Boot Flap

Prospect, Active

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-5
Latitude 63.3226
Longitude -146.3174
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Boot Flap prospect is at an elevation of 5,100 feet about three-quarters of a mile east of the lower Eureka Glacier and 6.8 mile northwest of the junction of Eureka Creek and Broxton Gulch. It is about 5.5 mile south of peak 6563 and about 0.3 mile south of the center of section 25, T. 18 S., R. 7 E.

Geologic setting

Geologic description

The Boot Flap prospect is associated with a east-trending, northward-dipping sill-like body of mafic and ultramafic rocks that are part of a Middle Triassic unit informally called the Eureka complex (Rose, 1966; Nokleberg and others, 1992 [MF]; 1992 [Open-File]; Bittenbender and others, 2007). The complex is mostly gabbro and serpentinized peridotite that occur along strands of the Broxson Gulch thrust fault (W.T. Ellis, unpublished data, 1996). The complex structurally overlies light-colored fine-grained andesite, dacite, and graywacke that are part of the Pennsylvanian to Permian, Slana Spur Formation.
The prospect was examined and sampled by several companies in the 1990s and 2000s and by the Alaska Division of Mines and Minerals, the U.S. Geological Survey, and the U.S. Bureau of Land Management at various times from the late 1980s to 2007.
The Boot Strap prospect as sampled by Bittenbender and others (2007) is in a sill of ultramafic rocks 50 to 200 feet thick that may extend for at least 5 miles based on aeromagnetic evidence. The sill which is largely gabbro has a base of serpentinized ultramafic rocks. It overlies volcanic rocks and underlies porphyritic granitic rocks.
The mineralization consists of: 1) disseminated sulfides in the serpentine; 2) up to 5 percent, net-textured pyrrhotite, with lesser chalcopyrite, pentlandite, and magnetite in olivine gabbro; and 3) gossan zones leached of sulfides in the gabbro (Bittenbender and others, 2007). Two representative samples of the serpentine contained up to 1,290 parts per million (ppm) chromium, 586 ppm, copper, 2,260 ppm nickel, 52 parts per billion (ppb) platinum, and 56 ppb palladium. Two samples of gossan from the gabbro contained 711 ppm copper, 1,515 ppm nickel, 112 ppb platinum, and 83 ppb palladium. Samples of the gabbro contained up to 17 ppb platinum, 28 ppb palladium, 1,75 ppm nickel, and 430 ppm chromium.
Geologic map unit (-146.319666118291, 63.322176126424)
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 Ultramafic rocks at the bottom of the sill are moderately to strongly serpentinized.

Production and reserves

Workings or exploration The prospect was examined and sampled by several companies in the 1990s and 2000s and by the Alaska Division of Mines and Minerals, the U.S. Geological Survey, and the U.S. Bureau of Land Management at various times from the late 1980s to 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