Unnamed Occurrence (ARDF - MH121; ridge between middle and east forks in Broxson Gulch), Delta River District, Southeast Fairbanks Borough, Alaska, USA
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Location: This occurrence is at an elevation of 4,900 feet on the north side of the ridge between the locally named middle and east forks of the stream(s) in Broxson Gulch (see figure 2 of Rose, 1965). It is in the NE1/4NE1/4 section 19, T. 18 S., R. 9 E., Fairbanks Meridian. The occurrence corresponds to locality 19 on figure 2 of Rose (1965), to locality 18 of MacKevett and Holloway (1977), and to locality 47 in table 2 of Nokleberg and others (1991).
Geology: This occurrence is in amphibolitized 'serpentinite' inferred to be in the hanging wall of a major thrust fault (Rose, 1965, figure 2, locality 19). Boulders of massive sulfide material were found along a 20-foot-wide zone on the north side of the ridge. Mineralized material assayed 0.9 percent copper, a trace of zinc, and less than 0.1 percent nickel (Rose, 1965). Fifty feet south of this zone a layer of pyrrhotite a few inches thick crops out for several feet. The amphibole 'serpentinite' in this area is considerably pyritized and sheared. Sample 79IL029A of float that contained pyrite, pyrrhotite, pentlandite, and chalcopyrite assayed 500 parts per million (ppm) cobalt (Nokleberg and others, 1991, locality 47). Later sampling determined higher metal values and a wider suite of metals (Foley, 1992). The massive sulfide lenses in the Broxson Gulch area sampled by Foley assayed as much as 2.4 percent copper, 0.66 percent nickel, 0.1 percent cobalt, 13 ppm silver, 416 ppm gold, and 137 parts per billion each platinum and palladium.
Workings: This occurrence was discovered by Rose (1965). It subsequently was examined by Nokleberg and others (1991) and Foley (1992). The area is currently claimed by MAN Resources.
Age: Late Triassic, the age of the host rock.
Alteration: The amphibole 'serpentinite' is considerably pyritized and sheared (Rose 1965).
Commodities (Major) - Cu; (Minor) - Ag, Au, Co, Ni, Pd, Pt, Zn
Development Status: None
Deposit Model: Ni-Cu-PGE in differentiated mafic-ultramafic sill.
4 entries listed. 4 valid minerals.
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Foley, J.Y., 1992, Ophiolite and other ultramafic metallogenic provinces in Alaska (west of the 141th meridian): U.S. Geological Survey Open-File Report 92-20-B, 55 p. 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. 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. Rose, A.W., 1965, Geology and mineral deposits of the Rainy Creek area, Mt. Hayes quadrangle, Alaska: Alaska Division of Mines and Minerals Geologic Report 14, 57 p., 1 sheet, scale 1:36,000.