Orogenic gold mineralization in the Paleoproterozoic collisional belt of Central India

The Paleoproterozoic Mahakoshal belt, located within the Central Indian Tectonic Zone, records prolonged crustal growth, accretion, subduction, and gold metallogeny between ca. 2.1 Ga and 1.6 Ga. This study integrates geology, structure, petrography, fluid inclusions, stable isotopes (C-O-S), and in situ sulfide chemistry to assess the fluid evolution and ore genesis associated with this orogenic gold metallogeny. Mineralization is hosted in quartz-carbonate ± sulfide veins within metasediments that show polyphase deformation (ca. 1.9–1.7 Ga) and related granite magmatism (ca. 1.8–1.7 Ga). Auriferous fluids migrated along NNE-SSW discrete shear zones, precipitating gold as blebs, stringers, and specks within arsenopyrite-scorodite-pyrite assemblages. Gold occurs with sulfides and bismuth, indicating transport as bisulfide complexes [Au(HS)2−] with Bi-rich melt extracting gold from granitic-hydrothermal fluids. Gold fineness (878–998) is consistent with orogenic gold systems. Fluid inclusion studies reveal low- to moderate-salinity (1.8–15.9 wt% NaCl equivalent), aqueous and carbonic fluids, with homogenization temperatures of 175–375 °C. Raman spectroscopy indicates CH4-CO2-N2–rich phases, while arsenopyrite thermometry records 322–397 °C and sulfur fugacity (log fS2) of −10.5 to −6.7. These reflect cooling, fluid-rock interactions, and mixing with meteoric water. Stable isotopic data (δ13C: −3.4‰ to 0.0‰; δ18O: −15‰ to −11‰; δ34S: −2.55‰ to +14.45‰) indicate metasediments and granites as the principal source of the ores, with minor mantle input. Based on a multiproxy investigation, we propose a genetic model linking Au mineralization to subduction-related fluids interacting with carbonaceous wall rocks under reduced fS2, contemporaneous with collision of the North and South Indian blocks along the Central Indian Tectonic Zone at ca. 1.7–1.6 Ga.