Abstract: The northern margin of the North China Craton is one of the prospective belts for critical metal mineralization, where rare-rare earth element (REE) deposits share similar metallogenic backgrounds but exhibit diverse mineralization styles. Among them, the Yushugou Nb-Ta-REE deposit is a typical alkaline rock/alkaline granite-type rare-REE deposit in this region. The ore bodies are primarily hosted within quartz syenite intrusions, occurring as layered or vein-like structures, with ore minerals dominated by columbite-tantalite and fergusonite, accompanied by bastnäsite. The wall-rock alteration is weak and shows a gradual transition with the ore bodies. For the first time, this study employs SHRIMP U-Pb zircon dating to precisely constrain the U-Pb age of the metallogenic intrusion at 1724.1 ± 7.1 Ma (Middle Proterozoic, Sibao Orogeny). Rock geochemical characteristics indicate that the quartz syenite belongs to the peraluminous, alkaline-calc-alkaline, tholeiitic series. It exhibits a right-sloping V-shaped REE pattern with LREE enrichment, weak negative Eu anomalies, slight positive Ce anomalies, and a pronounced tetrad effect, negative εNd(t) values and relatively old Nd isotope second-stage model ages, indicating that the ore-forming materials were derived from a mixed source of lower crust and depleted mantle, with the metallogenic process controlled by highly evolved magma melt-fluid interactions. In summary, the Yushugou deposit formed during the Sibao period in a tectonic setting transitioning from continental rifting to a passive continental margin. The mineralization process was associated with lithospheric underplating and delamination triggered by upwelling asthenosphere, which not only modified the syenite crystalline basement through mantle-derived magmatism but also facilitated the enrichment of Nb, Ta, and REE elements, leading to large-scale polymetallic mineralization. This study highlights that crust-mantle interaction in rift-related extensional settings is a critical indicator for exploring highly evolved alkaline magma-related rare-REE deposits.