Genesis of the Jinying gold deposit, southern Jilin Province, NE China: Constraints from geochronology and isotope geochemistry

Abstract The Jinying gold deposit is located in southern Jilin Province in northeast China and is representative of the large Early Cretaceous gold deposits in this area. To better understand ore genesis of this deposit, a multi-isotope integrated analysis of U–Pb–Rb–Sr–He–Ar–S has been carried out. Laser ablation inductively coupled plasma–mass spectrometry (LA–ICP–MS) dating of zircons from the granodiorite porphyry and dioritic porphyrite in the study area yields ages of 172.1 ± 1.2 Ma and 122.5 ± 0.8 Ma, suggesting that corresponding intrusion occurred in the Middle Jurassic and the Early Cretaceous. Rb–Sr dating of the pyrite yields an isochron age of 120 ± 3 Ma, suggesting that gold mineralization occurred in the Early Cretaceous. The fluid inclusions in pyrite yield 3He/4He ratios clustered within a small range from 0.08 to 0.13 Ra, 40Ar/36Ar ratios between 331.6 and 351.3, and mantle He in the range of 1.0–1.6%, indicating that the ore-forming fluids originated from a mixed crustal and mantle source. The in situ S isotopic values of pyrite vary between + 0.1 ‰ and + 2.8 ‰, suggesting that the ore-related sulphur came from the deep magmatic source. Combined with the geological history of the study area, it can be concluded that the gold mineralization was possibly related to the extensional setting associated with the rollback of the Palaeo-Pacific Plate.


Introduction
Southern Jilin Province, located in the northeastern margin of the North China Craton (NCC, Fig. 1a), is an important polymetallic metallogenic district that hosts numerous Ni, Fe, Cu and Au deposits (Fig. 1b), and over 20 large-, medium-and small-scale Au deposits have been found in this area.For example, the world-famous Jiapigou gold district contains proven gold reserves of 180 tons or more (Sun et al. 2013;Deng et al. 2014;Zhang et al. 2021;Chen et al. 2022).With advanced exploration, several gold deposits have been discovered in southern Jilin Province, including the Songjianghe (Zhang et al. 2019), Toudaoliuhe (Han et al. 2020), Laosandui and Jinying (known as Banmiaozi) gold deposits.Thus, this area shows great potential for ore prospecting and has been recognized as an important gold province in China.
Jinying is a large-scale gold deposit and currently contains 34 t of gold (Chen, 2019).Previous researches have been focused on the geology (Liu et al. 2009;Su & Zang 2010;Xing et al. 2012;Li et al. 2015), whole-rock geochemistry (Zhang, 2015;Chen, 2019), ore-forming fluid (Zhang, 2015;Men et al. 2016;Chen, 2019) and geochronology (Zhang, 2015;Chen, 2019).However, the ore genesis and mineralization time at Jinying deposit remain controversial.For example, Zhang (2015) argued that Au mineralization occurred at 170 Ma based on the zircon U-Pb age of granodiorite porphyry, as well as the zircon U-Pb age of 131 Ma for dioritic porphyrite (Chen, 2019).The deposit formed during the subduction of the Palaeo-Pacific Plate (Zhang, 2015) or in the following extensional setting (Chen, 2019).In addition, the ore-forming fluids originated from a mixture of magmatic water and meteoric water (Men et al. 2016) or magmatic water with meteoric water and formation water (Chen, 2019).
In view of the above scientific problems, this work carried out sulphide Rb-Sr and LA-ICP-MS zircon U-Pb geochronological analyses and He-Ar-S isotopic analyses of the Jinying gold deposit.We aim to determine the timing of gold mineralization, tectonic setting and sources of ore-forming materials and fluids, which have important implications for the genesis of the Jinying gold deposit.
The exposed oldest strata in the study area are Archaean TTG rocks, and supracrustal rocks consist of amphibolite, plagiogneiss, granulite and magnetite-quartzite.The Palaeoproterozoic Laoling Group consists of metamorphic conglomerate, quartzite, phyllite, schist and marble.The Neoproterozoic Qingbaikouan System mainly consists of feldspathic quartz sandstone, arkose and conglomerate.The Jurassic Linzitou and Shiren Formations consist of andesite, andesitic tuff, rhyolite and glutenite.The Cretaceous Xiaonangou Formation sediments consist of conglomerate and glutenite (Fig. 1b).The Quaternary sediments consist of clay and gravel (JBGMR, 1988).The fault system in the study area is dominated by the NE-trending Benxi-Tonghua and Yalujiang faults (Chu et al. 2021).Igneous rocks in the area comprise the Late Palaeozoic-Early Mesozoic mafic complex, alkali-granite and associated mafic rocks, and the Mesozoic granitic complex (Zhang, 2002).Mesozoic magmatic activity in the study area can be subdivided into three stages: the Late Triassic, the Early-Middle Jurassic and Cretaceous (Chu et al. 2021).Multiple stages of magmatic activity and geotectonic processes formed abundant Au deposits in this area (Sun et al. 2006(Sun et al. , 2023;;Han et al. 2022).

Deposit geology
Proterozoic sediments and metasedimentary rocks are the main rocks in the Jinying gold deposit, and they were subdivided into five units: Palaeoproterozoic Zhenzhumen Formation and Neoproterozoic Diaoyutai, Nanfen, Qiaotou and Wanlong Formations (Fig. 2).The Zhenzhumen Formation is composed of dolomite marble and quartz-bearing dolomite marble.The Diaoyutai Formation occurs in the central and northwest parts of the deposit and is mainly composed of quartz sandstone and hematite-bearing quartz sandstone.The Nanfen Formation is composed of siltstone, micritic limestone and shale.The Qiaotou Formation occurs in the southeastern part of the deposit and is mainly composed of quartz sandstone and siltstone.The Wanlong Formation is mainly exposed in the southeast of the deposit and consists mainly of laminated limestone.The structures of the Jinying deposit are dominated by NE-and NW-trending faults, and the NE-trending faults, which are closely related to mineralization.Intrusive rocks in the mining area include granodiorite porphyry and dioritic porphyrite.Granodiorite porphyry is exposed in the south part of the study area (Fig. 2), and dioritic porphyrite is exposed in the northeast part of the study area, as a small-scale rock mass (Fig. 2), but altered dioritic porphyrite can be seen at depth of drill holes 7, 10, 14, 16 and 30 (Fig. 3, Chen et al. 2020).Nine orebodies have been discovered in this deposit, and they mainly occur in the silicified breccia zone near the unconformity between the quartz sandstone and the silicified dolomitic marble (Fig. 4).They are controlled spatially by faults of No. F102 and F100 and therefore occur in a bedded shape, with dip SE at 48°-61°, and an average gold grade of 2.33-13.66g/t (Chen, 2019).The ore minerals comprise native gold (Fig. 5a-d), pyrite (Fig. 5e), marcasite (Fig. 5e), chalcopyrite (Fig. 5f, g), arsenopyrite, galena, sphalerite, hematite (Fig. 5c, d).Quartz, barite and sericite constitute the gangue mineral association.The alteration types are characterized by silicification, baritization, sericitization, kaolinization and carbonation.The hydrothermal processes can be divided into four paragenetic stages: quartz-pyrite stage, quartz-gold-pyrite stage, barite-chalcedony-gold-hematite stage and pyrite-marcasite stage (Xing et al. 2012).

4.a. Sampling
For zircon U-Pb dating, one granodiorite porphyry sample was collected from an outcrop in the southern part of the deposit, and one dioritic porphyrite sample was collected from tunnel 160.For the He-Ar isotope analysis, five pyrite samples were collected from tunnel 160.Sixteen pyrite samples were collected from tunnel 365, of which nine for Rb-Sr isotope analyses and seven for in situ sulphur isotope analyses.
Granodiorite porphyry is grey in colour, porphyritic texture and massive structure, and the phenocrysts consist of plagioclase, quartz, biotite and minor K-feldspar and hornblende.The plagioclase crystals are platy with lengths varying from 0.5 to 3 mm and are characterized by sericitization.The K-feldspar grains anhedral with lengths varying from 1 to 2 mm.The quartz grains show anhedral shape with lengths varying from 0.5 to 8 mm.The matrix is composed of quartz, feldspar and biotite, with minor accessory magnetite, zircon and apatite (Fig. 5h).Dioritic porphyrite is grey, porphyritic texture, massive structure, and the phenocrysts are mainly plagioclase, quartz, biotite and hornblende.The plagioclase crystals are platy with lengths varying from 1 to 10 mm and are characterized by sericitization.The quartz grains are xenomorphic with lengths varying from 0.5 to 5 mm.The biotite is platy with lengths varying from 0.5 to 2 mm and is characterized by chloritization.The hornblende crystals are rhombic with lengths varying from 0.5 to 5 mm.The matrix is composed of quartz, plagioclase and biotite, with minor accessory magnetite, zircon and apatite (Fig. 5i).

4.b.1. Zircon U-Pb dating
Zircon grains were separated using conventional heavy liquid and magnetic techniques, followed by hand selection under a binocular microscope.U-Pb isotopic analyses were performed using an Agilent 7500 mass spectrometer connected to a 193 nm ArF excimer laser ablation system at the MNR Key Laboratory of

Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences (CAGS).
Detailed operating conditions for the laser ablation system, the LA-ICP-MS instrument and data reduction were described by Hou et al. (2009).Errors in individual analyses by LA-ICP-MS are provided at the 1σ level, while errors in pooled ages are noted at the 95% confidence level.Concordia diagrams and weighted mean calculations were made using the Isoplot program (Ludwig, 2003).

4.b.2. Rb-Sr isotope analysis
The samples were crushed to a 40-80 mesh size and hand-selected under a binocular microscope, yielding samples of >99% purity.Sulphide grains were crushed to a <200 mesh size before analysis and then washed in an ultrasonic bath and dried.Rb and Sr isotopic analyses were performed on a VG-354 mass spectrometer with five collectors at the Nantai Geological Testing Institute, Nanjing, China.The analytical procedures were consistent with those described by Wang et al. (2007aWang et al. ( , 2007b)).During analysis, the reproducibility and accuracy of Sr isotope measurements were periodically checked by running the NBS987 standard reference material and laboratory standard La Jolla with a mean 87 Sr/ 86 Sr value of 0.710342 ± 0.000040 (certified value: 0.710340 ± 0.000260) based on the standard 86 Sr/ 88 Sr = 0.1194.The accuracy of the Rb/Sr ratios was better than 1%.

4.b.3. He-Ar isotope analysis
He-Ar isotopic analyses of five pyrite samples were conducted using a Helix SFT noble gas isotope mass spectrometer at the MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS.The measurement procedure consisted of crushing, purification and mass spectrometry.All weighed pyrite samples were measured under high vacuum conditions for analysis, with n × 10 −9 mbar in the crush and purification system and n × 10 −10 mbar in the mass spectrometer system.The details can be found in Liu et al. (2018).

4.b.4. In situ S isotope
Seven pyrite samples (BMZ6, BMZ7, BMZ8 BMZ9, BMZ10, BMZ13, BMZ14) for in situ sulphur isotope analyses were analysed using a laser ablation coupled multicollector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS) at the MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS.The laser fluence was 5.0 J/cm 2 , with a frequency of 4 Hz and spot diameter of 40-50 μm.The ablation method consisted of single-point ablation with a high-purity carrier gas.A standard-sample bracketing method (SSB) was employed to correct for instrumental mass fractionation, calibrated via a Balmat pyrite standard (Crowe & Vaughan, 1996), and the matrix effect was no more than 0.5‰.

5.d. In situ S isotope compositions
The in situ S isotopic compositions of pyrite are listed in Table 4.The δ 34 S values of pyrite have a relatively narrow range from þ 0.1 ‰ to þ 2.8 ‰ (Fig. 9a, b) and an average of 1.6 ‰ (n = 24).

6.a. Timing of gold mineralization
The volume of dioritic porphyrite increases towards deep levels, suggesting a considerable flux of dioritic magmas (Chen et al. 2020).At the No. 7 drill hole, the dioritic porphyrite is featured by sericitization and kaolinization at a depth of 51 metres.On either side in contact with the gold-bearing silicified breccia, the mineralized alteration shows a gradual trend of evolution from strong to weak.Moreover, mineralized altered dioritic porphyrite breccia was found in drill holes 10, 14, 16 and 30.All these ideological facts show that the genesis of the gold deposit is closely related to the dioritic porphyrite.These data indicate that the sulphur of the Jinying deposit was derived from a magmatic source.
It is generally recognized that there are three potential sources of He and Ar isotopes (Turner et al. 1993;Stuart et al. 1995;Burnard et al. 1999): (1) air-saturated water (ASW, e.g.meteoric water or seawater) with a 3 He/ 4 He ratio of 1Ra=1.4× 10 −6 and a 40 Ar/ 36 Ar ratio of 295.5; (2) mantle-derived fluids with 3 He/ 4 He ratios generally of 6-9 Ra and 40 Ar/ 36 Ar >40000; and (3) crustderived fluids with 3 He/ 4 He ratios of 0.01 to 0.05 Ra and 40 Ar/ 36 Ar >45000.The 3 He/ 4 He ratios of the pyrite from Jinying range from 0.08 to 0.13 Ra, which are slightly higher than those of crust-derived fluids.In the plot of 3 He vs. 4 He (Fig. 10a), all of the data are located between the crust and mantle helium isotopic compositions, indicating that the ore-forming fluids of the Jinying gold deposit were derived from mixed mantle and crustal sources.
For Ar isotopes, the obtained 40 Ar/ 36 Ar values of fluid inclusions range from 331.6 to 351.3 and are slightly higher than those of ASW (295.5, Fig. 10b).In the 3 He/ 4 He (R/Ra) vs. 40 Ar/ 36 Ar diagram (Fig. 10b), all of the data plot between the crustal and mantle end-members, indicating that the ore-forming fluids might be a mixture of two end-member fluids.These He-Ar isotope data are similar to those from the Early Cretaceous magmatichydrothermal Au deposits in the Liaodong.Likewise, the 3 He/ 4 He and 40 Ar/ 36 Ar values of pyrite from Wulong range from 0.15-0.54R/Ra and 297-315 (Zhang et al. 2020).For the Xinfang gold deposit, the 3 He/ 4 He and 40 Ar/ 36 Ar values of pyrite range from 0.14-0.62R/Ra and 1008-7100 (Zhang et al. 2022a).Moreover, the proportion of mantle 4 He is calculated as He mantle (%) = (R sample -R crust )/(R mantle -R crust ) × 100%, where R mantle = 8, R crust = 0.01 and R represents the 3 He/ 4 He ratios of the fluids in the mantle, crust, and sample (Tolstikhin, 1978;Kendrick et al. 2001).The calculated results indicate a mantle He range of 1.0-1.6%,indicating that the ore-forming fluids were dominantly crustal fluids with inputs of minor amounts of mantle fluids.

6.c. Ore genesis and tectonic implications
The sulphur isotopic compositions of pyrite suggested that the sulphur of the Jinying gold deposit has a magmatic source.Their He-Ar isotopic compositions suggest that the ore-forming fluids were derived from mixed mantle and crustal sources.The timing of gold mineralization is similar to the timing of emplacement of spatially related dioritic porphyrite in the deposit, implying that the mineralization was related to the intrusive activity.Based on the above arguments, it is reasonable to interpret the Jinying gold deposit is a magmatic-hydrothermal deposit.
The study area is located within the eastern edge of the NCC, which records the evolution and the final closure of the Palaeo-Asian Ocean, as well as the overprinting of the Palaeo-Pacific tectonic regimes during the Mesozoic (Sengör et al. 1993;Sengör & Natal'in, 1996;Li, 2006;Wu et al. 2011;Xu et al. 2013).Multiple stages and complicated geotectonic processes led to the formation of abundant magnesite, talcum, boron, lead-zinc and gold deposits in this area (Shen et al. 2020;Li et al. 2023;Zhang et al. 2023).The  (Zhu et al. 2015;Wu et al. 2019), respectively.In this study, we determined that magmatism and mineralization at Jinying occurred during the Early Cretaceous, and the formation of the deposit likely occurred in an extensional setting controlled by the rollback of the Palaeo-Pacific Plate.This interpretation is extensional-related settings, lithospheric thinning and delamination occurring spatially from west to the east with accompanying by upwelling asthenospheric mantle.In this case, the hot asthenospheric mantle provided enough heat to melt the delaminated lower crust and react with it, producing adakitic magmas in this area (Chen et al. 2020;Xuan et al. 2022), where magmatic differentiation formed ore-bearing fluids.The orebearing fluids then ascended along the fault and mixed with meteoric water or metamorphic water, which was accompanied by complicated physical and chemical changes that would have led to and final closure of the Palaeo-Asian Ocean in the late Palaeozoic-early Mesozoic as well as overprinted and modified by Palaeo-Pacific Plate tectonic regimes during the Mesozoic-Cenozoic (Sengör

Figure 1 .
Figure 1.(Colour online) (a) Tectonic map of the Proterozoic Liao-Ji belt, northeastern margin of the North China Craton (Zhao et al. 2005); (b) geological map of southern Jilin Province showing the locations of major deposits (Chu et al. 2021).

Figure 2 .
Figure 2. (Colour online) Geological map of the Jinying gold deposit.

Figure 4 .
Figure 4. (Colour online) Cross-section showing the geology along exploration Line 34.

Figure 6 .
Figure 6.Representative CL images of analysed zircons extracted from granodiorite porphyry and dioritic porphyrite in the Jinying gold deposit.
northern margin of the NCC is the most important gold belt in China, and many previous studies have examined the mineralization age and tectonic setting of gold deposits.The results show that gold mineralization occurred in the Permian-Triassic, Jurassic and Early Cretaceous (Li et al. 2018; Zeng et al. 2021; Zhang et al. 2022b; Song et al. 2023; Zhao et al. 2023), formed during closure of the Palaeo-Asian Ocean, subduction of the Palaeo-Pacific Plate and an extensional setting associated with rollback of the Palaeo-Pacific Plate

Table 1 .
LA-ICP-MS zircon U-Pb dating results of intrusions in the Jinying gold deposit In this study, the Rb-Sr age of 120 ± 3 Ma for pyrite associated with Au mineralization in the ore vein provides evidence of an Early Cretaceous Au mineralization age.Zircon U-Pb dating indicates that the crystallization age of the dioritic porphyrite was 122.5 ± 0.8 Ma, whereas the granodiorite porphyry yielded a relatively older age of 172.1 ± 1.2 Ma.These ages indicate that dioritic porphyrite and gold mineralization were largely synchronous and that mineralization and magmatism occurred in the Early Cretaceous.The age interpreted for the Jinying deposit is similar to that of many other magmatichydrothermal ore deposits in eastern Liaoning and southern Jilin.

Table 2 .
Rb-Sr isotopic analyses of pyrite from the Jinying gold deposit Plot of sulphide Rb-Sr isochron for the Jinying gold deposit.He-Ar isotopic compositions indicate that the ore-forming fluids mainly originated from a mixture of crustal and mantle components.In situ S isotope compositions of pyrite indicate that the ore-related sulphur source was derived from deep magma.(3) The Early Cretaceous diagenesis and mineralization formed in an extensional setting associated with rollback of the Palaeo-Pacific Plate.This work was jointly supported by the Science & Technology Fundamental Resources Investigation Program (Grant No. 2022FY101704), the National Natural Science Foundation of China Acknowledgements.

Table 3 .
He-Ar isotopic compositions of fluid inclusions trapped in pyrite from the Jinying gold deposit

Table 4 .
In situ sulphur isotope results of ore minerals in the Jinying gold deposit