Mining is the process of extracting valuable minerals buried beneath the ground. The location where these valuable minerals are extracted from is called a mine. The deepest mine in the world is AngloGold Ashanti's Mponeng mine in south-west Johannesburg, South Africa, which goes to a depth of over 2.5 miles. Evidence of human mining efforts has been found dating back to the beginning of history. The Bible even refers to mining in Genesis, where it mentions that men had tools of bronze and iron.
Types of mining
Mining can be either surface mining or sub-surface (underground) mining.
The type of mining further depends on what is being mined. For example, surface mining of coal is strip mining. Surface mining of precious metals such as gold is placer mining. A quarry is an open-pit surface mine for the mining of materials such as slate and gravel.
Sub-surface mining is called hard rock mining if the mining is for hard minerals such as precious metals, and soft rock mining if it is for soft minerals such as coal. Underground mines are also categorized by the direction of entry underground. A drift mine enters the earth horizontally, a slope mine enters the earth at a downward slope, and a shaft mine uses a vertical or steeply inclined downward shaft to enter the mine.
For specific types of mining and minerals mined, see:
Dangerous gases such as methane can accumulate in mines and can explode if ignited, and the inhalation of dusts is also a health issue, so underground mines must be ventilated, typically with large fans located above ground which keep air circulating through the mine. Another hazard in underground mines is blackdamp, which refers to an accumulation of gases such as carbon dioxide and nitrogen with the oxygen level too low to sustain life. Blackdamp can be detected using a safety lamp, the flame of which will flare up in the presence of methane and diminish or extinguish in the presence of blackdamp, or in modern use an electronic air quality detector is used. In earlier times a canary might have been used to detect both blackdamp and methane as the bird would be quite dead by the time the gases reached levels dangerous to miners.
In addition, mines must be inspected for unstable conditions which might result in a cave-in, and other hazardous conditions. Timber framing is installed inside underground mines, but contrary to popular misconception this is not to reinforce the mine and prevent collapse, as no timber framing can support the vast tonnage above the mine passage. Rather, it is to warn of unstable conditions and an imminent collapse and give miners advance notice to escape. If the timber framing breaks or starts making loud creaking noises, this is a warning that a cave-in is likely.