Golden Center Mine

Site Name

Primary: Golden Center Mine
Secondary: Rock Roche Mine
Secondary: Dromedary Mine
Secondary: Berriman Mine
Secondary: Garage vein
Secondary: Sleep vein
Secondary: Church Hill vein

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Commodity

Primary: Gold
Secondary: Silver

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Location

State: California
County: Nevada
District: Grass Valley

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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: Nevada County Planning Dept. and City of Grass Valley

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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

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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: R
Description: Wolf Creek Fault Zone, Gillis Hill Fault, Melones Fault Zone

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Alterations

Alteration Type: L
Alteration Text: Ankeritic, sericitic, and pyritic replacement of wall rocks adjacent to veins

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Rocks

Name: Granodiorite
Role: Host
Age Type: Host Rock
Age Young: Early Cretaceous

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Pyrite
Ore: Galena
Gangue: Chalcedony
Gangue: Chalcopyrite
Gangue: Sphalerite
Gangue: Quartz
Gangue: Calcite

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Comments

Comment (Geology): An important structural feature in the district is a group of "crossing" vertical or steeply dipping fractures that strike northeast, about normal to the long axis of the granodiorite body. In places they are simple fractures; elsewhere they form sheeted fracture zones several feet wide. Some are tight, some are open and form watercourses, and few contain any quartz. Two main stages of primary or hypogene mineralization are recognized - 1) a hypothermal stage represented by one vein and one mineralized crossing, in which magnetite, pyrrhotite, pyrite, and specularite were deposited, and 2) a mesothermal stage, in which the gold quartz veins were formed. The mesothermal stage is further divided into two sub-stages - an older one, in which quartz is the principal gangue mineral, and a younger one, marked by the deposition of carbonates. Pyrite and arsenopyrite, deposited in the quartz stage, are the earliest sulfides of the gold-quartz veins. Sphalerite, chalcopyrite, and galena are somewhat later. No secondary or supergene minerals have been noted except limonite, calcite, and gypsum, which are being deposited in the oxidized zone. The distribution of gold in the ore shoots is extremely erratic and assays of adjacent vein samples commonly differ widely. Some ore shoots have a pitch length of several thousand feet, but most are much smaller. Adjacent to veins and crossing fractures, the wall rocks are generally highly altered. Ankerite, sericite, and pyrite have replaced the original rock-forming minerals. Lesser amounts of chlorite and epidote have been found. The wall rock has not been replaced by quartz. LOCAL GEOLOGY The principal veins in the Golden Center Mine are the Dromedary, Garage, Church Hill, and Sleep. All strike north and northeast and dip west or northwest and all are contained wholly within granodiorite (Johnston, 1940). Most of the quartz in the various veins is massive and milky. Combs and sheared and brecciated textures are common. Locally, chalcedony fills the interstices in combs and cements quartz breccias. Pyrite, galena, and chalcopyrite are the principal sulfides. Dromedary Vein The Dromedary vein is the main producing zone in the mine. It has an average strike of N 35? E and an average dip of 38? NW. In the main shaft, the strike of the vein is approximately north-south, but north of the shaft, the strike swings to the northeast where the vein is intersected by a series of strong crossing fractures. The angular divergence in strike between the vein and the crossings ranges between 0? and 30?. The vein is repeatedly offset on the crossings, which dip 70? to 90?, forming a series of steps (Johnston, 1940, figure 47). The Dromedary vein was readily followed in the shaft to the 1,100-level and stoping established the continuity of the vein on the north side of the shaft. Below the 1,100-foot level the shaft cut a strong crossing, along which much water circulated and upon which the vein abruptly steepened. Beyond the crossing at the 1,300-foot station the vein was not found. Garage vein The Garage vein, which strikes northeast and dips 38? NW, roughly paralleling the Dromedary vein and lying in its hanging wall, was first encountered on the 500-foot level crosscut. The Garage vein is less broken than the Dromedary vein. The quartz ranges from 2 or 3 to 20 inches thick. Usually it is frozen to one wall; commonly to both walls. In places it fills a splintered fracture several feet wide, forming a sheeted zone of narrow quartz seams.

Comment (Identification): The Golden Center Mine is a consolidation of the Rock Roche, Dromedary, and Berriman mines.

Comment (Location): Location selected for latitude and longitude represents the Golden Center Mine main shaft symbol on the 1949 version of the USGS Grass Valley 7.5-minute quadrangle. On later vesrions of the map the symbol has been replaced by State Highway 49 improvements.

Comment (Development): The Golden Center Mine, located within the town limits of Grass Valley, is a consolidation of the previous Rock Roche, Dromedary, and Berriman Mine properties along with other mineral rights under the town of Grass Valley totaling 150 acres. The mine was first worked in the early 1850s, again in 1863, and from 1868 to 1874, when the ore is reported to have ranged from between $10 and $60/ton. In 1912, the mine was acquired by the Grass Valley Mining Company, which sunk the present (Johnston, 1940) shaft to the 1,100-foot level and crosscut on the 500-level to the Garage, Sleep, and Church Hill veins. In 1931, the mine was acquired by Cooley Butler of Los Angeles. Between 1931 and 1934, the shaft was deepened to the 1,300-foot level, and the 1,100-foot crosscut to the Garage and Church Hill veins was driven. Total value of the mine's production between the 400- and 1,300-level has been estimated at $2,250,000 (Johnston, 1940).

Comment (Economic Factors): Total production from the Golden Center Mine is estimated at $2,250,000 (Johnson, 1940).

Comment (Workings): A map of the underground workings in the Golden Center Mine is included in Johnston (1940, Plate 25, page 74).

Comment (Commodity): Ore Materials: Free-milling fine to coarse gold in quartz. Auriferous pyrite and galena.

Comment (Commodity): Gangue Materials: Quartz, calcite, chalcedony, chalcopyrite, sphalerite

Comment (Geology): Church Hill vein Like the Garage vein, which it parallels, the Church Hill vein was first found on the 500-foot crosscut near its junction with a footwall split called the Sleep vein. A short distance east of the discovery point, an ore shoot was encountered. A winze was sunk at the junction of the Church Hill and Sleep veins and a sublevel driven through the ore. On the sublevel, the shoot was about 135 feet long and averaged 14 inches of quartz that contained a little over 2 ounces of gold per ton. Structurally, the Church Hill vein more closely resembles the Garage vein than the Dromedary vein, for the vein walls are close together and the quartz is commonly frozen to them. Ribbon structure and quartz breccias are also present on the 500- and 1,100-foot levels.

Comment (Geology): REGIONAL GEOLOGY The Golden Center Mine is within the Grass Valley District, home to California's two largest underground gold mines, the Empire and the Idaho-Maryland. The district is located in the northern portion of the Sierra Nevada Foothills Gold Belt. This belt averages 50 miles wide and extends for about 150 miles in a north-northwest orientation along the western slope of the Sierra Nevada range. The Foothills Gold Belt roughly coincides with the Foothills Metamorphic Belt, which can be subdivided into four major lithotectonic belts: Western Belt, Central Metamorphic Belt, Feather River Peridotite Belt, and Eastern Belt. The Grass Valley District lies within the Central Belt, where in the Grass Valley area it is marked by an 8-mile-wide north-trending assemblage of two accreted terranes that range from Late Triassic to Late Jurassic in age. The Central Belt is bounded on the east and west by regional-scale tectonic suture zones; the Wolf Creek Fault Zone on the west and the Gills Hill Fault/Melones Fault Zone on the east. The oldest rocks in the area are those of the Carboniferous-Triassic metasedimentary Calaveras Complex. Originally clastics, these rocks were converted to schistose or slaty rocks during the Late Paleozoic orogeny and locally into a contact-metamorphic biotite gneiss by intruded granodiorite during Late Mesozoic time. The slates of the Jurassic Mariposa Formation, which outcrop in a small part of the area, are relatively unaltered. Igneous rocks in the district include granodiorite, diabase, porphyrite, amphibolite schist, serpentinite, gabbro, diorite, quartz porphyry, and various dike rocks (Johnston, 1940). The veins of the Grass Valley and neighboring Nevada City districts are not connected with or continuations of the famous Mother Lode vein system to the south. The last veins of the Mother Lode end about 20 miles to the south. Also, the Grass Valley veins differ in general character from those of the Mother Lode. Generally, the Grass Valley veins are narrower and produce a higher-grade ore than those of the Mother Lode. The veins trend in two primary directions. One set trends N-S (dipping E or W), and the other trends E-W (dipping N or S). The major feature of the Grass Valley District is a body of Lower Cretaceous granodiorite and diabase five miles long from north to south and half a mile to two miles wide (probably the apex of a larger batholitic mass). It which is intruded into older sedimentary and igneous rocks, including diabase of the Mesozoic-Paleozoic Lake Combie Complex, and is itself cut by various dike rocks. Gold-quartz veins cut the granodiorite and diabase (and in some cases, serpentinite) throughout the district. Most of the veins strike generally north, parallel to the intrusive body, and display gentle dips averaging 35?. Others strike northwest, parallel to a diabase contact with the granodiorite. The veins fill minor thrust faults that occur within fracture zones of various width and degree of fracturing. The maximum measured reverse displacement is 20 feet (Johnston, 1940). In all veins, quartz is the principal vein material and occurs in four textural types: 1) Comb quartz that forms crustifications and lines vugs, 2) massive milky quartz with a granular texture that displays many sharp crystal faces and has not undergone deformation, 3) sheared quartz developed with little or no dilation of the vein fracture and commonly showing ribbon or shear-banding structures, and 4) brecciated quartz formed where vein movement dilated the interwall space (Johnston, 1940). Gold occurs in quartz and in sulfides, principally pyrite. Although specimen ore has been found, most ore from the district occurs as fine and coarse free-milling gold in ores averaging between 0.25 to 0.5 ounces per ton.

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References

Reference (Deposit): Clark, W.B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 191, p. 53.

Reference (Deposit): Johnston, W.G., Jr., 1940, The gold quartz veins of Grass Valley, California: U.S. Geological Survey Professional Paper 194, 101 p.

Reference (Deposit): Koschmann, A.H., and Bergendahl, M.H., 1968, Gold-producing districts of the United States: U.S. Geological Survey Professional Paper 610, 283 p.

Reference (Deposit): Lindgren, W., 1896a, Geologic atlas of the United States - Nevada City Special Folio: U.S. Geological Survey Folio 29.

Reference (Deposit): MacBoyle, E.M., 1919, Mines and mineral resources of Nevada County: Sixteenth Annual Report of the State Mineralogist, California State Mining Bureau, p. 1-270.

Reference (Deposit): Additional information on the Golden cemter Mine is contained in File No. 331-9277 (CGS Mineral Resources Files, Sacramento)

Reference (Deposit): Lindgren, W., 1896b, Gold-quartz veins of Nevada City and Grass Valley: Seventeenth Annual Report of the U.S. Geological Survey, Part 2, p. 1-262

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