Determination of gold and the platinum group elements in geological samples by ICP-MS after nickel sulphide fire assay: difficulties encountered with different types of geological samples.

Problems involved in the determination of Au and the platinum group elements by the nickel sulphide fire assay (NiS-FA) procedure for black shale samples, samples containing magnetite, and samples containing As, Cu, and Fe were studied. The interference of the graphite in black shale samples was eliminated either by roasting the sample prior to fusion or by adding an oxidant to the fusion flux. Addition of a reducing agent to samples, containing the oxygen-rich mineral magnetite, enabled the NiS-FA procedure to be carried out for this sample type. The interference of Cu on Rh in the ICP-MS determination was corrected by establishing a linear correlation between the interference of Cu on (103)Rh and (105)Pd.