Princeton Mine

Site Name

Primary: Princeton Mine
Secondary: New Princeton
Secondary: Princeton Extension
Secondary: Lewis Brothers (Northwest Extension of Princeton)

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Commodity

Primary: Gold
Secondary: Silver

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Location

State: California
County: Mariposa
District: Mount Bullion 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: Mariposa 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: 1852
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

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Structure

Type: L
Description: The vein system follows what is interpreted to be a reverse fault hosted in slate.

Type: R
Description: Mineralized quartz veins are associated with subsidiary faults of the Melones Fault Zone

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Alterations

Alteration Type: L
Alteration Text: None specifically reported, although there is mention that slate is severely bleached and hydrothermally altered near the vein in the New Princeton workings.

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Rocks

Name: Slate
Role: Host
Age Type: Host Rock
Age Young: Late Jurassic

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Pyrite
Gangue: Quartz

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Comments

Comment (Geology): REGIONAL GEOLOGY The Princeton 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 Mariposa County consists of 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 Mariposa 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.

Comment (Commodity): Commodity Info: Most of the ore mined averaged about 0.2 to 0.3 ounces of gold per ton. Except for ore produced at the shallowest depths, the Princeton Mine was characteristically one of large ore bodies of relatively low grade.

Comment (Commodity): Ore Materials: Native gold, auriferous sulfides (pyrite)

Comment (Commodity): Gangue Materials: Quartz

Comment (Deposit): The deposit at the Princeton Mine consists of a typical gold- and sulfide-bearing hydrothermal quartz vein within metamorphic rock. The Princeton vein occupies a fault that cuts slate of the Jurassic Mariposa Formation. The slate contains thin beds of dark-colored graywacke and is cut by felsic dikes, some of which intersect the vein. The vein lacks the massive, multiple characteristics of the Mother Lode farther north in the county. The vein system strikes N54-57W and dips 45-60NE. Vein matter, which is ribboned milky quartz that carries numerous parallel sheets of included wall rock, varies from 4 to 8 feet wide. Parts of the vein that constitute ore carry a considerable amount of pyrite. Native gold is seldom visible, but minor amounts of galena, sphalerite, and tetrahedrite are commonly seen. Locally, the slate is severely bleached and hydrothermally altered near the vein. The richest ore was found within 100 feet of the surface, while relatively high-grade ore continued to the 600-level. Ore below this depth to the 1,200-level was more typically low- to moderate-grade with one barren zone. The main ore shoot in the mine was distinguished from the rest of the vein by the prominence of pyrite.

Comment (Development): After its discovery in 1852, the Princeton Mine became the most productive mine in Mariposa County and at various times was the largest gold producer in California. The mine was idle between 1875 and 1900, and then resumed production until 1915. After another period of idleness, activity took place from 1921 to 1927. Small tonnages of ore and tailings were milled in the 1930's, but no sustained mining is known to have been carried on since then. Amalgamation processes were used at this mine.

Comment (Workings): The Princeton Mine was developed by standard shafts, crosscuts, drifts, raises, and stopes. Within Mariposa County, the extent of the workings is exceeded only by those at the Pine Tree-Josephine Mine several miles to the north. The main shaft, which was caved and inaccessible in the mid-1950's, is 1,660 feet deep on the incline and reaches a vertical depth of about 1,250 feet. It has 9 levels, the longest of which is about 2,100 feet. Drifts approximate about 11,500 feet, while there are over 3,000 feet of crosscuts and raises. Stoping extended from the lowest level to the surface. Lesser workings were developed elsewhere on the Princeton property, but these had insignificant production compared to the workings of the main shaft. Julihn and Horton (1940) provided a sectional view of the workings in the plane of the vein.

Comment (Economic Factors): Clark (1970) reported a production value of $5 million for this mine.

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). The mineralization is generally 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 certain 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 generally associated with appreciable amounts of pyrite, chalcopyrite, pyrrhotite, galena, sphalerite, and arsenopyrite. LOCAL GEOLOGY The Princeton vein, which is believed to be part of the Mother Lode system, occupies a fault that cuts slate of the Jurassic Mariposa Formation. The slate contains thin beds of dark-colored graywacke and is cut by dikes described by Bowen and Gray (1957) as sheared, fine-grained granitic porphyry. The porphyry may be the same rock that Clark (1970) described as pyritic metarhyolite, which in places contains gold. Some of these dikes intersect the vein. The trace of the vein is not well-defined at the surface and lacks the massive, multiple characteristics of the Mother Lode at a few mines farther north in the county. The vein is en echelon with veins at adjacent mines; it is probable that the Mother Lode in this vicinity consists of several separated veins rather than one or two major persistent features.

Comment (Geology): The Princeton vein system strikes N54-57W and dips 45-60NE. The enclosing host rock strikes N35W and dips 70NE. Vein matter, which is ribboned, milky quartz that carries numerous parallel sheets of included wall rock, varies from 4 to 8 feet wide. Parts of the vein that constitute ore carry a considerable amount of pyrite. Native gold is seldom visible, but minor amounts of galena, sphalerite, and tetrahedrite are commonly seen. Locally, the slate is severely bleached and hydrothermally altered near the vein. The richest ore was found within 100 feet of the surface, in places running about $70 gold/ton. Relatively high-grade ore continued to the 600-level. Ore below this depth to the 1,200-level was more typically low- to moderate-grade with one barren zone. Ore at the 1,400 and 1,600 levels was too low-grade for mining. The main ore shoot in the mine was distinguished from the rest of the vein by the prominence of pyrite. One ore shoot was reported to be 600 feet long and about two feet thick.

Comment (Identification): The Princeton Mine was one of the most productive mines in Mariposa County. In its early days, the mine was part of the vast Las Mariposas land grant owned by John C. Fremont.

Comment (Location): Location selected for latitude and longitude is a prospect symbol about one-half mile southwest of the town of Mt. Bullion on the USGS 7.5-minute Bear Valley quadrangle. This symbol may represent the main working of the mine, which was a shaft.

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References

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): Strand, R.G., 1967, Mariposa Sheet: California Division of Mines and Geology Geologic Map of California, scale 1:250,000.

Reference (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.

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): Bateman, P.C. and Krauskopf, K.B., 1987, Geologic map of the El Portal Quadrangle, west-central Sierra Nevada, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-1998, scale 1:62,500.

Reference (Deposit): Bowen, O.E., Jr. and Gray, C.H., Jr., 1957, Mines and mineral resources of Mariposa County, California: California Journal of Mines and Geology, v. 53, nos. 1-2, p. 35-343.

Reference (Deposit): Castello, W.O., 1921, Mariposa County: California State Mining Bureau, 17th Annual Report of the State Mineralogist, p. 86-143.

Reference (Deposit): Clark, W. B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 193, p. 94-96.

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. 72-73.

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): Evans, J.R. and Bowen, O.E., 1977, Geology of the southern Mother Lode, Tuolumne and Mariposa counties, California: California Division of Mines and Geology Map Sheet 36, scale 1:24,000.

Reference (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.

Reference (Deposit): Kistler, R.W., Dodge, F.C.W. and Silberman, M.L., 1983, Isotopic studies of mariposite-bearing rocks from the south-central Mother Lode, California: California Geology, v. 36, no. 9, p. 201-203.

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

Reference (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.

Reference (Deposit): Krauskopf, K.B., 1985, Geologic map of the Mariposa quadrangle, Mariposa and Madera Counties, California: U.S. Geological Survey Geologic Quadrangle Map GQ-1586, scale 1:62,500.

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.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 Division of Mines Bulletin 108, 240 p.

Reference (Deposit): Moore, L., 1968, Gold resources of the Mother Lode Belt, El Dorado, Amador, Calaveras, Tuolumne, and Mariposa counties, California: U.S. Bureau of Mines Technical Progress Report 5, p. 1-22.

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