Age and genesis of hydrothermal Ni-PGE-Te mineralisation in the Gondpipri mafic-ultramafic complex, central India: constraints from zircon U-Pb geochronology and magnetite-pyrite geochemistry

The Gondpipri layered mafic-ultramafic intrusion at the western margin of the Bastar Craton in Central Indiacomprises leucogabbro, gabbronorite, and websterite. The intrusion hosts both magmatic and hydrothermal Ni-platinum group element (PGE) mineralisation. In this study, we use in-situ measured trace element composition of pyrite and magnetite and zircon U-Pb geochronology to elucidate hydrothermal processes and their timing. Secondary platinum group minerals (PGMs) occur as veins and fracture fillings in sulfide and oxide minerals together with hydrothermal zircon clusters within chlorite alteration. Electron microprobe (EPMA) analysis reveals that magmatic PGMs are enriched in Pt, Pd, and Rh, whereas the hydrothermal PGMs are characterized by higher Fe, S, Te, Bi, and Ni. A semi-metal collector model (Bi-Te) is proposed for PGE in the Heti Ni-PGE prospect, where an immiscible Bi-Te melt exsolves and acts as a collector for formation of primary PGM following precipitation of Pd tellurides, tsumoite, melonite and hessite upon cooling of temperature hydrothermal fluids. Two generations of pyrite (Py-I and Py-II) and magnetite (Mag-I and Mag-II) are identified. Py-I and Py-II exhibit distinctive concentrations of Co, Se, and Au, while Mag-I and Mag-II have variable concentrations of REEs, Cr, Ti, Ga, V, Ba, and Sr. Selenium geothermometry of pyrite indicates that hydrothermal mineralisation occurred within a temperature range of 200 degrees C to 475 degrees C. The Ni-PGM-Bi-Te mineralisation is associated with an unusual cluster of megacrystic zircons, which are likely hydrothermal origin. Uranium-lead (U-Pb) dating of five zircons using LA-ICPMS yields a concordia age of 2524 +/- 7 Ma, interpreted as the age of the hydrothermal sulfide-hosted Ni-Te-Bi-PGE mineralization.