Mining
mining was once to dipping on or near the surface .
but today mines can reach deep into the crust.
one mines in South Africa has reached a depth of 3.8 km (2.4 miles) .
although most mines are less than 1.8 km (1.1miles)deep .
but surface or open-cast mining remains generally cheaper and still accounts for most of the world’
mineral production .
Quaryying is a kind of surface mining .it is especially important for extracting kaolin (clay)for ceramics and building stones such as granite limstone marble sandstone and slate .
the search for minerals in alluvial deposits such as river gravels remains important.
these deposits may contain tough or heavy minerals such as diamond gold or platinum.
underground mining was once dangerous .
but most modern mines are equipped with safety equipment and are well -ventilated .
some minerals can be obtained from great depths
without digging a mine .For example halite (rock salt)and potash dissolve in water they can be extracted in soultion by water whice is pumped down to the deposits and then brought back to the surface .
sulphur does not dissolve in water but it can be mined by pumping hot steam down to the deposit . the steam melts the sulphur which is then forced to the surface by compressed air.
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