Feasibility Study and Technical Report - Pretivm

Table 13.23Occurrences of Gold in Leach ResiduesGold Distribution (%)Sample IDAu(g/t)Microscopic SubmicroscopicElectrum Pyrite ArsenopyriteGold inOtherMineralsTotalLeach Residue C8 (VOK) 10.4 12.5 72.9 2.1 12.5 100.0Leach Residue C11 (West Zone Footwall) 8.3 21.8 52.1 7.5 18.6 100.0During the 2010 to 2011 test program, cyanidation tests were conducted on the flotationconcentrates using a combination of gravity concentration and flotation concentration.The sodium cyanide concentration used was 3 g/L and the slurry pH was adjusted bylime to 10.5. Figure 13.22 shows the effect of leach retention time on gold extraction. Ata leach retention time of 27 hours, the leaching process extracted between 73 and 86%of the gold and between 73 and 82% of the silver. An increase in the leach retentiontime beyond 72 hours improved the gold and silver recoveries by up to approximately10%.Figure 13.22 Bulk Concentrate Leach Retention Time Test Results (2010 to 2011)During the 2009 to 2010 test work, leach tests were also conducted on head samplesand concentrate samples. The leaching test results on the head samples aresummarized in Table 13.24. The tests were conducted at a pH of 10.5 and a sodiumcyanide concentration of 3 g/L, with three different primary grind sizes.Pretium Resources Inc. 13-34 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC