Multiple isotope (He-Ar-Zn-Sr-Nd-Pb) constraints on the genesis of the Jiawula Pb-Zn-Ag deposit, NE China

Abstract

• Mantle fluid and atmospheric water are two most important sources for the ore-forming fluid of the Jiawula deposit. • Zn isotopic variation was most likely caused by kinetic Rayleigh fractionation. • Coeval magma played a key role in the formation of the deposit. The large Jiawula Pb-Zn-Ag deposit is located in the Manzhouli area, northeast China. The Pb-Zn-polymetallic mineralization in the Jiawula deposit is present as ore veins distributed in Early Mesozoic sedimentary and magmatic rocks and was controlled by NWW to NNW trending faults. He and Ar isotope analysis results of fluid inclusions hosted in pyrite show that 40 Ar/ 36 Ar ratios are 280.5–300.1, which is close to the atmospheric value (295.5). 3 He/ 4 He ratios vary from 40.15 × 10 −7 to 71.68 × 10 −7 . The calculated mantle He are in a range of 35.8–64.0%, with an average of 51.0%. He-Ar isotopic data reveals that the ore-forming fluids of the Jiawula deposit were derived from mixture of two fluid end-members: (1) mantle-derived fluid, which has provided a considerable proportion of He; and (2) crustal fluid, which is characterized by almost atmospheric Ar and crustal He. The sphalerite from the Jiawula deposit have a narrow range of δ 66 Zn JMC values, varying from 0.15 to 0.307‰, with a mean value of 0.236‰. We suggest that the variation of Zn isotope values of sphalerite from the Jiawula deposit was most likely caused by kinetic Rayleigh fractionation. The Zn isotope analysis result, combined with previous S isotopic data, indicate that the ore-forming material of the Jiawula deposit was derived from a single source. The intrusive rocks in the deposit have low initial 87 Sr/ 86 Sr ratios, relatively high ε Nd (t) values, and young T DM2 Nd model ages, indicating a high proportion of juvenile material in the petrogenesis. Combined with Sr-Nd-Pb isotopic data of intrusive rocks that are coeval with mineralization in the deposit, He-Ar-Zn isotope analysis results, and previous studies, we propose that the mantle component in the ore-forming fluid and material of the Jiawula deposit was most probably derived from the simultaneous magma, which was derived from partial melting of crust with involvement of mantle magma in an extensional setting during the late Jurassic to the early Early Cretaceous.