Occurrence, Inactive

Commodities and mineralogy

Main commodities Th; U
Other commodities Sn; Zr
Ore minerals thorite; uranothorite
Gangue minerals feldspar; hematite; quartz

Geographic location

Quadrangle map, 1:250,000-scale MG
Quadrangle map, 1:63,360-scale A-3
Latitude 62.046
Longitude -154.068
Nearby scientific data Find additional scientific data near this location
Location and accuracy This unnamed occurrence is located at the base of a cliff face on the east side of an unnamed, glacially carved, second order tributary of the Middle Fork of the Kuskokwim River. The occurrence is about three kilometers upstream from the mouth of the unnamed tributary and immediately downslope from an active valley glacier terminous at an elevation of 3,950 feet (1,204 m) in the NE1/4 sec. 32, T. 23 N., R. 26 W., of the Seward Meridian. The reporter briefly visited the site in 1982.

Geologic setting

Geologic description

The occurrence consists mainly of several feldspar-hematite-quartz veins infilling joints and fractures in the Windy Fork composite pluton about one mile from the contact zone with sandstone and limestone of the Lower to mid-Paleozoic Dillinger subterrane (Reed and Miller, 1980; Gilbert and others, 1988; Bundtzen, Harris, and Gilbert, 1997). The individual joint fillings are 3 to 6 centimeters thick and continue for 2 to 3 meters along strike. Much of the mineralization trends N65W. Feldspars are typically altered to a clay matrix; quartz is the 'smoky' variety due to radioactive(?) decay (Gunter and others, 1993). Green-to-purple fluorite is common in talus but was not recognized in place.
Composite grab samples of quartz-feldspar-hematite joint-filled material reported by Reed and Miller (1980) contain up to 490 ppm uranium and 376 ppm thorium.
Geologic map unit (-154.070230986811, 62.0453663327056)
Mineral deposit model Thorium-Rare Earth veins (Cox and Singer, 1986; model 11b).
Mineral deposit model number 11b
Age of mineralization Late Tertiary, based on age (25Ma) of Windy Fork composite pluton (Solie and others, 1991).
Alteration of deposit Feldspars are altered to clay minerals; quartz is a 'smokey' variety, possibly due to radioactive decay.

Production and reserves

Workings or exploration
The occurrence was found by the late Bruce Reed while conducting mineral resource investigations and regional geologic mapping for the U.S. Geological Survey in the western Alaska Range (Reed and Miller, 1980).
Composite grab samples of quartz-feldspar-hematite joint-filled material as reported by Reed and Miller (1980) contain up to 490 ppm uranium and 376 ppm thorium.
Indication of production None
Reserve estimates None estimated.

Additional comments

See Eudialyte Prospect (MG036).