| Basis for focus area |
Distribution of ultramafic rocks in ophiolite belts, MRDS records of chromite occurrences; outlines of Cr provinces in Thayer and Lipin (1979) and Peterson (1984). |
| Identified resources |
Identified resources and historical production of chromium (chromite). |
| Production |
The chromite deposits of the Sierra Nevada foothills, the Klamath Mountain district, and the Coastal Ranges shipped nearly 600,000 tons of chromite (Thayer and Lipin, 1979). Seventy-one chromite deposits in Del Norte County, California had yielded about 60,000 long tons chromite ore by 1944 (Wells and others, 1946). Siskiyou County: ~25,000 tons (Wells and Cater, 1950); Shasta, Tehama, Trinity, and Humboldt counties (1957): ~55,000 tons (Wells and Hawkes, 1965). |
| Status |
Past mining; no current mining or exploration. |
| Estimated resources |
The chromite deposits of the Sierra Nevada foothills, the Klamath Mountain district, and the Coastal Ranges have about 150,000 ton of chromite in identified reserves (Thayer and Lipin, 1979). ~275,000 tons in Siskiyou County (Wells and Cater, 1950). |
| Geologic maps |
Wells and others (1949), scale 1:96,000; Cater and Wells (1953), scale 1:50,000; Irwin (1994), scale 1:500,000; Jenks and others (2007), scale 1:100,000; Jennings and others (2010), scale 1:750,000; Wells and others (1946), multiple scales; California Geological Survey Regional Geologic Maps and Geologic Atlas of California, scales 1:250:000. |
| Geophysical data |
Mostly inadequate Rank 2,3 and 5 aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
Josephine peridotite. |
| Deposits |
Oregon: Esterley Chrome mine (MRDS dep_id: 10042731), Big Bear (MRDS dep_id: 10043130), Black Bear No. 1 & 2 (MRDS dep_id: 10043135), (many more); California: French Hill Chrome mine (MRDS dep_id: 10048022), Big Red Mountain Chrome mine (MRDS dep_id: 10103902), (many more). |
| Evidence from mineral occurrences |
MRDS; Dow and Thayer (1946). |
| Geochemical evidence |
Chromium in stream sediment sample (see Whittington and others, 1985); assay data in Wells and others (1946). |
| Geophysical evidence |
No single geophysical method gives unequivocal identification of buried massive pods of chromite. It is possible that a combination of gravity, magnetic, and seismic data, and complex resistivity, might be used to explore successfully if used in a systematic fashion. |
| Evidence from other sources |
Ultramafic intrusions are known to host podiform chromite bodies, but most known deposits are small (see Dow and Thayer, 1946; Wells and others, 1946). |
| Cover thickness and description |
Many deposits at the surface, but some are underground. |
| Authors |
Laurel G. Woodruff, Catherine Wesoloski, Greg Marquis. |
| New data needs |
Updated geologic mapping, geochemistry, aeromagnetic and radiometric surveys. |
| Geologic mapping and modeling needs |
Updated geologic mapping. |
| Geophysical survey and modeling needs |
High resolution, Rank 1, aeromagnetic surveys would be useful in delineating serpentine, ultramafics, but unclear if a new geophysical survey would be effective. |
| Digital elevation data needs |
Lidar inadequate. |
