Abstract:  Hydrothermal copper mineralization in the Dashihu-Dataizi area of Ji’an area, southern Jilin Province is closely related to the intermediate-acid complexes such as monzonite diorite, diorite porphyrite, monzonite porphyry and syenite granite. In order to determine the lower limit of metallogenic ages and geodynamic background, the lithography, zircon U-Pb isotopic geochronology, geochemistry and zircon Lu-Hf isotope of the medium-acid complex have been studied on the basis of field investigation. The results reveal that monzonite diorite, diorite porphyrite, monzonite porphyry and syenite granite are all products of the Early Cretaceous magmatism, and the zircon U-Pb crystallization ages are (122.7±1.8)(122.0±1.9)(120.1±1.5) and (121.4±1.9) Ma, respectively. The magma emplacement of the mineralized system occurred in the Early Cretaceous (122.7-120.1 Ma), indicating that the mineralization age of the Dashihu-Dataizi copper mineralization area was later than or approximately equal to 120.1 Ma. The geochemical data reveal that they are all enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), relatively depleted in high field strength elements (HFSEs) such as Nb, Ta and Ti, and the Eu anomaly is not obvious. All of them present high potassium calc-alkaline quasi-aluminous rocks, which are the products of different evolutionary sequences of homologous magmas. The results of zircon Lu-Hf isotope analysis shows that εHf(t) values of monzonite diorite range from -7.5 to -5.2 and TDM2 range from 1 647 to 1 500 Ma, and εHf(t) values of syenite granite range from -13.1 to -4.2 and TDM2 range from 2 004 to 1 445 Ma， fLu/Hf ranges from -0.99 to -0.95, indicating that the magma originated from the partial melting of ancient crustal materials in the Mesoproterozoic, during which there was the addition of mantle end-member materials, and the ancient materials were mixed during the ascent and emplacement of the syenogranite magma. Combined with relevant research results, it is concluded that the Early Cretaceous granitic magmatism in the study area was formed in the extensional environment formed by the subduction and roll-back of the Paleo-Pacific plate to Eurasia.

Key words: Dashihu-Dataizi copper mineralization area in Ji’an, zircon U-Pb geochronology, zircon Hf isotope, geochemistry, intermediate-acid complex, petrogenesis, geodynamics