Fire Assay and Digestion Strategies for Platinum‐Group Elements, Rhenium and Gold in Geological Materials: A Review of Matrix‐Dependent Workflows and Os Isotope Applications

Determination of platinum‐group elements (PGE), rhenium (Re) and gold (Au) in geological materials remains analytically demanding because of their low mass fractions, heterogeneous distribution and occurrence in refractory mineral phases. This review evaluates fire assay and digestion‐based strategies for Pt, Pd, Rh, Ir, Ru, Os, Re and Au, with emphasis on matrix‐dependent workflow selection and laboratory implementation. Fire assay is advantageous when larger test portions are required to reduce subsampling uncertainty, whereas Carius tube and high‐pressure asher digestion can provide lower procedural blanks and compatibility with isotope dilution and Re‐Os measurement. HF‐assisted digestion and alkaline fusion may be necessary for silicate‐bound or chromite‐hosted refractory phases. The review examines collector systems, post‐fusion dissolution, coprecipitation, chromatographic purification, Os separation, ICP‐MS/MS interference control and emerging fire assay‐LA‐ICP‐MS approaches. No single workflow is universally superior: performance depends on analyte suite, mineralogy, test portion mass, procedural blank, decomposition efficiency, recovery, instrumental interferences and intended data use. Accordingly, practical selection criteria are proposed for routine PGE‐Au determination, expanded PGE‐Re‐Au determination, Re‐Os applications, Os isotope ratio measurement and refractory geological materials. Validation requirements – including blank assessment, recovery, bias, precision, detection capability and measurement uncertainty – are integrated into the proposed workflow framework.