Penn-Alaska

Prospect, Inactive

Commodities and mineralogy

Main commodities Ag; Au; Zn
Other commodities Pb; Sb
Ore minerals chalcopyrite; galena; pyrite; sphalerite; stibnite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale A-1
Latitude 58.2208
Longitude -134.1418
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Penn-Alaska prospect is at an elevation of approximately 200 feet on the west side of Taku Inlet, 1.2 miles north of Bishop Point and 1.5 miles southwest of Cooper Point. It is in the NW1/4 section 21, T. 42 S., R. 69 E. of the Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

The Penn-Alaska prospect is in interlayered black phyllite and altered mafic volcanic rocks. The volcanic rocks are marked by a 20-foot-thick, brightly yellow-stained band that contains pyrite, rare sphalerite, galena, chalcopyrite, and stibnite (Redman and others, 1986). The phyllite contains both disseminated and thinly banded pyrite. The altered mafic volcanic rocks contain ankerite, quartz and albite. The deposit was discovered before 1906 and developed by three adits that total 948 feet, a 200 foot drift, an open cut, and several trenches. U.S. Bureau of Mines samples contain up to 3.9 ppm silver, 0.1 ppm gold, 0.17 percent zinc (Redman and others, 1986).
This prospect is in the Juneau Gold Belt, which consists of more than 200 gold-quartz-vein deposits that have produced nearly 7 million ounces of gold. These gold-bearing mesothermal quartz vein systems form a 160-km-long by 5- to 8-km-wide zone along the western margin of the Coast Mountains. The vein systems are in or near shear zones adjacent to west-verging, mid-Cretaceous thrust faults. The veins are hosted by diverse, variably metamorphosed, sedimentary, volcanic, and intrusive rocks. From the Coast Mountains batholith westward, the host rocks include mixed metasedimentary and metavolcanic sequences of Carboniferous and older, Permian and Triassic, and Jurassic-Cretaceous age. The sequences are juxtaposed along mid-Cretaceous thrust faults (Miller and others, 1994). The sequences are intruded by mid-Cretaceous to middle Eocene plutons, mainly diorite, tonalite, granodiorite, quartz monzonite, and granite. Sheetlike tonalite plutons emplaced just east of the Juneau Gold Belt and undeformed granite and granodiorite bodies that are emplaced farther to the east are between 55 and 48 Ma (Gehrels and others, 1991). The structural grain of the belt is defined by northwest-striking, moderately to steeply northeast-dipping, penetrative foliation that developed between Cretaceous and Eocene time (Miller and others, 1994). The majority of the veins in the Juneau Gold Belt strike northwest. Isotopic dates indicate that the auriferous veins in the Juneau Gold Belt formed between 56 and 55 Ma (Miller and others, 1994; Goldfarb and others, 1997).
Geologic map unit (-134.143555288705, 58.2204728057802)
Alteration of deposit Mafic volcanic rocks are altered to ankerite, quartz and albite.

Production and reserves

Workings or exploration The deposit was discovered before 1906 and developed by three adits that total 948 feet, a 200 foot drift, an open cut, and several trenches.
Indication of production None

References

MRDS Number A012028

References

Gehrels, G.E., McClelland, W.C., Samson, S.D., and Patchett, P.J., 1991, U-Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska: Canadian Journal of Earth Sciences, v. 28, no. 8, p.1285-1300.
Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190.
Miller, L.D., Goldfarb, R.J., Gehrels, G,E., and Snee, L.W., 1994, Genetic links among fluid cycling, vein formation, regional deformation, and plutonism in the Juneau gold belt, southeastern Alaska: Geology, v. 22, p. 203-206
Reporters J.C. Barnett and L.D. Miller (Juneau, Alaska )
Last report date 12/15/2001