Determination of precious metals in rocks and ores by microwave plasma-atomic emission spectrometry for geochemical prospecting studies

Methods were designed and developed for the quantitative determination of Au, Ag, Pt and Pd in several rock and ore reference samples by a new analytical technique, microwave plasma-atomic emission spectrometry (MP-AES). Two-gram samples dissolved in 100 ml using aqua regia digestion was directly used without any separation or a pre-concentration step for the determination of Au and Ag. On the other hand, NiS fire-assay technique followed by tellurium co-precipitation separation and pre-concentration step was adopted on 5 g samples to separate Pt and Pd from rock matrix for the determination of these two elements. Detection limits obtained are in the 0.5–5 ng/ml range for all these metals. MP-AES detection limits were compared with those of other well-established techniques, such as F-AAS, GF-AAS, INAA, ICP-AES and ICP-MS. The results obtained for Au, Ag, Pt and Pd were compared with those obtained by well-established analytical techniques such as F-AAS and ICP-MS. Precision and accuracy of the methods were demonstrated using replicate analyses of some international precious metal ore reference materials. Precisions of