Unnamed (Fish Lake)

Occurrence, Active

Commodities and mineralogy

Main commodities Cr
Ore minerals chromite
Gangue minerals olivine; serpentine

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-4
Latitude 63.2172
Longitude -145.9316
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is located on the hill southeast of Fish Lake at an elevation of 3,900 feet. It is in the NW1/4NE1/4 section 1, T. 20 S., R. 9 E., Fairbanks Meridian. The site corresponds to locality S72 in table 2 of Nokleberg and others (1991) and represents localities S73 and S74, which were similar occurrences within a mile of this one.

Geologic setting

Geologic description

The rocks in the area of this occurrence are part of the Fish Lake mafic-ultramafic intrusive complex of Late Triassic age, which may be a lopolithic feeder of the Nikolai basalt flows of the Wrangellia terrane (W.T. Ellis, oral communication, 1998). Serpentinized olivine-pyroxene cumulate in the complex contains sparsely disseminated chromite. Grab samples contain 5,000 (or more) parts per million chromium (Nokleberg and others, 1991, see sample 9ZN022A).
The Fish Lake ultramafic-mafic complex is a south-dipping layered intrusion of dunite, peridotite, and gabbro that varies from less than 3,000 feet thick to more than 7,000 feet thick and extends for more than 24 miles in length (W.T. Ellis, oral communication, 2001). The complex intrudes the Tangle Formation of Permian age (Nokleberg and others, 1991). It may connect with the Tangle complex at depth below the Amphitheater synform. Magmatic mineralization is synchronous with emplacement of the Fish Lake complex , which is part of a 120-mile-long belt of mafic-ultramafic and associated rocks in the east-central Alaska Range.
Geologic map unit (-145.933850399699, 63.2167794874023)
Mineral deposit model Disseminated chromite in a layered mafic-ultramafic complex.
Age of mineralization Late Triassic.
Alteration of deposit The olivine-pyroxene cumulate inclusion is serpentinized.

Production and reserves

Workings or exploration
Exploration on the Fish Lake property has been by American Copper and Nickel Company working with Fort Knox Gold Resources Inc. Exploration through 2001 included rock sampling, hand trenching, airborne and ground geophysical surveys, and completion of eight diamond drill holes (W.T. Ellis, oral communication, 2001).
The area is on active claims of Fort Knox Gold Resources.
Indication of production None

References