Primary fluid exsolution in porphyry copper systems: evidence from magmatic apatite and anhydrite inclusions in zircon,Mineralium Deposita

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Primary fluid exsolution in porphyry copper systems: evidence from magmatic apatite and anhydrite inclusions in zircon
Mineralium Deposita ( IF 4.4 ) Pub Date : 2020-09-14 , DOI: 10.1007/s00126-020-01013-4
Jin-Xiang Li , Guang-Ming Li , Noreen J. Evans , Jun-Xing Zhao , Ke-Zhang Qin , Jing Xie

It is well known that ore-forming melts associated with porphyry Cu deposits were oxidized and enriched in chlorine (Cl), sulfur (S), and water (e.g., Streck and Dilles 1998; Cooke et al. 2005; Richards 2011; Wang et al. 2018). In fact, the effective partitioning of Cl and S into exsolved fluids is a very important process in the formation of porphyry Cu systems (e.g., Sillitoe 2010; Richards 2011). However, the timing of primary fluid exsolution and the behavior of Cl and S during late-stage magma evolution are still poorly understood. Apatite, a common accessory phase in igneous rocks, incorporates oreforming elements (S, F, and Cl) into its crystal structure (e.g., Piccoli and Candela 2002; Zhang et al. 2012). Importantly, apatite trapped as inclusions in other igneous minerals can record the original volatile content of the magma (e.g., Scott et al. 2015; Stock et al. 2016, 2018; Zhu et al. 2018), eliminating diffusion effects associated with late-stage melts and/or fluids (Brenan 1993; Kusebauch et al. 2015). Additionally, magmatic anhydrite is an important indicator of S-rich and oxidized melts (e.g., Luhr 2008; Xiao et al. 2012; Masotta and Keppler 2015; Hutchinson and Dilles 2019), such as those related to porphyry Cu deposit formation (Audétat 2004; Richards 2011; Sun et al. 2015). However, magmatic anhydrite is rare in ore-forming magmatic intrusions, possibly due to dissolution by late-stage exsolved fluids (Chambefort et al. 2008). Previous studies on anhydrite inclusions and apatite phenocrysts in ore-bearing and fresh igneous rocks suggest that anhydrite crystallization could be an important process in reducing S contents during magma evolution (Streck and Dilles 1998; Chambefort et al. 2008). This study investigates apatite and anhydrite inclusions in zircon from ore-forming intrusions in the Duolong porphyry CuAu deposit, central Tibet (Fig. 1). Petrography and chemical analyses of apatite and anhydrite inclusions are used to elucidate volatile evolution and primary fluid exsolution in oreforming magmas.

更新日期：2020-09-14

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