Partitioning of palladium, iridium, platinum, and gold between sulfide liquid and basalt melt at 1200°C

Abstract

Iron-nickel monosulfide and basalt glass containing trace amounts of PGE equilibrated at 1200°C, and fo 2= 10 −9.2 (close to the wustite-magnetite buffer) and fs 2= 10 −0.9, have been analyzed for noble metals by radiochemical and instrumental neutron activation analysis. The average contents of PGE in coexisting Fe-Ni sulfide and basalt glass, respectively, are Pd, 50 ppm and 0.5 ppb; Ir, 50 ppm and 0.5 ppb; Pt, 100 ppm and 10 ppb; and Au, 0.7 ppm and 0.8 ppb. The sulfide liquid-silicate melt partition coefficients ( D values) for the noble metals are (9 ± 7) × 10 4 for Pd, (1 ± 0.7) × 10 5 for Ir, (9 ± 6) × 10 3for Pt, and (1 ± 0.9) × 10 3 for Au. The noble metals are strongly partitioned into sulfide liquid, but the affinity of Pd and Ir for sulfide liquid is about 50 times greater than that of Pt and about 500 times greater than that of Au. The D values indicate that equilibrium partitioning between immiscible sulfide liquid and basalt magma would result in fractionation of the noble metals, which differs significantly from that generally observed in nature.