OVERVIEW OF THE IMPACT OF MINING ON THE ... - IIED pubs

2.4.4 Siltation
Siltation is the process whereby fine solid particles build up on the bed of a river or lake and is the result of an
excessive load of suspended solids in a river or rivers. Mining operations produce large quantities of dust and
finely powdered rock, with much rock having been ground to particle sizes below 0.2 mm. Though the materials
that are dumped after removal of the commodity being mined have fine particle size and reasonable physical
characteristics that could permit plant growth and retain adequate amounts of water, these materials have been
formed from hard unweathered material and so may not contain much of the finest clay material and lack
organic or microbial activity. The result is that mine dumps may be very unstable, easily blown by wind when
they are dry and eroded by heavy rain when wet. The action of rain and wind thus removes fine particles into
nearby water systems, leading to a build up of suspended solids and ultimately siltation.
2.4.5 Water use
Mining operations are major users of water, most notably for:
1. Cooling;
2. Underground operations, such as hydraulic drills; and
3. Processing, such as flotation and leaching.
Larger mines also frequently use large quantities of water to supply nearby residential areas
attached to the mines, such as mine housing units.
In arid and semi-arid areas, the quantity of water used by a mining operation places it in
direct competition for water with other water users, especially domestic, agriculture and the
aquatic environment. This “competition” becomes heightened when the mining operation is
also responsible for any deterioration in water quality as a result of effluent discharges.
Typically, however, the authority responsible for granting the mining permit will also work in
collaboration with the authority responsible for granting permits for water abstraction and
effluent treatment and discharge. When this collaboration is effective, it ensures that the
quantity of water used by the mining operation is within the allowable limits posed by the
available water within the catchment concerned. If insufficient water is available in the
catchment, and the social and economic opportunities offered by the mining operation are
sufficiently attractive, additional water may be brought in from a neighbouring catchment.
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