Placer County California Gold Production
MICHIGAN BLUFF DISTRICT
The Michigan Bluff district is in southern Placer County, about 5 miles east of Foresthill.
The total gold production of the district through 1959 was about 300,000 ounces. In recent years activity has slackened, and during 1942-59 less than 100 ounces per year was reported.
No details on geology or history could be found.
OPHIR DISTRICT
The Ophir district, near Auburn, is the most productive lode-gold district of Placer County; it also has produced significant amounts of placer gold. The first reported production from the quartz mines was in 1867, when the Green Emigrant mine yielded $100,000 (Logan, 1936, p. 28). In the 1870's many mines were developed, and although not all prospered, the district continued to be moderately active until 1921. From about 1936 to 1942 the mines were very productive, but during 1942-59 less than 100 ounces per year was produced. The chief lode mines were the Crater, Bellevue, Oro Fina, and Three Stars. Total estimated lode production of the district through 1959, including Logan's (1936, p. 29) estimate of $3 million (145,300 ounces), is about 255,500 ounces.
Placers along the American River in the Ophir district were worked as early as 1850, but these shallow gravels were exhausted by 1880 (Logan, 1936, p. 49). The production for these years is unknown. In the late 1930's, dredges started working the gravels near Loomis and in a few years recovered more than 73,000 ounces of gold.
The geology of the district was briefly described by Logan (1936, p. 8-9). Granite, which is the eastern part of a batholith, is intruded into am-phibolite schist. The ore deposits are near the contact and are found in both the granite and in the schists. The gold occurs in lenticular quartz veins and is associated with small amounts of pyrite, galena, sphalerite, and copper sulfides.
RISING SUN MINE
The Rising Sun mine, 11/2 miles west of Colfax, with an estimated total production of $2 million in gold (Logan, 1936, p. 34), is the leading lode-gold producer in Placer County.
Opened in 1866, the mine produced continuously until 1884. Thereafter it was in operation for several brief periods, the most recent on record was in 1932. The Rising Sun deposit is in a zone of altered diabase, serpentine, and slate of the Mariposa Formation of Jurassic age, near a large stock of gabbro. The main vein averaged 18 inches in width and contained rich pockets of free gold in quartz (Logan, 1936, p. 34).