Metals cannot be farmed, or made artificially, so they have to be extracted from the earth. Only a few can be found on the surface of the earth, such as gold nuggets on river beds. These are collected by placing obstacles in the path of the flowing water, and sorting through the trapped deposits for gold (or tin or platinum) nuggets. This form of mining is called placer mining.
Most other metals (in the form of ores) must be dug out of the earth. Some deposits are close to the surface, and are mined by methods like strip mining and open cast mining. In both of these cases, the soil and rock over the metal deposits are removed with large shovels. The ore is carried away to factories for smelting and extraction of pure metal. Open-cast mines can be very big. For example, the open cast copper mine in Bingham, Utah is wider than 35 football fields and about 900 meters deep.
When the metal deposits are deep below the surface of the earth, vertical or sloping shafts are dug into the ground. Water and other materials are removed from the shaft. Then, miners go down into the shaft and break off metal ores from the walls surrounding the shaft using hand-held tools. The ores are transported up using mechanical equipment.
Some of the deepest underground mines are in South Africa. The East Rand gold mine reached went down to 3,585 meters in 2003. The Western Deep Levels gold mine, also in South Africa, reached a depth of 3,581 meters in 1977. As mining technology improves, these mines could go down as far as 5,000 meters in the future. TauTona mine, part of the Western Deep Levels, is already approaching a depth of about 3,900 meters in 2009. Compared to this, one of the deepest mines in Europe is a 1,100 meters deep salt and potash mine at Boulby on the northeast coast of England.
The business of mining metals from large pits or the deep underground poses serious safety and health issues and environmental concerns.
Safety: Historically, mining was such a dangerous activity that it was mainly performed by slaves, prisoners, and the very poor. Mining involves removing dirt, rock and other materials to create large holes in the ground. Explosives are commonly used to loosen rocks around the mining area. A large number of mine accidents also occur during the use of explosives in metal mines. Mines also use some of the heaviest equipment man has built, such as earth movers, bulldozers, shovels, and cranes. Many accidents occur during the operation of such machinery.
In 2006, about 4,800 miners in China were killed in mine accidents involving blasts, floods and other accidents. In United States, the number stood at about 70 in 2006, of which about 30% are in non-coal mines.
Underground mining is especially hazardous. The walls around the deep mine shafts can collapse, or roofs can cave in, sending miners to almost certain death. Other dangers include, flooding, poor ventilation, and fires. Deep down in the mine shafts, many flammable gases like methane accumulate. The sparks given off by mining equipment, such as lights, sets the gas on fire leading to terrible fires and explosions. Even if miners escape being burnt, such fires suck up the oxygen in the mine shaft, and suffocate the miners.
In olden times, caged canaries were lowered into mine shafts to detect poisonous gases like methane. As long as the bird kept singing, miners knew the shaft was safe. When the canary stopped singing due to gas poisoning, the miners would leave the shaft and come up to the surface. Until Sir Humphrey Davy (1778 - 1829), the British chemist invented the safety lamp (now called the Davy lamp) for use in underground mines, thousands of miners lost their lives to mine explosions. The Davy lamp placed wire gauze around the flame of the lamp, preventing the gases from coming in contact with the flame. Many lives were saved.
Modern mining equipment such as electrical lamps has improved the safety of mines. Still, accidents occur quite often. Ignorance, negligence, and violation of safety standards are usually the most common causes of mine accidents. It is extremely important miners be trained about the dangers of mining, and how to work safely. Such training can reduce the number of mine accidents dramatically. It is believed that 60-75% of all mine accidents resulted from errors that could have been avoided.
Health Effects: Apart from safety, workers in mines also face serious health issues. A common form of health hazard in metal mines is the dusty environment. Dust produced during mining causes major illnesses when inhaled in large quantities. It could lead to pneumoconiosis, or black lung disease. Other illnesses result when the dust contains silica and asbestos. Poisonous gases from the incomplete combustion of explosives used during mining also threaten miners’ health. Miners also have to operate powerful tools in cramped conditions, hurting their hands, backs and legs. The sound from these tools in the closed mine shafts is so loud that many miners go partially or fully deaf, especially if protective ear covers are not provided.
In many uranium mines, the radiation risk comes less from the uranium being mined and more from the radioactive radon gas that mixes with the air that miners breathe.
More risks arise in mining radioactive metals like uranium, due to exposure to radiation and inhaling radioactive dust particles. Radiation poses a significant risk to the miners, and the extent of damage depends on the dose. Heavy doses of radiation can destroy cells within days or weeks, and can kill the exposed person. Lower doses often go undetected, and effects become visible only after several years.
Around the world, government and legislative bodies put in rules to improve the safety and health conditions of miners minimize such effects. Levels are set for how much hazardous substances miners can be exposed to. But when things go wrong, these levels can be easily exceeded, exposing miners to severe damage, even death.
Environmental Effects: Mining can have serious negative impacts on the environment, in the short term as well as the long term. Mining operations can destroy scenic places, destroy the habitat of animals and plants, and even force local residents to move out. One method of mining blows off entire mountain-tops! A form of placer mining, called hydraulic mining, popular in California during the gold rush, was pronounced a “public and private nuisance” due to its effects the rivers and irrigation systems.
Many of the half-million abandoned gold, silver, and copper mines in the American West are draining dangerous concentrations of acid into nearby streams. A few have been cleaned up, although it’s usually an expensive and difficult process.
The continuous noise, frequent blasts, and severe dust pollutions cause much suffering to local communities who lived there before the mining companies moved in. In the long term, mines release many toxic substances that can pollute the air and water supply. Water pollution often kills off the native plants and animals, and even threatens people. Cutting down the trees increases soil erosion. When all the minerals have been mined, the mines have a bare and desolate look. The holes in the ground might be filled with coal ash or even sewage material; sometimes, these giant holes are not filled at all, and stand out like ugly scars on the surface of the earth.
Six years after the collapse of a dam of a mine in 1998 in Aznalcollar in Spain, which flooded about 4,000 hectares of adjoining land, concentrations of cadmium, lead, mercury, copper etc., in soil samples were found to be well above acceptable values.
Most nations in the world have made laws to control the negative effects of mining. By these laws, mining companies are required to minimize the damage they cause to the environment. When they finish extracting all the minerals, they are supposed to return the place as near to its original state as possible. While such laws are upheld in a few countries, they are widely ignored in some of the largest mines in the world. This is one of the reasons why we must recycle our metals. The more metal we recover from scrap, the less new metal needs to be mined.
Mining is often not the last step in the extraction of metals. Other than a few metals like gold and silver are mined in their pure form. Most other metals are chemically reactive, and their ores contain compounds of the metals rather than the metal itself. Extracting metals from their ores is usually a long and tedious process. During this process, many noxious fumes that pollute the air and toxic chemicals that seep into the ground (to pollute the water supply) are produced. The working conditions in metal processing factors can also be quite dangerous, with very high temperatures, molten metals, and poisonous gases. These present safety and health issues similar to the mining industry.
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Absolute Astronomy: Article on mining
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