Sheep Ranch Mine

Site Name

Primary: Sheep Ranch Mine
Secondary: Washington Mine
Secondary: Wallace and Ferguson Mine
Secondary: Chavanne Mine
Secondary: Pioche Mine
Secondary: American Mine
Secondary: Chavanne Claim
Secondary: Wallace Claim
Secondary: McNair Claim
Secondary: Location Claim
Secondary: Aspinwall Claim
Secondary: Northstarv Claim
Secondary: Salamanda Claim
Secondary: Admiral Dewey Claim
Secondary: Rosco Claim
Secondary: Alabama Claim
Secondary: Franklin Claim
Secondary: Lodi Claim
Secondary: Eureka Claim
Secondary: Elk Claim
Secondary: Hurricane Claim
Secondary: Toom Claim

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Commodity

Primary: Silver
Primary: Gold
Tertiary: Lead
Tertiary: Zinc
Tertiary: Copper
Tertiary: Iron

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Location

State: California
County: Calaveras
District: Sheep Ranch District

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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 Department

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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: 1867
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, lens

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Structure

Type: R
Description: Melones Fault Zone, Bear Mountain Fault Zone, Foothills Fault System, Calaveras-Shoo Fly Thrust

Type: L
Description: Parallel veins in unnamed fractures.

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Alterations

Alteration Type: L
Alteration Text: Negligible? None described.

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Rocks

Name: Mica Schist
Role: Host
Description: siliceous and graphitic
Age Type: Host Rock
Age Young: Triassic
Age Old: Carboniferous

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Chalcopyrite
Ore: Sphalerite
Ore: Pyrite
Ore: Galena
Gangue: Quartz

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Comments

Comment (Deposit): The Sheep Ranch gold deposit consists of hydrothermal quartz veins within metasedimentary rocks of the Carboniferous-Triassic Calaveras Complex. During the Late Jurassic Nevadan Orogeny, the Calaveras Complex and overlying Jurassic Mariposa Formation were metamorphosed and folded into a complex series of parallel northwest-trending folds and reverse-fault complexes in which the gold deposits of the Mother Lode region were emplaced. Primary among the complexes are the Melones Fault Zone (MFZ) and Bear Mountain Fault Zone (BMFZ), which host the Mother Lode Gold Belt (MLGB) and the West Gold Belt (WGB), respectively. All the gold mining districts lying to the east of the MLGB are included in the East Gold Belt (EGB). The Sheep Ranch deposit is in the EGB about 10 miles northeast of the MLGB. The mining operation consisted of as much as 200 acres comprising 21 patented claims and exploited at least five parallel gold-bearing quartz veins including the main "Sheep Ranch" vein, which was claimed for a distance of about 9,500 feet along its surface strike. The quartz occurs either as continuous undulatory veins or as a succession of disconnected or en echelon lenses that strike N55?W and dip 70-75? northeast. Ribboning is common. The main Sheep Ranch vein is the hanging-wall vein of the series and averages from 1-3 feet thick with swellings up to 5 feet. Much of the quartz is typically bluish gray-grayish black, a color that is characteristic of the Sheep Ranch deposit. The deposit is a true fissure-vein system, with irregular distribution of ore occurring as a series of ore shoots within the veins. Ore shoots rake about 50 degrees to the east and are often localized or enriched at vein intersections or where veins intersect igneous dikes. Low-grade and barren zones occur in the quartz veins between the ore shoots. While no site-specific geochemical data are available, the gold-bearing quartz veins are thought to be mesothermal deposits contemporaneous with the gold-bearing veins of the MLGB. Fluid-inclusion and paragenetic mineral-assemblage studies of quartz veins in the Alleghany District of the northern Sierra Nevada (Coveney, 1981) and in the Coulterville District of the southern MLGB (Weir and Kerrick, 1987) are consistent in placing mineralization temperatures at between 200?- 325?C and pressures up to 2.5 kilobars. Unlike many important mines in the MLGB and the WGB, the Sheep Ranch deposit shows little alteration of the wall rock and unusually low concentrations of associated sulfides.

Comment (Development): In 1917, the Monticali Mines Syndicate was formed to explore and evaluate the reopening of the mine. They dewaterd the mine of 50,000,000 gallons and deepened it to the 1700-foot level. In doing so, they discovered rich ore and the Golden Gate Exploration Company was formed to take over operation of the mine. Stoping was largely confined between the 1500- and 1700-foot levels with minor development work on the 1000- and 1400-foot levels. The mill process was converted from amalgamation to cyanidation, which increased recovery to almost 95%. During Golden Gate Exploration's operations, the mine produced 30,832 tons of ore averaging 0.58 oz/ton (or $11.93/ton) resulting in $367,877 (at $20.67/oz for gold). Later, the dump was worked. Despite the evidence that ore shoots at the lower 1700-foot level were as good as ore elsewhere in the mine, Golden Gate Exploration closed the mine in 1922. Reasons given for closure included incompetent labor, high costs, inadequate equipment for the 1,700 foot depth, scarce and inefficient labor available during the postwar period, and stealing of high-grade ore. Despite the hiring of detectives to thwart it, an estimated at 50% of the mine's production was lost to high-grading, which was considered one of the principle reasons for closure. The St. Joseph Lead Company reopened the mine in 1936. The mine was dewatered and the mine workings were retimbered and rehabilitated. A new headframe and 180-ton ore bin were erected, and the mill was overhauled. Ore was treated in the 150-ton mill equipped with a 28-inch primary gyratory crusher , a secondary 6 x 6-foot ball mill, Bendelari and Pan-American jigs, flotation cells, and filter presses. The main shaft was deepened to the 2100-foot level and a secondary shaft was sunk to 3,100 feet. Despite promising shows at the 2500-foot level, an east drift at the 2700-foot level encountered very little ore within the projected extension of the ore body. At the 2900-foot level, an east drift was driven 730 feet, but found only massive barren quartz. The mine was deepened to 3,100 feet and drifted to the east in hopes the ore shoot would reappear at depth. Development at the 3100-foot level proved otherwise, and it was concluded the mine had bottomed. The decision to permanently close the mine came in early 1942. During St. Joseph Lead's operation, the mine produced 139,709 tons of ore between 1938-1942. During its final years of operation, gold and silver were recovered from both the ore shoots and limited quantities of sulfide concentrates. Ore values averaged 0.45 ounce/ton gold and 0.055 ounces /ton silver. Concentrates yielded 0.12 ounce gold and 0.02 ounce silver per ton. The Sheep Ranch Mine has remained idle since its closure in 1942. Shortly after closure, all mine and mill buildings and equipment were dismantled and removed. While there have been proposals to process the remaining tailings in recent decades, none have been implemented on a systematic or significant scale. Currently, little remains of the Sheep Ranch Mine but overgrown waste rock and tailings piles. A crude wire fence surrounds the open mineshaft. The mine shaft and waste piles are accessible just north of the Pioneer Hotel. The lands are private property and posted. Permission to enter should be obtained before accessing the mine site.

Comment (Geology): Stratigraphy During the middle Paleozoic, the western edge of the North American continent lay east of the present day Sierra Nevada and was dominated by a passive continental margin. The onset of late Paleozoic convergence caused the evolution of a persistent offshore island arc and associated subduction zone. Up until the late Triassic, most of the land mass comprising the western Sierra Nevada was accreted to the continent as heterogeneous marine and magmatic arc allochthonous terranes scraped from the descending crustal plate. The contact between the native basement Paleozoic sequence and the accreted terranes has been called the Sierra Foothills Suture (Saleeby, 1981). Accretion of oceanic island-arc terranes along the suture belt choked the subduction zone and induced subduction to move west to the area of the Coast Ranges during the Mesozoic. Some researchers have interpreted the faults of the Foothills Fault System (FFS) to be sutures between allochthonous terranes (Moores, 1972; Schweickert and Cowan, 1975). Throughout the western two-thirds of Calaveras County, two primary northwesterly trending belts of metamorphosed and folded rocks form the basement complex and represent remnants of these accreted sediments. On the east is the older Calaveras Complex of Carboniferous to Triassic age (Dickinson,1981). The Calaveras Complex consists largely of black siliceous mica schist, amphibolite schist, argillite, phyllite, metachert, recrystallized limestone and metavolcanic rock. These rocks were originally deposited as hemipelagic and clastic basinal sediments including detrital and limestone muds and siliceous ooze deposited in an island arc sequence. Numerous localized occurrences of mafic and ultramafic rocks exist within the Calaveras Complex and represent metamorphosed volcanic rock and ophiolite sequences. West of the Calaveras Complex, and separated from it by the Melones Fault Zone (MFZ), is the Mariposa Formation (Upper Jurassic), which consists mainly of metamorphosed black slate and graywacke deposited as marine turbidites and volcaniclastic fan deposits of island- arc origin. Various metavolcanic units associated with this island-arc environment are locally assigned to other formations such as the Logtown Ridge and Copper Hill. The accreted terranes west of the MFZ are collectively referred to as the Foothill Terrane. Basement in the eastern third of the county consists of unroofed Mesozoic intrusive rocks of the Sierra Nevada Batholith ranging from granite to gabbro, with granodiorite being the most common. During the Late Jurassic, the Nevadan Orogeny began to elevate the Sierra Nevada. Deformation resulted from the collision of an oceanic island arc in the foothills terranes with a convergent margin on the west edge of the North American continent. Calaveras through Mariposa sediments were metamorphosed, folded into a series of complex northwesterly trending folds, and thrust faulted. Near the end of the Jurassic and into the Early Cretaceous, plutons of the granitic Sierra Nevada Batholith intruded the folded rocks. Its emplacement renewed faulting and resulted in hydrothermal gold mineralization of contemporary and earlier fracture systems.

Comment (Development): Surface exposures of a high-grade gold-bearing quartz vein are believed to have been discovered in about 1867 and claimed by C.P. Ferguson and Tom Smith. The original claim was 1600 feet in length by 200 feet wide. Shortly thereafter, W.A. Wallace bought Smith's interest, and during early development the mine was known as the Wallace and Ferguson Mine. Additional claims were added over time. Later these claims would become the main Sheep Ranch Mine. Wallace erected a 5-stamp mill to crush the ore. Using only crude and rudimentary methods, by 1871 they developed the mine to a depth of 94 feet along a quartz vein 8 to 20 inches thick. Ore valued at $34 to $44/ton was treated in arrastras. By 1877, the mine had been developed to 200 feet and had produced approximately $300,000. In 1877, the Sheep Ranch Mine and claims were acquired by James Ben Ali Haggin (Homestake and Anaconda Mines) and Senator George Hearst (father of William Randolph Hearst). They erected a 20-stamp mill and actively operated the mine as the Sheep Ranch Company until 1893. Development occurred through the main Sheep Ranch shaft to a depth of 1400 feet. During this time the mine was stoped for a length of 1400 feet to a depth of 1300 feet yielding approximately $4,000,000 from 400,000 tons of ore averaging about 0.5 troy ounces per ton. The ore was often so rich in free gold as to yield superb specimen rock. Sulfides in the form of pyrite, chalcopyrite, galena, and sphalerite accounted for less than 0.5% and were not considered worthwhile to retain. During this period, the competing Chavanne Mining Company developed the Chavanne ore shoot east of the Sheep Ranch main shaft to a depth of 600 feet deep with stoping up to about the 300-level. To avoid litigation regarding claim lines, the Chavanne mine was purchased by the Sheep Ranch Company for $100,000. The Pioche Mine adjoining on the west, with a shaft to 200 feet, was also purchased. From time to time, more adjoining gold-bearing quartz claims covering discoveries on the same vein were acquired until a total of 9 patented claims were owned covering the strike of the vein. In addition to the holding on the main vein, an additional group of claims, several of which are patented, was acquired covering more or less the parallel footwall vein. High operating costs forced the closure of the mine in 1893. Problems included costly steam-power generation and difficult metallurgy. Wood consumption for steam generation proved to be one of the biggest expenses. In 1888, 12-14 cords of wood were used per day. By 1892, all available timber in the immediate vicinity was consumed resulting in flooding of the mine to the 300 foot level, where a 2500-foot long tunnel drains the mine to the northwest into ONeil Creek. Amalgamation was the only practicable recovery process available at the time and yielded a recovery of only 75-80% (later operations were able to recover up to 95% by cyanidation). Reopened in 1898 by W.H. Clary, the Sheep Ranch Mine was deepened to 1,300 feet and operated until 1907. During this period, an east drift on the 1300-foot level found ore extending over twelve hundred feet and was stoped continuously for the full distance as it was on the upper levels. 43,150 tons of ore (worth about $440,000) of an average value of $10.65/ton was mined and milled between 1898 and 1907. Twenty stamps crushed the ore. Amalgamation was used inside the stamp mill battery and on outside plates and sluices with a 80% recovery. Inadequate financing, however, precluded the opening of enough stopes to bring the mill to capacity and profitability. In 1900, a shaft was commenced on the Lodi claim, one of the Sheep Ranch group, about 700 feet southwest of the main shaft. Whereas, in former years very rich ore was taken from the Lodi vein, no information is available regarding the sinking and development of this shaft.

Comment (Economic Factors): The Sheep Ranch Mine is considered the most productive gold mine of the East Gold Belt having produced in excess of $7,000,000 in native gold between its opening in the 1860s until final closure in 1942. Ore generally averaged 0.5-0.6 ounces per ton. The most prolific period in the mine's history was between 1877 and 1893 when over 400,000 tons of ore worth over $4,000,000 was produced. During the bulk of the mine's operation, sulfides in the form of pyrite, chalcopyrite, galena, sphalerite were encountered in concentrations of less than 0.5% and were considered insufficient to warrant the use of concentrators. During the early days of operation, the small amounts of sulfide concentrates collected assayed only $16 - $30 per ton. In the final years of operation, St Joseph Lead recovered less than $4.00 per ton from concentrates. Upon closure, no significant reserves remained in the known ore shoots. However, the quartz veins persisted at depth, and the presence of undiscovered ore shoots within them is a possibility.

Comment (Commodity): Commodity Info: Free-milling native gold is present in quartz veins. Ore has also been highly valued as high-grade specimen material and jewelry-grade gold in blue-black quartz. The very low sulfide content (<0.5%) has never been considered worthwhile to process.

Comment (Workings): The Sheep Ranch Mine is the deepest gold mine of the East Gold Belt. By the time of its closure in 1942, the Sheep Ranch Mine was developed as an underground mine to a depth of 3,100 feet via a 2,100 foot inclined main shaft and a secondary shaft sunk from the 2,100-foot level to the 3,100-foot level. The main shaft is in the hanging wall about 70 feet from the main Sheep Ranch vein, which strikes N55? W and dips 70-75? to the northeast. Ore shoots within the vein rake about 50? to the east. Drifts were driven along the vein from the main shaft at 100 foot intervals on 22 levels; the maximum length driven on the vein was 2,600 feet. From the 2,100-foot level to the 3,100-foot level, east and west drifts were driven at 200 foot intervals. At the 300-foot level, the Pioche Adit extended 2,500 feet to the west of the shaft and acted as a drain tunnel for the mine. Prior to its operation by the St Joseph Lead Company in 1936, the Sheep Ranch ore shoot was stoped continuously from the 1,300-foot level to the surface averaging 1,400 feet in length, 1,300 feet high, and 5 feet wide. More limited stoping was conducted east and west of the main shaft on the 1,400- through 1,700-foot levels. West of the main shaft, the Pioche ore shoot was mined from the surface to the 300 foot level where it intersected the Pioche drainage adit. East of the main shaft, the Chavanne ore shoot was mined from the surface to 600 feet in depth and 400 feet in length. Below 600 feet it was not mined, with the exception of very limited stoping of the 1,300-foot level where an easterly drift from the main shaft cut a poorly mineralized ore shoot 1,400 feet east of the main shaft. Below the 2,100-foot level, east- and west-trending drifts were driven at the 2,300-, 2,500-, 2,700-, 2,900-, and 3,100-foot levels. The drifts showed declining ore values with depth until the 2,900- and 3,100-foot levels, which encountered barren quartz in the main vein. The mine was subsequently closed.

Comment (Geology): INTRODUCTION The Mother Lode region has been subdivided into three gold-producing trends that share similarities in origin and character, yet exhibit differences in mineralization and ore material. The Mother Lode Gold Belt (MLGB) and the West Gold Belt (WGB) trends are manifested in two parallel zones of major structural disturbance resulting from compressional tectonic forces associated with the Late Jurassic Nevadan Orogeny. Northwest-trending reverse faults dominate this trend and ore deposits occur within the associated mineralized anastomosing faults, fissures, and shear zones. The MLGB, being closely associated with the Melones Fault Zone (MFZ), is generally 1-2 miles wide and extends 125 miles along the Sierra Nevada foothills. The WGB extends nearly as far, is associated with the Bear Mountain Fault Zone (BMFZ), and comprises all gold deposits west of the narrowly defined MLGB. Similarly, the East Gold Belt (EGB) encompasses all gold deposits east of the MLGB. Neither the WGB nor the EGB has undergone as extensive or systematic study as has the MLGB. The EGB it is notable for its relative paucity of identified significant gold deposits. Unlike the other gold belts, which display a marked longitudinal continuity of productive vein systems within the belts, the EGB deposits are fewer, smaller, and generally isolated and localized. Part of this distribution may in fact be related to the absence of, or ill definition of, an extensive longitudinal fault system analogous to the MFZ or BMFZ. Mineralization of the MLGB and WGB is characterized by both mesothermal deposition within faults, fissures, and shear zones generally in slate and greenstone, and secondary alteration of wall rock. Individual veins range from structures over 3000 feet long and over 50 feet wide to tiny veinlets. The overall zones frequently contain several parallel veins separated by hundreds of feet of highly altered country rock containing small quartz veins and occasional bodies of low-grade metasomatic ore. In the EGB, mineralization is largely confined to mesothermal deposition of free gold within white to black quartz veins. Little significant mineralization of host rock has been noted. REGIONAL SETTING The Mother Lode region has been studied extensively since the mid-nineteenth century in respect to understanding the regional stratigraphic and structural framework. Since many prolific gold mines are located in the region, numerous studies of specific mines were conducted. The progress of development of many of the lode mines is chronicled in the California State Mineralogist Reports commencing in 1880. Classic studies include Knopf's (1929) and Logan's (1935) studies of the geology and mining in the Mother Lode. Julihn and Horton's (1938) report on the mines of the Mother Lode addresses more specifically the mines of Calaveras County. Modern plate tectonic principles have inspired a reassessment of the evolution of the Sierra Nevada and the Mother Lode region. Important contributions include those by Dickinson (1981), Saleeby (1981), Burchfield and Davis (1981), and Schweickert and others (1988), which discuss the tectonic evolution of California and the Sierra Nevada.

Comment (Geology): It is clear from numerous field studies that the gold mineralization of the Mother Lode region took place after the Nevadan Orogeny (approximately 155 Ma). The origin and age of the hydrothermal fluids responsible for the gold mineralization in the Mother Lode region continues to be debated, however (Bohlke, 1999). Similarly, the specific regional tectonic events that stimulated this mineralization have not been conclusively established. A classical interpretation is that the gold-bearing quartz veins were precipitated from aqueous solutions during emplacement of plutons that comprise the Sierra Nevada Batholith. This interpretation lacks, however, specificity regarding the origin of the mineralizing fluids or the source of the contained mineral species. Studies in the areas of tectonic history, plate tectonics, thermodynamics, and geochemistry have advanced, but not conclusively resolved, our understanding of the source of these fluids. The primary interpretations for the origin of the fluids include metamorphic devolitilization and downward circulating meteoric waters. In places, stable-isotope compositions of hydrothermal minerals and fluid-inclusion characteristics from veins in the Mother Lode are consistent with metamorphic devolitilization in heterogeneous mixed carbonate-silicate rocks at depth, which could have produced a CO2-rich solution. Other studies of fluids extracted from gold-quartz veins in the Mother Lode reveal hydrogen-isotope distributions similar to modern precipitation, suggesting deeply circulating meteoric waters could be largely or partially responsible (Nesbitt and others, 1986). While it is reasonably certain that meteoric water entered the veins at some point, it has not yet been established if it commingled with and comprised a significant fraction of the ascending CO2-rich ore fluids during mineralization or if it entered the veins sometime later. The origin of the gold and other metallic elements remains problematic (Bohlke, 1999). While not conclusive, hydrothermal experiments and fluid-inclusion studies have suggested aqueous sulfide species may have been responsible for the solubility of the gold, and the low chlorinity and acidity of the fluids may have prevented the dissolution and transport of much larger amounts of the base metals Fe, Cu, Zn, and Pb. If the gold was carried in the form of an aqueous solution of sulfides, it is possible for it to have precipitated from solution in response to various combinations of cooling, mixing, degassing, sulfide precipitation, and increasing or decreasing fluid pH or oxidation state (Seward, 1991). The actual source of the metallic elements is thought to be a variety of rocks below or within the metamorphic cover through which the fluids ascended to sites of mineralization. The contribution from magmatic sources associated with the extensive Sierran plutonism is uncertain. Direct dating of the Mother Lode veins has been accomplished by Rb-Sr and K-Ar dating of the hydrothermal mica, mariposite, a clearly identifiable product of the carbonate metasomatism associated with the gold veins (Bohlke, 1999). Data summarized by Bohlke and Kistler (1986) for veins in the Melones Fault Zone indicated Early Cretaceous ages between 108 and 127 Ma. These dates have lead various researchers to date mineralization correlative with various major tectonic-plutonic events that occurred around the same time. Many workers have suggested these dates imply a connection with post-Nevadan subduction and arc magmatism. Others have suggested that these dates are too young, arguing that radiometric dates may be younger than initial crystallization ages for minerals subjected to high temperatures (Landefeld, 1990). In either case, mineralization appears to be confined temporally to magmatic activity associated with subduction and associated emplacement of the Late Jurassic-Early Cretaceous plutons associated with the Sierra Nevada batholith.

Comment (Location): The location point selected for latitude and longitude is the main shaft symbol for Sheep Ranch Mine as shown on the USGS Murphys 7.5-minute quadrangle map. The mine is located on private property at the west end of the town of Sheep Ranch. Access is by paved road from Murphys via Sheep Ranch Road or from San Andreas via Fricot City Road to the town of Sheep Ranch, then west approximately a half mile on Main Street to a dead end at the Pioneer Hotel. The mine shaft is located approximately 500 feet to the north.

Comment (Commodity): Ore Materials: Native gold, chalcopyrite, sphalerite, pyrite, galena

Comment (Commodity): Gangue Materials: Quartz

Comment (Identification): The Sheep Ranch Mine was initially known as the Wallace and Ferguson Mine until 1877. After 1877, additional claims were acquired until the Sheep Ranch Mine property encompassed 21 patented claims covering 200 acres.

Comment (Environment): The Sheep Ranch Mine is located in the East Gold Belt of the Mother Lode region of California, on the west side of the Sierra Nevada Mountain Range and about 100 miles east of San Francisco. The mine is in central Calaveras County on the western outskirts of the small community of Sheep Ranch (population 32), which derived its name from a large sheep corral that once encompassed the town. The area is rural and sparsely populated with the nearest town of any size being Murphys (population 1,712), five miles to the south. Topography is dominated by gently rolling and deeply weathered low-relief foothills underlain by deformed and metamorphosed sedimentary rocks, which support a cover of mixed oak, pine, and manzanita. Quartz veins punctuate the topography, many of which were found to be gold-bearing. The climate is intermediate between the Mediterranean climate of California's Central Valley and the more severe alpine climate of the higher mountains. Temperatures range from freezing in the winter to 100 degrees in the summer. Mean annual precipitation is between 25-30", most of which falls during the rainy winter months between November and May. The area is dissected by many small steams, the smaller of which are intermittent.

Comment (Geology): Cretaceous-through-Eocene erosion stripped away thousands of feet of rock including portions of the lode-gold deposits. As much as 6 miles of rock is estimated to have been removed from the central Sierra Nevada (Bateman and Eaton, 1976). Liberated gold enriched placer deposits in adjacent drainages. Oligocene-Miocene volcanism blanketed the higher elevations of the Sierra Nevada with rhyolitic ash falls and flows and the lower elevations with ash, which preserved the auriferous Eocene gravels under a cap of rhyolitic tuff. Volcanic activity continued, with periods of quiescence, until the late Miocene/early Pliocene wherein vulcanism reached its peak dispensing large volumes of andesitic lava flows, ash, and mud flows. The total of these volcanic episodes buried the Eocene channels to depths of several hundred feet. Erosion was renewed in the late Pliocene by the elevation of the present Sierra Nevada via uplift along its eastern front and westward rotation. Rivers carved deep canyons and much of the volcanic cover was removed. Local scouring of Eocene placers redeposited gold in channels of Quaternary to present-day age. Elsewhere, the relict placers remained preserved under a volcanic veneer. Local reexposure and the continued stripping of the lode-gold deposits also enriched the younger placers. Structure The Mother Lode region is best characterized by northwesterly striking and easterly dipping beds dissected by two parallel longitudinal reverse-fault and fissure systems: the Melones Fault Zone (MFZ) and the Bear Mountain Fault Zone (BMFZ). Collectively, the MFZ and BMFZ comprise what has been called by Clark (1964) the Foothills Fault System (FFS). The FFS is considered by some to represent a suture between allochthonous terranes accreted by subduction during the late Paleozoic to early Jurassic. The dominant structural element is the MFZ, a major Upper Jurassic reverse fault complex that trends about N30?W, with fault planes dipping from 70 degrees northeast to vertical. The MFZ hosts the Mother Lode Gold Belt and extends 125 miles, paralleling the Sierra Nevada from El Dorado County to Mariposa County where it terminates against the Sierra Nevada Batholith. Gold-bearing veins have been deposited in fault planes as well as ancillary fractures and fissures. For much of its length, Paleozoic rocks of the Calaveras Complex on the east are thrust against Jurassic metasedimentary and metavolcanic rock. While veins and ore bodies associated with the MFZ make up much of the MLGB, the two are not identical. Many of the faults are younger than the MFZ and appear to be contemporaneous with the later Jurassic Sierra Nevada Batholith. Veins do not generally follow the schistosity or cleavage of the rocks, but cut across it, both in strike and dip, usually at acute angles. In the Angels Camp area, at least four periods of faulting have occurred suggesting that faulting and mineralization may have been episodic into the early Cretaceous. Mineralization has also replaced sheared rock locally. In the BMFZ, deformation is more obvious as evidenced by intensely folded and overturned folds and repeated beds. Many folds are nearly isoclinal and overturned to the southwest with limbs dipping 65-85? northeast and bedding generally subparallel to the faults.

Comment (Geology): In the EGB of Calaveras County, bedrock is predominantly micaceous schist of the Calaveras Complex that has been folded, faulted and invaded by intrusive rocks. Interpretation of these rocks is difficult due to their structural complexity and the near total destruction of bedding by metamorphism and shearing, and the absence of marker horizons. These rocks are characterized by northwesterly striking beds and foliation (paralleling the Sierra Nevada), and steep easterly or northeasterly dips. Schistosity is the dominant planar element. It strikes northwest-southeast and dips steeply to the northeast paralleling the FFS. Faulting and fracturing appear to be less frequent than in the MFZ or BMFZ, but the EGB's poorer exposures, absence of bedding, and remoteness may mask more significant structural complexity. The EGB does, however, appear to lack a singular regionally persistent and mineralized longitudinal fault trend analogous to the MFZ or BMFZ. Instead, smaller gold-bearing veins occur in localized northwest-southeast trending faults and fracture systems of limited extent giving rise to a number of deposits such as at Sheep Ranch. Of possible significance locally within the EGB, however, is the presence of a major structure known as the Calaveras-Shoo Fly Thrust (Wagner and others, 1981). This structure is a major boundary between the Calaveras Complex on the west and an older Paleozoic unit, termed the Shoo Fly Complex, on the east. Approximately seven miles northeast of the MFZ and only 2 miles southwest of the Sheep Ranch Mine is a significant shear zone approximately one-half- to three-quarters-mile wide, which has been mapped for approximately 30 miles paralleling the MFZ . While this zone is poorly understood, it is interpreted to be the result of a deeper reverse fault system similar to the MFZ. Dips along this system range from 70? to the northeast to vertical. Metallogeny The Mother Lode region is noted for it profusion of hydrothermal gold-bearing quartz veins and numerous mining districts throughout the FFS and EGB. Most significant surface deposits have probably been discovered given the intense scrutiny the area was subjected to during the latter half of the 19th century. However, there are undoubtedly undiscovered deposits in the region. Likely deposits would occur where the veins do not outcrop or where surface exposures do not reflect mineralized ore shoots at depth. Zones of barren quartz commonly separate known ore shoots within veins. Others may be concealed under a veneer of Eocene-or-younger volcanic cover. The discovery of new lode deposits will depend on identification of previously undiscovered faults or fracture zones within the known structural trends or new parallel trends. Due to its lack of exposures and lesser scrutiny, the EGB may offer additional potential in as yet unrecognized fracture zones. GEOLOGY AT SHEEP RANCH MINE In the EGB, several lode gold mines occur in quartz veins within mica schist of the Calaveras Complex. The veins in the East Belt are generally narrower and richer than those in the MLGB or WGB, but do not occur on well-defined, persistent longitudinal structural elements such as the MFZ or BMFZ. Stratigraphy The detrital marine sediments of the Calaveras Complex are so severely metamorphosed and deformed at Sheep Ranch that original bedding features have been destroyed. The only recognizable planar element is a strongly defined schistosity striking northwest-southeast and dipping 65-80? to the northeast, and closely paralleling the producing ore veins. In the Sheep Ranch Mine, the host rock consists of brownish to bluish-black siliceous mica schist and graphitic schist. Intrusive Jurassic granodiorite, diorite, and ultramafic rocks commonly form thin dikes within the schist and are cut by the ore-bearing veins. Veins are usually richer where the veins intersect igneous dikes or where veins intersect one another.

Comment (Geology): The thickness of the Calaveras Complex has not been determined, but measurements of more then 35,000 feet have been obtained in the Sierra foothills. However, this number does not account for repetition of beds by significant faulting or folding. The extensive reverse faulting and near isoclinal folds associated with the FFS, the well-developed schistosity, and the fractures and shear zones in and near Sheep Ranch all suggest that the true thickness of the Calaveras Complex is much less. Structure Local structure is difficult to determine due to the destruction of bedding features and marker horizons by metamorphism. The dominant structural feature within the Calaveras Complex rocks at Sheep Ranch is a pronounced schistosity which trends northwest-southeast and dips steeply to the northeast. The main Sheep Ranch vein strikes N55?W and dips 70-75? northeast and is in the hanging wall of a series of at least five known parallel veins. The deposits are considered true fissure filling emplacements resulting from ancillary fractures associated with deeper-seated reverse faulting similar to, but less extensive than, that expressed in the FFS. Wagner and others (1981) show the Calaveras-Shoo Fly Thrust as passing approximately through the settlement of Sheep Ranch. It was not established from research for this geologic summary, however, if the Sheep Ranch deposit is genetically associated with this structure. Alteration No detailed information exists regarding the extent of wall rock alteration in the Sheep Ranch deposit. It is clear, however, that little significant alteration was ever encountered or exploited as a lower-grade ore. The lack of widespread alteration may be attributable to the nature of the host rock in the Sheep Ranch Mine, which consists almost entirely of siliceous mica schist and graphitic schist. In contrast, many of the mines in the MLGB and WGB exhibit extensive zones of carbonate alteration in the host rocks. The degree of alteration is often correlative with the mineralogic composition and relative permeabilities of the rocks, with alteration being extensive in metavolcanic and ultramafic rocks and weak in metasedimentary units. Rocks composed of minerals with a high Mg/Fe ratio, such as serpentine, display enhanced fluid permeabilities when in contact with CO2-rich hydrothermal fluids and are much less stable than metasedimentary rocks with low Mg and Fe contents (Landefeld, 1990). An example of this phenomenon is well-displayed in the Royal-Mountain King Mine in the WGB where the correlation between alteration and rock type is pronounced. Alteration of hanging-wall greenstone consists of extensive quartz-sericite-ankerite-mariposite assemblages containing disseminated gold, which extend up to 250 feet from the veins. In contrast, footwall argillite and phyllite display little alteration, which consists of localized pyrite dissemination and bleaching attributed to leaching and remobilization of organic carbon. The predominance of compositionally similar schists in the Sheep Ranch Mine might explain the lack of alteration. Mineralization Because there is no known study of the geochemistry of the ore deposit at Sheep Ranch, a summary of some of the regional geochemical conditions is presented as follows:

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References

Reference (Deposit): Bradley, W., 1936, Mines and mineral resources of Calaveras County: California Division of Mines 13th Report of the State Mineralogist, p. 236-239.

Reference (Deposit): Miscellaneous information on Sheep Ranch deposit is contained in File Number 330-2461 (CDMG Mineral Resources Files, Sacramento) and in files of the Anaconda Geological Documents Collection at the University of Wyoming.

Reference (Deposit): Collection number Ms 231.

Reference (Deposit): Additional miscellaneous information on Sheep Ranch Mine is also on file with:

Reference (Deposit): Burchfiel, B.C. and Davis, G.A., 1981, Triassic and Jurassic tectonic evolution of the Klamath Mountains - Sierra Nevada geologic terrane, in Ernst, W.G., editor, The geotectonic development of California (Rubey Volume I): Prentice-Hall, Englewood Cliffs, New Jersey, p. 50-70.

Reference (Deposit): Clark, L.D., 1954, Geology and mineral deposits of the Calaveritas quadrangle, Calaveras County, California: California Division of Mines Special Report 40, 23 p.

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, L.D., 1964, Stratigraphy and structure of part of the western Sierra Nevada metamorphic belt, California: U.S. Geological Survey Professional Paper 410, 70 p.

Reference (Deposit): Clark, W.B., 1970, Gold districts of California: California Divisions of Mines and Geology Bulletin 193, p. 115-116.

Reference (Deposit): Clark, W.B, and Lydon, P.A., 1962, Mines and mineral resources of Calaveras County, California: California Division of Mines and Geology County Report No. 2, p. 69-70.

Reference (Deposit): Coveney, R.M., Jr., 1981, Gold quartz veins and auriferous granite at the Oriental Mine, Alleghany, California: Economic Geology, v. 76, p. 2176-2199.

Reference (Deposit): Crawford, J.J., 1896, Calaveras County gold: California State Mining Bureau 13th Report of the State Mineralogist, p. 288, 318.

Reference (Deposit): Dickinson, W.R., 1981, Plate tectonics and the continental margin of California, in Ernst, W.G., editor, The geotectonic development of California (Rubey Volume I): Prentice-Hall, Englewood Cliffs, New Jersey, p. 1-28.

Reference (Deposit): Eric, J.H. and others, 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 p.

Reference (Deposit): Hamilton, F., 1914, Mines and mineral resources of parts of California: California State Mining Bureau 14th Report of the State Mineralogist, p. 104-105.

Reference (Deposit): Fischer, E. and Miller, B., 1998, Sheep Ranch pioneers: Las Calaveras, Quarterly Bulletin of the Calaveras County Historical Society, v. XLVII, October, 8 p.

Reference (Deposit): Hamilton, F. 1923, Mining in California - Activities of the State Mining Bureau: California State Mining Bureau 19th Report of the State Mineralogist, p. 17.

Reference (Deposit): Holt Atherton Department of Special Collections

Reference (Deposit): Stockton, CA 95211

Reference (Deposit): University of the Pacific Library

Reference (Deposit): P. O. Box 721

Reference (Deposit): Calaveras County Historical Society

Reference (Deposit): San Andreas, CA 95249

Reference (Deposit): (In addition to historical data, this collection includes an impressive photo catalog)

Reference (Deposit): Ireland, W., 1888, Calaveras County: California State Mining Bureau 8th Annual Report of the State Mineralogist, p. 131-133.

Reference (Deposit): Hanks, H.G, 1886, Calaveras County: California State Mining Bureau 6th Annual Report of the State Mineralogist - Part II, p. 30.

Reference (Deposit): Julihn, C.E. and Horton, F.W., 1938, Mines of the southern Mother Lode region, Part I - Calaveras County: U.S. Bureau of Mines Bulletin 413, p. 110-112.

Reference (Deposit): Nesbitt, B. E. and others, 1986, Dual origins of lode gold deposits in the Canadian Cordillera: Geology, v. 14, p. 506-509.

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

Reference (Deposit): Preston, E.B., 1892, California State Mining Bureau 11th Annual Report of the State Mineralogist, p. 175-176.

Reference (Deposit): Root, L.L., 1925, Mining in California: California State Mining Bureau 21st Annual Report of the State Mineralogist, p. 158-159.

Reference (Deposit): Landefeld, L.A., 1990, The geology of the Mother Lode Gold Belt, Foothills Metamorphic Belt, Sierra Nevada, California: in Landefeld, L.A. and Snow, G., editors, Yosemite and the Mother Lode Gold Belt: geology, tectonics, and the evolution of hydrothermal fluids in the Sierra Nevada of California: American Association of Petroleum Geologists, Pacific Section, Guidebook 68, p 117-124.

Reference (Deposit): Logan, C.A., 1935, Mother Lode gold belt of California: California State Division of Mines Bulletin 108, 240 p.

Reference (Deposit): Moore, L., 1968, Gold resources of the Mother Lode Belt of California: U. S. Bureau of Mines Technical Progress Report 5 - Heavy Metals Program, 22 p.

Reference (Deposit): Moores, E.M., 1972, Model for a Jurassic island arc - continental margin collision in California: Geological Society of America, Abstracts with program, v. 4, p. 202.

Reference (Deposit): Saleeby, J., 1981, Ocean floor accretion and volcanoplutonic arc evolution of the Mesozoic Sierra Nevada, in Ernst, W.G., editor, The geotectonic development of California (Rubey Volume I): Prentice-Hall, Englewood Cliffs, New Jersey, p. 132-181.

Reference (Deposit): Schweickert, R.A. and Cowan, D.S., 1975, Early Mesozoic tectonic evolution of the western Sierra Nevada, California: Geological Society of America Bulletin, v. 86, p. 1329-1336.

Reference (Deposit): Schweickert, R.A. and others, 1988, Deformational and metamorphic history of Paleozoic and Mesozoic basement terranes in the western Sierra Nevada metamorphic belt, in Ernst, W.G., editor, Metamorphism and crustal evolution of the western United States (Rubey Volume VII): Prentice-Hall, Englewood Cliffs, New Jersey, p. 789-822.

Reference (Deposit): Seward, T.M., 1991, The hydrothermal geochemistry of gold, in Foster, R.P., editor, Gold metallogeny and exploration: Blackie, Glasgow, p. 37-62.

Reference (Deposit): Wagner, D.L. and others, 1981, Geologic map of the Sacramento quadrangle, California: California Division of Mines and Geology Regional Map Series Map 1A, scale 1:250,000.

Reference (Deposit): Weir, R.H. and Kerrick, D.M., 1987, Mineralogic, fluid inclusion, and stable isotope studies of several gold mines in the Mother Lode, Tuolumne and Mariposa Counties, California: Economic Geology, v. 82, p. 1659-1682.

Reference (Deposit): Bohlke, J.K. and Kistler, R.W., 1986, Rb-Sr, K-Ar, and stable isotope evidence for the ages and sources of fluid components in gold-quartz veins of the northern Sierra Nevada foothills metamorphic belt, California: Economic Geology, v. 81, p. 296-322.

Reference (Deposit): Bohlke, J.K., 1999, Mother Lode gold, in Moores, E.M. and others, editors, Classic Cordilleran concepts: A View from California: Geological Society of America Special Paper 338, p. 55-67.

Reference (Deposit): Bateman, P.C. and Eaton, J.P., 1967, Sierra Nevada batholith: Science, v. 158, p. 1407-1417.

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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.