Mining+Maps



** Mining District Descriptions **
 * Alma ** – This large district in the Mosquito Range northwest of Fairplay produced gold, silver and base metals from the Laramide age veins and replacement deposits (metal sulfides replace Paleozoic dolomite). The London Mine was producing gold as recently as the early 1990’s. The Sweet Home Mine, formerly a silver mine, currently produces fine crystals of the state mineral rhodochrosite.
 * Aspen ** – Glitzy Aspen used to be a gritty mining town of the old west. It was one of Colorado’s largest silver-producing districts, and famous for the extreme rich ‘bonanza’ pockets of nearly pure silver it yielded occasionally. Lead and a little gold were also produced in some mines. Most of the ore occurs as bedding-parallel veins related to folding and faulting of the sedimentary host rocks. Laramide-age igneous intrusions are present and related to the ore deposition.
 * Boulder County Tungsten District ** – This district, located just south and west of Gold Hill was one of the largest tungsten-producing area of the United States. Ferberite, a tungsten-bearing mineral, was the principal ore mineral. Ferberite was mined from quartz veins associated with elongated, fault-controlled ‘breccia reefs’.
 * Breckenridge ** – Discovered in 1859, Breckenridge was one of Colorado’s most prolific gold producing areas. Most of the gold has come from the large placer deposits in deep gravels of the Blue River and other gulches. Narrow but rich quartz-sulfide veins also contributed to the gold output. Lead, zinc, and some copper were also mined here
 * Climax Mine ** – Although not currently operating, this mine has been the largest primary molybdenum producer in the world. Molybdenite occurs mainly in veinlets with quartz. The composite Climax stock is the source of the mineralization. It is not mined out.
 * Creede ** – Famous silver mining camp of the old west, discovered in 1883. It is a classic example of volcanic rock-hosted epithermal vein deposit. Silver and lesser gold ore occurs in quartz veins which were formed in open fractures and fissures created by faulting and subsidence of the Creede Caldera. Deposits of this type are the subsurface expression of fossil hot spring systems.
 * Cripple Creek ** – Cripple Creek is by far the largest single gold-producing district in Colorado. Over 22 million ounces has been produced since its discovery by a local rancher in 1891. Gold is found in a quartz and telluride veins and as disseminated deposits in phonolite breccias. The deposits are related to an igneous intrusive complex. In 1999, the Cresson Mine produced 231,000 ounces and was the only large-scale gold mine operating in the state.
 * Gilman ** – Gilman is similar to but smaller than the Leadville district. It produced large amounts of zinc, lead, silver, gold, and copper. It was discovered I 1879. Base metal sulfides including sphalerite, galena, and chalcopyrite replaced limestones and dolomites, probably during Laramide time. The district is just a few miles south of Vail.
 * Gold Hill ** – Discovered in 1859, this is Boulder County’s most productive gold producing district. It also produced silver, copper, lead, and zinc. Ore occurs in steeply dipping quartz veins with PreCambrian granodiorite. The mineralization, like most other districts of the Colorado Mineral Belt formed during the Laramide orogeny.
 * Henderson Mine ** – The Henderson Mine is the world’s largest currently operating primary producer of steel-strengthening metal, molybdenum. In 1998, the mine produced 30.1 million pounds of ‘moly’ from 6.9 tons of ore. The sulfide mineral, molybdenite occurs in veins and fractures within the Red Mountain Stock, a quartz monzonite intrusive. Molybdenum production began in the area at the smaller but geologically-related Urad deposit during World War 1.
 * Lake City ** – Silver-lead ore was discovered in the district in 1871. Epithermal quartz-sulfide veins similar to those at Silverton host the ore. The Tertiary-age volcanic rocks which host the mineralized veins are of the same origin as those at Silverton. In addition to silver and lead, gold, zinc, and copper were produced.
 * Leadville ** – The Leadville area was the most prolific metal mining district in Colorado. It produced vast quantities of lead, zinc and silver, as well as gold and some copper. Iron and manganese were also mined and shipped to the steel furnaces in Pueblo. The last significant mine to operate in the district, the Black Cloud, ceased mining in 1999. Most of the ore was mined from sulfide replacement bodies in dolomite. Gold was first mined from placer deposits in California Gulch.
 * San Luis Mine ** – Battle Mountain Gold Company mined this gold deposit in the early and mid-1900s. It is currently being reclaimed and environmentally monitored. The low-grade deposit occurs in faulted and fractured PreCambrian metamorphic rocks and is probably related to the extensional tectonics of the Rio Grande Rift zone.
 * Summitville ** – Gold, silver and copper-producing district. Over 500,000 ounces of gold were produced since its discovery in 1870. Ore minerals occur in veins, fracture zones, and breccias in a quartz porphyry intrusive related to the Summitville and Platoro calderas. The calderas represent resurgent volcanic centers and are thought to be 23 million years old.
 * Sunday Group Mines ** – Uranium and vanadium production began most recently in 1997 from deposits in the Salt Wash Member of the Morrison Formation. This region of the Colorado Plateau has been an exceptionally prolific producer of uranium and vanadium since 1898 when 10 tons of carnotite ore was mine and shipped to Marie and Pierre Curie for their Nobel Prize-winning research on radioactive substances.
 * VOCABULARY ** **–**
 * Base Metal – ** common metal which is easily removed from the surrounding rock.
 * Caldera ** – A large basin-shaped depression caused by the collapse of a volcano.
 * Epithermal ** – A hydrothermal mineral deposit formed within 1 mile of the surface at temperatures between 50 and 200 degrees Celsius.
 * Laramide Orogeny ** (mountain building) – occurred 95 – 23 million years ago. It was a time of deformation, particularly in the eastern Rocky Mountains. Intrusives and ore deposits occurring at this time in the mountain states is called the ‘Laramide’.
 * Ore ** – A naturally occurring material from which minerals can be removed to make a reasonable profit.
 * PreCambrian ** – a geologic era occurring more than 530 million years ago. Little if any life forms are preserved in these ancient rocks.
 * Stock ** – An igneous intrusion that is less than 40 square miles in size.
 * Vein ** – A fault or fracture where mineral deposits are found.