Abstract
The Okcheon metamorphic belt in South Korea has gained significant attention due to the widespread occurrence of black slates enriched in uranium and vanadium. This study aims to investigate the origin of black slate in the Boeun region by petrographic features and chemical properties. Based on the mineralogical composition and organic carbon concentration, the black slate was subdivided into coaly slates. Within these coaly slates, the sulfide veins contain diverse sulfide species resulting from the mixing of magmatic hydrothermal fluids and seawater. Additionally, these veins have undergone hydrothermal alteration. Moreover, noteworthy concentrations of uranium (average: 66 ppm) and vanadium (average: 0.9%) was detected within the coaly slate. The formation of dominant uranium minerals, such as uraninite, is associated with quartz, sulfides, phosphate minerals (e.g., xenotime, monazite, apatite), coal material, and muscovite. Uranium accumulation exhibits positive correlations with total sulfur (TS), phosphorus pentoxide (P2O5, total organic carbon (TOC), and total iron (Fe2O3) contents. Moreover, they are genetically associated with redox-sensitive elements such as Mo, V, Zn, Ni, Co, and Cu. In the case of muscovite within the coaly slate is considered a primary source of vanadium (average: 1.6%) and displays positive correlations with total nitrogen (TN), aluminum oxide (Al2O3), gallium (Ga), niobium (Nb), zirconium (Zr), chromium (Cr), and rare earth elements (REE) contents. The isotopic signatures of carbon, nitrogen, sulfur, and iron in the study area suggest that the accumulation of uranium and vanadium in the coaly slate was facilitated within a submarine hydrothermal environment.
