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Bunker (main)

Minor podiform chromite deposit, 22 of 30 in Placer county (in California)

Sections of this page: [Geologic] - [Economic] - [Reference]

Geologic Information
Other namesBlue Bird
CountryUnited States
State or provinceCalifornia
Geographic location:39°2'20"N, 120°45'36"W
(-120.76, 39.038889)
Geographic context: (click for info)
Deposit typeminor podiform chromite
Model typeMinor Podiform
Deposit formlenses, pods, stringers
Deposit texturecoarse-grained massive, disseminated
Ore typeUnknown
Age of depositpre-Early Devonian-Jurassic (388±17 Ma U-Pb zircon from felsic igneous rocks; 174 Ma K-Ar white mica from blueschists)
Age (m.y.)388million years
Area of deposit74.42sq m
Ore body length122m
Ore body width0.61m
Host rock typedunite
Host rock length134000
Host rock width7000
Paleotectonic settingsuprasubduction
Ophiolite zonetectonite
Deposits < 10kmpodiform chromite
Rocks within 5kmdunite
harzburgite or lherzolite
diabase dikes
mudflow breccia
rhyolite tuff
Geologic map unit-120.76, 39.0388888888889
Nearby scientific dataFind additional scientific data near this location
Economic Information
Discovery date1880s
Startup date1880s
Tonnage0.000411million metric tons
Mine depth26m
Ore depth0m
Cr2O3 grade35percent
Rh grade0.004g/t
Ir grade0.04g/t
Ru grade0.15g/t
Pd grade0g/t
Pt grade0g/t
Fe %12percent
Cr:Fe ratio2.4
Reference information
CommentsAnalysis <0.001 ppm Pd, <0.01 ppm Pt. Cr/Fe 2.27 to 2.53. Feather River Belt. Placer County.
Burnett, J.L., and Jennings, C.W., 1962, Geologic map of California, Chico sheet: California Division of Mines and Geology, scale 1:250,000.
Mayfield, J.D., and Day, H.W., 2000, Ultramafic rocks in the Feather River Belt, northern Sierra Nevada, California, in Brooks, E.R., and Dida, L.T., eds., Field guide to the geology and tectonics of the northern Sierra Nevada, National Association of Geoscience Teachers Far-Western Section Fall Conference 2000: California Division of Mines and Geology Special Publication 122, p. 1-15.
Rynearson, G.A., 1951, Chromite deposits in the northern Sierra Nevada, California (Placer, Nevada, Sierra, Yuba, Butte, and Plumas counties), in Geological investigations of chromite in California, Part 3--Sierra Nevada: California Division of Mines Bulletin 134, pt. 3, ch. 5, 321 p.
Carlson, C.A., Wilson, S.A., Carlson, R.R., Bradley, L., Cornell, J., Gent, C., Gass, W., Groeneboer, H., Haffty, J., Haubert, A., Love, A., McDade, J.M., Moore, R., Riley, L., Moring, B.C., Singer, D.A., and Page, N. J, 1985, Analyses for platinum group elements in samples from podiform chromite deposits, California and Oregon: U.S. Geological Survey Open-File Report 85-442, 15 p.
Ehrenberg, S.N., 1975, Feather River ultramafic body, northern Sierra Nevada, California: Geological Society of America Bulletin, v. 86, p. 1235-1243.
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