Geochronology of Potoumian Cu polymetallic deposit in Yangchun basin, zircon trace element and geological implications

The Potoumian Cu polymetallic deposit, located in Yangchun basin of Yunkai area, is a skarn deposit related to medium - to fine-grained granodiorite. The ore bodies mainly occurred as lamellar, stratiods and lenses in shape, controlled by NE and NNE- striking faults. In this study, we present detailed geologic characteristics of the deposit and carried out chronological studies of LA-ICP- MS zircon U-Pb ages for the ore-bearing granitoids and molybdenite Re-Os ages for the Potoumian deposit. Zircon U-Pb analyses yields an age of 163. 5 ± 0. 55Ma for the medium- to fine-grained granodiorite. Precise Re-Os dating of molybdenite shows that the Re-Os model ages of four samples range from 162. 9Ma to 163. 9Ma, with a weighted mean age of 163. 3 ± 1. IMa. These dating results suggest that the timing for the granodiorite and Cu polymetallic mineralization are simultaneously formed in the late stages of the Middle Jurassic, which is firstly reported in the Yangchun basin. The rhenium content of molybdenite samples are in the range of 30. 5×10-6 ~41. 7×10-6, implying that Cu and Mo were derived from the crust-mantle mixed source. The CeIV/III values of zircons in the granodiorite from the Potoumian Cu polymetallic deposit are from 198 to 987, which suggest that its magma has a high oxygen fugacity and good metallogenic potential. The forming temperature of the granodiorite calculated by zircon Ti thermometer are from 597°C to 782°C, indicating that its magma is probably closely related to a subducted environment. These results, together with geological records in South China, suggest that the formation of the Potoumian deposit is corresponding to the period of the large-scale mineralization in the Middle-Late Jurassic of South China. This highlights potential for discovery of additional deposits and extends the favorable interval for exploration for porphyry-skarn Cu polymetallic deposits around 170 ~ 150Ma in the Yangchun basin, and also provides new information for further discussing on the geodynamic settings of the Qin-Hang metallogenic belt. © 2018 Yanshi Xuebao/Acta Petrologica Sinica.All Rights Reserved.