Unnamed (Johns Hopkins Inlet)

The Unnamed (Johns Hopkins Inlet) is a copper mine located in Alaska.

About the MRDS Data:

All mine locations were obtained from the USGS Mineral Resources Data System. The locations and other information in this database have not been verified for accuracy. It should be assumed that all mines are on private property.

Mine Info

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Site Name

Primary: Unnamed (Johns Hopkins Inlet)

Commodity

Primary: Copper
Secondary: Tungsten
Secondary: Tin
Secondary: Molybdenum
Secondary: Silver
Secondary: Gold

Location

State: Alaska
District: Juneau

Land Status

Not available

Holdings

Not available

Workings

Not available

Ownership

Not available

Production

Not available

Deposit

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

Physiography

Not available

Mineral Deposit Model

Not available

Orebody

Not available

Structure

Not available

Alterations

Alteration Type: L
Alteration Text: Widespread sulfidation of intrusive and volcanic rocks, now reflected in iron-stained rocks.

Rocks

Name: Volcanic Rock (Aphanitic)
Role: Associated
Age Type: Associated Rock
Age Young: Late Cretaceous

Analytical Data

Not available

Materials

Ore: Cassiterite
Ore: Chalcopyrite
Ore: Molybdenite
Ore: Pyrrhotite

Comments

Comment (Geology): Age = Possibly Cretaceous, based on age of granitic plutons in the area.

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

Comment (Workings): Workings / Exploration = Surface occurrence only. A Bureau of Mines select sample (7SO44) of a pyrrhotite lens contained 1,300 ppm copper. 30 ppm molybdenite, 1.5 ppm silver and greater than 0.05 ppm gold; also reported from the same area is a float sample of hornfels that contained 0.41 percent copper, 250 ppm zinc, 7 ppm silver, 700 ppm tin and 793 ppm tungsten (Kimball and others, 1978, p. C147, C172). MacKevett and others (1971, table 9, no. 74) found 150 ppm copper and 30 ppm molybdenum in a grab sample of an iron-stained granitic intrusion in the area.

Comment (Deposit): Other Comments = Moderately large occurrence of iron-stained granitic pluton and hornfelsed volcanic and sedimentary rocks, not adequately prospected. The area is Glacier Bay National Park and Preserve.

Comment (Geology): Geologic Description = Interlayered volcanic and sedimentary rocks of Permian age occur west of an approximately concordant granitic intrusion of Cretaceous age that extends northerly across Johns Hopkins Inlet (Brew and others, 1978, plate 1A). Kimball and others (1978) note intermixed diorite and mixed sedimentary and volcanic rocks in the area, and, at this occurrence, there is a conspicuous iron-stained zone about 0.25 mile wide. Grab samples (rock in place) contained from 10 to more than 30 ppm molybdenum (Kimball and others, 1978, fig. C38, p. C147-149). A selected sample (7S044) from a thin (0.2 foot) lens of pyrrhotite in sulfidized volcanics contained 1300 ppm copper, 30 ppm molybdenum, 1.5 ppm silver, and >0.05 ppm gold. A float sample of hornfels (Kimball and others, 1978, location 30, p. C172) from the same area contained 4100 ppm copper, 7 ppm silver, 0.15 ppm gold, 700 ppm tin and 793 ppm tungsten. The sample contained visible chalcopyrite and pyrrhotite.

Comment (Deposit): Model Name = Skarn, massive sulfide type.

Comment (Exploration): Status = Inactive

References

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): 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.

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