Murchie Mine

Site Name

Primary: Murchie Mine
Secondary: Lone Star
Secondary: Big Blue

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Commodity

Primary: Gold
Primary: Silver

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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: 1861
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

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Structure

Type: R
Description: Weimar Fault Zone, Gillis Hill Fault

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Alterations

Alteration Type: L
Alteration Text: None reported in documents researched. MacBoyle (1919) stated that the wallrock of the Big Blue Vein is unaltered.

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Rocks

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

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

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Comments

Comment (Workings): The Big Blue and Independence veins were developed by an inclined shaft, which was 1,150 feet deep in the early 1900?s, and by at least seven drift levels. Johnston (1938), in his survey of quartz veins of the Nevada City District, collected samples from at least as deep as a 1,450-foot level in the Murchie Mine. Logan (1935) reported that workings were 1,600 feet deep in 1934, although it is not clear if that figure is vertical or inclined. The mine may have been developed ultimately to a depth of about 2,000 feet. Because the veins are in granodiorite with hard, well-defined walls, little timbering was required.

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 (Geology): LOCAL GEOLOGY The Murchie Mine is entirely within the southernmost part of the Yuba Rivers Pluton. It has been developed mostly along four main quartz veins, which are part of the system of ore-producing bodies in the Nevada City District: the Big Blue and Alice Belle are members of an east-west-trending set of veins that is dominant in the east part of the district, while the Lone Star and Independence are members of a minor system of veins that trend north-south in this area. Crawford (1896) also mentioned a Coe Vein, south of the Big Blue. The following summary of the Murchie vein complex is largely from MacBoyle (1919) and Lindgren (1896b): The strike of the Big Blue Vein is nearly east-west and the dip averages 85N. The vein averages about 4 feet in width, but ranges from one to 10 feet. The Independence Vein, which crops out about 800 feet east of the main shaft on the Big Blue, strikes north and dips 36W. The walls of the veins are composed of hard unaltered granodiorite; fault gouge is present on the Big Blue (Johnston, 1938). The Big Blue Vein follows a lamprophyric dike rock, breaking across it from one wall to the other and in some places leaving the dike altogether. 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. Tellurides of both gold and silver were also reportedly observed. Although ore shoots in the mine are irregular, they are of high grade and typical of the Nevada City Mining District. Johnston (1938) observed that quartz veins in the Murchie Mine contained all of the following textures of vein quartz: comb (vug), massive (complete vug-filling), brecciated (vein movement producing dilational cavities), and sheared (vein movement producing little or no dilational cavities). Shearing was responsible for much of the overall ribbon, or banded, texture in the veins. These textures are important because they indicate that the veins developed by successive movement (dilation) along a fissure with several episodes of subsequent deposition of quartz. Johnston (1938) documented at least three episodes of movement and deposition at the Murchie Mine.

Comment (Commodity): Commodity Info: According to Johnston (1938), the ?ratio of concentration of the Murchie ore in 1931 was 40 to1.? It is assumed from the context of this statement that the ratio represented gold to silver. The ratio, however, appears to be in contradiction to statements by MacBoyle (1919, p. 41, 203) that the ore carried more silver than those of other mines in the district. In general, ores of the Nevada City District are notable for their high silver content.

Comment (Commodity): Ore Materials: Native gold, auriferous sulfides (pyrite, chalcopyrite, galena, sphalerite), gold- and silver-bearing telluride

Comment (Commodity): Gangue Materials: Quartz

Comment (Location): Location selected for latitude and longitude is the Murchie Mine shaft symbol on the USGS 7.5-minute North Bloomfield quadrangle.

Comment (Development): Part of the mine site was hydraulically mined in the 1800?s. Up until World War I, the Murchie Mine had been worked at intervals since 1861. From 1878 to 1884, it was a large producer. It was then closed from 1884 to 1894, and was known to have been operated from 1902 to 1909. The mine was acquired by the Empire Star Mines Company in the 1930?s, at which time it became a major producer of gold and silver until its closure during World War II. In 1933, the mine produced nearly 80,000 tons of ore that contained an average of 0.415 ounces/ton gold and 1.48 ounces/ton silver. Most development on and production from this mine was on the Big Blue Vein. Although much less developed than the Big Blue Vein, the Lone Star and Alice Belle veins reportedly produced some rich ore in the early history of the property. As of the early 1900?s, two main ore shoots had been developed, one 350 feet east of the main shaft and one west of the shaft. The east shoot was 500 feet in length, averaged 6 feet wide, and reportedly yielded $15-20/ton. In the early 1970?s, two dumps remained on the property. The larger dump consisted of granodiorite and greenstone-dike material, which was used for construction fill. The smaller dump consisted of sand-sized mill tailings, which were used for construction sand. Amalgamation processes were used at this mine. In the 1800?s to early 1900?s, tailings were disposed of in Deer Creek.

Comment (Economic Factors): MacBoyle (1919) reported total production from the Murchie Mine at about $1,150,000 as of 1918. The mine also produced substantial amounts of gold and silver during the 1930?s when operated by the Empire Star Mines Company.

Comment (Environment): The Murchie Mine is situated on the south side of the forested canyon of Deer Creek. Rural residential development is nearby.

Comment (Deposit): The Murchie 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 has been developed mostly along four main quartz veins, which are part of the system of ore-producing bodies in the Nevada City District: the Big Blue and Alice Belle are members of an east-west-trending set of veins that is dominant in the east part of the district, while the Lone Star and Independence are members of a minor system of veins that trend north-south in this area. These deposits are similar to those of the adjacent Grass Valley Mining District to the south, which is notable for its world-class production. The following summary of the Murchie vein complex is largely from MacBoyle (1919) and Lindgren (1896b): The strike of the Big Blue Vein is nearly east-west and the dip averages 85N. The vein averages about 4 feet in width, but ranges from one to 10 feet. The Independence Vein, which crops out about 800 feet east of the main shaft on the Big Blue, strikes north and dips 36W. The walls of the veins are composed of hard unaltered granodiorite; fault gouge is present on the Big Blue (Johnston, 1938). The Big Blue Vein follows a lamprophyric dike rock, breaking across it from one wall to the other and in some places leaving the dike altogether. 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. Tellurides of both gold and silver were also reportedly observed. Although ore shoots in the mine are irregular, they are of high grade and typical of the Nevada City Mining District. At the Murchie Mine, Johnston (1938) documented at least three episodes of movement and deposition along the vein-filled fissures.

Comment (Identification): The Murchie Mine was originally known as the Lone Star Mine.

Comment (Geology): REGIONAL GEOLOGY The Murchie 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):

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References

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): 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): Logan, C.A.,1930, Nevada County: Twenty-sixth Annual Report of the State Mineralogist, California Division of Mines, p. 118-119.

Reference (Deposit): Logan, C.A.,1935, Nevada County: California Journal of Mines and Geology, v. 31, p. 13.

Reference (Deposit): Logan, C.A.,1941, Mineral resources of Nevada County: California Journal of Mines and Geology, v. 37, no. 3, p. 380.

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): 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): 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): 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): 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, Principal gold-producing districts of the United States: U.S. Geological Survey Professional Paper 610, 283 p.

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

Reference (Deposit): Crawford, J.J., 1896, Nevada County: Thirteenth Annual Report of the State Mineralogist, California State Mining Bureau, p. 250.

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. 285-296.

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.

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