Remote sensing detection and geological interpretation of the Idaho Primitive Area

Abstract

Lithologic and structural analyses were performed on igneous and metsunorphic terrain of the Idaho Primitive Area using Landsat imagery. Results were correlated with published geologic studies to determine a comprehensive history of the region and reports on 51 mines in and near the Primitive Area to establish possible controls of mineralization. Seven penetrative lineament systems are defined from edge enhancements and 3-D displays of MSS Band 5 and 7 imagery, a complete drainage overlay, and detailed spot checks of RBV imagery. Four of the systems were caused by three systems of shearing and the conjugate jointing accompanying the Cretaceous Laramide Orogeny. The other three systems resulted from northwest trending folding in the Eocene and two episodes of high-angle faulting in the Miocene.

Interpretation of MSS Band 5 and 7 and REV imagery, i^-'.SS color composites from early Spring and late Summer, and psuedocolor density slices of the color composites provided a diagnostic pattern for Precambrian schists and gneisses with which one contact with Cretaceous intrusives is redefined and a previously unreported exposure identified. In addition, two exposures of an unidentified unit within the Idaho Batholith are proposed based on persistant changes in image tone and density.

Gold, silver and other mineralization of veins in all the fractures and shear zones in the Primitive Area was caused by rising fluids from magma of the Idaho Batholith and later igneous activity. The best production is attributed to the two systems formed earliest in the Cretaceous. Prospects for future exploitation are deemed excellent.