Solubility of palladium in picritic melts: 1. The effect of iron

In order to improve our understanding of HSE geochemistry, we evaluate the effect of Fe on the solubility of Pd in silicate melts. To date, experimentally determined Pd solubilities in silicate melt are only available for Fe-free anorthite-diopside eutectic compositions. Here we report experiments to study the solubility of Pd in a natural picritic melt as a function of pO2 at 1300 °C in a one atm furnace. Palladium concentrations in the run products were determined by laser-ablation-ICP-MS. Palladium increases from 1.07 ± 0.26 ppm at FMQ-2, to 306 ± 19 ppm at FMQ+6.6. At a relative pO2 of FMQ the slope in log Pd concentration vs. log pO2 space increases considerably, and Pd concentrations are elevated over those established for AnDi melt compositions. In the same pO2 range, ferric iron significantly increases relative to ferrous iron. Furthermore, at constant pO2 (FMQ+0.5) Pd concentrations significantly increase with increasing XFeO-total in the melt. Therefore, we consider ferric Fe to promote the formation of Pd2+ enhancing the solubility of Pd in the picrite melt significantly.The presence of FeO in the silicate melt has proven to be an important melt compositional parameter, and should be included and systematically investigated in future experimental studies, since most natural compositions have substantial FeO contents.