Zircon U-Pb and Pyrite Re-Os Isotope Geochemistry of ‘Skarn-Type’ Fe-Cu Mineralization at the Shuikoushan Polymetallic Deposit, South China: Implications for an Early Cretaceous Mineralization Event in the Nanling Range

: The Shuikoushan deposit is an economic ‘skarn-type’ polymetallic Pb-Zn deposit in South China. The deposit is located at the southern margin of the Hengyang basin in the northern part of the Nanling Range. Recently, economic Fe-Cu mineralization that occurs spatially connected to skarns along the contact zone between the granodiorite and limestones was discovered in the lower part of this deposit. Detailed zircon U-Pb geochronological data indicate that the granodiorite was emplaced at 153.7 ± 0.58 Ma (Mean Square of Weighted Deviates ( MSWD ) = 2.4). However, the pyrite Re-Os isochron age reveals that Fe-Cu mineralization formed at 140 ± 11 Ma ( MSWD ) = 8.1), which post-dates the emplacement of the granodiorite, as well as the previously determined timing of Pb-Zn mineralization (157.8 ± 1.4 Ma) in this deposit. Considering that Fe-Cu mineralization was connected with the contact zone and also faults, and that sulﬁde minerals commonly occur together with quartz and calcite veins that crosscut skarns, we interpret this mineralization type as being related to injection of post-magmatic hydrothermal ﬂuids. The timing of Fe-Cu mineralization (140 ± 11 Ma) is inconsistent with a long-held viewpoint that the time interval of 145 to 130 Ma (e.g., Early Cretaceous) in the Nanling Range is a period of magmatic quiescence with insigniﬁcant mineralization, the age of 140 Ma may represent a new mineralization event in the Nanling Range.


Introduction
The Shuikoushan Pb-Zn-Au ore field, located at the northwestern margin of the Cathaysian block ( Figure 1a) and the middle part of the Nanling Range in South China, is one of the most important non-ferrous ore fields in China. The main mineral deposits in this ore field include the Shuikoushan Pb-Zn polymetallic deposit, the Kangjiawan Pb-Zn deposit, the Longwangshan Au deposit, and the Xianrenyan Au deposit (Figure 1b). The geological and geochemical characteristics of the ore deposits in this ore field have been investigated by numerous studies, and two general genetic models such as skarn-type investigated by numerous studies, and two general genetic models such as skarn-type related to contact metamorphism and hydrothermal vein-type, which resulted by infilling hydrothermal fluids into fractures have been proposed to account for their formations [1][2][3][4][5].  [2,5]); the location of the Shuikoushan deposit is outlined using a blue dashed square.
The Shuikoushan deposit is an economic 'skarn-type' polymetallic Pb-Zn deposit, with an average grade of 1.57 wt. % Pb, 5.72 wt. % Zn, and 0.50 wt. % Cu [6]. Previous studies conducted on this deposit have focused on geochemical characteristics and genesis of Pb-Zn mineralization. For example, based on geological mapping and zircon U-Pb geochronological work, Pb-Zn mineralization in this deposit was found to be spatially related to granodiorites that have zircon U-Pb ages ranging from 153 to 163 Ma (Table 1) [1][2][3][7][8][9]. Re-Os isochron age of the molybdenite from the Pb-Zn ore body of this deposit reveals that the timing of Pb-Zn mineralization is 157.8 ± 1.4 Ma, coinciding with the age of granodiorites in this deposit [9]. It is thought that Pb-Zn mineralization and granodiorites in the Shuikoushan deposit are genetically linked [9]. Recently, the drilling program made the discovery of the No. 3 concealed granodiorite and a spatially related Fe-Cu ore body at depths from −295 to −1050 m in this deposit ( Figure 2). The discovery enlarges the mineral reserve and indicates a potential for prospecting other resources in the Shuikoushan deposit [4]. In addition, the Mesozoic granitoids in the Nanling Range are known to host Pb-Zn-W-Sn as the dominant mineralization types [10,11], the discovery of the Fe-Cu ore body in the Shuikoushan deposit may enrich the mineralization diversity  [2,5]); the location of the Shuikoushan deposit is outlined using a blue dashed square.
The Shuikoushan deposit is an economic 'skarn-type' polymetallic Pb-Zn deposit, with an average grade of 1.57 wt. % Pb, 5.72 wt. % Zn, and 0.50 wt. % Cu [6]. Previous studies conducted on this deposit have focused on geochemical characteristics and genesis of Pb-Zn mineralization. For example, based on geological mapping and zircon U-Pb geochronological work, Pb-Zn mineralization in this deposit was found to be spatially related to granodiorites that have zircon U-Pb ages ranging from 153 to 163 Ma (Table 1) [1][2][3][7][8][9]. Re-Os isochron age of the molybdenite from the Pb-Zn ore body of this deposit reveals that the timing of Pb-Zn mineralization is 157.8 ± 1.4 Ma, coinciding with the age of granodiorites in this deposit [9]. It is thought that Pb-Zn mineralization and granodiorites in the Shuikoushan deposit are genetically linked [9]. Recently, the drilling program made the discovery of the No. 3 concealed granodiorite and a spatially related Fe-Cu ore body at depths from −295 to −1050 m in this deposit ( Figure 2). The discovery enlarges the mineral reserve and indicates a potential for prospecting other resources in the Shuikoushan deposit [4]. In addition, the Mesozoic granitoids in the Nanling Range are known to host Pb-Zn-W-Sn as the dominant mineralization types [10,11], the discovery of the Fe-Cu ore body in the Shuikoushan deposit may enrich the mineralization diversity in the Nanling Range. Albeit these significant meanings, the research on Fe-Cu mineralization in this deposit is still at a very initial stage. It is unclear whether the No. 3 granodiorite is co-genetic with other granodiorites in the Shuikoushan deposit and formed contempora-neously with Fe-Cu mineralization, and what is the genesis of Fe-Cu mineralization. In addition, the granitoid magmatism and related Pb-Zn-W-Sn mineralization events in the Nanling Range were determined to have occurred mainly between 151 and 160 Ma [12][13][14][15][16][17][18][19], coeval with Pb-Zn mineralization in the Shuikoushan deposit [9]. It is unclear whether or not Fe-Cu mineralization in this deposit is also coeval with mineralization events in the Nanling Range. Investigating this may provide implications for discovering similar types of mineralization in a much broader region. To address these problems, the emplacement age of the No. 3 granodiorite and the timing of Fe-Cu mineralization needs to be constrained. in the Nanling Range. Albeit these significant meanings, the research on Fe-Cu mineralization in this deposit is still at a very initial stage. It is unclear whether the No. 3 granodiorite is co-genetic with other granodiorites in the Shuikoushan deposit and formed contemporaneously with Fe-Cu mineralization, and what is the genesis of Fe-Cu mineralization. In addition, the granitoid magmatism and related Pb-Zn-W-Sn mineralization events in the Nanling Range were determined to have occurred mainly between 151 and 160 Ma [12][13][14][15][16][17][18][19], coeval with Pb-Zn mineralization in the Shuikoushan deposit [9]. It is unclear whether or not Fe-Cu mineralization in this deposit is also coeval with mineralization events in the Nanling Range. Investigating this may provide implications for discovering similar types of mineralization in a much broader region. To address these problems, the emplacement age of the No. 3 granodiorite and the timing of Fe-Cu mineralization needs to be constrained.  The Pb-Zn ore body is distributed mainly along the contact zone between the No. 2 granodiorite and fractured limestone, whereas the Fe-Cu ore body is distributed along the contact zone between the No. 3 granodiorite and Lower Permian Qixia limestone, note that several lenses of skarns are seen within the Fe-Cu ore body.
In this study, U-Pb zircon dating of the No. 3 concealed granodiorite was performed to constrain the emplacement age of this intrusion. Re-Os isotope system is known to be a powerful tool for dating sulfide minerals [21,22], thus the timing of Fe-Cu mineralization can be determined based on this method. Although the molybdenite is commonly used for Re-Os isotopic dating, it has been demonstrated that sulfide minerals with lower Re and Os concentrations such as pyrite and arsenopyrite are also suitable for Re-Os isotopic The Pb-Zn ore body is distributed mainly along the contact zone between the No. 2 granodiorite and fractured limestone, whereas the Fe-Cu ore body is distributed along the contact zone between the No. 3 granodiorite and Lower Permian Qixia limestone, note that several lenses of skarns are seen within the Fe-Cu ore body.
In this study, U-Pb zircon dating of the No. 3 concealed granodiorite was performed to constrain the emplacement age of this intrusion. Re-Os isotope system is known to be a powerful tool for dating sulfide minerals [21,22], thus the timing of Fe-Cu mineralization can be determined based on this method. Although the molybdenite is commonly used for Re-Os isotopic dating, it has been demonstrated that sulfide minerals with lower Re and Os concentrations such as pyrite and arsenopyrite are also suitable for Re-Os isotopic dating, and the Re-Os radiogenic system of pyrite can be used as a high-precision geochronometer [23,24]. As the Fe-Cu ore body in the Shuikoushan deposit contains abundant pyrite but lacks molybdenite, we carried out the pyrite Re-Os isochron dating to determine the timing of Fe-Cu mineralization in this study. The obtained ages are combined with whole-rock trace element compositions and trace element and Hf isotope compositions of zircons to evaluate the relationship between the No. 3 granodiorite and other granodioritic intrusions in the Shuikoushan deposit, the potential linkage between the No. 3 granodiorite and Fe-Cu mineralization, and the genesis of this mineralization type.

Regional Geological Setting
The Nanling Range in South China contains abundant Mesozoic granitoid intrusions that host significant metallic mineralization [25,26]. These intrusions were previously considered as S-type granitoids based on their relatively high initial Sr 87 /Sr 86 ratios of 0.710-0.735 [25,27], but were then re-identified as I-or A-type granitoids formed from highly fractionated magmas [28,29]. Particularly, recent studies identified several small granodioritic intrusions with relatively low initial Sr 87 /Sr 86 ratios in the Range and regarded this as an I-type signature for the intrusions [9,30]. Mesozoic granitoids in Southern Hunan are hosts to numerous W-Sn and Pb-Zn ore deposits, which form a significant part of mineralization in the Nanling Range. Among which, W-Sn deposits are commonly related to granite plutons emplaced at 160 to 150 Ma [15,[31][32][33], whereas Pb-Zn deposits are usually associated with I-type granodiorite intrusions [34,35].
The Shuikoushan ore field in Southern Hunan is located in the suture zone between the Yangtze and Cathaysia blocks. The basement of this ore field consists of Precambrian metamorphic rocks that were overlain by Sinian to Mesozoic cover sedimentary successions [2,36]. The strata in this field are composed mainly by the Late Triassic marine carbonate and Late Triassic to Cretaceous clastic molasses Formations. Structures in the ore field consist mainly of anticline and syncline that have nearly north-south axial direction, as well as some thrust faults that strike nearly from north to south [2].
Seventy-two igneous bodies that cover a total surface area of~4.5 km 2 have been discovered in this ore field. The lithology of these igneous bodies consists mainly of granodiorite and granite porphyry. The Yagongtang and Laoyachao granodiorites are two relatively large igneous bodies in the ore field, both intruded the Yagongtang inverted anticline [3]. The Yanshannian subvolcanic complex (133.9 to 199.6 Ma), composed mainly of dacite porphyry, andesitic tuff, rhyolite, and flow breccia, is also exposed in this ore field [37]. It is thought that Pb, Zn, and Au mineralization in this ore field is closely spatially related to the intermediate-felsic rocks of the Yanshannian subvolcanic complex [6].

Ore Deposit Geology
The Shuikoushan polymetallic deposit is located in the center of the Shuikoushan ore field (Figure 1b). The eastern part of this deposit is adjacent to the Kangjiawan Pb-Zn deposit and the western part is adjacent to the Longwangshan Au deposit (Figure 1b The granodioritic intrusion in this deposit was subdivided into numerous bodies by local miners, among which, No. 2, No. 3, and No. 4 are the main ones. No. 2 and No. 4 granodiorites are exposed and located at the western and eastern sides of the deposit, respectively, separated by a fault, whereas the No. 3 granodiorite is concealed and was discovered based on the drilling program ( Figure 2a). The three rock bodies cover an area of~2.7 km 2 in total and occur as lopolith and laccolith, which intruded the overturned anticline and/or fault (Figure 2a,b) [37]. The deposit contains two main mineralization types, such as Pb-Zn and Fe-Cu. Pb-Zn mineralization occurs dominantly along the margins of the No. 2 and No. 4 granodiorites, with minor within the (siliceous) marlstone of the Dangchong Formation. In contrast, Fe-Cu mineralization occurs along the eastern margin of the concealed No. 3 granodiorite (Figure 2b). There are also several thin lenses of Au mineralization found along the contact between the No. 4 granodiorite and fractured limestone (Figure 2a), details about Au mineralization can be referred to [6]. Various types of hydrothermal alteration, including chloritization, sericitization, skarnization, silicification, marbleization and hornfelization, are widespread along the contact zone between the granodiorites and country rocks. Among them, the skarnization and silicification are spatially related to Pb-Zn and Fe-Cu mineralization, whereas the chloritization is spatially related to Au mineralization [6].
Pb-Zn mineralization in the Shuikoushan deposit has been described in detail by previous studies [1-3,7-9]-only a brief description is given here. Fourteen lenticular and podiform-like Pb-Zn ore bodies were discovered, the occurrence of which is basically controlled by the contact zone between the No. 2 and No. 4 granodiorites and country rocks (e.g., the limestone of the Qixia and Huitian Formations), and include the hydrothermal vein-type, the cryptoexplosive breccia-type, and the skarn-type. Ore minerals consist mainly of galena, sphalerite, pyrite, native Au, with small amounts of pyrrhotite, hematite, arsenopyrite, chalcopyrite, bornite, chalcocite, argentite, molybdenite, and native Ag. Gangue minerals are calcite, quartz, garnet, diopside, wollastonite, epidote, apatite, with small amounts of feldspar, fluorite, and barite. According to the exploration report [6], the average content of the Pb-Zn ore body is 1.66 wt. % Pb and 6.95 wt. % Zn.
Fe-Cu mineralization in the Shuikoushan deposit is spatially related to skarns that occurred along the eastern contact zone between the No. 3 granodiorite and country rocks (e.g., the limestone of the Qixia Formation and the marlstone of the Dangchong Formation) (Figures 2b and 3a-c). The ore body of this mineralization type is buried at depth between −295 to −1050 m and can be termed as a 'blind' ore body (Figure 2b). The ore body is 1200 m long along the strike, up to~700 m long toward the dipping direction, and 3.68 to 175.87 m (30. 58 m on average) in thickness. The ore body is dominantly cylindrical, lenticular, sack-like, and stratified in shapes, but locally it can occur as veins within fissures of metamorphic rocks (Figure 3a,b). The occurrence of the ore body was controlled by the contact zone and faults and varies at different positions relative to the contact zone. For example, the ore body on the eastern side of the contact zone has a NW strike and dips to SW with a dipping angle of 55 to 70 degrees. In contrast, the 'lense-shaped' ore body located on the northern side of the contact zone has a NS or NNE strike and dips to SW with a dipping angle of 80 to 85 degrees for the upper part of the ore body and 50 to 60 degrees for the lower part of the ore body ( Figure 2b). The average content is 22.2 wt. % Fe, 0.62 wt. % Cu, 0.3 ppm Au, and 9.35 ppm Ag [6]. Ore minerals consist mainly of magnetite, pyrite, chalcopyrite, pyrrhotite, galena, and sphalerite, with trace amounts of molybdenite and native Ag, which are mainly anhedral to subhedral and show complex replacement and crosscutting relationships (Figure 4a-k). Gangue minerals are garnet, diopside, quartz, calcite, chlorite, and epidote.

Paragenetic Sequence of Fe-Cu Mineralization
Based on crosscutting relationships of ore and gangue minerals, as well as textures of ore minerals, paragenetic sequence of Fe-Cu mineralization was determined, which comprises two main episodes. From the oldest to the youngest, they are the skarn episode and the quartz-sulfide episode ( Figure 5). The skarn episode refers to the calcareous skarn that comprises anhydrous silicate minerals such as garnet and diopside, hydrous silicate

Paragenetic Sequence of Fe-Cu Mineralization
Based on crosscutting relationships of ore and gangue minerals, as well as textures of ore minerals, paragenetic sequence of Fe-Cu mineralization was determined, which comprises two main episodes. From the oldest to the youngest, they are the skarn episode and the quartz-sulfide episode ( Figure 5). The skarn episode refers to the calcareous skarn that comprises anhydrous silicate minerals such as garnet and diopside, hydrous silicate minerals such as epidote and chlorite, as well as a high amount of magnetite ( Figure 5). Epidote, chlorite, and magnetite commonly occur together, which either crosscuts or replaces the garnet and diopisde (Figure 4a), based on which, the skarn episode was further subdivided into the garnet-diopside skarn and magnetite stages ( Figure 5). The quartz-sulfide episode is characterized by abundant sulfide minerals, which include pyrite, chalcopyrite, pyrrhotite, sphalerite, and galena. Sulfide minerals commonly occur together with hydrothermal quartz and calcite veins (Figure 4b-e), and either crosscut the magnetite (Figure 4b-d,g) or replaced the garnet-diopside skarn (Figure 4f). This affirms that the quartz-sulfide episode occurred later than the skarn episode. Textures such as the replacement of massive pyrite by galena and sphalerite, chalcopyrite inclusion in sphalerite, and the replacement of chalcopyrite by sphalerite that resulted in the 'chalcopyrite disease' texture ( Figure 4h-k) are all evidence that the galena-sphalerite assemblage formed later than the pyrite-chalcopyrite assemblage, and thus the quartz-sulfide episode was further subdivided into the pyrite-chalcopyrite and galena-sphalerite stages. The pyritechalcopyrite stage comprises pyrite, chalcopyrite and pyrrhotite. The galena-sphalerite stage comprises galena, sphalerite, and minor pyrite, as well as some gangue minerals such as quartz and a small amount of carbonates.
Minerals 2021, 11, x 8 of 26 minerals such as epidote and chlorite, as well as a high amount of magnetite ( Figure 5). Epidote, chlorite, and magnetite commonly occur together, which either crosscuts or replaces the garnet and diopisde (Figure 4a), based on which, the skarn episode was further subdivided into the garnet-diopside skarn and magnetite stages ( Figure 5). The quartzsulfide episode is characterized by abundant sulfide minerals, which include pyrite, chalcopyrite, pyrrhotite, sphalerite, and galena. Sulfide minerals commonly occur together with hydrothermal quartz and calcite veins (Figure 4b-e), and either crosscut the magnetite (Figure 4b-d,g) or replaced the garnet-diopside skarn ( Figure 4f). This affirms that the quartz-sulfide episode occurred later than the skarn episode. Textures such as the replacement of massive pyrite by galena and sphalerite, chalcopyrite inclusion in sphalerite, and the replacement of chalcopyrite by sphalerite that resulted in the 'chalcopyrite disease' texture ( Figure 4h-k) are all evidence that the galena-sphalerite assemblage formed later than the pyrite-chalcopyrite assemblage, and thus the quartz-sulfide episode was further subdivided into the pyrite-chalcopyrite and galena-sphalerite stages. The pyrite-chalcopyrite stage comprises pyrite, chalcopyrite and pyrrhotite. The galena-sphalerite stage comprises galena, sphalerite, and minor pyrite, as well as some gangue minerals such as quartz and a small amount of carbonates.

Sample Collection
Ten samples of the No. 3 granodiorite were collected. The samples are medium-to coarse-grained and show porphyritic-like texture. They comprise a decreasing amount of plagioclase (22 to 28 modal%), orthoclase (19 to 23 modal%), quartz (20 to 30 modal%),

Sample Collection
Ten samples of the No. 3 granodiorite were collected. The samples are medium-to coarse-grained and show porphyritic-like texture. They comprise a decreasing amount of plagioclase (22 to 28 modal%), orthoclase (19 to 23 modal%), quartz (20 to 30 modal%), hornblende (10 to 18 modal%), and biotite (8 to 18 modal%), with minor amounts of apatite and zircon. Each of the samples was cut into three parts; one part was pulverized into powders for whole-rock analysis, another part was made into polished thin sections for petrography, the last part was crushed and prepared for hand-picking zircon separates. Five pieces of Fe-Cu ores were also sampled in order to obtain pyrite separates for Re-Os isotopic analysis. Locations of the collected Fe-Cu ores are given in Table 2. Powdered samples of the No. 3 granodiorite were sent to ALS Minerals-Chemex (Guangzhou) Co., Ltd. for whole-rock analysis, using an Agilent 7700× inductively coupled plasma-mass spectrometer (ICP-MS). The powdered samples (~2 g) were mixed homogeneously with lithium borate and placed in a furnace at 1000 • C for melting. After that, the melt was cooled, dissolved with 100 mL of 4% nitric acid solution, and then analyzed by ICP-MS. Quality control was conducted based on ALS Chemex quality-control procedures that involve analyses on a wide array of standards, blanks, and duplicates (e.g., GBM 306-12, GBM 315-13, NCSDC 73303, OREAS 195) that were included with each batch of samples. The standard deviation of the standard is better than 3%. The precision is better than 5% for most elements. The obtained whole-rock major and trace element analytical results are given in Table 3.

U-Pb Dating and Trace Elements in Zircon
Based on petrographic observations, zircon grains were sorted using a combination of heavy liquid and magnetic separation techniques. Transparent, crack-and inclusion-free zircon grains with good crystal shapes were hand-picked and mounted in epoxy resin. After the resin was fully cured, the epoxy disc was polished until the zircon was exposed. Cathodoluminescence (CL) and back-scattered electron (BSE) images of zircon grains were obtained using a JEOL-JXA-8100 electron probe micro-analyzer at China Metallurgical Geology Bureau, aiming to characterize the internal textures of zircon grains and identify suitable targets for spot analyses. The operating conditions include an acceleration voltage of 15 kV and a beam current of 2 × 10 −8 A. Nineteen zircon grains that are 100 to 180 µm long and 60 to 120 µm wide with an aspect ratio of 1.6 to 3.0 were analyzed. The CL images show that the analyzed zircons have typical oscillatory zoning textures ( Figure 6).  Trace element compositions and U-Pb isotope ratios of zircons were acquired using a laser ablation inductively coupled-plasma spectrometry (LA-ICP-MS) at China Metallurgical Geology Bureau. The Thermo Scientific XSeries 2 ICP-MS instrument was coupled to a Compex Pro 193 nm ArF excimer laser ablation system. The ablation pits are ~30 μm Trace element compositions and U-Pb isotope ratios of zircons were acquired using a laser ablation inductively coupled-plasma spectrometry (LA-ICP-MS) at China Metallurgical Geology Bureau. The Thermo Scientific XSeries 2 ICP-MS instrument was coupled to a Compex Pro 193 nm ArF excimer laser ablation system. The ablation pits are~30 µm in diameter and~40 µm in depth. The density of the laser energy was 8.5 J/cm 2 and ablation frequency was 8 Hz. Helium gas was used as a carrier gas. Multiple spots per grain were analyzed to test both grain-to-grain and intra-grain variability. Standards were analyzed throughout the sequence to allow for drift correction. A NIST 610 silicate glass standard was used as a monitor standard for trace elements to assess the accuracy and precision of the runs. 90 Zr was used as the internal standard assuming stoichiometric values for zircon, in order to calibrate the trace element concentrations of zircons. The obtained trace element compositions of zircons are tabulated in Table 4. The standard GJ-1 zircon (599.8 ± 4.5 Ma; [38]) was used for calibration of the acquired zircon U-Pb isotope ratios. The standard Plesovice zircon (337.13 ± 0.37 Ma; [39]) was treated as an unknown sample during analysis, in order to check the accuracy of the acquired zircon U-Pb isotope ratios. Off-line data reduction was carried out using the ICPMSDataCal software (version 11, the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, China) [40]. Concordia diagram and weighted mean calculations were performed using the ISOPLOT software [41]. The obtained zircon U-Pb geochronology results are tabulated in Table 5.

Zircon Lu-Hf Isotopes
In situ zircon Lu-Hf isotope analysis was performed using a Nu Plasma IImulticollector inductively coupled plasma-mass spectrometer (ICP-MS) equipped with a GeoLas 2005 laser ablation system (MC-ICPMS) at Nanjing FocuMS Technology Co., Ltd. (Nanjing, China). Analyses were performed on the pits ablated for previous U-Pb isotope analysis. The ablation pits are~50 µm in diameter and~40 µm in depth, with ablation time of 40 s and repetition rate of 8 Hz. Five standard zircons (GJ-1, 91500, Plešovice, Mud Tank, Penglai) were analyzed between every 10 samples to monitor the reproducibility of the zircon Hf isotopic data. The average 176 Lu/ 177 Hf for GJ-1 is 0.282008 ± 0.000025 (2σ standard deviation (SD)), for 91,500 is 0.282307 ± 0.000031, for Plešovice is 0.282482 ± 0.000013, for Mud Tank is 0.282504 ± 0.000044, and for Penglai is 0.282906 ± 0.000010 [39,[42][43][44]. Raw count rates for 172 Yb, 173 Yb, 175 Lu, 176 (Hf + Yb + Lu), 177 Hf, 178 Hf, 179 Hf, 180 Hf, and 182 W were measured, and isobaric interference corrections for 176 Lu and 176 Yb on 176 Hf were made, details were given in Ref. [45]. The off-line processing of analytical data was performed using ICPMSDataCal software, including the selection of samples and blank signals and the correction of isotope mass fractionation [40]. The obtained zircon Hf isotopic compositions are tabulated in Table 6.

Pyrite Re-Os Dating
Pyrite Re-Os isotope analysis was carried out using a Triton thermal ionization mass spectrometer (TIMS) at the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences.~0.1 to 0.8 g sample powder (spiked with 185 Re and 190 Os), 2.5 mL concentrated HCl and 7.5 mL concentrated HNO 3 were frozen in Carius tubes, which were sealed and heated to 240 • C for 24 to 48 h. After decomposition and cooling, the Carius tubes were opened and centrifuged and the supernatant was transferred to a 30 mL PFA flask. Osmium was separated using 4 mL CCl 4 solvent extraction and back extraction following the HBr method of [48]. The residual solution underwent anion exchange through a column for Re extraction.
Isotope abundances in OsO 3 − (mass numbers: 233, 235, 236, 237, 238, 240) was measured using the secondary electron multiplier (SEM) dynamic jumping method. The results were acquired using the stepwise deoxidation method, i.e., using the isothermal model for oxygen calibration, and then, the mass fractionation was calibrated using 192 Os/ 188 Os = 3.08271 [49]. Finally, the dilution of the diluent was calculated to determine the contribution of the 187 Os/ 188 Os to the sample. Re contents were obtained using an Xseries-2 inductively coupled plasma mass spectrometer. The results were corrected using the Re and Os blanks. Specific dating methods and procedures were described in [3,50,51]. The obtained pyrite Re-Os isotopic compositions are tabulated in Table 7.  (Table 3). On plots of K 2 O versus SiO 2 and A/CNK versus A/NK, rocks are plotted mainly in the shoshonite-high-K calc-alkaline field and the metaluminous field, respectively (Figure 7a,b). Rocks have total rare earth element (REE) contents ranging from 200 to 260 ppm, and display patterns of enrichment of light REE (LREE, 161 to 215 ppm) relative to heavy REE (HREE, 36 to 56 ppm) (Table 3, Figure 8a). In terms of Eu anomalies (Eu/Eu* = (Eu) N /[(Sm) N × (Gd) N ] 0.5 ), except for one sample that displayed a negative Eu anomaly (Eu/Eu* = 0.76), all show no obvious Eu anomalies (Eu/Eu* = 0.84 to 0.98) (Figure 8a). In addition, rocks all display pronounced Nb and Ta negative anomalies relative to large ion lithophile elements (LILE, e.g., Rb and K) and LREE (e.g., La) (Figure 8b). In general, rocks of the No. 3 granodiorite have similar REE and trace element patterns with other granodiorites in the Shuikoushan deposit (Figure 8a,b), except that the latter show obvious negative Sr anomalies due to the early fractionation of plagioclase (Figure 8b).
Isotope abundances in OsO3 − (mass numbers: 233, 235, 236, 237, 238, 240) was measured using the secondary electron multiplier (SEM) dynamic jumping method. The results were acquired using the stepwise deoxidation method, i.e., using the isothermal model for oxygen calibration, and then, the mass fractionation was calibrated using 192 Os/ 188 Os = 3.08271 [49]. Finally, the dilution of the diluent was calculated to determine the contribution of the 187 Os/ 188 Os to the sample. Re contents were obtained using an Xseries-2 inductively coupled plasma mass spectrometer. The results were corrected using the Re and Os blanks. Specific dating methods and procedures were described in [3,50,51]. The obtained pyrite Re-Os isotopic compositions are tabulated in Table 7.

Whole-Rock Major and Trace Element Compositions of the No. 3 Granodiorite
Rocks have SiO2, K2O, and Na2O contents ranging from 55.8 to 62.3 wt.%, 2.4 to 4.2 wt.%, and 2.9 to 3.1 wt.%, respectively (Table 3). On plots of K2O versus SiO2 and A/CNK versus A/NK, rocks are plotted mainly in the shoshonite-high-K calc-alkaline field and the metaluminous field, respectively (Figure 7a,b). Rocks have total rare earth element (REE) contents ranging from 200 to 260 ppm, and display patterns of enrichment of light REE (LREE, 161 to 215 ppm) relative to heavy REE (HREE, 36 to 56 ppm) (Table 3, Figure 8a). In terms of Eu anomalies (Eu/Eu* = (Eu)N/[(Sm)N × (Gd)N] 0.5 ), except for one sample that displayed a negative Eu anomaly (Eu/Eu* = 0.76), all show no obvious Eu anomalies (Eu/Eu* = 0.84 to 0.98) (Figure 8a). In addition, rocks all display pronounced Nb and Ta negative anomalies relative to large ion lithophile elements (LILE, e.g., Rb and K) and LREE (e.g., La) (Figure 8b). In general, rocks of the No. 3 granodiorite have similar REE and trace element patterns with other granodiorites in the Shuikoushan deposit ( Figure  8a,b), except that the latter show obvious negative Sr anomalies due to the early fractionation of plagioclase (Figure 8b).     (Table 4). Based on the Ti-in-zircon thermometer of [53], the zircon crystallization temperature is estimated to be 547 to 782 °C. It is noted that the No. 10 zircon grain likely contains rutile micro-inclusions, as this grain contains anomalously high Ti contents (45.2 ppm) and has crystallization temperature of up to ~900 °C (Table 4).

Zircon U-Pb Geochronology
Zircon grains (n = 19) have Th and U concentrations in the range of 108 to 567 ppm (257 ppm on average), and 195 to 614 ppm (349 ppm on average), respectively. Their Th/U varies from 0.44 to 0.94 (0.72 on average) ( Table 5). When ignoring the No. 10 zircon that may contain rutile micro-inclusions, they have 206 Pb/ 238 U ages of ca. 147 to ca. 165 Ma. Most of the ages are clustered within the range of ca. 151 to ca. 157 Ma (Figure 9a,b, Table 5). It is noted that three zircon grains (No. 09, 14, and 16) have much older ages (ca. 162 to ca. 165 Ma) than ages of the rest (ca. 147 to ca.159 Ma) (Figure 9a,b), and the age difference is obviously beyond the 1σ uncertainty of the obtained ages (Table 5). To better constrain the age of the No. 3 granodiorite, the three relatively old zircons were ignored in case that they are inherited in origin. On the U-Pb concordia diagram, data of the rest zircon grains are plotted basically on or close to the concordia line (Figure 9a). The concordia diagram yields a mean 206 Pb/ 238 U discordant age of 153.7 ± 0.58 Ma (1σ standard deviation, MSWD = 2.4) (n = 15, Figure 9a) [54]), consistent with the weighted average age of 154 ± 3.1 Ma (1σ standard deviation, MSWD = 2.1) (Figure 9b).  (Table 4). Based on the Ti-in-zircon thermometer of [53], the zircon crystallization temperature is estimated to be 547 to 782 • C. It is noted that the No. 10 zircon grain likely contains rutile micro-inclusions, as this grain contains anomalously high Ti contents (45.2 ppm) and has crystallization temperature of up to~900 • C (Table 4).

Zircon U-Pb Geochronology
Zircon grains (n = 19) have Th and U concentrations in the range of 108 to 567 ppm (257 ppm on average), and 195 to 614 ppm (349 ppm on average), respectively. Their Th/U varies from 0.44 to 0.94 (0.72 on average) ( Table 5). When ignoring the No. 10 zircon that may contain rutile micro-inclusions, they have 206 Pb/ 238 U ages of ca. 147 to ca. 165 Ma. Most of the ages are clustered within the range of ca. 151 to ca. 157 Ma (Figure 9a,b, Table 5). It is noted that three zircon grains (No. 09, 14, and 16) have much older ages (ca. 162 to ca. 165 Ma) than ages of the rest (ca. 147 to ca.159 Ma) (Figure 9a,b), and the age difference is obviously beyond the 1σ uncertainty of the obtained ages (Table 5). To better constrain the age of the No. 3 granodiorite, the three relatively old zircons were ignored in case that they are inherited in origin. On the U-Pb concordia diagram, data of the rest zircon grains are plotted basically on or close to the concordia line (Figure 9a). The concordia diagram yields a mean 206 Pb/ 238 U discordant age of 153.7 ± 0.58 Ma (1σ standard deviation, MSWD = 2.4) (n = 15, Figure 9a) [54]), consistent with the weighted average age of 154 ± 3.1 Ma (1σ standard deviation, MSWD = 2.1) (Figure 9b).

Zircon Hf Isotopic Compositions
Nineteen zircon grains were analyzed for Hf isotopes (Table 6), among which, three old zircons may be inherited in origin and are ignored in this section. The zircon 176 Lu/ 177 Hf and 176 Hf/ 177 Hf ranges from 0.001108 to 0.001729 (0.001483 on average), and 0.282406 to 0.282481 (0.282446 on average), respectively ( Table 6). The zircon εHf(t) ranges from −9.6 to −7.0 (−8.3 on average). The two-stage model ages (T DM2 ) were calculated to be 1.64 to 1.81 Ga (1.72 Ga on average), similar to the age of the basement rocks in the Shuikoushan ore field [36].

Zircon Hf Isotopic Compositions
Nineteen zircon grains were analyzed for Hf isotopes (Table 6), among which, three old zircons may be inherited in origin and are ignored in this section. The zircon 176 Lu/ 177 Hf and 176 Hf/ 177 Hf ranges from 0.001108 to 0.001729 (0.001483 on average), and 0.282406 to 0.282481 (0.282446 on average), respectively ( Table 6). The zircon εHf(t) ranges from −9.6 to −7.0 (−8.3 on average). The two-stage model ages (TDM2) were calculated to be 1.64 to 1.81 Ga (1.72 Ga on average), similar to the age of the basement rocks in the Shuikoushan ore field [36].

Pyrite Re-Os Geochronology
The average Re and common Os contents of pyrite separates, plus with 2σ standard deviation, are in the range of 5.632 ± 0.125 to 26.898 ± 0.562 ppb, and 0.03028 ± 0.00006 to 0.05748 ± 0.00010 ppb, respectively. The 187 Re/ 188 Os ranges from 2026 ± 45 to 11718 ± 91 (2σ standard deviation), and 187 Os/ 188 Os ranges from 9.79 ± 0.04 to 105.24 ± 0.52 (2σ standard deviation). It is noted that the pyrite separate from ore sample ZK2071-11 is exceptive in that it has much lower Re contents and also lower 187 Os/ 188 Os than the other four pyrite separates (Table 7). This pyrite separate was ignored in order to obtain reliable Re-Os isochron age of Fe-Cu ore mineralization. Using the ISOPLOT software (Model 3, the Berkeley Geochronology Center, Berkeley, CA, USA) [55], a regression analysis was performed, and the intercept on ordinate indicates that the initial 187 Os/ 188 Os ratio of the pyrite is 6.2 ± 3.1 (2σ standard deviation). The obtained isochron age (average value ± 2σ standard deviation) is 140 ± 11 Ma (MSWD = 8.1) (Figure 10).

Pyrite Re-Os Geochronology
The average Re and common Os contents of pyrite separates, plus with 2σ standard deviation, are in the range of 5.632 ± 0.125 to 26.898 ± 0.562 ppb, and 0.03028 ± 0.00006 to 0.05748 ± 0.00010 ppb, respectively. The 187 Re/ 188 Os ranges from 2026 ± 45 to 11718 ± 91 (2σ standard deviation), and 187 Os/ 188 Os ranges from 9.79 ± 0.04 to 105.24 ± 0.52 (2σ standard deviation). It is noted that the pyrite separate from ore sample ZK2071-11 is exceptive in that it has much lower Re contents and also lower 187 Os/ 188 Os than the other four pyrite separates (Table 7). This pyrite separate was ignored in order to obtain reliable Re-Os isochron age of Fe-Cu ore mineralization. Using the ISOPLOT software (Model 3, the Berkeley Geochronology Center, Berkeley, CA, USA) [55], a regression analysis was performed, and the intercept on ordinate indicates that the initial 187 Os/ 188 Os ratio of the pyrite is 6.2 ± 3.1 (2σ standard deviation). The obtained isochron age (average value ± 2σ standard deviation) is 140 ± 11 Ma (MSWD = 8.1) ( Figure 10).

Emplacement Age and Source of the No. 3 Concealed Granodiorite
It is known that before using zircon U-Pb ages to constrain the emplacement age of intrusions, it is necessary to confirm that the dated zircon is magmatic in origin so that the obtained ages are meaningful. This is done by considering the following two lines of evi- Figure 10. The pyrite Re-Os isochron age of Fe-Cu mineralization in the Shuikoushan deposit.

Emplacement Age and Source of the No. 3 Concealed Granodiorite
It is known that before using zircon U-Pb ages to constrain the emplacement age of intrusions, it is necessary to confirm that the dated zircon is magmatic in origin so that the obtained ages are meaningful. This is done by considering the following two lines of evidence. Firstly, zircon grains have Th/U (0.44 to 0.94) within the range of magmatic zircons (Th/U > 0.1) [56], and it has been demonstrated that Th/U can be used to distinguish between magmatic, metamorphic, and hydrothermal zircons [57,58]. Secondly, zircon grains show strong enrichments in LREE relative to HREE, have negative Eu anomalies and positive Ce anomalies (Figure 11), and show oscillatory zoning (Figure 6), which are typical of magmatic zircons. Therefore, the obtained zircon U-Pb age (153.7 ± 0.58 Ma) can reliably represent the emplacement age of the No. 3 granodiorite. The obtained age is similar to the reported ages of other granodiorites (163 to 153 Ma) in the Shuikoushan ore field (Table 1). This, together with their similar REE and trace element patterns (Figure 8), indicate that the No. 3 granodiorite is co-genetic with other granodiorites in the Shuikoushan ore field.
Minerals 2021, 11, x FOR PEER REVIEW 19 of 26 Figure 11. Chondrite normalized rare earth element distribution diagram of zircon grains from the No. 3 granodiorite. Reference fields of hydrothermal and magmatic zircons according to [56], chondrite values according to [52].
The source of the No. 3 granodiorite is evaluated based on in-situ zircon Hf isotopic compositions [47,59]. On the diagram of zircon εHf(t) versus age (Ma), all data points are plotted in or near the field of the lower crust (Figure 12), indicating that materials of this intrusion were likely derived from the lower crust, consistent with the source of other granitoids in the Shuikoushan ore field [2,3]. As the No. 3 granodiorite has zircon twostage Hf model age (T2DM) (1809 to 1644 Ma, Table 6) similar to the age of the basement rocks in the Shuikoushan ore field [36]), we consider the No. 3 granodiorite, as well as other granitoids in the Shuikoushan ore field were likely derived from partial melting of the Paleoproterozoic basement rocks that are composed mainly by metagreywackes [60]. When looking at a much broader scale, the W-Sn-Pb-Zn mineralization related granitoids in the Nanling Range are also thought to be derived from partial melting of the lower crustal materials [61], thus the lower crust, particularly the Paleoproterozoic basement metagreywackes may be a common source for granitoids in the whole Nanling Range. Figure 11. Chondrite normalized rare earth element distribution diagram of zircon grains from the No. 3 granodiorite. Reference fields of hydrothermal and magmatic zircons according to [56], chondrite values according to [52].
The source of the No. 3 granodiorite is evaluated based on in-situ zircon Hf isotopic compositions [47,59]. On the diagram of zircon εHf(t) versus age (Ma), all data points are plotted in or near the field of the lower crust (Figure 12), indicating that materials of this intrusion were likely derived from the lower crust, consistent with the source of other granitoids in the Shuikoushan ore field [2,3]. As the No. 3 granodiorite has zircon two-stage Hf model age (T 2DM ) (1809 to 1644 Ma, Table 6) similar to the age of the basement rocks in the Shuikoushan ore field [36]), we consider the No. 3 granodiorite, as well as other granitoids in the Shuikoushan ore field were likely derived from partial melting of the Paleoproterozoic basement rocks that are composed mainly by metagreywackes [60]. When looking at a much broader scale, the W-Sn-Pb-Zn mineralization related granitoids in the Nanling Range are also thought to be derived from partial melting of the lower crustal materials [61], thus the lower crust, particularly the Paleoproterozoic basement metagreywackes may be a common source for granitoids in the whole Nanling Range. In summary, our results indicate that the No. 3 granodiorite has the same source and is formed by a common magmatic event with other granodiorites in the Shuikoushan deposit and ore field. As only the No. 3 granodiorite is spatially related to Fe-Cu mineralization, whereas others are often spatially related to Pb-Zn mineralization, it does not seem that the No. 3 intrusion itself has a unique 'gene' to form Fe-Cu mineralization in this deposit.

Timing and Source of Fe-Cu Mineralization in the Shuikoushan Deposit
The examined pyrite separates yield consistent isochron ages (Figure 10), suggesting that the Re-Os system of pyrite separates may have remained closed. In addition, homogenization temperatures of fluid inclusions in sulfide minerals in the Shuikoushan ore field vary in the range of 112.0 to 417.7 °C [9]. These temperature are much lower than the pyrite Re-Os closure temperature (> 500 °C) [62], indicating that the Re-Os system of pyrite separates is resistant to any subsequent metamorphism or deformation and can record the timing of crystallization. Therefore, our pyrite Re-Os isochron age provides an important constraint on the timing of Fe-Cu mineralization in the Shuikoushan deposit, which is 140 ± 11 Ma ( Figure 10).
Even considering errors, the timing of Fe-Cu mineralization still post-dates the emplacement age of the No. 3 granodiorite (153.7 ± 0.58 Ma), and also the timing of Pb-Zn mineralization in the deposit (157.8 ± 1.4 Ma) [60]. Integrating observations such as: (1) the occurrence of Fe-Cu mineralization being controlled by the contact zone of the No. 3 granodiorite with the country rocks, and also by faults [4] (Figure 2b), and (2) that sulfide minerals in this mineralization type mainly occur together with quartz and calcite veinlets that crosscut the magnetite and garnet-diopside skarn (Figures 3 and 4), we consider that the Fe-Cu mineralization in the Shuikoushan deposit was likely produced by post-magmatic hydrothermal fluids after the emplacement of the No. 3 granodiorite. This argument is consistent with the presence of brecciation zones in fold hinge and fault intersections in the vicinity of the ore body, which is evidence of extensive focusing and mixing of hydrothermal fluids [63].
The source of ore-forming materials for Fe-Cu mineralization is then evaluated through combining the Re contents, 187 Re/ 188 Os, and initial 187 Os/ 188 Os of pyrite separates In summary, our results indicate that the No. 3 granodiorite has the same source and is formed by a common magmatic event with other granodiorites in the Shuikoushan deposit and ore field. As only the No. 3 granodiorite is spatially related to Fe-Cu mineralization, whereas others are often spatially related to Pb-Zn mineralization, it does not seem that the No. 3 intrusion itself has a unique 'gene' to form Fe-Cu mineralization in this deposit.

Timing and Source of Fe-Cu Mineralization in the Shuikoushan Deposit
The examined pyrite separates yield consistent isochron ages (Figure 10), suggesting that the Re-Os system of pyrite separates may have remained closed. In addition, homogenization temperatures of fluid inclusions in sulfide minerals in the Shuikoushan ore field vary in the range of 112.0 to 417.7 • C [9]. These temperature are much lower than the pyrite Re-Os closure temperature (>500 • C) [62], indicating that the Re-Os system of pyrite separates is resistant to any subsequent metamorphism or deformation and can record the timing of crystallization. Therefore, our pyrite Re-Os isochron age provides an important constraint on the timing of Fe-Cu mineralization in the Shuikoushan deposit, which is 140 ± 11 Ma ( Figure 10).
Even considering errors, the timing of Fe-Cu mineralization still post-dates the emplacement age of the No. 3 granodiorite (153.7 ± 0.58 Ma), and also the timing of Pb-Zn mineralization in the deposit (157.8 ± 1.4 Ma) [60]. Integrating observations such as: (1) the occurrence of Fe-Cu mineralization being controlled by the contact zone of the No. 3 granodiorite with the country rocks, and also by faults [4] (Figure 2b), and (2) that sulfide minerals in this mineralization type mainly occur together with quartz and calcite veinlets that crosscut the magnetite and garnet-diopside skarn (Figures 3 and 4), we consider that the Fe-Cu mineralization in the Shuikoushan deposit was likely produced by post-magmatic hydrothermal fluids after the emplacement of the No. 3 granodiorite. This argument is consistent with the presence of brecciation zones in fold hinge and fault intersections in the vicinity of the ore body, which is evidence of extensive focusing and mixing of hydrothermal fluids [63].
The source of ore-forming materials for Fe-Cu mineralization is then evaluated through combining the Re contents, 187 Re/ 188 Os, and initial 187 Os/ 188 Os of pyrite separates [21,[64][65][66][67]. The Re contents (5.6 to 26.9 ppb, average at 15.8 ppb) and 187 Re/ 188 Os (2026 to 42,709, average at 13,367) of pyrite separates are typical of sulfides with low-level highly radiogenic Os (LLHR) ( Table 7), similar to Re-Os isotopic features of pyrites from the crust [67,68]. The initial 187 Os/ 188 Os ratio of pyrite separates (6.2 ± 3.1, Figure 10) is significantly higher than that of the mantle (0.105 to 0.152) [21,69], but is close to that of the continental crust (3.63) [70]. These indicate that the ore-forming materials of Fe-Cu mineralization were mainly derived from the crust. To be consistent with this argument, sulfides in ores of the Shuikoushan deposit also have crustal signatures of 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb that range from 18.4 to 18.5, 15.7 to 15.8, and 38.6 to 39.1, respectively [20]. It is therefore likely that Fe-Cu mineralization in the Shuikoushan deposit shares the same material source with the No. 3 granodiorite, which, as mentioned earlier, is related to the Paleoproterozoic basement metagreywackes.

A Genetic Model of Fe-Cu Mineralization in the Shuikoushan Deposit
Based on above discussions, the following conditions need to be considered in order to establish a genetic model for the formation of Fe-Cu mineralization in the Shuikoushan deposit. They include: (1) Fe-Cu mineralization is spatially confined within the contact zone between the No. 3 granodiorite and country rocks (limestones of the Qixia and Huitian Formations), where abundant skarns occurred (Figures 2b and 3a), (2) sulfide minerals of this mineralization type crosscut the early formed skarns and magnetite (Figures 3a and 4), (3) this mineralization type formed post the emplacement of the No. 3 granodiorite and is likely related to injection of hydrothermal fluids, and (4) the ore-forming materials of this mineralization type were derived from the Paleoproterozoic basement rocks, similar to the source of the No. 3 granodiorite. By integrating these conditions, a genetic model is proposed, which involves three main events. Firstly, the No. 3 granodiorite intrusion was emplaced into the surrounding country rocks (e.g., limestones), the thermal metamorphism at the contact zone produced magnetite and skarns of the skarn episode (Figures 2b and 5). Secondly, post-magmatic hydrothermal fluids transported Fe-Cu sulfide components either from the basement rocks, or through remobilization of these components from the skarns and/or granodiorite. Thirdly, Fe-Cu sulfide minerals, along with quartz were precipitated within the contact zone/faults due to changes in temperature, pressure, etc., and crosscut the early formed skarns and magnetite (Figures 3a and 4). It is noted that the proposed genetic model is just a preliminary one because the source of the post-magmatic hydrothermal fluids cannot be ascertained on the basis of the data in this study. Nevertheless, this study for the first time quantified the timing relationship between Fe-Cu mineralization and the No. 3 granodiorite in the Shuikoushan deposit, which provides an important basis for understanding the genesis of this mineralization type in the deposit.

Implication for the Early Cretaceous Mineralization Event in the Nanling Range
The timing of Pb-Zn-W-Sn mineralization, as well as the emplacement ages of host granoitoids in the Nanling Range have been determined to be 151 to 160 Ma [12][13][14][15][16][17][18][19] ( Table 8). The granodiorites (including the No. 3 intrusion) and Pb-Zn mineralization in the Shuikoushan deposit have obviously similar ages with Pb-Zn-W-Sn mineralization and host granoitoids in the Nanling Range (Table 8), indicating that the magmatism and associated Pb-Zn mineralization in this deposit can be placed into the metallogenic context of the Nanling Range [9]. The newly discovered Fe-Cu mineralization in the Shuikoushan deposit, however, is exceptive as the timing (140 ± 11 Ma) is much younger than that of Pb-Zn-W-Sn mineralization in the Nanling Range.
The time interval of 145 to 130 Ma was commonly considered as a period of magmatic quiescence and thus insignificant ore formation in the Nanling Range [15,33,44,77]. However, a recent study by [78] reported an age of 145 to 142 Ma for the muscovite granite in the Dengfuxian pluton in the Nanling Range, and an age of ca. 137 Ma for W-Sn bearing quartz veins that crosscut the Dengfuxian muscovite. Similarly, several other studies also reported 145 to 130 Ma W-Sn mineralization in the North Jiangxi Province and the Southeastern Coastal metallogenic belt that are near the Nanling Range [33,[79][80][81][82]. Together with the obtained age (140 ± 11 Ma) of Fe-Cu mineralization in the Shuikoushan deposit, we consider that the mineralization barren interval of 145 to 130 Ma in the Nanling Range may need to be re-visited, and that the Early Cretaceous polymetallic mineralization events are also important and deserve further attentions in the Nanling Range.

Conclusions
Based on zircon isotopic studies of the No. 3 granodiorite and Re-Os isotopic dating of pyrites collected from Fe-Cu ores in the Shuikoushan deposit, the following conclusions are made: (1) The No. 3 granodiorite was emplaced at 153.7 ± 0. 58 Ma, similar to other granitoids in the Shuikoushan ore field and Nanling Range. Fe-Cu mineralization in the deposit formed at 140 ± 11 Ma, much younger than the No. 3 granodiorite. The younger Fe-Cu mineralization is interpreted as being related to injection of post-magmatic hydrothermal fluids. (2) The Late Paleoproterozoic basement in the Shuikoushan ore field provides rockforming materials and ore-forming metals of granodiorites and Fe-Cu mineralization in this region. (3) The Early Cretaceous may also be an important mineralization epoch in the Nanling Range.