U–Pb geochronology, geochemistry, and H–O–S–Pb isotopic compositions of the Leqingla and Xin'gaguo skarn Pb–Zn polymetallic deposits, Tibet, China

Journal of Asian Earth Sciences 115 (2016) 80–96

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U–Pb geochronology, geochemistry, and H–O–S–Pb isotopic compositions of the Leqingla and Xin’gaguo skarn Pb–Zn polymetallic deposits, Tibet, China Liqiang Wang a,b,⇑, Wenbin Cheng c, Juxing Tang a, Haoran Kang a, Yan Zhang d, Zhuang Li c a

MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China School of Earth Sciences and Resources, China University of Geosciences Beijing, Beijing 100083, China Chengdu University of Technology, Chengdu 610059, China d Key Laboratory of Gold Mineralization Processes and Resource Utilization Subordinated to the Ministry of Land and Resources, Jinan 250013, China b c

a r t i c l e

i n f o

Article history: Received 11 May 2015 Received in revised form 13 August 2015 Accepted 14 September 2015 Available online 25 September 2015 Keywords: Geochronology Geochemistry Isotopic compositions Ore-forming fluids and metals Leqingla Xin’gaguo Gangdese

a b s t r a c t The Leqingla and Xin’gaguo deposits are two representative skarn Pb–Zn polymetallic deposits of the Gangdese Pb–Zn polymetallic belt, Tibet, China. LA-ICP-MS zircon U–Pb dating of the mineralizationrelated biotite granites from both the Leqingla and Xin’gaguo deposits yielded weighted mean ages of 60.8 Ma and 56.5 Ma, respectively, which can be inferred as their mineralization ages. The Leqingla biotite granite is characterized by high Al2O3, total Fe, Na2O, and low K2O. In comparison, the Xin’gaguo biotite granite is characterized by relative higher K2O but lower Al2O3, total Fe, and Na2O. Geochemical and mineralogical characteristics indicate that the Leqingla and Xin’gaguo biotite granites are calc-alkaline I-type granite and High K calc-alkaline I-type granite, respectively. Both the Leqingla and Xin’gaguo biotite granites are enrichment in LREE and LILEs and depletion in HFSEs, and they were formed at the India–Asia collision stage. d18O and dD values for the Leqingla and Xin’gaguo deposits are 8.8‰ to 5.3‰ and 140.4‰ to 90.1‰, 4.5‰ to 7.0‰ and 117.3‰ to 81.0‰, respectively, indicating magma fluids mixed with meteoric water in ore-forming fluids. d34S values ( 11.6‰ to 0.3‰) of ore sulfides from the Leqingla deposit show characteristics of biogenetic sulfur isotope compositions, suggesting sulfur for the Leqingla deposit were sourced from wall rocks of the Mengla and Luobadui Formation, which are rich in organic materials. d34S values of ore sulfides from the Xin’gaguo deposits show bimodal distribution ( 5.0‰ to 1.6‰ and 1.6–2.1‰), indicating sulfur in the Xin’gaguo deposit were derived from both wall rocks and magma. In the Leqingla deposit, most ore sulfides have the similar Pb isotopic compositions with that of the mineralization-related biotite granite, suggesting the biotite granite supplied most of the ore-forming metals. Pb isotopic compositions of ore sulfides and Hf isotopic compositions of biotite granite show that the majority of ore-forming metals are derived from mantle components of partial melting of the Neo-Tethys Ocean slab, with some upper crust materials of the Lhasa terrane. Pb isotopic compositions of ore sulfides from the Xin’gaguo deposit are similar to that of the Leqingla deposit, indicating they have the similar sources of ore-forming metals. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction The Gangdese metallogenic belt within the Lhasa terrane is one of the most important metallogenic belts in China. In recent decades, a large number of porphyry Cu and porphyry Cu-(Mo) deposits have been discovered in the southern of the Gangdese, ⇑ Corresponding author at: MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China. E-mail address: [email protected] (L. Wang). http://dx.doi.org/10.1016/j.jseaes.2015.09.018 1367-9120/Ó 2015 Elsevier Ltd. All rights reserved.

such as the Qulong Cu-(Mo) deposit, the Jiama Cu-(Mo) deposit, the Tinggong Cu deposit, the Chongjiang Cu deposit, the Zhu’nuo Cu deposit, and the Jiru Cu deposit. These deposits constitute the Gangdese porphyry copper belt (GPCB) (Fig. 1). Lately, some skarn Pb–Zn polymetallic deposits were discovered immediately north of the GPCB (Fig. 1), which have constituted the skarn Pb–Zn polymetallic belt in the Gangdese region. The Leqingla and adjacent Xin’gaguo deposits are two representative deposits in the skarn Pb–Zn polymetallic belt (Fig. 1). The Leqingla deposit was discovered in 2005, with proven 408,000 t Zn, 145,000 t Pb, 8,090,000 t TFe, and 3200 t Cu, at an average grade of 5.71% Zn, 2.03% Pb,

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Fig. 1. Simplified geologic map of the Gangdese metallogenic belt showing major porphyry Cu–Mo deposits and skarn Pb–Zn deposits (modified after Zhu et al. (2011) and Wang et al. (2015a,b)). The numbers denoting the porphyry deposits are as follows: 1 – Tangbula; 2 – Sharang; 3 – Chongmuda; 4 – Bangpu; 5 – Chengba; 6 – Jiama; 7 – Qulong; 8 – Lakang’e; 9 – Dabu; 10 – Tinggong; 11 – Chongjiang; 12 – Jiru; 13 – Xiongcun; 14 – Zhu’nuo. The numbers denoting the skarn deposits are as follows: 1 – Yaguila; 2 – Dongzhongla; 3 – Dongzhongsongduo; 4 – Mengya’a; 5 – Longmala; 6 – Lawu; 7 – Hahaigang; 8 – Jialapu; 9 – Lietinggang; 10 – Narusongduo.

56.27% TFe, and 0.41% Cu (Liu, 2008; Zhang et al., 2008). The Xin’gaguo deposit was discovered in 2006, with proven 63,000 t Zn at 5.55%, and 37,000 t Pb at 3.49% (Cheng, 2011). Detailed geological mapping suggests that mineralization in the Leqingla and Xin’gaguo deposits are similar. Mineralization in the two deposits were caused by biotite granite intrusions. Some basic geological studies and isotope chemistry of the Leqingla deposit have been reported in Chinese (Fan et al., 2007; Zhang et al., 2008, 2012; Fei, 2014). In comparison, almost no researches on the Xin’gaguo deposit have been reported. Mineralization ages and geologic setting of both deposits, chemistry of the related intrusions, and origin of ore-forming fluids and metals are unclear as yet. Therefore, we present new zircon U–Pb, and whole rock chemistry data of biotite granites for both the Leqingla and Xin’gaguo deposits and H–O–S–Pb data of the Xin’gaguo deposit and Hf isotope composition of the Leqingla biotite granite. Combined with previously published isotope data of the Leqingla deposit, we provide insights into the formation of these two deposits in this paper. 2. Geological setting and metallogenic events The Lhasa terrane, constrained by the Bangong–Nujiang suture zone in the north and Indus–Yarlung-suture zone in the south, can be divided into northern, central, and southern subterranes (Zhu et al., 2011). The Leqingla deposit is located in the central Lhasa subterrane, while the Xin’gaguo deposit is located in the southern margin of the central Lhasa subterrane (Fig. 1). The Nyainqêntanglha Group as the basement in the central Lhasa subterrane consists mainly amphibolite facies (and, locally, granulite facies) metamorphic rocks, such as orthogneiss, schist, amphibolite, and marble (Allègre et al., 1984; Pan et al., 2004; Zhu et al., 2013), with ages of 748–690 Ma (Hu et al., 2005; Zhang et al., 2010; Dong et al., 2011). The basement is covered with widespread Permo-Carboniferous sedimentary rocks containing continental arc volcanic rocks, and abundant glacial-marine diamictites (Zhu et al., 2013). The Jurassic–Lower Cretaceous sedimentary rocks with abundant volcanic rocks and

the Paleocene–Eocene Linzizong volcanic succession are also the important part of the basement sedimentary cover (Pan et al., 2004, 2006; Zhu et al., 2010, 2013). The Lhasa terrane underwent complex tectono-magmatic evolutions of northward subduction of the Neo-Tethys Ocean, collision of India–Asia continents, and E–W extension of the Lhasa terrane. In Late Triassic–Jurassic or earlier, northward subduction of the Neo-Tethys Ocean has caused widespread volcanic rocks and granitoid intrusions along the southern margin of the southern Lhasa subterrane (Chu et al., 2006; Zhu et al., 2008; Ji et al., 2009a). Metallogenic event related to the northward subduction of the Neo-Tethys Ocean is the Xiongcun porphyry Cu–Au mineralization (Lang et al., 2014; Tang et al., 2015). After closure of the Neo-Tethys Ocean, continental collision of India–Asia initiated at the early Paleocene (65 Ma) (Yin and Harrison, 2000; Mo et al., 2003, 2007). Initiation of the India–Asia collision has induced the Gangdese granitoid batholiths of Paleocene (Chu et al., 2006), the widespread Linzizong volcanic succession (Mo et al., 2007), Paleocene–Eocene granitoids (Li et al., 2014; Wang et al., 2015b) and porphyries (Gao et al., 2012; Huang et al., 2012; Ji et al., 2012; Zhao et al., 2014; Zheng et al., 2014). Several porphyry- and skarn-type deposit related to the India–Asia collision have been recognized, including the Sharang porphyry Mo deposit (Zhao et al., 2014), the Jiru porphyry Cu–Mo deposit (Zheng et al., 2014), the Yaguila skarn Pb–Zn–Ag deposit (Gao et al., 2011), the Narusongduo skarn Pb–Zn–Ag deposit (Ji et al., 2012), the Chagele skarn Pb–Zn deposit (Gao et al., 2012), the Hahaigang skarn Pb–Zn–W–Mo deposit (Li et al., 2014), the Longmala skarn Pb–Zn deposit, the Mengya’a skarn Pb–Zn deposit (Wang et al., 2015b), and the Leqingla and Xin’gaguo Pb–Zn deposits studied in this article. The E–W crustal extension of the Lhasa terrane during the Miocene produced NS-striking normal faulting systems and induced the Miocene potassic calc-alkaline magmas, ultra-potassic magmas, and potassic Cu-bearing porphyry intrusions (Miller et al., 1999; Hou et al., 2009). The Gangdese Porphyry Copper Belt is a Miocene metallogenic belt which formed on the geological setting of the E–W extension of the Lhasa terrane (Hou et al., 2009).

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3. Ore deposit geology 3.1. Leqingla deposit The strata exposed are mainly the Middle Permian Luobadui Formation, the Upper Permian Mengla Formation, the Upper Triassic to Lower Jurassic Jialapu Formation, and the Eocene Nianbo Formation (Fig. 2a). The Luobadui Formation is exposed in the southern of the deposit, containing andesite, tuff, and limestone. The Mengla Formation hosting most of the orebodies outcrops widely in the central-southern and northern of the deposit, including sandstone, mudstone, and limestone. Rocks of the Jialapu Formation exposed in the central of the deposit, mainly consist of sandstone, siltstone, and mudstone. The Nianbo Formation is exposed in the northwestern part, and mainly consists of

pyroclastic rocks. The main structures in the Leqingla deposit comprise E-striking and NW-striking faults. The Mengla and Jialapu Formations were intruded by the biotite granite and diorite porphyry. The biotite granite has caused the skarn and mineralization. Detailed descriptions of the biotite granite are included in the Section 4 of this paper. Skarn (diopside, actinolite, epidote, garnet, and chlorite) is the most important wall-rock alteration in the Leqingla deposit, followed by silicification, and carbonate. Skarn is present at the contact between the biotite granite and the limestone of the Mengla Formation. The actinolite, epidote and chlorite alteration is closely related to magnetite mineralization, whereas sphalerite and galena mineralization is associated with silicification. The Leqingla deposit consists of six Pb–Zn polymetallic orebodies and four iron orebodies. Most of the orebodies are stratiform and lense-like,

Fig. 2. Simplified geologic map (a) and cross-section of the Leqingla Pb–Zn–Fe deposit and (b) (modified after Zhang et al. (2012)).

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occurred in the skarn of the Mengla and Luobadui Formations surrounding the biotite granite (Fig. 2a and b). The iron ores may be massive, disseminated, banded, and brecciated, and the massive ores (Fig. 3a) comprise most of the iron resource in the Leqingla deposit. Ore minerals of iron orebodies are dominantly magnetite, with skarn gangue minerals, such as garnet, diopside, actinolite, and epidote (Fig. 3e and f). The Pb–Zn polymetallic ore textures are mainly disseminated, banded and massive (Fig. 3b–d). Primary ore minerals are sphalerite, galena, and chalcopyrite, with minor pyrite and pyrrhotite (Fig. 3g–i). Gangue minerals are quartz, calcite, diopside, actinolite, epidote, and chlorite (Fig. 3b–d). Based on mineral assemblages, wall-rock alteration, ore textures, paragenetic sequence, cross-cutting relationships of ore veins, the ore-forming process can be divided into four stages: Stage I is a progade skarn stage that is characterized by garnet and diopside. There are little ore minerals at this stage. Stage II is a retrograde stage that is marked by formation of assemblages of actinolite–magnetite–epidote–chlorite (Fig. 3a, e, and f). This stage represents the main stage of magnetite mineralization. Stage III is a quartz-sulfides stage that is characterized by formation of sulfides assemblages of sphalerite–galena–chalcopyrite–pyrite–pyrrhotite and lots of quartz. This is the main stage of sphalerite, galena,

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and chalcopyrite mineralization. At this stage, skarn minerals were always eroded and replaced by these sulfides and quartz (Fig. 3b and d). Stage IV is a carbonate stage, with amounts of calcite veins formed. These calcite veins could crosscut the sulfides (Fig. 3c and i). This stage is also associated with minor sphalerite, galena, and pyrite. 3.2. Xin’gaguo deposit The exposed stratigraphic units are the Lower Cretaceous Takena Formation consisting of sandstone, siltstone, and limestone, the Upper Cretaceous Shexing Formation consisting of mudstone, siltstone, and sandstone, and the Eocene Dianzhong Formation containing tuff only (Fig. 4a). The Takena Formation is enriched in organic matter and hosts most of the Pb–Zn polymetallic orebodies and iron orebodies. The Xin’gaguo deposit is characterized by faults that strike northwest, northeast, and nearly south to north. The Pb–Zn polymetallic mineralization could be observed in some of the NW-striking faults, which could be broken by the NE- and SN-striking faults. Intrusions in the Xin’gaguo deposits include the diorite and the biotite granite. Field investigations demonstrate that skarn and magnetite mineralization developed

Fig. 3. Photographs and photomicrographs showing ore textures, ore minerals, and alteration minerals of different mineralization stages for the Leqingla Pb–Zn–Fe deposits. (a) Massive iron ore with fine grained magnetite; (b) disseminated lead-zinc ore with chalcopyrite, pyrrhotite, actinolite, diopside, epidote, and chlorite; (c and d) lead-zinc ore with calcite and quartz veins; (e and f) diopside, actinolite at stage II and they could be cross-cut and replaced by magnetite and quarzt of stage III; (g–i) major minerals assemblages of stage III, ore minerals are generally sphalerite, galena, chalcopyrite, pyrite, and pyrrhotite and the gangue mineral is usually quartz. Mt – magnetite; Po – pyrrhotite; Sp – sphalerite; Cp – chalcopyrite; Gn – galena; Act – actinolite; Di – diopside; Epi – epidote; Cc – calcite; Qtz – quartz.

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Fig. 4. Simplified geologic map (a) and cross-section of No. 6 prospecting line (b) of the Xin’gaguo Pb–Zn deposit (modified after Cheng (2011)).

very well on the contact zone between the limestone of the Takena Formation and the biotite granite, indicating that the biotite granite was the ore-forming intrusions. Detailed descriptions of the biotite granite are included in the Section 4 of this paper. The hydrothermal alteration of the Xin’gaguo deposit is similar to the Leqingla deposit. They mainly include the skarn (garnet, diopside, actinolite, epidote, and chlorite), silicification, and carbonate alteration. The alteration is zoned from the biotite granite to wall rocks. According to the mineral assemblages and alteration intensity, the alteration could be divided into three zones: (1) garnet–diopside skarn zone; (2) actinolite–epidote–chlorite skarn zone; (3) silicification–carbonate zone. The Xin’gaguo deposit consists of twenty Pb–Zn polymetallic and iron orebodies. The iron orebodies were located along the contacts between the Takena Formation and the biotite granite intrusions (Fig. 4a), with lenticular shape. However, the iron orebodies are small with low ore grade, and they are not economic. The Pb–Zn polymetallic orebodies were always lenticular, stratiform and veins (Fig. 4b). The iron ores are always disseminated and massive (Fig. 5a), while the Pb–Zn polymetallic ores have massive, disseminated, banded structures (Fig. 5b–d). Ore minerals of the iron ores are mainly magnetite, with minor hematite (Fig. 5e). The major ore minerals in the Pb–Zn polymetallic ores are sphalerite, galena, pyrite, and chalcopyrite, with minor arsenopyrite, pyrrhotite, and marcasite (Fig. 5f–i). The primary gangue and alteration minerals are garnet, diopside, actinolite, epidote, chlorite, quartz, and calcite. Similar to the Leqingla deposit, ore-forming process in the Xin’gaguo deposit could be also divided into four stages: (1) the prograde skarn stage; (2) the retrograde stage representing the main stage of magnetite mineralization; (3) quartz-sulfides

stage representing the main stage of Pb–Zn polymetallic mineralization; (4) carbonate stage. 4. Sampling and analytical methods 4.1. Zircon U–Pb geochronology and in situ Hf isotope analyses Samples for U–Pb dating and Hf isotope analyses were collected from biotite granite outcrops in both the Leqingla (LQLYT-1) and Xin’gaguo (XGGYT-7) deposits. Biotite granites in these two deposits are generally gray-white with light pink in color (Fig. 6a and d). Mineral compositions of both the Leqingla and Xin’gaguo biotite granite are similar, which contain quartz (23%), plagioclase (40%), alkali feldspar (22%), biotite (12%), and amphibole (2%), as well as accessory minerals (e.g., magnetite, zircon) (1%) (Fig. 6b–c, e–f). Mineral grains of the Leqingla biotite granite are relatively coarser than that of the Xin’gaguo biotite granite (Fig. 6a–f). Zircon grains were separated by heavy liquids and magnetic techniques and then purified by hand-picking under a binocular microscope. Representative zircon grains were mounted in an epoxy resin and polished down to expose the grain center. Before isotopic analyses their internal structures were examined by cathodoluminescence (CL). Zircon U–Pb dating was conducted using a Neptune multi-collector inductively coupled plasma mass spectrometer equipped with a New Wave 193 nm laser sampler at the Tianjin Institute of Geology and Mineral Resource, China Geological Survey. Detailed analytical procedures are described in Geng et al. (2012). The data processing was conducted using ICPMSDataCal software (Liu et al., 2010) and IsoplotEx 3 software

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Fig. 5. Photographs and photomicrographs showing ore textures and ore minerals of the Xin’gaguo Pb–Zn deposit. (a) Massive magnetite ore with a little hematite; (b) massive lead-zinc ore; (c) disseminated lead-zinc ore, sphalerite and galena cross-cut and replace garnet skarn; (d) banned lead-zinc ore, sphalerite and galena replace the actinotite–epidote–chlorite skarn; (e) main minerals of iron ores are magnetite and a little hematite and they could be cross-cut by pyrite of mineralization stage III; (f–i) ore minerals at mineralization III are mainly sphalerite, and galena, with some chalcopyrite, pyrite, pyrrhotite, marcasite, arsenopyrite. Mt – magnetite; Ht – hematite; Po – pyrrhotite; Sp – sphalerite; Cp – chalcopyrite; Gn – galena; Mar – marcasite; Apy – arsenopyrite; Grt – garnet; Act – actinolite; Di – diopside; Epi – epidote; Cc – calcite; Qtz – quartz.

(Ludwig, 2003). Common Pb was corrected by following the method of Andersen (2002). In situ Hf isotopic analyses were conducted on the same zircon grains that were analyzed for U–Pb dating. The Hf isotopic compositions were determined using a Neptune MC-ICP-MS equipped with a Newwave UP213 laser ablation system at MLR key laboratory of Metallogeny and Mineral Assessment of Institute of Mineral Resources Chinese Academy of Geological Sciences. Detailed analytical procedures and data acquisition processes were described by Wu et al. (2006). 4.2. Major and trace elements analyses Samples of the Leqingla and Xin’gaguo biotite granite were collected from open pits and outcrops. All the biotite granite samples collected were fresh. Whole rock major and trace elements compositions were determined at Analytical Laboratory Beijing Research Institute of Uranium Geology. Major elements analyses were conducted using a Philips PW2404 XRF with testing precision greater than 1%. Trace elements analyses were performed using a Finnigan MAT Element XR ICP-MS, with RSD (10 min) <1% and RSD (4 h) <5%.

4.3. H–O–S–Pb isotope analyses Two quartz samples from the sphalerite–galena ores of the quartz-sulfides mineralization stage (stage 3) and one quartz and two calcite samples of the post-ore stage (stage 4) from the Xin’gaguo deposit were selected for hydrogen and oxygen analyses. Hydrogen and oxygen isotope analyses were conducted at Analytical Laboratory Beijing Research Institute of Uranium Geology. The hydrogen and oxygen isotopic compositions were determined using a Finnigan-MAT 253 mass spectrometer. The analytical precisions are better than ±0.2‰ for d18O and ±2‰ for dD. The values of d18O and dD are reported relative to Vienna standard mean ocean water (V-SMOW). Nine sulfide samples from the sphalerite–galena ores were chosen for sulfur and lead isotope analyses. Sulfur and lead isotope analyses were also conducted at Analytical Laboratory Beijing Research Institute of Uranium Geology. The sulfur isotopic compositions were determined using a Finnigan MAT 251 mass spectrometer. The precision for d34S is better than ±0.2‰, and the data are reported relative to Vienna Canon Diablo Troilite (VCDT) sulfide. For lead isotope analyses, samples were dissolved in a mixed solution of hydrofluoric acid and perchloric acid, followed

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Fig. 6. Photographs and photomicrographs showing features of the Leqingla (a–c) and Xin’gaguo (d–f) biotite granites. (a) Gray-white biotite granite from Leqingla deposit; (b and c) mineral compositions of the Leqingla biotite granite; (d) biotite granite from the Xin’gaguo deposit; (e and f) the Xin’gaguo biotite have the similar mineral compositions with the Leqingla biotite granite, but mineral grains are more finer. Pl – plagioclase; Kf – potassium feldspar; Bt – biotite; Qtz – quartz; Ser – sericite; Mt – magnetite.

by basic anion exchange resin to purify Pb. Next, the samples were analyzed using an ISOPROBE-T Thermal Ionization Mass Spectrometer instrument. The data of the Pb isotopic composition were provided in the form of (value ±2r). The precisions for 204Pb/206Pb and 208 Pb/206Pb are better than 0.005%.

(Wu and Zheng, 2004). Three discordant data spots (spots 9, 10 and 12) were excluded. The remaining 14 spots have 206Pb/238U ages ranging from 53.6 ± 0.8 to 60.6 ± 1.3 Ma, which yield a weighted mean 206Pb/238U age of 56.5 ± 1.3 Ma with an MSWD of 5.4 at the 95% confidence level (Fig. 8b).

5. Results

5.2. Major and trace elements

5.1. Zircon U–Pb ages

Major and trace elements contents for biotite granites from both the Leqingla and Xin’gaguo deposits are listed in Table 2. SiO2 contents of the Leqingla biotite granite range from 65.51 to 67.82 wt.%. The Leqingla biotite granite samples are characterized by high Al2O3 (16.83–17.92 wt.%), total Fe (2.74–4.23 wt.%), and Na2O (4.45–5.61 wt.%), but low K2O (1.67–2.35 wt.%). Geochemically, the rocks are calc-alkaline (Fig. 9a), and weak to strong peraluminous, with an alumina saturation index (ASI; Al2O3/ (CaO + Na2O + K2O)) of 1.06–1.18 (Fig. 9b). In contrast, the Xin’gaguo biotite granite samples are high-K, calc-alkaline (Fig. 9a), and metaluminous, with ASI values of 0.93–1.00 (Fig. 9b). Compared with the Leqingla biotite granite, rocks of the Xin’gaguo biotite granite have relatively higher SiO2 (68.18–69.42 wt.%) and K2O (3.02–3.40 wt.%), but lower Al2O3 (14.57–15.02 wt.%), total Fe (2.94–3.66 wt.%), and Na2O (3.75–4.28 wt.%). K2O/Na2O ratios for the Leqingla and Xin’gaguo biotite granites are 0.30–0.52 and 0.71–0.86, respectively. The Leqingla biotite granite samples have total rare earth element (RREE) concentrations of 70.43–122.99  10 6, LREE/HREE of 3.58–5.36, with (La/Yb)N of 3.07–5.96. The chondritenormalized REE patterns of these rocks (Fig. 10a) shows an obvious light REE enrichment, with marked positive Eu anomalies (dEu = 1.28–2.50). In the primitive mantle-normalized spider diagram (Fig. 10b), large ion lithophile elements (LILE; e.g., Rb, Th, K, and Sr) are enriched, while high field strength elements (HFSE; Ta, Nb, P, and Ti) are relatively depleted. Positive Eu and Sr anomalies indicate that materials from melting of plagioclase have been

Twenty-five and seventeen analytical data obtained from the Leqingla and Xin’gaguo biotite granite samples, respectively, are listed in Table 1. The CL images show that zircon grains from the Leqingla biotite granite are euhedral and prismatic, with crystal lengths from 110 to 250 lm and length-to-width ratios from 2:1 to 4.5:1. Zircon grains are mainly colorless and transparent, and show oscillatory zoning (Fig. 7a). U and Pb contents of the analyzed zircons are 109–475 ppm and 270–625 ppm, respectively, with Th/U ratios of 0.4–0.8, indicating a magmatic origin (Wu and Zheng, 2004). The 25 spots have 206Pb/238U ages varying from 59.0 ± 0.7 to 63.8 ± 0.6 Ma. These age data could be divided into two groups. The first group of data containing spots 2, 4, 14, 20, 22, 24 and 25 show a weighted mean age of 63.1 ± 0.4 Ma (n = 7, MSWD = 0.7). The second group yield a weighted mean age of 60.8 ± 0.4 Ma (n = 18, MSWD = 1.9) (Fig. 8a). The older age of 63.1 ± 0.4 Ma could represent the time of crystallization in the deep magma chamber, while the younger age of 60.8 ± 0.4 Ma reflects the emplacement time of the biotite granite. Zircon grains from the Xin’gaguo biotite granite are subhedral pyramids and prisms, with crystal lengths from 100 to 300 lm and length-to-width ratios from 1:1 to 4:1. The CL images reveal that zircon grains have simple structures and oscillatory zoning (Fig. 7b). U and Pb contents are 87–558 ppm and 161–484 ppm, respectively, with Th/U ratios 0.5–1.2, indicating magmatic origin

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L. Wang et al. / Journal of Asian Earth Sciences 115 (2016) 80–96 Table 1 Isotopic data of U–Pb age determinations on zircon of biotite granites for the Leqingla (LQLYT-1) and Xin’gaguo (XGGYT-7) deposit. Sample no.

Element (ppm)

LQLYT-1

Th

U

01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

117 173 156 138 217 151 267 255 237 278 275 131 254 109 222 364 206 243 158 392 337 298 475 183 195

291 343 336 318 405 320 436 385 414 451 417 291 305 270 349 510 346 446 316 573 485 444 625 287 340

0.40 0.50 0.46 0.43 0.54 0.47 0.61 0.66 0.57 0.62 0.66 0.45 0.83 0.40 0.64 0.71 0.59 0.55 0.50 0.68 0.70 0.67 0.76 0.64 0.57

XGGYT-7 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17

86.9 331 158 270 165 124 558 298 125 277 218 101 167 383 110 123 233

161 335 286 277 258 219 484 363 182 327 290 195 293 348 181 163 285

0.5411 0.9883 0.5533 0.9746 0.6386 0.5639 1.1528 0.8203 0.6887 0.8471 0.7518 0.5182 0.5717 1.0992 0.6092 0.7513 0.8182

Th/U

Isotope ratio 206

Pb/238U

Age (Ma) 1r

207

0.0097 0.0098 0.0095 0.0099 0.0096 0.0094 0.0096 0.0093 0.0096 0.0093 0.0095 0.0094 0.0094 0.0098 0.0096 0.0092 0.0096 0.0095 0.0096 0.0099 0.0095 0.0098 0.0094 0.0098 0.0099

0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0002 0.0001

0.0093 0.0085 0.0089 0.0085 0.0087 0.0091 0.0086 0.0084 0.0098 0.0087 0.0091 0.0094 0.0091 0.0089 0.0094 0.0094 0.0085

0.0003 0.0001 0.0001 0.0001 0.0001 0.0002 0.0001 0.0001 0.0002 0.0001 0.0002 0.0002 0.0002 0.0001 0.0002 0.0002 0.0001

Pb/235U

1r

207

0.0649 0.0694 0.0628 0.0848 0.0730 0.0655 0.0701 0.0692 0.0628 0.0623 0.0638 0.0739 0.0686 0.0682 0.0770 0.0785 0.0839 0.0792 0.0750 0.0656 0.0741 0.0644 0.0716 0.0814 0.0737

0.0113 0.0041 0.0080 0.0081 0.0050 0.0041 0.0045 0.0058 0.0054 0.0049 0.0068 0.0088 0.0050 0.0120 0.0056 0.0152 0.0057 0.0053 0.0099 0.0044 0.0048 0.0075 0.0054 0.0131 0.0075

0.0671 0.0597 0.0712 0.0627 0.0568 0.0609 0.0582 0.0541 0.1499 0.1207 0.0636 0.1318 0.0606 0.0602 0.0746 0.0670 0.0704

0.0074 0.0041 0.0039 0.0037 0.0050 0.0047 0.0035 0.0034 0.0134 0.0077 0.0037 0.0066 0.0039 0.0037 0.0059 0.0054 0.0051

Pb/206Pb

1r

206

0.0487 0.0516 0.0481 0.0619 0.0551 0.0506 0.0530 0.0537 0.0477 0.0487 0.0488 0.0571 0.0531 0.0506 0.0584 0.0619 0.0635 0.0603 0.0565 0.0480 0.0563 0.0478 0.0551 0.0600 0.0542

0.0086 0.0031 0.0063 0.0061 0.0038 0.0032 0.0034 0.0045 0.0041 0.0038 0.0052 0.0069 0.0036 0.0092 0.0042 0.0118 0.0043 0.0042 0.0075 0.0032 0.0037 0.0057 0.0038 0.0097 0.0057

0.0573 0.0521 0.0585 0.0527 0.0482 0.0500 0.0494 0.0479 0.1076 0.1020 0.0521 0.1049 0.0482 0.0492 0.0595 0.0538 0.0600

0.0078 0.0036 0.0033 0.0031 0.0044 0.0039 0.0030 0.0032 0.0088 0.0066 0.0033 0.0058 0.0031 0.0030 0.0049 0.0049 0.0043

Pb/238U

1r

207

61.9 62.6 60.7 63.8 61.6 60.2 61.6 60.0 61.3 59.6 60.8 60.3 60.2 62.8 61.3 59.0 61.5 61.1 61.8 63.5 61.2 62.7 60.5 63.1 63.2

0.7 0.5 0.6 0.6 0.5 0.6 0.5 0.7 0.6 0.5 0.4 0.8 0.9 0.6 0.5 0.7 0.5 0.5 0.6 0.5 0.4 0.5 0.4 1.1 0.6

59.7 54.4 57.2 54.6 56.0 58.4 55.1 53.6 62.9 55.8 58.4 60.3 58.6 57.3 60.6 60.6 54.8

1.7 0.8 0.9 0.9 0.9 1.0 0.9 0.8 1.2 0.9 1.1 1.0 1.0 0.8 1.2 1.3 0.9

Pb/235U

1r

207

Pb/206Pb

64 124 62 92 118 113 88 96 94 61 63 91 225 67 94 77 100 96 73 64 73 63 70 107 82

11 7 8 9 8 7 6 8 8 5 7 11 16 12 7 15 7 6 10 4 5 7 5 17 8

63 1552 106 904 1485 1442 870 1121 1027 133 141 1002 2762 222 1031 672 1161 1081 471 101 466 89 417 1151 660

419 114 311 202 130 121 134 168 174 185 252 244 112 422 146 409 135 138 295 156 144 284 155 320 226

65.9 58.9 69.9 61.7 56.1 60.1 57.4 53.5 142 116 62.6 126 59.7 59.4 73.1 65.8 69.1

7.1 3.9 3.7 3.5 4.8 4.5 3.3 3.3 12 7 3.6 6 3.7 3.5 5.5 5.1 4.8

502 287 550 317 109 195 169 94.5 1761 1661 287 1722 109 167 583 361 606

302 159 116 140 213 16 141 161.1 49 119 117 102 144 144 180 204 156

1r

Fig. 7. Cathodoluminescence (CL) images of zircons from the Leqingla (a) and Xin’gaguo (b) biotite granites. The solid line circles represent U–Pb age analysis spots and the dashed line circles represent Hf isotopes analysis spots.

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L. Wang et al. / Journal of Asian Earth Sciences 115 (2016) 80–96

Fig. 8. LA-ICP-MS zircon U–Pb concordia diagrams for biotite granites from the Leqingla (a) and Xin’gaguo (b) deposits.

Table 2 Major elements (wt.%), trace elements (10 Sample no.

SiO2 Al2O3 Fe2O3 FeO CaO MgO K2O Na2O MnO TiO2 P2O5 LOI Total K2O + Na2O K2O/Na2O A/CNK A/NK R1 R2 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y RREE LREE/HREE (La/Yb)N dEu Rb Th U Pb Ba Zr Hf Nb Ta Sr

6

) compositions of biotite granites from the Leqingla (LQL) and Xin’gaguo (XGG) deposits.

Leqingla biotite granite

Xin’gaguo biotite granite

LYT-2

LYT-3

LYT-4

LYT-8

XGGYT-7

XGGYT-9

XGGYT-11

XGGYT-12

66.56 16.83 1.16 2.99 2.65 0.78 1.67 5.56 0.06 0.46 0.11 1.16 99.98 7.23 0.30 1.07 1.54 1838 641 16.1 29.5 3.71 15.6 3.53 1.84 4.05 0.801 5.41 1.17 3.22 0.595 3.76 0.615 34.3 89.90 3.58 3.07 1.49 86.4 8.49 2.05 25.7 454 169 5.14 10.6 0.729 447

67.82 17.42 0.77 1.97 2.15 0.80 2.35 5.03 0.11 0.51 0.07 0.97 99.96 7.38 0.47 1.18 1.61 2027 606 14.1 24.6 3.04 12.3 2.68 2.11 2.48 0.544 3.42 0.614 2.12 0.294 1.86 0.269 18.8 70.43 5.07 5.44 2.50 130 9.77 2.36 54.9 891 210 5.93 12.6 0.748 498

66.11 16.89 0.87 3.36 3.01 0.78 2.04 5.05 0.06 0.47 0.12 1.23 99.98 7.09 0.40 1.06 1.61 1884 678 23.8 44.7 5.54 22.5 4.8 1.96 4.54 0.881 5.31 1.12 3.13 0.589 3.61 0.51 32.5 122.99 5.25 4.73 1.28 105 7.08 1.79 18.2 453 197 5.69 11.1 0.748 406

65.51 17.92 0.42 3.08 2.69 0.81 1.68 5.61 0.08 0.60 0.12 1.45 99.97 7.29 0.30 1.12 1.62 1763 669 19.2 35.4 4.45 18.4 4.16 2.06 3.85 0.778 4.61 0.868 2.41 0.421 2.31 0.371 24.8 99.29 5.36 5.96 1.57 66.3 11.9 1.83 32.3 643 234 6.78 15.8 0.967 389

69.04 14.57 1.32 1.90 2.98 1.18 3.40 3.96 0.06 0.40 0.16 1.01 99.98 7.36 0.86 0.93 1.43 2236 658 30.7 63.4 6.88 26 4.68 1.43 4.39 0.718 4.01 0.755 2.35 0.367 2.47 0.394 23.3 148.54 8.61 8.92 0.96 108 15.9 3.08 12 582 75.3 2.84 7.51 0.63 341

68.18 14.58 1.61 2.05 3.22 1.43 3.06 3.94 0.08 0.46 0.18 1.16 99.95 7.00 0.78 0.93 1.49 2250 697 45.3 86.1 9.02 31.2 5.23 1.39 5.62 0.804 4.15 0.688 2.51 0.347 2.35 0.371 21.3 195.08 10.58 13.83 0.78 101 12.8 2.46 13.7 593 93.4 3.32 7.12 0.60 347

69.42 14.74 1.46 1.5 2.79 1.02 3.18 3.75 0.05 0.38 0.15 1.53 99.97 6.93 0.85 1.00 1.53 2427 639 34.8 65.8 6.9 25.4 3.77 1.24 4.33 0.624 3.1 0.506 1.9 0.265 1.73 0.265 14.9 150.63 10.84 14.43 0.94 91.5 13.3 2.18 12.9 527 94.2 3.19 6.62 0.88 298

68.36 15.02 1.54 1.4 2.82 1.24 3.02 4.28 0.04 0.39 0.16 1.66 99.93 7.30 0.71 0.97 1.46 2214 661 17.2 31.2 3.65 15.1 2.94 1.18 2.31 0.428 2.52 0.47 1.44 0.232 1.51 0.238 26.3 80.42 7.79 8.17 1.38 120 7.21 1.48 12.4 475 42.6 2.00 5.99 0.49 426

L. Wang et al. / Journal of Asian Earth Sciences 115 (2016) 80–96

89

Fig. 9. Geochemical analyses of biotite granites from the Leqingla and Xin’gaguo deposits showing: (a) A/NK vs A/CNK diagram of Maniar and Piccoli (1989), and (b) K2O vs SiO2 diagram of Rollinson (1993).

Fig. 10. Chondrite-normalized REE patterns and primitive mantle normalized trace element diagrams for the biotite granites from the Leqingla (a and b) and Xin’gaguo (c and d) deposits. The values of chondrite and primitive mantle are from Sun and McDonough (1989).

mixed into magma source (Yang et al., 2006). RREE, LREE/HREE, and (La/Yb)N values of the Xin’gaguo biotite granite are 80.42– 195.08  10 6, 7.79–10.84, and 8.17–14.43, respectively. All the samples are enriched in light REE, and most of them have slightly negative Eu anomalies (Fig. 10c). The primitive mantle-normalized spider diagram shows that the Xin’gaguo biotite granite are obvious depletion of HFSE (Nb, Ta, P, and Ti), and enrichment of LILE (Rb, Th, and K) (Fig. 10d).

5.3. Hydrogen-oxygen isotopes Hydrogen and oxygen isotopic compositions of the Xin’gaguo and Leqingla deposits are listed in Table 3. The d18O and dD values of three quartz samples of Xin’gaguo vary from 0.7‰ to 12.1‰ and 117.3‰ to 81.0‰, respectively. The d18O values of ore-forming fluids in quartz samples calculated with the equation 1000 lnaquartz-water = 3.38  106 T 2–3.40

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L. Wang et al. / Journal of Asian Earth Sciences 115 (2016) 80–96

(Clayton et al., 1972) vary from 4.5‰ to 7.0‰. The d18O and dD values of two calcite samples of Xin’gaguo vary from 9.3‰ to 11.4‰ and 103.4‰ to 105.6‰, respectively. The d18O values of ore-forming fluids in calcite samples calculated with the equation 1000 lnacalcite-water = 2.78  106 T 2–2.89 (O’Neil et al., 1969) vary from 1.9‰ to 3.9‰. The d18O values of ore-forming fluids of mineralization stages I, II, III and IV of the Leqingla deposit are 3.4‰, 2.8‰ to 5.3‰, 4.2‰ to -1.4‰, and 8.8‰ to -4.8‰, respectively. The dD values of oreforming fluids from mineralization stages I, II, III and IV are 138.6‰, 140.4‰ to 132.2‰, 139.8‰ to 90.1‰, and 102.0‰ to 97.0‰, respectively.

5.6. Zircon Hf isotope The Lu–Hf isotopic data of zircon grains obtained from the Leqingla biotite granite (LQLYT-1) are listed in Table 6. Nineteen zircon grains have 176Lu/177Hf ratios of 0.001173– 0.003550, with an average value of 0.002123, and 176Hf/177Hf ratios of 0.282799–0.282900, with an average value of 0.282850, yielding calculated eHf (t) values of 2.273–5.723, with an average value of 4.004. 6. Discussion 6.1. Constrain on the mineralization ages

5.4. Sulfur isotopes Sulfur isotopic compositions of the Xin’gaguo deposit together with sulfur isotope data published previously of the Leqingla deposit are presented in Table 4. d34S values of two marcasite samples from the Xin’gaguo deposit range from 2.0‰ to 2.1‰, averaging 2.1‰; two chalcopyrite samples have d34S values from 2.4‰ to 2.1‰, averaging 2.3‰; d34S values of seven sphalerite range from 3.1‰ to 1.9‰, averaging 0.3‰; and d34S values of four galena samples are from 3.9‰ to 5.0‰, with an average value of 4.4‰. d34S value of one pyrrhotite sample from the Leqingla deposit is 0.3‰; d34S values of four pyrite samples vary from 5.9‰ to 2.0‰, averaging 4.5‰; d34S values of eight chalcopyrite range from 8.7‰ to 2.1‰, averaging 5.4‰, d34S values of nine sphalerite samples range from 11.6‰ to 7.2‰, averaging 8.5‰; and d34S values of fourteen galena range from 11.6‰ to 5.6‰, averaging 8.5‰.

No reliable mineralization ages have been reported for both the Leqingla and Xin’gaguo deposits, due to lack of appropriate minerals for metallogenic chronology analyses. Generally, in skarn type ore deposits systems, the emplacement age of the mineralization-related intrusion could constrain the upper limit of the mineralization age (Chen et al., 2014; Liu et al., 2015). The biotite granite crops out close and at the contact of the orebodies and display skarn at their contact in the Leqingla deposit (Fig. 2a and b). The biotite granite is therefore the mineralization-related intrusion of the Leqingla deposit. The mineralization age of the Leqingla deposit should be slightly later than the biotite granite emplacement age. Field geological investigation and drill core logging of the Xin’gaguo deposit show that skarn and Pb–Zn–Fe mineralization occur generally at the contact between the biotite granite and limestone of the Takena Formation (Fig. 3a and b), indicating the biotite granite as the mineralization-related granitoid. The age of the Xin’gaguo mineralization could be therefore inferred from the emplacement age of the biotite granite intrusion.

5.5. Lead isotopes

6.2. Magma genetic types and tectonic setting

Lead isotopic compositions of the Xin’gaguo deposit together with previously published data of the Leqingla deposit are listed in Table 5. 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of eleven ore sulfides from the Xin’gaguo deposit vary from 18.505 to 18.644, 15.561 to 15.671, and 38.504 to 38.951, respectively. 206Pb/204Pb, 207 Pb/204Pb, and 208Pb/204Pb ratios of sixteen ore sulfides from the Leqingla deposit are 18.451–18.671, 15.588–15.708, and 38.463–39.106, respectively.

Two samples of the Leqingla biotite granite have A/CNK values of 1.12 and 1.18, respectively, showing S-type granite affinity (Chappell and White, 2001). However, the Leqingla biotite granite has high Na2O contents (5.03–5.61 wt.%) and low P2O5 contents (0.07–0.12 wt.%), which are obviously different with the S-type granite (Chappell and White, 1974; Chappell, 1999). In Fig. 11, samples data show decrease in P2O5 contents with increasing SiO2 contents. Moreover, Al-rich minerals in S-type granite, such

Table 3 Oxygen and hydrogen isotope compositions for the Leqingla and Xin’gaguo deposit. d18Omineral (‰)

d18Ofluid (‰)

Deposit

Sample

Stage

Mineral

Th (°C)

Leqingla

LQL12-7-4 LQL12-3-7 LQL12-2-1 LQL12-7-8 LQL12-3-3 LQL12-4-3 LQL12-5-11 LQL12-2-3 LQL12-1-1 KL1-1-2 KL1-1-3 KL1-2-4

I II II II III III III III III IV IV IV

Garnet Actinolite Actinolite Epidote Quartz Quartz Quartz Quartz Quartz Quartz Quartz Quartz

286 325 323 286 251 251 251 234 323 174.4 218.4 144.1

3.3 2.4 4.7 6.6 4.7 6.0 5.4 7.1 4.7 7.8 5.8 7.2

3.4 2.8 5.0 5.3 4.2 2.9 3.5 2.6 1.4 5.7 4.8 8.8

138.6 140.4 138.3 132.2 90.1 139.8 136.1 130.7 126.1 97.0 98.0 102.0

Fei (2014)

XGGPD5-8 XGGPD5-9 XGGPD3kd-3 XGGPD2kd-1 XGGPD5kd-1

III III IV IV IV

Quartz Quartz Quartz Calcite Calcite

345.4 355.4 357.8 246.1 243.6

1.2 0.7 12.1 9.3 11.4

4.2 4.5 7.0 1.9 3.9

81.0 92.3 117.3 103.4 105.6

This study

Xin’gaguo

dDfluid (‰)

Reference

Liu (2008)

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L. Wang et al. / Journal of Asian Earth Sciences 115 (2016) 80–96 Table 4 Sulfur isotope compositions of sulfides from the Leqingla and Xin’gaguo deposit. d34S(‰)

Deposit

Sample

Mineral

Leqingla

LD05-1-1 LD05-3-3 LD02-1-2 LD05-3-1 LD07-1 LD08-1 LD02-1-2 LD01-3 LD03-P3 S1 S4 S7 S9 S10 S11 S12 LQL12-1-1 LQL12-2-6

Mineralized limestone Mineralized limestone Galena Galena Galena Galena Sphalerite Sphalerite Sphalerite Galena Galena Galena Galena Galena Galena Galena Sphalerite Sphalerite

ZD1-1 ZD2-2 ZD2-2 ZD2-5 ZD5-4 XGGPD5-4 XGGPD5-7 XGGPD5-3

Marcasite Marcasite Sphalerite Sphalerite Sphalerite Sphalerite Galena Chalcopyrite

Xin’gaguo

9.0 8.6 10.3 11.4 10.8 11.6 8.8 8.0 7.2 5.6 6.0 6.1 6.9 7.3 7.0 7.3 11.6 8.1 2.1 2.0 1.9 1.6 1.8 2.7 4.7 2.1

d34S(‰)

Reference

Sphalerite Sphalerite Sphalerite Galena Chalcopyrite Chalcopyrite Chalcopyrite Chalcopyrite Chalcopyrite Chalcopyrite Chalcopyrite Chalcopyrite Pyrite Pyrite Pyrite Pyrite Pyrrhotite Sphalerite

8.0 7.7 7.3 10.4 5.8 8.7 5.6 2.1 4.3 4.8 5.5 6.1 5.7 2.0 4.4 5.9 0.3 8.4

Fei (2014)

Galena Sphalerite Chalcopyrite Galena Sphalerite Galena Sphalerite

5.0 2.9 2.4 3.9 3.1 3.9 1.6

Reference

Sample

Mineral

Zhang et al. (2008)

LQL12-3-6 LQL12-4-3 LQL12-4-4 LQL12-3-3 LQL12-8-7 LQL12-5-8 LQL12-6-10 LQL12-8-3 LQL12-8-5 LQL12-8-6 LQL12-8-12 LQL12-8-14 LQL12-6-10 LQL12-8-3 LQL12-8-5 LQL12-8-12 LQL12-8-4 LQL12-3-3 XGGPD5-11 XGG-04 XGG-04 XGG-05 XGG-05 XGG-06 XGG-06

Liu (2008)

Fei (2014) This study

This study Zang et al. (2007)

Table 5 Lead isotope compositions of sulfides from the Leqingla and Xin’gaguo deposit. Deposit

Sample

Mineral

206

Leqingla

LD02-1-2 LD05-3-1 LD02-1-2 LD01-3 S1 S4 S7 S9 S10 S11 LQL12-5-8 LQL12-3-3 LQL12-6-10 LQL12-8-5 LQL12-8-5 LQL12-8-12

Galena Galena Sphalerite Sphalerite Galena Galena Galena Galena Galena Galena Chalcopyrite Galena Pyrite Pyrite Chalcopyrite Pyrite

18.575 18.558 18.547 18.553 18.600 18.571 18.572 18.577 18.552 18.561 18.650 18.568 18.659 18.671 18.451 18.650

ZD1-1 ZD2-2 ZD2-2 ZD2-5 ZD5-4 XGGPD5-3 XGGPD5-4 XGGPD5-7 XGGPD5-11 XGG-05 XGG-06

Marcasite Marcasite Sphalerite Sphalerite Sphalerite Chalcopyrite Sphalerite Galena Galena Galena Galena

18.577 18.553 18.563 18.554 18.571 18.644 18.538 18.568 18.578 18.505 18.515

Xin’gaguo

Pb/204Pb

as muscovite and garnet are not observed in the Leqingla biotite granite. These geochemical and mineralogical characteristics above mean that the Leqingla biotite granite could be classified as I-type granite (Chappell and White, 2001). A/CNK values (0.93–1.00) of the Xin’gaguo biotite granite are much lower than 1.1, and P2O5 contents (0.15–0.18 wt.%) are also lower than S-type granite (P2O5 contents >0.20 wt.%; Chappell, 1999). In SiO2–P2O5 diagram (Fig. 11), all samples show negative correlations between SiO2 and P2O5. These geochemical characteristics mentioned above indicate that the Xin’gaguo biotite granite belongs to I-type granite (Chappell and White, 2001).

207

Pb/204Pb

208

Pb/204Pb

Reference

15.620 15.606 15.590 15.590 15.642 15.615 15.612 15.621 15.601 15.608 15.708 15.612 15.700 15.689 15.588 15.693

38.681 38.629 38.580 38.576 38.776 38.665 38.666 38.689 38.621 38.640 38.968 38.646 39.057 39.106 38.463 38.955

Zhang et al. (2008)

15.645 15.615 15.627 15.624 15.637 15.671 15.604 15.635 15.647 15.561 15.584

38.779 38.680 38.720 38.712 38.743 38.951 38.644 38.746 38.792 38.504 38.574

This study

Liu (2008)

Fei (2014)

Zang et al. (2007)

The Leqingla and Xin’gaguo biotite granites analyzed in this study are enriched in LREE and LILE (e.g., Rb, K, and Ba), and depleted in HFSE (e.g., Nb, Ta, P, and Ti), especially in P and Ti. In Rb-(Y + Nb) (Fig. 12a) and Ta–Yb (Fig. 12b) diagrams, all the samples are plotted into the VAG (volcanic arc granites) fields. These geochemical characteristics seem to indicate that the Leqingla and Xin’gaguo biotite granites are arc affinity and are induced by Neo-Tethys subduction. However, emplacement ages of the Leqingla and Xin’gaguo biotite granite are 60.8 Ma and 56.5 Ma, respectively, which are consistent with the emplacement time of the Paleocene–Eocene intrusions in Gangdese batholith (Mo et al.,

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L. Wang et al. / Journal of Asian Earth Sciences 115 (2016) 80–96

Table 6 Zircon in situ Hf isotopic data of the biotite granite from the Leqingla deposit. Sample no.

176

Y/177Hf

2r

176

Lu/177Hf

01 02 03 04 05 06 07 08 08 10 11 12 13 14 15 16 17 18 19

0.061261 0.105695 0.088378 0.074166 0.104715 0.151490 0.100428 0.139951 0.050772 0.065557 0.082486 0.101919 0.088688 0.124058 0.067080 0.105616 0.082070 0.060468 0.088071

0.001175 0.001259 0.000742 0.001486 0.002027 0.003551 0.003469 0.001919 0.000754 0.002327 0.001884 0.003458 0.001858 0.001727 0.000898 0.003523 0.003690 0.000760 0.001499

0.001611 0.002576 0.002163 0.001737 0.002433 0.003550 0.002247 0.003120 0.001173 0.001471 0.001998 0.002444 0.001966 0.002743 0.001514 0.002372 0.001784 0.001516 0.001917

2r

176

Hf/177Hf

0.000045 0.000030 0.000016 0.000033 0.000042 0.000081 0.000074 0.000047 0.000015 0.000048 0.000025 0.000116 0.000036 0.000021 0.000017 0.000081 0.000075 0.000045 0.000043

0.282872 0.282802 0.282875 0.282799 0.282896 0.282843 0.282888 0.282900 0.282830 0.282886 0.282854 0.282821 0.282822 0.282864 0.282850 0.282822 0.282852 0.282853 0.282813

Fig. 11. P2O5 vs SiO2 diagram of biotite granites from the Leqingla and Xin’gaguo deposits.

2005; Wen et al., 2008; Ji et al., 2009b) and ages of the Linzizong volcanic rocks (Zhou et al., 2004; Mo et al., 2008; Lee et al., 2009). The Paleocene–Eocene intrusions of the Gangdese batholith

2r

176

Hf/177Hfi

0.000019 0.000022 0.000017 0.000020 0.000023 0.000022 0.000022 0.000023 0.000019 0.000020 0.000029 0.000020 0.000024 0.000024 0.000021 0.000024 0.000022 0.000016 0.000016

0.2828699 0.2827987 0.2828728 0.2827967 0.2828931 0.2828391 0.2828856 0.2828966 0.2828286 0.2828845 0.2828519 0.2828178 0.2828194 0.2828611 0.2828485 0.2828193 0.2828498 0.2828512 0.2828106

eHf(t)

TDM1 (Ma)

TDM2 (Ma)

4.863 2.317 4.898 2.273 5.636 3.694 5.369 5.723 3.347 5.285 4.161 2.942 2.998 4.527 4.051 2.966 4.103 4.157 2.757

548 666 551 655 525 622 533 529 601 525 579 636 626 576 577 633 579 573 638

825 987 820 990 773 897 790 766 920 794 867 945 941 845 875 942 872 868 959

fLu/Hf 0.95 0.92 0.93 0.95 0.93 0.89 0.93 0.91 0.96 0.96 0.94 0.93 0.94 0.92 0.95 0.93 0.95 0.95 0.94

and the Linzizong volcanic rocks have the similar geochemical characteristics with the Leqingla and Xin’gaguo biotite granites, such as, the similar REE patterns, enrichment in LILE, depletion in HFSE (Ji et al., 2009b). They were also plotted into the VAG area in Rb-(Y + Nb) and Ta–Yb diagrams (Ji et al., 2009b). However, researches show that the Linzizong volcanic rocks were formed in syn-collision setting of the India–Asia collision and the coeval granitoids of the Gangdese batholith also belonged to syncollision granitoids (Mo et al., 2003, 2005, 2008). The Leqingla and Xin’gaguo biotite granites have the similar emplacement ages and geochemical compositions with the Paleocene–Eocene granites of the Gangdese batholith and the Linzizong volcanic rocks. Geologically, the Nianbo Formation and Dianzhong Formation of the Linzizong volcanic succession outcrop in the Leqingla and Xin’gaguo deposits (Figs. 2 and 4), respectively, indicating the two deposits underwent the India–Asia collision exactly. Moreover, near the Leqingla and Xin’gaguo deposits, there are two other skarn deposits having similar mineralization characteristics with them, named Lietinggang and Jialapu (Fig. 1). Researches show that they both formed during the India–Asia collision (Yang et al., 2014, 2015; Fu et al., 2013), meaning that Pb–Zn–Fe mineralization in

Fig. 12. Discrimination diagrams of Pearce et al. (1984) for tectonic setting of the Leqingla and Xin’gaguo biotite granites. syn-COLG-syncollision granites; VAG-volcanic arc granites; WPG-within plate granites.

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this area were indeed formed on the syn-collision setting of India– Asia. Therefore, we conclude that the biotite granites and Pb–Zn polymetallic and Fe mineralization in the Leqingla and Xin’gaguo were formed at the India–Asia collision stage. The arc characteristics of the biotite granites studied in this paper could be generated by HFSE-rich minerals, such as rutile, ilmenite, and apatite remain in magma sources during the partial melting. 6.3. Source of ore-forming fluids and metals 6.3.1. Leqingla deposit The d18O values of ore-forming fluids are between 8.8‰ and 5.3‰, and the dD values range from 140.4‰ to 90.1‰. In the dD vs. d18O diagram (Fig. 13), all the data points are plotted between the magmatic water field and meteoric water line, with the d18O values gradually decreasing form the early stage to the late stage, which indicates mixing sources of magmatic water with a significant input of meteoric water (Rye, 1993). The d34S values of 36 sulfide samples extend a relatively wide range of 11.6‰ to 0.3‰, concentrating at the range of 9.0‰ to 4.3‰ (Fig. 14a). The sulfide samples are enriched in light sulfur isotope and show characteristics of biogenetic sulfur. In the Leqingla deposit, the Mengla and Luobadui Formations hosting major of the Pb–Zn ore bodies, contain lots of organic clastic (Li et al., 2004; Zhang et al., 2012). d34S values of two mineralized limestone from the Mengla Formation are 9.0‰ and 8.6‰, which are consistent with that of ore sulfides, indicating that wall rocks of the Mengla and Luobadui Formations could be considered as the possible source of the biogenic sulfur of the ore-forming fluids. All the sulfide samples of the Leqingla deposit have narrow range of 206Pb/204Pb ratios, but wide ranges of 207Pb/204Pb, and 208 Pb/204Pb ratios. In the 207Pb/204Pb vs 206Pb/204Pb diagram (Fig. 15), ore sulfide data points show an approximate linear distribution, which could be considered as a mixing line, indicating mixing of two different Pb reservoirs (Andrew et al., 1984). Four sulfide data points are near the upper crust curve and are also plotted in the area of the Lhasa terrane basement, showing that Pb of the Leqingla deposit could be derived partially from the crustal basement of the Lhasa terrane. Other sulfide data points are distributed near the orogen curve, with some data points plotted between the orogen and mantle curves. This characteristic suggests that

Fig. 14. Histograms of sulfur isotopic compositions of the Leqingla and Xin’gaguo deposits. Cp – chalcopyrite; Gn – galena; Sp – sphalerite; Po – pyrrhotite; Py – pyrite; Mar – marcasite.

Fig. 15. Pb isotope compositions of ore sulfides from the Leqingla and Xin’gaguo deposits (modified after Zartman and Doe (1981)). Pb isotope compositions of the Lhasa terrane, Leqingla biotite granite, and Indian Ocean MORB are sourced from Gariépy et al. (1985), Fei (2014), Sun (1980) and Cohen and O’Nions (1982), respectively. Fig. 13. dD–d18O isotopic compositions for the Leqingla and Xin’gaguo deposits. The primary magmatic and metamorphic water boxes are from Taylor (1974), the meteoric water lines for China and Tibet are from Zheng et al. (1983), and the geothermal water area is from Zheng et al. (1982).

mantle-like components could also be involved in the Leqingla mineralization. Moreover, most of the ore sulfide data points overlap very close to the Pb isotope compositions for the biotite granite

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(Fig. 15), indicating that the mineralization-related biotite granite provide the major metals of the Leqingla deposit. eHf (t) values of the Leqingla biotite granite are positive and display small variations. As shown in Fig. 16, all the eHf (t) values distribute in the domain between chondrite and depleted mantle, which indicate that mantle contributions were existed exactly in the magma sources. Zircon U–Pb age (60.8 Ma) in this paper shows that the Leqingla mineralization maybe occurred at the stage of India–Asia collision. In this period, partial melting of the Neo-Tethys Ocean slab induced mantle composition adding into the magmatism in this area (Mo et al., 2008). The Neo-Tethys Ocean slab, therefore, could be another source for the Leqingla Pb isotope compositions.

suggests that most of the sulfur of the ore-forming fluids in the Xin’gaguo deposit was mainly derived from sedimentary rocks enriched in organic of the Takena Formation. Pb isotope compositions of the Xin’gaguo deposit are similar to that of the Leqingla deposit. In the 207Pb/204Pb vs 206Pb/204Pb plot (Fig. 15), Xin’gaguo sulfide data points also contribute the Pb isotope mixing line. Zircon U–Pb age (56.5 Ma) shows that mineralization of the Xin’gaguo also happened at the stage of India–Asia collision. In addition, the Xin’gaguo deposit is located immediately south of the Leqingla deposit. Hence, sources of the Pb of the Xin’gaguo deposit should be similar with the Leqingla deposit. 7. Conclusions

6.3.2. Xin’gaguo deposit dD and d18O values of two quartz samples of stage III range from 92.3‰ to 81.0‰, and from 4.5‰ to 4.2‰, respectively. One quartz sample and two calcite samples of stage IV have dD values of 117.3 to 103.4‰, and d18O values of 1.9–7.0‰. dD and d18O values of all the samples are lower than the magmatic water (dD = 50 to 85‰, d18O = 5.5–10‰; Taylor, 1974). In the dD vs. d18O diagram (Fig. 13), all the data points distribute in the field between the primary magmatic water and the meteoric water, also indicating a mixing source of magmatic water with a significant input of meteoric water during the main ore and post ore stages. The d34S values of 15 sulfide samples range from 5.0‰ to 2.1‰ and show a bimodal distribution (d34S = 5.0 to 1.6‰ and 1.6– 2.1‰) (Fig. 14b). All the samples for sulfur isotope analyses were gathered from sphalerite–galena ores of stage III (Fig. 5f–i), therefore, this bimodal distribution of sulfur isotope is not the result of different mineralization stages. In addition, mean d34S values of marcasite, sphalerite, chalcopyrite, and galena samples show the trend of d34Smarcasite > d34Ssphalerite > d34Schalcopyrite > d34Sgalena, showing the equilibrium crystallization between these sulfides and equilibrium sulfur isotopic fractionation during the ore-forming process (Barnes, 1979), indicating the bimodal distribution of sulfur isotope is not caused by sulfur isotope fraction. Hence, the bimodal distribution of sulfur isotope means that the sulfur sources of the Xin’gaguo deposit could be complicated. Two marcasite samples and three sphalerite samples show positive d34S values, ranging from 2.0‰ to 2.1‰ and 1.6‰ to 1.9‰, respectively. The average d34S value of these five samples is 1.9‰, indicating that parts of sulfur in the ore-forming fluids of the Xin’gaguo deposit were derived from a magmatic source (Ohmoto and Rye, 1979; Faure, 1986). The other ten sulfide samples have negative d34S values, averaging 3.2‰, also showing characteristics of biogenetic sulfur. This

(1) Emplacement ages of the Leqingla and Xin’gaguo biotite granites are 60.8 Ma and 56.5 Ma, respectively, which could be inferred as the upper limit of the mineralization ages for both the Leqingla and Xin’gaguo deposits. (2) Major elements compositions show that the Leqingla and Xin’gaguo biotite granites are calc-alkaline and high K calc-alkaline, respectively, and they should be classified as I-type granites. REE and trace elements geochemical characteristics, together with emplacement ages suggest that biotite granites and the Pb–Zn polymetallic mineralization in the Leqingla and Xin’gaguo deposits were formed at the India–Asia collision stage. (3) H–O isotopic compositions show ore-forming fluids in both the Leqingla and Xin’gaguo deposits were derived from magma source mixed with mounts of meteoric water. (4) S isotopic analyses suggest that sulfur in ore-forming fluids of the Leqingla deposit was mainly from wall rocks of the Mengla and Luobadui Formation. Sulfur in ore-forming fluids of the Xin’gaguo deposit were mainly from wall rocks of the Takena Formation with some magma sulfur. (5) Pb isotopic compositions of ore sulfides from both the Leqingla and Xin’gaguo deposits have shown that ore-forming metals for these two deposits were derived from a mixture of two reservoirs of the Lhasa terrane basement and the Neo-Tethys Ocean slab.

Acknowledgement This research project is financially supported jointly by the National Natural Science Foundation of China Grant 41403040, Scientific Research Fund of the China Central Non-Commercial Institute Grant K14l6, the Geological Survey Program of the mineral resources potential evaluation Grant 12120114068401, 12120113036200, and 12120114050901, and the Research Fund for the Doctoral Program of Higher Education of China Grant 20125122120013. We are grateful to Jianzhen Geng for his help in zircon U–Pb isotopic dating and Kejun Hou for the in situ Hf isotope analyses. We thank Lujun Dang for his assistance in fieldwork. Special thanks to Professor M. Santosh and the anonymous reviewer for their constructive suggestions. References

Fig. 16. Diagram showing Hf isotopic composition of the Leqingla biotite granite.

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