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Accepted Manuscript
Early Carboniferous adakitic rocks in the area of the Tuwu deposit, eastern
Tianshan, NW China: Slab melting and implications for porphyry copper min-
eralization
Yin-Hong Wang, Chun-Ji Xue, Jia-Jun Liu, Jian-Ping Wang, Jun-Tao Yang,
Fang-Fang Zhang, Ze-Nan Zhao, Yun-Jiang Zhao, Bin Liu
PII: S1367-9120(14)00445-3
DOI: http://dx.doi.org/10.1016/j.jseaes.2014.09.032
Reference: JAES 2113
To appear in: Journal of Asian Earth Sciences
Received Date: 1 April 2014
Revised Date: 23 September 2014
Accepted Date: 23 September 2014
Please cite this article as: Wang, Y-H., Xue, C-J., Liu, J-J., Wang, J-P., Yang, J-T., Zhang, F-F., Zhao, Z-N., Zhao,
Y-J., Liu, B., Early Carboniferous adakitic rocks in the area of the Tuwu deposit, eastern Tianshan, NW China: Slab
melting and implications for porphyry copper mineralization, Journal of Asian Earth Sciences (2014), doi: http://
dx.doi.org/10.1016/j.jseaes.2014.09.032
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Early Carboniferous adakitic rocks in the area of the Tuwu deposit, eastern Tianshan,
NW China: Slab melting and implications for porphyry copper mineralization
Yin-Hong Wang a, *, Chun-Ji Xuea, Jia-Jun Liua, Jian-Ping Wanga, Jun-Tao Yangb, Fang-Fang
Zhanga, Ze-Nan Zhaoa, Yun-Jiang Zhaob, Bin Liua
aState Key Laboratory of Geological Processes and Mineral Resources, China University of
Geosciences, Beijing 100083, China;
bNo. 1 Geological Party, Xinjiang Bureau of Geology and Mineral Exploration, Changji
831100, China
Abstract: Existing geochronological and geochemical data for the Early Carboniferous
magmatic rocks in the eastern Tianshan, Xinjiang, have been interpreted in a variety of theories
regarding petrogenesis and geodynamic setting. The proposed settings include rift, back-arc
basin, passive continental margin, island arc, ridge subduction, and post-collisional
environment. To evaluate these possibilities, we present new SHRIMP zircon U–Pb
geochronology and geochemical data, whole-rock geochemical, Hf isotope, and S isotope data
for tonalitic rocks and ores associated with the Tuwu porphyry copper deposit located in the
center of the late Paleozoic Dananhu–Tousuquan arc, eastern Tianshan. SHRIMP zircon U–Pb
dating indicates that the magmatic activity and thus associated copper mineralization occurred
��������������������������������������������������������������
*Corresponding author at: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, 29 Xue-Yuan Road, Haidian District Beijing 100083, China. Tel.: +86 10 8232 2346 (office); fax: +86 10 8232 2970 E-mail address: [email protected]
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ca.332 Ma. The tonalitic rocks are calc-alkaline granites with A/CNK values ranging from
1.16 to 1.58; are enriched in K, Rb, Sr, and Ba; and are markedly depleted in Nb, Ta, Ti, and
Th. They show geochemical affinities similar to adakites, with high Sr, Al2O3, and Na2O
contents and La/Yb ratios; low Y and Yb contents; and slight positive Eu anomalies. In situ Hf
isotopic analyses of zircons yielded positive initial εHf(t) values ranging from 6.9 to 17.2. The
δ34S values of the ore sulfides range from -3.0‰ to +1.7‰, reflecting a deep sulfur source. Our
results indicate that the paleo-Tianshan oceanic slab was being simultaneously subducted
northward beneath the Dananhu-Tousuquan arc, and southward beneath the Aqishan-Yamansu
arc during the Early Carboniferous. The Tuwu adakitic tonalitic rocks were derived from the
partial melting of the subducted paleo-Tianshan oceanic slab, which was subsequently
hybridized by mantle wedge peridotites. The slab-derived magmas have considerably high
copper contents and are highly oxidized, thus leading to porphyry copper mineralization. Such
Early Carboniferous tonalitic rocks that are widespread in the eastern Tianshan define a
province with high potential for copper mineralization.
Keywords: Eastern Tianshan; Tuwu porphyry Cu deposit; Subduction-related adakite;
Tonalite; SHRIMP zircon U–Pb dating; Hf isotope; S isotope
1. Introduction
The Central Asian Orogenic Belt was formed by the amalgamation of various continental
blocks, arc complexes, and accretionary wedges (Pirajno, 2010; Xiao et al., 2010;
Rojas-Agramonte et al., 2011; Goldfarb et al., 2014; Mao et al., 2014). The eastern part of the
Tianshan in northwestern China is part of the southern margin of the orogenic belt (Fig. 1a), and
it separates the Junggar Basin to the north from the Tu-Ha Basin to the south (Fig. 1b). The
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eastern Tianshan is characterized by widespread Carboniferous to Permian granitoids (Chen et
al., 2005b; Wu et al., 2006a), and lesser Devonian granitoids (Li et al., 2006c; Zhou et al., 2010)
and Triassic granitoids (Li et al., 2002; Zhang et al., 2005; Zhou et al., 2010). These eastern
Tianshan granitoids have attracted much attention because they are often associated with
Cu-Au-Fe-Ag mineralization. However, the petrogenesis and geodynamic setting of the
granitoids are still a matter of debate, with suggested settings such as rift (Qin et al., 2002),
back-arc basin (Xu et al., 2003), passive continental margin (Li et al., 2003), island arc (Rui et
al., 2002; Mao et al., 2005; Zhang et al., 2008), ridge subduction environment (Sun et al., 2010,
2011), or post-collision setting (Wang and Xu, 2006a; Gu et al., 2006; Zhou et al., 2008). Some
studies suggest that the porphyry copper-related granitic intrusions in the eastern Tianshan may
have an adakitic affinity (Wang et al., 2001; Liu et al., 2003; Han et al., 2006; Zhang et al.,
2010). The intrusions are mostly tonalitic, granodiorite, and granodioritic porphyry in
composition (Zhang et al., 2004). However, due to the lack of systematic, high-quality
geochronological and geochemical data, the petrogenesis and geodynamic setting of the
adakitic granitoids are poorly understood. As part of the magmatism research in the eastern
Tianshan, this paper thus provides SHRIMP zircon U–Pb geochronological, whole-rock
geochemical, Hf isotope, and S isotope data for the Tuwu intrusive rocks and ores, and
discusses granitoid petrogenesis, the associated porphyry Cu mineralization, the crust–mantle
interaction process, and eastern Tianshan geodynamic setting.
2. Geological setting and deposit geology
The eastern Tianshan region is one of the important producers of Cu (+/-Ni), Au, Fe, and
Ag in China (Zhai et al., 1999; Mao et al., 2008; Deng et al., 2011). The eastern Tianshan may
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be divided into three major tectonic units, the Dananhu–Tousuquan arc, the
Kangguer–Huangshan ductile shear belt, and the Aqishan–Yamansu arc, which are separated
by the regional-scale Kangguer and Yamansu crustal-scale faults (Fig. 1c). The
Dananhu–Tousuquan arc is situated north of the Kangguer fault, is mainly composed of
Devonian to Carboniferous volcanic and intrusive rocks, and contains several porphyry Cu
deposits of different sizes, including the Tuwu, Yandong, Linglong, and Chihu deposits (Fig.
1c). The base of the Dananhu–Tousuquan arc is represented by basaltic to andesitic volcanic
rocks, with locally overlying Lower Carboniferous carbonates and calcareous mudstones (Mao
et al., 2005). The Kangguer–Huangshan ductile shear belt lies between the Kangguer and
Yamansu faults, an area in which most rocks have undergone greenschist facies metamorphism
and ductile deformation, and where there are a number of orogenic Au deposits (e.g., Kangguer)
and magmatic Cu–Ni sulfide deposits (e.g., Huangshan and Huangshandong). The
Aqishan–Yamansu arc is located between the Yamansu and Aqikuduke faults, mainly
comprises Early Carboniferous basalt, andesite, dacite, and tuff of the Yamansu Formation and
Late Carboniferous rhyolite of the Tugutubulake Formation (Ma et al. 1993). The arc hosts
numerous Fe (-Cu) and Cu-Ag-Pb-Zn skarn deposits (e.g., Yamansu). The structural
architecture of the eastern Tianshan is characterized by a series of E-W-trending regional faults,
including the Dacaotan, Kangguer, Yamansu, and Aqikuduke faults (Qin et al., 2003).
The Tuwu porphyry Cu deposit is located in the middle of the Dananhu-Tousuquan arc and
is about 1–3 km north of the Kangguer fault (Fig. 2a). Tuwu, discovered in 1997, is the largest
deposit in the eastern Tianshan, with total Cu reserves of 2.04 million tonnes (Zhang et al.,
2006). The country rocks in the Tuwu area, have well-developed schistosity, strike
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approximately E–W, and dip to the south at 43°to 63°. They can be divided into three lithologic
sections of the Carboniferous Qieshan Group (Fig. 2b).The stratigraphically lowest section is
composed of volcaniclastics and tuff; the middle section is composed of basalt and andesite,
with intercalated dacite and basaltic andesite; and the upper section is composed of sandstone
and polymictic conglomerate, intercalated with tuff and andesite (Wang et al., 2001). The
overlying rocks of the Jurassic Xishanyao Formation consist chiefly of sandstone, siltite,
mudstone, and conglomerate, and they form an angular unconformity with the strata of the
Qieshan Group (Fig. 2b). Intrusive bodies, mostly tonalite and diorite porphyries (Fig. 2b and
3a), were emplaced into the Early Carboniferous volcanic rocks (Fig. 2b and 4b). The tonalitic
rocks are associated with porphyry-style Cu mineralization and surrounding alteration (Zhang
et al., 2004, 2006; Shen et al., 2012, 2014). Within the eastern Tianshan, 23 mineralized stocks
and plugs have been identified, and the largest of these at Tuwu occupies a surface outcrop of
~0.03 km2, with all other bodies occupying areas of <0.01 km2. The intrusions are mostly
irregular in shape where exposed (Fig. 2b).
The Tuwu porphyry Cu deposit consists of the Tuwu and Eastern Tuwu orebodies (Fig. 2b),
which are situated <200 m apart from one another. The mineralization occurs as thick tabular
bodies, and there is no distinct boundary between orebodies and subeconomic wall rocks. Using
a cut-off grade of 0.20% Cu to outline the orebodies, the Tuwu orebody has a continuous length
of 1400 m, a width ranging from 7.6 to 125m, and an average grade of 0.44% Cu. The Eastern
Tuwu orebody is about 1300 m in length, its width varies from 8.0 to 87.1m, and it has an
average grade of 0.30% Cu (Zhang et al., 2006). The orebodies have a thick lenticular surface
morphology, strike nearly E–W direction, and dip to the south at angles of 61°–67° (Fig. 4). The
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orebodies extend down-dip for more than 600 m (Fig. 4), and the Cu mineralization occurs
predominantly in tonalitic rocks (Liu et al., 2003; Zhang et al., 2004; Han et al., 2006).
Ore styles in the Tuwu porphyry Cu deposit mainly include disseminated (Fig. 5a), vein
(Fig. 5b), veinlet and disseminated (Fig. 5c), and scaly (Fig. 5d). Hydrothermal alteration is
zoned from the center of the tonalitic rocks to the margin with the wall rocks as follows: (1)
quartz-core zone, (2) biotite zone, (3) phyllic zone, (4) chlorite –epidote –albite zone, and (5)
argillite zone (Wang et al., 2001). Ore textures mainly include fine- to medium-grain sulfides or
hypidiomorphic-xenomorphic granular textures (Fig. 5e and f). Chalcopyrite is the main ore
mineral in the Tuwu deposit, with minor bornite, pyrite, molybdenite, chalcocite, digenite, and
magnetite. Gangue minerals are quartz and plagioclase, which are associated with sericite,
chlorite, and biotite (Wang et al., 2001).
3. Samples and analytical techniques
Tonalite samples for this study were collected from the Tuwu ore district (Fig. 2b). The
porphyries were altered to variable degrees by formation of biotite, sericite, and propylitic
assemblages. Thus, to best measure the chemical composition, the least altered samples were
chosen for major element, trace element, SHRIMP zircon U–Pb, and Lu–Hf isotope analyses.
These samples are defined as tonalite based on the IUGS classification, but they are also called
plagiogranite porphyry in the literature (Rui et al., 2002; Zhang et al., 2004, 2006; Shen et al.,
2012). They show porphyritic texture and massive structure, and mainly consist of plagioclase
(30–45%), quartz (10–20%), and biotite (5–10%), with accessory minerals that include zircon
and phosphates (Fig. 3b). Plagioclase is charactered by idiomorphic or hypidiomorphic tabular
texture, showing superficial weak sericite alteration (Fig. 3c). Quartz shows xenomorphic
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granular textures and distinct wavy extinction (Fig. 3d). Biotite was mainly yellow-brown in
color, with a hypidiomorphic–xenomorphic flaky or fragmental texture (Fig. 3d).
Zircons were separated from rock samples using flotation and electromagnetic methods at
the Hebei Regional Geological Survey located in Langfang. Zircons were documented with
transmitted and reflected light micrographs as well as cathodoluminescence (CL) images to
reveal their internal structures. The CL imaging was performed at the electronic probe lab of the
Geological Institute of the Chinese Academy of Geological Sciences (CAGS), under an
operating power of 15 kV and 4 nA. Under the guidance of zircon CL images, the zircons were
analyzed for U–Pb isotopic composition and U, Th, and Pb concentrations using a SHRIMP II
ion microprobe with a spot size of 30 μm at the Beijing Ion Probe Centre of the CAGS. Testing
conditions and processes were after Liu et al. (2006). Common lead correction was performed
using 204Pb, with a single testing error of 1σ and a 206Pb/238U weighted average age error of 2σ.
The zircon U–Pb isotope data are presented in Table 1.
Whole-rock compositions were analyzed at the test center of the Beijing Research Institute
of Uranium Geology. Major element analysis was conducted using a Philips PW2404 XRF
with testing precision greater than 1%. Trace element analysis was performed using a Finnigan
MAT Element I ICP-MS, with RSD (10 min) < 1% and RSD (4h) < 5%. For the testing methods,
refer to Gao et al. (2002). The whole-rock geochemical data are presented in Table 2.
In situ Hf isotope analysis was done on zircon grains using a Neptune MC-ICP-MS and a
NewWave UP213 ultraviolet LA-MC-ICP-MS at the MLR Key Laboratory of Metallogeny and
Assessment. During the analyses, He was used as the carrier gas. Depending on zircon size, the
ablating diameter was set at either 55 or 40 μm. International standard zircon sample GJ1 was
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used as a reference. Details of instrumental conditions and test process were given in Wu et al.
(2006b) and Hou et al. (2007). The weighted average of 176Hf/177Hf of the GJ1 zircon samples
was 0.282015 ± 31 (2SD, n = 10), which is in agreement with the values reported in the literature
(Elhlou et al., 2006; Hou et al., 2007). The initial 176Hf/177Hf ratios and εHf(t) values were
calculated with reference to the chondritic reservoir (CHUR) at the time of zircon growth from
magmas. The decay constant for 176Lu of 1.867×10−11 year-1 (Soderlund et al., 2004), and the
chondritic 176Hf/177Hf ratio of 0.282772 and 176Lu/177Hf ratio of 0.0332 (Blichert-Toft and
Albarède, 1997) were adopted. The depleted mantle model ages (TDM) used for basic rocks
were calculated with reference to the depleted mantle at the present-day 176Hf/177Hf ratio of
0.28325, which is similar to that of the average mid-ocean ridge basalt (MORB) (Nowell et al.,
1998) and 176Lu/177Hf=0.0384 (Griffin et al., 2000). Zircon Hf isotope crustal model ages (TcDM)
were calculated using an average continental crustal 176Lu/177Hf ratio of 0.015 (Griffin et al.,
2002). The zircon Hf isotopic data are presented in Table 3.
The δ34S values for sulfides were determined on SO2 obtained by placing a sulfide–CuO
composite (at weight ratio of 1/7) into a vacuum system heated to 980oC. Sulfur isotopes were
measured using a Finnigan MAT251 mass spectrometer at the test center of the Beijing
Research Institute of Uranium Geology. Isotopic data were reported in permil relative to the
Canyon Diablo Triolite (CDT) standard for sulfur. Total uncertainties were estimated to be
better than ± 0.2‰ for δ34S. The sulfur isotopic data are presented in Table 4.
4. Results
4.1. SHRIMP zircon U–Pb geochronology
Tonalite sample TW702-59 (N 42°06′57″, E 92°36′15″) from the Tuwu porphyry Cu
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deposit was chosen for SHRIMP zircon U–Pb analysis. The analytical data are presented in
Table 1. Zircons from the sample are colorless with no obvious inclusions. They are euhedral
and elongate prismatic, with a length to width ratio from 2:1 to 4:1. In zircon CL images, all
grains exhibit well-developed oscillatory zoning (Fig. 6a). The 238U and 232Th contents of
analyzed zircons are 45–144 ppm and 21–91 ppm, respectively, with Th/U ratios ranging from
0.29 to 0.79. These ratios are higher than those of metamorphic zircons (typically <0.1), but
consistent with those of magmatic zircons (Hoskin and Schaltegger, 2003). Therefore, the
SHRIMP zircon U-Pb dating results are interpreted to provide the age of magma crystallization.
Fifteen spot analyses were carried out on zircon grains of the tonalite sample (TW702-59).
Except for four older discordant data spots (9, 11, 12, and 15), the remaining 11 analyses have
206Pb/238U ages ranging from 320.3 to 348.6 Ma, with a weighted mean of 332.3±5.9Ma
(MSWD = 1.5) (Fig.6b). This is interpreted as the age of tonalite emplacement. In summary, the
SHRIMP zircon U-Pb dating indicates that the tonalitic rocks in Tuwu were emplaced in the
Early Carboniferous.
4.2. Whole-rock geochemistry
Whole-rock geochemical data for the Tuwu tonalite samples are presented in Table 2. The
Tuwu tonalite samples are characterized by a limited range in SiO2 (65.34%–68.21%), and plot
in the granodiorite field on a Na2O+K2O vs. SiO2 diagram (Fig. 7a). All tonalite samples record
Al2O3 contents greater than 15% and high Na2O concentrations (2.98%-4.65%). They have
relatively low K2O contents (1.28%–2.49%), and plot in the field of calc-alkaline granites (Fig.
7b). The A/CNK values of the samples (Al2O3/[CaO+Na2O+K2O], molratio) range from 1.16 to
1.58, which is characteristic of peraluminous granite (Fig. 7c). Most of tonalite samples have
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slightly high Mg# values of 40–42, except for two samples with low values of 36 and 37 (Table
2). The CaO, TFe2O3, and P2O5 contents of the tonalite samples range from 1.67% to 2.53%,
3.35% to 5.05%, and 0.13% to 0.15%, respectively. In the Harker diagrams for selected major
oxides (Fig. 8), CaO, TFe2O3, MgO, MnO, P2O5, and TiO2 contents are linearly correlated with
SiO2 contents.
The samples from the Tuwu deposits have steep heavy rare earth element (HREE) patterns
(Fig. 9a) and display slight positive Eu anomalies (Eu/Eu* = 0.93–1.12). High (La/Yb)N ratios
(8.24–10.87) indicate pronounced LREE/HREE fractionation. These features are observed in
the chondrite-normalized REE distribution pattern (Fig. 9a). The samples show strong
enrichment in large ion lithophile elements (K, Rb, Sr, and Ba) relative to high field strength
elements (Nb, Ta, Ti, and Th), and pronounced positive U and Pb anomalies in primitive
mantle-normalized trace element patterns (Fig. 9b). Tuwu tonalite samples also have low
concentrations of Yb (0.84–1.15ppm) and Y (7.51–9.53 ppm). These characteristics, together
with high Sr contents (261–669ppm) and Sr/Y ratios (35–82), indicate that the samples can be
classified as adakites as defined by Defant and Drummond (1990) (Fig. 10a).
4.3. Zircon Hf isotopes
In situ Hf isotope analyses of zircons from the tonalite sample (TW702-59) are shown in
Fig.6a. The zircon Hf isotopic data and calculated results are given in Table 3, and the Hf
isotopic evolution diagram is shown in Fig. 11. Except for four older data spots (9, 11, 12, and
15), the remaining 11 analyses have variable Hf isotopic compositions, with 176Hf/177Hf ratios
of 0.282798–0.283081, εHf(t) values ranging from +6.9 to +17.2, and corresponding two-stage
Hf isotopic crustal model ages (TCDM) values ranging from 239 to 902Ma.
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4.4. S isotopes
Sulfur isotopic compositions for chalcopyrite and pyrite samples from the Tuwu deposit
are presented in Table 4. The δ34S values of six pyrite samples range from +0.2‰ to +1.7‰,
and the δ34S values of four chalcopyrite samples range from –3.0‰ to +0.4‰. In addition, Rui
et al. (2002) and Han et al. (2006b) also obtained δ34S values for sulfides in Tuwu-Yandong ore
field that ranged from –0.9‰ to +1.3‰. Therefore, sulfur isotopes in the Tuwu porphyry Cu
deposit exhibit a narrow range, with an average δ34S value of 0.2‰, very close to meteoritic
values, suggesting an upper mantle source for the sulfur in the Tuwu deposit.
5. Discussion
5.1. Geochronology
Previous studies of most granites in the eastern Tianshan reported that they were formed
between 386 Ma and 228Ma (Fig. 1c; Table 5), and magmatic activity in this region can be
divided into four stages (Zhou et al., 2010; Wang et al., 2014): Late Devonian (386–369 Ma) (Li
et al., 2006c; Tang et al., 2007; Zhou et al.,2010), Early Carboniferous (349–329 Ma) (Sun et al.,
2012; Wang et al., 2014), Late Carboniferous–Late Permian (322–252 Ma) (Mao et al., 2002;
Wu et al., 2006c;) and Early and Middle Triassic (246–228 Ma) (Li et al., 2006a; Yang et al.,
2011). The Late Devonian granitic intrusions mainly occur on the eastern margin of the Tu-Ha
Basin in the eastern Tianshan. They are represented by Jingerquan, Xianshuiquan, and
Sidingheishan bodies, mainly consisting of biotite granite and granodiorite. The Early
Carboniferous granitic intrusions are widely distributed in the middle and western parts of the
eastern Tianshan. They include the Hongshi, Shiyingtan, Xifengshan, Hongyuntan, Yandong
and Tuwu intrusions, mainly consisting of moyite, syenogranite, granodiorite, dioritic
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porphyrite, and tonalite. The Late Carboniferous–Late Permian granites are mainly distributed
in Kangguer-Huangshan ductile shear belt, and include Bailingshan, Kangguer, Weiquan,
Chihu, Huangshan, Sanchakou, and Shuangchagou, which comprise granite porphyry, rhyolite
porphyry, quartz-syenite porphyry, granodiorite, and tonalite. The Early and Middle Triassic
granites are locally exposed as the Weiya, Donggebi, Baishan, and Tudun bodies, and they are
notably less common than the earlier three stages. There is an overall trend in the magmatic
activity in the area, with more of the older intrusions being emplaced in the east and younger
bodies in the middle and west along the length of the Kangguer ductile shear zone.
The internal structure of the large zircon grains from the Tuwu tonalite shows that they
possess good crystal form, uniform composition, and clear oscillatory zoning, which is typical
of magmatic zircons (Fig. 6a). This suggests that zircons were formed by crystallization in the
magmatic system. Our calculated SHRIMP zircon U–Pb age for the Tuwu tonalite of 332.3±5.9
Ma (MSWD = 1.5) is interpreted to represent the age of Tuwu tonalitic body emplacement and
is consistent with ages for the Tuwu–Yandong porphyry Cu mineralization of ca.340–330 Ma
(Liu et al., 2003; Chen et al., 2005a).
Rui et al. (2002) previously obtained a Re–Os isochron age of 323Ma for molybdenite
from the Tuwu porphyry Cu deposit. Qin et al. (2002) used K–Ar and 39Ar–40Ar methods to
determine the ages for hydrothermal sericite and copper sulfide-bearing quartz from the
Tuwu–Yandong region and obtained age of 341 Ma and 347 Ma, respectively. Zhang et al.
(2004) obtained a Re–Os isochron age of 343 Ma for veinlet-hosted and disseminated
molybdenite from the Yandong area. Zhang et al. (2010) obtained a Re–Os isochron age of 326
Ma for molybdenite from the Yanxi porphyry Cu deposit. In summary, these isotopic age data
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suggest that the mineralization ages for the Tuwu–Yandong porphyry Cu deposits range from
340 Ma to 320 Ma. Therefore, the mineralization at the Tuwu porphyry Cu deposit occurred
simultaneously with intrusion of the tonalitic host rock or slightly later.
5.2. Petrogenesis
The petrochemical signature of magmatic rocks records significant information on magma
source region, magmatic process, and tectonic setting (Pearce et al., 1984; Sylvester, 1998;
Barbarin, 1999); therefore, it is important to have a clear understanding of the petrogenetic
history of the Tuwu tonalitic rocks. Apatite is typically assumed to provide a reliable criterion
to distinguish magma types (e.g. S-, I-type) (Chappell and White, 1992; Wolf and London,
1994; Wu et al., 2003; Li et al., 2006b, 2007). Apatite reaches saturation in metaluminous and
weekly metaluminous magmas and the apatite solubility will reduce with the decrease of
temperature and the increase of SiO2 content, but it remains highly soluble in highly
peraluminous magmas (Wolf and London, 1994). These studies indicate that P2O5 and SiO2 in
I–type and A–type granites are negatively correlated, whereas the P2O5 in S–type granite
increases or remains unchanged with an increase in SiO2 (Li et al., 2007, Wu et al. 2007a;
Cheng and Mao, 2010). The P2O5 content of the Tuwu tonalite ranges from 0.13% to 0.15%,
and decreases with increasing SiO2. The results are consistent with an I-type granite (Fig. 13a).
The Y vs. Rb and Th vs. Rb diagrams (Fig. 13c and d) also show the same trend. The Th- and
Y-rich minerals will not crystallize from a metaluminous I-type granite during early stages of
magmatic differentiation, consequently resulting in high Th and Y abundances and a positive
correlation between Y and Rb, and Th and Rb in differentiated I-type granites (Li et al., 2007;
Zhu et al., 2009b). Based on the above interpretations, we suggest that the Tuwu tonalite is an
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I-type granite.
The term adakite was introduced by Kay (1978) and has been used to describe high-Al
(Al2O3>15%) and Na-rich andesitic to dacitic, extrusive or intrusive rocks with a high Sr
content (>600 ppm), strongly fractionated REE patterns (HREE depleted, LREE enriched),
and positive Sr and Eu anomalies (Defant and Drummond, 1990). Based on the whole rock
geochemical data, the Tuwu tonalitic rocks display an adakitic major and trace element
geochemical affinity. They have high Al2O3 and Na2O contents ranging from 15.53% to
16.83%, and 2.98% to 4.65%, respectively. They also have a high Sr concentration (261–669
ppm), and low Y and Yb concentrations (7.51–9.53 ppm and 0.84–1.15 ppm, respectively).
Therefore, the above data indicate that the Tuwu tonalitic rocks display characteristics similar
to adakites. Furthermore, in (Sr/Y) vs. Y and (LaN/YbN) vs. YbN discrimination diagrams (Fig.
10a and b), the Tuwu tonalitic rocks also plot well within the adakitic field.
Several hypotheses have been suggested for the origin of rocks with geochemical
characteristics similar to those of adakitic rocks. The various processes proposed for the genesis
of adakitic rocks include: (1) partial melting of a subducted oceanic slab (Rapp et al., 1999;
Escuder et al., 2007); (2) partial melting of thickened or delaminated lower crust (Gao et al.,
2004; Hou et al., 2004); (3) assimilation and fractional crystallization processes involving
basaltic magma (Macpherson et al., 2006; Richards and Kerrich, 2007); (4) mixing of felsic and
basaltic magmas (Streck et al., 2007); and (5) partial melting of subducted continental crust
(Wang et al., 2008, 2010). We suggest that the Tuwu adakitic tonalitic rocks were most likely
generated by partial melting of subducted oceanic slab based on both geochemical and isotopic
data. This interpretation is supported by the following lines of evidence:
15 �
(1) The Tuwu tonalitic rocks are geochemically similar to slab-derived adakites. Most
samples may be defined as calc-alkaline granites with relatively low K2O contents
(1.28%–2.49%) (Fig. 7b), similar to slab-derived adakites in the northern Tianshan (Wang et al.,
2007) formed by partial melting of subducted oceanic crust. The Tuwu tonalitic rocks also have
slightly high Mg# values of 40–59, and this characteristic is consistent with those of adakites
derived by partial melting of a subducted slab (Defant and Drummond, 1993). Melts from
basaltic lower crust are characterized by Mg# less than 40 regardless of degree of melting,
whereas those with Mg# greater than 40 can be obtained only with a mantle component (Rapp
and Watson, 1995). Therefore, the slightly high Mg# values indicate that interaction between
subducted oceanic crust and mantle wedge peridotite could have formed the Tuwu adakitic
magmas.
(2) The trace element signatures of the Tuwu tonalitic rocks are compatible with the partial
melting of a subducted oceanic slab. The assimilation and fractional crystallization of parental
basaltic magmas would result in positive correlation between Sr/Y, and particularly Dy/Yb
ratios with increasing SiO2 (Macpherson et al., 2006; Tang et al., 2010), but there are no such
obvious correlations in our data (Fig.13a and b). The data clearly plot along a partial melting
trend in the La/Sm versus La and La/Yb versus La diagrams (Fig. 13c and d), indicating that
partial melting of the source, rather than fractional crystallization, was the dominant process.
Moreover, the Tuwu tonalitic rocks have low Y and Yb concentrations, and a geochemical
affinity to MORB in the Sr/Y versus Y diagram (Fig. 10a), which is consistent with other
ore-forming adakitic rocks from the Tuwu–Yandong porphyry Cu belt (Zhang et al., 2006).
(3) The Tuwu tonalitic rocks have slight positive Eu anomalies (Eu/Eu* = 0.93–1.12) and
16 �
positive zircon εHf(t) values (+6.9 – +17.2), similar to a subducted oceanic slab (Mo et al., 2005;
Zhu et al., 2009a). Additionally, the zircons from all samples show an inhomogeneous Hf
isotopic composition, with variations of as much as 10.3 ε units, indicating interaction between
the subducted crust with less radioactive Hf geogenesis and mantle sources with more
radioactive Hf geogenesis (Bolhar et al., 2008). This is because the zircon Hf isotope system
has a high closure temperature (Patchett, 1983; Cherniak and Watson, 2003), and the isotope
ratio remains unchanged during partial melting or fractional crystallization. This is consistent
with the explanation from various workers regarding Hf isotopic inhomogeneity in zircon
(Griffinet al., 2002; Li et al., 2007; Bolhar et al., 2008). Therefore, the Tuwu tonalitic magmas
likely reflected interaction between a subducted slab and mantle wedge peridotite.
In summary, the hypothesis of partial melting of a subducted oceanic slab is our favored
interpretation for the genesis of the Tuwu tonalitic rocks, although there might have been minor
interaction between slab-derived magmas and mantle wedge peridotite during magma ascent.
Moreover, based on the formation conditions for adakites (Martin, 1999; Rapp et al., 1999;
Defant et al., 2002), we suggest that the Tuwu ore-bearing tonalitic rocks formed during fast
and oblique convergence between the paleo-Tianshan oceanic plate and the
Dananhu-Tousuquan island arc (Defant and Drummond, 1990; Oyarzun et al., 2001).
5.3. Implications for Cu mineralization
Different mineral deposit types are associated with different geodynamic environments,
and thus have distinct distribution in time and space (Meyer and Saager, 1985; Deng et al.,
2013, 2014; Mao et al., 2014; Santosh et al., 2014). With respect to porphyry copper deposits,
the relationship between subduction environments and adakitic rocks is well documented
17 �
(Sillitoe, 1972; Richards and Kerrich, 2007; Hou and Cook, 2009; Shen et al., 2014). Numerous
porphyry and other hydrothermal base and precious metal deposits are shown to be associated
with adakitic rocks in various parts of the world, such as the late Miocene Los Pelambres
porphyry Cu deposit in the Andes (Reich et al., 2003), the Eocene-Oligocene Yulong porphyry
Cu-Mo belt in eastern Tibet (Hou et al., 2003; Cooke et al., 2005), and the mid-Miocene
Gangdese porphyry Cu belt in southern Tibet (Hou and Cook, 2009). The three largest
porphyry Cu deposits in the world, E1 Teniente, Chuquicamata, and Río Blanco–Los Bronces,
are considered by many workers to be related to adakites derived by partial melting of a
subducted oceanic slab (Reich et al., 2003; Jiang et al., 2012).
The adakites derived from partial melting of a subducted slab have been shown to be
fertile for Cu mineralizations (Thiéblemont et al., 1997; Defant et al., 2002; Mungall, 2002), so
that a very favorable tectonic setting for the generation of porphyry Cu deposits is above
subduction zones (Sillitoe, 1972; Defant et al., 2002; Reich et al., 2003; Yang et al., 2012, 2014).
The adakitic magmas derived from slab melting in the Tuwu area were favorable melts for the
generation of porphyry Cu mineralization as evidenced by:
(1) The δ34S values of sulfides from the Tuwu porphyry Cu deposit range from –3.0 to
+1.7 ‰, with an average value of +0.2 ‰, which is very close to that of meteorite, implying that
the sulfur was probably derived from a mantle source. Thus, we suggest that the mantle
probably played an important role in providing water and sulfur to the Tuwu magma.
(2) Slab-derived adakitic magmas, together with the metasomatized mantle wedge,
provide relatively large amounts of chalcophile elements (Cu) and volatiles, such as H2O and
Cl, to a porphyry Cu magmatic-hydrothermal system (McDonough and Sun, 1995; Rudnick
18 �
and Gao, 2003; Ling, et al. 2009; Sun et al. 2010, 2011). Such magmas resulted in the
favorable conditions for porphyry Cu mineralization in the Tuwu area (Liu et al., 2010; Sun et
al., 2010).
(3) As chalcophile elements are mainly hosted in sulfides in the mantle (Fleet et al., 1996;
Ballard et al., 2002; Mungall, 2002), the removal of chalcophile elements from the mantle and
their incorporation into magmas can only occur if sulfides are absent in the melted source rocks.
This requires a high oxygen fugacity, with values of log fO2 >FMQ+2 (FMQ represents
fayalite–magnetite–quartz oxygen buffer; Mungall, 2002). The biotite in the Tuwu tonalitic
rocks is rich in magnesium, with Mg/(Mg + Fe + Mn) values ranging from 0.35 to 0.60, and
abundant hematite and magnetite are observed in the ores (Rui et al., 2002; Zhang et al., 2004,
2006). The mineralized porphyries are cut by numerous quartz-sulfide and chlorite-sulfide
veinlets, and locally by carbonate veinlets with minor amounts of sulfides. Therefore, the
adakitic magmas derived from partial slab melting in the Tuwu area are considered to have had
a high oxygen fugacity that was particularly favorable for porphyry Cu mineralization.
5.4. Geodynamic setting
SHRIMP zircon U–Pb dating and geochemical data obtained in this study and by previous
workers show that widespread granitic intrusions occurred in the eastern Tianshan at ca.
340-320 Ma. Magmatism and mineralization in the Tuwu area occurred in the period at ca. 332
Ma, with the mineralization being coeval with or slightly younger than emplacement of the
Tuwu tonalite.
Studies on Carboniferous andesites and granitoids in northern Xinjiang have revealed that
these rocks display an obvious subduction-related component as evidenced by positive bulk
19 �
εNd(t) and zircon εHf(t) values (Sun et al., 2008; Tang et al., 2010; Su et al., 2012; Wang et al.,
2014). There is also a broad consensus that the northern part of Xinjiang experienced
post-collisional magmatism in the latest Paleozoic (Wang and Xu, 2006b; Zhou et al., 2008;
Chen et al., 2012; Yang et al., 2012). The eastern Tianshan is suggested to have been in a
post-collision extensional setting since Early Permian, as supported by an ophiolite as young as
~310 Ma and widespread bimodal volcanic rocks (Qin et al., 2002, 2003; Su et al., 2012). A few
workers, however, favor subduction until Late Permian and Early Triassic based on the
presence of Permian mafic–ultramafic complexes suggested to have formed in an island arc
setting (Xiao et al., 2004; Ao et al., 2010; Su et al., 2012). In the Rb vs. (Y+Nb), Rb vs. (Ta+Yb),
and Nb vs. Y tectonic discrimination diagrams (Pearce et al., 1984), and Rb–Hf–Ta diagram, all
granitoid samples plot within the oceanic arc field (Figs. 10a, b, and c), indicating that the Tuwu
tonalitic rocks have characteristics of island arc granites that were formed in a
subduction-related setting.
Subduction zones have been considered as very favorable tectonic settings for the
generation of porphyry Cu deposits (Sillitoe, 1972; Defant et al., 2002; Reich et al., 2003).
Previous studies have shown that the simultaneous southward and northward subduction of the
paleo-Tianshan oceanic plate in the Carboniferous formed the Aqishan–Yamansu and the
Dananhu-Tousuquan arcs, respectively (Wang et al., 2006a; Han et al., 2006b; Zhang et al.,
2010). In the Aqishan–Yamansu arc belt, the Fe (-Cu) and Cu-Ag-Pb-Zn skarn deposits are
widely distributed, including Yamansu, Hongyuntan, Bailingshan, and Weiquan. These
deposits formed during emplacement of granitic intrusions, with associated hydrothermal
activity resulting in the replacement of Carboniferous and Neoproterozoic carbonate and calcic
20 �
clastic rocks (Mao et al., 2005). The Aqishan–Yamansu arc belt formed throughout the
Carboniferous (Li et al., 2003) along the northern margin of the Central Tianshan (Mao et al.,
2005). The Carboniferous Dananhu-Tousuquan arc was generated by the northward subduction
of the paleo-Tianshan plate (Xiao et al., 2004; Mao et al., 2005; Chen et al., 2012). During the
Early Carboniferous dual subduction, the Tuwu adakitic magma were generated by partial
melting of the paleo-Tianshan slab and subsequent hybridization of the mantle wedge
peridotites (Fig. 16). Such slab melts initially have high Cu contents and are highly oxidized,
and thus play a crucial role for generating deposits such as the Tuwu porphyry Cu system (Sun
et al., 2011). Given that adakitic rocks can only form at temperatures above 700� and at
depths greater than 70–85 km, regardless of whether subduction occurs at normal dips or
shallower angles (Sajona et al., 1993; Gutscher et al., 2000; Zhu et al., 2009a), the
paleo-Tianshan oceanic slab must have subducted beneath the Dananhu-Tousuquan sub-arc
mantle to depths of at least 70–85 km during the Early Carboniferous. In such an environment,
generation of Cu-rich adakitic magmas is favored. We therefore speculate that the widespread
Carboniferous–Permian magmatic rocks in the eastern Tianshan hold more potential for Cu
mineralization than is presently recognized.
6. Conclusions
(1) SHRIMP zircon U–Pb dating indicates that magmatic events occurred at ca.332 Ma in
the Tuwu area, and the associated Tuwu porphyry Cu deposit formed during the same period.
(2) The Tuwu tonalite is calc-alkaline; enriched in K, Rb, Sr, and Ba; markedly depleted in
Nb, Ta, Ti, and Th; and shows geochemical affinities similar to those of adakites. The Tuwu
tonalitic rocks have positive εHf(t) values ranging from +6.9 to +17.2, and these εHf(t) values are
21 �
inhomogeneous, with variations of as much as 10.3ε units. The geochemical and isotopic data
for the tonalitic rocks indicate that they were probably derived from the partial melting of a
subducted oceanic slab, and subsequently hybridized by peridotite in the mantle wedge.
(3) The Tuwu adakitic rocks and associated porphyry Cu mineralization in the eastern
Tianshan were generated in an arc setting, and they likely resulted from the northward
subduction of the paleo-Tianshan ocean plate beneath the Dananhu-Tousuquan island arc
during the Early Carboniferous.
Acknowledgements
We are very grateful to the Editor-in-Chief Bor-ming Jahn and three anonymous
reviewers for their constructive comments and assistance in improving the manuscript. We
thank Lianhui Dong, Chief Engineer of Xinjiang Bureau of Geology and Mineral Exploration,
for his great support and assistance during our fieldwork. We also thank Prof. Yusheng Zhai
and Prof. Dicheng Zhu of the China University of Geosciences (Beijing) for a helpful scientific
review of an earlier version of the manuscript. This research was financially supported by the
Program of the China Geological Survey (1212011085471 and 1212011220923), by the Key
Program of National Natural Science Foundation of China (41030423), by the Major Basic
Research Program of People’s Republic of China (2014CB440903), by the Specialized
Research Fund for the Doctoral Program of Higher Education of China (20130022110001), and
by the 111 Project under the Ministry of Education and the State Administration of Foreign
Experts Affairs, China (B07011).
22 �
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Figure Captions:
Fig. 1. (a) Location of the study area in the Central Asia Orogenic Belt (modified from Zhang et al.,
2009). (b) Sketch map showing geologic units of the Tianshan (modified from Chen et al., 2012). (c)
Simplified geological map of the eastern Tianshan (modified from Huang et al., 2013).
Fig. 2. (a) Geological map of the Tuwu–Yandong district (modified from Shen et al., 2012). (b)
Geological sketch map of the Tuwu porphyry Cu deposit (modified from Pan et al., 2013).
Fig. 3. (a) Field photograph of diorite porphyrite and tonalite. (b) Hand specimen of tonalite. (c)
Photomicrographs of tonalitic rock, showing mineral components and alteration, under
crossed-polarized light. (d) Tonalitic rock with porphyritic texture, under crossed-polarized light.
Abbreviations: Bt-biotite; Pl-plagioclase; Ser- sericite; Q-quartz; Kf- K-feldspar.
Fig. 4. Cross section along section Line 7 with orebody (a) and lithologies (b) in the Tuwu porphyry
deposit (modified from Han et al., 2006).
Fig. 5. Mineralization in the Tuwu porphyry deposit. (a) Disseminated chalcopyrite with
xenomorphic granular texture. (b) Chalcopyrite veins. (c) Pyrite with enterolithic structure. (d)
Scaly molybdenite. (e) Chalcopyrite replacing early pyrite. (f) Chalcopyrite. Photomicrographs are
taken under reflected light (a, b, c, d, e, f). Abbreviations: Ccp-Chalcopyrite; Py-Pyrite;
Mo-Molybdenite.
39 �
Fig. 6. Cathodoluminescence(CL) image of representative zircons (a) and Concordia diagram (b)
for zircons from the Tuwu granites.
Fig. 7. Classification and series diagrams of the Tuwu granites. (a) Na2O+K2O vs. SiO2 plot diagram
(Rickwood, 1989).(b) K2O vs. SiO2diagram (Rollinson, 1993). (c) A/NK vs. A/CNK plot diagram
(Maniar and Piccoli, 1989).
Fig. 8. Harker diagram of granites in the Tuwu porphyry Cu deposit.
Fig. 9. (a) Chondrite-normalized REE and (b) primitive mantle-normalized trace element abundance
spider diagram for the Tuwu granites (normalized data are from Boynton, 1984, and Sun and
McDonough, 1989).
Fig. 10�Plots of (a) Sr/Y vs.Y and (b) (La/Yb)N vs. YbN for the Tuwu granites (modified after Defant
and Drummond, 1990). Data sources: Li et al., 2002; Han et al., 2006; Zhang et al., 2004, 2006.
Fig. 11. (a) εHf(t) vs. U-Pb age diagram. (b) Histograms of zircon εHf(t) values. (c) Histograms of
zircon Hf-isotope crust model age (TCDM).
Fig. 12. Histogram of sulfur isotope composition of sulfides from the Tuwu porphyry copper deposit.
Fig. 13. Diagrams for granitoid classification for samples from the Tuwu granites. (a) P2O5 vs. SiO2
diagram. (b) Na2O vs. K2O diagram. (c) Th vs. Rb diagram (Li et al., 2007). (d) Y vs. Rb diagram (Li
40 �
et al., 2007).
Fig. 14. Dy/Yb vs. SiO2, Sr/Y vs. SiO2, La/Sm vs. La and La/Yb vs. La diagrams for the Tuwu
granites. Data sources: Li et al., 2002; Han et al., 2006; Zhang et al., 2004, 2006.
Fig. 15. Tectonic discrimination diagrams for the Tuwu granites. (a) Rb vs. (Y+Nb) diagram (Pearce
et al., 1984). (b) Rb vs. (Yb+Ta) diagram (Pearce et al., 1984). (c) Nb vs. Y diagram (Pearce et al.,
1984). (d) Rb/30-Hf-3×Ta diagram (Harris et al., 1986). WPG, within-plate granites; VAG, volcanic
arc granites; Syn-COLG, syn-collision granites; Post-COLG, post-collision granites; ORG, ocean
ridge granites. Data sources: Li et al., 2002; Han et al., 2006; Zhang et al., 2004, 2006.
Fig. 16. Schematic showing the geodynamic setting of the Tuwu porphyry Cu deposit in the eastern
Tianshan.
Table Captions:
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�� �* �/� �*���� �*��)� �*��)� �* 0/� �* �.� �*)� � �*.. � �* 0��
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�� *�/� *)�� *��� *..� *.�� *)�� */�� *.)� �*���
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LOI = loss on ignition; A/NK = molecular Al2O3 / (Na2O + K2O); A/CNK = molecular Al2O3 / (CaO + Na2O + K2O); Mg# = 100×molar Mg2+/ (Mg2+ +
Fe2+), calculated by assuming TFeO = 0.9 × TFe2O3; Data sources: a-this study, b-Zhang et al., (2004), c-Li et al., (2002)
�
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�
Table 5. Summary of geochronological data for granitoids in the eastern Tianshan.
44 �
Locations Dated rocks Dating method Ages/Ma Data sources
Shiyingtan Moyite LA-ICP-MS zircon U-Pb 342±11 Zhou et al. (2010)
Hongshi Syenogranite SHRIMP zircon U-Pb 344±4 Sun et al. (2012)
Kangguer Rhyolite porphyry Rb-Sr isochron 300±13 Zhang et al. (2002)
Quartz-syenite porphyry Rb-Sr isochron 282±16 Zhang et al. (2002)
Hongyuntan Granodiorite LA-ICP-MS zircon U-Pb 328.5±9.3 Wu et al. (2006a)
Bailingshan Granodiorite LA-ICP-MS zircon U-Pb 317.7±3.7 Zhou et al. (2010)
Weiquan Granodiorite 39Ar-40Ar 276±2.8 Mao et al. (2002a)
Granodiorite SHRIMP zircon U-Pb 297±3 Wang et al. (2005)
Xifengshan Moyite LA-ICP-MS zircon U-Pb 349±3.4 Zhou et al. (2010)
Yandong Dioritic porphyrite SIMS zircon U-Pb 340±3 Shen et al. (2014)
Tonalite SIMS zircon U-Pb 332.2±2.3 Shen et al. (2014)
Tonalite SHRIMP zircon U-Pb 335±3.7 Wang et al. (2014)
Tonalite SHRIMP zircon U-Pb 333±4 Chen et al. (2005a)
Tuwu Tonalite SHRIMP zircon U-Pb 332.3±5.9 This study
Tonalite SHRIMP zircon U-Pb 334±3 Chen et al. (2005a)
Tonalite SHRIMP zircon U-Pb 333±2 Liu et al. (2003)
Chihu Tonalite SHRIMP zircon U-Pb 322±10 Wu et al. (2006c)
Donggebi Fine-grained granite SHRIMP zircon U-Pb 227.6±1.3 Yang et al. (2011)
Weiya Quartz-syenite SHRIMP zircon U-Pb 246±6 Zhang et al. (2005)
Dioritic porphyrite SHRIMP zircon U-Pb 233±8 Zhang et al. (2005)
Fine-grained granite SHRIMP zircon U-Pb 237±8 Zhang et al. (2005)
Tudun Moyite LA-ICP-MS zircon U-Pb 246.2±2.6 Zhou et al. (2010)
Huangshan Moyite LA-ICP-MS zircon U-Pb 288±17 Zhou et al. (2010)
Sanchakou Tonalite SHRIMP zircon U-Pb 278±4 Li et al. (2004)
Shuangchagou Granodiorite LA-ICP-MS zircon U-Pb 252.4±2.9 Zhou et al. (2010)
Jingerquan Granite LA-ICP-MS zircon U-Pb 376.9±3.1 Zhou et al. (2010)
Xianshuiquan Granodiorite SHRIMP zircon U-Pb 369.5±5.6 Tang et al. (2007)
Sidingheishan Biotite granite SHRIMP zircon U-Pb 386±5 Li et al. (2006c)
Baishan Biotite granite SHRIMP zircon U-Pb 239±8 Li et al. (2006a)
1 Tab
le3
Hf i
soto
pic
data
for z
ircon
s fro
m th
e Tu
wu
gran
ites i
n th
e ea
ster
n Ti
ansh
ana)
Spot
A
ge//M
a 17
6 Yb/
177 H
f 17
6 Hf/17
7 Hf
± 2σ
17
6 Lu/17
7 Hf
176 H
f/177 H
f(t)
176 H
f/177 H
f
CH
UR
(T)
ε Hf(0
) ε H
f(t)
T DM
/Ma
T DM
C/M
a f L
u/H
f
TW70
2-59
, Ton
aliti
c ro
ck, 3
32.3
5.9
Ma
(11
spot
s, w
ithou
t spo
ts 9,
11,
12,
and
15)
, εH
f(t)=
6.9
~ 17
.2
TW70
2-59
-1
321.
3
0.11
4568
0.
2829
50
0.00
0017
0.
0020
15
0.28
2938
0.
2825
72
6.3
12
.9
440
50
6
-0.9
4
TW70
2-59
-2
340.
0
0.18
2536
0.
2830
62
0.00
0032
0.
0029
69
0.28
3043
0.
2825
61
10.3
17
.1
283
25
4
-0.9
1
TW70
2-59
-3
335.
3
0.12
9431
0.
2829
76
0.00
0024
0.
0023
14
0.28
2962
0.
2825
64
7.2
14
.1
404
44
2
-0.9
3
TW70
2-59
-4
323.
6
0.13
3702
0.
2829
24
0.00
0026
0.
0022
31
0.28
2911
0.
2825
71
5.4
12
.0
480
56
5
-0.9
3
TW70
2-59
-5
348.
6
0.15
8374
0.
2829
78
0.00
0024
0.
0033
86
0.28
2956
0.
2825
55
7.3
14
.2
414
44
7
-0.9
0
TW70
2-59
-6
333.
1
0.21
9734
0.
2830
73
0.00
0029
0.
0033
29
0.28
3052
0.
2825
65
10.6
17
.2
270
23
9
-0.9
0
TW70
2-59
-7
331.
3
0.16
8966
0.
2830
04
0.00
0026
0.
0028
21
0.28
2987
0.
2825
66
8.2
14
.9
369
38
8
-0.9
2
TW70
2-59
-8
320.
3
0.23
4525
0.
2830
32
0.00
0027
0.
0055
92
0.28
2999
0.
2825
73
9.2
15
.1
354
36
8
-0.8
3
TW70
2-59
-9
352.
7
0.20
9396
0.
2830
81
0.00
0025
0.
0049
80
0.28
3048
0.
2825
53
10.9
17
.5
270
23
5
-0.8
5
TW70
2-59
-10
339.
0
0.20
3264
0.
2830
24
0.00
0029
0.
0048
39
0.28
2993
0.
2825
61
8.9
15
.3
359
36
8
-0.8
5
TW70
2-59
-11
354.
8
0.20
0718
0.
2828
77
0.00
0030
0.
0048
54
0.28
2844
0.
2825
51
3.7
10
.4
593
69
6
-0.8
5
TW70
2-59
-12
350.
3
0.18
4403
0.
2829
57
0.00
0024
0.
0032
07
0.28
2936
0.
2825
54
6.5
13
.5
444
49
1
-0.9
0
TW70
2-59
-13
335.
2 0.
2783
84
0.28
2798
0.
0001
54
0.00
6290
0.
2827
59
0.28
2564
0.
9
6.9
74
8
902
-0
.81
TW70
2-59
-14
333.
2 0.
1590
34
0.28
2950
0.
0000
32
0.00
3210
0.
2829
30
0.28
2565
6.
3
12.9
45
5
516
-0
.90
TW70
2-59
-15
353.
8 0.
2313
09
0.28
2867
0.
0000
40
0.00
5216
0.
2828
32
0.28
2552
3.
4
9.9
61
5
724
-0
.84
a)ε H
f(t) =
100
00( {
[ (17
6 Hf /
177 H
f) S -
(176 Lu
/ 17
7 H f)
S(e
λt -
1) ]
/ [ (
176 H
f / 17
7 Hf) C
HU
R, 0
- (17
6 Lu /
177 H
f) CH
UR
( (eλt
- 1) ]
- 1
}. T
DM
= 1
/ λ
ln{1
+ [
(176 H
f / 17
7 Hf) S
- (17
6 Hf /
177 H
f) DM
] /
[(17
6 Hf /
177 H
f) S -
(176 H
f / 17
7 Hf) D
M] }
. TD
MC=
T DM
- ( T
DM
- t )
[ ( f c
c- f s)
/ ( f
cc- f
DM
) ]. f
Lu/H
f = (17
6 Lu /
177 H
f) S /
(176 Lu
/ 17
7 Hf) C
HU
R –
1, w
here
, λ =
1.8
67×1
0-11 /
a (S
oder
lund
et a
l., 2
004)
; (17
6 Lu /
177 H
f) S a
nd (17
6 Hf /
177 H
f) S a
re th
e m
easu
red
valu
es o
f the
sam
ples
; (17
6 Lu /
177 H
f) CH
UR =
0.0
332
and
(176 H
f / 17
7 Hf) C
HU
R, 0
= 0
.282
772
(Blic
hert-
Toft
and
Alb
arde
199
7 );
(176 Lu
/ 17
7 Hf) D
M =
0.03
84 a
nd (17
6 Hf /
177 H
f) DM
=0.
2832
5 (G
riffin
et a
l., 2
000)
; (17
6 Lu /
177 H
f)m
ean
crus
t = 0
.015
; fcc
= [ (
176 Lu
/ 17
7 Hf)
mea
n cr
ust /
(176 Lu
/ 17
7 Hf) C
HU
R]
– 1;
f s =
f Lu/
Hf; f D
M =
[ (17
6 Lu /
177 H
f) DM
/ (17
6 Lu /
177 H
f) CH
UR] –
1; t
= c
ryst
alliz
atio
n tim
e of
zirc
on.
Tab
le
1 T
able
4
Sulfu
r iso
topi
c da
ta o
f the
Tuw
u po
rphy
ry C
u de
posi
t in
the
east
ern
Tian
shan
Sam
ple
no.
Min
eral
s δ34
S‰
TW-9
Py
rite
1.7
TW-1
0 Py
rite
0.8
TW-1
1 Py
rite
0.2
TW-0
05-5
22-5
C
halc
opyr
ite
0.3
TW-0
05-5
22-5
Py
rite
1.6
TW-0
05-5
10-8
C
halc
opyr
ite
0.4
TW-1
5 C
halc
opyr
ite
-1.9
TW-1
6 Py
rite
1.0
TW-1
4 Py
rite
0.4
TW-1
2 C
halc
opyr
ite
-3.0
Tab
le
Figure
1
Figure
1
Fig. 3. (a) Field photograph of diorite porphyrite and tonalite. (b) Hand specimen of tonalite. (c) Photomicrographs of tonalitic rock, showing mineral components and alteration, under crossed-polarized light. (d) Tonalitic rock with porphyritic texture, under crossed-polarized light. Abbreviations: Bt-biotite; Pl-plagioclase; Ser- sericite; Q-quartz; Kf- K-feldspar.
Figure
1
Figure
1
Fig. 5. Mineralization in the Tuwu porphyry deposit. (a) Disseminated chalcopyrite with xenomorphic granular texture. (b) Chalcopyrite veins. (c) Pyrite with enterolithic structure. (d) Scaly molybdenite. (e) Chalcopyrite replacing early pyrite. (f) Chalcopyrite. Photomicrographs are taken under reflected light (a, b, c, d, e, f). Abbreviations: Ccp-Chalcopyrite; Py-Pyrite; Mo-Molybdenite.
Figure
1
Fig. 6. Cathodoluminescence (CL) image of representative zircons (a) and Concordia diagram (b) for zircons from the Tuwu granites.
Figure
1
Figure
1
Fig. 8. Harker diagram of granites in the Tuwu porphyry Cu deposit.
Figure
1
Figure
1
Figure
Fig. 11. (a) εHf(t) vs. U-Pb age diagram. (b) Histograms of zircon εHf(t) values. (c) Histograms of zircon Hf-isotope crust model age (TC
DM).
Figure
Fig. 12. Histogram of sulfur isotope composition of sulfides from the Tuwu porphyry copper deposit.
Figure
Figure
Figure
Figure
Fig. 16. Schematic showing the geodynamic setting of the Tuwu porphyry Cu deposit in the eastern Tianshan.
Figure
45 �
Highlights:
1) Zircon U–Pb dating data indicate that the magmatic events might have occurred around 332 Ma in
the Tuwu region, and the Cu mineralization occurred during the same period as that of the magmatic
rocks formation in the region or slightly later.
2) All the Tuwu tonalitic rocks are calc-alkaline or high–k calc–alkaline, enriched in K, Rb, Sr, and
Ba, makedly depleted in Nb, Ta, Ti, and Th, and show geochemical affinities similar to those of
adakites.
3) The adakitic tonalitic rocks geochemical and isotopic data indicate that they were probably derived
from the partial melting of a subducted oceanic slab, and subsequently hybridized by peridotite in the
mantle wedge.
4) The Tuwu adakitic tonalitic rocks and associated Cu mineralization were generated in an arc
setting, and resulted likely from the northward subduction of the paleo-Tianshan ocean crust beneath
the Dananhu-Tousuquan island arc belt during the Early Carboniferous.