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Congress

Prospect, Undetermined

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Commodities and mineralogy

Main commodities Cu
Other commodities Zn
Ore minerals chalcopyrite; pyrrhotite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale SI
Quadrangle map, 1:63,360-scale C-7
Latitude 57.731
Longitude -136.2817
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Congress prospect is at sea level about 0.4 mile northwest of the south tip of Hill Island. The prospect is near the southeast corner of sec. 2, T. 48 S., R. 56 E. It is location P-52 of Bittenbender and others (1999), location 24 of Cobb (1972, 1978), and MAS no. 0021140027 (U.S. Bureau of Land Management, 2002). The location is accurate within 0.2 mile.

Geologic setting

Geologic description

Johnson and Karl (1985) map the rocks in the area of this prospect as hornfelsed, Cretaceous graywacke and argillite interbedded with sparse, lenticular beds of recrystallized basalt ('greenstone'). The formation is cut by many steeply-dipping, mainly northwest-striking faults.
Cobb (1978), citing Overbeck (1919) and Reed and Coats (1941), reports that the prospect is a sulfide-bearing lens of schistose greenstone in graywacke. The sulfides are sparse chalcopyrite and pyrrhotite that occur in small quartz bodies and on foliation surfaces. The mineralized zone is 10 to 12 feet thick and was explored by a 25-foot tunnel.
Bittenbender and others (1999), citing Still and Weir (1981), describe this prospect as a copper- and zinc-bearing volcanogenic massive sulfide deposit in greenstone. A 12-foot zone of silicified greenstone contained 0.58 percent copper and 0.086 percent zinc.
Geologic map unit (-136.283530617571, 57.7306275161543)
Mineral deposit model Volcanogenic massive-sulfide deposit?
Alteration of deposit Greenstone is silicified.

Production and reserves

Workings or exploration The deposit was explored by a 25-foot-long tunnel (Cobb, 1978).
Indication of production Undetermined

Additional comments

The prospect is in West Chichagof-Yakobi Wilderness.

References

MRDS Number A013262

References

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.
Overbeck, R.M., 1919, Geology and mineral resources of the west coast of Chichagof Island: U.S. Geological Survey Bulletin 692-B, p. 91-136.
Reed, J.C., and Coats, R.R., 1941, Geology and ore deposits of the Chichagof mining district, Alaska: U.S. Geological Survey Bulletin 929, 148 p.
Still, J.C., and Weir, K.R., 1981, Mineral land assessment of the west portion of western Chichagof Island, Southeast Alaska: U.S. Bureau of Mines Open-File Report 89-81, 269 p., 12 sheets.
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]
Reporters H.C. Berg (U.S. Geological Survey)
Last report date 10/16/2004