The quest for wealth
Mining is as old as civilization itself, symbolizing the human raceâs search and dreams for the earthâs riches. Over the centuries techniques have been developed to reap these riches.
There are three main mining techniques in use worldwide â open-cast, drift and deep underground mining. A fourth technique, known as panning is more a technique of early mining history but is still used today by amateur prospectors around the world.
In the 19th century, panning methods â applied since the time of the ancient Egyptians â were used by prospectors to find minerals, especially precious metals and gems, washed down ancient river passages and settled in pockets in the bedrock.
Â The equipment of prospectors consisted of a shovel and a sieve or pan into which the mineral-rich gravel was scooped. The miners who thronged to California, the Klondike and Australia in the gold rush mostly used panning.
Panning has now been replaced by geochemistry, which traces deposits back to their source by analysing samples of soil, stream sediments and plant material.
2. Open-cast mining
This technique entails the gathering of mineral deposits where they lie close to the earthâs surface. Excavators remove coverings of soil or clay, and the ore-bearing rock is then broken up by blasting and removed to crushers.
Alternatively, water is used to flush the ore-rich rock from unwanted material. Because the ore is âopenâ â on the surface â giant excavating machinery can be used, making the mining process quick and relatively cheap.
The Big Hole in Kimberley, South Africa is the worldâs deepest open-cast mine (but not in use anymore). It is about 1.2 kilometres deep and its perimeter is about 1.6 kilometres.
3. Drift mining
This technique is used for deposits relatively near the surface, but not so near as to make open-cast mining economically viable. Large shafts or âdriftsâ are driven into the earth â often a hillside â more or less horizontally. This enables conveyer belts and trucks to remove ore directly from the working area to the surface.
4. Deep underground mining
This technique is used to reach seams hundreds of metres below the earthâs surface. However, this is a very expensive technique due to the fact that long vertical shafts and tunnels have to be driven to reach the ore, then the ore has to be moved a considerable distance to reach the surface, and the size of the tunnels restricts the use of large excavating machinery. It is therefore a very labour-intensive industry.
There are numerous challenges facing deep underground mining.Â Â The most important one is the heat. At 5 km below the earth, the temperature reaches 160 70F and therefore massive and expensive cooling plants are needed to allow workers to survive at such depths. Another problem is the weight of the rock. At 3.5 km the pressure of rocks above the workers is 9,500 tonnes per square metre.
The deepest mine in the world is currently the Western Deep mine in South Africa which penetrates 3.5 km into the Earth's crust.