Geological study and significance of typical gold deposits in eastern Qinzhou-Hangzhou metallogenic belt: Constraint from Tianjingshan gold deposit in south Anhui Province

Abstract

The eastern part of Qinzhou-Hangzhou metallogenic belt, including Jiangxi, Anhui and Zhejiang province, is located in the southeastern Jiangnan Orogen. A large amount of copper‑gold polymetallic deposits are distributed in the belt, represented by Jinshan super-large gold deposit in Jiangxi province, Tianjingshan large gold deposit in Anhui province and Huangshan medium gold deposit in Zhejiang province.The LA-ICP-MS U-Pb zircon dating for Lingshan and Hanjia intrusions of Tianjingshan gold deposit yield 794.7 ± 5.2 Ma and 765.9 ± 3.7 Ma, respectively, indicating they are all formed in the Jinningian. According to the different geochemical characteristics and field features, Hanjia intrusion shouldn't be altered by Lingshan intrusion, and was not formed in Yanshanian. The Ar-Ar analyses of chlorite for gold-bearing mylonite yield a spectrum age of 331.5 ± 3.2 Ma, firstly identifying Hercynian metallogenic event. The sulfur isotopes of pyrites from gold-bearing quartz veins show that the metallogenic fluids are complex, maybe metamorphic fluids mixed with meteoric water or magmatic water. Integrating with previous studies, Tianjingshan orogenic-type gold deposit with multiple stages and large time span of mineralization is formed by the collision-amalgamation of Yangtze block and Cathaysia block, which the Jinningian is the period of initial gold enrichment, and the Hercynian is an important metallogenic period.Based on contrastive analyses, these three typical gold deposits have similar metallogenic process as follows: the gold rich materials are derived from Neoproterozoic strata and Jinningian intrusion; then the ore-bearing metamorphic fluids resulted from regional metamorphism are mixed with meteoric water or magmatic water, and results in ore-bearing fluids enriched in CO2 and depleted in salinity; finally, the gold in the fluids is enriched in the low degree thrusting brittle- ductile shear zone due to the change of temperature, press and other conditions controlled by the fault. Therefore, these typical gold deposits were directly relate to the collision- amalgamation of Yangtze block and Cathaysia block and have a large time span of mineralization, which the altered-rock type gold deposit was formed at the Jinningian while the quartz vein type gold deposit was formed in Hercynian. Comprehensively, Tianjingshan gold deposit has the typical features of orogenic gold deposit. Significantly, the orogenic type gold deposit can provide important guidance and experience on deep and regional mining exploration.