Glacier Lake

Prospect, Active

Alternative names

Forbes

Commodities and mineralogy

Main commodities Cu; Ni; Pd; Pt
Other commodities Au; Co; Ir; Os; Rh
Ore minerals chalcopyrite; pentlandite; pyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-4
Latitude 63.3515
Longitude -145.662
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Glacier Lake prospect is at an elevation of about 3,700 feet. It is south of the terminus of the Canwell Glacier, about 2.3 miles east-southeast of Millers Roadhouse and about 0.5 mile west-southwest of the center of section 16, T. 18 S., R. 11 E. Figure 22 of Bittenbender and others (2007) is a geologic map of the prospect.

Geologic setting

Geologic description

The oldest unit in the area is the Pennsylvania to Early Permian, Slana Spur Formation which consists mainly of volcaniclastic sedimentary rocks (Nokleberg and others, 1992 [MF]; 1992 [Open-File]); Bittenbender and others, 2007). It hosts the Canwell mafic-ultramafic complex that varies from dunite to gabbronorite and includes much serpentinized rock. Both of these units are intruded by Cretaceous quartz diorite to granodiorite. The rocks at the Glacier Lake prospect are serpentine intruded by granodiorite and quartz diorite (Bittenbender and others, 2007).
The Glacier Lake prospect was discovered in 1962 by R.B. Forbes of the University of Alaska (Forbes, 1962; Hanson, 1963). Several companies explored the prospect within the next few years, including Newmont Mining Company (Barker and others, 1988). The property was examined and sampled by the Alaska Division of Mines and Minerals in 1963 (Kaufman, 1963) and by the U.S. Bureau of Mines from 1981 to 1984 (Barker, 1988). Claims were held by Northridge Exploration from 1997 to at least 2002. Falconbridge optioned the property in 1997 and the property was examined for Pacific Northwest Capital Corp. in 2002 (Freeman, 2002). The Bureau of Land Management examined and sampled the prospect in 2004 (Bittenbender and others, 2007). The work on the property includes considerable geologic mapping and sampling and several geophysical surveys.
The area of mineralization is about 25 feet long and 3 feet wide (Hanson, 1963; Barker, 1988; Bittenbender and others, 2007). It is at the contact of a nearly circular outcrop about 25 feet in diameter of granodiorite and quartz diorite (perhaps a roof pendant?) that is surrounded by serpentinite, serpentinized gabbro, peridotite and irregular masses of the granitic intrusive rocks. Pyrrhotite, chalcopyrite, and pentlandite occur in a narrow zone at a contact of peridotite and gabbro; chalcopyrite and pyrite are disseminated in the granodiorite and quartz diorite. The gabbro locally contains quartz lenses with 20 to 50 percent pyrrhotite; chalcopyrite and pentlandite. Disseminated sulfides are present in serpentinized peridotite away from the contact. Local hydrothermal alteration is characterized by secondary chlorite, epidote, mica, and anthophyllite veins near the contact of the serpentinite and quartz diorite.
There are two interpretations of the source of the mineralization. Barker (1988) and some industry geologists concluded that the mineralization is a result of the intrusion of Cretaceous quartz diorite into the ultramafic rocks. Rose (1965) and Bittenbender and others (2007) thought that it is a magmatic segregation in the mafic and ultramafic rocks.
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). 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). Samples collected by Bittenbender and others (2007) along 24.5 feet of the mineralization averaged 122 ppb gold, 450 ppb platinum, 658 ppb palladium, 560 ppm cobalt, 1.97 percent copper, and 2.59 percent nickel.
Geologic map unit (-145.66425468481, 63.3510889774377)
Mineral deposit model Intrusion-related copper-nickel-PGE deposit or a magmatic segregation deposit in a ultramafic-mafic complex.
Age of mineralization Interpreted as either related to a Cretaceous quartz diorite to granodiorite intrusion or as a magmatic segregation deposit in a Triassic ultramafic-mafic complex.
Alteration of deposit The peridotite and gabbro are extensively silicified and serpentinized near the quartz diorite-granodiorite contact. Local hydrothermal alteration is characterized by secondary chlorite, epidote, mica, and anthophyllite near the contact of the serpentinite and quartz diorite.

Production and reserves

Workings or exploration The Glacier Lake prospect was discovered in 1962 by R.B. Forbes of the University of Alaska (Forbes, 1962; Hanson, 1963). Several companies explored the prospect within the next few years, including Newmont Mining Company (Barker and others, 1988). The property was examined and sampled by the Alaska Division of Mines and Minerals in 1963 (Kaufman, 1963) and by the U.S. Bureau of Mines from 1981 to 1984 (Barker, 1988). Claims were held by Northridge Exploration from 1997 to at least 2002. Falconbridge optioned the property in 1997 and the property was examined for Pacific Northwest Capital Corp. in 2002 (Freeman, 2002). The Bureau of Land Management examined and sampled the prospect in 2004 (Bittenbender and others, 2007). The work on the property includes considerable geologic mapping and sampling and several geophysical surveys.
Indication of production None
Reserve estimates None.
Production notes None.

References

MRDS Number A011795

References

Barker, J.C., 1988, Distribution of platinum-group elements in an ultramafic complex near Rainbow Mountain, east-central Alaska Range, IN Vassilou, A.H., Hausen, D.M., and Carson, D.J.T, eds, Process Mineralogy VII, Applications to mineral beneficiation: Proceedings of the Metal Society SME/AIME Joint [Annual] Meeting, Denver, Colo., p. 197-220.
Bittenbender, P.E., Bean, K.W., Kurtak, J.M., and Deininger, James Jr., 2007, Mineral assessment of the Delta River Mining District area, east-central, Alaska: U.S. Bureau of Land Management, Alaska Technical Report 57, 675 p.
Freeman, C.J., 2002, Forbes-Emerick: Avalon Development Corp., Prospect submittal summary, CPG #6901, 7 p.
Wells, K., 1998, Report on the 1997 work program for Falconbridge Exploration U.S., Inc. on the Forbes Nickel Project (PN 5-998)-Mt. Hayes quadrangle, Alaska: Unpublished report, Falconbridge Exploration U.S., Inc., 41 p.
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