Refractory gold/copper sulfide concentrates from an active mine in the US were leached by PressureOxidation (POX) using different conditions. The POX residues containing gold and small amounts ofresidual copper were assessed for gold extraction. The gold contents of two residues nominated asSample 1 and 2 were 2.96 g/t and 1.76 g/t, respectively. XRD analysis showed the main mineral phasesin Sample 1 were 41.0 % hematite and 25.2 % iron sulfate, while in Sample 2 hematite accounted for69.6 % and there was no iron sulfate. Gold deportment analysis showed 32 % and 24 % free goldpresented in Samples 1 and 2 respectively with the remaining gold sub-microscopic gold. Hematiteand iron sulfates were the dominant carriers of the sub-microscopic gold in Sample 1 and hematitein Sample 2.Gold extraction from the POX residues was assessed using sodium cyanide and alternative lixiviantthiosulfate. Cyanidation was carried out using 100 mg/L, 250 mg/L, and 500 mg/L NaCN and thegold extraction was gradually increased from 35 % up to 99 %. Cyanide consumption ranged from0.29 kg/t to 2.19 kg/t while lime consumption varied from 5.98 to 197.4 kg/t, which was directly relatedto the iron sulfate content. Three thiosulfate salts (Na-, (NH4)-, and Ca-) were tested to investigate thegold leaching with sodium hydroxide, ammonium hydroxide, and calcium hydroxide as pH controlreagents. Leaching result using (NH4)2S2O3 was comparable to cyanide due in part to the dissolutionof copper present in ammoniacal thiosulfate solution forming a cupric-amine complex. Na2S2O3 andCaS2O3 were weaker lixiviants for the POX residues in this study.
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