| Basis for focus area |
Northgate district was the second largest fluorite producer in Colorado. Cenozoic age mineralization occurs in veins in faults or breccia zones associated with Precambrian quartz monzonite stock and gneiss. Bulk of the fluorspar veins occur in Precambrian quartz monzonite and within arkose of the White River Formation indicating a middle(?) Tertiary source. Fluorspar is reported to occur in two parallel northwesterly trending faults zones about 2 miles apart. Polygon includes general area around mine locations, MRDS occurrences, and west/northwest trending faults from the regional 1:250,000 geological map. |
| Identified resources |
Identified fluorite resources; historical production of fluorite. |
| Production |
Area was mined between about 1922 and 1973 (Schwochow and Hornbaker, 1985). Production includes 15,000 tons fluorite between 1922 and 1927 and about 115,700 tons between 1941 and 1945. Larger scale production started in 1951. Between 1952 and 1973, the value of fluorite production from the Northgate district was about $25 million and accounted for about 47.8% of the Colorado fluorite production during this timeframe (Shawe, 1976; Schwochow and Hornbaker, 1985). |
| Status |
Past mining of fluorspar, ending around 1973. |
| Estimated resources |
Average grades of between 40 and 50% CaF2 with a range between 10 and 90% CaF2 in some veins (Shawe, 1976). Schwochow and Hornbaker (1985, page 62) indicate, ".......high-grade fluorspar stringers containing more than 80% CaF2. At one mine, a 3- to 6-ft-wide vein averaged 60% CaF2, and an 8- to 11-ft width averaged 40 to 50% CaF2. An approximate 5-ft width across the Fluorine-Camp Creek vein contained 70% to 80% CaF2, and a 16-foot width contained more than 30%." Brady (1975) indicates a production and reserves of greater than 250,000 short tons at Northgate district. |
| Geologic maps |
Steven (1960), scale 1:24,000; Madole (1991), scale 1:100,000. |
| Geophysical data |
Inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
North and northwest-trending Laramide and younger (late Tertiary) fault zones containing veins and breccias. Steven (1960) indicates association with Laramide and/or middle Tertiary intrusives due to mineralization in the White River Formation. |
| Deposits |
Camp Creek Claims (MRDS dep_id: 10142618), Fluorine Vein Properties (MRDS dep_id: 10215435), Northgate Fluorspar District. |
| Evidence from mineral occurrences |
MRDS. |
| Geochemical evidence |
Historical mining and production of fluorspar. Some studies indicate anomalous detections of Mo associated with deposits. Steven (1960) report Mn-oxides coat fractures associated with fluorite mineralization. |
| Geophysical evidence |
No data. |
| Evidence from other sources |
This is a historical fluorspar mining district. |
| Comments |
Vermiculate is associated with Precambrian ultramafic masses (Steven, 1960), and is probably a separate mineralizing event than the event that resulted in the Cenozoic fluorite mineralization. |
| Cover thickness and description |
Faults and breccia zones are thought to extend to depths over 1,000 feet below the surface. |
| Authors |
Michael K. O'Keeffe, Joshua M. Rosera. |
| New data needs |
1:24,000 scale geologic mapping at two quadrangles to fill in existing 1:24,000 scale geologic map of the Northgate District. Geophysical survey to delineate breccia zones or connection with potential Tertiary intrusions at depth or nearby. Lidar data would also be needed. |
| Geologic mapping and modeling needs |
1:24,000 scale geologic mapping at two quadrangles to fill in existing 1:24,000 scale geologic map of the Northgate District. |
| Geophysical survey and modeling needs |
Rank 1 aeromagnetics and aeroradiometrics would help put things into context. |
| Digital elevation data needs |
Lidar in progress. |
