Airborne Magnetic and Radiometric Survey, Colorado Mineral Belt, Mid Block, 2023

This data release provides digital flight-line and gridded data for a high-resolution airborne magnetic and radiometric survey over the central portion of the Colorado Mineral Belt, central Colorado. The Colorado Mineral Belt is a broad, northeast-southwest trending alignment of historic mining districts that have produced multiple types of commodities, including critical minerals that are vital to the Nation's security and economy. The survey was acquired as part of the USGS Earth Mapping Resource Initiative (Earth MRI) to improve our understanding of the fundamental geologic framework underpinning the Colorado Mineral Belt. This release covers the central portion of the belt (“mid” block), which includes a wide swath from the Powderhorn mining district to the southwest, the Brown’s Canyon mining district to the east, and the Spring Creek mining district in the north, including parts of Gunnison, Chaffee, and Saguache Counties. Previous reports have identified several critical minerals in this region, including beryllium, fluorspar, graphite, lithium, manganese, niobium, REEs, tantalum, titanium, uranium, vanadium, and zinc. Data for this survey were acquired by NV5 Geospatial, Inc. and is sub-contractors Precision GeoSurveys, Inc. and EDCON-PRJ, Inc under contract with the USGS. The survey was flown in two segments, with the first in October 2023 and the second July through August of 2024, following a break in operations for winter weather. The survey used a helicopter equipped with a magnetometer mounted in a stinger extending from the nose of the aircraft and a gamma-ray spectrometer stowed onboard. The helicopter pilots followed pre-planned flight paths in a grid-like pattern, with north-south lines spaced 200 meters apart and east-west lines spaced 1,000 meters apart. Lines were flown 100 meters above ground as much as possible to maximize detection of gamma-rays and resolve details of the magnetic field. This clearance could be realized in areas of low relief but higher clearances, as much as 200-500 meters, were required over rugged terrain and populated areas for safety reasons. Areas with restricted airspace, such as Wilderness Areas, were avoided. A total of 40,111 linear kilometers of data were collected along the lines, covering a 6,863 square-kilometer irregular area. EDCON-PRJ performed extensive data processing after completion of flying and delivered the final data and report in November 2024.