|Leaching by sodium cyanide is the modern way of gold processing during which the tiniest particles are caught forming water-soluble cyanides. Zinc powder is used for obtaining gold from the water solution:|
2Na[Au(CN)2] + Zn = Na[Zn(CN)4] + 2Au.
Leach may be used gold extraction from abandoned mining stock piles, making actually a new deposit. The method of gold mining, the underground leaching is also potentially productive: cyanide solution is pumped into drill holes; the gold is absorbed into rock pores, after which the solution is pumped out from the hole with gold and other metals forming stable cyanide complexes.
Copper, lead-zinc or uranium mining byproducts are another, rather poor source of gold. Large copper mines, often recover considerable amounts of gold along with other metals, like complex metal ores which contain small amounts of gold. Such ores processing includes gold extraction when it is profitable.