Joint interpretation of aero-radiometric and magnetic survey data for ultramafic rocks in the Yugu area, South Korea

We conducted an airborne geophysical survey using a helicopter to acquire aero-radiometric and magnetic data around Yugu area in Gongju, South Korea. The presence of ultramafic rocks in the Yugu area was previously identified through regional geological and geochemical surveys. As part of a broad preliminary investigation, the airborne geophysical survey aimed to refine the precise location, boundaries, and subsurface extent of the ultramafic bodies. We presented 2D mapping results of radiometric and magnetic data respectively, and introduced joint interpretation with mafic-ultramafic index, which simultaneously incorporates both the field data. This approach clearly delineated only ultramafic bodies and adjusted their boundaries more accurately by slightly shifting them to the west. Furthermore, we performed 3D inversion of magnetic data to estimate the subsurface distribution of the ultramafic rocks. Finally, a preliminary interpretation of ultramafic bodies was achieved using only geophysical properties by integrating the 2D mafic-ultramafic index mapping and 3D magnetic inversion results. The well-matched results with the mafic-ultramafic values above 2 and isosurface of magnetic susceptibility of 0.02 delineated the ultramafic bodies into two major northwestern and southeastern regions. Higher thresholds with mafic ultramafic values above 3 and magnetic susceptibility of 0.04 further refined the ultramafic bodies into three regions: northwest, northeast, and south. This case study provides an improved interpretation of ultramafic bodies by integrating airborne radiometric and magnetic data and will offer valuable insights for wide-area geophysical exploration with similar objectives.