Surface mining is the primary method used to extract coal and
bitumen reserves found in Alberta. Although not widespread,
surface mining involves an intense, local alteration of the
landscape, the removal of large quantities of overburden (soil,
glacial till bedrock) to expose the hydrocarbon resource buried
beneath. When mining operations are completed, they usually
leave a series of open pits that must be reclaimed.
Surface mining is best suited to widespread fault seams of
materials, such as clay and coal, or compact near-surface
bodies, such as some types of uranium. The choice of open pit
mining or underground mining in the case of uranium depends on
the depth of the deposit, how easily the rocks and soil on top
of the ore can be removed and, finally, economics, as the amount
of overburden that must be removed to expose the seam varies.
Surface mining is generally less costly and more flexible
than underground mining. This type of mining also recovers a
higher percentage of coal in a deposit. This type of mining
involves removing the topsoil or surface earth, also called
overburden, from the area to be mined. This is often done with
huge draglines that have buckets. The cover soil removed is
stockpiled for later reclamation. Up to 69 cubic metres of earth
may be removed, all at one time. Sometimes the use of explosives
is required to crumble the overburden. Stripping the topsoil
reveals the coal seam. The coal seam is then mined
using
"shovels". These shovels can remove up to 16 cubic metres of
coal at one time.
Generally, extraction technology in non-mountainous areas
involves the use of massive draglines in order to remove the
overburden and expose the coal seams. Power shovels and trucks
are used to haul the coal to a nearby processing facility. Some
general environmental pressures include noise levels (machinery,
blasting), air quality (coal dust), water quality and stream
diversions, soil and vegetation removal. Reclamation of open pit
coal mines tends to be more difficult in mountainous areas
because of the naturally shallow soil depth and greater
variations in topography.
Surface Mining
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