Granite Mountain Electromagnetics Geophysical Survey

The Granite Mountain airborne electromagnetic survey covers a portion of the Iditarod Quadrangle across part of the Kuskokwim Mountains in western interior Alaska, southwest of McGrath. The Iditarod Quadrangle is a prime exploration target, which includes historically productive mining districts and contains geologic structures and rock units known to host gold and other metallic mineral deposits. The survey was conducted to characterize subsurface electrical resistivity variations and to support geologic mapping and mineral resource evaluation. These data provide a framework for identifying concealed lithologic contacts, structural features, and alteration zones that may indicate areas of elevated mineral potential. Time-domain electromagnetic data were acquired using the helicopter-mounted VTEM Terrain system from August 12 to September 14, 2025, by Geotech Ltd. A total of 2516 line-kilometers were flown over a single survey block measuring 916.5 square kilometers. The block was flown with northwest-southeast line orientation and a nominal spacing of 400 meters, along with northeast-southwest oriented tie lines with a nominal spacing of 4000 meters. Mean ground clearance was 47 meters, with a nominal survey speed of 87 km/hr. Geotech Ltd. provided initial resistivity models produced via simple inversion using a technique termed Resistivity Depth Imaging (RDI). These models are referred to in the provided data files as 'geotech_rdi.' Aqua Geo Frameworks then produced a spatially constrained inversion model (referred to in the data files as 'agf_sci'), which incorporates both along-track and cross-track constraints. The Aqua Geo Frameworks model is recommended for end-users as it resolves finer-scale structures, including faults. We also provide a 3D voxel dataset registered to elevation rather than raw depth for the agf_sci model.

Publications

• GPR 2026-4. Granite Mountain airborne electromagnetic survey, Kuskokwim Region, Alaska.