Application of Geothermal Energy to Mineral Processing: Cyanide Heap-Leaching of Low-Grade Gold Ore

Abstract

The advent of cyanide heap-leaching for low-grade gold and silver ores has resulted in an unprecedented increase in the output of mines throughout the world. This simple and economical process entails open-pit mining, milling, and stacking ore, which is then soaked with a dilute solution of sodium cyanide. The cyanide solution dissolves both gold and silver, which is subsequently recovered by additional processing. Many of these mines are located in remote, inaccessible areas and are subject to severe climatic conditions. Some operations are terminated during extreme cold or rainy seasons. As a result of United States Department of Energy sponsored investigations conducted by the Division of Earth Sciences, University of Nevada, Las Vegas, and the Mackay School of Mines, University of Nevada, Reno, some operating mines in Nevada were found to be co-located with geothermal resources suitable for use in cyanide heap-leaching operations. Low-to moderate-temperature geothermal resources may be used to heat the cyanide circuit, providing a low-cost method of maintaining the operation during freezing conditions. This paper describes the results of bench-scale heap-leaching experiments using a simulated geothermal source to increase metal dissolution rate. In addition, examples from two active mines that utilize geothermal energy in commercial-scale operations are included. The implications for co-development of gold and geothermal resources in Central America are discussed.