In Situ Geochemical and Sulfur Isotopic Composition of Pyrites from the Jiepailing Tin–Beryllium Polymetallic Deposit, Southern Hunan Province, China: Implications for Ore-Forming Processes

Abstract

The Jiepailing deposit in southern Hunan is a typical large to super-large polymetallic tin deposit enriched in beryllium and other rare metals. To enhance the understanding of the mineralization processes of the Jiepailing deposit, detailed mineralogical, in situ geochemical, and sulfur isotopic analyses were conducted on pyrite closely associated with tin–polymetallic mineralization. Five types of pyrite have been identified in the deposit: (1) euhedral to subhedral medium- to coarse-grained pyrite (PyI) in tungsten–tin ore; anhedral fine-grained pyrite (PyII) in tin polymetallic–fluorite ore; anhedral fine-grained or aggregate pyrite (PyIII) in lead–zinc ore; euhedral to subhedral coarse-grained pyrite (PyIV) in beryllium–fluorite mineralization; and subhedral to anhedral fine-grained pyrite (PyV) in carbonate veinlets developed in the wall rock. Backscattered electron imaging indicates consistent structural features across the five types of pyrite. In situ trace element analysis reveals differences in trace element concentrations among the pyrite types. PyI is relatively enriched in Sn, Cu, and Co. In contrast, PyIII is enriched in Pb, Zn, Sn, and Ti, while PyIV and PyV are enriched in Ag and Sb. PyI has a Co/Ni ratio more than 1, while the Co/Ni ratios in the other four types of pyrite are less than 1. LA-MC-ICP-MS in situ sulfur isotope analysis shows δ³⁴S values ranging from 2.5‰ to 5.8‰ (average 4.3‰, PyI), 2.5‰ to 5.8‰ (average 4.3‰, PyII), −7.6‰ to 9.5‰ (average 3.9‰, PyIII), −3.7‰ to 10.6‰ (average 3.6‰, PyIV), and 6.8‰ to 14.1‰ (average 9.2‰, PyV). Based on previous studies, regional geological background, deposit characteristics, and the in situ trace element and sulfur isotope compositions of pyrite, it is inferred that the various ore bodies in the Jiepailing deposit are products of Late Cretaceous magmatic–hydrothermal activity. The early ore-forming fluid originated from magmatic sources and during the migration into the wall rock and shallow formations, mixed with fluids primarily derived from atmospheric precipitation. Temperature, pressure, and composition changed of the ore-forming fluid which carried a large amount of substances, leading to tungsten–tin, tin polymetallic–fluorite, lead–zinc, and beryllium–fluorite mineralization, followed by carbonation during the late-stage mineralization.

1. Introduction

The Xiangnan region, part of the Nanling tungsten–tin metallogenic belt, is a significant area for rare metal exploration in Hunan Province [1,2,3,4,5,6]. There are a series of large to super-large nonferrous metal deposits developed in the area, including Shizhuyuan, Xianghualing, Furong, Huangshaping, Baoshan, Shuikoushan, Yaogangxian, etc. [7,8,9,10]. The Jiepailing tin polymetallic deposit, a typical rare element-rich deposit in this area, not only has a large amount of tin, copper, lead, zinc, fluorite mineralization, but also a large-scale beryllium mineralization with a reserve of about 1.027 million tons [11,12], belonging to a super-large deposit. This makes it an ideal subject for discussing the metallogenic mechanisms of metals in the Nanling belt and advancing the understanding of mineral exploration in the region.

Previous studies have extensively examined the geology, petrology, mineralogy, geochronology, and geochemistry of the Jiepailing deposit [13,14,15,16]. The mineralization is characterized by four distinct ore types: tungsten–tin ore bodies within fault zones in deep carbonate rocks; quasi-layered tin polymetallic–fluorite ore bodies in the external contact zone of deep granitic porphyry; lead–zinc ore bodies in the contact zone between granitic porphyry and surrounding rocks; and beryllium–fluorite ore bodies within interlayered fractured zones in shallow wall rocks [16]. Beryllium minerals, primarily hydroxyl–herderite, chrysoberyl, and phenakite, are widespread in the shallow beryllium–fluorite ore bodies and altered host rocks and are typically found along the margins of beryllium-rich muscovite–fluorite veins [13,15]. The granitic porphyry in the district was identified by some researchers as the parent rock for the Jiepailing tin polymetallic mineralization [17,18]. There are 19 granitic porphyry outcrops as dikes in the mining area for observation. Granitic porphyry is light grayish-gray, porphyritic structure, with the phenocryst scales about 0.5~1.5 cm, mainly quartz, potassium feldspar, and plagioclase, and the content of phenocrysts about 30%~55%. The matrix is mainly quartz, feldspar, biotite, etc., and the content is about 45%~70% [17]. Furthermore, the 19 granitic porphyry dikes exposed in the mining area were subcategorized into three phases of magmatic activities according to petrology and interspersed relationship: a giant phenocryst granitic porphyry with intense cryptocrystalline brecciation, a medium-grained granitic porphyry with minor cryptocrystalline breccia, and a plagioclase-rich medium- to fine-grained granitic porphyry. All three phases are enriched in W, Sn, Be, and volatiles such as F and Li, with higher total rare earth elements than other typical granitic intrusions [17,18].

The zircon U-Pb ages of ore-bearing granitic porphyry are 92 ± 1.0 Ma (MSWD = 1.5) and 92 ± 1.6 Ma (MSWD = 1.05) [14,19], while the ⁴⁰Ar-³⁹Ar plateau age of biotite in tungsten–tin ore bodies shows that the tin mineralization age is ~91.1 ± 1.1 Ma [20], and muscovite ⁴⁰Ar-³⁹Ar plateau ages from greisen indicate 92.1 ± 0.7 Ma [11], suggesting that mineralization slightly postdates rock formation. In situ trace element analyses of fluorite show similar Y/Ho ratios across different phases, indicating a consistent source of the mineralizing fluids [18]. Sulfur isotopes of sulfide minerals in shallow beryllium–fluorite ore are within the δ³⁴S range of the granitic porphyry, and lead isotopes also resemble those in feldspar from the granitic porphyry, suggesting that the ore-forming materials likely originated from the granitic porphyry [21]. However, the Nb-Ta mineral U-Pb concordant age from deep greisen-type ore is 89 ± 2 Ma, and the similarities between cassiterite, Nb-Ta minerals, and the deep concealed iron–lithium muscovite granite in terms of microstructure and trace element content suggest a closer genetic relationship between deep tin polymetallic mineralization and the iron–lithium muscovite granite [12]. Therefore, integrating the spatial–temporal and material associations between shallow granitic porphyry and fluorite mineralization implies that the Jiepailing tin polymetallic mineralization is likely a multi-type, multi-stage magmatic–hydrothermal event.

Previous studies show that the element partition of pyrite and other sulfides is affected by different physicochemical conditions and fluid components, which could provide key information of metallogenic process, e.g., source of the ore-forming fluid, fluid evolution, and physicochemical conditions [22,23,24,25,26,27,28]. Pyrite is one of the common metal sulfides in the Jiepailing deposit, which is widely distributed in the tungsten–tin, tin polymetallic–fluorite, lead–zinc and beryllium–fluorite ore bodies and even in the carbonate wall rock. Therefore, these types of pyrites provide an ideal research target to probe into the source and evolution of the ore-forming fluids. In the present study, detailed mineralogical and in situ trace element and sulfur isotope analyses were conducted, aiming to provide some insights into the ore-forming conditions, source of ore-forming fluids, and ore-forming process of the Jiepailing deposit.

2. Regional Geological Setting

The Nanling tungsten–tin metallogenic belt, located in the interior of the South China Block, is the most crucial tungsten–tin metallogenic belt both in China and globally, as well as a vital source of rare metals in China [28,29]. The Xiangnan region, situated in the midsection of the Nanling belt within the Caledonian–Indosinian fold zone of the South China Fold System in the South China Block, experiences intense tectonic–magmatic activities and has undergone multiple tectonic evolution stages [8,20]. The region is characterized by the development of nearly a hundred Caledonian to Yanshanian period plutons, providing favorable metallogenic conditions. Concentrated large to super-large tungsten–tin polymetallic deposits, such as Yaogangxian, Xianghualing, Shizhuyuan, and Huashaping, are found in the area, featuring granite-type, greisen-type, skarn-type, cassiterite–sulfide-type, and quartz vein-type mineralization, commonly accompanied by rare metals, dispersed metals, or rare earth metals [11]. For instance, Shizhuyuan is associated with Bi, Nb, and Ta mineralization, Xianghualing with Be mineralization, and Yaogangxian with Bi mineralization. The Jiepailing deposit, a representative of tin polymetallic mineralization in this region, is also the earliest discovered beryllium-rich tin polymetallic deposit in the Nanling metallogenic belt, located in Yizhang County in southwestern Xiangnan, within the southwestern segment of the Chaling–Linwu fault zone in the Chenzhou section [29] (Figure 1).

3. Deposit Geology

3.1. Geology of the Jiepailing Area

The exposed strata in the Jiepailing mining area mainly consist of the Carboniferous System, with minor scattered distributions of Cretaceous System. The former is composed of the Shidengzi, Ceshu, Zimenqiao Formation, and Hutian Groups, with the Lower Carboniferous Shidengzi Formation being the primary host for mineralization [13]. The Shidengzi Formation is prominently exposed in the central and southern parts of the mining area, with its lithology divided into upper and lower sections: the upper section comprises approximately 300 m of muddy limestone, while the lower section consists of around 100 m of bioclastic limestone interbedded with muddy dolomite and dolomitic limestone [16]. The Ceshui Formation, about 120 m thick, mainly features siltstone, shale, and carbonaceous slate, predominantly distributed in the central–eastern part of the mining area [16,17]. The Zimenqiao Formation, a shallow marine carbonate rock, is approximately 50 m thick, primarily composed of medium-thick bedded limestone in the lower section and dolomite in the upper section [11]. The Middle-Upper Carboniferous Hutian Group also consists of shallow marine carbonate rocks, with a total thickness of about 420–450 m, distinguished from the Zimenqiao Formation carbonates by lighter colors, with limited distribution within the mining area [11,17].

The Jiepailing mining area lies in a secondary complex anticline at the southwestern edge of the NE-SW trending Xinhua–Xiaoxiang tectonic belt and the southern end of the Leiyang–Linwu longitudinal tectonic belt. The anticline axis trends NE 23–25°, dipping NNE with an inclination of approximately 5–8° [13,14,18]. The area features well-developed fault structures, forming a chessboard pattern divided into NE-trending compressive shear reverse faults, NW-trending extensional normal faults, and nearly EW-trending translational shear normal faults (Figure 2). The NNE-trending faults primarily control the distribution, exposure, and extension of granitic porphyry, tin–polymetallic and beryllium–fluorite ore bodies [13,16,17]. Additionally, widespread cleavage in the Carboniferous strata, oriented approximately 15° with steep dips approaching 90°, is commonly filled with later hydrothermal minerals, forming beryllium-rich muscovite–fluorite veins [15,17,18].

Granitic porphyry dikes are exposed along the anticline axis, intruding to the surface with a discontinuous distribution and aligning with major structural features [14]. Early exploration suggested that these dikes might converge at a certain depth. The granitic porphyry exhibits intense alteration, often appearing light grey to greyish-white, with some parts showing a bluish-grey color, displaying a porphyritic texture and massive structure. Phenocrysts in the porphyry are primarily composed of potassium feldspar and quartz, constituting about 30%–55%, while the matrix consists of quartz, potassium feldspar, and muscovite, making up about 45%–70% [11,15]. The granitic porphyry is characterized by high silicon, alkali-rich, and low calcium content, with W, Sn, Cu, Pb, Be, and volatile elements like F, B, and Li with concentrations higher than the corresponding Clarke values, indicating a Late Cretaceous magmatic activity product [14].

3.2. Orefield Characteristics

In the Jiepailing deposit, nearly 50 ore bodies have been identified, which can be classified into four major categories: tungsten–tin ore bodies, tin polymetallic–fluorite ore bodies, lead–zinc ore bodies, and beryllium–fluorite ore bodies (Figure 3). These tungsten–tin ore bodies are primarily distributed in the Lower Carboniferous Shidengzi Formation, occurring as gently inclined sheeted and vein-type deposits, with retained tin metal reserves of 96,000 tons [11,13,18]. These ore bodies are controlled by secondary fault zones related to the F4 fault, trending approximately NNE and dipping towards SE [13].

The tin polymetallic–fluorite ore bodies are vein-like or stockwork, occurring in the outer contact zone of the granitic porphyry and the fracture zones of the Shidengzi Formation, controlled mainly by stratigraphic and fault structures, with an average thickness of 15.99 m [13,16].

The lead–zinc ore bodies are jointly controlled by contact zones and faults, developing along the outer contact zone between porphyritic granite and the surrounding rocks. They strike NNW and dip SW, with a strike length of approximately 130 m and a dip extension of about 50 m. The ore body thickness ranges from 3.94 to 4.63 m, averaging 4.36 m [13].

The beryllium–fluorite ore bodies are found in fracture zones within near-surface strata, with the largest being the No. I beryllium-rich muscovite–fluorite ore body, which accounts for over 95% of the total Sn-Be-F resources in the area [13]. This ore body exhibits a massive stratiform structure, trending NE (20–25°), extending approximately 700 m, dipping SE (14–55°), with a depth extension of 160–350 m, an average thickness of 16.5 m, and an average width of 250 m [13,16]. In the beryllium–fluorite ore body, beryllium minerals typically form mineral associations with fluorite and muscovite, often developing at the edges of beryllium-rich muscovite–fluorite veins, resulting in significant beryllium mineralization [13]. Based on the total number of drill holes in the Jiepailing deposit, the average thickness of the fluorite ore bodies is 48.72 m, with Zk1305 being the largest diameter drill hole (with a thickness of 120.06 m) and Zk1343 the smallest (with a thickness of 2.0 m) [16]. The average grade of CaF₂ is 37.50%, and the average grade of BeO is 0.26% [11].

3.3. Alternation and Mineralization

The Jiepailing mining area has undergone multiple cycles of tectonic–magmatic–hydrothermal activity, resulting in widespread hydrothermal alteration. The alteration types are diverse, including albitization, fluoritization, polymetallic pyritization, chloritization, silicification, muscovitization, and carbonation [16]. These alternations exhibit a close genetic relationship with various metallogenic types and demonstrate pronounced vertical zoning from deep to shallow.

Greisenization can be divided into early and late stages based on alteration intensity. The early stage is characterized by the replacement of potassium feldspar phenocrysts in the granitic porphyry by ore minerals, such as quartz and muscovite. Simultaneously, in the fracture systems of the surrounding rocks, a significant amount of metallic minerals, including ferberite, cassiterite, and chalcopyrite, occur, coexisting with non-metallic minerals like fluorite, potassium feldspar, quartz, and muscovite.

The late-stage alteration cause to tin polymetallic–fluorite mineralization is primarily composed of metallic minerals such as cassiterite, chalcopyrite, stannite, pyrite, and orpiment, along with alteration minerals like fluorite, sericite, tourmaline, corundum, chlorite, quartz, and calcite (Figure 4a,d,e).

Topazization and fluoritization are dominated by extensive fluorite deposition, particularly in the exocontact zone of intermediate granitic porphyry where dense stockwork-veinlet fluorite networks develop. Local occurrences of brecciated fluorite are observable. Fluorite phenocrysts display spherical morphology with coarse-grained to pegmatitic textures, constituting distinct topaz–fluorite ore bodies (Figure 3). Chloritization and silicification predominantly occur in both endo- and exocontact zones of granitic porphyry intrusions. The exocontact zones host abundant metallic sulfides (pyrite, chalcopyrite, sphalerite, galena) forming lead–zinc ore bodies (Figure 3 and Figure 4b,g).

Minor cassiterite and helvite are contemporaneously developed, with the latter exclusively occurring as disseminated grains in quartz vein interstices within the endocontact zone. Sericitization combined with fluoritization are predominantly developed in shallow distal areas from the intrusion. Fluorite associates with muscovite and sericite in interlayer fracture zones near the surface, forming the largest beryllium–fluorite ore bodies in the Jiepailing deposit through stockwork-veinlet systems (Figure 3 and Figure 4c). Subordinate pyrite aggregates and sporadic cassiterite occur as nodular masses within muscovite–fluorite veins (Figure 4h).

Carbonatization features extensive calcite veinlets in shallow wall rocks containing carbonate minerals (calcite, dolomite) with minor pyritization, muscovitization, and fluoritization. Similar carbonatization is observed in fractures of deep-seated granitic porphyry. Notably, magnetite veinlets fill pyrite fractures during carbonatization, accompanied by fine-grained cassiterite–pyrite intergrowths (Figure 4i). This phenomenon is interpreted to result from secondary mineralization events driven by concealed deep-seated intrusions [15].

Pyrite is a common metallic sulfide in the Jiepailing deposit, occurring in tungsten–tin ore bodies, tin polymetallic–fluorite ore bodies, lead–zinc ore bodies, beryllium–fluorite ore bodies, and carbonate wall rock. It typically occurs as subhedral to anhedral grains, ranging from 100 to 500 μm in size, with a pale brass color. Pyrite is disseminated or occurs in aggregates within greisen gangue (Figure 4a,b,f), or as irregular fine veins filling muscovite–fluorite veins, along with sphalerite, galena, and chalcopyrite (Figure 4g). Some pyrite grains exhibit euhedral crystal forms and coarse-fractured textures (Figure 4e,h,i). It commonly associates with chalcopyrite (Figure 4f,g,h), sphalerite (Figure 4f,g,h), galena (Figure 4f,g), magnetite (Figure 4h,i), and cassiterite (Figure 4e,h,i), distributed within fine-grained fluorite, muscovite, and feldspar. Backscattered electron imaging and scanning electron microscope energy spectrum analysis show that the different types of pyrite lack zoning structures, suggesting a uniform composition (Figure 4e,gߝi).

Galena appears lead-gray, with grain sizes ranging from 2 to 100 μm, and often coexists with pyrite, sphalerite, and chalcopyrite. It is occasionally found as individual minerals or aggregates within gangue, and sometimes enclosed within pyrite and sphalerite (Figure 4d,f–g). Chalcopyrite, with its characteristic copper-yellow hue, typically exhibits anhedral grain structures, replacing or enveloping early-formed pyrite, sphalerite, and galena within their crystal lattices or interstices. Rarely, chalcopyrite occurs as single grains within gangue quartz (Figure 4d), but it frequently appears as bleb-like inclusions within sphalerite crystal lattices or fractures (Figure 4f–h). Sphalerite, mainly found in altered granitic porphyry and wall rocks, is black–brown, 0.01 to 0.5 mm in size, and anhedral. Besides partial replacement by pyrite (Figure 4f–g), sphalerite also occurs independently, developing as subhedral to anhedral grains (Figure 4d,h).

4. Samples and Analytical Methods

4.1. Samples

Samples were collected from various ore types at the Jiepailing deposit, including tungsten–tin ore bodies, tin polymetallic–fluorite ore bodies, lead–zinc ore bodies, beryllium–fluorite ore bodies, and carbonate wall rock. The samples underwent detailed hand-specimen and microscopic petrographic studies to analyze their mineralogical features. Based on the microstructural characteristics of pyrite particles, crystal forms, and associated mineral compositions, pyrite in different ores and wall rock were classified into five distinct types: PyI, PyII, PyIII, PyIV, and PyV.

PyI occurs in tungsten–tin ore bodies, where pyrite predominantly appears granular, coexisting with potassium feldspar and quartz. Typically displaying euhedral crystal structures, pyrite particles range in size from 2 μm to 200 μm and are often found as discrete minerals within quartz grains, with surface features showing small pores filled with potassium feldspar and fluorite (Figure 5b,c). Some pyrite samples exhibit uneven compositions under backscattered electron (BSE) imaging, showing band-like structures, while micro-fine to droplet chalcopyrite can be seen internally within sphalerite (Figure 5a). Pyrite particles with larger grain sizes often exhibit various-sized surface pores or cracks, commonly filled by later-formed chalcopyrite and other metallic minerals (Figure 5a); droplet chalcopyrite is distributed within sphalerite.

PyII is found in tin polymetallic–fluorite ore bodies, where pyrite is often associated with granular fluorite, occurring within fractured zones of the surrounding rocks. Pyrite crystals typically display semi-euhedral to euhedral structures, ranging in size from 50 μm to 500 μm. They are frequently observed as single particles or aggregates exposed within fluorite veins, often accompanied by occurrences of corundum, sphalerite, galena, chalcopyrite, and other sulfides within pyrite grains or fractures (Figure 5d–f).

PyIII is associated with lead–zinc ore bodies, where pyrite and sphalerite are primarily found intergrown with muscovite and fluorite, forming vein-like structures cutting through gravelly fluorite. Pyrite crystals mostly exhibit euhedral structures with grain sizes ranging from 200 μm to 1 mm, while sphalerite generally appears as euhedral crystals ranging from 50 μm to 200 μm, often occurring as banded or vein-like structures exposed within muscovite–fluorite veins (Figure 5g–i). Sphalerite, galena, and chalcopyrite typically replace pyrite along its edges or within fractures, with sphalerite showing internal droplet or granular chalcopyrite. Additionally, pyrite surfaces often exhibit small pores and fractures, with occasional inclusions of sphalerite, chalcopyrite, or galena (Figure 5g,h).

PyIV is found within beryllium–fluorite ore, characterized by coarse-grained pyrite particles ranging from 500 μm to 2 mm. Larger pyrite grains commonly exhibit fractured structures with inclusions of galena, chalcopyrite, and other metal sulfides (Figure 5j,k). Some pyrite samples also show abundant magnetite along pyrite fractures (Figure 5k).

PyV occurs within carbonate wall rocks, where pyrite particles typically appear semi-euhedral to euhedral with fine-grained structures (5 μm to 100 μm). These pyrite particles are often found individually or in aggregate forms within muscovite–calcite veins, with pyrite grains showing fractures and pores containing inclusions of calcite and other vein minerals (Figure 5l).

4.2. Analytical Methods

Detailed petrographic observations of sample thin sections were conducted using a Leica DM2700P digital microscope at East China University of Technology. Representative pyrite grains from PyI, PyII, PyIII, PyIV, and PyV were selected for backscattered electron (BSE) imaging, in-situ trace element analysis, and sulfur isotope analysis.

Conducting micrometer-level observations on pre-analyzed pyrite samples by scanning electron microscopy (SEM) at the State Key Laboratory of Nuclear Resources and Environment in East China University of Technology allowed for the detection of microscopic inclusions or the assessment of the uniformity of sample components. Electron backscatter diffraction (BSE) images were captured, and energy-dispersive X-ray spectroscopy (EDS) was utilized for compositional analysis.

In Guangzhou Tuoyan Testing Technology Co., Ltd. (Guangzhou, China), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was employed to perform in situ trace element analysis on polished thick sections of pyrite. The laboratory utilized a New Wave Research 193 nm ArF excimer laser ablation system in conjunction with a Thermo Scientific iCap-RQ quadrupole ICP-MS. The excimer laser generated deep ultraviolet light focused on the sample surface through a homogenized optical path, with a laser beam spot diameter of 30 µm, operating at a frequency of 6 Hz and an energy density of 3.0 J/cm². Helium was used as the carrier gas during laser ablation, with argon serving as the compensation gas to adjust sensitivity. The analysis covered a total of 36 elements, including S, Fe, Be, Ti, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Zr, Ag, Cd, In, Sn, Sb, Te, Au, Pb, Bi, Mo, V, Cr, Re, W, Sr, Th, U, Sc, Hf, Ta, Nb, and Tl. Glass standard materials NIST SRM 610, NIST SRM 612, and MASS-1 were used for external calibration with internal standards [30]. Proportionate standard materials BHVO-2G and BIR-1G were employed as control samples [31,32]. Each sample point was analyzed for 85 s, comprising 40 s of blank signal and 45 s of sample signal. Offline processing of analysis data, including selection of sample and blank signals and correction for instrument sensitivity drift, was carried out using the IOLITE V 1.4 software’s 3D Trace Elements DRS mode [33]. Further details of the testing methods can be found in references [30,34].

Sulfide mineral sulfur isotopic analysis was performed using LA-MC-ICP-MS, conducted by Guangzhou Tuoyan Testing Technology Co., Ltd. The system included an ASI RESOlution M50-LR 193 nm excimer laser ablation coupled with a Nu Plasma 1700 multi-collector ICP-MS. Helium was used as the carrier gas during the ablation process, with argon as the auxiliary gas. The experimental setup utilized a beam spot size ranging from 25 to 37 μm and operated at a frequency of 3 Hz, with a laser energy of 3.6 J/cm². Sulfur isotopes were analyzed using L4, Ax, and H5 Faraday cups for 32S, 33S, and 34S signals, respectively, at a resolution greater than 12,000 to minimize interference from other gas peaks. During testing, pyrite sample Py-4 (δ³⁴S _V-CDT = 1.7 ± 0.3‰, 2SD), sphalerite sample NBS123 (δ³⁴S_V-CDT = 17.8 ± 0.2‰, 2SD), chalcopyrite sample Cpy-1 (δ³⁴S_V-CDT = 4.2 ± 0.3‰, 2SD), and galena sample CBI-3 (δ³⁴S_V-CDT = 28.5 ± 0.4‰, 2SD) were used as standards. Laboratory internal standard materials such as chalcopyrite Cpy-1/GC, pyrite Py-4/PTST-2, and sphalerite NBS123/PTST-3 were added during each test of 8 points to improve the accuracy of monitoring data, utilizing the cross-test method (SSB) to correct the data. The δ34S test achieved high precision of less than 0.1‰.

5. Results

5.1. Trace Element Compositions of Pyrite

The results of in situ LA-ICP-MS testing of different types of pyrite from the Jiepailing ore deposit are presented in

Table 1. In situ trace elements (ppm) of pyrite by LA-(MC)-ICP-MS from the Jiepailing deposit.

Point	Co	Ni	Zn	As	Sn	Pb	Bi	TI	Mn	Cu	Mo	Ag	Cd	Sb	Co/Ni
PyI@1	16.6	-	-	285	5.9	-	-	-	-	74.6	0.46	-	-	-	-
PyI@2	4.62	-	-	1038	-	3.48	0.42	-	-	-	0.32	0.05	-	-	-
PyI@3	8.68	0.9	-	1261	0.56	0.03	-	-	-	389	0.38	-	-	-	9.64
PyI@4	0.89	-	-	36.6	-	1.80	0.17	-	-	-	0.33	-	-	-	-
PyI@5	2.46	-	3.14	97.9	0.30	1.01	0.05	0.04	3.21	4.81	0.49	0.03	-	-	-
PyI@6	1.28	0.67	-	7.19	-	0.51	0.03	-	-	-	0.36	-	-	-	1.91
PyI@7	-	-	-	277	-	0.06	0.06	-	-	0.40	0.38	-	-	-	-
PyI@8	0.17	-	-	58.2	-	0.11	0.20	-	-	-	0.24	-	-	-	-
PyI@9	5.60	-	-	7.21	56.2	79.1	3.49	-	-	-	0.47	-	-	-	-
PyI@10	-	-	-	104	11.0	10.5	1.16	-	-	83.6	0.31	-	-	-	-
PyI@11	0.14	-	-	114	4.54	-	-	-	-	5937	-	-	-	-	-
PyI@12	19.4	-	6.34	79.3	1.86	31.2	3.73	0.01	-	889	0.56	0.68	-	0.17	-
PyI@13	2.05	-	-	4.50	-	0.89	0.01	-	-	3.88	0.36	-	-	-	-
PyI@14	1.01	0.76	-	25.9	-	0.03	-	-	-	3.86	-	-	-	-	1.33
PyI@15	1.20	-	-	1.13	-	0.26	0.02	-	-	23.5	0.31	-	-	-	-
PyI@16	7.80	5.47	-	12.0	-	0.68	-	0.004	-	2.99	-	-	-	-	1.43
PyI@17	20.6	2.29	-	505	-	2.27	0.42	0.008	-	-	0.42	-	-	-	9.00
PyI@18	8.35	1.88	-	268	-	-	-	-	-	-	0.17	-	-	-	4.44
Average	6.30	2.00	4.74	232	11.5	8.80	0.81	0.02	3.21	674	0.37	0.25	-	0.17	3.15
PyII@1	1.96	1.29	-	72.5	16.6	4.60	0.26	0.15	19.1	1.24	0.26	-	-	-	1.52
PyII@2	10.8	98.0	45.6	1509	-	39.4	4.21	0.01	-	4.92	0.41	-	-	0.08	0.11
PyII@3	8.70	35.0	6765	44.5	21.7	678	31.5	2.16	976	4.92	1.02	-	-	-	0.25
PyII@4	10.6	25.5	-	57.1	-	0.08	-	-	-	-	0.40	-	-	-	0.42
PyII@5	5.94	20.4	795	13.7	-	45.1	0.35	-	-	14.7	-	-	-	-	0.29
PyII@6	15.5	109	37.2	7.96	-	27.6	1.23	-	-	2.02	0.37	-	-	-	0.14
PyII@7	17.7	13.4	7.11	12.6	5.16	21.3	0.02	0.17	33.2	2.84	0.33	-	-	-	1.32
PyII@8	12.7	84.7	-	55.5	0.13	3.31	0.24	0.05	1.22	0.80	0.88	-	-	-	0.15
PyII@9	2.25	13.4	-	14.0	0.31	6.01	0.25	0.04	35.9	1.37	0.46	-	-	0.14	0.17
PyII@10	17.6	176	9798	79.0	16.4	2925	14.0	11.9	1.82	165	0.44	-	-	0.17	0.10
PyII@11	102	527	-	68.3	-	3.54	-	0.007	-	0.69	0.35	-	-	-	0.19
PyII@12	13.0	41.4	-	6146	-	-	-	-	-	0.49	0.25	1.00	-	0.96	0.31
PyII@13	11.1	139	3.54	7.20	0.23	18.5	-	0.07	-	7.65	0.90	-	-	0.08	0.08
Average	17.7	98.8	2493	622	8.65	314	5.78	1.62	178	17.2	0.51	1.00	-	0.29	0.18
PyIII@1	-	9.06	-	60	-	159	0.18	0.04	19.0	0.37	0.74	-	44	-	-
PyIII@2	0.71	30.8	-	2069	2.52	-	0.01	-	-	1.39	0.47	0.30	-	-	0.02
PyIII@3	1.08	214	-	287	0.15	19.1	0.20	0.20	41.4	2.79	0.55	0.91	0.35	-	0.01
PyIII@4	2.40	29.1	-	-	-	0.18	0.01	-	-	1.79	0.39	0.10	-	0.23	0.08
PyIII@5	2.00	69.6	-	1497	5.51	18.1	0.02	0.10	594	2.27	0.30	0.25	-	0.22	0.03
PyIII@6	1.33	48.2	-	3376	0.30	0.34	0.06	-	-	119	-	7.78	-	2.43	0.03
PyIII@7	0.85	23.6	-	52.1	-	0.54	0.06	-	-	8.13	0.32	0.37	-	0.15	0.04
PyIII@8	2.93	132	-	4.55	-	0.11	-	-	-	-	0.33	-	-	-	0.02
PyIII@9	1.29	171	-	11.3	0.14	2.86	-	0.02	3.59	7.75	0.30	1.64	-	0.84	0.01
PyIII@10	0.71	10.7	5.89	1045	-	214	0.33	0.2	31.3	2.39	0.30	-	0.47	-	0.07
PyIII@11	1.65	434	5.46	14,238	-	188	1.58	0.11	1.82	6.83	0.32	0.07	5.44	0.10	0.00
PyIII@12	10.2	396	216	1.10	-	1771	0.24	1.64	19.7	24.2	0.31	1.97	63.6	0.10	0.03
PyIII@13	1.57	72.0	-	15.8	-	13.6	0.03	0.13	2.99	7.38	0.77	0.14	-	0.12	0.02
PyIII@14	5.94	46.1	-	12.2	-	9.30	0.02	0.05	1.60	3.81	1.06	0.53	-	0.19	0.13
PyIII@15	4.52	31.9	-	12.8	-	31.4	0.03	0.19	27.8	-	2.25	-	-	-	0.14
PyIII@16	0.55	162	-	2.26	-	6.72	-	0.03	-	-	0.28	-	-	-	0.00
Average	2.52	118	75.8	1512	1.72	162	0.21	0.25	74.3	14.5	0.58	1.28	22.8	0.49	0.02
PyIV@1	2.00	5.36	-	645	-	0.81	0.03	0.01	0.50	0.58	0.32	20.8	-	0.20	0.37
PyIV@2	0.21	0.94	48.7	1.56	-	2.52	1.79	1.22	714	0.47	0.37	-	-	2.40	0.22
PyIV@3	0.19	6.79	121	-	-	3.00	3.77	-	-	0.67	-	6.52	0.67	-	0.03
PyIV@4	0.25	0.80	-	778	-	20.7	2.80	-	-	1.41	0.45	0.02	-	-	0.31
PyIV@5	0.32	10.9	-	5.80	-	9.63	0.22	0.16	18.3	6.88	0.41	0.61	-	0.18	0.03
PyIV@6	2.22	2.58	130	16,618	-	976	0.31	0.20	21.0	0.68	0.32	-	1.18	1.32	0.86
PyIV@7	1.44	-	-	5849	-	3.32	-	0.03	-	-	0.62	0.04	-	0.34	-
PyIV@8	0.52	-	-	1019	-	0.08	-	-	-	3.55	0.54	0.04	-	0.07	-
PyIV@9	0.34	16.0	-	13.1	-	22.7	0.03	0.29	2.91	-	0.79	5.02	-	0.12	0.02
PyIV@10	-	3.97	-	5.97	-	10.4	-	0.01	-	-	0.53	28.0	-	65.7	-
PyIV@11	-	4.28	-	13.6	-	13.7	-	0.04	0.67	0.69	0.51	57.1	0.25	0.18	-
PyIV@12	1.57	16.6	-	4.24	-	26.5	-	0.32	-	3.54	0.37	0.82	0.45	-	0.09
PyIV@13	2.32	15.5	-	14.6	0.26	19.8	0.01	0.07	1.25	1.15	0.69	0.05	-	0.15	0.15
PyIV@14	0.36	1.42	-	7.70	-	12.9	0.01	0.06	5.04	-	0.30	0.86	-	-	0.25
Average	0.98	7.10	99.9	1921	0.26	80.2	1.00	0.22	95.5	1.96	0.48	9.99	0.64	7.07	0.14
PyV@1	1.04	1.07	-	886	-	0.11	0.01	0.001	-	-	0.29	0.07	-	1.89	0.97
PyV@2	-	-	-	865	-	0.24	0.06	-	-	0.68	0.47	3.37	-	-	-
PyV@3	-	-	-	5020	-	0.10	0.05	-	-	-	0.47	4.92	-	0.41	-
PyV@4	0.26	2.63	-	5.45	-	0.07	-	-	-	-	0.45	0.01	-	-	0.10
PyV@5	0.64	4.20	-	22.9	-	0.18	-	-	-	-	0.4	1.33	-	0.31	0.15
PyV@6	1.16	3.63	-	4571	-	0.05	-	-	-	-	0.38	0.08	-	-	0.32
PyV@7	-	-	-	2515	-	-	-	-	-	-	0.29	0.59	-	-	-
PyV@8	-	-	-	3379	-	0.03	0.03	-	-	0.46	-	0.05	-	-	-
PyV@9	-	-	-	11.5	-	1.18	0.04	0.00	-	0.52	0.42	0.12	-	0.08	-
PyV@10	-	-	-	1926	-	0.16	0.03	-	-	-	0.31	35.4	-	0.62	-
PyV@11	0.13	-	-	120	-	0.02	0.01	-	-	0.42	0.27	0.13	-	1.13	-
PyV@12	0.11	0.85	3.69	3558	-	12.5	1.37	0.08	-	4.7	0.44	-	-	15.9	0.13
PyV@13	2.67	-	9.61	137	-	0.25	0.23	-	-	1.93	0.58	-	-	0.50	-
PyV@14	-	-	-	714	-	-	-	0.00	-	0.56	0.34	0.01	-	0.08	-
PyV@15	0.19	-	-	122	-	-	0.01	-	-	-	0.29	0.17	-	0.26	-
PyV@16	0.21	-	-	9592	-	-	-	-	-	1.42	0.24	0.11	-	-	-
PyV@17	-	-	-	5.15	-	-	-	-	-	1.17	0.25	0.34	-	-	-
PyV@18	-	-	-	17.0	-	0.02	-	-	-	-	0.27	0.12	-	-	-
PyV@19	-	-	-	128	-	-	-	-	-	0.33	0.23	-	-	-	-
PyV@20	0.64	-	-	8.14	-	0.02	-	-	-	0.88	0.38	-	-	-	-
PyV@21	0.23	-	-	3.22	-	-	-	-	-	-	0.32	-	-	-	-
Average	0.66	2.48	6.65	1600	-	1.07	0.18	0.02	-	1.19	0.35	2.93	-	2.12	0.27

. PyI consists of 18 points, PyII consists of 13 points, PyIII consists of 16 points, PyIV consists of 14 points, and PyV consists of 21 points. The analysis indicates varying ranges of chalcophile elements (Cu, Pb, Zn, Ag, Bi, As), siderophile elements (Sn, Co, Ni), as well as Mo, Tl, Mn, Cd, and Sb. Some elements such as Te, Ti, W, V, Cr, and Au are partially above the detection limits, with points showing notably high concentrations likely influenced by mineral inclusions. Elements including Sc, Ge, Re, Sr, Zr, Nb, Se, REE, Hf, Ta, W, Hg, Th, U, and Be are detected in very low amounts above detection limits, mostly below or near detection limits, with minimal variation among different types of pyrite, which is not discussed further in this paper.

Comparative analysis of average trace element content among different types of pyrite (Figure 6) shows similar spider diagrams, reflecting a common origin. PyI exhibits a higher Co-to-Ni ratio compared to other types of pyrite, relatively enriched in Cu, Sn, and other high-temperature elements. PyII is relatively enriched in Ni and Cd, while PyIII shows enrichment in Co, Pb, Zn, Bi, Ti, and Mn. PyIV is relatively enriched in As, Ag, and Sb, with similar ranges of Sn content among PyII, PyIII, and PyIV. In the PyV, apart from enrichment in elements such as As, Ag, and Sb, other ore-forming elements are lower compared to PyI, PyII, PyIII, and PyIV. The Mo content in all stages of pyrite is approximately consistent with a narrow distribution range (Figure 6).

5.1.1. PyI

This type of pyrite exhibits relatively uniform contents of Bi, Tl, Mo, and Ag, with values ranging from 0.01 to 3.73 ppm (mean 0.81 ppm), 0.004 to 0.04 ppm (mean 0.02 ppm), 0.17 to 0.56 ppm (mean 0.37 ppm), and 0.03 to 0.68 ppm (mean 0.25 ppm), respectively. Other elements show relatively larger variations in content, with Co and Ni ranging from 0.14 to 20.6 ppm (mean 6.30 ppm) and 0.67 to 5.47 ppm (mean 2.00 ppm), respectively, resulting in a Co/Ni ratio ranging from 1.33 to 9.64 (mean 4.62). Chalcophile elements such as Cu, Pb, and As exhibit ranges of 0.40 to 5937 ppm (mean 674 ppm), 0.03 to 79.1 ppm (mean 8.80 ppm), and 1.13 to 1261 ppm (mean 232 ppm), respectively. PyI notably lacks in Pb, Zn, Mn, Tl, Ag, Cd, and Sb content (Figure 6).

5.1.2. PyII

This type of pyrite exhibits relatively uniform contents of Bi, Tl, Mo, and Sn, with values ranging from 0.005 to 1.58 ppm (mean 0.21 ppm), 0.02 to 1.64 ppm (mean 0.25 ppm), 0.28 to 2.25 ppm (mean 0.58 ppm), and 0.14 to 5.51 ppm (mean 1.72 ppm), respectively. Other elements show relatively larger variations in content. Co ranges from 0.55 to 10.2 ppm (mean 2.52 ppm), while Ni ranges from 9.06 to 434 ppm (mean 118 ppm), resulting in a Co/Ni ratio ranging from 0.003 to 0.14 (mean 0.04). Chalcophile elements such as Cu, Pb, and As exhibit ranges of 0.37 to 119 ppm (mean 14.5 ppm), 0.11 to 1771 ppm (mean 162 ppm), and 1.10 to 14,238 ppm (mean 1512 ppm), respectively. Silver (Ag) and antimony (Sb), as copperophile elements, show ranges of 0.07 to 7.78 ppm (mean 1.28 ppm) and 0.10 to 2.43 ppm (mean 0.49 ppm), respectively, while tin (Sn) and bismuth (Bi) are notably depleted (Figure 6).

5.1.3. PyIII

This type of pyrite exhibits relatively uniform contents of Bi, Tl, Mo, and Sn, with values ranging from 0.02 to 31.5 ppm (mean 5.78 ppm), 0.007 to 11.9 ppm (mean 1.62 ppm), 0.25 to 1.02 ppm (mean 0.51 ppm), and 0.13 to 21.7 ppm (mean 8.65 ppm), respectively. Other elements show relatively larger variations in content. Co ranges from 1.96 to 102 ppm (mean 17.7 ppm), while Ni ranges from 1.29 to 527 ppm (mean 98.8 ppm), resulting in a Co/Ni ratio ranging from 0.08 to 1.52 (mean 0.39). Chalcophile elements such as Zn, Pb, and As exhibit ranges of 3.54 to 9798 ppm (mean 2493 ppm), 0.08 to 2925 ppm (mean 314 ppm), and 7.20 to 6146 ppm (mean 622 ppm), respectively, while silver (Ag), cadmium (Cd), and antimony (Sb) are notably depleted (Figure 6).

5.1.4. PyIV

This type of pyrite exhibits relatively uniform contents of Bi and Tl, with values ranging from 0.01 to 3.77 ppm (mean 1.00 ppm) and 0.01 to 1.22 ppm (mean 0.22 ppm), respectively. Mo content ranges from 0.30 to 0.79 ppm (mean 0.48 ppm). Co and Ni contents are lower, ranging from 0.19 to 2.32 ppm (mean 0.98 ppm) and 0.80 to 16.6 ppm (mean 7.10 ppm), respectively, resulting in a Co/Ni ratio ranging from 0.02 to 0.86 (mean 0.23). Cobalt (Co) and tin (Sn) are notably depleted (Figure 6).

5.1.5. PyV

This type of pyrite exhibits significantly lower trace element contents compared to other types of pyrite (Figure 6). Mo and chalcophile elements Bi, Cu, and Pb exhibit values ranging from 0.23 to 0.58 ppm (mean 0.35 ppm), 0.007 to 1.37 ppm (mean 0.18 ppm), 0.33 to 4.70 ppm (mean 1.19 ppm), and 0.02 to 12.5 ppm (mean 1.07 ppm), respectively. Co and Ni are detected slightly above detection limits, with contents ranging from 0.11 to 2.67 ppm (mean 0.66 ppm) and 0.85 to 4.20 ppm (mean 2.48 ppm), respectively, resulting in a Co/Ni ratio ranging from 0.10 to 0.97 (mean 0.33).

5.2. Sulfur Isotope Compositions

This research employed LA-MC-ICP-MS microanalysis to conduct in situ S isotope testing on metal sulfides from different ores of the Jiepailing deposit. These sulfides include: pyrite, sphalerite, and chalcopyrite in tungsten–tin ore bodies; pyrite, sphalerite, and galena in tin polymetallic–fluorite ore bodies; pyrite, sphalerite, and galena in lead–zinc ore bodies; pyrite, sphalerite, chalcopyrite, and galena in beryllium–fluorite ore bodies; and pyrite in carbonate wall rocks. A total of 52 analytical points were analyzed, with results presented in

Table 2. In situ sulfur isotopic composition of different types of pyrite and other sulfide in the Jiepailing deposit.

Point	Mineral	δ34SV-CDT/‰	2SE
PyI@01	Pyrite	3.3	0.2
PyI@02		5.4	0.2
PyI@03		4.7	0.2
PyI@04		2.8	0.2
PyI@05		3.7	0.2
PyI@06	Sphalerite	2.5	0.2
PyI@07		5.3	0.2
PyI@08	Chalcopyrite	5.5	0.3
PyI@09		5.8	0.3
PyII@01	Pyrite	6.9	0.2
PyII@02		−5.1	0.2
PyII@03		4.3	0.2
PyII@04		3.9	0.2
PyII@05		−1.9	0.2
PyII@06	Sphalerite	7.9	0.1
PyII@07		7.2	0.1
PyII@08	Galena	−3.8	0.2
PyII@09		−7.6	0.2
PyIII@01	Pyrite	6.2	0.2
PyIII@02		5.1	0.2
PyIII@03		5.8	0.2
PyIII@04		5.1	0.2
PyIII@05	Sphalerite	9.5	0.2
PyIII@06		7.3	0.1
PyIII@07		7	0.2
PyIII@08		8.8	0.2
PyIII@09	Galena	1.6	0.3
PyIII@10		8	0.2
PyIII@11		1.6	0.2
PyIV@01	Pyrite	9	0.2
PyIV@02		−2.1	0.2
PyIV@03		6.8	0.2
PyIV@04		3	0.2
PyIV@05		0.9	0.2
PyIV@06		4.4	0.2
PyIV@07	Sphalerite	10.6	0.1
PyIV@08		7.6	0.1
PyIV@09		8.1	0.2
PyIV@10		8.3	0.1
PyIV@11	Chalcopyrite	9.2	0.3
PyIV@12		−0.1	0.4
PyIV@13		−2.8	0.3
PyIV@14		1.6	0.3
PyIV@15	Galena	−3.7	0.2
PyIV@16		−3.5	0.2
PyV@01	Pyrite	6.8	0.2
PyV@02		7.2	0.2
PyV@03		7.2	0.2
PyV@04		14.1	0.2
PyV@05		10.2	0.2
PyV@06		10	0.2
PyV@07		9.3	0.2

(Figure 7). The δ³⁴S values for all sulfide analytical points ranged from −7.6‰ to 14.1‰ (mean 4.6‰), indicating significant variability in sulfur isotope composition across the Jiepailing deposit. For pyrite, δ³⁴S values ranged from −5.1‰ to 14.1‰ (mean 5.1‰) across twenty-seven points; for sphalerite, from 2.5‰ to 10.6‰ (mean 7.5‰) across twelve points; for chalcopyrite, from −2.8‰ to 9.2‰ (mean 3.2‰) across six points; and for galena, from −7.6‰ to 8.0‰ (mean −1.1‰) across seven points.

In tungsten–tin ore bodies, pyrite (PyI) exhibited δ³⁴S values ranging from 2.8‰ to 5.4‰ (mean 4.0‰) at five analytical points, while sphalerite (SpI) showed δ³⁴S values ranging from 2.5‰ to 5.3‰ (mean 3.9‰) at two analytical points. In tin polymetallic–fluorite ore bodies, pyrite (PyIII) had δ³⁴S values ranging from −5.1‰ to 6.9‰ (mean 1.6‰) at five analytical points, and sphalerite (SpIII) showed δ³⁴S values ranging from 7.2‰ to 7.9‰ (mean 7.6‰) at two analytical points. In lead–zinc ore bodies, pyrite (PyII) exhibited δ³⁴S values ranging from 5.1‰ to 6.2‰ (mean 5.6‰) at four analytical points, while sphalerite (SpII) showed δ³⁴S values ranging from 7.0‰ to 9.5‰ (mean 8.1‰) at two analytical points. In beryllium–fluorite ore bodies, pyrite (PyIV) had δ³⁴S values ranging from −2.1‰ to 9.0‰ (mean 3.7‰) at six analytical points, and sphalerite (SpIV) showed δ³⁴S values ranging from 7.6‰ to 10.6‰ (mean 8.7‰) at four analytical points. Pyrite in carbonate wall rocks (PyV) exhibited δ³⁴S values ranging from 6.8‰ to 14.1‰ (mean 9.2‰) at seven analytical points.

The δ³⁴S values of metal sulfides varied significantly across different ores: in the tungsten–tin ore bodies (Py I), sulfides exhibited δ³⁴S values ranging from 2.5‰ to 5.8‰ (mean 4.3‰), with a relatively concentrated distribution. In the tin polymetallic–fluorite and lead–zinc ore bodies (PyII-III), sulfides exhibited δ³⁴S values ranging from −7.6‰ to 9.5‰ (mean 3.9‰), indicating the most dispersed distribution. In the beryllium–fluorite ore bodies (Py IV), sulfides exhibited δ³⁴S values ranging from −3.7‰ to 10.6‰ (mean 3.6‰), with a scattered distribution. In the carbonate wall rock (PyV), sulfides exhibited δ³⁴S values ranging from 6.8‰ to 14.1‰ (mean 9.2‰), showing a moderately dispersed distribution.

6. Discussion

6.1. Chemical Characteristics of Pyrite

Pyrite is widely distributed in various geological environments and can incorporate numerous trace elements (As, Co, Ni, Cu, Zn, Se, Ag, Sb, Au, Pb, Bi, Hg, and Tl) into its crystal through various mechanisms [10,24,25,26]. Previous studies have shown that the occurrence states of trace elements in pyrite are mainly of three types: (1) they are incorporated into the mineral lattice in the form of isomorphous substitution; (2) they are present in visible micron-sized mineral inclusions; (3) they are present as invisible nanoparticle inclusions [35,36]. Specifically, elements such as Co, Ni, As, Se, Mn, and Mo enter the pyrite lattice mainly in the form of isomorphism or nanoparticles, while elements such as Cu, Pb, Zn, Bi, Ti, Tl, Te, Sn, Sb, Au, Ag, Th, U, Cr, V, and W mainly exist in the form of fine mineral daughter crystals [24,37,38,39,40].

When a certain element is distributed in pyrite in the form of isomorphism, the spectral line of the element time-resolved signal plots is flat, closely resembling that of Fe, with no significant fluctuation. When the elements occur in the form of fine mineral inclusions or nanoparticles, the spectral lines show obvious fluctuations on the element time-resolved signal plots [24,25,26,27,37,38]. Therefore, the micro-scale in situ analysis of pyrite can not only obtain the content of characteristic elements, but also determine the occurrence form of elements in pyrite through the changes of the element time-resolved signal, combined with other chemical behaviors [10,24,26,28].

In the element time-resolved signal plots of various types of pyrite, the spectral lines of Co and Ni rarely show significant fluctuations, indicating that they mainly exist in the pyrite in the form of solid solutions(Figure 8). In addition, the contents of Co and Ni are significantly increased in the PyIII type, which may be closely related to the development of pyrite in lead–zinc ore bodies, indicating that the rapid precipitation of pyrite may enhance the isomorphic substitution ability of Co and Ni.

The signal of As in various pyrites in the mining area is relatively stable, which further indicates that As also replaces S in the form of isomorphism and enters the pyrite lattice. The As content in each generation of pyrite is relatively stable. Considering that tungsten–tin ore bodies, tin polymetallic–fluorite ore bodies, and lead–zinc ore bodies all develop arsenopyrite and tetrahedrite, it is speculated that their ore-forming fluids are similar and all of them are As-bearing fluids [24,26].

Mn is another element that exists in the PyV lattices by replacing S in the form isomorphism, which is characterized by relatively stable spectral lines in the element time-resolved signal plots [26]. The content of Mn in PyI, PyII, and PyIII was close to each other and showed a gradual increase trend. The relationship between the solubility of Mn and temperature may reflect the gradual decrease in environmental temperature during the formation of PyI, PyII, and PyIII.

The ionic radius of lead is larger than that of Fe²⁺, which limits the ability of lead to enter the lattice of pyrite in the form of isomorphism [10]. Therefore, lead mainly exists in pyrite in the form of micron- to nanoscale mineral inclusions. In each type of pyrite in Jiepailing, lead and zinc show strong peaks or protrusions on the element time-resolved signal plots, indicating that they mainly exist in pyrite in the form of mineral inclusions (Figure 8).

Studies also show that Bi, Ag, Cd, and Sb are typically incorporated into the galena lattice in solid solution form. In the five types of pyrite from the mining area, Ag, Bi, and Sb exhibit a positive correlation with lead (Figure 9), and their contents are relatively low, with irregular “concave–convex” peaks in the element time-resolved signal plots. Therefore, it is inferred that lead exists in pyrite as fine galena inclusions, while Ag, Bi, and Sb exist in solid solution within these galena inclusions [24,40].

Copper shows significant “spikes” and “valleys” on the element time-resolved signal plots, indicating that copper mainly exists in pyrite as mineral inclusions. In the Jiepailing mining area, chalcopyrite mainly develops in the tungsten–tin ore bodies, followed by the tin polymetallic–fluorite ore bodies and lead–zinc ore bodies. Correspondingly, copper content is higher in PyI, while it significantly decreases in PyII, PyIII, PyIV, and PyV, showing no correlation with Pb, Zn, Bi, or As(Figure 9). Usually, after copper is formed as an independent mineral in the ore-forming fluid, the copper content in the fluid will be greatly reduced [39,40].

During mineralization, mineral crystallization is typically influenced by the chemical composition, temperature, and pressure of the fluid. The content, distribution, and occurrence states of trace elements in minerals record changes in these environmental conditions. Based on the occurrence and variation characteristics of elements such as Co, Ni, As, Mn, Cu, and Pb in the Jiepailing mining area, as well as the mineral assemblages and spatial relationships of the ore bodies, it is inferred that the formation of the five types of pyrite may originate from the same hydrothermal system [41].

6.2. Sources of Ore-Forming Fluid

The sulfur isotope composition of sulfides serves as crucial geochemical evidence for determining the sources of ore-forming materials and exploring ore-forming mechanisms [41,42,43,44,45,46]. The widespread application of sulfur isotope geochemistry in studying ore deposit formation processes has become a central focus of current research in the field [41,42,43,44,45,46,47,48]. The in situ sulfur isotope information of sulfides allows for the reconstruction of mineral formation processes within fluids, thereby delving into key scientific questions concerning the sources and mechanisms of ore formation. Similar to micro-area in situ trace element analysis of sulfides, recent advancements in in situ sulfur isotope analysis techniques, including point analysis, have been widely applied in studying various types of ore deposit formation environments, sources of ore-forming materials, and mechanisms of ore formation such as those in rare metal deposits, magmatic–hydrothermal environments, and their evolution processes, enrichment, precipitation, and mineralization mechanisms [47,48,49,50,51].

Previous studies indicated that using the single mineral grain powder method, the δ³⁴S values of metal sulfides in the Jiepailing fluorite ores ranged from −1.0‰ to +7.5‰ [21]. In contrast, this study employing metal sulfide LA-MC-ICP-MS in situ testing revealed a wider range of δ³⁴S values from −7.6‰ to 14.1‰ (mean 4.6‰; range 21.7‰), demonstrating significantly greater variability in sulfur isotopes compared to the single mineral grain powder method. This approach ensures more accurate determination of sulfur isotopic values for individual sulfide minerals, distinguishing itself by preventing errors that may arise in other methods [47].

The sulfur isotope composition of sulfides in ore deposits serves as a tracer for determining the sources of ore-forming materials and fluid evolution mechanisms, helping to identify sulfur sources in ore-forming fluids and further exploring the formation processes of ore deposits [52,53,54]. Through comprehensive identification methods such as field surveys, hand specimens, optical microscopy, and scanning electron microscopy, the Jiepailing deposit is primarily characterized by metal sulfides such as pyrite as the main sulfur-bearing minerals. No evidence of sulfate minerals (e.g., anhydrite, gypsum) was found in the ore bodies or surrounding rocks, indicating that sulfur in the ore-forming fluids mainly exists in the form of HS⁻ and S²⁻.

Therefore, the total sulfur isotope value (δ³⁴S_ΣS) in ore-forming fluids is approximately equivalent to the sulfur isotope composition of metal sulfides [55,56,57]. The relationship between δ³⁴S values of metal sulfides in the Jiepailing deposit is δ³⁴S_sphalerite > δ³⁴S_pyrite > δ³⁴S _chalcopyrite > δ³⁴S_galena, which does not follow the thermodynamic equilibrium fractionation principle obtained experimentally for coexisting sulfides δ³⁴S values, namely δ³⁴S_pyrite > δ³⁴S_sphalerite > δ³⁴S_chalcopyrite > δ³⁴S_galena, indicating that sulfur isotopes of sulfides in the deposit are not in equilibrium fractionation [58,59]. Hence, δ³⁴S values of sulfides in this deposit generally do not represent δ³⁴S_ΣS values in ore-forming fluids but are noticeably lower. Therefore, the δ³⁴S_ΣS value of ore-forming fluids in the Jiepailing deposit should be higher than the average δ³⁴S value of sulfides [47,60].

Extensive studies on sulfur isotopes have identified five sources of sulfur in hydrothermal deposits: (1) mantle-derived sulfur, typically with δ³⁴S values near 0‰ and a range of 0 ± 3‰ [61]; (2) crustal-derived sulfur, with a wide range of δ³⁴S values [61,62]; (3) seawater-derived sulfur, characterized by modern seawater δ³⁴S values (approximately +20‰), which can represent sulfur isotopes of sulfates in marine evaporite rocks [62]; (4) biogenic sulfur, typically characterized by large negative δ³⁴S values [63,64]; and (5) mixed sulfur, characterized by mixed sulfur isotope values ranging from +5‰ to +15‰ [59,61].

The in situ sulfur isotope values of sulfide minerals measured in this study range from −7.6‰ to 14.1‰, with an average value of 4.59‰. This indicates that the δ³⁴S values of the mineralizing fluids in the study area exhibit a more complex range compared to the common sulfur sources typically found in hydrothermal deposits. Previous studies on hydrothermal deposits have shown that the sulfur isotope composition of sulfide minerals is not solely determined by the sulfur isotopes of the mineralizing material in the source region. It is also influenced by physicochemical conditions, such as oxygen fugacity, pH, and temperature, during the evolution of the mineralizing hydrothermal fluids [54,55,56,57,58,59,60,61,62,63,64,65].

As shown in Table 2 and Figure 7, the δ³⁴S values of different types of pyrite from the Jiepailing deposit range as follows: 2.5‰ to 5.8‰ (PyI), −7.6‰ to 7.9‰ (PyII), 1.6‰ to 9.5‰ (PyIII), −3.7‰ to 10.6‰ (PyIV), and 6.8‰ to 14.1‰ (PyV). According to extensive research, the factors leading to negative δ³⁴S_V-CDT values in mineralizing fluids are primarily related to several situations: (1) the initial stage of the mineralizing fluid is already enriched in light sulfur, closely linked to biogenic processes; (2) the mineralizing fluid undergoes water–rock reactions or fluid mixing during its evolution, resulting in negative δ³⁴S_V-CDT values with relatively small absolute values [66,67].

Based on the δ³⁴S value range of PyI, it is inferred that the mineralizing fluids associated with tungsten–tin mineralization should have higher δ³⁴S values, closer to the sulfur source range of granite (Figure 10). This is consistent with previous studies suggesting that the granitic porphyry or deep granite in the region is the parent rock for tungsten–tin mineralization. However, the δ³⁴S values of PyII, which developed in the tin polymetallic ore body, and PyIV, found in the shallow fluorite ore body, exhibit some negative values. This suggests that the fluids may have undergone water–rock reactions or fluid mixing.

Studies on quartz fluid inclusions in the tungsten–tin and tin polymetallic–fluorite ore bodies of the Jiepailing deposit show that the homogenization temperatures of fluid inclusions associated with tin mineralization range from 250 °C to 350 °C, indicating that the mineralizing fluids are of medium to high temperature [68]. The δD values (−42.3‰ to −85‰) and δ¹⁸O values (4.64‰ to 9.08‰) of the mineralizing fluids calculated from the H-O isotopes of quartz fall within or close to the magmatic water range, with contributions from atmospheric precipitation [18]. Therefore, the variation in δ³⁴S values of sulfides within the tin polymetallic–fluorite, lead–zinc, and beryllium–fluorite ore bodies suggests that the mineralizing fluids in the Jiepailing deposit may have undergone fluid mixing.

Therefore, based on the variation characteristics of δ³⁴S values in different types of pyrite, the tungsten–tin mineralizing fluids in the high-temperature stage exhibit relatively high positive δ³⁴S values, reflecting that the early mineralizing fluids originated from a magmatic system associated with granite. In contrast, the δ³⁴S value range of PyII and PyIV, which developed in the shallow fluorite ore body, reflects that after the fluids extensively infiltrated the fracture system within the surrounding rocks, they mixed with other fluids, including atmospheric precipitation, resulting in a broader δ³⁴S value range for the mineralizing fluids [69].

6.3. Fluid Evolution of Multi-Stage Ore-Forming

The trace element composition of minerals indirectly reflects rich ore-forming information and processes such as temperature and redox changes in ore-forming fluids [70,71]. Specifically for metal sulfides, which are often associated with magmatic–hydrothermal systems, variations in trace element content or ratios in minerals can to some extent reflect the physical and chemical conditions of the ore-forming fluids during crystallization, and can be used to infer the sources of ore-forming fluids [70], thereby aiding in exploration for ore deposits [64]. Pyrite is the most common mineral in the Jiepailing ore district, developed throughout various polymetallic mineralizations including the early-stage tungsten–tin mineralization to tin polymetallic–fluorite mineralization, and the late-stage lead–zinc and beryllium–fluorite mineralization, and even in the carbonate wall rock. Therefore, conducting in situ trace element analysis of pyrite from different ores in the district can elucidate the sources of ore-forming materials and fluid evolution.

Previous studies indicate significant differences in Co/Ni ratios in pyrite crystals of different genetic origins, and within different mineralization stages of the same type of deposit [63]. Researchers suggested that Co, compared to Ni, is more sensitive to temperature changes: as the temperature of the ore-forming fluid increases, Co is more likely to enter the pyrite lattice in a solid solution form, typically resulting in a higher Co/Ni ratio in pyrite, indicating higher fluid temperatures; conversely, lower temperatures result in lower Co/Ni ratios [72]. On the other hand, studies show that sedimentary or sedimentary-reformed pyrite typically has lower Co and Ni contents, with Co/Ni ratios usually <1. In hydrothermal (vein-type) deposits, the Co and Ni contents and Co/Ni ratios of pyrite vary widely, with Co/Ni ratios ranging from 1.17 to 5.00. In porphyry, skarn, and volcanic vent sulfide deposits, pyrite Co and Ni contents and Co/Ni ratios vary greatly, with Co/Ni ratios ranging from 1.1 to 4.6, 3 to 23.5, and 5 to 50, respectively [10,63,73]. Based on these characteristics, previous researchers have used a Co-Ni binary plot of pyrite to classify different genetic types of deposits.

The Co/Ni ratio of pyrite in the Jiepailing deposit ranges from 0.003 to 9.63 (mean 0.76), indicating significant differences in ore-forming fluids between different ores. Pyrite with a Co/Ni ratio greater than 1 reflects ore-forming fluids with higher environmental temperatures, closely related to magmatic–hydrothermal processes. Pyrite with a Co/Ni ratio less than 1 reflects lower crystallization temperatures, suggesting an origin closer to sedimentary or reformed environments, with a significant contribution from non-magmatic sources [43]. Pyrite samples from different ores in the Jiepailing deposit were plotted for Co and Ni content on a Co-Ni genetic plot [24,68] (Figure 11). PyI-type pyrite is predominantly located in the lower left quadrant of the hydrothermal genesis area, indicating that the ore-forming fluids for this type of pyrite were influenced by magmatic–hydrothermal processes.

Overall, PyI-type pyrite is enriched in high-temperature elements such as Sn and Cu, while depleted in As, Mn, Ag, and Sb, consistent with the geochemical characteristics of high-temperature hydrothermal pyrite. In contrast, PyII, PyIII, PyIV, and PyV-type pyrite have Co/Ni ratios primarily located below the sedimentary genesis area, with higher concentrations of Pb, Zn, Tl, Mn, Ag, Cd, and Sb, indicating influences from metamorphic hydrothermal or atmospheric precipitation during magmatic–hydrothermal processes, leading to the enrichment of ore-forming elements in late-stage pyrite. Additionally, the gradual decrease in Co/Ni ratios in late-stage ore-forming fluids reflects a gradual decrease in temperature during the formation of PyII, PyIII, PyIV, and PyV-type pyrite. In summary, within the Jiepailing deposit, the decrease in Co/Ni ratios and Co + Ni contents in pyrite throughout multiple stages of mineralization indicates a continuous decrease in ore-forming fluid temperature. Early-stage ore-forming materials primarily originated from magmatic–hydrothermal processes, whereas the influx of significant non-magmatic materials during intermediate to late stages resulted in pyrite formations with sedimentary characteristics [63].

In the Jiepailing deposit, quartz inclusion thermometry reveals homogeneous temperatures in the tungsten–tin ore bodies ranging between 250 and 350 °C [68], in the lead–zinc ore bodies between 170 and 260 °C [74], and in the carbonate wall rock, quartz inclusion temperatures are primarily within 110–190 °C [74]. This reflects higher temperatures in the early stages of mineralization, with relatively minor temperature variations during the carbonate wall rock and lead–zinc mineralization, consistent with the characteristics indicated by trace elements in pyrite. Furthermore, H-O isotope studies on quartz indicate that δD values (−42.3‰ to −85‰) and δ¹⁸O values (4.64‰ to 9.08‰) of the ore-forming fluids are consistent with magmatic water ranges [74].

In summary, it is believed that the tin–polymetallic ore-forming fluids in the Jiepailing originate from deep-seated magmas. During the evolution of ore-forming fluids, they were influenced by mixing with atmospheric precipitation, leading to changes in fluid composition and physicochemical conditions. This resulted in the coexistence of different types of pyrite during the rare metal element mineralization process.

Previous studies suggest that elements such as W, Cu, Pb, and Zn typically undergo mineralization in medium- to low-temperature fluids ranging from 200 to 400 °C, whereas Sn can mineralize over a broader temperature range [75,76,77]. Additionally, early high-temperature fluids to some extent increased the solubility and activity of rare metal elements in ore-forming fluids, promoting complexation with halide elements (F-, Cl-) and rare metal elements. Subsequently, significant temperature decreases led to extensive precipitation and mineralization of rare metal elements [77,78,79,80,81,82].

Considering the regional geological background, geological characteristics of the deposit, and the evolution mechanism of ore-forming fluids in the Jiepailing area, it is inferred that during the late Yanshan period and multiple tectonic stages, granitic magma carrying abundant ore-forming elements such as W, Sn, Pb, Zn, Be, Cu, and F intruded into carbonate formations. Ore-forming fluids formed through magma cooling and degassing ascended along fault structures in the core of the Jiepailing anticline, causing greisenization, topalization, and fluoritation to occur near concealed plutons, forming tin–copper and topaz–fluorite ores. Thus, PyI-type pyrite formed during this stage is enriched in Cu, Sn, and other elements, with lower concentrations of As, Tl, Ag, Cd, Sb, Cr, V, Mn, and Ga, and a Co/Ni ratio mostly >1, indicating higher early-stage ore-forming fluid temperatures. Pyrite of PyII type in the tin polymetallic–fluorite exhibits lower Co/Ni ratios, reflecting a gradual decrease in fluid temperatures.

As ore-bearing fluids continued to ascend, they extensively entered interlayered fractured zones, mixing with pre-existing fluids in open systems through shallow structural fractures and fissures. This process progressively lowered fluid temperatures and pressures, resulting in substantial unloading of elements such as Pb, Zn, As, and Cd into mineralization. This led to the formation of PyIII-type pyrite in the upper part of the tungsten–tin ore bodies containing lead–zinc ore bodies. Subsequently, as fluid temperatures and pressures continued to decrease, PyIV-type pyrite formed in the beryllium–fluorite ore bodies, with some PyV-type pyrite forming in the surrounding carbonate wall rocks at shallow depths.

7. Conclusions

1. The Jiepailing Sn polymetallic deposit hosts five types of pyrite, developed in five types of ores: tungsten–tin ore bodies (PyI), tin polymetallic–fluorite ore bodies (PyII), lead–zinc ore bodies (PyIII), beryllium–fluorite ore bodies (PyIV), and carbonate wall rock (PyV).

2. PyI is enriched in high-temperature elements such as Cu and Sn, while PyII, PyIII, PyIV, and PyV are enriched in medium-temperature elements such as Pb and Zn, as well as medium- to low-temperature elements like As, Ag, and Mn, with most Co/Ni ratios formed early to late falling below those indicative of magmatic to sedimentary origins, reflecting a gradual decrease in temperature during the evolution of ore-forming fluids, possibly due to the influence of metamorphic or meteoric water.

3. Sulfur isotopic characteristics of sulfides indicate that ore-forming fluids result from mixing between mantle and metamorphic wall rock during the water–rock interaction progress.

4. Granitic magma carrying abundant ore-forming elements such as W, Sn, Pb, Zn, Be, Cu, and F intruded into carbonate formations. Ore-forming fluids formed through magma cooling and degassing ascended along fault structures, resulting in tungsten–tin and tin polymetallic–fluorite ore bodies forming. As ore-bearing fluids continued to ascend to shallow depths, they interacted extensively along host rock fractures, generating lead–zinc ore bodies. Subsequent temperature decreases in the system facilitated significant precipitation of Be and F elements, forming beryllium–fluorite ore bodies.