On the Potential of Nuclear Magnetic Resonance for Assessing Water Content and Saturation in Mine Tailings

Nuclear magnetic resonance (NMR) exploits the interaction between atomic nuclei and an external magnetic field. Recent advancements in small-diameter probes have expanded NMR applications for shallow subsurface investigations (<100 m); however, existing efforts in tailings engineering remain scarce. This study evaluates NMR’s potential to characterize water content and saturation in mine tailings. Tailings with varying particle size distributions and mineralogies, along with Ottawa sand and kaolinite, were analyzed using two NMR systems with different signal-to-noise ratios and magnetic fields. The study examines the influence of magnetic susceptibility, mineralogy, gradation, echo time, signal-to-noise ratio, and tailings pond water on NMR measurements. NMR-derived water content and saturation estimates were compared against controlled target volumetric and gravimetric measurements. Results indicate that magnetic susceptibility is a key limiting factor: NMR performed well for paramagnetic tailings with low magnetic susceptibility (<1.0 E-3) but poorly for ferromagnetic tailings with high magnetic susceptibility (>1.9E-2). However, low magnetic susceptibility alone does not guarantee reliable performance, as mineralogy and the presence of elements such as iron (Fe) also play a role. Additionally, the results show that shorter echo times and higher signal-to-noise ratios are beneficial. While gradation and tailings pond water primarily influenced NMR decay curves, they had minimal impact on water content estimates for the examined paramagnetic tailings. Finally, the study conducts error propagation evaluations to assess the degree of confidence in estimating volumetric water content and degree of saturation for different scenarios in tailings engineering.