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.
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, Germany, and Kiruna, Sweden (Steuer et al. 2020; Smirnova et al. 2020). The second phase focused on the application of the method to several deposits in Germany, Namibia (Becken et al. 2023) 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 (Stolz et al. 2022). 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 (Rochlitz et al. 2023) in DESMEX II in order to be able to generate three-dimensional conductivity models based on the measured data. With that, an extended synthetic study was done to optimize survey design (Nazari et al. 2023). In DESMEX-real, the inversion algorithms are further developed towards large-scale inversion of extended areas of different resolution using hierarchical approaches aiming at geological models for the Harz mining region.
Additional to mineral deposits, groundwater questions are coming into the focus to demonstrate the transferability of the methods into other fields of interest.
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 September 2023, 10 flight areas (blue) in the area around Schulenberg were measured. In 2024, the whole region will be completed by 5-10 flights south of Clausthal-Zellerfeld.
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 lengths depending on distances from the transmitter, and the inversion of single and multiple transmitter data sets.
Federal Ministry of Education and Research (BMBF) in the frame of the program Fona (033R385D)