Unnamed Occurrence (ARDF - MH096; west of the terminus of Eureka Glacier), Valdez Creek District, Southeast Fairbanks Borough, Alaska, USA
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Geology: This occurrence is in the westernmost exposure of the Fish Lake ultramafic complex, a large layered lopolith of Late Triassic age considered to be comagmatic with the Upper Triassic Nikolai Greenstone (Nokleberg and others, 1991). This occurrence consists of sulfide minerals disseminated in the ultramafic complex. Chalcopyrite and pyrrhotite form about 5 to 7 percent of the olivine-clinopyroxene wehrlite. The wehrlite is about 100 feet stratigraphically below locally pegmatitic gabbro. Grab samples of sulfide-bearing wehrlite contained as much as 1,180 parts per million (ppm) copper, 1,650 ppm nickel, 58 parts per billion (ppb) palladium, and 50 ppb platinum (W.T. Ellis, unpublished data, 1996).
Workings: The occurrence is covered by active Fort Knox Gold Resources claims (W.T. Ellis, unpublished field notes, 1996).
Age: Late Triassic, synchronous with emplacement of the mafic-ultramafic rocks.
Alteration: The wehrlite is weakly serpentinized.
Commodities (Major) - Cu, Ni; (Minor) - Pd, Pt
Development Status: None
Deposit Model: Ni-Cu-PGE in differentiated mafic-ultramafic sill.
3 entries listed. 2 valid minerals.
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Nokleberg, W.J., Lange, I.M., Roback, R.C., Yeend, Warren, and Silva, S.R., 1991, Map showing locations of metalliferous lode and placer mineral occurrences, mineral deposits, prospects, and mines, Mount Hayes quadrangle, eastern Alaska Range, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1996-C, 42 p., 1 sheet, scale 1:250,000.