Pt-Pd MINERALS FROM THE UPPER ZONE OF THE EASTERN BUSHVELD COMPLEX, SOUTH AFRICA

Although the upper zone of the eastern Bushveld Complex is generally known to contain concentrations of the platinum-group elements only in the low-ppb range, samples from a sulfide-enriched anorthosite in the footwall of lower magnetite layer 2 were found to contain several platinum-g1oup minerals (PCM. Detailed rnicroscopic and microprobe analyses revealed the presence of the Pt-PdBi-Te minerals michenerite, moncheite, merenskyite and froodite, as weu as a little sperrylite, In all Pt-Pd-Bi-Te minerals, 1:l subslitution between Pt and Pd, as well as between Te and Bi, confirms the well-documented partial solid-solution series between merensklte and michenerite, between moncheite and insizwaite, and the complete solidsolution series between moncheite and merenskyite. The textural association of the PGM with silicates rather than sulfides, the lateral restriction of the mineralization to a few meters. and the extensive alteration of silicates, sulfides and titaniferous magnetite in some samples are interpreted as evidence for the formation of the PGM ftom hydrothermal fluids. The upper and lower limits in temperature for these fluids, as derived from the stabilities of michenerite and plagioclase, are in the order of 490o and 400oC, respectively.