Rainy Breccia

Prospect, Active?

Commodities and mineralogy

Main commodities Cu; Ni; Pd; Pt
Other commodities Co
Ore minerals chalcopyrite; magnetite; pentlandite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-4
Latitude 63.3328
Longitude -145.9002
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Rainy Breccia prospect is at an elevation of about 5,600 feet, 2.9 miles north of the junction of the North and West Forks of Rainy Creek. It is 0.6 mile south-southwest of the center of section 19, T. 18 S., R. 10 E.

Geologic setting

Geologic description

The Rainy Breccia prospect is near the north margin of the Late Triassic, Rainy Creek ultramafic-mafic complex that intrudes volcanic and sedimentary rocks of the Tetelna Volcanics and the Slana Spur Formations, both of Pennsylvanian and Permian age (Stout, 1976, Nokleberg and others, 1992 [MF]; 1992 [Open-File]; Bittenbender and others, 2007). The complex is up to 5,000 feet thick, dips shallowly north, and can be traced for more than 15 miles. It is mainly serpentinized dunite with subordinate peridotite, pyroxenite, and gabbro. The base of the complex is a layered gabbro as much as 1,500 feet thick.
The prospect was discovered by the American Copper and Nickel Company (ACNC) in 1995 and later examined and sampled by the Bureau of Land Management (Bittenbender and others, 2007). As described by W.T. Ellis (oral communication, 2001), the Rainy Breccia prospect is in breccia that consists of subrounded clasts of dunite in a dark-colored gabbronorite matrix. The unit is several hundred feet long and approximately 50 feet thick. The breccia strikes S65E and dips 75N. The mineralization in the matrix consists of up to 6 percent disseminated pyrrhotite and magnetite, with traces of chalcopyrite and pentlandite as inclusions in the pyrrhotite. A grab sample of the sulfide-bearing breccia contained 0.12 percent nickel, 0.15 percent copper, 0.01 percent cobalt, 26 parts per billion (ppb) palladium, and 25 ppb platinum.
Bittenbender and others (2007) examined the area but were not certain that they located the the prospect described by Ellis. They did locate two breccia zones with disseminated sulfides in the immediate area; one with peridotite clasts in a leucogabbro matrix and the other brecciated peridotite. However, their samples had low base- and precious-metal values. The best contained 135 parts per million (ppm) copper, 1,285 ppm nickel, 13.9 ppb platinum, and 16 ppb palladium.
Geologic map unit (-145.90245951493, 63.3323838984474)
Mineral deposit model Nickel-copper-PGE mineralization in a differentiated mafic-ultramafic sill.
Age of mineralization Genetically related to the emplacement of a Late Triassic mafic-ultramafic complex.
Alteration of deposit Irregular serpentinized zones occur along the breccia contact.

Production and reserves

Workings or exploration The prospect was discovered by the American Copper and Nickel Company (ACNC) in 1995 and was later examined and sampled by the Bureau of Land Management (Bittenbender and others, 2007).
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