Copper mining in the United States has been a major industry since the rise of the northern Michigan copper district in the 1840s. In 2007 the United States produced 1.19 million metric tonnes of copper, worth $8.8 billion, making it the world's third largest copper producer, after Chile and Peru. The nation produces 63% of the copper it uses, relying on imports from Chile, Canada, Peru, and Mexico for the remaining 37%. Top copper producing states in 2007 were (in order) Arizona, Utah, New Mexico, Nevada, and Montana.
Copper mining activity has increased in recent years 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.
For the leading mines, see Lists of copper mines in the United States.
Alaska is not currently a significant copper producer.
Russian explorers discovered copper on the Kasaan Peninsula of Prince of Wales Island in southeastern Alaska about 1865. Mining began in the period 1895-1900, and continued until shortly after World War I. Copper is present as chalcopyrite, occurring with magnetite, pyrite, garnet, epidote, diopside, and hornblende, in replacement deposits in greenstone. Gold and silver were recovered as byproducts.
Copper was discovered at Prince William Sound in 1897. Deposits were associated with pillow basalts alterered to greenstone. The basalts are interbedded with slate and greywacke, faulted, and intruded by granitic rocks. The principal mines were the Beatson-Bonanza mine at Latouche and the Ellamar mine, which accounted for 96% of the copper produced. Other mines were the Midas mine near Valdez, the Threeman mine, and the Fidalgo-Alaska mine at Port Fidalgo, Alaska. Mining began in 1900, and continued until 1930. Total production was 96,000 tonnes of copper.
Historically, the largest copper mining distrct in Alaska was the Nizina district, the principal mines of which (Erie mine, Jumbo mine, Bonanza mine, Mother Lode mine, and Green Butte mine) were at Kennecott, Alaska, four miles north of McCarthy. The copper is present as chalcocite in veins and irregular replacements in the Triassic Chitistone Limestone. Some silver was also produced as a byproduct. The mine at Kennecott gave rise to Kennecott Copper Corporation, which outlasted the mine, and is still a major mining company. The deposit was discovered in 1900, and once a railroad connection was built, the mine operated from 1911 to 1938, after which Kennecott became a ghost town. The town is now a historical park.
Arizona has been a major copper producer since the 1800s. In 2006 Arizona was the leading copper-producing state in the US, producing a record five billion dollars worth of copper.
The Napoleon mine at Copperopolis in Calaveras County opened in 1860, and was so productive that it ignited a boom in other copper-mining properties from 1862 to 1866. The boom stimulated development of copper mines along the Foothill copper belt, a 250-mile long zone of copper deposits in the Sierra Nevada foothills, running from Butte County in the northwest to Fresno County in the southeast. Production nearly ceased after 1868 when the shallow oxidized ore was exhausted, and the deeper sulfide ores were found to be poorer in gold and silver. The Foothills belt yielded 91 thousand tonnes of copper and 23 thousand tonnes of zinc.
Most California copper production came from the West Shasta district in northern California. Gold prospectors discovered the copper deposits of Shasta County in 1848, but no metal was produced until 1879, when some silver was produced from the Iron Mountain Mine. The copper was in massive sulfide deposits in the Devonian Balaklala Rhyolite. The principal mines were the Iron Mountain Mine, Mammoth Mine, and the Balaklala Mine. Copper production began in 1894, and continued off-and-on until 1976. Total production was 320 thousand tonnes of copper, 93 million pounds of zinc, 36 million troy ounces of silver, and 520,000 ounces of gold. The district also produced pyrite for sulfuric acid.
The Island Mountain mine in Trinity County operated from 1915 to 1930, and produced 4100 tonnes of copper, 140,000 ounces of silver, and 8,600 ounces of gold. The orebody is a massive sulfide deposit of pyrite, chalcopyrite, and pyrrhotite along a shear zone in the Franciscan Formation.
The Harborside mine, near Brooksville mined copper and zinc from an open pit from 1968 to 1972.
The underground Black Hawk mine near Blue Hill produced copper, zinc, and lead from 1972 to 1977.
Native Americans mined copper from small pits on the Keweenaw Peninsula of northern Michigan as early as 3000 B.C. In the American era, the first successful copper mine, the Cliff mine, began operations in 1845, and many others quickly followed. The last major copper mine in Michigan, the White Pine mine, shut down in 1995, after unsuccessfully applying for a permit to convert the underground mine to an in-situ leaching operation.
Franconia Minerals is exploring three copper-nickel deposits in St. Louis County. Like the Northmet deposit, the deposits are in the Duluth Complex.
Copper is recovered as a byproduct of lead mining in the Lead Belt of southeastern Missouri.
In 2006, Montana was the fourth-largest copper-producing state in the country.
Butte, Montana was once the nation’s most prolific copper-mining district. Miners first came to Butte in 1864 to mine placer gold. Hard rock silver mining began in 1874, then rich copper veins were discovered in 1882. The district quickly switched from silver to copper, and by 1887, Butte was the leading copper-producing district in the United States. The Anaconda Copper Mine was the world's most productive copper mine from 1892 through 1903, and intermittently for years thereafter. Open-pit mining began at the Berkeley Pit in 1955; the Berkeley Pit has been inactive for years, and continues to fill with acidic water. Through 1964, Butte produced 7.3 million tonnes of copper, 2.2 million tonnes of zinc, 1.7 million tonnes of manganese, 380 thousand tonnes of lead, 645 million troy ounces of silver, and 2.5 million ounces of gold. The only remaining active copper mine at Butte is the Continental pit, operated by Montana Resources
Some copper is also produced by Troy unit silver mine in the northwest corner of the state, and by two platinum mines in the Stillwater igneous complex: the Stillwater mine and the East Boulder project.
The largest copper producer in Nevada has been the Ely district (also called the Robinson district) in White Pine County. A Native American showed mineralization to prospectors in 1867, and the district started in a small way as a lode gold producer. A railroad link in 1906 made it economically possible to start large scale open pit mining of the large porphyry copper deposits, and the first copper was produced in 1908. Mining was halted in recent years due to low copper prices, but the open pit was reopened in 2004 by Quadra Mining Ltd In 2007, the mine produced 121 million pounds (55 thousand tonnes) of copper, plus byproduct molybdenum.
Newmont's Phoenix mine in Lander County produced 6.2 million pounds (2800 tonnes) of copper in 2007, as a byproduct of gold mining.
Another copper deposit was discovered about 1712, and the Schuyler mine extracted ore and shipped it in casks to the Netherlands. The success of the Schuyler mine led to more prospecting and discovery of more deposits.
The Santa Rita mine in southwest New Mexico was the first copper mine in what is now the western United States. Spaniards began mining copper there about 1800. The district still produces copper, from the large Chino Mine open pit.
Native Americans had mined turquoise associated with the copper deposits at present-day Tyrone in Grant County, New Mexico. Modern mining followed the discovery of turquoise and copper by American prospectors in 1870. The first copper was shipped from the Tyrone district in 1879.
Some copper has been produced from three deposits in sandstone of the Triassic Chinle Formation in the Nacimiento Mountains near Cuba, New Mexico. The copper is present as sulfides (most commonly chalcocite) and malachite associated with organic material; some native silver is also present.
New Mexico is currently the nation’s number-three copper-producing state. Copper is produced from two large open-pit porphyry copper operations in Grant County: the Chino Mine and the Tyrone mine. Both mines are owned and operated by Phelps Dodge. In 2007, the two mines produced 249 million pounds (113 thousand tonnes) of copper, as well as 13 thousand ounces of gold and 209 thousand ounces of silver.
Copper and silver occur in a sandstone roll-front-type deposit in the Wellington sandstone of Permian age at Paoli, Garvin County, Oklahoma. About 1900, several wagon loads of ore were shipped from the deposit.
By 1732 the Gap mine in Lancaster County was operating, owned by shareholders including Gouverneur Morris and Thomas Penn. The mine shut down due to water problems about 1755. The mine reopened as a nickel mine about 1850, and produced some byproduct copper along with the nickel until it shut down in 1893.
In 1889, the Ducktown Sulphur, Copper, gold and Iron Company bought the properties, and began producing copper and iron from the deeper high-sulfide ores, which previous companies were unable to work successfully. The ores were treated by open roasting in which the ore was piled in large stacks with alternating layers of wood, and burned. The method released large quantities of sulfur dioxide, which killed much of the vegetation in the immediate area. Open roasting was replaced by pyritic smelting in 1904, and the smelters began recovering the most of the sulfur in the form of sulfuric acid rather than releasing it to the atmosphere. Froth flotation was added in the 1920s.
The Burra Burra Mine site in Ducktown is now home to a museum dedicated to the interpretation of the region's copper mining history.
In 2006, Utah was the nation's number two producer of copper.
The Bingham Canyon Mine southwest of Salt Lake City has been one of the world’s largest copper producers for more than 100 years. The mine, owned and operated by Kennecott Utah Copper (a division of Rio Tinto Group), is a large open pit in a porphyry copper deposit. (The Bingham Canyon Mine and the Chuquicamata copper mine in Chile each claim to be the largest open-pit mine in the world.) It continues to be a major source not only of copper, but also of molybdenum, gold, and silver. The value of metals produced in the year 2006 alone was $1.8 billion.
Constellation Copper's Lisbon Valley copper mine in San Juan County, southwest Utah began mining in 2005, and produced its first copper in 2006. The copper deposit is in sandstones of the Dakota Sandstone and Burro Canyon Formation. The primary copper mineral is chalcocite, which is thought to have been deposited from solutions ascending through the Lisbon Valley Fault. Above the water table, chalcocite has been oxidized to malachite, azurite, tenorite, and cuprite. On November 30, 2007, Constellation announced that it would stop mining in 2008, because of unexpectedly low copper recovery. The company will continue to recover copper by heap-leaching already-mined ore as long as profitable.
Western Utah Copper has applied for a permit to start an open-pit copper mine near Milford. Western Utah Copper estimates that their Milford properties will yield 100 thousand tonnes of copper, 115,000 ounces (3.58 tonnes) of gold, and 11.5 million ounces (358 tonnes) of silver over a five-year period. Western Utah Copper merged into Copper King Mining Corporation on January 31, 2008.
The Elizabeth deposit was discovered in 1793 and started mining in 1809 as the first copper mine in the state; it was also the last copper mine to operate in the state when it closed in 1958. The Elizabeth mine is now a federal Superfund site due to acid mine drainage.
The Toncrae deposit near Floyd was mined for iron (from the gossan) from about 1790-1850. Copper was mined from 1854-1855, 1905-1908, and 1938-1947. The deposit is a massive sulfide, composed mainly of pyrrhotite and magnetite. The main copper ore minerals are chalcocite and covellite.
Copper was discovered in 1843 at what became known as the Copper Creek mine near Mount Sterling in Crawford County, southwest Wisconsin. About 5500 pounds (2.5 tonnes) of copper were produced from the deposit between 1843 and 1852. The Plum Creek copper mine, also in Crawford County, was discovered near Wauzeka in the 1850s, and mined in 1860 and 1861. Both the Copper Creek and Plum Creek deposits are in limestone.
Douglas County, in the northwest corner of the state, was heavily prospected in the 1800s for native copper deposits in Keweenawan-series rocks, similar to deposits found in Keweenawan rocks in Michigan. A number of mines were started, but none proved profitable.
The copper deposit of the Flambeau mine was discovered in 1969 1.5 miles south of Ladysmith in Rusk County, and produced from an open pit from 1993 to 1997. Total production was 160 thousand tonnes of copper, 3.3 million ounces (100 tonnes) of silver, and 330 thousand ounces (10 tonnes) of gold. Kennecott reclaimed and revegetated the site to specifications of a state-approved reclamation plan. The Wisconsin Department of Natural Resources continues long-term vegetation and groundwater monitoring of the site to assure that the reclamation was done successfully.
Although no copper mines have operated in Wyoming in recent years, there are several properties with large-tonnage copper-silver porphyries (Tertiary) in the Absaroka Mountains east of Yellowstone, stratabound copper-silver-zinc massive sulfides (Triassic-Jurassic) in the Lake Alice district in the overthrust belt of Western Wyoming, several volcanogenic massive sulfide (copper, lead, zinc, silver) deposits in the Encampment district, a potentially major stratabound copper-gold paleoplacer (Proterozoic) at the Ferris-Haggarty property in the Sierra Madre, a Proterozoic copper-gold porphyry at the Copper King property in the Laramie Range, and other properties of interest (Hausel, 1997).
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