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

Mining methods vary widely and depend on the location, type and size of mineral resources. Surface mining
methods are most economical in situations where mineral deposits occur close to the surface (e.g. coal, salts and
other evaporite deposits or road quarry material) or form part of surface deposits (e.g. alluvial gold and diamonds,
and heavy mineral sands). Typical surface mining methods include: strip mining and open pit mining, as well as
dredge, placer and hydraulic mining in riverbeds, terraces and beaches. These activities always disrupt the
surface and this, in turn, affects soils, surface water and near-surface ground water, fauna, flora and all alternative
types of land-use (Fuggle & Rabie, 1996; Ashton, 1999).
Shallow underground mining, up to about 50 metres below the surface, includes bord (room) and pillar mining
(often used in coal mines), where pillars of the mineral seam are left to support overlying material. Many of the
gold and copper mines in Zimbabwe, Zambia and the Democratic Republic of Congo are sited on historical
workings that employed a variety of shallow underground mining techniques (Mendelsohn, 1961). In some of the
older South African coalmines in the Witbank area, roof collapse has occurred after the mines were closed,
allowing air to enter the old workings and promoting spontaneous combustion in the residual coal. Some of the
abandoned workings in the Witbank area have continued to burn for many years and have resulted in unplanned
surface collapse as well as ground and surface water contamination through acidification and salinization of local
aquifers and streams (Wells et al., 1996; Fuggle & Rabie, 1996). Spontaneous combustion of exposed coal
seams and stockpiles of coal fines is also experienced at the Hwange collieries in Zimbabwe and the Maamba
Colliery in Zambia (SADC, 2001).
A variety of deep underground mining techniques are required to extract ores located deep beneath the earth’s
crust. Deep mining techniques include specialized ore extraction techniques, such as block caving and longwall
mining, and require sophisticated infrastructure to ensure mine safety and maintain safe working environments.
The principal environmental impacts associated with deep underground mining (for example, in gold, platinum,
chrome and copper mines) are linked to the mine wastes and blasting residues brought to the surface by mine dewatering
activities. These cause water pollution from leachates, as well as visual pollution, changes in land use,
excessive dust, and surface subsidence as a result of mine dewatering activities.
Offshore (sub-marine) mineral deposits such as diamonds, oil and gas, heavy mineral sands, phosphorite,
glauconite and manganese occur off the shores of southern Africa and some of these are already exploited in
various ways. These offshore mining activities differs according to the specific locality and the effects of the mining
operation on intertidal, sub tidal or deep-sea marine environments (Gurney et al., 1996). Many offshore mining
operations are vulnerable to inclement weather conditions that pose added risks of fuel and material spills and loss
of human life (Ashton, 1999).
Besides the rate and method of mining, the location, variety and scale of mine infrastructure also influences the
nature and extent of impacts. Typical mine infrastructure includes: haul roads and ore dumps; ventilation shafts;
surface facilities (e.g. offices, workshops, car parks and warehouses); tailings and waste rock disposal areas and
methods; transport and service corridors (e.g. railway lines, roads, pipelines, conveyers, airstrips, port facilities,
power, water and gas corridors); product stockpiles; ore processing facilities; chemicals and fuel storage and the
locations of towns and housing facilities (Australian Environmental Protection Agency, 1995-1996; Fuggle & Rabie,
1996; Ashton, 1999; Weaver & Caldwell, 1999).
Each mineral ore reacts in distinct ways when brought to the surface and comes into contact with air and water,
affecting or altering the type of impact that may be expected from the mining operation. Whilst many
environmental impacts can be fairly severe, it is important to acknowledge that several sophisticated mitigation
measures have been devised through the sharing of best practice approaches in the mining industry.
2.3 Phases of mining and mineral processing operations
The typical life cycle of a mining operation consists of a number of simultaneous or sequential phases and
activities. For example: prospecting, development (including verification of the quantity and quality of ore and its
amenability to various extraction and processing methods), construction, operation, staff housing and support,
product stockpiling, mineral processing, waste management, rehabilitation and eventually, closure. The typical life
span of a mine is in the region of 25 years although this can vary from less than 1 year to well over 100 years
(Fuggle & Rabie, 1996).
xlv