Brewster

Mine, Inactive

Alternative names

Brewster Quartz

Commodities and mineralogy

Main commodities Au
Other commodities Cu; Pb; Zn
Ore minerals chalcopyrite; galena; gold; pyrite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale SR
Quadrangle map, 1:63,360-scale C-6
Latitude 60.6694
Longitude -149.2452
Nearby scientific data Find additional scientific data near this location
Location and accuracy The mine is at an elevation of 1,750 feet, on Groundhog Creek, about a half-mile from the confluence of Bench Creek. It is in the E1/2 or NE1/4 section 27, T. 7 N., R. 1 W., of the Seward Meridian. A one-mile trail reportedly exists from the confluence to the workings. This location is accurate to within 300 feet. This is location 34 of Cobb and Richter (1972), location 23 of MacKevett and Holloway (1977), location 35 of Cobb and Tysdal (1980), and location S-271 of Jansons and others (1984).

Geologic setting

Geologic description

The host rock at the Brewster mine is slate and graywacke of the Valdez Group of Late Cretaceous age (Cobb and Tysdal, 1980). Bedding of the sedimentary country rock strikes S20W.
This deposit consists of discontinuous sulfide-bearing pods and stringers of quartz that are localized along a fault that strikes N 15 to 20 E and dips vertically. The hanging wall of the fault is slate and the footwall is graywacke. The quartz in the wider pods is coarsely crystalline and includes small cavities lined with interlocking quartz crystals. The sulfide minerals are sparse and include chalcopyrite, galena, sphalerite, and pyrite. Some specimens contain visible gold, and select ore yields some free gold on panning (Wimmler, 1926).
Workings consist of a 65-foot adit and a 10-foot drift. A small prospector mill was erected on the site in 1926.
Geologic map unit (-149.247325548988, 60.6688216331708)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Cretaceous or younger; the veins cut rocks of the Valdez Group of Late Cretaceous age.

Production and reserves

Workings or exploration
Workings consist of a 65-foot adit and a 10-foot drift. The adit bears N20W and the drift bears N70W (Wimmler, 1926). A small prospector mill was erected on the site in 1926. The mill consisted of a laboratory-size jaw crusher, an Ellis Independence ball mill, and an amalgamator. A two-horsepower gasoline engine provided the power to run the mill.
No assay results are reported, although in 1926 ten tons of ore was estimated to contain $150 of gold (Wimmler, 1926) or about 5 to 10 ounces of gold (Jansons and others, 1984).
The U.S. Bureau of Mines searched for the prospect in 1980 and 1982 but did not find it (Hoekzema and Sherman, 1983).
Indication of production Yes; small
Production notes Reported production is 5 to 10 ounces of gold (Jansons and others, 1984).

Additional comments

The deposit offers no encouragement for further development (Wimmler, 1926).

References

MRDS Number A010367

References

Hoekzema, R.P., and Sherman, G.E., 1983, Mineral investigations in the Chugach National Forest, Alaska (Peninsula study area): U.S. Bureau of Mines in-house report; held at U.S. Bureau of Land Management Alaska State Office, Anchorage, 524 p.
Reporters Jeff A. Huber (Anchorage)
Last report date 3/9/2000