Unnamed (east side of Dundas Bay)

Site Name

Primary: Unnamed (east side of Dundas Bay)

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Commodity

Primary: Copper
Secondary: Zinc
Secondary: Gold
Secondary: Silver
Secondary: Lead
Secondary: Molybdenum

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Location

State: Alaska
District: Juneau

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Occurrence
Operation Type: Unknown
Years of Production:
Organization:
Significant:

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Physiography

Not available

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Mineral Deposit Model

Model Name: Massive sulfide, kuroko

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: Local oxidation of copper minerals.

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Rocks

Name: Meta-Basalt
Role: Associated
Age Type: Host Rock
Age Young: Late Silurian

Name: Meta-Basalt
Role: Associated
Age Type: Associated Rock
Age Young: Late Devonian

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Analytical Data

Not available

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Materials

Ore: Chalcopyrite
Ore: Galena
Ore: Malachite
Ore: Pyrite
Ore: Sphalerite
Gangue: Quartz

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Comments

Comment (Exploration): Status = Inactive

Comment (Commodity): Gangue = Muscovite (sericite)

Comment (Geology): Age = Devonian-Silurian with possible remobilization during the Cretaceous.

Comment (Deposit): Model Name = Volcanogenic, cupriferous metarhyolite -- similar to kuroko massive sulfide (Cox and Singer, 1986; model 28a).

Comment (Deposit): Other Comments = Although the reported grade of the deposit is subeconomic, its size and possible volcanogenic nature encourages further exploration and the mapping of the Devonian-Silurian volcanic stratigraphy. ? the site is in Glacier Bay National Park and Preserve.

Comment (Reference): Primary Reference = Kimball and others, 1978

Comment (Geology): Geologic Description = Pyritic quartz-mica semischist, that possibly is a metarhyolite,and metabasalt appear to occur within a unit that elsewhere consists mainly of graywacke and argillite of Silurian and Devonian age (Brew and others, 1978). Foliated granitic rocks crop out west of the pyritic schists. The granitic rocks are inferred to be extensive, but are covered by water in Dundas Bay. ? the pyritic semischist, which is the mineralized unit, forms a steep, north trending body from 100 feet to more than 1000 feet thick. It in sharp contact with adjacent metabasalt. Pyrite is more abundant than chalcopyrite in the semischist unit, but chalcopyrite is generally present. The semischist is cut locally by veinlike zones that contain relatively abundant chalcopyrite.? the occurrence is probably syngenetic and volcanigenic. Chalcopyrite may have been remobilized into the vein-like zones during Cretaceous metamorphism.? Selected samples of the semischist unit contained as much as 1 ppm silver and 2000 ppm copper (MacKevett and others, 1971, table 9). Kimball and others (1978) reported 2 ppm silver, 320 ppm copper, and 230 ppm zinc in a 50 foot long chip sample of the semischist. Molybdenum is commonly present and assayed as much as 100 ppm in a 12 foot chip sample. Moerlein (1968) collected 35- and 20-ft. chip samples from a northwest-striking shear zone within the semischist; his samples contained, respectively, 0.51 and 0.34 percent copper.

Comment (Workings): Workings / Exploration = Claims reportedly staked for gold, lead, zinc and copper were reported in the east Dundas Bay area by Wright and Wright (1937). In the 1966 examination by the U.S. Geological Survey, only surface exposures were examined and sampled. A chip sample collected across 40-feet of semischist contained 1000 ppm copper; a malachite stained zone contained 2000 ppm copper (MacKevett and others, 1971). Moerlein (1968) found as much as 0.51 percent copper in a northwest trending shear zone within the pyritic semischist unit. Samples of semischist collected by the U.S. Bureau of Mines (Kimball and others, 1978) showed anomalous silver, molybdenum, and zinc as well as copper. Maximum reported molybdenum content was 100 ppm.

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References

Reference (Deposit): Cobb, E.H., 1972, Metallic mineral resources map of the Mount Fairweather quadrangle, AK: U.S. Geological Survey Miscellaneous Field Study Map MF-436, 1 sheet, scale 1:250,000.

Reference (Deposit): Moerlein, G.A., 1968, Geology and drilling results, Nunatak molybdenum prospect, Walper property, southeastern Alaska: Unpublished report available at U.S. Bureau of Land Management Library at Juneau, Alaska.

Reference (Deposit): Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources, in Brew, D. A., and others, Mineral resources of the Glacier Bay National Monument wilderness study area, Alaska: U.S. Geological Survey Open-File Report 78-494, p. C1-C375.

Reference (Deposit): MacKevett, E.M., Jr., Brew, D.A., Hawley, C.C., Huff, L.C., and Smith, J.G., 1971, Mineral resources of Glacier Bay National Monument, Alaska: U.S. Geological Survey Professional Paper 632, 90 p., 12 plates, scale 1:250,000.

Reference (Deposit): Brew, D.A., Johnson, B.R., Grybeck, D., Griscom, A., Barnes, D.F., Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources of the Glacier Bay National Monument Wilderness Study Area, Alaska: U.S. Geological Survey Open-File Report 78-494, 670 p.

Reference (Deposit): Wright, F.E. and Wright, C.W., 1937, The Glacier Bay National Monument in southeastern Alaska, its glaciers and geology: U.S. Geological Survey manuscript report, 224 p.

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