Unnamed (on tributary to Middle Fork of Kuskokwim River)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Ag; Cu; Pb
Other commodities Fe; Mo; Ni; V; Zn
Ore minerals galena; marcasite; pyrite
Gangue minerals sericite

Geographic location

Quadrangle map, 1:250,000-scale MG
Quadrangle map, 1:63,360-scale A-3
Latitude 62.21
Longitude -154.449
Nearby scientific data Find additional scientific data near this location
Location and accuracy This unnamed occurrence is located near the juncture of two second order tributaries to an unnamed stream draining into Middle Fork of Kuskokwim River. It is at an elevation of 2,700 feet (823 m) in the SW1/4 sec. 34, T. 25 N., R. 28 W., of the Seward Meridian. The reporter visited the site in 1998; at station no. 98BT441.

Geologic setting

Geologic description

The unnamed occurrence consists of stratiform pyrite-marcasite-galena bands parallel to sedimentary bedding in black, carbonaceous shale of the Lower Ordovician to Lower Silurian, Post River Formation, a unit of the Dillinger subterrane (Gilbert and others, 1988; Bundtzen, Harris, and Gilbert, 1997). The mineralization occurs in several outcrops at creek level that can be traced for about 75 meters; the sulfide-bearing bands are about 3 meters thick. However, individual sulfide-bearing layers are rarely more than 5 centimeters thick, and are isoclinally deformed as are the sedimentary interlayers. Microprobe analysis showed galena grains impregnated in the pyrite-rich layers.
One grab sample of massive pyrite-marcasite-galena mineralization contained 2.4 grams/tonne silver, 135 ppm copper, 11.60 percent iron, 39 ppm molybdenum, 255 ppm nickel, 176 ppm lead, 168 ppm vanadium, and 208 ppm zinc.
Geologic map unit (-154.451238923606, 62.2093663211359)
Mineral deposit model Sedimentary exhalative lead-zinc? (Cox and Singer, 1986; model 31b).
Mineral deposit model number 31b?
Age of mineralization Lower Paleozoic if mineralization is syngenetic.

Production and reserves

Workings or exploration The reporter investigated the site in 1998 (T.K. Bundtzen and G.M. Laird, written communication, 1998). One grab sample of massive pyrite-marcasite-galena mineralization contained 2.4 grams/tonne silver, 135 ppm copper, 11.60 percent iron, 39 ppm molybdenum, 255 ppm nickel, 176 ppm lead, 168 ppm vanadium, and 208 ppm zinc.
Indication of production None
Reserve estimates None.

Additional comments

See other possible sedimentary exhalative prospects in McGrath quadrangle (MG049, MG051, MG064, MG071, MG072, and MG074).

References