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Unnamed (near Sylburn Harbor)

Occurrences, Undetermined

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Commodities and mineralogy

Main commodities Ag; barite; Pb; Zn
Ore minerals barite; galena; pyrite; sphalerite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale A-5
Latitude 55.174
Longitude -131.574
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site represents six occurrences near the north base of the peninsula between Sylburn Harbor and Port Chester. The occurrences are in sections 20 and 21, T. 77 S., R. 92 E., of the Copper River Meridian. The map site is at the approximate center of this group of occurrences. The site corresponds to loc. 20a-f in Karl (1992). The location is accurate within about 0.15 mile.

Geologic setting

Geologic description

The country rocks in the area of this site include recrystallized Upper Triassic carbonate and clastic rocks, rhyolite, and basalt; Silurian trondhjemite; and greenstone derived from undivided Silurian and Ordovician volcanic, sedimentary, and intrusive rocks (Berg, 1972 [I 684]; Berg and others, 1988; Karl, 1992). The rocks are folded and locally intensely sheared, sericitized, and permeated with hydrothermal hematite. The rocks were regionally metamorphosed to greenschist-grade phyllite and semischist in Late Cretaceous time.
The occurrences consist of quartz-barite-calcite-sulfide fissure veins as much as three feet thick, in sheared, siliceous phyllite, greenstone, rhyolite, and limestone (Karl, 1992, loc. 20a-f). Sulfide minerals, inferred from sample analyses, probably are mainly pyrite, galena, and sphalerite.
Samples of sulfide-bearing quartz, calcite, and barite veins contained up to 20 ppm Ag, 2% Pb, more than 1% Zn, and 100 ppm Ni; a sample of limestone contained 1000 ppm Ba, 100 ppm Pb, and 500 ppm Zn; a sample of greenstone contained 200 ppm Zn, 100 ppm Co, 100 ppm Cr, and 100 ppm Ni; and samples of rhyolite and rhyolite tuff breccia contained up to 1 ppm Ag, 1% Ba, and 200 ppm Cu (Karl, 1992, loc. 20a-f).
Geologic map unit (-131.575680041287, 55.1736556096929)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c)
Mineral deposit model number 22c
Age of mineralization Fissure veins probably are Late Cretaceous or younger.
Alteration of deposit Country rocks locally are sericitized and permeated with hydrothermal hematite.

Production and reserves

Workings or exploration Samples of sulfide-bearing quartz, calcite, and barite veins contained up to 20 ppm Ag, 2% Pb, more than 1% Zn, and 100 ppm Ni; a sample of limestone contained 1000 ppm Ba, 100 ppm Pb, and 500 ppm Zn; a sample of greenstone contained 200 ppm Zn, 100 ppm Co, 100 ppm Cr, and 100 ppm Ni; and samples of rhyolite and rhyolite tuff breccia contained up to 1 ppm Ag, 1% Ba, and 200 ppm Cu (Karl, 1992, loc. 20a-f).
Indication of production None

References

MRDS Number 10307685

References

Berg, H.C., 1972, Geologic map of Annette Island, Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-684, 8 p., 1 sheet, scale 1:63,360.
Berg, H.C., Elliott, R.L., and Koch, R.D., 1988, Geologic map of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Mineral Investigations Series Map I-1807, 27 p., scale 1:250,000.
Reporters H.C. Berg, USGS
Last report date 7/7/1999