Unnamed Occurrence (ARDF - KC051; east of Swan Lake), Ketchikan District, Ketchikan Gateway Borough, Alaska, USA
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Location: This occurrence is about 2.0 miles east of Swan Lake, on the crest of a north-northeast-trending ridge at an elevation of 3650 feet. The site is on the boundary between sections 19 and 20, T. 72 S., R. 92 E., of the Copper River Meridian. It corresponds to loc. 50.1 in Elliott and others (1978). The location is accurate within 0.1 mile.
Geology: The country rocks near this prospect are pelitic schist and gneiss, and subordinate andesitic and basaltic metavolcanic rocks, that are intruded by Cretaceous stocks, sills, and dikes of feldspar-porphyritic granodiorite, and by small metadiorite plutons of undetermined age (Berg and others, 1988). The strata were regionally metamorphosed to upper greenschist or amphibolite grade in Cretaceous time, and, near some of the granodiorite contacts, subsequently contact metamorphosed to hornblende hornfels. The premetamorphic age range of the strata is unknown. Berg and others (1988, p. 17) assigned them an undivided Mesozoic or Paleozoic age. More recent studies suggest that at least some of the strata may be as old as Precambrian (Crawford and others, 2000). This occurrence consists of sparsely disseminated, minute particles of molybdenite in a rusty-weathering, 45-foot-thick granodiorite(?) sill that intrudes pelitic paragneiss (Elliott and others, 1978). An analysis of the molybdenite-bearing rock showed 150 ppm Mo (Koch and Elliott, 1978 [OFR 78-156A]). The molybdenite may be a late-stage hydrothermal mineral in the granodiorite.
Workings: An analysis of the molybdenite-bearing rock showed 150 ppm Mo (Koch and Elliott, 1978 [OFR 78-156A]).
Age: Cretaceous?
Alteration: Locally conspicuous iron-staining.
Commodities (Major) - Mo
Development Status: None
Deposit Model: Porphyry Mo, low-F? (Cox and Singer, 1986; model 21b)
Mineral List
1 entry listed. 1 valid mineral.
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References
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. Koch, R.D., and Elliott, R.L., 1978, Analyses of rock samples from Ketchikan quadrangle, southeastern Alaska: U.S. Geological Survey Open-File Report 78-156-A, 162 p., 1 sheet, scale l:250,000.
