APPLICATION OF THE MINERAL SYSTEMS APPROACH FOR SUSTAINABLE CRITICAL MINERAL EXPLORATION AND RESEARCH IN KENTUCKY

A challenge of the energy transition away from fossil fuels is the limited supply of critical minerals needed for advanced technology that cannot be fulfilled by recycling alone. Part of this challenge is the very low probability of success for finding economic mineral deposits. A key to sustainable mineral exploration is the application of the holistic mineral systems approach, which improves our understanding of the processes that lead to the formation of economically viable deposits, thus increasing the probability of success. The U.S. Geological Survey has developed a mineral system framework for the country, which forms the basis of the critical mineral research at the Kentucky Geological Survey (KGS). Initial goals are to identify and characterize the components of each mineral system that has the potential to host critical minerals in Kentucky.

Of particular interest are areas with multiple types of deposits that formed as a result of overlapping mineral systems. For example, the mineralized areas of the Illinois–Kentucky Fluorspar District have been classified into at least three mineral systems: magmatic REE (rare earth element-bearing igneous dikes), basin brine path (Mississippi Valley-type lead, zinc, and low-REE fluorspar deposits), and hybrid magmatic REE/basin brine path (high-REE fluorspar). Tectonic reactivation of Precambrian-aged basement faults of the Reelfoot rift–Rough Creek Graben system, preceding the break-up of Pangea, likely was the driving force that resulted in magma emplacement, and changes in the regional geothermal gradient and topography. These, in turn, probably resulted in magmatic or magmatic–hydrothermal systems, as well as a terrestrial hydrothermal (non-magmatic basinal fluids) system. The magmas and geologic successions, which interacted with the magmatic and non-magmatic fluids, served as ligand and metal sources. The ligands and metals were then transported by these fluids to the site of deposition, typically in Mississippian carbonates. Here the minerals were trapped (precipitated) due to chemical and physical changes, such as change in temperature and pressure, pH and redox, mixing of fluids with different chemistries, etc. Understanding the details of these factors and processes is the subject of on-going research at KGS and elsewhere.