Explained by Bruce M. Gamble, Robert G. Eppinger, John W. Cady, Stanley E. Church, Byron R. Berger, Gregory T. Spanski
On the choice of deposit models
Although no massive sulfide deposits are known in this tract, the presence of the appropriate rock types suggest that the tract is geologically permissible for Besshi massive sulfide deposits as described by Cox (1986).
On the delineation of permissive tracts
This tract covers the area of the Koyukuk magmatic arc, which consists of Upper Jurassic(?) and Lower Cretaceous andesitic volcanics and subordinate sedimentary rocks (Patton and others, 1989; Nokleberg and others, 1994). The tract includes areas underlain by Koyukuk rocks as inferred from aeromagnetics. Locally stream sediment samples contain anomalously high concentrations of As, Sb, Pb, Cu, Au, Ag, and W.
Important examples of this type of deposit
No Besshi massive sulfide deposits are known in this tract.
On the numerical estimates made
No estimate of the number of undiscovered deposits was attempted because of the highly speculative nature of this model for this area.
Cox, D.P., 1986, Descriptive model of Besshi massive sulfide, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 136.
Nokleberg, W.J., Moll-Stalcup, E.J., Miller, T.P., Brew, D.A., Grantz, Arthur, Reed, J.C., Jr., Plafker, George, Moore, T.E., Silva, S.R., and Patton, William W., Jr., 1994, Tectonostratigraphic terrane and overlap assemblage map of Alaska: U.S. Geological Survey Open-File Report 94-194, 45 manuscript p., scale 1:2,500,000.
Patton, W.W., Jr., Box, S.E., Moll-Stalcup, E.J., and Miller, T.P., 1989, Geology of west-central Alaska: U.S. Geological Survey Open-File Report 89‑554, 41 p.