Unnamed (near the junction of Fall and Michigan Creeks)

Occurrence, Probably inactive

Commodities and mineralogy

Main commodities As; Au; Cu
Other commodities Ag; Co; Pb; Ti; Zn
Ore minerals arsenopyrite; cassiterite; chalcopyrite; marcasite; molybdenite; pyrite; pyrrhotite; rutile; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale WI
Quadrangle map, 1:63,360-scale B-3
Latitude 67.3051
Longitude -151.2404
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is based on several mineralized rock samples collected in an area about 0.2 mile in diameter (Dillon and others, 1981: Plate 1, samples 467 to 472 and 474 and 475). The area is about 0.2 mile northwest of the junction of Fall and Michigan Creeks. The occurrence is at an elevation of about 1,550 feet, 0.4 mile south-southwest of the center of section 25, T. 29 N., R. 17 W. The location is accurate.

Geologic setting

Geologic description

Dillon and others (1981) collected mineralized rock samples at several sites in an area about a half mile in diameter. The mineralization consists of layers and veins of massive pyrrhotite, chalcopyrite, sphalerite, arsenopyrite, cassiterite, rutile, pyrite, and possible molybdenite. The pyrrhotite is partly altered to marcasite. Eight samples collected by Dillon and others contained up to 82,000 parts per million (ppm) arsenic, 700 ppm cobalt, 1,360 ppm copper, 8.28 ppm gold, 135 ppm lead, 50 ppm tin, and 329 ppm zinc. The sulfide layers and veins are up to 30 cm. thick in actinolite-biotite felsite interlayered with marble and garnet-quartz-albite-muscovite schist. Hornfelsed calc-silicate rocks along the contact with the felsite contain disseminated pyrite(?). Dillon and others (1986) map the area as Devonian and Devonian(?) interlayered felsic and mafic intrusive and extrusive rocks, locally mixed with clastic sedimentary rocks. They indicate that the upper Devonian felsic schist is regionally associated with copper deposits.
The area was examined by Kurtak and others (2002) as part of a regional mineral assessment . The only sample they collected of a felsitic rock had only 111 ppm copper and 196 parts per billion (ppb) gold; i.e., not nearly the metal values in samples analyzed by Dillon and others (1981).
Geologic map unit (-151.243129505365, 67.3046477062719)
Mineral deposit model Volcanogenic massive sulfides or skarn?
Age of mineralization Devonian or younger based on the age of the host rocks.
Alteration of deposit Alteration of pyrrhotite to marcasite; oxidation of sulfides, development of skarn.

Production and reserves

Workings or exploration Only surface sampling by government agencies (Dillon and others, 1981; Kurtak and others, 2002).
Indication of production None
Reserve estimates None.
Production notes None.

References

MRDS Number A011991; A011992; A011993

References

Kurtak, J.M., Klieforth, R.F., Clark, J.M., and Maclean, E.A., 2002, Mineral investigations in the Koyukuk mining district, northern Alaska: Final Report: U.S. Bureau of Land Management Technical Report 50, v. 1 and 2, 845 p.
Reporters J.M. Britton (Anchorage); D.J. Grybeck (Contractor, USGS)
Last report date 2/1/2011