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 mineralization occurs in tracts to the north and west that have generally similar geology.
On the delineation of permissive tracts
The tract was drawn to include the entire area of Miocene rhyolitic volcanism southwest of the Pleistocene Snake River plain and south of the Idaho part of the Ore-Ida graben (Bond, 1978). The tract is underlain by two large Miocene caldera complexes, Juniper Mountain and Bruneau-Jarbidge (Ekren and others, 1982; Bonnichsen, 1982). Extensive rhyolitic ashflow tuffs erupted from the calderas, and these are overlain by Miocene basaltic lavas. A minor amount of older metamorphic and granitic rock is also included within the tract, since veins may extend into these lithologies, as they do in the Silver City area in the tract to the north.
Important examples of this type of deposit
No examples of this deposit type are known within the tract, and little is known about the exploration history.
On the numerical estimates made
The lack of known deposits within the tract and the dearth of information available on any exploration activity precluded estimation of the number of undiscovered deposits of this type.
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.
Bond, J.G., 1978, Geologic map of Idaho: Idaho Bureau of Mines and Geology, scale 1:500,000.
Bonnichsen, Bill, 1982, The Bruneau-Jarbidge eruptive center, southwestern Idaho, in Bonnichsen, Bill and Breckenridge, Roy M., eds., Cenozoic geology of Idaho: Idaho Bureau of Mines and Geology Bulletin 26, p. 237-254.
Eckren, E.B., McIntyre, D.H., Bennett, E.H., and Marvin, R.F., 1982, Cenozoic stratigraphy of western Owyhee County, Idaho, in Bonnichsen, Bill and Breckenridge, Roy M., eds., Cenozoic geology of Idaho: Idaho Bureau of Mines and Geology Bulletin 26, p. 215-236.