Reconnaissance petrography of the Idaho batholith in Valley County, Idaho

The purpose of this report is to describe the rocks comprising a part of the Idaho batholith in west-central Idaho (see index map, Figure 1). The study is a by-product of an investigation of placer deposits containing radioactive minerals, monazite and euxenite, by the U. S. Geological Survey on behalf of the Division of Raw Materials of the U. S. Atomic Energy Commission (Mackin and Schmidt, 1956).

Tracing of the valuable minerals to their source by panning of alluvium and residual soil made it evident that their distribution in the bedrock forms definite patterns roughly paralleling the west border of the batholith. The petrographic study was undertaken to clarify the relationships of the radioactive heavy minerals to the structure of the batholith, and for what light it might shed on the ultimate origin of these minerals.