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Measurements via helicopter in the Western Harz: First 3-D conductivity models

As part of the DESMEX-REAL research project, further scientific investigations are taking place in the Harz Mountains. From September 18 to 23, 2023, the LIAG (Hannover), the Federal Institute for Geosciences and Natural Resources (BGR, Hannover), the University of Münster, the Leibniz Institute for Photonic Technologies (Jena) and the companies Supracon (Jena) and iMAR Navigation (St. Ingbert) will conduct geophysical explorations in the western Harz using the BGR helicopter. Initial 3-D conductivity models depicting the various conductive layers in the subsurface are already available.

Distribution of good conductive structures in the subsurface looking north for the central area of the 2022 survey, for which a detailed 3D geological model is being developed. Most of the good conductors near the surface can be associated with the existing villages and their infrastructure. The deeper, elongated structures show the expected SW-NE strike direction in the Upper Harz Devonian Saddle. Translated with DeepL.com (free version)

Distribution of good conductive structures in the subsurface looking north for the central area of the 2022 survey, for which a detailed 3D geological model is being developed. Most of the good conductors near the surface can be associated with the existing villages and their infrastructure. The deeper, elongated structures show the expected SW-NE strike direction in the Upper Harz Devonian Saddle. Source LIAG.

Overview of the flight areas of the DESMEXreal campaign of 2023 in the area of Schulenberg in the Upper Harz.

Overview of the flight areas of the DESMEXreal campaign of 2023 in the area of Schulenberg in the Upper Harz. Source LIAG.

The aim of the DESMEX-REAL research project, which is planned to run until 2025 and is funded by the German Federal Ministry of Education and Research (BMBF) and in which the University of Cologne, the Clausthal University of Technology, the Lower Saxony State Office for Mining, Energy and Geology (Hanover) and the Geologische Landesuntersuchung GmbH Freiberg are also involved, is to set up a so-called real laboratory in the "old mining region of the Upper Harz". The project combines state-of-the-art geophysical measuring methods for the efficient exploration of mineral raw material deposits with knowledge gained from archival data of past mining activities in the Upper Harz.

In the course of the project, a total of three larger measurement campaigns are planned. For this purpose, helicopter measurement flights and ground geophysical investigations will take place. In this year's campaign, the flights, which will each start from the Hildesheim airfield, will cover several measuring areas in the Oker, Bad Harzburg, Schulenberg, Altenau, Clausthal-Zellerfeld and Kamschlacken regions.

First measurement results in the 3-D conductivity model from the subsurface

The project uses a so-called semi-airborne electromagnetics method that can be used to make statements about the electrical conductivity of geological structures. It combines dipole transmitters - grounded power cables on the ground - with highly sensitive magnetic field sensors located in flight probes towed by helicopter on a cable 50 to 70 meters above ground. Two different measuring probes with different sensor technology are used.

The evaluation software developed at LIAG creates three-dimensional models of electrical conductivity based on the measured data, which can provide indications of mineralization in the subsurface down to a depth of about 1 kilometer from all of the approximately 30 measurement flights. Interim results are already available. The 3-D models show the different electrical conductivities of the sediment and rock bodies. According to geological interpretation, this allows conclusions to be drawn about faults in the subsurface and potentially existing ore bodies. For the highly complex analysis of the data, researchers have developed inversion algorithms that can account for arbitrary 3-D geometries of the topography as well as the transmitters and receivers.

"Using the procedures developed here at LIAG to analyze the data with this novel method, we can visualize the subsurface in three dimensions based on electrical conductivity down to a depth of one kilometer, and thus existing ore deposits," explains Dr. Thomas Günther, project manager at LIAG. "This was previously not possible at this scale and in such detail."

For representatives of the media, there will be the opportunity to accompany the measurement campaign on site on Thursday, September 21, 2023. Here are both photo and film recordings of the start of the helicopter from 9 am at the airfield in Hildesheim and of the parallel measurement work on the ground. The latter will be coordinated by the LIAG (contact: Insa Cassens, 0511 643 3820). Registration is requested by Monday, September 18, 2023, at the e-mail address info(at)bgr.de. Further information can also be obtained by calling 0170 8569662.

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