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Unnamed (Johns Hopkins Inlet)

Occurrence, Inactive

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Commodities and mineralogy

Main commodities Cu
Other commodities Ag; Au; Co; Mo
Ore minerals chalcopyrite; chrysocolla; limonite; malachite; molybdenite

Geographic location

Quadrangle map, 1:250,000-scale MF
Quadrangle map, 1:63,360-scale D-3
Latitude 58.9
Longitude -136.993
Nearby scientific data Find additional scientific data near this location
Location and accuracy The occurrence is on a north-facing point into Johns Hopkins Inlet, almost due south of Orange Point; it is in section 24, T. 34 S., R. 50 E., of the Copper River Meridian. The location is accurate to within 0.25 mile. The location is approximately the same as number 65 of MacKevett and others (1971), number 15 of Cobb (1972) and number 29 of Kimball and others (1978).

Geologic setting

Geologic description

Argillite, phyllite, and slate of Permian and Permian (?) age are cut by a small foliated granite pluton of Cretaceous age (Brew and others, 1978, plate IA). Kimball and others (1978, p. C149, fig. C38 ) reported volcanic rock, chert, and sulfides. MacKevett and others (1971, table 9, p. 52) reported a 100- to 200-foot wide altered zone in granitic rocks which extended several hundred feet on strike: fracture surfaces were stained with malachite, chrysocolla, and limonite.
A grab sample collected by the U.S. Geological Survey contained 1500 ppm copper and 30 ppm molybdenum. Float samples collected by the U.S. Bureau of Mines (Kimball and others, 1978) contained as much as 4,600 ppm copper, 7 ppm silver, and 0.05 ppm gold. A rock sample collected by the Bureau contained more than 2000 ppm molybdenum and 610 ppm copper.
Geologic map unit (-136.994879188644, 58.899593003767)
Mineral deposit model Mineralized shear zone; possible volcanogenic mineralization.
Age of mineralization Cretaceous?

Production and reserves

Workings or exploration There are no mine workings. A grab sample representative of a shear zone in granitic rock contained 1500 ppm copper and 30 ppm molybdenum (MacKevett and others, 1978, sample 65, table 9). The U.S. Bureau of Mines (Kimball and others, 1978) collected float samples at about 150 feet elevation, in an area underlain by hornfels, that contained 4600 ppm copper, 300 ppm cobalt, 7 ppm silver, and 0.05 gold (p. C-172). A selected sample of a veinlet in hornfels at about 300 feet elevation contained greater then 2000 ppm molybdenum and 610 ppm copper.
Indication of production None

Additional comments

The area has numerous iron-stained areas, contact zones, and has widespread weak geochemical anomalies in copper and molybdenum. Favorable area for contact or intrusive-related shear zone-type deposits. The area is in Glacier Bay National Park and Preserve.

References

MRDS Number A013142

References

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., 7 sheets.
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.
Cobb, E. H., 1981, Summaries of data and lists of references to metallic and selected non-metallic mineral occurrences in the Mt. Fairweather quadrangle, Alaska, Supplement to Open-file Report 78-316: U. S. Geological Survey Open-File Report 81-249B, 15 p.
Cobb, E.H., 1981, Summaries of data on and lists of references to metallic and selected nonmetallic mineral occurrences in the Mt. Fairweather 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 81-249-A, 20 p.
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.
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.
Reporters C.C. Hawley (Hawley Resource Group)
Last report date 4/8/1999