Cretaceous magmatism and metallogeny in the Bangong–Nujiang metallogenic belt, central Tibet: Evidence from petrogeochemistry, zircon U–Pb ages, and Hf–O isotopic compositions

    Cretaceous magmatism and metallogeny in the Bangong–Nujiang metallogenic belt, central Tibet: Evidence from petrogeochemistry, zircon U–Pb ages, and Hf–O isotopic compositions Guang-Ming Li, Ke-Zhang Qin, Jin-Xiang Li, Noreen J. Evans, JunXing Zhao, Ming-Jian Cao, Xia-Nan Zhang PII: DOI: Reference:

S1342-937X(15)00238-5 doi: 10.1016/j.gr.2015.09.006 GR 1518

To appear in:

Gondwana Research

Received date: Revised date: Accepted date:

24 May 2015 2 September 2015 14 September 2015

Please cite this article as: Li, Guang-Ming, Qin, Ke-Zhang, Li, Jin-Xiang, Evans, Noreen J., Zhao, Jun-Xing, Cao, Ming-Jian, Zhang, Xia-Nan, Cretaceous magmatism and metallogeny in the Bangong–Nujiang metallogenic belt, central Tibet: Evidence from petrogeochemistry, zircon U–Pb ages, and Hf–O isotopic compositions, Gondwana Research (2015), doi: 10.1016/j.gr.2015.09.006

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ACCEPTED MANUSCRIPT Cretaceous magmatism and metallogeny in the Bangong–Nujiang metallogenic belt, central Tibet: Evidence from petrogeochemistry,

a, b

, Ke-Zhang Qin

a, b

, Jin-Xiang Li

, Noreen J. Evans d, Jun-Xing

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Zhao a, Ming-Jian Cao a, Xia-Nan Zhang a, e

Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese

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a

b, c

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Guang-Ming Li

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zircon U–Pb ages, and Hf–O isotopic compositions

Academy of Sciences, Beijing 100029, China

CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China

c

Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan

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D

b

d

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Plateau Research, Chinese Academy of Sciences, Beijing 100085, China John de Laeter Center for Isotope Research, TIGeR, Applied Geology, Curtin University, Perth,

WA 6945, Australia

University of Chinese Academy of Sciences, Beijing 100049, China

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e

*Corresponding author. Present address: Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China.

Tel.:

+86

10

82998187;

Fax:

+86

10

62010846;

E-mail:

[email protected].

Abstract Porphyry Cu–Au and porphyry–skarn Cu ± Au ± Mo deposits are widely 1

ACCEPTED MANUSCRIPT distributed in the Bangong–Nujiang metallogenic belt, central Tibet. Zircon U–Pb dating has revealed that Cretaceous ore-bearing intrusions related to Cu ± Au ± Mo

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mineralization formed in two periods (118–115 Ma and 90–88 Ma). These primarily

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high-K calc-alkaline series intrusions show light rare earth element enrichment

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(LaN/YbN=6.06–20.2) and negative to no Eu anomaly (Eu*/Eu=0.39–1.02). On primitive mantle-normalized diagrams, all the intrusions show strong enrichments in large ion lithophile elements (e.g., Cs, Rb, and K), depletions in Nb, Ta, and Ti, and

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negative Ba anomalies characteristic of arc magma. These intrusions show a wide

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range of zircon εHf(t) values from –6.3 to +10.9 and 18O values from 5.82 to 10.82 ‰, suggesting variable contributions from mantle and crustal sources. Considering the

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~100 Ma Lhasa–Qiangtang collision, the 118–115 Ma magmas and related deposits

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were likely formed by melting of subduction metasomatized mantle wedge in a continental arc setting during northward subduction of the Bangong–Nujiang ocean,

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and then further evolved in the upper crust as a result of MASH processes. The younger 90–88 Ma ore-bearing magmas were potentially derived from melting of

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previously metasomatized lithospheric mantle during slab tear and break-off after the Lhasa–Qiangtang collision.

Keywords: Petrogenesis, Zircon U–Pb ages, Zircon Hf–O isotopes, Bangong–Nujiang metallogenic belt, Tibet

1. Introduction Porphyry deposits provide more than 75 %, 90 % and 20 % of the global industrial demand for Cu, Mo and Au, respectively (Sillitoe, 2010), and, therefore, are

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ACCEPTED MANUSCRIPT the focus of attention of both mining companies and economic geologists. The currently proposed tectonic settings conducive to formation of porphyry deposits

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include subduction-related continental margin arc (e.g., Andean), island arc (e.g., West

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Pacific; Sillitoe, 2010; Richards, 2011), and collisional environments (e.g., Gangdese

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in southern Tibet; Hou et al., 2004; 2009; Li et al., 2011a; Zhao et al., 2014; Yang et al., 2015). It is well documented that southern Tibet hosts a widely distributed series of porphyry deposits

in

the Gangdese

metallogenic

belt,

including the

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subduction-related Jurassic Xiongcun porphyry Cu–Au deposit (Lang et al., 2014) and

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additional collision-related porphyry Cu–Mo deposits (e.g., Qulong, Tinggong, and Jiama; Hou et al., 2004; Qu et al., 2004; Li et al., 2011a; Yang et al., 2009, 2015; Xiao

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et al., 2012; Zhao et al., 2014, 2015). In contrast, central Tibet is host to the majority

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of Jurassic skarn Fe–Cu deposits (Zhang et al., 2011; Chen et al., 2014) and Cretaceous porphyry-skarn Cu–Au deposits (Li et al., 2011b, 2013a, 2015; Wang et al.,

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2013; Zhang et al., 2015; Zhu et al., 2015), including those recently discovered in the Bangong–Nujiang metallogenic belt which form the focus of in this study. Previous

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studies indicate that the early Cretaceous Duolong porphyry Cu–Au deposit was formed in a continental arc (Li et al., 2013a) or post-collisional setting (Qu et al., 2015), whereas the late Cretaceous Gaerqiong–Galale and Balazha porphyry-skarn Cu–Mo–Au deposits were possibly formed after the Lhasa–Qiangtang collision (Zhang et al., 2015). Meanwhile, extensive Jurassic–Cretaceous intermediate-felsic magmas and volcanic rocks in central Tibet were formed by southward or northward subduction of the Bangong–Nujiang ocean and after the collision between the Lhasa and Qiangtang blocks (e.g., Li et al., 2014b, 2015b; Wang et al., 2014; Chen et al., 2015b; Fan et al., 2015; Sun et al., 2015a). However, the petrogenesis and tectonic setting of these deposits are still poorly constrained.

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ACCEPTED MANUSCRIPT Typically, ore-bearing intrusions mostly experience widespread hydrothermal alteration, altering their Sr–Nd isotopic character and precluding them from being

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used to trace magmatic sources/characteristics. However, zircon is resistant to

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hydrothermal alteration and usually retains primary isotopic signatures (eg. Hf–O)

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which can be used to constrain petrogenesis (e.g., Valley, 2003; Kemp et al., 2007; Li et al., 2010; Li et al., 2013a). In this study, we present new petrogeochemistry, zircon U–Pb ages and Hf–O isotopic compositions of ore-bearing and fresh intrusions from

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five typical porphyry-skarn deposits in the Bangong–Nujiang metallogenic belt. The

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purpose is to reconstruct the geochronologic framework of porphyry-skarn Cu ± Mo ± Au mineralization, and to constrain petrogenesis and tectonic setting of ore-related

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intrusions.

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2.1. Regional geology

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2. Geologic setting

The Tibetan plateau consists of five blocks (from north to south: Qaidam,

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Kunlun, Qiangtang, Lhasa, and India), separated by four Mesozoic and Cenozoic sutures (Ayimaquin–Kunlun, Jinshajiang, Bangong–Nujiang, and Indus–Yarlung, respectively; Fig. 1a; Yin and Harrison, 2000; Zhu et al., 2013; Zhang et al., 2012). The Bangong–Nujiang suture zone (BNS), including the Rutog–Dongcuo and Shiquanhe–Yongzhu subzone (Fig. 1b), is characterized by a > 1200 km-long east–west belt of mainly Jurassic–Cretaceous flysch, mélange, and ophiolitic fragments (Pan et al., 2012; Shi et al., 2008; Yin and Harrison, 2000). The ages of ophiolites and radiolarians from this zone indicate that the Bangong–Nujiang ocean existed at least from the Carboniferous to Early Cretaceous (Pan et al., 2012; Shi, 2007; Shi et al., 2008; Fan et al., 2014; Wang et al., 2015), and that it may have closed

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ACCEPTED MANUSCRIPT ~ 100 Ma (Baxter et al., 2009; Liu et al., 2014b; Zhang et al., 2012). Extensive Jurassic-Cretaceous arc intrusions and volcanic rocks occur in the northern Lhasa

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block (close to BNS), southern Qiangtang block, and within the BNS (e.g., Zhu et al.,

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2011; Li et al., 2014b; Li et al., 2014c; Liu et al., 2014a, 2015; Wang et al., 2014; Sui

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et al., 2013; Chen et al., 2015a; Sun et al., 2015b). Jurassic skarn Fe–Cu deposits (e.g., Fuye, Caima; Zhang et al., 2011; Chen et al., 2014) and Early Cretaceous porphyry Cu–Au deposits (e.g., Duolong, Qingcaoshan, and Bainong; Li et al., 2011b, 2013a;

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Li et al., 2012; Zhou et al., 2013; Zhu et al., 2015) are distributed in the north of the

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BNS, while Late Cretaceous porphyry-skarn Cu ± Mo ± Au deposits (e.g., Gaerqiong–Galale and Balazha; Yu et al., 2011; Zhang et al., 2015) occur in the north

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Lhasa block and along the Shiquanhe–Yongzhu subzone (Fig. 1b). The detailed

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geological characteristics of the five typical porphyry-skarn deposits are detailed below and summarized in Table 1.

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2.2. Geology of ore deposits

Qingcaoshan porphyry Cu–Au deposit: This deposit is located 170 km northwest

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of Gerze County, on the southern edge of the Qiangtang block, and north of the western segment of the Bangong–Nujiang metallogenic belt (Fig.1b). It contains proved metal resources of 0.3 Mt at 0.3 % Cu and 3t at 0.3 g/t Au. Granodiorite, granodiorite porphyrite, quartz diorite porphyrite, diorite dyke, granite porphyry, and diabase intruded into the middle Jurassic Quemocuo Formation, which consists of conglomerate, sandstone, and metamorphic siltstone and slate (Fig. 2a). Granodiorite porphyry and quartz diorite porphyrite comprise the ore-bearing intrusions, spatial associated

with

alteration

and

mineralization.

Biotitization,

silicification,

chloritization, tourmalinization, and argillic alteration mainly occur in ore-bearing intrusions (Table 1), whereas hornfels are widely developed in wall rocks and include 5

ACCEPTED MANUSCRIPT hydrothermal biotite and sphene. In addition, Cu–Au mineralization is mainly developed in ore-bearing intrusions and hornfelsic wall rocks. Veinlets of varying

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composition (biotite, quartz-calcite, quartz-actinolite, quartz-sphene-chalcopyrite, and

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quartz ± pyrite ± chalcopyrite) are extensively developed in this deposit.

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Duolong porphyry Cu–Au deposit: This deposit is located 100 km northwest of Gerze County and divided into the Duobuza (Fig. 2b) and Bolong sections. This work focues on the Duobuza region which has been proved resources of 2.7 Mt at 0.94%

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Cu and 13t at 0.21g/t Au (Li et al., 2012). The EW–trending ore-forming granodiorite

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porphyry, exposed over a 2000m long by 100 m area on the surface, intruded into the middle Jurassic Quse Formation (mainly sandstone). The Tertiary Kangtuo Formation

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is only found in the north, consisting of conglomerate and sandstone (Fig. 2b).

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Hydrothermal alteration is widely developed in this deposit, including potassic, intermediate argillic, and propylitic alteration zones. However, phyllic alteration is not

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well developed, and quartz-sericite veins occur only locally (Table 1). Cu–Au mineralization is distributed in the potassic and propylitic alteration zones. The

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hypogene mineralization displays a degree of vertical variation that manifests as a stockwork of disseminated veinlets in the upper part of the ore body, gradually transitioning to sparsely disseminated ore in the lower part. The hypogene ore minerals are primarily chalcopyrite and magnetite, followed by pyrite, with lesser amounts of chalcocite, bornite and native gold. In general, hydrothermal magnetite closely coexists with chalcopyrite, consistent with the mineralization characteristics of a typical porphyry Cu–Au deposit (Sillitoe, 2010). Gaerqiong–Galale skarn Au–Cu ore district: This ore district, including the Gerqiong (24 t Au) and Galale (40 t Au) Au–Cu deposits, is located in the northwest, 40 km from Gegyai County and south of the Bangong–Nujiang metallogenic belt (Fig.

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ACCEPTED MANUSCRIPT 1b). Quartz diorite, granodiorite, granite porphyry, and diorite porphyrite intruded into the Early Jurassic Duoai Formation, which consists of volcaniclastic rocks and

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carbonate. Garnet-bearing skarn occur along the contact zone between granodiorite

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and wall rocks, and has been telescoped by late stage hydrothermal minerals

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(actinolite, epidote, and chlorite etc). The alterations types in these intrusions mainly include sericitization, epidotization, chloritization and silicification (Table 1). Au–Cu mineralization is developed in the contact zone between the granodiorite and marble.

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Magnetite formed at an early stage in the garnet-diopside skarn and was telescoped by

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late stage calcite-quartz-sulfide assemblages. The ore minerals are magnetite, chalcopyrite, bornite, pyrrhotite, pyrite, molybdenite, native gold, electrum and native

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silver (Table 1).

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Galale skarn Au–Cu–Fe deposit is located 4 km northeast of Gaerqiong. Au–Cu–Fe mineralization is developed in the calc-magnesian skarn and in the contact

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zone between the granodiorite and the Early Cretaceous Jiega Formation (dolomite and dolomitic marble; Fig. 2d). From the granodiorite outwards, the alteration zones through

garnet-diopside-serpentine

skarn

(magnetite

±

pyrite),

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progress

forsterite-diopside-phlogopite-serpentine skarn (magnetite ± chalcopyrite ±pyrite), skarnization (forsterite-serpentine-phlogopite) dolomite (chalcopyrite + magnetite) and dolomite (Zhang et al., 2015). The ore minerals are magnetite, native gold, with minor chalcopyrite and bornite (Table 1). Balazha porphyry-skarn Cu–Mo deposit：The deposit is located ~ 50 km south of Zhongcang village and south of the Shiquanhe–Yongzhu suture (Fig. 1b). The exposed Middle Permian Xiala Formation is composed of dolomite and dolomitic limestone. The Zenong Group, exposed in the western and northeastern part of this deposit, consists of gray conglomerate, sandstone, and mudstone interbedded minor

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ACCEPTED MANUSCRIPT volcanic and volcaniclastic rocks. The Balazha intrusive complex is composed of biotite monzonitic granite, monzonitic granite porphyry, granite porphyry and quartz

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diorite porphyrite (Fig. 2e). Magnesian skarn with Cu–Mo mineralization is formed at

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the contact zone between monzonitic granite and the Xiala Formation. In addition,

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veinlet-disseminated Mo mineralization is primarily found in the granite porphyry. The hydrothermal alteration in ore-bearing intrusions includes biotitization, K-feldspathization, chloritization, tourmalinization, chloritization, silicification and

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argillic alteration (Table 1). The ore minerals are chalcopyrite, chalcocite, bornite,

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molybdenite, and pyrite.

3. Sampling and petrography

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Samples were collected from the Qingcaoshan, Duolong, and Bainong porphyry

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Cu–Au deposits, Balazha porphyry-skarn Mo deposit and Gaerqiong–Galale

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porphyry-skarn Cu–Au deposit, and include diorite, diorite porphyrite, granodiorite, granodiorite porphyry, quartz diorite porphyrite, granite, granite porphyry (Fig. 3; for sample locations see Fig. 2). These intrusions show equigranular and porphyritic

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texture, and consist of amphibole, biotite, plagioclase, quartz, and K-feldspar (Fig. 3a–i), with accessory zircon, apatite, titanite, and Fe–Ti oxides (each <1 %). Some ore-bearing samples experienced variable degrees of potassic, phyllic, and argillic alteration.

4. Analytical methods 4.1. Major and trace element analyses Twenty-four samples of ore-related intrusions from five porphyry and porphyry-skarn Cu ± Au ± Mo deposits were powdered in an agate mortar. Loss–on–ignition (LOI) was measured as the weight loss of the samples after 1 h of 8

ACCEPTED MANUSCRIPT baking at a constant temperature of 1000oC. Sample powders (0.5 g) were fused with 5 g of lithium tetraborate (Li2B4O7) at 1050oC for 20 min. Major elements were then

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analyzed on fused glass disks with an AXIOS X–ray fluorescence spectrometer (XRF)

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at the Analytical Laboratory Beijing Research Institute of Uranium Geology

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(ALBRUG), China. The accuracy and reproducibility were monitored using the Chinese national standard sample GSR1 (granite; Supplementary Data Table 1), with a relative standard deviation from recommended values of better than 1%.

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Trace elements were determined using an ELEMENT inductively coupled plasma

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mass spectrometer (ICP–MS) at ALBRUG. Sample powders (40 mg) were dissolved in 1 ml of distilled 20 N HF and 0.5 ml of 7.5 N HNO3 in Teflon screw-cap capsules,

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then enclosed with alloy steel sleeves and heated at 170°C for 10 days. The solutions

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were dried and redissolved with 2 ml of 7.5 N HNO3 in the capsules. Finally, the solutions were diluted in 1% HNO3 to 50 ml before analysis. The standard sample

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GSR1 (Supplementary Data Table 1) was used to monitor the analytical accuracy and reproducibility, with a relative standard deviation of better than 3%. Major and trace

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element results are listed in Supplementary Data Table 1. 4.2. Zircon U–Pb geochronology Zircon crystals were obtained from crushed rock using a combination of heavy liquid and magnetic separation techniques. Individual crystals were hand-picked under a binocular microscope, mounted in epoxy and polished to expose the cores of the grains. The sites for zircon U–Pb age and Hf isotope analysis were selected on the basis of cathodoluminescence (CL) images (Fig. 4), which were obtained using a LEO1450VP scanning electron microscope (SEM) at IGGCAS (Institute of Geology and Geophysics, Chinese Academy of Sciences), Beijing, China. Fourteen zircon U–Pb isotopic analyses were conducted on a Neptune 9

ACCEPTED MANUSCRIPT MC–ICP–MS equipped with a 193-nm laser at IGGCAS. During the analyses, a laser repetition rate of 6~8 Hz at 100 mJ and spot size of 40–60 μm were used. Every 5

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sample analyses was followed by analysis of a suite of zircon standards including

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Harvard zircon 91500 (Wiedenbeck et al., 1995), GJ-1 (Jackson et al., 2004) and

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NIST SRM 610. Detailed analytical techniques have been described by Wu et al. (2006) and Xie et al. (2008). For zircon U–Pb age analysis, 207

Pb/235U (235U=238U/137.88), and

208

207

Pb/206Pb,

206

Pb/238U,

Pb/232Th ratios were corrected using 91500 as

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the reference material. Common Pb contents were evaluated using the method

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described by Andersen (2002).

One zircon U–Pb isotopic analyses was conducted on a Cameca IMS–1280

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SIMS at IGGCAS. Detailed analytical procedures have been described by Li et al.

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(2009). The measured compositions were corrected for common Pb using the measured non-radiogenic 204Pb. The corrections are sufficiently small to be insensitive

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to the choice of common Pb composition, and an average of present-day crustal composition (Stacey and Kramers, 1975) was used for the common Pb. The age

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calculations and concordia diagrams were generated using ISOPLOT (ver 3.0) (Ludwig, 2003). Uncertainties for individual analyses (ratios and ages) are quoted at the 1σ level, whereas the errors on concordia and weighted mean ages are quoted at the 2σ level. Zircon U–Pb isotopic data are listed in Supplemental Data Table 2. 4.3. Zircon in-situ Hf–O isotopes Zircon Hf–O isotope analyses were conducted on the same zircon grains that were previously analyzed for U–Pb ages. During data acquisition for Hf isotopes, a 176

Hf/177Hf isotopic ratio of 0.282300 is recommended as the standard value for 91500

(Wu et al., 2006), which is used to correct the Hf isotopic measurements. Detailed analytical techniques have been described by Wu et al. (2006) and Xie et al. (2008). 10

ACCEPTED MANUSCRIPT Zircon standard GJ-1 analysed as an unknown sample yielded a weighted

176

Hf/177Hf

ratio of 0.282010±0.000009 (2σ, n=36), consistent with the recommended Hf isotopic 176

Hf/177Hf was calculated

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ratio (0.282000±0.000005, Morel et al., 2008). Initial

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according to the corresponding spot age, and the value of εHf(t) calculated relative to

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the chondritic reservoir with a 176Hf/177Hf ratio of 0.282785 and 176Lu/177Hf of 0.0336 (Bouvier et al., 2008). Single-stage Hf model ages (TDM) were calculated relative to the depleted mantle which is assumed to have a linear isotopic growth from Hf/177Hf=0.279718 at 4.55Ga to 0.283250 at present, with a

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176

176

Lu/177Hf ratio of

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0.0384 (Vervoort and Blichert-Toft, 1999; Griffin et al., 2000). Two-stage Hf model ages (TDMC) were calculated by assuming a mean

176

Lu/177Hf value of 0.015 for the

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average continental crust (Griffin et al., 2002).

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Zircon oxygen isotopes were also measured using the Cameca IMS-1280 SIMS at IGGCAS. The Cs+ primary ion beam was accelerated at 10 kV with an intensity of

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approximately 2 nA and rastered over a 10 μm area with a spot diameter of 20 μm (10 μm beam diameter +10 μm raster). Oxygen isotopes were measured in multi-collector

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mode using two off-axis Faraday cups. Uncertainties on individual analyses are reported at the 1σ level. The internal precision of a single analysis was generally better than 0.2‰ for the 18O/16O ratio. Values of δ18O were standardized to VSMOW (Vienna Standard Mean Ocean Water) and reported in standard per mil notation. The instrumental mass fractionation factor (IMF) was corrected using the 91500 zircon standard with (δ18O)VSMOW = 9.9‰ (Wiedenbeck et al., 2004). The measured

18

O/16O

ratio was normalized using VSMOW compositions and then corrected for the instrumental mass fractionation factor. The Penglai zircon standard analyzed during the course of this study yield a weighted mean of δ18O = 5.29 ± 0.08 ‰ (95% confidence level, n=46), which is consistent within error with the reported value of

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ACCEPTED MANUSCRIPT 5.31 ± 0.10‰ (Li et al., 2010). Detailed working conditions and analytical procedures have been described by Li et al. (2010) and zircon Hf–O isotopic data are listed in

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Supplemental Data Table 3.

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5. Results 5.1. Zircon U–Pb ages

The dated zircons are mostly euhedral, and reveal prismatic forms with mean

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crystal sizes of 100–350 μm (Fig. 4). Most zircons show obvious oscillatory zoning

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(Fig. 4) and Th/U ratios of 0.10–13.43, consistent with those of igneous zircons (Corfu et al., 2003). Thus, the zircon U–Pb ages can be interpreted as representing the

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emplacement age of the host rocks. At the Qingcaoshan porphyry Cu–Au deposits,

11QX-15 yielded

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two granodiorite 11QL-8 and 11QX-14-1, and one porphyaceous granodiorite Pb/238U weighted mean ages of 118.8 ± 0.9 Ma (2σ, MSWD =

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0.1), 118.6 ± 0.7 Ma (2σ, MSWD = 0.2), and 118.8 ± 0.7 Ma (2σ, MSWD = 0.2; Fig. 5), respectively. Ore-bearing granodiorite porphyry 11QL-6 and quartz diorite

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porphyrite 11QX-18 yielded slightly younger 206Pb/238U weighted mean ages of 115.8 ± 1.1 Ma (2σ, MSWD = 1.2) and 116.4 ± 1.0 Ma (2σ, MSWD = 0.1; Fig. 5), consistent with the published age of 114.6 ± 1.2 Ma (2σ, MSWD = 1.1; Zhou et al., 2013) within errors. Zircons from the fresh fine-grained granite porphyry 11QX-10 yielded yield the youngest

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Pb/238U ages of 112.7 ± 0.6 Ma (2σ, MSWD = 1.2; Fig.

5). The ore-bearing granodiorite porphyry D2308-511 from the Duolong porphyry Cu–Au deposit (Dubuza section) yielded a zircon SIMS U–Pb age of 118.0 ± 1.0 Ma (2σ, MSWD = 0.8), consistent within error with previous published ages of ~ 117–118 Ma under errors (Li et al., 2011b, 2013a, 2015a). At the Bainong porphyry Cu–Au prospect, two diorite (11BNZK-1 and 11BN-4-2) and one diorite porphyrite 11BN-4

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ACCEPTED MANUSCRIPT yielded relatively consistent

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Pb/238U ages of 115.3 ± 1.0 Ma (2σ, MSWD = 0.7),

116.6 ± 1.2 Ma (2σ, MSWD = 0.1), and 115.8 ± 1.1 Ma (2σ, MSWD = 0.1; Fig. 5),

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respectively.

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Pb/238U weighted mean age of 91.7 ± 1.4 Ma (2σ, MSWD = 0.3).

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yielded a zircon

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Granodiorite 11GLQ-2 from the Gaerqiong porphyry-skarn Cu–Au deposit

At the Balazha porphyry-skarn Mo deposit, the ore-bearing granite 11BLZ-1-1 had a zircon

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Pb/238U weighted mean age of 90.6 ± 0.7 Ma (2σ, MSWD = 1.0; Fig. 5),

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overlapping with the published age of 92.1 ± 1.2 Ma within uncertainty (Wang et al.,

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2013). The monzonitic granite porphyry 11BLZ-4 and ore-bearing granite porphyry 11BLZ-6 yielded 206Pb/238U weighted mean ages of 89.6 ± 0.5 Ma (2σ, MSWD = 0.2)

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and 88.7 ± 0.9 Ma (2σ, MSWD = 0.2; Fig. 5), consistent within uncertainty with the

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published age of 88.0 ± 1.6 Ma (Yu et al., 2011).

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5.2. Major and trace elements

The studied samples from the Qingcaoshan, Duolong, and Bainong deposits mostly belong to the high-K calc-alkaline and shoshonitic series, with a few plotting

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in the calc-alkaline field, whereas the samples from the Gaerqiong–Galale and Balazha deposits show characteristics of the calc-alkaline and high-K calc-alkaline rocks (Fig. 5a). With the exception of one granite porphyry 11QX-10 (from a highly fractionated felsic magma), all samples are unfractionated granites (Fig. 5b). Most studied

samples

show

light

rare

earth

element

(LREE)

enrichment

(LaN/YbN=6.06–20.2; Fig. 7a, b) and negative to no Eu anomaly (Eu*/Eu=0.39–1.02), except three samples from the Duolong deposit that show obviously positive Eu anomalies (Eu*/Eu=1.33–2.14). Samples from the Bainong deposit have the highest total content of REE (Fig. 7a, b). On extended trace element diagrams (Fig. 7c, d), all of the samples show strong enrichments in large ion lithophile elements (LILE: e.g., 13

ACCEPTED MANUSCRIPT Cs, Rb, and K), depletions of high field strength elements (HFSE: e.g., Nb, P, and Ti) and Pb positive anomalies.

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5.3. Zircon Hf and O isotopes At the Qingcaoshan deposit, zircons from the 116 Ma ore-bearing granodiorite

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porphyry and quartz diorite porphyrite show εHf(t) of –0.9 to +2.6 (mean = 0.5 ± 0.8; Figs. 8a, 9a), which are slightly higher than zircons from the 118 Ma granodiorite

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(εHf(t) = –3.5–+1.7, mean = –0.6 ± 0.9). The 112 Ma fine-grained granite porphyry has the lowest zircon εHf(t) (–6.3 to –1.5; mean = –4.5 ± 0.7; Fig. 8a). One

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granodiorite has a zircon δ18O of 7.90–9.00 ‰ (mean = 8.36 ± 0.26 ‰), consistent with those of two ore-bearing granodiorite porphyry samples and quartz diorite

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porphyrite (δ18O = 7.63–9.02 ‰, mean = 8.34 ± 0.27 ‰; Figs. 10a, 11a). The 118 Ma

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ore-bearing granodiorite porphyry from the Duobuza deposit has a zircon εHf(t)

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signature of 1.6 to 5.0 (mean = 3.8 ± 0.7; Fig. 8b) and δ18O values of 5.82–7.37 ‰ (mean = 6.44 ± 0.29 ‰), which are very consistent with previously published Hf–O isotopic compositions (Li et al., 2013a, 2015a). The diorite porphyrite from the

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Bainong Cu–Au prospect has a zircon εHf(t) value of 2.6 to 10.9 (mean = 6.9 ± 1.0; Fig. 8c) and δ18O of 5.97–7.92 ‰ (mean = 7.28 ± 0.24 ‰; Fig. 10c), similar with those of diorite (εHf(t) = 2.7 to 9.9, mean = 6.9 ± 0.9; δ18O = 5.97–8.33 ‰, mean = 7.09 ± 0.25 ‰). The 90 Ma granodiorite from the Gaerqiong deposit has a zircon εHf(t) of 7.4 to 9.6 (mean = 8.6 ± 1.0; Fig. 8d) and δ18O of 5.46–7.46 ‰ (mean = 6.44 ± 0.25 ‰; Fig. 10d). At the Balazha porphyry Mo deposit, zircons from the 90 Ma granite have relatively consistent εHf(t) values ranging from 4.0 to 6.0 (mean = 5.0 ± 0.9; Fig. 8e) and δ18O of 7.44–8.85 ‰ (mean = 8.06 ± 0.27 ‰; Fig. 10e). In contrast, zircons from the 88 Ma ore-bearing granite porphyry show a wide range of εHf(t) (–1.7 to +5.8; 14

ACCEPTED MANUSCRIPT mean = 3.4 ± 0.8; Fig. 8e) and consistent δ18O values of 7.43–8.89 ‰ (mean = 8.02 ± 0.26 ‰; Fig. 10e). The 89 Ma monzonitic granite porphyry also has variable εHf(t) of

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(–4.5 to 6.0; mean = 2.1 ± 0.9; Fig. 8e) and consistent δ18O of 7.35–10.82 ‰ (mean =

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8.03 ± 0.27 ‰; Fig. 10e).

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6. Discussion

6.1. Geochronologic framework of porphyry-skarn Cu ± Mo ± Au deposits from the

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Bangong–Nujiang metallogenic belt

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Previous studies indicated that extensive Jurassic–Cretaceous (180–110 Ma) arc-like magmas are distributed in the northern Lhasa and southern Qiangtang terrane,

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and formed during subduction of Bangong–Nujiang ocean (e.g., Li et al., 2014b; Liu

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et al., 2014a, 2015; Zhu et al., 2011; Sui et al., 2013). Ages of ophiolites and radiolarians indicate that the Lhasa–Qiangtang collision may have occurred ~ 100 Ma

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(Baxter et al., 2009; Liu et al., 2014b; Zhang et al., 2012). Therefore, 95–80 My old mafic-felsic magmas, located in the northern Lhasa and southern Qiangtang terrane,

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are likely related to the Lhasa–Qiangtang collision (Wang et al., 2014; Sun et al., 2015a). Combined with published ages for ore-bearing intrusions in the Bangong–Nujiang metallogenic belt (Li et al., 2011b, 2013a; Zhang et al., 2015; Zhu et al., 2015), our new zircon U−Pb age data (Table 2) indicate two distinct mineralization stages: 118–115 Ma and 91–88 Ma, with the exception of a few small Jurassic skarn Fe–Cu deposits (Zhang et al., 2011). The first period coincided with the end of Bangong–Nujiang ocean subduction (Fig. 12), reinforcing the previously published supposition that long-lived subduction is beneficial for formation of large ore deposits (Richards, 2011, 2013). The mineralization stage occurred during Lhasa–Qiangtang collision, similar to collision-related Cu ± Mo ± Au deposits in

15

ACCEPTED MANUSCRIPT Gangdese metallogenic belt in southern Tibet (e.g., Hou et al., 2004, 2009; Li et al., 2011a; Zhao et al., 2014).

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6.2. Petrogenesis of Cretaceous ore-bearing intrusions from the Bangong–Nujiang

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metallogenic belt

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Cretaceous ore-bearing intrusions from the Bangong metallogenic belt show strong enrichments in LILE (e.g., Cs, Rb, and Th), depletions of HFSE (e.g., Nb), and

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negative Ti anomalies (Fig. 7c, d), consistent with arc-type melts (e.g., Hawkesworth et al., 1993; Pearce and Peate, 1995; Chai et al., 2015). TiO2 and MgO content have

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distinctly negative correlation with SiO2 among different deposits and various samples in an individual deposit (e.g., Qingcaoshan; Fig. 13a, b), mainly controlled by

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different lithologies and fractional crystallization of amphibole, biotite, and magnetite.

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P2O5 content decreases with increasing SiO2 content, and Th content increases with

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increasing Rb content (Fig, 13c, d), consistent with the evolution trend of I-type granites (Chappell and White, 1992). Therefore, during the two mineralization periods, Cretaceous ore-bearing intrusions formed from I-type arc magmas and underwent

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various degree of fractional crystallization. Many excellent studies have indicated that zircon Hf–O analysis is a powerful tool for elucidating magmatic source and evolution (e.g., Kemp et al., 2007; Li et al., 2013a). Most Cretaceous intrusions from the Bangong–Nujiang metallogenic belt show positive zircon εHf(t) values (Figs. 9, 11), indicating that they are dominantly derived from depleted mantle melting. However, all the Cretaceous ore-bearing intrusions show enriched zircon δ18O values (from 5.82 to 10.82 ‰; Figs. 10, 11) relative to mantle (δ18O=5.3±0.3‰, Valley et al., 1998), indicating various degrees of 18

O-enriched crustal contamination to into mantle-derived melts. Previous studies

have shown the existence of old crust in the Lhasa and Qiangtang block, supported by 16

ACCEPTED MANUSCRIPT intermediate-felsic intrusions with lower zircon εHf(t) values (up to –20; Zhu et al., 2011; Li et al., 2014a). Moreover, north of the Bangong–Nujiang metallogenic belt,

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the Early Cretaceous ore-bearing intrusions from the Qingcaoshan porphyry Cu–Au

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deposit have obviously lower zircon εHf(t) and higher δ18O values than those from the

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Duolong and Bainong deposits (Fig. 11a). Zircon mean εHf(t) and δ18O values of the Qingcaoshan ore-bearing intrusions have obviously negative and slightly positive correlation with Th/Yb ratios, respectively (Fig. 13e, f). These lines of evidence

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possibly may indicate that crustal contamination has a role in the petrogenesis of

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Qingcaoshan ore-bearing magmas. In the south of the Bangong–Nujiang metallogenic belt, Late Cretaceous ore-bearing intrusions from the Balazha porphyry-skarn Cu–Mo

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deposit also show lower zircon εHf(t), higher δ18O values, and higher Th/Yb ratios

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(Figs. 11b, 13e, 13f) than those from the Gaerqiong–Galale porphyry-skarn Cu–Au deposit, suggesting a higher degree of crustal contribution for the Balazha deposit.

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Moreover, the granite porphyry and monzonitic granite porphyry from the Balazha deposit show a wide range of zircon εHf(t) values (–1.8 to +5.9 and –4.5 to +6.0).

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Combined with consistent zircon Hf–O isotopic compositions (zircon εHf(t) = 3.98 to 6.0) in granite from this deposit, large variations in zircon Hf isotopic compositions in individual samples from the Balazha deposit may be caused by crustal contamination during zircon growth (e.g., Griffin et al., 2002; Belousova et al., 2006; Yang et al., 2007; Shaw and Flood, 2009). Interestingly, the granite and granite porphyry of the Balazha deposit show relatively consistent zircon δ18O values (7.35–10.82 ‰) with variable εHf(t) values (–4.5 to 6.0), speculatively indicating contamination of a homogeneous

18

O crustal source during zircon crystallization (Figs. 8e,11b). In

contrast, ore-bearing intrusions from the Gaerqiong–Galale porphyry-skarn Cu–Au deposit have relatively higher zircon εHf(t) (7.4 to 9.6), lower δ18O values

17

ACCEPTED MANUSCRIPT (5.46–7.46 ‰), and lower Th/Yb ratios (Figs. 11b, 13e, 13f), likely indicating minor crustal contamination. In summary, Cretaceous ore-bearing intrusions from the

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Bangong–Nujiang metallogenic belt may have formed by mixing of mantle- and

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crust-derived melts, and subsequently experienced various degrees of fractional

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crystallization and crustal contamination during emplacement.

6.3. A geodynamic scenario for Cretaceous ore-bearing intrusions from the

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Bangong–Nujiang metallogenic belt

Jurassic–Cretaceous (180–110 Ma) arc-type intermediate-felsic magmas are

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distributed in the southern Qiangtang terrane (Guynn et al., 2006; Li et al., 2013b, 2014b, 2015; Liu et al., 2014, 2015; Qu et al., 2009; Du et al., 2011; Zhang et al., formed

by

MASH

processes

(melting,

assimilation,

storage

and

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2011),

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homogenization; Hildreth and Moorbath, 1988) or in the ‘deep crustal hot zone’

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(Annen et al., 2006) during northward subduction of the Bangong–Nujiang ocean. As discussed above, ore-bearing intrusions from the Duolong, Qingcaoshan, and Bainong deposits in the southern Qiangtang block show characteristics of typical arc-type

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magmas (Fig. 7) with various contributions from mantle and crust sources as indicated by zircon εHf(t) of and δ18O signatures (Figs. 11a). Therefore, a similar petrogenetic model to that previously proposed (Fig, 14a; Li et al., 2013a, 2014b, 2015a) is preferred here, namely that these ore-bearing intrusions were likely derived from melting of subduction metasomatized mantle, ascended and underwent MASH process at the base of the lower crust, and then experienced AFC (crustal contamination

and

fractional

crystallization)

process

during

emplacement.

Importantly, subduction metasomatized mantle is rich in Cl and S and has a high oxidation state (Richards, 2011), which partitions Cu and Au-bearing sulfides into melts during partial melting. The Cl, S, Cu, and Au-rich melts contribute to the 18

ACCEPTED MANUSCRIPT formation of early Cretaceous porphyry Cu–Au deposits in the Bangong–Nujiang metallogenic belt.

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Most case studies and numerical models suggest that slab break-off (and

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subsequent slab tear propagation) is an important step and occurs ~ 10–25 Ma after

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collision (e.g., Davies and Von Blanckenburg, 1995; Dilek and Altunkaynak, 2009; van Hunen and Allen, 2011). Ages of ophiolites and radiolarians indicate that the collision between the Lhasa and Qiangtang terrane likely occurred about 100 Ma (e.g.,

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Baxter et al., 2009; Liu et al., 2014b; Zhang et al., 2012; Wang et al., 2015). A model

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of slab break-off, subsequent slab tear propagation from east to west, and sinking is proposed for to explain the petrogenesis and spatial-temporal distribution of Late

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Cretaceous magmatism (94–80 Ma) along the Bangong–Nujiang suture. Late

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Cretaceous magmatism decreases in age from east to west, with 94 My old andesitic porphyrites and rhyolites from Baingoin (Wang et al., 2014), 91 My old basaltic and

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andesitic volcanic rocks from Minqianri and Adang (Nyima; Ma and Yue, 2010), 91 My old Mg-rich andesitic and dacitic volcanic rocks from Zhuogapu (Nyima; Wang et

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al., 2014a), 90 My old ore-bearing granitic intrusions from the Balazha deposit, 90 My old andesitic and dacitic volcanic rocks from Azhang (Coqen; Sun et al., 2015a), 89 My old granite from the Sebuta deposit (Huang et al., 2013), 88–89 My old ore-bearing intrusions from the Gaerqiong–Galale deposit, and 86 My old quartz monzonite from Rutog (Li et al., 2014a). Break-off of the Bangong–Nujiang oceanic slab led to asthenosphere mantle upwelling and melting of previous subduction metasomatized mantle to form basaltic melts, which mixed with crust-derived melts to form the late Cretaceous mafic-intermediate volcanic rocks, intermediate-felsic intrusions and associated porphyry-skarn Cu ± Mo ± Au deposits (Fig, 14b). The late Cretaceous ore-forming magmas may have inherited their metallogenic character from

19

ACCEPTED MANUSCRIPT the source arc magmas (Li et al., 2011a; Richards, 2011; Wang et al., 2014b, c), which are similar with early Cretaceous magmas for porphyry Cu–Au deposits. Mo-bearing

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ore-forming magmas (Balazha) have likely experienced more crustal contamination as

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indicated by high zircon δ18O and low εHf(t) values (Fig, 11b). Subsequently, slab

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sinking resulted in extensive 83–75 Ma mafic-intermediate magmatisms along the BNS which extended to the south Qiangtang terrane (Fu et al., 2015; Li et al., 2013b; Wu et al., 2014; Zhao et al., 2008). At 95–70 Ma slab break-off and subsequent

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sinking generally led to the addition of mantle material, as indicated by the high

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zircon εHf(t) and low 18O signatures in these intrusions (e.g., Gaerqiong; Fig. 11b) and volcanic rocks (εHf(t) = 3.1–16.0; Fu et al., 2015; Wang et al., 2014; Sun et al.,

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2015a).

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7. Conclusions

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(1) Our new data combined with previously published ages indicate that Cretaceous porphyry-skarn Cu ± Mo ± Au deposits in the Bangong–Nujiang metallogenic belt mainly formed between 118–115 Ma and 90–88 Ma.

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(2) Cretaceous intrusions from the porphyry-skarn Cu ± Mo ± Au deposits dominantly show characteristics of high-K calc-alkaline continental arc magmas, with enrichments in LILE (e.g., Cs, Rb, and K), and depletions of Nb, Ta, Ti, and Ba. The first stage intrusions (118–115 Ma) intrusions mainly have positive zircon εHf(t) values and high 18O values, suggest mixing between mantle-derived mafic magmas and crustal-derived felsic melts which underwent MASH during northward subduction of the Bangong–Nujiang ocean. The second stage (90–88 Ma) intrusions have a similar petrogenesis but show a higher proportion of mantle-derived melts, and formed by slab break-off after the Lhasa–Qiangtang collision.

20

ACCEPTED MANUSCRIPT

Acknowledgments

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This article was funded by the "Strategic Priority Research Program" of the

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Chinese Academy of Sciences (Grant No. XDB03010303), the Natural Science Foundation Project (Grant No. 41472074), the Ministry of Science and Technology of China (973Project 2011CB403106), “Industry Program” of Ministry of Land and

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Resources (201011013), and the Tibetan Large Deposit Metallogenic Specialization (Grant No. 1212011221073). We obtained specific guidance and assistance from

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Yue-Heng Yang concerning the analyses of LA–ICP–MS zircon geochronology and in-situ Hf isotopes, and from Xian-Hua Li and Qiu-Li Li referring to zircon O

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analyses at the Institute of Geology and Geophysics, Chinese Academy of Sciences.

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This manuscript benefited from constructive comments by the editor Ze-Ming Zhang

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implications for the tectonic evolution of the Lhasa Terrane. Geological Magazine

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drift and growth. Earth and Planetary Science Letters 301, 241–255. Zhu, X.P., Li, G.M., Chen, H.A., Ma, D.F., Huang, H.X, 2015. Zircon U–Pb, 40

Ar/39Ar dating of the Bolong Porphyry

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Molybdenite Re–Os and K-feldspar

Cu–Au Deposit, Tibet, China. Resource Geology 65, 122–135.

Figure Captions Fig. 1. Sketch tectonic map (a) of the Himalayan–Tibetan orogen (Zhai et al., 2011; Tang and Zhang, 2014), and (b) geological map mainly showing spatial and temporal distribution of Jurassic–Cretaceous intrusions and porphyry-skarn Cu ± Mo ± Au deposits along the BNS, central Tibet.

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ACCEPTED MANUSCRIPT Fig. 2. Geological map and sample locations of the Qingcaoshan (a, modified from No. 2 Geological Party, Tibet Bureau of Geology and Exploration of Mineral

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Resources, 2012), Duobuza (b, Li et al., 2013), Bainong porphyry Cu–Au deposits,

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Galale (c), Gaerqiong (d) porphyry Cu–Au deposits (Zhang et al., 2015), and Balazha

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porphyry-skarn Mo deposits (e, Wang et al., 2013) in the Bangong–Nujiang metallogenic belt, central Tibet.

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Fig. 3. Photomicrographs of intermediate–felsic intrusions from porphyry-skarn Cu ±

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Mo ± Au deposits in the Bangong–Nujiang metallogenic belt, central Tibet. (a) porphyaceous granodiorite; (b) granite porphyry; (c) granodiorite porphyry; (d) quartz

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diorite porphyrite; (e) granodiorite porphyry; (f) diorite porphyrite; (g) granodiorite;

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(h) granite; (i) granite porphyry. Mineral abbreviations: Pl = plagioclase, Amp =

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amphibole, Kfs = K-feldspar, Bt = biotite and Q = quartz.

Fig. 4. Representative Cathodoluminescence (CL) images of zircons from

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intermediate-felsic intrusions with analytical numbers, U–Pb ages, εHf(t), and δ18O values (scale bar = 100 μm). The analyzed spots of the zircon U–Pb age, in-situ O and Hf isotope are represented by the red, yellow, and blue circles, respectively.

Fig. 5. Zircon U–Pb concordia diagrams and weighted mean ages of intermediate-felsic intrusions from porphyry-skarn Cu ± Mo ± Au deposits in the Bangong–Nujiang metallogenic belt, central Tibet.

Fig. 6. Diagrams of K2O + Na2O versus SiO2 (a; Middlemost, 1994) and (K2O+Na2O)/CaO versus Zr+Nb+Ce+Y (b; Whalen et al., 1987) of ore-bearing

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Fig. 7. Chondrite-normalized REE patterns (a, b) and primitive mantle-normalized

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element diagrams (c, d) for ore-bearing intrusions along the BNS. Normalizing values

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for REE and trace elements are from Sun and McDonough (1989).

Fig. 8. Histograms (a–e) of zircon εHf(t) values and diagrams of εHf(t) values versus

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Age (Ma) of intermediate-felsic intrusions from porphyry–skarn Cu ± Mo ± Au

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deposits in the Bangong–Nujiang metallogenic belt, central Tibet.

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Fig. 9. Zircon εHf(t) values versus age (Ma) diagram of intrusions from the ~

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118–115 Ma porphyry Cu–Au deposits in the northern of BNS (a) and ~ 90–88 Ma porphyry-skarn Cu ± Mo ± Au deposits in the southern of BNS (b). Published zircon

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U–Pb ages and Hf isotopic data shown for intermediate-felsic intrusions are from Li et

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al. (2014b) and Zhu et al. (2011).

Fig. 10. Histograms of zircon δ18O values (a–e) and diagrams of age (Ma) versus δ18O values (f) of intermediate-felsic intrusions from porphyry–skarn Cu ± Mo ± Au deposits in the Bangong–Nujiang metallogenic belt, central Tibet.

Fig. 11. Plots of zircon εHf(t) versus δ18O values of intrusions from the ~ 118–115 Ma porphyry Cu–Au deposits in the northern of BNS (a) and ~ 90–88 Ma porphyry-skarn Cu ± Mo ± Au deposits in the southern of BNS (b). Hf–O isotopic data of Bolong porphyry Cu–Au deposit from Li et al. (2013a).

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Lhasa–Qiangtang collision. Age data from Li et al. (2011b, 2013a, 2014), Liu et al.

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(2015a), Zhang et al. (2015) and Zhu et al. (2011, 2015).

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(2014a, 2015), Wang et al. (2014), Wang et al. (2013), Yu et al. (2011), Sun et al.

Fig. 13. Compositional variations of ore-bearing intrusions along the BNS, indicating

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evolution trend of I-type granites, fractional crystallization and crustal contamination.

Fig. 14. Geodynamic and petrogenetic models for Cretaceous ore-bearing intrusions

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Table Captions

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Table 1 Characteristics of mineral deposits in the Bangong–Nujiang metallogentic belt, central Tibet

Abbreviations: Act–actinolite, Ab–albite, Alu–alunite, Au–native gold, Bt–biotite, Bn–bornite,

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Cal–calcite, Cb–carbonate minerals, Cc–chalcocite, Cpy–Chalcopyrite, Chl–chlorite, Cm–clay minerals, Cv–covellite, Dck–dickite, Dg–digenite, Di–diopside, El–electrum, En–enargite, Ep–epidote, Fsp–feldspar, Gn–galenite, Gr–garnet, Gyp–gypsum, Hem–hematite, Hbl–hornblende, Hu–humite, Ilm–ilmenite, Kl–kaoline, Lm–limonite, Mt–Magnetite, Mo–molybdenite, Ol–Olivine, Phl–phlogopite, Py–pyrie, Prl–pyrophyllite, Po–pyrrhotite, Q–quartz, Ser–sericite, Srp–serpentine, Tn–tennatite, Tur–tourmaline, Tr–tremolite , and Wo–wollastonite. (1) Zhang et al., 2011; (2) Chen et al., 2014; (3) Li et al., 2013a.

Table 2 Summary of zircon U–Pb ages and Hf–O isotopic compositions for the intrusive rocks related to Cu ± Mo ± Au mineralization, central Tibet

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ACCEPTED MANUSCRIPT Table1 Characteristics of mineral deposits in the Bangong-Nujiang metallogentic belt, central Tibet

Skarn

Fe , Cu , A u, A g

Thick massive limestone of the Middle Permian Longge group

165.1 ±1.5(1 )

Granod iorite

Duob uza

Bolon g

Rong na

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Porphy ry Cu-Au

Cu , A u

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Qingc aosha n

Porphy ry Cu-Au

Cu ,A u

Porphy ry Cu-Au

Cu , A u

Porphy ry-high sulphid ation epither mal Cu(Au)

Sanstone and siltstone of Midddle Jurassic Quemocuo group

Cu ,A u

Quartz sandstone, feldspathic quartz sandstone of Lower Jurassic Quse group Quartz sandstone, feldspathic quartz sandstone of Lower Jurassic Quse group（J1q） Feldspar quartz sandstone and lithic sandstone with dark gray to black silty slate of

Granod iorite porphy ry

Granod iorite porphy ry

Granod iorite porphy ry

Granod iorite porphy ry

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Gangue mineral s

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Biotite monzo nitic granite, granod ionite porphy ry, granite porphy ry

Alteration type

Ore minera ls

Skarnization , hornfels and silicification

Mt, Hem, Py, Cpy, Sph, Ag

Cal, Di, Gr and Q etc

De pos it sca le

Ore grade

Sm all

TFe 44.15 %~63. 28%

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Fe

Fine grained lithic quartz sandstone and micrite, lenticular limestone of Triassic Rigangpeicuo formation

157.4 ±3.1(2 )

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Fuye

Skarn

Wall rocks

Age of mag matis m (Ma)

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Caim a

Type

M eta ls

Associ ated magma tic rocks

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Depo sit/oc curre nce

115.8 ±1.1

118± 1

118.5 ± 1.0(3)

Early Creta ceous

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Skarnization , actinolitizati on and silicification , carbonatizat ion silicification , hornfels, chloritizatio n, biotitization, actinolitizati on, tourmaliniza tion Magnetite, potassic, silicification , chloritizatio n, argillic, gypsificatio n Magnetite,p otassic,silici fication,chlo ritization,arg illic, gypsificatio n,tourmalini zation

Potassic, phyllic, and advanced argillic

Mt, Hmt, late Py and Cpy

Gr, Di, Q, Chl,Ep and rarely Ab, Cb

Sm all

TFe63. 55%～ 65.0% 、 Cu0.84 %、 Au7.68 ×106、 Ag55.5 ×10- 6

Py, Cpy, Mo, Dg

Q, Chl, Bt, Cal

Lar ge

Cu0.3 %、 Au0.3p pm

Cpy, Py, Bn, Mt, Mo, Au etc

Fsp, Q, Chl and Ser

Lar ge

Cu0.51 %, Au0.2g /t

Cpy, Py, Bn, Mt, Gn, Mo

Q, Chl, Bt, Tur,Gy p, Cal

Lar ge

Cu0.47 %, Au0.22 g/t

Py, Bn, Cpy, Tn, Cv, Cc, Dg, En and

Q, Ser, Alu, Prl,Kl, Dck

Gia nt

Cu0.55 %, Au0.09 g/t

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Mo etc

Baino ng

Porphy ry Cu-Au

Cu , A u

Cu , A u

group（J1q） Quartz sandstone, siltstone of Lower Jurassic Quse

Granod iorite porphy ry

Early Creta ceous

Diorite porphy rite

Galal e

Balaz a

Skarn

Porphy ry-skar n

A u, Cu , Fe

Cu , M o

Dolomite and dolomitic marble Cretaceous Jiega Group

Granod iorite

Dolomitic limestone of Permian Xila group

Monzo nitic granite, graniti c porphy ry

Lar ge

Cu0.40 %, Au0.21 g/t

Cu0.35 %, Au0.21 g/t

Fsp, Q, Chl and Ser,Gp, Cal etc

Lar ge

Silicificatio n, argillization and chloritizatio n

Cpy, Py, Mt

Q, Chl and Cm

occ urr enc e

Calcium Skarnization ,chloritizatio n,epidotizati on,sericitizat ion,silicifica tion, carbonatizat ion

Cpy, Py, Bn, Cc, Dg, Po, Mt, Hem, Au and El

Gr, Di, Act, Tr , Wo, Fsp, Hbl, Bt and Ser, Cal, etc., followe d by Ep, Chl and Phl, etc

Lar ge

Cu0.94 %, Au2.27 g/t

88.3± 0.9

magnesian skarnization, chloritizatio n,epidotizati on,carbonati zation

Main Mt, Au; minor Cpy, Bn, Cc, Dg, copper , Lm, Ilm etc

Ol, Di, Phl, Gr, Ep, Chl and Cal, Act, Q, etc

Lar ge

Au2.98 g/t, Cu0.91 %

90.6± 0.7; 88.7± 0.9

Calc-magne sian skarnization, chloritizatio n,tourmalini zation,silicif ication,argill ization

Cpy, Py, Mt, Po, and Mo

Gr, Ol, Hu, Srp, Di, Bt, Chl, Q, Fsp and Cm

Mi ddl e

Cu2-3 %, Mo0.0 4%

115± 1.1

TE

CE P

Skarn

Granod iorite, diorite porphy rite

Fsp, Q, Chl and Ser

Cpy, Py, Mt

91.7± 1.4

AC

Gaerq iong

Carbonate rocks and volcaniclastic rocks of Cretaceous Duo’ai Group

Cpy, Py, Mt

Potassic, phyllic, argillic

group（J1q）

A u, Cu , Fe

Potassic, phyllic, argillic,horn fels

IP

120.0 ±1.0

SC R

group（J1-2s） Quartz sandstone, feldspathic quartz sandstone of Lower Jurassic Quse

Granod iorite porphy ry

NU

Porphy ry Cu-Au

Cu ,A u

MA

Natin g

Porphy ry Cu-Au

D

Naru o

Feldspar quartz sandstone and lithic sandstone with dark gray to black silty slate of Lower-middle Jurassic Sewa

T

group（J1-2s）

Abbreviations: Act-actinolite, Ab-albite, Alu-alunite, Au-native gold, Bt-biotite, Bn-bornite, 54

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

SC R

IP

T

Cal-calcite ; Cb-carbonate minerals; Cc-chalcocite, Cpy-Chalcopyrite, Chl-chlorite, Cm-clay minerals, Cv-covellite, Dck-dickite; Dg-digenite, Di-diopside-, El-electrum; En-enargite, Ep-epidote, Fsp-feldspar, Gn-galenite, Gr-garnet, Gyp-gypsum, Hem-hematite, Hbl-hornblende, Hu-humite, Ilm-ilmenite; Kl-kaoline, Lm-limonite, Mt-Magnetite, Mo-molybdenite, Ol-Olivine, Phl-phlogopite, Py-pyrie, Prl-pyrophyllite, Po-pyrrhotite, Q-quartz, Ser-sericite, Srp-serpentine, Tn-tennatite, Tur-tourmaline, Tr-tremolite , Wo-wollastonite (1)Zhang et al., 2011;(2)Chen et al., 2014;(3)Li et al., 2013.

55

ACCEPTED MANUSCRIPT Table2 Summary of zircon U–Pb ages and Hf–O isotopic compositions for the intrusive rocks related to Cu ± Mo ± Au mineralization, central Tibet

11QX-1

Quartz diorite

8

porphyrite

11QX-1

Fine-grained granite

0

porphyry

11QX-1 4-1

Duobuza

Porphyraceous

5

granodiorite

D2308-5 11 11BNZ

Bainong

K-1 11BN-4-

Granodiorite porphyry Diorite Diorite

CE P

2 11BN-4 Gaerqion

11GLQ-

g

2

11BLZ-

AC

Balaza

Granodiorite

11QX-1

1-1

Diorite porphyrite Granodiorite Granite

11BLZ-

Monzonitic granite

4

porphyry

11BLZ6

-0.9 to

1.1

2.6

118.9 ±

-1.9 to

0.9

1.1

Granite porphyry

T

Granodiorite

115.8 ±

7.63 to 9.02

IP

11QL-8

(Ma)

SC R

Granodiorite

δ18O (‰)

εHf(t)

7.90 to 9.00

116.4 ±

-0.6 to

7.74 to

1.0

1.4

8.74

112.7 ±

-6.3 to

0.5

-1.5

NU

11QL-6

Age

LA-ICP-MS LA-ICP-MS LA-ICP-MS

-

LA-ICP-MS

-

LA-ICP-MS

0.7

1.5

118.8 ±

-3.5 to

0.7

1.7

118.0 ±

1.6 to

5.82 to

1.0

5.0

7.37

115.3 ±

2.7 to

5.97 to

1.0

7.5

8.33

116.6 ±

6.0 to

0.2

9.9

115.0 ±

2.6 to

5.98 to

1.1

10.9

7.92

91.7 ±

7.4 to

5.46 to

1.4

9.6

7.46

90.6 ±

4.0 to

7.44 to

0.7

6.0

8.85

89.6 ±

-5.3 to

7.35 to

0.5

6.0

10.82

88.7 ±

-1.8 to

7.43 to

0.9

5.8

8.89

56

method

LA-ICP-MS

-2.6 to

“–” means not analyzed.

U–Pb dating

-

118.6 ±

MA

han

Rock type

D

Qingcaos

Sample

TE

Deposits

-

SIMS LA-ICP-MS LA-ICP-MS LA-ICP-MS LA-ICP-MS LA-ICP-MS LA-ICP-MS LA-ICP-MS

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

SC R

Graphical abstract

57

ACCEPTED MANUSCRIPT Highlights

Ore-bearing intrusions formed in two periods of ~ 118–115 Ma and ~ 90–88

T



Zircon εHf(t) and 18O values suggest contributions from mantle and crustal

SC R



IP

Ma.

sources.

~ 118–115 Ma intrusions likely formed in a continental arc setting.



~ 90–88 Ma magmas likely formed by slab break-off after Lhasa–Qiangtang

NU



AC

CE P

TE

D

MA

collision.

58