Singhbhum Copper Belt - Chapri, Mosaboni, Pathargarh, Kendadih, Surda, Rakha, Dhobani, Jaduguda
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The Singhbhum Copper Belt lies within the major Singhbhum Thrust/Shear zone over a trend length of approximately 160 km. The most intense mineralisation however is in a 50 to 60 km interval in the central and south-central sections of the shear zone. It includes the Chapri, Mosaboni, Pathargarh, Kendadih, Surda, Dhobani and Rakha deposits. Others include: Turamdih, Ramchandrapahar, Nandup, Bayanbil, Dhadkidih, Jharkhand and Jaduguda Cu-U.
The Singhbhum Thrust is an arcuate structure that lies along the northern margin of the Singhbhum Craton and is believed to be part of the Central Indian Suture zone which forms the southern margin of the Aravalli Craton. On a regional scale the Singhbhum Thrust marks a sharp change in the metamorphic grade and trend of the sequences on either side. To the south, with the exception of the 'older metamorphics', the sequences are generally of greenschist facies rocks with a structural trend from around 30°, to north-south in the south. To the north, across the shear, they change to a generally east-west trending suite of amphibolite facies, with the development of sillimanite (Sarkar, et al., 1971).
Published resource figures for the more significant mines and occurrences include:
Rakha - 64 Mt @ 1.55% Cu (Res., Chintock & Bishop, 1994)
Mosaboni - 17 Mt @ 1.73% Cu (Res., Chintock & Bishop, 1994)
Surda - 29 Mt @ 1.73% Cu (Res., Chintock & Bishop, 1994)
Roam-Siddeshwar - 32 Mt @ 1.25% Cu (unspecified source, 1978)
Tamapahar - 25 Mt @ 1.2% Cu (unspecified source, 1978)
Turamdih - 12.6 Mt @ 1.6% Cu (Res., @ 1% Cu cut-off, unspecified source, 1978).
The mines of the Singhbhum Copper Belt are operated as the Indian Copper Complex, owned by Hindustan Copper Limited. The Copper Belt is the site of ancient workings from 2000 BC to the sixth century AD. Repeated attempts to mine on the belt from the middle of the 19 th century to the 1920's met with successive failures until an operation was started on the Mosaboni mine in 1927. That operation was nationalised in 1972 to become a unit of Hindustan Copper Limited (Khan, 1976).
Geology & Structure
The Singhbhum Copper Belt is within a zone of over-thrust and shearing which varies in width from a few hundreds metres to 2.5 km in width at the Mosaboni Mine, and around 1 km wide at Surda. The thrust generally dips gently to the north at angles of between 30° and 50°, and is very persistent with depth, having been traced down dip as far as 2.7 km. The shear plane acts as the loci of ultramafic and mafic igneous activity and of soda-metasomatism and apatite-magnetite-uranium-copper mineralisation within the district (Johnson, 1973).
In general the thrust zone thickens from east to west. In the south-east it involves rocks of the Iron Ore Series, which belong to the Singhbhum Craton to the south, the Dhanjori volcanics of the Singhbhum Group to the north and 'soda granites' which are largely a migmatitic/ metasomatic alteration product. In the middle, and further west, it involves chlorite schists which are believed to be after Dhanjori basic volcanics, meta-sediments of the Iron Ore Series, 'soda granites', and granophyres and granite gneisses which were intruded along the thrust zone (Sarkar, et al., 1971).
Deformation apparently took place in two phases. The first involved folding, accompanied by progressive regional metamorphism, and the development of an assemblage including staurolite and kyanite. Folding in the first phase was generally isoclinal and overturned to the west. Bedding, S1, was all but obliterated with the schistosity S2 being the best developed foliation outside of the shear zone (Sarkar, et al., 1971).
The first phase of deformation was followed, after a hiatus, by intense shear movement accompanied by retrogressive metamorphism, or degradation of rocks within the shear zone, to produce chlorite, muscovite, biotite and chloritoid. This formed a strong S3 foliation and a well developed set of lineations, which include elongated boudins, clasts and amygdales, slickensides, grooves, mineral lineations, etc.. Extensive development of shear planes with mutually parallel striae, grooving and mineral lineation accompanied the development of zones of mylonites and blasto-mylonites synchronously with the retrograde metamorphism (Sarkar, et al., 1971).
Open folds and warps of mesoscopic to megascopic dimensions influenced S1, S2 and S3, while a number of post shearing transverse faults have affected the shear zone (Sarkar, et al., 1971).
According to Sarkar, et al. (1988), the ore mineralisation within the Singhbhum Copper Belt has taken place in more than one rock type, most related to the Dhanjori volcanics. In the richest Mosaboni-Badia section, it is in the chlorite schists and within a 'soda feldspar' rich zone of metasomatism. They further add that detailed structural studies have indicated that within the Singhbhum Copper Belt, sulphide mineralisation is mainly stratabound, occurring within certain stratigraphic horizons adjacent to Dhanjori volcanics, although it is structurally controlled on macroscopic to microscopic scales. Ore is localised in both S2 and S3 foliations, while down-dip lineations, 'puckers' and gentle folds control the trends of the richer ore shoots. Lineations observed parallel to the shoots include, elongated boudins, slickensides, grooves, mineral lineations, etc..
In the vicinity of the Mosaboni mine, garnetiferous mica schists, phyllites, quartzites and quartz-kyanite schists of the Chaibasa Formation (Singhbhum Group), have been thrust over metamorphosed mafic volcanics of the Dhanjori Formation to the south. Rocks within the shear zone are highly sheared and mylonitised equivalents of siliceous rocks, quartzites and granites, and are characterised by soda rich feldspars (Khan, 1976). The shear zone itself varies from a few hundred metres to 2.5 km in width and contains slices of sheared Dhanjori epi-diorite and quartzite, sometimes accompanied by kyanite-hornblende-mica schist and soda-feldspathised schist. It dips on average at 30°NE, generally varying from 25° to 30°, although in places it gets up to 50°. Schistosity, strain slip cleavage and shear planes are developed throughout the thrust zone in the mine. The S2 foliation within the thrust zone is sub-parallel to the S3 shear planes (Johnson, 1973).
Mineralisation at Mosaboni is found close to the footwall of the thrust belt in two sheet like lodes that each average around 1.8 m in thickness and are generally 12 m apart. These are known as the 'Main Lode' and the 'West Lode', representing the hangingwall and footwall lodes respectively. They parallel the structural planes of the shear and follow two well defined shear channels over an aggregate length of around 5 km, with barren/poorly mineralised intervals in the plane of the lode between the ore shoots. The width of the mineralised lode varies from a few cm's to 11 m within these lodes (Khan, 1976; Johnson, 1973). Known mineralisation extends down plunge for at least 2.6 km (Sarkar, et al., 1971).
These lodes are confined to a zone of quartz-biotite-chlorite schist within the 'soda granite' and is regarded to post date the soda-metasomatism. The West Lode occurs about 50 m above the contact between the 'soda granite' with the underlying, 40 m thick sheared and feldspathised Dhanjori epidiorite, the base of which defines the lower limit of the shear (Johnson, 1973). The lodes consist of sheeted orebodies formed by sulphides infilling close spaced inter-locking fractures and by occasional massive sulphide pods and bands. These fractures and bands are defined by the S2 and S3 foliations. The orebodies at Mosaboni generally have sharp boundaries, although elsewhere they may also have assay limits. Some blebs of disseminated sulphides and small stringers may occur between the two lodes. Individual orebodies/shoots within th lodes vary in strike length from a few tens of metres to >1000 m, but are generally more extensive down-plunge (Temby, 1978; Johnson, 1973).
The sulphide minerals consist predominantly of chalcopyrite, followed by pyrite and pyrrhotite, accompanied by magnetite and minor pentlandite, millerite, violarite, sphalerite and molybdenite. The gangue minerals are quartz, biotite, chlorite and sericite in variable proportions (Sakar, et al., 1971). Magnetite-apatite are also occasionally gangue minerals. Quartz veins are not always mineralised. The sulphides are enriched in Co, Ni, Ti and V, as are the rocks of the Singhbhum Shear Zone, a relationship that has been quoted to support the derivation of metals from the rocks of the shear zone (Johnson, 1973).
Surda is some 6.5 km to the north-west of Mosaboni, and again is found close to the footwall of the shear zone. The thrust belt is around 1 km wide at this point, with a similar dip to that at Mosaboni and is within similar rocks (Johnson, 1973).
In 1973 there were seven sheeted lodes that were being tested and/or exploited. Six were called 'Hangingwall Lodes', developed in sheared quartzite and quartz-chlorite-biotite schist. One lode occurs within epidiorite below the thrust and is termed the 'Footwall Lode'. However nowhere are there more than three at any one interval. The ore zone has a strike length of 1800 m, and is up to 35 m wide. The average lode width is 7 m, and the dip from 35 to 45°NE. Each lode exhibits several sheet like orebodies formed by sulphides infilling irregular fractures. The fractures are not as closely spaced, nor are the individual orebodies as distinct as at Mosaboni, with assay boundaries (Johnson, 1973; Sarkar, et al., 1988).
Mineralisation is more commonly associated with quartz lenses and veins than at Mosaboni. The mineral assemblage is similar to that at Mosaboni, with the exception of the presence of uraninite associated with magnetite-apatite in four of the hangingwall lodes (Johnson, 1973).
Rakhais around 15 km to the north-west of Mosaboni. Ore occurs as disseminations, stringers and veinlets, massive sulphide veins and replacement patches in different structural units and lithologies. The richer zones forming lodes alternate with lean to barren widths of up to 2 m. Nine such lodes with strike lengths of 200 to 300 m and widths of 1 to 9 m occur in an en echelon pattern with sinistral overlaps that follow along strike and down the dip of 40°NE. This pattern leads to the overlap of two to three lodes at a given point. The lodes exhibit pinch and swell structures in gentle antiforms and synforms with a down-dip, north-easterly plunge (Sarkar, et al., 1988).
In addition to copper, Rakha averages 0.011% Mo, 0.08% Ni, 0.01% Co, 100 ppm Sn, 2 g/t Ag and 0.2 g/t Au. Co values tend to be fairly constant between the various mines, although Ni and Mo vary considerably.
Pathargora is between Mosaboni and Surda, being 3 km to the NNW of Mosaboni, and forms part of the same mineralised zone as those two deposits. In 1973 there were two lodes known, one on the contact between the 'soda granite' and the epidiorite, while the second was within the epidiorite. The latter is called the 'Footwall Lode'. Mineralisation is almost continuous with the Mosaboni block, although the lodes are not directly correlatable. Pathargora is separated from Surda by the Pathargora Fault, a cross fault with a displacement of 2.5 km (Johnson, 1973). Mineralisation varies from a few cm's in width, to as much as 12 m, and dips from 30 to 45°NE (Sarkar, et al, 1988).
Jaduguda is approximately 5 km to the north-west of Rakha. The individual lenses of mineralisation average 2.5 m in width, ranging up to 5 m, and have a strike length of 1100 m. Mineralisation is found within the shear zone, as at the copper mines. Most of the other uranium mines have very low Ni and Mo, although Jaduguda averages 0.21% Ni, 0.035% Mo and 0.013% Co (Temby, 1978).
As with copper the uranium is structurally controlled. Uraninite occurs as micro veinlets in meta-sediments in the thrust and along joint planes, and sometimes as minute disseminations in the host rock. The most favourable host rocks are mylonitised chlorite-sericite schist, granular chloritic rocks, quartzite, apatite-magnetite, tourmalinite, quartz-magnetite breccia, biotite schist and sheared magnetite-quartzite. Ore zones occur as en echelon lenses up to 20 m thick, but averaging 2 to 3 m, and up to 100 m in length. They are confined to well defined zones along the thrust sub-parallel to the foliation in the host rock. In general uranium and copper ore lenses are separate, although usually close together. Typically sulphides are found towards the footwall of the thrust, with uranium in the hangingwall of the mineralised zone. In the eastern copper mines some uranium is found in the copper lodes, as well as in separate lodes in the hangingwall. At Jaduguda chalcopyrite is subordinate (Johnson, 1973).
Apatite-magnetite mineralisation is also found within the shear zone, again occurring in veins, lenses and dissemination within biotite-chlorite host rocks. These veins are generally from 0.5 to 10 m in thickness and have been mined for both iron and apatite. They appear to be found mostly in the central to south-eastern part of the belt, while uranium is more common in the central section (Temby, 1978).
The paragenetic sequence, from earliest to latest is apatite, magnetite, ilmenite, uraninite-pyrite-molybdenite-sphalerite, chalcopyrite, pyrrhotite-pentlandite, and pyrite (Johnson, 1973). The first generation pyrite apparently formed between 490 and 325°C, from depth to shallower levels, while chalcopyrrhotite (Cu bearing pyrrhotite) and pyrrhotite were at around 340°C (Rao, 1964).
The most recent source geological information used to prepare this summary was dated: 2011.
Record last updated: 10/11/2014
This description is a summary from published sources, the chief of which are listed below.
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References to this deposit in the PGC Literature Collection:
Banerji A K 1981 - Ore genesis and its relationship to volcanism, tectonism, granitic activity and metasomatism along the Singhbhum shear zone, eastern India: in Econ. Geol. v76 pp 905-912|
Changkakoti A, Gray J, Morton R D, Sarkar S N 1987 - The Mosaboni Copper deposit, India - a preliminary study on the nature and genesis of the ore fluids: in Econ. Geol. v82 pp 1619-1625|
Gangadharam E V, Rao K K and Aswathanarayana U, 1963 - Distribution of radioactivity in the Mosaboni copper mine, Bihar, India : in Econ. Geol. v.58 pp. 506-514|
Pal D C, Chaudhuri T, McFarlane C, Mukherjee A and Sarangi A K, 2011 - Mineral Chemistry and In Situ Dating of Allanite, and Geochemistry of Its Host Rocks in the Bagjata Uranium Mine, Singhbhum Shear Zone, India - Implications for the Chemical Evolution of REE Mineralization and Mobilization: in Econ. Geol. v.106 pp. 1155-1171|
Rao K Kameswara 1964 - Geothermometric measurements of sulfide minerals, Mosabhoni copper mine, Singhbhum District, Bihar : in Econ. Geol. v.59 pp. 136-141|
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