SYSTEMATIC REE PARTITIONING IN CUBO-DODECAHEDRAL FLUORITE FROM BELGIUM REVEALED BY CATHODOLUMINESCENCE SPECTRAL IMAGING AND LASER ABLATION-ICP-MS

摘要

Geochemistry of the rare earth elements (REE) in fluorite is widely used in ore geology. However, bulk analysis may be biased by compositional heterogeneity in crystals. Here we report a systematic REE partitioning in cubo-dodecahedral fluorite crystals from Belgium using cathodoluminescence (CL) spectral imaging and laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS) analysis. The light REE (LREE) are markedly enriched, and heavy REE (HREE) depleted in the 11101 sector relative to the 11001 sector. The partition coefficient K_(|110|/|100|) is >10 for LREE and <1 for HREE. Very contrasting REE patterns and ratios are thus recorded from the same crystal. CL can be used for imaging compositional heterogeneities since REE are known CL activators in fluorite. However, CL imaging is found of limited application when the REE lines are masked by the strong Eu~(2+) emission. Spectral imaging of other REE lines solved this problem by producing sharp and contrasted compositional images.