Gold extraction or recovery from its ores may require a combination of comminution, mineral processing, hydrometallurgical, and pyrometallurgical processes to be performed on the ore.
Ancient techniques of mining gold
1) placer mining- Gold mining from alluvium ores was once achieved by techniques associated with placer mining such as simple gold panning and sluicing, resulting in direct recovery of small gold nuggets and flakes. Placer mining techniques since the mid to late 20th century have generally only been the practice of artisan miners.
2) Hydraulic mining was used widely in the Californian gold rush, and involved breaking down alluvial deposits with high-pressure jets of water. Hard rock ores have formed the basis of the majority of commercial gold recovery operations since the middle of the 20th century where open pit and or sub-surface mining techniques are used.
Gold occurs principally as a native metal, usually alloyed to a greater or lesser extent with silver (as electrum), or sometimes with mercury (as an amalgam). Native gold can occur as sizeable nuggets, as fine grains or flakes in alluvial deposits, or as grains or microscopic particles embedded in other rocks.
Ores in which gold occurs in chemical composition with other elements are comparatively rare. They include calaverite, sylvanite, nagyagite, petzite and krennerite.
Gold refining and parting
Gold parting is primarily the removing of silver from gold and therefore increasing the purity of gold. The parting of gold from silver has been done since ancient times starting in Lydia in the 6th century BC. Various techniques have been practised; salt cementation from ancient times, parting using distilled mineral acids from medieval times, and in modern times using chlorination using the Miller process and electrolysis using the Wohlwill process.
How was gold extracted?
In the old days it was extracted from mines with pick axes. Gold nuggets were dug from veins of crystal quartz that often included silver, mercury, and lead.
Today most of that ore has been tapped, and new methods are employed. The gold is no longer even visible to the naked eye--it is dust, scattered throughout an ore body in a zone. Strip mined ore is piled on slanted V shaped sheets of plastic where it is sprayed with a solution of cyanide. The cyanide bonds with the gold which settles into a pond. The pond is drained, the rich ore scooped up and further processed to recover the gold.
A profitable ore body may contain as little as 0.02 oz of gold per ton of ore.
I have toured several gold mining operations in northern Nevada, and have staked claims for other mines there.