Pennsylvania Mine [1] (Pennsylvania Consolidated Qtz; Pennsylvania-W.Y.O.D.; Pennsylvania vein; Pennsylvania-Wyod; Wyod), Empire Star group (Empire Star Mines Company holdings), Grass Valley, Grass Valley Mining District, Nevada County, California, USAi

Regional Level Types
Pennsylvania Mine [1] (Pennsylvania Consolidated Qtz; Pennsylvania-W.Y.O.D.; Pennsylvania vein; Pennsylvania-Wyod; Wyod)	Mine
Empire Star group (Empire Star Mines Company holdings)	- not defined -
Grass Valley	Valley
Grass Valley Mining District	Mining District
Nevada County	County
California	State
USA	Country

A former Au-Pb-Ag-Zn occurrence/mine located in center East boundary of sec. 34, T16N, R8E, MDM, about 1.2 km SE of Grass Valley proper (just outside city limit), on private (patented) land. Discovered in 1855. The property comprises 16.44 acres. MRDS database stated accuracy for this location is 100 meters. The location point selected by the USGS for latitude and longitude represents the Pennsylvania Mine shaft symbol on the USGS Grass Valley 7.5-minute quadrangle.

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 (period values); for 1891, $53,500 (period values); for 1892, $108,700 (period values); and for 1893, $143,360 (period values). As of 1896, the shaft was 1,400 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 (period values) (Johnston, 1940).

Mineralization is a vein 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 Early Cretaceous granodiorite and Mesozoic-Paleozoic diabase. The ore body is tabular, a seam, irregular shoots with sheared quartz, massive and comb.. It has a strike of N & a dip of 20-40W, at a thickness of 1.22 meters. There are 2 veins averaging 12 to 18 inches (30 to 45 cm) thick and carrying 2% sulfides. Controls for ore emplacement included mineralization that occurs as erratic shoots within mesothermal gold-bearing quartz deposited within fracture zones. Local alteration includes ankeritic, sericitic, and pyritic replacement of wall rocks adjacent to veins.
Local rocks include Mesozoic granitic rocks, unit 3 (Sierra Nevada, Death Valley area, Northern Mojave Desert and Transverse Ranges).

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.

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 32W. Long known as a minor surface vein as small as 3-6 inches (7.5 to 15 cm) wide, it was found to develop with depth in the early 1890's. Followed downward, the vein widened to 10 inches (25 cm) at 500 feet, 2 feet (60 cm) at 620 feet, and 2.5 feet (75 cm) 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 (60 cm) 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 (period values).

Regional geologic structures include the Wolf Creek Fault Zone, Gillis Hill Fault and the Melones Fault Zone.

Workings include underground openings with an overall depth of 1,402.08 meters and comprised of inclined shafts, drifts, a tunnel, crosscuts, 14 or 15 levels, a winze, stopes and a patented crosscuts connecting the Pennsylvania Mine with the Empire Mine. The underground workings of the Pennsylvania-W.Y.O.D. mines as of 1940 are described by Johnston (1940, figs. 60, 62 and pl. 31).

Ore materials include free-milling fine to coarse gold in quartz plus auriferous pyrite, galena, and arsenopyrite. Gangue materials include quartz, calcite, chalcedony, chalcopyrite and sphalerite.

Production statistics: Year: 1892 (estimated): 36 grams Au/metric ton; Year: 1893: 28 grams Au/ton.

At the 500 foot level, the W.O.Y.D. vein yielded $18 to $20 (period values) Au/ton. At the 700 level it was $50 Au/ton plus sulfides averaging $250 to $300 (period values). Production grade values based on Au at $20.67 ounce. For additional yearly production figures, see Johnson (1940), page 83.

Total production from the Pennsylvania-W.Y.O.D. is estimated at about $1,400,000.

Analytical data results: 1 ton concentrate averaged 2.5 to 4.5 ounces Au and 5 to 8 ounces Ag.

Other Databases

Link to USGS MRDS:	10007461

Localities in this Region

Other Regions, Features and Areas containing this locality

References