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Kagati Lake

Prospect, Inactive

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Commodities and mineralogy

Main commodities Au; Hg; Sb
Ore minerals cinnabar; orpiment; realgar; stibnite
Gangue minerals calcite; quartz; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale GO
Quadrangle map, 1:63,360-scale D-3
Latitude 59.92
Longitude -159.91
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Kagati Lake prospect is in uplands in the headwaters of Atmugiak Creek, 5.5 miles northeast of Kagati Lake. It is at an elevation of about 3,400 feet above the small, east-headwater lake to Atmugiak Creek. It is locality 1 of Hoare and Cobb (1977) and of Cobb and Condon (1972).

Geologic setting

Geologic description

The Kagati Lake prospect is within a Cretaceous granitic pluton (Hoare and Coonrad, 1978). It was discovered and prospected by 1927 (Malone, 1962) but explored mostly in the 1950s (Sainsbury and MacKevett, 1965). North-northwest-trending fractures and shear zones up to 1,200 feet long and approximately parallel to steep joints in the host granitic rock control mineralization. Cinnabar, some closely associated with realgar, stibnite, and minor orpiment, forms veinlets and fills fractures in the shear zones. Individual cinnabar masses are 2 to 24 inches wide, but are observed only for lengths up to 10 feet due to limited exposure. Quartz, some vuggy, and clay accompany the cinnabar; secondary antimony minerals and iron-oxides are also present. Frost (1990, p. C5) describes the veins as zoned with margins of blue-green to brown tourmaline needles extending into a core of quartz and calcite; cinnabar and stibnite crystals with some realgar and orpiment are scattered through quartz in the cores of the veins. Gold values up to 2.9 ppm were obtained on vein material (Frost, 1990; Gray and others, 1990).
Geologic map unit (-159.912237736911, 59.9192511474176)
Mineral deposit model Epithermal mercury- and antimony-bearing veins in granitic rock
Age of mineralization Late Cretaceous or Tertiary. The mineralization postdates the host granitic pluton, which yielded a K/Ar age of 71.1 +/- 2.1 Ma on biotite (Hoare and Coonrad, 1978).
Alteration of deposit Silicification and oxidation.

Production and reserves

Workings or exploration Exploration includes pits, trenches, and dozer stripping; surface mapping was completed in the 1950s (Sainsbury and MacKevett, 1965).
Indication of production None

References

MRDS Number A010299

References

Cobb, E.H., and Condon, W.H., 1972, Metallic mineral resources map of the Goodnews quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-447, scale 1:250,000.
Frost, T.P., 1990, Geology and geochemistry of mineralization in the Bethel quadrangle, southwestern Alaska, in Goldfarb, R.J., Nash, J.T., and Stoeser, J.W., eds., Geochemical studies in Alaska by the U.S. Geological Survey, 1989: U.S. Geological Survey Bulletin 1950, p. C1-C9.
Gray, J.E., Frost, T.P., Goldfarb, R.J., and Detra, D.E., 1990, Gold associated with cinnabar- and stibnite-bearing deposits and mineral occurrences in the Kuskokwim River Region, Alaska, in Goldfarb, R.J., Nash, J.T., and Stoeser, J.W., eds., Geochemical studies in Alaska by the U.S. Geological Survey, 1989: U.S. Geological Survey Bulletin 1950, p. D1-D6.
Hoare, J.M., and Cobb, E.H., 1977, Mineral occurrences (other than mineral fuels and construction materials) in the Bethel, Goodnews, and Russian Mission quadrangles, Alaska: U.S. Geological Survey Open-File Report 77-156, 98 p.
Hoare, J.M., and Coonrad, W.L., 1978, Geologic map of the Goodnews and Hagemeister Island quadrangles region, southwestern Alaska: U.S. Geological Survey Open-File Report 78-9-B, 2 sheets, scale 1:250,000.
Malone, Kevin, 1962, Mercury occurrences in Alaska: U.S. Bureau of Mines Circular 8131, 57 p.
Sainsbury, C.L., and MacKevett, E.M., Jr., 1965, Quicksilver deposits of southwestern Alaska a description of the quicksilver mines and prospects, with special emphasis on the structural controls of ore deposition: U.S. Geological Survey Bulletin 1187, 89 p.
Reporters Travis L. Hudson
Last report date 3/20/2001