DESMEX (Deep Electromagnetic Sounding for Mineral Exploration)
Country / Region: Germany
Begin of project: March 1, 2015
End of project: February 28, 2019
Status of project: September 17, 2019
DESMEX (Deep Electromagnetic Sounding for Mineral Exploration) is a joint project funded by the German Federal Ministry for Research and Education (BMBF) in frame of the program r4 – Innovative technologies for resource efficiency – Provision of raw materials of strategic economic importance.
The aim of the project is to set up a semi-airborne exploration system to explore mineral deposits in Germany, which will be tested exemplarily on an ore deposit.
The work of BGR on this project is divided into two working groups. One group is involved in the development and the test flights of the airborne sensors to be developed, the reconnaissance survey of the test area on field scale and the performance of the main semi-airborne surveys (Airborne Geophysics). The other group is responsible for the determination of the geophysical quantities on a laboratory scale (Petrophysics) and the scaling up to the field scale.
Scheme of the semi-airborne exploration method
Source: BGR
Subproject Airborne Geophysics
In recent years, the focus of the BGR Airborne Geophysics Group was in groundwater exploration. Due to the limited exploration depth so far, there were only individual projects for ore exploration (Siemon, 2013: Erzgebirge Geyer). The BGR is therefore very interested in expanding its range of methods in order to be able to make statements about the geology of the subsurface at depths of up to about 1 kilometer.
Development of airborne sensors and test flights. The BGR provides its helicopter for the necessary flight tests, as well as an airborne probe for the induction coil magnetometers and participates in necessary modifications of the probe and ground-based tests of the prototype.
Reconnaissance survey. A large-scale reconnaissance survey is carried out with the existing methods of the BGR Airborne Geophysics Group. With helicopter-borne electromagnetics, the near-surface structures of the selected survey area are to be investigated. Existing magnetic data will be complemented by the newly acquired data of airborne magnetics and later modeled together. The results of the airborne survey will help in the main experiment in planning the location of power sources, in the determination of anthropogenic and geological disturbances, as well as in creating a near-surface starting model for later inversions and modeling.
Flight execution of the developed airborne probes and creation of a reservoir model. In the main experiment, the BGR conducts the survey flights with the newly developed sensors and flight probes over the selected test area. The BGR participates in the creation of the deposit model by integrating the results of geophysics and petrophysics, and develops the physical parameterization of the model as far as possible.
Subproject Petrophysics
Geophysical measurements, whether airborne or ground-based, provide the distributions of physical quantities in the subsurface (geophysical models). The measured physical quantities are material-dependent and can therefore provide information about the extent and depth of geological structures. However, geophysical models are often ambiguous, and the measurements often can not be clearly assigned to a particular material or to a characteristic mineralogical or geochemical material parameter.
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In the Petrophysics subproject, extensive petrophysical investigations are carried out on representative sample material (ore as well as its surrounding rock) in order to gain in-depth knowledge of the physical parameters measured in the field (specific electrical resistance, magnetic susceptibility, chargeability) with relevant mineralogical-geochemical properties that characterize the deposit. Our goal is to develop solutions for how to conduct a stock analysis of the deposit through the complex interaction of mineralogy, petrophysics, geochemistry and geophysical exploration, based on the semi-airborne measurement methodology to be developed in the project.
Results
Reconnaissance survey
A reconnaissance survey with the standard geophysical helicopter-borne system of the BGR Airborne Geophysics Group took place in May 2015 between the cities of Schleiz and Greiz (Thuringia). The result is the distribution of the electrical resistivity down to 150 m.
Publications
A. Steuer, T. Martin, B. Siemon und U. Meyer, 2016. Projekt DESMEX: Lagerstättensuche in Thüringen - Vorerkundung mit HEM. 76. Jahrestagung der Deutschen Geophysikalischen Gesellschaft, Abstract Poster
Technical report
(Also available via the BGR product center for download)
Petrophysical investigations
For the geophysical exploration of mineral resources, knowledge about the petrophysical properties of the expected rocks is essential. The petrophysical investigations we carried out had the following objectives: on the one hand the target mineral antimonite, on the other hand the possible secondary rocks should be characterized petrophysically.
Publications
T. Martin, S. Costabel, T. Günther, 2016. Methods for measuring complex resistivity spectra of rock samples in the context of mineral exploration, International Workshop on Induced Polarization (IP), 4th International Workshop on Induced Polarization, Abstract, Poster.
Technical report
Exploration of mineral resources in Thuringia
The first main experiment with the semi-airborne method took place in October 2017 in the vicinity of the former mining area Schleiz (Thuringia) and Mühltroff (Saxony). The two flight probes developed in the project were used here for the first time.
In East Thuringia until the 1950s antimonite mining was operated to a depth of about 200 m. Whether the deposits extend to even greater depths is still unclear. From airborne- and ground geophysical reconnaissance surveys in Thuringia, the electrical properties of the subsurface are known at depths down to 150 m. It turned out that in the Schleiz area striking, electrically conductive structures can be seen that extend into the Mühltroff / Sachsen area. It is believed that this is Graptolite schist. This clear contrast in electrical conductivity is particularly well suited to investigating the extent to which these structures can be traced to great depths with the new measuring systems.
Publications
C. Nittinger, M. Cherevatova, M. Becken, T. Martin, H. Petersen, A. Steuer, U. Meyer, B. Siemon, U. Matzander, B. Friedrichs, W. Mörbe, P. Yogeshwar, B. Tezkan, R. Rochlitz and T. Günther, 2017. A Novel Semi-airborne EM System for Mineral Exploration - First Results from Combined Fluxgate and Induction Coil Data, Second European Airborne Electromagnetics Conference, DOI: 10.3997/2214-4609.201702154
M. Cherevatova, C. Nittinger, M. Becken and T. Günther, 2018. 3D Inversion of the Semi-airborne Electromagnetic Data from Schleiz, Germany, Second European Airborne Electromagnetics Conference, DOI: 10.3997/2214-4609.201702151
Meyer, U., Petersen, H., Costabel, S., Steuer, A., Cherevatova, M., Becken, M., Nittinger, C., Günther, T., Yogeshwar, P., Mörbe, W. and Tezkan, B., 2018. Results from the Main DESMEX Experiment South of Greiz, Germany, 2nd Conference on Geophysics for Mineral Exploration and Mining, DOI: 10.3997/2214-4609.201802722
Smirnova, M., Becken, M., Nittinger, C., Yogeshwar, P., Mörbe, W., Rochlitz, R., Steuer, A., Costabel, S., Smirnov, M. Y., and the DESMEX Working Group, 2019. A novel semi-airborne frequency-domain CSEM system. Three-dimensional inversion of semi-airborne data from the flight experiment over an ancient mining area near Schleiz, Germany. Geophysics, 84 (5), 1-12, DOI: 10.1190/geo2018-0659.1
Steuer, A., Preugschat, B., Cherevatova, M., Mörbe, W., Yogeshwar, P., Günther, T., Rochlitz, R., Schiffler, M., Siemon, B., Costabel, S., Müller F. and the DESMEX Working Group, 2019b. Validation of semi-airborne 3D inversion results using airborne and ground-based EM methods, as well as geological models and borehole measurements. EGU General Assembly, 07.-12.04.2019, Vienna, Austria, Abstract, Poster.
Flight report
New methods to explore the largest iron-ore mine in the world at Kiruna
The second main experiment took place in October 2018 at Kiruna in northern Sweden. The measurement flights are intended to better determine the extent of the largest underground iron-ore mine in the world in depth. The iron-ore deposit in Kiruna has so far been mined to a depth of around 1,300 meters and is therefore well suited to apply the newly developed methods.
Publication
Smirnova, M., Juhojuntti, N., Becken, M., Smirnov, M., Yogeshwar, P., Steuer, A., Rochlitz R., Schiffler, M., 2019. Combined 3D Inversion of Ground and Airborne Electromagnetic Data over Iron Ore in Kiruna. Near Surface Geoscience Conference & Exhibition 2019, 8-12 September 2019, The Hague, Netherlands, DOI: 10.3997/2214-4609.201902430
Flight report
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