Gunsight Notch

Prospect, Inactive

Commodities and mineralogy

Main commodities Au; Cu
Other commodities As
Ore minerals arsenopyrite; bornite; chalcopyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale D-5
Latitude 58.9687
Longitude -135.4426
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Gunsight Notch prospect is 1.5 miles west of Lynn Canal and 3.5 miles west of Sullivan Island. It is at an elevation of about 3,240 feet, 0.5 mile north of peak 4720, in the NE1/4 section 32, T. 33 S., R. 60 E. of the Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

The Gunsight Notch prospect, which was discovered by Placer Dome U.S. in 1989, is a lens of semi-massive to massive arsenopyrite, bornite, chalcopyrite, and pyrrhotite. The sulfides occur in a volcaniclastic unit 80 feet below the contact of a marble-schist unit. Samples contain up to 6 ppm gold and up to 0.13% copper (Bull and others, 1989). Although the stratabound, volcaniclastic-hosted, sulfides suggest a volcanogenic origin, Placer Dome U.S. geologists interpreted the deposit as a pre- or syn-metamorphic, hydrothermal-replacement deposit, possibly related to a pluton (Bull, 1991).
This deposit is one of many in the Dream prospect area that includes numerous veins, stockworks, stratabound and stratiform sulfide deposits (also see JU002, JU006, JU009, JU011, JU013, JU014, JU016, JU019), most of which occur near a volcaniclastic-marble contact. The U.S. Bureau of Mines (Clough and Redman, 1989), International Curator Resources, Ltd. (Huber and Barnett, 1988), and Placer Dome U.S. (Bull and others, 1989) explored the area in the late 1980s and developed a general lithology of the area. They divide the rocks into four major rock units. From the base up, they are: 1) a volcaniclastic unit approximately 2000 feet thick that consists of albite-chlorite schist, chlorite schist, and chlorite-quartz-sericite schist that may in part be metaplutonic as well as metavolcanic; 2) a unit 800 feet thick of micaceous marble, pelitic schist, graphite schist, gray to white, cliff-forming marble, chlorite-amphibole schist, greenstone, and phyllitic graphite schist; and 3) a unit of very fine-grained chlorite-sericite-biotite schist over 1000 feet thick that includes metatuff and pelitic, mafic and graphitic schist. The upper contact of this unit is a thrust fault that trends N-S for several miles; quartz veining is common along the thrust contact. The rocks overlying the thrust are middle- to upper-greenschist-facies graphitic schist, argillite, phyllite, and marble. The metamorphic grade of the rocks varies from mid- to upper-greenschist facies in the south, to amphibolite facies in the north. There have been at least two stages of folding.
The Dream prospect area was the site of extensive exploration and mapping from 1987 through 1990 by International Curator Resources Ltd. and Placer Dome U.S. The area was covered by 600 federal mining claims in 1989 and more than 5000 feet of drilling was completed by the end of 1990 (Swainbank and others, 1991).
The general area consists of metamorphosed Silurian and Devonian clastic rocks, limestone, and volcanic units; Permian limestone and siltstone; and small plutons of Tertiary and Cretaceous granodiorite (Brew and Ford, 1985).
Geologic map unit (-135.444446025125, 58.9683755848456)
Mineral deposit model Possibly a metamorphosed Kuroko massive sulfide deposit (Cox and Singer, 1986; model 28a) or a metamorphosed polymetallic replacement deposit (Cox and Singer, 1986; model 19a)
Mineral deposit model number 28a or 19a

Production and reserves

Workings or exploration The area has been the site of extensive exploration and mapping from 1987 through 1990 by International Curator Resources Ltd. and Placer Dome U.S. The area was covered by 600 federal mining claims in 1989 and more than 5000 feet of drilling had been completed by the end of 1990 (Swainbank and others, 1991).
Indication of production None

References

References

Reporters J.C. Barnett and L.D. Miller (Juneau, Alaska )
Last report date 12/15/2001