Klamath Mountains chromite

Region West, Northwest
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

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.