Rare earth elements, or REE, are used in modern society in televisions, computers, cellphones, military equipment, and smart weapons systems. These metals are also used by the medical industry in magnetic resonance imaging and in medical products.
The igneous rocks in the Western Kentucky Fluorspar District of the New Madrid Rift System are considered alkaline ultramafic rocks that are slightly enriched in REE. These rocks are rare and only occur in several hundred locations in the world. They have a complex history of emplacement, fractionation, metasomatism, and alteration, and are overprinted with Mississippi Valley-type mineralization. They are classified as lamprophyres and peridotites, and the rare mineralogy of the district suggests that there may be other facies of these rocks, such as carbonatite, kimberlite, and lamproite. The rare minerals wüstite and moissanite also suggest a deep lithospheric and asthenospheric mantle contribution to these igneous rocks and raise the level of interest in the igneous complex, which occurs in a Midcontinent rift system.
The petrogenesis of these rocks allows them to fractionate and concentrate REE by natural means, and although this study’s limited dataset did not reveal any economic deposits, there could still be economic quantities in western Kentucky. If higher concentrations of REE are found in the igneous dikes in the area, the economics and mining of the dikes might be feasible. Millions of tons of fluorite and thousands of tons of sphalerite, galena, and barite have been mined in the district, and small amounts of REE have been detected in the fluorite. Other elements of interest are titanium, niobium, iridium, cobalt, molybdenum, zirconium, and lithium, which suggest other elemental phases of mineralization. Many of these rare minerals and elements have never been described in the Western Kentucky Fluorspar District, and future research is warranted to further classify them.
Report of Investigations 8
Digital Object Identifier (DOI)
Anderson, Warren H., "Mineralogy and Chemistry of Rare Earth Elements in Alkaline Ultramafic Rocks and Fluorite in the Western Kentucky Fluorspar District" (2019). Kentucky Geological Survey Report of Investigations. 55.