Geochronological and Geochemical Constraints on the Origin of the Hutouya Polymetallic Skarn Deposit in the East Kunlun Orogenic Belt, NW China

The Hutouya polymetallic skarn deposit lies in the Qimantagh area of the East Kunlun Orogenic Belt, NW China. Skarnization and mineralization at the deposit are closely associated with contemporary felsic intrusions. In this paper, zircon U-Pb ages and zircon Hf isotope as well as whole-rock geochemical and whole-rock Sr-Nd isotope data are reported for intrusive rocks and crystal tuff of the Elashan Formation in the Hutouya area. Moreover, Re-Os ages and S-Pb isotopes are also reported for the ore minerals in the Hutouya deposit. The Zircon laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U-Pb age of granodiorite and Re-Os isochron age of molybdenite suggest that mineralizations occurred at ca. 227 Ma and that the granodiorite and molybdenite are closely related petrogenetically. All the granitoids in the Hutouya deposit are high-K calc-alkaline and metaluminous to weakly peraluminous I-type granitoids. Among them, the ore-forming granitoids were derived by the mixing of crust-derived (either juvenile or ancient mature lower crust) and mantle-derived magmas, whereas the non-ore-related granite porphyry was generated by the partial melting of a single ancient mature lower crust. The magmas of all the granitoids underwent extensive fractionation–crystallization during the process of rising and emplacement. The sulfur of the analyzed samples from the northern and middle zone of Hutouya deposit (including No. II, III, IV, and VI ore belts) belongs to deep magmatic sulfur, while the sulfur of samples from the southern zone of Hutouya deposit (No. VII ore belt) includes not only deep magmatic sulfur but also a contribution of strata sulfur. All the ore mineral samples in the Hutouya deposit have similar Pb compositions that are consistently derived from a mixed source of upper crust and mantle. Tectonic discrimination diagrams indicate a post-collisional setting for all granitic rocks of the Hutouya skarn deposit, which is therefore considered a product of a the post-collision extensional system and is consistent with other porphyry-skarn deposits within the East Kunlun Orogenic Belt.


Introduction
The East Kunlun Orogenic Belt (EKOB; Figure 1a,b) is one of the most significant polymetallic belts in China [1], with many studies of its numerous porphyry-and skarn-type deposits having been undertaken in recent years (Table 1). In particular, the Qimantagh area (Figure 1b,c), located in the northern EKOB, is the top priority of researchers for skarn and porphyry-type Fe-Cu-Pb-Zn-Mo-W-Sn deposits, including the Galinge Fe skarn deposit [2], Tawenchahan skarn Fe-Cu-Zn deposit [3], Tectonic map of the EKOB (modified after [9]; the square frame represents the location of Qimantag area). (c) Geological map showing the main mineral deposit types in the Qimantag area (modified after [10]). (b) Tectonic map of the EKOB (modified after [9]; the square frame represents the location of Qimantag area). (c) Geological map showing the main mineral deposit types in the Qimantag area (modified after [10]). The Hutouya district includes seven major Fe-Cu-Pb-Zn skarn deposits accompanied by Mo-W-Sn-Ag mineralization, which are referred to as ore belts Nos. I-VII ( Figure 2). The submitted Cu-Pb-Zn metal resources of ore belts Nos. VII, VI, and II are ca. 60 × 10 4 t, 20 × 10 4 t, and 5 × 10 4 t, respectively, indicating they correspond to large-scale deposits and have important economic value [24]. To date, several issues need more reasonable research and interpretation as the prospecting work has deepened; thus, many scholars have become attracted to the discussion of the ore genesis in this deposit [6,[24][25][26]. Although previous studies have investigated igneous rocks in this area, we notice that (1) most of them focused on the monzogranites in the Hutouya [24,26], but the ore-forming granodiorites of ore belts No. I and III have attracted less attention; (2) it still remains unknown whether all the granitic rocks in the Hutouya deposit belong to A-type granite [27]; (3) Sr-Nd-Hf isotopic data for granitoids are urgently needed to compare the magma sources between the ore-forming and non-ore-related granitoids; (4) the petrogenesis of a variety of rock types within the Hutouya deposit has not been systematically studied-especially the crystal tuff of the Elashan Formation-since many Pb-Zn-Ag deposits related to the volcanic strata were discovered [28]; (5) to date, the commonality and difference of ore-forming materials on S-Pb isotopes within different ore belts of the Hutouya deposit is unclear.
In this work, in order to address the above issues, we provide new geochronological and geochemical data for the Hutouya deposit, including molybdenite Re-Os dating, zircon LA-ICP-MS U-Pb dating, zircon Hf isotopic compositions, whole rock major and trace elements, and Sr-Nd isotopic compositions of ore-related granitoids, non-ore-related granitoids, and crystal tuff, as well as ore-mineral S-Pb isotopic compositions, which will place important constraints on the origin of the Hutouya polymetallic skarn deposit.  (11) skarn; (12) fractured and altered zone; (13) orebody; (14) stratigraphic boundary; (15) anticline; (16) reverse fault; (17) sampling site.

Regional Geology
The EKOB extends east-west (E-W) for >1000 km in the western part of the Central Orogenic Belt. The respective northern and southern boundaries of the EKOB are marked by the Qaidam Block and Bayan Har-Songpanganzi Terrane (Figure 1a,b), and this belt records the earliest history of assembly of the northern Tibetan Plateau [29,30]. The EKOB is divided into three parts by deep regional fractures: the North Kunlun, Central Kunlun, and South Kunlun belts by the boundaries between these units-from north to south, the North Kunlun fault (NKF), Middle Kunlun fault (MKF), and South Kunlun faults (SKF) [30][31][32] (Figure 1b). The Precambrian basement of the north Kunlun and Central Kunlun belts is the Paleoproterozoic Jinshuikou Group, which formed at ca. 1800-1600 Ma and underwent granulite facies metamorphism in the Paleozoic [33]. The Precambrian basement of the South Kunlun Belt is composed of the Proterozoic Wanbaogou Group, Kuhai Group, and the early Paleozoic Naij Tal Group [31].
Previous sufficient research works have identified two stages of the Phanerozoic orogeny and related magmatic events in the EKOB: the late Neoproterozoic-Devonian and Carboniferous-Triassic, which correspond to the evolution of the Proto-Tethys and Paleo-Tethys oceans, respectively [31,[34][35][36][37]. The Hutouya deposit, one of the typical Cu-Fe-Pb-Zn polymetallic skarn deposits, is located in the northwestern EKOB (Figure 1b,c). As previously stated, fragments of the Paleo-Tethyan Oceanic crust have been identified by their 308 Ma MORB-type basaltic lavas and 333 Ma OIB-type gabbro [38][39][40]. During the Late Permian to Triassic, numerous igneous rocks formed in the subduction and continental collision settings during the Paleo-Tethyan Ocean evolution in the EKOB [41,42]. As previously stated, a large amount of Permian-early Triassic granitoids (ca. 263-240 Ma) with the geochemical characteristics of Andeans-type granites formed in an active continental margin setting within the EKOB [42,43]. In addition, the marine facies sedimentary formations in the forearc basin, including the Upper-Permian Gequ Formation, the Lower-Triassic Hongshuichuan Formation, and Mid-Triassic Naocangjiangou Formation, are believed to be formed in a tectonic setting of ocean subduction within the EKOB related to the evolution of Paleo-Tethys ocean during the Late-Permian to Mid-Triassic [44]. In summary, the Paleo-Tethyan oceanic crust in the EKOB was still in a subduction setting before the Middle Triassic. Subsequently, a continental collision event occurred in the late Middle Triassic (after ca. 240 Ma). Moreover, the Middle to Upper Triassic Babaoshan Formation comprises terrigenous clastic and volcanic rocks in angular unconformity with an underlying marine sequence, indicating that the EKOB entered a collision setting after the late Middle Triassic [20,45]. During the Late Triassic, the EKOB tectonic regime was transformed from a collision compressional to post-collision extensional system following the closure of the Paleo-Tethys Animaqen Ocean [46].

Deposit Geology and Sample Descriptions
The Hutouya polymetallic deposit is ≈345 km west of Golmud, Qinghai Province, NW China. The strata in the Hutouya mining area are characterized with a large time span, including the mid-Proterozoic Langyashan Formation limestone, Ordovician-Silurian Tanjianshan Formation marble, mafic volcanic rocks with clasolite, Lower Carboniferous Dagan'gou Formation limestone, Upper Carboniferous Di'aosu Formation dolomitic limestone, and marble and Upper Triassic Elashan Formation crystal tuff with rhyolitic tuff breccia. Fold and fault structures occur in the mining area. A near-E-W transpressive fault and fold system formed by north-south (N-S)-directed compression is the ore-controlling structure of the deposit ( Figure 2). The Hutouya deposit is a large deposit, including seven main ore belts in the area. Ore belts No. I, II, III, and VI in the middle part of the Hutouya deposit, named the "inner contact skarn zones", emerge as the contact area among the ore-forming intrusions, carbonate strata, and host Fe-Cu-Mo mineralization ( Figure 2). In addition, ore belt No. VII, in the southern part of Hutouya deposit, named the "outer contact skarn zone", emerges as the main Pb-Zn ore body bounded by carbonate strata and the fracture zones. By contrast, small granodiorite and granite porphyry dykes, without a contact area between granitoids and carbonate strata, appeared in the No. IV and V ore belts in the northern part of the Hutouya deposit, which is different from the No. VII ore belt ( Figure 2). Based on the current field geology, a large polymetallic mineralization contact zone between the ore-forming intrusions and the carbonate strata probably exists in the deep part of the No. IV and V ore belts. The specific features of the main ore belts and sample locations are described below: (  Figure 2). The crystal tuff samples (37 • 05 47 N, 91 • 38 17 E) were also taken to examine the magmatism within the Hutouya deposit. The granodiorite sample (JR) was grayish white in surface outcrops. Microscopic examination revealed a granodiorite mineral composition ( Figure 3a) composed mainly of plagioclase (≈45%; 0.6-1.0 mm), alkali feldspar (≈20%; 1.3-1.9 mm), quartz (≈20%; 0.6-1.0 mm), biotite (≈5%; 0.5-1.5mm) and amphibole (≈10%; 0.3-0.5 mm) with accessory minerals including zircon and apatite. The fresh face of the monzogranite sample (DH10) was light gray with a massive structure ( Figure 3b) and a mineral composition of quartz (≈45%; 0.75-3.0 mm), plagioclase (≈35%; 1-2 mm), alkali feldspar (≈20%; 1.3-1.9 mm) and biotite (≈5%; 0.6-0.75 mm). The granite porphyry sample (HT) exhibited a porphyritic texture. The phenocrysts were mainly plagioclase (≈15%; 0.5-1.0 mm), K-feldspar (≈10%; 0.5-1.0 mm), quartz (≈30%), and biotite (≈2%). The groundmass was dominated by felsic minerals, biotite, and minor accessory minerals (Figure 3c). Most plagioclase was subhedral and short columnar in shape, with albite twinning and minor surface kaolinization and carbonate. K-feldspar was mostly subhedral short columnar, with Carlsbad twinning and surface kaolinization. The groundmass mainly comprised microcrystalline quartz and feldspar, and the main accessory minerals were apatite, zircon, and corundum. The Hutouya crustal tuff sample (DH09) was grayish green, with a crystalline-pyroclast tuffaceous texture. Crystal pyroclasts (≈30%) included predominantly quartz and pegmatolite ( Figure 3d). Quartz pyroclasts were angular with visible embayments.
The main ore mineral samples of the Hutouya deposit were sphalerite, galena, magnetite, and chalcopyrite, followed by molybdenite, arsenopyrite, pyrophyllite, and small amounts of chalcocite, pyrrhotite, and pyrite. The ore mineral analytical samples in this study were collected from the No. IV ore belt and No. VI ore belt within the Hutouya deposit. The ore texture was predominantly metasomatic in structure and exsolution (Figure 3e-i). In particular, the molybdenite was flaky with bending deflection and showed a dissemination structure in the photomicograph (Figure 3e). The chalcopyrite was brass yellow. Microscopic examination revealed an allotriomorphic texture (Figure 3f-h) and milk-drop texture (Figure 3f). The pyrrhotite was cream yellow, tinged slightly pink, and anhedral in texture in the photomicrograph (Figure 3g). The galena was pure white by reflection. Microscopic examination revealed an allotriomorphic granular texture with black delthrium in the surface (Figure 3h). The sphalerite was shown to be dark gray by reflection and exhibited an allotriomorphic graular texture in the photomicrograph (Figure 3f,i). Gangue minerals mainly included calcite, garnet, diopside, fluorite, and quartz.

Zircon U-Pb Dating
The results of zircon U-Pb dating are given in Supplementary Material Table S1, and their concordia diagrams are presented in Figure 4a-c. Zircons from the Hutouya granitic rocks and crystal tuff were generally light gray and columnar. All analyzed zircons were euhedral with lengths of 70-

Zircon U-Pb Dating
The results of zircon U-Pb dating are given in Supplementary Material Table S1, and their concordia diagrams are presented in Figure 4a-c. Zircons from the Hutouya granitic rocks and crystal tuff were generally light gray and columnar. All analyzed zircons were euhedral with lengths of 70-120 µm and aspect ratios of 1-3. Their oscillatory growth zoning indicated a magmatic origin [47]. The 206 Pb/ 238 U ages of zircons from sample JR-N ranged from 232 to 221 Ma, with a weighted-mean age of 227.1 ± 3.

Molybdenite Re-Os Dating
Re-Os analysis results for seven molybdenite samples are summarized in Supplementary Material Table S2. Re and 187 Os contents were 169.0-278.8 ppm and 403.8-669.4 ppm, respectively. Common Os (≈0.01 ppb) may have been derived from analytical artifacts and was negligible compared with 187 Os. Therefore, the molybdenite Re-Os ages were considered reliable [48]. The seven molybdenite samples from skarn ores yielded consistent model ages of 230-225 Ma (Supplementary Material Table S2), with an Re-Os isochron age of 227 ± 6 Ma (MSWD = 1.5) and an initial 187 Os content of 0 ± 14 ppm ( Figure 4d). Furthermore, the Re content is commonly used to trace ore-forming materials [49], and the higher Re contents (169-278 ppm) recorded here may imply the involvement of mantle underplating [50].

Whole-Rock Major and Trace-Element Compositions
Whole-rock major and trace-element compositions of 23 representative samples of granitic rocks and crystal tuff are given in Supplementary Material Table S3 and are described separately for each rock type below.

Whole-Rock Major and Trace-Element Compositions
Whole-rock major and trace-element compositions of 23 representative samples of granitic rocks and crystal tuff are given in Supplementary Material Table S3 and are described separately for each rock type below.     In the primitive-mantle-normalized trace-element spider diagram (Figure 6b), all samples display enrichment in LILEs (e.g., Rb, Th, U, and REEs), strong depletion in HFSEs (e.g., Nb, Ta, Ti, and P) and weak negative Sr anomalies. They had strong negative Eu anomalies (Eu/Eu* = 0.58-0.63), which is indicative of the possible crystal fractionation of plagioclase.

Sr-Nd Isotopic Compositions
The results of Sr-Nd isotopic analyses of the Hutouya monzogranite and crystal tuff are given in Supplementary Material Table S4

Zircon Hf Isotopic Compositions
Hf isotopic data for zircons from the Hutouya granitic rocks and crystal tuff are given in Supplementary Material Table S5
Pb isotopic compositions for the 15 sulfide mineral samples together with previous published data are given in Supplementary Material

Age of Mineralization
Accurate dating is crucial to the understanding of an ore deposit, and here, we discuss new dating results for the granitic rocks, crystal tuff, and molybdenite of the Hutouya deposit. Our zircon U-Pb dating of the crystal tuff indicates that its eruption occurred at 222.7 ± 2.5 Ma, and our zircon U-Pb dating of the granitic rocks indicates the emplacement and crystallization of granodiorite and granite porphyry at 227.1 ± 3.6 Ma and 222.1 ± 1.0 Ma, respectively. The molybdenite Re-Os isochron ages (227.5 ± 5.5 Ma) and zircon U-Pb dating of granodiorite are concordant within error at ca. 227.5

Zircon Hf Isotopic Compositions
Hf isotopic data for zircons from the Hutouya granitic rocks and crystal tuff are given in Supplementary Material Table S5  The predominantly negative εHf(t) values indicate that the magma was derived from reworked Mesoproterozoic crustal components.
Pb isotopic compositions for the 15 sulfide mineral samples together with previous published data are given in Supplementary Material

Age of Mineralization
Accurate dating is crucial to the understanding of an ore deposit, and here, we discuss new dating results for the granitic rocks, crystal tuff, and molybdenite of the Hutouya deposit. Our zircon U-Pb dating of the crystal tuff indicates that its eruption occurred at 222.7 ± 2.5 Ma, and our zircon U-Pb dating of the granitic rocks indicates the emplacement and crystallization of granodiorite and granite porphyry at 227.1 ± 3.6 Ma and 222.1 ± 1.0 Ma, respectively. The molybdenite Re-Os isochron ages (227.5 ± 5.5 Ma) and zircon U-Pb dating of granodiorite are concordant within error at ca. 227. 5 Ma. Thus, these ages indicate that magmatism and related skarn mineralization in the Hutouya deposit occurred during the Late Triassic. As stated previously, the closure temperature of the zircon U-Pb isotopic dating system and the Re-Os isotopic dating system is 800 • C and 500 ± 50 • C [56,57]. Therefore, the formation of the Hutouya deposit is related to the separation and exsolution of ore-forming fluids that occurred after the magma cooled rapidly from 800 to 500 ± 50 • C at ca. 227 Ma.

Genetic Types of the Igneous Rocks
The identification of the genetic type of felsic igneous rocks is critical to the understanding of their magma sources, magmatic evolution and tectonic settings [58]. Granitic rocks can be classified as either I, S, or A-types [59,60]. Our granodiorite, granite porphyry, and monzogranite samples had high K contents, low (Zr + Nb + Ce + Y) contents, and low (10,000 × Ga/Al) ratios. In ( Ma. Thus, these ages indicate that magmatism and related skarn mineralization in the Hutouya deposit occurred during the Late Triassic. As stated previously, the closure temperature of the zircon U-Pb isotopic dating system and the Re-Os isotopic dating system is 800 °C and 500 ± 50 °C [56,57]. Therefore, the formation of the Hutouya deposit is related to the separation and exsolution of oreforming fluids that occurred after the magma cooled rapidly from 800 to 500 ± 50 °C at ca. 227 Ma.

Genetic Types of the Igneous Rocks
The identification of the genetic type of felsic igneous rocks is critical to the understanding of their magma sources, magmatic evolution and tectonic settings [58]. Granitic rocks can be classified as either I, S, or A-types [59,60]. Our granodiorite, granite porphyry, and monzogranite samples had high K contents, low (Zr + Nb + Ce + Y) contents, and low (10,000 × Ga/Al) ratios. In ((Na2O + K2O)/CaO) − (10,000 × Ga/Al) ( Figure 8a) and ((Na2O + K2O)/CaO) − (Zr + Nb + Ce + Y) (Figure 8b) diagrams, all samples were plotted in the I and S-type granite and non-fractionated granite fields, respectively. A-type granites generally consist of alkaline minerals such as richterite, aegirine, and fayalite, unlike the granitic rocks of the Hutouya deposit, which are therefore not A-type granites. The mean A/CNK ratios of the Hutouya granitic rocks is 0.96, unlike S-type granites (A/CNK > 1.1) [61]. The solubility of P2O5 is high in strongly peraluminous melts but low in metaluminous or weakly peraluminous melts. Therefore, the P2O5 content increases in peraluminous S-type melts during crystal fractionation but decreases in I-type melts [62,63,64]. The Hutouya granitic rock samples generally have high SiO2 contents and are high-K calc-alkaline and metaluminous to weakly peraluminous rocks. Additionally, their trends are not in accordance with S-type granites in the P2O5-SiO2 diagram; on the contrary, they resemble the I-type granite trend (Figure 9h). The lack of Al-rich minerals such as cordierite and muscovite also supports their I-type rather than S-type origin [61]. Moreover, the low initial 87 Sr/ 86 Sr ratios of monzonitic granite ranging from 0.70635 to 0.70798 are clearly different from S-type granites (initial 87 Sr/ 86 Sr > 0.710) [65]. Therefore, we conclude that the Hutouya granitoids are I-type granites. A-type granites generally consist of alkaline minerals such as richterite, aegirine, and fayalite, unlike the granitic rocks of the Hutouya deposit, which are therefore not A-type granites. The mean A/CNK ratios of the Hutouya granitic rocks is 0.96, unlike S-type granites (A/CNK > 1.1) [61]. The solubility of P 2 O 5 is high in strongly peraluminous melts but low in metaluminous or weakly peraluminous melts. Therefore, the P 2 O 5 content increases in peraluminous S-type melts during crystal fractionation but decreases in I-type melts [62][63][64]. The Hutouya granitic rock samples generally have high SiO 2 contents and are high-K calc-alkaline and metaluminous to weakly peraluminous rocks. Additionally, their trends are not in accordance with S-type granites in the P 2 O 5 -SiO 2 diagram; on the contrary, they resemble the I-type granite trend (Figure 9h). The lack of Al-rich minerals such as cordierite and muscovite also supports their I-type rather than S-type origin [61]. Moreover, the low initial 87 Sr/ 86 Sr ratios of monzonitic granite ranging from 0.70635 to 0.70798 are clearly different from S-type granites (initial 87 Sr/ 86 Sr > 0.710) [65]. Therefore, we conclude that the Hutouya granitoids are I-type granites.

Magma Sources and Petrogenesis
As mentioned above, all the igneous rocks from the Hutouya deposit are high potassium calcalkaline to shoshonite series, metaluminous to weakly peraluminous I-typed granites. Generally, the calc-alkaline I-type granites can be generated by the partial melting of mafic to intermediate igneous rocks [66] by mantle-derived basaltic magmas, which underwent extensive assimilation and fractional crystallization [67] or by the mixing of crust and mantle-derived magma [68].  Table S3); positive Rb and K anomalies; and negative Nb, Ta, P, and Ti anomalies (Figure 6b). Such characteristics are consistent with crust-derived rocks [69,70]. In addition, the granodiorite and monzogranite samples were unassociated with any contemporaneous gabbros and basalts in the Hutouya area. All these factors exclude the possibility that they could be generated directly by the partial melting of mantle peridotite. Moreover, experimental studies indicate that the Mg # value is an effective way to evaluate the magma melts. In general, the dehydration melting of the basaltic lower crust generates low Mg # (<40) melts, whereas the melts with mantle components involved can produce Mg # (>40) [71,72]. According to the results, the granodiorite samples had a relatively low Mg # value ranging from 27 to 29, which indicates that the melts were derived from mafic lower crust. Notably, the Mg # value of the monzogranite samples ranged from 42 to 55, which likely suggests an involvement of mantle-derived components. Furthermore, the Nb/Ta ratios of the granodiorite and monzogranite samples ranged from 13.96 to 17.31 (mean value = 15.88) and from 6.52 to 11.08 (mean

Magma Sources and Petrogenesis
As mentioned above, all the igneous rocks from the Hutouya deposit are high potassium calc-alkaline to shoshonite series, metaluminous to weakly peraluminous I-typed granites. Generally, the calc-alkaline I-type granites can be generated by the partial melting of mafic to intermediate igneous rocks [66] by mantle-derived basaltic magmas, which underwent extensive assimilation and fractional crystallization [67] or by the mixing of crust and mantle-derived magma [68] Table S3); positive Rb and K anomalies; and negative Nb, Ta, P, and Ti anomalies (Figure 6b). Such characteristics are consistent with crust-derived rocks [69,70]. In addition, the granodiorite and monzogranite samples were unassociated with any contemporaneous gabbros and basalts in the Hutouya area. All these factors exclude the possibility that they could be generated directly by the partial melting of mantle peridotite. Moreover, experimental studies indicate that the Mg # value is an effective way to evaluate the magma melts. In general, the dehydration melting of the basaltic lower crust generates low Mg # (<40) melts, whereas the melts with mantle components involved can produce Mg # (>40) [71,72]. According to the results, the granodiorite samples had a relatively low Mg # value ranging from 27 to 29, which indicates that the melts were derived from mafic lower crust. Notably, the Mg # value of the monzogranite samples ranged from 42 to 55, which likely suggests an involvement of mantle-derived components. Furthermore, the Nb/Ta ratios of the granodiorite and monzogranite samples ranged from 13.96 to 17.31 (mean value = 15.88) and from 6.52 to 11.08 (mean value = 9.66), respectively. Both of the granitoids are above the average Nb/Ta ratios of the lower crust (8.3; [73]) and below the average Nb/Ta ratios of mantle-derived rocks (17.4; [54]), further indicating that a certain number of mantle-derived components were involved in the generation of the granodiorite and monzogranite. Isotopically, zircon Hf isotopic analysis is an effective and widely used method to trace the source of magmas [74][75][76]. All the granodiorite samples had similar zircon Hf isotopic compositions with εHf(t) values of 0.0-6.2. In the εHf(t)-age diagram (Figure 7a), they were plot between the depleted mantle and chondrite lines. In addition, the T DM2 ages ranged from 1123 to 930 Ma (Supplementary Material Table S5), implying that the granodiorite could be derived from reworked Meso-Neoproterozoic juvenile components. The monzongranite samples had a narrow range of high I Sr values (0.70635-0.70798) and low εNd(t) values (−5.01 to −4.11) with the T DM2 ages of 1406-1333 Ma, suggesting that the monzongranite may have been sourced from the partial melting of ancient lower crustal material. Notably, the monzongranite samples showed similar Sr-Nd compositions to other Triassic granitoids, plotting in the overlap field of the EKOB continental arc magmas and the EKOB-enriched lithospheric mantle (Figure 7b), which implies that the EKOB enriched lithospheric mantle might have been involved during the generation and/or evolution of the primary magma of the monzongranite.
All the granodiorite and monzongranite samples displayed low Sr (80.79-434.00 ppm), high Y (11.40-23.90 ppm), and high Yb (1.57-2.01 ppm) values, with low Sr/Y ratios (5.3-37.54), thus belonging to normal arc rocks rather than typical adakitic rocks [60]. The relatively high Yb concentrations (1.57-2.01 ppm) and relatively flat HREE characteristics (Figure 6a) indicate that partial melting occurred above the stable region of garnet [61]. Therefore, there was no garnet residue in the source. The granodiorite samples show a good linear relation in the Harker diagrams, which implies a strong fractionation of primary magma (Figure 9b In summary, the ore-forming granitoid intrusions were generated by the mixing of crust and mantle-derived magma. The mafic magma was generated by the partial melting of enriched lithospheric mantle and underplated on the bottom of lower crust. As the upwelling enriched lithospheric mantle-derived magma, which rose to the bottom of the lower crust, the partial melting of juvenile (i.e., the Hutouya granodiorite) and ancient mature lower crust (i.e., the Hutouya monzongranite) occurred, which then mixed with mantle-derived magmas. Then, the mixed magmas underwent extensive fractionation-crystallization during the process of rising and emplacement. (Figure 10c,d). In summary, the ore-forming granitoid intrusions were generated by the mixing of crust and mantle-derived magma. The mafic magma was generated by the partial melting of enriched lithospheric mantle and underplated on the bottom of lower crust. As the upwelling enriched lithospheric mantle-derived magma, which rose to the bottom of the lower crust, the partial melting of juvenile (i.e., the Hutouya granodiorite) and ancient mature lower crust (i.e., the Hutouya monzongranite) occurred, which then mixed with mantle-derived magmas. Then, the mixed magmas underwent extensive fractionation-crystallization during the process of rising and emplacement.

Non-Ore-Related Granite Porphyry and Crystal Tuff
All the granite porphyry and crystal tuff samples contained high concentrations of SiO2 and Al2O3 and low concentrations of MgO, Cr, Co, and Ni (Supplementary Material Table S3). All the concentrations mentioned above are in accordance with crust-derived rocks [77]. The low Nb/Ta ratios of both the granite porphyry (6. 39-8.25) and crystal tuff (6.33-8.17) indicate that the magmas of granite porphyry and crystal tuff probably originated solely from the anatexis of the lower crust. In addition, the low Mg # values of the granite porphyry  further imply that the magma was derived from crustal material. In contrast, the relatively high Mg # values of the crystal tuff (51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61)(62)(63)(64)(65) imply that the mantle-derived components were involved in the magma. The high concentrations of  Table S3). All the concentrations mentioned above are in accordance with crust-derived rocks [77]. The low Nb/Ta ratios of both the granite porphyry (6.39-8.25) and crystal tuff (6.33-8.17) indicate that the magmas of granite porphyry and crystal tuff probably originated solely from the anatexis of the lower crust. In addition, the low Mg # values of the granite porphyry  further imply that the magma was derived from crustal material. In contrast, the relatively high Mg # values of the crystal tuff (51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61)(62)(63)(64)(65) imply that the mantle-derived components were involved in the magma. The high concentrations of Y (12.25-33.33 and 10.90-17.60 of granite porphyry and crystal tuff samples, respectively) and relatively flat HREE pattern (Figure 6a) indicate the presence of residual amphibole [78].
The isotope geochemical data also contribute some proof of the magma source. The non-ore-related granite porphyry samples displayed the following features: their zircon εHf(t) values and T DM2 ages ranged from −5.34 to −0. 85 Ma and 1518 to 1312 Ma, respectively, indicating that the primary magma may have been derived from the partial melting of the Mesoproterozoic lower crust (Figure 7a); the nature of the magma source of crystal tuff was revealed through zircon Sr−Nd−Hf isotopic compositions; the εHf(t) values of −4.0 to +0.3 and T DM2 ages of 1345-1106 Ma indicate that the primary magma may have originated from the partial melting of the Mesoproterozoic lower crust with a minute quantity of mantle components; and the fairly negative εNd(t) values (−5.43 to −4.69) and T DM2 ages of 1442-1382 Ma also imply that the magma of the crystal tuff was derived from the partial melting of the Mesoproterozoic lower-crustal material.
In the Harker diagrams, the non-ore-related granite porphyry and crystal tuff samples show a slight fractionation of magmas with few relative negative correlations (Figure 9b-h). Plagioclase crystallization is indicated by their negative Eu anomalies (Eu/Eu* = 0.34-0.84 and 0.58-0.63 for the granite porphyry and crystal tuff samples, respectively; Figure 6a). Amphibolite crystallization is indicated in the (Hf/Sm) − (Zr/Y) diagram (Figure 10d). The crystallization and differentiation of K-feldspar is indicated in the Sr-Ba diagram (Figure 10a). The P and Ti negative anomalies of all the granite porphyry and crystal tuff samples suggest the fractionation-crystallization of apatite and the Fe-Ti oxides.
In summary, non-ore-related granite porphyry was generated by the partial melting of a single ancient mature lower crust, with its primary magma undergoing fractionation-crystallization during the process of rising and emplacement. In contrast, the crystal tuff of the Elashan Formation originated from the mixing of lower crust material and mantle-derived components and also underwent fractionation-crystallization in the process of magma rising. To date, many Pb-Ag polymetallic deposits (such as Hariza, Dongshan, Narimalahei, and Zamashan) closely hosted in the continental volcanic rocks of the Elashan Formation have been discovered in the eastern section of the EKOB [29]; therefore, we infer that the acid volcanic rocks of the Elashan Formation, with mixed magma sources, should probably also possess great prospecting potential in the western section of the EKOB.

Sources of Ore-Forming Materials
Sulfur obviously plays an important role in the mineralization and precipitation of metal sulfide deposits, and S isotopic data provide important information about the sources of ore-forming materials [79,80], as gained from sulfur isotopic characteristics of hydrothermal fluids [81]. The absence of sulfate minerals in all ore belts of the Hutouya deposit shows that the ore-forming hydrothermal fluid is a single component that did not experience complex strong fractionation. For this reason, the values of the δ 34 S sulfide from the sulfide mineral samples can approximately represent the values of δ 34 S fluid in the ore-forming hydrothermal solution (δ 34 S sulfide ≈ δ 34 S fluid ; [82,83]). Overall, our data, together with the previous studies, show that the δ 34 S values from the major ore minerals range from 0.6‰ to 9.8‰ with a mean value of 4.5 (Supplementary Material Table S6). The mean δ 34 S value is higher than the mantle-derived sulfur (0‰; [84]), meteoritic sulfur (from −3‰ to +3‰; [85]), and the reduced sulfur in sediments (<0‰; [86]), while it is lower than the oceanic carbonate (Cambrian-Triassic δ 34 S = 15-35‰; [87]) and approximately equal to deep magmatic sulfur (from −5‰ to +5‰; [81]), which indicates that the S predominately originated from magmatic sulfur. In addition, the δ 34 S peaks intervals of sulfide mineral samples from the No. IV ore belt in the north zone (0.8-5.0‰; Supplementary Material Table S6; Figure 11b,c) are similar to ore belts No. II, III and VI in the middle zone, named the "inner contact skarn zones" (0.6-6.8‰; Supplementary Material Table S6; Figure 11b,c), which are more approximate to the deep magmatic sulfur (from −5‰ to +5‰; [81]), while they are significantly lower than the VII ore belt in the southern zone (6.5-9.8‰, except for one chalcopyrite sample of 1.6‰; Figure 11a-c). In consideration of all the ore bodies bounded by carbonate strata and fracture zones in the No. VII ore belt, named the "outer contact skarn zones", located in the southern part of the Hutouya deposit, the higher δ 34 S peak intervals are likely due to the influence of the sulfur from the strata. Therefore, we conclude that concealed ore-forming intrusions and "inner contact skarn zones" probably existed deep within the No. IV, V ore belts of the northern zone within the Hutouya deposit, which shows greater metallogenic potential in the deep zone of the northern part of the Hutouya deposit. located in the southern part of the Hutouya deposit, the higher δ 34 S peak intervals are likely due to the influence of the sulfur from the strata. Therefore, we conclude that concealed ore-forming intrusions and "inner contact skarn zones" probably existed deep within the No. IV, V ore belts of the northern zone within the Hutouya deposit, which shows greater metallogenic potential in the deep zone of the northern part of the Hutouya deposit.  Lead isotope compositions can be used to indicate the evolution of the crust, the source of metallogenic minerals, and the genesis of deposits [88]. According to our data, together with previous studies, all the samples from the Hutouya deposit showed mean µ values of 9.55 (Supplementary Material Table S7), which is slightly lower than the mean value of the upper crust (9.58; [89]). The mean ω value (36.34; Supplementary Material Table S7) was between the mean value of the mantle (31.84; [90]) and upper crust (41.86; [90]). The mean Th/U ratio (3.68; Supplementary Material Table S7) was slightly lower than the mean Th/U ratio of the upper crust in China (3.76; [91]). All these data indicate that the Pb is likely derived from a mixed source of predominating crust-derived Pb and little mantle-derived Pb [92]. To further clarify the source of Pb in the Hutouya deposit, Pb isotopic data were also plotted in the Pb-isotope tectonic model diagram (Figure 12a,b) and tectonic environment discrimination diagram (Figure 12c,d). In a ( 207 Pb/ 204 Pb)-( 206 Pb/ 204 Pb) diagram (Figure 11a), the samples were plot mainly between the orogenic and upper crust evolution line with a proximate linear correlation. In a ( 208 Pb/ 204 Pb)-( 206 Pb/ 204 Pb) diagram (Figure 11b), the samples were plotted mostly on the orogenic evolution line. In tectonic environment discrimination diagrams (Figure 12c,d), the samples mainly fell in the orogen fields. Therefore, we conclude that Pb in the Hutouya deposit was sourced from the upper crust and the erosion zone of the orogenic belt [93]. In the ∆γ-∆β diagram, all the samples were mainly plotted in the field of "3a", which indicates that the Pb was derived from mixed lead from upper crust and mantle subduction ( Figure 13). Therefore, the Pb of all the mineral samples from the Hutouya deposit was derived from a mixed source: the majority from the crust and a small amount from the mantle. Lead isotope compositions can be used to indicate the evolution of the crust, the source of metallogenic minerals, and the genesis of deposits [88]. According to our data, together with previous studies, all the samples from the Hutouya deposit showed mean μ values of 9.55 (Supplementary  Material Table S7), which is slightly lower than the mean value of the upper crust (9.58; [89]). The mean ω value (36.34;Supplementary Material Table S7) was between the mean value of the mantle (31.84; [90]) and upper crust (41.86; [90]). The mean Th/U ratio (3.68; Supplementary Material Table  S7) was slightly lower than the mean Th/U ratio of the upper crust in China (3.76; [91]). All these data indicate that the Pb is likely derived from a mixed source of predominating crust-derived Pb and little mantle-derived Pb [92]. To further clarify the source of Pb in the Hutouya deposit, Pb isotopic data were also plotted in the Pb-isotope tectonic model diagram (Figure 12a,b) and tectonic environment discrimination diagram (Figure 12c,d). In a ( 207 Pb/ 204 Pb)-( 206 Pb/ 204 Pb) diagram ( Figure  11a), the samples were plot mainly between the orogenic and upper crust evolution line with a proximate linear correlation. In a ( 208 Pb/ 204 Pb)-( 206 Pb/ 204 Pb) diagram (Figure 11b), the samples were plotted mostly on the orogenic evolution line. In tectonic environment discrimination diagrams (Figure 12c,d), the samples mainly fell in the orogen fields. Therefore, we conclude that Pb in the Hutouya deposit was sourced from the upper crust and the erosion zone of the orogenic belt [93]. In the ∆γ-∆β diagram, all the samples were mainly plotted in the field of "3a", which indicates that the Pb was derived from mixed lead from upper crust and mantle subduction ( Figure 13). Therefore, the Pb of all the mineral samples from the Hutouya deposit was derived from a mixed source: the majority from the crust and a small amount from the mantle. Figure 12. (a,b) Pb-isotope tectonic model diagram [89]; and (c,d) tectonic environment discrimination diagram [89] for the Hutouya deposit (LC-lower crust; UC-upper crust; OIV-Ocean Intraplate Volcanism; OR-orogenic belt; A, B, C and D represent the dense domain in each field).
In summary, the sulfur of all the analyzed samples from the northern and middle zone of the Hutouya deposit (including ore belts Nos. II, III, IV, and VI) was derived from deep magmatic sulfur, while the S of all the analyzed samples from the southern zone of the Hutouya deposit (ore belt No. VII) was derived from deep magmatic sulfur and the contribution of strata sulfur. All the ore mineral samples showed that Pb was consistently derived from a mixed source of upper crust and mantle in the Hutouya deposit.
Minerals 2020, 10, x FOR PEER REVIEW 19 of 30 Figure 12. (a,b) Pb-isotope tectonic model diagram [89]; and (c,d) tectonic environment discrimination diagram [89] for the Hutouya deposit (LC-lower crust; UC-upper crust; OIV-Ocean Intraplate Volcanism; OR-orogenic belt; A, B, C and D represent the dense domain in each field). In summary, the sulfur of all the analyzed samples from the northern and middle zone of the Hutouya deposit (including ore belts Nos. II, III, IV, and VI) was derived from deep magmatic sulfur, while the S of all the analyzed samples from the southern zone of the Hutouya deposit (ore belt No. VII) was derived from deep magmatic sulfur and the contribution of strata sulfur. All the ore mineral samples showed that Pb was consistently derived from a mixed source of upper crust and mantle in the Hutouya deposit.

Geodynamic Background
An understanding of the geodynamic background of the EKOB is important for elucidating regional metallogenic processes [95,96,97,98]. The EKOB records several different orogenic phases and corresponding orogeneses, in which the orogeny related to the consumption of Paleo-Tethys oceans is an important and complex episode [99,100].
According to data in our study, the Late Triassic granitic rocks and crystal tuff from the Hutouya deposit are calc-alkaline I-type granites. In Nb-Y, and Rb-(Yb + Ta) diagrams (Figure 14), most samples were plotted in the (volcanic arc granites (VAG) + syn-collision granites (Syn-COLG)) and Post-COLG fields, respectively, similar to other Late Triassic high-K calc-alkaline to shoshonite I-type granites in the EKOB, which were supposed to form in a post-collision extensional setting [46,101]. In addition, the presence of Late Triassic A-type granites and adakites suggests that lithosphere delamination occurred and that the EKOB as in post-collision extension [30,102,103,104,105].
In the EKOB, a series of large and medium-scale skarn-porphyry Fe-Cu (Mo-Pb-Zn) polymetallic deposits have been generated, and their related ore-forming intrusions were formed during the Late Triassic ( [20,106]; Table 1). As previously stated, the Late Triassic post-collision extensional tectonic setting in the EKOB triggered the event of strong mantle-source magma underplating with the emergence of mafic-ultramafic rocks [107,108,109]. In addition to the maficultramafic rocks, numerous intermediate-felsic rocks derived from a mixing source of mantle and crust also developed (ca. 237-204 Ma; [46]). Therefore, intermediate-felsic rocks were likely generated from the partial melting of a thickened crust heated by strong mantle-derived magma underplating in decompression caused by the post-collision extension during the Late Triassic. This provided

Geodynamic Background
An understanding of the geodynamic background of the EKOB is important for elucidating regional metallogenic processes [95][96][97][98]. The EKOB records several different orogenic phases and corresponding orogeneses, in which the orogeny related to the consumption of Paleo-Tethys oceans is an important and complex episode [99,100].
According to data in our study, the Late Triassic granitic rocks and crystal tuff from the Hutouya deposit are calc-alkaline I-type granites. In Nb-Y, and Rb-(Yb + Ta) diagrams ( Figure 14), most samples were plotted in the (volcanic arc granites (VAG) + syn-collision granites (Syn-COLG)) and Post-COLG fields, respectively, similar to other Late Triassic high-K calc-alkaline to shoshonite I-type granites in the EKOB, which were supposed to form in a post-collision extensional setting [46,101]. In addition, the presence of Late Triassic A-type granites and adakites suggests that lithosphere delamination occurred and that the EKOB as in post-collision extension [30,[102][103][104][105].
In the EKOB, a series of large and medium-scale skarn-porphyry Fe-Cu (Mo-Pb-Zn) polymetallic deposits have been generated, and their related ore-forming intrusions were formed during the Late Triassic ( [20,106]; Table 1). As previously stated, the Late Triassic post-collision extensional tectonic setting in the EKOB triggered the event of strong mantle-source magma underplating with the emergence of mafic-ultramafic rocks [107][108][109]. In addition to the mafic-ultramafic rocks, numerous intermediate-felsic rocks derived from a mixing source of mantle and crust also developed (ca. 237-204 Ma; [46]). Therefore, intermediate-felsic rocks were likely generated from the partial melting of a thickened crust heated by strong mantle-derived magma underplating in decompression caused by the post-collision extension during the Late Triassic. This provided abundant ore-forming material as well as a heat source for regional mineralization under the influence of the strong crust-mantle interaction and magmatism in EKOB [23,106], as with the ore-forming granitoid intrusions from the Hutouya deposit in this study. Our results for the magmatism and mineralization ages of the Hutouya polymetallic deposit confirm its association with the Paleo-Tethys evolution of the EKOB.
abundant ore-forming material as well as a heat source for regional mineralization under the influence of the strong crust-mantle interaction and magmatism in EKOB [23,106], as with the oreforming granitoid intrusions from the Hutouya deposit in this study. Our results for the magmatism and mineralization ages of the Hutouya polymetallic deposit confirm its association with the Paleo-Tethys evolution of the EKOB.

Conclusions
Our new geochronological and geochemical data for Late Triassic granitoids, crystal tuff, molybdenites, and other ore minerals of the Hutouya Cu-Fe-Pb-Zn polymetallic deposit allow us to draw the following conclusions: (1) Zircon LA-ICP-MS U-Pb and molybdenite Re-Os dating reveals that the emplacement of granitoids and mineralization of the Hutouya deposit occurred at ca. 227 Ma; (2) The ore-forming granitoids were generated by the mixing of crust-derived (either juvenile or ancient mature lower crust) and mantle-derived magma. The non-ore-related granite porphyry was generated by the partial melting of a single ancient mature lower crust. The granitic magmas underwent extensive fractional crystallization during the process of rising and emplacement; (3) The crystal tuff was derived from a mixed magma source of lower crust material and mantlederived components, and the Elashan Formation probably has great prospecting potential in the western EKOB; (4) Sulfur in the northern and middle zone of the Hutouya deposit was derived from deep magmatic sulfur, while the S of the southern zone of Hutouya deposit was derived from both deep magmatic sulfur and strata sulfur. All the ore mineral samples show that the Pb was consistently derived from a mixed source of upper crust and mantle in the Hutouya deposit; (5) The new data for granitoids and crystal tuff in the the Hutouya area suggest that they were formed at 227-222 Ma in a post-collision extensional geodynamic setting, with the Paleo-Tethys Bayankala Ocean having closed before the Late Triassic.
Supplementary Materials: The following are available online at www.mdpi.com/xxx/s1, Table S1: LA-ICP-MS zircon U-Pb data for the granitic rocks and crystal tuff of the Hutouya deposite, Table S2: Re-Os isotopic data for molybdenite of the Hutouya deposit, Table S3: Geochemical compositions of granitic rocks and crystal stuff from the Hutouya deposit (major elements are presented in wt %; trace elements are presented in ppm), Table  S4: Whole-rock Sr-Nd isotopic compositions from the monzonitic granite and crystal stuff of the Hutouya deposit, Table S5: Hf isotopic compositions of zircons from the granoditic rocks and crystal stuff of the Hutouya

Conclusions
Our new geochronological and geochemical data for Late Triassic granitoids, crystal tuff, molybdenites, and other ore minerals of the Hutouya Cu-Fe-Pb-Zn polymetallic deposit allow us to draw the following conclusions: (1) Zircon LA-ICP-MS U-Pb and molybdenite Re-Os dating reveals that the emplacement of granitoids and mineralization of the Hutouya deposit occurred at ca. 227 Ma; (2) The ore-forming granitoids were generated by the mixing of crust-derived (either juvenile or ancient mature lower crust) and mantle-derived magma. The non-ore-related granite porphyry was generated by the partial melting of a single ancient mature lower crust. The granitic magmas underwent extensive fractional crystallization during the process of rising and emplacement; (3) The crystal tuff was derived from a mixed magma source of lower crust material and mantle-derived components, and the Elashan Formation probably has great prospecting potential in the western EKOB; (4) Sulfur in the northern and middle zone of the Hutouya deposit was derived from deep magmatic sulfur, while the S of the southern zone of Hutouya deposit was derived from both deep magmatic sulfur and strata sulfur. All the ore mineral samples show that the Pb was consistently derived from a mixed source of upper crust and mantle in the Hutouya deposit; (5) The new data for granitoids and crystal tuff in the the Hutouya area suggest that they were formed at 227-222 Ma in a post-collision extensional geodynamic setting, with the Paleo-Tethys Bayankala Ocean having closed before the Late Triassic.
Supplementary Materials: The following are available online at http://www.mdpi.com/2075-163X/10/12/1136/s1, Table S1: LA-ICP-MS zircon U-Pb data for the granitic rocks and crystal tuff of the Hutouya deposite, Table S2: Re-Os isotopic data for molybdenite of the Hutouya deposit, Table S3: Geochemical compositions of granitic rocks and crystal stuff from the Hutouya deposit (major elements are presented in wt %; trace elements are presented in ppm), Table S4: Whole-rock Sr-Nd isotopic compositions from the monzonitic granite and crystal stuff of the Hutouya deposit, Table S5: Hf isotopic compositions of zircons from the granoditic rocks and crystal stuff of the Hutouya deposit, Table S6: δ 34 S isotopic data for sulfides from the Hutouya deposit, Granitic (JR-N and HT-N) and crystal tuff (DH09-N) samples were selected for zircon U-Pb dating, with zircons being handpicked under a binocular microscope after separation by magnetic and heavy-liquid techniques at the Geological Laboratory of the Regional Geological Survey, Langfang, Hebei Province, China. Zircons were mounted in epoxy resin and polished to expose internal surfaces. Cathodoluminescence was used to image internal structures and to aid in the selection of optimal analysis sites.
Zircons from the Hutouya granodiorite (sample JR-N) were dated at the State Key Laboratory of Continental Dynamics, Northwest University, Xi'an, China, by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The ICP-MS instrument was an Aligent 7500a equipped with a 193 nm ArF-excimer Geolas 200M LA system (MicroLas, Göttingen, Germany), with a laser spot size of 30 µm, energy of 32-36 mJ and repetition rate of 10 Hz. He was used as the carrier gas. The detailed operating procedures have been described by Yuan et al. (2004) [110]. The US National Institute of Standards and Technology (NIST) standard reference material SRM610 was used to optimize instrument settings. The zircon 91500 was used as an external standard for the corrections of U-Pb isotope fractionation effects. Zircon standard GJ-1 was used as a secondary standard to supervise the deviation of age measurement/calculation. 29 Si and NIST 610 were used as an internal standard and external standard for the calibrations of the zircon analyses, respectively. Elemental concentrations and isotopic ratios were calculated using GLITTER program (v4.0, Macquarie University, Sydney, Australia). Ages were calculated using Isoplot 3.0 [111] and common-Pb correction followed the method of Andersen (2002) [112]. All zircon isotope ratios and age uncertainties are quoted at the 1δ level. Four analyses of the standard GJ-1 gave weighted mean 206 Pb/ 238 U ages of 610.6 ± 9.7 Ma (MSWD = 0.0023, n = 4), which agreed well with the recommended 206 Pb/ 238 U ages of 613 ± 6Ma (2δ, n = 20) [113].
Zircons from the Hutouya granite porphyry (HT-N) and crystal tuff (DH09-N) were dated at the State Key Laboratory of Geological Processes and Mineral Resources (LGPMR), China University of Geosciences, Wuhan, China, using an Agilent 7500a ICP-MS instrument equipped with a Geolas 2005 LA system. The detailed equipment and operating procedures have been described by Hu et al. [114]. He was used as the carrier gas. Standard zircon 91,500 was used for external calibration of the U-Pb isotope fractionation effects. Zircon standard GJ-1 was used as a secondary standard to supervise the deviation of age measurement/calculation. NIST SRM610 was used for the external calibration of the zircon analyses. Si was used as an internal standard for the external calibration of the zircon analyses. Elemental concentrations and isotopic ratios were calculated using the ICPMS-DataCal program [115,116]. Ages were calculated using Isoplot 3.0 [111]. All zircon isotope ratios and age uncertainties are quoted at the 1δ level. Four analyses of the standard GJ-1 gave weighted mean 206 Pb/ 238 U ages of 607.9 ± 5.3 Ma (MSWD = 0.29, n = 5), which agreed well with the recommended 206 Pb/ 238 U ages of 613 ± 6Ma (2δ, n = 20) [113].

Appendix A.2. Molybdenite Re-Os Dating
Re-Os isotopic analyses were performed at the National Research Center of Geoanalysis, Chinese Academy of GeoSciences, Beijing, China. Samples were dissolved in Carius tubes, and Re-Os concentrations and isotopic ratios were determined using a TJA X-series ICP-MS instrument (Thermo Electron Corporation, Waltham, MA, USA). Analytical procedures have been described by Du et al. (1994Du et al. ( , 2004 [117,118] and (Qu, 2003) [119]. Ages were calculated using Isoplot 3.0, with uncertainties given as 2σ. The standard sample is GBW04436 (JDC) of China national standard.

Appendix A.3. Whole-Rock Major and Trace-Element Analyses
Whole-rock major and trace-element analyses were conducted at the Analysis Center of Jilin University, Jilin Province, China, using fresh samples without altered or weathered surfaces, crushed, and powdered to ≈200 mesh. Major-element compositions were determined by the ZSX Primus II automatic X-ray fluorescence spectrometer with uncertainties of <3% according to the national standard of China (GBW 07103 and GBW 07121). Trace-element compositions were determined by Agilent 7500a ICP-MS instrument according to the national standard of China (GBW 07103). Procedures are described by Gao et al. (2002) [120].

Appendix A.4. In Situ Zircon Hf Isotopic Analyses
Hf isotopic compositions of zircons from granodiorite (JR-N) and crystal tuff (DH09-N) were determined by the Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Bremen, Germany) in combination with a Geolas 2005 excimer ArF laser ablation system (Lambda Physik, Göttingen, Germany) that was hosted at the state Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences in Wuhan. A "wire" signal smoothing device was included in this laser ablation system, by which smooth signals were produced even at very low laser repetition rates down to 1 Hz [121]. The energy density of laser ablation used in this study was 5.3 J cm −2 . Helium was used as the carrier gas within the ablation cell and was merged with argon (makeup gas) after the ablation cell. As demonstrated by our previous study, for the 193 nm laser, a consistent two-fold signal enhancement was achieved in helium compared to in argon gas [122]. We used a simple Y junction downstream from the sample cell to add small amounts of nitrogen (4 mL min −1 ) to the argon makeup gas flow [114]. Compared to the standard arrangement, the addition of nitrogen in combination with the use of the newly designed X skimmer cone and Jet sample cone in Neptune Plus improved the signal intensity of Hf, Yb, and Lu by a factor of 5.3, 4.0, and 2.4, respectively. All data were acquired on zircon in single spot ablation mode at a spot size of 44 µm in this study. Each measurement consisted of 20 s of acquisition of the background signal followed by 50 s of ablation signal acquisition. Detailed operating conditions for the laser ablation system and the MC-ICP-MS instrument and analytical method were the same as described by   [123]. The major limitation for accurate in situ zircon Hf isotope determination by LA-MC-ICP-MS is the very large isobaric interference from 176 Yb and, to a much lesser extent 176 Lu on 176 Hf. It has been shown that the mass fractionation of Yb (β Yb ) is not constant over time and that the β Yb that is obtained from the introduction of solutions is unsuitable for in situ zircon measurements [124]. The under or over-estimation of the β Yb value would undoubtedly affect the accurate correction of 176 Yb and thus the determined 176 Hf/ 177 Hf ratio. We applied the directly obtained β Yb value from the zircon sample itself in real-time in this study. The 179 Hf/ 177 Hf and 173 Yb/ 171 Yb ratios were used to calculate the mass bias of Hf (β Hf ) and Yb (β Yb ), which were normalized to 179 Hf/ 177 Hf = 0.7325 and 173 Yb/ 171 Yb = 1.132685 [125] using an exponential correction for mass bias. Interference of 176 Yb on 176 Hf was corrected by measuring the interference-free 173 Yb isotope and using 176 Yb/ 173 Yb = 0.79639 [125] to calculate 176 Yb/ 177 Hf. Similarly, the relatively minor interference of 176 Lu on 176 Hf was corrected by measuring the intensity of the interference-free 175 Lu isotope and using the recommended 176 Lu/ 175 Lu = 0.02656 [126] to calculate 176 Lu/ 177 Hf. We used the mass bias of Yb (β Yb ) to calculate the mass fractionation of Lu because of their similar physicochemical properties. Off-line selection and the integration of analyte signals, and mass bias calibrations were performed using ICPMSDataCal [115]. The 176 Hf/ 177 Hf ratios of the standard zircon TEMORA and GJ-1 were 0.282684 ± 0.000002 (1SD, n = 12) and 0.282006 ± 0.000009 (1SD, n = 10), respectively, similar to the commonly accepted 176 Hf/ 177 Hf ratios of 0.282684 ± 0.000036 (2SD) [127] and 0.282000 ± 0.000005 (2SD) [128] measured using the solution MC-ICP-MS method.
Hf isotopic compositions of zircons from the granite porphyry (HT-N) were determined at the Beijing Yanduzhongshi Testing Technology, Beijing, China, using a Neptune Plus MC-ICP-MS instrument and NewWave UP213 LA system. Procedures are described by Wu et al. (2006) [129]. The laser spot diameter was 30 µm, the repetition rate was 8 Hz, the beam fluence was 16 J/cm 2 , and the ablation time was 31 s. As the 176 Lu/ 177 Hf ratio in zircons was <0.002, the isotopic interference of 176 Lu with 176 Hf was negligible. The fractionation coefficient of Yb was based on the mean 173 Yb/ 172 Yb ratio for each spot, and the interference of 176 Yb on 176 Hf was deducted accordingly. A 173 Yb/ 172 Yb ratio of 1.35274 was adopted. The 176 Hf/ 177 Hf ratios of the standard zircon PLE was 0.282481 ± 0.000007 (2SD, n = 18), similar to the commonly accepted 176 Hf/ 177 Hf ratios of 0.282482 ± 0.000013 (2SD) measured using the solution MC-ICP-MS method [130].