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Emerging renewable energy technologies and low-carbon transportation rely heavily on the unique optical and magnetic properties of the rare earth elements. The medium to heavy rare earth elements, neodymium to lutetium, are most sought by industry but are the least abundant in nature. Only a small proportion of known rare earth element deposits are enriched in these elements. Identifying additional sources of medium to heavy rare earth elements for resource exploration requires improved understanding of the mechanisms responsible for the formation of such highly fractionated deposits. Here we report the results of experiments demonstrating a mechanism that could lead to enrichment of medium to heavy rare earth elements in ore-forming hydrothermal systems. In our experiments, we simulated natural hydrothermal systems by heating a column containing apatite and fluorite through which we pumped a chloride-rich solution bearing rare earth elements. Analysis of our experiments shows that the fluoride mineral fluocerite can serve as a precursor phase that fractionates rare earth elements before it is subsequently converted to a thermodynamically more stable mineral. Our findings identify geological settings in which fluocerite is observed or predicted to occur as potential exploration targets for deposits enriched in medium to heavy rare earth elements.

Lead poisoning is a preventable condition caused by exposure to environmental sources such as lead-containing dust or lead-painted consumer products. The history of lead poisoning prevention has been defined to some extent by the quality of the analytical methods available for lead measurements whether in environmental samples or biological tissues and fluids. The quality of blood lead methods has improved so greatly over the last three decades that we now know far more about the adverse health effects from low-level exposures. Recent evidence suggests that effects such as deficit in IQ occur below the current (periodically revised) U.S. CDC threshold of 10 μg/dL, such that no safe threshold appears to exist for children. Improvements in analytical techniques have also had an impact on the environmental measurement quality, yet many environmental thresholds have remained unchanged for decades. In light of our current understanding of the adverse health effects at low levels of exposure, new thresholds for lead in children’s products have been introduced by the U.S. CPSC. The adequacy of current analytical techniques to detect lead accurately at the new, lower thresholds is questionable. XRF offers the advantage of being rapid and nondestructive compared to techniques such as AAS that require extensive sample preparation. However, the accuracy of handheld XRF determinations of lead in painted toys is generally limited. A brief comparative study on the performance of several analytical techniques for the determination of lead in toys is presented at the end of this paper.