Unnamed (northwest of Fourteenmile Lake)

Prospect, Active

Commodities and mineralogy

Main commodities Cu; Ni; Pd; Pt
Ore minerals chalcopyrite; pyrrhotite
Gangue minerals serpentine

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-4
Latitude 63.0943
Longitude -145.83
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is at an elevation of 4,650 feet, about 1.5 miles northwest of Fourteenmile Lake. It is in the NW1/4SE1/4 section 16, T. 21 S., R. 10 E., Fairbanks Meridian.

Geologic setting

Geologic description

This occurrence consists of float of gabbro, gabbronorite, pyroxenite, olivine melagabbro, and dunite (W.T. Ellis, oral communication, 2001). The rocks are variably serpentinized, and some contain as much as 8 percent sulfide, chiefly in pyrrhotite and chalcopyrite. A sample of sulfide-bearing gabbro contained 0.18 percent nickel, 0.05 percent copper, 46 parts per billion (ppb) palladium, and 15 ppb platinum (W.T. Ellis, oral communication, 2001). Another sample of coarse-grained pyroxenite with 8 percent pyrrhotite and minor chalcopyrite contained 0.12 percent nickel, 0.07 percent copper, 22 ppb palladium, and 35 ppb platinum.
The bedrock source of the float is the Tangle ultramafic-mafic 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, 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 intrudes 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 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 (-145.832236551091, 63.0938771928071)
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
A sample of sulfide-bearing gabbro contained 0.18 percent nickel, 0.05 percent copper, 46 parts per billion (ppb) palladium, and 15 ppb platinum (W.T. Ellis, oral communication, 2001). Another sample of coarse-grained pyroxenite with 8 percent pyrrhotite and minor chalcopyrite contained 0.12 percent nickel, 0.07 percent copper, 22 ppb palladium, and 35 ppb platinum.
The prospect 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