Unnamed (east of Gakona Glacier)

Occurrence, Undetermined

Alternative names

JS

Commodities and mineralogy

Main commodities Ag; Au; Cu; Pd; Pt
Ore minerals bornite; chalcopyrite; covellite; digenite; magnetite; pyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-3
Latitude 63.2308
Longitude -145.0992
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is at an elevation 6,400 feet on a sharp ridge east of Gakona Glacier. It is about 5.3 miles north-northeast of the center of Devils Lake in the terminus of Gakona Glacier and near the northeast corner of section 32, T. 19 S., R. 14 E.

Geologic setting

Geologic description

Rose (1967) identified gabbro, pyroxenite, peridotite, and dunite here. Nokleberg and others (1992 [MF]; 1992 [Open-File]) included them in their 'ultramafic and associated rocks' unit that occur as klippen above thrust faults. The ultramafic rocks are thrust over volcanic and sedimentary rocks of the Pennsylvanian and Permian, Slana Spur Formation. Nokleberg and others suggest that an Early Cretaceous (123-126 Ma) age from the ultramafic unit probably represents regional metamorphism. However, Bittenbender and others (2007) suggest that Early Cretaceous ages on biotite and hornblende in similar rocks indicates primary crystallization.
Bittenbender and others (2007) identified several mineralized occurrences along the ridge in this vicinity. The rocks at the mineralized occurrences are mainly gabbro, pyroxenite and and peridotite that commonly contains patches of fresh biotite with minor tremolite and calcite (Bittenbender and others, 2007). The rocks are cut by thin, locally altered, pegmatitic gabbro dikes. The dikes contain 2-3 percent, chalcopyrite, bornite, and pyrrhotite, with minor digenite, covellite, and pyrite. Magnetite is a common accessory mineral and locally comprises up to 10 percent of the rock. At one location, 5-6 square feet in area, Bittenbender and others (2007) collected 5 iron-stained samples. The best contained 29 parts per billion (ppb) gold, 3.9 parts per million (ppm) silver, 363 ppb platinum, 72 ppb palladium, and 7,570 ppm copper. A 5.3-foot sample contained 17 ppb gold, 1.1 ppm silver, 258 ppb platinum, 68 ppb palladium, and 3.320 ppm copper. Other iron-stained occurrences in the area may be up to 100 feet long and 50 feet wide (Rose, 1967).
Geologic map unit (-145.101423529898, 63.230397296281)
Mineral deposit model Disseminated copper-PGE minerals in thin gabbro dikes that cut mafic and ultramafic rocks.
Age of mineralization Unclear, possibly Early Cretaceous but may be older.
Alteration of deposit Rocks are generally fresh but thin mineralized gabbro dikes are locally altered.

Production and reserves

Workings or exploration Only limited surface sampling by state and federal agencies.
Indication of production None
Reserve estimates None.
Production notes None.

References

References

Reporters W.T. Ellis (Alaska Earth Sciences), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (USGS); D.J. Grybeck (Contractor, USGS)
Last report date 5/13/2012