Glacier Lake; Forbes Prospect, Delta River Mining District, Southeast Fairbanks Census Area, Alaska, USAi

Regional Level Types
Glacier Lake; Forbes Prospect	Prospect
Delta River Mining District	Mining District
Southeast Fairbanks Census Area	Census Area
Alaska	State
USA	Country

Location: This prospect is at an elevation of 3,600 feet on the southwest valley wall of lower Canwell Glacier. Access to the property is by a mile-long trail from the end of a dirt road (not shown on the 1984 topographic map) on the east side of the Richardson Highway about a mile south of Millers Roadhouse. The prospect is in the NW1/4SE1/4 section 16, T. 18 S., R. 11 E., Fairbanks Meridian. The prospect is locality 2 in Rose (1965), locality 14 in Cobb (1979 [OFR 79-238]), and locality S104 in table 2 of Nokleberg and others (1991).
Geology: The prospect is in a roof pendant of Upper Triassic serpentinized peridotite and melagabbro in a stock of Cretaceous(?) quartz diorite (Rose, 1965). Pyrrhotite, chalcopyrite, and pentlandite occur in a narrow zone along the contact between the peridotite and gabbro, and chalcopyrite and pyrite are disseminated in the quartz diorite (Barker, 1988). The gabbro locally contains lenses composed of 20 to 50 percent pyrrhotite; chalcopyrite and pentlandite along with quartz and disseminated sulfides are present in serpentinized peridotite away from the contact. The mineralized zone is approximately 25 feet long by 3 feet wide (Hanson, 1963). Grab samples of a massive sulfide lens in gabbro and of quartz diorite with disseminated sulfides at the contact of serpentinized peridotite contained as much as 16,000 parts per million (ppm) copper, 7 ppm silver, 700 ppm cobalt, and more than 5,000 ppm nickel (Nokleberg and others, 1991).
Workings: The Glacier Lake prospect was discovered in 1962 by R.B. Forbes of the University of Alaska (Hanson, 1963). Since then the prospect has been intermittently explored by claimholders, and the claims are currently (2002) controlled by Northeast Exploration (W.T. Ellis, oral communication, 2002). Exploration to date has been primarily surface trenching and airborne and ground geophysical surveys. Samples containing disseminated sulfides assayed from 1.9 to 6.0 percent copper, 1.0 to 1.5 percent nickel, and a trace to 0.4 ounce of gold per ton; a massive sulfide lens assayed 1.1 percent copper, 6.6 percent nickel, and 0.04 ounce of gold per ton (Hanson, 1963). A 3-foot chip sample across the contact of peridotite and diorite assayed 2.1 percent copper, 0.05 percent nickel, a trace of gold, and 0.35 ounce of silver per ton, and a massive sulfide sample contained 8.1 percent nickel (Rose, 1965). The U.S. Bureau of Mines collected nine mineralized samples that averaged 1.46 percent copper, 2.89 percent nickel, 0.07 percent cobalt, 25 parts per billion (ppb) gold, 90 ppb iridium, 495 ppb palladium, 410 ppb platinum, 57 ppb rhodium, and 29 ppb ruthenium (Barker, 1988).
Age: The deposit occurs in Late Triassic ultramafic-mafic rocks and Cretaceous (?) quartz diorite. Mineralization is Late Triassic, synchronous with emplacement of a 120-mile-long belt of mafic-ultramafic and associated rocks in the east-central Alaska Range.
Alteration: The peridotite and melagabbro are extensively silicified and serpentinized near the quartz diorite contact.

Commodities (Major) - Cu, Ni, Pd, Pt; (Minor) - Au, Co, Ir, Os, Rh
Development Status: None
Deposit Model: Ni-Cu-PGE in differentiated mafic-ultramafic sill; Porphyry Cu (?) (Cox and Sin

Other Databases

Link to USGS - Alaska:	MH216

Other Regions, Features and Areas containing this locality

References