How to extract gold
The story of the present mine Englishman Timothy Green:
"Descent to the gold mine is like a journey into the realm of Pluto. You can even leave the surface of all his clothes, including underwear, and, dressed in a white shroud, enter the steel cage, which is two minutes sweeps down through the rock a mile thick. Down there - loud, hot, wet world, illuminated by the dancing flames of lamps on their helmets of miners. It suffices to ten minutes walk along the gallery, pierced in the rock, the natural temperature is above 100° Fahrenheit (above 38° C), and any visitor through a mixture of sweat from getting wet and damp. Then, through the constant drone of air conditioners and trucks rumbling sound is heard pneumatic drills, penetrate into the solid rock. On the one hand the tunnel opened a narrow opening that leads down a slope of almost 25 °.
It has no more than 40 inches (about 1 m) tall and elaborately supported legs, upholstered in blue rubber. It is working to develop. It seems that in making rock crushes on all sides, tiny flakes falling from the ceiling into puddles of warm water to which a person kneeling or lying down. Behind a veil of water, which must absorb dust, iglopodobnoe tip drill a hole cut in the rock, which struck a circle in red ink. The entire length of making a continuous line of red paint represents a four-wire, which, even for the inexperienced eye of the observer, it looks much different than the rock above and below. This is a tightly knit bunch of white pebbles, among which here and there in a miner's lamp beam slightly glistening specks of gold. This vein or reef, like the meat between slices of bread in a sandwich. This mine is "Free State Geduld" in the Orange Free State (province of South Africa.) - One of the very few where the gold among the gravel can be seen with the naked eye, as there developed one of the richest reef ever discovered in South Africa.
With the average content of 26.4 g of gold per ton of ore, the mine was processed about 2 million tons of ore which was mined 53 tons of metal. But the highest rate gave mine "West Drifonteyn" - 31.4 grams per tonne. This mine has given 89 tons of gold. These two giant mine had the lowest production costs. They were respectively 14.1 and 15.3 dollars per ounce at the average market price of about $ 40 per ounce.
That made the 10-year inflation to the cost of gold, evidenced by such data. In 1981, costs at the mine "Drifonteyn West" were the lowest in the industry, but they were already $ 112 per ounce, it has grown more than 7 times. On mine, "Free State Geduld," they were equal to 177 dollars - 12 times more than 10 years ago. But the gold price of 400 dollars an ounce for powerful companies that owned these mines, and high profits.
Greene says about gold mining at a depth of a mile (1,600 m). Currently, the mine often go to a depth of 3000-3500 m, where the natural temperature of rock for a few degrees higher. Under these conditions, cooling, ventilation, drainage and water supply, fighting rubble, vertical and horizontal transport are complex technical problems. Despite mechanization, the labor of miners difficult and dangerous. By the way, the mechanization of South Africa gold production falls far short of the U.S. and Canada. The reason is simple: cheap labor of black workers. Number of employees at each of the major mines more than 20 thousand of them Africans are on average about 90%. Underground work, their share is even higher: underground white only perform the work of technicians, craftsmen, fuzes. At most mines, the Africans are not allowed to explosive materials. "Gold mining industry for many years, very slowly implemented the mechanization of underground work - writes Green - because it was often cheaper to just send a dozen more African than to invent a machine."
Extraction of ore under the ground and pass it to the surface - the most important, but only pepper link in the technological chain of production of gold. Ore processing and smelting of metal carried in special factories with a complete cycle. In the structure of capital construction costs of a typical mine in South Africa, these costs make up about 15%.
The ore goes through several stages of crushing, grinding and sorting. Extraction of gold from ore, turned into pulp, is produced cyanidation or other methods. Smelting plants in the South African mining gives the rough ingots of gold weighs about 1000 ounces (about 31 kg), containing from 85 to 90% pure. The final purification (refining) is produced by electrolysis at a central refinery, owned by the Chamber of Mines of South Africa. This is an influential association of entrepreneurs, who performs many economic and political functions, including recruiting labor for mines and industry is in a relationship with the government.
With gold refinery comes as standard ingots (bars). Weight of these bars is usually 402 an ounce (about 12.5 kg), the sample - 996. International rules allow the weight of traditional bars (rounded up) from 10.9 to 13.8 kg and a sample of not less than 995. These ingots - the raw material for future applications of gold.
The main advantage of alluvial mining is that it does not require deep mines and often is open. Usually absent and the cost of ragging. Engineering thought long and has done much work for the mechanization and increased productivity in the extraction of gold from placer deposits. Now in etay industry dredges used (a kind of floating factories gold) hydromonitors (water guns for the erosion of sand containing gold), and suction dredger pulpovody, excavators, bulldozers and other machinery. Further processing of gold-pulp gold recovery and do not differ from the same process with the gold ore.
Approximately 3-4% of gold production falls on a passing prey. The greatest value it has in the U.S., Canada, Australia and the Philippines. For example, in Canada, which is second only to South African gold producer in the early 80s on a passing prey accounted for about 30%. Gold is usually extracted from ores, in which the main minerals are copper, zinc, silver, lead. Gold recovery somewhat complicates the process and increases the cost of enrichment and metallurgical processing of ore, but pays off, even at relatively low concentrations of gold. In this way, by using integrated feedstock.
On the island of Bougainville, which is part of the newly independent state of Papua New Guinea, there are rich deposits of copper, whose development began by foreign companies in the 70s. Tailwind gold mining on the island was at the end of the decade about 20 tons per year, then declined somewhat, as the situation of the world economic slowdown has decreased the production of copper. Large reserves of copper-gold ores are present in some other parts of Papua New Guinea.
High gold prices have caused a revival in many countries, and exploration work on the gold ore. In the U.S., Canada and other countries have been discovered some deposits that are suitable for industrial development. However, fundamentally the distribution pattern of production by major countries and ways had not changed. At least until the end of the century a crucial role in the production of gold will play its South African mining conglomerate.