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Gahnite occurs in diverse rock types and metamorphosed mineral deposits. The gahnite geochemistry is being used as an exploration tool for zinc sulfide deposits. In the present study, the geochemistry of gahnite and associated minerals viz. sphalerite, garnet, sillimanite, staurolite, anthophyllite, biotite, ilmenite, and chlorite, and their petrography have been used in studying the genesis, metamorphic evolution, deposit characterization, and exploration significance of seven Palaeoproterozoic volcanogenic massive sulfides (VMS) deposits in the Betul belt in the Central Indian Tectonic Zone, India. Different textural types of gahnites are recognized in the Betul belt. Field investigations of textural and geochemical characteristics suggest that the gahnites were formed by multiple geological processes: desulfidation of sphalerite, breakdown of almandine garnet, and zincian staurolite, and chloritization of zincian biotite corresponding with regional metamorphism. The temperature conditions of gahnite formation are estimated to be ~600–650°C using empirical Ti in biotite thermometry. The elemental concentrations in gahnites vary from Zn/Fe ratio 2–4; Co 1–30 ppm; Ga 14–573 ppm and Mn 126–3422 ppm, indicating that bimodal volcanics and volcano‐sedimentary rocks as protolith. High Mn content in gahnite suggests an influx of magmatic‐hydrothermal fluid in the protolith. Variations of trace elements (Mg vs. Al/V, Ti vs. Co/Mn, Co vs. V/Ga, Mn vs. Zn/Fe) and high‐temperature of gahnite formation attest to sensu stricto VMS type mineralization in Betul belt, which is entirely different from SEDEX, Broken Hill‐type, and non‐sulfide deposits. Principal component analysis of trace elements shows the geochemical variations at a few deposits and reveals that gahnites were formed as a result of the competing effect of fS2‐fO2 and governed by bulk rock composition. [ABSTRACT FROM AUTHOR]

We present the findings on in situ trace element geochemistry of sulphides by LA‐ICPMS, sulphur isotope, and hydrothermal fluid evolution of copper ± gold mineralization at Dubarpeth, Central India. Mineralization is associated with chloritized‐silicified alteration zones, structurally localized along the terrain boundary fault between Archean TTG quartz diorite (2.5 Ga) of Western Bastar Craton and Paleo‐Mesoproterozoic cover sediments of Pranhita–Godavari (PG) Valley. Studies reveal that the Cu ± Au mineralization occurs in the form of dissemination, stringers, and veins along the microfaults and fractures. We infer three stages of mineralization based on the field observations and petrography studies. The early stage is characterized by the quartz–pyrite–chalcopyrite assemblage, while the middle stage is represented by quartz–chlorite–chalcopyrite ± pyrite. Calcite ± epidote is conspicuous in the late stage. Fluid inclusion microthermometry and Raman spectroscopy studies indicate that the early‐stage veins are mainly aqueous rich, mixed carbonic‐aqueous, and minor vapour‐rich aqueous inclusions. FIs in the early stage displayed evidence of vein formation during episode of fluid immiscibility with the homogenization temperatures and salinities up to 259°C and 27 wt.% NaCl equiv., respectively, indicating initial ore‐forming fluids of moderate temperature, moderate to high salinity in H2O–CO2–NaCl systems. Copper mineralization stage is liquid‐ and vapour‐rich (H2O–CO2–CH4 + N2) aqueous inclusions, with homogenization temperatures of 174–221°C and salinities of 6.37 to 13.9 wt.% NaCl equiv. This temperature range has been further supported by empirical chlorite thermometry based on Fe/Mg, AlIV, and AlV. The sulphur isotope values of pyrite and chalcopyrite showed δ34S interval of 2.29‰ to −10.85‰, characteristic of highly oxidized nature of the fluids and attributing sulphur source to magmatic origin. The ore‐forming fluids gradually became SO2−4 enriched and relatively oxidized during Cu mineralization. High Co–Ni trace element signatures of pyrite by LA‐ICPMS substantiate this observation, further indicating remobilization from a magmatic‐hydrothermal fluid. The presence of CH4 favours either a source of deep crustal nature or a mantle for the ore‐bearing fluid. We suggest that initial ore‐forming fluids are magmatic in origin that has been further cooled and diluted by mixing with meteoric water. Fluid boiling and mixing facilitated hydrothermal alteration and mineralization in the vicinity of the fault zone, which is perhaps activated during initiation of Paleo‐Mesoproterozoic segment of the Godavari Rift. The tectono‐magmatic setting, mineral assemblage, hydrothermal alteration, FIs, and trace element behaviour of pyrite (As–Co–Ni) suggest that the Dubarpeth Cu deposit is a high sulphidation epithermal vein type of deposit that is similar to those described for the shear/fault‐controlled epithermal deposits found elsewhere in the world. [ABSTRACT FROM AUTHOR]

• Western Bastar Craton (WBC) hosts Archean TTGs, sanukitoids, Proterozoic granites. • Paleoarchean (3250–3150 Ma) Nd model ages of mafic enclaves may be the age of protolith. • Both high- and low-REE TTGs emplaced at 2544–2496 Ma in a subduction setting. • Mul granite emplaced in anorogenic setting during 1666–1547 Ma linked to Cu-Au metallogeny in WBC. • WBC preserves a record of events related to Ur, Columbia, and Rodinia supercontinents. The Bastar Craton is one of the oldest cratonic nuclei of the Indian shield, comprising Paleoarchean to Mesoproterozoic crust that preserves the record of protracted crustal evolution and metallogeny. This study describes whole-rock geochemistry, U-Th-Pb ages of zircon and monazite from Neoarchean TTGs, sanukitoids, and Paleo- to Mesoproterozoic granites, and Sm-Nd isotope data from mafic enclave within TTGs of the Western Bastar Craton (WBC). The TTGs and sanukitoids represent Neoarchean crust formed by collision-accretion processes. The TTGs are of two types: low-HREE and high-HREE with both groups derived from low-K mafic sources. The sanukitoids have moderate SiO 2 (55.1–65.1 wt%, average = 61.7 wt%), Mg# (20–36, average = 24.7), Ni (10–40 ppm; average = 14 ppm), Sr (339–528; average = 418 ppm) and moderate to high concentrations of incompatible elements like Rb (26–112 ppm, average = 48), Ba (482–2300 ppm, average = 1542), Zr (69–593 ppm, average = 334 ppm), Nb (3.8–14.8 ppm, average = 8.7 ppm), Y (13.2–24.5 ppm, average = 19.5 ppm), and REE (91–301 ppm, average = 212)]. They post-date TTG emplacement and formed by mixing between metabasalt-derived and mantle wedge-derived melts in an arc environment. The Mul granite represents a younger Paleo- to Mesoproterozoic suite of granites that was derived by reworking of pre-existing crust. U–Pb ages of zircon constraints the TTG magmatism to 2544–2496 Ma, while Nd-model ages (3259–3142 Ma) of mafic enclaves within the TTG suggest the presence of Paleoarchean crust in the WBC. Zircon and monazite ages indicate that the emplacement of the Mul granite was synchronous with 1666–1547 Ma regional tectonothermal event. These granites were produced by reworking of older granitoid crust. The Neoarchean TTGs/sanukitoids were affected by 1666–1547 Ma tectonothermal event which constitutes a widely documented Paleo- to Mesoproterozoic orogeny in the Central Indian Tectonic Zone and Bhopalpatnam granulite belt to the south of the WBC. Copper and gold mineralization in the Thanewasna belt along the craton's western margin is linked to this tectono-magmatic event. In the global supercontinent outlook, the WBC preserves the imprints of Neoarchean events related to the Ur supercontinent as well as Paleo-Mesoproterozoic and Neoproterozoic (Grenville-age) events associated with the Columbia and Rodinia supercontinent [ABSTRACT FROM AUTHOR]