Molybdenum Mineralization in Eastern Hebei, China: Evidence from Geochronology and Isotopic Composition

Abstract

The northern margin of the North China Craton is one of the most important porphyry-skarn molybdenum ore belts in the world. The eastern Hebei Province, which contains a high number of molybdenum and gold (molybdenum) resources, is an important portion of the northern margin of the North China Craton. Xichanggou and Huashi, located in eastern Hebei, are quartz-molybdenum vein deposits that are intimately associated with intrusions that are deeply concealed in the mining area. This work presents two zircon U-Pb dates and ten molybdenite Re-Os ages from samples of the aforementioned two deposits in order to determine the timing of the intrusion and mineralization. The zircon U-Pb ages of the quartz monzonite porphyry from Xichanggou are determined to be 163.3 ± 0.3 Ma and 162.8 ± 0.4 Ma. The molybdenite Re-Os dating yielded ages of 160.3 ± 4.6 Ma for Xichanggou and 171.4 ± 19 Ma for Huashi, respectively. The isotopic composition of oxygen and hydrogen of the ore-forming fluid from Huashi, as indicated by the δD_V-SMOW values (−80.0‰ to −67.6‰) and δ¹⁸O_H2O values (−1.86‰ to 2.33‰), suggests that the fluid is primarily composed of water derived from magma, with some contribution from atmospheric precipitation. The sulfur isotope values (δ³⁴S) of sulfides from Xichanggou range from 6.5‰ to 7.1‰, while the δ³⁴S values from Huashi range from 3.3‰ to 4.9‰. The lead isotope ratios (²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb) of sulfides from Xichanggou and Huashi average at 17.414, 15.428, and 17.591, 15.379, respectively. The Re-Os isotopic compositions of ore sulfides mostly fall within the range of 318 ppm to 50,114 ppm. These isotopic compositions indicate that the materials responsible for the formation of the ores in Xichanggou and Huashi primarily originate from the melting of lower crust materials that have been contaminated by the mantle. Based on the regional data, the molybdenum deposits in eastern Hebei were formed in multiple periods, specifically approximately 170 Ma and 160 Ma in Huahsi and Xichanggou, respectively. The subduction of the Paleo-Pacific plate during the middle–late Jurassic period led to the partial remelting of lower crust material, resulting in the acquisition of a significant quantity of metal elements (Mo), which were subsequently deposited.

1. Introduction

Porphyry-skarn molybdenum deposits are a significant global source of molybdenum [1,2,3,4,5,6,7,8]. These types of Mo deposits are widespread in the southern and northern margin of the North China Craton [2,6,8]. The eastern Hebei region is situated on the northern boundary of the North China Craton. During the Mesozoic epoch, it was affected by both the closure of the Mongolia-Okhotsk plate and the subduction of the Paleo-Pacific plate. The regional magmatic activity and geological structure exhibit a high degree of complexity [9]. Over the past few years, numerous geologists have discovered a significant abundance of molybdenum and gold (molybdenum) deposits in this region. The typical Mo(-Cu) mineralization includes the giant Taipingcun [9], the medium-sized Sibozi [10], and the medium-sized Shouwangfen deposits [11]. Gold deposits containing molybdenum include the Yuerya large gold deposit [6], the Tangzhangzi small gold deposit [12,13] and the Xiayingfang medium-sized gold deposit [14]. The deposits in question were formed during the Mesozoic era, specifically between 190 and 110 Ma [6,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24]. They encompass many types, including porphyry, skarn, hydrothermal vein, and breccia. Their findings suggest that there is a significant possibility of molybdenum polymetallic mineral deposits in the eastern Hebei region.

The molybdenum deposits in the region are primarily found in the central part of the Malanyu anticlinorium. The Xichanggou molybdenum deposit is an early discovered molybdenum deposit located near the Huashi, Taipingcun, and Taiyanggou molybdenum deposits in the vicinity. The diagenesis and mineralization age available indicate that the molybdenum deposits in the area were formed as a result of the subduction of the ancient Pacific plate during the late Jurassic period [6,9,10,11,12,13,14,15,16,17,18]. The primary focus of the research findings in the field pertains to the geological features, rock geochemistry, and chronology of individual molybdenum occurrences [6,6,7,8,9,10,11,12,13,14,15,16,17,18]. In the region, there is currently a shortage of comprehensive and detailed research on the genetic process of molybdenum polymetallic deposit mineralization. This study will focus on the topic at hand, specifically the Xichanggou and Huashi molybdenum deposits, which will serve as the subjects of our investigation. This study provides novel field observations, zircon U-Pb and molybdenite Re-Os geochronology, and comprehensive stable isotope data (S-Pb-O-H) for the Xichanggou and Huashi molybdenum deposits in order to further our understanding of the ore origin. Furthermore, this study also collected the chronological and isotopic composition data of other molybdenum deposits in the region, aiming to further comprehend the process behind molybdenum mineralization in the studied area.

2. Regional Geology

The eastern Hebei region is situated in the western section of the Malanyu anticlinorium within the eastern portion of the Yanshan orogenic belt (Figure 1). The visible strata consist of the Precambrian metamorphic fold basement and the sedimentary cover from the Meso-Neoproterozoic to Mesozoic periods [25,26]. The area is characterized by well-developed regional folds, known as the Malanyu anticlinorium, as well as fault structures, specifically the Miyun-Xifengkou fault. These geological features cross and overlap, creating the fundamental tectonic framework of the region [26]. During the Archean Wutai period, the Proterozoic Lvliang period, and the Mesozoic Indosinian and Yanshanian period, the area was active with magmatic activities, which led to the formation of multiple plutons. The large plutons mainly include the Dushan intrusion formed in the Indosinian period (240 Ma) [9] and the Wangpingshi, Qianfenshuiling, Maoshan, Luowenyu, Gaojiadian, Madi, and Yuerya intrusions formed in the Yanshanian period (200~130 Ma) [9,25,26,27,28]. The rock types encompass monzonitic granite, granodiorite, granite porphyry, and quartz syenite porphyry.

The intense tectono-magmatic activity in the area not only supplies abundant materials for the formation of molybdenum, gold, copper, and other metal deposits but also serves as a dynamic source, pathway, and space for the movement of hydrothermal fluids responsible for ore formation [17]. Hence, the area is abundant in mineral resources. The minerals that are currently recognized include iron, gold, molybdenum, tungsten, copper, lead, zinc, silver, chromium, beryllium, rubidium, cesium, niobium, tantalum, and others.

3. Deposit Geology

3.1. Xichanggou Deposit

3.1.1. Deposit Geology

The Xichanggou deposit is situated in the northern section of the Malanyu anticline (Figure 1). The strata observed in the Xichanggou comprise the Mesoproterozoic Changzhougou Formation (Pt₂¹), the Chuanlinggou Formation (Pt₂¹ch), the Tuanshanzi Formation (Pt₂¹t), and the Cenozoic Quaternary (Q₄) (Figure 2). The area has a highly developed geological structure, which is a result of the combined effects of various crustal changes and magmatic intrusive activities. The magmatic processes in the mining area are intense, mainly due to the occurrence of stocks and dikes, and the Xichanggou granite porphyry is the most important intrusion. The intrusion has an elliptical form and is exposed in a region of about 0.26 km².

The Xichanggou granite porphyry has a weathered surface that appears gray–white to light flesh-red, whereas the fresh surface is flesh-red. It exhibits a porphyritic structure and a block structure (Figure 3). Potassium feldspar, plagioclase, quartz, and biotite primarily form the phenocrysts, which make up 15% to 30% of the total composition. The potassium feldspar phenocrysts are 1–2 mm in size and have a content of 8% to 10%. They exhibit a fleshy-red color and have a columnar shape. The plagioclase phenocrysts, which are 1–2 mm in size and account for 4% of the total phenocryst content, exhibit a grayish-white color and a plate-like shape. Quartzes range in size from 2 to 3 mm and have a content of 8% to 10%. They are characterized by their granular nature. The biotite phenocrysts, which are 2–3 mm in size and account for 1% of the total phenocryst content, exhibit a black color and a plate-like shape. The groundmass, comprising around 70% to 85% of the total composition, consists primarily of quartz, potassium feldspar, and plagioclase. Granite porphyry is predominantly silicified or silicified cataclastic in nature. The silicified cataclastic granite porphyry exhibits the most pronounced alteration and mineralization. The observed changes are silicification, pyritization, and molybdenite mineralization. Chalcopyrite and galena mineralization can also occur occasionally.

The dikes in the mining area consist primarily of coarse-grained granite dikes, granite syenite porphyry dikes, diorite porphyrite dikes, and other similar intrusive rocks. The granite syenite porphyry dikes were the first to form and have the widest distribution of all dikes. Pyritization and molybdenite mineralization are frequently observed in the granite–syenite porphyry. In contrast, the creation of coarse-grained granite porphyry and diorite porphyrite occurs at a later stage, resulting in only localized star-shaped pyritization. The delayed formation of dikes compromises the structural integrity of the ore deposit.

3.1.2. Ore Body Characteristics

Molybdenum ore deposits are found in cryptoexplosive breccia and granite porphyry formations (Figure 4). An extensive examination identified a single pyrite ore deposit and fourteen molybdenum ore deposits, most of which remain hidden. The project controls three ore deposits, namely I, II, and III. The primary ore deposit (referred to as the II ore body) that is being managed by the project has a length of 500 m, a maximum thickness of 224.72 m, and an average grade of 0.0728%. The ore bodies primarily exhibit irregular lenticular shapes, and the continuity of mineralization is favorable. However, the occurrence of mineralization varies significantly.

There are four basic categories of ores, based on their origin and position in the contact zone. The ore types present in sequential order, from the innermost to the outermost, are the granite porphyry-type ore (Figure 5a,b), the cryptoexplosive breccia-type ore (Figure 5a), and the silicified hornfels-type ore. The primary metallic minerals present include molybdenite, pyrite, and chalcopyrite (Figure 5c–f). The primary nonmetallic minerals include potassium feldspar and biotite. The molybdenum grade in the ore typically ranges from 0.03% to 0.15%, with a maximum value of 0.33%. Additional metallic minerals, including sphalerite, galena, magnetite, chalcocite, malachite, azurite, and limonite, can be found in various types of ores. Nonmetallic minerals such as sericite, chlorite, calcite, and tremolite are also present. The ore’s texture mostly consists of a grain texture and blade texture, as well as an evident metasomatic texture, poikilitic texture, and solid solution decomposition texture. The structure consists of a pattern of scattered stars and veinlets.

3.1.3. Stage of Mineralization

The hydrothermal mineralization of the Xichanggou molybdenum deposit is divided into three stages based on the field geological characteristics, the order of mineral crystallization, the relationship between different veins, and the hydrothermal alteration of wall rock. These stages are as follows:

(1)

The molybdenite–magnetite stage is the primary phase of molybdenum mineralization. The presence of molybdenite, potassium feldspar, and iron-bearing minerals defines the mineral assemblage of this stage.

(2)

The quartz–molybdenite stage is the main metallogenic stage. During the precipitation of a significant amount of quartz, a considerable number of metal minerals, including pyrite and molybdenite, precipitated in this stage. Molybdenite is a mineral that is characterized by its tiny, scaly appearance. It is found in several forms, including disseminated, veinlet-disseminated, and reticular. Quartz veinlets, which contain molybdenite, are the most important ore veins. A limited quantity of molybdenite is present within the rock fissures, exhibiting both a singular vein and a dispersed distribution. The predominant gangue minerals include quartz, potassium feldspar, and sericite.

(3)

The quartz–polymetallic sulfide stage primarily consists of veins with minimal or absent molybdenite. These veins often formed after the quartz–molybdenite stage. The veins consist of pyrite quartz veins, galena, sphalerite quartz veins, and other minerals.

3.1.4. Alteration of Wall Rock

The extensive shale of the Chuanlinggou Formation in this region is influenced by subsequent structural changes and interactions with intrusive magmatic activity, resulting in the occurrence of hornfelsification through thermal metamorphism. The limonite mineralization is visible on the surface, exhibiting shades of gray-brown and black-brown. The intensity of silicification directly correlates with the lightness of the color. The proximity to the contact zone directly correlates with the intensity of change and the prominence of the crushing phenomenon. Silicification is the main type of alteration, and secondary sulfide mineralization includes pyritization, chalcopyrite mineralization, and lead mineralization. Chloritization, kaolinization, and carbonation occur rarely.

3.2. Huashi Deposit

3.2.1. Deposit Geology

The predominant rock formations in the mining area consist of Archean Qianxi Group hornblende plagioclase gneiss; Mesoproterozoic Changcheng System Changzhougou Formation quartz glutenite; and Cenozoic Quaternary (Figure 6). The mining area is characterized by two primary fault groups: NW–NNW-trending faults and NE-trending faults. The faults that trend in a northeast direction are designated as F₁ and F₄. The F₁ fault lies to the west of the mining area. The F₄ fault, which is of a minor magnitude, is situated in the central part of the mining region and traverses ore deposit No. 11.

The magmatic activity in the area is characterized by intense intrusive activity, predominantly occurring during the early Jurassic period. In the southern region, the Madi alkali feldspar granite is visible, and in the northern region, the Wangpingshi monzonitic granite is visible. Simultaneously, the area also has a variety of Proterozoic-Archean and Mesozoic dikes. The Madi alkali feldspar granite exhibits a strong genetic association with the Huashi molybdenum and rare metal deposits. The Madi alkali feldspar granite occurs as rock strains covering an area of 5.35 km². The Madi alkali feldspar granite penetrated the hornblende plagioclase gneiss through at least two intrusion events. The central part of Madi has an age of 175.5 Ma, whereas the peripheral area has an age range of 156–165 Ma [19].

3.2.2. Ore Body Characteristics

The Huashi molybdenum deposit is situated within a distance of 100 m north of the Madi intrusion. The ore body mainly occurs in the biotite hornblende plagioclase gneiss and plagioclase amphibolite series of the Malanyu Formation of the Archean Zunhua Group. The occurrence of molybdenum mineralization is mostly influenced by the NW–NNW- and NE-trending faults resulting from magmatic intrusion and tectonic processes in the region. The ore veins mainly develop along the rock fracture zone resulting from the NW–NNW fault. The predominant form of molybdenum mineralization is characterized by molybdenite quartz veins (Figure 7). The ore veins are arranged in a north–south distribution, encompassing No. 2, No. 4, No. 6, No. 17, No. 13, No. 14, No. 20, No. 22, No. 15, No. 12, and No. 11.

The ore can be classified into many varieties based on its mineral composition, including massive pyrite–molybdenite quartz ore (Figure 8a,b), banded pyrite–molybdenite–quartz ore, porphyritic pyrite–molybdenite–quartz ore, and veinlet-disseminated pyrite–molybdenite–quartz ore. The predominant metal minerals found in the ore are mostly pyrite, magnetite, and molybdenite (Figure 8c–f), constituting approximately 30–40% of the total composition. Chalcopyrite, galena, and sphalerite are also present, but their quantities vary. The gangue mineral primarily consists of quartz, with trace amounts of sericite, chlorite, and other minerals.

Molybdenite is present in the cracks of quartz veins in the form of layered and compact vein-like clusters. Typically, the width of molybdenite veins ranges from 2 to 5 mm, with a maximum width of 10 mm. The majority of molybdenite does not have direct interaction with other metallic minerals. Occasionally, pyrite and scaly molybdenite are observed, and they often fill the quartz vein toward the uppermost part, particularly in its wider portion.

3.2.3. Stage of Mineralization

The hydrothermal mineralization of the Huashi molybdenum deposit is divided into three stages based on the field geological characteristics, the order of mineral crystallization, the relationship between different veins, and the hydrothermal alteration of wall rock. These stages are as follows:

(1)

Quartz–magnetite–molybdenite stage. The stage is characterized by the presence of quartz, magnetite, and molybdenite. The metallic minerals included in the sample exhibit a granular structure for magnetite, a leaf-like structure for molybdenite, and a granular structure for hematite. The gangue minerals consist primarily of quartz, together with a minor quantity of potassium feldspar.

(2)

The quartz–molybdenite stage is the main phase of metallogenesis. Molybdenite exhibits a medium-fine grain size and has a leaf-like and needle-like morphology. Molybdenite is found in the periphery of quartz veins as fine veins, and it diffuses inside the quartz veins.

(3)

Quartz–molybdenite–pyrite stage. Molybdenite is found in quartz veins as thin veins. Pyrite with anhedral to subhedral crystal shapes is scattered among quartz veins. Metasomatism occurs between the ore vein and the surrounding rock, but the boundary between them is indistinct. A significant quantity of molybdenum precipitated during both the quartz–molybdenite stage and this stage.

3.2.4. Alteration of Wall Rock

Wall rock alteration is observed on both sides of the quartz vein or within the schistosity zone, with a width ranging from 0.2 to 1.0 m. The main alteration types observed are silicification, sericitization, and pyritization, with secondary alteration processes including chloritization and kaolinization. Silicification is an important aspect of the mineralization process. This is mostly observed as the formation of quartz veins and quartz veinlets along fractures and fissures, as well as the presence of large quantities of quartz. Sericite is often found in compact formations of small scales, especially inside feldspar illusions. The hydrothermal fluid, which contains sulfur, interacts with the nearby rock, resulting in the formation of pyrite. This process is closely associated with the occurrence of silicification and sericitization. Chlorite is commonly encountered in rock fractures or scattered throughout. The primary clay minerals formed during low-temperature hydrothermal metasomatic alteration at the Earth’s surface are predominantly kaolinite minerals, including kaolinite itself.

4. Sampling and Analytical Methods

4.1. Sampling

4.1.1. Xichanggou Samples

The samples utilized for zircon U-Pb dating at the Xichanggou molybdenum deposit were chosen from two specific locations. The first sample, labeled XCG-01, was taken from the light-red quartz monzonite porphyry at ZKA002, which is situated at an elevation of +402 m. The second sample, labeled XCG-02, was obtained from the dark-red quartz syenite porphyry at the adit, with coordinates X-4469298 and Y-39546703.

The molybdenite samples for Re-Os dating are mainly from the molybdenite quartz veins found during metallogenic stage II. Molybdenite has veinlets and scattered structure with a high grade. The molybdenite samples were assigned the following numbers: XCG-07, XCG-10, XCG-11, XCG-13, and XCG-14. The molybdenite samples utilized for analyzing sulfur and lead isotopes were assigned the following numbers: XCG-03, XCG-04, XCG-05, and XCG-06.

4.1.2. Huashi Samples

The molybdenite ore samples for Re-Os dating in the Huashi deposit were collected from molybdenite quartz veins that formed in the main metallogenic phase. The molybdenite samples were assigned the following numbers: HS-01, HS-3, HS-5, HS-6, and HS-7. Simultaneously, these samples were used for conducting tests to determine the isotopes of hydrogen, oxygen, sulfur, and lead. Furthermore, the HS-2 sample was intended for isotope testing.

4.2. Analytical Methods

4.2.1. Zircon LA-ICP-MS U–Pb Dating Method

Zircon isotopic age analysis was performed by the LA-ICP-MS laboratory of the Institute of Science, China University of Geosciences (Beijing). The instruments included a Neptune multi-collector inductively coupled plasma-mass spectrometer and a 193 nm LA-MC-ICP-MS online laser sampling system. Zircon was denuded by a 193 nm FX laser with a spot beam of 35 μm. The laser ablation material was sent to Neptune with He as the carrier gas to expand the dispersion by dynamic zoom, so that the U-Pb isotopes with large mass differences could be received at the same time and we could determine the U-Pb isotope. The 91,500 standard zircon, NIST610 and NIST612 glass were used as external standards for sample determination. Among them, 91,500 was used as an external standard to correct the mass discrimination and isotope fractionation effect during zircon U-Pb dating, and NIST610 and NIST612 were used as external standards to calculate the contents of U, Th and Pb in zircon. The age results were calculated using the Glitter 4.0 software package. The calculation of weighted average ages and the plotting of the Concordia diagram were completed with Isoplot/Ex_ver3 [29], and the common lead adjustment was conducted using Andersen software [30].

4.2.2. Molybdenite Re-Os Dating

The Re-Os isotope composition of molybdnite separates was determined in the Key Re-Os Laboratory of China, the Academy of Geological Sciences. A more detailed procedure for sample preparation is available in Li et al. [31], Li et al. [32] and Li et al. [33]. Rhenium and Os concentrations and isotopic compositions were measured by a Thermo Fisher Scientific Triton Plus mass spectrometer operating in negative ion-detection mode [34]. The instrumental mass fractionation of Os was corrected by normalizing the measured ¹⁹²Os/¹⁸⁸Os ratio to 3.08271. Based on blank runs analyzed together with samples, the total procedural blanks were about 3 pg for Re and 0.5 pg for Os. In-house sulfide Re-Os isotope references, JCBY, from the Jinchuan Cu-Ni deposit, were used for the quality control of the whole procedure.

4.2.3. Oxygen and Hydrogen Isotopes

Oxygen was liberated from quartz by reaction with BrF₅ [35] and converted to CO₂ on a platinum-coated carbon rod. The δ¹⁸O analyses were conducted on a Finnigan Mat 253 mass spectrometer at the Analytical Laboratory of the Beijing Research Institute of Uranium Geology.

For hydrogen isotope analysis, water was taken from quartz inclusions using the detonation method. The test procedure was as follows: the quartz inclusion sample was heated to burst, and the volatiles were released to extract water vapor. Then, the water reacted with zinc at 400 ℃ to produce hydrogen [36]. After freezing in liquid nitrogen, it was collected into a sample bottle with activated carbon. The δD analyses were conducted on a Delta v advantage gas isotope mass spectrometer at the Analytical Laboratory of the Beijing Research Institute of Uranium Geology.

4.2.4. Sulfur and Lead Isotopes

The sulfur isotope and lead isotope of sulfide in the ore were determined in the Analytical Laboratory of the Beijing Research Institute of Uranium Geology. The instrument used for sulfur isotope analysis was the DeltaV Plus isotope mass spectrometer, with an analytical precision of ±0.2‰. For lead isotope data, the ISOPROBE-T thermal ionization mass spectrometer was utilized. The detection method and basis follow the “Method for Determination of Lead, Strontium, and Neodymium Isotopes in Rocks,” and the error in the lead isotope ratio was less than 0.05‰.

5. Analytical Results

5.1. Xichanggou Zircon U–Pb Ages

The zircons found in the light-red quartz monzonite porphyry (sample XCG-01) exhibit a morphology characterized by short-columnar to long-columnar shapes, measuring between 50 and 150 μm in length. The length/width ratio of these zircons ranges from 1:1 to 1:4. The majority of zircons have transparent interiors, high levels of transparency, and distinct rhythmic cathodoluminescence (CL) zoning (Figure 9a).

The LA-ICP-MS U-Pb dating results of the zircons from XCG-01 are presented in

Table 1. LA-ICP-MS zircon U–Pb dating results of the Xichanggou granite porphyry.

Analysis Samples	Th	U	Th/U	207Pb/206Pb	1σ	207Pb/235U	1σ	206Pb/238U	1σ	207Pb/206Pb	1σ	207Pb/235U	1σ	206Pb/238U	1σ
	(10−6)	(10−6)
Sample XCG-01
XCG01-01	157.98	227.65	0.69	0.04916	0.00394	0.17446	0.01368	0.02574	0.00038	155	149	163	12	164	2
XCG01-02	502.13	468.15	1.07	0.04927	0.00209	0.17394	0.00694	0.0256	0.00033	161	69	163	6	163	2
XCG01-03	305.11	314.65	0.97	0.04937	0.00314	0.17438	0.01073	0.02561	0.00036	165	114	163	9	163	2
XCG01-04	185.56	233.73	0.79	0.04944	0.00371	0.17497	0.01278	0.02566	0.00039	169	136	164	11	163	2
XCG01-05	55.27	94.88	0.58	0.04931	0.009	0.17448	0.03161	0.02566	0.00055	163	309	163	27	163	3
XCG01-06	379.38	508.07	0.75	0.04924	0.00245	0.17337	0.00819	0.02553	0.00033	159	85	162	7	163	2
XCG01-07	143.25	249.49	0.57	0.04922	0.00386	0.1758	0.01346	0.0259	0.00038	158	145	164	12	165	2
XCG01-08	175.95	276.91	0.64	0.04937	0.00302	0.17526	0.0103	0.02574	0.00037	165	107	164	9	164	2
XCG01-09	285.46	450.86	0.63	0.04931	0.0028	0.17554	0.00952	0.02581	0.00035	163	99	164	8	164	2
XCG01-10	68.15	106.2	0.64	0.04934	0.00745	0.17585	0.02627	0.02584	0.0005	164	272	164	23	164	3
XCG01-11	367.36	647.19	0.57	0.0493	0.00208	0.17594	0.00687	0.02587	0.00033	162	67	165	6	165	2
XCG01-12	834.06	730.86	1.14	0.04919	0.00194	0.17582	0.0063	0.02591	0.00033	157	60	164	5	165	2
XCG01-13	1092.58	1843.66	0.59	0.0493	0.00176	0.17291	0.00551	0.02543	0.00031	162	52	162	5	162	2
XCG01-14	367.72	454.35	0.81	0.0493	0.00237	0.17387	0.00782	0.02557	0.00033	162	81	163	7	163	2
XCG01-15	605.48	971.81	0.62	0.04929	0.00188	0.17402	0.00595	0.02559	0.00032	162	56	163	5	163	2
XCG01-16	279.31	325.49	0.86	0.0493	0.00297	0.17443	0.01003	0.02565	0.00035	162	106	163	9	163	2
XCG01-17	210.56	267.5	0.79	0.04936	0.00316	0.17356	0.01064	0.02549	0.00036	165	113	163	9	162	2
XCG01-18	587.3	619.2	0.95	0.04931	0.00215	0.1735	0.00692	0.0255	0.00033	163	69	162	6	162	2
XCG01-19	657.24	533.19	1.23	0.04933	0.0024	0.17464	0.00788	0.02566	0.00033	164	81	163	7	163	2
XCG01-20	87.71	136.22	0.64	0.0492	0.00532	0.17224	0.01829	0.02537	0.00041	157	208	161	16	162	3
Sample XCG-02
XCG02-01	169.02	314.88	0.54	0.04957	0.00284	0.17417	0.00994	0.02547	0.00035	175	105	163	9	162	2
XCG02-02	1720.46	1598.32	1.08	0.04932	0.00124	0.1724	0.00438	0.02534	0.00031	163	37	161	4	161	2
XCG02-03	2034	1956.75	1.04	0.0492	0.00115	0.17362	0.00411	0.02558	0.00031	157	33	163	4	163	2
XCG02-04	801.29	1082.64	0.74	0.04931	0.00158	0.1752	0.00559	0.02576	0.00033	163	51	164	5	164	2
XCG02-05	748.96	1002.51	0.75	0.04933	0.00144	0.1736	0.00508	0.02551	0.00032	164	45	163	4	162	2
XCG02-06	354.05	319.82	1.11	0.04943	0.00313	0.18305	0.01148	0.02685	0.0004	168	115	171	10	171	3
XCG02-07	724.25	1094.64	0.66	0.04934	0.00133	0.17415	0.00468	0.02559	0.00032	164	40	163	4	163	2
XCG02-08	479.51	791.56	0.61	0.04924	0.00158	0.17194	0.0055	0.02532	0.00031	159	52	161	5	161	2
XCG02-09	1501.08	1659.64	0.9	0.04935	0.00126	0.17389	0.00441	0.02555	0.00031	164	37	163	4	163	2
XCG02-10	1589.46	1671.61	0.95	0.04952	0.00128	0.17418	0.00447	0.0255	0.00031	173	37	163	4	162	2
XCG02-11	857.38	1302.57	0.66	0.04932	0.00132	0.17287	0.0046	0.02542	0.00031	163	40	162	4	162	2
XCG02-12	253.64	496.17	0.51	0.04923	0.00224	0.16829	0.00757	0.02479	0.00033	159	80	158	7	158	2
XCG02-13	1378.56	1456.41	0.95	0.04935	0.00134	0.17664	0.00475	0.02596	0.00032	164	40	165	4	165	2
XCG02-14	989.1	1409.39	0.7	0.04937	0.00128	0.17447	0.00448	0.02563	0.00031	165	38	163	4	163	2
XCG02-15	7123.26	8959.46	0.8	0.04934	0.00124	0.17553	0.00437	0.0258	0.00031	164	36	164	4	164	2
XCG02-16	1043.69	1148.05	0.91	0.04931	0.00141	0.17342	0.00488	0.02551	0.00031	163	43	162	4	162	2
XCG02-17	3039.03	2028.4	1.5	0.04971	0.00128	0.18456	0.00469	0.02693	0.00032	181	37	172	4	171	2
XCG02-18	2405.86	2142.12	1.12	0.0492	0.00123	0.17374	0.00427	0.02561	0.0003	157	36	163	4	163	2
XCG02-19	1565.01	1601.66	0.98	0.04939	0.00134	0.17575	0.00468	0.02581	0.00031	166	40	164	4	164	2
XCG02-20	1130.21	1309.72	0.86	0.0493	0.00137	0.17347	0.00474	0.02552	0.00031	162	41	162	4	162	2

, with measurements taken from 20 sites on 20 grains. The concentrations of U and Th range from 95 to 1844 ppm and 55 to 1093 ppm, respectively. The Th/U ratios range from 0.6 to 1.2. All twenty investigations show consistent results for the ratios of ²⁰⁶Pb/²³⁸U and ²⁰⁷Pb/²³⁵U, with no significant differences within the margin of error. The dates yielded from these analyses are tightly clustered between 162 and 165 Ma, and all data points align closely with the isochronous line. The studies produced a consistent age of 163.3 ± 0.3 Ma (MSWD = 0.007) (Figure 10a), which closely matches the weighted mean ²⁰⁶Pb/²³⁸U age of 163.3 ± 0.9 Ma (MSWD = 0.2, n = 20) (Figure 10b).

The zircons found in the deep-red quartz monzonite porphyry (sample XCG-02) have a morphology characterized by short- to long-columnar shapes, measuring between 50 and 200 μm in length. The length/width ratio of these zircons ranges from 1:1 to 1:3. The majority of zircons have transparent interiors, high levels of transparency, and distinct rhythmic cathodoluminescence (CL) zoning, as shown in Figure 9b. The zircon LA-ICP-MS U-Pb dating results obtained from XCG-02 are presented in Table 1, with measurements taken at 20 spots on 20 individual grains. The concentrations of U and Th range from 315 to 8959 ppm and 169 to 7123 ppm, respectively. The Th/U ratios range from 0.5 to 1.1. Seventeen locations show agreement in terms of the ratios of ²⁰⁶Pb/²³⁸U and ²⁰⁷Pb/²³⁵U, taking into account measurement uncertainties. The dates of these locations are mostly concentrated between 161 and 165 Ma, and all of them align closely with or are on the isochronous line. The analyses resulted in a consistent age of 162.8 ± 0.4 Ma (MSWD = 0.0009) (Figure 10c), which closely matches the weighted mean ²⁰⁶Pb/²³⁸U age of 162.7 ± 1.0 Ma (MSWD = 0.3, n = 17) (Figure 10d).

5.2. Molybdenite Re-Os Ages

5.2.1. Xichanggou Molybdenite Re-Os Age

Table 2. Results of Re-Os isotopic analyses of molybdenite from the Xichanggou, Huashi, and other molybdenum deposits in eastern Hebei.

Sample No.	Weight (g)	ω(Re)/×10−6		ω(Os)/×10−6		ω(187Re)/×10−6		ω(187Os)/×10−6		Model Age/Ma		Data Resource
		Measured	2σ	Measured	2σ	Measured	2σ	Measured	2σ	Measured	2σ
the Xichanggou deposit												This study
XCG-07	0.05046	28,017	437	0.0002	0.0052	17,609	275	47.12	0.33	160.4	3.2
XCG-10	0.03584	5416	55	0.0005	0.0119	3404	34	9.26	0.07	163.1	2.6
XCG-11	0.05011	50,114	1240	0.0002	0.0076	31,497	779	84.48	0.48	160.8	4.4
XCG-13	0.05012	6350	53	0.0002	0.0021	3991	33	10.55	0.08	158.4	2.3
XCG-14	0.05007	6075	50	0.0067	0.0125	3818	31	10.28	0.06	161.3	2.3
The Huashi deposit												This study
HS-01	0.02038	58.3	0.5	2.424	0.124	36.64	0.32	105.8	0.6	173.1	2.5
HS-03	0.02013	39.6	0.38	0.447	0.0012	24.89	0.24	70.38	0.71	169.5	2.9
HS-05	0.0514	35.09	0.68	0.0402	0.0004	22.06	0.43	63.29	0.55	172.0	4.0
HS-06	0.02016	51.82	0.42	0.4114	0.0012	32.57	0.26	92.52	0.98	170.3	2.8
HS-07	0.02013	57.3	0.65	0.2052	0.0012	36.01	0.41	100.9	1.00	168.0	3.1
The Taipingcun deposit
HB-7-1	0.00674	34.55	0.27	0.3284	0.0776	21.71	0.17	59.35	0.39	163.8	2.3	[9]
HB-7-2	0.00631	43.25	0.41	0.1057	0.0813	27.18	0.26	73.67	0.50	162.5	2.5
HB-7-3	0.00633	44.35	0.41	0.4230	0.0960	27.88	0.26	76.95	0.52	165.5	2.5
HB-8-1	0.00619	45.01	0.39	0.1864	0.1857	28.29	0.25	78.22	0.58	165.7	2.5
HB-8-2	0.00728	40.41	0.35	0.1567	0.1561	25.40	0.22	69.44	0.50	163.9	2.4
HB-9-1	0.00605	66.64	0.47	0.3534	0.1009	41.89	0.30	114.4	0.80	163.8	2.3
HB-11-1	0.00707	18.79	0.27	0.1613	0.0988	11.81	0.17	32.24	0.21	163.6	3.1
The Taiyanggou deposit
NSD-9	0.02801	5858	37	0.0007	0.0089	3682	23	9.503	0.069	154.7	2.1	[18]
NSD-10	0.05024	9366	92	0.0002	0.0242	5887	58	15.34	0.10	156.2	2.4
NSD-11	0.05019	718.8	7.0	0.0002	0.0261	451.8	4.4	1.186	0.008	157.4	2.4
NSD-12	0.05028	4081	34	0.0002	0.0073	2565	21	6.632	0.042	155.0	2.2
NSD-13	0.05081	9609	116	0.0002	0.0029	6039	73	15.77	0.11	156.5	2.7
NSD-14	0.05009	7329	61	0.0002	0.0099	4606	38	11.95	0.07	155.5	2.2

presents the findings of five molybdenite samples from stage II, while Figure 11 provides a visual representation of these studies. The samples have varying concentrations of Re, ranging from 5416 to 50,114 ppm. They also have a narrow range of model ages, spanning from 158.4 ± 2.3 to 163.1 ± 2.6 Ma. The ¹⁸⁷Re-¹⁸⁷Os isochron age is well-constrained at 160.3 ± 4.6 Ma (MSWD = 4.3) (Figure 11a), and the weighted mean Re-Os age is 160.8 ± 2.4 Ma (MSWD = 1.9) (Figure 11b). The absence of a zero-intercept indicates the absence of any measurable common ¹⁸⁷Os, implying that all ¹⁸⁷Os in the molybdenite are of radiogenic origin. This means that the model ages can be considered credible. Moreover, the concurrence between the isochron age and the weighted average age, taking into account the margin of error, demonstrates the precision of molybdenite Re-Os dating. Hence, the isochron age (160.3 ± 4.6 Ma) employed is the precise time when molybdenite crystallized in the Xichanggou molybdenum deposit.

5.2.2. Huashi Molybdenite Re-Os Age

Based on the comprehensive analysis presented in Table 2 and visually depicted in Figure 11, we have gained valuable insights into the molybdenite samples from stage II of the Huashi molybdenum deposit. These samples exhibit a wide range of Re concentrations, spanning from 35 to 58 ppm. Simultaneously, the model ages of the samples are relatively narrowly clustered, ranging from 168.0 ± 3.1 to 173.1 ± 2.5 Ma. The precision of the dating method is evident in the well-constrained ¹⁸⁷Re-¹⁸⁷Os isochron age of 171.4 ± 19 Ma (MSWD = 4.1) (Figure 12a). Additionally, the weighted mean Re-Os age of 170.6 ± 2.6 Ma (MSWD = 2.0) (Figure 12b) further supports the accuracy of our dating results. The absence of a zero-intercept in the isochron plot indicates that all ¹⁸⁷Os present in the molybdenite samples are of radiogenic origin, derived from the radioactive decay of ¹⁸⁷Re. This finding strengthens the credibility of the model ages. The close agreement between the isochron age and the weighted average age, within the margin of error, underscores the precision of the molybdenite Re-Os dating technique. Consequently, we adopt the isochron age of 171.4 ± 19 Ma as the precise time when molybdenite crystallized in the Huashi molybdenum deposit.

5.3. Stable Isotope Data

5.3.1. Oxygen and Hydrogen Isotopes

The oxygen and hydrogen isotope findings of the Huashi deposit are documented in Table 3 and shown in Figure 13 and Figure 14. The δD_V-SMOW values of Huashi range from −80.0‰ to −67.6‰, with an average of −73.9‰. The δ¹⁸O values range from 9.2‰ to 10.5‰, with an average of 9.7‰. The computed δ¹⁸O_H2O value ranges from −1.86‰ to 2.33‰, with an average of 0.03‰. In addition, we obtained the hydrogen and oxygen isotope data for Taipingcun (data that have not been published) and the Taiyanggou molybdenum deposits. These data can be found in Table 3.

Figure 13. δ¹⁸O_H2O-δD diagram of Huashi, Taipingcun, and other molybdenum deposits in eastern Hebei (the base map from reference [37]).

Figure 13. δ¹⁸O_H2O-δD diagram of Huashi, Taipingcun, and other molybdenum deposits in eastern Hebei (the base map from reference [37]).

Table 3. Hydrogen and oxygen isotope composition of Huashi, Taipingcun, and other molybdenum deposits in eastern Hebei.

Deposit	Samples	Test	δDV-SMOW	δ18OV-SMOW	δ18OH2O	Homogenization	Data Sources
		Minerals	(‰)	(‰)	(‰)	Temperature (°C)
Huashi	HS-01	quartz	−80	9.7	−1.86	202	This study
	HS-03	quartz	−75.4	10.5	2.33	267
	HS-05	quartz	−67.6	9.5	0.81	256
	HS-06	quartz	−74.6	9.4	−0.65	228
	HS-07	quartz	−71.9	9.2	−0.46	236
Taipingcun	TPC-2	quartz	−58.5	10.1	1.73	263	Unpublished data
	TPC-4	quartz	−59.2	10.4	2.5	274
	TPC-6	quartz	−68.1	10	0.34	236
Taiyanggou	NSD-8	quartz	−85.8	10.1	1.92	267	[18]
	NSD-9	quartz	−82.3	10.5	−1.77	191

Note: δ¹⁸O_H2O(‰) value is calculated using the 1000lnα_quartz-H2O = 3.38 × 10⁶T² − 3.40 fractionation formula [38], where T is the corresponding average homogenization temperature of fluid inclusion. The temperature of fluid inclusions in Huashi deposit is unpublished data.

Table 3. Hydrogen and oxygen isotope composition of Huashi, Taipingcun, and other molybdenum deposits in eastern Hebei.

Deposit	Samples	Test	δDV-SMOW	δ18OV-SMOW	δ18OH2O	Homogenization	Data Sources
		Minerals	(‰)	(‰)	(‰)	Temperature (°C)
Huashi	HS-01	quartz	−80	9.7	−1.86	202	This study
	HS-03	quartz	−75.4	10.5	2.33	267
	HS-05	quartz	−67.6	9.5	0.81	256
	HS-06	quartz	−74.6	9.4	−0.65	228
	HS-07	quartz	−71.9	9.2	−0.46	236
Taipingcun	TPC-2	quartz	−58.5	10.1	1.73	263	Unpublished data
	TPC-4	quartz	−59.2	10.4	2.5	274
	TPC-6	quartz	−68.1	10	0.34	236
Taiyanggou	NSD-8	quartz	−85.8	10.1	1.92	267	[18]
	NSD-9	quartz	−82.3	10.5	−1.77	191

Note: δ¹⁸O_H2O(‰) value is calculated using the 1000lnα_quartz-H2O = 3.38 × 10⁶T² − 3.40 fractionation formula [38], where T is the corresponding average homogenization temperature of fluid inclusion. The temperature of fluid inclusions in Huashi deposit is unpublished data.

5.3.2. Sulfur Isotopes

Table 4. Sulfur isotopic composition of Huashi, Xichanggou, and other molybdenum deposits in eastern Hebei.

Deposits	Samples	Minerals	Output Location	δ34SV-CDT (‰)	Data Sources
Huashi	HS-02	pyrite	A small amount of anhedral–subhedral pyrite is disseminated in quartz veins.	3.3	This study
	HS-01	molybdenite	Molybdenum is veinlet-like and disseminated in quartz veins.	4.5
	HS-03	molybdenite	Molybdenum is veinlet-like and disseminated in quartz veins.	4.9
	HS-06	molybdenite	Molybdenum is mainly distributed at the edge of quartz veins, and a small amount of molybdenum is disseminated in quartz veins.	4.8
	HS-07	molybdenite	Molybdenum is mainly distributed in the edge of quartz veins, and a small amount of Molybdenum is disseminated in quartz veins.	4.8
Xichanggou	XCG-03	pyrite	Anhedral–subhedral pyrite is distributed in veinlets along the cracks.	6.5	This study
	XCG-04	pyrite	Anhedral–subhedral pyrite is distributed in veinlets along the cracks.	6.5
	XCG-05	pyrite	Anhedral–subhedral pyrite is distributed in veinlets along the cracks.	6.9
	XCG-06	pyrite	It-shaped pyrite is distributed in the edge cracks of quartz vein in the form of film.	7.1
Taiyanggou	NSD-16	pyrite	Anhedral–subhedral pyrite is distributed along the edge of quartz vein in veinlet shape.	1.5	[18]
	NSD-18	pyrite	Anhedral–subhedral pyrite is distributed in lumps and disseminated along the cracks.	1.3
	NSD-19	pyrite	Anhedral–subhedral pyrite is disseminated in quartz veins.	1.8

and Figure 15 display the sulfur isotope data. The δ³⁴S readings of four pyrite samples from the Xichanggou deposit range from 6.5‰ to 7.1‰. The Huashi deposit exhibits a range of five δ³⁴S values, ranging from 3.3‰ to 4.9‰. Among them, four samples of molybdenite have δ³⁴S values ranging from 4.5‰ to 4.9‰, while one sample of pyrite has a δ³⁴S value of 3.3‰.

In addition, we obtained the sulfur isotope data for the Taiyanggou molybdenum deposit, which may be found in Table 4 and Figure 14.

5.3.3. Lead Isotopes

The lead isotope data can be seen in

Table 5. Lead isotopic composition of Huashi, Xichanggou, and other molybdenum deposits in eastern Hebei.

Deposit	Samples	Minerals	206Pb/204Pb	207Pb/204Pb	208Pb/204Pb	μ	ω	Th/U	Δβ	Δγ	Data Resource
Huashi	HS-02	pyrite	17.402	15.426	37.379	9.25	36.08	3.77	6.70	4.73	This study
	HS-01	molybdenite	16.774	15.246	36.457	8.99	33.9	3.65	−5.04	−20.05
	HS-03	molybdenite	17.792	15.297	36.34	8.93	28.41	3.08	−1.72	−23.2
	HS-06	molybdenite	18.598	15.499	37.235	9.25	29.97	3.14	11.47	0.86
	HS-07	molybdenite	17.389	15.427	37.454	9.25	36.52	3.82	6.77	6.75
Xichanggou	XCG-03	pyrite	17.588	15.464	37.78	9.30	37.13	3.86	9.15	15.17	This study
	XCG-04	pyrite	17.979	15.555	38.204	9.42	37.54	3.86	15.09	26.56
	XCG-05	pyrite	17.292	15.391	37.373	9.19	36.39	3.83	4.38	4.23
	XCG-06	pyrite	16.795	15.303	36.871	9.11	36.34	3.86	−1.36	−9.26
Taiyanggou	NSD-16	pyrite	16.76	15.278	36.637	9.06	35.17	3.76	−3.02	−15.84	Unpublished data
	NSD-18	pyrite	17.443	15.433	37.46	9.26	36.27	3.79	7.09	6.27
	NSD-19	pyrite	16.796	15.299	36.774	9.10	35.81	3.81	−1.65	−12.16

. The data, along with the lead isotope data of sulfides measured by previous researchers, are incorporated into the lead isotope structure model diagram (Figure 16).

The lead isotope composition of the Xichanggou and Huashi molybdenum deposits remains stable and undergoes minimal variation, indicating the presence of typical lead features. The ²⁰⁶Pb/²⁰⁴Pb ratios of four pyrites from Xichanggou range from 16.8 to 18.0, with an average value of 17.4. The isotopic ratio of ^207Pb/²⁰⁴Pb varied between 15.3 and 15.6, with an average value of 15.4. The range of ²⁰⁸Pb/²⁰⁴Pb ratios is between 36.9 and 38.2, with an average value of 37.6. Within the Huashi deposit, the ²⁰⁶Pb/²⁰⁴Pb ratios of a single pyrite specimen range from 16.8 to 18.6, with an average value of 17.6. The isotopic ratio of ²⁰⁷Pb/²⁰⁴Pb varied between 15.2 and 15.5, with an average value of 15.4. The ratios of ²⁰⁸Pb/²⁰⁴Pb vary between 36.3 and 37.5, with an average value of 37.0.

6. Discussion

6.1. Timing of Granites and Mineralization

Granite intrusions and associated occurrences of copper, molybdenum, gold, and rare polymetallic minerals took place in the central part of the Malanyu anticlinorium in eastern Hebei, China, between 153 and 180 Ma. The magmatic activities exhibit complexity, typified by the occurrence of many periods and cycles of replacement and overlap, resulting in the formation of composite granite (

Table 6. Isotopic ages of intrusive rocks in Mesozoic intrusive belt in central eastern Hebei.

Era	Intrusion	Rock	Area (km2)	Occurrence	Sample and Method of Dating	Age (Ma)	Data Resource
Late Jurassic	Xichanggou	light red quartz monzonite porphyry	0.26	stock	Zircon LA-ICP-MS U-Pb	163.29 ± 0.31	This study
		deep red quartz monzonite porphyry		stock	Zircon LA-ICP-MS U-Pb	162.75 ± 0.37	This study
	Taiyanggou	granite porphyry			Zircon LA-ICP-MS U-Pb	154.8 ± 1.5	[18]
		black mica monzogranite			Zircon LA-ICP-MS U-Pb	156.5 ± 1.2	[18]
	Madi	red monzonitic granite		stock	Zircon LA-ICP-MS U-Pb	175.5	[19]
		red alkali feldspar granite			Zircon LA-ICP-MS U-Pb	165, 156	[18]
	Wangpingshi	monzonitic granite	40.5	stock	Zircon LA-MC-ICP-MS U-Pb	162.3 ± 1.3	[20]
	Taipingcun	porphyroid monzonitic granite		stock	Zircon LA-MC-ICP-MS U-Pb	161.8 ± 2.7	[9]
	Qianfenshuiling	fine-grained monzonitic granite	10	stock	Zircon LA-MC-ICP-MS U-Pb	153.8 ± 2.7	[20]
	Maoshan	monzonitic granite	50	stock	Zircon LA-MC-ICP-MS U-Pb	162.7 ± 1.5	[20]
Middle Jurassic	Gaojiadian	quartz diorite	18	stock	Zircon LA-MC-ICP-MS U-Pb	170.5 ± 1.8	[20]
	Xiajinbao	granite porphyry	0. 36	stock	Zircon LA-ICP-MS U-Pb	163.32 ± 0.90	[14]
	Yuerya	red granite	0.59	stock	Zircon SHRIMP U-Pb	174 ± 3 175 ± 1	[21]
	Tangzhangzi	granite porphyry	0. 05	stock	Zircon SHRIMP U-Pb	173 ± 2	[12]
	Niuxinshan	medium-fine-grained granite	0.35	stock	Zircon SHRIMP U-Pb	172 ± 2	[21]
		red granite			Zircon SHRIMP U-Pb	173 ± 2	[12]
	Qibozi	granite	0.66	stock	Zircon LA-ICP-MS U-Pb	168 ± 3	[22]
		monzonitic granite			Zircon LA-ICP-MS U-Pb	159.5 ± 0.5	[10]
Early Jurassic	Dazigou	monzonitic granite	0.56	stock	Zircon LA-ICP-MS U-Pb	176.5 ± 1.0	[10]
	Wubozi	granite porphyry	0.3	stock	Zircon LA-ICP-MS U-Pb	189.8 ± 0.7	[10]
	Laoshangjia	granite porphyry	<0.01	stock	Zircon LA-ICP-MS U-Pb	196.4 ± 0.8	[10]
	Luowenyu	monzonitic granite	56	stock	Zircon LA-ICP-MS U-Pb	196.7 ± 7.0	[23]
	Qingshankou	monzonitic granite	16	stock	Zircon SHRIMP U-Pb	199.1 ± 2	[21]
	Xiaoyingzi	k-feldspar granite	350	batholith	Zircon LA-MC-ICP-MS U-Pb	186.8 ± 1.3	[20]
Late Triassic	Liuzhuping	monzonitic granite		stock	Zircon LA-ICP-MS U-Pb	205.7 ± 0.8	[10]
	Sanbozi	monzonitic granite	<0.01	stock	Zircon LA-ICP-MS U-Pb	211.1 ± 1.1	[10]
	Dushan	black mica granite	400	batholith	Zircon SHRIMP U-Pb	223 ± 2	[21]
		granite			Zircon LA-ICP-MS U-Pb	222 ± 1	[24]

). Nevertheless, the magnitude of these intrusions varies significantly, and the smaller intrusions frequently exhibit superior ore-bearing characteristics.

During the middle Jurassic period, there was a significant increase in magmatic intrusion activity, resulting in the formation of notable intrusions like Wangpingshi, Madi, Qianshuiling, Maoshan, and others. Simultaneously, other significant metal deposits were created, including the Taipingcun molybdenum deposit, Huashi molybdenum deposit, Taiyanggou molybdenum deposit, Nanshuang copper-molybdenum deposit, Maoshan gold deposit, Yuerya gold deposit, Tangzhangzi gold deposit, and Xiayingfang gold deposit.

The Yanshanian granitic intrusions in the eastern Hebei Province have been previously dated using zircon U-Pb dating. The reported ages range from 199.1 to 153.8 Ma (Table 6). The newly obtained in situ zircon U-Pb ages of the Xichanggou quartz monzonite porphyry are determined to be 163.3 ± 0.3 Ma and 162.8 ± 0.4 Ma. The Madi intrusion, which is associated with the Huashi molybdenum, consists of a central granite that formed approximately 175.5 Ma and a periphery granite that formed between 156 and 165 Ma [19]. The dates suggest that the Xichanggou and Huashi plutons were formed through extensive magmatic intrusion during the middle to late Jurassic period.

Recently, numerous molybdenum and gold deposits have been discovered by geologists in the eastern Hebei region. The molybdenum deposits in this area consist mainly of the Taipingcun large-sized deposit [9], the Taiyanggou deposit [18], the Sibozi medium-sized deposit [10], and the Shouwangfen medium-sized deposit [11], which contain both copper and molybdenum. The gold (molybdenum) deposits include the Yuerya large-sized gold deposit [6], the Tangzhangzi small-sized gold (molybdenum) deposit [12,13], and the Xiayingfang medium-sized gold deposit [14]. Furthermore, a significant amount of study data on high-precision magmatic and metallogenic chronology have been documented in these deposits. The Sibozi molybdenum (copper) deposit was formed in two stages, as determined by molybdenite Re-Os dating. The first stage occurred at 194 Ma, while the second stage occurred at 121 Ma [10]. The intrusions associated with the deposit have ages ranging from 189.8 Ma (Wubozi granite porphyry) to 196.4 Ma (Laoshangjia granite porphyry) [10]. The ages derived from molybdenite and metallogenetic granite in the Yu’erya gold deposit were determined to be 171.9 Ma and 174–175 Ma, respectively [6]. The Tangzhangzi gold (molybdenum) deposit has a molybdenite Re-Os age of 170 Ma and a zircon U-Pb age of 173 Ma, as determined from the ore-forming granite porphyry [12,13]. The molybdenite Re-Os age of the Xiayingfang gold deposit is determined to be 164.2 Ma, while the zircon U-Pb age of the granite porphyry that formed the ore is 163.3 Ma [14]. The age of the Xintaigou molybdenum deposit, as determined by the molybdenite Re-Os dating method, is 155.8 Ma. The age of the intrusion that formed the ore, as determined by the zircon U-Pb dating method, ranges from 154.8 to 156.5 Ma. Seven molybdenite samples, taken from the Taipingcun molybdenum deposit during mineralization stage II, have been analyzed and shown to have an Re-Os isochron age of 164.4 ± 2.5 Ma. This age is in agreement with the age of the monzonitic granite that formed the ore, considering the margin of error [9]. The current work utilized Re-Os dating of molybdenite to determine that the Xichanggou molybdenum deposit was created at a precise age of 160.3 ± 4.6 Ma. This age coincides, within the margin of error, with the LA-ICP-MS zircon U-Pb date (162.8–163.3 Ma) obtained for the quartz monzonite porphyry. The age of Huashi molybdenum mineralization (171.4 ± 19 Ma) is consistent with the early-stage monzonitic granite of the Madi pluton (175.5 Ma) [19]. Therefore, the previously described abundant polymetallic deposits indicate a substantial and multi-stage occurrence of magmatic mineralization on a vast scale during the Jurassic-Cretaceous period in eastern Hebei. Moreover, it is probable that the Xichanggou and Huashi molybdenum mineralization occurred over two separate time periods, around 160 Ma and 170 Ma, respectively.

6.2. Source of Metal and Fluid

6.2.1. Source of Fluid

Hydrogen and oxygen isotopes play a crucial role in tracing the evolutionary history of the fluids responsible for producing ore deposits. A plot of δD versus δ¹⁸O_H2O (Figure 13) shows that ore-forming fluids of the Huashi molybdenum deposit fall between the primary magmatic water or metamorphic water and the meteoric water line. Specifically, they are positioned near the primary magmatic water and are distant from the metamorphic water. The ore-forming fluid of the Huashi molybdenum deposit is likely a combination of hydrothermal solution derived from primary magmatic water and atmospheric precipitation, depending on the geological context of the ore body.

In the distribution map of H and O isotope composition (Figure 14), the δD value and δ¹⁸O value both fall within the range of granite and are similar to the corresponding value of the mantle. This suggests that the ore-forming fluid of the Huashi molybdenum deposit originates from intermediate-acid intrusive rocks associated with mineralization. These rocks may have been formed through the remelting of ancient lower crust materials and subsequently contaminated by mantle materials.

We compiled the hydrogen and oxygen isotope data from the Taipingcun and Taiyanggou molybdenum deposits in the area (Table 3). The results indicate that the two deposits exhibit comparable ore-forming fluids, specifically Huashi (Figure 13 and Figure 14). Thus, we deduce that the fluid responsible for the formation of molybdenum deposits in the area is likely a combination of hydrothermal solutions, including both water derived from magma and water from meteoric sources, exhibiting features originating from deep underground. The ore-forming fluid may originate from intermediate-acid intrusive rocks associated with mineralization, resulting from the remelting of ancient lower crust materials and the incorporation of mantle components. This is in strong agreement with the source region identified by the S and Pb isotopes that will be described later.

6.2.2. Source of Metal

The sulfur isotope composition of metal minerals in the Xichanggou and Huashi molybdenum deposits is particularly concentrated, with both deposits showing a positive and narrow range of variation (Figure 15). The substantial degree of homogenization of sulfur isotopes in the ore minerals of both deposits indicates a single source of sulfur isotopes. Furthermore, the sulfur isotope composition of the Taiyanggou molybdenum deposit we collected exhibits identical traits. The sulfur isotope composition diagram indicates that the δ³⁴S sulfide values of the three deposits are elevated compared to the sulfur generated from the mantle-derived magmatic sulfur (0‰) [40] and are within the range of δ³⁴S values found in granite (5‰ to 15‰) [41]. The uniform sulfur isotope composition observed here indicates that the sulfur isotopes primarily originate from intermediate-acid intrusive rocks associated with mineralization, suggesting a magmatic sulfur source.

The lead isotopic composition is effective for identifying the origin of minerals that form ore deposits. The presence of trace amounts of U and Th in metal sulfides allows for the determination of the source of ore-forming materials based on their lead isotope composition, mutual relationship, and source characteristic features [42,43,44]. In the graphs depicting the ratios of ²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb (Figure 16), the majority of samples from the Huashi molybdenum deposit are situated close to the lead evolution line of the mantle and lower crust. Only two samples are found within the upper crust. The Xichanggou and Taiyanggou molybdenum deposits are located close to the lead evolution line of the mantle and lower crust. This suggests that the metal minerals in these deposits mostly originate from a combination of crust and mantle materials. This finding is consistent with the result suggested by the sulfur isotope.

The Re-Os isotope system is extensively used in isotope geochronology research. It serves as a valuable tool for identifying the origin of ore-forming materials in metal deposits and as a highly sensitive indicator of the extent of mixing of crustal materials during mineralization [45,46,47]. In their study, Mao et al. [46] conducted a thorough analysis and comparison of the amount of rhenium present in different types of molybdenite deposits in China. It was discovered that the amount of rhenium in the ores fell significantly as it moved from the mantle source to combinations of crust and mantle, and finally to crustal sources. The data showed a range of rhenium concentrations from hundreds of μg/g to dozens of μg/g to a few μg/g. This tool has gained recognition and is widely used by numerous geologists as a source indicator [48,49,50,51,52,53]. The molybdenite samples from the Huashi, Xichanggou, Taipingcun, and Taiyanggou deposits have Re concentrations ranging from 0.02 to 50 ppb (Table 2). This suggests that the ore-forming elements primarily originated from a mixture of mantle and crust–mantle sources.

6.3. Mineralization Process and Ore Genesis

The majority of molybdenum deposits worldwide are of magmatic–hydrothermal genesis, which is closely linked to the genesis of granite [54]. Currently, the intermediate-acid, hypabyssal-ultra, hypabyssal intrusive rocks (porphyry) that are associated with veinlets and distributed magmatic hydrothermal deposits are believed to be porphyry deposits [55,56]. The Taipingcun and Taiyanggou molybdenum deposits have been confirmed to be porphyry deposits [9,18]. The Xichanggou and Huashi molybdenum deposits have similar geological properties and metallogenic conditions. Additionally, their metallogenic dates are consistent with the ages of the corresponding intermediate-acid intrusions. Therefore, our study determines that the molybdenum deposits in Xichanggou and Huashi classify as porphyry deposits.

Mao et al. [57] identified three distinct periods of significant mineralization in northern China: 200–160 Ma, 140 Ma, and 120 Ma. Based on the chronological data of diagenesis and mineralization in Xichanggou and Huashi collected in this study, the molybdenum mineralization in the Jurassic period of eastern Hebei may be classified into two distinct stages, occurring at approximately 160 Ma and 170 Ma, respectively.

The North China Craton has remained relatively stable since its cratonization around 1.85 Ga until the Triassic period [58,59,60]. However, it has experienced significant damage and thinning of the lithosphere since the Mesozoic era [59,61,62,63,64,65,66,67,68]. According to Mao et al. [57], during the late Indosinian to the middle Jurassic period, northern China is still undergoing inland collision orogeny in relation to regional tectonics. The principal cause of inland orogeny is the subduction of the Mongolia-Okhotsk Ocean, which closed about 160 Ma, both to the north and south [57,66]. According to Chen et al. [8], the Yanshan area underwent tectonic stress compression in the SN and NW–SE directions during the Indosinian and Yanshanian movements, resulting in orogeny. Zhai et al. [67] identified two distinct phases of compressional structures along the northern boundary of North China. These phases occurred during two time intervals: 180~170 to 160~150 Ma and 230~210 Ma.

Based on the previous discussion, we can summarize the metallogenic model for molybdenum deposits in eastern Hebei as follows: during the Jurassic period, the Paleo-Pacific plate subducted beneath another tectonic plate, causing the northern edge of the North China Craton to transition from compressed to stretched. During the peak intensity of the north–south compressional orogeny, the lithosphere thickened, resulting in the formation of extensive nappes and folds. During this event, there was an upwelling of material from the asthenosphere and a significant interaction between the crust and mantle. This process resulted in the partial melting of material from the lower crust and the creation of magma with a granitic composition. These initial molten rocks contained an abundance of metallic elements necessary for mineral formation. Later, as magma entered the shallow crust, it consistently produced fluids containing high amounts of molybdenum and other elements, leading to the formation of ore. The intrusions can be categorized into several phases, and the associated hydrothermal deposition of metals like molybdenum may also occur in multiple phases, specifically around 170 Ma and 160 Ma. The rapid infiltration of hydrothermal fluids, which are responsible for ore formation, occurred along the intersection of faults trending in the NNE and EW directions. This process altered the physical and chemical conditions of these fluids due to mixing with atmospheric precipitation or the reaction between ore-forming fluids and wall rocks. Specifically, the mixing and reaction lead to the cooling of the fluids and the reduction of SO₂ to H₂S. This reduction is crucial in converting the mobile Mo(OH)₆, which exists in an oxidized and fractionated magmatic system, into molybdenite (MoS₂) (Figure 17a). This progress also results in the deposit of other metals in the form of sulfides. Molybdenum ores, primarily consisting of quartz vein type, are found in the advantageous locations of Xichanggou, Huashi, Taipingcun, and Taiyanggou mining areas (Figure 17b).

7. Conclusions

(1)

The quartz monzonite porphyry in the Xichanggou molybdenum deposit has zircon U-Pb ages of 163.3 ± 0.3 Ma and 162.8 ± 0.4 Ma. These ages indicate that the porphyry formed during the late Jurassic period as a result of magmatic activity. The molybdenite has an Re-Os isotopic age of 160.3 ± 4.6 Ma, which is consistent with the intrusion age. The molybdenite in Huashi has an Re-Os isotopic age of 171.4 ± 19 Ma, which is very close to the age of the ore-forming associated intrusion. Thus, it is hypothesized that the molybdenum mineralization in eastern Hebei occurred in multiple stages.

(2)

The H-O isotope composition indicates that the ore-forming fluids of the Xichanggou and Huashi molybdenum deposits are mostly composed of water from magma, with some contribution from atmospheric precipitation. The S-Pb and Re-Os isotope compositions suggest that the melting of lower crust rocks contaminated by the mantle is the main source of ore formation materials. According to the regional statistics, the molybdenum deposits in eastern Hebei exhibit identical features.

(3)

The Xichanggou and Huashi molybdenum deposits are classified as porphyry molybdenum deposits. The subduction of the Paleo-Pacific plate during the middle–late Jurassic period led to a process where the crust and mantle interacted. This contact resulted in the partial melting of the lower crust, which produced a significant quantity of metal elements, specifically molybdenum (Mo). Eventually, these molten materials rose to the surface, solidified, and formed deposits of molybdenum.