Comparison of LAM-ICP-MS and micro-pixe results for palladium and rhodium in selected samples of Noril'sk and talnakh sulfides

Comparisons of PGE measurements by laser-ablation microprobe (LAM-ICP-MS) with micro-PIXE analyses on the same sulfide grains were made in order to assess data quality. Pyrrhotite, pentlandite and chalcopyrite from a few samples of disseminated ores of the Noril'sk I intrusion and massive ore from the Talnakh deposit, Russia, were analyzed for Pd and Rh by micro-PIXE and for all PGE by LAM-ICP-MS. Micro-PIXE analyses employed focused proton beams of 8 × 15 μm for grains in heavy-mineral separates and 15 × 20 μm for grains in hand samples. These represent analyzed volumes of about 2.350 μm³ in pyrrhotite and 5,900 μm³ for Pd in pentlandite. LAM analyses were performed with a focused, 266-nm laser beam fired at 0.3 mJ/pulse and 10 Hz, resulting in 35-40 μm spots and analyzed volumes of about 85,000 μm³. Fused pyrrhotite standards separately doped with Pd, Ru, and Rh were synthesized for LAM-ICP-MS, and calibrated against sintered pyrrhotite PGE standards of Ballhaus & Sylvester (2000). The level of Pd, Ru and Rh varies by -4 to 9% (1σ) in the fused pyrrhotite standards at a 50-μm sampling scale. The LAM and micro-PIXE results for the natural sulfides are quite comparable, with the large majority of determinations falling within 33% of each other for both Pd and Rh on the same spot. This agreement is considered encouraging for use of the LAM-ICP-MS for trace PGE analysis, considering the large differences in volumes analyzed, and in probable trace-element heterogeneity in the grains and standards. The reasonable concordance of most Pd and Rh results by LAM-ICP-MS and micro-PIXE indicates the potential of the LAM-ICP-MS technique. LAM analyses of the natural sulfides for Pt, Ir and Os were made using the standards of Ballhaus & Sylvester (2000). Platinum is more enriched in pentlandite (n = 10) than in pyrrhotite (3.2 ± 1.2 versus 0.73 ± 0.60 ppm) from Noril'sk (MP6-97), but Ir (0.94 ± 0.32 versus 1.38 ± 0.13 ppm) is only slightly higher in pyrrhotite (n = 10), whereas Os (-0.5 ppm) is comparably enriched in both minerals. Noril'sk chalcopyrite contains trivial amounts of all PGE except Pd (6.6-15 ppm).