Eb No. 4 Prospect, Delta River District, Southeast Fairbanks Borough, Alaska, USA
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Geology: The Eb No. 4 prospect is hosted by the Fish Lake mafic-ultramafic complex, a lopolithic feeder of Late Triassic age of the Nikolai basalt flows (Nokleberg and others, 1991). The prospect lies in lower portion of the gabbroic unit of the second magmatic cycle of the Fish Lake ultramafic complex (W.T. Ellis, unpublished data, 1996). The prospect consists of float of sulfide-bearing coarse-grained pyroxenite; samples assay as much as 0.1 percent copper, 0.08 percent nickel, 140 parts per billion (ppb) palladium, and 85 ppb platinum. The metallic minerals are mainly pyrrhotite, along with chalcopyrite and pentlandite. The deposit does not crop out, but a good geophysical conductor is present that has been interpreted to be caused by sulfide accumulations (W.T. Ellis, unpublished data, 1996). Twelve hundred feet along strike a drill hole intersected 54 feet of pyroxenite grading 0.1 percent copper, 0.15 percent nickel, 198 ppb palladium, and 123 ppb platinum. This pyroxenite contained from 7 to 10 percent sulfides (W.T. Ellis, unpublished data, 1996).
Workings: The occurrence is on active Fort Knox Gold Resource claims.
Age: Late Triassic, the age of the host rock.
Commodities (Major) - Cu, Ni, Pd, Pt
Development Status: None
Deposit Model: Ni-Cu-PGE in differentiated mafic-ultramafic sill.
3 entries listed. 3 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.