Geochemistry and Genetic Significance of Scheelite in the Nanwenhe Tungsten Deposit, Yunnan Province, Southwestern China

Abstract

The Nanwenhe tungsten deposit is located in the southeastern Yunnan Laojunshan mineral district and is hosted in the Paleoproterozoic Mengsong Group strata. It can be divided into two periods and four stages: skarn (early and late) and the vein type (feldspar–quartz–scheelite–tourmaline and calcite. There are two types of scheelite occurrences: one in skarn (Sch-1) and the other in feldspar–quartz–scheelite–tourmaline veins (Sch-2). The latter is further divided into two types: Sch-2a and Sch-2b. The REE content and Eu anomaly of skarn scheelite (Sch-1) are affected by early mineral crystallization; Sch-2a in feldspar–quartz–scheelite–tourmaline veins forms in a Na⁺-rich environment, and Eu²⁺ released into the fluid through hydrolysis may have largely entered tourmaline, resulting in the weak positive Eu anomaly of Sch-2a; the negative Eu anomaly of Sch-2b is likely inherited from the metamorphic fluid. The mineralization is likely closely related to the metamorphic fluid activity generated by the tensional structural environment at the end and after the regional uplift, forming ore by reducing fluids associated with regional metamorphism. The Laojunshan mineral district hosts several tungsten and tin polymetallic deposits and occurrences that share similar geological characteristics with the Nanwenhe tungsten deposit. No granite bodies related to mineralization have been identified within the mining area. Therefore, research on the genesis of the Nanwenhe tungsten deposit holds significant value for guiding exploration efforts.

1. Introduction

China possesses abundant tungsten (W) ore resources, with reserves exceeding 50% of the world’s total [1]. The types of tungsten deposits are diverse and can be categorized based on metallogenic element associations and primary geological characteristics, including porphyry-type, greisen-type, skarn-type, and quartz-vein-type deposits [2]. Tungsten deposits in China are predominantly concentrated in the South China region, mainly within the Nanling area and the Jiangnan orogenic belt, while deposits in other areas are sporadically distributed. The metallogenic epochs primarily include the Caledonian, Indosinian, and Yanshanian periods, with the Yanshanian period (180–80 Ma) producing the largest number of tungsten deposits [3].

In recent years, large- and medium-sized tungsten deposits have been successively discovered in the southeastern Yunnan region [4]. It lies at the southwestern end of the Nanling polymetallic metallogenic belt, which exhibits intense tectonic–magmatic activity with multi-phase characteristics [5,6]. Around the Yanshanian period, Gejiu, Bozhushan, and Laojunshan composite granite bodies, a series of large-scale tin, tungsten, copper, lead, and zinc deposits formed, making this area an important polymetallic (Sn-W) metallogenic belt in China [4]. Among these, the Laojunshan ore cluster, located in the southeastern part of the metallogenic belt, lies in the northwestern part of the Laojunshan–Song Chay metamorphic dome. It has undergone extensive tectonic–magmatic activity and metamorphism and possesses significant rare metal metallogenic potential [7,8,9,10,11,12,13].

The Nanwenhe tungsten deposit, an important component of the Laojunshan ore cluster, is hosted in the Paleoproterozoic Mengdongyan Group strata and controlled by Mesozoic thrust nappe structures [12]. The largest exposed pluton within the Laojunshan ore cluster is the Cretaceous Laojunshan granite, which has long been a focus of attention for its relationship to Nanwenhe tungsten deposit. The ore bodies of the Nanwenhe tungsten deposit primarily occur in skarns of the Nanyangtian Formation and were once considered a typical skarn-type deposit [12]. However, scheelite categorized based on its occurrence into quartz-vein type is also identified. Hence, the genesis of the “skarn” (or “pseudo-skarn”) remains a matter of debate to this day. Additionally, no large granite intrusions related to mineralization have been found in the mining area, raising questions about whether it is truly a skarn-type deposit related to magmatic activity. This study focuses on the Nanwenhe tungsten deposit in the Malipo area of Yunnan Province. Based on field observations, systematic petrographic studies, and genetic mineralogy of hydrothermal minerals, we delineate the chemical composition of scheelite during different mineralization stages and discuss its genesis. The results provide guidance for understanding the genesis of tungsten deposits in this region to aid in future exploration efforts.

2. Geological Setting and Ore Deposit Geology

2.1. Geological Setting

Southeastern Yunnan is located at the tectonic junction of the Yangtze Plate, Cathaysia Plate, and Indochina Plate, where the Tethyan–Himalayan tectonic domain interacts with the circum-Pacific tectonic domain. Since the Proterozoic, this region has undergone multiple large-scale tectonic movements, resulting in an exceptionally complex history of magmatic and geological structural evolution [10]. Along the NW-trending Ailaoshan–Red River tectonic belt, the Gejiu, Bozhushan, and Laojunshan granite bodies are distributed parallelly from west to east. Around these intrusions, a series of large to super-large tungsten–tin polymetallic deposits have formed [4].

The Laojunshan ore cluster is located in Malipo, Wenshan Prefecture, southeastern Yunnan Province, representing an important tungsten–tin polymetallic metallogenic district in southeastern Yunnan (Figure 1). It lies on the western extension of the South China Caledonian Fold System, specifically within the southeastern Yunnan fold belt between the South China Fold System and the Yangtze Paraplatform. The Laojunshan ore cluster occupies the northwestern part of the Laojunshan–Song Chay metamorphic dome (Figure 1), bordered by the Youjiang foreland basin to the north and adjacent to the Sanjiang orogenic belt to the west. The Laojunshan granite, situated at the center of the ore cluster, is surrounded by several large deposits including the Xinzai tin deposit, Nanwenhe tungsten deposit, Dulong tin–zinc polymetallic deposit, and Saxi tungsten–beryllium deposit (Figure 2) [14].

The region has experienced multi-phase and multi-stage magmatic activities, resulting in widespread distribution of magmatic rocks in areas such as Gejiu, Wenshan, and Maguan. Neoproterozoic magmatic rocks are exposed on the western side of the Wenshan–Malipo fault zone and mainly manifest as highly weathered residual granite bodies. Caledonian ultramafic–mafic intrusive rocks are mainly distributed in the western and southern parts of the Nanwenhe–Song Chay dome and occur as dykes and sills within the Cambrian strata. Hercynian–Indosinian ultramafic–mafic intrusive rocks are primarily found in the Maguan and Malipo areas, with some occurrences in Vietnam as well, and are primarily concentrated in the Middle to Late Permian in terms of age. Yanshanian magmatic rocks consist of acidic intrusions, including the Laojunshan granite and the Pia Oac complex located outside China (Figure 1). The Yanshanian Laojunshan granite body is a composite pluton with multiple intrusive phases, which can be divided into early, middle, and late stages according to the time of emplacement. The early-stage rock type is porphyritic biotite granite, the middle-stage rock type is two-mica granite, and the late-stage rock type is granite porphyry.

The regional strata in the Laojunshan ore cluster have been subjected to varying degrees of metamorphism. The exposed strata range from the Proterozoic to Middle–Late Cambrian, Devonian, Carboniferous, Triassic, and Quaternary systems (Figure 2) [12]. The main ore-hosting formations include the Paleoproterozoic Mengdongyan Group and Neoproterozoic Xinzai Formation. Specifically, the Nanwenhe tungsten deposit occurs in skarns of the Nanyangtian Formation; the Saxi tungsten–beryllium deposit is hosted in granulites of the Saxi Formation; tulong and Xinzai tin–polymetallic deposits are contained within the Xinzai Formation.

2.2. Ore Deposit Geology

The Nanwenhe mining area is located in the eastern part of the Laojunshan W-Sn polymetallic ore cluster region. It extends 8.6 km in length from north to south and 5–6.5 km in width from east to west, covering a mineralization area of up to 60 km², with resource reserves reaching a large-scale deposit. It is the largest tungsten deposit in southeastern Yunnan in terms of resource reserves. The exposed strata in the Nanwenhe mining area primarily consist of the Nanyangtian Formation of the Paleoproterozoic Mengdongyan Group (Pt₁n). Pt₁n₁ is dominated by phyllite, with lithologies including two-mica phyllite, mica phyllite, two-mica plagioclase gneiss, and tourmaline quartzite, interlayered with minor amounts of skarn. Pt₁n₂ is the main ore-hosting horizon, with lithologies such as tourmaline quartzite and skarn. Pt₁n₃ has lithologies of two-mica phyllite and two-mica plagioclase gneiss, interlayered with minor amounts of skarn lenses. The attitude is relatively gentle. The mining area is situated in the core of the Laojunshan–Song Chay metamorphic dome, where tectonic activity is frequent, with developed faults and folds [16]. The mining area exhibits frequent magmatic activity with multi-phase characteristics, including the Silurian Laochengpo orthogneiss, the Yanshanian Laojunshan granite pluton, and the Cretaceous Kouha granite porphyry (Figure 3). The Nanwenhe tungsten deposit trends NE and is mainly divided into the Nanyangtian, Dayutang, and Maoping ore sections, distributed sequentially from north to south (Figure 3). The ore bodies occur in the skarn of the Paleoproterozoic Nanyangtian Formation of the Mengdongyan Group, primarily exhibiting layered and stratiform shapes. The average grade of the ore bodies is w(WO₃) = 0.30%–0.58%.

The Nanwenhe tungsten deposit can be divided into three mineralized zones, from bottom to top: Zone III, Zone II, and Zone I (Figure 3). Zone III is located at the base of the middle section and the top of the lower section of the Nanyangtian Formation. The main host rocks are garnet skarns, with minor amounts of diopside skarns, tourmaline quartzites, and tourmaline–quartz veins. Mineralization is relatively strong in garnet skarns, where scheelite predominantly occurs, while diopside skarns exhibit weaker mineralization. Zone II contains less ore, with skarns serving as the wall rocks and mica schists occurring along the margins. Cross-cutting quartz stockworks are well-developed, and scheelite is found within quartz veins. Locally, coarse-grained scheelite occurs in skarns. Zone I is hosted in dense hornblende schists and skarns. A reticulated quartz vein system is observed, with the veins confined to the layers. Zone I contains disseminated scheelite mineralization.

3. Samples and Analytical Methods

Samples were selected from the Nanwenhe tungsten deposit for geochronological and geochemical analyses. The studied samples were all collected from the Nanyangtian ore block of the Nanwenhe tungsten deposit, including surface outcrop samples, tunnel samples, and deep drill core samples (Figure 3).

In situ LA-ICP-MS trace element analyses were conducted on scheelite from both the late skarn stage of skarn mineralization and the feldspar–quartz–scheelite–tourmaline stage of vein-type mineralization. These analyses were performed at Collaborative Innovation Center for Exploration of Strategic Mineral Resources at China University of Geosciences (Wuhan). The measurements were carried out using an Agilent Technologies 7900 single-quadrupole inductively coupled plasma mass spectrometer (ICP-MS) (Santa Clara, CA, USA) coupled with a 193 nm ArF excimer laser ablation system. The analyses were conducted with a laser repetition rate of 8 Hz and a spot size of 32 μm. The energy density was set at 4.7 J/cm² for scheelite analysis. Helium was used as the carrier gas during sample ablation. Each analytical point consisted of approximately 30 s of background signal acquisition followed by 40 s of data signal acquisition. The NIST SRM standard reference material was used as an internal standard for mass and time drift correction. The acquired data were processed offline using ICPMSDataCal software (10.9) [16].

4. Results

4.1. Petrographical Characteristics of Scheelite

In the Nanwenhe tungsten deposit, two types of scheelite occurrences have been identified. One formed during the skarn mineralization stage and is hosted in skarn; the other formed during the vein mineralization stage and is hosted in feldspar–quartz veins, with the microscopic characteristics shown in Figure 4.

The CL images of scheelite in the Nanwenhe tungsten deposit (Figure 5) show that both types of scheelite occurrences do not exhibit zoning structures and are relatively homogeneous, indicating a stable ore-forming environment. Based on the occurrence, the scheelite in feldspar–quartz veins is further divided into two types, Sch-2a and Sch-2b, which replaces Sch-2a along fractures.

4.2. The Trace Element Composition of Scheelite

In situ LA-ICP-MS compositional analysis can obtain high-precision in situ mineral compositional results, define the nature of the ore-forming fluid, and further constrain the genesis of the deposit. The trace element analysis results of scheelite are shown in Figure 6. The results show that the elements relatively enriched in scheelite are Sr, Y, Nb, Mo, and Pb, with contents close to or greater than 10 ppm. In Sch-1, the contents are Sr (58.17–70.48 ppm), Y (33.29–33.30 ppm), Nb (14.26–49.04 ppm), Mo (28.84–35.58 ppm), and Pb (3.65–7.14 ppm); in Sch-2a, the contents are Sr (112–137 ppm), Y (16.93–64 ppm), Nb (3.68–24.85 ppm), Mo (19.40–41.31 ppm), and Pb (6.40–9.04 ppm); in Sch-2b, the contents are Sr (95.96–149 ppm), Y (59.56–249 ppm), Nb (8.08–37.37 ppm), Mo (14.97–25.08 ppm), and Pb (9.18–10.61 ppm). Scheelite in skarn has low Sr. Sch-2a in feldspar–quartz veins has lower Mo, Y, and Nb than Sch-2b that replaces Sch-2a.

4.3. The Rare Earth Element (REE) Composition of Scheelite

The ΣREE values are 28.43–47.28 ppm for Sch-1, 59.30–89.85 ppm for Sch-2a, and 339–472 ppm for Sch-2b. Overall, scheelite from the feldspar–quartz–scheelite–tourmaline stage (Sch-2a and Sch-2b) is more enriched in REEs than that from the late skarn stage (Sch-1). The REE distribution pattern diagram (Figure 7) shows that Sch-1 has weak differentiation between light and heavy REEs, with LREE/HREE ratios of 2.03–3.10, is slightly enriched in LREEs, and has an overall flat pattern. Eu shows a positive anomaly; Sch-2a has LREE/HREE ratios of 1.83–2.56, is enriched in MREEs, and has an arc-shaped pattern. The Eu-positive anomaly is weak; Sch-2b has LREE/HREE ratios of 0.82–1.04 and is enriched in MREEs and HREEs. The Eu anomaly is opposite to that of the previous two stages, showing Eu-negative anomaly.

5. Discussion

5.1. The Chemical Characteristics of Ore-Forming Fluid

Early mineral fractional crystallization can affect the Eu anomaly and the degree of the anomaly. The crystallization of accessory minerals rich in rare earth elements (REEs), such as apatite and titanite, which are associated with skarn scheelite, can lead to a significant reduction in REEs in the fluid [17,18]. Theoretically, when the ore-forming fluid reacts with the host rock through hydrolysis, the breakdown of plagioclase in the host rock releases Eu²⁺, which can cause a strong positive Eu anomaly in ore-forming fluid [19]. The relatively flat REE distribution pattern curve of skarn scheelite may indicate that the crystallization of early minerals reduced the Eu anomaly in the ore-forming fluid, which is reflected in the Eu anomaly of skarn scheelite. The formation of a large amount of apatite also indicates that the ore-forming fluid is rich in P, a phenomenon also observed in the Zhuxi deposit [20]. Scheelite (Sch-2a) from the feldspar–quartz–scheelite–tourmaline stage exhibits a weak positive Eu anomaly (Figure 7). Scheelite in this stage occurs in feldspar–quartz veins, but the small amount of plagioclase in the veins has a low REE content and does not cause a weak Eu anomaly [21]. The weak differentiation of light and heavy REEs under the condition of F-rich ore-forming fluid may also lead to a weak positive Eu anomaly [22]. When the fluid is rich in F, it promotes the formation of complexes between F and REEs, Y, and other elements, increasing the content of these elements in the fluid. However, the low levels of REEs and Y in Sch-2a indicate that the ore-forming fluid is not F-rich (Figure 7). Nevertheless, the large amount of tourmaline formed in this stage absorbed the Eu²⁺ released into the fluid through hydrolysis. Since tourmaline typically exhibits a significant Eu-positive anomaly, this absorption could result in a weak positive Eu anomaly in scheelite. Additionally, the relatively low REE contents in Sch-2a may be attributed to the crystallization of tourmaline. In the later stages, after the crystallization of accessory minerals is complete and hydrolysis weakens, the formed Sch-2b is more likely to reflect the characteristics of the ore-forming fluid itself. In summary, the ore-forming fluid of the Nanwenhe tungsten deposit is P-rich.

The Mo content in scheelite can serve as an indicator of the redox state of the ore-forming fluids. Under oxidizing conditions, Mo exists as Mo⁶⁺ and substitutes for W⁶⁺ in scheelite due to their similar coordination numbers, ionic radii, and valence states. However, under low f_O2 conditions, Mo⁶⁺ tends to be reduced to Mo⁴⁺ and precipitates as MoS₂ instead. In the Nanwenhe tungsten deposit, the average Mo contents of Sch-1, Sch-2a, and Sch-2b are 32.85 ppm, 34.61 ppm, and 18.81 ppm, respectively. These consistently low Mo concentrations suggest that the Nanwenhe tungsten deposit formed under relatively reducing conditions.

5.2. The Source of Ore-Forming Materials

The Nanwenhe tungsten deposit is located near the Laojunshan granite. Existing studies have shown that the formation age of the Laojunshan granite ranges from 92 to 84 Ma [11], which is significantly different from the garnet dating results of the mineralization stage of the Nanwenhe deposit [23]. In addition, no intrusive bodies that have temporal and spatial relationships with the Nanwenhe tungsten deposit have been found in the Nanwenhe area, which makes it difficult to determine the source of the ore-forming materials.

During the dating of the Laojunshan pluton, Di et al. (2013) [24] discovered metamorphic zircons with an age of 155 Ma. Previous studies have found that two stages of skarnization in the Nanyangtian deposit (ca. 203 Ma and ca. 141–146 Ma). Two garnet samples together yield a Tera–Wasserburg lower intercept age of 203.2 ± 8.7 Ma, whereas two vein-type vesuvianite samples yield ages of 144.4 ± 3.7 Ma and 145.9 ± 3.1 Ma, identical within error to the ages of 141.5 ± 7.2–145.5 ± 2.9 Ma obtained from micro-disseminated and veinlet-like scheelite. The above dating results and the geological observations that ore-barren garnet cut by later quartz–scheelite–(garnet)–(vesuvianite) hydrothermal veins suggest two stages of skarnization in the Nanyangtian deposit (ca. 203 Ma and ca. 141–146 Ma), whereas the W mineralization occurred during ca. 141–146 Ma. It is inferred that the age of ~203 Ma is related to Indosinian regional metamorphism and associated migmatization–hydrothermal activity [23].

Regional geochronological data indicate that the Laojunshan–Song Chay metamorphic dome had ceased uplifting by 165 Ma, and deep-seated magmatic activity had also stopped, until the intrusion of Yanshanian granite magma from 92 to 84 Ma prompted further uplift of the Laojunshan–Song Chay metamorphic dome. In combination with the study of Vladimirov et al. (2019) [25] and the ore-forming ages of 141–146 Ma, it is likely that regional metamorphism occurred in the Middle to Late Jurassic. The W content in the ore of the Nanwenhe tungsten deposit is approximately 42–4277 ppm [26]. The upper and lower crustal W contents are 2 ppm and 0.7 ppm, respectively, with an average of 1.9 ppm [27,28]. In South China, the W content in the Proterozoic strata does not exceed 12 ppm [29]. The W content in the Nanyangtian Formation of the Mengsong Group is about 19 ppm [28], while the world average for granite is 1.5 ppm [30]. The crustal evolution in South China already enriched the W element, and the metamorphic fluids generated by regional metamorphism likely extracted W from the crust and transported it to shallower depths for mineralization.

The host rock also provides important chemical substances in the process of generating ore and alteration minerals. The ore mineral of the Nanwenhe tungsten deposit is scheelite, and a large amount of Ca is required for the formation of scheelite. For scheelite in skarn, the reaction between the ore-forming fluid and the carbonate rock can provide the necessary Ca for the precipitation of scheelite. For scheelite in feldspar–quartz veins, Ca may come from the breakdown of plagioclase in the host rock, which releases Ca through hydrolysis reactions between the ore-forming fluid and the host rock, promoting the formation of scheelite. Hydrolysis reactions provide the necessary ore-forming elements for the precipitation of tungsten-bearing minerals [31,32]. The higher the CO₂ content in the fluid, the lower the pH of the fluid (Equation (1)):

CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃⁻ ↔ 2H⁺ + CO₃²⁻

(1)

Ore-forming fluids with low pH can carry high concentrations of tungsten. At temperatures > 300 °C, the solubility of tungsten-bearing species (H₂WO₄ and HWO₄⁻) in solution increases significantly [33,34,35,36,37]. The interaction between these acidic fluids and carbonate wall rocks leads to rock dissolution, increasing Ca²⁺ concentration and pH in the fluid (Equation (2)). Experimental studies have demonstrated that this reaction serves as a key trigger for tungsten mineral precipitation [35,36,37,38]. In the case where the wall rocks are metasedimentary rocks, intense alteration occurs on both sides of the ore-bearing quartz veins due to water–rock reactions, causing plagioclase decomposition to release the necessary Ca and triggering tungsten mineral precipitation [39]. Then, Ca²⁺ and WO₄²⁻ react and precipitate as CaWO₄ (Equation (3)). In the Nanwenhe tungsten deposit, both reactions occurred: scheelite formed during the skarn mineralization stage and the vein-type mineralization stage. Additionally, during the vein-type mineralization stage, intense water–rock reactions led to the formation of abundant tourmaline.

CaCO₃ + H⁺ → Ca²⁺ + CO₂ + H₂O

(2)

Ca²⁺ + WO₄²⁻ → CaWO₄

(3)

5.3. The Genesis Mechanism of the Deposit

Most discovered skarn-type tungsten deposits are genetically associated with magmatic rocks, commonly hosted at the contact zones between calc-alkaline intrusive rocks and carbonate sequences. However, a distinct strata-bound skarn tungsten deposit subtype exists where no associated intrusive rocks are observed in the vicinity. These orebodies typically exhibit stratiform morphology, occurring predominantly within regionally metamorphosed sequences or volcanic successions, and extend continuously for hundreds of meters along lithological contacts [40,41]. Since the tungsten ore bodies in the Nanwenhe tungsten deposit are mainly hosted in the skarn of the Nanyangtian Formation, the Nanwenhe tungsten deposit is currently generally considered to be a skarn-type tungsten deposit, which is different from the typical skarn-type tungsten deposit. There is a genetic controversy over the feldspar–quartz veins containing ore. This study found that the feldspar–quartz veins locally cut through the skarn body. The ore minerals occur in the quartz veins, and there is obvious hydrothermal alteration around the veins, with the formation of typical hydrothermal minerals– tourmaline. This phenomenon is consistent with the characteristics of quartz-vein-type tungsten deposits. Niu (2021) [21] conducted detailed studies on the temperature, composition, isotopes, and characteristic mineral assemblages of fluid inclusions in the Nanyangtian ore section of Nanwenhe tungsten deposit and concluded that the Nanwenhe tungsten deposit has the characteristics of both types of deposits. They found the ore-forming fluid belongs to the simple NaCl-H₂O type. Fluid experienced a gradual decrease in fO₂ and a continuous increase in pH, leading to the precipitation of abundant scheelite.

This study systematically investigates the characteristics of scheelite from the Nanwenhe tungsten deposit and found that the main ore-hosting rocks of the Nanwenhe tungsten deposit are garnet skarn, diopside skarn and tremolite skarn, and large-grained scheelite in the skarn. The edge of the skarn contains phyllite, with quartz veinlets cutting through the layers, and scheelite occurs in the quartz veins. The occurrence of the ore mineral scheelite in both skarn and feldspar-quartz veins is a typical characteristic of the Nanwenhe tungsten deposit. The two types of scheelite have different mineral associations (Figure 4). In terms of geochemical characteristics, scheelite in skarn has low Sr, which is significantly different from that in feldspar–quartz veins. The REE distribution pattern diagrams also show different characteristics. Therefore, this study indicates that the Nanwenhe tungsten deposit has the characteristics of both skarn deposits and quartz-vein-type deposits and belongs to a polygenetic composite deposit.

The Laojunshan ore cluster is situated within the southern Youjiang Basin, northwestern flank of the Laojunshan–Song Chay dome. Ore deposits in this district predominantly occur along contact zones between Late Mesozoic granites and metamorphic country rocks. During the Mesozoic, the Youjiang Basin—located at the southwestern margin of the South China Block—underwent multiple tectonic events including the Indosinian orogeny, post-orogenic extension, NW-directed Jurassic thrusting, and Cretaceous extension. These processes triggered polyphase magmatism and mineralization [42,43]. The Song Chay dome underwent detachment deformation during the Late Triassic to Early Jurassic period [12]. Due to the subduction of the Pacific Plate beneath the South China Block during the Early Jurassic, the South China Block transitioned from the Tethyan tectonic domain to the Pacific tectonic domain, resulting in the formation of NE- and NNE-trending folds and thrust nappes [44]. Additionally, numerous Late Jurassic–Early Cretaceous tectonothermal events occurred in a regional episodic extensional setting. In the Early Jurassic, by ∼200 Ma, that décollement was folded and cooled down to a temperature of ∼300 °C. P–T estimates suggest that metamorphism coeval with a décollement with top to the north shear culminated at ∼580 °C and ∼4.5 kbar (∼16 km depth) for [5]. The mineralization (141–146 Ma) may represent that regional metamorphic events occurred in the Nanwenhe area, and the mineralization is likely closely related to the metamorphic fluid activity generated by multiple tectonothermal events that occurred during the tensional structural environment at the end and after the regional uplift.

6. Conclusions

(1) Field geological observations have revealed that the tungsten ore bodies in the Nanwenhe tungsten deposit mainly occur in skarn, with some ore bodies hosted in feldspar–quartz veins in skarn and phyllite, constituting the typical skarn-type and quartz-vein-type ores in the Nanwenhe tungsten deposit.

(2) The Nanwenhe tungsten deposit is divided into two mineralization periods and four mineralization stages, including the skarn mineralization period (early skarn stage and late skarn stage) and the vein mineralization period (feldspar–quartz–scheelite–tourmaline stage and calcite stage).

(3) Studies on the trace elements of scheelite indicate that hydrolysis is an important mechanism for the formation of scheelite in the Nanwenhe tungsten deposit. During the skarn mineralization period, the ore-forming fluid reacted with the surrounding carbonate rocks to form skarn-type ore bodies. In the vein mineralization period, the ore-forming fluid reacted with the surrounding phyllite. Hydrothermal alteration occurred on both sides of the veins due to hydrolysis reactions, and the breakdown of plagioclase promoted the formation of scheelite within the veins. At the same time, hydrolysis released Eu²⁺ into the fluid, which dominated the Eu anomaly characteristics of the rare earth elements in scheelite.