subject: The Nature of the mining Industry [print this page] The Nature of the mining Industry The Nature of the mining Industry
Surface mining of coal typically uses the method known as strip mining, which is usually more cost-effective than underground mining and requires fewer workers to produce the same quantity of coal. In strip mining, workers use huge earthmoving equipment, such as power shovels or draglines, to scoop off the layers of soil and rock covering the coal seam. Once the coal is exposed, it is broken up by using explosives, and then smaller shovels lift it from the ground and load it into trucks. Mining companies are required by Federal, State, and local laws to restore the mined land after surface mining is completed; as a result, the overburden and topsoil are stored after removal so that they can be replaced and native vegetation replanted.
Underground mining is used when the coal deposit lies deep below the surface of the earth. When developing an underground mine, miners first must dig tunnels deep into the earth near the place where the coal is located. Depending on where the coal seam is in relation to the surface, tunnels may be vertical, horizontal, or sloping. Entries are constructed so that miners can get themselves and their equipment to the ore and carry it out, while allowing fresh air to enter the mine. Once dug to the proper depth, a mine's tunnels interconnect with a network of passageways going in many directions. Using the room-and-pillar method, miners remove sections of the coal as they work the coal seam from the tunnel entrance to the edge of the mine property, leaving columns of coal in place to help support the ceiling together with long steel bolts. This process is then reversed, and the remainder of the ore is extracted, as the miners work their way back out. In the case of longwall mining of coal, self-advancing roof supports, made of hydraulic jacks and metal plates, cover the area being mined. As coal is removed, the entire apparatus advances, allowing the ceiling in the mined area to cave in as the miners work back towards the tunnel entrance. Underground mining does not require as extensive a reclamation process as surface mining; however, mine operators and environmental engineers still must ensure that ground water remains uncontaminated and that abandoned mines do not collapse.
The metal ore mining industry segment covers the extraction of metal ores, primarily gold, silver, iron, copper, lead, and zinc. These naturally occurring minerals have a variety of industrial purposes: gold and silver are primarily used in jewelry and high-end electronics, iron is used to produce steel, copper is the main component of electrical wiring, lead is used in batteries, and zinc is used to coat iron and steel to reduce corrosion and as an alloy in the making of bronze and brass.
Most metals do not exist in concentrated form but rather in small traces in rock called "ore". Indistinguishable from regular rocks to the untrained eye, some ores that contain only a fraction of a percent of metal are mined. As a result, a massive amount of rock must be extracted from the ground in order to obtain a useable amount of metal. As a result of this, and because metal ores are less common than coal, metal mines can be much larger than coal mines and operate in more extreme environmentswhile coal mines are rarely more than a few hundred feet underground, gold mines, for example, can be over a mile below the surface.
Like coal mines, metal ore mines are found in both surface and underground varieties, depending on where the ore deposit is located. In addition to strip mining, surface ore mines also use the open-pit mining technique. These mines are huge holes in the ground that are mined by blasting rock from the sides and bottom with explosives, carrying out the broken up material in trucks, and then repeating the process. Open pit mines can grow to be hundreds of feet deep and several miles wide. Underground mining of ore is less common, typically only occurring when rich veins of ore are discovered or mineral prices are high enough to justify the added expense.
A significant amount of processing is needed to convert ore into usable metal. The mining industry includes initial mineral processing and preparation activities that are located together with mines as part of the extraction process. Further processing is classified under the primary metal manufacturing industry.
The nonmetallic mineral mining and quarrying industry segment covers a wide range of mineral extraction. The majority of the industry produces crushed stone, sand, and gravel for use in construction of roads and buildings. Other important minerals produced are clays, primarily for ceramics, water filtration, and cement making; gypsum, the primary material used in wallboard; salt, used in foodstuffs and as an ice remover; phosphate, for use in fertilizers; and sulfur, the main component of sulfuric acid, a major industrial input. Most of these minerals are found in abundance close to the surface, so underground mining is uncommon in this industry segment.
Surface mining for stone is also known as "quarrying". In quarrying operations, workers use machines to extract the stone. Stoneprimarily granite and limestoneis quarried by using explosives to break material off from a massive rock surface. The resulting rocks are crushed further and shipped off for the production of asphalt or concrete. Some high-quality stone, such as marble and certain types of granite, is quarried in large blocks, known as dimension stone, and used as a building material by itself.
The final industry segment is support activities for mining. The activities of this industry are often the same as those of the other industry segments, but the work is done by contract companies that specialize in one aspect of resource extraction. For example, the majority of drilling for new oil wells is done by specialty drilling companies; other support companies specialize in exploration for new resource deposits or operation of offshore oil rigs.
Recent developments. Many resources produced by the mining industry, particularly metals, oil, and gas, are relatively rare and are part of a global market that is highly sensitive to changes in prices. During the 1990s, commodity prices were relatively stable at low levels, causing production to stagnate and limiting the creation of new drilling and mining operations. In recent years, prices have become more volatile, with large increases followed by rapid declines. Exploration and production has likewise risen and stabilized or declined along with prices. Coal is less susceptible to world market conditions, but it also has seen price increases in recent years that have led to expanded production. Demand for nonmetallic minerals is primarily affected by the level of activity in the construction industry, particularly the building of new roads and highways.
Employment in the mining industry has been affected significantly by new technology and more sophisticated mining techniques that increase productivity. Most mining machines and control rooms are now automatic or computer-controlled, requiring fewer, if any, human operators. Many mines also operate with other sophisticated technology such as lasers and robotics, which further increases the efficiency of resource extraction. As a result, mine employment has been falling over time, particularly of workers who are involved in the extraction process itself. These new technologies and techniques have also increased specialization in the industry and led to expanded use of contract mining services companies for specific tasks. These companies also allow mining firms to more easily adjust production levels in response to changes in commodity prices.
