Mining is the working of pits or excavations from which minerals (coal, metals, salt, iron, and so forth) are extracted from \Tore deposits\t or large aggregations. Glass sands, gems, fertilizers such as potash, phosphates, and nitrates are also mined, as well as petroleum and natural gas. Increasingly, the ocean is being mined for \Lmanganese nodule\ls and other minerals. Quarrying is the extraction of stone, either in blocks or as aggregate (sand and gravel), from open excavations. This article discusses the history and present technologies associated with mining and quarrying in general. Descriptions of the special techniques used to mine a particular substance (for example, \Tcoal\t; \Tgold\t; \TSALT\t; \Tpetroleum\t) will be found in the article on that substance. Since ancient times mining has had a fundamental political impact on society. Wars have been fought to acquire minerals. The institution of slavery received much of is legitimacy from the need to use slaves in the onerous and often life-threatening work of mining. The exploration of Latin America and the opening of the American West were both accelerated by the presence of gold and silver in those new lands. Colonization of many areas of the world was in part due to the need of Europe to acquire the metals to feed the factories of the Industrial Revolution. Today, world politics and world trade are shaped in large measure by the locations of mineral and energy reserves. DEVELOPMENT OF MINING TECHNOLOGY Mining is one of the oldest human activities. Archaeologists in South Africa (one of the leading mineral producers in the world) have reported evidence that an iron mine there was worked, probably for the pigments associated with iron ores, 43,000 years ago. The earliest metals used by Neolithic peoples were probably gold and copper, for they occur "free" of other chemicals. Gold was extracted from stream beds, and copper from seams exposed on the earth's surface. The Egyptians mined copper and turquoise in the Sinai Peninsula about 3400 BC. Some pieces of beaten copper found in eastern Anatolia may date from 10,000 BC. Copper was the first metal used in tools, and in some cases it served as a medium of exchange. Bronze, a mixture of copper and tin, was the first commonly used alloy, appearing about 3000 BC. Iron smelting began between 1900 and 1400 BC. (See \TBronze Age\t; \TIron Age\t.) Early mining was probably for the most part alluvial--that is, from free metals that had been washed out of gravel occurring on or near the surface. Underground mining was undertaken by 1300 BC in the Nubian desert, and one surviving mine is 450 m (1,500 ft) long and was excavated to a depth of 89 m (292 ft). Underground mines in the Tyrol were worked from about 1600 to 400 BC. Copper ore was heated on the mine face by fires in the shaft, and cold water was thrown on the ore to break it loose. Chunks were then reduced with bronze hammers. Flint for tools was mined in Belgium and England by 2000 BC, using flint axes and wedges, pikes, and rakes fashioned from deer antlers. Both the Greeks and Romans carried on intensive mining activities, but after the fall of the Roman Empire, European mining experienced a decline from which it did not recover until the 11th century. References to coal mining survive from the 13th century. By the medieval period, the ancient reverence for the Earth as a living Mother, and ores as living substances gotten from her womb, had been replaced by the simple notion of minerals as a resource to be exploited for the greater wealth of society. At the same time, that new wealth demanded larger quantities of metals for new enterprises and devices, such as the cannon. Medieval mining techniques had probably changed little from Roman practice, but when the first books on the subject appeared in the 16th century (notably, Agricola's De re metallica, 1556), they showed that basic mining operations--draining and ventilating the mines, carrying the ore to the surface, and crushing and washing it preparatory to working it--were all undergoing mechanization. Improvements in drainage through the use of waterpower, especially, were soon transferred to other industries. The first useful steam engine, Thomas \TSavery\t's "Miner's Friend" of 1699, was developed to drain mines. As coal mines grew deeper after 1750, the problems of draining water, ventilation (especially because of dangerous gases), and getting the ore to the surface all increased. Improved steam engines solved the drainage problem. Ventilation was handled by auxiliary shafts for better circulation and by fires in the mines to draw in fresh air and expel the old heated air. Coal and other ores were removed from the face by picks and blasting. Ore was still transported through the mines by human (and sometimes animal) power during the mid-19th century, and women were often used to carry the broken ore, in baskets, up ladders in the shafts. All mine tasks were difficult and dangerous, although 19th-century improvements--including the safety lamp, underground tracks for coal carts, steam hoists, and the power drill--bettered working conditions to some extent. In the mining of metals, there were few changes in mining techniques between 1750 and 1850, but between 1875 and 1900 tonnage of the five leading nonferrous base metals (copper, lead, zinc, nickel, tin) rose from 268,000 to 1,955,000, and mining on a large scale spread from its historic sites in Britain, Sweden, Bohemia, and Spain. A worldwide search for ores was undertaken, and the skills of the chemist and engineer were more often employed. Power drills for making shot holes for explosives were used in hard-rock mines after the 1860s. After 1900, diesel locomotives were used to haul ores underground; the Leyner water drill (1907) reduced the dust caused by drilling; tungsten carbide-tipped drills during the 1930s increased efficiency at the work face. In coal mines, mechanical cutters at the face after 1900 forced the introduction of convey or belts to carry the material away more rapidly. Strip mining--that is, stripping away the shallow overlay to get at ore from the surface--has become widespread for coal and other ores as powerful machines have become available to dig and remove vast amounts of materials. PROSPECTING Since the 18th century the prospector's luck and experience have been increasingly augmented by a firmer grasp of scientific principles and, especially since World War II, a recourse to sophisticated technology. Most of the ore outcrops--telltale deposits on or near the earth's surface--have already been discovered, and modern prospecting relies heavily on geological techniques that suggest the presence of underground ores. A geological survey begins with mapping the area of exploration. Such a map will note surface features and the various types of surface rock--as well as estimations of the depth of rock formations--and structural features, such as faults and fractures. On the basis of the maps, target areas are selected for evaluation. Test holes are cut using drilling bits permeated with artificial diamonds, and core samples are evaluated. Geophysical testing techniques include seismic surveys, which test the elapsed time between the firing of an explosive charge in a surface feature and the detection of the resulting sound waves as they are reflected back from rock beds or other mineral deposits. The time lapse, the duration of the sound waves, and other evidence indicate the type of subsurface material. Geiger counters measure radioactivity and point to the presence of such radioactive minerals as uranium. Various types of instruments measure magnetic, gravitational, electric, and thermal properties, aiding in determining the types of materials buried in underground rock. Measurements are carried out on the ground or, very often, from specially equipped airplanes. In 1972 the National Aeronautics and Space Administration (\TNASA\t) launched the satellite Landsat 1, which began a program of remote sensing of earth-resource data. With images covering up to 33,675 km2 (13,000 mi2), the more recent Landsat D series of satellites will scan for several different wavelengths simultaneously. Coupled with powerful computers, such sensors can discover the surface signatures of mineral wealth over large areas of land. Landsat D's thematic mapper scanner uses a new 2.2-micron infrared band that detects so-called clay "alteration zones." These zones have been created by the decay of original rock into clay under the influence of mineralizing fluids and are often associated with mineral deposits. MINING METHODS Ore deposits vary greatly in their physical characteristics. Ore may be excavated by means of a series of horizontal, vertical, or inclined workings in veins and in more irregular ore deposits, or by openings, known as rooms, in flat deposits. The various excavation methods, the ore's removal from underground, and the measures taken to support the mine to prevent cave-ins, are all activities included in the meaning of the special mining term stoping. Stoping The mining methods that can be applied to a given ore body depend on the nature and size of the supports required to maintain the backs and the walls of an excavation, and on the requirements for permanently supporting the overlying and surrounding rocks and overburden to prevent movement and subsidence. Some mines are naturally supported and need little extra aid. These are generally relatively small bodies of ore. Artificially supported stopes use additional measures to support the mine opening, shafts, and working areas. In cut-and-fill stoping, the ore is excavated by working upward in vertical or steeply dipping veins. As the broken ore is removed, waste rock, sand, or some other filling material is run into the opening, leaving sufficient room so that further mining can be done. In narrow veins timber may be used for support. In square-set stopes, the walls and back of the working area are supported by regular framed timbers forming a skeleton enclosing a series of contiguous rectangular spaces and providing continuous support in all directions. The ore is excavated so as to provide just enough room for installing the next set of timbers. In block caving, a thick block of ore is partly cut off from surrounding blocks by a series of drifts (mine openings). The block is then undercut and caves in under its own weight. This method is employed primarily for mining low-grade ores because it is done on a large scale and at low cost. Two or more stoping methods may be used independently in the same mine. The actual mining involves drilling, blasting, mucking (material removal), and the various operations on the surface necessary to remove the ore and to transport the miners. In recent years improvement in these processes has come largely through seeking greater energy efficiency, higher labor productivity (especially through the replacement of people by machines), more continuous production methods, increased durability of equipment, and operating flexibility. Drilling shot holes and blasting the ore is still a standard process. Continuous mining machines are found primarily in the working of coal where a single machine cuts, breaks, and loads the coal. Such machines work efficiently only on large veins of a mineral. Other mines may use conveyor belts to transport chunks of ore to loading areas. Broken ore may be removed from the mine by electric- or diesel-powered railroad cars or by hoists pulled up the mine shaft. Surface mining The two chief methods of surface mining are placer and open-pit, or strip, mining. Placer mining is used today primarily for gold or tin recovery out of stream beds. (\Lplacer deposit\ls, by contrast, are underground mineral deposits--especially gold, diamonds, and titanium--originally formed by the action of water on rock.) Because the mined material is heavier than the debris surrounding it, washing stream-bed gravel will cause it to settle out of the water while the waste material is carried away. Open-pit methods are applied to ore deposits that are exposed or near ground surface. Overlying waste materials must be removed prior to mining the ore, an operation known as stripping. The mining site itself is basically a series of interconnected, slope-sided bench steps or mounds. The width and height of each bench is determined by ground conditions and by the type of mining equipment used. The slopes between benches must provide them with stability. Open-pit mining follows the same sequence of operations as underground mining: drilling, blasting, and loading and removing of waste and ore. Notably missing are the support systems required in underground mining. Drilling is accomplished with drills similar to those used for oil-field work, although they are smaller in size. The holes range up to 0.3 m (1 ft) in diameter and are loaded with bulk explosives. (The explosive Anfo is the most common blasting agent in open-pit mines.) After the blast the broken material is loaded onto rail cars, trucks, or conveyor systems. Although truck and power-shovel combinations remain standard for clearing the rubble, hydraulic excavators are being experimented with. Shovels are capable of digging at up to 47 m3 (60 yd3) per bite, driven by motors of more than 4,000 hp. Trucks with 120-ton capacity are common, but continuous hauling techniques featuring conveyor systems used in conjunction with in-pit crushers are beginning to be used. Microcomputers are employed, to route and dispatch trucks and for other ground-support purposes. The destruction of large land areas that are often agriculturally productive, the vast amount of spoil (and the dangers of hazardous materials leeching out of disposal heaps), the enormous amounts of water often needed to process the ores, and increasing public environmental sensitivity make strip mining a continuing problem of public policy. QUARRYING Quarrying is the method used to surface-mine such rock as marble, sandstone, granite, and limestone for buildings and other purposes. When the rock is removed in blocks, it is called "dimension" stone, and the quarries that are created by dimension cutting characteristically have steep faces transversed by stepped-down benches. Dimension stone is normally split off the face, rather than blasted, to preserve its shape and strength, and work is done selectively. Typically, holes are made along a line, then the intervening material is either sawed through or cracked by wedges inserted in the holes to expand them. Sometimes a chiseling machine is used to cut a channel into softer stone. Aggregate quarry mining is done by blasting and produces a rubble, different sizes of which are useful for different purposes. The components of an aggregate plant would include a mechanism (perhaps conveyor belts) to bring the rubble to the "scalper," which screens it to remove waste, a crusher to reduce the rubble to a number of useful dimensions (fine, medium, and course sand, for example), screens to sort the several dimensions, a washer to clean the aggregate, and storage facilities for the finished product. Major considerations of quarry location and design include the accessibility of the deposit, plenty of water for washing (and a place to waste or reclaim it), and a topography that will allow the raw material to flow downhill from quarry to processing plant. Large amounts of sand and gravel are used in conjunction with cement to produce concrete. Water seepage, land restoration, and waste disposal create environmental problems for both types of quarries. Aggregate quarries also have dust, noise, and blasting vibration problems, as these works must (for transportation reasons) be located near markets, typically large metropolitan areas. Worked-out quarries have sometimes been used for sanitary landfills. MINING WORLDWIDE Although the United States is a net importer of minerals, it dominates the world's mineral production and produces more than 50% of the world total of industrially important mine products. Industrially useful minerals, and especially the more exotic metals used in specialty steels and in such newer technologies as fiber optics and electronics, now possess great strategic importance, and the extraction of ores in less-developed nations is a primary source for the industrial world. U. S. interests in the early 1980s, for example, had invested over $7 billion directly in overseas facilities for mining, smelting, and refining nonfuel minerals. U. S. production of nonfuel minerals increased during the late 1980s, while the mining of metals--such as nickel, iron ore, tungsten, and molybdenum--declined. Gold production, however, increased dramatically, spurred by the development of leaching techniques that make the mining of low-grade ores economical. The world's only mine built to extract the rare metals gallium and germanium as principal products was opened in Utah in 1986. Extraction of the minerals used in construction--aggregate, sand and gravel, gypsum, and crushed stone--increased, as did the mining of cement components. (As an example of the internationalization of the mining industry, six of the ten major U. S. cement plants had been purchased by foreign companies by 1988.) All 50 states contribute to mining production, with Florida leading in the total amount of materials handled, followed by Arizona, Minnesota, and Texas. Most extraction now takes place in surface mines. The Utah copper mine Bingham Canyon is the world's largest surface excavation, and by 1988 plans had been completed to increase its size even further by using new excavation technologies. These include giant-scale equipment such as a hydraulic shovel capable of lifting 26 cubic meters (6 cubic yards). Worldwide, hydraulic cement is the leading mineral commodity by weight. Others include iron ore, peat, and salt. Mineral production around the world is remarkably concentrated. Seventy percent of the world's supply of minerals is produced by fewer than 200 mines, and the 1,000 largest mines account for 90% of production in the nonsocialist nations. Leading producers include Canada for silver, nickel, and zinc; the United States for lead and molybdenum; South Africa for platinum, vanadium and gold; the \TUSSR\t for chromium, tungsten, and manganese; Zaire for cobalt, and Turkey for boron. Mine safety issues continue to be a source of contention in the United States, as they are throughout the world. Critics of the Mine Safety and Health Administration (MSHA), which promulgates safety rules for U. S. mines, say that it must be more rigorous in its inspection standards and in its approval of the safety plans designed by mine owners. The toxic wastes produced by mining and smelting operations also present major safety problems. A new technique for extracting valuable materials from flue exhausts and mining wastes would--if it proves economically feasible--facilitate environmentally safe mining production. Carroll Pursell Bibliography: Blunden, J., Mineral Resources and Their Management (1985); Crowson, P., Minerals Handbook, 1986-87 (1986); Gregory, C. E., Rudiments of Mining Practice (1983); Pit and Quarry Handbook, 75th ed. (1982-83); Skinner, G. J., Earth Resources, 3d ed. (1986); Temple, John, Mining: An International History (1972); U.S. Department of the Interior, Geologic Survey, Studying the Earth from Space (1977); Van Rensburg, W. C., Strategic Minerals, 2 vols. (1986); Weiss, Alfred, ed., World Mining and Metals Technology (1976).