The extraction of gold from its ores becomes economically viable when the concentration of the metal is greater than 0.5 ppm (0.5 grams per ton); in large open pit mines the typical concentration is between 1 and 5 ppm; for minerals excavated in underground mines, the average concentration is about 3 ppm.
To be visible to the naked eye, gold in one of its minerals must have a concentration of about 30 ppm; this explains why even in gold mines it is rare to see it. Gold is extracted from alluvial deposits by run-off and from rock minerals by extractive metallurgy.
Metal refining is often accompanied by chlorination or electrolysis. Since 1880, South Africa has been the source of about two-thirds of the gold mined in the world. The city of Johannesburg was built on top of one of the largest oil fields in the world.
The deposits in the South African states of Orange and the Transvaal are among the deepest mines in the world. The Boer War of 1899-1901 between the Boers and the British was partly due to exploitation rights and litigation over South African mine ownership.
Gold as an asset: where it is mostly mined on the planet
However, since 2007, South Africa's leading position has been surpassed by China, whose production in 2008 reached up to 260 tons of gold, an increase of 59% since 2001.
Other major producers include the United States, mainly in Alaska, South Dakota and Nevada; Australia, mainly in the state of Western Australia; Peru and Russia. Unaffected by most chemical compounds, it practically reacts only with aqua regia and cyanide ion.
With mercury it forms an amalgam, but not a chemical compound. It is found in its native state in the form of nuggets, grains and flakes in rocks and alluvial deposits. It has been used since ancient times to mint coins and, before the advent of fiat money, it was used as a countervalue for the currency issues of the States, as was the case within the so-called gold standard.
It is also used in jewellery, dentistry and in the electronics industry. Its ISO code as currency is XAU, equivalent to an ounce of metal. Over time, gold has become the symbol of purity, value and loyalty.
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