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Thetis Prospects, Chichagof District, Sitka Borough, Alaska, USA

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Location: There may be several old workings in the vicinity and the location used here is an adit that was found by Bittenbender and others (1999) The Thetis prospect is at an elevation of about 850 feet, about 0.7 mile north-northeast of Mount Verstovia in the NW1/4SW1/4 sec. 28, T. 55 S., R. 64 E. The prospect is location P-115 of Bittenbender and others (1999), location 55 of Cobb (1972, 1978), and MAS no. 0021140016 (U.S. Bureau of Land Management, 2002). The location is probably accurate but Cobb (1972, 1978) places it about a mile to the northeast based on a 1898 map by Becker that is probably more diagrammatic than precise.
Geology: The Thesis prospect was located in 1888 (DeArmond 1997). By 1898, the prospect had been developed by two adits, a sawmill, and 2 prospecting mills (Becker, 1898). He described the deposit as a reticulated quartz vein 2 1/2 feet thick with calcite, pyrrhotite, and galena. A mill test of the ore indicated that it contained about $7 in gold (about 0.35 ounce of gold per ton) and $1 in silver. Becker described the host rock as schistose diorite. But modern mapping by Loney and others (1975) assign the rocks to the Jurassic and Triassic, Khaz Formation which consists of graywacke, greenschist, metachert, phyllite, and minor limestone--all cataclastically deformed. Bittenbender and others (1999) located and sampled a 30-foot adit here that cut a quartz vein less than a foot thick, and several thin quartz veinlets The gold values in 4 samples were below the detection limit.
Workings: In 1898, the workings consists of two adits, a sawmill, and two prospecting mills. One 30-foot adit was located by Bittenbender and others (1999).
Age: Triassic or younger based on the age of the host rock.
Production: Apparently none.

Commodities (Major) - Au, Pb
Development Status: None
Deposit Model: Low-sulfide gold-quartz vein (Cox and Singer, 1986; model 36a).

Mineral List

5 entries listed. 5 valid minerals.

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Becker, G.F., 1898, Reconnaissance of some gold fields of southern Alaska, with some notes on general geology: U.S. Geological Survey 18th annual report, Part 3, p. 7-86. Bittenbender, P., Still, J.C., Maas, K., and McDonald, M., Jr., 1999, Mineral resources of the Chichagof and Baranof Islands area, southeast Alaska: Bureau of Land Management, BLM-Alaska Technical Report 19, 222 p. Cobb, E.H., 1972, Metallic mineral resources map of the Sitka quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-467, scale 1:250,000. Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Sitka quadrangle: U.S. Geological Survey Open-File Report 78-450, 124 p. DeArmond, R.N., 1997, Haleys and Silver Bay, in Around and About Alaska: Sitka Sentinel, series of 29 Articles, April to October, 1997. Loney, R.A., Brew, D.A., Muffler, L.J.P., and Pomeroy, J.S., 1975, Reconnaissance geology of Chichagof, Baranof, and Kruzof Islands, southeastern Alaska: U.S. Geological Survey Professional Paper 792, 105 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]

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