Mining today: open-cut and underground mining
Gold mining has changed significantly since the early days of exploration. Where gold was traditionally mined using alluvial methods such as panning or cradling, the majority of gold today is found using two methods - open-cut mining and underground mining.
Open-cut mining is preferable to underground mining as it is generally safer and requires considerably less financial outlay, however many of the richest gold deposits are found beneath the ground's surface.
In open-cut mining, surface rocks and layers of earth are stripped away using enormous earth shifters. Over a period of time, the mine is excavated in a series of layers, known as benches. Safety levels are established at various intervals within the mine to reduce the risk of rock falls.
Benches provide access for trucks and other large vehicles to enter the site and allow for drilling and ore sampling at different levels. This is crucial as the miners and geologists need to determine the depth of the gold deposits.
As vast amounts of rock are removed by the machines and then crushed, it can be sifted through for gold. This method can be very profitable as the removed rock may yield three or four grams of gold per tonne.
Drills are used to break down the rock and, in some cases, explosives will also be used. Today, the most common explosive used is ammonium nitrate. As it has about half the power of dynamite, mining engineers can control the effects of explosions, minimising the damage caused to the surrounding area. This also means that risks to mining staff are reduced.
If the gold deposits are of a high standard and run below the base of the mine, the company may then decide to excavate further and establish an underground mineshaft.
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For gold deposits that lie well below the surface, underground mining is employed. This method is extremely costly and involves far greater danger to mine workers. For these reasons, the company involved needs to be guaranteed of finding at least four grams of gold per tonne of ore removed.
In underground mining, a deep vertical shaft is sunk into the ground. These shafts can be up to 1000 metres deep. The shaft provides access for machinery and for miners, who are lowered into the shaft in large cages. Horizontal tunnels, known as stopes are dug at various depths and the miners work along these to access the gold.
Vehicles gain access to the various levels of the mine through a spiral tunnel known as a decline. As mineshafts become deeper, the risk of cave-ins or collapses increases. Underground mines operate under strict safety protocols. These include the way the mineshafts are dug and constructed, the methods of support for the walls and ceiling of the mine and the use of special machines to provide adequate ventilation and lighting.
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Technological advances in recent years have led to the discovery of a new and potentially very rich source of gold - the ocean. Gold is found frequently in seawater as it has been deposited in the oceans for millions of years. Researchers are currently exploring ways to extract large amounts of gold from the sea.
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