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Pick and Shovel

Minor podiform chromite deposit, 7 of 13 in San Luis Obispo county (in California)

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

Geologic Information
Other namesSafety
CountryUnited States
State or provinceCalifornia
Geographic location:35°21'35"N, 120°40'14"W
(-120.670556, 35.359722)
Geographic context: (click for info)
Deposit typeminor podiform chromite
Model typeBanded Podiform
Deposit formirregular zone
Deposit texturemassive, disseminated
Ore typeMetallurgical
Age of depositMiddle Jurassic (163.3±1.1 Ma, U-Pb apatite-feldspar isochron in gabbro)
Age (m.y.)163million years
Host rock typeserpentinized dunite
Host rock length20000
Host rock width4250
Paleotectonic settingsuprasubduction
Ophiolite zonetransition
Deposits < 10kmpodiform chromite
Rocks within 5kmserpentine
Geologic map unit-120.670555555556, 35.3597222222222
Nearby scientific dataFind additional scientific data near this location
Economic Information
Discovery date1870
Startup date1870
Tonnage0.003million metric tons
Ore depth0m
Cr2O3 grade53percent
Cr %37.93percent
Fe %12.02percent
Cr:Fe ratio3.16
Al2O3 %12.61percent
Si2O2 %0.9percent
Reference information
CommentsProduction from 1870 to 1917 unknown, but reported to be large. Production from 1918 to 1944 was 2,100 t ore (Walker and Griggs, 1953). Chromite ore analyses range from 47-88% chromite, 53.87-54.85% Cr2O3. Estimated total tonnage of 3,000 t. Analysis 55.42% Cr2O3, 12.61% Al2O3, 8.10% Fe2O3, 8.19% FeO, 13.70% MgO, 0.16% MnO, 0.16% CaO, 0.13% TiO2, 0.90% SiO2, 37.93% Cr, 12.02% Fe, 3.16 Cr/Fe, 48.1% Cr2O3 in ore, 87% chromite in ore (Stevens, 1944). San Luis Obispo County.
Choi, S.H., Shervais, J.W., and Mukasa, S.B., 2008, Supra-subduction and abyssal mantle peridotites of the Coast Range ophiolite, California: Contributions to Mineralogy and Petrology, v. 156, p. 551-576.
Walker, G.W., and Griggs, A.B., 1953, Chromite deposits of the southern Coast Ranges of California, in Geological investigations of chromite in California, Part 2--Coast Ranges: California Division of Mines Bulletin 134, pt. 2, ch. 2, 88 p.
Jennings, C.W., 1958, Geologic map of California, San Luis Obispo sheet: California Division of Mines and Geology, scale 1:250,000.
Hopson, C.A., Mattinson, J.M., Pessagno, E.A., Jr., and Luyendyk, B.P., 2008, California Coast Range ophiolite--Composite Middle and Late Jurassic oceanic lithosphere: Geological Society of America Special Paper 438, p. 1-101.
Stevens, R.E., 1944, Composition of some chromites of the Western Hemisphere: The American Mineralogist, v. 29, nos. 1 and 2, 34 p.
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