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Gold mining in Colorado

Gold mining in Colorado, a state of the United States, has been an industry since 1858, and played a key role in the establishment of the state of Colorado.

Explorer Zebulon Pike heard a report of gold in South Park, present-day Park County, Colorado in 1807.

Gold discoveries in Colorado began around Denver, traced the placer gold to its source in the mountains west of Denver, then followed the Colorado Mineral Belt in a southwest direction across the state to its terminus in the San Juan Mountains. The Cripple Creek district, far from the mineral belt, was one of the last gold districts to be discovered.

Denver-area placers

A gold discovery in 1858 in the vicinity of present-day Denver sparked the Pike's Peak Gold Rush. In 1858, prospectors focused on the placers east of the mountains in the sands of Cherry Creek, Clear Creek, and the South Platte River. However, the placer deposits on the plains were small, and when the first rich discoveries were made in early 1859 in the mountains farther west, the miners abandoned the placers around Denver.

Although the economic portions of the gold placers around Denver were quickly exhausted, producers of construction aggregate in the area sometimes recover small amounts of gold from their sand and gravel washing. The plains counties of Adams, Arapahoe, Denver, and Elbert are each credited with having produced small amounts of gold.

Central City-Idaho Springs district

On January 5, 1859, during the Pike's Peak Gold Rush, prospector George A. Jackson discovered placer gold at the present site of Idaho Springs, where Chicago Creek empties into Clear Creek. It was the first substantial gold discovery in Colorado. Jackson, a Missouri native with experience in the California gold fields, was drawn to the area by clouds of steam rising from some nearby hot springs. Jackson kept his find secret for several months, but after he paid for some supplies with gold dust, others rushed to Jackson's diggings. The settlement was first called Spanish Bar, later renamed Idaho Springs, after the hot springs.

On 1859-05-06, John H. Gregory found a gold-bearing vein (the Gregory Lode) in Gregory Gulch between Black Hawk and Central City. Within two months many other veins were discovered, including the Bates, Gunnell, Kansas, and Burroughs. Other early mining towns in the district included Nevadaville and Russell Gulch.

Hardrock mining boomed for a few years, but then declined in the mid-1860s as the miners exhausted the shallow parts of the veins that contained free gold, and found that their amalgamation mills could not recover gold from the deeper sulfide ores.

Nathaniel P. Hill built Colorado's first successful ore smelter in Blackhawk in 1868. Hill's smelter could recover gold from the sulfide ores, an achievement that saved hardrock mining in the district. Other smelters were built nearby. Through 1959, the district produced about 6.3 million troy ounces (196 tonnes), mostly from sulfide veins in gneiss and granodiorite.

The early gold discoveries were at the northeast end of the Colorado Mineral Belt, a large alignment of mineral deposits that stretches northeast-southwest across the mountainous part of Colorado. From Idaho Springs, prospectors followed the Colorado Mineral Belt west along Clear Creek, then over the mountain passes to South Park and to the headwaters of the Blue River.

Breckenridge district

Placer gold was discovered in the Breckenridge, or Blue River district, in 1859. Lode deposits were developed in the 1880s, as prospectors followed the gold to its source veins in the hills. Gold in some upper gravel benches north of the Blue River was recovered by hydraulic mining. Gold production decreased in the late 1800s, but revived in 1908 by gold dredging operations along the Blue River and Swan River. The Breckenridge mining district is credited with production of about one million troy ounces (about 31 tonnes) of gold.

The gold mines around Breckenridge are all shut down, although some are open to tourist visits. The characteristic gravel ridges left by the gold dredges can still be seen along the Blue River and Snake River, and the remains of a dredge are still afloat in a pond off the Swan River.

South Park districts

Prospectors discovered rich placer deposits on the west side of South Park in 1859. The deposits were in valleys on the east side of the Mosquito Range. The principal districts were the Alma-Fairplay district on the headwaters of the South Platte River, and the Tarryall district along Tarryall Creek northwest of Como, Colorado. Important lode gold deposits were later discovered above Alma. A floating dredge worked the floor of the South Park valley east of Fairplay from 1941 to 1952, leaving the distinctive gravel ridges that can still be seen. Production from the Tarryall district was 67 thousand ounces, almost all from placers. The Alma-Fairplay district produced 1.55 million ounces, more than two-thirds of which came from lode deposits.

Leadville district

The history of the Leadville district began with the discovery of placer gold in 1860 at Oro City. The placers were exhausted within four years, but lode gold was discovered in 1868. The gold discoveries led to the discovery of the silver deposits in 1877, and the founding of the city of Leadville. The Leadville district produced 3.2 million ounces (101 tonnes) of gold, mostly as a byproduct of silver mining. (See main article: Leadville mining district)

Summitville district

Prospectors found placer gold in 1870 in the Wrightman Fork of the Alamosa River. Gold veins were discovered in 1871, and large-scale production started in 1875 after the construction of a mill. Operations were continuous until 1906, then sporadic after that. Gold production up to 1990 was 520 thousand ounces.

In 1985, Summitville Consolidated Mining Company, a subsidiary of Galactic Resources of Vancouver, British Columbia started open pit heap-leach mining at the Summitville mine. Mining ceased in 1992, and remediation started. However, Galactic Resources declared bankruptcy in December 1992, and the US Environmental Protection Agency stepped in to prevent releases of pollution from the property. The EPA declared it a federal Superfund site in May 1993. The total cost of environmental cleanup at the site has been estimated to be between $100 and $120 million.

In 1998, the general manager and the environmental manager of the mine pleaded guilty to federal pollution charges, and were each sentenced to six months probation and $20,000 fines.

Sneffels-Red Mountain-Telluride district

The Sneffels-Red Mountain-Telluride district, in San Miguel and Ouray counties at the southwest end of the Colorado Mineral Belt, was discovered in 1875. The district is within and adjacent to a Tertiary volcanic caldera. Deposits are chimneys and veins in Tertiary volcanics and intrusives, and in older sedimentary rocks. Production through 1959 was 6.8 million ounces of gold, as well as considerable silver, lead, and copper.

Cripple Creek district

Although known as the "Pike's Peak Gold Rush" because Pike's Peak was a landmark visible 100 miles out on the plains, the early gold and silver discoveries in Colorado were all far away from Pike's Peak. Located a few miles southwest of Pike's Peak, the Cripple Creek district, the most productive gold-mining district in Colorado, was not discovered until 1891. The towns of Cripple Creek and Victor were established to serve the mines and miners of the district. Among its principal mines was Stratton's Independence mine, at Victor, Colorado. Gold production up to 1990 was 21 million ounces (worth about US$17 billion at 2008 prices), making it the largest gold-producing district in Colorado, and the third-largest in the United States (after Carlin, Nevada and Lead, South Dakota).

The Cripple Creek mining district covers a Miocene volcanic caldera filled with quartz latite porphyry. The ore bodies are veins and replacement zones within the quartz latite. The ore minerals are gold and silver tellurides, with accessory fluorite.

The Cripple Creek & Victor Gold Mining Company formed in 1976 as a joint venture to restart mining in the district. From 1976 to 1989, the company produced 150,000 ounces of gold by reprocessing tailings and mining two small surface deposits. The Cripple Creek & Victor Gold Mining Company began the first large-scale open pit mining in the district in 1994. The Cresson mine open pits are located a few miles north of Victor. Mining continues today under the ownership of AngloGold Ashanti, producing about 330,000 troy ounces (10.3 tonnes) of gold annually, valued at about US$270,000,000 (2008 prices).

Gold mining today

Three Colorado mines continue to produce gold. The Cripple Creek & Victor mine at Victor, an open-pit heap leach operation owned by AngloGold Ashanti, is the leading producer, with 8.8 tonnes (283,000 troy ounces) of gold in 2006. Other active gold mines in the state are underground Golden Wonder mine near Lake City, and the Cash and Rex mines in the Gold Hill mining district in Boulder County, Colorado.