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Larson

Prospect, Inactive

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Commodities and mineralogy

Main commodities Cu
Ore minerals malachite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale MC
Quadrangle map, 1:63,360-scale C-8
Latitude 61.7026
Longitude -143.8772
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is on a ridge along the south valley wall of the Kotsina River. It is at an elevation of about 5,050 feet, 5,700 feet northeast of elevation 6830 and 2,600 feet south of the center of section 12, T. 2 S., R. 8 E. of the Copper River Meridian. This is locality 168 of MacKevett (1976) and locality 9 of MacKevett and others (1978). The location is accurate to within about 100 feet. Cobb and MacKevett (1980) included this prospect under the name 'Larson'.

Geologic setting

Geologic description

The deposit at this prospect consist of fractures in a fault zone cutting Triassic Nikolai Greenstone that are stained with malachite. The greenstone is locally amygdaloidal and quartz occurs in veins and as amygdule fillings (Moffit and Mertie, 1923). The deposits were explored by two adits. The widespread deposition of copper in Triassic greenstone and limestone of the area is thought to have accompanied regional deformation and low-grade metamorphism in the Late Jurassic or Early Cretaceous (MacKevett and others, 1997). Copper-bearing minerals were deposited in the underlying Nikolai Greenstone at about 112 Ma (Silberman and others, 1980).
Geologic map unit (-143.879291764312, 61.7021384375832)
Mineral deposit model Basaltic Cu (Cox and Singer, 1986; model 23)
Mineral deposit model number 23
Age of mineralization Cretaceous? The widespread deposition of copper in Triassic greenstone and limestone of the area is thought to have accompanied regional deformation and low-grade metamorphism in the Late Jurassic or Early Cretaceous (MacKevett and others, 1997). Copper-bearing minerals were deposited in the underlying Nikolai Greenstone at about 112 Ma (Silberman and others, 1980).
Alteration of deposit Oxidation.

Production and reserves

Workings or exploration The deposits were explored by two adits.
Indication of production None

Additional comments

The locality is in the Wrangell-Saint Elias National Park and Preserve.

References

References

Cobb, E.H., and MacKevett, E.M., Jr., 1980, Summaries of data on and lists of references to metallic and selected nonmetallic mineral deposits in the McCarthy quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-885, 156 p.
MacKevett, E.M., Jr., 1976, Mineral deposits and occurrences in the McCarthy quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-773-B, 2 sheets, scale 1:250,000.
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.
MacKevett, E.M., Jr., Smith, J.G., Jones, D.L., and Winkler, G.R., 1978, Geologic map of the McCarthy C-8 quadrangle, Alaska: U.S. Geological Survey Geologic Quadrangle Map GQ-1418, 1 sheet, scale 1:63,360.
Moffit, F.H., and Mertie, J.B., Jr., 1923, The Kotsina-Kuskulana district, Alaska: U.S. Geological Survey Bulletin 745, 149 p.
Silberman, M.L., MacKevett, E.M., Jr., Connor, C.L., and Mathews, A., 1980, Metallogenic and tectonic significance of oxygen isotope data and whole-rock potassium-argon ages of Nikolai Greenstone, McCarthy quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-2019, 31 p.
Reporters Travis L. Hudson (Applied Geology, Inc.)
Last report date 1/12/2003