| Basis for focus area |
The Denver Basin focus area includes a series of sandstone roll-front deposits in the Cretaceous Fox Hills and Laramie Formations (Chenoweth, 1980). Deposits in the Denver Basin do not crop out; they were discovered through shallow drilling accompanied by radiometric surveying, radon surveys and water sampling. There has been no production from this area with the exception of test mining at the Grover deposit. There has been at least one NI 43-101 report on the Centennial Project (Voss, 2010). See Reade (1976) for information about exploration for U in the Denver Basin. Exploration was also conducted south of this area within the Denver Basin. |
| Identified resources |
Identified resources for uranium. |
| Production |
Test mining (Kirkham and others, 1980) at the Grover deposit, otherwise no production. |
| Status |
Past exploration, and potentially current exploration. |
| Estimated resources |
The Centennial deposit contains an in-place Inferred NI 43-101 compliant resource of 7.6 million lbs of U3O8 (average grade 0.114% U3O8, 0.5 grade-thickness product cut-off) (Voss, 2010). Also, Reade (1976, page 30, figure 6) reports that a portion of the Grover deposit has 550,878 lbs of Measured reserves, 119,709 lbs of Indicated, and 215,454 lbs of Inferred (886,041 lbs total U3O8). Additional reserves found in the saddle area of the front would increase this reserve total to 1,007,000 lbs eU3O8 with a 0.05% cut-off (the average grade of the deposit is estimated to be 0.14% eU3O8) (Reade, 1976). The Pawnee deposit is estimated to contain 1 million lbs of eU3O8 (average grade of 0.07%) (Kirkham and others, 1980). Reserve estimates at the Keota deposit suggest 5,000,000 to 10,000,000 lbs of U3O8 (Kirkham and others, 1980). |
| Geologic maps |
Horton and others (2017), scale 1:500,000; Braddock and Cole (1978), scale 1:250,000. |
| Geophysical data |
Inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
Cretaceous Fox Hills Sandstone and Laramie Formations. The Grover deposit reportedly occurs in a medium- to fine-grained carbonaceous, feldspathic fluvial channel sandstone of the Laramie Formation (Reade, 1976). The Centennial Project is hosted in the Fox Hills Sandstone. |
| Deposits |
Centennial, Grover, Keota mine (MRDS dep_id: 10087755), Sand Creek, Pawnee. |
| Evidence from mineral occurrences |
MRDS; International Atomic Energy Agency (2020b); U.S. Environmental Protection Agency (2006). |
| Geochemical evidence |
No data. |
| Geophysical evidence |
No data. |
| Evidence from other sources |
Reade (1976) describes a U exploration program completed in many parts of the Denver Basin between 1969 and 1972, mostly centered in the northern portion of the Denver Basin north of Greeley, Colorado. Results are generally unknown. |
| Comments |
Several boxes of U exploration drill hole logs and other information associated with the Denver Basin were donated to the Colorado Geological Survey a number of years ago. However, the logs and information have not been compiled. |
| Cover thickness and description |
The top of the Centennial deposit is between 85 and 250 below the surface (Voss, 2010). |
| Authors |
Susan Hall, Michael K. O'Keeffe. |
| New data needs |
A 1:100,000 scale geologic map (Eaton sheet), compilation of publicly available drill logs from uranium exploration (see Colorado Geological Survey). |
| Geologic mapping and modeling needs |
Eaton sheet geologic map (1:100,000 scale), subsurface modeling of available exploration logs if available (see Colorado Geological Survey). |
| Geophysical survey and modeling needs |
High resolution aeroradiometric and electromagnetic data may be very helpful. |
| Digital elevation data needs |
Lidar is adequate. |
