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Uranium mining in Colorado, United States, goes back to 1872, when pitchblende ore was taken from gold mines near Central City, Colorado. The Colorado uranium industry has seen booms and busts, but continues to this day. Not counting byproduct uranium from phosphate, Colorado is considered to have the third largest uranium reserves of any US state, behind Wyoming and New Mexico.〔J. Keller and others, ''Colorado'', Mining Engineering, May 2006, p. 76.〕 Uranium price increases from 2001 to 2007 prompted a number of companies to revive uranium mining in Colorado. However, price drops and financing problems in late 2008 have forced some companies to cancel or scale back uranium-mining projects. There are no currently producing uranium mines in Colorado.〔Mark Jaffe, "Mine woes run deep", ''Denver Post'', 4 December 2008, p. B1.〕 ==Front Range province== Hydrothermal uranium deposits are present through a widely spaced area in the Front Range of the Rocky Mountains, in Larimer, Boulder, Gilpin, Clear Creek, and Jefferson counties. The first uranium identified in the USA was pitchblende from the Wood gold mine at Central City, Colorado in 1871.〔F.B. Moore and C.R. Butler (1952) ''Pitchblende Deposits at the Wood and Calhoun Mines Central City Mining District Gilpin County, Colorado'', US Geological Survey, Circular 186.〕 Pitchblende orebodies were also discovered in the Calhoun mine, the Kirk mine, and some others. About 122,000 pounds (55 metric tons) of uranium oxide (U3O8) were shipped at irregular intervals from six gold mines in the Central City district from 1872 to about 1916.〔William L. Chenowith (1980) ''Uranium in Colorado'', in ''Colorado Geology'', Denver: Rocky Mountain Association of Geologists, p. 217.〕 The uranium boom of the late 1940s revived the search for uranium orebodies in the gold and silver mines of the Front Range. Again, uranium was produced from a number of mines, but the orebodies were small and discontinuous. Pitchblende was discovered in 1948 in the Caribou silver mine at the town of Caribou, Boulder County. A small amount of uranium ore was produced.〔F.B. Moore, W.S. Cavender, and E.P. Kaiser (1957) ''Geology and uranium deposits of the Caribou Area, Boulder County, Colorado'', US Geological Survey, Bulletin 1030-N.〕 In 1949 janitor and weekend prospector Fred Schwartzwalder discovered uranium at an abandoned copper prospect in Jefferson County about ten miles northeast of Central City and eight miles north of Golden.〔Robert J. Wright and Donald L. Everhart (1960) Uranium, in Mineral Resources of Colorado First Sequel, Colorado Mineral Resources Board, p.349〕 The deposit consists of Tertiary hydrothermal veins filling fracture zones oriented predominantly NNW-SSE in gneiss, schist, and quartzite of the Precambrian Idaho Springs Formation. The chief ore mineral is pitchblende, which occurs with adularia and ankerite. Schwartzwalder could interest no one in his discovery, so he drove the first adit of the Schwartzwalder mine by himself, made the first ore shipment in 1953, and sold the mine in 1955.〔George R. Downs and Allan G. Bird, ''The Schwartzwalder uranium mine, Jefferson County, Colorado'', Mountain Geologist, Oct. 1965, v.2, n.4, pp. 183–191.〕 The Schwartzwalder mine was the source of more than 99% of the uranium produced from the Front Range province. The mine operated until 1995, producing 17 million pounds (7700 metric tons) of uranium oxide.〔J.W. Keller and C.J. Carroll, ''Colorado'', Mining Engineering, May 2001, p.68.〕 The mine is owned by General Atomics subsidiary the Cotter Corporation, which estimates that there are an additional 16 million pounds (7300 metric tons) of uranium oxide resource remaining in the mine. The Copper King mine, in Larimer County about 25 miles northwest of Fort Collins and 5 miles northeast of Red Feather Lakes contained a skarn deposit that was worked unsuccessfully for zinc in 1920 and 1936. Prospectors found uranium at the abandoned mine in 1949, and it was worked for uranium from 1951 until 1953. The uranium occurs as pitchblende in a hydrothermal vein deposit in Precambrian granite. Although the zinc skarn and the pitchblende vein are exposed in the same workings, the pitchblende appears to have been deposited much later.〔P.K. Sims, George Phair, and R.H. Moench (1958) ''Geology of the Copper King Uranium Mine, Larimer County, Colorado'', US Geological Survey, Bulletin 1132-D.〕 Other vein-type uranium mines in the Front Range were the Fairday A. M. mine near Jamestown in Boulder County, and the Wright Lease mine near Ideledale in Jefferson County.〔Robert J. Wright and Donald L. Everhart (1960) ''Uranium'', in ''Mineral Resources of Colorado First Sequel'', State of Colorado Mineral Resources Board, pp. 352–353.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Uranium mining in Colorado」の詳細全文を読む スポンサード リンク
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