SOURCE-TO-SINK ASSESSMENT AND PROVENANCE OF POTENTIAL PLACER MONAZITE CRITICAL MINERAL RESOURCES IN THE SOUTHEASTERN BLUE RIDGE, PIEDMONT, AND COASTAL PLAIN PROVINCES

Monazite (Mnz) is the most widespread REE-bearing mineral in the crust, forming in magmatic (primarily S-type granites), metamorphic (primarily metapelites across the full range of grades), and sedimentary diagenetic systems. Our prior work demonstrated the utility of detrital Mnz as a sedimentary provenance proxy and as a complement to detrital zircon in provenance analysis. Here we examine (1) Mnz fertility and age distributions of southern Appalachian crystalline basement lithologies, and (2) U-Pb ages of detrital Mnz in modern and ancient fluvial systems to evaluate the origin of placer monazite deposits long recognized as potential REE mineral deposits in the southeast. Mnz in metapelites of the Blue Ridge and Inner Piedmont is abundant at middle to high grade as revealed by full-section Ce X-ray maps. In situ ages of Mnz in the Blue Ridge and Inner Piedmont are exclusively 460-440 Ma (Taconian). East of the Brevard Fault Zone into the Piedmont, Mnz ages in bedrock are younger at 360-320 Ma (Neo-Acadian and Alleghanian). Mnz is abundant in heavy-mineral concentrates (HMC) of first-order streams draining peraluminous granites, metapelites, and Bt-gneisses of the Piedmont, along with variable ilmenite, zircon, rutile, garnet, and aluminosilicates. These co-produced minerals are critical to making potential placer Mnz deposits economic. Preliminary Mnz ages in HMC of the Chesnee-Cowpens area (NC-SC border) are 360-320 Ma. Granitic and meta-granitic rocks are also potential Mnz sources (e.g. Pacolet granite: new zircon U-Pb age of 324 + 2 Ma). An expanded dataset for full source-to-sink assessment of Mnz provenance in the Coastal Plain will include Mnz ages from the following: (1) bedrock of the Piedmont province in SC and western NC; (2) fluvial sediments of the Broad River from its sources in NC through the Piedmont to the Fall Line; (3) HMC from first order streams in quadrangles surrounding the Chesnee-Cowpens area and through which the Broad River flows; (4) HMC from the USGS NURE archive for Cretaceous and Paleocene strata just SE of and parallel to the Fall Zone; (5) Holocene coastal sands in SC. LASS-ICP-MS U-Pb dating of Mnz is a high-throughput, high-spatial resolution method that permits building a large-n dataset able to resolve potential age complexities known to characterize metamorphic Mnz.