Spectral induced polarization in anisotropic rocks with electrically conductive inclusions: synthetic model study

Abstract

Summary Electrically conductive minerals (e.g. graphite, pyrite, chalcopyrite, and magnetite) occur in the various geological contexts. They might represent economic resources or serve as indicators of such resources. In addition, they can be sources of contamination of soil and groundwater. Therefore, characterization of rocks containing electrically conductive inclusions is an important task in many sectors of science and economy. We conducted laboratory measurements to study the impact of the shape, composition, size, and passivation character of electrically conductive inclusions on the induced polarization (IP) parameters. This paper presents results of time domain IP measurements performed on 22 synthetic models, which were made of sieved sand mixed with electrically conductive particles. We carried out the IP measurements while varying orientation of the electrical field relative to the long axis of the inclusions. We found that the total chargeability of the models (M) strongly depended on the volumetric content (ξ), shape, and characteristic size (l) of the inclusions. It also depended on the angle between the electrical field direction and the orientation of the long axis of the inclusions (α), which made the models anisotropic. Experimental relationships between M, ξ, l, and α were found consistent with predictions of the generalized Maxwell-Garnett mixing equation in the tensor form. In contrast to M, the relaxation time (τ) of the studied models was almost independent of $\alpha $. Exceptions were the models with cylindrical electrically conductive particles, which showed a strong relationship between τ and$\,\,\alpha $. Despite the previous assumptions, no unique relationship between τ and the characteristic length of electrically conductive inclusions was observed. However, for all particle shapes, $\tau $ was proportional to the surface area of the particles. We also studied how passivated areas on the surface of the inclusions modified the spectral IP parameters. We found that passivation of electrically conductive inclusions led to anisotropy of M, while τ remained almost unaffected by the orientation of the polarizing field. Based on the experimental data, we show that the polarization magnitude of electrically conductive inclusions is proportional to the normal component of the electrical current density on their surface. We also show that the relaxation time is proportional to the area of the active surface of the inclusions. The obtained relationships highlight the importance of the interfacial polarization mechanism of the electrically conductive inclusions.

Study of the passive method of induced polarization at the copper deposit “Zhaman-Aibat”

“…The authors of [14] provide data that the use of the induced polarization method in the frequency domain is less preferable than in the time domain, which often leads to an increase in the observation…”

Numerical Simulation Study on the Relationships between Mineralized Structures and Induced Polarization Properties of Seafloor Polymetallic Sulfide Rocks

“…It was indicated that a portion of the electrons within the vein metal sulfides with high tortuosities did not participate in the IP effects. Gurin et al (2021) [22] proposed an active-surface theory in the study of the IP properties of anisotropic rocks with metallic particles. According to this theory, the relaxation time constant is positively associated with the area of the active surface.…”

“…The total chargeability of rocks containing sheet-like metal sulfides is less affected by their size and orientation relative to the direction of the polarizing field. The above dependence in rocks containing rod-like sulfides is much stronger [19][20][21][22]. However, studies on the effects of mineralized structures on the IP properties of seafloor polymetallic sulfides are currently lacking.…”

Induced Polarization of Metal Grains: Simulations of Three‐Dimensional Electric Fields

“…These studies empirically deduced the relationship between the IP signal and the characteristic of geological samples, including metals (Ntarlagiannis et al., 2010; Placencia‐Gómez & Slater, 2016; Placencia‐Gómez et al., 2013; Slater et al., 2005, 2006; Wu et al., 2005). Some recent studies used simple laboratory conditions and artificial metals to determine the parameters of phenomenological models (Gurin et al., 2013, 2015, 2020). In addition, recent numerical simulations investigated the detailed physico‐chemical process coupled with the electrical field on the surface of metals (Bücker, Undorf, et al., 2019; Bücker et al., 2018).…”