Source characteristics and fluid evolution of the Beiyingxigou Pb-Zn-Ag deposit, central North China Craton: An integrated stable isotope investigation

The Beiyingxigou quartz vein and alteration type Pb-Zn-Ag deposit forms part of the metallogenic region southwest of the Mapeng batholith in the Central North China Craton. The quartz vein-type polymetallic deposit is associated with intermediate-felsic intrusives emplaced with Mesoarchean metamorphic basement. The mineralization is dominantly controlled by N-S and NW-SE trending faults. We identify four distinct stages of mineralization associated with the hydrothermal activity: pyrite phyllic stage, quartz-pyrite stage, quartz-polymetallic sulfide stage, and quartz-carbonate stage. Among these, the first two stages and the quartz-polymetallic sulfide stage represent the early and main metallogenic stages, respectively. Here we present results from integrated stable isotope studies (S, Pb, He-Ar and H-O) to deduce the possible sources of the mineralizing fluids and metals. The delta S-34 values recorded in the sulfide minerals of the early and main metallogenic stages show ranges of +0.4 parts per thousand to +2.2 parts per thousand, and -11.4 parts per thousand to -6.8 parts per thousand, respectively. The data illustrate two distinct pulses of hydrothermal fluids with delta S-34 mean values of 1.1 parts per thousand and -8.7 parts per thousand. The S isotopes of pyrite and galena, sphalerite from the early and main metallogenic stages suggest a mixed source from the Mesozoic magmatism and the Precambrian basement. We infer that the slow cooling magma at the main metallogenic stage led to a larger interaction with the country rocks and resultant contamination, as compared to the early-middle metallogenic stage. The lead isotopic composition of pyrite, galena and sphalerite from the early to main stages shows restricted ranges with Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 ratios of 15.720-16.275, 15.068-15.140 and 38.688-41316, respectively. The data are all characterized by lower crustal nature, suggesting the contribution of Pb from both the Mesozoic intrusions and the basement rocks in the region. The He-3/He-4 and Ar-40/Ar-36 ratios of fluid inclusions from the Beiyinxigou Pb-Zn-Ag deposit show a range of 0.01-0.23 Ra and 270.2-298.1, respectively. The He-4 and Ar-40 concentrations vary from 26.6 to 340.6 (10(-7) cm(3) STP/g) and 165.6 to 357.9 (10(-7) cm(3) STP/g), respectively, suggesting dominantly crustal contribution. The delta O-18(Q) values of quartz and the delta D-18(w) values show ranges of 10.9 parts per thousand to 13.6 parts per thousand and -85.2 parts per thousand to -57.8 parts per thousand, respectively. The calculated delta O-18(w) values of the mineralizing fluids show a range of 3.7 parts per thousand to 7.5 parts per thousand. Our data suggest that the hydrothermal fluids were a mixture of both magmatic and meteoric water. The results presented in this study link the Beiyinxigou Pb-Zn-Ag deposit to metallogeny associated with Mesozoic magmatism in the North China Craton. (C) 2013 Elsevier B.V. All rights reserved.