Unnamed (at head of Geroe Creek)

Prospect, Probably inactive

Alternative names

MAS

Commodities and mineralogy

Main commodities Au; Cu; Mo
Other commodities Pb
Ore minerals chalcopyrite; molybdenite; pyrite
Gangue minerals chlorite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale CH
Quadrangle map, 1:63,360-scale C-4
Latitude 67.6804
Longitude -148.814
Nearby scientific data Find additional scientific data near this location
Location and accuracy This deposit is best exposed in cliffs at the head of the west, headwater tributary of Geroe Creek, in the southwest quarter of section 13, T. 33 N., R. 6 W. A block of 239 claims was staked over this deposit in the mid-1970s.

Geologic setting

Geologic description

Placid Oil Company staked a block of 239 claims over this prospect in 1975-1976. There apparently has been little industry work since then although the the area was examined by the Bureau of Land Management in their study of the Koyukuk mining district (Kurtak and others, 2002).
This prospect is one of several quartz stockworks and altered zones in the northeast-trending belt of Devonian peraluminous biotite-muscovite granite of the Baby Creek batholith and Devonian, metaluminous biotite-hornblende granite and granodiorite of the Horace Mountain pluton (Brosgé and Reiser, 1964; Newberry and others, 1986). Porphyritic phases occur locally in these plutons, and DeYoung and others (1997) report that the mineralizing intrusives are porphyritic meta-granodiorite and biotite meta-granite. The country rocks are mainly Paleozoic schist and marble, and peraluminous meta-granodiorite. DeYoung and others (1997) note the absence of skarn in the calcareous rocks adjacent to these plutons. The veinlets in the stockworks at this prospect contain disseminated molybdenite, chalcopyrite, and pyrite, accompanied by intense quartz-sericite-chlorite-(+/- epidote) alteration. Eakins and others (1983) report grades of up to 0.1 percent molybdenum, Nokleberg and others (1987) report that zones as much as several meters thick in the plutons contain 0.6 percent copper, 0.02 percent molybdenum, and 0.1 gram of gold per tonne. Kurtak and others (2002) identified a limonite-stained, altered area about 2,000 feet wide at the head of Geroe Creek that has disseminated pyrite and a gray mineral that is probably molybdenite. A sample contained 5,212 parts per million (ppm) molybdenum and 106 ppm lead. Minor chalcopyrite and copper staining are found occasionally and a float sample contained 1,457 ppm copper and 37 parts per billion gold.
Geologic map unit (-148.816751556188, 67.680006777265)
Mineral deposit model Porphyry Cu-Mo (Cox and Singer, 1986; model 21a).
Mineral deposit model number 21a
Age of mineralization Devonian or younger based on Early Devonian Pb/Pb zircon ages from the Baby Creek batholith and Horace Mountain plutons that are similar to the igneous rocks that hosts this deposit (Dillon and others, 1996).
Alteration of deposit Sericitization and propylitization of porphyritic host rocks; veinlets in stockworks are accompanied by intense quartz-sericite-chlorite-(+/- epidote) alteration.

Production and reserves

Workings or exploration Placid Oil Company staked a block of 239 claims over this prospect in 1975-1976. There has apparently been little industry work since then although the area was examined and sampled by the Bureau of Land Management in their study of the Koyukuk mining district (Kurtak and others, 2002).
Indication of production None
Production notes None.

Additional comments

MAS No. 0020310026

References

MRDS Number A012140

References

Kurtak, J.M., Klieforth, R.F., Clark, J.M., and Maclean, E.A., 2002, Mineral investigations in the Koyukuk mining district, northern Alaska, 2 vols.: Bureau of Land Management, Alaska Technical Report 50, 845 p.
Newberry, R.J., Dillon, J.T., and Adams, D.D., 1986, Regionally metamorphosed calc-silicate-hosted deposits of the Brooks Range, northern Alaska: Economic Geology, v. 81, p. 1728-1752.
Young, L.E., St. George, P., and Bouley, B., 1997, Porphyry copper deposits in relation to the magmatic history and palinspastic restoration of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral deposits of Alaska: Economic Geology Monograph 9, p. 306-333.
Reporters J.M. Britton (Anchorage, Alaska); D.J. Grybeck (Contractor, U.S. Geological Survey)
Last report date 4/18/2010