The cyanide process, or cyanidation (MacArthur-Forrest Process), discovered in 1887, is the method in which copper, silver, and gold are extracted from their ores. (…) Basic procedures are as follows for the extraction of gold:
1. Contacting the finely ground ore with a dilute solution of sodium (or potassium) cyanide in the presence of atmospheric oxygen causes the dissolution of gold, along with the production of sodium cyanoaurite and sodium hydroxide, otherwise known as the Elsner Reaction:
Vat leaching (when more than 20g of gold per ton is present): The ore and solvent are put in large tanks for hours to dissolve the gold.
Heap leaching (for low-grade ores): Solutions of sodium cyanide are sprayed to dissolve the gold.
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Gold cyanidation (also known as the cyanide process or the MacArthur-Forrest process) is a metallurgical technique for extracting gold from low-grade ore by converting the gold to water soluble aurocyanide metallic complex ions. It is the most commonly used process for gold extraction
http://en.wikipedia.org/wiki/Cyanide_process