Platinum-group minerals of concentrates from the Driekop platinum pipe, Eastern Bushveld Complex - Tribute to Eugen F. Stumpfl

Platinum-group mineral concentrates originating from the Driekop platinum mine, South Africa, collected and first described by E. F. STUMPFL (1961), were investigated. Driekop is one of several zoned dunite pipes crosscutting the layered mafic and ultramafic sequence of the Eastern Bushveld Complex. Three similar pipes were locally extraordinarily rich in platinum, with Pt/Pd of 80, and were the first to be mined for PGE in the Bushveld Complex. The concentrates from Driekop contain single and polyphase grains, 5 to 500 mu m in size, with dominant geversite-insizwaite, sperrylite, Pt-Fe alloy, and minor Rh-Ir-Pt-Ru sulpharsenides, stibiopalladinite, moncheite, ruthenium, osmium, and laurite. "Exotic" minerals comprise Pt-Pd-Bi-Sb phases, namely stumpflite, unnamed (Pt, Pd)(Sb, Bi), unnamed (Pt, CU)(3)(Sb, Bi, Sn)(4), genkinite, sobolevskite, as well as unnamed Cu-Pt compound, unnamed [RhSbS], unnamed [Pd2CuSb], cherepanovite, Sn-bearing phases of the rustenburgite-atokite and tatyanaite-taimyrite solid solution series, and Pt-Pd-Bi-Fe oxides. The most common mineral association in polyphase grains comprises ferroan platinum-geversite-stibiopalladinite-rustenburgite stumpflite, (Pt, Pd)(Bi, Sb) or genkinite. Textures are indicative of exsolution from a high-temperature Pt-rich, and S-poor phase which experienced complex sub-solidus reactions, probably aided by metasomatic reactions involving hydrothermal fluids. Such reactions produced complex Pt-Pd-Sb-Bi-Te-Sn assemblages at temperatures in the hydrothermal range. These observations confirm the interpretation of RUDASHVESKY et al. (1992) for the Onverwacht and Mooihoek pipes: a high-temperature magmatic assemblage of metal alloys (ferroan platinum), associated with olivine, is replaced and overprinted by low-temperature assemblages associated with secondary silicates such as amphibole, carrying sperrylite, stibiopalladinite and PGE sulpharsenides.