Zircon U-Pb ages and Hf isotopic characteristics of mineralized porphyries in the Mordaoga area,northern-central Da Hinggan Mountains,and their metallogenic significance

Granitoids are developed in Mordaoga area of Eerguna block,northern-central Da Hinggan Mountains.On the basis of granite batholith,the Taipingchuan porphyry Mo-Cu deposit was discovered.Metallogenic host rocks are granite porphyry,granodiorite porphyry and granodiorite,which are characterized by high-K calc-alkalic series,adakite magmatic affinity and slightly negative anomalies of Eu.In order to study the ages and sources of the mineralized porphyry and the relationship between the intrusive body and the Taipingchuan porphyry Mo-Cu deposit,zircon this paper reports U-Pb ages and Hf isotope characteristics of granite porphyry and granodiorite porphyry related to the porphyry molybdenite deposit.LA-ICP-MS zircon U-Pb dating results reveal that the Taipingchuan mineralized porphyries have ages of 183.6 Ma,193.7 Ma and 199.1 Ma,suggesting that granitoids were formed in early Jurassic and might stand for magmatic intrusion activities related to the closure of Mongolia-Okhotsk Ocean.Zircon Hf isotope characteristics indicate that three mineralized porphyry samples have zircon eHf(t)values ranging from-3.2 to 0.4,-3.1 to 1.8 and-3.7 to-1.1,with model ages of 1 322 Ma,1 276 Ma and 1 394 Ma respectively,implying that magma originated from the crustal growth and accretion of Meso-Neoproterozoic.Combined with previous zircon Hf isotope data obtained from Eerguna block,the authors hold that crustal growth and accretion took place in Meso-Neoproterozoic,and partial melting occurred in early Jurassic and resulted in the formation of granitic magma and mineralization in Eerguna block.The Taipingchuan mineralized porphyries are comparable with Wunugetushan porphyry in that they have similar tectonic setting,geochemical characteristics and ages of the host porphyry.It is thus inferred that the ore-forming age of the Taipingchuan porphyry molybdenite deposit should be 195 to 180 Ma.