Geochemical Characteristics and Genetic Significance of Garnet in the Dulong Sn-Polymetallic Deposit, Yunnan Province, Southwestern China
by
, , , and
Tong Liu
1
,
Shao-Yong Jiang
1,2,*,
Dong-Fang Li
1,
Suo-Fei Xiong
1,
Wei Wang
1 and
Shugang Xiao
2 1
State Key Laboratory of Geological Processes and Mineral Resources, Collaborative Innovation Center for Exploration of Strategic Mineral Resources, School of Earth Resources, China University of Geosciences, Wuhan 430074, China
2
Expert Workstation, Geological Team 308, Yunnan Bureau of Nonferrous Geology, Kunming 650214, China
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(9), 911; https://doi.org/10.3390/min15090911
Submission received: 10 July 2025
/
Revised: 24 August 2025
/
Accepted: 26 August 2025
/
Published: 27 August 2025
(This article belongs to the Special Issue Recent Developments in Rare Metal Mineral Deposits)
Abstract
The Dulong Sn-polymetallic deposit in Yunnan Province of southwestern China serves as a unique case study for unraveling the evolution of skarn systems and tin mineralization. Four distinct garnet types (Grt I to Grt IV) were classified based on petrographic observations. Compositional analysis reveals a progression from Grt I to Grt III, marked by increasing andradite components, and elevated tin concentrations, peaking at 5039 ppm. These trends suggest crystallization from Sn-enriched magmatic-hydrothermal fluids. In contrast, Grt IV garnet exhibits dominant almandine components and minimal tin content (<2 ppm). Its association with surrounding rocks (schist) further implies its metamorphic origin, distinct from the magmatic origin of the other garnet types. Combined with previously published sulfur and lead isotopic data, as well as trace element compositions of garnet, our study suggests that Laojunshan granites supply substantial ore-forming elements such as S, Pb, W, Sn, In, and Ga. In contrast, elements such as Sc, Y, and Ge are inferred to be predominantly derived from, or buffered by, the surrounding rocks. The geochemical evolution of the garnets highlights the critical role of redox fluctuations and fluid chemistry in controlling tin mineralization. Under neutral-pH fluid conditions, early-stage garnets incorporated significant tin. As the oxygen fugacity of the ore-forming fluid declined, cassiterite precipitation was triggered, leading to tin mineralization. This study reveals the interplay between fluid redox dynamics, garnet compositional changes, and mineral paragenesis in skarn-type tin deposits.
1. Introduction
Skarn deposits are an important type of polymetallic resource worldwide, such as tin, tungsten, copper, and iron [1,2,3]. Their mineralization is usually closely related to the metasomatism reaction between magmatic hydrothermal fluids and carbonate rocks [1,2,3]. Garnet is widely present in different skarn zones. It can record the physicochemical conditions of ore-forming fluids, especially in terms of oxygen fugacity and pH [4,5,6].
Previous studies have shown that the composition of garnet in typical skarn deposits mainly fluctuates between grossular and andradite, and the changes in their end-member ratios usually reflect the changes of oxygen fugacity [6,7,8,9]. The Dulong Sn-polymetallic deposit located in eastern Yunnan, northwestern China, is a typical skarn deposit with well-developed skarn alteration. Garnet is widely distributed within the skarn zones of the Dulong deposit. Previous studies on garnet from Dulong have suggested, based on garnet U–Pb dating, that the mineralization age of the deposit is contemporaneous with the formation of the Laojunshan pluton, occurring at approximately 80–90 Ma. In this study, we report the newly discovered occurrence of metamorphic garnet in the deposit. However, the implications of the presence of metamorphic garnet for the mineralization process of the Dulong deposit should be further investigated.
Therefore, this study focuses on garnet from the Dulong Sn-polymetallic deposit, conducting a detailed study on petrography and major and trace element compositions via LA-ICP-MS analysis. The aim of this study is to systematically analyze the major and trace element variations (especially Sn, and rare earth elements) of garnet from different types in an attempt to (1) reconstruct the physicochemical evolution of hydrothermal fluids, (2) explore the genesis and indicative significance of almandine-dominant garnet in the Dulong deposit, and (3) further evaluate the potential implications of garnet’s chemical composition in the study of the mineralization mechanism of skarn tin deposits.
2. Geological Setting and Ore Deposit Geology
2.1. Geological Setting
The strata in the regional range from the Proterozoic to the Cenozoic (except for the Jurassic and Cretaceous) is the geological setting for this study. The strata in the research area are mainly composed of Paleozoic rocks, with Cambrian strata being the most developed, which mainly composed of schists, quartz schists, and plagio-amphibolites [10].
The deposit distribution in the area is significantly influenced by faults (Figure 1). Three typical northwest faults in the area are the Wenshan-Malipo Fault, Nanwenhe Fault, and Maguan-Dulong Fault. The Wenshan-Malipo Fault is an important boundary of regional geological units, located in the northern part of the Dulong Sn-polymetallic deposit. The fault was formed during the Late Devonian period and underwent multiple activities in the Early Triassic and Early Carboniferous periods, and it is an important controlling part of the magmatic rocks, strata, and ore deposit in this area. Along the southwest of the fault, there are mainly exposed Cambrian schist, gneiss, marble, and Yanshanian granite samples [11]. In addition to large-scale deep faults, this area also includes other relatively small faults, mainly distributed in a northeast and north–south direction. Although the nature and evolution time of the faults are not exactly the same, the overall activity time is similar to the tectonic evolution time of deep faults, which together constitute the complex tectonic geological background of the study area. At the same time, it plays an important controlling role in regional magmatic activity and the formation and enrichment of tin polymetallic deposits [12].
Magmatic rocks are highly developed in the region, with an exposed area of approximately 600 m2. The magma eruption during the Hercynian period was mainly composed of basic volcanic rocks, the magma eruption during the Indosinian period was mainly composed of felsic volcanic rocks and intrusions, and the Yanshanian period was mainly composed of felsic intrusions, which is the most closely related to mineralization in this area. The Dulong granites are the ore-forming rocks in the mining area [13]. The Dulong-Laojunshan pluton is a metamorphic core complex that can be divided into three sub-stages [14,15]. Among them, the first-stage granite in Yanshanian has the largest scale and is directly in contact with the surrounding rocks. The second-stage granite intrudes into the first-stage granite, occupying the central part of the Dulong rock mass. The main lithology is biotite granite. The third-stage granite has the smallest scale, and the main lithology is granite porphyry. In addition, there are no volcanic rocks in the study area, but there are some volcanic rocks in the northern area of Malipo County (Figure 1).
2.2. Ore Deposit Geology
The strata in the ore district belong to the Cambrian Longha Formation, Tianpeng Formation, and a small amount of the Neoproterozoic Mengdong Group (Figure 2). The Tianpeng Formation is particularly closely related to the Dulong Sn-polymetallic deposit and is the main ore-bearing strata of the deposit. The Longha Formation is distributed on the west of the mining area, mainly composed of dolomite. The Tianpeng Formation, as the main ore-bearing strata in the mining area, is mainly composed of marble, schist, and a small amount of granulite [14,15].
The ore district has undergone multiple tectonic activities and transformations since the Neoproterozoic period, and is part of the Laojunshan complex anticline. There are five obvious fault zones in the mining area, which can be divided into the Maguan-Dulong fault, F0, F1, F2, and F4 [15]. Among them, the F0 and F1 faults are relatively large in scale and are the two main ore-controlling structures in the mining area, while F4 is the fault that separates ore bodies. The F0 fault is mainly distributed in the northeast of the ore district and the southwest of the Laojunshan rock mass. The F1 fault is distributed in a north–south direction, and is an important ore-conducting and hosting structure within the mining area. In the Dulong ore district, the contact zone is divided into three zones based on spatial relationships: inner, middle, and outer. The rock mass of the inner contact zone is syenogranite. The middle zone is characterized by three alteration zones: a diopside-wollastonite-grossular zone, a chlorite-epidote-actinolite zone, and a silicification-calcite zone. There is no distinct boundary between the middle and outer zones. The outer zone consists primarily of unaltered schist and marble.
The Dulong Sn-polymetallic deposit consists of five ore sections from north to south, namely Tongjie, Manjiazhai, Lazizhai, Wukoudong, and Nandangchang, all of which are located in the Tianpeng Formation (Figure 2) [14,15]. They are mainly composed of magnetite, sphalerite-pyrrhotite-chalcopyrite, and sphalerite-galena. The ore bodies are controlled by skarn alteration zone. Within the Neoproterozoic Xinzhaiyan Formation, the orebodies are primarily developed as layers, lenses, and vein-like bodies. The largest ore body, No. 13, has a length of 2432 m from north to south and a width of 228 m from east to west. The thickness of the ore body ranges from 1 to 55 m, with an average thickness of about 15 m. The deposit hosts approximately 5.0 Mt of Zn, 0.4 Mt of Sn, 0.2 Mt of Pb, and 7 kt of In [15].
3. Samples and Analytical Methods
3.1. Samples
The samples for this study were collected from skarns in the Cambrian clastic and carbonate rocks in the Tongjie–Jinshipo–Manjiazhai area of the Dulong deposit (Figure 3). The sampling locations are shown in Table 1. All of them are drill-core samples from four different cores, with lengths of approximately 5–10 cm.
Garnet, as a representative mineral of skarn alteration, mainly exists in the early skarn stage, with only a few appearing in the late skarn stage (Figure 3). The classification of garnet types is primarily based on lithological characteristics. Based on spatial relationships, they are divided into two main categories: garnet occurring in skarn and garnet occurring in schist. Furthermore, garnet within the skarn is subdivided into three types according to differences in mineral assemblages, which are described in detail in the following sections. Grt-I, as the earliest appearance of garnet, is mostly dark brown in color under a microscope, often coexisting with diopside, which are all anhydrous silicate minerals, without the presence of sulfides. Grt-II strongly influenced by later hydrothermal alteration, often associated with chlorite. Grt-III is lighter in color compared to Grt I, with an increase in coexisting carbonate minerals. Grt-IV, light red in color, is often found in schist, with a small amount of sulfide coexistence.
3.2. LA-ICP-MS Major and Trace Elements Analysis
In this study, the major and trace element concentrations of garnets were determined using a NWR 193 HE laser ablation system coupled to an Agilent 7900 single-quadrupole ICP mass spectrometer at the LA-ICP-MS laboratory in the Collaborative Innovation Center for Exploration of Strategic Mineral Resources, China University of Geosciences (Wuhan). The ablation of the samples was performed using helium as the carrier gas. Each spot analysis incorporates approximately 30 s of background acquisition followed by 40 s data acquisition from the sample. A spot size of 32 μm was used together with a repetition rate of 8 Hz and an energy density of ~3.5 J cm−2. Every 8–10 sample analyses were followed by several analyses of external reference materials. In this work, NIST SRM 610 was used as quality control (QC) reference material to correct the instrumental time-dependent sensitivity drift, and multiple external standards (NIST 610, NIST 612, BCR-2G, BHVO-2G and BIR-1G) were selectively used for external calibration. The off-line selection and integration of background and analyte signals, time-drift correction, and quantitative calibration were performed using ICPMSDataCal 10.9 [17].
4. Results
4.1. Garnet Major Element Analysis
The garnet major elements results are listed in Table 2. Endmember calculations were based on 12 oxygens. The data show that Dulong garnets are predominantly calcareous; only Grt-IV belongs to the aluminum series. From Grt-I to Grt-III, the grossular component gradually decrease, with an average of 74.5, 65.7, and 44.2, respectively, while the andradite component increase (Table 2, Figure 4). From Grt-I to Grt-III, the andradite component gradually increases (FeO: from 7.14–9.51 to 15.3 wt.%–17.4 wt.%), whereas the grossular component gradually decreases (Al2O3: from 16.3–18.4 to 9.43 wt.%–11.0 wt.%). The contents of CaO, MgO, and MnO of three generations of garnet (Grt-I–III) are nearly consistent, showing minor variations. In contrast, Grt-IV displays a distinct composition, with the highest Al2O3 contents (19.8 wt.%–21.1 wt.%), elevated FeO contents (25.5 wt.%–27.6 wt.%) and MnO contents (4.51 wt.%–7.10 wt.%), and lower CaO contents (5.11 wt.%–5.96 wt.%).
4.2. Garnet Trace and Rare Earth Element Analysis
The garnet trace and rare earth element analytical results are listed in Table 3 and Table 4. The total rare earth elements (REEs) of four generation garnets are 8.56–24.5 ppm (mean 16.6 ppm, Grt-I), 3.91–42.7 ppm (mean 14.2 ppm, Grt-II), 27.9–34.0 ppm (mean 30.3 ppm, Grt-III), and 61.8–469 ppm (mean 223 ppm, Grt-IV, Figure 5). The LREE contents of garnets are 6.65–15.9 ppm (mean 10.5), 0.29–1.74 ppm (mean 0.79 ppm), 10.3–14.9 ppm (mean 12.6 ppm), and 0.39–5.21 ppm (mean 1.16 ppm), respectively. The HREE contents of garnets are 1.91–15.5 ppm (mean 6.17), 3.59–40.9 ppm (mean 13.4 ppm), 17.0–19.1 ppm (mean 17.7 ppm), and 61.4–469 ppm (mean 222 ppm), respectively. The LREE/HREE ratios of garnets are 0.58–3.60 (mean 2.36), 0.04–0.15 (mean 0.08), 0.59–0.78 (mean 0.71), and 0–0.02 (mean 0.01).
5. Discussion
5.1. Geochemical Characteristics of Dulong Garnet
As mentioned earlier, from Grt-I to Grt-III, the andradite (Ca3Fe2Si3O12) components of garnet increase, while Grt-IV has a distinct major element composition with almandine (component of garnet is Fe3Al2Si3O12) as the dominant end-member, which is an uncommon feature in skarn deposits (Figure 4). This observation contrasts with the garnet chemistry documented in most typical skarn deposits [6,7,8,9]. For example, garnets from the Niukutou deposit exhibited oscillatory evolution between grossular- and andradite-rich components across different generations [6]. Grossular and andradite are found in the endoskarn of the Jiama deposit. Proximal exoskarns were dominated by andradite, while distal stratabound skarns mainly contained grossular [8]. Similarly, there was a compositional evolution from andradite to grossular in garnets from the Yemaquan deposit [7]. Similarly, a comparable conclusion was reached in the Kendekeke deposit [9]. Together, these studies indicate that garnet compositions in skarn deposits predominantly fluctuate between grossular- and andradite-rich components, with little to no evidence of almandine as a significant component. Therefore, what triggered the occurrence of almandine in the Dulong deposit?
A review of the literature on almandine indicates that it usually forms during metamorphic processes, and is commonly found in metamorphic rocks such as schist, gneiss, and amphibolite [19,20,21]. This observation brings us back to the specific sample in which Grt-IV was identified. The sample, numbered 917-2, is a schist. Considering the occurrence of almandine in metamorphic settings, as discussed above, we interpret Grt-IV to be a metamorphic product of the surrounding schist in the Dulong Sn deposit, which may be the product of regional metasomatism. However, the precise timing of the metasomatic event remains unconstrained. Nevertheless, a comparison of the geochemical characteristics between Grt-IV and the other types (from Grt-I to Grt-III) can provide valuable insights.
In order to visually identify the similarities and differences between the two garnet types, principal component analysis (PCA) was employed. The PCA reveals that the distribution of four garnet types based on the selected trace elements, with PC1 and PC2 explaining 71.5% and 18.7% of the total variance, respectively (Figure 6). From the perspective of garnet origin, skarn-type garnets (Grt-I–III) are enriched in elements such as W, Sn, In, and Ga, whereas metamorphic garnets (e.g., Grt-IV) show higher concentrations of Sc, Y, Ge, and rare earth elements (Figure 6, Figure 7 and Figure 8). Combined with these garnet origins, this geochemical contrast suggests that, in the Dulong deposit, elements such as W, Sn, In, and Ga were predominantly sourced from magmatic fluids, while Sc, Y, and Ge were primarily derived from the surrounding rocks (schist). This inference is further supported by two previous studies [22,23]. Gallium in the Dulong deposit is predominantly hosted in Al-rich minerals within the ore-related granite, with its distribution primarily controlled by temperature [22]. In addition, Indium is mainly hosted in chalcopyrite and garnet (andradite) [23]. Given the widespread occurrence and abundance of garnet in the deposit, it may contribute significantly to the proportion of total In.
5.2. Physicochemical Conditions During Garnet Deposition
Oxygen fugacity: Uranium (U) can serve as a sensitive proxy for oxygen fugacity due to its multiple oxidation states, primarily U4+ and U6+. In reduced conditions, U act as U4+ and more likely substitutes Ca2+, which means that U contents in garnet can reflect the oxygen fugacity variations [24]. In the Dulong Sn-polymetallic deposit, garnet U content is generally very low. Those of Grt-IV fall below the detection limit. Therefore, we prefer select Sn as an indicator of oxygen fugacity. Sn, like U, is a variable element, having two oxidation states, Sn2+ and Sn4+. In oxidized conditions, Sn4+ is dominant and its ionic radius (0.69 Å) is similar with Fe3+ (0.65 Å) in the Y-site of garnet, making it possible to substitute Fe3+ in garnet [6]. In reduced and moderately oxidized conditions, Sn (II)-Cl complexes are dominant and stable. In very acidic solutions, however, the Sn (IV)-Cl-OH complexes become relatively important as the oxygen fugacity increases and the temperature decreases [25]. In the Dulong Sn-polymetallic deposit, Sn contents in four garnet types are as follows: 698–1711 ppm (Grt-I, average 1069 ppm), 3537–5039 ppm (Grt-II, average 4472 ppm), 284–928 ppm (Grt-III, average 730 ppm), and 0.59–1.40 ppm (Grt-IV, average 0.98 ppm). This trend of decreasing Sn content indicates that, from skarn to the surrounding rocks, the oxygen fugacity gradually decreases, which is also confirmed by the Eu anomalies in different garnet types (Figure 7). Simultaneously, the Sc content of Grt I–III increases with the increase in andradite components, which can substitute Fe3+. However, for different origins of garnets, there is a significant difference in Sc contents: the metasomatism garnets have higher Sc content, indicating that Sc contents in the Dulong deposit are mainly from the surrounding rocks (Figure 7 and Figure 8).
pH: Garnet REE patterns and Eu anomalies can record the fluid pH changes during garnet formation [26]. The neutral fluid conditions are characterized by HREE enrichment, LREE depletion, and negative Eu anomalies, while the mildly acidic fluid conditions are characterized by HREE depletion, LREE enrichment, and positive Eu anomalies. In the Dulong Sn-polymetallic deposit, all four garnet types show left-leaning REE patterns, LREE depletion, and HREE enrichment, suggesting the fluid condition is neutral (Figure 5).
5.3. Implications
5.3.1. Mineralization Age and Sources
Although the metamorphic time of Grt-IV cannot be accurately constrained, we can attempt to discuss the mineralization age of the Dulong deposit and the emplacement age of the Laojunshan granites. Numerous studies have employed cassiterite U–Pb geochronology to constrain the timing of mineralization at the Dulong tin deposit. Previous researchers applied LA-MC-ICP-MS to cassiterite and reported ages ranging from 82 to 96.6 Ma [27], utilized TIMS and obtained a U–Pb age of 79.8 Ma [28], while LA-ICP-MS analyses and reported ages between 82.1 and 88.5 Ma [10]. These age results are broadly consistent with the emplacement ages of the Laojunshan granites [28], supporting a genetic link between magmatism and tin mineralization. Simultaneously, in the region, previous researchers reported that the age of molybdenite using Re-Os dating is 83.4 Ma from the Kafang deposit in the Gejiu ore district [29], the garnet and cassiterite LA-ICP-MS U-Pb age ranges from 79.7 to 81.8 Ma from the Malage deposit in Gejiu ore district [16], and the cassiterite U–Pb age ranges from 85.8 to 88.4 Ma [30]. These mineralization ages in the region collectively confirm the existence of large-scale mineralization in southeastern Yunnan during late Yanshanian (Table 5).
As for the origin of the ore-forming material source, previous researchers reported δ34S values of sulfides ranging from −1.3‰ to 2.9‰, suggesting a magmatic origin, and also reported the lead (Pb) isotopic composition of sulfides, including pyrite, pyrrhotite, sphalerite, and arsenopyrite, suggesting that the origin of Pb is mainly derived from the lower crust (206Pb/204Pb: 17.573–18.574; 207Pb/204Pb: 15.526–15.746; 208Pb/204Pb: 38.077–39.158) [31]. And, for the fluid evolution of the Dulong deposit, the results of the Li isotope indicate that, in the early stage, the ore-forming fluids were predominantly magmatic in origin, whereas in the late stage, after extensive water–rock interactions, the fluids were mainly derived from external sources [32]. Combined with the observation that Grt I–III formed in skarn is enriched in W, Sn, In, and Ga—elements typically associated with magmatic fluids—and that Grt-IV formed in schist is enriched in Sc, Y, and Ge—elements likely sourced from the surrounding rocks, we infer that the Laojunshan granites contributed significant amounts of ore-forming elements such as S, Pb, W, Sn, In, and Ga. In contrast, elements like Sc, Y, and Ge appear to have been predominantly buffered or contributed to by the surrounding rocks.
5.3.2. Implications for Skarn Mineralization
The compositional evolution of garnet in different types of the Dulong Sn deposit provides valuable insights into the fluid evolution and mineralization process during the formation of skarn. Firstly, the transition from Grt-I to Grt-III is characterized by an increase in the andradite component and a decrease in the grossular component, which is similar to many typical skarn deposits. Grt IV (almandine) is a product of regional metamorphism, indicating that metamorphic garnet may also occur in skarn deposits. This reminds us to pay attention to the surrounding rocks of the studied deposits when conducting research on garnet in skarn deposits in the future.
Secondly, from Grt-I to Grt-III belong to the andradite-grossular series, which are products dominated by magmatic hydrothermal fluids. Grt IV is almandine-dominant garnet, which is a product dominated by metamorphic fluids. Simultaneously, by comparing the trace element contents of these garnets, it can be found that, in the Dulong Sn deposit, the Sn content from Grt-I to Grt-III is >1000 ppm, while Grt IV has a lower Sn content, indicating that the Sn content in magmatic hydrothermal fluids is higher than in the metamorphic fluids.
Finally, studying the evolution of physical and chemical properties of ore-forming fluids by different trace elements in garnet reveals that the pH of ore-forming fluids is approximately neutral under the surrounding rock buffer. Simultaneously, the decrease in oxygen fugacity of ore-forming fluids corresponds precisely to the precipitation of cassiterite under reducing conditions in the final stage, leading to mineralization.
6. Conclusions
- (1)
- The garnet in the Dulong Sn-polymetallic deposit can be divided into four types (from Grt-I to Grt-IV). In the early stage (from Grt-I to Grt-III), the andradite-grossular series was the dominant component, showing obvious Sn enrichment, which was formed in early Sn-rich and oxidized magmatic hydrothermal fluids, while Grt-IV is dominated by almandine and occurs within schist, suggesting that it likely formed as a product of regional metamorphism rather than from hydrothermal processes. Combined with previously published sulfur and lead isotopic data, our study suggests that the Laojunshan granites supplied substantial ore-forming elements such as S, Pb, W, Sn, In, and Ga. In contrast, elements such as Sc, Y, and Ge are inferred to be predominantly derived from, or buffered by, the surrounding rocks.
- (2)
- All garnets exhibit similar REE patterns of LREE depletion, HREE enrichment, and are left-leaning, indicating that the ore-forming fluid has a neutral pH and is controlled by the buffering of the surrounding rocks. Simultaneously, the changes in Sn content in various types of garnet suggest that, from skarn to the surrounding rocks, the oxygen fugacity gradually decreases, indicating that the compositional evolution of garnet effectively records the changes in fluid oxygen fugacity and pH. This indicates that garnet can serve as an important geochemical indicator of changes in the ore-forming condition of skarn tin deposits.
Author Contributions
Conceptualization, S.-Y.J.; investigation, T.L., S.-Y.J., D.-F.L., S.-F.X., W.W. and S.X.; data curation, T.L. and D.-F.L.; writing—original draft preparation, T.L. and D.-F.L.; writing—review and editing, S.-Y.J.; project administration, S.-Y.J. All authors have read and agreed to the published version of the manuscript.
Funding
This research was financially supported by projects from the National Natural Science Foundation of China (grant no. 42321001) and the Expert Workstation, Geological Team 308, Yunnan Bureau of Nonferrous Geology, Kunming (202405AF140108).
Data Availability Statement
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.
Acknowledgments
The authors sincerely thank staff and lab assistant in the LA-ICP-MS laboratory at the Collaborative Innovation Center for Exploration of Strategic Mineral Resources for their invaluable support and assistance in conducting the analyses. Special thanks to the anonymous reviewers for their valuable and constructive comments on the manuscript.
Conflicts of Interest
The authors declare no conflicts of interest.
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Figure 2.
Geological map of the Dulong Sn-polymetallic deposit (adapted from [13]).
Figure 2.
Geological map of the Dulong Sn-polymetallic deposit (adapted from [13]).
Figure 3.
Typical skarn samples from the Dulong Sn-polymetallic deposit. (a) Boundary between skarn and marble; (b) hand specimen of skarn; (c) scheelite–quartz vein crosscutting skarn; (d) schist; (e) skarn hand specimen; (f) photomicrograph showing garnet under transmitted light. Abbreviations of minerals: Grt—garnet; Ep—epidote; Cal—calcite; Sch—scheelite; Qz—quartz; Chl—chlorite.
Figure 3.
Typical skarn samples from the Dulong Sn-polymetallic deposit. (a) Boundary between skarn and marble; (b) hand specimen of skarn; (c) scheelite–quartz vein crosscutting skarn; (d) schist; (e) skarn hand specimen; (f) photomicrograph showing garnet under transmitted light. Abbreviations of minerals: Grt—garnet; Ep—epidote; Cal—calcite; Sch—scheelite; Qz—quartz; Chl—chlorite.
Figure 4.
Classification in the garnet component from the Dulong deposit. Gray area means that the garnet field for skarn-type Sn deposits [18].
Figure 4.
Classification in the garnet component from the Dulong deposit. Gray area means that the garnet field for skarn-type Sn deposits [18].
Figure 5.
REE distribution patterns in garnets from the Dulong deposit.
Figure 6.
Principle component score for Dulong garnet. PC1 refers to the direction of the maximum variance in the dataset. PC2 captures the second-largest amount of variance after accounting for the variation already explained by PC. The orange axis represents the loadings, which are the correlation coefficients between the original variables and the principal components, with values ranging from −1 to 1.
Figure 6.
Principle component score for Dulong garnet. PC1 refers to the direction of the maximum variance in the dataset. PC2 captures the second-largest amount of variance after accounting for the variation already explained by PC. The orange axis represents the loadings, which are the correlation coefficients between the original variables and the principal components, with values ranging from −1 to 1.
Figure 7.
Binary diagram illustrating the variations in Eu/Eu* and the contents of total REE, Sc, and Sn in four garnet types. (a) total REE contents–Eu/Eu*; (b) Sc content–Sn content.
Figure 7.
Binary diagram illustrating the variations in Eu/Eu* and the contents of total REE, Sc, and Sn in four garnet types. (a) total REE contents–Eu/Eu*; (b) Sc content–Sn content.
Figure 8.
(a–f) Box plot with overlapping dots illustrating W, Ga, In, Sc, Ge, and Y values in four garnet types.
Figure 8.
(a–f) Box plot with overlapping dots illustrating W, Ga, In, Sc, Ge, and Y values in four garnet types.
Table 1.
Sampling location of Dulong Sn-polymetallic deposit.
| Number | Mineral | Location | Sampling Depth |
|---|---|---|---|
| 913-6 | Grt-III | Jinshipo | 253.2 m |
| 921-13 | Grt-I | Jinshipo | 185.2 m |
| 125-5 | Grt-II | Jinshipo | 357.8 m |
| 917-2 | Grt-IV | Jinshipo | 54.5 m |
Table 2.
Major element results and calculated endmember components of garnets from the Dulong Sn-polymetallic deposit.
Table 2.
Major element results and calculated endmember components of garnets from the Dulong Sn-polymetallic deposit.
| Sample | Type | SiO2− wt% | TiO2 | Al2O3 | * FeO | MnO | MgO | CaO | Total | *** Si | Ti | Al | ** Fe3+ | ** Fe2+ | Mn | Mg | Ca | **** Gro | And | Pyr | Spe | Alm |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 921-13-1 | Grt-I | 38.3 | 0.96 | 18.0 | 7.14 | 0.63 | 0.07 | 34.5 | 99.6 | 2.95 | 0.06 | 1.63 | 0.36 | 0.10 | 0.04 | 0.01 | 2.85 | 77.0 | 18.1 | 0.27 | 1.37 | 3.27 |
| 921-13-2 | Grt-I | 38.5 | 0.13 | 16.3 | 9.51 | 0.81 | 0.05 | 34.3 | 99.6 | 2.98 | 0.01 | 1.49 | 0.52 | 0.10 | 0.05 | 0.01 | 2.85 | 69.0 | 25.7 | 0.19 | 1.77 | 3.33 |
| 921-13-3 | Grt-I | 37.4 | 0.13 | 17.9 | 8.08 | 0.69 | 0.05 | 35.4 | 99.7 | 2.90 | 0.01 | 1.64 | 0.43 | 0.10 | 0.05 | 0.01 | 2.94 | 74.5 | 20.6 | 0.19 | 1.47 | 3.20 |
| 921-13-4 | Grt-I | 37.6 | 0.22 | 17.5 | 8.31 | 0.66 | 0.05 | 35.3 | 99.6 | 2.92 | 0.01 | 1.60 | 0.45 | 0.09 | 0.04 | 0.01 | 2.93 | 73.6 | 21.9 | 0.19 | 1.41 | 2.93 |
| 921-13-6 | Grt-I | 38.5 | 0.15 | 18.4 | 7.33 | 0.86 | 0.05 | 34.4 | 99.7 | 2.97 | 0.01 | 1.67 | 0.35 | 0.13 | 0.06 | 0.01 | 2.84 | 76.6 | 17.2 | 0.19 | 1.85 | 4.14 |
| 921-13-7 | Grt-I | 38.9 | 0.01 | 18.2 | 7.44 | 0.70 | 0.06 | 34.2 | 99.5 | 3.00 | - | 1.65 | 0.35 | 0.13 | 0.05 | 0.01 | 2.82 | 76.5 | 17.5 | 0.23 | 1.52 | 4.29 |
| 125-5-1 | Grt-II | 36.7 | 0.81 | 14.6 | 12.1 | 0.93 | 0.06 | 33.8 | 99.0 | 2.90 | 0.05 | 1.36 | 0.68 | 0.12 | 0.06 | 0.01 | 2.86 | 60.5 | 33.2 | 0.23 | 2.04 | 4.03 |
| 125-5-2 | Grt-II | 36.6 | 0.26 | 16.6 | 9.61 | 0.82 | 0.09 | 35.1 | 99.1 | 2.87 | 0.02 | 1.54 | 0.54 | 0.09 | 0.05 | 0.01 | 2.95 | 69.0 | 25.9 | 0.34 | 1.75 | 2.99 |
| 125-5-3 | Grt-II | 37.2 | 0.32 | 15.7 | 10.6 | 0.80 | 0.08 | 34.4 | 99.1 | 2.92 | 0.02 | 1.45 | 0.59 | 0.11 | 0.05 | 0.01 | 2.89 | 65.6 | 28.9 | 0.31 | 1.74 | 3.48 |
| 125-5-4 | Grt-II | 36.9 | 0.84 | 15.1 | 11.5 | 0.98 | 0.06 | 33.8 | 99.2 | 2.90 | 0.05 | 1.40 | 0.63 | 0.13 | 0.07 | 0.01 | 2.85 | 62.4 | 31.1 | 0.23 | 2.14 | 4.12 |
| 125-5-5 | Grt-II | 37.2 | 0.44 | 16.3 | 9.34 | 0.83 | 0.12 | 34.9 | 99.1 | 2.91 | 0.03 | 1.50 | 0.54 | 0.07 | 0.05 | 0.01 | 2.92 | 69.0 | 26.5 | 0.46 | 1.79 | 2.30 |
| 125-5-6 | Grt-II | 37.0 | 0.16 | 16.1 | 10.0 | 0.85 | 0.09 | 34.9 | 99.1 | 2.90 | 0.01 | 1.49 | 0.57 | 0.09 | 0.06 | 0.01 | 2.93 | 67.4 | 27.7 | 0.34 | 1.83 | 2.80 |
| 913-6-1 | Grt-III | 37.0 | 0.66 | 11.0 | 15.3 | 0.57 | 0.13 | 34.7 | 99.4 | 2.93 | 0.04 | 1.03 | 0.99 | 0.03 | 0.04 | 0.02 | 2.95 | 48.3 | 49.0 | 0.51 | 1.26 | 0.83 |
| 913-6-2 | Grt-III | 36.6 | 0.54 | 9.8 | 16.8 | 0.42 | 0.13 | 35.0 | 99.3 | 2.92 | 0.03 | 0.92 | 1.11 | 0.01 | 0.03 | 0.02 | 2.99 | 43.6 | 54.4 | 0.51 | 0.93 | 0.46 |
| 913-6-3 | Grt-III | 36.3 | 0.56 | 9.5 | 17.4 | 0.41 | 0.11 | 35.0 | 99.3 | 2.90 | 0.03 | 0.90 | 1.14 | 0.02 | 0.03 | 0.01 | 3.00 | 41.9 | 56.0 | 0.43 | 0.91 | 0.68 |
| 913-6-6 | Grt-III | 37.1 | 0.52 | 9.4 | 16.8 | 0.43 | 0.10 | 34.9 | 99.3 | 2.96 | 0.03 | 0.89 | 1.12 | - | 0.03 | 0.01 | 2.98 | 43.0 | 55.6 | 0.39 | 0.96 | - |
| 917-2-1 | Grt-IV | 41.0 | 0.08 | 19.8 | 25.5 | 5.67 | 1.20 | 5.88 | 99.1 | 3.25 | - | 1.85 | - | 1.69 | 0.38 | 0.14 | 0.50 | 17.9 | - | 5.11 | 13.7 | 60.9 |
| 917-2-2 | Grt-IV | 40.5 | 0.07 | 20.2 | 27.2 | 4.59 | 1.46 | 5.11 | 99.1 | 3.22 | - | 1.89 | - | 1.81 | 0.31 | 0.17 | 0.43 | 15.3 | - | 6.09 | 10.9 | 63.7 |
| 917-2-3 | Grt-IV | 39.6 | 0.07 | 20.5 | 27.6 | 4.51 | 1.46 | 5.34 | 99.1 | 3.16 | - | 1.93 | - | 1.84 | 0.30 | 0.17 | 0.46 | 15.7 | - | 6.00 | 10.5 | 63.7 |
| 917-2-4 | Grt-IV | 39.8 | 0.08 | 20.3 | 26.7 | 5.22 | 1.34 | 5.61 | 99.1 | 3.18 | - | 1.91 | - | 1.78 | 0.35 | 0.16 | 0.48 | 16.6 | - | 5.56 | 12.3 | 62.2 |
| 917-2-5 | Grt-IV | 38.7 | 0.08 | 20.5 | 25.9 | 6.94 | 1.13 | 5.80 | 99.1 | 3.11 | - | 1.94 | - | 1.74 | 0.47 | 0.14 | 0.50 | 17.1 | - | 4.65 | 16.2 | 59.8 |
| 917-2-7 | Grt-IV | 38.0 | 0.10 | 20.8 | 25.9 | 7.10 | 1.12 | 5.90 | 98.9 | 3.07 | 0.01 | 1.98 | - | 1.75 | 0.49 | 0.13 | 0.51 | 17.1 | - | 4.54 | 16.3 | 58.9 |
| 917-2-8 | Grt-IV | 38.0 | 0.09 | 21.0 | 26.5 | 6.44 | 1.20 | 5.95 | 99.2 | 3.06 | 0.01 | 1.99 | - | 1.78 | 0.44 | 0.14 | 0.51 | 17.1 | - | 4.82 | 14.7 | 59.7 |
| 917-2-9 | Grt-IV | 37.5 | 0.08 | 21.1 | 26.7 | 6.47 | 1.20 | 5.96 | 99.0 | 3.03 | - | 2.01 | - | 1.81 | 0.44 | 0.14 | 0.52 | 17.1 | - | 4.79 | 14.7 | 59.8 |
* Total Fe as FeO; ** calculated from stoichiometry; *** atomic proportions based on 12 cations; **** endmembers, %.
Table 3.
Rare earth element composition of garnet (ppm).
| Sample | La | Ce | Pr | Nd | Sm | Eu | Gd | Tb | Dy | Ho | Er | Tm | Yb | Lu |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 921-13-1 | 0.04 | 0.52 | 0.21 | 3.62 | 3.86 | 0.73 | 3.49 | 0.53 | 3.96 | 0.88 | 2.91 | 0.43 | 2.91 | 0.40 |
| 921-13-2 | 0.15 | 1.11 | 0.59 | 7.80 | 2.56 | 0.83 | 1.20 | 0.12 | 0.65 | 0.15 | 0.59 | 0.08 | 0.72 | 0.11 |
| 921-13-3 | 0.16 | 0.83 | 0.51 | 8.15 | 4.63 | 1.57 | 2.67 | 0.28 | 1.43 | 0.33 | 1.07 | 0.18 | 1.61 | 0.24 |
| 921-13-4 | 0.03 | 0.61 | 0.30 | 5.19 | 2.67 | 0.78 | 1.57 | 0.21 | 1.35 | 0.23 | 0.52 | 0.14 | 0.41 | 0.05 |
| 921-13-6 | 0.01 | 0.54 | 0.27 | 4.80 | 2.31 | 0.68 | 1.60 | 0.19 | 1.12 | 0.14 | 0.31 | 0.06 | 0.25 | 0.04 |
| 921-13-7 | 0.13 | 0.72 | 0.46 | 3.84 | 0.82 | 0.68 | 0.61 | 0.07 | 0.48 | 0.05 | 0.25 | 0.06 | 0.35 | 0.04 |
| 125-5-1 | - | 0.01 | 0.01 | 0.08 | 0.31 | 0.65 | 2.05 | 0.62 | 5.86 | 1.37 | 3.96 | 0.56 | 3.97 | 0.45 |
| 125-5-2 | 0.01 | - | - | 0.10 | 0.20 | 0.09 | 0.65 | 0.20 | 1.57 | 0.31 | 1.10 | 0.17 | 1.08 | 0.12 |
| 125-5-3 | - | 0.01 | - | 0.02 | 0.24 | 0.02 | 0.65 | 0.19 | 1.66 | 0.43 | 1.02 | 0.14 | 1.12 | 0.18 |
| 125-5-4 | - | 0.03 | 0.03 | 0.33 | 0.64 | 0.71 | 3.58 | 1.05 | 10.2 | 3.01 | 9.59 | 1.50 | 10.4 | 1.59 |
| 125-5-5 | - | 0.02 | 0.02 | 0.25 | 0.56 | 0.09 | 1.06 | 0.25 | 2.06 | 0.49 | 1.26 | 0.17 | 0.87 | 0.10 |
| 125-5-6 | - | 0.01 | - | 0.08 | 0.16 | 0.07 | 0.51 | 0.11 | 1.00 | 0.22 | 0.65 | 0.08 | 0.91 | 0.11 |
| 913-6-1 | 0.25 | 2.23 | 0.80 | 5.57 | 2.92 | 0.77 | 3.24 | 0.72 | 4.89 | 0.94 | 3.18 | 0.47 | 3.17 | 0.41 |
| 913-6-2 | 0.20 | 2.09 | 0.52 | 4.21 | 2.88 | 0.41 | 3.71 | 0.76 | 4.54 | 1.05 | 3.59 | 0.49 | 3.08 | 0.38 |
| 913-6-3 | 0.17 | 2.03 | 0.68 | 5.79 | 3.35 | 0.64 | 4.25 | 0.70 | 5.02 | 0.95 | 2.83 | 0.41 | 2.54 | 0.43 |
| 913-6-6 | 0.18 | 1.93 | 0.66 | 7.16 | 4.15 | 0.84 | 5.11 | 0.74 | 5.06 | 1.06 | 2.87 | 0.45 | 3.22 | 0.55 |
| 917-2-1 | - | - | - | 0.02 | 0.33 | 0.23 | 3.77 | 2.99 | 46.8 | 14.4 | 48.0 | 7.12 | 44.7 | 6.14 |
| 917-2-2 | - | - | - | 0.02 | 0.36 | 0.29 | 4.97 | 2.48 | 32.7 | 9.04 | 31.6 | 5.02 | 33.1 | 4.56 |
| 917-2-3 | - | - | - | 0.08 | 0.13 | 0.39 | 4.20 | 2.34 | 29.8 | 7.78 | 28.6 | 4.51 | 33.5 | 4.88 |
| 917-2-4 | 0.01 | - | - | 0.07 | 0.10 | 0.21 | 3.82 | 1.63 | 21.6 | 4.89 | 14.4 | 1.83 | 11.9 | 1.33 |
| 917-2-5 | - | - | - | 0.02 | 0.23 | 0.26 | 3.92 | 2.97 | 69.4 | 31.0 | 137 | 23.7 | 175 | 25.6 |
| 917-2-7 | 0.04 | 0.08 | - | 0.07 | 0.26 | 0.16 | 3.98 | 2.91 | 61.2 | 24.3 | 108 | 21.2 | 178 | 28.3 |
| 917-2-8 | - | 0.01 | - | 0.05 | 0.30 | 0.17 | 4.48 | 3.07 | 55.2 | 16.6 | 53.5 | 7.46 | 45.6 | 6.31 |
| 917-2-9 | 0.02 | - | - | 0.37 | 0.20 | 4.62 | 3.02 | 55.3 | 16.5 | 52.2 | 6.86 | 42.4 | 5.65 | 29.2 |
Table 4.
Trace element composition of garnet (ppm).
| Sample | Type | In | Ga | Ge | Y | Sc | Sn | W |
|---|---|---|---|---|---|---|---|---|
| 921-1 | Grt-I | 13.1 | 25.3 | 3.66 | 25.7 | 3.02 | 1239 | 9.27 |
| 921-2 | Grt-I | 9.67 | 17.0 | 3.75 | 5.36 | 2.01 | 728 | 0.38 |
| 921-3 | Grt-I | 9.49 | 24.2 | 2.35 | 10.4 | 2.13 | 905 | 3.83 |
| 921-4 | Grt-I | 38.0 | 21.8 | 1.74 | 5.94 | 3.03 | 1133 | 4.15 |
| 921-5 | Grt-I | 19.5 | 20.7 | 1.59 | 3.75 | 1.93 | 698 | 8.45 |
| 921-6 | Grt-I | 16.4 | 20.1 | 2.01 | 2.49 | 1.89 | 1711 | 6.77 |
| 125-1 | Grt-II | 83.1 | 25.7 | 2.34 | 43.0 | 2.56 | 4214 | 12.1 |
| 125-2 | Grt-II | 43.8 | 22.6 | 0.13 | 10.3 | 2.31 | 4599 | 63.4 |
| 125-3 | Grt-II | 44.3 | 24.0 | 1.24 | 11.9 | 2.18 | 5039 | 58.0 |
| 125-4 | Grt-II | 74.0 | 22.4 | 2.21 | 93.7 | 3.05 | 3537 | 12.6 |
| 125-5 | Grt-II | 43.8 | 22.0 | 0.72 | 13.8 | 1.95 | 4665 | 54.9 |
| 125-6 | Grt-II | 42.8 | 24.9 | 0.78 | 7.34 | 2.48 | 4779 | 48.0 |
| 913-1 | Grt-III | 8.43 | 23.1 | 2.33 | 29.5 | 12.3 | 284 | 0.70 |
| 913-2 | Grt-III | 18.4 | 23.1 | 1.65 | 29.7 | 13.3 | 928 | 1.76 |
| 913-3 | Grt-III | 17.9 | 24.4 | 4.54 | 29.0 | 14.0 | 812 | 1.55 |
| 913-4 | Grt-III | 17.4 | 28.2 | 6.79 | 29.8 | 12.0 | 896 | 1.37 |
| 917-1 | Grt-IV | 0.02 | 7.19 | 38.8 | 424 | 164 | 1.19 | 0.03 |
| 917-2 | Grt-IV | - | 7.80 | 30.9 | 277 | 147 | 0.74 | 0.05 |
| 917-3 | Grt-IV | 0.02 | 7.03 | 22.1 | 237 | 124 | 1.40 | - |
| 917-4 | Grt-IV | 0.02 | 6.70 | 31.2 | 162 | 102 | 1.07 | 0.02 |
| 917-5 | Grt-IV | 0.01 | 7.25 | 49.1 | 970 | 183 | 0.96 | 0.06 |
| 917-6 | Grt-IV | 0.03 | 6.74 | 47.5 | 834 | 190 | 0.90 | 0.04 |
| 917-7 | Grt-IV | - | 7.29 | 44.1 | 521 | 167 | 0.59 | 0.05 |
Table 5.
The age of mineralization and the intrusion emplacement of Dulong, Gejiu, and Bainiuchang deposit in the Yunnan province.
Table 5.
The age of mineralization and the intrusion emplacement of Dulong, Gejiu, and Bainiuchang deposit in the Yunnan province.
| Mineral | Method | Age | MSWD * | Reference |
|---|---|---|---|---|
| Cassiterite | LA-MC-ICP-MS U-Pb | 96.6 ± 3.5 Ma | 8.1 | [27] |
| 93.6 ± 1.6 Ma | 5.8 | |||
| 82.0 ± 2.5 Ma | 11 | |||
| TIMS U-Pb | 79.8 ± 3.2 Ma | 3.2 | [28] | |
| LA-ICP-MS U-Pb | 88.5 ± 2.1 Ma | 1.0 | [10] | |
| 82.1 ± 6.3 Ma | 1.6 | |||
| Zircon | SHRIMP U-Pb | 92.9 ± 1.9 Ma | 0.7 | [28] |
| 86.9 ± 1.4 Ma | 3.7 | |||
| Molybdenite | Re-Os | 83.4 ± 2.1 Ma | - | [29] |
| Garnet | LA-ICP-MS U-Pb | 81.8 ± 1.1 Ma | 2.0 | [16] |
| 81.8 ± 1.8 Ma | 1.6 | |||
| 80.4 ± 2.0 Ma | 1.2 | |||
| Cassiterite | LA-ICP-MS U-Pb | 80.2 ± 0.2 Ma | 1.0 | |
| 79.7 ± 0.6 Ma | 1.2 | |||
| Cassiterite | LA-ICP-MS U-Pb | 85.8 ± 0.5 Ma | 1.5 | [30] |
| Zircon | LA-ICP-MS U-Pb | 85.3 ± 0.4 Ma | 1.7 | [30] |
| 84.7 ± 0.5 Ma | 2.4 |
*: The mean square of weighted deviates (MSWD) quantifies the degree to which the scatter of isotopic data points deviates from that expected for the best-fit line or Concordia curve.
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Liu, T.; Jiang, S.-Y.; Li, D.-F.; Xiong, S.-F.; Wang, W.; Xiao, S. Geochemical Characteristics and Genetic Significance of Garnet in the Dulong Sn-Polymetallic Deposit, Yunnan Province, Southwestern China. Minerals 2025, 15, 911. https://doi.org/10.3390/min15090911
AMA Style
Liu T, Jiang S-Y, Li D-F, Xiong S-F, Wang W, Xiao S. Geochemical Characteristics and Genetic Significance of Garnet in the Dulong Sn-Polymetallic Deposit, Yunnan Province, Southwestern China. Minerals. 2025; 15(9):911. https://doi.org/10.3390/min15090911
Chicago/Turabian StyleLiu, Tong, Shao-Yong Jiang, Dong-Fang Li, Suo-Fei Xiong, Wei Wang, and Shugang Xiao. 2025. "Geochemical Characteristics and Genetic Significance of Garnet in the Dulong Sn-Polymetallic Deposit, Yunnan Province, Southwestern China" Minerals 15, no. 9: 911. https://doi.org/10.3390/min15090911
APA StyleLiu, T., Jiang, S.-Y., Li, D.-F., Xiong, S.-F., Wang, W., & Xiao, S. (2025). Geochemical Characteristics and Genetic Significance of Garnet in the Dulong Sn-Polymetallic Deposit, Yunnan Province, Southwestern China. Minerals, 15(9), 911. https://doi.org/10.3390/min15090911
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