Columbia District

Site Name

Primary: Columbia District
Secondary: Columbia Basin

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Commodity

Primary: Gold

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Location

State: California
County: Tuolumne
District: Columbia District

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Land Status

Land ownership: State Park
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: California Department of Parks and Recreation

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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: District
Operation Category: Past Producer
Operation Type: Surface
Discovery Year: 1850
Years of Production:
Organization:
Significant: Y
Deposit Size: L

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Physiography

Not available

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Mineral Deposit Model

Model Name: Placer Au-PGE

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Orebody

Form: Irregular

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Structure

Not available

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Alterations

Not available

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Rocks

Name: Clay, Mud
Role: Host
Age Type: Host Rock
Age Young: Quaternary

Name: Gravel
Role: Host
Age Type: Host Rock
Age Young: Quaternary

Name: Gravel
Role: Host
Age Type: Host Rock
Age Young: Tertiary

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Analytical Data

Not available

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Materials

Ore: Gold
Gangue: Quartz

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Comments

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 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 Columbia District is underlain by metasedimentary rock of the Calaveras Complex, which here consists of carbonate rock, argillite, phyllite, chert, and minor amphibolite, all of which are cut in places by a metavolcanic dike swarm. Remnants of Tertiary and Quaternary gravels are present on top of this complex and, along with various pocket veins in the underlying and nearby bedrock, were the sources of the placer gold in the district. The carbonate rocks harbored most of the gold because of their favorable physical character for trapping the gold. The numerous crevices and potholes produced by weathering and erosion of the highly soluble rock provided ideal sites for concentration of the gold carried across this karst landscape by streams.

Comment (Geology): The Columbia District is within the Sierra Nevada foothills, 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.

Comment (Identification): This district encompasses an approximately one-square mile area of extensive placer mining, which when combined with the adjacent areas of Springfield and Shaws Flat and when compared to any equal-sized area in the world, was the richest ever documented (Julihn and Horton, 1940). It also includes the former settlement of Springfield to the southwest.

Comment (Commodity): Ore Materials: Native gold

Comment (Development): During the 1850?s and early 1860?s, the diggings at Columbia were enormously productive; estimates of production of $100,000 per week were reported. The district declined in the late 1860?s and exhibited only a shadow of its former activity by the 1890?s even though small amounts of mining continued into the 1900?s. Much of the district is now a state historic park or under residential ownership. A small community college is on the east edge.

Comment (Economic Factors): For its area of about two square miles, the Columbia District is considered by some to be the largest producer of placer gold in the world. Julihn and Horton (1940) reported production of at least $55 million, while Clark (1970) reported estimates that range from at least $87 million to as high as $150 million.

Comment (Deposit): The deposit at Columbia District is composed of very coarse placer gold entrapped by a low-relief karst terrain. Most of the gold was likely removed during the gold rush period except for that resource still remaining in the deepest cavities of the carbonate bedrock. The gold consists of metal released from weathering and erosion of quartz veins in the underlying metamorphic bedrock of the Columbia Basin and that transported short distances from other placer deposits and the nearby rich gold-bearing ?pocket? quartz veins of the surrounding hills. The transported gold was moved by an early Tertiary stream, which headed near Yankee Hill, and by small Quaternary streams, all of which flowed over the carbonate bedrock and deposited both gold and gravel in the many crevices and potholes. The gravel in this district is notably angular, which suggests very short distances of transport. Large amounts of clay are also present in the cavities in the carbonate rock. Together, the gravel and clay form the host for the placer gold.

Comment (Geology): The Columbia Basin is a small geomorphic feature (approximately one square mile) that represents a preserved Tertiary valley. Lindgren (1911) believed that an early, pre-volcanic Tertiary channel flowed from south to north through the basin after rising to the east near Yankee Hill. He believed that the slow degradation of this valley during pre-volcanic time concentrated the coarse gold to an extraordinary degree in the flat central basin. Deep potholes developed in the limestone proved to be exceptionally effective gold riffles. According to Lindgren (1911), this valley was covered by volcanic deposits later in the Tertiary. Nearly all of this cover was removed during the Quaternary, which exhumed the paleo-valley. At that time, the process of concentration of the gold resumed. Turner and Ransome (1898) in the their folio on the Big Trees 30? Quadrangle described the Columbia District as follows: ?The gravels formerly washed on an extensive scale near Columbia are of a character somewhat different from that of gravels met with in other portions of the quadrangle. They rest upon limestone which, previous to or during their deposition, was dissolved and eroded away in a remarkably irregular manner. Where the gravels have been removed the exposed limestone presents a very rugged surface. The gold and gravels were caught in the deep crevices between the fantastically shaped projecting points of limestone, as in huge natural riffles. Much of the material found in these cavities is said to have been fine clay, and was the matrix in which, according to Whitney, various bones of extinct mammals, particularly those of the mammoth, were found. Although probably in the main of Neocene age, the auriferous deposits on the limestone in the vicinity of Columbia, with the exception of the patch about half a mile northwest of the town, are not typical well-rounded stream gravels, but are composed of subangular, little-worn fragments, largely quartzose, which appear to have been washed into the crevices by small streams from the waste of the rocks in the immediate neighborhood. Much of the cherty material may have been derived directly from the limestone area, for the soil covering portions of the latter is full of similar siliceous fragments. The deposits may thus be in part of Pleistocene age. The soil and detrital material over most of the limestone area west and south of Columbia has been so thoroughly worked over by the early miners that it is often impossible to determine what may have been the original character of the surficial deposits in a given spot.?

Comment (Workings): This district was developed as a placer-mining center. Standard small-scale hand methods were dominantly used at the beginning of the gold rush. These processes were used to scour the crevices and potholes in the underlying carbonate rock, which served as traps for the placer gold. In the deeper cavities, the gold-bearing sediment was hoisted to the surface by whims and water wheels and then run through sluices. Some hydraulic mining was done on small remnants of Tertiary gravels in the southern part of the district. According to Julihn and Horton (1940): ?The early miners excavated the gravel by hand from between the limestone pinnacles of the bedrock and hoisted it in buckets by derricks to raised platforms at the head of sluice boxes. Thousands of men worked at the diggings, and the yield per cubic yard of clay and gravel they handled was enormous.? They also reported that the subdued terrain caused drainage problems such that the miners were unable to mine below the water table. Consequently, many deep pockets in the limestone were never bottomed.

Comment (Location): Location selected for latitude and longitude is the town of Columbia, which is approximately in the center of the placer district.

Comment (Commodity): Gangue Materials: Metamorphic rock, igneous rock, quartz

Comment (Commodity): Commodity Info: the gold in the placer deposits of Tuolumne County was notably very coarse, with many large nuggets recovered from this district. Julihn and Horton (1940) described the gold as very coarse, and the finding of a nugget weighing a pound or so was so usual as to attract little attention. Five nuggets reportedly weighing 33-1/2 to 72 pounds were found in the early days.

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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): Turner, H.W. and Ransome, F.L., 1898, Geologic atlas of the United States, Big Trees Folio, California: U.S. Geological Survey Folio 51, scale 1:125,000.

Reference (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.

Reference (Deposit): Wagner, D.L. and others, 1981, Geologic map of the Sacramento Quadrangle, California: California Department of Conservation, Division of Mines and Geology Regional Geologic Map Series, Map No. 1A, scale 1:250,000.

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

Reference (Deposit): Lindgren, W., 1911, Tertiary gravels of the Sierra Nevada: U.S. Geological Survey Professional Paper 73, p. 212-213.

Reference (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.

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): 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): 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): Clark, W. B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 193, p. 30.

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.

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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.