Gravel Pit

Occurrence, Active

Commodities and mineralogy

Main commodities Cu; Ni; Pd; Pt
Other commodities Au
Ore minerals pyrrhotite
Gangue minerals olivine; serpentine

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-4
Latitude 63.056
Longitude -145.7501
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is in a gravel pit at an elevation of 3,650 feet on the north side of the Denali Highway, 1.9 miles southeast of Fourteenmile Lake. It is in the NW1/4NW1/4 section 36, T. 21 S., R. 10 E., Fairbanks Meridian.

Geologic setting

Geologic description

Peridotite in a borrow pit on the side of the Denali Highway contains as much as 1 percent disseminated pyrrhotite and traces of platinum group elements (L.D. Hulbert, oral communication, 2001). The peridotite probably is part of the Tangle ultramafic-mafic complex of Late Triassic age. Two grab samples collected by MAN Resources respectively contained 0.11 percent nickel, 0.01 percent copper, 67 ppb palladium, and 146 ppb platinum and 0.27 percent nickel, 0.09 percent copper, 58 parts per billion (ppb) palladium, 51 ppb platinum, and 51 ppb gold (L.D. Hulbert, oral communication, 2001).
The Tangle complex is a north-dipping layered intrusion of dunite, peridotite, and gabbro that varies from less than 2,000 feet thick to more than 4,000 feet thick and extends for more than 12 miles in length (W.T. Ellis, oral communication, 2001). The complex is believed to be a lopolithic feeder of the Nikolai basalt flows of the Wrangellia Terrane (W.T. Ellis, oral communication, 2001). The complex intrudes the Tangle Formation of Permian age (Nokleberg and others, 1991). It may connect with the Fish Lake complex at depth below the Amphitheater synform. Magmatic mineralization is synchronous with emplacement of the Tangle 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 (-145.752330782595, 63.0555770419033)
Mineral deposit model Ni-Cu-PGE in differentiated mafic-ultramafic sill.
Age of mineralization Late Triassic.
Alteration of deposit The peridotite is locally serpentinized.

Production and reserves

Workings or exploration
Two grab samples collected by MAN Resources respectively contained 0.11 percent nickel, 0.01 percent copper, 67 parts per billion (ppb) palladium, and 146 ppb platinum and 0.27 percent nickel, 0.09 percent copper, 58 ppb palladium, 51 ppb platinum, and 51 ppb gold.
The occurrence is on active claims of MAN Resources.
Indication of production None

References

Reporters W.T. Ellis (Alaska Earth Science), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (USGS)
Last report date 6/17/2002