A study of isotope geochemistry and sources of ore-forming materials of the Bianjiadayuan silver polymetallic deposit in Linxi, Inner Mongolia

Located in the southern part of the Da Hinggan Mountains metallogenic belt, the Bianjiadayuan silver polymetallic deposit is a typical hydrothennal vein-type deposit. Stable (C, H, O and S) and radiogenic (Pb) isotopes of the Bianjiadayuan silver poly-metallic deposit were analyzed with the purpose of determining the source of the ore-forming fluids and materials. The δ D_H2O-SMOW and δ ¹⁸O_H2O-SMOW of the ore-forming fluids are -138.5‰--111.7‰, and -8.85‰-9.38‰, respectively, showing that they came from the mixing of magmatic water and meteoric water. The δ¹³C_PDB and ¹⁸O_SMOW of the hydrothennal calcite vary from -7.7‰ to -2.67‰ and from -0.41‰ to 6.03‰, respectively, indicating that the hydrothennal calcite was formed at two ore-forming stages. At the early stage, the ore-forming fluids were similar to magmatic water and the CO₂ was related to the magma, whereas at the late stage, the ore-forming fluid was derived from meteoric water. The δ³⁴S values of polymetallic ore in the Bianjiadayuan deposit range from 0.7‰ to 4.4‰, suggesting that the formation of the Ag-Pb-Zn orebody was closely related to magmatism and the sulfur probably came from the magma source. The ratios of lead isotopes in sulfides range from 38.1 to 38.634 for ²⁰⁸Pb/²⁰⁴Pb, 15.518 tol5.681 for ²⁰⁸Pb/²⁰⁴Pb, and 18.155 to 18.284 for ²⁰⁸Pb/²⁰⁴Pb, respectively, indicating that the mineralization might have been induced by the magmatism, and the lead in the deposit was mainly derived from deep-seated magmatic source. The mineralization took place in a low δ ³⁴S_{Σ s} and equilibrium system. The Bianjiadayuan deposit can be genetically regarded as a volcanicsubvolcanic hydrothennal vein-type silver polymetallic deposit.