HIGH-RESOLUTION AIRBORNE MAGNETIC AND RADIOMETRIC SURVEY OF THE REPUBLIC GRABEN, OKANOGAN AND KETTLE METAMORPHIC CORE COMPLEXES, KOOTENAY ARC AND SURROUNDING REGIONS, NORTHEASTERN WASHINGTON STATE

Northeastern Washington is arguably the most geologically varied region of the state, with exposures spanning Precambrian to modern day. Proterozoic metasedimentary sequences of diverse lithology and thickness formed along the convergent margin of Rodinia; volcanic, intrusive, and sedimentary units accreted throughout Paleozoic and Mesozoic time; and extension during the late Paleozoic to Cenozoic exhumed multiple metamorphic core complexes. The resulting mineralogic diversity of this geologic landscape is a target for the USGS Earth Mineral Resources Initiative (EMRI) focused on identifying areas of critical-mineral potential. To this end, the EMRI conducted a high-resolution airborne survey, known as the Republic survey, to ascertain the magnetic and radiometric properties of the region. The resulting data are intended for rigorous modeling and interpretation of the geology and structure in this region and will be used to evaluate the potential for undiscovered resources and will contribute to USGS and Washington DNR-related mineral and geothermal resource assessments of the region.

In this presentation, we showcase the recently obtained Republic survey, which is a low-altitude survey flown by helicopter over rugged terrain 80-100 m above ground along lines spaced 200 m apart. The survey covers 16,885 km², an area containing roughly 33% of Washington’s known metallic mineral resources and 25% of its critical-mineral resources. The Republic survey is designed to image the subsurface geology and structure of a large portion of northeastern Washington and is positioned to capture variability both along-strike and orthogonal to the regional tectonic fabric. New data reveal a variety of information that were not clearly identifiable from older datasets. New observations include detailed structure and magmatism of the Okanagan and Kettle metamorphic core complexes, the Republic and Toroda Creek grabens, and the Kootenay arc, along with the association of mineralogical zones with structural and depositional fabric.