At Northam Platinum Mine in South Africa intense potholing of the Merensky Reef has led to the development of several mineralogically different reef types in proximity to one other, which results in differing processing performance. In particular, the nature and texture of the valuable sulfide minerals, as well as the nature of the gangue minerals and degree of alteration in the various reef types affects both milling throughput and flotation recovery. The three major ore types being processed and thus selected for this study are the Normal reef, NP2 reef and P2 reef. The focus of this study was to investigate the relationship between changes in mineralogy and the effect of copper sulfate addition at two grind sizes on the laboratory batch flotation performance obtained with the three reef types. The best results were obtained with the NP2 reef in terms of expected industrial throughput, recovery and grade of all base-metal sulfides despite this reef type having the lowest feed grade of sulfide minerals. The biggest difference was in the recovery and grade of pyrrhotite. The better performance of the NP2 reef ore relative to the Normal and P2 reefs has been attributed to the equigranular nature of the reef type together with its feldspathic mineralogy. In contrast, the Normal and P2 reefs are orthopyroxene rich and are associated with more alteration minerals. The Normal reef contained the greatest amount of alteration minerals which correlated to the poorest flotation performance in terms of recovery and grade at all conditions tested. Whereas addition of copper sulfate did not affect the flotation of the sulfides in the NP2 reef ore, it significantly improved the overall performance of the base-metal sulfides in the Normal and P2 reefs, especially for pyrrhotite. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.