Rift-induced structurally controlled hydrothermal barite veins in 1.6 Ga granite, Western Bastar Craton, Central India: Constraints from fluid inclusions, REE geochemistry, sulfur and strontium isotopes studies

Abstract

Expressive granitic magmatism and a complex system of fault and shear zones are the main features associated with the crustal evolution and metallogeny in the Western Bastar Craton (WBC), Central India. The barite mineralization in WBC, Central India, occurs as veins and fracture fillings along faults are activated or reactivated as a consequence of rifting of – 1.5–1.6 Ga Pranhita-Godavari (PG) basin. The barite mineralization is hosted in ca. 1.6 Ga Mul granite of WBC. We present the first comprehensive, integrated field and laboratory studies approach using structural mapping, fluid inclusion, Sulfur, and Sr-Isotope geochemistry, mineral, and REE geochemistry to characterize barite mineralization ore-forming processes, a fluid source, and structural control. The host granite is intensely altered with evidence of hydrothermal mineralization in the form of silicification and hematitisation. Both sulfide-free (Brt-I) and sulfide-bearing (Brt-II) barites occur in the study area. Besides, barites with fluorite (Brt-III) were also observed in minor concentrations. The mineralization is associated with quartz-calcite vein, and the barite is accompanied by galena, pyrite, and chalcopyrite. Petrographic observations, fluid inclusion, and isotope data suggest a bimodal evolution of the mother brine viz. the oxidative source forms sulfide-free high-salinity brine and reductive low-salinity sulfide-bearing aqueous fluid formed by interaction with reducing agent causing hydrothermal barite mineralization in the study area. The source for the hydrotherms responsible for the formation of barite and galena in association with the quartz-barite vein is, in all probability, granitic magma. Incompatible elements like Ba, Pb and volatiles like S, preferentially concentrated in late magmatic hydrothermal fluids, got emplaced along the structurally weak zones in the interior of the granite pluton. The combined 87Sr/86Sr and δ34S‰ data suggest mixing fluids from diverse sources, including magmatic, marine, and crustal fluids. Low 87Sr/86Sr (<0.707) and high δ34S(>10‰) are indicative of alteration products of granite that were subsequently mixed with submarine hydrothermal fluid mobilized through the Mesoproterozoic PG rift system. This regional rifting event provided pathways for fluid flow and ore formation along faults/fracture systems (F2 and F3 fault systems) in the host Mul granite of WBC. The F2 fault system, sympathetic to the PG rift, is deep-seated and contains mainly barites of magmatic origin besides the minor marine signature. The F3 cross faults, developed across the gneissic foliation of TTG gneisses and charnockites, can be traced to the PG basin's younger marine sediments, host barites of dominantly marine signature.The Ba ± F mineralization in the study area is a perspective for regional exploration for REE-Ba-F in central India and elsewhere in a similar geological milieu. The epigenetic-submarine hydrothermal vein-type barite mineralization hosted in granite, WBC differs from Sedex, VMS, Carlin, or Orogenic type barite deposits, which has a great deal of replicability and suitability for future exploration targeting.