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Khetri Copper Belt - Kolihan, Madhan, Kudhan, Chandmari, Akwali, Banwas, Singhana, Alwar |
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Rajasthan, India |
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Cu Au
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Super Porphyry Cu and Au
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The Neoproterozoic Khetri and Alwar IOCG related copper Belts are located ~190 km SW of New Delhi, in the states of Rajasthan and Haryana, in northwestern India.
They lie within the 100 to 200 km wide Aravalli mobile belt (Singh et al., 2010) on the northwestern margin of the Archaean Aravalli-Bundelkhand proto-continent (Meert et al., 2010; or Aravalli craton of Naqvi and Rogers, 1987). The Aravalli-Bundelkhand proto-continent is bounded to the north by the current Himalayan Fold Belt and to the south by the continental scale, eastnortheast-trending, Proterozoic Narmada-Son lineament and the parallel Satpura mobile belt immediately to its south. These structures also mark the northern limit of the Dharwar (East and West), Bhandara (Bastar) and Singhbhum cratons, which are each separated by northnorthwest-trending sutures, and form the bulk of Peninsular India.
The northeast-trending Great Boundary fault divides the Aravalli-Bundelkhand proto-continent into the main Bundelkhand craton to the east and the Aravalli block (Meert et al., 2010; or Mewar craton of Rao and Reddy, 2002), which broadly coincides with the Aravalli Mobile Belt, to the west. The Aravalli and Satpura mobile belts would appear to be continuous from the southern to western margins of the Aravalli-Bundelkhand proto-continent.
Much of the Bundelkhand craton is occupied by the Bundelkhand Igneous Complex, which includes the late Bundelkhand Granite (2492±10 Ma). These intrude older Archaean granite-greenstone enclaves and gneisses formed between 3.2 and 2.5 Ga. The exposed basement to the Aravalli block comprises the 3.3 to 2.45 Ga Banded Gneissic Complex (or Mewar Gneisses), composed of migmatites, tonalite-trondhjemite-granodiorite gneisses, meta-sedimentary rocks and sporadic greenstone belts/ amphibolites, intruded by the 2530±3.6 Ma Berach Granite (Meert et al., 2010; Singh et al., 2010 and sources quoted therein). The stabilised metamorphic basement of the Aravalli block was unconformably overlain by the 2.15 to 1.8 Ga Aravalli Supergroup. This unit comprises shallow water, stromatolite-bearing facies in the east, and deep water carbonate-pelite facies to the west. These facies-domains are separated by the gabbro-norite (ophiolite?)-bearing Rakhabdev shear zone, interpreted to define a subduction zone, along which the Aravalli basin closed at 1.8 Ga (the absence of any preserved magmatic arc would challenge this interpretation). The sequence is also cut by 1.85 Ga granites (Singh et al., 2010).
Within the Aravalli mobile belt, the Aravalli Supergroup succession is overlain by the >5 km thick Delhi Supergroup, which comprises the basal Raialo Group (carbonate, conglomerate and sandstone, with mafic and felsic volcanic rocks), overlain by the Alwar Group (conglomerate and sandstone), which is followed in turn by the Ajabgarh Group (stromatolitic carbonate, siltstone and shale). Minor felsic and mafic volcanic rocks occur throughout the Ajabgarh and Alwar Groups. The age of this succession is poorly constrained, between 1.7 and 0.8 Ga (Meert et al., 2010; Singh et al., 2010).
The Aravalli mobile belt is composed of a series of terranes. These terranes are separated by major shear zones, and represent the surface expression of different stratigraphic levels and degrees (depths) of metamorphism, e.g., in some terranes, the Aravalli Supergroup is only metamorphosed to low- to medium grades, while in others it has been modified to granulite facies and subjected to migmatisation (Singh et al., 2010). The main pulse of metamorphism took place between 1725 and 1621 Ma, at the onset of the Delhi Orogenic Cycle. Two distinct phases of magmatism are also recognised, the first between 1810 and 1660 Ma in the south, and largely between 1810 and 1780 Ma in the north, have an A-type geochemistry, attributed to an extensional setting (Meert et al., 2010).
The second, younger ~0.85 to ~0.73 Ga (with some examples ~1.0 Ga) 'Erinpura Granite' pulse is best represented to the south, although it is also developed in the Khetri area, to the north. This extensive young granite phase temporally overlaps the bimodal 0.77 to 0.75 Ga Malani Igneous Suite (MIS), which forms the largest felsic magmatic province in India, covering an area in excess of 55 000 km2 (Li et al., 2008; Singh et al., 2010; Vallinayagam and Kumar, 2010). It is characterised by voluminous magmatism that began with minor basaltic, followed by predominant felsic volcanic rocks and then by granitic emplacement, with a final, predominantly felsic magmatic cycle, and minor mafic dyke swarms. The MIS includes both peralkaline and peraluminous phases and is interpreted to represent 'anorogenic magmatism', related either to crustal melting during extension or to an active 'hot spot' (Eby and Kochhar, 1990; Bhushan, 2000; Sharma, 2004).
The MIS constitutes the bulk of the exposed basement (below superficial cover) in the Marwar terrane, which forms the western margin to the Aravalli mobile belt, although the complex also overlaps well into the core of the mobile belt, mainly in the form of intrusive roots. No Archaean basement is exposed, or indicated by isotopic signatures within the Marwar terrane, suggesting it marks the western edge of the Archaean craton. The MIS is unconformably overlain by the red beds and evaporites of the Neoproterozoic to Cambrian Marwar basin (Meert et al., 2010).
To the east of the Aravalli mobile belt (i.e., east of the Great Boundary fault), the bulk of the Bundelkhand craton is covered by the extensive, flat lying, 600 to 4500 m thick, Mesoproterozoic (1.7 to 1.0 Ga) Vindhyan Supergroup. This unit is made up of a sequence that includes conglomerates, sandstones, shales and a variety of limestones, including stromatolites (Meert et al., 2010; Naqvi and Rogers, 1987).
The tectonic framework, geological setting and distribution of main iron oxide-alkali altered mineralisation in the Aravalli-Bundelkhand Craton, Northwestern India. Note that only the mineral occurrences of the Khetri-Alwar district are shown (after Knight
et al., 2002; Meert et al., 2010; Singh et al., 2010).
Mineralisation within the Khetri district is controlled by shear zones, related to the major northeast-southwest trending Kaliguman lineament. It is hosted by the Mesoproterozoic Delhi Supergroup, described above. In the Khetri-Alewar district, the sequence comprises shallow-water, locally evaporitic, sedimentary, and lesser mafic and felsic volcanic rocks. This sequence is likely to have been deposited within a series of intra-cratonic rift basins, developed over an Archaean basement (Knight et al., 2002, and sources cited therein). A regionallycontinuous, stratigraphically conformable, breccia horizon, the Hornstone Breccia (Heron, 1917), is developed near the contact between the Alwar and Ajabgarh groups. It comprises angular fragments of quartz and quartzite in a massive iron oxide-rich chert matrix, interpreted to represent a breccia formed by evaporite dissolution (cf., Corella Formation, Mt Isa; Blake et al., 1990).
The Delhi Supergroup rocks of both the Khetri and Alwar districts have been metamorphosed to low- to mid-amphibolite facies, deformed into northeast-southwest striking, doublyplunging folds, and intruded by numerous 1.7 to 1.5 Ga syntectonic, and 0.85 to 0.75 Ga post-tectonic granitoids. The latter are broadly coeval with the Erinpura Granite and MIS events and comprise biotite- and hornblendebearing tonalite to syenite, containing accessory magnetite, titanite, allanite, apatite and fluorite, and are geochemically characterised by Al2O3/(CaO+Na2O+K2O) ratios of <1.1, low Al and Ca, high Th and HFSE, and enrichment in LREE, indicating A-type affinities (Knight et al., 2002).
District-scale Alteration and Mineralisation
The Khetri line of deposits extends over a strike-length of >10 km and contains ~140 Mt @ 1.1 to 1.7% Cu, 0.5 g/t Au. It is hosted by garnet-chlorite schists, andalusite- and graphitebearing biotite schists, and feldspathic quartzites, within sub-vertical northeast-striking shear zones. Mineralisation forms sub-vertical lens-like zones of stockwork, massive and vein-hosted chalcopyrite-pyrite-pyrrhotite with magnetite and hematite (Knight et al., 2002).
This belt of copper deposits occurs on the western margin of a regional 50 x 100 km zone of calc-silicate and albite-haematite alteration that overprints and crosscuts metamorphic fabrics, and contains widespread Cu±Au±Ag±Co±Fe±REE±U mineralisation. The calc-silicate assemblages occur as coarse-grained clinopyroxene-hornblende-epidote-apatite-scapolitetitanite- magnetite. The albite-hematite alteration comprises albite-amphibole (actinolite)-hematite-magnetite-calcite, with variable K feldspar, biotite, epidote, scapolite, titanite, apatite and fluorite, and locally abundant pyrite and chalcopyrite. The albite-hematite alteration is spatially related to vein systems and breccias, which commonly contain copper and gold mineralisation, massive magnetite-hematite vein-deposits, fluorite and rare uraninite occurrences. Alteration is zoned, with calc-silicates found dominantly on the margins of the regional alteration system, while albite-hematite forms a central core, locally overprinting calc-silicate assemblages.
Mineralisation-style within the system is also zoned, from i). chalcopyrite-pyrite-pyrrhotite in graphitic schists at Akwali; and ii). chalcopyrite-pyrite-pyrrhotite-magnetitehematite at Khetri, both in the northwest; iii). magnetite-hematite-chalcopyrite-pyrite in albite-haematite alteration, in the core, and iv). hematite-chalcopyrite-barite to the east. A SHRIMP U-Pb titanite age from the albite-hematite-amphibole-calcite-titanite assemblage constrains the timing of regional alteration to 847±8 Ma, which overlaps the fission-track ages of garnet from ore assemblages at the Madhan-Kudhan Cu mine at Khetri (897±125 Ma). As such, this mineralisation temporally overlaps the post tectonic A-type granitoids of the district (Knight et al., 2002).
A study on the Madan-Kudan deposit by Baidya et al. (2021) recognised four vein types: Type 1 pyrite ±chalcopyrite ±magnetite ±biotite ±scapolite ±amphibole ±chlorite; Type 2 chalcopyrite-pyrrhotite-pyrite-magnetite-amphibole-chlorite; Type 3 chalcopyrite-pyrrhotite-pyrite-dolomite-quartz; and Type 4 chalcopyrite-pyrrhotite-biotite. On the basis of texture and major and trace element chemistry, pyrite is grouped into Pyrite-1A, Pyrite-1B and Pyrite-1C within Type 1 veins; Pyrite-2 within Type 2 veins; Pyrite-3A and Pyrite-3B in Type 3 veins. This sequence was interpreted to reflect changing fluid composition and taken to suggest sulphide mineralisation was associated with Na-Ca-K alteration in Type 1 and 2 veins; carbonate alteration in Type 3 veins; and K-Fe-Mg alteration in Type 4 veins. The isotopic composition of C and O in dolomite from Type 3 veins was interpreted to suggest the ore fluid contained mantle-derived carbon, possibly related to a carbonatite, which was mixed with an isotopically heavier fluid or exchanged isotopes with crustal rocks. The strong positive correlation between Au and Cu was interpreted to reflect 'coupling' of the two in the pyrite structure. In contrast, Pb, Zn, Bi and Ag are found in mineral inclusions. Intragrain Fe, Co, As and Ni variability in pyrite was interpreted to suggest replacement by coupled dissolution-precipitation and formation of overgrowths were important. Pyrite-1A contains up to 3.3 wt.% Co and Co/Ni ratios of 500 to 16 000 that had not previously been reported. The Co/Ni ratios of Khetri Copper Belt pyrite are similar to those from iron oxide-apatite and other IOCG deposits, although the latter do not have a characteristic Co/Ni ratio but have consistently high Co concentrations of up to 1 wt.% or more. This paragraph is drawn from the abstract of Baidya et al. (2021).
The most recent source geological information used to prepare this decription was dated: 2021.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Baidya, A.S., Saha, R., Pal, D.C. and Upadhyay, D., 2023 - Fingerprinting alteration and mineralization in the iron oxide Cu-Au (IOCG) system using biotite chemistry and monazite geochronology: constraints from the Khetri Copper Belt, western India: in Mineralium Deposita v.58, pp. 1445-1476.
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Baidya, A.S., Sen, A., Pal, D.C. and Upadhyay, D., 2021 - Ore-forming processes in the Khetri Copper Belt, western India: constraints from trace element chemistry of pyrite and C-O isotope composition of carbonates: in Mineralium Deposita v.56, pp. 957-974.
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Das Gupta S P, 1970 - Sulfide deposits of Saladipura, Khetri copper belt, Rajasthan: in Econ. Geol. v.65 pp. 331-339
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Knight J, Joy S, Lowe J, Cameron J, Merrillees J, Nag S, Shah N, Dua G and Jhala K 2002 - The Khetri Copper Belt, Rajasthan: Iron Oxide Copper-Gold Terrane in the Proterozoic of NW India: in Porter T M (Ed.), 2002 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide v.2 pp. 321-341
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Li, X.-C., Zhou, M.-F., Williams-Jones, A.E., Yang, Y.-H. and Gao, J.-F., 2019 - Timing and genesis of Cu-Au) mineralization in the Khetri Copper Belt, northwestern India: constraints from in situ U-Pb ages and Sm-Nd isotopes of monazite-(Ce): in Mineralium Deposita v.54, pp. 553-568.
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Porter T M, 2010 - Current Understanding of Iron Oxide Associated-Alkali Altered Mineralised Systems: Part II, A Review: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide v.3 pp. 33-106
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Zhu, Z., 2016 - Gold in iron oxide copper-gold deposits: in Ore Geology Reviews v.72, pp. 37-42.
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| References in PGC Publishing Books: | |
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Knight J, Lowe J, Joy S, Cameron J, Merrillees J, Nag S, Shah N, Dua G, Jhala K, 2002 - The Khetri Copper Belt, Rajasthan: Iron Oxide Copper-Gold Terrane in the Proterozoic of NW India , in Porter T M, (Ed.), Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective, v2 pp 321-341
 Abstract
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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