The treatment of a copper sulphide-bearing gold ore by direct cyanide leaching, ammonia pretreatment and ammoniacal cyanide leaching was investigated. Dissolution behaviour of gold and copper in these leaching systems was demonstrated. Severe interference by the copper containing sulphides with cyanide leaching of gold is observed at rho(NaCN)<= 5 g/L. This is consistent with speciation calculations. Ammonia pretreatment is shown to readily eliminate the copper interference, allowing almost complete extraction of gold with concomitantly low reagent consumption in subsequent cyanide leaching. In ammoniacal cyanide system, Box-Behnken experimental design shows the main and interaction effects of NH3, NaCN and Pb(NO3)(2). The concentrations of NH3 and NaCN are statistically confirmed to be significant factors affecting extraction of gold while the effect of Pb(NO3)(2) is limited. Increasing the concentration of NH3 improves the selectivity and extent of gold extraction and reduces the cyanide consumption. The contribution of reagent interactions to gold extraction is statistically insignificant. These findings highlight that ammonia pretreatment and ammonia-cyanide leaching are promising approaches for the treatment of gold ores with high copper sulphide content.