Lone Mountain Occurrence, Bristol Bay Region District, Dillingham Borough, Alaska, USA
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Geology: Lone Mountain is centered on a Cretaceous or Tertiary felsic stock surrounded by hornfels (Hoare and Coonrad, 1978). The iron-stained hornfels, which is locally gossan, contains disseminated pyrite and small quartz-pyrite veinlets. Quartz veinlets are also locally present in iron-stained parts of the stock near the contact zone. Stream-sediment samples from the area contain anomalous amounts of As, Bi, Cu, Pb, Mo, W, or Zn (Cieutat and others, 1988; Hessin and others, 1978 [OF 78-9-Q; OF 78-9-M]). Hornfels and veinlet samples collected near the eastern contact mostly contain anomalous amounts of copper (up to 900 ppm Cu) and up to 1.2 ppm Ag, 0.01 ppm Au, 26 ppm Bi, 7.2 ppm Mo, 30 ppm Sn, and 50 ppm W (Kilburn and others, 1992). One iron-stained, carbonate-cemented breccia contained 460 ppm As, 0.15 ppm Au, 1.9 ppm Hg, and 11 ppm Sb.
Workings: Reconnaissance geochemical sampling has been completed in the area (Cieutat and others, 1988; Hessin and others, 1978 [OF 78-9-Q; OF 78-9-M]).
Age: Probably Late Cretaceous or Early Tertiary. Mineralization is probably related to the granitic pluton in the area, which is part of a regionally extensive Upper Cretaceous and Lower Tertiary plutonic suite (Hoare and Coonrad, 1978).
Alteration: Silicification and oxidation.
Commodities (Major) - Cu; (Minor) - Ag, Au, W
Development Status: None
Deposit Model: Polymetallic veins (Cox and Singer, 1986; model 22c)
2 entries listed. 2 valid minerals.
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Cieutat, B.A., Goldfarb, R.J., and Specman, W.S., 1988, Analytical results and sample locality map of stream-sediment, heavy-mineral-concentrate, and organic material samples from the Goodnews, Hagemeister Island, and Nushagak quadrangles, southwest Alaska: U.S. Geological Survey Open-File Report 88-591, 187 p., plate. Hessin, T.D., Taufen, P.M., Seward, J.C., Quintana, S.J., Clark, A.L., Grybeck, Donald, Hoare, J.M., and Coonrad, W.L., 1978, Geochemical and generalized geological map showing distribution and abundance of copper in the Goodnews and Hagemeister quadrangles region, southwestern Alaska: U.S. Geological Survey Open-File Report 78-9-M, 2 sheets, scale 1:250,000. Hessin, T.D., Taufen, P.M., Seward, J.C., Quintana, S.J., Clark, A.L., Grybeck, Donald, Hoare, J.M., and Coonrad, W.L., 1978, Geochemical and generalized geological map showing distribution and abundance of molybdenum, tin, and tungsten in the Goodnews and Hagemeister quadrangles region, southwestern Alaska: U.S. Geological Survey Open-File Report 78-9-Q, 1 sheet, scale 1:250,000. 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. Kilburn, J., Box, S.E., Goldfarb, R.J., and Gray, J.E., 1992, Geochemically anomalous areas in the eastern Goodnews Bay 1 degre x 3 degree quadrangle, southwest Alaska, in Bradley, D.C., and Ford, A.B., eds., Geologic studies by the U.S. Geological Survey in 1990: U.S. Geological Survey Bulletin 1999, p. 156-162.