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. |
