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Abstract

Rare-earth elements and other critical minerals are key components to transition economies towards a greener and more sustainable footprint. In all phases of mining operations (exploration, extraction and ore processing), real-time and stand-off sensors with low detection thresholds have the potential to improve the economic and environmental impact of producing critical minerals. Upgrading ore body modelling as well as realizing sorting and processing efficiencies are two use cases. Laser-ablation dual comb spectroscopy is a broadband technique that uses two mode-locked lasers to measure the absorption spectrum of laser-produced plasmas. It requires minimal sample preparation, has millisecond measurement times, and has the resolution of continuous wave laser based spectroscopies. These properties make it an ideal candidate for real-time sensing in mining workflows, yet its potential in mining remains unexplored. This work describes the construction, characterization, and use of a laser-ablation dual comb spectroscopy system optimized for detecting rare-earth elements in ores. The system was built using two commercial mode-locked lasers whose repetition rates were stabilized with respect to one another for measurement repeatability. The systems measurement spectrum is centered around the second harmonic of the two mode-locked lasers, ranging from 518-532 nm, and its spectral resolution ranges from 1-10 pm. Its ability to detect rare earth elements in mineral matrices was tested by measuring a dilution series of pellets made from calibrated ore powders with traces of CeO₂, La₂O₃, and Sm₂O₃. Limits of detection of Ce, La, and Sm were estimated from the measurements to be 50 ± 1 ppm, 65 ± 0.1 ppm, and 63 ± 0.1 ppm, respectively.