SURFACE MINING

                      

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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