Unnamed (on the west side of Tarr Inlet)

Site Name

Primary: Unnamed (on the west side of Tarr Inlet)

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Commodity

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

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Location

State: Alaska
District: Juneau (Glacier Bay subdistrict)

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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: Porphyry Cu

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: Alteration is mentioned but not described in Brew and others (1978).

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Rocks

Role: Host
Age Type: Host Rock
Age Young: Cretaceous

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Analytical Data

Not available

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Materials

Ore: Arsenopyrite
Ore: Chalcopyrite
Ore: Pyrite
Ore: Sphalerite
Gangue: Quartz

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Comments

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

Comment (Reserve-Resource): Reserves = Brew and others (1978) judged the mineralized zones to be too small and too low-grade to be economic.

Comment (Deposit): Model Name = Mineralized veins and shear zones in a quartz monzodiorite, possibly a porphyry copper occurrence (Cox and Singer, 1986: model 17?).

Comment (Deposit): Other Comments = the deposit is within Glacier Bay National Park and Preserve where exploration and development is restricted.

Comment (Exploration): Status = Inactive

Comment (Geology): Age = Host rock is Cretaceous.

Comment (Geology): Geologic Description = The following description is summarized from Brew and others, 1978. Mineralization is found along altered fault and shear zones in quartz monzodiorite that makes up the Tarr Inlet Knob. The quartz monzodiorite contains large xenoliths of shale and volcanics. Porphyritic granite, probably in the form of small plugs, occurs at two sites on the knob. The altered and mineralized fault and shear zones are up to 200 feet thick and are often brightly iron-stained. Most of the mineralization occurs along altered fault zones that are oriented N20-30W and N10-30E. The deposit consists of pyrite, chalcopyrite, sphalerite, arsenopyrite, and quartz. The prospect is generally similar to the Margerie (SK020) prospect located about 2.5 miles to the west and both may have been mineralized by the same process. Most of the more significant mineralization has been found on the east side of the Tarr Inlet Knob below the 500-foot elevation. Samples of the richer portions of the mineralized zone that vary from 3 feet to 16 feet wide contain up to 3,300 ppm copper, 5,000 ppm zinc, 3,100 ppm lead, 50 ppm silver, and 0.15 ppm gold. A 1/2-foot sample contained 0.48% copper, 4.3% zinc, 100 ppm silver, 1,500 ppm lead, and 0.15 ppm gold.? the Tarr Inlet Knob is in the Geikie province of Brew and others (1978) near its western margin. It is along the Brady Glacier fault zone, the eastern edge of the Tarr Inlet suture zone, which forms the western boundary of the Geike province. Movement along these structures is probably responsible for the fault and shear zones which localize the mineralization at this site. The faulting and mineralization must be younger than the Cretaceous intrusive rocks at Tarr Inlet Knob.

Comment (Geology): Age = The mineralization must be younger than the Cretaceous age of the host intrusive rocks (Brew and others, 1978).

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References

Reference (Deposit): Cobb, E.H., 1981, Summaries of data on and lists of references to metallic and selected nonmetallic mineral occurrences in the Skagway quadrangle, Alaska; Supplement to Open-File Report 78-316; Part A, Summaries of data to January 1, 1980: U.S. Geological Survey Open-File Report 81-82-A, 11 p.

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): 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.

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): Cobb, E.H., 1981, Summaries of data and lists of references to metallic and selected nonmetallic mineral occurrences in the Skagway quadrangle, Alaska, Supplement to Open-File Report 78-316, Part A in Summaries of data to January 1, 1980: U.S. Geological Survey Open-File Report 81-82-A, 11 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.

Reference (Deposit): MacKevett, E.M., Jr., Brew, D.A., Hawley, C.C., Huff, L.C., and Smith, J.G., 1967, Mineral resources of Glacier Bay National Monument, Alaska: U. S. Geological Survey Open-File Report 151, 176 p.

Reference (Deposit): Still, J.C., 1991, Bureau of Mines mineral investigations in the Juneau mining district, Alaska, 1984 - 1988, v. 2, Detailed mine, prospect, and mineral occurrence descriptions, section B, Glacier Bay subarea: U.S. Bureau of Mines of Mines Special Publication, 69 p.

Reference (Deposit): 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 approx. 1:600,000.

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