Oneida Mine

Site Name

Primary: Oneida Mine

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Commodity

Primary: Gold
Secondary: Silver

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Location

State: California
County: Amador
District: Jackson-Plymouth

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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: Amador 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: Underground
Discovery Year: 1860
Years of Production:
Organization:
Significant: Y

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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, pinch and swell

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Structure

Type: L
Description: Melones Fault zone

Type: R
Description: Bear Mountains Fault zone, Melones Fault zone

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Alterations

Not available

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Rocks

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

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: Quartz
Gangue: Slate

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Comments

Comment (Commodity): Commodity Info: Ores values ranged up to $40 per ton.

Comment (Commodity): Ore Materials: Free milling gold in quartz with auriferous sulfides, principally pyrite and arsenopyrite

Comment (Commodity): Gangue Materials: Quats, slate, greenstone

Comment (Geology): REGIONAL GEOLOGY The Oneida Mine is located 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. Locally, the Mesozoic rocks are capped by erosional remnants of Eocene auriferous gravels and once extensive volcanic rocks of Tertiary age. 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. In Amador County, the structural belts are internally bounded by the Melones and Bear Mountains fault zones. Schweickert and others (1999) provide one interpretive overview of the regional geology of this part of the Sierra Nevada. Gold deposits in the Plymouth - Jackson district occur within the north and northwest trending mile-wide Mother Lode Belt, which is dominated by gray to black slate of the Upper Jurassic Mariposa Formation and associated greenstone and amphibolite schist bodies assigned to its Brower Creek Volcanics member. In Amador County, the Mother Lode Belt approximately parallels Highway 49 southeastward from Plymouth through the town of Jackson. The geology of this segment has been mapped by Zimmerman (1983) and Duffield and Sharp (1975). The lode gold deposits along this stretch are responsible for most of the gold production in the county, which has been reported to be 7.68 million ounces (Koschman and Bergendahl, 1968). Clark (1970) placed the value of this production at $180 million. The Amador County portion of the belt was one of the most productive gold mining areas in the United States, and the Plymouth - Jackson district in Amador County was the most productive part of the belt. The Mariposa Formation contains a distal turbidite, hemipelagic sequence of black slate, amphibolite, schist, and fine-grained tuffaceous rocks, and volcanic 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. Massive greenstone of the Upper Jurassic Logtown Ridge Formation lies west of the Mother Lode Belt. The contact between the Logtown Ridge and Mariposa Formation is generally gradational (Zimmerman, 1983). The Logtown Ridge Formation consists of over 9,000 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. Metasedimentary rocks, chiefly graphitic schist, metachert, and amphibolite schist of the Calaveras Complex (Carboniferous to Triassic) are to the east. Mother Lode Gold Quartz Veins Mother Lode-type veins fill voids created within faults and fracture zones. The Mother Lode Belt consists of a vein system ranging from a few hundred feet to a mile or more in width. The vein system consists of a fault zone containing several parallel veins separated by hundreds of feet of highly altered country rock containing small quartz veins and occasional bodies of low-grade ore. Veins are generally enclosed within numerous discontinuous fault fissures within Mariposa Formation slate, associated greenstone, amphibolite schist, or along lithologic contacts. Mineralized fault gouge is abundant.

Comment (Development): Most of the important lode gold deposits in Amador County Mother lode were discovered in the 1850s while rich Tertiary placer deposits were being worked. One of the important and richest of the early mines on the Mother Lode, the Oneida Mine was founded in the 1860s. Early hanging wall ores yielded as much as $40 a ton, with average yields of $22 per ton in 1867 and $16 per ton in 1868 (Logan, 1934). The mine was operated intermittently from the 1860s until the late 1890s when extensive development work was done and a new mill erected. By 1871, there were three shafts at 300 feet, 700 feet, and 800 feet, and the vein had been drifted for a length of 800 feet on the 700-foot level with 2 ore shoots reportedly 700 feet and 400 feet long. These old workings finally reached a depth of about 1000 feet, after which the property lay idle until 1896 (Logan, 1934). In 1896, a new vertical shaft was started which eventually struck the Oneida vein on the 1900-foot level. This shaft was bottomed at a depth of 2280 feet, and an inclined winze was sunk 250 feet deeper at a point 280 feet north of the shaft. The mine was worked extensively from the 1200 foot to the 2200-foot level (Logan, 1934). On the 1200-foot level, the vein was drifted 2700 feet. On the 1500-foot level 2050 feet, and on the 2000 level about 2300 feet (Logan, 1934). Ore was stoped from the latter level to the old workings. By 1900, the old inclined shaft which had been sunk by the former operators to a depth of 1350 feet has been cleaned out and a new 60 stamp mill was under construction. The plan is to extend the inclined shaft downward and to connect it and the new vertical shaft at various levels (Storms, 1900). Operations continued until 1914, after which the mine was idled. Only fragmentary figures are available for the earlier production. For 8 months prior to June 1, 1867, a yield of $135,000 from 7710 tons of ore was reported. For less than four months in 1868 the output was $60,400 from $16 ore. By 1872, the average yield dropped to $10 a ton (Logan, 1934). For the period 1898 to 1910 inclusive, the production was about $1.5 million. The yield during this time was from $2.00 to $3.75 a ton. The total production of the Oneida Mine has been estimated at $2.5 million (Logan, 1934).

Comment (Economic Factors): Clark (1970) reported that the Oneida Mine produced about $2.5 million.

Comment (Geology): Ore Genesis Several mechanisms have been suggested as the source of the Mother Lode gold deposits. The most widespread belief is that plutonic activity magmatically differentiated vein constituents or provided the heat to circulate meteoric fluids or to metamorphose the country rocks to liberate the vein constituents. Knopf (1929) proposed that carbon dioxide, sulfur, arsenic, gold, and other constituents were emitted from a crystallizing magma but the components were carried by meteoric water in a circulation system driven by plutonic heat. Most theories suggest that gold deposits formed at temperatures of 300 to 350 degrees centigrade with a possible magmatic or metamorphic origin. Zimmerman (1983) proposed that the Mother Lode veins were generated by and localized near a major late Nevadan shear zone, the mechanism of ore genesis being the shearing and redistribution of mass within a major fault zone. He suggested that the early reverse faults had strike slip component, which is evident in the correlation of expected strike-slip dilatant zones with the geometries and steeply raking attitudes of the ore shoots. Fault movement and shearing would cause recrystallization of the rocks within the fault zone, releasing the more mobile elements including gold and most of the other vein constituents. Moreover, the heat generated by shearing would contribute to the metamorphism of the rocks in the fault zone and cause fluid circulation in the fault zone. Mineral laden auriferous fluids generated by this shearing channeled into the fault fracture system into dilatant zones, which represented avenues of increased flow and lower strain LOCAL GEOLOGY The Oneida vein occupies a fissure chiefly in slate near the contact with greenstone to the west (Tucker, 1914). The vein strikes N 27? E and dips 65?east and averages 5 feet wide. At its maximum it is 20 feet wide. The vertical shaft intersected the vien at the 1900-foot level where the hanging wall is greenstone and the foot wall black Mariposa slate, with heavy gouge on the foot wall (Storms, 1900). Ore shoots have a northerly ternd. The main ore shoot is 8 feet wide by 150 feet long and is near the shaft. North of this is an irregularly shaped ore body. A small but rich ore body was developed to the north of this on the 1000-foot level. The best ore was on the 1500-foot level, although there was production down to the 2000-foot level where some coarse gold was found in the thin quartz seam (Carlson & Clark, 1954). Ore in the lower workings is low grade Ore is free milling gold in quartz with auriferous pyrite, arsenopyrite, and minor amounts of sphalerite and galena.

Comment (Deposit): The Oneida Mine produced from typical Mother Lode type fracture filling mesothermal gold-quartz veins. The principal vein was the Oneida vein, striking N 27? E and dipping 65?east. The vein averaged 5 feet wide but thickened to as much as 20 feet. Ore is free milling gold in quartz with auriferous pyrite, arsenopyrite, and minor amounts of sphalerite and galena. Ore quality progressively declined with depth ranging from as high as $40 per ton in the upper workings to about $2 per ton near the mine's bottom of 2280 feet.

Comment (Workings): The Oneida Mine workings included a 2280-foot vertical main shaft in the hanging wall, a 1350- foot 65 ?inclined shaft, and two other shallow inclined shafts (Carlson & Clark, 1954). Levels were driven on the main shaft at 200', 350', 400', 500', 600', 700', 800', 900', 1000', 1100', 1200', 1500', 1700', 1800', 1900', 2000', 2100', 2200'. On the 1200 foot level, the vertical shaft is connected with the inclined shaft by a 500 foot crosscut. Drifts: 1200-foot level: N 1200 ft., S 1500 ft. 1500-foot level: N 1400 ft., S 650 ft. 1700 foot level: N 250 ft., S 150 ft. 1800-foot level: N 750 ft., S 1505 ft. 1900-foot level: N 250 ft., S 200 ft. 2000-foot level: N 1100 ft., S 1200 ft. 2200-foot level: N 450 ft., S 250 ft. Winzes: On the 2200-foot level, a 62? inclined winze was sunk on the vein 280 feet north of the shaft to a depth of 250 feet. The Oneida workings are connected on the 1800-foot level with the South Eureka Mine. Ore was milled in a 60 stamp mill. When in full operation, 40-50 men were employed at the mine and mill ((Carlson & Clark, 1954).

Comment (Geology): Mineralization is characterized by steeply dipping massive gold-bearing tabular quartz veins striking north to northwest and dipping between 50 to 80? east. Veins are discontinuous along both strike and dip, with maximum observed unbroken dimensions of 6,500 feet in either direction (Zimmerman, 1983), but individual veins more commonly range from structures 3,000 feet long and 10 to 50 feet wide to tiny veinlets. In rare instances, veins are known to reach as much as 200 feet thick (Keystone Vein). Veins may be parallel, linked, convergent, or en echelon, and commonly pinch and swell. Few can be traced more than a few thousand feet. At their terminations, veins pass into stringer zones composed of numerous thin quartz veinlets or into gouge filled fissures (Knopf, 1929). Ores consist of hydrothermally deposited minerals and altered wall-rock inclusions. Gold occurs as free gold in quartz and as auriferous pyrite and arsenopyrite. Quartz is the dominant mineral component in the veins, comprising 80-90% or more with ankerite, arsenopyrite, pyrite, albite, calcite, dolomite, sericite, apatite, chlorite, sphalerite, galena, and chalcopyrite in lesser amounts of a few percent or less. Cumulative sulfides generally range 1% - 3% of the rock (Carlson and Clark, 1954; Zimmerman, 1983). Ore grade material is not evenly distributed throughout the veins, but was localized in ore shoots, which tend to occur at vein intersections, at intersections of veins and shear zones, or at points where the veins abruptly change strike or dip (Moore, 1968). Ore shoots generally display pipe-like geometries raking steeply in the veins at 60-90%. Horizontal dimensions of the ore shoots are commonly 200-500 feet, but pitch lengths were often much greater, and often nearly vertical. Pockets of high grade ore are relatively abundant. Single masses of gold containing over 2,000 ounces and single pockets containing more than 20,000 ounces have been found. Silver is subordinate. Gold fineness averages 800. While most of the Mother Lode ore shoots mined have been less than 300 feet in strike length, many have extended down dip for many thousands of feet. In the deeper mines, mining continued to almost 6,000 feet on the dip of the vein with no evidence of bottoming. Cessation of operations in the deep Kennedy (5912') and Argonaut (5570') mines was caused by increasing costs at the greater depths rather than an absence of ore. Milling ore was generally low to moderate in grade (1/7 to 1/3 ounce per ton). Alteration Wall rocks have invariably been hydrothermally altered, having been partially to completely converted to ankerite, sericite, quartz, pyrite, arsenopyrite, chlorite, and albite with traces of rutile and leucoxene (Knopf, 1929). The mineralization is usually adjacent to the veins in ground that has been fractured and contains small stringers and lenses of quartz.. Locally, greenstone bodies (altered volcanic rocks) adjacent to the quartz veins contain enough disseminated auriferous pyrite in large enough bodies to constitute what has been called "gray ore". Altered slate wallrock commonly contains pyrite, arsenopyrite, quartz, chlorite, and sericite with or without ankerite (Zimmerman, 1983). Large bodies of mineralized schist also form low-grade ore bodies throughout the Mother Lode. This ore consists of amphibolite schist which has been subjected to the same processes of alteration, replacement, and deposition that formed the greenstone gray ores. The altered schist consists mainly of ankerite, sericite, chlorite, quartz, and albite. Gold is associated with the pyrite and other sulfides that are present. Pyrite comprises about 8 percent of the rock. The average grade of mineralized schist is about 0.1 oz per ton (Moore, 1968).

Comment (Identification): The Oneida Mine is located 1.5 miles northwest of Jackson in the famous Mother Lode Gold Belt in the Sierra Nevada foothills. The mine lies between the adjoining Kennedy Mine on the south and the South Eureka Mine on the north. It is within the Jackson - Plymouth district which was the most productive district of the Mother Lode belt with an estimated total production of about $180 million (Clark, 1970). The Oneida Mine is credited with $2.4 million. (Clark, 1970)

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

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References

Reference (Deposit): Clark, W. B., 1970, Gold districts of California: California Divisions of Mines and Geology Bulletin 193, p. 69-76.

Reference (Deposit): Carlson, D.W., and Clark, W.B., 1954, Mines and mineral resources of Amador County: California Division of Mines, California Journal of Mines and Geology, v. 50, p. 188.

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): Irelan, W., Jr., 1888, El Dorado County, Church Mine: California State Mining Bureau, 8th Annual Report of the State Mineralogist, p. 79.

Reference (Deposit): Logan, C.A., 1934, Mother Lode gold belt of California: California Division of Mines Bulletin 108, p. 111-112.

Reference (Deposit): Schweickert, R.A., Hanson, R.E., and Girty, G.H., 1999, Accretionary tectonics of the Western Sierra Nevada Metamorphic Belt in Wagner, D.L. and Graham, S.A., editors, Geologic field trips in northern California: California Division of Mines and Geology Special Publication 119, p. 33-79.

Reference (Deposit): Storms, W.H., 1900, The Mother Lode region of California: California Mining Bureau Bulletin 18, p 60-63.

Reference (Deposit): Tucker, W.B., 1914, Amador County, Oneida Mine: California State Mining Bureau, 14th Annual Report of the State Mineralogist, p. 39.

Reference (Deposit): Additional information on the Oneida Mine is available in file no. 332-5917 (CGS Mineral Resources Files, Sacramento).

Reference (Deposit): Zimmerman, J.E., 1983, The Geology and structural evolution of a portion of the Mother Lode Belt, Amador County, California: unpublished M.S. thesis, University of Arizona, 138 p.

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