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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.〔 〕 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. 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. Once the ore is mined it can be treated as a whole ore using a dump leaching or heap leaching processes. This is typical of low-grade, oxide deposits. Normally, the ore is crushed and agglomerated prior to heap leaching. High grade ores and ores resistant to cyanide leaching at coarse particle sizes, require further processing in order to recover the gold values. The processing techniques can include grinding, concentration, roasting, and pressure oxidation prior to cyanidation. ==History== The smelting of gold began sometime around 6000 - 3000 BC.〔Gold Field Mineral Services (GFMS)-(goldavenue.com) & I Podleska and T Green - (goldavenue ) Retrieved 2012-07-01〕〔Carnegie Mellon University Dept. of Material Science and Engineering - () Retrieved 2012-07-01〕〔G Leick - (Historical Dictionary of Mesopotamia ) Scarecrow Press, 16 Dec 2009 Retrieved 2012-07-01 ISBN 0810863243〕 According to one source the technique began to be in use in Mesopotamia or Syria.〔R.J. Forbes - (Studies in Ancient Technology, Volume 1 ) Brill Archive, 1993 Retrieved 2012-07-01〕 In ancient Greece, Heraclitus wrote on the subject.〔M Y Treister - (The Role of Metals in Ancient Greek History ) BRILL, 1996 Retrieved 2012-07-01 ISBN 9004104739〕 According to de Lecerda and Salomons (1997) mercury was first in use for extraction at about 1000 BC,〔B Lottermoser - (Mine Wastes: Characterization, Treatment and Environmental Impacts ) Springer, 2 Aug 2010 Retrieved 2012-07-22 ISBN 3642124186〕 according to Meech and others (1998), mercury was used in obtaining gold until the latter period of the first millennia.〔R Eisler - (Mercury Hazards to Living Organisms ) CRC Press, 14 Mar 2006 Retrieved 2012-07-21 ISBN 0849392128〕〔(secondary)L Drude De Lacerda, W Salomons - (Mercury from Gold and Silver Mining: A Chemical Time Bomb? ) Springer, 1998 Retrieved 2012-07-21 ISBN 3540617248〕〔(secondary) Guido Küstel - (Nevada and California processes of silver and gold extraction ) F. D. Carlton, 1863 Retrieved 2012-07-21〕〔(secondary) A Tilloch - (Philosophical Magazine, Volume 52 ) Retrieved 2012-07-21〕 A technique known to Pliny the Elder was extraction by way of crushing, washing, and then applying heat, with the resultant material powdered.〔JM Stillman - (Story of Alchemy and Early Chemistry ) Kessinger Publishing, 1 Jan 2003 Retrieved 2012-07-22〕〔(primary source "Pliny") S Venable - (Gold: A Cultural Encyclopedia ) ABC-CLIO, 2011 Retrieved 2012-07-22 ISBN 0313384312〕〔(secondary) M Page - (The First Global Village: How Portugal Changed the World ) Leya, 2006 Retrieved 2012-07-22 ISBN 9724613135〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「gold extraction」の詳細全文を読む スポンサード リンク
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