7-mile Gold

Prospect, Active?

Commodities and mineralogy

Main commodities Au; Cu
Ore minerals chalcopyrite; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale A-1
Latitude 55.19942
Longitude -132.0251
Nearby scientific data Find additional scientific data near this location
Location and accuracy The 7-Mile Gold prospect, which is exposed in road cuts and a borrow pit, is about 0.8 mile southeast of hill 1360, and near the northeast corner of section 17, T. 77 S., R. 89 E.

Geologic setting

Geologic description

The 7-Mile Gold prospect is one of the deposits in the Kael-7 Mile Trend (CR188), a belt of mineralization about 4 miles long and 0.5 mile wide. The rocks in the area consist mainly of marble and minor chlorite schist, cut by greenstone dikes and sills. They are part of the Wales Group of Late Proterozoic and Cambrian age (Eberlein and others, 1983; Brew, 1996). The mineralization is stratiform and and consists of breccia veins or zones (Hedderly-Smith, 1993, 1999 [Inventory]). The clasts in the breccia vary from fresh marble to ferroan(?) dolomite to silicified marble. The matrix is mainly quartz; locally the matrix may contain up to 50 percent pyrite and chalcopyrite but it generally contains only a few percent of sulfides.
The mineralization in the Kael-7 Mile Trend was discovered in 1988 by a Sealaska geologist. The discovery (CR 186) was soon leased to the American Copper and Nickel Company, who mapped and sampled the belt, and drilled 26 shallow holes in 1990 and 1991, mainly on geochemical anomalies. At least one hole was drilled on the 7-Mile Gold prospect. Three holes totaling 2,837 feet were drilled in 1994, one at the Roy Creek prospect (CR191) at the east end of the belt, and two at the west end.
As described by Maas and others (1991), the deposit at this prospect is a 30-foot-thick, silicified marble-breccia zone with masses and blebs of pyrite and chalcopyrite. The zone trends N 55-80 E. The mineralization is exposed in road cuts and a borrow pit, but the best mineralization is in large blocks of sulfide-rich marble in rubble in the cuts and on the pit floor. Maas and others (1991) collected several sets of samples: 1) 4 samples, 6 to 10 feet long, of the footwall and hanging wall of the mineralized zone contained 18 to 165 parts per billion (ppb) gold and 17 to 154 parts per million (ppm) copper; 2) 7 samples, 2 to 8 feet long, of the silicified breccia contained 105 to 566 ppb gold and 11 to 182 ppm copper; and 3) 2 sulfide-rich samples of rubble in the pit contained 0.388 and 0.784 ounce of gold per ton, 5.5 and 14.5 ppm silver, and 1.0 and 2.18 percent copper.
Geologic map unit (-132.026773911078, 55.199065236875)
Mineral deposit model Stratiform Au-Cu breccia zones in marble.
Age of mineralization Younger than the Late Proterozoic or Cambrian host rocks.
Alteration of deposit Silicification and dolomitization of marble.

Production and reserves

Workings or exploration Extensive sampling of mineralized road cuts and a borrow pit by government and industry geologists. At least one shallow hole drilled in 1990. Maas and others (1991) collected several sets of samples: 1) 4 samples, 6 to 10 feet long, of the footwall and hanging wall of the mineralized zone contained 18 to 165 parts per billion (ppb) gold and 17 to 154 parts per million (ppm) copper; 2) 7 samples, 2 to 8 feet long, of the silicified breccia contained 105 to 566 ppb gold and 11 to 182 ppm copper; and 3) 2 sulfide-rich samples of rubble in the pit contained 0.388 and 0.784 ounce of gold per ton, 5.5 and 14.5 ppm silver, and 1.0 and 2.18 percent copper.
Indication of production None

References

References

Hedderly-Smith, D.A., 1993, Gold-copper mineralization in the Dolomi-Chasina Point area, Prince of Wales Island, Alaska (abs.): Alaska Miners Association, Juneau Branch, Conference Juneau, Abstracts of Professional Papers, p. 13-14.
Hedderly-Smith, D.A., 1996, Report of the 1994 and 1995 work in the Kitkun Bay area-Sealaska minerals reconnaissance project: Sealaska Corporation, 83 p. (Unpublished report held by the Sealaska Corporation, Juneau, Alaska.)
Hedderly-Smith, D.A., 1999, Inventory of metallic mineral prospects, showings and anomalies on Sealaska lands, 1988 through 1998: Sealaska Corporation, Juneau, Alaska, 217 p. (internal report held by Sealaska Corporation, Juneau, Alaska).
Reporters D.J. Grybeck (Applied Geology)
Last report date 5/1/2004