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DESMEXreal

The project "Real laboratory Upper Harz Mountains (DESMEX-real)" investigates in the frame of the BMBF program "research for sustainable development" (FONA) a modern large-scale exploration strategy for mineral deposits in the traditional mining area Upper Harz.

Project history

This project follows two the preceding two projects, DESMEX and DESMEX II. In the first phase, a new semi-airborne (i.e. transmitter on the ground and receiver in the air) exploration methodology for ore deposits was developed (Becken et al. 2020) and tested on demonstration cases in Schleiz and Kiruna. The second phase focused on the application of the method to several deposits in Germany, Namibia and Spain in rather local scales. Additionally to helicopters, drones have been used as alternatives to helicopters. Morover, alternative methods like AFMAG (audio-frequency magnetotellurics) have been added. The third phase of the project, DESMEX real, is a so-called real laboratory with the aim of investigating deposits in the district scale, by using the former mining are of the upper Harz mountains.

Apart from the joint measuring campaigns, the focus of the work at LIAG is on the software development. While in DESMEX the finite-element modelling package custEM was created (Rochlitz et al. 2019), it was extended to inversion in DESMEX II in order to be able to generate three-dimensional conductivity models based on the measured data. In DESMEX-real, the inversion algorithms are further developed towards large-scale inversion of extended areas of different resolution using hierarchical approaches.

Additional to mineral deposits, groundwater questions are coming into the focus to demonstrate the transferability of the methods into other fields of interest.

Survey plan

In the course of DESMEX II, two areas in the Harz mountains were already covered by extensive flight campaigs using four flight areas each. In 2020, the Northern part near Goslar was measured, also including the world-class ore deposit Rammelsberg (red color). In 2021, four other areas close to the historical mining town Bad Grund were measured (white colors). Like in other demonstration sites, we used both traditional induction coils and supra-conducting magnetometers and compared those data (Stolz et al. 2022).

In September 2022, the first of three planned campaigns was measured within the DESMEX-real project in the vicinity of the mining village Lautenthal. Thirteen flight areas (black colors), each with an associated transmitter inside, covered the area between the 2020 and 2021 data so that in total a triangular area of 15-20 km side length has been covered. In 2023 and 2024, the area will be extended towards Southeast. Data analysis, time series processing and subsequent inversion, is ongoing and will finally lead to geological 3D models.

Inversion

Based on the 3D frequency-domain finite-element modelling code custEM for arbitrary CSEM setups and topography, we implemented a flexible, 3D inversion routines for semi-airborne CSEM data based on inversion framework pyGIMLi. In DESMEX-real our responsibility is to implement a multi-scale 3D inversion scheme of magnetic field data. Next step is process the Data with Different Cycle length, that these data are used in different distances from the transmitter for example lower cycles are used near transmitter, this job is done by IPHT and you can see it as sounding in one data position in figure 2 and after combination of different cycles at different distances form transmitter we started the inversion for example transmitter number 2 in BadGrund and you can see the result of it as conductive body in 3D resistive domain in figure 3. As you can see in the map many flight areas overlapping and this feature makes these data sets good example and real data suitable for multi-scale inversions.

Publications from the project

  • Rochlitz, R., Becken, M. & Günther, T. (2023): Three-dimensional inversion of semi-airborne electromagnetic data with a second-order finite-element forward solver. Geophys. J. Int., accepted.
  • Rochlitz, R., Seidel, M. & Börner, R.-U. (2021): Evaluation of three approaches for simulating 3-D time-domain electromagnetic data. - Geophysical Journal International, 227 (3), 1980-1995. doi:10.1093/gji/ggab302
  • Werthmüller, D., Rochlitz, R., Castillo-Reyes, O. & Heagy, L. (2021): Towards an open-source landscape for 3-D CSEM modelling, - Geophysical Journal International 227(1): 644-659. doi:10.1093/gji/ggab238
  • Becken, M., Nittinger, C., Smirnova, M., Steuer, A., Martin, T., Petersen, H., Meyer, U., Matzander, U., Friedrichs, B., Rochlitz, R., Günther, T., Mörbe, W., Yogeshwar, P., Tezkan, B., Schiffler, M. & Stolz, R. (2020): DESMEX: A novel system development for semi-airborne electromagnetic exploration. - Geophysics, 85(6): E239-E253, doi:10.1190/geo2019-0336.1
  • Steuer, S., Smirnova, M., Becken, M., Schiffler, M., Günther, T., Rochlitz, R., Yogeshwar, P., Mörbe, W., Siemon, B., Costabel, S., Preugschat, B., Ibs-von Seht, M., Zampa, L.S. & Müller, F. (2020): Comparison of novel semi-
    airborne electromagnetic data with multi-scale geophysical, petrophysical and geological data from Schleiz, Germany
    , J. Appl. Geophys. 182: 104172, doi:10.1016/j.jappgeo.2020.104172
  • Rochlitz, R., Skibbe, N. & Günther, T. (2019): custEM: customizable finite element simulation of complex controlled-source electromagnetic models. Geophysics 84(2): F17-F33, doi:10.1190/geo2018-0208.1

Team

Project Scientist
Dr. Raphael Rochlitz

Project lead
Dr. Thomas Günther

Funding

Federal Ministry of Education and Research (BMBF) in the frame of the program Fona-r4

Duration: 01.07.2019-30.06.2023