|Economic gold extraction can be achieved from ore grades as little as 0.5g/1000kg (0.5 parts per million, ppm) on average
in large easily mined deposits. Typical ore grades in open-pit mines are 1-5 g/1000 kg (1-5 ppm), ore grades in underground
or hard rock mines are usually at least 3 g/1000 kg (3 ppm) on average. Since ore grades of 30g/1000kg (30 ppm) are usually
needed before gold is visible to the naked eye, in most gold mines the gold is invisible.
|Since the 1880s, South Africa has been the source for a large proportion of the world's gold supply. Production in 1970 accounted for 79% of the world
supply, producing about 1,000 tonnes. However, production in 2005 was just 294 tonnes according to the British Geological
Survey. This sharp decline was due to the increasing difficulty of extraction and changing economic factors affecting the
industry in South Africa.
|The city of Johannesburg was built atop the world's greatest gold finds. Gold fields in the Free State and Gauteng provinces
are deep and require the world's deepest mines. The Second Boer War of 1899-1901 between the British Empire and the Afrikaner
Boers was at least partly over the rights of miners and possession of the gold wealth in South Africa.
|Other major producers are United States, Australia, China and Peru. Mines in South Dakota and Nevada supply two-thirds of gold used in the United States. In South America, the controversial project Pascua Lama aims at exploitation of rich fields in the high mountains of Atacama
Desert, at the border between Chile and Argentina. Today about one-quarter of the world gold output is estimated to originate from artisanal or small scale mining.
|After initial production, gold is often subsequently refined industrially by the Wohlwill process or the Miller process. Other
methods of assaying and purifying smaller amounts of gold include parting and inquartation as well as cuppelation, or refining
methods based on the dissolution of gold in aqua regia.
|The world's oceans hold a vast amount of gold, but in very low concentrations (perhaps 1-2 parts per billion). A number of
people have claimed to be able to economically recover gold from sea water, but so far they have all been either mistaken
or crooks. Reverend Prescott Jernegan ran a gold-from seawater swindle in America in the 1890s. A British fraud ran the same
scam in England in the early 1900s.
|Fritz Haber (the German inventor of the Haber process) attempted commercial extraction of gold from sea water in an effort
to help pay Germany's reparations following the First World War. Unfortunately, his assessment of the concentration of gold in sea water was unduly
high, probably due to sample contamination. The effort produced little gold and cost the German government far more than the
commercial value of the gold recovered. No commercially viable mechanism for performing gold extraction from sea water has
yet been identified. Gold synthesis is not economically viable and is unlikely to become so in the foreseeable future.
|The average gold mining and extraction costs are $238 per troy ounce but these can vary widely depending on mining type and
ore quality. In 2001, global mine production amounted to 2,604 tonnes, or 67% of total gold demand in that year. At the end
of 2001, it was estimated that all the gold ever mined totalled 145,000 tonnes.