Mining
Mining is the extraction of minerals and rocks from the earth. The history of mining stretches back to prehistoric times when gold, copper, and silver were apparently the first metals mined. Egyptians mined copper and tin as far back as 3700 b.c.. A German scholar, Gergius Agricola, wrote an early comprehensive study of mining methods in the Middle Ages in his De re metallica. In the United States, mining did not begin until the late 18th century, when a Missouri lead belt began continuous production. Metal ores were found in the western part of the United States in the middle of the nineteenth century causing the California gold rush. Mining is still a major industry in the United States.
There are several methods to find potential deposits for inspection. Trenching and testpitting are used when there is only loosely packed matter covering the deposit. If the surface is harder or featured stratified layers, drills are used to take samples. Many types and sizes of drills exist for this purpose. After a sample is analyzed and a mining operation is put in place, there are two basic mining types utilized: open-pit and underground mining.
Open-pit mining, also known as surface mining or opencast mining, is employed when the material to be mined is at or near the surface. Open-pit mining is usually done in layers with materials at the edges removed. Thus, the pit is enlarged gradually. At the beginning of mining operation, if the material is slightly underground, the loose earth has to be stripped back. This is usually done by backhoes or blasting, though drilling is sometimes used. If blasting is involved, it is done with dynamite, bag powder or ammonium nitrate. Flame piercing is another option. Flame piercing involves jets of burning fuel oil, or kerosene and oxygen, which dissolves the rock into a pit. As the ore or other minerals are mined, they are picked up by shovels or drag lines, though some operations use bucket-wheel excavators. One major issue in open-pit mining is keeping the pit slopes stable. However, compared to open-pit mining, underground mining is more costly, has more safety concerns, and is more complex overall.
There are several types of underground mines, each suited to a particular type of mineral deposit. A drift mine is used when the material to be mined approaches the surface at one point but the majority is located in a hill. A tunnel is inserted into the hillside. When the material to be mined is found completely underground, but not at extreme depths. A slanting entrance is built to meet the deposit, and the mined ore is taken to the surface by cars. Shaft mines are used when the mineral deposit is far underground. Two or more vertical shafts are built to the deposit area, one for hoisting the ore to the surface and the other to provide air, sometimes pushed with fans, to the miners. Because of the nature of underground mining, drilling and blasting are important to reaching deposits. Drills can be small, one-man drills (like jackhammers) or much bigger. Blasting is a quicker way to reach deposits or advance the mining area, and is accomplished with dynamite, ammonium nitrate, and bag powder. For miners to work underground, several issues have to be addressed, including ventilation, drainage, escape routes, and lighting their working area. The safety of miners is a major concern, and stability of the mine, especially the prevention of cave-ins, remains an important safety concern.
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