Platinum-Group Element Distribution in Some Ore Deposits: Results of EPMA and Micro-PIXE Analyses

Abstract.

The distribution of platinum-group elements (PGE) in the Main Sulfide Zone of the Great Dyke of Zimbabwe, in the arsenide ores of Vammala and Kylmäkoski mines in Finland, and in the chromite-Ni arsenide ores from the Ronda and Beni Bousera massifs (Spain and Morocco) has been studied by means of different optical and microanalytical techniques. The results show a bimodal distribution of PGE in the ores from the Great Dyke and the Vammala and Kylmäkoski mines where Pd, Pt and, to lesser extent, Rh occur both as discrete platinum-group minerals and in solid solution in sulfides, arsenides and sulfarsenides. In the ores from Ronda and Beni Bousera, platinum-group elements occur only in solid solution in arsenides and sulfarsenides.

Trace electron probe (EPMA) and micro-PIXE analyses of Pd in sulfides, arsenides and sulfarsenides produce comparable results at concentration levels well above their limit of detection (LOD). These are 27–29 ppm by EMPA and 2.5–7 ppm by micro-PIXE. Whereas trace EPMA on arsenides and sulfarsenides measure Pt concentrations above 33–35 ppm, the proximity of the Pt L lines and the As Kα line severely degrade de detection limit for Pt in micro-PIXE analyses, increasing the LOD up to 440 ppm. The rest of PGE were randomly detected by both methods at concentrations close to their LOD.