geochemistry, zircon u–pb and molybdenite re–os dating of ... · of the ore ﬂuids and mo...

Geochemistry, zircon U–Pb and molybdenite Re–Os dating of the Taolaituoporphyry Mo deposit in the Central Great Hinggan Range: implications for the

geodynamic evolution of northeastern China

CHEN WU1*, TIAN JIANG1, CHU WU2, HANSHI LI1,3, ZHENG LI 4 and WENCAN LIU1,5

1School of Earth Science and Resources, China University of Geosciences, Beijing, China2School of Water Resources and Environment, China University of Geosciences, Beijing, China

3School of Economics, Peking University, China4Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

5Institute of Geological Survey, China University of Geosciences, Beijing, China

The Taolaituo porphyry-type molybdenum deposit is located in the eastern Inner Mongolia Autonomous Region in China. The mineralizationoccurs mainly as veins, lenses and layers within the host porphyry. To better understand the link between the mineralization and the host ig-neous rocks, we studied samples from the underground workings and report new SHRIMP II zircon U–Pb and Re–Os molybdenite ages, andgeochemical data from both the molybdenites and the porphyry granites. Five molybdenite samples yield a Re–Os isochron weighted meanage of 133.0 ± 0.82Ma, whereas the porphyry granitoids samples yield crystallization ages of 133 ± 1Ma and 130.4 ± 1.3Ma. The U–Pb andRe–Os ages are similar, suggesting that the mineralization is genetically related to the Early Cretaceous porphyry emplacement. Re contents ofthe molybdenites range from 21.74 to 42.45 ppm, with an average of 32.69 ppm, whereas δ34S values vary between 3.7‰ and 4.2‰, which istypical of mantle sulphur. The 206Pb/204Pb, 207Pb/ 204Pb and 208Pb/204Pb vary in the ranges of 18.276–18.385, 15.566–15.580 and38.321–38.382, respectively. The Taolaituo Early Cretaceous granitoids are A-type granites. These observations indicate that the molybde-nites and the porphyry granites were derived from a mixed source involving young accretionary materials and enriched subcontinental lith-ospheric mantle. A synthesis of geochronological and geological data reveals that porphyry emplacement and Mo mineralization in theTaolaituo deposit occurred contemporaneously with the Early Cretaceous tectonothermal events associated with lithospheric thinning, whichwas caused by delamination and subsequent upwelling of the asthenosphere associated with intra-continental extension in northeast China.Copyright © 2015 John Wiley & Sons, Ltd.

Received 5 January 2015; accepted 21 July 2015

KEY WORDS Taolaituo area; porphyry-type deposit; zircon U–Pb dating; molybdenite Re–Os ages; S–Pb isotopic geochemistry; A-type granites

1. INTRODUCTION

Economic molybdenum deposits in the world includeporphyry-type, skarn-type and hydrothermal vein-type(Chen et al., 2000; Mao et al., 2005, 2014). The GreatHinggan Range is located in the eastern section of the CentralAsian Orogenic Belt, which reflects superposition of thePalaeozoic Palaeo-Asian and Mesozoic Western Pacific mar-ginal tectonic-metallogenic magmato-tectonic styles (Maoet al., 2014). The Great Hinggan Range, well known for itsvariety of ore systems (Chen et al., 2011; Li et al., 2012; Zhaiet al., 2013, 2014; Mao et al., 2014), hosts a number of skarn,

porphyry and epithermal ore deposits, which are believed tobe related to the widespread distribution of Mesozoicmagmatism (Sengör and Natal’in, 1996; Mao et al., 2003,2005; Chen et al., 2007; Zhai et al., 2013, 2014). TheTaolaituo area is located on the southeastern margin of theSiberian Block, in a region that was affected by thePalaeo-Asiatic tectonomagmatic and circum-Pacific tectono-magmatic domains (Wu et al., 2002, 2005a,b). The explora-tion degree is relatively high in the southern segment of theGreat Hinggan Range, which bears Pb– Zn, Ag, Cu, Mo,Sn and rare earth element (REE) deposits (Qin et al., 1999;Wu et al., 2011a; Li et al., 2012; Zhou et al., 2012; Liuet al., 2014; Zhai et al., 2014). A few large and medium-sizeddeposits have been discovered in the northern segment(Liu et al., 2014), but the size and number of deposits inthe north are far less than those in the south.

*Correspondence to: Chen Wu, School of Earth Science and Resources, ChinaUniversity of Geosciences, Beijing, China. E-mail: [email protected]

Copyright © 2015 John Wiley & Sons, Ltd.

GEOLOGICAL JOURNALGeol. J. 51: 949–964 (2016)Published online 27 August 2015 in Wiley Online Library(wileyonlinelibrary.com). DOI: 10.1002/gj.2711

In the Xing’ an–Mongolian Orogenic Belt of northeastChina, several Early Cretaceous A-type granitic plutonsare reported, such as the Nianzishan (125±8Ma, Rb–Srwhole rock isochron) (Li and Yu, 1993), Baerzhe (122±5Ma, Rb–Sr whole rock isochron) (Jahn et al., 2000),Woduhe (129±5Ma, Rb–Sr whole rock isochron) (Jahnet al., 2000), Shangmachang (106±2Ma, zircon U–Pb)(Wu et al., 2002), Jiazishan (139±1.5Ma, zircon U–Pb)(Wu et al., 2014a), and Hulunhu (alkali rhyolite, 127±5Ma,Rb–Sr whole rock isochron) (Ge et al., 2007), in the GreatHinggan Range. Because A-type granite and alkaline rocksform in either post-orogenic or anorogenic setting, thissuggests that the Early Cretaceous giant igneous eventaccompanied regional extension.

A few studies have been carried out on the Taolaituodeposit, generally focusing on geological characteristics(Wu et al., 2002, 2005a,b). However, the timing of magmaemplacement, ore genesis and physico-chemical conditionsof the ore fluids and Mo mineralization are poorlyconstrained. Accurate dating of ore deposits is critical forproperly evaluating their relationship to tectonic evolutionsand magmatic events (Stein et al., 1997; Mao et al., 2014).Molybdenite Re–Os dating is a powerful tool for preciseage determination of ore deposits (Mathur et al., 2000;Creaser et al., 2002; Gilmer et al., 2003; Selby and Creaser,2003; Mao et al., 2006, 2008; Wu et al., 2014a,b). In thiscontribution, we present new S and Pb isotopic composi-tions of the main sulphides along with U–Pb ages ofmagmatic zircon and the Re–Os isochron age of molybde-nite from the Taolaituo deposit to constrain the sources ofores and the relationships between Mo mineralization andregional geodynamic evolution. This work contributes to abetter understanding of ore genesis, timing of the oresystem, and the Mesozoic geodynamic evolution of thecentral-southern segment of the Great Hinggan Range innortheast China.

2. REGIONAL GEOLOGY

The Great Hinggan Range is located in the eastern section ofthe Central Asian Orogenic Belt between the Siberian Cra-ton and North China Craton (Jahn et al., 2000; Jahn, 2004;Wu et al., 2011b). The Central Asian Orogenic Belt is a gi-ant accretionary orogen bounded by the Siberian, Tarim andNorth China Cratons (Fig. 1) and is considered to have beenthe world’ s largest site of juvenile crust formation in thePhanerozoic Eon (Shi et al., 2010). The Central Asian Oro-genic Belt is an important region for Cu, Fe, Sn, Ag, Au andpolymetallic and rare metal (Li, Be, Nb, Ta and REE) miner-alization in the world (Dawei et al., 2003). New Sr–Nd–Pbisotope mapping results obtained from this area suggest thatduring the Mesozoic Era crustal growth mainly occurred

around the collisional sutures and/or along the majorlithosphere-scale faults (Guo et al., 2010). The Great HingganRange area was mainly affected by N–S-trending compressionbetween the Siberia Craton and the North China Craton prior tothe Early Jurassic. After the Middle–Late Jurassic, the maintectonic influence was the oblique subduction to the northwestof the Pacific Plate towards the east of the Eurasian continent(Liu et al., 2014), which formed a series of lattice fault systemswith the coexistence of three fault systems that exhibitNE-NNE-trending, E–W-trending and NW-trending, respec-tively. The regional stratigraphy of the Great Hinggan Rangecan be divided into four units as follows: (1) Precambrianmetamorphic basement; (2) early Palaeozoic metamorphosedvolcanic and sedimentary rocks; (3) late Palaeozoic metamor-phic grades and extensive exposures; and (4) Jurassic andCretaceous intermediate–felsic volcanic and sedimentary rocks(Lin et al., 1998; Zhou et al., 2012).Widespread magmatism occurred across the Great Hinggan

Range region (Fig. 1), including multiphase plutonic and vol-canic activity. The Great Hinggan Range area is known forlarge outcroppingMesozoic granite and volcanic rocks (Wanget al., 2006; Ge et al., 2007; Zhang et al., 2008) (Fig. 1). TheMesozoic Era was the most important period for magmatic ac-tivity in northern China, with some of these granites being as-sociated with Cu, Mo, Fe, Sn, Pb–Zn and Ag mineralization(e.g. Mao et al., 2005; Wu et al., 2005a; Zhang et al., 2010a,b). On the basis of isotopic dating, the granites have beendivided into two magmatic stages: early and late Yanshanian,which are separated at 135Ma (Xiao et al., 2004). The intru-sive rocks in the Great Hinggan Range were mainly formedin the late Palaeozoic and Mesozoic with a small amount inthe early Palaeozoic (Fig. 1), and massive intermediate–acidicintrusive rocks were mainly developed in the Mesozoic (Wuet al., 2005b; Liu et al., 2014). Most of the typical porphyryCu–Mo or Mo–Cu deposits in the Great Hinggan Range areahad been studied (Qin et al., 1999).

3. GEOLOGY OF TAOLAITUO MO DEPOSIT

The Taolaituo Mo deposit is situated to the north of Aershancity in the eastern Inner Mongolia Autonomous Region inChina (Fig. 1). Although the degree of exploration activityin this area is not extensive, it still shows good potentialfor Mo mineralization. The rocks exposed in the miningarea are mainly meta-sedimentary rocks of the ProterozoicGeda Formation, Ordovician Luohe Formation sedimentaryrocks, and Jurassic Manketouebo Formation volcano-sedimentary rocks (Fig. 2) (Gong et al., 2014). The meta-sedimentary rocks of the Proterozoic Geda Formation aremainly composed of metamorphic sandstone and schist.The Ordovician Luohe Formation sedimentary rocks aremainly metamorphic sandstone, silty slate and limestone.

C. WU ET AL.950

Copyright © 2015 John Wiley & Sons, Ltd. Geol. J. 51: 949–964 (2016)DOI: 10.1002/gj

The Jurassic Manketouebo Formation volcano-sedimentaryrocks are widely exposed and are composed of anintermediate–acidic volcanic series, which are mostly tafflava. The faults are well developed in the ore district andmainly exhibit as two NNE-trending, NE-trending and minorNW-trending faults. The porphyry molybdenum deposits,which are controlled by NE–NNE-trending structures, morethan 30km long and 50 to 80m wide, have a close spatial re-lationship with the Mo orebody.The intermediate–acidic intrusive rocks are relatively well

developed in four phases consisting of Silurian quartz diorite,

Carboniferous quartz diorite and biotite granodiorite, Jurassicred fine-grained granite rocks, and Cretaceous granite porphyry(Gong et al., 2014). The Silurian quartz diorite is exposed in theeast of the Mo deposit and intrudes the Ordovician sedimentaryrocks. The Carboniferous quartz diorite and biotite granodioriteare exposed in the centre of the Mo deposit, expanding in an E-W direction. The Jurassic red fine-grained granite rocks are ex-posed in the north of the Mo deposit, intruding into the Ordovi-cian sedimentary rocks. And the Cretaceous granite porphyry isdistributed in the southwest of the Mo deposit, comprising thepink granite porphyry, orthophyre and fine-grained granite

Figure 1. Sketch regional geological map of the Great Hinggan Range and its adjacent areas in NE China (modified after Wu et al., 2014a,b). The bluecircles show the main porphyry (Cu)–Mo deposits distribution of the Great Hinggan Range. The blue box shows study area Fig. 2. NCB: North ChinaBlock; SCOB: South China orogenic belt; YZC: Yangtze Craton; SGT: Songpan–Ganzi terrane; QB: Qaidam basin; QT: Qiangtang terrane; LT: Lhasaterrane; and QOB: Qinling orogenic belt. TXOB: Tianshan-Xiangan orogenic belt. This figure is available in colour online at wileyonlinelibrary.

com/journal/gj

TAOLAITUO PORPHYRY-TYPE DEPOSIT 951


porphyry. The chert is relatively well developed. The Taolaituoigneous complex was emplaced at the intersection of the NNE-fault, NE-fault and, as mentioned above, also has a close spatialrelationship with the Mo orebody.

There are approximately 38 ore belts in the Taolaituo oredistrict. At present, more than 70 ore veins have been foundin the ore belts. The Mo orebodies are stratoid structure,as produced in quartz veins and Cretaceous volcano-sedimentary rocks. The Mo orebodies are mainly hidden,and only small parts are exposed at the surface. The currentlydominant Mo orebody extends over 2000m with a width of100–1000m and a vertical thickness generally of 30m; withgrades ranging from 0.06wt.% to 0.13wt.%. Ore mineralsare molybdenite, galena, sphalerite, chalcopyrite, pyrite, py-rolusite and malachite. The ores show cataclasticand metasomatic texture, with disseminated, veinlet-disseminated and massive structure. The gangue mineralsare predominantly quartz, calcite, plagioclase feldspar,sericite and minor phlogopite and K-feldspar.

The alteration of wall rock is strong, and zoning from thecentre of the porphyry body outward consists of potassic,sericitic, argillic and propylitization zone. There are noclear boundaries between mineralization zones, as theyshow a grading relationship. Potassic, sericitization,kaolinitization, montmorillonitization, chloritization andepidotization are absent, but there are silicification,fluoritization and carbonatization. The potassic, silicifica-tion and fluoritizations are closely related to the Mo miner-alization. According to the mineral assemblages and orefabrics, as well as the cross-cutting relationships of veins,the mineralization process can be preliminarily dividedinto five stages. The first stage is a pyrite + quartz stage,and the minerals were produced as pyrite + quartzveins and magnetite + pyrite + quartz veins. The secondstage is a quartz +molybdenite stage including moly-bdenite + quartz veins, pyrite +molybdenite + quartz veins,magnetite + pyrite +molybdenite + quartz veins and pyrite+ chalcopyrite +molybdenite + quartz veins. The

Figure 2. A sketched geological map of the Taolaituo area based on our own field observations and mapping. The black dashed box shows the location of theTaolaituo deposit and distribution from this study. This figure is available in colour online at wileyonlinelibrary.com/journal/gj

C. WU ET AL.952


molybdenite is distributed as disseminations or films inquartz veins. The third stage is a molybdenite +K-feld-spar + quartz stage with molybdenite +K-feldspar + quartzveins, pyrite +molybdenite +K-feldspar + quartz veins andpyrite + chalcopyrite +molybdenite +K-feldspar + quartzveins. The fourth stage is a fluorite +K-feldspar + quartzstage with pyrite + fluorite + quartz veins and pyrite + fluo-orite +K-feldspar + quartz veins. The last stage is a carbon-ate stage with calcite and chlorite veins.

4. SAMPLE DESCRIPTION AND ANALYTICALMETHODS

4.1. SHRIMP U–Pb analytical method

In this study, the five Taolaituo porphyry granitoid sampleswere collected from underground workings at drilling no.zk27 and no. zk17. The fine-grained porphyry granite(TLT1) from 370m level of drilling no. zk27 has a porphyritictexture with approximately 10% phenocrysts that are mainlycomposed of plagioclase (5%), K-feldspar (2%) and quartz(3%), with accessory zircon, apatite, magnetite and molybde-nite. The pink porphyry granite (TLT2) from 417.5m levelof drilling no. zk17 has a porphyritic texture with approxi-mately 15% phenocrysts that are mainly composed of plagio-clase (2%), K-feldspar (10%) and quartz (3%), with accessoryzircon, apatite, magnetite, pyrite and molybdenite. The otherporphyry granite samples (TLT3, TLT4 and TLT5) are alsofrom the underground workings at drilling no. zk427 leveland no. zk427 level, but different levels. The granitoidsamples were sent to the Institute of Hebei Regional Geologyand Mineral Survey in Langfang, Hebei Province, China, formineral separation. Sample preparation included standardcrushing, heavy liquid and paramagnetic techniques for pick-ing out zircon grains. Representative zircon from the sampleswas selected using a binocular microscope. The zircon grainsweremounted in epoxy with standard zircon (TEMORA), sec-tioned in half and polished. Reflected and transmitted lightphotomicrographs and cathodoluminescence (CL) scanningelectron microscope images were prepared to determine theinternal structures of the grains and to target areas within therim of zircon grains for analysis (Fig. 3). U–Pb isotopes wereanalysed on the SHRIMP II at the Ion Probe Centre of theInstitute of Geology, CAGS, Beijing, following the proce-dures described in Song et al. (2002). All data were processedusing the SQUID and ISOPLOT/Ex macros of Ludwig(2004). Measured 204Pb was used to correct for common Pb.The reported analytical precision for the U/Pb ratio is 1σ andthe weighted mean age is reported as 2σ. The zircon grainscollected from the Taolaituo plutonic rocks are irregular ortabular in shape, and range from 50 to 120μm in size. TheCL images show that these zircons are broken and display

clear zoning or core–mantle–rim structure (Fig. 3). Reflectedand transmitted light show that a few zircon grains developedcracks or voids, which might have been influenced by thermalevolution during late metamorphism.

4.2. Re–Os analytical method

Five molybdenite samples were collected from drilling coresfor Re–Os dating. Gravitational and magnetic separationwas applied and then handpicked under a binocular micro-scope (purity >99%). The molybdenite in the samples isfine-grained (<0.1mm), thus avoiding the decoupling ofRe and Os within large molybdenite grains (Stein et al.,2003; Selby and Creaser, 2004). Re–Os isotope analysiswas performed in the Re–Os Laboratory, Institute of Geol-ogy and Mineral Resources, in Tianjin, China. An ICP-MS(TJA X-series), made by Thermo Electron Corporation(Waltham, MA, USA), was used. The analytical proceduresfollowed are those of Shirey and Walker (1995). The modelages were calculated following the equation t= [ln(1 + 187Os/187Re)]/λ, where λ is the decay constant of187Re, 1.666 * 10�11/year�1 (Smoliar et al., 1996). The dataare presented in Table 3.

4.3. Major and trace-elemental analyses

Major and trace-elemental analyses were carried out in theInstitute of Geology and Mineral Resources in Tianjin,China. Major oxide concentrations were determined bywavelength-dispersive X-ray fluorescence spectrometry(XRF) on fused glass beads using a Philips PW 2400 spec-trometer with matrix correction following a procedure de-scribed by Norrish and Hutton (1969). Chinese nationalrock standard GSR-1 (granite) was used as reference mate-rial. Accuracies of the XRF analyses are estimated to be ap-proximately 1% (relative) for SiO2 and approximately 2%(relative) for the other oxides. Trace-element compositionswere analysed by inductively coupled plasma mass spec-trometry (ICP-MS) of nebulized solutions using a VGPlasma-Quad Excell ICP-MS at the Institute Of Geologyand Mineral Resources in Tianjin, China. The detailed ana-lytical procedures are described by Liang et al., (2000).About 50±1mg of powdered sample was digested in Teflonbombs using mixed HF and HNO3.

103Rh was used as an in-ternal standard solution to monitor drift (Liang et al., 2000).Two multi-element standard solutions—one containing Li,Ba, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Cs, Ba, Pb, Th, U,Sc, Y and 14 REEs and the other containing W, Mo, Nb,Ta, Zr and Hf—were employed for external calibration.The reference standards were the same as those used forthe XRF analyses. The accuracies for most of the trace ele-ments are estimated to be better than approximately 5%



(relative). Geochemical data are presented in Table 4 for ma-jor oxides and in Table 5 for trace elements.

4.4. Sulphur and lead isotopic compositions analyses

For S isotope determinations, a mixture of sample powdersand Cu2O was heated under oxidizing conditions to produceSO2 for analysis. Isotopic ratios were obtained on a FinniganMAT-251 at Beijing Institute of Nuclear Geological Re-search with VCDT standard, and the analytical precisionwas better than ±0.01‰. For Pb isotope determinations,sample powders were attacked with mixed HF and HNO3

in a Savillex Teflon screwcap beaker on a 100 °C hotplatefor 7 days. Pb was separated and purified with anion resinexchange technique with an HBr as the eluant. Isotopic ra-tios were obtained on the Finnigan MAT-262 TIMS atBeijing Institute of Nuclear Geological Research. Repeatedanalyses of NBS981 gave 204Pb/ 206Pb=0.05897±15,207Pb/206Pb=0.91445±80 and 208Pb/206Pb=2.16170±180.

5. ANALYTICAL RESULTS

5.1. SHRIMP U–Pb ages

A total of 44 zircons were analysed, and the SHRIMP II an-alytical data are presented in Tables 1 and 2. Most zircongrains of the porphyry granitoid sample are transparent and

colourless under the optical microscope. Concentric zoningis common, and no inherited cores were observed. Thesezircons have highly variable Th and U contents(79–2750ppm), but their Th/U ratios range from 0.48 to2.23, indicating a magmatic origin (Th/U> 0.4). Zircongrains of the quartz orthogranitoid sample have uniform Uconcentrations ranging from 47 to 248 ppm and variableTh concentrations, with Th/U between 0.46 and 1.42, sug-gesting a magmatic origin. Two samples were analysed,and all analyses are concordant or nearly concordant andcluster as a single population with a weighted mean206Pb/238U age of 130.4 ± 1.3Ma (MSWD=3.6, the pinkporphyry granitoid sample), 133±1Ma (MSWD=2.9, thefine-grained porphyry granitoid sample), which representsthe crystallization age of the pluton and was used for the cal-culation of initial isotopic ratios of the other isotopic systems(Fig. 4).

5.2. Re–Os ages

Results of molybdenite Re–Os dating are listed in Table 3.The concentrations of Re and 187Os range from 21.74 to42.45 ppm and 30.31 to 58.83 ppb, respectively. FiveTaolaituo molybdenite samples have a narrow range ofRe–Os ages varying from 132.2 to 133.9Ma. The TaolaituoMo Re–Os data, processed using the ISOPLOT/Ex program(Ludwig, 2004), yielded an isochron age of 133.0 ±0.82Ma(MSWD=0.37) and an initial 187Os of 0.11± 0.72 ppb

Figure 3. Cathodoluminescence (CL) images of zircons from representative samples. White circles with white outlines are analysed spots. The numerals areages in Ma.

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Table 1. Zircon SHRIMP II dating results of the Early Cretaceous fine-grained porphyry granite sample from the Taolaituo Mo deposit

Spot Pb(*10�6) U(*10�6) 232Th/238U 207Pb/206Pb ±%

Isotopic ratios Ages

206Pb/238U ±% 207Pb/235U ±% 206Pb/238U ±%

TLTG-01 12 464 1.0601 0.0527 4.75 0.0209 0.92 0.1518 4.80 133 1TLTG-02 24 991 0.8687 0.0488 2.14 0.0208 0.80 0.1402 2.23 133 1TLTG-03 15 433 2.4395 0.0530 5.38 0.0201 1.31 0.1469 5.57 128 2TLTG-04 6 236 0.8244 0.0506 4.32 0.0210 1.20 0.1469 4.48 134 2TLTG-05 102 4510 0.7298 0.0494 1.17 0.0199 0.89 0.1319 1.47 127 1TLTG-06 6 219 1.0293 0.0506 5.45 0.0210 1.05 0.1464 5.67 134 1TLTG-07 4 151 0.7916 0.0494 4.09 0.0209 1.29 0.1424 4.17 133 2TLTG-08 17 662 0.9538 0.0482 4.07 0.0211 1.14 0.1400 4.33 134 2TLTG-09 85 3744 0.6276 0.0501 1.15 0.0203 1.00 0.1337 1.53 130 1TLTG-10 7 256 1.5723 0.0492 4.54 0.0211 1.05 0.1429 4.58 134 1TLTG-11 6 223 1.1806 0.0483 2.43 0.0210 1.18 0.1400 2.49 134 2TLTG-12 61 3017 0.2374 0.0512 0.90 0.0205 1.07 0.1452 1.61 131 1TLTG-13 9 361 0.8749 0.0478 2.67 0.0212 1.01 0.1398 2.86 135 1TLTG-14 130 6176 0.2780 0.0468 1.42 0.0215 1.15 0.1386 1.64 137 2TLTG-15 7 298 0.9117 0.0468 4.04 0.0211 1.27 0.1362 4.04 135 2TLTG-16 15 594 0.9294 0.0513 3.89 0.0210 0.86 0.1483 3.97 134 1TLTG-17 7 298 0.8718 0.0508 3.71 0.0214 1.21 0.1498 3.75 136 2TLTG-18 7 304 0.8238 0.0517 3.52 0.0214 1.10 0.1522 3.52 136 1TLTG-19 23 889 1.0913 0.0511 2.52 0.0207 0.94 0.1462 2.69 132 1TLTG-20 9 361 0.7872 0.0511 4.23 0.0210 1.02 0.1477 4.28 134 1TLTG-21 11 387 1.4318 0.0481 3.71 0.0210 1.06 0.1390 3.71 134 1TLTG-22 7 285 0.9920 0.0531 4.08 0.0203 1.27 0.1489 4.08 130 2TLTG-23 6 252 0.7086 0.0508 4.11 0.0206 1.01 0.1438 4.14 131 1TLTG-24 13 596 0.8325 0.0476 4.89 0.0201 0.95 0.1320 4.99 128 1TLTG-25 22 924 0.8246 0.0461 2.85 0.0203 1.00 0.1287 2.91 129 1

Errors are 1-σ.

Table 2. Zircon SHRIMP II dating results of the Early Cretaceous pink porphyry granite sample from the Taolaituo Mo deposit

Spot Pb(*10�6) U(*10�6) Th(*10�6) 232Th/238U

Isotopic ratios Ages

206Pb/238U Errors 207Pb/235U Errors 206Pb/238U ±%

TLT-01 3.53 150.66 111.01 0.74 0.0204604 0.0002207 0.1365031 0.0040147 130.6 1.4TLT-02 13.24 586.67 397.61 0.68 0.0204282 0.0002725 0.1399174 0.0062903 130.4 1.7TLT-03 6.60 208.56 197.32 0.95 0.0207390 0.0002212 0.1384809 0.0031628 132.3 1.4TLT-04 7.85 337.77 232.97 0.69 0.0202459 0.0002001 0.1346917 0.0032612 129.2 1.3TLT-05 27.62 1335.30 539.32 0.40 0.0225281 0.0001984 0.1641397 0.0013080 143.6 1.3TLT-06 8.24 341.56 264.40 0.77 0.0201005 0.0001797 0.1335258 0.0029433 128.3 1.1TLT-07 27.88 1096.78 841.44 0.77 0.0205655 0.0003630 0.1422292 0.0058744 131.2 2.3TLT-08 17.95 1104.78 372.47 0.34 0.0212240 0.0002187 0.1415540 0.0021636 135.4 1.4TLT-09 13.93 609.47 400.16 0.66 0.0209730 0.0002136 0.1397736 0.0022408 133.8 1.3TLT-10 19.91 847.64 645.34 0.76 0.0195422 0.0001526 0.1295912 0.0013573 124.8 1.0TLT-11 50.71 2275.09 1465.29 0.64 0.0198994 0.0001731 0.1360694 0.0014475 127.0 1.1TLT-12 29.10 1305.71 800.70 0.61 0.0203922 0.0001873 0.1361336 0.0013619 130.1 1.2TLT-13 37.74 1714.35 1124.48 0.66 0.0201365 0.0001627 0.1358025 0.0011463 128.5 1.0TLT-14 22.76 952.09 696.77 0.73 0.0207905 0.0002795 0.1383485 0.0020292 132.6 1.8TLT-15 16.96 520.03 533.47 1.03 0.0200894 0.0001830 0.1383913 0.0018099 128.2 1.2TLT-16 6.45 259.76 187.19 0.72 0.0205033 0.0001787 0.1363830 0.0016734 130.8 1.1TLT-17 10.27 366.19 376.57 1.03 0.0205279 0.0001712 0.1354212 0.0012684 131.0 1.1TLT-18 15.97 565.44 440.75 0.78 0.0212910 0.0002747 0.1428967 0.0028186 135.8 1.7TLT-19 7.29 239.77 242.84 1.01 0.0200263 0.0001752 0.1693133 0.0025316 127.8 1.1TLT-20 24.10 1026.46 801.73 0.78 0.0188578 0.0001774 0.1324402 0.0018452 120.4 1.1

Errors are 1-σ.



(Fig. 5). The nearly identical model age and isochron agesuggest that the analytical results are reliable.

5.3. Major and trace-element geochemistry

A total of five granitic samples (Fig. 6A)were analysed for ma-jor and trace-element compositions. The loss on ignition (LOI)for most samples is about 1wt.%. In general, the granitic sam-ples are characterized by high SiO2 contents (76.18–77.32wt.%) and have low Al2O3 contents (12.16–13.00wt.%). Totaliron oxide contents (in the form of Fe2O3) vary from 1.08 to1.10wt.%. The contents of CaO and Na2O are 0.24 to0.64wt.% and 3.36 to 3.64wt.%, respectively. The K2Ocontent ranges from 4.78 to 4.98wt.%. Other oxides are lessthan 1wt.% (i.e. MgO= 0.09–0.14wt.%, MnO=0.01 to0.07wt.%, TiO2=0.13–0.20wt.% and P2O5=0.02–0.05wt.%).According to the K2O versus SiO2 diagram (Le Maitre, 1984;Rickwood, 1989) (Fig. 6B), all samples fall in the fieldof the high K calc-alkaline series. Chondrite-normalizedREE patterns invariably show relative enrichment of lightrare earth elements (LREEs) with high (La/Yb)N ratios(Fig. 6D). Significant negative Eu anomalies are evident.However, some samples show distinctive, rather different,REE patterns. The granitoids share all the featurescommon to A-type granitoids in terms of trace elementgeochemistry. They are typically high in Ga, Zn, Zr,Nb and Y, and low in Ba and Sr, with some variationin Rb (Collins et al., 1982; Whalen et al., 1987). In thespider diagrams (Fig. 6C), all the granitic rocks showthe characteristic negative anomalies in Ba, Nb, Ta, Sr,P, Eu and Ti (Tables 4-5).

5.4. Sulphur and lead isotopic compositions

A total of two samples (Table 6) were analysed for lead iso-topic and sulphur isotopic compositions. Their δ34S valuesvary between 3.7‰ and 4.2‰, which is typical of mantlesulphur. The 206Pb/204Pb, 207Pb/ 204Pb and 208Pb/204Pbvary in the ranges of 18.276–18.385, 15.566–15.580 and38.321–38.382, respectively.

6. DISCUSSION

6.1. Petrogenesis of the granites

The Early Cretaceous Taolaituo granitoids have all thegeochemical characteristics of A-type granitoids. The plutoncontains moderate to high total alkalis (K2O+Na2O=8.17–8.62wt.%). The ACNK(Al/Ca+Na+K>1) is higherthan that of a typical I-type granitoids, showing ametaluminous–peraluminous nature (i.e. Loiselle andWones, 1979; Douce, 1997). The extremely low P2O5 abun-dances and the absence of phosphate minerals also suggestthat the Taolaituo Early Cretaceous pluton is an A-type gran-itoid rather than an S-type leucogranitoid (King et al., 1997;Bonin, 2007). The trace-element compositions of the granit-oids also show characteristics of A-type granites, includingenrichment in HFSEs (e.g. Zr, Nb and Y) and REEs and ex-treme depletion in Ba, Sr, P, Ti and Eu. Other trace-elementratios such as Nb/Ta (11.7–13.2) and Zr/Hf (19.87–29.3)are also consistent with those in typical A-type granites(e.g. Eby, 1992; Martin et al., 1994). The extremely lowSr content is important in discriminating A-type granites

Figure 4. SHRIMP II zircon U–Pb concordia diagrams of the different granitoids from the Taolaituo Mo deposit. (A) Taolaituo fine-grained porphyry granitoidand (B) Taolaituo pink porphyry granitoid. This figure is available in colour online at wileyonlinelibrary.com/journal/gj

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from calc-alkaline granites, as Sr contents in A-type granitesare only about 33–50% of those in the calc-alkaline varietiesat the same SiO2 level (Douce, 1997). Various discriminationdiagrams are also used to constrain the tectonic environmentof the granitoids. Samples in this study plot in the field of‘volcanic arc granite’ or ‘syn-collision granite’ in the dia-grams of Pearce et al. (1984) (Fig. 6E and F). Followingthe discrimination diagrams of Whalen et al. (1987), samplesfall into the field of ‘A-type granites’ (Fig. 7).Granitoid samples from the study area feature enrichment

and positive anomalies of the large-ion lithophile element

(LIL) group (Rb, Th, U and K) and LREE with flat and neg-ative anomalies of the high field strength (HFS) elements(Ba, Nb, Ta, Sr, P and Ti) and heavy REEs (HREEs). Thesecharacteristics had a similar magma source to that of coevalvolcanic rocks (Wu et al., 2014a). The source of the late Me-sozoic volcanic rocks is thought to have been from enrichedlithospheric mantle. Re-melting of these residues cannot pro-duce granitic liquids with high (Na2O+K2O)/Al2O3 andTiO2/MgO ratios that are characteristic of A-type granitoids(e.g. Eby, 1990, 1992; Turner et al., 1992; Douce, 1997;Wei et al., 2002; Bonin, 2007). Mantle–crust interaction in

Figure 5. Re–Os isotopic isochron diagram of molybdenite from the Taolaituo Mo deposit. The ISOPLOT software of Ludwig (2004) was used to calculate theisochron age, decay constant: λ (187Re) = 1.666 * 10�11/year (Smoliar et al., 1996), uncertainties are absolute at 2σ with error of 1.01% at the 95% confidence

level, initial 187Os ng/g = 0.11 ± 0.72. This figure is available in colour online at wileyonlinelibrary.com/journal/gj

Table 3. Result of Re–Os isotopic analyses of molybdenite from the Taolaituo Mo deposit

Drill no.Sampleno.

Weight(g)

Re μg/g 187Re μg/g 187Os ng/g Model age (Ma)

Measured 2σ Measured 2σ Measured 2σ Measured 2σ

ZK17-03 TLT1 0.05422 42.45 0.36 26.68 0.23 58.83 0.47 132.2 1.9ZK17-04 TLT2 0.05150 39.54 0.48 24.85 0.30 55.50 0.45 133.9 2.2ZK27-02 TLT3 0.03057 21.74 0.17 13.66 0.10 30.31 0.27 133.0 1.9ZK27-03 TLT4 0.03099 35.57 0.27 22.36 0.17 49.45 0.44 132.6 1.9ZK27-04 TLT5 0.03049 24.15 0.18 15.18 0.11 33.66 0.30 133.0 1.9

Uncertainty for the calculated ages is 1.01% at the 95% confidence level.



Figure 6. Geochemistry diagrams for the five granitoids from the Taolaituo area. (A) SiO2 versus (K2O +Na2O) diagram for intrusive rocks (after Middlemost,1994). (B) K2O versus SiO2 diagram for intrusive rocks (after Le Maitre, 1984; Rickwood, 1989). (C) N-MORB-normalized spider diagram for the granitoids.Normalization values are from Sun and McDonough (1989). (D) Chondrite-normalized REE diagram for the granitoids. Normalization values are from Boynton(1984). (E) and (F) (Yb + Ta) versus Rb diagram and Yb versus Ta diagram for granitoids, respectively (Pearce et al., 1984). VAG: volcanic arc granites; ORG:ocean ridge granites; WPG: within-plate granites; Syn-COLG: syn-collision granites. Quoted geochemistry data for the two granitoids are shown in Tables 4

and 5. This figure is available in colour online at wileyonlinelibrary.com/journal/gj

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the Early Cretaceous Taolaituo pluton is manifested by bothits trace-element and isotopic compositions.Wu et al. (2011b), Fu et al. (2012), and Zhou et al. (2012)

proposed that Late Jurassic to Early Cretaceous graniteswere formed and significantly affected by the subductionprocess, which resulted in regional lithospheric thickening,

and subsequent delamination of the thickened lithospheredue to its gravitational instability during the Early Creta-ceous. As discussed above, trace-element geochemistry ofthe Early Cretaceous Taolaituo granitoids suggests that themagma was enriched in mantle materials and that crustal as-similation was minor, but some crustal contamination oc-curred. We conclude that young accretionary materials andenriched continental lithospheric mantle were the meltsource of the Early Cretaceous Taolaituo pluton. We pro-pose that the Early Cretaceous Taolaituo A-type graniteswere the product of extension in eastern Inner Mongolia af-ter the delamination of thickened lithospheric mantleresulting from subduction of the Pacific plate (Fig. 8).

6.2. Ore-forming material source, timing of magmaemplacement and Mo mineralization

Through field investigation and geochemical study, combinedwith S and Pb isotopic tracing and Re–Os isotopic dating, wehave demonstrated that ore sulphides of the porphyry Mo belthave the same S and Pb isotopic compositions, as that of ore-bearing porphyries. We collected two pyrite and molybdenitesamples from Taolaituo deposit. The δ34S values of pyritesamples are similar to the δ34S values of magmahydrothermalism (Ohmoto and Goldhaber, 1997). Re contentsof the molybdenites range from 21.74 to 42.45ppm, with anaverage of 32.69ppm (Table 3). Their δ34S values vary be-tween 3.7‰ and 4.2‰ (Table 6), which are typical of mantleS. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios arebroadly consistent with this interpretation (Table 6).

In this study, we obtained two grantoids zircon SHRIMPII U–Pb weighted mean ages of 133±1Ma and 130.4± 1.3Ma, and Re–Os isochron age for five molybdenite sam-ples of 133.0 ± 0.82Ma (Re–Os isochron age for Taolaituodeposit). Both U–Pb age and Re–Os isochron age are identi-cal within analytical error, indicating that the porphyry gran-itoid emplacement and the Mo mineralization occurredapproximately at the same time, Early Cretaceous.

Table 6. Result of S and Pb isotopic compositions of ore-bearing porphyries

Location Sample no. Mineral δ34S‰ 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb

TLT deposit ZK17-01 Pyrite 4.2 18.278 15.566 38.321TLT deposit ZK17-02 Molybdenite 3.7 18.385 15.580 38.382

Table 4. Major element data for five granitoids from the Taolaituo Mo deposit

Sample no. SiO2 Al2O3 Fe2O3 FeO MgO CaO Na2O K2O MnO P2O5 TiO2 LOITotal majorelement (%)

TLT1 76.18 13.00 0.44 0.23 0.11 0.64 3.64 4.98 0.01 0.03 0.15 0.58 99.98TLT2 77.32 12.38 0.25 0.58 0.14 0.28 3.39 4.78 0.07 0.04 0.17 0.76 99.40TLT3 77.03 12.16 0.32 0.35 0.14 0.24 3.45 4.83 0.05 0.03 0.14 0.64 99.38TLT4 77.18 12.46 0.41 0.25 0.09 0.49 3.36 4.79 0.02 0.02 0.13 0.19 99.39TLT5 76.28 12.88 0.36 0.55 0.12 0.56 3.52 4.92 0.04 0.05 0.20 0.55 100.03

Table 5. Trace element data for five granitoids from the TaolaituoMo deposit

Traceelement

TLT1(ppm)

TLT2(ppm)

TLT3(ppm)

TLT4(ppm)

TLT5(ppm)

La 47.76 41.11 38.90 18.90 39.50Lu 0.29 0.38 0.36 0.20 0.08Nd 10.73 18.90 9.36 12.94 16.53Pr 3.82 5.79 2.89 5.04 7.37Sm 1.60 2.85 1.66 3.14 2.73Tb 0.21 0.36 0.31 0.32 0.34Tm 0.16 0.30 0.32 0.20 0.24Ce 51.36 61.40 40.50 42.76 44.22Dy 1.20 2.23 1.99 1.51 1.49Er 0.76 1.55 1.46 1.30 0.69Eu 0.28 0.40 0.18 0.38 0.96Gd 1.46 2.30 1.60 2.41 2.73Ho 0.24 0.45 0.44 0.26 0.25Yb 1.22 2.26 2.31 1.66 0.60V 10.00 16.60 10.70 13.76 11.82Cr 4.00 5.37 3.80 5.35 5.01Co 0.34 1.58 1.67 1.13 1.63Ga 20.90 22.40 22.10 21.70 21.60Cs 4.93 2.29 5.59 2.31 3.07Rb 445.70 156.00 279.80 237.50 130.00Ba 130.20 152.00 132.83 565.30 577.00Th 40.26 16.80 39.03 18.19 14.35U 21.17 5.76 8.83 6.65 3.05Y 2.98 2.88 3.01 2.25 7.65Ta 0.76 1.24 1.12 1.31 0.41Nb 8.94 16.40 12.87 14.94 6.16Sr 54.00 63.70 50.00 176.00 144.00Hf 5.32 7.39 5.42 4.92 5.96Zr 105.80 217.00 138.50 129.50 181.70Pb 32.70 15.10 34.97 12.19 18.57



6.3. Regional mineralization and geodynamic evolution

Mineral systems in the central part of Inner Mongolia, includ-ing skarn, porphyry and epithermal mineral deposits, wereformed during the Palaeozoic and Mesozoic eras (Chenet al., 2009). Mesozoic ore deposits are related to lithosphericthinning, caused by the upwelling of the asthenosphere under

continental extension in eastern China (Zhang et al., 2010a).The dynamic setting of these geological processes may belinked to the subduction of the Izanagi Plate beneath theEurasian Plate during the Early Cretaceous (Mao et al.,2005; Zhang et al., 2010b). The subduction of the IzanagiPlate may have changed direction from west to north ornorthwest, which caused a transition in the tectonic regime

Figure 7. (a) K2O versus Na2O diagram (Collins et al., 1982) for the five Taolaituo Early Cretaceous plutonic rocks. (b) (10000 * Ga/Al) versus Nb diagram forA-type granitoids (Whalen et al., 1987); and (c) (10000 *Ga/Al) versus Zr diagram for A-type granitoids (Whalen et al., 1987). Both samples plot into the field

of A-type granitoids. This figure is available in colour online at wileyonlinelibrary.com/journal/gj

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from compression to extension and subsequently inducedlarge-scale delamination of the thickened lower crust and lith-ospheric mantle (Zhang et al., 2010b;Wu et al., 2014a,b). The

shortening and thickening of the crust delamination andconsequent upwelling of the asthenosphere promoted theemplacement of Yanshanian granitoids (Wu et al., 2005a,b).

Figure 8. Model diagrams of Mesozoic tectonic evolution and metallogeny in the regional (Mao et al., 2005; Wu et al., 2014a). Notes: (A) Post-collisionalextension and associated mantle upwelling; (B) subduction of the Pacific Plate beneath the Eurasian continental margin, slab break-off and upwelling of as-thenospheric mantle and crustal melts to produce high K calc-alkaline intrusions; and (C) extension of the back-arc area and lithospheric thinning, enablingthe immense emplacement of Cretaceous granitoids and the formation of large-scale Mo mineralization. This figure is available in colour online at

wileyonlinelibrary.com/journal/gj



The magmatic fluids originated from granitic magmas orthe deep magma chambers during the Mesozoic Era sup-plied significant amounts of sulphur and other base metalsto form large-scale hydrothermal deposits in NE China.

It should be noted that the Late Jurassic to Early Creta-ceous interval is an important Sn–Fe–Cu–Mo–Pb–Znpolymetallic mineralization peak in northern China (Maoet al., 2005). Izanagi Plate subduction also triggered inten-sive magmatism and mineralization events in the GreatHinggan Range in NE China. Subduction-related oredeposits in these belts during the Late Jurassic to EarlyCretaceous period shared a tectonic setting of lithosphericthinning and magmatic underplating (Zhang et al., 2009).Several studies suggest that the collision between the Sibe-rian Craton and the North China–Mongolia Block mighthave been ongoing until the closure of the Mongolia–Okhotsk Ocean in the Late Jurassic (Li, 1998; Zorin,1999; Deng et al., 2005; Mao et al., 2005, 2014). Subduc-tion of the Palaeo-Pacific Ocean beneath the East Asiancontinental margin began during the Middle Jurassic(Isozaki, 1997), and that extrusion and crustal thickeningreached a climax in Late Jurassic time. Wu et al. (2011b)proposed that those granitoids were formed and signifi-cantly affected by the subduction process, which resultedin regional lithospheric thickening and subsequent delami-nation of the thickened lithosphere due to its gravitationalinstability during the Early Cretaceous. Large-scale magmaactivity and the NE-trending or NNE-trending tectonicsystem were the far-field response of the Palaeo-PacificPlate beneath the Eurasian Block in the Early Cretaceous,which was the main formation period of the porphyrygranitoids (Fig. 8).

The Taolaituo deposit is controlled by the NNE-trendingand NE-trending faults, and the ages of the emplacementof porphyry granitoids and the Mo mineralization corre-spond with the large magmatic event. The two porphyrygranitoids also have the (high-K) calc-alkaline chemistry,enabling us to conclude that the origin of the Taolaituodeposit was linked to the strong folding and thrusting, thegeodynamic regime of which was associated with continu-ous subsidence of oceanic slab and subsequently the magmasource region underwent metasomatism and concentration ofancient subducted oceanic slab fluids after the closure of thePalaeo-Asian Ocean. Our geochemical studies indicate thatthe host granitoids in the Taolaituo Mo deposit are A-typegranite, formed in an extensional setting (Figs. 7 and 8).The geodynamic scenario proposed for this Early Cretaceousgiant igneous event is that continental breakup and rapidplate motion (including Pacific Plate subduction), resultedin large-scale lithospheric delamination, leading to astheno-sphere upwelling, and subsequent crustal melting in anextensional setting (Wu et al., 2005a; Wu et al., 2014a,b)(Fig. 8).

7. CONCLUSIONS

The Geochemistry data zircon SHRIMP II U–Pb and Re–Osmolybdenite dating of the Taolaituo deposit in eastern InnerMongolia enable us to draw the following conclusions.

(1) Zircon SHRIMP II U–Pb ages indicate that the porphyrygranitoids were intruded at about 130.4 ±1.3Ma and133.0 ± 1.0Ma (related to Taolaituo Mo mineralization).Re–Os dating of five molybdenite samples gives anisochron age of 133.0 ± 0.82Ma. The nearly identicalU–Pb and Re–Os ages suggest that the mineralizationand porphyry alteration followed the intrusive activitywithin a short period of time.

(2) The Re content of molybdenite is similar to that foundin deposits associated with mantle magmatic inputs.This conclusion is supported by δ34 SCDT of sulphides,and these values are interpreted to reflect a deep mag-matic source of the sulphur contained within the oreminerals of the deposit, and the 206Pb/204Pb, 207Pb/204Pband 208Pb/204Pb ratios are broadly consistent with thisinterpretation. Young accreted materials and enrichedcontinental lithospheric mantle were the dominantsources of Tailaituo Early Cretaceous plutonic rocks.

(3) Intrusive activity and Mo mineralization occurred contem-poraneously with the tectonic and magmatic events duringthe Early Cretaceous tectonothermal event that affected thisregion during an extensional regime. Formation of theEarly Cretaceous Tailaituo and the Early CretaceousA-type granitoids are related to extension followinglithospheric delamination in eastern China associated withsubduction of the Izanagi Plate. The formation of these de-posits coincides with lithospheric thinning, which wascaused by delamination and subsequent upwelling of theasthenosphere under extensional tectonic regime in NEChina. The geodynamic setting for the geological processesshould be linked to the subduction of the Izanagi Platebeneath the Eurasian Plate during the Early Cretaceous.

ACKNOWLEDGEMENTS

We sincerely thank the editor Professor M. Santosh andanonymous reviewer for comments that improved the finalversion of this paper. This work was supported by the ChinaUniversity of Geosciences (Beijing) and was generouslysupported by 1 :50,000 Regional Geological Survey Pro-gram in Inner Mongolia (grant number 1212011120700);Comparative study of the deep structure and mineralizationconditions in eastern section of the Sino-Mongolian border(grant number 1212011085490); and 1 :50,000 RegionalGeological Survey Program in Qilian area (grant number1212011121188).

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