Mining has played an important role in the development of the United States. In the past, the discovery of minerals such as gold and silver resulted in population shifts and economic growth. Extraction of minerals and coal continues to provide the foundation for local economies in some parts of the country. Products of this industry are used as inputs for consumer goods, processes, and services provided by all other industries, including agriculture, manufacturing, transportation, utilities, communication, and construction. Uses of mined materials include coal for energy, copper for wiring, gold for satellites and sophisticated electronic components, and a variety of other minerals as ingredients in medicines and household products.

Besides mining coal and metallic and nonmetallic minerals, employers in this industry explore for minerals and develop new mines and quarries. Metallic minerals include ores, such as bauxite-from which aluminum is extracted-copper, gold, iron, lead, silver, and zinc. Nonmetallic minerals include stone, sand, gravel, clay, and other minerals such as lime and soda ash, used as chemicals and fertilizers. This industry also includes initial mineral processing and preparation activities, because processing plants usually operate together with mines or quarries as part of the extraction process.

Mining is the process of digging into the earth to extract naturally occurring minerals. There are two kinds of mining, surface mining and underground mining. Surface mining, also called open-pit mining or strip mining, is undertaken if the mineral is near the earth’s surface. This method usually is more cost-effective and requires fewer workers to produce the same quantity of ore than does underground mining. In surface mining, after blasting with explosives, workers use huge earthmoving equipment, such as power shovels or draglines, to scoop off the layers of soil and rock covering the mineral bed. Once the mineral is exposed, smaller shovels are used to lift it from the ground and load it into trucks. The mineral also can be broken up using explosives, if necessary. In quarrying operations, workers use machines to extract stone used primarily as a building material. Stone, such as marble, granite, limestone, and sandstone, is quarried by splitting blocks of rock from a massive rock surface.

Underground mining is used when the mineral deposit lies deep below the surface of the earth. When developing an underground mine, miners first must dig two or more openings, or tunnels, deep into the earth near the place where they believe coal or minerals are located. Depending on where the vein of ore is in relation to the surface, tunnels may be vertical, horizontal, or sloping. One opening allows the miners to move in and out of the mine with their tools and also serves as a path for transporting the mined rock by small railroad cars or by conveyor belts to the surface. The other opening is used for ventilation.

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. Long steel bolts and pillars of unmined ore support the roof of the tunnel. Using the room-and-pillar method, miners remove half of the ore as they work the ore seams from the tunnel entrance to the edge of the mine property, leaving columns of ore to support the ceiling. 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, are moved ahead, allowing the ceiling in the mined area to cave in as the miners work back towards the tunnel entrance.

Once all the minerals or coal have been extracted, the mine and its surrounding environment must be restored to the condition that existed before mining began. In surface mining, the layers of topsoil, or overburden, that were removed in order to reach the mineral are used to fill in the mine and reshape the land. This ensures that native plants and animals will be able to thrive once again. Underground mining does not require as extensive a reclamation process; however, mine operators and environmental engineers still must ensure that ground water remains uncontaminated and that abandoned mines will not collapse. The reclamation process is highly regulated by Federal, State, and local laws, and reclamation plans often must be approved before mining permits will be granted.

During the 1990s, production of both minerals and coal increased. Given the more volatile price of metal, its production fluctuated more than that of nonmetallics. However, employment in both sectors declined significantly, as new technology and more sophisticated mining techniques increased productivity, allowing growth in output while employing fewer workers. 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 decrease the number of workers needed to mine materials.