Mineralization Age and Ore-Forming Material Source of the Yanshan Gold Deposit in the Daliuhang Gold Field in the Jiaodong Peninsula, China: Constraints from Geochronology and In Situ Sulfur Isotope

Abstract

The newly discovered Yanshan gold deposit within the Qixia–Penglai mineralization belt is situated within the Daliuhang goldfield of Daliuhang Town, approximately 45 km southeast of Penglai City, the Jiaodong Peninsula. Quartz-vein–type gold orebodies are mainly distributed among the Guojialing granite and are controlled by NNE-trending faults. Native gold primarily occurs within the interiors of pyrite grains, forming inclusion gold and fracture gold. In this study, LA-ICP-MS zircon U-Pb dating and in situ sulfur isotope analysis of gold-bearing pyrite were conducted to constrain the ore genesis of the Yanshan gold deposit. Guojialing monzogranite and porphyritic granodiorite yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 130 ± 2 Ma (MSWD = 1.8) and 131 ± 2 Ma (MSWD = 1.8), respectively, indicating that magmatism and gold mineralization occurred during the Early Cretaceous period. The in situ sulfur δ³⁴S values of euhedral crystalline pyrite (Py1) formed in the early stage ranged from 3.21% to 5.35‰ (n = 11), while the in situ sulfur δ³⁴S values of pyrite (Py2) formed in the later stage ranged from 6.32‰ to 9.77‰ (n = 10), suggesting that the sulfur of the Yanshan gold deposit primarily originates from magmatism, with contamination from stratigraphic materials. Granitoids are highly likely to provide the thermal drive for fluid activity; however, the origins of the fluids and ore-forming materials remain difficult to determine. Based on geological features, geochronological data, and in situ sulfur isotopic analysis, this study concludes that the Yanshan gold deposit is a mesothermal magmatic hydrothermal vein-type gold deposit. The mineralization of the Yanshan gold deposit is related to the subduction of the Mesozoic Paleo-Pacific Plate beneath the Eurasian continent and is mainly controlled by steep dip faults. This study provides theoretical guidance for further exploration and prospecting of the Yanshan gold deposit.

1. Introduction

The Jiaodong region is the most important gold resource base in China, with a total gold reserve of over 5800 t [1,2,3] and remaining predicted gold reserves exceeding 4000 tons, accounting for more than 1/4 of the country’s total (Figure 1a). The Jiaodong region is the largest gold-mining area in China and the third largest in the world [4,5,6,7,8,9,10]. The Jiaodong gold mineralization belt primarily comprises three major metallogenic regions: Zhaoyuan–Laizhou, Laizhou–Qixia, and Muping–Rushan (Figure 1b; [2,3,5,6,7]). The Jiaodong gold concentration area in Shandong Province is densely populated with three giant gold deposits (>1000 tons), over 30 large- and medium-sized gold deposits, and hundreds of small gold deposits. It exhibits the following characteristics: regional concentration, large scale, abundant reserves, and short mineralization period (125–115 Ma) [11,12,13,14,15,16]. This rare intracontinental dynamic gold mineralization process has garnered significant attention from numerous scholars in the geoscience community [3,15,16,17,18,19,20,21,22]. The Jiaodong gold deposit concentration area is the outcome of regional-scale geological mineralization, with its formation and evolution controlled by the continental lithosphere and deep faults. It is associated with the subduction of the Pacific Plate and the transformation of the geodynamic system [16]. The ore-forming process of gold refers to the sum of various geological processes that concentrate gold elements to form gold deposits in the crust. This is the product of multiple activities, long-term evolution, a high concentration of gold ore-forming materials during a specific stage of geological history, and tectonic environment [16,17,18,19,20,21,22].

The Yanshan gold deposit is situated within the renowned Qixia–Penglai mineralization region (Figure 1b). The geotectonic setting of the deposit pertains to the Jiaobei uplift, located in the northeastern section of the Jiaoliao uplift region within the North China Craton. The Yanshan gold deposit is primarily situated in the contact zone between the Mesozoic Linglong and Guojialing granites. It is controlled by the NE–NNE-trending Huluxian and Xiaogujia faults (Figure 2). Over ten gold deposits (including Shuigou, Shijia, Daliuhang, Shijinhe, and Yanshan gold deposits) are scattered across the footwall of this fault zone, with a cumulative proven resource exceeding 100 tons. This goldfield is known as the Daliuhang goldfield. Currently, the exploration of the deep and peripheral areas of the Yanshan gold deposit has revealed immense mineralization potential; however, theoretical research is considerably lacking. The available literature primarily focuses on ore-forming geological conditions [22] and the possibility of prospecting the Yanshan gold deposit. This limitation hinders further research and exploration of deposits. Three scientific issues regarding this deposit remain unresolved. Firstly, the mineralization age of the Yanshan gold deposit has not yet been clearly defined. Although extensive research has been conducted on the diagenetic and mineralization chronology of gold deposits in the region, due to the relatively late discovery of this deposit, there is a lack of direct high-precision isotopic chronological data targeting the main mineralization stage (such as ⁴⁰Ar/³⁹Ar dating of gold-bearing quartz veins or Re-Os dating of gold-bearing sulfides). More critically, multiple stages of intrusive rocks have developed within the mining area, including diorite porphyrite, granite porphyry, and xenoliths of Archean basement rock series (Figure 2). Currently, there is a lack of reliable evidence able to determine the temporal and spatial coupling relationship between mineralization events and specific magmatic activities—with which stage of intrusive rocks does gold mineralization have a genetic connection? Is it controlled by deeply concealed rock masses? Resolving this issue is crucial for establishing a regional metallogenic dynamic model. Secondly, the source of the ore-forming materials of this deposit remains unclear. Some scholars have suggested that the ore-forming materials of the deposit originate from the strata, whereas others argue that they originate from granitic intrusions [23]. Lastly, the ore genesis of the Yanshan gold deposit remains controversial. Some researchers suggest that the deposit is formed by both mesothermal hydrothermal replacement and silica-rich hydrothermal filling, while others classify it as a mesothermal hydrothermal vein-type gold deposit [18,19,20,21,22,23].

Based on these three scientific issues, this study conducts LA-ICP-MS zircon U-Pb dating of the intrusions related to gold mineralization in order to determine the mineralization age of the Yanshan gold deposit. In situ sulfur isotopic analysis of gold-bearing pyrite is conducted to identify the source of ore-forming materials in the Yanshan gold deposit. Through a comprehensive analysis of the research presented in this paper, an analysis of the regional tectonic evolution, and comparative studies of gold deposits within the area, the ore genesis of the Yanshan gold deposit is conclusively determined. This study has significant theoretical implications for the future prospecting and exploration of deposits.

Figure 2. Regional geological map and distribution map of gold deposits in the study area (modified from Ma et al., 2020 [23]).

Figure 2. Regional geological map and distribution map of gold deposits in the study area (modified from Ma et al., 2020 [23]).

Figure 3. (a) Geological map of the mining area of the Yanshan Gold Deposit (modified from Ma et al., 2020 [23]); (b) Cross-sectional view of the exploration line of ore body No. ① (modified from Ma et al., 2020 [23]).

Figure 3. (a) Geological map of the mining area of the Yanshan Gold Deposit (modified from Ma et al., 2020 [23]); (b) Cross-sectional view of the exploration line of ore body No. ① (modified from Ma et al., 2020 [23]).

2. Geological Background

The Yanshan gold deposit is situated within the Daliuhang goldfield of Daliuhang Town, approximately 45 km southeast of Penglai City, Shandong Province (Figure 1b and Figure 2). Geotectonically, it occupies a central position within the southeastern gold mineralization zone of Penglai, which lies on the eastern fringe of the Jiaobei uplift, itself situated on the southeastern margin of the North China Craton. It is characterized by widespread magmatic activity and fault-controlled mineralization. The region has experienced multiple stages of tectonic evolution, including Mesozoic lithospheric thinning and intense magmatism related to the subduction of the Paleo-Pacific Plate, which provided favorable conditions for gold enrichment [2,3,4,5,6,7,8,9,10,11,12,13,14,15,24].

Regional geological studies indicate that the exposed strata in the area, from oldest to youngest, comprise the Jiaodong Group of the Neoarchean, the Jingshan Group and Fenzishan Group of the Paleoproterozoic, the Penglai Group of the Neoproterozoic, the Laiyang Group, Qingshan Group, and Wangshi Group of the Mesozoic Cretaceous, as well as the Quaternary. These strata are distributed around the Mesozoic intrusive bodies, with some Precambrian strata occurring as inclusions or relics within them (Figure 2). The Archean Qixia sequence TTG rock series, the Jiaodong Group, and the Paleoproterozoic Fenzishan Group collectively constitute the metamorphic basement within the region (Figure 2). The Jiaodong Group, predominantly comprising plagioclase amphibolites and biotite granulites, is distributed in Mesozoic granites in the form of smaller, isolated, island-like and lentil-shaped residual bodies. The Qixia sequence TTG rock series is found near Daxindian Town and is composed of banded tonalite and gneissic granodiorite. The Paleoproterozoic Fenzishan Group is located in the eastern part of the study area, characterized by rock types such as biotite granulite, aluminum-rich schist, leptite, and marble, with a high degree of metamorphism; this ranges from greenschist to low amphibolite facies [2]. The Penglai Group of the Sinian system is situated in the southeast corner, consisting of phyllite, slate, quartzite, limestone, and marble; this represents a suite of shallowly metamorphosed sedimentary rocks deposited in coastal and shallow marine environments. The Cretaceous Qingshan Group comprises andesite and andesitic volcaniclastic rocks, distributed within the Zangjiazhuang Basin (Figure 2).

Magmatic activity was predominantly concentrated in the Precambrian and Mesozoic eras. Specifically, the Precambrian intrusive rocks primarily comprise the TTG rock series, which consists of tonalite, trondhjemite, and granodiorite, exhibiting prominent schistosity or gneissosity and predominantly occurring in the form of rock stocks. The Mesozoic era witnessed intense magmatic activity, resulting not only in the formation of extensive Linglong granite and Guojialing granodiorite bodies but also in the development of numerous vein rocks, including lamprophyres, granite porphyries, quartz diorite porphyrites, and diabase porphyrites (Figure 2). These vein rocks cut through the Linglong and Guojialing rock bodies, serving as indicators of potential mineral deposits in the region. The primary faults are oriented in the NE–NNE direction, with significant examples including the Wulipu fault, Milukuang fault, Huluxian fault, and Xiaogujia fault; this is in addition to their secondary and lower-order faults. These faults and their secondary low-order faults control the production of rock veins and gold deposits in the area (Figure 2).

3. Deposit Geology of the Yanshan Gold Deposit

The outcropping strata in the Yanshan mining area are dominated by Quaternary alluvial deposits, while Precambrian metamorphic basement rocks occur locally (Figure 3a). The relics of the Neoarchean Jiaodong metamorphic rock group occur as lenticular inclusions within the Jiuqu and Bijiaoshan unit plutons, while the lithology is mainly composed of plagioclase hornblendite and biotite gneiss. Three groups of fault systems, namely NE-, NNE-, and NS-trending faults, developed in the mining area, with the NE–NNE trending faults controlling the distribution of ore bodies (Figure 3a). The most prominent of these faults is the Huluxian fault, with alteration zones and ore bodies predominantly occurring in the secondary faults of its footwall [23,24,25,26,27,28]. These faults vary in size but share a nearly parallel strike, all dipping towards the SE; their angles of dip predominantly range from 43° to 70°, with a minority ranging between 70° and 90°. The intrusive rocks are roughly delineated by the Huluxian fault, with Guojialing granite located in the east and Linglong granite in the west (Figure 3a). These two types of granite serve as direct ore-hosting wall rocks and occur in the form of batholiths. These magmatic activities are closely associated with gold mineralization, as evidenced by the presence of ore-bearing altered fractures within granitic rocks. The contact zone between these two granite types controls the distribution of the industrial ore bodies within the gold mine. The primary dike rocks consist mainly of Mesozoic quartz diorite porphyries, diorite (porphyritic) rocks, and lamprophyres, with the occurrence of granite porphyries and pegmatites (Figure 3a). Most of these dike rocks formed during post-mineralization.

The Yanshan gold deposit is situated within the brittle faults of the Guojialing granite body, which is positioned in the footwall of the Huluxian fault (Figure 3a). Seven mineral veins of industrial significance have been identified within the mining area, with a total of gold metal content of 4.8 tons and an average grade of 5.29 × 10⁻⁶ g/t [23]. The ore-hosting faults comprise NE–NNE-oriented fault zones, which strike between 5° and 64°, dip SE, and are inclined at angles ranging from 50° to 89°. The ore bodies within these veins are predominantly thin and vein-like (Figure 3a,b), with an average thickness of approximately 1 m. They exhibit shapes such as veins, lenses, and pods, often displaying gentle undulations along the dip and local areas of expansion and contraction. The sections in which faults transition from steep to gentle are frequently associated with thicker ore bodies and enriched gold deposits (Figure 3b). The exploration depth of the largest, the No. 8 ore vein, has surpassed −900 m, and it remains open along both the dip and strike directions. The geological features of some gold ore bodies are shown in

Table 1. Characteristics of other ore bodies in the Yanshan ore district.

Ore Bodies	Elevation (m)	Ore Body Shape	Occurrence (°)		Scale		Average Thickness (m)	Average Grade (×10−6)
			Dip Direction	Dip Angle	Length (m)	Oblique Depth (m)
④-2	−233~−261	Vein	120	81	20	20	1.12	3.27
M3-1	−247~−313	Vein	120	85	120	20	0.76	3.66
M4-1	−417~−534	Vein	120	81	70	80	1.12	3.13
M9-1	−107	Vein	110	70	20	20	2.7	1.38
M1-1	−362	Vein	100	54			0.34	6.74
M3-2	−615	Vein	120	87			0.68	4.43
M5-1	−79	Vein	120	87			0.25	31.88
M6-1	−107	Vein	120	82			0.47	22.85

.

The gold ores are characterized by gold-bearing pyrite veins and polymetallic sulfide quartz veins (Figure 4a–e). The types of ore structure are dominated by veinlet-disseminated structures (Figure 4a–c), with mottled and compact massive structures being commonly encountered. The types of mineralization mainly include gold-bearing pyrite-sericite altered granitic rock, followed by gold-bearing pyrite-sericite rock and gold-bearing quartz vein rock. The industrial classification is low-sulfur gold ore. The ore textures primarily consist of euhedral to subhedral granular and interstitial textures, with the common occurrence of fractured, metasomatic, and metasomatic residual textures. The metallic minerals in the ore are dominated by pyrite and native gold, accompanied by a minor amount of metallic sulfides such as galena and sphalerite (Figure 4f–i). The non-metallic minerals encompass quartz, feldspar, sericite, chlorite, calcite, and others (Figure 4m–o). Native gold primarily occurs within the interiors of pyrite grains, forming inclusion gold and fracture gold (Figure 4f,j–l).

Hydrothermal alteration surrounding the orebodies and fractures is well developed, including silicification, sericitization, choritization, K-feldspar alteration, and carbonation (Figure 4b,c,m–o). The alteration assemblages exhibit clear temporal relationships: (1) K-feldspar alteration represents a precursor stage predating mineralization; (2) pyritization, sericitization, and silicification constitute the coeval alteration suite most closely associated with gold deposition, defining the main ore-forming stage; (3) chloritization occurs multiphasically throughout mineralization; and (4) carbonatization represents a late stage of ore-forming hydrothermal activity. The alteration has a narrow range, with widths generally ranging from several meters to over ten meters. Characterized by the presence of K-feldspar alteration that formed first, successively overprinted by silicification and sericitization, the intensity of alteration decreases gradually. Pyritization and carbonatization were also observed. Silicification and sericite mineralization are closely related to gold mineralization.

The mineralization process of the Yanshan gold deposit is divided into three stages: early quartz-pyrite, quartz-sericite-native gold-polymetallic sulfide, and late quartz-carbonate.

Quartz–pyrite stage (I): in this stage, pure white quartz is predominantly formed, with coarse-grained euhedral pyrite (Py1, Figure 4f,g,i) crystallization observable in both the quartz and surrounding granodiorite (Figure 4a–e). Minor disseminated pyrite, associated with poor gold mineralization, exhibits a variety of crystal habits. The grains were partially euhedral but mostly exhibited a granular texture. At this stage, because the magmatic hydrothermal fluid has recently intruded into the strata and the temperature is relatively high, the surrounding rock undergoes silicification (Figure 4m,n).

Quartz–sericite–native gold–polymetallic sulfide stage (II): This stage is predominantly characterized by the formation of substantial amounts of soot-gray quartz and sericite (Figure 4m,o), accompanied by minor chlorite. This stage also witnesses the abundant occurrence of polymetallic sulfides, such as pyrite (Py2, Figure 4f–j) and galena (Figure 4j), as well as native gold. This represents the major gold mineralization stage. At this stage, the surrounding rock undergoes sericitization and chloritization. Because gold precipitates and forms deposits at this stage, the grade of gold is positively correlated with the intensity of sericitization.

Quartz–carbonate stage (III): This stage is characterized by the presence of grayish-white quartz and abundant calcite. This stage forms quartz–calcite veinlets that cut through earlier quartz–sulfide veins. Occasionally, disseminated pyrite is observed within quartz–carbonate veins.

4. Sampling and Analytical Methods

The Guojialing granite series within the mining area of the Yanshan gold deposit is predominantly composed of monzogranite and porphyritic granodiorite, which mainly controls the production of gold deposits. We carefully selected a monzogranite sample (22GJL01) and a porphyritic granodiorite sample (22GJL02, Figure 5) for LA-ICP-MS zircon U-Pb dating.

The monzogranite (Figure 5a,c) exhibits a flesh-red color, with a medium-to-fine-grained texture and massive structure. It is primarily composed of plagioclase (~35%), potassium feldspar (~30%), quartz (~25%), and biotite (~10%). The porphyritic granodiorite (Figure 5b,d) exhibits a grayish-black hue, featuring a porphyritic texture and massive structure. Phenocrysts account for 20% of the rock mass and consist of plagioclase (~10%), quartz (~6%), biotite (~2%), and hornblende (~2%). Matrix (~80%) shows fine-grained texture and is composed of plagioclase, K-feldspar, quartz with minor biotite and hornblende.

4.1. LA–ICP–MS Zircon U–Pb Dating

The initial concentrations of zircon grains isolated from the Guojialing porphyritic granodiorite and monzogranite samples were determined via magnetic and heavy liquid separation. Subsequent hand-picking under a binocular microscope at the Integrity Geological Service Corporation (Langfang City, Hebei Province, China) yielded grains for analysis. These grains were epoxy-mounted, polished to expose crystal interiors, and preliminarily examined using reflected and transmitted light microscopy. To visualize their internal structures and guide spot selection for U–Pb dating, cathodoluminescence (CL) imaging was performed using a Japan Electron Optics Laboratory (JEOL) (Akishima City, Japan) scanning electron microscope (Figure 6). We targeted areas exhibiting oscillatory zoning, typically near grain rims, to ensure that the chosen spots reflected the final crystallization age of the Pulang porphyry intrusion. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb isotopic analyses were conducted at the Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Natural Resources (Changchun, Jilin Province, China), using an American Agilent 7500c quadrupole ICP-MS coupled to a 193 nm ArF excimer laser (COMPexPro 102, Coherent, Saxonburg, PA, USA) featuring an automatic positioning system. A laser spot diameter of 32 μm was used. To ensure data quality, the zircon standard 91500 (for isotope ratio fractionation correction) and NIST 610 silicate glass (for elemental concentration calculations, using Si as the internal standard) were analyzed after every six unknown samples. The uncertainties for isotope ratios and derived ages are reported at the 2σ level. Details of the analytical process and data reduction methodology are described by Hou et al. [29], and the isotope data were calculated using the GLITTER 4.0 [30]. Concordia diagrams and weighted-mean age calculations were produced using ISOPLOT 3.0 [31]. Common Pb was corrected according to the method proposed by Anderson [32].

4.2. In Situ S Isotope Analysis

In the experimental procedure, the in situ determination of the sulfur isotopes of sulfides was performed on an experimental platform at Guangzhou Tuoyan Analytical Technology Co., Ltd. (Guangzhou, China) in China. We selected three pyrite samples for in situ sulfur isotope analysis. The detection system consists of a Neptune Plus multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) manufactured by Thermo Scientific Inc., Waltham, MA, USA, which operates in conjunction with an NWR 193 nm ArF excimer laser ablation device equipped with a TV2 sample cell and manufactured by Elemental Scientific Lasers (Bozeman, MT, USA). The experimental parameters were as follows: laser energy density of 3.5 J/cm², pulse repetition rate of 6 Hz, and ablation spot diameter of 25–30 μm. Helium gas with a flow rate of 0.7 L/min was used as the carrier gas to transport the ablation products, and then argon gas with a flow rate of 0.96 L/min was introduced for aerosol mixing. The detection process was carried out in low-resolution mode, and the signal data of ³⁴S, ³³S, and ³²S were simultaneously collected through three Faraday cups, namely L3, C, and H3. Data were acquired in the transient signal acquisition mode (TRA). The integration time for a single signal cycle was 0.131 s, the background correction period was set to 15 s, the sample signal accumulation period was maintained for 40 s, and the flushing time between two tests was set to 70 s. The sulfur isotope composition was characterized using the following formula: δ³⁴S = [(³⁴S/³²S sample value/³⁴S/³²S standard ratio) − 1] × 10³. The final data were normalized and converted based on the Vienna Canyon Diablo Troilite standard (δ³⁴SV-CDT). The quality control scheme included the following elements: (1) using matrix-matched pyrite reference materials as a reference; (2) constructing a “reference material–quality control sample–reference material” cycle detection sequence; (3) cross-comparison testing (SSB), with five measurements of standard samples inserted before and after a single test cycle; (4) using the average value of the ³⁴S/³²S ratios of adjacent standard samples as the calibration base for unknown samples; and (5) introducing an internal pyrite standard to enhance the assessment of the data’s reliability. The measured value of δ³⁴S for the control sample WS-1 in the verification experiment was 1.1‰, which was within the error range recommended in the literature. The operational specifications and technical details of this method have been systematically described in the studies by Bao et al. [33], Yang et al. [34,35], and Chen et al. [36].

5. Analytical Results

5.1. Zircon U–Pb Age

The zircon U-Pb dating results for the Guojialing monzogranite (22GJL01) and porphyritic granodiorite (22GJL02), obtained via LA-ICP-MS, are summarized in Table 1 and graphically represented in Figure 5 and

Table 2. LA-ICP-MS zircon U-Pb isotope analyses of granite from the Yanshan gold deposit.

Lithology	Spot Name	Concentrations (ppm)							Ages (Ma)
		Th (ppm)	U (ppm)	Th/U	207Pb/235U	1σ	206Pb/238U	1σ	207Pb/235U	1σ	206Pb/238U	1σ
Monzogranite	22GJL01-1	150.41	336.23	0.45	0.1546	0.0092	0.0207	0.0004	144	7	130	2
	22GJL01-2	186.04	350.26	0.53	0.1439	0.0097	0.0194	0.0003	142	6	127	2
	22GJL01-3	263.13	423.92	0.62	0.1352	0.0071	0.0203	0.0004	130	6	131	2
	22GJL01-5	308.58	511.52	0.60	0.1454	0.0087	0.0203	0.0004	137	7	129	2
	22GJL01-6	91.18	154.26	0.59	0.1626	0.0160	0.0217	0.0005	150	12	137	4
	22GJL01-7	170.61	256.47	0.67	0.1577	0.0184	0.0214	0.0005	142	12	134	4
	22GJL01-9	349.18	493.27	0.71	0.1445	0.0073	0.0197	0.0003	136	7	127	2
	22GJL01-10	238.69	401.15	0.60	0.1423	0.0071	0.0206	0.0003	136	6	130	2
	22GJL01-11	542.50	673.23	0.81	0.1341	0.0063	0.0201	0.0003	129	5	128	2
	22GJL01-12	174.67	289.41	0.60	0.1313	0.0099	0.0209	0.0004	126	8	135	3
	22GJL01-13	240.79	417.18	0.58	0.1550	0.0105	0.0204	0.0004	145	9	134	3
	22GJL01-14	327.87	507.82	0.65	0.1292	0.0062	0.0201	0.0003	125	6	128	2
	22GJL01-15	350.31	506.12	0.69	0.1279	0.0057	0.0204	0.0003	124	5	129	2
	22GJL01-16	192.02	248.52	0.77	0.1378	0.0085	0.0199	0.0004	131	8	130	3
	22GJL01-17	149.27	264.31	0.56	0.1540	0.0112	0.0208	0.0005	144	8	133	3
	22GJL01-18	209.35	325.45	0.64	0.1472	0.0076	0.0203	0.0004	137	7	129	2
	22GJL01-19	386.52	525.35	0.74	0.1333	0.0065	0.0198	0.0003	129	7	126	2
	22GJL01-20	429.69	961.58	0.45	0.1519	0.0061	0.0216	0.0003	143	5	136	2
Porphyritic granodiorite	22GJL02-1	238.19	372.75	0.64	0.1463	0.0098	0.0203	0.0005	139	9	130	3
	22GJL02-2	326.60	529.13	0.62	0.1361	0.0065	0.0201	0.0003	131	7	127	2
	22GJL02-3	324.92	459.16	0.71	0.1324	0.0069	0.0202	0.0004	128	7	130	2
	22GJL02-4	362.16	581.29	0.62	0.1435	0.0071	0.0207	0.0004	137	6	133	2
	22GJL02-5	346.78	425.82	0.81	0.1356	0.0075	0.0205	0.0004	129	7	129	2
	22GJL02-6	281.34	429.89	0.65	0.1348	0.0078	0.0201	0.0004	128	6	127	2
	22GJL02-7	278.94	492.07	0.57	0.1609	0.0099	0.0216	0.0004	151	8	136	3
	22GJL02-8	188.67	359.12	0.53	0.1449	0.0116	0.0198	0.0005	137	10	126	3
	22GJL02-9	252.61	282.33	0.89	0.1230	0.0082	0.0198	0.0004	121	7	128	2
	22GJL02-10	228.51	341.22	0.67	0.1456	0.0115	0.0209	0.0005	136	10	132	3
	22GJL02-12	371.85	545.37	0.68	0.1441	0.0065	0.0213	0.0003	136	6	136	2
	22GJL02-13	251.77	336.25	0.75	0.1425	0.0093	0.0199	0.0004	135	8	126	2
	22GJL02-14	149.82	262.81	0.57	0.1457	0.0126	0.0212	0.0005	137	11	132	3
	22GJL02-15	263.61	417.51	0.63	0.1535	0.0083	0.0212	0.0004	143	7	132	2
	22GJL02-16	249.69	467.80	0.53	0.1681	0.0095	0.0225	0.0004	155	7	142	3
	22GJL02-17	314.51	537.42	0.59	0.1472	0.0068	0.0196	0.0003	141	6	128	2
	22GJL02-18	275.33	420.25	0.66	0.1385	0.0125	0.0203	0.0005	133	9	134	3
	22GJL02-19	465.32	677.56	0.69	0.1515	0.0079	0.0219	0.0004	139	7	132	2
	22GJL02-20	358.90	482.52	0.74	0.1442	0.0085	0.0207	0.0004	136	8	131	2

. The zircon grains analyzed in both samples predominantly exceed 100 μm in length, display euhedral morphology, and exhibit transparency. Cathodoluminescence (CL) imaging further reveals well-developed columnar textures and oscillatory zoning patterns (Figure 6a,b). The Th/U ratios for zircons in 22GJL01 and 22GJL02 range from 0.45 to 0.77 and from 0.47 to 0.89, respectively, consistent with their magmatic origins (Table 2; [37,38]).

For the monzogranite (22GJL01), the ²⁰⁶Pb/²³⁸U ages of 20 zircon grains ranged from 126 ± 2 Ma to 1125 ± 12 Ma, revealing two distinct populations (Figure 6c): a dominant Early Cretaceous group (130 ± 2 Ma, 1σ, MSWD = 1.8, n = 18) and a subordinate Neoproterozoic group (685 ± 8 Ma, n = 2). According to previous studies, younger ages constrain the emplacement of the granodiorite porphyry, while older ages likely reflect inheritance from the Sulu orogenic belt or Yangtze Craton basement. Similarly, porphyritic granodiorite (22GJL02) yielded ²⁰⁶Pb/²³⁸U ages ranging from 126 ± 2 Ma to 2274 ± 20 Ma, clustering into two groups (Figure 6d): a predominant Early Cretaceous cluster (131 ± 2 Ma, 1σ, MSWD = 2.3, n = 19) and an Archean–Paleoproterozoic cluster (2274 ± 20 Ma). The former defines the intrusion age of the monzogranite porphyry, whereas the latter is attributed to zircon inheritance from the North China Craton basement.

5.2. Sulfur Isotope Composition

In situ sulfur isotope analysis was performed on different pyrite grains from three samples (YS-1, YS-2, andYS-4), yielding a total of 21 spot measurements (

Table 3. Sulfur isotope analysis of pyrite in the Yanshan gold deposit.

Deposit	Sample	δ34Sv-CDT (‰)	Reference
Yanshan gold deposit	YS-1 (Py1)	3.34	This study
	YS-2 (Py1)	3.21
	YS-3 (Py1)	5.35
	YS-4 (Py1)	5.22
	YS-5 (Py1)	4.92
	YS-6 (Py1)	3.52
	YS-7 (Py1)	3.88
	YS-8 (Py1)	4.94
	YS-9 (Py1)	4.14
	YS-10 (Py1)	3.57
	YS-11 (Py1)	5.16
	YS-12 (Py2)	8.88
	YS-13 (Py2)	7.22
	YS-14 (Py2)	6.32
	YS-15 (Py2)	7.71
	YS-16 (Py2)	8.93
	YS-17 (Py2)	9.45
	YS-18 (Py2)	6.75
	YS-19 (Py2)	7.60
	YS-20 (Py2)	7.79
	YS-21 (Py2)	9.77
Daliuhang gold deposit	SD45B1-1	6.81	[39]
	SD45B1-2	5.08
	SD44B1-5	6.78
	SD44B1-6	6.76
	SD44B1-7	6.52
	SD44B1-8	5.78
	SD46B1-3	6.64
	SD46B1-4	6.59
	SD47B1-1	4.87
	SD47B1-2	4.82
	SD47B1-3	4.97
	SD44B1-1	6.39
	SD44B1-2	6.79
	SD44B1-3	6.81
	SD44B1-4	5.93
	SD46B1-1	7.04
	SD46B1-2	6.49
	SD47B1-4	5.1
	SD47B1-5	6.05
Heilangou gold deposit	HLI-1	7.2	[40]
	HLI-4	6.8
	HLII-2	6.7
	HLI-10	6.9
	HLII-11	9.5
	HLI-21	8.0
	HLH-1	8.4
	HLH-3	6.3
Hexi gold deposit	HX-11	7.6	[40]
	HX-12	7.4
	HX-13	7.5
	HX-14	8.0
	HX-15	8.5

). Notably, the δ³⁴S values of pyrite can be clearly divided into two groups. The isotopic values of euhedral pyrites (Py1; 3.21–5.35‰, n = 11) are systematically lower than those of anhedral pyrites(Py2; 6.32–9.77‰, n = 10). This may imply that the fluid exchanged materials with the wall rocks during migration or evolution, or that there were multiple stages of fluid mixing, resulting in an overall increase in δ³⁴S values.

6. Discussion

6.1. Mineralization Age

Zircon U–Pb geochronology plays a pivotal role in elucidating the temporal linkages between mineralization and associated magmatic events [17]. In the Yanshan gold deposit, granitic samples from the Guojialing granodiorite predominantly contain prismatic, short-columnar zircon grains. Cathodoluminescence (CL) images reveal distinct oscillatory zoning patterns (Figure 6a,b), which are indicative of a magmatic origin. LA-ICP-MS zircon U-Pb dating of monzogranite (22GJL01) and granodiorite (22GJL02) yielded concordant ages of 130 ± 2 Ma and 132 ± 2 Ma, consistent with the zircon U–Pb ages previously reported, ranging from 123 to 135 Ma (Figure 6c,d; [17,40,41,42,43,44]). Three discordant age outliers were identified and interpreted as inherited zircons captured from country rocks during magma emplacement. The geological characteristics of the Yanshan gold deposit demonstrate a close genetic relationship between Guojialing granodiorite and gold mineralization, as evidenced by the following: (1) Gold orebodies hosted within the Guojialing granodiorite, with orientations controlled by NE-trending structures. (2) Widespread silicification, sericitization, and chloritization are spatially associated with gold mineralization in the granodiorite, where positive correlations exist between Au grade and the intensity of silicification–sericitization. (3) Regional mineralization studies constrain the gold mineralization event to 116–128 Ma (

Table 4. Geochronological data compilation of the Jiaodong Peninsula.

Location	Deposit Name	Age(Ma)	Analysis Method	Source(s)
Zhaoyuan-Laizhou gold belt	Dayingezhuang	119.1 ± 1.2	Sericite Ar-Ar	[36]
	Sanshandao	117.6 ± 3.0	Sericite Rb-Sr	[45]
	Cangshang	121.3 ± 0.2	Sericite Ar-Ar	[46]
	Jiaojia	120.5 ± 0.6	Mscovite and sericite Ar-Ar	[47]
		119.2 ± 0.2
	Shangzhuang	126.2 ± 1.9	Molybdenite Re-Os	[48]
	Wang’ershan	119.2 ± 0.5	Sericite Ar-Ar	[49]
		120.7 ± 0.6
	Xincheng	120.7 ± 0.2	Muscovite and sericite Ar-Ar	[47]
		120.2 ± 0.3
	Linglong	122 ± 11	Pyrite Rb-Sr	[50]
		122.7 ± 3.3
		123.0 ± 4.2
Muping-Rushan gold belt	Denggezhuang	118 ± 9	Sericite Rb-Sr	[51]
	Jinqingding	117 ± 3	Hydrothermal zircon U-Pb	[52]
	Guocheng	116.2 ± 2.4	Quartz fluid inclusion Rb-Sr	[53]
	Liaoshang	116	Geological constrain	[53]
	Pengjiakuang	120.9 ± 0.4	Sericite Ar-Ar	[54]
		119.1 ± 0.2
	Fayunkuang	128.49 ± 7.2	Pyrite Rb-Sr	[55]
Penglai-Qixia gold belt	Daliuhang	120.5 ± 1.7	Monazite U-Pb	[56]
	Qixia	125.8 ± 1.7	Pyrite Rb-Sr	[57]
	Hushan	120.0 ± 3.0	Monazite U-Pb	[58]
	Ankou	119.61 ± 0.70	Sericite Ar-Ar	[59]
	Heilangou	120.09 ± 0.71	Sericite Ar-Ar
	Qijiagou	117.81 ± 0.69	Sericite Ar-Ar

), peaking at ~120 Ma [36,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59]. The close correlation between the Guojialing granodiorite and gold mineralization further highlights that the Early Cretaceous, driven by contemporaneous magmatic and hydrothermal activities, was a critical period for large-scale gold mineralization on the Jiaodong Peninsula.

Previous geochronological and geochemical investigations have demonstrated that lithospheric destruction of the North China Craton began during the Late Triassic, with continental extension commencing at 160–150 Ma, coinciding with the generation of continental crust-derived granites [13,14,18,19,27,58]. During the Early Cretaceous, an extensional tectonic regime associated with lithospheric thinning developed in eastern North China. This extension facilitated asthenospheric upwelling, which triggered partial melting of an enriched lithospheric mantle. This mantle enrichment was the result of prior metasomatism by subducted components derived from the Yangtze continental crust, followed by contributions from the Paleo-Pacific slab [14,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79]. The resultant volatile-rich mantle-derived melts underwent underplating at the base of the lower crust. This process introduces significant heat and fluid, inducing crustal anatexis and generating silicic crustal melts. Subsequent large-scale interactions and hybridization occur between these crustal melts and the mantle-derived melts, forming extensive crust–mantle magma mixing zones within the deep crust [1,2,3,17,19,26,27,75,80].

These hybrid magmas ascended through pre-existing and extension-related structural weaknesses via diapiric ascent and/or dike propagation. Their migration culminated in the emplacement of plutons.

During the late-stage crystallization differentiation of these magmas, ore-forming fluids exsolved from the evolving melt. These hydrothermal fluids, enriched with gold and other metals, migrated preferentially along magma–wall rock contacts and regional-scale structural discontinuities (e.g., faults and fractures).

This fluid mobilization event ultimately led to regional-scale gold mineralization. The temporal and spatial association between Guojialing magmatism and gold mineralization is fundamentally controlled by unique crust–mantle interaction processes that occur during lithospheric extension. These processes provided essential metal sources (derived from the enriched mantle and potentially the lower crust), thermal energy required to drive fluid circulation, and the requisite structural pathways and chemical gradients required for efficient gold transport and deposition.

6.2. Sources of Ore-Forming Material

Sulfur isotopes are an effective tool for tracing the source of ore-forming materials. Studies have shown that sulfur has three sources: mantle sulfur (δ³⁴S = 0, with a range of 0 ± 3‰), modern seawater sulfur (δ³⁴S = +20‰), and reduced (sedimentary) sulfur (δ³⁴S with negative values) [81]. Sulfur from different sources exhibits distinct δ³⁴S characteristics. The δ³⁴S values of sulfides formed in hydrothermal fluids are influenced by temperature, pH, and the fugacity of oxygen and sulfur, and do not always equal the total δ³⁴S values of hydrothermal sulfur [82,83]. Under low oxygen fugacity, sulfur exists as HS⁻ and S²⁻, and the δ³⁴S values of sulfides are close to the total δ³⁴S values of the fluid [84,85].

The in situ sulfur isotopic values of the Yanshan gold deposit range from 3.21‰ to 9.77‰ (average 6.08‰), with a relatively concentrated distribution; these values are higher than those in the mantle (δ³⁴S = 0, with a range of 0 ± 3‰), indicating that the sulfur source is not entirely derived from mantle-derived magma (Figure 7). Research has shown that the δ³⁴S values in euhedral–subhedral pyrite grains range from 3.21‰ to 5.35‰, with an average value of 4.30‰; meanwhile, the sulfur isotopic values in subhedral–anhedral pyrite grains range from 6.32‰ to 9.77‰, with an average value of 8.04‰. This suggests that during the early stages of mineralization, the ore-forming material originated from the mantle or magma, with later-stage contributions from host rocks. The sulfur in ore-forming fluids mainly originates from magmatic rocks with high δ³⁴S values (3.57‰–9.77‰) [63] or from the occurrence of high-oxygen mantle degassing in subduction zones [64]. Therefore, the ore-forming materials of the Yanshan gold deposit are primarily derived from magma or the mantle, with some admixture of crustal material. The δ³⁴S values of other gold deposits in the Qixia–Penglai mineralization belt are listed in Table 3. The δ³⁴S values of the Daliuhang gold deposit range from 4.82‰ to 7.04‰, with an average value of 6.12‰ [39]; those of the Heilangou gold deposit range from 6.3‰ to 9.5‰, with an average value of 7.48‰ [40]; and those of the Hexi gold deposit range from 7.4‰ to 8.5‰, with an average value of 7.8‰ [40]. Therefore, the sulfur isotopic values of the Yanshan gold deposit are lower. The main reasons for this may be the dominant contribution of early low δ³⁴S mantle/magmatic sulfur, contamination of the crustal wall rock, and differences in sulfur isotope fractionation during ore-forming fluid evolution. However, the range in the δ³⁴S values (3.21‰–9.77‰) of the Yanshan gold deposit generally overlaps with that of the Daliuhang (4.82‰–7.04‰) and Heilangou (6.3‰–9.5‰) gold deposits, indicating that the mineralization of these gold deposits is related to magmatic activity.

6.3. Ore Genesis

There are two main viewpoints regarding the ore genesis of the Yanshan gold deposit. Some researchers believe that the deposit is a gold deposit formed by the superposition of both mesothermal hydrothermal replacement and silica-rich hydrothermal filling processes [86], while others classify it as a mesothermal hydrothermal vein-type deposit [23]. Based on the comprehensive geological characteristics and the in situ sulfur isotopic data, this study suggests that the Yanshan gold deposit is a mesothermal magmatic–hydrothermal vein-type gold deposit.

The ore body is mainly controlled by the Daliuhang fault (NNE-trending), similar to the magmatic–hydrothermal gold deposits of the Jiaodong Peninsula [87]. The ore minerals in the Yanshan gold deposit mainly include metal sulfides, such as pyrite, chalcopyrite, galena, and sphalerite, as well as native gold and electrum. The alteration of the wall rocks mainly includes silicification, sericitization, and potassic alteration. The in situ sulfur isotopic characteristics of the sulfides suggest that the ore-forming materials of the deposit primarily originate from the mantle or magma, with the involvement of host rocks. However, the δ³⁴S values of orogenic gold deposits are often inherited from the crustal wall rocks (such as sedimentary rocks or regional metamorphic rocks), and due to the isotopic fractionation of crustal materials, their range is wider (usually −10‰ to +10‰, with some reaching −20‰ to +20‰), significantly deviating from the characteristic isotopic sulfur values of the mantle (−3‰ to +3‰). This is inconsistent with the typical features of orogenic gold deposits. In the Yanshan gold deposit, cathodoluminescence (CL) images of zircon grains from Guojialing granodiorite exhibit a distinct oscillatory zoning pattern (Figure 6), indicating a magmatic origin. The U-Pb dating of zircons from the Guojialing granodiorite yields ages of 130 ± 2 Ma and 132 ± 2 Ma. These findings are related to the early Cretaceous magmatic activity of the Jiaodong Peninsula [88].

The tectonic basement of the Jiaodong Peninsula comprises Proterozoic metamorphic and Mesozoic intrusive rocks [64]. Since the Jurassic, the superimposition of the ancient Pacific tectonic system has led to the partial melting of the lower crust beneath the Jiaodong Peninsula, triggering large-scale Mesozoic magmatic activity [89]. A series of Mesozoic magmatic rocks dominated by monzogranites and granodiorites was formed from west to east [3]. In the Late Early Cretaceous (120 ± 5 Ma), the entire Jiaodong region was in an extensional tectonic environment due to the retreat of the subducting Pacific Plate (Figure 8) [90]. Lithospheric thinning and mantle material upwelling, along with strong interactions between the crust and mantle, led to the formation of hydrothermal fluids with crust–mantle mixing characteristics [86]. Extensional faults provide not only a good channel for ore-forming fluid migration but also function as a favorable space for ore-forming fluid enrichment and orebodies. The ore-bearing structure of the quartz vein-type gold deposit is opposite to that of the altered rock-type gold deposit (Figure 9). The quartz vein-type gold deposit is mainly controlled by a steep-dipping fault (Figure 9). The relatively steep dip fault is the expansion zone, which is a favorable section for quartz vein-filling. The decompression space is easily formed in the extensional shear segment of the main fault or in secondary extensional or tensional shear faults, in which the ore-forming fluid is filled with ore-forming minerals [91] under the action of pumping, forming quartz vein-type gold deposits.

7. Conclusions

The mineralization of the Yanshan gold deposit is dominated by quartz–sulfide vein-type gold mineralization, where native gold is regularly observed within pyrite grains and in the interstices of quartz crystals.

Studies on mineralization chronology have revealed that the deposit has a close temporal–spatial association and genetic connection with the Guojialing granites (including monzogranite and porphyritic granodiorite) in the mining area. The zircon U-Pb Concordia ages of these two types of granite are 130 ± 2 Ma and 131 ± 2 Ma, respectively, which clearly indicates that the gold mineralization event occurred in the Early Cretaceous period.

Regarding the source of sulfur, in situ sulfur isotope analysis of gold-bearing pyrite indicates a predominantly magmatic origin. Although granitoids are highly likely to have provided the thermal drive for fluid activity, the precise origins of the fluids and ore-forming materials remain difficult to constrain.

Based on a comprehensive analysis of the above-mentioned mineralization characteristics, mineralization age, material source, and regional tectonic setting, it can be determined that the Yanshan gold deposit is a magmatic–hydrothermal vein-type gold deposit. Thus, its formation was controlled by the subduction of the Paleo-Pacific Plate and is a direct product of magmatic–hydrothermal activities under this tectonic regime.