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Soulsby Mine

Past Producer in Tuolumne county in California, United States with commodity Gold
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Sections on this page
  1. Identification information
  2. Geographic coordinates
  3. Site location context
  4. Geographic areas
  5. Public Land Survey System information
  6. Commodities
  7. Materials information
  8. Alteration
  9. Mineral occurrence model information
  10. Host and associated rocks
  11. Nearby scientific data
  12. Ore body information
  13. Controls for ore emplacement
  14. Economic information about the deposit and operations
  15. Mining district
  16. Land status
  17. Bibliographic references
  18. General comments
  19. Reporter information

Geologic information

Identification information

Deposit ID 10310683
Record type Site
Current site name Soulsby Mine

Comments on the site identification

  • The original mine was called the Soulsby, which was later consolidated with several other adjacent mines (Johnson and Bradbury, Platt, Gilson, Churchill). It is the largest producer in the East Belt of gold mineralization. Despite this standing, there is relatively little easily available information on this deposit.

Geographic coordinates

Geographic coordinates: -120.26188, 37.98675 (WGS84)
Location accuracy 100(meters)
Relative position About seven miles directly east of the downtown section of the city of Sonora.

Site location context

Political divisions (FIPS codes)

Tuolumne(county)

California(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Standard(quadrangle 1:24,000 scale)

Oakdale(quadrangle 1:100,000 scale)

San Jose(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Upper Tuolumne(hydrologic unit)

San Joaquin(hydrologic accounting unit)

San Joaquin(hydrologic subregion)

California(hydrologic region)

Geographic areas

Country State County
United States California Tuolumne

Public Land Survey System information

Meridian Township Range Section Fraction State
Mount Diablo 002N 016E 31 NW California

Comments on the location information

  • Location selected for latitude and longitude is the Soulsby Mine southern ?prospect? symbol on the USGS 7.5-minute Standard quadrangle.

Commodities

Commodity Importance
Gold Primary

Comments on the commodity information

  • Commodity Info: Although its mineralization was erratic, the Soulsby vein system yielded about $1 million per 100 feet of depth from an average width of only 18 inches.
  • Ore Materials: Native gold, auriferous sulfides (pyrite, galena, sphalerite, and chalcopyrite).
  • Gangue Materials: Granodiorite, quartzite, quartz, diorite

Materials information

Materials Type of material
Gold Ore
Pyrite Ore
Galena Ore
Sphalerite Ore
Chalcopyrite Ore
Quartzite Gangue
Quartz Gangue
Diorite Gangue

Alteration

  • (Local) None reported

Mineral occurrence model information

Model code 273
USGS model code 36a
Deposit model name Low-sulfide Au-quartz vein
Mark3 model number 27

Host and associated rocks

  • Host or associated Host
    Rock type Metamorphic Rock
    Rock type qualifier reportedly quartzite
    Rock unit name Calaveras Complex or Shoo Fly Complex
    Stratigraphic age (youngest) Mesozoic
    Stratigraphic age (oldest) Paleozoic
  • Host or associated Host
    Rock type Plutonic Rock > Granitoid > Granodiorite
    Rock unit name Standard Pluton
    Stratigraphic age (youngest) Jurassic
  • Host or associated Host
    Rock type Plutonic Rock > Mafic Intrusive Rock > Diorite
    Stratigraphic age (youngest) Mesozoic

Nearby scientific data

(1) -120.26188, 37.98675
ListMap

Economic information

Ore body information

  • General form Tabular, pinch and swell

Controls for ore emplacement

  • Ore shoots within quartz veins

Comments on the geologic information

  • The Soulsby Mine is within the Sierra Nevada Mountains, where bedrock consists of northerly trending tectonostratigraphic belts of metamorphosed sedimentary and volcanic rocks and associated intrusive rocks that range in age from 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 Mariposa County, lode gold deposits occur in three distinct belts - the West Belt, the Mother Lode Belt, and the East 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 in Tuolumne County consists of sparse, widely scattered gold deposits located west of the Mother Lode vein system, which represents the Mother Lode Belt. 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 is cut by the northwest-trending Bear Mountains fault zone, which separates an assemblage of metavolcanic and metasedimentary rocks of Jurassic age on the southwest from a more disrupted and diverse assemblage of metavolcanic, metasedimentary, plutonic, ultramafic, and melange rocks on the northeast. The metavolcanic rocks consist generally of volcanic and volcanic-sedimentary rocks of island arc affinity. These rocks are mostly mafic to intermediate in composition and include flows, breccias, and a variety of layered pyroclastic rocks. Some silicic rocks are present also. Various formation names assigned to the metavolcanic assemblages include Gopher Ridge, Copper Hill, Logtown Ridge, and Penon Blanco the metasedimentary rocks are dominantly distal turbidites and hemipelagic sequences of black slate. Assigned formation names include Mariposa, Salt Spring Slate, and Merced Falls Slate.

    The northwest-trending Mother Lode Belt traverses western Tuolumne County and is associated with the Melones Fault Zone. The rocks of this belt are typically metavolcanic, metasedimentary, and ultramafic, some of which have been hydrothermally altered to assemblages as described below. Mother Lode Belt 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, chromium-bearing mica, 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.
  • 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). The mineralization is usually 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 comprises about 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 East Belt is dominantly argillite, phyllite and phyllonite, chert, and metavolcanic rocks of Paleozoic-Mesozoic age. Carbonate rocks (marble) are also present locally. The phyllite and phyllonite are dark to silvery gray. The chert is mostly thin-bedded with phyllite partings. The Upper Paleozoic-Lower Mesozoic metasedimentary and metavolcanic rocks of the East Belt have been assigned to the Calaveras Complex by most investigators (Earhart, 1988). The Lower Paleozoic metamorphic rocks farther east have been assigned to the Shoo Fly Complex. More recently, some geologists have reinterpreted some assemblages along and immediately east of the Melones Fault Zone as separate Jurassic units (Schweickert and others, 1999). The metamorphic complexes 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

    The Soulsby Mine is developed mainly in a quartz-vein system, the Soulsby, which cuts granodiorite of the Jurassic Standard Pluton, a roof pendant of metamorphic rock of either the Calaveras Complex or Shoo Fly Complex, and diorite dikes. Julihn and Horton (1940) reported the metamorphic rock as quartzite. The vein system strikes N10W to N20W and has an average dip of about 80NE, although in places it is vertical or has a steep dip to the west. It averages about 18 inches in width where mined and consists of a single vein in the north part of the deposit, which then splits into two veins in the south part after the system enters the granodiorite body. Diorite dikes are reportedly present along the vein system, although their relationship to the ore is not clear from available reports on the deposit. Ore comprises native gold and auriferous sulfides (pyrite, galena, sphalerite, and chalcopyrite).

Economic information about the deposit and operations

Operation type Underground
Development status Past Producer
Commodity type Metallic
Deposit size Medium
Significant Yes
Discovery year 1856

Mining district

District name Soulsbyville District

Land status

Ownership category Private
Area name Tuolumne County Planning Department

Comments on the workings information

  • Workings consist of several shafts with associated drifts and some crosscuts. It may have reached a maximum vertical depth of about 750 feet.

Comments on other economic factors

  • Clark (1970) reported a production value of $5.5 million for this mine and at least $20 million for the Soulsby District making it the most productive in the East Belt of the Sierra Nevada. Julihn and Horton (1940) credited the mine, in consolidation with the Gilson, with a production of at least $6.75 million.

Comments on development

  • The deposit was discovered in 1852 or 1856 depending on the historic source consulted. Mining took place at least as late as 1911.

Reference information

Bibliographic references

  • Deposit

    Clark, W. B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 193, p. 121-123.

  • 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. 72-73.

  • 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.

  • Deposit

    Higgins, C.T., 1997, Mineral land classification of a portion of Tuolumne County, California, for precious metals, carbonate rock, and concrete-grade aggregate: California Division of Mines and Geology Open-File Report 97-09, 85 p.

  • Deposit

    Julihn, C.E., and Horton, F.W., 1940, Mineral industries survey of the United States - Mines of the southern Mother Lode Region, Part II - Tuolumne and Mariposa counties: U.S. Bureau of Mines Bulletin 424, 179 p.

  • Deposit

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

  • Deposit

    Koschmann, A.H., and Bergendahl, M.H., 1968, Principal gold-producing districts of the United States: U. S. Geological Survey Professional Paper 610, 283 p.

  • Deposit

    Logan, C.A., 1949, Mines and mineral resources of Tuolumne County, California: California Journal of Mines and Geology, v. 45, no. 1, p. 47-83.

  • 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.

  • Deposit

    Wagner, D.L., Bortugno, E.J., and McJunkin, R.D., 1990, Geologic map of the San Francisco-San Jose Quadrangle, California: California Department of Conservation, Division of Mines and Geology Regional Geologic Map Series, Map No. 5A, scale 1:250,000.

  • 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.

General comments

Subject category Comment text
Deposit The Soulsby Mine exploited a typical East Belt gold deposit, which is characterized by a tabular hydrothermal quartz-vein system. The system cuts granodiorite of the Jurassic Standard Pluton, a roof pendant of metamorphic rock of either the Calaveras Complex or Shoo Fly Complex, and diorite dikes. The vein system strikes N10W to N20W and has an average dip of about 80NE, although in places it is vertical or has a steep dip to the west. It averages about 18 inches in width where mined and consists of a single vein in the north part of the deposit, which then splits into two veins in the south part after the system enters the granodiorite body. Diorite dikes are reportedly present along the vein system, although their relationship to the ore is not clear from available reports on the deposit. Ore comprises native gold and auriferous sulfides (pyrite, galena, sphalerite, and chalcopyrite).

Reporter information

Type Date Name Affiliation Comment
Reporter 18-AUG-2006 Higgins, Chris T. California Geological Survey CGS (Formerly CDMG)
Editor 01-SEP-2007 Schruben, Paul G. U.S. Geological Survey Converted from S&A FileMaker format to Oracle. Edit checks on rocks, units, and ages with Geolex search, and other fields.

Beyond USGS

Supplemental information added by qvyshift.com. Not part of the original USGS MRDS record.

External references

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Authoritative California resources

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