The PGE contents of chromite separated from peridotite layers of Archaean maficultramafic flows, Abitibi belt (Canada), indicate enrichment in Os-Ir-Ru (600 ppb) relative to Pd-Au (<5 ppb). Evidently, chromite was a sink for Ir-Os-Ru during melt-chromite fractionation in each of the flows. However, an additional phase, probably olivine, is required to explain the bulk Ir content of the sulphide-poor peridotites. In contrast, the chromite Pt contents range from <10 ppb to 400 ppb, with large variation in Pt/Ru (0.02-2.76) and Pt/Pd (5-400) ratios. The Pt enrichment may be related to the presence of Pt spinel structure compounds in oxidised melt, reflecting Fe-Ti spinel-related mineralisation in higher pyroxenite-gabbro layers.
Stone, B., & Crocket, J. H. (2003). Platinum-group element contents of chromites from mafic-ultramafic layered flows, Abitibi greenstone belt, Ontario: implications for geochemical fractionation and mineral exploration. Mineralogy and Petrology, 78, 139-147. https://doi.org/10.1007/s00710-003-0231-x