Unnamed (east of peak 6346)

Prospect, Active

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-4
Latitude 63.3249
Longitude -145.981
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is on the southeast side of a ridge about 0.4 mile southeast of the top of peak 6346 at an elevation of about 5,900 feet. It is on the west side of the North Fork Rainy Creek about 0.4 mile west of the center of section 26, T. 18 S., R. 9 E., Fairbanks Meridian.

Geologic setting

Geologic description

This prospect is in the Late Triassic, Rainy complex, a shallowly north-dipping ultramafic-mafic body that varies from less than 100 feet to more than 5,000 feet thick and extends for more than 12 miles (Nokleberg and others, 1992 Open-file]; Nokleberg and others, 1992 [MF]; Bittenbender and others, 2007). It is largely dunite with lesser peridotite and gabbro. A discontinuous marginal gabbro extends along most of the southern (lower) contact and is more discontinuous along the northern (upper) contact (W.T. Ellis, oral communication, 2001). The body intrudes the Pennsylvanian-Permian, Slana Spur Formation of the Wrangellia terrane.
The prospect was found by the American Copper and Nickel Company (ACNC) in 1994. Working in conjunction with Fort Knox Gold Resources Inc. they sampled and mapped it, did airborne and ground geophysical surveys over it, and diamond drilled one hole (W.T. Ellis, oral communication, 2001). Sampled by the Bureau of Land Management in the early 2000s (Bittenbender and others, 2007).
The prospect is in the footwall of the complex in a layered marginal gabbro. The layer, which is up to 1,500 feet thick at the prospect includes gabbronorite, coarsely-crystalline clinopyroxene gabbro, wehrlite, and mineralized mafic gabbro. The mineralized gabbro contains 5 to 15 percent disseminated pyrrhotite with minor chalcopyrite and pentlandite and is iron and copper stained. Two samples contained 0.15 to 0.23 percent copper, 0.12 to 0.21 percent nickel, 153 to 180 parts per billion (ppb) palladium, 58 to 72 ppb platinum, and 18 to 51 ppb gold (W.T. Ellis, oral communication, 2001).
Bittenbender and others (2007 collected two samples from the mineralized gabbro. A sample with about 5 percent pyrrhotite and chalcopyrite contained 29 ppb gold, 75 ppb platinum, 236 ppb palladium, 1,690 parts per million (ppm) copper, and 1,045 ppm nickel. They also sampled a thin dike of leucocratic, pegmatitic gabbro dike that had disseminated chalcopyrite; an analysis showed insignificant precious and base metals.
Geologic map unit (-145.983261995111, 63.324481998056)
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 Mafic and ultramafic rocks are variably serpentinized.

Production and reserves

Workings or exploration The prospect was found by the American Copper and Nickel Company (ACNC) in 1994. Working in conjunction with Fort Knox Gold Resources Inc. they sampled and mapped it, did airborne and ground geophysical surveys over it, and diamond drilled one hole (W.T. Ellis, oral communication, 2001). Sampled by the Bureau of Land Management in the early 2000s.
Indication of production None
Reserve estimates None.
Production notes None.

References