AN INVESTIGATION OF REE MINERAL POTENTIAL WITHIN EXPLORATORY CORE SAMPLES FROM THE SOUTHEASTERN MISSOURI IRON METALLOGENIC PROVINCE

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 in southeastern Missouri are of particular interest because known reserves of REE-bearing minerals exist in the Pea Ridge iron ore deposits. Other igneous-hosted iron deposits in the area surrounding the Pea Ridge mine may also be potential sources of these minerals.

This research focuses on the mineralogy, petrology, and geochemistry of ten core samples obtained from three exploration wells located within 15 - 30 km of the Pea Ridge iron ore mine. To better understand the relationship of these samples to the Pea Ridge REE deposits, these cores were analyzed for potential REE minerals using polarized-light microscopy (PLM), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS).

Preliminary PLM and SEM/EDS investigations indicate that the Precambrian basement consists primarily of porphyritic rhyolite containing quartz and plagioclase with minor biotite and hornblende. Euhedral to subhedral magnetite and Fe-Ti oxides are abundant in the core samples, comprising 50–75% of the mineral assemblage. Primary phenocrysts of plagioclase (~1 cm) show pervasive sericitization and saussuritization. The presence of secondary phases such as chlorite, actinolite, epidote, calcite, titanite, allanite, and quartz indicate greenschist facies alteration conditions. These secondary mineral phases are observed forming veins, filling fractures, and located within altered plagioclase phenocrysts. SEM/EDS analyses confirm the presence of REE-bearing phases such as epidote, allanite, titanite, and apatite. Although the REE-bearing phases are not abundant in these cores, these findings still highlight the region's potential as a domestic source of critical minerals, contributing to sustainable resource development in the United States.