|Quadrangle map, 1:250,000-scale||SI|
|Quadrangle map, 1:63,360-scale||B-1|
|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 descriptionThe 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.|
|Workings or exploration||The deposit was explored before 1904 by several trenches.|
|Indication of production||None|
Additional commentsThe prospect is now within the Wilderness Area of the Admiralty Island National Monument that is closed to mineral exploration and development.
Berg, H.C., and Cobb, E.H., 1967, Metalliferous lode deposits of Alaska: U.S. Geological Survey Bulletin 1246, 254 p.
Herbert, C.F., and Race, W.H., 1964, Geochemical investigations of selected areas in southeastern Alaska, 1964: Alaska Division of Mines and Minerals Geochemical Report 1, 75 p.
Herbert, C.F., and Race, W.H., 1965, Geochemical investigations of selected areas in southeastern Alaska, 1964 and 1965: Alaska Division of Mines and Minerals Geochemical Report 6, 67 p., 4 sheets, scale 1:63,360.
Lathram, E.H., Loney, R.A., Berg, H.C., and Pomeroy, J.S., 1960, Progress map of the geology of Admiralty Island, Alaska: U.S. Geological Survey Miscellaneous Investigations Map I-323, 1 sheet, scale 1:250,000.
Loney, R.A., 1964, Stratigraphy and petrography of the Pybus-Gambier area, Admiralty Island, Alaska: U.S. Geological Survey Bulletin 1178, 103 p.
Race, W.H., and Rose, A.W., 1967, Geochemical and geological investigations of Admiralty Island, southeastern Alaska: Alaska Division of Geological and Geophysical Surveys, Geochemical Report 8, 45 p.
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]
Wright, C.W., 1906, A reconnaissance of Admiralty Island, in Spencer, A.C. and Wright, C.W., The Juneau Gold Belt, Alaska; and A Reconnaissance of Admiralty Island, Alaska: U. S. Geological Survey Bulletin 287, p. 138-161.
|Reporters||Donald Grybeck (U.S. Geological Survey)|
|Last report date||5/5/2005|