Genesis of the Linghu Au deposit in Xiaoqinling Region, Henan province, China: Constraints from fluid inclusions and isotope systematics

摘要

The Linghu Au deposit is located within the northeastern part of the Xiaoqinling region in the southern margin of the North China Craton. Field investigations, cross-cutting relationships, and mineral paragenetic associations have identified three stages of hydrothermal activity. To determine the origin and evolution of ore-forming fluids, and better understand genesis of the Linghu Au deposit, we have undertaken a series of studies including fluid inclusion and He-Ar-H-O-S-Pb isotope systematics. Fluid inclusion study indicates that the early stage of gold mineralization was characterized by a high-temperature and low-salinity H2O-CO2-NaCl hydrothermal fluids that have delta D values of - 82.0 to - 78.6 parts per thousand and delta O-18(H2O) values of 5.3 to 6.4 parts per thousand. The intermediate stage of gold mineralization involved moderate temperature H2O-CO2-NaCl hydrothermal fluids with delta D and delta O-18(H2O) values of - 92.7 parts per thousand to - 87.9 parts per thousand and - 1.4 parts per thousand to 0 parts per thousand, respectively. Pyrite samples from this mineralization stage have He-3/He-4 and Ar-40/Ar-36 ratios of 0.26-0.31 Ra and 2834.7-4300.6, respectively. The last mineralization stage involved (low-temperature and low-salinity NaCl-H2O system of hydrothermal fluids with relatively lower delta D values of - 93.1 to - 92.3 parts per thousand and delta O-18(H2O) values of - 5.7 to - 5.2 parts per thousand. Moreover, sulfides in ores yielded delta S-34 values of - 3.6 to 5.9 parts per thousand, with an average of 2.65 parts per thousand. The sulfides have Pb-206/Pb-204 ratios of 17.101-17.804, Pb-207/Pb-204 ratios of 15.438-15.554, and Pb-208/Pb-204 ratios of 37.438-38.654. The results of fluid inclusions and H-O, S-Pb, and He-Ar isotopes indicate that hydrothermal fluids associated with the early stage of mineralization originated from magmatic fluids, with sulfur and lead being derived from both units of the Taihua Group and a Late Triassic magmatic-hydrothermal system. All of these data indicate that the Linghu gold deposit formed as a result of magmatic-hydrothermal mineralizing processes.