Location
This district is in northwestern El Dorado County. It consists of the northwest segment of the Mother Lode gold belt, which splits at Garden Valley (the east segment continues through Georgetown). This segment of the belt is several miles wide and extends from the point of the split northwest through Greenwood and Spanish Dry Diggings to the Middle Fork of the American River, a distance of about eight miles.
History
Placer mining began in this area shortly after the beginning of the gold rush. The town was named for Caleb and John Greenwood, who established a trading post here in 1850. The district flourished during the 1850s, when the American River was mined and the seam deposits hydraulic ked on a large scale. The river was mined by diverting the main stream with a series of flumes, tunnels, and wingdams. The gold-bearing gravels were removed from the bedrock and sent through sluices or long toms. Major mining activity continued through the early 1900s, much of the later placer mining done by Chinese. This district was quite productive again during the 1930s, when the Sliger, Taylor, and Grit lode mines were active. Since about 1955, numerous skin divers have been mining the Middle Fork of the American River by small-scale methods.
Geology
There are two northwest-trending belts of slate of the Mariposa Formation (Upper Jurassic) 1/2 to one mile apart. Chert, impure quartzite, and slate lie to the west, and greenstone and amphibolite schist lie in the center and to the east. A number of small lenticular bodies of serpentine and talcose schist are enclosed in the bedrock, which is deeply weathered in places.
Ore Deposits
There are several wide and sometimes extensive zones of quartz veins and veinlets and mineralized schist containing free gold and auriferous pyrite. Where deeply weathered, the bedrock was eroded, and the gold in the seams and vein lets remained and became concentrated. Such deposits are known as seam deposits or "seam diggings". The upper portions were mined by hydraulicking, and later the unweathered veins at depth were mined by conventional underground methods. Considerable specimen material has been recovered from this district, including crystallized gold. The famous Fricot nugget of crystallized gold (201 ounces), which was taken from the Grit mine in 1865, is on display in the Division of Mines and Geology exhibit in the Ferry Building, San Francisco. Milling-grade ore bodies commonly averaged 1/5 to more than 1/2 ounce of gold per ton. Some of the veins were mined to inclined depths of 2000 feet.
Mines
Admiral Schley, Argonaut $100,000+, Bazocoo, Cedarburg, Centennial, Esperanza $100,000+, Eagle, French Hill $100,000+?, Greenwood, Grit, Hines-Gilbert $100,000+, Homestake, Maltby, Nancy Lee, Oakland Cons., Railroad Hill, Red Mount, Revenge, Rosecranz $ 100,000+, San Martin, Sebastopol, Sliger $2.85 million, Taylor $1 million.
Bibliography
Clark, W. B., and Carlson, D. W., 1956, EI Dorado County, Grit, Rosecronz, and Sliger mines: California Jour. Mines and Geology, vol. 52, pp. 415-416, 423-424, and 425-426.
Fairbanks, H. W., 1890, Geology of the Mother lode region: California Min. Bur. Rept. 10, pp. 81-82.
Lindgren, Waldemar, and Turner, H. W., 1894, Placerville folio, California: U. S. Geol. Survey, Geol. Atlas of the U.S., folio 3, pp. logan, C. A., 1935, Mother lode gold belt of California, Seam mines: California Div. Mines Bull. 108, pp. 43-47.
Preston, E. 8., 1893, Taylor mines: California Min. Bur. Rept. 11, p.205.
Ransome, F.L., 1900. Mother lode district folio, California: U.S. Geol. Survey, Geol. Atlas of the U.S., folio 63, 11 pp.
