PGE Distribution and Mineralogy in the LG-6 and Middle Group Chromitite Layers, Thaba Mine, Bushveld Complex

Here we present information about concentrations, distribution and mineralogy of platinum group elements (PGE) in the sequence of chromitite layers from LG-6 to MG-4 at the Thaba mine in the north-western sector of the Bushveld Complex in South Africa. The information is based on assay analyses of drill core samples and studies of platinum group minerals and base-metal sulfides by mineral liberation analysis. Total concentrations of PGE gradually increase with the stratigraphic height from the LG-6 layer to MG-4. Detailed sampling of the LG-6, LG-6A, MG-1 and MG-2 layers revealed uneven vertical distribution of PGE with the highest concentrations at the footwall contacts. Pt-Pd ratios vary broadly from one layer to another and tend to increase from top to bottom within the individual layers. The assemblage of platinum group minerals in the LG-6 and LG-6A layers comprises equal proportions of (Pt,Pd)S, malanite and laurite, and minor amounts of Fe-Sn alloys sperrylite. PGE tellurides and bismuthotellurides are largely absent. In contrast, the PGE mineralogy of the MG-1 and MG-2 layers is dominated by laurite.