Unnamed Occurrence (ARDF - KC017), Misty Fiords National Monument, Ketchikan District, Prince of Wales-Outer Ketchikan Borough, Alaska, USA
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Location: This occurrence is at an elevation of about 100 feet in the canyon walls of the stream draining Leduc Lake, just before the stream enters Leduc River, 2 miles above its confluence with Chickamin River. The site is in section 36, T. 68 S., R. 94 E., of the Copper River Meridian. It corresponds to loc. 17 in Elliott and others (1978). The location is accurate within about 0.1 mile.
Geology: The country rocks in the area of this occurrence are pelitic paragneiss, subordinate quartzofeldspathic paragneiss, and minor marble. These metamorphic rocks form roof pendants, screens, and inclusions in Tertiary or Cretaceous foliated granodiorite and quartz diorite of the Coast Range batholith (Berg and others, 1977, p. 124-126; Berg and others, 1988). The metamorphic rocks probably represent marine argillaceous, clastic, and minor carbonate strata that underwent high-grade regional metamorphism in Cretaceous or Tertiary time. The premetamorphic age of the strata is uncertain, but they probably are mainly Paleozoic and may be as old as Precambrian (Berg and others, 1988, p. 26; Gehrels and others, 1990; Crawford and others, 2000). The occurrence is a poorly-exposed, rusty-weathering zone in paragneiss about 900-1800 feet wide and 2.5 miles long (Berg and others, 1977, area M-2, p. 124-126). Some of the rocks contain a little pyrrhotite and traces of chalcopyrite. Four chip samples of the accessible part of the zone, representing two separate horizons totalling about 200 feet thick, contained 30-160 ppm Cu, 10-90 ppm Pb, 80-400 ppm Zn, 5-50 ppm Mo, and 0.5-2.0 ppm Ag. A six-foot-thick layer of graphitic marble contained negligible amounts of these metals.
Workings: Four chip samples of the accessible part of the iron-stained zone, representing two separate horizons totalling about 200 feet thick, yielded values of 30-160 ppm Cu, 10-90 ppm Pb, 80-400 ppm Zn, 5-50 ppm Mo, and 0.5-2.0 ppm Ag (Berg and others, 1977, p. 124-126). A six-foot-thick layer of graphitic marble contained negligible amounts of these metals.
Alteration: Locally conspicuous iron-staining.
Commodities (Major) - Cu; (Minor) - Ag, Mo, Pb, Zn
Development Status: None
Deposit Model: Disseminated base-metal sulfides in metamorphic roof pendant
2 entries listed. 2 valid minerals.
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Berg, H.C., Elliott, R.L., Smith, J.G., Pittman, T.L., and Kimball, A. L., 1977, Mineral resources of the Granite Fiords Wilderness Study Area, Alaska, with a section on aeromagnetic data by Andrew Griscom: U.S. Geological Survey Bulletin 1403, 151 p. 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. Crawford, M.L., Crawford, W.A., and Gehrels, G.E., 2000, Terrane assembly and structural relationships in the eastern Prince Rupert quadrangle, British Columbia, in H.H. Stowell and W.C.McClelland, eds., Tectonics of the Coast Mountains, southeastern Alaska and British Columbia: Geological Society of America Special Paper 343, p. 1-21. Elliott, R.L., Berg, H.C., and Karl, S.M., 1978, map and table describing metalliferous and selected non-metalliferous mineral deposits, Ketchikan and Prince Rupert quadrangles, Alaska: U.S. Geological Survey Open-File Report 78-73-B, 17 p., 1 sheet, scale 1:250,000. Gehrels, G.E., McClelland, W.C., Samson, S.D., Patchett, P.J., and Jackson, J.L., 1990, Ancient continental margin assemblage in the northern Coast Mountains, southeast Alaska and northwest Canada: Geology, v. 18, no. 3, p. 208-211.