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Lower Crash

Prospect, Active?

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Commodities and mineralogy

Main commodities Au; Cu; Pd; Pt
Other commodities As; Cr; Hg; Mn
Ore minerals chalcopyrite; magnetite; pentlandite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-5
Latitude 63.3146
Longitude -146.2585
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Lower Crash prospect is at an elevation of about 4,700 feet, about 5.0 miles northwest of the junction of Broxson Gulch and Eureka Creek. It is on the east side of a southeast-flowing tributary of Eureka Creek that is locally called Landslide Creek. It is about 0.5 mile north-northwest of the center of section 32, T. 18 S., R. 8 E.

Geologic setting

Geologic description

The Lower Crash prospect is in an east-trending, northward-dipping sill of Late Triassic, ultramafic and mafic rocks that is part of Triassic Eureka complex (Rose, 1966; Nokleberg and others, 1992 [MF]; Nokleberg and others, 1992 [Open-File]. The rocks at the prospect consist mainly of peridotite, gabbro and serpentine. The peridotite contains up to 5 percent sulfides, mainly pyrrhotite with sparse chalcopyrite, and pentlandite.
The prospect was found by industry in about 1990 and they may have dug a 50-foot trench on the mineralization (Bittenbender and others, 2007). Bittenbender and others (2007) collected six rock-chip samples; they contained up to 56 parts per billion (ppb) gold, 93 ppb platinum, 91 ppb palladium, 1,385 parts per million (ppm) copper, and 2,590 ppm nickel.
They also collected several samples below the prospect in the complex; one notable float sample contained 2.59 percent copper, 11.6 ppm silver, 282 ppm arsenic, 150 ppb gold, 668 ppm chromium, 0.68 ppm mercury, 2,490 ppm manganese, and 115 ppb palladium.
Geologic map unit (-146.260764896646, 63.3141769293863)
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 the ultramafic rocks.

Production and reserves

Workings or exploration Found by industry in the 1990s; they may have dug a 50-foot trench. Examined and sampled by the Bureau of Land Management in the 2000s.
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.
Nokleberg, W. J., Aleinikoff, J. N., Dutro, J. T., Lanphere, M. A., Silberling, N. J., Silva, S. R., Smith, T. E., and Turner, D. L., 1992, Map, tables, and summary of fossil and isotopic age data, Mount Hayes Quadrangle, eastern Alaska range, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1996-D, 43 p., 1 sheet, scale 1:250,000.
Nokleberg, W.J., Aleinikoff, J. N., Lange, I. M.; Silva, S. R., Miyaoka, R. T., Schwab, C. E., Zehner, R. E., Bond, G. C., Richter, D. H., Smith, T. E., and Stout, J. H., 1992, Preliminary geologic map of the Mount Hayes quadrangle, eastern Alaska Range, Alaska: U.S. Geological Survey Open-File Report 92-594, 39 p. 1 sheet, scale 1:250,000.
Nokleberg, W.J., Lange, I.M., Roback, R.C., Yeend, Warren, and Silva, S.R., 1991, Map showing locations of metalliferous lode and placer mineral occurrences, mineral deposits, prospects, and mines, Mount Hayes quadrangle, eastern Alaska Range, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1996-C, 42 p., 1 sheet, scale 1:250,000.
Stout, J.H., 1976, Geology of the Eureka Creek area, east-central Alaska Range: Alaska Division of Geological and Geophysical Surveys Geologic Report 46, 32 p., 1 plate, scale 1:63,360.
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