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Unnamed (near Gillett Pass)

Occurrence, Inactive

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Commodities and mineralogy

Main commodities Cr
Other commodities Ni
Ore minerals chromite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-1
Latitude 63.0761
Longitude -144.2809
Nearby scientific data Find additional scientific data near this location
Location and accuracy The occurrence is about 1.2 miles west of Gillett Pass at an elevation of about 4,200 feet. It is in the SW1/4SE1/4 section 16, T. 15 N., R. 6 E., Copper River Meridian. It corresponds to locality 6 of Richter (1967), locality 32 on figure 6 of Cobb (1979 [OFR 79-238]), locality 53 of MacKevett and Holloway (1977), and locality 144 in table 2 of Nokleberg and others (1991). The location is a general one in a dunite body that is exposed for a strike length of about 2 miles.

Geologic setting

Geologic description

Low-grade chromite deposits occur in a lenticular body of dunite about 2 miles long and one-half mile wide; the dunite is a near-vertical body within the Denali Fault zone (Richter, 1967). The dunite is partly enclosed by amphibolite and pyroxenite that extend to the east beyond the dunite mass. Chromite occurs in gneissoid layers in the ultramafic rocks. On the basis of representative samples, the dunite contains about 1.2 percent chromic oxide and 0.4 percent nickel. The nickel possibly occurs in olivine and its alteration products. At places chromite is segregated into massive lenses. The largest lens found by Richter (1967) was about 1 foot long and 2 inches thick, but he noted that the body was poorly exposed and that larger bodies of chromite could exist. No samples were analyzed for platinum group metals.
Geologic map unit (-144.283131639311, 63.0757134805609)
Mineral deposit model Chromite disseminated in layered mafic-ultramafic complex (Cox and Singer, 1986; model 8a).
Mineral deposit model number 8a
Age of mineralization Late Triassic (?).
Alteration of deposit Serpentinization of dunite.

Production and reserves

Workings or exploration There are no workings.
Indication of production None

References

MRDS Number A011782

References

Cobb, E.H., 1979, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Mount Hayes quadrangle, Alaska: U.S. Geological Survey Open-File Report 79-238, 140 p.
MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000.
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.
Richter, D.H., 1967, Geology of the upper Slana-Mentasta Pass area, southcentral Alaska: Alaska Division of Mines and Minerals Geologic Report 30, 30 p., 2 sheets, scale 1:63,360.
Reporters W.T. Ellis (Alaska Earth Sciences), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (USGS)
Last report date 7/14/2003