Geology , Geochronology and Geochemistry of Weilasituo Sn-Polymetallic Deposit in Inner Mongolia , China

The recently discovered Weilasituo Sn-polymetallic deposit in the Great Xing’an Range is an ultralarge porphyry-type deposit. The mineralization is closely associated with an Early Cretaceous quartz porphyry. Analysis of quartz porphyry samples, including zircon U-Pb dating and Hf isotopies, geochemical and molybdenite Re-Os isotopic testing, reveals a zircon U-Pb age of 138.6 ± 1.1 Ma and a molybdenite Re-Os isotopic age of 135 ± 7 Ma, suggesting the concurrence of the petrogenetic and metallogenic processes. The quartz porphyry has high concentrations of SiO2 (71.57 wt %–78.60 wt %), Al2O3 (12.69 wt %–16.32 wt %), and K2O + Na2O (8.85 wt %–10.44 wt %) and A/CNK ratios from 0.94–1.21, is mainly peraluminous, high-K calc-alkaline I-type granite and is relatively rich in LILEs (large ion lithophile elements, e.g., Th, Rb, U and K) and HFSEs (high field strength elements, e.g., Hf and Zr) and relatively poor in Sr, Ba, P, Ti and Nb. The zircon εHf(t) values range from 1.90 to 6.90, indicating that the magma source materials were mainly derived from the juvenile lower crust and experienced mixing with mantle materials. Given the regional structural evolution history, we conclude that the ore-forming magma originated from lower crust that had thickened and delaminated is the result of the subduction of the Paleo–Pacific Ocean. Following delamination, the lower crustal material entered the underlying mantle, where it was partially melted and reacted with mantle during ascent. The deposit formed at a time of transition from post-orogenic compression to extension following the subduction of the Paleo–Pacific Ocean.


Introduction
The southern Great Xing'an Range (SGXR) in southeastern Inner Mongolia is part of the eastern section of the Central Asian Orogenic Belt (Xing'anling Mongolian Orogenic belt).The SGXR is a superimposed compound structural region that has experienced processes associated with the evolution of the Paleo-Asian Ocean and the subduction of the Paleo-Pacific Ocean [1][2][3].Multistage tectonic, magmatic, sedimentary and metamorphic events characterize the metallogenic background of the SGXR and have resulted in the development of extensive granitic plutonic rocks, intermediate-acidic volcanic-sedimentary rocks and Paleozoic strata [4][5][6].Additionally, these events have given rise to associated porphyry-type molybdenum deposits, magmatic hydrothermal vein-type Sn-polymetallic (Pb-Zn-Ag) deposits, and skarn-type Pb-Zn-Ag deposits (Figure 1).The metallogenic  [25]).(B) Simplified geologic map of the southern Great Xing'an Range (modified after [26]).
The Weilasituo deposit is a large recently discovered porphyry-type Sn-polymetallic deposit in the SGXR.Notably, most Sn-polymetallic deposits in this area are hydrothermal vein-type deposits and the porphyry-type Sn-polymetallic deposits are rare.The Weilasituo porphyry-type Sn-polymetallic deposit has estimated reserves of 93,127 t Sn at 1.35%, 15,800 t W at 0.44%, 32,540 t Zn at 1.63% and 9175 t Cu at 1.91% [16].Recent studies have examined the geological characteristics, geochemistry, geochronology, and metallogenic mechanism of the Weilasituo Sn-polymetallic deposit [16,17,27,28], and have applied several geochronological methods to constrain the timing of petrogenesis and metallogenesis.The zircon U-Pb ages of the quartz porphyry are 138 ± 2 Ma and 135.7 ± 0.9 Ma [16,27].The molybdenite Re-Os isochron ages are 135 ± 11 Ma and 125.7 ± 3.8 Ma [16,27].The cassiterite U-Pb ages of the disseminated mineralization and vein-like mineralization are 138 ± 6 Ma and 135 ± 6 Ma, respectively [17].Geochemical studies have determined the mineralized rock (i.e., the quartz porphyry) is a highly differentiated I-type granite by fractional crystallization [17].[25]).(B) Simplified geologic map of the southern Great Xing'an Range (modified after [26]).
The Weilasituo deposit is a large recently discovered porphyry-type Sn-polymetallic deposit in the SGXR.Notably, most Sn-polymetallic deposits in this area are hydrothermal vein-type deposits and the porphyry-type Sn-polymetallic deposits are rare.The Weilasituo porphyry-type Sn-polymetallic deposit has estimated reserves of 93,127 t Sn at 1.35%, 15,800 t W at 0.44%, 32,540 t Zn at 1.63% and 9175 t Cu at 1.91% [16].Recent studies have examined the geological characteristics, geochemistry, geochronology, and metallogenic mechanism of the Weilasituo Sn-polymetallic deposit [16,17,27,28], and have applied several geochronological methods to constrain the timing of petrogenesis and metallogenesis.The zircon U-Pb ages of the quartz porphyry are 138 ± 2 Ma and 135.7 ± 0.9 Ma [16,27].The molybdenite Re-Os isochron ages are 135 ± 11 Ma and 125.7 ± 3.8 Ma [16,27].The cassiterite U-Pb ages of the disseminated mineralization and vein-like mineralization are 138 ± 6 Ma and 135 ± 6 Ma, respectively [17].Geochemical studies have determined the mineralized rock (i.e., the quartz porphyry) is a highly differentiated I-type granite by fractional crystallization [17].
In addition to the extensively exposed Holocene strata, the other rocks in the area include the Xilin hot complex, quartz diorite, cryptoexplosive breccia and buried quartz porphyry (Figure 2A,B).The Xilin hot complex is a combination of brown amphibole-plagioclase and biotite-plagioclase gneiss, both intensely metamorphosed and deformed.The quartz diorite is less extensively exposed and subject to NE-trending faults [42].The cryptoexplosive breccia is spatially linked with the quartz porphyry in the upper part and it usually occurs at the contact between the Xilin hot complex and the quartz porphyry [17].The buried quartz porphyry, whose overall morphology is unknown to date, lies approximately 400 m beneath the surface.The quartz porphyry samples recovered from a drillhole have an off-white color, a massive structure and a porphyritic texture (Figure 3A,B).The main minerals are K-feldspar (65%-70%), quartz (25%-27%) and biotite (3%-5%).

Mineralization and Alteration
The mining area is currently under mineral exploration, and ores have been encountered and verified by drilling.Ore bodies in the area come in three forms: (I) shallow quartz vein-type ore bodies, (II) moderate-depth cryptoexplosive breccia-type ore bodies, and (III) deep quartz porphyry-type ore bodies (Figure 2B).

Mineralization and Alteration
The mining area is currently under mineral exploration, and ores have been encountered and verified by drilling.Ore bodies in the area come in three forms: (I) shallow quartz vein-type ore bodies, (II) moderate-depth cryptoexplosive breccia-type ore bodies, and (III) deep quartz porphyry-type ore bodies (Figure 2B).
Fifteen shallow quartz vein-type ore bodies of medium size or greater have been detected.These vein-like or stratiform subparallel ore bodies strike 25°-205°, dip towards 115° at 11°-54°, and The faults in the area trend primarily NE-SW and secondarily sub-E-W (Figure 2B).They are developed in the quartz diorite and, as the main ore-controlling structures, provided spaces for mineralization.The NE-trending faults F 1 , F 2 , F 3 and F 4 strike 20     , and extend approximately 30-900 m with widths of 0.3-14 m.The E-W-trending faults (F 5 and F 6 ), located above or outside of the quartz porphyry, strike 85    , and extend approximately 20-800 m [17].

Mineralization and Alteration
The mining area is currently under mineral exploration, and ores have been encountered and verified by drilling.Ore bodies in the area come in three forms: (I) shallow quartz vein-type ore bodies, (II) moderate-depth cryptoexplosive breccia-type ore bodies, and (III) deep quartz porphyry-type ore bodies (Figure 2B).
Fifteen shallow quartz vein-type ore bodies of medium size or greater have been detected.These vein-like or stratiform subparallel ore bodies strike 25   , and exhibit a fairly simple morphology with basically continuous strike and some branching-reconnecting along dip.These orebodies extend 32-1400 m horizontally and 43-1300 m vertically, and their thicknesses range from 0.1 to 13 m.The cryptoexplosive breccia-type ore bodies are found in the cryptoexplosive breccia.Their morphology is associated with the internal structural morphology of the cryptoexplosive breccia.Local quartz vein-type ore bodies are found to cut the breccia-type ore bodies, adding to the complexity of these ore bodies.The quartz porphyry-type ore bodies found at the upper contact of the quartz porphyry bodies occur in lenticular form and are morphologically similar to the ore bodies above the quartz porphyry bodies, and those found inside the quartz porphyry bodies occur in a vein-like form.Seven ore bodies of industrial size, represented by Sn #200 (Figure 2B), represent more than 80% of the total quartz porphyry-type ore-body resources in the area.The ore bodies vary in size, extending dozens of meters to 400 m horizontally and 70 m vertically.Their thickness ranges from 1 to 10 m.
Three types of mineralization that are recognized in the Weilasituo deposit: stockwork mineralization, disseminated mineralization and vein-like mineralization.Stockwork mineralization exists both inside and outside the quartz porphyry and inside the cryptoexplosive breccia pipe.Disseminated mineralization occurs in the quartz porphyry.Vein-like mineralization occurs outside the quartz porphyry and inside the cryptoexplosive breccia pipe.
The mineralization level decreases with increasing depth.Stockwork and disseminated mineralization have resulted in disseminated and vein-like ores (Figure 4A-D).The ore minerals are mainly cassiterite + wolframite + sphalerite with lower amounts of chalcopyrite + arsenopyrite + tetrahedrite.Disseminated mineralization is the most important form of mineralization (Figure 4H-L).Vein-like mineralization is typically found in cracks and faults on top or outside of the quartz porphyry (Figure 2B) and is responsible for vein-like ores.The ore minerals include cassiterite + wolframite + sphalerite and less amounts of chalcopyrite + tetrahedrite + pyrrhotite + molybdenite + galena.Breccia pipe mineralization occurs in steep breccia pipes (Figures 2B and 4F), with no distinct boundary with the country rock.Disseminated and spots of cassiterite, chalcopyrite and dark sphalerite occur commonly as fragments in the breccia, suggesting that the breccia mineralization occurred after the disseminated mineralization.In addition, vein-like Sn-polymetallic mineralization was found to cut into the quartz porphyry-related breccia pipe mineralization (Figure 2B), suggesting that vein-like mineralization occurred after breccia mineralization.
The Sn-polymetallic metallogenic system in the Weilasituo deposit presents a high-to-low-temperature alteration zone from the quartz porphyry outward.The center of alteration is a Na-Ca-Rb alteration combination, surrounded by greisenization with high-level Na-Ca-Rb alteration.Stockwork and disseminated mineralization can be observed, typically in the quartz porphyry-type and breccia-type ore bodies.The alteration minerals are albite + amazonite + topaz + celestine + muscovite + epidote + fluorite (Figure 4A-C).Greisenization alteration mainly occurs in the vein-like orebodies on top or outside of the quartz porphyry, although some can also be found in the overlying breccia pipes.The alteration is controlled by fissures and faults [17].The alteration minerals include muscovite + quartz + topaz + fluorite + zircon (Figure 4E).

Sampling and Analytical Methods
Unaltered quartz porphyry samples for LA-ICP-MS U-Pb dating, zircon Lu-Hf isotope analysis and whole rock geochemistry analysis were collected from drillhole ZK809.Molybdenite samples for Re-Os isotopic analysis were also gathered from drillhole ZK809 of the porphyry Sn-W-Rb mineralization zone.

Zircon LA-ICP-MS U-Pb Dating
Two zircon U-Pb isotopic dating samples (ZK809-1 and ZK809-2) were analyzed at the Key Laboratory for Sedimentary Basin and Oil and Gas Resources, Ministry of Land and Resources.A GeoLasPro 193 nm laser system and an SF-ICPMS Element 2 were used for ablation and mass

Sampling and Analytical Methods
Unaltered quartz porphyry samples for LA-ICP-MS U-Pb dating, zircon Lu-Hf isotope analysis and whole rock geochemistry analysis were collected from drillhole ZK809.Molybdenite samples for Re-Os isotopic analysis were also gathered from drillhole ZK809 of the porphyry Sn-W-Rb mineralization zone.

Zircon LA-ICP-MS U-Pb Dating
Two zircon U-Pb isotopic dating samples (ZK809-1 and ZK809-2) were analyzed at the Key Laboratory for Sedimentary Basin and Oil and Gas Resources, Ministry of Land and Resources.A GeoLasPro 193 nm laser system and an SF-ICPMS Element 2 were used for ablation and mass spectrometry, respectively.High-purity He gas was used as the carrier gas for the ablated material.The test was conducted with a laser wavelength of 193 nm, a beam spot of 32 µm, a pulse frequency of 6 Hz, and a laser energy of 6 J/cm 2 .Before the test, the instrument was tuned to the optimal state using the NIST610 standard so that the 139 La and 232 Th signals were the highest and the oxide yield for 232 Th 16 O/ 232 Th was less than 0.3%.GJ-1 zircon standard specimens were used as external criteria to calibrate the fractionation and mass discrimination of U-Pb isotopes, and Plěsovice zircon standard specimens were used as control specimens to monitor the stability of the analytical process.A set of standard specimens was inserted every five samples.Laser sampling of each sample included 20 s of background acquisition, 50 s of ablation sampling and 10 s of cell flushing.ICPMSDataCal was used to process the analysis data offline [43].

Molybdenite Re-Os Dating
Five molybdenite Re-Os isotope dating samples (ZK809-1 to ZK809-5) were obtained by separating the molybdenite samples collected from the drillhole (in basically the same way as for zircon) to a size far smaller than 2 mm to avoid decoupling.Re-Os isotopic testing was conducted at the Re-Os isotopic laboratory of the National Geological Test Center.A TJA X-series ICP-MS was used to determine isotopic ratios.For low Re-Os samples, a Thermo Fisher Scientific HR-ICP-MS Element 2 was used.For Re, mass numbers 187 and 185 were selected, and mass number 190 was used to monitor Os.For Os, mass numbers 186-190 and 192 were selected, and mass number 185 was used to monitor Re.Blank values of Os, Re and 187 Os measured by the TJA X-series ICP-MS were (0.0031 ± 0.0005) × 10 −9 , (0.00023 ± 0.00008) × 10 −9 , and (0.00039 ± 0.00005) × 10 −9 , respectively, which were far smaller than the Os and Re measurements from the samples and the standard specimens and were therefore insignificant with respect to the test results.Common Os was calculated through the measured 192 Os/ 190 Os ratio according to the atomic and isotopic abundance charts.The uncertainties in Os and Re concentrations included weighing errors for the samples and thinner, calibration errors for the thinner, fractionation calibration errors for mass spectrometry, and isotopic ratio measurement errors for the samples in question.The confidence degree can reach 95%.The uncertainties in the model age also included this uncertainty (1.02%).The confidence degree was 95%.National standard materials (GBW04435 (JDC)) were used as standard specimens to monitor the reliability of the chemical process and analysis data.The principles and processes of Re-Os isotope analysis are detailed in Du et al. [44].

Whole Rock Geochemistry
Eight collected samples were crushed to 200-mesh powder.Major elements were analyzed on an Axios MaxX fluorescence spectrometer.FeO was titrated through a 50-mL burette.The sample was first placed in a Li 2 B 4 O 7 solution at a ratio of 1:5, melted at 1050-1250 • C, formed into thin glass sections and analyzed with approximate accuracies of 1% for SiO 2 and 2% for other oxides.Rare earth elements (REEs) and trace elements were analyzed on an X-series 2 instrument.A sample of whole-rock powder (200 mesh) weighing 50 mg was placed in a Teflon flask, dissolved with HNO 3 and HF solutions for 2 days, further dissolved by adding HClO 4 , dried by distilling, and then diluted to 50 mL with a 5% HNO 3 solution before being analyzed for trace elements.During analysis, two GBW series specimens were measured: one for calibrating Li, Ba, Cr, V, Co, Ni, Zn, Cu, Ga, Sr, Rb, Cs, Ba, Pb, U, Th, Sc, Y and REEs and the other for calibrating Mo, W, Nb, Ta, Hf and Zr.The analysis errors were less than 5%.Major elements, trace elements and REEs were measured at the testing center of the Shenyang Geological Survey Center, Ministry of Land and Resources.

Zircon Lu-Hf Isotope
In situ analysis of the zircon Hf isotope composition of the quartz porphyry from the Weilasituo deposit was conducted at the State Key Laboratory for Mineral Deposits Research, Nanjing University using a Neptune Plus MC-ICP-MS equipped with a New Wave UP193 laser microprobe.
The data acquisition and instrumental conditions were similar with Wu et al. [45].The analyses were mainly conducted with a repetition rate of 8 Hz and a beam diameter of 35 mm.Ar and He carrier gases were used to transfer the ablated sample from the laser ablation cell to the ICP-MS torch through the mixing chamber.Atomic masses 172, 173, 175-180 and 182 were measured simultaneously in the static collection mode.Corrections of isobaric interferences of 176 Lu and 176 Yb on 176 Hf were based on, Wu et al. [45], and Yang et al. [46].The performance conditions and analytical accuracy were monitored by the 91500 and Mud Tank zircon standards ( 176 Hf/ 177 Hf = 0.282507 ± 6 [47]).The initial Hf values (ε Hf ) were calculated by using the decay constant of 1.865 × 10 −11 per year [48] for 176 Lu and the chondritic model with 176 Lu/ 177 Hf = 0.0332 and 176 Hf/ 177 Hf = 0.282772 [49].Depleted mantle Hf model ages (T DM ) were calculated by using the 176 Lu/ 177 Hf ratios of the zircon.These ages refer to a model of depleted mantle with a current 176 Hf/ 177 Hf ratio of 0.28325 which is similar to the average of MORB [50], which has a 176 Lu/ 177 Hf ratio of 0.0384 [51] and assumes an average continental crust ratio (f CC ) of −0.55 [52].

Zircon U-Pb Dating
Pb isotopic age analysis was conducted on 52 zircon grains from the two quartz porphyry samples (ZK809-1 and ZK809-2).The analytical results are shown in Table 1.All the zircon grains analyzed are idiomorphic crystals that are 35-100 µm long.The aspect ratios are approximately 3:1-1:1 (Figure 5).As the U and Th concentrations are exceptionally high (for most of the analysis points, U is 8721-48,802 × 10 −6 but can reach 165,623 × 10 −6 ; and Th is 819-13,033 × 10 −6 but can reach 734,544 × 10 −6 ), most of the zircon grains from the two samples display weak zonal structures (Figure 5).Those showing obvious zones yield ages older than 189 Ma, suggesting they are inherited zircons.The Th/U ratio lies mostly in the 0.10-0.38range, which also points to a magmatic origin.The zircon 206  Nanjing University using a Neptune Plus MC-ICP-MS equipped with a New Wave UP193 laser microprobe.
The data acquisition and instrumental conditions were similar with Wu et al. [45].The analyses were mainly conducted with a repetition rate of 8 Hz and a beam diameter of 35 mm.Ar and He carrier gases were used to transfer the ablated sample from the laser ablation cell to the ICP-MS torch through the mixing chamber.Atomic masses 172, 173, 175-180 and 182 were measured simultaneously in the static collection mode.Corrections of isobaric interferences of 176 Lu and 176 Yb on 176 Hf were based on, Wu et al. [45], and Yang et al. [46].The performance conditions and analytical accuracy were monitored by the 91500 and Mud Tank zircon standards ( 176 Hf/ 177 Hf = 0.282507 ± 6 [47]).The initial Hf values (εHf) were calculated by using the decay constant of 1.865 × 10 −11 per year [48] for 176 Lu and the chondritic model with 176 Lu/ 177 Hf = 0.0332 and 176 Hf/ 177 Hf = 0.282772 [49].Depleted mantle Hf model ages (TDM) were calculated by using the 176 Lu/ 177 Hf ratios of the zircon.These ages refer to a model of depleted mantle with a current 176 Hf/ 177 Hf ratio of 0.28325 which is similar to the average of MORB [50], which has a 176 Lu/ 177 Hf ratio of 0.0384 [51] and assumes an average continental crust ratio (fCC) of −0.55 [52].

Zircon U-Pb Dating
Pb isotopic age analysis was conducted on 52 zircon grains from the two quartz porphyry samples (ZK809-1 and ZK809-2).The analytical results are shown in Table 1.All the zircon grains analyzed are idiomorphic crystals that are 35-100 μm long.The aspect ratios are approximately 3:1-1:1 (Figure 5).As the U and Th concentrations are exceptionally high (for most of the analysis points, U is 8721-48,802 × 10 −6 but can reach 165,623 × 10 −6 ; and Th is 819-13,033 × 10 −6 but can reach 734,544 × 10 −6 ), most of the zircon grains from the two samples display weak zonal structures (Figure 5).Those showing obvious zones yield ages older than 189 Ma, suggesting they are inherited zircons.The Th/U ratio lies mostly in the 0.10-0.38range, which also points to a magmatic origin.The zircon 206

Molybdenite Re-Os Geochronology
Table 2 presents the Re-Os isotopic results of nine molybdenite samples from the deposit.The test results indicate that w(Re) = 55.2-712.5 ng/g, w(Os) = 0.152-9.222ng/g, w( 187 Re) = 34.71-447.80ng/g, and w( 187 Os) = 0.0216-1.041ng/g.As the relative concentration of common Os is higher than that of 187 Os, the isochron age (135 ± 7 Ma) was interpreted as the formation time of the molybdenite (Figure 7), which indicates that mineralization of the Weilasituo Sn-polymetallic deposit occurred in the early stage of the Early Cretaceous.

Molybdenite Re-Os Geochronology
Table 2 presents the Re-Os isotopic results of nine molybdenite samples from the deposit.The test results indicate that w(Re) = 55.2-712.5 ng/g, w(Os) = 0.152-9.222ng/g, w( 187 Re) = 34.71-447.80ng/g, and w( 187 Os) = 0.0216-1.041ng/g.As the relative concentration of common Os is higher than that of 187 Os, the isochron age (135 ± 7 Ma) was interpreted as the formation time of the molybdenite (Figure 7), which indicates that mineralization of the Weilasituo Sn-polymetallic deposit occurred in the early stage of the Early Cretaceous.

Molybdenite Re-Os Geochronology
Table 2 presents the Re-Os isotopic results of nine molybdenite samples from the deposit.The test results indicate that w(Re) = 55.2-712.5 ng/g, w(Os) = 0.152-9.222ng/g, w( 187 Re) = 34.71-447.80ng/g, and w( 187 Os) = 0.0216-1.041ng/g.As the relative concentration of common Os is higher than that of 187 Os, the isochron age (135 ± 7 Ma) was interpreted as the formation time of the molybdenite (Figure 7), which indicates that mineralization of the Weilasituo Sn-polymetallic deposit occurred in t   Therefore, these rocks belong to the high-K calc-alkaline series (Figure 8A, [53]).The Al 2 O 3 values vary from 12.69 wt %-16.32 wt %, the A/CNK values range from 0.94 to 1.21, and the A/NK values range from 1.40 to 1.75, indicating that these samples are high-K calc-alkaline, weakly meta aluminous to peraluminous rocks (Figure 8B; [54]).In the TAS diagram (Figure 8C
On the standard trace element primitive mantle-normalized diagram (Figure 8F), the quartz porphyry samples display similar variations with very low Sr contents (3.09-17.45ppm) and fairly high Yb contents (3.25-7.64ppm), suggesting that the provenance pressure was less than 0.8-1.0GPa [60].The samples are relatively rich in large-ion lithophile elements (LILEs) such as Rb, Th, U, K as well as the high field strength elements (HFSEs) Hf and Zr and relatively poor in Ba, P, Sr, Ti and Nb, suggesting significant differentiation in the provenance of the quartz porphyry and implying the involvement of subduction zone processes.

Lu-Hf Isotopes
After zircon LA-ICP-MS U-Pb dating, microscale zircon Lu-Hf isotope analysis was conducted on the quartz porphyry samples from the Weilasituo deposit (ZK809-1 and ZK809-2).The analytical results are shown in Table 4.The zircons in the quartz porphyry have the similar Hf isotopic compositions.The 176 Hf/ 177 Hf and ε Hf (t) values at the 25 measuring points are 0.282742-0.282882and 1.90-6.90,respectively.The ε Hf (t) isotopic calculations all plot between the chondritic meteorite and depleted mantle evolution lines (Figure 9B), as well as in the Phanerozoic igneous region of the eastern Central Asian Orogen (Figure 9A).The gray figures are quoted from [20,61,62].At all the analysis points, T DM2 vary from 1069 to 747 Ma.As the zircon f Lu/ Hf value is substantially lower than that in felsic crust (0.72, [63]) and mafic crust (0.34, [64]) and the T DM2 is close to the age of the source materials retained in the crust, the result indicates that the quartz porphyry magma originated from lower crustal materials.
On the standard trace element primitive mantle-normalized diagram (Figure 8F), the quartz porphyry samples display similar variations with very low Sr contents (3.09-17.45ppm) and fairly high Yb contents (3.25-7.64ppm), suggesting that the provenance pressure was less than 0.8-1.0GPa [60].The samples are relatively rich in large-ion lithophile elements (LILEs) such as Rb, Th, U, K as well as the high field strength elements (HFSEs) Hf and Zr and relatively poor in Ba, P, Sr, Ti and Nb, suggesting significant differentiation in the provenance of the quartz porphyry and implying the involvement of subduction zone processes.

Lu-Hf Isotopes
After zircon LA-ICP-MS U-Pb dating, microscale zircon Lu-Hf isotope analysis was conducted on the quartz porphyry samples from the Weilasituo deposit (ZK809-1 and ZK809-2).The analytical results are shown in Table 4.The zircons in the quartz porphyry have the similar Hf isotopic compositions.The 176 Hf/ 177 Hf and εHf(t) values at the 25 measuring points are 0.282742-0.282882and 1.90-6.90,respectively.The εHf(t) isotopic calculations all plot between the chondritic meteorite and depleted mantle evolution lines (Figure 9B), as well as in the Phanerozoic igneous region of the eastern Central Asian Orogen (Figure 9A).The gray figures are quoted from [20,61,62].At all the analysis points, TDM2 vary from 1069 to 747 Ma.As the zircon fLu/ Hf value is substantially lower than that in felsic crust (0.72, [63]) and mafic crust (0.34, [64]) and the TDM2 is close to the age of the source materials retained in the crust, the result indicates that the quartz porphyry magma originated from lower crustal materials.

Magmatic-Metallogenic Age Context
The determination of the precise age of mineralization and closely associated intrusions is essential for understanding genetic processes and locating economic deposits [65,66].Presently, several high-precision and accurate isotopic dating methods exist to determine petrogenetic and metallogenic ages, such as zircon U-Pb [16,25], molybdenite Re-Os [16,25], and cassiterite U-Pb dating [17].
The zircon LA-ICP-MS U-Pb ages we obtained are 138.0 ± 1.1 Ma and 138.6 ± 1.1 Ma, which agree with the zircon U-Pb age of the quartz porphyry (138 ± 2 Ma and 135.7 ± 0.9 Ma) and the cassiterite age of the disseminated mineralization (138 ± 6 Ma) obtained by previous studies [16,17].In addition, the molybdenite Re-Os isochron age (135 ± 7 Ma) we obtained also agrees with the molybdenite Re-Os isochron age (135 ± 11 Ma), and the cassiterite U-Pb age of the vein-like mineralization (135 ± 6 Ma) obtained by previous studies.Taking into account previous findings, we assume a petrogenetic age range of 138.0-138.6 Ma, which coincides with the age of the disseminated mineralization (138 ± 6 Ma).The vein-like mineralization formed at 135 ± 7 Ma, which was slightly later than the disseminated mineralization.These results indicate that the petrogenesis, as well as the metallogenesis, of the deposit occurred during the early Early Cretaceous.The petrogenetic ages of the various deposits found in the area have been widely examined and summarized over the past years.The results mostly correspond to the Mid-Triassic, Early to middle Jurassic and Early Cretaceous [67], with the Early Cretaceous becoming the most prevalent age.The Early Cretaceous deposits include more hydrothermal Pb-Zn-Ag (Sn-Cu), skarn-type Pb-Zn-Ag (Sn-Fe) and porphyry-type Cu-Mo deposits than porphyry-type Sn (W) deposits.
The study area lies at the eastern end of the Central Asian Orogen, which is sandwiched between the North China Block and the Siberian Plates.The study area was influenced by the evolution and closure of the Paleo-Asian Ocean during the Paleozoic and by the circum-Pacific tectonic domain from the Mesozoic to the Cenozoic [27,68].Many studies have disconnected the magmatism of late Mesozoic in the SGXR from the subduction of the Pacific Plate [4,69], however, it is evident that the Early Cretaceous magmatism occurred throughout East China.This evidence suggests that the geodynamics underlying the formation of granite during this period must be taken into account.We believe the Pacific Plate played an important role in this magmatism [70].During the Early Cretaceous, northern China is thought to have experienced a post-orogenic extensional collapse, an environment of post-arc extension closely followed by the subduction of the Paleo-Pacific Plate [26,[71][72][73].In the Nb-Y tectonic discrimination diagram, the sample points plot within the volcanic arc + syn-collisional granite fields (Figure 10C).In the Rb-Y + Nb diagram, the sample points are all distributed within the syn-collisional granite field (Figure 10D).
As discussed above, we have dated the petrogenesis and metallogenesis of the Weilasituo deposit to the early stage of the Early Cretaceous and conclude that the deposit was affected by the Early Cretaceous compression associated with the Paleo-Pacific Plate.

Petrogenesis and Magma Source
It is of great significance to determine the genetic type of granitoids so that one can understand the magma source, magmatism, and tectonic setting [75,76].According to the (Zr + Nb + Ce + Y)-FeO T /MgO diagram (Figure 11A) and the SiO2-FeO T /MgO diagram (Figure 11B), the quartz porphyry from the Weilasituo deposit exhibit no characteristics of A-type granites.In addition, the rocks are rich in silica (average SiO2 = 73.07wt %) and alkalis (average Na2O + K2O = 9.71 wt %) with Na2O/K2O ratios from 1.37 to 2.94, Al2O3 from 12.69 wt % to 16.32 wt %, and A/CNK ratios from 0.94 to 1.21.These features are typical of high-K calc-alkaline peraluminous granite.The low MgO content (<0.3 wt %) is also indicative of S-type granites [77].
In all the samples, the P-contents of quartz porphyry is very low (0.010%-0.043%) and P2O5 decreases with increasing SiO2 (Figure 11C), while Th increases with Rb (Fig 11D ), both of which are important gauges for discriminating I-type granites [77].The Nb/Ta ratios of the quartz porphyry mostly range from 2.65 to 3.62 (<5) in Table 3, which is a sign of differentiation of peraluminous granite [78].In the Nb-Nb/Ta diagram and Ta-Nb/Ta diagram (Figure 12A and B), the degree of differentiation of the quartz porphyry samples reaches more than 90%.The Zr/Hf ratios of quartz porphyry range from 1.36 to 3.65 (<25), and the U and Th concentrations are high in zircon, which are typical features of highly differentiated granite [79].In the Zr-Zr/Hf diagram (Figure 12C), the ratio of Zr/Hf decreases with decreasing Zr content.In the Nb-Y/Ho diagram (Figure 12D), the Y/Ho ratio decreases with the increasing Nb content.The above two characteristics are typical of highly differentiated granite [80].Additionally, the relatively low total REE contents, the relatively flat "seagull" pattern in the standard REE chondrite-normalized diagram (Figure 8E), the relatively

Petrogenesis and Magma Source
It is of great significance to determine the genetic type of granitoids so that one can understand the magma source, magmatism, and tectonic setting [75,76].According to the (Zr + Nb + Ce + Y)-FeO T /MgO diagram (Figure 11A) and the SiO 2 -FeO T /MgO diagram (Figure 11B), the quartz porphyry from the Weilasituo deposit exhibit no characteristics of A-type granites.In addition, the rocks are rich in silica (average SiO 2 = 73.07wt %) and alkalis (average Na 2 O + K 2 O = 9.71 wt %) with Na 2 O/K 2 O ratios from 1.37 to 2.94, Al 2 O 3 from 12.69 wt % to 16.32 wt %, and A/CNK ratios from 0.94 to 1.21.These features are typical of high-K calc-alkaline peraluminous granite.The low MgO content (<0.3 wt %) is also indicative of S-type granites [77].
In all the samples, the P-contents of quartz porphyry is very low (0.010%-0.043%) and P 2 O 5 decreases with increasing SiO 2 (Figure 11C), while Th increases with Rb (Figure 11D), both of which are important gauges for discriminating I-type granites [77].The Nb/Ta ratios of the quartz porphyry mostly range from 2.65 to 3.62 (<5) in Table 3, which is a sign of differentiation of peraluminous granite [78].In the Nb-Nb/Ta diagram and Ta-Nb/Ta diagram (Figure 12A,B), the degree of differentiation of the quartz porphyry samples reaches more than 90%.The Zr/Hf ratios of quartz porphyry range from 1.36 to 3.65 (<25), and the U and Th concentrations are high in zircon, which are typical features of highly differentiated granite [79].In the Zr-Zr/Hf diagram (Figure 12C), the ratio of Zr/Hf decreases with decreasing Zr content.In the Nb-Y/Ho diagram (Figure 12D), the Y/Ho ratio decreases with the increasing Nb content.The above two characteristics are typical of highly differentiated granite [80].Additionally, the relatively low total REE contents, the relatively Minerals 2019, 9, 104 20 of 28 flat "seagull" pattern in the standard REE chondrite-normalized diagram (Figure 8E), the relatively abundant LREEs with LREE/HREE ratios of 1.48-3.91(suggesting distinct differentiation), the very low contents of Sr (<400 ppm), the high contents of Yb (>2 ppm), (La/Yb) N = 0.37-1.09, the intensely negative Eu anomalies (δEu = 0.01-0.46, Figure 8F) and the relatively high abundances of the LILEs Rb, U, Th, and K compared to the relatively low abundances of Ba, P, Sr, Ti are all indicative of a highly differentiated I-type granite [81].abundant LREEs with LREE/HREE ratios of 1.48-3.91(suggesting distinct differentiation), the very low contents of Sr (<400 ppm), the high contents of Yb (>2 ppm), (La/Yb)N = 0.37-1.09, the intensely negative Eu anomalies (δEu = 0.01-0.46, Figure 8F) and the relatively high abundances of the LILEs Rb, U, Th, and K compared to the relatively low abundances of Ba, P, Sr, Ti are all indicative of a highly differentiated I-type granite [81].Overall, we assume that the metallogenesis-related quartz porphyry in the deposit is a peraluminous, high-K calc-alkaline I-type granite as previously stated by Wang et al. [17].
Using the bulk rock Zr composition to represent the melt composition (Table 3) in the model of Watson and Harrison [83], zircon-saturation temperatures (T Zircon ) were calculated for the quartz porphyry of the Weilasituo deposit.The T Zircon of the quartz porphyry ranges from 616 • to 727 • (averaging 678 • ), thus corresponding to a low T Zircon value.In general, highly fractionated granitic magmas generally feature high primary temperatures or large amounts of various volatiles during the later stage.Although the T Zircon of the quartz porphyry is low, the hydrothermal fluid of the Weilasituo depositwas characterized by high-Na, high-F contents [17], which would have been favorable for the differentiation of the quartz porphyry.In addition, volatiles in the residual melt, such as H 2 O, Li, F, and Cl, tend to increase with crystallization [84], thus promoting the differentiation of magma.Overall, we assume that the metallogenesis-related quartz porphyry in the deposit is a peraluminous, high-K calc-alkaline I-type granite as previously stated by Wang et al. [17].
Using the bulk rock Zr composition to represent the melt composition (Table 3) in the model of Watson and Harrison [83], zircon-saturation temperatures (TZircon) were calculated for the quartz porphyry of the Weilasituo deposit.The TZircon of the quartz porphyry ranges from 616° to 727° (averaging 678°), thus corresponding to a low TZircon value.In general, highly fractionated granitic magmas generally feature high primary temperatures or large amounts of various volatiles during the later stage.Although the TZircon of the quartz porphyry is low, the hydrothermal fluid of the Weilasituo depositwas characterized by high-Na, high-F contents [17], which would have been favorable for the differentiation of the quartz porphyry.In addition, volatiles in the residual melt, such as H2O, Li, F, and Cl, tend to increase with crystallization [84], thus promoting the differentiation of magma.
Partial melting test results for common crustal rocks have revealed that this type of granite can be produced by the partial melting of water-bearing calc-alkaline to high-K calc-alkaline rocks, and mafic to intermediate metamorphic rocks in the earth's crust.In theory, granitoids can forme in many ways, including assimilation-fractional crystallization, magma mixing, or melting of the lower crust [85].Magma mixing generates supercooled particles and magmatic inclusions [86].However, no dioritic inclusions were found in the Weilasituo granites.Hence, the granites did not experience significant magma mixing.The zircons from the Weilasituo granites yield 206 Pb/ 238 U ages that are younger than 200 Ma and Th/U values that are greater than 0.1.These data suggest that the zircons were not inherited as a result of contamination by the surrounding host rocks or assimilation.Furthermore, the La-La/Sm diagram (Figure 10A) and the Th-Th/Nd diagram (Figure 10B) also illustrate the presence of partially melted magma in the quartz porphyry from the deposit.All these findings confirm that partial melting controlled the formation of the magma [87].Partial melting test results for common crustal rocks have revealed that this type of granite can be produced by the partial melting of water-bearing calc-alkaline to high-K calc-alkaline rocks, and mafic to intermediate metamorphic rocks in the earth's crust.In theory, granitoids can forme in many ways, including assimilation-fractional crystallization, magma mixing, or melting of the lower crust [85].Magma mixing generates supercooled particles and magmatic inclusions [86].However, no dioritic inclusions were found in the Weilasituo granites.Hence, the granites did not experience significant magma mixing.The zircons from the Weilasituo granites yield 206 Pb/ 238 U ages that are younger than 200 Ma and Th/U values that are greater than 0.1.These data suggest that the zircons were not inherited as a result of contamination by the surrounding host rocks or assimilation.Furthermore, the La-La/Sm diagram (Figure 10A) and the Th-Th/Nd diagram (Figure 10B) also illustrate the presence of partially melted magma in the quartz porphyry from the deposit.All these findings confirm that partial melting controlled the formation of the magma [87].
The Hf isotope composition of the Late Cretaceous granite in this area is summarized.The Hf isotope composition is the same as that of other rocks from the same era, suggesting that these rocks shared the same magma source.The ε Hf (t) value of the rock is positive, and the T DM2 model ages are 1069-747 Ma, and thus exhibit a large range.Therefore, the materials in the source region mainly came from the juvenile lower crust with some degree of mixing with mantle source materials, which is consistent with the conclusions based on the Sr-Nd isotope [17].
These data suggest that the subduction of the Paleo-Pacific Plate caused the lower crust to thicken and delaminate.The delaminated material then entered the underlying mantle, where it partially melted.As the resulting magma ascended, it reacted with the mantle before intruding into the shallow crust and solidifying in the form of the quartz porphyry.

Metallogenic Implications
Because the mineralization of the deposit occurred after the intrusion of the quartz porphyry, the mineralization had an inherently close genetic, spatial and temporal relationship with the quartz porphyry [17].Thus, the ore-forming fluids of Sn-polymetallic mineralization were derived from the highly differentiated quartz porphyry.
Sn, W and Rb are highly incompatible elements.These elements are much more abundant in the crust than in the mantle [88].Partial melting can lead to the enrichment of these elements in the presence of favorable complexing agents [89].
Chen et al. [90] and Chen and Fu [91] discussed the mechanism of granitic magma formation via the partial melting of thickened lower crust and established three models.(1) During a major period of continent orogenic movement, the strong collision between continental plates compresses and shortenes the crust, resulting in thickening and shearing of the lower crust.The temperature rise caused by the thickening of the lower crust and the heat generated by tectonic shearing may lead to partial melting of the lower crust, potentially assisted by the addition of external fluids.(2) After the main orogenic movement, the crust is in the state of tectonic decompression, which affects the thickening of the crust.This process leads to the dehydration of water-bearing minerals, and the addition of these fluids causes the partial melting of the crust.(3) After the main orogenic movement, gravitational instability results in lithospheric delamination of over-thickened crust results in mantle upwelling and the under-plating of the lower crust.These events cause partial melting of the lower crust.
At least in the late Mesozoic, the Great Xing'an Range had the characteristics of a post-collisional environment from the existing paleomagnetic evidence [92].In recent years, studies in this region have found mafic granulite xenoliths and mafic-ultramafic cumulate xenoliths from the Early Mesozoic (based on 40 Ar- 39 Ar ages, whole-rock K-Ar isochron ages, and Rb-Sr whole-rock isochron ages in a range of 220 to 237 Ma) and the late Mesozoic (based on zircon U-Pb ages in a range of 120 to 140 Ma).These rocks are believed to be the result of both upwelling and asthenospheric underplating [93].Therefore, we believe that the granites associated with the Weilasituo are the result of the third mechanism discussed above.
Based on geochronological and geochemical research on the intermediate-acidic intrusive rocks exposed in the area and given the deposit geology and regional tectonics, we assume the following diagenetic and metallogenic dynamic processes.From the Late Jurassic to the Early Cretaceous, the subduction of the Paleo-Pacific Ocean caused the lower crust to thicken and delaminate.The delaminated material then entered the underlying mantle, where it partially melted.The roof of a magma chamber can become enriched in Sn, W, Mo and other elements by convection-driven thermogravimetric diffusion [94].During the subsequent ascent of this magma, a portion mixed with remelted old crust and became calc-alkaline magma, which rose to the shallow crust and was emplaced in weak locations resulting from local extension, corresponding to the quartz porphyry emplacement.This process caused the ore minerals, Sn in particular, to leach out of the quartz porphyry (Figure 13A).During 138-135 Ma, due to the local extension, fractures and faults developed in the surrounding rocks above the quartz porphyry, and these fractures acted as conduits for the continuous upward migration of fluid.The increase in fluid pressure eventually exceeded the lithostatic pressure of the surrounding rocks, leading to cryptoexplosion and the formation of the breccia pipe.After the emplacement of the quartz porphyry, a large amount of metal-rich magmatic volatiles were released (Figure 13B).Because the magma was rich in Cl and F, Sn tendeds to migrate in the form of SnCl 2 .The high F activity in the magma lowereds the viscosity and enableds the segregation of a less viscous, highly enriched residual fluid [95].At approximately 135 Ma, ore-bearing hydrothermal fluid passed through the fractures, cleavages, and faults, and reacted with the surrounding rocks ("Xilin hot complex") as follows: SnCl 2 + 3(Na,K)A1Si 3 O s + 2H 2 0 → SnO 2 (cassiterite) + KAl 3 Si 3 O 10 (OH) 2 + 6SiO 2 + 2NaCl + H 2 .Sn crystallized as cassiterite and was accompanied by the precipitation of other metallogenic elements.These processes formed the Weilasituo Sn-polymetallic deposit (Figure 13C).breccia pipe.After the emplacement of the quartz porphyry, a large amount of metal-rich magmatic volatiles were released (Figure 13B).Because the magma was rich in Cl and F, Sn tendeds to migrate in the form of SnCl2.The high F activity in the magma lowereds the viscosity and enableds the segregation of a less viscous, highly enriched residual fluid [95].At approximately 135 Ma, ore-bearing hydrothermal fluid passed through the fractures, cleavages, and faults, and reacted with the surrounding rocks ("Xilin hot complex") as follows：SnCl2 + 3(Na,K)A1Si3Os + 2H20 → SnO2(cassiterite) + KAl3Si3O10(OH)2 + 6SiO2 + 2NaCl + H2.Sn crystallized as cassiterite and was accompanied by the precipitation of other metallogenic elements.These processes formed the Weilasituo Sn-polymetallic deposit (Figure 13C).

Conclusions
Integrating zircon U-Pb and Re-Os dating, whole-rock geochemistry, and Hf isotopic data presented here with the results of previous research leads to the following conclusions: (1) The zircon U-Pb ages of the ore-forming porphyry (quartz porphyry) samples from the Weilasituo Sn-polymetallic deposit are 138.0 ± 1.1 Ma and 138.6 ± 1.1 Ma; the molybdenite Re-Os age is

Figure 5 .
Figure 5.Typical CL images of zircons and analyzed spots from the quartz porphyry in the Weilasituo Sn-polymetallic deposit.

Figure 5 .
Figure 5.Typical CL images of zircons and analyzed spots from the quartz porphyry in the Weilasituo Sn-polymetallic deposit.

Figure 6 .
Figure 6.U-Pb Concordia diagram of zircon of quartz porphyry (A,C); weighted mean ages of zircon U-Pb dating for quartz porphyry (B,D).

Figure 7 .
Figure 7. Re-Os isochron ages of quartz porphyry of the Weilasituo Sn-polymetallic deposit.

Figure 6 .
Figure 6.U-Pb Concordia diagram of zircon of quartz porphyry (A,C); weighted mean ages of zircon U-Pb dating for quartz porphyry (B,D).

Figure 6 .
Figure 6.U-Pb Concordia diagram of zircon of quartz porphyry (A,C); weighted mean ages of zircon U-Pb dating for quartz porphyry (B,D).

Figure 7 .
Figure 7. Re-Os isochron ages of quartz porphyry of the Weilasituo Sn-polymetallic deposit.

Figure 7 .
Figure 7. Re-Os isochron ages of quartz porphyry of the Weilasituo Sn-polymetallic deposit.
; [55]), the data points plot within the granite zone; in the Na 2 O-K 2 O diagram (Figure 8D; [56]), some of the samples plot within the potassium zone, while the remainder plot within the sodium zone.The quartz porphyry is relatively poor in Mg, with Mg concentrations ranging from 0.09 wt %-0.19 wt %.Minerals 2019, 9, 104 13 of 29

Figure 13 .
Figure 13.(A) Schematic model of the Late Jurassic to Early Cretaceous geodynamic evolution and associated ore deposits in the Great Xing'an Range.(B) Schematic model for the Weilasituo Sn-polymetallic deposit during 138-135 Ma. (C) Schematic model for the Weilasituo Sn-polymetallic deposit at 135 Ma.

Figure 13 .
Figure 13.(A) Schematic model of the Late Jurassic to Early Cretaceous geodynamic evolution and associated ore deposits in the Great Xing'an Range.(B) Schematic model for the Weilasituo Sn-polymetallic deposit during 138-135 Ma. (C) Schematic model for the Weilasituo Sn-polymetallic deposit at 135 Ma.

Table 1 .
LA-ICP-MS zircon U-Pb dating data of quartz porphyry of Weilasituo deposit.

Table 2 .
Results of Re-Os isotopic analyses of greisen stage from the Weilasituo Sn-polymetallic deposit.Whole-rock geochemical measurements of quartz porphyry samples from the Weilasituo deposit are shown in Table 3.The samples are rich in silicon, alkalis and aluminum.The analyses indicate SiO 2 , Na 2 O + K 2 O and Na 2 O/K 2 O ranges of 71.57wt %-78.60 wt %, 8.85 wt %-10.44 wt %, and 1.37-2.94.

Table 4 .
Zircon Hf isotopic composition for zircons from quartz porphyry from the Weilasituo Sn-polymetal deposit.