Origin of the ore-forming fluids and metals of the Bangpu porphyry Mo-Cu deposit of Tibet, China: Constraints from He-Ar, H-O, S and Pb isotopes

The Bangpu porphyry Mo-Cu deposit is a representative Mo-dominated deposit besides the Sharang porphyry Mo deposit in the Gangdese metallogenic belt. The Mo-Cu mineralization has a close relationship with the monzogranite porphyry and diorite porphyrite. We identify three stages during the ore formation: a pre-ore stage, a main-ore stage with Mo-Cu deposited dominantly, and a post-ore stage. In this study, He-Ar, H-O, S and Pb isotopic compositions of the Bangpu deposit were determined. Based on these determinations, integrated isotope geochemistry studies were performed to constrain the possible sources of the ore-forming fluids and metals. The He-3/He-4 and Ar-40/Ar-36 ratios of fluid inclusions exhibit a range of 0.12209-0.36370 Ra and 275.6-346.1, respectively. The He-4 and Ar-40 concentrations vary from 1.51 to 3.57 (10(-7) cm(3) STP g(-1)) and 0.49 to 931 (10(-7) cm(3) STP g(-1)), respectively. He-Ar isotopic compositions suggest dominantly crustal-derived fluid with minor amount of meteoric water in the main ore stage. The delta D-fluid and delta D-fluid values vary from -1.3 parts per thousand. to 3.9 parts per thousand and -140.5 parts per thousand to -73.7 parts per thousand, respectively, indicating that magma fluids mixed with meteoric water. The average delta S-34 value of the sulfides (0.3 parts per thousand) in the main-ore stage is close to the ore-forming porphyries, indicating a magmatic source. The lead isotopic components of ore sulfides exhibit restricted ranges with Pb-206/Pb-204, Pb-207/Pb-204, and Pb-208/Pb-204 ratios of 18.450-18.728, 15.602-5.672, and 38.715-39.211, respectively and mu values in the range of and 9.46-9.58, indicating ore-forming metals of primarily an upper crust source with a small amount of mantle materials. Compared to the Bangpu deposit, the ore metals derived from mantle are even greater in the Jiama and Qulong deposits, which leads to Cu being the dominant mineralization in the Jiama and Qulong deposit. (C) 2014 Elsevier Ltd. All rights reserved.