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Copper mining in the United States has been a major industry since the rise of the northern Michigan copper district in the 1840s. In 2014 the United States produced 1.37 million metric tonnes of copper, worth $9.7 billion, making it the world's fourth largest copper producer, after Chile, China, and Peru. Copper was produced from 27 mines in the US. Top copper producing states in 2014 were (in descending order) Arizona, Utah, New Mexico, Nevada, and Montana. Minor production also came from Idaho, and Missouri. As of 2014, the US had 35 million tonnes of known remaining reserves of copper, the fifth largest known copper reserves in the world, after Chile, Australia, Peru, and Mexico.〔(''Mineral Commodity Summary'' ) - U.S. Geological Survey - January 2015〕 Copper in the US is used mainly in construction (43%) and electric equipment (19%). In 2014, the nation produced 69% of the copper it used, relying on imports from Chile, Canada, Peru, and Mexico for the remaining 31%.〔 Copper mining activity increased in the early 2000s because of increased price: the price increased from an average of $0.76 per pound for the year 2002, to $3.02 per pound for 2007.〔D.R. Wilburn, "Exploration review," ''Mining Engineering'', May 2008, p.47.〕 A number of byproducts are recovered from American copper mining. In 2013, American copper mining produced 28,500 metric tons of molybdenum, worth about $700-$800 million, which was 47% of total US production.〔(Molybdenum ) US Geological Survey, Minerals Yearbook 2013.〕 In 2014, copper mining produced about 15 metric tons of gold, worth $600 million, which represented 7% of US gold production.〔(Gold ) US Geological Survey, Commodity Updates, 2015〕 Other byproducts of the copper extraction process included silver, and minor amounts of rhenium and platinum-group metals. Sulfuric acid is recovered at copper smelters.〔US Geological Survey, (Sulfur ), Minerals Yearbook, 2012.〕 ==Ore grades== From the start of copper mining in the Michigan copper district, ore has been divided into two classes. The rock with higher copper content was smelter ore, also called direct shipping ore, and required no treatment before going to the smelter. The rock with less copper was called milling ore, or concentrating ore, and required crushing and separation of ore minerals from the waste rock to produce copper concentrate, which was sent to the smelter. Because metallic minerals have higher specific gravities than most gangue (waste) minerals, concentrating the milling ore was done in various gravity classifiers. The early Michigan copper mines used buddles. Later copper mining used improved gravity-classification machinery, including jigs, vanners, and Wilfley tables. A revolutionary development in American copper mining took place when mining engineer Daniel Cowan Jackling conceived of mining the huge but low-grade copper ore body at Bingham Canyon, Utah, using steam shovels in a big open pit. Steam shovels had previously been used in the iron mines of the Mesabi Range, in Minnesota, but had not been used in copper mining. Jackling incorporated the Utah Copper Company in 1903, and in 1906 began excavating. From the start, the Bingham Canyon Mine was one of the leading copper-producing mines in the world, and returned a good profit mining ore with less than two percent copper.〔Horace J. Stevens, ''The Copper Handbook'', v8 (Houghton, Mich: Horace Stevens, 1908) 1377-1381.〕 Mining by open-pit model using large-scale mechanization was copied by other US mines, in Ely, Nevada (1908), Santa Rita, New Mexico (1910), and Ajo, Arizona (1917). The entire output of these mines was low-grade milling ore. The open-pit mining of porphyry copper deposits was adopted worldwide. In the 1910s and 1920s, copper mills adopted the froth flotation method, which had been developed in Australia. Whereas the old gravity methods of concentration, using jigs and Wilfley tables recovered 60 to 80 percent of the copper in the ore, froth flotation recovered 90 to 95 percent.〔George J. Young, ''Elements of Mining'', 4th ed. (New York: McGraw-Hill, 1946) 3.〕 The Bingham Canyon mill installed froth flotation in 1918. Large-scale mining of low-grade orebodies became predominant, and the amount of direct-shipping ore mined fell drastically in the first half of the 20th century, and by 1960, the contribution of direct-shipping ore was insignificant. Improvements in low-cost mining and ore processing allowed the average ore grade of milling ore to decline. 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「Copper mining in the United States」の詳細全文を読む スポンサード リンク
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