To reveal the deep structure of the granitic-pegmatitic type lithium and other rare metal mineral system, a Magnetotelluric (MT) survey was conducted in the Dahongliutan area of the Western Kunlun. Through 3D resistivity inversion of the MT data, two high-resistivity bodies were detected within the depth range of 0-20 km, reflecting the large-scale felsic magma and the partially concealed eastern granite basement of Dahongliutan. A widespread high-conductivity anomaly observed at depths of 20-80 km reflects the large-scale felsic magma reservoir formed by crustal remelting extending deep into the upper mantle. The mineralization host rocks, the granite basement of Dahongliutan, are shown to be rooted and represent a massive magma reservoir extending deep into the upper mantle, providing the source materials and heat for the formation of the giant Dahongliutan granitic-pegmatitic type lithium deposit. In comparison with the Songpan-Ganzi Jiajika super-large granitic-pegmatitic type lithium deposit, although the exposed granite in Jiajika is limited, the 3D resistivity inversion model of the MT data also reveals a widespread high-conductivity anomaly extending into the upper mantle, indicating the presence of a large-scale felsic magma reservoir. The difference lies in the shallower erosion depth in Jiajika, where the overlying granite intrusion has not been eroded. Therefore, Dahongliutan exhibits a "hot dome" feature with extensive granite outcrops resulting from deep erosional processes, while Jiajika represents a "gneiss dome" feature with the country rocks surrounding the granite subjected to thermal metamorphism. The giant ore belt of rare metal mineralization, including lithium, in Western Kunlun-Songpan-Ganzi, which hosts two super-large deposits of late Triassic age at its ends, is the product of large-scale crustal remelting and felsic magmatism. The saturation of H2O is a key factor in the exceptional enrichment of lithium and other rare metals in the granitic-pegmatitic type lithium deposits. Moreover, the "pre-enrichment" of lithium during different stages of differentiation and evolution in the felsic magma reservoir, intrusive granites, and pegmatites lays an essential foundation for the formation of massive granitic-pegmatitic type lithium deposits.