PARTITIONING OF RUTHENIUM, RHODIUM, AND PALLADIUM BETWEEN SPINEL AND SILICATE MELT AND IMPLICATIONS FOR PLATINUM GROUP ELEMENT FRACTIONATION TRENDS

High temperature (1450 and 1300°C), one atmosphere trace element partitioning experiments were made in the CaO-MgO-SiO2-Al2O3 system to investigate the chemical compatibility of Ru, Rh, and Pd in magnesium aluminate spinels coexisting with silicate melts. Spinel/melt partition coefficients indicate that Rh and Ru are highly compatible with values near 90 and 20, respectively. These high partition coefficients contrast sharply with partitioning behavior for Pd under similar conditions. Palladium is rather incompatible with partition coefficients of less than 0.02. Platinum group elements, generally considered a geochemically coherent group, may thus be fractionated with respect to one another when spinel is a magmatic phase. © 1990.