Unnamed (Disk Island)

Prospect, Inactive

Commodities and mineralogy

Main commodities Cu
Ore minerals chalcopyrite; pyrite; pyrrhotite
Gangue minerals epidote; quartz

Geographic location

Quadrangle map, 1:250,000-scale SR
Quadrangle map, 1:63,360-scale B-2
Latitude 60.486
Longitude -147.6565
Nearby scientific data Find additional scientific data near this location
Location and accuracy The prospect is located in the NW1/4 section 35, T. 5 N., R. 10 E., of the Seward Meridian. It is situated at sea level on the southwest shore of Disk Island. This is location 92 of Cobb and Richter (1972), location 120 of MacKevett and Holloway (1977), location 196 of Cobb and Tysdal (1980), and location S-084 of Jansons and others (1984). This location is accurate to within a quarter of a mile. This description includes other copper-stained breccia zones near the prospect and exposed along the beach for about 2 miles.

Geologic setting

Geologic description

The prospect consists of a 10-foot-long adit driven on a greenstone breccia zone that is as much as 4.5 feet wide, strikes N 55 W, and dips 75 E (Johnson, 1918 [B 662, p. 211]). The zone is traceable for about 50 feet. It is healed by quartz and epidote and contains as much as 5 percent pyrite and traces of chalcopyrite (Kurtak and Jeske, 1986). Several other mineralized zones within greenstone and pillow basalt of the Orca Group (of early Tertiary age) occur on the south side of Disk Island (Cobb and Tysdal, 1980; Nelson and others, 1985). Sulfide minerals in these zones are pyrite, pyrrhotite, and a trace of chalcopyrite, which is irregularly distributed throughout the breccia, shear, and fracture zones. The largest of these zones is a 15- by 40-foot exposure of intensely fractured pillow flow containing an estimated trace of chalcopyrite and 5 percent pyrite; the pyrite occurs as blebs, fracture fillings, and fine disseminations. Copper-stained, fractured and brecciated zones are exposed along the beach in this general area for about 2 miles. Nine samples collected from the adit and from various zones along the beach contained from 58 ppm copper to 0.43 percent copper and from 50 ppm to 0.81 percent zinc (Kurtak and Jeske, 1986). The adit sample contained the highest copper value.
Geologic map unit (-147.658493763154, 60.4853911900544)
Mineral deposit model Cyprus massive sulfide (Cox and Singer, 1986; model 24a)
Mineral deposit model number 24a
Age of mineralization Tertiary or younger; the mineralization is in rocks of the Orca Group of Tertiary age.
Alteration of deposit Silicification and epidotization are reported, but no details are provided (Johnson, 1918 [B 662, p. 211]).

Production and reserves

Workings or exploration The workings consist of a single 10-foot-long adit driven on a greenstone breccia zone that is as much as 4.5 feet wide, strikes N 55 W and dips 75 E (Johnson, 1918 [B 662-C, p. 211]). Nine samples collected from the adit and from various zones along the beach contained from 58 ppm copper to 0.43 percent copper and from 50 ppm to 0.81 percent zinc (Kurtak and Jeske, 1986). The adit sample contained the highest copper value.
Indication of production None

References

MRDS Number A010382

References

Hoekzema, R.P., and Sherman, G.E., 1983, Mineral investigations in the Chugach National Forest, Alaska (Peninsula study area): U.S. Bureau of Mines in-house report; held at U.S. Bureau of Land Management Alaska State Office, Anchorage, 524 p.
Reporters Jeff A. Huber and Carol S. Huber (Anchorage)
Last report date 12/9/2000