Geology, geochemistry and isotopic geochemistry are reported for the subvolcanic rocks from the Ashele Cu-Zn deposit. The rocks are basaltic andesites belonging to low-K tholeiite series, and are characterized by intermediate SiO₂ (51.90%～52.85%), MgO (4.44%～5.08%), Al₂O₃ (14.94%～16.11%), TiO₂ (0.99%～1.03%) values and low K₂O (0.01%～0.27%) content. They have low REE values (ΣREE=38.07×10^-6～41.70×10^-6) and exhibit LREE depletion with LREE/HREE ratio of 0.57～0.61 and (La/Yb)_N ratio of 0.84～0.91, and positive Eu anomaly. The trace elements are characterized by enrichment of Sr, Ba, and Th and depletion of Nb, Ta, Zr and Hf. They show both compositional characteristics of the mid-ocean ridge basalt (MORB) and the island arc basalt (IAB). Relatively high εNd(t) values (+6.9～+7.6) suggest that their primitive magma was possibly generated by partial melting of a metasomatic mantle source modified by the subducted slab-derived fluid rather than by the slab-derived melt. Combined with the tectonic evolution of the southern margin of the Altay, the authors hold that the southern margin of the Altay was in an active continental margin setting during the late Paleozoic, and the Ashele Basin was in an island arc or forearc setting.