Sedanka Island

Prospect, Inactive

Alternative names

Biorka

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale UN
Quadrangle map, 1:63,360-scale D-1
Latitude 53.7917
Longitude -166.2
Nearby scientific data Find additional scientific data near this location
Location and accuracy Locality is 4 km south of Biorka Village, 0.9 km east of Udamat Bay on Sedanka Island. The locality corresponds to locality 3 of Cobb (1972, MF-446), it is accurate within about 300 m. It is also equivalent in part to anomaly no. 15 of Christie (1974).

Geologic setting

Geologic description

Quartz and ankerite in nearly vertical veins in N 60øW striking fractures in diorite that forms hanging wall of fault that strikes N 80øE and dips 55øS. Richest mineralization near fault; fine-grained greenstone of footwall is barren. Veins contain sphalerite, abundant pyrite, a small amount of chalcopyrite and argentiferous(?) galena, and a small amount of gold. Pyrite also disseminated throughout diorite. Deposit along fault has been exposed for 70 m along strike, with mineralization zone a maximum of 18 m high and averaging more than 13 meters. Ore shoot extends at least 14 m beyond sampled zone, with fault traceable for at least 900 m west, and possibly 3.2 km east of mineralized zone, but no mineralization has been detected outside of the sampled area. Ores deposited at temperature below 138ø C (Drewes and others, 1961, p. 658).
Geologic map unit (-166.20190959098, 53.7908523139186)
Mineral deposit model Polymetallic vein
Mineral deposit model number 22c
Alteration of deposit Christie (1974) reports pervasive development of chlorite and minor sericite and quartz veinlets near diorite.

Production and reserves

Workings or exploration A 70 by 12 m area of tundra overburden was stripped by hydraulic methods and explosives, and 29 channel samples collected along strike of deposit for 75 m during USBM investigations in 1945 (Webber and others, 1946). Average analysis of 29 samples along narrow mineralized zone was 6.8 percent Zn. Average of 19 samples was 9.1 percent Zn, 0.24 percent Pb, 0.45 percent Cu, 0.04 oz/ton Au, 1.4 oz/ton Ag. Benefication tests showed that concentrates contained 0.3 percent Cd. Sampling in 1979 by Resource Associates of Alaska (Butherus, 1979) produced gold values ranging from 200 ppb to 12 ppm (0.348 oz/t). Christie (1974) did not visit the 'zinc' occurrence, however reconnaissance mapping in the area and limited sampling resulted in samples yielding up to 205 ppm copper, 1,000 ppm zinc, 3.1 ppm silver, and 0.34 ppm gold.
Indication of production None

References

MRDS Number A013233

References

Butherus, D.L., Gressitt, E.E., Pray, Jim, Corner, N.G., Lindberg, P.A., and Fankhauser, R.E., 1979, Exploration and evaluation of the Aleut Native Corporation Lands 1979: Unpublished Resource Associates of Alaska report prepared for Houston Oil and Minerals Corporation and available from The Aleut Corporation, 69 p., 1 appendix.
Randolph, D.B., 1991, Unalaska project, 1990 final report: Battle Mountain Exploration Company, Alaska District, 62 p., 5 appendices, 15 plates, various scales. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Reporters L.P. Niles; S.W. Bie; F.H. Wilson
Last report date 3/18/1996