HIGH-RESOLUTION GEOPHYSICS FOR CHARACTERIZING STRUCTURE WITHIN THE IDAHO COBALT BELT, SALMON, IDAHO

The U.S. Geological Survey (USGS) is engaged in the Earth Mapping Resources Initiative (EMRI), a national effort to map large portions of the USA, prioritizing areas with high potential for critical mineral resources. One focus of EMRI is to collect high-resolution aeromagnetic and aeroradiometric data sets that can be integrated with geologic and other geophysical data to significantly refine characterization of subsurface geology and structure that support mineral resource studies. EMRI products include publicly available datasets and accompanying geologic interpretations, in order to stimulate subsequent advanced investigations in both the public and private sector.

The Idaho Cobalt Belt (ICB) is a belt of Proterozoic meta-sediments, some of which are enriched in cobalt, copper, and gold. It is home to the Blackbird and several other important Co-Cu deposits. Historically, these deposits have produced over 2 Mt of ore, and the prospect of the ICB containing undiscovered resources is high.

Newly published high-resolution aeromagnetic and aeroradiometric data across the ICB are helping characterize its geologic stratigraphy and structure and highlight focus areas worthy of further exploration, with aeroradiometric data highlighting the very near surface – within the top meter – and aeromagnetics highlighting deeper geologic structures in the top few kilometers. The ICB survey, flown in Sept 2021, provides high-resolution baseline data (200 m line spacing, 200 m average flight height) to improve surface geologic mapping and serve as a catalyst for 3D geologic mapping of prospective mineral-rich regions. The data show that important contact relations in the shallow subsurface (< 500 m) such as those within subunits of the Apple Creek Formation tend to favor Co-Cu mineralization.

The baseline data also provide a regional context to more local data collection efforts – unpiloted areal system hyperspectral, field magnetic susceptibility, XRF, and radiometric measurements collected in ground campaigns. The Colorado School of Mines, Idaho Geological Survey, and the USGS are collaboratively engaging in these efforts to identify the most geologically promising areas for undiscovered critical mineral resources in the ICB.