| Basis for focus area |
USMIN W site CO00048, Ftr_ID Mr00030 is the polygon for the San Juan area W. The Colorado Geological Survey updated this focus area, based on Cement Creek (the outline from the USMIN W publication) and added the Eureka district to the east as well as some other areas to the south. These areas generally had a higher concentration of past W producers taken from MRDS. There are other producers/occurrences nearby to the west and the north not included in this polygon. |
| Identified resources |
Indicated resources for tungsten. Historical production of antimony, fluorite, manganese, and tungsten. |
| Production |
Minor production. |
| Status |
Past mining. |
| Estimated resources |
1956 Inferred reserves 700 metric tons W. |
| Geologic maps |
Horton and others (2017), scale 1:500,000; Luedke and Burbank (1987, 2000), scale 1:24,000; Burbank and Luedke (1964, 1966), scale 1:24,000. |
| Geophysical data |
Inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
A down-fault block, more or less circular and about 8 miles in diameter, is situated in the Silverton area. This fault block has been called the Silverton caldera. Stocks of monzonite and diorite have been intruded into a ring-fault zone. Known W deposits are adjacent to or within the caldera or occur in or near igneous stocks or vein systems (Belser, 1956). |
| Deposits |
Over 40 mines, prospect, and properties have been described (see Belser, 1956). The area provided by the USMIN program contains all or a portion of the following mining districts: Animas, Eureka, Cement Creek, Animas Forks, Mineral Point, Poughkeepsie, Upper Uncompahgre, Red Mountain, Camp Bird, Imogene Basin, Sneffels, Upper San Miguel, Telluride, Iron Springs, and Ophir (USMIN Site_ID: CO00048). |
| Evidence from mineral occurrences |
MRDS; USMIN (W); Belser (1956). |
| Geochemical evidence |
Manganese is associated with polymetallic fissure veins (for example, King Group mine) and possibly by supergene enrichment (for example, see MRDS Fairview record; dep_id: 10018491). There is a manganese-fluorite association. Fluorite mines are also associated with polymetallic Ag-Au-Pb-Zn mineralization. |
| Geophysical evidence |
Subdued magnetic anomalies indicate extensive alteration in Silverton Caldera. |
| Evidence from other sources |
No data. |
| Comments |
The known W deposits are adjacent to or within the caldera or occur in or near igneous stocks or strong vein systems. The ore mineral hübnerite is often associated with fluorite. A small amount of scheelite occurs in some veins. |
| Cover thickness and description |
Deposits associated with volcanic rocks. Potentially variably buried. |
| Authors |
Jane M. Hammarstrom, Joshua M. Rosera, Michael K. O'Keeffe. |
| New data needs |
Report containing data/GIS compilation of historical data and description of deposits. |
| Geologic mapping and modeling needs |
No mapping needed. |
| Geophysical survey and modeling needs |
EM being flown, rank 3 aeromagnetic. |
| Digital elevation data needs |
Lidar in progress or complete. |
