Mount Henry Clay Prospect, Skagway District, Juneau District, Haines Borough, Alaska, USA
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Geology: According to Still (1984 [OF 118-84]), the Mt. Henry Clay prospect is located within the Glacier Creek volcanic-sedimentary sequence that hosts all of the Glacier Creek volcanogenic massive-sulfide occurrences. The sequence includes basalt, which locally display good pillow structures, andesitic flows and tuffs, and minor sedimentary rocks. The andesitic flows and tuffs in the vicinity of Mt. Henry Clay are mostly altered to chloritic phyllites. Exposed mineralization consists of sphalerite-barite-pyrite-chalcopyrite boulders up to 6 feet in diameter that are found along a sliver of rock that extends for a distance of 1/2 mile beneath the toe of a small triangular-shaped hanging glacier. Bedrock exposures of mineralization were not found and the source of the mineralized boulders is probably beneath the glacier. Assays of the mineralized float are variable; the highest grade samples contain 20 to 44% zinc, 5% barium, and several percent copper. Ore-grade mineralization was not found in place, but elevated levels of zinc, copper, barium, lead, silver, and gold were found in altered andesites in the area. Diamond drilling by Kennecott Exploration intersected felsic schists that contained barite-sphalerite mineralization underlain by pyrite-chalcopyrite stringer zones in chloritized basalt. Their drill core assays included intervals from 20 to 161 feet thick that contained up to 0.70% zinc and 0.44% copper. Drilling by Stryker Resources and Freeport Resources on the Canadian side of the border returned similar values. (Still and others, 1991; Rosenkrans and Jones, 1985). Eleven drill holes, 7 by Kennecott Exploration and 4 by Granges, Inc. totaling 8,719 feet, identified two mineralized horizons but did not intercept high grade mineralization comparable to the surface boulders. Rubicon Minerals interprets the Mount Henry Clay prospect to to be on a mineral trend along or near the apex of a shallowly plunging, northwest-trending antiform that extends to the southeast through the Cap (SK060) and Nunatak (SK058) prospects. (Rubicon Minerals, 1998). The Mt. Henry Clay prospect and other similar prospects in the Mt. Henry Clay area are probably correlative with the Windy Craggy deposit in Canada and the Greens Creek deposit on Admiralty Island and are therefore Late Triassic (Still, 1984 [OF 118-84]); Newberry and others, 1997).
Workings: Stryker Resources drilled 5 holes totaling 2,787 feet in length on extensions of this occurrence on the Canadian side of the border in 1985 (Still and others, 1991; Rosenkrans and Jones, 1985). Eleven drill holes, 7 by Kennecott Alaska Exploration and 4 by Granges, Inc. totaling 8,719 feet identified two mineralized horizons but did not intercept high grade mineralization comparable to boulders found at the surface (Rubicon Minerals, 1998).
Age: The Mt. Henry Clay prospect and other similar prospects in the Mt. Henry Clay area are probably correlative with the Windy Craggy deposit in Canada and the Greens Creek deposit on Admiralty Island and are therefore Late Triassic (Still, 1984 [OF 118-84]; Newberry and others, 1997).
Alteration: Chloritic.
Commodities (Major) - Ag, Au, Ba, Cu, Pb, Zn
Development Status: No
Deposit Model: Probably a Besshi- or Kuroko-type volcanogenic massive sulfide (Cox and Singer,
Mineral List
11 entries listed. 10 valid minerals.
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References
Forbes, R.B., Gilbert, W.G., and Redman, E., 1989, Geologic setting and petrology of the metavolcanic rocks in the northwestern part of the Skagway B-4 quadrangle, southeastern Alaska: Alaska Division of Geological and Geophysical Surveys Public-Data File 89-14, 46 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. 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. Redman, E.C., 1983, Reconnaissance geology of the Glacier Creek area, Skagway B-4 quadrangle, Alaska, in Appendix B of 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. Rosenkrans, D.S., and Jones, B.K., 1985, Jarvis Glacier project, 1985 annual progress report: Kennecott Alaska Exploration report, 30 p. (Unpublished material available at the Juneau Mineral Information Center, U.S. Bureau of Land Management, Juneau, Alaska). 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.
