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The Summitville mine was a gold mining site in Rio Grande County, Colorado south of Del Norte. It is remembered for the environmental damage caused in the 1980s by the leakage of mining by-products into local waterways and then the Alamosa River. ==History== Charles Baker's group of prospectors found traces of placer gold in the San Juan Mountains in 1860 at Eureka, Colorado. The group was forced out in 1861 by the Ute Tribe , who had been awarded the area in a US treaty. Gold was discovered in Wightman Fork, on South Mountain, which is the same location of present-day Summitville. More prospectors returned in 1871, when lode gold was found in the Little Giant vein at Arrastre Gulch, near Silverton, Colorado. The miners were allowed to stay after the Brunot Treaty of 13 Sept. 1873. In exchange for giving up 4 million acres, the Southern Ute Indian Reservation received $25,000 per year. Gold veins were found at 11,500 feet on South Mountain in 1873 and the town was founded when stamp and amalgamation mills were built.〔Voynick, S.M., 1992, Colorado Gold, Missoula: Mountain Press Publishing Company, ISBN 0878424555〕 By 1885 there were more than 250 individual claims in operation. The site was soon mined out, with the weather of the 3,500 m high site adding to difficulties. The site was re-opened on a number of occasions for gold or other metals but with little success, and prior to the site's acquisition in 1984 the last survey was in the early 1970s for copper. The total amount of gold extracted from the site from 1873 until 1959 was around 257,600 troy ounces (8,012 kg). In 1984 an area of was acquired by the Canadian-based Galactic Resources Ltd. subsidiary Summitville Consolidated Mining Company, Inc. (SCMCI). They began a new large-scale open pit operation covering . New techniques were used to extract gold from otherwise uneconomic ore. The mining involved the treatment of pyritic ore with a sodium cyanide solution to leach the gold out of the ore—heap leaching (see also cyanide process). The solution (leachate) was then removed from the ore and the valuable metals extracted using activated carbon. SCMCI leached around 10 million tons of ore on a heap leach pad. The mining operations were finished in October 1991 with the leaching continuing until March 1992, when Galactic Resources filed for bankruptcy. A total of 294,365 troy ounces (9,155.8 kg) of gold and 319,814 troy ounces (9,947.3 kg) of silver were recovered. SCMCI then closed the site and converted on-site equipment for the detoxification process, with around 160 million U.S. gallons (610,000 m³) of stored water needing treatment. After the company insolvency proceedings were completed in a British Columbia court, the US Government declared the site a superfund cleanup site and spent $155,000,000 of public funds cleaning up the site. 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「Summitville mine」の詳細全文を読む スポンサード リンク
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