Title: “On-the-Rocks” Field Trip The Cripple Creek Gold Mining District, Teller County, Colorado
Trip Leader: Marc Melker, Mine Geologist, Cresson Gold Mine
Date: Saturday, July 21, 2001
Publication: The Outcrop, July 2001, p. 15-16
Discovered in 1891 by a cowpoke named Bob Womack, described as a “part-time cowboy, full-time drinker”, the Cripple Creek mining district has produced in excess of 21 million ounces of gold, making it the third largest-producing gold district in the United States. The district’s epithermal precious metal deposits are hosted within and adjacent to an Oligocene (~32 Ma) diatreme-intrusive complex. The complex consists of a large mass of heterolithic breccia composed of Tertiary igneous rock fragments as well as Precambrian igneous and metamorphic rock fragments. The diatreme breccia is intruded by a series of Tertiary alkaline rocks including phonolite, plagioclase phonolite, tephriphonolite, phonotephrite, and lamprophyre.
Gold ore in the historic mines occurred predominantly as gold-silver tellurides (calaverite and sylvanite) in narrow, high-grade sheeted vein systems. Most of the gold was recovered between 1891 and 1959. Most of the historic mines of the district were closed by 1962, but exploration in the last ten years has delineated several large zones of low-grade, disseminated gold mineralization. The largest of these bulk-minable deposits is the Cresson deposit, which is currently being mined by open pit methods. The Cresson mine is operated by the Cripple Creek and Victor Mining Company, a joint venture between Anglogold and Golden Cycle.
Gold mineralization in the district and Cresson deposit is controlled by both structural and lithologic factors. Both low-grade disseminated gold mineralization and high-grade gold-telluride veins are hosted by individual fractures, faults, and sheeted fracture zones, as well as structural intersections and shear-zone-induced en echelon vein zones. These structurally favorable zones provided conduits for ascending gold-bearing fluids and localized gold mineralization. Lithology-related hosts for gold mineralization include dike margins, igneous contacts, and breccia bodies. These lithologic settings are interpreted as favorable hosts to gold mineralization due to contrasts in porosity, permeability, and rock competency, in addition to the effect of fluid damming along dike margins and igneous contacts. Breccias provided open space for the migration of gold-bearing fluids and for gold deposition.
The field trip will depart at 8:00 a.m. from the RTD Park-n-Ride located at Yosemite and East Caley Ave. Take 1-25 to Arapahoe Road. Go west one block to Yosemite and north to Caley Avenue. Please be at the Park-n-Ride by 7:45, as we will depart at 8:00. Carpools are recommended for the drive to Cripple Creek. The route from Denver will be via 1-25 south to Colorado Springs, then west on U.S. 24 to Divide, and then south on Colorado Highway 67 to Cripple Creek. The field trip will begin at the Cripple Creek and Victor Mining Company offices, southeast of Cripple Creek at the former Carlton Mill, and then proceed with a tour of the Cresson open pit mine and the ADR plant. The field trip is estimated to finish at the RTD Park-n-Ride at approximately 5:30 p.m. For reservations call Denis Foley.
Participants are responsible for their own food and drink, as well as dressing appropriately (layered clothing) for weather and field conditions, including hats, gloves, and sunscreen. Bring hiking boots and rock hammers (steel-toed boots if you have them). Also, the mine is short on hard hats. Let Denis know if you can bring your own when you register. We will need to let the mine folks know how many we can bring.