Collaborative Research: GEO-CM: Quantifying the role and composition of mineralizing fluids in carbonatite-hosted rare earth element deposits

Critical minerals are minerals that modern society depends on. Rare earth elements are one group of critical minerals and are used in defense and energy technologies. Today, most rare earth elements are produced outside the United States, which could make U.S. supplies less secure. These deposits are hard to find because they are often small and easy to miss. At Mountain Pass, California, hot fluids helped form a rich rare earth deposit and may have changed nearby minerals in ways that make the deposit easier to find. This project will study those fluids by measuring chemical changes in minerals from Mountain Pass. Researchers will use those changes to estimate what the fluids were like when the deposit formed. The results may help improve the search for valuable rare earth deposits, which will benefit American prosperity and security. Carbonatites host over half of rare earth element (REEs) projects but commonly have minimal surface expression, making exploration expensive and time-consuming. This project will expand exploration to include alteration halos in systems with hydrothermal mineralization. A growing consensus suggests that most high-grade carbonatite REE mineralization is hydrothermal, but there is a scarcity of data on mineralizing fluid compositions in natural systems. This project will examine regional fluid alteration patterns linked to mineralization at the Mountain Pass carbonatite-hosted REE deposit to improve models of ore formation and develop more reliable exploration indicators. Field mapping and petrological studies across the intrusive suite and alteration halo will provide geologic context for the temporal and spatial evolution of the fluids. Mineral assemblages and geochemistry will be integrated with modeling to reconstruct fluid compositions. This integrated workflow can serve as a blueprint for studying other magmatic-hydrothermal systems. Coupling geochemical data from natural systems with experimentally derived thermodynamic properties of fluids provides a framework for integrating natural and experimental geochemistry in a broad range of systems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.