Combined fibre-optic sensing and nodal recorders for seismic characterization of mine tailings

As the mining industry shifts toward more responsible and lower-impact practices, mine tailings are increasingly regarded as a secondary resource that can be sourced into society. However, poor knowledge of subsurface geometry at many historical tailings sites leads to uncertainties in volume and resource estimates. High-resolution seismic imaging serves as a tool for improved characterization of such sites. Here, we present the results of a seismic survey conducted in 2024 on tailings at Blötberget in central Sweden. The data were acquired using a combined and partly collocated sparse 3D nodal array, landstreamer and distributed acoustic sensing (DAS) systems. The objective was to characterize the tailings and to optimize the acquisition and processing strategies for our application. Through 2D reflection seismic imaging, layer-based refraction travel time modelling and travel time tomography, we obtained well-constrained P-wave velocities for the tailings on the order of 300-350 m/s. Additional 3D travel time modelling yielded volumetric estimates, from which we estimate a total tailings tonnage of approximately 4 Mt. Finally, we demonstrated that surface DAS can serve as a complementary recording system, capable of delineating the tailings when fibre cable-ground coupling conditions are favourable. The survey serves as a pilot for future mine tailings investigations and related near-surface characterization efforts, and we highlight the benefits of using multi-element seismic recording arrays for such purposes.