National mineral assessment tract PC23 (Epithermal vein, Comstock)

Tract PC23
Geographic region Pacific Coast
Tract area 3,040sq 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). Hot-spring mercury mineralization at the Idaho Almaden mine near Weiser (Andserson, 1941) indicates the existence of extinct geothermal systems in this tract. Deeper parts of these systems may include veins of the Comstock type (Mosier and others, 1986).
On the delineation of permissive tracts
The tract was drawn around the Miocene Payette Formation, host rock of the Idaho Almaden mine, northwest of the western Snake River plain (Bond, 1978). The Miocene Payette Formation consists of fluvial arkosic sedimentary materials derived from the Idaho batholith and is capped by lavas of the Columbia River Basalt Group. The surrounding area where the Payette Formation may occur within a kilometer of the surface beneath rocks of the overlying Columbia River Basalt Group was also included.
Important examples of this type of deposit
No examples of this deposit type are known in the tract. However, the existence of an extinct Au-bearing hot-spring hydrothermal system at the Idaho Almaden mine near Weiser suggests the possibility that Comstock-type vein systems may occur at depth. Gold occurs in subeconomic grades in the Idaho Almaden deposit.
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
Anderson, Alfred L., 1941, Geology of the Idaho Almaden quicksilver mine: Idaho Bureau of Mines and Geology Pamphlet 55, 9 p.
Bond, J.G., 1978, Geologic map of Idaho: Idaho Bureau of Mines and Geology, scale 1:500,000.
Mosier, D.L., Singer, D.A., and Berger, B.R., 1986a, 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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