Ore geology, and H, O, S, Pb, Ar isotopic constraints on the genesis of the Lengshuibeigou Pb-Zn-Ag deposit, China

摘要

The Lengshuibeigou Pb-Zn-Ag deposit is located in the Qinling superlarge metallogenic belt, China. The Pb-Zn-Ag orebodies are hosted in the Proterozoic Luanchuan Group. The ore types are hydrothermal veins and skarns type. The ore-forming process can be divided into three stages: (1) quartz-pyrite; (2) quartz-sulphide; and (3) quartz-carbonate. This paper used stable and radiogenic isotopes to study the characteristics of the Lengshuibeigou Pb-Zn-Ag deposit. The temperature and salinity of fluids tend to decrease from the early skarn and quartz- pyrite stages to the late quartz-carbonate stage. The ranges of δ~(18)O_(H2O) (SMOW) and δD_(H2O) (SMOW) values of the ore-forming fluids range from -0.03 to +4.97‰ and from -83.00 to -72.00‰, respectively. The δ~(34)S_(V-CDT) values of pyrite, sphalerite and galena from the skarntype and hydrothermal-type vein ores range from +0.34 to +5.88‰, which is similar to those of porphyry-type Mo-W deposits in the area, but is different from those in the strata. The sulphur in both types of ores may have been derived from magmatic sources. The ranges of ~(206)Pb/~(204)Pb, ~(207)Pb/~(204)Pb and ~(208)Pb/~(204)Pb ratios in the sulphide ores are 17.457-17.765, 15.423-15.606 and 37.712-39.012, respectively, which are comparable with those of feldspars in porphyry granites in the Nannihu ore field and less radiogenic than those in the host strata. These new data support the likelihood that the fluids and metals associated with Lengshuibeigou Pb-Zn-Ag deposit were carried by the porphyry magmatic system. The ~(40)Ar/~(39)Ar plateau age of 137.9 ± 0.4 Ma age obtained from the Lengshuibeigou Pb-Zn-Ag deposit is likely its mineralization age. This paper is useful not only for interpretation of the genesis of the magmatic-hydrothermal deposits but also significant for mineral exploration in the area especially for finding large deposits in large magmatic districts where various types of base metal deposits might occur.