Location
This district is at the south side of Oroville Table Mountain three miles north of Oroville. It includes the Monte de Oro area. It is both a lode and placer-mining district. Morris Ravine and other nearby ravines were first placer-mined during the gold rush. Drift and lode mining began soon afterward and continued until around World War I. There was some work again during the 1930s. The Morris Ravine mine has been intermittently worked in recent years.
Geology
The bedrock in the district consists of amphibolite with smaller amounts of slate and phyllite. The slate contains fossil ferns. The bedrock is overlain by sedimentary and volcanic rocks of Oroville Table Mountain, a mesa-like hill consisting of thick beds of sands, tuffs, clays and auriferous channel gravels capped by black basalt. Fossil leaves also have been found in the clays.
Ore Deposits
The channel gravels are quartz-rich, well-cemented, and interbedded with sands and clays. The gold ranges from fine to coarse. A few small diamonds have been recovered here. The veins usually are narrow but the Banner vein has been mined to a depth of 1000 feet. The ore bodies are large but low in grade (1/10 ounce of gold/ton). Small rich pockets were mined also. Sulfides are spotty but often rich.
Mines
Placer: Monte de Oro, Morris Ravine, Perkins and Goodall, Yuba. Lode: Banner $1 million, Bumble Bee $100,000+
Bibliography
Creely, R. S., 1965, Geology of the Oroville Quadrangle: California Div. Mines ond Geology Bull. 184, 86 pp.
Lindgren, Waldemar, 1911, Tertiary gravels of the Sierra Nevada: U.S. Geol. Survey Prof. Paper 73, pp. 86-89.
Logan, C. A., 1930, Butte County, Bonner mine: California Div. Mines Rept. 26, pp. 369-370.
O'Brien, J. C., 1949, Butte County, gold: California Jour. Mines and Geology, vol. 45, pp. 426-433.
Waring, C. A., 1919, Butte County, gold-quartz mines: California Min. Bur. Rept. 15, pp. 211-224.
