Laser-induced breakdown spectroscopy analysis of palladium in rock ore

An emerging geochemical analytical technique, laser-induced breakdown spectroscopy (LIBS), was applied to determine the concentration of palladium (Pd) in a one-meter-long quarter-core ore sample from the Lac des Îles palladium mine (Ontario, Canada). This paper demonstrates for the first time the analytical applicability of LIBS as a large-scale, high-performance analyzer for assessing the palladium content of ore. Principal component analysis of LIBS spectra shows three main mineralogical phases: a major silicon-rich and moderately iron-rich (5%) phase, a sulfide-rich phase, and a predominantly silicate phase. To calibrate the LIBS instrument, we used three sets of certified reference materials in the form of compressed powders with a quasi-homogeneous concentration of palladium ranging from around one part per million (ppm) to 500 ppm. Pearson correlation between the unknown spectra and the reference material spectra was used to select the appropriate reference material for quantitative Pd analysis for each single laser shot on the core sample. The palladium concentration of the three sides of nine quarter-core solid fragments was determined by LIBS using the Pd line at 348.115 nm and the average Pd concentration was compared to that obtained from the mine laboratory assay results for the remainder of the core. The LIBS analysis highlighted the significant heterogeneity of the palladium distribution on the surface of the ore and revealed that the sulfide-rich zones are particularly rich in palladium.