Mineral chemistry and U-Th-Pb geochronology of critical mineral-enriched breccia samples from Hicks Dome, southern Illinois

Mineralized breccias at Hicks Dome, Illinois host abundant fluorspar, Pb-Zn sulfides, barite, rare earth elements (REE), and high field strength elements (HFSE). The REE+HFSE mineralogy of breccias between 600 and 900 meters were examined and mineral compositions were determined by electron probe microanalysis (EPMA), using a JEOL 8530F Plus field emission electron microprobe at the U.S. Geological Survey (USGS), Denver Microbeam Laboratory. The U-Th-Pb isotopic compositions and trace element concentrations of apatite were measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at the USGS-LTRACE laboratory in Denver, Colorado.