An exceptionally preserved Precambrian magmatic-to-epithermal pathway in the Bastar Craton, central India

Well-preserved epithermal Cu-Zn-Au mineralization is rare in the Precambrian. The NW-trending Mesoproterozoic Minjhari-Bamhani deposit in the Bastar Craton in central India represents the first documented example of a vertically zoned porphyry-linked epithermal system in the Indian Shield. The Minjhari-Bamhani deposit transitions from a porphyry-proximal system at Minjhari to an intermediate-sulfidation (IS) system at Bamhani-Denwari. The Minjhari sector exhibits phyllic alteration (quartz-sericite) associated with quartz veins and breccias that host pyrite, chalcopyrite, tennantite, and gold. Fluid inclusion data indicate boiling of high-salinity (up to 33 wt% NaCl equivalent), CO2-CH4-bearing magmatic-hydrothermal fluids at temperatures up to 315 °C. The adjacent Bamhani area displays classic IS textures such as colloform banding and comb quartz, together with significant Zn-Pb enrichment, likely precipitated from low-temperature (as low as 125 °C) and moderately saline fluids resulting from mixing of magmatic and meteoric waters. Sulfur isotope values from both regions (δ34S: −2.57‰ to +4.14‰ Vienna Canyon Diablo Troilite) are consistent with a dominant magmatic sulfur source, with minor crustal input observed in the distal regions. Downhole increases in copper grades, spatially and genetically linked to potassic alteration (K-feldspar–biotite–chalcopyrite), point to a deeper, concealed copper-rich source at Minjhari. The Minjhari-Bamhani system exemplifies a preserved Mesoproterozoic magmatic-hydrothermal continuum, highlighting significant exploration potential for concealed, deep-seated porphyry Cu-Au roots and structurally controlled epithermal base-metal (Pb-Zn) mineralization within the Bastar Craton.