mutual precipitation of amorphous hydrox­ ides of .multivalent iron. The possibility of the for­ mation of magnetite as a result of the dehydration and crystallization of a gel containing both Fe2+ and Fe3+ has been experimentally confirmed (Berz, 1 922). 2 Lepidocrocite represents periods of lower hydro­ thermal activity under conditions of excess oxygen and lower Fe2+ contents in the solution. These conditions are favourable for the high oxidation rates of iron necessary to form lepidocrocite. 3 Goethite and hematite are in all probability the products of lepidocrocite transformation. This alter­ ation is apparently greatly hindered by the presence of amorphous silica and hydrated Mn02, and thus takes time. This is confirmed by extremely low con­ tents of goethite and hematite in the uppermost part of the section where l�pidocrocite is almost the only 3 mineral phase of Fe +. Mechanism of formation of manganese oxyhydroxides

Unlike the oxidation zone I of the Atlantis-II Deep, the water layer of the Thetis Deep is more alkaline, there is a deficit of oxygen as a result of the preceding Fe2+ oxidation, and much lower Mn2+ concen­ trations. These conditions obviously obstruct the

Iron-manganese oxyhydrox ides, the Red Sea rapid growth o f the mass o f suspended Mn02 particles due to their coagulation. It is possible that due to slower coagulation the hydrated structures with low ordering initially appear and in them, from above and below, the adsorbed Mn2+ cations and H 2 0 molecules attach to the fragments of insular octahedron Mn4+ layers. The intraphase oxidation­ reduction reactions between Mn4+ and adsorbed Mn2+ slow down due to high hydration of the poly­ meric microaggregates. Condensation, adhesion and reorientation of these microaggregates probably re­ sult in the layer by layer alternation of two­ dimensional associations of Mn4+ and Mn2+ . Concurrently with the formation of an increasingly well-crystallized structure, an intraphase Mn4+ and Mn2+ oxidation-reduction interaction probably takes place producing trivalent manganese. This stage apparently correlates with the low-ordered X­ phase containing disproportionate layers occupied by Mn4+ , Mn3+ and Mn2+ cations.

71

layers are transitional to those of seawater and have low Fe2+ and high Mn2+ contents. In the Thetis Deep, the iron ore material contains a predominant magnetite -lepidocrocite association and the manganese component is represented mostly by asbolanes. This basin has no stratified brines and the mineral-forming environment is alkaline, low temperature and oxygenated. The changes in con­ centration in the solution of Fe2+ and Mn2+ ions are controlled by changes in their supply from hydro­ thermal brines.

ACKNOWLEDGEMENTS

The authors express their sincere thanks to two anonymous reviewers and J . Parnell for critical reading of the manuscript and numerous valuable corrections. We also are indebted to A. Sivtsov for selected-area electron diffraction, N. Gorkova for supplying electron micrographs and B. Smoliar for assistance in the preparation of the manuscript.

CONCLUS IONS

The bulk of the iron and manganese oxyhydroxides in the ore material of the Atlantis-II and Thetis Deeps is formed by oxidation of Fe2+ and Mn2+, supplied by hydrothermal brines, and by precipi­ tation of amorphous hydrated particles from the brine. Subsequent processes of their transformation into individual crystalline phases depend on the composition of particles and are controlled by a complex of effects, including oxidation-reduction, coordination, colloidal-chemical, adsorptive, sedi­ mentary and diagenetic processes. These transform­ ations are also influenced by the kinetics of gel dehydration. All these effects are shown to be deter­ mined by distinct physico-chemical parameters of the mineral-forming medium. The differences be­ tween these parameters in the water layers of the studied basins result in the formation of different mineral associations. In the ore material of the Atlantis-11 Deep, goethite and hematite predominate among the fer­ ruginous phases; the manganese phases are rep­ resented mainly by todorokite and well-crystallized m;:mganite . This set of minerals is controlled by the differentiated conditions related to the stratification of the water layer, the lower layers of which have low pH values, higher temperatures, a sharp de­ ficiency in oxygen, and a high concentration of Mn2+ and Fe2+ ions; the parameters of the upper

REFERENCES

H. & RICHTER, H. ( 1973) Die rezente hydrothermal-sedimentare Lagerstatte Atlantis-II-Tief im Roten Meer. Geol. Rund. 62, 697 - 741. Bii.CKER, H . & ScHOELL, M. ( 1972) New deeps and metal­ l iferous sediments in the Red Sea. Nature 240, 153- 158. BERZ, K.C. ( 1922) Uber Magneteisen in Marinen pp. 569-577. Centralblatt fi.ir Ablagerungen, M ineralogic, Geologie und Palaeontologie, Stuttgart. BIGNELL, R . D . , CRONAN, D.S. & TOOMS, J . S . ( 1976) Red Sea metalliferous brine precipitates. Geol. Ass. Canada Spec. Pap. 14, 147- 149. B ISCHOFF, J . ( 1969) Red Sea geothermal brine deposits, their mineralogy, chemistry and genesis. In: Hot Brines and Recent Heavy Metal Deposits in the Red Sea (Ed. by E .T. Degens & D.A . Ross ) , pp. 368-401. Springer, Berlin. BREWER, R . G . & SPENCER, O . W . ( 1969) A note on the chemical composition of the Red Sea brines. In; Hot Bii.CKER,

Brines and Recent Heavy Metal Deposits in the Red Sea

(Ed. by E.T. Degens & D.A. Ross) , pp. 174- 179. Springer, Berlin. BuruzovA, G . Y u . ( 1984a) Mineralogy and certain aspects of genesis of metalliferous sediments in the Red Sea, Communication 1. Litho!. Miner. Resources 2, 3 -23. B uruzovA, G . Y u . ( 1984b) Mineralogy and certain aspects of genesis of metalliferous sediments in the Red Sea, Communication 2 . Litho!. Miner. Resources 4, 11-32. B uTUZOVA, G.Yu. ( 1985) Singularities of hydrothermal­ sedimentary ore genesis in the Rift Zone of the Red Sea. Litho/. Miner. Resources 5, 39-55.

G. Yu. But uzova et al.

72

Metal Deposits in the Red Sea.

CHUKHROV,

F.V.,

L . P . , GORSHKOV, A . I . & ( 1975a) Beta-hydroxide of iron and

ERMILOVA,

BuGELSKI, Y u . Y u .

akaganeite. In: 1-!ypergenic Oxides of Iron in Geological Processes (Ed. by N . V. Petrovskaya) , pp. 6 1 -70. Nauka, Moscow. CHU KHROV, F.V . , ERMILOVA, L.P. , GORSHKOV, A . l . , ZHUKHLISTOV, A . P . , SIDORENKO, O . V . , ZVYAGIN , B . B . , B E LYATSKJ, V . V . , SAPOLNOVA, L.P. & KHOKHLOVA, M . M . ( 1975b) Experimental data o n the conditions o f iron oxide formation (Ed. by N . Y . Petrovskaya), pp. 1 1 -33. Nauka, Moscow. CHU KHROV, F . V . , GORSHKOV, A . I . , D RJTS, V . A . , SHTERENBERG, L . E . , SIVTSOV, A . V . & SAKHAROV, B . A . ( 1983) Mixed-layered minerals asbolane-buserite and asbolanes in oceanic Mn-Fe concretions. lzv. AN SSSR (Ser. geol. ) 5, 9 1 - 100. CHU KHROV, F.Y . , GoRSHKov, A . l . , DRITS, V.A . , SivTsov , A . V . , UsrENSKAYA, T. Y u . & SAKHAROv B .A . ( 1984) Structural varieties of buserite. Izv. AN SSSR (Ser. geol . ) 10, 65-74. CHU KHROV, F.V . , SAKHARov, B . A . , GoRSHKov, A . I . , D RJTS, V . A . & BARJNOV, N . N . ( 1987) A new mixed­ layered phase of oceanic Fe- Mn nodules. Litho!. Miner. Resources 5, 1 12- 120. DEGENS, E.T. & Ross, D . A . ( 1969) Hot Brines and Recent Metal Deposits in the Red Sea. Springer, Berlin, 600pp.

Springer, Berlin, 600 pp. J.P. & BISCHOFF, J.L. ( 1973) New data on the stratigraphy, extent and geologic history of the Red Sea geothermal deposits. Econ. Ceo!. 68, 553 -564. HARTMANN, M. ( 1979) Untersuchungen von suspendieren Material in den hydrothermal Laugen des Atlantis- l l­ Tiefs . Ceo!. Rund. 62, 742-754. HOLM, N . G . , WADSTEU , T. & DOWLER, U . l . ( 1982) �­ Fe00H (akaganeite) in Red Sea Brine. Etud. Ceo!. 38, 367 - 3 7 1 . MANCEAU, A . , GoRSHKOv, A . I . & DRJTS, V . A . ( 1990) Structure of Fe and Mn hydrous oxides. I. Crystal chemistry of Mn, Fe, Co and Ni in Mn hydrous oxides by X-ray absorption spectroscopy and electron diffraction. Amer. Mineral. (submitted ) . MISSACK, E . A . ( 1988) Mineralogy a n d phase relations of the massive sulphides and metalliferous sediments of the axial rift valley, Red Sea. Heidelberger Geowissen­ Schaftliche Abhandlungen 23, 2 13pp. MuRRAY, G.W. ( 1979) Iron oxides. In: Marine Minerals , Short course notes, Vol. 6, pp. 47- 107. Mineralogical Soc. Am. , Washington. SHANKS, W . C . III ( 1983) Economic and exploration signifi­ cance of Red Sea metalliferous brine deposits. In: Unconventional Mineral Deposits , pp. 1 57 - 1 7 1 . Am. Inst. Min. Eng. HACKEH,

Spec. Pubis int. Ass. Sediment. (1990) 11,73-88

Mineoka Umber: a submarine hydrothermal deposit on an Eocene arc volcanic ridge in central Japan A. I I J I MA*, Y. WATANABE*, S. 0 G I HA RA* and K. YA M A ZA K It *Geological Institute, University of Tokyo, Hongo 7-3-1, Tokyo II3, Japan;t Mitsui Coal Mining Company, Muromachi 2-1-1, Nihonbashi, Tokyo 103, Japan

ABSTRACT

A strata-bound iron-manganese umber, extending for 2 km along strike, overlies the top surface of an Eocene submarine tholeiitic pillow lava of the Mineoka terrain in the southern Boso Peninsula, 70 km southeast of Tokyo. The Mineoka Umber is divided into lower metalliferous and upper argillaceous segments, changing upwards gradually to ferruginous, spicule-rich shale. The metalliferous umber contains 41-54 wt% F�03 and 8·0- 16·8 wt% Mn02 + MnO, comprising massive aggregates of very fine goethite, amorphous calcic manganese oxides and pyrolusite. The Mineoka Umber formed during submarine hydrothermal activity following basaltic volcanism. Direct evidence of the hydrothermal origin is the discovery of an umber-filled pipe, a conduit for hydrothermal water, within the pillow lava beneath the strata-bound umber. Away from this conduit, the MnO : Mn02 ratio in the strata-bound umber decreases, reflecting the redox potential of the umber formation, and thus the content of pyrolusite increases. The high concentrations of rare earth elements and the strong negative cerium anomaly in the umber are also explained by the submarine hydrothermal origin. Calcites filling pores 3 and contraction cracks in the pipe umber have 61 C and 6180 values of -8·5 to -10·6%o and -14·3 to -20-4%o PDB, respectively. These values suggest precipitation from heated Eocene seawater at 55-68°C. The metal-carrying hydrothermal water was probably much hotter than the calcite­ precipitating water. Abundant spicules in the overlying shale are thought to represent a school of sponges that fed on the nutrient-rich water. The Mineoka Umber accumulated at the foot of an Eocene arc volcanic ridge in the supra-subduction zone off the Japanese continental arc.

INTRODUCTION

(Robertson & Boyle, 198 3). T heir depositional setting is still controversial. The Cyprus Umbers were once considered to have formed on the T roodos Oceanic Ridge; their modern analogue is a metalliferous red clay on the East Pacific Rise (Eiderfield et al. , 197 2; Robertson & Hudson, 1973; Robertson, 1975; Robertson & Fleet, 1976). Robertson & Fleet (1986) have reasoned that metal­ liferous sed iments from the Oman Ophiolite as well as the Cyprus Umbers formed on a volcanic ridge above the subduction zone. However, Karpoff et al. (1988) considered the Oman metalliferous sedi­ ments to have a spreading oceanic ridge origin. The Mineoka -Setogawa-Kobotoke Tectonic Belt, which comprises extensively folded and faulted marine strata of Palaeogere to middle Miocene age

T he Mineoka Umber deposit is mainly composed of manganese oxides and hydrated ferric oxides. A short note by T asaki et al. (1980) reported the occurrence of the umber from a roadside cut along the Skyline Road of the Mineoka Hills in the Mineoka terrain of the southern Boso Peninsula. Another hematitic umber deposit was reported briefly by lijima et al. (1981) from Setodani in the Setogawa terrain of central Shizuoka, the western portion of the Mineoka- Kobotoke-Setogawa Tectonic Belt (Fig. 1). T he two umber deposits are closely associated with Eocene submarine b asaltic pillow lavas and they are considered to be related to submarine hydrothermal activity following the b asaltic volcanism. Similar metalliferous sediments occur in the Cretaceous of the Tethys region Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

73

A. Jijima et al.

74

141

140

139

36

TOKYO

35 -

0

I' 138

I

I=======:Oi50

"'

c

I f

I C

�m

Fig. 1. Locality map. Strata and rocks of the Mineoka-Kobotoke-Setogawa Tectonic Belt are hatched. Locality of the

Setogawa Umber marked by a cross.

and intrusive ultramafic rock masses, developed from an arc volcanic ridge and a forearc basin in the arc­ trench gap on the Pacific Ocean side of central Japan (Watanabe, 198 9). Recently a strata-bound umber has been excavated at two quarries of the Chiba Kenzai Industrial Company in the Mineoka Hills, within 2 km distance from the original locality re­ ported byTasaki et al. (1980). Its occurrence, mineral assemblage, chemical composition and carbon and oxygen stable isotopic composition are described in this paper. Furthermore, its origin and site of deposition are discussed.

GEOLOGICAL SETTING Stratigraphy

The Mineoka Hills are situated in the eastern portion of the Mineoka-Kobotoke-Setogawa Tectonic

Belt. Here Palaeogene and Lower Miocene marine strata of the Mineoka Group are extensively dis­ turbed by tectonic movements and by intrusion of ultramafic rocks. The Mineoka Group is subdivided into four stratigraphic formations as shown in Fig. 2. T he lowest Kamogawa Formation, more than 200 m thic k , is mainly composed of pillow lavas, pillow breccia and massive lavas of tholeiitic, picritic and alkali basalts. A dacitic tuff brecc ia to vitric tuff, with a thickness of 60 m, is interbedded with the basalts. Middle Eocene nannofossils, such as Coc­ colithus eopelagicus and Reticu/ofenestra cfr. um­ bilica, were found in interpillow limestone in the pillow lava at Arayashiki on the coast of Kamogawa (Watanabe, 198 9). T he Shirataki Formation, up to 250 m thick, represents a hemipelagic biogenic facies. Its lower and midd le parts consist of. bedded calcareous quartzose c hert, which originated from calcareous diatomite, and bedded siliceous micritic limestone with an interc alation of 30 m thick, silicic

Mineoka Umber, Japan

AGE

THICKNESS

FORMATION

HATCHO Fm.

:;:::::

HEGURI Fm.

--- - - - ---- - 1 - ------ 1----- -- - 1------- 1------- ----- --1----- -- - - - - --

LITHOLOGY

(m)

FAULT

EARLY MIOCENE

75

1000

50

300

Flysch

Siliceous mudstone

Glauconitic sandstone

.......

OLIGOCENE

300

SHIRATAKI Fm.

Bedded chert and micritic limestone Silicic tuff (30 m)

'-l\/\./\1\ LATE EOCENE FAULT

6.5 1-2.5 MIDDLE EOCENE

KAMOGAWA Fm.

--·raul

r:-:: pault/ \ 1 '\

\./'-/'\./"\/

80

Chocolate shale MINEOKA UMBER Pillow basalt

60

Silicic tuff

50

Pillow basalt

FAULT

Fig. 2. Columnar section of the Mineoka Group in the Mineoka terrain.

vttnc tuff. Its upper 80 m thick part grades into b edded siliceous shale. L ate Eocene to early Oligocene nannofossils such as Coccolithus pelagicus and Dictyococcites cfr. bisectus were collected from the lower micritic limestone at Shirataki, while Theocotyle sp. nov. of late Oligocene radiolaria was found in the upper siliceous shale (Iijima et al., 198 4). Latest Eocene planktonic foraminifera were also reported from the calcareous chert at Shirataki (Suzuki et a!. , 198 4). Although the above two for­ mations are in contact with each other at thrust faults, the Shirataki Formation probably overlies the Kamogawa Formation, as inferred from the micro­ fossil biostratigraphy. The Shirataki Formation is conformably overlain by the siliceous mudstone of the 50-300 m thick Heguri Formation, containing early Miocene radiolaria. Glauconitic sandstone,

less than 1 m thick, occurs locally at the b ase of the Heguri Formation. The Mineoka Group terminates with a non-volcanic sandy turb idite facies of the Hatcho Formation , more than 1000 m thick, which contains early Miocene radiolaria. Depositional environment

T he Mineoka and Setogawa Umbers were deposited at the foot of the Eocene submarine volcanic ridge off th_e Japanese continental arc. Silt- to sand-sized terrigenous grains were not derived from the conti­ nental arc during the umber deposition. A glau­ conitic sandstone bed is intercalated between bedded chert of the Shirataki Formation and siliceous mud­ stone of the Heguri Formation. The lowermost Miocene glauconitic sandstone contains 20-40 vol%

A. Iijima et a!.

76

authigenic glauconite pellets and siliceous clay matrix. This sandstone and the glauconitic sand­ stones at the base of the Miocene siliceous sediments in the northeastern Honshu arc ( Iijima et a!., 198 8) suggest an offshore bank environment of 50-500 m water depth. Late Eocene to Oligocene hemipelagic, biogenic, calcareous and siliceous sediments of the Shirataki Formation, as well as the Mineoka U mber, probably acc umulated at the foot of the volcanic ridge at depths greater than the offshore bank. A volcanic island, which is represented by massive tholeiite lava flows with clinkers and an overlying basaltic boulder conglomerate, existed near Heguri and Arakawa, about 20 km west of the Mineoka Umber. T hus, open ocean water depths were not reached.

OCCURRENCE AND SAMPLE DESCRIPTION

Figure 3 shows the geological map of the Mineoka Hills near Sengensan and Otsukayama, where the Mineoka Umber is distributed. Strata of the Mineoka Group are sliced into several thrust sheets. The umber is observed at three localities near the ridge of the Mineoka Hills (Fig. 3). Locality 1 reported by

Tasaki et al. (1980) is at a roadside cut on the southeastern side of Otsukayama along the Mineoka S kyline Road. This umber is disturbed by faults. Locality 2 at the Sengensan Quarry is the site where the umber is best observed, in three trenches. Locality 3 at the Iimor iyama Quarry is the place in which field evidence for the hydr othermal origin of the umber was obtained. However, the umber has already been covered by mine waste and can no longer be seen at localities 2 and 3. The Mineoka Umber directly overlies the pillow basalt of the Kamogawa Formation. The contact was best ob­ served on the cut-faces of the trenches at locality 2, where all strata are overturned toward the south (Fig. 4a, b). The strata-bound umber with a thickness of 2200 mm covers the uneven surface of the pillow lava. At the contact, the pillows are oxidized through a depth of approximately 1000 mm and they change colour from dark green to reddish brown. In con­ trast, the umber is gr adationally over lain by c hocolate-brown, sponge spicule-rich ferruginous shale with a thickness of over 5000 mm. The top of the shale is c ut by a thrust fault where it is in contact with a younger light-grey sandstone. At locality 3, the top of the 1600 mm thick umber is in faulted contact with a sheared pillow basalt. Elsewhere, sheared umber and overlying chocolate-brown shale

Early Miocene

Fig. 3. Geological map of the Mineoka Hills in the environs of Sengensan and Otsukayama, showing localities 1-3 of the

basalts of the Kamogawa Formation; S Mineoka Umber. Basalt masses encircled by broken line are landslide blocks. K bedded chert and micritic limestone of the Shirataki Formation with a silicic tuff interbed; Gl glauconitic sandstone at the base of the Heguri Formation; hatched serpentinite; stipple younger sandstone. =

=

=

=

=

Mineoka Umber, Japan

77

(a)

Fig. 5. Cross-section of the umber-filled pipe with white

(b)

Fig. 4. Photographs showing the Mineoka Umber exposed

on the cut-faces of the Sengensan Quarry (locality 2) . (a) Overturned pillow basalt (B), umber (U), chocolate­ brown shale (S), thrust (arrow), and younger sandstone (Y). Scale is 1 m. (b) Enlargement of umber-basalt contact (arrow) in (a).

calcite veinlets within pillow basalt, about 1 m below the strata-bound umber, locality 3. Hammer is 30 em length.

p illow lava about 1 m beneath the bottom of the 1600 mm thick strata-bound umber at locality 3 of the Iimoriyama Quarry (Fig. 5). The cross-section of this ore body is almost circular with 480 mm dia­ meter. In its outer part it shows radial and concentric fr actures. White calcite precip itated in veinlets and in contraction cracks which are probably due to dehydration of the umber. In its inner par t, calcite fills micropores of the umber. This occurrence suggests that the calcite is almost coeval with umber formation. As a whole, the umber appears to fill a p ip e standing nearly perpendicular to the contact between the strata-bound umber and the pillows. T he umber is not brecciated but massive: therefore the pipe was a hydrothermal conduit, not just a filler from above.

METHODS

were recognized within four small pits along the east-west strike by the Mineoka Skyline Road b e­ tween localities 1 and 2. Consequently, the umber at these localities is considered to represent one single bed. This would mean that the Mineoka strata­ . b ound Umber extends for at least 2 km along strike. The Mineoka Umber is generally dull in lustre, massive and structureless. A t locality 2 of the Sengensan Quarry however, several intercalations of steel-grey, metallic-lustred manganiferous bands, 5-10 mm thick, occur in the basal 600 mm thick segment of the umber. Similar b ands are also r ecognized at locality 1. It is very difficult to p repare thin sections because the umber easily disintegrates when in contact with water. A round-shaped umber body occurs within the

Wet c hemical analyses were made for specimens collected from localities 2 and 3. Sampling positions are shown in Fig. 6. Concentrations of minor and trace elements were obtained by XRF analysis using the pressed-powder-disc method. Mineral identifi­ cation was p erformed by ordinary X-ray powder diffraction (XRD) analysis. Fracture surfaces of some chips that were taken from the metalliferous umber at localities 2 and 3 were examined under a scanning electron micro­ scope (SEM). Semiquantitative c hemical analysis of pyrolusite and amorphous manganese oxides in the umber was performed on a JEOL 840 SEM with electron dispersive system. Instrumental neutron activation analysis (INAA )

78

A. Iijima et al.

LOCALITY +2 No. I w 1< ...J 0 (.) 0 I (.)

a: w aJ ::;: :l < :.:: 0 w z ::;:

>w >< ...J (.) (/) :l 0 a: w LJ.. ...J ...J < 1w ::;:

LOCALITY +3 (INTERVAL)

Sh-2

(450-460)

Sh-1

(230-240)

2-6

(205-215)

2-5

(170-180)

2-4

(120-130)

2-3 2-2

2-1

Bc,Bm 3::

0 ...J ...J Cl.

1...J < (/) < aJ

No.

(INTERVAL)

3-4

(140-150)

( 75- 85)

3-3

( 75- 85)

( 50- 60)

3-2

( 50- 60)

10- 20)

3-1

10- 20)

FAULT

Ocm

Ocm

Fig. 6. Columnar sections of the UMBER PIPE

was undertaken for each specimen collected from the lower metalliferous umber (No. 2-2), the upper argillaceous umber (No. 2-5) and the basal part of the overlying shale (No. Sh-1) at locality 2 of the Sengensan Quarry. The specimens were irradiated for neutron activation in the TRIGA 2 nuclear reactor at Rikkyo University at the following con­ 2 2 dition: thermal neutron flux 1 x 101 n/(cm S) and irradiation time 12-24 h. Gamma-ray spectra were measured with a Ge(Li) detector at the Radio­ isotopic Centre, University of Tokyo. Stable carbon and oxygen isotopic compositions of sparry calcites in the umber-filled pipe at locality 3 were analysed on a Finnigan MAT DELTA-E mass spectrometer at the Geological Institute, University of Tokyo. This was done to estimate the temperature of hydrothermal water from which the manganese oxides precipitated. For comparison, the isotopic composition of calcites in late Eocene micritic lime­ stone of the Shirataki Formation at Shirataki was analysed. The precision is within 0.02%o and 0.04%o for the <513Cr08 and <5180r08 values, respectively.

Mineoka Umber at localities 2 and 3, showing sample numbers and sampling positions for various analyses.

RESULTS Chemical composition and mineral assemblages

The results of chemical analyses and the mineral assemblages are shown in Tables 1 and 2 and Fig. 7. At locality 2, the lower 1400 mm thick segment of the 2200 mm thick umber is metalliferous and con­ tains more than 50% ferric oxide and manganese oxides in total, and 70% in its basal part including the steel-grey, metallic-lustred bands. At locality 3, the 1600 mm thick umber is metalliferous, containing a total of 51-59% Fe203 and manganese oxides. In the metalliferous segments, ferric oxide consists almost exclusively of hydrous goethite. At locality 2, Mn02 predominates over MnO, and the MnO: Mn02 ratio tends to increase upward from 0·05 to 0·15. In contrast, MnO predominates over Mn02 at locality 3, except in the uppermost part. The pipe-filling umber itself however shows low MnO: Mn02 ratios (0·21: 0·22) and has a similar chemical composition when compared with the metalliferous segment of locality 2. The only

79

Mineoka Umber, Japan , w

� ;i

(em)] 450

Oz :s � ():?:

��

1

250

()(!)

a: w (!) :::2 ::J <{ :>::: 0 w z :::2

�

><{

Ni+Co.f.Cu

200

_J

() 150 (/) ::J

.

-

.

-

-

.

.

. .

� 100 <{ Iw :::2

Zr 50 0

.

.

. . -

.

. .

.

. . · - -

- - -

Zn

w

lL _J _J

- . -

10

20

30

40

0 50 (wt.%)

v

� 500

800 (ppm)

Fig. 7. Stratigraphic distribution of element contents and ratios for the Mineoka Umber at locality 2.

exception is the high CaO content that results from calcite in cement and veinlets. Pyrolusite is the only crystalline manganese oxide phase detected on the diffractograms of the Mineoka Umber. According to Tasaki et al. (1 980), pyrolusite is the main con­ stituent at locality 1. At localities 2 and 3 however, most manganese oxides in the metalliferous umber are present in an amorphous phase, except for the appearance of a weak X-ray reflection at 28·5° (28 CuK) for pyrolusite in the steel-grey, metallic­ lustred bands at localjty 2. Here, the concentrations of Mn02 and Fe203 gradually decrease upwards together with the water content, whereas other components such as Si02, Al203 and alkalis gradually increase. Small amounts of quartz, montmorillonite and illite were detected in the metalliferous umber. The upper 8 00 mm thick segment of the 2200 mm thick umber at locality 2 is argillaceous, regardless of its dark-brown colour. The concentrations of iron and manganese oxides appear to decrease abruptly to less than 15% at the boundary between the lower metalliferous and the upper argillaceous segments. Ferric oxide accounts for almost all of the iron, although goethite was not detected. Mn02 dis­ appears, whereas the content of MnO is almost constant in the upper segment from the top of the lower metalliferous segment (1- 37-2-06% ). In con­ trast, most other components , with the exception of

CaO and P205, are much more abundant in the argillaceous segment than in the metalliferous seg­ ment. The high contents of Si02 and K20 are par­ ticularly characteristic. Quartz, illite and chlorite are the main constituents of the upper argillaceous umber. Quartz does not occur as detrital grains but as authigenic aggregates that originated from sili­ ceous organisms, such as sponge spicules, radio­ larian skeletons and possibly diatoms, which are transformed to quartz probably through opai-CT during burial diagenesis. At locality 3 the upper argillaceous segment is missing, probably due to the fault at the top of the umber. The concentrations of minor elements in the strata­ bound umber at locality 2 are generally low, as shown in Table 1 and Fig. 7. The copper, vanadium and zinc contents decrease upwards; they decrease rapidly at the boundary between the lower metal­ liferous and upper argillaceous segments, corre­ sponding to the contents of ferric oxide and manganese oxides. In contrast, the zirconium con­ tent increases upward. Values of (Ni+Co +Cu)x 10 decrease upwards , resulting from the generally lower copper concentration in the higher parts of the section. The basal part of the overlying chocolate-brown ferruginous shale has a chemical composition similar to the upper argillaceous umber. The composition of the upper part of the shale is comparable to that of

00 0

Chemical composition and mineral assemblage of the Mineoka Umber deposit (2-1 to 2-6), the underlying pillow basalt (Ba-c and Ba-m), and the overlying chocolate-brown shale (Sh-1 and Sh-2) at locality 2, the Sengensan Quarry in the Mineoka Hills

Table l.

Si02 (%) Ti02 AhOo Fe203 Fe O Mn02 MnO MgO CaO Na20 K20 H20 ( - ) H20 ( + ) P20s Total Mn0+Mn02 Fe203 MnO -Mn02 Ba (ppm) Co Cr Cu Ni Rb Sr Th* U* v

Zn Zr

2-4

Ba-c

Ba-m

2-1

2-2

2-3

47·37 1·83 14·79 5·14 4·99

47·32 1·67 13·67 7·54 3-40

0·22 7·38 10·26 2·79 0·33 6·75 2·62 0·14

0·19 7-10 10·12 3·40 0·96 4·71 0·19 0·19

8·61 0-40 4·31 54·27 <0·1 15·52 0·85 1·30 1-07 0·13 0·79 11·70 0·89

9·76 0·38 6·01 50·91 <0·1 15·91 0·93 1·39 1·39 0·17 0·93 0-47 11·13 1·06

19·76 0·47 7·25 44·13 <0·1 9·84 0·59 1·87 2·05 0·26 1·81 0·70 10·02 1·55

21·53 0·50 7·96 41·82 <0·1 9·58 1-43 1·98 2·35 0·27 1·86 0·32 9·96 1-43

100·61

100·37

100·34

100·54

100-40

100·09

0·02

0·02

0·30

0·33

0·24

0·27

0·055

0·058

0·060

0·149

OAO

769 68 49 502 249 108 206 215 224 70

880 56 56 464 184 4 236 2 9 216 215 81

929 77 77 457 150 18 176

939 79 79 436 147 17 176

190 227 107

191 229 107

2-6

Sh-1

Sh-2

50·52 0·68 15·73 12·01 <0·1

54-48 0·82 17-08 9·69 <0·1

52·86 0·59 17·33 8-48 <0·05

45·61 2·04 16·51 12-48 1·74

2·06 3-48 2·34 0·62 3·98 1-10 6·21 0·84

1·37 3·35 1·32 0·70 4·15 0·72 5·66 0·38

1·25 2·74 3-01 0·68 3·85 2·59 6·29 0-47

0·19 3-06 8·26 2·97 1·26 1-45 4-45 0·26

99·67

99·82

100·19

100·28

0·17

0·14

0·15

0·02

2-5

928 38 38 266 262 103 231 7 4 121 175 163

853 120 120 164 210 127 184 125 153 174

18 3

::t. ...... ..:::·

§' I:> �

�

Table

1. (continued)

Ba-c

Ba-m

2-1

2-3

2-4

+ + + + + + +

2-5

2-6

218 112 299 45·3 16·7 16 16·3 2·05

624 44 750 123 19·9 18 38·1 4·90

La* Ce* Nd* Sm* Eu* Tb* Yu* Lu* Goethite Pyrolusite Amorphous Mn oxides Smectite Chlorite Illite Quartz Plagioclase Olivine Cpx.

2-2

+ +

+

+ +

+ +

+ +

+

+ +

Sh-1

Sh-2

94·8 165 120 22·2 5·19 4·6 7·75 1·19

�

s·

"' C) ;:>;.,

� o-

+

"' _..,

+

.......

� ., + + +

+ + +

+ + +

+ + +

;::s

+ + +

* INAA analysis. Other minor and trace elements are analysed by XRF.

co

82

A. Jijima et at.

2. Chemical composition and mineral assemblages of the Mineoka Umber deposits (3-1 to 3-4) and the pipe-filling umber (Pu-o and Pu-i) at locality 3, the l imoriyama Quarry in the Mineoka Hills. Those of the Setogawa Umber deposit (S-U) and the host shale (S-sh) are also shown

Table

Pu-o

Pu-i

3-l

3-2

3-3

3-4

S-U

S-sh

Si02 (%) Ti02 Alz03 Fe203 FeO Mn02 MnO MgO CaO Na20 KzO HzO ( ) HzO (+) Pz05 NiO

14·12 0·53 6·64 45·61 <0·1 8·79 1·87 1·62 3·31 0·06 6·46 9·59 6·75 0·87 0·18

10·63 0-41 6·11 48·75 <0·1 7-42 1·61 1·18 6·51 0·06 0·20 11·03 5·02 1·13 0·12

13·03 0-45 7·24 47·66 <0·1 4·00 5·99 1·77 3·39 0·03 0·53 3·47 11·27 1·57

8·27 0·26 5·66 44·17 <0·1 5·97 9·35 1·23 2·24 0·03 0·30 11-00 10·88 0·94

9·21 0·36 6·63 42·98 <0·1 4·26 8·27 1·57 2·73 0·03 0·62 12·03 10·92 0·96

12·36 0·41 7·77 45·63 <0·1 5·50 4·26 1·85 1·90 0·15 0·41 6·96 11·77 1·05

21·04 0-45 9·74 45·65 5·39

53·25 0·71 1 3·52 15·78 2·74

0·20 3·96 5·98 0·31 0·25 0·45 3·71 2·96

0-48 2·87 1·03 1 -19 2·43 1·16 4·07 0·53

Total

100-48

100·28

100·50

100-40

100·67

100·45

100·09

99·76

0·23

0·19

0·21

0·35

0·29

0·21

-

Mn0+Mn02 Fez03 Cr (ppm) Ni Goethite Hematite Pyrolusite Amorphous Mn oxides Smectite Chlorite I llite Quartz Calcite Plagioclase

21

15

23 905

22 503

21 518

35 240

+

+

+

+

+

+

+ +

+ +

+

+

+

+ +

+

+

+

+

+

27 188

56 156

+

+ +

+ + + +

Fig. 8. Scanning electron

micrograph of pyrolusite in the steel-grey, metallic-lustred band in the metalliferous umber. Sample No. 2-2 from locality 2. (A) Pyrolusite crystals. (B) Microcrystalline aggregates of pyrolusite showing the same dimensions as the spherular aggregates of amorphous calcic manganese oxides.

Mineoka Umber, Japan

the underlying pillow basalt: illite, chlorite and small amounts of detrital plagioclase derived from basaltic material. Most of the quartz originated from sili­ ceous organisms.

83 M n

Amorphous aggregate

SEM observation and EDX analysis

Pyrolusite

Crystalline manganese oxides were recognized in the steel-grey, metallic-lustred band at locality 2 (Fig. Sa). The crystals appear to have a tetragonal prismatic habit and are less than 10 !A-m in length. A semiquantitative energy dispersive X-ray (EDX) analysis of these crystals does not show elements other than manganese (Fig. 9). Based on the above evidence and XRD analysis the crystals are identified as pyrolusite. Pyrolusite sometimes occurs in small voids among the amorphous aggregates of manganese oxides. Microcrystalline aggregates of pyrolusite frequently show dimensions equivalent to the spherular aggregates of amorphous manganese oxides (Fig. Sb).

c M

p

M Pyrolusite crystal

p

Amorphous manganese oxides with todorokite-like composition

Two morphological types of amorphous aggregates of manganese oxides were observed under the SEM (Figs 10a,b). One type is a lepisphere-like, spherular aggregate with a diameter of 10-15 !A-m. The spherular aggregate consists of micron-scale curly ribbons or meshes, resembling todorokite in deep-sea manganese nodules reported by Iizasa (1988). The other type is a wafer-like aggregate

Fig. 10. Scanning electron

micrograph of aggregates of amorphous calcic manganese oxides in the metalliferous umber. Sample No. 2-1 of locality 2. (A) Spherular aggregates. (B) Wafer-like aggregates.

M n

p

5. 020

Fig. 9. Energy dispersive X-ray semiquantitative analysis

of the Mineoka Umber.

A. lijima et a/.

84

which consists of septa that are arranged subparallel to each other in intervals of less than 5 r-tm. This type of aggregate is rather uncommon when compared with the spherular aggregates. The semiquantitative EDX analysis reveals that both types of amorphous aggregates have the same chemical composition. As shown in Fig. 8, the amorphous aggregates consist mainly of manganese with a significant amount of calcium (several per­ cent). Small peaks of silicon, aluminium and mag­ nesium are probably at background level. The chemical composition of these aggregates can be estimated from the bulk composition of the pyrolusite-free metalliferous umber, assuming that each of the oxides results from the umber-forming constituent minerals (Table 3). It is estimated that approximately half of the water content is due to the presence of goethite, and that the remaining half is associated with montmorillonite. Therefore, the composition of the amorphous aggregates is roughly estimated to be 15·52% Mn02, 0·85% MnO and 1·07% CaO, which are normalized to 8 9·0% Mn02, 4· 9% MnO and 6·1% CaO. The CaO content is probably a maximum value, because small amounts of CaO may contribute to montmorillonite and apatite(?). This estimation is consistent with the result of the EDX analysis. The MnO: Mn02 ratio of the amorphous aggregates is variable, as can be seen in the values for the bulk composition of

different arrays (see Table 1). In the strata-bound umber and pipe-filling umber, the MnO: Mn02 ratio has a range from 0·21-1· 94. REE d istribution pattern

The result ofiNAA is shown in Table 1 and Fig. 11. The three specimens generally have a slightly heavy rare earth element (HREE)-depleted pattern. The concentrations of the lanthanides, except for cerium, decrease upwards from the lower metalliferous umber to the overlying shale through the upper argillaceous umber, and are much hjgher than those of the North American Shale Composite (Haskin & Haskin, 1966). In contrast, the concentration of cerium increases upwards, resulting in a strongly negative cerium anomaly for the Mineoka Umber. The REE pattern of the Mineoka Umber is very simjlar to that of the Cyprus Umber reported by Robertson & Fleet (1976), although the con­ centrations of the lanthanides are much higher in Mineoka than in Cyprus. Stable carbon and oxygen isotopic composition of associated calcites

The micritic calcites of the Shirataki limestone have 3 01 CroB values of +0· 9% and + 1·1%o (Table 4), suggesting a marine planktonic origin. In contrast,

Estimation of the chemical composition (in percentages) of amorphous calcic manganese oxides in the metalliferous segment of the Mineoka Umber at locality 2

Table 3.

Bulk composition of the metalliferous umber (sample No. 2-1) Si02 Ti02 Alz03 Fez03 FeO Mn02 MnO MgO CaO Na20 KzO HzO (+, -) PzOs

8·61 0·40 4·31 54·27 <0·1 15·52 0·85 1·30 1·07 0·13 0·79 12·20 0·89

Total

100·34

Essentially montmorillonite Montmorillonite Essentially goethite Essentially amorphous aggregates Essentially amorphous aggregates Montmorillonite Largely amorphous aggregates Montmorillonite Montmorillonite Goethite (6·1%) and montmorillonite (approximately 6·0%) ?

Composition of the amorphous calcic manganese oxides is roughly estimated as follows: Mn02 1 5·52 89·0 MnO 0·85 4·9 CaO 1·07 (maximum) 6·1 Total

1 7-44

100·0

85

Mineoka Umber, Japan 10000

w

Fig. 1 1 . The chondrite-normalized

concentrations of REEs in the metalliferous umber (1 sample No. 2-2), the argillaceous umber (2 sample No. 2-5) and the overlying ferruginous shale (3 sample No. Sh-1) at locality 2. The North American Shale Composite (N) is shown for comparison. =

=

=

Table 4.

1a: Cl z 0 :I: u

1000

w

100

--' 0..

1\

�\'/'IF� -----------\fl- ---

::;: < en

10

J .......

\

La

Ce

- - -Nd

� ------

-- -- -

� ' �

--

Sm

-

Eu

---·---

,__

�·

--- ---

Tb

1 2 3

N_

_____

Yb

Lu

Stable oxygen and carbon isotopic composition of calcites in the Mineoka Umber and the Shirataki limestone

013CPDB (%o)

01R0PDB (%o)

Temperature (0C)

Pore-cement calcite in the inner part of the umber pipe

-14·3

-9-4

60·1

Veined calcite in the inner part of the umber pipe (1) (2)

-17·9 -20-4

-10-4 -8·5

66·5 54·5

Veined calcite in the outer part of the umber pipe

-16-4

-10·6

67·9

1·1 0·9

-7·3 -10·6

Calcite in micritic limestone of the Shirataki Formation (1) (2)

the sparry calcites with a nearly pure composition in veins and cements of the umber-filled pipe have 613CPDB values of -14· 3 to -20·4%o which are much lower than those of the limestone (Table 4). These 613 C-depleted calcites precipitated in the pipe approximately 5 m below the seafloor and indicate a hydrothermal origin. The 6180p08 values of the micritic calcites are -7· 3 and -10·6%o, much lower than those of the older Tertiary marine planktonic fossils. The Shirataki limestone recrystallized at temperatures approximately between 80 and 120°C during burial diagenesis. This is inferred from zone III (analcime­ quartz) of the zeolitic burial diagenesis of the inter­ calated silicic vitric tuff (Iijima, 1986). The original oxygen isotopic composition of microfossil calcites most probably changed during recrystallization. The sparry calcites in the umber-filled pipe possess 0180ros values of -8·4 to -10·6%o (Table 4). No

significant differences in the oxygen isotopic com­ position of the calcites were recognized between cement and veins, nor between the inner and outer parts of the pipe. Temperatures of the hydrothermal water from which the calcites precipitated can be calculated from the 6180 values of the calcites, assuming that the hydrothermal water would be heated Eocene seawater with a 6180 value of -1·2%o SMOW (Savin & Yeh, 19 8 1), and that the calcites did not recrystallize in the course of diagenesis. The temperatures calculated are 55-68°C. DISCUSSION Hydrothermal origin

The aforementioned geologic occurrence of the Mineoka U mber strongly suggests formation during hydrothermal activity which followed middle Eocene

86

A. Jijima et al.

submarine basaltic volcanism. Direct evidence for the hydrothermal origin is the existence of the umber-filled pipe at locality 3 (the limoriyama Quarry), because the pipe undoubtedly acted as a conduit for the hydrothermal water. It is interesting that the thickness of the metalliferous umber is 1600 mm and more above the conduit, decreasing to 1200 mm at locality 2 (570 m southeast of locality 3). The REE patterns in both the lower metalliferous and upper argillaceous segments of the Mineoka Umber are characterized by a strong negative cerium anomaly. ln contrast, REE patterns in deep-sea iron-manganese nodules, particularly from greater than 3500 m depth, show a strong positive cerium anomaly (Piper, 1974). Oceanic deep waters, pelagic biogenic sediments and pelagic authigenic minerals such as phillipsite are cerium-depleted (Piper, 1974). Matsumoto et al. (1985) investigated the con­ centrations of REEs in Pacific pelagic sediments and pointed out that red and brown clays with very slow sedimentation rates in the central Pacific have normal or even slightly cerium-enriched patterns, whereas red metalliferous clays on the East Pacific Rise show a strong negative cerium anomaly. Matsumoto et al. attributed the strong negative cerium anomaly of the metalliferous clays to their submarine hydrothermal origin. We therefore interpret the strongly cerium­ depleted patterns of the Mineoka Umber to be indicative for a submarine hydrothermal origin. At least the basal part of the overlying chocolate-brown, spicule-rich and ferruginous shale seems also to be affected by the hydrothermal water, considering the high REE concentrations in this part of the section. There are also similarities in the REE pattern when compared with the umber, regardless of the slight negative cerium anomaly. Abundant spicules in the shale suggest that a school of sponges fed on the nutrient-rich warm water, which can be seen as additional support for a hydrothermal origin for the umber. The sparry calcites filling pores and contraction cracks in the umber pipe precipitated from hydro­ thermal water at 55-6 8°C, as calculated from their 6180 values. The temperature of the metal-carrying hydrothermal solution that preceded the calcite­ precipitating water was probably much higher (>100°C). The amorphous aggregates of colloidal calcic manganese oxides of the Mineoka Umber suggest rapid precipitation when the manganese­ enriched hot solution mixed with the cold seawater. The rate of sedimentation for the Mineoka Umber and the overlying chocolate-brown shale was prob-

ably much greater than the 18 mm/ 103 a for the hemipelagic biogenic sediments from the Shirataki Formation, because planktonic organisms such as radiolarian skeletons are rarely found, even in the shale. The pyrolusite of the steel-grey, metallic-lustred bands appears to have crystallized from the spherular aggregates of the amorphous manganese oxides, because a transitional morphology between the spherular aggregates and the microcrystalline pyro­ lusite was observed under the SEM (Fig. 8b). Pyrolusite generally forms under more oxidizing conditions when compared with the amorphous aggregates of calcic manganese oxides, which still contain variable amounts of MnO. The MnO: Mn02 ratio in the strata-bound metalliferous umber de­ creases from 0 77 to 1·94 at locality 3, where the pipe-filling umber exists, to 0·05-0·15 at locality 2, where small amounts of pyrolusite occur. Pyrolusite dominates at locality 1 (Tasaki et al., 1980), which is most distant from locality 3. It is therefore concluded that the conditions became more oxidizing with in­ creasing distance from the conduit at locality 3. The ratios between manganese and iron oxides in the metalliferous umber are comparable in the different localities: 0·24-0·33 at locality 2 and 0·19-0·35 at locality 3. Consequently, a separation of manganese and iron during precipitation has not been identified. ·

Site of d eposition

The Mineoka Umber was deposited on a submarine volcanic ridge during the Eocene. The ridge ex­ tended from the southern Boso Peninsula to central Shizuoka in the Mineoka- Kobotoke-Setogawa Tectonic Belt (Fig. 1). At Setodani, in the Setogawa terrain, a small lenticular body of ferruginous umber of 500 x 200 mm size occurs in a radiolarian black shale of the Takisawa Formation, about 10m above a basaltic pillow lava (Table 2). The Setogawa Umber consists of microcrystalline aggregates of hematite, chlorite and limited quartz, which suggest a diagenetic modification. The Setogawa Umber has also been interpreted to have formed by submarine hydrothermal activity following the basaltic volcanism (lijima et a/., 1981). There are two different theories for the ongm of submarine pillow basalts of the Mineoka­ Kobotoke-Setogawa Tectonic Belt: 1 accretion of the oceanic crust (Ogawa & Taniguchi, 1988); and

Mineoka Umber, Japan 2 an arc volcanic ridge. The following points favour the arc volcanic ridge theory: (a) the bulk chemical composition of the pillow basalt from the Kamogawa Formation matches that of the island arc tholeiites (Arai & Uchida, 1 978); (b) the distribution patterns of minor and trace elements in the tholeiite of the Kamogawa Formation and in the alkali basalt of the Setogawa terrain coincide with those of island arc basalts (Watanabe, 1989); (c) a dacitic tuff, >60 m thick, is closely associated with basalts of the Kamogawa Formation in the Mineoka Hills. On Kuroshima Isle at the base of the pier of the Kamogawa fishing port and in the north of Wada, it changes to a lapilli tuff/tuff breccia, suggesting that it erupted on the basaltic volcanic ridge ; (d) two tectonic blocks composed of crystalline schists and amphibolite crop out at the Kamogawa fishing port. The pelitic to psammitic biotite schist consists of biotite, quartz, microcline and plagioclase (Kanehira et al. , 1968), and its K/ Ar age is 38 Ma (Yoshida, 1974). Moreover, a large float of mylonitized and albitized biotite granite has recently been found on Kainagisa Beach in the south of the Kamogawa fishing port. The biotite schist and mylonitized granite are considered to have formed the basement of the arc volcanic ridge and to have been uplifted together with ultramafic rock masses. We therefore conclude that the Mineoka Umber accumulated on the arc volcanic ridge in the suprasubduction zone off the Japanese continental arc during the Eocene, when the Sea of Japan was not yet open, except for a late Oligocene embayment in the south (Iijima et al., 1988). A very similar setting is now postulated for the Troodos, Oman and Baer-Bassit settings. However they are primitive arcs built up before the genesis of major calc-alkaline edifices (Robertson & Fleet, 1986).

CONCLUSION

The Mineoka Umber, which is mainly composed of manganese oxides and hydrated ferric oxides, formed during submarine hydrothermal activity that followed basaltic volcanism. It was deposited at the foot of an arc volcanic ridge in the suprasubduction zone off the Japanese continental arc during the Eocene, when the Sea of Japan was not yet open. The temperature of the metal-carrying solution was probably much higher than the 55-68°C of the metal-free water from which calcite precipitated in pores and cracks of the conduit-filling umber.

87 ACKNOWLEDGEM ENTS

This study was partly supported by a Grant-in-aid for Cooperative Research (A) from the Ministry of Education, Science and Culture (Project No. 60303010). We are indebted to the Chiba-Kenzai I ndustrial Company for permission to collect the umber samples. We are grateful to S. Roy, B.R. Bolton and J.R. Hein for their invaluable dis­ cussion and comments at the lAS ISOSRMD Beijing meeting. Our thanks are due to J. Parnell, A.H. F. Robertson and B. Pracejus for critical reading of the typescript, H. Haramura for wet chemical analysis, H. Matsuda for isotopic analysis, R. Matsumoto for advice on interpretation of the isotopic compositions, and T. Fukuhara for preparing the typescript.

R E F E RENCES

ARAI, S. & UcHIDA, T. (1978) Highly magnesian dunite from the Mineoka Belt, central Japan. J. Japan. Ass. Min. Petrol. Econ. Geol. 73, 176-179 . ELDERFIELD, H . , GASS, I . G . , HAMMOND, A. & BEAR, L . M . (1972) The origin o f ferromanganese sediments associ­ ated with the Troodos Massif of Cyprus. Sedimentology 19, 1 -19. HASKIN , L.A. & HASKIN, M.A. (1966) Rare earths in European shale: a redetermination. Science 145, 507-509. lmMA, A. (1986) Occurrence of natural zeolites. Clay Sci. 26, 90-103. IuiMA, A. , MATSUMOTO, R. & IGUCHI, T. (1981) Occurrence and properties of the Setogawa 'Umber'. Abstracts Paper, Geol. Soc. Japan, 235. liHMA, A. , TADA, R. & WATANABE, Y. (1988) Devel­ opments of Neogene sedimentary basins in the North­ eastern Honshu Arc with emphasis on Miocene siliceous deposits. J. Fac. Sci. Univ. Tokyo , Section II , 2 1 , 417- 446. lUIMA, A., WATANABE, Y . & MATSUMOTO, R. (1984) Geo­ logic age of the Setogawa-Mineoka Tectonic Belt. In: Biostratigraphy and International Correlation of the Paleogene System in Japan (Ed. by T. Saito & H. Okade), pp. 69-74. Yamagata Univ., Yamagata. IlZASA, K. (1988) Metasomatism in manganese nodules. Bull. Sci. Univ. Tokyo 7, 21-24. KANEHIRA, K. , OKJ, Y . , SANADA s . , YAKOU, K. & ISHIKAWA, F. (1968) Tectonic blocks of metamorphic rocks at Kamogawa, southern Boso Peninsula. J. Geol. Soc. Japan, 74, 529 - 534. KARPOFF, A.M., WALTER, A.V. & PFLUMIO, C. (1988) Metalliferous sediments within lava sequences of the Sumail Ophiolite (Oman) : Mineralogical and geo­ chemical characterization, origin and evolution. Tec­ tonophysics , 1 5 1 , 223-245. MATSUMOTO, R . , MINAI, Y. & IIHMA, A. (1985) Manganese content, cerium anomaly, and rate of sedimentation as aids in the characterization and classification of deep-sea

88

A. Iijima et al.

sediments. I n : Formation of Active Ocean Margins (Ed. by N. Nasu). pp. 913-939. Terrapub, Tokyo. OGAWA, Y. & TANIGUCHI, H. (1988) Geology and tectonics of the Miura - Boso Peninsulas and the adj acent area. Mod. Ceo!. 12, 147-168. PIPER, D.Z. ( 1974) Rare earth elements in the sedimentary cycle: a summary. Chemical Ceo!. 14, 285-304. RoBERTSON, A.H.F. ( 1975) Cyprus Umbers: basalt­ sediment relationships on a Mesozoic oceanic ridge. J. Ceo/. Soc. Land. 131, 51 1-531. ROBERTSON, A.H.F. & BoY LE, ] .F. ( 1983) Tectonic setting and origin of metalliferous sediments in the Mesozoic Tethys. I n : Hydrothermal Processes at Seafloor Spreading Centres (Ed. by P.A. Rona) , pp. 595-663. NATO. Conf. Ser. , Plenum Press, New York. RoBERTSON , A.H.F. & FLEET, A.J. ( 1976) The origins of rare earths in metalliferous sediments of the Troodos Massif, Cyprus. Earth Planet. Sci. Letts 28, 385-394. ROBERTSON , A.H.F. & FLEET, A.J. ( 1986) Geochemistry and palaeo-oceanography of metalliferous and pelagic sediments from the Late Cretaceous Oman Ophiolite. Marine Petrol. Ceol. 3, 315-338.

ROBERTSON , A.H.F. & HuDSON , J.D. ( 1973) Cyprus umbers: chemical precipitates on a Tethyan ocean ridge. Earth Planet. Sci. Letts, 18, 93-101. SAVIN, S . M. & YEH , H . W . ( 1981) Stable istopes in ocean sediments. I n : The Sea. The Oceanic Lithosphere , Vol. 7 (Ed . by C. Emiliani) , pp. 1521- 1554. Wiley­ lnterscience, New York. SuzuKI, Y . , KoNDO, K. & SAITO, H. ( 1984) Latest Eocene planktonic foraminifers from the Mineoka Group, Boso Peninsula. J. geol. Soc. Japan 90, 497-499. TASAKI, K . , INOMATA, M. & TASAKI, K. ( 1980) Umbers in pillow lava from the Mineoka Tectonic Belt, Boso Peninsula (Short notes). J. geol. Soc. Japan 86, 413-416. WATANABE, Y . (1989) Evolution of the forearc basin of the Setogawa- Kobotoke - Mineoka Tectonic Belt, central Japan. Unpubl. PhD Thesis, Geological I nstitute, Univ. Tokyo. YosHIDA, Y. (1974) Discovery of foraminifers from the Mineoka Hills, Chiba. Chishitsu News, Ceol. Survey Japan , 233, 30-36.

Spec. Pubis int. Ass. Sediment. ( 1990) 1 1 , 89-108

Mineralogy, geochemistry and genesis of manganese-iron crusts on the Bezymiannaya Seamount 640, Cape Verde Plate, Atlantic l. M . V A R E N T S O V*, V . A . D R I T S*,

and

A .I. G O R S CH K O Vj

1 *Geological Institute of the USSR Academy of Sciences, 7 Pyzhevsky per. , 109017 Moscow, USSR; "1nstitut e of Ore Geology and Mineralogy of the USSR Academy of Sciences, 35 Staromonetny per. , 109017 Moscow, USSR

ABSTRACT

Manganese-iron oxyhydroxide encrustations overgrow and impregnate hydrothermally phosphatized Middle Eoce;1e limestones, which blanket the Bezymiannaya Seamount 640 (the Rocett Seamount) on the Cape Verde plate. In chemical composition, the manganese-iron crusts are transitional between hydrothermal and hydrogenetic types . The major minerals are iron vernadite and manganese feroxyhyte. The presence of goethite, mixed-layered asbolane-buserite, magnesium asbolane, and birnessite in the crusts is interpreted as a result of postdepositional transformations of the initial manganese-iron oxyhydroxide material.

INTRODUCTION

the Rocett Seamount) is situated about 750 km west- southwest of the rise of the Cape Verde Islands, a large volcanic structure of the Cape Verde plate composed of oceanic crust of early Cenozoic (Palaeogene) age. The base of the Bezymiannaya Seamount 640 lies at depths of 4500- 5000 m, and the top of the seamount is at 640 m. This rise is a submeridionally oriented block of oceanic crust about 74 km long. According to subsea photography and sample collection , the seamount surface is covered with moderately lithified limestones of lower Middle Eocene age. Moreover, the lime­ stones exhibit an increasingly shallow-water character towards the top of the seamount. The hydrothermal alteration of limestones irregularly increases in the same direction (recrystallizatio n , silicification, phosphatization, etc) . The intensity of formation of the manganese- iron oxyhydroxide crusts increases from the middle part of the slopes towards the top (Fig. 1 ) .

Manganese- iron oxyhydroxide crusts occur on the surface of seamounts, guyots, ridges and various rises on the ocean floor. There is a definite distinction between the manganese - iron oxyhydroxide crusts of hydrothermal origin and hydrogenetic origin , which is evident i n the geological settings o f the deposits and their structure, mineralogy and geo­ chemical characteristics (Crorian, 1976; Toth , 1980; Cronan et a/ . , 1 982; Varentsov et a/ . , 1983 ; Aplin & Cronan, 1985; Thompson et a/., 1 985; Lalou et a/., 1986; Carlo et a/ . , 1 987). The most common, how­ ever, are the manganese-iron encrustations formed as a combined accumulation of components of dif­ ferent genesis. An important problem in the miner­ alogy and geochemistry of oceanic manganese-iron ore formation is the objective and substantiated esti­ mation of the contribution of hydrothermal and hydrogenetic sources. The studies described here were based on materials collected during the first cruise of RV 'Akademik Nikolai Strakhov' and on the data of geological - geophysical studies on the Bezymiannaya Seamount 640. The samples were collected by a dredge and a shovel sampler. The Bezymiannaya Seamount 640 (on some maps: Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

METHODOLOGY

The samples were studied in thin section under the microscope, and by X-ray diffraction and other 89

90

I. M. Varentsov, V . A . Drits and A./. Gorschkov

m

STn39

15

5

25

35

45 47.41

km

lt'\�;e1h �2 �31tli141e¥1s

r 16 !II]y rz=lal-· _:_.=-Jgjv v v 11o

Fig. 1. Sublatitudinal lithological profile across the central part of the Bezymiannaya Seamount 640. Arrows show stations of sample collection (dredge). (1) Biogenic limestone: (2) biogenic limestone with relatively weak alteration; (3) altered limestone; (4) altered limestone, rudaceous; (5) altered limestone with manganese-iron oxyhydroxide crusts on bedding planes; (6) manganese-iron oxyhydroxide crusts; (7) modern coral structures; (8) foraminiferal sand; (9) silty mud; and (10) basalt.

physical methods of analysis (Varentsov et al., 1989). The study of mineral composition was much more effective using electron microdiffraction, in combi­ nation with microprobe energy dispersive X-ray (EDX) analysis. The chemical composition of samples was deter­ mined by classical wet chemical analysis combined with the plasma spectroscopy of small masses (about 0· 1 g) . Heavy metals and trace elements were de­ termined by emission spectroscopy. High concen­ trations of cobalt, antimony and silver were deter­ mined by instrumental neutron activation analysis.

GEOLOGICAL SETTING,

STRUCTURE,

AND MINERAL COMPOSITION

Three stations (34, 38 and 39) were selected for the study of m ineralogy and geochemistry of manganese - iron oxyhydroxide crusts and of changes in the substrate rocks (Fig. 1 ) . The description of samples, hauled at these stations, and their mineral compositions are given in the captions to Figs 2a,b and 3a,b. Moreover, the structural and crystallo­ chemical characteristics of the manganese- iron oxy-

hydroxide minerals discussed below are given in a previous paper (Varentsov et al., 1989 ) . 1 Station 34 was set up on the eastern slope of the Bezymiannaya Seamount 640 with coordinates 1 5°51-0'N, 36°07 ·0'W 1 5°50·0'N , 36°08·0'W; the depth interval was 2 100- 1400 m. Blocks of altered phosphatized limestone were torn off the parent deposit and collected; they are covered with a crust 50- 100 mm thick and intensively impregnated by manganese - iron oxyhydroxides. Samples 1 -34-D-11 1 5-(A) (Fig. 2a) and 1-35-D-1 1 5-(2) (Fig. 3a) were selected for detailed study of mineralogy and geochemistry as characteristic manganese -iron crusts and typical substrate rocks. 2 Station 38 (Fig. 1) is located at the top western part of the Bezymiannaya Seamount 640 with coor­ dinates 1 5°51-s'N and 36°09·7'W. Blocks of deeply altered bioclastic limestones were torn from the parent rock; they are up to 400 mm in size with an uneven lumpy surface covered with crust growths of manganese- iron oxyhydroxides. 3 Station 39 (Fig. 1) is at the top of the Bezymian­ naya Seamount 640. A plate-like block (200 x 700 mm) was broken off the parent deposit by a dredge; the block is composed of manganese - iron

Manganese- iron crusts, Bezymiannaya Seamount 640

(a)

91

1-34-D-1-115-A

Fig. 2. (a) Structure of manganese-iron oxyhydroxide crust on altered substrate, a recrystallized, phosphatized limestone.

Sample 1-34-D-1-115-(A), the Bezymiannaya Seamount 640. a, the upper finely botryoidal crust (40 mm), black manganese-iron oxyhydroxides with ochre (iron oxyhydroxides) and white cavities filled mainly with relict material residual after limestone dissolution . The material is mostly represented by manganese feroxyhyte, iron vernadite and subordinate quantities of goethite. b, relics of substrate represented by white recrystallized phosphatized limestone. c, black, dull, sooty manganese-iron oxyhydroxides impregnating substrate (40-80 mm) . They are represented mostly by iron vernadite, manganese feroxyhyte and subordinate amounts of goethite. The presence of relict patchy areas of the substrate is characteristic (see b ) . d, patches and lens-like areas of ochrous material which is a rather early product of substitution (b ) embedded in the mass of manganese-iron oxyhydroxides (c). They are represented by goethite, manganese feroxyhyte, an almost isotropic iron X-phase, probably vernadite, calcite, with admixtures of kaolinite, traces of chlorite, francolite and hydroxyl apatite. (b) Structure of crust of manganese-iron oxyhydroxides on altered substrate, a hydrothermally reworked (intensively phosphatized) limestone. Sample 1-39-D-126, the Bezymiannaya Seamount 640. a, the upper crust of manganese-iron oxyhydroxides with rough botryoidal surface (20 mm). The material contains mostly iron vernadite and manganese feroxyhyte with an admixture of goethite. b, a part of manganese-iron oxyhydroxide crust with microlayered structure (10-15 mm). Iron vernadite dominates with a somewhat subordinate amount of manganese feroxyhyte and admixture of goethite. c, a shiny, massive, dense, rather homogeneous material of manganese-iron oxyhydroxides (10-20 mm) composed predominantly of iron vernadite with lesser amounts of manganese feroxyhyte, admixture of goethite, and rather small quantities of mixed-layered asbolane-buserite. d, intensively reworked material of initial limestone almost entirely composed of phosphates; it is locally intensively impregnated and substituted by manganese-iron oxyhydroxides (20 mm). d-1, phosphate (hydroxyl apatite and francolite) interlayer intensively impregnated by manganese-iron oxyhydroxides (10 mm). e, the lower crust composed of loose sooty manganese-iron oxyhydroxides (20 mm). Iron vernadite and manganese feroxyhyte dominate with admixture of goethite and very small amounts of mixed-layered asbolane-buserite.

(a) u

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Fig. 3. (a) Distribution of values of ratios AI: Ti, Si: Ti, Mn : Ti, Fe: Ti and P: Ti in the components of a crust of manganese-iron oxyhydroxides and in the

altered substrate, an intensively hydrothermally phosphatized limestone. Sample 1-34-D-115-(2) (Table 1); the Bezymiannaya Seamount 640. Mineral composition: (1) The upper crust of manganese-iron oxyhydroxides. Manganese feroxyhyte and iron vernadite dominate with subordinate amounts of goethite and traces of quartz. (2) The lower crust of manganese-iron oxyhydroxides. The major components are manganese feroxyhyte and iron vernadite with subordinate amounts of goethite and admixture of mixed-layered asbolane-buserite. (3) Altered cream-coloured rock (phosphatized limestone) confined in the limestone mass. The material is represented by calcite and francolite with admixture of hydroxyl apatite. (4) Altered cream-coloured fragments of breccia (recrystallized phosphatized limestone with admixture of kaolinite and siliceous material). Major components are calcite with admixture of kaolinite, traces of mica, chlorite, francolite and hydroxyl apatite. (5) Phosphatized basalts, the Cruiser Seamount (Table 1). (6) Iron vernadite. (7) Manganese feroxyhyte. (8) Goethite. (9) Mixed­ layered asbolane-buserite. (10) Calcite. (11) Francolite. (12) Hydroxyl apatite. (13) Kaolinite. (b) Distribution of values of ratios AI: Ti, Si: Ti, Mn: Ti, Fe : Ti and P: Ti in the components of a crust of manganese-iron oxyhydroxides and in the altered substrate, an intensively hydrothermally phosphatized limestone. Sample 1-38-D-124; the Bezymiannaya Seamount 640. Mineral composition: (1) The upper crust of manganese-iron oxyhydroxides (2-15 mm). The major phases are iron vernadite, manganese feroxyhyte, magnesium asbolane with subordinate amounts of mixed-layered asbolane-buserite and admixture of goethite and traces of birnessite. (2) The lower crust of manganese-iron oxyhydroxides (2-15 mm). It is mostly composed of iron vernadite with subordinate quantities of manganese feroxyhyte and asbolane-buserite and admixture of goethite. (3) Light grey-cream-coloured material of the general mass of altered rock (intensively phosphatized limestone). The major components are francolite, hydroxyl apatite, admixture of calcite and probably farringtonite (?). (4, 5) As (3). (6, 7) Buff-coloured veinlets of phosphate pigmented by iron oxyhydroxides. The major components are hydroxyl apatite and francolite with probable admixture of hureauLite and brushite. (8) Iron vernadite. (9) Manganese feroxyhyte. (10) Magnesium asbolane. (11) Mixed-layered asbolane-buserite. (12) Goethite. (13) Birnessite. (14) Hydroxyl apatite and fancolite.

� ;::!

Q ;:

;;

0\

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\0 VJ

94

I. M. Varentsov, V.A. Drits and A.!. Gorschkov

oxyhydroxides (80-90% ). The middle part of the plate contains finely grained phosphatized rock with typical white, rose- and orange-coloured patches and local patches of unaltered bioclastic limestone (Fig. 2b). GEOCHEMISTRY

ganese-iron oxyhydroxide crust accumulations belong to deposits whose appearance was essentially affected by hydrothermal processes. At later stages, these deposits experienced a hydrogenetic influence, as distinctly shown in the trend of the continuum from hydrothermal deposits to hydrogenetic ones (Fig. 4).

Distribution of titanium, aluminium and silicon

The manganese : iron ratios

It has been established that in manganese - iron oxyhydroxide crusts of hydrogenetic origin (Ridout et al. , 1984; Aplin & Cronan , 1985; Hein et a!., 1988) the titanium content reaches 0·34-0·48% , whereas in the hydrothermal manganese - iron oxy­ hydroxides (Cronan, 1976; Toth, 1980; Varentsov et a/ . , 1983) the titanium concentration is no more than 0 · 1 % (at aluminium up to 0· 1 -0·3% ) . In the ana­ lysed crusts the content of titanium changes from 0·6 to 1 · 1 % and that of aluminium reaches 2·43% . In the light of these data, the higher titanium and aluminium values characterize them as residual from the dissolution of the substrate. This conclusion is on the whole also true for silicon (Figs 3a,b; Tables 1 and 2). There is a well-defined tendency for the intensity of accumulation of manganese- iron oxy­ hydroxide growths to increase towards the top of the seamount. The thickness of manganese -iron oxy­ hydroxide growths is directly controlled by the in­ tensity of hydrothermal alteration of limestone and its phosphatization which develops irregularly and by patches, as shown in Figs 2 and 3.

The manganese: iron ratios in oxyhydroxide growths vary within a limited range and normally are close to 1 · 0 (Tables 1 and 2; Fig. 5). In the studied samples the lower or bottom crusts are either slightly more ferruginous than the upper ones or insignificantly different. It should be emphasized that laterally the total manganese content of crusts increases towards the top of the seamount accompanied by the general rather deep substitution and intensive development of oxyhydroxide phases. Thus, about three-quarters of the initially limestone plate (Fig. 5) is made up of manganese and iron compounds, the remaining part being composed of the phosphate material which almost entirely substitutes the bioclastic limestone.

Analysis of aluminium-manganese relationships

The analysis of aluminium-manganese relationships (Tables 1 and 2; Fig. 4) and their comparisons with data on hydrothermal and hydrogenetic crusts and nodules allow us to identify three major genetic fields from the correlation diagram: (I) the field of hydrothermal accumulations with extensive vari­ ations of manganese-iron contents but extremely low aluminium concentrations, less than 0·25% (Cronan, 1976; Toth, 1980; Cronan et al., 1982; Varentsov et al. , 1983); (II) the field of points corresponding to manganese-iron oxyhydroxide deposits of the intermediate group between the hydrothermal and hydrogenetic crusts; (III) the field of hydrogenetic crusts whose boundary is drawn tentatively along the line of the aluminium concen­ tration value of more than 2·5% . Therefore , accord­ ing to aluminium- manganese relations, the man-

The distribution of ratios Ni : Mn, Cu : Fe, Ba : Ti

The behaviour of heavy metals in the process of crust formation can be illustrated by the distribution of Ni : Mn and Cu: Fe ratios in the crusts. This distribution is characterized by the absence of any considerable variations, as can be shown by the representative example near the top station 39 (Fig. 1 ) where manganese, iron and phosphate mineralization are most intensive. Unlike heavy metals, the B a : Ti distribution clearly shows an increase in this ratio from the surface layers to the lower parts of the crust on the boundary with the phosphatized substrate , for ex­ ample in sample 1-39-D-126 (Fig. 5) . As in the manganese-iron crusts from the Krylov Seamount, also situated on the Cape Verde Abyssal Plate of the eastern Atlantic (Varentsov et al., 1989), such re­ lations may imply the lessening of the role of hydro­ thermal components in ore-bearing solutions, which are mixtures of hydrothermal water and seawater, at the late stages of accumulation. Analyses of nickel-manganese relationships

From the analysis of nickel-manganese relation-

Table 1. Chemical composition of manganese-iron crusts and the altered substrate (an intensively hydrothermally phosphatized limestone): samples 1-34-D-1-115-(A); 1-34-D-115-(2); the

Bezymiannaya Seamount 640; and of alkalic basaltoids of the subsea Cruiser Rise, Cape Verde Plate, eastern Atlantic (major components: wt%; heavy metals: ppm)

Sample Component Si

Ti

AI

a

b

Cruiser Seamount

l-34-D-115-(2)

1-34-D-1-115-(A) d

c

a

b

c

d

2

4

6

7

8

1·457

2·414

0·948

10·816

1·733

1-485

0·658

4·128

16·168

17-335

9·317

9·826

12·646

0·839

0·078

1·012

0·623

1·003

0·839

0·012

0·108

1·677

1·725

1-414

0·91

1·725

1·09

1-19

0·984

3·544

1·264

1-428

0·587

2·343

8·157

8·205

5·517

4-772

8·131

0·2798

1·322

15·762

13·908

13·91

17·153

Fe (total)

18·345

1·021

13-575

14·89

16·925

18·471

Mn (total)

16·889

0·31

12·7

10·207

16·913

16·301

0·194

0·279

0·108

0·093

0·186

0·403

0·155

1·152

0·88

1-14

1·387

1·315

1·345

0·386

0·808

2·466

2·714

1·236

1·236

0·494

2·209

34·034

11·133

1·716

2·567

1·952

37·051

30·774

4·683

6·921

16-481

16·688

6·099

0·271

0·323

0·546

0·362

0·34

0·34

3·073

0·253

0·55

0·681

4·679

4-452

1·397

1·091

0·378

1·469

1-195

1·573

1·247

0·297

0·252

2·404

1·974

1-491

1·603

2·1

0·274

0·241

0·208

0·697

0·232

0·241

0·116

0·49

0·697

0·697

0·739

0·78

-

-

13-904

11·449

11·498

1·858

1·531

Mg

Ca

p

Na

K

Fe3+

-

-

-

Fe2+

Mn2+

Mn4+ Ba Ni

-

0·341

0·139

0·07

0·163

0·108

10·155

16·752

16·196

0·116

0·009

0·081

0·072

0·108

0·116

0·125

0·22

0·008

0·157

0·252

0·212

0·354

0·008

16·752

12·36

350

<50

315

310

300

370

<50

<50

Cu

120

<65

<65

230

140

200

<65

<65

135

>1000

>1000

>100

>1000

<50

9157

2150

v

Co

Co* Pb

Ga

Mo

Mn:Fe Sb*

Ag*

>1000 7385

103·0

<65

<65

80·0

<65

6425

<65

14·3

78

<50

= 1000

410

>1000

>1000

<50

<50

<55

<55

<55

<55

<55

<55

<55

>110·0

>110·0

>110·0

>110·0

0·92

0·30

1·00

0·22

-

0·88

6·0

6·3

0·69

0·21

52·8

63-1

49-4 0·52

0·69

0·94

0·661

60·7

<55

6-4

2·192

<65

>1000 >110·0

16-492

0·016

<65

<65

2·4096

0·863

11·715

0·018

Cr

<65

12·98

4·3

The characteristics of components of manganese-iron oxyhydroxide crusts and of the substrate, a hydrothermally phosphatized limestone, samples 1-34-D-1-115-(A), 1-34-D-115-(2), are given in captions to Figs 2a, 3a. The chemical composition of hydrothermally altered, phosphatized alkaline basaltoids from the Cruiser Seamount, eastern Atlantic, is also given for comparison; samples 2,4,6,7,8 (data by B.P. Zolotarev and Y.A. Eroschev-Shak). * Determinations by instrumental neutron activation analysis.

\0 a-

Table 2. Chemical composition of iron-manganese crusts and of altered substrate (an intensively hydrothermally phosphatized limestone); samples 1-38-D-

124: 1-39-D-126; the Bezymiannaya Seamount 640, Cape Verde Plate, eastern Atlantic (major components: wt%; heavy metals: ppm) Sample

1-38-D-124

Component

a

b

Si Ti AI Fe (total) Mn (total) Mg Ca

0·602 0·635 0·926 13·275 21·022 1·592 4·254 0·71 1·425 0·299

0·85 0·701 1·016 15·135 20·705 1·658 2·724 0-445 1·373 0·315

-

-

0·163 20·872 0·143 0·354 <65 320 <65 >1000 14134 >1000 <55 >110·0 1·58

0·116 20·59 0·134 0·346 <65 325 <65 >1000 12745 >1000 <55 >110·0 1·37 14·5

p

Na K Fe3+ Fe2+ Mn2+ Mn4+ Ba Ni Cr

v

Cu Co Co* Pb Ga Mo Mn : Fe Sb* Ag*

1-39-D-126 c 0·299 0·018 0-460 0·546 0·194 0·507 35·435 15·14 1·514 0·149 0·266 0·28

d 1·196 0·03 0·783 6·064 0·317 0·627 31·56 11·58 1·158 0·307

b

c

d

e

0·99 0·928 0·92 17·198 18·003 1·254 2·159 0·345 1·217 0·241

0·794 0·701 0·577 14·534 20·937 1·278 2·488 0·395 1·313 0·299

0·822 0·635 0·608 15·282 20·975 1·14 2·36 0·32 1·202 0·274

1·597 0·252 1·106 5·861 4·327 0·724 27·485 10·945 0·934 0·291

1·139 1·03 1·01 15·988 18·22 1·375 2·638 0·34 1·514 0·257

0·147 17·87 0·116 0·322 <65 325 <65 >1000 11256 >1000 <55 >110·0 1·05

0·062 20·891 0·143 0·322 <65 315 <65 >1000 12980 >1000 <55 >110·0 1-44 71·9

0·139 20·84 0·143 0·307 <65 340 <65 >1000 12644 >1000 <55 >110·0 1·37

0·217 4·114 0·036 0·149 130 130 <150 >1000 1947 340 <55 46·5 0·74 15·0

-

0·009 0·008 120 <50 <65 <SO 19·2 <50 <55 <6·0 0·36

a

0·008

82·9

0·05 16·1 0·013

0·108 18·123 0·108 0·275 <65 310 (1000) <150 >1000 11739 >1000 <55 >110·0 1-14

Characteristics of components of manganese-iron oxyhydroxide crusts and of the substrate, a hydrothermally phosphatized limestone, are given in captions to Figs 3b and 5; samples 1-38-D-124; 1-39-D-126. * Determinations by instrumental neutron activation analysis.

:--

s:

�

.... "' ;::,

<:;;a

·""' :<::: � \:::1 :::!. <:;;�

� � -

() a

�

" ;::;>;a ""'

Manganese- iron crusts, Bezymiannaya Seamount 640

Mn

97

(/o,wr) 60.0

f.

2.

J. 4.

I·

11I· Iq I

20,0

I

'

'

ll\

II

X

',

i� . 1 41.

_ _

I 0'........

I

I

10.

•

12.

�

14.

-x-x-x

13.

l-·---

®

I

-·-·-

1

X

•

•

•

@

II. &.

ill

j

'

7.

8.

9.

I

I�� \ 10.0

t:,.

11£, 5. 0 6. 0

40,0

.30.0

0

@)

....._

I

X

•

0

y .... J I I

X

.,x

(0

2.0

4,0

6.0

8,0

10,0

Al(/o, wr)

Fig. 4. Aluminium-manganese relationships in the components of crusts of manganese-iron oxyhydroxides and in the altered substrate, an intensively hydrothermally phosphatized limestone. Samples: 1-34-D-1-115-(A); 1-34-D-115-(2); 1-38D-124; 1-39-D-126 (Tables 1 and 2), the Bezymiannaya Seamount 640. The data on hydrothermal and hydrogenetic manganese oxyhydroxide crusts and diagenetic nodules of the ocean are shown for comparison (Cronan, 1976; Cronan eta!., 1982; Toth, 1980). (1) Components of crust of manganese-iron oxyhydroxides; sample 1-34-D-l-115-(A) (a, c, d). (2) Substrate, phosphatized limestone; sample 1-34-D-1-115-(A) (b). (3) Components of crust of manganese-iron oxyhydroxides; sample 1-34-D-115-(2) (a, b) . (4) Substrate, components of phosphatized limestone; sample 1-34-D-1-115-(2) (c, d) . (5) Phosphatized alkalic basalts; the Cruiser Seamount, eastern Atlantic. (6-8) Manganese oxyhydroxide crusts and nodules from the ocean (Cronan, 1976; Cronan et al., 1982; Toth, 1980): 6-hydrothermal; ?­ hydrogenetic; 8-diagenetic. (9) Components of crust of manganese-iron oxyhydroxides; sample 1-38-D-124 (a, b). (10) Components of the substrate, a phosphatized limestone; sample 1-38-D-124 (c, d) . (11) Components of crust of manganese-iron oxyhydroxides; sample 1-39-D-126 (a-c, e). (12) Substrate, a phosphatized limestone; sample 1-39-D126 (d). Fields of manganese-iron oxyhydroxide crusts: I-hydrothermal; II-mixed; III-hydrogenetic. (13) Borderline of hydrothermal crust field. (14) Borderline of hydrogenetic crust field.

ships (Fig. 6) the fields of hydrothermal ( I ) , tran­ sitional (II), and hydrogenetic ( I I I ) crust growths are distinctly separated on the correlation diagram . The studied components o f manganese -iron crusts of the Bezymiannaya Seamount 640 belong to de­ posits of intermediate origin. These crust growths, which were formed under a strong hydrothermal influence, have experienced extensive hydrogenetic effects, i . e. the accumulation of heavy metals from the bottom seawater.

Geochemical behaviour of cobalt

The geochemical behaviour of cobalt displays two well-expressed tendencies: (a) clear association with manganese; and (b) increasing cobalt concentration with decreasing of water depths, i.e. towards the summit areas of the seamount (see Tables 1 and 2). Similar contents of cobalt and manganese were re­ ported from the seamounts of the central Pacific (Aplin & Cronan , 1985; Hein et al. , 1988).

1-39-D-126

25

0

X X

x

)(

X )(

X

X )(

x )(

){

(%)

75

"GEclx x

1fr,4 1 .. Ill� fiiif X X X

X

X

X

x

X

X

_}(_

)( X

50

X "

Fe

X

X

FR

OH

x

X.

X

-APT

X

x

x

x

X

X

X

x

){ �X )(

X

)(

Mn/Fe

Ni/Mn

Cu/Fe

Ba/Ti

0.20 0 1P 2.0 0 0.02 0.04 0 0,0002 0,0006. 0 0105 0.10 0.15 I I lv<:A:>. I I KAXA1 I • lv
)( X

)(

X

JLJ!. 11 �B)

?

?

?

-1 �2 �3 .4 ITJii]5 �6 ��f:��1tl7 g9 BFrF1I �11

ii""F*

-

VRT

Mn·F

I'

�

�u·ut.t

Fig. 5. Distribution of values of Mn: Fe, Ni: Mn, Cu: Fe and Ba: Ti ratios in the components of the crust of manganese-iron oxyhydroxides and in the altered substrate, an intensively hydrothermally phosphatized limestone. Sample 1-39-0-126 (Table 2); the Bezymiannaya Seamount 640. Mineral composition: (1-6) (see Fig. 2b). (7) Iron vernadite. (8) Manganese feroxyhyte. (9) Mixed-layered asbolane-buserite. (10) Goethite. (11) Francolite and hydroxyl apatite.

Manganese- iron crusts, Bezymiannaya Seamount 640

Distribution of antimony and silver

The distribution of antimony and silver reveals con­ siderable association with manganese and increasing concentrations towards the summit areas (see Tables 1 and 2). It is of interest that values of antimony and silver concentrations are several times higher than the average contents of these metals for oceanic manganese- iron nodules and crusts.

GENESIS Accumulation of manganese-iron oxyhydroxide crusts

Crusts , patches, deep impregnation by manganese­ iron oxyhydroxides of phosphatized calcareous rocks, covering like a blanket the alkalic basalts of the Bezymiannaya Seamount 640, are extensively distributed on this topographic high. The intensity of development of crust growths increases from the middle part of the slopes (station 34; Figs 1 , 2 and 3), where their thickness seldom exceeds 2-40 mm, to the top of the seamount (station 39; Figs 1, 2b and 5) , where their thickness is no less than 60- 1 00 mm. The crusts are composed of globular and micro­ layered accumulations of manganese -iron oxyhy­ droxides (Figs 7 and 8) . These formations are poss­ ibly the products of substitution of the calcareous deeply phosphatized substrate: the mass of oxy­ hydroxide patches distinctly contains relics of foraminiferal shells, nannofossils and other bio­ detritus. The relationship between the formation of crust accumulations and manganese-iron oxy­ hydroxide patches and dissolution of limestones is also manifested in relatively higher titanium and aluminium contents which represent residual matter after dissolution (Tables 1 and 2). It is important to note that the formation of phosphates, represented mostly by francolite and, to a lesser degree, by hydroxyl apatite, is associated with earlier hydro­ thermal alterations of limestones in the substrate which preceded the massive deposition of man­ ganese-iron hydroxides. Phosphatization of basalts of the substrate is also observed in other regions of the Cape Verde plate (the Cruiser Rise, the Krylov Seamount). Accumulation of manganese- iron oxyhydroxides occurred as a result of hydrolythic precipitation ac­ companied by autocatalytic oxidation in the process of adsorption of transition metals involving micro-

99

biological phenomena. These processes took place during the mixing of hydrothermal solutions with near-bottom or interstitial seawater (Varentsov & Pronina, 1973; Craig, 1974; Varentsov, 1976; Varentsov et al. , 1979a ,b, 1983). The values of Ba : Ti ratios perceptibly decrease from the lower interlayers to the surface parts of the crust accumulations (Fig. 5) . The M n : Fe ratios can be regarded as an indicator of Eh and pH gradient. These ratios are distinctly different in various parts of the crust deposit on the Bezymiannaya Seamount 640. The values are rather low for the crusts of the middle part of the slope (station 34, Mn : Fe0·685: 0·999 , average 0·885; Table 1) but are higher near the top (station 39, Mn : Fe- 1 ·047: 1 · 584, av­ erage 1 · 326; Table 2). The comparison of these data leads to the conclusion that towards the summit of the seamount pH and Eh values notably increase , affecting the composition of crust growths. The Mn : Fe ratios are fairly close to those of the seamounts of the Cape Verde plate (Varentsov et al., 1989); they are observed in oxyhydroxide crusts from the hydrothermal field 'TAG' which is a part of the Mid-Atlantic Ridge at 26°N (Lalou et al., 1986). Lalou et al. ( 1986) demonstrated that the tempera­ ture of hydrothermal sources increases with depth , with a concomitant increase in iron content. If the total hydrothermal activity covered the time interval from 20 to 4 kyr, then the manganese oxyhydroxide deposition continued from 16 to 4 kyr, which means that during the interval from 20 to 16 kyr an accumu­ lation of iron compounds predominated. These data present evidence of a distinct separation of manganese and iron in the transport by hydro­ thermal solutions mixed in variable proportions with seawater, both in time and laterally, in the process of movement of the Cape Verde Plate towards the African continent. The hydrothermal activity was particularly inten­ sive during the accumulation of relatively old inter­ layers of manganese - iron oxyhydroxide crusts at the time when this part of the Cape Verde Plate was near the axial zone of the Mid-Atlantic Ridge. A hole drilled on the Mid-Atlantic Ridge south of the Kane transform fault passed through a sequence of volcanic rocks in the field of active hydrothermal activity (Detrick et al., 1 986) . This is another case of intensive manganese - iron oxyhydroxide mineraliz­ ation and extensive activity of the 'black smokers' in the zone of the Mid-Atlantic Ridge marked by massive accumulation of iron, copper and zinc sulphides. A similar situation might also have oc-

100

J. M. Varentsov, V . A . Drits and A.l. Gorschkov

Ni

('fo, wr.) @

1.

f,OO

0,75

0,50

't.

8 �

6.

•

7.

@ @

9,

@

5.

I

I I I I I I I I

8.

I I I I I

10.

(:;

A II. � 12.

][

13. -x-x-x-

x x x x x x x �x x� x ,x x x x x x x x x x x x � //8� iLl / A? 1I / /0 8 / / / 0 / -/-if.-.-.- 0;;- L - - - .-.- . -.- / / / l /

-

0.25

@

3.

I

0

2.

-

-

-

-

-

-

·

-

·

-

-

·-.

-

-

-

.-.-.-.

-

.

-

-

-

-

-

.

-

-

-

·

·-

/

10.0

20,0

30,0

40.0

50,0

Mn ("/o,wr.)

Fig. 6. Manganese-nickel relationships in the components of crusts of manganese-iron hydroxides and in the altered

substrate, an intensively hydrothermally phosphatized limestone . Samples: 1-34-D-1-115-(A); 1-34-D-115-(2); 1-38-D-124; 1-39-D-126 (Figs 2-5; Tables 1 and 2). The Bezymiannaya Seamount 640. The data on hydrothermal and hydrogenetic manganese-iron crusts and diagenetic nodules of the ocean are shown for comparison (Cronan, 1976; Toth, 1980; Cronan eta!., 1982). (1) Components of manganese-iron oxyhydroxide crust; sample 1-34-D-1-115-(A) (a, c, d) . (2) Substrate, a phosphatized limestone; sample 1-34-D-1-115-(A) (b). (3) Components of manganese-iron oxyhydroxide crust; sample 134-D-115-(2) (a, b). (4) Substrate, components of phosphatized limestone; sample 1-34-D-115-(2) (c, d) . (5-7) Manganese-iron oxyhydroxide crusts and nodules from the ocean (Cronan, 1976; Toth, 1980; Cronan et al., 1982): 5hydrothermal, 6-hydrogenetic, ?-diagenetic. (8) Components of manganese-iron oxyhydroxide crusts; sample 1-38-D124 (a, b). (9) Components of the substrate, a phosphatized limestone; sample 1-38-D-124 (c, d). (10) Components of manganese-iron oxyhydroxide crusts; sample 1-39-D-126 (a-c, e). (11) Substrate, a phosphatized limestone; sample 1-39D-126 (d). Genetic fields of manganese-iron oxyhydroxide crusts; I-hydrothermal, U-mixed; III-hydrogenetic. (12) Borderline of hydrothermal crust field . (13) Borderline of hydrogenetic crust field.

curred in the early Palaeogene when this part of the Cape Verde Plate was situated near that area of the axial zone of the Atlantic.

MINERAL COMPOSITION OF MANGANESE-IRON OXYHYDROXIDE CRUSTS

The data on the distribution of minerals manganese - iron oxyhydroxide crusts and

m

m

the the

substrate rocks are shown by generalized schemes in Figs 3 and 5. Although the schemes represent with considerable approximation the quantitative re­ lations of mineral phases composing individual interlayers, nonetheless on the whole they show the true relations. The comparative analysis of these schemes gives certain data on the distribution of manganese-iron minerals both in the secti9n of the crusts and along the profile of the Bezymiannaya Seamount 640 from the middle part of the slope to the summit through stations 34-38-39 (Fig. 1).

Manganese- iron crusts, Bezymiannaya Seamount 640

Fig. 7. Scanning electron micrographs of

manganese-iron oxyhydroxide crusts (mostly iron vernadite and manganese feroxyhyte). Sample 1-34-D-1-115-(A); the Bezymiannaya Seamount 640 (a, b) (Photomicrographs with increasing magnification.) Indistinctly layered step­ like growths of manganese-iron oxyhydroxides . (c-e) (Photomicrographs with increasing magnification .) Growth of small apatite crystals on the walls of channel caverns in the mass of manganese-iron oxyhydroxides .

101

Fig. 8. Scanning electron micrographs of manganese-iron oxyhydroxide crusts (mostly iron vernadite and manganese francolite). Sample 1-34-D- 1- 1 15-(A). The Bezymiannaya Seamount 640. (a) Small crystals of apatite growing on the surface of channel microcavities in the mass of manganese-iron oxyhydroxide crust . (b) Crystallization of a fine microlayered structure of manganese-iron oxyhydroxide crust with local caverns and globular texture. (c and d) Indistinctly microlayer�d structure of manganese-iron oxyhydroxide crust. (e) Areas of intensive development of microcavernous porosity in indistinctly layered mass of manganese-iron oxyhydroxide crust (relict products of limestone dissolution and its substitution by manganese-iron oxyhydroxides). (f) Remnants of coccoliths, and a part of manganese­ iron oxyhydroxide crust with globular texture.

Manganese- iron crusts, Bezymiannaya Seamount 640

1 In all studied samples (except sample 1-38-D-124; Fig. 3b) the upper crust interlayers 2-7 to 3035 mm thick are composed mostly of manganese feroxyhyte and iron vernadite with subordinate amounts of goethite. 2 I n the lower and therefore older crust interlayers lying directly on the substrate (deeply phosphatized limestone), the relative quantities of manganese feroxyhyte are perceptibly less and of iron vernadite are greater than in the surface interlayer. Moreover, these old interlayers show the presence of asbolane­ buserite, a mixed-layered mineral. 3 It is of interest to note that the mineral compo­ sition of oxyhydroxide crusts , growing at the base of plate-like blocks of altered limestones, differs from that in the superficial parts of crusts and has an affinity with relatively old interlayers of the crust lying directly on the substrate (e.g. sample 1-39-D126, Fig. 5). The difference in the mineral com­ position of crusts growing on the top and at the base of plates of altered limestones is manifested by sample 1-34-D-1 15-(2) , i .e. the crust at the base contains a notable admixture of mixed-layered as­ bolane -buserite, besides iron vernadite , manganese feroxyhyte and subordinate amounts of goethite. 4 A special case of sample 1 -38-D-124 (Fig. 3b) shows relatively thin (2 - 15 mm) crusts composed of a fairly wide set of minerals. The major phases of the upper crust are iron vernadite, manganese fer­ oxyhyte, magnesium asbolane , subordinate amounts of mixed-layered asbolane - buserite, goethite and traces of birnessite. The composition of the lower crust is somewhat different: iron vernadite domi­ nates and manganese feroxyhyte is in subordinate quantities. In order to know how the change in mineral composition of microlayers of oxyhydroxide crusts is connected with the variations of components ac­ cumulated in the course of depositional history and how significant are the postdepositional transform­ ations, it is necessary to take into account the geo­ chemistry of manganese, iron and other elements (Tables 1 and 2). In most cases the manganese and iron content rather insignificantly changes along the section of the crusts , and normally Mn : Fe is close to 1 . In the intervals of crust sections, which show perceptible variations of Mn : Fe ratio (e.g. sample 1-39-D126 from the top part of the seamount, in which the surface layer 0-20 mm thick (a) has Mn : Fe 1 ·047 , whereas an interlayer 20-35 mm thick (b) has Mn : Fe 1 ·44 1 ) , these variations reflect =

=

103

an increase in the relative quantity of iron verna­ dite and a corresponding decrease 111 manganese feroxyhyte. In previous research (Varentsov et a!. , 1989) , fairly detailed crystallochemical characteristics of iron vernadite, manganese feroxyhyte and other minerals were given. We should mention only the major aspects which are necessary to discuss the postdepositional changes. Iron vernadite

I n typical hydrogenetic crusts the accumulation rates of manganese -iron oxyhydroxides which produce iron vernadite are, as a rule , rather low. Iron ver­ nadite is a mineral which experienced minimal postdepositional alteration . Manganese feroxyhyte

The manganese feroxyhyte structure is described by Chukhrov et a/. ( 1975, 1976) and Varentsov et a/. ( 1 989). The energy dispersive spectra of the studied particles record the presence of iron and manganese (at Fe > Mn) thus giving grounds to call this phase manganese feroxyhyte. It has been established that feroxyhytes (o'-FeOOH) are relatively unstable products of fairly rapid oxidation of Fe2 + in weakly alkalic or weakly acid media which transform into goethite in an oxidizing environment (Chukhrov et al. , 1975; Murray, 1979). The observed maximal quantities of manganese feroxyhyte in the surface interlayers (in this case 'a' interlayer 0-20 mm thick) of rather thick crusts (e.g. sample 1-39-D126, Figs 2 and 5) can be interpreted in this context, as can the presence of subordinate amounts of goethite. The experiments have shown (M urray, 1979) that the formation of goethite ( cx-FeOOH) as a result of direct oxidation of Fe2+ or hydrolysis of Fe3+ is hardly probable in subsea near-bottom conditions or in the area of hydrothermal vents, because the synthesis of this mineral is inhibited by the presence of Cl - ions in the system. Therefore , the reduction of quantities of this phase in older interlayers of crust growths, caused by the relative instability of manganese feroxyhyte, results in a respective increase of relative quantities of goethite and other minerals, which shall be discussed later. Mixed-layered asbolane-buserite

In the manganese- iron oxyhydroxide crusts the

104

I. M. Varentsov, V . A . Drits and A.!. Gorschkov

mixed-layered asbolane- buserite phases dominate only in the lower relatively old interlayers of rather thick crusts (e.g. interlayer 'c' is 35-65 mm thick; sample 1-39-D- 126; Fig. 2b). They are also ob­ served in most of the bottom crusts (Figs 3a and b ) , o r i n the crust growths (2- 15 mm) , which experi­ enced notable postdepositional alterations (Fig. 3a) . It can be supposed that the mixed-layered asbolane ­ buserite mineral was formed as a result of trans­ formations of iron vernadite in the process of dehydration and aging of the oxyhydroxide material of the crusts. This process is stimulated by the presence in vernadite of relatively long two­ dimensional fragments, which can be regarded as nuclei of octahedral Mn4 + layers. Moreover, the mixed-layered asbolane- buserite should be con­ sidered as one of the early products of diagenetic mineral formation. It is natural to suppose that the mixed-layered mineral preceded the formation of birnessite (Chukhrov et al. , 1987 ) , which perhaps appeared later than buserite( I ) . Although the latter was not found in the studied crusts, its presence in this series of transformations is highly probable. Asbolanes

The structure of the minerals of this group is de­ scribed in a number of papers (Chukhrov et al. , 1983a ,b, 1987). Perceptible amounts of magnesium asbolane (Fig. 3b) were identified in the upper thin crust (215 mm) accompanied by iron vernadite, manganese feroxyhyte and mixed-layered asbolane-buserite. There are grounds to suppose that the observed magnesium asbolane is the product of solid phase transformations occurring in the following suc­ cession : iron vernadite (manganese feroxyhyte?) ----> buserite(I) ----> mixed-layered asbolane-buserite ----> magnesium asbolane (Chukhrov et al. , 1987 ) .

vernadite and manganese feroxyhyte. It was also noted that the existence of the intermediate vanished buserite( l ) phase, preceding the formation of mixed-layered asbolane -buserite and magnesium asbolane, can be assumed. The presence of birnessite in this sample is also evidence in favour of this assumption.

THE MODEL OF FORMATION OF MANGANESE -IRON CRUSTS AND NODULES

In previous papers (Varentsov & Pronina, 1973; Varentsov, 1976; Varentsov et al. , 1979a, b ; Varentsov e t al. , 1989) i t has been noted that man­ ganese -iron oxyhydroxide crusts are extremely important for the understanding of the processes of formation of oceanic ores since they are relatively simple deposits. The relative simplicity of crust structure and the often clearly delineated stratifi­ cation offer possibilities for the study of the evolution of the ore-forming medium and of the succession of postdepositional transformations of manganese­ iron oxyhydroxides (Shterenberg et al. , 1986; Chukhrov et al. , 1987). The data discussed above on the distribution of manganese and iron phases and the analysis of the structural features of these min­ erals (Chukhrov et al. , 1987) produce the generalized scheme shown in Fig. 9.

Fe + M n ( solution + suspe nsion )

t

Mn ( Ill). Mn +

Fe OO H , m H z O u orp h m

( n � O ·S )

Birnessite

There are small amounts of birnessite in the studied crusts (sample 1-38-D- 124; Fig. 3b) with pre­ dominant contents of iron vernadite, manganese feroxyhyte and lesser quantities of magnesium as­ bolane, mixed-layered asbolane-·buserite and goethite. According to the supposition expressed earlier, the presence in this crust of mixed-layered asbolane ­ buserite, magnesium asbolane and goethite is the consequence of diagenetic transformations of iron

( !V l 0 1 - S + n · m H z O u m orph

I

'

I

Mn

fl

Fe-ver nudite

\

feroxyhyte

l

::::.

I

ite-I (7 )

\\ I G o e t h i te I I B i r ness i te I

1--

M ixed layered usbolun e buserite

' I Asbolune I

Fig. 9. Generalized scheme for transformation of manganese-iron oxyhydroxide minerals.

Manganese- iron crusts, Bezymiannaya Seamount 640

Despite obvious differences in the environments of formation of the crusts on the seamounts and the sedimentary-diagenetic manganese- iron nodules from the near-Equatorial Pacific Zone (Skorniakova, 1984) , common features are established in the formation and transformation sequences of manganese-iron oxyhydroxide phases. Uspenskaya et al. ( 1987, 1988) have shown that manganese- iron concretions deposited in the radio­ larian oozes of the sublatitudinal zone between the Clarion - Clipperton Fractures are mostly concen­ trically layered with an alternation of layers of well­ crystallized dendrites and globules (MD layer 0·2 5 mm thick) and of layers of thin microlaminated isotropic or weakly isotropic material with dendrites and globules (TLD layer). The essentially manga­ nese MD layers have dominant amounts of buserite (I) in the outer and middle parts of the concretions and lesser quantities of asbolane- buserite. Nearer to the nucleus of the concretion the relative amount of birnessite and buserite(II) increases and that of buserite(I) correspondingly decreases. The presence of asbolane-buserite is also definitely established. The TLD layers are represented mainly by asbolane­ buserite and by a somewhat lesser amount of buserite (I). In order to understand this sequence of trans­ formations, it is essential to keep in mind that the outer TLD layers contain perceptible quantities of fine iron vernadite , which resembles iron vernadite from hydrogenetic concretions and crusts. Sorem & Fewkes ( 1 979) attempted to build up a single pattern of the structural - textural features of the concentric structure and the mineral composi­ tion and chemistry of the major components of manganese- iron concretions from the Equatorial Pacific Zone. It was established that the interlayers equivalent to MD layers are composed of predomi­ nantly manganese oxyhydroxides or 10 A manga­ nates (average wt% Mn 35· 8 1 ; Fe 1 ·28 ; Ni 1 ·74; Cu 1 ·25; Co 0·07; Zn 0·23 ) , whereas the content of poorly-crystallized and almost X-ray-amorphous material of layers corresponding to TLD is made up of mostly iron-manganese (average wt% Mn 19·42; Fe 16· 94; Ni 0·27; Cu 0· 16; Co 0·31 ; Zn 0·01) (Sorem & Fewkes, 1979). The alternation of M D and TLD layers in the concretions from the Clarion­ Clipperton Fracture Zone also reflects the regional variations of sedimentary conditions in this part of the Pacific and, in particular, the alternation of hiatus intervals in sedimentation with periods of high biological productivity; this alternation of MD and TLD layers is in good agreement with the

105

sediment section (Von Stackelberg, 1987). To obtain a better insight into the formation of concretions from the Clarion - Clipperton Zone and to compare them with crusts , it seems necessary to analyse rep­ resentative examples of hydrogenetic- diagenetic growth (Von Stackelberg, 1987 ) . The upper part of a typical concretion is built up of layered and dense material which looks black and optically amorphous in the reflected light under the microscope. The lower part near the base of the concretion has a less structurally distinct fabric and is composed of light­ grey material with relatively higher reflectivity. The boundary between these two parts of the concretion coincides with the sediment-water interface . The part of the concretion lying above this interface is exposed to interaction with bottom seawater. I n other words, this model concretion was formed a s a result of accumulation of manganese - iron oxy­ hydroxide material on both sides. According to X­ ray diffraction data, there are essential differences: the upper part is composed predominantly of 2·4 A manganate (i.e. verandite) and the lower part of 10 A manganate. This information leads to the conclusion that below the sediment-water interface the diagenetic processes dominated and above it hydrogenetic processes prevailed; the relationships between them could have changed during the geo­ logical history of their formation. Despite distinct differences in the modes of growth of these con­ cretions, the trend in the manganese-iron oxy­ hydroxide transformations is similar to the scheme discussed earlier for crusts.

CONCLUSIONS

The Bezymiannaya 640 Seamount is a submeridi­ onally oriented block of oceanic crust covered with moderately lithified limestone which dates from the early Middle Eocene. From the middle parts to the summit of the seamount the hydrothermal alter­ ation of limestones increases (mostly by phospha­ tization , calcitization, silicification) , together with an increase in the intensity of growth of manganese­ iron oxyhydroxide crusts. The crusts are composed of globular structures; microlaminated accumulations of manganese - iron oxyhydroxides which developed as the products of substitution of the deeply phosphatized limestone substrate. The association between the formation of crust growths and patches of manganese-iron oxy­ hydroxides and the dissolution of limestones is

106

/. M. Varentsov, V . A. Drits and A.!. Gorschkov

evident also in the relatively high titanium and aluminium contents which represent residual matter. In their chemical composition , the manganese ­ iron oxyhydroxide crusts compose a relatively homogeneous group between typical hydrothermal and hydrogenetic deposits. In these crusts, the hydrogenetic accumulation of heavy metals was superimposed on manganese - iron oxyhydroxide phases deposited under a strong influence of hydro­ thermal solutions, in particular at the early stages of accumulation . This circumstance is clearly illustrated by the features in the distribution of barium, which is a hydrothermal component in these environments. The Mn : Fe ratio values are rather low (0·885) for the crusts from the middle parts of the slope, but they increase for the crusts in the summit areas (average 1 ·326) . Hydrothermal activity was particu­ larly intensive during the formation of the older interlayers of manganese-iron oxyhydroxide crusts at the time when this part of the Cape Verde Plate was situated near the axial zone of the Mid-Atlantic Ridge; as it moved further east, the role of hydro­ genetic factors increased. The two major minerals composing the surficial and the least altered crust interlayers are iron vernadite and manganese feroxyhyte. The manganese feroxyhytes are relatively unstable prod­ ucts which transformed into goethite. The mixed­ layered asbolane - buserite is usually found in the lower interlayers of fairly thick crusts and in most of the foot-wall crusts. The presence of this mineral is interpreted as a result of postdepositional trans­ formations of iron vernadite and manganese fer­ oxyhyte. Magnesium asbolane was identified in perceptible quantities in the upper thin (2- 15 mm) crust from the middle part of the slope, and also iron vernadite, manganese feroxyhyte , and mixed­ layered asbolane - buserite with admixtures of goe­ thite and birnessite. Crystallochemical data imply that magnesium asbolane is the product of trans­ formations occurring in the following succession : iron vernadite (manganese feroxyhyte) ---'> buserite(I ) --" mixed-layered asbolane- buserite ---'> magnesium asbolane. Birnessite is interpreted as a product of dehydration of once present but now absent buserite(I). The suggested succession of postdepo­ sitional alterations of the oxyhydroxide material of manganese - iron crusts is on the whole in agreement with the trend in transformations of material in hydrogenetic-diagenetic manganese- iron con­ cretions from the radiolarian zone of the East Equatorial Pacific.

ACKNOWLEDGEMENTS

We are grateful to B . P . Zolotarev, V.A. Eroschev­ Shak and 1 . 1 . Bebeshev (Geological Institute of the USSR Academy of Sciences) for preliminary de­ scription of the recovered samples. For their assistance in analysing crust components we thank our colleagues N.l. Kartoshkina and N. Yu. Vlasova for their help in processing the data and preparing the materials and N . D. Serebryannikova for her assistance in scanning electron microscopy. Constructive criticism of the anonymous reviewers and editorial processing by J. Parnell (The Queen's University of Belfast) were useful and improved the work.

REFERENCES

A.P. & CRONAN, D.S. (1985) Ferromanganese oxide deposits from the Central Pacific Ocean. 1. En­ crustations from the Line Islands Archipelago. Geochim. cosmochim. Acta 49, 427-436. CARLO, E., McMuRrY, G. & KIM, K. (1987) Geochemistry of ferromanganese crust from Hawaiian Archipelago. 1. Northern survey areas. Deep Sea Res. 34, 441-467. CHUKHROV, F.V., DRITS, V.A. & GORSHKOV, A.l. (1987) Structural transformations of Mn-oxides in oceanic Fe­ Mn nodules. Izv. A N SSSR (ser. geol.) 1, 3-14 (in Russian) . CHUKHROV, F.V., Zv LAG tN , B . B . , GoRSHKOV, A.l. & ERMILOVA, L.P. (1975) Delta-Fe hydroxides. In: Hypergenetic Fe-oxides in Geological Processes (Ed. by N.Y. Petrovskaya), pp . 70-84. Nauka, Moscow (in Russian). CHUKHROV, F.V . , ZVLAGIN , B . B . , GORSHKOV, A.l., ERMILOVA, L.P., KOROVUSHKJN , V.Y., R U D N ITSKAYA, E.S., & YAKU BOVSKAYA, N. Yu . (1976) Feroxyhyte, a new FeOOH modification. lzv. AN SSSR (ser. geol.), 5, 5-24 (in Russian). CRAIG, H. (1974) A scavenging model for trace elements in the deep sea. Earth Planet. Sci. Lett. 23, 149 - 159. CRON A N , D.S. (1976) Manganese nodules and other ferro­ manganese oxide deposits . In: Chemical Oceanography Vol. 5, 2nd edn. (Ed. by J.P. Riley & R . Chester), pp. 2 17-265. Academic Press, London. CRONAN , D.S. , GLASBY, G.P., MOORBY, S.A., THOMSON , J . , KNEDLER, K.E. & McD o u GALL, J.C. (1982) A sub­ marine hydrothermal manganese deposit from the south-west Pacific Island Arc. Nature 298, 456-458. DETRICK, R . S., HONNOREZ, J., ADAMSON, A.C. , BRASS , G . W . , GILLIS, K . M . , H U MPHERIS, S.E. , MEVEL, c . , MEYER, P . S . , PETERSEN, N., RAUTENSCHLEIN, M., SHIBATA, T. , STAUDIGEL, H., WOOLRIDGE, A. & YAMAMOTO, K. ( 1986) Forages dans Ia dorsale media­ Atlantique: resultats preliminaires du Leg 106 du Joides­ Resolution (Ocean Drilling Program). C. R. Acad. Sci. (ser. 2, 303) 7, 597-602. HEtN, J.R. , Sc H WAB, W . C . & D Avts , A.S. ( 1988) CobaltAPLIN,

Manganese- iron crusts, Bezymiannaya Seamount 640

and platinum-rich ferromanganese crusts and associated substrate rocks from the Marshall Islands. Marine Ceo!. 78, 255-283. LALO U , C., THOMPSON , G., RONA, P.A., BRICHET, E. & JEHANNO, C. ( 1986) Chronology of selected hydrother­ mal Mn oxide deposits from the transatlantic geotraverse 'TAG' area, Mid-Atlantic Ridge 26°N. Geochim. Cosmochim. Acta 50, 1737-1743. M uRRAY, J.W. ( 1979) Iron oxides. In: Marine Minerals, Course Notes, Vol. 6 (Ed. by R.G. Burns), pp . 47-98. Mineralogical Society of America, Washington. RIDOUT, P.S., CARPENTER, M.S.N. & MORRIS, R.J. ( 1984) Analysis of metalliferous encrustation from a seamount in the Gulf of Guinea. Chem. Ceo!. 42, 2 19-225 . SHTERENBERG, L.E., ALEKSANDROVA, V.A., ILYICHEVA, L.V., SivTsov, A.V. & STEPANOVA, K . L. ( 1986) Post­ depositional alterations in oceanic Fe-Mn concretions and crusts. lzv. AN SSSR (Ser. Geol.) 1 , 80-88 (in Russian). SKORNIAKOVA, N .S. ( 1984) Morphogenetic types of Fe-Mn concretions from the radiolarian belt of the Pacific. Litho!. Min. Deposits 5, 67-83 (in Russian). SoREM, R.K. & FEWKES, R.H. (1979) Manganese nodules. Research Data and Methods ofInvestigation . IFI/Pienum Data, New York, 723pp. THOMPSON , G ., MOTfL, M . & RONA, P.A. ( 1985) Mor­ phology, mineralogy and chemistry of hydrothermal de­ posits from the 'TAG' area, 26°N Mid-Atlantic Ridge. Chem. Ceo!. 49, 243-257. ToTH, J.R. (1980) Deposition of submarine crusts rich in manganese and iron. Ceo!. Soc. Am. Bull. 91, 44-54. USPENSKAYA, T.Yu., GoRSHKov, A.l. & SJVrsov, A.V. (1987) Mineral composition and inner structure of Fe­ Mn concretions from the Clarion-Clipperton fracture zone. Izv. AN SSSR (Ser. Geol.) 3, 9 1 - 100 (in Russian). UsPENSKAYA, T.Yu . , GoRSHKOv, A.I . & SJVrsov, A . V. ( 1988) Structure and mineral composition of oceanic nodules Izv. AN SSSR (Ser. Geol.) 4, 88-97 (in Russian) .

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l.M., BAKOVA, N . Y . , DIKOV, Yu.P., T.S. & GIOVANOLI , R. (1979a) On the model of Mn, Fe, Ni, Co ore formation in Recent Basins: experiments with synthesis of Me-hydroxide phases on Mn304. Min. Deposita 14, 281-296. VARENTSOV, J.M., BAKOVA, N . Y . , DIKOV, Yu.P., GENDLER, T.S. & GIOVANOLI, R. ( 1979b) Synthesis of Mn, Fe, Ni, Co oxide-hydroxide phases on manganese oxides: on a model for transition metal ore formation in Recent Basins. Acta Mineral. -Petrograph. (Szeged) XXIV/I, 63-90. VARENTsov, I . M ., D RITS, V.A., GoRSHKOv, A . !., Swrsov, A.V. & SAKHAROV, B.A. ( 1989) Formation of Mn-Fe crusts in the Atlantic: mineralogy, geochemistry of major and trace elements, the Krylov Seamount. In: Genesis of Sediments and Basic Problems of Lithology (Ed. by V.N. Kholodov), pp. 58-78. Nauka, Moscow (in Russian) . VARENTSOV, I.M. & PRONINA, N . Y . (1973) On the study of mechanisms of iron -manganese ore formation in Recent Basins: the experimental data on nickel and cobalt. Min. Deposita ( Berl. ) 8, 161-178. VARENTSOV, J.M., SAKHAROV, B.A., D RITS, V.A., TSIPURSKY, S.l., CHOPOROV, D . YA. & ALEXANDROVA, V.A. (1983) Hydrothermal deposits of the Galapagos Rift Zone, Leg 70: mineralogy and geochemistry of major components. In: Initial Reports of the Deep Sea Drilling Project, Vol. 70 (Ed. by 1 . Honnorez, et a!. ) , pp. 235-268. U S Government Printing Office, Washington. VoN STACKELBERG, U. ( 1987) Growth history and variability of manganese nodules of the Equatorial North Pacific . In: Marine Minerals. Advances in Research and Resource Assessment (NATO ASI Series, Series C. Mathematical and Physical Sciences, Vol. 194) (Ed. by P.G. Teleki, M .R. Dobson, J.R. Moore & U. von Stackelberg), pp. 189-204. Reidel, Dordrecht.

VARENTSOV,

GENDLER,

Spec. Pubis int. Ass. Sediment.

(1990) 11, 109-118

Microbiota from middle and late Proterozoic iron and manganese ore deposits in China L. Y I N Nanjing Institute of Geology and Palaeontology, Academia Sinica, Chi-Ming-Ssu, Nanjing, People's Republic of China

ABSTRACT

Abundant microfossils have been discovered in middle and late Proterozoic iron and manganese ore deposits in eastern Guizhou Province, western Hunan Province, western Liaoning Province and Gansu Province. On the basis of microfossil assemblages and radiometric dating, the age of the iron and manganese ore deposits is considered to be in the range 1200-750 Ma. A number of microfossils of Sphaerocongregus (or Bavlinella) have been found in rhodochrosite in these deposits. Based on the different preservation of microfossils in relation to the iron and manganese contents, it can be inferred that cyanobacteria are directly or indirectly implicated in the genesis of these iron and manganese ore deposits.

INTRODUCTION

Late Proterozoic manganese ore deposits inter­ bedded with tillites are widely distributed in South China. Some manganese ores in Sichuan, Guizhou, Hunan, Hubei and Jiangxi Provinces have industrial value. However, there are different views about the geological age of these manganese ore deposits and their genesis (see Ji, 1985; Xu, 1987). In order to understand them better, the biostratigraphy of manganese ore deposits in the Songtao district of eastern Guizhou Province and the Huayuan district of western Hunan Province has been studied with the help of the 405 Geological Team of the Hunan Geological Bureau and the 103 Geological Team of the Guizhou Geological Bureau. A number of organic-walled microfossils have been identified from these sediments by means of palynological maceration and thin section studies, and numerous coccoid microfossils were photographed using the scanning electron microscope (SEM). The results not only strongly support the recognition of which manganese ore deposits in eastern Guizhou Province and western Hunan Province were formed during the ' Nantuo glacial epoch' of the late Proterozoic, but also provide important evidence for the genesis of manganese ore deposits in South China. Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

In addition, organic-walled microfossils have been obtained from iron and manganese ore deposits in Wafangzi, Chaoyang County, Liaoning Province and Jingtieshan, Jiuquan district and Gansu Province. Middle and late Proterozoic iron and manganese ore deposits in China occur as iron and manganese carbonates interbedded with black shales formed under anaerobic conditions. Important questions in such environments, are which microorganisms could live, and what effects could be attributable to micro­ organisms, such as transportation and enrichment of iron and manganese. In this paper, this subject is not discussed in depth. At the present level of knowl­ edge, the facts are presented for certain Chinese deposits and their significance is suggested.

SEQUENCES OF IRON AND MANGANESE ORE DEPOSITS, AND THEIR MINERAL ASSOCIATIONS

A brief summary of the geology of the deposits examined is given below. 109

l lO

L. Yin

Songtao district of eastern Guizhou Province

The Datangpo Formation is 90-570 m thick; the upper part consists of yellow-green mudrock inter­ bedded with fine sandstone, the middle part is composed of yellow-green mudrock and silty mud­ stone and the lower part is grey-black shale, usually containing manganese carbonate near the bottom. This formation is underlain conformably by the Liaoghekou Formation and overlain disconformably by the Nantuo tillites. Manganese ore deposits occur at the bottom of the Datangpo Formation in this district. Ore bodies, strata-bound and lenticular, extend laterally up to 400 m and are up to 7·65 m thick. Manganese carbonate appears as dense, massive and striped beds, containing 10-25% Mn. The ratio of Mn: Fe is 4·75-6·79 and the ratio of P: Mn is 0·0075-0·0163. The manganese ore is characterized by a high con­ tent of phosphorus and a low content of iron. A rhodochrosite-calcite series of manganese carbon­ ates is present, ranging through rhodochrosite, calcium rhodochrosite, calcium-magnesium rho­ dochrosite, magnesium-manganese calcite and manganese calcite. Huayuan district of western Hunan Province

The Minle Formation is 218 m thick; the upper part is made up of grey shales and dark-grey silty shales and the lower part consists of dark-grey silty shales interbedded with thin beds of black shale and grey­ black striped manganese carbonate (Fig. 2). Massive manganese carbonate occurs at the bottom of this formation with a thickness of 0·75 m. This formation is underlain conformably by the Chunmu Formation and overlain conformably by the Nantuo Formation. Manganese ore deposits in this district are dated at 728 ± 27 Ma by means of a rubidium-strontium whole-rock isochron (see Geological Team of Hunan Geological Bureau, 1984). The characters of the mineral deposit are similar to those of the manganese ore deposits in eastern Guizhou Province. The manganese carbonates are mainly rhodochrosite, calcium rhodochrosite, mag­ nesium rhodochrosite, calcium-magnesium rhodo­ chrosite, magnesium-calcium rhodochrosite and manganese dolomite. Chaoyang district of western Liaoning Province

Manganese ore beds are situated in the Tieling For­ mation. The age of the manganese-bearing series is about 1200 Ma.

The thickness of the Tieling Formation in this district is about 70 m. The upper part is made up of thick bedded siliceous limestone, the middle part is a manganese-bearing series and the lower part consists of laminated dolostone with lenticular quartzose sandstone at the top. The underlying Hongshuizhuang Formation, with a thickness of 130-170 m, consists of black carbonaceous shales and is in conformable contact with the Tieling For­ mation. Lower Cambrian conglomerates overlap the Tieling Formation with unconformity. The manganese-bearing series is mainly composed of mudrocks with some dolomitic conglomerates at the bottom, and siliceous limestone at the top. In the mudrock series, manganese ore occurs as stratiform and lenticular ore bodies, associated with siltstone and shales. The manganese ore belongs to the iron­ manganese class with Mn 16-33%, Fe 15-20% and Mn: Fe ratio of 1-2. The phosphorus content in primary carbonate ores is 0·004-0·006% and the sulphur content is 0·5- 1%.

MICROBIAL FOSSILS

A number of sphaeromorphic microfossils, dis­ playing individuals, pairs or groups of cells with more than three vesicles, have been obtained using standard palynological techniques from iron and manganese ore deposits of the Datangpo Formation of eastern Guizhou Province, the Minle Formation of western Hunan Province, the Tieling Formation of western Liaoning Province and the strata of Gansu Province. Most of them occur as bud-like forms or forms with infillings (see Fig. 3). Some specimens exhibit morphological features similar to forms previously reported and are determined as Leio­ minuscula, Lophominuscula, Protosphaeridium, Asperatopsophosphaera, Trachysphaeridium and Bavlinella. These form-taxa usually occur in late Riphean and Vendian strata in the USSR and North Europe (see Timofeev, 1959, 1966, 1973; Vidal, 1976). In addition, numerous coenobium-type fossils­ Sphaerocongregus valiabiris (or Bavlinella faveo­ lata) and their degradational remains were identified from sections of manganese ore etched by HCl (10-15%) before examination by SEM. The organic-walled microfossils Sphaerocongregus (or Bavlinella) have been mostly reported from late Proterozoic strata, especially from glacial deposits, in Scandinavia, Greenland, North America, China

Microbiota from iron and manganese deposits

111

Fig.

1. Map showing the localities of iron and manganese ore deposits in China discussed in this paper. (A) Huayuan manganese ore deposit, western Hunan Province; (B) Songtao manganese ore deposit, eastern Guizhou Province; (C) Wafangzi manganese ore deposit, western Liaoning Province; (D) Jingtieshan iron ore deposit, Gansu Province.

0

A

B

c

E

lL 0 ::J -+c 0 z

Fig.

2. Stratigraphic sections of the

Minle Formation from Huayuan district of western Hunan Province (A), the Datangpo Formation from Songtao district of eastern Guizhou Province (B) and the Tieling Formation from the Chaoyang district of western Liaoning Province (C). (1) Sandy shale; (2) sandy dolomite; (3) manganese ore beds; (4) black shale; (5) tillites; (6) dolomite; (7) shale; and (8) limestone.

u 0 N 0 L Q) ...... 0 L 0..

E

u.. ::J E

c

::J _c u

and elsewhere (Manum, 1968; Moorman, 1974; Vidal, 1976; Knoll et al., 1981; Mansuy & Vidal, 1983; Yin, 1987). Sphaerocongregus variabilis Moorman, 1974, the type species of genus Sphaerocongregus Moorman, 1974, was recognized as the synonym of Bavlinella faveolata Shepeleva, 1962, by Vidal (1976). How­ ever, Volkova (1974) concluded that Bavlinella Shepeleva, 1962, is a junior synonym of Pyrito­ sphaera Love, 1958 and that Bavlinella forms, like

1::-_:.::::1 ESC9

2

�

3

�

4

I-:-..:.-:-:-I

5

ES::::j � .E5:9

6 7

8

Pyritosph aera, arose as a result of the modifications of acritarch tests, films or threads of organic matter, and exines of spores (pollen) in the formation of framboidal pyrite. Foster et al. (1985) reported organic-walled microfossils Sphaerocongregus from the early Cambrian Heatherdale Shale, on the Fleurieu Peninsula, South Australia and they con­ cluded that members of Sphaerocongregus are dif­ ferent from Bavlinella in having a compound wall of coccoid subunits and an extremely shallow negative

L. Yin

112

A

D

E

G

F

Fig.

J

M

3. Microfossils from middle and late Proterozoic iron and manganese sediments in China. All photomicrographs are from organic­ walled microfossils obtained by maceration. Scale in figure equals 15 f.tm in (A)-(H),(J),(K) and 10 f.tm in (I),(L) and (M). (A),(E),(F),(G) and (J) are from the Datangpo Formation of eastern Guizhou Province; (B) is from the Tieling Formation of western Liaoning Province; (C),(D),(H),(I) and (K) are from the Minle Formation of western Hunan Province; (L), (M) are from the strata of Gansu Province.

THE RELATIONSHIP BETWEEN

reticulum between these subunits. It is recognized here that the Bavlinella faveolata (Shepeleva, 1962) Vidal, 1976 is the same as the Sphaerocongregus variabilis Moorman, 1974 colonial microfossils. They are both fossil representations of a particular bio­ logical form rather than secondary structures, due to their restricted stratigraphic distribution and relationship with a -particular environment. SEM studies reveal that the fossils are coenobia and have hollow, cell-like subunits (Fig. 4). They represent certain biological forms with an affinity with living coccoid cyanobacteria, such as Entophysalis (see Cloud et al., 1975), Xenococcus and Dermocarpa (see Knoll et al., 1981).

MICROBIOTA AND IRON AND MANGANESE MINERALS

These studies have indicated that the morphological features, quantity and distribution among the micro­ biota are related to the iron and manganese content in iron and manganese ore deposits. In rocks con­ taining minimal iron-manganese contents, such as black shale and carbonate, the microbiota is domi­ nated by larger forms, which can be considered to be vegetative cells or cysts of eukaryotic alg�e. With increasing iron and manganese content in the sedi­ ments, larger forms of microfossils decrease dis­ tinctly and a few forms display either infillings of

Microbiota from iron and manganese deposits

113

Fig. 4. Scanning electron micrograph of Sphaerocongregus (or Bavlinella) from late Proterozoic manganese ore, Huayuan district, western Hunan Province.

iron or manganese minerals, or exhibit irregular shapes. In richer iron and manganese ores, cyano­ bacterial fossils ( Sphaerocongregus) rather than eukaryotic microplankton are predominant. It is well known that low-diversity microbiota dominated by morphologically simple taxa appear to be diagnostic for inshore coastal environments, while higher diversity microbiota containing a hetero­ geneous array of morphologically complicated forms indicate more open-shelf conditions (Vidal, 1981). The sedimentary environments in the sequences discussed in this paper would be inshore coastal or lagoonal facies, because microbiotas in these sequences are all characterized by low diversity. Based on sulphur isotopic analysis, o34S for pyrite in manganese ore in Huayuan, western Hunan Prov­ ince is 46·6-58·59% (Geological Team of Hunan Geological Bureau, 1984). This high value of o34S supports the suggestion that the manganese ore deposits may have been deposited in a semi-enclosed bay. In such an ecological environment, micro­ organisms were restricted by stressed physical and chemical conditions, such as high concentrations of nutrients or high salinity. Knoll et al. (1981) de­ scribed microfossils from the late Proterozoic min­ eral rock formation in North America and they suggested that stressed conditions were caused by an influx of glacial meltwater, thus allowing one organ­ ism (like Bavlinella faveolata) to proliferate and dominate in such an environment. In the present study, a number of Sphaerocongregus (or Bavlinella) were found in manganese carbonate of a postglacial epoch in eastern Guizhou Province and western Hunan Province. The presence of a single genus of microfossils in this particular environment is in agreement with the finding of Knoll et al. (1981). No glacial sediments have been seen in iron and manganese deposits of either the Chaoyang district

of western Liaoning Province or the Jiuquan district of Gansu Province. So, glacial activity was probably not significant in these districts during the formation of the iron and manganese ore deposits. However, the diversity and the morphology of microfossils in the iron and manganese deposits from rocks asso­ ciated with the ore beds in these districts are variable. Possibly, stressed conditions not only resulted from an anomalous salinity and temperature regime as­ sociated with the influx of glacial meltwater, but the oxygen content in the water was also an important control on both the diversity and the morphology of the microorganisms. It is considered that the normal balance between oxygen and carbon dioxide in the basin only existed when iron and manganese ions were in low ionic concentrations. The photic zone, with more oxygen, is more suitable for aerobic organisms. When iron and manganese became more abundant, the oxi­ dation of these metal ions (Fe2+ and Mn2+) would have depleted the oxygen available. Most original aerobic organisms could not be sustained by such anaerobic conditions and only a few forms of cyanobacteria, characterized by facultative photo­ autotrophy (i.e. with capability in both aerobic and anaerobic conditions), could continue development because they are capable of anoxygenic photo­ synthesis. The interpretation discussed above is shown in relation to the microorganisms in Fig. 5. On the other hand, microorganisms may play an important role in the iron and manganese cycles, interacting with iron and manganese in several ways. It is well known that the influence of microorganisms on iron and manganese geochemistry is significant. This is because fluctuations of conditions, such as pH and Eh in water are paralleled by variations in the nature of microbial populations (Edmunds et al., 1982). In the material dealt with in this paper, it is

114

L. Yin

_J �z_! .

Oz.-

Fig. B

found that shales containing abundant microfossils are always superjacent to the iron or manganese ore beds (see Fig. 2). It is considered that the biochemistry of microbial populations was an im­ portant influence on the solution, transport and precipitation of the iron and manganese. In previous studies, including both modern bio­ logical experiments and fossil records, it has been shown that microorganisms play a significant role in the precipitation of iron and manganese. However, these organisms are commonly filamentous bacteria, like Metallogenium (Nealson, 1983). No filamentous bacteria have been seen in the present material. There were two possible reasons for this. One is that the ecological environment was not suitable for the development of filamentous organisms. The other reason may be that diagenesis, including the recrys­ tallization of iron-manganese carbonate, could eliminate the filamentous organisms. Although at present, we cannot say that there is a definite relationship between cyanobacteria, like Sphaerocongregus (or Bavlinella), and the genesis of iron and manganese ore, it is certain that their biochemical functions (i.e. photosynthesis, respiration, adhesion, etc.) could alter the Eb and pH of water and influence the oxidation and re­ duction of iron and manganese, as well as form organic chelates of these metals. On the other hand,

5. Schematic diagram showing the distribution of microfossils in different environments.

it is well known that iron is readily cbelated by a variety of organic molecules including oxalates, citrates, burnie acids, tannins and siderophores, and that the hydrous oxides of manganese are themselves strong chelators of Mn2+ and other cations, and adsorption/desorption processes play a major role in the geochemistry of manganese (see Nealson, 1983). So, the biochemjcal functions of microorgarusms were closely concerned with the geochemistry of iron and manganese during the formation of iron and manganese ores. Here we consider the manganese ore of western Hunan Province and eastern Guizbou Province as examples for interpretation of the relationship be­ tween microorganisms and manganese. As discussed above, the sedimentary environment was a semi-enclosed basin. Initially, there were numerous but low-diversity planktonic micro­ organisms in the water, and their activities bad increased the oxygen content and pH of the water. When manganese ions entered the basin, mainly in the form of manganese bicarbonate from the conti­ nent, volcanic eruption and hydrothermal solution, their oxidation caused exhaustion of oxygen in the water. In such an ecological environment, only cer­ tain cyanobacteria survived because they are capable of anoxygenic photosynthesis. Manganese adhered to mucilage, including carbohydrate polymers, on

Microbiota from iron and manganese deposits

their walls, and organic chelates of metals could also form. The chelates impregnated and mineralized the cell walls of the cyanobacteria. In addition, the enzymes enolase, superoxide dismutase and PEP carboxykinase in organisms all require manganese (see Nealson, 1983) although the question is open as to whether or not cyanobacteria can obtain energy for growth by the oxidation of manganese. Sub­ sequently, the manganese accumulated in the cells of organisms. Such direct and indirect relationships between the organisms and manganese allowed the gradual deposition of manganese minerals in the basin. Meanwhile, the water became more reduced by both the oxidation and the accumulation of manganese minerals, so that microorganisms like cyanobacteria could not normally survive and dead cells accumulated at the bottom of the basin. The cell walls were degraded by sulphur-reducing bac­ teria and cells were partially or entirely replaced by various manganese minerals, which caused further manganese mineralization in the sediments. This interpretation seems to be supported by the fact that microfossils appear to be more abundant in the man­ ganese ore deposits with an increase in manganese

Fig.

6. Scanning electron micrograph of Sphaerocongregus (or Bavlinella) and their degraded forms from late Proterozoic manganese ore, Songtao district, eastern Guizhou Province.

115

content, and the fossils are also more degraded in manganese-rich sediments (Figs 6 and 7). The colonial microfossils shown in Fig. 6A were obtained from striped manganese carbonate. How­ ever, in dense, massive manganese-rich carbonate, cell-like residues are as in Fig. 6C or in Fig. 7B. In addition, organic components such as bitumen, satu­ rated hydrocarbons, aromatic hydrocarbons and phenanthrenes, have been determined from massive manganese-rich carbonate of western Hunan Province (Geological Team of Hunan Geological Bureau, 1984). The data also indicate organic ac­ tivity during the deposition of the manganese-rich sediments. Although all of the above speculations and inter­ pretations are mainly based on the morphology of microfossils and textural features of iron and manganese ores, it may be surmised that the bio­ logical and physiological functions of coccoid cyano­ bacteria directly or indirectly affected both the transport and the deposition of iron and manganese minerals. This only happened in suitable conditions, characterized by low atmospheric oxygen level and rich sources of iron and manganese ions, such as

116

L. Yin

genetic association between coccoid microorganisms and iron and manganese minerals.

CONCLUSIONS

Based on the microfossil material available from iron and manganese ore deposits, the following conclusions were reached: 1 The diversity of microbiota in iron and manganese deposits is relatively low and generally has little biostratigraphic significance. 2 Sphaerocongregus (or Bavlinel/a) seems to have been a cyanobacterium of facultative photoauto­ trophy, i.e. sustainable in both aerobic and anaer­ obic conditions, in that it not only occured in a stressed environment controlled by anomalous sal­ inity and temperature associated with an influx of glacial meltwater, but then also developed in anaerobic conditions containing iron and manganese minerals. 3 Coccoid cyanobacteria po�sibly play a role in the genesis of iron and manganese ore deposits, by direct or indirect biochemical effects.

ACKNOWLEDGEMENTS

Fig.

7. Scanning electron micrograph showing the degraded forms of Sphaerocongregus? (A) From late Proterozoic manganese ore of the Songtao district of eastern Guizhou Province; (B) From late Proterozoic manganese ore of the Huayuan district of western Hunan Province.

I thank L. Wang, D. Cao and X. Zhan (Nanjing Institute of Geology and Palaeontology, Academia Sinica) for assistance in preparing the specimens, producing the SEM micrographs and in drafting, J. Ostwald (BHP Central Research Laboratories, Australia) for critical review and J. Parnell (The Queen's University of Belfast) for editorial help. The costs of field studies and laboratory investi­ gations were covered by the National Nature Science Foundation of China.

REFERENCES

BANDOI'ADHYAY, P.C. (1989) Proterozoic microfossils from manganese orebody, India.

Nature, 339,

376-378.

CLOUD, P., MooRMAN, M.A. & PIERCE D. (1975) Sporu­ ,

develop in enclosed water basins. Previous reports of microfossils from early Proterozoic banded iron formations in China (Yin, 1979), late Proterozoic banded manganese formations in China (Xu, 1987), and a late Proterozoic manganese ore body in India (Bandopadhyay, 1989) all seem to support the

lation and ultrastructure in a late Proterozoic cyano­ phyte: some implications for taxonomy and plant phylogeny. Q. Rev. Bioi. SO, 131-149. EDMUNDS, K.L.H., BRASSELL, S.C. & EGUNTON, G. (1982) The organic geochemistry of benthic microbial eco­ systems. In: Mineral Deposits and the Evolution of the Biosphere (Ed. by H.D. Holland & M. Schidlowski), pp. 31-50. Dahlem Konferenzen, 1982, Berlin. Springer, New York.

117

Microbiota from iron and manganese deposits FAN, D.L. (1959a) Wafangzi ferro-manganese ore deposits in China. Geol. Rudn. Mestorozhd 4, 78-89 (in Russian). FAN, D.L. (1959b) The pyrosmalite in Wafangzi ore deposit in China. Dokl. Akad. Nauk. USSR (ser. geol. 6) 126, 1338-1347 (in Russian). FoGG, G.E., STEWART, W.D.P., FAY, P. & WALS BY, A.E. (1973) The Blue-green Algae. Academic Press, New York, 459pp. FOSTER, C.B., CERNOVSKIS, A. & O'BRIEN, G.W. (1985) Organic-walled microfossils from the Early Cambrian of South Australia. Alcheringa 9, 259-268. GEOLOGICAL TEAM OF HUNAN GEOLOGICAL BUREAU (1984) Bulletin on geological characters and mineralogical pat­ tern of Minle manganese ore deposits in Huayuan region of Hunan Province. Monograph of mineral deposit (18), 122pp. (in Chinese). JI, J.F. (1985) Fossil cyanophytes from Early Sinian manganese and iron-bearing moraine formation in Southern China and their geological significance. In: Selected papers

from

the

1st National

Fossil Algal

pp. 213-218. Geological Publishing House, Beijing (in Chinese, with English abstract). KNOLL, A.H. & AwRAMJK, S.M. (1983) Ancient microbial ecosystems. In: Microbial Geochemistry (Ed. by W.E. Krumbein), pp. 267-315. Blackwell Scientific Publications, Oxford. KNOLL, A.H., BucK, N. & AwRAMIK, S.M. (1981) Strati­ graphic and ecologic implications of late Precambrian microfossils from Utah. Am. J. Sci. 281, 247-263. MANSUY, C. & VIDAL, G. (1983) Late Proterozoic Briaverian microfossils from France: taxonomic affinity and implications of plankton productivity. Nature 302, 606-607. MANUM, S. (1968) Microfossils from late Precambrian sedi­ ments around Lake Mjosa, Southern Norway. Norg. Geol. Unders. 251, 45-52. MooRMAN, M.A. (1974) Microbiota of the late Proterozoic Hector Formation, Southwestern Alberta, Canada. J. Paleontol. 48 , 524-539. NEALSON, K.H. (1983) The microbial iron cycle. In: Symposium,

Geochemistry (Ed. by W.E. Krumbein), pp. 159-190. Blackwell Scientific Publications, Oxford. TIMOFEEV, B.V. (1959) Ancient flora of the Baltic area and its stratigraphic significance. Trudy VNJGRI 129, Leningrad (in Russian) 320pp. TiMOFEEV, B.V. (1966) Microphytological investigations of ancient formations. Acad. Sci. USSR Lab. Precambr. Geol. Geochronol. Nauka, Leningrad, 145pp. (in Russian). TIMOFEEV, B.V. (1973) Microphytofossils from the Ukraine. Acad. Sci. USSR Jnst. Ceo!. Geochronol. Pre­ cambr. Nauka, Leningrad, 58pp. (in Russian). VIDAL, G. (1976) Late Precambrian microfossils from the Visingso Beds in southern Sweden. Fossils and Stra/a 9, 1-57. VIDAL, G. (1981) Aspect of problematic acid resistant, organic-walled microfossils (acritarchs) in the Upper Proterozoic of the North Atlantic region. Precambr. Res. 15, 9-23. VOLKOVA, N.A. (1974) Types of damage to the body of Precambrian and Cambrian acritarchs. Paleont. Zh. 4, 101-108 (in Russian). Xu, Z.L. (1987) Algal fossils from late Precambrian Banded Manganese Formation (BMF), Xianhtan, Hunan Province of China. Acta Botanica Sinica 29, 104-110 (in Chinese, with English abstract). YIN, L.M. (1979) Microflora from the Anshan Group and the Liaohe Group in East Liaoning with its stratigraphic significance. In: Selected works for a scientific symposium on iron-geology of China, sponsored by Academia Stratigraphy and Palaeontology, Sinica, 1977. pp. 39-60. Science Press, Beijing (in Chinese, with English abstract). YIN, L.M. (1987) Microbiotas of latest Precambrian sequences in China. In: Stratigraphy and Palaeontology Microbial

of

Systemic

Boundaries

in

China

(Precambrian­

Vol. 1, pp. 415-522 (compiled by Nanjing Institute of Geology and Palaeontology, Academia Sinica). Nanjing University Publishing House.

Cambrian Boundary)

Spec.

Pubis

in!.

Ass.

Sediment. (1990)

ll,

119-138

Metal precipitation related to Lower Ordovician oceanic changes: geochemical evidence from deep-water sedimentary sequences in western Newfoundland

*

J. W . BOTSFORD* and D.F. SANGSTERt centre for Earth Resources Research, Memorial University of Newfoundland, St. John's, Newfoundland Canada, AlB 3X5; '"Geological Survey of Canada, 601 Booth St., Ottawa, Canada KIA 0£8

ABSTRACT

Lower Palaeozoic deep-water sedimentary sequences arc preserved within the Humber Arm Allochthon in western Newfoundland, where they have been thrust westward and now structurally overlie coeval shallow-water sequences. Of particular interest are the laterally equivalent Cow Head and Northern Head Groups, base-of-slope shale-rich sediment apron deposits which span the latest Middle Cambrian to late Early Ordovi cian. A pronounced Early Ordovician change in oceanic conditions is particularly evident i n the Northern Head Group, based upon: (1) a marked increase in bioturbation; (2) anomalously high manganese and barium content; and (3) changes in carbon : sulphur ratios. All suggest a transition to a new depositional regime characterized by ventilated depositional and early diagenetic conditions. This is much more subtly reflected i n the Cow Head Group; the contrast is ascribed to alo ng-strike differences in original margin morphology which the two groups embody. The contrast extends to sulphides within shales through the section. I n the Northern Head Group, anomalous metal (zinc, copper and lead) concen­ trations (up to 300 ppm) occur within Lower Ordovician (Lower Arenigian) shales. Disseminated sulphides within this horizon appear remobilized and rcplacive . On the other hand, localized metal concentrations within the Cow Head Group are scattered throughout the entire stratigraphic interval and are generally associated with organic carbon. The sulphur isotopic profiles of early precipitated pyrite through the stratigraphic in terval in both groups are also suggestive of a marked Lower Ordovician change from stratified to ventilated conditions based upon a decrease in1'r'4S values in the Late Tremadocian. Immediately following this, o34S values display a positive deflection suggestive of a temporary return to stratified conditions in the Arenigian. These apparent circu lation changes may have controlled redox conditions, and in turn have governed metal mobilization and precipitation.

REGIONAL GEOLOGY

The Humber Zone assemblage of western Newfoundland (Williams, 1979) records : ( 1) the establishment of a passive continental margin in the Late Precambrian/Early Cambrian; (2) continental

margin sedimentation spanning the Cambrian to Middle Ordovician; (3) the destruction of the margin during Middle Ordovician Taconic orogenesis; and (4) subsequent deformation during Acadian oro­ genesis. The Early Cambrian Labrador Group is a siliciclastic-carbonate sequence which represents the basal part of the autochthonous sedimentary sequence. This is overlain by a thick (approximately 1500 m) carbonate platform sequence (Port au Port Group , St George Group) spanning the Middle

* Present address: Newfoundland and Labrador Science and Technology Advisory Council, 114 Empire Ave . , St John's, Newfoundland, A l C 3G2. Also at: t Derry Laboratory for Sedimentary Geochemistry and Mineral Deposits, Ottawa-Carleton Geoscience Centre, Ottawa, Canada.

Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

1 19

120

1. W.

Botsford and D. F. Sangster

Cambrian to Early Ordovician (Fig. 1). The autoch­ thonous platform sequence was dominated by shallow-water sedimentation, and is generally poor in shale. Equivalent deep-water strata are preserved in two major allochthons, the Humber Arm Allochthon in the south and the Hare Bay Allochthon in the north. Block-faulting and foundering of the platform pre­ ceded emplacement of these allochthons, and is recorded in the deposition of the Middle Ordovician Table Head Group atop the platform sequence ( Klappa et a/., 1980; Stenzel & James, 1987). The Humber Arm and Hare Bay Allochthons are broadly similar in that they comprise thrust slices of predominantly sedimentary lithologies in the lower part, overlain by volcanic and igneous slices of oceanic affinity, and capped by ophiolite complexes ; all are separated by melange zones of variable thickness. Both allochthons were emplaced west­ ward during the Middle Ordovician Taconic Orogeny, now structurally overlie the autochthonous

AUTOCHTHONOUS PLATFORMAL SEQUENCE

ci a: 0 w ..J 0

0

:i ci a: 0 � 0

..J

platform sequence and are bounded by melange (Figs 1 and 2). The internal stratigraphy is both clearest and most complete in the Humber Arm Allochthon, where the structural history is presently better understood. The sedimentary succession here is exposed in imbricate thrust slices, modified by later (Acadian) compression. Humber Arm Allochthon

The Humber Arm Allochthon is centred on the Bay of Islands and extends from the Port au Port Peninsula in the south to the Cow Head area in the north (Fig. 2). A succession of deep-water sedi­ mentary units, time-equivalent to the platform sequence outlined above, is exposed in the lower part of the Humber Arm Allochthon (Fig. 3), and termed the Humber Arm Supergroup (Stevens, 1970). At the base, red and green shale and sand­ stone of the ?Lower Cambrian Summerside Formation occur. This passes upward into the

HUMBER ARM ALLOCHTHON

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Fig. 1. Schematic summary illustrating tectonostratigraphic relationships of Lower Palaeozoic e lements in western Newfoundland.

Metal-rich shales, Newfoundland

12 1

HARE BAY ALLOCHTHON

HUMBER ARM ALLOCHTHON

HUMBER ARM SUPERGROUP BAY OF ISLANDS OPHIOLITE SUITE

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PORT A U PORT A UTOCHTHONOUS CAMB R O

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ORDOVICIAN PLATFORMAL SEDIMENTS POST-TACONIC SEDIMENT

Fig. 2. Generalized geologic map of the Humber Arm Allochthon.

Lower-Middle Ordovician Irishtown Formation which contains quartzitic sandstone, conglomerate and shale. These units are probably the deep-water time-equivalents of the Labrador Group. These are overlain by upper Middle Cambrian to Lower Ordovician deep-water carbonate slope de­ posits derived from adjacent platform carbonates. In the Bay of Islands area this sequence is termed the Northern Head Group (Botsford, 1988), while laterally equivalent and coeval strata to the north are termed the Cow Head Group (James & Stevens , 1986) (Fig. 3). The Northern Head Group comprises the upper Middle Cambrian to Lower Ordovician Cooks Brook Formation and the Lower Ordovician (Arenigian) Middle Arm Point Formation (Fig. 3). Both groups are conformably overlain by flysch (Fig. 3), termed the Eagle Island Formation in the Bay of Islands area (Botsford, 1988) and the Lower

25

50

75

D

100 km

Head Formation in the Cow Head area (Williams et al., 1985). The Humber Arm Allochthon is struc­ turally thin at its northern and southern extremities, so that only the Cow Head Group and Lower Head Formation are preserved, in imbricate slices, in the Cow Head area. The Humber Arm Supergroup constitutes the most complete and intact record of deep­ marine conditions through the late Middle Cambrian to earliest Middle Ordovician in western Newfoundland. Because of the stratigraphic control available for the Northern Head and Cow Head Groups, these two sequences are particularly useful for documenting changes in deep-marine depo­ sitional conditions which may bear on the mobility and precipitation of metals; discussion in ensuing sections is directed toward this.

J. W. Botsford and D. F. Sangster

122

Groups comprise carbonate gravity deposits and shale, differences between them reflect an irregular carbonate margin morphology which has controlled their deposition under local palaeoceanographic conditions (Botsford, 1988) (see below).

MELANGE

c:i a: 0

SEDIMENTOLOGY

0 <j MELANGE

��.

�t '"

COW HEAD AREA

�

�

0

0

MELANGE

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Fig. 3. Schematic summary of the Humber Arm Supergroup, in the Humber Arm Allochthon, illu strating the relationship between the Bay of Islands and Cow Head areas. Legend as per Fig. 1 .

Relationship o f the Northern Head and Cow Head Groups

The Cow Head and Northern Head Groups are laterally equivalent toe-of-slope sediment apron deposits (James & Stevens, 1986; Botsford, 1988). Both are roughly 400 m thick, and comprise car­ bonate conglomerates, bedded lime grainstone , chert and shale (Fig. 3). Shale occurs interbedded with conglomerate, ribbon and parted limestone, and dolostone. A pronounced proximal (northwest) to distal (southeast) transition is evident in the Cow Head Group. Proximal Cow Head Group facies are domi­ nated by coarse carbonate conglomerate with minor interbedded shale , while distal facies are dominated by shale. A similar but more subtle depositional polarity is evident in the Northern Head Group. While both the Northern Head and Cow Head

A marked change in sedimentological and ich­ nological character occurs within the deep-water sequences of the Humber Arm Supergroup sugges­ tive of a widespread change in depositional con­ ditions. This is pronounced in the Northern Head Group and more subtly reflected in the Cow Head Group. In general faunal communities in marine environments decrease in diversity, size and numbers of individuals with decreasing oxygen levels, from commonly rich, diverse communities under aerobic conditions, to a restricted (commonly vermiform) infaunal community under dysaerobic conditions to a complete lack of benthos under anaerobic con­ ditions (Rhoads & Morse, 197 1 ; Byers, 1977). Within the Northern Head Group, shales of the lrishtown and Cooks Brook Formations contain abundant organic carbon and are very poorly bio­ turbated. This suggests deposition from the late Middle Cambrian to the Late Tremadocian under poorly oxygenated conditions. A marked change is apparent at the (Late Tremadocian) base of the Middle Arm Point Formation. Shales of the Middle Arm Point and Eagle Island Formations are charac­ terized by ( 1) a marked increase in the diversity and intensity of bioturbation (Botsford, 1988); (2) di­ minished organic carbon content; and (3) the appearance of oxidized red (locally interbedded with green) shales. This is suggestive of deposition under better oxygenated conditions. Trace fossil diversity in 'neritic' and 'flysch' facies remained relatively constant through the Lower Palaeozoic (Seilacher, 1978) and it is considered unlikely that the increase in bioturbation level within the Northern Head Group is the result of any marked evolutionary change.

GEOCHEMISTRY

Coincident with the sedimentological contrast de­ scribed above are changes in geochemical aspects including: (a) manganese content, (b) barium con­ tent and (c) sulphur-carbon relationships, which

123

Metal-rich shales, Newfoundland

are reviewed here for shales through both the Northern Head and Cow Head Groups. Manganese

There is a contrast of manganese abundance between the Northern Head and Cow Head Groups. The manganese content of Northern Head Group shales (Fig. 4) increases markedly from low 'background' levels through the Cooks Brook Formation to anomalously elevated levels, of up to 6·5 wt% MnO within the Middle Arm Point and lowermost Eagle Island Formations. Manganese in this enriched inter­ val occurs in three principal forms: ( 1) diagenetic finely crystalline manganese carbonate disseminated in red and green shale; (2) diagenetic manganese carbonate bands, up to 3 em thick, in red and green shale; and (3) manganese-iron carbonate which has overgrown individual grains within dolomitic silt­ stones. Manganese is only present within carbonate minerals. Based on petrographic evidence and field relation­ ships this manganese carbonate precipitation oc­ curred very early in the diagenetic sequence, very near the seafloor before compaction and prior to extensive and protracted silica and carbonate cemen­ tation (Botsford, 1 988). This style of manganese precipitation appears to be consistent with models of early upward diffusion of reduced manganese under shallow burial, and precipitation across a 'diagenetic front' (e.g. Wilson et a/., 1986). This has been described and modelled for an oxidative front and

precipitation of manganese oxides (Lynn & Bonatti, 1965). We suggest that under somewhat lower Eh and higher bicarbonate concentration this precipi­ tation has occurred not as oxides but manganese carbonates. Recent analogues of this style of precipi­ tation have been described by Calvert & Price ( 1970a) and Pederson & Price ( 1982). Models of early, shallow-burial diagenesis (reviewed in Hesse, 1 986) indicate that bottom-water conditions, such as dissolved oxygen levels, can readily be responsible for chemical gradients at shallow burial. An analogous relationship between manganese oxides and carbonates is illustrated in Cretaceous and Tertiary shallow-water manganese ore deposits (Frakes & Bolton, 1984; Bolton & Frakes, 1985). Here manganese oxides have been precipitated in the shallowest, best-oxygenated portions of the basin, while laterally equivalent manganese carbon­ ates have been precipitated at greater water depths, under apparently lower but still mildly positive Eh. No manganese enrichment occurs in proximal Cow Head shales, and only very subtle enrichment occurs in distal shales from the Arenigian portion of the section (Fig. 5). Barium

The stratigraphic distribution of barium within shales displays a pattern similar to that of manganese within the Humber Arm Supergroup. A pronounced enrichment of barium in shale (up to 8000 ppm) is evident through the Arenigian part of the Northern

a

"' a

Fig. 4. Stratigraphic distribution of manganese within shales of the Northern Head Group and adjacent units. Elevated concentrations of manganese above the Cooks Brook-Middle Arm Point boundary indicate the precipitation of manganese carbonate resulting from elevated Eh levels.

a

a

o

4

2 � ..

.. E

MnO

<wt.%)

6

J. W. Botsford and D. F. Sangster

124

Distal setting

Proximal setting

Cow Head

Martin Pt.

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m

11m

pb

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Fig. 5. Stratigraphic distribution of manganese in shales (black) of the Cow Head Group in proximal (Cow Head) and distal (Martin Point) settings.

Head Group section (Fig. 6), but absent in the Cow Head Group. In the Middle Arm Point Formation (Northern Head Group) barite occurs within shale as early precipitated, euhedral crystals, generally fine crystal­ line but ranging up to 4 mm. Petrographic evidence indicates that this authigenic barite was coprecipi­ tated with manganese carbonate, i.e. very early in the diagenetic sequence, again prior to compaction or any cementation. Models of progressive sediment reduction under shallow burial indicate that under anoxic bottom­ water conditions, active sulphate reduction will occur at, or near, .the seafloor and the early diagenetic

precipitation or preservation of sulphate minerals is highly unlikely. Such appears to be the case through the Cambrian portion of the Northern Head Group. Under more oxidizing conditions, an oxidizing zone of variable thickness will exist at the top of the sediment column, where sulphate is stable. The principal source of sulphate in pore waters of this zone will be: (1) diffusion from overlying seawater; and (2) upward diffusion, from the underlying zone of sulphate reduction, of reduced sulphur which is reoxidized (Berner, 1980). Such a diagenetic en­ vironment clearly represents suitable conditions for the precipitation of sulphate minerals (i.e. barite) and the distribution of barite illustrated in Fig. 6 is

125

Metal-rich shales, Newfoundland

400

·I

�

'�1,,,

i'"" lo

a

"

B

0

"

n

Fig. 6. Stratigraphic distribution of barium within shales of the Northern Head Group and adjacent units. Enrichment within the Middle Arm Point Formation indicates the precipitation of authigenic barite related to the preservation of sulphate under elevated Eh levels.

consistent with a transitiOn to better oxygenated seafloor conditions in the Lower Ordovician. Two mechanisms may bear on the preservation of authigenic barite and manganese carbonate during ensuing burial: 1 Middle Arm Point shales which host these authigenic minerals contain essentially no organic carbon. The bacterially driven oxidation of organic carbon is essentially the 'engine' which drives the continuing reduction of sediment through progres­ sive burial. If contained carbon were consumed early (i.e. at shallow levels) in the Middle Arm Point diagenetic system, through a combination of dimin­ ished initial supply or extensive consumption in the oxidation zone, then Eh may have stabilized until lithification was essentially complete. 2 Silica occurs as an early and pervasive cement in the Middle Arm Point and may locally have effected the early closure of the diagenetic system, isolating barite and manganese carbonate from subsequent dissolution.

Sulphur-carbon relationships

Review

Studies of recent and ancient sediments indicate that sulphur-carbon relationships are indicative of early depositional conditions. Pertinent reviews may be found in Berner (1970, 1984), Leventhal (1979, 1983, 1987) and Raiswell & Berner (1985). Under 'normal marine' oxygenated bottom-water conditions, sul­ phur and carbon maintain a linear relationship in

0

0

4 Ba

6

8

(ppm x1000)

sediments due to S : C stoichiometry established during progressive microbial sulphate reduction. The S : C ratio in this case is 0·357 (Leventhal, 1983; Raiswell & Berner, 1985). Under anoxic conditions, sulphate reduction commences in the water column above the seafloor, resulting in the precipitation of 'excess' sulphide (providing there is sufficient iron present to precipitate pyrite). Hence 'anoxic' sedi­ ments display higher sulphur : carbon ratios (wt% sulphur : wt% organic carbon). Notwithstanding the complicating factors of: ( 1) addition of late pyrite, not related to early burial; and (2) variations in sedimentation rate (cf. Leventhal, 1 983) which may obscure these initial ratios, this approach may allow the better discrimi­ nation of: ( 1) anoxic conditions which promoted the early precipitation of sulphides in the ambient water column; and (2) relatively oxygenated depositional settings. A further potential complication is the loss of carbon during burial and thermal maturation. This has most likely taken place in the Humber Arm Supergroup and probably accounts for the high (rela­ tive to thermally immature sediments) sulphur : carbon ratios presented below. A survey of illite crystallinity and conodont alteration indices (CAl) was conducted through the sequences sampled and these parameters are consistent throughout (e.g. CAl = 1 - 1· 5). (These data are not considered directly relevant and are omitted for brevity, but available upon request.) Hence the thermal maturity of the sequences discussed is considered consistent for the internal comparison presented here.

J. W. Botsford and D. F. Sangster

126

Cambrian and earliest Ordovician, but gave way to a better oxygenated setting briefly through the Late Tremadocian. Poorly oxygenated conditions were re-established in the Arenigian , and appear to have changed to better oxygenated conditions again in the latest Arenigian, immediately preceding the deposition of the Lower Head Sandstone. Data from the proximal environment are sparser and more scattered, but do not conflict with this interpretation.

Northern Head Group and adjacent units

Because of temporal variations in depositional con­ ditions the S : C ratio can be more meaningfully inter­ preted when examined with stratigraphic control. Because the sulphur : carbon ratio gives a measure of oceanic bottom-water conditions the variation in this ratio through a stratigraphic interval should indicate temporal variation in depositional environ­ ments. Figure 7 shows sulphur : carbon variations through the Irishtown Formation, Northern Head Group and lowermost Eagle Island Formation. Data reach a maximum at the Irishtown-Cooks Brook Formation boundary, and although somewhat scat­ tered are generally greater than values for normal marine sediments and suggestive therefore of anoxic or poorly oxygenated bottom-water conditions, through deposition of the uppermost Irishtown and Cooks Brook Formations. A marked decrease in ratios , indicative of the transition to oxygenated 'normal marine conditions' occurs in the (Arenigian) Middle Arm Point Formation.

Summary and discussion

An Early Ordovician change in oceanic conditions is recorded in the deep-water sediments of the Humber Arm Supergroup, but the response to this change was different in the laterally equivalent Northern Head and Cow Head Groups. In the Northern Head Group this change occurred at the Cooks Brook-Middle Arm Point Formation boundary. Evidence for a change in oceanic con­ ditions includes : 1 A marked increase in bioturbation at the forma­ tion boundary; 2 The establishment of a new early diagenetic regime represented by (a) hematite, (b) authigenic manga­ nese carbonate, and (c) authigenic barite; 3 A marked decrease in S : C ratios indicating a transition to better oxygenated conditions in the Middle Arm Point. Considered together, this evidence is consistent

Cow Head Group

Sulphur: carbon ratios indicate that temporal vari­ ations in depositional conditions also occurred in the Cow Head Group (Fig. 8). In the distal environment, locally elevated S : C values suggest that poorly oxygenated conditions occurred during the Late 500

400

elevated S within authigenic sulphate

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Metal-rich shales, Newfoundland Cow Head

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with an Early Ordovician 'ventilation event' which persisted from the Late Tremadocian through the Late Arenigian in the Northern Head Group. While this Early Ordovician transition to more oxidizing deep-water conditions is dramatic in the Northern Head Group, the change is much more subdued and temporary in the Cow Head Group. In the Cow Head Group S : C ratios suggest that weakly oxygenated conditions were established in the Late Cambrian, to be temporarily replaced by more oxy­ genated conditions during the latter part of the Tremadocian. Poorly oxygenated conditions were again re-established at the Tremadocian-Arenigian boundary, particularly in the proximal environment. The absence of abundant authigenic manganese car­ bonate and barite suggests that pronounced changes

in early diagenetic conditions related to a sudden change in redox conditions did not occur in the Cow Head Group. This contrast between the Northern Head and Cow Head Groups has been ascribed to variability in the carbonate margin and slope mor­ phology, which influenced local palaeoceanographic conditions and resulted in the more extensive and continuous deposition of biogenic debris in the Cow Head area (Botsford, 1988). Notwithstanding these lateral and facies vari­ ations, the abundance of organic carbon in Middle Cambrian to Early Ordovician sediments is con­ sistent with an episode of extensive black shale de­ position, suggestive of poorly aerated deep-marine bottom water, worldwide (cf. Leggett et a/., 1981). The appearance of more oxidizing conditions in the

J. W. Botsford and D. F. Sangster

128

Late Tremadocian of the Northern Head and Cow Head Groups is approximately coincident with an Early Ordovician interval sparse in black shale worldwide, suggesting that this oxygenated episode may reflect global oceanic conditions. BASE METALS Introd uction

Localized enrichments of base metals (zinc, lead, copper and nickel) are apparent in shales of the Humber Arm Allochthon, but in detail differ in magnitude and mode of occurrence between the Northern Head and Cow Head Groups. Individual enrichments in the following order of magnitude occur in the Northern Head Group: zinc-400 ppm, lead-300 ppm, copper-350 ppm and nickel130 ppm. Lead occurs at these anomalous concen­ trations only in the Northern Head Group and enrichments of the other metals do occur in the Cow Head Group but are not as profound. Anomalously high nickel contents can be at­ tributed to two contrasting styles of occurrence. First, nickel is associated with disseminated sulphides in shales (see discussion below). Second, nickel oc­ curs in detrital silicate grains in ophiolite-derived flysch (Lower Head, Eagle Island Formations) cap­ ping both allochthonous sequences. Northern Head Group

Abundant pyrite occurs in an approximately 10 m interval at the base of the Northern Head Group, near the Irishtown -Cooks Brook Formation bound­ ary. Here, several beds of carbonate pebble con­ glomerate, ranging in thickness from 20 to 400 mm, are partially to completely replaced by pyrite (Fig. 9a). The only lithology which is never replaced is black, phosphatic shale, which comprises up to 10% of individual beds. In some instances, where replace­ ment is complete, field textures are suggestive of detrital pyrite, but petrographic examination indi­ cates that this is a relatively fine crystalline (30 �J.m), pebble-by-pebble replacement of an original carbon­ ate conglomerate, with interstitial ferroan carbonate cement. This unit overlies a 40 m thick black shale sequence at the top of the Irishtown Formation and occurs within the most intensely anoxic interval developed in the Humber Arm Supergroup. No base metal sulphides have so far been observed.

The stratigraphic distributions of lead, zinc, copper and nickel within the Northern Head Group (Fig. 10) show a pronounced enrichment in Arenigian shales at the top of the Middle Arm Point and base of the Eagle Island Formation. Petro­ graphic and SEM/EDX (scanning electron microscopy/energy diverted X-ray analysis) examin­ ation revealed the presence of chalcopyrite, galena, sphalerite and locally pentlandite all occurring as highly disseminated blebs and grains, 10-50 �tm in size, and within very thin veinlets. Sulphide blebs are commonly irregular, inter­ grown and locally replacive with the clay matrix. Where sulphides have been noted within adjacent thin sandstones, they occur as late pore fillings, sur­ rounding detrital grains and locally replacing inter­ stitial matrix and cement (Fig. 9b). Intergrown galena-sphalerite (Fig. 9c) and galena-chalcopyrite also occur in cubic habit. Veinlets of galena or chalcopyrite up to 0.25 mm in width occur intergrown with vein-filling potassium fieldspar and quartz (Fig. 9d). All metal anomalies in the Northern Head Group and adjacent units occur in bedded sediment. Sam­ pling of associated melange units has yielded only background concentrations of zinc, lead, copper and nickel. Cow Head Group

Figures 11 and 12 illustrate the stratigraphic distri­ bution of zinc, lead, copper and nickel within proxi­ mal and distal facies shales of the Cow Head Group. In contrast to the Northern Head Group, zinc and copper anomalies within Cow Head Group shales are not concentrated at one stratigraphic horizon, but are scattered from the Upper Cambrian to the Lower Ordovician. Compared to Northern Head Group shales, concentrations of lead, nickel, zinc and copper are consistently lower. While the stratigraphic distribution of metal en­ richments is scattered, it is interesting to note that all but one (85-20; Fig. 12) occur within parts of the section characterized by poorly oxygenated depo­ sitional conditions. Detailed SEM/EDX examin­ ation indicates that most enriched metal occurrences are related to the presence of organic carbon. In some cases, sphalerite, chalcopyrite and ?pyrrhotite replace delicate framboidal pyrite (Fig. 13a), which is locally associated with organic matter. In other cases, blebs of sphalerite, with minor pyrite, sur­ round (Fig. 13b) or occur directly within (Fig. 13c)

Metal-rich shales, Newfoundland

129

Fig. 9. Sulphide occurrences in the Northern Head Group. (a) Thin beds of carbonate conglomerate completely replaced by pyrite (py) within laminated black shale (sh); base of the Cooks Brook Formation (late Middle Cambrian), Seal Cove, Middle Arm, Bay of Islands. (b) SEM/EDX photomicrograph (backscatter mode) illustrating pore-filling chalcopyrite blebs (arrows), with small inclusions of galena (bright areas), within thin sandstone bed at base of Eagle Island Sandstone. Surrounding silicate grains are opaque in backscatter mode but adjacent detrital chromite grain (Ch) can be seen; Eagle Island Formation, Bay of Islands area; magnification and scale in micrometres at lower right. (c) SEM/EDX photomicrograph (backscatter mode) illustrating intergrowth galena (gal)- sphalerite (sph) grain within (opaque) shale matrix; Middle Arm Point Formation, Bay of Islands area; magnification and scale in micrometres at lower right. (d) SEMI EDX photomicrograph (scanning mode) of veinlet within Middle Arm Point Formation shale illustrating intergrown chalcopyrite (Cp) and potassium feldspar (fsp) cross-cutting shale (sh); magnification and scale in micrometres at lower right.

flattened fragments of organic material (which can frequently be identified as graptolite fragments). All of these sulphides have precipitated relatively early in the diagenetic history of the shales, prior to

compaction or any cementation. It is of further interest to note that the style of sulphide occurrence is different in sample 85-20 within Tremadocian 'normal marine' sediments.

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Fig. 13. Sulphide occurrences in the Cow Head Group. (a) SEM/EDX photomicrograph (scanning mode) illustrating framboids comprising finel y intergrown chalcopyrite and pyrrhotite within Cow Head Group shale; Western Brook Pond; magnification and scale in micrometres at lower right. (b) SEM/EDX photomicrograph (backscatter mode) illustrating the association of sphalerite (and minor pyrite) blebs (bright areas) with flattened fragments of organic material ( flattened black area ) . This style dominates sulphide occurrences in the Cow Head Group; magnification and scale in micrometres at lower right. (c) SEM/EDX photomicrograph (backscatter mode); detail of above illustrating the presence of sphalerite (bright areas) within flake of organic material; magnification and scale in micrometres at lower right. (d) Chalcopyrite (Cp) replacing detrital chert grain in sample 85-20 from Tremadocian shale of the Cow Head Group; magnification and scale in m icrometres at lower right.

Here chalcopyrite occurs replacing chert and other grains (Fig. 13d) reminiscent of the replacive style of precipitation described for sulphides in the Northern Head Group. Discussion

Metal enrichments in shales of the Northern Head Group and Cow Head Group appear to have oc­ curred at different times and by contrasting pro­ cesses. In the first case, precipitation of zinc, copper, lead and nickel sulphides appears to have been

a stratigraphically confined, relatively late event, through vein and pore filling and replacement, not directly related to the presence of organic carbon. By contrast, sulphides in the Cow Head Group appear to have been relatively early and only in one example have been extensively remobilized. This contrast in sulphide occurrence may be related to several factors. While transition metals are generally mobile in the divalent (reduced) form, precipitation as sul­ phides will occur under reducing conditions in the presence ofH2S (Jacobs & Emerson, 1982; Maynard,

J. W. Botsford and D. F. Sangster

134

1983). Transport mechanisms may include the forma­ tion of complexes involving chloride or organic matter. Concentration of metals in organic material may commence during the life-cycle of organisms, and combined with the behaviour of these metals outlined above, is thought to account for the common association of sulphide mineralization with (organic­ rich) black shale (Vine & Tourtelot, 1970; Calvert & Price, 1970b; Maynard, 1983). Preliminary evidence suggests that these processes of metal enrichment, related to the presence of organic carbon, controlled localized sulphide precipi­ tation in Cow Head Group shales. This does not, however, appear to be the principal factor controlling anomalous occurrences of lead , zinc , copper and nickel in the Northern Head Group, since this en­ richment occurs in an interval which represents the highest levels of dissolved oxygen in the depositional and early diagenetic environment. Factors responsible for this localized enrichment may include: ( 1) the transport of metals , within detrital grains or as complexes, during deposition of the Eagle Island Sandstone ; (2) the in situ mobiliz­ ation of metals under a redox gradient during early diagenesis (cf. Klinkhammer et al. , 1982); or (3) contrasting burial and deep diagenetic history. As previously discussed, comparable illite crystallinity indices and conodont alteration indices in the two groups suggest that the last alternative is not likely.

SUL P HU R ISOTOPES Introd uction

To assess further the relationship of sulphide precipi­ tation and postulated changes in oceanic conditions sulphur isotopic values in pyrite have been deter­ mined in shale from the Northern Head and Cow Head Groups. Pyrites selected for isotope determi­ nation are of known or readily inferred age and span the entire stratigraphic sequence under consideration. Secular trends in sulphur isotopic values may be used to identify episodes of oceanic stagnation, and associated widespread reducing conditions , and ven­ tilated, relatively oxidizing conditions, which may have been a factor in controlling base metal mobility (cf. Goodfellow & Jonasson, 1984; Goodfellow, 1987). In the Cambrian-Devonian sedimentary se­ quence of the Selwyn Basin, for example (ibid. ) , anoxic events related to oceanic stratification are

characterized by isotopically heavy pyrite sulphur, where 634S is roughly +30%o. Ventilated episodes are defined by less positive isotopic values, where ()34S approaches roughly +5%o. The nature of the sulphur reservoir present in bottom water at any given time is indicated most directly by early diagenetic pyrite (or its metastable precursor), precipitated at the onset of bacterial sulphate reduction during shallow burial. Ensuing generations of pyrite tend to be coarser crystalline and more euhedral and may incorporate sulphur of uncertain isotopic history. In general, it appears that pyrite precipitated first in the diagenetic sequence incorporates the isotopically lightest sulphur , and that ensuing pyrite generations become progressively isotopically heavier (e.g. Raiswell, 1982). A chemical technique recently developed at the Geological Survey of Canada (Hall et al. , 1988) facilitates the extraction, separation and sulphur isotope determination of this highly disseminated, fine-crystalline, early precipitated pyrite which com­ monly occurs in the shale samples of this study. The majority of sulphur isotopic analyses reported in this study are of this type of sulphide occurrence. The sulphur isotopic signatures for 1 1 samples of burrow­ filling and fine nodular pyrite from the Cow Head Group have also been determined. Four samples from the Northern Head and Cow Head Groups have yielded sufficient authigenic barite to establish the sulphur isotopic signature in this sulphate. Chemical separation of pyritic and baritic sulphur was performed using the techniques of Hall et al. (1988). Sulphur isotopic determinations were then performed at Geochron Laboratories, Cambridge , Massachusetts, on a contract basis. Temporal changes in sulphur isotopic signature

A pattern of temporal change in 634S values is most clearly displayed by the Northern Head Group (Fig. 1 4), in part because of sampling density, and is confirmed by data from the Cow Head Group (Fig. 15). Based upon the principles briefly outlined above , this temporal variation is remarkably consis­ tent with the postulated Lower Ordovician ventil­ ation event discussed in previous sections. Northern Head Group

Sulphur isotopic signatures in the Northern Head Group are heaviest near the (uppermost Middle Cambrian) Cooks Brook -Irishtown Formation

Metal-rich shales, Newfoundland

135

.

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D e p o s i t i o n a l /e a r l y d i a g e n e t i c c o n d i t i o n s

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S u l p h u r I s o t o p i c s i g n a t ure o r :

I n d i c a t e d b y o t h e r p a r a m e t e r s (se d i m e n t o l o g y , s h a l e g e o c h e m . , S IC r e l a t i o n s h i p s )

Fig. 1 4 . Sulphur isotopic signature (%o) of finely disseminated pyrite in shales of the Northern Head Group and adjacent units. The sulphur isotopic signature of authigenic barite in three shale samples is also shown.

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f i n e l y d i s s e m i n a t e d p y r i te In

v e n t i l a t ed c o n d i t i o n s

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A n o m a r o u s m e t a l c o n c e n tra t i o n s

boundary, where b34S values close to + 30%o occur (Fig. 14). This coincides with the most pro­ nounced anoxic conditions , as indicated by sulphur ­ carbon relationships discussed previously (see Fig. 7). A progressive upward change to lighter-pyrite sulphur in the Early Ordovician is evident, and is most pronounced in the Middle Arm Point Forma­ tion, where o34S values approaching 30%o occur. Here again sulphur isotope data mirror other evi­ dence in suggesting the onset of ventilated conditions in the Early Ordovician. Of particular i nterest is the return, in the Arenigian, to a heavier isotopic signa­ ture, ranging from roughly 0 to +22%o. This stratigraphic interval coincides with the anomalous concentrations of zinc , lead, copper and nickel within the uppermost Middle Arm Point Formation (see Fig. 10). The significance of this relationship is un­ clear. It may be that the sulphur isotope signature is indicating a subtle return, not otherwise apparent, to more stratified conditions conducive to the pre­ cipitation of sulphides. -

Cow Head Group

The transition from isotopically heavy pyrite sui-

phur in the Cambrian to a lighter signature in the Ordovician is also evident in the Cow Head Group. Furthermore the presence of isotopically heavier sulphur in the Arenigian is evident in the proximal setting (Fig. 15) , coincident with the return to poorly oxygenated conditions described in previous sec­ tions. Isotopic data for the same interval in the distal setting is not presently available. Sulphur isotopic signature of barite in the Northern Head and Cow Head Groups

The sulphur isotopic signature of authigenic barite in the Northern Head Group (Fig. 14) and Cow Head Group (Fig. 15) falls within the range of b34S values established for pyrite sulphur in surrounding samples. This is surprising since fractionation associ­ ated with sulphate reduction normally results in a considerable separation of sulphide and sulphate signatures. Only one (Northern Head Group) sample could be interpreted as distinct from the pyrite sulphur field, and falls within the o34S range of +30%o in dicated for Cambro-Ordovician sulphate by Claypool et a!. ( 1980). The reason for this conver­ gence of pyrite and barite isotopic signatures is not

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Fig. 15. Sulphur isotopic signature (%o) of: (a) finely disseminated pyrite (open squares); (b) burrow-filling or fine nodular pyrite (filled squares); and (c) authigenic barite (si ngle sample) in shales of the Cow Head Group.

c o n d it i o n s

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Metal-rich shales, Newfoundland

clear. It may be related, however, to the model outlined by Berner (1980) of upward diffusion of reduced sulphur from a zone of bacterially driven sulphate reduction (where it was fractionated) and the subsequent reoxidation of this sulphur and incor­ poration in authigenic sulphate. Barite is only found in 'ventilated' samples.

SUMMARY AND

DISCUSSION

Localized enrichments of metals (300+ ppm) in shales occur in two princip al styles and settings in the allochthonous Lower Palaeozoic sequences of western Newfoundland. The contrasting nature of these occurrences appears to be related to fundamen­ tal differences in depositional and early diagenetic conditions. In the Northern Head Group, anomalous metals in Arenigian shales are found in sphalerite, galena, chalcopyrite and locally pentlandite which occur as highly disseminated replacements and pore and vein fiUings. In contrast, zinc, copper and nickel sul­ phides scattered throughout Cambrian-Ordovician shales of the Cow Head Group are associated with organic matter and show only localized evidence of subsequent remobilization. The sedimentology, shale geochemistry, sulphur­ carbon relationships and sulphur isotopes indicate a significant change in the marine environment, from Cambrian- Early Ordovician anoxic conditions to a ventilation event commencing in the Late Tremadocian. These conditions appear to have con­ tinued through the Arenigian in the Northern Head Group, while S : C profiles suggest a return to more reducing conditions in the Cow Head Group. The occurrence of sulphides outlined above ap­ pears to be related to these temporal variations in oceanic conditions. The most profound buildup of sulphides consists of pyrite at the (Upper Middle Cambrian) base of the Cooks Brook Formation in the Northern Head Group. The replacive and vein-filling style of sulphide occurrence in the Northern Head Group (and locally within the Cow Head Group) may reflect a redox­ related mobilization of metals within sediments de­ posited during the Lower Ordovician ventilation episode. It is possible that the precipitation of these sulphides may be related to a return to more stratified conditions during the Arenigian. In the Northern Head Group this is subtly suggested by the o34S profile which briefly returns to more positive values

and may indicate an episode of stratified, reducing conditions conducive to H2S formation and sulphide precipitation. It is interesting to note that most of the platform­ hosted base metal occurrences in western Newfoundland are localized in the Lower Ordovician St George Group. It is not clear what the relation­ ship is between this mineralization and the Lower Ordovician 'ventilation event' postulated in this study. Unknown is the timing of metal mobility (in deep-marine shales) and the dewatering of this sedi­ mentary sequence. Dewatering during collisional orogenesis may have commenced as early as the Middle Ordovician Taconic orogeny, but regional geologic considerations suggest that the most signifi­ cant compression occurred later, during the Acadian.

ACKNOWLEDGEMENTS

This study forms part of a collaborative project undertaken through the Canada-Newfoundland Mineral Development Agreement ( 1984-89), DSS Contract 23233-7-0223/0 1 -ST. Many of the results are also based upon fieldwork, sampling and analysis supported by the Natural Science and Engineering Research Council funding to N.P. James, whose advice regarding sedimentological and regional geological aspects is gratefully acknowledged. The cooperation and technical support of the Newfoundland Department of Mines and Geological Survey of Canada are also acknowledged. Reviews by E. Cameron, W. Goodfellow and R. Raiswell substantially improved the manuscript.

REFERENCES

R . A . ( 1970) Sedimentary pyrite formation. A m . J. Sci. 268 , 1-23. BERNER, R.A. ( 1980) Early Diagenesis: a Theoretical Approach . Princeton U niversity Press , Princeton, 241pp. BERNER, R . A . ( 1984) Sedimentary pyrite formation: an update. Geochim. cosmochim. A cta 48, 605 - 6 15 . BoLTON , B . R . & FRAKES, L . A . ( 1985) Geology and genesis of manganese oolite, Chiatara, Georgia , USSR. Geol. Soc. Am. Bull. 96, 1398- 1406. BoTSFORD, J . W . ( 1988) Depositional history of Middle BERNER,

Cambrian to Lower Ordovician deep- water sediments,

western Newfoundland. Unpublished PhD Thesis, Memorial University of Newfoundland, 509pp. BOUVIER, J . L . & A BB EY , S. ( 1980) Simultaneous determi­ nation of water, carbon dioxide and sulfur i n rocks by Bay of Islands,

138

J. W. Botsford and D. F. Sangster

volatization and non-dispersive infrared absorptiometry. J. Spectros. 25, 126- 132. BYERS, C.W. ( 1977) B iofacies patterns in euxinic basins: a general model. I n : Deep Water Carbonate Environments (Ed. by H . E . Cook and P. Enos), pp . 5 - 18. Spec. Publ . Soc. Econ. Paleont. Miner. 25. CALVERT, S.E. & PRICE , N .B. ( 1970a) Composition of manganese nodules and manganese carbonates from Loch Tyre, Scotland . Contrib. Min. Petrol. 29, 2 1 5 - 233. CALVERT, S . E . & PRtCE, N . B . ( 1 970b) Minor metal contents of recent organic-rich sediments off southwest Africa . Nature 227 , 593-595. CLAYPOOL, G . E . , HOLSER, W . T . , SAKI, l . R. & ZAK, I . ( 1980) The age curves for sulfur and oxygen isotopes i n marine sulfate a n d their mutual interpretation. Chem. Ceo!. 28 , 199-260. FRAKES, L . A . & BOLTON , B . R . ( 1984) Origin of manganese giants: sea-level rise and oxic-anoxic history. Geology 12, 83-86. GooDFELLOW , W. (1987) Anoxic stratified oceans as a source of sulphur in sediment-hosted stratiform Zn- Pb deposits (Selwyn Basin, Yukon, Canada). Chem. Geol. 65, 359-382. GoODFELLOW, W . & JoNASSO N , I. ( 1 984) Ocean stagnation and ventilation defined by o34S secular trends in pyrite and barite, Selwyn Basin, Yukon. Geology 12 , 583-586. HALL, G . E . M . , PELCHAT, J. & LOOP, J. (1988) Separation and recovery of various sulphur species in sedimentary rocks for stable sulphur isotope determination. Chem. Geol. 67, 34-45. HESSE, R . ( 1 986) Early diagenetic pore water/sediment interaction: modern offshore basins. Geosci. Can. 13, 165- 196. JACOBS, L . & EMERSON , S. (1982) Trace metal solubility in an anoxic fjord. Earth Planet. Sci. Lett. 60, 237-252. JAMES, N . P . & STEVEN S , R . K . ( 1 986) Stratigraphy and Can.

Correlation ofthe Cambro-Ordovician Cow Head Group, Western Newfoundland. Geological Survey of Canada, Bulletin 366. KLAPPA , C . F . , 0PALINSKl, P . R . & JAMES, N . P . (1980) Middle Ordovician Table Head Group of Western Newfoundland: a revised stratigraphy. Can. J. Earth Sci. 17, 1007- 1019. KLINKHAMMER, G., HEGGIE, D .T. & GRAHAM, D.W. ( 1 982) Metal diagenesis in oxic marine sediments. Earth Planet. Sci. Lett. 6 1 , 2 1 1 -219. KRAUSKOPF, K.B. (1967) Introduction t o Geochemistry. McGraw-Hill, New York, 72 lpp. LEGGErr, J . K . , McKERRow, W . S . , CocKs, L . R . M . & RICHARDS, R . B . ( 1981) Periodicity in the early Palaeozoic marine realm. J. Geol. Soc. Lond. 138, 1 67 - 176. LEVENTHAL, J . ( 1979) The relationship between organic carbon and sulfide sulfur in recent and ancient marine and euxinic sediments. EOS 60, 283. LEVENTHAL, J. ( 1983) An i nterpretation of carbon and

sulfur relationships i n Black Sea sediments as indicators of environments of deposition. Geochim. cosmochim. A cta 47, 133 - 137 . LEVENTHAL, J . ( 1987) Carbon and sulfur relationships in Devonian shales from the Appalachian Basin as an indicator of environment of deposition. Am. J. Sci. 287, 33-49. LYNN , D . C . & BoNATTl, E. ( 1965) Mobility of manganese in diagenesis of deep-sea sediments. Marine Ceo!. 3, 457-474. MAYNARD, J . B . ( 1 980) Sulfur isotopes of iron sulfides in Devonian-Mississippian shales of the Appalachian Basin: control by rates of sedimentation. Am. J. Sci. 280, 772-786. MAYNARD, J . B . ( 1983) Geochemistry of Sedimentary Ore Deposits. Springer, New York, 305pp. PEDERSEN, T.F. & PRICE , N . B . ( 1982) The geochemistry of manganese carbonate in Panama Basin sediments. Geochim. Cosmochim. Acta 46, 59-68. RAISWELL, R . (1982) Pyrite texture, isotopic composition and the availability of iron. Am. J. Sci. 282, 1244- 1263. RAISWELL, R . & BERNER, R . A . ( 1985) Pyrite formation in euxinic and semi-euxinic sediments. Am. J. Sci. 285 , 710-724. RHOADS, D . C . & MoRSE, J . W . ( 1971 ) Evolution and eco­ logic significance of oxygen-deficient marine basins. Lethaia 4, 413 -428. SEtLACHER, A. ( 1978) Use of trace fossils for recognizing depositional environments. In: Trace Fossil Concepts (Ed. by P . B . Basan) , pp. 1 67 - 18 1 , SEPM Short Course No. 5 . STENZEL, S . R . & JAMES, N . P . (1987) Death and destruction of an

early

Paleozoic

carbonate

platform,

western

Program with Abstracts, Society of Economic Paleontologists and Mineralogists Mid-Year Meeting, AustilL STEVENS, R . K . ( 1970) Cambro-Ordovician flysch sedimen­ Newfoundland.

tation and tectonics in west Newfoundland and their

Geological Associ­ ation of Canada, Special Paper No . 7 , pp. 165- 177. VtNE, J . D . & TouRTELOT, E . B . ( 1970) Geochemistry of black shale deposi ts - a summary report. Econ. Geol. 85, 253-272. WtLLIAMS, H. ( 1979) Appalachian Orogen in Canada. Can. J. Earth Sci. 16, 792-807. WILLIAMS, H . , JAMES, N . P . & STEVENS, R . K . ( 1985) Humber Arm Allochthon and nearby groups between Bonne Bay and Portland Creek, western Newfoundland. In: Current Research , Part A. Geological Survey of Canada, Paper 85 - 1 A , pp. 399-406. WILSO N , T . R . S . , THOMSON , 1 . , HYDES, D . J . , COLLEY, S . , CALKIN, F . & SORENSEN , J . ( 1986) Oxidation fronts in pelagic sediments: diagenetic formation of metal-rich layers. Science 232, 972-975. bearing on a proto-Atlantic Ocean .

Spec.

Pubis inl. Ass. Sediment. (1990) 11, 139-146

Origin of iron carbonate layers in Tertiary coastal sediments of Central Kalimantan Province (Borneo), Indonesia G .R .

SIEFFERMANN

ORSTOM-UGM Cooperation, Sekip K 3, Yogyakarta, Indonesia

ABSTR ACT

Siderite layers, brown coals and quartzitic sands are an important part of the Tertiary section of the Rungan River Basin in Central Kalimantan Province, Indonesia. The siderite layers consist of grey, fine­ grained, indurated rocks. The depositional setting in Borneo during the Upper Tertiary was that of a large coastal lowland area with peat swamps and tropical giant podzols, much like the modern landscape. This environment seems to have been favourable for the formation of siderite. A relationship can be suggested between iron carbonate sedimentation and deferrification of onshore sedimentary continental formations through a pedological podzolization process. The iron was probably removed from the soils by 'black' waters which were rich in iron-complexing organic compounds. The iron carbonate was probably formed in tidal lagoons, in a brackish environment under reducing conditions. The depositional setting shows that the origin of the iron in siderite layers must be sought laterally, probably hundreds of kilometres away, in bleached siliceous formations, associated with coal beds which are the former peat deposits. This mode of occurrence may have application to other sequences where such distinct lateral relationships are less obvious.

INTRODUCTION Since 1979, Indonesian and ORSTOM scientists,

DESCRIPTION OF THE OUTCROPS

within the framework of scientific cooperation be­ tween Indonesia and France, have produced soil

Siderite

maps covering large parts of Central Kalimantan Province (Brabant & Muller, 1981; ORSTOM &

The most conspicuous outcrops of bedded siderite

Dept Transmigrasi, 1981). Numerous observations

are located on the Rungan River, between its conflu­

and analyses are available for the post-Miocene

ence with the Manuhing River and the town of

sediments of the Central Kalimantan Coastal Plain

Tumbang Jutuh (Fig. 1). On this stretch, the Rungan

(Sumartadipura, 1976).

River cuts its valley through post-Miocene sedi­ ments. Three main siderite outcrops can be ob­

The outcrops of these sediments reveal sandy sometimes intercalated with gravels and

served within the river channel between July and

clayey horizons, siderite, and coal beds. An analysis

November, when the water level of the river is low.

layers,

The siderite consists of a very hard rock, forming

of the modern depositional setting of the coastal plain was carried out as a basis for interpreting the

nearly continuous layers between

nature and formation of these outcrops. This paper

thickness. The layers are so hard that they form

outlines the characteristics of the main outcrops

small rapids in the river (Fig.

2).

200 and 300 mm in

The rock has a very

and describes the

pale yellowish-grey colour which changes gradually

present coastal landscape and geochemistry of units

into dark reddish-violet, especially after a week of

within it.

air exposure. This change in colour is not just super-

along the Rungan River (Fig.

1)

Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

139

C. R.

140

10

20

Sieffermann

30

Fig. 1. Coal and siderite outcrops

c::::? SIDERITE

/COAL

�LIMESTONE

along the Rungan River, Borneo, Indonesia.

Fig. 2. Outcrop of siderite layers in

the Rungan River, in Central Kalimantan (Borneo).

Iron carbonate layers in coastal sediments, Borneo

141

ficial; after two weeks a depth of and after two months a

20 mm is affected, 100 mm thick block becomes

completely dark red up to the centre. This change in colour undoubtedly corresponds to an oxidation process. Submerged under the river water the sider­ ite acquires only a very superficial yellow crust.

Clay beds The indurated siderite layers are mainly underlain by fine soft bluish-grey clay. Frequently, organic matter in the form of leaves and other plant frag­ ments can be observed in these clay layers. The overlying sediments above the siderite are silty with an upwards increasing amount of sand, and a minor amount of quartz gravels.

Coal beds Between the second and third outcrop of siderite (Fig.

1),

five coal beds can be observed. Coals have

not been observed to directly overlie the siderite. The rank of the coal is brown coal and the total thickness reaches

800

mm (Fig.

3).

Perfectly pre­

served tree trunks can be found within the coal layers, indicating a depositional environment of forest peat, similar to that described by Cecil

(1985)

et al.

for the Central Appalachian Basin during the

Carboniferous and comparable to the current peat belt in Kalimantan to the south (Fig.

Fig. 3. Outcrop of Miocene coal on the Rungan River, in Central Kalimantan (Borneo).

4). instead appears to be more like that of coastal sedimentation under a periodic marine influence,

ANALYTICAL DATA

mainly

because

of

its

montmorillonite-chlorite

In its X-ray diffraction pattern, the siderite has all

content, its bluish colour and reducing character­

the characteristic reflections of iron carbonate

istics, and the absence of goethite and hematite.

(3·58,

with the siderite

An explanation for the genesis of the siderite is

is an interstratifi.ed montmorillonite-chlorite. In a

more problematic. A good approach to understand

12·8 A,

its deposition is to look at geochemical mechan­

and after glycerol

isms of the modern coastal plain of the Indonesian

2·79, 2·34

and

2·13 A). Associated

normal state, the main peak for this phase is shifting after· heating to treatment to

)4·7 A.

11·8 A,

Fine quartz, illite and dis­

Central Kalimantan Province.

ordered kaolinite are often associated with these minerals. The bluish-grey clay underlying the siderite contains the same montmorillonite-chlorite min­

THE MODERN COASTAL LANDSCAPE

eral, associated with disordered kaolinite, illite, and a small amount of quartz.

Millions of hectares of poorly drained coastal plains

The rivers are transporting a different mineral

of the Indonesian Islands are covered with peat. The

suite today. In order of abundance, disordered kao­

peat zone of Kalimantan is situated in relation to the

linite, quartz, illite and goethite dominate the river­

other landscape units in a well-defined sequence upslope from the peat is a wide zone of

ine clay fraction in accordance with the dominant

(Fig.

oxisol and ultisol cover of the island's interior. The

deferrified tropical giant podzols; further inland is a

clay mineral mixture associated with the siderite

zone including coal and siderite; and at the centre of

4):

G.R.

142

0

50

Igneous, volcanic and m�tamorphic rocks

� � L...:.J

;Jtf;,'fJ; §

}

Sieffermann

100Km

Post Mioc�n� s�dim�nts with coal and Sid�rit� lay�rs

with Oxisols and Ultisols covn

D�f�rrifi�d PODZOL 5 Thick ombrog�nous PEAT Coastal PEAT on brackish wat�r s� dim�nts

the island is a vast oxisol landscape developed on

Fig. 4. Succession of soil types in Central Kalimantan Province.

The oxisols

crystalline and volcanic rocks. Towards the coastal

In the upstream units, the oxisol formation is con­

area, thinner peats overlie predominantly clayey,

trolled by two mechanisms: weathering and erosion.

brackish

water

sediments

contammg

pyrite,

montmorillonite-chlorite and sometimes siderite.

1 Weathering destroys completely the minerals of the crystalline and volcanic rocks through a hydroly­ sis process. The less-soluble elements remain and form the characteristic minerals of the oxisols; mainly

GEOCHEMISTRY OF MODERN COASTAL LANDSCAPE

kaolinites, iron and aluminium oxides and hydrox­ ides. Such processes have been well studied during the last

The geochemistry of each of the landscape zones represented in Fig.

4

is different.

30 years by Bonifas (1959), Millot (1964), ( 1965), Lelong ( 1967), Tardy (1969) and Sieffermann (1973). These authors have shown that Delvigne

Iron carbonate layers in coastal sediments, Borneo

143

during hydrolysis, nearly two-thirds of the weathered

The hardpan forms a nearly permanent water table

rock is removed in soluble, ionic form. It is easy to

with only lateral outflow.

forget this because the process is invisible. The hydrolysis of

parts of andesite gives only

part of

Such podzols have been extensively reported dur­ ing the last 30 years by Viera & Oliveira-Filho

quantity of soil we can see in Borneo, on the Matto

( 1962), ( 1964), Klinge (1967, 1969), Andriesse ( 1969, 1970), Turenne (1970, 1975), Flexor et al. ( 1975) and Thompson ( 1986). The

Grosso Shield in Brazil, or in the Congo Basin, an

normal, undisturbed vegetation on such soils is

equal amount of silica has been transported to the

forest.

3

soil and the remaining

2 parts disappear.

1

Half of the

dissolved rock is silica. In other words, for each

Altenmuller & Klinge

coastal zone of sedimentation.

At its southern limit, the giant podzols are overlain

2 Erosion affects all soils and removes the soil

by ombrogenous thick peats as represented in Fig.

minerals formed during the weathering process in

The great contrast in these soils, between the white

5.

the form of suspensions in the rivers. In equatorial

quartz sand horizon and the iron and organic hard­

regions, the soils represent an equilibrium between

pan, is not caused by a change in depositional source

the weathering and the erosion processes. This re­

materials or by facies changes resulting in different

moval of 'soil minerals' can be seen and measured: it

parent materials, but by thousands of years of clay

is the solid transport. These two mechanisms are

mineral breakdown through rainwater percolation

represented on the right-hand side of Fig.

The giant podzols have been formed from fluviatile

5.

sedimentary clayey sands, similar to those deposited by modern rivers, and composed mainly of quartz

The giant podzols

gravels and sands, kaolinites and iron hydroxides.

This unit occurs over thousands of square kilometres

The percolation of the equatorial rainwater through

and forms a very flat landscape. The giant podzols

such sediments created the bleached horizon in which

can be morphologically compared with those of tem­

only quartz remains. If the past rainfall was compar­

perate climates, but differ from temperate podzols

able to the modern rainfall, a column of

by the greater thickness of their horizons. They are

rainwater has percolated slowly through these soils

characterized by a white quartz sand horizon, often

during the last

more than

5

m thick.

2

.J4VA SEA

f----

SOOm-

200m100m 35m-

--�--=-""-

30 000 years.

organic compounds has been described by Bruckert

r-----

SOUTH

About 200 Kilom
I

PODZOLS --PEAT -----11-

[

1

I

�----_,...--

sedimentation area

Lateritic weathering area De- ferrificatioo md de- aluminization area

Soluble Al and Fe organic compounds

Neoformat ions

(

Siderite Fe- Chlorite

C

+

weathering and genesis of new minerals in the coastal landscape of Kalimantan.

Soil minerals

__,/' �

(�

2:1 Clay minerals

Fig. 5. Transfer of elements during

w��

•'

I

Pyrite

OXISOLS and

I

Peat accumulation area

Coastal

km of

The removal of the iron and aluminium through

m thick, overlying an iron and alu­

minium hardpan, frequently more than

50

Soluble fr action

.

tons:

lSi 04r--

Ca++, Mg++, K•, Na• etc ... in river water

River transport

.

�

Er o s

.,__..--

�

J+

Soil minerals: Ka olinite Goethite Hematite Gibbsite

G.R.

144 (1970), (1975).

Sieffermann

Razzaghe-Karimi Tancredi

(1974), and Turenne et a!. (1975) proposed that the iron

to the genesis of the siderite and pyrite. Siderite may be the dominant mineral in reducing freshwaters

removed from the soils was later available to make

(Postma,

siderite and iron chlorite in Quaternary sediments

be

of the Amazon Delta. Tancredi

(Casagrande

et al.

therefore

1982;

more

Giresse,

frequent

1987),

in

et a!., 1977;

whereas pyrite may

seawater Postma,

environments

1982).

suggested a relationship between siderite formation

The clays surrounding the siderite layers of the

and deferrification of white kaolin deposits, pro­

Rungan River suggest brackish water sedimentation,

cesses that fit the situation in Indonesia. A similar

even though the salt has been washed away since the

mechanism was proposed by Bubenicek

Tertiary. More field investigations have to be under­

(1970)

for

the iron chlorites and siderite of the important iron

taken in order to understand the genesis of the

ore deposit of Lorraine (France). These processes

siderite and pyrite.

are shown in the central part of Fig.

There is little data available for iron carried by

5.

inland groundwater to the coastal area. However, the heavy clayey texture of the sediments, their

The coastal sedimentation zone

topographic position which is less than

1

m above

The coastal sedimentation zone is characterized by

the mean sea level, the presence of salt which induces

its clay mineral suites.

dispersion of clays and consequently the impervious­

1 Inherited clays and minerals arrive detritally from

ness of the clay layers, suggest that groundwater

the inland environment; these are mainly disordered

iron discharge may play a role only in short distance

kaolinites,

transport.

small amounts of quartz, and minor

amounts of mica.

2 Clay mineral of

2: 1

type; mainly interstratified

montmorillonite-chlorite and iron-bearing clay min­ erals with chlorite X-ray characteristics. These minerals can represent up to

30%

2: 1

CONCLUSION

of the clays of the

coastal unit.

In the coastal area of Central Kalimantan Province, minerals

the fine sediments are a mixture of inherited detrital

are almost absent in the solid load of rivers draining

components and newly formed aggradational clays

It should be emphasized that such

2: 1

tropical oxisol areas. A similar absence of such

incorporating cations from the seawater. Within this

minerals was observed in South America in the solid

clay mineral mixture, neoformed minerals such as

transport of the tropical Xingu River (Gibbs,

siderite and pyrite are being produced.

The most plausible explanation is that minerals of

1967). these 2: 1

the coastal sedimentation zone are

This modern depositional setting can be directly applied

to

post-Miocene

sediments

in

Central

formed by aggradation of degraded clay particles

Kalimantan, in which indurated siderite layers are

coming from the inland units. The river water carries

underlain by clays having a mineralogical compo­

soluble silica derived from the inland soils where

sition much like those of the modern analogue.

equatorial weathering occurs. This silica could con­

Deferrification of onshore sedimentary continental

tribute to the growth of small clay crystals in the

formations

sedimentation area, with incorporation of potassium

podzolization processes can be inferred from such

and magnesium ions from seawater in the new struc­

features

ture. Such transformations by the aggradation of

hardpans.

as

through

the

agency

bleached quartz

of

sands

pedological and

organic

inherited clays related to the environment have been extensively reported by Dietz

(1949),

Grim & Johns

Nelson

( 1960)

(1941), Grim et a!. (1957, 1959), & Murray (1960).

(1954),

and Pinsak

Powers

ACKNOWLEDGEMENTS

3 Neoformed siderite and pyrite. The iron in these two minerals is undoubtedly derived from inland,

The author wishes to express his deepest gratitude

either in the form of soluble iron-organic compounds

to J. Parnell (The Queen's University of Belfast),

or from the destruction of detrital goethite and

E.I. Robbins (US Geological Survey, Reston) and

hematite. Goethite and hematite disappear in the

M.J. McFarlane (University of Reading), for their

reducing brackish water environment of the coastal

invaluable suggestions and their great contribution

sedimentation zone, and their iron may contribute

to the correction of this text.

Iron carbonate layers in coastal sediments, Bomeo REFERENCES

H . J. & KLINGE, H. (1964) Micromorpho­ logical lllvestigations on the development of podzols in the Amazon Basin. Soil micromorphology Proc. 2nd. Int. Wk. Mtg. Soil Micromorph. Arnhem, pp. 295-305. ANDRIESSE, J.P. (1969) A study of the environment and characteristic of tropical podzols in Sarawak. Geoderma 2, 201-207. ANDRIESSE, J.P. (1970) The development of podzol mor­ phology in the Tropical Lowlands of Sarawak (Malaysia). Geoderma 3, 261-279. BoNIFAS, M. (1959) Contribution c) !'etude geochimique de !'alteration laterique. These Doc. es Sciences, Strasbourg. Mem. Serv. Carte Geol. Als. Lorr. 17, 159pp. BRABANT, P. & MuLLER, D. (1981) Reconnaissance Survey ALTE � MULLER,

in

Central

Kalimantan.

Soil

and

Land

Suitability.

Indonesia-ORSTOM Transmigration Project PTA-44, 136pp. Dept of Transmigration, Jakarta. BRUCKERT, S. (1970) Influence des composes organiques solubles sur Ia pedogenese en milieu acide. These Sci. Univ. Nancy, 250pp. BuBENICEK, L. (1970) Geologie des gisements de fer de Lorraine. These Sci. Univ. Nancy. Pub!. IRSID 48, 146pp. CASAGRANDE, D.J., SIEFFERT, K., BERSCHINSKJ, C. & SuLTON, N. (1977) Sulfur in peat forming systems of the Okefenokee Swamp and Florida Everglades: origin of sulfur 111 coal. Geochim. Cosmochim. Acta 41, 161-167. CECIL, C.B., STANTON, R.W., NEUZIL, S.G., DULONG, F.T., RuPPERT, L.F. & PIERCE, B.S. (1985) Paleoclimate controls on late Paleozoic sedimentation and peat forma­ tion 1n the Central Appalachian Basin (USA). Int. J. Coal Geol. 5, 195-230. DELVIGNE, J. (1965) Pedogenese en zone tropicale. La formation des mineraux secondaires en milieu ferral­ litique. Mem. ORSTOM 13, 177pp. DIETZ, R.S. (1941) Clay minerals in recent marine sedi­ ments. Thesis, Univ. illinois. Summary in Am. Min. 27. FLEXOR, J.M., OLIVEIRA, J.J., RAPAIRE, J.L. & StEFFERMANN, G. (1975) La degradation des illites en montmorillonite dans I' Alios de podzols tropicaux humo­ ferrugineux du Reconcavo Bahianais et du Para (Bresil). Cah. ORSTOM (ser. Pedol.) Xill, 41-48. GIBBS, R.J. (1967) Geochemistry of the Amazon River system. Geol. Soc. Am. Bull. 78, 1203-1232. GJRESSE, P. (1987) Les depots Quaternaires du lac Barombi-Mbo (Ouest Cameroun). Geodynamique 2, 132-133. GRIM, R.E., DIETZ, R.S. & BRADLEY, W.F. (1949) Clay mineral composition of some sediments from the Pacific Ocean of the California Coast and the Gulf of California. Bull. Geol. Soc. Am. 60, 1785-1808. GRIM, R.E. & JoHNS, W.O. (1954) Clay mineral investi­ gations of sediments in the Northern Gulf of Mexico. Clays Clay Min. (2nd Nat!. Conf. 1953), 81-103. KLINGE, H. (1967) Podzol soils: a source of blackwater

145

rivers in Amazonia. In: Atas do Simposio s6bre a biota amazonica. Limnologia, 117-125. KLINGE, H. (1969) Climatic conditions in lowland tropical podzol areas. Trop. Ecol. 10, 222-239. LELONG, G.F. (1967) Nature et genese des produits d'alteration de roches cristallines sous clima/ lropical hunude (Guyane Fram;aise).

These Sci. Univ. Nancy,

182pp. MILLOT,

G. (1964)

Geologie des Argiles.

Masson, Paris,

499pp. B.W. (1960) Clay mineralogy of the bottom sedi­ ments, Rappahannock River, Virginia. Clays Clay Min. (7th Nat!. Conf. 1958), 135-148. ORSTOM & DEPT. TRANSMIGRASI (1981) Reconnaissance survey in Central Kalimantan. Phase I Maps. 21 maps 11250 000. ORSTOM-Transmigrasi Project PTA-44. Dept of Transmigration, Jakarta. PINSAK, A.P. & MURRAY, H.H. (1960) Regional clay min­ eral patterns in the Gulf of Mexico. Clays Clay Min. (7th Nat! Conf. 1958), 162-178. PoSTMA, D. (1982) Pyrite and siderite formation in brackish and fresh water swamp sediments. Am. J. Sci. 282, 1151-1183. PowERS, M.C. (1957) Adjustment of land derived clays to the environment. J. Sedim. Petrol. 27, 355-372. PowERS, M.C. (1959) Adjustment of clays to chemical change and the concept of the equivalence level. Clays Clay Min. (6th Nat!. Conf. 1957), 309-326. RAZZAGHE-KARIMI, M. (1974) Evolution geochimique et NELSON,

mineralogique des micas et phyllosilicates en presence

These Univ. Paris VI, 96pp. G. (1973) Les sols de quelques regions vol­ caniques du Cameroun. These Sci, Strasbourg. Mem. ORSTOM 66, 183pp. SuMARTADIPURA, A.S. (1976) Geologic map of Tewah quadrangle, Central Kalimantan, 1: 100 000 scale. Geol. Survey of Indonesia, Bandung. TANCREDI, A., SIEFFERMANN, G., BESNUS, Y., FUSIL, G. & DELIBRIAS, G. (1975) Presence et formation de niveaux de siderite dans les sediments recents du delta Amazonien. Bull. Groupe fram;. Argiles XXVII, 13-29. TARDY, Y. (1969) Geochimie des alteralions. Eludes des d'acides organiques.

SIEFFERMANN,

arenes

et

des

eaux

de

quelques

massif�·

criswllins

These Sci. Strasbourg. Mem. Serv. Carte. Geol. AIs. Lorr., 270pp. THOMPSON, C.H . (1986) Giant podzols on Pleistocene dunes in eastern Australia. XIII Congr. Int. Soc. Soil Science, Hamburg ill, 1295-1296. TuRENNE, J.F. (1970) Influence de Ia saison des pluies sur Ia dynamique des acides humiques dans les profils ferral­ htiques et podzoliques sous savane en Guyane Fran�aise. Cah. ORSTOM, Pedol. Vill, 419-450. TuRENNE, J.F. (1975) Mode d'humification et differentiation podzolique dans deux toposequences guyanaises. These, Univ. Nancy, 175pp. VIERA, L.S. & OLIVEIRA-FILHO, J.P.S. (1962) As caatingas do Rio Negro. Bol. Tee. lnst. Agron. Norte 42, 1-42. d'Europe et d'Afrique.

Spec. Pubis int. Ass. Sediment. (1990) 11, 147-156

Mineral deposits in Miocene lacustrine and Devonian shallow-marine facies in Yugoslavia

J. OBR AD O V I C

and

N. V A SIC

Faculty of Mining and Geology, University of Beograd, Djusina 7, I 1000 Beograd, Yugoslavia

ABSTRACT Miocene lacustrine facies in Serbia, Yugoslavia, contain sedimentary zeolites, bentonites, oil shales with authigenic minerals, magnesites and borates. Some of these mineral deposits are of diagenetic origin, including the alteration of volcanic glass. In some cases hot waters of volcanic origin migrated through serpentines that underlie the lake basins, bringing magnesium to the lake water. Boron was derived by the leaching of volcanic and pyroclastic rocks by meteoric waters. Devonian marine shallow-water facies in western Macedonia include oolitic ironstone deposits. Oolitic ironstones (mostly chamositic clays) were deposited within a clastic sequence composed of clays, silts and sands which were subsequently metamorphosed. All primary structures were destroyed by metamorphism and/or tectonic activity. The internal fabrics of the chamosite ooids are mostly tangential, although in some cases they are radial. The iron had a multiple origin, including streams which drained weathered terrains and possibly upwelling deep basin waters.

INTRODUCTION

chamosite ooids with both tangential and radial­ concentric fabric are recognizable.

In Yugoslavia, especially in Serbia, many non­ metallic mineral deposits occur in lacustrine facies of Tertiary age including sedimentary zeolites (Obradovic, 1988), bentonites, oil shales (Obradovic & Jovanovic, 1987), borates and sedimentary magnesites (Obradovic et al., 1984). Their formation is related to the diagenetic alteration of volcanic glass (bentonites, zeolites), or to other processes (sedimentary magnesites, borates and others) m alkaline-saline lakes. A Devonian ironstone formation is mined in western Macedonia. Many geologists (Page, 1958; Harder, 1966; Kleut, 1966, 1968; Obradovic & Karamata, 1982; Karamata, et al., 1982, 1988) have investigated the Tajmiste ironstone deposit, but some problems remain unresolved. The oolitic ironstone ores from Tajmiste are a shallow-marine facies, within a sequence of clastic sediments. Re­ crystallized limestones occur only at the top of the series. Although the ironstone formation has experi­ enced metamorphism and/or tectonic deformation, Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

LACUSTRINE FACIES

Many lake basins existed in Serbia in Neogene times. The lakes became established in the Palae­ ogene, and lasted until the Upper Miocene or Pliocene. All of them were freshwater lakes (Fig. 1), situated in graben-like intermontane basins near the marginal part of the Pannonian Sea. Under the influence of contemporaneous vol­ canism (heating of water), vertical movements of fault blocks (shallowing and deepening in different parts of the lake) and a dry, arid climate, the lake water changed from fresh to alkaline and saline (Obradovic, 1983). This occurred at a certain stage of lake development and often only in some parts of the lake. Because of subsequent subsidence and water inft.ow, all lakes reverted to freshwater en­ vironments. According to Pantie & Mihajlovic 147

1. Obradovic and N. Vasic

148

c-·,

- - ·.._ r,\ .;- ·--···: � .

(�) /

)

'·

)

Fig. 1. Palaeogeographic reconstruction of Miocene environments in Yugoslavia. After Grubic (1980). (1) Land, (2) lakes, (3) sea, (4) land-sea boundary, (5) islands, (6) volcanic centres (dacite-andesite), (7) Slanci Basin, (8) Valjevo-Mionica Basin, (9) Jarandol Basin, (10) Vranje Basin. I, Adriatic Basin; II, Pannonian Basin; III, Dacian Basin; IV, land with lakes.

( 1977), a comparison between fossil floras collected over a wide area in Central and Southern Europe shows that the dry climatic zone shifted from the north, southwards throughout the Miocene.

marl and tuff were deposited in the lake. The prod­ ucts of the diagenetic alteration of the tuffs were bentonite, clinoptilolite and analcime. Oil shales

Zeolites

In Serbia, a dry period occurred in the Middle Miocene (Table 1). At that time sedimentary zeolites (the product of the diagenetic alteration of volcanic glass) were formed in many lake basins. These zeolites are mostly referrable to clinoptilolite, as in the Slanci Basin and the Vranje Basin at Zlatokop (Obradovic & Dimitrijevic, 1987). At Zlatokop in the Vranje Basin, zeolitized quartz-latitic tuffs are interbedded with marly sedi­ ments of Middle Miocene age (Fig. 2). The tuffs are separated from the marly sediments by layers of laminated silicified tuffs containing analcime and lenses of black chert. The tuffs are predominantly fine-grained volcanic ash and rare crystals of quartz, plagioclase (30-35% An) and biotite. The tuffs are on average about 80% zeolitized, and constitute up to 90% of the rock volume. The zeolite corresponds to calcium clinoptilolite. In some lake basins, including the Slanci Basin, lacustrine sediments overlie a fluvial floodplain and swamp succession. Clay, dolomitic and tuffaceous

The lacustrine facies includes two types of oil shale. The first is carbonate-rich and the second is silici­ clastic. The first type, in the Valjevo-Mionica Basin, includes dolostones and rarely dolomitic marlstones with laminae of kerogen. Moulds of gypsum crystals are very common in the carbonate rocks. It is possible to distinguish three series. The lower series contains varved and laminated pelites (mostly marlstones) and laminae of kerogen and rare beds of searlesite. The middle series contains tuffaceous material and varved pelites (tuffaceous dolostones and dolomitic marlstones) with laminae of kerogen and beds of searlesite in association with analcime and potassium feldspar crystals. The upper series consists of carbonate rocks with rare laminae of kerogen. A younger siliciclastic formation lies transgressively upon them (Obradovic & Jovanovic, 1987). In another type of oil shale, in the Vranje Basin of Oligo-Miocene age, laminae of kerogen alternate with laminae of shale or clay, but the authigenic minerals mentioned above have not been discovered in them.

Table 1. Lacustrine facies and their characteristics Slanci Basin

Vranje Basin Zlatokop

Jarandol Basin

Valjevo-Mionica Basin

Age

Lower-Upper Miocene

Lower Miocene-Pliocene

Lower- Upper Miocene

Late Lower-Late Upper Miocene

Character of the lake water

Freshwater with coal

Freshwater with floral remains

Freshwater with coal and floral remains

Freshwater with oil shales

Saline-alkaline (volcanic glass-bentoniteclinoptilolite-analcime)

Saline-alkaline (volcanic glass-clinoptiloliteanalcime)

Saline-alkaline (magnesites with the moulds of borate,

Saline-alkaline (searlesite, analcime and K feldspar) with oil shales

2;::

phosphate and sulphate

s· "' .,

!:?.. !:>..

�

0 "' :::;: -"'

minerals; early diagenetic dolomitization of CaC03 mud) Freshwater fossil remains

Freshwater floral remains

Freshwater fossil remains

Freshwater floral remains, oil shales

Contemporaneous volcanic products

Tuffs and tuffites

Volcanic rocks, tuffs and tuffites

Volcanic rocks, tuffs and tuffites

Tuffs and tuffites

Tectonic activity

Strong

Strong

Strong

Strong

Climate

Wet Dry (Middle Miocene) Wet

Wet Dry (Middle Miocene)

Wet Dry (Middle Miocene)

Wet

Wet

Wet Dry (Middle Miocene) Wet

�

CrQ 0 "'

1:) "'

;::;·

�

\C

COLUMN

LITHOSTRATIGRAP HIC FROM ZLATOKOP - VRANJE

LACUSTRINE

BASIN

44

2 2 2 2

2

"

�

a: w

i+ + �+

2

a. ::E 0 <.>

TUFFACEOUS

MARLY

MARLSTONE

TUFFITE

TUFFACEOUS MARLSTONE

2 e:

-' ' '-

I

2

w z w

:

"" w �

z 0 " a:

"' <.>

I

2

(.)

SILICIFIED

TUFF

SILICIFIED AND

WITH ANALCIME

TUFF

WITH ANALCIME

WITH LENSES OF

BLACK CHERT

+

0 E

MAR LSTONE

+

�

g

v

v

'I v

v v

w ...J c c

v v

v v

�

v

v

v

v

v v

w

z

v v

v v

"' � "'

�

ffi �

TUFF

WITH

3:

CUNOPTILOUTE

v v v

v

;:: g ...J ..

v v

SILICIFIED TUFF

TUFF

v v v v

v

CL!NOPTILOLITE

� "

v v

v

"'

v v

G

WITH

w z

MAALSTONE

2 N

0

1----_1

MARLSTONE

�

MARLY

' [2Z]

TUFF

In }I

TUFFACEOUS

�

SILICIFIED TUFF

I� I

BLACK

2

WITH ANALCIME

J: <J)

v v

PARALLEL LAMINATION

't

TUFFITE

FLORA

Fig. 2. Lithostratigraphic column for Zlatokop, Vranje Lacustrine Basin.

MARLSTONE

CHERT

REMAINS

0

Mineral deposits, Yugoslavia

Sedimentary magnesites and borates

In the tectonically active Jarandol Basin, several subenvironments can be distinguished. In one of them, in a shallow-water dolomitic carbonate com­ plex, deposits of sedimentary magnesite (Bela Stena =white rock) occur (Obradovic et al., 1984). Ultra­ mafic and volcanic rocks and locally Triassic dolo­ mites underlie these lake sediments. The Bela Stena deposit is a lens-shaped body that once contained about four million tons of magnesite. The magnesites are bedded in layers of different thickness, mostly 400-500 mm, which were more or less destroyed by diagenetic modification, slumping and tectonic ac­ tivity. The characteristics of the magnesite deposits are given in Table 2. Electron microprobe analyses show that the content of MgO varies from 38·72 to 46·19% . The highest content is characteristic of the massive type of magnesite. The source of magnesium was the ultramafic rocks; hot waters of volcanic origin migrated through them, bringing magnesium to the lake. Also, magnesium may have been derived by leaching of the ultramafic rocks by meteoric waters. At the time of most intense faulting hydrothermal solutions precipitated magnesium and other components as a nodular and porous type of magnesite deposit along the fault zones. Bedded massive and laminated magnesite pass laterally into dolomitic and magnesitic marl­ stones. Due to vertical fault movements some parts of the magnesite deposits were exposed to subaerial conditions. The magnesite became dried and frag­ mented to produce what is known as the brecciated type (Obradovic et al., 1990). Desiccation cracks commonly occur in this deposit. In magnesite, es­ pecially in the porous type, moulds of gypsum and lueneburgite [Mg3B2(0H)6(P0)4 ·6H20] crystals occur. Crystals of lueneburgite up to 3 mm in size were found. In the same lake basin (Fig. 3), a deposit of boron

151

minerals was discovered in fine-grained clastic sedi­ ments, representing a very shallow-water environ­ ment. In the outer part of the basin, colemanite (2[Ca2B60u·5H20]) and howlite (Ca2B5Si09(0H)5) occur in association with bitumen, calcite and gypsum, forming the lens-shaped body. In the central part of the basin, in the same fine­ grained siliciclastic subenvironment, ulexite (2[NaCaB506(0H)6-5H20]), colemanite and tinca­ lonite (Na2B405(0H}4-3H20) were found. All these boron minerals are typical of playa lake deposits. The boron was probably derived by the leaching of volcanic and pyroclastic rocks by meteoric waters.

DEVONIAN SHALLOW-MARINE CHAMOSITIC IRONSTONE

In western Macedonia a Devonian shallow-marine sequence contains oolitic ironstone deposits. Fossils found in limestones from the area surrounding the mine indicate a late Lower Devonian to Middle Devonian age. The oolitic ironstones, primarily chamosite clays, in the Tajmiste deposit, western Macedonia, were deposited within a clastic series of claystones, shales and sandstones, which were subsequently metamor­ phosed into quartzites, phyllites and schists. There are several important beds of ironstone. It is possible to distinguish three stratigraphic units: a lower unit under the ores, the unit containing the ores and an upper unit above the ores. The first unit is composed of fine-grained sediments with rare sandstones (metamorphosed to phyllite and quart­ zites), the second unit includes the ores within sand­ stones and shales (quartzites, slates and phyllites), and the third unit is metamorphosed sandstones, shales and claystones (quartzites and phyllites) with limestones at the top. Coarsening-upward sequences are characteristic for the lower and middle units.

Table 2. Characteristics of magnesites from the Bela Stena deposit Sedimentary features

Types

Environment

Bedding

Laminated

Lake basin, shallow water with temporary

Lamination Desiccation cracks Kerogen of sapropelic type Floral remains

Massive Cavernous

subaerial conditions pH= 8-10 Alkaline-saline water (moulds of sulphate, borate

Algal structure Tufa

Brecciated Nodular

·

and phosphate minerals; occurrences of lueneburgite) Contemporaneous volcanism

LITHOSTRATIGRAPHIC COLUMN

FROM

LACUSTRINE

A PART

OF JARANDOL

BASIN

..

OELUVIUM ALLUVIUM

DOLOMITE AND DOLOMITIC MARL

9' 2

BORON MINERALIZATION

2 2

MAGNESITE

LUTITE:

2

TUFF, TUFFITE, MARL,

CLAY

ARENITE: SANDSTONE 1 TUFF 1 TUFFITE

2

� �

2

RUDITE: CONGLOMERATE, VOLCANOC

ANDESITE

2

PARALLEL WAVY

2

L AMINATION

L AMINATION

GRADED

BEOOING

CONVOLUTION FLORA

Fig. 3. Lithostratigraphic column from a part of Jarandol Lacustrine Basin.

COAL

REMAINS

���C

LITHOSTRATIGRAPHIC COLUMN

OF

IRONSTONE

FROM

FORMATION

TAJMISTE

RECRYSTALLIZED LIMESTONE

Co SCHIST Co PHYLLITE

C.a SCHIST

RECRYSTALLIZED LIMESTONE

METASANDSTONE

z

:'!

2

> w c

2

z 0

PHYLLITE

METASHALE PHYLLITE METASANDSTONE PHYLLITE METASANDSTONE

2 w ..J c c �

Co

-

Ca-Se

"' w "­ "­ �

PHYLLITE

Se-Ca -

2

Ca-se-Co METASHALE Sd-Co-Mt ORE

METASANDSTONE Co- Sd ORE METASANDSTONE Sd-Co

ORE

METASANDSTONE Sd-Co

ORE

METASANDSrONE

a:: w

�

METASHALE

Co-Mt-Sd ORE

METASHALE

"' w "' 0

� i z

2 ii'

�

-

w � c c

;;

Sd-Co ORE Set-Co

PHYLLITE

METASANDSTONE

PHYLliTE

METASHALE

� � . � -

z

2 ii'

!E "'

� g

PHYLLITE

METACL ASTIC ROCK

ORE

Co

CHLORI TE -CHAMOSI TE

Co

CALCITE

Se

SERICITE

Sd

SIDERITE

Mt

MAGNETITE

2

Fig. 4. Lithostratigraphic column of ironstone formation from Tajmiste.

RECRYSTALLIZED LIMESTONE

PARALLEl L AMINATION

154

J. Obradovic and N. Vasic

Most primary structures were destroyed by meta­ morphism and/or tectonic activity. Only in a few cases can parallel lamination be distinguished (Fig. 4). According to Harder ( 1966, 1989), the different iron ores can be distinguished by using the chemical compositions of the ores. The Minette type of iron ore is geochemically characterized by high contents of Ti02 (more than 0·15% ), P205 (more than 1% ), V205 (about 0· 1% ) and Al203 (more than 4% ). These contents are lower in exhalative iron ores (Lahn-Dill type) than in the ores of the Minette type. According to these data, ironstones from the Tajmiste deposit correspond more closely to the Minette type than to the exhalative type. Chemical analyses (Tables 3 and 4) show that ironstone ores show some differentiation in their chemical compo­ sition, but they do correspond to the Minette type. Although some pyroclastic rocks are found in the Tajmiste deposit, basic volcanic rocks occur 50 km distant from it, and are covered by thick deposits of Palaeozoic rocks, so there is unlikely to be a genetic connection between them and the Tajmiste ironstones. The fabric of the ores is oolitic, rarely pisolitic. The ooids are mostly less than 0·5 mm, and rarely from 0·5 to 0·8 mm in size. The ooids are composed of chamosite with tangential and radial structure, and rarely of siderite and magnetite. In some cases

Table 3. Chemical analysis of iron ores

Si02 Ti02 AI203 F�03 FeO MnO MgO CaO Na20 K20 P20s s Org.mat. H20 H20

(1) (3)

1000° 110°

2

3

7·73% 0·36 3·00 22·22 35-45 0·15 0·50 2·42 0·09 0·11 2·80 1·04 0·38 23·75

19·68% 0-48 3·92 8·53 43·88 0·16 0·99 1·04 0·09 0·11 1·13 1·03 1-49 17·50

7·14% 0·39 7·23 5·32 43-97 0-48 1·98 3·05 0·12 0·80 2·58 0·69 0·64 25-43 0·18

100·00%

100·03%

100·00%

Chamosite-siderite ore; siderite-chamosite ore

(2)

chamosite-siderite ore;

Classical gravimetric methods were employed for oxides and water (analyst: D. Nikolic).

Table 4. Spectrochemical trace element analyses of iron ores (ppm)

2

3

15 500 150 5000 80 100 100 200

15 600 500 3000 10 30 150 200

50 500 700 500 5 50

Ba Nb Zr

*

*

*

*

*

*

*

y

*

*

*

Sr

*

*

*

Pb Zn Cu Mn Co Ni Cr

v

*

50 300 *

4 *

111·52 61·03 2100 *

27-44 274·54 152·03 178·52 3·50 124·09 38·18 129·09

* Not determined. Analyst for samples 1, 2, 3, B. Milanovic, Beograd; for sample 4, D. Opper, Koln.

the nuclei of the ooids are visible, but usually this is not the case. Siderite commonly replaced chamosite, but the magnetite is of metamorphic origin. The ooids were deformed by metamorphism. In some cases two or three ooids have coalesced with a common outer cortex. The tangential fabric in the ooids suggests that besides ooids similar to lateritic ooids (radial­ concentric fabric) there are others. The tangential fabric is probably produced by the mechanical ac­ cretion of detrital clay (kaolinite) and hydrated iron oxide minerals (Bhattacharyya & Kakimoto, 1982). Ooids with radial fabrics, resembling lateritic pisoids, are also composed of chamosite, which was partly replaced by siderite at the late diagenetic stage. In the region surrounding the deposit there is no ex­ posed weathering crust or occurrence of laterites. Because of this the origin of this kind of ooid is questionable, but it is believed that they correspond to a weathering crust. Until now there has been no satisfactory general model for the interpretation of the origin of these ironstones. We did not find any evidence that the investigated ooids represent the diagenetic ferru­ ginization of calcareous ooids. The tangential fabric of the ferruginous ooids originated, according to Bhattacharyya & Kakimoto (1982), by the mechan­ ical accretion of suspended hydrated iron oxides and detrital clay minerals, especially kaolinite, around the nucleus, in water with some degree of agitation. The chamosite formed from the kaolinite during the early stages of diagenesis in an iron-rich environment.

155

Mineral deposits, Yugoslavia

The ongm of the iron is probably polygenetic. The chemical composition of the Tajmiste ironstones shows a similarity between them and the Minette type of ironstones, indicating that the iron originated from weathered terrains. Some differences between the Minette type and the Tajmiste ironstones, like the occurrences of goethite in the Minette type, indicate that iron was not only supplied by streams which drained weathered terrains but that the up­ welling of deep basinal waters may also have been an important source of iron.

there is no exposed weathering crust or occurrence of laterites. The origin of this kind of ooid is therefore questionable, but it is believed that they correspond to a weathering crust. The origin of the iron is probably polygenetic. The data indicate that iron was not simply supplied by streams which drained weathered terrains, although this source was important. We cannot exclude the upwelling of deep basinal waters as an important source of iron. ACKNOWLEDGEMENTS

CONCLUSIONS

Miocene lacustrine rocks in Serbia contain authigenic zeolites, bentonites, magnesites and borate deposits. Climate and contemporaneous volcanic activity had a strong influence on the diagenetic processes and alteration of the lacustrine facies. A dry, semi-arid to arid climate and vertical movements of fault blocks with contemporaneous dacitic-andesitic vol­ canism influenced the chemistry of the lake water, changing it, generally in the Middle Miocene, to alkaline and saline. These conditions made possible the alteration of volcanic glass to bentonites and zeolites, the deposition of magnesite and the occur­ rence of borate, silicoborate, phosphate and sulphate minerals. They also influenced the diagenetic forma­ tion of authigenic minerals (searlesite, analcime, potassium feldspar) in oil shale. Devonian shallow-marine rocks in western Macedonia are characterized by the occurrence of oolitic ironstone deposits composed of chamosite and siderite, with magnetite, pyrite, chlorite­ thuringite, ankerite, apatite, stilpnomelane, min­ nesotaite, quartz and rare calcite. The ironstone deposits occur within clastic sediments, which were metamorphosed to quartzites, slates and phyllites. In a shallow subtidal environment, rich in organic substances and in mildly agitated waters, ooids were formed by the mechanical accretion of suspended hydrated iron oxides and detrital clay minerals around the nucleus (ooids with tangential fabric). During early diagenesis chamosite was formed, and later the chamosite was replaced by siderite. Ooids are cemented by fine-grained siderite, rarely with chamosite or dark amorphous chamositic masses. Ooids with radial fabrics, resembling lateritic pisoids, are also composed of chamosite, which was partly replaced by siderite at the late diagenetic stage. In the region surrounding the deposit now

We gratefully acknowledge the help of S. Karamata who offered helpful suggestions. We would like to thank J. Parnell for his editing of the manuscript and suggestions for its improvement. 0. Mudronja assisted in the preparation of the figures. REFERENCES BHAlTACHARYYA, P.D. & KAKIMOTO, K.P. (1982) Origin of ferriferous ooids: an SEM study of ironstone ooids and bauxite pisoids. J. Sediment. Petrol. 52, 849-859. GRUBIC, A.

(1980) Yugoslavia -an Outline of Geology of Yugoslavia, Excursion 201A -202c (Ed. by A. Grubic), 26th Int. Geol. Congress, Paris, 5-92. HARDER, H. (1966) Kiinnen die Mazedonischen Eisenerze aus Verwitterungsliisungen gebildet worden sein. Ref. VI Savetovanja geol. Jugoslav., Ohrid II, 659-673. HARDER, H. (1989) Mineral genesis in ironstones: a model based upon laboratory experiments and petrographic observations. In: Phanerozoic Ironstones, Vol. 46 (Ed. by T.P. Young & W.E.G. Taylor), pp. 9-18. Spec. Publ. Geol. Soc. KARAMATA, s., 0BRADOVIC, J. & NIKOLIC, D. (1982) Study of the characteristics of Fe ores from Western Macedonia-on the example of the Mine Tajmiste. Part II. Unpubl. studies (in Serbo-Croatian). KARAMATA, S., 0BRADOVIC, J. & NIKOLIC, D. (1988) Study of the characteristics of Fe ores from Western Macedonia-on the example of the Mine Tajmiste. Part

111. Unpubl. studies (in Serbo-Croatian).

(1966) Mineral composition of Tajmiste Mine. Ref VI Save10vanja geol. Jugoslav. Ohrid. II, 506-514

KLEUT, D.

(English summary). KLEUT, D. (1968) Phosphorus in the Tajmiste iron ore deposit. Rad. Ins/. za geol. rud. islr. i isp. nukl. i dr. min.

sir., Beograd 4, 125-139. 0BRADOVIC, J. (1983) Some aspects of sedimentation in Neogene Lake Basins in Serbia, Yugoslavia. 4th !AS

Regional Meeting, 18-20 April 1983, Abstracts, 120-121. 0BRADOVIC, 1. (1988) Occurrences and genesis of sedi­ mentary zeolites in Serbia, Yugoslavia. In: Occurrences, Properties and Ulilization of Natural Zeolites (Ed. by D. Kallo & H.S. Sherry), pp. 59-69. Academiai Kiado.

J. Obradovic and N. Vasic

156 Budapest. 0BRADOVIC, J. & DtMITRJJEVIC, R.

(1987)

Klinoptilolizirani

tuf Zlatokopa kod Vranja (Ciinoptilolized tuffs from Zlatokop, Vranje Lake Basin). Glas SA N U 51, 7-19 (English summary).

origin. 5th !AS European Regional Meeting on Sedi­ mentology, 9-11 April 1984, Marseille, France, Abstracts, 330-331. OBRADOVIC, J., KARAMATA, S., KELTS, K., 0BERHAENSLI, H. & VASIC, N. (1990) Lake sedimentation and occurrence of sedimentary magnesite (in press).

0BRADOVIC, J. & JovANOVIC, 0. (1987) Neke karakteristike sedimentacije u neogenom Valjevsko-Mionickom Basenu (Some characteristics of Neogene sedimentation,

PAGE, B.M. (1958) Chamosite iron-ore deposit near Tajmiste, Western Macedonia, Yugoslav. Econ. Geology

Valjevo-Mionica lake basin). Glas SA N U 51, 53-63 (English summary). 0BRADOVIC, J. & KARAMATA, S. (1982) Study of character­ istics of Fe ores Western Macedonia-on the example of the Mine Tajmiste. Part I. Unpubl. studies (in Serbo­

PANTie, N. & MIHAJLOVIC, D.J. (1977) Neogene flore Balkanskog kopna i njihov znacaj za paleoklimatologiju, paleobiogeografiju i biostratigrafiju (Flores Neogenes provenant du Continent Balkanique et leur importance

Croatian). 0BRADOVIC, J., KARAMATA, S. & VAS IC , N. (1984) Sedi­ mentary magnesite from 'Bela Stena' deposit and its

53 (1), 1-21.

au point de vue de Ia Paleoclimatologic, Paleobio­ geographic et Biostratigraphie). Geol. Anali Balk. Pol.

XL, 103-125.

Copper Deposits

Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

Spec. Pubis int. Ass. Sediment. (1990) 11, 159-172

Syngenetic and paleokarstic copper mineralization in the Palaeozoic platform sediments of West Central Sinai, Egypt M. A . E L S H A R K A WI*, M. M. E L A RE Ft an d A . A B DEL M O TE LI Bt *Geology Depar tmen t, Facul ty of Science, Kuwai t Universi ty , Kuwai t; tceology Depar tmen t, Facul ty of Science, Cairo Universi ty, Egyp t

ABSTRACT

Copper in the form of carbonate, chloride, silicate, sulphate and phosphate minerals is encountered within the Palaeozoic sediments of the Urn Bogma region, West Central Sinai, Egypt. They are classified into two contrasting genetic types: ( 1 ) strata-bound to stratiform malachite confined within a certain stratigraphic level of Cambro-Ordovician clastic sediments; and (2) strata-bound copper carbon­ ate, chloride, silicate, sulphate and phosphate confined within a buried Carboniferous karst profile. The geometric distribution patterns of the malachite of the first type represent a high degree of congruence with the primary, deformational and biogenic sedimentary structures of the enclosing rocks . The malachite was formed syngenetically during the accumulation of the host sediments in fluviodeltaic environments. In the second type, the geometric distributions of the copper minerals and the chemistry and mineral composition of the host karst products reveal that these copper minerals are of pedogenic origin, deposited from solutions in a paleosol developed during the Carboniferous karst event. The variation in the pH and Eh conditions of the paleosol environment and the related biogenic processes are suggested to be the main factors controlling the leaching of the copper and its migration and redeposition within the subsoil and topsoil horizons of the paleokarst profile.

INTRODUCTION

The copper minerals of the Urn Bogma region at­ tracted the attention of the ancient Egyptians (5000 BC or even earlier). They were used throughout the Predynastic periods of Ancient Egypt. Ancient workings for copper of Pharaonic time occur in West Central Sinai at many localities in the Urn Bogma region ( Lucas & Harris, 1962). The region is occu­ pied mainly by upper Proterozoic basement rocks followed unconformably by sedimentary successions of Cambro-Ordovician and Carboniferous ages ( Fig. 1). The present work is concerned with the distri­ bution, mode of occurrence and possible genesis of the copper minerals occurring in the Palaeozoic succession of this area. The copper occurs in the form of carbonate, chloride, phosphate, silicate and sulphate minerals and is confined within a certain Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

stratigraphic level of the Cambro-Ordovician sedi­ ments and in a Carboniferous buried paleokarst profile. The work is based on detailed field and megascopic investigations supported by stratigraphic and sedimentologic observations, geometric in­ terpretation and identification of organic matter. The identity of the copper and clay minerals was verified by X-ray diffraction (XRD) and the chemical analysis of the paleokarst profile was carried out by X-ray fluorescence (XRF). The mechanisms of formation of the Palaeozoic copper minerals involve fluvial (Cambro­ Ordovician), karst and pedogenetic processes (Carboniferous) with an overprint from diagenetic processes. Certain palaeoclimatic and palaeoen­ vironmental conditions are postulated as a result of the present study. 159

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Copper mineraliza tion, Sinai An epigenetic hydrothermal origin as a result of Tertiary volcanicity was proposed by most of the authors who have studied the copper minerals of this area, including Barron (1907), Ball (19 16), Davey ( 1948), Soliman ( 1961), Gindy (1961) and Hilmy & Mohsen ( 1965). Segev ( 1984) postulated a hydro­ thermal hypogene origin for associated gibbsite in Urn Bogma. El Shazly et a t. ( 1963) considered the copper minerals as oxidation and leaching products of primary copper sulphides present in the basement rocks of West Central Sinai. Magaritz & Brenner (1979) attributed the copper and manganese associ­ ation of Urn Bogma to copper and manganese migration during marine diagenesis.

LITHOSTRATIGRAPHY OF THE PALAEOZOIC SEDIMENTS The Cambro-Ordovician sediments

The Cambro-Ordovician sediments are represented by a clastic sequence underlying the Carboniferous dolomitic rocks in the Urn Bogma region. Litho­ stratigraphic details are included in Fig. 1. Weissbrod ( 1969) assigned them to the Cambrian, then Issawi & Jux ( 1982) used trace fossils to extend their age to cover the Cambro-Ordovician. Soliman & El Fetouh ( 1969) subdivided these sediments into three forma­ tions; the Sarabit El Khadim Formation, Abu Hamata Formation and Adedia Formation. The

Abu Hamata Formation is equivalent to the Timna Formation of Israel (Weissbrod, 1969). Kora ( 1984) introduced the Nasib Formation to include the upper part of the Abu Hamata Formation as shown in Table 1. The Carboniferous sediments

The Carboniferous sediments are dominated by carbonates and divided into a lower Urn Bogrna Formation and a conformably overlying Abu Thora Formation (Kora, 1984). The modified lithostrati­ graphic succession is shown in Table 2. El Sharkawi et a/. ( 1990) proved that the Lower Dolostone 'Ore Member' and the overlying Marly Dolostone-Siltstone Member of Kora ( 1984) rep­ resent a typical soil profile of a paleokarst surface. This profile was buried by the rocks of the Upper Dolostone Member. This is manifested by: (1) de­ velopment of dissolution features of different forms; (2) formation of intrakarstic sediments; (3) wall­ rock alterations of the parent carbonate rocks; (4) formation of calcrete; and (5) development of paleosol sediments covering the karstified rocks and filling the dissolution features. The Urn Bogma Formation (the lower karstified carbonates and the Upper Dolostone) was subjected to another episode of karstification during the Quaternary (EI Sharkawi eta/., 1990). This is mani­ fested by the formation of stepped terraced escarp­ ments, favouring the retreat of the slopes of the

Table 1. Lithostratigraphic succession of the Cambro-Ordovician sediments

Formation

Main lithology and environment

Adedia (25-55 m)

Sandstone with minor siltstone and shale Occasional conglomerates at base Fluviomarine environment

Nasib (=45m)

Deltaic sediments differentiated into: Upper variegated member (=25m), subdivided into: (a) Upper laminated siltstone and shale (b) Middle green, 3 .5 m thick cupriferous beds, micaceous siltstone and shales, subordinate sandstone (c) Lower alternating beds of shales and siltstone 2 Lower white member consisting of conglomerate and sandstone, manganiferous (=20 m)

Abu Hamata (12-36 m)

Sandstone, siltstone, shale, glauconitic and algal subarkoses Neritic environment

Sarabit El Khadim (7- 17 m)

Basal conglomerate, alternations of sandstone and siltstone Continental shelf, very calm shore

Basement rocks

161

162

M.A. El Shar ka wi, M. M. El Arefand A. A bdel Moteli b

Table 2. Lithostratigraphic succession of the Carboniferous sediments

Formation

Main lithology and environment

Member

Sandstone with shale intercalations Coal in the upper part, with Lepidodendron sp. and Sigillaria sp.

Abu Thora (>100 m) Upper Dolostone

Yellow to pink dolostone with occasional yellow shales Warm shallow-marine environment

Unconformity

Urn Bogma ( =41 m)

Marly Dolostone­ Siltstone

Karstified member, siltstone representing soil cover, cupriferous

Lower Dolostone

Extensively karstified dolomitic rocks with intrakarstic product housing manganese ores and caliche nodules.

Unconformity

Basement rocks and Cambro-Ordovician sediments

main wadis of the area and development of karren morphogenetic karst features. The uppermost sur­ faces of these karstified rocks are encrusted by surficial calcareous and siliceous duricrusts (calcrete and silcrete). The ultimate result of this younger karstification is the complete denudation of the Upper Dolostone Member and subsequent destruc­ tion of the underlying paleokarst profile. The distribution of copper minerals in the Palaeozoic sediments is indicated on the individual stratigraphic successions in the six studied sites in ' the Urn Bogma region (Fig. 1).

STRATA-BOUND TO STRATIFORM MALACHITE IN THE CAMBRO­ ORDOVICIAN SEDIMENTS

Malachite is found in the clastic rocks of the Nasib Formation. It is mostly confined to the middle green part of the variegated member of this unit. In the overlying Adedia Formation and underlying Abu Hamata Formation, no malachite or other copper minerals are observed. No traces of copper sulphides or any other sulphide minerals are detected in polished sections. Malachite occurs as small col­ loform globules, up to 4 mm in diameter, usually associated with kaolinite. The cupriferous sediments consist of rhythmic alternations of laminated shale, micaceous siltstone and very fine-grained sandstone

(Fig. 1). The shale layers are of green colour and some layers are stained by a violet colouration. The clay minerals constituting the shale layers are kao­ linite, illite and chlorite. The uppermost surfaces of ·the shale layers are dominated by shrinkage features and scour-and-fill structures. The interlayered silt­ stones and sandstones exhibit well-defined sedimen­ tary structures including horizontal and undulating lamination, cross-lamination, ftaser bedding, graded bedding, ripple marks, load casts, load balls and pillows. Biogenic structures are also recorded and include tracks and vertical burrows. The sandstones are subarkosic, composed mainly of subangular to subrounded quartz grains with subordinate alkali feldspar and opaques. The matrix is made up of green kaolinite together with less abundant illite. The grains are usually cemented by calcite and malachite. Both in the field and on a hand specimen scale, the geometric forms of the malachite and the associ­ ated green kaolinite exhibit a high degree of congru­ ence with the primary, depositional, deformational and biogenic structures of the enclosed rocks. The geometrical classification of the various forms of the malachite and the associated kaolinite, detected under the binocular microscope, is subdivided into 14 types, illustrated in Fig. 2. The close congruence of the geometric patterns of the malachite with the sedimentary structures suggests that the malachite was deposited during the accumu­ lation and dewatering of the host clay sediments.

Copper mineralization, Sinai STRATA-BOUND COPPER MINERALS IN THE CARBONIFEROUS BURIED KARST PROFILE

The Carboniferous karst profile is subdivided into three distinctive horizons corresponding to the typi­ cal paleosol profile (EI Sharkawi et al., 1 990). These are the parent carbonate horizon, the subsoil horizon and the topsoil horizon. The parent carbonate horizon includes the fresh or slightly weathered dolostone, which still exhibits the original textures and mineral compositions. The subsoil horizon constitutes the upper parts of the parent carbonate. It is characterized by: (1) abun­ dant distribution of solution features with structural modification, pulverization and brecciation of the parent carbonate; (2) advanced degree of dedolo­ mitization and formation of dedolomite and concen­ tration of sesquioxides of iron and manganese with clays; and (3) development of crustified calcareous nodules (calcrete). The topsoil horizon constitutes the uppermost erosion surface of the paleokarst profile and consists mainly of alternating multicoloured layers of kaoli­ nitic shales, ochres and nodules of alunite and gypsum together with copper minerals. These sedi­ ments merge gradually downwards into the altered dolostones and the associated weathering products of the underlying subsoil horizon. Organic remains were recognized in the topsoil section (Fig. 3) within the green, black and red shales. The plant remains are dominated by palynomorphs, woody particles and insoluble opaque organic detritus. The paly­ nomorphs are differentiated into spores and pollen grains. The spores include Tr i lete sp., Denso5porites sp., Dictytr i letes sp. and Mutticellaesporites sp. as­ sociated with a few badly preserved unidentified microspores. The pollen grains are dominated by small land-derived forms related to the genus Sp heripollen i tes. The occurrence of land-derived pollen grains and spores and the absence of marine dinoflagellate cysts and acritarchs indicate a continental origin for the studied sediments. Therefore, the sediments of the topsoil horizon are of continental origin de­ posited under subaerial pedogenetic conditions during the karstification of the Lower Dolostone Member of the Urn Bogma Formation. Different associations of megascopic copper minerals including carbonate, chloride, silicate, sul­ phate and phosphate minerals are intimately associ­ ated with this Carboniferous karst profile. These

163

copper minerals are mainly distributed within the red kaolinitic layers of the topsoil horizon. The close association between these copper minerals and the buried soil profile reflects the role of subaerial weathering in the concentration of the copper during the Carboniferous karstification event. The copper minerals of this type are highly altered and leached in the localities of Gebel Sarabit El Khadim and Gebel Adedia. This alteration is attributed to the effect of subsequent Quaternary karstification (EI Sharkawi et al., 1990). The identified copper minerals include malachite (Cu2C1(0Hh), (Cu2C03(0H)z), atacamite paratacamite (Cu2(0HhCI), pseudomalachite (CuAir, turquoise (Cu5(P04h(OH)4-H20), (P04)4(0H)s-4H20) and chrysocolla (CuSi03· H20). Other minerals including lungite (Cu4(S04) (CunAl(S04)spangolite (OH),;H20), (0H)12CI·3H20), bultgenbachite (Cu10(N03)(Cul'1(S04)C14connellite (0HbCidH20), (0Hb·3H20), antlerite (Cu3(S04)(0H)4) and chalcanthite (CuS04·5H20) were also recorded by Hilmy & Mohsen (1965). According to Hilmy & Mohsen, copper sulphate minerals occur as fissure fillings in the ferruginous shales overlying the manganese ore at Gebel Sid El Banat, which cor­ respond to the topsoil horizon of the present work. Malachite occurs as aggregates of globules up to 1 mm in diameter displaying a colloform structure. It is usually associated with other copper minerals and widely distributed among the topsoil and subsoil horizons. The atacamite has a blackish-green colour and a green streak. It occurs as aggregates of mas­ sive grains of sand size and is commonly associated with malachite in the topsoil horizon. Widespread veinlets of atacamite and gypsum occur cutting across the rock of the underlying subsoil horizon. Para­ tacamite, the dimorph of atacamite, is green and usually occurs as thin crusts associated with the gypsum and alunite nodules of the topsoil horizon. Pseudomalachite has a green to blackish-green colour and occurs as thin colloform crusts within the red kaolinitic and ochreous layers of the topsoil horizon. It is always associated with black plant remains. Turquoise has sky blue to bluish-green colours and a green streak. It is commonly present in the subsoil horizon. In some instances, turquoise fills strata-bound veinlets within the topsoil horizon The geometrical forms of these copper minerals and their relationship with the host karst sediments are classified as follows: 1 Geometrical forms of copper minerals in the top-

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Copper m ineralization, Sinai

LITHOLOGY

165

LITHOLOGIC DESCRIPTION

Unconformity and gypsum capped rich crust. Stratified alunite and gypsum nodules intercalated with organic matter.

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Fig. 2. [opposite] Geometric distribution patterns of the malachite in the copper-bearing sediments of the Nasib Formation. (1) Stratiform malachite arranged parallel to the lamination of the enclosing shale, siltstone or sandstone. (2) Strata-bound

malachite randomly distributed within the host sediment. (3) Strata-bound malachite distributed along the top surfaces of the ripple marks. (4) Fine stratiform discontinuous streaks of malachite and kaolinite conformable with the original lamination of the host sediments . (5) Strata-bound discontinuous streaks forming a planar non-parallel flaser structure. (6) Strata-bound to stratiform concave-upward streaks corresponding to a !laser structure produced by oscillation ripples . (7) Strata-bound discontinuous streaks filling, together with shale laminae, small scale grooves. These grooves are developed along the uppermost surfaces of coarser material and represent a scour-and-fill structure. (8) Fine discontinuous streaks filling shallow burrow pipes. In some instances , the streaks are confined with the upper convex relief capping the burrows which characterize the bottom surfaces of the overlying shale layers. (9) Strata-bound discontinuous and branched streaks of malachite and kaolinite forming a bifurcated flaser structure . ( 10) Stratiform laminae parallel to the internal lamination of the host sediment. ( 11) Stratiform undulated laminae developed along the horizontal bedding planes of the host sediment. ( 12) Stratiform distributed spots or streaks arranged parallel to the cross-lamination of the host sandstone. ( 13) Stratiform interrupted concave-upward streaks developed along the top surfaces of the shale layers , indicating buried mud cracks. Some of these streaks are loaded by gravel and sand grains. ( 14) Strata-bound veinlets of malachite cutting across some layers of the host sediment.

166

M.A . El Shar ka wi, M.M. El Arefand A . A bdel Moteli b

soil horizon. The details of the topsoil horizon are illustrated in Figs 1 and 3. The geometric forms encountered in this horizon are: (a) Stratiform lenticular masses, up to 400 mm long and 100 mm thick, encountered within the red and green shales. The laminae of the host red shales follow the outer boundaries of these lenses. The lenses consist of pseudomalachite, malachite and atacamite with kaolinite. (b) Strata-bound discrete pockets, up to 200 mm in diameter, of pseudomalachite randomly dis­ tributed within the green and kaolinitic shales. The cupriferous bodies exhibit lamination. (c) Stratiform fine lamination of malachite and chrysocolla intercalated with the green, red and blackish-red shales. The copper laminae are closely congruent with the primary lamination of the host sediment. The intercalated shale laminae include abundant plant remains. (d) Stratiform fine streaks of malachite with or without atacamite, up to 40 mm long. They are enclosed within the siltstone layers. (e) Strata-bound minute spots of malachite, up to 0.5 mm in diameter, distributed within the red kaolinitic shales. (f) Strata-bound veinlets cutting across the red kaolinitic shales. These veinlets consist of one of the following associations: malachite, atacamite and gypsum with or without malachite, turquoise and paratacamite, and chrysocolla, atacamite and gypsum. (g) Strata-bound veinlets of atacamite cutting across the iron pisolites. (h) Strata-bound thin crusts of paratacamite encountered within the gypsum and alunite nodules. 2 Geometrical forms of copper minerals in the subsoil horizon: (a) Strata-bound pockets of turquoise, up to 30 mm in diameter, encountered within the shaly materials of the intrakarstic sediments. (b) Strata-bound veinlets of atacamite, malachite and gypsum cutting across the manganese nodules and crusts which fill the subsurface solution cavities. 3 Copper minerals in exposed and altered Carbon­ iferous karst. In the exposed and altered Carbon­ iferous karst terrains, only turquoise and malachite are recorded. This type of karst is represented by an accumulation of terrigenous sediments mixed with manganese oxides. The turquoise and malachite occur as fine detrital grains embedded within the

residual accumulations. Other copper minerals seem to have been leached and removed during the mech­ anical and chemical weathering which accompanied the Quaternary karstification event. GEOCHEMISTRY OF THE CARBONIFEROUS PALEOKARST PROFILE AND THE FORMATION OF ASSOCIATED COPPER MINERALS

The paleokarst profile of Abu Hamata (Fig. 3) was sampled and analysed for major and trace elements (Tables 3 and 4). Two samples (samples 1 and 2) represent the parent stylolitic dedolomitized calca­ renite and the overlying dedolomite of the subsoil horizon respectively. The other five samples are from the topsoil sediments collected from different levels. The intercalated layers of gypsum and alunite of the topsoil and the highly manganiferous varieties of the subsoil horizon are not represented. The analysed samples were carefully selected to avoid any megascopic gypsum, alunite, copper and manganese minerals. Each spot sample weighed about 1 kg, and was crushed, quartered and analysed by XRF against relevant clay and dolomite standards. The frequency of the major elements throughout the soil profile (Table 3) shows that: 1 the overall trend of the analysed samples of the topsoil horizon is characterized by high values of Si02, Al203 and Fe203, a low value of MgO and a depletion of CaO. In contrast, the samples of the subsoil and parent carbonate rocks are characterized by high values of CaO, MgO, a low value of Fe203 and very low values of Si02 and Al203; 2 the content of MgO decreases, and CaO increases, from the parent rock towards the subsoil; 3 the K20 content reaches up to 5·43% in the topsoil samples but is only a fraction of 1% in the underlying subsoil and bed rock; 4 Na20 is mostly depleted in the subsoil and bed rock samples and ranges from 0·1 to 1·01% in the topsoil samples; 5 P205 fluctuates between 0·09 and 0·42% in the topsoil sediments and is represented by much lower values in the underlying subsoil and parent carbonate rocks; 6 Ti02 content is relatively high in the topsoil samples reaching up to 1·48% in comparison to its content in the subsoil and bed rock samples; 7 MnO is represented by fractions of 1% up to 2·63% in the analysed samples.

•

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Table 3. Major element content

7* 6 5 4 3 2 1

Si02

Ti02

AI203

F�o3t

MnO

MgO

CaO

K20

Na20

P20s

Loi*

Total

57·44 49·96 50·27 47·37 55·69 7·36 2·77

1·18 0·82 0·90 1-48 1·09 0·17 0·08

15·00 12·82 13·38 19·76 18·19 0·36 0·24

6·99 12·04 23·34 8·87 11·93 2·93 1·31

0·02 2·63 0·07 0-45 0·05 2-19 0·14

0·79 8·68 1-70 4·38 2·31 14·05 19·75

0·25 0·82 0·10 0-45 0·58 31·81 29·92

3·17 2·64 2·78 5-43 3·96 0·35 0·19

0·10 0-42 0·35 1·01 0-45 0·01 0·01

0·09 0·17 0·10 0·09 0-42 0·01 0·01

14·21 6·76 3-81 7·30 5·08 40·35 45·06

99·24 97·76 96·80 96·59 99·75 99·59 99-48

Code: 1 Stylolitic calcarenite (bed rock); 2 ·Dedolomite (subsoil); 3 "'"'""''" 4 Green shale; Topsoil 5 Ferruginous shale; 6 Green shale, cupriferous; 7 Green shale. * See Fig. 3. t Total iron oxide. * Loss on ignition to 1000°C

� �"'

l

..., � s· "' ..., :::,

:::-: N

:::,

::::-. 0

?

v,

s· �. Table 4. Trace element content of Abu Hamata paleokarst profile (in ppm)

7* 6 5 4 3 2 1

Rb

Ba

Pb

Sr

La

Ce

Nd

y

Th

Zr

Nb

Zn

Cu

Co

Ni

Sc

v

Cr

Ga

49 83 89 171 128 22

74 1282 76 105 93 1610 125

135 69 146 221 31 172 101

143 192 200 126 179 88 35

92 84 108 155 127 259

155 176 220 241 242 207

66 75 102 133 162 342

68 72 69 82 1 15 231

29 16 12 27 21 1

524 412 431 715 524 110

72

58 423 498 1020 446 567 61

151 476 438 178 470 74 110

7 35 44 42 23 61

17 97 58 328 93 291

15 13 16 16 17 14

350 555 1480 1430 193 286 10

346 614 1310 1140 625 544 9

26 20 19 29 28 9

-

so so

84 69 15

-

* As in Table 3.

......

0\ -...]

M.A . El Shar ka wi, M.M. El Arefand A. Abdel Moteli b

168

ln the subsoil horizon, the analysed sample is relatively enriched in barium, lanthanum, dymium, yttrium, cobalt and nickel (Table

4)

neo­ when

factors controlling the leaching, migration and rede­ position of these elements. The rhythmic strati­ graphic distributions of the redeposited iron- and

compared with the topsoil samples while rubidium,

aluminium-bearing minerals, e.g. goethite and alu­

strontium, thallium,

nite, within the topsoil sediments indicate seasonal

zirconium, niobium, copper

and gallium are relatively depleted. ln the topsoil

changes in the Eh and pH conditions of the soil

there is a pronounced increase in the content of

environment, which in turn clepenclecl on variations

thallium, zirconium and copper. The increase in

in the palaeoclimate or the soil moisture regime.

thallium and zirconium is attributed to the detrital

The close relation between the alunite and gypsum

components of the pedogenetic paleokarstic sedi­

suggests

ments while copper is attributed to the deposition of

periods of evaporation. Potassium in the topsoil

copper minerals from solution in the topsoil.

sediments may have been derived by leaching from

The chemical composition of the analysed topsoil

that

allochthonous

alunite

was

deposited

potassium-bearing

during

minerals,

the

e.g.

samples reflects their lithological characters and is

feldspar, mica and illite, or during the diagenesis of

similar to that of ferruginous laterites or latosols

the residual clays in an acidic medium.

(Bear,

1967).

Kaolinite and sesquioxicles of iron and

manganese are the most abundant mineral constitu­ ents of all the studied topsoil sections. The kaolinitic and iron layers are intercalated with thin layers of gypsum and alunite and indurated iron pisolites.

Manganese is mobile in the relatively acidic parts of the soil profiles and may be carried in solution to the lower parts, where the pH is higher (Lelong

al., 1976).

et

This may explain the general scarcity of

MnO in the present topsoil horizon and the concen­

Kaolinite is a good indicator of a former wetter

tration of the manganese ore in the karst solution

climate. It is favoured by a high-leaching acidic

features of the subsoil horizon by an eluviation

environment but also remains stable for long time intervals

in

neutral

and

alkaline

environments

process during soil formation. Silicon is one of the main constituents of the

(Birkland, 1984). Because of the high solubility of K+, Ca2 +, Si032- and o- ions in weathering con­

leaching conditions, silicon is leached easily as bases.

ditions, the salt accumulations in the soil profiles

It tends to form SiOl- ions which remain soluble

reflect a diminishing in soil moisture under ariel

over a large pH range.

kaoLinite

conditions or clue to seasonal oscillations of the water table level (Birkland,

1984).

The depletion of CaO in the topsoil was the result

and

chrysocolla.

Under

very

humid

The occurrence of phosphorus in the present top­ soil sediments is attributed to the abundance of the organic matter distributed in this horizon. The or­

of the complete dissolution of dolomite in the humid

ganic matter is responsible for leaching, absorption

regime, i.e. during the eluviation process. Calcium

and accumulation of phosphorus as organic phos­

tends to migrate to lower horizons, forming redepo­

phate complexes and/or phosphoric acid (Bear,

sited CaC03 (ancient caliche and freshwater calcite

1967).

cement), under suitable alkaline conditions and a low C02 content.

The phosphorus is the main constituent of

the pseuclomalachite as well as turquoise.

The main forms of iron in the studied topsoil sections are residual ochres, indurated pisolites of

DISCUSSION

goethite (ferricrete) and hematite associated with kaolinite. Aluminium is the main constituent of the

Two modes of occurrence of cupriferous sediments

residual kaolinite, turquoise and alunite. Iron can

are recognized in the platform Palaeozoic sediments

migrate in the acidic medium of the exposed soil

of

waters and is converted to ferric ions in a more

Ordovician sediments is represented by strata-bound

alkaline medium (Hem,

1963).

In the bicarbonic

Sinai.

Copper

mineralization

in

Cambro­

to stratiform malachite in clastic sediments while the •

moderately acid medium, iron becomes relatively

younger Carboniferous copper mineralization en­

soluble, while aluminium remains immobile (Lelong

compasses a variety of strata-bound copper minerals

et al., 1976;

Krauskopf,

1979).

Aluminium is soluble

confined

within

a

fossilized

karst

profile.

The

when the environment is sufficiently oxidizing and is

Cambro-Ordovician occurrence is similar to the

deposited owing to small increases of pH (Lelong e t

Cambrian cupriferous sediments of Timna (Bartura

a l., 1976).

Thus the relative mobility o f the iron and

aluminium and Eh-pH conditions, are the essential

& Wurtzburger, (Bender,

1974)

1974)

in Israel and Wadi Dana

in Jordan.

169

Copper mineralization, Sinai The copper in the Cambro-Ordovician and Car­ boniferous clastic sediments can be envisaged as a surface leaching product of copper sulphide minerals from the Precambrian rocks of the Arabo-Nubian Shield. These sediments surround the border of the copper-mineralized Precambrian rocks in Jordan (Burgath et al.,

1984)

and in Egypt (El Shazly et al.,

moisture regimes or periods of evaporation and under neutral to alkaline conditions. The fact that in some instances the copper minerals form strata-bound veinlets cutting through certain karst or karst alter­ ation products may be related to the mobilization of the above-mentioned ions during subsequent acidic leaching and their redeposition. Copper is comparatively soluble in the acidic

It is debatable whether copper was present

1955).

in the Lower Dolostone Member or brought into

environment

solution during the pedogenetic evolution of the

changes in physico-chemical conditions of the sol­

recorded

ution during pedogenesis can precipitate metals such

karst profile. Nevertheless, Soliman

0·5%

(1961)

copper in the large dolomite crystals of the

of

the

weathering

processes.

as c0pper as stable minerals (Lelong

The

et a!., 1976).

Lower Dolostone. The bed rock and subsoil are

The neutralization of acidic waters by reactive wall

depleted in copper relative to the topsoil at the Abu

rocks such as carbonates causes dissolved copper to

Hamata site (Table

4).

The intimate association of

copper mineralization with faults and volcanism in the Cretaceous to Neogene sedimentary rocks of Israel

(II ani et a/., 1987)

could not be extended to

precipitate (Guilbert & Park,

Eh and pH

1986).

changes and the formation of complex chlorides dominate the geochemical behaviour at

low temperature

(White,

1968;

of copper

Rose,

1976;

explain the studied Palaeozoic sediments in Sinai

Maynard,

where copper mineralization is never recorded con­

solubility under oxidizing conditions at moderate to

centrated in the vicinity of faults or tied to the

low pH. Iron is less soluble under these conditions.

Tertiary basalts.

In their passage through a carbonate formation the

1983)

and there is a large field of copper

The syngenetic Cambro-Ordovician malachite is

dilute copper solutions will precipitate brochantite

intimately associated with clay minerals and displays

and atacamite. The stability field of these minerals is

a strong congruence with the sedimentary structures.

similar and their formation depends only on the

It is believed that malachite was probably formed

concentration of so/- and Cl- anions in the sol­

from a bicarbonate solution saturated in copper and

ution (Kern & Weissbrod,

was deposited under severe arid conditions.

Barton & Bethke

The copper-mineralized karstified Carboniferous

(1960),

1967).

According to

the relevant reaction for

the formation of atacamite is:

sediments have no counterpart in neighbouring countries. The karstified nature of the enclosing sediments was overlooked by previous investigators who erroneously described it as a normal strati­

The cupric solution reacts with C02 derived from the carbonate or the carbonic acid to form malachite

graphic succession. The dolomitic (mainly ferroan

by the following reactions:

dolomite) and dedolomitized subsoil of the karst profile

is

intimately

developed

with

manganese mineralization (El Sharkawi

extensive

eta!., 1990).

2Cu 2+ + Col- + 20H-

-->

According to Guilbert & Park

CuzC03 (0Hh

(1986),

malachite is

The clayey topsoil is admixed with strata-bound

favoured in more dilute cupriferous water or by a

copper carbonate, chloride, silicate, sulphate and

lower Pco2, although the stability field of malachite (Kern & Weissbrod, 1967) in terms of the pH and

phosphate minerals, and hence mineralogically dis­ tinguished from the copper mineralization of the

copper concentration in the solution at various partial

Cambro-Ordovician sediments. The fate of leached

pressures of C02 shows that the malachite crystal­ lization is only slightly_ dependent on the Pco2.

copper during karstification depends on many factors as reflected in the diverse mineralogical composition. The stratified arrangement of the copper minerals within the kaolinitic shales of the topsoil horizon

According to Kern & Weissbrod

(1967),

brochantite

or atacamite will be precipitated if the Cu 2+ con­

centration is high enough. On the other hand, at a

and their close relation with gypsum and alunite

very low Cu 2+ concentration, azurite, malachite or

indicate that these copper minerals were deposited from a pore soil solution containing Cu2+, Cl-,

tenorite can precipitate and in such circumstances

SOi- C032-, POl-, SiOl- and AlH ions and

the C02 content of the atmosphere above the sol­ ution has scarcely any influence on the stability of

were entrapped within the shale laminae. The for­

these minerals. Chrysocolla has to be formed from a

mation of copper minerals prevailed during low

cupric solution containing available soluble silica. In

170

M . A . El S har ka wi , M. M. El Arefan d A. Abde l Mo te li b

supergene processes, the soluble silica may combine

REFERENCES

with copper to form chrysocolla as follows: 4Cu 2 + + 4Si0/- + 6H2 0

�

Cu4H4Si40w(OH)s

The occurrence of pseudomalachite in the organic­ rich layers of the topsoil may indicate the reaction of the cupric solution with organic phosphorus and/or phosphoric acids to form this mineral when leaching was not strong enough to remove phosphorus. On the other hand, the presence of turquoise in the form of strata-bound veinlets or pockets within the sediments of the subsoil horizon suggests th€ mi­ 3 gration of Cu2+, AJ + and PO - from the upper

/

acid-leached parts of the soil into the lower horizon and their redeposition.

CONCLUSIONS Workable copper deposits are known to occur in the Palaeozoic

platform

sediments

surrounding

the

northeast margin of the Arabian Shield. In the Urn Bogma region, two modes of copper occurrence were recognized:

(1)

strata-bound to stratiform

malachite in the Cambro-Ordovician ftuviodeltaic sediments; and

(2)

strata-bound copper carbonate,

chloride, silicate, sulphate and phosphate minerals in a buried Carboniferous karst profile. The Cambro-Ordovician occurrence is similar to the copper deposits in Timna and Wadi Dana in neighbouring

countries.

It

is

anticipated

that

Cambro-Ordovician malachite at Urn Bogma was syngenetically deposited under a ftuvi odeltaic en­ vironment. The Carboniferous paleokarstic copper deposit has no counterpart in the neighbouring countries and the copper minerals are of supergene origin deposited during the pedogenic evolution of the paleokarst surface. The recognition of paleokarst in the Carbon­ iferous,

the

intimate

development

of

copper

minerals within the topsoil horizon capping the Lower Dolostone Member of the karst profile and the unconformable cap of the Upper Dolostone Member could be used as a prospecting guide for workable copper deposits in the region.

ACKNOWLEDGEMENTS We thank N.A. El Ella for the identification of the spores and pollen grains in the topsoil and J. Parnell for correcting the English.

J. (1916) The Geography and Geology of West Central Sinai- Egypt. Surv. Dept . , Cairo, 219pp. BARRON , T. (1907) The Topography and Geology of the Peninsula of Sinai (Western Portion) . Surv. Dept. , BALL,

Cairo, 241pp. P . B . & BETHKE, P . M . (1960) Thermodynamical properties of some synthetic zinc and copper minerals. Am. J. Sci. (A) 258, 21 -34. BARTURA, Y. & WURTZBURGER, U. (1974) The Timna Copper Deposit, pp. 277-285. Centenaire de Ia Soc. Geol. de Belgique. Gisement Stratiformes et Provinces Cupriferes, Liege. BEAR, F . E . (1967) Chemistry of the Soil. American Chemi­ cal Society Monography Series. Reinhold, New York, 512pp. BENDER, F. ( 1974) Geology of Jordan . Contribution to the Regional Geology of the Earth. Gebruder Borntraeger, Berlin, 196pp. BIRKLAND, P . W . ( 1984) Soils and Geomorphology. Oxford University Press, New York, 372pp . B u RGATH, K . P . , HAGEN, D. & SIEWERS, V. ( 1984) Geo­ chemistry, geology and primary copper mineralization in wadi Araba, Jordan. Geol. Jb (B) 53, 3-53. DAVEY , J.C. (1948) Report on Southern Sinai. Mining Mag. 78, 44-152 and 212-214. E L SHARKAWI, M . A . , E L AREF, M.M & ABDEL MoTELIB, A. (1990) Manganese deposits in a Carboniferous paleokarst profile, Urn Bogma region, west-central Sinai , Egypt. Min Deposita 25 , 34-43. EL SHAZLY, E . M . , AsDEL NASER, S . & SHUKRI, B . ( 1955) Contributions to the mineralogy of copper deposits in Sinai . Geol. Surv. Egypt, Bull. 1 , 13pp. EL SHAZLY, E . M . , SHUKRI, N . M . & SALEEB, G.S. (1963) Geological studies of Oleikat, Marahil and Urn Sakran manganese-iron deposits, West Central Sinai. J. Geol. UAR 7, 1 -27. GINDY, A.R. ( 1961) The origin of copper mineralizations in Central Sinai , UAR. Proc. 4th Arab Sci. Congr. , Cairo , 607-634. GuiLBERT, J . M . & PARK, G . F . (1986) The Geology of Ore Deposits . Freeman, New York , 985pp. HEM , J . D. (1963) Chemical equilibria and rate of manga­ nese oxidation. US Geol. Surv., Water Supply Bull. (A) 1667, 64pp. HILMY, E. & Mo HSEN , L. (1965) Secondary copper minerals from West Central Sinai. J. Ceo!. UAR 9, 1 - 12. ILANI, S., FLEXER, A. & KRONFELD , J. (1987) Copper mineralization in sedimentary cover associated with tectonic elements and volcanism in Israel. Min. Deposita 22, 269-277. IssAWI, B. & Jux, U. (1982) Contributions to the strati­ graphy of the Paleozoic rocks in Egypt. Ceo!. Surv. Egypt, Bull. 64, 28pp. KERN, P. & WEISSBROD, A. (1967) Thermodynamics for Geologists. Freeman, Cooper and Company, San Francisco, 304pp . KORA, M. ( 1 984) The Paleozoic outcrops in Urn Bogma area, Sinai. PhD Thesis , Mansoura Univ . , Egypt , 280pp. KRAUSKOPF, K . B . (1979) Introduction to Geochemistry . McGraw-Hill, New York, 817pp. LELONG , F. , TARDY , Y., GRANDIN, G . , TRESCASES, J . J . & BARTON ,

.

Copper m iner alization , Sin ai BouLANGE, B. (1976) Pedogenesis, chemical weath­ ering and processes of formation of some supergene ore deposits. In: Handbook of Strata-bound and Strati­ form Ore Deposits , Vol. 3 (Ed. by K.H. Wolf) , pp. 93 - 173. Elsevier, Austerdam. LucAS, A. & HARRIS, J.R. ( 1962) Ancient Egyptian Ma­ terials and Industries , 4th edn. Edward Arnold, London, 523pp. MAGARITZ, M. & BRENNER, L B . (1979) The geochemistry of a lenticular manganese ore deposit (Urn Bogma ) . Min. Deposita 14, 1 - 13. MAYNARD, J . B . ( 1983) Geochemistry of Sedimentary Ore Deposits. Springer, New York, 305pp. RosE, A.W. (1976) The effect of cuprous chloride com­ plexes in the origin of red-bed and related deposits. Econ. Geol. 72, 1036- 1048.

171

A. (1984) Gibbsite mineralization and its genetic implication for the Urn Bogrna manganese deposits, Southwestern Sinai. Min. Deposita 19, 54-62. SoLIMAN, S . M . (1961) Geology of the manganese deposits of Urn Bogma, Sinai and its position in the African manganese production. 1st Iron and Steel Congr. Proc., Min. Ind., Cairo , 1 - 2 1 . S OLIMAN, S . M . & EL FETOUH, M . ( 1969) Petrology o f the Carboniferous sandstones in West Central Sinai. J. Geol. UAR 13, 6 1 - 143. WEISSBROD, T. ( 1969) The Paleozoic of Israel and adjacent countries (part 2), the Paleozoic outcrops of South­ western Sinai and their correlation with those of Southern Israel. Geol. Surv. Israel, Bull. 48, 32pp. WHITE, D .E. (1968) Environment of generation of some base-metal ore deposits. Econ. Geol. , 63 301 -335. SEGEV,

·

Spec. Pubis int. Ass. Sediment. (1990) 11, 173-180

Geochemical data for the Dongchuan- Yimen strata-bound copper deposits, China C. R A N Department o f Geology, Kunming Institute of Technology, Kunming, Yunnan Province, China

ABSTRACT Trace element, organic carbon, stable isotope and fluid inclusion data are reported for the Dongchuan­ Yimen type strata-bound copper deposits Yunnan, China. The trace element data show that the ore materials were derived from the host rocks and underlying beds, and that bismuth, lead and zinc were additionally introduced through deep fractures. The ore-forming fluid was a hot connate brine. The sulphur was derived from sulphate-reducing bacteria, and carbon was derived from marine carbonate. Organic carbon played an important part in the metallogenesis. In the Kangdian Axis, two deep fractures controlled the sedimentation of a cupriferous algal reef limestone. Copper was subsequently mobilized into vein deposits.

INTRODUCTION

The Dongchuan-Yimen copper deposits are large (economically mineable) and occur in an algal reef carbonate development in the Proterozoic Kunyang Group in the South Kandian Axis (Fig. 1, Table 1). The ore bodies include stratiform and vein types. The main horizons which contain the stratiform ores are: (1) the lower algal dolomite of the Luoxue Formation and a transitional bed underlying it; and (2) the black bed of the Shishan Member of the Luzhijiang Formation and a transitional bed under­ lying it. They are the products of two transgressive cycles, and are tidal flat-bay-lagoon facies. Purple beds underlie both of these beds. The stratiform ores are of diagenetic origin, and were remobilized into vein deposits (Fig. 2; Ran, 1983). GEOCHEMICAL DATA Trace element geochemistry

Trace element data for beds and ore deposits of the mining area are recorded in Table 2. The coefficients of trace element enrichment were evaluated using the ratio of the analysed value of the elements to the Clarke value of elements in the crust (Li, 1981). The Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun 173 and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

elements with a coefficient of greater than 2 are enriched elements, coefficients in the range 2-0·5 are elements at levels close to the Clarke value, and coefficients less than 0·5 are deficient elements. Silver, copper, tin, molybdenum and boron are enriched in strata of the Luoxue and Yinmin For­ mations, barium and lead are at normal levels and other elements are deficient. Silver, copper, tin, molybdenum, barium, lead and bismuth are enriched in the ore deposits. The silver contents in the strata are 0·26 to 12 ppm (average 2·3 ppm), but in bornites they exceed 100 ppm and in chalcopyrites the values range from 5·2 to 50 ppm. Bismuth is absent in the Yinmin purple bed, the Luoxue dolomite and dia­ genetic deposit, and is occasionally present in the transitional beds, but ranges from 56·3 to 195 ppm in remobilized deposits; so bismuth is probably not derived from the host sequence. Gallium is generally in the range 2-8 ppm in the host rocks, but at 12-30 ppm in chalcopyrite. In the Shishan Member, Yimen, silver, copper, lead, molybdenum, gallium, tin, boron and barium are mostly enriched elements, lanthanum, titanium, vanadium, nickel, cobalt and yttrium are normal and the others are deficient. In the Shishan-Fengshan ore deposit, copper, silver,

174

C. Ran

I

Proterozoic ( Kunyang Subgroup)

Proterozoic

z

(Sinian)

Mz

Mesozoic

I

Major fault

Fig. 1. Geological sketch map of the south of the Kangdian Axis, highlighting the Kunyang Group.

tin and molybdenum are enriched elements, prob­ ably derived from the host rocks. In summary, the lithophile elements titanium, chromium, stron­ tium, yttrium, niobium, lanthanum and vanadium are mostly deficient, except barium and boron; the siderophile elements nickel and cobalt are mostly deficient or normal and the chalcophile elements copper, silver, tin, lead, bismuth and gallium are mostly enriched. The chalcophile elements were enriched within the Yinmin purple bed, transitional bed, Luoxue dolomite and three beds of the Shishan Member to make these strata favourable source beds. The trace element distributions in the strata and ore deposits at different horizons are similar, which suggests an inheritance of metals from the strata to the ore deposits. The association and contents of most trace elements in the Lala copper mine of the Hekeu Formation are similar to those in the Luoxue and Yinmin Formations. The total rare earth element content (La to Lu + Y) in the Yinmin-Luzhijiang Formations of the Kunyang Group, 209·23 ppm, the ratio of LREE: HREE which is 18·53, and the ratio Eu: Eu* 0·70, are compatible with derivation from an evolved crustal source. =

Organic geochemistry

The contents of organic carbon in the Dongchuan­ Yimen copper mine are recorded in Table 3. The average organic carbon content in the host rocks is

I

\\

1�� -

� � � � � � � ��

iang Fm. u L zhij Heishan Fm. Fm. uoxue L------------Yinmin Fm.

II

Fig. 2. Two-stage model of mineralization for the Dongchuan- Yimen strata-bound copper deposits. Mineralization occurred in syndiagenetic (I) and epigenetic (II) stages in cupriferous sediments of the Kunyang Group. Arrows indicate direction of brine movement; ore bodies are black.

Table 1. Composite Precambrian stratigraphy and ore-bearing sedimentary formation in Kangdian Axis Formation

Thickness (m)

Lithological character

Chengjiang

Ore-bearing sedimentary formation Ferruginous molasse formation

Developing stage of geosyncline Rejuvenated

(or Dengying)

Type of ore deposits

Cupriferous horizon

Sedimentary iron

uplifting

(Jinning movement] Proterozoic Kunyang Group Upper

>3419

Sandstone and slate intercalated with limestone and andesite, with conglomerate at the base

Upper ferruginous terrigenous formation

Subsidence and rejuvenated uplifting

Sedimentary, metasedimentary iron

tJ ()

[Manyingou movement(?)] Luzhijiang (Middle)

32-3035

Upper siliceous banded dolomite, and

Fengshan veined

limestone with stromatolites

Major

copper

Lower carbonaceous, argillaceous, tuffaceous dolomite and tuff

Shishan stratiform copper

Major

limestone, black slate

115-1900

Middle greyish-green, yellowishgreen silty banded slate intercalated

Luoxue (Middle)

40-500

�

s 6-

Carbonate formation

Subsidence

Stromatolitic dolomite, argilloarenaceous dolomite intercalated

Daqinggou stratiform copper

Minor

Luoxue stratiform copper

Major

with thin-bedded slate Yinmin (Middle)

20-1300

I

"'

Cupriferous algal reef

with thin-bedded dolomite Lower black slate intercalated with dolomite and tuff

� ;:s

� � �

Upper blue-grey thin-bedded Heishan (Middle)

� g.. ;;::

() ;;:: ;:s !::>..

�

"' ....

!::>..

Xikuangshan stratiform Cu-Fc Sedimentary­

Cyclothem composed of purple slate, dolomite and sandstone- slate, with conglomerate at the base

Minor

�

() �. 1:;"

metamorphosed­ hydrothermal iron

[Dongchuan movement(?}] Lower

>7525

Sandstone and slate intercalated with limestone and tuff

Lower ferruginous terrigenous formation

Subsidence

Sedimentary, sedimentary­ metamorphosed­ hydrothermal iron

[Palaeo-Dongchuan movement (?)] Hekou

>1250

Green schist

Copper-iron-bearing spilitekeratophyre formation

Subsidence

Dahongshan volcanic­ hosted Cu-Fe

:3 Vl

-.] a-

-

Table 2. Average content of trace clements in Dongchuan- Yimen copper deposits (in ppm) Strata and ore deposits

Yinmin purple beds Transitional beds Luoxue dolomite Shishan purple beds Shishan transitional beds Shishan black beds Fengshan dolomite Fengshan diapir body Lata copper deposits Luoxue- Yinmin diagenetic deposits Luoxue- Yinmin remobilized deposits Shishan diagenetic deposits Shishan weakly remobilized deposits Fengshan intensely remobilized deposits Element abundance in crust

Number of samples

Ba

B

Cr

Cu

Pb

Ga

Ni

5 5 6 4 5 5 5 3 2 5 8 8 5 12

519 344 414 9775 1049 458·6 32·8 446 16·6 1976 837 103 131·2 135·9 390

56 67 30·7 95·8 1 19·6 18·2 4-4 43·4

22·6 . 16·3 6·1 43 60·3 23·9 2·4 48·7

9·1

4·7 2·3

399 483 725 228 294 279 so 228 >1000 >1000 >1000 >1000 >1000 >1000 63

2-4 6·9 7·1 33-6 68·9 339·0 40·6 12·3 18·6 50·5 43·9 195 325·9 330 12

6·6 6·8 4·9 25-4 139 48·0 3·8 27·8 42·5 4·6 14·9 42·8 25-4 37·5 18

16·5 13-6 11·1 43 72-7 70·1 4·5 24-4 850 11-4 13·0 91·9 275·8 27·3 89

131 13

6-4 110

Bi

-

22 -

Nb

Mo

Sn

10·2 3·6 6·8 10·2 10

16·2

1·8 57·9 3·1 2-4 3·8 79·2 9-4 7·7

8·09 13·6 15·1 19

18·9 36·6 39·6 47·8 38·3 1·3

6·2 7·9 12-4 6·0 10·6 1·8 22 23·3 90 30·6 36·2 73-0 49·3 32 1·7

10·8 0·6

188·9 56·3 35·1 60 30 4·3X10-3

0

(after Li, 1981) Strata and ore deposits

Yinmin purple beds Transitional beds Luoxue dolomite Shishan purple beds Shishan transitional beds Shishan black beds Fengshan dolomite Fengshan diapir body Lata copper deposits Luoxue- Yinmin diagenetic deposits Luoxue-Yinmin remobilized deposits Shishan diagenetic deposits Shishan weakly remobilized deposits Fengshan intensely remobilized deposits Element abundance in crust

Number of samples

v

Ag

5 5 6 4 5 5 5 3 2 5 8 8 5 12

64-4 93·3 47·2 92·8 152·6 311-4 33·5 138 33·5 18-4 19-4 42·9 25·8 34-4 140

0·94 4·80 1-20 0·98 1·80 7·34 1·86 1 4·6 81·6 52·2 9·6 8·7 16·7 0·08

Co

10·8 10·1 27·4 9·8 21·7 24·7 2·9 44·3 >1000 10·7 8-40 44-4 89-4 42·3 25

Sr

35·6 23·8 31-4 194·0 66·1 197·6 54-4 77-3 9·8 6·8 50·0 1·5 0·65 480

La

y

Ti

Zn

Be

7·2 101·6 2·5 35·9 53·6 47·83 3·6 36·7 258

11·2 12·2 3·2 11·7 12·8 15·6 3·2 29 15 2-4 4·6 9·6 6·75 8·1 24

1310 1518 359 4775 8230 4820

4 15 44·5 86·4

0·3

39

190 11·7 90 386 125 1231 580 596 6400

20 237 383 986 94

(after Li, 1981) Determined by Central Laboratory of Yunnan Bureau of Geology and Mineral Resources using ICP-AES quantitative analysis (1986) .

2·6 3·4 0·8 2·3 3·7

1·3

Co:Ni

Sr:Ba

0·65 0·74 2-47 0·23 0·30 0·35 0·64 1·82 1·18 0·94 0·65 0-48 0·33 1·55 0·28

0·07 0·07 0·08 0·02 0·06 0-43 1·66 0·17 0·06 0·01 0·01 0·49 0·01 0·01 1·23

;:.;, � ;:s

177

Dongchuan- Yimen strata-bound copper deposits

Table 3. Contents of organic carbon (%) in Dongchuan- Yimen copper mine Strata or ore deposits

Number of

Average

Range

0·050 0·040 0·040 0·028 0·036 0·196 0·070 0·060 0·210 0·230 0·660 0·200 0·400

0·02-0·10 0·01-0·07 0·03-0·07 0·02-0·04 0·01-0·06 0·12-0·23 0·05-0·09 0·02-0·13 0·16-0·28 0·14-0·33 0·11-2·06 0·04-0·56 0·30-0·53

samples Yinmin Formation Transitional bed Luoxue Formation Shishan purple bed Shishan light bed Shishan black bed Purple diapir body Fengshan dolomite Luoxue-Yinmin diagenetic deposits Luoxue-Yinmin remobilized deposits Shishan diagenetic deposits Shishan weakly remobilized deposits Fengshan intensely remobilized deposits

12 15 15 4 7 5 3 6 5 6 5 5 4

Determined by Yunnan Research Institute of Petroleum Geology (1986).

0·03-0·07% , but that in copper sulphide minerals is much higher than in the host rocks at 0·2-0·66% (2·06% maximum value). Besides disseminated organic carbon, there is earthy bitumen in epigenetic minerals in the Yimen copper mine, globular bitu­ men in dolomites, methane, carbon dioxide and organic matter in inclusions in dolomites. The reflectance (Ro) of bitumen in the Yimen copper mine is 4·3-6·2% , and it is weakly aniso­ tropic. The uncorrected homogenization tempera­ tures of fluid inclusions in the dolomite are 107-234°C. The organic carbon content of dolomite (C) is 0·05% and its chloroform-bitumen extract (A) is 0·0076%, so the transformed ratio (A: C = 0·152) is high. The extractive ratio and the maturity of soluble organic matter are higher (OEP = 0·93). The pristane: phytane ratio (Pr: Ph = 0·14) is low. The source organic matter was mainly marine algal kerogen. The high content of organic carbon in the ore deposit suggests that it may have played an important part in the process of copper mineral­ ization. Possible roles for the organic matter include the solubilization of metals by organic acids, a cata­ lyst for sulphate reduction, and a reductant for sulphide deposition (Saxby, 1976). Isotope geochemistry

Stable isotope data for sulphur, hydrogen, oxygen and carbon for the copper mine have been determined.

Isotopic composition of sulphur

The determined sulphur isotope compositions of copper sulphides (bornite, chalcocite, chalcopyrite; analysed by the Nonferrous Metallic Geological Institute, Guilin, China, 1985) b34ScoT are in the range -10 to + 16·7%o for the Dongchuan diagenetic deposits, from -0·1 to + 15·2%o for the Dongchuan remobilized deposits, from -4·5 to +14·9%o for the Shishan diagenetic deposits and from -1·5 to + 19·5%o for the Shishan-Fenshan remobilized deposits. The narrow difference between these ranges of values suggests that the sulphur had a simjlar source. The sulphur isotopic composition has a wide range (from -10 to 19·5%o) and is predomi­ nantly positive. It is suggested that the sulphur was mainly derived from bacterial sulphate reduction in marine strata. The data are similar to those from copper sulphides in the White Pine copper deposit (in USA) and the Katanga copper deposit (in Zaire) whose values of b34S range from -10 to + 18%o and from -15·3 to + 19·2%o respectively, and many other strata-bound sulphide deposits in marine rocks (Sangster, 1976). Isotopic composition of hydrogen and oxygen

The isotopes of hydrogen and oxygen can be used to discriminate the source of water in ore-forming fluids (Tu, 1988), but at the present time the technique has its limitations and the data may be susceptible to different interpretations. Additionally, there is no definite location of connate water in the bD-6180 cross-plot. On the basis of recent research (Tu,

178

C. Ran

1988), the composition of connate water is located approximately in the area between the meteoric water line and the region of metamorphic water and magmatic water composition in the ()D-6180 diagram (Fig. 3). The isotopic compositions of hydrogen and oxygen in minerals from the Dongchuan-Yimen copper mine are recorded in Table 4. Determined values of 6180 for vein minerals are calculated into 6180H,o (SMOW) values which range from 0·51 to 12·85%o. The value of 6DH,o (SMOW) for solutions in fluid inclusions ranges from -34·5 to -83·9%o. These values plot in the areas of metamorphic water, magmatic water and connate water in the ()D-6180 diagram (Fig. 3). There is no evidence for meta­ morphism or magmatism in the region. Considering the value of soi-: Cl- (see below), it can be reasoned that the water in the ore-forming fluids was possibly connate water. Some of these values do not plot in the area of connate water in the diagram because of isotopic exchange between the fluids and wall rocks during fluid migration. Isotopic composition of carbonate carbon

The average 613C (PDB) value in dolomite veins of the Shishan, Yimen and Luoxue-Yinmin diagenetic

¥ Sea water 3

0 ::;: Vl 0

-40

•

� 0

0 '-0

1 1 1 I 1 le

_

1 I I

Metamorphic water

e

,__'::;-..__Juvenile water

-80

-120

-20

-10

0

10

20

6180 (%o) SMOW Fig. 3. oD-6180 cross-plot for fluid inclusions in five carbonate samples from the Dongchuan- Yimen copper mine (see Table 4).

deposits is -0·74%o, for the Luoxue-Yinmin remobilized deposits it is -0·84%o, for the Shishan weakly remobilized deposit it is -1·64%o, and for the Fengshan intensively remobilized deposit it is 0·16%o. These ranges are narrow, from -2·79 to + 1·30%o (Table 4), and consistent with derivation of the carbon from marine carbonate. However the

parentheses)

Shishan LuoxueYinmin Luoxue-

Type

Diagenetic Diagenetic

Remobilized

Yinmin

Sample number 28 D30 D14 D116 D41 D40

Analysed mineral

013Co%o (PDB)

Dolomite Dolomite

- 2·79

Dolomite Quartz Dolomite Dolomite

0·18 0-40 (- 0·74)

o13C%o (PDB)

- 2·71

0180o%o (SMOW)

0180H,o%o (SMOW)

ODH,o%o (SMOW)

17·61 18·83 18·73 (18·39)

5·31 6·53

- 59·7*

6·43 (6·09)

(- 71·8)

Fengshan

Weakly remobilized

Intensively remobilized

15·88

7·42 6·18

S30

Dolomite

- 2·39

S16 1

Dolomite Dolomite

-1·08 -1·44 (-1·64)

18-2

Dolomite Dolomite

- 1·57 - 1·06

19·64 11·91

8·99 3·45

Dolomite Dolomite Dolomite

1·30 1·14

20·07 19·56 18·34

12·32 8·91 7·17

19·62 (18·19)

12·85 (8·95)

19 F40 F22 F38 F

Calcite

-83·9

- 16·41 - 0·84

(6·80) Shishan

0·85 0·32 (0·16)

13·98 15·58 16·85

- 0·87

-34·5* (-51·55)

1·09 0·51 0·97 (0·86)

- 46·7*

-61·3

* Determined by Institute of Geochemistry, Academia Sinica. All others determined by Isotope Section of Beijing University.

I I

, --, - - - - - - ---

Table 4. Isotopic compositions of carbon, hydrogen and oxygen in Dongchuan-Yimen copper mine (averages in

Mineral deposits

:

, --- --- - - - -- -

: �_

Table 5. Composition of fluid inclusions in Dongchuan- Yimen copper mine. (Determined by Institute of Geochemistry, Academia Sinica.) I::J

Analysed results 3 (ppm x 10 ) Type

Mineral deposits Shishan

Diagenetic Weakly remobilized

Fengshan Intensively remobilized

Luoxue-

Diagenetic

Yinmin Remobilized

*

Part of Ca

2+

Number of samples

Analysed minerals

S26 S22

Dolomite Dolomite

S1 S5

Dolomite quartz Dolomite

5

Dolomite

15-2 F22

K+

27·9 43·8 4·9 3·0 8·7 30·8 15·1

+

*Ca2+

14-4 30·0

3·5 12·8

22·4 3-3

2·2

Na

* Mi +

soi-

+ + Na : K

2+ Na+:Ca 2+ Mg

+

so42-: o-

F-

o-

0·4 4·1

5·7 7·7

50·0 67-8

20·2 54·8

0·52 0·69

3-69 1·78

0-40 0·71

1·9 0·3 10·5

2·9 0·2

76·0 6·0

6·1 1-4

4·50 1·11

5·43 5·05

2·3

82·8

302·0

3·87

0·18

0·08 0·24 3·60

180·8 86·3 101·8

14·7 45·5 454·5

4·07 2·23 1·83 0·99

1-11 0·87 0·13

0·08 0·53 2·50

3·34

0·05 0·18

10·50 4·70

33·7

0-4 182·0

125·8

57·0 6-4 393·9 287·5 149·0

56·0 32·6 79·1

10·8 40·0

38·8 12·7

0·7 6·1

36·6 71-8

416·7 340·0

I

F3

Dolomite Dolomite Quartz

F4 15-1

Dolomite Dolomite

33·9 15·5 8·6

33·8 62·3 15-4 28·7

D30 D14

Dolomite quartz Dolomite

16·1 18·9

18·5 11-4

2·6 149·5

2·3 22·1

6·6 0·9

77-2 58·8

182·6 132·4

1·15 0·60

3·74 0·07

1·67 2·25

D40 D96

Quartz dolomite Dolomite

35·1 20·8

19·8 31·7

8·7 806·3

4·9 85·7

1·5 1-1

93·3 142·9

8·6 1071-4

0·56 1·53

l-45

0·09 7·50

-

0·04

pH

0 ;: OQ "' ;:>:: "' ;:

8·11

:::;; � "' ;: "'

�

s 67·83

0 >:: ;: "'"'

�

"' ..,

"'-

8·06

�

0 "'

�·

2+ and Mg in inclusion in dolomite probably derived from host minerals.

-.) 'D

-

180

C. Ran

o 13C,

value of -16-41%o for the solution in fluid inclusions suggests that organic matter contributed to the composition of the solution.

sol-: Cl- (3·0) were relatively high during the remobilization stage.

CONCLUSIONS

Fluid inclusion geochemistry

The fluid inclusions in minerals of the copper mine have been grouped into six classes: (I) pure liquid inclusions; (lA) liquid inclusions (with gas); (II) gaseous inclusions; (III) liquid carbon dioxide­ bearing inclusions; (IV) crystal-bearing (NaCl, KCl) inclusions; and (V) organic matter-bearing in­ clusions. Classes (I) and (IA) are widespread and abundant. Class (II) inclusions are also common in remobilized deposits, but other classes are less abundant. In the remobilized deposits, the size of inclusions is bigger (4-10 !A-m), they are more abundant, more variable in type, and yield higher homogenization temperatures than the diagenetic deposits. The results of salinity and temperature determination of the inclusions (Table 5) are that the homogenization temperature is generally in the range 105-140°C for the Yimen diagenetic de­ posits, 150-200°C for the Dongchuan deposit and 150-280°C for remobilized deposits. The salinity range is 12·5-23·2 wt% for both deposits, and clearly the ore-forming fluids were hot brines. The chemical composition of the brine (Table 5) shows that the contents of N a+ (or K+), Cl - or sol-in this region are high compared with modern heavy metal-bearing solutions in some seas (Jiang, 1983). The values of S042-: Cl - (mostly >0·14) show that the water type is neither pure chloride brine nor choride brine ( sensu Jiang, 1983), but a sodium-sulphate­ chloride water whose total mineralization and value of SO/-: Cl- are higher. In the genetic classification for hot brines of Jiang (1983) this brine has affinities with shallow connate water. A growth fault (fault I in Fig. 1) at the margin of the depositional basin may have allowed brine flow and a source of heat. Research on inclusions in various vein minerals shows that there were two stages of hot brine cor­ responding to the two types of deposits (diagenetic and vein). The temperature of the hot brine during the diagenetic stage was relatively low and the ratios of Na+: K+ (average 0·74) and of SO/-: Cl­ (average 1·26) were also relatively low, but the temperature and ratios of Na+ : K+ (2-4) and of

Reforming metals were deposited within the marine sediments of the Yinmin and Luoxue Formations and the Shishan Member of the Luzhijiang Formation. Metals were concentrated from the cupriferous sedi­ ments by hot brine flowing through deep faults, with the influence of organic matter, to form copper sulphides as stratiform ore deposits. Sulphide pre­ cipitation was engendered by bacterial sulphate reduction. Intensive faulting introduced hotter brine to the strata and remobilized the metals into new vein ore bodies.

ACKNOWLED GEMENTS

I thank the National Natural Science Foundation of China for their support for our project, and Z. Zhijun, G. Jianguo, H. Meifang, L. Weihua, W. Linjang and 0. Xiangwei for participating in work for this project.

REFERENCES JiANG, Q.J. (1983) The role of hot vadose brine mineral­ ization and the genetic indicators of the ore deposits.

Min. Deposits, Beijing, China 2, 57-59. L1, T. (1981) Table of Abundance of Chemical Elements. Geology & Prospecting Publishing House, Beijing, China.

RAN, C. Y. (1983) On genetic model of Dongchuan type strata-bound copper deposit. Scientia Sinica (B) 26,

983-995.

SANGSTER, D.F. (1976) Sulphur and lead isotopes in strata­ bound deposits. In: Handbook of Strata-bound and Stratiform Ore Deposits, Vol. 2 (Ed. by K.H. Wolf), pp. 219-236. Elsevier, Amsterdam. SAXBY, J.D. (1976) The significance of organic matter in ore genesis. In: Handbook ofStrata-bound andStratiform Ore Deposits, Vol. 2 (Ed. by K.H. Wolf), pp. 111-128. Elsevier, Amsterdam. Tu, G. Z. (1988) Geochemistry ofStrala-bound Ore Deposil

in China, Vol. 3, pp. 18-20. Science Press, Beijing, China.

Metal Enrichments Associated with Organic Matter

Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

Spec.

Pubis

int.

Ass.

Sediment. (1990)

11,

183-192

Metal enrichments in organic materials as a guide to ore mineralization J.

P A RNELL

Department of Geology, Queen's University, Belfast BT7 INN, UK

ABSTRACT The determination of metal enrichments in organic materials can contribute to the geochemical exploration for metalliferous ore deposits. An enrichment in metals can develop at several stages in the geological evolution of organic matter, from living tissue through kerogen and liquid hydrocarbons to solid hydrocarbon products. Scenarios for enrichment include: (1) uptake by organic matter from groundwaters flowing through ore deposits;

(2)

organic matter caught up in metal-rich hydrothermal

systems; and (3) organic matter with a signature of low-level synsedimentary metal concentrations which were subsequently remobilized into ore deposits. Some solid bitumens are so enriched in metal that they constitute the actual ore body. Uranium is especially found enriched within organic materials, including bitumens which precipitate around uranium minerals due to radiation-induced polymerization, but many other metals also form enrichments.

INTRODUCTION

material to become metal-enriched. This paper discusses how metal enrichments within organic materials may be a significant guide to metalliferous ore exploration.

The occurrence of organic materials in ore deposits and other concentrations of metals is extremely widespread. In many cases the organic material played a geochemical role in the concentration of metals but was not itself enriched in metals. However some organic materials are enriched with metals. Metal concentration can be envisaged in several types of organic material, which represent different stages in the geological evolution of organic matter. Living organisms utilize and may take up a large number of elements including metals (see below). The decay of dead organisms yields organic acids and other compounds which may complex with metal ions. The degradation of sulphur-rich organic matter by anaerobic bacteria, and bacterial sulphate re­ duction both yield hydrogen sulphide which can help to precipitate metals as sulphides within organic-rich sediment. Mixed sequences of organic-rich and organic-poor sediment contain redox boundaries which facilitate metal precipitation. Finally epi­ genetic organic materials (migrating petroleum, and bitumens and pyrobitumens of diverse origin) can cause the reduction or complexing of metals. At each of these stages it is possible for the organic Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

METAL ENRICHMENT IN ORGANIC MATERIALS

A large number of elements are concentrated by biological activity. M;�my metals are taken up by micro-organisms for use in enzymes or for other metabolic functions, and some organisms can con­ centrate them by several orders of magnitude (see Robbins, 1983 and references therein for review of in­ teractions between biomass and nutrients). Much data show that terrestrial plant matter in particular ac­ cumulates metals. For example peat bogs concen­ trate uranium and other metals through adsorption and the binding action of humus (Boyle, 1982). Cannon et at. (1968) showed that plants on a tailings dump were concentrating substantial quantities of base metals. Determinations of metals in young coniferous trees suggest that they can be used as a 183

J. Parnell

184

sampling medium in geochemical prospecting (King 1984). Once organisms have died, the degraded tissues may still absorb some metals, and it is found that the metal concentrations in organic-rich sediments in an anoxic environment are much higher than those in the overlying water column. Further enrichment of metals can occur during the diagenesis of the organic­ rich sediment. Metals are already being remobilized during early diagenesis and transported or deposited according to the redox conditions. The relative importance of different metals may change, because some organometallic complexes are quite stable during diagenesis, while others break down as the temperature rises. Vanadium and nickel complexes are particularly stable and these metals will substitute for others which are progressively lost (Lewan & Maynard, 1982). Vanadium and nickel are also im­ portant components of petroleum and bitumens, in which they are concentrated within certain organic fractions, particularly the heavy fractions rich in asphaltenes and sulphur. In addition to vanadium and nickel, elements regularly concentrated within petroleum and bitumens include copper, cobalt, chromium, molybdenum, lead, manganese and iron (Erickson et al., 1954; Bell, 1960). The availability of significant quantities of organic materials and metals together is particularly likely in certain types of lake basin. In tectonically active lacustrine basins, such as in rift systems, there may be rapid erosion of the crystalline basement which

et al.,

may be quite rich in metals and even contain mineral deposits which can be recycled into the lake system. Metals may also be introduced by vulcanism and hot spring activity, and the extensive circulation of groundwaters through fractured bedrock in a fault­ bounded system will enhance leaching of metals from the basement. The metals, and other species like phosphate, will include nutrients to support the biomass in the lake, and within a deep stratified lake the dead organic matter and the metals and phos­ phate will become locked up in the anoxic bottom sediments. Without the organic matter there is no anoxic environment where the metals and phosphate can be concentrated. But the mere existence of an organic-rich sediment and its anoxic environment is not a guarantee of concentrating metals, because the influx of metals varies considerably in space and time (Fig. 1). While inflowing rivers are draining off a crystalline basement there is a good chance that those waters are metal-rich. But as the watershed is gradually worn down and the reworking of sediment becomes more important, the flux of new metals into the basin declines, and the higher beds in the succession may be relatively metal-poor. However, uplift of the basin margin may re-expose the basement and herald a new influx of metal-rich waters. It is also possible that metals are available but do not reach the sapro­ pelic facies at the lake centre because they are filtered out by some other facies beforehand. That other facies may also be organic-rich, in the form of

POOR RICH

LAKE \\I

1/

Q , If,

RICH

POOR

�9 ""

RICH Fig. I. Schematic scenario for input of metals into a lake basin. Input may be metal-rich by erosion of granitic and volcanic terrains, or metal-poor due to filtering effect of lake-margin vegetation and reworking of sediment to progressively greater maturities.

Metal enrichments in organic materials

lake-matgin vegetation. Some lacustrine oil shales are known to pass laterally into coal at the basin margins (see below), and in those systems one might expect that metals will be concentrated in the coals rather than in the oil shales. The factor of over riding importance to metal enrichment is the availability of metals from the rocks in the watershed. The rocks which form the basement to the lake system may be particularly concentrated in certain metals which will be reflected as enrichments in the lake sediments. Volcanic rocks in rift systems may particularly give up copper, nickel and iron, while granites may yield uranium, molybdenum, tungsten and lead. Examples of ancient lake sequences in which metal enrichments reflect the nature of the underlying basement are discussed below. Lacustrine basins contain extensive redox boundaries that are favourable to the precipi­ tation of metals as they often include rhythmic alternations between fine-grained lacustrine beds which may be organic-rich, and oxidized fluvial or aeolian red beds. Metal enrichments in organic materials can be significant to metal exploration in four ways: 1 The organic material could be enriched in metal that has been taken up from groundwaters flowing off a metal ore deposit, i.e. the organic matter is younger than the ore deposit. The enrichments of metals in present day plants are examples of this. 2 The organic material may contain metal enrich­ ments which are a signature of more limited levels of enrichment in the host sediments. If the enrichments in the sediments were later remobilized and concen­ trated into an ore deposit, then the organic material used as a sampling medium is older than the ore deposit. 3 The organic material could be so enriched in the metal that it constitutes the actual ore. Further metal concentrations could occur in the vicinity, or the metal may be restricted to the organic material. 4 The organic material could be an epigenetic prod­ uct (bitumen, pyrobitumen) generated at the same time as the ore deposit, particularly in a hydro­ thermal environment. Traces of the ore metal may occur as a signature within the organic material. Examples of these scenarios are given below.

185

of metal anomalies which reflect mineralization in the watershed (Fig. 2). In the Mid-Tertiary Lough Neagh Basin of Northern Ireland, the inflowing drainage was predominantly across early Tertiary basalts, and Precambrian schists which are mineralized by gold­ bearing quartz veins. Lacustrine lignitic sediments in the basin are enriched in vanadium, nickel and iron which are derived from the basalts (Parnell et al., 1989), and in gold which has been recycled from the Precambrian (Sunday Telegraph, 1987). In central Scotland a thick sequence of Carbon­ iferous lacustrine oil shales includes some of the richest oil source rocks in Europe (Parnell, 1988a). They have carbon contents up to 30% but do not contain significant quantities of metals (Pb <40 ppm, Zn < 160 ppm, Cu <50 ppm). They occur in

Fig. 2. Three palaeolake basins in northern Britain in

Post-ore organic material

Organic materials in ancient lake basins in the northern United Kingdom provide several examples

which metal signatures in source terrains are reflected as enrichments in organic-rich lake sediments: gold, iron, nickel and vanadium enrichments in lignite of Tertiary (i) Lough Neagh Basin; copper enrichments in stromatolites of Carboniferous (d) oil shale group: uranium and lead enrichments in fish fossils of Devonian (c) Orcadian Basin.

186

J. Parnell

a basin which had already existed through much of the Devonian, and the drainage was largely through older sandstones which were not mineralized. There is also a lateral transition from some oil shale seams to coal at the lake margin. No data exist for these coals, which are not exposed at present. However some coals higher in the sequence do contain limited concentrations of base metal sulphides which suggests that metals may have been filtered out by vegetation. There was also limited drainage off some Devonian basaltic lavas and newly extruded Car­ boniferous basaltic lavas which are copper-rich, and copper mineralization is accordingly developed in lacustine stromatolites in the oil shale sequence (Parnell, 1983). In the north of Scotland a lake system in the Devonian Orcadian Basin received drainage directly off Caledonian granites, some of which are miner­ alized by uranium and lead. The chemistry of the Devonian sediments closely reflects that of the base­ ment (Plant et al., 1986). Uranium and lead are

enriched within the lake sediments, particularly in the vicinity of a small granite outcrop in Orkney (Fig. 3). Fish fossils in the sediments are enriched in uranium (Davidson & Atkin, 1953; Bowie & Atkin, 1956; Diggle & Saxon, 1965). Autoradiographic studies showed that more radioactivity is associated with hydrocarbons infilling cavities in the fish bone than with the carbonate-fluorapatite bone itself. New electron microprobe �Wdies show that the hydrocarbon in the bone contains numerous discrete crystals of uraninite (Fig. 4). A regional survey (Fig. 3) using the thick warty bone fragments of coccosteid fish yielded bulk concentrations up to 4668 ppm uranium and the highest values were recorded in the vicinity of the granite outcrop noted above. The sediments containing the fossils are also enriched in uranium (Michie & Cooper, 1979) but to a much lesser degree, in a smaller region (particularly around the granite outcrop), and only at certain horizons. Thus not only is the uranium anomaly in the basin more easily detected by analysing the

206 Pb 204Pb

u

I

�;f

� 'G 1723

{'

�{1

649

�� I I

18·2

\.. ' ....,

'

..

'·

..

'

•

:

0

,·,

' " 1.._..,'/1

A

B

40 Km

/

Fig. 3. (A) Anomalous concentrations of uranium (ppm) in coccosteid fish bones, and (B) zonation of anomalous lead isotope composition around granite outcrop G, in Devonian Orcadian Basin. Normal

18·2.

For location see Fig.

2.

206

04 PbP Pb composition for basin is

Metal enrichments in organic materials

Fig. 4. Backscattered electron micrograph of fish bone, consisting of apatite (grey) with spheres of bitumen (black) containing uraninite crystals (bright). Field width =

250

�lin.

fossils (and was first detected thus) but in some parts of the basin the fossils are the only evidence for the anomaly. Lead isotope data for galenas (Parnell & Swainbank, 1985) provide independent evidence for a focus of mineralization around the granite (Fig. 3), but the anomaly in isotopic composition does not occur over as wide an area as the uranium anomaly in the fossils. It is not possible to date the timing of the uranium enrichment of the bones, but contem­ poraneous fish debris is known to act as a sink for metals (Tlig, 1988) and the Devonian occurrences are likely to be syndiagenetic. A similar example of uranium uptake by fish debris is reported from Australia by Ramsden et al. ( 1982). A widespread product of the interaction of metals with organic materials is the formation of metal­ rich, organic-rich nodules at the cores of reduction spots in red beds. The organic matter at the cores of some spots is detrital (fragments of plant matter) but those nodules which are mineralized tend to have spherical cores which clearly developed postcom­ paction by accretion of migrating hydrocarbons. The nodules contain metals characteristic of red bed mineralization (uranium, copper, vanadium, selenium) and typically have a mineralogy of coffinite, roscoelite (vanadium mica), vanadium oxides/hydroxides, vanadium-rich clays, copper nickel arsenides and selenides, and organic carbon. One model for their formation is through the juxta­ position of metal-bearing groundwaters in red bed sediments with hydrocarbons migrating along cross-

187

cutting fractures (Parnell & Eakin, 1987). The nodules are useful in assessing regional metal anomalies. In any continental basin there is probably enough uranium, vanadium and copper available to be remobilized into trace quantities of ore minerals within these centimetre-scale structures, but where metals reach very high levels they may be more significant. For example in several cases where the uranium content of the nodules is greater than 0·5% it is possible to identify more extensive uranium mineralization, either in the basement rocks of the basin watershed or in the organic-rich facies of lake sediments. 1 Organic-rich nodules in Devonian red beds in Easter Ross, Scotland, are mineralized with about 1% uranium, mainly as a component of xenotime (Parnell, 1985). The uranium enrichment reflects a regional uranium anomaly in the crystalline base­ ment rocks below the Devonian sediments (Watson & Plant, 1979). 2 Uraniferous hydrocarbon nodules in Permian red beds in Oklahoma are thought to be the product of hydrocarbons migrating up fault planes from a deep reservoir interacting with uranium-rich ground­ waters (Curiale et a!., 1983). Granites in the basin watershed are uranium-rich, and uranium ore miner­ alization occurs within the coarse sediment between the granites and the finer-grained red beds (Fig. 5). 3 Organic-rich nodules from the Permian Lodeve Basin, France, occur in red beds, in a sequence which also contains lacustrine black mudrocks. The organic-rich nodules are significantly mineralized by uranium (Fig. 6) in the form of coffinite, ac­ companied by roscoelite, clausthalite (lead selenide) and copper arsenides. The black mudrocks are mineralized with a major economic uranium deposit. Some uranium is dispersed within the mudrocks, but much is concentrated within solid bitumens in brecciated fracture systems (Landais eta!., 1987), so that in this case the nodules are pre-ore. Perhaps the largest regional metal anomaly in hydrocarbons is the high level of vanadium found in oils and bitumens throughout much of South America (Kapo, 1978). The anomaly is so marked that Gold (1984, 1985) has suggested that it reflects a vanadium anomaly in the mantle which was trans­ ferred to the upper crust through a flux of abiogenic hydrocarbons. An alternative, more conventional explanation is suggested here. In the case of Venezuela, the anomaly may in part reflect ore deposits in the local basement. Kapo ( 1978) has suggested that waters flowing over deposits of

188

J. Parnell

��-="tj} Permian U Conglomerate Q U

S.W. OKLAHOMA

Red Beds

Ordovician

Cambrian granite

(Curiale et al 1983)

� �

•

Uranium

in

groundwaters

Petroleum along faults

Uraniferous hydrocarbons

��--����-=--��= +

+ +

+

+

+

+

Fig. 6. Backscattered electron micrograph of organic-rich core of reduction spot from Permian Lodeve Basin, France, showing concentration of coffinite, roscoelite and copper-bearing phases (all bright) around detrital quartz grains. Field width = 250 �un.

vanadium, nickel and copper transported the metals and reprecipitated them in organic-rich sediments including coals (Fig. 7). The vanadium enrich­ ments were conveyed to subsequently generated hydrocarbons. Organic material as an ore

For a metal-rich hydrocarbon to have value as an ore in its own right, the hydrocarbon must be very

Fig. 5. Origin of uraniferous hydrocarbon nodules in southwest Oklahoma, through intersection of petroleum migrating along faults with red bed groundwaters draining off uranium-rich granites. (Based on Curiale et al., 1983.)

abundant and/or the metal must be a very scarce one. The vanadiferous hydrocarbons in South America are locally both sufficiently abundant and enriched to have been considered as potential vanadium ores (Abraham, 1945). Several mines in central Peru contain bitumen which was ashed to a vanadium­ rich concentrate (Baragwanath, 1921). The most important deposit, at Minas Ragra, is the richest vanadium ore body ever recorded. The Minas Ragra bitumen is a highly sulphur-rich variety ('quisqueite') in which the vanadium occurs segregated out as inclusions and veinlets of the vanadium sulphide patronite. Detailed examination of the bitumen shows that it consists of several phases of varying sulphur content which may represent successive periods of hydrocarbon mobilization (Fig. 8). A thick vein of patronite adjacent to the bitumen may have segregated out during the thermal maturation of the bitumen by an igneous intrusion (McKinstry, 1957). Pilot projects for the extraction of vanadium and nickel from solid bitumens have also been set up elsewhere, including the USSR (Shabad, 1984). Uranium-rich hydrocarbon deposits are very widespread, and in a few cases are large enough to constitute viable ore deposits. Deposits in the USSR and France in which the uranium is largely confined to bitumen are described by Zubov & Kotel'nikov ( 1968) and Landais & Connan ( 1980) respectively. Kerogen, in the form of cyanobacterial mats, also hosts a major fraction of the uranium in Precambrian deposits in Canada and the Witwatersrand

Metal enrichments in organic materials

0

189

Km

300

Trinidad

f) VENEZUELA Columbia

N Fig. 7. Distribution of vanadium­ nickel-rich petroleum and vanadium-copper-rich coal in basinal areas, relative to vanadium-nickel-copper ore deposits in basin watersheds, Venezuela. (After Kapo, 1978.)

0 Ore deposit •

Coal rich in V, Cu

•

Petroleum rich in V, Ni

Fig. 8. Backscattered electron micrograph of sulphur-rich pyrobitumen from Minas Ragra, Peru, showing multiphase nature. Earliest bitumen (dark grey) cut by bitumen vein (light grey) cut and displaced by later bitumen vein (bright); phases distinguished by different sulphur contents. Small black masses are vanadium-enriched but appear darker because of lower sulphur content. Field width = 280 >UTI.

(Willingham et al., 1985). In many more deposits, only a limited proportion of the uranium may be held within organic materials, but in these cases the organic materials are a good sampling medium for

r

prospecting the deposits. For example in the Moonta copper deposit, South Australia, radioactivity was first detected from organic material, and only sub­ sequently was torbernite mineralization recorded (Mawson, 1944). The copper lode, in Precambrian schists and quartz-porphyry, has yielded radioactive organic materials where it is intersected by cross­ courses (Davidson & Bowie, 1951; Mumme, 1965). The organic material (which appears to be a type of bitumen) contains abundant inclusions of a mineral referrable to xenotime (with 22% uranium substi­ tution for yttrium and coupled substitution of silicon for phosphorus) and a variety of copper sulphides (Fig. 9). Several examples of uranium-enriched bitumen occur in uranium prospects in the Scottish Devonian lake basin discussed above (Michie & Cooper, 1979). As the uranium anomaly in the basin was first detected as syndiagenetic enrichments in fish, this is also an example of an organic sampling medium which predates formation of the ore. Uranium-rich bitumens may be formed by two distinct processes. Pre-existing uranium-bearing minerals can cause the precipitation of solid bitumen around the minerals by the polymerization/conden­ sation of migrating fluid hydrocarbons, a con­ sequence of radiation. Alternatively uranium may be precipitated from metal-bearing fluids on contact

J. Parnell

190

case all the uranium is likely to be within the bitumen, but much bitumen may not contain uranium. Ore coeval with organic material

Fig. 9. Backscattered electron micrograph of carbonaceous matter from Moonta copper mines, South Australia, showing inclusions (bright) of uranium-rich xenotime (diffuse boundaries) and chalcopyrite­ covelline (sharp boundaries). Field width =

300 J.tm.

with fluid or solid hydrocarbons, by reduction and adsorption. In the former situation all solid bitumen is likely to be uranium-rich but some uranium may be unassociated with hydrocarbons. In the latter

Ni

A INiAsI AsSb

An example of the fourth scenario for the formation of uranium-rich bitumens is in a set of vein-hosted deposits around the Irish Sea (Fig. 10) . The uranium in these deposits is restricted to solid bitumens. The bitumens contain inclusions of uraninite, nickel­ cobalt arsenides and at one locality bismuth­ antimony sulphides ( Parnell, 1988b ) . In the same region, nickel, cobalt, arsenic, bismuth and antimony also form ore deposits (Fig. 10) , although at some bitumen localities the only trace of these metals is within the bitumen. The chemistry of the bitumens is therefore useful as a pointer towards the nature of ore deposits in the region.

DISCUSSION

In the assessment of how metal enrichments in organic materials can be used as a guide to metal

A tf

lf-,-,,-o ' --:: iC N W B :-:iS ::-:b --::-c 1 --, U

: BITUMEN OCCURRENCE WITH METALLIFEROUS INCLUSIONS : ORE DEPOSIT

D

: LOWER PALAEOZOIC OUTCROP

Fig. 10. Occurrence of metals as inclusions in bitumens around the Irish Sea, relative to ore deposits of those metals in the same region.

Metal enrichments in organic materials

anomalies, it is important to consider how the metals come to be associated with the organic matter. Four mechanisms may be distinguished for metal enrich­ ment in organic materials (Parnell, 1988c). 1 The metals in hydrocarbons may be inherited from the hydrocarbon source rock as organometallic complexes. Source rocks contain variable quantities of organophilic metals, including vanadium and nickel, which may have been inherited in turn from the living tissues. 2 Uptake of metals by hydrocarbon fluids, from the rocks through which the fluids migrate. 3 Enrichment at sites of mixing between metal­ bearing fluids and hydrocarbon-bearing fluids. 4 Enrichment of uranium and/or thorium in bitu­ mens precipitated through the effects of radiation (see above). The enhanced precipitation of bitumens around radioactive sources results in this type of enrichment being widespread. These mechanisms have varying import for the possible roles of organic materials as signatures of regional metal anomalies. The uptake of metals from groundwaters flowing off a metalliferous deposit, and enrichment of organic materials coeval with an ore deposit, could involve all except the inheritance mechanism. Pre-ore organic material with a signature of enrichments in the host sediment could be either syngenetic or epigenetic. Syngenetic organic material could have inherited the metal in the case of organophilic elements whereas epigenetic organic material could be involved in any mechan­ ism. The unusual occurrences of organic materials which are ores are produced by the radiation mech­ anism in the case of uranium-thorium ore, and probably by the inheritance mechanism in the case of vanadium ore. On a cautionary note, it cannot be assumed that organic matter will contain a signature of any ore deposit in the vicinity. Some metals are much more readily taken up by organic matter than others (e.g. tin and tungsten very rarely form enrichments). The circumstances of fluid migration may be such that the organic matter does not have the opportunity to take up the metal. It is also important to appreciate that in some ore deposits wltich contain significant quantities of organic materials, those materials may not exhibit enrichments. For example the bitumen commonly encountered in Mississippi Valley type lead-zinc deposits generally does not contain lead or zinc enrichments. In order to further understand the degrees to which organic materials become enriched in metals,

191

Table 1. Behaviour of metal relative to organic material during progressive evolution of organic matter Organic material

Metal

Living organic matter

Metals used as enzymes Other metabolic functions

Decay of organic matter,

Adsorption of metals

conversion to kerogen

Release of organic acids with complexed metals Sulphate reduction to metal sulphides

Hydrocarbon products

Reduction and complexing

Alteration of hydrocarbons

Progressive enrichment of

of metals

metals Mineral exsolution Graphitization

Loss of heteroatoms Expulsion of metals from graphite structure

and the processes involved, it will be necessary to make a detailed assessment of the metal flux at different stages in the evolution of organic matter (Table 1). Generally, there is a progressive enrich­ ment in metals through the maturation of organic matter, generation of petroleum and alteration to complex solid hydrocarbons, and then a loss of metals as they cannot be accommodated by the ordered structure developed during graphitization. This simple trend belies the many complex processes which have yet to be systematically investigated.

ACKNOWLEDGEMENTS

I am grateful to A. Thickpenny and J. Arthurs for critical reading of the manuscript. The Peruvian bitumen was kindly supplied by the British Museum (Natural History) (sample regd. no. 1908, 413), and J. McCrae and E. Mulqueeny provided valuable technical assistance.

REFERENCES ABRAHAM, H.

( 1945) Asphalts and Allied Substances,

5th

edn. Van Nostrand, New York.

BARAGWANATH, J.G. (1921) The vanadiferous asphaltites of central Peru. Eng. Mining. JI. 1 1 1, 778-781. BELL, K.G. (1960) Uranium and other trace elements in petroleum and rock asphalts. 365B.

US Geol. Surv. Prof. Paper

1. Parnell

192

BOWIE, S.H.U. & ATKIN, D. (1956) An unusually radio­ active fossil fish from Thurso, Scotland. Nature 177, 487-488. BOYLE, R.W. (1982) Geochemical Prospecting for Thorium and Uranium Deposits. Elsevier, Amsterdam. CANNON, H.L., SHACKLEITE, H.T. & BASTRON, H. (1968) Metal absorption by Equisetum (Horsetail). US Ceo!. Surv. Bull. (A) 1278, 1-21. CURIALE, J.A., BLOCH, S., RAFALSKA-BLOCH, J. & HARRISON, W.E. (1983) Petroleum-related origin for uraniferous organic-rich nodules of southwestern Oklahoma. Bull. Am. Ass. Petrol. Ceo/. 67, 588-608. DAVIDSON, C.F. & ATKIN, D. (1953) On the occurrence of uranium in phosphate rock. C. r. 19th Congr. Ceo!. Int. 11, 13-31. DAVIDSON, C.F. & BowiE, S.H.U. (1951) On thucholite and related hydrocarbon-uraninite complexes. Bull.

Ceo/. Surv. GB 3, 1-19. DIGGLE, W.R. & SAXON, J. (1965) An unusually radioactive fossil fish from Thurso, Scotland. Nature 208, 400-401. ERICKSON, R.L., MYERS, A.T. & HORR, C.A. (1954) As­ sociation of uranium and other metals with crude oil, asphalt and petroliferous rock. Bull. Am. Ass. Petrol. Ceo/. 38, 2200-2218. GoLD, T. (1984) Contributions to the theory of an abiogenic origin of methane and other terrestrial hydrocarbons. Proc. 27th Int. Ceo/. Congr. 13, 413-442. GoLD, T. (1985) The origin of natural gas and petroleum, and the prognosis for future supplies.

Ann. Rev. Energy

10, 53-77.

KAPO, G. (1978) Vanadium: key to Venezuelan fossil hydrocarbons. In: Bitumens, Asphalts and Tar Sands (Ed. by G.V. Chilingarian and T.F. Yen), pp. 155-190. Elsevier, Amsterdam. KING, H.D., CURTIN, G.C. & SHACKLEITE, H.T. (1984) Metal uptake by young conifer trees. US Ceo/. Surv. Bull. 1617, 1-23. LANDAIS, P. & CoNNAN, J. (1980) Relation uranium­ matiere organique dans deux bassins Permiens Francais: Lodeve (Herault) et Cerilly-Bourbon-L'Archambault (Allier).

Bull. Cent. Rech. Explor-Prod. Elf-Aquitaine

4, 709-757.

LANDAIS, P., CONNAN, J., DEREPI'E, J.M., GEORGE, E., MEUNIER, J.D., MONTHIOUX, M., PAGEL, M., PIRONON, J. & PoTY B. (1987) Alterations of organic matter: a clue for uranium ore genesis. Uranium 3, 307-342. LEWAN, M.D. & MAYNARD, J.B. (1982) Factors controlling enrichment of vanadium and nickel in the bitumen of organic sedimentary rocks. Geochim. cosmochim. Acta 46, 2547-2560.

McKINSTRY, H. (1957) El Vanadio en el Peru (review).

Econ. Ceo/. 52, 324-325. MAWSON, D. (1944) The nature and occurrence of ura­ niferous mineral deposits in South Australia. Trans. Roy. Soc. S. Aust. 68, 334-357. MICHIE, U. MeL. & CooPER, D.C. (1979) Uranium in the Old Red Sandstone of Orkney. Rep. Inst. Ceo/. Sci. 78/ 16. MuMME, l.A. (1965) An hypothesis on the origin of

thucholite mineralization at the Wallaroo-Moonta mining field, South Australia. Trans. Roy. Soc. S. Aust. 89, 255-256. PARNELL, J. (1983) Stromatolite-hosted mineralization in the Oil Shale Group, Scotland. Trans. Inst. Min. Metall. (B) 92, 98-99. PARNELL, J. (1985) Uranium/rare earth-enriched hydro­ carbons in Devonian sandstones, northern Scotland. N. lb. Miner. Mh. (H) 3, 132-144. PARNELL, J. (1988a) Lacustrine petroleum source rocks in the Dinantian Oil Shale Group, Scotland: a review. In: Lacustrine Petroleum Source Rocks (Ed. by A.J. Fleet, K. Kelts & M.R. Talbot), pp. 235-246.

Spec. Pub!.

Ceo!. Soc. London 40. PARNELL, J. (1988b) Mineralogy of uraniferous hydro­ carbons in Carboniferous-hosted mineral deposits, Great Britain. Uranium 4, 197-218. PARNELL, J. (1988c) Metal enrichments in solid bitumens: a review. Min. Deposita 23, 191-199. PARNELL, J. & EAKIN, P. (1987) The replacement of sand­ stones by uraniferous hydrocarbons: significance for petroleum migration. Min. Mag. 51, 505-515. PARNELL, J., SHUKLA, B. & MEIGHAN l.G. (1989) The lignite and associated sediments of the Tertiary Lough Neagh Basin. Irish J. Earth Sci. 10, 67-88. PARNELL, J. & SWAINBANK, l.G. (1985) Galena mineral­ ization in the Orcadian Basin, Scotland: geological and isotopic evidence for sources of lead. Min. Deposita 20, 50-56. PLANT, J.A., FORREST, M.D., HODGSON J.F., SMITH, R.T.S. & STEVENSON, A.G. (1986) Regional geochemistry in the detection and modelling of mineral deposits. In: Applied Geochemistry in the 1980s (Ed. by I. Thornton & R.J. Howarth), pp. 103-139. Graham & Trotman, London. RAMSDEN, A.R., DICKSON, B.L. & MEAKlNS, R.L. (1982) Origin and significance of the Toolebuc gamma-ray anomaly in parts of the Eromanga Basin. J. Ceo!. Soc.

Aust.

29, 285-296.

RoBBINS, E.l. (1983) Accumulation of fossil fuels and metallic minerals in active and ancient rift lakes.

Tectonophysics 94, 633-658. SHABAD, T. (1984) Growing interest in Soviet resources of bitumen, heavy oil and tar sands. Sov. Geog. 25, 702-704. SuNDAY TELEGRAPH (1987) Financial News, 24 May, p. 26. TuG, S. (1988) Fish debris as chemical scavengers of zirconium and lanthanum in oceanic environments - Zr and Hf fractionation in marine phosphates. Chem. Ceo!. 69, 59-71. WATSON, J.V. & PLANT, J. (1979) Regional geochemistry of uranium as a guide to deposit formation. Phil. Trans. Roy. Soc. Land. (A) 291, 321-338.

WILLINGHAM, T.O., NAGY, L.A., KRJNSLEY, D.H. & MosSMAN, D.J. (1985) Uranium-bearing stratiform organic matter in paleoplacers of the lower Huronian Supergroup, Elliot Lake-Blind River region, Canada. Can. J. Earth Sci. 22, 1930-1944. Zusov, A.I. & KOTEL'NIKOV, G.N. (1968) Vein asphaltites in a uranium deposit. Sov. At. Energy 24, 637-641.

Spec. Pubis int. Ass. Sediment. (1990) 11, 193-202

Relationships between organic matter and metalliferous deposits in Lower Palaeozoic carbonate formations in China R . Jl A , D . Ll U and Institute of Geochemistry, Academia Sinica,

PO

Box

J.

FU

1131,

Wushan, Guangzhou, China

ABSTRACT Organic matter in carbonate rocks from Cambrian to Devonian age in China is distributed inhomoge­ neously, and asphalts occur in two belts in northern and southern China. Some metal deposits are associated with the two asphalt belts. Based on the characteristics of soluble organic matter, reflectance and the structure of the asphalts associated with metal deposits, it is inferred that most of the vanadium, nickel, molybdenum and uranium deposits were formed in stable pressure and temperature conditions, while arsenic and mercury deposits were formed in open system conditions near to natural gas pools. A comparison of the content of metallic elements in asphalts, black shale and carbonate shows that most metallic elements in asphalts could be derived mainly from black shales, but some lead, tin, silver, zinc and manganese were possibly contributed from hydrothermal solutions. The metallic elements in minerals associated with organic matter are mainly chalcophile and variable-valency elements. Accord­ ing to simulated experiments the combination between organic matter and metals occurs during two particular stages, when Ro is less than

1·2% and greater than 2%.

INTRODUCTION

lationship between organic matter and metalliferous deposits, including the relationship between oil and ore deposits in sedimentary rocks (Connan, 1977), hydrothermal maturation of organic matter in gold deposits (Ilchik & Brimhall, 1986), relationships between oil-gas fields and ore deposits (Tu, 1988), the significance of organic matter in strata-bound ore deposits (Rashid, 197 1; Lu & Yuan, 1986), charac­ teristics of organic matter in mercury- gold deposits (Fu & Liu, 1983; Chen et at., 1987), vanadium­ nickel minerals in carbonaceous asphalt (Liu & Lin, 1984; Zhang et al., 1984) and the relationship between uranium precipitation and organic matter (Wang, 1983; Hu et at., 1988). The occurrence of organic matter distributed in metalliferous deposits in China has been reported in many papers (e.g. Fu & Liu, 1983; Liu & Lin, 1984). This paper reports the results of field work and experimental simulations in the laboratory.

Carbonate formations are widely distributed through Precambrian to Devonian sequences in China. Excepting some gas fields in Sichuan and Shanxi Provinces, productive fields are not found in these rocks. However, a lot of solid asphalt representing the products of migration, accumulation and degra­ dation of oil is exposed at the surface in the carbon­ ates (Liu et al., 1985; Liu & Fu, 1989). There are two asphalt belts in Lower Palaeozoic strata in China. One belt is usually associated with oil seep­ ages, and is called the oil-bearing asphalt belt, located from east to west in northern China, includ­ ing the southern Talimo Basin, the Ordos Tableland, south of Yanshan Mountain to Tanshan City. The second belt, called the carbonaceous asphalt belt, is located around the Jiangnan Swell in southern China (Fig. 1). In some cases there is much solid asphalt in metalliferous ore deposits, including mercury, zinc, lead, copper, gold and uranium deposits. There has been much recent research on the reSediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

193

194

R. Jia,

D.

Liu and J. Fu

Xi'an 0

Changsha� GuiyangA &;.� 0

;.

0 Fig. 1. Major occurrences of asphalts in China.

CHARACTERISTICS OF ORGANIC MATTER IN METALLIFEROUS DEPOSITS Abundance and maturation of organic matter

The contents of organic matter in Precambrian to Devonian rocks in some provinces of China are shown in Table 1. The values of TOC (%), A (ppm), and HC (ppm) represent the quantity of total organic carbon, total soluble organic matter and saturated hydrocarbons, respectively. The abundance of organic matter in the tin­ polymetallic deposit in Dachan, Guangxi Province is listed in Table 2. In this deposit it is found that carbonate is light-coloured and silicified carbonate is dark-coloured. The results show that the amount of organic matter in the silicified carbonate is 1- 3 times greater than that in the carbonate strata, which possibly indicates that the organic matter may have migrated and become enriched in the silicified rock due to the action of hydrothermal solutions.

The relationship between the abundance and maturation of organic matter in different deposits is shown in Fig. 2. The TOC content and maturation (reflectance, Ro) of organic matter in each deposit show a wide range. The contents of organic matter are highest in nickel, vanadium, uranium and molybdenum deposits, but lower in mercury and arsenic deposits. However, research in the field and analyses in the laboratory indicate that the mercury and arsenic deposits are associated with both natural gas and solid asphalt, while the nickel, vanadium, uranium and molybdenum deposits are only associ­ ated with solid asphalt. In accordance with the reflectance measurements with Ro over 2%, there are few oil occurrences (Fu et al., 1983) and most of the metalliferous deposits are only associated with asphalt and natural gas. Soluble organic matter

The composition and alkane characteristics of sol­ uble organic matter in Cambrian- Devonian car-

195

Organic matter and metalliferous deposits

Table l. Abundance of organic matter in Middle- Upper Proterozoic and Lower Palaeozoic carbonate rocks in China Northern China

Strata Ordovician

c (%)

0·03-0·55 [0·13 (76)]*

A (ppm) HC (ppm) Cambrian

C (%)

41-650 [210 (32)] 22-579 [108 (26)] 0·02-0·30 [0·10 (53)]

A (ppm) HC (ppm) Proterozoic

Sichuan

C (%)

15-1056 [171 (25)] 19-756

HC (ppm)

0·06

0·10

0·10

0·05

29

50

Jianghan

Zhejiang

Hunan

<5

24 0·07

0·09

0·33

0·17

77

10

61

<5

25

[ 92 (25)]

0·02-0·48 [0·12]

A (ppm)

Yunnan

0·08-0·10

0·14

0·18 <5

0·04-0·55

20-690 [95]

54 34·3

8-410 [52]

* Average value [ ]; number of samples ( ).

Table 2. Average amount of TOC (%) in different strata of Sn-polymetallic ore deposit* Unit

Devonian 3-2d

Petrography Lenticular

Lenticular

carbonate

silicified carbonate 1·5 (7)

TOC (%) Number

0·11 (10)

Lenticular carbonate

Carbonate

Silicified carbonate

0·028

0·078 (4)

0·15 (11)

(95)

Devonian 3-1

Devonian 3-2a

Devonian 3-2b

Devonian 3-2c

Carbonate Silicified carbonate 0·43 (5)

0·076 (7)

Silicified carbonate

Silica rock

1·31

0-43

(7)

(8)

* Data from Lu (1986).

R"

(%)1 12

10

u

IL_

Sn

-� l r_p,���

IMn.Ni

.vi

_______ c _ " __

Fig. 2. Cross-plot of Ro (%) and TOC (%) for organic matter in

Chinese ore deposits.

bonate rocks in southern China are listed in Table 3, which shows that the saturated fraction is more abundant than the aromatic fraction. The amount of non-hydrocarbons increases with maturation. The organic matter in Lower Palaeozoic deposits is probably the product of oil evolution.

10

15

20

Corg

(% J

The pristane : phytane (Pr: Ph) and the C21- : C22+ alkane ratios are indicators of maturity and environment; the lower the ratios, the more reducing the environment arid the more mature the organic matter (Liu & Jia, 1990). The data for saturated hydrocarbons in some deposits (Table 4)

R.

196

Jia, D. Liu and J. Fu

Table 3. Composition (%) of soluble organic matter in carbonate formation of Cambrian-Devonian systems, China Area

Petrology

Layer

Saturated CH

Aromatic CH

Non-CH + Asphalt

E. Guizhou E. Guizhou E. Guizhou E. Guizhou Northern China

Carbonate Limestone Limestone Limestone

D2-3 S2 01

27·41 30·16 75·35

68·84 54-45 19·79

39·30

4·15 15·42 4·87 7·08

Carbonate

01

48·34

12·76

44·66

Carbonate

E

31-36

12·02

56·12

Northern China E,

El

53-62

Cambrian.

Table 4. Character of saturated hydrocarbons in some deposits, southern China Ore & Area

Main peak

CPI

nC21-:nC22+

Pr:Ph

E

nC14-nC30 nC14-nC30 nC14-nC31

C16 C17 C17

1·053 1·263 1·136

6·957 2·931 3·582

1·15 1·30 0·59

Sl

nC14-nC36 nC15-nC31

C17 C23

1·084 1·131

2-414 0·441

0·89 0·33

E

Hg, Guizhou (SE) Hg, Guizhou (NE)

E

Pb-Zn, Hunan Pb-Zn, Hunan V-Ni, Anhui E,

Range of n-alkane

Layer

E

Cambrian.

show that the most highly reducing and most mature sequence was the source of organic matter in the vanadium-nickel- uranium deposits, and the least mature was the source of organic matter in the mercury deposits. Insoluble organic matter

During the evolution of the parent organic matter, some hydrocarbons migrated as liquids, a part of H/C 1.5

/

which was degraded to leave a residue called solid asphalt. The 0 C and H: C ratios of the asphalts associ­ ated with metallic deposits allow them to be plotted on a Van Krevelen diagram (Fig. 3). The hydrogen content of the asphalt samples is very low, and the oxygen content is highly variable, especially in the samples from the tin-polymetallic deposit. These asphalts are rich in carbon and have no effective potential for oil or gas. They are derived from

:

/

(/ \

1.0

\ I I I I I I I

0.5 5il I 1•1

Fig. 3. Aromatic H : C and 0 : C ratios of asphalts plotted on the

/•3 .3. fs-----:1·---/�;--5�;------- ----- --------0.4 0.1 0.2 0.3 /

Van Krevelen diagram. (From

-- -...---- -- --- -

Hu et a!., 1988 and Tu, 1988. ) (1) Uranium deposit in Proterozoic-Cambrian, Guangxi; (2) tin-polymetallic

/

deposit, in Devonian, Guangxi; (3) lead-zinc deposit in Cambrian-Carboniferous, Jiangsu; ( 4) lead-tin deposit in

(___ _

0/C

Cambrian, Shanxi; (5) lead-tin deposit in Devonian, Hunan.

Organic matter and metalliferous deposits

liptinite-rich hydrogen precursors (in the marine pre-Devonian). These asphalts were highly altered by hydrothermal solutions (Lu, 1986; Yang, 1988). X-ray diffraction (XRD) of different coal rank vitrinites shows that the Z8 angle of OOZ diffraction is changed from 17° to Z6°. The Z8 angle at 17-zoo represents aliphatic straight-chain and aliphatic ring structures, and the Z8 angle at Z4-Z6° represents aromatic structure. Besides the OOZ diffraction, there is a peak at 43° representing 100 diffraction in highly mature vitrinite. X-ray diffraction also offers information about asphalt structure, especially the degree of aromati­ city. We regard the d002 parameter as an important measurement of asphalt maturity and oil-gas po­ tential (Fu et a/., 1983). The d002 and d1oo para­ meters represent the vertical separation of aromatic nuclei along the OOZ and 100 directions. The Lc and

dooz

3.40

3.42

3.44

3.46

Fig. 4. Cross-plots of d002 and Lc, and dlOO and La, for some Chinese asphalts. Samples 0 10,

016 and Gu2 from tin­

polymetallic deposit, Guangxi; H2114, Wa-5 and Dz-5 from mercury deposit, Guizhou; H22o from lead-tin deposit, Hunan; and H221 from asphalt vein; Guizhou.

0.08

197

La parameters represent the size of aromatic nuclei along the OOZ and 100 directions. X-ray diffraction analysis of different asphalts shows that the relation­ ships between asphalt/oil-gas and metallic deposits are: ( 1) in general, oil is associated with asphalt with an OOZ diffraction at about 17- zoo, and 100 diffrac­ tion is not found; (Z) the OOZ diffraction is at 17-Z6° (two peaks are combined) and 100 diffraction is visible in some asphalts associated with mercury deposits; (3) the OOZ diffraction at Z6° and 100 diffraction at 43° are very clear in asphalt associated with lead, zinc and tin deposits. The cross-plots of d002 with Lc and d 100 with La are shown in Fig. 4, reflecting the degree of crystal­ linity of asphalts sampled from different deposits (Qin et al., 1987). The degree of crystallinity depends on: (1) the carbonization of asphalts- the higher the carbon content, the higher the asphalt crystallization;

R.

198

Jia, D. Liu and J. Fu

and (2) the temperature and pressure, which at higher levels produce more crystalline asphalt. A compari­ son of asphalts from different deposits suggests that mercury deposits formed in relatively low-pressure systems containing natural gas (rich in hydrogen), but the lead, zinc and tin deposits formed in the relatively closed systems far from gas pools, because the degree of asphalt crystallization is greater in the latter deposits.

the average contents in black shales, except Sb, Sn, Ag, Pb, Zn and Mn. Possibly some Sb, Sn, Ag, etc. was contributed from hydrothermal solutions. Minerals in asphalts

Some minerals found in asphalts in southern China are listed in Table 5. The metallic elements in the minerals are mainly chalcophile elements and most of them are variable-valency elements. There are temporal and regional variations in the enrichment of metallic elements in asphalts. For example va­ nadium and nickel minerals occur mainly in asphalts in Cambrian, Silurian and Devonian rocks around the Jiangnan Swell, but lead and zinc minerals occur particularly in asphalts along the juncture of Yunnan, Guizhou and Guangxi Provinces and south of Qinglin Mountain.

METALLIC ELEMENTS AND MINERALS IN ASPHALT Abundance of metallic elements in asphalt

The abundance of metallic elements in asphalt is compared with the average abundance in carbon­ ates (Geological Department of Nanjing University, 1987) and black shales (Fan et a!., 1973) in Fig. 5. It was found that: ( 1) the following elements are not present in the asphalts-Ta, Hf, Sc, Ge, In, Ga, W, Nb, Zr, Co, Be, Li, U, Th, La, Ce, Y, Yb, Au, K and Na; (2) the abundance of Ag, Pb, Zn, V and Ni in asphalts is 100 to 10 000 times greater than the average abundance in carbonates; and (3) the con­ tents of metallic elements are generally lower than

SIGNIFICANCE OF ORGANIC MATTER IN METAL ORES Direct combination of organic matter with metals

Living organisms contain many enzymes which con­ tain metallic ions, i. ncluding Na, K, Fe, Cu, Zn, Mn,

1:� (a)

M1 ppm (Asphalt) M2ppm Black shale)

0

0

0 0

0 -2

0

0

2

0

0

0

0

0

0

0

-4

•

2 (b)

MJPPm CAsphaltJ MaPPm (Carbonate)

• •

•

0 -2

•

•

4

•

• •

•

•

•

-4 Sr

Ba

Pb

Zn

Sb

v

Mo

Sn

Ti

Fig. 5. Metal abundances in asphalts. (a) Compared with average for black shale (Fan

Mn

Ni

Cu

Ag

eta/., 1973). (b) Compared with average for carbonate rock (Geological Department, Nanjing University). Ml, M2, M3 represent amount of metallic

elements in asphalt, black shale and carbonate, respectively.

199

Organic matter and metalliferous deposits Table 5. Some minerals recorded in asphalt Name Pyrite Marcasite Jordisite Bravoite Millerite Polydymite Gersdorffite Sulvanite Sphalerite Galena Violarite Tetrahedrite Uraninite

Formula FeS FeS MoSz (Ni, Co, Fe)S2 NiS Ni3S4 NiAsS

Location

Reported

Stratigraphy

Hunan

E

and S

Fan T. Yang X. Chen N. (1973-1985)

Cu3VS4 ZnS PbS (Fe, Ni)3S4 5CuS·2(Cu, Fe)S·2As2S3 UOz

Montroseite Karelianite

Mo, Ca, Mg and Se ions, which are important in metabolic processes (Chen & Li, 1983). The content of some metallic elements in living. organisms is generally higher (up to 10 000 times) than that of the surrounding medium. For example, the contents of metallic elements in plants growing in the sea compared with those of the seawater are: Ag, B, Mo, Rb >10 times >100 times W, K, Li, Ca Al, Au, Ba, Cd, Co, Cs, Cu, Hg >1000 times As, Cr, Fe, Mn, P, Pb, Ti, Zn >10 000 times (data from Yang, 1989). In addition, organic acids produced by the de­ composition of living organisms allow the formation of organometallic complexing, such that the abun­ dances of lead, zinc, copper and nickel in humic 2 acids are 104, 103, 103 and 10 times more than the average abundance in shales respectively (Rashid, 1971; Lu & Yuan, 1986).

Guangxi . Simulated in lab.

Z-E

Chen R. (1983) Hu K. (1987)

Guangxi

D

Liu D. Lin M. (1983)

[UOzS04JZ- +CH4 ____,. U02 +H2S +COl- +H20 Na4[UOz(C03h] + H2S ____,. U02 + S + 2Na2C03 + C02 + H20 2HgS + CH4 ____,. 2Hg + C + 2H2S As a result, some metal ore is associated with organic matter. Simulated experiments of uranium precipitation by organic matter support the possibility of the above reactions (Hu et al., 1988). The experimental results show that there are two stages of uranium uptake in the evolution of organic matter, at Ro <1·2% and >2% (Fig. 6). The mechanisms of the two stages of uranium enrichment are different. In the first stage (Ro <1·2%), the enrichment is mainly by absorption and complexing. When Ro >2%, the enrichment is mainly through reduction of metallic elements and consequent precipitation to ore. Some of the vanadium and nickel ore in the asphalt vein surrounding the Jiangnan Swell may be formed by the latter process.

Reduction of metal ions by organic matter

The content of organic carbon in the uranium ore­ bearing rocks in Zazipin, Guangxi Province, ranges from 4·27 to 19·14%, but the partition of uranium in the organic matter is only 0·1-1% (Hu et al., 1988). Native mercury has been found in mercury ore deposits which are rich in organic matter (Chen et al., 1987). The role of organic matter may have been to reduce metal ions to minerals. Examples may include

SUMMARY

1 Organic matter in carbonate rocks from Cambrian to Devonian age is distributed inhomogeneously. Although the average TOC is less than 0·1% in most regions, oil-bearing asphalts and carbonaceous as­ phalts outcrop in two belts in northern and southern China, respectively. 2 Some metal deposits are associated with the two

200

R.

Jia, D. Liu and J. Fu

Table 6. Partition of uranium in host rock and organic matter Sample

Slate Slate Slate Ore

8818-41 18 5-52 D20 D2

U content in kerogen (ppm)

Org. matter

in host rock (ppm)

7·2 10·4 36-4 1560·0 26300·0

6·5 5·5 7·0 83·0 39·0

U content

Lithology

Ore

:i

§

"0 Q) ..0 .... 0 "' ..0 -<

Partition of U in org. matter

(%)

(%)

3·92 4·80 10·72 19·14 4·27

3·5 2·5 2·1 1·0 0·01

When Ro >2%, metal precipitation is dominated by the reduction of metallic ions to ore minerals by organic matter.

., 50 � c " 0

content

40 ACKNOWLEDGEMENTS

30

20

0.5

1.0

1.5

2.0

2.5

3.0

3.5RO%

Fig. 6. Relationship between amount of absorbed uranium (�tg) and Ro (%) of organic matter, from experimental precipitation of uranium by organic matter.

This study was funded by National Scientific In­ vestment Bureau grant No. 86040129. We thank X. Chen and Q. Chen for reading the paper and offering good suggestions. X. Yan kindly supplied data for minerals in black shale.

REFERENCES

asphalt belts. Most V, Ni, Mo and U deposits are associated with solid asphalt, while most As and Hg deposits are related to both solid asphalt and natural gas. Based on the asphalt structure, the former deposits are concluded to have formed in stable conditions of pressure and temperature, while the latter deposits formed in open system conditions near to natural gas pools. 3 Ta, Hf, Sc, Ge, In, Ga, W, Nb, Zr, Co, Be, Li, U, Th, La, Ce, Y, Yb, Au, K and Na have not been found in asphalts. The abundance of Ag, Pb, Zn, V and Ni in asphalts is 100-10 000 times greater than the average abundance in carbonates; the content of metallic elements in the asphalts is generally less than the average in black shales, except Sb, Sn, Ag, Zn and Mn. Possibly some Sb, Sn, Ag, etc. was contributed from hydrothermal solutions. 4 The metallic elements in minerals associated with organic matter are mainly chalcophile elements. 5 The combination between organic matter and metals occurs in two stages. At the stage when Ro <1·2%, processes are dominated by complexing and absorption of metallic elements by enzymes in living organisms and by organic acids from dead organisms.

H. & LI, W. (1983) Molecular Enzymology, 130-177. People's Sanitation Publishing House. CHEN, Q., JI A, R. & Liu, D. (1987) Some characteristic CHEN,

pp.

features of organic matter and metals in Danzhai mercury-gold deposit. In: Annual Research Reports of the Organic Geochemistry Laboratory, 1986, Institute of Geochemistry, Academia Sinica, pp. 145-158. Guizhou People's Publishing House. (1977) Relationship between oil and ore in the Saint-Privat barite deposit, Lodeve Basin. In: Forum on

CoNNAN, J.

Oil and Ore in Sediments, pp. 167-187. Imperial College London. FAN, T., YANG, X. & C!iEN , N. (1973) Petrological and geochemical characteristics of a nickel-molybdenum multi element-bearing Lower-Cambrian black shale from a certain district in south China.

Geochemica 3,

143-160.

Fu, J., JIA, R. & LIU, D. (1983) Organic geochemical criterion of evaluation for oil-gas prospect in carbonate strata. In: Symposium on Petroleum Science, Chinese Academy of Sciences, pp. 131-138. Science Publishing House, Beijing.

Fu, J. & LIU, D. (1983) Evolution of organic matter and origin of sedimentary deposits (II) hydrocarbons orig­ inating from

coal and strata-bound deposits.

Sedimentol. Sinica, 1, 13-28.

Acta

GEOLOGICAL DEPARTMENT OF NANliNG UNIVERSITY (1987)

Geochemistry, pp. 80-92. Science Publishing House, Beijing.

201

Organic matter and metalliferous deposits ILCHIK, R.P. & BR I M HALL , G.H. (1986) Hydrothermal maturation of indigenous organic matter at the Alligator Ridge gold deposit, Nevada. Econ. Ceo!. 81, 298-306. Hu, K., ZHANG, Z., ZHING, B. & JIA , R.

(1988) The role

of organic matter in the formation of the Chanziping uranium deposit. In: Annual Research Reports of the

Organic Geochemistry Laboratory, Chinese Academy of Sciences, pp. 161-177. Science Publishing House, Beijing. L1u, B. & ]lA, R. (1990) Characteristics of normal and iso­ alkanes in Middle-Upper Proterozoic source rocks and thermal alteration experiments of kerogen. Geochemica 3 (in press). L1u, B., LIANG, D., FANG, J., JIA, R. & Fu, J.

Organic

matter

maturity

and

oil-gas

(1985)

prospect

in

Middle- Upper Proterozoic and Lower Paleozoic carbonate rocks in northern China. Geochemica 2,

150-162.

Guangxi Province. Thesis, the Institute of Geochemistry, Academia Sinica, Guiyan. Lu, J. & YU AN , Z. (1986) Experimental studies of organic-Zn complexes and their stability. Geochemica 1, 66-77.

Q1N, G., ZHAN, X. & LAO , Y.

diffraction of kerogen.

(1987) Research on X-ray Acta Sedimentol. Sinica 5, 1,

26-36. RASHID, N.A.

(1971) Role of humic acids of marine origin and their different molecular weight fractions in com­ plexing di- and tri-valent metals. Soil Sci. , 3, 298-306. Tu, G. (1988) The relationship between Hg, As, ore deposits and natural gas fields. In: Stratabound Deposits in China, Vol. 3 (Ed. by G. Tu), pp. 27-36. Science Publishing House, Beijing. WANG, J. (1983) Natural organic substance and oil-gas prospect: its implication in uranium mineralization.

Geochemica 3, 294-302. (1989) The action of organic matter on forming ore deposits in stratabound deposits. In: Stratabound Deposits in China, Vol. 3 (Ed. by G. Tu), pp. 255-310.

L1u, D. & Fu, J.

YANG, W.

Science Publishing House, Beijing. L1u, D. & LIN, M. (1984) Discovery of some vanadium and nickel minerals from anthraxolite and discussion of their origin. Scientia Sinica (B), XXVll (11), 1197-1202. Lu, G. (1986) Research on sedimentology and sedimentary

ZHANG, A., PAN, Z. & E NG , C.

(1989) Asphalts and stratabound deposits in carbonate rocks. In: Organic Geochemistry of Car­ bonates Applied to Evaluating Origin of Oil-Gas Fields and Stratabound Deposits (Ed. by J. Fu), pp. 172-193.

geochemistry of late Devonian system in Danchang basin,

Science Publishing House, Beijing.

(1984) The geochemistry of vanadium in Yang Jiabao stone coal of Upper Cam­ brian. In: Selected papers of Sedimentological and

Organic Geochemical Meeting, Beijing, pp. Science Publishing House, Beijing.

263-274.

Spec.

Pubis int. Ass. Sediment. (1990) 1 1, 203-216

Comparative geochemistry of metals and rare earth elements from the Cambrian alum shale and kolm of Sweden J . L E V E N T H AL US Geolog ical Survey, Federal Center MS 973, Denver CO 80225, USA

ABSTRACT

The Cambrian Alum Shale Formation of Sw eden is a metal-rich black shale. The metal distribution , however, varies with stratigraphy as well as organic carbon content and shows increases for certain metals in areas of tectonism. In the non-metamorp hosed areas, the elements uranium, molybdenum, vanadium and lead are enriched by factors of 2-4 relative to other black shales. The organic-rich (50% organic carbon) kolm of the Upper Cambrian shale is more enriched in uranium (0·5 % ), radiogenic-lead (200 ppm), yttrium (800 ppm) and heavy rare earth elements (HREE, e.g. ytterbium 45 ppm), but depleted in other elements (molybdenum, vanadium, nickel) . Normalizing to aluminium accounts for the major and rock-forming elements in the kolm that are the same as the surrounding shale, but not for uranium, lead, yttrium and HREE in kolm. In many shales, increased metal or trace element contents can be accounted for by parallel increases in organic matter, pyrite or p hosphate as hosts or sites. However, increases in content of trace elements are often not correlated with the content of hosts (sites) for the metal and trace element contents in non-metamorphosed alum shale or kolm. Therefore a combination of unusual source rocks (rich in uranium and other elements) coupled with selective element transport and efficient concentration by organic matter in an unusual depositional environment is suggested as a method of element enrichment. In the metamorphosed areas, the carbon content of the Cambrian shales is similar to the non­ metamorp hosed areas but vanadium (0·2% ), nickel (500 ppm), zinc (500 ppm), cadmium (10 ppm) and barium (1500 ppm) are greatly increased. Epigenetic addition of metals from external source(s), rather than internal redistribution, is suggested to account for increased amo unts of metals (vanadium, nickel, zinc, cadmium and barium) in the metamorphosed/tectonically affected areas.

INTRODUCTION

(Thickpenny, 1984, and references therein). The geochemistry of the Swedish alum shale is presented in the summary papers by Armands (1972), Edling (1974), Hessland & Armands (1978), and Andersson et at. (1983, 1985). The work reported here began in 1979 with a suite of core samples from Ranstad, courtesy of D. Gee (Swedish Geological Survey) and A. Andersson (Swedish Alum Shale Co) and a few hand specimens from J. Erdman (US Geological Survey); these were supplemented by additional core samples from Narke and Jamtland supplied by D. Gee. The initial interest was in extending the earlier inorganic geochemical work and new empha­ sis on the study of the organic matter association and

The Alum Shale Formation of Scandinavia is an organic-rich marine sequence of middle Cambrian to early Ordovician age (Andersson et al., 1985, and references therein). The Alum Shale Formation in Sweden (Figs 1 and 2) is generally between 15 and 35 m thick (in central Sweden). Locally it can be separated into Upper, Middle and Lower Members based on interlayered carbonate concretions (stinkstones) or other lithological characteristics and well-preserved marine fauna. The shales are rep­ resented by black laminated, dark-brown organically banded and grey mudstones and referred to as alum shales because of their potassium, aluminium and sulphate content. The sedimentation rate is esti­ mated to have been between 1 and 5 mm/1000 years Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

203

204

1.

Leventhal

SOUTHEASTERN BALTOSCANDIA

I

' 0 z I-<(

'

_J

' z

'G: SWEDEN /

LEGEND

f.::.·.J

t

N

I

• l':c\\\/'1 CJ

Post-Cambrian Cambrian, on-shore Cambrian, off-shore Precambrian

0

control on uranium and other anomalous elements (Leventhal, 1981, 1983, 1986). Since then a number of other workers have reported results on various aspects of geology and geochemistry (Andersson eta/ . 1983, 1985; Thickpenny, 1987), sedimentology (Thickpenny, 1984; Dworatzek, 1987), carbon iso­ topes (Buchardt et a/., 1986), and organic geo­ chemistry and radiation effects (Leventhal et al., 1986; Dahl et a/. , 1988a, b; Lewan & Buchardt, 1989). However none of these recent reports deals with the kolm which is the most enriched in uranium and organic matter. The uranium- and organic carbon-rich kolm nodules were studied in detail by Davidson (1961) and Cobb & Kulp (1961) and have been mentioned in many reports, but have only been further studied by Parnell (1984), who identified uranium- and

100

200

300 km

Fig. 1. Map showing Cambrian Alum Shale Formation in south­ eastern Baltoscandia. (From Andersson et al., 1985.) Note localities of interest (names out­ lined): Himtland in the north; Narke in the centre; Sydbillingen/ Ranstad samples are from Vastergotland (B-F ) .

cerium-rich minerals in the kolm. The kolm is part of the Pel tura scarabaeoides zone of the Upper Cambrian Olenid Series and is thickest in the Mt Billingen area (Armands 1972; Dahlman & Gee, 1977). Andersson etal. (1985) describe the kolm in more detail: it is restricted to the P. scarabaeoides zone and occurs as lenses and ( <10 em thick) bands in two levels (i.e. Billingen) or three levels (i.e. Vastra Falbygden). A brief report of the organic geochemistry of the kolm and its comparison to other uranium-enriched organic matter were pre­ sented in Leventhal et al. (1986). The summary papers by Armands (1972), Hessland & Armands (1978), Andersson et al. (1983) and Andersson etal . (1985) on the geochemistry of the alum shale mention the kolm but give no new data. This may be due to its thin and discontinuous nature such that it

205

Black s hale geoc hem istry

ALUM SHALE (RANSTAD)

U-1 ...J -< :r: (/) Q..

0 f-

Peltura scarabaeoides 5 c :::: ..c

6

·� E: 7 :::: c "'

::; -- 8 Ezz:Z%Z:Z:z:.::z:;2?Zj} Bottom shale

9 Great stinkstone

11 Fig. 2. Schematic section of the Alum Shale Formation at Ranstad. (From Andersson et al., 1985.) Note two kolin layers in the uranium-rich zone between 5.5 and 7.5 m below the Ordovician.

is not considered to be of major economic import­ ance despite early attempts to mine it for radium. However, it appears that although the kolm is extremely unusual in its geochemistry it may actually help to understand the geochemistry of the alum shale formation as a whole. In most reports, the kolm has been treated as a more organic-rich part of the alum shale formation, although it also has been suggested that it may be a migrated bitumen, based on microscopic examination of polished blocks (J. Dahl, pers. comm.). However, the mineral con­ tent of the kolm is around 40%, much higher than in

12�------,_--�

Middle Cambrian

c::Jshale

� Stinkstone- Kolm

a bitumen, and the major element abundances are proportional to the surrounding shale. In addition, although the kolm is present in the Mt Billingen (Ranstad) area where there has been intrusion of a diabase sill nearby, kolm also occurs at Narke, where there is no evidence of igneous activity and the organic matter in the shales is less mature. In this paper, a summary of results of the geo­ chemical characterization of kolm are presented (Leventhal, 1988). The origin and geochemistry of the kolm have not been reported or discussed in many studies. This may be because it is 1zotmerely an

206

J. Leventhal

extension of the alum shale in many of its geo­ chemical properties: the uranium content is much higher than expected based on extrapolation of uranium and organic carbon contents of the sur­ rounding shale. Neither is the uranium correlated with phosphate or other potential hosts or sulphur content. In most shales the sulphur content is related to the organic content; this is not true for the kolm. In fact, the sulphur content of the kolm is actually lower than the sulphur content of shale because the iron content of the kolm is lower and in both shale and kolm the iron appears to be completely sul­ phidized (i.e. iron is all as FeS2; Leventhal, 1983). Thus, many of the correlations of metals with organic carbon or sulphur that are found for many black shales (for example, Leventhal & Hosterman, 1982; Leventhal et al. , 1981) and the alum shale have not been found for the kolm. Thus the kolm has been, at least, a component that did not fit in with the shale geochemistry and, at most, something of an enigma. Also in this paper, the geochemistry of the uranium-rich upper unit from Ranstad and Narke in southern Sweden is contrasted with the vanadium­ rich Cambrian alum shale from Jamtland, in the Caledonian front, where the organic matter is thermally mature (Gee, 1980). Both of these shales are contrasted with the kolm.

REGIONAL GEOLOGY AND SAMPLES Sydbillingen area

In this area the shale is 22-24 m thick and is at or only a few tens of metres below the present land surface. The beds are flat-lying and undisturbed (Andersson et al. , 1983, 1985). Shale samples in this study were from Sydbillingen core 16/74 near Ranstad from four depths, two in the uranium-rich unit (of the P. scarabaeoides zone) and two below this in the Middle Member (A. pisiformiszone). The kolm samples were hand specimens collected in the Ranstad open pit mine. In this area there is a diabase sill that lies approximately 100 m above the Cambrian strata which has caused some local heating (Cobb & Kulp, 1961; Dahl et al. , 1988a, b). This is supported by Rock-eva! results (see Leventhal etal. , 1986, for explanation and references) that show that T ax is 427 -440°C and HI (hydrogen index) values m are between 100 and 200 mg/g org. carbon (Leventhal & Daws, new data).

Narke area

This area is somewhat different from Ranstad because the Middle Member is absent; the alum shale is approximately 12-19 m thick and is buried about 30 m below the present surface (Andersson et al . , 1983, 1985). Shale samples were from six in­ tervals of core from the Kvarntorp 11/53 borehole and the kolm was a hand specimen. At Narke the organic matter is thermally immature (Rock-eva! T x 422°C, HI is between 400 and 500 mg/g org. C) ma (Leventhal & Daws, new data).

Jamtland area

In this region of the Caledonian front the alum shale is deformed and has been subjected to low grade metamorphism (Andersson eta/. , 1985; Snail, 1988). Regional overthrusting has resulted in tectonic rep­ etition of the alum shale beds (total thicknesses up to around 150 m) Andersson et al. , 1985, fig. 19). Samples were from the southern Storsjon-Myrviken drilling project and were from cores Myrviken 78001 and 78004. No kolm has been recognized from this tectonically disturbed area. Rock-eva! results con­ firm the overmaturity of the organic matter ( Tmax is greater than 460°C and the HI is only 5-20 mg/g org. C) (Leventhal & Daws, new data). The maturity of the organic matter for the entire alum shale implies that there has also been a Caledonian ther­ mal effect due to loading of thrust sheets and prob­ ably also from heated fluids that may have been heated and expe!Jed during the thrusting.

ANALYTICAL METHODS

Most major, minor and trace elements were measured after mixed acid digestion of samples by inductively coupled plasma-atomic emission spec­ troscopy (Lichte et al. , 1987). However Si02 was measured by X-ray fluorescence (Taggart et al. , 1987), and uranium was measured by delayed neutron activation analysis (McKown & Millard, 1987).

Rare earth elements were measured by three methods: ICP analysis, instrumental neutron acti­ vation analysis (Baedecker & McKown, 1987) and radiochemical neutron activation analysis (Wandless, 1987). Organic geochemical methods are described in Leventhal et al. (1986).

Table 1. Detailed analytical results for kolm samples

Sample

Org C

s

Fe

AI

(% )

(% )

(% )

(% )

49·9 53-4 52·9

1 1·7 3·2 7·7

9 2·4 5·8

2·1 H 1·5

Ranstad H Ranstad I Narke

Ranstad H Ranstad I Narke

u (ppm)

5940 4960 4 1 00

Mo ( ppm)

v (ppm)

89 130 51

290 410 100

Si02

K

Ca

Mg

Ti

Na

p

(% )

(% )

(% )

(% )

(% )

(% )

(% )

12·2 20·1

1·3 2·1 0·62

0·36 0·22 0·23

0·21 0·3 0·25

-

0·1 5 0·21 0·09

0·04 0·06 0·05

0·08 0·12 0·05

Ni (ppm)

Zn (ppm)

Cd (ppm)

Pb (ppm)

98 92 48

50 375 7

<2 5 <2

250 220 240

Co (ppm)

Li ( ppm )

Sc (ppm)

Sr (ppm)

Nb ( ppm)

9 11 8

40 50 37

42 56 22

5 <4 5

30 29 24

Cu ( ppm) 54 69 48

As ( ppm)

Mn ( ppm)

Ba ( ppm )

50 180 160

200 280 150

360 515 120

Cr ( ppm)

O:l s-

'"' ?;"' ;:;I;)

24 31 19

� OQ

"' C) '"' ;:;"'

Table 2. Representative results for alum shale and kolm

Sample

Kolm Sydbillingen Narke Jii mtland SD0-1 Avg Shale

(% )

u ( ppm)

Mo ( ppm)

v (ppm)

Ni (ppm)

Zn ( ppm)

Cd ( ppm)

Pb (ppm)

Cu ( ppm)

As ( ppm)

Mn ( ppm)

Ba (ppm)

2 6-4 5·3 6·6 6·6 8

4500 410 220 240 53 4

90 260 200 340 160 3

290 695 460 2000 160 130

95 245 160 510 1 10 68

200 90 90 410 60 95

3 <2 <2 11 <2 <2

230 48 35 40 36 20

60 150 130 1 30 62 45

150 1 30 70 1 00 70 13

240 390 200 430 340 850

400 490 350 1 200 410 580

Org C

s

Fe

A1

(% )

(% )

(% )

50 12 16 13 10·2 1·6

7·7 8 6 4·3 5·5 0·24

5·8 7 6 3·9 6·6 4·7

SiOz p ( ppm ) (% ) 500 800 700 1100 600 700

;:s �;;·

�

15 46 52 50 59

N

s

208

J. Lev enth al

Table 3. Rare earth elements in kolm, shale and standards Eu

( ppm)

La

Ce

Nd

Sm

Kolm H Ranstad O pen p it mine

14 16

35 40

41 40

25

Kolm l Ranstad Open pit mine

24

61

45

6 7

Kolm Narke

7

22

42

Shale core 16/74 Sydbillingen 6·0 m

45 41

85 74

37 33

Myrviken 78004 Shale 7799083 Ja mtland

42 37

82 57

41 32

North Am. shale

32

73

SD0-1

36

64

6·3

Tb

Gd 44

67

8-4

8·1

<2 1 ·5

7· 1

<2 1·1

5·7

33

5·7

1·2

5·2

35

7·5

1 ·2

6·9

y

Method

860

RNAA ICP

37

690

!CP

67

1 200

!CP

53

reP

Yb

Dy

Lu

6·5

45 47

7·3

4 3-4

5·9

4 3·2

0·52

0·9

5·8

3· 1

0-48

27

H68

1-1

6·9

3·4

0·53

40

ICP

6·2

RNAA

0-45 43

ICP INAA

Methods: RNAA, radiochemical neutron activation analysis; ICP, ind uction cou pled p lasma; INAA, instrumental neutron activation analysis; H68, Haskin et al. 1968.

1000

NEW DATA

Table 1 gives the detailed chemical analyses for three kolm samples. Table 2 gives representative values for selected elements for the kolm samples for the uranium-rich portion of the alum shale from southern Sweden (Sydbillingen and Narke, 10 sam­ ples), for alum shale from the Jamtland Caledonides (Storsjon, 9 samples), for USGS SD0-1 black shale standard (data from Leventhal et al. 1978 and un­ published), and for 'average shale' (Turekian & Wedepohl, 1961). Rare earth element (REE) data for the kolm samples and for specific samples of shale from Ranstad (Narke is similar), for Jamtland, and for North American shale composite (NAS: Haskin eta!., 1968) are given in Table 3. Alum shale representative values ·are derived from unpublished USGS data and are quite similar to the results listed in Andersson et al. (1985). The complete set of geochemical data will be presented elsewhere (Leventhal et al., in preparation).

D ISCUSSION OF

RESULTS

Figure 3 shows selected element contents as ratios to average shale. At the left side are the major con­ stituents of shales (except silicon) and organic carbon and sulphur. It is clear from this diagram that the kolm is enriched in organic carbon and depleted

100 so

20 Ill Ill ....

10

....

""

:z: A. en ::E "" " en >

""

5

1.0

0.5

s

AI

Mo

Pb

v

Cu

P

0.1��--�--�_,,_L-,--L-r�-,,-�

org C

Fe

U

As

Zn

Ni

Ba

Mn

Fig. 3. Ratios of selected major and trace constituents of kohn, shale from Sydbillingen/Ranstad (Ran) and shale from Jamtland (Jamt); data from Table 2. The ratios of each value to average shale of Turekian & Wede pohl ( 1961) are taken. Sec text for discussion.

209

Black shale geoch emistry

in aluminium relative to the other sample groups. Examination of the detailed data (Leventhal, un­ publ. data) shows that aluminium and also other major elements (silicon, potassium, magnesium, titanium, sodium, calcium) are diluted by the organic carbon. The trace elements are shown on the right side of Fig. 3; the elements are ordered in decreasing enrichment for the kolm (relative to average shale). Relative to average shale, the samples of kolm and alum shale are enriched in most of these metals (Fig. 4) except manganese, phosphorus and barium. In particular, the alum shale and kolm samples are all greatly enriched in uranium and molybdenum and to lesser degrees in the other plotted elements relative to average shale. However, there are differences in the degrees of enrichment in the shale and kolm that need to be considered. The kolm is most enriched in uranium and lead. A simple calculation shows that approximately

1000 100 50

• .

•

20

Kolm Ran

Jamt

10 5

Ill

..1

IILUI

:Eel ccz Ill

300 ppm lead will result from decay of the uranium in kolm in 500 Ma. However, in their detailed isotope work on uranium and lead, Cobb & Kulp (1961) report that kolm has probably lost daughters in the uranium decay series (radium, radon and/or lead) by diffusion and/or leaching. It is important to note that the kolm is enriched only in uranium (and lead by uranium decay) and organic carbon relative to the adjacent alum shale and not in other elements, such as molybdenum, vanadium, copper, etc., that are often enriched in organic-rich units. The shale samples from Sydbillingen are enriched in uranium, molybdenum, arsenic, lead, vanadium, nickel and copper (in that order) relative to average shale. In contrast, alum shale samples from Jiimtland, on the Caledonian front, are enriched in vanadium, nickel, zinc, barium and phosphorus (in that order), but not uranium, relative to the samples from southern Sweden (Sydbillingen and Niirke). The element enrichments of the kolm and Jiimtland samples will be discussed. It is assumed that the element contents in the Sydbillingen samples (southern Sweden) represent normal syn­ genetic non-metamorphosed shale. The Jiimtland samples are especially enriched in vanadium, nickel, zinc and barium relative to the Sydbillingen samples. The tectonic events on the Caledonian front were probably accompanied by heated fluids during thrusting. This suite of enriched elements could be derived by the interaction of hot water and rocks in the Caledonian cover and basement, the latter including subordinate basic rocks. Table 4 gives the abundances for selected elements in basaltic and granitic rocks. Although manganese is not en­ riched in the Jiimtland samples relative to average

1.0

Table 4. Geochemical abundances (ppm) of selected samples from Turekian & Wede pohl ( 1961)

0.5

Element

Basalt

Granite

v Mn Ni Cu Zn As y Mo Ba Ce Yb Pb u

250 1600 130 87 105 2 21 1·5 330 48 2·1 6 1

65 100 10 20 50 1·7 37 1 ·2 630 86 3·7 17 3

La Ce

Nd Sm

Yb

Tb

Eu Gd

Dy

y Lu

u Mo

orgC

Fig. 4. Ratios of rare earth elements and yttrium in kohn , Sydbillingen/Ranstad (Ran) and Himtland (Jamt) samples (data from Table 2) to 'North American shale' (NAS, values from Haskin et al., 1968) . Also shown are ratios of molybdenum, uranium and yttrium to average shale (from Fig. 3) . See text for discussion .

210

1. Lev enth al

shales this could be because of the solubility of manganese under reducing conditions. The enrich­ ment in vanadium, which is greater than the other elements, could also have come from the circulation of the heated waters interacting with the overlying vanadium-rich Ordovician Dictyonema-bearing shales that have been reported locally in these Himtland shales (Gee, pers. comm. , 1989). Alternative explanations could involve differing source areas for vanadium and uranium or facies controls in enrichment and deposition. Along these lines, Gee (1981) and Sundblad & Gee (1984) suggest that the high vanadium contents of the black shales in the higher Caledonian thrust sheets are syngenetic and related to the Dictyonema-bearing shales, based on stratigraphic relationships.

Rare earth element abundances and distribution

Another set of interesting geochemical comparisons are shown in Table 3 for the REE. The kolm shows an enrichment in the REE that increases with the increasing atomic number. This is shown in Fig. 4, where the REE are ordered by increasing atomic number and their concentrations in the samples plotted relative to NAS values (Table 3). Also in­ cluded are yttrium, molybdenum and uranium that are enriched by even greater factors than the heaviest REE; but note that organic carbon is not nearly as enriched as uranium. The lightest REE actually appear to be depleted, but if the organic content of the kolm is taken into account (as a diluent) then the light (L) REE are very near normal NAS values. Rare earth elements have been used as geo­ chemical tracers for both low temperature (usually marine chemistry) and high temperature (magma and mineral formation) processes (Taylor & McLennan, 1985). Rare earth element enrichments and abundance patterns for the kolm are unusual: they require discussion in terms of possible element sources and transport and concentration mech­ anisms. Thus, it is necessary to consider REE abundances from possible source rocks (from high temperature processes) and transport and concen­ tration (low temperature processes) to explain the abundance and distribution of REE in the kolm. Certain sedimentary minerals are enriched in heavy (H) REE, for example apatite pellets and glauconite from offshore Peru (Piper et al. 1988; also see McArthur & Walsh, 1984, for review and discus­ sion). One study of the clay mineral fraction of

samples related to a Jurassic sandstone-hosted uranium ore in New Mexico, USA, reported REE enrichment (but not HREE enriched) near epi­ genetic uranium ores and suggested transport of REE by organic complexing and/or adsorption on colloidal species (Della Valle & Brookins, 1983). Some igneous minerals are also enriched in HREE: sphene, zircon, xenotime and clinopyroxene (Sawka & Chappell, 1988). These minerals are not present as hosts for REE in the kolm, and only sphene or clinopyroxene could have sourced the REE during weathering with subsequent preferential enrichment in the kolm. Another possible source of REE is the erosion of uranium deposits or weathering of source rocks that subsequently contribute to uranium deposits. This possibility can be considered for the Swedish uranium deposits in the Precambrian basement. The uranium-enriched granites of Sweden give ages of 1000-850 Ma (Wilson & Fallick, 1982): they often contain mineral assemblages that are enriched in REE, such as zircon and sphene (Smellie, 1982). In a study of the Lilljuthatten uranium deposit (420 Ma) the source rock was postulated to be the 1650 Ma Olden Granite (Stuckless & Troeng, 1984). Although the Olden Granite is in northern Sweden it could have also been a source rock during the Cambrian. The REE of this granite show a flat to increasing REE abundance for REE heavier than europium, with Yb : Sm > 1. The sites of the REE also need to be considered because the REE abundances in the kolm are dif­ ficult to explain. If the REE were sited in clay minerals, as they often are, their contents should be decreased, as are the aluminium and other clay­ forming elements, because of the relatively smaller amount of clay (due to dilution by the increased amount of organic matter) in the kolm. Although this is true for the light REE (such as lanthanum and cerium), the REE samarium through lutetium are enriched. The REE are probably not present in phosphate because phosphorus is depleted in the kolm (Fig. 3) relative to both average shale and to the alum shales. Part of this is due to dilution by organic matter, although many organic-rich samples are enriched in phosphorus. Detrital heavy minerals are also not a possible site for the REE because elements characteristic of heavy minerals (zircorium, neodymium, hafrium and thorium) are not en­ hanced (in fact, they are low: Zr 150, Nb 5, Hf <5, Th 4 ppm). Thus, if the REE and yttrium are not located in the clay, phosphate or heavy minerals,

Black shale geochemistry

they must be associated with another site, perhaps the organic matter. In an electron microprobe study, Parnell (1984) was able to identify that some of the cerium and uranium occurred in the phosphate minerals xeno­ time and monazite. However, this does not account for the occurrence of other REE and yttrium. A consideration of the material balance of the phos­ phorus and REE (Table 1) shows that whereas the REE could theoretically be accommodated in phos­ phate minerals (only cerium was identified by Parnell, 1984), the yttrium is too abundant to be sited wholly in phosphate. Further microprobe work may determine if there are mineral hosts for the other abundant REE (neodymium and ytterbium) and especially yttrium. Unusual REE abundances and distributions have been found to be associated with uranium deposits (McLennan & Taylor, 1979, 1980; Fryer & Taylor, 1987; Leventhal et al., 1987). These unusual REE patterns and enrichments are also commonly associ­ ated with granitic host rocks (Taylor & Fryer, 1984), where HREE were enri�hed in the fluid phase during transport by carbonate complexing (McLennan & Taylor, 1979) at hydrothermal temperatures. How­ ever these uranium deposits are mainly epigenetic unconformity vein-type deposits hosted in Pro­ terozoic rocks that were associated with heated fluids. This is in sharp contrast to the alum shale and kolm of syngenetic-sedimentary origin that have never been heated above 60-80°C at Narke and only slightly higher at Sydbillingen based on Rock­ eva! and burial history. Another way to consider the REE problem is to . examine seawater as a likely source. De Baar etal. (1985) reported that present day seawater is pro­ gressively enriched in HREE with depth (data to 3250 m) by preferential scavenging of the LREE by settling particles. A somewhat different explanation was given by Klinkhammer et al. (1983) who also reported HREE enrichment at depth in the Pacific Ocean, but attributed it to regeneration of REE at hydrothermal vents where iron and manganese oxides preferentiaUy scavenge the LREE. In the Cariaco Trench seawater, a sharp discontinuity in the REE abundance is seen at the oxic-anoxic boundary where two effects are noted (De Baar et al., 1988): the cerium and europium show anomalies that are related to their possible +4 and +2 oxidation states, respectively. Of more relevance to the present problem is the reduction of iron oxides that had scavenged the REE, with subsequent

211

formation of iron sulphides and release of adsorbed REE, in this case mainly LREE. Hoyle eta/. (1984) reported on the behaviour of REE during the mixing of river and seawater where the REE in the organic-rich Luce River are chiefly associated with iron -organic matter colloids rather than being in solution. In experiments using different salinities to simulate mixing they found that approxi­ mately 70-80% of the REE were removed from the water during the salinity increase from 0 to 10%o; most of this change occurred in the 0-5%o region. Hoyle et al. (1984) explained this as being due to flocculation of the organic matter colloids. They also found that the HREE formed stronger complexes with the organic colloids than the LREE and thus were preferentially removed (e.g. 95% Yb vs 60% La) in the estuary. By way of contrast; they observed essentially no removal of REE from an organic-poor river in conditions simulating the estuary from sal­ inities 0 to 25%o. The problem with the above interpretation is that the nearshore precipitation of REE is indirect, being due to their complexation to organic matter (or iron-organic matter) colloids. In Cambrian times there were no land plants and therefore no soil organic matter to form organic matter colloids in river water. Thus the well-documented regime of the present day river-estuary removal of REE by organic flocculation in the estuary did not occur during the time of deposition of the alum shale. In another study, Sholkovitz & Elderfield (1988) studied REE in Chesapeake Bay and the related Susquehanna River and estuary. They found that the dissolved REE were strongly enriched in HREE compared to the particulate (colloidal) fraction. The basin becomes anoxic at depth and the HREE are depleted in the oxygen-poor deep waters. They also found that the sediments were enriched in LREE over HREE (relative to average shale), whereas the sediment pore waters were enriched in HREE over LREE (but lower corrcentrations by a factor of 106 than in sediments). They believe that the Chesapeake Bay system is more complex than the stable redox conditions in the Cariaco Trench and involves an indirect coupling to the redox cycle of manganese. Another factor to consider is the REE complex­ ation by carbonate and oxalate anions at low temperature (Cantrell & Byrne, 1987). Their exper­ imental work shows that the HREE are more ef­ fectively complexed (Yb 75%) than the LREE (La 20%) by the carbonate anion (e.g. Yb(C03)z -) that

212

J.

Leventh al

would predominate in seawater. Thus, the LREE could be removed early (estuary and nearshore), leaving the HREE to be enriched in the deeper basin offshore (Goldstein & Jacobsen, 1988). It has been suggested (B. Dahlman, in Cobb & Kulp, 1961) that the kolm was deposited in the central axis of the basin; this can partly explain the HREE enrichment. However, Thickpenny (1984, 1987) and Andersson et a!. (1985) favour deposition of the alum shales in an exceedingly stable epicontinental sea below wave base but offer no explanation for the kolm. GENERAL SUMMARY

The Scandinavian alum shale is an unusual metal­ rich black shale with several additional anomalies: the stratigraphically controlled geochemically unique kolm and the tectonically disturbed vanadium-rich shale on the Caledonian front. The alum shale in southern Sweden in the Sydbillingen and Narke regions is flat-lying and undisturbed by significant burial or deformation. It is enriched in organic matter of marine origin that was deposited offshore at a depth of at least 100 m to allow stratification of the water column and formation of a lower stable euxinic layer. The euxinic bottom waters caused efficient trapping, by reduction, of metals and the preservation of organic matter and associated metals. A low sedimentation rate also enhanced metal contents because of a lack of clastic dilution. As a result, iron was completely sulphidized and all reducable metals were fixed in the sediment as sulphides or associated with organic matter. The suite of enriched metals (uranium, molybdenum, vanadium, arsenic, nickel, copper, lead) could have come from either a basic source (richer in vanadium, nickel and copper) or a granitic source (richer in uranium) or, more likely, a combination of these such as basalt for most metals and erosion of a uranium deposit for the uranium. The lead is mostly radiogenic and the elevated arsenic and molybdenum contents could have come from either basalts or granites, where these elements are equally abundant. The alum shales on the Caledonian front have undergone low grade metamorphism and during this process heated waters probably leached associated metasediments and/or underlying basement rocks and added vanadium, nickel, zinc, copper and barium (but not uranium) during the Caledonian Orogeny, about 100 my after the shale was de­ posited. The vanadium in the Cambrian shales could

have been added during water circulation by mobil­ ization of vanadium from the overlying Dictyonema shale. Other enriched metals (nickel, zinc and cop­ per) are a suite that is most likely derived from a basic (basaltic or gabbroic) source. This in­ terpretation is reasonable, based on the tectonic history and basement rocks of the area. The kolm enrichment in uranium, molybdenum, yttrium and HREE is less easy to explain. It requires some combination of the following: a unique source, selective transport and/or specific concentration mechanisms. The uranium and REE are not derived directly from heavy minerals because the elements zironium, hafrium, and thorium, which are usually associated with heavy minerals, are not enriched in the kolm. The stratigraphic control and richness in organic carbon of the kolm suggest a unique de­ positional setting, with low dilution by clastic mat­ erial, a rich source for uranium and HREE and extremely low sedimentation rates. The high organic content of the kolm may be due to the lack of clastic dilution, higher organic productivity or a greater thickness of the euxinic water column or some com­ bination of these. From sulphur and iron data, the iron is completely sulphidized (Leventhal, 1983), indicating that the environment of deposition must have been euxinic so that high preservation of organic matter was effected. However, the euxinic condition probably held for the adjacent shale as well, based on the sulphur intercept on the SIC plot (Leventhal, 1979, 1987; Thickpenny, 1987). Thus there is no problem in the preservation of organic matter and sulphides even at very low sedimentation rates. Because preservation was not unique to the kolm, low clastic dilution and/or high productivity of organic matter must have caused the kolm 's organic richness. Selective enrichment of HREE by carbonate com­ plexing noted by McLennan & Taylor (1980) at increased temperatures is also possible at low tem­ perature in seawater (Cantrell & Byrne, 1987). Thus, removal of LREE by selective adsorption on iron and manganese oxides in the estuary or near shore coupled with carbonate complexation of HREE may account for the enrichment in the kolm. The suggestion of 'organic complexing' by Della Valle & Brookins (1983) has not been tested. The epigenetic uranium deposits studied by Della Valle & Brookins are however enriched in organic matter (Leventhal, 1986). An argument against this suggestion is the observation that many organic-rich shales, including the alum shale, do notshow HREE

213

Black shale geochemistry

enrichments. It is possible that severe (or pref­ erential) weathering of a rock that is rich in this suite of elements (or heavy minerals), such as a granite, could have contributed them. A host rock similar to the Olden Granite is such a rock. Another possibility is the contribution of uranium and HREE from destruction (weathering and erosion) of an existing uranium deposit. This is illustrated by the geo­ chemistry of the Pine Creek Geosyncline uranium deposits that are enriched in HREE and also in yttrium (McLennan & Taylor, 1980) but is only partly analogous to the deposits related to the Swedish Olden Granite (Stuckless & Troeng, 1984) which show less depletion in HREE. Destruction (by uplift or faulting) and weathering of a local, existing vein-type uranium deposit at the time of sedimentation of the kolm could account for the uranium enrichment. This fortuitous timing of de­ struction of an unusual uranium- and HREE-bearing ore at the time of kolm formation may not seem a very probable event, but the alum shale is very unusual and an even more unusual event may be necessary to account for the unusual elements in the kolm. Selective concentration of HREE in the kolm as a result of removal of LREE by adsorption in the nearshore and/or selective complexation/transport of HREE further into the basin where the kolm was formed could account for the REE pattern. The high organic carbon content of the kolm requires that the basin be starved, that the kolm be formed at water depths of at least 100 m to maintain water column stratification below wave base and/or pos­ sibly that production of organic matter was greater. ACKNOWLEDGEMENTS

I especially thank D.G. Gee (formerly with Swedish Geological Survey, now at Institute of Geology, University of Lund, Sweden) who provided the carefuLly chosen representative samples and also provided important geological information, dis­ cussions of the results and helpful review of the paper. I thank J. Erdman, USGS, for providing several samples and my USGS colleagues F. Lichte, D. McKown, E. Daws and M. Stanton for detailed analytical chemical results. I thank B. Hofmann, J. Hatch, A. Thickpenny and B. Buchardt for very complete reviews of the manuscript. REFERENCES ANDERSSON ,

A . , DAHLMA N , B. & G EE , D. ( 1983) Kerogen

and uranium resources in the Cambrian Alum Shales of the Billingen-Falbygden and Narke areas. Sweden. Geol. Foren. Stockholm Forh. 104, 197-209. A N DERSSON, A . , DAHLMAN , B ., GEE, D . & S NALL, S . ( 1 985) The Scandinavian Alum Shales. Svcr. Gcol. Unders. Ser. (Ca) N R56, Uppsala, 50pp . ARMANDS, G. ( 1972) Geochemical studies of uranium, molybdenum and vanadium in a Swedish Alum Shale. Stockholm University Contrib. Geol. 27, 1-148 (in Swedish) . BAEDECKER, P . & M c KowN , D . ( 1 987) Instrumental neu­ tron activation analysis of geological sam p les. USGS Bull. 1770, H1-14. BucHARDT, B . , CLAUSEN, 1. & THOMSEN , E. (1986) Carbon isotope composition of lower Paleozoic kerogen. Organic Geochem. 10, 127- 1 34. CANTRELL, K . & BYRNE, R . ( 1987) Rare earth element complexation by carbonate and oxalate ions. Geo­ chim. cosmochim. Acta 51, 597-605 . CoBB, 1. & K ULP , 1. ( 1961) Isoto pic geochemistry of uranium and lead in the Swedish kolm and its associated shale. Geochim. cosmochim. Acta 24, 226-249. CROCK, 1. & LICHTE, F . ( 1982) Determination of rare earth elements in geological materials by ICP­ AES. Anal. Chem. 54, 1 329- 1333. DAHL, 1. HALLBERG, R . & K APLAN , l. ( 1988a) The effects of radioactive decay of uranium on elemental and isotopic ratios of alum shale kerogen. Appl. Geochem. 3, 583-589. DAHL, 1. HALLBERG, R. & KAPLAN , l. ( 1 988b) Effects of irradiation from uranium decay on extractable organic matter in the alum shales of Sweden. Organic Geochem. 12, 559-571 . DAHLMAN , B . & GEE, D . ( 1977) Oversikt over Billingen-Falbygdens geologi. In: Betakande av exampel Suaens Billingen-tredningen, Billingen 4, offentliega utredninger 1977, Vol. 47, pp . 2 19-255. Industri departmentet, Stockholm (in Swedish). DAVIDSON, C. ( 1961) The kolm de posits of Sweden. Mining Mag. 105, 201-207. D E BAAR, H . , B A CON , M. & B REWER, P. ( 1985) Rare earth elements in the Pacific and Atlantic Ocean. Geochim. cosmochim. Acta 49, 1943- 1959. D E BAAR, H . , GERMAN, C . , ELDERFIELD, H. & VAN GAA N S , P . ( 1988) Rare earth element distributions in anoxic waters of the Cariaco Trench. Geochim. cosmochim Acta 52, 1203-12 19. DELLA VALLE, R.S. & B ROO KINS , D . G. (1983) Geo­ chemical studies of the Grants mineral belt, New Mexico. In: The Signii f cance of Trace Elemems in Solving Petrogenic Problems, 793-818. pp . Theo phrastus, Athens. DwORATZEK, M. ( 1987) Sedimentology and Petrology of Carbonate Intercalations in the

Upper

Olenid Shale Facies of Southern Sweden.

Cambrian

Sver. Geol.

Unders. Ser. (C) N R 819, U ppsala, 73pp . B. ( 1 974) Distribution of Uranium in the

EDLING ,

Upper

Cambrian

Alum

Shale

fi"om

Ranstad,

Pubis Paleontol. Inst., Univ . Uppsala. S pec. Vol. 2, 1 1 8pp . (in Swedish) . FRYER, B . J . & T AYLOR, R . P . ( 1987) Rare-earth element distribution in uranini tes: im plications for ore gen­ esis. Chem. Geol. 63, 10 1-108. Billingen,

Vastergotland.

2 14

J. Leven tha l

D . G . ( 1980) Basement-cover relationshi ps in the central Scandinavian Caledonides. Ceo/. Foren. Stockholm Forhandl. 102 , 455-474. GEE, D . G. ( 1981) The D ictyonema-bearing phyllites at Nordaunevoll, eastern Trondelag, Norway . Norsk Geologisk Tidsskrift, 6 1 , 91-95. GoLDSTEIN S . & JACOBSEN S. ( 1988) Rare earth elements in river water. Earth Planet. Sci. Lett. 89 , 35-47. HASKI N , L . . HASKI N , M . . FREY, F. & WILDEMAN, T . ( 1968) Relative and absolute abundances terrestrial of the rare earth elements . In: Origin and Distri­ bution of the Elements (Ed. by L. Ahrens) pp . 8899 12. Pergamon Press, Oxford . HESSLA N D , I . & ARMANDS, G. ( 1978) Alunskiffer Under­ lagsmaterial geologi. Utredning Fran Stcuens Industri, (SIND 1978 : 3) Stockholm, pp . 1- 146, 1-94 and 1-38 (in Swedish). HOYLE, J., ELDERFIELD, H., GLEDHILL, A. & GREAVES, ( 1984) The behaviour of rare earth el­ ements during mixing of river and sea waters. Geochim. cosmochim. Acta 48 , 143- 149. KLINKHAMMER, G . , ELDERFIELD, H. & H U DSON , A. ( 1983) Rare earth elements in seawater near hydrothermal vents. Nature 305, 185- 188. LEVENTHAL, 1. ( 1979) The relationshi p between carbon and sulfur in recent and ancient marine and euxinic sedi­ ments . EOS Trans. Am. Geophys. Union 60, 282. LEVENTHAL, 1. ( 1981) Origin, distribution and controls of syngenetic metals in black shales and resource imp li­ cations. Ceo!. Soc. Am. Abstracts 13, 497. LEVENTHAL, J. ( 1983) Organic carbon, sulfur and iron relationshi ps in ancient shales as indicators of de position. EOS Trans. A m. Geophys. Union 64, 739. LEVENTHAL, 1. ·(1 986) Roles of organic matter in ore deposits. In: Organics and Ore Deposits (Ed. by W . Dean), pp . 7-20. Denver Region Ex ploration Ge­ ologists Symposium, Wheat Ridge, Colorado. LEVENTHAL, J. ( 1 987) Carbon and sulfur relationshi ps in Devonian Shales from the Appalachian basin as an indicator of environment of de position. Am. I. Sci. 287, 33-49. LEVENTHAL, 1. ( 1 988) Comparative geochemistry of metals and trace elements from Cambrian Alum Shale of Sweden. In: International Symposium on Sedimentology Related to Mineral Deposits, pp . 1 22-123 . Beijing. LEVENTHAL, J . , CROCK, J . & MALCOLM , M. ( 1981) Geo­ chemistry of trace elements and uranium in D evonian Shales of the Appalachian Basin. US Ceo!. Survey Open File Report, 81-778, 76 pp . LEVENTHAL, J . , CROCK, J . , MOUNTJOY, W. & T HOM AS , J . ( 1978) Results o f analysis o f USGS black shale standard SD0- 1 : US Ceo!. Survey Open File Report, 78-447, l l pp . LEVENTHAL, J . , DAws, T. & FRYE, J . (1 986) Organic geochemical analysis of organic matter associated with uranium . Appl. Geochem. 1 , 24 1 - 247 . LEVENTHAL, J . , GRAU C H , R . , THRELKELD, C . , LICHTE, F . & HARPER, C. ( 1 987) Unusual organic matter associated with uranium from Cluff Lake, Canada. Econ. Ceo!. 82, 1 169- 1176. LEVENTHAL, J. & HoSTERMAN, J. ( 1 982) Chemical and mineralogical analysis of Devonian black shale samples GEE.

from Kentucky, Ohio, Virginia and Tennessee. Chem. Ceo/. 37, 239-264. LEWAN , M. & B ucHARDT, B. ( 1 989) Irradiation of organic matter by uranium decay in the alum shale, Sweden. Geochim. cosmochim. Acta. 53, 1 307- 1322. LICHTE, F . , GoLIGHTLY , D. & LAMOTHE, P. ( 1 987) Induc­ tively coupled plasma-atomic emission sp ectrosco py . In: Methods for Geochemical Analysis (Ed . b y P . Baedecker) . US Geol. S urvey Bull . 1770, B 1-B10. McARTHUR, J . & WALSH, J . ( 1984) Rare-earth geo­ chemistry of phosp horites. Chem. Ceo!., 47, 19 1-220. McKow N , D . & MILLARD, H. ( 1987) Determination of uranium by delayed neutron counting. In : Methods for Geochemical Analysis (Ed. by P . Baedecker). US Geo l . Survey B ul l . 1770, 1 1- 12 . McLEN N AN , S . & TAYLOR, S . ( 1979) Rare earth element mobility associated with uranium mineralization. Nature 282, 247-250. McLENNAN, S . M . & TAYLOR, S . R . (1980) Rare earth elements in sedimentary rocks, granites and uranium deposits of the Pine Creek geosyncline. In: Proceedings of International Uranium Symposium on the Pine Creek

(Ed . by J . Ferguson & A. Goleby ) , pp . 175-190. International Atomic Energy Agency , Vienna. PARNELL, J. ( 1984) The distribution of uranium in kolm: evidence from backscattered elecron imagery . Ceo!. Foren. Stockholm Forhandl. 106, 231-234. PIPER, D . , BAEDECKER, P . , CROCK, J . , B U R N ETT, W . & LOEBNER, B . ( 1 988) Rare earth elements i n the p hos p hatic-enriched sediment of the Peru shelf. Marine Ceo!. 80 , 269-285. SAWKA, W . & CHAPPELL, B . ( 1 988) Fractionation of U, T h and R E E i n a vertically zoned granodiorite , Sierra Nevada batholit h , California , USA. Geochim. cosmo­ chim. Acta 52, 1 13 1 - 1 143. SHOLKOVITZ, E . & ELDERFIELD, H. ( 1 988) Cycling of dis­ solved rare earth elements in Chesapeake Bay . Global Biogeochem. Cycles 2, 157-176. SMELLIE, J. ( 1 982) Radioactive mineral p hases from Pre­ cambrian Granites within the Olden window, Jamtland, N. Sweden. OCED Nuclear Energy Agency . Proc. Symp. Uranium Exploration Methods, Paris, 1982, pp . 415-428. SNALL, S. ( 1988) Mineralogy and maturity of t he alum shales of south-central Himt land. Sweden. S ver. Ceo/. Unders. (C) 818, Upp sala, 46 pp . STUCKLESS, J . & TROEN G , B . ( 1984) Uranium mineralization in response to regional metamorphism at Lilljuthatten, Sweden. Econ. Ceo!. 79, 509-528. SuN DBLAD, K. & GEE, D . ( 1 984) Occurrence of a uraniferous-vanadiferous grap hiteic p hyllite in the Koli Nappes of the Stekenjokk area, central Swedish Caledonides. Ceo!. Foren. Stockholm Forhandl. 106, 269-274. TAGGART, J . , LINDSAY, J . , ScoTT, B . , VIVIT, D . , BARTEL, A. & STEWART, K . ( 1987) Analysis of geologic materials by wavelength dis persive X-ray fluorescence spectrometry. In: Methods for Geochemical A nalysis (Ed. by P . Baedecker) . U S Geol. S urvey Bull. 1770, E 1 -:- E19. TAYLOR, R. & FRYER, B . ( 1984) Rare earth element litho­ geochemistry of granitoid mineral de posits. Can. Inst. Min. Met. Bull. 76, 74-84. Geosyncline

Black shale geochem istry

S. & M cL ENNAN , S. ( 1 985) The Continental Crust: Blackwell Scientific, Oxford, 312pp . THtCKPENNY, A. (1984) The sedimentology of the Swedish Alum Shales. I n : Fine Grained Sediments: Deep Water Processes and Environments (Ed. by D . Stow & D . Pi per) , Spec. Pub! . , pp . 5 1 1 -526. Geol. Soc. 1 5 . Black­ well Scientific Publications, Oxford . THtCKPE N N Y , A. ( 1987) Palaeo-oceanography and depo­ sitional environment of the Scandinavian alum shales: sedimentological and geochemical evidence. I n : Marine Clastic Sedimentology (Ed. by J . K . Leggett & G . TAYLOR,

its Composition and Evolution.

215

Zuffa pp ) , pp . 156- 17 1 . Graham & Trotman, London. K. & WEDEPOHL, K. ( 1961) Distribution of elements in the earth's crust. Ceo/. Soc. Am. Bull. 72, 175- 192. WAND LESS, G. ( 1987) Radiochemical neutron activation analysis of geological materials. US Ceo/. Surv. Bull. 1770, J l - 8. WtLSON , M . & FALLlCK, A . ( 1 982) The relationshi p between uranium-enriched granites and hydrothermal mineraliz­ ation in northern Sweden. OCED Nuclear Energy Agency, Proc. Symp. Uranium Exploration Methods, Paris, 1982, pp . 293-306.

TuREKlAN ,

Spec. Pubis int. Ass. Sediment. (1990) 11, 217-224

Uranium enrichment in the Permian organic-rich Walchia shale, Intra-Sudetic Depression, southwestern Poland S.

WOLKOWICZ

Geological Survey of Poland, Rakowiecka 4, 00-975 Warsaw, Poland

ABSTRACT

The Lower Permian section of the Intra-Sudetic depression includes black shales of lacustrine origin. Of these shales, the Walchia shale ( Ratno Dolne Member) has the widest distribution. The rocks are further subdivided into several complexes according to lithology. They represent sedimentary environ­ ments varying from oxidized and unoxidized parts of the pelagic zone to the littoral and coastal plain. Horizons with uranium mineralization occur within beds of organic-rich pelagic sediment. Facies analysis and studies of organic matter suggest that the mineralization was syndiagenetic and occurred in rocks below wave base. The presence of migrated bitumens on fracture surfaces and a correlation between uranium and organic carbon contents suggest the possibility of reconcentration of uranium within migrated bitumens.

INTRODUCTION The Intra-Sudetic Depression is a substantial region

of the Sudety Mountains (northeast part of the Bohemian Massif; Fig.

1).

The development of the

Depression began in the Early Carboniferous and

lain by

of

poorly sorted

the Radkow

(Dziedzic,

1961).

Anomalous

conglomeratic

Formation,

uranium

dated

as

sandstones

Saxonian

concentrations,

some

of

had a multiphase history including infill with Car­

economic value, are known from several lithostrati­

(Fig.

Depression (Fig.

boniferous, Permian, Triassic and Cretaceous rocks

1).

The sediments of early Carboniferous to

early Triassic are of the molasse type. The Carbon­

iferous sequence is mainly represented by continen­

graphic units of the Permian in the Intra-Sudetic

tal sediments with mudstone units including coal may be subdivided into

cyclothems (Fig.

2).

four

WALCHIA SHALE

mega­

Each of these cyclothems begins

This paper describes those

SEDIMENTOLOGY OF THE

seams. Lower Permian rocks, also continental in

character,

2).

found in the Walchia shale.

with fluvial conglomerates and sandstones, usually

Rocks of the Walchia shale form several complexes

mudstones.

here defined by the first appearance of dark-coloured

oxidized, and ends with mainly unoxidized lacustrine Fairly

thick

complexes

of

volcanic

rocks are known from the contact of the third and

fourth megacyclothems in the Slupiec Formation (Kozlowski,

1963).

trachybasalts,

The volcanogenic rocks include

latites,

rhyolites,

rhyolite tuffs (Nowakowski,

Kubicz et al.,

1986).

1968;

andesites

Gorecka,

and

1982;

Tectonic movements at the end

varying in lithology. The base of the Walchia shale is silty-sandy or, locally, clay rocks in the section.

The subtuffite complex,

45

m thick, is built of mud­

stones and sandstones with horizontal and cross­ bedding, dispersed pyrite and (in the upper part) carbonized plant remains (Fig.

3).

The basal part

also includes two carbonate beds each

2

m thick.

of the Autunian resulted in a break in sedimentation

The beds are of similar magnitude over distances of

the Walchia shale (Ratno Dolne Member) are over-

characterized by intercalations of brown-red ripple-

and partial restructuring of the depression. Rocks of

Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun 2 17 and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

about

12

km. The middle part of the complex is

S. Wolkowicz

2 18

Fig. 1. Location of the studied area

and geological map of the southeastern part of the Intra­ Sudetic Depression. (After Nemec et a!., 1982. ) (1-9) Sedimentary and volcanic rocks: (1) Upper Cretaceous; (2-4) Lower Permian: (2) Radkow Formation, (3) Slupiec Formation, (4) Krajanow Formation; (5-7) Upper Carboniferous: (5) Ludwikowice Formation, (6) Zacler Formation, (7) Walbrzych Formation; (8) Lower Carboniferous, Szczawno Formation; (9) Lower Permian volcanics (undifferentiated). (10-13) Surrounding units: (10) Gory Bardzkie, (11) Klodzko metamorphics, (12) gabbros and diabases of Klodzko area; ( 13) Sowie Gory Block; (14) state boundary, (15) boreholes.

�. "'· ...... ....

5 km

0

�----'

./ .,J'r·f":,..,...

C]1 r=::a2 �3 �4 OJ] �6 10 �11 �12 OliliiiJ �8 �9 EEEl]13 l.r-�'114 5

.

7

15

.

.

Stratigraphy

Lithostro.ti gro.phy

Relative intensity of uranium mineralization

Lithology

low c

.� c 0 X d VJ

.

Radkciw

Formation

0 0

3

0 _J

0

0

0

0

S.i:"upiec

0

0

0

( Walchia Shale)

Zagorzyn

K

u. Anthraces ia Shale

---:-

Krajanow Member

• 0 .

0

0

0 0 0 0 0

.

. .

� /

;....__•

.

,-..._,

'"'-'

-

.

0

'

0

0

0

.

0

0 0 0

. -------

�

�

�,..__,

Member

. .

0

�

.

L.Anthracosia Shale -- - ---

---

c

---=---=--

�--:--:-

�

.

0

---=

-

Ludwikowice Upper Carboniferous

0

. .

high

0

.

......:...

�

.

Formation

0

0

0

0

Volcanic Complex

. 0 . "

. 0

�wierki

0

0

-

Member

------

0

0

------ -- --

·-

c :::J +:::J
0

.

0

-

Formation

c d

0

0

'

-

�

0:: w

0

0

'

0

�::� �� --

Member

:L 0:: w o_

0

.

Ratno Dolne z
0

.

0 0 0

0

.

0

0

. .

.

0

.

0

�

Fig. 2. Permian stratigraphy of

southeastern Intra-Sudetic Depression, indicating levels of anomalous uranium concentration.

VII

VIII

IX

� �

i5. E 0 u

50 VII

VIII

u <9

pu

100

�

"

i5. E " u

150

I I I

� "

i5. E 0 u

1?/� �. §. 1111?,

I I

I I

1

111112 .-- 3 ,..,..,...,.... 4

v11

vu

2

"��� � 61 5

� � ��J C>
Fig. 3. Borehole log Wambierzyce IG-12 (W-12), and

�

i5. E

8

section of complex III in the Wambierzyce lG-15 (W-15) borehole: (l) the studied lithologic complex; (II) thickness (depth) in metres; (III) lithologic column: (1) mudstone, (2) silty mudstone, (3) muddy siltstone, (4) siltstone, (5) sandy siltstone, (6) silty sandstone, (7) sandstone, (8) conglomerate; (IV) colour of rock: (1) grey and black, (2) variegated, (3) brown and red; (V) erosional boundaries; (VI) sedimentary structures: (1) horizontal bedding, (2) cross-bedding, (3) ripple marks, ( 4) flaser bedding, (5) wavy bedding, (6) erosional channels, (7) mud cracks and mud flakes, (8) rain prints; (VII) bioturbation: ( l) single, (2) few, (3) numerous, (4) very numerous, (5) interior mould of branches, (6) coprolites, (7) floral remains, (8) fish remains; (VIII) interpretation of sedimentary palaeoenvironments: pu, pelagic anoxic, po, pelagic oxic, L, littoral, cp, coastal plain, af, alluvial fan; (IX) uranium­ rich horizons.

S. Wo/kowicz

220

laminated sandy rocks and moulds of branches.

environment and partly in the coastal plain zone.

predominantly oxidized pelagic zone of the lacustrine

horizontal lamination was deposited in both the

Rocks of the subtuffite complex originated in the basin.

The

exception

is

the

brown-red

sandy

intercalations, which were deposited in the littoral

zone of the basin.

The subtuffite complex is overlain by a horizon of

The calcareous grey-black clay-silty series with oxidized and unoxidized pelagic zone. Towards the southeast, i.e. in the direction in which the basin was

becoming shallower (borehole W - 15), sedimentation

was in the littoral zone or even in an alluvial fan

rhyolitic tuffs 25-40 m thick. Deposition of the tuffs

environment.

levelling of the basin floor, and was followed by

above complex III. This series, assigned to complex

throughout the area. The rocks assigned to the

calations (Fig.

resulted in shallowing of the sedimentary basin and

sedimentation

of

brown-red

supratuffite complex are about

silty-sandy

30

erally display cross-bedding (Fig.

rocks

m thick and gen­

3)

and thorough

bioturbation. Mud cracks, mud flakes and rain prints

are known from the middle part and erosional

boundaries are fairly common. The rocks displaying

mud cracks, mud flakes and rain prints originated in

a coastal plain zone, and the remaining rocks were deposited in the littoral zone of the lacustrine basin. Rocks of complex I are overlain by a

40-60

Black clay-silty rocks reappear in the section

IV, is characterized by limited sandy mudstone inter­

complex IV is

80-100

m thick and very similar to

both the oxidized and unoxidized parts of the pelagic

zone of the basin.

URANIUM- POLYMETALLIC MINERALIZATION

in pyrite and organic matter, include asphaltite lenses

The Walchia

the upper part of the complex,

lead, zinc, copper and vanadium. The anomalous

and smell bituminous. Bituminous limestones from known as the

Ruprechtice horizon in the Czech part of the de­

pression (Tasler eta/.,

1979),

are characterized by

a fine lamination of algal origin. The rocks were

·

mm thick

the complex II described above. It was deposited in

m

are fairly rich

1-10

and show marked epigenetic deformation. The whole

with intercalations of bituminous limestones. The

3),

Its basal part displays inter­

carbonate. Individual laminae are

series of laminated or structureless black mudstones latter, assigned to complex II (Fig.

3).

calations of alternating laminae of mudstone and

shale includes

numerous

horizons

enriched in uranium and other metals, especially horizons may be assigned to four groups. The first group is related to the subtuffite complex and com­

prises three horizons (Fig.

3).

The uranium mineral­

formed in the anoxic-pelagic zone of the basin.

ization is found in mudstones, and sometimes in

frequent in the upper part of complex II. These

asphaltite lenses. The weighted mean contents of

limestone, mark the transition to complex III, of

to

alternating beds of red sandy-silty rocks, and grey­

other metals are also high at this level (zinc up to

Erosional boundaries become progressively more

boundaries, and intercalations of calcareous sandy very variable lithology. Complex III consists of black clay-silty or rarely sandy beds which are

usually calcareous and contain pyrite and organic

matter in amounts up to

10%.

In the southeastern

part of the studied area (borehole

W-15;

Fig.

3)

all

carbonates with pyrite, dispersed organic matter and uranium for layers

100

0·90-1· 50

m thick range from

60

ppm. The mineralization is richest in the

uppermost horizon of this group. The contents of

2700 ppm, 1 10 ppm).

lead up to

400

ppm, molybdenum up to

The second group of anomalies is related to com­

plex II and comprises two to four horizons (Fig.

3).

the rocks of complex III are brown-red in colour,

The mineralization is connected here with clay

In that area

their weighted mean contents of uranium are from

because some rocks which were originally grey­ black were oxidized (Wolkowicz,

1988).

the complex is composed of several sandstone­

mudstone cycles with subordinate intercalations of

mudstones and conglomerates and the total thickness

is estimated at about

120 m.

The changes in lithology

reflect rapid changes in environment during sedi­ mentation. is

The

characterized

brown-red

by

silty-sandy

bioturbation

and

series

numerous

erosional boundaries. It was deposited in the littoral

shales. The horizons are

40

to

80

0·20-1·50

m thick and

ppm.

The third group of anomalies corresponds to

complex III (Fig.

3),

in which the mineralization is

associated with laminated calcareous shales with

laminae and streaks of organic matter, asphaltite

lenses and dispersed pyrite and galena. The horizons vary from

0·75

to

1·20

m in thickness and the mean

contents of uranium in the most strongly mineralized

Uranium-rich shale

horizon are from 120 to 200 ppm. The uranium mineralization is accompanied by increased contents of zinc, lead, molybdenum, vanadium and arsenic. The fourth group of anomalies is weakly devel­ oped, and related to complex IV.

GEOCHEMISTRY OF ORGANIC

MATTER IN THE WALCHIA SHALE

In the present study attention was focused on the organic matter in the Walchia shale, because of the possible role of organic matter in the concentration of metals in black shales (see Szalay, 1964; Breger, 1974; Nakashima et al., 1984). The Walchia shale was deposited in a sedimentary basin about 50 km wide, and the zone of mixing due to surface waves extended down to depths of 8-20 m, depending on wind force (Sly, 1978). Sedi­ ments deposited at greater depths are richer in organic matter than those formed in the zone of mlXlllg. The content of organic matter varies from 0·2 to over 10% in the unoxidized Walchia shale rocks characterized by uranium mineralization. The cor­ relation coefficient for the contents of organic carbon and uranium (72 samples) is high, at +0·60 (data in Fig. 4). The uranium mineralization was found to be limited almost exclusively to the finest grained rocks: mudstones, silty mudstones and carbonates of the shaly type in the classification of Lundegard & U

221

Samuels ( 1980). Coarser grain sizes, resulting from higher energy sedimentary environments, appear unfavourable for the concentration of uranium m this case. Studies on organic matter were also aimed at a more precise reconstruction of the depositional environment of the uranium-bearing rocks (Table 1). There is a high variability in the content of bitumens (from 1·2 to 13·5%) in the total organic carbon, and the highest content of bitumens is found in rocks of complex II (Table 1). Analyses of iso­ prenoids show a low pristane: phytane ratio (Pr: Ph 0·78 to 2· 1), which indicates a strongly reducing sedimentary environment (Didyk eta/., 1978; Tissot & Welte, 1978). Low CPI (carbon preference index) values indicate relatively mature organic matter and may also indicate a predominantly aquatic origin (Hunt, 1979). The n-alkane distribution for the majority of samples peaks at Cl8 (Fig. 5). The exception is a sample from a uranium-bearing layer (with uranium content of 272 ppm), characterized by two n-alkane maxima at C18 and C25 and also the lowest CPI value (0·61) and a low ratio of saturated to aromatic hydrocarbons (Table 1). However, some differences in the geochemical characteristics of this sample may be due to the effects of radiation from uranium on the organic matter, as observed widely elsewhere (e.g. Landais & Connan, 1980). The content of hydrocarbons in bitumens is also important for estimating the potential for remobil=

[ppm]

600

500

400

300

Fig. 4. Correlation between

uranium (U) and organic matter (Corg) .

6

8

10

12

Corgo/o

222

S.

Wolkowicz

Table 1. Characteristics of organic matter in the Walchia shale

Depth (m)

Lithological complex

U content (ppm)

Total Bitumen organic extract (BE) carbon (TO C) (%)

BE/TOC

(%)

Pristane: Phytane

CPI

(%)

32·5 56·5 114·0 124·5 139·2 192·7 194·2 199·0 217·0 297·0

IV IV III III III II II II II subtuff.

9·0 23·7 3·2 272-0 12-0 4·2 12·0 4·2 5·5 7·0

% 40

u�4.2

[ppm]

u� 270

[ppm]

0·6 0·6 0·6 3·9 1·8 2·7 1·6 0-4 0·4 0·2

30

20

10

%

40

0·008 0·014 0·007 0·064 0·078 0·365 0·047 0·054 0·033 0·016

Hydrocarbon content in bitumen

(%)

1·3 2·3 1·2 1·6 4·3 13·5 2·9 13·5 8·2 8·0

1·2

1·2 0·6

1·9 0·8 2·1 1·8

0·85 0·99 0·96 0·92 0·82

18 52 34 35 43 55 50 69 55 43

Intra-Sudetic Depression are related to a deep lacus­ trine sedimentary environment. This environment saw the accumulation of planktonic organic matter of mainly aquatic origin. Concentrations of uranium in the Walchia shale are closely related to the con­ tent of organic matter, and are inferred to be syndia­ genetic. High contents of hydrocarbons within bitumens and the presence of migrated bitumens on fracture surfaces suggest the possibility of recon­ centration of uranium within the migrated bitumens.

30

REFERENCES

20

10

LA. (1974) The role of organic matter in the accumulation of uranium: the organic geochemistry of the coal-uranium association. Proc. Symp. IAEA Athens, pp. 99-124. DIDYK, B.M., SIMONEIT, B.R.T., BRASSELL, S.C. & EGLINTON, G. (1978) Organic geochemical indicators of paleoenvironmental conditions of sedimentation. Nature 272, 216-222. DziEDZIC, K. (1961) Lower Permian of the Intra-Sudetic Basin. Studia Geol. Pol. 6, 1-121. GORECKA, A. (1982) Some remarks on Permian volcanic rocks in the vicinities of Tlumaczow (eastern part of the Central Sudetic Depression). Kwart. Geol. 26, 599-607. HUNT, J.M. (1979) Petroleum Geochemistry and Geology. WH Freeman, San Francisco, 617pp. KozLOWSKI, S. (1963) The geology of Permian volcanites in the Central part of the Inner Sudetic Basin (Lower Silesia). Pr. Geol. Kom. Nauk Geol. PAN 14, 1-84. KuBICZ, A., MoLENDA, R. & ZuPNIK, K. (1986) Notes on Permian pyroclastics from Nowa Ruda Region. Kwart. AGH Geologia 12,77-108. LANDAIS, P. & CONNAN, J. (1980) Relation uranium­ matiere organique dans deux bassins permiens· francais: Lodeve (Herault) et Cerilly-Bourbon-l'Archambault (Allier). Bull. SNEA 4, 709-757. LUNDEGARD, P.D. & SAMUELS, N.D. (1980) Field classifiBREGER,

Fig. 5. Distribution of n-alkanes in samples with uranium

content of 4.2 and 270 ppm.

ization of the uranium. The hydrocarbon contents in the bitumen extracts are high, usually in the range 34-69% (Table 1). This, together with a strong correlation of uranium and organic carbon and the presence of migrated bitumen on the surfaces of fractures suggest the possibility of migration of uranium. Such phenomena have been reported from Lodeve (Massif Central, France) by Landais & Connan ( 1980), and from Scotland by Parnell ( 1985). CONCLUSIONS

Mineralized Lower Permian black shales from the

Uranium-rich shale

cation of fine-grained sedimentary rocks. J. Sedim. Petrol. 50, 781-786. NAKASHIMA, S., DISNAR, J.R., PERRUCHOT, A. & TRICHET, 1. (1984) Experimental study of mechanism of fixation and reduction of uranium by sedimentary organic matter under diagenetic or hydrothermal conditions. Geochim. cosmochim. Acta 48, 2321-2330. NEMEC, W., POREBSKI, S.J . & TEISSEYRE, A.K. (1982) Explanatory notes to the lithotectonic Molasse Profile of the Intra-Sudetic Basin, Polish Part (Sudety Mts, Carboniferous- Permian). In: Tectonic Regime of Molasse Epochs. Report on Activities of Working Group 3.3 (Ed. by H. Lutzner & G. Schwab), pp. 267-278. Potsdam. NowAKOWSKI, A. (1968) Permian volcanites of the Suche Mts in the Intrasudetic Basin. Ceo!. Sudetica 4, 289-400.

PARNELL, J.

223

(1985) Uranium/rare earth-enriched hydro­ carbons in Devonian sandstones, northern Scotland. N. lb. Miner. Mh. H. 3, 132-144. SLY, P.G. (1978) Sedimentary processes in lakes. In: Lakes, Chemistry, Geology, Physics (Ed. by A. Lerman), pp. 65-90. Springer, New York. SzALAY, A. (1964) Cation exchange properties of humic acids and their importance in the geochemical enrich­ ment of UO/ + and other cations. Geochim. cosmochim. Acta 28, 1605-1614. TISSOT, B. & WE LTE, D.H. (1978) Petroleum Formation and Occurrence. Springer, New York. WOLKOWICZ, S. (1988) On the sedimentation of the Lower Permian Walchia Shales from Ratno Dolne (Intra­ Sudetic Depression). Przegl. Geol. 36, 214-218.

Index

References to figures appear in italic type References to tables appear in bold type.

Abu Hamata

metals in

165, 166, 167, 169 161, 162

cobalt

Abu Thora Formation akaganeite

Algoma type iron formations alum shale, metals in

see

33,37

metals and

rare earth elements, Sweden aluminium mineralization alunite

168

copper

Datangpo Formation

193-9

fossils from

119-120, 121, 122

sedimentology

122

hydrocarbons, metals in

187-91

60, 61,

see

39, 42-3,

109

Dongchuan-Yimen copper deposits

Groote Eylandt

stratigraphy geochemistry

169

barium precipitation

Bezymiannaya Seamount

isotope

177-8, 180

organic

175,177

hydrolithic sediments 173, 176

analytical data Eagle Island Formation

103, 104,106

122,123,

126,129-30 Egypt

see

Urn Bogma region, Sinai

188-91, 221-2

iron carbonate layers,

Borneo brochantite : buserite

Fengshan copper deposits ferrihydrite

60-2 114,143-4,168

iron oxyhydroxides

57-8

in Atlantis-II Deep

186-7

in Thetis Deep iron vernadite

Cahuasas Formation carbonate deposition

58,59, 64, 69, 70

Groote Eylandt manganese norm

19, 20

methodology

26-7

Datangpo Formation;

151, 152-3, 154-5

Datangpo manganese deposits

4, 5-7, 8-9, 10-13

Guacamaya Formation

18, 19

Mineoka Umber Newfoundland

deposits; iron and manganese

Tetzintla mine

organic matter and metalliferous deposits, China Chipoco facies chrysocolla

21,22,23,24, 25

Clarion-Clipperton Fracture Borneo

140, 141

Hatcho Formation

75

Heguri Formation

75

hematite

105

howlite

177-8,180

84-5 134-5,136,137 23

120 Japan

see

Mineoka Umber

Jarandol Basin

58,59, 65, 69, 70

Hequing manganese deposit

163,166,169-70

coal

Hare Bay Allochthon

45-6

Dongchuan deposits

Dongchuan-Yimen copper deposits, China; Lijiang basin;

68-71

103, 105,106

isotope geochemistry

3-4,14

96, 99

58-9,63-5,

71

ironstone

Cape Verde Plate

139, 140, 141

iron mineralization

58,59, 60, 65

62, 105 goethite

see

178, 179

fossils, metal enrichments in

169

outcrops

141

142-4

iron-manganese oxyhydroxides

151 see

iron carbonate layers, Borneo formation

640

113-16 see

manganese and iron facies in

151

Bezymiannaya Seamount

110-12

iron and manganese facies

see

manganese-iron crusts,

bitumen, metals in

109-10

microbial fossils

179, 180

trace element

123-5

Bela Stena magnesite deposit

175

geology

microbiota and minerals

fluid inclusion 124-5,134, 135,136,137

122, 126,128,

iron and manganese deposits, China

44-9

manganese norm

birnessite

l rishtown Formation

130, 134-5

manganese deposits

62-3,65-8 Australia

190

39-40, 41, 42-

3

59-62, 63-5

manganese oxyhydroxides

Irish Sea, uranium mineralization

39-40

110-12

geological setting

58, 63,71

iron oxyhydroxides

China

137 geology

103-4,105,106

169

Atlantis-Il Deep

Borneo

125-8

134-5, 136,

69,103

atacamite

borates

sulphur-carbon ratios

159,

121,122,123,

123-5,

128-9, 130-2, 133-4 sulphur isotopes

126-9,131-2, 133-7

asphalt beds, China

barite

Dongchuan-

copper mineralization, Sinai Cow Head Group

187-8

asbolane-buserite

azurite

see

Yimen copper deposits

99

asbolanes

128-9, 130-2, 133-4, 137

161,168-70

America, South

122-5

metal distribution

151

copper deposits

166,168

antimony

geochemistry

colemanite

63-4

Humber Arm Allochthon

185-6

99

149, 151, 152-3

55

151

Huayacocotla Formation Huizachal Formation

Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

225

19

18,19-20

Kalimantan Province Kamogawa Formation

139-44 75-6, 87

Index

226 Kangdian axis kaolinite

174, 175

Thetis Deep

168

manganite

Karadzhal deposits

Northern Head Group

69,70-1

63, 67-8

metal enrichments in organic

33

materials

183-5

organic material as an ore lacustrine basins, metals in lacustrine oil shales

Lake Superior type iron formations lead

matter see organic matter and

128-9, 130-2, 133-4,137

lepidocrocite

58,59,60, 65, 69,70

Liangiiehe Formation Lijiang Basin

Sweden

52-3

manganese mineralization Lough Neagh Basin

206, 207, 208

53-6 161, 162

characteristics

194-8

significance

198

198-9

oxisol formation, Borneo

microbial fossils

142-3

110-16 Permian Lodeve Basin

Mid-Atlantic Ridge

151

magnesium

109-10

magnetite

39,69, 70

Minas Ragra

malachite

162, 163,164, 166, 169

Mineoka-Kobotoke-Setogawa

hydrolithic sediments globular distribution

32-3,34-6,

37-8,105 related facies

see also iron and manganese deposits in China manganese deposits, Datangpo 39, 42-3,44-9

manganese feroxyhyte manganese goei�ite

103

66-7,70

manganese-iron crusts,

Poland

73, 74

76-7

site of deposition

147

147-8, 149, 150, 151

ironstone

151,152-3, 154-5

Minle Formation

154,155

110, 111

112

89-90

17-18,

90,92-3, 94,95-6,

97, 98, 100

geological setting and structure

22,23,42,43,46, 47

33

Rocett (Bezymiannaya) Seamount see manganese-iron crusts on the

Rungan River deposits

24-7

petrography

21-2

stratigraphy

18-21

Moonta copper deposit

189, 190 San Andres Member

mineral composition model of formation

104-5

Nantuo Formation

deposits

40, 42

natural gas, metalliferous deposits in

manganese mineralization 53-6

Nazas Formation

Mexico, East

17-18,23-4,27

Newfoundland see Humber Arm

39,43-9, 114-16

manganese oxyhydroxides Atlantis-!I Deep 65-8,71

60,61, 62-3,

nickel

94,97,128-9,130-2, 133-4,137

normalization techniques 8-9, 10-13

20,22,23,24,

sea level and sedimentation

20

Allochthon

168

33

'Santiago' Formation 26,27

194

Lijiang Basin

South China

21,22,24,25

San Francisco manganese-iron

100,103-4

91

139,140,

141,144

90,94

structure

57-8 see also

Bezymiannaya Seamount 640

22-5

palaeogeography

99

geochemistry

189

84,86,174,

210-13 Red Sea sediments

rhodonite

manganese mineralization mineralogy

radioactive organic materials rare earth elements

rhodochrosite

23-4,27

analytical methods

82, 83, 86

Atlantis-II Deep; Thetis Deep

Molango district 89,101-2,

pyrolusite

86-7

Minette-type iron ore

106-7

163,170

136

85-6

mineral deposits, Yugoslavia facies

Datangpo Formation

pseudomalachite pyrite

74-6

occurrence and samples

168

Proterozoic Datangpo Formation see

73-4,76,87

geological setting

21

143-4

Poland see uranium enrichment, potassium

77-9,80-1,82,83-5

fossils from

Bezymiannaya Seamount 640

analysis

origin

31-2

Formation

Mineoka Umber

187,188

168

podsols, Borneo

188,189

tectonic belt

123, 124

manganese and iron facies in

122,

123,124-5,126, 130, 135

104,106

phosphorus

Pimienta Formation

103

Middle Arm Point Formation

209

magnesium asbolane

Sinai

193,

metals and minerals in asphalt

112-16

genesis

221-2

199-200

110-16

sequence of deposits

manganese

45-7, 48 65

microbiota-mineral relationships

179

magnesite

163,174,177

deposits, China

210-12

206

deposits 178,

203-6,209-13

in Walchia shale

microbiota from iron and manganese

151

Luoxue-Yimen copper deposits

shale

in copper minerals

organic matter and metalliferous

208-9

Mexico, East see Molango District

microbial fossils

185

Lower Dolostone Member

regional geology

in alum

in Red Sea sediments

rare earth enrichments

53

manganese geochemistry

organic matter

in manganese deposits

203-6

discussion of results

51-3

basin evolution

lueneburgite

metals and rare earth elements, analysis

53

basin analysis

metalliferous deposits, China

40, 42

organic materials

185-8

metalliferous deposits and organic

32,33, 37

148,185-6

see metal enrichments in

190

post-ore organic material

154

oil shales

organic materials, metal enrichment

ore coeval with material

185

Lahn-Dill type iron ore

188-

90,191

184-5

122,123-9,

130, 133,134-7

3-4,5-7,

26-7,

46,47 Setogawa Umber Shirataki limestone

75-6, 86-7 85

Shishan-Fengshan copper deposits 177,178 siderite

139,140, 141, 144

Index silicon Sinai

Tielin Formation

168

silver

97, 99 see

Urn Bogma Region, Sinai

Slanci Basin sodium

148, 149

209

Songgui Formation

51,53, 54

stratafer sediments

31-2

sulphate minerals, stability

Tiesiao Formation

Valjevo-Mionica Basin

todorokite

60,61, 66-7

vanadium

134-5,

metals and rare earth

elements, Sweden

minerals

see

in alum shale

'Taman Mixto'

161, 162

Tepexic Formation Tetzintla mine Thetis Deep

20, 21-2, 26

18,19, 23,26

see

Dongchuan-Yimen copper deposits

185,186-7,

Yugoslavia

uranium enrichment, Poland

see

mineral deposits

Yugoslavia

217,

218

68-71

manganese oxyhydroxides

39-40

Yimen copper deposits

14 188-90,191, 199

iron oxyhydroxides 70-1

Yangtze Craton 204, 205,206, 208-

in organic matter

21,22,24

21

uranium enrichment,

Poland

162-3, 164, 166

uranium

Taman Formation

148, 149

Walchia shale, uranium enrichment

160,161-2,165

Upper Dolostone Member

152-3, 154

184,185,188

159, 161,

166 ; 167, 168

lithostratigraphy

136,137

Tajmiste ironstones

209-10

159

168-70 geochemistry

148, 149

187-8, 189

Vranje Basin

151

Urn Bogma region, Sinai copper mineralization

125-8

sulphur isotopic analysis

in alum shale

163,166, 170

Venezuela ulexite

128,

189-90

40, 42

151

124-5,

129, 133-4,137

sulphur-carbon ratios

uranium-rich bitumen

tincalonite turquoise

177

see

110, 111

112

in organic matter

sulphide ores, Newfoundland

Sweden

fossils from

227

69,

organic matter in shale

221-2

sedimentology of shale

217,219

uraniurn-polymetallic mineralization

220-1

zeolites zinc

148

128-9, 130-2, 133-4,137

Zlatokop-Vranje Basin

150