Milli-PIXE determination of trace elements in osmium-rich platinum-group minerals from the Witwatersrand basin, South Africa

Osmium-rich platinum-group minerals (PGM), like osmiridium or native osmium , are an integral, though rare, part of the mineralogy of the Witwatersrand paleoplacer. Usually these grains are small, on average <100 mu m in size, and the characteristics of their source areas are unknown. In the mineralog ical literature on these PCM in the Witwatersrand gold reefs, no informatio n on the trace elements in these minerals is available. The milli-PIXE syst em at the van de Graaff accelerator at the Atomic Energy Corporation of Sou th Africa was used in a first attempt to determine a range of minor and tra ce elements, such as Co, Cu, Fe, Rh and Ru, in PGM from the Witwatersrand b asin. This attempt is directed towards fingerprinting individual grains and to obtain possible information on the sources for these grains. It also se rves as a first step towards a database of trace elements, which could allo w a genetical classification of Os-rich PGM of unknown provenance. (C) 1999 Elsevier Science B.V. All rights reserved.