In this paper, the influence of the oxidation state of pyrite and arsenopyrite on the flotation of an auriferous sulphide ore was investigated by different techniques. including electrode, pulp potentials. DRIFT spectroscopy and microflotation tests. In addition. the gold and sulphide recoveries were also investigate. in a laboratory-scale cell, as a function of pulp potential and reagent concentration. It was verified that the presence of oxidation products on the sulphide mineral surface demands a higher collector concentration in order to achieve a satisfactory sulphide recovery. The electrochemical behaviour of pyrite and arsenopyrite indicated that a nitrogen atmosphere can lead to a low pulp potential. which inhibits the formation of oxidation products, enhancing both the free gold and sulphide recoveries. Although copper sulphate activates even oxidised sulphide surfaces. it does not improve free gold recovery. (C) 2002 Elsevier Science Ltd. All rights reserved.