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  3. Alaska Resource Data File (ARDF)

Unnamed (east of Mentasta Lake)

Occurrence, Inactive

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Commodities and mineralogy

Main commodities Ag; Cu
Ore minerals bornite; chalcopyrite
Gangue minerals calcite; epidote

Geographic location

Quadrangle map, 1:250,000-scale NB
Quadrangle map, 1:63,360-scale D-6
Latitude 62.8878
Longitude -143.6552
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is 3,500 feet east of the Mentasta Lodge on the Glenn Highway. It is at an elevation of about 3,000 feet in the SW1/4 of section 23, T. 13 N., R. 9 E. of the Copper River Meridian. This is locality 7 of Richter (1967) and locality 3 of Richter and others (1975). The location is accurate within a few hundred feet.

Geologic setting

Geologic description

Bornite and minor chalcopyrite fill vesicles and form irregular segregations disseminated through a 400-foot-thick section of Triassic, Nikolai Greenstone (Richter, 1967, 1976). The host metabasalt is highly epidotized and locally cut by veinlets of red jasper. The bornite is associated with calcite and epidote. A grab sample containing copper minerals assayed 1.1 percent copper, 0.02 ounce of gold per ton, and 0.02 ounce of silver per ton (Richter, 1967). Alteration and copper mineralization in Nikolai Greenstone is thought to have accompanied regional deformation and low-grade metamorphism in the Late Jurassic to Early Cretaceous (MacKevett and others, 1997).
Geologic map unit (-143.657397773952, 62.8874244176783)
Mineral deposit model Basaltic copper (Cox and Singer, 1986; model 23)
Mineral deposit model number 23
Age of mineralization Cretaceous? Alteration and copper mineralization in the Nikolai Greenstone is thought to have accompanied regional deformation and low-grade metamorphism in the Late Jurassic to Early Cretaceous (MacKevett and others, 1997).
Alteration of deposit Epidotization.

Production and reserves

Workings or exploration There are no known workings but some surface prospecting has probably occurred.
Indication of production None

References

MRDS Number A011379

References

MacKevett, E.M., Jr., Cox, D.P., Potter, R.W., III, and Silberman, M.L., 1997, Kennecott-type deposits in the Wrangell Mountains, Alaska--High-grade copper ores near a basalt-limestone contact, in Goldfarb, R.J., and Miller, L.D., eds., Mineral deposits of Alaska: Economic Geology Monograph 9, p. 66-89.
Richter, D.H., 1967, Geology of the upper Slana-Mentasta Pass area, southcentral Alaska: Alaska Division of Mines and Minerals Geologic Report 30, 30 p., 2 sheets, scale 1:63,360.
Richter, D.H., 1976, Geologic map of the Nabesna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-932, 1 sheet, scale 1:250,000.
Richter, D.H., Singer, D.A., and Cox, D.P., 1975, Mineral resources map of the Nabesna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-655-K, 1 sheet, scale 1:250,000.
Reporters Travis L. Hudson (Applied Geology)
Last report date 11/24/2002