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Production and disposal of mill tailings in the Coeur D'Alene mining region, Shoshone County, Idaho; preliminary estimates

1998; United States Department of the Interior; Linguagem: Inglês

10.3133/ofr98595

2332-4899

Keith R. Long,

Coal and Its By-products

The Coeur d'Alene mining region in northern Idaho has produced 34,300 metric tons of silver, 7,288,300 metric tons of lead, and 2,870,000 metric tons of zinc since the discovery of polymetallic veins in the region during the 1880s.This output accounts for 18, 17, and 6 percent, respectively, of the nation's production of silver, lead, and zinc.The total value of this metal production exceeds 26 billion in 1997 dollars.The Coeur d'Alene mining region is the largest silver-producing mining district in the world, exceeding even that of the Cerro Rico de Potosf district in Bolivia.Due to the relatively low grade of many of the lead-zinc-silver ores mined, methods of concentration were introduced at the beginning of commercial mining operations in 1886.About 130 million metric tons of metal-bearing material was treated by various methods of concentration from 1886 to 1997, generating 109 million metric tons of mill tailings as a waste product.Until 1968, most mill operators disposed of mill tailings directly into the South Fork of the Coeur d'Alene River or its tributaries.After 1968, all mill tailings have been stored in tailings impoundments or returned to the mines for use as stope fill.A preliminary accounting of the production and disposal of mill tailings shows that about 56 million metric tons of tailings containing 2,200 metric tons of silver, 800,000 metric tons of lead, and at least 650,000 metric tons of zinc were disposed of or otherwise lost into the Coeur d'Alene River or its tributaries.Another 13.2 million metric tons of tailings containing 400 metric tons silver, 200,000 metric tons lead, and at least 290,000 metric tons zinc were stockpiled along the floodplain of the Coeur d'Alene River, principally west of the town of Kellogg.The remaining production of mill tailings was either placed in one of several tailings impoundments, starting with that of the Bunker Hill & Sullivan Mining & Concentrating Co., west of Kellogg in 1928, or used as stope fill, beginning in 1949 at the Dayrock mine.These impoundments were typically built from, and built upon, older stockpiles of mill tailings.Mitigation of fugitive mill tailings has been a major management issue in the region since the turn of the century.In 1904, two impoundments were built on the South Fork of the Coeur d'Alene River to contain mill tailings, one near the town of Osburn, the other near the confluence of Pine Creek and the South Fork, and a third impoundment built on Canyon Creek just above its confluence with South Fork.The Osburn and Canyon Creek dams were partly breached by flooding in 1917; the Pine Creek dam was breached in 1933.Meanwhile, mine and mill operators purchased pollution easements from property owners along the Coeur d'Alene River.By 1900, mill tailings had reached Lake Coeur d'Alene and had impacted as much as 25,000 acres of floodplain along the river.From 1932 to 1946, mine and mill operators dredged more than 15 million metric tons of tailings-contaminated sediments from the river at Cataldo Mission Flats, stockpiling recovered material on the floodplain.Many millions tons more of tailings were dredged from 1946 to the 1960s.Some of these tailings-contaminated sediments, along with tailings removed from the Central Impoundment Area at the Bunker Hill mine, were used to construct the road bed of Interstate 90, which follows the river valley.Since 1900, some 6 million metric tons of tailings have been reclaimed from creeks and dumps for reprocessing.These operations recovered 149 metric tons of silver, 51,000 metric tons of lead, and 56,000 metric tons of zinc.Unknown quantities of tailings and tailings-contaminated sediments have been removed for such uses as railroad ballast, brick-manufacture, and fill.The amount of tailings and tailings-contaminated sediments remaining in the Coeur d'Alene River system cannot yet be determined.