Sweepstake Prospect (Mining Co.), Prince William Sound Mining District, Valdez-Cordova Census Area, Alaska, USAi

Regional Level Types
Sweepstake Prospect (Mining Co.)	Prospect
Prince William Sound Mining District	Mining District
Valdez-Cordova Census Area	Census Area
Alaska	State
USA	Country

Location: This prospect is located between 1,600 and 1,800 feet elevation on the northeast valley wall of Avery River, about 2 miles east of Port Wells. It is in the N1/2 section 6, T. 10 N., R. 9 E., of the Seward Meridian. This is location 94 of Condon and Cass (1958), location 82 of Cobb and Richter (1972), location 94 of MacKevett and Holloway (1977), location 148 of Cobb and Tysdal (1980), and location S-140 of Jansons and others (1984). This location is accurate to within half a mile.
Geology: The host rock at this prospect is sedimentary strata of the Valdez Group of Late Cretaceous age (Cobb and Tysdal, 1980). The deposit consists of quartz veins containing arsenopyrite, pyrite, pyrrhotite, chalcopyrite, and gold. Minor gangue minerals include brown-weathering carbonate, feldspar, and chlorite. The workings consist of a 110-foot adit at 1,600 feet elevation, a shaft at 1,630 feet elevation, a 22-foot adit at 1,700 feet elevation, and a shaft at 1,800 feet elevation. Improvements included a two-stamp mill. The upper shaft was sunk on a 5-foot-wide shear zone with a 16- to 18-inch-wide quartz vein. The shear strikes N65W and dips 45W. About 20 feet northwest of the shaft, the vein pinches out to four inches wide and occurs along the hanging wall of the shear (Johnson, 1914 [B 592-G, p. 219-220]). The veining in the lower working is described as thin, discontinuous, quartz veins generally parallel to the shear margins. Some ore was shipped from the lower shaft in 1912 (Johnson, 1914 [B 592-G, p. 219-220]). No assay results are reported.
Workings: The workings consist of a 110-foot adit at 1,600 feet elevation, a shaft at 1,630 feet elevation, a 22-foot adit at 1,700 feet elevation, and a shaft at 1,800 feet elevation. A Hammond two-stamp mill crushed ore, which then passed across three face plates and then on to a concentrate table (Hoekzema and Sherman, 1983). The U.S. Bureau of Mines collected seven chip samples in 1979 and 1980. The samples contained from nil to 35 ppm gold. The 35-ppm chip sample was taken from a surface outcrop near the shaft (Hoekzema and Sherman, 1983). The U.S. Bureau of Mines sampled the exposed vein and short adit in 1979 and 1980. Five grab samples contained as much as a trace of gold and silver. A select grab sample contained 1.02 ounces of gold per ton and 1.05 ounces of silver per ton. A 24-inch chip sample contained 0.25 ounce of gold per ton and 0.24 ounce of silver per ton (Jansons and others, 1984).
Age: Cretaceous or younger; the veins cut rocks of the Valdez Group of Late Cretaceous age.
Alteration: Sulfides locally altered to limonite.
Production: Several tons of ore of the best ore were shipped about March of 1912 (Johnson, 1914 [B 592-G, p. 219]), but the returns were not made public. Tysdal (1978 (MF-880A]) estimated a total recovery from this deposit of less than 769 ounces of gold.
Reserves: The U.S. Bureau of Mines estimated a resource of 500 tons of ore with a grade of 0.3 ounce each of gold and silver per ton (Hoekzema and Sherman, 1983).

Commodities (Major) - Au, Cu; (Minor) - Ag
Development Status: Yes; small
Deposit Model: Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)

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Link to USGS - Alaska:	SR101

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References