Comparison between Nickel-Sulfur Fire Assay Te Co-precipitation and Isotope Dilution with High-Pressure Asher Acid Digestion for the Determination of Platinum-Group Elements, Rhenium and Gold

The accurate determination of platinum-group elements (PGE), rhenium and gold is important in both fundamental research and ore deposit studies. Questions have been raised by some authors as to whether the nickel-sulfur fire assay technique (NiS-FA) efficiently collects all the PGE. On the other hand, most isotope dilution (ID) techniques can only treat small test portion masses (2 g was used for high-pressure asher digestion; HPA) and this makes them more vulnerable to nugget effects. We determined PGE concentrations in ten reference materials with the aim of comparing the performance characteristics of the two methods. Both methods determine Ru, Pd, Os, Ir and Pt and we found that there were no significant systematic differences in the recovery. The advantages of NiS-FA were that: (a) it is capable of determining Rh and Au; (b) the relatively large test portion mass (15 g) reduces the nugget effect and (c) it is faster and less expensive than HPA-ID. The advantages of HPA-ID were that: (a) it determined Re and (b) it had low level blanks, lower detection limits and hence better precision in low-level homogeneous samples. Each technique had advantages and limitations; they should be considered as complementary rather than competing techniques.L'analyse quantitative des elements du groupe du platine (EGP), du rhenium et de l'or est importante pour la recherche fondamentale et la prospection. Certains doutes existent concernant l'efficacite de la pyro-analyse par nickel-soufre (PA-NiS) pour quantifier les EGP. D'un autre cote, la plupart des techniques d'analyse par dilution isotopique (DI) ne peuvent qu'analyser de petites masses d'echantillon (2 g pour la digestion haute pression; DHP-DI), les rendant vulnerable a l'effet de pepite. Nous avons quantifie les EGP dans dix materiaux de reference pour comparer les performances de chaque methode. Chaque methode peut quantifier le ruthenium, palladium, osmium, iridium et le platine. Les resultats ne montrent pas de differences significatives. Les avantages de la PA-NiS sont : (a) sa capacite de determiner l'or et le rhodium, (b) la masse d'echantillon plus elevee (15 g) reduisant ' l'effet de pepite ' et (c) sa rapidite et son cout moins eleve. Les avantages de la DHP-ID sont : (a) capacite de determiner le rhenium et (b) blancs plus bas, limites de detection plus basses donc plus de precision pour l'analyse en basses teneurs des materiaux geologiques homogenes. Chaque technique a des avantages et des limites et devraient etre considerees comme complementaires plutot que competitives.