Petrogenesis and tectonic settings of the Late Carboniferous Jiamantieliek and Baogutu ore-bearing porphyry intrusions in the southern West Junggar, NW China

Journal of Asian Earth Sciences 75 (2013) 158–173

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Petrogenesis and tectonic settings of the Late Carboniferous Jiamantieliek and Baogutu ore-bearing porphyry intrusions in the southern West Junggar, NW China Ping Shen a,⇑, Wenjiao Xiao a, Hongdi Pan b, Lianhui Dong a,c, Chaofeng Li a a b c

Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China Collage of Earth Sciences, Chang’an University, Xi’an 710054, China Xinjiang Bureau of Geology and Mineral Resources, Urumqi 830000, China

a r t i c l e

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Article history: Received 22 March 2013 Received in revised form 10 July 2013 Accepted 16 July 2013 Available online 24 July 2013 Keywords: Zircon U–Pb age Sr–Nd–Pb isotope Jiamantieliek Baogutu West Junggar Xinjiang

a b s t r a c t Porphyry Cu deposits occurred in the southern West Junggar of Xinjiang, NW China and are represented by the Baogutu and newly-discovered Jiamantieliek porphyry Cu deposits. Petrographical and geochemical studies show that both Jiamantieliek and Baogutu ore-bearing intrusions comprise main-stage diorite stock and minor late-stage diorite porphyry dikes and are the calc-alkaline intermediate intrusions. Based on U–Pb zircon SHRIMP analyses, the Jiamantieliek intrusion formed in 313 ± 4 Ma and 310 ± 5 Ma, while, based on U–Pb zircon SIMS analyses, the Baogutu intrusion formed in 313 ± 2 Ma and 312 ± 2 Ma. Rocks in the Jiamantieliek intrusion are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) with negative Nb anomaly. Their isotopic compositions (eNd(t) = +1.6 to +3.4, (87Sr/86Sr)i = 0.70369–0.70401, (207Pb/204Pb)i = 15.31–5.41) suggest a mixing origin from depleted to enriched mantle sources. In the Baogutu intrusion, the rocks are similar to those of the Jiamantieliek intrusion. Their Sr-Nd-Pb isotopic composition (eNd(t) = +4.4 to +6.0, (87Sr/86Sr)i = 0.70368–0.70385, (207Pb/204Pb)i = 15.34–5.42) shows a more depleted mantle source. These features suggest generation in an island arc. The Jiamantieliek and Baogutu intrusions have similar characteristics, indicating that a relatively uniform and integrated source region has existed in the southern West Junggar since the Palaeozoic. A larger contribution of calc-alkaline magma would be required to generate the Jiamantieliek intrusion, which may reflect the development of magma arc maturation towards the western section of the southern West Junggar. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction The Central Asia Orogenic Belt (CAOB) is the largest Phanerozoic juvenile crustal growth orogenic belt in the world (Sßengör and Natal’in, 1996; Jahn et al., 2000, 2004; Xiao et al., 2008, 2009, 2010) and have plentiful mineral sources (Seltmann and Porter, 2005; He and Zhu., 2006; Zhu et al., 2007; Shen et al., 2010a,b, 2013). As a part of the CAOB, the West Junggar terrain in Xinjiang (NW China) is economically important, not only as a potential target for Cu–Au– Mo–W–Cr exploration (Shen et al., 1993; He and Zhu, 2006; Zhu et al., 2007; Shen et al., 2010a,b, 2012, 2013), but also as a critical area to study the subduction-accretion history of the CAOB. The West Junggar terrain largely comprises Palaeozoic volcanic arcs in the northern West Junggar and accretionary complexes in the southern West Junggar (e.g., Windley et al., 2007; Xiao et al., 2008, 2009, 2010; Zhang et al., 2011a,b), which were accreted onto ⇑ Corresponding author. Tel.: +86 10 82998189; fax: +86 10 62010846. E-mail address: [email protected] (P. Shen). 1367-9120/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2013.07.024

the Kazakhstan plate as the Tarim, Kazakhstan and Siberian plates converged (Jahn et al., 2000; Chen and Jahn, 2004; Chen and Arakawa, 2005; Xiao et al., 2008). This geodynamic process led to the formation of voluminous granitoids and small ore-bearing stocks. The former are I- and A-type granites with highly-depleted isotopic signatures (eNd(t) = +6.4 to +9.2) (Jahn et al., 2000; Chen and Jahn, 2004; Chen and Arakawa, 2005; Han et al., 2006). The latter are diorites that are associated with the porphyry copper deposits (e.g. Baogutu and newly-discovered Jianmantieke) in the southern West Junggar (Fig. 1b, Shen et al., 2009, 2013). Previous studies were mainly concentrated on the voluminous granitoids in the area (e.g. Jahn et al., 2000; Hu et al., 2000; Chen and Jahn, 2004; Chen and Arakawa, 2005; Han et al., 2006; Zhou et al., 2008), with few attention to these ore-bearing stocks. In addition, the intrusions tectonic setting of the southern West Junggar is controversial. They have been attributed either to subduction-related sources in an island arc setting (Xiao et al., 2008, 2009; Shen et al., 2009; Geng et al., 2009, 2011; Tang et al., 2009, 2010; Zhang et al., 2011a) or to depleted mantle contributions in a post-collisional extensional setting

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Fig. 1. A Schematic map of the Central Asian Orogenic Belt (Xiao et al., 2009; Shen et al., 2010a) showing principal porphyry copper deposits (1 – Baogutu; 2 – Tuwu; 3 – Yandong; 4 – Wunuhetushan; 5 – Duobaoshan; 6 – Erdenet; 7 – Tsagaan-Suvarga; 8 – Oyu Tolgoi; 9 – Boshekul; 10 – Samarsk; 11 – Borly; 12 – Kounrad; 13 – Sayak; 14 – Aktogai; 15 – Koksai; 16 – Taldy Bulak; 17 – Kal’makyr). Fig. 1B. Geological map of the West Junggar region, showing the location of the Jiamantieliek and Baogutu porphyry copper deposits occurred in the southern West Junggar.

(Chen and Arakawa, 2005; Han et al., 2006; Zhou et al., 2008). These models clearly have significantly different implications for intrusion petrogenesis and associated mineralisation. In this paper, we first report the major elements, trace elements and Sr–Nd–Pb isotopic geochemical data for whole rocks and for U–Pb zircon SHRIMP ages from the Jiamantieliek ore-bearing intrusion in the Barluk Mountains. For comparison, we have also added new results for the Baogutu intrusion in the Kelamay Region relating to 10 whole-rock major and trace element analyses, and four Sr–Nd–Pb isotope ratios. Our aim was to provide constraints to the tectonic setting and associated ore-bearing magma in the West Junggar, Xinjiang. All these factors have significant implications for

understanding the continental growth and associated mineralisation in the CAOB. 2. Geological outline The West Junggar terrain is bound by the Altai orogen to the north and by the Tianshan orogen to the south and extends westward to the Junggar–Balkhash region in adjacent Kazakhstan and eastward to the Junggar Basin in North Xinjiang, NW China. The southern West Junggar is located between latitudes 45°050 and 46°150 north and longitudes 82°150 and 86°000 east (Fig. 1b). Geologically, the southern West Junggar is characterised by several

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northeast-trending faults, including the Barluk, Mayile and Darbut faults, and fault-bounded accretionary complexes. This is very different from the northern West Junggar where the major faults and fault-bounded blocks are mainly E–W oriented (Fig. 1b, Xiao et al., 2008; Shen et al., 2012a). The Barluke Mountains are located in the western part of the southern West Junggar (Fig. 1b). The fossil-dated Devonian strata occur widely across the Barluke Mountains, close to the border with China–Kazakhstan (Fig. 1b; BGMRXUAR, 1993), and comprise the volcano-sedimentary strata of the Middle Devonian Barluk and Tielieketi Groups. The Barluk Group is composed of siltstone, tuff and minor basalt; the Tielieketi Group consists of greywacke, tuffaceous mudstone and tuffaceous siltstone. These Devonian sequences are intruded by Carboniferous–Permian intrusions in the Barluk Mountains. The Carboniferous intrusions include peridotite, gabbro, diorite and quartz diorite stocks, and the Permian intrusions include diorite, quartz diorite and adamellite stocks (BGMRXUAR, 1993). Structurally, the Barluk Mountains are characterised by the northeast-trending Barluke fault. There are NW-trending faults that are almost orthogonal to the Barluk fault. The Jiamantieliek intrusion is found in the western part of the Barluk fault (Fig. 1b). The Kelamay Region, located in the southeastern section of the West Junggar, is characterised by the occurrence of Lower Carboniferous volcano-sedimentary strata (Fig. 1b). There are three Early Carboniferous stratigraphic units: from oldest to youngest, they are the Tailegula, Baogutu and Xibeikulasi groups (Shen and Jin, 1993). The Tailegula group consists of a succession of basic volcanic and volcaniclastic rocks intercalated with chert. The Bao-

gutu group includes tuffaceous siltstone, silt tuff and felsic tuff. The Xibeikulasi group consists of greywacke and sandstone. These Early Carboniferous sequences were intruded by ore-bearing stocks at about 320 Ma (Fig. 1b; Shen et al., 2012b; Tang et al., 2009). The Baogutu intrusion is placed to the south of the Darbut fault; the main structures in this area are a series of approximately N-trending faults and folds, which are almost orthogonal to those found to the north of the Darbut fault (Fig. 1b). The Xibeikulasi, Baogutu and Tailegula groups have a synclinal structure, in which the Xibeikulasi group forms the core and the Baogutu and Tailegula groups form the flanks. The studied Baogutu intrusion occurs within the eastern flank of the syncline. 3. Ore-bearing intrusions 3.1. Jiamantieliek Some granitoids that occur in the Barluk Mountains are represented by the Jiamantieliek intrusion hosting the Jiamantieliek porphyry copper deposit (Fig. 2). The Jiamantieliek intrusion was intruded into the volcano-sedimentary strata of the Middle Devonian Barluk and Tielieketi Groups and now occupies localised dilatant sites created by a structural intersection of NW- and NE-trending faults (Fig. 2). The intrusion is irregular in shape at the surface, and its total area is 9 km2. We established a profile of over 400 m in length through the Jiamantieliek ore-bearing intrusion (Fig. 2). There were at least two intrusive phases within this intrusion, based on cross-cutting relationships; these were the main-stage stock, in which occurred

Fig. 2. A Geological map of the Jiamantieliek porphyry copper deposit (modified after BGMRXUAR, 1993). Line AA0 shows the location of the profile through the studied area. Fig. 2B Geologic cross section along AA0 (meaurede by authors). It also shows the locations of main samples.

P. Shen et al. / Journal of Asian Earth Sciences 75 (2013) 158–173

abundant alteration and mineralisation, and the minor late-stage dikes. Main-stage stock is widespread in the study area (Fig. 2a), consisting of diorite and quartz diorite. Diorite and quartz diorite have a granular to weakly porphyritic texture (Fig. 4a). Diorite contain plagioclase (60–65%), hornblende (15–20%), biotite (5–10%), and minor quartz (<5%) and accessory opaque oxides, zircon, and apa-

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tite. Quartz diorites have similar mineralogies to the diorites, but are distinguished by more quartz (<10% by volume, up to 15–20 % by volume). Plagioclases (An = 30–40) of the diorite and quartz diorite show typically andesite zoning (Fig. 4a), corresponding to andesine. The main-stage stock makes abrupt contacts with the wall rocks of the intrusion. Several small bodies of porphyry cutting the main-stage diorite stock have been mapped (Fig. 2b).

Fig. 3. A Geological map of the Kelamay Region in the southern West Junggar region (modified after Shen and Jin, 1993), showing the location of the studied Baogutu intrusion and associated deposit. Fig. 3B. Geological map of the Baogutu intrusion. Dots indicate the position of drill holes, and pentagons show the location of the samples used in this study (Shen et al., 2010a).

Fig. 4. Photomicrographs of the main rocks from Jiamantieliek and Baogutu intrusions. (A) Jiamantieliek main-stage diorite with granular texture; (B) Jiamantieliek late-stage diorite porphyry with porphyritic texture; (C) Baogutu main-stage diorite with granular texture; (D) Baogutu late-stage diorite porphyry with porphyritic texture. All photomicrographs were captured under transmitted lights. Abbreviations: Pl: plagioclase; Hb: hornblende.

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They are referred to here as late-stage diorite porphyry and quartz diorite porphyry. Sharp contacts between the late-stage and mainstage rocks are exposed mainly on the eastern rim of the Jiamantieliek intrusion (Figs. 2a and b). The late-stage porphyries are characterised by a porphyritic texture. Phenocrysts of plagioclase, hornblende, and biotite in diorite porphyry and quartz diorite porphyry are typically 2–3 mm in diameter and account for 20–30 vol.% of the rock. Microcrystalline plagioclase, hornblende and minor quartz define the groundmass, which occupies 70– 80 vol.% of the porphyries (Fig. 4b). 3.2. Baogutu Our previous work includes descriptions of the petrology, mineralisation and geochronology of the Baogutu deposit (Shen et al., 2010a,b, 2012b), the main characteristics of which are summarised in the following sections. The Baogutu intrusion contained metal, at levels of 63  104 tonnes Cu, 1.8  104 tonnes Mo and 14 tonnes Au, and is associated with a Carboniferous intrusion that was emplaced into the Lower Carboniferous volcano-sedimentary sequences of the Baogutu and Xibeikulasi Groups. Two intrusive phases at Baogutu are the main-stage diorite stock and minor late-stage diorite porphyry dikes. Sharp intrusive contacts have been observed between the

main-stage diorites and late-stage diorite porphyries (Fig. 3b). Alteration and mineralisation were closely related to the mainstage diorites. The main-stage diorite stock includes granular to weakly porphyritic diorite (Fig. 4c) and weakly porphyritic quartz diorite. Diorite contains plagioclase (40–50%), hornblende (25–30%), biotite (5– 10%), minor clinopyroxene (<5%) and quartz (<5%), and rare titanite, rutile, apatite, magnetite, and zircon. Quartz diorites have similar mineralogies to the diorites, but are distinguished by less pyroxene (<3–5% by volume) and more quartz (<10% by volume, up to 15% by volume). The late-stage diorite porphyry dikes are diorite porphyry and quartz diorite porphyry, which have the porphyritic texture (Fig. 4d). Phenocrysts are plagioclase, hornblende, and minor biotite, which are 1–2 mm in diameter and account for 10–20 vol.% of the rock. The groundmass is microcrystalline plagioclase, hornblende and minor quartz which occupies 80 vol.% of the porphyries. 4. Methods and results 4.1. Methods Seventeen representative samples from the Jiamantieliek intrusion were petrographically selected for chemical analyses. The location of samples is shown in Fig. 2b. They are the main-stage

Table 1 Major (wt%) and trace element (ppm) abundance of the rocks from the Jiamantieliek main-stage diorite stock and Late-stage diorite porphyry dikes. Stages

Main-stage diorite stock

Sample Rocks

ZK2-36 QD

YJ1-100 QD

YJ1-81 QD

YJT2 D

YJ1-175 D

ZK2-0 QD

YJ1 D

ZK2-207 D

ZK2-260 D

JMP-3-5 QD

JMP-7 QD

Late-stage diorite porphyry dikes YJ1-54 DP

YT3-1 QDP

JMP-5-4 QDP

JMP-5-5 QDP

JMP-5-6 QDP

SiO2 Al2O3 Fe2O3 FeO MgO CaO Na2O K2O MnO TiO2 P2O5 LOI Total Mg# Rb Sr Y Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ta Pb Th U Zr Hf RREE

66.78 15.02 1.89 1.90 1.98 3.92 4.77 2.20 0.07 0.61 0.18 0.48 99.80 0.65 41.90 624 13.90 5.59 0.89 705 17.80 33.80 4.05 15.40 2.90 0.94 2.59 0.47 2.67 0.52 1.53 0.22 1.52 0.25 0.37 13.70 4.64 1.09 71 2.46 85

65.34 15.69 1.98 1.80 2.22 3.42 4.49 2.68 0.07 0.59 0.18 0.94 99.40 0.69 42.32 643 12.79 5.40 1.35 698 14.42 27.05 3.48 13.78 2.75 0.90 2.53 0.38 2.28 0.47 1.34 0.21 1.36 0.20 0.39 7.79 3.86 0.90 136 3.87 71

65.49 15.63 1.92 2.09 2.25 3.50 4.45 1.80 0.08 0.64 0.18 1.34 99.37 0.66 22.24 677 13.30 5.85 2.42 463 18.17 33.39 4.00 15.33 2.86 0.85 2.59 0.41 2.32 0.47 1.33 0.21 1.36 0.22 0.47 14.49 5.17 1.36 137 4.02 84

68.09 14.04 2.99 1.35 1.78 2.78 4.02 2.45 0.07 0.61 0.18 1.09 99.45 0.70 36.50 551 13.50 4.89 1.27 722 16.30 31.50 3.44 14.50 2.71 0.94 2.44 0.41 2.41 0.46 1.33 0.22 1.37 0.20 0.32 37.80 3.90 1.32 48 1.61 78

66.11 15.27 2.65 1.60 2.05 2.45 4.71 3.04 0.07 0.60 0.18 1.19 99.92 0.70 64.80 551 14.20 4.84 0.85 1044 15.00 29.10 3.45 14.60 3.00 1.12 2.64 0.44 2.46 0.42 1.37 0.22 1.40 0.22 0.34 8.51 4.25 1.14 42 1.56 75

66.33 15.15 2.02 1.65 1.91 3.87 4.74 2.31 0.07 0.59 0.17 0.94 99.75 0.68 42.50 585 12.90 5.09 0.69 627 18.40 33.50 3.90 14.90 2.86 0.85 2.44 0.42 2.44 0.49 1.41 0.23 1.34 0.23 0.40 11.20 5.68 1.19 72 2.51 83

56.69 15.60 4.91 3.55 4.60 6.81 3.89 1.29 0.12 0.94 0.19 1.29 99.88 0.70 49.20 665 24.40 4.69 2.77 464 16.60 33.70 4.37 19.00 4.40 1.33 4.00 0.72 4.33 0.81 2.60 0.40 2.60 0.36 0.30 3.64 3.14 0.88 139 3.37 95

66.17 14.77 2.22 1.95 2.07 3.83 4.44 2.33 0.07 0.66 0.17 0.94 99.62 0.66 42.60 915 13.00 5.20 1.56 736 17.50 33.20 3.70 14.40 2.83 0.93 2.51 0.45 2.54 0.49 1.42 0.21 1.36 0.24 0.41 9.55 4.75 2.04 57 2.25 82

64.47 15.15 1.94 2.05 1.78 4.09 4.21 2.24 0.08 0.62 0.17 3.07 99.87 0.61 42.00 371 13.00 5.33 1.45 591 17.50 33.30 3.87 14.80 2.70 0.86 2.60 0.49 2.60 0.49 1.45 0.21 1.41 0.22 0.39 10.20 4.75 2.29 57 2.17 83

65.20 15.93 2.28 1.85 2.08 4.02 4.40 2.38 0.08 0.57 0.17 1.00 99.95 0.67 43.30 613 14.60 5.52 1.20 740 20.60 37.80 4.40 16.80 3.36 1.01 3.36 0.47 2.92 0.52 1.62 0.24 1.53 0.25 0.45 8.31 6.20 0.87 80 2.87 95

65.10 16.12 2.41 1.75 2.11 3.94 4.37 2.35 0.07 0.59 0.17 1.00 99.98 0.68 45.00 620 14.20 5.14 1.41 760 18.20 33.00 3.97 15.60 3.25 1.03 2.94 0.46 2.53 0.55 1.52 0.20 1.39 0.25 0.40 8.74 4.82 0.92 75 2.61 85

57.49 16.56 2.60 3.62 4.71 4.83 3.55 2.00 0.08 0.81 0.19 3.04 99.48 0.70 61.17 681 19.03 5.01 2.25 553 20.02 36.85 4.73 18.33 3.71 1.18 3.69 0.58 3.56 0.74 2.02 0.30 1.90 0.29 0.35 3.28 3.84 1.49 112 3.36 98

65.02 15.40 2.30 2.05 2.07 4.41 4.88 1.91 0.07 0.63 0.19 0.78 99.71 0.65 37.20 687 13.50 4.61 0.65 599 15.90 30.90 3.72 14.10 2.78 0.98 2.48 0.48 2.62 0.50 1.46 0.24 1.53 0.24 0.35 11.70 4.31 1.68 151 3.79 78

65.07 16.25 2.40 1.70 2.10 4.20 4.45 2.29 0.07 0.58 0.18 0.69 99.97 0.69 36.30 684 12.80 5.16 0.73 716 20.00 33.70 3.87 15.20 2.94 0.98 2.52 0.48 2.26 0.46 1.56 0.25 1.38 0.24 0.38 6.85 5.02 1.55 123 3.96 86

64.71 16.04 2.27 1.90 2.16 3.74 4.60 2.68 0.07 0.59 0.18 1.04 99.98 0.67 50.80 705 13.80 5.21 0.98 851 20.80 34.30 3.98 15.40 3.04 1.10 2.80 0.47 2.48 0.46 1.54 0.22 1.45 0.24 0.43 10.00 5.36 1.66 138 4.02 88

65.17 15.82 2.32 1.85 2.14 3.84 4.49 2.16 0.06 0.59 0.18 1.35 99.97 0.68 34.20 724 12.70 4.91 1.01 741 19.70 31.80 3.65 15.00 2.99 0.92 2.56 0.42 2.36 0.46 1.42 0.24 1.40 0.26 0.41 5.36 5.02 1.68 127 3.40 83

Abbreviations: D: diorite; QD: quartz diorite; DP: diorite porphyry; QDP: quartz diorite porphyry.

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diorite and quartz diorite and late-stage diorite porphyry and quartz diorite porphyry. The six samples from the main-stage diorite stock were selected for Rb, Sr, Sm, Nd and Pb isotope compositions analyses. We also selected two samples (YJ1-21, YJ1-175) from the main-stage diorite stock and late-stage diorite porphyry dikes at Jiamantieliek, respectively, for zircon separation (the location of samples is shown in Fig. 2b). For comparison, ten representative samples from the Baogutu main-stage stock and late-stage diorite porphyry dikes were selected for chemical analyses. The four samples were selected for Rb, Sr, Sm, Nd and Pb isotope compositions analyses. All measurements were carried out at the Institute of Geology and Geophysics, Chinese Academy of Sciences in Beijing, excepting for SHRIMP zircon U–Pb dating, which were carried out in the Beijing SHRIMP Center, Chinese Academy of Geological Sciences in Beijing. 4.1.1. Major and trace elements About 0.5–1.0 kg samples were crushed and quartered. 100-g sample was milled and analysed for major oxides, rare earth elements (REE), selected trace elements and Rb, Sr, Sm, Nd and Pb isotope compositions. Major elements were analysed by XRF-1500 Sequential X-ray Fluorescence Spectrometry, with wet chemical

determination of FeO and loss-on-ignition. Analytical precision based on certified standards and duplicate analyses are expressed in terms of relative percentages, which range from ±0.01% to ±0.20%. A PQ2 Turbo inductively Coupled Plasma Mass Spectrometer (ICP-MS) was used to analyse trace elements and REE. 100-g of sample was digested in beakers using a hot HF + HNO3 mixture followed by a HF + HNO3 + HClO3 mixture to ensure complete dissolution and then taken up in 1% HNO3 (dilution factor of 500). The measurement error and drift were controlled by regular analysis of standard samples with a periodicity of 10%. Analysed uncertainties of ICP-MS data at the ppm level are better than ±3%–±10% for trace elements, ±5–±10% for REE. 4.1.2. Sr–Nd–Pb isotopes Rb, Sr, Sm and Nd isotope compositions were analysed according similar procedure that described by Chen et al. (2002). Procedural blanks were <100 pg for Sm and Nd and <50 pg for Rb and Sr. The 87 Sr/86Sr ratios were normalised to 86Sr/88Sr = 0.1194 and the 143 Nd/144Nd ratios to 146Nd/144Nd = 0.7219. Typical within-run precision (2rm) for Sr and Nd was estimated to be ±0.000010 and ±0.000013, respectively. The measured values for the JMC Nd standard and NBS987 Sr standard were 143Nd/144Nd = 0.511937 ± 7

Table 2 Major (wt%) and trace element (ppm) abundance of the rocks from the Baogutu main-stage diorite stock and Late-stage diorite porphyry dikes. Stages

Main-stage diorite stock

Late-stage diorite porphyry dikes

Sample BGT5- BGT5- BGT5- BGT5- ZK2111 2 3 4 60 Rocks D QD QD QD D

ZK211144 D

ZK211263 D

ZK201616 QD

ZK202295 QD

ZK106350 DP

ZK011664 DP

ZK011666 DP

ZK106242 QDP

ZK106246 QDP

ZK106279 QDP

ZK106267 QDP

SiO2 Al2O3 Fe2O3 FeO MgO CaO Na2O K2O MnO TiO2 P2O5 LOI Total Mg# Rb Sr Y Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ta Pb Th U Zr Hf RREE

57.72 17.01 1.50 4.55 4.51 6.94 4.03 1.31 0.08 0.88 0.24 0.89 99.71 0.64 41.22 739 14.9 2.96 2.913 418.9 14.19 29.57 4.45 18.25 4.00 1.18 3.39 0.49 2.84 0.56 1.53 0.22 1.43 0.21 0.21 3.86 2.61 1.29 93 2.84 82

57.72 15.29 2.56 5.20 4.93 5.10 3.42 2.16 0.07 0.86 0.13 2.39 99.83 0.63 129 542 20.6 2.74 7.69 429 10.4 22.4 3.04 13.70 3.12 0.89 3.03 0.61 3.63 0.72 2.07 0.34 1.94 0.33 0.17 3.87 1.89 1.39 50 1.73 66

57.13 15.81 2.61 5.30 4.16 7.21 4.07 1.03 0.12 0.94 0.21 1.33 99.92 0.59 34.4 655 16.4 3.09 1.78 486 13.8 29.3 3.90 16.90 3.69 1.29 3.13 0.59 3.14 0.60 1.68 0.25 1.48 0.27 0.18 5.09 2.17 0.61 36 1.13 80

57.84 16.04 1.16 4.20 4.69 7.45 5.04 0.75 0.08 0.98 0.21 1.45 99.89 0.67 35.2 632 17.6 3.27 4.58 262 11.8 29.6 4.10 17.70 3.90 1.23 3.28 0.59 3.46 0.66 1.84 0.30 1.79 0.31 0.22 4.87 1.72 0.77 36 1.24 81

58.53 14.95 3.88 5.65 3.06 3.55 3.85 2.16 0.03 0.73 0.17 3.30 99.86 0.49 111 471 19.2 4.6 5.89 408 24.2 48.6 5.85 22.40 4.22 1.04 3.54 0.60 3.37 0.68 2.06 0.34 2.24 0.38 0.32 3.74 5.52 1.70 149 3.79 120

58.32 15.93 1.83 5.40 3.74 6.93 3.77 1.08 0.10 0.80 0.19 1.80 99.89 0.55 32.8 658 14.8 2.46 1.84 466 13.3 28.4 3.82 16.00 3.44 1.03 2.85 0.49 2.83 0.52 1.54 0.24 1.43 0.23 0.15 2.35 2.83 0.69 44 1.58 76

58.92 15.60 1.58 5.40 4.03 7.09 3.83 0.78 0.10 0.82 0.20 1.53 99.88 0.57 25.5 681 15.9 2.63 2.19 382 13.6 29 4.02 17.00 3.74 1.06 2.99 0.54 2.96 0.55 1.64 0.25 1.59 0.25 0.17 2.32 2.42 0.64 47 1.76 79

60.73 15.66 0.73 5.70 3.08 5.80 3.87 1.61 0.04 0.76 0.16 1.74 99.88 0.49 75.7 488 19 3.37 3.68 462 14.6 30.9 3.99 16.50 3.58 1.02 3.11 0.59 3.47 0.72 2.01 0.32 2.05 0.34 0.24 2.54 3.73 1.09 108 2.89 83

61.80 14.27 1.84 3.70 2.66 4.53 3.86 1.58 0.03 0.67 0.14 4.74 99.82 0.56 75.4 451 20.1 3.81 3.13 457 13.9 29.6 3.86 16.30 3.78 1.14 3.28 0.63 3.71 0.74 2.11 0.34 2.11 0.35 0.27 3.40 4.39 1.31 101 2.93 82

61.35 15.42 0.81 6.00 3.01 5.65 4.12 1.44 0.03 0.76 0.15 1.16 99.90 0.47 70.6 556 20.9 3.78 4.72 303 14.6 31.4 4.05 17.00 3.79 1.04 3.39 0.64 3.72 0.74 2.15 0.34 2.19 0.37 0.24 3.30 3.88 1.12 116 3.17 85

64.98 14.64 0.73 4.25 2.37 4.50 4.12 2.16 0.03 0.66 0.15 1.34 99.93 0.50 59.3 496 20.7 4.15 2.46 941 17.6 36.2 4.57 18.90 4.06 1.18 3.50 0.64 3.62 0.75 2.21 0.37 2.11 0.37 0.29 5.43 5.04 1.46 123 3.38 96

58.95 17.88 1.74 1.87 4.35 7.56 4.41 0.72 0.04 0.82 0.18 1.13 99.65 0.81 43.33 746 15.11 2.48 2.28 222 10.77 29.7 4.15 18.63 3.79 1.21 3.36 0.53 2.91 0.57 1.71 0.22 1.45 0.23 0.14 2.96 3.29 1.13 94 2.61 79

62.05 15.73 2.03 3.44 3.91 5.44 4.16 0.65 0.06 0.69 0.14 1.22 99.52 0.67 14.63 559 14.5 3.2 0.99 354 10.86 22.97 3.20 14.95 2.77 0.92 2.87 0.39 2.50 0.49 1.37 0.21 1.36 0.21 0.21 2.97 4.09 1.03 132 3.90 65

59.98 17.76 0.87 1.64 4.41 7.52 4.46 0.67 0.03 0.88 0.21 1.10 99.53 0.83 36.42 707 15.48 2.69 0.92 240 8.8 28.1 4.03 19.22 4.31 1.27 3.78 0.55 3.09 0.59 1.74 0.24 1.56 0.23 0.15 2.98 1.94 0.55 85 2.51 78

59.92 18.07 0.62 1.24 4.81 7.85 4.75 0.37 0.03 0.83 0.10 0.95 99.54 0.87 13.28 748 17.44 2.69 0.65 221 5.6 16.81 2.66 13.84 3.45 1.14 3.53 0.55 3.16 0.62 1.72 0.27 1.59 0.23 0.14 2.77 1.58 0.40 93 2.71 55

55.68 16.92 1.92 4.76 5.01 7.07 3.87 1.40 0.09 0.88 0.20 1.51 99.34 0.65 40.01 722 13.3 2.76 2.113 411.8 10.06 21.25 3.18 13.15 3.15 0.98 2.71 0.41 2.42 0.49 1.35 0.20 1.29 0.19 0.16 4.14 1.22 0.56 58 1.70 61

Data sources: Shen et al. (2009); the other this study. Abbreviations: D: diorite; QD: quartz diorite; DP: diorite porphyry; QDP: quartz diorite porphyry.

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(2rm, n = 12) and 86Sr/88Sr = 0.710226 ± 12 (2rm, n = 12), respectively, during the period of data acquisition. Pb isotopic ratios were analysed with the same mass spectrometer; analytical precision is better than ±0.1‰.

4.1.3. SHRIMP zircon U–Pb dating Zircon grains were separated using standard techniques involving heavy liquid and magnetic separation for SHRIMP study. Representative grains were handpicked using a binocular microscope, mounted in an epoxy resin disc, and then polished and coated with a gold film. All zircons were documented with transmitted and reflected light micrographs as well as cathodoluminescence (CL) images to reveal their internal structures, and the mount was vacuum-coated with high-purity gold prior to SHRIMP analysis. U, Th, and Pb analyses of the two samples (YJ1-21, YJ1-175) were carried out using SHRIMP II. The operating conditions followed those of Williams (1998). Handpicked zircons were mounted in epoxy together with Temora (417 Ma) and SL13 (U content 238 ppm, 572 Ma) zircon standards, cut in half, and polished. U–Th–Pb isotopic ratios were determined relative to the TEMORA standard zircon (Black et al., 2003), and their concentrations were calibrated relative to SL13 reference zircon. The instrumental techniques are similar to those described by Compston et al. (1992). Data were reduced according to the procedure of Williams (1998), using ISOPLOT (Ludwig, 1999) and SQUID (1.02) software. The analytical data are presented as 1r error boxes on the concordia plots, and uncertainties in mean ages are quoted at the 95% confidence level (2r). The decay constants used in age calculations are 238U = 0.155125 Ga1 and 235U = 0.98485 Ga1.

4.2. Results 4.2.1. Major and trace elements Major and trace element concentrations of the studied samples are listed in Tables 1 and 2 and plotted in Figs. 5–7, respectively. The loss on ignition (LOI) for all rocks analysed in this study ranged from 0.48 wt.% to 4.74 wt.% , which probably resulted from postmagmatic fluid-rock interactions. All major oxides were LOI-free normalised before petrogenetic interpretation. The investigated rocks from the Jiamantieliek intrusion have a sub-alkaline character and a limited range of SiO2 content (56–66%) except for one outlier of 68% (Table 1; Fig. 5A). In the diagram for SiO2 vs. K2O (Fig. 5B), samples were shown to have a relatively wide range of K2O, from medium-K calc-alkaline to high-K calc-alkaline. Na, K and low-field-strength elements are mostly mobile and susceptible to change during alteration (e.g., Humphris and Thompston, 1978), whilst the high-field-strength elements and REE are essentially immobile during all but the most severe seafloor-hydrothermal alterations (e.g., Pearce, 1975; Wood et al., 1979) and during high-salinity, oxidised fluid-rock interactions at temperatures >400 °C (Dongen et al., 2010). At Baogutu, the orebearing rocks were subjected to fluid-rock interactions at temperatures <400 °C (Shen et al., 2010a), while at Jiamantieliek the fluidrock interactions took place in temperatures conditions of <400 °C (unpublished data). Thus, immobile elements are referred to in the following classification. Most samples from the Jiamantieliek were plotted in the gabbro to diorite fields with sub-alkaline character in the Zr/TiO2 vs. Nb/Y diagram (Fig. 5C); this was consistent with the above-mentioned results for the use of transmitted light petrography. Minor samples are plotted in the diorite field and close to the boundary between

Fig. 5. Classification diagrams of the analysed samples from Jiamantieliek and Baogutu intrusions. (A) total alkalis vs. silica; (B) SiO2 vs. K2O; (C) Zr/TiO2 vs. Nb/Y; (D) SiO2 vs. Mg#.

P. Shen et al. / Journal of Asian Earth Sciences 75 (2013) 158–173

165

Fig. 6. Chondrite normalised (Nakamura, 1974) REE distribution and patterns of trace elements normalised (Sun and McDonough, 1989) to E-MORB for the Jiamantieliek intrusions.

Fig. 7. Chondrite normalised (Nakamura, 1974) REE distribution and patterns of trace elements normalised (Sun and McDonough, 1989) to E-MORB for the Baogutu intrusions.

the diorite and granodiorite. Together with the results of the detailed thin section petrography (quartz <20%), these samples are quartz diorites. Therefore, it was possible to classify the

Jiamantieliek intrusion, by its petrography and immobile elements, which ranges from diorite to quartz diorite. In addition, all samples showed a high Mg# character, with Mg# >0.4 (Fig. 5D).

166

Table 3 Nd–Sr–Pb isotopic data for the Jiamantieliek and Baogutu intrusions. Jiamantieliek

Baogutu

Sample

ZK2-260

001-191

YJ1-100

YJ1-8(1)

JMP-3-5

YJ1-54

BGT-600

ZK211-263

ZK201-616

ZK202-295

BGT5-1

BGT5-2

BGT5-3

BGT5-4

Rocks Rb Sr 87 Rb/86Sr 87 Sr/86Sr 2rm T(Ma) I(Sr) Sm Nd 147 Sm/144Nd 143 Nd/144Nd 2rm (143Nd/144Nd)i eNd(t) Tdm U Th Pb (206Pb/204Pb)m (207Pb/204Pb)m (208Pb/204Pb)m (206Pb/204Pb)i (207Pb/204Pb)i (208Pb/204Pb)i

D 19.7 874 0.065 0.70412 14 313 0.70383 5.77 28.31 0.1233 0.512779 12 0.51252 2.8 610 3.57 3.81 1.91 23.81 15.70 39.96 17.41 15.34 37.74

D 16.1 646.4 0.072 0.70402 10 313 0.70369 1.92 9.75 0.1193 0.512812 10 0.51256 3.4 544 0.90 3.86 7.79 18.25 15.41 37.80 17.89 15.33 37.31

QD 42.2 679.2 0.18 0.70465 10 313 0.70386 2.44 12.16 0.1216 0.512802 13 0.51255 3.2 567 1.36 5.17 14.49 18.52 15.37 38.08 18.23 15.31 37.72

QD 22.3 714 0.090 0.70441 13 313 0.70401 2.83 15.11 0.1133 0.512773 12 0.51254 2.6 587 0.58 1.78 6.38 18.32 15.46 37.93 18.04 15.41 37.65

QD 43.9 631 0.202 0.70461 8 313 0.70371 2.74 14.4 0.1153 0.512724 9 0.51248 1.6 677

DP 64.3 679 0.274 0.70519 14 310 0.70396 3.32 16 0.1254 0.512734 8 0.51247 1.9 688

D 3.66 794.7 0.013 0.70371 11 313 0.70365 3.35 13.51 0.1498 0.512915 13 0.51260 5.4 481 0.13 0.30 2.20 18.12 15.47 37.95 17.93 15.45 37.82

D 16.4 659.6 0.072 0.70387 11 313 0.70355 2.97 13.2 0.136 0.512902 12 0.51261 5.2 456 0.38 1.17 4.62 18.28 15.45 38.06 18.03 15.41 37.80

D 24.1 638.9 0.109 0.70422 12 313 0.70372 1.98 9.69 0.1233 0.512846 11 0.51258 4.1 503 1.07 2.90 3.11 19.07 15.47 38.71 17.98 15.32 37.75

D 5.3 937.4 0.016 0.7039 10 313 0.70388 1.69 6.65 0.1536 0.512938 13 0.51261 5.9 457 0.50 0.39 1.84 18.26 15.49 38.06 17.43 15.46 37.85

D 39.9 770.8 0.15 0.70438 10 313 0.70370 3.68 17.32 0.1286 0.512859 9 0.51257 4.3 522

QD 14.73 634 0.067 0.70405 9 313 0.70374 3.21 14.14 0.1372 0.512887 10 0.51258 4.9 525

D 34.16 750.4 0.132 0.70445 13 313 0.70385 4.11 18.7 0.1327 0.512865 11 0.51257 4.4 537

D 13.27 770.6 0.05 0.70392 12 313 0.70369 3.67 13.57 0.1636 0.512947 10 0.51258 6.0 618

Rb, Sr, Sm, Nd, U, Th and Pb in ppm. (m) is the measured value, (i) is the initial value, (t) is the idealised crystallization age. The 87Sr/86Sr ratios are normalised to 86Sr/88Sr = 0.1194 and the 143Nd/144Nd ratios to 146Nd/144Nd = 0.7219.

eNd(t) = [{(143Nd/144Nd)m/(143Nd/144Nd)CHUR}  1]104, using (143Nd/144Nd)CHUR = 0.512638 (DePaolo, 1988). Initial (i) values calculated at 313 Ma. The model ages were calculated using a linear isotopic ratio growth equation: = (1/k)ln{1 + [(143Nd/144Nd)m  0.51315]/[(147Sm/144Nd)m  0.2137] (0.51315 and 0.2137 from Miller and O’Nions, 1985). Decay constants used are 1.42  1011a1 for 87Rb, 6.54  1012a1 for 147Sm, for U = 1.55125  1010a1, 235U = 9.8485  1010a1 and 232Th = 4.9475  1011a1 (Steiger and Jäger, 1977). Blank: not analysed. Data sources: Shen et al. (2009); the other this study. Abbreviations: D: diorite; QD: quartz diorite; DP: diorite porphyry.

tDM 238

P. Shen et al. / Journal of Asian Earth Sciences 75 (2013) 158–173

Intrusions

P. Shen et al. / Journal of Asian Earth Sciences 75 (2013) 158–173

Comparison of the Baogutu and Jiamantieliek intrusions revealed that the Baogutu rocks are similar to those of Jiamantieliek except that they are less enriched in SiO2 and alkline, and contain lower KO2 and variable Mg# (Figs. 5A–D). The Baogutu can be classified as ranging from diorite to quartz diorite. All samples from the Jiamantieliek intrusion exhibited coherent chondrite-normalised (Nakamura, 1974) patterns of rare earth elements (REE), characterised by a relative enrichment of light rare earth elements (LREE) and nearly flat heavy rare earth element

167

(HREE) segments, without Eu anomalies (Figs. 6A and C). They also have similar enriched mid-oceanic ridge basalt (E-MORB)-normalised (Sun and McDonough, 1989) trace element patterns, characterised by a negative Nb anomaly and enrichment in large ion lithophile elements (LILE) (Figs. 6B and D). The Baogutu rocks have similar REE patterns and E-MORB-normalised trace element patterns to those of the Jiamantieliek rocks, except that they have more variable REE patterns and a slightly low RREE and LILE (Fig. 7). All rocks displayed a negative Nb-anomaly.

Fig. 8. Initial (313 Ma) isotope characteristics (after DePaolo, 1981; Alibert, 1985; Deckart et al., 2005) of the Jiamantieliek and Baogutu intrusions from this work and our previous work (Shen et al., 2009). (a) eNd(t) vs. (87Sr/86Sr)i diagram (the early to middle Proterozoic crust from Hu et al., 2000). (b) (143Nd/144Nd)i vs. (87Sr/86Sr)i, (c) (143Nd/144Nd)i vs. (206Pb/204Pb)i, (d) (87Sr/86Sr)i vs. (206Pb/204Pb)i, (e) (207Pb/204Pb)i vs. (206Pb/204Pb)i, and (f) (208Pb/204Pb)i vs. (206Pb/204Pb)i. The diagram shows mixing lines with percentages of mixing between N-MORB and EMI or EMII end-members. DM, depleted mantle; BSE, bulk silicate Earth; EM1 and EM2, enriched mantle; HIMU, mantle with high U/Pb ratio. Symbols are the same as in Fig. 5.

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P. Shen et al. / Journal of Asian Earth Sciences 75 (2013) 158–173

4.2.2. Sr–Nd–Pb isotopes The measured and initial (back-calculated to 310 Ma) isotopic ratios are reported in Table 3. All samples from the Jiamantieliek and Baogutu intrusions showed a limited range in their 143Nd/144Nd and 87Sr/86Sr ratios (Fig. 8). In details, initial 87Sr/86Sr ratios for the Jiamantieliek intrusion ranged from 0.70369 to 0.70401; their Nd isotopes displayed small variations of between 0.51247 and 0.51256, and eNd(t) from +1.6 to +3.4. Their Pb initial ratios were less variable (206Pb/204Pb = 17.41–18.23, 207Pb/204Pb = 15.31–15.41 and 208 Pb/204Pb = 37.31–37.74). Initial 87Sr/86Sr ratios of the Baogutu main-stage diorite and quartz diorite were from 0.70355 to 0.70388, their Nd isotopes from 0.51257 to 0.51261 and the eNd(t) from +4.1 to +6.0. Their initial Pb ratios were also less variable 207 (206Pb/204Pb = 17.43–18.03, Pb/204Pb = 15.32–15.46, and 208 204 Pb/ Pb = 37.75–37.85).

mean age for the 17 remaining samples was determined to be 310 ± 5 Ma (Fig. 9d). This age was interpreted as the crystallisation age of the late-stage porphyry. 5. Discussion 5.1. Ages The Jiamantieliek intrusion includes the main-stage stock and late-stage dikes. The geochronological data provide direct support for the occurrence of two intrusive events. The U–Pb zircon SHRIMP age of the diorite is 313 ± 4 Ma and the diorite porphyry is 310 ± 5 Ma. In our previous work, we determined the U–Pb zircon SIMS ages of the Baogutu intrusion at 313 ± 2 Ma and 312 ± 2 Ma for the main-stage diorite and late-stage diorite porphyry, respectively. These data indicate that the Jiamantieliek and Baogutu ore-bearing intrusions were the product of a shortlived magmatic activity. Tang et al. (2009) have determined a zircon LA-ICPMS U–Pb age of 314 ± 2 Ma and 313 ± 3 Ma for Stocks II and III, respectively, in the Kelamay Region (Fig. 3A). Our Re– Os dating of molybedenite from the Baogutu deposit indicates that mineralisation occurred at around 312 Ma (Shen et al., 2012b). Based on these data, we suggest that the ore-bearing magma and associated Cu-Au-Mo mineralisation in the southern West Junggar occurred in the Late Carboniferous. This is consistent with the orebearing magma and mineralisation ages in the North Balkash Region, Kazakhstan, determined as 316 Ma by SHARMP zircon dating of the ore-bearing porphyry and 315 Ma by Re–Os dating of molybedenite from the Borly porphyry Cu–Mo deposit (Fig. 1a; Chen et al., 2010). The southern West Junggar in China may be correlated with the North Balkhash porphyry copper ore belt in Kazakhstan.

4.2.3. Zircon U–Pb ages All analyses illustrated the variability in U concentrations, which ranged from 65 to 408 ppm. Thorium ranged from 27 to 436 ppm and Th/U ratios varied between 0.41 and 1.07. All of the zircon Th/U ratios were greater than 0.1, therefore indicating a magmatic origin for the zircons. Sample YJ1-175: this was a diorite selected from the main-stage stock of the Jiamantieliek intrusion. Analyses of 14 magmatic zircons were obtained from this sample (Table 4). The calculated weighted mean age was 313 ± 4 Ma (Fig. 9b). This age was interpreted as the crystallisation age of the main-stage stock. Sample YJ1-21: this was a diorite porphyry selected from the late-stage dike of the Jiamantieliek intrusion. Analyses of 18 magmatic zircons were obtained from this sample (Table 4). Excluding one outlaying age result of 250.4 ± 7.0 Ma, the calculated weighted

Table 4 SHRIMP zircon U–Pb isotopic data for the main-stage diorite and late-stage diorite porphyry at Jiamantieliek. Th/U

207

YJ1-175; main-stage diorite YJ1-175-1 132 82 YJ1-175-2 116 65 YJ1-175-3 174 85 YJ1-175-4 145 79 YJ1-175-5 161 74 YJ1-175-6 129 66 YJ1-175-7 113 52 YJ1-175-8 97 54 YJ1-175-9 183 102 YJ1-175-10 114 66 YJ1-175-11 161 94 YJ1-175-12 244 205 YJ1-175-13 128 65 YJ1-175-14 309 243

0.62 0.56 0.49 0.54 0.46 0.51 0.46 0.56 0.56 0.57 0.58 0.84 0.51 0.79

0.0521 0.0470 0.0534 0.0489 0.0478 0.0570 0.0484 0.0560 0.0549 0.0516 0.0547 0.0516 0.0464 0.0478

3.7 5.5 3.5 6.1 4.5 3.4 6.2 3.6 2.9 5.1 3.1 2.7 6.3 3.4

0.3488 0.3065 0.3686 0.3467 0.3327 0.4001 0.3319 0.3808 0.3692 0.3478 0.3944 0.3497 0.3283 0.3314

4.3 5.9 4.0 6.7 5.0 4.1 6.6 4.2 3.5 5.5 3.8 3.4 6.7 3.9

YJ1-21; late-stage diorite porphyry YJ1-21-1 65 27 YJ1-21-2 176 134 YJ1-21-3 137 100 YJ1-21-4 165 88 YJ1-21-5 72 32 YJ1-21-6 176 86 YJ1-21-7 99 41 YJ1-21-8 176 137 YJ1-21-9 224 175 YJ1-21-10 408 436 YJ1-21-11 141 87 YJ1-21-12 92 46 YJ1-21-13 279 152 YJ1-21-14 127 82 YJ1-21-15 90 57 YJ1-21-16 169 85 YJ1-21-17 104 47 YJ1-21-18 212 87

0.42 0.76 0.73 0.54 0.44 0.49 0.42 0.78 0.78 1.07 0.62 0.50 0.54 0.65 0.64 0.50 0.45 0.41

0.0470 0.0465 0.0556 0.0524 0.0439 0.0471 0.0441 0.0535 0.0521 0.0509 0.0453 0.0473 0.0506 0.0531 0.0543 0.0558 0.0454 0.0517

15.6 6.6 3.2 5.2 12.0 6.2 11.6 3.0 3.4 2.5 9.4 7.7 5.5 4.5 6.4 3.0 14.2 3.5

0.3142 0.3164 0.3826 0.3502 0.2397 0.3226 0.3014 0.3492 0.3432 0.3397 0.3075 0.3380 0.3555 0.3850 0.3593 0.3901 0.3097 0.3440

15.8 6.9 3.9 5.6 12.4 6.5 12.0 3.6 3.9 3.1 9.7 8.0 5.8 5.0 6.8 3.6 14.4 4.0

Sample/spot

U (ppm)

Th (ppm)

Pb/206Pb

±%

207

Pb/235U

±%

206

Pb/238U

±%

207

Pb/206Pb

±

207

0.0485 0.0473 0.0501 0.0514 0.0505 0.0509 0.0497 0.0493 0.0488 0.0489 0.0523 0.0492 0.0513 0.0503

2.2 2.2 2.1 2.8 2.1 2.2 2.3 2.2 2.0 2.2 2.1 2.0 2.2 2.0

305.6 297.6 315.1 323.1 317.3 319.9 312.7 310.1 307.0 307.5 328.6 309.4 322.7 316.4

6.5 6.4 6.3 8.7 6.5 6.7 6.9 6.6 6.0 6.6 6.7 6.2 7.0 6.0

0.0485 0.0494 0.0499 0.0484 0.0396 0.0496 0.0496 0.0473 0.0478 0.0484 0.0493 0.0518 0.0510 0.0526 0.0480 0.0507 0.0495 0.0483

2.7 2.1 2.1 2.1 2.8 2.1 2.9 2.1 2.0 1.9 2.1 2.2 2.0 2.2 2.3 2.1 2.3 2.0

305.0 310.7 313.9 304.9 250.4 312.3 312.2 297.9 301.1 304.8 310.1 325.7 320.6 330.3 302.3 318.8 311.5 303.8

8.1 6.3 6.5 6.2 7.0 6.3 8.8 6.0 5.9 5.7 6.4 7.1 6.2 7.0 6.7 6.4 7.1 6.1

Pb/235U

±

206

Pb/238U

305.7 299.5 314.8 324.7 319.2 318.3 314.3 308.8 306.1 307.8 327.9 309.8 325.3 318.3

6.6 6.5 6.4 8.8 6.6 6.8 7.0 6.7 6.1 6.7 6.8 6.3 7.1 6.1

306.1 298.9 316.3 323.9 318.8 317.4 313.7 309.8 307.5 308.1 327.1 310.4 324.3 318.0

7.3 7.1 6.9 9.6 7.0 7.4 7.5 7.4 6.7 7.3 7.5 7.2 7.7 6.9

307.1 313.0 312.8 304.9 252.6 314.3 315.5 297.5 301.2 305.3 312.8 327.9 321.5 330.3 301.7 317.6 314.2 304.1

7.9 6.4 6.6 6.3 7.0 6.4 8.8 6.1 5.9 5.8 6.4 7.2 6.3 7.1 6.8 6.5 6.9 6.1

308.2 315.1 311.2 304.9 252.2 313.1 316.8 298.6 301.0 306.9 313.9 326.1 322.3 332.4 300.2 319.8 313.0 303.4

8.4 7.3 7.5 6.8 7.6 6.9 9.4 7.0 6.8 7.0 7.1 7.8 6.8 7.9 7.5 7.0 7.5 6.5

±r

P. Shen et al. / Journal of Asian Earth Sciences 75 (2013) 158–173

169

Fig. 9. (a) and (c) SEM cathodoluminescence (CL) images of sectioned zircon grains from the Jiamantieliek main-stage diorite stock (sample YJ1-175) and late-stage diorite porphyry dike (sample YJ1-21) in the Barluke Mountains. Circle and numbered spots indicate the locations of SHRIMP analysis with the measured age in Ma. (b) and (d) Concordia plots of SHRIMP U–Pb isotopic analyses of zircon.

5.2. Petrogenesis 5.2.1. Jiamantieliek intrusion The Jiamantieliek intrusion consists of diorite and diorite porphyry, with SiO2 contents ranging from 56 to 68 wt%, Al2O3 from 14 to 16 wt% and MgO from 1.78 to 4.71 wt% (Table 1). High Sr concentrations ranged from 551 to 915 ppm, except for one value of 371 ppm and low 87Sr/86Sr ratios between 0.70369 and 0.70401. The Yb content ranged from 1.3 to 1.9 ppm, except for one outlier of 2.6 ppm, and the Y value ranged from 12.9 to 17.9 ppm except for two outliers of 19.0 ppm and 24 ppm (Table 1). Compositionally, samples from the Jiamantieliek intrusion are similar to those of modern adakites (Defant et al., 1991). However, compared to adakites, the Jiamantieliek intrusion has slightly lower abundances of REE and LILE (Fig. 6) and variable Sr/Y ratios (Fig. 10). They also contain a high content of MgO and a low SiO2 content (Fig. 5) relative to adakites (Defant et al., 1991). In the Sr/Y vs. Y (Defant and Drummond, 1993) and (La/Yb)n vs. Ybn (Defant and Drummond, 1990) diagrams, the Jiamantieliek intrusion plots in a transitional adakite to normal arc field (Fig. 10). The Jiamantieliek rocks have less

variable Zr contents, but variation in Zr/Nb ratios, suggesting that partial melting process played a role in their petrogenesis (Fig. 11). In addition, the Jiamantieliek intrusion is enriched in LILEs and LREEs, with a marked negative Nb anomaly (Fig. 6). The above data demonstrate that the Jiamantieliek intrusion has a genetic affinity between the adakites and diorites occurred in the normal arc. The former implies that the melt of the Jiamantieliek intrusion could be a product of the partial melting of a Junggar oceanic slab. The latter indicates that they were derived from a subduction-modified mantle source. The melt of the Jiamantieliek intrusion was therefore a product of the partial melting of a Junggar oceanic slab and later interaction with the subduction-modified mantle during ascent. Experimental studies have demonstrated that Mg# is a useful index in discriminating melts purely derived from the crust from those involved in the mantle. Melts from the basaltic lower crust are characterised by low Mg# (<0.4) regardless of melting degree, whereas those with Mg# >0.4 can only be obtained when a mantle component is involved (Rapp and Watson, 1995). The Jiamantieliek dioritic rocks have a relatively high Mg# content (0.61–0.70) (Table 1; Fig. 5D), indicating the involvement of mantle components.

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Jiamantieliek intrusive rocks were derived from a depleted mantle source mixed with subducted EM-I. The lower positive eNd(t) value, which corresponds to Nd mean crustal residence ages in the range of 544–688 Ma (Table 3) for the Jiamantieliek samples, indicated an involvement of Neoproterozoic primitive crust in the formation of the Barluke magmatic arc. 5.2.2. Baogutu intrusion The Baogutu dioritic rocks also have a genetic affinity with the adakites and diorites. In the Sr/Y vs. Y and (La/Yb)n vs. Ybn diagrams, the samples plot in the transitional adakite to normal arc field (Fig. 10). In the Zr/Nb–Zr diagram (Fig. 11), the Baogutu dioritic rocks display a comparable trend to the partial melting process (Fig. 11). In comparison with the Jiamantieliek intrusion, the Baogutu rocks are derived from a more depleted mantle source, with minor mixing of subducted EM-I (Figs. 8a and b). The isotopic signature of the Baogutu intrusion (eNd(310) = +4.1 to + 6.0; ISr = 0.70355–0.70385) and the corresponding Nd model ages (474–537 Ma, except for one outlier of 618 Ma, Table 3) both support less involvement of Neoproterozoic primitive crust in the formation of the Kelamay magmatic arc. The Jiamantieliek and Baogutu intrusions have similar characteristics, indicating that a relatively uniform and integrated source region has existed in the southern West Junggar since the Palaeozoic. This suggests that this source region is related to the long-lasting residual oceanic basin and related lithospheres since the Palaeozoic in North Xinjiang. A greater contribution from an enriched mantle source and more involvement of the Neoproterozoic crust would be required to have generated the Jiamantieliek intrusion in the Barluk Mountains. 5.3. Tectonic setting and mineralisation implications Fig. 10. (a) Diagram of Sr/Y vs. Y (Defant and Drummond, 1993). Fig. 10B. Diagram of (La/Yb)n vs. Ybn (Defant and Drummond, 1990).

Fig. 11. Zr/Nb–Zr diagram showing that the studied dioritic rocks are controlled by partial melting.

This result is supported by the isotopic data. Based on Nd–Sr–Pb isotope systematics, the Jiamantieliek intrusive magmas generally lie on a mixing line between the N-MORB and EM-I or EM-II component (Figs. 8a–d). Moreover, modelling based on the Sr, Nd and Pb isotopic composition indicated that the composition of all samples can be explained by mixing between about 70–80 wt% of melts with N-MORB characteristics (from a DM source) and 20–30 wt% of a sedimentary end-member, isotopically similar to EM-I or EM-II (Figs. 8b–d). Lead isotopic ratios of the samples indicated an EM-I source (Figs. 8e and f), which can be considered as an end-member of the mixing process in the genesis. Therefore, the

5.3.1. Tectonic setting Confirming which series a rock belongs to is very important in discriminating the tectonic setting of intrusive rocks. In the SiO2 vs. K2O diagram (Fig. 5B), most samples from the Jiamantieliek intrusion plot on the medium-K calc-alkaline field and to a minor degree on the high-K calc-alkaline field. Calc-alkaline rocks are typical constituents of mature island arcs (e.g. Miyashiro, 1974). Most samples were enriched in LREE (Fig. 6) had Nb/Yb ratios between EMORB and OIB (Fig. 12A). On discrimination diagrams these samples plotted on the volcanic arc granitoid field (Fig. 12B). Their ISr values ranged from 0.70369 to 0.70401 and eNd(t) from +1.6 to +3.4, with Nd model ages ranging between 544 and 688 Ma. Their Pb initial ratios were less variable (206Pb/204Pb = 17.41–18.23, 207 Pb/204Pb = 15.31–15.41 and 208Pb/204Pb = 37.31–37.74). Based on these characteristics, we inferred that the rocks from the Jiamantieliek intrusion formed in an island are setting. The Baogutu intrusive rocks have a transitional calc-alkaline to tholeiite character (Fig. 5B). Tholeiitic rocks may be associated with emerging island arcs (e.g. Miyashiro, 1974), mid-ocean ridges and back-arc basin spreading centres (e.g. Gill, 1976). Most diorites were enriched moderately in LREE (Fig. 7) and had E-MORB-like Nb/Yb ratios (Fig. 12A). Their isotopic composition (eNd(t) = +4.4 to +6.0, ISr = 0.70368–0.70385) matched that of a depleted mantle source. Thus, it is very likely that the Baogutu intrusive rocks were also formed within an island are setting. 5.3.2. Tectonic evolution In comparison to the Jiamantieliek intrusion, the Baogutu intrusion has a transitional tholeiite to calc-alkaline character (Fig. 5B), with moderate enrichment in LREE and LILE (Figs. 6 and 7), low and E-MORB-like Nb/Yb ratios (Fig. 12A) and a high eNd(t) (+4.4 to +6.0), suggesting that the Jiamantieliek intrusion could have formed in a normal island arc setting, while the Baogutu intrusion formed in a

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Fig. 12. (A) Th/Yb–Nb/Yb diagram (Pearce and Peate, 1995; Sayit and Goncuoglu, 2009) and (B) Ta–Yb diagram for the Jiamantieliek and Baogutu intrusions. WPG = within plate granitoid, VAG = volcanic arc granitoid, Syn-COLG = syn-collision granitoid, ORG = ocean ridge granitoid. Symbols are the same as in Fig. 10.

Fig. 13. Cartoon showing the geodynamic setting in the southern West Junggar, double subduction systems might have result in the formation of ore-bearing intrusions, as suggested by Zhang et al. (2011a,b).

relatively immature island arc setting. Therefore, there is a development of magmatic arc maturation towards the northwestern part of the southern West Junggar. Most recently, some researchers consider that the Carboniferous Junggar Ocean may have been northwestward subducting beneath the Kelamay arc in the Early Carboniferous (Tang et al., 2009, 2010; Geng et al., 2009, 2011; Yin et al., 2010; Yang et al., 2012). On the basis of detailed field mapping and ages of the ophiolitic mélanges and coherent sedimentary rocks, Zhang et al. (2011a, 2011b) proposed there were double subduction systems in the Darbut area of the southern West Junggar in the Late Carboniferous. Our study about the Early Carboniferous volcanic rocks (submitted for publication) in the Kelamay region (southern West Junggar) supported the double subduction model. Therefore, an alternative model for their formation invokes a double subduction model, as proposed by Zhang et al. (2011a, 2011b). In this model (Fig. 13) subduction along the Durbut fault was synchronous towards the northwest and southeast during the Late Carboniferous (310–313 Ma), creating the Kelamay intra-oceanic arc in the southeastern Darbut fault and the Barluk intra-oceanic arc in the northwestern Darbut fault. In this scenario, (1) melting of the subducted slab released melts/fluids which metasomatised the lithospheric mantle, creating an enriched mantle source; (2) mixing between the depleted- and enriched- mantle produced diorites and quartz diorites of the Jiamantieliek and Baogutu intrusions. This geodynamic process led to the formation of subductionrelated intrusions and associated porphyry copper deposits in the southern West Junggar (Shen et al., 2009, 2013), represented by

the Baogutu ore-bearing intrusions and associated deposits in the Kelamay Region and the newly-discovered Jiamantieliek ore-bearing intrusions and associated deposits in the Barluk Mountains (Fig. 1b). 5.3.3. Mineralisation implications In general, most porphyry copper deposits are generated in magmatic arc settings and associated with calc-alkaline magma (Hedenquist and Lowenstern, 1994; Richards, 2005; Sillitoe, 2010). In this contribution, we recognise that the ore-bearing intrusions of the southern West Junggar are calc-alkaline intermediate rocks and proposed that they form in an island arc setting. This island arc setting and associated with calc-alkaline magma is favourable for the formation of the porphyry Cu ore deposits in the Kelamay Region and the Barluk Mountains. Furthermore, the maturation of the magmatic arc and the increase in calc-alkaline magma content from the Kelamay Region to the Barluk Mountains are favourable for the formation of the Jiamantieliek porphyry-type ore deposit, although the Jiamantieliek deposit is still being explored. 6. Conclusions (1) Both Jiamantieliek and Baogutu intrusions are the intermediate intrusions that comprise main-stage diorite stock and late-stage diorite porphyry dikes. The Jiamantieliek intrusion formed in 313 ± 4 Ma and 310 ± 5 Ma and the Baogutu intrusion formed in 313 ± 2 Ma and 312 ± 2 Ma.

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(2) The Jiamantieliek rocks are calc-alkaline rocks and enriched in LREE and LILE with distinct negative Nb anomaly, suggesting generation in a normal island arc setting. Baogutu rocks are similar to those of the Jiamantieliek intrusion except for moderate enrichment in LREE and LILE and E-MORB-like Nb/ Yb ratios with tholeiite signature, indicative of a relative immature island arc setting. (3) The Jiamantieliek intrusion isotopic compositions (eNd(t) = +1.6 to +3.4, (87Sr/86Sr)i = 0.70369–0.70401, (207Pb/204Pb)i = 15.31– 15.41) match a mixing source of depleted mantle and EM-I, whereas the Baogutu intrusion isotopic compositions (eNd (t) = +4.4 to +6.0, ISr = 0.70368–0.70385) reveal a more depleted mantle source. They formed in an intra-oceanic arc setting. (4) The Jiamantieliek and Baogutu intrusions have similar characteristics, indicating that a relatively uniform and integrated source region has existed in the southern West Junggar since the Palaeozoic. The magmatic arc maturation developed from east to west in the southern West Junggar, and is favourable for the formation of the porphyry-type ore deposits in the Barluk Mountains.

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