Hard-rock mines have existed for thousands of years.
Mining is one of the oldest of all human endeavors, with archaeological evidence of ancient mines dating back thousands of years. Minerals can be extracted from the earth either from the surface or from underground. Underground mining is perhaps more familiar to many people, calling up images of workers toiling deep below the earth's surface in search of ore.
Description
Any site where tunnels, shafts or inclines are developed to access subsurface minerals can be defined as an underground mine. Hard-rock mining refers to the underground development and extraction of ore, either by drilling and blasting or by using huge mechanized boring units. Ore is defined as any rock that can be mined for a profit. Modern hard-rock technology contrasts sharply with the traditional pick-and-shovel mining of earlier times.
Hard Rock vs. Soft Rock
In hard-rock mining, workers advance the tunnel by drilling and blasting the working face. The rock is then removed by mucking machines. Hard-rock techniques are used to remove minerals such as gold, silver, lead, zinc and copper, which usually occur as veins and seams within the host rock. In contrast, the term soft-rock mining encompasses underground mining of soft minerals such as coal, gypsum and potash, which are removed by machines such as shearer-loaders and plows.
Methods
Many hard-rock mining methods are used to remove ore and waste rock. The oldest method, stoping, involves reinforcing underground passageways with timbers as they are advanced. Due to the slow progress, this is probably the most expensive method of underground mining. More modern methods include various types of caving techniques where the rock is often undercut and allowed to cave by gravity. Block-and-fill caving is the lowest-cost of all underground mining methods.
Examples
The deepest hard-rock mines in the world are in the West Witswatersrand district southwest of Johannesburg, South Africa. Owned and operated by gold-mining giant AngloGold Ashanti, the Mponeng Mine is still being developed by stoping at depths well over 10,000 feet below the surface. In the United States, the Homestake Mine near the town of Lead, South Dakota, still holds the record as the deepest mine in the Western Hemisphere at over 8,000 feet below the surface.
Resources
The National Mining Hall of Fame and Museum in Leadville, Colorado, features some remarkable exhibits of hard-rock mining and its history.The National Mining Association is the primary mining trade organization in the United States. This body represents the American mining industry to the government and educates the public about all facets of mining including methods and technology.
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