Advances in sulfur species analysis in geological materials: methods, challenges, and future directions

Sulfur has a significant impact on environmental geochemistry, mineral formation, magmatic evolution and biogeochemical cycling, among other geological processes. Accurate identification and quantification of sulfur species in geological materials remain analytically challenging due to their complex mineral matrix, variable oxidation states, and susceptibility to change during sample preparation. This review offers a thorough evaluation of current developments in the investigation of sulfur species in a variety of geological materials, such as rocks, ores, sediments, and fluid inclusions. The strengths, limitations, and analytical performance of several established and emerging techniques, including X-ray Absorption Spectroscopy (XANES/EXAFS), Electron Probe Microanalysis (EPMA), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), Ion Chromatography-High-Performance Liquid Chromatography (IC-HPLC), combustion-based methods, Raman spectroscopy, and synchrotron-based microanalytical tools were assessed. The preservation of oxidation states, detection limits, matrix effects, and method standardization are all given special consideration. To improve accuracy and resolution in sulfur speciation, current trends such as multi-method integration, microscale and nanoscale analytical advancements, and machine learning-assisted data interpretation are explored. Lastly, we highlight important knowledge gaps and suggest future lines of inquiry for improving analytical robustness, creating reference materials, and building high-resolution, non-destructive characterisation procedures. The importance of analytical innovation in advancing our understanding of sulfur behaviour in geological systems and enabling broader applications in geochemical modelling, environmental monitoring, and mineral exploration is highlighted in this review.