|Quadrangle map, 1:250,000-scale||VA|
|Quadrangle map, 1:63,360-scale||C-3|
|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 descriptionDunite, 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.|
|Workings or exploration||Considerable reconnaissance surface observations and sampling have been carried out.|
|Indication of production||None|
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.
Cobb, E.H., and Matson, N.A., Jr., 1972, Metallic mineral resources map of the Valdez quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-438, 1 sheet, scale 1:250,000.
Dahlin, D.C., Kirby, D.E., and Brown, L.L., 1985, Chromite deposits along the Border Ranges fault, southern Alaska; Part 2--Mineralogy and results of beneficiation tests: U.S. Bureau of Mines Information Circular 8991, 37 p.
Foley, J.Y., and Barker, J.C., 1985, Chromite deposits along the Border Ranges fault; Part 1 -- Field investigations and descriptions of chromite deposits: U.S. Bureau of Mines Information Circular 8990, 57 p.
Foley, J.Y., Barker, J.C., and Brown, L.L., 1986, Chromite resources in Alaska, in Daellenbach, C.B., compiler, Chromium-chromite; U.S. Bureau of Mines assessment and research: U.S. Bureau of Mines Information Circular 9087, p. 23-29.
Foley, J.Y., Burns, L.E., Schneider, C.L., and Forbes, R.B., 1989, Preliminary report of platinum group element occurrences in Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 89-20, 32 p., 1 map sheet, scale 1:2,500,000.
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.
Winkler, G.R., Miller, R.J., MacKevett, E.M., Jr., and Holloway, C.D., 1981, Map and summary table describing mineral deposits in the Valdez quadrangle, southern Alaska: U.S. Geological Survey Open-File Report 80-892-B, 2 sheets, scale l:250,000.
|Reporters||Travis L. Hudson|
|Last report date||12/14/2001|