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 quarry 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. Another type of surface mining is Hydraulic Mining. This type of mining involves high pressure water. Water is sprayed at an area of rock and gravel and breaks it up, dislodging ore and placer deposits. The water/ore mixture is then milled. This is a very destructive way to mine and has been outlawed in most areas.

Underground mining, also called hard-rock mining or shaft 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, shafts and 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 railroad cars, trucks or by conveyor belts to the surface. The other opening is used for ventilation. Most shaft or tunnel mines would eventually flood as they hit the water table and as a result, the water would have to be continually pumped out or the mine would be abandoned.

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 minerals 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.