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Mining is the extraction of valuable minerals or other geological materials from the earth, usually (but not always) from an ore body, vein or (coal) seam. Materials recovered by mining include bauxite, coal, copper, gold, silver, diamonds, iron, precious metals, lead, limestone, nickel, phosphate, oil shale, rock salt, tin, uranium and molybdenum. Any material that cannot be grown from agricultural processes, or created artificially in a laboratory or factory, is usually mined. Mining in a wider sense comprises extraction of any non-renewable resource (e.g., petroleum, natural gas, or even water).
The oldest known mine on archaeological record is the "Lion Cave" in Swaziland. At this site, which by radiocarbon dating the mine dates around 4,100 BC, paleolithic humans mined mineral hematite, which contained iron and was ground to produce the red pigment ochre. Mines of a similar age in Hungary and are believed to be sites where Neanderthals may have mined flint for weapons and tools.
Ancient Egyptians mined malachite at Maadi. At first, Egyptians used the bright green malachite stones for ornamentations and pottery. Later, between 2,613 and 2,494 BC, large building projects required expeditions abroad to the area of Wadi Maghara in order "to secure minerals and other resources not available in Egypt itself." Quarries for turqoise and copper were also found at "Wadi Hamamat, Tura, Aswan and various other Nubian sites" on the Sinai Peninsula and at Timna.
The Celts, who were native to Britain, had mined minerals for centuries, but when the Romans came, the scale of the operations changed dramatically. The Romans needed what Britain had: especially the gold, silver, and lead.
Britain's gold mines were located in Wales at Dolgellau and Dolaucothi. The Romans discovered the Dolaucothi vein soon after their invasion, and a settlement was soon set up in the Cothi Valley. The mine produced Welsh gold. There were many iron mines in Roman Britain. The index to the Ordnance Survey Map of Roman Britain lists 33 iron mines: 67% of these are in the Weald and 15% in the Forest of Dean. The majority of mine workers were slaves. The work conditions were terrible, and up to 12% of miners died every year.
Black powder was first used in mining in Banská Štiavnica, Slovakia in 1627. In 1762, the world's first mining academy was established in the same town.
In North America there are ancient, prehistoric copper mines along Lake Superior that formed from volcanic activity 1280 million years ago. "Indians availed themselves of this copper starting at least 5000 years ago," and copper tools, arrowheads, and other artifacts that were part of an extensive native trade network have been discovered. In addition, obsidian, flint, and other minerals were mined, worked, and traded. While the early French explorers that encountered the sites made no use of the metals due to the difficulties in transporting it, the copper was eventually traded throughout the continent along major river routes. In Manitoba, Canada, there also are ancient quartz mines near Waddy Lake and surrounding regions.
In the early colonial history of the Americas, "native gold and silver was quickly expropriated and sent back to Spain in fleets of gold- and silver-laden galleons." Turquoise dated at 700 A.D. was mined in pre-Columbian America. In the Cerillos Mining District in New Mexico, estimates are that "about 15,000 tons of rock had been removed from Mt Chalchihuitl using stone tools before 1700."
Mining in the United States became prevalent in the 19th century. As with the California Gold Rush in the mid 1800s, mining for minerals and precious metals alongside ranching and exploration for oil and gas fields was very important in the Westward Expansion to the Pacific coast. With the exploration of the West, mining camps were established and "expressed a distinctive spirit, an enduring legacy to the new nation;" Gold Rushers would experience the same problems as the Land Rushers of the transient West that preceded them. Aided by railroads, many traveled West for work opportunities in mining. Western cities such as Denver and Sacramento originated as mining towns.
Steps of process
Mining techniques can be divided into two basic excavation types:
The science of extractive metallurgy is a specialized area in the science of metallurgy that studies the extraction of valuable metals and minerals from their ores, especially through chemical or mechanical means. Mineral processing (or mineral dressing) is a specialized area in the science of metallurgy that studies the mechanical means of crushing, grinding, and washing that enable the separation (extractive metallurgy) of valuable metals or minerals from their gangue (waste material).
Environmental issues can include erosion, formation of sinkholes, loss of biodiversity, and contamination of groundwaters and surface water by chemicals from the mining process and products.
Modern mining companies in some countries are required to follow environmental and rehabilitation codes, ensuring the area mined is returned to close to its original state. In some countries with pristine environments, such as large parts of Australia, this is impossible despite the best intentions. Some mining methods have devastating environmental and public health effects.
Mining can have adverse effects on surrounding surface and ground water if protection measures are not exercised. The result can be unnaturally high concentrations of some chemical elements, notably arsenic and sulfuric acid, over a significantly large area of surface or subsurface. Coal mining releases approximately twenty toxic chemicals, of which 85% is said to be managed on site. Combined with the effects of water and the new 'channels' created for water to travel through, collect in, and contact with these chemicals, a situation is created in which massive contamination can occur. In well-regulated mines, hydrologists and geologists take careful measures to mitigate any type of water contamination that could be caused by mines. In modern American mining, operations must, under federal and state law, meet standards for protecting surface and ground waters from contamination, including acid mine drainage (AMD). To mitigate these problems water is continuously monitored at coal mines. The five principal technologies used to control water flow at mine sites are: diversion systems, containment ponds, groundwater pumping systems, subsurface drainage systems, and subsurface barriers. In the case of AMD, contaminated water is generally pumped to a treatment facility that neutralizes the contaminants.
Some examples of environmental problems associated with mining operations are:
Although such issues have been associated with some mining operations in the past, modern mining practices have improved significantly and are subject to close environmental scrutiny. Modern mining practises aim to lessen environmental impacts from mining, and the ultimate aim is to return the local environment to as close to pristine as is possible. In many cases, the most significant environmental impact longer-term is visual, with pits and mine dumps prominent landscape features.
To ensure completion of reclamation (restoring mine land) most governments and regulatory authorities around the world require that mining companies post a bond to be held in escrow until productivity of reclaimed land has been convincingly demonstrated. Since 1978 the mining industry has reclaimed more than 2 million acres (8,000 km²) of land in the United States alone. This reclaimed land has renewed vegetation and wildlife in previous mining lands and can even be used for farming and ranching.
For further reading on reclamation of former mining sites, see Restoration ecology.
While exploration and mining can sometimes be conducted by individual entrepreneurs or small business, most modern-day mines are large enterprises requiring large amounts of capital to establish. Consequently, the mining sector of the industry is dominated by large, often multinational, mostly publicly-listed companies. See for a list. However, what is referred to as the 'mining industry' is actually two sectors, one specializing in exploration for new resources, the other specializing in mining those resources. The exploration sector is typically made up of individuals and small mineral resource companies dependent on public investment. The mining sector is typically large and multi-national companies sustained by mineral production from their mining operations.
Miners today do more than just dig tunnels in the Earth's subsurface. There are many different jobs, direct and indirect, in the mining industry, ranging from engineers and lab technicians to geologists and environmental specialists. Beyond employment directly linked to mine-site activity, the modern mining industry also employs many other professionals, including accountants, lawyers, sales representatives, public relations specialists, not to mention thousands of men and women involved who manufacture the machines and equipment necessary to mine minerals.
Employment in the mining industry offers highly competitive wages and benefits, especially in rural or remote areas. According to the Bureau of Labor Statistics (BLS), wages for coal miners are 30% higher than the wage earned by the average American. Employees possessing at least a bachelor's degree in mining or geological engineering can earn a median pay of over $80,000 annually.
The US Bureau of Labor Statistics estimates that 675,000 are employed in the natural resources and mining sector. Estimated employment by selected specific commodity (including mine, mill, smelter, and quarry workers) listed below is from US Geological Survey Mineral Commodity Surveys:
The mining industry has an experienced but aging workforce with a mean average age of 50 years and median of 46 years. Indeed, while the industry will require new employees to meet future demand, the largest dilemma currently facing mine operators is finding employees to fill vacancies left by a generation of miners, mine engineers, senior managers, technical experts and others who are set to retire between 2005 and 2015. However, the industry is struggling to meet that demand due to current low enrollment levels in mining education programs at American colleges and universities.
Mining is regulated under a comprehensive federal safety law (Federal Mine Safety and Health Act) that is administered by the Department of Labor's Mine Safety and Health Administration (MSHA). Currently under federal law, and enforced by MSHA each U.S. miner must have an approved worker training program in health and safety issues, including at least 40 hours of basic safety training for new underground miners with no experience; 24 hours for new miners at surface mines with no experience; plus eight hours of annual refresher training for all miners.
Safety has long been a controversial issue in the mining business especially with sub-surface mining. While mining today is substantially safer than it was in the previous decades, mining accidents are often very high profile, such as the Quecreek Mine Rescue saving 9 trapped Pennsylvania coal miners in 2002.
Mining ventilation is often seen to be a safety concern for many miners and their families. Poor ventilation of the mines causes exposure to harmful gases, heat and dust inside sub-surface mines. These can cause harmful physiological effects, even death. The concentration of methane and other airborne contaminants underground can generally be controlled by dilution (ventilation), capture before entering the host air stream (methane drainage), or isolation (seals and stoppings).
Methane gas is a common source of ignition for explosions in coal mines and can propagate into the more violent coal dust explosions. Explosions can be prevented or mitigated by eliminating ignition sources, minimizing methane concentrations and coal dust accumulations, generalized rock dusting, and by using passive and active barriers to suppress propagating explosions. High temperatures and humidity may result in heat-related illnesses, including heat stroke which can be fatal. Dusts can cause lung problems, including silicosis, asbestosis and pneumoconiosis (also known as miners lung or black lung disease).
A ventilation system is set up to course a stream of air through the working areas of the mine. The air circulation necessary for the effective ventilation of a mine is generated by one or more large mine fans, usually located above ground. In the United States, the main fans at coal mines are required to be above ground. Air flows in one direction only, making circuits through the mine such that each main work area receives a supply of fresh air.
Mining is regulated under the federal Mine Safety and Health Act by MSHA, which employs nearly one safety inspector for every four coal mines. Underground coal mines are thoroughly inspected at least four times annually by MSHA inspectors. In addition, miners can report violations, request additional inspections. Miners with such concerns for their work safety cannot be penalized with any threat to the loss of employment.
Heavy machinery is needed in mining to break and remove rocks of diverse hardness and toughness. Bulldozers, drills, explosives and trucks are important for digging into the land, especially in surface mining.
Underground mining, like continuous mining, tends to be more technologically sophisticated because of the dangers and expense of subsurface tunneling.
Trams are used to transport miners, minerals and waste.
Mining machinery manufacturers include Joy Mining Machinery, Bucyrus International, Caterpillar, Komatsu, Volvo, Hitachi, Terex, Dresser Industries, Kawasaki, Eimco Elecon India Limited, and Liebherr.
Placer mining is a type of surface mining, usually for gold, tin, and other metals, and gemstones. Ore, typically unconsolidated gravels, is fed into machinery that may consist of a hopper, shaking screen or trommel which frees the minerals from the gravels. The target minerals are then concentrated using sluices or jigs.
The number of abandoned mines in the United States remains an unknown, ranging "from the National Park Service's tally of 2,500 on its lands, to the Mineral Policy Center's assessment of 560,000 abandoned mines on public and privately owned lands."   Many of these abandoned mines are associated with abandoned neighboring towns often referred to as ghost towns. Experts strongly warn against entering or exploring old or abandoned mines.
In the U.S., the estimation is that approximately 25% of the abandoned mine lands (AML) sites pose physical safety hazards. Old mines are often dangerous and can contain deadly gases, snakes and other dangerous animals. Since weather may have eroded the earth/rock surrounding it, the entrance to an old mine in particular can be very dangerous. Old mine workings, caves, etc. are commonly hazardous simply due to the lack of oxygen in the air (a condition in mines known as blackdamp). Blackdamp is a deadly killer which provides no warning to any individual or group of individuals entering such an environment.
Every year, dozens are injured or killed in recreational accidents on mine property. It is only fair to note, however, that the majority of the deaths are unrelated to mine exploration. Drownings in open quarries and ATV accidents on abandoned mine properties are the main cause of accidental death. The U.S. Department of Labor notes that since 1999, "more than 200 people have died in recreational accidents at surface and underground active and abandoned operations across the country."  Due to these circumstances, MSHA (Mine Safety and Health Administration) launched the "Stay Out – Stay Alive" campaign, which is a national public awareness campaign aimed at warning and educating children and adults about the dangers of exploring and playing on active and abandoned mine sites.
In the U.S., the Abandoned Mine Land Initiative, launched by the Western Governor's Association and the National Mining Association is also an effort focusing on reporting the number of high-priority AML sites. The initiative identifies, measures and reports on the progress of current reclamation cleanup programs on an annual basis. In the Americas region, the United Nations Environment Programme (UNEP) and the Chilean Copper Commission (COHILCO) co-hosted a workshop to address the problem of abandoned or "orphaned" mines. Including a representative from the UN, ten countries were represented from North, Central and South America with an eleventh participant being Japan.
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|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Mining". A list of authors is available in Wikipedia.|