Sliger Mine, French Hill, Spanish Dry Diggings (Spanish Dry Diggins), Greenwood District, Northwest Segment Mother Lode, El Dorado County, California, USAi

Regional Level Types
Sliger Mine	Mine
French Hill	Hill
Spanish Dry Diggings (Spanish Dry Diggins)	Diggings
Greenwood District	Mining District
Northwest Segment Mother Lode	Lode
El Dorado County	County
California	State
USA	Country

A former lode Au-Ag occurrence/mine located in secs. 25 & 36, T13N, R9E, MDM, 0.6 km (0.4 mile) WNW of French Hill (coordinates of record) and 1.9 km (1.2 miles) WSW of Spanish Dry Diggings, E of the Middle Fork American River (6 miles WNW of Georgetown), on private land. Discovered in 1864. MRDS database stated accuracy for this location is 100 meters.

The Sliger Mine is located within the Greenwood District in northwestern El Dorado County, at the northwest end of the Mother lode Gold belt. Discovered in 1864, the mine was operated during the 1870s, and again between 1922 and 1942, before being idled at a depth of 2,000 feet, and having produced about $2,625,000. During its early days of operation, the Sliger Mine was known for specimen gold which was desired by collectors and jewelry makers.

The Sliger Mine was originally discovered in 1864, but work did not start until 1872 or 1873. By 1874, an adit had been run 375 feet, cutting the vein at a depth of 200 feet, and a shaft had been sunk to connect with it (Logan, 1934). By 1874, the mine had produced a reported $125,000 (Logan, 1934). By the time the shaft reached the 300-foot level, the mine was reported to have produced $225,000 in gold (Logan, 1938). During the 1870s the mine was known as a producer of specimen gold, which was used in jewelry.

The mine was inactive for many years until 1922, when the Sliger Gold Mining Company reopened the mine and deepened the shaft to 500 feet on the dip of the vein. They also added a 15-stamp mill. Milling began in January, 1929, and good ore was produced during the two following years. In an attempt to save money, the shaft was not properly supported and caved in early 1931 (Logan, 1934). Late in 1931, C.L. Wright and associates leased the mine, rehabilitated the shaft, and installed a new 100-ton ball mill and flotation plant. In 1932, a winze was sunk 100 feet from the 500-foot level and a drift 200 feet long on the 600 foot level was driven entirely within ore, which crosscuts showed to be 32 feet wide. Ore averaged $10 per ton (Logan, 1934). In 1932, work was also started on the surface outcrop of the vein near the south boundary of the Sliger claim. Shortly after, a lawsuit was filed by the owner of the neighboring South Sliger claim. The suit was resolved in 1934, with the purchase of the claim by the Middle Fork Mining Company. By 1934, the stamps had been replaced by two-stage crushing in Blake and Symonds crushers, a ball mill, flotation, and gravity concentration. The ball mill worked in closed circuit with two Dorr classifiers. From the mill, the pulp passed over a Deister Overstrom concentrator which captured 75%-80% of the gold in a high-grade concentrate. The table tailings were sent to a conditioner, then six Kraut rougher cells and two cleaner cells. Mill capacity was about 70 tons a day, but the mill, more often than not, produced about 50 tons a day (Logan, 1934).

The Middle Fork Gold Mining Company continued operations until May, 1937, when the mine was closed pending financing of further development work. Over 80,000 tons of good ore was produced during 4 years 1932-1935. In August 1937, the Mountain Copper Company leased the mine and did some exploration. They sank the shaft another 350 feet to a depth of 1,350 feet. About 500 feet of drifting and 1,500 feet of diamond drilling was done. Early in 1938, the company gave up its option and the Middle Fork Gold Mining Company once gain operated it between 1938 and 1942, processing as much as 100 tons of ore per day. In 1942, the mine was idled at a depth of 2,000 feet, and by 1953 most of the surface equipment had been sold. In the decade from 1932 to 1942, 309,000 tons of ore were mined from which $2,625,000 of gold was recovered .

Mineralization is a vein deposit (Mineral occurrence model information: Model code: 273; USGS model code: 36a; Deposit model name: Low-sulfide Au-quartz vein; Mark3 model number: 27) hosted in rocks of the Mariposa Formation (Late Jurassic slate). The ore body strikes N and dips 63E. The deposit is comprised of slate with numerous quartz stringers in a fault zone between a Mariposa slate footwall and serpentine band hanging wall. The country rock is amphibolite. The ore zone is 30 feet wide with lensoid (?) ore shoots without definite walls, but merging into lower grade rock. It is believed that Au-bearing solutions rose along favorable slate bands to the fault where they spread to form the ore shoots. Finely disseminated pyrite and arsenopyrite are present. 40% of the Au is in the free state and 60% is in sulfides. The ore tenor is nearly unchanged from the 300 foot level to the 2,000 foot level. Controls for ore emplacement included erratic ore shoots in quartz veinlets and disseminated auriferous sulfides in adjacent hanging wall. Local alteration includes silicification of the slate wall rock. Local rocks include Mesozoic volcanic rocks, unit 2 (Western Sierra Foothills and Western Klamath Mountains).

Local and regional geologic structures include a fault zone (Melones Fault Zone).

The Sliger Mine developed the footwall side of a Mother Lode quartz-vein system developed along a reverse fault within rocks of the Mariposa Formation. The vein is in fault contact between a body of black Mariposa Formation slate on the footwall and a band of ankerite and serpentine on the hanging wall, within amphibolite schist country rock (Clark and Carlson, 1956). The slate is thought to have been caught up in the intrusive from which the amphibolite was derived (Logan, 1934).

The principle ore body strikes north and dips 63? E, with lenticular north-raking ore shoots (Logan, 1934). The width of the ore generally varied from 14 inches to 19 feet, but on the 600-foot level the ore reportedly reached 32 feet thick. The ore body is in part a replacement deposit (Logan, 1934. The ore is composed of silicified slate containing numerous quartz veinlets with free gold, fine disseminated pyrite, and smaller amounts of arsenopyrite. Ankerite is present (Clark and Carlson, 1956).

Sulfides comprised about up 3.7% of the ore and contained from $75-$375 (period values) per ton (Logan, 1934; Logan, 1938). Recovery from the stamps was 80% and ore values ranged from $5-$15 (period values) per ton (Logan, 1934).

Workings include surface and underground openings comprised of a 2,000 foot inclined shaft and open stopes. Little detailed information is available regarding the the Sliger Mine underground workings.

Production data are found in: Clark, Wm. B. & D.W. Carlson (1956).

Production statistics: Year: 1937; Period: 1934-1937: Au @ 7 grams/metric ton ($5 to $15 per ton (period values)).

$2,625,000 (period values) was recovered during the period 1932 to 1942. A small amount of Au was produced in 1864.

Analytical data results: Au as high as 925 fine.

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Link to USGS MRDS:	10006860

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