Big Canyon Mine

Site Name

Primary: Big Canyon Mine

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Commodity

Primary: Gold
Tertiary: Silver

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Location

State: California
County: El Dorado
District: Shingle Springs 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: El Dorado 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 and replacement
Operation Type: Surface-Underground
Discovery Year: 1880
Years of Production:
Organization:
Significant: Y
Deposit Size: S

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Physiography

Not available

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Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

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Orebody

Form: Tabular

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Structure

Type: L
Description: Big Canyon fault zone

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

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Alterations

Alteration Type: L
Alteration Text: Pyrite-carbonate-albite alteration of basaltic metatuff and netadiorite

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Rocks

Name: Diorite
Role: Host
Description: meta-
Age Type: Host Rock
Age Young: Paleozoic

Name: Tuff
Role: Host
Description: basaltic meta-
Age Type: Host Rock
Age Young: Paleozoic

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Pyrite
Gangue: Calcite
Gangue: Albite
Gangue: Tuff
Gangue: Diorite

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Comments

Comment (Geology): REGIONAL GEOLOGY The Big Canyon area is within the Sierra Nevada foothills, where bedrock consists of north trending tectonostratigraphic belts of metamorphosed sedimentary, volcanic, and intrusive rocks that range in age from late Paleozoic to Mesozoic. Locally, the Mesozoic rocks are capped by erosional remnants of a once extensive conglomerate and tuff of Tertiary age. The structural belts, which extend about 235 miles along the western side of the Sierra, are flanked to the east by the Sierra Nevada Batholith and to the west by sedimentary rocks of the Cretaceous and Jurassic Great Valley sequence. The structural belts are internally bounded by the Melones and Bear Mountains fault zones. These steeply dipping major faults, along with an unnamed normal fault that parallels Big Canyon Creek, separate diverse geologic terranes of oceanic crust and magmatic arc affinities. All the belts are characterized by extensive faulting, shearing, and folding (Earhart, 1988). In the El Dorado County area, gold deposits occur in the West Belt, the Mother Lode Belt, and the East Belt. The Mother Lode Belt is responsible for most of the gold produced in the county. There has also been substantial gold produced from the West Belt and East Belt (Clark and Carlson, 1956). The West Belt consists of widely scattered gold deposits located west of the Mother Lode vein system. Gold occurs in irregular quartz veins in schist and granitic rocks, altered mafic rocks, and as gray ore in greenstone. The West Belt has been further divided by some authors into an eastern component composed of an ophiolitic melange and a western component composed of Jurassic rocks of the Copper Hill volcanics (Duffield and Sharp, 1975; Saleeby, 1982; Clark, 1964). The Copper Hill volcanics consist of mafic to felsic flows and pyroclastic rocks that are metamorphosed to greenschist and amphibolite facies. The Bear Mountains fault zone separates the melange from the Copper Hill volcanics. The Big Canyon Mine is located in the melange belt, which is locally separated from the Mother Lode Belt by the Big Canyon Fault zone. The Mother Lode Belt consists of the Upper Jurassic Logtown Ridge and Upper Jurassic 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, graywacke, conglomerate, 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 Belt mineralization is characterized by steeply dipping gold-bearing quartz veins that traverse western El Dorado County. The belt trends north through Nashville, northeast through Placerville, and northwest to Garden Valley. At Garden Valley, the Mother Lode Belt splits. The west branch extends northwest through Greenwood, and the east branch extends north through Georgetown to the Georgia Slide area (Busch, 2001). The Mother Lode veins are generally enclosed in Mariposa Formation slate with associated greenstone. The vein system ranges from a few hundred feet to a mile or more in width. Within the zone are numerous discontinuous or linked veins, which may be parallel, convergent, or en echelon. The veins commonly pinch and swell. Few can be traced more than a few thousand feet. Mother Lode type veins fill voids created within faults and fracture zones and consist of quartz, gold and associated sulfides, ankerite, calcite, chlorite, and sericite (Clark and Carlson, 1956).

Comment (Development): The Big Canyon Mine was discovered in the early 1880s. Little is known about the first few years of operation except that a twenty-stamp mill was on the property prior to 1888. Afterward, the mine became one of the most productive mines in El Dorado County having produced more than $3+ million in gold during two periods of operation, 1893-1901 and 1934-1940. Between 1893 and 1901, Hayward, Hobart, and Lane operated the mine, producing $720,000 from 180,000 tons of ore (Logan, 1938). During that period mining reached the 500 foot level. In 1934, the Mountain Copper Company acquired the property. Mountain Copper sank a new shaft, erected a mill, and operated the mine on a large scale until 1940. From 1934-1940, Mountain Copper Company produced another $2,368,000. The workings were extended deeper and along strike; the average dip of the veins was about 35? east and the strike was S 25? W. The ores from the upper levels were successfully treated by amalgamation, but that was not effective on the deeper pyritic ores, which were treated by flotation. On February 26, 1937, water from Big Canyon Creek flooded the mine. Within 52 hours, 30,000 gallons of water had poured into the mine and a pond several hundred feet long formed at the surface. Later in 1937 an open pit was developed to reach below the 100-foot level (Nash, 1988). The mine was forced to close in 1940 by the War Production Board Limitation Order. The mine has been idle since 1940 (Earhart, 1988). In 1983, Gold Fields Mining Corp. acquired the mineral rights, with plans to develop the property as an open pit mine. Surface exploration and coring (about 12,000 m of core) between 1983-1985 identified many zones with gold grades in the range of 3-7 grams/ton (Nash, 1988). Plans to open the open-pit mine were scuttled by environmental opposition. In 1986, an El Dorado County company acquired the mine and continued feasibility studies.

Comment (Commodity): Ore Materials: Mineralized pyrite-carbonate-albite alteration of basaltic metatuff, metadiorite, and breccia with 5-15% auriferous pyrite carryiong 80% of the gold. The remaining 20% is free gold.

Comment (Economic Factors): The Big Canyon Mine produced more than $3 million in gold from two main periods of operation (1893-1901 and 1934-1940). Ores consist of free gold, auriferous pyrite, and pyrrhotite in pyrite-carbonate-albite wallrock alteration zones and in vein fillings in faulted and brecciated mafic rocks. Free gold constituted about 20% of the total contained gold with the remainder in pyrite, and pyrrhotite. During 1934-40, ores yielding $5 or more per ton were considered economical. Exploration coring by Gold Fields Corp in the 1980s identified many zones with gold grades in the range of 3-7 grams/ton (Nash, 1988).

Comment (Commodity): Gangue Materials: Calcite, albite, carbonate, metatuff, metadiorite

Comment (Workings): The mine was originally developed by a vertical shaft sunk to a depth of 200 feet, and then sunk an additional 540 feet on a 40? incline to the east. The ore was stoped out to the surface from the 500-foot level of this shaft during the early operations of the mine. The mine had a 20-stamp mill before 1888. After the Mountain Copper Company acquired the mine in 1934, a new 620-foot three-compartment shaft on a 45? incline was sunk 400 feet north of the old shaft. Drifts were extended several thousand feet along the strike of the ore body. The ore was mined in open stopes. In 1937, after the underground workings were flooded, some ore in the upper portion of the mine was mined by open pit methods (Clark and Carlson, 1956). From the mine, the ore was belt conveyed to the mill. The mill had a capacity of 300 tons/day. It was equipped with two 7 by 6 foot ball mills, two Dorr classifiers, and five Fagergren flotation cells and a cleaner cell. Concentrate was sent through a Dorr thickener and a Oliver filter. Concentrates were shipped to a smelter in Tacoma. A crew of 150 men worked at the mine and mill (Clark and Carlson, 1956).

Comment (Geology): The Melones Fault Zone separates the Mother Lode Belt from the East Belt. The East Belt lies in the south central part of El Dorado County approximately 15 miles east of the Mother Lode belt. The East Belt traverses the county from the southern county line, north through Omo Ranch and Grizzly Flat, and apparently terminates near the Hazel Creek Mine east of Jenkinson Reservoir (Busch, 2001). The Eastern Belt is dominantly argillite, phyllite and phyllonite, and chert of Paleozoic age. The phyllite and phyllonite are dark to silvery gray. The chert is mostly thin bedded with phyllite partings. Other rocks in the Eastern Belt include a Jurassic granodiorite pluton near the Cosumnes River and small bodies of Jurassic serpentinite, gabbro, diorite, and limestone. The Paleozoic metasedimentary rocks of the Eastern Belt have been assigned to the Shoo Fly Complex by most investigators. Lode deposits of the East Belt consist of many individual gold-bearing quartz veins enclosed in 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 (Clark and Carlson, 1956) LOCAL GEOLOGY The Big Canyon Mine lies within the eastern melange belt of the West Gold Belt. In the vicinity of the mine, the melange consists of detached blocks that were derived from oceanic crust and island arc terranes. The detached blocks are as much as 2 miles long, in a matrix of mostly serpentinite. Serpentinite and basalt that compose the matrix of the melange are vestiges of a dismembered ophiolite. According to Earhart (1988), the Big Canyon deposit is at the intersection of three branching faults, which are parts of a major fault zone that parallels Big Canyon Creek. The steeply dipping ore zone is exposed for about 150 feet in a northerly direction along strike on the western side of a glory hole. The ore occurs along a fault that separates metasedimentary rocks on the east from basalt and basaltic tuff to the west. The host rock is a breccia that contains silicified and pyritized fragments primarily from the basaltic wall rocks. The breccia matrix consists of calcite, ankerite, quartz, chlorite, and tremolite. According to Nash (1988), the deposit is structurally controlled by numerous closely spaced fractures withinin the east dipping Big Canyon fault zone. The Big Canyon structure is a series of sub-parallel high angle faults in a zone more than 100 meters wide with branching low angle faults that cut off blocks between the high angle faults (Nash, 1988). Gold occurs in veins and in faulted and brecciated Paleozoic basaltic metatuff and metadiorite displaying pyrite-carbonate-albite alteration zones up to 100 feet thick (Nash, 1988). The main ore body strikes N 25?E and dips 35? - 40? east and southeast. The ore shoot that was mined during the 1930s had a maximum length of 450 feet and was as much as 50 feet wide (Clark and Carlson, 1956). Gold mineralization is consistently associated with fracture filling and pyrite-carbonate-albite alteration of basaltic metatuff and metadiorite wall rocks in are in fault contact with serpentinite, slate, and black argillite. PCA alteration was caused by metasomatic processes by which S, CO2, and Na were added to the rocks during both vein filling and replacement reactions.

Comment (Location): Location selected for latitude and longitude is the Big Canyon Mine symbol on the USGS 7.5 minute Latrobe quadrangle

Comment (Deposit): The Big Canyon Mine produced free gold and auriferous sulfides from structurally controlled fractures in the Big Canyon fault zone. Gold is associated with mesothermal zones of pyrite-carbonate-albite alteration of mafic rocks (basaltic metatuff and metadiorite) and vein filling. Free gold accounts for about 20% of the contained gold with auriferous pyrite and pyrrhotite responsible for 80%. Earhart (1988) described the gold deposits of the Big Canyon area as follows: ?The area contains two distinct types of gold deposits. The older gold deposits are hosted by detached blocks of pyritic chert and associated banded iron-formation. These deposits , formed by sea-floor exhalative porcesses in an island-arc environment, were moved by gravity to their present chaotic setting during formation of the melange. Younger gold occurrences, including the Big Canyon deposit, are associated with hydrothermally altered fault zones that are younger than the formation of the melange. They are akin to the fault-controlled auriferous quartz veins in the Mother Lode belt east of the Big Canyon area.?

Comment (Geology): The orebody formed by Cretaceous hydrothermal alteration of the fault zones by gold-bearing Mother Lode type mineralizing fluids which ascended along fractures within the east dipping Big Canyon fault zone (which may merge at depth with the Mother Lode Fault system four miles to the east). Fractures apparently acted as a structural control for ore deposition. The deposits are thought to have formed from alkaline, CO2 rich fluids of moderate temperature (300-400?C?) and pressure (1-2 kilobars?) of metamorphic origin (Nash, 1988). For information on geochemical controls, see Nash (1988), Earhart (1988), Loucks and Mavogenes (1999), and Bohlke and Kistler (1986). Sulfide minerals occur as disseminations and fracture fillings in both the matrix and the fragments of the breccia, but are most abundant in the matrix. Surface exposures contain as much as 5% sulfides and intervals of 2-3 feet in drill cores contain as much as 15 percent sulfides. Gold values vary directly with sulfide content. Auriferous pyrite is the main sulfide, but some pyrrhotite and arsenopyrite is in the ore. Sulfides are responsible for 80% of the gold produced. The remaining gold occurs as fine free milling gold. Exploration coring by Gold Fields Corp in the 1980s identified many zones with gold grades in the range of 3-7 grams/ton (Nash, 1988).

Comment (Identification): The Big Canyon Mine is located in the Shingle Springs District of western El Dorado County in the foothills of the Sierra Nevada Mountains. The deposit was first mined from the early 1880s to 1901, then again between 1934-1940. The Big Canyon mine was one of the largest in El Dorado County, producing $720,000 in gold from 1893- 1901, and $2,380,000 from 1934-1940 (Clark and Carlson, 1956) . The deposit is structurally controlled by numerous closely spaced fractures in the Big Canyon Fault zone. Gold is associated with zones of pyrite-carbonate-albite alteration of mafic rocks and vein filling, both as free gold, auriferous pyrite, and pyrrhotite.

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References

Reference (Deposit): Busch, L.L., 2001, Mineral land classification of El Dorado County, California: California Geological Survey Open-File Report 2000-03.

Reference (Deposit): Clark, L.D., 1964, Stratigraphy and structure of part of the western Sierra Nevada metamophic belt, California:

Reference (Deposit): 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. 117.

Reference (Deposit): Clark, W.B. and Carlson, D.W., 1956, Mines and mineral resources of El Dorado County: California Division of Mines, California Journal of Mines and Geology, v. 52, p. 408.

Reference (Deposit): Duffield, W.A., and Sharp, R.V., 1975, geology of the Sierra Foothills melange and adjacent areas, Amador County, California: U.S. Geological Survey Professional Paper 827, 30 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): Logan, C.A., 1938, Mineral resources of El Dorado County: California Division of Mines, 34th Report of the State Mineralogist, p. 220-223.

Reference (Deposit): Logan, C.A., 1926, El Dorado County: California State Mining Bureau, 22nd Report of the State Mineralogist, p.413

Reference (Deposit): Loucks, R.R., and Mavrogenes, J.A., 1999, Gold solubility in supercritical hydrothermal brines measured in synthetic fluid inclusions: Science, v. 284, p. 2159-2163.

Reference (Deposit): Loyd, R.C., Anderson, T.P., and Bushnell, M.M., 1983, Mineral land classification of the Placerville 15-minute quadrangle, El Dorado and Amador counties, California: California Division of Mines and Geology Open-File Report 83-29, 38 p.

Reference (Deposit): Nash, T.J., 1988, Geology and geochemistry of the Big Canyon area, El Dorado County, California: U.S. Geological Survey Professional Paper 1854, 40 p.

Reference (Deposit): Saleeby, J., 1982, Polygenetic ophiolite belt of the California Sierra Nevada: Geochronological and tectonostratigraphic development: Journal of Geophysical research, v. 87, n0. 8, p. 1803-1824.

Reference (Deposit): Additional information on the Big Canyon Mine is contained in File No. 322-5979 (CGS Mineral Resources Files, Sacramento)

Reference (Deposit): Tucker, W.B., and Waring, C.A., 1916, Mines and mineral resources of El Dorado, Placer, Sacramento, and Yuba counties, California State Mining Bureau, Fifteenth Report of the State Mineralologist, p. 293.

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 of gold-bearing quartz veins in the northern Sierra Nevada foothills metamorphic belt, California: Economic Geology, v. 81 p. 296-322.

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