Bandarita Mine

Site Name

Primary: Bandarita Mine
Secondary: Bandaretta
Secondary: Eclipse
Secondary: Goodwin

---

Commodity

Primary: Gold
Secondary: Silver

---

Location

State: California
County: Mariposa
District: Kinsley District

---

Land Status

Not available

---

Holdings

Not available

---

Workings

Not available

---

Ownership

Not available

---

Production

Not available

---

Deposit

Record Type: Site
Operation Category: Past Producer
Deposit Type: Hydrothermal vein
Operation Type: Underground
Discovery Year: 1856
Years of Production:
Organization:
Significant: Y
Deposit Size: S

---

Physiography

Not available

---

Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

---

Orebody

Form: Tabular

---

Structure

Type: R
Description: Sonora Fault

---

Alterations

Alteration Type: L
Alteration Text: None reported except for vague references by Thompson (1934) to alteration of the dikes.

---

Rocks

Name: Granodiorite
Role: Host
Age Type: Host Rock
Age Young: Mesozoic

Name: Hornfels
Role: Host
Description: quartz-biotite
Age Type: Host Rock
Age Young: Mesozoic
Age Old: Paleozoic

Name: Slate
Role: Host
Age Type: Host Rock
Age Young: Mesozoic
Age Old: Paleozoic

---

Analytical Data

Not available

---

Materials

Ore: Galena
Ore: Sphalerite
Ore: Tetrahedrite
Ore: Arsenopyrite
Ore: Gold
Ore: Pyrite
Gangue: Quartz

---

Comments

Comment (Geology): REGIONAL GEOLOGY The Bandarita 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 (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 Bandarita Mine is situated in the East Belt of gold mineralization of the Sierra Nevada. The deposit consists of a main gold-bearing quartz vein in slate that is part of the Paleozoic-Mesozoic Calaveras Complex. Regionally, this complex also includes phyllite, metachert, schist, metavolcanic rock, and metacarbonate rock. Other reported rocks associated with the deposit include quartz-biotite hornfels and granodiorite. The granodiorite is present as four individual north-trending dikes that intersect the vein at approximately right angles. Thompson (1934) observed that some of the dikes were altered and leached. The vein strikes N84W and dips 47SW. Its width varies from 2 to 10 feet. Ore consists of quartz with native gold, pyrite, galena, sphalerite, arsenopyrite, and tetrahedrite. The best ore contained considerable tetrahedrite. Thompson (1934) concluded that this ore formed on fault planes that exhibited much movement, which produced a quartz-slate gouge in places. He reported the presence of native gold in the gouge as well as in some of the altered dikes.

Comment (Identification): The Bandarita Mine, as discussed here, exploited this gold deposit as a single operation. Various other mining claims are also present in the immediate area.

Comment (Location): Location selected for latitude and longitude is the Bandarita Mine adit symbol (west side of river) on the USGS 7.5-minute Buckhorn Peak quadrangle.

Comment (Workings): Workings at this mine consist of adits, crosscuts, drifts, and stopes, some of which are daylighted. The mine is developed by a 1,364-foot crosscut adit and by six adits driven along the strike of the vein. The crosscut adit intersects the vein about 850 feet vertically from the surface. Stoping along three ore shoots in one adit ranged from 75 to 650 feet to the surface. Thompson (1934) estimated at least 5,000 feet of workings.

Comment (Commodity): Ore Materials: Native gold, auriferous sulfides (pyrite, galena, sphalerite, tetrahedrite, and arsenopyrite).

Comment (Commodity): Gangue Materials: Quartz, fault gouge

Comment (Deposit): The deposit at the Bandarita Mine consists of a typical gold- and sulfide-bearing hydrothermal quartz vein within metamorphic wall rock. The vein is reportedly in slate, quartz-biotite hornsfels, and granodiorite. The granodiorite is present as four individual north-trending dikes that intersect the vein at approximately right angles. The vein strikes S84W, dips 47SE, and ranges in thickness from 2 to 10 feet. Gold is present both in native form and in sulfides; the gold content was reportedly roughly proportional to the quantity of tetrahedrite present. Thompson (1934) concluded that the ore is present on fault planes along which much movement has taken place. Here, the quartz and slate have been crushed to a gouge.

Comment (Development): Opened in 1856, this mine was worked almost continuously until 1887 and then sporadically afterward. Its most productive period was 1881-1887. It was last known to be operated from 1937 to 1943 when $40,000 in gold and silver were obtained from 7,362 tons of ore mined from the Goodwin ore shoot. Amalgamation processes were used at this mine.

Comment (Commodity): Commodity Info: the Goodwin ore shoot reportedly averaged 0.57 ounces of gold per ton. Bowen and Gray (1957) reported that in 1874 a single mill cleanup yielded 25 pounds of gold from 100 tons of ore. Ore that averaged $25/ton was obtained from at least one location in the main crosscut working.

Comment (Economic Factors): Clark (1970) reported a production value of $1.52 million for this mine. In 1940, it was reported that there were still 275,000 tons of gob remaining in the old stopes.

---

References

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

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): 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): 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. 85.

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

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): Thompson, G.L., 1934, Report on the property of Bandarita Consolidated Gold Mining Company, North Fork of Merced River, Mariposa County, California: Unpublished consulting report, 12 p.

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.

---

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.