Jenny Lind District

Site Name

Primary: Jenny Lind District

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Commodity

Primary: Gold
Secondary: Platinum
Secondary: Silver

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Location

State: California
County: Calaveras
District: Jenny Lind

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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: Calaveras County Planning Dept.

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: Various private owners

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Production

Not available

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Deposit

Record Type: District
Operation Category: Past Producer
Deposit Type: Stream placer
Operation Type: Surface
Discovery Year: 1849
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: Placer Au-PGE

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Orebody

Form: Irregular

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Structure

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

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Alterations

Not available

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Rocks

Name: Gravel
Role: Host
Description: shoreline
Age Type: Host Rock
Age Young: Tertiary

Name: Gravel
Role: Host
Description: stream
Age Type: Host Rock
Age Young: Tertiary

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Analytical Data

Not available

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Materials

Ore: Gold
Gangue: Quartz
Gangue: Magnetite
Gangue: Ilmenite
Gangue: Zircon
Gangue: Garnet

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Comments

Comment (Workings): Little specific information is available regarding the individual mining operations in the Jenny Lind district. The earliest placer mining exploited the Quaternary Calaveras River gravels and was by means of a miner's pan. By 1850, rockers were in use throughout the district. Rockers were quickly supplemented and replaced by the long tom. By the early 1850s, hydraulic mining became the dominant method of mining the Tertiary terrace gravels. Hydraulic mining persisted until the Sawyer Decision in 1884 severely curtailed hydraulic mining. Hydraulic mining virtually ceased by 1905. In 1903, the Calaveras Gold Dredging Company introduced bucket-line dredging of the unconsolidated Quaternary gravels to the district. By the 1930s, dragline dredging came into prominence since it allowed the working of many small properties that were not rich or large enough to warrant the capital investment in a bucket-line dredge. Clark and Lydon (1962) and Tucker (1915) provide a more detailed description of the equipment and techniques employed in dredging operations.

Comment (Economic Factors): No detailed information is available regarding the early placer production in the Jenny Lind district. Clark (1970) estimated total production to be more than 100,000 ounces of gold. Values recovered by dredging ranged from 10 to 30 cents per yard.

Comment (Commodity): Ore Materials: Placer Gold

Comment (Commodity): Gangue Materials: Quartz, igneous and metamorphic gravels, magnetite, ilmenite, zircon, and garnet

Comment (Development): Placer gold deposits in the gravels of the modern Calaveras River and tributary creeks of the Jenny Lind district were first worked during the early years of the gold rush, and hydraulic mining of the Tertiary shoreline and deltaic terrace gravels followed. Dredging operations commenced in 1903 when the Calaveras Gold Dredging Company began operations on the Calaveras River near Jenny Lind. In 1908 and 1910, the Isabel Dredging Company and the Butte Dredging Company, respectively, commenced dredging on the south side of the Calaveras River near Jenny Lind. By 1913, all three companies were operating concurrently within the district (Tucker, 1915).

Comment (Deposit): The Jenny Lind district is noted for its rich placer gold deposits within river and floodplain gravels of the modern Calaveras River. The placer gold was derived from erosion of bedrock gold-quartz veins in the Mother Lode and East Gold belts of the Sierra Nevada and from reworked auriferous gravels deposited by the ancestral Tertiary Mokelumne River. Gravel deposits were generally 20 to 40 feet deep and of low grade, yielding 10 to 30 cents per yard. Dragline and bucket dredging were the principal means of mining.

Comment (Geology): REGIONAL GEOLOGY The Jenny Lind District 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. 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. 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. In Calaveras County, mesothermal gold-quartz veins of the Mother Lode and East Gold belts are responsible for most of the gold produced. However, rich placer gravels of the ancestral Tertiary Calaveras and Mokelumne rivers and their modern counterparts were also exploited, primarily by hydraulic mining and dredging respectively. The placer gold was derived from the upstream erosion of the Mother Lode and East Gold belt bedrock veins. Mother Lode Belt mineralization is generally characterized by steeply dipping gold-bearing quartz veins that traverse western El Dorado through Tuolumne counties. 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). The Melones Fault zone separates the Mother Lode Belt from the East Gold Belt. The East Belt is dominantly argillite, phyllite and phyllonite, chert, and metavolcanic rocks of Paleozoic-Mesozoic age that have been assigned to the Calaveras Complex by most investigators. Lode deposits of the East Belt consist of many individual gold quartz veins within rocks of the Calaveras Complex, Shoo Fly complex, or in granitic rocks. Most of the veins trend northward and dip steeply. East Belt veins are smaller and narrower than those of the Mother Lode, but commonly are more chemically complex, and richer in grade. Regionally, the northern Sierra Nevada experienced a long period of Cretaceous to early Tertiary erosion, after which it underwent extensive Oligocene to Pliocene volcanism. The oldest of the Tertiary units are basal Eocene auriferous gravels, which were preserved in paleochannels eroded into basement and adjacent bench gravels deposited by the predecessors of the modern Calaveras and Mokelumne rivers. Farther west, in the vicinity of the Jenny Lind district, the Eocene Calaveras River discharged to the Ione sea which occupied much of the Central Valley during this period. Auriferous deltaic sand and gravels were deposited at the river's mouth and shoreline gravels were distributed in a northwest-southeast trend along the ancient shoreline. In contrast to the earlier volcanism, Tertiary volcanism was continental and deposited on top of the eroded basement rocks, channel deposits, and Mesozoic intrusives. An important widespread unit of intercalated rhyolite tuffs and intervolcanic channel gravels is the Oligocene-Miocene Valley Springs Formation. The youngest volcanic unit, the Miocene-Pliocene Mehrten Formation, consists largely of andesitic flows overlying the Valley Springs Formation.

Comment (Identification): The Jenny Lind district extends between Jenny Lind and Milton in western Calaveras County. It extends westward into eastern San Joaquin County and northeastern Stanislaus County. The district has yielded more than 100,000 ounces of gold (Clark, 1970). Auriferous Quaternary-age river and floodplain gravels deposited by the modern Calaveras River were the principal deposits. As much as 40 feet thick, these low-grade gravels yielded 10 to 30 cents per yard and were largely exploited by dragline and bucket dredging operations between 1903 and 1951. Tertiary-age auriferous gravels of the ancestral Calaveras River were also exploited by hydraulic mining methods until hydraulic mining was curtailed by the Sawyer decision in 1884. Tertiary gravels included ancient river gravels as well as deltaic and shoreline sands near the ancient river's mouth where it entered the Ione Sea. No information is available regarding the early placer production in the Jenny Lind, but the district is thought to have produced more than 100,000 ounces of gold. (Clark, 1970).

Comment (Location): Location selected for latitude and longitude is the community of Jenny Lind on the USGS 7.5 minute Valley Springs quadrangle

Comment (Geology): Pliocene-Pleistocene uplift of the Sierra Nevada caused existing drainages to cut down through the volcanic Valley Springs - Mehrten sequence and carve deep river gorges into the underlying basement rocks. During this process, the rivers became charged with placer-gold deposits from both newly eroded basement rocks and from the reconcentration of the eroded Tertiary placers. The discovery of these modern Quaternary placers in the American River is what sparked the California Gold Rush which led the discovery of similar deposits in Calaveras River gravels in the Jenny Lind district. LOCAL GEOLOGY The principal placer deposits of the Jenny Lind district consist of unconsolidated Quaternary gravels in and adjacent to the modern Calaveras River, its floodplain deposits and those of its tributary streams. Secondary deposits included older terrace and Tertiary shoreline gravels associated with the ancestral Calaveras River. Dredging depths ranged from 20 to 40 feet, with the average nearer 20 feet overlying a substrate of soft clay. The gravels are generally coarse and unconsolidated, and are sometimes overlain by heavy clay and loam which reaches as much as 10 feet deep and causes much difficulty in dredging (Winston, 1910). In places, the gravels are also overlain by hydraulic mine tailings. Recovered gold values ranged from 10 cents to 30 cents per yard and hydraulic tailings were around 10 cents per yard. There are a number of narrow gold-quartz veins in greenstone in the eastern portion of the district.

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References

Reference (Deposit): Tucker , W. B., 1915, Calaveras County, gold dredging: California Mining Bureau report 14, pp. 124-127.

Reference (Deposit): Clark, W. B., 1970, Gold districts of California: California Divisions of Mines and Geology Bulletin 193, p. 80.

Reference (Deposit): Clark. W. B., Lydon, P.A., 1962, Mines and mineral resources of Calaveras County, California: California Division of Mines and Geology County Report No. 2, p. 76-93.

Reference (Deposit): Logan, C.A., 1919, Calaveras River area: California Mining Bureau Bulletin 85, pp. 32-35.

Reference (Deposit): Logan, C.A., 1936, Calaveras County, ancient shore line deposits: California Division of Mines Report 32, pp. 324-325.

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California Gold

"Where to Find Gold in California" looks at the density of modern placer mining claims along with historical gold mining locations and mining district descriptions to determine areas of high gold discovery potential in California. Read more: Where to Find Gold in California.