63 Maarten A. T. M. Broekmans (ed.), Proceedings of the 10th International Congress for Applied Mineralogy (ICAM), DOI: 10.1007/978-3-642-27682-8_9, Ó Springer-Verlag Berlin Heidelberg 2012 EFFECT OF ALTERATION ON THE MINERALOGY AND FLOTATION PERFORMANCE OF PPM PLATINUM ORE Megan Becker 1* , Mpho Ramonotsi 1,2 , Jochen Petersen 1 1 Department of Chemical Engineering, University of Cape Town, Private Bag, Rondebosch, 7701 Cape Town, South Africa. 2 Boynton Investments, Private Bag X11, 0067 Highveld, South Africa. Abstract The 2.05-Ga Bushveld Complex in South Africa, host to many lucrative ore deposits (e.g. platinum group elements (PGE)), is surprisingly pristine and unaltered, given its geological age. In some areas, however, there is evidence of low-temperature weathering and alteration, most commonly observed when the ore is near the surface. The Pilanesburg Platinum Mines (PPM) operation in South Africa treats ore from an open pit and routinely suffers from low and erratic PGE flotation recoveries. This article investigates the effect of low-temperature alteration on the mineralogy and flotation performance of the PPM “silicate reef” ore. Bulk density measurements of the various lithologies show a clear decrease in density with decreasing depth, and similarly, a decrease in PGE flotation recovery. Various factors from the mineralogical investigation show supporting evidence that loss of platinum group minerals (PGM) recovery is due to low-temperature alteration. Several recovery improvement strategies are also investigated. Keywords: PGM, alteration, oxidation, liberation, flotation 1 INTRODUCTION Precious metals are known to have superb physicochemical properties such as their high conductivity, catalytic activity and corrosion resistance. South Africa is currently one of the world leaders in the production of the platinum group elements (PGE) which are sourced entirely from the Bushveld Igneous Complex. The Merensky Reef is one of the principal ores in the Complex that is mined for the PGE. The Merensky Reef is a “texturally heterogeneous pegmatoidal feldspathic pyroxenite”, bounded by thin chromitite layers [1]. The base metal sulphide (BMS) assemblage primarily consists of pyrrhotite, pentlandite and chalcopyrite that occur interstitial to the silicates. The valuable platinum group minerals (PGM) show a strong association with the BMS, often occurring along BMS grain boundaries, included in the BMS, or hosted as solid solution PGE. The Pilanesburg Platinum Mines (PPM) project is located on the western limb of the Bushveld Complex, just west of the Pilanesburg Alkaline Igneous Complex where rocks from the Critical Zone outcrop on the Tuschenkomst Farm [2]. At PPM, PGE mineralisation occurs within the Merensky Reef, the Merensky footwall, Upper Pseudo Reef, Pseudo Harzburgite Reef, the Lower Pseudo Reef and the UG2 Chromitite (Figure 1). The Pseudo Reef is a distinctive feldspathic harzburgite layer containing PGE mineralisation, also bounded by thin chromitite layers, and normally situated ~15 m below the Merensky Reef. * Correspondence to: megan.becker@uct.ac.za