| Basis for focus area |
Chromite-bearing black sands in present beaches and adjacent braided beaches stretch over 200 km along the coast of northwestern California and southwestern Oregon. |
| Identified resources |
Historical production of chromium (chromite), gold, and PGE. |
| Production |
Gold and minor Pt production circa 1850-1930s. Exploration began during WWII, and by 1955 52,000 tons of chrome-bearing concentrate had been shipped. |
| Status |
Past mining; no current mining or exploration. |
| Estimated resources |
The known reserves of Measurable and Indicated ore, minus what was mined in 1943, are 1,913,000 long tons sand in deposits averaging more than 5% Cr2O3, and 1,212,000 long tons sand in deposits averaging between 3 and 5% Cr2O3 (Griggs, 1945). |
| Geologic maps |
McClaughry and others (2013), scale 1:24,000; Dott (1971), scale 1:250,000. |
| Geophysical data |
Inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
Black beach sands in modern and older raised beaches. |
| Deposits |
Southwest Oregon beach sands (MRDS dep_id: 10127508). |
| Evidence from mineral occurrences |
MRDS; Griggs (1945). |
| Geochemical evidence |
No data. |
| Geophysical evidence |
Unknown. |
| Evidence from other sources |
None. |
| Comments |
Foreshore coastal beach areas are transitory, which complicated estimates of historical resources. Beach-face retreat in the winter of 1982-83 exposed underlying placers containing the economic minerals garnet, zircon, ilmenite, and chromite (Peterson and others, 1986). |
| Cover thickness and description |
Exposed. |
| Authors |
Jane M. Hammarstrom, Laurel G. Woodruff. |
| New data needs |
None requested at this time. |
| Geologic mapping and modeling needs |
Recent mapping at 1:24,000. |
| Geophysical survey and modeling needs |
None requested at this time. |
| Digital elevation data needs |
Lidar in progress over southern portion of the focus area; incomplete in northern half. |
