Heap leaching of gold was pioneered in the United States in 1973 at Placer Development's Cortez open pit in Nevada and proved on a larger scale at Pegasus Gold's Zortman Landusky mine in Montana.
Although it is low cost, recovery rates average only sixty to seventy per cent, significantly less than with conventional milling.
But it has enabled low-grade ores, which otherwise might not be economically viable, to be processed. In the United States, where heap leaching is used most extensively, half of all production is won by this method. See also Biological Leaching.
In Peru, Barrick gold has its largest gold mine....Pierina...which produced nearly 650,000 oz in 2005.
It uses heap leach on low-grade ore with about 1 gm/ton of gold.
Its cash cost are $138 per oz..very cheap indeed.
Heap leaching has certain limitations, such as water use, but it is now used for most low grade sulphides.
In CMM's Golden Chapune Peru project, which has up to 18 million oz of gold, heap leaching should be able to recover about 2/3 of the gold resources in place.
Note that the sampled grades are in the 1.5 to 3 gm /ton range..much more than that at Pierina.
In theory, therefore, at the average grade of 2.25 gms/ton, Chapune would hold about 13 million oz of gold, of which about 9 million oz would be recoverable by heap leaching.
In other words, a 500,000 oz per year mine, with a mine life of about 16 years, at a cash cost below $200 /oz.
That is a tremendous resource,and may be Peggy's short and cheap route to making CMM a 1 million oz gold producer within 2-3 years.
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