Madhya Pradesh, India
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The Malanjkhand copper-molybdenum deposit is located in the Balaghat district of Madya Pradesh state in central India (#Location: 22° 1' 14"N, 80° 42' 53"E)
The Malanjkhand copper deposit is hosted within a multi-phase, tonalite-granodiorite-adamellite-granite-trondhjemite pluton that has yielded a date of 2362±58 Ma, which intrudes the broader enveloping Malanjkhand granodiorite-adamellite-granite pluton, which also hosts much of the ore and the Archaean Amgaon Group (Jain, et al., 1995; Sikka, 1989). Sarkar, et al., (1996) quote dates of between 2100 and 2400 Ma, as detailed below.
The age of the major phase of the granitoid complex hosting the copper deposit has been constrained by Uâ€“Pb dating on zircons (~2476±8 Ma; Panigrahi et al., 2004). Stein et al. (2004, 2006) provided Re-Os models and isochron dates (ranging from 2491 to 2439 Ma) of molybdenite from the mine pit and from the leucogranite. The molybdenite age spectrum overlaps those of zircon and indicates protracted or episodic hydrothermal activity, interpreted by Stein et al. (2004) as discrete deformation episodes and molybdenite deposition (after Panigrahi et al., 2008).
The host pluton lies immediately adjacent to, and within, the Central Indian Suture zone, some 600 km to the west of the Singhbhum Copper Belt. The granitoids of the pluton and the ores are cut by dolerite dykes and small gabbroic bodies of Middle Proterozoic age. The mineralised intrusives are unconformably overlain by the Middle Proterozoic clastics of the Sausar Group (Sikka, 1989).
The host granitoids have been subdivided into four groupings, as follows (Sarkar, et al., 1996):
• G1 - a moderately coarse grained, porphyritic granite containing alkali-feldspar megacrysts up to 2 cm long, in a quartzo-feldspathic matrix, with minor biotite, epidote-zoisite, sericite, titanite and carbonate;
• G2 - is an overall coarse grained rock that varies from tonalite, through granodiorite to trondhjemite, consisting mainly of quartz and sodic andesine, with important accessories of magnesio-hornblende, biotite, epidote and titanite. Feldspars range from 0.25 to 6.5 mm. This is the principal host lithology to ore and has been altered to an alkali feldspar rich variant with more pervasive alteration of hornblende surrounding the ore (Sarkar, et al., 1996). In earlier literature this has been mapped as a separate phase of pink adamellite rocks, occurring as a 1.8 x 0.8 km body within the larger pluton, with two ages, 1816±73 Ma and 1684±67 Ma (Panigrahi, et al., 1991). These may be metamorphic ages. Dating of G2 has yielded ages of between 2199±178 Ma and 2425±321 Ma (Sarkar, et al., 1996).
• G3 - is similar to G2 except that it has little or no hornblende. Accessory biotite, epidote and titanite influence the colour.
• G4 - is an aplite that intrudes both G1 and G2 and is characterised by the presence of alkali feldspar phenocrysts (up to 2.5 mm), in a fine grained quartzo-feldspathic matrix.
Magnetite is a common accessory in all four of the granitoid rocks, while accessory pyrrhotite, chalcopyrite and molybdenite have been noticed in some samples. Texturally G1, G2 and G3 are granoblastic-unfoliated and do not show gneissose or schistose fabrics, except where locally highly strained (Sarkar, et al., 1996).
All of the granitoids are cut by a series of gabbro and dolerite intrusives/dykes which also cut the ore (Sarkar, et al., 1996).
Mineralisation & Alteration
Mineralisation at Malanjkhand occurs as an arc shaped, 1.8 km-long and N-S oriented quartz reef complex, containing chalcopyrite-pyrite mineralization, hosted by granitoid G2, and is closely associated with a zone of silicification which is apparently controlled by sub-parallel brittle-ductile shear zones. Silicification within these shear zones coalesced at an upper level forming a massive quartzose body referred to as the 'quartz reef' (Sarkar, et al., 1996). It has been classified as a stockwork in some references (Sikka, 1989), although according to Sarkar, et al., (1996), it is more akin to a composite vein or lode. The mineralised zone dips at 65 to 70° to the east. There is another set of quartz veins in the area, distributed along a discrete set of fractures, although these have no associated ore, and were apparently formed prior to the introduction of the orebody (Sarkar, et al., 1996).
Primary mineralisation is present in four forms (Panigrahi et al., 1991), namely: i). as 'reef quartz' associated ore over an average width of 70 m; ii). as sulphide-rich quartz and quartzo-feldspathic veins and stringers in the hydrothermally altered granitoid on the margins of the zone of silicification and veining; iii). pegmatoid ore; andiv). disseminated sulphides.
These last three types occur within the enclosing pink granitoid where ore minerals are intimately associated with quartz, K-feldspar, chlorite, biotite, and epidote. The disseminated mineralisation is very much the subordinate, and occurs as disseminated sulphides at the interstices of silicate minerals, or a veinlets of sulphides ±quartz ±calcite ±chlorite. The 'reef mineralisation' is apparently the younger (Sarkar, et al., 1996).
The mineralised quartz veining/silicification zone contains chalcopyrite and pyrite, with subordinate magnetite, minor/accessory sphalerite, molybdenite, chalcocite and bornite, and trace cassiterite and cobaltite. The silicate gangue of the veins is predominantly quartz, with minor orthoclase, muscovite, chlorite and epidote, and trace zircon and apatite (Sikka, 1989; Sarkar, et al., 1996). Molybdenum levels are generally <100 ppm, averaging 40 ppm in the ore, although locally they may be several times greater. Mo and Au are generally higher towards the margins of the orebody (Sarkar, et al., 1996).
The crystallisation sequence seems to comprise magnetite (±cassiterite), followed by pyrite. Emplacement of chalcopyrite and sphalerite partly overlapped with that of pyrite as it is both included within un-fractured pyrite, as well as along fractures within the same mineral. Magnetite continued throughout. Molybdenite is earlier than chalcopyrite at least (Sarkar, et al., 1996).
The conspicuous hydrothermal alteration types associated with the mineralisation are silicification, replacement of andesine by alkali-feldspars, replacement of hornblende by biotite, epidote, chlorite, etc., increase of the Mg:Fe ratio in biotite, and the appearance of hypogene hematite and muscovite in minor phases (Sarkar, et al., 1996).
Beyond the limits of the intense silicification, other alteration has been traced for approximately 100 m into the hanging wall and 200 m into the footwall. This zone is characterised by a relatively fine grain size and a reddish-pink colouration, commonly referred to as "pink granitoid", when compared to the grey color of the rest part of the pluton, which are devoid of any ore mineral and low in abundance of K-feldspar. The dominant feldspars are K-feldspar, followed by albite. On its outer margin this alteration zone gradually changes to G2, or occurs as veins in that rock type. The colouration is due largely to the presence of hematite dust in the alkali feldspar (Sarkar, et al., 1996).
After the final phases of mineralisation, the ores were subjected to shear constrained deformation, as evidenced by the presence of fragmental vein quartz and altered wall rock, as well as striae within the ores. Chalcopyrite and sphalerite show evidence of plastic deformation and recrystallisation (Sarkar, et al., 1996).
Sarkar, et al., (1996) interpret the sequence of events that led to the development of the hypogene mineralisation, as commencing with fracturing of the host rock; emplacement of barren vein quartz; development of pronounced wall rock alteration accompanied by disseminated mineralisation and then the ultimate stage of intense silicification accompanied by the main copper ore. This was followed by post-mineralisation deformation related to dynamic shearing and the recrystallisation of chalcopyrite and sphalerite.
Oxidation extends from 3 to 40 m below the surface, but in places is known to a depth of 120 m (Sikka, 1989). The cap to the orebody comprises a strongly oxidised zone containing chalcocite, as well as sulphates, carbonates, oxides and chlorides of copper, native copper, and cobalt arsenide. The major phases in the secondary ore are Fe-oxides, chalcocite and malachite, followed by bronchantite. Minor phases include bornite, covellite, azurite, etc.. Malachite is the most obvious mineral in the cap, which also contains alunite. A moderately oxidised zone is also present near the interface with the hypogene ore, containing chalcocite and tarnished primary minerals. The total oxide reserve has been quoted at 7.5 Mt @ 0.8% Cu (Sikka, 1989; Sarkar, et al., 1996).
Published reserve and resource estimates include:
790 Mt @ 0.83% Cu, 0.2 g/t Au, 6 g/t Ag (Total resource., 1988 @ a 0.2% Cu cut-off, Sikka, 1989).
420 Mt @ 1.43% Cu at a 0.45% Cu (Total resource., 1988 @ a 0.45% Cu cut-off, Sikka, 1989).
based on 32 000 m of drilling in 112 holes (Sikka, et al., 1991)
145.7 Mt @ 1.28% Cu (Proved reserve, 1994, Chintock & Bishop, 1994)
90 Mt @ 1.3% Cu (Reserves, 1995, Sarkar, 1996)
58.8 Mt @ 1.2% Cu (Start-up open pit Reserve, 1979, Sikka, 1989)
9.2 Mt @ 1.4% Cu (Production, 1982-1988, Sikka, 1989).
The most recent source geological information used to prepare this summary was dated: 2008.
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:
Panigrahi K K, Bream B R, Misra K C and Naik R K 2004 - Age of granitic activity associated with copper–molybdenum mineralization at Malanjkhand, Central India: in Mineralium Deposita v39 pp 670-677|
Panigrahi M K, Mookherjee A, 1997 - The Malanjkhand copper (+molybdenum) deposit, India: mineralization from a low-temperature ore-fluid of granitoid affiliation: in Mineralium Deposita v32, pp 133-148|
Panigrahi M K, Naik R J, Pandit D and Misra K C, 2008 - Reconstructing physico-chemical parameters of hydrothermal mineralization of copper at the Malanjkhand deposit, India, from mineral chemistry of biotite, chlorite and epidote: in Geochemical Journal v.42 pp. 443-460|
Sarkar S C, Kabiraj S, Bhattacharya S, Pal A B, 1996 - Nature, origin and evolution of the granitoid-hosted early Proterozoic copper-molybdenum mineralization at Malanjkhand, Central India: in Mineralium Deposita v31 pp 419 - 431|
Sikka D B, Petruk W, Nehru C E and Zhang Z, 1991 - Geochemistry of secondary copper minerals from Proterozoic porphyry copper deposit, Malanjkhand, India: in Ore Geology Reviews v6 pp 257-290|
Stein H J, Hannah J L, Zimmerman A, Markey R J, Sarkar S C and Pal A B 2004 - A 2.5 Ga porphyry Cu-Mo-Au deposit at Malanjkhand, central India: implications for Late Archean continental assembly: in Precambrian Research v134 pp 189-226|
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