Boundary; Boundary Glacier Prospect, Skagway District, Juneau District, Haines Borough, Alaska, USA
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Geology: Still and others (1991) describe this prospect as: 'Narrow bands of iron-stained metasedimentary rocks and altered metabasalt that crop through glacial ice.' 'Float and bedrock samples of sedimentary and volcanic rocks contain up to 0.034 ppm gold, 1.214 ppm silver, 280 ppm zinc, 1,390 ppm copper, 390 ppm cobalt, 400 ppm arsenic, and 200 ppm nickel.' 'A barite rich band hosted in white phyllite contained 47% barium.' Rubicon Minerals (1998) in an unpublished Executive Summary, cites work by Kennecott Alaska Exploration that describes Boundary as: '...quartz-sericite-pyrite schist and felsite with chalcopyrite.' Rubicon also cites Kennecott samples with maximum values of 6.5% copper, 16 ppm lead, 3,610 ppm zinc, 12 ppm silver, and 1.980 ppm gold. Sample descriptions from Still and others (1984) mention phyllite, white phyllite, sericite schist, greenstone and quartzite. These rock types are similar to those at baritic massive sulfide prospects like the Main Zone/Palmer (SK066) and RW Zone (SK067) deposits, and Rubicon Minerals (1998) considers Boundary to be a volcanogenic massive-sulfide system. The phyllitic rocks may reflect a felsic volcanic or altered mafic volcanic protolith. If Boundary is a volcanogenic massive sulfide system correlative with the Windy Craggy deposit in Canada and the Greens Creek deposit on Admiralty Island, then this prospect and others like it in the Mt. Henry Clay area are probably Late Triassic (Still, 1984 [OF 118-84]; Newberry and others, 1997).
Age: If Boundary is a volcanogenic massive-sulfide deposit correlative with the Windy Craggy deposit in Canada and the Greens Creek deposit on Admiralty Island, then this prospect and others like it in the Mt. Henry Clay area are probably Late Triassic (Still, 1984 [OF 118-84]; Newberry and others, 1997).
Alteration: Quartz-sericite (?).
Commodities (Major) - Barite, Cu; (Minor) - As, Co, Zn
Development Status: None
Deposit Model: Besshi- or Kuroko-type massive sulfide (?) (Cox and Singer, 1986; models 28a? o
5 entries listed. 4 valid minerals.
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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. Newberry, R.J., Crafford, T.C., Newkirk, S.R., Young, L.E., Nelson, S.W., and Duke, N.A., 1997, Volcanogenic massive sulfide deposits of Alaska, in Goldfarb, R.J. and Miller, L. D., eds., Mineral deposits of Alaska: Economic Geology Monograph 9, p. 120-150. Rubicon Minerals, 1998, Palmer VMS Project, southeast Alaska, Executive Summary: Unpublished report by Rubicon Minerals Corporation, Vancouver, British Columbia, 25 p. Still, J.C., 1984, Stratiform massive sulfide deposits in the Mt. Henry Clay area, southeast Alaska: U.S. Bureau of Mines Open-File Report 118-84, 65 p. 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. Still, J.C., Weir, K.R., Gilbert, W.G., and Redman, E.C., 1984, Stream-sediment, float, and bedrock sampling in the Porcupine mining area, southeast Alaska: U.S. Bureau of Mines Open-File Report 173-84, 16 p., 1 sheet.