| Basis for focus area |
Polymetallic Au-Ag quartz veins distributed around the Idaho batholith in Idaho and southwest Montana and in the Blue Mountains of northeast Oregon. A multipart focus area based on favorable tracts (X10 in Oregon and X11 in Idaho and Montana) for Polymetallic Au-Ag, vein and disseminated deposits (Box and others, 1996). |
| Identified resources |
Identified resources and historical production of gold and silver prior to 1950. |
| Production |
Unknown. |
| Status |
Past mining. |
| Estimated resources |
Median size of veins in Idaho: 14,000 t @ 13 g/t Au and 0 to 55 g /t Ag (Bliss, 1994). |
| Geologic maps |
Horton and others (2017), scale 1:500,000. |
| Geophysical data |
Inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
In and around the Idaho batholith, most polymetallic Au-Ag veins occupy steeply dipping faults and fissures, and many of them are localized within or near roof pendants or inclusions of metasedimentary rocks in the Idaho batholith (Box and others, 1996). |
| Deposits |
Idaho: Atlanta district, Hailey gold belt, Rocky Bar, Elk City, and Warren districts; Oregon: Cracker Creek, Cornucopia, Greenhorn, Granite, and Rock Creek mining districts. |
| Evidence from mineral occurrences |
MRDS; Box and others (1996). |
| Geochemical evidence |
Arsenopyrite, pyrite, galena, sphalerite, chalcopyrite, tetrahedrite, and stibnite are common. Bournonite, proustite, argentite, and electrum are sparse. Huebnerite, scheelite, hessite, cinnabar, and zinc-mercury sulfides are rare. |
| Geophysical evidence |
Unknown. |
| Evidence from other sources |
Focus areas include scattered arsenic and tellurium occurrences from MRDS and other databases. |
| Comments |
Grade-tonnage model for Blue Mountain-type Au-Ag polymetallic (Bliss, 1994): mean deposit size is 76,000 t, Au grades 13 to 23 g/t Au, 2 to 300 g/t Ag (Box and others, 1996). |
| Cover thickness and description |
Exposed at the surface. |
| Authors |
Reed S. Lewis, Virginia S. Gillerman, Christopher A. Tate, Jane M. Hammarstrom. |
| New data needs |
Geophysics. |
| Geologic mapping and modeling needs |
None requested at this time. |
| Geophysical survey and modeling needs |
High resolution, Rank 1 aeromagnetic and aeroradiometric coverage. |
| Digital elevation data needs |
Lidar variable over large focus area. |
