A mine is an excavation made in the earth for the purpose of extracting minerals.
A surface mine is therefore an open-air excavation made for the purpose of
minerals removal and its application is to all mineral deposits amenable to
surface mining.
Surface mining involves the excavation of ore from the surface
by removing overburden (non-mineralized soil and rock that cover an ore body)
and waste rock (poorly mineralized or very low-grade soil and rock that are
within the ore body or surrounding it) to expose higher-grade minerals. In
general, overburden is removed as efficiently and rapidly as possible, usually
with little comminution. Overburden piles compose the largest volume of wastes generated
by surface extraction activities (Beard 1990). Although surface mining is generally
limited to near surface deposits of about 160 meters in depth, due to the
development of modern technology surface mining has successfully excavated much
deeper deposits.
Advantages of surface mining operations, as compared to
underground operations, include flexibility in production rates without
deterioration of workings, relative safety for workers, ability to practice
selective mining and grade control, and low cost per ton of ore recovered.
Surface mining also has lower development and maintenance costs than
underground mining because it requires fewer specialized systems. expanded
development, however, some surface mines with large amounts of prestripping waste
could have higher costs than established underground mines.
There are five basic types of surface
mining:
1. Placer mining
2. Open pit mining
3. Auger
mining
4. Glory hole
5. Solution mining/ In-situ
leaching
Under each of these, there are
different methods of approach:
Placer mining: (i)Ground sluicing
(ii)Hydraulicking
(iii)Dredging
Open-pit: (i)Single bench
(ii)Multiple bench
(iii)Strip mining
(iv)Quarry mining
Auger
mining: Is a surface mining technique used to recover additional coal from
a seam located behind a highwall
produced either by stripping or open-pit mining
Glory hole:Is a combination of open-pit and underground haulage system below an already existing open pit.
Solution mining:it involves
pumping of a leachate solution into the ore body via borehole,
which circulates through the porous rock dissolving the ore and
is extracted via a second borehole.
PLACER
MINING
GROUND
SLUICING
Utilizes natural flow of water to disintegrate a
placer deposit and transport the broken material through a sluice.
Concentration of the valuable mineral is carried out in the sluice. In operation,
the flow of water is directed continuously against the toe of the deposit is
about 2.5 meters in thickness and over the top of face if the deposit is thicker
(Figure 39). In order to enhance efficient operation, there must be adequate
water supply available for a period long enough for the operation and the
deposit must be favourably situated in relation to natural gradient and dumping
space. When the supply of water is insufficient for continuous operation,
storage reservoirs are constructed for steady water supply as water is released
periodically through an automatic or hand-operated valve. This periodic release
exercise is known as “booming”.
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