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Paleoproterozoic U Mineralization in Huayangchuan Deposit, Xiaoqinling Area: Evidence From the U-Rich Granitic Pegmatite

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12 June 2023

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Abstract
The Huayangchuan uranium deposit, located in the west of the Xiaoqinling belt on the southern margin of the North China Craton, is a polymetallic deposit dominated by U, Nb, Pb, and rare earth elements. The Huayangchuan uranium deposit, discovered in the 1950s, has long been known as a carbonatite-type uranium deposit. Recently, new geological work has found uranium mineralisation in many granitic pegmatite veins in the Huayangchuan deposit and adjacent areas. Here, we report a systematic investigation of the petrography, whole-rock geochemistry, zircon U-Pb ages, and in situ Lu-Hf isotopic characteristics of newly discovered U-rich granitic pegmatite veins in the west of Huayangchuan deposit. The petrological results showed that the lithology of the samples is equivalent to that of granite. The U-Pb ages of zircon were 1826.3 ± 7.9 and 1829 ± 11 Ma. Microscopically, the symbiotic characteristics of zircon, betafite, and uraninite exist in the intergranular fissures of K-feldspar and quartz, reflecting metallogenic phenomena in the rock formation process. Almost all whole-rock samples were rich in SiO2 (64.37–70.69 wt.%), total alkalis (K2O+Na2O = 8.50–10.30 wt.%), and Al2O3 (12.20–14.41 wt.%), but poor in Ti2O (0.23–0.73 wt.%), MgO (0.38–0.90 wt.%), P2O5 (0.14–0.83 wt.%), MnO (0.04–0.57 wt.%). Additionally, they showed enrichment of LILEs (such as Rb, Ba, Th, U, and K), depletion of HFSEs (such as Ta, Nb, P, Ti, and Hf), no alkaline dark minerals, and the characteristics are typical of intraplate A1-type granite. The A1-type granite displayed low zircon εHf(t) values (-19.42– -15.02) with zircon two-stage Hf model aged 3.10–2.76 Ga, indicating that the U-rich granitic pegmatite was derived predominantly from partial melting of the ancient continental crust (such as the early Taihua group formed in Archean-Neoarchean). Combined with the above results and regional geological data, the U-rich granitic pegmatite discovered in the Huayangchuan deposit was related to granite magma activity that formed in a post-collisional regime after the Luliang movement in the late Palaeoproterozoic. This study suggests that future uranium prospecting work in this area should focus on late Palaeoproterozoic U-rich granitic pegmatites.
Keywords: 
Southern Margin of North China Craton
;  
Xiaoqinling
;  
Huayangchuan
;  
Uranium
;  
Pegmatite
;  
Paleoproterozoic
;  
Mineralization age
Subject: 
Environmental and Earth Sciences  -   Geochemistry and Petrology

1. Introduction

The Huayangchuan U deposit in the Qinling Orogenic Belt (Central China; QLOB) was discovered during the 1950s. In the last decade, the Huayangchuan deposit has been recognised as a giant carbonate-hosted U-polymetallic deposit characterised by dominant U with abundant Nb, rare earth elements (REE), and Pb resources [1,2,3]. Since its discovery, it has been famous worldwide for the rare presence of carbonatite-related U–Nb–REE mineralisation [4,5,6]. Many studies have been published on carbonatites in Huayangchuan, including their chronology, petrography, and geochemistry, all of which point to an igneous origin of carbonatites in QLOB in the evolutionary background of the Late Triassic [7,8,9,10,11,12,13]. Apart from Huayangchuan, the district also contains other large deposits, such as the Xigou carbonatite-related Mo deposit and Huanglongpu carbonatite-related Mo–Pb(-Re) deposit. Regionally, these typical deposits are part of the Triassic carbonatite metallogenic belt of North Qinling.
Recently, new geological work has discovered U mineralisation in many granitic pegmatite veins in the Huayangchuan deposit and in adjacent peripheral areas. The U and Nb contents of some of the granitic pegmatite veins reached industrial grade. Field observations and laboratory research have shown that the metallogenic characteristics of U-rich granitic pegmatite veins are different from those of U-rich carbonate veins in the Huayangchuan deposit area. However, studies on the chronology, petrography, and geochemistry of U-rich granitic pegmatite veins are scarce and only a few have been conducted. In this study, we present an investigation of the petrography, whole-rock geochemistry, zircon U–Pb ages, and in situ Lu–Hf isotopic data for the U-rich granitic pegmatite veins in the Huayangchuan deposit. Integrating our new results for U-rich granitic pegmatites, we discuss the industrial minerals, diagenetic and metallogenic epoch, petrogenesis, and tectonic setting. The study of U-rich granitic pegmatites indicates that late Palaeoproterozoic U-mineralisation occurred in the Huayangchuan deposit, which can provide a new target for U-prospecting in this area and should attract our attention.

2. Regional and Deposit Geology

The Qinling Orogenic Belt (QLOB), an important tectonic unit in central China (Figure 1a), has undergone a prolonged and complex tectonic evolution [14]. The Huayangchuan deposit is located in Shaanxi Province, central China, and geologically located in west of the Xiaoqinling tectonic belt on the southern margin of the North China Craton (Figure 1a,b). The Xiaoqinling tectonic belt is a metamorphic core complex (Figure 1c), and its exposure range is limited by a series of deep and large boundary fault zones [15]. Various magmatic rocks and veins of different ages intrude into the metamorphic core complex, making the uranium deposit in this area with complex genesis by “ancient basement, deep fault, and magmatism”.
According to the metallogenic characteristics of uranium in the area, the geological bodies closely related to uranium mineralisation mainly include the Taihua group, Huayangchuan fault zone, and Laoniushan and Huashan granites. Local stratigraphic units in the Huayangchuan area comprise the Archean Taihua group, which is a high-grade metamorphosed and the main outcropping sequence. The Taihua group provided magma sources and materials for various diagenetic and metallogenic events. Major faults (e.g., Taiyao, Xiaohe, Huayangchuan, and Luonan–Luanchuan; Figure 1c) are all NE- or EW-trending, superimposed by NS-trending secondary faults and fractures. The NE-trending Huayangchuan Fault controls the major distribution of ore bodies in Huayangchuan. In Huayangchuan, the magmatic rocks mainly comprise Proterozoic granite and pegmatite, Triassic carbonatite dikes, and Jurassic-Cretaceous granitoids (Figure 2).
Numerous U-rich granitic pegmatite veins have been found in the western and peripheral areas of the Huayangchuan deposit. Geological field observations showed that the U-rich granitic pegmatite intruded into the Taihua Group in a large single vein (Figure 3a,b). Its exposed width was over 1–3 m, length reached 100 m, extension direction was nearly E–W, and dip angle was approximately 50°–70°. The chloritisation and weathering of the contact zone formed by pegmatite and the surrounding rock were evident (Figure 3a,b), indicating that the contact zone was a weak area where fluids could easily act. The U and Nb contents in some granitic pegmatite veins reached high industrial grade. Extension of some U-rich granitic pegmatite veins can be observed deep underground through drilling.

3. Sample Characteristics

The studied pegmatite samples were collected from the western Huayangchuan deposit (Figure 2). Two representative U-rich granitic pegmatite samples were tested for petrography, whole-rock geochemistry, zircon U–Pb ages, and in situ Lu–Hf isotopes.

3.1. Petrographic Characteristics of Samples

The U-rich granitic pegmatites were mainly composed of quartz (approximately 15–25 wt.%), K-feldspar (approximately 50–60 wt.%), plagioclase (approximately 10–20 wt.%), and small amounts of biotite, hornblende, and accessory minerals. Its total mineral composition was approximately equivalent to that of granite. The contact boundary formed by gneissic xenoliths of the Taihua Group in the U-rich granitic pegmatites was observed under a polarising microscope (Figure 4a). The rock-forming minerals of the U-rich granitic pegmatites exhibited an evidently coarse pegmatitic texture (Figure 4b). In addition, zircon particles with good crystal forms were observed between the inter-crystalline fractures of K-feldspar and quartz (Figure 4c). Meanwhile, intrusion of quartz veinlets into the plagioclase fissure of gneiss was observed (Figure 4d), which suggests that the magmatic hydrothermalism occurred during the formation of U-rich granitic pegmatite.

3.2. Characteristics of Uranium and Zircon

Scanning electron microscopy (SEM) showed that the main uranium minerals in the U-rich granitic pegmatite were betafite and a small amount of uraninite. The symbiotic relationship between zircon and uranium minerals provides supporting evidence for the age of diagenesis and mineralisation.

3.2.1. Betafite

Betafite is mainly hosted in the intergranular fissures of rock-forming minerals in the U-rich granitic pegmatite, showing a relatively complete crystal morphology (Figure 5a,b). The aggregation of betafites was also observed in the U-rich granitic pegmatite (Figure 5c,d). In addition, the filling of quartz, K-feldspar, and other minerals can also be observed in the holes in the betafite (Figure 5d). These characteristics reveal that betafites and rock-forming minerals were formed during the diagenetic process at the same stage. Theoretically, betafite is an equiaxed octahedral crystal. However, the crystal shape of betafite in the U-rich granitic pegmatite was incomplete, and the developed fractures often extended into rocks (Figure 5a,b). These characteristics indicate that the U-rich granitic pegmatite may have been affected by tectonic stress in the later stages, which often destroyed the crystal form of the betafite.

3.2.2. Uraninite

Uraninite in U-rich granitic pegmatite is characterised by low content and fine grain size and is associated with betafite, which indicates that it is closely related to the material source and genesis. Under a scanning electron microscope, some uraninite was seen wrapped in betafite (Figure 5a), and some uraninite existed on the outer edge (Figure 5b) or internal fissure of the betafite (Figure 5c). Because the crystallisation temperature of uraninite is higher than that of betafite, the formation of uraninite wrapped in betafite may have occurred earlier than that of betafite. During the diagenesis of U-rich granitic pegmatites, uranium minerals gradually change from uraninite to betafite with a decrease in temperature. The uraninite grains that grew in the internal fissures of betafite or on the outer edge of betafite were probably formed by the recrystallisation of U from betafite.

3.2.3. Zircon

The genetic type of zircons and the symbiotic relationship between zircons and ore minerals are important bases for determining the age of diagenesis and mineralisation. Zircons with a columnar shape and intact crystal form can be observed under a scanning electron microscope (Figure 5e,f), which showed the same characteristics as zircon in the cathodoluminescence (CL) images. All these show the characteristics of magmatic zircons. Zircons occurred in the intergranular fissures of K-feldspar and were associated with uraninite (Figure 5f). The above occurrence characteristics of zircons indicate mineralisation of the U-rich granitic pegmatite during diagenesis. Therefore, the zircon age can provide supporting chronological evidence for diagenesis and mineralisation.

4. Analytical Methods

4.1. Zircon U–Pb Geochronology

Zircon crystals were separated using heavy-liquid and magnetic methods. Separated zircons were carefully handpicked under a binocular microscope. The selected high-quality zircons were further mounted in epoxy resins and finally polished to approximately half their thickness for analysis. CL images were captured at the Xi’an Center of Geological Survey, CGS (China) to investigate internal structures of analysed zircons and to select target positions for U–Pb dating and Hf isotopic analysis. Zircon U–Pb dating with a beam size of 30 μm was conducted using LA–ICP–MS at the Key Laboratory for the study of focused Magmatism and Giant ore Deposits, MLR, Xi’an Center of Geological Survey, CGS (China), using a system of a Geolas 200 M equipped with a 193 nm ArFexcimer laser. Zircon 91500, GJ-1, and NIST610 were used as reference materials for U–Pb dating and instrument optimisation. The U–Th–Pb ratios were calculated using Glitter 4.4. Concordia diagrams and weighted mean calculations were performed using the Isoplot/Ex.3 software [16]. Common Pb compositions were calibrated using the method described by Andersen [17].

4.2. Major and Trace Element Analyses

Twenty fresh whole-rock samples were collected for major and trace element analyses. Major- and trace-element analyses were performed at the Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits in Xi’an, (China). Whole-rock geochemical analyses were performed using X-ray fluorescence (XRF) and ICP-MS, with analytical errors <3 wt.% for most elements. Loss on ignition (LOI) was estimated using an electronic analytical balance at constant temperature of approximately 1000 °C. The detailed procedures followed are as described by Yang et al. [18].

4.3. Zircon Hf Isotopic Analyses

Zircon Lu–Hf isotope measurements were performed using a Geolas-Pro laser ablation system coupled to a Neptune multiple-collector inductively coupled plasma mass spectrometry (ICP–MS). Details of the instrumental conditions and acquisition were similar to those described in previous studies [19]. A stationary laser ablation spot with a beam diameter of 32 μm was used for the analyses. During the analysis, zircon GJ-1 was used as the reference standard, yielding a weighted mean 176Hf/177Hf ratio of 0.281990–0.282070. The present-day chondritic ratios of 176Hf/177Hf and 176Lu/177Hf are 0.282772 and 0.0332 [20], respectively. The decay constant for 176Lu is 1.865 × 10-11a-1 [21]; these values were used to calculate the εHf values. In addition, the depleted mantle single-stage (TDM1) and two-stage model ages (TDM2) were calculated with reference to present-day 176Hf/177Hf ratios of 0.28325 and 176Lu/177Hf ratios of 0.0384 obtained from the depleted mantle [22].

5. Analytical Results

5.1. Zircon U–Pb Age

Older zircons (>1000 Ma) usually exhibit Pb loss. Under the same initial conditions and geological environment, 206Pb and 207Pb isotopes have synchronous variation characteristics and can maintain a relatively stable ratio [23]. Therefore, the 206Pb/238U age was used for zircons younger than 1000 Ma and the 206Pb/207Pb age was used for zircons older than 1000 Ma to represent the formation age of zircons. Two representative U-rich granitic pegmatite samples from the western Huayangchuan deposit were dated to determine their diagenetic and metallogenic ages. Most zircons from the samples were translucent–transparent crystals. They had a size range of 150–300 μm long and 100–200 μm wide, with length:width ratios of 2:1–3:1. The CL images of the zircon grains (Figure 6a) displayed clear concentric oscillatory zoning coupled with high Th:U ratios (most were 0.11–0.89, average = 0.56) (Table 1, Table 2), suggesting a magmatic origin [24]. Meanwhile, the chondrite-normalised REE patterns of the zircons were similar to those of typical magmatic zircons (Figure 7a,c), with elevated HREE/LREE ratios (Figure 7b,d), significant positive Ce anomalies, and positive correlations between Th and U [25]. The results of LA–ICP–MS zircon analyses are listed in Table 1, Table 2, as shown in Figure 8a‒d. Analyses of forty-three grains from two groups of zircon samples formed a concordant population with a weighted mean 206Pb/207Pb age of 1829 ± 11 Ma (MSWD = 1.5, n = 21; Figure 8b) and 1826.3 ± 7.9 Ma (MSWD = 0.97, n = 22; Figure 8d) , respectively. This age was interpreted as the diagenetic age of the U-rich granitic pegmatite.

5.2. Major Element Compositions

The major and trace element test data are presented in Table 3 and Table 4 . Most of the U-rich granitic pegmatite samples from the Huayangchuan deposit had low LOI values, indicating that these samples were relatively fresh. The samples were characterised by high concentrations of SiO2 (64.37–70.69 wt. %) and total alkalis (Na2O + K2O = 8.50–10.30 wt.%), higher Al2O3 (12.20–14.41 wt.%), but relatively lower concentrations of Ti2O (0.23–0.73 wt.%), MgO (0.38–0.90 wt.%), P2O5 (0.14–0.83 wt.%), and MnO (0.04–0.57 wt.%). Meanwhile, they had low Rittmann index (σ=2.6–4.9, average = 3.8) values. In the SiO2 vs. Na2O + K2O diagram (Figure 9a), SiO2 vs. K2O diagram (Figure 9b) and SiO2 vs. Na2O +K2O-CaO diagram (Figure 9c), most samples were placed in the alkaline granite field, shoshonitic series and A-Type granite, and generally exhibited metaluminous characteristics (A/CNK = 0.8–0.9, Figure 9d), respectively. In addition, it can also be seen that the U-rich granite pegmatite samples have different major element characteristics with the Paleoproterozoic Yuantou granite [27], Huashan granite and TTG gneiss of Taihua group (Figure 9a–d).

5.3. Trace Element Compositions

The content of rare earth elements (ΣREE) in the U-rich granitic pegmatite samples had a range from 430.50–1286.18×10-6 (Table 3), indicating that the REE in the U-rich granitic pegmatite had the characteristics of high total amount but very uneven distribution. In the chondrite-normalised diagrams (Figure 10a), all samples showed LREE-enriched and HREE depletion with (La/Yb)N =14.36–54.66. Meanwhile, the HREE exhibited a relatively flat patterns with (Gd/Yb)N =2.05–3.46 and weak negative Eu anomalies (δEu=0.57–1.19) (Figure 10a). Moreover, all of the U-rich granitic pegmatite samples were enriched in large-ion lithophile elements (such as Rb, Ba, K, and Pb) and radioactive elements (such as Th and U), and depleted in high field strength elements (such as Ta, P, Ti, Zr, and Hf) (Figure 10b). Obviously, the combination and enrichment characteristics of the trace elements in the U-rich granitic pegmatite samples were also consistent with the actual ore-forming elements(such as U,Nb,Pb, and REE). Compared with the Yuantou granite [27], Huashan granit and TTG gneiss of Taihua group, the U-rich granite pegmatite sample has a higher total amount of rare earth elements (Figure 10a), as well as Th, U, Pb and other trace element combinations (Figure 10b). This feature is also consistent with the actual metallogenic element combinations (such as U, Nb, Pb, REE, etc.) in this area.

5.4. In Situ Zircon Hf Isotopic Compositions

Twenty zircon grains from the two groups of zircon samples were analysed for their Hf isotopic compositions. The results of the Lu–Hf analysis are presented in Table 5. These measured zircons have homogeneous Hf isotopic compositions and relatively high 176Hf/177Hf ratios (0.281359–0.281539), with depleted εHf (t) values varying from -19.42–-15.02 (Table 5, Figure 11a). Correspondingly, their single- (tDM1) and two-stage (tDM2) model ages ranged from 2.61 to 2.41 Ga and 3.10 to 2.76 Ga (Table 5, Figure 11b), respectively. The Hf isotope composition of the zircon indicates that the Late Palaeoproterozoic U-rich granitic pegmatite in Huayangchuan was probably formed by the reworking or remelting of crustal material from the Middle Archean to the Neoarchean.

6. Discussion

6.1. Constraints from zircon age of Paleoproterozoic U mineralization

Based on field observations, the U-rich granitic pegmatite intruded into the Taihua Group in a large single vein, and the intrusive contact boundary with the Taihua Group was clearly visible (Figure 3a,b), showing the characteristics of magmatic rock intrusion. The CL images of zircons from U-rich granitic pegmatite samples also showed general characteristics of magmatic zircons [24]. The REE characteristics of the zircons were consistent with those of typical magmatic zircons (Figure 7a,c). The highly positive correlation of U and Th in zircon showed the characteristics of magmatic genesis (Figure 7b,d), reflecting that the zircon isotope system was still well sealed without the migration of U and Th. Under the polarising and scanning electron microscopes, zircon grains displayed an intact crystal form (Figure 3c, Figure 5e,f) and an association with uraninite (Figure 5f). Combined with the massive occurrence of betafites in the intergranular fissures of rock-forming minerals (Figure 5a–d), we speculate that the zircons had mineralisation characteristics in the diagenetic stage. Therefore, the zircon U–Pb dating results obtained in this study were 1826.3 ± 7.9 and 1829 ± 11 Ma (Figure 8b,d), which not only indicated the diagenetic age of U-rich pegmatite but also represented the age of uranium mineralisation in the same period.
Generally, orogenic belts on the margins of ancient continental blocks are important uranium metallogenic regions. First, ancient land blocks are often rich in large-ion lithophilic elements (e.g., Rb, Ba, Th, U, and K), which can easily provide material sources for uranium polymetallic mineralisation. Second, the crust and mantle materials on the margin of the ancient continental region have strong material interactions and frequent magmatic activities, which can create favourable geological conditions for the large-scale enrichment of ore-forming materials. Therefore, the marginal zone of the ancient continent often had favourable uranium polymetallic mineralisation conditions that controlled the temporal and spatial distribution of uranium polymetallic deposits [30,31]. Regionally, a large number of late Palaeoproterozoic (2.0–1.8 Ga) uranium polymetallic deposits are distributed along the collisional orogenic belt along the marginal zone of the ancient continental North China Craton. Typical deposits include the Lianshanguan uranium deposit in the Liaoning Province, the Pinglu uranium deposit in the Shanxi Province, and the Hongshiquan uranium deposit in the Gansu Province [30,31]. In conclusion, the chronological research results of U-rich granitic pegmatite in this study show that uranium mineralisation in the late Palaeoproterozoic (1829 ± 11 and 1826 ± 7.9 Ma) also occurred in the Xiaoqinling area of the southern margin of the North China Craton, which implies that the tectonic–magmatic–mineralization events were produced during the ultimate cratonisation process of the North China Craton in the late Palaeoproterozoic (2.0–1.8 Ga) [32,33,34].

6.2. Rock Type of U-rich granitic pegmatite

Lithologically, A-type granites can be further divided into peralkaline and aluminous types [35]. Peralkaline A-type granite with a high degree of magmatic differentiation was formed during the latest time series of magmatic activity. They are often associated with iron–magnesia rocks (such as mafic inclusions, xenoliths, and intrusive veins) and often contain alkaline dark minerals (such as aegirine, aegirine–augite, sodium amphibole, sodium iron amphibole, and olivine) [36]. The peralkaline A-type granite is characterised by high SiO2, rich total alkalis (K2O+Na2O), and relatively poor MgO and low CaO; they usually enrich large-ion lithophile elements (LILEs: such as Rb, Th, U, and K), and depletion of high field strength elements (HFSEs: such as Zr, Nb, Ta, and Ti) [37]. Their ΣREEs are usually several times or even dozens of times greater than that of other types of granites and they have strong negative δEu anomalies in the chondrite-normalised diagrams [38]. They usually also have high K2O/Na2O values, A/CNK ratios >1, and 10000 × Ga/Al ratios >2.6. Compared to peralkaline A-type granites, aluminous A-type granites have a relatively low degree of magmatic differentiation [39], therefore, they also show slightly different mineral and geochemical characteristics. The aluminous A-type granite is relatively rich in aluminium (Al2O3 >12 wt.%), but the A/CNK and 10000 × Ga/Al value are relatively low. They have a high content of light REE, thus showing more obvious characteristics of light and heavy rare earth fractionation, butδEu is usually not obvious [38]; The dark minerals of aluminous A-type granites are mainly ordinary hornblende or biotite [40].
The U-rich granitic pegmatite samples in this study were characterised by high SiO2 (64.37–70.69 wt.%) , total alkali values (K2O + Na2O = 8.50–10.30 wt.%), and Al2O3 (12.20–14.41 wt.%), and relatively low Ti2O (0.23–0.73 wt.%), MgO (0.38–0.90 wt.%), P2O5 (0.14–0.83 wt.%), and MnO (0.04–0.57 wt.%). Most of the U-rich granitic pegmatite samples belonged to the A-type granite in the SiO2 vs. Na2O+K2O-CaO diagram and showed alkaline and alkaline calcareous series (Figure 9c). The A/CNK values of these samples had a range from 0.8 to 0.9 (Table 3), and most of them were metaluminous (Figure 9d) in the A/CNK vs. A/NK diagram; The 10000 × Ga/Al ratios of the samples were 2.83–3.99 (average = 3.41) (Table 3), and most of them fell into the range of A-type granite in the 10000 × Ga/Al vs. (K2O+Na2O) diagram (Figure 12a), 10000 × Ga/Al vs.Y diagram (Figure 12b), 10000 × Ga/Al vs. (Na2O + K2O)/CaO diagram (Figure 12c) and Zr+Nb+Ce+Y vs. (Na2O + K2O)/ CaO diagram (Figure 12d), which also shows different rock type characteristics from the Huashan granite and TTG of Taihua group. The trace elements of the U-rich granitic pegmatite samples also showed enrichment of large-ion lithophile elements (typically Rb, Ba, K, and Pb) and radioactive elements (such as Th and U), and depletion of high-field strength elements (such as Ta, Nb, P, Ti, and Hf (Figure 10b). The U-rich granitic pegmatite samples also have a high total content of rare earth elements (ΣREE), but fractionation characteristics of LREE and HREE are obvious, and negative δEu anomalies are relatively weak (Figure 10a). No dark alkaline minerals were observed in the U-rich granitic pegmatite samples (Figure 4). In summary, the U-rich granitic pegmatites of the late Palaeoproterozoic in the Huayangchuan deposit were equivalent to aluminous A-type granites.

6.3. Tectonic Setting of U mineralization

Type A granites are generally formed in tensile or extensional tectonic settings [36]. The tectonic settings of A-type granites can be divided into non-orogenic and post-orogenic types [41]. Globally, A-type granites were very rare before the Palaeoproterozoic but began to appear in large quantities during the late Palaeoproterozoic (early Mesoproterozoic) [42]. This phenomenon implies a transition of the tectonic system from compression to extension during the continental evolution [43]. During the late Palaeoproterozoic (2.0–1.8 Ga), all kinds of rocks in the basement of the North China Craton underwent strong metamorphism and deformation [44]. This process lasted at least 150 Ma, which was the widespread land–land collision events, and this tectonic event was known as the Luliang movement [45]. The Luliang movement promoted a unified crystalline basement in the North China Craton. A series of magmatic activities occurred in the North China Craton after the Luliang movement. For example, Yang (2020) [46] obtained zircon U–Pb ages of felsic pegmatite, granodiorite, and monzogranite in the Xiaoqinling area on the southern margin of the North China Craton, which were aged approximately 1926, 1808, and 1807 Ma, respectively, reflecting tectonic magmatism after the end of the Luliang movement. Thereafter, the bimodal volcanic rocks of Xiong’er group (1.80–1.75 Ga) [47], the volcanic–sedimentary formation of Changcheng group (1.68–1.62 Ga) [48], and the contemporaneous or later (1.72–1.60 Ga) basic dyke swarms [49], all these indicate that the Xiaoqinling area on the southern margin of the North China Craton had been in a continuous regional extensional environment since the Luliang movement.
In the SiO2 vs. lg[Ca/( Na2O + K2O)] diagram(Figure 13a)and R1 vs. R2 diagram(Figure 13b), most of the U-rich granitic pegmatite samples plotted in a extensional and non-orogenic tectonic setting. In the Y vs. Nb diagram(Figure 14a), Yb vs. Ta diagram(Figure 14b), Y+Nb vs. Rb diagram(Figure 14c) and Yb+Ta vs. Rb diagram(Figure 14d), most of the U-rich granitic pegmatite samples are generally in an intra-plate granite tectonic setting (WPG) [50]. In the Y-Nb-3×Ga diagram(Figure 15a), Y-Nb-3×Ce diagram(Figure 15b) and Yb+Ta vs. Rb diagram(Figure 15d), most of the U-rich granitic pegmatite samples belong to intraplate A1-type granite [36]. Therefore, the above results indicate that the Xiaoqinling belt in the southern margin of the North China Craton was already in a non-orogenic extensional setting when the U-rich granitic pegmatites were formed (1826.3 ± 7.9 and 1829 ± 11 Ma). The reconstruction scheme of the Columbia supercontinent in the late Paleoproterozoic (2.0‒1.8 Ga) provided the location of the North China Craton. At this time, the southern margin of the North China Craton was located in the intraplate rift zone of the Colombian supercontinent [51], which had the non-orogenic tectonic conditions of a plate margin or intraplate rift.

6.4. Rock and mineralisation genesis of U-rich granitic pegmatite

Currently, there are four viewpoints on the genetic model of A-type granite: first, the crustal rocks are partially melted to form I-type granite, and then the residual materials are partially melted again to form A-type granite [54]; however, experimental petrology and actual observations proved that the residual crustal material cannot differentiate A-type granite [55]. Second, A-type granite is formed by the partial melting of the crystalline basement or metamorphic sedimentary rocks [35]. Third, A-type granite is formed by crust–mantle magmatic mixing [56]. Fourth, the separation crystallisation of mantle-derived alkaline basalt directly forms A-type granite [57]. The studied U-rich granitic pegmatite samples have the characteristics of high SiO2, Al2O3, and total alkalis, low MgO, TiO2, and P2O5, and enrichment in large-ion lithophiles and radioactive elements (such as Rb, Ba, Th, U, K, and Pb) and depletion of high-field-strength elements (such as Ta, Nb, P, Ti, and Hf). These whole-rock geochemical characteristics support the conclusion that the magma source of the U-rich granitic pegmatite samples was felsic crustal material, rather than mantle-derived mafic magma. In addition, experimental petrology has proved that felsic rocks in the shallow crust (depth ≤20 km) can produce A-type granites melt through dehydration, high temperature, and partial melting [58]. In fact, the lithology of Taihua Group as the basement were composed of “supracrustal rock” and “TTG suite” (Trondhjemite, Tonalite, and Granodiorite), whose material composition clearly belongs to the evolved felsic crust. The formation ages of Taihua Group were approximately 2.8, 2.5, 2.3 and 1.97–1.8 Ga [32,34,59], reflecting the multi-stage cyclic evolution of the crust in this area. The formation age of the early Taihua Group (approximately 2.8 Ga) is much older than that of the later U-rich granitic pegmatite and is very close to the two-stage model age (TDM2) of the zircon Hf isotope (3.10–2.76 Ga). This evidence indicates that the materials of the early Taihua Group (such as the Middle Archean) were probably the magma source of the later Taihua Group (such as the Late Palaeoproterozoic).
Therefore, we can speculate that the formation process of U-rich granitic pegmatite in this study was as follows: after the Late Palaeoproterozoic (1826.3 ± 7.9 and 1829 ± 11 Ma) Luliang movement, the tectonic setting in this area gradually transitioned to an extensional background [27]. The subduction plates broke off and triggered asthenospheric mantle upwelling, resulting in partial melting of the lithospheric mantle, and the generated basic magma rose and underplated the middle-lower crust, prompting partial melting of the early Taihua Group formed in the Archean-Neoarchean (3.10–2.76 Ga). As extension continued, a series of A-type granites gradually formed, such as in the Yuantou and Huayangchuan areas (Figure 16a). The Taihua Group formed in the Archean-Neoarchean was rich in uranium and other radioactive elements, and the uranium-rich granitic pegmatites in this area were directly formed during the magmatic activity in the late Palaeoproterozoic (1826.3 ± 7.9 and 1829 ± 11 Ma) (Figure 16b). These U-rich granitic pegmatites also provided material sources for later (Indosinian and Yanshanian) uranium mineralisation in the Huayangchuan area or underwent superimposed transformation to form new deposit types, reflecting the ultra-long evolutionary history of uranium mineralisation and uranium deposits with complex genesis in the Huayangchuan area.

7. Conclusion

  • The U-rich granitic pegmatites were formed in the late Palaeoproterozoic (1826.3 ± 7.9 and 1829 ± 11 Ma). The symbiotic phenomena of the magmatic zircons with betafite and uraninite in the samples showed metallogenic characteristics during the diagenetic period.
  • Based on the classification criteria and rock characteristics of A-type granite, the major elements, trace elements, and mineral compositions of most U-rich granitic pegmatite samples had the characteristics of intraplate A1-type granite
  • The U-rich granitic pegmatites were formed after the Luliang movement in the late Palaeoproterozoic, and the tectonic system gradually transitioned from a continent–continent collision to an extensional setting. The partial melting of the early Taihua Group materials formed in the Archean-Neoarchean triggered a series of tectonic granitic magmatic activities.
  • The early Taihua Group formed in the Archean-Neoarchean as mature crust material rich in uranium, which provided uranium-rich magma for the formation of uranium-rich granite pegmatite in the late Palaeoproterozoic. Existing uranium-rich geological bodies also provided material sources for later uranium mineralisation in the Huayangchuan deposit.

Author Contributions

Putao Li——Conceptualization, Methodology, Formal analysis, Investigation, Resources, Data curation, writing- original draft, Writing-review & editing, Visualization. Yongjun Li——Writing-review & editing, Supervision. Pingyang Gu——Investigation, Resources, Data curation, Project administration. Shiping He——Investigation, Data curation. Yujun Zhuang——Investigation, Data curation. Ruiming Chen——Investigation, Data curation.

Funding

This research was financially supported by the Geological Survey Project of the China Geological Survey (Grant No. DD20160014, DD20190069, and DD20221636).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article.

Acknowledgments

We are very grateful to Qingqing Kang, Peng Li, Lei Li, and Hongjun Jiang of Geological Party No. 224, Sino Shaanxi Nuclear Industry Group, for their assistance in the field sampling work, and the reviewers for their constructive comments and suggestions which improved the quality of the manuscript.

Conflicts of Interest

There is no conflict of interest for this work.

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Figure 1. (a) Geologic sketch map of China; (b) Regional tectonic map of Qinling Orogen; (c) Geologic map of the Huayangchuan district (modified from [2]) .
Figure 1. (a) Geologic sketch map of China; (b) Regional tectonic map of Qinling Orogen; (c) Geologic map of the Huayangchuan district (modified from [2]) .
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Figure 2. Simplified geologic map of the Huayangchuan deposit (modified from [13]).
Figure 2. Simplified geologic map of the Huayangchuan deposit (modified from [13]).
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Figure 3. Representative images of U-rich granitic pegmatite veins (a)-(b); Ore images of U-rich granitic pegmatite veins (c)- (d).
Figure 3. Representative images of U-rich granitic pegmatite veins (a)-(b); Ore images of U-rich granitic pegmatite veins (c)- (d).
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Figure 4. (a) Boundary between pegmatite and gneiss xenolith; (b) Pegmatitic texture; (c) Zircon with intact crystal form; (d) Quartz veinlets in gneiss fractures. Qz: Quartz, Pl: Plagioclase, Kf: K-feldspar, Zr: zircon.
Figure 4. (a) Boundary between pegmatite and gneiss xenolith; (b) Pegmatitic texture; (c) Zircon with intact crystal form; (d) Quartz veinlets in gneiss fractures. Qz: Quartz, Pl: Plagioclase, Kf: K-feldspar, Zr: zircon.
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Figure 5. (a) Betafite and its encapsulated uraninite; (b) Betafite and its internal fissure uraninite; (c) Betafite and its edge growing uraninite; (d) Betafite aggregates between K-feldspar and quartz; (e) Zircon between K-feldspar and albite; (f) Zircon from intergranular fissures of K-feldspar. Qz: Quartz, Kf: K-feldspar, Ab: Albite, Bnr: Betafite, U: Uraninite, Alt: Allanite, Ep: Epidote, Spn: Sphene, Zr: Zircon.
Figure 5. (a) Betafite and its encapsulated uraninite; (b) Betafite and its internal fissure uraninite; (c) Betafite and its edge growing uraninite; (d) Betafite aggregates between K-feldspar and quartz; (e) Zircon between K-feldspar and albite; (f) Zircon from intergranular fissures of K-feldspar. Qz: Quartz, Kf: K-feldspar, Ab: Albite, Bnr: Betafite, U: Uraninite, Alt: Allanite, Ep: Epidote, Spn: Sphene, Zr: Zircon.
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Figure 6. Cathodoluminescence images of zircons from U-rich granitic pegmatite.
Figure 6. Cathodoluminescence images of zircons from U-rich granitic pegmatite.
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Figure 7. (a) Chondrite-normalised trace multi-element patterns of zircons sample D43-Zr; (b) Th–U element correlation diagram of zircons sample D43-Zr; (c) Chondrite-normalised trace multi-element patterns of zircons sample D45-Zr; (d) Th–U element correlation diagram of zircons sample D45-Zr (Chondrite values are from [26]).
Figure 7. (a) Chondrite-normalised trace multi-element patterns of zircons sample D43-Zr; (b) Th–U element correlation diagram of zircons sample D43-Zr; (c) Chondrite-normalised trace multi-element patterns of zircons sample D45-Zr; (d) Th–U element correlation diagram of zircons sample D45-Zr (Chondrite values are from [26]).
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Figure 8. (a) Zircon U–Pb concordia diagrams of sample D43-Zr; (b) Weighted average of zircon U–Pb ages of sample D43-Zr; (c) Zircon U–Pb concordia diagrams of sample D45-Zr; (d) Weighted average of zircon U–Pb ages of sample D45-Zr.
Figure 8. (a) Zircon U–Pb concordia diagrams of sample D43-Zr; (b) Weighted average of zircon U–Pb ages of sample D43-Zr; (c) Zircon U–Pb concordia diagrams of sample D45-Zr; (d) Weighted average of zircon U–Pb ages of sample D45-Zr.
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Figure 9. (a) SiO2 vs.Na2O+K2O diagram; (b)SiO2 vs.K2O diagram (modified from [28]); (c)SiO2 vs.Na2O+K2O-CaO diagram (modified from [29]); (d) A/CNK vs. A /NK diagram(modified from [29]).
Figure 9. (a) SiO2 vs.Na2O+K2O diagram; (b)SiO2 vs.K2O diagram (modified from [28]); (c)SiO2 vs.Na2O+K2O-CaO diagram (modified from [29]); (d) A/CNK vs. A /NK diagram(modified from [29]).
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Figure 10. (a) Chondrite-normalised REE patterns; (b) Primitive mantle-normalised trace multi-element patterns (Chondrite and primitive mantle values are from [26]).
Figure 10. (a) Chondrite-normalised REE patterns; (b) Primitive mantle-normalised trace multi-element patterns (Chondrite and primitive mantle values are from [26]).
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Figure 11. (a) εHf(t) vs. t (Ma) diagram of zircons; (b) T DM2 diagram of of zircons.
Figure 11. (a) εHf(t) vs. t (Ma) diagram of zircons; (b) T DM2 diagram of of zircons.
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Figure 12. (a) 10000 × Ga/Al vs. Na2O + K2O diagram; (b) 10000 × Ga/Al vs.Y diagram; (c) 10000 × Ga/Al vs. (Na2O + K2O)/ CaO diagram ; (d) Zr+Nb+Ce+Y vs. (Na2O + K2O)/ CaO diagram (modified from [37]).
Figure 12. (a) 10000 × Ga/Al vs. Na2O + K2O diagram; (b) 10000 × Ga/Al vs.Y diagram; (c) 10000 × Ga/Al vs. (Na2O + K2O)/ CaO diagram ; (d) Zr+Nb+Ce+Y vs. (Na2O + K2O)/ CaO diagram (modified from [37]).
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Figure 13. (a)SiO2 vs. lg[Ca/( Na2O + K2O)] diagram (modified from [52]); (b)R1 vs. R2 diagram (modified from [53]).
Figure 13. (a)SiO2 vs. lg[Ca/( Na2O + K2O)] diagram (modified from [52]); (b)R1 vs. R2 diagram (modified from [53]).
Preprints 76375 g013
Preprints 76375 g014
Figure 14. (a) Y vs. Nb diagram; (b) Yb vs. Ta diagram; (c) Y+Nb vs. Rb diagram; (d) Yb+Ta vs. Rb diagram (modified from [50]).
Figure 14. (a) Y vs. Nb diagram; (b) Yb vs. Ta diagram; (c) Y+Nb vs. Rb diagram; (d) Yb+Ta vs. Rb diagram (modified from [50]).
Preprints 76375 g014
Preprints 76375 g015
Figure 15. (a) Y-Nb- 3×Ga diagram; (b)Y-Nb- 3×Ce diagram; (c)Y/Nb vs. Rb/Nb diagram (modified from [36]).
Figure 15. (a) Y-Nb- 3×Ga diagram; (b)Y-Nb- 3×Ce diagram; (c)Y/Nb vs. Rb/Nb diagram (modified from [36]).
Preprints 76375 g015
Preprints 76375 g016
Figure 16. (a) Rock genesis pattern drawings of Paleoproterozoic U-rich granitic pegmatite; (b)Mineralisation genesis pattern drawings of Paleoproterozoic U-rich granitic pegmatite.
Figure 16. (a) Rock genesis pattern drawings of Paleoproterozoic U-rich granitic pegmatite; (b)Mineralisation genesis pattern drawings of Paleoproterozoic U-rich granitic pegmatite.
Preprints 76375 g016
Table 1. LA–ICP–MS dating results of zircons from the U-rich granitic pegmatite (D43-Zr).
Table 1. LA–ICP–MS dating results of zircons from the U-rich granitic pegmatite (D43-Zr).
Site number Isotopic contents(×10-6) Th/U Isotopic ratios Ages (Ma)
232Th 238U 206Pb 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ
D43-Zr 1 98.43 259.74 337.46 0.38 0.11004 0.00265 5.13454 0.12013 0.33794 0.00424 1800 25 1842 20 1877 20
D43-Zr 2 167.28 265.39 365.40 0.63 0.11386 0.00211 5.22471 0.09341 0.33234 0.0037 1862 17 1857 15 1850 18
D43-Zr 3 1089.61 843.28 1167.14 1.29 0.11265 0.00151 5.1857 0.06662 0.33343 0.00334 1843 11 1850 11 1855 16
D43-Zr 4 447.03 509.84 711.98 0.88 0.11331 0.00179 5.23058 0.07961 0.33435 0.00351 1853 14 1858 13 1859 17
D43-Zr 5 345.90 780.87 1084.87 0.44 0.11019 0.00167 5.14842 0.07508 0.33843 0.0035 1803 13 1844 12 1879 17
D43-Zr 6 100.15 140.18 197.50 0.71 0.11122 0.0033 5.18751 0.14954 0.33786 0.00476 1819 32 1851 25 1876 23
D43-Zr 7 515.44 577.08 813.96 0.89 0.11263 0.00166 5.24234 0.07419 0.33718 0.00346 1842 12 1860 12 1873 17
D43-Zr 8 205.12 390.15 545.44 0.53 0.11288 0.00221 5.21629 0.09842 0.33479 0.00381 1846 18 1855 16 1862 18
D43-Zr 9 100.38 189.16 266.94 0.53 0.11239 0.00386 5.21178 0.174 0.33595 0.00519 1838 38 1855 28 1867 25
D43-Zr 10 199.06 320.95 457.25 0.62 0.11313 0.00369 5.28373 0.1672 0.33838 0.00508 1850 36 1866 27 1879 24
D43-Zr 11 286.62 347.43 498.58 0.82 0.10964 0.00436 5.26711 0.20378 0.34807 0.00598 1793 45 1864 33 1925 29
D43-Zr 12 53.58 126.46 179.43 0.42 0.11239 0.00614 5.21294 0.27797 0.33607 0.00723 1838 65 1855 45 1868 35
D43-Zr 13 119.28 266.05 372.73 0.45 0.10876 0.00362 5.21221 0.16861 0.34727 0.00518 1779 37 1855 28 1922 25
D43-Zr 14 1283.81 2329.27 3302.17 0.55 0.10729 0.0014 5.04289 0.06241 0.34059 0.00334 1754 10 1827 10 1890 16
D43-Zr 15 142.68 189.51 269.85 0.75 0.10974 0.00536 5.10878 0.24319 0.33736 0.00672 1795 58 1838 40 1874 32
D43-Zr 16 53.86 207.76 294.53 0.26 0.10862 0.00412 5.07892 0.18737 0.33885 0.00557 1776 43 1833 31 1881 27
D43-Zr 17 190.37 443.75 594.51 0.43 0.10451 0.00372 4.36696 0.15106 0.30281 0.00462 1706 41 1706 29 1705 23
D43-Zr 18 115.23 433.07 619.64 0.27 0.10778 0.00275 5.18861 0.12828 0.34889 0.00444 1762 27 1851 21 1929 21
D43-Zr 19 136.61 248.62 364.45 0.55 0.10921 0.00315 5.27281 0.14784 0.34991 0.0048 1786 31 1864 24 1934 23
D43-Zr 20 41.31 157.21 215.51 0.26 0.10369 0.00713 4.30494 0.28889 0.30088 0.0074 1691 87 1694 55 1696 37
D43-Zr 21 125.59 233.32 326.21 0.54 0.11463 0.00352 5.21009 0.15489 0.3294 0.00479 1874 33 1854 25 1835 23
D43-Zr 22 77.29 231.59 318.26 0.33 0.10444 0.00449 4.19583 0.17523 0.29115 0.00509 1704 51 1673 34 1647 25
D43-Zr 23 13.50 209.90 294.81 0.06 0.11053 0.00523 5.15281 0.23697 0.33787 0.00674 1808 55 1845 39 1876 32
D43-Zr 24 144.01 298.90 430.19 0.48 0.1123 0.00323 5.20516 0.14507 0.33594 0.00466 1837 31 1853 24 1867 22
D43-Zr 25 142.41 282.60 403.90 0.50 0.11201 0.00275 5.21895 0.12386 0.3377 0.00426 1832 25 1856 20 1876 21
D43-Zr 26 118.14 273.18 388.65 0.43 0.10738 0.00336 5.1433 0.15635 0.34715 0.00505 1755 34 1843 26 1921 24
D43-Zr 27 92.52 143.41 210.65 0.65 0.10916 0.00331 5.13968 0.15094 0.34125 0.00485 1785 33 1843 25 1893 23
D43-Zr 28 184.27 300.53 438.35 0.61 0.10907 0.00258 5.15027 0.11775 0.34222 0.00421 1784 24 1844 19 1897 20
D43-Zr 29 275.79 443.79 645.12 0.62 0.11055 0.00186 5.17060 0.08305 0.33899 0.00356 1808 15 1848 14 1882 17
D43-Zr 30 224.04 291.71 424.84 0.77 0.11036 0.00184 5.19606 0.08258 0.34124 0.00357 1805 15 1852 14 1893 17
Table 2. LA–ICP–MS dating results of zircons from the U-rich granitic pegmatite (D45-Zr).
Table 2. LA–ICP–MS dating results of zircons from the U-rich granitic pegmatite (D45-Zr).
Site number Isotopic contents(× 10-6) Th/U Isotopic ratios Ages (Ma)
232Th 238U 206Pb 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ
D45-Zr 1 228.10 365.61 485.22 0.62 0.11534 0.00222 5.18495 0.09539 0.32637 0.00352 1885 18 1850 16 1821 17
D45-Zr 2 128.28 309.54 441.36 0.41 0.11556 0.00250 5.15581 0.10680 0.32387 0.00369 1889 21 1845 18 1809 18
D45-Zr 3 80.33 235.43 396.67 0.34 0.11476 0.00283 5.13976 0.12210 0.32510 0.00397 1876 26 1843 20 1815 19
D45-Zr 4 237.05 458.37 608.01 0.52 0.11492 0.00233 5.12766 0.09936 0.32386 0.00358 1879 20 1841 16 1809 17
D45-Zr 5 139.49 331.45 484.36 0.42 0.11286 0.00484 5.18060 0.21601 0.33314 0.00580 1846 50 1849 35 1854 28
D45-Zr 6 189.41 386.22 554.32 0.49 0.10886 0.00461 4.99192 0.20586 0.33278 0.00569 1780 50 1818 35 1852 28
D45-Zr 7 94.63 268.34 358.87 0.35 0.10978 0.00564 5.03454 0.25229 0.33272 0.00662 1796 62 1825 42 1852 32
D45-Zr 8 100.94 330.15 315.84 0.31 0.11174 0.00551 5.04625 0.24235 0.32761 0.00636 1828 59 1827 41 1827 31
D45-Zr 9 250.90 624.89 866.61 0.40 0.11229 0.00348 5.05149 0.15160 0.32634 0.00458 1837 34 1828 25 1821 22
D45-Zr 10 235.17 389.51 457.12 0.60 0.11280 0.00290 5.06802 0.12589 0.32590 0.00409 1845 27 1831 21 1818 20
D45-Zr 11 38.51 145.62 192.54 0.26 0.11372 0.00394 5.08833 0.17119 0.32456 0.00490 1860 39 1834 29 1812 24
D45-Zr 12 55.93 177.01 254.71 0.32 0.11150 0.00375 5.07163 0.16582 0.32992 0.00486 1824 38 1831 28 1838 24
D45-Zr 13 72.56 161.74 263.65 0.45 0.11352 0.00273 5.09377 0.11822 0.32543 0.00396 1857 25 1835 20 1816 19
D45-Zr 14 173.63 401.95 521.82 0.43 0.11311 0.00204 5.03004 0.08685 0.32252 0.00344 1850 17 1824 15 1802 17
D45-Zr 15 180.93 390.31 511.79 0.46 0.11196 0.00202 5.02322 0.08669 0.32538 0.00347 1831 17 1823 15 1816 17
D45-Zr 16 139.81 299.29 395.54 0.47 0.11398 0.00206 5.06457 0.08754 0.32223 0.00344 1864 17 1830 15 1801 17
D45-Zr 17 363.32 496.56 686.98 0.73 0.11286 0.00167 5.04589 0.07128 0.32423 0.00324 1846 12 1827 12 1810 16
D45-Zr 18 307.15 462.25 645.57 0.66 0.11135 0.00174 5.01952 0.07507 0.32691 0.00332 1822 14 1823 13 1823 16
D45-Zr 19 391.09 564.46 708.34 0.69 0.11097 0.00161 4.97956 0.06916 0.32542 0.00324 1815 12 1816 12 1816 16
D45-Zr 20 179.55 495.74 694.59 0.36 0.11071 0.00170 5.02653 0.07396 0.32925 0.00334 1811 13 1824 12 1835 16
D45-Zr 21 257.02 397.13 577.63 0.65 0.11092 0.00171 5.00038 0.07406 0.32693 0.00333 1815 13 1819 13 1823 16
D45-Zr 22 323.16 487.96 678.09 0.66 0.11120 0.00166 5.02863 0.07181 0.32793 0.00331 1819 13 1824 12 1828 16
D45-Zr 23 200.79 325.30 465.12 0.62 0.11064 0.00269 4.95459 0.11685 0.32474 0.00401 1810 25 1812 20 1813 20
D45-Zr 24 141.25 362.66 495.12 0.39 0.11155 0.00586 5.02813 0.25715 0.32690 0.00693 1825 62 1824 43 1823 34
D45-Zr 25 38.10 358.15 559.24 0.11 0.11060 0.00213 5.04176 0.09387 0.33061 0.00367 1809 18 1826 16 1841 18
D45-Zr 26 106.97 234.35 308.37 0.46 0.11053 0.00321 5.10190 0.14402 0.33478 0.00458 1808 32 1836 24 1862 22
D45-Zr 27 79.38 271.86 341.08 0.29 0.10930 0.00263 5.02578 0.11715 0.33349 0.00410 1788 25 1824 20 1855 20
D45-Zr 28 415.24 1008.82 1003.89 0.41 0.11021 0.00187 5.19751 0.08529 0.34206 0.00363 1803 15 1852 14 1897 17
D45-Zr 29 155.56 326.47 508.54 0.48 0.10724 0.00305 5.08513 0.14076 0.34397 0.00461 1753 31 1834 23 1906 22
D45-Zr 30 241.24 915.28 1372.88 0.26 0.11082 0.00265 5.05000 0.11732 0.33056 0.00408 1813 25 1828 20 1841 20
Table 3. Measured contents of major (wt. % ), rare earth, and trace elements (ppm) of the U-rich granitic pegmatite.
Table 3. Measured contents of major (wt. % ), rare earth, and trace elements (ppm) of the U-rich granitic pegmatite.
Sample D43-YH1 D43-YH2 D43-YH3 D43-YH4 D43-YH5 D45-YH1 D45-YH2 D45-YH3 D45-YH4 D45-YH5
SiO2 69.92 67.82 70.69 64.37 65.68 66.73 67.05 66.24 66.49 66.13
Al2O3 12.50 13.06 12.50 14.41 14.19 14.41 14.38 14.33 14.35 14.37
Fe2O3 2.20 3.35 2.55 4.10 3.65 3.46 3.29 3.52 3.72 3.74
FeO 0.88 1.15 0.95 1.40 1.23 1.54 1.33 1.41 1.49 1.50
CaO 2.04 2.22 1.82 1.72 1.84 1.37 1.37 1.23 1.53 1.46
MgO 0.84 0.52 0.38 0.86 0.84 0.88 0.82 0.89 0.86 0.90
K2O 5.95 5.91 5.57 6.98 6.22 5.22 5.76 5.65 5.02 5.40
Na2O 3.07 3.17 2.93 3.23 4.08 4.35 3.96 4.11 4.27 4.06
TiO2 0.26 0.50 0.23 0.65 0.70 0.70 0.66 0.71 0.72 0.73
P2O5 0.83 0.17 0.14 0.22 0.22 0.20 0.19 0.22 0.21 0.22
MnO 0.57 0.07 0.04 0.06 0.05 0.07 0.07 0.08 0.06 0.07
LOI 1.43 1.49 1.32 1.55 0.82 0.62 0.63 1.00 0.79 0.82
Tatal 100.49 99.43 99.12 99.55 99.52 99.55 99.51 99.39 99.51 99.40
K2O+Na2O 9.02 9.08 8.50 10.21 10.30 9.57 9.72 9.76 9.29 9.46
A/CNK 0.8 0.8 0.9 0.9 0.8 0.9 0.9 0.9 0.9 0.9
A/NK 1.1 1.1 1.2 1.1 1.1 1.1 1.1 1.1 1.2 1.1
σ 3.0 3.3 2.6 4.9 4.7 3.9 3.9 4.1 3.7 3.9
R1 2089 1881 2269 1350 1328 1532 1577 1486 1585 1546
R2 383 391 336 368 378 332 328 316 347 342
Rb 64.1 85.9 117 148 118 114 172 187 134 175
Ba 3180 2910 5100 1950 2160 2290 2360 2780 2250 2750
Th 260.00 45.10 79.00 77.50 68.40 60.70 87.60 98.50 76.00 102.00
U 234.00 321.00 289.33 200.50 181.00 89.00 173.00 237.50 109.50 211.50
Ta 0.30 2.18 0.71 1.58 2.10 2.14 2.50 2.86 2.62 2.84
Nb 317.0 104.0 116.0 167.0 156.3 131.3 158.0 201.3 151.0 176.0
Pb 4000 1220 1650 799 870 454 445 835 664 798
Sr 109 146 87.4 118 62.3 132 98.4 138 198 183
Zr 125 34 30.6 33.9 34.3 29.9 38.4 47.6 39.4 48
Hf 22.6 23.0 26.4 25.0 23.9 21.6 26.3 28.5 24.2 27.8
Y 282 100 156 203 243 204 284 336 246 320
Ga 63.50 22.00 28.40 37.10 45.80 39.30 53.50 62.90 47.00 60.40
La 245 76.3 95.4 117 148 125 165 204 153 192
Ce 43.70 13.20 13.80 16.40 19.70 16.40 21.90 26.10 19.10 25.70
Pr 15.00 2.76 2.61 2.76 3.13 2.62 3.41 4.39 3.38 4.23
Nd 33.70 9.86 9.77 11.80 13.60 11.40 14.90 18.60 13.60 17.60
Sm 4.94 1.46 1.30 1.64 1.65 1.37 1.88 2.49 1.90 2.46
Eu 25.10 7.46 6.52 8.14 7.66 6.79 8.77 11.00 8.44 11.60
Gd 4.77 1.48 1.25 1.47 1.40 1.25 1.53 1.90 1.58 2.15
Tb 13.60 4.02 3.44 3.66 3.71 3.26 3.96 5.00 4.21 5.69
Dy 2.05 0.59 0.52 0.55 0.52 0.46 0.57 0.75 0.63 0.76
Ho 13.30 3.80 3.22 3.13 3.19 2.69 3.52 4.39 3.79 4.46
Er 2.03 0.57 0.50 0.48 0.46 0.38 0.54 0.66 0.58 0.63
Tm 1269.69 430.50 613.73 770.13 946.82 745.92 1065.48 1286.18 878.21 1216.68
Yb 5.10 5.76 9.05 9.94 11.86 11.31 12.14 11.51 10.35 10.78
Lu 14.36 17.83 32.82 43.93 51.60 51.37 54.66 51.85 43.97 48.60
REE 4.06 4.77 7.11 7.79 7.76 7.82 8.16 8.10 8.10 7.83
LREEN/HREEN 2.05 2.10 2.46 3.06 3.46 3.44 3.43 3.44 2.91 3.20
(La/Yb)N 1.19 0.73 0.68 0.60 0.58 0.58 0.57 0.61 0.64 0.60
(La/Sm)N 0.90 0.92 0.98 0.94 0.97 0.84 0.92 0.94 0.79 0.92
(Gd/Yb)N 3.42 3.33 3.99 3.28 3.18 2.83 3.45 3.76 3.19 3.65
δEu 69.92 67.82 70.69 64.37 65.68 66.73 67.05 66.24 66.49 66.13
δCe 12.50 13.06 12.50 14.41 14.19 14.41 14.38 14.33 14.35 14.37
10000×Ga/Al 2.20 3.35 2.55 4.10 3.65 3.46 3.29 3.52 3.72 3.74
NOTE: Abbreviations- LREE: light rare earth element; HREE: heavy rareearth element; REE: rare-earth element; LOI: loss on ignition; σ = (K2O+Na2O)2/(SiO2-43); Mg# = Mg2+/(Mg2+ + Fe2+) molar ratio; R1 = 4Si4+-11 × (Na+ + K+) - 2 × (Fe3+ + Fe2+ + Ti4+) molar ratio; R2 = 6Ca2+ + 2Mg2+ + Al3+, molar ratio; A/CNK = 2Al3+/(Ca2+ + 2Na+ + 2K+) molar ratio; A/NK = Al3+/(Na+ + K+) molar ratio; δEu = EuN/SQRT (SmN × GdN) ; δCe = 2CeN/(LaN × PrN). Symbol with “N” denotes the values normalised to chondrite (modified from [26]).
Table 4. Measured contents of major (wt. % ), rare earth, and trace elements (ppm) of the Surrounding rock and Huanshan granite.
Table 4. Measured contents of major (wt. % ), rare earth, and trace elements (ppm) of the Surrounding rock and Huanshan granite.
Sample D54-YH1 D54-YH2 D54-YH3 D54-YH4 D54-YH5 D63-YH1 D63-YH2 D63-YH3 D63-YH4 D63-YH5
SiO2 71.86 71.27 69.24 70.49 67.91 73.63 72.63 74.88 74.56 73.38
Al2O3 15.04 15.56 15.65 15.59 16.08 14.41 14.70 13.74 14.23 14.71
Fe2O3 1.48 1.61 1.80 1.95 2.09 0.88 1.01 0.66 0.75 0.95
FeO 0.44 0.43 0.71 0.50 0.72 0.58 0.62 0.43 0.39 0.54
CaO 1.89 2.13 3.18 2.56 3.63 0.99 1.04 0.96 0.82 1.04
MgO 0.61 0.47 0.89 0.53 1.01 0.30 0.32 0.25 0.22 0.26
K2O 1.72 1.59 1.98 1.53 2.02 4.25 4.49 4.67 4.52 4.46
Na2O 5.99 6.11 5.52 6.07 5.47 4.07 3.97 3.72 3.95 3.97
TiO2 0.22 0.23 0.28 0.26 0.29 0.20 0.20 0.13 0.14 0.18
P2O5 0.06 0.06 0.08 0.07 0.09 0.06 0.07 0.04 0.05 0.06
MnO 0.03 0.03 0.04 0.05 0.05 0.06 0.06 0.04 0.04 0.05
LOI 0.23 0.16 0.33 0.11 0.36 0.30 0.61 0.29 0.09 0.12
Tatal 99.57 99.66 99.70 99.71 99.72 99.73 99.71 99.81 99.76 99.72
K2O+Na2O 7.71 7.70 7.50 7.60 7.49 8.32 8.46 8.39 8.47 8.43
A/CNK 1.0 1.0 0.9 1.0 0.9 1.1 1.1 1.1 1.1 1.1
A/NK 1.3 1.3 1.4 1.3 1.4 1.3 1.3 1.2 1.2 1.3
σ 2.1 2.1 2.1 2.1 2.3 2.3 2.4 2.2 2.3 2.3
R1 2201 2146 2115 2111 2028 2421 2329 2542 2472 2391
R2 380 404 538 453 596 262 271 250 238 268
Rb 62.2 42.7 69.7 53.1 73.8 208 201 174 201 214
Ba 2030 1400 1280 1070 1130 1480 1560 1040 1300 1520
Th 6.27 3.90 5.11 3.59 3.61 25.00 24.40 16.60 19.80 24.00
U 8.48 5.83 1.48 3.32 0.98 2.17 2.06 1.78 2.32 2.11
Ta 0.28 0.23 0.28 0.27 0.29 1.46 1.26 0.78 1.05 1.31
Nb 41.70 30.80 10.40 17.90 8.17 22.50 20.00 12.70 17.00 21.00
Pb 277.00 191.00 183.00 205.00 170.00 41.80 43.40 39.90 36.50 38.90
Sr 1530 1280 1020 1340 988 579 580 425 477 552
Zr 125.00 113.00 144.00 145.00 142.00 29.40 150.00 84.50 103.00 161.00
Hf 3.50 3.01 3.74 3.99 3.62 0.96 4.34 2.41 3.00 4.82
Y 23.00 29.10 30.00 15.60 28.50 11.50 10.80 6.06 6.80 9.95
Ga 18.3 16.7 20.9 19.7 20.1 21.8 21.0 16.8 18.7 20.8
La 49.60 23.10 31.60 20.80 24.50 33.30 25.20 15.60 19.80 23.50
Ce 75.80 34.20 46.80 35.20 40.10 83.20 67.00 43.80 50.20 65.20
Pr 8.25 4.06 5.44 3.85 4.86 7.75 6.10 3.66 4.57 5.64
Nd 26.90 13.10 16.90 12.50 14.40 24.50 19.20 11.40 14.30 18.10
Sm 4.06 1.96 2.44 1.95 2.27 3.95 3.36 1.93 2.36 3.15
Eu 1.36 0.71 0.84 0.67 0.81 1.00 0.90 0.58 0.70 0.89
Gd 2.67 1.47 1.79 1.42 1.81 2.94 2.46 1.45 1.73 2.38
Tb 0.38 0.20 0.24 0.21 0.26 0.41 0.35 0.23 0.27 0.32
Dy 1.55 0.89 0.97 0.93 1.18 2.04 1.77 1.02 1.24 1.70
Ho 0.29 0.18 0.18 0.18 0.22 0.36 0.34 0.19 0.22 0.32
Er 0.74 0.48 0.52 0.49 0.62 1.03 1.00 0.55 0.62 0.89
Tm 0.11 0.07 0.08 0.08 0.10 0.15 0.14 0.09 0.10 0.14
Yb 0.68 0.46 0.45 0.48 0.62 0.96 0.97 0.55 0.61 0.90
Lu 0.10 0.07 0.07 0.07 0.10 0.15 0.14 0.09 0.09 0.14
REE 172.49 80.95 108.32 78.83 91.84 161.74 128.93 81.13 96.81 123.27
LREEN/HREEN 10.92 8.77 10.51 8.20 7.63 7.65 6.74 7.08 7.44 6.76
(La/Yb)N 49.41 34.02 47.57 29.35 26.77 23.50 17.60 19.21 21.99 17.69
(La/Sm)N 7.68 7.41 8.15 6.71 6.79 5.30 4.72 5.08 5.28 4.69
(Gd/Yb)N 3.18 2.59 3.23 2.40 2.37 2.48 2.06 2.14 2.30 2.14
δEu 1.25 1.27 1.22 1.22 1.21 0.89 0.95 1.05 1.05 0.99
δCe 0.82 0.79 0.79 0.88 0.84 1.20 1.26 1.35 1.23 1.32
10000×Ga/Al 2.30 2.03 2.52 2.39 2.36 2.86 2.70 2.31 2.48 2.67
NOTE: Abbreviations- LREE: light rare earth element; HREE: heavy rareearth element; REE: rare-earth element; LOI: loss on ignition; σ = (K2O+Na2O)2/(SiO2-43); Mg# = Mg2+/(Mg2+ + Fe2+) molar ratio; R1 = 4Si4+-11 × (Na+ + K+) - 2 × (Fe3+ + Fe2+ + Ti4+) molar ratio; R2 = 6Ca2+ + 2Mg2+ + Al3+, molar ratio; A/CNK = 2Al3+/(Ca2+ + 2Na+ + 2K+) molar ratio; A/NK = Al3+/(Na+ + K+) molar ratio; δEu = EuN/SQRT (SmN × GdN) ; δCe = 2CeN/(LaN × PrN). Symbol with “N” denotes the values normalised to chondrite (modified from [26]).
Table 5. Hf isotope results of zircons from the U-rich granitic pegmatite.
Table 5. Hf isotope results of zircons from the U-rich granitic pegmatite.
Site number Age (Ma) 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf ±2σ ƒLu/Hf εHf (t) TDM1 (Ga) TDM2 (Ga)
D43-Hf 1 1800 0.028578 0.000703 0.281458 0.000026 -0.98 -17.96 2.49 2.91
D43-Hf 2 1862 0.019464 0.000491 0.281447 0.000027 -0.99 -16.48 2.49 2.91
D43-Hf 6 1819 0.012029 0.000361 0.281430 0.000025 -0.99 -18.04 2.51 2.95
D43-Hf 9 1838 0.016209 0.000414 0.281464 0.000025 -0.99 -16.41 2.46 2.84
D43-Hf 10 1850 0.011812 0.000311 0.281407 0.000022 -0.99 -17.99 2.53 2.98
D43-Hf 12 1838 0.013678 0.000342 0.281413 0.000026 -0.99 -18.11 2.53 2.96
D43-Hf 21 1874 0.016944 0.000438 0.281359 0.000024 -0.99 -19.23 2.61 3.10
D43-Hf 23 1808 0.017472 0.000438 0.281431 0.000024 -0.99 -18.38 2.51 2.93
D43-Hf 25 1832 0.017730 0.000468 0.281436 0.000024 -0.99 -17.61 2.50 2.90
D43-Hf 29 1808 0.040893 0.000984 0.281420 0.000027 -0.97 -19.42 2.56 2.99
D45-Hf 8 1828 0.022944 0.000590 0.281423 0.000020 -0.98 -18.34 2.53 2.96
D45-Hf 9 1837 0.027094 0.000690 0.281484 0.000022 -0.98 -16.04 2.45 2.83
D45-Hf 10 1845 0.031770 0.000795 0.281511 0.000023 -0.98 -15.02 2.42 2.77
D45-Hf 11 1860 0.011456 0.000315 0.281452 0.000019 -0.99 -16.12 2.47 2.85
D45-Hf 12 1824 0.008961 0.000246 0.281485 0.000019 -0.99 -15.79 2.42 2.80
D45-Hf 13 1857 0.018569 0.000512 0.281492 0.000019 -0.98 -15.03 2.43 2.78
D45-Hf 14 1850 0.035348 0.000940 0.281490 0.000019 -0.97 -15.83 2.46 2.83
D45-Hf 26 1808 0.046560 0.001192 0.281539 0.000022 -0.96 -15.47 2.41 2.76
D45-Hf 27 1788 0.024690 0.000661 0.281465 0.000021 -0.98 -17.95 2.48 2.90
D45-Hf 30 1841 0.078297 0.002007 0.281534 0.000025 -0.94 -15.82 2.47 2.82
NOTE: εHf(t) = ((176Hf/177Hf)S - (176Lu/177Hf)S × (eλt-1))/((176Hf/177Hf)CHUR,0 - (176Lu/177Hf)CHUR × (eλt-1))-1) × 10,000; tDM1(Ma) = 1/λ × ln(1+((176Hf/177Hf)S-(176Hf/177Hf)DM)/((176Lu/177Hf)S-(176Lu/177Hf)DM)); tDM2(Ma) = tDM1-(tDM1-t)(( ƒCC-ƒS)/( ƒCC-ƒDM)); ƒLu/Hf = (176Lu/177Hf)S/(176Lu/177Hf)CHUR-1; ƒCC,ƒS, and ƒDM are ƒLu/Hf values of continental crust, zircon samples and depleted mantle, respectively. Subscript with “S” denotes zircon samples analysed. Subscript with “CHUR” denotes Chondrite standard library. Subscript with “DM” denotes depleted mantle. (176Lu/177Hf)CHUR = 0.0332; (176Hf/177Hf)CHUR,0 = 0.282772; (176Lu/177Hf)DM = 0.0384; (176Hf/177Hf)DM = 0.28325; λ = 1.865 × 10-11ar-1.
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