mining
Surface mining operations, known as open-pit, open cast or open cut mines, are as their names suggest, open to the earth’s surface. Underground mines, in contrast, involve exploiting
deep-lying ore bodies that are reached from the surface by incline or vertical shafts. Whether a mine is a surface or underground operation depends on a variety of safety, environmental,
economic, geological and geotechnical factors. In general, surface mines present more advantageous opportunities to use the large scale mechanization that makes production safer, more
efficient and more economical. However, many deposits are too small, irregular or deeply buried to be reached by surface methods and must be mined via underground methods. Transportation
represents a large proportion of mining activity. In surface mines this is mostly transport of the mined ore and waste, while men and materials must also be transported to their working sites
in underground mines.
Processing
Once mined ore has been recovered from the earth, we process it to remove as much waste material – gangue – as possible. This begins with the use of huge crushers and mills to reduce the size
of the ore to liberate the valuable minerals so that they can be recovered and concentrated. Depending on the minerals present in the ore, concentration processes such as gravity separation,
flotation or chemical leaching may be employed. Each technique uses the physical or chemical properties of the minerals to exploit the difference between valuable material and gangue. Coal,
for example, is lighter than most rock particles, while conversely, diamonds are much heavier, and gravity processes that can exploit these differences in density are generally employed. Lead
and zinc often occur together in orebodies, but can be separated by froth flotation processes that exploit the different chemical properties of the respective minerals.