14 DAY TRIAL // 1.Mining started in the Neolithic (New Stone Age), 12,000 years ago, when people gathered grit from the surface of the ground, and later from subterranean deposits. At first, grit mines were made of vertical wells, up to 2 m (6.6 ft) wide and 10 m (33 ft) deep. Tunnels were excavated at the bottom of the well, until grit deposits were found. The tools used for digging were deer antlers and shovels made of the shoulder blade of large animals.
5,000 years ago, Egyptians mined gold, silver, copper and turquoise, but they focused on surface or shallow deposits. Thousands of prisoners worked in dangerous conditions in the subterranean gold mines located at the border with Ethiopia in 50 BC. The Egyptian miners made wood fires near the rock and when the rock got extremely heated, they cooled it down by throwing water. The sudden cooling determined a crack in the rock, which could be broken by using picks and pinions battered with the hammers into the cracks. Sometimes, the rock broke suddenly, killing many miners.
Slaves were also used by Greeks and Romans in order to mine gold, silver, tin, copper, lead and iron. Being chemically inert, gold often appeared as nuggets or powder. But other metals usually appeared in chemical compounds called ores. The ores had to be processed for obtaining the metal. The Romans spread mining in Europe and Africa.
2.Vapor engines, developed around 1700, boosted the mining technology. They helped venting and draining the subterranean mines and the lift-up to the surface of the heavy cargoes. Vapor trains on railways enabled the extraction of large amounts of material. In two centuries, mining turned into a well planned industry. But with all the complex technology, millions of people have died in mines. About 50,000 miners die annually.
3.Nowadays, some coal mines have completely automatic computerized systems, which control the machines working on the coal front and transport the coal to the surface. The coal extracted from the front is automatically loaded into trolleys, transported to a well and unloaded at the surface into vans. This way, human accidents and huge coasts with the miners are decreased.
But this technology can be applied only in the case of exploitation of soft material, like coal or phosphates. Instead, rocks containing metal ores are often hard, and breaking them is more difficult to do.
4.The irregular shape of some deposits makes it impossible for the automatic technology. That's why most metal deposits are still exploited by using explosives for shooting the exposed fronts. Holes 2.5-5 cm (1-2 in) wide at a distance of 2-3 m (6.6-10 ft) are made into the front of the ore. Explosive loads are located in these holes, then detonated, causing the ore's breaking off. A 3 m hole loaded with 2 kg (4.4 pounds) of explosive would produce about 3 tonnes of ore. Sometimes, simultaneous or successive detonations are made, involving more than 1 tonne of explosives. The burned gases must be vented out.
5.Surface operations make 70% of the mining production. In some surface operations, a 20-time-larger cover is removed for exposing the proper deposit. This way, mining operations remove annually about 50 billion tonnes of material. The scale varies a lot: some lone prospectors still search the river bed sands for gold or opal, while some small mines (with 2-3 workers) extract some thousands of tonnes of ore annually. On the other hand, huge mines in South Africa have up to 15,000 miners extracting millions of tonnes of gold ores from deep mines.
6.The gold mine Western Deep Levels from Carletonville, South Africa, is 3.7 km (2.3 mi) deep (the world's record)! The air used for venting the tunnels at such depths must be cooled down first in huge fridge installations, as the rocks' temperature is extremely high.
7.The world's largest surface mine is the copper mine Bingham Canyon, Utah, U.S., that detaches about 250,000 tonnes of useless rocks, together with 100,000 tonnes of copper ore, daily. The ore contains 0.7% copper and the bottom of the mine is located at a depth of 600 m (2,000 ft)!
8.Surface mines can be quarries, when the ore masses extend to the depths and a hole is formed as the ore is removed. Granite, slate, limestone and other rocks are exploited from quarries. Detachment mines are surface mines in which the deposit has a limited depth, but it extends on a large horizontal surface. The cover is removed on sections for getting to the ore. This technique is suitable for coal deposits located near the surface. Serra Pelada (Brazil) is the world's largest gold quarry.
Surface exploitation is also the dredging of the river and sea beds for materials varying from diamonds to sand and gravel. Commercial sea mining is made down to 60 m (200 ft) using excavators with cup wheel, bucket or suction pumps. Manganese recovered from the bottom of the Pacific Ocean at depths of 900 m (3,000 ft) is made with special pumps. At greater depths, there are more mineral resources than on the land.
Derrick mining involves the sinking of a derrick from the surface to the target deposit. Sulfur is exploited through the Frasch process, involving conducts that go through the derrick and transport water heated over the boiling point. This water melts the sulfur, which can be pumped to the surface. Solution mining involves the use of a solvent passed through the derrick. The solvent dissolves the subterranean deposits, and the resulting solution is pumped to the surface for mineral extraction. Salt can be exploited this way.
Hydraulic mining is used for soft surface deposits, like kaolin. The ore is taken using high pressure water jets. The water transports the material to a processing plant.
9.In subterranean mining, crumbling can be employed for large masses. Tunnels are made into the ore, and when shot, they will crumble.
The hewing exploitation is made systematically, at various levels. This can be made through chambers and pillars that sustain the roof. Low-quality coal deposits, difficult to exploit through conventional methods, are ignited in the subterranean. Low-quality coal gases are then extracted through special drill wells.
The dissolving technique can be applied to subterranean metal deposits, but the ore mass is first broken. A weak acid is let out over the broken rocks. The acid dissolves the metal content, which is then pumped to the surface.