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
The presence of placer Au deposits in the greenschist facies rocks of the Ruby and Nixon Fork terranes, and local geochemical anomalies support a potential for low-sulfide Au-quartz veins.
On the delineation of permissive tracts
This tract is defined by the metamorphic basement of the Ruby and Nixon Fork terranes, which comprises Precambrian(?) and Paleozoic pelitic schists, metabasites, quartzites, orthogneiss, and marbles (Patton and others, 1989; Nokleberg and others, 1994). Permissive deposit types are placer gold and low-sulfide gold-quartz vein. Arsenic is the most common stream sediment anomaly; Zn, W, Cu, and rare Au, Ag and Bi are present locally.
Important examples of this type of deposit
No low-sulfide Au-quartz veins are known in the tract, but the geologic environment and the presence of placer Au deposits in the Ruby district suggest that low-sulfide Au-quartz veins may be present.
On the numerical estimates made
No estimate of the number of undiscovered low-sulfide Au-quartz vein deposits was attempted.
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.