Heliborne em and magnetism for hydrogeological characterization in an obduction context - A new-caledonian example

Summary Airborne Time Domain ElectroMagnetic (TDEM) and magnetic (MAG) surveys have successfully been used for environmental studies. In igneous provinces, TDEM and MAG data may be jointly interpreted for the characterization of the geological environment. In May 2015, a heliborne survey was conducted in New-Caledonia Island (south-west in the Pacific Ocean) over a small area nearby Kone for hydrogeological characterization. The area is hosted by pre-Late Cretaceous metamorphic unit, Cretaceous formations, two volcanic facies and peridotite massifs, relic of the ophiolite nappe. TDEM and MAG data were separately and jointly interpreted in order to characterize the Kone area. Separately, results obtained from the two methods provided new information on the hydrogeological environment and allow delineating the precise limits of the different geological formations. Jointly, the multilayered results were interpreted using a hierarchical ascendant clustering algorithm. Through a statistical classification of three MAG grids and three TDEM grids, it was possible to propose a predictive geological map for the Kone area. The input will help to better manage the groundwater resources and will be used to position new exploration wells.