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. (1st May 2015)

• Record Type: Journal Article
• Authors: Wang, Liqiang; Tang, Juxing; Cheng, Wenbin; Chen, Wei; Zhang, Zhi; Lin, Xin; Luo, Maocheng; Yang, Chao
• Is Part Of: Journal of Asian earth sciences. Volume 103(2015)
• Page Start: 276
• Page End: 287
• Publication Date: 2015-05-01
• Subjects: Isotope geochemistry -- Sources of ore-forming fluids and metals -- Bangpu deposit -- Gangdese metallogenic belt; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2014.07.041
• Languages: English
• ISSNs: 1367-9120

Abstract

Highlights: Integrated isotope geochemistry was studied of the Bangpu deposit. Ore-forming fluids in Bangpu were mainly from porphyry magma with meteoric water. Ore metals of the Bangpu deposit were mainly derived from the upper crust. Ore metals of the Qulong and Jiama deposits have more mantle components. Mantle composition causing the different metal associations of the three deposits. Abstract: 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 3 He/ 4 He and 40 Ar/ 36 Ar ratios of fluid inclusions exhibit a range of 0.12209–0.36370 Ra and 275.6–346.1, respectively. The 4 He and 40 Ar concentrations vary from 1.51 to 3.57 (10 −7 cm 3 STP g −1 ) and 0.49 to 9.31 (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 δ 18 Ofluid and δDfluid values vary from −1.3‰ to 3.9‰ and −140.5‰ to −73.7‰, respectively, indicating that magma fluids mixed with meteoric water. The average δ 34 S value of the sulfides (0.3‰) 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 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb ratios of 18.450–18.728, 15.602–5.672, and 38.715–39.211, respectively and μ 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.