West Fork-Post River (ARDF #MG073) Ag, Cu

West Fork-Post River

Occurrence, Inactive

Commodities and mineralogy

Main commodities	Ag; Cu
Other commodities	Zn
Ore minerals	chalcopyrite; pyrrhotite; sphalerite

Geographic location

Quadrangle map, 1:250,000-scale	MG
Quadrangle map, 1:63,360-scale	A-2
Latitude	62.01
Longitude	-153.88
Nearby scientific data	Find additional scientific data near this location
Location and accuracy	The West Fork-Post River occurrence is located on an east facing bluff of the west fork of Post River; it is at an elevation of approximately 4,000 feet (1,220 m) in the NE1/4 sec. 8, T. 22 N., R. 25 W., of the Seward Meridian. The occurrence, which corresponds to locality number 19 in Cobb (1972), is located to within 460 m.

Geologic setting

Geologic description The West Fork-Post River occurrence consists of small lenses and disseminations of pyrrhotite associated with a swarm of northwest-trending mafic dikes that cut argillite of the Early to Late Silurian Terra Cotta Mountains Sandstone, a unit of the Dillinger subterrane (Bundtzen and others, 1988; Bundtzen, Harris, and Gilbert, 1997). Samples collected by Reed and Elliott (1968, C 596) contained semi-massive pyrrhotite and minor chalcopyrite and sphalerite. Values from selected grab samples on the surface run up to 45.7 grams/tonne silver, 1.50 percent copper, and 0.07 percent zinc.
Geologic map unit	(-153.882230476209, 62.0093690663369)
Mineral deposit model	Polymetallic vein (Cox and Singer, 1986; model 22c).
Mineral deposit model number	22c

Production and reserves

Workings or exploration	The West Fork-Post River was discovered by the late Bruce Reed during mineral investigations for the U.S. Geological Survey in the 1960s (Reed and Elliott, 1968, C 596). Values from selected grab samples collected by Reed and Elliott (1968, C 596) contain up to 45.7 grams/tonne silver, 1.50 percent copper, and 0.07 percent zinc.
Indication of production	None
Reserve estimates	None.
Additional comments Similar to Veleska-South prospect (MG050) in McGrath B-2 quadrangle.

References

MRDS Number	A015041
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. Cobb, E.H., 1972, Metallic mineral resources map of the McGrath quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-379, 1 sheet, 1:250,000 scale. Cobb, E.H., 1976, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Iliamna, Lake Clark, Lime Hills, and McGrath quadrangles, Alaska: U.S. Geological Survey Open-File Report 76-485, 101 p. MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous mineral deposits in the western part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-F, 38 p., 1 sheet, scale 1:1,000,000. Reed, B.L. and Elliott, R.L., 1968, Geochemical anomalies and metalliferous deposits between Windy Fork and Post River, southern Alaska: U.S. Geological Survey Circular 569, 22 pages. Reed, B.L., and Elliott, R.L., 1968, Results of stream sediment sampling in parts of the southern Alaska Range: U.S. Geological Survey Open-File Report 68-223, 18 p., 1 sheet, 1:500,000 scale.
Reporters	T.K. Bundtzen (Pacific Rim Geological Consulting)
Last report date	10/30/1998