National mineral assessment tract PC25 (Epithermal vein, Comstock)

Tract PC25
Geographic region Pacific Coast
Tract area 17,200sq km
Deposit type Epithermal vein, Comstock
Deposit age Tertiary

Deposit model

Model code 25c
Model type descriptive
Title Descriptive model of Comstock epithermal veins
Authors Dan L. Mosier, Donald A. Singer, and Byron R. Berger
URL https://pubs.usgs.gov/bul/b1693/html/bull5nqr.htm
Source https://pubs.er.usgs.gov/publication/b1693

Rationale

Explained by Stephen E. Box and Arthur A. Bookstrom
On the choice of deposit models
Epithermal Au-Ag quartz-adularia vein deposits are hosted in subaerial, intermediate to felsic volcanic rocks (Mosier and others, 1986). Comstock-type vein 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.
On the numerical estimates made
The lack of known deposits within the tract and the dearth of information available on any exploration activity prevented the team from estimating the number of undiscovered deposits of this type.
References
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.
Mosier, D.L., Singer, D.A., and Berger, B.R., 1986, Descriptive model of Comstock epithermal veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 150.

Geographic coverage

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