Mount Brock

Occurrence, Inactive

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

Schorr, A.E., 1991, Alaska Place Names, 4th edition: Anchorage, Alaska, The Denali Press, 191 p.
Reporters T.C. Crafford (T. Crafford & Associates, Anchorage)
Last report date 2/4/2001