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Mount Brock

Occurrence, Inactive

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Alternative names

Mount Brack

Commodities and mineralogy

Main commodities Ag; Cu; Pb; Zn
Other commodities Au; Sb
Ore minerals arsenopyrite; chalcopyrite; galena; pyrite; sphalerite
Gangue minerals ankerite; calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale SK
Quadrangle map, 1:63,360-scale A-4
Latitude 59.11
Longitude -136.28
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is in Glacier Bay National Park and Preserve about 0.8 miles northwest of the summit of Mount Brock; it is on a ridgetop at an elevation of approximately 3,900 feet. It corresponds to location 6 of Cobb (1972 [MF424]). A more detailed location is shown in Figure C-67 of Brew and others (1978). Note: Mount Brock is shown on some maps as Mount Brack. Schorr (1991) asserts that the correct name is Mount Brock, named for Canadian geologist R.W. Brock who visited Muir Inlet in 1913.

Geologic setting

Geologic description

The following description is summarized from Brew and others (1978).
The prospect consists of hydrothermal quartz-calcite veins 0.1- to 1.8-foot thick that contain chalcopyrite, sphalerite, galena, pyrite, arsenopyrite, and ankerite in Devonian and Permian andesite, graywacke, limestone, hornfels, and siltstone. The veins strike north and dip to the east. Altered zones (presumably altered zones around or between the veins) are sparsely mineralized. The veins contain up to 1.3% copper, 0.9% lead, 4.2% zinc, 0.7% antimony, 70 ppm silver, and traces of gold. The mineralization must be younger than the Permian age of some of the host rocks and is probably the same age as nearby Cretaceous intrusive rocks.
Geologic map unit (-136.281890181622, 59.1096094317392)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c?
Age of mineralization No older than Permian based on age of host rocks and probably Cretaceous, based on the age of nearby intrusive rocks (Brew and others, 1978).
Alteration of deposit Alteration is mentioned but not described.

Production and reserves

Indication of production None
Reserve estimates According to Brew and others (1978), the individual veins are neither rich enough nor extensive enough to be economic and the veins are not close enough together to be mined as a unit.

Additional comments

The deposit is within Glacier Bay National Park and Preserve where exploration and development is restricted.

References

MRDS Number A013120

References

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 1:600,000.
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 Skagway quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-424, 1 sheet, scale 1:250,000.
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.
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 67-151, 176 p.
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.
Schorr, A.E., 1991, Alaska Place Names, 4th edition: Anchorage, Alaska, The Denali Press, 191 p.
Still, J.C., 1991, Section B: Glacier Bay subarea, in U.S. Bureau of Mines, Mineral investigations in the Juneau Mining District, Alaska, 1984-1988: Volume 2 - Detailed mine, prospect, and mineral occurrence descriptions: U.S. Bureau of Mines Special Publication VOL. 2B, 69 p., 3 sheets.
Reporters T.C. Crafford (T. Crafford & Associates, Anchorage)
Last report date 2/4/2001