Candle Hills Electromagnetics Geophysical Survey

The Candle Hills airborne electromagnetic survey covers a portion of the McGrath and Iditarod quadrangles, southwest of McGrath, across part of the Kuskokwim Mountains in western interior Alaska. Time-domain electromagnetic data were acquired using the helicopter-mounted VTEM Terrain system on August 5-12, 2025, by Geotech Ltd. A total of 1060 line-kilometers was flown over a single survey block measuring 369.5 square kilometers. The block was flown with a 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 44 meters, with a mean survey speed of 86 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 2026-3. Candle Hills airborne electromagnetic survey, Kuskokwim region, Alaska.