Unnamed (southwest Gravina Island)

Prospect, Undetermined

Commodities and mineralogy

Main commodities Ag; Au
Other commodities Barite
Ore minerals barite; chalcopyrite; galena; sphalerite
Gangue minerals carbonate; quartz

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale A-6
Latitude 55.198
Longitude -131.824
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is at sea level on the northeast shore of the unnamed cove about 0.3 mile south of Nelson Cove on southwest Gravina Island. The site is in section 15, T. 77 S., R. 88 E., of the Copper River Meridian. It corresponds to loc. 52.1 in Elliott and others (1978). The location is accurate within 0.1 mile.

Geologic setting

Geologic description

The country rocks in the general area of this prospect are complexly folded and faulted Upper Triassic carbonate, clastic, and basaltic volcanic strata (Berg, 1973; Berg and others, 1980). The deposit consists of a 3-foot-wide fault breccia in a mafic dike(?) that is structurally mixed with the Upper Triassic sedimentary and volcanic rocks. The breccia weathers orange or red, and contains quartz, carbonate, barite, and small amounts of unidentified sulfide minerals, which also are sparsely disseminated in the adjacent country rocks. Analyses of samples of the breccia and the adjacent country rocks showed up to 70 ppm Ag, 0.15 ppm Au, more than 0.5% Ba, 700 ppm Cu, 1.5% Pb, and more than 1% Zn (Koch and Elliott, 1978 [OFR 78-156A]). The analytical data indicate that the unidentified sulfide minerals probably include sphalerite, chalcopyrite, and argentiferous galena. In 1969, workings that probably date to the early 1900s consisted of an approximately 21-foot-long adit.
Geologic map unit (-131.825676840113, 55.1976523672044)
Mineral deposit model Polymetallic veins? (Singer and Cox, 1986; model 22c)
Mineral deposit model number 22c?
Age of mineralization The mineralized fault breccia is Late Triassic or younger.
Alteration of deposit Local iron-staining.

Production and reserves

Workings or exploration In 1969, workings that probably date to the early 1900s consisted of an approximately 21-foot-long adit. Analyses of samples of the breccia and the adjacent country rocks showed up to 70 ppm Ag, 0.15 ppm Au, more than 0.5% Ba, 700 ppm Cu, 1.5% Pb, and more than 1% Zn (Koch and Elliott, 1978 [OFR 78-156A]).
Indication of production None

References