CONTRIBUTION OF SOUTHERN AFRICAN ORE DEPOSITS TO THE GEOCHEMISTRY OF THE PLATINUM GROUP METALS.

A review and classification of South African platinoid-bearing ores leads to a documentation of the main problems of the geochemistry of the platinum group metals. The question of the lattice substitution of base metal cations by the platinum metals is investigated but is not supported. The most preferential collection of the platinoids is found to occur within base metal sulfides, but the siderophile tendency of platinum and the chalcophile behavior of palladiun affect their separation in the sulfide environment of igneous rocks. This noncoherence of the principal platinoid metals constitutes the main theme of this paper. The behavior of the platinoids in the minor exogenic cycle is examined. Some of the main conclusions reached include the fact that palladium suffers depletion during weathering and transport. Refs.