Geophysical Multimethod Joint Analysis for Assessing Multi-Layer Covers on Mine Tailings at Two Different Scales

Mine tailings storage is a major challenge for the mining industry due to the risks associated with contaminated mine drainage. Tailings can contain sulfides that, when exposed to atmospheric oxygen and precipitation, generate acidity that can spread downstream from tailings storage facilities. To mitigate this issue, the construction of multi-layer cover systems designed to divert infiltrating water from the tailings represents a promising solution. However, such cover systems are susceptible to deteriorate over time, and their effectiveness must therefore be regularly assessed.

Unlike traditional destructive methods, non-invasive geophysical techniques offer a rapid and cost-effective solution for analysing these cover systems. However, each geophysical technique has its own limitations when used individually. In particular, the ERT-IP (Electrical Resistivity Tomography and Induced Polarization) and MASW (Multi-channel Analysis of Surface Waves) methods can be used to characterize the volumetric properties of soils, such as variations in electrical resistivity and seismic velocities, but often lack the precision to delineate fine interfaces clearly. GPR (Ground Penetrating Radar) and seismic refraction, on the other hand, offer a better resolution for identifying the boundaries between layers but have difficulty in accurately describing the physical properties in volume.

This project aims to demonstrate the potential of a multimethod approach that combines these techniques by jointly analyzing the results to leverage their respective advantages while overcoming individual limitations and biases. Ultimately, the goal is to develop a joint inversion methodology to further refine the imaging of multi-layer cover systems, which are generally shallow and are made from a large range of materials.

This study presents the results from a field campaign conducted on a tailings storage facility where inclined multi-layer cover systems have been constructed to limit water infiltration (~1 m thick). Two longitudinal profiles were analyzed at two different scales. A high-resolution profile (32 m-long, 7% slope), with 64 collocated geophones and electrodes spaced by 50 cm intervals was used to focus on fine-scale variations in the cover layer system. Measurements were taken before, during, and after an infiltration test. A longer profile (100 m-long), with 64 collocated geophones and electrodes spaced by 1 m covered two instrumented sections (a 7% slope and a 28% slope) to provide a larger-scale view and greater depth of investigation. The ERT-IP data (collected using the Wenner protocol) and seismic data were coupled with GPR profiles conducted in continuous mode using 200 MHz and 1500 MHz antennas. All geophysical datasets were surveyed to allow comparison between techniques.

The results are interpreted jointly, in order to exploit the interface detection capabilities of GPR and refraction techniques along with the volumetric characterization provided by ERT and MASW at two different scales, which could improve the applicability of geophysical methods to assess the in situ performance of multi-layer cover systems installed on tailings storage facilities across larger scales.