DETERMINATION OF PRECIOUS METALS IN ROCKS BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY USING NICKEL SULFIDE CONCENTRATION - COMPARISON WITH OTHER PRETREATMENT METHODS

The nickel sulfide fire assay followed by inductively coupled plasma mass spectrometry was used to determine the platinum group elements and gold in the certified reference material SARM 7 of felspathic pyroxenite and in the two new reference materials CHR-Pt+ and CHR-Bkg of chromitite. These results and results of reagent blank studies are reported. The nickel sulfide fire assay was also compared with the other commonly used pre-treatment methods, i.e., lead fire assay and aqua regia leach. The comparison was made using the above reference materials and 12 samples from different ore types of the Keivitsa mafic layered intrusion in northern Finland. Various rock types, quartz carbonate rock, hornblendite and peridotite, were selected to study dependence of the results on the type of sample. The highest recoveries, considering all elements, were obtained by nickel sulfide fire assay. However, lead fire assay gave higher values for gold, palladium and platinum for our samples than the nickel sulfide fire assay. The results obtained by aqua regia leach support its use for preliminary ore analysis preceding fire assay for gold, platinum and palladium and for some rock types for rhodium and ruthenium.