Road Cut II

Site Name

Primary: Road Cut II

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Commodity

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

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Location

State: Alaska
District: Juneau (Skagway 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: Prospect
Operation Type: Unknown
Years of Production:
Organization:
Significant:

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Physiography

Not available

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Mineral Deposit Model

Not available

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: Epidotization.

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Rocks

Role: Host
Age Type: Host Rock
Age Young: Late Triassic

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Analytical Data

Not available

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Materials

Ore: Sphalerite
Ore: Pyrite
Ore: Chalcopyrite
Gangue: Epidote

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Comments

Comment (Workings): Workings / Exploration = In 1986-1987 the U.S. Bureau of Mines made shallow excavations and sampled the bedrock and rubble. They also ran two 440-foot-long magnetometer lines across the beach and road and up the escarpment that forms the eastern edge of the Chilkat Fault near milepost 5 of the Mud Bay Road. A prominent magnetic low indicates a fault zone that strikes N37W about 35 feet east of the Mud Bay road (Still, 1988). An approximately 30-foot-long adit in metabasalt is located several hundred feet southeast of milepost 4 on the Mud Bay road. No mineralization was seen in the adit, but a band of metabasalt adjacent to the adit contains chalcopyrite (Still, 1988).

Comment (Geology): Geologic Description = According to Still (1988), spotty gold-copper-zinc mineralization extends for at least a mile, between mileposts 4 and 5 on the Mud Bay Road. Mineralization consists of epidote-altered metabasalt and epidote bands up to 2 feet thick that contain pyrite, chalcopyrite, and locally sphalerite. Samples contain up to 0.21 ppm gold, 2.5 ppm silver, 0.69% copper, and 1.83% zinc. This mineralization may be continuous with the Road Cut prospect (SK006). From the descriptions of Still (1988), it appears that mineralization at both prospects occurs along fault and shear zones that are subsidiary shears and splits of the Chilkat fault. If so, then the age of the mineralization is probably Tertiary or youngersince most movement along the Chilkat Fault has probably been post-Mesozoic (Lanphere, 1978). Plafker, Hudson and Silberling (1979) and Plafker and Hudson (1980) cite fossil evidence for a Late Triassic (Karnian) age for the metabasalts on the Chilkat Peninsula. The age of a nearby ultramafic body is probably 108-109 m.y. based on potassium-argon ages from a pyroxenite at Battery Point (MacKevett and others, 1974).

Comment (Geology): Age = the age is not well established. It can be no older than the Late Triassic age of the metabasalt that hosts the prospect (Plafker, Hudson and Silberling, 1979; Plafker and Hudson, 1980). If the structures that localize the mineralization are related to the Chilkat Fault, then the age of the mineralization is probably Tertiary or younger as most movement on the Chilkat Fault has been post-Mesozoic (Lanphere, 1978).

Comment (Reference): Primary Reference = Still, 1988

Comment (Exploration): Status = Inactive

Comment (Deposit): Other Comments = This prospect is within a mile of the Chilkat State Park.

Comment (Deposit): Model Name = Base metal sulfides with some precious metal values along a shear zone in metabasalt.

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References

Reference (Deposit): Winkler, G.R., and MacKevett, E.M., Jr., 1970, Analyses of bedrock and stream-sediment samples from the Haines-Porcupine region, southeastern Alaska: U.S. Geological Survey Open-File Report 369, 91 p., 1 sheet, scale 1:125,000.

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 A, Haines-Klukwan-Porcupine subarea: U.S. Bureau of Mines of Mines Special Publication, 214 p.

Reference (Deposit): Still, J.C., 1988, Gold-copper Mineralization of the Chilkat Peninsula and Islands: U.S. Bureau of Mines Open-File Report 49-88, 39 p., 11 sheets.

Reference (Deposit): 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.

Reference (Deposit): Plafker George, Hudson, T.L., and Silberling, N.J., 1979, Upper Triassic fossils from a sequence of volcanic and sedimentary rocks on the Chilkat Peninsula, southeastern Alaska, in Johnson, K.M., and Williams, J.R., eds., The United States Geological Survey in Alaska: Accomplishments during 1978: U.S. Geological Survey Circular 804-B, p. B107-B110.

Reference (Deposit): MacKevett, E.M., Jr., Robertson, E.C., and Winkler, G.R., 1974, Geology of the Skagway B-3 and B-4 quadrangles, southern Alaska: U.S. Geological Survey Professional Paper 832, 33 p.

Reference (Deposit): Lanphere, M.A., 1978, Displacement history of the Denali fault system, Alaska and Canada: Canadian Journal of Earth Sciences, v. 115, p. 817-822

Reference (Deposit): Plafker, George, and Hudson, T., 1980, Regional implications of Upper Triassic metavolcanic and metasedimentary rocks on the Chilkat Peninsula, southeastern Alaska: Canadian Journal of Earth Sciences, v. 17, p. 681-689.

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