Abstract: Eudialyte is a critical ore mineral enriched in zirconium, niobium, and rare earth elements (Zr-Nb-REE), and often occurs in peralkaline rocks. Its composition records key information from magma genesis, evolution, to hydrothermal activities, providing important insights for evaluating the metallogenic potential of alkaline rocks. The Bashisuhong complex is located in the junction zone between the Northern Tarim Basin and the South Tianshan Orogen, where aegirine-augite syenite dikes host Zr-Nb-REE mineralization. These dikes, exhibiting a gray-black to purplish-red coloration, display irregular contact boundaries with the marble and locally visible plastic flow structures. Wollastonite-rich wall-rock xenoliths are commonly observed within these dikes, indicating material exchange with the marble. The dikes are 0.33–3.71 m wide, extend 30–170 m, and are generally oriented east-west. Gangue minerals primarily consist of perthite, aegirine-augite, and wollastonite, while ore minerals are mainly eudialyte, apatite, and titanite. Eudialyte is predominantly euhedral, with grain sizes ranging from 0.1 to 5 mm, and exhibits well-developed straight oscillatory zoning. Their trace element characteristics are controlled by charge-and-radius-controlled (CHARAC) substitution mechanisms, indicating a typical magmatic origin. Both whole-rock and eudialyte samples exhibit light rare earth element (LREE) enrichment and heavy rare earth element (HREE) depletion, accompanied by significant negative Eu and Sr anomalies, indicating extensive fractional crystallization of plagioclase in the primary magma of the syenite dikes and compositionally similar to alkaline basalt. When alkaline magma intruded into marble, assimilation of the marble introduced substantial CaO components. This assimilation not only supplied critical materials for eudialyte formation but also, through increased CaO content, enhanced Cl solubility and lowered the solidus temperature, thereby facilitating further magma evolution and achieving supernormal enrichment of rare metals. Therefore, the interaction between alkaline magma and marble represents a crucial mechanism for eudialyte mineralization in the junction zone between Northern Tarim Basin and South Tianshan Orogen, making their contact zones promising targets for rare metal exploration.