Unnamed (west mouth of Shag Cove)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Cu
Other commodities Ag; Co; Zn
Ore minerals azurite; bornite; chalcopyrite; cuprite; malachite; pyrite; pyrrhotite
Gangue minerals quartz; sheared wall rock minerals

Geographic location

Quadrangle map, 1:250,000-scale MF
Quadrangle map, 1:63,360-scale C-2
Latitude 58.645
Longitude -136.345
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is at an elevation of about 100 feet on the west side of Shag Cove at the mouth of Geikie Inlet, and on a small island just offshore. The location is accurate within 0.1 mile. The site location number 49 of MacKevett and others (1971), number 46 of Cobb (1972), and number 93 of Kimball and others (1978). Kimball and others (1978) reported other mineral occurrences in the area.

Geologic setting

Geologic description

Schist, marble, and hornfels derived from sedimentary and volcanic rocks of Paleozoic age crop out west of Shag Cove. A major northwest-striking fault underlies the Cove and is one of the major faults of the Glacier Bay area. A splay off the master fault appears to separate the metamorphic terrane from granitic rocks of Cretaceous age about 0.3 mile southwest of the cove (Brew and others, 1978).
The mineralized structure is a 65-foot-wide shear zone that strikes northeast and dips steeply northwest, apparently between the master and splay faults, both of which strike northwest.
The shear zone contains quartz veins and subparallel sulfide-rich pods. Pyrrhotite and pyrite are the most abundant sulfide minerals. Chalcopyrite and bornite, partly oxidized to azurite, malachite and cuprite?, occur in lesser amounts. Sulfide-rich pods of pyrite, pyrrhotite and bornite also occur on the small island off the point at the north end of Shag Cove. A sample from a 3-foot-long sulfide pod in the shear zone contained 3000 ppm copper, 700 ppm zinc, 200 ppm cobalt, and 1 ppm silver (MacKevett and others, 1978, p. 51, table 9). A selected sample from a pod exposed on the island contained 1.5 ppm silver, 260 ppm copper, and 100 ppm cobalt (Kimball and others, 1978, p. C366-367).
Geologic map unit (-136.346830301658, 58.6446265179486)
Mineral deposit model Polymetallic vein of probable igneous affiliation (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c
Age of mineralization Cretaceous or younger.
Alteration of deposit Local oxidation of copper minerals.

Production and reserves

Workings or exploration There are no workings. The occurrence on the mainland contains as much as 3000 ppm copper, 700 ppm zinc, 200 ppm cobalt, and 1 ppm silver. A selected sample of a sulfide pod which crops out on the island contained 1.5 ppm silver, 260 ppm copper and 100 ppm cobalt. Kimball and others (1978) reported occurrences of sulfide-bearing quartz veins 1/2 mile from the mouth of the cove and of sulfide-rich pods and sulfide-bearing quartz veins about 1 1/2 miles from the mouth of the cove.
Indication of production None

Additional comments

The site is in Glacier Bay National Park and Preserve.

References