Complex conductivity characteristics of soil samples and reshaped samples from ion-adsorption type REE deposit in South China

This is the authors' abstract. We don't add key points for this paper.

Weathering-crust ion-adsorption deposits in South China are the source of approximately 95% of global mid-heavy rare earth element (REE) supply, where REE predominantly exist as weakly adsorbed ions on clay minerals. Despite advances in ore-forming theory, the exploration and environmental monitoring technologies for REE have progressed slowly. REE adsorption onto clays creates electrical double layers (EDLs), which are a key structure known to generate induced polarization (IP) responses that could be a promising non-invasive method for mapping REE mineralization and enrichment patterns within the weathering crust, as well as for real-time monitoring of in-situ leaching environments. This study integrated spectral induced polarization (SIP) with the physicochemical characteristics of ion-adsorption REE deposits to investigate (i) the complex-conductivity of samples collected from a representative profile, and (ii) reshaped samples prepared under controlled conditions that simulate the critical metallogenic factors. Single-variable experiments on reshaped samples demonstrated that low-frequency polarization was controlled by the soil's adsorbed capacity, whereas increasing the REE concentration enhanced the bulk conductivity. The results of soil samples revealed a layered geoelectric structure, wherein within individual horizons, chargeability scaled linearly with total mass fraction of rare earth oxide (TMFREO). The overall polarization response is produced by a combination of Stern-layer and diffusion-coupling mechanisms. These findings demonstrated that SIP could effectively distinguish horizons with distinct physicochemical properties. For accurate estimation of TMFREO from chargeability, complete water saturation was essential to account for the contribution of diffusion-coupling polarization.