THE MINERALOGICAL CONTROLS ON RARE EARTH ELEMENT ENRICHMENT AND DISTRIBUTION AT FRANKLIN AND STERLING HILL, NJ

Rare earth elements (REEs) are crucial in everyday products like computers, automobiles, and handheld devices and will be in even higher demand as we transition to renewable energy sources. However, we are experiencing global shortages of REEs. As such, quantifying how REEs may substitute at the trace level (<1000 ppm or <0.1 wt%) and in which minerals will provide a framework for exploration of low concentration deposits, establish more efficient extraction techniques during mining, and help sustain our growing dependence on critical elements. This study identifies key minerals within the Sterling Hill deposit in Franklin, New Jersey, with trace level REE substitution to better understand mineralogical controls on the partitioning of critical elements.

The mineral diversity at Sterling Hill, which includes more than 365 unique mineral species, provides an ideal location to evaluate mineralogical and crystal chemical controls and how they may dictate REE partitioning. Here, we observe silicate and carbonate mineral groups, which contain large, 8- or 12-fold, coordinated cations such as calcium and potassium, were more likely to contain higher concentrations of light REEs (9 of 18 and 5 of 6 with light REEs > 10ppm, respectively) than other mineral groups examined. Minerals that exclusively contained elevated concentrations of heavy REEs included franklinite, willemite, zincite, tephroite, and sussexite. These preliminary data demonstrate mineralogical controls may strongly influence REE behavior in more common geologic environments, particularly for trace level substitution. As REE dependance continues to grow, secondary, trace-level REE resources may become more critical to meeting demand and, as such, crucial to further exploration and extraction.