Natural polycomponent solid solutions of the Ru-Os-Ir-Pt-Fe system from the eastern Witwatersrand (South Africa)

This study presents compositional features of platinum-group element mineralization derived from the Late Archaean placers in the eastern part of the Witwatersrand basin. The significant presence of platinum-group minerals, formed by polycomponent solid-solution series in the system Ru-Os-Ir-Pt(+/- Fe), was determined using an electron microprobe analysis. Compositional data indicate that the source for polycomponent solid solutions of the Ru-Os-Ir-Pt-Fe system was the Archaean mantle of the Earth, slightly differentiated with respect to platinum-group elements.