Unnamed Occurrence (ARDF - MD005), McGrath District, Yukon-Koyukuk Borough, Alaska, USA
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Location: Occurrence is situated on a north-south oriented ridge 2 miles (3.2 km) south of Sischu Creek at an elevation of 1,350 feet (411 m) in Section 9, T. 18 S., R. 29 E., of the Kateel River Meridian. Location is accurate to within 500 feet (152 m).
Geology: Miller and others (1980) report anomalous uranium and thorium levels in slightly porphyritic, fine-grained rhyolite. No ore minerals were identified. Two areas of strongly radioactive rhyolite, each about 4 miles long by 1 to 2 miles wide (6.4 km by 0.8 km), are separated by 2 miles (3.2 km) of ridgeline. Age is inferred to be early Tertiary, based on isotopic ages of Sischu Volcanics (Moll and others, 1981). Miller and others (1980) report values of 16.4 ppm uranium and 73.8 ppm thorium from grab samples. Clautice and others (1993) report lower uranium and thorium values than those reported by Moll and others (1981), but up to 900 ppm rubidium, and elevated cerium levels.
Workings: Miller and others (1980) report values of 16.4 ppm uranium and 73.8 ppm thorium from grab samples. Clautice and others (1993) report lower uranium and thorium values than those reported by Miller and others, (1980), but up to 900 ppm rubidium, and elevated cerium levels.
Age: Inferred to be early Tertiary, based on isotopic ages of Sischu Volcanics (Moll and others, 1981).
Commodities (Major) - Th, U; (Minor) - Ce, Rb
Development Status: No
Deposit Model: Volcanogenic Uranium (Cox and Singer, 1986; model no. 25f)
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Clautice, K.H., Bowman, N.D., Clough, J.G., Gilbert, W.G., Kline, J.T., Smith, T.E., and Blodgett, R.B., 1993, Land selection Unit 8 (Kantishna River, Ruby, and Medfra quadrangles); References, lead isotope, geochemical and major oxide data: Alaska Division of Geological and Geophysical Surveys, 42 p., 1 sheet, scale 1:250,000. Miller, T.P., Moll, E.J., and Patton, W.W. Jr., 1980, Uranium and thorium rich volcanic rocks of the Sischu Creek area, Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-803, 9 p. Moll, E.J., Silberman, M.L., and Patton, W.W. Jr., 1981, Chemistry, mineralogy, and K-Ar ages of igneous and metamorphic rocks of the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811-C, 15 p., 2 sheets, scale 1:250,000.