Geological and geochemical characteristics and prospecting potential of the Daqiao hot spring-type gold deposit in the west Qinling Orogen

摘要

Great breakthroughs have recently been made in discovery of gold deposits in the west Qinling Orogen, which is an important component of the Central China Orogen, the most important gold metallogenic region in China, with numerous developed gold deposits. The Daqiao gold deposit is located in the west Qinling region of the Central China Orogen at the convergence of the Minxian-Dangchang-Liangdang and Zhouqu-Chengxian thrust and nappe tectonic belts. The gold orebodies exist in the silicolites occurring in a funnel shape at the lithologic unconformity between the Triassic lower limestone and argillaceous slate; ore types are dominated by siliceous breccia type, and ores are dominated by brecciated, filmy, crusty, veinlet-mesh vein, and porous structures, with silicification and kaolinization developed widely. The silicolites have Si-30=-0.7-0.4 parts per thousand and O-18=12.8-17.9 parts per thousand; their formation temperature calculated with an oxygen isotope thermometer is 108-182 degrees C. These features indicate characteristics of hot spring-type gold deposits. The S-34 values of the pyrite (from 1.6 parts per thousand to 9.41 parts per thousand in the early period and -11.6 parts per thousand to 9.82 parts per thousand in the late period) and the lead isotope results show that the metallogenic materials were from a mixture of magmas and strata in the early period and from strata in the late period. The zircon SHRIMP U-Pb age of the granodiorite related to mineralization is 230.9 +/- 1.9Ma. A comprehensive study of the Daqiao gold deposit indicates that it is a hot spring-type gold deposit, formed in an intracontinental orogenic environment.