2022 Volume 56 Issue 3 Pages 74-95
The Changjiang U ore field developed typical granite-related U mineralization in the Zhuguangshan complex, China. Pitchblende is the most important ore mineral in these mineralizations. In this study, the mineralogy and geochemistry of pitchblende were investigated by electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) to identify the genesis of the Changjiang U ore field. Pitchblende exhibits colloidal, fragmented, spherulitic and fine-grained crystals in U ores. Its geochemical compositions are similar to those of other granite-related U deposits in South China, which have elevated contents of U, Sr, As and W; low contents of Pb, Th, Zr, Nb, Ta, Hf, Co, Ni and rare earth elements (REEs); and variable amounts of Ca, Si, Bi, Y, V and Zn. These geochemical signatures suggest that mineralization occurred through hydrothermal genesis and that the hosting Youdong and Changjiang granites acted as the dominant U sources. The uraninite in these granites might be the major U source mineral. Uranium mineralization occurred under the following conditions: low temperature (<250°C), low oxygen fugacity (log fO2 = –29.5 – –25.5), weakly acidic (pH = 5.3–5.9), high CO32– and F– contents and a silicon-saturated solution. Rapid changes in the physicochemical conditions of the ore-forming fluid are responsible for the precipitation of pitchblende. Combined with previous studies, we propose that U-rich granites, Cretaceous-Tertiary crustal extensions, regional faults and hydrothermal alterations were the critical factors for U formation in the Changjiang ore field.
The South China U Province (SCUP) is the most important U metallogenic region in China and has produced major U products during the past several decades (Hu et al., 1993, 2008; Dahlkamp, 2009; Bonnetti et al., 2018). Based on the lithology of host rocks, the U deposits in the SCUP have been classified as granite-related, volcanic-related and carbonaceous-siliceous-pelitic-related U deposits (Du et al., 1982; Min, 1995; Min et al., 1999; Hu et al., 2008; Luo et al., 2015). These deposits mainly occur in the granites of the Nanling magmatic belt, in the volcanic rocks of the Ganhang volcanic belt and in the carbonaceous and siliceous pelitic sedimentary rocks along the Jiangnan Orogen (Hu et al., 2008; Luo et al., 2015; Zhang et al., 2020). The granite-related U deposits in the SCUP generally display close spatial and genetic relationships with several typical granitic complexes, such as Miao’ershan, Taoshan, Guidong and Zhushuangshan (Min et al., 2005; Hu et al., 2008; Zhao et al., 2011, 2016; Chi et al., 2020; Zhang et al., 2020, 2021). These deposits formed in six episodes, namely, ~140 Ma, ~120 Ma, ~100 Ma, ~90 Ma, ~70 Ma and ~50 Ma, which kept pace with the activity of Cretaceous–Paleogene mafic magma and a red bed basin in this region (Hu et al., 2004, 2008; Luo et al., 2015, 2017).
The Changjiang ore field, a large-scale granite-related U ore field in the SCUP, is situated in the Zhuguangshan granitic complex of the Nanling magmatic belt (Fig. 1, Dahlkamp, 2009; Huang et al., 2010; Zhang et al., 2017a, 2017b). It was discovered in the late 1950s, covers a mineralization area of approximately 60 km2 and is hosted by Triassic Youdong granite and Jurassic Changjiang granite. There are five endogranitic U deposits, namely, Shulouqiu (SLQ), Mianhuakeng (MHK), Changpai (CP), Youdong (YD) and Changkeng (CK), and several occurrences, which contain >10,000 tons of ore with recoverable ore grades of 0.10–0.50% (Fig. 2, Zhang et al., 2017a). Since the 1980s, the geology and geochemistry of these deposits have been extensively studied to reveal their genesis (Hu et al., 2008; Huang et al., 2010; Bonnetti et al., 2018; Zhang et al., 2017a, 2017b, 2018, 2021; Zhong et al., 2019; Sun et al., 2021). However, the metallogeny of these U deposits is still controversial. For example, several models have been proposed to explain the U mineralization in the Changjiang ore field, including magmatic-hydrothermal (Jin and Hu, 1988), hotspot (Li, 2006), mantle-derived mineralizer (Hu et al., 2008; Luo et al., 2015; Zhang et al., 2017b), supergene (Fu et al., 2016), and basin models (Zhang et al., 2017a, 2020).
Geological sketch displaying the distribution of granite intrusions and U deposits in the Zhuguangshan complex from northern Guangdong Province, China, from Deng et al. (2011).
(a) Geological sketch of the Changjiang U ore field showing the relationship among the U deposits, magmatic rocks and faults from Zhang et al. (2017a); (b–d) simplified geological cross-sections.
Uraninite (UO2) is a cubic crystal tetravalent U mineral and a magmatic U-bearing accessory mineral in granite (Fryer and Taylor, 1987; Zhang et al., 2021). Pitchblende, a fine-grained aggregate of uraninite, is an important ore mineral in many U deposits worldwide (Cuney, 2009, 2014). Its chemical formula is ideally UO2 but is actually (U4+1–x–y–zU6+xREE3+yM2+z)O2+x–(0.5y)–z (Janeczek and Ewing, 1992). Pitchblende with a fluorite-type structure can accommodate a large number of impurities (e.g., W and Mo) and trivalent (e.g., Y and rare earth elements (REEs)) and divalent (e.g., Pb and Ca) cations. In many previous studies, its geochemical compositions have been widely used to trace the source, physicochemical conditions and hydrothermal fluid of U deposits (Fryer and Taylor, 1987; Janeczek and Ewing, 1992; Mercadier et al., 2011; Frimmel et al., 2014; Bonnetti et al., 2018). Thus, pitchblende has been considered an ideal tool to reveal the metallogenic mechanism of U deposits that occur in different geological backgrounds (Depiné et al., 2013; Spano et al., 2017; Zhang et al., 2017c, 2021; Martz et al., 2019; Grare et al., 2021).
In this study, the mineralogy and geochemistry of pitchblende are investigated and used to trace the metal source, physicochemical environments and genesis of the Changjiang U ore field. Our study provides new insight into the interpretation of the metallogenic mechanism of granite-related U deposits in South China.
The South China Block is composed of the Yangtze Block and the Cathaysia Block, which contain Mesozoic granitoid-related polymetallic mineralization, such as W, Sn, Mo, Au, Pb-Zn, Nb-Ta, U, Cu and REE deposits (Hu et al., 2004, 2008; Hu and Zhou, 2012; Pirajno, 2013; Zhang et al., 2020). The Yangtze Block is composed of an Archean-Paleoproterozoic metamorphic basement, whereas the Cathaysia Block consists of Neoproterozoic subblocks, including the Yunkai, Nanling, and Wuyi massifs (Wang et al., 2020). Enormous Triassic and Jurassic igneous rocks widely cover the South China Block, and most of them are spatially and genetically close to polymetallic deposits, such as the Zhuguangshan complex associated with uranium mineralization (Hu and Zhou, 2012; Bonnetti et al., 2018, 2020).
The Zhuguangshan complex (>4000 km2) is located in the middle part of the Nanling magmatic belt, which intruded into Cambrian, Ordovician, Devonian and Carboniferous sedimentary rocks. This complex was formed by a multistage granitic batholith, including Silurian, Triassic, and Jurassic granites and minor Jurassic–Cretaceous mafic dikes (Fig. 1, Zhou et al., 2006; Zhang et al., 2018). The Silurian intrusions in this area are migmatitic granite, gneissic granite and granodiorite. Triassic and Jurassic intrusions include medium- to coarse-grained biotite granite and two-mica granite. Most granites within the Zhuguangshan complex are geochemically classified as peraluminous S-type granites (Zhu, 2010; Huang et al., 2012, 2014). It is noteworthy that this complex has elevated U concentrations of 9–27 ppm (Dahlkamp, 2009; Zhang et al., 2018), several times that of the upper continental crust (2.7 ppm, Rudnick et al., 2003). Three stages of diabasic dykes (~140 Ma, ~105 Ma and ~90 Ma) have been identified in the Zhuguangshan district (Li et al., 1997). These diabasic dykes with lengths of 200–1000 m and widths of 5–30 m occur along E-W-, NE-, and N-S-trending faults.
In the Zhuguangshan area, the fault system mainly consists of NE-, NW-, E-W-, and N-S-trending faults (Fig. 1). The NE-trending Nanxiong fault belongs to a regional deep-large fault with a low-angle dip and experienced multiple tectonic activities during the Jurassic–Cretaceous period (Li and Zou, 2011). This fault delineates the boundary of the Zhuguangshan complex and the Nanxiong red basin (Fig. 1). The Zhuguangshan complex has been separated by several NE-trending faults, forming five fault depressions in the SE part (Shu et al., 2004).
Seven economic U ore fields (Lujing, Changjiang, Chengkou, Baishun, Lanhe, Sanjiu, and Quanan ore fields) and occurrences are present in the Zhuguangshan complex (Fig. 1, Huang et al., 2010; Zhong et al., 2019). Seven large-scale U deposits are located in these ore fields, including the Mianhuakeng (MHK), Dongkeng, Lujing and Lanhe deposits. In these deposits, most ore bodies are hosted in NE- and N-S-trending fracture structures (Sun et al., 2021). Two types of U ores have been identified in these deposits, termed red ore and black ore (Dahlkamp, 2009), which occur in the Changjiang and Baishun ore fields, respectively.
In the Changjiang U ore field, the rocks that dominantly crop out are the Triassic Youdong granite and Jurassic Changjiang granite, and sedimentary and metamorphic rocks are absent (Fig. 2). The intrusion age of the Youdong granite is ca. 226 Ma, and that of the Changjiang granite is ca. 160 Ma (Zhang et al., 2017b, 2018). The Youdong granite is a medium- to coarse-grained two-mica granite with K-feldspar (33%), plagioclase (28%), quartz (30%), biotite (5%) and muscovite (5%). This granite has an accessory mineral assemblage of zircon, uraninite, apatite, monazite and ilmenite (Fig. 3a–b). The Changjiang granite is a medium- to fine-grained granite consisting of K-feldspar (35%), plagioclase (30%), quartz (30%) and biotite (5%). Its accessory mineral assemblages are zircon, uraninite, apatite, monazite, allanite, xenotime, uranothorite and magnetite (Fig. 3c–d). A few granitic and diabasic dykes occur along E-W- and NE-trending faults. In this ore field, the major faults are the NE-trending MHK, Lizhou, and Huangxishui faults, N-S-trending faults and the NW-trending Youdong fault. The N-S-trending faults are silicified fractured zones with widths of 2–3 m and lengths of 5–10 km.
BSE images of U-bearing minerals in the Youdong and Changjiang granites. (a–b) Uraninite, monazite, zircon, apatite and xenotime hosted by the Youdong granite. (c–d) Uraninite, zircon, monazite and apatite hosted by Changjiang granite. (e) Uraninite hosted by monazite in Changjiang granite. (d) Altered monazite and U silicate phases in Changjiang granite. Alt Mnz = altered monazite, Ap = apatite, Bt = biotite, Chl = chlorite, Kfs = K-feldspar, Qtz = quartz, Xtn = xenotime, Zr = zircon.
Three large-scale (SLQ, MHK, and CP) and two small-scale (KD and YD) U deposits were verified in the Changjiang ore field (Fig. 2a). The SLQ deposit is hosted by the Changjiang granite (Fig. 2b). However, MHK and CP deposits are hosted by both the Youdong and Changjiang granites (Fig. 2c–d). Most of the ore bodies 1–20 m wide and 50–600 m long occur in the high-angle N-S-trending fractured zones. Among them, the No. 9 ore body is the largest and contains more than 60% of the U resources in the Changjiang ore field. The vertical length of the No. 9 ore body exceeds 1100 m (from the 500 m level to the –647 m level), with the ore grade varying from 0.10% to 1.50% (Fig. 2c, Huang et al., 2010).
The ore bodies are U-bearing red microcrystalline quartz, grayish white calcite and purple black fluorite veins 30–200 mm in width. Pitchblende is the main ore mineral in these veins and occurs as botryoidal aggregates, angular pebbles, veins, veinlets and stockworks. The U–Pb ages of pitchblende suggest that the main U mineralization in the Changjiang ore field formed at ~70 Ma (Huang et al., 2010; Zhang et al., 2017b; Zhong et al., 2019). The gangue minerals include microcrystalline quartz, fluorite, calcite, pyrite and galena. The hydrothermal alterations around the ore bodies include hydromicazation, silicification, chloritization, hematitization, sericitization, fluoritization and carbonatation.
Based on microscopic observations and previous studies (Zhang et al., 2017a), the mineral paragenesis of mineralization and alterations in the Changjiang ore field can be divided into four stages: the magmatic, pre-ore, syn-ore and post-ore stages (Fig. 4). The magmatic stage includes K-feldspar, plagioclase, quartz, biotite, muscovite and minor accessory minerals in the Youdong and Changjiang granites. The pre-ore stage is characterized by the mineral assemblages of abundant chlorite, sericite and hydromuscovite; local quartz and albite; and trace pyrite, calcite and hematite. Biotite in granite is completely replaced by chlorite, and feldspar is replaced by sericite and hydromuscovite. The K-feldspar crystal is partly altered to albite. The syn-ore stage contains microcrystalline quartz, chlorite, purple–black fluorite, nebulous hematite, hydromuscovite, sericite, colloidal pyrite, grayish calcite and pitchblende. The post-ore stage consists of jade-green fluorite, white calcite, euhedral pyrite and comb-like quartz.
Mineral paragenesis in the Changjiang U ore field, including the magmatic, pre-ore, syn-ore and post-ore stages.
Four Youdong and Changjiang granite samples and two diabase samples were selected from drill cores in the Changjiang ore field. Six mineralized samples were selected from the No. 9 ore body in drill cores and mining tunnels, and the sampling locations are marked in the geological cross-sections (Fig. 2b–d). These samples were made into thin sections for in situ analysis and powders for geochemical analysis.
The whole-rock U, Th and REE contents were analyzed at the American Laboratory Services (ALS) Chemex (Guangzhou, China) Co., Ltd. The analysis process contained the dissolution of 40 mg powder samples in HF and HNO3, dilution to 1% HNO3, and analysis via Agilent 7850 ICP–MS. The analytical precision of ICP–MS is better than ±5% for REEs, Th and U.
The microscopy investigation of samples was carried out at the State Key Laboratory of Nuclear Resources and Environment, East China University of Technology (China) using an optical microscope (Zeiss Axio Scope. A1), scanning electron microscopy (SEM, Nova NanoSEM 450) and JEOL JXA-8100 EPMA. The EPMA operating conditions were as follows: a 15 kV accelerating voltage, a beam current of 50 nA and a beam diameter of 1–5 μm. The analyzed data were corrected by the built-in ZAF program. The analysis standards were metal and natural minerals, including UO2 (U), thorianite (Th), PbCr2O4 (Pb), rhodonite (Mn), periclase (Mg), anorthite (Ca), Fe2O3 (Fe), rutile (Ti), albite (Si), jadeite (Na), barite (Ba), apatite (P) and plagioclase (Al). The limit of detection is 200 ppm. The analysis error was better than 1.5% for major elements and 5.0% for trace elements.
Trace element analysis was carried out on pitchblende using LA–ICP–MS at Wuhan Sample Solution Analytical Technology Co., Ltd., Wuhan, China. The detailed operating conditions of the laser ablation system and the ICP–MS instrument and data processing were described by Zong et al. (2017). Laser sampling was performed using a GeoLasPro laser ablation system that consisted of a 193 nm COMPexPro ArF excimer laser and a MicroLas optical system. An Agilent 7700e ICP–MS instrument was used to acquire ion-signal intensities. Helium was applied as a carrier gas to transport the aerosol from the ablation cell to the ICP–MS instrument. Argon as the make-up gas was mixed with the carrier gas via a T-connector before entering the ICP. Rare earth elements (139La, 140Ce, 141Pr, 146Nd, 147Sm, 153Eu, 157Gd, 159Tb, 163Dy, 165Ho, 166Er, 169Tm, 172Yb and 175Lu) and twenty trace elements (9Be, 49Ti, 51V, 52Cr, 59Co, 60Ni, 66Zn, 75As, 88Sr, 89Y, 90Zr, 93Nb, 95Mo, 118Sn, 137Ba, 178Hf, 181Ta, 182W, 209Bi and 232Th) were analyzed. The spot size of the laser system was 32–44 μm depending on the size of the target minerals. In this study, the frequency and energy density of the laser were set to 3 Hz and 5 J/cm–2, respectively. Certified USGS glass standards NIST 610, BVHO-2G, BIR-1G and BCR-2G (Pearce et al., 1997) were used as reference materials to calibrate the trace element compositions in the analyzed minerals. The U content of pitchblende obtained by the electron probe was used as the internal standard to correct the trace element results. Every spot analysis consisted of a background acquisition of approximately 20–30 s followed by 50 s of data acquisition. The Excel-based software ICPMSDataCal 10.9 was used to perform offline selection and integration of background and analyzed signals, time-drift correction and quantitative calibration for trace element analysis (Liu et al., 2008).
In the SLQ deposit, U mineralization presents a close relationship with microcrystalline quartz and fluorite (Fig. 5a). In backscattered electron (BSE) images, U mineralization is characterized by abundant pitchblende, pyrite, microcrystalline quartz and fluorite (Fig. 5b–c). Biotite was completely replaced by chlorite. Pitchblende shows fragmented, spherulitic and fine grains cemented by microcrystalline quartz and fluorite (Fig. 5c).
Photographs and BSE images of representative U ores in the Changjiang U ore field. (a) Fluorite vein related to uranium mineralization (sample SLQ1603). (b) Botryoidal pitchblende associated with fluorite and pyrite. (c) Pitchblende associated with fluorite and microcrystalline quartz. (c) Calcite and pitchblende occur at the diabase (sample MHK1519). (e) Globular pitchblende cemented by calcite. (f) Pitchblende associated with calcite. (g) Microcrystalline quartz vein related to uranium mineralization (sample CP1603). (h) Subidiomorphic pitchblende associated with microcrystalline quartz. (i) Idiomorphic pitchblende associated with microcrystalline quartz, pyrite and galena. Abbreviations: Ab = albite, Cal = calcite, Chl = chlorite, Cof = coffinite, Fl = fluorite, Gn = galena, Hem = hematite, Hym = hydromica, Micro Qtz = microcrystalline quartz, Pit = pitchblende, Py = pyrite, Qtz = quartz. Red circles represent the locations of the LA–ICP–MS spots.
In the MHK deposit, U mineralization is closely related to calcite, pyrite, hematite, and microcrystalline quartz (Fig. 5d). The BSE images show that pitchblende is cemented by idiomorphic calcite and microcrystalline quartz (Fig. 5e). In sample MHK1519, part of the globular pitchblende transformed into coffinite (Fig. 5f). Abundant idiomorphic pitchblende occurs along the pyrite rims and is cemented by microcrystalline quartz. Galena is commonly cemented by pitchblende.
In the CP deposit, U mineralization is associated with hematite, microcrystalline quartz, calcite, pyrite and albite (Fig. 5g). Abundant pyrite, pectinate quartz and calcite occur as veins in sample CP1601. In BSE images, there are irregular, fragmental and spherulitic morphologies of pitchblende, which show a close relationship with pyrite and microcrystalline quartz (Fig. 5h–i). In sample CP1603, a notable amount of spherulitic pitchblende is identified, which is usually in the form of aggregates (Fig. 5h). The spherulitic pitchblende is locally surrounded by xenomorphic pyrite and galena (Fig. 5i).
Pitchblende geochemistry from oresThe major and trace element compositions in pitchblende from the SLQ, MHK and CP deposits are listed in Table 1 and shown in Fig. 6, which present comparable geochemical signatures. Their compositions are similar to the pitchblende of granite-related U deposits in South China, such as the Xiwang deposit (Zhao et al., 1988; Bonnetti et al., 2018). The major elements are characterized by high UO2 (81.3–89.4%, median = 85.9%), varietal CaO (3.57–9.89%, median = 6.93%) and SiO2 (0.60–4.50%, median = 1.72%) and low Na2O (<0.46%), FeO (0.09–1.74%), Al2O3 (<1.05%), MnO (0.22–0.84%), P2O5 (<0.23%), MgO (<0.07%), TiO2 (<0.49%), BaO (<0.32%), ThO2 (<0.09%) and PbO (<2.21%) contents. Most of the ThO2 in pitchblende is below the detection limit of the electron probe (<0.01%).
| Elements / Spots | Sample MHK1519 | Sample CJ16153 | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | |
| Na2O | 0.39 | 0.40 | 0.39 | 0.27 | 0.25 | 0.30 | 0.37 | 0.42 | 0.17 | 0.12 | 0.08 | 0.05 | 0.08 | 0.20 | 0.08 | 0.26 | 0.35 | 0.09 | 0.03 | 0.18 |
| SiO2 | 2.45 | 2.38 | 2.35 | 2.22 | 2.31 | 2.22 | 2.35 | 2.41 | 1.34 | 1.00 | 1.27 | 1.34 | 1.09 | 1.37 | 1.06 | 1.80 | 1.28 | 1.88 | 1.18 | 1.99 |
| FeO | 0.69 | 0.70 | 0.67 | 0.68 | 0.65 | 0.70 | 0.62 | 0.69 | 0.21 | 0.32 | 0.11 | 0.12 | 0.16 | 0.17 | 0.16 | 0.09 | 0.20 | 0.11 | 0.32 | 0.16 |
| Al2O3 | 0.25 | 0.27 | 0.18 | 0.21 | 0.20 | 0.18 | 0.19 | 0.20 | bdl | 0.09 | 0.07 | 0.06 | 0.08 | 0.05 | 0.14 | 0.83 | 0.91 | 0.09 | 0.10 | 0.90 |
| MnO | 0.36 | 0.31 | 0.36 | 0.32 | 0.28 | 0.28 | 0.24 | 0.30 | 0.77 | 0.49 | 0.57 | 0.56 | 0.51 | 0.55 | 0.67 | 0.48 | 0.41 | 0.64 | 0.56 | 0.53 |
| P2O5 | 0.07 | 0.10 | 0.01 | 0.09 | 0.09 | 0.08 | 0.11 | 0.07 | bdl | 0.04 | 0.01 | 0.17 | bdl | bdl | 0.04 | 0.08 | 0.02 | 0.03 | bdl | 0.12 |
| MgO | 0.03 | 0.03 | 0.02 | 0.01 | 0.05 | 0.02 | 0.02 | 0.01 | bdl | 0.04 | 0.01 | bdl | bdl | bdl | bdl | 0.04 | 0.04 | bdl | bdl | 0.02 |
| UO2 | 88.9 | 89.4 | 89.4 | 87.6 | 87.0 | 88.3 | 88.4 | 88.6 | 86.9 | 85.3 | 86.8 | 88.0 | 86.3 | 85.2 | 87.0 | 84.6 | 86.6 | 85.1 | 86.2 | 85.9 |
| TiO2 | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | 0.03 | 0.02 | 0.05 | 0.11 | bdl | bdl | bdl | bdl | 0.09 | bdl |
| CaO | 5.73 | 5.62 | 5.30 | 5.40 | 6.24 | 5.39 | 5.56 | 5.31 | 6.36 | 7.15 | 6.76 | 5.56 | 7.82 | 8.94 | 4.79 | 6.54 | 4.95 | 8.09 | 9.75 | 7.47 |
| BaO | 0.18 | 0.16 | 0.11 | 0.06 | 0.05 | 0.14 | 0.06 | 0.08 | 0.01 | bdl | 0.15 | 0.17 | 0.13 | bdl | 0.20 | bdl | bdl | 0.11 | 0.01 | 0.07 |
| ThO2 | 0.01 | bdl | bdl | bdl | 0.01 | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | 0.01 | bdl | bdl | bdl | bdl |
| PbO | 0.79 | 0.89 | 0.87 | 1.03 | 0.80 | 0.78 | 1.06 | 0.77 | 0.48 | 0.26 | 0.60 | 0.44 | 0.45 | 0.26 | 0.62 | 0.35 | 0.19 | 0.58 | 0.66 | 0.15 |
| Total | 99.9 | 100.2 | 99.7 | 97.9 | 97.9 | 98.4 | 99.0 | 98.9 | 96.2 | 94.8 | 96.4 | 96.5 | 96.7 | 96.9 | 94.8 | 95.1 | 95.0 | 96.7 | 98.9 | 97.5 |
| Ta | bdl | 0.05 | bdl | bdl | 0.03 | bdl | 0.06 | 0.03 | 0.49 | 0.49 | 0.64 | 0.95 | 0.90 | 0.75 | 0.28 | 0.16 | 0.65 | 0.16 | 0.07 | bdl |
| W | 3332 | 4552 | 3963 | 5005 | 5046 | 3204 | 3002 | 3330 | 1123 | 1240 | 780 | 2089 | 2750 | 2440 | 2537 | 2362 | 2344 | 3401 | 3622 | 3531 |
| Th | bdl | bdl | 0.07 | bdl | 0.09 | bdl | bdl | bdl | 0.10 | 0.02 | 0.01 | 0.07 | 0.09 | 0.05 | bdl | 0.27 | 0.09 | 0.03 | 0.02 | 0.09 |
| Be | 65.3 | 68.2 | 73.0 | 86.4 | 87.6 | 90.4 | 76.7 | 89.9 | 80.3 | 86.4 | 115.1 | 12.4 | 28.4 | 16.7 | 40.7 | 35.0 | 27.3 | 55.6 | 57.6 | 38.6 |
| V | 1535 | 1436 | 1493 | 1328 | 1434 | 1182 | 1155 | 1610 | 54.5 | 57.4 | 54.4 | 17.3 | 20.0 | 22.0 | 16.7 | 19.8 | 18.4 | 17.6 | 22.1 | 16.5 |
| Cr | 15.7 | 1.7 | 4.4 | 5.4 | 17.9 | 20.3 | 1.4 | 14.2 | bdl | bdl | 9.21 | 17.9 | 9.22 | 19.6 | 8.23 | 17.9 | 19.2 | bdl | 17.2 | 21.6 |
| Co | bdl | bdl | bdl | 0.79 | 0.09 | bdl | 0.35 | bdl | 0.53 | 0.46 | 0.39 | bdl | bdl | 0.57 | 0.08 | bdl | bdl | bdl | bdl | 0.01 |
| Ni | bdl | 0.41 | bdl | bdl | 3.51 | bdl | bdl | bdl | bdl | bdl | 1.72 | 1.37 | 0.06 | bdl | bdl | 3.06 | bdl | 1.39 | 1.33 | bdl |
| Zn | 8.00 | 2.83 | 3.33 | 15.69 | 2.01 | bdl | 7.07 | 9.84 | bdl | 1.77 | 4.30 | bdl | bdl | 9.80 | 0.07 | 2.67 | 3.60 | 8.87 | 5.43 | 3.07 |
| Sr | 531 | 588 | 520 | 633 | 577 | 401 | 469 | 618 | 1089 | 1035 | 989 | 141 | 194 | 147 | 287 | 357 | 272 | 235 | 230 | 223 |
| Y | 130 | 214 | 90 | 247 | 190 | 596 | 657 | 177 | 515 | 610 | 644 | 525 | 648 | 599 | 645 | 574 | 729 | 831 | 784 | 736 |
| Zr | 0.09 | 0.02 | 0.10 | 0.08 | 0.45 | 0.67 | 0.75 | 3.83 | 3.62 | 3.81 | 2.73 | 0.35 | 2.63 | 0.26 | 0.08 | 0.65 | bdl | 0.19 | 0.27 | |
| Nb | 0.34 | bdl | 0.43 | bdl | bdl | 2.75 | 3.65 | 0.29 | 0.31 | 0.45 | 1.05 | 11.6 | 26.2 | 18.0 | 13.9 | 11.6 | 36.9 | 13.5 | 13.1 | 12.0 |
| Mo | 33 | 33 | 28 | 33 | 33 | 31 | 19 | 27 | 0.72 | 2.52 | 0.71 | 3.24 | 4.18 | 4.47 | 8.19 | 8.69 | 6.83 | 2.21 | 5.10 | 4.16 |
| Sn | 5.85 | 1.12 | bdl | bdl | 5.34 | 16.22 | bdl | 11.53 | 4.70 | bdl | bdl | 14.1 | 1.77 | 4.87 | 0.82 | bdl | bdl | bdl | bdl | 7.81 |
| Ba | 391 | 364 | 331 | 433 | 377 | 253 | 312 | 427 | 15.8 | 9.3 | 52.6 | 25.8 | 30.4 | 32.5 | 36.6 | 52.8 | 53.6 | 47.2 | 51.7 | 36.3 |
| As | 529 | 484 | 523 | 472 | 506 | 589 | 515 | 499 | 298 | 270 | 383 | 215 | 274 | 236 | 357 | 293 | 364 | 336 | 376 | 316 |
| Hf | bdl | 0.22 | 0.25 | 0.22 | 0.23 | 0.24 | 0.36 | 0.26 | 0.38 | 0.38 | 0.23 | 0.26 | bdl | 0.53 | 0.22 | 0.03 | 0.31 | bdl | 0.60 | bdl |
| Bi | 4.06 | 1.00 | 0.39 | 1.33 | 0.99 | 40.6 | 84.5 | 7.03 | 0.01 | 0.17 | 3.34 | 392 | 81.5 | 250 | 35.6 | 23.8 | 25.5 | 49.7 | 23.5 | 19.1 |
| La | 128 | 69 | 35 | 55 | 62 | 287 | 250 | 99 | 980 | 939 | 946 | 259 | 326 | 291 | 243 | 216 | 239 | 364 | 342 | 324 |
| Ce | 197 | 52 | 63 | 59 | 40 | 682 | 564 | 102 | 2100 | 2115 | 1831 | 947 | 1233 | 1074 | 905 | 826 | 893 | 1221 | 1218 | 1110 |
| Pr | 21.2 | 4.0 | 7.5 | 6.5 | 3.0 | 74.4 | 59.8 | 8.9 | 46.9 | 50.9 | 41.7 | 46.4 | 57.8 | 53.9 | 40.5 | 32.6 | 57.4 | 61.3 | 59.6 | 57.5 |
| Nd | 83 | 26 | 31 | 30 | 17 | 378 | 300 | 52 | 169 | 194 | 173 | 210 | 248 | 236 | 192 | 165 | 248 | 277 | 261 | 240 |
| Sm | 21.23 | 3.15 | 4.45 | 6.45 | 2.86 | 105 | 124 | 10.9 | 48.2 | 50.4 | 53.5 | 67.2 | 94.3 | 71.8 | 56.5 | 57.0 | 93.2 | 87.3 | 89.3 | 85.6 |
| Eu | 7.41 | 1.08 | 3.08 | 4.07 | 1.32 | 40.9 | 33.5 | 5.01 | 4.98 | 5.19 | 6.27 | 12.05 | 16.5 | 13.9 | 9.12 | 6.68 | 12.3 | 11.3 | 12.4 | 11.4 |
| Gd | 20.7 | 10.3 | 7.16 | 17.0 | 9.42 | 130 | 129 | 23.4 | 50.2 | 58.6 | 59.8 | 58.8 | 79.2 | 66.9 | 59.6 | 53.9 | 82.8 | 76.7 | 78.2 | 75.6 |
| Tb | 2.05 | 1.03 | 0.75 | 1.70 | 0.53 | 19.9 | 25.5 | 3.55 | 7.57 | 8.62 | 8.70 | 15.4 | 19.3 | 15.4 | 11.6 | 12.1 | 20.5 | 17.3 | 16.9 | 16.7 |
| Dy | 11.01 | 3.78 | 1.99 | 11.4 | 3.51 | 121 | 152 | 16.3 | 57.6 | 59.1 | 62.8 | 107 | 147 | 123 | 86.6 | 81.2 | 148 | 150 | 137 | 121 |
| Ho | 2.26 | 1.46 | 0.79 | 2.27 | 0.89 | 21.5 | 24.3 | 3.22 | 10.5 | 10.7 | 12.0 | 22.4 | 29.7 | 23.9 | 20.1 | 17.5 | 31.8 | 29.6 | 24.9 | 26.4 |
| Er | 4.24 | 2.62 | 1.90 | 5.30 | 3.19 | 60.7 | 59.7 | 5.46 | 26.4 | 30.9 | 32.5 | 71.8 | 110 | 82.2 | 62.0 | 58.3 | 116 | 105 | 96.7 | 88.7 |
| Tm | 1.14 | 0.31 | bdl | 0.64 | 0.42 | 5.83 | 8.66 | 0.48 | 4.63 | 4.85 | 5.17 | 13.1 | 18.6 | 16.5 | 10.2 | 9.72 | 20.7 | 17.9 | 17.5 | 15.8 |
| Yb | 4.62 | 3.01 | 2.17 | 2.63 | 2.55 | 46.0 | 53.7 | 4.00 | 30.4 | 32.0 | 31.9 | 89.0 | 138 | 105 | 65.6 | 60.0 | 151 | 127 | 113 | 99.9 |
| Lu | 0.77 | 0.71 | 0.36 | 0.46 | 0.44 | 4.80 | 6.25 | 0.55 | 3.28 | 3.96 | 4.05 | 10.5 | 15.6 | 15.1 | 8.62 | 9.58 | 17.8 | 16.1 | 13.1 | 13.0 |
| ΣREE | 505 | 178 | 159 | 202 | 147 | 1977 | 1791 | 335 | 3540 | 3563 | 3269 | 1930 | 2531 | 2188 | 1770 | 1606 | 2133 | 2561 | 2480 | 2286 |
| LREE | 458 | 155 | 144 | 161 | 126 | 1567 | 1331 | 278 | 3350 | 3354 | 3052 | 1542 | 1974 | 1740 | 1446 | 1304 | 1544 | 2022 | 1983 | 1828 |
| HREE | 47 | 23 | 15 | 41 | 21 | 410 | 459 | 57 | 191 | 209 | 217 | 388 | 557 | 449 | 324 | 302 | 589 | 540 | 497 | 457 |
| LREE/HREE | 9.80 | 6.68 | 9.51 | 3.88 | 6.02 | 3.82 | 2.90 | 4.88 | 17.6 | 16.1 | 14.1 | 3.97 | 3.55 | 3.88 | 4.46 | 4.32 | 2.62 | 3.74 | 3.99 | 4.00 |
| δEu | 0.49 | 0.49 | 0.74 | 0.51 | 0.72 | 0.28 | 0.32 | 0.56 | 0.30 | 0.29 | 0.34 | 0.57 | 0.56 | 0.60 | 0.47 | 0.36 | 0.42 | 0.41 | 0.44 | 0.42 |
| δCe | 0.84 | 0.51 | 0.88 | 0.64 | 0.45 | 1.10 | 1.08 | 0.65 | 1.48 | 1.53 | 1.35 | 1.93 | 2.01 | 1.93 | 2.01 | 2.13 | 1.78 | 1.81 | 1.90 | 1.82 |
| Elements / Spots | Sample SLQ1601 | Sample SLQ1603 | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | |
| Na2O | 0.03 | 0.08 | 0.06 | 0.06 | 0.11 | bdl | 0.04 | 0.07 | 0.04 | 0.08 | 0.05 | 0.17 | 0.19 | 0.05 | 0.17 | 0.05 | 0.16 | 0.09 | 0.14 | 0.12 | 0.05 | 0.06 |
| SiO2 | 1.35 | 1.67 | 2.89 | 1.80 | 3.78 | 1.61 | 1.59 | 3.51 | 3.21 | 1.06 | 3.67 | 4.50 | 4.50 | 3.24 | 2.57 | 2.36 | 2.59 | 2.73 | 3.18 | 2.53 | 1.34 | 3.12 |
| FeO | 0.31 | 0.31 | 0.47 | 0.28 | 0.50 | 0.35 | 0.30 | 0.20 | 0.20 | 0.16 | 0.43 | 0.34 | 0.27 | 0.37 | 0.48 | 0.52 | 0.30 | 0.13 | 0.23 | 0.15 | 0.12 | 0.33 |
| Al2O3 | 0.13 | 0.13 | 0.34 | 0.12 | 0.72 | 0.13 | 0.12 | 0.54 | 0.47 | 0.14 | 1.05 | 0.42 | 0.42 | 0.40 | 0.29 | 0.30 | 0.26 | 0.41 | 0.40 | 0.37 | 0.06 | 0.27 |
| MnO | 0.24 | 0.44 | 0.63 | 0.39 | 0.47 | 0.40 | 0.24 | 0.32 | 0.40 | 0.67 | 0.66 | 0.55 | 0.64 | 0.84 | 0.67 | 0.63 | 0.54 | 0.23 | 0.43 | 0.37 | 0.56 | 0.68 |
| P2O5 | 0.05 | bdl | 0.04 | 0.01 | bdl | 0.02 | 0.04 | bdl | 0.04 | 0.04 | 0.01 | bdl | bdl | bdl | 0.04 | 0.07 | 0.02 | 0.02 | bdl | 0.01 | 0.17 | 0.01 |
| MgO | 0.05 | 0.02 | 0.02 | 0.02 | bdl | 0.03 | 0.04 | 0.03 | bdl | bdl | 0.06 | 0.02 | bdl | bdl | bdl | bdl | bdl | 0.02 | 0.07 | 0.05 | bdl | bdl |
| UO2 | 82.2 | 83.0 | 82.1 | 84.8 | 83.1 | 84.2 | 83.3 | 83.6 | 84.4 | 89.0 | 83.2 | 83.9 | 85.2 | 85.3 | 87.2 | 86.3 | 85.3 | 84.2 | 84.5 | 84.5 | 86.0 | 81.3 |
| TiO2 | bdl | bdl | 0.13 | bdl | 0.13 | 0.02 | 0.13 | 0.12 | 0.02 | bdl | 0.44 | bdl | bdl | bdl | 0.01 | 0.03 | bdl | bdl | bdl | bdl | 0.02 | 0.02 |
| CaO | 8.66 | 9.89 | 6.75 | 7.25 | 6.86 | 9.61 | 7.00 | 8.22 | 8.98 | 5.79 | 4.31 | 7.52 | 7.53 | 7.68 | 6.84 | 7.43 | 8.70 | 8.48 | 9.16 | 8.66 | 6.56 | 8.82 |
| BaO | bdl | bdl | 0.09 | 0.12 | 0.05 | bdl | bdl | 0.32 | 0.17 | 0.20 | 0.14 | 0.05 | 0.05 | bdl | 0.08 | 0.17 | 0.14 | 0.07 | 0.14 | 0.18 | 0.17 | bdl |
| ThO2 | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | 0.02 | bdl |
| PbO | 0.91 | 0.54 | 0.50 | 0.52 | 0.12 | 0.78 | 0.83 | 1.07 | 0.74 | 0.04 | 0.64 | 0.32 | 0.39 | 0.55 | 0.74 | 0.67 | 0.70 | 1.39 | 1.14 | 1.47 | 0.17 | 2.06 |
| Total | 93.9 | 96.1 | 94.0 | 95.3 | 95.8 | 97.1 | 93.6 | 98.0 | 98.7 | 97.2 | 94.7 | 97.8 | 99.1 | 98.4 | 99.0 | 98.6 | 98.7 | 97.7 | 99.4 | 98.4 | 95.2 | 96.7 |
| Ta | 0.07 | bdl | 0.13 | 0.15 | bdl | 0.09 | 0.12 | 0.16 | bdl | 0.08 | 0.31 | 0.17 | 0.07 | 0.34 | 0.72 | 0.80 | 0.41 | 0.47 | bdl | 0.10 | 0.14 | 0.09 |
| W | 2068 | 3432 | 3168 | 2770 | 2740 | 2073 | 2048 | 2644 | 2456 | 1899 | 3145 | 3584 | 2833 | 3958 | 3578 | 3639 | 3496 | 3087 | 2479 | 2677 | 3519 | 3089 |
| Th | 0.06 | 0.03 | 0.02 | 0.08 | bdl | bdl | bdl | 0.08 | 0.09 | bdl | bdl | 0.06 | 0.05 | 0.09 | 0.05 | bdl | 0.09 | 0.01 | 0.03 | 0.09 | 0.01 | bdl |
| Be | 42.8 | 69.7 | 58.6 | 72.4 | 60.3 | 62.9 | 53.0 | 84.9 | 79.3 | 53.0 | 53.6 | 34.1 | 37.5 | 41.1 | 65.5 | 50.5 | 89.9 | 60.3 | 67.9 | 79.3 | 89.8 | 93.4 |
| V | 51.4 | 70.2 | 69.0 | 64.4 | 63.2 | 66.2 | 56.4 | 68.3 | 76.1 | 54.0 | 96.4 | 29.2 | 17.3 | 42.1 | 35.8 | 43.0 | 47.7 | 45.9 | 40.5 | 36.3 | 41.8 | 36.8 |
| Cr | bdl | 16.7 | bdl | 0.74 | 0.66 | 2.08 | 4.25 | 2.91 | bdl | bdl | 11.2 | bdl | 2.06 | 3.62 | bdl | 1.33 | 2.45 | bdl | 8.68 | 2.85 | bdl | 8.52 |
| Co | 0.26 | 0.23 | 0.38 | bdl | bdl | bdl | 0.20 | 0.15 | bdl | bdl | 0.50 | bdl | bdl | bdl | 0.61 | 0.80 | 0.12 | 0.18 | 0.24 | bdl | 0.22 | bdl |
| Ni | bdl | 2.93 | bdl | 0.55 | 1.19 | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | 0.03 | 1.63 | bdl | 0.72 | 0.58 | bdl | 1.97 | bdl | 0.56 |
| Zn | 0.99 | 1.65 | 2.71 | 1.55 | 0.14 | 4.00 | 0.69 | 0.98 | 6.21 | 1.61 | 0.09 | 2.66 | bdl | 0.03 | 2.14 | 1.60 | 3.31 | 2.08 | 0.81 | 2.09 | bdl | 22.14 |
| Sr | 71.5 | 100 | 92.7 | 94.0 | 82.8 | 92.6 | 83.1 | 96.2 | 110 | 64.3 | 116 | 149 | 83.6 | 202 | 115 | 165 | 141 | 128 | 119 | 132 | 115 | 145 |
| Y | 2036 | 2389 | 2864 | 1719 | 2223 | 5127 | 4880 | 6584 | 6045 | 4598 | 6563 | 579 | 832 | 435 | 1778 | 3588 | 2280 | 1719 | 1677 | 1754 | 1583 | 1688 |
| Zr | 2.99 | bdl | 0.19 | 0.36 | bdl | 0.02 | bdl | 0.66 | 0.05 | 0.02 | 0.15 | 0.09 | 0.88 | 1.01 | 0.09 | 1.30 | 0.72 | 1.69 | 1.41 | 0.52 | 0.40 | 0.07 |
| Nb | 2.45 | 12.22 | 9.93 | 14.21 | 1.56 | 2.94 | 7.19 | 14.77 | 17.77 | 5.57 | 123.00 | 70.53 | 49.83 | 169.91 | 88.76 | 255.63 | 94.55 | 46.17 | 1.65 | 2.43 | 15.79 | 4.19 |
| Mo | 388 | 504 | 352 | 390 | 364 | 183 | 116 | 406 | 224 | 154 | 191 | 126 | 48 | 707 | 374 | 1521 | 1080 | 645 | 551 | 480 | 279 | 523 |
| Sn | bdl | 0.20 | 2.06 | 1.00 | 2.60 | 3.35 | bdl | 1.70 | 11.70 | 4.50 | 4.91 | 2.07 | 5.16 | 7.68 | 4.62 | 10.90 | 2.64 | bdl | 3.81 | 1.60 | bdl | 1.62 |
| Ba | 22.9 | 32.4 | 27.1 | 34.2 | 21.7 | 35.1 | 35.1 | 34.0 | 34.5 | 25.1 | 38.9 | 14.1 | 26.6 | 27.0 | 26.5 | 28.5 | 26.8 | 27.5 | 30.8 | 36.1 | 29.5 | 37.3 |
| As | 842 | 1366 | 918 | 1248 | 999 | 657 | 595 | 988 | 602 | 766 | 810 | 898 | 836 | 977 | 909 | 1853 | 909 | 576 | 387 | 400 | 997 | 707 |
| Hf | 0.14 | 0.11 | bdl | 0.11 | bdl | bdl | 0.33 | 0.80 | bdl | 0.18 | 0.39 | bdl | bdl | 0.11 | 0.12 | 0.16 | bdl | bdl | 0.09 | bdl | 0.32 | bdl |
| Bi | 726 | 6138 | 1422 | 1428 | 995 | 1194 | 799 | 1109 | 985 | 686 | 940 | 2827 | 1476 | 6644 | 3422 | 1128 | 4792 | 4211 | 4689 | 4868 | 3796 | 4611 |
| La | 708 | 1266 | 1229 | 1173 | 878 | 1395 | 1145 | 1460 | 1439 | 912 | 2085 | 927 | 729 | 1412 | 912 | 1050 | 1168 | 1053 | 1171 | 1190 | 1117 | 1186 |
| Ce | 1988 | 2813 | 2774 | 2410 | 2241 | 4931 | 4307 | 5785 | 5777 | 3782 | 7200 | 1772 | 1538 | 2345 | 2577 | 3769 | 3152 | 2641 | 2916 | 3026 | 2399 | 2891 |
| Pr | 276 | 524 | 508 | 455 | 295 | 534 | 496 | 723 | 666 | 425 | 945 | 184 | 188 | 242 | 312 | 495 | 390 | 318 | 353 | 360 | 283 | 342 |
| Nd | 1131 | 1937 | 1970 | 1685 | 1191 | 2321 | 2183 | 3130 | 2902 | 1844 | 3919 | 726 | 753 | 854 | 1269 | 2108 | 1596 | 1262 | 1440 | 1507 | 1238 | 1412 |
| Sm | 179 | 286 | 331 | 252 | 192 | 471 | 500 | 694 | 692 | 444 | 940 | 117 | 144 | 133 | 236 | 466 | 292 | 241 | 266 | 263 | 224 | 251 |
| Eu | 38.6 | 56.5 | 60.8 | 52.0 | 42.7 | 90.7 | 87.3 | 124 | 118 | 79.7 | 157 | 15.1 | 19.2 | 14.6 | 39.3 | 72.2 | 46.6 | 34.4 | 38.4 | 37.6 | 32.1 | 36.1 |
| Gd | 237 | 302 | 364 | 219 | 250 | 651 | 618 | 892 | 814 | 585 | 1019 | 104 | 141 | 88.7 | 244 | 433 | 295 | 257 | 275 | 315 | 231 | 286 |
| Tb | 37.4 | 50.1 | 61.2 | 41.3 | 40.1 | 130 | 133 | 183 | 171 | 118 | 217 | 19.4 | 24.9 | 19.3 | 45.5 | 93.8 | 56.6 | 45.0 | 49.6 | 55.1 | 39.2 | 49.8 |
| Dy | 191 | 288 | 339 | 228 | 215 | 747 | 806 | 1044 | 1047 | 713 | 1340 | 107 | 145 | 114 | 260 | 554 | 328 | 253 | 293 | 309 | 251 | 288 |
| Ho | 39.6 | 60.6 | 74.3 | 46.3 | 44.9 | 159 | 169 | 234 | 226 | 158 | 279 | 22.9 | 30.0 | 20.5 | 47.0 | 108 | 66.4 | 52.9 | 59.7 | 67.9 | 47.7 | 59.4 |
| Er | 112 | 183 | 208 | 134 | 126 | 479 | 509 | 700 | 691 | 478 | 866 | 75.6 | 98.3 | 70.1 | 147 | 327 | 190 | 155 | 190 | 190 | 152 | 178 |
| Tm | 19.9 | 38.5 | 39.8 | 25.9 | 21.0 | 85.7 | 89.6 | 124 | 132 | 83.8 | 157 | 12.7 | 16.9 | 12.7 | 23.6 | 56.2 | 33.8 | 27.4 | 33.1 | 33.5 | 27.6 | 33.3 |
| Yb | 134 | 276 | 295 | 193 | 146 | 560 | 619 | 797 | 849 | 542 | 1080 | 86.1 | 118 | 89.1 | 169 | 371 | 209 | 176 | 216 | 216 | 168 | 197 |
| Lu | 22.6 | 46.1 | 50.0 | 34.7 | 26.6 | 100 | 102 | 144 | 144 | 98.2 | 171 | 14.0 | 18.6 | 13.6 | 26.5 | 56.6 | 37.4 | 30.3 | 35.3 | 37.4 | 29.6 | 32.8 |
| ΣREE | 5113 | 8126 | 8305 | 6949 | 5708 | 12654 | 11763 | 16033 | 15669 | 10261 | 20373 | 4182 | 3964 | 5427 | 6307 | 9961 | 7861 | 6546 | 7335 | 7607 | 6238 | 7242 |
| LREE | 4320 | 6882 | 6874 | 6027 | 4839 | 9743 | 8718 | 11915 | 11594 | 7487 | 15245 | 3740 | 3372 | 5000 | 5346 | 7961 | 6645 | 5549 | 6184 | 6383 | 5292 | 6117 |
| HREE | 793 | 1244 | 1431 | 922 | 870 | 2910 | 3045 | 4118 | 4074 | 2774 | 5128 | 442 | 592 | 428 | 961 | 2000 | 1217 | 997 | 1151 | 1224 | 945 | 1125 |
| LREE/HREE | 5.45 | 5.53 | 4.80 | 6.54 | 5.56 | 3.35 | 2.86 | 2.89 | 2.85 | 2.70 | 2.97 | 8.46 | 5.69 | 11.69 | 5.56 | 3.98 | 5.46 | 5.57 | 5.37 | 5.21 | 5.60 | 5.44 |
| δEu | 0.57 | 0.58 | 0.53 | 0.66 | 0.59 | 0.50 | 0.48 | 0.48 | 0.48 | 0.47 | 0.48 | 0.41 | 0.40 | 0.39 | 0.49 | 0.48 | 0.48 | 0.42 | 0.43 | 0.40 | 0.43 | 0.41 |
| δCe | 1.08 | 0.83 | 0.84 | 0.79 | 1.05 | 1.37 | 1.37 | 1.34 | 1.41 | 1.45 | 1.22 | 0.98 | 0.98 | 0.89 | 1.16 | 1.25 | 1.12 | 1.09 | 1.08 | 1.10 | 1.00 | 1.08 |
| Elements / Spots | Sample CP1603 | Sample CP1601 | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | |
| Na2O | 0.26 | 0.24 | 0.27 | 0.04 | 0.10 | 0.17 | 0.46 | 0.20 | 0.40 | 0.09 | 0.06 | 0.01 | 0.16 | 0.07 | 0.09 | 0.04 | 0.07 | 0.10 | 0.11 | 0.11 |
| SiO2 | 1.93 | 1.78 | 2.24 | 0.87 | 0.60 | 1.00 | 0.95 | 1.61 | 0.91 | 1.31 | 0.88 | 1.14 | 1.07 | 1.42 | 0.96 | 2.24 | 1.50 | 1.23 | 1.20 | 1.08 |
| FeO | 0.45 | 1.10 | 1.74 | 1.19 | 1.41 | 1.25 | 1.03 | 1.32 | 0.86 | 0.11 | 0.20 | 0.10 | 0.49 | 0.40 | 0.43 | 0.60 | 0.70 | 0.55 | 0.54 | 0.60 |
| Al2O3 | 0.16 | 0.15 | 0.32 | 0.01 | bdl | 0.03 | 0.03 | 0.02 | 0.01 | 0.05 | 0.02 | 0.02 | 0.06 | 0.14 | 0.08 | 0.28 | 0.05 | 0.06 | 0.03 | 0.09 |
| MnO | 0.41 | 0.54 | 0.52 | 0.61 | 0.39 | 0.70 | 0.57 | 0.73 | 0.58 | 0.52 | 0.56 | 0.61 | 0.36 | 0.59 | 0.22 | 0.74 | 0.68 | 0.48 | 0.49 | 0.42 |
| P2O5 | 0.04 | 0.18 | 0.08 | 0.23 | 0.28 | 0.13 | 0.30 | 0.20 | 0.25 | bdl | 0.03 | 0.03 | 0.04 | 0.07 | 0.04 | 0.02 | bdl | 0.03 | 0.10 | 0.02 |
| MgO | bdl | bdl | bdl | bdl | bdl | 0.03 | bdl | 0.06 | 0.01 | bdl | bdl | bdl | bdl | 0.01 | bdl | bdl | 0.03 | 0.06 | 0.01 | 0.01 |
| UO2 | 85.9 | 84.6 | 83.6 | 83.6 | 86.2 | 87.7 | 87.4 | 83.4 | 84.9 | 86.2 | 86.5 | 85.9 | 88.1 | 85.8 | 87.0 | 83.8 | 86.6 | 85.9 | 86.0 | 86.0 |
| TiO2 | bdl | bdl | bdl | 0.49 | 0.46 | bdl | bdl | 0.45 | bdl | 0.06 | bdl | 0.10 | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl |
| CaO | 8.05 | 6.39 | 8.77 | 3.57 | 3.77 | 4.31 | 4.10 | 4.91 | 3.73 | 4.13 | 4.63 | 5.93 | 7.64 | 7.77 | 6.43 | 7.78 | 7.27 | 9.42 | 8.08 | 7.11 |
| BaO | bdl | 0.10 | 0.10 | 0.24 | 0.13 | bdl | 0.02 | bdl | bdl | 0.01 | 0.13 | bdl | 0.10 | 0.02 | 0.10 | bdl | 0.03 | 0.09 | 0.11 | bdl |
| ThO2 | bdl | bdl | bdl | bdl | bdl | bdl | 0.01 | bdl | bdl | 0.05 | bdl | 0.09 | bdl | 0.01 | bdl | bdl | bdl | bdl | bdl | 0.01 |
| PbO | 1.03 | 0.64 | 1.18 | 1.15 | 0.98 | 0.77 | 0.96 | 0.89 | 1.33 | bdl | 0.03 | 0.03 | 1.63 | 2.16 | 2.21 | 0.59 | 2.10 | 1.31 | 1.76 | 1.30 |
| Total | 98.2 | 95.7 | 98.8 | 92.0 | 94.3 | 96.1 | 95.8 | 93.8 | 93.0 | 92.5 | 93.0 | 94.0 | 99.7 | 98.5 | 97.6 | 96.1 | 99.0 | 99.2 | 98.4 | 96.7 |
| Ta | 0.04 | bdl | 0.03 | bdl | 0.05 | 0.01 | 0.02 | 0.09 | 0.05 | 0.19 | 0.03 | bdl | 0.04 | 0.09 | bdl | bdl | 0.03 | bdl | 0.32 | 0.20 |
| W | 3631 | 4294 | 4012 | 4773 | 3872 | 4683 | 5375 | 4048 | 4153 | 3923 | 4064 | 4003 | 2573 | 2345 | 2223 | 2536 | 2647 | 2428 | 2584 | 2958 |
| Th | 0.07 | 0.01 | 0.04 | 0.05 | bdl | 0.04 | bdl | 0.05 | 0.07 | 0.01 | bdl | 0.02 | 0.02 | bdl | bdl | 0.03 | 0.02 | 0.03 | 0.01 | 0.02 |
| Be | 47.5 | 53.9 | 49.5 | 47.4 | 46.9 | 83.9 | 74.2 | 52.3 | 64.7 | 46.2 | 54.9 | 43.7 | 29.2 | 18.3 | 28.6 | 51.6 | 67.9 | 14.8 | 19.8 | 20.6 |
| V | 124 | 145 | 131 | 133 | 124 | 202 | 197 | 155 | 145 | 161 | 162 | 133 | 334 | 306 | 306 | 350 | 362 | 286 | 335 | 362 |
| Cr | bdl | 0.43 | bdl | bdl | 5.66 | 11.4 | bdl | bdl | 11.95 | bdl | 7.47 | 20.1 | bdl | bdl | 0.31 | bdl | 0.16 | 0.96 | bdl | 19.6 |
| Co | bdl | 0.37 | 0.48 | bdl | 0.15 | bdl | bdl | 0.02 | 0.24 | bdl | bdl | 0.55 | 0.31 | 0.48 | bdl | 0.54 | 0.38 | 0.34 | 0.27 | bdl |
| Ni | bdl | bdl | 1.21 | bdl | bdl | bdl | 4.29 | 0.80 | 0.68 | 4.07 | 0.98 | 0.24 | 1.64 | 2.61 | bdl | bdl | 1.88 | 0.48 | 1.19 | bdl |
| Zn | 2.31 | bdl | 7.25 | 0.69 | 7.53 | 5.64 | 7.70 | 5.74 | 0.49 | 4.91 | 3.55 | 9.43 | 884 | 844 | 836 | 385 | 3.70 | 91.0 | 224 | 408 |
| Sr | 119 | 133 | 118 | 131 | 127 | 251 | 202 | 164 | 175 | 135 | 137 | 125 | 117 | 90.0 | 96.6 | 161 | 189 | 61.5 | 55.2 | 58.6 |
| Y | 809 | 624 | 522 | 632 | 579 | 580 | 399 | 621 | 1695 | 842 | 750 | 814 | 619 | 469 | 510 | 602 | 658 | 410 | 477 | 557 |
| Zr | bdl | bdl | 0.21 | 0.05 | bdl | bdl | bdl | 0.04 | bdl | 0.10 | 0.23 | 0.25 | 0.06 | 0.12 | 0.16 | 0.30 | 0.45 | bdl | 0.02 | 0.09 |
| Nb | 0.62 | 0.16 | 0.56 | 0.34 | 0.20 | 0.51 | 0.11 | 0.02 | 18.34 | 0.14 | bdl | 0.35 | 0.25 | 0.25 | 0.19 | 0.37 | 0.92 | 0.64 | 35.0 | 23.6 |
| Mo | 53.4 | 54.7 | 49.8 | 52.5 | 54.3 | 24.9 | 49.3 | 50.1 | 30.9 | 58.8 | 64.8 | 55.7 | 47.6 | 45.8 | 26.0 | 14.0 | 7.76 | 27.0 | 71.1 | 74.1 |
| Sn | bdl | 3.36 | bdl | 2.70 | bdl | 4.23 | 1.36 | bdl | bdl | bdl | 2.00 | 14.92 | 6.78 | 16.9 | 18.0 | 13.7 | 11.1 | 16.5 | 59.4 | 49.4 |
| Ba | 14.5 | 18.6 | 18.2 | 21.5 | 17.9 | 48.1 | 38.8 | 35.0 | 33.0 | 23.6 | 22.2 | 22.6 | 40.8 | 40.2 | 34.4 | 62.0 | 45.3 | 27.6 | 22.8 | 27.8 |
| As | 1079 | 1179 | 1097 | 1091 | 1026 | 1393 | 1112 | 1153 | 1187 | 1049 | 1088 | 1000 | 348 | 303 | 359 | 463 | 539 | 272 | 146 | 161 |
| Hf | bdl | bdl | 0.12 | bdl | bdl | 0.02 | 0.10 | bdl | 0.08 | 0.01 | 0.09 | 0.11 | 0.15 | bdl | 0.10 | bdl | 0.33 | 0.30 | 0.20 | 0.08 |
| Bi | 626 | 784 | 411 | 598 | 302 | 74.4 | 71.0 | 189 | 383 | 287 | 494 | 1382 | 286 | 172 | 233 | 579 | 892 | 137 | 228 | 163 |
| La | 356 | 314 | 277 | 314 | 272 | 185 | 155 | 263 | 343 | 307 | 305 | 347 | 909 | 777 | 900 | 1050 | 982 | 614 | 504 | 581 |
| Ce | 322 | 216 | 175 | 204 | 205 | 176 | 119 | 256 | 586 | 292 | 235 | 303 | 2925 | 2552 | 2712 | 2863 | 2863 | 2694 | 2704 | 3197 |
| Pr | 46.4 | 33.4 | 23.3 | 27.8 | 25.1 | 19.0 | 10.3 | 30.1 | 74.5 | 33.1 | 28.0 | 57.1 | 342 | 290 | 290 | 307 | 323 | 345 | 427 | 489 |
| Nd | 215 | 139 | 90.3 | 113 | 110 | 77.0 | 51.7 | 126 | 317 | 139 | 120 | 250 | 1419 | 1221 | 1331 | 1304 | 1380 | 1480 | 1928 | 2247 |
| Sm | 74.1 | 39.9 | 25.8 | 34.2 | 28.1 | 24.5 | 17.8 | 39.7 | 116.1 | 42.3 | 38.1 | 70.5 | 312 | 268 | 257 | 241 | 286 | 353 | 556 | 702 |
| Eu | 5.64 | 3.38 | 2.57 | 2.60 | 2.30 | 1.99 | 1.01 | 2.77 | 11.01 | 4.32 | 2.43 | 6.43 | 39.4 | 35.0 | 37.7 | 37.3 | 35.7 | 43.6 | 61.5 | 68.4 |
| Gd | 68.2 | 46.8 | 36.1 | 47.5 | 46.2 | 37.4 | 29.0 | 49.5 | 155 | 66.9 | 47.8 | 81.6 | 205 | 162 | 169 | 180 | 180 | 170 | 227 | 280 |
| Tb | 12.2 | 7.97 | 5.40 | 7.78 | 6.27 | 5.86 | 4.05 | 8.41 | 27.2 | 9.27 | 6.67 | 13.7 | 19.8 | 18.2 | 17.0 | 16.5 | 19.9 | 23.1 | 37.5 | 44.7 |
| Dy | 80.5 | 55.2 | 33.9 | 44.8 | 40.3 | 38.8 | 22.8 | 47.2 | 201 | 59.4 | 51.3 | 80.3 | 105 | 86.7 | 73.1 | 74.6 | 89.7 | 104 | 195 | 221 |
| Ho | 15.0 | 11.9 | 7.03 | 9.76 | 9.01 | 8.43 | 5.18 | 9.25 | 36.3 | 12.1 | 10.8 | 15.4 | 15.3 | 13.8 | 12.8 | 12.5 | 13.3 | 15.5 | 27.4 | 33.3 |
| Er | 48.0 | 33.2 | 22.6 | 27.6 | 27.4 | 23.8 | 14.7 | 26.9 | 106 | 35.2 | 27.9 | 49.3 | 36.6 | 26.9 | 27.3 | 27.6 | 31.6 | 39.7 | 69.6 | 80.4 |
| Tm | 6.67 | 4.79 | 3.61 | 4.42 | 3.22 | 3.33 | 2.27 | 4.82 | 15.9 | 5.73 | 4.37 | 6.03 | 4.52 | 4.38 | 4.06 | 3.27 | 4.93 | 5.65 | 11.5 | 12.8 |
| Yb | 44.4 | 34.6 | 19.2 | 26.2 | 26.5 | 20.7 | 10.4 | 23.0 | 102.2 | 34.0 | 29.2 | 48.1 | 27.8 | 30.7 | 21.2 | 23.3 | 25.4 | 32.6 | 84.6 | 95.5 |
| Lu | 5.55 | 5.46 | 2.41 | 3.98 | 3.49 | 2.78 | 1.76 | 2.76 | 13.87 | 3.99 | 3.39 | 6.23 | 3.71 | 3.75 | 3.07 | 3.16 | 2.29 | 3.58 | 8.55 | 8.88 |
| ΣREE | 53.4 | 54.7 | 49.8 | 52.5 | 54.3 | 24.9 | 49.3 | 50.1 | 30.9 | 58.8 | 64.8 | 55.7 | 47.6 | 45.8 | 26.0 | 14.0 | 7.76 | 27.0 | 71.1 | 74.1 |
| LREE | bdl | 3.36 | bdl | 2.70 | bdl | 4.23 | 1.36 | bdl | bdl | bdl | 2.00 | 14.9 | 6.78 | 16.9 | 18.0 | 13.7 | 11.1 | 16.5 | 59.4 | 49.4 |
| HREE | 14.5 | 18.6 | 18.2 | 21.5 | 17.9 | 48.1 | 38.8 | 35.0 | 33.0 | 23.6 | 22.2 | 22.6 | 40.8 | 40.2 | 34.4 | 62.0 | 45.3 | 27.6 | 22.8 | 27.8 |
| LREE/HREE | 1079 | 1179 | 1097 | 1091 | 1026 | 1393 | 1112 | 1153 | 1187 | 1049 | 1088 | 1000 | 348 | 303 | 359 | 463 | 539 | 272 | 146 | 161 |
| δEu | bdl | bdl | 0.12 | bdl | bdl | 0.02 | 0.10 | bdl | 0.08 | 0.01 | 0.09 | 0.11 | 0.15 | bdl | 0.10 | bdl | 0.33 | 0.30 | 0.20 | 0.08 |
| δCe | 626 | 784 | 411 | 598 | 302 | 74.4 | 71.0 | 189 | 383 | 287 | 494 | 1382 | 286 | 172 | 233 | 579 | 892 | 137 | 228 | 163 |
Note: bdl = below detectable limit
Major element diagrams of pitchblende and coffinite in ores from the Changjiang U ore field. (a) UO2 vs. SiO2. (b) UO2 vs. CaO. (c) UO2 vs. FeO. (d) UO2 vs. PbO. (e) CaO vs. PbO. (f) SiO2 vs. SiO2 + CaO + FeO.
The trace element compositions of pitchblende show high contents of As, Sr and W, low contents of Nb, Ta, Sn, Th and Hf and varied contents of Bi, Y, V, Zn and Mo (Table 1, Fig. 7). Some trace elements present several orders of magnitude of variation, such as Be (12.4–115 ppm, median = 55.3 ppm), V (16.5–1609 ppm, median = 69.6 ppm), Zn (bdl–884 ppm, median = 2.95 ppm), Sr (55.2–1089 ppm, median = 139 ppm), Nb (bdl–256 ppm, median = 2.84 ppm), Mo (0.71–1521 ppm, median = 49.9 ppm), Ba (9.32–433 ppm, median = 33.5 ppm) and Bi (0.01–6644 ppm, median = 387 ppm). A few trace elements have very low contents, most of which are below the detection limit of inductively coupled plasma mass spectrometry (ICP–MS), such as Ta (<0.95 ppm), Th (<0.27 ppm), Cr (<21.6 ppm), Co (<0.80 ppm), Ni (<4.29 ppm), Hf (<0.80 ppm) and Zr (<3.83 ppm).
Box plots of the trace element contents of pitchblende in ores from the Changjiang U ore field.
Significantly, a small number of trace elements, such as V, Ba, Zn and Mo, in pitchblende are quite variable from one sample or deposit to another (Table 1, Fig. 7). Sample MHK1519 from the MHK deposit has higher V and Ba contents (median = 1435 ppm and 370 ppm, respectively) than the other five samples (V median = 63.8 ppm and Ba median = 30.6 ppm). Sample CP1603 from the CP deposit has the highest Zn contents (median = 407 ppm), except for spot No. 5. Sample CJ16153 from the MHK deposit has the lowest Mo contents (median = 4.17 ppm).
The pitchblende in all the samples is characterized by very low REE contents (0.01–2.04%, median = 0.36%) with weak negative Eu anomalies (Eu/Eu* = 0.13–0.74, median = 0.44, Fig. 8a–c). All the REE patterns present enrichment in light rare earth elements (LREEs) compared with heavy rare earth elements (HREEs) (LREEs/HREEs = 1.86–12.1, median = 4.80). It is worth noting that a small number of pitchblende REE patterns show significant differences between each individual deposit. The REE signatures of samples from the SLQ deposit display minor fractionated and “gull-winged” patterns (Fig. 8a). In the MHK deposit, sample CJ16153 has higher HREE contents than sample MHK1519 (Fig. 8b). In the CP deposit, sample CP1601 shows higher LREE contents than sample CJ1603 (Fig. 8c).
Chondrite-normalized REE patterns of pitchblende. (a) Pitchblende in the SLQ deposit. (b) Pitchblende in the MHK deposit. (c) Pitchblende in the CP deposit. (d) Pitchblende in hydrothermal vein-type deposits. (e) Pitchblende in magmatic/intrusive-type, volcanic-related and sandstone-hosted roll-front deposits. (f) Pitchblende in unconformity-related and synmetamorphic-type deposits. (in d–f, the REE data in uraninite are from Mercadier et al., 2011; Frimmel et al., 2014). Chondrite normalization values are from Anders and Grevesse (1989).
A small amount of coffinite was observed in sample MHK1519 of the MHK deposit. On the BSE image (Fig. 5f), coffinite shows a gray color and replaces the globular pitchblende. It seems that coffinite is the product of the later hydrothermal alteration of pitchblende. The major elements of coffinite are listed in Table 2. Compared with the pitchblende in the MHK deposit, coffinite has higher SiO2 contents (11.1~26.9%, median = 15.5%) and lower UO2 contents (57.6~73.6%, median = 62.7%) (Fig. 6).
| Elements | MHK1519.1 | MHK1519.2 | MHK1519.3 | MHK1519.4 | MHK1519.5 | MHK1519.6 | MHK1519.7 | MHK1519.8 | MHK1519.9 | MHK1519.10 |
|---|---|---|---|---|---|---|---|---|---|---|
| Na2O | 0.05 | 0.20 | 0.02 | 0.05 | 0.05 | 0.32 | 0.05 | 0.17 | 0.15 | 0.07 |
| SiO2 | 14.5 | 26.9 | 16.5 | 14.1 | 22.1 | 12.8 | 13.4 | 11.1 | 19.8 | 20.1 |
| FeO | 0.06 | 0.04 | bdl | 1.18 | 1.29 | 0.79 | 1.38 | 0.75 | 0.13 | 0.24 |
| Al2O3 | 0.94 | 0.74 | 0.22 | 0.47 | 0.65 | 0.35 | 0.26 | 0.87 | 0.68 | 0.59 |
| MnO | 0.13 | 0.24 | bdl | 0.27 | bdl | 0.61 | 0.21 | 0.10 | 0.06 | 0.02 |
| P2O5 | 0.21 | 0.05 | bdl | 0.07 | 0.19 | bdl | bdl | 0.01 | 0.16 | 0.11 |
| MgO | 0.05 | 0.08 | 0.12 | 0.02 | 0.16 | 0.10 | 0.03 | 0.05 | 0.02 | 0.04 |
| UO2 | 73.6 | 57.6 | 63.4 | 62.0 | 58.5 | 65.2 | 68.5 | 72.5 | 59.7 | 60.2 |
| TiO2 | 0.04 | 0.11 | bdl | 0.13 | 0.07 | 0.07 | 3.62 | bdl | 0.02 | 0.66 |
| CaO | 2.35 | 4.17 | 5.92 | 2.61 | 1.66 | 3.24 | 2.46 | 3.37 | 1.00 | 1.48 |
| BaO | 0.20 | bdl | 0.14 | 0.21 | 0.04 | 0.27 | bdl | bdl | bdl | bdl |
| ThO2 | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl | bdl |
| PbO | 0.02 | 0.76 | bdl | 0.11 | 0.05 | 0.17 | 0.94 | 0.27 | bdl | bdl |
| Total | 92.2 | 90.9 | 86.3 | 81.2 | 84.8 | 84.0 | 90.8 | 89.1 | 81.7 | 83.5 |
Note: bdl = below detectable limit
The U, Th and REE data of granites and diabase from the Changjiang ore field are listed in Table 3 and Fig. 9a–d, coupled with the data from Zhu (2010), Huang et al. (2012, 2014) and Fu (2015). The Youdong and Changjiang granites show high U contents (mean = 12.5 ppm and 18.2 ppm, respectively) and varying Th contents (mean = 3.93 ppm and 37.3 ppm, respectively) and Th/U values (mean = 3.24 and 2.21, respectively) (Fig. 9d). Both have high total REE (ΣREE) contents (170–322 ppm and 76.9–207 ppm, respectively) with moderate to strong fractionation between LREEs and HREEs ((La/Yb)N = 10.5–22.2 and 2.48–11.8, respectively, Fig. 9a–b). Two granites have weak negative Eu and Ce anomalies (mean Eu/Eu* = 0.24 and 0.24 and mean Ce/Ce* = 0.98 and 0.92, respectively).
| Granite Sample | Changjiang granite | Youdong grantie | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CJ1626 | CJ1529 | 8a | 9a | 10a | 06225b | 06220b | M5102b | M15103b | M15104b | M15122b | M15123b | CJ1525 | CJ1538 | 0621c | |
| Th | 26.6 | 24.7 | 37.5 | 30.8 | 30.1 | 47.6 | 38.1 | 43.5 | 30.3 | 39.9 | 45.6 | 53.2 | 42.3 | 36.7 | 51.1 |
| U | 18.1 | 13.9 | 15.1 | 13.1 | 14.5 | 14.1 | 31.4 | 34.2 | 12.5 | 14.2 | 18.0 | 19.3 | 14.2 | 12.0 | 11.4 |
| Th/U | 1.47 | 1.78 | 2.49 | 2.35 | 2.08 | 3.38 | 1.21 | 1.27 | 2.42 | 2.81 | 2.53 | 2.76 | 2.98 | 3.06 | 4.50 |
| La | 28.7 | 31.1 | 29.6 | 28.8 | 21.8 | 43.0 | 27.7 | 11.8 | 15.8 | 25.4 | 25.2 | 33.6 | 55.2 | 47.0 | 63.5 |
| Ce | 67.4 | 52.8 | 52.5 | 49.3 | 40.4 | 74.6 | 60.7 | 27.1 | 30.8 | 59.4 | 50.8 | 67.3 | 127 | 100 | 141 |
| Pr | 5.99 | 8.41 | 6.81 | 6.72 | 5.09 | 10.2 | 7.56 | 3.61 | 4.03 | 6.72 | 6.20 | 7.92 | 11.1 | 11.7 | 16.7 |
| Nd | 22.7 | 40.0 | 26.3 | 26.7 | 20.5 | 38.9 | 30.4 | 16.8 | 14.3 | 23.5 | 23.4 | 31.1 | 40.4 | 38.8 | 62.1 |
| Sm | 4.99 | 7.63 | 5.93 | 6.93 | 5.42 | 8.13 | 7.39 | 4.05 | 2.07 | 3.37 | 3.25 | 3.87 | 8.02 | 8.40 | 12.3 |
| Eu | 0.54 | 0.34 | 0.35 | 0.34 | 0.25 | 0.75 | 0.54 | 0.16 | 0.31 | 0.45 | 0.37 | 0.35 | 0.68 | 0.70 | 0.59 |
| Gd | 4.42 | 8.59 | 4.97 | 6.50 | 5.17 | 7.71 | 7.93 | 4.26 | 2.80 | 4.71 | 4.08 | 4.92 | 7.14 | 7.55 | 10.5 |
| Tb | 0.73 | 1.48 | 0.76 | 1.16 | 0.92 | 1.40 | 1.58 | 0.81 | 0.34 | 0.50 | 0.44 | 0.47 | 1.02 | 0.98 | 1.43 |
| Dy | 4.15 | 9.41 | 4.03 | 6.61 | 5.13 | 8.73 | 10.3 | 4.83 | 2.41 | 4.25 | 3.70 | 3.87 | 4.79 | 4.73 | 6.90 |
| Ho | 0.82 | 1.95 | 0.73 | 1.22 | 0.92 | 1.69 | 2.09 | 1.00 | 0.50 | 0.96 | 0.71 | 0.76 | 0.85 | 0.78 | 1.08 |
| Er | 2.51 | 5.95 | 2.13 | 3.47 | 2.51 | 5.22 | 6.45 | 3.27 | 1.45 | 2.69 | 2.25 | 2.12 | 2.09 | 2.09 | 2.82 |
| Tm | 0.38 | 0.97 | 0.30 | 0.50 | 0.34 | 0.84 | 1.01 | 0.49 | 0.24 | 0.46 | 0.28 | 0.29 | 0.28 | 0.25 | 0.36 |
| Yb | 2.66 | 6.62 | 1.94 | 3.20 | 2.16 | 5.67 | 6.53 | 3.21 | 1.62 | 2.96 | 2.01 | 1.92 | 1.68 | 1.67 | 2.28 |
| Lu | 0.38 | 1.03 | 0.30 | 0.47 | 0.32 | 0.87 | 1.03 | 0.52 | 0.23 | 0.42 | 0.33 | 0.30 | 0.24 | 0.25 | 0.32 |
| Granite Sample | Youdong grantie | Diabase | |||||||||||||
| 06134c | 06135c | 06213c | 06214c | 06222c | CJ1533 | CJ1534 | 601d | 602d | 603d | 604d | 605d | 674d | 691d | 692d | |
| Th | 38.6 | 39.2 | 34.7 | 39.7 | 32.2 | 4.14 | 4.08 | 3.66 | 3.19 | 3.22 | 3.98 | 4.18 | 2.54 | 2.20 | 2.38 |
| U | 12.7 | 9.3 | 15.5 | 11.2 | 13.6 | 0.88 | 0.92 | 1.68 | 3.03 | 4.33 | 1.85 | 1.04 | 8.89 | 0.71 | 6.68 |
| Th/U | 3.03 | 4.22 | 2.24 | 3.56 | 2.37 | 4.70 | 4.43 | 2.18 | 1.05 | 0.74 | 2.15 | 4.02 | 0.29 | 3.10 | 0.36 |
| La | 32.1 | 44.9 | 32.8 | 39.7 | 32.2 | 19.0 | 19.5 | 17.1 | 15.4 | 15.6 | 19.0 | 17.3 | 16.4 | 18.0 | 20.6 |
| Ce | 69.0 | 87.9 | 68.6 | 88.2 | 72.3 | 34 | 34.5 | 34.2 | 29.9 | 30.5 | 33.8 | 39.1 | 36.3 | 40.2 | 44.8 |
| Pr | 8.31 | 12.70 | 9.23 | 10.92 | 8.77 | 5.92 | 5.94 | 4.16 | 3.63 | 3.72 | 4.39 | 4.52 | 4.85 | 5.57 | 6.10 |
| Nd | 35.8 | 45.2 | 35.4 | 42.4 | 33.9 | 33.0 | 32.1 | 17.8 | 15.8 | 16.1 | 18.4 | 19.8 | 21.1 | 25.3 | 27.2 |
| Sm | 7.07 | 9.91 | 7.56 | 8.78 | 7.08 | 6.43 | 6.28 | 4.01 | 3.54 | 3.68 | 4.00 | 4.59 | 4.06 | 5.08 | 5.28 |
| Eu | 0.55 | 0.71 | 0.59 | 0.66 | 0.51 | 2.10 | 2.02 | 1.24 | 1.28 | 1.21 | 1.18 | 1.67 | 1.15 | 1.77 | 1.77 |
| Gd | 5.91 | 8.55 | 6.09 | 7.01 | 5.75 | 8.11 | 8.00 | 4.07 | 3.64 | 3.70 | 4.06 | 4.85 | 3.78 | 4.64 | 4.88 |
| Tb | 0.95 | 1.27 | 0.93 | 1.06 | 0.89 | 1.23 | 1.25 | 0.65 | 0.59 | 0.60 | 0.67 | 0.78 | 0.68 | 0.79 | 0.82 |
| Dy | 5.05 | 6.42 | 4.91 | 5.52 | 4.66 | 8.02 | 7.70 | 3.90 | 3.51 | 3.59 | 3.95 | 4.69 | 4.04 | 4.46 | 4.64 |
| Ho | 0.84 | 1.01 | 0.81 | 0.92 | 0.79 | 1.63 | 1.63 | 0.79 | 0.71 | 0.72 | 0.78 | 0.93 | 0.75 | 0.83 | 0.86 |
| Er | 2.41 | 2.79 | 2.18 | 2.42 | 2.09 | 4.60 | 4.57 | 2.22 | 2.01 | 2.05 | 2.19 | 2.69 | 2.15 | 2.31 | 2.41 |
| Tm | 0.33 | 0.35 | 0.30 | 0.33 | 0.30 | 0.64 | 0.65 | 0.33 | 0.29 | 0.29 | 0.32 | 0.38 | 0.31 | 0.31 | 0.33 |
| Yb | 2.07 | 2.22 | 1.78 | 1.98 | 1.73 | 4.14 | 4.21 | 2.06 | 1.85 | 1.84 | 2.01 | 2.36 | 1.95 | 2.03 | 2.13 |
| Lu | 0.29 | 0.31 | 0.25 | 0.28 | 0.25 | 0.64 | 0.64 | 0.31 | 0.28 | 0.29 | 0.30 | 0.37 | 0.29 | 0.30 | 0.31 |
Note: The date with superscript a, b, c and d are from Fu. (2015), Huang et al. (2014), Huang et al. (2012) and Zhu. (2010), respectively.
Chondrite-normalized REE patterns of the Youdong granite (a), Changjiang granite (b) and diabase (c). Th vs. U diagram of these two granites (d). Chondrite-normalized REE patterns of uraninite in the Youdong granite (e) and Changjiang granite (f).
The diabase samples in the Changjiang U ore field have low Th and U contents (2.20–4.18 ppm and 0.71–8.89 ppm, respectively) with low Th/U ratios of 0.29–4.70 (Table 2). All the samples show low ΣREE contents (82.5–129 ppm). In the chondrite-normalized REE patterns, these samples exhibit right-declining REE patterns, with weak positive Eu anomalies (0.87–1.10) and (La/Yb)N values of 3.10–6.52 (Fig. 9c).
Uraninite REE compositions from granitesThe results of the REE analysis of uraninite from the Youdong and Changjiang granites are listed in Table 4 and are coupled with the data from Zhang et al. (2021). The uraninite in both granites has “gull-winged” chondrite-normalized REE patterns with high ΣREE contents (123864–219476 ppm and 44655–59373 ppm, respectively) and weak negative Eu anomalies (Eu/Eu* = 0.01–0.02 and 0.01–0.02, respectively, Fig. 9e–f). However, the ΣREE contents of uraninite from the Youdong granite are higher than those from the Changjiang granite (mean = 168574 ppm and 51626 ppm, respectively).
| Samples | Youdong granite | Changjiang granite | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CJ1525-7 | CJ1525-8 | CJ1525-9 | CJ1525-10 | CJ1538-5 | CJ1538-6 | CJ1538-7 | ZK304-5-1a | ZK211-2-1a | ZK211-2-2a | ZK211-2-3a | ZK211-2-4a | ZK211-2-5a | ZK211-2-6a | ZK211-2-7a | |
| La | 711 | 442 | 1231 | 1282 | 583 | 943 | 803 | 243 | 151 | 161 | 162 | 228 | 175 | 161 | 171 |
| Ce | 7330 | 4341 | 12055 | 13335 | 4566 | 9569 | 7102 | 3428 | 2869 | 3060 | 3091 | 3916 | 3389 | 3082 | 3292 |
| Pr | 2057 | 1297 | 3323 | 3600 | 1201 | 2829 | 1913 | 733 | 664 | 691 | 711 | 911 | 739 | 713 | 739 |
| Nd | 23845 | 15312 | 36690 | 38507 | 14020 | 34097 | 22468 | 5458 | 5168 | 5509 | 5795 | 7278 | 5895 | 5812 | 6018 |
| Sm | 15554 | 11859 | 25363 | 26758 | 11374 | 25451 | 17039 | 4183 | 4982 | 5205 | 5611 | 6590 | 5673 | 5653 | 5801 |
| Eu | 62.8 | 71.2 | 89.8 | 104 | 111 | 59 | 138 | 52.9 | 33.4 | 34.7 | 38.0 | 33.8 | 32.7 | 36.2 | 39.7 |
| Gd | 23022 | 19158 | 32649 | 34652 | 18584 | 34185 | 24677 | 5958 | 6461 | 7061 | 7351 | 8591 | 7364 | 7434 | 7716 |
| Tb | 6259 | 5407 | 8634 | 9395 | 5366 | 8871 | 6655 | 1544 | 1642 | 1833 | 1912 | 2183 | 1955 | 1876 | 2020 |
| Dy | 37156 | 32996 | 47525 | 51366 | 33582 | 48697 | 38183 | 9745 | 10194 | 11661 | 11141 | 11001 | 12045 | 12451 | 13226 |
| Ho | 6621 | 6177 | 7983 | 8608 | 6284 | 7963 | 6701 | 2202 | 1901 | 2244 | 2352 | 2783 | 2306 | 2234 | 2365 |
| Er | 16270 | 15245 | 18103 | 19338 | 16007 | 18281 | 15968 | 5881 | 5205 | 6015 | 6314 | 7351 | 6085 | 5965 | 6091 |
| Tm | 1631 | 1466 | 1591 | 1754 | 1594 | 1621 | 1472 | 746 | 787 | 892 | 938 | 1075 | 921 | 879 | 924 |
| Yb | 10502 | 9492 | 9260 | 10182 | 10562 | 9468 | 9160 | 4088 | 5117 | 5706 | 5980 | 6740 | 5785 | 5739 | 6000 |
| Lu | 672 | 600 | 561 | 598 | 697 | 550 | 541 | 394 | 532 | 586 | 618 | 693 | 588 | 595 | 619 |
| ∑REE | 151693 | 123865 | 205057 | 219477 | 124531 | 202581 | 152819 | 44656 | 45706 | 50659 | 52014 | 59374 | 52953 | 52630 | 55022 |
| LREE | 49559 | 33323 | 78752 | 83585 | 31855 | 72947 | 49464 | 14098 | 13867 | 14661 | 15408 | 18957 | 15904 | 15457 | 16061 |
| HREE | 102135 | 90542 | 126305 | 135892 | 92676 | 129634 | 103356 | 30558 | 31839 | 35998 | 36606 | 40417 | 37049 | 37173 | 38961 |
| LREE/HREE | 0.49 | 0.37 | 0.62 | 0.62 | 0.34 | 0.56 | 0.48 | 0.46 | 0.44 | 0.41 | 0.42 | 0.47 | 0.43 | 0.42 | 0.41 |
| Eu* | 0.01 | 0.01 | 0.01 | 0.01 | 0.02 | 0.01 | 0.02 | 0.03 | 0.02 | 0.02 | 0.02 | 0.01 | 0.02 | 0.02 | 0.02 |
| Ce* | 0.90 | 0.85 | 0.91 | 0.94 | 0.92 | 0.86 | 0.92 | 1.19 | 1.14 | 1.17 | 1.15 | 1.13 | 1.21 | 1.14 | 1.17 |
Note: The date with superscript a is from Zhang et al. (2021).
In the Changjiang U ore field, uranium mineralization is closely related to both Triassic Youdong and Jurassic Changjiang granites. Ore bodies occur along N-S-trending faults within granites, reflecting that ore formation postdates the emplacement of the host granites (Sun et al., 2021). Indeed, there is a large gap of >90 Ma between the mineralization (~70 Ma, Huang et al., 2010; Zhong et al., 2019) and the hosting granites in this ore field. The chondrite-normalized REE patterns of pitchblende from ore samples exhibit enrichment in LREEs, medium-strong fractionation between LREEs and HREEs, and weak negative Eu anomalies (Fig. 8a–c). The REE patterns of pitchblende in these deposits are similar to those of hydrothermal vein-type U deposits (e.g., the Bois Noris U deposit in the French Hercynian belt) and differ from those of other type U deposits worldwide (Fig. 8d–f, Mercadier et al., 2011; Frimmel et al., 2014). Thus, we propose that the U mineralization in the Changjiang ore field was hydrothermal, excluding the U source of magmatic hydrotherms.
The incorporated elements generally occupy pitchblende structures (e.g., Ca2+, Th4+, REE3+, and Y3+) or occur as minute mineral inclusions in pitchblende crystals (Mercadier et al., 2011; Frimmel et al., 2014). The function in which these elements are usually considered to be specific to trace the sources of pitchblende has been demonstrated in many previous studies (Frimmel et al., 2014; Bonnetti et al., 2018; Grare et al., 2021; Zhang et al., 2021). Therefore, the REE pattern of pitchblende can be considered as a powerful tool for tracing sources (Mercadier et al., 2011; Spano et al., 2017; Bonnetti et al., 2018, 2020); for example, the pitchblende in the Shituling deposit from South China shows very similar REE signatures to the Maofeng granite, which is considered the major U source for U mineralization (Bonnetti et al., 2018). There are significant differences in REE patterns between pitchblende in ores and diabase (Fig. 8a–c, Fig. 9a–c) and low Cr, Co and Ni contents in pitchblende (Table 1), suggesting that it is impossible for the diabase to be the U source. The REE patterns show that samples SLQ1601, SLQ1603, CP1603 and MHK1519 are close to the Changjiang granite, whereas samples CJ16153 and CP1601 are comparable to the Youdong granite. A close genesis relation appears between the U mineralization and the two granites. The high W contents (780–5374 ppm, Table 1) in pitchblende from the Changjiang ore field are comparable to the Wittichen U deposits occurring in the Hercynian granites of Central Europe, in which the hosting W-rich granite is deemed the primary U source (Cathelineau et al., 1990; Förster, 1999; Frimmel et al., 2014). The Zhuguangshan complex has high W contents of approximately 5.97–37.5 ppm and hosts several later Jurassic W-Mo deposits (e.g., the Neidong deposit) (Xue, 2011). The Youdong and Changjiang granites are peraluminous S-type granites with high U contents (9.27–15.5 ppm and 12.5–34.2 ppm, respectively), variable Th contents (32.2–51.1 ppm and 24.7–53.2 ppm, respectively) and erratic Th/U values (2.24–4.50 and 1.21–3.38, respectively) (Table 2, Huang et al., 2012, 2014; Zhang et al., 2017b, 2018). It is suggested that most of the U in granites is located in uraninite, and a significant fraction of U was released during alteration (Friedrich et al., 1987; Cuney et al., 1990). Indeed, uraninite grains are easily found in both the Youdong and Changjiang granites (Fig. 3a, c), and U can be released from uraninite through hydrothermal alteration (Qi et al., 2014; Zhang et al., 2017a, 2021). The partial comparability between the REE patterns of uraninite in the granites and pitchblende in the ores also indicates a genetic link (Fig. 8a–c, Fig. 9e–f). These signatures suggest that the U sources of the Changjiang ore field were derived from the Youdong and Changjiang granites, and the uraninite in both granites seems to be the major U source mineral.
Physicochemical conditions of mineralizationThe geochemical imprinting of pitchblende is a function of the physicochemical conditions (e.g., temperature, redox state, and fluid composition) during its formation (Alexandre and Kyser, 2005; Mercadier et al., 2011; Ballouard et al., 2017; Grare et al., 2021). Uraninite generally occurs as cube-shaped grains at high temperatures and fine-grained aggregates at low temperatures (namely, pitchblende, Frimmel et al., 2014). Th4+ is available and soluble in a high-temperature environment and can easily occupy the position of U4+ in the uraninite structure during crystallization (Cuney and Kyser, 2008; Depiné et al., 2013; Cuney, 2009). As a result, uraninite has a high Th content. In contrast, due to the limited solubility of Th4+ in low-temperature hydrothermal fluids, pitchblende has a low Th content (Alexandre et al., 2015; Cuney, 2009). The U/Th values of uraninite and pitchblende are indicators to differentiate between high (>350°C) and low temperatures (<350°C) (Frimmel et al., 2014). Similar to Th4+ behavior, the REEs in pitchblende are also sensitive to its formative conditions. Uraninite, due to the U4+ that is substituted by REE3+, has higher ΣREE contents (>1%) than pitchblende (<1%) (Fryer and Taylor, 1987; Alexandre and Kyser, 2005; Mercadier et al., 2011; Frimmel et al., 2014). In BSE images, the pitchblende grains from the SLQ, MHK and CP deposits in the Changjiang ore field exhibit botryoidal, globular, colloidal and vein shapes rather than cubic crystals (Fig. 5). The Th contents in pitchblende are almost negligible (<0.27 ppm), and most Th contents are below the detection limit of ICP–MS (0.01 ppm) (Table 1). A large proportion of pitchblende in this ore field has low ΣREE contents (0.01–2.04%, median = 0.36%) (Fig. 8a–c). The topography and geochemistry of pitchblende in ores suggest a low-temperature ore-forming environment. Furthermore, this relatively low ore-forming temperature (<250°C) has also been evidenced by alteration mineral assemblages around ore bodies, which contain abundant chlorite, hydromica, sericite and illite (Fig. 5, Du et al., 1982). This hypothesis is strongly supported by the results of the chlorite geothermometer (230°C, Guo et al., 2012) and the homogeneous temperatures of fluid inclusions in quartz linked with U mineralization (220°C, Zhang et al., 2017a).
The REE patterns of pitchblende in ores from the Changjiang ore field are similar to the REE patterns of pitchblende from the Bois Noris U deposit in the French Hercynian belt, which is characterized by low salinity (3–8% eq. NaCl) and temperature (150–250°C) of the ore-forming fluid (Fig. 8a–d, Cuney, 1978; Mercadier et al., 2011). This implies that the ore-forming fluid in the Changjiang ore field had low-salinity hydrothermal fluid. Previous studies confirmed that Eu3+ and Eu2+ behavior is dominantly a function of the redox conditions of hydrothermal solutions (Sverjensky, 1984). The low Eu/Eu* values in the range of 0.13–0.74 (mean = 0.39) represent the obvious negative Eu anomalies of pitchblende in this ore field, suggesting reducing conditions. The relatively high Mo (median = 49.9 ppm), As (median = 592 ppm) and V (median = 69.6 ppm) contents (Fig. 7) also indicate a relatively reductive environment. Pitchblende has high W contents, suggesting ore-forming fluid with high W contents. The higher ΣREE, Mo and Bi contents in pitchblende from the SLQ deposit than in the MHK and CP deposits probably indicate higher ore-forming temperatures. Additionally, the mineralization in the Changjiang ore field is closely related to microcrystalline quartz, calcite and fluorite, reflecting that the ore-forming fluid is a silicon-saturated solution with elevated contents of CO32– and F– ligands. These ligands facilitate U migration from U-rich source rocks in hydrothermal solution.
Hydrothermal alteration of mineral assemblages around ore bodies is widely used as an indicator of the physicochemical parameters of ore-forming fluids in hydrothermal U deposits (Romberger, 1984; Zhang et al., 2019). The mineral assemblages related to U mineralization in the Changjiang ore field are characterized by chlorite, sericite, hematite, pyrite, calcite, fluorite and pitchblende. This suggests that the ore-forming fluid shares low log fO2 values ranging from –29.5 to –25.5 and pH values of approximately 5.3–5.9 (Fig. 10). Moreover, Jin and Hu (1988) indicated that pitchblende formed in a weakly acidic fluid with pH values of 3.5–5.5. The gas phase compositions in quartz-associated fluid inclusions are dominantly CO2, H2 and CH4, meaning that the reductive ore-forming fluid was responsible for U mineralization (Chen and Liu, 1990; Zhang et al., 2017a). Thus, the precipitation of pitchblende occurs with low oxygen fugacity and in a relatively acidic environment.
Log fO2-pH diagram showing the distribution of uranyl complexes, solubility of uranium oxides, distribution of iron phases, relative stability of chalcopyrite and bornite and relative stability of potassium and magnesium silicates at 200°C in an aqueous system containing 10 ppm Fe, 100 ppm F, 10000 ppm S, 10000 ppm K, 100 pm Mg and 1 m NaCl at a PCO2 of 10 atm (modified from Romberger, 1984). The Changjiang U ore field plots in the gray area. Sch. = schoepite, Chl. = chlorite, Ksp. = adularia, Ser. = sericite, bn = bornite, ccpy = chalcopyrite, Mg-Mont = magnesian montmorillonite, Alu. = alunite.
Generally, the granite-related U deposits in the SCUP are spatially and genetically associated with Triassic and Jurassic peraluminous granites, which were derived from partial melting from pelitic sedimentary sources (Zhao et al., 2016; Chen et al., 2012; Zhang et al., 2018, 2021; Chi et al., 2020). In these granites, U is dominantly composed of tetravalent ions (U4+) hosted in accessory minerals (e.g., uraninite, monazite, and xenotime) (Cuney and Friedrich, 1987; Chen et al., 2012; Zhang et al., 2017a). Among them, uraninite hosts the vast majority of U in granite (>80%), which is easily leached by oxidized fluid, especially Th-poor uraninite (Cuney and Friedrich, 1987, Cuney, 2009, 2014). In the Changjiang ore field, uraninite, which is characterized by low Th, Y, and REE contents, has been identified in both the Youdong and Changjiang granites (Qi et al., 2014; Zhang et al., 2021). The similarity of REE patterns between pitchblende from ores and hosting granites reflects genetic relationships (Fig. 8a–c, Fig. 9a–b). Such high W contents in pitchblende from the SLQ, MHK and CP deposits indicate a close connection between the mineralization and hosting granites. The hydrothermal fluid possibly leaches W from the surrounding W-rich hosting granites or early formed W deposits. Simultaneously, the U hosted by the accessory minerals of the granites releases and forms U- and W-rich ore-forming fluids.
The close relationship between mafic dikes and mineralization has been widely studied in U deposits worldwide. Zhang et al. (2018) summarized the function of mafic dikes in U mineralization, which could have (1) provided mineralizer CO2 for U migration in fluid (Wang et al., 1991; Hu et al., 2008; Luo et al., 2015), (2) created favorable conditions for U leaching from U-rich rocks and transference along the fault (Rogers and Bird, 1987; Wang et al., 1991), (3) served as reducing agents for U precipitation due to the presence of Fe2+-bearing phases (e.g., pyrite, amphibole, and pyroxene) (Tappa et al., 2014; Wang et al., 1991, 2015), and (4) provided a favorable position for U precipitation (Wang et al., 1991, 2015; Zhong et al., 2019). In the Changjiang ore field, the U mineralization age (~70 Ma) is much younger than the emplacement ages of diabasic dykes (~140 Ma, ~105 Ma and ~90 Ma, Li et al., 1997; Zhang et al., 2018), excluding mineralizer CO2 directly from mantle-derived mafic magma. Notably, the NE-trending faults (e.g., Mianhuakeng and Huangxishui faults) in the Zhuguangshan complex not only control the U deposits but also constrain the sites of hot springs (up to 98°C) (Huang et al., 2010; Zhou, 2016). These hot springs are enriched in soluble F– and CO32– ligands, which play a key role in U migration in solution (Li, 1992; Hu et al., 2008). According to drilling exploration, most U mineralization is hosted by microcrystalline quartz veins in granite, and only a small amount of U mineralization is hosted by diabase. Therefore, we propose that diabasic dikes in the Changjiang U ore field may locally serve as favorable reductive agents for pitchblende precipitation. This crucial mineralizer CO2 for U mineralization probably comes from the NE-trending fault systems in the Zhuguangshan district (Wang et al., 2015; Zhong et al., 2019). No vital function of diabasic dykes for U mineralization in this study area is confirmed by the low Co, Ni and Cr contents of pitchblende in ores and differentiable REE patterns between pitchblende in ores and diabase.
The transport and precipitation of uranium in hydrothermal fluids are controlled by the oxygen fugacity (fO2) of the solution (Cuney, 1978, 2009; Ling, 2011; Bonnetti et al., 2018). The H-O isotope data of ore-forming fluid in the Changjiang ore field suggest that the fluid initially originated from meteoric water (Zhang et al., 2017a; Chi et al., 2020). Meteoric water percolating along faults could combine with mantle-derived mineralizer CO2 triggered by Cretaceous–Tertiary crustal extensional events to form CO2-rich oxic fluids (Hu et al., 2008; Luo et al., 2015, 2017). These fluids could leach U from the Youdong and Changjiang granites through water-rock interactions and transport soluble U6+ as soluble UO2(CO3)22–, UO2(CO3)34– and UO2F24– complexes in fluids (Cuney, 1978; Leroy, 1978; McLennan and Taylor, 1979; Min et al., 1999; Zhang et al., 2019). This is proven by the presence of calcite and fluorite in U-bearing hydrothermal veins. This process results in various hydrothermal alterations (e.g., chloritization, hydromicazation and sericitization) around the faults. Pitchblende precipitation may be triggered by CO2 degassing, decreases in T, P, Eh and pH values, and reductions in U6+ to U4+ in fluid (Turpin et al., 1990; Hu et al., 2008; Cuney, 2009; Dolníček et al., 2014; Luo et al., 2015, 2017; Wang et al., 2015). The abundant Fe2+-bearing minerals (e.g., biotite and chlorite) in the Youdong and Changjiang granites serve as favorable reductive agents for pitchblende precipitation.
In summary, the formation of U mineralization in the Changjiang ore field may be controlled by U-rich granite, Cretaceous–Tertiary crustal extension, regional faults within granite and hydrothermal alteration. The fracture zones with intensive hydrothermal alterations should receive more attention in the future exploration for granite-related U deposits in the Zhuguangshan district.
1. Pitchblende was the main ore mineral in the Changjiang U ore field and was characterized by high U, Sr, As and W contents; varying Ca, Si, Bi, Y, V, Zn and Mo contents; and low Pb, Th, Zr, Nb, Ta, Hf, Co, Ni and REE contents. These geochemical signatures suggest hydrothermal genesis.
2. The hosting Youdong and Changjiang granites were the major U sources for mineralization. The uraninite in these granites appeared to be the main U source mineral.
3. Uranium mineralization developed in a typical environment with the following conditions: low temperature (<250°C), low oxygen fugacity (log fO2 = –29.5 – –25.5), weakly acidic (pH = 5.3–5.9), high CO32– and F- densities and a silicon-saturated fluid.
4. U-rich granite, crustal extension, regional faults and hydrothermal alteration were the critical factors for U formation.
We express our sincere thanks to Xinwen Guo and You Xu from Research Institute No. 290 for their help in the field. We are grateful to Wei Gao at the Wuhan SampleSolution Analytical Technology Co., Ltd. for the helping with LA-ICP-MS analyses. This work was supported by National Natural Science Foundation of China Projects (No. 42002095, 41862010, 42162013, 41902075, 41772066) and the China Uranium Industry Co. LTD. - East China Institute of Technology Innovation Partnership Fund (NRE2021-05, NRE2021-09).
