Determination of the precious metals in milligram samples of sulfides and oxides using inductively coupled plasma mass spectrometry after ion exchange preconcentration

A method for the quantitative separation of six precious metals (Ru, Rh, Pd, Ir, Pt and Au) from large amounts of transition elements (especially Fe, Ni, Cu and Zn) in dilute hydrochloric acid solutions using a strongly acidic cation exchange resin, Amberlite CG-120, is described. The method has been applied to the determination of precious metals in small amounts (2-20 mg) of high purity sulfide and oxide mineral separates using inductively coupled plasma mass spectrometry (ICP-MS). Solid limits of detection for a 20 mg sample are less than 4 ng g ^-1 for Ru, Rh, Ir, Pt, and Au, and 29 ng g - 1 for Pd. Precision and accuracy are demonstrated by replicate analyses of sub-samples of a nickel sulfide fire assay bead of the reference material, SARM-7, which show good agreement with certified values and relative standard deviations of less than 8%. Poorer precision and accuracy was obtained for Au because of heterogeneity and inefficient collection in the nickel sulfide bead. Analyses of sulfide and magnetite minerals from Sudbury, Canada, copper-nickel sulphide ores demonstrate the method's usefulness in studying the genesis of precious metal ore deposits.