Ore-localization in the Khetri copper belt, Rajasthan, India

Chowdhury, M. K. Roy; Gupta, S.

doi:10.2113/gsecongeo.60.1.69

Cited by 30 publications

(15 citation statements)

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“…Here, the mineral assemblage has been suggested to have formed by large-scale ironmagnesium metasomatism during epigenetic mineralization (Dasgupta, 1964b;Roychowdhury and Dasgupta, 1965). The present paper provides an account of the geological setting, origin, and conditions of metamorphism of two recently discovered massive zinc-lead-copper deposits, which occur in association with cordierite-anthophyllite rocks belonging to the Delhi system.…”

Section: Introductionmentioning

confidence: 79%

Genesis and metamorphism of two stratiform massive sulfide deposits at Ambaji and Deri in the Precambrian of western India

Deb¹

1980

Economic Geology

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Massive, stratiform, zinc-lead-copper ores occur at Ambaji anti Deri, located 8 km apart, in Gujarat and Rajasthan, resl)ectively. The ores are concentrated in lensoid bodies of metamorphosed magnesian and calc-magnesian rocks, such as cordieriteanthopl•yllite-chlorite rocks, quartz-chlorite-tremolite schists, and diopside-forsterite marble, enclosed within argillaceous and arenaceous metasediments or orthoamphibolites. The rocks belong to the lower part of the Ajabgarh series of Precambrian Delhi system. The host rocks and ores were subjected to an earlier low-grade regional metamorphism under greenschist facies conditions and a superimposed hornblende hornfels facies thermal metamorphisriL apparently related to the intrusion of granite and alkali syenite plutons at Ambaji and Deri, respectively.The P-T conditions of the last n•etamorphic episode have been estimated by comparing the mineral assemblages having a hornfelsic fabric with experimentally determined mineral reactions. Based on the stability relations of Mg-A1 chlorites, anthophyllite, magnesian cordierite, and the assemblage diopside-tremolite-calcite-quartz, it is inferred that thermal n•dtamorphism took phtce in the temperature range of 525 ø to 625øC at 2 to 4 kb pressure, with a mean condition of 575øC/3 kb. The average mole percent FeS in sphalerite from the buffered assemblage sphalerite-pyrrhotite-pyrite, in •,vell-annealed Deri ores, is 16.3_ 0.2, which for the temperature range mentioned corresponds to a pressure range of 3.8 to 3.1 kb, according to Scott's (1973) geobarometer. The fugacities of O 2 and S2 are determined by the mineral assemblage and vary considerably from rock to rock. A log [o• log [s.o diagram at the mean P-T of thermal metamorphism (3.45 kb and 575øC) has been prepared and contoured with the sphalerite composition in chlorite-anthophyllite rock from the Ambaji-Deri area.The compositions of coexisting sulfides and silicates from the magnesian assemblages were studied with the electron microprobe. The iron sulfide coexisting with Mg chlorite, anthophyllite, and Zn-rich pleonaste is pyrite and the Mg enrichment appears to be due to the original bulk composition of these rocks rather than the iron extracted during metamorphism.From a number of geological features it is inferred that the host rocks of sulfide ores were formed essentially by isochemical metamorphism of sedimentary calc-magnesian and magnesian concentration accumulated in a transitional shelf environment. The metals were derived from basalt, which was subsequently metamorphosed to amphibolite, and were concentrated syngenetically and/or diagenetically with the magnesian sediments. A model of consanguinous origin is presented which invokes the derivation of the metals, the concentration of the magnesia, the nonbacteriogenic reduction of seawater sulfate, and the concentration of stratiform sulfides by ska-water-basalt interactions under near-shore peritidal conditions.

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Section: Introductionmentioning

confidence: 79%

Genesis and metamorphism of two stratiform massive sulfide deposits at Ambaji and Deri in the Precambrian of western India

Deb¹

1980

Economic Geology

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“…The Khetri complex is characterised by the Cu (with minor Au and Ag) and iron sulphide (with minor Cu–Au) mineralisation (Roy Chowdhury & Das Gupta, ). Additionally, U mineralisation occurs throughout the Khetri complex with minor REE, Mo, Fe, Co, fluorite, and magnetite deposits (Baidya et al, ; Chen, Zhou, Li, Gao, & Hou, ; Knight et al, ).…”

Section: Discussionmentioning

confidence: 99%

Chlorine‐rich amphibole and biotite in the A‐type granites, Rajasthan, NW India: Potential indicators of subsolidus fluid–rock interaction and metallogeny

2018

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The A-type granites in the northern Delhi fold belt, Rajasthan, India, comprise Clenriched amphibole and biotite. These hydrous phases, in general, show significant variation in the Cl and F contents on the scale of individual intrusions and also at times on thin-section scale. This variation of the hydrous phases that equilibrated with the fluid is principally controlled by the variation in the fluid activity ratios of a Cl -/a OHand a F -/a OH -. The activity gradients in the fluid developed due to the interaction between the granites and an externally derived Cl-bearing fluid coupled with limited integrated fluid flux. The fraction of the fluid that reached the least albitised granite was highly Cl-rich as a consequence of preferential extraction of water from the grain-boundary fluid for the formation of hydrous phases like epidote and sericite. The occurrence of Cl-rich amphibole and biotite coupled with the variation in their halogen contents in the A-type granites can act as potential indicators of hydrothermal fluid activity and the subsequent mineralisation in a region.

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“…The last major metamorphic event has been dated at 950-910 Ma through chemical dating of monazite (Kaur et al 2006;Pant et al 2008). Previous workers have reported widespread post-metamorphic hydrothermal alterations (Roy Chowdhury and Das Gupta 1965;Kaur et al 2012;Knight et al 2002). Roy Chowdhury and Das Gupta (1965) reported Fe-Mg metasomatism, chloritization, biotitization, sericitization and silicification.…”

Section: Geological Backgroundmentioning

confidence: 94%

“…Previous workers have reported widespread post-metamorphic hydrothermal alterations (Roy Chowdhury and Das Gupta 1965;Kaur et al 2012;Knight et al 2002). Roy Chowdhury and Das Gupta (1965) reported Fe-Mg metasomatism, chloritization, biotitization, sericitization and silicification. Knight et al (2002) demonstrated that the NKCB rocks have been overprinted by regionally pervasive calc-silicate and sodic alteration.…”

Section: Geological Backgroundmentioning

confidence: 94%

Textures and compositions of cobalt pentlandite and cobaltian mackinawite from the Madan-Kudan copper deposit, Khetri Copper Belt, Rajasthan, India

2018

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The Khetri Copper Belt (KCB), a part of the Proterozoic Delhi-Aravalli fold belt in western India, hosts several Cu deposits, which are known to contain considerable Au, Ag, Co and Ni. Although many Cobearing phases have been reported from the KCB and adjacent areas, detailed textural and geochemical data are either unavailable or scant except for mackinawite. In this study, we describe the textures and compositions (determined by EPMA) of two very rare Co-rich phases, namely cobaltian mackinawite (containing up to 12.68 wt.% Co, 1.90 wt.% Ni and 2.52 wt.% Cu) and cobalt-pentlandite (containing up to 49.30 wt.% Co and 10.19 wt.% Ni), identified based on composition, from the Madan-Kudan deposit. To the best of our knowledge, neither cobalt-pentlandite nor such highly Co-rich mackinawite have previously been reported from this area. The common sulphide minerals viz. chalcopyrite, pyrrhotite and rare pyrite occur in chalcopyrite-pyrrhotite ± pyrite-magnetite-chlorite-blue amphibole (Cl-rich hastingsitepargasite-sadanagaite) ± marialitic scapolite ± allanite ± uraninite veins in amphibole-bearing feldspathic quartzite and garnetiferous chlorite schist. Cobaltian mackinawite is invariably associated with chalcopyrite and occurs as exsolution and inclusion within chalcopyrite or outside, but at the contact of chalcopyrite. On the other hand, cobalt-pentlandite is invariably associated with pyrrhotite and shows similar textural relation with pyrrhotite as that of mackinawite with chalcopyrite. Mineralogically diverse undeformed sulphide veins comprising Cl-rich amphibole and locally Cl-rich marialitic scapolite suggests epigenetic hydrothermal mineralization involving Cl-rich saline fluid in the Madan-Kudan deposit. Transport of metals, derived from a mafic source rock with high intrinsic Ni:Co ratio, by Cl-rich fluid can suitably explain the high Co:Ni ratio of the studied ore minerals. Presence of such highly Co-rich phases and other circumstantial evidences, enumerated in this work, are consistent with variants of Fe oxide (-Cu-Au) (IOCG) style mineralization, at least for some stages of mineralization in the Madan-Kudan deposit.

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Ore-localization in the Khetri copper belt, Rajasthan, India

Cited by 30 publications

References 1 publication

Genesis and metamorphism of two stratiform massive sulfide deposits at Ambaji and Deri in the Precambrian of western India

Genesis and metamorphism of two stratiform massive sulfide deposits at Ambaji and Deri in the Precambrian of western India

Chlorine‐rich amphibole and biotite in the A‐type granites, Rajasthan, NW India: Potential indicators of subsolidus fluid–rock interaction and metallogeny

Textures and compositions of cobalt pentlandite and cobaltian mackinawite from the Madan-Kudan copper deposit, Khetri Copper Belt, Rajasthan, India

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