Murchie Mine (Lone Star Mine; Big Blue Mine; Murchie and Starr; Coe vein; Big Blue vein; Independence vein), Willow Valley, Nevada City Mining District, Nevada County, California, USAi

Regional Level Types
Murchie Mine (Lone Star Mine; Big Blue Mine; Murchie and Starr; Coe vein; Big Blue vein; Independence vein)	Mine
Willow Valley	Valley
Nevada City Mining District	Mining District
Nevada County	County
California	State
USA	Country

A former lode Au-Ag occurrence/mine located in secs. 8, 9, 16 & 17, T16N, R9E, MDM, 0.8 km (0.5 mile) SSW of Willow Valley (town) and about 2 miles E of Nevada City proper. Discovered in 1861. Owned & operated by the Empire Star Mines Co., Ltd., California (1941). MRDS database stated accuracy for this location is 100 meters.

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 (period values)/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.

Mineralization is a Mesozoic deposit (Mineral occurrence model information: Model code: 273; USGS model code: 36a; Deposit model name: Low-sulfide Au-quartz vein; Mark3 model number: 27), hosted in the Jurassic granodiorite of the Yuba Rivers Pluton and Mesozoic lamprophyre. The ore body is tabular/irregular, strikes N-S and E-W and dips 0W-65N at a thickness of 3.05 meters. Controls for ore emplacement
involved ore shoots within quartz veins. Lindgren (1896b) reported that the principal ore shoots on the Big Blue Vein dip to the west and appear to follow the lines of intersection with the flat veins. A lamprophyric dike follows the Big Blue for some distance.Local alteration is absent. None was reported in documents researched. MacBoyle (1919) stated that the wallrock of the Big Blue Vein is unaltered. Local rocks include Mesozoic granitic rocks, unit 3 (Sierra Nevada, Death Valley area, Northern Mojave Desert and Transverse Ranges).

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 Au and Ag. 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.

Regional geologic structures include the Weimar Fault Zone and Gillis Hill Fault.

Workings include underground openings with a length of 304.8 meters and an overall depth of 381 meters. 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.

commodity information: According to Johnston (1938), the ratio of concentration of the Murchie ore in 1931 was 40:1. It is assumed from the context of this statement that the ratio represented Au to Ag. 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. Ore materials: native gold, auriferous sulfides (pyrite, chalcopyrite, galena, sphalerite), gold- and silver-bearing tellurides. Gangue materials: quartz.

Production data are found in: MacBoyle, E.M. (1919); Logan, C.A. (1935); Goodwin, Joseph Grant (1957).

MacBoyle (1919) reported total production from the Murchie Mine at about $1,150,000 (period values) 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.

Production statistics: Year: 1932 (period = 1905 to 1932) (estimated): ^143,000 pounds Cu and 50,000 pounds Pb. Year: 1933 (estimated): ^0.415 ounce Au and 1.48 ounces Ag/ton. Recovery percentages: Ag: 42grams/metric ton; Au: 12 grams/metric ton. Concentrates were worth $100 to $200 (period values)/ton.

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Link to USGS MRDS:	10101281

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