Zircon as a Monitoring Tool for the Magmatic–Hydrothermal Process in the Granitic Bedrock of Shitouping Ion-Adsorption Heavy Rare Earth Element Deposit, South China

: The Shitouping pluton in Jiangxi Province, southern China, hosts an ion-adsorption heavy rare earth element (HREE) deposit identiﬁed by a recent geological survey. This study reveals the HREE pre-enrichment mechanism during the magmatic–hydrothermal process of granitic bedrock based on the comprehensive study of zircon structure and composition. Zircon from the Shitouping pluton, composed of syenogranite and monzogranite, can be categorized into three types based on structure and compositions. The Type-1 zircons, the predominate type in monzogranite, are early magmatic zircons with prismatic crystals and bright oscillatory zoning in CL images. In contrast, the late magmatic-hydrothermal zircons (Type-2 and Type-3) mainly occur in the syenogranite. The Type-2 zircons occur as dark CL images and euhedral crystals crystallized during the late magmatic stage. The Type-3 zircons with irregular zoning and abundant mineral inclusions in BSE images are possibly formed via intense hydrothermal alteration during the hydrothermal stage. The increase in Y/Ho ratios from Type-1 to Type-3 zircon indicates that the Shitouping syenogranites underwent magmatic to hydrothermal evolution. Compared with Type-1 and Type-2 zircons, Type-3 zircons exhibit the highest concentrations of F and HREEs. The signiﬁcant increase in HREE concentrations both in zircons and bulk-rock composition of syenogranite can be attributed to the introduction of HREE-rich ﬂuids during magma evolution. Therefore, we propose that the increase in HREE contents in zircon reﬂect the exsolution of HREE-rich ﬂuids during a late stage in the magma evolution, which is an important factor controlling HREE enrichment in Shitouping syenogranites and furthermore in the generation of ion-adsorption HREE deposits.


Introduction
Rare earth elements (REE) are indispensable strategic resources in high-technology industries, such as green energy, semiconductor materials and medicine [1].It is essential to clarify the genesis of heavy REE (HREEs: Gd-Lu + Y) deposits due to their low crustal abundance compared with light REEs (LREEs: La-Eu) [2].Ion-adsorption HREE deposits are characterized by HREEs/LREE ratios greater than 1 and high HREE contents in the weathering crusts of the granites [3,4].Such deposits in South China and adjacent areas provide almost all of the HREE resources in the world [5].Recent studies have shown that these granitic parent rocks are already enriched in HREEs during their petrogenesis [6][7][8][9][10][11][12][13].It is traditionally accepted that the bedrocks of ion-adsorption HREE deposits should be the HREE-type (HREEs/LREEs > 1) granite [6][7][8], because the supergene process is not enough

Geological Background
The Shitouping deposit is located in the eastern part of the Nanling tectono-magmatic zone of South China (Figure 1a), which is also a major W-Sn-REE-Nb-Ta metallogenic region [4].The metallogenic mineralization is spatially associated with large volumes of Yanshanian (late Middle Jurassic-Late Cretaceous) granitic rocks.More than 150 ionadsorption REE deposits have been discovered in this tectono-magmatic zone [9], and almost all HREE deposits, such as the Zudong and Gucheng deposits [1,11], are hosted in weathering crusts of Yanshanian granitic rocks (Figure 1a).
The Shitouping pluton is located in the southern part of Jiangxi Province and covers an area of about 200 km 2 (Figure 1b).These granites intruded on the Late Neoproterozoic metamorphic sedimentary rocks, Ordovician weakly deformed biotite granodiorite [35], and the earliest Cretaceous (145~143 Ma) silica volcanic rocks [36,37].This pluton is mainly composed of medium-to coarse-grained biotite monzogranites and syenogranites with limited volume of fine-grained granite occurring as dykes or stocks (Figure 1b).The biotite monzogranites mainly consist of plagioclase, K-feldspar, quartz, biotite and minor Fe-Ti oxide mainly enclosed by biotite.Plagioclase (oligoclase) has calcium-rich cores and fresh sodium-rich rims and tends to form clusters.The REE-bearing accessory minerals include zircon, apatite, and monazite as well as a small amount of bastnäsite and synchysite-(Ce) associated with sericite.On the contrary, the syenogranites have lower proportions of plagioclase (albite), biotite, Fe-Ti oxide, apatite, and monazite, but higher proportions of hydrothermal HREE-and Nb-bearing minerals closely associated with fluorite [10].They Minerals 2023, 13,1402 3 of 13 are co-genetic with monzogranites showing identical Nd-Hf isotope compositions [10], and should be more evolved units characterized by stronger Ba, Sr, P, Ti, and Eu negative anomalies (Figure 2).Both of the two granites are LREE-type granites and the syenogranites containing abundant hydrothermal HREE-fluorocarbonates and higher total HREE contents can be assumed to be the main bedrock of the large-scale Shitouping ion-adsorption HREE deposits [10].
synchysite-(Ce) associated with sericite.On the contrary, the syenogranites hav proportions of plagioclase (albite), biotite, Fe-Ti oxide, apatite, and monazite, bu proportions of hydrothermal HREE-and Nb-bearing minerals closely associat fluorite [10].They are co-genetic with monzogranites showing identical Nd-Hf compositions [10], and should be more evolved units characterized by stronger B Ti, and Eu negative anomalies (Figure 2).Both of the two granites are LREE-type and the syenogranites containing abundant hydrothermal HREE-fluorocarbona higher total HREE contents can be assumed to be the main bedrock of the lar Shitouping ion-adsorption HREE deposits [10].synchysite-(Ce) associated with sericite.On the contrary, the syenogranites have lower proportions of plagioclase (albite), biotite, Fe-Ti oxide, apatite, and monazite, but higher proportions of hydrothermal HREE-and Nb-bearing minerals closely associated with fluorite [10].They are co-genetic with monzogranites showing identical Nd-Hf isotope compositions [10], and should be more evolved units characterized by stronger Ba, Sr, P, Ti, and Eu negative anomalies (Figure 2).Both of the two granites are LREE-type granites and the syenogranites containing abundant hydrothermal HREE-fluorocarbonates and higher total HREE contents can be assumed to be the main bedrock of the large-scale Shitouping ion-adsorption HREE deposits [10].

Analytical Methods
Three samples of syenogranites and one sample of monzogranites were collected for examining zircon internal structure and geochemical analysis, and the detailed sample location is in Figure 1b.The crystals in polished section were documented with reflected light photomicrographs as well as with backscattered electron (BSE) and cathodoluminescence (CL) images to reveal their textures.The CL images were obtained using a Tescan MIRA3 LM instrument equipped with a CL detector at the Nanjing Hongchuang Geological Exploration Technology Service Co., Ltd.(NHEXTS), Nanjing, China.
The major element compositions of zircon were determined using NHEXTS with a JEOL JXA-iSP100 Electron Probe Microanalyzer (EPMA).The accelerating voltage, beam current and diameter were 15 kV, 20 nA, and 2~5 µm, respectively.The peak counting time was 10 s for F; 20 s for Si and Zr; 40 s for Fe, P, Ca, and Al; and 60 s for Ti, U, Y, Yb, Hf, and Th, respectively.The background counting time was half of the peak on the high and low background positions.Standards used for data correction were diopside for Si, Ca and Mg, cubic zirconia for Zr, albite for Al, garnet for Y, apatite for P, uranium for U, thorium for Th, titanium oxide for Ti, hafnium for Hf, ytterbium of Yb, hematite for Fe, and rhodonite for Mn.All the data were corrected using the ZAF (atomic number, absorption and fluorescent excitation) correction method [38] for the matrix effect.The accelerating voltage, beam current, pixel interval, and dwell time of EPMA mapping of zircon were 15 kV, 50 nA, 0.5 µm, and 50 ms, respectively.
Zircon trace element analyses were undertaken at the State Key Laboratory of Nuclear Resources and Environment, East China Institute of Technology, China, using the Agilent 7900 ICP-MS connected to a GeoLasHD laser ablation system (λ = 193 nm).All analyses were carried out with a beam diameter of 32 µm and a repetition rate of 5 Hz with an energy of 90 mJ.NIST SRM 610 and NIST SRM 612 glass [39] were used as external standards.

Zircon Morphology and Structure
Zircon in the Shitouping granites can be classified into three types (i.e., Type-1, Type-2, and Type-3) based on morphology and textures.Type-1 zircon grains showing euhedral prismatic crystals are commonly intergrown with magnetite and enclosed in biotite (Figure 3a).They show needle apatite inclusion in transmitted-light microscopic images and a chemically homogeneous interior in BSE images as well as well-developed multiple oscillatory growth zones in CL images (Figure 3d).
Type-2 zircon grains are commonly enclosed with biotite.They are euhedral or subhedral crystals with slightly dusty appearance (Figure 3b), and are without oscillatory growth zones in CL images (Figure 3e).Some zircon grains show irregular zoning in BSE images with cusped edges and a cataclastic texture (Figure 3g).They contain mineral inclusions that are closely associated with hydrothermal Nb-and REE-bearing minerals (Figures 3h,i and 4).
Type-3 zircon grains are mainly intergrown with magnetite (Figure 3c), and they display patchy, cloudy, or very irregular zoning in CL images (Figure 3f,g).They usually coexist with hydrothermal minerals (Figure 3g), and are heterogeneous with randomly distributed pores as well as thorite, xenotime, and irregular Fe, Nb-bearing mineral inclusions under BSE.
Overall, the monzogranite sample No. HC-17 only contains Type-1 zircon grains, whereas the other three samples from syenogranites encompass all three types of zircon.

Zircon Compositions
Major and trace element compositions of the zircon samples are listed in Supplementary Tables S1 and S2, respectively.The three zircon types show distinct major and trace elements compositions.Type-1 zircon grains contain the highest SiO 2 (33.32

Genesis of the Zircons
Zircon showing variable textures and compositions could demonstrate the geophysical-geochemical evolution of the parental magma, and altered zircon would retain the

Genesis of the Zircons
Zircon showing variable textures and compositions could demonstrate the geophysicalgeochemical evolution of the parental magma, and altered zircon would retain the chemical compositions of the volatile-rich fluids exsolved from highly fractionated granite [41][42][43][44][45][46][47].In this study, all of the three types of zircon grains are closely associated with early crystalline minerals, and the chemical compositions of zircon could reveal the magmatic characteristics during its crystallization.
Type-1 zircons are mainly found in less evolved monzogranite.The observed magmatic textures, characterized by the presence of needle apatite inclusions and well-developed oscillatory zoning, suggest that these zircons crystallized from a primary cal-alkaline magma [41].Additionally, they exhibit consistently high SiO 2 and ZrO 2 contents, elevated ZrO 2 /HfO 2 ratios, and significantly high EPMA analytical total contents (Figure 6a,b; Table S1), implying they crystallized from a volatile-undersaturated magma [21].Therefore, the Type-1 zircon grains should be the primary magmatic zircon crystallized during the early magmatic stage.Type-2 zircon grains are predominantly found in the highly evolved syenogranite.They exhibit a dark appearance without oscillatory growth zones in CL images and contain thorite, coffinite, and minor HREE-bearing mineral inclusions, which appear as white spots in BSE images (Figures 3h and 4).This is clearly distinct from Type-1 zircon grains that contain needle-shaped apatite inclusions.Some Type-2 zircons occur as intergrowths within Type-1 zircons and display a dark core with a bright rim in CL images (Figure 3e), suggesting that Type-2 zircon likely originated from the hydrothermal alteration of the Type-1 zircon.Furthermore, some Type-2 zircon grains are observed as intergrowths with secondary minerals, such as thorite and xenotime, which typically crystallized in the late stage of magmatic evolution in most cases (Figure 3h).These zircon grains containing relatively low analytical totals (Figure 6a) were generally considered as the result of radiation damage [19, 21,22], which is also consistent with higher U and Th contents compared with Type-1 zircon grains.Zircons characterized by high U-Th contents and coexistence with late-stage crystalline accessory minerals imply they are crystallized from residual melt in the late magmatic stage [21,25].In some cases, cataclastic structure and amorphous domains at the edges of zircons can be observed due to exsolution of hydrothermal fluids, leading to irregular zoning patterns BSE images (Figure 3g) [18].Moreover, Type-2 zircon grains contain higher incompatible elemental (e.g., Nb and Ta) contents than Type-1 zircon (Figure 7a), which is also associated with late fluid influence.Therefore, it can be inferred that Type-2 zircon grains should have undergone crystallization from a residual melt with an enriched volatile composition during the later magmatic stage.Type-3 zircon grains are closely associated with Type-2 zircon grains occurring in the syenogranites.They exhibit irregular zoning in BSE images and contain mineral inclusions similar to those found in the Type-2 zircon grains.However, the presence of abundant randomly distributed pores, mineral inclusions, and irregular zoning patterns (Figure 3f,g) within the Type-3 zircon grains imply that they underwent intense hydrothermal Type-3 zircon grains are closely associated with Type-2 zircon grains occurring in the syenogranites.They exhibit irregular zoning in BSE images and contain mineral inclusions similar to those found in the Type-2 zircon grains.However, the presence of abundant randomly distributed pores, mineral inclusions, and irregular zoning patterns (Figure 3f,g) within the Type-3 zircon grains imply that they underwent intense hydrothermal alteration [30,31] and formed via a dissolution-reprecipitation process [42][43][44].The coexistent relationship of Type-3 zircon grains with other hydrothermal minerals (such as synchysite-(Y) and fluorite) further supports their hydrothermal origin (Figure 3g).Meanwhile, Type-3 zircon samples exhibits lowest analytical totals and the lowest SiO 2 and ZrO 2 contents (Table S2), which can be attributed to the presence of volatiles and H 2 O within the zircon domains [43].Furthermore, compared with other zircon grains, Type-3 zircon grains exhibit highest concentrations of total non-formula cations (Table S1) as well as non-quadrivalent charged cations (Figure 6d), such as Al 3+ , Ca 2+ , and Mg 2+ , implying that these zircon grains were also generated by a diffusion-reaction process [19,29].The evolutionary trend line between HREE (Y and Yb) and P of Type-3 zircon grains exhibits a distinct deviation from the coupled xenotime-type substitution trending line (Figure 6c), implying a more complex charge-balance mechanism or multiple mechanisms in hydrothermal fluids [29].In addition, the logarithm of REE distribution coefficient between minerals and melts (Table S3) exhibits a simple parabolic relationship with the ion radius, which is considered as the crystal structure strain model [49].Most REEs of Type-1 and Type-2 zircon grains Minerals 2023, 13, 1402 9 of 13 fall on the parabola, except for Ce and La (Figure 8a,b), which are largely affected by their valences and detection error.On the contrary, the Type-3 zircon grains have more elements (La, Ce, Pr, Nd) sensibly deviating from the simulated parabolic behavior (Figure 8c), which can also serve as the result of the interaction between zircon and hydrothermal fluids.Therefore, it can be inferred that Type-3 zircon grains should generated by the intense hydrothermal alteration of magmatic zircon in a volatile oversaturated environment.
that these zircon grains were also generated by a diffusion-reaction process [19,29].The evolutionary trend line between HREE (Y and Yb) and P of Type-3 zircon grains exhibits a distinct deviation from the coupled xenotime-type substitution trending line (Figure 6c), implying a more complex charge-balance mechanism or multiple mechanisms in hydrothermal fluids [29].In addition, the logarithm of REE distribution coefficient between minerals and melts (Table S3) exhibits a simple parabolic relationship with the ion radius, which is considered as the crystal structure strain model [49].Most REEs of Type-1 and Type-2 zircon grains fall on the parabola, except for Ce and La (Figure 8a,b), which are largely affected by their valences and detection error.On the contrary, the Type-3 zircon grains have more elements (La, Ce, Pr, Nd) sensibly deviating from the simulated parabolic behavior (Figure 8c), which can also serve as the result of the interaction between zircon and hydrothermal fluids.Therefore, it can be inferred that Type-3 zircon grains should generated by the intense hydrothermal alteration of magmatic zircon in a volatile oversaturated environment.
Figure 8.The simulated parabolic behavior between zircon-melt trace element partition coefficients and ionic radius [49].Data are taken from the average values of Type-1 zircon to whole-rock compositions of monzogranite as well as Type-2 and Type-3 zircon to whole-rock compositions of syenogranite, respectively (Table S3).

Monitor the Magmatic Process
Magmatic-hydrothermal evolution processes are ubiquitous in granitic bedrock of the ion-adsorption HREE deposits in South China [6][7][8][9][10][11][12][13].Fractionation of early crystalline LREE-rich minerals such as apatite and monazite could result in the relative enrichment of HREE in the residual melt with higher HREEs/LREEs ratios.Our previous study showed that the syenogranites should be the higher evolved granite characterized by lower proportions of accessory minerals, as well as lower Zr/Hf, Nb/Ta, and K/Rb ratios, compared with monzogranites [10].This magmatic evolution process could also be traced by zircon.The monzogranites mainly contain well-developed oscillatory primary magmatic zircons representing an early-crystallized phase from less evolved magmatism.On the contrary, the syenogranites contain almost all late magmatic-hydrothermal zircons.Type-2 zircon grains containing relatively higher HfO2 content compared with Type-1 zircon grains suggests that they are late-crystallized zircon during magmatic evolution (Figure 6b) [50,51].Volatiles will increase in the residual melt and become oversaturated in the hydrothermal fluids during the fractionation of granitic magma.The significant Figure 8.The simulated parabolic behavior between zircon-melt trace element partition coefficients and ionic radius [49].Data are taken from the average values of Type-1 zircon to whole-rock compositions of monzogranite as well as Type-2 and Type-3 zircon to whole-rock compositions of syenogranite, respectively (Table S3).

Monitor the Magmatic Process
Magmatic-hydrothermal evolution processes are ubiquitous in granitic bedrock of the ion-adsorption HREE deposits in South China [6][7][8][9][10][11][12][13].Fractionation of early crystalline LREE-rich minerals such as apatite and monazite could result in the relative enrichment of HREE in the residual melt with higher HREEs/LREEs ratios.Our previous study showed that the syenogranites should be the higher evolved granite characterized by lower proportions of accessory minerals, as well as lower Zr/Hf, Nb/Ta, and K/Rb ratios, compared with monzogranites [10].This magmatic evolution process could also be traced by zircon.The monzogranites mainly contain well-developed oscillatory primary magmatic zircons representing an early-crystallized phase from less evolved magmatism.On the contrary, the syenogranites contain almost all late magmatic-hydrothermal zircons.Type-2 zircon grains containing relatively higher HfO 2 content compared with Type-1 zircon grains suggests that they are late-crystallized zircon during magmatic evolution (Figure 6b) [50,51].Volatiles will increase in the residual melt and become oversaturated in the hydrothermal fluids during the fractionation of granitic magma.The significant deficits of the analysis totals for Type-2 and Type-3 zircon grains (Figure 6a) can be attributed to volatile substitution [13,19], which is closely correlated with the magmatic to hydrothermal transition processes.Therefore, abundant hydrothermal Type-3 zircons with highest concentrations of total non-formula cations imply that syenogranites should be the evolved phase, having undergone intense fluid metasomatism during the magmatic-hydrothermal process [19,21].In conclusion, the variable compositions from early magmatic to late hydrothermal metamict zircon in the Shitouping granites could reveal the magmatic evolution processes of this intrusion.

Fluids Metasomatism Recorded by the Zircon
Previous studies have shown that hydrothermal zircon compositions would retain the variable geochemical characteristics of exsolution fluid during the magmatic-hydrothermal transition [23][24][25][26][27][28][29].The syenogranites contain Type-3 zircon grains generated from a volatile oversaturated environment suggesting that syenogranites underwent intense fluid metasomatism.The relatively high F content (0.71-1.16 wt%) in Type-3 zircon grains indicates a significantly elevated F concentration in the exsolution fluid from the highly evolved granitic system.The presence of this phenomenon also serves as evidence of the paragenetic relationship between zircon and fluorite (Figure 4).Fluorine can prolong magma fractional crystallization by reducing magma viscosity, forming fluoride complexes with incompatible elements (e.g., REE, U, Hf, Nb, Ta) that trigger the deposition of hydrothermal minerals during the late stages of magmatic evolution [52,53].This is also consistent with the bulk-rock geochemistry and mineral assemblages of abundant Nb-bearing minerals and hydrothermal HREE-fluorocarbonates closely associated with fluorite in syenogranites [10].The relative higher Y/Ho ratio in Type-3 zircon grains (Figure 7b) is also considered as the evidence of F-rich fluids metasomatism in most cases [22].Moreover, the late magmatic fluids exhibit enrichment in HREEs, but are not in a state of saturation, as evidenced by the hydrothermal HREE-bearing minerals presented as the rim of Type-2 zircon identified by EPMA mapping (Figure 4).The positive correlation observed between Y/Ho ratios and HREE concentrations (Figure 7b) from early to late zircon grains suggest that postmagmatic fluids were gradually enriched in HREEs during the magma differentiation.This is consistent with the hydrothermal xenotime occurring as the rims of thorite and magmatic xenotime (Figure 3h).The highest HREE contents with detectable Yb 2 O 3 in Type-3 zircon grains and the paragenetic relationship between Type-3 zircon and synchysite-(Y) (Figure 3g) reveal that the exsolution of fluids enriched in HREEs plays a crucial role in promoting hydrothermal precipitation of HREE minerals.Previous studies have demonstrated that fluoride can be considered as an "adhesive" that promote REE-minerals deposition due to their strong complexation ability with REE ions [54][55][56].Thus, we argue that the exsolution of HREE-and F-rich fluids during the magmatic-hydrothermal transition stage is the critical reason driving the migration and precipitation of HREEs and further HREEs mineralization in the Shitouping deposit.

Implication for HREE Mineralization in South China
The outcropping of a large number of granitic intrusions in South China can be attributed to the late Mesozoic subduction and retreat of the paleo-Pacific plate [6][7][8][9][10][11][12][13].It should be noted that only a small proportion of Yanshanian granites develop HREE deposits in their weathering crusts, and granitic bedrocks of ion-adsorption HREE deposits were formed over a wide range of time periods, including the Late Jurassic formation of Dabu Granite [13], emplacement of the Shitouping pluton in the Early Cretaceous [10], and crystallization of Gucheng Granite in the late stage of Early Cretaceous [11].Meanwhile, the highly evolved granite associated with W-Sn-Li polymetallic mineralization in the Nanling region was also predominantly concentrated during the Late Yanshanian [57].The Mikengshan Granite, located east of this investigated Shitouping pluton, exhibiting identical age and bulk-rock isotope compositions, is closely associated with Sn mineralization rather than REE mineralization [37].The coexistence of polymetallic deposits with REE deposits suggests that the occurrence of REE mineralization is primarily independent of regional geological background and geodynamic processes.On the contrary, these bedrocks of ion-adsorption HREE deposits that experienced intense HREE-and F-rich fluid metasomatism are the primary factors contributing to the pre-enrichment of HREE [11,13].The accessory minerals that crystallized during the initial magmatic stage can provide compelling evidence for unveiling hydrothermal fluid metasomatism and subsequent HREE mineralization in granites.

Conclusions
Our study shows that zircons from the Shitouping monzogranites and syenogranites can be classified into three types based on textures and compositions.Type-1 zircon grains crystallized early in the granitic magma are well-developed oscillatory primary magmatic zircons, while Type-2 zircon grains are subhedral crystals crystallized from the residual melt.Anhedral Type-3 zircon grains showing distinctive amorphous textures with pores and numerous hydrothermal minerals should be the product of fluid metasomatism in a volatile oversaturated environment.The increasing of Y/Ho ratios from Type-1 to Type-3 zircon indicates that Shitouping granites underwent magmatic to hydrothermal evolutions.Syenogranites contain abundant hydrothermal Type-2 and Type-3 zircons compared with monzogranites indicating that they are a more evolved phase that underwent intense fluid metasomatism during the magmatic-hydrothermal process.Moreover, Type-3 zircon grains containing highest HREE contents reflect the exsolution of HREE-rich fluids during the magma evolution, which is an important factor controlling HREE enrichment in Shitouping syenogranites and further generation of ion-adsorption HREE deposits.

Supplementary Materials:
The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/min13111402/s1,Table S1: EPMA results of zircon from Shitouping granites.Table S2: LA-ICP-MS trace element results of zircon from Shitouping granites.Table S3: Trace element partition coefficients of the three types of zircon to host melt (whole-rock composition) and the ionic radii.

Figure 1 .
Figure 1.Simplified geological map of Yanshanian granites and volcanism in South Chin distribution of ion-adsorption REE deposits (a) [9] and the main type granites of Shitoupin as well as sample location in this study (b) JX: Jiangxi Province; FJ: Fujian Province; HN Province; GD: Guangdong Province; GX: Guangxi Province.

Figure 2 .
Figure 2. Primitive mantle (PM)-normalized trace element diagrams (a) and chondrite-no REE patterns (b) of whole rock compositions for different granites of the Shitouping pluto

Figure 1 .
Figure 1.Simplified geological map of Yanshanian granites and volcanism in South China and the distribution of ion-adsorption REE deposits (a) [9] and the main type granites of Shitouping pluton as well as sample location in this study (b) JX: Jiangxi Province; FJ: Fujian Province; HN: Hunan Province; GD: Guangdong Province; GX: Guangxi Province.

Figure 1 .
Figure 1.Simplified geological map of Yanshanian granites and volcanism in South China and the distribution of ion-adsorption REE deposits (a) [9] and the main type granites of Shitouping pluton as well as sample location in this study (b) JX: Jiangxi Province; FJ: Fujian Province; HN: Hunan Province; GD: Guangdong Province; GX: Guangxi Province.

Figure 4 .
Figure 4. Transmitted-light photomicrograph, BSE, and CL images, and EPMA mappings revealing the distribution of major element of Type-2 zircon.Fl: Fluorite.

Author
Contributions: L.G.: writing-original draft preparation, data curation and funding acquisition; X.W.: writing-review and editing; D.Z.: experimental testing; W.Z.: sampling; M.C.: writing-review, editing and software.All authors have read and agreed to the published version of the manuscript.Funding: This research was funded by the Geological Exploration Project of Jiangxi province Finance (No. 20220014) and Science and Technology Innovation Project of Department of Natural Resources of Jiangxi province (No.ZRKJ20232526).