This study is aimed at explaining the effect of copper activation in flotation systems which contain free gold and gold locked in pyrrhotite and pyrite. Unlike other studies, the effect of the sequence and amount of copper added to the slurry in relation to the xanthate conditioning period is investigated and the results are discussed in terms of how the two gold bearing types respond to true particle-bubble attachment and entrainment during flotation. The results indicate that increasing the dosage of copper sulphate increases the entrainment of refractory gold when the copper is added before the potassium amyl xanthate (PAX), because there is a greater flux of water upwards to the froth, which results in a decrease in the amount of sulphide material that is attached to the air bubbles. When the true flotation of refractory gold decreases, there is also a higher degree of entrainment. True flotation of free gold increases since there is a larger proportion of non-mineralised surface sites on the bubbles where attachment can take place. When copper sulphate is added after the collector the recovery of free gold increases dramatically so that there is an overall increase in total gold recovery of up to 6% compared with the usual sequence of adding the copper first. (C) 2000 Elsevier Science B.V. All rights reserved.