Geochemical and Geochronological Constraints on a Granitoid Containing the Largest Indosinian Tungsten (W) Deposit in South China (SC): Petrogenesis and Implications

: Chuankou tungsten (W) ore ﬁeld, with an estimated WO3 reserve exceeding 300,000 tonnes, is so far the largest Indosinian (Triassic) granite-related W ore ﬁeld in South China. However, the precise emplacement ages, Trace elements within the zircons and whole-rock geochemistry yielded evidence of the close relationship between W mineralization and G-1 and G-2 granitoids of the Chuankou ore ﬁeld. The batholith of the Chuankou ore ﬁeld was formed 20–10 Ma later than the peak age of the collisions orogeny and formed in a post-collisional setting.


Introduction
South China (SC) is renowned for its extensive magmatism and the giant ore deposit clusters of W, Sn, Mo, Bi, Pb, Zn, Sb, U, Be, Nb, Ta, and REEs in the Yanshanian period [1][2][3][4][5]. These ore deposits host more than 90% of China's W resources; over 56% of global W resources [1 -3]. Extensive research has been carried out around Yanshanian W mineralization and related igneous rocks using high-precision geochronological data [2,[6][7][8][9][10][11][12][13][14][15][16]. In contrast, the Indosinian igneous rocks and W deposits have been not widely concerned since they are small in size and bear minimal U, Nb, and Ta deposits [17][18][19]. Recently, Sample reports on Indosinian W-Sn mineralization (the Miao'ershan W-Mo deposit, Hehuaping Sn deposit, Xiane'tang Sn deposit, Xitian Sn deposit, Nanyangtian W-Mo deposit, and Qingshan W deposit) have come to the forefront [2,12,[20][21][22][23][24] (Figure 1b). Due to the unique spatial and Previous research has identified the close genetic relationships between W deposits and granitoids in the South China block (SCB). Numerous studies have shown that W-bearing granitoids generally present S-and/or A-type granitoid affinities and are enriched in SiO2 and volatiles (e.g., Li and F) [25,26]. Recently, Zhang et al. [27] and Jiang et al. [28] confirmed that W-bearing granitoids are highly fractionated I-type granite based on the investigation of Yanshannian W deposits from Jiangxi Province and Guangdong Province. However, Huang et al. [29] proposed that W-bearing granitoids from Indosinian Yuntoujie W deposits are obvious highly fractionated S-type granite affinities. Therefore, further research is needed to solve the issue of whether the W-bearing granitoids are highly fractionated I-type or S-type.
The Chuankou W ore field is situated in the middle of the SCB and has been identified as the largest W ore field of SC with a total W metal content of over 300,000 tonnes ( Figure 1a). Moreover, there are 14 important W deposits distributed in the ore field (Table 1). Bai et al. [30] suggested that the host rocks of the Chuankou W deposit were formed 170 to 160 Ma. Peng et al. [31] suggested zircon U-Pb dating of host rocks to around 220 Ma and a molybdenite Re-Os to 221 Ma for the Sanjiaotan W deposit. However, up to now, the precise emplacement ages, sources of granitoids from the Chuankou ore field, and their relationship with W mineralization have been less studied and are still not well understood. Previous research has identified the close genetic relationships between W deposits and granitoids in the South China block (SCB). Numerous studies have shown that Wbearing granitoids generally present S-and/or A-type granitoid affinities and are enriched in SiO 2 and volatiles (e.g., Li and F) [25,26]. Recently, Zhang et al. [27] and Jiang et al. [28] confirmed that W-bearing granitoids are highly fractionated I-type granite based on the investigation of Yanshannian W deposits from Jiangxi Province and Guangdong Province. However, Huang et al. [29] proposed that W-bearing granitoids from Indosinian Yuntoujie W deposits are obvious highly fractionated S-type granite affinities. Therefore, further research is needed to solve the issue of whether the W-bearing granitoids are highly fractionated I-type or S-type.
The Chuankou W ore field is situated in the middle of the SCB and has been identified as the largest W ore field of SC with a total W metal content of over 300,000 tonnes ( Figure 1a). Moreover, there are 14 important W deposits distributed in the ore field (Table 1). Bai et al. [30] suggested that the host rocks of the Chuankou W deposit were formed 170 to 160 Ma. Peng et al. [31] suggested zircon U-Pb dating of host rocks to around 220 Ma and a molybdenite Re-Os to 221 Ma for the Sanjiaotan W deposit. However, up to now, the precise emplacement ages, sources of granitoids from the Chuankou ore field, and their relationship with W mineralization have been less studied and are still not well understood.

Ore Deposit Geology
The Proterozoic metamorphic basement exposed in the center of the ore field contains a metamorphic silty slate and an argillaceous slate of the Neoproterozoic Wuqiangxi Formation of Banxi group. These are the most important host rocks of the quartz vein-type wolframite. The Paleozoic strata are exposed in the margin of the ore field and are unconformably covered above the metamorphic basement. It is composed of siliceous sedimentary breccia and shale with of the Devonian Yanglinao Formation (D2y), shale of the Carboniferous Yanguan Formation (C1y), and the diluvial layer of the Quaternary. Among them, the siliceous sedimentary breccia of Yanglinao Formation (D2y) has been confirmed as one of the wall rocks of the vein-type scheelite in the Yanglinao deposit ( Figure 2). The Chuankou W ore field is exposed in the core of the Chuankou uplift, which is composed of a series of anticlines. The Chuankou uplift belongs to the eastward extension of the Qiyangshan zigzag-shaped structural ridge axis. Two groups of folds were developed: (1) the early E-W-direction fold belt and (2) the late N-S-direction fold belt. Fault structures in the ore field are oriented mainly in an NNW direction and NEE direction. The ENE-direction fault clusters are early faults that occur near the internal contact zone between the granitoids and surrounding rocks. The NNW-direction fault clusters are deep normal faults, which control the ore body's occurrences, orientation and enrichment ( Figure 2).
Granitoids of the Chuankou ore field are exposed in the core of the Chuankou uplift with an area of 15 km 2 . According to fieldwork in this research, four main magmatic stages could be observed ( Figure 2). The emplacement sequence is biotite monzogranite (G-1) → two-mica monzogranite (G-2) → fine-grained granite (G-3) → granite porphyry (G-4) (Figure 3a-d).

Ore Deposit Geology
The Proterozoic metamorphic basement exposed in the center of the ore field contains a metamorphic silty slate and an argillaceous slate of the Neoproterozoic Wuqiangxi Formation of Banxi group. These are the most important host rocks of the quartz veintype wolframite. The Paleozoic strata are exposed in the margin of the ore field and are unconformably covered above the metamorphic basement. It is composed of siliceous sedimentary breccia and shale with of the Devonian Yanglinao Formation (D2y), shale of the Carboniferous Yanguan Formation (C1y), and the diluvial layer of the Quaternary. Among them, the siliceous sedimentary breccia of Yanglinao Formation (D2y) has been confirmed as one of the wall rocks of the vein-type scheelite in the Yanglinao deposit ( Figure 2). The Chuankou W ore field is exposed in the core of the Chuankou uplift, which is composed of a series of anticlines. The Chuankou uplift belongs to the eastward extension of the Qiyangshan zigzag-shaped structural ridge axis. Two groups of folds were developed: (1) the early E-W-direction fold belt and (2) the late N-S-direction fold belt. Fault structures in the ore field are oriented mainly in an NNW direction and NEE direction. The ENE-direction fault clusters are early faults that occur near the internal contact zone between the granitoids and surrounding rocks. The NNW-direction fault clusters are deep normal faults, which control the ore body's occurrences, orientation and enrichment ( Figure 2).
Granitoids of the Chuankou ore field are exposed in the core of the Chuankou uplift with an area of 15 km 2 . According to fieldwork in this research, four main magmatic stages could be observed ( Figure 2). The emplacement sequence is biotite monzogranite (G-1) → two-mica monzogranite (G-2) → fine-grained granite (G-3) → granite porphyry (G-4) (Figure 3a-d).
(3) Fine-grained granite (G-3) is widely exposed at the region and intrudes into the G-2 and metamorphic slate as veins about 30-50 cm in width. G-3 is dark to gray in color and has a fine-grained texture. The minerals assemblage includes quartz, plagioclase, K-feldspar, and muscovite. Generally, the mineral crystals of G-3 are smaller than 0.5 mm. Slight alteration were developed in K-feldspar crystals (Figure 4b,c,l).
(3) Fine-grained granite (G-3) is widely exposed at the region and intrudes into the G-2 and metamorphic slate as veins about 30-50 cm in width. G-3 is dark to gray in color and has a fine-grained texture. The minerals assemblage includes quartz, plagioclase, K-feldspar, and muscovite. Generally, the mineral crystals of G-3 are smaller than 0.5 mm. Slight alteration were developed in K-feldspar crystals (Figure 4b,c,l).
(4) Granite porphyry (G-4) is only exposed on the north side of Chishui Village roads. It occurs as a vein and intrudes into G-2 with a width of 15-20 m. G-4 exhibits a large structure and porphyritic texture. The phenocrysts (approximately 30 vol.% of the whole rocks) are 0.5-2 mm in size and composed of quartz (30 vol.% of total phenocrysts), potassium feldspar (60 vol.% of total phenocrysts), and a small amount of plagioclase and muscovite (less than 10 vol.%). The matrix is microgranular, which occupies 70 vol.% of all rocks (Figure 4f,k).

Alteration and Mineralization
Field observation shows that hydrothermal alteration occurred in the contact zone between the granitoids and Neoproterozoic strata and its adjacent area. The alteration types contain silicification, greisenization, potash feldspathization, tourmalinization, carbonatization, argillization. Greisenization, and silicification as the main high-temperature hydrothermal alterations that are widely developed at the top of the contact zones between the G-2 and Neoproterozoic strata. In addition, greisenization occurred intensely along the margins between barren or fertile quartz veins. The interior of the veins developed potassium feldspar, tourmaline, and calcite.

Alteration and Mineralization
Field observation shows that hydrothermal alteration occurred in the contact zone between the granitoids and Neoproterozoic strata and its adjacent area. The alteration types contain silicification, greisenization, potash feldspathization, tourmalinization, carbonatization, argillization. Greisenization, and silicification as the main high-temperature hydrothermal alterations that are widely developed at the top of the contact zones between the G-2 and Neoproterozoic strata. In addition, greisenization occurred intensely along the margins between barren or fertile quartz veins. The interior of the veins developed potassium feldspar, tourmaline, and calcite.
The mineralization types of the Chuankou ore field include altered granite-type scheelite and molybdenite, quartz vein-type wolframite, and veinlet-disseminated-type scheelite. Among them, the altered granite-type scheelite and molybdenite occur in the top greisenization zone of two-mica monzogranites (Maowan, Hubeichong, and Baishui deposits); generally, low ore grades and limited spatial scales. Quartz vein-type wolframite occurs in the fault zone above the granitoids (Nanwan and Hunaglong deposits). Ore-bearing veins are along the NNE direction, and the angle of inclination is 70 • to 80 • . Veinlet-disseminated scheelite has economic value only in the Yanglinao deposit, and it occurs in the siliceous breccia belt (D 2 y) as a mesh vein structure.

Geochoronology
Zircon grains were separated for U-Pb age dating at the Langfang Regional Geology and Mineral Resources Survey Institute. The bulk samples were crushed to 60-80 mesh (3) The low-to middle-temperature hydrothermal period. The quartz and sulfide stage shows no obvious mineralization of W. The minerals assemblage is composed by chalcopyrite, sphalerite, pyrite, and arsenopyrite. (Figure 6i-l) (4) Low-temperature hydrothermal period. Low-temperature minerals (fluorite and calcite) and a small amount of sulfide (sphalerite and galena) are the dominant minerals in this period.

Geochoronology
Zircon grains were separated for U-Pb age dating at the Langfang Regional Geology and Mineral Resources Survey Institute. The bulk samples were crushed to 60-80 mesh size, and zircons were separated using gravity and electromagnetic techniques and hand-picked under a binocular microscope. The samples were then mounted on epoxy resin, smoothed and polished, and finally gold coated. The zircons were examined using transmitted and reflected light and cathodoluminescence (CL) microscopy. Zircon U-Pb dating was performed at the Institute of Mineral Resources, CAGS, Beijing, using a Finnigan Neptune inductively coupled plasma mass spectrometer (MC-ICP-MS) with a new wave UP213 laserablation system. Helium was used as the carrier gas, and the beam diameter was 30 µm with a 10 Hz repetition rate and laser power of 2.5 J/cm 2 . Eight ion counters were used to simultaneously receive the 238 U, 235 U, 232 Th, 208 Pb, 207 Pb, 206 Pb, 204 Pb, and 202 Hg signals, whereas data for 208 Pb, 232 Th, 235 U, and 238 U were collected on a Faraday cup. Zircon GJ-1 was used as standard, and Plešovice zircon was used to optimize the mass spectrometer. U, Th, and Pb concentrations were calibrated using 29 Si as an internal standard and zircon M127 (U: 923 ppm; Th: 439 ppm; Th/U: 0.4750) as an external standard [42]. 207 Pb/ 206 Pb, and 206 Pb/ 238 U were calculated using the ICP-MS DataCal 4.3 program. Common Pb was not corrected because of high 206 Pb/ 204 Pb. Abnormally high 204 Pb data were deleted. The Plešovice zircon was dated as unknown and yielded a weighted mean 206 Pb/ 238 U age of 337 ± 2 Ma (2SD, n = 12), which is in good agreement with the recommended 206 Pb/ 238 U age of 337.13 ± 0.37 Ma (2SD) [43]. Age calculations were performed, and Concordia diagrams were generated using the Isoplot/Ex 3.0 software [44].

Geochemistry
Whole-rock major, trace, and rare earth element concentrations were analyzed at the National Geological Experiment Test Center, Beijing. Whole-rock major, trace, and rare earth element concentrations were analyzed at the National Geological Experiment Test Center, Beijing. Whole-rock major elements were analyzed using a plasma spectrometer (PE8300). All results were normalized against the Chinese rock reference standard JY/T015-1996 [45]. The analytical uncertainties were less than ±2%.

Sr-Nd Isotope
Fresh samples were ground with an agate mill and powders were spiked with mixed isotope tracers, dissolved in Teflon capsules with HF + HNO 3 acid, and separated by conventional cation-exchange techniques. The isotopic measurements were performed on a VG-354 mass spectrometer at the Institute of Geology and Geophysics, Chinese Academy of Sciences [46]. The mass fractionation corrections for Sr and Nd isotopic ratios were based on 86 Sr/ 88 Sr = 0.1194 and 146 Nd/ 144 Nd = 0.7219. Repeat analyses yielded an 87 Sr/ 86 Sr ratio of 0.71023 ± 0.00006 for the NBS-987 Sr standard and an 143 Nd/ 144 Nd ratio of 0.511845 ± 0.000012 for the La Jolla standard. Detailed descriptions of the analytical techniques can be found elsewhere-in [47] and references therein.
(2) G-1: The length/width ratios of zircons are close to 1-2. The sizes of zircons range from 100 to 150 µm ( Figure 7). The U content ranges from 249.1 to 1094.1 ppm, Pb content ranges from 12.1 to 124 ppm, and Th content ranges from 132.1 to 1072 ppm. Th/U ratios are from 0.23 to 1.81, and 206 Pb/ 238 U ages are from 206.6 ± 6.3 to 232.9 ± 7.1 Ma. The concordance age of the zircon grains is 230.8 ± 1.6 Ma (MSWD = 0.31).
(3) G-3: Zircons are columnar crystals with grain sizes ranging from 50 to 150 µm, typical of acidic magmatic zircons, with Th/U ratios of 0.12-2.07, Pb content from 17.9 to 265.71 ppm, Th content from 54.46 to 1425.03 ppm, and U content from 295.74 to 12,287.53 ppm. The obtained 206 Pb/ 238 U ages reveal two notably different groups: the first group is from 200.5 ± 3.51 to 203.9 ± 3.55 Ma with a concordance age of 203.1 ± 1.6 Ma (MSWD = 7.2). The 206 Pb/ 238 U age of the second group ranges from 218.2 ± 4.11 to 226.8 ± 4.05 Ma, and the concordance age is 224.8 ± 1. 6        (2) G-1: The length/width ratios of zircons are close to 1-2. The sizes of zircons range from 100 to 150 μm (Figure 7). The U content ranges from 249.1 to 1094.1 ppm, Pb content ranges from 12.1 to 124 ppm, and Th content ranges from 132.1 to 1072 ppm. Th/U ratios

Geochemistry
Thirteen samples from the Chuankou ore field were analyzed and the analysis results are listed in Table 3.   (12.91-16.47 wt.%) and characterized by low Na 2 O (0.12-3.54 wt.%) and ALK (3.52-6.91 wt.%) contents. G-4 has the lowest Na 2 O content (0.08 wt.%), MnO content (0.04 wt.%), and has the highest K 2 O contents (4.77-4.79 wt.%). In the SiO 2 versus ALK diagram, the granitoids plot into the subalkaline granite field (Figure 9a). In the SiO 2 vs. K 2 O diagram and Si vs. ALK-Ca diagram, all the samples plot into the high-K calc-alkaline field (Figure 9b,d). In the A/NK-A/CNK diagram, samples plot into the peraluminous field, implying that the granitoids of the Chuankou ore field belong to the high-K calc-alkaline and peraluminous series (Figure 9c).

Geochemistry
Thirteen samples from the Chuankou ore field were analyzed and the analysis results are listed in Table 3.
G-1 is characterized by high SiO2 ( In the SiO2 versus ALK diagram, the granitoids plot into the subalkaline granite field (Figure 9a). In the SiO2 vs. K2O diagram and Si vs. ALK-Ca diagram, all the samples plot into the high-K calc-alkaline field ( Figure  9b,d). In the A/NK-A/CNK diagram, samples plot into the peraluminous field, implying that the granitoids of the Chuankou ore field belong to the high-K calc-alkaline and peraluminous series (Figure 9c).  0.06~0.23) (Figure 10a). The values of LaN/YbN range from 0.93 to 2.39. Rb, Hf, and U are enriched and Ba, Sr, and Ti are depleted (Figure 11a). Rb/Sr ratios vary from 14.26 to 34.48, K/Rb ratios range from 42.96 to 73.83, and Rb/Ba ratios range from 6.04 to 7.88. The value of Zr + Nb + Y + Ce ranges from 97.9 to 155.75 ppm. The chondrite-normalized REE patterns of G-3 are similar to G-2. The δEu values of G-3 range from 0.02 to 0.45, and the values of LaN/YbN range from 0.75 to 6.87 (Figure 10c). Rb, Hf, and Th are enriched and Ba, Sr, P, and Ti are depleted (Figure 11c) Figure 10d). Zr, Hf, Rb, Th, and U are enriched and Ba, Sr, P, and Ti are depleted ( Figure  11d). The Rb/Sr ratios vary from 13.06 to 13.20, K/Rb ratios range from 87.19 to 87.83, and Rb/Ba ratios range from 1.32 to 1. 34. The values of Zr + Nb + Y + Ce range from 281.59 to 284.42 ppm.

Zircon Geochemistry and Ce 4+ /Ce 3+ Ratios
The trace element compositions of zircon grains from the granitoids in the Chuankou ore field are shown in Table 4. Most of the Ti, Sr, and Ta contents of zircon grains are much closer to the values range proposed by Hoskin and Schaltegger [49] (Nb: up to 62 ppm; Sr ≤ 3 ppm; Ti: up to 75 ppm), which could be interpreted as normal magmatic zircon with various microscopic mineral inclusions, such as rutile and

Zircon Geochemistry and Ce 4+ /Ce 3+ Ratios
The trace element compositions of zircon grains from the granitoids in the Chuankou ore field are shown in Table 4. Most of the Ti, Sr, and Ta contents of zircon grains are much closer to the values range proposed by Hoskin and Schaltegger [49] (Nb: up to 62 ppm; Sr ≤ 3 ppm; Ti: up to 75 ppm), which could be interpreted as normal magmatic zircon with various microscopic mineral inclusions, such as rutile and ferrotapiolite [50]. The ΣREE contents of G-1 range from 787.62 to 2080.54 ppm, those of G-2 range from 935.37 to 11,137.50 ppm, and those of G-3 range from 1387.73 to 4694.70 ppm. The chondritenormalized REE patterns reveal an obvious enrichment of HREEs and depletion of LREEs but depletion of LREEs and connect with a magmatic origin [51]. All samples commonly show positive Ce anomalies and negative Eu anomalies in the zircons ( Figure 12). However, there is an obvious difference in the degree of Ce and Eu anomalies in that G-1 and G-2 contain more negative Eu anomalies and positive Ce anomalies (δEu = 0.03-0.28; δCe = 1.56-189.58) than G-3 (δEu = 0.12-0.47, with a value of 1.41; δCe = 1.04-8.81). Despite this difference, all zircon grains in the study appear to be magmatic in origin and do not show geochemical evidence of metamorphic, hydrothermal overprinting or radiationinduced damage. Ballard et al. [52] proposed a detailed calculation formula for the Ce 4+ /Ce 3+ ratio: The zircon-melt partition coefficients for Ce 3+ and Ce 4+ were estimated using the model described by Ballard [31,56]. Due to the absence of detailed field observations and efficient constraints on geochronology, the magmatic process and evolution of granitoids from the Chaunkou ore field remain unclear.
In this study, zircon U-Pb geochoronological analysis of the four main phases (G-1-G-4) was carried out. G-1 is exposed at the depth of the Maowan and Tangjiangyuan deposits. The formation age of G-1 is 230.8 ± 1.6 Ma (MSWD = 0.31). G-2 is the dominant part and represents approximately 70% of the granitoids in size. The formation age of G-2 is 222.1 ± 0.56 Ma, which is similar to the results of 223.1-224. 6 Ma within the allowed error range [57]. G-3 intruded into G-2 as a dyke, and two groups of concordance ages can be identified. The first group of 224.8 ± 1.6 Ma (MSWD = 0.047) is consistent with G-2 and suggests that the zircons might be xenocrysts. The second group is 203.1 ± 1.6 Ma (MSWD = 7.2), representing the formation age. G-4 intruded into G-2 as larger veins with width from 0.5 to 3 m. The field observations and analysis results confirm the conclusion that G-4 formed at 135.5 ± 2.4 Ma (MSWD = 1.3).
In summary, the Chuankou ore field experienced at least four stages of magmatism. The emplacement sequence is G-1 (phase I), G-2 (phase II), G-3 (phase III), and G-4 (phase IV).

Genesis Type
The granitoids of the Chuankou ore field are peraluminous, reflected in both the major element ratios (A/CNK ranging from 1.110 to 4.238) and the secondary and accessory minerals (spessartine, muscovite, biotite and tourmaline). The granitoids are commonly enriched in Rb, Zr, Hf, Th, and U, whereas they are depleted in Ba, Sr, P, and Ti. In addition, total alkali content ranges from 3.57 to 7.53 ppm, FeO T /MgO ratios range from 2.40 to 13.98, and Zr + Nb + Ce + Y values range from 97.9 to 284.42 ppm. These indexes are significantly lower than the global average of A-type granite (350 ppm) [58]. In the Zr + Nb + Ce + Y vs. ALK and Zr + Nb + Ce + Y vs. FeO T /MgO diagrams, samples plot into the FG field suggesting that the granitoids from the Chuankou ore field have an affinity for fractionated I/S-type granite (Figure 13a,b). Thirdly, in the A (Al-Na-K)-C (Ca)-F (Fe 2+ + Mg) ternary diagram, samples plot in the S-type granite field, also indicating an S-type granite affinity ( Figure 14). In summary, the Chuankou ore field experienced at least four stages of magmatism. The emplacement sequence is G-1 (phase I), G-2 (phase II), G-3 (phase III), and G-4 (phase IV).

Genesis Type
The granitoids of the Chuankou ore field are peraluminous, reflected in both the major element ratios (A/CNK ranging from 1.110 to 4.238) and the secondary and accessory minerals (spessartine, muscovite, biotite and tourmaline). The granitoids are commonly enriched in Rb, Zr, Hf, Th, and U, whereas they are depleted in Ba, Sr, P, and Ti. In addition, total alkali content ranges from 3.57 to 7.53 ppm, FeO T /MgO ratios range from 2.40 to 13.98, and Zr + Nb + Ce + Y values range from 97.9 to 284.42 ppm. These indexes are significantly lower than the global average of A-type granite (350 ppm) [58]. In the Zr + Nb + Ce + Y vs. ALK and Zr + Nb + Ce + Y vs. FeO T /MgO diagrams, samples plot into the FG field suggesting that the granitoids from the Chuankou ore field have an affinity for fractionated I/S-type granite (Figure 13a,b). Thirdly, in the A (Al-Na-K)-C (Ca)-F (Fe 2+ + Mg) ternary diagram, samples plot in the S-type granite field, also indicating an S-type granite affinity ( Figure 14).

Origin
In this study, granitoids from the Chuankou ore field are characterized by high 87 Rb/ 86 Sr ratios (varying from 13.5591 to 152.3436) and extremely high 87 Sr/ 86 Sr ratios (from 0.751712 to 1.292048). The initial 87 Sr/ 86 Sr values range from 0.67995 to 0.85226, which is beyond the range of normal continental crust and primitive mantle. Thus, these data cannot be used to trace the source of magma due to the hydrothermal alteration during the W mineralization process.
Conversely, the activities of Sm and Nd and the relevant isotopic composition remain unchanged in the evolution and alteration process. The Sm-Nd isotopic composition could be considered as a reasonable indicator for the source region. In this research, ε Nd (t) values of granitoids from the Chuankou ore field are −10.77 for G-1, −7.74 to −9.3 for G-2, and −6.53 to −10.07 for G-3. The samples plot in the Cathaysia basement field in the T(Ma) vs. ε Nd (t) diagram (Figure 15b). The calculated T DM2 and ε Nd (t) values (2090 Ma for G-1, 1684 to 1764 Ma for G-2, and 1471 to 1669 Ma for G-3) reveal a crustal origin by partial melting. G-1 was derived from the metamorphic basement in the Paleoproterozoic Era, while G-2 and G-3 were of homogeneous origin in the Mesoproterozoic Era. Significantly negative correlations of the formation ages with T DM2 (2090 Ma → 1684 to 1764 Ma → 1471 to 1669 Ma) and ε Nd (t) (−10.77 → −9.3 to −7.74 → −10.07 to −6.53) indicate that the proportion of crustal components in the source area decreased gradually; however, the composition of the mantle shows an obvious increasing trend. In the AMF vs. CMF diagram, the granitoids plot near the region of metapelitic sources and metagraywackes far from the metamorphic basalt and tonalite field. This indicates that the source rocks of granitoids from the Chuankou ore field are mainly crystal schists and gneisses formed by metamorphic Proterozoic mudstones and metagraywackes (Figure 15a). affinity for fractionated I/S-type granite (Figure 13a,b). Thirdly, in the A (Al-Na-K)-C (Ca)-F (Fe 2+ + Mg) ternary diagram, samples plot in the S-type granite field, also indicating an S-type granite affinity (Figure 14).

Origin
In this study, granitoids from the Chuankou ore field are characterized by high 87 Rb/ 86 Sr ratios (varying from 13.5591 to 152.3436) and extremely high 87 Sr/ 86 Sr ratios (from 0.751712 to 1.292048). The initial 87 Sr/ 86 Sr values range from 0.67995 to 0.85226, which is beyond the range of normal continental crust and primitive mantle. Thus, these data cannot be used to trace the source of magma due to the hydrothermal alteration during the W mineralization process.
Conversely, the activities of Sm and Nd and the relevant isotopic composition remain unchanged in the evolution and alteration process. The Sm-Nd isotopic composition could be considered as a reasonable indicator for the source region. In this research, εNd(t) values of granitoids from the Chuankou ore field are −10.77 for G-1, −7.74 to −9.3 for G-2, and −6.53 to −10.07 for G-3. The samples plot in the Cathaysia basement field in the T(Ma) vs. εNd(t) diagram (Figure 15b). The calculated TDM2 and εNd(t) values (2090 Ma for G-1, 1684 to 1764 Ma for G-2, and 1471 to 1669 Ma for G-3) reveal a crustal origin by partial melting. G-1 was derived from the metamorphic basement in the Paleoproterozoic Era, while G-2 and G-3 were of homogeneous origin in the Mesoproterozoic Era. Significantly negative correlations of the formation ages with TDM2 (2090 Ma → 1684 to 1764 Ma → 1471 to 1669 Ma) and εNd(t) (−10.77 → −9.3 to −7.74 → −10.07 to −6.53) indicate that the proportion of crustal components in the source area decreased gradually; however, the composition of the mantle shows an obvious increasing trend. In the AMF vs. CMF diagram, the granitoids plot near the region of metapelitic sources and metagraywackes far from the metamorphic basalt and tonalite field. This indicates that the source rocks of granitoids from the Chuankou ore field are mainly crystal schists and gneisses formed by metamorphic Proterozoic mudstones and metagraywackes (Figure 15a).

Magmatic Process
During the granitic magmatism process, Ti was mainly absorbed in ilmenite, rutile, titanite, biotite and anatase. The separation of Ti-bearing phases at relatively moderate to low temperatures would have led to a significant depletion of Ti, Nb, Ta. Eu, Sr, and Ba which existed stably by substituting into the K + site in the K-feldspar and/or Ca 2+ site in plagioclase. P is the dominant component of apatite. There is significant depletion of Sr, Ba, P, and Ti of granitoids from the Chuankou granitoids, indicating obvious fractional crystallization of feldspar, biotite, Ti-bearing minerals, and apatite in magmatic processes [59]. In addition, the Eu/Eu* ratios, Rb/Sr ratios, Sr, and Ba could be used as markers to identify fractional crystallization. The correlations between Rb/Sr and Sr, Ba and Sr, and Eu/Eu* and Ba suggest that the fractional crystallization of K-feldspar, plagioclase and biotite was the main genetic mechanism (Figure 16a-d). For the REEs (La and Yb), carrier minerals included zircon, apatite, allanite, and monazite. The correlations between

Magmatic Process
During the granitic magmatism process, Ti was mainly absorbed in ilmenite, rutile, titanite, biotite and anatase. The separation of Ti-bearing phases at relatively moderate to low temperatures would have led to a significant depletion of Ti, Nb, Ta. Eu, Sr, and Ba which existed stably by substituting into the K + site in the K-feldspar and/or Ca 2+ site in plagioclase. P is the dominant component of apatite. There is significant depletion of Sr, Ba, P, and Ti of granitoids from the Chuankou granitoids, indicating obvious fractional crystallization of feldspar, biotite, Ti-bearing minerals, and apatite in magmatic processes [59]. In addition, the Eu/Eu* ratios, Rb/Sr ratios, Sr, and Ba could be used as markers to identify fractional crystallization. The correlations between Rb/Sr and Sr, Ba and Sr, and Eu/Eu* and Ba suggest that the fractional crystallization of K-feldspar, plagioclase and biotite was the main genetic mechanism (Figure 16a-d). For the REEs (La and Yb), carrier minerals included zircon, apatite, allanite, and monazite. The correlations between between La and La/Yb suggests that the melt was constrained by the fractional crystallization of allanite and monazite (Figure 16e). In addition, there are no obvious xenoliths (metamorphic slate in the Proterozoic) near the stratigraphic contact belt and no significant correlation between SiO 2 content and ε Nd (t) values. This implies that the fractional crystallization process was relatively clear for the felsic melt rather than for the extensive assimilation-fractional crystallization (AFC) process (Figure 16f). between La and La/Yb suggests that the melt was constrained by the fractional crystallization of allanite and monazite (Figure 16e). In addition, there are no obvious xenoliths (metamorphic slate in the Proterozoic) near the stratigraphic contact belt and no significant correlation between SiO2 content and εNd(t) values. This implies that the fractional crystallization process was relatively clear for the felsic melt rather than for the extensive assimilation-fractional crystallization (AFC) process (Figure 16f). Furthermore, Zr + Nb + Y contents of the Chuankou complex vary from 75.57 to 187.05 ppm, and the Rb/Ba ratios range from 1.33 to 39.41. An obvious negative correlation trend is exhibited on the Zr + Nb + Y versus Rb/Ba diagram, coinciding with the Sandy Cope granite field, indicating the common regulations of highly fractionated granite ( Figure 17).

Relationships between Host Rocks and Tungsten Mineralization
There are three main substitution mechanisms of scheelite in the concent REEs: (1) 2Ca 2+ ↔ Na + + REE 3+ , (2) Ca 2+ + W 6+ ↔ REE 3+ + Nb 5+ , and (3) 3Ca 2+ ↔ 2R (□ vacancy) [60,61]. A significant comparative study between REE patterns of from the Chuankou ore field and Sch-3 was performed and showed high correla In addition, the Sr isotopic composition (Isr) of G-1 (0.72109) is close to the composition of Sch-1 and Sch-3, which is derived from magmatic-hydr conditions without significant fluid/rock interactions and fluid mixing. In addit G-2, and G-3 are highly fractionated S-type granite and contain W concentration several to ten times higher than average crustal concentrations (1.9 ppm and respectively [62]). This characteristic is very similar to the host rocks of we Dahutang superlarge W deposits [63].
To date, the Chuankou W deposit has been identified as the largest Indo deposit in the SCB and contains quartz vein type-, veinlet type-, and altered type-W ore bodies. Cai et al. obtained a formation age of 224.6 ± 1. 31 Ma for th two mica monzogranites [57], which are generally thought to be host disseminated wolframite and scheelite. The ore formation ages of quartz v mineralization ranged from 224 to 230 Ma [31,56,64]. These data are consistent 206 Pb/ 238 U ages of G-1 (230.8 ± 1.6 Ma) and G-2 (222-224 Ma). Field observations h shown the close spatiotemporal relationship between G-1, G-2, and W minera However, the ages of G-3 and G-4 are 203.1 ± 1.6 Ma and 135.5 ± 2.4 Ma (MSW respectively. Seemingly, these intrusions were emplaced after W mineralization. Systematic evidence indicates that the host rocks of the Chuankou W ore fi G-1 and G-2. However, how did W separate from the intrusions and becom concentrated in a limited spatial area? Generally, rutile was the main W-bearing during the early stage of magmatic activity, while wolframite and scheelite do the later stage of magmatic to hydrothermal activity. Because the six-coordina could be substituted by W 6+ accompanied by a double substitution of Fe to mai charge balance [65], W could be concentrated in large amounts in rutile significantly depleted in the residual melt and fluid. However, the granitoids Chuankou ore field (G-1 and G-2) contain 0.26-0.35 wt.% MgO and 1.29-1.77 w

Relationships between Host Rocks and Tungsten Mineralization
There are three main substitution mechanisms of scheelite in the concentration of REEs: (1) 2Ca 2+ ↔ Na + + REE 3+ , (2) Ca 2+ + W 6+ ↔ REE 3+ + Nb 5+ , and (3) 3Ca 2+ ↔ 2REE 3+ + ( vacancy) [60,61]. A significant comparative study between REE patterns of G-1/G-2 from the Chuankou ore field and Sch-3 was performed and showed high correlation [54]. In addition, the Sr isotopic composition (I sr ) of G-1 (0.72109) is close to the medium composition of Sch-1 and Sch-3, which is derived from magmatic-hydrothermal conditions without significant fluid/rock interactions and fluid mixing. In addition, G-1, G-2, and G-3 are highly fractionated S-type granite and contain W concentrations that are several to ten times higher than average crustal concentrations (1.9 ppm and 0.6 ppm, respectively [62]). This characteristic is very similar to the host rocks of well-known Dahutang superlarge W deposits [63].
To date, the Chuankou W deposit has been identified as the largest Indosinian W deposit in the SCB and contains quartz vein type-, veinlet type-, and altered granite type-W ore bodies. Cai et al. obtained a formation age of 224.6 ± 1. 31 Ma for the altered two mica monzogranites [57], which are generally thought to be host rocks of disseminated wolframite and scheelite. The ore formation ages of quartz vein-type mineralization ranged from 224 to 230 Ma [31,56,64]. These data are consistent with the 206 Pb/ 238 U ages of G-1 (230.8 ± 1.6 Ma) and G-2 (222-224 Ma). Field observations have also shown the close spatiotemporal relationship between G-1, G-2, and W mineralization. However, the ages of G-3 and G-4 are 203.1 ± 1.6 Ma and 135.5 ± 2.4 Ma (MSWD = 1.3), respectively. Seemingly, these intrusions were emplaced after W mineralization.
Systematic evidence indicates that the host rocks of the Chuankou W ore field were G-1 and G-2. However, how did W separate from the intrusions and become vastly concentrated in a limited spatial area? Generally, rutile was the main W-bearing mineral during the early stage of magmatic activity, while wolframite and scheelite dominated the later stage of magmatic to hydrothermal activity. Because the six-coordination Ti 4+ could be substituted by W 6+ accompanied by a double substitution of Fe to maintain the charge balance [65], W could be concentrated in large amounts in rutile and was significantly depleted in the residual melt and fluid. However, the granitoids from the Chuankou ore field (G-1 and G-2) contain 0.26-0.35 wt.% MgO and 1.29-1.77 wt.% FeO T and belong to the normal ilmenite-series granite, indicating an obvious absence of rutile in the early crystalline phase [63,66]. In addition, W is a lithophilic element in the bulk silicon earth (BSE), and the multiple stages of partial melting and separation crystallization would have caused a strong concentration of W in the late period of the residual melt phase. Thus, G-1 and G-2 granitoids have significant potential for the mineralization of W.
In addition, with increasing oxygen fugacity, the mineralization series of Sn → W → Mo → Cu (Mo) → Cu (Au) was carried out in succession [67]. The occurrence of W mineralization could be attributed to the reduced granitic magmas that typically belong to the ilmenite series [68,69]. A possible contribution from W 4+ may have only been at the very lowest oxygen fugacity accessible to the experimental method in the melt [70][71][72]. Zircon is a common accessory mineral in intermediate-acid igneous rocks and is stable during later hydrothermal alteration and physiochemical processes. Due to its similar ionic radii and electrovalence, Ce 4+ is more easily absorbed in zircon crystals than light rare earth metal ions (such as Ce 3+ ) that occupy the site of Zr 4+ under oxidizing conditions. Hence, zircon can be invoked as a tracer for the evaluation of relative oxygen fugacity based on its Ce 4+ /Ce 3+ ratios. In this paper, the value of Ce 4+ /Ce 3+ was calculated as 0.33-93.28, which is much lower than the host rocks of well-known, large-scale, porphyry Cu-Au deposits, such as Chuquicamata-El Abra [50], and typical Cu-Au (Mo) deposits from the SCB, such as Dabaoshan porphyry Mo deposits (Ce 4+ /Ce 3+ = 356-1300; Li et al.) [73] and Dexin porphyry Cu deposits (Ce 4+ /Ce 3+ = 495-1922) [53]. In contrast, the Ce 4+ /Ce 3+ ratios were closer to those of W and Sn-bearing granitoids, such as the Guposhan, Qitianling, and Xuehuading granitoids, suggesting a significant metallogenetic potential of W and Sn [69] ( Figure 18). mineralization could be attributed to the reduced granitic magmas that typically belong to the ilmenite series [68,69]. A possible contribution from W 4+ may have only been at the very lowest oxygen fugacity accessible to the experimental method in the melt [70][71][72].
Zircon is a common accessory mineral in intermediate-acid igneous rocks and is stable during later hydrothermal alteration and physiochemical processes. Due to its similar ionic radii and electrovalence, Ce 4+ is more easily absorbed in zircon crystals than light rare earth metal ions (such as Ce 3+ ) that occupy the site of Zr 4+ under oxidizing conditions. Hence, zircon can be invoked as a tracer for the evaluation of relative oxygen fugacity based on its Ce 4+ /Ce 3+ ratios. In this paper, the value of Ce 4+ /Ce 3+ was calculated as 0.33-93.28, which is much lower than the host rocks of well-known, large-scale, porphyry Cu-Au deposits, such as Chuquicamata-El Abra [50], and typical Cu-Au (Mo) deposits from the SCB, such as Dabaoshan porphyry Mo deposits (Ce 4+ /Ce 3+ = 356-1300; Li et al.) [73] and Dexin porphyry Cu deposits (Ce 4+ /Ce 3+ = 495-1922) [53]. In contrast, the Ce 4+ /Ce 3+ ratios were closer to those of W and Sn-bearing granitoids, such as the Guposhan, Qitianling, and Xuehuading granitoids, suggesting a significant metallogenetic potential of W and Sn [69] (Figure 18). Figure 18. The Ce 4+ /Ce 3+ versus EuN/EuN* diagram. The data of blue field named Porphyry Cu-Mo-Au are from [49,70] and there in, the orange field are from [74].
Blevin [75] carried out important work on the granite in the Lachlan fold belt and proposed the parameters to estimate the redox state of granite [75]: (1) The calculated results show that the redox state (ΔOx1) of G-1 ranges from 0.03 to 0.31, that of G-2 ranges from 0.09 to 0.91, that of G-3 ranges from 0.41 to 1.68, and that of G-4 is 0.35. The ΔOx2 of G-1 ranges from −1.19 to −0.16, that of G-2 ranges from −0.70 to 0.32, that of G-3 ranges from −0.06 to 0.56, and that of G-4 is −0.13. Obviously, G-1 and most G-2 had the lowest degree of oxidation. This condition provides an opportunity to remove substantial W from magma to hydrothermal fluids. Indeed, the slightly higher values of ΔOx1 and ΔOx2 in G-3 and G-4 indicate that W would have remained in biotite or muscovite by substitution with the Al 3+ and/or Ga 3+ site instead of expulsion from the melt. Further investigation is needed for the relationship between G-3, G-4 granitoids, and regional W mineralization.  [49,70] and there in, the orange field are from [74].
Blevin [75] carried out important work on the granite in the Lachlan fold belt and proposed the parameters to estimate the redox state of granite [75]: The calculated results show that the redox state (∆Ox1) of G-1 ranges from 0.03 to 0.31, that of G-2 ranges from 0.09 to 0.91, that of G-3 ranges from 0.41 to 1.68, and that of G-4 is 0.35. The ∆Ox2 of G-1 ranges from −1.19 to −0.16, that of G-2 ranges from −0.70 to 0.32, that of G-3 ranges from −0.06 to 0.56, and that of G-4 is −0.13. Obviously, G-1 and most G-2 had the lowest degree of oxidation. This condition provides an opportunity to remove substantial W from magma to hydrothermal fluids. Indeed, the slightly higher values of ∆Ox1 and ∆Ox2 in G-3 and G-4 indicate that W would have remained in biotite or muscovite by substitution with the Al 3+ and/or Ga 3+ site instead of expulsion from the melt. Further investigation is needed for the relationship between G-3, G-4 granitoids, and regional W mineralization.

Metallogenesis and Geodynamic Implications
During the early Middle Triassic, the intense collision and extensive metamorphism between the Indo-China block and Sibumas-Qingtang block exerted far-reaching effects on the SCB [76,77]. In addition, the southeastward subduction and collision of the North China block (NCB) with the South China block (SCB) overlapped due to the closure of the Paleo-Tethys Ocean. The SCB experienced multidirectional compression and extensive shortening, accompanied by thickening of the continental lithosphere [78][79][80][81][82]. During the late Mesozoic period, due to the tectonic regime transformation from Paleotethys dominant to paleo-Pacific tectonic dominant, the tectonic axis changed from the E-W direction to the NE-SW direction [40,83]. The tectonic regime is characterized by multiple stages of compression and extension, resulting in the formation of extensive magmatism and mineralization [9,39,[84][85][86].
Indosinian  (Figure 1b). A possible "V"-shaped distribution model in the region indicates that the central belts of W deposits are relatively older than the others. The western and eastern parts have significantly lower values than those in the central part, which may represent the reactivation of the Proterozoic Qin-Hang tectonic belt under the Indosinian collision orogenetic regime of SC.
Regional Sr-Nd isotopic compositions show that ε Nd (t) values of Indosinian granitoids range from −14.4 to −8 [17,90]. The two-stage depleted mantle model ages of Indosinian granitoids range from 1.63 to 2.09 [17,90]. In general, the T DM2 values better match the formation ages of the Paleoproterozoic metamorphic basement of the SCB [82]. On the other hand, Yanshanian T DM2 values range from 1.04 to 2.28, especially in Northeast Jiangxi. The Nanling area and coastal zone of Fujian and Zhejiang Provinces show multiple belts of low T DM values (<1.6 Ga) and high ε Nd (t) values (>−9), which might match the Mesoproterozoic basement [38,[91][92][93]. Numerous research data confirm that the main source of Yanshanian W mineralization was the Mesoproterozoic metamorphic basement, such as the Shuangqiaoshan group [81,94,95], which has an abnormal enrichment of W content-ten times more than the concentration of the average crust (11.7 ppm of the Shuangqiaoshan group) [96]. The more ancient basement identified in this study suggests a relatively deeper derivation of Indosinian W mineralization. Many valuable insights have been reported regarding the tectonic mechanism of W mineralization in the SCB, and the consensus suggests that the large Yanshanian W mineralization in the SCB was constrained closely by the paleo-Pacific plate regime, which mainly includes the extension of the Shi-Hang belt [38], a mantle plume [7,97], back-arc extension and lithospheric thinning [98], and slab subduction [99,100]. However, a distinct dynamic mechanism was identified in which Indosinian magmatism and mineralization extended approximately east-west in a zone that formed under the extension of a post-collisional setting, which could have been linked to the closure effects of the ancient Tethys Ocean. This setting reflects a relative "free" extension space of the overall compression regime [40,101].
Studies have recently revealed two dominant mineral assemblages and two stages of tectonic regimes in the Indosinian in SC [48,95]. G-1, G-2, and G-3 formed about 20-10 Ma later than the peak period of orogeny triggered by the collage of the SCB, North China craton, and Indo-China block. This reflects a post-collisional setting, which is parallel to the contemporaneous A-type granite in the SCB. In the late stage of the magmatic processes of G-1 and G-2, fertile magmatic fluid converged on the upper part of the granitoids and filled the internal fissure of the slate with the formation of extensive greisenization and granite-type wolframite (Maowan, Wubeichong, and Baishui) and quartz vein-type wolframite (Huanglong, Nanwan, and Sanjiaotan) interior contact belt. The continuous migration of ore-forming fluid up to the interbedded limestone and shale of the Devonian Yanglinao formation occurred (D 2 y). Adequate fluid-rock interactions and abundant Ca 2+ ion reservoirs from the strata made it possible for large-scale dissemination and veinlet scheelite to form (Figure 19b). Ma later than the peak period of orogeny triggered by the collage of the SCB, North China craton, and Indo-China block. This reflects a post-collisional setting, which is parallel to the contemporaneous A-type granite in the SCB. In the late stage of the magmatic processes of G-1 and G-2, fertile magmatic fluid converged on the upper part of the granitoids and filled the internal fissure of the slate with the formation of extensive greisenization and granite-type wolframite (Maowan, Wubeichong, and Baishui) and quartz vein-type wolframite (Huanglong, Nanwan, and Sanjiaotan) interior contact belt. The continuous migration of ore-forming fluid up to the interbedded limestone and shale of the Devonian Yanglinao formation occurred (D2y). Adequate fluid-rock interactions and abundant Ca 2+ ion reservoirs from the strata made it possible for large-scale dissemination and veinlet scheelite to form (Figure 19b).
(2) Granitoids from the Chuankou ore field had significantly high contents of Si and Al and low contents of alkali, Fe, Mg, Mn, and Ca. The granites are commonly enriched in Rb, Zr, Hf, Th, and U but depleted in Ba, Sr, P, and Ti, indicating obvious highly fractionated S-type granite affinities. The Chuankou complex was derived from the partial melting of the Cathaysia basement and underwent significant fractionation of K-feldspar, plagioclase, biotite, Ti-bearing minerals (except rutile), zircon, apatite, allanite, and monazite.
(3) G-1 and G-2 showed a more reductive state than G-3 and even typical host rocks of porphyry copper deposits were identified to have an obvious correlation with W mineralization of the Chuankoou ore field.
(4) Indosinian W deposits were formed in a post-collision setting triggered by the collisional orogeny of SC in the late Paleozoic to early Mesozoic. However, the Yanshanian W deposits reflect strengthened crust-mantle interactions which resulted from the multistage extension of the SCB caused by the westward subduction of the paleo-Pacific plate.
(2) Granitoids from the Chuankou ore field had significantly high contents of Si and Al and low contents of alkali, Fe, Mg, Mn, and Ca. The granites are commonly enriched in Rb, Zr, Hf, Th, and U but depleted in Ba, Sr, P, and Ti, indicating obvious highly fractionated S-type granite affinities. The Chuankou complex was derived from the partial melting of the Cathaysia basement and underwent significant fractionation of K-feldspar, plagioclase, biotite, Ti-bearing minerals (except rutile), zircon, apatite, allanite, and monazite.
(3) G-1 and G-2 showed a more reductive state than G-3 and even typical host rocks of porphyry copper deposits were identified to have an obvious correlation with W mineralization of the Chuankoou ore field.
(4) Indosinian W deposits were formed in a post-collision setting triggered by the collisional orogeny of SC in the late Paleozoic to early Mesozoic. However, the Yanshanian W deposits reflect strengthened crust-mantle interactions which resulted from the multistage extension of the SCB caused by the westward subduction of the paleo-Pacific plate.