| Basis for focus area |
A massive late-Cambrian carbonatite stock forms the core of the Iron Hill carbonatite complex. The carbonatite stock is enriched in REE, Nb, and Th; the adjacent pyroxenite unit is enriched in these elements also and in substantial amounts of Ti. Numerous historical Mn producers associated with the late-Cambrian intrusion. Lesser amounts of Be, fluorite and V. |
| Identified resources |
Identified resources for niobium, thorium, titanium, REE, uranium, and vanadium; historical production of fluorite, manganese, and vermiculite. |
| Production |
Alexite mine had small production of rock with 21 to 38% Mn. |
| Status |
Past mining. Since 1990, Teck Resources Ltd. has owned many of the patented claims within this intrusive complex. Its interests have focused on the substantial titanium resource within the pyroxenite unit of the complex. In 2010, it appeared that Teck Resources was not actively conducting work at this property. |
| Estimated resources |
Resources estimates for the Iron Hill Carbonatite deposit indicate that 3.4 billion tons of carbonatite would contain about 140,000 tons ThO2 (41 ppm), 1,900,000 tons Nb2O5 (570 ppm); 13,500,000 tons combined REO (3,970 ppm), and 43,000 tons U3O8 (12.7 ppm) (Armbrustmacher, 1980). In addition, 419 million tons of reserve of rock averaging about 12% TiO2; 50,000 tons V in a million tons of magnetite-ilmenite-perovskite rock (Olson and Hedlund, 1981). Also see Van Gosen (2009) and Staatz, Armbrustmacher and others (1979). |
| Geologic maps |
Hedlund and Olson (1973, 1975), scale 1:24,000; Hedlund (1974), scale 1:24,000; Olson (1974), scale 1:24,000; Olson and others (1975), scale 1:24,000; Olson and Hedlund (1973), scale 1:24,000. |
| Geophysical data |
Inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
The Iron Hill carbonatite complex is exposed for 31 km2 (12 mi2 ) near the small town of Powderhorn, about 35 km (22 mi) south-southwest of Gunnison, Colorado. The intrusion is alkaline with a prominent carbonatite stock at its core. Other favorable rocks include the pyroxenite and other alkaline rocks. An occurrence of manganese within the basal vitrophyre of the Oligocene Sapinero Mesa tuff is mentioned in an "Unnamed Manganese Prospect" (MRDS dep id: 10014422). |
| Deposits |
Iron Hill carbonatite deposit (MRDS dep_id: 10142743), White Earth, Cebolla mining district, Alexite manganese mine, Dubois mine. |
| Evidence from mineral occurrences |
MRDS; USMIN. |
| Geochemical evidence |
This Ti-Nb-REE deposit has been documented by several authors, apparently associated with minor Mn mineralization (for example, psilomelane) and locally fluorite and beryllium. |
| Geophysical evidence |
Regional geophysical maps both show expression of the Cimarron fault; regional magnetic maps show anomalies associated with Iron Hill and a string of smaller anomalies located along the Cimarron fault. These geophysical expressions suggest that airborne geophysics will be a good tool for understanding geology and perhaps mineralization related to the fault. |
| Evidence from other sources |
No data. |
| Comments |
Original Powderhorn district footprint from USMIN. Boundary modified to include 1:24,000 scale quadrangle boundaries. Barium, Sr, and Zr inferred from the mineral system/deposit type table (Hofstra and Kreiner, 2020). |
| Cover thickness and description |
Recent erosion has removed most of the volcanic rocks that once covered the Iron Hill complex, exposing much of the bedrock of the intrusive complex. |
| Authors |
Michael K. O’Keefe, Matthew L. Morgan, V.J.S. (Tien) Grauch, Joshua M. Rosera. |
| New data needs |
1:24,000 scale geologic mapping, geochemical sampling, and geophysical survey. |
| Geologic mapping and modeling needs |
New 1:24,000 scale geologic mapping of the Rock Creek Park quadrangle is required to fill gaps in previous geologic mapping. This quadrangle follows the trace of the Cimarron fault to the southeast where alkaline intrusives may exist at depth below younger Paleogene volcanic cover. Lipman (2012) mapped the eastern portion of this quadrangle at a 1:50,000 scale; however, the western half needs to be mapped. |
| Geophysical survey and modeling needs |
Rank 1 aeromagnetic and radiometric data will provide insight into other alkaline/carbonatite intrusions at depth. 200 m line spacing on E-W lines, 100 m nominal terrain clearance; helicopter magnetics and radiometrics. |
| Digital elevation data needs |
Lidar is available for Gunnison County but not for the quadrangle in Saguache County. However, only a portion of one quadrangle needs to be mapped in Saguache County. |
