A mine can be described as any attempt to extract minerals or other materials from the ground. These materials include metals such as gold, copper, nickel, and aluminum, fuels such as coal, peat, oil, and gas, and industrial materials such as gravel, limestone, or quartz. The most common abandoned mines in the West are hardrock mines, which extracted copper, gold, iron ore, lead, molybdenum, phosphate rock, platinum, potash, silver, uranium, and zinc.
In general, there are three types of mining operations:
Due to modern technology and the ability to move huge quantities of material, surface mining has become a more economically and technically feasible operation. Although there are several types of surface mining, open pit mining is the most common method used for the majority of metals in the U.S.
Open pit mining involves the removal of overburden with large excavators and hauling equipment. It is commonly used for low grade ores, where large amounts of materials must be processed to get enough of the target mineral to make it profitable. An open pit is usually widest at the top and has a series of levels, called benches, which get more towards the bottom.
Other types of large scale surface mining operations include strip mining and mountaintop removal. Placer mining involves removing target minerals from sand and gravel in a streambed or former stream channel using simple tools or mechanized dredging equipment.
Underground mining involves tunneling into the earth to reach a deposit of valuable minerals. Although not utilized extensively by modern mining companies, underground mining was a very common practice during the opening and settling of the American West. It is still used today in situations where the metals are too deep to make surface mining economically feasible.
Underground mining used to involve sinking a shaft (vertical tunnel) or adit (horizontal tunnel) into bedrock using picks, shovels, and explosives. Modern underground mines are more highly mechanized and require little manual labor. After reaching valuable metal deposits, the ore is moved to the surface with conveyors or shuttles for processing.
Although underground mining usually results in minimal surface disturbance when compared to other types of mining, the resulting network of tunnels can stretch for many miles, at different levels below ground. The underground tunnels are supported with timber, concrete, and steel and often becomes get with groundwater, which reacts with oxygen and the metals, causing acidic mine drainage.
Solution mining, also called in situ, is used when mineral deposits are concentrated and too deep below the earth’s surface to make other mining methods feasible. This technology is often used for uranium and copper.
Instead of physically removing the ore body, solution mining involves a series of wells which pump chemical solvents directly into the ground to dissolve the ore. The solution is then pumped back to the surface through a different set of wells so that it can be processed. Although there is little surface disturbance involved in solution mining, it can pollute groundwater supplies due to the infiltration of the chemical solvents or dissolved metals.
Mineral processing is a series of physical, chemical and biological processes used to concentrate minerals and metals for human use. In general, there are three distinct stages in mineral processing.
The first step in mineral processing is usually crushing or grinding the ore. This step, called comminution, tends to make the valuable minerals more easily accessible.
The second step in mineral processing is call separation. Often, the type of separation technique used at a mine site will have a large impact on the type of environmental problems found there. The following techniques are commonly used by the mining industry to separate the valuable minerals from the waste rock and other material.
The final stage in mineral processing is beneficiation, or smelting. By heating the concentrated metals to high temperatures, leftover wastes and impurities are burned off.