BOS

Prospect, Active

Commodities and mineralogy

Main commodities Au; Cu; Ni; Pd; Pt
Ore minerals chalcopyrite; pentlandite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-5
Latitude 63.3345
Longitude -146.3224
Nearby scientific data Find additional scientific data near this location
Location and accuracy The BOS prospect as identified by Bittenbender and others (2007) is at the terminus of a hanging glacier about 0.7 mile east-northwest of elevation 6568 and about 6.3 miles northwest of the junction of Eureka Creek and Broxson Gulch. It is about 0.3 mile south of the center of section 24, T. 18 S., R. 7 E. The location is accurate.

Geologic setting

Geologic description

The BOS prospect is in the Late Triassic, Eureka mafic-ultramafic complex. The host for the complex is Pennsylvanian to Permian rocks of the Slana Spur Formation which is intruded by Late Jurassic to Cretaceous granodiorite (Nokleberg and others, 1991). At the prospect, the complex is mainly a sill-like body of serpentinized peridotite, with lesser pyroxenite and gabbro (Bittenbender and others, 2007). The complex crops out along strands of the Broxson Gulch thrust fault (W.T. Ellis, oral communication, 2001).
As described by W.T. Ellis (oral communication, 2001) the mineralization consists of coarsely-crystalline clots and disseminations of pyrrhotite, chalcopyrite, and pentlandite in olivine melagabbro and feldspathic peridotite. Sulfide abundance rarely exceeds about 5 percent. A float sample contained 117 parts per billion (ppb) gold, 393 ppb platinum, 493 ppb palladium, 0.14 percent copper, and 0.4 percent nickel.
Bittenbender and others (2007) could not locate mineralized rock at the Ellis's supposed location and samples they took in that area had insignificant metal values. However, after talking with industry geologists in 2004, they determined that the most likely location for what is commonly known as the BOS prospect is at the coordinates used for this record. (The Ellis location may be about a mile to the northwest but it uncertain whether there are two sites of mineralization or confusion about the location of a single location.) A sample collected by Bittenbender and others (2007) across 1 foot of peridotite with about 1 percent chalcopyrite contained 36 ppb gold, 106 ppb platinum, 86 ppb palladium, 594 parts per million (ppm) copper, and 2,030 ppm nickel. A sample of serpentinite with disseminated sulfides contained 11 ppb gold, 292 ppb platinum, 308 ppb palladium, 1,145 ppm copper, and 3,710 ppm nickel. The prospect is at the toe of a small ice field and may extend under the ice.
Geologic map unit (-146.324667121348, 63.3340764554379)
Mineral deposit model Nickel-copper-PGE mineralization in a differentiated mafic-ultramafic complex.
Age of mineralization Genetically related to the emplacement of a Late Triassic mafic-ultramafic complex.
Alteration of deposit Moderate to strong serpentinization of ultramafic rocks.

Production and reserves

Workings or exploration Examined and sampled by American Copper and Nickel Company in the early 2000s and by Pure Nickel Inc. as part of their MAN project. As of 2001, the prospect was on claims held by Pure Nickel. 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