A process mineralogical investigation of platinum group minerals from the UG2 Reef facies types at Booysendal South mine, South Africa: A comparative study

Abstract

The milling and flotation performance of ore at Northam Platinum’s Booysendal South mine, situated on the eastern limb of the Bushveld Complex, was investigated with particular emphasis on the recovery of platinum group elements (PGEs) from the geologically complex Upper Group 2 (UG2) Reef. Two reef morphologies are distinguished within the mine lease area. The first morphology comprises a relatively coherent chromitite package, where the Leader chromitite (UL) conformably overlies the Main Member chromitite (UM), or where the two chromitite units are bifurcated by a thin internal pyroxenite parting not exceeding 0.5 m in thickness. In contrast, the second morphology is characterised by pronounced internal waste development, in which the UL, the UM, or both chromitite layers are bifurcated by single or multiple pyroxenite units, with cumulative pyroxenite thicknesses reaching up to 10 m. This lithological variability delineates two principal facies types: the ‘normal’ UG2 Reef and the UG2 split reef facies, furthermore, eight theoretical mine resource-cuts were identified and altogether represent the facies types defined.

Drill core samples were used to characterise the ore which included petrographic analysis, assay data, and bench-scale milling and flotation tests. Laboratory rougher flotation results demonstrate that the ‘normal’ UG2 Reef facies (e.g., N_full cut) display superior metallurgical performance, characterised by higher PGE head grades, enhanced PGE recovery, and higher enrichment ratios. In contrast, selected UG2 split reef facies (SR_UMC2, SR_UMC3, and SR_full cut) exhibit markedly poorer flotation performance. This behaviour reflects a combination of factors such as high proportions of naturally floating gangue (NFG), increased water recoveries resulting in reduced drainage and froth stability, and intricate mineral associations. The main influence imposing poor metallurgical performance is the internal waste pyroxenite between chromitite units.