Sheep Hill

Prospect, Undetermined

Alternative names

Dust Mountain (west)

Commodities and mineralogy

Main commodities Cr
Other commodities Ni; PGE
Ore minerals chromite; chromium spinel; pge minerals
Gangue minerals olivine; pyroxene

Geographic location

Quadrangle map, 1:250,000-scale VA
Quadrangle map, 1:63,360-scale C-3
Latitude 61.5818
Longitude -144.9887
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is near the summit of hill 5,140, on the divide between Bernard and Dust Creeks. It is in the NE1/4 section 26, T. 3 S., R. 2 E., of the Copper River Meridian. This prospect is approximately located, perhaps to within one-half mile. It is locality 43B of Winkler and others (1981 [OFR 80-892-B]).

Geologic setting

Geologic description

Dunite, pyroxenite, and peridotite of the Tonsina ultramafic complex (Winkler and others, 1981 [OFR 80-892-A]; Burns, 1985; Foley and others, 1988) contain disseminated chromite, some podiform chromite, and local anomalous concentrations of nickel and platinum-group metals. At Sheep Hill, two low-grade, high-iron deposits with 5 percent chromite contain some PGE values (Foley and Barker, 1985; Foley and others, 1986; Dahlin and others, 1985; Foley and others, 1988, 1989). Samples from a 210- by 300-foot area contain as much as 927 ppb PGEs, including 515 ppb platinum (Pt) and 412 ppb palladium (Pd); Pt/Pt+Pd ratios range from 0.57 to 0.75. The PGEs are commonly associated with chromium spinel (Foley and others, 1988). The Tonsina ultramafic complex may be a deep part of large gabbroic plutons in the root zones of the Jurassic Talkeetna arc (Winkler and others, 1981 [OFR 80-892-A]; Burns, 1985). Because the Tonsina ultramafic complex contains granulites and tectonized harzburgite and dunite, it may have some mantle components and may in part be older than Jurassic mafic and ultramafic intrusives of the region (Burns, 1985).
Geologic map unit (-144.990803670805, 61.5813178304516)
Mineral deposit model Podiform chromite (Cox and Singer, 1986; model 8a)
Mineral deposit model number 8a
Age of mineralization The Tonsina ultramafic complex may be deep parts of large gabbroic plutons in the root zones of the Jurassic Talkeetna arc (Winkler and others, 1981 [OFR 80-892-A]; Burns, 1985). Because the Tonsina ultramafic complex contains granulites and tectonized harzburgite and dunite, it may have some mantle components and may in part be older than Jurassic mafic and ultramafic intrusives of the region (Burns, 1985).
Alteration of deposit Minor serpentinization is probably present.

Production and reserves

Workings or exploration Considerable reconnaissance surface observations and sampling have been carried out.
Indication of production None

References

MRDS Number A011494

References

Burns, L.E., 1985, The Border Ranges ultramafic and mafic complex, south-central Alaska; Cumlative fractionates of island-arc volcanics: Canadian Journal of Earth Science, v. 22, p.1020-1038.
Foley, J.Y., Mardock, C.L., and Dahlin, D.C., 1988, Platinum-group metals in the Tonsina ultramafic complex, southern Alaska, in Vassiliou, A.H., Hausen, D.M., and Carson, D.J.T., Process Mineralogy VII: The Metallurgical Society, p. 165-195.
Reporters Travis L. Hudson
Last report date 12/14/2001