Volcanic-hosted Be-(Li-F-REEs-U) mineralization at the world-class Spor Mountain deposit, Utah, USA: Insights into source rocks, geochemical signatures, and macro-to-microscale concentration processes

Beryllium (Be) is among the most important rare metals in the world and is used to produce complex alloys and ceramics critical for the telecommunication, aerospace, medical, and defense industries. Global Be supplies are primarily obtained from bertrandite [Be₄Si₂O₇(OH)₂] mined from the Spor Mountain deposit, Utah, U.S.A, in a region dominated by Miocene-Oligocene alkaline rhyolitic tuffs and lavas. Ore occurs primarily in lithic-rich, phreatomagmatic, base-surge deposits containing carbonate debris in a basal tuff. The tuff is part of a package of rare-metal-rich rhyolite lava flows, pyroclastic deposits, and discordant fluorite-bearing pipes. Pb-Nd-Sr isotope and trace element data, together with mineral associations (1) map the flux of Be, Li, F, REEs, and U in the magmatic-to-hydrothermal system, (2) reveal the role of fluid-rock interactions and recrystallization processes in concentrating metals, and (3) place constraints on timescales of bertrandite-fluorite-opal precipitation. Geochemical models indicate that high-grade ore formed under pH-buffered conditions when F-rich fluids leached metals from glassy tuff, reacted with carbonate xenoliths, and deposited Be and other rare metals in complexly layered nodules composed of Mn-oxide, Li-smectite, calcite, fluorite, opal, and bertrandite. U-Pb age dates and coupled 29-element analyses of discrete opal layers by the SHRIMP-RG method show an almost continuous record of opal deposition. The results establish timescales of high-grade opaline ore formation with major influxes of Be, F, REEs, and Li from ~16 Ma to 10 Ma and of Mn and U at <6 Ma. The interplay of periodic infusions of Be-rich magma, ash, and gas with shallow-circulating, heated fluids led to large-scale remobilization of Be and concentration of high-grade Be ore in the tuff. Fluid-rock interaction and recrystallization had limited effects on other rare elements (Li, REEs) in tuff and rhyolite. These new data shed light on the magnitude of the metallogenic processes and magmatic-to-hydrothermal system required to form a world-class volcanic-hosted beryllium deposit. Additional Be occurrences in Utah, Nevada, New Mexico, and Texas highlight the potential for additional resources of volcanic-related Be and co-product Li-F-REEs in the western United States and globally.