Phase Relationships and Distribution of S, Fe, Co, Ni, Re, Os, and Pt between Metal and Sulfide Melts in the Basalt–Fe–FeS–C System at 1400°C and 4 GPa

Abstract

The immiscibility of a Fe–FeS–C melt into Fe-metal (Mc) and Fe-sulfide (Ms) liquids has been studied in the basalt–Fe–FeS–C system at 4 GPa and 1400°C. The partition (D) and distribution (Kd) coefficients of S, Fe, Co, Ni, Re, Os, and Pt between the Mc and Ms melts are determined. The partition coefficients D served as indicators of the siderophilic and chalcophilic properties of each element, and Kd characterized their interelemental ratios during fractionation. In the Fe–Os–Co–Re series with D > 1, siderophilic properties prevail, which increase with increasing values of the partition coefficients: 1.2–1.5–1.6–12.6. In the Ni–Pt–S series with D < 1, chalcophilic properties prevail, which increase with decreasing D: 0.9–0.6–0.1. The values of the distribution coefficients Kd Re/Os (8.4) and Pt/Os (0.4) indicate the fractionation of Re and Pt relative to Os, with enrichment of rhenium in a metallic melt and platinum in a sulfide melt and a shift in the fractionation of the Re/Os and Pt/Os relations and related systems of ¹⁸⁷Re/¹⁸⁷Os and ¹⁹⁰Pt/¹⁸⁶Os isotopes. The genetic relationship of magmatic sulfide mineralization in intrusive of the Upper Norilsk (ore-bearing) and Lower Norilsk (ore-free) types with metal–sulfide immiscibility of sulfide magma is evidenced by the similarity of the Re/Os ratio in the Upper Norilsk intrusive with the ratio in the Ms component, and in the Lower Norilsk intrusive with the Mc component.