Pennsylvania Mine Project, Pennsylvania Mining District, Lincoln County, Nevada, USAi

Regional Level Types
Pennsylvania Mine Project	Project
Pennsylvania Mining District	Mining District
Lincoln County	County
Nevada	State
USA	Country

Structure: The Caliente caldera complex consists of an 80 km E-W by 35 km N-S area of nested calderas in this part of the southeastern Great Basin. It is bounded on its north and south sides by E-W shear zones that provided magmatic pathways for stratovolcanoes, volcanic domes, breccia pipes, and other volcanic vents. The E-W zones also provided fluid pathways that resulted in adjacent hydrothermal gold deposits of the Pennsylvania, and other mining districts. The E-W shear zones are interpreted as transverse zones, which are broad belts of accommodation that enabled crust north and south of them to extend at different rates, amounts, and methods. Rocks in the mine area are cut by both NE- and NW- striking faults.

Alteration: Argillization and silicification are the dominant alteration types in the mine area. Host rocks in the mine area are thoroughly kaolinized and silicified. Chloritically altered intrusive outcrops nearby.

Commodity: Ore Materials: chalcopyrite, malachite, azurite, brochantite, gold, other very fine-grained gray sulfides Gangue Materials: clay, iron oxides, quartz, pyrite, calcite

Deposit: The main Pennsylvania deposit consists of a mile-long sheeted quartz vein system and quartz-cemented breccia that was emplaced along a shear zone. The property also contains several gold skarn zone targets. In th emain vein system, intervening wall rock fragments and lenses consist of altered andesite, mapped as Miocene ash-flow tuff. The quartz is light green to tan to gray in color, sugary to massive in texture and characteristically vuggy with some gossany portions. The vugs are filled with euhedral iron-stained prismatic quartz. Fissure-type banding is common as is quartz after calcite texture and coarse white calcite vein material. Most of the veins are subparallel with a general N-NW strike and shallow E-NE dip. The outcrop is sheared (fractured) both parallel to and at a high angle to the sheeted vein system. The dominant NW- shearing and veining reflect a major NE-striking 30E-dipping fault that bounds the inferred southern limit of the Caliente caldera complex. The contact of intrusive with limestone is not well exposed, but orientation is probably NE-SW. Weathered, chloritically altered intrusive outcrops at bottom of trench just NW of the adit. Host rock has iron-stained fractures and carries a small amount of oxidized pyrite. An inclined shaft follows an iron-stained, silicified, gossan replacement zone in altered limestone. Mineralized dump rock is red-black, very dense and composed almost wholly of magnetite. Magnetite also occurs in calcite-veined tactite and as replacement pods in the limestone. Limestone shows various types of alteration including silication, marbelization, and replacement or staining by iron-oxides (gossan). The rock is banded, very dense, and contains lenses and veins of calcite and oxidized pods and crystals of magnetite, copper oxides, pyrite, and chalcopyrite. An elongate prospect in the NW part of mine area exposes propylitized, silicified, brecciated andesitic volcanics cut by mafic dikes and a N25W shear zone 10-30 ft wide that hosts the main Pennsylvania sheeted quartz vein system. Many of the veins are fissure-type, composed of bands of finely crystalline or chalcedonic quartz with open drusy quartz-encrusted centers. The quartz carries the minerals mentioned above and encloses altered andesite and possibly some sedimentary fragments. Some of the fragments are mineralized, containing pyrite, chalcopyrite and iron oxides. Several fragments display early stage vitreous quartz veinlets. The breccia itself is commonly crosscut by late-stage open-centered fissure veins. The rocks exposed in the trenches above the prospects are altered pink-gray, rhyolite ash-flow tuff. Within the trench, the rocks are bleached, argillized (kaolinized?) and sheared. The rocks are hydrothermally altered to bright red, yellow, and orange colors at the northwest end of the trench. They are clay-altered and show calcite and clay veining.

Deposit type: Polymetallic veins

Development: Early exploration in the district was for silver. The U. S. Government explored it for copper in 1943, driving a "new" incline 230 ft n of the "old" incline, 500 ft down dip from the outcrop, thence 500 feet north and 200 feet south, drifting in quartz breccia with minor mineralization. Bear Creek Mining Company (Kennecott) began exploration in 1967, staking an additional 26 "Alta" claims around Johnston's claims. Homestake began exploration here in 1968, followed by Western Ventures in 1969 and Cordilleran Exploration in the early 1970s and Westward Energy and Resources, Inc. in 1983. Area is staked and there is recent surface exploration at and adjacent to the mine sites (1983). Although there was no activity at the time of NBMG examination in 1983, several core boxes and modern equipment indicated that the property had been recently drilled. The open pit operation appeared to date from about 1980. Orange flagging on outcrops at west edge of pit indicated recent sampling of the property at that time. Royal Standard Minerals, Inc. acquired the Caliente property in the Pennsyvania Mine area in the 1990s. In 1996, Royal Standard was assessing the ore potential of the partially developed resource on the property. Forty-eight new lode claims were staked to control the entire Pennsylvania quartz vein system, including the high-grade Jumbo open pit and several gold skarn zone targets on the property. Based on previous drilling, the high-grade Jumbo zone was believed to contain 10,000 to 30,000 tons grading 0.126 opt gold. This mineralization remains open down plunge toward the east.Based on assay results from a 1997 sampling program, Royal Standard planned an infill diamond drilling program to prove up and expand the reserve base of the Jumbo zone on its Caliente property. The mile-long gold-bearing sheeted quartz vein-breccia system has been partially developed by the Jumbo pit. Previous exploration identified a resource of 700,000 tons grading 0.039 opt gold in the central area of the system. The former heap leach pile contains about 50,000 tons of 0.03 opt gold and 0.80 opt silver which may also be classified as reserves. Deep exploration and evaluation of several gold skarn targets on the property were also planned.

Ore(s): E-W shear zones associated with the Caliente caldera complex provided fluid pathways that resulted in adjacent hydrothermal gold deposits of the Pennsylvania and other mining districts.

References

Other Databases

Link to USGS MRDS:	10310471

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