Unnamed Occurrence (ARDF - TL008), Yentna District, Matanuska-Susitna Borough, Alaska, USA

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This prospect is located within Denali National Park and Preserve.
Location: Reed and others (1978, locality 24 and 25) locate this occurrence in the southwest quarter of Section 25, T. 31 N., R. 14 W., of the Seward Meridian on a nunatak within the Dall Glacier in Denali National Park and Preserve.
Geology: Reed and others (1978) describe this coincident mineral occurrence of a quartz-molybdenite vein cutting Paleozoic and (or) Mesozoic (Reed and Nelson, 1980) or Late Cretaceous/early Tertiary (?) (Foley and others, 1997) chromite-bearing dunite. The quartz-molybdenite vein is 20 to 50 centimeters thick, with as much as 20 volume percent molybdenite as foliated tabular crystals up to 5 centimeters in diameter. It is probably genetically related to the middle Tertiary (38 m.y.) granodiorite of Mt. Foraker (Reed and Nelson, 1980) and may indicate porphyry molybdenum/copper potential (Reed and others, 1978). The dunite is part of the Dall trend described in TL002, 003, TL009 - 012, and TL055.
Workings: Reconnaissance mapping, stream silt and rock sampling are all that have been done here. Chromium content of 0.7 to 1% from typical dunite is given in Reed and others (1978). The average of 3 microprobe analyses of one sample was 58.4% Cr2O3, 21.1% FeO, 8.9% MgO, and 9.7% Al2O3.
Age: Mesozoic and (or) Paleozoic (Reed and Nelson, 1980) or Late Cretaceous/early Tertiary (?) (Foley and others, 1997) chromite-bearing dunite. Tertiary; vein hosted quartz-molybdenite presumed to be related to the middle Tertiary (38 m.y.) granodiorite (Reed and others, 1978).

Commodities (Major) - Cr, Mo
Development Status: None
Deposit Model: Podiform chromite (Cox and Singer, 1986; model 8a); vein is possibly related to

References

Foley, J.Y., Light, T.D., Nelson, S.W., and Harris, R.A., 1997, Mineral occurrences associated with mafic-ultramafic and related alkaline complexes in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 396-449. MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000. Reed, B.L., and Nelson, S.W., 1980, Geologic map of the Talkeetna quadrangle: U.S. Geological Survey Miscellaneous Investigations Map I-1174, 1 sheet, scale 1:250,000. Reed, B.L., Nelson, S.W., Curtin, G.C., and Singer, D.A., 1978, Mineral resources map of the Talkeetna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-870-D, 1 sheet, scale 1:250,000.

Mineral List

Chromite

Molybdenite

Quartz

3 entries listed. 3 valid minerals.