Sericite 40 Ar/ 39 Ar Dating and Indosinian Mineralization in the Liushuping Au–Zn Deposit, West Qinling Orogen, China

: The Liushuping deposit, located on the northeast margin of the Bikou Block, is the middle-sized gold-zinc deposit (with ore reserves of 15.67 × 10 4 t Zn and 2.2 t Au) in the Mianxian–Lueyang– Yangpingguan area. The orebodies occur in the meta-dolomite of the Duantouya and Jiudaoguai formations controlled by the Jiudaoguai syncline. The ore-forming process has experienced hydrothermal period and epigenetic oxidation period, and the hydrothermal period can be divided into two stages. The hydrothermal sericite sample collected from stage 2 yielded a well-deﬁned 40 Ar/ 39 Ar isotopic plateau age of 215.70 ± 0.37 Ma, and an 39 Ar/ 36 Ar- 40 Ar/ 36 Ar normal isochron age of 215.35 ± 0.38 Ma, indicating that the metallogenic age of the Liushuping is the Late Triassic (ca. 215 Ma). The I Sr (t) of sphalerite is higher than that of the Bikou Group but similar to the Duantouya Formation, indicating that the ore-forming ﬂuids may mainly originate from the metamorphic dehydration of the Duantouya Formation. The Liushuping Au–Zn deposit is consistent with that of the Qinling Indosinian orogeny and mineralization, which are related to oceanic subduction during the Late Triassic.


Introduction
The Qinling Orogenic Belt (QOB) is well-endowed with mineral systems in China [1-3] (Figure 1a), including a large number of orogenic deposits formed during the Indosinian period (ca. 220 to 190 Ma) [2][3][4][5]. The Mianxian-Lueyang-Yangpingguan area (MLY) is located in the Southwest of the QOB (Figure 1), bounded by the Hanjiang Fault and the Mian-Lue Suture to the south and north, respectively (Figure 1b). The MLY area belongs to the northeast part of the Bikou Terrane and hosts a large number of mineral deposits, i.e., gold, nickel, zinc, and lead, which is known as the "Golden Triangle" [6]. The Liushuping is a gold-zinc deposit discovered in recent years, with proven zinc reserves of 15.67 × 10 4 t and gold reserves of 2.2 t. Previous studies mainly focused on geological characteristics of the deposit [7,8] and stratigraphic division [9]. However, the ore-forming process and its relationship with regional metamorphism and magmatism are ambiguous.
Hydrothermal mica is a common mineral in the gold deposit, and its precise 40 Ar- 39 Ar plateau age can represent the precipitation age of gold [10][11][12][13][14][15]. Strontium isotope data of ore minerals, especially sulfides, can be used to evaluate the nature and source of the ore-forming fluids [16][17][18][19][20][21][22][23][24][25]. In this contribution, we selected hydrothermal sericites from the main stage to restrict the age of the Liushuping gold-zinc deposit. In addition, Sr isotope of sphalerites are used to trace the source of ore-forming fluids. The magmatic rocks include the quartz albite porphyry exposed in the south of the ore district, diorite in the north, and plagiogranite in the northwest, as well as serpentinized ultrabasic rocks ( Figure 2). The fault structure in the ore district can be divided into three groups, nearly EW-, NE-, and NW-trending, respectively. The nearly EW-trending The magmatic rocks include the quartz albite porphyry exposed in the south of the ore district, diorite in the north, and plagiogranite in the northwest, as well as serpentinized ultrabasic rocks ( Figure 2). The fault structure in the ore district can be divided into three groups, nearly EW-, NE-, and NW-trending, respectively. The nearly EW-trending faults are F1, F2, F3, and F7 that penetrate the ore district, and F5 and F6 appear in the eastern part of the ore district. The NE-trending faults F11 and F12 cut through the ore bodies and the strata and are cut by the latest NW-trending faults F8 and F9 ( Figure 2).
The Jiudaoguai syncline consists of a set of sedimentary strata, i.e., the Duantouya Formation and the Jiudaoguai Formation unconformable on the volcanic rocks of the Bikou Group ( Figure 2). The southern limb strata dip to the NE with a dip angle of 20-45 • , and the northern limb strata dip to the SE with a dip angle of 40 to 70 • . The Zn-Au ore bodies in the Liushuping occur in the northern and southern limbs of the Jiudaoguai syncline.
The Liushuping deposit consists of two ore prospects: the south ore prospect is located in the southern limb of the Jiudaoguai syncline and contains 5 Au-Zn orebodies, while the north ore prospect is located in the northern limb of the syncline and contains 12 Zn-(Pb) orebodies ( Figure 2).
The ore bodies from the south ore prospect have different ore-bearing strata, and their occurrences are relatively consistent ( Figure 3). The Au-Zn1 ore body occurs in altered limy dolomite of the Duantouya Formation and is controlled by the interlayer fracture zone. It has a lenticular shape with an average thickness of 0.85 m, with 310 • striking and NNW-dipping. The exposed length of the surface is about 300 m, and the average Au grade is 2.45 g/t. The Au-Zn2, Au-Zn3, and Au-Zn4 ore bodies are produced in the thick dolomite of the Jiudaoguai Formation. The Au-Zn2 ore body is narrow and long, outcrop about 500 m, and more than 900 m together with an alteration zone. It is generally NE-dipping with an inclination angle of 46 to 65 • . The east side is cut by F11 and F9. The ore body has the longest extension, and all four boreholes can be seen ( Figure 3). The thickness of the single-engineering ore body is 0.78-3.47 m, and the average thickness is 3.06 m. The single-engineering gold grade is up to 11.81 g/t, and the average zinc grade is 4.82%. The exposed thickness of the Au-Zn3 ore body is large, extending up to 500 m, and generally contains gold, with a gold grade up to 5.08 g/t. The Au-Zn4 ore body has a relatively small outcrop, about 300 m in length. It can be seen from the borehole with a large thickness of 2.76 m on average. The gold-rich ore bodies are concentrated in the eastern section. the Au-Zn5 ore body occurs in chlorite sericite slate and chlorite sericite slate containing carbonate nodules of the Jiudaoguai Formation. The ore body is dominated by sphalerite with weak gold mineralization, extending about 500 m from east to west ( Figure 2).
The orebody of the north ore prospect occurs in the dolomite of the Jiudaoguai Formation on the northern limb of the Jiudaoguai syncline, which is controlled by the interlayer fracture zone. The overall trend of the orebodies is northeast with a dipping southeast and dip angle of 57−67 • , which is nearly parallel to the strata in the ore deposit ( Figure 2). The length of a single orebody is between 560 m and 1160 m, and the thickness is between 0.48 m and 10.09 m. The orebody generally contains zinc and lead, with average grades of 1.81-3.81% and 0.35-0.36%, respectively.  The orebody of the north ore prospect occurs in the dolomite of the Jiudaoguai Formation on the northern limb of the Jiudaoguai syncline, which is controlled by the interlayer fracture zone. The overall trend of the orebodies is northeast with a dipping southeast and dip angle of 57−67°, which is nearly parallel to the strata in the ore deposit ( Figure  2). The length of a single orebody is between 560 m and 1160 m, and the thickness is between 0.48 m and 10.09 m. The orebody generally contains zinc and lead, with average grades of 1.81-3.81% and 0.35-0.36%, respectively.
The ore is mainly pyritized limy dolomite and dolomite, and ferritization is common ( Figure 4). The ore contains a massive (Figure 4a,b), vein (Figure 4c), and disseminated structure (Figure 4d,e). The massive ore is dominated by coarse-grained pyrite ( Figure  4f,g), interspersed with irregular vein-like sphalerite (Figure 4a,b). In vein-like and disseminated ores, there are few coarse-grained pyrites, and sphalerite-pyrite veins often appear irregular (Figure 4h-j). In the disseminated ores, the sphalerite and transparent minerals are coexistence and present a grid-like feature (Figure 4j), and coarse-grained pyrite is cracked (Figure 4i,j). All ore rocks that are characterized by coarse-grained pyrite are replaced by sphalerite (Figure 4f  The ore is mainly pyritized limy dolomite and dolomite, and ferritization is common ( Figure 4). The ore contains a massive (Figure 4a  . Photographs and photomicrographs showing the ore rocks from drilling ZK801 of the Liushuping Au-Zn deposit: (a,b) massive structure ore rocks are dominated by coarse-grained pyrites that interspersed with irregular vein-like sphalerite; (c) vein structure ore rock; (d,e) disseminated structure ore rocks, and ferritization; (f) coarse-grained pyrites in the massive ore rock; (g) coarse-grained pyrites replaced by sphalerite and clustered fine-grained pyrite (Py2) in the massive ore rock; (h) the vein-like ores are dominated by sphalerite and clustered fine-grained pyrite (Py2); (i,j) disseminated ores are dominated by sphalerite and clustered fine-grained pyrite (Py2), coarsegrained pyrites are severely fragmented; (k) coexistence of quartz, sericite, calcite, and sphalerite to replace coarse-grained pyrites (Py1), the same position as photo (f) under orthogonal polarization; (l) coexistence of quartz, sericite, calcite, and sphalerite to replace coarse-grained pyrites (Py1), the same position as photo (g) under orthogonal polarization; (m) coexistence of quartz, sericite, dolomite, and sphalerite to replace coarse-grained pyrites (Py1), the same position as photo (h) under orthogonal polarization; (n) coexistence of quartz, sericite, serpentine, and sphalerite, the same position as photo (i) under orthogonal polarization; (o) coexistence of quartz, sericite, serpentine, carbonates, and sphalerite in the disseminated ore, the same position as photo (j) under orthogonal polarization. Abbreviations: Cal-Calcite; Dol-Dolomite; Py-pyrite; Q-quartz; Ser-sericite; Srp-Serpentine; Sph-sphalerite.
According to the petrographic and mineralographic observations, two types of pyrite can be distinguished, i.e., coarse-grained pyrite (Py1) and fine-grained pyrite (Py2). Coarse-grained pyrites (Py1) are generally developed in massive ore (Figure 5b), usually showing fragmented texture ( Figure 5b) and replacement texture (Figures 4f,g and 5d). Fine-grained pyrites (Py2) are euhedral or subhedral and often appear in clusters ( Figure  5c,e,f) closely associated with sphalerite, indicating the products are of the same stage (Figure 5e-g). Fine-grained pyrites (Py2) are more common in vein-like and disseminated ores (Figure 4i,j). Sphalerite and fine-grained pyrite (Py2) replaced coarse-grained pyrite, showing a metasomatic texture and/or metasomatic residual texture (Figure 5f,g). Some ores, especially disseminated ores, show the appearance of ferritization (Figure 4d,e), which is more obvious under the microscope. In addition, the pyrite has weathered into limonite and formed a pseudomorphic pyrite (Figure 5h  . Photographs and photomicrographs showing the ore rocks from drilling ZK801 of the Liushuping Au-Zn deposit: (a,b) massive structure ore rocks are dominated by coarse-grained pyrites that interspersed with irregular vein-like sphalerite; (c) vein structure ore rock; (d,e) disseminated structure ore rocks, and ferritization; (f) coarse-grained pyrites in the massive ore rock; (g) coarsegrained pyrites replaced by sphalerite and clustered fine-grained pyrite (Py2) in the massive ore rock; (h) the vein-like ores are dominated by sphalerite and clustered fine-grained pyrite (Py2); (i,j) disseminated ores are dominated by sphalerite and clustered fine-grained pyrite (Py2), coarsegrained pyrites are severely fragmented; (k) coexistence of quartz, sericite, calcite, and sphalerite to replace coarse-grained pyrites (Py1), the same position as photo (f) under orthogonal polarization; (l) coexistence of quartz, sericite, calcite, and sphalerite to replace coarse-grained pyrites (Py1), the same position as photo (g) under orthogonal polarization; (m) coexistence of quartz, sericite, dolomite, and sphalerite to replace coarse-grained pyrites (Py1), the same position as photo (h) under orthogonal polarization; (n) coexistence of quartz, sericite, serpentine, and sphalerite, the same position as photo (i) under orthogonal polarization; (o) coexistence of quartz, sericite, serpentine, carbonates, and sphalerite in the disseminated ore, the same position as photo (j) under orthogonal polarization. Abbreviations: Cal-Calcite; Dol-Dolomite; Py-pyrite; Q-quartz; Ser-sericite; Srp-Serpentine; Sph-sphalerite.
According to the petrographic and mineralographic observations, two types of pyrite can be distinguished, i.e., coarse-grained pyrite (Py1) and fine-grained pyrite (Py2). Coarsegrained pyrites (Py1) are generally developed in massive ore (Figure 5b Sphalerite and fine-grained pyrite (Py2) replaced coarse-grained pyrite, showing a metasomatic texture and/or metasomatic residual texture (Figure 5f,g). Some ores, especially disseminated ores, show the appearance of ferritization (Figure 4d,e), which is more obvious under the microscope. In addition, the pyrite has weathered into limonite and formed a pseudomorphic pyrite (Figure 5h,i).
According to the characteristics of ores, as well as the petrographic and mineralographic observations, the deposit is mainly divided into the hydrothermal period and epigenetic oxidation period ( Figure 6). The hydrothermal period can be further divided into two stages: stage 1 is mainly composed of coarse-grained pyrite, and stage 2 consists of fine-grained pyrite, sphalerite, quartz, dolomite, calcite, sericite, and serpentine. Limonite is the product of the epigenetic oxidation period. According to the characteristics of ores, as well as the petrographic and mineralographic observations, the deposit is mainly divided into the hydrothermal period and epigenetic oxidation period ( Figure 6). The hydrothermal period can be further divided into two stages: stage 1 is mainly composed of coarse-grained pyrite, and stage 2 consists of fine-grained pyrite, sphalerite, quartz, dolomite, calcite, sericite, and serpentine. Limonite is the product of the epigenetic oxidation period.

40 Ar/ 39 Ar Geochronology
One sample of hydrothermal sericite was collected for 40 Ar/ 39 Ar dating (ZK802-H46) from a disseminated ore from the Liushuping drilling ZK802. The samples were crushed into 20 mesh and obtained 0.2 g mica with handpicking under a binocular microscope. The mica was disaggregated, and fragments with no porphyroblasts were reserved. The mica separates for 40 Ar/ 39 Ar dating were preliminarily purified from the fragments through a conventional heavy liquid, magnetic technique, and ultrasonic cleaning.
The 40 Ar/ 39 Ar analyses were performed at the Western Australian Argon Isotope Facility at Curtin University, Australia. The sample was step-heated using a 110 W Spectron Laser Systems, with a continuous Nd-YAG (IR; 1064 nm) laser rastered over the sample for 1 min to ensure a homogenously distributed temperature. The gas was purified in a stainless-steel extraction line using two SAES AP10 getters, a GP50 getter, and a liquid nitrogen condensation trap. Ar isotopes were measured in static mode using a MAP 215-50 mass spectrometer (resolution of ~500; sensitivity of 4 × 10 −14 mol/V) with a Balzers SEV 217 electron multiplier mostly using 9 to 10 cycles of peak-hopping. The data acquisition was performed with the Argus program written by M.O. McWilliams and ran under a LabView environment. The raw data were processed using the ArArCALC software (Version 2.5.2, by Anthony Koppers in Oregon State University, Corvallis, Oregon, United States; http://earthref.org/tools/ararcalc) [30] and the ages have been calculated using the decay constants recommended by [31]. Blanks were monitored every 3 to 4 steps, and typical 40 Ar blanks range from 1 × 10 −16 to 2 × 10 −16 mol. Our criteria for the determination of plateau were as follows: Plateaus must include at least 70% of 39 Ar. The plateau should be distributed over a minimum of 3 consecutive steps agreeing at a 95% confidence level and satisfying a probability of fit (P) of at least 0.05. Plateau ages (Table 1 and Figure 7) are given at the 2σ level and are calculated using the mean of all the plateau steps, each

40 Ar/ 39 Ar Geochronology
One sample of hydrothermal sericite was collected for 40 Ar/ 39 Ar dating (ZK802-H46) from a disseminated ore from the Liushuping drilling ZK802. The samples were crushed into 20 mesh and obtained 0.2 g mica with handpicking under a binocular microscope. The mica was disaggregated, and fragments with no porphyroblasts were reserved. The mica separates for 40 Ar/ 39 Ar dating were preliminarily purified from the fragments through a conventional heavy liquid, magnetic technique, and ultrasonic cleaning.
The 40 Ar/ 39 Ar analyses were performed at the Western Australian Argon Isotope Facility at Curtin University, Australia. The sample was step-heated using a 110 W Spectron Laser Systems, with a continuous Nd-YAG (IR; 1064 nm) laser rastered over the sample for 1 min to ensure a homogenously distributed temperature. The gas was purified in a stainless-steel extraction line using two SAES AP10 getters, a GP50 getter, and a liquid nitrogen condensation trap. Ar isotopes were measured in static mode using a MAP 215-50 mass spectrometer (resolution of~500; sensitivity of 4 × 10 −14 mol/V) with a Balzers SEV 217 electron multiplier mostly using 9 to 10 cycles of peak-hopping. The data acquisition was performed with the Argus program written by M.O. McWilliams and ran under a LabView environment. The raw data were processed using the ArArCALC software (Version 2.5.2, by Anthony Koppers in Oregon State University, Corvallis, OR, USA; http://earthref.org/tools/ararcalc, accessed on 10 May 2022) [30] and the ages have been calculated using the decay constants recommended by [31]. Blanks were monitored every 3 to 4 steps, and typical 40 Ar blanks range from 1 × 10 −16 to 2 × 10 −16 mol. Our criteria for the determination of plateau were as follows: Plateaus must include at least 70% of 39 Ar. The plateau should be distributed over a minimum of 3 consecutive steps agreeing at a 95% confidence level and satisfying a probability of fit (P) of at least 0.05. Plateau ages (Table 1 and Figure 7) are given at the 2σ level and are calculated using the mean of all the plateau steps, each weighted by the inverse variance in their analytical error. Miniplateaus are defined similarly except that they include between 50% and 70% of 39 Ar. Integrated ages (2σ) were calculated using the total gas released for each Ar isotope. Inverse isochrons include the maximum number of steps with a probability of fit ≥ 0.05. All sources of uncertainties were included in the calculation. weighted by the inverse variance in their analytical error. Miniplateaus are defined similarly except that they include between 50% and 70% of 39 Ar. Integrated ages (2σ) were calculated using the total gas released for each Ar isotope. Inverse isochrons include the maximum number of steps with a probability of fit ≥ 0.05. All sources of uncertainties were included in the calculation.

Sr Isotope Analysis
Five sphalerite samples were obtained from Stage 2 of the Liushuping Au-Zn deposit, which was crushed into finer than 10 mesh (420 microns), and the sulfides were handpicked under a binocular microscope. Around 10 to 50 mg of the powder was leached in acetone and washed with distilled and deionized water to remove contamination, then dried at 60 °C. The samples were then dissolved in a solution of HF + HNO3 + HClO4, dried, redissolved in 6 N HCl, redried, and redissolved again in 0.5 N HCl (for Sr and Nd

Sr Isotope Analysis
Five sphalerite samples were obtained from Stage 2 of the Liushuping Au-Zn deposit, which was crushed into finer than 10 mesh (420 microns), and the sulfides were handpicked under a binocular microscope. Around 10 to 50 mg of the powder was leached in acetone and washed with distilled and deionized water to remove contamination, then dried at 60 • C. The samples were then dissolved in a solution of HF + HNO 3 + HClO 4 , dried, redissolved in 6 N HCl, redried, and redissolved again in 0.5 N HCl (for Sr and Nd separation). The Sr and Nd fractions were separated following the standard chromatographic technique using AG50 × 8 and PTFE-HDEHP resins with HCl as eluent.
A TRITON thermal ionization mass spectrometer (TIMS, Thermo Fisher Scientific, Waltham, Massachusetts, United States) was used to measure the Sr isotopes at the Analytical Laboratory of the Tianjin Institute of Geology and Mineral Resources, China. The 87 Sr/ 86 Sr isotope ratios were normalized against the 86 Sr/ 88 Sr = 0.1194. The BCR-2 basalt Sr standard was used yielding 87 Sr/ 86 Sr ratios of 0.705009 ± 0.000008. The Sr isotopic compositions were measured with a thermal ionization ISOPROBE-T mass spectrometer.

Sericite 40 Ar/ 39 Ar Geochronology
The analytical results are listed in Table 1, and the corresponding plateau age and normal age are plotted in Figure 7. The 40 Ar/ 39 Ar plateau age of the spectra is defined by: (1) at least 10 contiguous steps of all the gas evolved from the sample and (2) their apparent ages in agreement with the integrated age of the plateau segment with invariability at the 2σ level of uncertainty. The temperatures at which sericite sample ZK802-H46 was measured ranged from 850 • to 1400 • C, corresponding to 18 steps of heating released (Figure 7;

Sr Isotopes of Sphalerite
The five sphalerite samples (stage 2) yield 87 Sr/ 86 Sr values of 0.728131-0.755716 (average 0.739492; Table 2) and calculated I Sr (t) values of 0.707447-0.752802 (average 0.730952; Table 2). To conduct a macro-comparison and analysis, we also summarized the Sr data from previous literature and listed it in Table 2.   [37] within analytical error, indicating the 40 Ar/ 36 Ar age of the sample to be reliable. The coincident plateau ages and normal isochrones ages can represent the actual metallogenic ages after systematic error corrections. The micropetrographic study indicates the coexistence of sericites and sphalerite (Figure 8a-c); hence, the age of sericite can represent the sphalerite mineralization. We thus conclude that the sphalerite mineralization with a small amount of gold in the Liushuping deposit occurred in Late Indosinian, which is consistent with the age of the Huachanggou Au deposit in the MLY (212-209 Ma [10]; Figure 1b).

Timing of Au-Zn Deposit Formation
One sericite sample from Liushuping yielded an 40 Ar/ 39 Ar isotopic plateau age of 215.28 ± 0.39 Ma, correlating with an 39 Ar/ 36 Ar-40 Ar/ 36 Ar normal isochron age of 215.70 ± 0.37 Ma. The initial 40 Ar/ 36 Ar values of the sericites are almost consistent with the atmospheric value of 298.56 ± 0.31 [37] within analytical error, indicating the 40 Ar/ 36 Ar age of the sample to be reliable. The coincident plateau ages and normal isochrones ages can represent the actual metallogenic ages after systematic error corrections. The micro-petrographic study indicates the coexistence of sericites and sphalerite (Figure 8a-c); hence, the age of sericite can represent the sphalerite mineralization. We thus conclude that the sphalerite mineralization with a small amount of gold in the Liushuping deposit occurred in Late Indosinian, which is consistent with the age of the Huachanggou Au deposit in the MLY (212-209 Ma [10]; Figure 1b).

Source of Ore-Forming Materials
As known, hydrothermal deposits are products of water-rock reactions between oreforming fluids and wall rocks. Therefore, the isotopic composition of wall rocks and oreforming fluids can be reflected by the isotopic composition of ore minerals [21,38]. In other words, we can infer the isotope compositions of the ore-forming fluids based on the isotope compositions of the unaltered wall rocks and the ores [23], and it has been widely used [18,23,24,39,40].

Source of Ore-Forming Materials
As known, hydrothermal deposits are products of water-rock reactions between ore-forming fluids and wall rocks. Therefore, the isotopic composition of wall rocks and ore-forming fluids can be reflected by the isotopic composition of ore minerals [21,38]. In other words, we can infer the isotope compositions of the ore-forming fluids based on the isotope compositions of the unaltered wall rocks and the ores [23], and it has been widely used [18,23,24,39,40].
The sphalerite I Sr (t) values of the Liushuping deposit (0.707447 to 0.752803 Table 2; Figure 9) varies greatly, overlapping with host rocks of the Duantouya Formation ( Figure 9). The average I Sr (t) value of sphalerite (0.730952) is much higher than the highest value of the Bikou Group (Figure 9), and close to the counterpart of the Duantouya Formation (0.733668), indicating that the ore-forming fluids mainly originate from sedimentary strata of the Duantouya Formation. Considering that the Jiudaoguai Formation contains Rb-rich carbonatite, even if there is no I Sr (t) data, we proposed the wall rocks of the Jiudaoguai Formation can also provide a high I Sr (t) source. Therefore, the ore-forming fluids may mainly come from the metamorphic fluids derived from the dehydration of the high Sr isotopes strata. s 2022, 12, x FOR PEER REVIEW 12 9). The average ISr(t) value of sphalerite (0.730952) is much higher than the highest v of the Bikou Group (Figure 9), and close to the counterpart of the Duantouya Forma (0.733668), indicating that the ore-forming fluids mainly originate from sedimentary s of the Duantouya Formation. Considering that the Jiudaoguai Formation contains Rb carbonatite, even if there is no ISr(t) data, we proposed the wall rocks of the Jiudao Formation can also provide a high ISr(t) source. Therefore, the ore-forming fluids mainly come from the metamorphic fluids derived from the dehydration of the hig isotopes strata.

Geodynamic Setting of Au-Zn Mineralization
The West Qinling Orogenic belt (WQO) was known as the third-largest gold prov in China containing more than 50 gold deposits with total gold resources up to 1100 [41], which also contained a large amount of copper, lead, and zinc resources. The av ble metallogenic ages for gold deposits in WQO are listed in Table 3. The predeces divided the WQO into the southern gold belt and northern gold belt [42]. The former distributed along the Mianlue suture zone from east to west, including the Mianluey Yangshan-Maonaoke, and Dashui deposits (Figure 1a). The latter was located in the s of the Shangdang suture zone and is composed of Fengxian-Taibai, Daqiao-L Zhaishang, and Zaozigou deposits from the east to west (Figure 1a). Throughou WQO, two gold metallogenic events in Indosinian and Yanshanian had been identi The former was from the end of the Triassic to the Early Jurassic (ca. 220 to 190 Ma), the latter was from the end of the Jurassic to the Early Cretaceous (ca. 150 to 130 Ma) (T 3; Figure 10). The Yanshanian gold metallogenic event was consistent with the met genic ages of gold deposits in the East Qinling, and the metallogenic peak was 135 [43,44], which was interpreted as the interaction between Eurasia and the Pacific plate or to be related to the far-field effect of plate reorganization during the Paleo-Pacific duction in eastern Eurasia [45].

Geodynamic Setting of Au-Zn Mineralization
The West Qinling Orogenic belt (WQO) was known as the third-largest gold province in China containing more than 50 gold deposits with total gold resources up to 1100 tons [41], which also contained a large amount of copper, lead, and zinc resources. The available metallogenic ages for gold deposits in WQO are listed in Table 3. The predecessors divided the WQO into the southern gold belt and northern gold belt [42]. The former was distributed along the Mianlue suture zone from east to west, including the Mianlueyang, Yangshan-Maonaoke, and Dashui deposits (Figure 1a). The latter was located in the south of the Shangdang suture zone and is composed of Fengxian-Taibai, Daqiao-Liba-Zhaishang, and Zaozigou deposits from the east to west (Figure 1a). Throughout the WQO, two gold metallogenic events in Indosinian and Yanshanian had been identified. The former was from the end of the Triassic to the Early Jurassic (ca. 220 to 190 Ma), and the latter was from the end of the Jurassic to the Early Cretaceous (ca. 150 to 130 Ma) ( Table 3; Figure 10). The Yanshanian gold metallogenic event was consistent with the metallogenic ages of gold deposits in the East Qinling, and the metallogenic peak was 135 Ma [43,44], which was interpreted as the interaction between Eurasia and the Pacific plate [43] or to be related to the far-field effect of plate reorganization during the Paleo-Pacific subduction in eastern Eurasia [45].   Figure 10. Summary diagram illustrating the ages of Au deposits in the West Qinling Orogen [11,12,42,45,[47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65]. Data sources are listed in Table 3.
The plateau age of the hydrothermal sericite sample obtained in this study is 215.28 ± 0.39 Ma, and the isochronal age is 215.70 ± 0. 37 Ma, indicating that the Liushuping Au-Zn deposit was formed in the late Indosinian period. This conclusion coincides with the Indosinian mineralization in the MLY (Figure 1b), such as the Huachanggou Au deposit (fuchsite 40 Ar/ 39 Ar, 212-209 Ma [11]) and the Jianchaling Au deposit (fuchsite 40 Ar/ 39 Ar 199-194 Ma [12]; pyrite Re-Os 206 Ma [42]). It means that an important metallogenic event occurred in the MLY from the Late Triassic to the Early Jurassic, which coincided with the Indosinian metallogenic of WQO.
Large-scale mineralization that occurred in the WQO in the late Indosinian was closely related to the scissors suture of the Tethys Ocean from east to west. Furthermore, the Triassic Qinling Orogen was analogous to the present-day Mediterranean Sea, contemporaneously accommodating oceanic plate subduction in the west and continental collision in the east, as well as a gradual transition from subduction to collision [2,3]. The Figure 10. Summary diagram illustrating the ages of Au deposits in the West Qinling Orogen [11,12,42,. Data sources are listed in Table 3.
The plateau age of the hydrothermal sericite sample obtained in this study is 215.28 ± 0.39 Ma, and the isochronal age is 215.70 ± 0. 37 Ma, indicating that the Liushuping Au-Zn deposit was formed in the late Indosinian period. This conclusion coincides with the Indosinian mineralization in the MLY (Figure 1b), such as the Huachanggou Au deposit (fuchsite 40 Ar/ 39 Ar, 212-209 Ma [11]) and the Jianchaling Au deposit (fuchsite 40 Ar/ 39 Ar 199-194 Ma [12]; pyrite Re-Os 206 Ma [42]). It means that an important metallogenic event occurred in the MLY from the Late Triassic to the Early Jurassic, which coincided with the Indosinian metallogenic of WQO.
Large-scale mineralization that occurred in the WQO in the late Indosinian was closely related to the scissors suture of the Tethys Ocean from east to west. Furthermore, the Triassic Qinling Orogen was analogous to the present-day Mediterranean Sea, contemporaneously accommodating oceanic plate subduction in the west and continental collision in the east, as well as a gradual transition from subduction to collision [2,3]. The onset of the continental collision between the Yangtze and the North China Cratons occurred between 200 and 190 Ma [66]. There are also ore-forming processes in which elements have accumulated to form various kinds of deposits, such as gold, silver, lead, zinc, etc. The metallogenesis of the Huachanggou gold deposit was explained to be related to the collision between the Yangtze terrane and the Qinling microplate, which was further interpreted to have completed the closure of the ocean basin and to have caused the collision between the Yangtze plate and the Qinling microplate before 209 Ma [11]. We also believe that, as the location of the arc point on the northwestern edge of the Yangtze plate, its collision may represent the initial collision between the Yangtze plate and the Qinling microplate [11]. Even at 206 Ma, the formation of the Jianchaling gold deposit still had oceanic subduction, and the mineralization continued until the continental collision in the Early Jurassic [12,42]. Therefore, the Liushuping Au-Zn deposit was formed in ca. 215 Ma, coeval with the end of the oceanic subduction.

Conclusions
(1) Two stages of hydrothermal mineralization are recognized in the Liushuping Au-Zn deposit; stage 1 is mainly coarse-grained pyrite, and stage 2 consists of fine-grained pyrite, sphalerite, and gangue minerals.
(3) The sphalerite I Sr (t) values of the Liushuping deposit (0.707447 to 0.752803) overlapping with host rocks of the Duantouya Formation (0.709824 to 0.812487), but higher than the Bikou Group, which means that ore-forming fluid may mainly originate from the Duantouya Formation.
(4) The Liushuping Au-Zn deposit is the product of metamorphic dehydration of the host rocks, which was formed by the northward subduction of the Yangtze plate under the Qinling microplate during the late Triassic.