Bird's Foot

Prospect, Active?

Commodities and mineralogy

Main commodities Cr; Cu; Ni
Other commodities Pd; Pt
Ore minerals chalcopyrite; chromite; magnetite; pentlandite; pyrrhotite
Gangue minerals olivine; serpentinite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-5
Latitude 63.3259
Longitude -146.38
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Bird's Foot prospect is at an elevation of about 5,300 feet, about a 0.3 mile west of lower Eureka Glacier, and 0.6 mile northeast of elevation 6120. It is near the center of section 27, T. 18 S., R. 7 E.

Geologic setting

Geologic description

The Bird's Foot prospect is in Upper Triassic ultramafic and mafic rocks that are faulted into a Tertiary to Cretaceous composite, granitic to dioritic pluton (Nokleberg and others, 1991). Rose (1966) mapped dunite bodies within diorite, quartz diorite, and gabbro in this area. The Broxson Gulch thrust appears to form the hanging wall of the ultramafic and mafic rocks and it has been inferred that dunite bodies lubricated the bottom of the thrust (Kurtak and others, 1992). The hanging wall of the thrust is schist.
The occurrence was found during geologic reconnaissance by the USGS in the early 1990s (Nokleberg and others, 1991) and examined by industry in about 2001 (W.T. Ellis, unpublished field notes, 2001). In 2001, the prospect was on claims of the MAN project of Pure Nickel Inc. Sampled by the Bureau of Land Management in 2003.
This occurrence consists of chromite and magnetite disseminated in a serpentinized olivine inclusion in metagranodiorite (Nokleberg and others, 1991). A grab sample contained more than 0.5 percent chromium.
As described by W.T. Ellis (unpublished data, 2001) rubble of olivine melagabbro and feldspathic peridotite hosts sulfide mineralization. The rubble appears to be derived from a sill-like body of Upper Triassic gabbro and serpentinized peridotite and dunite in the cliffs on the south side of the cirque to the west. The sulfide mineralization consists of coarsely-crystalline clots and disseminations of pyrrhotite, chalcopyrite, and pentlandite. The sulfides rarely exceed about 5 percent of the float.
Bittenbender and others (2007) collected several samples. Most grab samples from the extensive fresh peridotite at the prospect contained no metals of note. A float sample of iron-stained peridotite with 3 to 5 percent sulfides contained 553 parts per billion (ppb) platinum, 3,821 ppb palladium, 148 ppb gold, 2,190 parts per million (ppm) copper and 2,970 ppm nickel. Bittenbender and others (2007) concluded that the mineralized area is small and unlikely to be economic.
Geologic map unit (-146.382266949885, 63.3254750684792)
Mineral deposit model Disseminated chromite in layered mafic-ultramafic complex and nickel-copper-PGE mineralization in a differentiated mafic-ultramafic complex.
Age of mineralization Probably Late Triassic; synchronous with emplacement of the mafic-ultramafic rocks.
Alteration of deposit The ultramafic rocks are serpentinized.

Production and reserves

Workings or exploration The occurrence was found during geologic reconnaissance by the USGS in the early 1990s and examined by industry in about 2001 (W.T. Ellis, unpublished field notes, 2001). In 2001, the prospect was on claims of the MAN project of Pure Nickel Inc. Sampled by the Bureau of Land Management in 2003.
Indication of production None
Reserve estimates None.
Production notes None.

References

References

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.
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