Brown

Prospect, Inactive

Commodities and mineralogy

Main commodities Au; Cu
Ore minerals chalcopyrite; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale SI
Quadrangle map, 1:63,360-scale B-1
Latitude 57.4907
Longitude -134.119
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Brown prospect is at an elevation of about 1,000 feet, about 1.7 miles north of the southwest arm of Gambier Bay. The prospect is 0.4 mile southwest of the center of sec. 36, T. 50 S., R. 70 E. It is location 71 of Cobb (1972, 1978) and MAS no. 0021140035 (U.S. Bureau of Land Management, 2002). The location probably is accurate within 0.5 mile.

Geologic setting

Geologic description

The Brown prospect is near the contact of a thick Devonian marble unit within greenschist, phyllite, and metachert of the Devonian Gambier Bay Formation (Loney, 1964). The prospect has been mentioned several times over the years but apparently the only definitive descriptions are by Wright and Wright (1905) and Wright (1906). They describe the deposit as a 'ledge', a vein probably, that was exposed for more than 200 feet in open cuts. The host rock is mostly calcareous schist and the deposit is in brecciated limestone that is replaced by quartz with small masses of pyrite and chalcopyrite. Samples had low values in copper and gold. Apparently there has been little work on the prospect since the early part of the 20th century and Wright and Wright (1905) noted that it had not been active for several years before 1904.
Geologic map unit (-134.120736673344, 57.4903601875338)
Mineral deposit model Limestone replaced by quartz with low copper and gold values.
Age of mineralization Devonian or younger based on the age of the host rock.

Production and reserves

Workings or exploration The deposit was explored before 1904 by several trenches.
Indication of production None

Additional comments

The prospect is now within the Wilderness Area of the Admiralty Island National Monument that is closed to mineral exploration and development.

References

MRDS Number A013317

References

U.S. Bureau of Land Management, 2002, Alaska mineral locations database report (Sitka quadrangle), July 2, 2002, 205 p. [http://imcg.wr.usgs.gov/dem.html]
Reporters Donald Grybeck (U.S. Geological Survey)
Last report date 5/5/2005