Colorado Mineral Belt

The Colorado Mineral Belt (CMB) is an area with abundant ore deposits. The area stretches north-east from the La Plata Mountains in Southwestern Colorado to the Front Range near Boulder, Colorado. Most of the historic metal mining camps of Colorado lie in this area, the most important exception being the Cripple Creek District.

The CMB is most famous for gold; over 25 million troy ounces (778 t) of the metal have been extracted from the area. The gold deposits were first discovered in 1858. Further finds in 1859 prompted the Pikes Peak Gold Rush lasting until 1867; over 1.25 million troy ounces (39 t) of gold were produced in those eight years. By 1874, most significant deposits in the CMB had been found. The peak year of gold production in Colorado was 1900 and there are no major gold mines currently in operation in the CMB, leaving a number of sites as ghost towns.

Molybdenum deposits in the CMB are of continuing interest. In April, 2006, Phelps Dodge Corporation announced tentative plans to reopen the Climax molybdenum mine near Leadville, where operations closed in 1995. The Henderson mine in the same region has been an active producer even when the mine at Climax was closed. In 2006, a deep tunnel at the Henderson mine was under consideration as a deep-earth lab for particle physics.

Major historic sites of mining in the Belt included Central City in the Front Range, west of Denver (4.2 million troy ounces (131 t) of gold 1859-1960). In the San Juan Mountains the major finds were at Ouray, Silverton, Mount Sneffels, and Telluride where over 10 million troy ounces (311 t) of gold was mined. Extracting gold from river gravel placers was also popular and a number of sites such as Breckenridge and Fairplay yielded considerable quantities of gold. Gold was found in Leadville, on the Arkansas River, in the 1860s; Leadville was the site of the single richest placer gold strike in the entire Pikes Peak gold rush. But the richer lead, silver, and zinc lodes found from 1874 just as the era of new gold discoveries was beginning to play out, prompted more activity. The Leadville Mining District was the most productive silver-mining district in the state.

The ore deposits in the Colorado Mineral Belt lie within a zone that has been geologically active at intervals beginning from near the time of crustal accretion in central Colorado at least 1.6 billion years ago until the present. Parts of the CMB follow shear zones of Precambrian age. Those shear zones were active at several times during the Precambrian and also during the Paleozoic and Mesozoic. Igneous rocks intruded about 60 to 70 million years ago during the Laramide orogeny are associated with the belt and once were thought to be responsible for most of the ore deposits. Now many of the important ore deposits are thought to be genetically related to younger magmatism, some at least as young as about 25 million years. Today the zone is marked by relatively high heat flow and low seismic velocities in the crust.