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Unnamed (near West Fork of Post River)

Occurrence, Inactive

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Commodities and mineralogy

Main commodities Ag; Cu; Zn
Other commodities Ni
Ore minerals pyrite

Geographic location

Quadrangle map, 1:250,000-scale MG
Quadrangle map, 1:63,360-scale A-2
Latitude 62.029
Longitude -153.824
Nearby scientific data Find additional scientific data near this location
Location and accuracy This unnamed occurrence is located on a steep, southeasterly slope adjacent to the west fork of Post River at an elevation of 4,900 feet (1,494 m) in the NE1/4 sec. 3, T. 22 N., R. 25 W., of the Seward Meridian. The reporter sampled the site in 1982.

Geologic setting

Geologic description

This unnamed occurrence is shale-hosted Ag-Cu-Zn mineralization in the Lower Ordovician-to-Lower Silurian Post River Formation, a unit of the Dillinger subterrane (Bundtzen and others, 1988). Graptolites of the Monograptus spiralis zone were found in the shale at the occurrence.
A distinctive yellowish, sulfur bloom occurs in the mineralized zone, which is estimated to be about 2 meters thick. Disseminated pyrite was observed in one outcrop. Although isotopic data is lacking, Bundtzen, Harris, and Gilbert (1997) classified the occurrence as a sedimentary exhalative lead-zinc deposit. Two random chip-channel samples collected across the zone contained up to 1.37 percent zinc, 0.12 percent copper, 13.6 grams/tonne silver, and 196 ppm nickel.
Geologic map unit (-153.826229188683, 62.0283717624673)
Mineral deposit model Sedimentary exhalative lead-zinc? (Cox and Singer, 1986; model 31b).
Mineral deposit model number 31b?
Age of mineralization Inferred to be Lower Silurian, based on graptolite identifications (Bundtzen and others, 1988).
Alteration of deposit Sulfides oxidized to free sulfur.

Production and reserves

Workings or exploration The reporter sampled the occurrence in 1982. Two random chip-channel samples taken across the mineralized zone contained up to 1.37 percent zinc, 0.12 percent copper, 13.6 grams/tonne silver, and 196 ppm nickel.
Indication of production None
Reserve estimates None.

Additional comments

See other shale-hosted deposits in McGrath quadrangle such as MG049, MG029, MG051, MG071, MG064, and MG074.

References

MRDS Number 10307870

References

Bundtzen, T.K., Harris, E.E., and Gilbert, W.G., 1997, Geologic Map of the eastern McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 97-14, 34 p., 1 sheet, scale 1:125,000.
Bundtzen, T.K., Kline, J.T., Smith, T.E., and Albanese, M.D., 1988, Geology of the McGrath A-2 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report 91, 18 p., 1sheet, scale 1:63,360.
Reporters T.K. Bundtzen (Pacific Rim Geological Consulting)
Last report date 12/9/1998