Unnamed Occurrences (ARDF - KC173), Crab Bay, Annette Island, Ketchikan District, Prince of Wales-Outer Ketchikan Borough, Alaska, USA
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Geology: The country rocks in the area of the site are recrystallized, locally phyllitic, rhyolite, and massive, dolomitic limestone that conformably overlies the rhyolite (Berg, 1972 [I 684]; Berg and others, 1988). These Upper Triassic rocks were regionally metamorphosed to greenschist grade in Late Cretaceous time. The occurrences are quartz fissure veins in dolomite and at a dolomite-rhyolite contact (Karl, 1992a-d). The veins, which contain barite, galena, and sphalerite, have the character of ladder veins, and are most abundant at the dolomite-rhyolite contact. At a locality informally called 'Cave Creek,' exploration in the 1970s by private interests showed galena and sphalerite in quartz veins up to 3 feet thick, as well as disseminated galena and sphalerite, in a 75-foot-wide zone in dolomite. Their exploration reportedly also showed two other occurrences of sulfide-bearing quartz veins at the dolomite-rhyolite contact. A sample of a quartz vein contained 5000 ppm Ba (Karl, 1992, loc. 32a-d).
Workings: At a locality informally called 'Cave Creek,' exploration in the 1970s by private interests showed galena and sphalerite in quartz veins up to 3 feet thick, as well as disseminated galena and sphalerite, in a 75-foot-wide zone in dolomite. Their exploration reportedly also showed two other occurrences of sulfide-bearing quartz veins at the dolomite-rhyolite contact. A sample of a quartz vein contained 5000 ppm Ba (Karl, 1992, loc. 32a-d).
Age: Probably Late Cretaceous or younger.
Alteration: Dolomitization of limestone country rock.
Commodities (Major) - Ag, barite, Pb, Zn
Development Status: None
Deposit Model: Polymetallic veins (Cox and Singer, 1986; model 22c)
Mineral List
4 entries listed. 4 valid minerals.
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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. Karl, S.M., 1992, Map and table of mineral deposits on Annette Island, Alaska: U.S. Geological Survey Open-File Report 92-690, 57 p., 1 map, scale 1:63,360.