Microprobe measurements of PGM, pristine and secondary phases of samples of the Merensky Reef, Bushveld Complex, South Africa

Platinum-group elements (PGE) in the Bushveld Complex (South Africa) are mainly recovered from pristine, unweathered ores of the Merensky Reef, UG-2, and the Platreef. Weathered PGE ores are currently not mined due to uneconomic recovery rates achieved by conventional metallurgical methods although weathered ores can contain a high PGE content. In order to understand the behavior of PGE during weathering, five drill cores containing fresh and weathered Merensky Reef (originating from the Twickenham and Richmond properties of AngloPlatinum in the eastern Bushveld Complex), were studied by microprobe. Polished thick section of the samples with high PGE content was created and then analyzed after microscopic evaluation of the most promising section (with a high platinum-group mineral (PGM) content) In the pristine ores, the PGM occur dominantly as sulfides, arsenides, and tellurides. They are mainly found in contact or close to base metal sulfides (BMS). In the oxidized ores, discrete, relict PGM are rare, indicating remobilization of the PGE during weathering. Microprobe data reveal traces of PGE within secondary minerals (e.g. Fe-hydroxides, chlorites etc.).