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Gold is obtained by two principal mining methods--placer and vein mining--and also as a by-product of the mining of other metals. Placer mining is used when the metal is found in unconsolidated deposits of sand and gravel from which gold can be easily separated due to its high density. The sand and gravel are suspended in moving water; the much heavier metal sinks to the bottom and is separated by hand. The simplest method, called panning, is to swirl the mixture in a pan rapidly enough to carry the water and most of the gravel and sand over the edge while the gold remains on the bottom.
Panning is one of the original methods used by the forty-niners and is imortalized in story, art, and song . Then, a method that allowed for processing larger quantities of ore, is a sluice box, a U-shaped trough with a gentle slope and transverse bars firmly attached to the trough bottom. The bars, which extend from side to side, catch the heaviest particles and prevent their being washed downslope. Sand and gravel are placed in the high end, the gate to a water supply is opened, and the lighter material is washed through the sluice box and out the lower end. The materials caught behind the bars are gleaned to recover the gold. A similar arrangement catches the metal on wool, and may have been the origin of the legend of Jason's search for the GOLDEN FLEECE. Another variation of the placer method is called hydraulic mining. A very strong stream of water is directed at natural sand and gravel banks, causing them to be washed away. The suspended materials are treated much as if they were in a giant sluice box. Today's most important placer technique is dredging. In this method a shovel of several cubic meters capacity lifts the unconsolidated sand and gravel from its resting place and starts the placer process.
Vein, or lode mining, is the most important of all gold recovery methods. Although each ounce of gold recovered requires the processing of about 100,000 ounces of ore, there is so much gold deposited in rock veins that this method accounts for more than half of the world's total gold production today. The gold in the veins may be of microscopic particle size, in nuggets or sheets, or in gold compounds. Regardless of how it is found, the ore requires extensive extraction and refining. One-third of all gold is produced as a by-product of copper, lead, and zinc production. Copper, for example, must be electrolytically refined to raise its purity from 99% to more than 99.99% as required for many industrial purposes. In the refining process an anode of impure copper is electrolyzed in a bath in which the cathode is a very thin sheet of highly refined copper. As the process continues, copper ions leave the impure anode and are deposited as atoms on the cathode. Because impurities are not transported through the bath, as the anode is consumed, the impurities fall to the bottom as a sludge. This anode sludge contains gold in quantities sufficient to make recovery profitable. One-third of all gold is obtained from such by-products. Silver and platinum are also recovered from the copper anode sludge in quantities large enough to more than pay for the total refining process.
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Gold mining history resources. |
A general listing of gold mining history resources. GMHq's is the webs largest information resource for the recreational and small scale gold miner.
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09-Nov-2005 Hits: 79 Rating: 0.00 Votes: 0
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Gold |
Placer deposits have formed in the same manner throughout the Earth's history. ... Shortly after the start of World War II, gold mines were closed by the ...
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04-Jan-2006 Hits: 70 Rating: 0.00 Votes: 0
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