Underground mining process is done when the mineral stone, or precious metals found in very long distances to be at a depth of soil. Underground mining techniques used to excavate hard minerals, mainly those containing metals such as ore containing gold, silver, iron, copper, zinc, nickel, tin and lead, but also involves using the same techniques for excavating ores of gems such as diamonds. And The processing of underground gold mines is used where the depth of mineral ore below the surface makes open-cut mining uneconomic
The vast majority of current gold production comes from commercial hardrock mining operations. Underground hard rock mining refers to various underground mining techniques used to excavate hard minerals, mainly containing precious metals. Some hardrock mines are underground mines. A tunnel is drilled or blasted to the source of the ore, which is transported out for processing often by truck or rail.
A variety of specific techniques for the processing of underground gold mines can be used for mining the ore, such as block caving, which allows massive strip-mine scale underground excavation, or the more steretypical cut-and-fill and drift-and-fill techniques, where miners dig our out in long horizontal tunnels.
The ore from Underground mine is then processed in some manner to remove the gold. Usually this entails crushing the rock into powder and using some combination of gravity, centrifugation, and cyanidation processing to perform an initial separation of gold from rock.
Coarse gold may be removed by gravity concentration. The processing required to recover fine gold from crushed ore is determined by the free-milling or refractory nature of the ore.
In many cases this is followed by some form of cyanide treatment to precipitate out the remaining gold. Free-milling ore is ore from which gold can be recovered by crushing, grinding and cyanidation (treatment with a dilute cyanide solution) without additional processing. Free-milling oxide ores are suitable for direct cyanidation of the crushed and ground ore.
Mineral ore or treated concentrate is placed in a weak solution of sodium cyanide, which dissolves gold and forms a slurry of gold-bearing solution and barren solids. the gold is recovered from the gold-bearing solution in a process in which activated carbon are added to the slurry and the gold-bearing ions are adsorbed onto the surface. The slurry is moved through a number of linked tanks in a direction opposite to the slurry movement.
Activated carbon that has been filled with gold are removed and the gold is stripped from them by washing in a solution of hot cyanide. The carbon used in the process is recycled and an electric current is passed through the new solution, depositing the gold on a steel wool cathode. The gold laden cathode is treated with hydrochloric acid to dissolve any residual steel and the gold sludge is filtered and dried, ready for smelting. At this stage the gold-bearing material may contain silver and base metals.
Gold is smelted in a crucible furnace to produce unrefined bullion. In smelting, base metal impurities are oxidised and absorbed, leaving the precious metals to be poured into ingot moulds. Smelted gold is then refined.
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