To investigate the relationship between syenogranite and mineralization in the Xiahulin lead-zinc deposit, samples from the orebody and contact zone near the 90-meter adit of the No. 3 inclined shaft were collected for trace element and REE analysis in sphalerite, as well as for major element, REE, and trace element analysis in syenogranite (Section 4.3). The sample preparation and testing were conducted at the Analytical Laboratory of the Harbin Comprehensive Survey Center. The AXIOSMAX X-ray fluorescence spectrometer from Malvern Paralytical was utilized to measure the concentration of primary elements in the samples, employing the instru-ment’s quantitative analysis software. The major elements were analyzed by XRF with an accuracy of 97%–98%. The sample is pre crushed to 200 mesh, dried at 105°C for 2 h, taken out and cooled to room temperature in a dryer. Accurately weigh (0.5 ± 0.0002) g of the sample and (5 ± 0.0005) g of the mixed flux (Li₂B₄O₇-LiBO₂) on an analytical balance and place them in a porcelain crucible. Stir evenly and transfer the mixed sample into a platinum crucible (95% Pt+5% Au). Use a dropper with a rubber tip to add 300 g/L NH4NO₃ solution and 5 drops of 200 g/L NH₄Br solution. Place the platinum crucible into the melting machine that has been heated to 1,100°C, pre melt for 2 min, shake and spin for 8 min, and let it stand for 1 min. After the melting of the sample is completed, use crucible tongs to remove the platinum crucible and place it on the refractory brick. Let it cool naturally for about 5 min, peel it off, label it, and store it in a dryer for testing. For detailed experimental procedures, reference materials, and calculated LOD, please refer to relevant literature (Lv et al., 2023).

The trace element and REEs were analyzed using the XSERISEⅡ ICP-MS instrument manufactured by Thermo Fisher Scientific. Weigh 0.1 g of the sample into a PTFE inner tank of a closed dissolution apparatus, add 1 mL of HF and 0.5 mL of HNO₃, cover with a PTFE lid, and put it into a stainless steel sleeve. Tighten the steel sleeve lid and keep it at 190°C for 48 h in an oven. Remove, cool down, open the lid, take out the inner can, and heat it on an electric heating plate at 200°C to evaporate. Add 1 mL of HNO₃ and evaporate until dry to drive away hydrofluoric acid. Repeat this step twice, add 5 mL of HCl (1 + 1), seal again in a steel jacket, keep at 130°C for 3 h in an oven, remove and cool, dilute to 25 mL, and prepare 2 blank samples along with the experiment. For detailed experimental procedures, reference materials, and LOD, please refer to relevant literature (Zhao et al., 2021). The solution to be measured is introduced into the high-temperature plasma, and the mass spectrometer automatically calculates the concentration of each element. The analysis error of trace elements is generally less than 5%.

To determine the source of metallogenic materials in the Xiahulin lead-zinc deposit, in-situ micro-scale sulfur (S) and lead (Pb) isotope analyses were performed on metal sulfides from the main mineralization stage. Sulfur isotope analysis was conducted using LA-MC-ICP-MS at Kehui Testing Technology (Tianjin) Co., Ltd., employing a Neptune Plus multi-collector ICP-MS (Thermo Scientific) paired with a RESOlution SE 193 nm laser (testing environment: temperature requirement of 18°C–22°C, relative humidity<65%). Select a suitable area based on the scanned photos of the sample, and use a laser ablation system to ablate sulfides. Point erosion is used for erosion, with a diameter of 30 μm (sphalerite)/20 μm (pyrite), energy density of 3 J/cm², and frequency of 5 Hz. Using high-purity He as the carrier gas, the aerosol generated by erosion is blown out and sent to MC-ICP-MS for mass spectrometry testing. ³²S and ³⁴S are simultaneously received statically using Faraday cups, with an integration time of 0.131 s 200 sets of data are collected, taking approximately 27 s in total. Before formal testing, adjust the instrument parameters with sulfide standard samples to achieve the optimal state. To reduce the impact of matrix effects on test results, sulfides similar to the sample matrix were used as standard samples during the analysis process, and quality discrimination correction was performed using the standard-sample-standard cross method.

In situ lead isotope analyses of sulfide were performed on a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Bremen, Germany) equipped with a Geolas HD excimer ArF laser ablation system (Coherent, Göttingen, Germany) at the Wuhan SampleSolution Analytical Technology Co., Ltd., Hubei, China. In the laser ablation system, helium was used as the carrier gas for the ablation cell and was mixed with argon (makeup gas) after the ablation cell. The spot diameter ranged from 44 to 90 μm dependent on Pb signal intensity. The pulse frequency was from 4 to 10 Hz, but the laser fluence was kept constant at ∼5 J/cm². A new signal-smoothing and mercury-removing device was used downstream from the sample cell to efficiently eliminate the short-term variation of the signal and remove the mercury from the background and sample aerosol particles. The Neptune Plus was equipped with nine Faraday cups fitted with 10¹¹Ω resistors. Isotopes ²⁰⁸Pb, ²⁰⁷Pb, ²⁰⁶Pb, ²⁰⁴Pb, ²⁰⁵Tl, ²⁰³Tl, and ²⁰²Hg were collected in Faraday cups using static mode. The mass discrimination actor for Pb was determined using a Tl solution nebulized at the same time as the sample, using an Aridus II desolvating nebulizer. The mass fractionation of Pb isotopes was corrected by ²⁰⁵Tl/²⁰³Tl with the exponential law. Note that the optimized values of ²⁰⁵Tl/²⁰³Tl, which were calibrated from measuring two Pb isotope standards MASS-1 (USGS) and Sph-HYLM (sphalerite, in-house standard), replaced the natural Tl isotopic composition for the mass fractionation correction of Pb isotopes. The ²⁰²Hg signal was used to correct the remaining ²⁰⁴Hg interference on ²⁰⁴Pb, using the natural ²⁰²Hg/²⁰⁴Hg ratio (0.2301). In addition, the mass fractionation of ²⁰⁴Hg/²⁰²Hg was corrected by the ²⁰⁵Tl/²⁰³Tl normalization. In this case, we assumed identical mass fractionation factors for ²⁰⁴Hg/²⁰²Hg and ²⁰⁵Tl/²⁰³Tl. Sph-HYLM was used to monitor the precision and accuracy of the measurements after ten sample analyses, over the entire period of analysis. The obtained accuracy is estimated to be equal to or better than ±0.2‰ for ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁶Pb/²⁰⁴Pb compared to the solution value by MC-ICP-MS, with a typical precision of 0.4‰ (2σ). The more detail of the in situ Pb isotopic ratios analysis was described in Zhang et al. (2016). All data reduction for the MC-ICP-MS analysis of Pb isotope ratios was conducted using “Iso-Compass” software (Zhang et al., 2020).

To establish the petrogenesis and timing of mineralization in the Xiahulin lead-zinc deposit, zircon U-Pb dating was performed on the mineralization-associated rocks collected from the 90-meter adit of the No. 3 inclined shaft. The syenogranite exhibited a fresh, light-reddish color (Figure 4A) with a medium-grained granite texture and massive structure. It was primarily composed of quartz (40%, anhedral granular, colorless to smoky gray, 0.5–1.5 mm), plagioclase (20%, grayish white, subhedral tabular, 0.5–2 mm), and potassium feldspar (35%, light reddish, subhedral tabular, 0.5–1.5 mm) (Figure 4B), with minor biotite (5%, anhedral, often in aggregates).

U-Pb dating analyses were conducted by LA-ICP-MS at at Beijing Createch Testing Technology Co.,Ltd. Detailed operating conditions for the laser ablation system and the ICP-MS instrument and data reduction are the same as description by Hou et al. (2009). Laser sampling was performed using a RESOlution 193 nm laser ablation system. An AnalytikJena PQMS Elite ICP-MS instrument was used to acquire ion-signal intensities. Helium was applied as a carrier gas. Argon was used as the make-up gas and mixed with the carrier gas via a T-connector before entering the ICP. Each analysis incorporated a background acquisition of approximately 15–20 s (gas blank) followed by 45 s data acquisition from the sample. Off-line raw data selection and integration of background and analyte signals, and time-drift correction and quantitative calibration for U-Pb dating was performed by ICPMSDataCal (Liu et al., 2010). Zircon GJ-1 was used as external standard for U-Pb dating, and was analyzed twice every 5–10 analyses. Time-dependent drifts of U-Th-Pb isotopic ratios were corrected using a linear interpolation (with time) for every 5–10 analyses according to the variations of GJ-1 (i.e., 2 zircon GJ-1 + 5–10 samples +2 zircon GJ-1) (Liu et al., 2010). Uncertainty of preferred values for the external standard GJ-1 was propagated to the ultimate results of the samples. In all analyzed zircon grains the common Pb correction was not necessary due to the low signal of common ²⁰⁴Pb and high ²⁰⁶Pb/²⁰⁴Pb. U, Th and Pb concentration was calibrated by NIST 610. Concordia diagrams and weighted mean calculations were made using Isoplot/Ex_ver3. The zircon Plesovice is dated as unkown samples and yielded weighted mean ²⁰⁶Pb/²³⁸U age of 337.4 ± 3.4 Ma (2SD, n = 7), which is in good agreement with the recommended ²⁰⁶Pb/²³⁸U age of 337.13 ± 0.37 Ma (2SD) (Sláma et al., 2008).

The measurement of Hf isotopes in zircon micro-areas was conducted at the labor-atory of Kehui Testing Technology (Tianjin) Co., Ltd. The detection equipment used in this study is a laser ablation multi-receiver inductively coupled plasma mass spectrometer. The laser injection system employed is the RESOlution SE solid-state laser, while the analysis system utilized is the NEPTUNE plus multi-receiver plasma mass spectrometer. Cathodoluminescence (CL) imaging was used to acquire the internal structural information of zircon, and specific analysis locations were chosen accordingly. The duration of laser ablation is 27 s, the diameter of the spot beam is around 30 μm, the energy density is 6 J/cm², and the frequency is 6 Hz. To guarantee the correctness of the analysis procedure in this investigation, the researchers employed the Plesovice zircon standard sample as a reference. The detected ¹⁷⁶Hf/¹⁷⁷Hf ratio remained stable within the range of 0.282488 ± 20 (2SD, n = 6). The test results are consistent with the data published by Sláma et al. (2008), within the margin of error.

Table 1 presents the major element compositions of the Early Jurassic syenogranites from the Xiahulin lead-zinc deposit. The SiO₂ contents ranged from 59.42 to 78.21 wt% (most samples exceed 72.81 wt%, with only one at 59.42 wt% likely due to higher loss on ignition), Al₂O₃ = 9.56 to 12.63 wt%, Fe₂O₃ = 0.23 to 0.88 wt%, CaO = 0.23 to 0.37 wt%, Na₂O = 2.37 to 4.01 wt%, K₂O = 3.74 to 4.85 wt%, Na₂O + K₂O = 6.11 to 8.53 wt%, and Mg^# = 0.26 to 0.34. In the TAS (Figure 5A) and SiO₂-K₂O (Figure 5B) diagrams, the samples fell within the high-K calc-alkaline series, whereas in the Na₂O-K₂O diagram (Figure 5C), they were plotted within the potassic series. The A/CNK values ranged from 1.05 to 1.16, and the A/NK values from 1.08 to 1.20, categorizing them as peraluminous granite (Figure 5D).

Table 2 presents the trace and rare earth element (REE) data for syenogranites associated with mineralization in the Xiahulin lead-zinc deposit, along with individual sphalerite samples. The REE and trace elements in the syenogranite and sphalerite exhibit different characteristics, with syenogranites containing higher REE and trace element concentrations than sphalerite. The total REE content in the syenogranites ranged from 112.52 to 153.54 × 10⁻⁶, with an average of 137.40 × 10⁻⁶. The syenogranites displayed enrichment of light REEs (LREEs) over heavy REEs (HREEs), with LREEs from 83.73 to 88.73 × 10⁻⁶, HREEs from 23.78 to 32.49 × 10⁻⁶, and LREE/HREE ratios between 3.29 and 4.28. The chondrite-normalized REE patterns (Figure 6A) exhibited a slight rightward trend, enriched in LREEs and depleted in HREEs, accompanied by a distinct negative Eu anomaly (δEu = 0.07 to 0.09, average 0.08). The total REE content in the sphalerite ranged from 1.01 to 25.55 × 10⁻⁶, with an average of 7.18 × 10⁻⁶. The sphalerite displayed enrichment of light REEs (LREEs) over heavy REEs (HREEs), with LREEs from 0.88 to 21.98 × 10⁻⁶, HREEs from 0.12 to 3.57 × 10⁻⁶, and LREE/HREE ratios between 3.48 and 8.93. The chondrite-normalized REE patterns (Figure 6A) exhibited a distinct rightward trend, enriched in LREEs and depleted in HREEs, accompanied by a slight negative Eu anomaly (δEu = 0.57 to 0.93, average 0.64).

In the primitive mantle-normalized trace element spider diagrams (Figure 6B), both syenogranite and sphalerite samples exhibit significant negative Sr anomalies, which may be due to residual source areas such as plagioclase in the rocks and strong rock alteration. The higher Th/U values (8.3–19.11) in syenogranite may indicate its mantle derived origin. The Th/U value (0.05–1.99) in sphalerite is significantly lower than that in syenogranite, and the Zr content in sphalerite is also significantly lower than that in syenogranite, which should be due to the replacement and precipitation of minerals such as zircon during silicification and mineralization processes. The depletion of Ti and Nb elements in both syenogranite and sphalerite may indicate the involvement of crustal materials in magmatic processes.

In this study, pyrite and sphalerite from the third metallogenic stage of the Xiahulin lead-zinc deposit were selected for in-situ S and Pb isotope analysis using laser ablation-multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS), and the results are presented in Tables 3, 4. As indicated in Table 3, the sulfur isotope composition of metal sulfides in the main mineralization stage of the Xiahulin lead-zinc deposit is similar to that of typical hydrothermal vein type lead-zinc deposits in the region (Figure 7). The δ ³⁴S values of metal sulfides in the Xiahulin lead-zinc deposit are all greater than 0, ranging from+3.5‰ to+6.0‰, with an average value of+5.0‰, a range of R = 2.50, and a standard deviation of S = 0.95. It has a small fluctuation range, but has exceeded the fluctuation range of deep source sulfur. The ore-forming material may have been added by crustal materials or sedimentary rocks such as strata. The ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁶Pb/²⁰⁴Pb ratios remained stable at 38.362–38.386, 15.583–15.591, and 18.472–18.481, respectively. These minor variations within a concentrated range indicated that sulfides in the Xiahulin lead-zinc deposit exhibited normal lead characteristics (Du, 1988; Tan, 2011).

The zircons from the syenogranite in the Xiahulin mining area were highly transparent and well crystallized, appearing in aggregated and octahedral forms. The particle sizes ranged from 102 to 205 μm, indicating strong self-formation and distinct oscillatory zoning (Figure 8). The Th content of the zircons varied from 138.55 to 1849.39 ppm, while the U content ranged from 312.9 to 2540.93 ppm. The Th/U ratios, all above 0.4 and spanning from 0.41 to 1.04 (Table 5), indicated a magmatic origin (Wu and Zheng, 2004; Li, 2009).

The surface ages of the 17 measurement points were determined by the ²⁰⁶Pb/²³⁸U method, ranging from 197 to 211 Ma, with most clustering between 199 and 207 Ma. On the zircon U-Pb age concordia diagram, all data points were on or near the concordia line (Figure 9). The weighted average age was (203.8 ± 2.2) Ma (MSWD = 3.6; n = 17), indicating the crystallization age of the syenogranite closely associated with the mineralization of the Xiahulin lead-zinc deposit during the Early Jurassic.

The in-situ Hf isotope data for zircons from syenogranite (D0901) were collected from the inclined shaft of the Xiahulin lead-zinc mine and closely associated with mineralization, as detailed in Table 6. The magmatic zircons in sample D0901 exhibited the ¹⁷⁶Hf/¹⁷⁷Hf ratios from 0.282628 to 0.282846, with εHf(t) values ranging from −1.23 to +6.72. The two-stage Hf model ages (TDM2) ranged from 804 to 1309 Ma. The captured zircon (∼437 Ma) demonstrated a¹⁷⁶Hf/¹⁷⁷Hf ratio of 0.282620, εHf(t) value of +3.54, and a TDM2 of 1192 Ma. These results indicated that the primary magma was largely derived from partial melting of juvenile crustal material, with minor incorporation of ancient crustal components during magma evolution. The Hf isotope composition of this rock aligned with that of ore-related rocks in the Late Triassic to Early Jurassic porphyry copper-molybdenum deposits in the area (Figure 10).

Sulfur is a key ore-forming element in lead-zinc deposits, offering insights into sulfur sources and deposit genesis through its isotopic composition (Yang et al., 2018). The stable sulfur isotope composition of metal sulfides reflects the initial isotopic ratios and, along with other indicators, can reveal the provenance of ore-forming materials (Cao et al., 2000; Basuki et al., 2008). Sulfur isotopes generally originate from three main sources: mantle-derived sulfur (δ³⁴S ≈ 0‰ ± 3‰), modern seawater (δ³⁴S ≈ +20‰), and reduced sulfur with significantly negative δ³⁴S values (Chaussidon and Lorand, 1990). The fluctuation range of δ ³⁴S values (+3.5‰∼+6.0‰) of sulfur isotopes in sulfide during the main mineralization stage of the Xiahulin lead-zinc deposit is relatively small and close to 0, but it exceeds the fluctuation range of mantle sulfur and has a mixed characteristic of mantle sulfur and crustal sulfur, indicating the presence of crustal or sedimentary rock materials added during the mineralization process. The formation age of the Xiahulin lead-zinc deposit ore-forming rock body is Late Triassic-Early Jurassic, which should be produced at the same time as the related rock bodies of copper molybdenum deposits in the same period in the region. After comparative research, the δ ³⁴S characteristics of the Xiahulin lead-zinc deposit are slightly different from those of the Badaguan copper molybdenum deposit (δ ³⁴S is 1.5‰–2.0‰) and the Wunugetushan copper molybdenum deposit (δ ³⁴S is −0.2‰∼+3.4‰) (Xiang et al., 1998) in the middle section of the Erguna metallogenic belt in the region. The δ ³⁴S value is higher than that of the ore-forming rock bodies of the Wunugetushan and Badaguan deposits. Therefore, it can be said that there are crustal or sedimentary rock materials in the ore-forming process of the Xiahulin lead-zinc deposit. Join, it belongs to a mixed source.

Pb isotopes play a critical role in determining the metallogenic age and sourcing ore-forming materials, especially through the analysis of Pb isotope composition (Doe and Stacey, 1974; Zartman and Doe, 1981). Variations in the Pb isotope characteristic value μ indicate different sources: mantle (μ = 8.92) (Doe, 1979), orogenic belt (μ = 10.87), normal Pb (8.686–9.238) (Isotope Geology Laboratory of Yichang Institute of Geology and Mineral Resources, Ministry of Geology and Mineral Re-sources, 1979), and upper crust (μ = 9.58), each exhibiting distinct ranges. In the Xiahulin deposit, μ values are tightly clustered (9.38–9.42, avg. 9.40), bridging the mantle and upper crust, while ω values (34.95–35.17, avg. 35.10) exceeded the mantle values but remained below the crustal average (Zartman and Doe, 1981), suggesting a mixed Pb origin from both crustal and mantle sources.

To assess the temporal effects and trace the sources of ore-forming materials, the Δβ and Δγ values were computed using Geokit software (Table 4). In the Δγ–Δβ diagram by Zhu et al. (1998), Xiahulin sulfides fell within the mixed crust-mantle source range (Δβ: 17.36–17.88, avg. 17.60; Δγ: 25.35–26.05, avg. 25.70), affirming a combined crust-mantle lead origin. Both the Xiahulin and Bajiaguan samples plotted in the subduction zone lead range on the Δγ–Δβ diagram (Figure 9), indicating magmatic lead derived from upper crust-mantle mixing.

Hf isotope analysis of syngenetic syenogranite associated with Xiahulin mineralization revealed a primary magma origin primarily from juvenile crustal partial melting derived from mantle, with minor ancient crustal contamination during its evolution. Similar findings in the Taipingchuan (granodiorite porphyry) and Wunugetushan (monzogranite) copper-molybdenum deposits in the region highlighted mantle-derived young crustal material differentiation, followed by the incorporation of ancient crustal components (Cao, 2020; Zhang et al., 2022).

The trace element composition in rocks and sphalerite represents a certain geochemical significance, and the study of the geochemical characteristics of metallic minerals and mineralized rock bodies is of great significance for the research of the entire deposit. By analyzing the rare earth and trace characteristic parameters of syenogranite and sphalerite in the Xiahulin deposit (Table 2), although the rare earth and trace element characteristics in syenogranite and sphalerite are not consistent, their evolutionary characteristics of rare earth elements, Th/U, Nb, Sr, Zr, Ti and other trace elements indicate a certain degree of inheritance. The higher Th/U values in syenogranite indicate that the magma may have originated from mantle material, while the weak negative Nb anomaly exhibited by syenogranite to the obvious negative Nb anomaly in sphalerite suggests the involvement of crustal material in the mineralization process (Rollison, 2000). The negative Ti anomaly in syenogranite may indicate the involvement of crustal material in magmatic processes. The rare earth elements in sphalerite are lower than those in syenogranite, but the decrease in heavy rare earth elements is more significant, while the decrease in Eu is not significant. This may be due to the partial melting of plagioclase as a residual phase, which results in a significant decrease in the content of heavy rare earth elements in sphalerite during the gas-liquid and mineralization stages in contact with marble, due to the exchange of a large amount of alkali rich minerals.

The sulfur, lead, zircon Hf isotope trace elements and REE analyses collectively indicated that the metallogenic material source for the Xiahulin lead-zinc deposit was a mixture of crust and mantle components.

According to field observations underground, the lead-zinc mineralization in the Xiahulin deposit is closely related to the skarnization at the contact between syenogranite and marble. In addition, after analysis, there are certain differences in trace elements and rare earth elements between sphalerite and syenogranite, but it can be seen that there is some inheritance (Figure 6). Therefore, we believe that syenogranite should be the ore-forming rock of the Xiahulin lead-zinc deposit. The Rb-Sr isochron age of the sphalerite (191.9 ± 7.9 Ma) (unpublished data) aligned with the zircon LA-ICP-MS age of the syenogranite (203.8 ± 2.2 Ma), indicating Late Triassic to Early Jurassic diagenesis and mineralization. Moreover, a comparative analysis of the geochemical and zircon Hf isotope compositions of the ore-forming syenogranite and regional porphyry copper-molybdenum deposits revealed their coeval formations and shared tectonic settings.

Recent research has provided extensive data on the formation ages of porphyry Cu–Mo deposits in the Erguna Metallogenic Belt. Qin et al. (1999) reported a single-grain zircon U-Pb age of 188.3 ± 0.6 Ma for the ore-bearing monzogranitic porphyry in the Wunugetu deposit, along with an altered sericite K-Ar age of 183.5 ± 1.7 Ma. Li N. et al. (2007) identified a molybdenite Re-Os isochron age of 178 ± 10 Ma, suggesting Early to Middle Jurassic mineralization. In the Taipingchuan deposit, the ore-forming granodiorite porphyry yielded a zircon U-Pb age of 202 ± 5.7 Ma and a molybdenite Re-Os age of around 203 Ma (Chen et al., 2010), indicating Late Triassic mineralization. The quartz diorite porphyry serves as the ore-forming rock of the Baguan deposit, presenting a zircon U-Pb age of 217.6 ± 2.6 Ma and a molybdenite Re-Os model age of 222.4 ± 3.3 Ma. The Erdenet giant porphyry copper-molybdenum deposit in Mongolia records a quartz diorite U-Pb age of 240–246 Ma and a molybdenite Re-Os isochron age of 241 ± 3.1 Ma (Jiang et al., 2010), indicating Middle Triassic diagenesis and mineralization.

The Early Mesozoic porphyry copper-molybdenum and skarn-type lead-zinc mineralization in the Erguna block can be broadly divided into two stages. The first stage, which occurred in the Middle to Late Triassic, included certain deposits, such as the Erdenet deposit in Mongolia and the Baguan deposit in China. The second stage, spanning from the Late Triassic to Early Jurassic, led to the formation of the Taipingchuan, Wunugetu, and Xiahulin deposits in China. These stages cover approximately 20 Ma and have significant spatial impact on the region.

Isotopic dating revealed that the Baguan porphyry copper-molybdenum deposit formed in the Late Triassic, while the Taipingchuan copper-molybdenum and Xiahulin lead-zinc deposits developed from the Late Triassic to Early Jurassic. In contrast, the Wunugetu porphyry copper-molybdenum deposit originated in the Early Jurassic. During this period, the Erguna region was located at the intersection of the Paleo-Asian Ocean, Paleo-Pacific, and Mongolia-Okhotsk metallogenic domains. Therefore, understanding the tectonic setting of these copper-molybdenum-lead-zinc deposits is essential for interpreting the region’s tectonic evolution.

Tectonic setting discrimination diagrams (Figure 11), based on the lithology of ore-forming rock masses from the Baguan, Taipingchuan, and Xiahulin deposits, illustrate the tectonic evolution of the area, progressing from an intraplate environment to an island arc, then a volcanic arc, and finally a syn-collisional setting. Given that the ore-forming rock masses in this region originated from the upper mantle and were contaminated by crustal materials, they likely formed in an active continental margin setting associated with oceanic crust subduction. Recent geochemical studies of ore-forming rock masses from typical porphyry copper-molybdenum deposits along the Sino-Mongolian border and nearby regions have indicated that these deposits can be formed primarily in an island arc environment owing to oceanic crust subduction (Kuzmin and Antipin, 1993; Xu et al., 1998; Tang et al., 2018; Chen et al., 2010; Zhang et al., 2010).

Emerging evidence suggests that the Paleo-Asian Ocean likely closed during the Middle Triassic (Sun et al., 2004; Li J. et al., 2007; Liu et al., 2011). Although some scholars have proposed that the subduction of the Paleo-Pacific plate toward the Eurasian continent began in the Late Triassic (Peng and Chen, 2007), others argue that the Late Triassic igneous rocks in the eastern Jilin-Heilongjiang region and the Zhangguangcai Range reflect an extensional tectonic setting during this time (Xu et al., 2009; Wu et al., 2011). The presence of Early Jurassic calc-alkaline and bimodal volcanic rock assemblages in the eastern Jilin-Heilongjiang region (Yu et al., 2012; Xu W. et al., 2013; Xu et al., 2013 M.; 2019; Tang et al., 2018) suggests that the Paleo-Pacific plate subduction commenced in the Early Jurassic. Therefore, it is evident that the subduction timings of the Paleo-Asian Ocean and Paleo-Pacific Ocean cannot align with the mineralization ages of the copper-molybdenum-lead-zinc deposits in this region.

Most researchers have reported that the Mongolia-Okhotsk Ocean can be a major bay of the Paleo-Asian Ocean with localized subduction, which is closed in a “scissors-like” manner from west to east at the end of the Late Paleozoic due to the rotation of the Siberian Plate relative to the Central Mongolian Block. This closure occurred in stages, with the western segment closing in the Late Triassic and the eastern segment closing in the Late Jurassic (Zonenshain, 1990; Zorin, 1999; Mo et al., 2005; Mazukabzov et al., 2010). The Erdenet giant porphyry copper-molybdenum deposit in Mongolia, with diagenesis and mineralization ages of approximately 240 Ma (Jiang et al., 2010), formed in a continental marginal arc setting associated with the subduction of this oceanic crust. Lv et al. (2001) proposed that the Mesozoic era in the Manzhouli-Erguna region of China was part of the Mongolia-Okhotsk residual ocean tectonic domain. Recent data have suggested that the Taipingchuan porphyry copper-molybdenum deposit in China’s Erguna Block can be formed in the Late Triassic within an active continental margin arc setting, resulting from the subduction of the Mongolia-Okhotsk Ocean beneath the Erguna Block (Chen et al., 2010; Zhang et al., 2010). Wu et al. (2011) also indicated that Early Mesozoic granites in the northern Erguna block were related to the evolution of the Mongolia-Okhotsk Belt.

The above analysis suggests that the Mongolia-Okhotsk oceanic crust experienced bidirectional subduction during the Triassic. The porphyry copper-molybdenum deposits, including Baguan and Taipingchuan, and lead-zinc deposits, such as Xiahulin, in the Erguna block are closely linked to tectono-magmatic processes driven by the subduction of the Mongolia-Okhotsk Ocean. Specifically, during the Late Triassic to Early Jurassic, as the Mongolia-Okhotsk Ocean closed in a “scissors-like” manner, the oceanic crust subducted toward both the Siberian Plate and the Erguna block. Partial melting of lower crustal materials could incorporate minor mantle-derived components and generate granitic magmas enriched in Cu, Mo, Pb, and Zn, exhibiting the characteristics of adakitic and island arc magmatic rocks. This granitic magma, rich in ore-forming elements, ascended through tectonic fractures, forming porphyry bodies such as monzogranitic, quartz diorite, and granodiorite porphyries. As the temperature and pressure decreased and meteoric water mixed in, the ore-forming fluids underwent boiling and immiscibility, precipitating Cu, Mo, and other metals, forming certain deposits such as Baguan, Babayi, Taipingchuan, and Wunugetu. Concurrently, the syenogranitic magma engaged in contact metasomatism with the Ergunahe Formation marble, leading to skarnization. In the middle to late stages of mineralization, further reductions in temperature and pressure and the mixing of meteoric water reduced the solubility of Cu, Pb, and Zn, promoting their enrichment and precipitation, resulting in the lead-zinc deposits such as Xiahulin and Xijinuo Mountain.