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Calaveras Co., California, USA
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NOTE: The files of this county are under active revision, commencing July 6, 2014. Please do not make any changes until this process is completed, at which time a posting will be made under the California thread under the Localities forum, Mindat message board. Any questions, please contact Chet Lemanski. Thank you!



Welcome to Calavaras County!
History
The history of Calaveras County is much like that of other counties in the California Mother Lode. Hoards of miners came; water systems were developed; settlements grew up around the more successful and environmentally rich mining areas; transportation networks developed, first as trails and then as wagon roads; farms, orchards, and truck gardens sprang up; saloons and fandango halls, along with boarding houses provided entertainment, bed, bath, and sustenance; and the bare bones of civilization in the form of government, newspapers, and social lodges developed from a beautiful wilderness.

VALUABLE MINERAL RESOURCES OF CALAVERAS COUNTY, CALIFORNIA

From 1880 to 1960, Gold, Copper and Limestone have accounted for the greatest portion of wealth produced by Calaveras county. However, other important mineral commodities include Zinc, Silver, Lead, Chromite, Clay, Stone as well as Sand and Gravel.

Gold
Probably the best known collectible minerals found in Calaveras county are the fine, crystallized specimens of native gold in quartz that have been taken from some of the Mother Lode mines and many of the east and west belt mines. The largest and most famous specimen was the 195-pound mass of gold found at Carson Hill in 1854. Also, a number of large nuggets have been taken from placer deposits; a 94-ounce gold nugget was found south of Campo Seco in 1854. Gold is the best known mineral commodity of Calaveras county and was the chief attraction to the early-day settlers in the area. Since 1880, the value of the recorded gold output of the county has amounted to $78,031,158. However, the value of the total gold output of the county is much greater because of the vast yield from the rich surface placers mined during the gold rush, for which production records are not available. Since World War II, gold production in Calaveras county has followed a diminishing trend.



Asbestos
Chrysotile asbestos has been produced commercially in small quantities in Calaveras county. Serpentine, is the host rock for Chrysotile asbestos, and is abundant in the western portion of Calaveras county. The Asbestos is in cross-fiber seams and veinlets which appear as stockworks in the serpentine. Most of the veinlets are an inch or less in thickness and no more than a few feet in length. They branch, join other veins, or simply pinch out. Ore deposits consist of those portions of the serpentine which contain sufficient asbestos veinlets and seams to be of commercial value.



Chromite
Chromite is present as magmatic segregations in ultrabasic igneous rocks, especially serpentine. Serpentine crops out in three belts in western Calaveras county. The belts, which trend north-northwest, are not continuous, but consist of a series of irregular lenticular bodies. Most of the ore deposits consist of lenses and pods of massive chromite, or thin alternating layers of chromite and dunite. Relatively few disseminated deposits have been found. In some of the deposits, small amounts of the secondary chromium minerals uvarovite and kammererite are present.



Clay

Calaveras County, in the flush of early springtime.

The eocene Ione formation (located near Valley Springs) is the major source of raw material for the ceramic industry in northern california. It crops out in a belt of discontinuous patches along the western Sierran foothills. The most extensive exposures extend from northeastern Sacramento county across western Amador county to the extreme northwest corner of Calaveras county. The Ione formation covers an area of approximately 4 square miles in Calaveras county. The formation has been divided into an upper and a lower member. The upper member consisting of clayey sand and some clay, is mined for silica sand at Camanche and also at Ione in Amador county. The lower member, consisting of both clay and clayey sand, is the main source for commercial clay. The clay minerals are kaolinite and anauxite. Individual crystals of kaolinite are to fine-grained to be seen with the naked eye, but pearly flakes of anauxite are easily distinguishable. It is classified as fire clay, but most of the county's output is used as common clay, as in the manufacture of drain tile and sewer pipe.



Copper-Zinc
Calaveras county has been the principle source of copper and zinc in the Sierran Foothill copper belt.
Copper in the Foothill belt was first discovered in 1880 at what is now the Quail Hill mine. Soon afterward, the copper lodes at Copperopolis and Campo Seco were discovered, and the copper "boom" of the Civil War was in full sway. Smelters were erected, and by 1866, more than 5 million dollars worth of copper ore had been mined. The Union mine at Copperopolis was the source of more than half of this production. By 1867, a fall in the price of copper had ended the boom. From about 1880 to the end of World War I, the copper mines of Calaveras county were intermittently active . During World War II, copper mining in Calaveras county was revived on a major scale, and a considerable amount of byproduct lead, gold and silver were recovered. This area also became a major source of zinc. It had been produced as a byproduct as early as 1906, but ore dressing techniques had not been developed to the point where zinc-bearing copper ores could be economically treated. Since World War II, there has been minor activity at the Union and Keystone mines. Also, a considerable amount of zinc was produced at the Penn mine between 1948 and 1953. In May of 1958, small amounts of cement copper were being produced from the Penn, Star-Excelsior and Union mines.


Geological Overview of the Foothill copper belt
The foothill copper-zinc ore deposits are for the most part lenticular sulfide ore bodies developed by replacement along zones of faulting, shearing and crushing. The ore bodies consist of pyrite containing chalcopyrite, sphalerite, and smaller amounts of galena, tetrahedrite, bornite, gold, and silver. Other minerals that are present include Pyrrhotite, quartz, calcite, barite, chlorite, magnetite and hematite. In a few deposits, cobaltite, ilmenite, rutile and sphene have been observed. Outcrops of the orebodies are marked by gossan caps, some of which have been profitably mined for gold. The gossans usually do not extend to depths of more than 30 or 40 feet. The zone of supergene enrichment in most deposits of the Foothill belt ranges from within 20 to 60 feet of the surface. Chalcocite, the most plentiful secondary sulfide, is accompanied by smaller amounts of covellite. Copper and zinc minerals are also minor constituents of lode gold ores in the Mother Lode and East belt deposits, and copper minerals are found in tactite at the Garnet Hill and Moore Creek tungsten mines.



Limestone
The quarrying of limestone and the manufacture of cement by the Calaveras Cement Company is the most lucrative segment of the mineral industry in Calaveras county. Not only has the industry accounted for the largest portion of the mineral output of the county for a number of years, but the extensive limestone and dolomite deposits form some of the largest undeveloped reserves in the state. The term "limestone" here is used in a broad sense to include carbonate rocks ranging in mineral composition from nearly pure calcite to nearly pure dolomite. The largest deposits in the county are: the northern extension of the Sonora-Columbia limestone belt, the Murphys, Cave City, Kentucky House, and Gambetta deposits. Most Sierra Nevada limestone deposits are lenticular masses of recrystallized limestone and dolomite that are interbedded with metasedimentary and metavolcanic rocks of the Calaveras formation. Many have been intruded by granitic rocks. They range from small lenses less than a 1000 feet in length to those that are literally square miles in extent. Those deposits that lie east of the Mother Lode are medium to coarsely crystalline, while those to the west are mostly fine-grained. Although the west west-belt deposits are smaller, they are more uniform in composition and are commonly superior for some uses. Numerous deposits of marble are also found in Calaveras county, three of which have yielded small amounts of decorative facings and terrazzo. Solution caves and potholes are abundant in some of the Calaveras limestone deposits. Some of the potholes actually contained rich placer gold deposits that were mined during the gold rush. Veins and seams of secondary aragonite and calcite along joint planes are common. A few fossils ranging from Mississippian to Permian in age have been found in some of the limestone bodies in the Sierras, but fossil evidence is sparsely distributed.


The limestone caves of Calaveras county
Calaveras county is renowned for its abundance of limestone caverns which host some of the most spectacular formations in North America. They range in size from small openings only a few feet in extent to deep caverns hundreds of feet in length and depth that consist of numerous passageways and rooms that host marvelous formations including; flowstone, soda straws, curtains and sheets, stalagmites, stalactites and even the very rare sparkling, twisting "Helictites" as found at the renown Black Chasm Caverns. Many of the caves are on private land and are not well known. However, four Caverns are open to the public: Mercer Caverns, Moaning Caverns, California Caverns, and Black Chasm Caverns.


Quartz Crystal
Quartz crystals for use in the manufacture of quartz oscillators have been mined at Chili Gulch, 2 1/2 miles south of Mokelumne hill. Most of the state's crystal output has been from the Rough Diamond and Green Mountain drift mines located on the east side of Chili Gulch. Quartz crystal mined here in 1897-98 was used as ornamental material and a 5-inch flawless sphere and a 7-inch flawed sphere were both cut from quartz taken from this area.




Tungsten
During 1953 and 1954 tungsten ore was mined in the Garnet Hill area in northeastern Calaveras county. The sources of production were the Garnet Hill and Moore Creek mines. This is the only area in Calavera county where tungsten is known. The deposits were probably first prospected for copper during the 1860's but for many years following it was best known for the fine garnet and epidote crystals that were collected there. Both mines were prospected for tungsten during World War II, but there was no recorded production. Tungsten and various amounts of copper and molybdenum ore minerals are in north-trending tactite bodies at the crest of Garnet Hill, and south of Moore Creek half a mile to the southwest. These tactite bodies are roof pendants in granodiorite and were developed by contact metamorphism when calcareous rocks were intruded by the granodiorite. The tactite consists of coarse-grained garnet and epidote with smaller amounts of calcite and quartz. Most of the granodiorite adjacent to the tactite is gneissic. The ore bodies are zones within the tactite that contain disseminated fine-to-coarse-grained scheelite. These zones may be in or near the center of the tactite, or may extend across the entire width. Most of the scheelite grains are subhedral, but a few well-formed crystals several inches long have been found. Associated with the scheelite are various amounts of molybdenite, chalcopyrite, pyrite and bornite. At some places masses of copper-bearing sulfides 1 - 2 feet in diameter have been found. At the Moore Creek mine coarse flakes of molybdenite are abundant.



An overview of the Geology of Calaveras County



The rocks in Calaveras county are divided into two major groups -- the older bedrock series and the younger superjacent series. The bedrock series consists of broad northwest trending belts of steeply dipping, intensely folded and faulted metamorphic rocks of Paleozoic and Mesozoic age that have been intruded by large granitic masses and also by smaller bodies of basic and ultrabasic rocks.

Gold-Quartz veins are directly associated with the granitic intrusions and are thought to be derived from them. These renowned Gold bearing Quartz veins are divided into three belts: The East belt, the Mother Lode belt and the West belt, respectively. Copper and Zinc were deposited in western portions of the county and are considered an important part of the once prolific Foothill Copper Belt. Chromite deposits were formed during the intrusion of ultrabasic rocks and were actively mined for use in Copper smelters. The Superjacent series consists of nearly flat-lying beds of auriferous gravel, clay, sand and volcanic rocks of Quaternary age.




Rock Units



Calaveras formation
(Carboniferous and Permian)
A suite of undifferentiated metamorphic rocks that underlies extensive areas in the central and east-central portions of the county. The rocks of the group are Quartz-Mica Shist, Graphitic Shist, Slate, Quartzite, Chert and and re-crystallized Limestone and Dolomite. Present in smaller amounts are sheared Conglomerate, Chlorite and Talc Shist and massive Greenstone.

Amador group
(middle to Upper Jurassic)
This group consists of metamorphosed sedimentary and volcanic rocks West of the Mother Lode in western Calaveras county. The group is divided into two formations - the Consumnes and the Logtown Ridge. The Conumnes formation consists of Tuffaceous Siltstone and Sandstone, Clay Slate, Tuff, Quartzite and Chert. The Logtown Ridge consists of massive Greenstone, which can contain large phenocrysts of Augite and Plagioclase.

Mariposa formation
(Upper Jurassic)
This formation is in two northwest trending belts 1 to 2 miles wide, in the west and west-central portions of Calaveras county. It consists predominantly of carbonaceous Clay Slate with smaller amounts of sandy Tuff and Graywacke. In the northern part of the county the Mariposa formation hosts the Mother Lode Gold belt; but south of the town of San Andreas the belt trends east of this formation.

Serpentine and associated rocks
(Jurassic)
Northwest-trending lensoid Serpentine bodies are found along the Mother Lode belt in the Angels Camp-Carson Hill area.
Serpentine of the area can be massive or foliated and slickensided, ranging in color from green and black. Associated with the Serpentine are minor amounts of Gabbro, Pyroxenite, Talc Shist and near Carson Hill, Mariposite-Ankerite rock.

Granitic rocks
(Upper Jurassic Cretaceous)
This group includes Granite, Granodiorite, Quartz Diorite, Diorite and Gabbro; Hornblende Granodiorite being by far the most abundant type. The entire eastern portion of the county is underlain by Granodiorite with smaller, isolated bodies at Rich Gulch, Jesus Maria, Mokelumne Hill and San Andreas.

Ione formation
(Eocene)
The Ione formation consists of nearly flat lying beds in the low foothills of the northwestern portion of Calaveras county. In this county, it is predominantly clayey Quartzose sand and interbedded lenses of clay.

Auriferous gravels
(Tertiary)
The Auriferous gravels were deposited in stream channels during the Tertiary period and range from Eocene to Miocene in age. They are in isolated patches, which are remnants of ancient river channels, and in more extensive deposits that are overlain by a thick cover of volcanic rocks. The Eocene channel deposits are characterized by a high percentage of Quartz alluvium and by concentrations of Gold at or near bedrock. The later Tertiary channel deposits, known as the inter-volcanic deposits, are characterized by abundant Rhyolite and Andesite cobbles and are relatively lean in Gold as compared with the older eocene deposits.

Valley Springs formation
(Miocene)
This formation consists of nearly flat lying beds of white, vitreous Rhyolite Tuff with Interbedded gravel and breccia. In the western part of the county, this formation rests uncomformably on sand and clay of the Ione formation, but to the east it lies on auriferous channel gravel or Sierran bedrock.


Mineral List

Mineral list contains entries from the region specified including sub-localities
Actinolite
Albite
var: Cleavelandite
'Allanite'
Almandine
Altaite
Alunite
'Amphibole Asbestos'
Amphibole Supergroup
var: Byssolite
Andalusite
Andradite
Ankerite
Antigorite
Antimony
'Apatite'
Aragonite
var: Flos Ferri
Arsenopyrite
var: Danaite
'Asbestos'
'var: Mountain Leather'
Axinite-(Fe)
'Axinite Group'
Azurite
Baryte
Bementite
'Biotite'
Bismuth
Boothite
Bornite
Brochantite
Calaverite (TL)
Calcite
Chalcanthite
Chalcocite
Chalcopyrite
Chlorargyrite
'Chlorite Group'
Chromite
Chrysocolla
'Chrysoprase'
Chrysotile
Cinnabar
Clinochlore
var: Chromian Clinochlore
var: Kämmererite
var: Pennine
Cobaltite
Coloradoite
Copper
Coquimbite
Covellite
Cuprite
Diaspore
Dolomite
Emmonsite
Enstatite
Epidote
Erythrite
Fayalite
'Feldspar Group'
Ferrimolybdite
Ferro-actinolite
Freibergite
Galena
'Garnet'
'Garnierite'
Glaucophane
Goethite
Gold
var: Electrum
Graphite
Gypsum
var: Selenite
Hematite
Hessite
'Hornblende'
Ilmenite
Jamesonite
Jarosite
Kalinite
Kaolinite
'K Feldspar
var: Valencianite'

Laumontite
'Limonite'
Magnesiochromite
Magnesite
Magnetite
Malachite
'Manganese Oxides'
Marcasite
Margarite
Melonite (TL)
Millerite
Molybdenite
'Monazite'
Muscovite
var: Mariposite

var: Sericite
Nickeline
'Olivine'
Opal
'Orthochrysotile'
Orthoclase
Palygorskite
'Petrified Wood'
Petzite
Platinum
var: Ferroan Platinum

Powellite
'Prochlorite'
'Psilomelane'
Pyrite
Pyrolusite
Pyromorphite
'Pyroxene Group'
Pyrrhotite
Quartz
var: Jasper
var: Moss Agate
var: Rock Crystal
Reevesite
Rhodochrosite
Rhodonite
Riebeckite
Rutile
Scheelite
Schorl
'Serpentine Group'
Siderite
Silver
Skutterudite
var: Smaltite
'Smectite Group'
'Soapstone'
Spessartine
Sphalerite
Stibnite
Stilpnomelane
Sylvanite
Talc
'Tantalite'
Tellurium
Tenorite
Tephroite
Tetradymite
Tetrahedrite
Thorite
Titanite
'Tourmaline'
Tremolite
'Uraconite'
Uraninite
Uvarovite
Vesuvianite
Vivianite
'Wad
var: Cobaltian Wad'

Willemite
Zircon


164 entries listed. 112 valid minerals. 2 type localities (valid minerals).

Localities in this Region

USA
USA

The above list contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.

References

Patton, William (1855), Geology of a portion of Calaveras County; California Surveyor General, Annual Report 1854: California Legislature, 6th. session, A Jour. Ap. F: 86-88.

Goodyear, Watson Andrews (1867), Salt Springs Valley and the adjacent region in Calaveras County: California Academy of Science Proceedings: 3: 387-399.

Silliman, Benjamin, Jr. (1867a), A notice of the peculiar mode of the occurrence of gold and silver in the foothills of the Sierra Nevada, and especially at Whiskey Hill, in Placer County, and Quail Hill, in Calaveras County, California: California Academy of Natural Sciences Proceedings: 3: 349-351; […American Journal of Science, 2nd. series: 45: 92-95 (1868)]: .

Brown, J.A. (1890), Amador, Calaveras Counties: California Mining Bureau. (Report 10): 10: 98-123, 147-152.

Preston, E.B. (1893), Amador, Butte, Calaveras, El Dorado, Lassen, Monterey, Plumas, San Benito, Sierra, Tuolumne Counties, also Salton Lake: California Mining Bureau. (Report 11): 11: 139-178, 200-209, 241-242, 259-262, 323-333, 370-373, 387-393, 400-419, 493-513.

Storms, William H. (1894), Ancient Channel System of Calaveras County: California Mining Bureau (Report 12): 482-492.

Kerr, M.B. (1900), Register of Mines and Minerals, County of Calaveras, California, California Mines Bureau, 27 pp.

Ransome, Frederick Leslie (1900), Description of the Mother Lode district, California: USGS Geological Atlas, Mother Lode (No. 63), 11 pp.

Reid, John A. (1907b), The ore deposits in Copperopolis, Calaveras County, California: Economic Geology: 2: 380-417; […(abstract): Geol. Zentralbl., Band 11: 350 (1908)]:

Lindgren, Waldemar (1911), The Tertiary gravels of the Sierra Nevada of California: USGS Professional Paper 73, 226 pp.

Tucker, W. Burling (1915), Calaveras County: California Journal of Mines and Geology, California Mines Bureau (Report 14): 14: 70.

Tucker, W. Burling (1916), Amador, Calaveras, Tuolumne Counties: California Journal of Mines and Geology, California Mining Bureau. (Report 14): 14: 1-172; […(abstract): Geol. Zentralbl., Band 27: 396 (1922)]: .

Larsen, Esper Signius (1917), Durdenite from California: American Mineralogist: 2: 45-46.

Larsen, Esper Signius (1921), The microscopic determination of nonopaque minerals: USGS Bulletin 679, 294 pp.: 71.

Logan, Clarence August (1921), Auburn field division: California Mining Bureau. (Report 17): 17: 391-490.

Knopf, Adolf (1929), The Mother Lode system of California: USGS Professional Paper 157, 88 pp.; […(abstract): Engineering & Mining Journal: 128: 24 (1929); […Geol. Zentralbl., Band 41: 364-367 (1930)].

Franke, Herbert A. & C.A. Logan (1936), Mines and mineral resources of Calaveras County: California Division Mines (Report 32): 32: 226-364.

Logan, Clarence August and Franke, H. (1936), Mines and Mineral Resources of Calaveras Co.: California Division of Mines, California Journal of Mines & Geology, California Division of Mines (Report 32): 32(3): 311.

Durrell, Cordell (1944) Geology of the quartz crystal mines near Mokelumne Hill, Calaveras County, California California Division Mines (Report 40): 40: 423-433.

Cater, F.W., Jr. (1948b), Chromite deposits of Calaveras and Amador Counties, California: California Division Mines Bulletin 134, part 3, chapter 2: 33-60.

Heyl, George Richard (1948b), Ore deposits of Copperopolis, Calaveras County, California: California Division Mines Bulletin 144: 93-110.

Heyl, George Richard (1948c) The zinc-copper mines of the Quail Hill area, Calaveras County, California. California Division Mines Bulletin 144: 111-126.

Heyl, George Richard, Cox, M.W. and Eric, J.H. (1948) Penn zinc-copper mine, Calaveras County, California. California Division Mines Bulletin 144: 61-84.

Wiebelt, F.J., Sanborn, W.C., Trengrove, R.R., and Ricker, A.S. (1951) Investigaton of West Belt copper-zinc mines, El Dorado, Amador, Calaveras, and Mariposa counties. U.S. Bureau of Mines Report of Investigation 4760, 62 pp.

Clark, L.D. (1954), Geology and mineral deposits of the Calaveritas quadrangle, Calaveras County, California: California Division Mines Special Report 40.

Eric, J.H., A.A. Stromquist & C.M. Swinney (1955), Geology and mineral deposits of the Angels Camp and Sonora quadrangles, Calaveras and Tuolumne Counties, California: California Division Mines Special Report 41.

Clark, Wm. B. & P.A. Lydon (1962), Mines and mineral resources of Calaveras County, California: California Division of Mines & Geology County Report 2; [… Geological Society of America Proceedings, 1933: 312-313, 1934]: .

Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 174, 282.

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 5: 1-22.

Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 303.

Clark, William B. & Lydon, Philip A. (1963), Mines and Mineral Resources of Calaveras County, California, California Division of Mines and Geology, County Report No. 2. Pages 11-15.

Cooperative War Minerals Investment Project, Calaveras County No. 6 & 7: 19 (Holbrook and McGuire Mine).

Taliaferro, Nicholas Lloyd, Coop War Minerals Investigations California Chrome, Calaveras County, No. 4.

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Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
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