Sedanka Island; Biorka Prospect, Aleutians Mining District, Aleutians West Census Area, Alaska, USAi

Regional Level Types
Sedanka Island; Biorka Prospect	Prospect
Aleutians Mining District	Mining District
Aleutians West Census Area	Census Area
Alaska	State
USA	Country

Location: 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).
Geology: Quartz and ankerite in nearly vertical veins in N 60oW striking fractures in diorite that forms hanging wall of fault that strikes N 80oE and dips 55oS. 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 138o C (Drewes and others, 1961, p. 658).
Workings: 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.
Alteration: Christie (1974) reports pervasive development of chlorite and minor sericite and quartz veinlets near diorite.

Commodities (Major) - Au, Ag, Cu, Zn; (Minor) - Cd, Pb
Development Status: No
Deposit Model: Polymetallic vein

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Link to USGS - Alaska:	UN005

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References