A ductile to brittle shear zone–hosted Cu mineralization: Geological, geochronological, geochemical and fluid inclusion studies of the Lingyun Cu deposit, southern Tianshan, NW China

Ore Geology Reviews 94 (2018) 155–171

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A ductile to brittle shear zone–hosted Cu mineralization: Geological, geochronological, geochemical and fluid inclusion studies of the Lingyun Cu deposit, southern Tianshan, NW China

T

⁎

Yun Zhaoa, Chunji Xuea, , Yongsen Huangb, Xuefeng Wangc, Xiaobo Zhaoa, Guozhen Zhangd a

State Key Laboratory of Geological Processes and Mineral Resources, Faculty of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China 106 Geological Brigade of Sichuan Bureau of Geology and Mineral Resources, Chengdu 611130, China c Gold Seventh Team, Chinese People's Armed Police Force, Yantai 264000, China d Tianjin Institute of Geology and Mineral Resources, China Geological Survey, Tianjin 300170, China b

A R T I C L E I N F O

A B S T R A C T

Keywords: U–Pb, Re–Os and 40Ar/39Ar geochronology Fluid inclusion Lingyun Cu deposit Southern Tianshan

The Lingyun Cu deposit is located at the northern margin of the South Tianshan Accretionary Complex, NW China. In the Lingyun mine area, the rocks are cut by a NW–trending Yanxingshan ductile to brittle shear zone. All orebodies are hosted in crystal tuff. The sulfide mineralization in the Lingyun Cu deposit can be divided into early (E) and late (L) paragenetic stages. The E-stage is characteristic of fault-controlled sulfide assemblages (chalcopyrite + bornite+chalcocite)–quartz veins in the foliation fabric of the crystal tuff with albite + sericite ± epidote ± biotite assemblages. In the L-stage, the assemblages of ankerite + chalcopyrite + bornite + chalcocite are present in veinlets that cut the E-stage assemblages. The sulfide assemblages in the Lingyun deposit are characterized by striations in the metamorphosed crystal tuff. Ribbon-like silicate minerals in the crystal tuff share common deformation features with the sulfide assemblages. The host rock of the Lingyun Cu deposit yields a concordia age of ca. 405 Ma, indicating that the Aerbishibulake Formation formed during southward subduction of the South Tianshan Ocean beneath the Tarim Block. Moreover, crystal tuff samples show well developed negative Sr anomaly and positive Rb, Th, U, Nd and P anomalies, which are common in arc-related volcanic rocks. The ca. 297 Ma Re–Os isochron age yielded by sulfides is much younger than the host rock, which implies that the Lingyun Cu deposit is a typical epigenetic deposit. Both similar REE fractionated patterns between sulfide ores and crystal tuff and the high initial 187 Os/188Os ratio (18.54 ± 0.67) indicate significant crustal materials input. The 40Ar/39Ar plateau age of ca. 292 Ma from the ribbon-like sericite in crystal tuff is coeval with the mineralization occurrence in the Lingyun Cu deposit. By contrast, diorite dikes that crosscut the crystal tuff formed at ca. 221 Ma, which is much younger than the sulfide mineralization. Thus, the mineralization in the Lingyun deposit is likely to have been generated by shear zone activity rather than the intrusion of diorite dikes. Three types of fluid inclusions have been identified in the Lingyun Cu deposit: Aqueous (W-type), mixed aqueous–carbonic (M-type) and pure carbonic (C-type) inclusions. These three types of fluid inclusions are all found in the E-stage quartz whereas only the W-type fluid inclusions have been observed in L-stage ankerite. Fluid inclusions from the E-stage commonly contain CO2 and H2O, locally with N2 with low salinity, which are common in orogenic deposits. By contrast, L-stage fluid inclusions show low CO2 concentrations and salinity, indicating a significant inflow of meteoric water. Given the regional geology, ore geology, coeval ore-forming and deformation and fluid inclusion features, the Lingyun Cu deposit may be associated with the orogenic class of mineral systems.

1. Introduction Orogenic Au deposits, which are controlled by faults including deepcrustal shear zones, are one of the main sources of Au in the world

⁎

Corresponding author. E-mail address: [email protected] (C. Xue).

https://doi.org/10.1016/j.oregeorev.2018.01.012 Received 9 April 2017; Received in revised form 7 January 2018; Accepted 15 January 2018 0169-1368/ © 2018 Elsevier B.V. All rights reserved.

(Groves et al., 2003; Frimmel, 2008). The geological and geochemical characteristics of orogenic Au deposits have been well documented (e.g., Groves et al., 1998, 2003; Chen et al., 2004; Chen, 2006; Pirajno, 2009; Corrêa et al., 2015).

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In recent years, the findings for Ag, Mo, Pb–Zn, and Cu commodities in geologically, geochemically and structurally similar to orogenic-type deposits have been proposed (Chen et al., 2004; Deng et al., 2008; Zhang et al., 2009; Pirajno, 2010; Pirajno et al., 2011; Zheng et al., 2012). For example, a large number of orogenic-type deposits have been identified in China, including Tieluping (Chen et al., 2004) and Yindonggou (Zhang et al., 2009) Ag deposits, Weishancheng Ag–Au deposit (Zhang et al., 2011), Zhifang (Deng et al., 2008) and Longmendian (Li et al., 2011b) Mo deposits, Lengshuibeigou Pb–Zn deposit (Qi et al., 2007), Dahu Au–Mo deposit (Li et al., 2011a; Ni et al., 2012) and Wulasigou Cu deposit (Zheng et al., 2012). Most of the deposits mentioned above occur in the Qinling orogenic belt. The Tianshan orogenic belt, on the other hand, is characterized by continental scale strike-slip shear zones, which are generally ductile to brittle-ductile, with steeply dipping mylonitic foliations (Pirajno, 2010). Orogenic Au deposits have been discovered in the Tianshan orogenic belt whereas orogenic-type Cu deposits have not been reported to date. Therefore, the study of representative orogenic Cu deposits in the Tianshan orogenic belt is of significant interest. The Lingyun Cu deposit is a new discovery in southern Tianshan, NW China, with a reserve of 4.73 million tonnes (Mt) of ore at an average grade of 1.3 wt% Cu. The Cu orebodies are hosted by the Devonian metamorphosed crystal tuff, indicating a potential genetic relationship with the orogenic-related events. However, it is still unclear whether the Lingyun Cu deposit can be classified as orogenic class. In this paper, we first document the geological characteristics of the Lingyun Cu deposit. We then use zircon U–Pb, sericite 40Ar/39Ar and sulfide Re–Os geochronological methods to determine the ages of the host rock, as well as the deformation and mineralization events, which are crucial for understanding the genesis of the deposit. We then present the research results of fluid inclusions to investigate the evolution of the ore-forming fluids. Finally, a genetic model is proposed based on all the acquired data.

extends for ca. 2500 km from Xinjiang (NW China) to Kyrgyzstan, Uzbekistan and Kazakhstan (Windley et al., 1990; Gao et al., 1998). The Tianshan orogenic belt and adjacent regions in Chinese portion were subdivided into four distinct tectonic domains, the Kazakhstan-Yili Block (KYB), the North Tianshan Accretionary Complex (NTAC), the Central Tianshan Arc Terrane (CTA) and the South Tianshan Accretionary Complex (STAC) by the North Tianshan Suture Zone (NTSZ) in the north, Nikolaev Line-North Nalati Suture Zone (NNSZ) in the middle, and South Central Tianshan Suture Zone (SCTSZ) in the south (Fig. 1b, Gao et al., 2009; Jiang et al., 2014; Qian et al., 2009). The NTAC comprises abundant Paleozoic volcanic and sedimentary rocks (Gao et al., 1998; Jiang et al., 2014). The KYB is underlain by Precambrian basement, and the CTA is composed of a Precambrian metamorphic basement and Ordovician–Early Carboniferous arc and postearly Carboniferous sedimentary rocks (Charvet et al., 2011; Jiang et al., 2014; Long et al., 2011; Wilhem et al., 2012). The STAC consists predominantly of Lower Cambrian black shales and phosphoric silicates, Cambrian–Carboniferous marine non-marine carbonates, clastic rocks, cherts and interlayered volcanics (Carroll et al., 1995; Jiang et al., 2014). During the early Silurian to early Carboniferous, the South Tianshan Ocean is believed to have experienced northward subduction under the Yili-Central Tianshan Block (YCTB) and concurrent southward subduction beneath the Tarim Block (Jiang et al., 2014). The collision between the YCTB and the Tarim Block is believed to have occurred before Permian (e.g., Gao et al., 2011; Gao and Klemd, 2003; Jiang et al., 2014; Li et al., 2010; Wang et al., 2010; Wang et al., 2016a,b,c). The boundaries between the divisions of the CTA, NTAC, STAC and KYB are typically marked by strike–slip shear zones with both dextral and sinistral kynematics (Fig. 1a, Pirajno, 2010; Wang et al., 2007). Recent Ar–Ar geochronology in mylonites at the southern margin of the NNSZ yield plateau ages of 309.7 ± 2.2 Ma in the Kumishi (Xu et al., 2011) and 290.0 ± 2.4 Ma in the Gangou (Cai et al., 2012, Fig. 1b). In the northern margin of the SCTSZ, Ar–Ar geochronology in mylonitic rocks shows a small range: 298.2 ± 3.0 Ma and 292.4 ± 2.6 Ma in the Maanqiaonan, 280.2 ± 3.7 Ma in the Yaershabulake and 290 ± 11 Ma in the Aotulagelakebulake (Fig. 1b, Cai et al., 2012). These Ar–Ar ages were interpreted as the time of shearing of the main suture zone during a continent-continent collision (Cai et al., 2012). The Terekitinksy I-type granite in the Kyrgyzstan Tianshan yields concordant U–Pb zircon ages from 294 to 291 Ma, whereas the A-type granitic stocks have ages ranging from 299 to 295 Ma (Konopelko et al.,

2. Regional geological setting The Central Asian Orogenic Belt (CAOB), which is sandwiched between the Siberian East European, the Tarim and the North China cratons (Fig. 1a), is one of the largest accretionary orogens in the world (Şengör et al., 1993; Jahn et al., 2004; Wilhem et al., 2012; Windley et al., 2007; Xiao et al., 2009; Jiang et al., 2014). The Tianshan orogenic belt is situated along the south margin of the CAOB (Fig. 1a and b) and Paleozoic intrusions

Lingyun Cu deposit

Precambrian intrusions

Strike-slip fault

3 - South Central Tianshan Suture Zone( SCTSZ)

Ultramafic intrusions

Orogenic Au deposit

4 - North Tarim Fault

Meso- Cenozoic strata

1 - North Tianshan Suture Zone ( NTSZ ) 2 - Nikolaev Line-North Nalati Suture Zone(NNSZ)

0

Early Paleozoic strata

100 km

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ra l

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Lakes

Asia

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Urumqi Ar-Ar 310Ma

Ar-Ar 298Ma

Ar-Ar 290Ma Ar-Ar 280Ma

40° 83°

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Kumishi

Kangxi

Shiyingtan

Matoutan

86°

41°

BSR

88°

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91°

42°

Xingxingxia

CTA

87°

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NTAC

Kangguer

Kuerle

85°

lt

Hongshishan

Hongliuyuan

Ar-Ar 290Ma

84°

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North China

Hami

41°

Tarim Block

Orog Fig.1b

Tulufan

Wangfeng

STAC

n

Tarim

Ar-Ar 292Ma

CTA

Bayinbuluke

60° N

Siberian

nt

Precambrian strata

Junggar Terrane

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Ce

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20 ° E 80 ° N 60 °E 100 ° E 140 °E 80 ° N

European

Late Paleozoic strata

5 - Xingxingxia Fault 44°

60 °N

92°

93°

94°

95°

96°

97° 40°

Fig. 1. (a) Simplified tectonic map of the Central Asian Orogenic Belt (modified from Şengör et al. (1993)). (b) Geological map of the Chinese Tianshan showing the major suture zones and associated orogenic Au deposits (modified from Cai et al. (2012), Gao et al. (2009) and Jiang et al. (2014)).

156

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41°40ƍ 90° 30

41°40ƍ 91° 00

90°45

Fig.3 Lingyun Heibaishan Baijianshan Wolonggan Yanxingshan

41° 30

Yanxingshan shear zone 41°30

Xingeer f 42°00ƍ

42°00ƍ 89° 55ƍ

au

lt

92°

NTAC

00ƍ

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3

90°45 Kaw

Fig.2b

abul

Lingyun

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faul

Quaternary

t t

Aerbishimaibulake Formation

STAC 89° 55 41°01

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15 30 km N

Xingxingxia Group

a

N

b

CTA

Xi ng ee r fa ul

6 km

Yamansu Formation

Gancaohu Formation

Saaerming Formation

Chakou Formation

Baidingshan Formation

Beisainaertage Formation

Yangjibulake Formation

Nanxingeer Formation

Monzonite granite Shear zone

Quartz diorite

Diorite

Fault

Fe occurrence

Cu occurrence

Au occurrence

Fig. 2. (a) Simplified tectonic units of the Lingyun area. (b) Geological map showing locations of the Lingyun Cu deposit and other deposits. Modified from Chen (2008) and the First Geological Team of the Xinjiang Bureau of Geology and Mineral Resources (2008).

conformably overlain by the Lower Devonian Aerbishibulake Formation and unconformably underlain by clastic-carbonate sedimentary rocks of the Gancaohu Formation (Fig. 2b). The Yanxingshan ductile to brittle shear zone extends for more than 30 km in the Lingyun area, with a width of 100–200 m, parallel to the Kawabulake and Xingeer fault (Fig. 2a). The Lingyun Cu deposit and Baijianshan Au–Cu, Wolonggang Cu and Yanxingshan Au occurrences are distributed along the NW–trending Yanxingshan ductile to brittle shear zone (Fig. 2b).

2009). Both of them were attributed to post-collisional granitic magmatism along trans-crustal shear zones (Konopelko et al., 2007). The Kangguer–Huangshan ductile to brittle shear zone is the largest shear zone in the eastern part of the NTAC, with deformation activities ranging from 262.9 to 248.8 Ma (Chen et al., 2009). These shear zones hosts a number of orogenic Au deposits, such as Kangguer (Zhang et al., 2003, 2004), Matoutan (Han et al., 2006; Zhang et al., 2004), Kangxi (Mao et al., 2005), Shiyingtan (Mao et al., 2005; Zhang et al., 2004), Wangfeng (Zhang et al., 2012a,b) and Sawayaerdun (Chen et al., 2012a,b) in the Chinese Tianshan (Fig. 1b). Furthermore, many worldclass orogenic Au deposits, such as Muruntau (Bierlein and Wilde, 2010), Kumtor (Mao et al., 2004) and Jilau (Cole et al., 2000), have also been discovered in the Kyrgyz and Kazakhstan Tianshan. Most of these orogenic Au deposits in the Tianshan orogenic belt were formed during Permian, and are associated with the continent-continent collision. The Lingyun area is located at the northern margin of the STAC (Fig. 1b), sandwiched between the Kawabulake fault to the north and the Xingeer fault to the south (Fig. 2a). This area is mainly covered by clastic-carbonate sedimentary rocks of the Saerming Formation,

3. Geology of the Lingyun Cu deposit The Lingyun mine area is mainly covered by the Aerbishibulake Formation of Lower Devonian, which consists of marble, metamorphosed tuffaceous arkose and sodium-rich marine volcanic rocks or tuff. These rocks are cut by NW–trending Yanxingshan ductile to brittle shear deformation and subsequent fold structures, leading to the characteristic “∽” morphology on the surface (Fig. 3a). These complex and long-term activities are believed to have resulted in syndeformational metamorphism in the Lingyun mine area (e.g., Chen, 2008). The 157

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N 85 °

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Metamorphosed crystal tuff Metamorphosed sodium-rich tuff Metamorphosed crystal tuff Marble and metamorphosed tuffaceous arkose

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Quartz vein

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25

50 m

41°32'39"

50°

90°38'23"

90°39'07"

Diorite dike

Quartz-carbonate vein

Alteration zone

Fault

Shear zone

Cu orebody Zk

Position of drill hole

Fig. 3. (a) Simplified geological map of the Lingyun Cu deposit. Section line A–A′ indicates the location of the cross-section shown in (b). (b) A–A′ prospecting line of the Lingyun Cu deposit. Modified from the First Geological Team of the Xinjiang Bureau of Geology and Mineral Resources (2008).

crystal tuff and occur mainly as mm-scale veinlets (Fig. 5e and f). Sulfide minerals are composed of chalcopyrite, bornite and chalcocite, with minor pyrite, digenite, covellite and pyrrhotite (Fig. 5f–h). The gangue minerals consist of albite, ankerite, quartz, sericite, chlorite and calcite, with minor epidote and biotite. Gangue and sulfide minerals in the Lingyun deposit show common deformation features (Fig. 4c and d). The paragenetic stages, from early (E) to late (L), are recognized on the basis of crosscutting relationships and shown in Fig. 5. They are: (1) E-stage fault-controlled sulfide assemblages (chalcopyrite + bornite + chalcocite)–quartz veins in the foliation of the crystal tuff with albite + sericite ± epidote ± biotite assemblages (Fig. 5a and c); (2) L-stage, the assemblages of ankerite + chalcopyrite + bornite + chalcocite are present in veinlets that cut the Estage assemblages (Fig. 5b and d). Most of the sulfide ores in the Lingyun Cu deposit were formed in the E-stage.

rocks in this area have been strongly mylonitized, and silicate minerals show obvious alteration features. The silicate minerals and associated sulfide assemblages are characterized by elongated fabrics, parallel to the Yanxingshan shear zone. Wall–rock alterations including sericitization, chloritization, epidotization, albitization and carbonatization, have been observed in the Lingyun Cu deposit. The wall–rock alterations in the Lingyun mine area can be divided into two stages. The early (E) stage alterations of the crystal tuff are dominant, which is manifested by ribbon-like chlorite + sericite assemblages and augenlike albite + quartz crystals (Fig. 4a–d). The metamorphosed assemblages of the late (L) stage in greenschist facies are characterized by a “chlorite + albite ± epidote ± actinolite ± quartz” assemblage. In the Lingyun area, no igneous intrusion has been identified. Only a few EW– and NS–trending diorite dikes have been found, in which the EW–trending diorite dikes have been mylonitized, whereas the NS–trending diorite dikes show weak deformation (Figs. 3a and 4b). The NS–trending diorite dikes generally show subhedral granular texture, consisting of > 60% plagioclase, < 35% hornblende, < 5% quartz and minor magnetite, zircon and apatite (Fig. 4e and f). Twelve orebodies have been identified in sodium-rich marine volcanic rocks or tuff in the Lingyun mine area. All orebodies are along the Yanxingshan ductile to brittle shear zone, striking 270–305° and dipping to south with an angle of 67–75° (Fig. 3b). The orebodies are variable in size and the main orebodies are lenticular shaped, while the small orebodies occur as veinlets (Fig. 5a–d). The sulfide assemblages in the Lingyun deposit exhibit elongated striations in the metamorphosed

4. Samples and analytical methods 4.1. U–Pb zircon chronology Crystal tuff and diorite were collected from the Lingyun Cu deposit for U–Pb zircon geochronology. Zircon grains were separated by conventional heavy liquid and magnetic techniques, and then hand-picked under a binocular microscope. The selected zircon grains were mounted in epoxy and then polished to section the crystals for analysis. All zircons were photographed in transmitted, reflected and 158

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a

Fig. 4. Photographs and photomicrographs showing the characteristics of metamorphosed crystal tuff and diorite dike from the Lingyun Cu deposit. (a) The metamorphosed crystal tuff. (b) Diorite dikes intruded and crosscut the crystal tuff. (c and d) The minerals show obvious directional array in the crystal tuff in the relatively large (c) and small scale (d). (e and f) The texture of the diorite dike. Planepolarized light for (e) and cross-polarized light for (f). Abbreviations: Amp = amphibole, Pl = plagioclase, Qtz = quartz, Chl = chlorite, Ser = sericite.

b

(a)

Diorite dike Metamorphosed crystal tuff

ce

df Qtz

Pl

Ser

Chl Pl

Qtz

200 ȝm

2 mm

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f

(d)

(c)

Amp

Chl

Amp

Amp

Amp

Amp

Pl

Pl

200 ȝm

200 ȝm

extraction and alkali washing methods (Du et al., 2012). Analytical uncertainties related to the weighing of samples, 185Re and 190Os spike calibrations, abundances of the blank, isotopic compositions, mass spectrometric measurements, and decay constants are reported at the 2σ level. During the course of this study Re and Os blanks were 0.0017 ± 0.0000 ppb and 0.0002 ± 0.0000 ppb, which are much lower than the Re and Os concentrations in the analyzed samples (Table 1). The standard reference materials of JCBY yielded 38.6859 ppb for Re, 15.868 ppb for Os and 0.3344 ± 0.0005 for 187 Os/188Os, which are in good agreement with previous determinations (Re = 38.61 ± 0.54 ppb, Os = 16.23 ± 0.17 ppb, and 187 Os/188Os = 0.3360 ± 0.0002; 2σ; n = 56; Qu et al., 2009). The Re–Os data and isochron were regressed using the Isoplot/Ex v. 3.0 program (Ludwig, 2003).

cathodoluminescence (CL) light to reveal their internal structures prior to LA–ICP–MS analyses at the Tianjin Institute of Geology and Mineral Resources. The U–Pb isotope analyses were performed with a Newwave 193 nm FX laser coupled to a Finniagan Neptune multi–collector ICP–MS. A beam diameter of 32 μm was used in this study. Analyses of standard zircon SRM610 and GJ–1 were interspersed between the samples. Data were calculated using the ICPMSDataCal program (Liu et al., 2008). Uncertainties in individual analyses are reported at the 1σ level; errors on the ages are quoted at the 95% confidence level. Data reduction was performed using the Isoplot/Ex v. 3.0 program (Ludwig, 2003). 4.2. Re–Os geochronology Re–Os isotope analyses were performed in the National Research Center of Geoanalysis, Chinese Academy of Geological Sciences, Beijing. Three chalcopyrite samples separated from the veinlet-disseminated or veinlet ores of L2 orebody were collected for Re–Os geochronology. The Re–Os analyses were carried out on a Negative TIMS, following the procedures of Du et al. (2001, 2004, 2009) and Zhao et al. (2015). Accurately weighted chalcopyrite sample (∼0.7 g) were spiked with a Re–Os tracer solution with a known amount of 185Re and 190Os abundances. Samples and tracer solution were digested in 5 mL 10 mol/L HCl, 15 mL 16 mol/L HNO3 and 3 mL 30% H2O2 in a sealed Carius tube at 220 °C for 24 h. Rhenium and Os were separated using direct distillation and microdistillation techniques at 80 °C for 2 h (Li et al., 2010). The rhenium fraction was isolated by acetone

4.3. Sericite

40

Ar/39Ar geochronology

One crystal tuff sample for 40Ar/39Ar dating was collected from the country rock of the L1 orebody at the Lingyun Cu deposit. The sample was crushed to minus-80-mesh, from which the sericite flakes were separated using conventional heavy liquid, magnetic techniques and ultrasonic cleaning. Finally, 32.66 mg of sericite flakes was handpicked out using a binocular microscope. The sericite separates and the monitor standard ZBH-25 biotite with an age of 132.7 ± 1.2 Ma, wrapped in aluminum foil and shielded with cadmium foil, were irradiated with fast neutrons for 1444 min at the Chinese Academy of Nuclear Energy Sciences. Step-heating 40Ar/39Ar measurements were 159

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a

b

Ank

Bn Qtz

c

Ccp

e

d

Ser

Bn

f

Ser

Ccp Bn

Qtz

Ccp Qtz

Ser

Ank

200

g

f

m

h

Ccp Ccp

Bn

Bn Ccp 20ȝm

200ȝm

100ȝm

Fig. 5. Characteristics of ore-bearing veins and sulfide textures of different mineralization stages of the Lingyun Cu deposit. (a) E-stage bornite-quartz veins occur in the foliation of crystal tuff. (b) L-stage chalcopyrite-ankerite vein cut the E-stage foliation. (c) E-stage sulfide-quartz veins are parallel to the foliation and show wrinkle-style structure. (d) Taxitic chalcopyrite and bornite assemblages occur in the L-stage ankerite veins. (e and f) E-stage sulfide assemblages and silicate minerals show similar deformation orientation. Transmitted light for (e) and reflected light for (f). (g) Chalcopyrite and bornite show latticed exsolution texture. (h) Chalcopyrite and bornite show exsolution texture, and bornite replaces chalcopyrite. Abbreviations: Qtz = quartz, Ank = ankerite, Ser = sericite, Ccp = chalcopyrite, Bn = bornite.

conducted by MM-1200B Mass Spectrometer at the Ar–Ar Laboratory, Institute of Geology, Chinese Academy of Geological Sciences (Beijing). The detailed analytical procedures in this study can be found in Chen and Liu (2002). Mineral separates were step-heated in 9–10 steps at incrementally high power. All the measured data were corrected for mass discriminations, argon component, blanks and irradiation-induced mass interference. The correction factors of interfering isotopes produced during the irradiation were determined by the analysis of irradiated pure salts of K2SO4 and CaF2 ((36Ar/37Ar)Ca = 0.0002389, (40Ar/39Ar)K = 0.004782, (39Ar/37Aro)Ca = 0.000806). All 37Ar were corrected for radiogenic decay, the decay constant used is λ = 5.543 × 10−10 a−1. The errors are reported at 2σ deviations.

at the Beijing Research Institute of Uranium Geology. Trace elements and rare earth elements (REE) were measured using ICP–MS (FinniganMAT Element I), following the procedures of Dulski (1994). The analytical precision is generally better than 5%, and reference materials of GBW07106 and GBW07312 were used to monitor the analytical quality.

4.5. Fluid inclusion studies Representative samples from E-stage (sulfide assemblages–quartz veins) and L-stage (sulfide assemblages–ankerite veins) were selected for fluid inclusion studies. Fluid inclusions were carefully observed to identify their genetic and composition types, vapor-liquid ratios, and spatial clustering (Table 2, Fig. 6). Microthermometry was conducted using a Linkam THMS600 heating-freezing stage (from −198 to 600 °C) at the Institute of Geology and Geophysics, Chinese Academy of Sciences. The estimated accuracy is about ± 0.1 °C at temperatures below

4.4. Trace elements analyses A total of 7 fresh crystal tuff and 7 sulfide ore samples were collected from the Lingyun Cu deposit. All of these samples were analyzed 160

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Table 1 Zircon U–Pb LA–ICP–MS analytical data of the diorite dike and metamorphosed crystal tuff from the Lingyun Cu deposit. Spot No.

U

Th

Pb

ppm

ppm

ppm

Th/U

Isotope composition Pb/206Pb*

Age (Ma)

207

1σ

207

Pb*/235U

1σ

206

Pb*/238U

1σ

207

Pb/206Pb

1σ

207

Pb/235U

1σ

206

Pb/238U

1σ

207* 185* 219 203* 182* 208* 186* 218* 195* 223 225 221 194* 220 205* 225 220 221 206* 221 202* 1919* 222 199* 219 220 218

1 1 1 1 1 1 2 1 1 1 1 1 2 1 1 1 1 1 1 1 2 10 1 1 1 1 1

Sample no. L11, diorite 875 189 1* 2* 681 763 3 571 372 * 645 109 4 5* 935 1061 6* 651 246 885 1546 7* 8* 428 93 * 9 1070 741 10 349 159 11 619 264 12 707 307 13* 763 1300 14 1505 607 15* 875 876 16 840 1063 17 971 571 18 1067 189 19* 1076 660 20 1342 301 21* 1281 1671 22* 269 28 23 632 141 * 24 1024 752 25 944 293 26 1000 1315 27 1105 802

29 24 21 22 30 23 38 16 39 14 24 26 29 55 32 35 36 38 37 47 47 97 23 37 34 40 43

0.47 1.06 0.81 0.41 1.07 0.61 1.32 0.47 0.83 0.67 0.65 0.66 1.31 0.64 1.00 1.12 0.77 0.42 0.78 0.47 1.14 0.32 0.47 0.86 0.56 1.15 0.85

0.0581 0.0907 0.0508 0.0695 0.0712 0.0694 0.1985 0.0710 0.0951 0.0501 0.0496 0.0506 0.1034 0.0507 0.0671 0.0500 0.0507 0.0504 0.0594 0.0505 0.0587 0.1179 0.0505 0.0738 0.0510 0.0504 0.0516

0.0005 0.0007 0.0005 0.0009 0.0009 0.0006 0.0033 0.0013 0.0008 0.0008 0.0010 0.0005 0.0009 0.0004 0.0005 0.0005 0.0004 0.0005 0.0004 0.0003 0.0004 0.0005 0.0007 0.0004 0.0005 0.0004 0.0005

0.2610 0.3634 0.2415 0.3072 0.2805 0.3137 0.7995 0.3373 0.4033 0.2433 0.2434 0.2435 0.4347 0.2425 0.2986 0.2445 0.2427 0.2428 0.2667 0.2428 0.2577 5.6342 0.2438 0.3188 0.2425 0.2413 0.2441

0.0021 0.0030 0.0027 0.0042 0.0035 0.0029 0.0083 0.0063 0.0033 0.0041 0.0051 0.0022 0.0039 0.0021 0.0020 0.0030 0.0018 0.0021 0.0021 0.0016 0.0016 0.0280 0.0035 0.0020 0.0024 0.0020 0.0020

0.0326 0.0291 0.0345 0.0321 0.0286 0.0328 0.0292 0.0344 0.0308 0.0352 0.0356 0.0349 0.0305 0.0347 0.0323 0.0355 0.0347 0.0349 0.0326 0.0349 0.0318 0.3467 0.0350 0.0313 0.0345 0.0347 0.0343

0.0002 0.0002 0.0002 0.0002 0.0002 0.0002 0.0003 0.0002 0.0002 0.0002 0.0002 0.0002 0.0003 0.0002 0.0002 0.0002 0.0002 0.0002 0.0002 0.0002 0.0002 0.0018 0.0002 0.0002 0.0002 0.0002 0.0002

533 1440 230 913 964 911 2814 958 1530 198 177 221 1686 229 840 195 226 215 583 219 558 1924 219 1036 240 213 267

19 15 25 27 25 18 27 37 16 39 47 23 17 20 16 23 18 23 15 14 16 8 34 12 22 19 20

235 315 220 272 251 277 597 295 344 221 221 221 366 220 265 222 221 221 240 221 233 1921 221 281 221 220 222

2 3 2 4 3 3 6 5 3 4 5 2 3 2 2 3 2 2 2 1 1 10 3 2 2 2 2

Sample no. L10, crystal tuff 1* 690 563 2* 582 474 * 3 169 293 * 4 380 178 5* 488 390 6 557 1440 7* 420 328 8* 986 717 * 9 784 312 * 10 564 548 * 11 337 216 12* 333 481 13* 574 563 14* 278 365 15* 369 187 * 16 848 0 * 17 529 2994 * 18 572 50 19* 524 551 20* 521 559 21* 826 1904 26* 102 730 * 27 388 178 * 28 1011 1067 * 29 577 410 30* 484 503 31* 523 894 32* 904 2941 33* 577 1003 * 34 417 439 * 35 636 798 36 539 400 37* 446 261 38* 245 598 39 333 234 40* 271 358 41* 912 0 42 449 378 * 43 551 654 44 430 504 45 710 651 46* 550 399 47* 231 309

50 47 15 28 37 46 35 75 58 43 27 28 44 22 29 17 23 55 39 39 63 18 30 78 45 37 41 82 48 32 49 39 33 20 24 22 12 32 45 32 51 40 34

0.90 0.90 1.32 0.68 0.89 1.61 0.88 0.85 0.63 0.99 0.80 1.20 0.99 1.15 0.71 0.02 2.38 0.30 1.03 1.04 1.52 2.68 0.68 1.03 0.84 1.02 1.31 1.80 1.32 1.03 1.12 0.86 0.77 1.56 0.84 1.15 0.02 0.92 1.09 1.08 0.96 0.85 1.16

0.0646 0.0934 0.1129 0.0769 0.0696 0.0589 0.1068 0.0906 0.0810 0.0684 0.0861 0.1016 0.0722 0.0702 0.0950 0.1550 0.1235 0.0923 0.0643 0.0657 0.0633 0.0660 0.0999 0.0657 0.0866 0.0715 0.0641 0.2001 0.0771 0.0834 0.0843 0.0613 0.0800 0.0861 0.0622 0.1103 0.0723 0.0618 0.0923 0.0591 0.0605 0.0641 0.1134

0.001 0.001 0.003 0.001 0.001 0.001 0.002 0.004 0.003 0.001 0.002 0.001 0.001 0.002 0.002 0.004 0.003 0.001 0.003 0.001 0.001 0.001 0.002 0.001 0.001 0.001 0.001 0.003 0.001 0.002 0.001 0.001 0.001 0.002 0.001 0.002 0.002 0.001 0.002 0.001 0.001 0.001 0.002

0.5740 0.8686 1.0311 0.6967 0.6349 0.5320 0.9678 0.8018 0.7333 0.6195 0.8028 0.9217 0.6549 0.6378 0.8718 0.3320 0.4648 1.1027 0.5840 0.5954 0.5736 1.1467 0.9083 0.6111 0.8036 0.6630 0.5768 1.5996 0.7032 0.7490 0.7526 0.5563 0.7263 0.7794 0.5616 0.9255 0.1294 0.5570 0.8379 0.5334 0.5432 0.5789 1.6923

0.0118 0.0120 0.0270 0.0110 0.0105 0.0088 0.0185 0.0382 0.0247 0.0107 0.0207 0.0137 0.0109 0.0150 0.0196 0.0089 0.0118 0.0167 0.0299 0.0096 0.0079 0.0224 0.0161 0.0084 0.0139 0.0102 0.0102 0.0228 0.0102 0.0216 0.0129 0.0079 0.0117 0.0210 0.0111 0.0157 0.0027 0.0095 0.0220 0.0086 0.0075 0.0098 0.0273

0.0644 0.0674 0.0663 0.0657 0.0662 0.0655 0.0657 0.0642 0.0657 0.0657 0.0676 0.0658 0.0658 0.0659 0.0665 0.0155 0.0273 0.0867 0.0659 0.0657 0.0657 0.1260 0.0659 0.0675 0.0673 0.0673 0.0653 0.0580 0.0661 0.0651 0.0648 0.0658 0.0658 0.0657 0.0655 0.0609 0.0130 0.0654 0.0658 0.0655 0.0652 0.0655 0.1082

0.0006 0.0007 0.0007 0.0006 0.0006 0.0006 0.0006 0.0007 0.0006 0.0006 0.0007 0.0006 0.0006 0.0007 0.0006 0.0002 0.0003 0.0010 0.0007 0.0006 0.0006 0.0012 0.0007 0.0006 0.0007 0.0006 0.0006 0.0007 0.0006 0.0007 0.0006 0.0007 0.0006 0.0007 0.0006 0.0006 0.0001 0.0006 0.0006 0.0006 0.0006 0.0006 0.0011

762 1496 1846 1118 917 564 1745 1437 1221 880 1340 1653 991 933 1529 2402 2008 1473 751 797 719 806 1622 797 1352 971 743 2827 1125 1280 1299 650 1198 1340 681 1804 995 665 1474 570 621 745 1855

40 23 41 29 32 33 31 81 66 33 46 24 31 45 40 45 41 23 101 30 26 39 28 26 33 29 35 21 26 49 31 28 28 50 40 27 43 34 47 32 27 32 28

461 635 719 537 499 433 687 598 559 490 598 663 511 501 637 291 388 755 467 474 460 776 656 484 599 516 462 970 541 568 570 449 554 585 453 665 124 450 618 434 441 464 1006

9 402* 9 421* 19 414* 8 410* 8 413* 7 409 13 410* 28 401* 19 410* 8 410* 15 422* 10 411* 8 411* 12 412* 14 415* 8 99* 10 174* 11 536* 24 411* 8 410* 6 410* 15 765* 12 412* 7 421* 10 420* 8 420* 8 408* 14 363* 8 413* 16 407* 10 405* 6 411 9 411** 16 410* 9 409 11 381* 3 83* 8 409 16 411* 7 409 6 407 8 409* 16 662* (continued on next

161

4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 1 2 6 4 4 4 7 4 4 4 4 4 4 4 4 4 4 4 4 4 4 1 4 4 4 4 4 7 page)

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Y. Zhao et al.

Table 1 (continued) Spot No.

48* 49* 50 51 52 53* 54* 55 56* 57 58* 59* 60* 61 62* 63* 64 65* 66* 67* 68* 69 70 71* 72* 73 74 75* 76 77* 78* 79* 80 81 82 83* 84 85* 86 87 88 89 90* 91 92* 93 94 95* 96* 97 98* 99 100* 101 102* 103* 104* 105* 106 107* 108* 109 110* 111* 112 113

U

Th

Pb

ppm

ppm

ppm

302 560 441 277 829 303 916 563 476 346 786 776 407 427 2418 659 839 704 370 191 475 852 442 574 1841 617 278 748 406 734 398 610 203 444 503 484 486 539 480 468 585 802 393 354 197 150 364 376 297 190 645 175 648 180 630 614 288 1069 431 707 335 348 1862 144 349 330

112 198 244 139 480 298 89 471 1128 463 608 207 698 365 1 216 358 183 366 106 800 319 115 319 18 251 91 424 149 406 504 115 174 175 817 229 223 212 163 47 303 90 108 87 80 53 136 441 156 69 293 163 336 93 661 354 228 0 509 339 316 849 0 101 154 170

22 49 32 20 59 25 177 40 42 28 64 55 31 32 52 47 62 52 31 14 16 60 30 42 160 43 19 54 29 47 12 45 15 31 40 37 34 38 33 30 43 53 27 24 15 10 26 31 22 13 47 13 48 13 50 46 22 19 34 60 32 29 28 11 25 24

Th/U

Isotope composition Pb/206Pb*

0.61 0.59 0.74 0.71 0.76 0.99 0.31 0.91 1.54 1.16 0.88 0.52 1.31 0.92 0.02 0.57 0.65 0.51 0.99 0.75 1.30 0.61 0.51 0.75 0.10 0.64 0.57 0.75 0.61 0.74 1.12 0.44 0.93 0.63 1.27 0.69 0.68 0.63 0.58 0.32 0.72 0.34 0.52 0.49 0.64 0.60 0.61 1.08 0.73 0.60 0.67 0.97 0.72 0.72 1.02 0.76 0.89 0.02 1.09 0.69 0.97 1.56 0.01 0.84 0.66 0.72

Notes: Common Pb corrected using measured

Age (Ma)

207

1σ

207

Pb*/235U

1σ

206

Pb*/238U

1σ

207

Pb/206Pb

0.0848 0.0728 0.0605 0.0585 0.0615 0.0919 0.1376 0.0620 0.0662 0.0602 0.0695 0.0655 0.0954 0.0572 0.0708 0.0642 0.0614 0.0697 0.0791 0.0645 0.0697 0.0574 0.0571 0.0649 0.0791 0.0571 0.0550 0.1125 0.0618 0.0776 0.0585 0.0744 0.0569 0.0560 0.0573 0.0659 0.0581 0.0646 0.0579 0.0566 0.0616 0.0586 0.0632 0.0578 0.0953 0.0588 0.0580 0.0884 0.0642 0.0605 0.0646 0.0581 0.0791 0.0611 0.0826 0.0630 0.0679 0.1149 0.0584 0.0830 0.0720 0.0576 0.0515 0.0634 0.0608 0.0580

0.002 0.001 0.001 0.001 0.001 0.002 0.002 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.002 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.001 0.001 0.001 0.001 0.003 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.002 0.002 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

0.7698 0.8118 0.5468 0.5276 0.5492 0.8328 3.2309 0.5602 0.5993 0.5438 0.6770 0.5928 0.7881 0.5121 0.2174 0.5822 0.5577 0.6477 0.7316 0.5895 0.2545 0.5200 0.5145 0.5838 0.9682 0.5132 0.4896 0.9287 0.5606 0.6471 0.2026 0.7297 0.5089 0.5044 0.5130 0.6357 0.5240 0.5861 0.5179 0.5039 0.5581 0.5307 0.5730 0.5187 0.8716 0.5285 0.5253 0.8139 0.5814 0.5483 0.5862 0.5226 0.7173 0.5532 0.7488 0.5709 0.6150 0.2755 0.5243 0.8434 0.6521 0.5151 0.1177 0.5679 0.5473 0.5193

0.0157 0.0135 0.0083 0.0107 0.0097 0.0155 0.0443 0.0087 0.0111 0.0095 0.0107 0.0089 0.0185 0.0086 0.0073 0.0088 0.0104 0.0115 0.0119 0.0154 0.0083 0.0073 0.0081 0.0083 0.0155 0.0071 0.0088 0.0133 0.0082 0.0094 0.0051 0.0100 0.0106 0.0216 0.0073 0.0106 0.0078 0.0086 0.0076 0.0085 0.0110 0.0075 0.0097 0.0084 0.0262 0.0137 0.0083 0.0132 0.0099 0.0121 0.0091 0.0124 0.0102 0.0138 0.0151 0.0084 0.0150 0.0051 0.0083 0.0160 0.0129 0.0083 0.0018 0.0140 0.0101 0.0104

0.0658 0.0808 0.0655 0.0654 0.0647 0.0657 0.1703 0.0655 0.0657 0.0656 0.0707 0.0657 0.0599 0.0650 0.0223 0.0658 0.0658 0.0674 0.0670 0.0663 0.0265 0.0657 0.0654 0.0653 0.0887 0.0652 0.0646 0.0599 0.0657 0.0605 0.0251 0.0711 0.0649 0.0653 0.0650 0.0700 0.0654 0.0657 0.0649 0.0646 0.0658 0.0657 0.0658 0.0650 0.0663 0.0651 0.0657 0.0668 0.0657 0.0657 0.0658 0.0653 0.0658 0.0656 0.0657 0.0658 0.0657 0.0174 0.0651 0.0737 0.0657 0.0648 0.0166 0.0650 0.0653 0.0650

0.0006 0.0008 0.0006 0.0006 0.0006 0.0006 0.0018 0.0006 0.0006 0.0007 0.0007 0.0007 0.0006 0.0006 0.0004 0.0007 0.0007 0.0007 0.0007 0.0007 0.0003 0.0006 0.0007 0.0006 0.0012 0.0006 0.0006 0.0006 0.0006 0.0007 0.0002 0.0007 0.0006 0.0006 0.0006 0.0007 0.0006 0.0007 0.0006 0.0006 0.0006 0.0007 0.0006 0.0006 0.0007 0.0006 0.0007 0.0006 0.0006 0.0006 0.0007 0.0006 0.0006 0.0006 0.0006 0.0006 0.0006 0.0002 0.0006 0.0007 0.0012 0.0006 0.0002 0.0006 0.0006 0.0006

1311 1010 622 547 658 1465 2197 675 812 609 913 789 1537 498 952 748 655 921 1176 758 919 506 495 770 1175 496 411 1839 669 1136 547 1052 487 454 502 803 534 763 526 475 659 551 714 524 1534 561 531 1392 748 621 762 532 1174 644 1260 707 865 1878 545 1269 986 516 264 720 631 529

1σ

207

Pb/235U

37 29 30 42 36 32 20 31 36 36 28 28 38 35 36 31 35 34 29 53 64 28 32 26 23 28 38 28 29 37 53 25 44 99 28 33 29 27 30 35 40 29 34 33 49 55 33 28 34 46 27 51 26 52 39 29 49 24 32 32 36 33 32 49 37 42

580 603 443 430 445 615 1465 452 477 441 525 473 590 420 200 466 450 507 557 471 230 425 421 467 688 421 405 667 452 507 187 556 418 415 420 500 428 468 424 414 450 432 460 424 636 431 429 605 465 444 468 427 549 447 568 459 487 247 428 621 510 422 113 457 443 425

1σ

206

Pb/238U

1σ

12 10 7 9 8 11 20 7 9 8 8 7 14 7 7 7 8 9 9 12 8 6 7 7 11 6 7 10 7 7 5 8 9 18 6 8 6 7 6 7 9 6 8 7 19 11 7 10 8 10 7 10 8 11 11 7 12 5 7 12 10 7 2 11 8 9

411* 501* 409 409 404 410* 1014* 409 410* 409 440* 410* 375* 406 142* 411* 411 420* 418* 414* 168* 410 408 408* 548* 407 404 375* 410 379* 160* 443* 405 408 406 436* 408 410* 405 404 411 410 411* 406 414* 407 410 417* 410* 410 411* 408 411* 410 410* 411* 410* 111* 407 459* 410* 405 106* 406* 408 406

4 5 4 4 4 4 11 4 4 4 5 4 4 4 3 4 4 4 4 4 2 4 4 4 8 4 4 4 4 5 2 4 4 4 4 4 4 4 4 4 4 4 4 4 5 4 4 4 4 4 4 4 4 4 4 4 4 2 4 5 8 4 1 4 4 4

204

Pb. *The spots were excluded for calculating weighted average age.

Laser Raman spectroscopy of fluid inclusions was carried out using a LabRAM HR800 Raman micro-spectrometer at the Institute of Geology and Geophysics, Chinese Academy of Sciences. An argon ion laser with a wavelength of 514.5 nm and a source power of 20 mW × 100% was

−70 °C, ± 0.2 °C at temperatures from −70 to 100 °C, and ± 2 °C at high temperatures (100–500 °C). The heating rate was maintained from 0.2 to 5 °C min−1, but reduced to 0.1–0.5 °C/min close to phase-change conditions. 162

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Y. Zhao et al.

Table 2 Re–Os isotope data for chalcopyrite from the E-stage sulfides-quartz vein of the Lingyun Cu Deposit. Sample no.

Weight (g)

Total Re (ppb) ± 2σ

Common Os (ppb) ± 2σ

187

L2-138C2-3 L2-138C-3 L2-138C-2 JCBY Blank

0.6008 0.6902 0.6002 0.2048 1.0000

7.5534 ± 0.0558 11.4426 ± 0.0871 5.2014 ± 0.0384 38.6859 ± 0.2856 0.0017 ± 0.0000

0.0049 0.0015 0.0015 15.868 0.0002

0.0355 0.0393 0.0199 0.6904 0.0000

± ± ± ± ±

0.0000 0.0000 0.0000 0.1196 0.0000

Os (ppb) ± 2σ ± ± ± ± ±

0.0003 0.0003 0.0002 0.0052 0.0000

187

Re/188Os ± 2σ

187

Os/188Os ± 2σ

7385.2 ± 75.4 37308.2 ± 388.5 16504.2 ± 169.0 11.8 ± 0.1 38.0 ± 0.6

55.2710 ± 0.1266 204.0154 ± 0.4437 100.7375 ± 0.2328 0.3344 ± 0.0005 0.3494 ± 0.0033

Notes: JCBY, in-house standard sample, recommended values (38.61 ± 0.53 ppb for Re, 16.23 ± 0.17 ppb for Os and 0.3363 ± 0.0029 for 2009).

used in detection. The spectral range falls between 50 and 4000 cm−1 for the analysis of CO2, N2, and CH4 in the vapor phase. Final melting temperatures of ice (Tm-ice) and clathrate (Tm-clath) were measured to calculate salinities of NaCl–H2O (Bodnar, 1993) and NaCl–H2O–CO2 ± N2 (Collins, 1979) fluid systems, respectively. Densities of the NaCl–H2O fluid system were calculated using the equation of the Liu and Duan (1987), and the densities of the NaCl–H2O–CO2 ± N2 fluid system were estimated based on diagrams of Shepherd et al. (1985).

187

187

Os/188Os (initial)

18.5270 18.3940 18.6233 – –

Os/188Os) (Du et al., 2012; Qu et al.,

data yielded an isochron age of 297.9 ± 3.4 Ma (MSWD = 0.54) with an initial 187Os/188Os value of 0.680 ± 0.039 (Fig. 8). 5.3. Sericite

40

Ar/39Ar age

Argon loss occurred in the relatively low and high temperature steps (Table 3), which may indicate minor Ar loss from grain margins or secondary phase, possibly chlorite, respectively. Sericite sample yielded plateau ages based on 81.7% 39Ar released from six consecutive steps (Fig. 9). The combined plateau age calculated for the indicated steps is 292.3 ± 2.4 Ma (MSWD = 0.69) (Fig. 9b). Regressing the most radiogenic steps through the composition of atmospheric argon (40Ar/36Ar=274 ± 37) on an inverse isochron diagram (Fig. 9a) results in a date of 292.2 ± 4.6 Ma (MSWD = 2.1), which is within the error of the plateau age.

5. Results 5.1. U–Pb zircon geochronology results Zircons from crystal tuff of country rock are colorless, semi-transparent to transparent, stubby to prismatic euhedral, and generally 35–120 μm in length and 30–65 μm in width with a length to width ratio of 1:1 to 2:1. Most crystals display oscillatory or patchy linear zoning with variable luminescence in CL images (Fig. 6a–c). Typical igneous zircons are characterized by high Th/U ratios (> 0.4) whereas the metamorphic zircons show relatively low Th/U values (generally < 0.1). Among the one hundred and nine analyzed zircon grains, six zircons (spot 16, 41, 62, 72, 105 and 110) were excluded due to low Th/U values (< 0.1). In addition, six zircons (spot 17, 18, 47, 54, 68 and 78) were excluded because of their extremely light color, which may indicate the Pb loss. In summary, of the total of 109 analyses, each on a single crystal, about 67% are > 10% discordant, which was likely to result from the Pb losses due to a metamorphic event (Table 1). The remaining 36 analyses yield a concordia age of 405.4 ± 2.9 Ma (MSWD = 0.23, n = 36), which is considered to be the eruption age of the crystal tuff (Table 1). Zircons from the diorite vary from euhedral to anhedral with most occurring as initially equant to short or long prismatic crystals (Fig. 7a and b). The lengths of the crystals range from 36 to 110 μm with aspect ratios from 1:1 to 2:1. Most crystals display oscillatory or patchy linear zoning with variable luminescence in CL images (Fig. 7a and b). Among the 27 analyzed grains, one (spot 22) yielded old apparent ages of 1924 ± 8 Ma that may indicate inheritance from old zircons (Li et al., 2009; Zhu et al., 2009). About 52% zircon grains are > 5% discordant and abandoned, which was likely to result from the Pb losses due to a metamorphic event. The remaining 13 analyses present consistent 206 Pb/238U apparent ages of 221.0 ± 1.4 Ma (MSWD = 3.8) (Table 1; Fig. 7e), which is considered to be the crystallization age of the diorite dike.

5.4. Trace elements On the REE spider diagrams normalized to chondrites, the crystal tuff samples of the Lingyun Mine area are marked by strong enrichment in light rare earth elements (LREE) relative to heavy rare earth elements (HREE) (Table 4; Fig. 10b). The Eu/Eu∗ values of the samples vary from 0.71 to 0.9, indicating that parental magma has experienced minor plagioclase crystallization. Primitive mantle normalized incompatible trace elements patterns are characterized by a pronounced depletion of Sr and enrichment of Rb, Th, U, Nd and P (Table 4; Fig. 10b). We also note that the sulfide ores and crystal tuff show similar REE patterns (Table 5; Fig. 10a). 5.5. Types of fluid inclusions, microthermometry and laser Raman spectroscopy In this study, three types of fluid inclusions were identified based on their phases (L–V–S) at room temperature, phase transitions observed during heating and cooling, and laser Raman spectroscopy data. These are aqueous (W-type), mixed aqueous-carbonic (M-type) and pure carbonic (C-type) inclusions in the Lingyun Cu deposit. These three types of fluid inclusions are all found in the E-stage quartz whereas only the W-type fluid inclusions have been observed in L-stage ankerite. (1) W-type: These aqueous (H2O–NaCl) fluid inclusions usually appear as two-phase (liquid water and vapor water) fluid inclusions at room temperature (Fig. 11a). Morphologically, they show variations from oval, tubular or irregular shapes, and they vary in size from 1 to 5 μm. Trace content of CO2 has been identified in the vapor bubbles by laser Raman spectroscopy. The primary W-type fluid inclusions have been observed in E-stage quartz and L-stage ankerite (Fig. 11a–c). We also note that the W-type inclusions of the L-stage are rare and in small size. (2) M-type inclusions are composed of H2O, CO2 and minor N2 phases (Fig. 11a and d), with the CO2 phase accounting for 20%–80% of the volume. They vary from 2 to 7 μm in size, which are the main types of fluid inclusions observed in the E-stage quartz of the Lingyun Cu deposit.

5.2. Re–Os age of Cu mineralization The analyzed 3 chalcopyrite samples from Lingyun Cu deposit possess total Re and common Os abundances ranging from 5.2014 ± 0.0384 to 11.4426 ± 0.0871 ppb and from 0.0015 ± 0.0000 to 0.0049 ± 0.0000 ppb (Table 2), respectively. The samples have 187Re/188Os ratios varying from 7385.2 ± 75.4 to 187 37308.2 ± 388.5, with Os/188Os ratios range from 55.2710 ± 0.1266 to 204.0154 ± 0.4437. Regression of the Re–Os 163

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06

36

44

42

39

50

45

51

55

52

411±4 409±4 409±4 409±4 407±4 409±4 409±4 404±4

409±4 69

70

80

74

73

81

76

82

409±4 409±4 406±4 411±4 86

84

410±4 408±4 407±4 404±4 410±4 405±4 408±4 406±4 408±4 91

93

97

94

99

106

101

406±4 407±4 410±4 410±4 408±4 410±4 407±4 405±4 01

03

02

04

15

20

19

28

27

21

415±4 411±4 410±4 410±4 412±4 43

38

48

46

113

89

100 m

a

406±4 11

10

09

88

12

14

13

413±4 410±4 401±4 410±4 410±4 422±4 411±4 411±4 412±4

421±4 414±4 410±4

402±4

08

07

05

408±4

87

405±4 404±4 411±4 410±4

112

109

64

61

57

29

33

31

30

35

34

37

421±4 420±4 420±4 408±4 413±4 407±4 405±4 411±4 65 56

53

63

59

66

67

71

85

410±4 411±4 409±4 411±4 410±4 410±4 410±4 411±4 420±4 418±4 414±4 408±4 410±4 95

92

90

98

96

414±4 417±4 410±4 411±4

411±4

104

102

100

103

108

111

100 m

411±4 410±4 411±4 410±4 410±4 406±4

b

68

99 ± 1

174±2

83±1

142±3 169±2 160±2

111±2

106±1

363±4 381±4 375±4

100ȝm

77

440±5

436±4

379±5

536±6 418

420

0.067 238

Pb/ U

0.08 400

410

0.066 0.065

206

200

0.063 0.42

Mean =405.4±2.9Ma MSWD=0.23 0.46

0.50 207

0

1

e

765±7

662±7 1014±11

c

data-point error symbols are 1ı

207

2

410

406

400

0.064

0.04

Age (Ma)

data-point error ellipses are90% conf. 0.068

0.12 600

548±8

414

800

0.00

501±5

1000

206

238

459±2

1200

0.16

Pb/ U

443±4

d

0.20

375±4

Pb/ 2 3 5 U

0.54

0.58

402

0.62

Pb/ 2 3 5 U 3

4

398

Mean= 407.8±1.3Ma [0.32%] 95% conf. Wtd by data-pt errs only, 0 of 36 rej. MSWD= 0.29, probability = 1.000

Fig. 6. Cathodoluminescence (CL) images of zircons. (a) zircon grains were selected for calculating concordia and weighted mean ages and some zircon grains were abandoned due to Pb loss or > 10% discordant (b and c), U–Pb concordia plot (d) and weighted mean 206Pb/238U diagram (e) of the crystal tuff in the Lingyun mine area.

inclusions from E-stage quartz grains vary from −20.0 to −0.9 °C. Correspondingly, the salinities are ranging from 1.6 to 14.9 wt% NaCl eqv, with a majority from 2 to 4 wt% NaCl eqv. Homogenization occurred to the liquid phase between 130 and 370 °C. Based on the equation of Liu and Duan (1987), the calculated densities are ranging from 0.75 to 0.94 g/cm3. The Tm(CO2) of M-type fluid inclusions range from −62.5 to −58.2 °C and Clathrate melting temperatures are from 2.5 to 4.5 °C, with salinities ranging from 3.3 to 10.8 wt% NaCl eqv.

(3) C-type fluid inclusions consist of a large amount of CO2 with minor H2O liquid and N2 vapor at room temperature, including monophasic CO2 (vapor or liquid; Fig. 11c) and two-phase CO2 (VCO2 + LCO2). These fluid inclusions vary between 2 and 8 μm in size and occur in isolation within quartz grains. Microthermometric data of the Lingyun Cu deposit are summarized in Table 6. The ice melting temperatures (Tm(ice)) of W-type fluid 164

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Y. Zhao et al.

03

11

10

225±1

223±1

219±1 18

20

221±1

221±1

01

23

25

222±1

219±1

13

195±1

194±2

205±1

Pb/ 2 3 8 U

200

206

206

Pb/ 2 3 8 U

e

210

0.030

0.1 400

0.028

(d)

0

2

207

235

Pb/ U

4

230

230

e

0.0358

226

Age (Ma)

222

206

0.0346 218

f

0.3

207

0.52 3 5

Pb/ U

0.7

0.9

data-point error symbols are 1ı

224 222 220 218

0.0342

216 214

180

226

0.0354 0.0350

190

0.026 0.1

6

228

Pb/ 238 U

240 230

0.032

1200 800

0.0338

199±1

0.034

1600

0.2

0.0362

m

220

0.3

0.0

100

24

1924±8

0.036

2000

b

218±1

22

d

a

08

186±2

202±2

c

0.4

07

0.038

m

218±1

220±1

21

206±1

100

27

208±1

19

15

09

26

06

182±1

220± 1

225±1

220±1

05

203±1

185±1

17

16

14

221±1

04

02

207±1

12

Mean=221.0±1. 4[0.63%] 95% conf Wtd by data-point errors only MSWD=3.8,probability=0.000

0.0334 0.228 0.232 0.236 0.240 0.244 0.248 0.252 0.256 207

214

Mean=221.0±1.4 [0.63%] 95% conf. Wtd by data-piont errors only MSWD=3.8,probability=0.000

212

Pb/ 2 3 5 U

Fig. 7. Representative CL images of zircons for calculating concordia and weighted mean ages (a-b) and some zircons (c-d) were excluded because of > 5% discordant. The U–Pb concordia plot (e) and weighted mean 206Pb/238U diagram (f) of the diorite dikes that crosscut the crystal tuff.

temperature (Th) of the C-type fluid inclusions fall between 250 and 320 °C. The Tm(ice) of W-type fluid inclusions from L-stage ankerite range from −1.0 to −3.0 °C, with salinities from 1.7 to 5 wt% NaCl eqv. Homogenization occurred to the liquid phase between 135 and 150 °C and the estimated bulk densities are ∼0.9 g/cm3.

Total homogenization temperature (Th) of the M-type fluid inclusions fall between 238 and 378 °C. Most of Tm(CO2) values of C-type fluid inclusions vary from −63.6 to −61.4 °C, which is slightly lower the triple point of CO2 (56.6 °C). Clathrate melting temperatures of M-type fluid inclusions range from 1.2 to 3.6 °C, corresponding to salinities between 9.0 and 14.2 wt% NaCl eqv. The CO2 phase homogenizes to a liquid at temperatures from 3.0 to 19.1 °C. Total homogenization 165

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Y. Zhao et al.

data-point error ellipses are 2ı

to the formation of the Lingyun Cu deposit. The sulfide assemblages in the Lingyun Cu deposit are characterized by elongated striations in the crystal tuff. Ribbon-like sericite lamellaes from the crystal tuff show common deformation features with sulfide assemblages, plagioclase, quartz and chlorite (Fig. 4c and d), suggesting that the sericites formed by syndeformational metamorphism rather than by hydrothermal alteration. These sericites yielded a 40Ar/39Ar plateau age of ca. 292 Ma, indicating that syndeformational metamorphism is coeval with the mineralization event (ca. 297 Ma) in the Lingyun Cu deposit within the measurement uncertainties. Orogenic-type deposits are exclusively found in metamorphic terranes, which are structurally controlled and closely associated with major shear zones (Groves et al., 2003). Large-scale strike-slip shear zones were developed during the continent-continent collision in the Tianshan orogenic belt, accompanied by a number of orogenic-type deposits (e.g., Zhang et al., 2003; Han et al., 2006; Mao et al., 2005; Zhang et al., 2012a,b; Chen et al., 2012a,b). Increasing numbers of shear zone–hosted deposits and occurrences have been found in recent years along the Yanxingshan shear zone (e.g., Lingyun, Baijianshan, Wolonggang and Yanxingshan, Fig. 2b). In the Lingyun Cu deposit, orebodies occurred along the Yanxingshan ductile to brittle shear zone. Besides, both sulfide assemblages and silicate minerals show common elongated striations, which are similar to those from orogenic-type deposits (e.g., Groves et al., 2003; Chen et al., 2007; Pirajno, 2009). The collision between the YCTB and the Tarim Block is believed to have occurred before Permian, based on the precise dating of metamorphic events in the STAC (e.g., Gao et al., 2011; Gao and Klemd, 2003; Jiang et al., 2014; Li et al., 2010; Wang et al., 2010). Besides, mylonite samples at the south margin of the NNSZ (Xu et al., 2011; Cai et al., 2012) and the northern margin of the SCTSZ (Cai et al., 2012) yielded Ar–Ar ages ranging from 280 to 300 Ma, which was interpreted as the time of shearing of the main suture zone during a continentcontinent collision (Cai et al., 2012). Thus, the deformational phase in the Lingyun Cu deposit may be geodynamically linked with the collision between the YCTB and the Tarim Block.

220 L2-138C-3

187

188

Os/ Os

180 140 L2-138C-2

100 L2-138C2-3

60 20

Initial

0

Age = 297.9±3.4 Ma 188 Os/ Os =18.54±0.67 MSWD = 0.062

187

20000

10000 187

30000

40000

188

Re/ Os

Fig. 8. Re–Os isochron diagram of chalcopyrite from the Lingyun Cu deposit.

6. Discussion 6.1. Tectonic setting and ore genesis During the early Silurian to early Carboniferous, the South Tianshan Ocean is believed to have experienced southward subduction beneath the Tarim Block (Jiang et al., 2014). In the STAC, the Paleozoic subduction-related accretionary orogeny ended diachronously before Permian, followed by a continent-continent collision (Gao et al., 2011; Jiang et al., 2014). Many strike-slip faults in the Tianshan orogenic belt controlled the emplacement of mafic–ultramafic intrusions, alkaline mafic and felsic magmatism during the continent-continent collision (Pirajno, 2010), accompanied by shear zone activity. Although crystal tuff in the Lingyun mine area underwent low-grade metamorphism, we selected suitable analyses (see details in Section 5.1) to yield a concordia age of ca. 405 Ma (Fig. 6d), indicating that the Aerbishibulake Formation formed in a subduction environment. Moreover, crystal tuff samples show well developed negative Sr anomaly and distinct positive Rb, Th, U, Nd and P anomalies (Fig. 10b), which are common in arc volcanic rocks. The mineralization event of the Lingyun Cu deposit occurred at ca. 297 Ma (Fig. 8), which is much younger than the eruption of the host rocks. No magmatism has been identified in the Lingyun Cu deposit, and only a few diorite dikes that crosscut the crystal tuff have been observed. These diorite dikes formed at ca. 221 Ma (Fig. 7e), an age much younger than the mineralization (ca. 297 Ma). Thus, the magmatic origin is not the main factor contributing

Table 3 Analytical data of step heated

40

6.2. The origin and evolution of ore-forming fluids At the Lingyun Cu deposit, some fluid inclusions of the E-stage quartz (e.g., M- and C-types) show high homogenization temperatures and vapor/liquid ratios, and homogenize to a vapor phase. On the other hand, other fluid inclusions of this stage show relatively low homogenization temperatures and vapor/liquid ratios, which are homogenized to an aqueous phase. These fluid inclusions coexist in the same sample (Fig. 11c), indicating an occurrence of fluid immiscibility (e.g., Roedder, 1984). The activity of the Yanxingshan shear zone in syn- or/ and post-collision settings may be closely correlated with pressure fluctuations, which change the equilibrium of the ore-forming fluid system. The salinities (1.5–14.9 wt% NaCl eqv) and homogenization

Ar/39Ar dating for synkinematic sericites separated from the mylonitic crystal tuff. Ar (×10−14 mol)

(38Ar/39Ar)m

40

Sample weight = 32.66 mg

J = 0.003961

Plateau Age = 292.3 ± 2.4 Ma

0.0921 0.0122 0.0024 0.0013 0.0008 0.0009 0.0105 0.0188 0.0694 2.2818

0.0423 0.0175 0.0128 0.0126 0.0130 0.0130 0.0147 0.0179 0.0425 0.5577

41.23 92.54 98.58 99.14 99.51 99.46 93.64 88.99 68.60 3.47

T (°C)

(40Ar/39Ar)m

(36Ar/39Ar)m

Sample no. b504e

Sericites

700 770 820 870 920 960 1000 1040 1100 1400

44.9614 45.7355 46.4437 45.0771 44.7434 45.0706 47.2007 49.1349 64.2089 696.3503

(37Ar/39Ar)m

11.3142 2.9481 0.7779 0.0000 0.1583 0.5009 1.3945 2.2764 5.0472 29.2528

Note: Subscript “m” means measured isotopic ratios; F = 40Ar*/39Ar; J is the irradiation parameter.

166

Ar (%)

F

18.7083 42.4263 45.8132 44.6904 44.5295 44.8440 44.2487 43.8075 44.2292 24.7344

39

0.07 0.58 0.97 1.33 2.14 1.70 1.16 0.89 0.16 0.03

Age (Ma)

± 1σ (Ma)

129.0 280.2 300.8 294.0 293.0 295.0 291.3 288.7 291.2 169.0

8.5 2.7 2.8 2.7 2.7 2.7 2.7 2.7 4.7 46

temperatures (130–370 °C) of the E-stage fluid inclusions are obviously higher than those of the L-stage (1.7–5.0 wt% NaCl eqv and 135–150 °C, respectively) (Fig. 12), which can be considered as diagnostic of a significant inflow of meteoric water. Salinity decreasing from E-stage to L-stage, together with temperature, is comparable with the fluid mixing trend proposed by Kreuzer (2005). Fluid immiscibility and mixing are important mechanisms causing metal precipitation in the orogenic deposits (e.g., Chen et al., 2012a,b; Zhang et al., 2012a,b; Zheng et al., 2012), which may also contribute to the formation of the Lingyun Cu deposit. Ore-forming fluids of a metamorphic origin are rich in CO2 and low salinity (e.g., Chen et al., 2007; Groves et al., 1998, 2003; Pirajno, 2009). Fluid inclusions of E-stage in the Lingyun Cu deposit commonly contain CO2 and H2O, locally with N2 (Fig. 13), with low salinity (with a majority ranging from 2 to 4 wt% NaCl eqv). The ore-forming fluids of L-stage show low CO2 concentrations and salinity (most of them from 1.7 to 3.0 wt% NaCl eqv) due to a significant inflow of meteoric water. The abundant CO2-rich fluid inclusions from the Lingyun Cu deposit are generally comparable with those of other orogenic-type deposits (e.g., Chen et al., 2004, 2007; Groves et al., 2003; Pirajno, 2009). Besides, fluid mixing and subsequent fluid immiscibility during ore-forming fluid evolution have been reported in many orogenic-type deposits (e.g., Muruntau gold deposit, Bierlein and Wilde, 2010; Chen et al., 2004; Sawayaerdun gold deposit, Chen et al., 2012a,b; Wangfeng gold deposit, Zhang et al., 2012a,b). Given the regional geology, ore geology, coeval ore-forming and deformation occurrences, and fluid inclusion features, the Lingyun Cu deposit may belong to the orogenic class associated with the shear zone activity. However, further work needs to do to confirm this (e.g., Cu transportation and precipitation mechanisms).

6.3. Genetic model of the Lingyun Cu deposit In the early Devonian, the Aerbishibulake Formation was formed during southward subduction of the South Tianshan Ocean beneath the Tarim Block. During Carboniferous–Permian continent-continent collision, the major faults such as the SCTSZ were reactivated, leading to the formation of a series of transpressional strike-slip faults. The Yanxingshan ductile to brittle shear zone was formed in this period and

may be the second fault of the SCTSZ. Metamorphic devolatilization of the carbonaceous sediments and carbonate rocks (e.g., the marble of Aerbishibulake Formation) could have generated large amounts of CO2rich fluids that migrated upward along the Yanxingshan shear zone. Moreover, these fluids remobilized and extracted ore-forming elements from the country rocks during their upward movement. These ore-forming compositions precipitated extensively when they reached the brittle to ductile transition level (BDL) due to the mixing of meteoric fluids and subsequent fluid immiscibility. The fluid system evolved from CO2-rich (E-stage) to CO2-poor (L-stage) through meteoric water input. The crystal tuff in the Lingyun mine area shows similar REE fractionated patterns with the sulfide ores, which suggest that the crystal tuff may have provided some of the ore metals during formation of the Lingyun Cu deposit. Besides, the initial 187Os/188Os ratio (18.54 ± 0.67; Fig. 8) of chalcopyrite, which is much higher than the chondritic 187Os/188Os ratio of 0.125 at ca. 297.7 Ma (Meisel et al., 2001), indicate a significant input of crustal materials. In the late Triassic, diorite dikes intruded and crosscut the crystal tuff in the Lingyun Cu deposit.

7. Conclusions Both the silicate minerals and associated sulfide assemblages in the

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Table 6 Microthermometric data of fluid inclusions of the Lingyun Cu deposit. Stage

Host mineral

Type of FIs

Num.

Tm,ice (°C)

Early

Quartz Quartz Quartz Ankerite

W-type M-type C-type W-type

80 12 13 10

−20.0 to −0.9

Late

Tm, CO2 (°C)

Tm,cla (°C)

Th,CO2 (°C)

Th (°C)

Salinity (wt% NaCl eqv)

−62.5 to −58.2 −63.6 to −61.4

2.5 to 4.5 1.2 to 3.6

4.0 to 20.6 3.0 to 19.1

130–370 238–378 250–320 135–150

1.6–14.9 3.3–10. 8 9.0–14.2 1.7–5.0

−1.0 to −3.0

Notation: Tm,ice – final ice melting temperature; Tm, CO2 = final melting temperature of solid CO2; Tm,cla – melting of carbonic hydrite; Th,CO2 – homogenization temperature of carbon dioxide; Th – total homogenization temperature. Fig. 12. Histograms of homogenization temperatures and salinities of fluid inclusions in the Lingyun Cu deposit.

Compliance with ethical standards

thank Hongying Zhou, Jianzhen Geng, Wen Chen, Chao Li, Limin Zhou, Xinwei Li and Fagang Zeng for zircon LA–ICP–MS U–Pb, Sericite 40 Ar/39Ar and Re–Os analyses. Constructive reviews by Editor-in-Chief Franco Pirajno and Prof. Roberto Corrêa are greatly appreciated. This study was financially supported by the National Key R&D Program of China (2017YFC0601202), the Support Program for Postdoctoral Innovative Talents (No. BX201600136), the Fundamental Research Funds for the Central Universities (No. 53200759011), the National Science and Technology Support Program of China (No. 2011BAB06B02) and the Chinese Geological Survey Program (No.

The authors declare that this paper has fully complied with the research ethics of this journal, and there are no conflicts of interest. Acknowledgments Gang Chen, Junbao Gao, Yong Zheng, Liang Yu and Jiufa Li of the First Geological Team of the Xinjiang Bureau of Geology and Mineral Resources are appreciated for logistic support for field work. We also

a

300

b

400

300

200

Relative strength

Relative strength

250

150 100

CO 2 CO 2

100

H2O

50

H2O 200

CO 2

0 1000

500

1500

2000

2500

3000

3500

4000

1000

1500

2000

2500

3000

3500

c

4000

d

CO 2 800

300

CO 2 Relative strength

Relative strength

400

Co 2

200

100

N2

600

400

CO 2

200

H2O

N2

0 1000

1500

2000

2500

3000

Raman Shift (cm - 1 )

3500

4000

1000

1500

2000

2500

3000

Raman Shift (cm - 1 )

169

3500

4000

Fig. 13. Representative Raman spectra of fluid inclusions. (a) Spectrum for the liquid CO2 phase of two-phase M-type inclusions. (b) Spectrum for vapor bubbles of two-phase Mtype inclusions. (c) Spectrum for vapor bubbles of twophase M-type inclusions, showing high contents of CO2. (d) C-type fluid inclusions.

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