Objective Pegmatite-type Nb−Ta deposits represent a significant deposit type for niobium and tantalum resources. In China, these deposits are primarily developed within Phanerozoic orogenic belts. While important rare-metal pegmatite deposits like the Koktokay No. 3 pegmatite vein occur in the western Central Asian Orogenic Belt (CAOB), such deposits have rarely been reported in the eastern segment of this orogenic belt. The Majiagou deposit in western Liaoning Province, recently discovered along the southeastern margin of the CAOB near its junction with the northern North China Craton, remains poorly constrained in terms of metallogenic age and tectonic setting.

Methods This study presents detailed petrographic, geochronological, and geochemical investigations on the pegmatites from this deposit to elucidate their emplacement age, metallogenic epoch, and petrogenesis.

Results LA-ICP-MS U−Pb dating of columbite-group minerals (CGMs) yields a crystallization age of 263.5±3.2 Ma for the Nb−Ta pegmatites, indicating Middle Permian mineralization during the transitional stage from subduction to syn-collisional tectonics. Geochemical analyses reveal that the Majiagou Nb−Ta pegmatites exhibit characteristic features of high silica, aluminum, and alkali contents with low Ti, Fe, Mg, Ca, and P concentrations, showing peraluminous affinity. They display extremely low total rare earth element contents (ΣREE=4.77×10⁻⁶~15.94×10⁻⁶), relatively constant La_N/Yb_N ratios (2.11~9.70), and variable δEu values (0.51~3.31). The rocks are enriched in large-ion lithophile elements (LILEs: Rb, K, U, Sr) but depleted in high-field-strength elements (HFSEs: Nb, Ta, P, Zr, Ti), with low Nb/Ta ratios (in average 6.81).

Conclusions These characteristics indicate that the magma underwent extensive fractional crystallization, and the pegmatite may have formed from the partial melting of ancient crustal materials. The prolonged and complex orogenic evolution coupled with multi-stage granitic intrusions along the southeastern CAOB margin created favorable geological conditions for generating highly differentiated pegmatitic magmas, highlighting this region's potential for prospecting pegmatite-type Nb−Ta deposits.