Mining

Modern mining is an industry that involves the exploration for and removal of minerals from the earth, economically and with minimum damage to the environment. Mining is important because minerals are major sources of energy as well as materials such as fertilizers and steel. Mining is necessary for nations to have adequate and dependable supplies of minerals and materials to meet their economic and defense needs at acceptable environmental, energy, and economic costs. Some of the nonfuel minerals mined, such as stone, which is a nonmetallic or industrial mineral, can be used directly from the earth. Metallic minerals, which are also nonfuel minerals, conversely, are usually combined in nature with other materials as ores. These ores must be treated, generally with chemicals or heat to produce the metal of interest. Most bauxite ore, for example, is converted to aluminum oxide, which is used to make aluminum metal via heat and additives. Fuel minerals, such as coal and uranium, must also be processed using chemicals and other treatments to produce the quality of fuel desired.

There are significant differences in the mining techniques and environmental effects of mining metallic, industrial, and fuel minerals. The discussion here will mostly concentrate on metallic minerals. Mining is a global industry, and not every country has high-grade, large, exceptionally profitable mineral deposits, and the transportation infrastructure to get the mined products to market economically. Some of the factors affecting global mining are environmental regulations, fuel costs, labor costs, access to land believed to contain valuable ore, diminishing ore grades requiring the mining of more raw materials to obtain the target mineral, technology, the length of time to obtain a permit to mine, and proximity to markets, among others. The U.S. mining industry is facing increasing challenges to compete with nations that have lower labor costs—for example, less stringent environmental regulations and lower fuel costs.

Mining Life Cycle

Minerals are a nonrenewable resource, and because of this, the life of mines is finite, and mining represents a temporary use of the land. The mining life cycle during this temporary use of the land can be divided into the following stages: exploration, development, extraction and processing, and mine closure.

Exploration is the work involved in determining the location, size, shape, position, and value of an ore body using prospecting methods, geologic mapping and field investigations, remote sensing (aerial and satellite-borne sensor systems that detect ore-bearing rocks), drilling, and other methods. Building access roads to a drilling site is one example of an exploration activity that can cause environmental damage.

The development of a mine consists of several principal activities: conducting a feasibility study, including a financial analysis to decide whether to abandon or develop the property; designing the mine; acquiring mining rights; filing an Environmental Impact Statement (EIS); and preparing the site for production. Preparation could cause environmental damage by excavation of the deposit to remove overburden (surface material above the ore deposit that is devoid of ore minerals) prior to mining.

Extraction is the removal of ore from the ground on a large scale by one or more of three principal methods: surface mining, underground mining, and in situ mining (extraction of ore from a deposit using chemical solutions). After the ore is removed from the ground, it is crushed so that the valuable mineral in the ore can be separated from the waste material and concentrated by flotation (a process that separates finely ground minerals from one another by causing some to float in a froth and others to sink), gravity, magnetism, or other methods, usually at the mine site, to prepare it for further stages of processing. The production of large amounts of waste material (often very acidic) and particulate emission have led to major environmental and health concerns with ore extraction and concentration. Additional processing separates the desired metal from the mineral concentrate.

The closure of a mine refers to cessation of mining at that site. It involves completing a reclamation plan and ensures the safety of areas affected by the operation, for instance, by sealing the entrance to an abandoned mine. Planning for closure is often required to be ongoing throughout the life cycle of the mine and not left to be addressed at the end of operations. The Surface Mining and Control Act of 1977 states that reclamation must "restore the land affected to a condition capable of supporting the uses which it was capable of supporting prior to any mining, or higher or better uses." Abandoned mines can cause a variety of health-related hazards and threats to the environment, such as the accumulation of hazardous and explosive gases when air no longer circulates in deserted mines and the use of these mines for residential or industrial dumping, posing a danger from unsanitary conditions. Many closed or abandoned mines have been identified by federal and state governments and are being reclaimed by both industry and government.

Environmental Impacts

The environmental responsibility of mining operations is protection of the air, land, and water. Mineral resources were developed in the United States for nearly two centuries with few environmental controls. This is largely attributed to the fact that environmental impact was not understood or appreciated as it is today. In addition, the technology available during this period was not always able to prevent or control environmental damage.

Air. All methods of mining affect air quality. Particulate matter is released in surface mining when overburden is stripped from the site and stored or returned to the pit. When the soil is removed, vegetation is also removed, exposing the soil to the weather, causing particulates to become airborne through wind erosion and road traffic. Particulate matter can be composed of such noxious materials as arsenic, cadmium, and lead. In general, particulates affect human health adversely by contributing to illnesses relating to the respiratory tract, such as emphysema, but they also can be ingested or absorbed into the skin.

Land. Mining can cause physical disturbances to the landscape, creating eyesores such as waste-rock piles and open pits. Such disturbances may contribute to the decline of wildlife and plant species in an area. In addition, it is possible that many of the premining surface features cannot be replaced after mining ceases. Mine subsidence (ground movements of the earth's surface due to the collapse of overlying strata into voids created by underground mining) can cause damage to buildings and roads. Between 1980 and 1985, nearly five hundred subsidence collapse features attributed to abandoned underground metal mines were identified in the vicinity of Galena, Kansas, where the mining of lead ores took place from 1850 to 1970. The entire area was reclaimed in 1994 and 1995.

Water. Water-pollution problems caused by mining include acid mine drainage, metal contamination, and increased sediment levels in streams. Sources can include active or abandoned surface and underground mines, processing plants, waste-disposal areas, haulage roads, or tailings ponds. Sediments, typically from increased soil erosion, cause siltation or the smothering of streambeds. This siltation affects fisheries, swimming, domestic water supply, irrigation, and other uses of streams.

Acid mine drainage (AMD) is a potentially severe pollution hazard that can contaminate surrounding soil, groundwater, and surface water. The formation of acid mine drainage is a function of the geology, hydrology, and mining technology employed at a mine site. The primary sources for acid generation are sulfide minerals, such as pyrite (iron sulfide), which decompose in air and water. Many of these sulfide minerals originate from waste rock removed from the mine or from tailings. If water infiltrates pyrite-laden rock in the presence of air, it can become acidified, often at a pH level of two or three. This increased acidity in the water can destroy living organisms, and corrode culverts, piers, boat hulls, pumps, and other metal equipment in contact with the acid waters and render the water unacceptable for drinking or recreational use. A summary chemical reaction that represents the chemistry of pyrite weathering to form AMD is as follows:

"Yellowboy" is the name for iron and aluminum compounds that stain streambeds. AMD can enter the environment in a number of ways, such as free-draining piles of waste rock that are exposed to intense rainstorms, transporting large amounts of acid into nearby rivers; groundwaters that enter underground workings which become acidic and exit via surface openings or are pumped to the surface; and acidic tailings containment ponds that may leach into surrounding land.

Major U.S. Mining Laws and Regulations

Some major federal laws and regulations affecting the mineral industry include the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), commonly known as Superfund, enacted in 1980. This law requires operations to report releases of hazardous substances to the environment and requires cleanup of sites where hazardous substances are found. The Superfund program was established to locate, investigate, and clean up the worst abandoned hazardous waste sites nationwide and is currently being used by the U.S. Environmental Protection Agency (EPA) to clean up mineral-related contamination at numerous locations. The Federal Water Pollution Control Act, commonly referred to as the Clean Water Act, came into effect in 1977. The act requires mining operations to meet standards for surface water quality and for controlling discharges to surface water. The Resource Conservation and Recovery Act (RCRA), enacted in 1976, regulates the generation, storage, and disposal of solid waste and hazardous waste, using a "cradle-to-grave" system, meaning that these wastes are governed from the point of generation to disposal. The National Environmental Policy Act (NEPA), enacted in 1970, requires federal agencies to prepare EIS for major federal actions that may significantly affect the environment. These procedures exist to ensure that environmental information is available to public officials and citizens before actions are taken. NEPA applies to mining operations requiring federal approval.

Comparison of U.S. and International Mining Laws and Regulations

The European Union (EU) has developed a set of environmental directives that have had a significant effect on the mining industries of member nations. Each country's environmental laws derive from these directives. Among the key directives are the Environmental Impact Assessment Directive (similar to the EIS requirements of the United States), the Water Framework Directive (addresses concerns similar to those of the U.S. Clean Water Act), and the Waste Framework, Hazardous Waste, and Landfill Directives (all address concerns similar to those of the U.S. RCRA).

Examples of Mining Pollution and Reclamation

The Bunker Hill Mine complex is located in northwest Idaho in the Coeur d'Alene River Valley, and has a legacy of nearly a hundred years of miningrelated contamination since 1889. Operations ceased in 1982, and the EPA declared much of the area a Superfund site in 1983. The complex produced lead, zinc, cadmium, silver, and gold, as well as arsenic and other minerals and materials. Much of the mining pollution was caused by the dispersal of mining wastes containing such contaminants as arsenic, cadmium, and lead into the floodplain of the Coeur d'Alene River, acid mine drainage, and a leaking tailings pond. The metals contaminated soils, surface water, groundwater, and air, leading to health and environmental effects. Lead, in particular, was noted for its health effects on children in the area. EPA reports concerning lead poisoning state that experts believe blood levels as low as 10 micrograms per deciliter (μg/dl) are associated with children's learning and behavioral problems. High blood lead levels cause devastating health effects, such as seizures, coma, and death. Blood levels of children in areas near the complex ranged from about 35 to 65 μg/dl in the early 1970s to less than 5 percent in 1999, as remediation efforts progressed. EPA reports also state that children are at a greater risk from exposure to lead than adults because, among other reasons, children absorb and retain a larger percentage of ingested lead per unit of body weight than adults, which increases the toxic effects of the lead. Efforts by the federal government, the state of Idaho, and industry to remediate contaminated areas associated with the site are ongoing.

There are also many mines with successful reclamation plans. For example, the Ruby Hill Mine, which is an open pit gold mine in Eureka, Nevada, won a state award in 1999 for concurrent reclamation practices, such as using revegetation and employing mitigation measures to offset potential impacts to local wildlife.

The mining of asbestos, either as the primary mineral or included as an unwanted material while mining for the "target" mineral, is one of the more controversial issues facing the mining industry in the United States. Asbestos is the name given to a group of six naturally occurring fibrous minerals. Asbestos minerals have long, strong, flexible fibers that can be spun and woven and are heat-resistant. Because of these characteristics, asbestos materials became the most cost effective ones for use in such items as building materials (roof coatings and shingles, ceiling and floor tiles, paper products, and asbestos cement products) and friction products (automobile clutch, brake, and transmission parts).

Unfortunately, it has been found that long-term, high-level exposure to asbestos can cause asbestosis and lung cancer. It was also determined that exposure to asbestos may cause mesothelioma, a rare form of cancer. Workers can be exposed to asbestos during mining, milling, and handling of ores containing asbestos or during the manufacture, installation, repair, and removal of commercial products that contain asbestos. One of the more recent controversies involving asbestos is the exposure of workers and the local residents to asbestos found in vermiculite ore mined in Libby, Montana. The vermiculite ore was shipped nationwide for processing and was used for insulation, as a lightweight aggregate, in potting soils, and for agricultural applications. Mining of the Libby deposit ended around 1991 but elevated levels of asbestos-related disease have been found in the miners, millers, and the local population. Another major area of concern is naturally occurring asbestos found in rock outcrops in parks and residential areas.

see also Clean Water Act; Disasters: Environmental Mining Accidents; Mining Law of 1872; National Environmental Policy Act; Resource Conservation and Recovery Act; Smelting; Superfund.

Bibliography

Kesler, Stephen E. (1994). Mineral Resources, Economics and the Environment. New York: Macmillan.

Marcus, Jerrold J. (1997). Mining Environmental Handbook: Effects of Mining on the Environment and American Environmental Controls on Mining. London: Imperial College Press.

Ripley, Earle A.; Redman, Robert E.; and Crowder, Adele A. (1996). Environmental Effects of Mining. Delray Beach, FL: St. Lucie Press.

Sengupta, Mritunjoy. (1993). Environmental Impacts of Mining: Monitoring, Restoration, and Control. Boca Raton, FL: CRC Press.

internet resources

Brosius, Liz, and Swain, Robert S. (2001). "Lead and Zinc Mining in Kansas." Public Information Circular 17, Kansas Geological Survey. Available from http://www.kgs.ukans.edu.

Bureau of Land Management. (2001). "Abandoned Mine Lands Cleanup Program." Available from http://www.blm.gov/aml.

National Institute for Occupational Safety and Health. (1995)."Report to Congress on Worker's Home Contamination Study." NIOSH Report No. 95-123. Available from http://www.cdc.gov/niosh.

Michael J. McKinley

COAL-BED METHANE

Methane, a potent greenhouse gas trapped inside coal, can be released into the atmosphere when coal is mined. The 1993 President's Climate Change Action Plan encouraged the recovery of a possible 100 trillion cubic feet of this coal-bed methane for energy. This would reduce methane and carbon dioxide emissions overall, because burning methane produces less carbon dioxide than burning fossil fuels. Scientists from the United States Geological Survey are studying how to extract coal-bed methane without harming the environment. Current difficulties include how to dispose of the water that permeates coal beds and must be pumped off before methane can be released, and how to prevent methane migration. Methane, possibly from coal-bed methane mining, has been discovered in groundwater in residential neighborhoods.

Mining

Mining is the process by which commercially valuable mineral resources are extracted (removed) from Earth's surface. These resources include ores (minerals usually containing metal elements), precious stones (such as diamonds), building stones (such as granite), and solid fuels (such as coal). Although many specific kinds of mining operations have been developed, they can all be classified into one of two major categories: surface and subsurface (or underground) mining.

History

Many metals occur in their native state or in readily accessible ores. Thus, the working of metals (metallurgy) actually dates much farther back than does the mining industry itself. Some of the earliest known mines were those developed by the Greeks in the sixth century b.c. By the time the Roman Empire reached its peak, it had established mining sites throughout the European continent, in the British Isles, and in parts of North Africa. Some of the techniques used to shore up underground mines still in use today were introduced as far back as the Greek and Roman civilizations.

Exploration

Until the beginning of the twentieth century, prospecting (exploring an area in search of mineral resources) took place in locations where ores were readily available. During the California and Alaska gold rushes of the nineteenth century, prospectors typically found the ores they were seeking in outcrops visible to the naked eye or by separating gold and silver nuggets from stream beds. Over time, of course, the supply of these readily accessible ores was exhausted and different methods of mining were developed.

Words to Know

Adit: A horizontal tunnel constructed to gain access to underground mineral deposits.

Metallurgy: Science and technology of extracting metals from their ores and refining them for use.

Ore: A mineral compound that is mined for one of the elements it contains, usually a metal element.

Overburden: Rocky material that must be removed in order to gain access to an ore or coal bed.

Prospecting: The act of exploring an area in search of mineral deposits or oil.

Shaft: A vertical tunnel constructed to gain access to underground mineral deposits.

Surface mining

When an ore bed has been located relatively close to Earth's surface, it can be mined by surface techniques. Surface mining is generally a much preferred approach to mining because it is less expensive and safer than subsurface mining. In fact, about 90 percent of the rock and mineral resources mined in the United States and more than 60 percent of the nation's coal is produced by surface mining techniques.

Surface mining can be subdivided into two large categories: open-pit mining and strip mining. Open-pit mining is used when an ore bed covers a very large area in both distance and depth. Mining begins when scrapers remove any non-ore material (called overburden) on top of the ore. Explosives are then used to blast apart the ore bed itself. Fragments from the blasting are hauled away in large trucks. As workers dig downward into the ore bed, they also expand the circular area in which they work. Over time, the open-pit mine develops the shape of a huge bowl with terraces or ledges running around its inside edge. The largest open-pit mine in the United States has a depth of more than 0.5 mile (0.8 kilometer) and a diameter of 2.25 miles (3.6 kilometers). Open-pit mining continues until the richest part of the ore bed has been excavated.

When an ore bed covers a wide area but is not very deep, strip mining is used. It begins the same as open-pit mining, with scrapers and other machines removing any overburden. This step involves the removal of two long parallel rows of material. As the second row is dug, the overburden removed is dumped into the first row. The ore exposed in the second row is then extracted. When that step has been completed, machines remove the overburden from a third parallel row, dumping the material extracted into the second row. This process continues until all the ore has been removed from the area. Afterward, the land typically resembles a washboard with parallel rows of hills and valleys consisting of excavated soil.

Subsurface mining

Ores and other mineral resources may often lie hundreds or thousands of feet beneath Earth's surface. Because of this, their extraction is difficult. To gain access to these resources, miners create either a horizontal tunnel (an adit) or a vertical tunnel (a shaft). To ensure the safety of workers, these tunnels must be reinforced with wooden timbers and ceilings. In addition, ventilation shafts must be provided to allow workers a sufficient supply of air, which is otherwise totally absent within the mine.

Once all safety procedures have been completed, the actual mining process begins. In many cases, the first step is to blast apart a portion of the ore deposit with explosives. The broken pieces obtained are then collected in carts or railroad cars and taken to the mine opening.

Other techniques for the mining of subsurface resources are also available. The removal of oil and natural gas by drilling into Earth's surface are well-known examples. Certain water-soluble minerals can be removed by dissolving them with hot water that is piped into the ground under pressure. The dissolved minerals are then carried to the surface.

Environmental issues

In general, subsurface mining is less environmentally hazardous than surface mining. One problem with subsurface mining is that underground mines sometimes collapse, resulting in the massive sinking of land above

them. Another problem is that waste materials produced during mining may be dissolved by underground water, producing water solutions that are poisonous to plant and animal life.

In many parts of the United States, vast areas of land have been laid bare by strip mining. Often, it takes many years for vegetation to start regrowing once more. Even then, the land never quite assumes the appearance it had before mining began. Strip mining also increases land erosion, resulting in the loss of soil and in the pollution of nearby waterways.

[See also Coal; Minerals; Precious metals ]

mining extraction of solid mineral resources from the earth. These resources include ores, which contain commercially valuable amounts of metals, such as iron and aluminum; precious stones, such as diamonds; building stones, such as granite; and solid fuels, such as coal and oil shale. The search for and discovery of mineral deposits is called prospecting , or exploration. When a mineral deposit is found, it is studied to determine if it can be mined profitably. If so, the deposit can be worked or extracted by a variety of mining methods.

Surface Mining Methods

Strip mining (see coal mining ), open-pit (or open-cut) mining, and quarrying are the most common mining methods that start from the earth's surface and maintain exposure to the surface throughout the extraction period. The excavation usually has stepped, or benched, side slopes and can reach depths as low as 1,500 ft (460 m). In strip mining, the soft overburden, or waste soil, overlying the ore or coal is easily removed. In open-pit mining the barren rock material over the ore body normally requires drilling and blasting to break it up for removal. A typical mining cycle consists of drilling holes into the rock in a pattern, loading the holes with explosives, or blasting agents, and blasting the rock in order to break it into a size suitable for loading and hauling to the mill, concentrator, or treatment plant. There the metals or other desired substances are extracted from the rocks (see metallurgy ).

Underground Mining Methods

Under certain circumstances surface mining can become prohibitively expensive and underground mining may be considered. A major factor in the decision to operate by underground mining rather than surface mining is the strip ratio, or the number of units of waste material in a surface mine that must be removed in order to extract one unit of ore. Once this ratio becomes large, surface mining is no longer attractive. The objective of underground mining is to extract the ore below the surface of the earth safely, economically, and with as little waste as possible. The entry from the surface to an underground mine may be through an adit, or horizontal tunnel, a shaft (see shaft sinking ), or vertical tunnel, or a declined shaft. A typical underground mine has a number of roughly horizontal levels at various depths below the surface, and these spread out from the access to the surface. Ore is mined in stopes, or rooms. Material left in place to support the ceiling is called a pillar and can sometimes be recovered afterward. A vertical internal connection between two levels of a mine is called a winze if it was made by driving downward and a raise if it was made by driving upward.

A modern underground mine is a highly mechanized operation requiring little work with pick and shovel. Rubber-tired vehicles, rail haulage, and multiple drill units are commonplace. In order to protect miners and their equipment much attention is paid to mine safety. Mine ventilation provides fresh air underground and at the same time removes noxious gases as well as dangerous dusts that might cause lung disease, e.g., silicosis . Roof support is accomplished with timber, concrete, or steel supports or, most commonly, with roof bolts, which are long steel rods used to bind the exposed roof surface to the rock behind it.

Other Methods

Although surface and underground mining are the most common techniques, there are a number of other mining methods. In solution mining the valuable mineral is brought into a liquid solution by some chemical or bacteria. The resultant liquid is pumped to the surface, where the mineral or metal is taken out of solution by precipitation or by ion exchange (e.g., the Frasch process ). In glory-hole mining a steep-sided, funnel-shaped surface excavation is connected to tunnels below it. Rocks blasted off the sides of the excavation fall into the tunnels, from which they are then removed. Gopher mining is an old-fashioned method still used in very small mines. Narrow, small holes are driven in order to extract the ore (e.g., gold) as cheaply as possible. In placer mining no excavation is involved; instead, gravel, sand, or talus (rock debris) is removed from deposits by hand, hydraulic nozzles, or dredging. The ore is separated from the waste by panning or sluicing.

Environmental and Legal Concerns

Associated with mining are many environmental concerns. Large-scale excavation is often necessary to extract a small amount of ore. Ore extraction disrupts the topsoil and can displace local animals and plants, and sometimes native human populations. Runoff can contaminate nearby water sources with pollutants such as the mercury and sodium cyanide used in gold mining. Waste materials and smelters can cause sulfurous dust clouds that result in acid rain. Abandoned strip mines have often been used as unregulated landfills for hazardous wastes. Several pieces of legislation in the United States, the Surface Mining Control and Reclamation Act (1977) and the Comprehensive Environmental Response, Compensation, and Liability Act, or Superfund Act (1986), address these issues, but enforcement has been difficult.

Another act that affects mining in the United States is the 1872 Mining Act. This now controversial act, which was originally designed to encourage settlement of the West, allows mining companies to purchase land for $2.50 per acre. In the late 20th cent., despite many efforts at reform, the law and the $2.50 per acre price still stood, despite the fact that the ore contained in the land could be worth billions of dollars.

Bibliography

See R. Peele and J. A. Church, ed., Mining Engineer's Handbook (3d ed.; 2 vol., 1941); R. S. Lewis and G. B. Clark, Elements of Mining (3d ed. 1964); E. Pfleider, ed., Surface Mining (1968); G. C. Amstutz, Glossary of Mining Geology (1971); C. Gregory, A Concise History of Mining (1981); M. K. Tolba (United Nations Environment Programme), Saving Our Planet (1991); A. Warhurst, Environmental Degradation from Mining and Mineral Processing in Developing Countries (1994).

mining Mining is the process of extracting solid natural resources from the shallow parts of the Earth's crust. Mining has been carried out by man since it was first realized that materials within the ground could be valuable, whether as fuel, for tools, or as decorative materials in jewellery or for religious use. Mining is known to have taken place for thousands of years; there are early indications of the perceived importance of geology at a number of sites. In the remains of the gold–silver workings at Cassandra in Greece there is evidence that miners dug in search of faulted vein segments at some time prior to 300 bc. Their Athenian contemporaries, faced with the depletion of silver and lead ore at Laurium, recognized the significance of marble near a schist contact and sank more than a thousand shafts through barren rock, some to depths of 100 m, in search of hidden orebodies.

The materials that are recovered by mining operations can be divided into six general categories: coal and low-grade coals; metalliferous materials (non-ferrous); iron, including all types of iron ore; rock, including construction materials such as building stone; precious stones; and evaporite deposits.

The two main methods of extraction are opencast mining and underground mining. Opencast mining entails the excavation of open pits from the ground surface so that the raw materials can be transported from the mine to a processing plant or export point. Underground mining entails sinking shafts to reach the target resource and driving tunnels and adits, either inclined or horizontally.

Whether to extract a resource by opencast or underground mining depends on the depth of the ore or rock below the ground surface and the concentration of the material per unit volume. In historical times, underground mining was carried out at extremely shallow depths because of the lack of mechanical equipment for removing the overburden. As a result of advances in mechanization, underground mining is no longer carried out on an industrial scale at shallow depths. There is no comprehensive formula for the depth of a mine: each mine and its ore are unique. For example, as a result of highly efficient production methods, mines in the Witwatersrand gold fields of South Africa operate at depths in excess of 3000 m where the specific geological conditions are suitable.

The ‘bigger, faster, and deeper’ requirements of modern mining are often met by scaling up the mining equipment and giving that equipment enough room to work. This ‘up-scaling’ is generally accommodated easily in open-pit mines, but in underground workings the creation of large caverns brings with it problems of rock mechanics and increased risk of instability.

In subsurface ore mining, headings are driven into new ground, level drifts follow the ore, level crosscuts connect drifts, and vertical or inclined raises connect the workings from level to level. Underground mining systems consist of workings that may be naturally supported, may require artificial support, or may be allowed to collapse as part of a caving method, according to the orebody geometry and the engineering properties of the strata. Because very few mineral deposits are uniform, most mines make use of more than one method.

The three main underground mining methods are stoping, room-and-pillar mining, and longwall mining.

In stoping, ore is blasted or excavated in a vertical or inclined stope and extracted from the base of the stope for removal from the mine. Various methods are used, including sub-level open stoping, longhole stoping, and cut-and-fill stoping, according to the geometry of the orebody and the relative strengths of the orebody and wall rock.

Room-and-pillar mining is best suited to gently dipping and relatively uniform bedded deposits, provided that the deposits are not too deep and the rock is strong enough for the pillars to support the overlying strata. At depths beyond 1000 to 2000 m, hard-rock room and pillar mining methods are considered dangerous because of rock bursts and other results of high stress concentration. The limiting depth in coal mines is much less, in the region of 200 to 300 m, since the rocks of the Coal Measures tend to be weaker. Room-and-pillar mining was used extensively in the UK and Europe for the extraction of building stone, such as the Jurassic oolitic limestones of the Bath area.

Longwall mining began in the coalfields as a method of extracting seams at depths in excess of 200 m. It is by far the most common method of working in European coal mines where the shallower seams have been depleted. Longwall mining is best suited to deposits ranging in thickness from 1 to 2.5 m, dipping at less than 12°, with relatively incompetent rock and a fairly competent floor. The method lends itself to mechanization, especially in coal mines where fast-moving shearing machines move across a 100- to 200-m face and load the coal into conveyors without the need for blasting.

Other forms of mining take place, most notably solution mining (leaching) or brining of evaporite deposits, which is a long-established method. The process is extensively used in the mining of halite in Cheshire.

Brian J. Mcconnell

Mining has played a central role in American economic development.Coal, petroleum, natural gas, and uranium helped fuel industrialization. Iron, cement, copper, and other mine products were transformed into manufactured goods and buildings. Gold and silver have at times served as monetary metals. Mining and drilling contributed to the accumulation of numerous family fortunes, including those of the Guggenheims, Rockefellers, Hearsts, and Mellons. Historically, the growth of mining and the growth of the economy were strongly intertwined. Between 1880 and 1970, mining output was cyclical and the trend rate of growth for mining and real gross domestic product were similar. After 1970, however, mining output remained flat.

Iron, copper, and coal were originally mined from outcroppings at or near the earth's surface, and gold was panned in streams. As the demand for mine products increased, miners searched farther afield, dug deeper, and drilled in the ocean. The increased difficulty of tapping these resources led to increased capital investment and dramatic changes in mine technologies. Through the early 1920s, many mines depended on workers using hand tools and rule‐of‐thumb techniques, while mules and steam‐run hoists or pumps moved the materials to the surface. Increases in mine output required more mine workers, although technological improvements in blasting and machinery based on steam, compressed air, and then electricity contributed to steady growth in output per miner. After the 1920s the pace of technological change increased dramatically. New machinery dug, drilled, pumped, and clawed underground, and many mines began using large‐scale earth movers to strip the hillsides above the mine seams. Consequently, mine output rose nearly eight‐fold from the mid‐1920s to the 1970s despite a 40 percent reduction in the number of miners. The improvements in mining technology also cut accident rates in half. Mining remained dangerous, however, as evidenced by a series of mining disasters, including those in Mather, Pennsylvania (1928, 195 dead); Centralia, Illinois (1947, 111 dead); and West Frankfort, Illinois (1951, 119 dead).

Mining was often the leading edge of development in isolated areas. Gold rushes and silver rushes opened up California, Nevada, Arizona, and the Black Hills. When coal and copper mines opened in unpopulated and undeveloped areas, employers attracted workers from outside the region by establishing company towns with housing, stores, and schools. As the number of mines increased or other industries developed, company towns gave way to independent towns and cities. In some isolated regions, however, the population dwindled when the resource was depleted, leaving ghost towns behind.

During the employment booms in the early 1900s, mine owners competed fiercely for labor. Consequently, miners were often highly mobile; they earned high hourly wages to compensate for the dangers of mining, and employers hired an ethnically diverse workforce. Competition among numerous mines in combination with the miners’ use of collective action limited the employers’ abilities to exploit their monopoly power in company towns. Miners went on strike more frequently than other workers, and several violent episodes erupted in the mine fields. Mine workers often were leaders in the major union movements. The hardrock miner William D. (“Big Bill”) Haywood led the radical Industrial Workers of the World. The United Mine Workers of America, led by John L. Lewis, played a leading role in the American Federation of Labor and the Congress of Industrial Organizations.
See also Carnegie, Andrew; Hearst, William Randolph; Iron and Steel Industry; Labor Markets; Petroleum Industry; Rockefeller, John D.; Strikes and Industrial Conflict.

Bibliography

John Laslett, ed., The United Mine Workers of America: A Model of Industrial Solidarity?, 1996.
David Pearson , This Was Mining in the West, 1996.

Price Fishback

MINING

Mining activities have been carried out by humans for millennia. The first book on mining, (and the health hazards associated with it), was De re metallica by Agricola, published in Switzerland in the sixteenth century. Mining is among the most hazardous of all occupations. Mining activities take place all over the world, and are often a major source of a country's natural wealth.

There are many types of mining operations, ranging from precious metals, such as gold, to other metals, and to minerals such as asbestos, sand, granite, and iron ore. Nonmetal mining can take many forms, including coal mining, which supplies much of the world's energy, and the mining of other materials such as clay, diamonds, semiprecious stones, and related substances.

Mining can take place on the surface of the earth or in underground settings. Depending on where in the world it is carried out, it may utilize nothing more than manual labor, or extraordinarily large and sophisticated mining equipment may be involved. Mining operations can vary in size from several people working alone (often family members) to large facilities employing hundreds of workers.

Traumatic injuries of many types are associated with mining activities. In underground mines there is the ever-present danger of explosion, foul air, water hazards, and other difficulties related to the use of mechanized equipment in confined spaces. Many injuries also take place in the transportation and processing of ore and other mined products.

Depending on the nature of the material being mined, there may also be a risk of damage to various organs. Particularly vulnerable are the lungs, with many lung diseases associated with exposures related to mining. These include the pneumoconioses, or dust diseases of the lung, which are caused by coal, silica, asbestos, kaolin, talc, and many other dusts. There is also a risk of lung cancer posed by some of these materials, and the fumes from diesel vehicles that may be used in underground mining settings also pose a threat. In many underground mining operations there is a risk of exposure to radioactive materials, especially in the form of radon gas, which can lead to high rates of lung cancer.

Although most mining-related lung disease is entirely preventable with the use of good ventilation, respirators when necessary, and other precautions, not only do traumatic injuries remain high, but long-term health effects are still quite common. The National Institute of Occupational Safety and Health (NIOSH) regularly documents these issues, and releases data regarding the respiratory problems related to mining.

Organizations involved with overseeing mining activities include NIOSH, which certifies respirators for use, and the Mining Safety and Health Administration (MSHA), which directly oversees safety practice at working mines, including oversight of dust sampling. There is still considerable medical research being done related to mining activities.

Mining activities also have a high potential for adversely affecting the general environment through air pollution, the fouling of bodies of water through runoff, or the contamination of soil with waste products.

Arthur L. Frank

(see also: National Institute for Occupational Safety and Health; Occupational Lung Disease; Occupational Safety and Health )

Bibliography

Rosen, G. (1943). The History of Miner's Diseases. New York: Schumans.

mining n. the process of placing land or naval mines in order to destroy or damage ground vehicles, boats, or aircraft, or to kill or wound enemy forces.