Gondwana Research 35 (2016) 40–58 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr Geologic and geochemical insights into the formation of the Taiyangshan porphyry copper–molybdenum deposit, Western Qinling Orogenic Belt, China Kun-Feng Qiu a,b,⁎,RyanD.Taylorb,Yao-HuiSonga,c,Hao-ChengYua,d,Kai-RuiSonga,NanLia a State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China b U.S. Geological Survey, Box 25046, Mail Stop 973, Denver Federal Center, Denver, CO 80225-0046, USA c Airborne Survey and Remote Sensing Center of Nuclear Industry, Shijiazhuang 050000, China d The 7th Gold Detachment of Chinese Armed Police Force, Yantai 264004, China article info abstract Article history: Taiyangshan is a poorly studied copper–molybdenum deposit located in the Triassic Western Qinling collisional Received 24 January 2016 belt of northwest China. The intrusions exposed in the vicinity of the Taiyangshan deposit record episodic Received in revised form 24 March 2016 magmatism over 20–30 million years. Pre-mineralization quartz diorite porphyries, which host some of the de- Accepted 31 March 2016 posit, were emplaced at 226.6 ± 6.2 Ma. Syn-collisional monzonite and quartz monzonite porphyries, which also Available online 2 May 2016 host mineralization, were emplaced at 218.0 ± 6.1 Ma and 215.0 ± 5.8 Ma, respectively. Mineralization occurred Handling Editor: F. Pirajno during the transition from a syn-collisional to a post-collisional setting at ca. 208 Ma. A barren post- mineralization granite porphyry marked the end of post-collisional magmatism at 200.7 ± 5.1 Ma. The ore- ε − Keywords: bearing monzonite and quartz monzonite porphyries have a Hf(t) range from 2.0 to +12.5, which is much Geochronology more variable than that of the slightly older quartz diorite porphyries, with TDM2 of 1.15–1.23 Ga corresponding Geochemistry to the positive εHf(t) values and TDM1 of 0.62–0.90 Ga corresponding to the negative εHf(t) values. Molybdenite in Taiyangshan deposit the Taiyangshan deposit with 27.70 to 38.43 ppm Re suggests metal sourced from a mantle–crust mixture or – Porphyry copper molybdenum from mafic and ultramafic rocks in the lower crust. The δ34S values obtained for pyrite, chalcopyrite, and molyb- Western Qinling Orogenic Belt denite from the deposit range from +1.3‰ to +4.0‰, +0.2‰ to +1.1‰,and+5.3‰ to +5.9‰,respectively, 18 suggesting a magmatic source for the sulfur. Calculated δ Ofluid values for magmatic K-feldspar from porphyries (+13.3‰), hydrothermal K-feldspar from stockwork veins related to potassic alteration (+11.6‰), and hydro- thermal sericite from quartz–pyrite veins (+8.6 to +10.6‰) indicate the Taiyangshan deposit formed domi- nantly from magmatic water. Hydrogen isotope values for hydrothermal sericite ranging from −85 to −50‰ may indicate that magma degassing progressively depleted residual liquid in deuterium during the life of the magmatic–hydrothermal system. Alternatively, δD variability may have been caused by a minor amount of mixing with meteoric waters. We propose that the ore-related magma was derived from partial melting of the ancient Mesoproterozoic to Neoproterozoic middle to lower continental crust. This crust was likely metasomatized during earlier subduction, and the crustal magmas may have been contaminated with litho- spheric mantle derived magma triggered by MASH (e.g., melting, assimilation, storage, and homogenization) processes during collisional orogeny. In addition, a significant proportion of the metals and sulfur supplied from mafic magma were simultaneously incorporated into the resultant hybrid magmas. © 2016 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. 1. Introduction origin of porphyry deposits abound, but broadly form in two distinct tec- tonic settings (e.g., Richards, 2003; Hou et al., 2009; Pirajno and Zhou, Porphyry deposits are some of the world's most important reposito- 2015). Commonly these deposits occur in continental margin and ries of copper, gold, and molybdenum. They are defined as large volumes island-arc settings (Sillitoe, 1972; Cooke et al., 2005; Sillitoe, 2010; of hydrothermally altered rock centered on porphyry stocks, and are pre- Richards, 2011). In continental arc setting, such as in the Andes, flattening dominantly related to oxidized, felsic to intermediate calc-alkaline of a subducting oceanic slab, and associated crustal thickening and uplift magmas (Richards, 2003; Sillitoe, 2010; Lee, 2014). Hypotheses for the has been proposed to be essential for ore formation (Skewes and Stern, 1995; Cooke et al., 2005). In island-arc settings, such as throughout the western Pacific, porphyry deposits are associated with arc-parallel ⁎ Corresponding author at: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China. strike-slip faults and arc-transverse faults that are related to tearing of E-mail addresses: [email protected] (K.-F. Qiu), [email protected] (N. Li). the subducting slab (Richards, 2003). Alternatively, some porphyry Cu http://dx.doi.org/10.1016/j.gr.2016.03.014 1342-937X/© 2016 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58 41 (Mo–Au) deposits may form during the post-subduction collisional pro- mafic rocks, or lower crustal arc plutons and cumulates (e.g., Hou et al., cess, as observed in the Himalayan–Tibetan orogen (e.g., Hou et al., 2004; 2004; Shafiei et al., 2009; Lu et al., 2013; Chiaradia, 2014; Z.M. Yang Hou et al., 2009; Shafiei et al., 2009; Hou et al., 2013; Deng et al., 2014a; et al., 2014b, 2015d; Qiu et al., 2016); or (3) asthenosphere upwelling Hou et al., 2015; Lu et al., 2015; Z.M. Yang et al., 2015d, 2016), the in response to delamination, slab breakoff, back-arc extension, or oro- Qinling–DabieorogeninChina(e.g.,Li et al., 2013; Chen and Santosh, genic collapse (e.g., Jiang et al., 2006; Mair et al., 2011; Wang et al., 2014; Mao et al., 2014), the Zagros orogen in Iran (e.g., Singer et al., 2016). Although it is well acknowledged that a fertilized lithospheric or- 2005; Zarasvandi et al., 2005, 2007; Shafiei et al., 2009), and the Variscan igin is necessary for porphyry deposit formation due to the absence of a orogen of western and central Europe (e.g., Seltmann and Faragher, 1994). subduction-enriched asthenospheric mantle source (Chiaradia, 2014; The formation processes of ore-bearing porphyries in arc settings are Richards, 2014), some key problems on potential lithospheric source re- well understood and are acknowledged to be closely associated with gions are still elusive, which hampers our understanding of the genesis a subducting oceanic slab (e.g., Cooke et al., 2005; Sillitoe, 2010; of collisional porphyry systems and their targeting for exploration. Richards, 2014; Pirajno, 2016). However, post-subduction collisional The Western Qinling Orogenic Belt is a typical collisional orogen, and metallogeny is more complex and may involve a number of different was assembled by collision between the North China and South China processes and (or) magma, metal, and fluid sources. Potential broad- Blocks during the Late Triassic (Fig. 1; Chen and Santosh, 2014; Deng scale ore-forming processes include melting of: (1) orogenically thick- and Wang, 2015; Dong and Santosh, 2016). It hosts a belt of porphyry ened crust (e.g., Richards, 2009; Li et al., 2011; Xu et al., 2013; Deng deposits and occurrences that can be divided into five districts et al., 2014b); (2) previously subduction-modified lithosphere, includ- (i.e., Jiangligou-Nianmuer, Xiahe-Hezuo, Tiegou-Xingshigou, Hezuo- ing metasomatized mantle, juvenile lower crust formed by underplated Dewulu, and Wenquan-Huomaidi) (Fig. 1B; Table 1; GSBGME, 1979; Fig. 1. Generalized geological map of northwestern China (modified after Dong et al., 2011; Yang et al., 2015a), also showing the location and regional geology of the Western Qinling Orogenic Belt. (A) Tectonic subdivision of China, showing the location of the Western Qinling. (B) Regional geology with emphasis of Mesozoic granitoid distribution and five main mineral districts in the Western Qinling. See Table 1 for detailed information and data sources. Abbreviation: NCB = North China Block, SCB = South China Block, BK = Bikou Terrane, NQLOB = North Qilian Orogenic Belt, NQB = North Qinling Block, SQB = South Qinling Block, SP-GZOB = Songpan-Garzê Orogenic Belt, SZ1 = Wushan-Tianshui-Shangdan suture zone, SZ2 = Maqu-Nanping-Lueyang suture zone, TLF = Tan-Lu Fault, F1 = Baoji-Gouyuan Fault, F2 = Xinyang-Yuanlong (Baoji-Tianshui) Fault, F3 = Hezuo-Minxian-Dangchuan Fault, F4 = Diebu-Bailongjiang Fault, F5 = Lixian-Luojiapu Fault, F6 = Chengxian-Taibaishan Fault, F7 = Xihe Fault, F8 = Wudu Fault, F9 = Minjiang Fault, F10 = Pingwu-Qingchuan Fault. 42 K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58 Table 1 Summary of porphyry–skarn deposits in the five mineral districts in the Western Qinling, with geochronological data of mineralization and related granitoids. Mineral deposit Type Metal Tonnage Location Age (Ma) Mineral and method Reference Jiangligou-Nianmuer mineral district Xiekeng S Cu–Au Medium Xunhua, Qinghai 218 ± 2 Zircon LA-ICPMS U–Pb Sun et al. (2013), Guo et al. (2012), Zhang et al. (2006) Jiangligou P–SCu–Mo–W Medium Tongren, Qinghai 214 Molybdenite Re–Os He (2012), Li et al. (2010); Dong et al. (2010) Shuangpengxi P–SCu–Au Medium Tongren, Qinghai No data J. Zhang et al. (2014a), T. Zhang et al. (2014b), He (2012) Gangcha P–S Cu Prospect Tongren, Qinghai No data GSBGME (1979), J. Zhang et al. (2014a), T. Zhang et al. (2014b) Xiechangzhigou P–S Cu Prospect Tongren, Qinghai No data GSBGME (1979), Yin (2007) Langmujia P–S Cu Prospect Tongren, Qinghai No data Yin et al. (2005) Hongqika P–SCu–Au Prospect Tongren, Qinghai No data GSBGME (1979), Yin et al.