Owhat (Cobalt Creek)

Prospect, Active

Commodities and mineralogy

Geographic location

Quadrangle map, 1:250,000-scale RM
Quadrangle map, 1:63,360-scale C-1
Latitude 61.6622
Longitude -159.1114
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Owhat prospect is in the Russian Mountains in the cirque valley at the head of Cobalt Creek. The map site is at the approximate center of sec. 8, T. 18 N., R. 54 W., of the Seward Meridian.

Geologic setting

Geologic description

The Owhat, or Cobalt Creek prospect was discovered by Native prospectors before 1900 (Maddren, 1915; Holzheimer, 1926). The deposits include 8 to 10 sulfide-tourmaline-axinite-quartz veins or greisens in syeno-monzonite (Bundtzen and Laird, 1991). The individual greisens are several inches to more than 3 feet thick in a zone that is 5 to 26 feet thick; the average width of the zone is about 8 feet and it has been traced more than 280 feet vertically. The greisens trend northwest and dip steeply northeast near a contact with an axinite-bearing andesite porphyry dike. The mineralized zone has been traced on the surface for a distance of 870 feet, and extensions totaling 650 feet in both directions are indicated by the distribution of mineralized float. The deposit is mineralogically complex and includes arsenopyrite, aramayoite, bismuth, bismuthinite, bornite, chalcopyrite, galena, gold, marcasite, pekoite or gladite, pyrite, sphalerite, stephanite, stetefeldite and tetrahedrite in the sulfide-rich material in the quartz-tourmaline-axinite greisen. Multiple episodes of mineralization are indicated by cross-cutting relations among the veins. Late-forming minerals include arsenopyrite, chalcopyrite, and pyrite, but the youngest cross-cutting assemblages include bornite, stephanite, tetrahedrite, sphalerite, and lead-bismuth sulfides (Bundtzen and Laird, 1991). Microprobe analyses indicate that arsenopyrite contains 0.1 to 0.2 weight percent gold in its lattice structures. Bundtzen and Laird (1991) collected 16 chip-channel samples averaging 4.4 feet wide, along 860 feet of the greisen zone. The samples average 5.3 parts per million (ppm) gold, 13.4 percent arsenic, 0.21 percent antimony, 0.39 percent copper, 0.07 percent tin, 0.05 percent zinc, and 0.017 percent cobalt. Assuming dimensions, in feet, of 4.4 x 280 x 870, Bundtzen and Laird (1991) estimated that the resource at this prospect is 63,000 tons of material with the stated average grades. The syeno-monzonite host rocks are part of the Upper Cretaceous intrusive complex of the Russian Mountains (Bundtzen and Laird, 1991).
In August, 2009, Full Metal Minerals Corp. and Kinross Gold formed an alliance to explore properties in the Russian Mountains, northwest of Aniak (Full Metal Minerals Corp., 2009b, 2010). Six holes were drilled at the Owhat prospect to test a structure more than 200 meters long. Gold-silver-copper mineralization associated with quartz-tourmaline veining was cut in all the holes. The best intercepts are 1.1 meters with 8.59 grams of gold per tonne, 185.6 grams of silver per tonne, and 6.03 percent copper; 0.94 meters with 5.35 grams of gold per tonne, 150.0 grams of silver per tonne, and 9.97 percent copper; and 0.52 meters with 8.59 grams of gold per tonne, 680.0 grams of silver per tonne, and 10.35 percent copper.
Geologic map unit (-159.113765686738, 61.6614854221071)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c
Age of mineralization Late Cretaceous or Tertiary. The veins crosscut part of the intrusive complex of the Russian Mountains; quartz monzonite from this complex has a K/Ar age of 70.3 +/- 2.1 Ma (Bundtzen and Laird, 1991).
Alteration of deposit Silicification and tourmalinization.

Production and reserves

Workings or exploration Prior to 2009, the only workings were three shallow shafts as much as 40 feet deep and several surface trenches and pits, along about 800 feet of the deposit. Full Metal Minerals drilled 6 holes in late 2009.
Indication of production None
Reserve estimates Assuming the deposit is 4.4 feet deep, 280 feet wide, and 870 feet long, Bundtzen and Laird (1991) estimate that the resource at this prospect is 63,000 tons of material with average grades of 5.3 ppm gold, 13.4 percent arsenic, 0.21 percent antimony, 0.39 percent copper, 0.07 percent tin, 0.05 percent zinc, and 0.017 percent cobalt.
Production notes None.

References

MRDS Number A013415

References

Full Metal Minerals Corp., 2009a, Full Metal and Kinross acquire gold-silver targets in western Alaska; drilling commenced: http://www.fullmetalminerals.com/s/NewsReleases.asp?ReportID=360655&_Type=News&_Title=Full-Metal-and-Kinross-acquire-Gold-Silver-Targets-in-Western-Alaska-Drilli... (News release, August 20, 2009).
Full Metal Minerals Corp., 2009b, Full Metal intercepts 8.6 g/t Au, 185.6 g/t Ag and 6.03% Cu over 1.0 meters at Russian Mountain Project: http://www.fullmetalminerals.com/s/NewsReleases.asp?ReportID=376394&_Type=News&_Title=Full-Metal-Intercepts-8.6-gt-Au-185.6-gt-Ag-and-6.03-Cu-over-1.0-meters-at-...(News release, December 8, 2009).
Full Metal Minerals Corp., 2010, Kuskokwim region: http://www.fullmetalminerals.com/s/Kuskokwim.asp (as of February 23, 2010).
Reporters Travis L. Hudson and Madelyn A. Millholland (Applied Geology and Millholland & Associates); D.J. Grybeck (Contractor, U.S. Geological Survey)
Last report date 4/2/2010