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Gondwana Research 35 (2016) 40–58

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Geologic and geochemical insights into the formation of the Taiyangshan porphyry copper–molybdenum deposit, Western Qinling Orogenic Belt,

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, 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, 050000, China d The 7th Gold Detachment of Chinese Armed Police Force, 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 , 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 . 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 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--Shangdan 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. (2005) Dehelongwa P Cu–Au Medium Tongren, Qinghai No data Sun et al. (2013), Xiang et al. (1985) Tiewu S Cu–Au Small Tongren, Qinghai No data GSBGME (1979), Yin, 2007 Amangshaji P Au–Cu Prospect Gannan, No data GSBGME (1979) Nianmuer P Cu Prospect Gannan, Gansu 218.1 Biotite K–Ar GSBGME (1979), He (2012) Longdegang P Cu Prospect Gannan, Gansu 217 Whole rock Rb–Sr GSBGME (1979) Chuodamu P Cu Prospect Gannan, Gansu No data GSBGME (1979), Yin (2007) Yanglongqing P Cu Prospect Gannan, Gansu 200.2 Biotite K–Ar GSBGME (1979)

Xiahe-Ayishan mineral district Shuangyuangou P–S Cu Prospect Xiahe, Gansu No data GSBGME (1979), Yin (2007), Jin et al. (2005) Ayishan P Cu–W Prospect Xiahe, Gansu No data Xu et al. (2012), Wei (2013)

Tiegou-Xingshigou mineral district Xingshigou P–SCu–Mo Hezheng, Gansu No data GSBGME (1979) Tiegou P Cu–Mo–Au–Pb–Zn Hezheng, Gansu No data GSBGME (1979), Yin (2007)

Hezuo-Dewulu mineral district Dewulu P–S Cu Hezuo, Gansu 233.5 ± 1.5 Zircon LA-ICPMS U–Pb GSBGME (1979), Gao (2011) Zaozigou P Au Hezuo, Gansu 215.5 ± 2.1 Zircon SHRIMP U–Pb Liu et al. (2012)

Hezuo-Dewulu mineral district 216.6 ± 2.4 Zircon SHRIMP U–Pb Liu et al. (2012) 219.4 ± 1.1 Sericite Ar–Ar Sui and Li, 2014 SEG poster 230.0 ± 2.3 Sericite Ar–Ar Sui and Li, 2014 SEG poster Nikejiang P Cu Zhuoni, Gansu No data Yin (2007) Gangyi P Cu Xiahe, Gansu ~220 Zircon LA-ICPMS U–Pb Author's unpublished data Nanpan P–S Cu Xiahe, Gansu ~215 Zircon LA-ICPMS U–Pb Author's unpublished data Shanglangkamu P Cu Xiahe, Gansu No data GSBGME (1979), Yin (2007) Zaorendao P Au–Cu Xiahe, Gansu No data GSBGME (1979), Gao (2011)

Wenquan-Huomaidi mineral district Wenquan P Mo–Cu Medium Wushan, Gansu 226 Ma Biotite K–Ar GSBGME (1979), Han (2009) 224.6 ± 2.5 Zircon LA-ICPMS U–Pb Cao et al. (2011) 224 Biotite K–Ar Han (2009) 223.0 ± 7 Zircon SHRIMP U–Pb Zhang et al. (2006) 222.5 ± 2.8 Zircon LA-ICPMS U–Pb Cao et al. (2011) 221 Ma Biotite K–Ar Han (2009) 218.0 ± 2.0 Zircon SHRIMP U–Pb Zhang et al. (2006) 217.4 ± 2.0 Zircon LA-ICPMS U–Pb Wang (2011) 217.2 ± 2.0 Zircon LA-ICPMS U–Pb Wang (2011) 216.3 ± 1.4 Zircon LA-ICPMS U–Pb Xu et al. (2012) 214.4 ± 7.1 Molybdenite Re–Os Xu et al. (2012) 216.2 ± 1.7 Zircon LA-ICPMS U–Pb Zhu et al. (2009) 214.1 ± 1.1 Molybdenite Re–Os Zhu et al. (2009) 214.4 ± 1.7 Zircon LA-ICPMS U–Pb Zhu et al. (2011)

Wenquan-Huomaidi mineral district 217.3 ± 2.1 Zircon SHRIMP U–Pb Zeng et al. (2014) 216 ~ 207 Biotite K–Ar Han (2009) 210 Ma Biotite K–Ar Li et al. (1993) Yangposhan P Mo Prospect Tianshui, Gansu No data Wang (2011), Qiu et al. (2014) Chenjaidawan P Mo Prospect Tianshui, Gansu No data Wang (2011), Qiu et al. (2014) Xiaonancha P Mo Prospect Tianshui, Gansu No data Wang (2011), Qiu et al. (2014) Huangjiagou P Mo Prospect Tianshui, Gansu No data Wang (2011), Qiu et al. (2014) Yaozigou P Mo Prospect Tianshui, Gansu No data Wang (2011), Qiu et al. (2014) Xiaotanggou Mo Prospect Tianshui, Gansu No data Wang (2011), Qiu et al. (2014) Xigou P Cu Prospect Tianshui, Gansu No data Wang (2011), Qiu et al. (2014) Hongtonggou P Cu–Mo Small Tianshui, Gansu No data GSBGME (1979), Yin (2007) Taiyangshan P Cu–Mo Small Tianshui, Gansu 227.2 Biotite K–Ar 226.6 ± 6.2 Zircon LA-ICPMS U–Pb This study 218.0 ± 6.1 Zircon LA-ICPMS U–Pb This study 215.0 ± 5.8 Zircon LA-ICPMS U–Pb This study 200.7 ± 5.1 Zircon LA-ICPMS U–Pb This study 208.5 ± 1.3 Molybdenite Re–Os This study; GSBGME (1979) Tongniushan P Cu–Mo Prospect Tianshui, Gansu No data Yin (2007) Guojiashan P Cu Prospect Tianshui, Gansu No data Yin (2007) Moshangou P Mo Small Ningshan, Gansu No data Wang et al. (2012) Shentangou P–SCu–Mo Small Ningshan, Gansu 206.5 ± 1.9 Zircon LA-ICPMS U–Pb GSBGME (1979); Zongqi Wang, unpub. data 222.8 ± 1.8 Zircon LA-ICPMS U–Pb GSBGME (1979); Zongqi Wang, unpub. data 200.1 ± 7.3 Molybdenite Re–Os GSBGME (1979); Zongqi Wang, unpub. data K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58 43

Xiang et al., 1985; Luo, 1988; Lai, 1991; Li et al., 1993; Du et al., 2003; Yin none of these initial studies provided sufficient data to identify the spe- et al., 2005). However, few studies of any of these poorly developed dis- cific factors controlling Cu and Mo mineralization. tricts had been conducted before 2009 because of their difficult access. In this contribution, we document the alteration and vein mineral Recently, however, there has been an increase in exploration in the paragenesis by a combination of field mapping and core logging. Addi- belt and the first detailed research on deposit geology, geochronology, tionally, new detailed geological, geochemical, and geochronological and geochemistry (e.g., Han, 2009; Zhu et al., 2009; Cao et al., 2011; data for the granitic porphyries and mineralization at the Taiyangshan Gao, 2011; Wang, 2011; Zhu et al., 2011; Guo et al., 2012; He, 2012; porphyry deposit help to elucidate the evolution of the magmatic– Liu et al., 2012; Xu et al., 2012; Qiu et al., 2014; Zeng et al., 2014; J. hydrothermal system and establish a genetic model. Zhang et al., 2014a; T. Zhang et al., 2014b; Qiu et al., 2015). These studies suggest that the deposits constitute a metallogenically important belt of 2. Geological background porphyry systems formed in a post-collisional geodynamic setting. The Taiyangshan deposit (11,400 tonnes @ 0.54% Cu, 205 tonnes @ 2.1. Regional geology 0.12% Mo; Zhao et al., 2009) is located in the Western Qinling Orogenic Belt (Fig. 1), and has been operated as an open pit mine. Interest in the The convergence and collision between the South China Block Taiyangshan deposit dates back to the 1970s, when the Tianshui Insti- and the North China Block in northwestern China resulted in forma- tute of Gansu Nonferrous Metal Geological Exploration Bureau first re- tion of the Qinling Orogenic Belt (Fig. 1A; Meng and Zhang, 2000; ported copper and molybdenum mineralization and hydrothermally Ratschbacher et al., 2003; Dong et al., 2011; J. Zhang et al., 2014a, altered country rocks at Taiyangshan, and nearby at the Huomaidi and T. Zhang et al., 2014b). The early Paleozoic Wushan-Tianshui-Shangdan Hongtonggou deposits. Consequently, Bureau geologists carried out suture zone (also known as the Shangdan suture zone) to the north, more detailed study of the deposit geology and alteration in 2007 and the Middle Triassic Maqu-Nanping-Lueyang suture zone (also (Zhao et al., 2009). Han (2009) carried out preliminary geochemical known as the Mianlue suture zone) to the south separate the North and geochronological studies on igneous petrology of spatially associated Qinling Block and South Qinling Block (Fig. 1B; e.g., Dong et al., 2011; intrusions, reported biotite K–Ar ages for the stated mineralization- Luo et al., 2012; X.W. Li et al., 2015b; Dong and Santosh, 2016). related granitoid porphyries ranging from 224 to 207 Ma, and defined The Paleozoic to Mesozoic evolutionary history of the belt can be the Taiyangshan Cu-Mo deposit as the product of a Triassic magmatic– best described by three stages. These include an early to middle Paleo- hydrothermal system. Although the K–Ar data provided the first age es- zoic accretionary orogen along the southern side of the North China timate for the deposit, the age had a great deal of uncertainty. Moreover, Block; a late Paleozoic to Triassic collisional orogen along the Mianlue

Fig. 2. Schematic diagram showing the magmatic association, tectonic setting, and evolutionary history of the Qinling Orogenic Belt during the Phanerozoic. Compiled after Meng and Zhang (2000), Dong et al. (2011), Wang et al. (2013), Chen and Santosh (2014), Qiu et al. (2014, 2015), N. Li et al. (2015a), X.W. Li et al. (2015b), and Dong and Santosh (2016). 44 K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58 suture zone, with amalgamation of the South China Block to earlier ac- Block that were deformed between the North China and South Qinling creted terranes; and Jurassic to Cretaceous intracontinental tectonism Blocks in the early Mesozoic (Dong et al., 2011; Ji et al., 2014; Yang (Fig. 2;e.g.,Meng and Zhang, 2000; Ratschbacher et al., 2003; Dong et al., 2015a). The eastern boundary of the Triassic Western Qinling et al., 2011; Dong and Santosh, 2016). The Shangdan Ocean separated is commonly considered to be roughly located at the Baoji- the South China and North China Blocks at the start of the Phanerozoic. railway (the blue dash line in Fig. 1B; Zhang et al., 2007; Zeng et al., Subduction of the Shangdan Ocean slab on the basin's northern margin 2014), whereas, to the west, the boundary becomes obscured under caused formation of the North Qinling oceanic arc and development of young cover (Liu et al., 2014; N. Li et al., 2015a, X.W. Li et al., 2015b). the short-lived Cambrian–Ordovician Erlangping back-arc basin between The North Qinling Block (north part of the Triassic Western Qinling the arc and North China Block. As the basin closed at the end of the Ordo- Orogenic Belt), bounded to the southern-North China Block to the vician, the North Qinling arc was accreted to the North China Block. Silu- north and the Shangdan suture zone to the south, is predominantly cov- rian–Devonian rifting within the northern part of the South China Block ered by Precambrian rocks (Fig. 1B; Dong et al., 2011; Luo et al., 2012; led to fragmentation of the South Qinling Block, followed by Devonian– Yan et al., 2014; Dong and Santosh, 2016). The South Qinling Block Carboniferous closure of the Shangdan Ocean along the Shangdan suture (south part of the belt) is bounded between the Shangdan and Mianlue zone and opening of the Mianlue Ocean between the South Qinling and suture zones (Fig. 1B, Liu et al., 2014). It is characterized by a highly South China Blocks. During Permian to Early Triassic, the Mianlue oceanic deformed basinal flysch sequence, consisting of Devonian clastic crust began to subduct to the north beneath the South Qinling Block, and carbonate rocks with minor local Carboniferous and Permian eventually closing the ocean with the collision of the South China Block metasedimentary rocks (Dong and Santosh, 2016). Moreover, Devonian along the Mianlue suture zone in Norian time. Associated compressional sedimentary rocks are overlain by Triassic turbidites southward, deformation led to lateral escape structures along the major strike-slip and with small local Cambrian to Ordovician sedimentary rocks to the faults in the North Qinling Block or arc. Post-collisional collapse of the middle and west (Feng et al., 2002; Dong et al., 2011; Liu et al., 2014; thickenedorogencausedformationofEarly Jurassic fault bounded basins. Yang et al., 2015b). The Triassic Western Qinling is defined as the western part of the The Indosinian (early Mesozoic) granitoids that are closely associ- narrow belt of Paleozoic through Triassic rocks of the North Qinling ated with the porphyry deposits in the Western Qinling have been

Fig. 3. (A) Generalized geological map of the Taiyangshan deposit showing the hydrothermal alteration, and relationships between orebodies, related intrusive rocks, and their host sedimentary rocks. The original maps were provided by Gansu Institute of Nonferrous Metal Exploration and updated from our field investigation. (B) Sketch geological map of the cross section along A–A′ in Panel A. K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58 45 well studied due to their widespread exposure (Luo et al., 2012; Wang commonly present as dikes that are several meters in width (Fig. 3). et al., 2013; X.W. Li et al., 2015b). It is recognized that the granitoids The primary rock-forming minerals consist predominantly of comprise three distinct compositions and populations at 250–240 Ma, plagioclase, potassium feldspar, quartz, micas, and (or) amphiboles, 228–210 Ma, and 210–190 Ma (Wang et al., 2013; N. Li et al., 2015a, and accessory minerals are mainly iron-titanium oxides, apatite, and zir- X.W. Li et al., 2015b; Qiu et al., 2015; Dong and Santosh, 2016). They con, and microcrystalline minerals or glass. Characteristics of the pre-, correspond to the subduction-related, syn-collision, and post-collision syn-, and post-mineralization intrusions are summarized in Table 2. suites in the accretionary and ultimate collisional orogen developed be- Previous studies determined that the ore-hosting porphyries in the tween the North China and South China Blocks (Fig. 2). Taiyangshan deposit were predominantly formed in a syn-collision set- ting (Zhao et al., 2009; Song, 2015). They are metaluminous to slightly 2.2. Deposit geology peraluminous, and high-K calc-alkaline granitoids (Zhao et al., 2009; Song, 2015), and characterized by moderate LREE enrichments, slight The Taiyangshan deposit is located within the easternmost part HREE depletions (Song, 2015). Moreover, they are enriched in large- of the Triassic Western Qinling Orogenic Belt (Fig. 1B). The deposit ion lithophile elements (LILEs) and light rare earth elements (LREEs), is underlain by Devonian sedimentary rocks that have been intruded and depleted in high-field-strength elements (HFSEs), Nb, Ta, P and Ti, by Triassic dikes and small stocks. Local Triassic tuffaceous pebbly with negligible to slightly negative Eu anomalies. These chemical fea- sandstones, tuffaceous conglomerates, and dacitic to rhyolitic ignim- tures are consistent to those of the widespread 228–210 Ma granitoids brites, from bottom to top, crop out to the south and west of the deposit of the Western Qinling, which formed in a collisional setting (e.g., area (Fig. 3A). The northwest-striking and northeast-dipping Devonian Dong et al., 2011; Wang et al., 2013; N. Li et al., 2015a, X.W. Li et al., formations consist of quartz pebble sandstone and siltstone. The volca- 2015b; Dong and Santosh, 2016). nic and vocaniclastic rocks unconformably overlie the Devonian sedi- mentary rocks (Fig. 3B). Mapping of local geology in the mine area 3. Sample preparation and analytical methods was carried out concurrently with sampling for geochronological and geochemical analysis from outcrop, underground sites, and drill core. 3.1. Zircon LA-ICP-MS U–Pb geochronology Previous mapping, petrography, and microprobe studies by Zhao et al. (2009) determined alteration assemblages and their lateral extent Zircon grains were extracted from 5–10 kg whole-rock samples by (Fig. 3). Porphyry-style mineralization at Taiyangshan is associated with standard crushing, sieving, and heavy liquid and magnetic separation a very distinct and typical alteration sequence within the mineralized techniques. They were mounted in epoxy blocks and polished to obtain granitoids and their host rocks. These alteration types extend vertically an even surface, and then cleaned in an ultrasonic washer containing and laterally for as much as 100 m from the main mineralization. Assem- a5%HNO3 bath prior to laser ablation-inductively coupled plasma mass blages include an inner potassic zone, a surrounding zone of phyllic al- spectrometry (LA-ICP-MS) analysis. To identify the internal structure teration, and a peripheral zone of propylitic alteration (Fig. 3A). and texture of the zircon grains and to select potential positions for U– Potassic alteration is directly associated with abundant quartz Pb analysis, cathodoluminescence (CL) images of zircons were taken on stockworks and quartz + molybdenite + chalcopyrite + pyrite veins. a JXA-880 electron microscope and an image analysis software was used Structurally controlled quartz–pyrite–sericite veins, with distinct sericite under operating conditions of 20 kV and 20 nA, at the Institute of Mineral selvages, occur along fractures and faults, and postdate most porphyry Resources, Chinese Academy of Geological Sciences, Beijing, China. dikes and all stockwork veinlets (Figs. 4, 5, 6). The argillic alteration is Zircon U–Pb isotope analyses were carried out by LA-ICP-MS at spatially controlled by the NW-striking F2 fault in the mine (Fig. 3A). University of Technology, China, using a pulsed 193 nm ArF Excimer Detailed field observations indicating crosscutting relationships (COMPex PRO) with laser power of 10 mJ/cm2 pulse energy at a repeti- demonstrate that intrusive rocks include quartz diorite porphyry, mon- tion rate of 6 Hz coupled to an Agilent 7500a quadrupole ICP-MS. zonite porphyry, quartz monzonite porphyry, and porphyritic granite Helium was used as the carrier gas to provide efficient aerosol transport from early to late (Fig. 4). The ore-hosting quartz diorite porphyries to the ICP and minimize aerosol deposition. The diameter of the laser are exposed in the southeast part of the mine area and are cut by a ablation crater was 32 μm. Plesovice zircon, a new natural reference major NW-striking fault (Fig. 3A). They are crosscut by quartz– material for U–Pb isotopic microanalysis (Sláma et al., 2008), was ana- sericite–pyrite veins that are a few millimeters to centimeters in lyzed once every 10 analyses, and zircon 91500 was used as an external width (also termed D veins), and are intruded by all the other porphy- standard for U–Pb dating, and was analyzed twice every 5 analyses, in ritic intrusive types (Fig. 4A, C, E, F). The monzonite porphyries order to normalize isotopic fractionation during isotope analysis. The (Fig. 4B) are cut by quartz monzonite porphyries (Fig. 4E), both of NIST610 glass standard was used as an external standard to normalize which contain significant volumes of disseminated molybdenite, U, Th, and Pb concentrations of the unknowns. In addition, standard chalcopyrite, and pyrite. These two porphyry types are exposed pre- sample Mud Tank (Black and Culson, 1978) was used as an isotopic dominantly in the center of the mine, and spatially confined by the monitoring sample. The ICPMS DataCal program (Liu et al., 2010)was NW-striking F1 and F2 faults in areas of pervasive potassic alteration used for processing acquired data. Common Pb was corrected according (Fig. 3A, B). The porphyritic granite crosscuts the mineralized porphy- to the method proposed by Andersen (2002). The analytical results are ries and is itself barren (Fig. 4A). In summary, the bulk of the Cu–Mo reported with 1σ error. The weighted mean U–Pb ages (with 90% confi- mineralization is associated with the quartz monzonite and monzonite dence) were calculated at 2σ level and Concordia plots were produced porphyries, and occurs as stockwork veinlets (Figs. 4B–D, 5B, 6) and using ISOPLOT 3.23V (Ludwig, 2003).TheNIST610wasusedasanexter- disseminated ore in the porphyries and the surrounding Devonian nal standard to calculate the trace element contents of the unknowns, rocks (Figs. 4B–D, 6B). The main sulfide minerals at Taiyangshan are and the preferred values of element concentrations for the USGS refer- chalcopyrite, pyrite, and molybdenite, with lesser galena and sphalerite ence glasses are from the GeoReM database (http://georem.mpch- (Fig. 5). Associated gangue minerals include quartz, orthoclase, biotite, mainz.gwdg.de/). A detailed compilation of instrument and data acquisi- sericite, and potassium feldspar. tion parameters was presented in Liu et al. (2010).

2.3. Petrology and whole-rock geochemistry of porphyry stocks 3.2. In situ zircon Lu–Hf isotope analyses

The bulk of the Cu–Mo mineralization is hosted by the quartz In situ Hf isotope analysis of zircons was carried out on spots which monzonite, and monzonite porphyries in the Taiyangshan deposit. The had been analyzed for U–Pb ages by means of a 193-nm laser attached intrusions most closely associated with the mineralization are to a Neptune multi-collector ICP-MS (LA-MC-ICP-MS) at the Laboratory 46 K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58

Fig. 4. Macroscopic features of ores, associated granitoids and their host rocks at Taiyangshan. (A) Outcrop showing the barren porphyritic granite (PG) postdating the ore-bearing QMP which intruded the Devonian host rocks (DHRs). (B) Ore-bearing monzonite porphyry (MP) sample TY13U01 from underground exposures. (C) Pyrite–quartz vein with sericite halo crosscutting the ore-bearing MP and precursor quartz diorite porphyry (QDP). (D) Ore-bearing quartz monzonite porphyry (QMP) from surface outcrops. (E) Drill core samples showing relationship between ore-bearing QMP and MP. (F) Drill core samples showing relationship between barren PG and ore-bearing QDP. Mineral abbreviations through the text, including those in the figures, are after Whitney and Evans (2010). K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58 47

Fig. 5. Photomicrographs showing sulfides in the ore-bearing stockwork veins from the Taiyangshan deposit. Hand specimen (A) and thin section photograph (B) of stockwork veins cutting through K-feldspar phenocrysts in QMP. Chalcopyrite growing in the cracks (G) and edge (H) of pyrite, sphalerite associated with pyrite (G, J, K), and molybdenite aggregations (I) shown in C, D, E, and F, respectively. of Isotope Geology, Institute of Geology and Mineral Resources, The modal age (t) is calculated using the following formula: China, following the detailed analytical procedures described in Geng "# ! et al. (2011). A laser repetition rate of 10 Hz at 100 mJ was used for ab- 187 1 Os lating zircons and the spot diameters were 50 μm. Isotopes, including t ¼ ln 1 þ : λ 187Re 177Hf, 178Hf, 179Hf, 180Hf, 172Yb, 173Yb, 175Lu, 176(Hf + Yb + Lu), and 182W, were measured during the analytical process. Isobaric interfer- 176 176 175 ence of Lu on Hf was corrected based on the measured Lu In this formula, λ (187Re decay constant) = 1.666 × 10−11 year−1. value and the recommended 176Lu/175Lu ratio of 0.02655. Similarly, The blanks in this experiment are Re = 0.0253 ng and Os = 0.0001 ng. the 176Yb/172Yb value of 0.5887 and mean βYb value obtained during Hf analysis on the same spot were used for interference correction of 3.4. Stable isotope analyses 176Yb on 176Hf. During the analyses, the GJ-1 and 91500 zircon stan- dards yielded 176Hf/177Hf ratios of 0.282008 ± 24 (2σ, n = 17) and Sulfur isotope measurements were made on 25 concentrates of 0.282297 ± 18 (2σ, n = 16), respectively. These ratios are all consistent sulfide minerals separated from 16 rock samples (Table 3) at the U.S. with the recommended 176Hf/177Hf ratios of 0.282015 ± 19 (Elhlou Geological Survey Isotope Laboratory in Denver, Colorado. Mineral sepa- et al., 2006) for GJ-1 and 0.282302 ± 8 (Goolaerts et al., 2004)for ration using standard methods of concentration were performed by con- − − 91500. The decay constant for 176Lu of 1.865 × 10 11 year 1 (Scherer ventional preparation techniques including crushing, heavy liquid, and 176 177 et al., 2001) and present-day chondritic ratios of Hf/ Hf = magnetic separation. The purity of all concentrates was further checked 0.282785 and 176Lu/177Hf = 0.0336 (Blichert-Toft and Albarède, 1997) by examination under binocular microscopes, to make sure that the con- were used to calculate the εHf(t) values. centrates, which were fresh, non-oxidized and contaminant-free, were essentially monomineralic and purities were 95% to, more commonly, 3.3. Molybdenite Re–Os geochronology 99% or better. Aliquots of pyrite, chalcopyrite, and molybdenite were

combined with V2O5 and combusted in an elemental analyzer. Sulfur iso- Samples with sufficient molybdenite were carefully identified under tope ratios were determined by an on-line method using an elemental a microscope. Molybdenite was handpicked to produce a separate, analyzer coupled to a Micromass Optima mass spectrometer which was fresh, non-oxidized, and contaminant-free, with a purity of (Giesemann et al., 1994). Analytical results are generally reproducible better than 98%. within ±0.2‰ (2σ). Isotope data are reported in conventional δ notation Analyses were performed in the Re–Os Laboratory, National Re- relative to the Canyon Diablo Troilite (CDT) standard. search of Geoanalysis, Chinese Academy of Geological Sciences, using We conducted oxygen and hydrogen isotope analysis on six ore- a TJA X-series ICP-MS. The chemical separation process and analytical related sericite samples from quartz–pyrite–sericite veins, and oxygen methods are described by Du et al. (1994) and Smoliar et al. (1996). isotope analysis on four potassium feldspar samples from stockwork The uncertainty in each individual age determination is due to the veins and from unaltered intrusions (Table 3). Pure sericite aggregates 187Re decay constant, isotopic ratio measurements, and spike calibra- and potassium feldspar grains were obtained by crushing, washing, tion and weighing; the confidence level is 95%. and drying, and were then hand-picked under a binocular microscope. 48 K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58

Fig. 6. Samples for molybdenite Re-Os isotope analyses at the Taiyangshan porphyry deposit. (A) Qtz-Py-Cpy-Mo vein in QMP. (B) Disseminated Mo-mineralized QDP. (C) Qtz-Mo vein in MP. (D)Qtz-MoveininQDP.

Oxygen and hydrogen isotopes were analyzed at the USGS Isotope quartz monzonite porphyry (TY13S04), and barren porphyritic granite Laboratory in Denver, Colorado. Oxygen was extracted from 15–20 mg (TY13D03) are presented in Supplementary Table 1 and Fig. 7. Zircons silicate minerals by reaction with BrF5 and then reacted with carbon to separated from the quartz diorite porphyry are mostly transparent, col- give CO2 (Clayton and Mayeda, 1963), whereas hydrogen was liberated orless to pale yellow, and euhedral prismatic to elongated prismatic. as water by the fusion of the samples and then reacted with zinc to give They have lengths of ~150 to 200 μm and length/width ratios of 2:1

H2 (Coleman et al., 1982). The resultant CO2 was analyzed for oxygen iso- to 3:1. Moreover, concentric and typical magmatic oscillatory zoning topes using a Finnigan MAT-252 mass spectrometer, whereas the hydro- without inherited cores are revealed by CL images (Fig. 8). Results gen isotopes were obtained using a MAT 253. The precisions for O and H from 20 analyses indicate 495–1129 ppm U, 261–1693 ppm Th, and isotopes were ±0.1 and ±2‰ (1σ), respectively. The 18O/16OandD/Hra- Th/U ratios in the range of 0.60 to 1.50. All of these data are concordant tios are reported in normal δ-notation relative to V-SMOW standard. and yield a weighted mean age of 226.6 ± 6.2 Ma (MSWD = 2.20, n = 20; Supplementary Table 1; Fig. 7A). 4. Results Results for 13 analyses from the monzonite porphyry are 663 to 3485 ppm U, 336–813 ppm Th, and Th/U ratios ranging from 0.14 to 4.1. Zircon U–Pb ages 0.66. The zircons are colorless, transparent and euhedral, and most are short to long prismatic, with length-to-width ratios between 2:1 The LA-ICP-MS zircon U–Pb analytical data for the ore-hosting and 5:1. Their CL images (Fig. 8) display broad and concentric oscilla- quartz diorite porphyry (TY13D02), monzonite porphyry (TY13U01), tory zones. They are concordant and yield a weighted mean age of

Table 2 Lithology and mineralogy of the porphyritic granitoids at the Taiyangshan deposit.

Rocks Age (Ma) Texture Phenocrysts Groundmass Accessory

Quartz diorite porphyry 226.6 ± 6.2 Fine- to medium-grained porphyritic Pl, Am, Bt, Qtz Kfs, Qtz, Pl Zr, Mt, Apt, Rt Monzonite porphyry 218.0 ± 6.1 Medium-grained porphyritic Pl, Kfs, Qtz, Am Qtz, Kfs, Pl Mt, Apt, Zr Quartz monzonite porphyry 215.0 ± 5.8 Fine- to medium-grained porphyritic Pl, Kfs, Qtz, Am, Bt Qtz, Kfs, Pl, Am, Bt Mt, Zr Porphyritic granite 200.7 ± 5.1 Coarse-grained porphyritic Qtz, Kfs, Pl, Bt, Am Qtz, Pl, Kfs, Bt Zr, Mt, Apt, Rt

Abbreviations of minerals: Pl = plagioclase, Am = amphibole, Bt = biotite, Qtz = quartz, Kfs = K-feldspar, Zr = zircon, Apt = apatite, Rt = rutile, Mt = magnetite. K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58 49

Table 3 Current study sample descriptions.

Sample no. Sample description/common vein minerals Application in this study Locality

TY13U01 Ore-bearing mp Re–Os dating; U–Pb dating; sulfur isotope; hydrogen and oxygen isotope Underground Plan 1630 TY13D02 Ore-hosting qdp Re–Os dating; U–Pb dating; sulfur isotope Drill hole 24-2, depth 209 m TY13D03 Barren pg U–Pb dating Drill hole 24-2, depth 211 m TY13S04 Ore-bearing QMP Re–Os dating; U–Pb dating; sulfur isotope; hydrogen and oxygen isotope Surface outcrops TY13D05 Qtz + Mo vein Re–Os dating; sulfur isotope Drill hole 17-3, depth 275 m TY13D06 Qtz + Mo vein Re–Os dating; sulfur isotope Drill hole 17-3, depth 136 m TY13D07 Qtz + Mo ± Cpy vein truncated by Qtz + Py vein Re–Os dating; sulfur isotope; hydrogen and oxygen isotope Drill hole 17-3, depth 285 m TY13D08 Qtz + K-feldspar + Bt + Cpy ± Py vein Sulfur isotope Drill hole 17-3, depth 267 m TY13S09 Qtz + Py + Ser vein Hydrogen and oxygen isotope Surface outcrops TY13D10 Qtz + K-feldspar + Bt + Cpy ± Py vein Sulfur isotope; hydrogen and oxygen isotope Drill hole 17-3, depth 236 m TY13D11 Qtz + Py + Ser vein Sulfur isotope Drill hole 17-3, depth 288 m TY13D12 Qtz + Py + Ser vein Sulfur isotope Drill hole 17-3, depth 258 m TY13U13 Qtz + Py + Ser vein Sulfur isotope Underground Plan 1630 TY13U14 Qtz + Mo vein truncated later by Qtz + Py vein Sulfur isotope Underground Plan 1630 TY13U15 Qtz + Mo vein truncated later by Qtz + Py vein Sulfur isotope Underground Plan 1630 TY13D16 Qtz + Cpy ± Py vein Sulfur isotope Drill hole 24-1, depth 280 m TY13D17 Qtz + K-feldspar + Bt + Cpy ± Py vein Sulfur isotope Drill hole 23-2, depth 140 m TY13D18 Qtz + Cpy ± Py vein Sulfur isotope Drill hole 23-2, depth 334 m TY13U19 Qtz + Py + Ser vein Hydrogen and oxygen isotope Underground Plan 1680 TY13U20 Qtz + Py + Ser vein Hydrogen and oxygen isotope Underground Plan 1680

218.0 ± 6.1 Ma (MSWD = 1.50, n = 11; Supplementary Table 1; concentrations of 246–1191 ppm U and 150 to 829 ppm Th, and Th/U Fig. 7B, C). Two additional zircons gave anomalously old ages of ratios from 0.41 to 0.76 (Supplementary Table 1; Fig. 7E). The zircons 552 Ma and 628 Ma. They have no concentric oscillatory zones, and are short prismatic and have weak oscillatory zoning (Fig. 8). The re- much lower Th/U ratios compared to that of 218 Ma zircons. maining five zircons are transparent, colorless, elongated prismatic Thirteen zircon analyses from the quartz monzonite porphyry (up to 200 μm), and are oscillatory zoned. They have contents of contain 511–930 ppm U and 233–665 ppm Th, with Th/U ratios of 1217–1747 ppm U and 622–1047 ppm Th, with Th/U ratios from 0.41 0.46 to 0.72. The zircons are colorless, transparent, and euhedral with to 0.62 (Supplementary Table 1; Fig. 8), and yield a weighted mean length-to-width ratios between 1:1 and 2:1, and display CL images of age of 200.7 ± 5.1 Ma (MSWD = 0.53, n = 5) (Figs. 7E, F). oscillatory zoning (Fig. 8). They are concordant and yield a weighted mean age of 215.0 ± 5.8 Ma (MSWD = 1.20, n = 13; Supplementary 4.2. Lu–Hf isotopic composition Table 1; Fig. 7D). Six zircons separated from barren porphyritic granite are oval in Zircon Lu–Hf isotopic data are presented in Supplementary Table 2, shape, show weak oscillatory zoning, contain 172–534 ppm U and and illustrated in Fig. 9. The single stage depleted-mantle model ages

87–393 ppm Th, and have Th/U ratios from 0.45 to 0.95 (Supplementary (TDM1) are determined for each sample by calculating the intersection Table 1; Fig. 8). They have 206Pb/238U ages ranging from 419 ± 13.4 Ma of the zircon/parent-rock growth trajectory with the depleted-mantle to 491 ± 14.0 Ma (Fig. 7E). Nine of the twenty analyses spots have evolution curve (Vervoort and Blichert-Toft, 1999). The two-stage 206 238 Pb/ U ages ranging from 224 ± 6.4 Ma to 253 ± 7.2 Ma, have model ages (TDM2) are calculated for the source rock of the magma by

Fig. 7. Concordia (A, D, E, F) and Tera-Wasserburg (B, C) plots of U-Pb zircon geochronology results for QDP (A), MP (B, C), QMP (D) and PG (F), respectively. 50 K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58

Fig. 8. Cathodoluminescence images of representative zircons and 206Pb/238U ages of the individual analyzed spots.

assuming a mean 176Lu/177Hf value of 0.015 for an average continental 4.3. Re–Os isotopic dating crust (Griffin et al., 2002). For the quartz diorite porphyry sample, eighteen analyses were car- The hand-picked molybdenite grains were collected from both the ried out on the same spots used to measure U–Pb ages, among which, drill core and underground exposures in the Taiyangshan mine analyses TY13D02.05 and TY13D02.06 are excluded because they for Re–Os isotope analyses (Table 3). Molybdenite Re–Os isotope are statistical outliers. The remaining sixteen analyses discussed data and model ages calculated using the 187Re decay constant of in this study have ratios of 0.000724–0.001691 176Lu/177Hf and 1.666 × 10−11 year−1 (Smoliar et al., 1996) including uncertainties at 176 177 0.282573–0.282642 Hf/ Hf. They display εHf(t) values ranging the 2σ level are presented in Table 4. from −2.4 to +0.3, and corresponding TDM2 of 1.12–1.25 Ga (Supple- For the six samples from the Cu–Mo mineralization, the concentra- mentary Table 2, Fig. 9). tions of 187Re and 187Os range from 27.70 to 38.43 ppm and 60.99 We made 13 Lu–Hf isotopic analyses on the same spots used to deter- to 84.07 ppb, respectively. The Re–Os model ages vary from 206.7 ± mine U–Pb ages of the monzonite porphyry sample. Two zircons with 3.1 Ma to 209.9 ± 3.1 Ma, and give a weighted mean age of 208.5 ± ages of ~552 Ma and ~629 Ma have 176Lu/177Hf ratios of 0.001468 and 1.3 Ma (MSWD = 0.49) (Table 4; Fig. 10A). These analyses, processed 0.001519, 176Hf/177Hf ratios of 0.28263 and 0.282750, and positive using the ISOPLOT/Ex program (Ludwig, 2003), yield an isochron age 187 εHf(t) values of +6.7 and +12.5. The remaining eleven analyses for an of 207 ± 12 Ma (MSWD = 0.84), with initial Os = 0.5 ± 3.9 ppb estimated age at ca. 218 Ma have 176Lu/177Hf and 176Hf/177Hf ratios (Fig. 10B). ranging of 0.000888–0.001614 and 0.282625–0.282817. They display

εHf(t) values ranging from −0.6 to +6.1, and corresponding TDM2 4.4. Stable isotope geochemistry of 0.78–1.16 Ga (Supplementary Table 2, Fig. 9). Thirteen analyses of the sample of quartz monzonite porphyry show 176Lu/177Hf and Sulfur isotope data, obtained on 15 pyrite, 3 chalcopyrite, and 176Hf/177Hf ratios of 0.000635–0.002135 and 0.282583–0.282693. They 7 molybdenite grains from 18 rock samples, are summarized in display variable εHf(t) values ranging from −2.0 to +1.7, with corre- Supplementary Table 3 and shown in Fig. 11. Seven sulfide samples sponding TDM2 of 1.02–1.23 Ga (Supplementary Table 2, Fig. 9). were selected from disseminated mineralization and eighteen sulfide For the sample of porphyritic granite, twenty analyses show samples from stockwork veins. Sulfide separates have δ34Sinthe 176Lu/177Hf and 176Hf/177Hf ratios of 0.000542–0.001842 and range of +0.2 to 5.9‰,withanarithmeticmeanof3.1‰, similar 34 0.282622–0.282817, respectively. They have εHf(t) values ranging to those typical of porphyry deposits worldwide (Fig. 11). The δ S from −2.4 to +10.9 (Supplementary Table 2, Fig. 9). Six inherited or values of the 15 pyrites from both ore styles range from +1.3‰ captured zircons with 206Pb/238U ages ranging from 419 Ma to 491 Ma to +4.0‰ (Fig. 11), with an average value of +2.5‰. The range of have 176Lu/177Hf ratios of 0.000544–0.001842 and 176Hf/177Hf ratios of δ34S values for three chalcopyrite samples is +0.2‰ to +1.1‰, with 34 0.282628–0.282817. They show εHf(t) values ranging from +4.4 to an average of +0.5‰,andtheδ S values of seven molybdenite sam- +10.9, with corresponding TDM2 of 0.70–1.05 Ga. Nine analyses with ples are concentrated in a narrow range, from +5.3‰ to +5.9‰,with 206Pb/238U ages ranging from 223 Ma to 255 Ma have 176Lu/177Hf ratios an average of +5.6‰. of 0.000542–0.001124 and 176Hf/177Hf ratios of 0.282568–0.282681. The δD values for hydrothermal fluids in equilibrium with the hydro-

They display εHf(t) values ranging from −2.4 to +2.2, with TDM2 thermal sericite were calculated using the sericite–water equilibrium 6 −2 of 1.03–1.26 Ga. The remaining five magmatic analyses representing equation of Marumo et al. (1980): δDfluid = δDmineral +22.1×10 T − the emplacement age at ca. 201 Ma display εHf(t) values ranging from 19.1, and estimated using the trapping temperature of primary fluid in- −1.8 to +2.9, with corresponding TDM2 of 0.94–1.21 Ga (Supplementary clusions in quartz coexisting with the silicate minerals (350 °C: Kun- Table 2, Fig. 9). Feng Qiu, unpub. data). Oxygen isotope concentrations of the ore fluids K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58 51

Fig. 9. Results of Lu-Hf analyses of zircons from intrusive rock samples at Taiyangshan. (A, B) εHf(t) vs. t (Ma) diagrams. (C)HistogramsofεHf(t) values, and (D)Histogramsof corresponding two-stage Hf model ages.

18 18 were calculated using the muscovite–water (δ Ofluid = δ Omineral − 2008; Rusk et al., 2008a, 2008b). The measured and calculated oxygen 6 −2 18 2.38 × 10 T + 3.89), and K-feldspar–water equations (δ Ofluid = and hydrogen isotopes are listed in Supplementary Table 4. The 18 6 −2 δ Omineral − 2.91 × 10 T +3.41)ofZheng (1993). The magmatic two magmatic potassium feldspar grains from unaltered monzonite K-feldspar separated from unaltered parts of the ore-hosting por- and quartz monzontie porphyry have δ18O values of +13.3‰.Two phyries was used to determine δ18O of the magma. The K-feldspar hydrothermal potassium feldspar minerals separated from from the mineralized veins was used to approximate the δ18Oofthemag- stockwork veins show δ18O value of +12.5‰, and corresponding cal- 18 matic–hydrothermal ore-forming fluids. The sericite separated from culated δ Ofluid values are +11.6‰. Hydrothermal sericite displays quartz + pyrite + sericite veins was used to define the δ18OandδDvalues δDrangingfrom− 122 to − 87‰, which correspond to calculated 18 for late stage hydrothermnal fluids. Based on microthermometry studies δDfluid values from − 85 to −50‰,andδ Ofluid values from +8.6 18 (Kun-Feng Qiu, unpublished data), calculated equilibrium temperatures to +10.6‰.Onaδ Ofluid vs. δDfluid plot (Fig. 12), most samples are 350 °C (late fluid), 550 °C (ore fluid), and 650 °C (magma), which plot in or proximal to the magmatic water field, with those late are roughly consistent to those of typical porphyry deposit ( Z.M. Yang stage fluids nearer to the meteoric water line.

Table 4 Molybdenite Re–Os isotope analyses for samples at Taiyangshan.

Sample no. Weight (g) Sample description Re (μg/g) 187Re (μg/g) 187Os (ng/g) Modal age (Ma)

Content 2σ Content 2σ Content 2σ Age 2σ

TY13D07 0.00204 Qtz + Mo ± Cpy vein truncated by Qtz + Py vein 38.43 0.38 24.15 0.24 84.07 2.10 208.6 5.9 TY13D05 0.00206 Qtz + Mo vein 35.33 0.32 22.21 0.20 77.15 0.80 208.2 3.3 TY13U01 0.00218 Ore-bearing MP 29.28 0.24 18.40 0.15 63.49 0.63 206.7 3.1 TY13D06 0.00213 Qtz + Mo vein 32.81 0.27 20.62 0.17 71.74 0.61 208.4 3.0 TY13D02 0.00211 Ore-bearing QDP 32.67 0.26 20.53 0.16 71.69 0.58 209.2 2.9 TY13S04 0.00203 Ore-bearing QMP 27.70 0.24 17.41 0.15 60.99 0.51 209.9 3.1

Decay constant: λ187Re = 1.666 × 10−11 year−1 (Smoliar et al. 1996). 52 K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58

Fig. 12. Plot of calculated δDversusδOfororefluids of the Taiyangshan deposit. Additional Fig. 10. (A) Isochron age, and (B) weighted average Re–Os model age of the six data (Ohmoto, 1986; Bowman et al., 1987; Watanabe and Hedenquist, 2001; Khashgerel molybdenite samples from the Taiyangshan Cu–Mo deposit. et al., 2006; Valencia et al., 2008) of various typical porphyry ore deposits worldwide shown for comparison. Modified after Sheppard et al. (1971) with addition of data for andesite volcanic vapor 5. Discussion field from Giggenbach (1992), and felsic magmatic water field from Taylor (1992),and residual magmatic water field from Taylor (1974). 5.1. Timing and duration of the magmatic–hydrothermal system Yang et al., 2014a). Zircon U–Pb dating of ore-hosting porphyries at The determination of the precise age of mineralization and closely Taiyangshan recorded the emplacement of quartz diorite porphyries associated intrusions within a magmatic–hydrothermal system is at 226.6 ± 6.2 Ma, monzonite porphyries at 218.0 ± 6.1 Ma, and quartz essential for understanding genetic processes and locating economic monzonite porphyries at 215.0 ± 5.8 Ma (Fig. 13). The Re–Os analyses deposits (Richards, 2003; Qiu and Yang, 2011; Chiaradia et al., 2013; on molybdenite from disseminated and stockwork ores yield model

Fig. 11. (A) The range of sulfur isotope values (δ34S‰) for sulfides and sulfates from various rock reservoirs (data from Marini et al., 2011 and references therein), (B) sulfur isotope compositions of sulfides from the Taiyangshan Cu–Mo deposit, with comparison to those of sulfides and sulfates from typical porphyry deposits worldwide (data from Ohmoto and Rye, 1979 and Calagari, 2003 and references therein). K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58 53

of the mineralization in the Río Blanco-Los Bronces-Los Sulfatos belt of porphyry deposits spanned about 4 million years (Toro et al., 2012). These studies indicate that the magmatic–hydrothermal duration of the porphyry system could possibly last for several million years, al- though there is still some debate on how long it could last and what could be the leading factor that controls this.

5.2. Constraints on the source of magma

The above presented geology, petrography, and geochemistry indi- cate the monzonite porphyries and quartz monzonite porphyries are the causative intrusions responsible for mineralization, whereas the quartz diorite porphyries were only a host rock for mineralization. The

initial εHf(t) values (age corrected using U–Pb age for individual grains) of the monzonite porphyries and quartz monzonite porphyries fall in the gray area above the lower crust but below the depleted mantle lines (Fig. 9A, B, C). This indicates that their magmas could have been derived from either partial melting of ancient enriched lithospheric mantle or depleted mantle-derived melts that mixed with mature con-

tinental crust. Their εHf(t) values range from −2.0 to +12.5, which are much higher and more variable than those of the older quartz diorite porphyries (−2.4 to +1.2), further suggesting a more significant con- tribution from the lithospheric mantle for the monzonitic melts. This is also consistent with previous studies that the 228–210 Ma granitoids in the Triassic Western Qinling Orogenic Belt commonly have mafic microgranular enclaves, and have geochemical characteristics attributed to a mantle contribution (Zhang et al., 2007; Zhu et al., Fig. 13. Summary of age data for magmatic and hydrothermal events at Taiyangshan. 2009; Cao et al., 2011; Zeng et al., 2014). Additionally, the monzonite and quartz monzonite porphyries are metaluminous to slightly peraluminous, and are classified as high-K ages ranging from 206.7 ± 3.1 Ma to 209.9 ± 3.1 Ma (Fig. 13). A later calc-alkaline granitoids. They are enriched in LREEs and LILEs, and de- magmatic episode included emplacement of the barren porphyritic pleted in HREEs, HFSEs, Nb, Ta, P, and Ti, with negligible to slightly neg- granites at 200.7 ± 5.1 Ma. ative Eu anomalies (Zhao et al., 2009; Song, 2015). These chemical Magmatic activity in the Taiyangshan area was episodic during the features are consistent with those of the widespread 228–210 Ma gran- Late Triassic to Early Jurassic. The older quartz diorite porphyries acted itoids of the Western Qinling, which were generated by partial melting as a favorable ore hosts, however their emplacement preceded the ini- of a sub-continental lithospheric mantle in a collisional setting tiation of the magmatic–hydrothermal system responsible for porphyry (e.g., Dong et al., 2011; Wang et al., 2013; N. Li et al., 2015a, X.W. Li mineralization. The emplacement ages of the ore-hosting monzonite et al., 2015b; Dong and Santosh, 2016). Their high Rb/Zr and Ta/Nb, and quartz monzonite porphyries are within analytical uncertainty of and low K/Rb ratios are consistent with values for syn-collision the Re–Os ages of molybdenite mineralization. We thus propose that metaluminous intrusions that may be derived from the hydrated the monzonite and (or) quartz monzonite porphyries may be responsi- bases of continental thrust sheets (Duggen et al., 2005). Moreover, ble for porphyry-style mineralization. The later intrusion of the barren they have a TDM2 of 1.15–1.23 Ga, corresponding to positive porphyritic granites indicates that the magmatism in the Taiyangshan εHf(t) values, and TDM1 of 0.62–0.90 Ga, corresponding to negative mine area continued beyond the ore-forming event. εHf(t) values (Fig. 9D). This further suggests the monzonite porphyries In contrast to the pulsed nature of magmatism in Taiyangshan, and quartz monzonite porphyries at Taiyangshan resulted from partial porphyry mineralization was more limited in duration. All Re–Os melting of Mesoproterozoic to Neoproterozoic crustal rocks with addi- age data overlap in age, and seem to occur at the transition from a col- tional contributions from mantle–derived magmas triggered by MASH lisional to post-collisional setting (Fig. 13), regardless of the ore host processes. They were remelted at ca. 215 Ma, simultaneously with, or rock and mineralization style. The limited duration of the magmatic– shortly after, closure of the Mianlue Ocean and collision between the hydrothermal system at Taiyangshan is similar to that of many porphy- North China and South China blocks. ry systems around the world (e.g., Gangdese porphyry belt, Hou et al., 2003; Li et al., 2007; Rio Blanco porphyry deposit, Deckart et al., 2005; 5.3. Constraints on fluid and metal sources Nambijia skarn gold deposit and Pangui porphyry copper deposit, Chiaradia et al., 2009; Río Blanco-Los Bronces copper–molybdenum por- Rhenium and osmium isotopes have been used to not only deter- phyry district, Toro et al., 2012). Hou et al. (2003) reported that although mine timing of mineralization, but also the source of rhenium and, by magmatic–hydrothermal activitymay have lasted for 3–10million years, inference, ore metals (Suzuki et al., 1996). Rhenium concentrations in the mineralization event was less than 1 million years in length for three molybdenite decrease progressively from porphyry deposits with a porphyry copper deposits in the Miocene Gangdese belt of Tibet. Li et al. source being the mantle (N100 ppm), a mantle–crust mixture (tens (2007) argued that the magmatic–hydrothermal activity event lasted of ppm), and the crust (b10 ppm) (Mao et al., 1999). Similarly, Stein 0.5–5 million years in the Gangdese belt, which is much shorter than et al. (2001) suggested that molybdenite from deposits having a mantle the extensive period of magmatism. Moreover, Li et al. (2013) reported source generally have a higher Re content than that from crustally- that the well-constrained temporal correlations indicated that Mo min- derived ones, and very low Re contents (b20 ppm) are highly diagnostic eralization was caused by pulses of granitic magmatism, and that the of metamorphic derivation (Stein, 2006). As shown in Table 4, molybde- ore-forming magmatic–hydrothermal activity responsible for the nite grains have Re contents ranging from 28 to 38 ppm, implying that Yuchiling porphyry Mo system in the Qinling orogen lasted about the Taiyangshan porphyry deposit has a metal source dominated 8 million years. Magmatic–hydrothermal activity associated with most by mantle–crust mixture or mafic and ultramafic rocks in the lower 54 K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58 crust. Moreover, they have approximately the same Re concentration as −50‰ and the large variations characterize different paragenetic min- molybdenite from the neighboring Wenquan porphyry deposit eral assemblages at Taiyangshan. This may indicate that magma (20.47–33.52 ppm: Zhu et al., 2009), which is the one important degassing depletes residual liquid in deuterium by about 20‰,leaving porphyry deposit well documented in the Western Qinling to have a felsic magmatic water lighter than andesite volcanic vapors, and resid- metal source of a predominantly crust–mantle mixture (Zhu et al., ual magmatic water further depleted in deuterium. In addition, δDmay 2009; Cao et al., 2011; Zhu et al., 2011). be affected by some degree of mixing of the magmatic fluids with ex- Hydrogen, oxygen, and sulfur, the most frequently analyzed stable ternal meteoric waters (Fig. 12), as is discussed below. isotopes in porphyry copper systems, reveal sources of aqueous fluids The relatively low δD values characterize the hydrothermal sericite and sulfur, as well as processes that formed hydrothermal mineral collected from the late phyllic alteration stage. These sericite samples assemblages (John et al., 2010). The narrow range of sulfur isotope com- also have lower δ18O isotope fluid values that are nearer to the meteoric positions of sulfides from Taiyangshan is similar to typical porphyry water line, reflecting influx of meteoric water into the magmatic– deposits around the world (Fig. 11) and suggests a relatively homoge- hydrothermal system during the late part of the alteration processes. neous sulfur source. In addition, no significant variations in δ34Svalues We thus believe that the late phyllic alteration formed in the hydro- were observed between disseminated and stockwork vein ore, sug- static environment that overprinted the ore-bearing minerals formed gesting that the different types of ore have the same sulfur source. The in the lithostatic environment associated with the early potassic δ34S values for the sulfides at Taiyangshan are typical of magmatic sul- alteration. fur, further demonstrating that mineralization at the Taiyangshan deposit was magmatic–hydrothermal in origin. Hydrogen and oxygen isotope compositions for the ore fluids of the 5.4. Ore formation and insights into mineralization of a porphyry system at Taiyangshan porphyry deposit indicate multiple fluid sources in addi- the district scale 18 tion to time–space variations in fluid composition in the δ Ofluid vs. δDfluid plot (Fig. 12). Two hydrothermal potassium feldspars separated We propose a model such that the causative magma for ore forma- 18 from stockwork veins show calculated δ Ofluid at +11.6‰, and hydro- tion was derived from partial melting of the ancient Mesoproterozoic 18 thermal sericite displays δ Ofluid values from +8.6 to +10.6‰.These to Neoproterozoic middle to lower continental crust. This magma isotope compositions are similar to those for magmatic water (Taylor, mixed with magma derived from melting of the deeper fertile subconti- 1974): for example, they are similar to ore fluids that formed Bingham nental lithosphere, which had been modified by prior subduction pro- potassic and sericitic alteration, La Caridad potassic and sericitic alter- cesses prior to final collision in the West Qinling orogeny (Fig. 14A). ation, and some El Salvador muscovite alteration (Fig. 12). Calculated During MASH processes (melting, assimilation, storage, and homogeni- hydrogen isotope values for hydrothermal sericite range from −85 to zation; Hildreth and Moorbath, 1988), a significant proportion of the

Fig. 14. Genetic model of the magmatic–hydrothermal system at the Taiyangshan deposit. Modified after Hildreth and Moorbath (1988), Richards (2003), Shafiei et al. (2009), Dong et al. (2011),andRichards (2015). K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58 55 metals and sulfur were supplied from a mafic magma recycled into re- possible reason why some ca. 228–210 Ma granitoids are barren. Only sultant hybrid magmas (Fig. 14B). a conjunction of favorable factors at both the regional and local scales Porphyry deposits may form at various stages during back-arc ex- will ultimately allow the successful transfer of large amounts of Cu to tension prior to the onset of collision, syn-collisional crustal thickening, shallow levels after being initially concentrated within or at the base and post-collisional stress relaxation and crustal extension (Deng et al., of the lithosphere (Chiaradia, 2014). As a whole, many of the ca. 228– 2013; Richards, 2014; Q.F. Wang et al., 2014a; R. Wang et al., 2014b; 210 Ma syn-collisional granitoids in the Western Qinling Orogenic Belt Deng et al., 2015). Much research on porphyry deposits during the could have great potential for additional associated porphyry deposits. past decade in the Eastern Qinling (e.g., Chen and Santosh, 2014; Mao et al., 2014), Tibet (e.g., Hou et al., 2011; Deng et al., 2012; Yang et al., 2015c; Wang et al., 2016), and southeastern Europe, Turkey, and 6. Conclusions Iran (e.g., Shafiei et al., 2009; Z.M. Yang et al., 2009; Richards, 2015)in- dicates that collisional orogens are favorable targets for porphyry de- The intrusions exposed at the Taiyangshan deposit record episodic posit exploration due to fertilization of the lithosphere during magmatism spanning many millions of years. The quartz diorite por- subduction prior to final collision. Furthermore, more precise geochro- phyries intruded at ca. 226 Ma and are genetically unrelated to mineral- nological data for ore mineral precipitation and associated porphyry ization, but were favorable host rocks. The monzonite porphyries and emplacement allow us to place ore formation within a broader, well- quartz monzonite porphyries intruded as syn-collisional granites and constrained geologic context in the Triassic Western Qinling Orogenic are ore-bearing. Mineralization occurred during the transition from Belt (Fig. 15). a syn-collisional to a post-collisional tectonic setting at ca. 208 Ma. During the Late Triassic, the Mianlue Ocean closed due to collision Following mineralization, a barren porphyritic granite was emplaced between the South Qinling Block and South China Block, and the at the end of all post-collisional magmatism. widespread 228–210 Ma syn-collisional ore-bearing granitoids were The ore-bearing monzonite porphyries and quartz monzonite por- emplaced within the Western Qinling (Fig. 2;e.g.,Dong et al., 2011; phyries have εHf(t) values ranging from −2.0 to +12.5, which are Wang et al., 2013; Dong and Santosh, 2016). In addition, five main por- much more variable than those of the quartz diorite porphyries. The phyry copper districts are located across the Western Qinling Orogenic monzonitic rocks have TDM2 of 1.15–1.23 Ga, corresponding to their Belt. The widespread Late Triassic syn-collisional granitoids are spatially positive εHf(t) values, and TDM1 of 0.62–0.90 Ga, corresponding to and temporally related to these deposits (Fig. 15). The intrusions were their negative εHf(t) values. Their magmas were sourced from the derived by partial melting of the Mesoproterozoic to Neoproterozoic Mesoproterozoic to Neoproterozoic crust and metasomatized middle to lower continental crust, which mixed with magma derived Neoproterozoic sub-continental lithospheric mantle that melted at ca. from deeper subcontinental lithospheric mantle that had been modified 215 Ma, simultaneously with or just subsequent to collision of the by prior subduction. The hydrous and oxidized lithospheric mantle South China Block to the West Qinling orogeny and closure of the melts were more fusible than typical anhydrous lower crustal assem- Mianlue Ocean. blages (e.g., Wilkinson, 2013) due to the prior introduction of cumulates Isotopic results indicate that the sulfur in the Taiyangshan deposit from a subducted slab (Richards, 2015). This magmatic underplating re- ore fluids had a magmatic–hydrothermal source. The narrow range of sulted in mountain building in the Western Qinling, and aided melting of sulfur isotope values of sulfide minerals implies a homogenous sulfur the lithosphere during collision (Lee et al., 2012; Richards, 2015), which source; the values are also consistent with a magmatic source. Hydro- resulted in the subsequent formation of numerous ore deposits within gen and oxygen isotope compositions of ore-related minerals are also the belt (Fig. 2; Dong et al., 2011; Wang et al., 2013; Liu et al., 2014). consistent with magmatic–hydrothermal fluids being dominant in the An uneven distribution of the subduction-modified lithosphere mineralization process, with magma degassing during alteration events. within the Western Qinling Orogenic Belt (e.g. X.W. Li et al., 2015b; Concentrations of Re in molybdenite grains from 28 to 38 ppm imply Xiong et al., 2016) might lead to some areas that are fertile and others that the Taiyangshan porphyry deposit has a metal source dominated that are unproductive for porphyry deposits on the scale of tens to by a mantle–crust mixture or mafic and ultramafic rocks in the lower hundreds of kilometers (e.g., Wilkinson, 2013). This could be one crust. Moreover, the ~228–210 Ma syn-collisional granitoids in the

Fig. 15. Summary of geochronological data of the porphyry–skarn deposits in the Western Qinling, and their magmatic–hydrothermal association within early Mesozoic geologic context. The age data and mineral districts illustrated here are listed in Table 1. 56 K.-F. Qiu et al. / Gondwana Research 35 (2016) 40–58

Western Qinling Orogenic Belt could have a great potential for econom- Deng, J., Wang, Q.F., Li, G.J., Li, C.S., Wang, C.M., 2014a. Tethys tectonic evolution and its bearing on the distribution of important mineral deposits in the Sanjiang region, ically important porphyry deposits. SW China. Gondwana Research 26, 419–437. Deng, J., Wang, Q.F., Li, G.J., Santosh, M., 2014b. tectono-magmatic and metallogenic processes in the Sanjiang region, southwestern China. Earth-Science Acknowledgments Reviews 138, 268–299. Deng, J., Wang, Q.F., Li, G.J., Hou, Z.Q., Jiang, C.Z., Danyushevsky, L., 2015. Geology and gen- esis of the giant Beiya porphyry–skarn gold deposit, northwestern Yangtze Block, Drs. Craig Johnson and Cayce Gulbransen at USGS in Denver are China. Ore Geology Reviews 70, 457–485. thanked for providing access to stable isotope analysis facilities. We Dong, Y., Santosh, M., 2016. Tectonic architecture and multiple orogeny of the Qinling especially thank Senior Engineers Jun-Lie Zhou and Wang-Zhen Han Orogenic Belt, Central China. Gondwana Research 29 (1), 1–40. Dong, X.P., Du, Z.M., Liu, Q.Y., Duan, B., Zhang, X.J., 2010. Discussion about the geological at Gansu Nonferrous Metal Geological Exploration Bureau for their sup- characteristics and genesis of Xiekeng gold–copper mine, Qinghai Province. Mineral port in the field survey, and Erin Marsh at the U.S. Geological Survey in Exploration 18, 46–49 (in Chinese with English abstract). Denver for her assistance with the stable isotope analyses, and Richard Dong, Y.P., Zhang, G.W., Neubauer, F., Liu, X.M., Genser, J., Hauzenberger, C., 2011. Tectonic Goldfarb, Jun Deng, Li-Qiang Yang, and Lin-Nan Guo for their helpful evolution of the Qinling orogen, China: review and synthesis. Journal of Asian Earth Sciences 41 (3), 213–237. discussions. M. 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