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Uranium mining is the process of extraction of uranium ore from the ground. As uranium ore is mostly present at relatively low concentrations, most uranium mining is very volume-intensive, and thus tends to be undertaken as open-pit mining. It is also undertaken in only a small number of countries of the world, as the resource is relatively rarely found.
A prominent use of uranium from mining is as fuel for nuclear power plants.
Additional recommended knowledge
The first deliberate mining of radioactive ores took place in Jáchymov (also known by its German name, Joachimsthal), a silver-mining city in what is now the Czech Republic. Marie Curie used pitchblende ore from Jáchymov to isolate the element radium, a decay product of uranium; her death was from aplastic anemia, almost certainly due to exposure to radioactivity. Until World War II uranium mining was done primarily for the radium content. Sources for radium (contained in uranium ore) were sought for use as luminous paint for watch dials and other instruments, as well as for health-related applications (some of which in retrospect were incredibly unhealthy). The byproduct uranium was used mostly as a yellow pigment.
In the United States, the first radium/uranium ore was discovered in gold mines near Central City, Colorado. However, most American uranium ore before World War II came from vanadium deposits on the Colorado Plateau of Utah and Colorado.
Because of the need for the element for bomb research during World War II, the Manhattan Project contracted with numerous vanadium mining companies in the American Southwest, and also purchased uranium ore from the Belgian Congo, through the Union Minière du Haut Katanga, and in Canada from the Eldorado Mining and Refining Limited company, which had large stocks of uranium as waste from its radium refining activities. American uranium ores mined in Colorado were mixed ores of vanadium and uranium, but because of wartime secrecy the Manhattan Project would only publicly admit to purchasing the vanadium, and did not pay the uranium miners for the uranium content. (In a much later lawsuit, many miners were able to reclaim lost profits from the U.S. government.) American ores had much lower uranium concentrations than the ore from the Belgian Congo, but they were pursued vigorously to ensure nuclear self-sufficiency.
Similar efforts were undertaken in the Soviet Union, which did not have native stocks of uranium when it started developing its own atomic weapons program.
In the 20th century the United States was the world's largest uranium producer. Grants Uranium District in New Mexico was the largest United States uranium producer. The Gas Hills Uranium District, was the second largest uranium producer. The famous Lucky Mc Mine is located in the Gas Hills near Riverton, Wyoming. Canada has since surpassed the United States as the cumulative largest producer in the world.
Australia has the world's largest uranium reserves - 24 percent of the planet's known reserves. The majority of these reserves are located in South Australia. Almost all the uranium is exported, but under strict International Atomic Energy Agency safeguards to satisfy the Australian people and government that none of the uranium is used in nuclear weapons. Australian uranium is used strictly for electricity production, but frees other uranium to be used in weapons.
The Olympic Dam operation run by BHP Billiton in South Australia is combined with mining of copper, gold, and silver, and has reserves of global significance. There are three uranium mines in Australia (a limit currently imposed by the Austalian government), but more have been proposed. The most controversial was Jabiluka, to be built inside the World Heritage listed Kakadu National Park. The existing Ranger Uranium Mine is surrounded by the National Park as the mine area was not included in the original listing of the Park.
Uranium mining and export and related nuclear issues have often been the subject of public debate, and the anti-nuclear movement in Australia has a long history.
Canada is the largest exporter of uranium ore, with the largest mines located in Athabasca Basin in northern Saskatchewan.
Canada's first uranium discovery was in the Alona Bay area, south of Lake Superior Provincial Park in Ontario, by Dr. John Le Conte in 1847. But the Canadian uranium industry really began with the 1932 discovery of pitchblende at Port Radium, Northwest Territories. The deposit was mined from 1933 to 1940, for radium, silver, copper, and cobalt. The mine shut down in 1940, but was reopened in 1942 by Eldorado Mining and Refining Limited to supply uranium to the Manhattan Project. The Canadian government expropriated the Port Radium mine and banned private claimstaking and mining of radioactive minerals.
In 1947 the government lifted the ban on private uranium mining, and the industry boomed through the 1950s, spurred by high prices due to the nuclear weapons programs. Production peaked in 1959, when 23 mines in five different districts made uranium Canada’s number-one export. That same year, however, Great Britain and the United States announced their intention to halt uranium purchases in 1963. By 1963, seven mines were left operating, a number that shrunk to only three in 1972.
A price rise caused uranium to boom again in 1975.
In 1948, prospector Robert Campbell discovered pitchblende at Theano Point, in the area of Alona Bay, Ontario, and staked 30 claims. By November 1948 a rush had begun, and in the next three years, 5,000 claims would be staked in the area. A shaft and headframe were constructed, but abandoned before operations could begin; the mine proved unprofitable after uranium discoveries at Elliot Lake, Ontario.
The uranium-bearing pegmatite of Bancroft, Ontario began mining in 1952.
Uranium was discovered at Blind River-Elliot Lake area in 1949, and production began in 1955. The deposits are in Precambrian quartz-pebble conglomerates, similar to uranium deposits in Brazil and South Africa.
Pitchblende veins were discovered near Beaverlodge, Saskatchewan in 1935, and uranium mining started in 1953.
Today the Athabasca Basin in northern Saskatchewan hosts the largest high-grade uranium mines and deposits. Cameco, the world’s largest low-cost uranium producer, which accounts for 18% of the world’s uranium production, operates three mines and one dedicated mill in the region. Among the major mines are Cameco's flagship McArthur River mine, the developing Cigar Lake mine, the Rabbit Lake mine and mill complex, and the world's largest uranium mill at Key Lake. French-owned uranium syndicate Areva also operates the McClean Lake mill. Most of these mines are joint ventures between Cameco, Areva, and various other joint venture shareholders. Future mines currently in early development stages include Areva's Midwest Project (near McClean Lake), and Cameco's Millennium Project (near Key Lake). As of 2007, with uranium spot market prices well over the $100 USD/lb mark, Saskatchewan has become a hotbed of uranium exploration, with many junior exploration companies rushing to explore the highly valuable Athabasca basin.
Most uranium ore in the United States comes from deposits in sandstone, which tend to be of lower grade than those of Australia and Canada. Because of the lower grade, many uranium deposits in the United States became uneconomic when the price of uranium declined sharply in the 1980s.
Regular production of uranium-bearing ore in the United States began in 1898 with the mining of carnotite-bearing sandstones of the Colorado Plateau in Colorado and Utah, for their vanadium content. The discovery of radium by Marie Curie, also in 1898, soon made the ore also valuable for radium. Uranium was a by-product. By 1913, the Colorado Plateau uranium-vanadium province was supplying about half the world supply of radium. Production declined sharply after 1923, when low-cost competition from radium from the Belgian Congo and vanadium from Peru made the Colorado Plateau ores uneconomic.
Mining revived in the 1930s with higher prices for vanadium. American uranium ores were in very high demand by the Manhattan Project during World War II, although the mining companies did not know that the by-product uranium was suddenly valuable. The late 1940s and early 1950s saw a boom in uranium mining in the western US, spurred by the fortunes made by prospectors such as Charlie Steen.
Uranium mining declined with the last open pit mine shutting down in 1992 (Shirley Basin, Wyoming. United States production occurred in the following states (in descending order): New Mexico, Wyoming, Colorado, Utah, Texas, Arizona, Florida, Washington, and South Dakota. The collapse of uranium prices caused all conventional mining to cease by 1992. "In-situ" recovery or ISR has continued primarily in Wyoming and adjacent Nebraska as well has recently restarted in Texas. Rising uranium prices since 2003 have increased interest in uranium mining in the United States.
Uranium mining took place at Jáchymov from 1948 to 1964.
Uranium was mined from 1947 to 1990 from mines in Saxony. One of the former uranium producers is the Königstein mine, presently being flooded by Wismut GmbH, which plans to recover an estimated 2 million pounds (770 tonnes) U3O8 from the mine water.
In Hungary uranium mining began in the 1950s around Pécs to supply the country's first atomic plant in Paks. After the fall of communism, uranium mining was gradually given up because of the high production costs. That caused serious economic problems and a rise of unemployment in Pécs.
In Sweden uranium mining took place at Ranstadsverket between 1965 and 1969. The goal was to make Sweden self-supplying with uranium, but the mine was closed due to high costs. Since 2005 there have been investigations on opening new uranium mines in Sweden.
Namibia produces uranium at Rossing deposit, where an igneous deposit is mined from one of the world’s largest open pit mines. The mine is owned by a subsidiary of the Rio Tinto Group.
Niger is Africa’s leading uranium-producing nation. Uranium is produced from mines at Arlit owned by Compagnie Generale des Matieres Nucleares.
Niger's uranium came to world attention before the US invasion of Iraq, when it was asserted that Iraq had attempted to buy uranium from Niger (see Niger uranium forgeries).
South Africa produces uranium from deposits in Precambrian quartz-pebble conglomerates of the Witwatersrand Basin, at Brakpan and Krugersdorp, Gauteng.
Uranium prospecting is little different than other forms of mineral exploration with the exception of some specialized instruments for detecting the presence of radioactive isotopes.
The Geiger counter was the original radiation detector, recording the total count rate from all energy levels of radiation. Ionization chambers and Geiger counters were first adapted for field use in the 1930s. The first transportable Geiger-Müller counter (weighing 25 kg) was constructed at the University of British Columbia in 1932. H.V. Ellsworth of the GSC built a lighter weight, more practical unit in 1934. Subsequent models were the principal instruments used for uranium prospecting for many years, until geiger counters were replaced by scintillation counters.
The use of airborne detectors to prospect for radioactive minerals was first proposed by G.C. Ridland, a geophysicist working at Port Radium in 1943. In 1947, the earliest recorded trial of airborne radiation detectors (ionization chambers and Geiger counters) was conducted by Eldorado Mining and Refining Limited. (a Canadian Crown Corporation since sold to become Cameco Corporation). The first patent for a portable gamma-ray spectrometer was filed by Professors Pringle, Roulston & Brownell of the University of Manitoba in 1949, the same year as they tested the first portable scintillation counter on the ground and in the air in northern Saskatchewan.
Airborne gamma-ray spectrometry is now the accepted leading technique for uranium prospecting with worldwide applications for geological mapping, mineral exploration & environmental monitoring.
A deposit of uranium, discovered by geophysical techniques, is evaluated and sampled to determine the amounts of uranium materials that are extractable at specified costs from the deposit. Uranium reserves are the amounts of ore that are estimated to be recoverable at stated costs.
Types of uranium deposits
Many different types of uranium deposits have been discovered and mined.
Uranium deposits in sedimentary rock
Uranium deposits in sedimentary rocks include those in sandstone (in Canada and the western US), Precambrian unconformities (in Canada), phosphate, Precambrian quartz-pebble conglomerate, collapse breccia pipes (see Arizona Breccia Pipe Uranium Mineralization), and calcrete.
Sandstone uranium deposits are generally of two types. Roll-front type deposits occur at the boundary between the up dip and oxidized part of a sandstone body and the deeper down dip reduced part of a sandstone body. Peneconcordant sandstone uranium deposits, also called Colorado Plateau-type deposits, most often occur within generally oxidized sandstone bodies, often in localized reduced zones, such as in association with carbonized wood in the sandstone.
Precambrian quartz-pebble conglomerate-type uranium deposits occur only in rocks older than two billion years old. The conglomerates also contain pyrite. These deposits have been mined in the Blind River-Elliot Lake district of Ontario, Canada, and from the gold-bearing Witwatersrand conglomerates of South Africa.
Igneous or hydrothermal uranium deposits
Hydrothermal uranium deposits encompass the vein-type uranium ores. Igneous deposits include nepheline syenite intrusives at Ilimaussaq, Greenland; the disseminated uranium deposit at Rossing, Namibia; and uranium-bearing pegmatites. Disseminated deposits are also found in the states of Washington and Alaska in the US.
As with other types of hard rock mining there are several methods of extraction. The main methods of mining are box cut mining, open pit mining and in situ leaching (ISL)
In open pit mining, overburden is removed by drilling and blasting to expose the ore body which is mined by blasting and excavation via loaders and dump trucks. Workers spend much time in enclosed cabins thus limiting exposure. Water is extensively used to suppress airborne dust levels.
Underground uranium mining
If the uranium is too far below the surface for open pit mining, an underground mine might be used with tunnels and shafts dug to access and remove uranium ore. There is less waste material removed from underground mines than open pit mines, however this type of mining exposes underground workers to the highest levels of radon gas.
Underground uranium mining is in principle no different to any other hard rock mining and other ores are often mined in association (eg copper, gold, silver). Once the ore body has been identified a shaft is sunk in the vicinity of the ore veins, and crosscuts are driven horizontally to the veins at various levels, usually every 100 to 150 metres. Similar tunnels, known as drifts, are driven along the ore veins from the crosscut. To win the ore, the next step is to drive tunnels, known as raises when driven upwards and winzes when driven downwards through the deposit from level to level. These raises are subsequently used to develop the stopes where the ore is mined in the veins.
The stope, which is the workshop of the mine, is the excavation from which the ore is being extracted. Two methods of stope mining are commonly used. In the “cut and fill” method and open stoping method, the space remaining following removal of ore after blasting is filled with waste rock and cement. In the “shrinkage” method just sufficient broken ore is removed via the chutes below to allow the miners to work from the top of the pile to drill and blast for the next layer to be broken off; eventually leaving a large hole. Another method, known as room and pillar, is used for thinner flatter ore bodies. In this method the ore body is first divided into blocks by intersecting drives, removing ore while so doing, and then systematically removing the blocks, leaving sufficient for roof support.
Waste rock is produced during open pit mining when overburden is removed, and during underground mining when driving tunnels through non-ore zones.
Piles of these tailings often contain elevated concentrations of radioisotopes compared to normal rock. Other waste piles consist of ore with too low a grade for processing. The transition between waste rock and ore depends on technical and economic feasibility criteria. All these piles threaten people and the environment after shut down of the mine due to their release of radon gas and seepage water containing radioactive and toxic materials.
In some cases uranium has been removed from this low-grade ore by heap leaching. This may be done if the uranium contents is too low for the ore to be economically processed in a uranium mill. The leaching liquid (often sulfuric acid) is introduced on the top of the pile and percolates down until it reaches a liner below the pile, where it is caught and pumped to a processing plant. Due to the potential for extreme damage to the surrounding environment , this practice is no longer in use.
In-situ leaching (ISL), sometimes referred to as in-situ recovery (ISR) or solution mining, is performed by pumping liquids (weak acid or weak alkaline depending on the calcium concentration in the ore) down through injection wells placed on one side of the deposit of uranium, through the deposit, and up through recovery wells on the opposing side of the deposit - recovering ore by leaching. ISL is also used on other types of metal extraction such as copper. ISL is often cost-effective because it avoids excavation costs, and may be implemented more quickly than conventional mining. However, it is not suitable to all uranium deposits, as the host rock must be permeable to the liquids (as is often the case in sandstone).
Environmental impact studies are performed when evaluating ISL, because ground water can be affected. In-situ leaching is the only type of uranium mining currently being done in the United States (2006).
Recovery from seawater
The uranium concentration of sea water is low, approximately 3.3 mg per cubic meter of seawater (3.3 ppb). But the quantity of this resource is gigantic and some scientists believe this resource is practically limitless with respect to world-wide demand. That is to say, if even a portion of the uranium in seawater could be used the entire world's nuclear power generation fuel could be provided over a long time period. Some anti-nuclear proponents claim this statistic is exaggerated. Although research and development for recovery of this low-concentration element by inorganic adsorbents such as titanium oxide compounds, has occurred since the 1960s in the United Kingdom, France, Germany, and Japan, this research was halted due to low recovery efficiency.
At the Takasaki Radiation Chemistry Research Establishment of the Japan Atomic Energy Research Institute (JAERI Takasaki Research Establishment), research and development has continued culminating in the production of adsorbent by irradiation of polymer fiber. Adsorbents have been synthesized that have a functional group (amidoxime group) that selectively adsorbs heavy metals, and the performance of such adsorbents has been improved. Uranium adsorption capacity of the polymer fiber adsorbent is high, approximately tenfold greater in comparison to the conventional titanium oxide adsorbent. Commercial installations are planned for the near future.
Rise, stagnation, renaissance and opposition to uranium mining
In the beginning of the Cold War, to ensure adequate supplies of uranium for national defense, the United States Congress passed the U.S. Atomic Energy Act of 1946, creating the Atomic Energy Commission (AEC) which had the power to withdraw prospective uranium mining land from public purchase, and also to manipulate the price of uranium to meet national needs. By setting a high price for uranium ore, the AEC created a uranium "boom" in the early 1950s, which attracted many prospectors to the four corners region of the country. Moab, Utah became known as the Uranium-capital of the world, when geologist Charles Steen discovered such an ore in 1952, even though American ore sources were considerably less potent than those in the Belgian Congo or South Africa.
At the height of the nuclear energy euphoria in the 1950s methods for extracting diluted uranium and thorium, found in abundance in granite or seawater, were pursued. ORNL Review Scientists promised that, used in a breeder reactor, these materials would potentially provide limitless source of energy.
American military requirements declined in the 1960s, and the government completed its uranium procurement program by the end of 1970. Simultaneously, a new market emerged: commercial nuclear power plants. However, in the U.S. this market virtually collapsed by the end of the 1970s as a result of industrial strains caused by the energy crisis, popular opposition, and finally the Three Mile Island nuclear accident in 1979, all of which led to a de facto moratorium on the development of new nuclear reactor power stations.
In Europe a mixed situation exists. Considerable nuclear power capacities have been developed, notably in Belgium, France, Germany, Spain, Sweden, Switzerland and the UK. In many countries development of nuclear power has been stopped and phase out by legal actions. In Italy the use of nuclear power has been barred by a referendum in 1987. Ireland also has no plans to change its non-nuclear stance and pursue nuclear power in the future.
Since 1981 uranium prices and quantities in the US are reported by the Department of Energy.  The import price dropped from 32.90 US$/lb U3O8 in 1981 down to 12.55 in 1990 and to below 10 US$/lb U3O8 in the year 2000. Prices paid for uranium during the 1970s were higher, 43 US$/lb U3O8 is reported as the selling price for Australian uranium in 1978 by the Nuclear Information Centre.
Uranium prices reached an all-time low in 2001, costing US$7/lb, but has since rebounded strongly and in the last few months extremely so. In April 2007 the price of Uranium on the spot market rose to US$113.00/lb. This is very close to the all time high (adjusted for inflation) in 1977. The higher price has spurred expansion of current mines, construction of new mines and reopening of old mines as well as new prospecting.
Health risks of uranium mining
Because uranium ore emits radon gas, uranium mining can be more dangerous than other underground mining, unless adequate ventilation systems are installed. During the 1950s, many Navajos became uranium miners, as many uranium deposits were discovered on Navajo reservations. A statistically significant subset of these early miners later developed small cell carcinoma after exposure to uranium ore. Radon-222, a natural decay product of uranium, has been shown to be the cancer-causing agent. Some American survivors and their descendants received compensation under the Radiation Exposure Compensation Act in 1990.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Uranium_mining". A list of authors is available in Wikipedia.|