The major loss of base metals in beneficiation of the Merensky Reef ore occurs during the separation of the siliceous gangue from the platinum group and base metal sulphides by selective flotation. The paper examines the use of amine complexes in managing inadvertent activation of pyroxene in a pentlandite-pyroxene flotation system at pH 9. Zeta potential, time of flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy data have shown that pyroxene becomes copper activated in the presence of copper sulphate. When xanthate ions are added to the copper activated mineral system, true flotation of pyroxene occurs. Furthermore, the flotation and surface analysis data revealed that pyroxene could also be inadvertently activated by Ni(II) ions, which would result in a higher pyroxene recovery and thus lower selectivity. In the presence of ethylenediamine (EDA) the concentration of copper(II) and nickel(II) ions found on pyroxene and pentlandite surfaces was significantly reduced, although the effect was significantly more predominant on pyroxene. The mechanism for the removal of the activating ions from the mineral surfaces involves the formation of soluble stable metal-EDA chelates, which are removed into solution. (C) 2003 Elsevier Ltd. All rights reserved.