Carson Hill Mines

Site Name

Primary: Carson Hill Mines
Secondary: Morgan Mine
Secondary: Melones Mine
Secondary: Finnegan Mine
Secondary: Calaveras Mine
Secondary: Reserve Mine
Secondary: Stanislaus Mine

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Commodity

Primary: Gold
Secondary: Silver

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Location

State: California
County: Calaveras
District: Carson Hill

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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

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: 1850
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, 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

Alteration Type: L
Alteration Text: Ankeritic and sericitic alteration of wall rock with disseminated aurtiferous pyrite mineralization

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Rocks

Name: Schist
Role: Host
Description: chlorite and sericite schist
Age Type: Host Rock
Age Young: Paleozoic
Age Old: Mesozoic

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Analytical Data

Not available

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Materials

Ore: Petzite
Ore: Melonite
Ore: Hessite
Ore: Sylvanite
Ore: Calaverite
Ore: Gold
Ore: Pyrite
Gangue: Tetrahedrite
Gangue: Molybdenite
Gangue: Bornite
Gangue: Sericite
Gangue: Ankerite
Gangue: Chalcopyrite
Gangue: Quartz
Gangue: Galena
Gangue: Petzite

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Comments

Comment (Geology): Structure The Carson Hill area displays extensive structural upheaval with several stages and styles of shearing and faulting. Early shearing is evident in zones of intensely sheared rock that parallel the regional foliation. Later faulting is recorded in the Bull and Calaveras veins. Later brittle movement is evident in west dipping reverse faults and east-dipping low-angle thrust faults that offset the Bull and/or Calaveras veins. The west dipping reverse faults moved obliquely, offsetting the Bull vein by as much as 100 feet (Collum, 1990). The east dipping thrust faults, hosting the so-called "Flat" veins, also offset the Bull vein and the mineralized wall rock which envelops it. Three principal quartz vein systems exist at Carson Hill. The Bull and Calaveras vein systems are Mother Lode type fissure filling veins occupying reverse fault planes. The Calaveras vein lies west of the Bull vein, but the two veins converge to the north. A third vein system, the so-called "Flat veins", is comprised of fracture filling quartz veins occupying low-angle thrust fault planes. The Bull vein is the largest vein and formed the prominent ridge of Carson Hill until it was removed during open pit mining operations. It consists of a coarse massive barren or nearly barren vein of white quartz striking N 20?- 80? W and dipping 60?-70? NE (Carpenter, c. 1999). To the south it splits into two branches, the Stanislaus vein on the west and the Adelaide vein on the east. The Bull vein rarely contained more than 1/7 of an ounce of gold, and was more often nearly barren (Knopf, 1929; Clark and Lydon, 1962). The maximum dilation of the Bull vein shear zone is where it bends to strike N 80? W, at which point the vein is 50 feet thick. The Calaveras vein system strikes northwestward, dips 60? NE, and has an average thickness of 10 to 15 feet. It consists of quartz with interspersed talcose gouge, talc and sericite schist, and extensive masses of ankerite with mariposite. Country rock in the vicinity of the vein system is talcose and pyritic schist. Ore mined from the Calaveras vein in 1919-1920 yielded $3.88 per ton. The Flat veins consist of a series of five gently-dipping veins striking N30? - 40?W and dip 20? to 30? NE. These younger veins occupy thrust fault fissures that intersect the Bull vein at various intervals resulting in a maximum of 120 feet of measured offset at the 1100-foot level. Hanging Wall Rocks Hanging wall rocks consist of metavolcanics, principally meta-andesite, that strike N 20?- 40? W and dip 60?- 70? NE. These rocks are generally disturbed by the younger reverse faults, which parallel regional foliation and by the . Flat vein thrust faults. Adjacent to the Bull vein, hydrothermal alteration of the meta-andesite formed large low-grade ore bodies. The extent and distribution of alteration, mineralization, and emplacement of quartz-carbonate veining were controlled by dilation fractures established during fault movement, with alteration and mineralization diminishing with distance from the principal faults. Early quartz veins are typically crushed into unconsolidated breccias (Collum, 1990). Footwall Rocks Southwest of the Bull vein, the footwall geology is more complex. About 100 feet from the Bull vein is a large body of serpentinized-peridotite with irregular dikes and inclusions of gabbro and diorite within and at the contact of the serpentinite. The serpentinite is relatively unaltered except where highly sheared. In such places it has been metamorphosed and altered to a talc-carbonate rock that contains insignificant gold (Collum, 1990). Sandwiched between the serpentine and the Bull vein are lenses of metasediments altered to carbonaceous pyrite-ankerite schist with abundant quartz stringers that yielded low-grade ore (Carpenter, c. 1999). Similar to the hanging wall ores, fracture enhanced permeability controlled the extent and distribution of alteration.

Comment (Workings): The principal working entries for the consolidated Carson Hills mines were the Calaveras, Melones, and Morgan adits, the Morgan shaft, the underground Melones winze extending from the 1100-foot level to the 3000-foot level, and the lower winze extending from the 3000-foot to the 4500-foot level. The Melones adit was the main haulage way and was known as the 1100-foot level. These workings and the various levels are shown in longitudinal sections by Clark and Lydon (1962, page 48, figs. 6, 7). Cursory descriptions of the workings of some of the mines when individually operated are contained in the individual Mine discussions in the Exploration and Development History section of this record. Several mining methods, both surface and underground, were employed at Carson Hill. Large quantities of ore were mined from glory holes north of the summit of Carson Hill. Ore from the great Morgan glory hole and others, as well as the adjacent Union shovel pit, was drawn through an ore pass to the 200-foot level and trammed to the Morgan ore pass, which was just east of the Morgan shaft, where it was delivered to the 100-foot haulage level. The ore was hauled by electric trolley locomotives to the mill (Clark and Lydon, 1962). Much of the underground ore was mined from shrinkage stopes. The Flat veins were mined by open stoping with casual pillars. Square-set shrinkage stopes with subsequent waste filling were employed at the Calaveras Mine. The two principal mills at Carson Hill were the 100-stamp Melones mill, which operated from 1902 to 1919, and the 30-stamp mill of the Carson Hill Gold Mining Corporation, which was in operation from about 1920 to 1926 and 1933 to 1942. At the Melones mill, ore was sent through a gyratory breakers, a crusher, and the stamps. The pulp was classified and concentrated on Wilfley tables and Frue vanners. Concentrates were sent to a cyanide plant. At the Carson Hill Gold Mining Corp. mill, the ore went through jaw crushers, stamps, and conical ball mills, and was concentrated on Deister tables. Concentrates were sent to the cyanide plant at the Melones mill. Mill tailings were delivered by flume to the disposal area just east of Coyote Creek (Clark and Lydon, 1962). Operations in the 1980s consisted of open pit mining with extraction by heap leaching using a valley leach method, carbon in column adsorption, high temperature-low pressure glycol elution, and electrowinnowing.

Comment (Deposit): The Carson Hill Mines group produced about $26 million, primarily from large low-grade ore bodies consisting of auriferous pyritic chlorite and sericite schist. The ore bodies were formed by extensive hydrothermal alteration and mineralization of fractured metavolcanic and metasedimentary rocks within the shear zones of two principal quartz veins; the Bull vein and Calaveras vein. Unlike typical Mother Lode veins, these quartz veins were unusually low-grade to barren, with the bulk of the gold coming from disseminated sulfides in the altered wall rocks. Highly altered chlorite and sericite schist on both the footwall and hanging wall sides of the Bull vein were the host for most of the ore mined at Carson Hill. The largest and most productive ore body was the so-called "Hanging wall ore shoot" which measured 175 feet by 15 feet and averaged one-half ounce of gold per ton. Smaller ore bodies also occurred at the intersection of the Bull vein and the gently-dipping "Flat" veins. The largest mass of gold ever found in North America, the 195-pound "Calaveras Nugget", was discovered in a Flat vein. Gold bearing telluride minerals such as calaverite, sylvanite, hessite, melonite, and petzite were also recovered in the early shallow workings. Lack of modern processes for the extraction of gold from telluride ore prevented these minerals from being significant sources of gold

Comment (Development): In 1888, an ore body 40 feet wide was discovered on the Calaveras claim. The same year, the Calaveras Consolidated Gold Mining Company, Ltd., was organized to develop the find. It purchased several claims on the Calaveras vein, erected a 20-stamp mill and commenced development. This was the first operation in the area in which large low-grade ore bodies were mined commercially (Clark and Lydon, 1962). In 1898, the Melones Consolidated Mining Company was organized with Grayson and Boland as principal stockholders. This concern consolidated the Enterprise, Keystone, Last Chance, Melones, Mineral Mountain, Reserve, and Stanislaus claims, and later the South Carolina. Under the superintendency of W.C. Ralston and later W. G. Deveraux, a large amount of development work was done including driving the Melones adit northwestward from the south side of the hill. A new mill was erected just east of the adit, and the first 60 stamps began operation in 1902. The mill was increased to 100 stamps in 1905. This was the first mine on Carson Hill to employ modern technological methods including a large mill with full electrical power that could process large volumes of low-grade ore. Mining and milling costs were lower than any other mine on the Mother Lode belt (Clark and Lydon, 1962). Large quantities of ore were mined, the maximum having been 245,000 tons in 1918, the next to last year of operation by this concern. The total value of gold produced by the Melones Consolidated Mining Company was about $4.5 million (Logan, 1935). Meanwhile in 1917, Carson Hills Gold Mines, Inc. was formed under the direction of W, J. Loring with A.D. Stevenot as mine superintendent. The old Morgan Mine was purchased in 1918. In 1919 they also acquired and consolidated the Calaveras Group, Melones, South Carolina, Iron Rock, Relief, Irvine, Rider, Adelaide, Stanislaus, and other claims. A new adit, known as the Morgan adit was driven in a southerly direction from the north side of the hill. A rich new ore body was encountered in schist in the hanging wall of the large massive "Bull" vein. This proved to be the upward extension of high-grade ore previously mined some 1300 feet below on the 1600-foot level (Knopf, 1929). In the next few years, this "Hanging Wall" ore body was mined to a depth of 4550 feet and yielded more than $5 million. Mill heads averaged over $20 per ton at times, but the average grade of the ores was $12.60/ton (Burgess, 1848). Additional properties were absorbed including those of the Melones Mining Company, and the name of the concern was changed to Carson Hill Gold Mining Company. A new 30-stamp mill was erected west of the 100-stamp mill. This concern operated the properties until 1926 when increasing costs and a decline in ore grade caused them to close the mine. The value of production for the 7 years of operation was $7 million (Clark and Lydon, 1962). During these years, the Finnegan Mine was also being operated sporadically by a local family, prospecting the Finnegan and Melones veins and operating an old mill when sufficient ore was accumulated. In the mid-1920's, while working on the 1100-foot level, loose rock caused work to cease and shortly afterward the workings caved, creating a large landslide. In 1928, a 10-stamp mill was erected at the Finnegan Mine, but by the early 1930s, the Finnegan Mine was on its last legs with the only activity being dewatering of the workings.

Comment (Commodity): Gangue Materials: Quartz, galena, chalcopyrite, ankerite, sericite, bornite, molybdenite, teterahedrite, petzite

Comment (Development): Finnegan Mine The Finnegan Mine was located on the northeast slope of Carson Hill between the Reserve and Boston Consolidated claims. The mine was operated separately from the other Carson Hill group mines for much of its history. The mine was discovered in 1856 by John Finnegan. In 1867, a small rich ore shoot which yielded $80,000 to $100,000 was encountered on the property. During the latter part of the 19th century, the mine was almost continuously active. In 1894, it was being worked on a small scale for pockets. In the early 1900s it was worked chiefly by the open pit method, and in 1910, a $10,000 pocket was discovered. The open cuts of the Finnegan and the adjoining Reserve claim of the Melones Mining Company finally joined and a suit against the latter concern resulted. From about 1920 until about 1931, Lewis, Gilman, and Moore operated the mine. The ore body consisted of mineralized amphibolite schist as much as 100 feet thick on the footwall of the Bull vein. This was developed by open cut. To the east, a narrow west-dipping quartz vein was developed by a 350-foot inclined shaft. Melones Mine The Melones mine consisted of eight claims consolidated by the Melones Mining Company in 1895 and operated as a unit until 1919. They extended from the summit of Carson Hill south to the river and are on and east of the Bull vein. All of the claims had earlier histories. The Melones Mine was best known for the large quantities of low-grade ore mined and milled at low cost. The main working entry was the Melones adit, which extended 500 feet from portal to workings. Morgan Mine Located on the northwest slope of Carson Hill, the Morgan Mine produced the largest amount of gold in the area. Discovered in 1850, it had yielded at least $2.8 million by the end of 1851. In 1854, a large mass of gold was found on the property. The mine was active during the 1860s. It was idle during much of the following period until 1918, when it was acquired by the Carson Hill Gold Mining Company. In driving the Morgan adit, the famous Hanging wall ore shoot was discovered, consequently, the Morgan and adjoining Melones mine were major sources of ore from 1920 to 1926. This mine was again highly productive during the operations of the Carson Hill Gold Mining Corporation (1933-1942). The principal working entries were the Morgan adit, the Morgan shaft, and the immense Morgan glory hole.

Comment (Economic Factors): The Carson Hill district has produced over $27 million. The vast majority of this production ($26 million) came from the Carson Hill Mines group. Reported production from Carson Hill is about one million ounces of gold with an overall average grade of about 0.120 ounces/ton (Collum, 1990). The Hanging Wall ore body was the richest in the mine averaging about 0.5 ounce of gold per ton, while most of the low-grade ores ran about 0.1 ounce per ton. The very low-grade ore mined in the 1980s by Grandview resources ran only 0.046-0.057 ounce per ton.

Comment (Geology): 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). Mineralization often occurs adjacent to the veins in ground that has been fractured and contains small stringers and lenses of quartz. Locally, greenstone bodies adjacent to the quartz veins contain enough disseminated auriferous pyrite in large enough bodies to constitute what has been called "gray ore". Altered slate wall rock 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 that 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 may comprise as much as 8 percent of the rock. The average grade of mineralized schist is about 0.1 oz per ton. The Melones Fault zone separates the Mother Lode Belt from the East Belt. The Eastern Belt is dominantly argillite, phyllite and phyllonite, chert, and metavolcanic rocks of Paleozoic-Mesozoic age. The phyllite and phyllonite are dark to silvery gray. The chert is mostly thin bedded with phyllite partings. The Paleozoic-Mesozoic metasedimentary and metavolcanic rocks of the Eastern Belt have been assigned to the Calaveras Complex by most investigators (Earhart, 1988). Older Paleozoic metamorphic rocks have been assigned to the Shoo Fly Complex. The metamorphic complexes have are intruded in places by Mesozoic plutonic rocks. Lode deposits of the East Belt consist of many individual gold-bearing quartz veins enclosed in metamorphic rocks of possible Jurassic age, metamorphic rocks of the Calaveras Complex, 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. LOCAL GEOLOGY While the Carson Hill mines are within the Mother Lode belt, the geology of the Carson Hill area is much more complex and atypical of other productive Mother Lode areas. Bedrock, which is assigned either to the Calaveras Complex or unnamed units of Jurassic age, consists of a succession of northwest-striking, northeast dipping beds of mafic metavolcanic and associated metasedimentary rocks that have been intensely folded, faulted, and metamorphosed to upper greenschist facies. Bedrock units in the mine area include, from east to west: a hanging wall of augite-hornblende meta-andesite, interbedded carbonaceous and volcaniclastic metasedimentary rocks which grade into interbedded clay-rich and/or siliceous metasedimentary rocks, and a footwall of serpentinized peridotite. The serpentinized peridotite envelops and is in contact with numerous fragments of dikes of gabbro to diorite. For the purposes of this report, the hanging wall and footwall are located with reference to the main Bull vein around which mining was focused (Collum, 1990).

Comment (Identification): The Carson Hill mines are a collection of mines that operated independently and through various consolidations in the Carson Hill district of the Mother Lode belt. The Carson Hill district consists of that portion of the Mother Lode extending from Carson Flat southeast through Carson Hill to the town of Melones on the Stanislaus River. It has also been known as the Melones district. The Carson Hill mines were the largest source of lode gold in Calaveras County, contributing about $26 million of the district's total production of $27 million. The principal properties of the Carson Hill mines group were the Morgan, Melones, Reserve, Calaveras, Finnegan, and Stanislaus mines. Other claims that were consolidated with one ore more of these mines were the Adelaide, Carson, Enterprise, Iron Rock, Irvine, Kentucky, May Day, Mayflower, McMillan, Mineral Mountain, Point Rock, relief, South Carolina, and Union claims. Because of the complexity of the history of operations and various consolidations, all have been generally lumped together for this report, with only the more important mines being described in more detail. Most of the earlier information contained in this report is taken from Clark and Lydon ( 1962). Many more sources, containing additional or supplemental information are listed in the references following this report.

Comment (Location): Location selected for latitude and longitude is the Morgan Mine symbol on the USGS 7.5 minute Angels CAmp quadrangle

Comment (Commodity): Commodity Info: Principal ?Hanging wall ore body? averaged 0.5 oz. gold/ton. Assays of solitary large pyrite crystals averaged greater than 0.333 ounces per ton. 195 pound mass of gold (?Calaveras Nugget?) found in quartz vein (largest ever in North America). Telluride minerals never exploited due to extraction problems

Comment (Commodity): Ore Materials: Altered metavolcanic wall rocks containing disseminated auriferous pyrite Free milling gold ore shoots in quartz veins Telluride minerals: calaverite, sylvanite, hessite, melonite, and petzite

Comment (Development): In 1933, the Carson Hill Gold Mining Corporation was organized. The Morgan and Melones Mines were rehabilitated to the 3000-foot level where newly discovered ore bodies in the footwall area were exposed. These were mined from that depth to the surface. Operations were stimulated by the increase in the gold price to $35 an ounce in 1935, enabling the company to work downward to the 3500-foot level. It was during this time that the large pits were developed, including the Relief, the Union Shovel Pit (Morning Glory Hole), and the Footwall glory holes west and south of the Bull vein. The Calaveras Mine was also operated with mining on the upper levels. The capacity of the 30-stamp mill was increased to 20,000 tons per month. The peak year of production for this mill was 1939 when $937,156 worth of gold was sold. The Carson Hill Gold Mining Corporation continued operations until May, 1942 when the mill burned to the ground. During this period of operation 2,400,000 tons of ore were mined which yielded a total of $6.5 million. Any hope of rebuilding the mill and resuming operations was crushed by the enactment of Government Order L-208 (Gold Mine Closing Order) in 1942 to help the war effort. The properties of the Carson Hill Mines group lay idle until 1975 when they were acquired by Cyprus Mines Corporation. After evaluation of the properties, Cyprus abandoned the project. In 1984, Grandview Resources acquired the property. Following further evaluatiuons including 43,000 feet of reverses circulation drilling, the decision was made to proceed with mining. Permits to reopen the mine as an open pit operation were approved in 1985. Operations consisted of open pit mining with extraction by heap leaching using a valley leach method, carbon in column adsorption, high temperature-low pressure glycol elution, and electrowinnowing. Ore was produced at rates that ranged from 7,000 to 14,000 tons per day (Collum, 1990) with an average gold content ranging from 0.046-0.057 oz./ton. Recovery averaged between 70% to 75%. The first dore bar was poured in December, 1986. In 1988 Western Mining Corporation took over operations, but mining operations ceased in October, 1989, after dropping gold prices and a deteriorating heap leach recovery rate made operation uneconomic. During this short period, the mine produced 90,000 ounces of gold (Collum, 1990). The mine site underwent reclamation during the 1990s. The following is a brief summary of some of the principal early mines comprising the Carson Hill mines group (from Clark and Lydon, 1962): Calaveras Mine The Calaveras Mine, which was also known as the Calaveras Consolidated, originally consisted of several claims of which the Calaveras and Santa Cruz were the most important. The property is was on the southwest slope of Carson Hill west of the Melones Mine. Large-scale mining of low-grade ore bodies in the Carson Hill area began at the Calaveras Mine soon after 1889. The mine was a major source of ore during the later part of operations of the Carson Hill Mining Company (1918-1926). During the operations of the Carson Hill Mining Corporation (1933-1942), it was mined extensively both underground and in open cuts. The mine was developed by the 1500-foot Calaveras adit, the portal of which was just west of State Highway 49 at Melones, several raises, and two open cuts on the adjacent northern slope, known as the north and south pits. These workings were on the Calaveras vein system.

Comment (Geology): REGIONAL GEOLOGY The Carson Hill mines are within the Sierra 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 and are characterized by extensive faulting, shearing, and folding (Earhart, 1988). From El Dorado County southward into Tuolumne County, lode gold deposits occur in three distinct lithologic belts - the West Gold Belt, the Mother Lode Belt, and the East Gold Belt. The Mother Lode Belt is responsible for most of the gold produced. However, there has also been substantial gold production from the West Belt and East Belt. The West Belt consists of widely scattered gold deposits located west of the Mother Lode vein system. Gold occurs in irregular quartz veins and stringers in schist, slate, granitic rocks, altered mafic rocks, and as gray ore in greenstone. The West Belt can be divided into an eastern component composed of an ophiolitic melange and a western component composed of Jurassic rocks of the Copper Hill volcanics, Salt Springs slate, and Gopher Ridge volcanics. The Bear Mountains fault zone separates the melange from the Copper Hill volcanics. The Mother Lode Belt traverses western Calaveras County and consists of the upper Jurassic Logtown Ridge and 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, schist, amphibolite and chlorite schist, 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 mineralization is characterized by steeply dipping gold-bearing quartz veins and bodies of mineralized country rock adjacent to veins. Mother Lode veins are characteristically enclosed in Mariposa Formation slate with associated greenstone. The Mother Lode belt 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, limonite, talc, and sericite. Stringer veins are commonly found in both adjacent footwall and hanging walls. Mother Lode ores are generally low to moderate grade (1/3 ounce of gold or less per ton), but ore bodies can be large. Ore shoots are generally short, 200-300 feet being the average stope length. However, they persist at depth, some having been mined to several thousand feet (Clark and Lydon, 1962). Ore shoots are commonly localized at bulges in veins, shear zones, vein intersections, or near abrupt changes in strike or dip.

Comment (Geology): Alteration Rock competency is the primary factor controlling alteration and mineralization, the best ore zones being intensely sheared meta-andesite and metasedimary wall rocks of the Bull and Calaveras veins. The more brittle metavolcanic and metasedimentary rocks fractured more easily and allowed more pervasive circulation of the mineralizing fluids within the dilation zones. Carbonate metasomatism is typified by the nearly complete replacement of the wall rock by carbonate and sericite adjacent to the major veins, which diminishes away from the veins into unaltered meta-andesite or metasediments. These altered wall rocks provided most of the Carson Hill ore. Chlorite content increases gradually with distance from the veins. Pyrite concentration in the alteration halo is as high as 5 percent but decreases rapidly away from the veins (Collum, 1990). The size of the pyrite crystals are unusual for Mother Lode mines, often exceeding the size of a half dollar and ranging from 0.02 inch to 1.25 inch cubes. Assays of solitary large pyrite crystals averaged greater than 0.333 ounces per ton (Carpenter, c. 1999). Ore Bodies and Ore Minerals Telluride minerals such as calaverite, sylvanite, hessite, and petzite were also recovered in the early shallow workings with both calaverite and melonite, a rare nickel telluride, being first found and described at Carson Hill. Lack of modern processes for the extraction of gold from tellurides prevented their being a major source of production. While some gold is found in narrow zones of intensely sheared rock that are parallel to the regional foliation, most of the gold occurs in metasomatic alteration halos as disseminated auriferous pyrite within wall rocks where dilation zones were discordant to the regional foliation. Gold is also found in brittle fractures filled with quartz-carbonate veins. Coarse free-milling gold is also found in ore shoots where the Bull vein is cut by the yuonger Flat vein thrust faults (Collum, 1990). Gold is everywhere associated with sulfide minerals, the principal sulfide being pyrite. Minor amounts of galena, chalcopyrite, tetrahedrite, molybdenite, and bornite occur with gold and pyrite in the quartz-carbonate veins. Gold is also found on grain boundaries of carbonate minerals, sericite, quartz, and pyrite. Gold, along with carbonate and sulfide minerals fill fractures in the vein quartz. In the veins, gold is up to 200 microns in size and is found on the grain boundaries of carbonate minerals and pyrite (Collum, 1990). The most famous ore body was the so-called "Hanging Wall ore shoot" which occurred at a bend in the Bull vein in the Morgan and Melones mines. This shoot averaged 175 feet by 15 feet and averaged 0.5 ounce of gold per ton. This large body was mined from the surface to the 4550-foot level. The bulk of the ore consisted of auriferous pyritic schist. Other minerals present were chalcopyrite, galena, tetrahedrite, petzite, and molybdenite in various amounts. Ore from this shoot milled in 1919-1920 yielded $11 to $14 of gold per ton. A lower-grade ore shoot was also found on the footwall at the bend in the Bull vein in the Morgan and Melones mines. This ore body extended from the surface to the 2179-foot level and consisted of pyrite-ankerite schist with abundant quartz stringers. Unlike the higher grade ore of the Hanging Wall shoot, the average value of this ore was $2 to $2.50 per ton (Knopf, 1929) More conventional Mother Lode gold quartz ore shoots containing coarse native gold were encountered in the Morgan and Melones workings at the intersection of the Bull vein and the five Flat veins. The most productive ore shoot in this vein system was on the second lowest Flat vein between the 1100 and 1600-foot levels northeast of the Bull vein. Another Flat vein yielded the 195-pound "Calaveras Nugget:"

Comment (Development): The Carson Hill mines principal properties were the Calaveras, Finnegan, Melones, Morgan, Reserve, and Stanislaus mines. Others claims that were consolidated with one or more of these mines included the Adelaide, Carson, Enterprise, Iron Rock, Irvine, Kentucky, May Day, Mayflower, McMillan, Mineral Mountain, Point Rock, relief, South Carolina, and Union. Because of the complexity of the history of operations and various consolidations, all have been generally grouped together for this discussion, with only the more important mines being described in any detail. Carson Hill was named for James H. Carson, a soldier who came to California in 1847 and who discovered placer gold in nearby Carson Creek in 1848. Within 10 days, Carson and a small company of men reportedly had each taken out 180 ounces of gold, after which they left the area planning to return the following year. By 1849, word had gotten out, and when Carson returned he found the area swarming with miners and little left to claim. He left Carson Hill to prospect the Mother Lode farther south. Lode gold was first discovered in 1850 at the Morgan Mine on Carson Hill. The rich surface ores were easily crushed in hand mortars, and rock too poor for a hand mortar was ground in arrastras. From February 1850 until December 1851, it was reported that about $2.8 million was extracted and unknown sums stolen (Clark and Lydon, 1962). As much as $110,000 in gold was exposed with a single blast, and in 1854, a 195-pound mass of gold, the largest ever found in North America, was found ("Calaveras Nugget"). The nugget was eventually melted down after being exhibited at the Paris Exhibition in 1856. Telluride minerals were also recovered in quantity, but most were lost in unsuccessful attempts to extract the gold (Clark, 1970). After the rich shallow ores were exhausted, ore grade and gold production declined. In the late 1850s, G.K. Stevenot took possession of the Morgan Mine and erected a 3-stamp mill, the first quartz mill in the area (destroyed by fire in 1862). The Melones and Stanislaus Mining Company was then organized (with G. K. Stevenot as manager) to work the Melones and Stanislaus claims. By 1865, the two properties had been mined to a depth of 250 feet and a length of 400 feet. The ore was dry ground in a wooden tub-like device, and the concentrates were shipped to New York. Later an eight-stamp mill was erected on the property. In the meantime, the Finnegan Mine on the northeast slope of Carson Hill, which had been discovered in 1857, was active (Clark and Lydon, 1962). During the late 1860s and early 1870s, the mines were mostly idle, due largely to litigation over the Morgan Mine claims and milling difficulties. In 1869, the Morgan Mine was sold for back taxes of $115.19 to William Irvine. Lack of modern processes, an absence of a cheap labor force, and the necessity for large-scale operations made it expensive to mine and mill the lower-grade ores. Lacking sufficient capital, Irvine deeded the claim to the Morgan Mining Company of which he was a major stockholder. In 1876, the Morgan Mining Company reopened the mine and a tunnel was begun, which in 1878, struck the vein 200 feet below the outcrop. The Morgan Mine was operated intermittently until 1884, when it was acquired by Senator James G. Fair. Due to animosity between Fair and Irvine, Fair closed the Morgan Mine, refusing to allow it to be worked during his lifetime so that Irvine would not profit from his 25% interest (the mine remained closed until 1914 when the Calaveras Consolidated Mining Company bought the Morgan Mine from the Fair estate).

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References

Reference (Deposit): Moss, F. A., 1927, The geology of Carson Hill: Engineering and Mining Journal, vol. 124, no. 26, p. 1010-1012.

Reference (Deposit): Ransome, F. L., 1900, Mother Lode district folio: U. S. Geological Survey Geological Atlas of the U. S., folio 63, 11 p.

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, Calaveras County - Melones Consolidated mines: California Mining Bureau Bulletin 18, p 111-119.

Reference (Deposit): Carpenter, D., c. 1999, Unpublished draft report for the California Division of Mines and Geology.

Reference (Deposit): Eisenhauer, R. C., 1932, Preliminary report on the property of the Utica Mining Company: unpublished geological report for the Utica Mining Company.

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.

Reference (Deposit): Bowen, O. E., Jr., 1949, Calaveras County: California Division of Mines Bulletin 142, p. 37-40.

Reference (Deposit): Burgess, J. A., 1937, Mining gold on Carson Hill: Engineering and Mining Journal, vol. 136, no. 3, p. 111-114.

Reference (Deposit): Burgess, J. A., 1937, Mining methods at the Carson Hill mine, Calaveras County, California: U.S. Bureau of Mines Information Circular 6940, 15 pp.

Reference (Deposit): Burgess, J. A., 1948, Mining on Carson Hill: California Divisions of Mines Bulletin 141, p. 89-90.

Reference (Deposit): Clark, L.D., 1970, Geology of the San Andreas 15-minute quadrangle, Calaveras County, California: California Division of Mines and Geology Bulletin 195, 23 p.

Reference (Deposit): Clark, W. B., 1970, Gold districts of California: California Divisions of Mines and Geology Bulletin 193, p. 34-35.

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. 44-50.

Reference (Deposit): Collum, K.R., 1990, The geology of the Carson Hill gold mine, Calaveras County, California, in, Landefeld, L.A., and Snow, G. G., eds., Yosemite and the Mother Lode gold belt; geology, tectonics, and the evolution of hydrothermal fluids in the Sierra Nevada of California, Am. Assoc. of Petroleum Geologists, Pacific section Guidebook, 68, 200 p.

Reference (Deposit): Costello, J.G., and Cunningham, J., undated, History of mining at Carson Hill: Special publication of the Carson Hill Gold Mining Corporation, 15 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): Eric, J. A., Stromquist, A. A., and Swinney, C. M., 1955, Geology and mineral deposits of the Angels Camp and Sonora quadrangles, Calaveras and Tuolumne counties, California: California Division of Mines Special Report 41, 55 pp.

Reference (Deposit): Julihn, C.E., and Horton, F.W., Mineral industries survey of the United States - Mines of the southern Mother Lode Region, Part 1, Calaveras County, Utica and Gold Cliff mines: U.S. Bureau of Mines Bulletin 413, 140 p.

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

Reference (Deposit): Logan, C. A., 1935, Carson Hill mines: California Division of Mines Bulletin 108, p. 129-137.

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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.