Camanche Mining District, Calaveras County, California, USAi

Regional Level Types
Camanche Mining District	Mining District
Calaveras County	County
California	State
USA	Country

A placer Au-Ag-PGE (Pt) mining area with occurrences located in secs. 1-5 & 8-12, T4N, R9E and in secs. 5-8, T4N, R10E, MDM, on a stretch of the Mokelumne River between Lancha Plana in Amador County and Clements in San Joaquin County, on private land with various owners, and land administered by the U.S. Bureau of Reclamation. Discovered in 1849.

Mineralization is a stream placer deposit (Deposit model code 119; USGS model code 39a; BC deposit profile C01. C02; Deposit model name: Placer Au-PGE; Mark3 model number 54), hosted in unconsolidated Tertiary and Quaternary stream gravels (terrace and shoreline) of the Ione Formation (gravel & conglomerate). Local rocks include Miocene nonmarine rocks.

Location:This district extends along the Mokelumne River from the vicinity of Lancha Plana, Amador County, west through the Camanche-Wallace area, Calaveras County, to Clements, San Joaquin County, a distance of about 12 miles.

History:The creeks were first worked during the early part of the gold rush, and hydraulic mining of the terrace gravels followed. The town of Camanche was named for a town in Iowa. Later, the Chinese mined the river and reworked the old tailings. From 1904 to 1923, the river was dredged on a large scale by the American Dredging Company. Dragline dredging was done during the 1930s and bucket-line dredging from then until 1951. Much of the region was recently inundated by the Camanche reservoir. The output from dredging is estimated to be about $10 million.

Geology:The deposits consist of unconsolidated gravels in and adjacent to the Mokelumne River and floodplain deposits. Tightly packed shore gravels of Eocene age are found near Wallace. In the west portion of the dredging field, the gravels ranged from six to 50 feet deep while, in the east, they were six to 25 feet deep. Bedrock is clay and volcanic rock. Values recovered by dredging ranged from 10 to 25 cents per cubic yard (period values). The gold was fine grained and 850 to 900 in fineness.

Regional Geology:The Camanche 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 Amador and Calaveras counties, rich mesothermal gold-quartz veins of the Mother Lode Belt are responsible for most of the gold produced. However, rich placer gravels of the ancestral Tertiary Mokelumne and Calaveras rivers and their current recent 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 Eocene auriferous gravels, which were preserved in paleochannels eroded into basement and adjacent bench gravels deposited by the predecessors of the modern Mokelumne and Consumnes rivers. 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.REGIONAL GEOLOGY The Camanche 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 Amador and Calaveras counties, rich mesothermal gold-quartz veins of the Mother Lode Belt are responsible for most of the gold produced. However, rich placer gravels of the ancestral Tertiary Mokelumne and Calaveras rivers and their current recent 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 Eocene auriferous gravels, which were preserved in paleochannels eroded into basement and adjacent bench gravels deposited by the predecessors of the modern Mokelumne and Consumnes rivers. 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.

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 modern 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 to the discovery of similar deposits in Mokelumne River gravels in the Camanche district. LOCAL GEOLOGY The principal placer deposits of the Camanche district consist of unconsolidated Quaternary gravels in and adjacent to the current Mokelumne River, its floodplain deposits and those of tributary streams. Secondary deposits included older terrace and Tertiary shoreline gravels associated with the ancestral Mokelumne River. In the western portions of the dredging fields, the gravels ranged from 6 to 50 feet deep while, in the east, they were 6 to 25 feet deep, averaging about 20 feet. The gravels are underlain by a false bedrock of volcanic lava ash and clay. Overburden consists of from one to ten feet of silt and soil. Values recovered by dredging ranged from 10 to 25 cents per yard. The gold was fine-grained and 850 to 900 in fineness (Clark, 1970). Associated with the gold are heavy, resistant minerals such as magnetite, ilmenite, zircon, and garnet, as well as minor amounts of silver and platinum-group metals.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 modern 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 to the discovery of similar deposits in Mokelumne River gravels in the Camanche district. LOCAL GEOLOGY The principal placer deposits of the Camanche district consist of unconsolidated Quaternary gravels in and adjacent to the current Mokelumne River, its floodplain deposits and those of tributary streams. Secondary deposits included older terrace and Tertiary shoreline gravels associated with the ancestral Mokelumne River. In the western portions of the dredging fields, the gravels ranged from 6 to 50 feet deep while, in the east, they were 6 to 25 feet deep, averaging about 20 feet. The gravels are underlain by a false bedrock of volcanic lava ash and clay. Overburden consists of from one to ten feet of silt and soil. Values recovered by dredging ranged from 10 to 25 cents per yard. The gold was fine-grained and 850 to 900 in fineness (Clark, 1970). Associated with the gold are heavy, resistant minerals such as magnetite, ilmenite, zircon, and garnet, as well as minor amounts of silver and platinum-group metals.

Operations: American Dredging Co., 1904-23, three bucket-lines; Camanche Placers Ltd., 1935-, one bucket-line; Gold Gravei Products, 1935; Gold Hill Dredging Co., 1936-51, two bucket-lines; Lancha Plana Gold Dredging Co., 1926-40, one? bucket-line; Wallace Dredging Co., 1935-40, two bucket-lines.

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