| Basis for focus area |
Focus area is based on the outline of Proterozoic and Cambrian rock footprint in the statewide geological map. Focus area delineated based on Th and REE noted in veins, syenite dikes, fracture zones, and carbonatite dikes associated with Th-REE Cambrian alkaline complexes. |
| Identified resources |
Identified resources of REE and thorium. Historical production of barite, niobium (columbite), uranium, and vermiculite. |
| Production |
The Gem Park district (Goldenite and Silverite mines) produced a large tonnage of vermiculite along with unknown quantities of columbite. Numerous small pits produced barium. Floyd Watters mine produced a small quantity of U. |
| Status |
Past mining. Vermiculite mine near Gem Park may be in operation. No apparent exploration activity is underway in this district as of 2010. Many of the prospective vein and fracture-zone deposits occur on private land. There is currently exploration in the northeast portion of this property associated with a Broken-Hill type deposit in the Precambrian rocks. |
| Estimated resources |
Armbrustmacher (1988) estimated that the vein and fracture zone deposits of the Wet Mountains area contain the following resources: ThO2 reserves of 8,200 metric tons (64,200 tons) and probable potential resources of 145,600 metric tons (160,500 tons); ΣLREE reserves of 26,600 metric tons (29,300 tons) and probable potential resources of 66,500 metric tons (73,270 tons); total ΣHREE reserves of 17,700 metric tons (19,540 tons) and probable potential resources of 44,300 metric tons (48,850 tons). This estimate was based on average concentrations of 0.46% ThO2, 0.21% ΣLREEO, and 0.14% ΣHREEO. |
| Geologic maps |
Scott and others (1978), scale 1:250,000. |
| Geophysical data |
Inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
Thorium-REE deposits are exposed throughout an area of about 60 km (37 mi) north to south by 24 km (15 mi) west to east. Thorium and REE are found in veins, syenite dikes, fracture zones, and carbonatite dikes (Armbrustmacher, 1988) associated with ΣHREE Cambrian alkaline complexes (Olson and others, 1977) that intruded the surrounding Precambrian terrane. These ΣHREE alkaline complexes are the McClure Mountain Complex (Shawe and Parker, 1967; Armbrustmacher, 1984), the Gem Park Complex (Parker and Sharp, 1970), and the complex at Democrat Creek (Armbrustmacher, 1984). The presence of alkalic rocks, carbonatites, and layered mafic-ultramafic rocks at the surface and in drill holes indicates that additional intrusions could exist at depth at the three complexes. Drilling in the Gem Park complex has verified carbonatite bodies to a depth of 1,438 feet with concentrations exceeding 10,000 ppm REE and over 0.2% Nb (Papson, 1981). |
| Deposits |
Gem Park district (MRDS dep_id: 10311020), Goldenite, Silverite (MRDS dep_id: 10016566), Floyd Watters Ranch (MRDS dep_id: 10012579), Vermiculite mine, McClure Mountain. |
| Evidence from mineral occurrences |
MRDS. |
| Geochemical evidence |
Mineralized veins and fracture zones, which are distal to the Th-REE alkaline intrusive complexes, have the highest economic potential for Th and REE. Veins/dikes in the area are generally enriched in HREE compared to other deposits (for example, Mountain Pass) but vary from area to area. The arithmetic mean of 10 samples collected from fracture zones in one area (the old Haputa Ranch area) indicated concentrations of LREE at 1,478 ppm and 8,581 ppm HREE. Drilling in the Gem Park complex detected concentrations of REE of > 5.23% and Nb concentrations over 0.2% at depth. Numerous small mines produced barite in the area. Barite occurs in veins carrying quartz-barite-iron carbonate +/- Th-minerals (Christman and others, 1959). |
| Geophysical evidence |
Strong gradients in both regional gravity and magnetic data may indicate crustal boundaries that were involved in controlling mineralizing fluids that trend northeast north of Gem Park and McClure Mountain. |
| Evidence from other sources |
No data. |
| Comments |
Wet Mountain area footprint from USMIN and modified by the Colorado Geological Survey (CGS). CGS is currently compiling geochemistry results from this area in GIS. Additionally, CGS is digitizing existing geologic maps of this area. Note, this area overlaps other focus areas, including pegmatite districts and a potential deep porphyry system. Some other commodities (for example, fluorite) occur in the area, but may be associated with different mineral systems. As reported by the CGS, historical exploration at the Gem Park Complex (the furthest west intrusion) observed carbonatites, gabbro, REE-bearing minerals, fenitized rock, and magnetite bodies at depth. At least one of these drill holes extended to 1,438 feet below the ground surface. Logs of this hole indicate carbonatite veins with REE-bearing minerals down to the total depth (1,438 feet below ground surface [438 meters]); see Papson (1981). |
| Cover thickness and description |
The Cambrian (could also include Ordovician and younger) alkaline complexes outcrop at the surface and intrude Proterozoic metamorphic rocks and granite. Some areas have overlying Paleogene volcanic rocks as well as Quaternary cover. |
| Authors |
Ryan D. Taylor, Albert H. Hofstra, Joshua M. Rosera, V.J.S. (Tien) Grauch, Michael K. O'Keeffe, Joshua M. Rosera. |
| New data needs |
1:24,000 geologic mapping, compilation geologic maps, geochemistry (historical data does not include full suites of critical minerals, REE, etc.), geophysical survey. |
| Geologic mapping and modeling needs |
The Colorado Geological Survey acquired funding to digitize several existing 1:62,500 scale geologic maps through the USGS Data Preservation program. New 1:24,000 scale geologic mapping is required to fill in the patchwork of mostly 1:62,500/1:250,000 -scale geologic mapping in the area. This would include mapping the Hardscrabble quadrangle and include completion of the partial 1:24,000 scale geologic mapping (see Sharp, 1978) of the Westcliffe, Aldrich Gulch, and Rosita quadrangles. Creation of a compilation geologic map at 1:50,000 scale using the existing 1:24,000/1:62,500 scale geologic maps, one new 1:24,000-geologic map of the Hardscrabble quadrangle, and three partial 1:24,000-geologic maps. Field work is required to check the compiled units, fix any edge-matching issues, and to verify the geology for three 1:10,000 scale insets for the Gem Park, McClure Mountain, and Democrat Creek complexes (some of these are already partially completed at 1:10,000 scale associated with USGS reports). |
| Geophysical survey and modeling needs |
Rank 1 aeromagnetic and radiometric data will provide insight into larger carbonatite, alkali, and mafic/ultramafic intrusions at depth. Acquisition of such a survey is underway for 2020-2021 (Wet Mountains survey). |
| Digital elevation data needs |
Lidar available. |
