Fluid inclusion and stable isotope study of the Shagou Ag-Pb-Zn deposit, Luoning, Henan province, China: Implications for the genesis of an orogenic lode Ag-Pb-Zn system

The Shagou deposit, located in the eastern Qinling orogenic belt, central China and hosted by the Taihua Supergroup, is a large-sized Ag-Pb-Zn deposit and has proven reserves of 1.54 million tons of ore with grades of 767 g/t Ag, 13.24% Pb and 4.31% Zn. The ore-forming fluids have been previously interpreted as products of direct exsolution of a crystallizing magma or sudden decompression of the fluid exsolved from magma, defining the Shagou deposit as an intrusion-related system. In this study, the Shagou deposit has been identified as an orogenic type mineralization system. The hydrothermal ore-forming process can be divided into the early quartz-pyrite, middle quartz-polymetallic sulfides and late quartz-carbonate stages. Four types of fluid inclusions in quartz can be distinguished between PC, C, Wand PW types. The early and middle stage quartz contains the PC, C and W type fluid inclusions, while only W and PW type fluid inclusions can be observed in the late stage quartz. In the early stage, the W type fluid inclusions homogenized at 173-369 degrees C (concentrating at 200-240 degrees C), with salinities ranging from 5.4 to 8.3 wt.% NaCl equiv. But in the middle stage, the C and W type fluid inclusions homogenized at 112-313 degrees C (concentrating at 180-220 degrees C), with salinities ranging from 0.7 to 13.6 wt.% NaCl equiv. In the late stage, the W type fluid inclusions homogenized at 108-253 degrees C (concentrating at 160-200 degrees C), with salinities ranging from 2.1 to 8.1 wt.% NaCl equiv. The fluids may have experienced a boiling process or fluid mixing in the middle stage. The estimated trapping pressures of fluid inclusions in the middle stage ranged from 33 to 211 MPa, corresponding to a mineralization depth from 3.3 to 7.7 km. For the early stage fluids, the calculated delta(18)O(H2)o p and delta D(H2)o, values are 7.5-9.1%, - 962 to -1105%., respectively. For the middle stage fluids, these two values are 1.5-53%., -75.6 to -110.7%. but change to 1.0%0 and -87%. for the late stage, suggesting an evolution from metamorphic to meteoric in origin. In general, the Shagou Ag-Pb-Zn deposit is similar in many respects to typical orogenic type mineralization systems. (c) 2014 Elsevier B.V. All rights reserved.