Late Triassic magmatic activity in the Daqiao gold deposit of West Qinling belt: Zircon U-Pb chronology and Lu-Hf isotope evidence

The West Qinling area is one of the important gold ore concentration areas in China. The Daqiao gold deposit, located in the middle of the West Qinling area, has become a superlarge deposit with the growing Au reserves. Recent research reveals that the metallogenic process may be associated with magmatic activity in the area. The zircons LA-ICP-MS U-Pb dating results of 4 granodiorite samples collected in the mining area are concentrated mainly at 228Ma and 206Ma, forming two groups obviously and corresponding to the Late Triassic. The corresponding Hf-isotopic compositions of zircons show similar phenomena and can also be divided into two units. The ε_Hf(t) values are from -8 to 0, and the T_DM2 values are from 1300Ma to 1900Ma. It is inferred that the source came from the old crustal rocks of the Paleoproterozoic-Proterozoic period, and most of the ancient lava was derived from remelting process of the old materials, which came from the lower crust, mixed probably with a small amount of mantle components which were involved in diagenetic process. In combination with REE and trace elements researches, the authors hold that there probably existed two phases of magmatic activity in late Indosinian period in the mining area. The Daqiao gold deposit is the product of metallogenic activity caused by regional magmatism in the late Indosinian epoch in West Qinling belt.