Improvement of cyanidation practice at Goldcorp Red Lake Mine

Abstract

Goldcorp Red Lake Mine processes a mildly refractory high grade gold ore with 77.8 g/t Au and 1.9% arsenopyrite, 1.7% pyrite and 0.2% pyrrhotite at a grind of 77% −37 microns. A cyanidation study was conducted to determine the necessary retention time of the leach circuit and the optimal gold extraction and cyanide consumption. Results have shown that the gold leaching kinetics could be significantly improved by the addition 100–200 g/t lead nitrate directly in the grinding circuit, followed by a 6 h cyanidation. A 1 month trial indicated a throughput of 810 tpd can be sustained without detrimental effect on gold extraction. However, the mill is currently limited by the underground operation to a throughput ranging from 650 to 700 tpd for a 55 h retention time. In the event of future throughput increase over 810 tpd value, lead nitrate could become an essential part of the leaching efficiency. The experimental work indicated a gold extraction at 87.1–87.4% (tailings ∼9.8 g/t Au) which is similar to plant performance. The associated cyanide consumption was 0.7 kg/t. Gold dissolution can efficiently be conducted at an average cyanide concentration of 400 ppm. Previous control of cyanide concentration in the plant was 700 ppm in the first leach tank to 350 ppm NaCN at the end. Testwork realised in the mill allowed a 32% cyanide reduction predicted by the on-site cyanidation study. The new cyanide concentration is ranging between 500 ppm in the first leach tank and 300 ppm NaCN at the end of the leaching circuit. The cyanide consumption of the plant was reduced from 1.0 to 0.68 kg/t with reduction of effluent treatment costs. Grinding finer (91% −37 microns) slightly increased the gold extraction (tailings lower by 0.4 g/t) but lowers the leaching kinetics, increases cyanide consumption (35%) and the arsenic dissolution.