High Resolution Airborne Gravity Gradiometry, Electromagnetic and Magnetic data for Geothermal Assessment

Advances in airborne technologies has enabled rapid and efficient acquisition of high-resolution gravity, electromagnetic and magnetic datasets for geothermal assessment. HeliFalcon airborne gravity gradiometry (AGG) can acquire high quality gravity data in most terrains, which is ideal for detailed litho-structural mapping of tectonic, volcanic and igneous features (faults, lava domes, lava flows, intrusives, calderas, basins, sub-basins), and general geology. Helitem time-domain helicopter electromagnetics (AEM), operating at transmitter frequencies as low as 6.25Hz, provides enhanced exploration depth, and AEM data ideal for mapping subsurface resistivity distribution in 2D and 3D (and particularly low-resistivity clay-caps related to hydrothermal alteration), aquifers and lithological distribution. Resistivity depth slices and 3D iso-surfaces are used to image low resistivity zones, giving information on fluid sources, pathways, conduits at fault intersections, and alteration. Magnetic data, acquired simultaneously with the AGG and/or AEM data, provides complementary information for the mapping applications above, and can also map areas of magnetite destruction due to hydrothermal alteration. A geothermal case history from Japan is used to demonstrate how high-resolution airborne gravity, electromagnetic and magnetic datasets, can benefit geothermal assessment.