Development of the induced polarization theory with application to exploration of strategic raw materials

• Applicant: Professor Dr. Andreas Weller
• Subject Area: Geophysics
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 425975038

Within last two decades, Spectral Induced Polarization (SIP) method attracts researchers because it allows to remotely investigate interface properties of geo-materials. As a result, SIP is increasingly used in hydrogeology, contaminant hydrology, geotechnics and mineral exploration. However, to date many points in the physical and chemical theory of Induced Polarization (IP) phenomena are contradictory and understudied. First, the role of different mechanisms (interfacial mechanisms, diffusion of p- and n-charge carriers, electromagnetic induction, and Maxwell-Wagner effect) in polarization of metallic particles (MP) is unclear. Second, each mechanistic model of rock polarization describes only one mechanism (the Stern layer of the Electrical Double Layer polarization, the membrane polarization, or the Maxwell-Wagner polarization). No model includes all of the mechanisms. The objectives of the project are to fill the above-mentioned gaps. We expect: - to develop an unified model of IP of metallic particles;- to improve the mechanistic models of rock polarization.In order to validate these models, we will carry out an extensive series of laboratory experiments with natural samples of magmatic and hydrothermally altered rocks typical of some economically important ore deposits. However, natural samples (being highly heterogeneous) are always poorly sorted in terms of mineral composition and pore structure. Therefore, we will use well-controlled synthetic samples to clarify some aspect of the new models. As a result, we will compile a new extensive database of SIP data available for the scientific community for reuse.Moreover, to test the models we will reproduce numerically the phenomena responsible for IP based on solution of the Nernst-Plank - Poisson-Boltzmann differential equations with the COMSOL Multiphysics package. In addition, we address two methodological aspects of SIP data processing. First, it can be assumed that not all polarization responses indicate a Debye character. However, experimental data are frequently fitted with a Debye Decomposition (DD) procedure. We propose to extend the DD approach for non-Debye relaxation case. Then, field surveys are typically performed with the Time Domain (TD) technique, whereas petrophysical researches are carried out with the Frequency Domain (FD) technique. So, TD and FD data must be compared. However, for real lab, and, especially, field data the TD – FD transformation is not straightforward. For this reason, we plan to improve the TD - FD transformation technique. Finally, the theoretical and methodological results will be applied to ore exploration. We propose to develop a prototype of TD IP logging instrument, to test it within ore deposits, and to assess the information output of IP logging. If this task is successful, we believe to obtain a promising technology for ore exploration, which will be demanded by commercial and state enterprises.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Science Foundation, until 3/2022
• Cooperation Partner: Professor Dr. Konstantin Titov, until 3/2022