A mine is a place where all kinds of metals and stones that have economic value are accumulated. Mining or mining is the process of extracting valuable minerals or other materials from the ground and usually from mines. The materials obtained from these deposits include base metals, precious metals, iron, uranium, coal, diamonds, lime, salt, potash and other such materials. According to many factors such as economic and technical conditions and accessibility to the deposit, mining is done in two general ways, open and underground. The scientific exploration of Iran's mines started in 1939, and in that year a geological and exploration unit was established in the General Directorate of Mines. In 1996, 1,257 mining cooperatives were registered in the country, of which 730 units were active with a capital of 19,957 million Rials. Iran has the world's second oil reserves, eleven percent of the proven oil reserves of the earth, equivalent to 130 billion barrels, and the world's second gas reserves, eighteen percent of the proven natural gas reserves, equivalent to 26 trillion cubic meters. Other important mines of the country are: Coal, nickel, cobalt, silver, gold and uranium mines.