Sliger Mine

Site Name

Primary: Sliger Mine

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Commodity

Primary: Gold
Secondary: Silver

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Location

State: California
County: El Dorado
District: Greenwood District

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Land Status

Land ownership: Private
Note: the land ownership field only identifies whether the area the mine is in is generally on public lands like Forest Service or BLM land, or if it is in an area that is generally private property. It does not definitively identify property status, nor does it indicate claim status or whether an area is open to prospecting. Always respect private property.
Administrative Organization: El Dorado County Planning Dept.

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Past Producer
Deposit Type: Hydrothermal vein and replacement
Operation Type: Underground
Discovery Year: 1864
Years of Production:
Organization:
Significant: Y
Deposit Size: S

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Physiography

Not available

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Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

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Orebody

Form: Tabular

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Structure

Type: L
Description: Melones Fault Zone

Type: R
Description: Melones Fault Zone

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Alterations

Alteration Type: L
Alteration Text: Silicification of slate wall rock

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Rocks

Name: Slate
Role: Host
Age Type: Host Rock
Age Young: Late Jurassic

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Pyrite
Ore: Arsenopyrite
Gangue: Slate
Gangue: Calcite
Gangue: Quartz
Gangue: Ankerite

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Comments

Comment (Commodity): Commodity Info: Ore averaged about $5-$15 per ton. 40% of the gold was free gold, the remaining 60% in sulfides. Gold was 925 fine.

Comment (Commodity): Ore Materials: Free gold-bearing quartz veinlets and silicified slate carrying disseminated pyrite and arsenopyrite

Comment (Commodity): Gangue Materials: Slate, calcite, quartz, ankerite

Comment (Identification): 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.

Comment (Location): Location selected for latitude and longitude is the Sliger Mine shaft symbol on the USGS 7.5 minute Greenwood quadrangle

Comment (Workings): Little detailed information is available regarding the the Sliger Mine underground workings. The mine was developed by a 2,000 foot inclined shaft. Ore was mined in open stopes that were later filled with mill tailings (Clark and Carlson, 1956).

Comment (Geology): The Melones Fault zone separates the Mother Lode Belt from the East Belt. The East Belt lies in the south central part of El Dorado County approximately 15 miles east of the Mother Lode belt. The East Belt traverses the county from the southern county line, north through Omo Ranch and Grizzly Flat, and apparently terminates near the Hazel Creek Mine east of Jenkinson Reservoir (Busch, 2001). The Eastern Belt is dominantly argillite, phyllite and phyllonite, and chert of Paleozoic age. The phyllite and phyllonite are dark to silvery gray. The chert is mostly thin bedded with phyllite partings. Other rocks in the Eastern Belt include a Jurassic granodiorite pluton near the Cosumnes River and small bodies of Jurassic serpentinite, gabbro, diorite, and limestone. The Paleozoic metasedimentary rocks of the Eastern Belt have been assigned to the Shoo Fly Complex by most investigators. Lode deposits of the East Belt consist of many individual gold-bearing quartz veins enclosed in metamorphic rocks of the Shoo Fly Complex, or in granitic rocks. Most of the veins trend northward and dip steeply. An east-west set of intersecting faults may be a controlling factor in controlling deposition of ore. Ore deposits of the East Belt are smaller and narrower than those of the Mother Lode, but commonly are more chemically complex, and richer in grade. Gold is usually associated with appreciable amounts of pyrite, chalcopyrite, pyrrhotite, galena, sphalerite, and arsenopyrite (Clark and Carlson, 1956) LOCAL GEOLOGY 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 orebody 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 orebody is in part a replacement deposit (Logan, 1934. The ore has no definite wall, but merges into low-grade rock (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). It is believed that the ore forming solutions rose along several favorable bands in slate in the fault zone where they spread out to form ore shoots. Approximately 40% of the gold was free with about 60% contained in the sulfides (Clark and Carlson, 1956). Sulfides comprised about up 3.7% of the ore and contained from $75-$375 per ton (Logan, 1934; Logan, 1938). Recovery from the stamps was 80% and ore values ranged from $5-$15 per ton (Logan, 1934). Fineness ran as high as 925.

Comment (Deposit): The Sliger Mine produced free gold and auriferous sulfides from a system of quartz veinlets and silicified wall rock along a fault zone within the Upper Jurassic Mariposa Formation. The deposits consist of gold-quartz veinlets and zones of silicified slate in the footwall of a reverse fault zone. The north-striking ore body generally ranged from 14 inches to 19 feet wide, but achieved a maximum thickness of 32 feet on the 600-foot level. Approximately 40% of the gold was free disseminated gold with the remaining 60% being contained in sulfides (pyrite and arsenopyrite). Gold was 925 fine.

Comment (Development): 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 .

Comment (Economic Factors): Clark (1970) reported that the Sliger Mine produced approximately $2.65 million.

Comment (Geology): REGIONAL GEOLOGY The Sliger Mine is in the Sierra Nevada foothills of El Dorado County, where bedrock consists of north-trending tectonostratigraphic belts of metamorphosed sedimentary, volcanic, and intrusive rocks that range in age from late Paleozoic to Mesozoic. The structural belts, which extend about 235 miles along the western side of the Sierra, are flanked to the east by the Sierra Nevada Batholith and to the west by sedimentary rocks of the Cretaceous and Jurassic Great Valley sequence. The structural belts are internally bounded by the Melones and Bear Mountains fault zones and are characterized by extensive faulting, shearing, and folding (Earhart, 1988). In the El Dorado County area, gold deposits occur in the West Belt, the Mother Lode Belt, and the East Belt. The Mother Lode Belt is responsible for most of the gold produced in the county. There has also been substantial gold produced from the West Belt and East Belt (Clark and Carlson, 1956). The West Belt consists of widely scattered gold deposits located west of the Mother Lode vein system. Gold occurs in irregular quartz veins in schist and granitic rocks, altered mafic rocks, and as gray ore in greenstone. The West Belt has been further divided by some authors into an eastern component composed of an ophiolitic melange and a western component composed of Jurassic rocks of the Copper Hill volcanics (Duffield and Sharp, 1975; Saleeby, 1982; Clark, 1964). The Copper Hill volcanics consist of mafic to felsic flows and pyroclastic rocks that are metamorphosed to greenschist and amphibolite facies. The Bear Mountains fault zone separates the melange from the Copper Hill volcanics. The Mother Lode Belt consists of the upper Jurassic Logtown Ridge and upper Jurassic Mariposa formations. The Logtown Ridge Formation consists of about 6,500 feet of volcanic and volcanic-sedimentary rocks of island arc affinity. These rocks are mostly basaltic and include flows, breccias, and a variety of layered pyroclastic rocks. The overlying Mariposa Formation contains a distal turbidite, hemipelagic sequence of black slate, amphibolite, schist, and fine-grained tuffaceous rocks, and subvolcanic intrusive rocks. The thickness of the Mariposa Formation is difficult to ascertain due to structural complexities, but is estimated to be about 2,600 feet thick at the Cosumnes River (Earhart, 1988). The Sliger Mine is located within black slates, schist, and serpentinite of the Mariposa Formation. Mother Lode Belt mineralization is generally characterized by steeply dipping gold-bearing quartz veins that traverse western El Dorado County. The belt trends north through Nashville, northeast through Placerville, and northwest to Garden Valley. The Mother Lode veins are generally enclosed in Mariposa Formation slate with associated greenstone. The vein system ranges from a few hundred feet to a mile or more in width. Within the zone are numerous discontinuous or linked veins, which may be parallel, convergent, or en echelon. The veins commonly pinch and swell. Few can be traced more than a few thousand feet. Mother Lode type veins fill voids created within faults and fracture zones and consist of quartz, gold and associated sulfides, ankerite, calcite, chlorite, and sericite (Clark and Carlson, 1956). At Garden Valley, the Mother Lode Belt splits. The west branch extends northwest through the Greenwood District which includes the Sliger Mine, and the east branch extends north through Georgetown to the Georgia Slide area (Busch, 2001). In this area, there is a north- and northwest-trending belt of Mariposa Slate, with greenstone and green schist to the west and mica schist, slate, quartzite, amphibolite, and serpentine to the east (Clark, 1970).

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References

Reference (Deposit): Busch, L.L., 2001, Mineral land classification of El Dorado County, California: California Geological Survey Open-File Report 2000-03.

Reference (Deposit): Clark, L.D., 1964, Stratigraphy and structure of part of the western Sierra Nevada metamophic belt, California:

Reference (Deposit): U.S. Geological Survey Professional Paper 410, 70 p.

Reference (Deposit): Clark, W. B., 1970, Gold districts of California: California Divisions of Mines and Geology Bulletin 193, p. 51.

Reference (Deposit): Clark, W.B. and Carlson, D.W., 1956, Mines and mineral resources of El Dorado County: California Division of Mines, California Journal of Mines and Geology, v. 52, p. 425-426.

Reference (Deposit): Duffield, W.A., and Sharp, R.V., 1975, geology of the Sierra Foothills melange and adjacent areas, Amador County, California: U.S. Geological Survey Professional Paper 827, 30 p.

Reference (Deposit): Earhart, R.L., 1988, Geologic setting of gold occurrences in the Big Canyon area, El Dorado County, California: U.S. Geological Survey professional Paper 1576, 13 p.

Reference (Deposit): Lindgren, W. and Turner, H.W., 1894, Placerville folio, California: U.S. Geological Survey, Geological Atlas of the U.S., folio 3.

Reference (Deposit): Logan, C.A., 1934, Mother Lode gold belt of California: California Division of Mines Bulletin 108, p. 38, 46, 53.

Reference (Deposit): Logan, C.A., 1938, Mineral resources of El Dorado County: California Division of Mines, 34th Report of the State Mineralogist, p. 220-223.

Reference (Deposit): Saleeby, J., 1982, Polygenetic ophiolite belt of the California Sierra Nevada: Geochronological and tectonostratigraphic development: Journal of Geophysical research, v. 87, n0. 8, p. 1803-1824.

Reference (Deposit): Additional information on the Sliger Mine is contained in File No. 339-8774 (CGS Mineral Resources Files, Sacramento)

Reference (Deposit): Logan, C.A., 1926, El Dorado County: California State Mining Bureau, 22nd Report of the State Mineralogist, p.418-419.

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