Explained by Stephen E. Box and Arthur A. Bookstrom
On the choice of deposit models
Hot-spring Au-Ag deposits consist of precious metal-bearing siliceous sinters and silicified rocks cut by breccias and stockworks of veins and veinlets, which were deposited at or near the surface in and around felsic volcanic fields, usually associated with normal faults (Berger, 1986). Hot-spring Au-Ag deposits are known in the Republic mining district (Tschauder, 1989), although they appear to be small deposits in the upper part of associated Comstock-type deposits.
On the delineation of permissive tracts
The permissive tract was delineated to include the Eocene volcanic and volcaniclastic rocks of the Republic graben and adjacent areas of northeastern Washington (Stoffel and others, 1991). Volcanism and mineralization were broadly contemporaneous with detachment faulting above the Okanogan, Kettle, and Priest River metamorphic core complexes. Eocene, gold-bearing hydrothermal systems are known from several of these volcanic sequences.
Important examples of this type of deposit
The Republic and adjacent areas of northeastern Washington contains numerous volcanic-hosted Au-Ag deposits, prospects, and occurrences. Each of these appears to be primarily a Comstock vein system with a subordinate hot-spring deposit in its upper part. The Golden Promise mine in Republic is an important example of this type (Tschauder, 1986). The vein system has been mined for over 300 m down dip. The prominent vein system becomes a stockwork system in the upper part, and grades into an overlying hot-spring Au-bearing sinter, which has been mined as part of the underground mine .
On the numerical estimates made
Since Comstock veins in the area grade up into more disseminated hot-spring systems, our estimate for undiscovered Comstock deposits includes both deposit types as part of the same system (Mosier and others, 1986), and we do not make a separate estimate for hot-spring Au-Ag deposits.
Berger, B. R., 1986, Descriptive model of hot-spring Au-Ag deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 143.
Mosier, D.L., Singer, D.A., and Berger, B.R., 1986b, Grade and tonnage model of Comstock epithermal veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 151-153.
Stoffel, K.L., Joseph, N.L., Waggoner, S.Z., Gulick, S.W., Korosec, M.A., and Bunning, B.B., 1991, Geologic map of Washington-Northeast quadrant: Washington Division of Geology and Earth Resources, Geologic Map GM-39, scale 1:250,000.
Tschauder, R., 1986, Gold deposits in northern Ferry County, in Joseph, N.L., ed., Geologic guidebook for Washington and adjacent areas: Washington Division of Geology and Earth Resources Information Circular 86, p. 239-254.