Pennsylvania - W.Y.O.D. Mines

Site Name

Primary: Pennsylvania - W.Y.O.D. Mines

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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: 1855
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: Diabase
Role: Host
Age Type: Host Rock
Age Young: Mesozoic
Age Old: Paleozoic

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
Ore: Arsenopyrite
Gangue: Quartz
Gangue: Calcite
Gangue: Chalcedony
Gangue: Chalcopyrite
Gangue: Sphalerite

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Comments

Comment (Geology): In places, the wall rock is generally fresh and unaltered, but elsewhere, the granodiorite walls are highly altered by sericite and ankerite, and both ankerite and calcite occur with the vein quartz. Pyrite, galena, and sphalerite are the principal sulfides. The Pennsylvania vein displayed an unusually erratic distribution of gold, some of which occurred in scattered patches of high-grade specimen ore. The largest ore bodies were found north of the shaft between the first and third levels. X Vein The X vein, which was worked in the Pennsylvania and neighboring Empire and North Star mines, is characterized by its unusually persistent strike, heavy gouge, and evidence of post-quartz movement. The X vein (also called the No. 1 vein in the North Star Mine) strikes N 45? W and dips an average 35? southwest. It extends down-dip from the 700 foot level of the Pennsylvania Mine to the 8,600 foot level of the North Star Mine and has been worked from both mines. It has also been worked through a crosscut from the Empire shaft at the 4,600-foot level of the Empire Mine. The vein lies wholly in granodiorite and is characterized by the abundance and persistence of the gouge and breccia within the walls of the vein fracture, necessitating in places, much closer timbering than was required in other veins in the granodiorite. Extensive post-quartz movement is indicated by gouge seams that cross the quartz from wall to wall and by much crushed and broken quartz that has not been cemented by later vein materials. Recurrent movement is also indicated by younger gouge cutting older gouge. The width of the main vein fracture is highly variable, ranging from 1 foot to at least 30 feet and averaging between 5 and 10 feet. W.Y.O.D. Vein East of, and in the foot wall of, the Pennsylvania vein is the W.Y.O.D. vein. This vein strikes to the south and has an average dip of 32? W. Long known as a minor surface vein as small as 3-6 inches wide, it was found to develop with depth in the early 1890's. Followed downward, the vein widened to 10 inches at 500 feet, 2 feet at 620 feet, and 2.5 feet at 700 feet. South of the W.Y.O.D. Mine, the vein enters diabase and turns more southeasterly and increases in dip. The vein is generally narrow, locally reaching 2 feet wide and sometimes closing to a seam. The country rock is fractured and impregnated with pyrite and a little calcite. Cavities filled with quartz crystals are common in the vein. Comb, massive, and sheared quartz is the principal gangue material and is accompanied by minor amounts of carbonate. The ore consists of quartz with finely disseminated gold (806-832 fine) and averages $20 - $50 per ton. Pyrite, galena, sphalerite, and some arsenopyrite are the principal sulfides making up about 2% of the vein material and averaging 2.5 to 4.5 ounces of gold and 5 to 8 ounces of silver per ton. Annual production from the W.Y.O.D. vein in the W.Y.O.D Mine for the four years 1890-1893 was $26,000, $53,500, $108,700, and $143,360.

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

Comment (Workings): Underground workings of the Pennsylvania-W.Y.O.D. mines as of 1940 are described by Johnston (1940, figs. 60, 62 and pl. 31).

Comment (Development): Extending from the town of Grass Valley southeastward to the end of Osborne Hill is a series of north-northwest- striking veins that dip about 35? W. This system includes the Pennsylvania, W.Y.O.D. , and Empire mines, as well as several smaller old mines. The Pennsylvania vein was discovered in 1870, and the Pennsylvania claim was patented in 1879. By 1890, an inclined shaft 345 feet deep was sunk and 1,500 feet of drifts and crosscuts opened. By 1898, the shaft had been deepened to 700 feet and the drifts extended to a total of 3,000 feet. In 1890, an apex suit was begun by the Grass Valley Exploration Company, owners of the adjacent W.Y.O.D. Mine against the Pennsylvania Mining Co., which in turn filed a counter suit. In 1902, after the dispute had severely depleted the resources of both companies, the court decided in favor of the Pennsylvania Mining Co. In lieu of damages, the court awarded all the property of the Grass Valley Exploration Co. to the Pennsylvania Mining Co. In 1915, the Empire Mine & Investment Co. purchased the Pennsylvania and the W.Y.O.D. mines, consolidating them with their Empire Mine workings. The W.Y.O.D. ("Work Your Own Diggings") Mine was worked superficially until 1888. The production from 1890 was $26,000; for 1891, $53,500; for 1892, $108,700; and for 1893, $143,360. As of 1896, the shaft was 1400 feet deep on the incline with drifts extending a maximum distance of 700 feet south and 600 feet north. The total output of the W.Y.O.D. mine has been estimated at $1,400,000 (Johnston, 1940).

Comment (Economic Factors): Total production from the Pennsylvania-W.Y.O.D. is estimated at about $1,400,000.

Comment (Geology): REGIONAL GEOLOGY The Pennsylvania and W.Y.O.D. mines are 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 (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 hills southeast of Grass Valley are to a large degree shattered by jointing or sheeting, and numerous quartz veins are found parallel to these joints. The most prominent vein system dips west at moderate angles, but there is evidence of another contemporaneous system dipping at similar angles to the east. The veins lie chiefly in granodiorite while some are encased in diabase. The gold is generally high value, often coarse, and sulfides are moderate in quality. The principal veins in this system that were worked in the Pennsylvania and W.Y.O.D. mines were the Pennsylvania vein, X vein, and W.Y.O.D. vein. The Pennsylvania and W.Y.O.D. veins dip to the west, the W.Y.O.D. vein being the deeper of the two. Pennsylvania Vein The Pennsylvania vein strikes generally north and dips at an average angle of 40? W, but is characterized by numerous irregularities in strike and dip, as well as numerous splits, back-dipping cross-overs, and rolls in the vein. On the surface, the vein can be traced for 1,000 feet north of the shaft. The X vein joins the Pennsylvania vein between the 8,900- and 1,200-foot levels of the Pennsylvania Mine. The Pennsylvania can be followed north from its junction with the X vein for about 4,000 feet, but as it approaches the contact between granodiorite and the Calaveras Complex rocks, the vein undulates on strike and splits into many branches; here the gold content was too low to have justified mining. In the lower levels, the vein ranges from a mere seam to 3 feet or more in width but averages 1 foot wide. The vein walls are generally sharp. Gouge of variable width is present, and the quartz is commonly sheared and brecciated. Evidence of post-quartz movement is much less than on the X vein. The system of fissures dipping to the east cut the vein and there is a constant tendency throughout the mine for the main vein to throw off stringers into the easterly dipping fractures.

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

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

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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): 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): 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 Pennsylvania - W.Y.O.D. Mine is contained in File No. 339-5899 (CGS Mineral Resources Files, Sacramento)

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