Unnamed Occurrences (ARDF - DE053), Nichols Bay, Prince of Wales Island, Ketchikan District, Prince of Wales-Outer Ketchikan Borough, Alaska, USA
Location: This site represents two geologically similar occurrences along the west shoreline of Nichols Bay about 1.6 and 2.0 miles north-northwest of Point Nunez. One is near the center of section 4, T. 83 S., R. 89 E. The other, at the coordinates, is about at the center of the north boundary of the same section.
Geology: This site, first described by Gehrels and others (1983), represents two occurrences, about a half mile apart, in Silurian or Ordovician (Descon Formation) strata (Gehrels, 1992). The northern occurrence consists of several centimeter-thick, pyrite-rich layers in fragmental silicic volcanic rocks. Samples contained up to 0.5 parts per million (ppm) silver and 140 ppm zinc. The 10-meter-wide unit that contains the pyrite-rich layers may extend to the southern occurrence. The southern occurrence consists of several 2- to 6-centimeter-thick lenses that contain much pyrite and microscopic sphalerite, in locally fragmental, silicic volcanic rocks. The mineralized rock is interbedded with andesitic pillow breccia and massive flows; andesite dikes cut the mineralized lenses. Samples contained up to 0.7 ppm silver and 140 ppm zinc.
Workings: Only outcrop sampling.
Age: The massive-sulfide layers are contemporaneous with the deposition of the Silurian or Ordovician Descon Formation.
Commodities (Major) - Zn; (Minor) - Ag
Development Status: None
Deposit Model: Kuroko massive sulfide (Cox and Singer, 1986; model 28a).
| Pyrite|| Sphalerite|
2 entries listed. 2 valid minerals.
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Gehrels, G. E., 1992, Geologic map of southern Prince of Wales Island, southeastern Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-2169, 23 p., 1 sheet, scale 1:63,360. Gehrels, G. E., Berg, H. C., and Saleeby, J. B., 1983, Ordovician-Silurian volcanogenic marine sulfide deposits on southern Prince of Wales Island and the Barrier Islands, southeastern Alaska: U.S. Geological Survey Open-File Report 83-318, 10 p., 1 sheet.
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