Kupol mill leach operation in 2008-09

CIM Journal, Vol. 2, No. 2, 2011

J. Rajala, G. Deschênes, A. Romanov and G. Kolosay

The Kupol project, located in Far East Russia, treats a high-grade, free-milling ore containing 25.5 g/t Au, 298.3 g/t Ag, and 0.5% pyrite, with a P70 of 53 microns. Most of the gold occurs as electrum and the silver is predominantly present in the forms of acanthite, stephanite, pyrargyrite, and proustite. The mill reached the design throughput of 3,000 tpd six months after start-up. A Knelson concentrator recovers 10.4% gold and 0.5% silver. Leaching (14.5 hours pre-treatment and 116 hours cyanidation) of gravity tailings is performed with the CANMET Enhanced Leach Process (CELP), using only 490 ppm NaCN (cyanide consumption of 1.1 kg/t). The precious metals are recovered by countercurrent decantation and the Merrill-Crowe process. Calcium hypochlorite destroys cyanide and thiocyanate. Overall, gold and silver recoveries for 2008 were 95.4% and 85.6%, respectively (2.8% and 7.5% higher than targets). In the first eight months of 2009, gold and silver recoveries were 95.0% and 82.6%, respectively. By August 2009, the mill processed 1.42 million tons of ore with production of 1.1 million ounces of gold and 11.3 million ounces of silver. CELP performance was not affected by changes in feed grade and ore mineralogy. Additional modifications to the leaching strategy allowed further reduction in cyanide consumption and effluent treatment costs.

Keywords: Gold, Silver, Sulphide, Minerals, Cyanide, Kupol, Leaching