Mountaineer Mine

Site Name

Primary: Mountaineer Mine

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Commodity

Primary: Silver
Primary: Gold

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Location

State: California
County: Nevada
District: Nevada City 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: Nevada 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: 1880
Years of Production:
Organization:
Significant: Y
Deposit Size: S

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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: Weimar Fault Zone

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Alterations

Alteration Type: L
Alteration Text: The wallrock (granodiorite) adjacent to the Mountaineer Vein is comparatively fresh.

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Rocks

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

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Analytical Data

Not available

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Materials

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

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Comments

Comment (Geology): REGIONAL GEOLOGY The Mountaineer Mine is within the Nevada City District, which is adjacent to the Grass Valley District, home to California's two largest underground gold mines, the Empire and the Idaho-Maryland. The district is situated 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 Mountains. The Foothills Gold Belt approximately coincides with the Foothills Metamorphic Belt, which in this area can be subdivided into four major lithotectonic belts: Western Belt, Central Belt, Feather River Peridotite Belt, and Eastern Belt. The Nevada City District lies within the Central Belt, which in the Nevada City-Grass Valley area is marked by a 15-mile-wide north-trending assemblage of two accreted terranes that range from Paleozoic-Late Triassic to Late Jurassic in age. The Central Belt is bounded on the east and west by regional-scale tectonic zones: the Wolf Creek Fault Zone on the west and the Melones Fault Zone on the east. Although some early geologists considered the mines at Nevada City and those on Banner Hill as forming two separate districts, all of these mines are considered here to be part of the "Nevada City District." The oldest rocks in the Central Belt in this area are those of the Paleozoic-Triassic metasedimentary Calaveras Complex, which is exposed in the east part of the belt. Derived from marine sedimentary rocks, these were converted to schistose or slaty rocks during the Late Paleozoic orogeny and locally into a contact-metamorphic biotite gneiss by granodiorite intruded during the Late Mesozoic. Exposed in the west part of the belt, and underlying the two mining districts, are metamorphic rocks of the Jurassic Lake Combie Complex. Slate of the Jurassic Mariposa Formation is exposed in a small area southeast of the Nevada City-Grass Valley area. Igneous and metaigneous rocks in this area include granodiorite, diabase, porphyrite, amphibolite schist, serpentinite, gabbro, diorite, quartz porphyry, and various dike rocks (Johnston, 1940). The main host rocks for the ore deposits of the two districts are rocks of the Lake Combie Complex and younger granitic rocks that intrude them. The veins of the Nevada City and neighboring Grass Valley districts are not connected with, nor are they continuations of, the famous Mother Lode vein system to the south. The northernmost veins of the Mother Lode end about 20 miles to the south. The Nevada City District is at the southern end of a large body of Jurassic granodiorite called the Yuba Rivers Pluton (Saucedo and Wagner, 1992). Here, the granodiorite is in intrusive contact with a north-trending belt of older metamorphic rocks (Lake Combie Complex of Tuminas, 1983) that consist of slate, schist, diabase, gabbro, and serpentinite. The east part of the district is covered with younger Tertiary volcanic rocks in places. The veins in the vicinity of Nevada City are concentrated along or near the contact of the granodiorite body with the metamorphic complex and are arranged in two main systems: one trends west-northwest with steep dips to the north or south, while the other trends northerly with medium dips to the east and contains the most productive veins. In general, according to Koschmann and Bergendahl (1968), the veins of the Nevada City District are mineralogically similar to those of the Grass Valley District. There are several differences in the character of the veins between the two districts, however. One is that the Grass Valley veins contain larger amounts of coarse gold. The following characteristics of the Nevada City District are summarized from Lindgren (1896b), Hobson and Wiltsee (1893), and Johnston (1938):

Comment (Development): The Mountaineer Mine was operated at least as early as 1880, with the vein worked prior to that. The Mountaineer Vein was worked extensively for about 15 years prior to approximately 1896 and at intervals thereafter until either 1913 or 1916. It is not known if the mine was in production subsequent to 1913 or 1916, the last years of operation reported by MacBoyle (1919). Some work, including diamond drilling, was done in the mine as late as 1961 (Clark, 1961), but there was no indication of any production. Current conditions at the mine site are not known. Although five ore shoots were opened along the vein, only one was responsible for the main production. This shoot was about 100 feet north of the winze at the main tunnel level and had a rake of 40N on the vein. At the 400-level the vein pinched down to a small seam, but at the 500-level, the vein averaged 20 inches in width and the ore shoot was 160 feet in length. The mine utilized a 20-stamp mill in the 1800?s. In the 1800?s, any ore below $7/ton was not processed because of the narrowness of the vein and the extremely hard wallrock (Crawford, 1894). Before 1890, sulfide concentrates were processed at the nearby Champion Mine. Although not reported in the documents researched, it is assumed that amalgamation processes were used at this mine.

Comment (Economic Factors): MacBoyle (1919) and Clark (1961, 1970) estimated production at the Mountaineer Mine to be $2 million to $3 million.

Comment (Environment): The Mountaineer Mine is situated along the canyon of Deer Creek in a semi-developed, forested setting that is less than a mile downstream of the main commercial area of Nevada City.

Comment (Workings): The Mountaineer Vein is developed by a 2,000-foot drift adit driven north from the bank of Deer Creek. About 1,000 feet in from the adit portal, a 1,200-foot inclined winze was sunk along the vein. From this working, nine levels were drifted along the vein. Maximum drifting was 1,500 feet north and 2,200 feet south of the winze. Little timbering was required because of the hard wallrock (little or no hydrothermal alteration and no sheeting of wallrock). The mine reportedly produced considerable water.

Comment (Deposit): The Mountaineer Mine is in the southernmost part of a large body of Jurassic granodiorite associated with the northern portion of the Sierra Nevada Foothills Gold Belt . It exploits the Mountaineer Vein, which has been one of the main ore-producing bodies of a complex of gold-bearing quartz veins that comprise the lode-gold deposits of the Nevada City Mining District. These deposits are similar to those of the adjacent Grass Valley Mining District to the south, which is notable for its world-class production. As described by MacBoyle (1919) and Lindgren (1896b): The strike of the Mountaineer Vein is N18E and the dip averages 37SE, although there are many local irregularities. It averages about one foot in width, but at intervals it swells to a maximum width of 10 feet; in the wider parts, the ore is generally of lower grade. The narrowness of the vein compared to the nearby veins at the Champion-Providence Group suggests that there was less movement along the fissure occupied by the Mountaineer Vein. The walls of the vein are composed of unaltered granodiorite. Ore consists of ribbon quartz, which carries native gold and 3-4% sulfides. Sulfides are chiefly pyrite, with smaller amounts of sphalerite, chalcopyrite, and galena. The sulfides carry from $100-200 per ton in gold and silver. The percentage of silver in the ore is larger than in most mines of the Nevada City and Grass Valley mining districts. Crawford (1896) reported the presence of telluride on one ore shoot. The Mountaineer Vein extends for at least 5,000 feet north of Deer Creek. It also continues south of Deer Creek, but the ore there was of low grade. Five ore shoots were exploited in this mine, with one responsible for most of the production.

Comment (Geology): REGIONAL GEOLOGY (continued) The most productive veins in the vicinity of the town of Nevada City are near or along the contact between the metamorphic rocks and granodiorite. They do not tend to directly coincide with the contact itself. The veins of the district are generally larger than those at Grass Valley; they range from a few to as much as 40 feet in width with an average of about 2 to 6 feet. Overall, the veins of the district contain more silver than those at Grass Valley, and generally the contained sulfides are richer in gold. Sulfides are generally auriferous and can constitute as much as 20% of the vein material. Pyrite is the dominant sulfide, with lesser amounts of galena, sphalerite, chalcopyrite, arsenopyrite, and tetrahedrite. Molybdenite and tellurides are locally present. Compared to Grass Valley, however, the veins are lower in grade and rarely contain coarse or specimen gold. The gangue is mainly quartz, although calcite and ankerite are abundant and later than the quartz; minor gangue minerals locally include sericite, chlorite, epidote, and chalcedony. Study of the paragenesis of the district by Johnston (1938) indicated that vein-filling developed in two main stages: quartz first, then carbonate, with a transistion of deposition between the two types. The sulfides and gold were deposited during the quartz stage. Hydrothermal alteration of the wallrock consists of carbonate, sericitic, and pyritic. Replacement of wallrock by silica was not noted, although small fissures filled with carbonates and quartz can be common. In places, the veins are associated with dikes. All of the veins have some gouge, which indicates that they were emplaced along faults. Detailed studies of several veins indicate that they were formed by successive movement along the faults with subsequent deposition of quartz; at least four separate cycles of movement and deposition have been recognized. Ore shoots have been followed down-dip as much as 2,700 feet. The nearby Banner Hill part of the Nevada City District has some distinct differences from those closer to Nevada City proper. Among these differences are the narrowness of the veins and their prevailing east-west strike with low to moderate dips to the north or south; locally, north-south-striking veins are present. A few of the east-west-striking veins have nearly vertical dips. The east-west set appears to generally follow a system of joints or sheeting in the granodiorite country rock. Ores are commonly of high grade, with much silver and sulfides.

Comment (Identification): The Mountaineer Mine is developed on the Mountaineer Vein, which is just east of the highly productive Merrifield-Ural vein system that was exploited by the Champion Group of mines. Although the Mountaineer Mine property later included mines (Orleans, Fortuna) along the nearby Orleans Vein, which were not as productive, this report is confined to the deposit along the Mountaineer Vein only.

Comment (Commodity): Commodity Info: the mine is notable for its high percentage of silver.

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

Comment (Commodity): Gangue Materials: Quartz

Comment (Location): Location selected for latitude and longitude is based on narrative descriptions and on the location of the Mountaineer Mine as shown on the USGS Nevada City Special Map (Lindgren, 1896a). Modern quadrangle maps (Nevada City 7.5-minute) do not show the mine.

Comment (Geology): LOCAL GEOLOGY The Mountaineer Mine is entirely within the southernmost part of the Yuba Rivers Pluton. It is along the Mountaineer Vein, which has been one of the main ore-producing bodies in the Nevada City District. The Mountaineer Vein extends for at least 5,000 feet north of Deer Creek. It also continues a short distance south of Deer Creek, but the ore there was of low grade. About 150 feet east of the Mountaineer Vein is the Black Prince Vein, which has structural characteristics similar to the Mountaineer, but is of lower grade. The following summary of the Mountaineer Vein is from MacBoyle (1919) and Lindgren (1896b): The strike of the Mountaineer Vein is N18E and the dip averages 37SE, although there are many local irregularities. The vein averages about one foot in width, but at intervals it swells to a maximum width of 10 feet; in the wider parts, the ore is generally of lower grade. The narrowness of the vein compared to the nearby veins at the Champion-Providence Group suggests that there was less movement along the fissure occupied by the Mountaineer Vein. The walls of the vein are composed of unaltered granodiorite. Ore consists of ribbon quartz, which carries native gold and 3-4% sulfides. Sulfides are chiefly pyrite with smaller amounts of sphalerite, chalcopyrite, and galena. The sulfides carry from $100-200 per ton in gold and silver. The percentage of silver in the ore is larger than in most mines of the Nevada City and Grass Valley mining districts. Crawford (1896) reported the presence of telluride on one ore shoot. As of 1916, five ore shoots were exploited in this mine. The most productive shoot was about 1,100 feet north of the portal of the main adit at Deer Creek. Overall, the ore mined on this shoot prior to the middle 1890?s averaged $15/ton. Near the 1200-foot level, the ore reportedly averaged $11/ton. The other four were of small size or low grade. Ore in the thicker, more massive quartz away from the shoots reportedly carried $1.50-2.00/ton.

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References

Reference (Deposit): Crawford, J.J., 1894, Nevada County: Twelfth Annual Report of the State Mineralogist, California State Mining Bureau, p. 193-194.

Reference (Deposit): Clark, W.B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 193, p. 97-101.

Reference (Deposit): Clark, W.B., 1961, Mountaineer Mine: Unpublished Property Report, California Division of Mines, 1 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): Johnston, W.G., Jr., 1940, The gold-quartz veins of Grass Valley, California: U.S. Geological Survey Professional Paper 194, 101 p.

Reference (Deposit): Johnston, W.G., Jr., 1938, Vein-filling at Nevada City, California: Geological Society of America Bulletin, v. 49, no. 1, p. 23-34.

Reference (Deposit): Tuminas, A., 1983, Structural and stratigraphic relations in the Grass Valley-Colfax area of the northern Sierra Nevada, California: Ph.D. dissertation, University of California, Davis, 415 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): Saucedo, G.J. and Wagner, D.L., 1992, Geologic map of the Chico Quadrangle, California: California Department of Conservation, Division of Mines and Geology Regional Geologic Map Series, Map No. 7A, scale 1:250,000.

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): Crawford, J.J., 1896, Nevada County: Thirteenth Annual Report of the State Mineralogist, California State Mining Bureau, p. 254-255.

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

Reference (Deposit): Lindgren, W., 1896a, Geologic atlas of the United States - Nevada City Special Folio: U.S. Geological Survey Folio 29, 7 p..

Reference (Deposit): Hobson, J.B., 1890, Nevada City Mining District: Tenth Annual Report of the State Mineralogist, California State Mining Bureau, p. 384-385.

Reference (Deposit): Hobson, J.B. and Wiltsee, E.M., 1893, Nevada City Mining District: Eleventh Annual Report of the State Mineralogist, California State Mining Bureau, p. 287-288.

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