Details of the abstract

Title of paper Results from the DESMEX semi-airborne EM survey at the Gosetal/Rammelsberg
(Harz Mountains, Germany)
List of authors Thiede, A., Becken, M., Kotowski, P.O. and the DESMEX Working Group
Affiliation(s) University of Münster (Germany) Institute of Geophysics, University of Münster (Germany) Institute of Geophysics, University of Münster (Germany) Institute of Geophysics
Summary The nowadays depleted world-class SEDEX Rammelsberg deposit and its adjacent areas are a prime location
to test and demonstrate new geophysical exploration methods. Here, we present preliminary results of a semiairborne EM survey centered at the Gosetal and the Rammelsberg, which was conducted in September 2020 as part of the DESMEX II project. Previous airborne EM exploration surveys, carried out about a decade ago in that area, revealed a high-conductivity anomaly in the Gosetal, but subsequent drillings could not verify its existence. Therefore, the results of the airborne EM survey remained enigmatic. Semi-airborne EM has the potential to image deeper than pure airborne EM and may detect conductivity anomalies from the near surface to about 1000 m, including a possibly deeper root of the enigmatic Gosetal anomaly.
We installed four electrical dipole transmitters of 2-3 km length and injected an alternating current with a fundamental frequency of 9.26 and 4.63Hz and covered an area of about 45 km² with the Helicopter induction coil DESMEX system. EM Transfer functions were derived in the frequency range up to 4 kHz. Analysis of the data is complicated due to the presence of steep topography and over 500 m altitude differences in the surveyed area. Synthetic 3D modeling using the unstructured finite element code custEM shows that strong topographic effects are evident in the collected data and must thus be taken into account in any inversion. We discuss these effects as well as topography correction schemes for flat surface inversion models based on normal field corrections. Ongoing work is focused on comparison of 3D inversion applying the custEM code supporting complex survey geometry and the 3DINV code using corrected data on a flat surface model.
Session Keyword 3.0 Exploration, Monitoring and Hazards
File upload 3.0_results_from_the_desmex_s_thiede.pdf
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