Georgia Slide

Site Name

Primary: Georgia Slide

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Commodity

Primary: Gold

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Location

State: California
County: El Dorado
District: Georgetown 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
Operation Type: Surface-Underground
Discovery Year: 1849
Years of Production:
Organization:
Significant: Y
Deposit Size: M

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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: R
Description: Melones Fault zone

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Alterations

Not available

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Rocks

Name: Slate
Role: Host
Age Type: Host Rock
Age Young: Mesozoic
Age Old: Paleozoic

Name: Schist
Role: Host
Age Type: Host Rock
Age Young: Mesozoic
Age Old: Paleozoic

Name: Amphibolite
Role: Host
Age Type: Host Rock
Age Young: Mesozoic
Age Old: Paleozoic

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Pyrite
Gangue: Quartz
Gangue: Calcite
Gangue: Albite

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Comments

Comment (Deposit): Unlike the typical Mother Lode gold-quartz vein deposits, the Georgia Slide ?seam? deposits consist of an orebody approximately 4,000 feet long by 500 feet wide composed of 5 principle belts of slate, schist, and amphibolite country rock that contain numerous thin gold-quartz stringers and veinlets. The veinlets generally ran from less than 1 inch thick to over one foot. The enclosing country rock was heavily weathered to depths of 100-150 feet to produce ?seam? deposits,. which allowed hydraulic removal of the soft intervening material and sorting of quartz ore. The quartz ore was processed in hand mortars and small stamp mills. Milling ore usually yielded from 1/7 to 1/5 ounce per ton, but many high-grade deposits were found.

Comment (Geology): Small and localized portions of the Mother Lode Belt north of Placerville, particularly in the area of Georgia Slide are characterized by what have been described as "seam deposits". Unlike the typical Mother Lode veins, seam deposits consist of narrow gold bearing quartz veinlets within slate, amphibolite, or chlorite schist. These zones which are as much as several hundred feet thick and contain quartz veinlets in several systems that have definite dips and strikes. The richest portions of seam deposits are, for the most part, near the intersections of two or more systems of veinlets, or where one system intersects a larger quartz veins (Logan, 1934). Seam deposits were frequently heavily weathered and friable to depths of 100-150 feet, allowing the rich oxidized zone to be worked by hydraulic mining methods, before reaching unweathered rock, wherein lode mining methods were employed. 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)

Comment (Identification): The Georgia Slide Mine is located within the Georgetown District in northwestern El Dorado County. The district is located at the northeast end of the east branch of the Mother Lode belt, which extends from just north of Garden Valley north through Georgetown and the Georgia Slide area to the Middle Fork of the American River. The mine is noteworthy as the largest of the gold "seam deposits" in the Mother Lode having produced an estimated $6.5 million ($3 million from the Georgia Slide mines and $3.5 million from placer deposits in Oregon Canyon and Canyon Creek derived directly from the seam deposits). . Unlike the typical Mother Lode gold quartz veins, the Georgia Slide deposits were largely worked by applying hydraulic mining methods to thin quartz stringers within a largely weathered country rock matrix 150-200 feet thick.

Comment (Location): Location selected for latitude and longitude is the Georgia Slide site symbol on the USGS 7.5 minute Georgetown quadrangle

Comment (Workings): The Georgia Slide deposits were primarily mined using hydraulic mining methods. It is estimated that 3,500,000 cubic yards of material were removed from the Georgia Slide Mine by hydraulic mining, leaving an open pit about 1,000 feet long by nearly 600 feet wide. Several small underground lode mining operations continued in the unweathered portions of the deposit, but no record of the workings are available.

Comment (Geology): LOCAL GEOLOGY Unlike the typical Mother Lode veins, the Georgia Slide seam deposits consist of narrow gold-bearing quartz veinlets within slate, schist and amphibolite country rock. The Georgia Slide deposit is essentially an immense lens shaped orebody roughly 4,000 feet long by 500 feet in maximum width and composed of auriferous quartz stringers ranging from one inch to over 1 foot wide within a matrix of highly weathered green chloritic schist and interbedded black slate of the Calaveras Complex (Moore, 1968). The overall orebody strikes N 5? W and dips 80? East (Logan, 1926). The Georgia Slide Mine occurs in an area where deep bedrock weathering of lode deposits caused the concentration of residual gold. Over time, extensive chemical weathering and mechanical breakdown of the softer intervening amphibolite and schist lithologies left the thin quartz veinlets and gold remaining. The deposits are loose and oxidized to depths of 100-150 feet. Jenkins (1935) referred to these deposits as "residual placer" deposits, but more commonly the term "seam deposits" has been applied. The seams are gold and auriferous pyrite-bearing quartz stringers and veinlets within the schist and slate ranging from less than 1 inch to a foot or more in thickness (Clark and Carlson (1956). Some stringers swelled into lenses several feet thick. The richest portions of seam deposits are, for the most part, near the intersections of two or more systems of veinlets, or where one system intersects a larger quartz veins (Logan, 1934). In some places, calcite and albite are abundant. There were 5 principle belts of schist and slate in which the stringers were more abundant than elsewhere. The easternmost belt was 35 feet thick (Clark and Carlson, 1956). According to Preston (1892) much of the hydraulically mined material contained $2-$3 per ton in gold. Some of the gold mined from this deposit was beautifully crystallized. Milling ore usually yielded from 1/7 to 1/5 ounce per ton, but many high-grade deposits were found (Clark, 1970). In addition, there were several wide quartz veins containing finely disseminated free gold and pyrite were encountered below the oxidized zone. The veins contained ore shoots with stoping lengths of up to 500 feet.

Comment (Commodity): Commodity Info: Hydraulically mined material contained between $2-$3 per ton. Milling ore usually yielded 1/7 - 1/5 ounce per ton.

Comment (Commodity): Ore Materials: Free milling gold and auriferous pyrite

Comment (Commodity): Gangue Materials: Quartz, calcite, albite

Comment (Economic Factors): The Georgia Slide Mine is reported to have produced about $6.5 million from seam and placer deposits. Knopf (1929) estimated that the value of gold produced from the Georgia Slide seam deposits at $6.5 million ($3 million from the Georgia Slide mines and $3.5 million from placer deposits in Oregon Canyon and Canyon Creek derived from the seam deposits).

Comment (Development): The Georgia Slide mine is the best known and largest seam gold mine in El Dorado County. Mining in the area began here in 1849 by a party of placer miners from Oregon. They established the local community of Growlersburg, whose name was soon changed to Georgetown. The small mining community of Georgia Slide soon appeared to the north on the south side of Canyon Creek. By the middle of 1850, Georgia Slide was a lively mining camp. When the easily recovered placer deposits were depleted, the lode deposits were exploited by tunneling. While technically a lode deposit in place, the Georgia Slide deposit was found at an early date to be best worked by hydraulic mining until more competent unweathered bedrock was reached. By 1853, tunneling was replaced by hydraulic mining, which would continue until it was banned in 1895. The method of working involved blasting the bank to break hard portions and hydraulicking to dig the soft ground and move broken material into sluices to wash the material. Whenever quartz specimens containing gold were found, they were hand sorted and crushed in a hand mortar (Preston, 1892). Larger blocks of gold-bearing quartz were treated in stamp mills. The first mine to use hydraulic mining at Georgia Slide was the Beattie claim (36 acres) on the south side of Canyon Creek. By 1856, two other claims, the Blue Point (27 acres) and Pacific (6 acres) commenced hydraulic operations and later, these two claims along with the Mulvey Point and Parsons (20 acres) claims were consolidated with the Beattie to become the Georgia Slide Mine. The Beatty and Parsons claims were worked almost continuously from 1853 until 1895, when the use of a hydraulic mining on the claims was ordered stopped (Logan, 1926) the Blue Rock and Pacific claims were worked continuously from 1856-1895 (Logan, 1934). After the cessation of hydraulic mining in 1895, small amounts of ore were treated in several small stamp mills. In 1915, a 10-stamp mill was being operated to determine the gold content of the large amount of accumulated tailings (the hydraulic process only recovered 40-60 percent of the gold). Some commercial mining of these claims would continue until 1916 or later. Subsequently, a number of lessees worked the quartz stringers in search of high grade pockets (Clark and Carlson, 1956). In 1983, Callahan Mining Corp. and Nevada Resources, Inc. obtained a permit to conduct an exploration program at Georgia Slide. After spending $250,000 on the program, in 1988 Callahan Mining applied for a permit to open the Blue Rock Mine on the former Georgia Slide workings. The permit was not approved.

Comment (Geology): REGIONAL GEOLOGY The Georgia Slide Mine area is within the Sierra Nevada foothills, 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. All the belts 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). 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 Greenwood, 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 Calaveras Complex rocks, 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. 435-436.

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): Jenkins, O.P., 1935, Study of placers: California Division of Mines, 31st Report of the State Mineralogist, p. 157-158.

Reference (Deposit): Knopf, A., 1929, The Mother Lode system of California: U.S. Geological Survey Professional Paper 157, p. 88.

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., 1926, El Dorado County: California State Mining Bureau, 22nd Report of the State Mineralogist, p.437-438.

Reference (Deposit): Logan, C.A., 1934, Mother Lode gold belt of California: California Division of Mines Bulletin 108, p. 34.

Reference (Deposit): Moore, L., 1968, Gold resources of the Mother Lode Belt: El Dorado, Amador, Calaveras, Tuolumne, and Mariposa Counties, California: U.S Bureau of Mines, Technical Progress Report No. 5, p. 11.

Reference (Deposit): Preston, 1892, El Dorado County: California State Mining Bureau, 11th Annual Report of the State Mineralogist, p. 203-204.

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.

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California Gold

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