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Unnamed (east of headwaters of Windy Fork)

Occurrence, Inactive

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Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale MG
Quadrangle map, 1:63,360-scale A-2
Latitude 62.013
Longitude -153.926
Nearby scientific data Find additional scientific data near this location
Location and accuracy This unnamed occurrence is located on a moderately steep, southeast facing spur overlooking the headwaters of the west fork of Post River. It is about 3 kilometers east of the headwaters of the Windy Fork of the Kuskokwim River, at an elevation of 5,050 feet (1,540 m), in the NE1/4 sec. 7, T. 22 N., R. 25 W., of the Seward Meridian. The reporter sampled the site in 1982.

Geologic setting

Geologic description

The unnamed occurrence consists of shale-hosted Zn-Ag (Pb-Cu) mineralization in the Lower Ordovician to Lower Silurian Post River Formation, a unit of the Dillinger subterrane (Bundtzen, Harris, and Gilbert, 1997). The mineralized zone is parallel to bedding and is a distinctly sulfur-stained, carbonaceous shale bed about one meter thick. Only disseminated pyrite was identified in the zone. Although isotopic data is lacking, Bundtzen, Harris, and Gilbert (1997) regarded the occurrence as possible sedimentary exhalative(?) lead-zinc mineralization. Two random grab samples from the mineralized shale contained up to 0.86 percent zinc, 4.5 grams/tonne silver, 104 ppm copper, and 186 ppm lead (Bundtzen and others, 1988).
Geologic map unit (-153.928230837487, 62.0123680144277)
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 Ordovician to Lower Silurian (Bundtzen, Harris, and Gilbert, 1997), assuming it is a syngenetic deposit.
Alteration of deposit None.

Production and reserves

Workings or exploration The reporter and Kristi McDonald sampled the mineralized zone in 1982. Two random grab samples from the mineralized shale yielded up to 0.86 percent zinc, 4.5 grams/tonne silver, 104 ppm copper, and 186 ppm lead (Bundtzen and others, 1988).
Indication of production None
Reserve estimates None.

Additional comments

See other examples of shale-hosted mineralization in McGrath quadrangle (MG029, MG049, MG051, MG064, MG071).

References

MRDS Number 10307871

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