PROGRESS UPDATE ON THE ILLINOIS–KENTUCKY FLUORSPAR DISTRICT EARTH MRI PROJECT

The Kentucky Geological Survey has collaborated with the USGS on the Earth MRI program since 2019 to provide geological data and information on the critical mineral potential of the Illinois–Kentucky Fluorspar District. The District is a historically important production area of fluorspar, barite, and sphalerite, and is permissive for critical minerals, including rare earth elements (REE), germanium, and others. Phase 1 of this project concluded in 2021. Now in Phase 2, the project is focused on the development of a Geographic Information System (GIS)-based three-dimensional (3D) geological framework model of the District with accompanying fully integrated supporting datasets.

Seven stratigraphic surfaces have been incorporated into the 3D model that are adjacent to known or prospective areas of mineralization. These surfaces are the Kinkaid, Fort Payne, Renault, Aux Vases, Ste. Genevieve, St. Louis, and New Albany formations. Previously mapped polyline fault traces were classified and 291 of these were identified as major faults. These were incorporated into the model as 3D fault panels. USGS aeromagnetic survey data were used to define igneous features as polygons based on their magnetic signature. Known non-magnetic dikes were also incorporated. Additional features in the 3D model include boreholes, analyzed samples, and historic mines.

To date, over 50 archived mineral cores have been logged and sampled for geochemical and petrographic analyses. Detailed petrographic description of 130 thin sections confirmed the serpentinized lamprophyre classification of the igneous dikes found in the Kentucky part of the District. Geochemical data on 103 samples indicate that the total REE of the dikes in Kentucky range from 89 to 620 ppm, with an average of 326 ppm. The studied dikes are strongly carbonatized and preliminary data suggest that higher carbonate contents of dikes typically correspond to lower total REE content. Fluid inclusion analysis is currently underway to decipher the potential relationship between carbonate alteration and ore mineralization. Data on two fluorite samples (9 and 23 ppm) confirmed published low REE levels of fluorspar in Kentucky. However, sphalerite in the district may have high levels of germanium as indicated by measured Ge values as high as 1050 ppm.