Evolution of ore fluids in the Donggou giant porphyry Mo system, East Qinling, China, a new type of porphyry Mo deposit: Evidence from fluid inclusion and H–O isotope systematics Yong-Fei Yang a , Yan-Jing Chen a,b , Franco Pirajno c , Nuo Li a a Key Laboratory of Orogen and Crust Evolution, Peking University, Beijing 100871, China b Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, CAS, Guangzhou 510640, China c Centre for Exploration Targeting, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia abstract article info Article history: Received 1 July 2014 Received in revised form 2 September 2014 Accepted 8 September 2014 Available online 21 September 2014 Keywords: Ore fluids Fluid inclusion Isotope Porphyry Mo deposit Qinling Orogen Post-collision The Donggou Mo deposit in the eastern Qinling area, China, is a giant porphyry system discovered based on a targeting concept by using the tectonic model for collisional orogeny, metallogeny and fluid flow (CMF model). Mo mineralization is associated with the Donggou aluminous A-type granite porphyry and was formed during the Early Cretaceous in a tectonic regime of continental extension. The orebodies mainly occur as numerous veinlets in the host-rocks. Hydrothermal ore-forming processes include at least three stages, char- acterized by veinlets of (1) quartz + K-feldspar + minor molybdenite, (2) quartz + molybdenite ± beryl and (3) quartz + carbonate + fluorite. Three types of fluid inclusions (FIs) are distinguished in quartz and beryl in stages 1 and 2, i.e., aqueous (W-type), carbonic–aqueous (C-type) and solid-bearing (S-type), with only aqueous FIs observed in stage 3 minerals. S- type FIs contain variable daughter minerals including halite, chalcopyrite, calcite and an unidentified transpar- ent crystal, but only halite can dissolve during heating. Halite-bearing S-type FIs are mainly homogenized by halite dissolution at 182–416 °C, corresponding to salinities of 30.9–49.2 wt.% NaCl equiv.; minor halite- bearing S-type FIs are homogenized to liquid at 190–360 °C via vapor disappearance, with salinities of 29.1– 36.2 wt.% NaCl equiv. Other FIs in minerals of stages 1, 2 and 3 are homogenized at temperatures of 341–550 °C, 220–440 °C and 125–225 °C, with salinities of 8.0–18.3, 5.3–16.8 and 0.5–7.3 wt.% NaCl equiv., re- spectively. The estimated minimum trapping pressures are up to 141 MPa in stage 1 and up to 81 MPa in stage 2, respectively, corresponding to an initial mineralization depth of no less than 5 km. The quartz in veinlets yields δ 18 O values of 8.5–10.0‰, corresponding to δ 18 O H 2 O values of -2.9 to 5.9‰, while the δD H 2 O values of fluid inclu- sions range from -59 to -82‰. These data suggest that the ore fluids forming the Donggou deposit changed from high-temperature, high-salinity, CO 2 -rich magmatic to low-temperature, low-salinity and CO 2 -poor mete- oritic fluids via boiling and mixing, resembling those of other magmatic–hydrothermal systems in Qinling Orogen and Dabie Shan. This supports the notion that the porphyry systems generated in a post-collisional tec- tonic setting were initially CO 2 -rich, as indicated by abundant C-type and CO 2 -bearing S-type fluid inclusions. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The Qinling Orogen in China, suturing the Yangtze and Sino-Korea cratonic blocks (Fig. 1A, B), is a typical continental collisional orogen formed in the Mesozoic (Chen and Santosh, in press; Li et al., 2014c; Wang et al., 2013; Wu and Zheng, 2013; Zheng et al., 2013). Renowned by several discoveries of mineral deposits, especially Mo mineral systems, the Qinling Orogen has become one of the most ideal places in the world to study the relationship between collisional orogens and mineralization. In previous studies, Chen and Fu (1992) and Chen et al. (2000, 2004, 2005, 2007a, 2009b) proposed a tectonic model for collisional orogeny, petrogenesis, metallogenesis and fluid flow (referred to as the CMF, Pirajno, 2009, 2013). The eastern Qinling molybdenum belt (EQMB; Fig. 1C) has become one of the most important Mo provinces in the world, containing six giant Mo deposits (each with a reserve or resource of N 0.5 Mt Mo) and tens of small (b 0.01 Mt Mo), medium (0.01–0.1 Mt Mo) and large (0.1–0.5 Mt Mo) deposits, with a total resource of ~6 Mt Mo metal (Chen et al., 2009b, 2014; Li et al., 2012a, 2012b; Mao et al., 2011; Zhang et al., 2011). The principal characteristics of the Mo mineraliza- tion in the EQMB can be summarized as follows (Chen and Li, 2009; Chen et al., 2009b, 2014): (1) most of the important Mo deposits are located in areas with thick crust in the Huaxiong block (Yuan, 1996; Fig. 1B, C), to the north of the Luanchuan fault, such as the Jinduicheng porphyry Mo deposit (Li et al., 2014a; Zhu et al., 2010) and the Luanchuan Mo field (Bao et al., 2014; Yang et al., 2012, 2013a), which Ore Geology Reviews 65 (2015) 148–164 http://dx.doi.org/10.1016/j.oregeorev.2014.09.011 0169-1368/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Ore Geology Reviews journal homepage: www.elsevier.com/locate/oregeorev