As early as 6,000 years ago humans collected lumps of gold or copper or iron and fashioned ornaments, implements, and tools from the soft metals. But nuggets of relatively pure metal are rare; most of the earth's metallic resources are chemically bound within rock of lesser utility. Thus the history of man's use of the earth's mineral resources comprises two topics: mining (extracting rock from the earth) and metallurgy (separating metals from their host ores, purifying them, and transforming them into a useful state). Mining and the exploitation of mineral resources over history have been shaped by the relationship between societies' demand for particular minerals and human's ability to extract, purify, and work with those materials. Chance discoveries play a small role and attract the investment of time and money only if there is sufficient demand. Mining's growth in world trade has historically responded to technological advances in both mining and metallurgical techniques. Finally, minerals are nonrenewable and nonreplicable. The first quality gives every historical mining experience its classic boom and bust cycles; the second quality means that nations, firms, or individuals desiring minerals must trade (or fight) for them if they do not possess them at home. Thus long-distance trade has been a standard component of mining and metallurgy from its inception.
MINING AND WORLD TRADE
Villages and societies have traded metals and metallic objects for millennia. The bronze-making societies of the Mediterranean in the first millennium b.c.e., for instance, used local sources of copper but imported tin, then traded bronze objects through Europe, north Africa, and parts of Asia. The Romans spread mining and metallurgical techniques further north and east. Medieval Europe saw moderate levels of regional trade in metals, whereas East Asian societies during the same period developed the world's most advanced techniques and high-volume trade, centered especially in China. But a broader and sustained international trade in mineral resources did not develop until the Portuguese and Spanish voyages of discovery in the late fifteenth century. After 1500 new markets for European metal products as well as new sources of raw materials in Africa, India, East Asia, and the Americas opened to European commerce.
Precious metals dominated the early international trade of mineral resources. Rising European powers in the fifteenth and sixteenth centuries sought gold and silver to finance local, regional, and continental wars. Nowhere was this more evident than with the Hapsburg monarchs of the Holy Roman Empire and Spain, manifest in their extraction of silver from Spain's American colonies to finance European ambitions. Access to bullion, they believed, constituted the foundation of national wealth; at least it paid for large armies. Moreover, gold and silver were the only metals with sufficient value to bear the high transportation costs of both oceanic trade (on relatively small and slow sailing ships) and overland trade (on the backs of humans, draft animals, or animal-pulled carts).
In the Americas, gold, silver, and copper had long been used by indigenous societies to make ornaments and some tools. Metallurgical techniques were most developed among the Incas of the Andean highlands, where smelting furnaces, gilding and welding techniques, and the use of alloys were developed by 1000 b.c.e. (although well after similar developments in Eurasia). The European conquest of the Americas in the early sixteenth century effectively destroyed indigenous metalworking techniques. Although the Spanish quest for El Dorado failed to yield rich gold mines after the initial seizure of Aztec and Incan ornaments, within half a century rich sources of silver were located in central Mexico and the southern Andes. By century's end, Spain's American mines dominated world production of the white mineral. American silver sailed the Atlantic in well-defended Spanish fleets to Seville, and then flowed quickly through Europe to pay for the Hapsburg's armies, for Spanish imports, and for Spanish debts. American silver also flowed west from Acapulco to the Spanish port of Manila and hence to China in exchange for silks and porcelain. The Spanish silver peso—mined and minted in the Americas with largely indigenous labor—quickly became the standard coin for international commerce throughout the world.
International trade created its own demand for metals: copper and bronze and iron for ship parts and the armaments to protect them; silver and gold to finance expeditions and navies. European copper joined American gold and silver in the holds of ships bound for India and beyond, exchanged for fabrics, spices, and other Asian goods. Japan experienced its own silver boom in the sixteenth century, and Japanese silver (and later, copper) competed with European metals in other Asian markets. At the same time that new sources of silver and gold were linked to European trade routes, an increasingly vigorous intra-European trade in metals as well as in experienced miners and metallurgists stretched from the British Isles to Russia and from Scandinavia to the Mediterranean. Sovereigns, manufacturers, and artisans sought cheap metal and skilled practitioners to jump-start their own enterprises or further their political ambitions.
Although international trade in metals continued through the sixteenth and seventeenth centuries, the next major shift in the level and direction of mining history came in the second half of the eighteenth century. Early industrialization in Britain after 1750 and its spread to the United States and continental Europe offered two new stimuli to world mining: first, new technologies to mine and refine metals dramatically lowered the costs of production; second, industrialization created new markets for nonprecious minerals such as iron, copper, lead, tin, and coal.
Since the publication of Georgius Agricola's De Re Metalica in 1556, methods to dig tunnels, remove water, ventilate shafts, power machinery, and haul ore had changed relatively little. Then, between 1750 and 1850, a wide range of new technologies transformed each of these activities. The steam engine had perhaps the biggest impact. Initially applied to the debilitating problem of dewatering deep mines, steam power was then harnessed to rock drills, stamp mills, tramways, and to locomotives. The railroad dramatically altered the economics and geography of mining throughout the world, opening new regions to exploitation and increasing scale economies in mining and metallurgy, carrying ore at a fraction of previous costs. Blasting powder also came into widespread use at this time, speeding the extension of tunnels and shafts. In metallurgy, coal and then coke replaced charcoal in iron smelting by the mid-eighteenth century, and the puddling and rolling process invented by Henry Cort (1740–1800) further improved quality and reduced costs. Industrialization in Western Europe also motivated colonial endeavors through the nineteenth century, and South African gold, Malayan tin, and central African copper (among others) flowed to European consumers.
Britain and its colonial empire led world metal production through much of the nineteenth century, but by late century was overtaken by the United States. Technical advances during this second industrial revolution once again changed the face of international mining and metallurgy. Large-scale steel production offered the most dramatic new development after 1850, and the application of electricity to a host of mining and metallurgical processes at century's end cut costs and opened new possibilities. In between, the use of dynamite and diamond drills made deep-rock mining a bit safer and faster, steam shovels speeded open-pit mining, and newly developed flotation and cyaniding processes increased metal yields from copper, gold, and silver ores. All of these technical innovations created financial incentives to increase the scale of mining and metallurgical operations, and large corporations increasingly dominated both sectors of the industry.
In the early decades of the twentieth century Germany rose to the first rank of the world's metal producers, followed by the Soviet Union at mid-century and Japan after World War II. But despite the dominant position of particular nations over the last two centuries, the business of mining and metallurgy has remained essentially international. Germany's rise as an industrial and military power, for example, owed partly to Swedish iron, Canadian nickel, Malayan tin, Rhodesian chrome, Hungarian bauxite, Ukrainian manganese, and Southeast Asian petroleum, not to mention iron and coal deposits much closer to home. The great wars of the twentieth century drove international developments in metallurgy and gave rise to the new mining industries for nickel, aluminum, and uranium. Postwar economic growth in the United States, Europe, and Japan deepened global metal markets and brought new developments in science and technology that lowered costs and increased access to mineral resources. Although the economies of the world's high-income countries have recently moved away from a dependence on metal-based heavy industry, access to mineral resources remains of central importance to the economies of much of the rest of the world.
Although the stolen treasures of the Aztec and Incan empires promised rich bonanzas in gold mining, Minas Gerais in Portuguese Brazil proved the New World's only significant producer after the sixteenth century, joined by other sources around the world to supply European and Asian demand for the next couple of centuries. The great gold rushes of the nineteenth century began in Siberia, followed by the Sierra Nevada of California in 1848, just nine days before Mexico transferred the territory to the United States. California's gold helped grease the wheels of a world trade boom after 1850, as had Spanish American silver three centuries earlier. California's bonanza previewed strikes and subsequent rushes in Southeast Australia (1850s), Colorado (1850–1860s), Montana (1860s), and South Dakota (1870s). In the late 1880s miners opened the rich gold-bearing reefs in the Rand, South Africa, which yielded one-third of the world's gold by 1907. The last of the great gold rushes came in Western Australia, the Yukon, and Colorado in the 1890s. Low-cost large-scale production in the rich South African fields subsequently dominated twentieth-century gold production; investors had little incentive to open new mines elsewhere as the U.S. dollar price of gold was pegged at $35 an ounce from the 1930s until the 1970s.
In California, as in most of these classic rush settings, individuals armed with a bedroll, a mining pan, and not much else undertook early exploration and mining. As initial hordes exhausted the loose-lying placer deposits, following gold-bearing veins underground and separating the gold from more complex ores required new technologies and ever-greater financial resources. Especially after 1900 the development and diffusion of the cyanide-separation process and the application of electrical power to hard-rock mining increasingly favored highly financed international corporations. This was especially true in the goldfields of South Africa, but technological developments and financing requirements pushed the consolidation of mines and metallurgical facilities the world over.
For centuries, silver coins constituted a universally accepted medium of exchange with high and stable value, and silver was the world's most traded metal until the Industrial Revolution. Using the mercury-amalgamation process, Spanish mines in Mexico and at Potosí in lower Peru produced more silver than any other region of the world from 1550 to 1850. In bullion or coin, Spanish America's silver exports reached the Baltics, Russia, the Ottoman Empire, India, and especially China. Even the United States's first paper currency specified that bills were payable in Mexican silver pesos.
The biggest new silver strike of the nineteenth century came in 1858 when gold prospectors discovered rich silver ore in western Nevada. Over the following decades the Comstock lode became the richest mining field on earth. As with gold, new techniques and financial trends pushed consolidation. By 1899 most of the silver-smelting facilities of the American West had been gathered within the American Smelting and Refining Company and the Guggenheim family, who expanded the company's reach to include dominant positions in western U.S. metallurgy and in Mexican silver, lead, and copper production, as well as additional interests in Europe and Africa.
Late-century discoveries and the application of cyanide separation to silver boosted world production levels briefly, but the world's demand for silver had long been tied to its use as the foundation for much of the world's coinage. As nation after nation switched to gold-backed currencies in the late nineteenth century, international demand for silver fell and its price plummeted. By the early twentieth century silver had lost its prominent place in world mining, and industrial uses overtook coinage thereafter.
Iron is the earth's most plentiful metal, and its production dates from about 2000 b.c.e. Wrought iron, soft but strong, became the leading tool- and weapon-making material of Europe's forges and anvils from Roman times through the medieval era. Blast furnaces to produce pig (or cast) iron developed first in China, and were established in Europe by about 1500. Cast iron was too hard and brittle for most uses, but by the late eighteenth century blast-furnace improvements, the replacement of charcoal by coal and then coke, and Cort's new puddling process yielded iron of sufficient quality and quantity to supply Britain's growing industrial demands. Until then, British manufacturers had imported iron from Sweden and Russia, where cheap labor, abundant wood, and purer ores could outcompete Britain's home product, even with added transport costs. In the decades to follow, Britain's disadvantage disappeared. Technological advances loosened supply constraints as demand for iron in construction and industry expanded rapidly. British iron production roughly doubled each decade through the first half of the nineteenth century, and British iron products flooded world markets.
Beginning in the 1850s a series of furnace advances permitted the mass production of steel, an iron product harder than wrought and stronger than cast iron. The Bessemer, Siemens, and Thomas-Gilchrist processes appeared first in Britain, then spread rapidly to the United States. The combination of Great Lakes iron, Appalachian coal, Bessemer mills, cheap water transport, and the efforts of men such as Andrew Carnegie (1835–1919) made the United States the world's leader in steel production by the late nineteenth century. In 1901 the U.S. Steel Corporation became the biggest "trust" in an era of mammoth corporate combinations. Germany's industrial rise in the late nineteenth century was partially built on the exploitation of European iron and coal, and the great steel mills built through the Ruhr region surpassed British steel production by 1900 to lead Europe. Although the scale of steel production increased dramatically through the twentieth century and new production centers emerged (most notably in Japan), blast-furnace technologies remained the mainstay of the industry until well after World War II.
Sweden took the early lead in modern copper production, dominating European and world production until well into the seventeenth century. Leadership soon passed to the southwest of England, where Cornish copper and tin mines were among the first to use James Watt's new steam engine in the 1780s. The region's smelting center at Swansea in Wales comprised a small number of large firms using the most advanced smelting techniques to produce the world's cheapest copper. In the early nineteenth century British investors financed the modernization of Chile's copper mines, shipping the raw ore around Cape Horn to join Cornwall's ores in the Swansea smelters, which produced fully three-quarters of the world's copper.
In the second half of the nineteenth century new copper mines threatened the supremacy of this arrangement. These included Spain's Tharsis and Rio Tinto; the rich mines on Michigan's Lake Superior coast; and new large discoveries in the American West. For a time most of the world's copper ores continued to undergo final smelting in Britain's Swansea district, filling the harbor there with ships from the United States, Chile, and Spain. Increasingly, however, new smelters and new techniques broke Britain's hold and shifted the center of world production to the United States. Application of the new Bessemer and electrolytic processes to copper refining in the last decades of the nineteenth century allowed global production to expand eight-fold between the 1880s and the 1920s and drove industrial concentration. New open-pit mines opened in Utah, Alaska, Chile, the Belgian Congo, and elsewhere to fill demand for copper electrical wire and other new applications.
TIN AND OTHER METALS
Cornish mines and Welsh smelters led global tin production well into the nineteenth century. After 1860, however, cheaper tin from other parts of the world swamped European markets. The exhaustion of Britain's tin reserves combined with lower production costs elsewhere favored new tin centers in Malaya, Sumatra, Bolivia, and Nigeria.
In the twentieth century zinc, aluminum, and uranium joined the ranks of the world's important industrial metals. Aluminum became the first new metal of the twentieth century, with uses ranging from aircraft to cans. Like other minerals, aluminum was a truly international business. Bauxite deposits in Brazil, Asia, and France fed smelters in Switzerland and the United States. Large corporations dominated both sectors of the industry: ALCOA in the United States, and AEG, AIAG, and British Aluminum in Europe, all with worldwide interests. In aluminum, as with other minerals, the world's biggest companies coordinated production, prices, and global trade through much of the century.
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Tylecote, R. F. A History of Metallurgy, 2nd edition. London: Institute of Materials, 1992.
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.
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.
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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.
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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
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 is the process by which ores or related materials are extracted from Earth. Ore is defined as a rock or mineral, generally metallic, which can be mined, processed, transported, and sold at a profit. Therefore, the classification of an Earth material as ore depends as much on economics and technology as geology. Non-metallic substances that are commonly
mined but not considered to be ores include coal, phosphate, and sand and gravel. The term ground-water mining is sometimes used to describe the withdrawal of groundwater from an aquifer more rapidly than it is recharged by infiltration or underground flow from adjacent areas.
Mining can occur either at Earth’s surface in strip mines or open pit mines, or beneath the surface in underground mines. The method used depends on the depth, lateral extent, and economic value of the rock being mined. The deepest underground mine on Earth, which is 2.4 mi (3.8 km) deep, is a South African gold mine. The open-pit Bingham Canyon Mine near Salt Lake City, Utah, is more than 2.5 mi (4 km) wide and more than 0.6 mi (1 km) deep. It is the largest man-made excavation on Earth. Excavation of the pit began in 1906 and has continued into the early twenty-first century, producing primarily copper with smaller amounts of gold, silver, and molybdenum.
Many metals occur in their native state or in readily accessible ores. Thus, the extraction and working of metals dates much further back in time than does the mining industry. Some of the earliest known mines were those developed by the Greeks in the sixth century BC. As were mines for many centuries thereafter, the workers in these mines were slaves and prisoners of war. By the time the Roman Empire reached its peak, it had established mines throughout the European continent, in the British Isles, and in parts of North Africa. The first scientific description of mining operations was the book De Re Metallica by the Saxon physician Georgius Agricola (1494–1555). De Re Metallica, which remained an authoritative reference for nearly 200 years, was translated from Latin to English by mining engineer and former United States president Herbert Hoover (1874–1964) and his wife Lou Henry Hoover (1874–1944).
Surface mining is less expensive and safer than underground mining. About 90% of the rock and mineral resources mined in the United States and more than 60% of the nation’s coal is produced by surface mining techniques. Coal mining accounts for about half of all surface mining, extraction of sand, gravel, stone, and clay for another 35%, phosphate rock for about 5%, and all metallic ores, for about 13%.
There are four kinds of surface mines: open-pit mines, strip mines, mountaintop mines, and alluvial (or placer) mines. Open-pit mines consist of deep cone-shaped holes or pits that are excavated in rock that is first loosened by blasting. In order to prevent the sides of the pit from collapsing, open-pit mines must be continually widened as they are deepened. Open-pit mines are used when the ore is of low grade, meaning that the amount of metal per cubic meter or kilogram of rock is small, and disseminated, meaning that the metals are distributed throughout large volumes of rock rather than being concentrated in veins. The size of open-pit mines, which often take decades to excavate, makes it uneconomical to reclaim the pits by filling them with rock.
Strip mines consist of shallow excavations, typically 109 yd (100 m) or less, that are used to mine tabular bodies of rock such as coal. Soil and rock above the mined material, known as overburden, are removed and set aside. Because the strip mines consist of shallow excavations, the overburden can be economically replaced, re-contoured to resemble the original topography, and replanted.
Mountaintop mining came into widespread use in Appalachian coal fields following the 1997 passage of the Surface Mining Control and Reclamation Act by the United States Congress. Mountaintop mining is similar to strip mining in that the overburden above a tabular coal deposit is removed. Instead of being stockpiled and used to restore the original topography, however, the overburden is used to fill adjacent valleys. Although mountaintop mining is an inexpensive method of mining coal in mountainous areas, the filling of valleys can have negative environmental impacts. Mountain-top mining in Appalachia was the subject of lawsuits, many of them alleging violations of the Clean Water Act by mining companies engaged in mountain-top mining, during the early twenty-first century.
Alluvial mining is a form of surface mining used to recover heavy minerals such as gold from sand and gravel beds, including stream beds, known as placer deposits. In some cases these deposits can be removed mechanically by agitating the sand and gravel in simple pans. A more sophisticated and efficient way of separating placer minerals from the sand and gravel is a sluice box, a long, shallow box with wooden separators placed along its bottom. As sand and gravel is shaken in the sluice box, lighter sand grains are washed away and heavier metals are left behind. A particularly destructive form of alluvial mining is hydraulic mining, in which pressurized water is used to wash away large amounts of sand and gravel. Dredges are used in other large-scale alluvial mining operations.
Underground mining involves the excavation of tunnels and rooms beneath Earth’s surface. Compared to surface mining, underground mining is expensive and dangerous. Therefore, it is used primarily in situations where high-value ores such as gold are concentrated in narrow veins or other unusually rich deposits. Unlike surface mines, underground mines can also be excavated beneath bodies of water. Salt mines more than 328 yd (300 m) deep, for example, extend beneath Lake Erie near Cleveland, Ohio, and Detroit, Michigan.
The vocabulary of underground mining has developed over several centuries. Shafts are vertical passages excavated downward from Earth’s surface, whereas raises and winzes are vertical passages excavated upward and downward, respectively, between horizontal workings beneath the surface. An adit is a horizontal passage excavated into a hillside, whereas an incline is a sloping passage excavated inward from a hillside. Horizontal underground passages following the trend of the ore body are known as drifts. An open room beneath the surface is a stope and its roof is known as the back.
Underground mines are excavated using a variety of methods. Room-and-pillar mining is the excavation of large open rooms supported by pillars. Coal and rock salt (halite) are commonly mined using room-and-pillar methods. Longwall mining is a form of underground mining widely used in the coal industry. A coal seam is completely removed using specialized machines, leaving no support and allowing the overlying rock to slowly subside as the seam is mined. Open-stope mining, in contrast, consists of rooms without any supporting
Adit— A horizontal passage constructed into a hillside to gain access to underground mineral deposits.
Overburden— Material that must be removed in order to gain access to an ore or coal bed.
Panning— The process of separating metallic nuggets and flakes from sand and gravel by shaking them in a pan filled with water.
Placer— An accumulation of metallic flakes or nuggets, typically gold, in sand and gravel deposited by running water.
Raise— Vertical passages extending upward from a level in a subsurface mine.
Room-and-pillar— A technique for mining certain kinds of minerals, especially coal, in which vertical shafts of the mineral are left in place to support the roof of the mine.
Shaft— A vertical tunnel constructed downward from the surface to gain access to underground mineral deposits.
Sluice box— A device used to separate metals and metallic ores from sand and gravel.
Stope— An open room produced by the removal of ore and in which mining is occurring.
Subsidence— A sinking or lowering of Earth’s surface.
Winze— A vertical passage extending downward from a level in a mine.
pillars. It is employed if the ore body is small or the rock is strong enough to withstand collapse into the stope. Sublevel caving and block caving involve the excavation of vertical chutes and horizontal passages beneath an ore body, which is then allowed to collapse into the openings under its own weight. Gloryhole mining is a term used to describe caving methods that result in the formation of a crater or depression on the surface above the mine.
Certain water-soluble minerals can be removed from the Earth by dissolving them with hot water piped into the ground under pressure. This practice is known as solution mining. The minerals dissolve in the hot water and then are carried to the surface. In the Frasch process, a system of pipes is sunk into a known deposit of sulfur at some depth under ground. Steam forced into one pipe melts the sulfur, which is then extracted in a liquid form through a second pipe.
Hartman, H.L. and J.M Mutmansky. Introductory Mining Engineering. Hoboken, New Jersey: Wiley, 2002.
David E. Newton
William C. Haneberg
Mining is the process by which ores or related materials are extracted from the Earth . Ore is defined as a rock or mineral, generally metallic, which can be mined, processed, transported, and sold at a profit. Therefore, the classification of an Earth material as ore depends as much on economics and technology as geology . Nonmetallic substances that are commonly mined but not considered to be ores include coal , phosphate, and sand and gravel. The term groundwater mining is sometimes used to describe the withdrawal of groundwater from an aquifer more rapidly than it is recharged by infiltration or underground flow from adjacent areas.
Mining can occur either at Earth's surface in strip mines or open pit mines, or beneath the surface in underground mines. The method used depends on the depth, lateral extent, and economic value of the rock being mined. The deepest underground mine on Earth, which is 2.4 mi (3.8 km) deep, is a South African gold mine. The open-pit Bingham Canyon Mine near Salt Lake City, Utah, is more than 2.5 mi (4 km) wide and more than 0.62 mi (1 km) deep. It is the largest man-made excavation on Earth. Excavation of the pit began in 1906 and has continued into the early twenty-first century, producing primarily copper with smaller amounts of gold, silver, and molybdenum.
History of mining
Many metals occur in their native state or in readily accessible ores. Thus, the extraction and working of metals dates much further back in time than does the mining industry. Some of the earliest known mines were those developed by the Greeks in the sixth century b.c. As were mines for many centuries thereafter, the workers in these mines were slaves and prisoners of war. By the time the Roman Empire reached its peak, it had established mines throughout the European continent , in the British Isles, and in parts of North Africa . The first scientific description of mining operations was the book De Re Metallica by the Saxon physician Georgius Agricola (1494–1555). De Re Metallica, which remained an authoritative reference for nearly 200 years, was translated from Latin to English by mining engineer and former United States president Herbert Hoover (1874–1964) and his wife Lou Henry Hoover (1874–1944).
Surface mining is less expensive and safer than underground mining. About 90% of the rock and mineral resources mined in the United States and more than 60% of the nation's coal is produced by surface mining techniques. Coal mining accounts for about half of all surface mining, extraction of sand, gravel, stone, and clay for another 35%, phosphate rock for about 5%, and all metallic ores, for about 13%.
There are four kinds of surface mines: open-pit mines, strip mines, mountaintop mines, and alluvial (or placer) mines. Open-pit mines consist of deep cone-shaped holes or pits that are excavated in rock that is first loosened by blasting. In order to prevent the sides of the pit from collapsing, open-pit mines must be continually widened as they are deepened. Open-pit mines are used when the ore is of low grade, meaning that the amount of metal per cubic meter or kilogram of rock is small, and disseminated, meaning that the metals are distributed throughout large volumes of rock rather than being concentrated in veins . The size of open-pit mines, which often take decades to excavate, makes it uneconomical to reclaim the pits by filling them with rock.
Strip mines consist of shallow excavations, perhaps 109 yd (100 m) or less, that are used to mine tabular bodies of rock such as coal. Soil and rock above the mined material, known as overburden, are removed and set aside. Because the strip mines consist of shallow excavations, the overburden can be economically replaced, re-contoured to resemble the original topography, and replanted.
Mountaintop mining came into widespread use in Appalachian coal fields following the 1997 passage of the Surface Mining Control and Reclamation Act by the United States Congress. Mountaintop mining is similar to strip mining in that the overburden above a tabular coal deposit is removed. Instead of being stockpiled and used to restore the original topography, however, the overburden is used to fill adjacent valleys. Although mountaintop mining is an inexpensive method of mining coal in mountainous areas, the filling of valleys can have negative environmental impacts. Mountain-top mining in West Virginia was halted by a court order in 2002 on the grounds that the practice violated the Clean Water Act, but changes to the act may again make the method legal.
Alluvial mining is a form of surface mining used to recover heavy minerals such as gold from sand and gravel beds, including stream beds, known as placer deposits. In some cases these deposits can be removed mechanically by agitating the sand and gravel in simple pans. A more sophisticated and efficient way of separating placer minerals from the sand and gravel is a sluice box, a long, shallow box with wooden separators placed along its bottom. As sand and gravel is shaken in the sluice box, lighter sand grains are washed away and heavier metals are left behind. A particularly destructive form of alluvial mining is hydraulic mining, in which pressurized water is used to wash away large amounts of sand and gravel. Dredges are used in other large-scale alluvial mining operations.
Underground mining involves the excavation of tunnels and rooms beneath Earth's surface. Compared to surface mining, underground mining is expensive and dangerous. Therefore, it is used primarily in situations where high-value ores such as gold are concentrated in narrow veins or other unusually rich deposits. Unlike surface mines, underground mines can also be excavated beneath bodies of water. Salt mines more than 328 yd (300 m) deep, for example, extend beneath Lake Erie near Cleveland, Ohio, and Detroit, Michigan.
The vocabulary of underground mining has developed over several centuries. Shafts are vertical passages excavated downward from Earth's surface, whereas raises and winzes are vertical passages excavated upward and downward, respectively, between horizontal workings beneath the surface. An adit is a horizontal passage excavated into a hillside, whereas an incline is a sloping passage excavated inward from a hillside. Horizontal underground passages following the trend of the ore body are known as drifts. An open room beneath the surface is a stope and its roof is known as the back.
Underground mines are excavated using a variety of methods. Room-and-pillar mining is the excavation of large open rooms supported by pillars. Coal and rock salt (halite) are commonly mined using room-and-pillar methods. Longwall mining is a form of underground mining widely used in the coal industry. A coal seam is completely removed using specialized machines, leaving no support and allowing the overlying rock to slowly subside as the seam is mined. Open-stope mining, in contrast, consists of rooms without any supporting pillars. It is employed if the ore body is small or the rock is strong enough to withstand collapse into the stope. Sub-level caving and block caving involve the excavation of vertical chutes and horizontal passages beneath an ore body, which is then allowed to collapse into the openings under its own weight. Gloryhole mining is a term used to describe caving methods that result in the formation of a crater or depression on the surface above the mine.
Certain water-soluble minerals can be removed from the Earth by dissolving them with hot water piped into the ground under pressure . This practice is known as solution mining. The minerals dissolve in the hot water and then are carried to the surface. In the Frasch process, a system of pipes is sunk into a known deposit of sulfur at some depth under ground. Steam forced into one pipe melts the sulfur, which is then extracted in a liquid form through a second pipe.
Brown, Maurice Russell, and Herbert Ralph Rice. Mining Explained in Simple Terms. Toronto: Northern Miner Press, 1968.
Hustrulid, William A., and Richard L. Bullock, eds. Underground Mining Methods: Engineering Fundamentals and International Case Studies. Littleton, Colorado: Society for Mining, Metallurgy, and Exploration, 2001.
Thomas, L. J. An Introduction to Mining: Exploration, Feasibility, Extraction, Rock Mechanics. Sydney: Hicks Smith & Sons, 1973.
Charleston Gazette Online. "Mining the Mountains." 2002 [cited January 15, 2003]. <http://wvgazette.com/static/series/mining/>.
Kentucky Department for Surface Mining Reclamation and Enforcement. "Mining Education." November 20, 2002 [cited January 15, 2003]. <http://www.kyenvironment.org/nrepc/dsmre/NRDSMRE/dsmremay13/mining_education.htm>.
United Mine Workers of America. "What Coal Miners Do." [cited January 15, 2003]. <http://www.umwa.org/mining/colminrs.shtml>.
David E. Newton William C. Haneberg
KEY TERMS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
—A horizontal passage constructed into a hillside to gain access to underground mineral deposits.
—Material that must be removed in order to gain access to an ore or coal bed.
—The process of separating metallic nuggets and flakes from sand and gravel by shaking them in a pan filled with water.
—An accumulation of metallic flakes or nuggets, typically gold, in sand and gravel deposited by running water.
—Vertical passages extending upward from a level in a subsurface mine.
—A technique for mining certain kinds of minerals, especially coal, in which vertical shafts of the mineral are left in place to support the roof of the mine.
—A vertical tunnel constructed downward from the surface to gain access to underground mineral deposits.
- Sluice box
—A device used to separate metals and metallic ores from sand and gravel.
—An open room produced by the removal of ore and in which mining is occurring.
—A sinking or lowering of the Earth's surface.
—A vertical passage extending downward from a level in a mine.
From the moment humans discovered stone tools and salt, they have been extracting and using materials from the Earth. Every American will utilize approximately 2.4 million pounds of mined materials during their lifetime (calculated from Mineral Information Institute statistics). In spite of people's dependence on the products of extractive technologies and their associated sciences, mining is a highly controversial activity surrounded by ethical, political, social, and legal issues. Mining focuses attention on the metaphysical relationship of humans to the Earth, on the impact of their activities on the environment and other species, on issues of equity and sustainability, on human rights and democracy.
Mining is the extraction of metallic or nonmetallic materials from the Earth. The full cycle of mining involves exploration for the material required; mining sensu stricto, which is the physical removal of material from the Earth; processing, which is usually required to concentrate or clean the ore; the health, safety, and environmental issues associated with the full cycle of mining activities; and appropriate closure of the site when mining is completed (National Research Council 2002).
Surface mining, where material is separated directly from the surface of the Earth, is the oldest and most common method of mining. Underground mining, where the material is extracted via tunnels dug into the Earth, is used to work deeply buried ores. Mining technology has evolved greatly, but the basic concept of removing rock or minerals from the Earth has remained constant since prehistory. Nonentry mining, by which the valuable components of the rock are extracted without physically removing the surrounding rock, is still at an experimental stage.
The many ethical, social, and political challenges associated with mining can only be addressed within the context of the prevailing philosophical view of the relationship of human beings to the Earth and its resources. From prehistoric time through the sixteenth century, many cultures regarded Earth as animate. Ores grew and matured in the uterus of the Earth; mining was an interference with the natural order and was often accompanied by myths and rituals (Eliade 1962). In the Western world, the organic view of nature was superceded by a mechanical model during the Scientific Revolution: The Earth is inanimate, and its resources should be exploited for the benefit of humans (Merchant 1980). In the late twentieth century, scientists developed holistic syntheses that integrate humans, other living beings, and Earth in an all-encompassing, interdependent Earth system. Some philosophers emphasize the importance of the humanities in understanding the full dimensions of the human–Earth system relationship (Frodeman 2003). These cross-disciplinary concepts are the basis for most modern interpretations of the place and responsibilities of mining.
Polarized positions on the ethics of mining are strongly developed and there have been few true dialogs on the subject. One early-twenty-first century attempt to foster communication is the Mining, Minerals, and Sustainable Development Project, which concluded that economic, social, environmental, and governance issues must be addressed appropriately by all participants in order to meet the conflicting demands of society for the products of mining while still maintaining sustainability (International Institute for Environment and Development, and World Business Council for Sustainable Development 2002). Finding mechanisms whereby all the stakeholders can be involved in negotiating acceptable practices and compensation for mining has proved difficult. Some nongovernmental organizations and companies have promoted formal or informal democratic fora, but they have been difficult to implement in areas lacking good governance or a history of citizen participation.
Mining is inherently inequitable. Earth resources are not distributed evenly, and mines can only be located where there are suitable resources. Many of the social and environmental consequences of mining are concentrated at the mine site even if the consumer or ultimate beneficiary of the mine product, or the wealth it creates, is far away. Resolving these inequities are some of the major ethical and political challenges associated with mining.
A fundamental question concerns ownership and control of the mineral endowment. Does a nation, or a sovereign, or a dictator, own the mineral wealth of a country? Or is it instead the landowner, the owner of the mineral rights, the person or company who discovered the deposit, the artisan miners who may have worked the deposit, or the local community (however defined)? In many cases the owner of a mineral deposit is not competent to mine it. In capitalist societies the high financial risk of mineral exploration and mining is usually borne by corporations that also supply technical expertise, and in return expect a profit from their investment. Almost every country has devised a different formula for regulating mineral ownership and control, for calculating taxes, and for oversight of mining activities and their impact.
A mine may introduce large amounts of capital or people into an area, distorting the economic and social structure. Corruption may become a problem. Wars are fought over the control of resources, and illicit trade particularly in diamonds and columbite-tantalite has funded conflicts, such as those in Angola and Congo, in the twentieth and early-twenty-first centuries. Safeguarding the human rights of workers and local populations is also a concern. Disciplined and transparent governance by governments and companies is necessary to stabilize the impact of mining.
Economic analysis shows that the Earth is unlikely to run out of mineral resources in the twenty-first or twenty-second centuries, which is as far forward as such predictions can be made, but the total cost of mining (including environmental, social, and other external costs) may limit the willingness to produce minerals (Tilton 2003). The role of mining in sustainable development is controversial, and conclusions largely depend on what values or assets one wishes to sustain, and on the scale at which the question is examined. Tilton (2003) argues that mining can contribute to global sustainable development if the products and profits of present-day mining are used to provide other assets of equivalent or greater value to succeeding generations. Analyses that concentrate on preserving the lifestyle, economy, or environment of a particular location are more likely to conclude that mining is a temporary phenomenon which disrupts rather than sustains development.
Technological innovation may lessen the demand for mineral products and lower the environmental impact of mining, but intellectual innovation is also vital to resolve the social and cultural consequences of mining.
MAEVE A. BOLAND
Eliade, Mircea. (1978 ). The Forge and the Crucible: The Origins and Structures of Alchemy, 2nd edition, trans. Stephen Corrin. Chicago: The University of Chicago Press.
Frodeman, Robert. (2003). Geo-Logic: Breaking Ground Between Philosophy and the Earth Sciences. Albany: State University of New York Press.
International Institute for Environment and Development, and World Business Council for Sustainable Development. (2002). Breaking New Ground: Mining, Minerals, and Sustainable Development. The Report of the MMSD Project. London: Earthscan Publications Ltd.
Merchant, Carolyn. (1980). The Death of Nature: Women, Ecology, and the Scientific Revolution. San Francisco: Harper & Row.
National Research Council. (2002). Evolutionary and Revolutionary Technologies for Mining. Washington, DC: Committee on Technologies for the Mining Industries, National Academy Press.
Tilton, John E. (2003). On Borrowed Time? Assessing the Threat of Mineral Depletion. Washington, DC: Resources for the Future.
International Institute for Environment and Development, and World Business Council for Sustainable Development. "Breaking New Ground: Mining, Minerals, and Sustainable Development. The Report of the MMSD Project." Available from http://www.iied.org/mmsd/finalreport/.
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.
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.
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 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.
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.
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.
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.
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.
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 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 )
Rosen, G. (1943). The History of Miner's Diseases. New York: Schumans.