Warner Bay; Prospect Bay Prospect, Alaska Peninsula District, Lake and Peninsula Borough, Alaska, USA
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Location: This site is at or near sea level on the west side of Warner Bay just to the south of the spit (Berg and Cobb, 1967, locality 3; Cobb, 1972: MF-374; Cobb, 1980: OFR 80-909, locality 3; MacKevett and Holloway, 1977, locality 3; Cox and others, 1981, locality 11; Nokleberg and others, 1987, locality AP 9). Site location as plotted is accurate to within 1 mile.
Geology: This prospect is within the northeast part of the Devils Bay batholith (Detterman and others, 1981). This pluton is a multiphase granodiorite to tonalite which intrudes sediments of the Cretaceous Hoodo Formation. Potassium-argon dates of the pluton indicate a range of between 5 and 10 million years (Wilson, 1980). Atwood (1911) first described this prospect as a 50-foot wide crushed zone containing chalcopyrite, galena, pyrite, quartz and sphalerite. Later, more extensive investigation has shown that mineralization is exposed mostly in vertical cliffs extending down to sea level. Chalcopyrite and molybdenite occur as veinlets on joint surfaces spaced 5 to 10 centimeters apart (Cox and others, 1981). The extent of this mineralization has not been reported. Four samples collected by Resource Associates of Alaska in 1979 assayed as follows: 520 to 16,000 ppm copper, 280 to 9,110 ppm molybdenum, 0.4 to 2.5 ppm silver, 20 ppm tin, and 9-128 ppm tungsten. Cox and others (1981) list the grade of this mineralization at 0 to 0.07 percent molybdenum with a trace of copper. Nokleberg and others (1987) list an average grade of 0.03 percent copper with values up to 0.7 percent. Massive sulfide veins, ranging in width from 2 inches to 4 feet occur filling a northwest-trending nearly vertical fracture system. These are spaced approximately 100 feet apart over a distance of 3500 feet along the beach. Assays of this material by Resource Associates of Alaska returned values of up to 5.7 percent copper, 0.312 ounce gold per ton, 0.91 percent molybdenum, 1.25 percent lead, 395 ppm tungsten, and 10.8 percent zinc (Anderson and others, 1979). One sample reported 3000 ppm lanthanum. A breccia pipe, approximately 3 meters in diameter, occurs at the extreme north end of the showing. It contains clasts of propylitically altered granodiorite cemented by galena, pyrite, sphalerite, calcite, chlorite, and zeolites. The small tonnage in sight is estimated at >10,000 tonnes. Anderson and others (1979) give values for a high-grade sample as follows: 1600 ppm copper, 0.1 ppm gold, 4000 ppm lead, 2.3 ppm silver, 8 ppm tungsten, 400 ppm zinc. Four holes were drilled on the prospect in 1965 and 1966 by Pan American Exploration (now Amoco) for a total of 2432 feet Cobb (1980: OFR 80-909) reports drilling as recent as 1977.
Workings: Two short adits were driven in the early 1900's (Atwood, 1911). In the 1960's four holes were drilled for a total of 2432 feet. Some drilling has been reported as late as 1977. Bear Creek Mining Company visited the property in 1975 and Resource Associates mapped and sampled there in 1979.
Age: The age of mineralization is estimated at less than 6.5 million years (Wilson, 1980).
Alteration: Alteration of granodiorite host rock is limited to partial alteration (?) of amphibole to biotite and slight chloritization of biotite. Clasts of granodiorite in the breccia pipe exhibit propylitic alteration. Biotitic and sericitic alteration occur as thin selvages along veinlets.
Commodities (Major) - Ag, Au, Cu, Mo, Pb, Zn; (Minor) - Sn, W
Development Status: None
Deposit Model: Porphyry copper-molybdenum; polymetallic vein (Cox and Singer, 1986; models 21a
Mineral List
11 entries listed. 9 valid minerals.
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References
Anderson, G.D., Fitch, G.M., Lappie, D.W., Lindberg, P.A., and Fankhauser, R.E., 1979, Exploration and evaluation of Bristol Bay Native Corporation Lands, Vol. II, Book 1: Prepared for Houston Oil and Minerals Company by Resource Associates of Alaska, 78 p. (Report held by Alaska Earth Sciences, Inc., Anchorage, Alaska.) Atwood, W.W., 1909, Mineral resources of southwest Alaska, in Brooks, A.H., and others, Mineral resources of Alaska in 1908: U.S. Geological Survey Bulletin 379, p. 108-152. Atwood, W.W., 1911, Geology and mineral resources of parts of the Alaska Peninsula: U.S. Geological Survey Bulletin 467, 137 p. Berg, H.C., and Cobb, E.H., 1967, Metalliferous lode deposits of Alaska: U.S. Geological Survey Bulletin 1246, 254 p. Cobb, E.H., 1972, Metallic mineral resources map of the Chignik quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-374, 1 sheet, scale 1:250,000. Cobb, E.H., 1980, Summaries of data and lists of references to metallic and selected nonmetallic mineral deposits in fifteen quadrangles in southwestern and west-central Alaska: U.S. Geological Survey Open-File Report 80-909, 103 p. Cox, D.P., Detra, D.E., and Detterman, R.L., 1981, Mineral resource maps of the Chignik and Sutwik Island quadrangles, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF- 1053-K, 2 sheets, scale 1:250,000. Detterman, R.L., Miller, T.P., Yount, M.E., and Wilson, F.H.,1981, Geologic map the Chignik and Sutwik Island quadrangles Alaska: U.S. Geologic Survey Miscellaneous Investigations Series Map I-1229, 1 sheet, scale 1:250,000. Fields, E.D., 1977, 1976 Annual report: Alaska search, Chignik area-Bristol Bay region: Bear Creek Mining Company, 44 p., 22 map sheets. (Report held by the Aleut Corporation, Anchorage, Alaska.) Knappen, R.S., 1929, Geology and mineral resources of the Aniakchak District, in Smith, P.S., and others, Mineral Resources of Alaska, report on progress of investigations in 1926: U.S. Geological Survey Bulletin 797-F, p. 161-227. MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous mineral deposits in the western part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-F, 38 p., 1 sheet, scale 1:1,000,000. Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, D.J., Robinson, M.S., Smith, T.E., and Yeend, W., 1987, Significant metalliferous lode deposits and placer districts of Alaska: U.S. Geological Survey Bulletin 1786, 104 p., 2 plates, scale 1:5,000,000. Wilson, F.H., 1980, Late Mesozoic and Cenozoic tectonics and age of porphyry copper prospects, Chignik and Sutwik Island quadrangles, Alaska Peninsula: U.S. Geological Survey Open-File Report 80-543, 94 p., 5 sheets, scales 1:250,000 and 1 inch = 1,000 feet. Wilson, F.H., and Cox, D.P., 1983, Geochronology, geochemistry, and tectonic environment of porphyry mineralization in the central Alaska Peninsula: U.S. Geological Survey Open-File Report 83-783, 24 p.
