Helium and argon isotope geochemistry of the Tibetan Qulong porphyry Cu-Mo deposit, China
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ORIGINAL ARTICLE
Helium and argon isotope geochemistry of the Tibetan Qulong porphyry Cu-Mo deposit, China Keqiang Peng1,2 • Liyan Wu1
•
Yong Huang1 • Ke Jiang3
Received: 29 September 2020 / Revised: 7 November 2020 / Accepted: 17 November 2020 Ó Science Press and Institute of Geochemistry, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The Qulong porphyry Cu–Mo deposit, generated in the Miocene post-collisional extension environment of the Gangdese Copper (Molybdenum) Metallogenic Belt, is one of the largest porphyry Cu deposits in China. This study reports the noble gas isotopic compositions of volatiles released from fluid inclusion reserved in pyrite from the Qulong deposit. 3He/4He and 40Ar/36Ar ratios range from 0.54 to 1.015 Ra and 300–359, respectively. Concentrations of 4He and 40Ar range from 1.77 to 2.62 9 10-8 cm3 STP and 1.7–34 9 10-8 cm3 STP, respectively. The isotopic composition of noble gases indicates that the ore-forming fluids of the Qulong Cu–Mo deposit were a mixture of fluid containing mantle component, which is exsolved from the porphyry magma, and crustal fluid characterized by atmospheric Ar and crustal radiogenic He. The d34S values of pyrite and molybdenite range from - 0.52% to 0.31%, with an average of - 0.12%, indicating a magmatic origin. More mantle components were involved in the Cu–Mo deposit than in the Mo–Cu deposit in the Qulong-Jiama ore-district. Keywords He and Ar isotopes Sulfur isotope Qulong Cu–Mo deposit Ore-forming fluid Tibet China
& Liyan Wu [email protected] 1
State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
College of Eco-Environmental Engineering, Guizhou Minzu University, Guiyang 550025, China
1 Introduction The Qulong porphyry Cu–Mo deposit (PCD), located in the east part of the Gangdese copper Metallogenic Belt, about 50 km east of Lhasa city, is one of the largest porphyry Cu deposits in China, with reserves of 10.6 Mt [email protected]% and 0.5 Mt [email protected]% (Xiao et al. 2012). Many studies have been done on the geology (Yang 2008; Yang et al. 2009; Qin et al. 2014), petrology (Hu et al. 2015; Mo et al. 2006; Yang et al. 2011), mineralization (Meng et al. 2006), geochronology (Meng et al. 2003; Wang et al. 2006; Li et al. 2017a, b), magmatic-hydrothermal evolution (Li et al. 2017a; Yang et al. 2005, 2009), and thermal history (Zhao et al. 2016; Zhou et al. 2019) of the Qulong deposit. Approximately the same S and Pb isotope compositions of sulfide and ore-related porphyry show that the ore-forming materials are mainly from the porphyry magma (Qu et al. 2002, 2007; Meng et al. 2006). However, the contribution of the mantle is not clear. Among the noble gases, He and Ar are the most efficient for tracing the sources of ore-forming fluids because of the significant difference of isotopic compositions between end members. 3He/4He ratio of the upper mantle is 7–9 Ra (Graham, 2
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