Metallogenic controls on the granite-related W-Sn deposits in the Hunan-Jiangxi region, China: evidence from zircon trace element geochemistry

Yuannan Feng· Tingguang Lan · Lichuan Pan · Tingting Liu ·Shaohua Dong

Abstract The Nanling Range in South China is well known for its rich granite-related W–Sn deposits. To elucidate the controls of different granite-related W–Sn metallogenesis in the region, we chose five representative orerelated granites (Yanbei, Mikengshan, Tieshanlong, Qianlishan, and Yaogangxian intrusions) in the Hunan–Jiangxi region, and studied their magmatic zircon ages and trace element geochemistry. Our new zircon data showed the differences in ages, temperatures and oxygen fugacity of the ore-forming magmas. Zircon U–Pb ages of the Yanbei and Mikengshan intrusions are characterized by 142.4 ± 2.4 and 143.0 ± 2.3 Ma, respectively, whereas the Tieshanlong and Qianlishan intrusions are 159.5 ± 2.3 and 153.2 ± 3.3 Ma, respectively. The Sn-related intrusions were younger than the W-related intrusions. The Tiin-zircon thermometry showed that there was no systematic difference between the Sn-related Yanbei (680–744 °C)and Mikengshan (697–763 °C) intrusions and the W-related Tieshanlong (730–800 °C), Qianlishan (690–755 °C)and Yaogangxian (686–751 °C) intrusions. However, the zircon Ce4+/Ce3+ ratios of the Yanbei (averaged at 18.3)and Mikengshan (averaged at 18.8) intrusions are lower than those of the Tieshanlong (averaged at 36.9), Qianlishan (averaged at 38.4) and Yaogangxian (averaged at 37)intrusions, indicating that the Sn-related granitic magmas might have lower oxygen fugacities than those of the W-related. This can be explained by that, in more reduced magmas, Sn is more soluble than W and thus is more enriched in the residual melt to form Sn mineralization.The difference in source materials between the Sn-related and the W-related granites seems to have contributed to the different redox conditions of the melts.

Keywords W–Sn deposits · South China · Zircon trace element chemistry · Ti-in-zircon thermometry · Oxygen fugacity

1 Introduction

Physicochemical conditions of magmas, such as temperature, pressure, oxygen fugacity, and water content, impose key controls on the ore fertility and on what types of ore deposits are to be formed(Richards 2011,2013).Since oreforming intrusions are commonly altered, conventional whole-rock geochemistry cannot precisely constrain the nature of the ore-forming magmas.In recent years,with the rapid development of LA-ICP-MS technology, in situ mineral geochemical analyses have been widely used to determine the physicochemical features of the magmas.Zircon (ZrSiO4) is a common accessory mineral in many types of rocks, and an important carrier for REEs (rare earth elements), HFSEs (high field strength elements). It’s also physiochemically inert and contains high U and Th contents and very low common Pb contents (Watson et al.1997), making it an ideal candidate for U–Pb dating. The low solubility, high melting point and physical resistivity of zircon (Hoskin and Schaltegger 2003; El-Bialy and Ali 2013) enable it to retain the original trace element chemistry (except for radiogenic elements, e.g., U and Th).During the zircon crystallization, a specific suite of trace elements (e.g., Sc, Y, Ti, Hf, Th, U, Nb, Ta, V, P and REEs) is incorporated into the crystal lattice, and the variation of their concentrations indicates their geological formation processes (El-Bialy and Ali 2013). Currently,zircon trace element geochemistry were widely used to study the compositions (e.g., Heaman et al. 1990; Belousova et al. 2002; Hanchar and van Westrenen 2007), oxidation states (e.g., Ballard et al. 2002; Trail et al. 2012;Burnham and Berry 2014; Smythe and Brenan 2016) and crystallization temperatures (e.g., Watson and Harrison 2005; Watson et al. 2006; Ferry and Watson 2007) of the host magmas. Therefore,zircon is regarded as an effective petrogenetic/metallogenic indicator.

The Nanling Range in South China is a world-class W–Sn province, and hosts a large number of Yanshanian(Jurassic-Cretaceous) granitoids and associated W–Sn deposits (Hua et al. 2003;Chen et al. 2008, 2013; Li et al.2007; Hu and Zhou 2012; Wei et al. 2012; Hu et al.2012a, b, 2015, 2017a, b; Mao et al. 2013). Previous studies in this region were dedicated mainly to the petrography, geochronology and petrogenesis of the oreforming granitoids, whereas the critical factors controlling the W and Sn mineralization were poorly understood.Therefore,in this study,we select representative intrusions associated with W and Sn mineralization from the Nanling Range (e.g., the W-related Tieshanlong, Qianlishan and Yaogangxian granites and the Sn-related Yanbei and Mikengshan granites) to conduct whole-rock major and trace element analyses and LA-ICP-MS zircon U–Pb dating and trace element analyses,with the aim to discuss the physiochemical difference (mainly temperature and oxygen fugacity) between the W-related and Sn-related granitoids. Our studies intend to elucidate the critical factors controlling the W and Sn mineralization associated with the granitoids.

2 Regional geology

In this study, we focused on the famous W–Sn associated granitoids in southern Jiangxi (Huangsha W, Yanbei Sn and Taoxiba Sn deposits)and southern Hunan(Shizhuyuan W-polymetallic and Yaogangxian W deposits) areas in the Nanling Range (Fig. 1). The southern Jiangxi region is where the W deposits are most concentrated.Igneous rocks(ca. 600–66 Ma) are widely distributed in this region,among which granitic rocks (180–66 Ma) are the most pervasive, and include mainly biotite granite, granite porphyry and granodiorite complexes.The southern Hunan W–Sn polymetallic ore district contains a large number of diachronous and multiphase intermediate-felsic granitoids,whose distributions are controlled by the boundary between the uplift zone (ca. 600–400 Ma) and depression(409–205 Ma),as well as by the basement architecture and regional-scale deep faults.The granitoid belts in the region are mostly NE-trending and minor NW-trending (Wang 2008).

The Huangsha W deposit is located in the intersection between the E-W-trending Dayu-Ruijin fold belt and the NE-NNE-trending Yushan fold belt (Gan 1988), and is a large-scale, polymetallic sulfide-bearing quartz-vein-type W deposit in southern Jiangxi.Major strata exposed in the mine include the Cambrian, Devonian and Quaternary sequences, and multi-phase magmatic intrusions were documented (Li 2011). The Tieshanlong granite is metallogenically related to the Huangsha W deposit, and is located in the central part of Huangsha. The intrusion comprises medium-to coarse-grained porphyritic biotite granite. Rock-forming minerals mainly include quartz,plagioclase,muscovite and biotite,with accessory minerals of zircon and sphene (Li 2011). Huang et al. (2011)reported SHRIMP zircon U–Pb age of 168.1 ± 2.1 Ma for the Tieshanlong biotite granite. The Tieshanlong intrusive complex has very low εNd(t) values (- 15.5 to 11.8),indicating that the magmas were probably sourced from the Paleoproterozoic crustal basement (Li 2011).

The super-large Yanbei porphyry Sn deposit is located in the west of the intersection between the N-trending Shicheng-Xunwu fault and the Huichang ring-shaped structure,belonging to the southern Wuyi Mountains REM(rare earth metals)-W–Sn metallogenic belt. The deposit is hosted in the late Jurassic Huichang intermediate-felsic volcanic basin, and the orebodies are clustered along the contact between the granite porphyry and rhyolite porphyry(Mei et al.2007).The ore-related porphyritic granite of the Yanbei Sn deposit is grey and massive, and contains mainly quartz and K-feldspar and minor biotite.Accessory minerals include zircon, pyrite, chalcopyrite and cassiterite. The ore-related intrusion shows zircon U–Pb age of 137.4 ± 1.2 Ma. This intrusion has relatively high εNd(-t)values(- 9.9 to- 10.1),which fall into the fields of the Proterozoic Longquan and Mayuan groups crustal rocks(Liang 2017).

The Taoxiba Sn deposit (Huichang County, Jiangxi) is located in the northern part of the Mikengshan intrusion in the Xikengjing ore field,about 3 km away from the Yanbei Sn deposit.Tectonically, the Taoxiba deposit is situated in the intersection between the western margin of the Mesozoic volcanic-metallogenic belt of the SE China coast and the EW-trending South China Sn belt. The two belts collided with each other at ～400 Ma (Li 2011). The orerelated Mikengshan intrusive complex comprises mainly porphyritic biotite (K-feldspar) granite. The intrusion shows the zircon U–Pb age of 136.0 ± 1.7 Ma (Qiu et al.2006), and has relatively high εNd(t) values (- 3.6 to- 5.1),which might be derived from a crust-mantle mixed source (Qiu et al. 2005).

Fig. 1 Simplified geological map showing the structural framework of the South China and the distribution of ore deposits(Ore deposits in this study include:1-Huangsha W deposit,2-Yanbei Sn deposit,3-Taoxiba Sn deposit,4-Shizhuyuan W polymetallic deposit and 5-Yaogangxian W deposit) (modified after Mao et al. 2011; Hu et al. 2017a)

The Shizhuyuan W-polymetallic deposit is located at the eastern margin of the Hercynian-Indosinian depression of the South China Caledonian fold belt (Chen 1993). The ore-related Qianlishan granites (southeast of Chenzhou City, Hunan) are located in the middle part of the Nanling metallogenic belt, and may have formed in three phases:(I) porphyritic biotite granite (158–157 Ma), (II)equigranular biotite granite(158–155 Ma)and(III)granite porphyry (～154 Ma) (Wu et al. 2011; Chen et al. 2016).The various intrusive phases of the Qianlishan granites have overlapping ranges of initial Sr isotopic compositions.In the εNdversus εSrdiagram, almost all the plots fall on a horizontal line, consistent with the Yangtze continental crust-derived granite. This suggests that the Qianlishan granites were mainly sourced from the re-melting of crustal materials (Shen et al. 1995).

The Yaogangxian deposit in Hunan province is an important W deposit in the Nanling Range.The deposit and its host Yaogangxian granitic complex are located in the northern part of the Nanling tectonic belt(Peng et al.2006;Hu et al. 2012b). Zircon U–Pb ages of the medium- to coarse-grained two-mica granite, fine- to medium-grained two-mica granite and fine-grained muscovite granite are 169.5 ± 0.9 and 170.7 ± 1.5 Ma, 161.6 ± 0.7 and 162.6 ± 0.6 Ma, 156.9 ± 0.7 and 157.1 ± 0.7 Ma,respectively (Dong 2012). The coarse-grained two-mica granite is light grey, massive and porphyritic, and mainly contains quartz, K-feldspar and plagioclase with minor biotite and muscovite. Accessory minerals include apatite,garnet,zircon and xenotime(Dong 2012).The medium-to fine-grained two-mica granite comprises mainly quartz,K-feldspar, plagioclase, muscovite and biotite, with accessory minerals including apatite, garnet, zircon,xenotime and fluorite (Dong 2012). The fine-grained muscovite granite comprises mainly quartz, K-feldspar,plagioclase and muscovite, with accessory minerals of garnet, zircon and fluorite (Dong 2012). Published wholerock geochemical and Sr–Nd isotopic data suggest that the Yaogangxian granitic magmas were mainly sourced from Paleoproterozoic argillaceous rocks (Dong 2012).

3 Analytical methods

Whole-rock major and trace element analyses were conducted at the ASL Laboratory in Guangdong province.For major element analyses, Li2B4O7powders were admixed with 200 mesh whole-rock powders and then fused into glass discs.After that,a Philips PW2404 XRF analyzed the discs. Using basaltic to granitic rock standards(NCSDC73303, SARM-2, SARM-3, and SARM-4) to monitor the analytical quality, and the results indicate the accuracy better than 2%. For trace element analyses,whole-rock powders were dissolved in distilled HF + HNO3+ HClO4mixture, dried, and then digested with HCl. An Agilent 7700×ICP-MS analyzed the final solutions. The analytical uncertainties are within 5% for most elements, as indicated by the analytical results of the standard materials (GBM908-10, MRGeo08, OREAS460 and SY-4).

Zircon U–Pb dating and trace element analyses were performed at the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences,using a Geolas Pro 193 nm laser ablation system coupled with an Agilent 7900 ICP-MS. Analytical conditions were 32 μm laser beam and 6 Hz frequency.Zircon 91500 was used as an external standard, and elemental content calibration was performed using NIST SRM610 as an external standard and Zr as an internal standard.Details of the analytical processes were described in Liu et al. (2008, 2010a, b).

4 Results and discussion

4.1 Zircon U-Pb dating

Zircon U–Pb data are listed in Table S1,and the Concordia diagrams are shown in Fig. 2.

All the analyzed spots of the Qianlishan intrusion(sample CS007; Shizhuyuan W-polymetallic deposit),Tieshanlong intrusion (sample TSL02; Huangsha W deposit), Yanbei intrusion (sample YB01; Yanbei Sn deposit) and Mikengshan intrusion (sample LHS02;Taoxiba Sn deposit) fall on the Concordia, with their weighted mean206Pb/238U ages of 153.2 ± 3.3(MSWD = 3.2, n = 20), 159.5 ± 2.3 (MSWD = 2,n = 22), 142.4 ± 2.4 (MSWD = 2.6, n = 24) and 143 ± 2.3 Ma (MSWD = 2, n = 20), respectively. These zircon U–Pb ages indicate that the Sn-related granitoids(～140 Ma) formed much later than the W-related ones(＞150 Ma) in this study, suggesting that the magmas related to the Sn and W mineralization were probably derived from two independent magmatic events (Figs. 3,4).

4.2 Whole-rock major and trace elements

For major element compositions, all the studied intrusions are calc-alkaline (Rittmann index: 1.87–2.61), metaluminous to weakly peraluminous (A/CNK = 1.00–1.24).Compared with the other four intrusions, the Qianlishan granite is more felsic. In the primitive-mantle normalized spider diagram,all the five intrusions show obvious Ba,Sr,P and Ti depletions. The chondrite-normalized REE patterns of Yaogangxian show a weak tetrad effect, while those of the other four intrusions incline to right. The Yanbei intrusion contains the highest average ∑REE contents (380 ppm) and LaN/YbNratios (11.6). The Mikengshan, Tieshanlong and Qianlishan intrusions show medium ∑and, while the Yaogangxian intrusion shows the lowest average ∑(66.3 ppm),LaN/YbN(0.43)and strongest Ce anomaly(1.28)(Table 1).

Fig. 2 Zircon U–Pb Concordia diagrams of Qianlishan porphyritic biotite granite (a), Tieshanlong medium- to fine-grained porphyritic biotite granite (b), Yanbei porphyritic K-feldspar granite (c) and Mikengshan coarse-grained biotite granite (d)

Fig. 3 Plots of Na2O + K2O (wt%) versus SiO2 (wt%) (a) and Al2O3/(Na2O + K2O) molar versus Al2O3/(CaO + Na2O + K2O) molar (b)

4.3 Zircon geochemistry

The zircon Th/U ratios are all ＞0.1 (mostly ＞0.4), indicating typical magmatic zircons (Belousova et al. 2002;

Wu and Zheng 2004)(CL images in Fig. 5).The zircons in the Mikengshan intrusion contain distinctly higher REE,Th, U, Ta, Nb, Ce and Zr contents than those in the other four intrusions.The zircons in the Yanbei intrusion contain the lowest zircon Ti contents.All the intrusions show very similar zircon REE distribution patterns, as featured by LREE depletion, HREE enrichment and distinct positive Ce and negative Eu anomalies. Among the five intrusions,the zircons in the Mikengshan intrusion have the highest∑REE and LaN/YbN, while the Tieshanlong and Yaogangxian intrusions have the highest positive Ce anomalies and the highest negative Eu anomalies, respectively(Tables 2 and S2).

Fig. 4 Whole-rock chondrite-normalized REE distribution patterns (a) and primitive-mantle normalized spider diagram (b) (normalization values after Sun and McDonough 1989)

Ce anomaly in zircon is calculated from(Trail et al. 2011, 2012), where Dzrc/meltCe ,andrepresent the concentrations of Ce,La, and Pr in zircon to that of the melt, respectively. Eu anomaly in zircon is calculated from(Trail et al. 2011, 2012), where Dzrc/melt

4.4 Ti-in-zircon temperatures

Numerous studies have shown that Ti-in-zircon thermometry can effectively constrain the crystallization temperatures of zircons (Watson and Harrison 2005; Watson et al.2006; Ferry and Watson 2007). The Ti-in-zircon thermometer (Ferry and Watson 2007) is commonly given as,

The Yaogangxian and Yanbei intrusions contain accessory mineral of rutile (Li et al. 2007; Wang et al. 2014),thus the αTiO2can be set to 1.The estimation of αTiO2in the Tieshanlong, Qianlishan, Mikengshan granites was based on the method of Hayden and Watson(2007),which shows that logTimelt(ppm) = 7.95–5305/T(K) + 0.124FM (FM =1/Si × (Na + K+2(Ca + Mg + Fe))/Al (cation fractions). According to this method, only 582–592 ppm Ti could lead to the rutile saturation in the Tieshanlong,Qianlishan, Mikengshan granites. The above granites contain 659–905 ppm Ti, suggesting TiO2saturation in their melts. In addition, all the granites contain quartz grains. Therefore, the αSiO2and αTiO2of all the granites can be set to 1, the above equation can be simplified into:

According to Eq. (2),the calculated temperatures for the Mikengshan, Yanbei, Tieshanlong, Qianlishan and Yaogangxian granites are 697–763, 680–744, 730–800,690–755, 686–751 °C, respectively. The results show that there is no systematic difference in zircon crystallization temperatures between the W- and Sn-related granites(Figs. 6, 7).

4.5 Zircon Ce4+/Ce3+ indicator on magma oxygen fugacity

Ce anomaly in zircon can reflect the physicochemical conditions of zircon crystallization (Ballard et al. 2002;Pettke et al.2005;Barth and Wooden 2010;Claiborne et al.2010;Trail et al.2011,2012;Burnham and Berry 2012;Li et al. 2012). Previous studies suggested that zircon Ce3+and Ce4+are strongly fractionated with magma redox changes, but unaffected by the fractionation of minerals.This suggests that Ce4+/Ce3+ratios can effectively reflect the relative oxygen fugacity of magma (Ballard et al.2002). The zircon Ce3+and Ce4+can be calculated using the method of Ballard et al. (2002):

Table 1 Major (wt%) and trace (ppm) elements of the Yanbei, Tieshanlong, Mikengshan, Yaogangxian and Qianlishan granites

Fig. 5 CL images of zircons from a Yanbeiand, b Tieshanlong granites

Table 2 Zircon ∑REE, LaN/YbN, Ce and Eu anomalies for the five intrusions

Fig. 6 Chondrite-normalized zircon REE distribution patterns of the five intrusions studied (normalization values after Sun and McDonough 1989)

Fig. 7 Histogram of zircon Ce4+/Ce3+ ratio versus frequency

Experiments have shown that the solubility of W is higher than that of Sn in more oxidized melts, while Sn is more soluble in more reduced melts (Blevin et al. 1996;Linnen et al. 1996; Bhalla et al. 2005; Champion and Bultitude 2013; Che et al. 2013). The different oxygen fugacities of the W-related and Sn-related granites thus might have originally facilitated the W and Sn to be enriched in the more oxidized and more reduced magmas,respectively. Furthermore, the accessory minerals in the W-related Yaogangxian, Qianlishan, Tieshanlong are mainly magnetite, ilmenite, and sphene (Li 2011a; Tong 2013;Wang et al.2014),whereas in the Sn-related Yanbei and Mikengshan granites are magnetite, cassiterite, topaz,fluorite and monazite(Yu et al.2013;Li et al.2007;Liang 2017).This indicates that Ti-bearing minerals are enriched in the W-related granites while F-bearing minerals are enriched in the Sn-related granites. At higher oxygen fugacity, Sn is presented dominantly as Sn4+species(SnO2) (Linnen et al. 1996). Because Sn4+and Ti4+species have similar ionic radii,Sn4+will replace Ti4+to enter the Ti-bearing minerals. Fractional crystallization of the Ti-bearing minerals thus would make the melts gradually deplete in Sn,which is not favorable for late hydrothermal Sn mineralization(Linnen et al.1995;Blevin 2004;Bhalla et al. 2005; Wang et al. 2017). Actually, because of the high oxygen fugacity, cassiterite will also crystallize earlier, leading to the melts being depleted in Sn. On the contrary,in the conditions of F-enriched and low fO2,Sn is presented dominantly as an Sn2+species (Linnen et al.1996), the solubility of which is higher than the Sn4+(Bhalla et al. 2005; Che et al. 2013). If no Sn-bearing mineral was fractioned from the melts, the Sn2+would be gradually enriched in the residue melts and thus finally enter the magmatic-hydrothermal fluids, contributing to generate the ore-forming fluids (Wang et al. 2017).

Table 3 Zircon Ce4+/Ce3+ of the five intrusions

Sr–Nd–Hf isotopic studies showed that the Sn-related and the W-related granites have some difference in source materials,of which more mantle materials were involved in the Sn-related granites while more crustal materials were involved in the W-related(Li et al. 2009;Liu et al. 2010a;Liu 2011; Chen et al. 2013; Su and Jiang 2017). This indicates that the redox conditions of the different magmas were probably originally controlled by the source materials.

5 Conclusion

1. LA-ICP-MS zircon U–Pb dating (～140 Ma for Snrelated granites,and ＞150 Ma for W-related granites)indicates that the Sn-related and W-related magmas were derived from two independent magmatic events rather than from cogenetic evolutionary series due to fractional crystallization.

2. Zircon Ce4+/Ce3+ratios indicate that the granites related to the Sn mineralization (Yanbei and Mikengshan)had lower oxygen fugacities than those related to the W mineralization (Tieshanlong, Qianlishan and Yaogangxian). This finding supports the effective indication of zircon for magmatic oxygen fugacity.

AcknowledgementsWe gratefully acknowledge Liyan Wu and Youwei Chen for field sampling, Yanwen Tang and Jun Yan for experiments, and Leiluo Xu and Wei Gao for data processing. This work was supported by the National Basic Research Program of China(973 Program)(Grants No.2014CB440906),Innovation Team Program of Chinese Academy of Sciences (Overseas Famous Scholars Program) and ‘‘Light of West China’ Program of Chinese Academy of Sciences.