The oldest Mo porphyry mineralization in the Yangtze Valley Metallogenic Belt of eastern China: Constraints on its origin from geochemistry, geochronology and fluid inclusion studies at Matou

Accepted Manuscript The oldest Mo porphyry mineralization in the Yangtze Valley metallogenic belt of eastern China: Constraints on its origin from geochemistry, geochronology and fluid inclusion studies at Matou Guangming Li, Kezhang Qin, Guoxue Song, Leon Bagas PII: DOI: Reference:

S0169-1368(16)30215-3 http://dx.doi.org/10.1016/j.oregeorev.2017.09.006 OREGEO 2340

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Ore Geology Reviews

Received Date: Revised Date: Accepted Date:

17 April 2016 11 August 2017 11 September 2017

Please cite this article as: G. Li, K. Qin, G. Song, L. Bagas, The oldest Mo porphyry mineralization in the Yangtze Valley metallogenic belt of eastern China: Constraints on its origin from geochemistry, geochronology and fluid inclusion studies at Matou, Ore Geology Reviews (2017), doi: http://dx.doi.org/10.1016/j.oregeorev.2017.09.006

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The oldest Mo porphyry mineralization in the Yangtze Valley metallogenic belt of eastern China: Constraints on its origin from geochemistry, geochronology and fluid inclusion studies at Matou

Guangming Lia,b, Kezhang Qina,b, Guoxue Song a,b, Leon Bagasc

a

Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029 b

College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China

c

Centre for Exploration Targeting, The University of Western Australia, Crawley, WA 6009, Australia,

and MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS, Beijing 100037, China

Abstract

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The Matou Mo(-Cu) deposit, located in the Yangtze Valley Metallogenic Belt of central-eastern China, is a typical porphyry-type Mo deposit. The orebodies at the deposit are hosted by Matou porphyritic granodiorite, which is the largest intrusive in the area. Quartz vein-type and disseminated sulfide mineralization are well developed in the porphyry and near its contact with Silurian sandstone. Crosscutting relationships indicate that porphyritic granodiorite is the oldest phase in the pluton, which is crosscut by a porphyritic diorite containing traces of chalcopyrite, and later dolerite dykes. These phases have U-Pb zircon dates of 147 ± 3, 140 ± 1 and 135 ± 1 Ma, which confirms the cross-cutting relationships observed in the field. A Re-Os molybdenite isochron age of 147 ± 4 Ma indicates that the porphyritic granodiorite is the source of the oldest Mo mineralization in the metallogenic belt and was formed during achangeof the tectonic setting in the area, from an intracontinental orogeny to extensional tectonics. From 147 to 135 Ma, crust-mantle interaction played an important role in the formation of magmatic rocks at Matou. Systematic petrological and geochemistry investigations reveal that the three phases have a crust source with minor input from the mantle. Investigation of ore-forming fluid, H-O isotopes, S isotopes, and the Re content of molybdenite indicate that the ore-forming fluid and metals were derived from the lower crust. During the evolution of fluid from initial magmatic fluids (stage I) to ore-forming fluids (stage II), fluid boiling accompanied by the input of relatively cooler meteoric water led to the deposition of the Mo mineralization.

Keywords: Yangtze Valley Metallogenic Belt; Matou; Oldest Mo porphyry mineralization; Fluid boiling; CO2-rich inclusions; Crust-mantle interaction

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1.

Introduction

The “Middle-Lower Yangtze Valley” (MLYV) is an important Cu-Fe-Au metallogenic belt (or zone) in central-eastern China (Fig. 1). The belt is commonly referred to as the Yangtze Valley Metallogenic Belt (YVMB) and contains in excess of 200 polymetallic deposits including various combinations of Cu, Fe, Au, Mo, Zn, Pb, and Ag (Hu et al., 1977; Chang et al., 1991; Zhai et al., 1992; Qin and Ishihara, 1998; Qin et al., 1999; Li, 2001; Mao et al., 2003; Zhou et al., 2008; Li et al., 2010; Yang et al., 2011; Song et al., 2010, 2012, 2013). The Anhui Province is located in the southern part of MLYV and contains numerous Mo-Pb-Zn (-W) deposits and occurrences, but most are small in scale and have limited economic value (Zhou et al., 2003a). Exploratory work in the area has been relatively limited, but recent exploration has led to the discovery of the Qimen W-Mo, Gaojiabang W-Mo, and the Guilinzheng Mo deposits (Fig. 1) (Jiang et al., 2009; Fu and Du, 2010). Some occurrences, previously considered to be sub-economic, have also been found to contain economic resources, such as the Jitoushan and Baizhangya W-Mo deposits. In addition, Song (2010) suggested that there is potential for Mo-Pb-Zn mineralization near Chizhou in the southern part of the belt (Fig. 1). The Matou Mo deposit is ~30 km south of Chizhou,and located in the transition zone between the lower Yangtze depression and the “Jiangnan Ancient Continent” (Chang et al., 1991), here referred to as the Jiangnan Terrane (Figs. 1, 2a). It is a typical porphyry-type Mo deposit also containing scheelite and wolframite in quartz veins (Zhu et al.,2014). With reference to Carten et al.

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(1993), the Matou Mo deposit shares many common geological features with high-fluorine porphyry Mo deposits (e.g. Climax and Henderson, White et al., 1981; Seedorff and Einaudi, 2004), whereas the Luming and Daheishan Mo deposits in the Jilin-Heilongjiang Belt in NE China should be classified as fluorine-poor monzogranite–granodiorite porphyry Mo systems (e.g. Endako, Mutschler et al., 1981 and Selby et al., 2001; Li et al., 2014a). Molybdenite from Matou has a Re-Os age of ca. 150-146 Ma (Wang, 2012; Yang et al., 2014). This is at odds with the findings of Zhu et al. (2014), who suggested that porphyritic granodiorite associated with the Mo mineralization was emplaced at 140 ± 2 Ma. Furthermore, geochemistry of mineralized magmatic rocks, the source of the ore metals, and the ore-forming mechanism have not been adequately constrained until now. To determine the age of the Mo mineralization and the nature of the ore-forming fluid at Matou, this contribution documents geochemistry and geochronology of intrusions and characteristics of fluid inclusions, which will help better decipher the genesis of magmatism and Mo mineralization of the deposit. The results also provide a better understanding of the tectonic setting for ore-forming process in the region. 2.

Ore district geology

2.1. Rock types in the Matou area Silurian, Devonian, Carboniferous, and Permian sedimentary rocks are exposed in the Matou area (Fig. 2b). Early Silurian rocks in the area consist of the Gaojiabian, Fentou, and Maoshan formations, which are distributed close to porphyritic granodiorite and the

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relatively younger porphyritic diorite and dolerite (Fig. 2b), where hornfels is well developed in the Fentou Formation. Northwest- and north-trending faults are common around Matou and are crosscut by the Matou porphyritic granodiorite (Fig. 2a, b).A small intrusive stock of porphyritic diorite is present in the porphyritic granodiorite, and dolerite dykes cut both the granodiorite and Silurian sedimentary rocks. The Matou porphyritic granodiorite is grey and consists of plagioclase (36-45 vol.%), quartz (17-28 vol.%), K-feldspar (16-20 vol.%), biotite and hornblende (5-10 vol.%), and accessory minerals (2-5% vol.%). Phenocrysts (25-40 vol.%) include euhedral plagioclase, quartz, and biotite. The groundmass consists of quartz, feldspar, and subordinate biotite and amphibole. The rock has been altered, with K-feldspar and plagioclase partially replaced by clay minerals, and biotite and amphibole partially replaced by chlorite. The porphyritic diorite consists of plagioclase, K-feldspar, quartz, biotite, and a small amount of amphibole (Fig. 3b). Phenocrysts include euhedral plagioclase and K-feldspar. The groundmass consists of feldspar, quartz, biotite, and amphibole. The dolerite is dark green, weakly altered, and fine-grained (Fig. 3e). Minerals present are plagioclase (65-70 vol. %), pyroxene (25 vol. %), amphibole (2 vol. %), and accessory minerals including quartz, orthoclase, and chlorite (5 vol. %), and accessory chalcopyrite and pyrite. 2.1. Mo mineralization

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Porphyry Mo mineralization in eastern China is closely associated with small Middle Jurassic-Lower Cretaceous intrusions (Luo et al., 1991). Molybdenite is the only mineral of economic interest at Matou, and the mineralization is spatially associated with porphyritic granodiorite (Fig. 2). Molybdenite orebodies at Matou are frequently hosted by the Matou porphyritic granodiorite, and less commonly by hornfelsed sandstone assigned to the Silurian Fentou Formation. Ore minerals include molybdenite, pyrite, and minor amounts of chalcopyrite, galena,

and

sphalerite

(Fig.

3,

g-j).

Alteration

at

Matou

is

characterized

by

the

mineral

assemblage

clay-silica-chlorite-sericite-carbonate at the top of the Matou porphyritic granodiorite (Fig. 3, a-2). The alteration gradually diminishes outwards away from the granodiorite in the formation, and the Mo mineralization is closely associated with silica and sericite. Different typical types of veins are present in the Matou porphyritic granodiorite (Fig. 3d). These are: (a) early barren quartz veins referred to here as A veins; (b) ore-forming-stage quartz-Mo veins (B and D veins) where 80% of the molybdenite is between 1-10 mm in size, although it reaches up to 15 mm across; (c) later barren calcite veins (C veins), and (d) quartz-fluorite veins (E veins). Molybdenite is predominantly present in quartz-Mo veins cutting the porphyritic granodiorite or disseminations in the granodiorite. 3.

Analytical results

The results of major, trace, and rare earth element (REE) analyses for the Matou porphyritic granodiorite, porphyritic diorite, and dolerite are listed in Table 1. The analytical techniques are described in Appendix 1. The three Matou porphyritic granodiorite samples

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in this study show weakalteration and preserve primary minerals, with LOI values of 2.7-4.9% (Table 1). These characteristics indicate that alteration did not significantly influence their original chemical composition, but the collected data forthe porphyritic granodiorite have a variation range of K2O assays explaining the wide distribution shown in Fig. 4b (Table 1, samples of M1, M2, M4, M5, M6, M8). All of the three porphyritic diorite samplesshow weak chlorite alteration and preserve primary minerals, with LOI values of 5.5-7.7% (Table 1). These alteration results may account for some increase in K2O, and thus K2O is not included in the calculations in this contribution. The porphyritic granodiorite contains 62.9-64.6 wt.% SiO2, 2.17-2.28 wt.% MgO and 3.42-4.21 wt.% Na2O, and plots in the granodiorite field on the K2O+Na2O versus SiO2 diagram of Middlemost (1985) (Fig. 4a). The porphyritic diorite contains 57.1-58.1 wt.% SiO2, 1.35-2.23 wt.% Na2O and 2.98-3.93 wt.% K2O, and the dolerite contains 47.81-48.07 wt.% SiO2, 6.15-6.34 wt.% Mg and 1.31-1.32 wt.% K2O. All of these samples plot in the high-K calc-alkaline series on the K2O versus SiO2 diagram of Peccerillo and Taylor (1976) (Fig. 4b).

3.1. Trace elements and REE elements The rare earth element (REE) profiles for various intrusive rocks from the Matou area are shown in Fig.4c and the trace elements data are listed in Table 1 (refer to Appendix 1 for the methods used). The total REE concentration of the porphyritic granodiorite, porphyritic diorite, and dolerite range from 120 to 128 ppm, 214 to 226 ppm and 221 to 222 ppm, respectively. All of the samples

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show the characteristics of light REE (LREE) enrichment and heavy REE (HREE) depletion, with weak positive to obviously negative Eu anomalies (Fig. 4c). The (La/Yb)N ratio ranges from 7.5 to 25.5 and δEu values from 0.3 to 0.6. The Primitive-mantle normalized diagrams show consistent patterns of large ion lithophile elements, with positive U (0.54-3.50 ppm) and Pb (3.31-37.6 ppm) anomalies and depletions in Nb (12.3-24.1 ppm) and Ti (0.71-2.45 wt. %). All of the samples are characterized by the enrichment of large ion lithophile elements, including Th and U, and depletion of high-field-strength elements, showing notable negative of Nb, Ta, and Y , and changing Sr anomalies (Fig. 4d).

3.2. LA-ICP-MS U-Pb zircon ages Eighteen zircons from the Matou porphyritic granodiorite (Sample P5-1) were dated (Table 2; Appendix 1). The zircons have U concentrations of 61 to 648 ppm, Th concentrations of 122 to 594 ppm, and high Th/U ratios of 0.92 to 2.74. The U-Pb isotopic data are concordant within the error range, with a concordant age of 147 ± 3 Ma (MSWD = 1.4) (Fig. 5a). Twenty zircon grains from the porphyritic diorite (Sample P5-13) have U concentrations of 101 to 485 ppm, Th concentrations of 48 to 226 ppm, and high Th/U ratios of 0.27 to 0.69 (Table 2). The U-Pb isotopic data are concordant within the error range and have an age of 140 ± 1 Ma (MSWD = 0.86) (Fig. 5b). Nineteen zircon grains were analyzed from the dolerite (Sample P5-95) (Table 2), which assays 335 to 639 ppm U, 173 to 597 ppm Th, and has high Th/U ratios of 0.846 to 1.289. The U-Pb isotopic data are concordant within the error range, with a concordant

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age of 135 ± 1 Ma (MSWD = 0.95) (Fig. 5c).

3.3. Zircon Hf isotopic results Eighteen Hf isotopic analyses were completed on LA-ICP-MS U-Pb dated zircons from the Matou porphyritic granodiorite, and sixteen each from the dated zircons from the porphyritic diorite and dolerite (Table 3; Appendix 1). Zircons from the porphyritic granodiorite have 176Hf/177Hf ratios of 0.281202-0.282569, Hf model ages (TDM2)of 3120-1260 Ma, εHf(t) values of –23.6 to 5.1, and the ca. 164-145 Ma zircons have an average value of –6.9. Zircons from the porphyritic diorite have

176

Hf/177Hf ratios of

0.282368-0.282561, Hf model ages (TDM2) of 1550-1310Ma, and εHf(t) values between –7.2 and –3.6. Zircons from the dolerite have 176

Hf/177Hf ratios of 0.282531-0.282729, Hf model ages (TDM2) of 1370-990 Ma, and εHf(t) values ranging from –4.8 to 1.1.

3.4. Re-Os isotopic ages Six samples of molybdenite were analysed for their Re-Os model ages (Table 4; Appendix 1). The agesare 150± 3, 149 ± 3, 146 ± 2, 149 ± 3, 148 ± 2, and 148 ± 3 Ma defining a molybdenite Re-Os isochron age of 147 ± 4 Ma (MSWD = 1.6) (Fig. 6a). The molybdenite Re-Os weighted mean age of the six samples is 148 ± 2 Ma, which is consistent with the isochron age within error (Fig. 6b).

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3.5. Fluid inclusions Fluid inclusions were studied using an electron microscopy at room temperature (Appendix 1). The study revealed that two-phase aqueous (L+V) inclusions (type I) are dominant, and CO2-rich (Lwater+LCO2+VCO2) inclusions (type II) and daughter mineral-bearing multiphase (L+V+S) inclusions (type III) are minor in number. Type I inclusions usually have rounded, oval, elongated, and irregular shapes. The gas/liquid ratio of the inclusions ranges from 5 to 70%, with most between 20 and 40% (Table 5). Type II inclusions commonly appear as oval shapes with a gas/liquid ratio ranging from 15 to 40% (Table 5). Type III inclusions are rounded, oval and irregular in shape, and have a gas/liquid ratio between 10 and 45%, with most between 10-30% (Table 5). All of the fluid inclusions have coexisting gas and liquid. The homogenization temperatures for fluid inclusion from the mineralization stages are shown in Table 5 and Fig. 9. The homogenization temperature of the inclusions in quartz from the main ore-forming Mo stage ranges from 170° to 360° C with corresponding salinities in the range of 1.7-13.9%and 34.4-39.2% NaCl equiv (Table 3). Fluid inclusions in quartz from the later Mo-barren stage have homogenization temperatures between 130° and 257° C with corresponding salinities of 1.9-3.6% NaCl equiv (Table 5). Type III inclusions have the highest homogenization temperature and salinity. The salinity of type I inclusions is calculated using the ice melting temperature (Tm, ice) and the salinity-temperature formula of Hall et al., (1974). The salinity of type II inclusions is calculated using the clathrate disappearing temperature (Tc1) (Roedder, 1984), and the salinity of the type III inclusions are

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calculated by the temperature at which daughter phases (TS1) disappear using the formula of Bishcoff (1991). 3.5.3.

Composition of fluid inclusions

The composition of fluid inclusions in quartz examined with microthermometry was determined with a Raman microprobe spectrometry. Typical results from eleven analytical datasets are included in Fig. 7. The results show that the liquid-phases in the type I, II, and III fluid inclusions are rich in H2O (Fig. 7). The gas composition of the fluid inclusions is H2O, CO2, and H2S, and the daughter minerals are mainly transparent halite and opaque sulfide in the type III multiphase inclusions.

3.6. H-O-S isotopic results The majority of the δ34S values for sulfides associated with various mineralization types at Matou range from 3.03 to 3.69‰ (Table 6; Appendix 1). Two pyrite samples from sandstone have δ34S values between 7.42 and 9.67‰ (Table 4). The δ18OSMOW and ∆DSMOW values of quartz range from -0.91 to 0.1 and -50.6 to -48.8, respectively (Table 7). 4.

Discussion

4.1. Oldest porphyry Mo deposit in the YVMB and its geodynamic setting The oldest mineralizing event reported in the YVMB is ca. 147-145 Ma (Zhou et al., 2008; Li et al., 2010; Song et al., 2014). This event was earlier than the Cu-Au metallogenic peak during ca. 140-135 Ma along the belt (Song et al., 2014). A comparison of all of

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the geochronology data on magmatism and mineralization indicates that the ca. 147 Ma Matou Mo deposit is the oldest porphyry Mo deposit in the belt (Zhou et al., 2008; Li et al., 2010; Song et al., 2014) (Figs. 6, 8). Although the Laoyaling deposit from the Tongling area has the older Mo mineralization age of 234± 7 Ma in the YVMB (Yang et al., 2004), its mineralization was related to sedimentation and is very different from porphyry-type mineralization. Wang (2012) and Yang et al. (2014) report Re-Os Mo and U-Pb zircon ages for the Matou Mo deposit between ca. 150 and 146 Ma. In contrast, Zhu et al. (2014) report that the Matou porphyritic granodiorite was emplaced at 140 ± 2 Ma, similar in age to the other Cu-Au-related porphyries in the YVMB. Our studies indicate that the Matou porphyritic granodiorite, porphyritic diorite, and dolerite have U-Pb zircon ages of 147 ± 3, 140 ± 1 Ma, and 135 ± 1 Ma, respectively (Fig. 5). Our Re-Os model age determined from six molybdenite samples from Matouis 147 ± 4 Ma (Fig. 6). These results show that the age of the Mo mineralization is the same within error as the porphyritic granodiorite. The ca. 140 Ma porphyritic diorite and ca. 135 Ma dolerite are barren in mineralization and cut through the porphyritic granodiorite and orebodies placing a minimum age limitation ca. 140 Ma on the Mo mineralization. Zhai et al. (1992) suggested that mineralization in the YVMB at the northern margin of the Yangtze Craton took place during ca. 170-90 Ma with skarn-porphyry-type Cu-Au deposits forming at ca. 170-130 Ma, skarn-type Fe and Fe-Cu deposits at ca. 160-120 Ma, and porphyry-type Fe deposits at ca. 130-90 Ma. Mao et al. (2003) proposed that the belt has the same tectonic setting as the North China Craton during the Mesozoic and that most of the mineralization formed during the periods of ca. 190-160, ca. 140-135 and ca. 120 Ma. Chen et al. (2004), Zhou and Yue (2000), and Zhou et al.(2008) summarized the geochronology of magmatism and

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mineralization in the belt and proposed ore-forming stages at ca. 145-137, ca. 135-127, and ca. 126-123 Ma. Li et al. (2010) shown that Cu-Au(-Mo) mineralized porphyritic granites in the Jiurui and Edong mining districts in the belt were formed during two discrete magmatic events at ca. 146-145 and ca. 140 Ma. Song et al. (2014), who studied the magmatism and W-Mo mineralization in the Chizhou area, conclude that magmatism took place during three events at ca. 147-135, ca. 130-120, and ca. 115-110 Ma. The first event involved the emplacements of porphyritic granodiorite and monzogranite, which have a close association with W-Mo-Pb-Zn mineralization. These data indicate that the mineralizing events did not form arbitrarily in time and space, but are related to regional tectonic and magmatic events. Zhou et al. (2003) documented four deformation events during ca. 220-80 Ma in east China. These events are related to a collision between the North China and Yangtze cratons during ca. 220-200 Ma with a post-orogenic stage between ca. 200-170 Ma, intracontinental orogeny at ca. 170-150 Ma, and intracontinental extension during ca. 150-80 Ma. On passing, Mao et al. (2003) proposed that three episodes of gold mineralization took place in the region during ca. 250-180, ca. 170-140 and 130-100 Ma. Integrated studies show that almost all of the deposits along the YVMB were formed under an intracontinental extensional setting, and the oldest porphyry type Mo mineralization event at Matou took place during a transition from intracontinental orogeny to extension (Fig. 8).

4.2. Magma processes The emplacement and evolution of porphyry-type Mo deposits are complex and different from each otherin different pasts of the

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world, and many are associated with two or more magmatic events. For example, Chalukou is the biggest Mo deposit in China, and is associated with pre-ore Middle Jurassic monzogranite, Late Jurassic ore-related porphyritic granites, and Early Cretaceous post-ore porphyritic diorite and quartz monzonite porphyry (Li et al., 2014a). An alogous magmatism ispresent at the world-class Climax Mo deposit in Colorado of the USA (Seedorff and Einaudi, 2004), and the Shapinggou deposit in the Anhui Province of China(Ni et al., 2015). Unlike the many giant porphyry deposits documented by Selby and Creaser (2001), Seedorff (2004), Harris et al. (2008), Li et al. (2014a), Wang et al. (2014) and Ni et al. (2015), the Matou deposit does not have a long history characterized by repeated pulses of magmatism and hydrothermal activity. This is different from the model present by Audetat (2010) in which the high-Mo content of felsic end-members at the depositare derived from the fractional crystallization of a mafic magma. In this model, the melt’s Mo content decreases with the increasing degree of crystallization. In contrast, Matou is a relatively small and locally high-grade porphyry Mo deposit that lacks multiple and overprinting ore-related magmatic events, which is similar to the Max deposit of Canada (Lawler et al., 2010). 4.2.1. Porphyritic granodiorite(ca. 147 Ma)

The Matou porphyritic granodioriteis characterized by intermediate to high K2O (2.78–3.58 wt.%) and Na2O (3.42–4.21 wt.%) assays, with K2O/Na2O ratios of 0.66-0.93, and low to intermediate Mg#of 38-41..Melts from the basaltic lower crust are characterized by low Mg# (<40), whereas those with Mg#> 40 form when mantle material is involved (Shen and Pan, 2013). In this study, the Matou

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porphyritic granodiorite has relatively low MgO contents, which are similar to those of melts derived from a lower crust with input from the mantle. In addition, the porphyritic granodiorite is enriched in Rb, Ba, Th, U and K, depleted in Nb, Ta, P, and Ti, has a weak Eu anomaly(Figs. 5a-d), and has Nb/U, Ta/U and Ce/Pb ratios of 12.8-15.6, 0.55-0.68, and 1.21-2.79, respectively (Table 1). These values are much lower than those of MORB and OIB (i.e. Nb/U = 47, Ta/U = 2.7, and Ce/Pb = 25; Hofmann, 1988), but are close to those of the average crust (Nb/U = 12.1, Ta/U = 1.1, and Ce/Pb = 4.1; Taylor and McLennan, 1995) and upper continental crust (i.e. Nb/U = 8.9, Ta/U = 0.2, and Ce/ Pb = 3.2; Taylor and McLennan, 1995). The La/Yb vs La plot in Fig. 4f for samples from the Matou porphyritic granodioriteis indicative of a partial melting trend, and the lack of compositional variationsis characteristic of fractional crystallization. This indicates that the effects of partial melting at the source were much more important than fractional crystallization in controlling the geochemical composition of the granodiorite. The degree of fractionation (La/YbN =12.3-14.4) is very high and the magmatic evolution did not experience the process of fractional crystallization with plagioclase as the dominant phase, but garnet was a possible major residual mineral in their sources (Defant and Drummond,1990). Melts in equilibrium with phlogopite are expected to have relatively high Rb/Sr (>0.1) and low Ba/Rb (<20) ratios (e.g. Furman and Graham, 1999), which suggests that phlogopite was a more likely potassic phase in the source area rather than amphibole (Fig. 4e). Geochemical diagrams forthe porphyritic granodiorite show that ithas similar geochemical characteristics to the ca. 147-135 Ma intrusions at Tonglingin China (Song et al., 2014) (Fig. 4a-d). However, they are different from magmatic rocks related to W-Mo mineralization in the Chizhou area. Several mechanisms have been proposed for the origin of the ca. 147-135 Ma ore-bearing

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porphyries from Tongling, including a source involving partial melting of a delaminated lower continental crust (Wang et al., 2006), subducted Pacific oceanic crust (Sun et al., 2010; Wu et al., 2012), fractional crystallization of basaltic magma (Li and Jiang, 2009), slab melts with the assimilation of enriched mantle components (Xie et al., 2008), and crust-mantle interaction fractional crystallization with simultaneous crustal assimilation (AFC) (Chen et al., 1998; Du et al., 2007; Deng et al., 2007). Based on thecomparative study of ore-related magmatic rocks in this study, it is concluded that the mechanism of crust-mantle interaction, which is generally accepted in Tongling area, played an important role in the formation of Mo-related porphyritic granodiorite at Matou. The porphyritic granodiorite was probably derived from the mixing of a lower crustal source in the Yangtze Craton with a small input from the mantle. This interpretation is corroborated from zircon Hf isotope compositions and the inherited zircon ages (c.f. Kemp et al., 2006; Hou et al., 2011; Shu et al., 2014). Zircons εHf(t) values from the ca. 147 Ma Matou porphyritic granodiorite and their wide range are indicative of a lower crustal source with input from the mantle (Yang et al., 2012). The two-stage Hf model ages suggest that crustal growth took place during the Mesoproterozoic in the YVMB. As all of the inherited zircons in the Matou porphyritic granodiorite have ages between 2505 and 723 Ma with centralized values of between and 1100 and 700 Ma with clear oscillatory zoning (Fig. 5a, a-1; Table 2). This indicates that ca. 1100 and 700 Ma rocks are present in the source or the magma was contaminated on its ascent through the crust.

4.2.2. Porphyritic diorite (ca. 140 Ma)

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The ca. 140 Ma porphyritic diorite is different from many of the ca. 147-135 Ma W-Mo-related intrusions at Chizhou in that it intrudes the mineralizing Matou porphyritic granodiorite, has an intermediate silica composition, a higher alumina content, a lower alkalis (K2O+Na2O = 5.2-6.1%), is poor in Ti and Fe, and has higher La/Yb values range from 21.9 to 25.5. In addition, all of the diorite samples plot in the high-K calc-alkaline field on the K2O vs SiO2 diagram in Fig. 4b. The porphyritic diorite is enriched in light REE relative to heavy REE, and has a less pronounce Eu anomaly, which is indicative of garnet being a significant residual mineral in the source region (Defant and Drummond, 1990). Petrological and geochemical evidence notably indicates that the low degree of partial melting of the depleted mantle might be the main cause responsible for the enrichment in alkalis. Furthermore, zircons from the diorite have (176Hf/177Hf)i values of 0.282485-0.282558, εHf(t) values of −7.2 to −4.5, and TDM2 ages of 1460-1310 Ma. These characteristics indicate that the porphyritic diorite has a crustal source. The geochemical characteristics of Matou porphyritic diorite are very similar to diorite in the Tongling area of the YVMB. The major rock types at Tongling are pyroxene diorite-pyroxene monzodiorite, quartz diorite-quartz monzodiorite (Xie et al., 2012). Intermediate to felsicmagmatic rocks related to the mineralization at Tongling have a lower Si (SiO2= 45-65 %), are high-Kcalcic alkaline-shoshonitic and metaluminous, have a weak negative to positive Eu anomaly, enriched in LILEs such as Sr (661.6–1542 ppm) and Rb (55.42–139.46 ppm), and depleted in HFSEs such as Nb and Ti (Chen et a., 2016). Most of their εHf(t) values are between -4 and -20, which is also indicative ofa crustal-derived magma source (Song, 2010). It is generally held that the diorite have a mixed crustal and mantle source, and are genetically related to skarn-porphyry type Cu-Au-Fe-S deposits in the region (e.g., Qin and Ishihara, 1998;

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Mao et al., 2003; Yang et al., 2016). Based on the comparative study of geochemistry between the porphyritic diorite at Matou and Tongling, it is suggested here that both units are related to the same magmatism event related to an extensional setting during ca. 143-135 Ma, and both have a mixed crustal and mantle source. This is consistent with field observations in the Matou mine area, and Cu occurrences associated with heavily altered porphyritic diorite dykes in the south of Matou. Furthermore, the association of the Cu occurrences with the diorite indicates that the diorite must have prospectivity for economic Cu mineralization. 4.2.3.

Dolerite (ca. 135 Ma)

Mesozoic volcanic rocks are widely present in the Lower Yangtze region, which are commonly intruded by dolerite during an N-S orientated extensional event. During this tectonic event, most of the felsic magmatic rocks, A-type granites (e.g. Song, 2010; Su et al., 2013), and mafic dykes (e.g. dolerite at the Jitoushan W-Mo deposit; Song, 2010) were emplaced duringa strong interaction between the crust and mantle at ca. 110-130 Ma. Chang et al. (2012) propose that the 145-136 Ma high-K calc-alkaline intrusions and Cu-Au mineralization in the region formed during a strike-slip transpressional tectonic setting, but the ca. 135-127 Ma Shoshonitic volcanic rocks hosting Fe-S mineralization formed in a strike-slip extensional setting (Xie et al., 2008; Chang et al., 2012). Compared with the porphyritic granodiorite and diorite, the late (Early Cretaceous) dolerite at Matou has much lower silica (SiO2= 47.8-48.1%) and alkalis (K2O+Na2O = 4.2-4.4%) contents, and is rich in its Ti (TiO2= 2.41-2.45 %), Ca (CaO= 7.1-8.1 %), and Fe (FeO = 8.29-8.31%) contents (Table 1). The dolerite has a subdued Eu anomaly and no negative Ba or Sr anomalies. This implies that plagioclase was unstable in the magma and there was no fractionation of K-feldspar (Duan et al., 2015). The relatively high HREE

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abundance and the generally flat HREE patterns of the dolerite indicate a garnet-free magmatic source(Fig. 4c) (Zhang et al., 2015). The dolerite’s La/Yb values of 7.5-7.6 and the slightly negative Ce anomaly are indicative of a magma derived from the partial melting of oceanic crust or lithospheric mantle (Mandal et al., 2012). Thus, the magma source is deeper and the fractional crystallization is weaker than those of the older porphyritic granodiorite and diorite. The Early Cretaceous dolerite has (176Hf/177Hf)i values of 0.282527-0.282721,εHf(t) values of –5.7 to 1.1, and TDM2 ages of 1370-990 Ma (Table 3). The Hf isotopic values (εHf(t), –5.7 to 1.1) are slightly higher than that of the porphyritic granodiorite and diorite (Fig. 10), showing that the proportion of mantle material involved is slightly higher. Therefore, the doleritemay have derived from the mantle, with the mixing of a small proportion of crust material. A gradual decrease in silica, alumina and alkalis contents, and an increase in mantle components have been here recognized for the sources of the porphyritic granodiorite, porphyritic diorite, and dolerite at Matou. The average εHf(t) values increase gradually from the porphyritic granodiorite (–7.1) through the porphyritic diorite (–5.4) to the dolerite (–3.2) (Fig. 10), indicating that the proportion of mantle materials involved is higher in the younger intrusives.The gradual change in the petrochemistry of the magmatic rocks indicates that their tectonic setting gradually changed from ca. 147 to 135 Ma. Given that the ore-related magmatic rock is coeval with the oldest Mo deposit, the Matou porphyritic granodiorite was formed in an initial extensional tectonic setting from a magmatic source predominantly in the lower crust. Following continued extensional tectonics and lowering of pressures associated with the earlier

19

compressional tectonics, along with continued increasingin the supply of mantle material, the porphyritic diorite and dolerite were emplaced sequentially.

4.3. Evolution of ore-forming fluids The coeval relationship of the porphyritic granodiorite and Mo mineralization at Matou indicates that fluids associated with the mineralization were magmatic in origin. The early stage (Stage I) of the fluid, which can be found in quartz phenocryst from the porphyriticgranodiorite, consist of two-phase (L+V), daughter mineral-bearing multiphase (L+V+S), and CO2-rich phase (L+LCO2+VCO2) fluid inclusions, which represent the initial part of the mineralizing process (Song, 2010). Fluids containing Mo developed during Stage IIat 170°-360º C and salinities of 5-39.2% NaCl equiv. The Stage II fluid included H2O-CO2-NaCl enriched in H2O and CO2 (Figs. 7, 9a), and varied in composition from those relatively rich in CO2 (gas) to those relatively higher in salinity (Fig. 7). This indicates that fluid boiling took place during deposition of Mo (Fig. 9a). The succeeding Stage III fluid was barren forming at lower temperatures of 130° - 257ºC, and salinities between of 1.1- 8.2% NaCl equiv. (Fig. 9a). The Matou Mo deposit is very similar to the Shapinggou Mo deposit, which is a Climax-type Mo deposit in China (Ni et al., 2015). Fluid inclusion studies by Ni et al. (2015) show that ore-forming fluids at Shapinggou include co-existing CO2-rich and halite-bearing inclusions. Ni et al. (2015) suggest that fluid boiling in the H2O-CO2-NaCl system took place at the deposit in a relatively deep environment, and intensive fluid boiling primarily led to the formation of the giant Mo deposit. On the basis of the fluid inclusion

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types and changes of temperature and salinity, it is suggested that the Stage I fluid at Matou is characterized by a low- to moderate-salinityoriginated from the porphyritic granodiorite’s magma (c.f. Li et al., 2014a; Ni et al., 2015). As the fluid evolved, phase separation took place during decreases in pressure or temperature resulting in fluid boiling, Mo deposition and formation of the Stage II fluids. Further decreases in pressure or temperature and salinity resulted in the development of the Stage III fluids. This study is the first to recognize the existence of CO2-rich inclusions associated with Mo mineralization at Matou (Fig. 7). Similar characteristics are found in the Mo deposits present in the Qinling-Dabie Orogen between the North China Craton and Yangtze Craton to the south. Examples include Yuchiling (Li et al., 2012), Qian’echong (Yang et al., 2013), and Shapinggou (Ni et al., 2015) in the Henan Province. Suggested sources for the CO2-rich mineralizing fluids in the literature are magma derived from the mantle (Hu et al., 2008; Sverjensky et al., 2014), magma formed from partial melting of the lower crust (Baker, 2002; Chen and Wang, 2011; Ni et al., 2015), or from the upper crust (Lowenstern, 2001; Li et al., 2012). Lowenstern (2001) suggested that fluid boiling in the H2O-CO2-NaCl system is likely to be common even at mid-crustal levels. Chen and Wang (2011) proposed that ore bodies formed in the post-collisional tectonic setting are derived from the continental crust with a high CO2 content. These observations, including the data from the fluid inclusions presented here, indicates that the ore-forming fluid forming the Matou Mo was derived from the lower crust. Exsolution of the Stage I fluids was synchronous with the emplacement of the porphyritic granodiorite. The fluid then evolved into the ore-forming Stage II fluid (c.f. Li et al., 2011; Chen et al., 2012). At this stage, ore-forming fluids boiled resulting in phase

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separations and a significant change in the salinity of the mineralized fluids (Fig. 9a). The homogenization temperature and salinities of Stage II fluid inclusions decrease in temperature and salinity from the Stage II to Stage III fluids (Fig. 9a). The decreasing temperature and salinity could have been due to the intrusion of cooler, meteoricwater that mixed with magmatic fluid, the magma being the heat engine started to cool with time, or is associated with a decrease in pressure.

4.4. Source of metals and ore-forming fluids There is an increasing interest on the source of metals and sulfur in the study of porphyry-type ore deposits worldwide (e.g., Hedenquist and Lowenstern, 1994; Kinny and Maas 2003; Wu et al., 2007; Audetat, 2010; Zeng et al., 2013). There is evidence indicating that repeated addition of mafic magma in a compositionally zoned magma chamber leads to the deposition of S-Cu-Au-Mo in porphyry deposits (Hattori and Keith, 2001; Halter et al., 2002; Stern et al., 2007). The source of the metals, however, still seems to be a matter of debate. There are various references to Mo being derived from mafic magma or the mantle (e.g. Audetat, 2010; Pettke et al., 2010; Li et al., 2014a). Others propose that Mo is derived from the crust (e.g. Sinclair, 2007; Zhu et al., 2009). Although there is some opposition to the using of Re content for tracing the source of Mo (e.g. Berzina et al., 2005), there is a higher consensus it can be used for this purpose (e.g.Foster et al., 1996; Mao et al., 1999; Selby and Creaser 2001;Voudouris et al., 2009). Based on studies of the Re–Os isotopic compositions for intermediate and felsic associated with Mo deposits in China, it is found that Re content in ore reaches tens of ppm and is derived from a mixed crustal and mantle source (Mao et al.,1999; Li et al., 2007;Meng et al., 2007; Zhu et

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al., 2008; Song, 2010), whereas deposits with a crustal source have lower concentrations of Re with values of ≤ 1−n ppm. Song (2010) compared data on the Re content of Mo from 115 Mo-related deposits worldwide, including Cu-Mo deposits, Mo deposits and W-Mo deposits. The results show that there is a gradual decrease in Re from 70-1000 ppm in Cu-Mo deposits, 7-60 ppm in Mo deposits, to 0.1-8 ppm in W-Mo deposits, which is consistent with a decrease in the mantle contribution to the magma source for the mineralization. The Mo samples from the Matou deposit have a Re content between 84 and 155 ppm (Table 2) which, again, is indicative of a mixed crustal and mantle source for the ore-forming material. The Re content in molybdenite versus the zircon εHf(t) values plot in Fig. 11 shows that there are remarkable differences between porphyry Mo, W-Mo, Cu-Mo, and Cu-Au deposits. The Qulong (Cu-Mo) (Yang et al., 2011), Yulong (Cu-Au ) (Wang et al., 2011), Duobuza (Cu-Au) (Li et al., 2014b), Nuri (Cu-W-Mo) (Chen, 2015), and Baogutu Cu-Au porphyry deposits (Cao, 2014) plot in the top right corner of Fig.11, with Remolybdenite greater than 100 ppm and zircon εHf(t) value more than zero. This indicates that the deposits formed largely from a mantle-dominant source. In contrast, the Wenquan (Mo) (Zhu et al., 2011), Sharang (Mo) (Zhao et al., 2014a), Gaoaobei (W-Mo) (Wang et al., 2010), Jitoushan (W-Mo) (Song et al., 2012), Baizhangyan (W-Mo) (Song et al., 2013), Tangjiaping (Mo) (Wei et al., 2010), and Yuchiling (Mo) (Cheng et al., 2013) porphyry deposits plot in the bottom left corner of the figure with Remolybdenite less than 100 ppm and zircon εHf(t) values of less than zero. This indicates a crust-dominant source of metals. Other deposits at Wushan (Cu-Mo) (Zhao et al., 2014b), Baoshan (Cu-Mo) (Wang et al., 2010), Tongshankou (Cu-Mo) (Liet al., 2008), and Matou (Mo) plot in the bottom right corner of the figure with Remolybdenite more than 100 ppm and zircon εHf(t) values of

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greater than zero, indicates a crust-dominant source metals with some contribution from the mantle material. The distribution of measured and calculated hydrothermal fluid compositions on a conventional hydrogen versus oxygen isotope diagramis shown in Fig. 9b. The δ18Owater (9.4 to 10.5 per mil) and δD values (–48.3 to –50.6 per mil) for quartz samples from Stage II veins are not characteristic of magmatic water (δDwater = –80 to -40 per mil; δ18Owater = 5.5 to 9.0 per mil, Taylor and Hugh, 1974). However, the values are within the range for formational or meteoric water (Fig. 9b; Table 4), indicating a significant input of meteoric water or degassing of magma that is crystallizing (Rye, 1993; Liu et al., 2014). This is different from the Baizhangyan and Jitoushan W-Mo deposits that did not have a significant incursion of meteoric water during the formation of ore-forming fluids (Fig. 9b). The sulfur isotopesin metal deposits along the YVMB vary significantly with δ34S values from -15 to 20 (Fig. 8) (Chang et al., 1991; Song, 2010; Song et al., 2012). The δ34S values in most porphyry deposits are less varied from -5 to 8‰ (Fig. 11), which are broadly consistent with the magmatic sulfur range of -3 to 3‰ (Chaussidon et al., 1989). Eight sulfide samples from the Matou Mo deposit can be grouped into two distinct groups with δ34S of3.03 to 3.69‰ (Group 1) and 7.42 to 9.67‰ (Group 2), which indicate that there are two kinds of sources for sulfur (Fig. 9c; Table 5; Appendix 1). Group 1 is from six samples of Mo are within in the range of the sulfur isotopic values from most porphyry deposits in the world (Fig. 12). These include the Badaguan Cu-Mo deposit in NE China (Mi et al., 2016), Wenquan Mo deposit in Western Qinling Orogen (Xiong et al., 2016), Climax Mo deposit in the USA (Stein and Hannah, 1985), and others deposits from the YVMB (Chang et al.,

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1991). Chang et al.(1991) analyzed 398 sulfide samples from deposits and magmatic rocks in the belt and found that magmatic rocks have an average δ34S value of 5.5‰, and mineralization has an average δ34S value of 5‰. This is consistent with mixing of crust- and mantle-derived sulfur. Collectively, sulfur isotopic composition of the first groupis interpreted to reflect a predominantly crustal and lesser mantle origin for the sulfur inventory at the Matou deposit. The Group 2 δ34S values are from two samples of pyrite from sandstone at Matou and are higher than those of Group 1 (Fig. 9c; Table 5). This indicates that although the sedimentary rocks in the Matou area are not the prime source for the sulfur at the deposit, they have contributed sulfur to the main magmatic source. Therefore, the data presented above suggest thattheore-forming fluids and metals originated from granitic magmatismin the lower crust during the Jurassic. The ore-forming fluids (Stage II) originated from a magmatic source with continued input of meteoric water (Figs. 9, 12). Combining the discussion on the evolution processes of magma and ore-forming fluids above, a magmatic and hydrothermal model for the Matou deposit is presented in Figure 12. In the model, the ca. 147 Ma Matou porphyritic granodiorite developed during a transition from compressional to extensional tectonic settings. The magma was then contaminated when passing through the crust, and the associated fluids carried Mo from the magma and sulfur from the crust. The mineralized fluid then boiled during changes in temperatures or pressures resulting in Mo deposition along the contact between the porphyritic granodiorite and wallrock, and a phase separation of the fluid into saline-rich and CO2-rich (Fig. 12a). During ca. 140 Ma, increased tectonic extension orientated in a N-S direction led to the emplacement of mantle-derived mafic magma forming the porphyritic diorite at Matou, which intruded the porphyritic granodiorite rocks and Mo(-Cu) mineralization (Fig.

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12b). The N-S orientated extension diminished in intensity during or shortly after ca. 135 Ma with the intrusion of dolerite (Fig. 12b), and mantle-derived materials control the formation of magmatic rocks. 5.

Conclusions

There are three magmatic events in the Matou area , which are represented by the ca. 147 Ma porphyritic granodiorite, ca. 140 Ma porphyritic diorite, and ca. 135 Ma dolerite. The Mo mineralization is closely associated with the ca. 147 Ma porphyritic granodiorite. The oldest Mo mineralization event at Matou took place during the initial transition from compressional to extensional tectonics that culminated by or shortly after ca. 135 Ma. This event between 147 and 135 Ma was accompanied by magmatism represented by the three magmatic events at Matou, which originated from the lower crust and mantle. The extensional event was orientated in a N-S direction, and as it developed a change in magmatism is represented by the porphyritic granodiorite followed by the porphyritic diorite and finally the dolerite. This change in rock type represents a transition from crust-dominant to mantle-dominant magmatism. The Matou porphyritic granodiorite sourced predominantly from the lower crust with a minor contribution from the mantle. This magmatism, associated with magmatic fluids containing Mo and sulfur, reached the upper crust where the Mo mineralization was deposited. As the compressional tectonics diminished, the extensional setting continued with the intrusion of the porphyritic diorite and later dolerite. The porphyritic diorite may relate to the small scale copper mineralization located in the southern part of the Matou deposit.

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Three stages of fluids have been identified at Matou, which are the initial magmatic fluids (Stage I), ore-forming fluids (Stage II), and barren fluids (Stage III). The Stage II fluids were in the temperature range 170°-360º C with salinities of 5-39.2% NaCl equiv in an H2O-CO2-NaCl system. Two distinctive fluid inclusion types of rich in CO2 (gas) and rich in salinity can be found at the deposit, indicating the occurrence of fluid boiling during the fluid’s evolution from Stage I to Stage II. Combined evidence of the Re content of the molybdenite, comparative studies on the Re contents in molybdenite versus zircon εHf(t) values for different deposits in the region, H–O isotopic compositions of the ore-forming fluid (Stage II), and S-isotopic signatures of sulfides from Matou suggest that the ore-forming fluids and metals possibly originated from the Jurassic porphyritic granodiorite with a source from the lower crust. The increase in the incursion of meteoric water also played an important role in the mineralizing process.

Acknowledgements The Intellectual Innovation Project, Chinese Academy of Sciences (Grant No. KZCX1-YW-15-3) and NSFC grant (Grant No. 41102046) supported this study. Thanks go to Li Deting and Anhui Zhongke Mining Co., Ltd. for their valuable support in the field during this study. We are also grateful to Hu Zhaochu for help during zircon LA-ICPMS U-Pb dating and Lu-Hf analyses, Li He for help during major elements analyses, Yan Xin and Yang Saihong for help during zircon CL analyses. The editors and reviewers are thanked for their constructive and valuable comments, which greatly contributed to the improvement of the manuscript.

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Appendix 1 Analytical methods Major, trace and REE elements analysis Samples for major, trace and REE elements analysis were taken from PD301 and other drill-core material. Whole rock samples were ground into powders of ~200 meshes in size. For major element analysis, 0.5 g powders were accurately weighed and then ignited under 1000° C for about 60 min. The weight loss divided by original weight (0.5 g) is taken as a loss on ignition (LOI) as listed in Table 1. The ignited powders were then mixed with powders of 67 wt. % Li2B4O7+ 33 wt. % LiBO2 (5 g), and melted to make glass pellets. The pellets were then analyzed by X-ray fluorescence spectroscopy (XRF) with an AXIOS Minerals spectrometer at the IGGCAS. The analytical uncertainties were basically within 0.1–1% (RSD). Trace element abundances were obtained by inductively coupled plasma mass spectrometry (ICP-MS) using a Finnigan MAT Element spectrometer, with analytical uncertainties within 5% for most elements, at the IGGCAS. Whole rock powders (40 mg) were dissolved in distilled HF+HNO3 in 15 ml high-pressure Teflon bombs at 200 °C for 5 days, dried and then diluted to 50 ml for analysis. A blank solution was analyzed and the total procedural blank was 50 ng in weight for all trace elements. Indium was used as an internal standard to correct for matrix effects and instrument drift. Precision for all trace elements is estimated to be 5% and accuracy is better than 5% for most elements by analyses of the GSR-1 standard.

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Zircon LA-ICP-MS U-Pb analysis The locations of the samples for the U-Pb dating are shown in Fig. 5. Sample P5-12, P5-13, and P5-95 were all taken from PD301 adit. Sample P5-12 is porphyritic granodiorite with silica-, chlorite-, and sericite-alteration (Fig. 3a). Sample P5-13 (30°23′01″ N, 117°45′59″ E) is of porphyritic diorite that cuts through the sedimentary rocks and the porphyritic granodiorite. The diorite has moderate degree chlorite- and sericite-alteration. Sample P5-95 is dolerite with weak carbonate alteration. Zircon grains were separated using the standard methods involving heavy liquid and magnetic separation. The grains were then handpicked under a binocular microscope to choose the most suitable specimens for dating. The selected zircon grains were mounted in epoxy with standard zircon grains (91500) and then polished to expose the internal structures. Cathodoluminescence (CL) images (Fig. 5) show that all three samples are zoned. The zircons from sample P5-12 have the clearest concentric zonation, with most of the zircon grains intact. The size of the zircon grains ranges from 100 to 300 µm with a length to width ratio (aspect ratio) of up to 3:1. The zircons from sample P5-13 have moderately clear concentric zoning, have a size range of 60-300 µm and an aspect ratio of up to 3:1, and half of the zircon grains are intact. The zircons from sample P5-95 also have moderately clear concentric zoning, with a size range of 100-200 µm and an aspect ratio of up to 2:1. Most of the zircon grains are defective. Zircon U–Pb isotopic dating was performed with an Agilent 7500 ICP-MS instrument at the China University of Geosciences,

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Wuhan (CUG). Zircon 91500 was used as the external standard and NIST 610 was used to optimize the results of the U–Pb dating. The spot diameter was 45 µm. The analytical methodology is described in detail in Liu et al. (2010). Data reduction was performed with the ICPMSDataCal (Liu et al., 2010) and ISOPLOT (Ludwig, 2003). The uncertainties for individual analyses (ratios and ages) are quoted at the 1 σ level, whereas the errors in the Concordia and weighted mean ages are quoted at the 2σ level. The zircon U–Pb isotopic data are listed in Supplemental data Table 1.

Zircon Hf analysis The zircon Hf isotopes were measured in situ using a Neptune multi-collector ICP-MS (with a 193nm laser ablation microprobe attached) at IGGCAS, Beijing. Spot sizes of ~60 µm and a laser repetition rate of 10 Hz at 100 mJ were used. The raw count rates for 172

Yb,

173

Yb,

175

corrections for

Lu,

176

176

(Hf+Yb+Lu),

Lu and

176

177

Hf,

178

Hf,

179

Hf,

180

Hf, and

182

W were recorded simultaneously, and the isobaric interference

Yb on 176Hf were made based on precise determinations.

176

Lu was calibrated using the

175

Lu value,

whereas the 176Yb/172Yb ratio of 0.5887 and mean βYb value obtained at the same spot were employed for the interference correction of 176Yb on 176Hf (Iizuka and Hirata 2005). Details of this analytical technique can be found in Wu et al., (2007). During the analysis, the

176

Hf/177Hf and

176

The measured average

Lu/177Hf ratios of the standard zircon 91500 were 0.282299±0.000035 (2σ, n=29) and 0.00030, respectively. 176

Hf/177Hf ratio agrees with the ratios previously acquired by the solution method (0.282302±0.000008 (2σ),

Goolaerts et al., 2004; 0.282306±0.000008 (2σ), Woodhead et al., 2004).

49

Molybdenite Re-Os analysis Six veinlet-disseminated type molybdenite samples for the Re-Os dating were collected from PD301 adit (Fig. 2b) and were separated with a greater than 99% purity through shattering, water elutriating, and electromagnetic election, alcohol elutriating, and heavy liquid separation. Re-Os isotope analysis was performed at the Re-Os Laboratory of the National Research Center of Geoanalysis and the Chinese Academy of Geological Sciences (CAGS) in Beijing. The analytical protocol was as described in Shireyand Walker(1995), Duet al., (2001), and Qu et al., (2003). The Re blank was about 10 pg and the common Os was about l pg in the whole process. These values are much lower than the Re and Os content in the samples, and we thus assume that they do not influence the accuracy of the Re and Os isotopic measurements.

Fluid inclusions analysis Ten doubly polished sections of samples were prepared for fluid inclusion microthermometric analysis and Laser Raman microprobe analysis, to analyze fluid compositions and temperatures. Heating and cooling experiments were carried out using a Linkman THMS 600 programmable heating-freezing stage at the Fluid inclusions Lab of IGGCAS. The reproducibility of measurements was ±0.2° C below +30° C and ±2° C above 100° C, where the chips were centered in the specimen holder. Salinity is expressed as equivalent wt. % NaCl (Fan et al., 2006). In order to confirm fluid inclusion volatile species, representative samples were analyzed using a Renishaw

50

2000 Laser Raman micro-spectrometer equipped with a CCD detector and an Ar ion laser with a wavelength of 514.5 nm at IGGCAS. The measured spectrum of counts for 10 seconds, every 1 cm-1 (wave number) count one, 100 cm-1 to 4000 cm-1 to take the whole band a peak, the spot size of laser beam about 1µm, the spectral resolution of 2 cm-1. The results of heating, freezing and component analysis studies of inclusions are presented in Table 3 and Fig. 7.

Sulfur isotope analysis Six molybdenite samples with over 99% purity were prepared for sulfur isotope analysis through shattering, water elutriating, and electromagnetic election, alcohol elutriating and heavy liquid separation. Sulfur isotope analysis was performed at the stable isotope Laboratory, IGGCAS in Beijing. During sulfur isotopes testing, each sample weighed 15mg, and mixed with CuO powder evenly placed in a vacuum quartz tube, reacted 15min at a temperature of 1100° C. After purification, SO2 transferred to the sample tube. The 34

S/33S of SO2 composition was tested by Delta-S mass spectrometer in the determination of CDT relative to the δ (‰) form, and the

analysis accuracy is ± 0.2‰ (Chu et al., 2007).

H-O isotope analysis H-O isotope analysis was performed at Stable Isotope Laboratory of IGGCAS. Quartz samples from main Mo ore-forming stage are selected for hydrogen and oxygen isotopes analysis. For hydrogen isotope measurement thermal burst method was adopted extracted

51

H2O of fluid inclusions in samples reacted with Zn to take H2, and then it was fixed in a mass spectrometer for determination of hydrogen isotope. Using the conventional BrF5 testing method for oxygen isotope, test equipment for the MAT253 mass spectrometer, and to SMOW standard, hydrogen and oxygen isotope analysis precision is ±2 per mil and ±0.2 per mil. The conversion of δ18OPDB and δ18OSMOW used δ18OSMOW=1.03086×δ18 OPDB+30.86.

52

Figure captions Fig. 1. Regional tectonic sketch map of the Middle-Lower Yangtze Valley (modified after Mao et al., 2003 and Song et al., 2010).

Fig. 2. Maps showing: (a) regional geology of the Chizhou area; (b) local geology of the Matou Mo deposit; and (c) profile of the PD301 adit.

Fig. 3. Photographs and microphotographs of rocks from the Matou deposit: (a) hand specimen of the porphyritic granodiorite with microphotograph a-1 and a-2 of granodiorite; (b) hand specimen of the porphyritic diorite showing microphotographs b-1 and b-2 of porphyritic diorite; (c) hand specimen of Silurian sandstone with microphotographs c-1 and c-2 showing strong sericite alteration. Photographs of (d), (e), and (f) are of hand specimens of Mo, and microphotographs (g), (h), (i) and (j) are of ore minerals. Abbreviations: Bio-biotite, Cc-calcite, Chl-chlorite, Cpy-chalcopyrite, Moly-molybdenite, Pl-plagioclase, Py-pyrite, Q-quartz, Gal-galena.

Fig. 4. Geochemical diagrams of magmatic rocks from the Matou area: (a) SiO2 versus Na2O + K2 O diagram; (b) SiO2 versus K2O diagram; (c) REE distribution pattern diagram; (d) spider diagram of trace elements; (e) Rb/Sr versus Ba/Rb diagram; and (F) La versus La/Yb diagram. Data are from Tang et al. (1998), Zhang and Xu (2002), Qi et al. (2002), Wang et al. (2004), Hou (2005), Wang (2007), Lu (2008), Xie (2008), Wang (2009), Liu et al. (2012), Song et al. (2014).

Fig. 5. Zircon CL images and analyzed points for Samples P5-12 (granodiorite), P5-13 (diorite) and P5-95 (dolerite) from Matou, and their corresponding zircon U-Pb Concordia diagrams.

53

Fig. 6. Re-Os isochron and weighted mean age diagram of molybdenite from the Matou Mo deposit: (a) Re-Os isochron age; and (b) Re-Os isotopic weighted mean age.

Fig. 7. Microphotographs of different types of fluid inclusions from the Matou Mo deposit and the Raman composition of the inclusions.

Fig. 8. Geochronology of magmatism and Mo mineralization in the Yangtze Valley metallogenic belt (YVMB) and their corresponding tectonic settings (modified after Song, 2010). Data are from Tang et al. (1998), Hou (2005), Wang (2007), Lu (2008), Xie (2008), Zhou et al. (2008), Wang (2009), Liu et al. (2012), Song et al. (2014).

Fig. 9. Plots of: (a) salinity versus temperature for fluid inclusions; (b) H-O isotope diagram of quartz; and (c) sulfur isotope values of sulfide samples from the Matou Mo deposit. Sulfur isotope data are from Tang et al. (1998), Hou (2005), Wang (2007), Lu (2008), Xie (2008), Wang (2009), Song (2010), Song et al. (2013).

Fig. 10. Hf isotope histograms of zircons from magmatic rocks at the Matou deposit. Zircon Hf isotope data are from Hou (2005), Wang (2007), Lu (2008), Xie (2008), Zhou et al. (2008), Wang (2009), Liu et al. (2012), Song et al. (2012, 2013, 2014).

Fig. 11.Average εHf(t) values in zircon vs. average values of the Re concentration in Mo from porphyry-type W-Mo, Mo, Cu-Mo, and Cu-Au deposits in China. Data are from Yang et al. (2011), Wang et al. (2011), Wang (2012), Li et al. (2014a), Li et al. (2014b), Chen (2015), Cao (2014), Zhu et al. (2011), Zhao et al. (2014), Wang et al. (2010), Song et al. (2012), Song et al. (2013), Wei et al.

54

(2010), and Cheng et al. (2013).

Fig. 12 Sketch models of the Matou deposit showing: (a) the ore-forming mechanism; and (b) and generalized evolution of intrusive rocks.

55

FIG. 1.

56

FIG. 2.

57

58

FIG. 3.

59

60

FIG. 4.

61

62

FIG. 5.

63

64

FIG. 6.

65

FIG. 7.

FIG. 8.

66

FIG. 9.

67

FIG.10.

68

FIG. 11.

69

FIG. 12.

70

71

Tables Table 1. Whole-rock and trace element analyses for rocks from the Matou Mo deposit at Chizhou. Sample NO.

SiO2

TiO2

Al 2O3

Fe2O3

FeO

MnO

MgO

CaO

Na2O

K2O

P2O5

LOI

Total

Rb

Th

U

Sr

Pb

Mo

Nb

Ba

Ta

P5-16

64.2

0.71

15.8

1.04

2.05

0.06

2.17

2.90

4.14

3.58

0.21

3.11

100.0

142

8.30

1.87

510

14.2

23.2

24.0

651

1.02

P5-25

62.9

0.92

16.3

1.61

2.01

0.05

2.28

2.30

3.42

3.18

0.33

4.91

100.2

132

7.90

1.67

512

24.0

20.5

23.3

498

1.01

P5-45

64.6

1.13

16.8

1.18

1.97

0.04

2.19

1.80

4.21

2.78

0.45

2.71

99.9

122

7.50

1.47

514

33.8

17.8

22.6

545

1.00

P5-13

57.1

0.87

17.0

2.32

2.70

0.18

1.85

4.63

1.35

3.93

0.35

7.77

100.1

178

8.37

2.52

185

28.4

4.63

24.1

147

1.89

P5-13-1

58.1

0.91

16.7

2.01

2.89

0.20

1.96

4.71

2.17

2.98

0.56

6.03

99.3

164

9.11

3.01

171

33.0

3.98

23.8

167

1.45

P5-13-2

57.9

0.82

16.8

2.28

2.92

0.31

1.79

4.50

2.23

3.88

0.35

5.51

99.4

150

9.85

3.50

207

37.6

3.33

23.5

157

1.01

P5-95

48.1

2.41

15.5

4.45

8.19

0.25

6.15

8.13

2.84

1.31

0.47

1.53

99.3

38.5

2.66

0.54

519

4.65

12.3

411

0.74

P5-96

47.8

2.45

14.9

4.38

8.31

0.21

6.34

7.84

3.08

1.32

0.52

2.41

99.6

42.3

2.71

0.57

531

3.31

12.6

413

0.76

Sample NO.

La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Y

∑REE

δEu

La/Yb

P5-16

18.1

39.6

6.21

21.8

4.62

1.27

4.04

0.50

3.24

0.60

1.40

0.25

1.47

0.23

16.2

120

0.29

12.3

P5-25

18.9

40.2

7.31

22.9

5.51

2.07

3.94

0.40

3.11

0.80

1.30

0.28

1.42

0.24

15.3

124

0.44

13.3

P5-45

19.7

40.8

8.41

24.0

6.40

2.87

3.84

0.30

2.98

1.00

1.20

0.31

1.37

0.25

14.4

128

0.56

14.4

P5-13

38.7

77.0

9.52

38.8

7.91

2.33

7.18

1.02

5.02

0.74

1.90

0.25

1.52

0.19

22.1

214

0.31

25.5

P5-13-1

39.1

81.0

10.1

31.3

6.88

2.98

8.11

1.81

7.10

0.81

1.81

0.19

1.66

0.18

23.9

217

0.40

23.6

P5-13-2

39.5

85.0

10.7

33.8

7.85

3.63

7.04

1.60

6.18

0.88

1.72

0.13

1.80

0.17

25.7

226

0.49

21.9

P5-95

29.9

65.5

9.51

36.9

8.52

2.44

8.32

1.34

7.81

1.59

4.31

0.65

3.98

0.66

39.5

221

0.29

7.51

P5-96

30.4

64.3

9.66

38.1

8.41

2.52

8.19

1.29

8.15

1.66

4.48

0.67

4.02

0.61

40.0

222

0.30

7.56

Note: Rock types of samples in this paper, P5-16,P5-25, and P5-45 are from the Matou porphyritic granodiorite; P5-13, P5-13-1 and P5-13-2 are from porphyritic diorite; P5-95 and P5-96 are from dolerite.

72

Table 2. Zircon U-Pb isotopic analyses for rocks from the Matou Mo deposit, Chizhou. Sample No. P5-12-01 P5-12-02 P5-12-03 P5-12-04 P5-12-05 P5-12-06 P5-12-07 P5-12-08 P5-12-09 P5-12-10 P5-12-11 P5-12-12 P5-12-13 P5-12-14 P5-12-15 P5-12-16 P5-12-17 P5-12-18 P5-13-1 P5-13-2 P5-13-3 P5-13-4 P5-13-5 P5-13-6 P5-13-7 P5-13-8

Th/U

207

U

Th

Pb/

ppm 151

ppm 300

1.987

U 0.1687

111 76 80 83 160 260 179 71 154 120 61 648 65 143 106 86 226

283 179 182 179 281 559 207 223 325 243 107 594 177 319 237 122 294

2.564 2.360 2.266 2.140 1.758 2.151 1.160 3.125 2.112 2.016 1.752 0.916 2.740 2.227 2.245 1.419 1.299

0.1757 0.1677 0.1960 1.0901 0.1559 2.8402 4.5768 0.1463 0.2216 0.1790 10.9919 1.9882 3.4576 0.1680 0.1517 0.4745 0.1446

243 205 234 243 321 101 263 259

72 142 84 91 130 48 84 108

0.296 0.691 0.360 0.374 0.404 0.472 0.321 0.417

0.1536 0.1401 0.1509 0.1473 0.1402 0.7254 0.1320 0.1455

±σ

235

73

206

Pb/

±σ

238

206

Pb/

±σ

238

U 0.0238

0.13

U 152

8

3.49 3.67 47.06 7.84 8.81 6.42 7.58 11.41 2.05

0.0232 0.0230 0.0228 0.1187 0.0242 0.2250 0.3139 0.0230 0.0232 0.0233 0.4749 0.1807 0.1900 0.0228 0.0239 0.0258 0.0228

0.10 0.14 0.13 0.72 0.20 0.77 1.45 0.10 0.10 0.12 1.45 0.36 0.33 0.19 0.26 0.33 0.10

148 147 145 723 154 1308 1760 147 148 148 2505 1071 1121 145 152 164 145

6 9 8 42 13 41 71 6 6 8 63 20 18 12 16 21 6

2.91 3.99 2.70 2.77 2.89 2.65 4.59 2.82

0.0225 0.0218 0.0220 0.0215 0.0220 0.0814 0.0212 0.0218

1.53 1.54 1.52 1.67 1.53 1.58 1.56 1.54

143 139 140 137 141 504 135 139

2 2 2 2 2 8 2 2

2.80 3.15 3.93 4.80 16.73 4.21 19.28 38.84 1.92

P5-13-9 P5-13-10 P5-13-11 P5-13-12 P5-13-13 P5-13-14 P5-13-15 P5-13-16 P5-13-17 P5-13-18 P5-13-19 P5-13-20

216 260 243 357 392 191 306 335 250 485 454 233

70 105 98 178 165 52 111 133 109 226 218 90

0.324 0.403 0.405 0.498 0.421 0.271 0.364 0.397 0.438 0.467 0.480 0.385

0.1510 0.1485 0.1432 0.1395 0.1560 0.1456 0.1429 0.1471 0.1429 0.1568 0.1522 0.1406

2.93 3.10 3.32 4.65 3.64 4.25 4.42 3.15 3.83 2.96 2.71 5.45

0.0217 0.0224 0.0220 0.0218 0.0229 0.0218 0.0217 0.0216 0.0216 0.0226 0.0227 0.0216

1.56 1.53 1.53 2.02 1.53 1.53 1.54 1.53 1.55 1.56 1.51 1.59

138 143 140 139 146 139 139 138 138 144 145 138

2 2 2 3 2 2 2 2 2 2 2 2

P5-95-01 P5-95-02 P5-95-03 P5-95-04 P5-95-05 P5-95-06 P5-95-07 P5-95-08 P5-95-09 P5-95-10 P5-95-11 P5-95-12 P5-95-13 P5-95-14 P5-95-15 P5-95-16 P5-95-17 P5-95-18

500 582 529 525 368 335 305 537 486 443 511 381 577 639 391 422 396 505

438 432 562 469 255 194 181 368 415 354 431 295 597 544 215 247 223 414

0.875 0.742 1.064 0.894 0.691 0.579 0.594 0.685 0.853 0.799 0.845 0.775 1.034 0.852 0.551 0.585 0.564 0.821

0.15096 0.14549 0.13201 0.72544 0.14023 0.14726 0.15095 0.14058 0.14014 0.15218 0.15681 0.14294 0.14291 0.14562 0.15595 0.13950 0.14324 0.14847

2.93 2.82 4.59 2.65 2.89 2.77 2.70 5.45 3.99 2.71 2.96 3.83 4.42 4.25 3.64 4.65 3.32 3.10

0.0217 0.0218 0.0212 0.0814 0.0220 0.0215 0.0220 0.0216 0.0218 0.0227 0.0226 0.0216 0.0217 0.0218 0.0229 0.0218 0.0220 0.0224

1.56 1.54 1.56 1.58 1.53 1.67 1.52 1.59 1.54 1.51 1.56 1.55 1.54 1.53 1.53 2.02 1.53 1.53

131 135 135 133 136 136 137 138 136 136 137 133 136 135 132 134 133 133

2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

P5-95-19

343

173

0.505

0.15365

2.91

0.0225

1.53

138

2

74

Table 3. Zircon Hf isotopic analyses for rocks from the Matou Mo deposit at Chizhou. eHf(0)

eHf(t)

TDM (Ma)

TDMC(M a)

fLu/Hf

0.282520 0.282427 0.282567 0.282545 0.282454 0.282497 0.281906 0.281463 0.282495 0.282508 0.282543 0.281202 0.282247 0.281406 0.282532 0.282210 0.282438

-8.8 -12.1 -7.2 -7.9 -10.8 -9.6 -29.8 -45.6 -9.7 -9.2 -8.0 -53.8 -14.1 -47.6 -8.4 -19.8 -11.7

-5.6 -9.0 -4.0 -4.9 4.7 -6.3 -1.6 -7.1 -6.6 -6.1 -4.8 0.7 5.1 -23.6 -5.3 -16.6 -8.2

1029 1163 962 997 1108 1065 1858 2449 1064 1048 996 2793 1442 2548 1017 1458 1144

1380 1565 1290 1334 1263 1424 2076 2732 1431 1405 1336 2907 1517 3117 1360 1986 1537

-0.97 -0.97 -0.98 -0.97 -0.97 -0.97 -0.97 -0.98 -0.97 -0.97 -0.98 -0.97 -0.81 -0.97 -0.97 -0.98 -0.97

0.000020

0.282518

-8.8

-5.7

1060

1385

-0.94

0.282520

0.000007

0.282518

-8.9

-5.9

1030

1389

-0.98

0.282554 0.282542 0.282510 0.282510 0.282368 0.282486

0.000008 0.000007 0.000006 0.000008 0.000009 0.000010

0.282550 0.282540 0.282509 0.282507 0.282357 0.282485

-7.7 -8.1 -9.3 -9.3 -14.3 -10.1

-4.8 -5.1 -6.3 -6.3 -3.6 -7.2

1008 1002 1041 1054 1256 1073

1328 1346 1409 1411 1548 1457

-0.95 -0.97 -0.98 -0.97 -0.97 -0.98

No.

Age (Ma)

P5-12 01 P5-12 02 P5-12 03 P5-12 04 P5-12 05 P5-12 06 P5-12 07 P5-12 08 P5-12 09 P5-12 10 P5-12 11 P5-12 12 P5-12 13 P5-12 14 P5-12 15 P5-12 16 P5-12 17

152 148 147 145 723 154 1308 1760 147 148 148 2505 1071 1121 145 152 164

0.023227 0.026342 0.021634 0.025374 0.023923 0.026589 0.027768 0.016333 0.022655 0.025435 0.021235 0.030784 0.210582 0.025196 0.027185 0.019543 0.023322

0.000854 0.000969 0.000826 0.000960 0.000848 0.001011 0.000970 0.000562 0.000868 0.000961 0.000826 0.001016 0.006218 0.000894 0.001046 0.000743 0.000851

0.282523 0.282429 0.282569 0.282547 0.282466 0.282500 0.281930 0.281482 0.282498 0.282511 0.282546 0.281251 0.282373 0.281425 0.282535 0.282212 0.282440

0.000017 0.000014 0.000016 0.000017 0.000016 0.000018 0.000016 0.000015 0.000016 0.000018 0.000016 0.000019 0.000023 0.000017 0.000017 0.000017 0.000022

P5-12 18

150

0.055738

0.002036

0.282524

P5-13 01 P5-13 02 P5-13 03 P5-13 04 P5-13 05 P5-13 06 P5-13 07

143

0.021774

0.000749

139 140 137 141 504 135

0.053470 0.027164 0.020257 0.035476 0.035569 0.019544

0.001730 0.000876 0.000675 0.001099 0.001160 0.000636

176

Yb /177Hf

176

Lu/177Hf

176

Hf/177Hf

176

2σ

75

Hf/177Hfi

P5-13 08 P5-13 09 P5-13 10 P5-13 11 P5-13 12 P5-13 13 P5-13 14 P5-13 15

139 138 143 140 139 146 139 139

0.033385 0.042669 0.026969 0.033649 0.036376 0.019969 0.037278 0.035037

0.001102 0.001169 0.000880 0.001061 0.001192 0.000652 0.001017 0.001000

0.282561 0.282550 0.282536 0.282560 0.282534 0.282520 0.282539 0.282535

0.000006 0.000010 0.000006 0.000009 0.000010 0.000007 0.000010 0.000009

0.282558 0.282547 0.282533 0.282557 0.282531 0.282518 0.282537 0.282532

-7.5 -7.8 -8.4 -7.5 -8.4 -8.9 -8.2 -8.4

-4.5 -4.9 -5.3 -4.5 -5.5 -5.8 -5.3 -5.4

981 998 1011 982 1022 1027 1010 1016

1311 1333 1358 1313 1365 1387 1353 1362

-0.97 -0.96 -0.97 -0.97 -0.96 -0.98 -0.97 -0.97

P5-13 16 P5-95-01

138

0.030826

0.001038

0.282524

0.000007

0.282521

-8.8

-5.8

1032

1384

-0.97

131

0.151703

0.004320

0.282680

0.000010

0.282669

-3.3

-0.8

890

1096

-0.87

P5-95-02 P5-95-03 P5-95-04 P5-95-05 P5-95-06 P5-95-07 P5-95-08 P5-95-09 P5-95-10 P5-95-11 P5-95-12 P5-95-13 P5-95-14 P5-95-15

135 135 133 136 136 137 138 136 136 137 133 136 135 132

0.035451 0.063331 0.045711 0.068177 0.065174 0.118712 0.112853 0.060427 0.096515 0.061846 0.108754 0.093186 0.072847 0.069689

0.001069 0.001916 0.001378 0.002074 0.001992 0.003432 0.003221 0.001818 0.002801 0.001924 0.003135 0.002835 0.002088 0.002038

0.282555 0.282594 0.282531 0.282598 0.282560 0.282643 0.282645 0.282580 0.282596 0.282600 0.282729 0.282594 0.282614 0.282583

0.000009 0.000009 0.000010 0.000009 0.000011 0.000011 0.000012 0.000009 0.000009 0.000009 0.000014 0.000009 0.000009 0.000009

0.282552 0.282589 0.282527 0.282593 0.282555 0.282634 0.282637 0.282575 0.282588 0.282595 0.282721 0.282587 0.282609 0.282577

-7.7 -6.3 -8.5 -6.1 -7.5 -4.6 -4.5 -6.8 -6.2 -6.1 -1.5 -6.3 -5.6 -6.7

-4.8 -3.5 -5.7 -3.3 -4.7 -1.9 -1.8 -4.0 -3.5 -3.3 1.1 -3.6 -2.8 -4.0

990 955 1032 953 1006 923 914 974 977 947 786 979 931 975

1325 1251 1374 1244 1318 1163 1156 1279 1253 1239 992 1255 1213 1276

-0.97 -0.94 -0.96 -0.94 -0.94 -0.90 -0.90 -0.95 -0.92 -0.94 -0.91 -0.91 -0.94 -0.94

P5-95-16

134

0.069610

0.002077

0.282581

0.000009

0.282576

-6.7

-4.0

978

1277

-0.94

76

Table 4. Re-Os isotopic analyses of molybdenite from the Matou Mo deposit at Chizhou. Sample No.

Weight (g)

187

Re(µg/g)

187

Re (µg/g)

Osng/g

Model age (Ma)

Measured

2σ

Measured

2σ

Measured

2σ

Measured

2σ

M1

0.05045

137.1

1933

86146

1215

214.90

1.73

149.5

2.7

M2

0.05078

149.7

3004

94104

1888

233.13

1.83

148.5

3.4

M3

0.05050

149.6

1294

94003

813

228.93

1.97

146.0

2.1

M4

0.05072

84.2

1327

52932

834

131.11

1.03

148.5

2.9

M5

0.05066

154.6

1405

97184

883

240.16

2.14

148.1

2.2

M6

0.05080

104.6

1458

65730

917

161.78

1.39

147.6

2.7

77

Table 5. Fluid inclusions types and data from quartz at the Matou Mo deposit, Chizhou. Samples

Mineralogy

Host minerals

Inclusion types

V-L ratio (%)

Ti (℃)

Ts1 (℃)

Tc1 (℃)

Tht (℃)

Salt (equiv wt% NaCl)

P5-7

Qtz+Mo

Qtz

I

10 to 60(21)

-3.8 to -6.1(10)

197 to 274(21)

6.2 to 9.3(10)

P5-12

Qtz+Mo+Py

Qtz

I

5 to 70(16)

-3.9 to -10.1(12)

187 to 355(14)

6.3 to 14(12)

P5-16

Qtz+Mo

Qtz

I

15 to 40(12)

-1 to-4.5(8)

170 to 280(12)

1.7 to 7.2(8)

P5-40

Qtz+Mo

Qtz

I、III

10 to 50(11)

-5 to -9.3(7)

189.5-251.5(5)

321 to 360(10)

7.9-13.2(7) and 34.4 to 37.5(5)

P5-44

Qtz+Mo

Qtz

I、III

10 to 40(16)

-3.3 to -6.2(6)

210-278.5(6)

212 to 357(13)

5.4-9.5(6) and 35.3 to 39.2(6)

P5-59

Qtz+Mo

Qtz

I、II

5 to 65(15)

-2.1 to -4.2(7)

2.1-3.8(5)

220 to 334(10)

3.55 to 13.1(12)

P5-64

Qtz+Mo

Qtz

I、II

5 to 30(20)

-3.1 to -5(8)

1.5-3.2(2)

205 to 308(10)

5.11 to 13.9(10)

P5-90

Qtz+Mo+Py

Qtz

I

5 to 40(16)

-1.7 to-9.7(5)

188 to 309(8)

2.9 to 13.6(5)

P5-105

Qtz+Mo+Py

Qtz

I

5 to 35(22)

-2.6 to -7.6(10)

204 to 320(22)

4.3 to 11.2(10)

M2

Qtz+Py

Qtz

I

5 to 30(18)

-1.1 to -3.2(12)

130 to 198(15)

1.9 to 8.3(12)

M3

Qtz+Py

Qtz

I

5 to 25(20)

-0.6 to -2.1(13)

143 to 257(16)

1.1 to 3.6(13)

78

Table 6. Sulfur stable isotope analyses of sulfides from the Matou Mo deposit, Chizhou. Samples No.

Mineral

δ34s0/00

σ0/00

p5-7

Moly

3.32

0.009

p5-59

Moly

3.34

0.004

p5-105

Moly

3.03

0.002

p5-16

Moly

3.61

0.004

p5-90

Moly

3.63

0.009

M1

Moly

3.69

0.009

M2

Py

7.42

0.009

M3

Py

9.67

0.008

79

Table 7. H-O isotope results for sulfides from the Matou Mo deposit, Chizhou.

Deposit

Sample

Temperature

δ18O

δ18OSMOW

∆DSMOW

Mineral

(°C)

‰

‰

‰

bpd

quartz

162 to 342

11

3.4 to 5.9

-61.5

B22

scheelite

281 to 360

5.2

5 to 6.3

-68.8

BD180-330

scheelite

281 to 360

4.5

4.3 to 5.6

-62.1

BD180-350

garnet

377 to 412

9.2

10 to 10.3

-84.3

BD180-350

diopside

350

7.7

8.8

-83.1

BD180-350

calcite

137 to 190

11.2

-1.9 to 1.6

-63.2

p5-18

quartz

230

9.4

-0.56

-48.8

p5-25

quartz

213

10.5

-0.4

-50.6

p5-34

quartz

224

10.4

0.1

-48.3

p5-42

quartz

220

9.6

-0.91

-49.9

p5-65

quartz

243

10.1

0.81

-50.1

p510-3

quartz

286

10.3

2.9

-47.3

p580-8

quartz

244

10.8

1.6

-63.9

jt-27

quartz

238

10.1

0.6

-59.3

p320-10

quartz

252

10.7

1.8

-51.2

tc1-3

quartz

236

10.6

1

-60.9

Meteoric water

10 to -55

50 to -500

Seawater

0±

0±

Magmatic water

5.5 to 9.5

-40 to -85

Metamorphic water

5 to 25

20 to -65

Baizhangyan

Matou

Jitoushan

80

source

Song et al., 2013

This paper

Song et al., 2010

Wei and Wang，1988

Highlights 1) The oldest Mo porphyry mineralization event from Matou deposit took place under the transformation stage which was from intracontinental-orogeny stage to intracontinental extension stage . 2) There are three episodes of magmatic events in the Matou deposit: 147 Ma Matou porphyritic granodiorite, ca. 140 Ma porphyritic diorite, and ca. 135 Ma dolerite. The results are in accord with the cross-cutting relationships observed in the field. 3) A gradual decrease in silica, alumina and alkalis contents, and an increase in mantle components have been here recognized for the sources of the porphyritic granodiorite, porphyritic diorite, and dolerite at Matou. The gradual change in the petrochemistry of the magmatic rocks indicates that Matou porphyritic granodiorite was formed in an initial extensional tectonic setting, following continued extensional tectonics and lowering of pressures associated with the earlier compressional tectonics, along with continued increasing in the supply of mantle material, the porphyritic diorite and dolerite were emplaced sequentially. 4) Ore-forming fluids of the Matou Mo deposit are rich in CO2 and coexist with halite-bearing inclusions. It suggested that Mo mineralization was primarily caused by intensive fluid boiling in the H2O-CO2-NaCl system. Geochemistry characters, zircon Hf isotope values, Recontentration in molybdenite, CO2-rich fluid inclusions, H-O isotope data of quartz, δ34S values of the sulfides from the Mo ores indicate that the crust provide the dominating materials for mother rock and increase of formation water or meteoric water take part in the evolution process of Mo ore-forming fluids.

81

Graphical abstract As the oldest porphyry Mo deposit of YVMB, the Matou Mo deposit was formed under the early transformation stage that between intracontinental-orogeny stage and intracontinental extension stage. The ca. 147 Ma Matou porphyritic granodiorite developed during a transition from compressional to extensional tectonic settings. The magma was then contaminated when passing through the crust, and the associated fluids carried Mo from the magma and sulfur from the crust. The mineralized fluid then boiled during changes in temperatures or pressures resulting in Mo deposition along the contact between the porphyritic granodiorite and wall rock, and a phase separation of the fluid into saline-rich and CO2-rich. During ca. 140 Ma, increased tectonic extension orientated in a N-S direction led to the emplacement of mantle-derived mafic magma forming the porphyritic diorite at Matou, which intruded the porphyritic granodiorite rocks and Mo(-Cu) mineralization. The N-S orientated extension diminished in intensity during or shortly after ca. 135 Ma with the intrusion of dolerite, and mantle-derived materials control the formation of magmatic rocks.

82