Source Characteristics And Fluid Evolution Of The Beiyingxigou Pb-Zn-Ag Deposit, Central North China Craton: An Integrated Stable Isotope Investigation

The Beiyingxigou Pb-Zn-Ag Deposit is belong to the peripheral metallogenic belt of mapeng batholith, which is a quartz vein-type Pb-Zn-Ag Deposit lies in Fupingian and Wanzi cycle of Mesoarchean metamorphic rock series and is dominantly controlled by S-N and N-W trending faults. Yanshanian intermediate-acid intrusive and dikes are widely distributed in this region.The hydrothermal period of the Beiyingxigou Pb-Zn-Ag deposit is consist of 4 stages of mineralization:pyrite phyllic stage, quartz-pyrite stage(which is divided into pyrite-quartz and quartz-pyrite substage based on the content of pyrite and quartz), quartz-polymetallic sulfide stage, quartz-carbonate stage, the quartz-polymetallic sulfide stage is the main metallogenic stage.This paper synthesizes the main characteristics of stable isotope composition (S, Pb, He-Ar and H-O) and compares to the Shihu gold deposits in Fuping region to deduces possible sources of the mineralizing fluids and materials. We deduce the δ34S values of two-period(the early-middle and main metallogenic stage) hydrothermal fluid are 1.1‰ and -6.9‰, respectively. Bases on the S isotopic composition of paragenetic sulfide minerals, we calculate equilibrium temperature of the main ore-forming period change from 227.6 ℃ to 448.6℃, imply that the S of the main metallogenic stage came from magma. S isotope of the early-middle and main metallogenic stage are both dually controlled by Yanshanian magmatic rock and FuPing metamorphic. The lead isotopic composition changed in a restricted range, and these data are all concentrated in the lower crust field or near the lower crust line in Pb tectonic model diagram, which suggests the Pb isotope of the Beiyingxigou Pb-Zn-Ag deposit are derived from under crust principally which richer in thorium. The calculated results of the participated percentage of mantle helium are in the range of 0.08% to 3.99% with an average of 2.05%. Plotting the measured data of the inclusion-trapped noble gases in the sulfide mineral samples from the BeiyinxigouPb-Zn-Ag deposit on 3He vs.4He and R/Ra vs.40Ar/36Ar diagrams, the results suggests that the helium isotope mainly came from crust with little mantle material participating which are consistent with that of the Shihu gold deposit. Plotting D and 18O isotopic compositions of the Beiyingxigou Pb-Zn-Ag deposit together with the Shihu gold deposit on the δD versus δ18O diagram which suggests the hydrothermal fluid of the two deposits from the same region are both controlled by magmatic water and meteoric water.Combining all the data of the stable isotopic composition from the Beiyinxigou Pb-Zn-Ag deposit, we suggested that the metallogenic material had a closed relationship with Yanshanian intrusions and FuPing metamorphic complex. The magmatic hydrothermal fluid originated from lower crust rising rapidly along the structure paths and sparsely contaminated by country rock, and then stored in the proper structural position. The heat of magma melt country rock and made the ore-forming elements in strata transported into the magmatic hydrothermal fluid, which led to further enriched of the ore-forming elements. At the same time, the heat offered by the magma also made the meteoric water stored in the country rocks reactivated and mixed with magmatic water, which led to sediment of the metallogenetic matters. The source of metallogenic materials of the Shihu gold deposit is similar to thet of the Beiyinxigou Pb-Zn-Ag deposit. However, the mantle contributed more to the Shihu gold deposit relative to the Beiyingxigou Pb-Zn-Ag deposit, and the latter was contaminated more country rock matters than the former.