The solubility of palladium and ruthenium in picritic melts: 2. The effect of sulfur

Here we report the results of experiments where the solubilities of Ru and Pd have been measured in natural picritic melt, as a function of pO2 and in the presence of sulfur. Results show that the presence of sulfur in the silicate melt enhances the solubility of Ru in picrite by over an order of magnitude. These results can be used to quantify the preference that PGE have to associate with sulfur relative to oxygen. For example, Ru was found to be 880 ± 410 times more likely to associate with sulfur than with oxygen at pO2 around the fayalite-magnetite-quartz redox equilibrium. The preferential association of the PGE with S2− ligand indicates that once a sulfide melt exsolves, it will already be enriched in PGE precluding the need for it to actively scavenge PGE from a silicate melt.