Geochemistry of sulfide in mafic enclaves from Gushan granite: Implications for the role of contemporaneous mafic magma in the genesis of the large-scale Jiaodong gold province, eastern China

The Jiaodong gold province, located on the eastern side of the North China Craton, is the largest gold producer in China (Deng et al., 2020c). This region hosts many world-class gold deposits that generate around a quarter of the country’s gold supply (Wen et al., 2015). The proven reserves and potential resources in gold are estimated at over 2000 t and 5000 t, respectively (Deng et al., 2020c; Song et al., 2023b), and these large gold deposits were principally emplaced in a short time at ca. 120 Ma (Zhang et al., 2020). For these reasons, several researchers have carried out meticulous investigations in the area that have attempted to constrain the genesis of the gold deposits, though this is still a subject of open debate (Goldfarb and Santosh, 2014).

Conflicting hypotheses on the source of the mineralizing materials have rapidly emerged as investigations have increased. The ore-forming fluid was attributed to meteoric water (Shen et al., 2004) or thought to originate from the Precambrian crustal basement (Zhai and Santosh, 2013). It was also regarded as magmatic, derived from partial melting of the continental crust, mainly due to the orebodies being hosted by the Mesozoic granitic rocks (Li et al., 2013b, 2015a), or from partial melting of the mantle, as lamprophyres and other mafic dikes occur nearby and overlap (at ca. 130–120 Ma) the gold mineralization (Tan et al., 2012; Li et al., 2016; Yao et al., 2021). However, most researchers agree that the ore-forming materials could be related to the subducted westward Paleo-Pacific oceanic slab and oceanic floor sedimentary accretions and/or to the metasomatized lithospheric mantle (Deng et al., 2020c). Yet, researchers have not reached a consensus on how the ore-forming materials responsible for the precipitation of the gold in the Jiaodong gold province were transported from the mantle to the upper crust. Some authors suggest that the ore-forming fluid was mainly transported by devolatilization through trans-lithospheric fault zones without magmatic contribution (Goldfarb and Groves, 2015; Goldfarb and Santosh, 2014; Deng et al., 2020b, 2020c; Wang et al., 2020a). Others point out that the extensive Mesozoic magmatic activity may have been the principal carrier of the ore-forming fluid and materials from deep sources to the shallower crustal levels where the gold precipitated (Zhu et al., 2015; Li et al., 2022).

Recent deep drilling projects in the Linglong gold field revealed a concealed mineralized mafic intrusion at ~2,000 m deep in the footwall of the Zhaoping fault, which is termed the Xiejia diorite intrusion (DI). The intrusion was dated at ca. 120 Ma (Shen et al., 2016; Yao et al., 2021; Li et al., 2022, 2023), which is contemporaneous with the large-scale gold mineralization in the Jiaodong peninsula. The mineralized dioritic intrusive shows distinctive hydrothermal features and disseminated sulfides, with average Au contents of 0.32 g/t and locally up to 7.59 g/t, which suggests a genetic relationship between magmatic hydrothermal fluids and mineralization (Li et al., 2023). Inspired by the discovery of the intrusion, multiple articles were published (Shen et al., 2016; Yao et al., 2021; Li et al., 2022, 2023). Common key points are: (1) the large-scale gold mineralization derived from the metasomatized mantle, and (2) alkalic mafic magma from the mantle, including lamprophyre, dolerite, and intermediate magma formed by magma mixing of the mantle and crust (diorite, monzonite, syenite, etc.), played a critical role by transporting gold from the mantle to shallow crust (Li et al., 2022, 2023). However, the few outcrops of mafic dikes marked by syn-gold mineralization suggest a small volume of mafic magma compared to what could have supplied gold materials in the region. Besides, only three drilling out of 27 planned encountered the Xiejia DI, which suggests that the intrusion is likely an apophysis or a large dike. Thus, focusing on rare mantle-derived intrusions seems inadequate for confirming the relationship between large-scale gold mineralization and deep-seated mafic magmatism. Instead, it is critical to consider other available proxies to clarify this issue. Accordingly, we shifted our view to another type of intrusion that is contemporaneous with the gold mineralization, experienced mantle-crustal magma mixing, and hosts numerous mafic microgranular enclaves (MMEs). These MMEs could be a new and more available proxy for providing insight into the relationship between large-scale gold mineralization and mafic magma.

Gushan MMEs and their host granitic pluton are part of the Weideshan granitic suite. Previous studies of the granitic host and its MMEs have revealed that they formed through magma mixing and that the magma end-members involved are the metasomatized mantle and the ancient continental crust (Li et al., 2012; Koua et al., 2022). Geochemical analysis and petrological observations show that Gushan MMEs are enriched in water, volatiles, and ore-forming materials (Koua et al., 2022). Contrary to other MMEs in the region, Gushan MMEs have the advantage of containing measurable sulfide phases and, more importantly, being contemporaneous with large-scale gold mineralization. Thus, Gushan MMEs appear to be a valuable tool for investigating the implication of syn-gold mineralization of mafic magma in generating large-scale gold deposits.

In this study, data from laser ablation–inductively coupled plasma–mass spectrometric (LA-ICP-MS) trace elements and sulfur isotope analyses conducted on pyrites hosted in the Gushan MMEs were used to constrain the origin of the pyrites. Additionally, zircon U-Pb and molybdenite Re-Os isotopes were applied to quartz-molybdenite veins hosted by Gushan granite to constrain the timing of the hydrothermal event. The new geochemical and isotope data are compared with data from the contemporaneous gold-mineralized Xiejia DI to evaluate the role of syn-gold mineralization of mafic magma in generating large-scale gold deposits.

The Jiaodong gold province is situated at the boundary between the North China Craton and the Yangtze Craton, limited to the west by the Tan-Lu fault, to the north by the Bohai Basin, and adjacent to the Yellow Sea (Fig. 1). The NE-trending Wulian-Qingdao-Yantai fault separates the province into two Precambrian tectonic units: the Sulu orogenic belt in the southeast and the Jiaobei Terrane in the northwest. The former is an ultrahigh-pressure (UHP) metamorphic complex comprising Neoproterozoic granitic gneisses with secondary coesite-bearing eclogites, quartzite, and schist (Zhang, 2012). The Jiaobei Terrane, with a Precambrian metamorphic basement intruded by voluminous Mesozoic igneous and volcanic rocks (Zhang, 2012), comprises the Jiao-Lai Basin in the south and the Jiaobei Uplift in the north. The Jiaobei Uplift hosts ~90% of the proven gold resources and contains the largest gold deposits, mainly in the Jiaojia, Linglong, and Sanshandao gold fields (Fig. 2). The Jiao-Lai Basin was described as a Cretaceous pull-apart basin that consists of the mid–Early Cretaceous Laiyang Group, late Early Cretaceous Qingshan Group, and Late Cretaceous Wangshi Group (Tang et al., 2008).

The Mesozoic rocks are extensively distributed in the Jiaodong gold province and formed within the Late Triassic, the Late Jurassic, and the Early Cretaceous (Fig. 1). The Late Triassic syenites and mafic dikes were derived from the ancient and re-enriched lithospheric mantle (Gao et al., 2004; Yang and Wu, 2009) and are considered to be the result of collision/subduction of the Yangtze Craton beneath the lithosphere of the North China Craton at ca. 230–205 Ma (Yang et al., 2007). The Late Jurassic granitoids intruded the Precambrian basement between ca. 160 Ma and 150 Ma throughout the Jiaodong peninsula and are represented by the Linglong and Luanjiahe granites and were sourced from the partial melting of thickened crust (Li et al., 2019b; Yang et al., 2012). The Early Cretaceous granitoids, dated at ca. 130–110 Ma, intruded the Precambrian basement and the Late Jurassic granitoids and are classified within two groups: i.e., the Guojialing suite (ca. 130–125 Ma), which is concentrated in a small area of the Jiaobei Uplift, and the Weideshan granitic suite (ca. 121–110 Ma), which is widespread from west to east in the peninsula, including in the Gushan granitic pluton (Fig. 1; Goss et al., 2010; Li et al., 2012, 2019b; Yang et al., 2012). The Weideshan granitic suite was generated by the partial melting of the ancient lower crust, and most of the plutons host MMEs, which indicates that they interacted with mantle-derived melts during their formation (Goss et al., 2010; Li et al., 2012; Yang et al., 2012; Koua et al., 2021, 2022). The Linglong biotite granite and, to a lesser extent, the Guojialing granodiorite, host gold mineralization. Lamprophyres and mafic dikes are widespread within the gold deposits and were emplaced at ca. 130–114 Ma (Cai et al., 2013; Deng et al., 2017).

Early Cretaceous mafic dike swarms (135–81 Ma; with an age peak at ca. 120 Ma) invade the Precambrian basement and the Mesozoic granitoid rocks in the Jiaodong peninsula. They strike NE-NNE and were emplaced within the NNE- and NE-trending extensional brittle structures and display an intimate relationship with the gold mineralization (Cai et al., 2013). Geochemical and isotope data revealed three types of mafic dikes: i.e., the low-TiO₂ island-arc basalt (IAB)–like mafic dikes, the high-Mg adakitic-like diorite dikes, and the high-TiO₂ oceanic-island basalt (OIB)–like mafic dikes. The low-TiO₂ IAB-like mafic dikes originated from the partial melting of the metasomatized ancient lithospheric mantle, while the high-Mg adakitic-like diorite dikes formed through magma mixing of the ancient continental crust and the lithospheric mantle; both were emplaced at ca. 135–120 Ma (Deng et al., 2017; Liu et al., 2018). The high-TiO₂ OIB-like mafic dikes formed at ca. 120–81 Ma and originated from decompressional melting of the lithospheric mantle with an asthenospheric upwelling (Cai et al., 2013; Zheng et al., 2018).

The Jiaodong gold province comprises several large to super-large gold deposits (more than 100 t to 50 t of gold) principally concentrated along the Zhaoyuan-Laizhou, Qixia-Yantai, and Rushan-Mouping gold belts (Fig. 1; Mao et al., 2008). The gold deposits have been termed “Jiaodong type” by Deng et al. (2015) and Li et al. (2015a), “decratonic gold deposits” by Zhu et al. (2015), and more recently, “Jiaodong-type orogenic gold deposits” by Deng et al. (2020c), to highlight the singularity of the Jiaodong gold province compared to other well-classified gold deposits worldwide (Goldfarb and Santosh, 2014). The gold mineralization was classified into three types: (1) the Linglong type, (2) the Jiaojia type, and (3) the altered breccia type. The third type is principally concentrated in the detachment faults close to the northeastern margin of the Jiao-Lai Basin (Fig. 1; Tan et al., 2012). The Linglong type occurs within variable quartz-sulfide lodes. In contrast, the Jiaojia type is disseminated within strongly altered fractured rocks or stockworks (Li et al., 2015a). The different precipitation types can be found within the same deposit and share common characteristics, which indicates that they formed through a unique process and had the same source (Goldfarb and Santosh, 2014; Li et al., 2015a, 2016). Previous studies have constrained the ages of the gold mineralization to ca. 135–100 Ma by using ⁴⁰Ar-³⁹Ar, U-Pb, Rb-Sr, and Re-Os dating methods (Cai et al., 2018; Li et al., 2019a; Feng et al., 2020), and the peak of the mineralization is clustered at 120 ± 3 Ma (Li et al., 2015a; Deng et al., 2020c; Zhang et al., 2020). The Jiaodong gold province is structurally controlled by widely developed NNE-NE–trending regional faults and their secondary faults, which are the principal channels for the flow of magmas and fluids (Li et al., 2015a; Groves and Santosh, 2016; Zhang et al., 2020). Orebodies are concentrated along the faults, fractures, and hydrothermal alteration zones. The dip angles of these faults and fractures vary from the Linglong type (>60°) to the Jiaojia type (<45°). The NNE-NE–trending faults in the Jiaodong peninsula are the secondary faults of the Tan-Lu or Wulian-Yantai faults and formed through lithospheric extension related to the subduction and rollback of the Paleo-Pacific slab (Goldfarb and Santosh, 2014; Groves and Santosh, 2016; Zhu et al., 2015; Deng et al., 2020c).

The Linglong gold field is located at the northern section of the Zhaoping fault in the eastern part of the Jiaobei Uplift (Fig. 2) and covers an area of 70 km² for a total gold resource of ~1000 t. The site is structurally dominated by the northern segment of the Zhaoping fault, which is locally termed the Potouqing fault. This fault trends 50°–80°NE and dips 30°–40°SE (Guo et al., 2020). Linglong gold deposits are typically of the Linglong type as they host several auriferous quartz veins. Occasionally, they are associated with Jiaojia-type gold precipitation in local veins. The auriferous quartz veins occurred broadly parallel to the Potouqing fault along with barren intermediate to basic dikes and are exclusively hosted in the Late Jurassic Linglong biotite granite. Disseminated- and stockwork-style mineralization are generally sited in the Potouqing fault footwall, at the contact of the Late Jurassic Linglong biotite granite and Luanjiahe monzonitic granite, and in the footwall of the Jiuqu-Jiangjia fault. The general hydrothermal alteration is relatively weak in the wall rocks, notably around the auriferous quartz veins.

The Xiejia DI is a concealed intrusion that was revealed through three deep drill holes (72ZK1, 84ZK1, and 108ZK1) at ~2000 m (Fig. 3) in recent prospecting programs in the Linglong gold field (Shen et al., 2016). Drill hole 72ZK1 penetrated the intrusion from top to bottom, from 2080 m to 2193 m (Fig. 3B), 84ZK1 intersected the rock from 2332 m to 2390 m, while 108ZK1 traversed the concealed Xiejia DI from 2201 m to 2218 m. The drill-core samples are mainly biotite monzonite and monzodiorite, gray to dark gray, and medium- to fine-grained (Figs. 4A–4D). In general, the mineral assemblage comprises K-feldspar (35%–40%), plagioclase (20%–25%), biotite (15%–20%), quartz (5%–10%), and amphibole (<5%). Other accessory minerals comprise titanite, zircon, allanite, and apatite. Disseminated sulfides and magnetite are common, along with pervasive potassic alteration, silicification, and carbonatization in undeformed drill-core samples (Figs. 4E and 4F). Additionally, some samples contain explosive breccias, miarolitic cavities, skeletal and dendritic quartz, and aplite dikes, revealing a deuteric hydrothermal activity. The intrusion was primarily dated using a biotite Ar-Ar plateau age of 123 ± 1.5 Ma by Shen et al. (2016). More recently, magmatic and hydrothermal titanite LA-ICP-MS U-Pb ages of 120.7 ± 3.1 Ma, 120.9 ± 2.6 Ma, and 121.7 ± 3.9 Ma (Li et al., 2022, 2023) were obtained, as were magmatic zircon LA-ICP-MS U-Pb ages of 121.3 ± 0.9 Ma and 120.8 ± 1.1 Ma (Li et al., 2023). These dating measures confirm that the intrusion is contemporaneous with the large-scale gold mineralization. The Xiejia DI is metaluminous, high-K calc-alkaline, shoshonitic, enriched in light rare earth elements (LREE) and large ion lithophile elements (LILEs), depleted in high-field strength elements (HFSEs), and displays negative Nb, Ta, and Ti anomalies and enriched Sr-Nd-Hf isotope compositions (⁸⁷Sr/⁸⁶Sr = 0.707–0.708 and εNd(t) = −15.8 to −14; Yao et al., 2021; εHf(t) = −19.3 to −16.9; Li et al., 2023) identical to the contemporaneous Gushan MMEs and arc-like mafic dikes of the Jiaodong peninsula, which indicates that the Xiejia DI originated from the enriched lithospheric mantle (Yao et al., 2021). In situ laser ablation–multicollector–inductively coupled plasma–mass spectrometric (LA-MC-ICP-MS) sulfur isotope analyses on magmatic and hydrothermal pyrites from the Xiejia DI show a wide range of S-isotope composition (δ³⁴S_{Vienna-Canyon Diablo Troilite [V-CDT]}) values from −1.7‰ to 9.7‰, which overlap those measured for the Linglong gold deposits (Yao et al., 2021; Li et al., 2022, 2023), with the magmatic pyrites having the lowest δ³⁴S_V-CDT values and the hydrothermal pyrites having the highest δ³⁴S_V-CDT values (Li et al., 2022, 2023).

The Gushan granitic pluton is located ~20 km east of Laizhou city and ~35 km south of the Linglong gold field and intrudes the Late Jurassic Linglong suite over an exposed area of ~20 km² (Fig. 2). It is pale red to light gray in hand specimens and shows a porphyritic texture, with the mineral assemblage composed of K-feldspar, plagioclase, quartz, hornblende, and biotite. Accessory minerals are titanite, opaque oxides, zircon, and apatite. Gushan granite is the host of MMEs that are randomly distributed and represent <1% of the outcrop (Li et al., 2012). The MMEs are dioritic with globular and oval shapes and display fine- to medium-grained porphyritic textures (Figs. 5A and 5B). They contain more mafic minerals than their hosted granites and are composed of K-feldspar (30%–45%), plagioclase (30%–40%), hornblende (10%–20%), and biotite (5%–10%). Accessory minerals are clinopyroxene, opaque oxide, sulfide, titanite, zircon, and apatite. Phenocryst minerals are mainly hornblende and plagioclase with minor K-feldspar and biotite. Disequilibrium textures such as acicular apatite, plagioclase with reverse zoning and repeated resorption surfaces, and ocelli quartz (Figs. 5C–5E) are observed in the MMEs, which suggests that they formed through magma mixing (Koua et al., 2022). Most MME samples show alteration phenomena such as calcification carbonatization, chloritization, and kaolinization (Fig. 5F). Disseminated pyrite, chalcopyrite, magnetite, and ilmenite are well represented in the MMEs (Fig. 6). Furthermore, potassic alteration and several quartz-sulfide and quartz-molybdenite veins developed in the granite (Figs. 7A and 7B).

Gushan granite and its MMEs are comagmatic and were dated in our previous publications by LA-ICP-MS in situ zircon U-Pb isotope dating at 118.01 ± 0.34 Ma for the host rock and 120.38 ± 0.49 Ma for the MMEs (Koua et al., 2022). These ages are similar to those obtained earlier by Li et al. (2012). The MMEs and their host granite are metaluminous, high-K, I-type granitoids. They are enriched in LILEs (Rb, K, and Pb) and LREEs and depleted in HFSEs (e.g., Nb, Ta, P, and Ti). The host granite has high SiO₂ and lower MgO contents and originated from the reworking of ancient North China Craton lower crust (Li et al., 2012; Koua et al., 2022). The MMEs have low SiO₂ and high MgO, Ni, and Cr contents; their isotope compositions (I_sr = 0.710043–0.710243; εNd(t) = −18.8 to −18.6; εHf(t) = −19.4 to −7.13) are lower than those of the depleted mantle but similar to IAB-like mafic rocks from the enriched lithospheric mantle (Cai et al., 2013; Deng et al., 2017; Zheng et al., 2018), which indicates that they were derived from the enriched lithospheric mantle (Li et al., 2012; Koua et al., 2021).

Three representative samples of Gushan MMEs were collected in a stone pit, including GS-2, GS-6, and GS-4. Fresh to slightly altered samples from the Xiejia DI were collected in boreholes 72ZK1 (samples LJH-34, LJH-45, LJH-37, and LJH-62) and 84ZK1 (samples LJH-125 and LJH-130). Samples from quartz-sulfide veins developed in molybdenite-mineralized potassic granite were analyzed for pyrite trace elements (GS-10, GS-12, and GS-7) and molybdenite dating (GS-9 and GS-16). Two representative samples of molybdenite-mineralized potassic granites (GS-7 and GS-9) were analyzed for zircon U-Pb isotope dating.

Pyrites in Gushan MMEs are disseminated and represent the primary sulfide phase in the samples. They occur as isolated grains enclosed in amphibole, or in the interstices along the boundaries of amphibole grains, or in the matrix (Fig. 5C). The pyrite grains have an overall irregular shape and are fine-grained (~10–100 µm), with some microfractures and dissolution pits on their surfaces (Fig. 6A). Pyrite grains enclosed in amphibole have a size of between 10 μm and 60 μm (Fig. 5C); the interstitial pyrite grains and those in the matrix are between 10 μm and 100 μm (Figs. 5F and 6A–6D). Pyrite grains in the matrix are subhedral to euhedral and are usually associated with hydrothermal/alteration minerals, chlorite, epidote, carbonate, titanite, and magnetite (Figs. 6A–6D). Tiny grains of chalcopyrite and pyrrhotite occur at the contact with pyrite, or as inclusions through pyrite fractures or cavities, or as spots or droplets on the surface of the pyrite grains (Figs. 6D and 6E). Pyrite grains partly replaced by Fe-oxides (i.e., limonite overgrowths) are also observed in some samples (Figs. 6E and 6F), which suggests post-magmatic reactions. Due to the size of the laser ablation beam, only pyrites with a size/diameter of above 50 µm were considered for analysis.

No disseminated sulfide has been observed in the Gushan granite. However, numerous quartz-sulfide veins cross the rock (Figs. 7A and 7B). Pyrite dominates the sulfide phase in the quartz-pyrite veins, followed by chalcopyrite, sphalerite, and galena. Pyrite grains are subhedral and coarse-grained in the veins, with crystals that vary in size from large (500 µm) to huge (>500 µm; Fig. 7C). Brittle pyrites from dislocated crystals are also observed with angular shapes. The pyrites show numerous fractures and inclusions filled with quartz and chalcopyrite, and, on rare occasions, magnetite. Sphalerite and galena are less abundant and are intergrown with pyrite and chalcopyrite (Fig. 7D). Molybdenite was also observed and occurs as mineral aggregates in quartz veins (Fig. 7B). The morphology of the sulfides and their occurrences in quartz veins further suggest that they are hydrothermal sulfides.

Pyrites from the Xiejia DI represent the principal sulfide phase of the rock and are subhedral to anhedral and range from fine- to coarse-grained. They have varying sizes that can roughly be classified as small (≥50–100 µm), medium (100–500 µm), or coarse (≥500 µm; Fig. 8). They are disseminated in the interstices of the rock-forming minerals. Brittle pyrites from bigger, dislocated pyrites are also observed and have an angular shape. The pyrites show no systematic zoning, contain numerous inclusions of plagioclase and quartz in places, and are traversed by fractures (Figs. 8A and 8B). Minor chalcopyrite and pyrrhotite intergrew with the pyrites (Figs. 8C and 8F). Limonitites were also observed replacing the pyrite grains or overgrowing with them (Fig. 8E).

Re-Os isotope analyses were performed at the Laboratory for Sulfide and Source Rock Geochronology and Geochemistry at Durham University, UK. Molybdenite was dissolved and equilibrated with a mixed ¹⁸⁵Re and isotopically normal Os spike composition. The molybdenite preparation and separation for this work conformed to the existing protocols of Selby et al. (2007) and Li et al. (2017). The Re and Os isotope data were obtained by isotope dilution–negative thermal ionization mass spectrometry (ID-NTIMS; Creaser et al., 1991; Völkening et al., 1991). The average blanks were <3 pg for Re and <0.5 pg for ¹⁸⁷Os. The model age of the reference material Henderson molybdenite RM8599 was measured at 27.695 ± 0.038 Ma, consistent with the certified value of 27.66 ± 0.10 Ma (Markey et al., 2007; Zimmerman et al., 2014).

Two altered samples from molybdenite mineralized potassic granite were chosen for zircon U-Pb dating. Cathodoluminescence (CL) images were performed at Sample-Solution Analytical Technology Co., Ltd., Wuhan, China, using an Analytical Scanning Electron Microscope (JSM-IT100) and a GATAN MINICL system. Zircon U-Pb dating was conducted using LA-ICP-MS at the State Key Laboratory of Geological Processes and Mineral Resources (GPMR) of China University of Geosciences in Wuhan. Detailed operating conditions and data reduction were undertaken using methods described by Li et al. (2019a). Zircon 91500, GJ-1, Ple, and SRM610 were used as external standards. Zircon 91500 was analyzed twice for every five samples. Trace-element compositions of zircons were calibrated against multiple reference materials (BCR-2G and BIR-1G), combined with an internal standardization, ²⁹Si, to obtain the unknown trace element compositions. An uncertainty on entity analysis was recorded at the 1σ level, and the weighted mean ages for pooled U/Pb analyses are quoted at a 95% confidence interval. The data recorded were processed with ICPMSDataCal (Liu et al., 2010a). Concordia diagrams and estimations of weighted means were made with Isoplot (Ludwig, 2003).

LA-ICP-MS trace element analysis of sulfides was performed at the Wuhan Sample Solution Analytical Technology Co., Ltd. The process followed is identical to the process described by Zong et al. (2017). The sampling was conducted by a GeolasPro laser ablation system (COMPexPro 102 ArF excimer laser) coupled with a MicroLas optical system. The wavelength used was 193 nm, and the maximum energy was 200 mJ. The intensities of the ion signal were acquired by an Agilent 7700e ICP-MS. The spot size and frequency of the laser were set at 35 µm. The laser beam was fired at a 6 Hz repetition rate and 300 pulses. NIST 610 was chosen as the standard for calibrating the trace element compositions of pyrite, and no internal standards were used (Liu et al., 2008). The sulfide reference material MASS-1 (U.S. Geological Survey) was utilized as an unknown sample to validate the calibration method. Single-spot analysis included a background acquisition of ~20 s followed by 45 s of data acquisition from the samples. ICPMSDataCal 10.9 (Liu et al., 2010a) was used to process the raw data.

In situ sulfur isotope analyses of pyrite were performed at the State Key Laboratory for Geological Processes and Mineral Resources (GPMR) of China University of Geosciences using a Nu Plasma II multicollector–inductively coupled plasma–mass spectrometer (MC-ICP-MS) equipped with a Resonetics S155 193 nm ArF excimer laser ablation system. Helium served as a carrier gas in the laser ablation system and was mixed with argon in a cyclone coaxial mixer before insertion into the ICP torch. The laser ran with an energy of ~3 J/cm², and an integrating time of 1.023 s was set for the isotope. The laser spot’s diameter was calibrated at 33 μm with a repetition rate of 10 Hz and 40 s of ablation for each spot. ³⁴S/³²S analysis gave a precision rate of 3 × 10⁻⁵ (1δ). Standard sample bracketing (SSB) was used to determine the δ³⁴S_V-CDT = [(δ³⁴S = ((³⁴S/³²S)_sample / (³⁴S/³²S)_V-CDT) − 1)] × 10³ values of the samples throughout the MC-ICP-MS analytical sessions. (³⁴S/³²S)_sample is the measured ³⁴S/³²S in the sample, and (³⁴S/³²S)_V-CDT is defined as 0.044163 (Ding et al., 2001). International sphalerite, NBS-123 (sulfur isotopes in sphalerite; δ³⁴S_V-CDT = +17.1‰), and a local crystal of pyrite, WS-1 from the Wenshan polymetallic skarn deposit in the Yunnan Province of South China, served as standards and were employed to calibrate the mass bias for S isotopes. The δ³⁴S_V-CDT values (+1.1‰ ± 0.2‰) of WS-1 were determined by secondary ion mass spectrometry (SIMS) at the Chinese Academy of Geochemistry, Guangzhou, China. More details about WS-1 are available in Zhu et al. (2017). Standards were measured before and after every five-spot analysis to verify the accuracy of the calibration method. The true sulfur isotope ratios of unknown samples were calculated by correcting instrumental mass bias based on linear interpolation of two neighboring standards. The 2δ analytical error is estimated to be ± 0.3‰.

The Re-Os isotope compositions of two molybdenite samples hosted in potassic-altered Gushan granite are reported in Table 1. The Re and ¹⁸⁷Os concentrations of the molybdenite vary from 22.29 ppm to 23.32 ppm and 26.92–27.66 ppb, respectively. The Re-Os model ages of the two samples are 110.17 ± 0.6 Ma and 118.39 ± 0.5 Ma, respectively.

The results of U-Pb isotope dating of two altered samples from molybdenite-mineralized potassic granite are reported in Table 2 and Figure 9. Sixteen zircon grains from sample GS-9-1 yielded ²⁰⁶Pb/²³⁸U ages ranging from 126.71 Ma to 113.87 Ma, with a weighted mean age of 119.8 ± 2.1 (MSWD = 5.9). Nineteen U-Pb isotope analyses of sample GS-7-1 gave weighted mean ²⁰⁶Pb/²³⁸U ages ranging from 126.5 Ma to 112.3 Ma, with a weighted mean age of 119.4 ± 1.4 Ma (MSWD = 3.7).

LA-ICP-MS data for pyrite trace elements measured from Gushan MMEs (47 spots), quartz-sulfide veins (six spots), and the Xiejia DI (30 spots) are reported in Table 3 and Figure 10.

Generally, the concentrations of ore-forming metal components (Cu, Pb, Zn, Ag, and Au), siderophile (Co and Ni), and sulfophile (Se, Bi, and As) are below the detection limit, although some individual elements can be as high as hundreds of parts per million. The trace element compositions vary over several orders of magnitude. There is no systematic trace element difference between enclosed pyrite, interstitial pyrite, and pyrite in the matrix. Contents of Co and Ni are 5.8–8516 ppm (average 1306 ppm) and 23.2–2338 ppm (average 393 ppm), respectively. Sulfophile elements Se and Bi, and As compositions are below detection limit (b.d.l.) to 102 ppm, 0–12.84 ppm, and 0–667 ppm (average 59.6 ppm), respectively. The ores contain base metals. Cu is b.d.l. to 402 ppm, Pb is b.d.l. to 902 ppm, and Zn is b.d.l. to 109 ppm. Precious metals include Ag b.d.l. to 5.7 ppm and Au b.d.l. to 0.04 ppm, with one value (1.37 ppm) higher than the average.

Compared to Gushan MMEs, the pyrites here contain relatively low concentrations of Co (0.05–80 ppm), Ni (b.d.l. to 30.82 ppm), As (b.d.l. to 8.6 ppm; one value of 205.93 ppm is higher than average), Cu (0.28–21.64 ppm), Pb (0.08–7 ppm; one value of 145 ppm is higher than average), Zn (0.12–0.56 ppm), Ag (0–7 ppm), Bi (0–41.4 ppm), and Au (b.d.l. with one value at 0.07 ppm).

The pyrites contain higher concentrations of Co (7–1318 ppm, average 314.67 ppm) and Ni (1.6–1414 ppm, average 145.49 ppm), but lower concentrations of Cu (b.d.l. to 8.4 ppm), Zn (b.d.l. to 1.59 ppm), As (b.d.l. to 22.4 ppm), Ag (b.d.l. to 0.33 ppm), Sb (b.d.l. to 0.67 ppm), Au (b.d.l. to 0.04 ppm, with one high value of 0.39 ppm), Pb (b.d.l. to 29.14 ppm), and Bi (b.d.l. to 16.8 ppm; Fig. 10).

Thirty pyrite grains from Gushan MMEs were analyzed to measure their sulfur isotope compositions. The results are listed in Table 4 and illustrated in Figure 11. Pyrite in Gushan MMEs has δ³⁴S values ranging from 4.14‰ to 6.73‰, with an average of 5.13‰.

The Re-Os isotope sulfide dating method was used to constrain the mineralization age due to the measurement of high Re and low Os concentrations of sulfides and proved to be a potent and reliable tool for dating molybdenite mineralization and even hydrothermal events (Stein et al., 1997, 2003).

Molybdenite from the quartz-molybdenite veins in Gushan granite yields young model ages of 110.17 ± 0.6 Ma and 118.39 ± 0.5 Ma (Table 1), which correspond to the late Early Cretaceous. The two samples measured show distinctive ages with a gap of ~8 m.y., which is very large and in disagreement with expected harmonious Re-Os ages since the two molybdenite samples were collected from Gushan granite at the same spot. This may be due to the small amount of aliquant weighted for analysis (Selby and Creaser, 2004) or to the analytical procedures (Suzuki et al., 2001). The age discrepancies observed in the Re-Os ages of molybdenites cannot be attributed to the analytical procedures followed in this work since the model age of the reference material RM8599 gave reliable Re-Os ages of 27.695 ± 0.038 Ma, which agrees with the certified value (i.e., 27.66 ± 0.10 Ma) of Markey et al. (2007) and Zimmerman et al. (2014). Moreover, Liu et al. (2010b) previously calculated the ages of five molybdenite samples from the same Gushan pluton. The samples were analyzed at the Key Laboratory of Isotope Chronology and Geochemistry of the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences. The results show inconsistent ages of 111.8 ± 0.3 Ma, 117.5 ± 0.3 Ma, 118.5 ± 0.4 Ma, 121.3 ± 0.4 Ma, and 128.9 ± 0.5 Ma, which further indicates that analytical procedures were not the main reason for the large gap. This indicates that the aliquants weighted for analysis in this work were likely small to yield harmonious Re-Os ages. Selby and Creaser (2004) showed that the analysis of small sample aliquants (<20 mg) from the same mineral would not produce reliable or reproducible Re-Os ages for some molybdenite samples, whereas analysis of multiple larger aliquants from the same mineral would yield reproducible Re-Os ages. They demonstrated that coarse-grained molybdenite samples necessitate ≥40 mg of aliquant from a much larger mineral separate to avoid Re and ¹⁸⁷Os decoupling. However, in this study, the aliquants weighted for Re-Os molybdenite analysis were small (~20 mg), while the molybdenite grains in the Gushan granite are coarse-grained (~0.3–12 mm), with some as large as 20 mm. Thus, the variation in Re-Os ages observed in this study was likely induced by the small amount of aliquant weighted.

The Re-Os molybdenite ages in this study are within the range of Re-Os ages (i.e., 128–111.8 Ma) calculated by Liu et al. (2010b) and our calculated U-Pb zircon ages (i.e., 126.5–112.3 Ma), with weighted mean ages of 119.8 ± 2.1 Ma (MSWD = 5.9) and 119.4 ± 1.4 Ma (MSWD = 3.7), respectively (Fig. 9). The ages are also consistent with the zircon and titanite U-Pb ages of unaltered samples (120.7 ± 3.1 Ma, 121.3 ± 0.9 Ma, and 121.7 ± 3.9 Ma) or the titanite and monazite ages of hydrothermally altered samples (120.9 ± 2.6 Ma and 122.3 ± 4.3 Ma) from the Xiejia DI obtained by Li et al. (2022, 2023). These ages coincide with more recent gold mineralization ages dated at 120 ± 3 Ma (Deng et al., 2020a; Zhang et al., 2020) and three molybdenite samples with Re-Os model ages of 117.6 ± 1.6 Ma, 116.1 ± 1.6 Ma, and 115.5 ± 1.6 Ma from the Shangjiazhuang Mo deposit hosted in the Weideshan granitic suite (Li et al., 2013a). The geochronological coincidence determined using diverse methods on quartz-molybdenite veins, Gushan granite, and its MMEs; fresh and altered samples of the mineralized Xiejia DI; and some samples from large-scale gold deposits indicate that the hydrothermal event, the ore formation occurrence, and the emplacement of the Weideshan granitic suite (especially Gushan granite and the Xiejia DI) resulted from a single geological event rather than multiple events. Obviously, ca. 120 ± 3 Ma is the most significant time for the occurrence of the younger intrusions (i.e., Weideshan granitic suite), the magmatic-hydrothermal events, and the large-scale gold mineralization (Deng et al., 2020a; Yao et al., 2021; Koua et al., 2022; Li et al., 2022, 2023).

Pyrite (FeS₂) is by far the most dominant and widespread sulfide in the crust (Craig and Vokes, 1993); it is an Au-hosting mineral and can contain a large diversity of trace elements, which, coupled with S isotopes, are widely exploited to constrain the nature of the fluids from which it crystallized (Zhao et al., 2011; Koglin et al., 2010; Gregory et al., 2016; Song et al., 2019). Trace elements such as Co, Ni, As, Se, and Sb are commonly distributed in pyrite; Co and Ni can replace Fe through isomorphism, while As, Se, and Sb can substitute for S within the pyrite lattice (Li et al., 2021; Zhou et al., 2022; Song et al., 2023a). Generally, pyrite with higher Co-Ni contents precipitated under higher temperatures. In contrast, sulfophile elements As, Se, and Sb are more abundant at lower temperatures. Hence, the concentration of trace elements in pyrite may reflect the formation temperature (Chen et al., 1987; Li et al., 2021).

Pyrite grains in Gushan MMEs are subhedral to anhedral, fine-grained (<100 µm), and disseminated in the matrix. They are also enclosed in chloritized amphibole or kaolinized plagioclase phenocrysts and can occur along with hydrothermal magnetite, titanite, carbonate, and quartz (Figs. 5C, 5D, 5F, and 6A–6D). The small sizes and anhedral morphologies of these pyrite grains are identical to the disseminated hydrothermal pyrites in fresh monzonite samples from the Xiejia DI (Fig. 8) but unlike the huge (>500 µm) and euhedral hydrothermal-like pyrites in the quartz veins from the Gushan host granite (Fig. 7), which indicates a different genesis for Gushan MMEs, the Xiejia DI, and the quartz vein-hosted pyrites. In many studies, magmatic pyrite, compared to hydrothermal pyrite, displays higher Co and Ni concentrations (Tan et al., 2012; Chen et al., 2011; Gregory et al., 2016; Song et al., 2019). In this work, pyrite grains from the quartz-sulfide veins display Co (0.05–80 ppm) and Ni (b.d.l.–30.82 ppm) contents that are much lower than the Co and Ni concentrations in pyrite grains from the Gushan MMEs and the Xiejia DI (Figs. 10F and 12A), which suggests a hydrothermal origin for pyrites from the quartz-sulfide vein. As such, pyrites from Gushan MMEs and the Xiejia DI are likely of magmatic origin. However, numerous works have shown that magmatic sulfides are commonly hosted in ultramafic and mafic rocks and display high Ni (≥2200 ± 500 ppm) contents (Jochum et al., 1986), while those in felsic rocks or quartz veins are generally hydrothermal and have low Ni (~19–60 ppm) contents (Song et al., 2019; Zhao et al., 2011). Gushan MME pyrites have Ni contents higher (23.2–2338 ppm; average of 393 ppm) than the proposed Ni contents of felsic rocks, which suggests that pyrite from Gushan MMEs was unlikely to have formed in a felsic magma. These pyrites could not have formed in an ultramafic or mafic environment either, because sulfide that precipitated from ultramafic/mafic magma has significantly high Ni contents that are generally higher than the Co contents. This is the case for reported sulfide-bearing mafic dikes from the Guocheng gold deposit in the Jiaodong gold province (Ni = 2500–13,000 ppm; Tan et al., 2012) and pyrite-bearing mafic granulite xenoliths from Xikeer in the northwestern Tarim Basin (Ni = 602–11,496 ppm; Chen et al., 2011), and pyrite-bearing basalt and dolerite from the St. Ives gold district (Ni of 7354 ppm; Gregory et al., 2016). Pyrites from Gushan MMEs have low Ni contents compared to the reported pyrites that formed in ultramafic and mafic environments, which rules out the possibility that these pyrites formed in an ultramafic–mafic environment. Previous studies have shown that Gushan MMEs and the Xiejia DI originated from the mixing of magma derived from the mantle and crust (Li et al., 2012; Koua et al., 2022); thus, pyrites from these rocks could have eventually precipitated from a hybrid intermediate magma. However, disseminated, subhedral–anhedral pyrite, commonly associated with altered minerals (Figs. 5C, 5F, and 6A–6D), combined with relatively higher temperature and Co-Ni contents, suggest that pyrite from Gushan MMEs precipitated during the deuteric stage.

Pyrite is the predominant S-bearing mineral in the Gushan MMEs and mineralized Xiejia DI. Thus, it is reasonable to assume that the pyrite δ³⁴S_V-CDT values represent the bulk S-isotope composition of the ore fluids (Ohmoto and Rye, 1979). The S-isotope compositions of Gushan MME pyrites range from 4.14 to 6.73 (average 5.13; Fig. 9), which overlaps with the sulfur isotope compositions of pyrites from the Xiejia DI (+1.9‰ to +6.4‰; Li et al., 2022; +2.1‰ to +9.7‰; Li et al., 2023), the Early Cretaceous intermediate–mafic dikes in the Jiaodong province (δ³⁴S_V-CDT = 0.8‰–10.8‰; Huang, 1994; Zhang et al., 2014), and the gold-bearing ores (δ³⁴S_V-CDT = 0.8‰–10.8‰; Huang, 1994; Zhang et al., 2014). Thus, we can infer that these sulfurs have the same congenetic source, which is the metasomatized lithospheric mantle. However, sulfur isotope compositions of Gushan MMEs are more homogenous and relatively lower than those of the Xiejia DI, the Early Cretaceous intermediate–mafic dikes, and the gold-bearing ores (Fig. 13), which implies that Gushan MMEs assimilated or mixed with less sedimentary components than the two other rocks in the Jiaodong peninsula. The presence of abundant inherited zircon grains with old U-Pb ages from the ancient continental crust in the Xiejia DI (Li et al., 2023) and the Early Cretaceous intermediate–mafic dikes (Liu et al., 2009; Ji et al., 2022) further confirm the assimilation of much more sedimentary components in these rocks. In this regard, the sulfur isotope and trace element compositions of Gushan MMEs are much closer to those of the primitive source than the other mafic rocks. In summary, both pyrite trace elements and sulfur isotopes indicate that Gushan MMEs, the Xiejia DI, Early Cretaceous mafic dikes, and gold-bearing ores originated from the same metasomatized lithospheric mantle, but they experienced different degrees of crustal material assimilation and/or magma mixing, causing slight differences in their sulfur isotope compositions.

The gold deposits in the Jiaodong peninsula are mainly hosted in the Mesozoic granitic rocks and are structurally controlled by the NE-NNE faults and shear zones that intersect these granitoids (Fig. 1). All of the gold deposits in this region occurred in a short period between 135 Ma and 100 Ma, but most of the large-scale gold deposits clustered at 120 ± 3 Ma (Zhu et al., 2015; Zhang et al., 2020). Ongoing debate on the sources of the ore-forming fluids and materials responsible for the precipitation of the large-scale gold mineralization in the Jiaodong gold province reveals a lot of uncertainties about the genesis of the large-scale gold deposits (Groves et al., 2020; Wang et al., 2021a). Several sources have been proposed to account for the origin of the ore-forming fluids and materials, and the four most common are discussed below.

The large-scale gold mineralization in Jiaodong was classified as an orogenic gold deposit with the ore-forming fluids exsolved from the metamorphic crustal basement (i.e., Jiaodong Group) since the ore bodies are lode gold veins (Groves and Santosh, 2016). However, a recent detailed investigation led by Wang et al. (2021b) clearly eliminated the Precambrian metamorphic crustal basement as a potential source of ore fluids and metals of the gold deposits based on the relatively low Au contents (~0.18–0.47 ppb) of these rocks. Additionally, the metamorphic event, which could have scavenged Au, S, and other useful components from the Precambrian basement, was recorded ~1.8–1.9 b.y. earlier than the gold deposits (Goldfarb and Santosh, 2014; Goldfarb and Groves, 2015). Any mobilized materials from the Jiaodong Group would have been lost since then, making the Precambrian crustal basement irrelevant for generating gold mineralization in this area.

Mesozoic plutons in the Jiaodong peninsula show a good spatial relationship with the large-scale gold deposits, which were used to support the Jiaodong Mesozoic crustal-derived magmas being the principal source of the ore-forming fluids (Li et al., 2013b, 2015b) until precise geochronological dating revealed that most of these granitoids were emplaced before (ca. 160–125 Ma; Linglong and Congjia suite) or after (ca. 116–110 Ma; Aishan suite) the large-scale gold deposits. However, a few young plutons, such as the Gushan and Aishan granites, show a perfect temporal relationship with the large-scale gold deposits but host no gold deposits. Furthermore, the outcrops are volumetrically insignificant for providing the volumes of fluids needed to precipitate the large-scale gold deposits. Thus, crustal-derived magmas are difficult to reconcile as the dominant reservoir for the ore-forming fluid and metals.

Metamorphic fluids directly derived from dehydration of the subducted oceanic Paleo-Pacific slab and accreted sediments have been proposed to form the gold deposits (Goldfarb and Santosh, 2014; Groves and Santosh, 2016; Groves et al., 2020). It is believed that the movement changes of this plate, which was contemporary to the large-scale gold deposits, could have triggered its dehydration and the desulfidation of Au-rich pyrites in accreted sediments, which would eventually release tremendous volumes of gold into fluids that would move upward through trans-lithospheric faults to precipitate in the shallower crust of favorable structures (Deng et al., 2020c; Wang et al., 2021a). This suggests the direct transport of ore-forming materials without a transitional source, such as the lithospheric mantle or intermediary Mesozoic magmatism (Groves et al., 2020). Such a transportation mode implies the absence of interaction or little interaction with the surrounding environment, and it can be inferred that the geochemical features of the ore-forming materials should reflect the geochemical features of the westward Paleo-Pacific plate. However, Deng et al. (2020b) showed that sulfur isotopes recorded in the gold deposits differ from the Jurassic to Early Cretaceous seawater sulfate and sedimentary sulfides from the sediment wedge above the subducting oceanic plate. Furthermore, in a recent publication, Jiang et al. (2020) pointed out that the Sr-Nd isotope compositions of orebodies from the large-scale Xiadian gold deposit, which are similar to the arc-like mafic dikes (Ma et al., 2013; Liang et al., 2017), are different from those of the western Pacific pelagic sediments that should correspond to the Paleo-Pacific plate. Additionally, no slab-derived melts were reported in this region. Furthermore, the asthenospheric mafic melts have different Sr-Nd isotope signatures than the gold deposits (Ma et al., 2016; Zheng et al., 2018; Liu et al., 2020). This suggests that no direct devolatilization nor intermediate magma from the Paleo-Pacific plate was directly involved in generating large-scale gold deposits.

Thus, we propose a transitory source for ore-forming elements, most likely the metasomatized lithospheric mantle. This is further supported by the study of arc-like dolerite and lamprophyre dikes, which revealed that the lithospheric mantle was widely metasomatized by extensive dehydrated fluids and volatiles from the subducted Paleo-Pacific plate in the Mesozoic (Li et al., 2012, 2016; Ma et al., 2014b). Liang et al. (2019) and Wang et al. (2020b) measured a large quantity of water (2–4 wt%), LILEs, and volatiles in these rocks. In fact, if all of the ore-forming materials directly escaped from the subducted slab through the trans-lithospheric fault, the lithospheric mantle would not have achieved such a high level of metasomatism.

Many authors agree that the lithospheric mantle of the eastern North China Craton was the repository of the ore-forming materials (Deng et al., 2020b, 2020c; Jiang et al., 2020; Wang et al., 2021a). Saunders et al. (2018) identified the eastern block of the North China Craton as the most enriched in Au concentrations (median of 3.5 ppb versus global median of 1.2 ppb Au) and attributed this enrichment to the intense metasomatism of the lithospheric mantle by the subducted Yangtze craton in the Triassic, the oceanic slab in the Jurassic, and the upwelling of the asthenosphere (Deng et al., 2020a, 2020b; Groves et al., 2020). Besides the widespread metasomatism, the peak of the lithospheric destruction, asthenospheric upwelling, and lithospheric melting coincided perfectly with the precipitation of large-scale gold (Ma et al., 2014a; Zhang et al., 2020).

Many workers have shown the implications of mantle components in the generation of gold deposits (Jiang et al., 2020; Wang et al., 2021a; Wei et al., 2021), which suggests that the lithosphere in the Jiaodong peninsula is likely the repository of the ore-forming materials that precipitated the large-scale gold deposits. Also, several studies suggest the implication of crustal components, which were interpreted by some authors to be evidence of mantle and crust interaction (Li et al., 2012) or as crustal contamination that occurred when ore material ascended through crustal channels (Deng et al., 2020b).

However, how the gold attained the shallower level of the crust has yet to be explained. Deng et al. (2020b) proposed that the ore-forming materials from the lithosphere were transported through trans-lithospheric faults to the crust. Although this model appears suitable for explaining the formation of the gold deposits, there is a lack of direct evidence to substantiate its validity. In addition, ore-forming materials in the North China Craton were channeled through crustal-scale faults rather than lithospheric-scale faults (Groves et al., 2020). Importantly, there is no evidence connecting trans-lithospheric faults and crustal faults. In this regard, it is unlikely that the ore-forming materials were carried by devolatilization, and thus, an intermediary is required. Therefore, we argue that the ore-forming metals and fluids originated from the metasomatized lithospheric mantle and were transported into the upper crust by an intermediary-like Gushan MME and the Xiejia DI.

This work aims to identify the mechanism of gold transportation from the lithospheric mantle to the shallow crust. Previous research on the mineralized Xiejia DI has concluded that the gold in the Jiaodong peninsula derived from the enriched lithospheric mantle, and the syn-gold mineralization of mafic magma played a significant role by transferring gold from the deep lithospheric mantle to shallow crustal levels (Li et al., 2023). However, Groves and Santosh (2016) pointed out that the limited distribution of mafic dikes (lamprophyre, dolerite, and diorite) could not have provided the large volume of fluids and materials required to form the massive gold mineralization in the Jiaodong gold province. Likewise, it is reasonable to doubt whether the Xiejia DI could have transported so much gold due to its rare occurrence in the cores, considering that multiple holes in the area were drilled during previous decades.

This work sheds light on an alternative carrier of gold that could play a role similar to that of the Xiejia DI in transferring gold and ore-related components from the lithospheric mantle to the shallow crust. Previous workers have suggested that the Gushan MMEs also could have played a carrier role, as they share several features with the Xiejia DI and are extensively distributed within the late Early Cretaceous Weideshan granitic suite (Goss et al., 2010; Koua et al., 2022), which is widespread from west to east and is close in age to the large-scale gold mineralization (ca. 121–110 Ma) in the Jiaodong peninsula (Fig. 1).

Therefore, we infer that the magma from the lithospheric mantle injected gold and ore-related components into the Weideshan granitic suite during magmatic mixing processes. Consequently, the Weideshan granitic suite may have played an intermediary role by continuously transferring gold and ore-related components into the shallow crustal fault where gold precipitated.

This inference can be documented. First, polymetallic occurrences (Mo, W, Cu, Pb, Zn, and Ag), like those mineralized element associations observed in Gushan MMEs, are extensively distributed around the Weideshan granitic suite, especially in the central and eastern parts of the Jiaodong peninsula, forming four polymetallic mineralized concentration areas (SBGMR, 1991). Different sizes of Mo deposits, such as the large-scale Xingcun Mo-W and the small-scale Shangjiazhuang Mo deposits, are hosted in the Weideshan granitic suite (Li et al., 2013a). Molybdenite Re-Os dating on the Shangjiazhuang Mo deposit revealed an age close to that of the large-scale gold mineralization, which infers that molybdenum and gold mineralization in the Jiaodong area are coeval (Li et al., 2013a; Song et al., 2023b). Second, no reported polymetallic mineralization is hosted in the Linglong and Guojialing granitic suites, except for gold mineralization controlled by faults along the contact between the two suites. Moreover, a recent study on chalcophile elements of the Guojialing and Linglong host rocks and their MMEs shows that they are free of sulfides and have remarkably low S, Cu, Ag, and Au concentrations (Xu et al., 2022).

Consequently, the possibility that polymetallic mineralization hosted in the Weideshan granitic suite was caused by the Linglong and Guojialing granitic suites can be ruled out. The presence of sulfide in Gushan MMEs suggests that polymetallic mineralization hosted in the Weideshan granitic suite derived from the injection of mafic magma from the enriched lithospheric mantle. Based on the coeval formation of gold and molybdenum deposits with the Weideshan granitic suite in the Jiaodong peninsula, it is reasonable to assume that Au and Mo mineralization was caused by the emplacement of the Weideshan granitic suite.

However, most researchers deny this hypothesis mainly because there is no direct evidence of gold deposits being hosted in the Weideshan granitic suite (Deng et al., 2020c). A possible reason for the lack of gold occurrence in the Weideshan granitic suite can be attributed to a mineralization zoning process in which the high-temperature Mo-W deposits precipitated in the vicinity of the Weideshan granitic suite, and the low-temperature Au and Ag deposits were distal to the intrusion. This is in agreement with the distribution of the mineral deposits in the Jiaodong area, where the Mo-W polymetallic deposits mainly occur in the central and eastern parts associated with extensive Weideshan granitic suite outcrops, and gold deposits are distributed in the northwestern part of the Jiaodong peninsula with minor Weideshan granitic suite granite occurrences. Large-scale gold deposits, such as the Sanshandao, Jiaojia, and Linglong gold fields, follow this pattern of distribution (SBGMR, 1991). Moreover, Song et al. (2012, 2023b) advocated for gold mineralization of the Weideshan granitic suite and thought that the Weideshan granitic suite provided the necessary metallogenic material and heat engine.

Based on the discussion above and previous research, we proposed a genetic model for the syn-mineralization of mafic enclaves in the Jiaodong peninsula along the following lines. Large-scale lithospheric mantle-derived basaltic magma underplated the Archean lower crust and caused its partial melting to form the cool and depleted felsic magmas, which generated the Weideshan granitic suite. The injection of hot mafic magma pulses from a deep MASH zone, enriched in ore-forming fluids and metals, into the cooler felsic magma chambers was followed by the spontaneous interaction of hot mafic and cool felsic magma and the rapid cooling of the mafic magma. This cooling could have prompted a devolatilized reaction of the enriched mafic magma, which released a tremendous quantity of volatiles. This could explain the low Au content in the syn-mineralization mafic enclaves. Second-order faults formed or reactivated during the lithospheric thinning, and favorable structures might have eased the flux of volatiles, water, and ore-forming materials through the upper crust and offered auspicious loci for gold deposition (Li et al., 2012). The cool felsic magma from the host rock played the role of stopper as volatiles and ore materials were released into favorable structures where the gold precipitated (Fig. 14).

In summary, rather than drilling to find deep mafic intrusions like the Xiejia DI, we suggest that future mineral prospecting campaigns in the Jiaodong gold peninsula should investigate the Weideshan granitic suite, its MMEs, and their relationships to the gold mineralization.

1. The magmatic-hydrothermal event in the potassic-altered Gushan granite took place at ca. 120 Ma, which is coeval with the gold mineralization in the Jiaodong peninsula.

2. Pyrite grains hosted by Gushan MMEs are of hydrothermal origin and precipitated during the deuteric stage after magma mixing; trace element compositions in these pyrites are closer to the primitive mafic magma than pyrites from the Xiejia DI and quartz vein.

3. The ore-forming materials preferentially originated from the enriched lithospheric mantle, which was the repository for water, sulfur, and volatiles from the subducted Paleo-Pacific plate, rather than by direct release from the subducted sediments of the Paleo-Pacific plate.

4. The arc-like mafic magmas derived from the metasomatized lithospheric mantle at ca. 120 Ma were the intermediaries that transported the gold and other ore-forming components from the deep mantle to the shallow crustal levels.

5. During magma mixing, mantle-derived magma transferred gold and ore-related components into the Weideshan granitic suite, which played a critical role in transferring gold into the shallow crustal faults where gold precipitates. Future gold exploration campaigns should focus on the Weideshan granitic suite rather than the Xiejia DI and mafic dikes.

This project was financially supported by the Ministry of Science and Technology of China (grant no. 2016YFC0600104) and the National Natural Science Foundation of China (grant no. 41672074). Sanshandao Gold Mine, Jiaojia Gold Mine, Linglong Gold Mine of Shandong Gold Group, and Lingnan Gold Mine of Zhongkuang Gold Industry Co., Ltd., provided assistance with fieldwork. We are very grateful to these organizations and individuals. We also thank Science Editor Wenjiao Xiao and two anonymous reviewers for their critical and constructive comments that helped to improve the manuscript.