Deadfall

Prospect, Active

Alternative names

Powdermilk

Commodities and mineralogy

Main commodities Ag; Pb; Zn
Other commodities Ba; Cd
Ore minerals galena; pyrite; sphalerite
Gangue minerals barite

Geographic location

Quadrangle map, 1:250,000-scale BM
Quadrangle map, 1:63,360-scale B-4
Latitude 67.4616
Longitude -160.7957
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Deadfall prospect is just southeast of the confluence of the two major headwater forks of a major, unnamed, southeast flowing tributary of the Omar River. The coordinates are for the approximate center of the prospect which covers an area of 2 square kilometers in sections 24 and 25, T. 24 N., R. 10 W., of the Kateel River Meridian. The location is accurate.

Geologic setting

Geologic description

The Deadfall deposit consists of disseminations and clots under 2.5 centimeters in diameter of sphalerite, galena, and rare pyrite in Devonian light-gray dolostone (Schmidt and Allegro, 1988). The sphalerite is coarsely crystalline, locally zoned, and medium to dark brown and red. Barite forms veins in the dolostone. Soil samples from the western river bank exposure contain as much as 1,600 parts per million (ppm) lead, 420 ppm zinc and 7.2 ppm silver. Rock samples from the more oxidized, eastern exposure in the creek contain as much as 280 ppm lead, 230 ppm zinc, and 21 ppm silver. Rock samples contain as much as 20 percent sphalerite, 8 percent galena, and 5 percent pyrite.
The host dolostone strikes NE and dips nearly vertically; a synform structure is suggested (Schmidt and Folger, 1986). Some gray limestone occurs east of the prospect. The Deadfall deposit is similar to southeast Missouri lead-zinc deposits (Cox and Singer, 1986; model 32a) in host rock and mineralization. The sulfides are epigenetic with respect to the host dolostone. Mineralization may be structurally controlled by the synform.
In 2006, NovaGold Resources Inc. began working in the region and staked a large block of claims that covered this and other similar prospects nearby (TintinaGold Resources Inc., 2010). In 2007, NovaGold carried out extensive field work in the area, emphasizing geologic mapping and geochemical sampling. Their geochemical work indicates that the Deadfall prospect is part of a northwest-trending belt of mineralization up to 3 kilometers long and 0.5 kilometer wide. They sampled a 47-meter-long trench in recrystallized dolomite with disseminated coarse sphalerite and galena. Samples from a 12-meter section in the trench contained 10.1 percent zinc and 42.4 grams of silver per tonne; samples from the full 47 meters contained 6 percent zinc and 21.7 grams of silver per tonne.
Geologic map unit (-160.798565549876, 67.4609788147428)
Mineral deposit model Southeast Missouri Pb-Zn (Cox and Singer, 1986; model 32a).
Mineral deposit model number 32a
Age of mineralization Devonian?
Alteration of deposit Surficial weathering resulted in sparse iron oxide staining and local clay alteration.

Production and reserves

Workings or exploration The U.S. Geological Survey did reconnaissance mapping, took a line of 39 soil samples, and collected additional rock and pan concentrate samples (Zayatz and others, 1988). In 2006, NovaGold began working in the region and staked a large block of claims that covered this and other similar prospects nearby (TintinaGold Resources Inc., 2010). In 2007, they carried out extensive field work in the area emphasizing geologic mapping, geochemical sampling, and trench sampling.
Indication of production None

References

MRDS Number A015622
Reporters Anita Williams (Anchorage, AK); D.J. Grybeck (Contractor, U.S. Geological Survey)
Last report date 4/2/2010