The North Qaidam Orogenic Belt (NQOB) is a high-pressure/ultrahigh-pressure (HP/UHP) metamorphic belt located at the northeastern margin of the Qinghai-Tibetan Plateau (Figure 1a). It represents a Paleozoic continental collision zone between the Qaidam Block to the south and the Qilian Block to the north (Song et al., 2005; Zhang et al., 2008; Chen et al., 2022b; Lin et al., 2025). The NQOB, encompassing the Yeluotuoquan, Qianmeiling, Hongliugou, Tanjianshan, and Yuka areas, are a critical region for orogenic mineral deposits—particularly Au and base metals. These deposits are primarily hosted within specific lithological units, including carbonaceous phyllite and carbonate rocks of the Wandonggou Group and mafic volcanic rocks (metabasalt) of the Tanjianshan Group (Yu et al., 1998; Zhang et al., 2010; Fan, 2016). These deposits are controlled by a NW–SE-trending ductile shear zone, similar to other regional deposits such as the Qinglonggou and Jinlonggou deposits (Liu et al., 2005). Geological structures and magmatic activities have played a crucial role in the formation of polymetallic ore deposits in northwest China (Shi et al., 2004; Shi et al., 2006; Wu et al., 2001; 2007). The exposed stratigraphy comprises a Cambrian–Ordovician greenschist facies, metamorphosed sequence of arc-related volcanic and sedimentary rocks of Tanjianshan Group, Maojiushan sandstone and tuff, Yukahe schist and gneiss (Zhao et al., 2003; Chen et al., 2018a).

The gabbros intrude into the Tanjianshan Group, which consists of low-grade metamorphic volcanic-sedimentary rocks, including metabasalts, metabasaltic andesites, dacites, sericite schists, carbonaceous schists, marbles, metasandstones, and conglomerates (Huichu et al., 2003; Lei et al., 2022). The Tanjianshan Group contains the Shuangkoushan Au–Ag–Pb ore deposits, adjacent to a Pb–Zn magmatic-hydrothermal deposit and numerous orogenic Au deposits from other complexes in the region (Xietieshan and Luliangshan complexes, respectively; Deng and Wang, 2016; Sun et al., 2017; Cai et al., 2018). The exposed deformation features in the Shuangkoushan area include a NW-trending ductile shear zone, a brittle–ductile shear zone, and a NE-trending brittle fracture system. The formation and localization of the deposit were primarily controlled by these structural features.

The exposed lithologies in the Shuangkoushan area include tonalite, granodiorite, gabbro, mica quartz schist, quartzite, meta-sandstone with associated conglomerates, and Quaternary alluvium (Figure 2a). Additionally, mafic and ultramafic pyroclastic rocks were emplaced along thrust faults, with protolith ages ranging from 450 to 530 Ma (Sun et al., 2019; Cai et al., 2021; Lei et al., 2022; Jiang et al., 2024; Chen et al., 2025). Preliminary drilling has indicated that the Shuangkoushan ore deposit consists of distinct Au and Ag–Pb mineralization bodies, with total reserves exceeding 5 t of Au and 39 t of Ag, along with a significant amount of Pb (Meng, 2017). In the study area, both mineralized bodies are hosted within metabasaltic rocks of the Tanjianshan Group deposits, located at the western margin between the Xietieshan and Luliangshan complexes (Figures 1b,c). These metabasalts have undergone significant mylonitization and fragmentation (Chen et al., 2018b).

The Au ore body is primarily hosted in a NW–SE trending brittle-ductile shear zone, dipping 50°–75° to the NW. A total of 10 ore bodies have been identified through exploration, including following main ore bodies number: 10, 9, 4, and 5 with an average grade of 2.24 g/t (Figure 2b). Orebody No. 9 is approximately 172 m long and 3.7 m wide, with an average Au grade of 6.3 g/t. Orebody No. 10 consists of three orebody layers, extending a total of 2 km in length and 60 m in width, with a grade ranging from 1 to 3.8 g/t. Orebody No. 4 is about 700 m long and 2 m wide, with a grade of 1.02–3.6 g/t (Du, 2017). These ores are primarily classified as structurally altered rock and quartz-vein types (Yu et al., 2020). A critical aspect of recent research is the recognition of multistage pyrite formation—classified as Py1, Py2, Py3, and Py4—which plays a key role in constraining the mineralization sequence and fluid evolution. Each generation of pyrite exhibits distinct textural, compositional, and isotopic signatures that correlate with different mineralization stages. Arsenian pyrite (Py1) is the predominant ore mineral in the hypogene ores of area, occurring as subhedral or euhedral fine-grained infillings in quartz fractures (Yu et al., 2020). The gangue minerals mainly include quartz, sericite, and chlorite (Yu et al., 2020). Au occurs primarily as invisible Au in Py1, with grain sizes ranging from 10 μm to 70 μm. The Au size range can be observed in the photograph from the preliminary research work of this area by Chen et al. (2018b). Sulfide minerals appear as disseminations or infilling veinlets within brittle fracture zones and brittle–ductile shear fracture zones, displaying various metamorphic relationships and textures within the alteration zones (Yu et al., 2020). Py2 is porous and coexists with other sulfide minerals (Py1, Py3, etc.). Py2 metasomatized by Py3. Py3 is anhedral and forms in later stages, Py3 further metasomatized by chalcopyrite. The Au grade is positively correlated with pyrite content. Hydrothermal alteration in the Au mineralization stage is characterized by sericitization, silicification, and sulfidation, with no clear zonation.

The Ag–Pb orebodies contain reserves exceeding 39 t of Ag, with an average grade of 343.52 g/t, along with a significant amount of Pb, averaging 11.10% (Meng, 2017). These orebodies are controlled by NE-trending extensional faults and occur as infilling hydrothermal veinlets that cut through the earlier Au ore bodies (Figure 2a). The ore bodies form lens-shaped deposits at the surface and extend to depths greater than 330 m.

The predominant hypogene ore minerals include galena, stromeyerite (AgCuS), and pyrargyrite (Ag₃SbS₃), with minor amounts of chalcopyrite and sphalerite. Galena occurs as fine subhedral or euhedral grains filling fractures in pyrite (Py4) (Yu et al., 2020). Stromeyerite and pyrargyrite display solid-solution separation textures, typically enclosed by galena (Yu et al., 2020). The gangue minerals consist of quartz, calcite, sericite, and carbonaceous materials (Yu et al., 2020). Sulfide minerals occur as thin infilling veinlets within the brittle fracture zone (Yu et al., 2020). Hydrothermal alteration associated with Ag–Pb mineralization is characterized by silicification, sulfidation, and carbonatization.

The sample collection site is Shuangkoushan, located in the North Qaidam region of western China. During the field survey, two fresh rock samples were collected: one from the gabbro unit (95°3′0″E, 37°45′36″N) and another from the granitic gneiss unit (95°4′26.4″E, 37°46′12″N), both adjacent to the Shuangkoushan ore deposits for age dating (Figure 1c). An H–O isotope study was conducted on eight quartz samples collected near 95°4′12″E, 37°45′36″N from the Au and Ag–Pb ore bodies. Additionally, ten galena–chalcopyrite-bearing samples from the Ag–Pb ore body, collected from drill holes ZK01 (95°4′12″E, 37°45′36″N) and ZK02 (95°4′33.6″E, 37°43′48″N) (Figure 2a), and twenty-two pyrite-bearing samples from the Au ore body in the vicinity of 95°43′12″E, 37°46′12″N were subjected to in situ sulfur isotope analysis (Figure 1c). Approximately six fresh rock samples were also collected from Tanjianshan metabasalts—hosting Au–Ag–Pb deposits—near 95°4′12″E, 37°45′50.4″N for textural studies. Each sample, weighing approximately 1 kg, was placed in a labeled bag with a unique identification number and subsequently dispatched to the laboratory.

Sulfide-bearing rock samples were cut, polished to a mirror finish, and carbon-coated to ensure conductivity. A Scanning Electron Microscope (SEM) equipped with a Backscattered Electron (BSE) detector was used at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan). The SEM was operated at an accelerating voltage of 10–20 kV, with a moderate beam current and a working distance of 10–15 mm. BSE images were formed by detecting electrons backscattered from the sample surface, providing compositional contrast based on atomic number differences. This is crucial for distinguishing between different sulfide phases (Novikov, 2014). High-resolution grayscale images were obtained, clearly revealing the textural relationships among various sulfide phases. For further details on the procedure, refer to Čalkovský et al. (2023).

Crushing and zircon selection for the Gabbro (SK01) and Granitic Gneiss (GS01) samples were conducted at the Langfang Institute of Geological and Mineral Research Laboratory. Initially, samples were broken into small fragments, washed, dried, and then pulverized to 200 mesh. Zircons were separated using conventional heavy liquid and magnetic separation techniques, mounted in epoxy resin, and polished to expose grain centers.

Zircons were selected for isotopic analysis based on cathodoluminescence (CL) imaging, performed at the Wuhan Sample Solution Analytical Technology Co., Ltd., using an Analytical Scanning Electron Microscope (JSM-IT100) equipped with a GATAN MINICL system. Imaging was conducted with a 10.0–13.0 kV electric field and an 80–85 µA tungsten filament.

A total of thirty-five zircon grains underwent U–Pb dating and trace element analysis simultaneously using LA-ICP-MS at Wuhan Sample Solution Analytical Technology Co., Ltd. The laser ablation system consisted of a GeolasPro system, including a COMPexPro 102 ArF excimer laser (193 nm wavelength, 200 mJ maximum energy) and a MicroLas optical system. Ion signal intensities were measured using an Agilent 7700e ICP-MS. Helium was used as a carrier gas, while argon served as the make-up gas, mixed with helium via a T-connector before entering the ICP. A “wire” signal smoothing device was employed (Hu et al., 2015). Zircon 91,500 and glass NIST610 were used as external standards for U–Pb dating and trace element calibration, respectively. Each analysis included background acquisition for ∼20–30 s, followed by 50 s of data acquisition. Data processing, including background selection, integration, time-drift correction, and quantitative calibration, was performed using Excel-based ICPMSDataCal software (Liu et al., 2008). Concordia diagrams and weighted mean age calculations were generated using Isoplot/Ex_ver3. The laser ablation system and ICP-MS operating conditions, as well as data reduction methods, followed Zong et al. (2017).

Four quartz samples were collected from the Au ore body and four from the Ag–Pb ore body. Testing was conducted at the Analytical Testing Research Center of the Beijing Institute of Geology. The samples were first crushed, and a preliminary selection to 40–60 mesh was conducted under a stereo microscope to ensure that the quartz mineral purity exceeded 99‰. Isotopic analysis was performed using the DZ/T 0184.19-1997 water hydrogen isotope zinc reduction method. This involved drying the samples at a low temperature to remove adsorbed water and then heating to above 600°C to extract water from the fluid inclusions. The extracted water was then reacted with zinc to produce hydrogen, which was analyzed using mass spectrometry.

Oxygen isotopes were measured using the bromine pentafluoride (BrF₅) method following the DZ/T 0184.13-1997 standard for silicate and oxide minerals. In this method, BrF₅ reacts with quartz at 500°C–680°C under vacuum, releasing oxygen, which is then analyzed via mass spectrometry. The analytical precision was ±1‰ for hydrogen isotopes and ±0.2‰ for oxygen isotopes.

The homogenization temperature of the fluid inclusions in quartz and the mineral–water oxygen isotopic fractionation equation was used to calculate the δ¹⁸O_H₂O value of the fluid. The average temperature of the fluid was taken as the representative value, and the equation used for oxygen isotope equilibrium between quartz and water was: 10 3 ⁡ ln ⁡ α quartz − H 2 O = 3.42 × 10 6 T 2 − 3.40 (Clayton et al., 1972).

In-situ sulfur isotope analyses of the Au ore body and the Ag–Pb ore body were conducted on drill core samples. Au-bearing pyrite, primarily from the Au mineralization stage, was identified based on deformation intensity, metamorphic characteristics, and cross-cutting relationships observed from deep to shallow levels. Galena and chalcopyrite samples were also primarily collected from the Ag–Pb mineralization stage.

Polished thin sections were prepared, and suitable samples were selected through inspection under a reflected-light microscope. Sulfur isotope analysis was performed using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan). For clean ablation of pure sulfide phases backscattered electron (BSE) imaging also used to identifies zoning, inclusions, grain boundaries, and distinguishes sulfides from gangue minerals.

Sulfide samples were analyzed using a laser spot diameter of 30 μm, a repetition rate of 4 Hz, and a laser energy density of approximately 2.5 J/cm². To address instrumental drift and mass bias, a standard-sample bracketing (SSB) approach was applied, while the use of a femtosecond laser ablation system mitigated matrix effects during sulfur isotope analysis of sulfides, as demonstrated in prior studies (e.g., Zhang et al., 2013; Fu et al., 2017). Data processing for the LA-MC-ICP-MS analysis was performed using Iso-Compass software, following established protocols (Zhang et al., 2020). The analytical precision was ±0.2‰. For further details on the procedure, refer to Wang et al. (2024).

The detailed analytical results for the zircon U–Pb ages of gabbro (GS01) and granitic gneiss (SKS01) are presented in Supplementary Tables S1, S2, with Concordia diagrams and cathodoluminescence (CL) images shown in Figures 3, 4.

The zircons from GS01 are predominantly rounded or short columnar crystals with length-to-width ratios of 2:1 and exhibit no evidence of metamorphism or post-formation alteration (Figure 4a). In contrast, the zircons from SKS01 are generally long, prismatic, or euhedral, with length-to-width ratios of 2:1 or 3:1 (Figure 4b). The Th/U ratios of these zircons range from 0.23 to 1.14 and 0.03 to 0.4, respectively, consistent with those classified as magmatic origin (Belousova et al., 2002; Faisal et al., 2020; Phyo et al., 2025a; Phyo et al., 2025b).

A total of seventeen spots on seventeen zircon grains from GS01 were analyzed, yielding a weighted mean ²⁰⁶Pb/²³⁸U age of 448.5 ± 2.5 Ma (MSWD = 0.17; Figure 3a), representing the crystallization age of the Shuangkoushan gabbro intrusion.

For SKS01, eighteen zircon grains were analyzed, forming two distinct age groups. The first group, consisting of 11 measurements, yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 839.8 ± 5 Ma (MSWD = 0.69; Th/U average 0.16). The second group, comprising seven measurements, yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 924 ± 6.3 Ma (MSWD = 0.35; Th/U average 0.17), representing the crystallization age of the granitic gneiss (Figure 3b).

The results of the H–O isotopic analysis of quartz veins from the two metallogenic stages are presented in Supplementary Table S3. In the Ag-Pb mineralization stage, δD_V−SMOW values range from −108.2‰ to −113.8‰, with an average of −110.6‰. The δ18OH2O-SMOW values range from 6.45‰ to 6.55‰, with an average of 6.48‰. The δ18OV-SMOW values range from 14.1‰ to 14.3‰, with an average of 14.17‰. In contrast, during the Au mineralization stage, δDV−SMOW values range from −72.9‰ to −81.5‰, with an average of −76.2‰. The δ18OH2O-SMOW values range from 3.45‰ to 4.95‰, with an average of 3.97‰. The δ18OV_-SMOW values range from 10.4‰ to 13.9‰, with an average of 11.9‰.

The results of the in situ sulfur isotope analysis are presented in Supplementary Table S4. The tests were conducted on pyrite, galena, and chalcopyrite from drillhole samples representing different ore-bearing types at varying depths. The isotopic composition of pyrite from the Au mineralization stage shows significant variation, with δ³⁴S values ranging from +4.8‰ to +10‰, averaging +7.05‰. Within this dataset: Py1 ranges from +8.1‰ to +10‰ (average: +9.3‰), Py2 ranges from +5.9‰ to +7‰ (average: +6.4‰), and Py3 ranges from +4.8‰ to +5.6‰ (average: +5.4‰).

In contrast, the sulfur isotopic composition exhibits less variation in the Ag–Pb mineralization stage. The δ³⁴S values for galena range from +0.2‰ to +2.3‰ (average: +1.4‰), while those for chalcopyrite range from +1.0‰ to +3.3‰ (average: +1.9‰).

In the Shuangkoushan area, two main mineralization stages and five sub-stages have been identified based on cross-cutting relationships among ore-bearing veinlets, observed mineral textures, and assemblages. These stages (Figure 5) include syn-orogenic Au stage (pre-ore, quartz–pyrite, and polymetallic sulfide stage), and post-orogenic Ag–Pb stage (Ag–Pb stage and carbonate stage). Additionally, four types of pyrite were recognized based on textures and paragenetic relationships. During the pre-ore stage (I), the host rocks were subjected to intense tectonic reworking and alteration due to orogenic processes, including strong metamorphism and deformation (Yu et al., 2020). Au-bearing pyrite (Py1) began to pre-enrich the rocks, occurring mainly as fine subhedral grains—either sparsely disseminated or in bamboo-shaped veinlets—within altered mylonites along the shear zone. Some Py1 is intergrown with Py2 in quartz–pyrite veins (stage II), accompanied by gangue minerals such as serpentine, chlorite, epidote, and quartz (Figures 6a,b). Py1 frequently displays evidence of dissolution, metamorphism, and secondary overgrowth from subsequent hydrothermal events. Both Py1 and associated quartz were later crushed, transformed, and metamorphosed by fault activity and hydrothermal overprinting, experiencing both brittle and ductile deformations. Sericite alteration was widespread during this stage. Due to intense structural reworking and alteration, the original composition of the host rocks cannot be accurately determined.

The quartz–pyrite stage (II) represents the main phase of Au mineralization and corresponds to a transition from ductile to brittle deformation structures. Au-bearing pyrite (Py2) is typically subhedral and fine-grained, occurring in disseminated, veinlet-disseminated, and veinlet-type ores hosted in quartz fractures. Py2 often replaces or overgrows Py1 (Figure 6b). Gangue minerals include quartz and sericite. The dominant alteration style during this stage was quartz–pyrite alteration, with minor sericitization (Yu et al., 2020).

By the polymetallic sulfide stage (III), Au mineralization had significantly weakened. The primary minerals were quartz and sericite, with sparse ore minerals including pyrite (Py3) and chalcopyrite. Py2 was overgrown by Py3 (Figure 6c), which was in turn replaced by chalcopyrite. Silicification dominated the alteration assemblage, accompanied by minor pyrite alteration.

The Ag–Pb polymetallic sulfide stage (IV) marks the main phase of Ag–Pb mineralization. The ore bodies occur as veins or lenses that cut across the earlier Au-bearing zones (Figures 6a–c). It can observe in the field photograph from the preliminary research work of this area by Chen et al. (2018b). Many Au-bearing breccias were overprinted by Ag–Pb-bearing hydrothermal deposits. Pyrite (Py4) is mostly euhedral and occasionally displays weak zoning (Figures 6d, e).

In the carbonate stage (V), the mineral assemblage becomes simple in composition, dominated by quartz and calcite, with minor chalcopyrite and pyrite. These sulfides have been partially oxidized to malachite and limonite (Yu et al., 2020).

The metallogenic framework of northern Qaidam reflects its dynamic tectonic history. The formation ages of the ore deposits are consistent with the regional tectonic evolution, encompassing: oceanic subduction (520–460 Ma), continental collision (460–440 Ma), and Continental Exhumation with Orogenic Fluid Modification (430–420 Ma) (Chen et al., 2010; Shuguang et al., 2009; Zhang et al., 2015; Sun et al., 2019). The northern Qaidam margin and East Kunlun Mountains host thirteen structurally controlled Au deposits, each of which formed during successive phases of orogenic activity. The primary episodes of Au mineralization occurred during the Silurian-Triassic periods, with ages ranging from ∼425 Ma to ∼218 Ma. These ages decrease progressively from north to south (Zhang et al., 2005).

Geochronological data provide critical constraints on the timing of syn-orogenic Au mineralization and its transition to post-orogenic Ag-Pb systems. In the Shuangkoushan area, the formation of the metallic ore body was associated with the metabasaltic rocks of the Tanjianshan Group, which host numerous orogenic Au deposits, all controlled by the NW–SE-trending ductile shear zone of the North Qaidam Orogeny (Zhang et al., 2007). For instance, Fu et al. (2016) measured a sericite Ar–Ar age of 399 ± 4 Ma for the Xitieshan ductile shear zone. Xu et al. (2003) obtained muscovite Ar–Ar ages ranging between 402 Ma and 406 Ma for the Northern Qaidam ultra-high-pressure ductile shear zone (UP = 443–473 Ma and UHP = 420–426 Ma by Shuguang et al., 2009). Zhang et al. (2001) determined a muscovite Ar–Ar age of 401 Ma for the NW–SE-trending ductile shear zone in the Tanjianshan Group. Additionally, Zhang et al. (2007) reported a sericite Ar–Ar age of 409.4 ± 2.3 Ma from the NW–SE-trending ore-controlling shear zone of the Tanjianshan deposit, consistent with the earlier Ar–Ar age of 409 ± 2.3 Ma for metamorphic sericite from the similarly oriented (NW–SE) Au ore-controlling shear zone of the Qinglonggou deposit (Zhang et al., 2005). These ages fall within the period of ductile shear activity, indicating that ductile shear deformation and metamorphism played a major role in the formation of the Au deposits. The Shuangkoushan Au orebodies are also controlled by the NW–SE trending ductile shear zone, suggesting that they may have formed during this time. Furthermore, orogenic Au deposits worldwide are typically interpreted to have formed within collision or accretion zones during peak or late-collision metamorphism (Goldfarb et al., 2001). In this study, we obtained an LA-ICP-MS zircon U–Pb age of 448.5 ± 2.5 Ma for Shuangkoushan gabbro (Figure 3a; Supplementary Table S1), which is likely consistent with the formation age (443 ± 2.9 Ma; Yu et al., 2020) of the Shuangkoushan ore-bearing metabasaltic continental back-arc basin related rocks (Gao et al., 2011; Zhang et al., 2015; Sun et al., 2019). The age of the ductile shear zone and Au-bearing quartz vein (402 ± 4.2 Ma; Yu et al., 2020) in the Shuangkoushan area is younger than that of the host rocks, and therefore likely represents the timing of Au mineralization to some extent.

For the Ag–Pb mineralization stage, work by Xu (2012) on inclusions in galena and sphalerite yielded an Rb–Sr mineralization age of 347.9 ± 3.5 Ma. The zircon U–Pb age obtained for the granitic gneisses is 835 ± 6.3 Ma and 924 ± 6.3 Ma, indicating multistage crystallization (Figure 3b; Supplementary Table S2). These oldest ages represent the continental rifting stage of Rodinia, with corresponding ages (700–850 Ma) discovered by Zhu et al. (2015) on the northern margin of the Qaidam Basin. These results suggest that the Ag-Pb ore-forming fluids and metals were not sourced from the adjacent Neoproterozoic granitic gneiss. The North Qaidam granites age is 386–356 Ma postdate UHP metamorphism (438–420 Ma) of the deeply subducted continental crust, confirming their post-collisional origin (Sun G. C. et al., 2022).

Fluids transport thermal energy and ore-bearing minerals in various forms, such as hydrothermal fluids, CO₂-rich fluids, geothermal fluids, etc., (Deng et al., 2000; Kesler, 2005; Huan-zhang, 2008). Previous studies (Chen et al., 2023) have suggested that multiple fluid sources contribute to the formation of ore deposits: Hydrous fluids liberated by metamorphic dehydration (Yardley and Cleverley, 2015), Magmatic–hydrothermal fluids (Lang and Baker, 2001; Treloar et al., 2015), Deep metamorphic dehydration fluids or magmatic–hydrothermal fluids convecting with meteoric water during uplift (Jenkin et al., 1994), CO₂-rich fluids released when the mantle interacts with other hydrothermal fluids (Phillips and Evans, 2004). During the Au mineralization stage in the Shuangkoushan area, the values of δD_V-SMOW and δ¹⁸O_H2O-SMOW (Supplementary Table S3) are lower than typical values for orogenic Au deposits (δD_V-SMOW = −20‰ to −80‰; δ¹⁸O_H2O-SMOW = +5‰ to +10‰; Kerrich et al., 2000; Zheng and Chen, 2000). In the δD_V-SMOW vs. δ¹⁸O_H2O-SMOW plot (Figure 5), the Au samples trend between metamorphic fluids and meteoric water, with values lower than those of typical orogenic Au deposits (Groves et al., 1998; 2003; Goldfarb and Groves, 2015) and local deposits such as Hongliugou (Supplementary Table S5). However, these values align with the variations observed in orogenic Au deposits in China (Zhang, 2011; Fan et al., 2012; Wang, 2012). This suggests that the Au mineralization fluids originated from metamorphic fluids mixed with a substantial meteoric water component. During the Ag–Pb mineralization stage in Shuangkoushan, the samples in the plot trend toward magmatic water alongside meteoric water (Figure 7; Supplementary Table S3). This indicates that Ag–Pb mineralization fluids were sourced primarily from primitive magmatic water with a minor meteoric water component.

Previous studies have identified several sources of metals in ore deposits such as metamorphosed rocks (Phillips and Powell, 2010), intrusion-related primary magmatic sources (Lang and Baker, 2001; Hart et al., 2004), carbonaceous, pyrite-rich sedimentary rocks (Daliran, 2007; Gaboury, 2013), and metabasaltic rocks (Augustin et al., 2016). Among these, metabasaltic rocks have a greater potential to serve as a primary source of remobilized Au during the metamorphogenic formation of orogenic Au deposits such as, Wona-Kona Au deposit (Bierlein and Craw, 2009; Augustin and Gaboury, 2017). Evaluating the origins of metals and fluids particularly during the Au mineralization stage, requires identifying the source of sulfur (Chang et al., 2008).

The pyrite δ³⁴S values in this study ranging from +4.8‰ to +10.0‰ (Supplementary Table S4), overlap with those of biogenic sulfide (δ³⁴S = 2‰–46‰; Detmers et al., 2001) and metamorphic rocks (δ³⁴S = −20‰ to +20‰) but are higher than those of magmatic rocks (δ³⁴S = −1.1‰–3.5‰; McClenaghan, 2013). Previous research has indicated that there is no biological component in sulfides from volcanic rocks and that sulfur concentrations in minerals are largely preserved in ore deposits subjected to metamorphism up to the amphibolite facies. Beyond this stage, sulfur content increases with the degree of metamorphism, reaching up to 2000 μg/g in amphibolite facies fluids (Rauchenstein-Martinek et al., 2014; Rauchenstein-Martinek et al., 2016). As shown in Supplementary Table S4, the δ³⁴S value for pyrite gradually decreases from deep to shallow samples (9.3 → 6.9 → 6.1 → 5.4), correlating with a decrease in metamorphic intensity (Figure 8). Additionally, most orogenic Au deposits in the western part of North Qaidam, including the Yuka, Yeluotuoquan, Qianmeiling, and Hongliugou deposits, exhibit a spatial, temporal, and genetic association with Tanjianshan meta-basaltic rocks. These rocks are favorable for Au mineralization and show positive anomalies in elements such as Ag, As, Au, B, Bi, Sb, Te, and W (Groves et al., 1998). The Tanjianshan meta-basaltic rocks contain higher concentrations of Au, Cr, and Ni (Au: 19.09 × 10⁻⁹; Cr: 167.40 × 10⁻⁶; Ni: 64.36 × 10⁻⁶) compared to local average values (Au: 1.35 × 10⁻⁹; Cr: 55.4 × 10⁻⁶; Ni: 9.94 × 10⁻⁶). These characteristics are similar to those of Au-bearing greenstone belts worldwide (Henley et al., 1976; McKeag et al., 1989). Together with the deposit geology and H–O isotopic results (Figure 9), these findings suggest that the Au ore-forming material was sourced from the Syn-orogenic meta-basaltic rocks of the Tanjianshan Group, which have relatively high background Au values.

During the Ag–Pb mineralization stage in study area, δ³⁴S values for galena range from 0.2‰ to 2.3‰ (Supplementary Table S4), while those for chalcopyrite range from 1.0‰ to 3.3‰. These values fall within the typical range of magmatic sulfur (0‰ ± 3‰; Chaussidon and Lorand, 1990) and are consistent with those observed in the large-scale Xitieshan Pb–zinc deposits (galena δ³⁴S = 2.0‰–2.2‰; Wang et al., 2009; Zhu et al., 2010; Figure 10). This suggests that the Ag–Pb ore-forming material was primarily sourced from post-orogenic deep magma or Devonian granite.

The Qaidam Orogenic Belt is part of the northern margin of the North China Craton and has played a significant role in the formation of the Shuangkoushan Au–Ag–Pb deposit. The belt is characterized by a series of metamorphic and magmatic rocks, which have been shaped by the tectonic evolution of the region (Yang and Santosh, 2020; Li and Yan, 2023). The geological features, isotopic data, and comparison with orogenic deposits in the Shuangkoushan area (Supplementary Table S5) all indicate that the Au-Ag–Pb deposit formed through two distinct mineralization stages, which separately produced Au and Ag–Pb ore bodies at different times and during different phases (syn- and post-) of the North Qaidam orogeny. The syn-post tectonic framework of the Qaidam Orogenic Belt is a result of multiple tectonic phases, including Cambrian−Ordovician magmatic arc formation, Silurian−Devonian orogeny, Permian−Triassic magmatic arc, and Cenozoic collisional magmatism by UHPM exhumation and collapse (Wang et al., 2014; Chen et al., 2022a; Wang et al., 2023; Wu et al., 2024; Jiang et al., 2025).

The Shuangkoushan Au-ore body is a metamorphic-hydrothermal type deposit genetically associated with syn-orogenic metamorphism and deformation. In contrast, the Ag–Pb ore body is an intrusion-related magmatic-hydrothermal type deposit. It was genetically associated to magmatic activity along extensional faults during the post-collision orogeny. These deposits formed through ore-bearing hydrothermal infill, as ore-bearing magma crystallized and differentiated from deep to shallow depths during the regional post-collision extension period, superseding the earlier Au ore body. The Ag–Pb ore-forming fluids originated from deep magma or Devonian granite.

Based on the results of this study and the regional tectonic background of the area, a conceptual model suggests that the Shuangkoushan deposits underwent a two-stage mineralization process (Figure 11). Stage I: Subduction related Ordovician basaltic rocks with high background Au values underwent metamorphism and deformation during the syn-orogenic process. As a result, fluids were released through dehydration, extracting Au elements. The Au-bearing fluids ascended along faults. In the ductile to brittle–ductile transition zone, Au precipitated from the fluids and became enriched (Figure 11). Stage II: After regional metamorphism and deformation reached their peak, stress began to relax, leading to detachment along the fault zone. Deep crustal material underwent decompression and partial melting, generating an Ag–Pb-bearing magmatic melt that ascended along fault structures. Crystallization and differentiation occurred near the surface, filling tensile fractures that cut across the earlier Au ore body (Figure 11).