Platinum group elements in lamprophyre, picrobasalt, gabbro and basalts of the Phenai Mata and nearby areas: implications for Fe–Ni–Cu–PGE mineralization in the Deccan Large Igneous Province

Abstract

AbstractAmong the basaltic large igneous provinces (LIPs) world over, the Deccan Large Igneous Province (DLIP) is considered barren of metalliferous sulfide deposits, and especially platinum group minerals (PGMs). The tholeiitic basaltic magmas of the DLIP were found to lack sulfur saturation at all stages of its evolution. However, we found some incidences of Fe–Ni–platinum group element (PGE) mineralization in the cumulate gabbros of the Phenai Mata Igneous Complex (PMIC), as well as intrusive dykes of lamprophyre, picrobasalt and basalt in adjoining areas. To examine the metal potential of the gabbros, we adopted the following approach: (a) whole-rock PGE analysis of selected rocks; (b) preconcentration of the samples by communition, sieving and gravity-magnetic separation, followed by froth floatation, Ni-sulfide fire assay and geochemical analysis of the concentrates; and (c) direct scanning of samples using an electron probe microanalyser (EPMA). The geochemical proxies – namely, Pd/Ir, Cu/Ir, Ni/Pd and Ni/Cu – indicate that PMIC has distinct geochemical signatures compared to other parts of the DLIP. The results have further indicated an interesting suite of minerals comprising metal sulfides of Fe–Cu–Zn–Pb–Co–Ni. This metal-rich suite in the otherwise ‘barren’ Deccan Trap tholeiites is a result of accidental fertilization of metals into their sulfides due to the mixing of crustal sulfur.