GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.1 GNGTS 2024 polarizaton currents, ceases to be valid (Smith and Klein, 1996): the negatve data cannot be fted and the fast-decaying signals are modelled as strong resistors, generatng artfacts. To avoid the mis-modelling of EM-IP afected data, it is necessary to use a dispersive-resistvity model (such as the Cole & Cole one) to compute the forward response and considering the capacitve nature of the ground. This approach gives the opportunity to map, as well as the resistvity, the chargeability of the ground that is ofen related to signifcant economic (or signatures of) mineralizaton. At the same tme, it complicates the inversion process adding three more parameters and expanding the model space generatng equivalent domains. It follows that an appropriate parameters management during the inversion process is crucial to properly retrieve the ground descripton and to maximize the AIP sensitvity to geological and mineral targets. Geophysical and geological descripton The Airborne EM data have been acquired in spring 2022 with the NRG XCite Time Domain system, with a 25Hz base frequency, and the acquisiton lines are illustrated in black lines in fgure 1 . In the same area, 18 Iris VIP 1000 (transmiter) lines (0.125Hz of base frequency, 50% duty cycle) of ground Time Domain DCIP have been acquired (red lines in fgure 1). Figure 1. Survey locaton. In black the Airborne EM lines are displayed, in red the DCIP. In the base map of fgure 1 the local geology is shown. Two main domains are visible: a volcanic intrusive one in the north, where Rhyolite and Dacite are presented in red and green, and a more recent sedimentary domain that covers the outcrop is in yellow in the southern area. The main tectonic features are represented in black and outcrops in the northernmost part of the investgated area. Data modelling and inversion Among the diferences between Airborne and Ground IP, the most obvious are in the in footprint, depth of investgaton and spectral content, with AEM data’s frequency bandwidth usually a couple