On the prospects of identifying rare and rare earth metals in the black shale sequence of the Eastern segment of the Greater Caucasus

The expansion, updating, and comprehensive utilization of the mineral resource base for rare and rare-earth metals necessitate the search for and development of new deposits of non-traditional genetic types, including those localized within black shale formations. This study examines the distribution of rare and rare-earth elements (REE) in the black shale formation of the Eastern segment of the Greater Caucasus, where extensive research and exploratory drilling have led to the discovery of several deposits and occurrences of non-ferrous metals. The results of geochemical and mineralogical investigations reveal a high concentration of rare and rare-earth elements (REE) and other metals within the black shale formation. All lithological types of rocks constituting the black shale formation, as well as rocks from the near-deformation and hydrothermally metasomatized zones, were tested for this study. Comparative studies of the behavior of rare and rare-earth elements across various rock types indicated significant variations in their elemental spectrum and concentrations. Notably, elevated concentrations of rare-earth elements were observed in clay-rich rocks, attributed to the sorptive capacity of clay minerals. Analysis of the distribution of microelements in the rocks and main minerals of the black shale formation highlighted a considerable presence of rare, rare-earth, and other elements, with concentrations exceeding their Clarke values by several times. Distinct anomalous zones were identified for Au, Mo, Cs, La, Ce, Nd, Sm, and U, while anomalous zones were noted for Cd, Se, Hf, Yb, Lu, Eu, Tb, and Th. The geochemical characteristics related to the concentration of these elements were also determined. The findings indicate that the unique properties of graphitized clay shales and accessory minerals within the formation significantly influence the processes of concentration of rare and rare-earth elements, serving as sources of associated metals. This study further analyzes the geochemical and mineralogical characteristics of the black shale formation and delineates zones of mobilization and concentration for rare, rare-earth, and other elements.