By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Auriferous gravels have been highly productive in Yuba County. The Hammonton vicinity alone yielded $100 million in gold from the gravels along the Yuba River after dredging started in 1903 (O'Brien, 1952a, p. 148). Considerable placer gold has come from Tertiary gravels but much more has come from the Quaternary gravels.
Gold-bearing quartz veins have been mined in the Browns Valley-Smartville and Brownsville-Challenge-Dobbins districts where the veins are found in metamorphic rocks near the contact with a granodioritic body.
Total recorded production from 1880 through 1959 was 5,294,600 ounces: 4,387,100 ounces from placers and 907,500 ounces from lodes.
BROWNS VALLEY-SMARTVILLE AND BROWNSVILLE-CHALLENGE-DOBBINS DISTRICTS
These districts are discussed jointly here because of the paucity of published information regarding their individual history, geology, and production. The Browns Valley-Smartville district is in central Yuba County, in T. 16 N., R. 5 E. The Brownsville-Challenge-Dobbins district is in the northern part of the county, in Tps. 18 and 19 N., Rs. 6 and 7 E.
The gold deposits of these districts were described briefly by Lindgren and Turner (1895). In the Browns Valley-Smartville area, gold-bearing quartz veins occur in amphibolitic schists and diabase. The principal mine here was the Hibbert and Burris. In the Brownsville-Challenge-Dobbins area, gold-quartz veins are associated with masses of granodiorite.
Production from these districts is not known, but it may be assumed that it represents all the lode gold credited to Yuba Countyâ€”907,500 ounces from 1880 through 1959.
Metasedimentary rocks of the Calaveras Group are exposed in two northwest-trending beltsâ€”one passes through Camptonville, the other near Challenge. A younger group of greenstones and green schists is also exposed in this area, but their stratigraphic relations are not known (O'Brien, 1952a, p. 144-145). Intrusive rocks consisting of small bodies of diabase, gabbro, and peridotite, and of large masses of granodiorite of the Sierra Nevada batholith cut the metasedimentary rocks and greenstones.
The Hammonton district, in parts of Tps. 15 and 16 N., Rs. 4 and 5 E., is along the Yuba River in the southern part of Yuba County.
Beginning in 1903, large-scale dredging of the Quaternary gravels produced about $2 million in gold annually, and by 1949 the district had proÂ¬duced about $100 million in gold (O'Brien, 1952a, p. 145). In 1952 six dredges were in operation. Total production through 1959 was about 4,387,100 ounces.
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