Utica Mine

Site Name

Primary: Utica Mine

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Commodity

Primary: Gold
Secondary: Silver

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Location

State: California
County: Calaveras
District: Angels Camp

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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: City of Angels Camp

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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: 1850
Years of Production:
Organization:
Significant: Y
Deposit Size: M

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Physiography

Not available

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Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

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Orebody

Form: Tabular, pinch and swell

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Structure

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

Type: L
Description: Melones Fault Zone

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Alterations

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

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Rocks

Name: Amphibole Schist
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
Gangue: Calcite
Gangue: Talc
Gangue: Chalcopyrite
Gangue: Ankerite
Gangue: Sericite

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Comments

Comment (Development): The surface of the Utica claim was mined during the early part of the gold rush, and the ore was treated in arrastras. The Stickle claim was active during the 1860s. In 1871, it had been developed to a depth of 240 feet and was equipped with a 10-stamp mill. The Confidence claim was active in the 1880s, and its ore was treated in a five-stamp mill (Clark and Lydon, 1962). Later, C.D. Lane gained control of the Utica claim. Hobart and Hayward, who controlled numerous mines in the area were brought in as partners in the 1880s and shortly thereafter, the Utica Mining Company was organized and large scale development commenced in 1893. The other claims that now constitute the property (Brown, Confidence, Dead Horse, Jackson, Little Nugget, Raspberry, Stickle, and Washington claims) were gradually acquired and the mine was developed on a major scale. During the 1890s, the Utica Mine was one of the most productive in the nation - the output from January 1893 to September 1895 was $4,154,026 (Logan, 1934). More than 500 men were on the payroll. By 1900, the Cross vertical shaft bottomed at 1312 feet. Operations continued into late 1915 when the mine was shut down. Except for mill cleanups and small amounts of gold recovered from the dump in the 1930s, the mine has been idle since. McCurdy (1932) attributes the cessation of mining and exploration for the footwall portion of the Utica vein to inferior or obsolete equipment resulting in the overly high operating costs.

Comment (Economic Factors): The Utica Mine is thought to have produced about $17 million (Clark, 1970). Shallow ores yielded as much as $13.02 per ton but declined to $3.60 or less in the deeper levels.

Comment (Geology): The ore bodies in the Utica mine are not within simple veins like many Mother Lode deposits, but instead consist of numerous lenticular quartz-calcite stringer veins separated by various thicknesses of mineralized fissured mineralized amphibolite and chloritic and talcose schist. Nonetheless, the mineralized zone was designated the Utica vein (Bonanza vein in some records) in most mine records. The stringers are largely quartz, but carbonate is abundant, especially in the smaller fissures. The stringers strike about N 50? W and dip about 70-80? northeasterly, lying nearly in the planes of schistosity of the country rock (Eisenhauer, 1932). Both the quartz and nearby country rock contain free gold and auriferous pyrite. In the south portion of the mine the country rock is more highly sheared than in the north, and the ore bodies were more complex networks of stringers and mineralized country rock (Clark and Lydon, 1962). In the Stickle claim on the south side of the Utica Mine property, the ore body is separated into two longitudinal portions, by a horse of barren schist and stringers 30 to 50 feet wide. The westerly portion is the more important being from 60-90 feet wide, while the eastern part is only 20 or 30 feet wide. The richest ore was called "brown quartz", consisting of a fine granular aggregate of quartz, dolomite, and sometimes albite, with abundant small crystals of pyrite. The brown quartz does not always form well-defined veins or stringers, but is intimately associated with the country rock, and is in part an altered form of the country rock. The other vein minerals are free gold, sericite, and chalcopyrite. Gold is not visible in most of the ore, but occurs in considerable masses in certain rich streaks (Ramsome, 1900). The grade of ore varied greatly. During the first year's operation in 1894, the shallowest ores yielded as much as $13.02 per ton but declined to $3.60 or less per ton in following years. Occasionally small high-grade pockets were found. The stringers dip easterly but are nearly vertical. Pyrite and chalcopyrite are the only sulfides reported in the ore (Clark and Lydon, 1962). Ore averaged about 2% concentrates. The neighboring Gold Cliff Mine (also operated by the Utica Gold Mining Company) developed the Gold Cliff vein, a parallel deposit very similar to the Utica vein. The Gold Cliff vein system dips about 40? northeasterly and converges with the Utica vein on the 2700-foot level of the Utica Mine. Some mine accounts indicate that the junction of the Utica and Gold Cliff veins was prospected and found not to contain a large ore body as was originally expected. Other accounts and geological reports (McCurdy, 1932; Eisenhauer, 1932) indicate that the Utica vein system ends abruptly at a 150-foot thick, northeasterly dipping talc zone at the 800-foot level in the Stickle shaft. Elsewhere in the mine the equivalent talc zone occurred only as small "dislocated bunches" (Eisenhauer, 1932). Due to differences in the strike and dip of the Utica vein and talc zone, the bottom of the vein system gets progressively deeper from northwest to southeast. In the neighboring Lightner Mine (to the northwest), the talc zone also floored the ore body between the 500 and 600 foot levels. Geological interpretation in the lower workings and below the talc zone are sketchy and hampered by the lack of geological record keeping in the shallower zones by the Utica Gold Mining Company (Eisenhauer 1932). However, Eisenhauer (1932) and McCurdy (1932) interpret the thin talc zone to be a reverse fault plane above which the best ore occurred in the hanging wall.

Comment (Geology): Very little exploration was conducted below the talc zone to locate the Utica vein ore body on the footwall of the fault (Eisenhauer 1932). Limited cross cutting below the talc zone failed to locate the footwall portion of the Utica vein (Eisenhauer 1932). Eisenhauer (1932) notes that miners intimately familiar with the characteristics of the Utica vein ore described the ore below the talc zone as a stringer lead distinctly different in appearance and lower-grade from the brown quartz ore developed above the talc.

Comment (Commodity): Commodity Info: Ore values of $3.60 to $13.02 per ton. Ore averaged 2% sulfide concentrates

Comment (Commodity): Ore Materials: Quartz-calcite stringer veins containing free gold and auriferous pyrite, and mineralized schist wallrock

Comment (Commodity): Gangue Materials: Quartz, calcite, talc, chalcopyrite, ankerite, and sericite

Comment (Geology): The Angels Camp district is within the Sierra foothills, where bedrock consists of north trending tectonostratigraphic belts of metamorphosed sedimentary, volcanic, and intrusive rocks that range in age from late Paleozoic to Mesozoic. The structural belts, which extend about 235 miles along the western side of the Sierra, are flanked to the east by the Sierra Nevada Batholith and to the west by sedimentary rocks of the Cretaceous and Jurassic Great Valley sequence. The structural belts are internally bounded by the Melones and Bear Mountains fault zones and are characterized by extensive faulting, shearing, and folding (Earhart, 1988). From El Dorado County southward into Tuolumne County, lode gold deposits occur in three distinct lithologic belts - the West Gold Belt, the Mother Lode Belt, and the East Gold Belt. The Mother Lode Belt is responsible for most of the gold produced. However, there has also been substantial gold production from the West Belt and East Belt. The West Belt consists of widely scattered gold deposits located west of the Mother Lode vein system. Gold occurs in irregular quartz veins and stringers in schist, slate, granitic rocks, altered mafic rocks, and as gray ore in greenstone. The West Belt can be divided into an eastern component composed of an ophiolitic melange and a western component composed of Jurassic rocks of the Copper Hill volcanics, Salt Springs slate, and Gopher Ridge volcanics. The Bear Mountains fault zone separates the melange from the Copper Hill volcanics. The Mother Lode Belt traverses western Calaveras County and consists of the upper Jurassic Logtown Ridge and 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, schist, amphibolite and chlorite schist, fine-grained tuffaceous rocks, and subvolcanic intrusive rocks. The thickness of the Mariposa Formation is difficult to ascertain due to structural complexities, but is estimated to be about 2,600 feet thick at the Cosumnes River (Earhart, 1988). Mother Lode mineralization is characterized by steeply dipping gold-bearing quartz veins and bodies of mineralized country rock adjacent to veins. Mother Lode veins are characteristically enclosed in Mariposa Formation slate with associated greenstone. The Mother Lode belt vein system ranges from a few hundred feet to a mile or more in width. Within the zone are numerous discontinuous or linked veins, which may be parallel, convergent, or en echelon. The veins commonly pinch and swell. Few can be traced more than a few thousand feet. Mother Lode type veins fill voids created within faults and fracture zones and consist of quartz, gold and associated sulfides, ankerite, calcite, chlorite, limonite, talc, and sericite. Stringer veins are commonly found in both adjacent footwall and hanging walls. Mother Lode ores are generally low to moderate grade (1/3 ounce of gold or less per ton), but ore bodies can be large. Ore shoots are generally short, 200-300 feet being the average stope length. However, they persist at depth, some having been mined to several thousand feet (Clark and Lydon, 1962). Ore shoots are commonly localized at bulges in veins, shear zones, vein intersections, or near abrupt changes in strike or dip.

Comment (Workings): The Utica Mine was originally developed through he Utica North and Utica South Shafts until 1902, after which the 1470-foot vertical Cross shaft and the 1000-foot vertical Stickle shaft (650 feet to the northwest) became the main working entries. The Cross shaft was sunk in hard rock to provide a permanent opening prior to abandoning the Utica North and Utica South shafts which had been used to mine the upper portions of the Utica vein. Working levels in Cross and Stickle shafts were turned every 100 feet. About 960 feet northwest of the Cross shaft, on the 1400-foot level, a hoist station was cut and a winze was sunk to the 2850-foot level. On this level, a crosscut extended 300 feet to the northeast where an inclined winze extended to the lowest 3050-foot level were the latest work was done before the mine shut down in 1915. From the 1500-foot level a southwest crosscut is connected with the 1400-foot level of the neighboring Gold Cliff Mine. Details of mine workings are sketchy, but there are though to be over 100 miles of underground workings, a portion of which are shown by Clark and Lydon (1962, p. 73). Stoping operations on the Utica vein system were confined to between the surface and the 13th level (1700 feet) (Eisenhauer 1932). Stoping widths ranged from 10 to 100 feet. Square set stopes with waster filling and open stopes with pillars were the preferred mining methods (Clark and Lyndon, 1962). During the 1890s, ore was treated in a 120-stamp mill. Storms (1900) detail the processes of ore milling and processing at the turn of the century. In later operations, the ore was treated in a 300-ton mill equipped with 60 stamps and 36 Frue vanners (Clark and Lydon, 1962). Mine dumps are conspicuously absent since all waste rock was utilized underground as backfill.

Comment (Deposit): The Utica Mine produced over $17 million from ore bodies consisting of numerous lenticular quartz-calcite stringer veins separated by various thicknesses of fissured mineralized amphibolite and chloritic and talcose schist. The stringers strike about N 50? W and dip about 70-80? northeasterly, lying nearly in the planes of schistosity of the country rock. Both the quartz stringers and country rock contain free gold and auriferous pyrite, although most of the gold occurs within the mineralized schist. The grade of ore varied greatly. The shallowest ores yielded as much as $13.02 per ton but declined to $3.60 or less per ton in following years. Ore averaged about 2% concentrates yielding about $40 to $70 per ton.

Comment (Geology): Wall rocks have invariably been hydrothermally altered, having been partially to completely converted to ankerite, sericite, quartz, pyrite, arsenopyrite, chlorite, and albite with traces of rutile and leucoxene (Knopf, 1929). 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 Eastern Belt is dominantly argillite, phyllite and phyllonite, chert, and metavolcanic rocks of Paleozoic-Mesozoic age. The phyllite and phyllonite are dark to silvery gray. The chert is mostly thin bedded with phyllite partings. The Paleozoic-Mesozoic metasedimentary and metavolcanic rocks of the Eastern Belt have been assigned to the Calaveras Complex by most investigators (Earhart, 1988). Older Paleozoic metamorphic rocks have been assigned to the Shoo Fly Complex. The metamorphic complexes have are intruded in places by Mesozoic plutonic rocks. Lode deposits of the East Belt consist of many individual gold-bearing quartz veins enclosed in metamorphic rocks of possible Jurassic age, metamorphic rocks of the Calaveras Complex, metamorphic rocks of the Shoo Fly complex, or in granitic rocks. Most of the veins trend northward and dip steeply. An east-west set of intersecting faults may be a controlling factor in controlling deposition of ore. Ore deposits of the East Belt are smaller and narrower than those of the Mother Lode, but commonly are more chemically complex, and richer in grade. Gold is usually associated with appreciable amounts of pyrite, chalcopyrite, pyrrhotite, galena, sphalerite, and arsenopyrite. LOCAL GEOLOGY The geology of the Angels Camp district is complex. Bedrock, which is assigned either to the Calaveras Complex or unnamed units of Jurassic age, consists of a series of northwest-striking beds of amphibolite and chlorite schists, phyllite, greenstone, and metagabbro. Ore deposits occur either in amphibolite and chlorite schist or phyllite. There are three principal northwest striking vein systems in the district. In the westernmost system, the veins are in phyllite. In the center system, the veins are along the western margin of a northwest trending belt of metagabbro. In the eastern system, which includes the Utica Mine, the ore deposits occur in amphibolite and greenstone. To the east and west of the district, bedrock is composed of slate, impure quartzite, and micaceous schist (Clark, 1970).

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

Comment (Identification): The Utica Mine is located within the city of Angels Camp in southwestern Calaveras County, California. The gold mines in and around Angels Camp are part of the Angels Camp mining district, which is credited with producing at least $30 million in gold (Clark, 1970). The Utica Mine alone is thought to have produced in excess of $17 million at the old price of gold. The Utica Mine is one on the best-known gold mines in the Mother Lode, and is the consolidation of the Brown, Confidence, Dead Horse, Jackson, Little Nugget, Raspberry, Stickle, Utica, and Washington claims. The surface of the Utica claim was mined during the early part of the gold rush, but large-scale development was only conducted between 1893 and 1915 by the Utica Gold Mining Company. During the 1890s, the Utica Mine was one of the most productive in the nation - the output from January 1893 to September 1895 was $4,154,026 (Logan, 1934).

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References

Reference (Deposit): Eric, J.H., Stromquist, A.A., and Swinney, C.M., 1955, Geology and mineral deposits of the Angels Camp and Sonora quadrangles, Calaveras and Tuolumne counties, California: California Division of Mines Special Report 41, 55 p.

Reference (Deposit): Julihn, C.E., and Horton, F.W., Mineral industries survey of the United States - Mines of the southern Mother Lode Region, Part 1, Calaveras County, Utica and Gold Cliff mines: U.S. Bureau of Mines Bulletin 413, p. 136.

Reference (Deposit): Storms, W.H., 1900, The Mother Lode region - Calaveras County: California Mining Bureau Bulletin 18, p 111-119.

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

Reference (Deposit): McCurdy, E. S., 1932, Utica mining property: unpublished geological report for the Utica Mining Company.

Reference (Deposit): Zimmerman, J.E., 1983, The Geology and structural evolution of a portion of the Mother Lode Belt, Amador County, California: unpublished M.S. thesis, University of Arizona, 138 p.

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

Reference (Deposit): Clark, W. B., 1970, Gold districts of California: California Divisions of Mines and Geology Bulletin 193, p. 25-28.

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): Crawford, J. J., 1894, Utica-Stickles Mine: California State Mining Bureau, 12th Annual Report of the State Mineralogist, p. 98.

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