Marsha

Prospect, Active?

Commodities and mineralogy

Main commodities Cu; Ni; Zn
Ore minerals chalcopyrite; pentlandite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-4
Latitude 63.3436
Longitude -145.848
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Marsha prospect is at an elevation of about 4,300 feet, about 3.3 miles west of the mouth of Ann Creek. It is about 0.4 mile north-northwest of the center of section 21, T. 18 S., R. 10 E.

Geologic setting

Geologic description

The Marsha prospect is associated with 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 prospect is just south of the Broxson Gulch thrust fault and is between splays of imbricated thrust faults that juxtapose slivers of dark ultramafic rocks with volcaniclastic rocks of the Slana Spur Foundation. Both are intruded by gabbro dikes up to 30 feet thick.
From the late 1980s into at least the 1990s, the Marsha prospect was examined and sampled by several companies, including Teck Cominco America, Northeast Mining Company, MAN Resources Inc., and Nevada Star Resource Corp. but there are no workings on it. Examined and sampled by the Bureau of Land Management in the early 2000s (Bittenbender and others, 2007).
At least three discontinuous lenses and nodules of oxidized chalcopyrite, pyrrhotite, and pentlandite are along the contact of a gabbro dike and serpentinized ultramafic rock. The largest sulfide lens is about 6 feet by 5 feet in area. Samples contained up to 6.25 percent copper, 1,540 parts per million (ppm) nickel, and 1,470 ppm zinc. The mineralization is discontinuous and does not extend far along strike.
Geologic map unit (-145.850258902255, 63.3431852079222)
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 The ultramafic rocks are extensively serpentinized.

Production and reserves

Workings or exploration From the late 1980s into at least the 1990s, the Marsha prospect was examined and sampled by several companies, including Teck Cominco America, Northeast Mining Company, MAN Resources Inc., and Nevada Star Resource Corp. but there are no workings on it. Examined and sampled by the Bureau of Land Management in the early 2000s (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