Allison Ranch Mine

Site Name

Primary: Allison Ranch Mine

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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.

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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: 1854
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: Quartz
Gangue: Calcite
Gangue: Chalcedony
Gangue: Chalcopyrite
Gangue: Sphalerite

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Comments

Comment (Geology): REGIONAL GEOLOGY The Allison Ranch 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.

Comment (Location): The location point selected for latitude and longitude represents the Allison Ranch Mine symbol on the 1949 USGS Grass Valley 7.5-minute quadrangle.

Comment (Workings): A development map showing the underground workings in the Allison Ranch Mine is included in Johnston (1940, fig. 58).

Comment (Development): The Allison Ranch Mine was discovered in early 1854 during placer mining operations on Wolf Creek. The mine was one of the most famous early producers of the Grass Valley District. During the period 1854-1866, 46,000 tons of ore valued at $2,300,000 was mined. During the same period, the mine paid $1,200,000 in dividends. At that time, the mine had been developed by an inclined shaft to a depth of 475 feet and four levels had been driven about 700 feet along the vein. The mine was closed in October 1866 and reopened in April 1869. Between 1869 and 1871, the shaft was deepened to 600 feet and a drift was run for a distance of 500 feet south of the shaft. During this period, the production was between $200,000 and $250,000. The mine was idled in 1871, but was again reopened in 1896 when the property was acquired by Mackey & Flood of San Francisco. An extensive surface plant was installed and the inclined shaft was deepened to 1650 feet, but instead of following the vein the shaft was continued in granodiorite at a uniform angle. At the 800, 1,000, 1,200, 1,400, and 1,600 levels, crosscuts were driven east from the shaft intersecting the vein on each level. Drifts were then driven on the vein and average distance of 400 feet north and 1,000 feet south. Since the shaft was sunk near Wolf Creek, 1,000 gallons of water per minute had to he pumped. Over two miles of drifts were driven on the Allison Ranch, Cariboo, and Branch veins from 1896-1903. In 1902, a 20 stamp mill was completed. The ore during this period is said to have averaged $10 per ton and concentrates, $80 per ton. In 1903 the mine was again idled, but was reopened in 1918-1921, and again for a short period in 1926. When the mine was reopened in 1918, 1000 feet of new drifts were driven and a crosscut of several hundred feet was driven. At that time the shaft bottomed at 1675 feet and the mine had 11 levels. Its surface facilities included a 102-foot wooden head frame, a hoist capable of handling 2 tons from an incline depth of 2500 feet, a new Sullivan compressor rated at 1500 cubic feet, an Ingersol-Rand 500 cubic foot compressor, a shop, a mill equipped with 20 stamps weighing 1450 pounds each and a 100 ton capacity cyanide plant. The mine was closed in 1926 (Johnston, 1940).

Comment (Economic Factors): The Allison Ranch Mine produced $2,550,000 between 1854 and 1871. No production is available at this writing for the period 1896 to 1926.

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 Allison Ranch Mine is south and east of the Omaha Mine in the southwest part of the district. The mine is in the Allison Ranch vein, one of several veins that comprise the Omaha-Wisconsin-Hartery vein group, a system of veins that strikes north, dips west, and lies entirely within granodiorite. Other veins in the system include the Omaha, Lone Jack, Homeward Bound, Wisconsin, Hartery, Surprise, and Mary Ann-Phoenix, which produce in their namesake mines to the north. All mines in the vein system (except for the Phoenix) were closed and flooded by 1940 (Johnson, 1940). Like the other westward-dipping veins in the Omaha - Wisconsin-Hartery group, the Allison Ranch vein is narrow, averaging 1 foot thick in the upper levels and 1 - 1.5 feet at depth. Maximum width was five feet at depth. The vein strikes N 5? to N 15? E and dips 40?-45? W. There was a clayey parting on the hanging wall while the footwall lacks this parting. Near the surface, the decomposed ore was unusually rich. Twenty-one tons of this ore milled in 1855 yielded $370 per ton. There was a considerable percentage of sulfides chiefly pyrite, galena, and chalcopyrite. A footwall split is known as the Cariboo vein. This smaller vein varied from 4-10 inches thick but yielded rich ore carrying 10 -15 ounces of gold per ton. Pyrite, galena, and chalcopyrite were the principal sulfides. Both the Allison Ranch and Caribou veins are in granodiorite.

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

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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): 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 Allison Ranch Mine is contained in File No. 331-9467 (CGS Mineral Resources Files, Sacramento)

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

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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