113-3 Geochronologic and Microanalytical Characterization of REE Minerals within Exploratory Core Samples from the Southeastern Missouri Iron Metallogenic Province

Session: Mineralogical Characterization of Economic Resources: From Critical Minerals to Gemstones (Posters)

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Abstract:

With the increasing demand for Rare Earth Elements (REEs) and critical minerals due to their vital role in emerging technologies, the search for domestic deposits has intensified. The St. Francois Mountains (SFM) of southeastern Missouri contain Mesoproterozoic igneous rocks that host iron oxide-apatite (IOA) and iron oxide-copper ± gold ± cobalt (IOCG) mineral deposits. The Pea Ridge mine is of particular importance because of its IOA deposits and REE-bearing minerals.

This research focuses on the mineralogy, petrology, and geochemistry of ten core samples obtained from three exploration wells collected near the Pea Ridge mine. To better understand the relationship of these samples to the Pea Ridge REE deposits, these cores were analyzed using polarized-light microscopy (PLM), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). 

PLM and SEM/EDS investigations indicate that the core samples are porphyritic rhyolite, containing quartz and plagioclase with minor biotite and hornblende. Euhedral to subhedral magnetite are abundant, comprising ~50–75% of the mineral assemblage. Evidence of greenschist facies hydrothermal alteration is indicated by secondary minerals such as chlorite, actinolite, epidote, titanite, and allanite, with titanite forming reaction rims around magnetite. SEM/EDS analyses confirm the presence of REE-bearing phases, including epidote, allanite, titanite, and apatite. LA-ICP-MS analyses of epidote and allanite reveal steep LREE patterns with LREE concentrations ranging from 10,000 - 100,000x chondrite. Titanite REE patterns are relatively flat, but contain LREE >1,000x chondrite. U-Pb titanite geochronology yields a mean age of 1470 ± 24 Ma, which is identical to U-Pb zircon ages from the REE-bearing breccia pipe in the Pea Ridge mine. These findings support the interpretation that hydrothermally altered rocks near the Pea Ridge deposit possess substantial REE potential, reinforcing the southeastern Missouri region as a promising domestic source of critical minerals essential for sustainable resource development in the United States.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5610

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