PARTITIONING OF PLATINUM-GROUP ELEMENTS (OS, IR, RU, PT, PD) AND GOLDBETWEEN SULFIDE LIQUID AND BASALT MELT

New measurements on partitioning of platinum-group elements (PGE) Os, Ir, Ru, Pt, Pd, and Au between (Fe,Ni)-sulfide Liquid and basaltic mel t using low pressure, sealed silica glass tube, and controlled atmosph ere methods at 1200-1250 degrees C show an extremely wide variation, w hich spans much of the range reported in the literature. In spite of t heir geochemical coherence in natural high-temperature assemblages, PG E-Au apparently behave as seven different metals in individual laborat ory experiments with silicate melts. Sulfide/silicate partition coeffi cients, D, generally increase with run time, in a manner consistent wi th either serial change in chemical state of the metals in the silicat e melt or passivation of alloy phases. Ruthenium is the only metal pre sently investigated that exhibits reversible behaviour. Summary partit ion coefficients for the lowest PCE contents investigated under reduci ng conditions and low Ni contents remain unchanged, except for the add ition of a value of (4.4 +/- 2.4) x id for Ru. Absence of interference from the nugget effect and homogeneity and equilibration of silicate melt in the earlier experiments is demonstrated by new measurements on Ir in different grain-size fractions of glass. An additional set of p artition coefficients for 37 mol% NiS and 100-1000 ppm PGE in the sulf ide is: D(Os)= (30 +/- 6) x 10(3), D(Ir) = (26 +/- 11) x 10(3), D(Ru)= (6.4 +/- 2.1) x 10(3), D(Pt) = (10 +/- 4) x 10(3), and D(Pd) = (17 +/ - 7) x 10(3).