Get premium membership and access revision papers with marking schemes, video lessons and live classes.

Processing. Please wait.

In this Lesson we are going to learn about the Methods of Mining including open cast mining, underground mining and alluvial mining.

Answer Text:
Methods of Mining
1. Open Cast Mining
-Method of extracting minerals which are near the earth’s surface.
Types
a) Stripping
-Stripping off of the unwanted material lying on top of the mineral deposit and then digging to remove the mineral bearing rock if it’s soft or if it’s hard explosives may be used to loosen it and then huge power shovels are
employed to dig up the mineral deposits.
b) Hill-slope Boring
-Using boring instruments known as augers to drill out mineral deposit and bring it to the surface.
2. Underground Mining
-Method employed when the mineral lies very deep below the surface and the overburden is too thick to be removed by mechanical means.
Types
a) Shaft Method
- Method employed when the mineral bearing rock doesn’t out crop.

How it’s carried Out
• Vertical shafts are sunk into the earth’s crust to reach the layer with the mineral.
• Horizontal tunnels are dug from the vertical shaft to reach the mineral.
• Props are erected to support the roof to prevent it from collapsing.
• The mineral bearing rock is blasted loose by explosives.
• The deposit is transported on light rail or conveyor belt to the bottom of the shaft.
• It is then brought to the surface in a crane or a lift called cage.
b) Drift/Adit Mining
-Method employed when the mineral deposit can be reached from the valley sides.
• Horizontal tunnels (adits) are constructed from the side of the hill.
• Railway line is constructed into the mine to bring out the mineral e.g. mining of copper at Kilembe in Uganda.
c) Solution Method
- Method used in mining soluble minerals such as sulphur, salt, potash, etc.
• Superheated water is ejected into salt deposits.
• The mineral dissolves or melts.
• The solution is then pumped into the surface.
d) Drilling
-Method employed in exploitation of petroleum.
• Wells (oil derricks) are drilled.
• Oil and natural gas are brought to the surface under their own pressure or by pumping.
3. Alluvial/Placer Mining
-Method used to extract minerals occurring in alluvial deposits e.g. gold, tin, diamonds and platinum.
Types
a) Panning
It involves:
• Digging a mixture of sand, gravel and mineral from the river bed.
• Putting it in a pan and rotating the pan while tilted.
• The lighter sand or gravel is washed on the side leaving the heavier mineral at the bottom of the pan e.g. gold mining in Migori and R. Morun Beds in W. Pokot.
b) Dredging
• A dredger scoops water logged alluvium from the bed of a lake.
• The alluvium is passed over sloping channels with series of traps.
• Wastes are washed away and denser materials are left at the bottom of the trap e.g.mining of soda ash at L. Magadi.
c) Hydraulic Mining
- Method used when alluvial deposit occurs on a valley side.
• A powerful jet of water is directed at the deposit.
• Gravel and mineral collect at the valley because of the great pressure.
• The mineral grains are recovered and washed out.
d) Sub-marine Mining
- Method employed in extracting minerals in alluvial deposits lying deep down the ocean floor.
• A sub-marine dredger goes down the ocean floor.
• It scoops mineral deposit and rises to the surface.
• The alluvium is passed over sloping channels with series of traps.
• Wastes are washed away and denser materials are left at the bottom of the trap.