Abstract: Some metagabbro bodies intruded into high-grade metamorphic rocks on the southern margin of the Altai Mountains, Xinjiang, were originally considered as Late Paleozoic basaltic intrusions. Study of the Wuqiagou basic rocks exposed in Fuyun County indicates that these basic rocks were derived from partial melting of the upper mantle that had not been subjected to contamination with continental crustal material. The Wuqiagou basic rocks have Nd model ages of 945 and 977Ma and Sm? Juan Nd isochron ages of 974 ± 63.4Ma, which are consistent with each other. It implies a geological event of basaltic magma intrusion into the southern margin of the Altai in the early Neoproterozoic. The Nd model ages of high-grade metamorphic surrounding rocks range between 1435 and 1580Ma, being equivalent to the Mesoproterozoic Changchengian Period, which suggests that the Xemirxek Group formed in the Mesoproterozoic.