Summit Creek; Lost Silver Ledge Mine, Skagway District, Juneau District, Haines Borough, Alaska, USA
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Geology: According to Eakin (1919), the prospect contains narrow silver-lead veins less than 1 foot thick. The maximum metal content was reported to be $3 gold per ton (about 0.14 ounces of gold per ton), about 60 ounces silver per ton, and about 35% lead. One sample contained nearly 3% copper. Berg and others (1981) cite a maximum gold grade of 0.145 ounces per ton and comment that the veinlets contain argentiferous galena. As reported by Still and others (1991), this prospect consists of quartz-sulfide veins in dolomitic limestone. The veins do not continue into the adjacent slate. A vein that was mined from the surface in the 1930's is up to 0.4 feet wide and is adjacent to a felsic dike. Sulfides from the vein are primarily jamesonite with lesser amounts of galena and tetrahedrite. Samples contain up to 14.19 ppm gold, 871.6 ppm silver, 1,540 ppm zinc, 1.70% copper, and 42.5 % lead. The most prominent vein extends for several hundred feet vertically and samples of it contain 0.05 to 1.32 ppm gold, 346.0 to 3,423.1 ppm silver, 0.193 to 4.89% zinc, and 4.36 to 39.3% lead. The Devonian to Mississippian age of the host carbonate rock establishes a maximum age for the veins while the presence of an adjacent felsic dike suggests a Tertiary age based on the 29.3 + 1 to 33.0 + 1 m.y. age of nearby quartz diorite and granodiorite bodies (Gilbert and others, 1987).
Workings: Workings consist of a 5-foot adit and a stope on a high-grade silver lens mined by a local prospector, R.C. Manuel, in the 1930's. The stope is about 10 feet high, 3 to 5 feet wide, and 20 feet long. (Still and others, 1991).
Age: The Devonian to Mississippian age of the host carbonate rock establishes a maximum age for the veins while the presence of an adjacent felsic dike suggests a Tertiary age based on the 29.3 + 1 to 33.0 + 1 m.y. age of nearby quartz diorite and granodiorite bodies (Gilbert and others, 1987).
Production: Based on the size of the stope described by Still and others (1991), production was very small.
Commodities (Major) - Ag, Au, Pb, Zn; (Minor) - Cu
Development Status: Yes; small
Deposit Model: Polymetallic quartz-sulfide veins (Cox and Singer, 1986; model 22c).
4 entries listed. 4 valid minerals.
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Berg, H.C., 1984, Regional geologic summary, metallogenesis, and mineral resources of southeastern Alaska: U.S. Geological Survey Open-file Report 84-572, 298 p., 1 plate, scale 1:600,000. Berg, H.C., Decker, J.E., and Abramson, B.S., 1981, Metallic mineral deposits of southeastern Alaska: U.S. Geological Survey Open-File Report 81-122, 136 p., 1 sheet, scale 1:1,000,000. Cobb, E.H., 1972, Metallic mineral resources map of the Skagway quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-424, 1 sheet, scale 1:250,000. Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Mt. Fairweather and Skagway quadrangles, Alaska: U.S. Geological Survey Open-File Report 78-316, 123 p. Eakin, H.M., 1919, The Porcupine gold placer district, Alaska: U.S. Geological Survey Bulletin 699, 29 p. Gilbert, W.G., and Redman, E.C., 1989, Lode deposits, prospects, and occurrences of the Porcupine mining area, southeast Alaska: U.S. Bureau of Mines Open-File Report 17-89, 1 sheet, scale 1:39,600. Gilbert, W.G., Burns, L.E., Redman, E.C., and Forbes, R.B., 1987, Preliminary bedrock geology and geochemistry of the Skagway B-3 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 87-2, 2 sheets, scale 1:36,200. MacKevett, E.M., Jr., Robertson, E.C., and Winkler, G.R., 1974, Geology of the Skagway B-3 and B-4 quadrangles, southern Alaska: U.S. Geological Survey Professional Paper 832, 33 p., 1 plate. Still, J.C., 1991, Bureau of Mines mineral investigations in the Juneau mining district, Alaska, 1984-1988; Volume 2, Detailed mine, prospect, and mineral occurrence descriptions, Section A, Haines-Klukwan-Porcupine subarea: U.S. Bureau of Mines of Mines Special Publication, 214 p. Still, J.C., Gilbert, W.G., and Forbes, R.B., 1987, Final report of stream sediment, float, and bedrock sampling in the Porcupine mining area, southeast Alaska, 1983-1985: U.S. Bureau of Mines Open-File Report 36-87, 35 p., 8 sheets. Still, J.C., Hoekzema, R.B., Bundtzen, T.K., Gilbert, W.G., Wier, K.R., Burns, L.E., and Fechner, S.A., 1991, Economic geology of Haines-Klukwan-Porcupine area, southeastern Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 91-4, 156 p., 5 sheets, scale 1:63,360. Wells, D.E., Pittman, T.L., Brew, D.A. and Douglass, S.L., 1986, Map and description of the mineral deposits in the Juneau, Taku River, Atlin, and part of the Skagway quadrangles, Alaska: U.S. Geological Survey Open-File Report 85-717, 332 p., 1 sheet, scale 1:250,000.