| Basis for focus area |
Northeast-trend of mining districts cut across Eocene intrusions from Breckenridge to the town of Montezuma (Colorado Mineral Belt). Mineralization approximately follows Precambrian shear zone that extends from the east side of the Breckenridge mining district. Rhyodacite to rhyolite volcanic plugs occur within the shear zone, south of the Montezuma pluton. The plugs contain quartz-sericite-pyrite alteration and are anomalously enriched in base metals. |
| Identified resources |
Historical production of bismuth, copper, gold, lead, silver, and zinc. |
| Production |
Unknown. Difficult to ascertain exact production from lode deposits in specific mining districts (production from placers as well). |
| Status |
Past mining. |
| Estimated resources |
Unknown. |
| Geologic maps |
Lovering (1935) scale 1:62.500; Widmann and others (2003), scale 1:24,000; Keller and others (2017), scale 1:24,000; Barker and Wyant (1976), scale 1:24,000. |
| Geophysical data |
Inadequate: Rank 3 aeroradiometric and Rank 4 aeromagnetic coverage. |
| Favorable rocks and structures |
Volcanic plugs, breccias, and dikes that roughly follow the northeast-trend of Precambrian shear zones in the area. Mineralization and alteration cuts the southeast side of the 38.8 Ma Montezuma pluton (Neuerburg and others, 1974; Rosera and others, 2021). |
| Deposits |
Numerous small operations. Missouri (MRDS dep_id: 10018305, reported bismuth production),Wellington mine (MRDS dep_id: 10108375, one of the larger producers of Zn), Pennsylvania mine (MRDS dep_id: 10108421), Area includes all or portions of the following mining districts: Clear Creek, Park, Summit, Snake River, Peru, Chihuahua and (to the west) Jo Davis, Delaware Flats, Illinois Gulch, French Gulch, Avalanche (Bald Mt.), Lincoln, Middle Swan River, South Swan River, edge of Georgia Pass (these general areas are based on the Colorado Geological Survey historical metal mine online publication). |
| Evidence from mineral occurrences |
MRDS; Colorado Geological Survey historical metal mine database. |
| Geochemical evidence |
Sphalerite reported at numerous former producers. Bismuthinite reported at the Missouri mine. The Webster Pass porphyry has been drilled and surface samples indicate it contains anomalously high abundances of Zn, and Mn (as well as Cu, Pb, and Mo; Millan, 2005). |
| Geophysical evidence |
The central Colorado Mineral Belt is part of a large regional gravity low, interpreted to be upper crustal silicic intrusions. However, silicic magmas intruded the area episodically from the Cretaceous through the Oligocene; thus, the age of an inferred batholith with respect to individual mineral systems remains uncertain. |
| Evidence from other sources |
Unknown. |
| Comments |
Enrichment of Sb, As, Ga, Ge, In, Te, and W are inferred from the mineral system/deposit type table (Hofstra and Kreiner, 2020). More work is required to test if critical minerals are enriched in this focus area. |
| Cover thickness and description |
Variable. |
| Authors |
Joshua M. Rosera. |
| New data needs |
Geochemical characterization of historical ore material, more detailed gravity data could elucidate more details about the hypothesized buried batholith in the area, and 1:24,000 scale geologic mapping. |
| Geologic mapping and modeling needs |
1:24,000 scale mapping at the Montezuma and potentially the south end of the Gray's Peak quadrangles. |
| Geophysical survey and modeling needs |
High resolution Rank 1 aeromagnetics and aeroradiometrics needed, as well as gravity. |
| Digital elevation data needs |
Lidar is available-most is acquired and some is processed. |
