Geology and genesis of the Xiaguan Ag-Pb-Zn orefield in Qinling orogen, Henan province, China: Fluid inclusion and isotope constraints

摘要

The Xiaguan Ag-Pb-Zn orefield (Neixiang County, Henan Province), hosting the Yindonggou, Zhouzhuang, Yinhulugou and Laozhuang fault-controlled lode deposits, is situated in the Erlangping Terrane, eastern Qinling Orogen. The quartz-sulfide vein mineralization is dominated by main alteration styles of silicic-, sericite-, carbonate-, chlorite- and sulfide alteration. Major Ag-bearing minerals are freibergite, argentite and native Ag. The deposits were formed by a CO2-rich, mesothermal (ca. 250-320 degrees C), low-density and low salinity (< 11 wt.% NaCl equiv.), Na+-Cl--type fluid system. Trapping pressures of the carbonic-type fluid inclusions (FIs) decreased from ca. 280-320 MPa in the early mineralization stage to ca. 90-92 MPa in the late mineralization stage, indicating that the ore-forming depths had become progressively shallower. This further suggests that the metallogenesis may have occurred in a tectonic transition from compression to extension. Geological- and ore fluid characteristics suggest that the Xiaguan Ag-Pb-Zn orefield belongs to orogenic-type systems.