Source and Precipitation Process of Gold in the Linglong Gold Deposit, Jiaodong Peninsula: Constraints from Trace Elements of Pyrite and S-Pb Isotopes

Abstract

Jiaodong Gold Province is a globally rare giant gold cluster, with ongoing debates regarding its metallogenic material sources and mineralization mechanisms. This study focuses on the Linglong quartz-vein-type gold deposit within the Zhaoping Fault Zone, conducting in situ trace element and S-Pb isotope analyses of pyrite from different mineralization stages. The trace element characteristics were investigated to explore the sources of metallogenic materials, the evolution of ore-forming fluids, and the mechanisms of gold precipitation. The main findings are as follows: (1) In the Linglong gold deposit, gold primarily enters the pyrite lattice as a solid solution (Au⁺) through Au-As coupling. From the Py1 to Py3 stages, Co and Ni contents significantly decrease, while Cu, As, Au, and polymetallic element contents continuously increase. Additionally, Cu mainly replaces Fe²⁺ in the form of Cu²⁺, whereas Pb predominantly exists as micro inclusions of galena. (2) The S isotope (Py1: δ³⁴S = +7.60‰–+8.25‰, Py2: δ³⁴S = +6.15‰–+8.15‰, Py3: δ³⁴S = +6.90‰–+9.10‰) and Pb isotope (²⁰⁶Pb/²⁰⁴Pb = 16.95–17.715, ²⁰⁷Pb/²⁰⁴Pb = 15.472–15.557, ²⁰⁸Pb/²⁰⁴Pb = 37.858–38.394) systems collectively constrain the ore-forming materials such that they are dominated by metasomatized enriched lithospheric mantle, with simultaneous mixing of crustal materials. (3) The ore-forming fluid underwent a continuous evolution process characterized by persistently decreasing temperatures and a transition from mantle-dominated to crust–mantle mixed sources. The Py1 stage was predominantly composed of mantle-derived magmatic fluids uncontaminated by crustal materials, representing a high-temperature, closed environment. In the Py2 stage, the fluid system transitioned to an open system with the incorporation of crustal materials. Through coupled substitution of “As³⁺ + Au⁺ → Fe²⁺” and dissolution–reprecipitation processes, gold was initially activated and enriched. During the Py3 stage, pyrite underwent dissolution–reprecipitation under tectonic stress and fluid activity, promoting extraordinary element enrichment and serving as the primary mechanism for gold precipitation. Concurrently, bismuth–tellurium melt interactions further facilitated the precipitation of gold minerals.

1. Introduction

The Jiaodong gold ore concentration area is located on the southeastern margin of the North China Craton, with proven gold resource reserves approaching 6000 tons, making it a rare giant gold province in China and even the world [1,2,3]. The Jiaodong region hosts dozens of large and super large gold deposits, along with over a hundred medium and small gold occurrences [4,5,6]. The gold deposits in this region are genetically distinct from typical orogenic or magmatic hydrothermal deposits, hence termed as “Jiaodong type” gold deposits [7,8].

Regarding the sources of the ore-forming fluids and materials, there are currently four main controversial models: (1) orogenic gold deposits, proposing that the ore-forming fluids were derived from metamorphic dehydration [9,10]; (2) magmatic hydrothermal gold deposits: emphasizing the contribution of Mesozoic granites [11]; (3) subducted slab metasomatized mantle type gold deposits (Jiaodong type gold deposits), suggesting that the ore-forming materials originated from the Paleo-Pacific slab and the overlying mantle wedge [12,13]; (4) craton destruction model gold deposits, attributing the mineralization to hydrous basaltic magmatism [14]. Although these models are based on different geological evidence and theoretical reasoning, no consensus has been reached yet.

As the primary gold-bearing mineral permeating the entire mineralization process in the Jiaodong gold deposits, pyrite often exhibits polygenerational characteristics. Its complex structure and internal variations in trace elements can effectively reflect the properties and evolutionary processes of ore-forming fluids, as well as the mechanisms of gold enrichment and precipitation [15,16,17]. Although previous studies have been conducted, particularly in situ elemental and isotopic research on pyrite in the Jiaodong gold deposits within the region, exploring the sources of ore-forming materials, mineralization processes, hydrothermal evolution, genesis of deposits, and influencing factors of gold enrichment and mineralization [18,19,20,21,22,23], there remains a lack of unified understanding regarding the regularities of the mineralization system.

The Linglong gold deposit, a typical quartz-vein type, is located in the Zhaoping fault zone of the northwestern Jiaodong ore concentration area. Its mineralization process involves four consecutive stages: Py1 (pyrite–sericite–quartz), Py2 (quartz–pyrite), Py3 (quartz–polymetallic sulfide), and quartz–carbonate. This study focuses on Py1-Py3 pyrites, conducting high-resolution in situ microanalysis to measure trace element contents. Combined with sulfur–lead isotopes, it investigates trace element occurrence/enrichment mechanisms, constrains ore-forming material sources and fluid evolution, and provides geochemical insights into deposit genesis.

2. Regional Geology

The Jiaodong region is located on the eastern side of the Tanlu Fault and the western side of the Pacific subduction zone. It is mainly composed of two tectonic units: the Sulu terrane in the east and the Jiaobei terrane in the west, with the Wulian–Qingdao–Yantai Fault serving as the suture zone (Figure 1A). The Sulu terrane is an ultra-high-pressure metamorphic belt, while the Jiaobei terrane is divided into the Jiaobei Uplift in the north and the Jiaolai Basin in the south [24]. Mesozoic tectonomagmatic activity was intense, with Late Jurassic and Early Cretaceous magmatism widespread, including granite bodies and intermediate basic dykes [25,26].

Jiaodong has widespread Precambrian basement metamorphic rocks, including the Neoarchean Jiaodong Group (TTG gneiss dominated) in the Jiaobei Block and Proterozoic Jingshan, Fenzishan, and Penglai Groups (metamorphic sedimentary rock dominated) (Figure 1B) [27,28]. Mesozoic large-scale gold mineralization made Jiaodong rich in gold resources [29,30,31].

The tectonic characteristics of Jiaodong are mainly manifested as regional fault structures, dominated by NE-NNE and NW-NNW trending structures. Among them, the NE-NNE trending faults consist of extensional faults, which have derived a series of secondary faults, and gold mineralization is mainly controlled by the NE-NNE trending faults [32]. Eastward from the Yishu Fault, the NE-NNE-trending Sanshandao, Jiaojia, and Zhaoping Faults occur sequentially. Widely developed NE structures, formed by Early Mesozoic North China–Yangtze plate collision, consist of metamorphic basement folds and secondary faults, with EW faults later reworked. As secondary faults of the Yishu Fault, NE-NNE faults (including west to east Sanshandao, Jiaojia, Zhaoyuan–Pingdu, and Muru Faults) control nearly all proven gold mineralization and have experienced multiple compression extension episodes.

Figure 1. (A) Simplified Tectonic Map of Jiaodong; (B) Simplified geological map of the Jiaodong area (after [33]).

Figure 1. (A) Simplified Tectonic Map of Jiaodong; (B) Simplified geological map of the Jiaodong area (after [33]).

Intrusive rocks are extensively developed in the area, primarily comprising three types of granite: the Linglong type, Guojialing type, and Aishan type [34]. Linglong-type granite is mainly composed of the Linglong biotite granite and the Luanjiahe monzogranite. It is developed between the Zhaoping Fault and the Jiaojia Fault and is widely exposed. Zircon U-Pb dating by LA-ICP-MS indicates that the Linglong-type granite formed mainly between 166 and 149 Ma [35]. Guojialing-type granite shows an intrusive contact relationship with the Neoarchean Jiaodong Group and the Linglong-type granite. It is generally distributed in the Shangzhuang and Guojialing areas of Zhaoyuan, with an overall nearly E-W trend [36]. Zircon U-Pb ages show its emplacement occurred between 133 and 126 Ma, formed by the partial melting of the Precambrian metamorphic basement of the lower crust [37]. Aishan-type granite is mainly exposed in eastern Jiaodong and consists of undeformed alkaline granites. Zircon U-Pb ages indicate that the Aishan-type granite was emplaced mainly between 120 and 108 Ma and has a crust–mantle mixed origin [38,39]. Mafic dikes are widely distributed but typically small in volume. Zircon U-Pb dating shows that these basaltic dikes were emplaced between 130 and 110 Ma, derived primarily from low-degree partial melting of the lithospheric mantle [40].

3. Deposit Geology

The Linglong gold deposit is located in the northwestern part of the Jiaodong Peninsula, along the northern segment of the Zhaoyuan–Pingdu Fault. The mining area spans from Dongfeng in the east to Oujiakuang in the west, and from Taishang in the south to Dazhuangzi in the north. With a prospective gold reserve exceeding 1000 tons, it ranks as a world-class super-large gold deposit. The main exposed strata in the mining area consist of the Neoarchean Jiaodong Group and the Cenozoic Quaternary System. Jiaodong Group is predominantly composed of amphibolites, biotite gneisses, and schists (Figure 2), which occur as relatively small-scale layered or lenticular bodies. From the Paleoproterozoic to the Early Paleozoic, the metamorphic and deformational processes underwent a complex evolution, transitioning from ductile shear zones to brittle fracture zones, and further to mylonitization.

The structural framework of the Linglong gold deposit is primarily controlled by regional faults. These faults have been superimposed and compounded during multiple tectonic movements, forming a series of secondary faults with varying scales and dense distribution. Gold mineralization is closely associated with these ore-controlling faults, and ore enrichment zones are typically located within fault zones or at their intersections. The emplacement of orebodies is mainly controlled by first-order faults, with second-order faults developed in their footwalls, including the ore-forming Potouqing Fault and the post-ore-forming Linglong Fault. The most developed secondary faults in the mining area are the northeast–north–northeast trending ones, which are relatively small in scale, mainly distributed on both sides of the first-order faults, and belong to ore-forming structures. Compared with other ore-controlling structures, this set of faults exhibits significant control and modification effects on gold mineralization, showing a zonal distribution in the central and eastern parts of the mining area.

Mesozoic magmatism is highly developed within the mining area. The Linglong-type, Guojialing-type, and Luanjiahe-type granites are the main ore-hosting rocks in this region, with the Linglong-type granite being dominant. According to previous studies, starting from the northwest of the Potouqing Fault, the lithology gradually transitions from intermediate to basic as the frequency of dark dikes increases [42]. In the Linglong gold deposit, dikes and ore bodies often exhibit similar temporal and spatial characteristics, suggesting they may be products of cogenetic differentiation.

The ore types in the Linglong gold deposit mainly include altered rock type and quartz-vein-type ores. Altered rock type ores are dominated by pyrite-sericite rock and pyrite-sericitized granite (Figure 3A), while quartz-vein-type ores are represented by quartz-pyrite veins and quartz–polymetallic sulfide veins (Figure 3B,C). The two ore types exhibit distinct structural characteristics: the former primarily shows disseminated or stockwork-disseminated structures, while the latter commonly develops veinlet and stockwork structures. In terms of mineral assemblages, they share similarities, with metallic minerals dominated by pyrite, accompanied by sulfides such as chalcopyrite, galena, and sphalerite (Figure 3D,E); gangue minerals mainly consist of quartz, sericite, and calcite. Ore textures are diverse, including euhedral–subhedral granular texture, cataclastic texture, and interstitial texture; ore structures mainly include massive, stockwork, and banded structures. Based on their occurrence, gold-bearing minerals are classified into three types: intergranular gold distributed between pyrite and other mineral grains, inclusion gold enclosed within sulfide crystals, and fracture gold filling in sulfide fractures (Figure 3G–I).

The Linglong gold deposit exhibits typical wall-rock alteration zoning, whose spatial distribution generally shows symmetry centered around ore veins. From the ore vein to the surrounding rocks on both sides, the alteration zones are sequentially: silicification zone, pyrite-sericite zone, pyrite-sericitized granite zone, potassic-altered granite zone, and finally transitioning to unaltered biotite granite. Among them, K-feldspathization is distributed in the outer distal wall rocks, formed earlier than the sericitization stage, and the intensity of potassic alteration gradually weakens with increasing distance from the main fault. In contrast, sericitization alteration is extremely developed in the deposit, mainly distributed in the area adjacent to the main fault, and is a product of early ore-forming hydrothermal processes.

Based on the orebody occurrence, ore mineral assemblage characteristics, wall-rock alteration features, and vein cross-cutting relationships, the metallogenic process of the Linglong gold deposit is divided into 4 stages (Figure 4).

Stage I (Pyrite–Sericite–Quartz Stage): The sericite–quartz rock or pyrite–sericite–quartz rock characterized by the mineral assemblage of pyrite + quartz + sericite forms the early stage of mineralization. Pyrite is mostly distributed in euhedral–subhedral granular texture with well-developed crystals. Quartz shows dynamic recrystallization, and some pyrite is stretched, indicating that this stage experienced ductile deformation.

Stage II (Quartz–Pyrite Stage): As the middle mineralization stage, it is characterized by smoky gray quartz and widely exposed quartz–pyrite veins. The mineral assemblage is dominated by quartz and pyrite, with a small amount of chalcopyrite. Pyrite is mostly distributed as medium-coarse-grained irregular massive aggregates, partially as subhedral crystals, and occasionally undergoes late dissolution and replacement. Quartz is mostly smoky gray, medium-fine-grained subhedral crystals.

Stage III (Quartz–Polymetallic Sulfide Stage): This is the middle-late mineralization stage and also the late stage of gold mineralization, characterized by the development of polymetallic sulfide veins and smoky gray quartz veins. The mineral assemblage includes grayish-white quartz, pyrite, chalcopyrite, galena, sphalerite, etc. Metallic sulfides such as pyrite occur as medium-fine-grained aggregates, often cutting through the earlier quartz veins to form massive or banded ores. Quartz is light grayish-white, medium-coarse-grained euhedral–anhedral crystals. Native gold is mainly developed in the interstices of pyrite crystals, coexisting with polymetallic sulfides, occurring as intercrystalline gold.

Stage IV (Quartz–Carbonate Stage): As the late mineralization stage, it is characterized by a large number of calcite veins and low-gold-bearing quartz, with low sulfide content and a small amount of pyrite. Almost no gold mineralization occurs in this stage.

4. Samples and Analytical Methods

4.1. LA-ICP-MS Analysis of Trace Elements in Pyrite

Trace element concentrations in pyrite were determined using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at the National Research Center of Geoanalysis of China.

The analyses were performed on an ICP-MS (Agilent Technologies, Inc., Santa Clara, CA, USA) equipped with a 193 nm ArF excimer laser ablation system (Fremont, CA, USA). Argon gas was used as the supplementary gas, which was mixed with the carrier gas via a T-junction before entering the ICP. High cleaning efficiency was achieved under high flow rates of He (0.9 L/min) and Ar (0.9 L/min). For each analysis, a homogeneous laser spot with a diameter of 30 μm was employed, operating at 7 Hz with an energy density of 2 J/cm², with a measurement duration of 20 s and a total run time of 40 s. Reference materials NIST 610 and NIST 612 were used as external standards to construct calibration curves (National Institute of Standards and Technology, Gaithersburg, MD, USA). Based on MASS-1 (USGS), the analytical error for trace elements in sulfide minerals was less than 30%. A set of standard samples was analyzed after every 10 sample spot analyses.

4.2. LA-MC-ICP-MS Analysis of Sulfur Isotopes in Pyrite

In situ sulfur isotope analysis of pyrite was conducted at the National Research Center for Geoanalysis of China. The pyrite samples selected for testing were derived from the polymetallic sulfide stage of the Linglong gold deposit. Through processing of the test data, sulfur isotope composition data and related parameters of sulfides in the minerals were obtained. The laser ablation system employed was an NWR 193 nanosecond laser (Fremont, CA, USA), and the analysis was performed using a multi-collector inductively coupled plasma mass spectrometer (Thermo Scientific NEPTUNE Plus MC-ICP-MS) manufactured by Thermo Fisher Scientific (Karlsruhe, Germany). Helium was used as the carrier gas during laser ablation with a flow rate of 600 mL/min. The analysis uses a single-point mode with laser conditions of a large beam spot (44 μm) and low frequency (2 Hz), and the laser energy density is fixed at 5 J/cm². The system is integrated with a signal smoothing device to ensure signal stability under low frequency [43]. The Neptune Plus mass spectrometer is equipped with 9 Faraday cups and adopts a medium resolution mode (approximately 7000) to eliminate the influence of interference peaks. It uses three Faraday cups (L3, C, and H3) to statically receive ³²S, ³³S, and ³⁴S signals simultaneously. A single data acquisition is set with an integration time of 0.131 s, and 200 sets of data are continuously acquired to form a complete signal sequence of approximately 27 s. In this study, laboratory standard samples were used, and the testing sequence of “Standard Substance–Sample–Standard Substance” (SSB) was adopted for cross-validation and data correction.

4.3. LA-MC-ICP-MS Analysis of Galena Pb Isotopes

In this study, in situ Pb isotope experiments were conducted using LA-MC-ICP-MS at the National Research Center for Geoanalysis of China. Samples were selected from gold-bearing quartz-vein ores of the Linglong gold deposit and subjected to pretreatment procedures including numbering and wiping. For in situ Pb isotope analysis, a femtosecond laser ablation system (ASIJ-200–343 nm, Applied Spectra Inc., West Sacramento, CA, USA) was employed with a spot diameter of 2 μm, laser ablation energy of 80%, and a 2 μm line scan mode, with an ablation duration of approximately 15 s. Analyses were performed using a multi-collector inductively coupled plasma mass spectrometer (Thermo Scientific NEPTUNE Plus MC-ICP-MS). To optimize analytical quality, signal smoothing technology and a mercury removal device were introduced in the experiment, which helps improve signal stability and testing accuracy, while reducing gas background noise and mercury interference in samples. The mass spectrometer is equipped with 9 Faraday cups, capable of simultaneously receiving lead isotope signals including ²⁰⁸Pb, ²⁰⁷Pb, ²⁰⁶Pb, and ²⁰⁴Pb, as well as signals of ²⁰⁵Tl, ²⁰³Tl, and ²⁰²Hg. A single-standard Tl solution introduced via Aridus II membrane desolvation technology is mixed with ablation-generated aerosols before entering the ICP, and the ²⁰⁵Tl/²⁰³Tl ratio is used for real-time mass fractionation correction of lead isotopes.

5. Results

5.1. Trace Element Characteristics of Pyrite

Fifty-seven pyrite grains were analyzed using LA-ICP-MS in this study, including 12 points for Py1, 20 for Py2, and 25 for Py3. The test data are presented in Supplementary Table S1. Based on the pyrite analysis results, trace element boxplots for the three types of pyrite were generated (Figure 5). Analytical results show that concentrations of elements such as Co, Ni, Cu, Zn, As, Te, Ag, Sb, Au, Bi, and Pb are generally above the detection limit, with only some data points falling below it.

The composition of Py1 shows relatively high concentrations of Co (median 137.87 ppm) and Ni (median 31.53 ppm), with Co/Ni ratios ranging from 0.57 to 17.19. Au concentrations range from 0.01 to 0.09 ppm, while As concentrations range from 0.77 to 66.28 ppm. The concentrations of Cu, Zn, Ag, Bi, and Pb are mostly less than 1 ppm. Compared with Py1, Py2 has significantly lower concentrations of Co (median 3.94 ppm) and Ni (median 19.51 ppm). Au concentrations in Py2 are less than 0.80 ppm, and the concentrations of As, Cu, Zn, Te, Ag, Bi, and Pb are all higher than those in Py1. Compared with Py1 and Py2, Py3 has relatively lower contents of Ni and Co. The gold concentrations in Py3 range from 0.01 to 6.52 ppm, and the concentrations of As, Cu, Zn, Te, Ag, Bi, and Pb are all higher than those in both Py1 and Py2.

5.2. Sulfur Isotope Characteristics

LA-MC–ICP–MS sulfur isotope analysis was conducted on pyrite from three mineralization stages of the Linglong gold deposit (

Table 1. ³⁴S values of three stages of pyrite in the Linglong gold deposit.

Sample	Analyzed Minerals (Stage)	δ34S (‰, VCDT)	2σ
19LL17-1	Pyrite (Py1)	+7.80	0.10
19LL17-2	Pyrite (Py1)	+7.75	0.09
19LL17-3	Pyrite (Py1)	+8.10	0.14
19LL17-4	Pyrite (Py1)	+8.25	0.08
19LL37-1	Pyrite (Py1)	+7.70	0.11
19LL37-2	Pyrite (Py1)	+7.60	0.10
D007B1-1	Pyrite (Py2)	+8.15	0.13
D007B1-2	Pyrite (Py2)	+7.90	0.09
D007B1-3	Pyrite (Py2)	+8.05	0.08
D007B4-1	Pyrite (Py2)	+7.25	0.14
D007B4-2	Pyrite (Py2)	+7.55	0.10
D007B4-3	Pyrite (Py2)	+6.40	0.07
D012B1-1	Pyrite (Py2)	+6.15	0.11
D012B1-2	Pyrite (Py2)	+6.70	0.09
670-B1-3-1	Pyrite (Py3)	+8.21	0.10
670-B1-3-2	Pyrite (Py3)	+7.64	0.09
670-B1-3-3	Pyrite (Py3)	+7.37	0.14
670-B3-1	Pyrite (Py3)	+6.90	0.08
670-B3-2	Pyrite (Py3)	+8.40	0.11
670-B3-3	Pyrite (Py3)	+7.88	0.09
670-B3-4	Pyrite (Py3)	+8.10	0.10
670-B3-5	Pyrite (Py3)	+7.90	0.27
670-B4-1	Pyrite (Py3)	+7.30	0.08
670-B4-2	Pyrite (Py3)	+9.10	0.09

). The results show a range of δ³⁴S values from +6.15‰ to +9.10‰. The δ³⁴S values of Py1 stage pyrite range from +7.60‰ to +8.25‰, with an average of +7.9‰ (6 measurement points). The δ³⁴S values of Py2 stage pyrite range from +6.15‰ to +8.15‰, with an average of +7.3‰ (8 measurement points). The δ³⁴S values of Py3 stage pyrite range from +6.90‰ to +9.10‰, with an average of +7.9‰ (10 measurement points).

5.3. Lead Isotope Characteristics

Pb isotope test results and previous research data are shown in Supplementary Table S3. The ²⁰⁶Pb/²⁰⁴Pb ratios range from 16.95 to 17.715, with an average of 17.268 and a range of 0.765; ²⁰⁷Pb/²⁰⁴Pb ratios range from 15.472 to 15.557, with an average of 15.500 and a range of 0.085; ²⁰⁸Pb/²⁰⁴Pb ratios range from 37.858 to 38.394, with an average of 38.067 and a range of 0.536. The μ values (²³⁸U/²⁰⁴Pb) range from 9.38 to 9.54, which are higher than the μ values of normal lead (8.686–9.238); the ω values (²³²Th/²⁰⁴Pb) range from 39.73 to 45.13, exceeding the ω values of normal lead (35.55 ± 0.59); Th/U ratios range from 4.06 to 4.58, indicating relative enrichment of thorium-lead in this mining area. From the early mineralization stage to the main mineralization stage, the values of ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb all reach their maximum values during the main mineralization stage, suggesting possible contamination by highly radiogenic lead in the main mineralization stage.

6. Discussion

6.1. Occurrence State of Trace Elements in Pyrite

Trace elements in sulfides primarily occur in three forms: (1) solid solutions entering the crystal lattice through isomorphism; (2) nanoscale mineral inclusions; (3) microscale mineral inclusions [44]. Among these, isomorphic substitution is a universal mechanism for the occurrence of trace elements and serves as a carrier for numerous trace elements [45]. Correlation analysis of trace elements can effectively distinguish their occurrence forms [46].

The chemical properties of gold indicate that under hydrothermal conditions, it mainly exists in pyrite as solid solution gold (Au⁺) and nanoparticulate gold (Au⁰). Au⁺ most likely enters pyrite lattices through Au-As coupling, involving the chemical process:

Fe(S,As)₂ + 2Au(HS)⁰ → Fe(S,As)₂ + Au₂S + H₂S

During this process, As substitutes for S, distorting the pyrite lattice and allowing Au⁺ to enter [47]. Reich defined the solubility curve of solid solution Au in As-bearing pyrite [48]. In the Au-As binary diagram (Figure 6a), points above the gold solubility curve represent Au present as nanoscale gold minerals, whereas points below the curve indicate Au in solid solution form. All Au-As data points of pyrite from the Linglong gold deposit fall below the gold solubility curve, demonstrating that Au primarily exists in solid solution form. Au and As show no clear correlation in Py1, but exhibit a significant positive correlation in Py2 and Py3, indicating distinct coupling behaviors between Au and As during different mineralization stages.

In the Au-Ag binary diagram (Figure 6b), the data points exhibit a scattered distribution, suggesting possible variations in the occurrence forms of Ag across different mineralization stages. During the early mineralization stage (Py1), Ag content is relatively low and shows no clear correlation with Au, whereas in the later mineralization stages (Py2 and Py3), the correlation between Ag and Au becomes more pronounced.

Au shows no significant correlation with Sb in the three stages of pyrite (Figure 6c), indicating that the occurrence mechanism of Sb in pyrite differs from that of Au. Its enrichment may be influenced by changes in the redox conditions or pH of the fluids. Furthermore, Sb is more likely to exist as independent mineral phases rather than entering the pyrite lattice through isomorphic substitution.

In hydrothermal gold deposits, bismuth-chalcogen compounds (primarily S and Te) are often closely associated with gold [49,50]. In the Au-Bi and Au-Te binary diagrams (Figure 6d,e), the positive correlations in the Py2 and Py3 stages indicate a closer association of gold with bismuth and tellurium.

The occurrence mechanism of Cu in pyrite is jointly controlled by the redox state of ore-forming fluids and the Cu/Au ratio. In a strongly oxidizing environment, when the Cu/Au ratio is close to 1, Cu typically replaces Fe²⁺ in the crystal lattice in the form of [Au³⁺ + Cu⁺] complexes; when the system is under reducing conditions and the Cu/Au ratio is significantly higher than 1 (usually ranging from 1 to 100), Cu elements directly replace Fe²⁺ in the pyrite crystal lattice in the form of Cu²⁺ single ions [45]. Determination of fluid inclusions has shown that the ore-forming fluid of the Linglong gold deposit is in a reducing environment [51]. Combined with the characteristic that the Cu/Au ratios of pyrite in all three stages are greater than 1 (Figure 6f), it can be inferred that the copper in pyrite in the study area is mainly derived from the direct lattice replacement of Fe²⁺ by Cu²⁺.

The ionic radius of Pb²⁺ is 1.19Å, and that of Fe²⁺ is 0.74Å [52]. Therefore, without a specific crystal chemical environment, Pb is difficult to enter the pyrite lattice and often occurs in pyrite as lead-bearing mineral inclusions [53]. Pb has a high positive correlation with Ag and Bi (Figure 7a,b), indicating that Pb may occur in pyrite as galena inclusions.

6.2. Sources of Ore-Forming Materials

Previous studies have proposed various genetic models for the sources of gold ore-forming materials in the Jiaodong Gold Province, including Archean metamorphic basement rocks, Mesozoic granites, the subducted Paleo-Pacific Plate and its overlying metasomatized mantle, mixed subducted continental crustal materials, or basic magmas derived from partial melting of metasomatized lithospheric mantle [54,55,56,57,58,59,60,61]. Based on S-Pb isotope geochemical data and combined with regional geological settings, this paper evaluates the above models and further investigates the most likely material source of gold deposits in the Jiaodong area.

The migration and precipitation of gold are closely related to hydrogen sulfide, while sulfur is generally preserved in deposits as metal sulfides. The δ³⁴S values are typically influenced by temperature, fO₂, and pH [62,63,64]. Thermodynamic simulations of equilibrium sulfur isotope fractionation show that no significant sulfur isotope fractionation occurs between sulfides and fluids when the temperature drops to 300–250 °C, oxygen fugacity is under pyrite-pyrrhotite buffer conditions, and pH ranges from 3 to 4 [65]. For the Linglong gold deposit, the temperature during the main metallogenic stage ranges from 250 to 300 °C, with metallic sulfides mainly including pyrite, pyrrhotite, sphalerite, chalcopyrite, and galena, and pH ranging from 3 to 5 [66]. Thus, the sulfur isotope characteristics of sulfides can reflect the sulfur isotope composition of ore-forming fluids [66,67].

The δ³⁴S values of various mineralization types in the different gold metallogenic belts of the Jiaodong gold deposits exhibit generally consistent, high values (Figure 8, Supplementary Table S2, Zhaoping belt: δ³⁴S = +3.50‰–+9.10‰; Qixia belt: δ³⁴S = +4.40‰–+8.80‰; Muru belt: δ³⁴S = +3.50‰–+13.00‰; Jiaojia belt: δ³⁴S = +5.30‰–+12.72‰; Sanshandao belt: δ³⁴S = +4.67‰–+12.60‰). These values overlap with the δ³⁴S ranges of the main host rocks (Mesozoic granites and Precambrian metamorphic rocks) and intermediate-mafic dikes in the Jiaodong gold deposits (Figure 8, Supplementary Table S2, Mesozoic granites: δ³⁴S = +3.4‰–+9.9‰; intermediate-basic dikes: δ³⁴S = +3.4‰–+9.4‰). The Jiaodong Group metamorphic rocks cannot be the source layer for the mineralization. The metamorphism of the Jiaodong Group metamorphic rocks occurred nearly 2 billion years earlier than the mineralization event, and the water and related ore-forming elements within them had already been released through intense metamorphic dehydration and devolatilization. Furthermore, more compelling evidence comes from multiple sulfur isotope studies, which reveal that the ore-related pyrites in Jiaodong exhibit relatively constant Δ³³S values (approximately 0‰), with no signals of mass-independent fractionation of sulfur detected [55]. Therefore, the sulfur could not have been derived from the Archean metamorphic basement, also ruling out Mesozoic granites formed by the remelting of the Archean metamorphic basement as a source.

The δ³⁴S values of pyrite from the Linglong gold deposit overlap with those of intermediate-mafic dikes, and some orebodies of the Linglong gold deposit occur within or are distributed on both sides of lamprophyre dikes, suggesting a potential deep-seated connection between them. However, compared to the volume of gold orebodies, mafic dikes are relatively limited and are more likely to act as carriers rather than sources of the ore-forming materials. The δ³⁴S values of sulfur derived from the upper mantle are typically concentrated around 0 ± 3‰, which is significantly lower than the δ³⁴S values of the various metallogenic belts [68]. Therefore, the upper mantle cannot be the source of the ore-forming materials. The high δ³⁴S values of pyrite from the mineralization stage of the Linglong gold deposit may result from the mixing of seawater or magma oxidation. However, there is no evidence of marine sedimentation from the Paleozoic to Mesozoic on the Jiaodong Peninsula [69]. Even with appropriate consideration of sulfur isotope fractionation related to transport, the formation of the Linglong gold deposit still requires a sulfur source with relatively high δ³⁴S values. A comparison of sulfur isotope data among the Jiaodong gold deposits, seawater sulfate, and global sedimentary-orogenic gold deposits shows that the δ³⁴S values of pyrite from the Linglong gold deposit are much higher than those of global sedimentary-orogenic gold deposits from the Jurassic to Early Cretaceous (Figure 8). Thus, it is not the reduced sulfide from seawater sulfate in the sediments of the Mesozoic Paleo-Pacific Plate subduction that provided the high δ³⁴S fluids. This effectively negates the direct derivation of sulfur and associated gold from the Paleo-Pacific subduction system.

Figure 8. δ³⁴S values of sulfur isotopes in Jiaodong granites, metamorphic rocks, mafic dykes, and gold ores, as well as sulfur isotope compositions of sulfides in global sedimentary-orogenic gold deposits, in relation to geological ages based on temporal variations in marine sulfate curves (The sulfur isotope data are cited from the references in Liang et al. (2023) [66], Mao et al. (2005) [70], Zhu et al. (2019) [71], Yuan et al. (2019) [72], Xue et al. (2018) [73], Chen et al. (2010) [74], Yang et al. (2010) [75], Mills et al. (2015) [69], Li et al. (2015) [76], Liu et al. (2019) [77], Guo et al. (2009) [78], Feng et al. (2018, 2019) [79,80], Wang et al. (2013) [81], Zhang et al. (2014) [82], Huang (1994) [83] and Deng et al. (2020) [56]. For detailed data, please refer to Supplementary Table S2).

Figure 8. δ³⁴S values of sulfur isotopes in Jiaodong granites, metamorphic rocks, mafic dykes, and gold ores, as well as sulfur isotope compositions of sulfides in global sedimentary-orogenic gold deposits, in relation to geological ages based on temporal variations in marine sulfate curves (The sulfur isotope data are cited from the references in Liang et al. (2023) [66], Mao et al. (2005) [70], Zhu et al. (2019) [71], Yuan et al. (2019) [72], Xue et al. (2018) [73], Chen et al. (2010) [74], Yang et al. (2010) [75], Mills et al. (2015) [69], Li et al. (2015) [76], Liu et al. (2019) [77], Guo et al. (2009) [78], Feng et al. (2018, 2019) [79,80], Wang et al. (2013) [81], Zhang et al. (2014) [82], Huang (1994) [83] and Deng et al. (2020) [56]. For detailed data, please refer to Supplementary Table S2).

The high δ³⁴S values of auriferous pyrite require anomalously heavy sulfur source regions. Qiu et al. proposed that fluids, gold, and most sulfur were derived from the devolatilization of the Mesozoic westward-subducting Paleo-Pacific Plate and overlying sediments [55]. Subduction-related metamorphism induces the decomposition of pyrite into pyrrhotite, releasing H₂S and Au into the generated fluids. Plate-derived fluids metasomatize the overlying mantle, enriching volatiles including S and Au while preserving crustal δ³⁴S signatures. Deng et al. found that the δ³⁴S values of the Jiaodong gold deposits overlap with those of global Proterozoic sedimentary-orogenic gold deposits [56]. In the Late Neoproterozoic sedimentary rocks of the Yangtze Craton, diagenetic pyrite—dominantly hosted in black shales and carbonates—exhibits anomalously high δ³⁴S values. Globally, Au-rich diagenetic pyrite in Neoproterozoic sedimentary rocks constitutes an important source of gold and sulfur for orogenic gold deposits. Neoproterozoic rocks from the northern Yangtze Craton were subducted beneath the North China Craton; devolatilization of these rocks likely caused metasomatic enrichment of the mantle lithosphere, and the mixing of sedimentary heavy sulfur with mantle sulfur explains the δ³⁴S values of pyrite in the Jiaodong gold deposits. Thus, the metasomatically enriched lithospheric mantle represents a relatively reliable source of S, while the incorporation of crust-derived S information adds complexity to the interpretation of ore-forming material sources.

In addition, as shown in Figure 8, the overall distribution range of δ³⁴S values of pyrite from the three metallogenic stages is relatively narrow. The Py2 and Py3 stages exhibit the minimum and maximum values, respectively, while the Py1 stage lies between the two. The narrow distribution of δ³⁴S values suggests that the sulfur source of the ore-forming fluids maintained high consistency throughout the metallogenic process, which is mainly derived from the enriched metasomatized lithospheric mantle. The extreme values in the Py2 and Py3 stages may reflect minor material exchange between fluids and crustal materials during the middle to late metallogenic stages. Such minor fluctuations have not altered the dominance of the overall sulfur source, but rather indicate that the incorporation of crustal sulfur might be a gradual process, slightly intensified in the late metallogenic stage.

Lead isotopes are well-studied tools for tracing ore sources, mantle–crust interactions, and deposit genesis [84]. Their composition remains stable during physical/chemical processes (except radioactive decay or mixing), making them reliable for tracking material sources. However, low-salinity ore-forming fluids carry limited lead, which can be overwhelmed by other sources during migration, potentially complicating interpretations [56].

Linglong gold deposit lead isotopes show concentrated ratios, with rare outliers likely from radiogenic Pb contamination. Low μ (7.98–8.64) and ω (31.87–37.47) values indicate non-radiogenic Pb (

Table 2. Pb isotope data of ore galena from the Linglong gold deposit.

Sample	Analyzed Minerals	206Pb/204Pb	207Pb/204Pb	208Pb/204Pb	TCDT/Ma	μ	ω
670-B1-3-1	Galena	17.491	15.518	38.075	729	8.440	34.710
670-B1-3-2	Galena	17.494	15.518	38.078	727	8.450	34.720
670-B1-3-3	Galena	17.494	15.517	38.083	726	8.450	34.740
670-B1-3-4	Galena	17.492	15.516	38.080	726	8.440	34.730
670-B1-3-5	Galena	17.493	15.521	38.085	731	8.440	34.750
670-B1-3-6	Galena	17.492	15.518	38.083	728	8.440	34.740
670-B2-1-1	Galena	17.487	15.516	38.062	729	8.440	34.660
670-B2-1-2	Galena	17.493	15.520	38.083	730	8.440	34.740
670-B2-1-3	Galena	17.492	15.520	38.082	730	8.440	34.740
670-B2-1-4	Galena	17.490	15.517	38.080	728	8.440	34.730
670-B2-1-5	Galena	17.493	15.521	38.084	731	8.440	34.750
670-B2-1-6	Galena	17.495	15.519	38.084	727	8.450	34.750
670-B2-1-7	Galena	17.487	15.514	38.063	727	8.440	34.660
670-B2-1-8	Galena	17.495	15.519	38.077	727	8.450	34.720
670-B2-1-9	Galena	17.494	15.518	38.058	727	8.450	34.640
670-B2-1-10	Galena	17.494	15.518	38.087	727	8.450	34.760
670-B4-1-1	Galena	17.484	15.510	38.042	725	8.440	34.580
670-B4-1-2	Galena	17.494	15.516	38.085	724	8.450	34.750
670-B4-1-3	Galena	17.486	15.516	38.064	730	8.440	34.660
670-B4-1-4	Galena	17.495	15.518	38.083	726	8.450	34.740
670-B4-1-5	Galena	17.494	15.520	38.080	729	8.450	34.730
670-B4-1-6	Galena	17.495	15.519	38.085	727	8.450	34.750
670-B4-1-7	Galena	17.494	15.517	38.082	726	8.450	34.740
670-B4-1-8	Galena	17.238	15.472	37.883	857	8.180	33.930
670-B4-2-1	Galena	17.481	15.519	38.040	737	8.430	34.570
670-B4-2-2	Galena	17.206	15.448	37.829	853	8.150	33.720
670-B4-2-3	Galena	17.340	15.573	38.151	893	8.290	35.020
670-B4-2-4	Galena	17.270	15.442	37.808	801	8.210	33.630
670-B4-2-5	Galena	17.275	15.406	37.731	758	8.220	33.320
670-B4-2-6	Galena	17.203	15.430	37.751	836	8.150	33.400
670-B4-2-7	Galena	17.195	15.422	37.731	833	8.140	33.320
670-B5-1-1	Galena	17.379	15.588	38.271	882	8.330	35.500
670-B5-1-2	Galena	17.337	15.460	37.866	774	8.280	33.870
670-B5-1-3	Galena	17.267	15.446	37.785	808	8.210	33.540
670-B5-1-4	Galena	17.292	15.535	38.061	886	8.240	34.650
670-B5-1-5	Galena	17.233	15.500	38.008	890	8.180	34.440
670-B5-1-6	Galena	17.142	15.425	37.720	874	8.080	33.280
670-B5-1-7	Galena	17.274	15.548	38.154	912	8.220	35.030

), suggesting a mantle origin or minimal radiogenic Pb input. Single-stage model ages (652–940 Ma, avg. 804 Ma) predate host rock emplacement (166–149 Ma) and mineralization (120 Ma), but postdate Jiaodong Group protolith (3.4–2.6 Ga) and metamorphism (~1.8 Ga) [2,35,85]. This implies an ancient non-radiogenic Pb reservoir, not directly derived from host rocks or syn-mineral magmatism. Lead isotopes from Linglong and other Zhaoping Fault Zone deposits exhibit high-slope, mixed-source trends. Most data plot below the S-K 1975 curve and above the metasomatized lithospheric mantle (Figure 9), indicating a mixed source of crust and/or metasomatized lithospheric mantle.

In the ²⁰⁷Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb tectonic discrimination diagrams (Figure 10), the Pb isotopic composition of the Linglong deposit overlaps with most Jiaodong gold deposits, Precambrian metamorphic rocks, and the Early Cretaceous Guojialing granite (with crust–mantle mixed sources). Significant overlap also occurs with the Late Jurassic Linglong granite (derived from ancient lower crust remelting) and Early Cretaceous mafic dikes (from enriched lithospheric mantle melting). This indicates a potential genetic link between Linglong, other Zhaoping Fault Zone deposits, and these geological units. The Pb isotopic data plot between the lower crust and orogenic belt fields, closer to the lower crust. However, the extensive overlap makes pinpointing the ultimate Pb source ambiguous.

6.3. Evolution of Ore-Forming Fluids and Mechanism of Gold Precipitation

As the main gold-bearing mineral throughout the entire mineralization process in the Jiaodong gold deposits, the multi-generational structure and trace element composition of pyrite directly record the evolution of ore-forming fluid properties, mineralization processes, and gold precipitation mechanisms [18,93,94,95,96]. Both Co and Ni are siderophile elements that can replace Fe through isomorphism, so the Co/Ni ratio can indicate changes in ore-forming conditions [97]. Generally, a smaller Co/Ni ratio represents a lower formation temperature of pyrite [98,99]. Pyrites of different genetic types show significant differences in Co/Ni ratios: those of sedimentary origin are usually less than 1 [100], while those of magmatic-hydrothermal origin are generally greater than 1 [98,101,102]. The Co/Ni ratios of the Py1 stage are basically greater than 1, whereas 78% of the Co/Ni ratios in the Py2 and Py3 stages are less than 1 (Figure 7c; Supplementary Table S1), indicating that the ore-forming fluid underwent a temperature-decreasing process from the Py1 to Py3 stages.

Pyrite in the Py1 stage occurs as euhedral–subhedral granular crystals (Figure 3D) with smooth crystal surfaces, showing stable crystallization characteristics of a magmatic-hydrothermal system. Its high Co and Ni contents and Co/Ni ratio (>1) are consistent with the characteristics of pyrite in mantle-derived magmatic-hydrothermal deposits. Combined with the relatively low contents of Cu, Zn, and As, it indicates that the primary fluid in the early mineralization stage may have been dominated by mantle-derived magmatic fluid, uncontaminated by crustal materials [103]. The low Au (<0.09 ppm) and As (<66.28 ppm) contents and the absence of Au-As correlation (Figure 6a) suggest that Au mainly entered the crystal lattice as a dispersed solid solution (Au⁺) without significant precipitation and enrichment [48]. At this time, the fluid had a high temperature and stable chemical composition, belonging to a stable and closed ore-forming environment.

Pyrite in the Py2 stage develops obvious dissolution textures at the edges (Figure 3E). Intermittent fluctuations in fluid composition caused by multiple hydrothermal events generally lead to stage-wise precipitation of pyrite, accompanied by irregular boundaries and corrosion structures between alternating zones, indicating the reworking characteristics of dissolution-reprecipitation of early crystals by fluids [104]. In this stage, Co and Ni contents are significantly lower than those in Py1, with most Co/Ni ratios less than 1, while the contents of Cu, Zn, As, Te, Ag, Au, Bi, and Pb are significantly higher than those in Py1. This reflects a decreased proportion of mantle-derived fluid, a transition of the fluid system from closed to open, and the leaching and mixing of crustal materials, which diluted the mantle-derived signal [103]. The increased As content may be attributed to As in sedimentary rocks being released through fluid leaching and enriched in pyrite. Due to the larger ionic radius of As compared to S and Fe, the crystal lattice of As-rich pyrite exhibits obvious distortion. As³⁺ enters the pyrite lattice through the coupling mechanism of “As³⁺ + Au⁺ → Fe²⁺”, forming an “arsenic-bearing gold-pyrite” solid solution. While promoting elements such as Au to enter the pyrite lattice, it also facilitates dissolution-reprecipitation by late-stage fluids [105], thereby leading to the activation, migration, enrichment, and precipitation of Au [106,107].

Pyrite in the Py3 stage is characterized by fracture-filling and porous textures, with native gold and metal sulfides commonly filling the fractures, showing typical features of dissolution-reprecipitation [108]. At this stage, the contents of Cu, Zn, Au, and Ag in pyrite reach their peak values. Under tectonic stress, dislocation slip and creep of pyrite create a relatively open space at the interface between dislocated and undislocated areas in pyrite crystals, which is the most favorable site for Au activation and re-enrichment [105]. Invisible gold and other trace elements fixed inside pyrite can be reactivated during late metamorphic-deformation processes and/or water-rock reactions and reprecipitated at the grain edges or microfractures of pyrite [93]. The brittle fracturing may be caused by the accumulation of dislocation sliding, indicating characteristics of low-temperature deformation [109], which is consistent with the trend of gradual temperature decrease in the ore-forming fluid. The porous and fracture-filling textures formed by pyrite dissolution-reprecipitation are direct products of the transformation of ore-forming fluid from the “migration stage” to the “precipitation stage” and are also the controlling factors for the peak contents of elements such as Au, Cu, Zn, and Ag. By expanding fluid–mineral interaction interfaces, providing precipitation space, and responding to abrupt changes in fluid physicochemical conditions, they synergistically promote the super-enrichment of elements. Notably, the relatively significant enrichment of Te and Bi suggests the possible existence of local melt–fluid interaction. The presence of bismuth–tellurium melt not only provides an important transport carrier for gold but also promotes gold precipitation from hydrothermal fluids by forming stable gold–tellurium compounds (such as tellurobismuthite) [49,50,110].

7. Conclusions

(1)

Trace elements in pyrite show systematic variations across mineralization stages (Py1 → Py3), marked by decreasing Co and Ni and increasing Au, As, Cu, Pb, Zn, Bi, and Te. These trends reflect the continuous evolution of the ore-forming fluids. The early stage (Py1) involved high-temperature, reduced fluids dominated by mantle sources, representing a phase of gold pre-enrichment. During the main ore-forming stages (Py2–Py3), fluid temperature decreased, incorporation of crustal material increased, and water–rock reactions intensified. Gold precipitation was governed by two principal mechanisms: in Py2, Au⁺ coupled with As³⁺ and entered the pyrite lattice as a solid solution; in Py3, fluid immiscibility broke down gold complexes, while Bi–Te melts or complexes promoted further gold enrichment and the formation of visible gold.

(2)

The S isotope characteristics indicate that sulfur is mainly derived from fluids released by dehydration of the Paleo-Pacific Plate during subduction, and these fluids have metasomatized the overlying lithospheric mantle. The Pb isotope characteristics reflect the ore-forming fluid mixed with crust-derived materials during its ascent. The S-Pb isotope system jointly constrains that the ore-forming materials are mainly derived from the metasomatized lithospheric mantle, with the involvement of crustal materials.

(3)

The ore-forming fluid underwent a continuous evolutionary process from early high-temperature, mantle-derived dominance to late low-temperature, crustal-derived mixing. The Py1 stage was dominated by mantle-derived magmatic fluids that were not contaminated by crustal materials. The Py2 stage was accompanied by the incorporation of crustal materials and an increase in As content, triggering the coupled substitution of “As³⁺ + Au⁺ → Fe²⁺” and dissolution–reprecipitation, which promoted the initial activation and enrichment of gold. In the Py3 stage, dissolution–reprecipitation occurred in a low-temperature, open environment, forming fractures and porous structures that facilitated the supernormal enrichment of elements, representing the main mechanism for gold precipitation. Local bismuth–tellurium melt also contributed to gold precipitation.