Unnamed (on a tributary to Windy Fork) (ARDF #MG071) Ag, Zn

Unnamed (on a tributary to Windy Fork)

Occurrence, Inactive

Commodities and mineralogy

Main commodities	Ag; Zn
Other commodities	Mo
Ore minerals	pyrite; galena; sphalerite

Geographic location

Quadrangle map, 1:250,000-scale	MG
Quadrangle map, 1:63,360-scale	A-2
Latitude	62.13
Longitude	-153.926
Nearby scientific data	Find additional scientific data near this location
Location and accuracy	Occurrence is located in a bedrock outcrop on the north side of an unnamed west-flowing tributary stream to Windy Fork; it is at an elevation of 3,900 feet (1,189 m) in the NE1/4 sec. 31, T. 24 N., R. 25 W., of the Seward Meridian. The reporter investigated the site in 1983 and in 1997. Note that the occurrence is properly located in Bundtzen and others (1988; #8), but mislocated in Bundtzen, Harris, and Gilbert, (1997; #23).

Geologic setting

Geologic description This unnamed occurrence consists of three thin, stratiform sulfide layers in black shale of the Lower Ordovician to Lower Silurian Post, River Formation a unit of the Dillinger subterrane (Bundtzen, Harris, and Gilbert, 1997). The sulfide beds are isoclinally folded along with host strata and are believed to be syngenetic in origin. The occurrence is just below the contact between the Post River Formation and the mid-Silurian Terra Cotta Mountains Sandstone, and hence has an inferred age of Early Silurian. Three 6 centimeter thick sulfide layers mainly contain pyrite, with minor to trace disseminated sphalerite and galena (Bundtzen and others, 1988; Bundtzen Harris, and Gilbert, 1997). Grab samples of one sulfide bearing horizon contained 700 ppm zinc, 1.2 grams/tonne silver, and 31 ppm molybdenum.
Geologic map unit	(-153.928223777215, 62.1293747207759)
Mineral deposit model	Sedimentary exhalative lead-zinc? (Cox and Singer, 1986; model 31a).
Mineral deposit model number	31a?
Age of mineralization	Undated, inferred to be Early Silurian, based on stratigraphic evidence.

Production and reserves

Workings or exploration	The reporter first found the occurrence in 1983 (Bundtzen and others, 1988). Grab samples of one sulfide bearing horizon contained 700 ppm zinc, 1.2 grams/tonne silver, and 31 ppm molybdenum.
Indication of production	None
Reserve estimates	None.

References

MRDS Number	10307869
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	12/8/1998