u–pb and re–os geochronological evidence for the jurassic porphyry metallogenic event of the...

Journal of Asian Earth Sciences 79 (2014) 608–622

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Journal of Asian Earth Sciences

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U–Pb and Re–Os geochronological evidence for the Jurassic porphyrymetallogenic event of the Xiongcun district in the Gangdese porphyrycopper belt, southern Tibet, PRC

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⇑ Corresponding authors. Tel.: +86 18780259870 (X. Lang).E-mail addresses: [email protected] (X. Lang), [email protected] (J. Tang).

Xinghai Lang a,⇑, Juxing Tang b,⇑, Zhijun Li a, Yong Huang a, Feng Ding a, Huanhuan Yang a, Fuwei Xie a,Li Zhang c, Qin Wang a, Yun Zhou d

a College of Earth Science and Key Laboratory of Tectonic Controlled Mineralization and Oil Reservoir, Chengdu University of Technology, Chengdu, Chinab Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, Chinac Chengdu Center of China Geological Survey, Chengdu, Chinad Wuhan Center of China Geological Survey, Wuhan, China

a r t i c l e i n f o a b s t r a c t

Article history:Received 3 May 2012Received in revised form 6 August 2013Accepted 6 August 2013Available online 23 August 2013

Keywords:GeochronologyXiongcunGangdeseTibetPorphyry copper–gold deposit

Two large copper–gold porphyry deposits (No.I and No.II) were discovered in the last decade within theXiongcun district, which is located along the south margin of the Gangdese porphyry copper belt. Thesetwo deposits are hosted by two porphyries that were emplaced into the Early Jurassic volcano-sedimen-tary rock sequences of the Xiongcun Formation. The porphyries are both quartz diorite bodies, with oneof these distinguished by its large quartz eyes. Our new molybdenite Re–Os and zircon U–Pb dates forNo.I and No.II deposits and host intrusions reveal the presence of two Middle Jurassic ore-forming epi-sodes in the Xiongcun district. The No.II deposit is related to the 181–175 Ma quartz diorite porphyryand formed ca. 172.6 ± 2.1 Ma. The No.I deposit is related to the 167–161 Ma quartz diorite porphyrywith large quartz eyes and formed ca. 161.5 ± 2.7 Ma. Geochronological and geochemical features ofthe Jurassic ore-bearing porphyries in the Xiongcun district indicate that the porphyry copper–gold min-eralization formed in an island arc setting, which is related to the northward subduction of the Neo-Tethys oceanic plate. These observations, in combination with geochronological data reported at Gang-dese porphyry copper belt, indicated four major metallogenic events existed in the Gangdese porphyrycopper belt at 172–161 Ma, 65–48 Ma, 40–23 Ma, and 20–12 Ma. We have identified two mineralizationepisodes comprise Middle Jurassic metallogenic event (172–161 Ma) in the Xiongcun district, which pro-vides new constrains for the Middle Jurassic metallogenic event in the Gangdese porphyry copper belt.

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1. Introduction

Many precious- and base metal-bearing deposits have beendiscovered in the Gangdese porphyry copper belt in the southernTibet (Fig. 1). In the past decade, two large porphyry copper–golddeposits, No.I (also called Xietongmen or Xiongcun: Tang et al.,2007; Tafti et al., 2009) and No.II (also called Newtongmen: Taftiet al., 2009), have been discovered in the Xiongcun district, whichreveals a large porphyry copper–gold systems located in the Gang-dese porphyry copper belt. These two deposits lie about 3.4 kmapart (Fig. 2) and host a measured and indicated resources of morethan two million tonnes (Mt) copper, >200 tonnes (t) gold, and>1000 t silver; the average grades are 0.40% copper, 0.40 g/t goldand 3 g/t silver (Tang et al., 2012a).

The two intrusions that host the porphyry copper–gold depositsin the Xiongcun district were emplaced into the Early Jurassic vol-cano-sedimentary rock sequences of the Xiongcun Formation. Bothintrusions are quartz diorite porphyries but one of them containslarge quartz eyes. Numerous studies have been conductedthroughout this district (Zhang et al., 2007; Tang et al., 2007; Taftiet al., 2009; Lang et al., 2010). However, there is considerable con-troversy regarding the ages of magmatic–hydrothermal activity inthe Xiongcun district, e.g., Qin et al. (2005) suggested that the oreswere Mesozoic and Xu et al. (2006), Hou et al. (2006) and Qu et al.(2007a) suggested they were Eocene, whereas Tang et al. (2007)and Tafti et al. (2009) suggested ore formation in Jurassic.

Tafti et al. (2009) reported zircon U–Pb ages for the porphyriesin the No.I and No.II deposits as ca. 173–171 Ma and 173 Ma,respectively, and a molybdenite Re–Os age for the No.II depositof ca. 174 Ma. They considered this to be the only mineralizationepisode in the Xiongcun district. However, our research shows thata single mineralization episode cannot explain the ore-related

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Fig. 1. Regional tectonic map of southern Tibet (Modfield from Tafti et al. (2009) and Yin and Harrison (2000)). Abbreviations: GCT = Great counter thrust, Ts = Tertiarysedimentary rocks, Tv(lz) = Early Tertiary Linzizong volcanic rocks in the Lhasa Terrane, GnAm = Amdo gneiss, ITS = Indus-Tsangpo suture, and BNS = Bangong-Nujiang suture.

X. Lang et al. / Journal of Asian Earth Sciences 79 (2014) 608–622 609

characteristics in the Xiongcun district (Lang et al., 2011; Tanget al., 2012a; Huang et al., 2012). The existence of at least twoJurassic mineralization episodes is indicated by the obvious miner-alogical contrasts of the two deposits: abundant hypogene pyrrho-tite and andalusite, only minor magmetite, and an absence ofprimary anhydrite in the No.I deposit, contrast it with the No.II de-posit (Tang et al., 2012a; Lang, 2012). A detailed new geochrono-logic study can further define the absolute age(s) of themineralization and the related intrusive rocks to better understandthe ore genesis processes (e.g., Gustafson et al., 2001; Wilson et al.,2007; Mao et al., 2008), as well as to identify any problems withthe previous work by Tafti et al. (2009). Our new work providesfive U–Pb ages of magmatic zircons from the two ore-bearing por-phyries and eleven Re–Os ages of molybdenite from the No.I andNo.II deposits. These data add new constraints to the absolute tim-ing of magmatic and hydrothermal activity, and reveal the occur-rence of two distinct Jurassic mineralization episodes in theXiongcun district.

2. Regional geology

The Xiongcun porphyry copper–gold district is located along thesouthern margin of the Lhasa Terrane of the Himalayan–Tibetanorogen (Fig. 1; Yin and Harrison, 2000). Magmatic activity in thesouthern part of the Lhasa Terrane is related to the northward sub-duction of the Neo-Tethys oceanic plate and the subsequent colli-sion of India with Eurasian (Yin and Harrison, 2000; Mo et al.,2005; Li et al., 2011). Due to the northward subduction of theNeo-Tethys slab during the Jurassic and Cretaceous, arc volcanicrocks and granitoid intrusions formed along the southern marginof the Lhasa Terrane (Chu et al., 2006; Zhu et al., 2008; Ji et al.,2009), whereas the Xigaze fore-arc basin developed to the southduring the Cretaceous to early Tertiary (Fig. 1; Durr, 1996; Yinet al., 1994).

The continental collision of India and Eurasian is dated as Paleo-cene (Mo et al., 2002; Ding et al., 2005; Hou and Wang, 2008). TheLinzizong volcanism, voluminous granitoid batholiths, and Paleo-cene to Eocene porphyries formed in the southern Lhasa Terraneduring and immediately after the collision (Mo et al., 2008b;Dong et al., 2005; Chung et al., 2005). Several porphyry copper–

(molybdenum) deposits are related to the Early Tertiary porphyries(Zhang et al., 2008; Tang et al., 2009; Gao et al., 2011). Subse-quently, Eocene–Oligocene granitoids and porphyries were alsoemplaced in the southern Lhasa Terrane, which generated addi-tional porphyry and skarn copper ores (Mo et al., 2008a; Yanet al., 2010; Zhang et al., 2012).

Miocene magmatism in the southern Lhasa Terrane generatedalkalic (ultrapotassic) to high-K calc-alkalic volcanic rocks andhigh-K calc-alkalic porphyries (Pearce and Mei, 1988; Milleret al., 1999; Chung et al., 2005). The porphyries were emplaced be-tween 25 Ma and 10 Ma, commonly as small stocks and/or dikesthat intruded older magmatic and sedimentary rocks. They formedmany porphyry copper–molybdenum deposits and related skarndeposits (Qu et al., 2001; Hou et al., 2004; Li et al., 2011). TheGangdese porphyry copper belt is dominated by these Mioceneore deposits (Fig. 1), although the less widespread older depositsare also important sources of mineral resources.

3. District and deposit geology

3.1. Exploration history

The Xiongcun district is located 53 km west of Xigaze, Tibet.Stream sediments with anomalous copper, gold, and silver wereinitially discovered in 1989 by the Geophysics and Geochemis-try Survey Team of Jiangxi province while conducting a geolog-ical survey at the scale of 1:500,000. The 6th GeologicalExploration Team of Tibet, in cooperation with geologists fromChengdu University of Technology, conducted geochemical andgeological surveys in the area 2003. During this study, they rec-ognized disseminated mineralization and veinlets hosting cop-per and gold.

From 2004 to 2011, Tibet Tianyuan Minerals Exploration LTD. incooperation with Chengdu University of Technology and the Insti-tute of Mineral Resources of Chinese Academy of Geological Sci-ences carried out systemic exploration of the discovery. A total of63,215 m of core was drilled from 201 diamond drill holes. Fromthis exploration, two major copper–gold deposits (No.I and No.IIdeposits) were discovered. The No.II deposit is located 3.4 kmnorthwest of the No.I deposit (Fig. 2). The mineralization at the

Fig. 2. Generalized geological map of the Xiongcun district (simplified from Oliver et al. (2006)).

610 X. Lang et al. / Journal of Asian Earth Sciences 79 (2014) 608–622


No.II deposit is still open laterally in all directions and is awaitingadditional exploration, whereas the No.I deposit is moving forwardto the mine construction stage (Tang et al., 2012a). In addition tothe No.I and No.II deposits, there are several geochemical anoma-lies that have potential for additional discoveries in the Xiongcundistrict (Lang et al., 2012).

3.2. District geology

The strata exposed in the Xiongcun district are rocks of theEarly Jurassic Xiongcun Formation. These comprise tuff, sandstone,siltstone, argillite, and lesser limestone (Fig. 2; Tang et al., 2007).The tuff of the Xiongcun Formation is the main mineralized coun-try rock into which the ore-related intrusions were emplaced.

3.3. Structures

The most important structures are faults F1 and F2 (Fig. 2),which occur respectively along the hangingwall and footwall ofthe No.I deposit (Tang et al., 2012a). The faults are subparallel,E–W-trending at approximately 265–280�, and moderately to stee-ply north-dipping at about 40–75� (Oliver et al., 2006). Catacla-sites, lenticular fault-breccias, and discontinuous quartz ± sulfideextensional veins surround and occur within these two fault zones.Other faults are mainly steep post-mineralization structures thatare either NE-, N-, or NW-trending. An E–W-trending anticline isdeveloped to the south of the Xiongcun district (Fig. 2; Oliveret al., 2006).

3.4. Ore-bearing porphyries

Two mineralization-related porphyries have been identified inthe Xiongcun district. One is a quartz diorite porphyry with largequartz eyes (Figs. 2 and 3a), which is spatially and genetically asso-ciated with copper–gold mineralization in the No.I deposit. An-other is a quartz diorite porphyry (Figs. 2 and 3d) related tothe No.II copper–gold deposit, with phenocrysts of plagioclase(35–45%), hornblende (15%), and quartz (<10%; <1-cm-long)(Fig. 3k). These two porphyries are both quartz diorite bodies thathave been highly altered during mineralization. They are texturallyand mineralogically similar except for the fact that the one relatedto the No.I deposit commonly contains round to square quartzeyes, which are as much as 1.5 cm in diameter and account for10% to >15% of the rock (Fig. 3l). They were emplaced within an8-km-long, NW-trending corridor across the center of the Xiong-cun district (Fig. 2).

3.5. Orebodies and resources

The No.I deposit is a NW-elongated, tabular body that hasdimensions of about 1200 m by 600 m (Fig. 2). The orebody dipsto the northeast at about 35–55�, generally parallel to the bed-ding of the volcanic rocks. The ore-bearing porphyry and thecontact metamorphosed tuffs surrounding the porphyry hostveinlet-disseminated pyrite–pyrrhotite–chalcopyrite mineraliza-tion. The footwall to the deposit is the F1 fault, which separatesaltered volcanic rocks from the underlying quartz diorite por-phyry (Fig. 2). The porphyry itself experienced strong sodic–calcicalteration, but contains insignificant copper–gold mineralizationrelative to the adjacent country rocks. The deposit has a mea-sured and indicated resources of >1 Mt copper, >140 t gold, and>900 t silver; the average grade is 0.48% copper, 0.66 g/t gold,and 4.19 g/t silver.

The morphology of the No.II deposit is somewhat similar to thatof the No.I deposit. It is also a NW-trending, tabular body, and thedimensions of about 900 m by 500 m (Fig. 2). The orebody dips

approx. 26–70� to the northeast. Veinlets and disseminated pyr-ite–chalcopyrite mineralization is mainly hosted within the por-phyry itself. The mineralization is less well-developed up-dip tothe south, as alteration changes from potassic to strong sodic–cal-cic. Nevertheless, it is still open down-dip to the north and alongthe strike to the northwest and southeast. The footwall to the de-posit is an older quartz diorite porphyry with large quartz eyes(Fig. 2), which contains barren propylitic alteration and intrudedinto the ore-bearing quartz diorite porphyry (Fig. 3m and n). Thetexture and mineralogy of this barren porphyry are similar to thathosting the No.I deposit, but the quartz eyes of this barren por-phyry near the No.II deposit are larger in size (0.5–2 cm) and moreabundant (15–25 vol.%). The deposit has a measured and indicatedresources of >1.3 Mt copper, >60 t gold, and >180 t silver; the aver-age grade is 0.35% copper, 0.22 g/t gold and 1.30 g/t silver.

Supergene enrichment is weakly developed in these two depos-its. Most of the resources are hosted in the hypogene zone.

3.6. Hydrothermal alteration

Syn-mineralization hydrothermal alterations at the No.I depos-it predominately occur within the ore-bearing porphyry and thecontact tuffs proximal to porphyry, which includes four pervasiveassemblages. Early moderate potassic alteration (Fig. 3a, b, i, andj) consists of andalusite, biotite, muscovite (or sericite), and sul-fides (pyrite, chalcopyrite and pyrrhotite). Later poorly mineral-ized phyllic alteration, which overprints the early potassicalteration, is characterized by quartz, sericite, pyrite, and veryminor chalcopyrite. Strong silicification and stockworks (Fig. 3c)are related to intense development of quartz–sulfide veins inthe center of the orebody. The silicified rocks contain the highestgrade copper–gold–silver mineralization. Weak, late, peripheralpropylitic alteration, which consist of epidote, chlorite, carbonate,quartz, and sericite, is only locally observed, and is barren of min-eralization. The most important and widespread of the alterationassemblages at the No.I deposit are the potassic alteration andthe silicification and stockworks associated with quartz–sulfideveins.

Andalusite in the No.I deposit is of hydrothermal origin (Langet al., 2011; Huang et al., 2012), and is texturally similar to anda-lusite described at the EI Salvador and Elkhorn porphyry deposits(Steefel and Atkinson, 1984; Gustafson and Quiroga, 1995). Tex-tural and chemical evidence (Zhang et al., 2007; Lang et al., 2010,2011; Huang et al., 2012), as well as mineral stability relationshipsin the K2O–Al2O3–SiO2–H2O system (Burnham, 1979), suggest thatthe abundance of andalusite in the No.I deposit can be attributedto: (1) the tuff and ore-bearing porphyry being rich in Al2O3

(Al2O3 = 15.28–18.08%, A/CNK = 1.27–3.78), and (2) a hydrother-mal fluid at high temperature and with a low K+/H+ ratio (Langet al., 2011; Huang et al., 2012).

The No.II deposit is also characterized by four types of pervasivealteration, which mainly developed in the ore-bearing quartz dio-rite porphyry. Early and mineralization-related potassic alteration(Fig. 3e) is dominated by biotite, magnetite, K-feldspar, and sul-fides (pyrite and chalcopyrite). Early and only weakly mineralizedsodic–calcic alteration (Fig. 3f), commonly overprints the potassicalteration, and is composed of albite, epidote, actinolite, magnetite,chlorite, and quartz, with rare sulfides. Late and poorly mineralizedphyllic alteration forms a broad envelope surrounding the northernand eastern parts of the deposit. Late, weakly developed, barrenpropylitic alteration overprints the potassic alteration and phyllicalteration mainly at the center of the deposit, but is more extensivetowards the north. The principal mineral assemblage includeschlorite, quartz, and epidote. The mainly ore-related alteration inthe No.II deposit is the potassic assemblage.

Fig. 3. Photos of rock hand specimens and polarizing microscope images from the Xiongcun district. (a) Quartz diorite porphyry with large quartz eyes in the No.I deposit,potassic alteration; observing large quartz eyes and quartz–sulfide veins. (b) Tuff in the No.I deposit, potassic alteration; observing quartz–andalusite–biotite ± muscovite (orsericite)–sulfide veins. (c) Strong silicification in the No.I deposit. (d) Quartz diorite porphyry in the No.II deposit, weak potassic alteration; observing many gray plagioclasephenocrysts. (e) Quartz diorite porphyry in the No.II deposit, strong potassic alteration overprinted by weak phyllic alteration. (f) Quartz diorite porphyry in the No.II deposit,strong sodic–calcic alteration; observing actinolite veins. (g) Quartz diorite porphyry in the No.II deposit, weak potassic alteration overprinted by phyllic alteration; observingmany chorite–sulfide veins. (h) Quartz diorite porphyry in the No.II deposit, strong potassic alteration; observing many quartz–sulfide veins. (i) Tuff in the No.I deposit,potassic alteration; showing quartz, andalusite (prominency, no color) and minor sulfides (black). (j) Tuff in the No.I deposit, potassic alteration; sulfides (black) distributed inintergranular between the macrograin andalusite and biotite; muscovite developed in the contact zone between the sulfides and andalusite. (k) Quartz diorite porphyry in theNo.II deposit, plagioclase phenocrysts are gray, euhedral tabular crystal, and matrix suffers strong biotite alteration (sandy beige). (l) Quartz diorite porphyry with largequartz eyes in the No.I deposit, observing one big quartz eye (in the center of photo, gray grained) contains some sulfides (black). (m) Older quartz diorite porphyry with largequartz eyes in the No.II deposit, phenocrysts comprise quartz, plagiocalse and hornblende. (n) Older quartz diorite porphyry with large quartz eyes in the No.II deposit,phenocrysts comprise quartz, plagiocalse and hornblende; matrix comprises fine graind quartz, plagiocalse and hornblende. Abbreviations: 1 = Quartz–sulfide veins in theNo.I deposit, 2 = Quartz–andalusite–biotite ± muscovite (or sericite)–sulfide veins in the No.I deposit, 3 = Chlorite–sulfide veins in the No.II deposit, 4 = Actinolite veins in theNo.II deposit, 5 = Quatz–sulfide veins in the No.II deposit, Qz = Quartz, As = Andalusite, Bi = Biotite, Mu = Muscovite, Pl = Plagioclase, and Ho = Hornblende.


Fig. 4. Representative catholuminescence (CL) images of zircons from ore-bearing porphyries with analytical numbers and U–Pb ages. (a) Sample 7226-233.7, (b) Sample7224-159.9, (c) Sample 7235-123.4, (c) X-1, (e) Sample ZK5056-4.


3.7. Veins

Six main vein types, in terms of mineralogical characteristics,have been recognized in the No.I deposit, which are listed as fol-lows, from the oldest to the youngest: (1) Minor, weakly tomoderately mineralized magnetite–biotite–minor sulfide (pyrite ±chalcopyrite) veins; (2) moderately mineralized quartz–andalusite–biotite ± muscovite (or sericite)–sulfide (pyrite–chalco-pyrite ± pyrrhotite) veins or biotite–sulfide veins (Fig. 3b); (3)strongly mineralized quartz–sulfide (pyrite–chalcopyrite ± pyrrho-tite) veins (Fig. 3a); (4) minor, weakly to moderately mineralizedpyrite–chalcopyrite ± pyrrhotite veins; (5) barren pyrite veins,with minor quartz and sericite; and (6) minor, late polymetallicveins that contain abundant sphalerite, pyrite, and chalcopyrite,with minor galena and pyrrhotite. The main mineralized veins inthe No.I deposit are the quartz–andalusite–biotite ± muscovite(or sericite)–sulfide and quartz–sulfide veins.

Hydrothermal veins are also well developed in the No.II deposit.The major types of veins are listed as follows, from the earliest tothe youngest: (1) minor, moderately mineralized magnetite–bio-tite–sulfide (pyrite–chalcopyrite) veins; (2) strongly mineralized

Table 1Summary of ages of ore-bearing porphyries in the Xiongcun district.

Deposits Samplenumber

Rock types and sample locations

No.I X-1 Quartz diorite porphyry with large quartz eyes in 5021 dZK5056-4 Quartz diorite porphyry with large quartz eyes in 5056 d

No.II 7226-233.7 Quartz diorite porphyry in 7226 drill hole7224-159.9 Quartz diorite porphyry in 7224 drill hole7235-123.4 Quartz diorite porphyry in 7235 drill hole

quartz–sulfide (pyrite–chalcopyrite) veins (Fig. 3h); (3) weaklymineralized actinolite veins (Fig. 3f); (4) strongly mineralized chlo-rite–sulfide (pyrite–chalcopyrite) veins (Fig. 3e and g); (5) minor,weakly to moderately mineralized pyrite–chalcopyrite veins; (6)barren pyrite veins; and (7) barren anhydrite veins. The main min-eralized veins in the No.II deposit are the quartz–sulfide and chlo-rite–sulfide veins.

4. Sampling, analytical methods and results

4.1. Zircon U–Pb geochronology

4.1.1. Zircon SHRIMP U–Pb geochronology of ore-bearing porphyry inthe No.II deposit

Three samples of the ore-bearing porphyry (quartz diorite por-phyry) from drill cores (Sample 7226-233.7, 7224-159.9 and 7235-123.4; Fig. 2; Table 1) in the No.II deposit were chosen for zirconU–Pb dating. Sample 7226-233.7 show strong potassic alterationwith high-grade copper–gold mineralization; sample 7224-159.9shows moderate amounts of potassic alteration with weak miner-

Analyticalobjects

Analyticalmethods

Weighted average ages(Ma)

rill hole Zircon LA-ICP-MS 161.77 ± 0.66rill hole Zircon LA-ICP-MS 167.22 ± 0.72

Zircon SHRIMP 181.8 ± 1.5Zircon SHRIMP 175.7 ± 1.5Zircon SHRIMP 179 ± 2

Fig. 5. Zircon U–Pb concordia diagrams and weighted average 206Pb/238U age diagrams for ore-bearing porphyries in the Xiongcun district. Error bars are shown at the 1rlevel.


Table 2Re–Os data of molybdenite in the Xiongcun district.

Deposits Sample number Rock types and sample locations Analytical objects 187Re (ppm) 187Os (ppm) Model ages (Ma)

No.I X-I Quartz–sulfide vein in 5013 drill hole Molybdenite 7656.5 20.5 160.4 ± 2.3X5023-8 Quartz–sulfide vein in 5023 drill hole Molybdenite 3191.1 8.5 160.1 ± 2.3X5024-2 Quartz–sulfide vein in 5024 drill hole Molybdenite 3316.6 9.0 163.4 ± 2.3X5028-3 Quartz–sulfide vein in 5028 drill hole Molybdenite 6135.0 16.7 162.9 ± 2.9

No.II 7222-383.6 Quartz–sulfide vein in 7222 drill hole Molybdenite 1048.4 3.0 172.7 ± 2.57222-431.2 Quartz–sulfide vein in 7222 drill hole Molybdenite 1014.8 2.9 172.4 ± 2.57222-384.8 Quartz–sulfide vein in 7222 drill hole Molybdenite 1029.0 2.9 170.6 ± 2.3278-1 Quartz–sulfide vein in 7234 drill hole Molybdenite 1346.6 3.9 173.6 ± 2.5278-2 Quartz–sulfide vein in 7234 drill hole Molybdenite 1268.7 3.6 169.5 ± 2.6278-3 Quartz–sulfide vein in 7234 drill hole Molybdenite 1354.1 4.0 176.8 ± 2.5278-5 Quartz–sulfide vein in 7234 drill hole Moybdenite 1293.4 3.7 172.5 ± 2.4


alization; and sample 7235-123.4 shows moderate phyllic alter-ation with weak mineralization.

Zircons U–Pb ages of quartz diorite porphyry were obtainedusing the SHRIMP method. Williams (1998), Song et al. (2002),and Zhu et al. (2008) have described the analytical procedure,which is summarized below.

Zircon grains together with the zircon U–Pb standard TEMORA(Black et al., 2003), were cast in an epoxy mount, which was thenpolished to section the crystals in half for analysis. Zircons weredocumented with transmitted and reflected light micrographs, aswell as by cathodoluminescence (CL) images, to reveal their inter-nal structures, and the mount was vacuum-coated with a 500-nmlayer of high-purity gold. Under the guidance of zircon CL images(Fig. 4a–c), the zircons were analyzed for U–Pb isotopes and U,Th, and Pb concentrations using a SHRIMP II ion microprobe atthe Beijing SHRIMP Center, Chinese Academy of Geological Sci-ences. The U–Th–Pb ratios were determined relative to theTEMORA standard zircon corresponding to 417 Ma206Pb/238U = 0.0668 (Black et al., 2003), and the absolute abun-dances were calibrated to the standard zircon SL13. Analyses ofthe TEMORA standard zircon were interspersed with those of un-known grains, following operating and data processing proceduressimilar to those described by Williams (1998). The reference zirconwas analyzed after every fourth analysis. Measured compositionswere corrected for common Pb using the 204Pb method, and dataprocessing was carried out using ISOPLOT (Ludwig, 2003). Uncer-tainties on individual analyses (ratios and ages) are reported atthe 1r level, whereas the errors on the Concordia and weightedmean ages are quoted at the 2r level. The U–Pb zircon data arepresented in Appendix A.

The zircons of the tested samples show similar crystal forms(euhedral, prismatic forms with no resorption or inherited cores)with crystal sizes of 70–170 lm (Fig. 4a–c). All of the zircons showobvious oscillatory zoning (Fig. 4a–c) and Th/U ratios ranging from

Fig. 6. Molybdenite Re–Os weighted average ages of No

0.39 to 1.18 (higher than 0.1), which are in accordance with thoseof igneous zircons (Corfu et al., 2003; Bowring and Schmitz, 2003).Thus, the zircon U–Pb ages can be interpreted as representing theemplacement age of the ore-bearing porphyry in the No.II deposit.Samples 7226-233.7, 7224-159.9, and 7235-123.4, from the No.IIdeposit (Fig. 2; Table 1), yielded 206Pb/238U ages of 181.8 ± 1.5 Ma(2r, MSWD = 1.5), 175.7 ± 1.5 Ma (2r, MSWD = 0.37) and179 ± 2 Ma (2r, MSWD = 1.08), respectively (Table 1, andFig. 5a–f).

4.1.2. Zircon LA-ICP-MS U–Pb geochronology of ore-bearing porphyryin the No.I deposit

Tafti et al. (2009) dated the ore-related porphyry in the No.I de-posit using LA-ICP-MS method, however the ages (171.7 ± 1.1 Maand 171.3 ± 1.0 Ma) are significantly older than we obtainedmolybdenite Re–Os weighted average age (161.5 ± 2.7 Ma, see be-low) of the No.I deposit. So we dated the ore-related porphyry ofthe No.I deposit with same method (LA-ICP-MS) again.

Two samples of the ore-bearing quartz diorite porphyry withlarge quartz eyes from drill cores (samples X-1 and ZK5056-4;Fig. 2; Table 1) in the No.I deposit were chosen for zircon U–Pb dat-ing. The samples both show strong potassic alteration and copper–gold–silver mineralization.

Zircons U–Pb ages of the quartz diorite porphyry with largequartz eyes were obtained using LA-ICP-MS method at the Insti-tute of Mineral Resources, Chinese Academy of Geological Sciences.Hou et al. (2009), Tafti et al. (2009) and Li et al. (2011) have de-scribed analytical procedure, which is summarized below.

Before analysis, the sample surface was cleaned with ethanol toeliminate possible contamination. The sites for zircon U–Pb ageanalysis were selected on the basis of the CL imaging (Fig. 4d ande). During the analyses, a laser repetition rate of 6–8 Hz at100 mJ was used. The spot sizes are 40–60 lm. Every fifth sampleanalysis was followed by analysis of a suite of zircon standards, i.e.,

.I (a) and No.II (b) deposits in the Xiongcun district.

Fig. 8. Summary of the geochronology of the Xiongcun district (data listed inTable 1 and shown in Figs. 5 and 6).


Harvard zircon 91500 (Wiedenbeck et al., 1995), Australian Na-tional University standard zircon TEMORA 1 (Black et al., 2003),and NISTSRM 610. Each spot analysis consisted approximately of30 s background acquisition and 40 s sample data acquisition.The 207Pb/206Pb, 206Pb/2238U, 207Pb/235U (235U = 238U/137.88), and208Pb/232Th ratios are corrected using the Harvard Zircon 91500(Wiedenbeck et al., 1995) as the external calibrant. Common Pbcontents were evaluated using the method described by Andersen(2002). The age calculations and Concordia diagrams were gener-ated using ISOPLOT (Ludwig, 2003). The uncertainties for individ-ual analyses (ratios and ages) are quoted at the 1r level,whereas the errors on the Concordia and weighted mean agesare quoted at the 2r level. Zircon U–Pb analytic data are shownin Appendix B.

The zircons of the studied samples are mostly euhedral and inlong to short prismatic forms with mean crystal lengths of 180–320 lm (Fig. 4d and e). Most zircons show obvious oscillatory zon-ing (Fig. 4d and e), with the range of Th/U ratios varying from 0.40to 1.18, higher than 0.1, in accordance with those of igneous zir-cons (Corfu et al., 2003; Bowring and Schmitz, 2003). Thus, the zir-con U–Pb ages can be interpreted as representing the emplacementage of the ore-bearing porphyry in the No.I deposit. Samples X-1and ZK5056-4, from the No.I deposit (Fig. 2; Table 1), yielded206Pb/238U ages of 161.77 ± 0.66 Ma (2r, MSWD = 1.3) and167.22 ± 0.72 Ma (2r, MSWD = 1.3), respectively (Table 1;Fig. 5g–j).

In summary, these new age data from ore-bearing porphyriesindicate that the porphyry copper–gold deposits in the Xiongcundistrict are the products of the two magmatic episodes (Table 1),one in Early Jurassic (181.8 ± 1.5–175.7 ± 1.5 Ma) and the other inMiddle Jurassic (167.22 ± 0.72–161.77 ± 0.66 Ma). The porphyrymineralization of the No.I deposit is spatially and genetically asso-ciated with the Middle Jurassic quartz diorite porphyry with largequartz eyes, whereas the porphyry mineralization of the No.II de-posit is spatially and genetically associated with the Early Jurassicquartz diorite porphyry (Fig. 2). These contrast with previous con-clusions that both intrusions were emplaced coevally at ca. 173–171 Ma (Tafti et al., 2009).

4.2. Molybdenite Re–Os geochronology

We collected four molybdenite samples of quartz–sulfide veinsfrom drill cores (Fig. 2; Table 2) in the No.I deposit. One quartz–sul-fide vein (sample X-I) is from the porphyry host rock, whereas theother three veins (samples X5023-8, X5024-2, and X5028-3) arehosted in altered tuff. Seven molybdenite samples (7222-383.6,7222-431.2, 7222-384.8, 278-1, 278-2, 278-3, and 278-5; Fig. 2;Table 2) from quartz–sulfide veins, all contained within the miner-alized porphyry, were collected from drill cores in the No.II deposit.

Fig. 7. Rhenium concentrations (ppm) vs. Re–Os model ages (Ma) for

Molybdenite grains were dated using the Re–Os method at theRadiogenic Isotope Facility of the Institute of Mineral Resources,Chinese Academy of Geological Sciences. Du et al. (1995, 2004),Shirey and Walker (1995), and Qu et al. (2007b) have describedthe chemical separation procedure, which is summarized below.

The Carius tube method was used in this study for dissolution ofmolybdenite. The solution was prepared from 2 ml of 12 M HCl and6 ml of 15 M HNO3. Osmium is distilled twice. In the first distilla-tion step, OsO4 is distilled at 105–110 �C for 50 min, and is trappedin 10 ml of water. The residual rhenium-bearing solution is savedin a 50 ml beaker for rhenium separation. The water trap solutionplus 40 ml of water are distilled a second time for 1 h and trappedin 10 ml of water for determining of osmium isotope ratio. The rhe-nium-bearing solutions were treated with 20% NaOH and rheniumextraction was performed with acetone in a Teflon separation fun-nel. Finally, the rhenium and osmium isotopic analyses wereundertaken using a MAT262-NTIMS and TJA PQ Excel ICP-MS.The uncertainty in each individual age determination is about0.35% due to contributions from 187Re decay constant, isotopic ra-tio measurement, spike calibration, and spike weighing. Becausemolybdenite is inherently rhenium enriched and contains insignif-icant nonradiogenic osmium (Markey et al., 1998), it is assumedthat molybdenite does not contain any initial or common osmium,and all measured osmium is monoisotopic 187Os, the product of the

molybdenite from the Xiongcun district (data listed in Table 2).


decay of 187Re. Therefore, the Re–Os dating of molybdenite is basedon the simplified age equation: 187Os = 187Re (ekt � 1) (Stein et al.,2001a).

Samples X-1, X5023-8, X5024-2 and X5028-3, collected fromquartz–sulfide veins of the No.I deposit (Fig. 2; Table 2), yieldRe–Os model ages of 160.4 ± 2.3 Ma, 160.1 ± 2.3 Ma,163.4 ± 2.3 Ma and 162.9 ± 2.9 Ma, respectively (Table 2). The187Re contents of the four samples range from 3191 to 7657 ppm.The 187Os contents vary from 8.5 to 20.5 ppm. Using ISOPLOT soft-ware (Ludwig, 2003), we obtained a weighted average age of161.5 ± 2.7 Ma (MSWD = 2.0) (Fig. 6a).

Samples 7222-383.6, 7222-431.2, 7222-384.8, 278-1, 278-2,278-3, and 278-5, collected from the quartz–sulfide veins in theNo.II deposit (Fig. 2; Table 2), yield Re–Os model ages of172.7 ± 2.5 Ma, 172.4 ± 2.5 Ma, 170.6 ± 2.3 Ma, 173.6 ± 2.5 Ma,169.5 ± 2.6 Ma, 176.8 ± 2.5 Ma, and 172.5 ± 2.4 Ma, respectively(Table 2). The 187Re contents of the seven samples range from1015 to 1354 ppm. The 187Os contents vary from 2.9 to 4.0 ppm.Using ISOPLOT software (Ludwig, 2003), we obtain a weightedaverage age of 172.6 ± 2.1 Ma (MSWD = 3.4) (Fig. 6b).

The Re–Os age data indicate that there are two porphyry-re-lated hydrothermal episodes in the Xiongcun district, i.e., at161.5 ± 2.7 Ma and 172.6 ± 2.1 Ma (Fig. 6). The older mineralization(172.6 ± 2.1 Ma) is hosted by the 181.8 ± 1.5–175.7 ± 1.5 Ma quartzdiorite porphyry at the No.II deposit. The younger mineralization(161.5 ± 2.7 Ma) is hosted by the 167.22 ± 0.72 –161.77 ± 0.66 Maquartz diorite porphyry with large quartz eyes at the No.I deposit.These contrast with previous conclusions that both deposits wereformed coevally at ca. 174 Ma (Tafti et al., 2009).

5. Discussion

5.1. Jurassic metallogenic event in the Xiongcun district

For No.II deposit, previous geochronology data is very limited.Tafti et al. (2009) reported only one zircon U–Pb age of173.0 ± 0.9 Ma from an older quartz diorite porphyry with largequartz eyes surface outcrop near the deposit. We believe that sam-ple was collected from the same intrusion body Lang (2012) datedas 174.4 ± 1.6 Ma, which is an unmineralized porphyry and in-truded into No.II deposit from the south (Fig. 2). Here our three zir-con samples from ore-bearing quartz diorite porphyry in the No.II

Table 3Ore-forming ages in the Gangdese porphyry copper belt.

Deposits Ages (Ma)

Bangpu porphyry–skarn copper–polymetal deposit 15.32 ± 0.79Chongjiang porphyry copper–(molybdenum, gold) deposit 14.85 ± 0.69Jiama porphyry–skarn copper–polymetal deposit 15.18 ± 0.98Zhibula skarn copper–polymetal deposit 16.90 ± 0.64Chuibaizi porphryry copper–(molybdenum) deposit 20.70 ± 0.59Tinggong porphyry copper deposit 15.49 ± 0.36Dabu porphyry copper–(molybdenum) deposit 15.3 ± 0.80

14.6 ± 0.50–14.67 ± 0.20

Lakanger porphyry copper deposit 13.5–13.6Qulong porphyry copper–(molybdenum) deposit 16.41 ± 0.48Zhunuo porphyry copper–gold deposit 13.73 ± 0.62Bairong porphyry copper deposit 12 ± 0.1Tangbula porphyry molybdenum–copper deposit 20.9 ± 1.3Mingze porphyry copper–molybdenum deposit 30.26 ± 0.49Nuri skarn copper–tungsten–molybdenum depsoit 23.36 ± 0.49Chongmuda skarn copper–gold depsoit 40.3 ± 5.6Yaguila skarn lead–zinc–molybdenum deposit 65.0 ± 1.9Jiru porphyry copper deposit 48.3–50.8Sharang porphyry molybdenum deposit 51 ± 1.0No.I porphyry copper–gold deposit in Xiongcun district 161.5 ± 2.7No.II porphyry copper–gold deposit in Xiongcun district 172.6 ± 2.1

deposit yield results between 181.8 ± 1.5 Ma and 175.7 ± 1.5 Ma,which we conclude can represent the emplacement time of theore-bearing quartz diorite porphyry in No.II deposit. A singlemolybdenite Re–Os age from No.II deposit reported by Tafti et al.(2009) at 174.2 ± 0.2 Ma, which is in consistent with our molybde-nite Re–Os weighted average age of 172.6 ± 2.1 Ma and this can berepresented the mineralization age of No.II deposit. The slight dif-ference between the emplacement and mineralization time is sim-ilar to some hydrothermal deposits in China (Chen and Li, 2009;Wang et al., 2010b). The reason for this is attributed to hydrother-mal fluids form in the late evolutionary stage of granitic melt (Aud-tat et al., 2000; Balen and Broska, 2011).

For No.I deposit, Tafti et al. (2009) reported four zircon U–Pbages, two from barren quartz diorite porphyry in the footwall ofthe No.I deposit (Fig. 2) are 172.4 ± 2.0 Ma and 173.5 ± 1.0 Ma,the other two from ore-bearing quartz diorite porphyry with largequartz eyes are 171.7 ± 1.2 Ma and 171.3 ± 1.0 Ma. These ages aresignificantly older than we obtained molybdenite Re–Os weightedaverage age of 161.5 ± 2.7 Ma from the No.I deposit. Zircon age of167.22 ± 0.72 Ma to 161.77 ± 0.66 Ma from ore-related quartz dio-rite porphyry with large quartz eyes in the No.I deposit reportedhere is notably younger than those obtained by Tafti et al. (2009)for the same intrusions with same analytical method, whereas thisage is identical with molybdenite Re–Os weighted average agefrom the No.I deposit. So we consider that the ore-related quartzdiorite porphyry with large quartz eyes in No.I deposit probablyformed in 167.22 ± 0.72 Ma to 161.77 ± 0.66 Ma.

These new zircon U–Pb and molybdenite Re–Os ages indicatethere are two Middle Jurassic porphyry copper–gold mineraliza-tion episodes that comprise the Jurassic metallogenic event inthe Xiongcun district. This new understanding contrasts with pre-vious conclusions that only mineralization episode present in theXiongcun district (Tafti et al., 2009).

Mao et al. (1999, 2006) and Stein et al. (2001a) noted that rhe-nium concentrations in molybdenite can be diagnostic and used tofingerprint multiple episodes of temporally distinct, but spatiallyoverlapping mineralization. For example, two mineralization epi-sodes were observed in the Archean Boddington gold–copper por-phyry deposit, Western Australia (Stein et al., 2001b) and in theCadia porphyry district, New South Wales, Australia (Wilsonet al., 2007), on the basis of rhenium concentrations in molybde-nite. The rhenium concentrations in molybdenite from the two epi-

Analytical methods Data sources

Molybdenite Re–Os Meng et al. (2003a)Molybdenite Re–Os Rui et al. (2003)Molybdenite Re–Os Li et al. (2005)Molybdenite Re–OsMolybdenite Re–Os Rui et al. (2004)Molybdenite Re–OsMolybdenite Re–Os

14.8 ± 0.23 Molybdenite Re–Os Gao et al. (2012)Molybdenite Re–Os Hou et al. (2003)Molybdenite Re–OsMolybdenite Re–Os Meng et al. (2003b)Molybdenite Re–Os Zheng et al. (2007)sericite 40Ar/39Ar Li et al. (2007)Molybdenite Re–Os Wang et al. (2010a)Molybdenite Re–Os Yan et al. (2010)Molybdenite Re–Os Zhang et al. (2012)Molybdenite Re–Os Li et al. (2006)Molybdenite Re–Os Gao et al. (2012)Molybdenite Re–Os Zhang et al. (2008)Molybdenite Re–Os Tang et al. (2009)Molybdenite Re–Os This studyMolybdenite Re–Os This study

Fig. 10. Histogram of ore-forming ages in the Gangdese porphyry copper belt,showing the four distinct metallogenic events with the highest peak at ca. 15 Ma(Miocene) (data listed in Table 3).

Fig. 9. The location and ore-forming ages of major deposits in the Gangdese porphyry copper belt (Simplified from Tang et al. (2012b); data listed in Table 3).


sodes of mineralization in the Xiongcun district are also remark-ably different (1015–1354 ppm for the 172.6 ± 2.1 Ma molybdenitecompared to 3191–7657 ppm for the 161.5 ± 2.7 Ma molybdenite),further supporting the interpretation of the presence of twodistinct episodes of magmatic–hydrothermal activity in theXiongcun district (Fig. 7). The high rhenium content (1015–7657 ppm) in each of eleven molybdenite samples points to a man-tle source for the ore in the No.I and No.II deposits (Mao et al.,1999, 2008).

The time difference of the mineralization between the No.I de-posit (161.5 ± 2.7 Ma) and No.II deposit (172.6 ± 2.1 Ma) in theXiongcun district is about 10 m.y. (Fig. 8). Several studies have rec-ognized the occurrence of multiple, temporally discrete episodes ofmineralization in an ore district (e.g., Cannell et al., 2005; Lundet al., 2002; Wilson et al., 2007). The 10-m.y.-long time differencein Xiongcun district is not a typical of a porphyry district. However,the time difference between discrete magmatic hydrothermal epi-sodes can range from <2 m.y. (Indio Muerto district, Chile: Gustaf-son et al., 2001) to about 18 m.y. (Cadia District, Australia: Wilson

et al., 2007). The emplacement of the ore-bearing porphyry in theNo.I deposit (167–161 Ma) and No.II deposit (175–181 Ma) are alsotemporally distinct; the time difference is about 8 m.y. (Fig. 8).

5.2. Ore-forming geological setting

The convergence and collision between the Indian and Eur-asian continents occurred in the Paleocene (Mo et al., 2002; Dinget al., 2005; Hou and Wang, 2008). However, the initiation of thenorthward subduction of the Neo-Tethys oceanic plate is uncer-tain. Some geologists have suggested that the northward subduc-tion of the plate probably started in the Late Jurassic (Honeggeret al., 1982; Pearce and Mei, 1988; Zhu et al., 2009), and the LateJurassic to Early Cretaceous volcanic rocks in the Sangri Grouprecord this initial subduction. However, in recent years, newgeochronology shows Early Jurassic magmatism present in thesouthern Lhasa terrane (Chu et al., 2006; Zhu et al., 2008; Jiet al., 2009). Therefore, it is likely that the northward subductionof the Neo-Tethys plate began in the Early Jurassic or earlier (Moet al., 2005).

The Xiongcun district is located along the southern margin ofthe Lhasa Terrane. Porphyry copper deposits mainly form alongconvergent plate boundaries (Sillitoe, 2010). Kesler (1973) de-scribed porphyry copper–gold deposits that formed in island arcsettings of the southwestern Pacific margin. In contrast, porphyrycopper–molybdenum deposits also may occur in continental arcsettings, as along the eastern Pacific margin (e.g., Titley, 1990).The geological setting of the Xiongcun district appears to be similarto that hosting the porphyry copper–gold deposits in the south-west Pacific. Zircons from the two ore-bearing quartz diorite por-phyries in the Xiongcun district yielded the U–Pb ages of 181–175 Ma and 167–161 Ma, respectively, which is the time of north-ward subduction of the Neo-Tethys plate and long prior to India–Eurasia collision. In addition, geochemical characteristics of theore-bearing porphyries in the Xiongcun district are similar to thoseof magmatic rocks in island arc settings (Qu et al., 2007a; Taftiet al., 2009; Lang et al., 2010). The rocks also exhibit characteristicsof high initial eNd(t) values (+5.5939 to +5.9189), low initial 87-

Sr/86Sr values (0.704021–0.704409), and high eHf(t) values(+12.24 to +18.79) (Lang, 2012). These characteristics are consis-tent with the copper–gold-enrichment of magmas in island arc


settings that have experienced little or no crustal contamination(Solomon, 1990). Therefore, we conclude that the porphyry cop-per–gold deposits in the Xiongcun district formed in island arcsetting.

Originally, the Middle Jurassic Xiongcun porphyry copper–goldmineralization is likely formed in oceanic island arc, which weresubsequently accreted onto the southern margin of the Lhasa Ter-rane post-Jurassic. By Cretaceous, southern Lhasa Terrane hadevolved to a continental arc setting (Zhu et al., 2009). PorphyryCopper (e.g., Jiru: Zhang et al., 2008), copper–molybdenum (e.g.,Qulong: Meng et al., 2003b), copper–polymetal (e.g., Jima: Liet al., 2005), and molybdenum (e.g., Sharang: Tang et al., 2009)deposits formed at southern margin of the Lhasa Terrane in Paleo-cene–Miocene, which appears to be related to the variability inbasement components, with oceanic crust, metasomatised litho-spheric mantle, juvenile lower crust and continental crust all pres-

Table A1Summary of SHRIMP U–Pb zircon data.

Run no. W (B)/ppm Th/U Isotopic ratios

U Th 206Pb� 207Pb/206Pb ±1r 207P

Sample (7226-233.7): Ore-bearing quartz diorite porphyry in the No.II depositDrill hole 7226, depth 233.7 m; WGS84 coordinates: 636398 E, 3251163 N

1.1 189 84 4.65 0.46 0.0546 3.1 0.192.1 139 61 3.29 0.45 0.0546 3.8 0.183.1 244 133 6.13 0.57 0.0559 2.7 0.184.1 108 41 2.65 0.39 0.0619 4.5 0.185.1 160 69 4.08 0.45 0.0522 3.1 0.186.1 161 72 4.01 0.46 0.0564 2.9 0.217.1 211 128 5.18 0.63 0.0539 3.6 0.208.1 139 57 3.41 0.42 0.0567 3.4 0.20

9.1 276 211 7.01 0.79 0.0525 2.4 0.2010.1 175 76 4.27 0.45 0.0534 3.2 0.1911.1 230 199 5.77 0.90 0.0549 2.6 0.1912.1 147 69 3.55 0.48 0.0554 3.3 0.1913.1 147 63 3.60 0.44 0.0548 3.3 0.1814.1 120 67 2.85 0.58 0.0586 3.5 0.2015.1 229 112 5.68 0.51 0.0521 2.6 0.2116.1 136 160 5.79 0.70 0.0518 2.4 0.21


1.1 141 83 3.39 0.61 0.0512 3.1 0.172.1 168 66 4.04 0.41 0.0505 2.7 0.183.1 99 50 2.39 0.52 0.0535 3.3 0.184.1 199 89 4.81 0.46 0.0521 2.4 0.165.1 204 97 4.84 0.49 0.0549 2.4 0.186.1 157 99 3.80 0.65 0.0576 2.6 0.187.1 187 86 4.45 0.47 0.0556 2.4 0.208.1 122 52 2.89 0.44 0.0520 3.2 0.199.1 150 63 3.51 0.44 0.0598 2.7 0.19

10.1 210 141 4.99 0.69 0.0516 2.5 0.2111.1 184 79 4.43 0.44 0.0545 2.6 0.1912.1 172 85 4.10 0.51 0.0552 2.7 0.1813.1 215 145 5.15 0.70 0.0698 2.1 0.21


1.1 36 18 0.849 0.52 0.0737 6.9 0.322.1 81 60 1.95 0.76 0.0603 3.5 0.183.1 62 48 1.49 0.79 0.0654 4.4 0.214.1 87 70 2.13 0.83 0.0626 3.5 0.185.1 65 57 1.57 0.89 0.0688 3.8 0.236.1 80 55 1.93 0.71 0.0629 3.6 0.207.1 76 48 1.88 0.66 0.0681 3.5 0.218.1 139 159 3.42 1.18 0.0523 3.9 0.189.1 56 29 1.41 0.54 0.0690 4.1 0.18

10.1 100 90 2.52 0.93 0.0706 2.9 0.2611.1 67 58 1.61 0.90 0.0677 8.4 0.2612.1 59 47 1.54 0.83 0.0974 3.3 0.28

ent (Qu et al., 2007b; Cheng et al., 2010). The inferred temporal andspatial evolution of the Jurassic Xiongcun copper–gold deposits inthe southern Lhasa terrane is analogous to that of the Mesozoicporphyry copper–gold deposits in the British Columbia and Ordo-vician porphyry copper–gold deposits in the eastern Australian(Cooke et al., 1998).

In island arc settings, periodic magmatism leads to the forma-tion of multiple magmatic–hydrothermal ore deposits (Athertonand Petford, 1993; Wilson et al., 2007). At Xiongcun, this occurredat least twice in essentially the same location, but 10 m.y. apart.

5.3. Implications for metallogenic events and mineral exploration inthe Gangdese porphyry copper belt

According to existing geochronological data for porphyry andrelated skarn deposits in the Gangdese porphyry copper belt

Ages (Ma)

b/235U ±1r 206Pb/238U ±1r 206Pb/238U ±1r

8 7.8 0.02847 2.0 181.0 3.68 17 0.02743 2.0 174.5 3.45 14 0.02895 1.7 184.0 3.00 23 0.02795 2.2 177.7 3.87 9.7 0.02953 1.7 187.6 3.13 6.8 0.02898 1.5 184.2 2.81 6.7 0.02855 1.5 181.5 2.68 8.7 0.02840 1.7 180.5 3.1

0 6.6 0.02946 1.4 187.1 2.67 9.6 0.02833 1.6 180.1 2.996 4.3 0.02905 1.7 184.6 3.13 6.1 0.02788 1.6 177.3 2.80 6.9 0.02813 2.0 178.8 3.63 13 0.02753 2.3 175.1 3.974 3.8 0.02894 1.4 183.9 2.63 4.9 0.02862 1.4 181.9 2.5

Weighted mean 181.8 1.5

9 6.8 0.02782 1.9 176.9 3.41 6.7 0.02778 1.9 176.6 3.216 4.9 0.02791 1.5 177.4 2.70 11 0.02775 1.5 176.5 2.69 9.8 0.02746 1.5 174.6 2.60 12 0.02775 2.3 176.4 3.968 4.8 0.02763 1.4 175.7 2.496 3.6 0.02771 1.5 176.2 2.66 5.7 0.02695 1.5 171.4 2.55 5.3 0.02778 1.4 176.7 2.55 5.9 0.02782 1.4 176.9 2.56 11 0.02752 1.6 175.0 2.88 13 0.02749 1.7 174.8 2.9


6 14 0.02775 2.5 176.5 4.39 14 0.02756 1.7 175.2 3.07 18 0.02757 2.1 175.3 3.63 22 0.02788 2.0 177.3 3.42 41 0.02757 3.6 175.3 6.28 24 0.02781 2.2 176.8 3.91 29 0.02847 2.5 181.0 4.47 12 0.02843 1.5 180.7 2.65 35 0.02862 2.7 181.9 4.91 7.9 0.02922 1.6 185.7 3.08 8.7 0.02811 1.6 178.7 2.92 20 0.02919 2.5 185.4 4.6

Weighted mean 179 2


(Table 3, Fig. 9 and 10), four main metallogenic events can bewidely defined at: (1) 172–161 Ma, with only the deposits of theXiongcun district known at present time and which we haveshown to have formed in two discrete episodes; (2) 65–48 Ma,with several porphyry and skarn deposits formed that include Sha-rang, Jiru, and Yaguila; (3) 40–23 Ma, with several porphyry andskarn deposits, such as Mingze, Chongmuda, and Nuri; and (4)20–12 Ma, with numerous porphyry and skarn deposits that in-clude Chuibaizi, Dabu, Bairong, Chongjiang, Zhunuo, Tinggong, Lak-anger, Qulong, Jiama, Bangpu, Zhibula, and Tangbula.

Through the late 1990s, according to existing ore-forming ages,the metallogenesis in the Gangdese porphyry copper belt wereconsidered only to be associated with the collision of the Indianand Eurasian plates. However, the discovery of the Middle Jurassicore-forming episodes at the No.I and No.II porphyry copper–golddeposits in the Xiongcun district indicates that the Gangdese por-phyry copper belt is also associated with ores related to the north-ward subduction of the Neo-Tethys oceanic plate. Thus, mineralexploration in the Gangdese porphyry copper belt should also tar-get Jurassic subduction-related intrusive suites as potential hostsfor porphyry-type ore deposits.

6. Conclusions

The copper–gold porphyry deposits of the Xiongcun districtformed in two middle Jurassic mineralization episodes separatedby 10 m.y.. Quartz diorite porphyry intimately related to the No.IIdeposit were emplaced at 181–175 Ma. Seven molybdenite sam-ples from quartz–sulfide veins within No.II deposit yielded Re–Osweighted average age at ca. 172.6 ± 2.1 Ma. A second episode ofintrusive activity occurred at 167–161 Ma, based on two206Pb/238U weighted average ages for Quartz diorite porphyry withlarge quartz eyes that host mineralization in No.I deposit. At theNo.I deposit, porphyry copper–gold mineralization is recorded atca. 161.5 ± 2.7 Ma, according to the Re–Os weighted average agefrom four molybdenite samples in the quartz–sulfide veins. The

Table B1Summary of LA-ICP-MS zircon data.

Run no. W (B)/ppm Th/U Isotopic ratios

U Th 206Pb� 207Pb/206Pb ±1r 207P

Sample (X-1): Ore-bearing quartz diorite porphyry with large quartz eyes in the No.IDrill hole 5021, depth 340.2 m; WGS84 coordinates: 638898 E, 3249149 N

1.1 250 163 6.46 0.65 0.04961 0.00069 0.172.1 251 295 6.47 1.18 0.04958 0.00068 0.173.1 219 129 5.57 0.59 0.05161 0.00222 0.174.1 311 193 7.88 0.62 0.05167 0.00104 0.175.1 253 165 6.43 0.65 0.05101 0.00077 0.176.1 121 82 3.07 0.67 0.04942 0.00258 0.177.1 165 87 4.16 0.53 0.05330 0.00167 0.188.1 195 99 4.99 0.51 0.05109 0.00111 0.179.1 170 97 4.30 0.57 0.05066 0.00194 0.17

10.1 106 43 2.73 0.40 0.05007 0.00735 0.1711.1 212 156 5.44 0.73 0.05141 0.00109 0.1812.1 281 236 7.11 0.84 0.05135 0.00103 0.17

Sample (ZK5056-4): Ore-bearing quartz diorite porphyry with large quartz eyes in thDrill hole 5056, depth 65.4 m; WGS84 coordinates: 638596 E, 3249150 N

1.1 225 155 5.96 0.69 0.04997 0.00028 0.182.1 403 404 10.61 1.00 0.05155 0.00043 0.183.1 184 179 4.93 0.97 0.05051 0.00256 0.184.1 263 167 6.90 0.63 0.05039 0.00126 0.185.1 258 190 6.72 0.74 0.04964 0.00076 0.176.1 349 269 9.31 0.77 0.05192 0.00193 0.187.1 165 96 4.37 0.58 0.05001 0.00203 0.188.1 244 157 6.52 0.64 0.05053 0.00072 0.18

mineralogy and rhenium contents of molybdenite in both episodesare different.

The porphyry copper–gold deposits in the Xiongcun districtformed in island arc setting, which was related to the northwardsubduction of the Neo-Tethys oceanic plate. The geological settingof Xiongcun copper–gold porphyry deposits is similar to that of theporphyry copper–gold deposits of the modern-day southwesternPacific margin.

Middle Jurassic metallogenic event (172–161 Ma) in the Gang-dese porphyry copper belt is likely to be associated with subduc-tion-related intrusions emplaced at the �181–161 Ma. Theoccurrence of copper–gold mineralization with intrusions of mark-edly different ages should be an important consideration whenexploring the Gangdese porphyry copper belt.

Acknowledgments

This research was jointly supported by the National ScienceFoundation of China (Grant No. 41172077), the National Basic Re-search Program of China (Grant No. 2011CB403103), OpeningFoundation of Ministry of Land and Resources Key Laboratory oftectonic controlled mineralization and oil reservoir (Grant No.gzck2012003), China Geological Survey program (Grant No. Zi[2012]03-002-055). The authors express their appreciation forbeneficial direction from Reza Tafti, Jianbing Liu, James R. Lang,Mark Rebagliati, and Qi Deng, as well as constructive commentsby Jingwen Mao and two anonymous reviewers.

Appendix A

See Table A1.

Appendix B

See Table B1.

Ages (Ma)

b/235U ±1r 206Pb/238U ±1r 206Pb/238U ±1r

deposit

509 0.00243 0.02559 0.00010 162.86 0.63476 0.00245 0.02556 0.00011 162.70 0.70902 0.00936 0.02515 0.00056 160.15 3.51876 0.00466 0.02510 0.00050 159.82 3.13687 0.00272 0.02515 0.00013 160.15 0.79175 0.00983 0.02518 0.00046 160.31 2.92486 0.00897 0.02507 0.00058 159.60 3.65901 0.00394 0.02543 0.00024 161.89 1.48555 0.00602 0.02516 0.00026 160.19 1.61684 0.02347 0.02565 0.00037 163.25 2.33035 0.00358 0.02545 0.00017 161.99 1.04788 0.00356 0.02513 0.00019 159.98 1.18


e No.I deposit

183 0.00343 0.02638 0.00038 167.87 2.40647 0.00487 0.02622 0.00064 166.88 4.03548 0.01033 0.02663 0.00056 169.39 3.51216 0.00524 0.02617 0.00012 166.53 0.72793 0.00267 0.02605 0.00012 165.75 0.76951 0.00665 0.02647 0.00019 168.39 1.18125 0.00726 0.02630 0.00038 167.33 2.36430 0.00253 0.02644 0.00010 168.21 0.60



Appendix C. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.jse-aes.2013.08.009. These data include Google maps of the mostimportant areas described in this article.

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u–pb and re–os geochronological evidence for the jurassic porphyry metallogenic event of the...

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