Introduction

Magmatic fractionation and exsolution of a fluid phase from a cooling pluton plays an important role in metal enrichment for intrusion-related deposits1,2,3. Reheating of preexisting semi-solidified plutons triggered by the input of a new magma may lead to the exsolution of fluid and element transport, thus contributing to incremental extraction of metals from the magma and their precipitation in the cupola of plutons4,5. Successive magma inputs led to the repeated extraction and precipitation of metals to form ore at the vantage position2,6. The lifespan of the magmatic-hydrothermal system triggered by the emplacement of a set of successive plutons controls the timescale of the ore-forming process and thus the metal grades and tonnages of deposits. Therefore, establishing tight temporal ties between magmatism and its associated mineralization is key to understanding the contribution of magma to mineralization. It is generally considered that lifespans of magmatic-hydrothermal systems is less than 10 million years, and even shorter (< 2 Ma) for porphyry deposits7,8,9,10,11,12. Accordingly, a time interval between plutons and the associated mineralization of > 10 Ma is interpreted to indicate that they have no genetic ties.

The development of W, Sn, Pb, Zn, and rare earth element (REE) deposits is genetically associated with voluminous Mesozoic granites13,14,15,16,17,18,19,20. The Qianlishan granite complex (QGC) in China is located ~ 16 km southeast of Chenzhou city, Hunan Province. The QGC is centered in the well-known Shizhuyuan polymetallic ore zone (W–Sn–Mo–Bi–Pb–Zn) which includes the Shizhuyuan W–Sn–Mo–Bi deposit (W: 80 Mt, Sn: 40 Mt, Bi: 20 Mt, Mo: 10 Mt)21,22,23. The zoned QGC was formed by successive Mesozoic magmatic intrusions24,25,26, which are assumed to have provided heat and metals for mineralization. However, the classification and geochronology of the QGC and the mineralization time of the Shizhuyuan deposit remain debated. Previous research on the QGC obtained intrusion ages ranging from 183 to 131 Ma13,14,25,26,27,28,29 and the mineralization ages from 145 to 160 Ma28,30,31. Thus, some phases of the QGC may indeed have a genetic relationship with the deposit, whereas other phases may not.

This study revisited the classification and dating of the QGC and mineralization to to clarify their genetic relationship. We present zircon LA-ICP-MS dating results for the QGC and combine these with petrology and field observations to constrain the structure and intrusive history of the QGC. Precise Ar–Ar dating of muscovite from the mineralized greisen vein allows for place constraints on the timing of the Shizhuyuan W–Sn–Mo–Bi deposit. Our results suggest close temporal relationship between the QGC and associated mineralization.

Geological setting

The Nanling Range is located in the collision zone between the Yangtze Block and the Cathaysia Block (Fig. 1) where six main (buried) faults strike north and north-northeast. These blocks amalgamated during the early Neoproterozoic along the Qin-Hang deep fault zone17,32,33. This collision zone was reactivated in the early to late Mesozoic at 180–90 Ma, leading to the formation of numerous nonferrous and rare metal mineralized deposits, including W, Sn, Mo, Pb, Zn, U, Cu, Au, Ag and REEs34. The Shizhuyuan ore field is located approximately 16 km southeast of Chenzhou city, Hunan Province (Fig. 1). The faults are extensively developed in the ore field with strike directions of north-east, north–south and north-west (Fig. 2). The northeast and north–south faults control the distribution of the QGC and ambient mineral deposits. The Shizhuyuan ore field is located at the northern end of the Shizhuyuan-Taipingli synclinorium striking northeast. The ore field is surrounded by Sinian metasedimentary rocks, Devonian carbonate and clastic sedimentary rocks, the QGC and Quaternary sediments35 (Fig. 2). Sinian metasedimentary rocks occur only on the eastern edge of the ore field. These rocks are mostly weakly metamorphosed clastic sedimentary rocks. Specifically, the rocks comprise gray-green to gray-black, moderately thick, fine-grained quartz-rich sandstones, feldspathic sandstones, siltstones, phyllites and slate36. Devonian carbonate rocks and clastic sedimentary rocks are present as host rocks intensely altered by fracturing and magmatic activity (Fig. 2). From bottom to top, these rocks have been subdivided into four formations: (1) Tiaomajian Formation; (2) Qiziqiao Formation; (3) Shetianqiao Formation; and (4) Xikuangshan Formation. The first two formations belong to the Middle Devonian, and the last two to the Upper Devonian30. The Tiaomajian Formation (D2t) is > 358 m thick and occurs at the eastern and western sections of the ore field. It is mainly composed of gravel-bearing sandstones and conglomerates. The Qiziqiao Formation (D2q, > 520 m in thickness) occurs in the middle and southern parts of the ore field. It comprises micritic dolomites, limestones and dolomitic limestones. The Shetianqiao Formation (D3s, > 296 m in thickness), is present in the Shizhuyuan, Dongpo and Chaishan areas. It contains mainly banded micritic limestones. The Xikuangshan Formation (D3x, > 363 m in thickness) comprises thick-bedded limestones and dolomitic limestones containing flint concretions37. The Quaternary sediments are ~ 10 m thick, comprising slope wash. They are present only along the rivers in the northern part of the Shizhuyuan ore field.

Figure 1
figure 1

Geological map of the Nanling Range, South China (modified after Chen et al. (2016)14, copyright@ Elsevier, 2016). Faults: (1) Jiangshan–Shaoxing-Pingxiang Fault; (2) Zhenghe-Dapu Fault; (3) Changle-Nan’ao Fault; (4) Chenzhou-Linwu Fault; (5) Changlin-Guangchang buried Fault; (6) Wuzhou-Sihui buried Fault.

Full size image
Figure 2
figure 2

Schematic geological map of the Qianlishan district showing the QGC (modified after Chen et al. (2016)14, copyright@ Elsevier, 2016). The sample location and the obtained dates: (1) zircon LA-ICP-MS U–Pb dates from this study; (2) zircon SHRIMP U–Pb dates from Li et al. (2004)28; and (3) zircon LA-ICP-MS U–Pb dates from Chen et al. (2014)13.

Full size image

Petrography

Previous studies have indicated that the QGC (~ 10 km2) was intruded by lamprophyre and coeval mafic dikes. Since the mafic dikes are ~ 10 Ma younger than the QGC and the associated mineralization, they are not genetically related38. The QGC, which is spatially and temporally associated with W–Sn–Mo–Bi mineralization, can be subdivided into five Sections 13,14,22,30,37,38,39. The first section (S1) is a fine-grained porphyritic biotite granite (Fig. 3a,d) that outcrops within an area of ~ 4.0 km2 on the northern edge of the pluton. It is gray-white in color and comprises ~ 30 vol.% phenocrysts (2–7 mm in diameter), which are mostly potassium feldspar (~ 10 vol.%), plagioclase (~ 10 vol.%) and quartz (~ 10 vol.%), as well as minor biotite (~ 1 vol.%). The groundmass (0.3–1.0 mm in diameter) contains the same minerals. Dark inclusions within biotite, plagioclase, quartz and apatite occasionally occur in the S1 stocks and dikes. The accessory minerals in S1 are zircon, monazite, xenotime and ilmenite. The second section (S2) is a gray-white micro-fine-grained porphyritic biotite granite (Fig. 3b,e), occurring in the southern part of the pluton, with an outcrop area of ~ 1.1 km2. It contains phenocrysts of quartz (~ 17 vol.%) and feldspar (~ 13 vol.%) that range in size from 1 to 6 mm. The matrix is dominated by quartz, potassium feldspar, plagioclase and minor biotite (0.1–0.6 mm in diameter). Biotite is locally altered to chlorite (Fig. 3e). Accessory minerals in S2 are mainly zircon, monazite, xenotime, thorium, and apatite. The third section (S3) is a gray-white fine- to coarse-grained (mainly 0.3–0.8 mm in diameter) equigranular biotite granite (Fig. 3c,f) with an outcrop area of 4.4 km2. It contains quartz (~ 37 vol.%), plagioclase (~ 30 vol.%), alkali feldspar (~ 23 vol.%), biotite (~ 2 vol.%), and accessory minerals (< 3 vol.%) including zircon, monazite, and fluorite. Plagioclase (An = 0.01–0.03) occasionally exhibits overgrowth and argillization. The fourth section (S4) is a gray-white fine-grained (mostly 0.1–0.3 mm in diameter) equigranular two-mica granite (~ 0.1 km2; Fig. 3g,j), which comprises quartz (~ 40 vol.%), plagioclase (~ 31 vol.%), alkali feldspar (~ 22 vol.%), biotite (~ 2 vol.%), and muscovite (~ 1 vol.%). Plagioclase shows polysynthetic twinning, and alkali feldspar has Carlsbad twinning and perthitic texture. Primary and secondary muscovite were both found in this section. The primary muscovite grains present as euhedral intergranular sheets surrounded by plagioclase and quartz grains, whereas the secondary grains are distributed along the secondary fractures. The S4 has intruded into the first three sections, and pegmatite belts are often found on its top. The accessory minerals in this section are mainly zircon, thorite, topaz and fluorite. The fifth section (S5) represents a series of NE-striking (25–65°) granite porphyry dikes (Fig. 3h, 3k), comprising quartz (~ 15 vol.%), orthoclase (~ 8 vol.%), plagioclase (~ 15 vol.%) and minor biotite (~ 2 vol.%) phenocrysts (0.2–2 mm in diameter) within a matrix consisting mainly of quartz, orthoclase, plagioclase, and biotite. This section suffered strong alteration: (1) argillization was widely developed on the surface of plagioclase phenocrysts; (2) almost all biotite has been altered into chlorite and muscovite (Fig. 3k). Plagioclase comprises albite (An = 0.01 ~ 0.08) and andesine (An = 0.26 ~ 0.37). The Fe/(Fe + Mg) ratio of biotite is 0.74 ~ 0.7522,40. The accessory minerals mainly consist of euhedral to subhedral, prismatic allanite and apatite (60–150 μm × 10–60 μm wide), with a small number of zircon, monazite, fluorite, rutile and magnetite. All the studied zircon grains were generally wrapped in plagioclase, suggesting that they occurred as an early crystallization phase during crystal fractionation.

Figure 3
figure 3

Photographs of the Qianlishan granites. (a, d) porphyritic biotite granite (Section 1: GL-13); (b, e) microfine-grained porphyritic biotite granite (Section 2: 315–36); (c, f) middle- to large-grained equigranular biotite granite (Section 3: 490–21); (g, j) fine-grained equigranular biotite granite (Section 4: 490–10); (h, k) granite porphyry dikes (Section 5: 490–2); (i, l): muscovite vein with mineralization. Abbreviations: Qz , Quartz; Pl,  Plagiarize; Bt, Biotite; Ms, Muscovite (Whitney DL and Evans BW et al. 2010)53.

Full size image

Alteration and mineralization

Alteration

The alteration of the Shizhuyuan W–Sn–Mo–Bi deposit includes four types: a. skarnization; b. greisenization; c. marmarization; and d. feldspathization22.

Skarnization

The skarn located in the contact zone in the southeastern region of the QGC has experienced the most pervasive alteration in the Shizhuyuan deposit (Fig. 2). This skarn is approximately 1.2 km long, 1.0 km wide and 50–500 m thick (with an average thickness of 150–200 m). There are three types of skarns: a. original skarn; b. retrograde skarn; and c. veinlet skarn. The mineral assemblage of the skarn, whose parent rock is marble, comprises mainly garnet, pyroxene, idocrase and wollastonite22. The original skarn has been overprinted by a retrograde skarn. In comparison to the original skarn, the retrograde skarn contains much higher contents of fluorite, epidote, wolframite, scheelite, cassiterite, molybdenite, bismuthinite, magnetite, and pyrite39. Generally, mineralization occurs within the retrograde skarn rather than in the original skarn. Skarn veins crosscutting the margin of the retrograde skarn are tens to hundreds meters long and 10–50 cm wide. These skarn veins contain ores with grades of 1% to 6%22.

Greisenization

There are two types of greisen: massive greisen and vein-type greisen21. Massive greisen occurs mainly as discrete lenses in the upper section of the equigranular granites (S3 and S4); it contains quartz (~ 65%), mica (~ 16%), topaz (~ 8%), feldspar (~ 3%), chlorite (~ 2%) and fluorite (~ 1%). Compared with the massive greisen, the vein-type greisen has a similar mineral assemblage but with wider variations in mineral proportions: quartz (45–85%), mica (3–35%), topaz (5–40%), fluorite (2–10%), and feldspar (1–3%) as well as minor accessory minerals wolframite, scheelite, cassiterite, molybdenite, bismuthinite, magnetite, pyrite, and chalcopyrite (Fig. 3i,l). The vein-type greisen overlies the massive greisen, and it is distributed much more broadly (Fig. 4). Additionally, in Tunnel 490, a greisen vein is observed cutting through both the massive greisen and the skarn.

Figure 4
figure 4

Sampling locations in Tunnel 490 (after Lu et al., 2003, copyright@Society of Economic Geologists, 2003)39. (1) zircon LA-ICP-MS U–Pb dates from this study; (2) muscovite Ar–Ar dates of the Qianlishan granites and Greisen from Yin et al., 200229.

Full size image
Marmarization

The stockwork marble vein, which is located at the contact between the overlying marble and the underlying skarn, is 750 m long, 300–600 m wide and 20–200 m thick. This vein comprises mainly fluorite, mica, tourmaline, and feldspar. The mineral grains are smaller than 0.05 mm in diameter41.

Feldspathization

Stockwork feldspar is a light-colored altered rock located in the fractures of the skarn. It contains mainly potassium feldspar and plagioclase and occasional quartz, fluorite, garnet, and pyroxene42.

Mineralization

Based on their compositions, textures and ore characteristics, the ores are clearly zoned. Pervasive greisenization plays the dominant role in defining these ore type classification. Mao et al. (1998) classified the ores into four types26. From top to bottom, these are Type 1—Sn–Cu ore within vein-type greisen superimposed on the porphyritic biotite granites (S1 and S2); Type 2—Sn–Be–Cu ore within the fine stockwork greisen overprinting the marble; Type 3—which W–Sn–Mo–Bi ore within thick stockwork greisen and rare stockwork greisen superimposed on the skarn; and Type 4—W–Sn–Mo–Bi ore within massive greisen at the top of the equigranular biotite granite stock (Fig. 4). Of these ores, the Type 3 ore has the greatest tonnage and represents the main mineralization stage26,37.

Results

Zircon LA-ICP-MS age and trace elements

The zircons from Sample GL-13 (S1) are typically transparent, colorless to slightly brown, rectangular to prismatic crystals 100–150 μm long, with aspect ratios ranging from 2:1 to 3:1. Oscillatory zoning, with the occasional appearance of inherited cores, is common in these crystals (Fig. 5). The zircons from Sample 315–36 (S2) are mostly transparent, colorless to pale yellow, euhedral to subhedral crystals 100–200 μm long, with aspect ratios ranging from 2:1 to 3:1. The euhedral grains have concentric zoning with relatively bright cores in CL images (Fig. 5). Compared with those from the S1 and S2 granites, the zircons from the S3 granite (Sample 490–21) are similar in shape and color but are smaller (typically 50–100 μm long), with aspect ratios ranging from 2:1 to 1.5:1, and exhibit weak oscillatory zoning. The zircons of Sample 490–10 (S4) resemble those of Sample 490–21 in terms of their shape, color, and size (Fig. 5). The zircons of Sample 490–2 (S5) are characteristically long (100–250 μm), with aspect ratios ranging from 2:1 to 3:1. They are also transparent, colorless, and euhedral to subhedral. Oscillatory zoning is commonly visible in CL images (Fig. 5).

Figure 5
figure 5

Cathodoluminescence images of zircons with corresponding 206Pb/238U ages for the samples from the QGC.

Full size image

Zircon dates are summarized in Fig. 6 and Table 1. In total, 40 spots on zircon grains from Sample GL-13 were analyzed. Excluding the spots with abnormally high U content and associated with inherited zircons, 11 analyses yield a 238U/206Pb age of 155 ± 1.9 Ma (MSWD = 2.8, probability 0.002). Similarly, the weighted average 238U/206Pb age of Sample 315–36 (154.4 ± 0.88, MSWD = 1.05, probability 0.4) was obtained by pooling 14 analyses. The data for Sample 490–21 are too variable to constrain either an intercept age or a concordant age. Sample 490–10 has a slightly younger weighted average 238U/206Pb age (151.7 ± 3.1, MSWD = 2.3, probability 0.04) obtained by 6 analyses. Within error, this date is identical to those of Samples GL-13 and 315–36. Of forty analyses from Sample 490–2, 18 data points give a 238U/206Pb age of 153.7 ± 1.2 (MSWD = 2.2, probability 0.002). Trace element contents in zircon and calculated Ce anomalies and ‘Ti-in-zircon’ temperatures are presented in Table 2.

Figure 6
figure 6

Zircon LA-ICP-MS U–Pb concordia diagrams for the QGC. The data from Sample 490 are too distributed to constrain either intercept age or concordant age. Data processing was carried out using concordia intercept ages on the Tera-Wasserburg plot utilizing ISOPLOT (Ludwig, v. 3.75, 2012, copyright@ BGC Berkeley Geochronology Center, 2006, available from: http://www.bgc.org/isoplot_etc/isoplot.html).

Full size image
Table 1 LA-ICP-MS analyses of zircons in the QGC.
Full size table
Table 2 Zricon Trace element compositions, Ce anomalies, and Ti-in-zircon temperatures.
Full size table

Whole-rock major and trace element chemistry

Twenty representative samples were analyzed for their major and trace element compositions (Table 3). These samples are characterized by high SiO2 (70.32–78.28 wt%) and K2O (3.54–5.92 wt%) contents. Most of the samples plot in the fields of high-K calc-alkaline field, whereas seven samples plot in the shoshone field. The aluminum saturation index (ASI) values of the five phases of Qianlishan granites are 0.95–1.78, 1.04–1.05, 0.88–1.34, 1.04–1.2, and 1–1.2. The S1, S2, and S5 porphyritic granites have higher contents of K2O, CaO, MgO, TiO2, Zr, Sr, Ba, and P2O5 but lower contents of Na2O and Al2O3 than the other granites (Figs. 7, 8). Notably, fluorine concentrations of the S3 and S4 equigranular biotite granites (2500–10,400 ppm) are much higher than those of the S5 granite porphyry (< 2000 ppm), whereas the S1 and S2 porphyritic biotite granites have intermediate F contents (2000–6800 ppm). Moreover, S2, S3 and S4 have relatively high W contents (20–100 ppm), whereas S1 and S5 have lower W contents (< 20 ppm). In the primitive mantle-normalized diagrams (Fig. 9), S3 and S4 exhibit the strongest negative Ba, Sr, P, and Ti anomalies, whereas S1 and S2 show much smaller anomalies. S5 has trace element patterns similar to those of S1 and S2. As presented in Fig. 10 and Table 3, S3 and S4 have the lowest La/Yb (0.08–1.31) and δEu (0.002–0.011), followed by S1 and S2 with La/Yb (3.01–3.71) and δEu (0.15–0.25). S5 has the highest La/Yb (13.16–13.96) and δEu ((0.23–0.32).

Table 3 Major and trace element composition of samples from the main intrusive stages of the QGC.
Full size table
Figure 7
figure 7

Harker diagram for the QGC.

Full size image
Figure 8
figure 8

SiO2 vs Sr, Ba, Zr, P2O5, W and F for the QGC.

Full size image
Figure 9
figure 9

REE patterns for the QGC.

Full size image
Figure 10
figure 10

La/Y vs δEu for the QGC.

Full size image

Muscovite Ar–Ar age

The Ar–Ar analytical data of Sample YJW-8-B are summarized in Table 4. Age spectra and inverse isochrons are plotted in Fig. 11.

Table 4 Ar–Ar stepwise heating data for muscovite samples from the QGC and the Shizhuyuan deposit.
Full size table
Figure 11
figure 11

Plateau (a) and isochron (b) Ar–Ar age of muscovite from mineralizing greisen in the Shizhuyuan deposit. ISOPLOT software (Ludwig, v. 3.75, 2012, copyright@ BGC Berkeley Geochronology Center, 2006, available from: http://www.bgc.org/isoplot_etc/isoplot.html) was used for data processing.

Full size image

Muscovite from Sample YJW-8-B yields a plateau age of 154.2 ± 1.0 Ma (MSWD = 0.65) (Fig. 11a). All errors are quoted at the 2σ level. The plateau age comprises nine steps accounting for 85.9% of the total 39Ar released and agrees with the inverse isochron age of 154.0 ± 1.6 Ma (MSWD = 0.81) (Fig. 11b). The estimated initial 40Ar/36Ar is 296.9 ± 4.1%, which is identical to the present-day initial 40Ar/36Ar (295.5%). The characteristics of the spectra suggest the absence of argon loss and excess argon. In other words, the Ar–Ar system of the muscovite remained closed during the geological history of Sample YJW-8-B.

Discussion

Reclassification of granitic phases

Zoned plutons often require numerous magmatic intrusion pulses continuously emplaced over millions of years, because individual magmatic pulses commonly last for less than 100,000 years7,9,10,24,43. The QGC exhibits normal zoning with the most differentiated phases (S3 and S4) in the central part. Each phase can be distinguished by their emplacement age, mineral assemblage and geochemistry. Different classification schemes for the QGC have been suggested. According to some studies, the equigranular biotite granite (S3) and the porphyritic biotite granite (S1) have been classified as the QGC25,28,37,39. In contrast, other studies combined the porphyritic biotite granite (S1) with the porphyritic biotite granite (S2) that is located on the southern margin of the QGC13,14,22,31,38. Additionally, the porphyritic biotite granite (S1) has been considered a separate phase by Guo et al. (2015)27. To clarify the relationship between different rock types with the QGC, we have undertaken a systematic study of petrology, geochronology and geochemistry of all five sections of the pluton.

Previous geochronological investigations have used diverse methods and obtained a variety of results (Table 5, Fig. 12). For the porphyritic biotite granite (P1), Liu et al. (1997) obtained a potassium feldspar 40Ar/39Ar plateau age of 183.17 ± 3.75 Ma25. In contrast, Chen et al. (2016) obtained two zircon U–Pb ages of 157 ± 2 Ma and 158 ± 2 Ma using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)14. Similarly, Chen et al. (2014) obtained two zircon U–Pb ages of 160 ± 1 Ma and 156 ± 1 Ma using LA-ICP-MS13. Furthermore, Guo et al. (2015) obtained four younger ages based on zircon analyses using secondary ion mass spectrometry (SIMS): 153.4 ± 1.6 Ma, 152.5 ± 1.2 Ma, 154.5 ± 1.3 Ma and 152.3 ± 1.2 Ma, which were identical (within error) to the zircon ages of 153 ± 3 Ma27,28 determined using sensitive high-resolution ion microprobe (SHRIMP). Overall, the previous ages of the P1 granite range from 183.2 to 152.3 Ma.

Table 5 Ages of the QGC from this study and the literature.
Full size table
Figure 12
figure 12

Summary of the dating of the QGC from previous publications and this study. Zrn , Zirco; Kfs, K-feldspar; Bt, Biotite; Ms, Muscovite (Whitney DL and Evans BW et al. 2010)53. WR , whole-rock. Reference: 1. This study; 2. Chen et al. 201614; 3. Guo et al. 201527; 4. Li et al. 200428; 5. Yin et al. 200229; 6. Mao et al. 199826; 7. Liu et al. 199725; 8. Chen et al. 201413.

Full size image

The equigranular biotite granite (P2) can be classified into two groups. (1) One group consists of medium- and coarse-grained equigranular biotite granite, for which Liu et al. (1997) obtained a potassium feldspar 40Ar/39Ar plateau date of 162.55 ± 3.25 Ma25. In addition, Chen et al. (2016) obtained two slightly younger zircon U–Pb ages of 157 ± 2 Ma and 158 ± 2 Ma using LA-ICP-MS, which agreed with the younger zircon LA-ICP-MS U–Pb age of 155 ± 2 Ma obtained by Chen et al. (2014)13,14. However, Li et al. (2004) obtained a SHRIMP zircon U–Pb age of 151 ± 3 Ma, which was consistent with the muscovite 40Ar/39Ar age of 149.3 ± 3.5 Ma obtained by Yin et al. (2002)28,29. (2) The other group is fine-grained equigranular biotite granite, for which Yin et al. (2002) obtained a muscovite 40Ar/39Ar age of 137.4 ± 3.3 Ma29. In addition, Chen et al. (2016) did not classify the equigranular granite into two groups with distinct grain sizes, and they obtained two zircon U–Pb ages of 158 ± 2 Ma and 155 ± 1 Ma using LA-ICP-MS14. In summary, the P2 granite was emplaced at 137.4–162.6 Ma.

For the granite porphyry (P3), Chen et al. (2016) obtained a zircon U–Pb age of 154 ± 1 Ma14. Liu et al. (1997) obtained a potassium feldspar 40Ar/39Ar plateau date of 144.41 ± 2.83 Ma25. Together, these ages indicate that the emplacement of the P3 granite occurred at 154.0–144.4 Ma.

Bulk-rock Rb–Sr ages and potassium/mica (K/Ar)-Ar isochron ages are not reliable for dating the emplacement of granitic plutons because they can be affected by thermal disturbances caused either by prolonged fluid convection or tectonic processes14,44,45. In contrast, zircon U–Pb dating, which has closure temperatures of 700–800°C46,47, is a reliable tool for placing geochronological constraints on plutonic emplacement.

Here, LA-ICP-MS was used to carry out zircon U–Pb dating. Our new data indicate that the S1, S2, S4, and S5 granites were emplaced at 155 ± 1.9 Ma, 154.4 ± 0.88 Ma, 151.7 ± 3.7 Ma and 153.7 ± 1.2 Ma, which are identical within error (Table 5, Fig. 12).

The QGC (Si content > 70%) was formed by a felsic magma and experienced advanced differentiation, with a fractionation index of > 9222. During the fractionation process of felsic magma, although major elements have a limited range, trace elements that favor feldspars (Rb, Sr, Ba) and accessory minerals (Th, P, U, Zr, Sn, Ce, Y) show wide variation48,49. The variation diagrams (Figs. 7, 8) indicate that the contents of Na2O and Al2O3 increase from the S1 to S4 granites, whereas Ca and Mg decrease. The decrease in P with SiO2 content indicates fractionation of apatite. This is consistent with the presence of apatite in Sample GL-2 (S1) and the absence of apatite in Sample 490–10 (S4). The depletions in Sr, Ba, Nd, and Ti and the striking negative Eu anomalies (Fig. 9) indicate fractionation of plagioclase, K-feldspar and Ti-Fe oxides. In comparison with S1, S2 and S5, the S3 and S4 granites show much more pronounced depletions in Ti, P, Sr and Ba, as well as extremely negative Eu anomalies (Fig. 10). Extensive magmatic fractionation is further supported by the ratios of Zr/Hf, Nd/Ta, Th/U and Rb/Sr. With the increase in the degree of magmatic fractionation, Zr/Hf, Nd/Ta, Th/U and ratios decrease, but the Rb/Sr ratio increases50,51,52. The Zr/Hf ratios of all five sections are 18.36–20.55 (S1), 20.14–20.18 (S2), 7.43–8.28 (S3), 8.90–11.53 (S4), and 25.92–38.24 (S5). The Nb/Ta ratios are 5.92–6.61, 5.52–5.54, 1.06–1.44, 0.82–2.58, and 7.73–7.74, respectively. The sections have Th/U ratios of 1.84–2.13, 1.94–2.04, 0.89–0.91, 0.91–1.16, and 3.97–4.30, respectively. The Rb/Sr ratios show much wider range: 7.99–10.24, 10.38–12.75, 60.13–108.81, 36.41–165.2, and 5.23–6.05, respectively. All the variations in the ratios from S1 to S4 suggest an increased degree of magmatic fractionation. It is worth noting that the S5 granite does not follow the increasing trend of magmatic evolution from S1 to S4. The S5 granite composition suggests that it experienced the lowest degree of fractionation.

Based on the primitive mantle-normalized diagrams (Fig. 9), the QGC can be classified into three groups: 1) S1 and S2 porphyritic biotite granites; 2) S3 and S4 equigranular biotite granites; and 3) S5 granite porphyry. Group 1 shows relatively flat REE patterns characterized by moderate enrichments in light REEs (LREEs) (with La/Y ratios ranging from 2.50 to 3.71) and slightly negative Eu anomalies (Eu/Eu* = 0.144–0.249), suggesting that these samples have been weakly differentiated. In comparison, Group 2 has undergone strong fractional differentiation, as it exhibits flat REE patterns (with La/Y ratios ranging from 0.84 to 1.31) with much stronger Eu anomalies (Eu/Eu* = 0.001–0.011). In contrast, Group 3 is characterized by strong enrichments in LREEs, with La/Y ratios ranging from 13.16 to 13.96 and the weakest Eu anomalies (with Eu/Eu* ratios ranging from 0.31 to 0.222). On the primitive mantle-normalized spider diagrams (Fig. 9), both Group 1 and Group 3 show weak negative Ba, Sr, P, and Ti anomalies, whereas the anomalies of Group 2 are larger. All three groups record positive U and Th anomalies, but positive Ta anomalies occur only in Group 1 and Group 2.

Field observations indicate that a 0.4- to 1-m-wide baked margin is located at the contact between S2 and S3 and that NE-striking granite porphyry dikes (S5) cut through the other granites26, thus supporting our classification.. Additionally, positive Ce anomalies in zircon from S2 are strikingly higher than in zircon from S2, indicating that it was formed in a geochemical environment distinct from that of S2. Thus, S1 and S2 should be separated into individual groups. In summary, the QGC may be reasonably classified into four phases: P1, which contains S1; P2, which is composed of S2; P3, which comprises S3 and S4; and P4, which includes S5.

Genetic relationship between plutonism and mineralization

Liu et al. (1997) obtained a garnet/pyroxene Sm–Nd age for the QGC of 160.8 ± 2.4 Ma, which was consistent (within error) with the Sm–Nd age for the massive-type skarn of 157 ± 6.2 Ma obtained by Lu et al. (2003)25,39. In contrast, according to the analyses of samples from massive-type skarn and vein-type greisen, Li et al. (2004) obtained a much younger Sm–Nd age of 149 ± 2 Ma, which matched the molybdenite Re-Os age of 151 ± 3.5 Ma obtained by Li et al. (1996) and a quartz fluid inclusion Ar–Ar age of 153.7 ± 0.9 Ma obtained by Wang et al. (2016)28,30,31. Furthermore, Yin et al. (2002) used muscovite 40Ar/39Ar dating to suggest that the timing of greisenization and its associated W–Sn–Mo–Bi mineralization ranged from 145 to 148 Ma29. Collectively, the age discrepancy is up to ~ 20 Myr.

Based on our field observations, the W–Sn–Mo–Bi mineralization of the Shizhuyuan deposit is intimately associated with greisenization; therefore, muscovite Ar–Ar dating is ideal candidate for assessing the timing of hydrothermal mineralization. According to our analytical results, greisen-type mineralization occurred ca. 154.2 ± 1.0 Ma. Within error, this age is consistent with molybdenite Re-Os dating (151 ± 3.5 Ma) conducted by Li et al. (1996)31. Wang et al. (2016) obtained a muscovite Ar–Ar age of 153.7 ± 0.9 Ma by carrying out geochronological Ar–Ar dating on a fluid inclusion in quartz and coexisting muscovite30. This age also agrees with our dates.

In conclusion, the QGC has two impacts on the Shizhuyuan deposit. (1) Heat supply: According to the thermal model of Mclaren et al. (1999)5, the heat derived from the high-heat-producing granites reaches a maximum ~ 10 Myr after its emplacement. Furthermore, the thermal disturbances caused by the high-heat-producing granites can drive hydrothermal fluid convection, resulting in mineralization. For instance, the mineralization in the Mount Elliott Cu-Au deposits, Australia, was produced by hydrothermal convection driven by the heat released from its associated high-heat-producing granite. The volume heat of the QGC estimated by the U, Th, and K contents is 5.89–14.30 μWm−3 (volume heat of high-heat-producing granite > 5 μWm−3), indicating their high heat production. Therefore, when mineralization occurred, the heat anomaly resulting from the QGC was quite strong (nearly its maximum strength), which promoted the development of hydrothermal convection around the QGC, leading to the generation of the Shizhuyuan deposit. (2) Metal supply: Field observations reveal that the Shizhuyuan W–Sn–Mo–Bi deposit is located at the endo-contact of the skarn and the porphyritic biotite granite (S1, S2) and equigranular granite (S3, S4), demonstrating their close spatial relationship21,37. In addition, as shown in Fig. 8a, the W contents in the S1, S2, S3, and S4 granites are mostly 40–60 ppm; therefore, the QGC can supply sufficient metal for mineralization.

In summary, the QGC is temporally and spatially associated with the formation of the Shizhuyuan W–Sn–Mo–Bi deposit. Furthermore, the QGC provided heat and metals for these deposits.

Conclusions

  1. 1.

    According to zircon LA-ICP-MS dating, the emplacement time of the Qianlishan granite complex is constrained to 155–151.7 Ma.

  2. 2.

    Based on petrological and geochemical characteristics, the Qianlishan granite complex can be classified into four phases: porphyritic biotite granites (Phase 1, Section 1); porphyritic biotite granites (Phase 2, Section 2); equigranular biotite granite (Phase 3, Sections 3 and 4); and granite porphyry dikes (Phase 4, Section 5).

  3. 3.

    The Qianlishan granite complex is temporally and spatially associated with the formation of the Shizhuyuan W–Sn–Mo–Bi deposit (mineralization time: 154 Ma).