By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
The discovery of gold in El Dorado County in 1848 by James Marshall at Coloma, on the south fork of the American River 8 miles northwest of Placerville (Clark and Carlson, 1956, p. 371), was the widely publicized event that precipitated the fabulous gold rush to California in 1849. Soon thousands of gold seekers swarmed over the county, and in the 1850's it was one of the most populous areas in the State. With all the stream gravels being diligently worked, soon discoveries of vein deposits were made, and in 1851 lode mining began at Nashville (Clark and Carlson, 1956, p. 372). Since 1884, when legislation restricted hydraulic mining, lode mines have been the major source of gold in the county; however, the placers were rejuvenated briefly in the late 1930's, when large floating dragline dredges were introduced.
From 1880 through 1959, a total of 1,267,700 ounces of gold was mined in the county. From 1903, when systematic recording began, through 1958, about 190,600 ounces was mined from placers, and 534,000 ounces, from lode mines; data before 1880 have not been found.
The lode deposits are in quartz veins in the Mother Lode, in the East Belt, and in the West Belt. Lode gold also occurs in contact metamorphic and replacement deposits.The most productive placer deposits were in the Tertiary channels near Placerville and in the Grizzly Flat-Fairplay-Indian Diggings area (Clark and Carlson, 1956, p. 431). Placer deposits are also found along the American and Cosumnes Rivers.
GEORGIA SLIDE DISTRICT
The Georgia Slide district is in T. 12 N., R. 10 E., in the northwestern part of El Dorado County. This district, in the northern part of the Mother Lode, is characterized by its rich seams of gold that occur in narrow quartz veinlets that impregnate a zone several hundred feet wide in slate, amphibolite, and chlorite schist of the Mariposa Slate. Intersections of two vein systems, or of a large quartz vein, with a veinlet system are richest in gold. The upper parts of these veins were weathered extensively and the soluble components were removed, but the gold remained and was thus concentrated. In the 1860's and 1870's these deposits were worked by hydraulicking. After the residual mantle was removed, the unweathered deposits were mined by conventional underground methods (Clark and Carlson, 1956, p. 435). Gold production from this district through 1955 was estimated at $6 million (Clark and Carlson, 1956, p. 436). No activity has been reported in recent years.
MOTHER LODE, EAST BELT, AND WEST BELT DISTRICTS
The Mother Lode, East Belt, and West Belt districts, composing a zone 10 to 20 miles wide extending from north to south in western El Dorado County, are combined here because their individual production cannot be determined.
Most of the lode gold produced in the county to 1959 came from mines of the Mother Lode which were developed in the early 1850's. Two of these, the Union and Church mines, produced $600,000 in gold before 1868 (Clark and Carlson, 1956, p. 427). The Union was the largest in this district, with a total gold production of $2,700,000 to $5 million (Clark and Carlson, 1956, p. 427). Other mines with $1 million or more total production are the Big Canyon, Mount Pleasant, Pyramid, Sliger, Taylor, and Zantgraf.
From 1903 through 1958 the lode mines of the district produced roughly 500,000 ounces of gold. Total production could possibly be 1 million ounces or more.
The geology of this district is covered in the description of the Mother Lode in the California Gold Production Summary article.PLACERS IN TERTIARY GRAVELS
Placer gold has been mined from Tertiary gravels in three localities in El Dorado County: Georgetown in the northern part in T. 12 N., R. 10 E., Placerville in the west-central part in T. 10 N., R. 11 E., and Grizzly Flat about 18 miles south of Placerville in T. 9 N., R. 13 E.
The most productive channels in the county were at Placerville where a total of $25 million in gold was extracted after the 1860's (Clark and Carlson, 1956, p. 433). Production from the Georgetown and Grizzly Flat areas is not known. From 1903 through 1959 the production from these three areas totaled about 190,000 ounces. Annual production has been combined with that of the Mother Lode, East Belt, and West Belt districts by U.S. Bureau of Mines (1933-1966).
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