Shumagin; Choumagin Prospect, Alaska Peninsula District, Aleutians East Borough, Alaska, USA

Location: This prospect is at an elevation of about 300 feet, approximately 2,500 feet southwest of the head of Baralof Bay (Berg and Cobb, 1967, locality 7; Cobb, 1972 [MF 433], locality 4; MacKevett and Holloway, 1977, locality 4; Nokleberg and others, 1987, locality AP5; Wilson and others, 1988, locality 4). It is in the SE1/4 of sec. 19, T. 57 S., R. 74 W., of the Seward Meridian. This location is accurate.
Geology: The Shumagin gold deposit occurs in the Eocene to Oligocene Popof volcanic rocks (Wilson and others, 1995). The deposit is in the northeast section of the Aquila-Shumagin fault system, which strikes northeast across Unga Island. The deposit consists of auriferous, sulfide-bearing quartz-calcite veins in a fault that trends N 60 E and dips 80 to 85 southeast. The veins and fault can be traced approximately 4,000 feet along strike and to a depth of 765 feet. The mineralization is interpreted as a fault-controlled epithermal, volcanic-hosted vein deposit (White and Queen, 1989). The hanging wall is tuff, and the footwall is andesite. Movement on the fault is suggested to be high-angle reverse. The deposit comprises of four individual veins, two vein systems, and two fault breccia units. Within the fault, the mapped units from oldest to youngest are pyrite-rich cataclasite, clast-supported fault breccia, the Union vein, and matrix-supported quartz breccia (White and Queen, 1989). The total thickness of these units averages approximately 40 feet. Veins that are peripheral to or cut the main vein and fault system include the Lucky Friday and Greenbaum veins, the Vuggy Watercourse vein, and carbonate veins. Gold is most abundant in the Union vein, which generally is considered to be the principal gold deposit. The Union vein is a composite vein consisting of a 10-foot-wide zone of closely-spaced quartz veins in the hanging wall tuff. Individual veins are sinuous, vuggy, and generally less than 30 inches wide. Native gold occurs, with finely crystalline arsenopyrite, pyrite, galena, and sphalerite. Precious-metal grades range from a trace throughout wide zones to more than 10 ounces of gold and 150 ounces of silver per ton in narrow zones. A strong correlation exists between gold, silver, and tellurium, indicating that some of the precious metals probably occur as tellurides (White and Queen, 1989). Singer (1999) suggests that this is a Sado-type gold deposit. Atwood (1909) first described the prospect, whose workings at that time consisted of two tunnels 150 feet apart vertically. The lower one was 365 feet in length with a 75-foot crosscut. The upper tunnel was 79 feet in length with a 169-foot crosscut. During the period 1983 to 1987, Alaska Apollo Gold Mines diamond drilled 23 holes totalling 9,269 feet, drilled 44 percussion holes, and cut 13 trenches through the vein and fault. At that time the deposit was estimated to contain 300,000 tons of ore grading 0.5 ounce of gold per ton. In 1989 Ballatar Exploration core-drilled approximately 6,000 feet into the deposit. In 1986 Battle Mountain Exploration Company mapped and sampled the deposit and relogged the core. Analysis of the data indicated an ore shoot approximately 400 feet long, 5 to 30 feet thick, and plunging 45 degrees to the northeast in the plane of the fault (Ellis and Apel, 1990). A deep hole drilled by Alaska Apollo Gold Mines into the shoot cut 27 feet of rock containing 0.46 ounce of gold per ton at 600 feet down dip. The deposit was estimated by Battle Mountain Exploration company to contain 352,000 tons of ore grading 0.299 ounce of gold per ton. In 1990 Battle Mountain Exploration Company drilled a 1,022-foot core hole collared on Aleut Corporation land and inclined to hit the deposit at depth. The hole cut 18 feet of rock containing 0.47 ounce of gold per ton at 900 feet. In 1987 during road building, a 500-foot-long, faulted eastern extension of the Shumagin vein was uncovered, mostly on Aleut Corporation land. Battle Mountain Exploration Company mapped and sampled this section of vein. It was found to be a large, weakly mineralized, south-dipping vein structure, locally as much as 50 feet thick. Metal values obtained were as much as 680 ppb gold, 12.1 ppm silver, 234 ppm arsenic and 2,000 ppb mercury (Ellis and Apel, 1990).
Workings: Atwood (1909) described two tunnels with crosscuts at the time of his visit. During the period 1983-1987 Alaska-Apollo Gold Mines diamond drilled 23 holes totalling 9,269 feet. They also drilled 44 percussion holes and cut 13 trenches. In 1989 Ballatar Exploration diamond drilled approximately 6,000 feet into the deposit. From 1986 to 1990 Battle Mountain Exploration Company mapped and sampled the deposit and logged the drill core. They also drilled a 1,022-foot hole into the deposit where it dips south beneath Aleut Corporation land. In 1987 and 1988 the deposit was mapped and sampled in detail by the U.S. Geological Survey and Alaska Apollo Gold Mines.
Age: Eocene or younger.
Alteration: Strong argillic alteration is present as much as 148 feet from the Shumagin deposit. Quartz-sericite-pyrite alteration adjoins the Union vein and the matrix-supported quartz breccia. The presence of adularia is suspected (White and Queen, 1989). There are indications of a broad aureole of mercury and arsenic as much as 250 feet from the Union vein.
Reserves: A resource of 300,000 tons grading 0.5 ounce of gold per ton was estimated from the exploration work done by Alaska Apollo Gold Mines in 1983 to 1987. Battle Mountain Exploration Company evaluated the deposit in 1986 at 352,000 tons grading 0.299 ounce of gold per ton. Queen (1988) estimated a resource of 270,000 tons grading 0.49 ounce of gold and 1.97 ounces of silver per ton.

Commodities (Major) - Ag, Au; (Minor) - As, Cu, Hg, Pb, Te, Zn
Development Status: None
Deposit Model: Sado epithermal gold vein (Cox and Singer, 1986; model 25d)

References:
Angeloni, L.M., Wilson, F.H., and Sutley, Stephen, 1985, Map and tables showing preliminary rock geochemical data, Port Moller, Stepovak Bay, and Simeonof Island quadrangles, Alaska: U.S. Geological Survey Open-File Report 85-470, 179 p., 1 sheet, scale 1:250,000. Atwood, W.W., 1909, Mineral resources of southwest Alaska, in Brooks, A.H., and others, Mineral resources of Alaska in 1908: U.S. Geological Survey Bulletin 379, p. 108-152. Atwood, W.W., 1911, Geology and mineral resources of parts of the Alaska Peninsula: U.S. Geological Survey Bulletin 467, 137 p. Berg, H.C., and Cobb, E.H., 1967, Metalliferous lode deposits of Alaska: U.S. Geological Survey Bulletin 1246, 254 p. Cobb, E.H., 1972, Metallic mineral resources map of the Port Moller quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-443, 1 sheet, scale 1:250,000. Cobb, E.H., 1980, Summaries of data and lists of references to metallic and selected nonmetallic mineral deposits in fifteen quadrangles in southwestern and west-central Alaska: U.S. Geological Survey Open-File Report 80-909, 103 p. Ellis, W.T., and Apel, R.A., 1989, Unga/Alaska Peninsula 1989 final report: Battle Mountain Exploration Company report, 41 p., 28 map sheets at various scales. (Report held by the Aleut Corporation, Anchorage, Alaska.) Ellis, W.T., and Apel, R.A., 1990, Unga/Alaska Peninsula 1990 final report: Battle Mountain Exploration Company report, 49 p., 29 map sheets at various scales. (Report held by the Aleut Corporation, Anchorage, Alaska.) MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous mineral deposits in the western part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-F, 38 p., 1 sheet, scale 1:1,000,000. Martin, G.C., 1905, Gold deposits of the Shumagin Islands, in Brooks A.H., and others, Mineral resources of Alaska in 1904: U.S. Geological Survey Bulletin 259, p. 100-101. Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, D.J., Robinson, M.S., Smith, T.E., and Yeend, W., 1987, Significant metalliferous lode deposits and placer districts of Alaska: U.S. Geological Survey Bulletin 1786, 104 p., 2 plates, scale 1:5,000,000. Queen, L.D., 1988, Geologic report on Shumagin claims, Unga Island, Alaska: Report for Alaska Apollo Gold Mines, 7 p. (Unpublished report held by the U.S. Geological Survey, Anchorage) Riehle, J.R., ed., 1999, Introduction to the present study, previous studies, and a descriptive summary of the vein systems and their production history, 10 p., in A Geological and geophysical study of the gold-silver vein system of Unga Island, southwestern Alaska: U.S. Geological Survey Open-File Report 99-136, CD-ROM. Singer, D.A., 1999, Classifying the Shumagin and Alaska Apollo deposits, in Riehle, J.R., ed., A geological and geophysical setting of the gold-silver vein system of Unga Island, southwestern Alaska: U.S. Geological Survey Open-File Report 99-136, 6 p., CD-ROM. Webber, B.S., Moss, J.M., Rutledge, F.A., and Sanford, R.S., 1946, Reconnaissance examinations of parts of the Alaska Peninsula and Aleutian Islands southwestern Alaska: U.S. Bureau of Mines, unpublished report of investigations, 40 p. (Report held by the U.S. Geological Survey, Anchorage.) Wedow, Helmuth, Jr., White, M.G., and Moxham, R.M., 1952, Interim report on an appraisal of the uranium possibilities of Alaska: U.S. Geological Survey Open-File Report 52-165, 124 p. White, W.H., and Queen, L.D., 1989, Preliminary geologic and rock-chip geochemical data from drill core and trenches at the Shumagin gold deposit, Unga Island, Alaska: U.S. Geological Survey Open-File Report 89-361, 36 p. White, W.H., and Queen, L.D., 1996, Description of the Shumagin epithermal gold vein deposit, in Wilson, F.H., White, W.H., Detterman, R.L., and Case, J.E., Maps showing the resource assessment of the Port Moller, Stepovak Bay, and Simeonof Island quadrangles, Alaska Peninsula: U.S. Geological Survey Miscellaneous Field Studies Map MF-2155-F, 45 p., 2 map sheets, scale 1:250,000. Wilson, F.H., Detterman, R.L., Miller, J. W., and Case, J.E., 1995, Geologic map of the Port Moller, Stepovak Bay, and Simeonof Island quadrangles, Alaska: U.S. Geological Survey Miscellaneous Investigation Series Map I-2272, 1 sheet, scale 1:250,000. Wilson, F.H., White, W.H., and DuBois, G.D., 1988, Brief descriptions of mines, prospects, and mineral occurrences in the Port Moller and Stepovak Bay quadrangles, Alaska Peninsula: U.S. Geological Survey Open-File Report 88-666, 128 p., 1 plate, scale 1:250,000.