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

Abstract: Located in the southern part of the Da Hinggan Mountains metallogenic belt, the Bianjiadayuan silver polymetallic deposit is a typical hydrothermal 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. TheδDH2O-SMOW and δ18ОH2O-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 δ13CPDB and 18OSMOW of the hydrothermal calcite vary from -7.7‰ to -2.67‰ and from-0.41‰ to 6.03‰, respectively, indicating that the hydrothermal 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 to15.681 for 207Pb/204Pb, and 18.155 to 18.284 for 206Pb/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 δ34S∑S and equilibrium system. The Bianjiadayuan deposit can be genetically regarded as a volcanic-subvolcanic hydrothermal vein-type silver polymetallic deposit.