heap leaching

Heap leaching means leaching ores that have been mined, crushed, and transported on impervious pads for leaching by sprinkling and percolation of the solution through the ore. Barrick's Pierina Mine in Peru uses heap leaching to extract gold. Pierina is expected to produce more than 800,000 ounces of gold at a total cash cost of less than $50 per ounce in 1999, making it the world's lowest-cost major gold mine.


The facilities consist of a valley-fill heap leach pad and a conventional Merrill-Crowe gold and silver recovery plant. The ore is stacked in a lined containment area behind a retention dam. A leach solution is applied to the top of the ore and allowed to percolate through the heap. As the solution migrates through the ore, it leaches the gold and silver from the rock and holds it in a solution. The gold-bearing solution ("pregnant solution") is collected at the base of the leach pad in the pore space within the heap. The pregnant solution is pumped to the gold recovery plant where suspended solids are removed and the solution is then treated in a conventional Merrill-Crowe precious metal circuit. The same valley-fill system was successfully used at Barrick's Mercur Mine in Utah.