Spectral Induced Polarization Response of Clay Rock Samples with a High Value of Pyrite

Abstract

The induced polarization (IP) response in media containing clay and/or metallic minerals has been modeled in different research. Increasing the IP applications and measurements has revealed these models’ limitations. For instance, no model has described IP response in the media with metallic minerals higher than 22 percent. So, our goal in this contribution is to explain the IP response of clay-rich samples containing low- to high-grade pyrite, galena, and sphalerite from the Zn-Pb sedimentary-exhalative mine Koushk, central Iran. The samples’ background consists of clayey/micaceous minerals, including illite, muscovite, and chlorite, that, along with the metallic minerals, make the consecutive layers in some samples, while others have a different formation. The samples also contain some insulating grains such as quartz and gypsum. Therefore, there are different conduction and polarization mechanisms in them. These properties make our samples unique and substantial to study the IP response. To do this, we measured the samples’ complex conductivity, density, porosity, cation exchange capacity (CEC), and metallic/non-metallic minerals. Then, we investigated the relationship between electrical and petrophysical properties. The results showed that the chargeability has no relationship with CEC and is a complete representation of the metallic minerals’ polarization. The normalized chargeability depends linearly on the quadrature conductivity and is affected by the metallic minerals besides CEC. The content and type of clay/mica minerals control the CEC. Hence, the normalized chargeability is influenced by the metallic and non-metallic polarizable components. The conductivity linearly relates to metallic minerals’ content and, in vein mineralizations, has higher values than disseminated ones. Ultimately, comparing our samples’ IP response with Revil et al.’s and Pelton et al.’s models for chargeability, metallic minerals volume content, and time constant determined that increasing the metallic minerals makes the chargeability decrease and the time constant increase. So, in high-grade porous media or non-dispersive formations, chargeability is a function of the metallic minerals’ volume content and the time constant. Complex media like our samples are expected in geological environments. Hence, recognizing the parameters affecting IP response in these media helps to better understand their properties and, in general, IP response characteristics.

Keywords

• black shales
• chargeability
• time constant
• high-grade sulfides