Zircon U-Pb dating shows that tonalites in the Xiaoxinancha Au-Cu ore deposit from NE China were formed at (112±1) Ma. Different from adakitic magmas that were produced through partial melting of subducted oceanic slab and/or through crustal assimilation and fractional crystallization (AFC) of basaltic magma, the tonalitic magmas are interpreted as melts derived from partial melting of underplated basaltic crust. The moderate Sr/Y ratios (23～76) and weak HREE fractionation(e.g., (Dy/Yb) CN = 1.1～1.4) suggest that magma derived from the transition of garnet amphibole to amphibole residual phases. The ⁴⁰Ar- ³⁹Ar age of (110.1±1.5) Ma for separated hornblende from Au-Cu mineralization associated with Late-Paleozoic high-Mg diorites is consistent with the zircon U-Pb age of the tonalites, indicating that the regional Au-Cu mineralization was genetically related to the Early Cretaceous magmatism.