Strictly speaking, all “minerals” are obtained by mining, as that is one meaning of the word, although it is sometimes used to refer to other inorganic substances. Mining usually involves digging in the Earth’s crust, although a few minerals, such as gold, sometimes come to the surface naturally and are found in rivers or on the seashore. Metals, precious and semi-precious stones, and minerals such as sulphur and salt are all obtained by mining.
The location and shape of the deposit, strength of the rock, ore grade, mining costs, and current market price of the commodity are some of the determining factors for selecting which mining method to use.
Higher-grade metallic ores found in veins deep under the Earth’s surface can be profitably mined using underground methods, which tend to be more expensive. Large tabular-shaped ore bodies or ore bodies lying more than 1,000 feet (300 m) below the surface are generally mined underground as well. The rock is drilled and blasted, then moved to the surface by truck, belt conveyor, or elevator. Once at the surface, the material is sent to a mill to separate the ore from the waste rock.
Lower grade metal ores found closer to the surface can be profitably mined using surface mining methods, which generally cost less than underground methods. Many industrial minerals are also mined this way, as these ores are usually low in value and were deposited at or near the Earth’s surface. In a surface mine, hard rock must be drilled and blasted, although some minerals are soft enough to mine without blasting.
Placer mining is used to recover valuable minerals from sediments in present-day river channels, beach sands, or ancient stream deposits. More than half of the world’s titanium comes from placer mining of beach dunes and sands. In placer operations, the mined material is washed and sluiced to concentrate the heavier minerals.
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