| Basis for focus area |
Polymetallic sulfide veins and stockworks in and around Idaho Springs and Central City, most of which contain some sphalerite (Sims and others, 1963). District is composed of numerous small alkalic dikes and magmatic-hydrothermal veins that are in close spatial association with a northeast-trending shear zone in the northern Colorado Mineral Belt (Sims and others, 1963). Focus area approximately outlines historical mines and associated dikes from the state geological map. |
| Identified resources |
Historical production of copper, gold, lead, silver, uranium, and zinc. |
| Production |
Central City (1904 to 1953): ~9,000 tons Zn, >25 tons Au, >150 tons Ag, >70,000 tons Pb, and ~ 4,300 tons Cu (estimates from reports with partially overlapping time periods: 1859 to 1924, and 1904 to 1953 (Sims and others, 1963; Bryant and others, 1989). Idaho Springs: production "about two-thirds that of Central City district, with silver being more important than gold." (Bryant and others, 1989). |
| Status |
Past mining with no current mining. |
| Estimated resources |
Unknown. |
| Geologic maps |
Braddock (1967), scale 1:24,000; Kellogg and others (2008), scale 1:100,000; Sims and others (1963), scale 1:6,000; Sims (1964), scale 1:24,000; Taylor (1975), scale 1:24,000; Widmann and others (2000), scale 1:24,000. |
| Geophysical data |
Rank 3 aeroradiometric and Rank 4 aeromagnetic coverage. |
| Favorable rocks and structures |
Northeast- to east-trending veins, fissures, mineralized faults. |
| Deposits |
Central City district (500+ mines) and Idaho Springs. |
| Evidence from mineral occurrences |
MRDS. |
| Geochemical evidence |
Pyrite in quartz-pyrite veins contains 10 to 1000 ppm Ni and ~ 1 to 1000 ppm Co. Pyrite in base metal veins is enriched in As (average ~ 6500 ppm) and Sb (avgerage ~ 3300 ppm; Alford and others, 2020). Some additional trace and minor element chemistry of ore reported in Sims and others (1963), who also note Au hosted in telluride minerals. |
| Geophysical evidence |
Unknown. |
| Evidence from other sources |
Unknown. |
| Comments |
Uranium is not listed as a byproduct for this mineral system and deposit type in Hofstra and Kreiner (2020), but small quantities were produced from the district. Possible occurrence of Bi, Ga, Ge, In, and Te are inferred from the Hofstra and Kreiner (2020) mineral system/deposit type table. |
| Cover thickness and description |
Exposed to shallow cover. |
| Authors |
Joshua M. Rosera. |
| New data needs |
Better characterization of byproduct critical commodities in ores and waste rock. Secondary oxides could potentially be hosts for Ge as well, but no data appear to be reported for Ge. |
| Geologic mapping and modeling needs |
Detailed maps of veins and intrusions in the Central City district already exist (for example, Sims and others, 1963). The area has been mapped at 1:24,000 scale. |
| Geophysical survey and modeling needs |
High resolution aeromagnetic and aeroradiometric coverage. |
| Digital elevation data needs |
Lidar is adequate. |
