In-situ Determination of Rare Earth Elements in Scheelite by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry

Rare earth elements (REEs) composition and chondrite-normalized REEs patterns of scheelites can be used as an important basis to determine the genesis of deposits. In-situ determination is more conducive to analysis of ore-forming fluid evolution characteristics in terms of single minerals. REEs compositions in scheelite from auriferous quartz veins in Daping gold deposit were analyzed in-situ by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) coupled with 193 nm ArF excimer GeoLasPro laser ablation system and are reported in this paper. The results show that analysis of scheelite can yield precise and accurate data for REEs by using NIST 610 as the external standard and Ca as the internal standard. The cathode luminescence images show that the crystal composition of scheelite is relatively homogeneous. The experimental results show that they have very similar MREEs-enriched patterns with chondrite-normalized, which have very high ΣREEs(918.00-2094.97 μg/g), obvious positive anomaly of δEu(1.17-1.95), and no anomaly of Ce.However, the content of each element changes within a certain range, which reflects that the REEs distributions are not exactly homogeneous. Comparing the analysis results of in-situ Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry(LA-ICP-MS) and solution nebulization ICP-MS, the accuracy and reliability of the in-situ LA-ICP-MS method is demonstrated for the first time. Based on all the results, routine digestion and ICP-MS analytical method provide the average contents of a bulk sample. By comparison, LA-ICP-MS has the advantages of being a rapid method with high spatial resolution ( < 40 μm) and in-situ analysis, which is more important for scheelites which host an inhomogeneous rare earth elements distribution.