ZIMSEC O Level Geography Notes:Resource Exploitation:Mining: Types of Mining
OPEN CAST AND STRIPPING (SURFACE METHODS)
- The open cast method is used when mineral deposits occur in horizontal seams which are near the surface not more than 50 meters deep.
- This method involves blasting which is carried out of scatter rocks.
- The overburden is then removed using large mechanical excavators or draglines.
- Open cast mining is used to extract coal at Hwange, asbestos in Mashava, nickel at Trojan mine in Bindura.
Advantages of opencast
- It is a fairly cheap and simple method of extracting shallow seams
- It is safer compared to the alternatives as there is no risk of tunnel collapse, explosions or gas poisoning
- The open pit allows easy access for humans and machines
- Requires less machinery and investment
- There is high selectivity which allows the operators to quickly get rid of low grade ores
- Blasting causes structural damage to buildings as well as noise pollution.
- Use of explosive is a potential danger to miners.
- Opencast leaves the land scarred.
- Deforestation causes severe soil erosion. Mine dumps destroy the natural beauty of the land and landslides can occur on unstable dumps.
- Shaft method is used to extract deep seated ores over 50 metres deep.
- The method involves the sinking of vertical or inclined shafts down to the level of the seams.
- Horizontal tunnels are built following the seams.
- Shaft mining is used to extract coal at Hwange, chrome in Shurugwi and gold in Mazowe.
- The method allows extraction of deep seams.
- There is less deforestation.
- It is very expensive.
- Cave-ins and toxic gases are a great risk.
- Deep mines can cause earth tremors.
- Flooding can be a danger to miners.
- This method is used to extract minerals that appear on the sides of mountains and valleys.
- This form of mining involves building horizontal or inclined tunnels along the mineral seam.
- Other structure such as conveyor belts and railway lines are built to facilitate the extraction of the minerals.
- It is fairly cheap method and its safer than shaft mining method
- Can be drained using a force of gravity
- Minerals can be transported more easily and cheapily
- Tunnels can cave-in.
- Landslides can occur.
- Can only be constructed where topology permits
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