Original Investigation into the Petrogenesis and Metallogenic Significance of Rare Earth Element-Bearing Carbonatites in North East Nigeria

Carbonatite complexes are the world's primary source of light rare earth elements, and the discovery of carbonatite occurrences in North East Nigeria has potential significance for the country's critical mineral endowment, yet their petrogenesis and metallogenic characteristics have not been systematically investigated. This dissertation presents an original petrological, geochemical, and isotopic investigation of rare earth element-bearing carbonatite complexes in Adamawa and Taraba states, North East Nigeria. Field mapping, drill core logging, and sampling were conducted at three carbonatite bodies. Whole-rock major and trace element geochemistry, mineral chemistry by electron microprobe and LA-ICP-MS, and isotopic compositions of strontium, neodymium, and carbon-oxygen systems were determined. Geochronological dating was performed using U-Pb on apatite and baddeleyite. Results establish that the North East Nigerian carbonatites were emplaced at approximately 161 million years during rifting of the Benue Trough proto-rift, representing a previously undocumented episode of mantle-derived alkaline magmatism. Rare earth element total concentrations reach 4.8 percent oxide in the most enriched zones, associated with bastnaesite and synchysite mineralisation. Isotopic compositions indicate derivation from an enriched mantle source modified by long-term continental lithospheric residence. The dissertation proposes an original metallogenic model linking North East Nigerian carbonatite emplacement to Trans-Saharan lineaments and redefines the region's potential for rare earth element resources. Keywords: carbonatites, rare earth elements, petrogenesis, North East Nigeria, metallogenesis.