Abstract:The Ganshanebo REE deposit located in the middle sector of the North Qilian orogenic belt is the largest REE deposit in the North Qilian metallogenic belt. The orebodies are mainly hosted within the Early Devonian alkaline complex and the contact zone between the complex and country rocks. In order to confirm the intrusive age, lithogenesis and magma source characteristic of the alkaline complex, this study carried out zircon U- Pb dating, Hf isotopic and petrogeochemical analysis. The results show that the alkaline complex is composed of aegirine syenite, aegirine syenite porphyry, quartz syenitic porphyry and granite porphyry, and intruded into the Maozangsi granitiods. LA- ICPMS U- Pb zircon dating yielded an age of 409.7±5.8Ma, with a εHf(t) range of -0.15~+2.34m (average 1.03) and a tDM2(Hf) range of 1.2~1.1Ga. The major elements of alkaline complex are characterized by rich potassium (Na2O/K2O=0.35~0.85), high alkaline (K2O+Na2O=7.91%~11.09%) and low CaO (2.90% ~ 8.17%) and MgO (0.21%~1.30%), suggesting the complex belongs to potassic alkaline series rocks. High contents of rare earth elements (REE), and enrichment in Large Ion Lithophile Elements (LILE; Rb, Ba, Sr, U, etc), depletion in high field strength elements (HFSE, Nb, Ta and Ti), weak negative Eu anomalies (δEu=0.7~0.8), and LREEenriched, right- inclined REE distribution patterns suggest the geochemical characteristics of A- type rock suites. In combination with the regional geological feature and geodynamic settings, it can concluded that the alkaline complex formed in the post- orogenic tectonic setting and was the product of the intrusion of alkaline complex, which was triggered by the large- scale lithospheric extension starting at early Devonian after the closure of the North Qilian Ocean.