Fluid inclusions and isotopic characteristics of the Jiawula Pb-Zn-Ag deposit, Inner Mongolia, China

摘要

The large Jiawula Pb-Zn-Ag deposit is located in the Derbugan metallogenic belt of the northern Great Xing'an Range. The vein style orebodies of the deposit occur along NWW- to NNW-trending fault zones. The ore-forming process at the deposit can be divided into three stages: an early quartz-pyrite-pyrrhotite-chalcopyrite stage, a middle quartz-carbonate-pyrite-galena-sphalerite stage, and a late quartz-carbonate-pyrite stage. Sulfide Rb-Sr dating indicates that the Jiawula deposit formed at ca. 143-142 Ma. Four types of fluid inclusions have been distinguished in quartz veins including liquid-rich, gas-rich, H2O-CO2, and daughter mineral-bearing inclusions. The fluid inclusions of the early stage are mainly liquid-rich, gas-rich, and H2O-CO2 types, with a small number containing daughter minerals. Cumulatively, the types have homogenization temperatures, densities, and salinities of 304-438 degrees C, 0.35-137 g/cm(3), and 0.8-44.6 wt.% NaCl eqv., respectively. Inclusions of the middle stage are mainly liquid-rich and gas-rich types, with a small amount of H2O-CO2 and daughter mineral-bearing types; their homogenization temperatures, densities, and salinities vary from 242 degrees C to 297 degrees C, 0.71 to 1.44 g/cm(3), and 0.4 wt.% to 36.8 wt.% NaCl eqv., respectively. The late stage only comprises liquid-rich inclusions with homogenization temperatures, densities, and salinities of 181-238 degrees C, 0.81-0.90 g/cm(3), and 0.2-1.9 wt.% NaCl eqv., respectively. The ore-forming fluids of the Jiawula deposit are generally characterized by moderate temperature and low salinity and density, and belong to an H2O-NaCl-CO2 +/- CH4 system. The delta O-18(water) values calculated for ore-bearing quartz vary from -13.4 parts per thousand to -9.1 parts per thousand, and the delta Dv-SMOV values from bulk extraction of fluid inclusion waters vary from -166 parts per thousand to -133 parts per thousand, suggesting that the ore-forming fluids mainly consist of meteoric water with a small amount of magmatic water. The delta S-34(V-CDT) values range from 1.2 parts per thousand to 8.4 parts per thousand. The Pb-206/Pb-204, Pb-207/Pb-204, Pb-208/Pb-204 values of the ore minerals are in the ranges of 18.319-18.377, 15.499-15.596, and 38.094-38.314, respectively. Initial Sr-87/Sr-86 ratios of sulfides range from 0.712381 to 0.712770. The data for the S, Pb, and Sr isotopic systems indicate that the ore-forming metals and sulfur came from Mesozoic magma. The Jiawula deposit is a low-sulfidation epithermal Pb-Zn-Ag deposit, and fluid boiling is the dominant mechanism for the deposition of ore-forming materials. (C) 2014 Elsevier Ltd. All rights reserved.