The flotation performance of Hidden Valley primary ore in the presence of 10 ppm free cyanide is also included in Fig. 5. Au recovery of 80.7% was obtained at the end of flotation, which is obviously lower than its recovery in baseline flotation. Ag recovery had a similar dependence on free cyanide with 82.0% at the end of flotation. On the other hand, the addition of cyanide had little influence on the grade of Au and Ag in flotation concentrate, partially related to the decrease of mass recovery to 4.2% in the presence of free cyanide. The Fe and S recoveries were decreased to 5.7% and 4.2%, respectively, indicating a strong depressive effect of free cyanide on the flotation of iron sulphide minerals. It seems that the depression of Au and Ag was associated with the depression of iron sulphide minerals. Around 13% of the Au and 9.3% of the Ag may be depressed by free cyanide as a result of their associations with iron sulphide minerals. It is well known that cyanide has a strong depressive effect on iron sulphide minerals including pyrite, pyhrrotite, and arsenopyrite. The iron sulphide minerals carrying gold and silver were examined by mineralogy analysis in the following section. Furthermore, free cyanide concentrations at 30 ppm and 50 ppm were also tested but the recoveries showed no further decrease. Fig. 5 also shows the grade-recovery plots of flotation concentrate for Hidden Valley primary ore in the presence of 10 ppm cyanide in the form of cuprous cyanide. It is seen that cuprous cyanide species had a similar depression effect on Au, Ag and their bearing iron sulphide minerals as free cyanide, resulting in recoveries of 5.4% Fe, 4.7% S, 81.2% Au and 81.8% Ag at the end of flotation. Meanwhile, similar mass recoveries and concentrate grades of these elements were obtained with free cyanide and cuprous cyanide.