Fluid inclusions, C–H–O–S–Pb isotope systematics, geochronology and geochemistry of the Budunhua Cu deposit, northeast China: Implications for ore genesis

Journal Pre-proof Fluid inclusions, C-H-O-S-Pb isotope systematics, geochronology and geochemistry of the Budunhua Cu deposit, northeast China: implications for ore genesis Kaituo Shi, Keyong Wang, Xueli Ma, Shunda Li, Jian Li, Rui Wang PII:

S1674-9871(19)30175-6

DOI:

https://doi.org/10.1016/j.gsf.2019.09.010

Reference:

GSF 892

To appear in:

Geoscience Frontiers

Received Date: 10 April 2019 Revised Date:

27 July 2019

Accepted Date: 29 September 2019

Please cite this article as: Shi, K., Wang, K., Ma, X., Li, S., Li, J., Wang, R., Fluid inclusions, C-H-O-SPb isotope systematics, geochronology and geochemistry of the Budunhua Cu deposit, northeast China: implications for ore genesis, Geoscience Frontiers, https://doi.org/10.1016/j.gsf.2019.09.010. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

Fluid inclusions, C-H-O-S-Pb isotope systematics, geochronology and geochemistry of the Budunhua Cu deposit, northeast China: implications for ore genesis

Kaituo Shia, Keyong Wanga, b, c,*, Xueli Maa, Shunda Lia, b, Jian Lia, Rui Wanga a

College of Earth Sciences, Jilin University, Changchun 130061, China

b

College of Geology and Mining Engineering, Xinjiang University, Urumqi 830047,

China c

MNR Key Laboratory of Mineral Resources Evaluation in Northeast Asia,

Changchun 130061, China

*Corresponding author:

Tel: 86-13069004095 E-mail: [email protected]

Postal address: 2199 Jianshe Street, College of Earth Sciences, Jilin University, Changchun 130061, China E-mail addresses for all authors:

[email protected] (K.-T. Shi)

[email protected] (K.-Y. Wang) [email protected] (X.-L. Ma) [email protected] (S.-D. Li) [email protected] (J. Li) [email protected] (R. Wang)

Abstract 1

The Budunhua Cu deposit is located in the Tuquan ore-concentrated area of the southern Great Xing’an Range, NE China. This deposit includes the southern Jinjiling and northern Kongqueshan ore blocks, separated by the Budunhua granitic pluton. Cu mineralization occurs mainly as stockworks or veins in the outer contact zone between tonalite porphyry and Permian metasandstone. The ore-forming process can be divided into four stages involving stage I quartz–pyrite–arsenopyrite; stage II quartz–pyrite–chalcopyrite–pyrrhotite; stage III quartz–polymetallic sulfides; and stage IV quartz–calcite. Three types of fluid inclusions (FIs) can be distinguished in the Budunhua deposit: liquid-rich two-phase aqueous FIs (L-type), vapour-rich aqueous FIs (V-type), and daughter mineral-bearing multi-phase FIs (S-type). Quartz of stages I–III contains all types of FIs, whereas only L-type FIs are evident in stage IV veins. The coexisting V- and S-type FIs of stages I–III have similar homogenization temperatures but contrasting salinities, which indicates that fluid boiling occurred. The FIs of stages I, II, III, and IV yield homogenization temperatures of 265–396 °C, 245–350 °C, 200–300 °C, and 90–228 °C with salinities of 3.4–44.3 wt.%, 2.9–40.2 wt.%, 1.4–38.2 wt.%, and 0.9–9.2 wt.% NaCl eqv., respectively. Ore-forming fluids of the Budunhua deposit are characterized by high temperatures, moderate salinities, and relatively oxidizing conditions typical of an H2O–NaCl fluid system. Mineralization in the Budunhua deposit occurred at a depth of 0.3–1.5 km, with fluid boiling and mixing likely being responsible for ore precipitation. C–H–O–S–Pb isotope studies indicate a predominantly magmatic origin for the ore-forming fluids and materials. LA-ICP-MS zircon U–Pb analyses indicate that ore-forming tonalite porphyry and post-ore dioritic porphyrite were formed at 151.1 ± 1.1 Ma and 129.9 ± 1.9 Ma, respectively. Geochemical data imply that the primary magma of the tonalite porphyry formed through partial melting of Neoproterozoic lower crust. On the basis of available evidence, we suggest that the Budunhua deposit is a porphyry ore system that is spatially, temporally, and genetically associated with tonalite porphyry and formed in a post-collision extensional setting following closure of the Mongol–Okhotsk Ocean. 2

Keywords: Fluid inclusion; C–H–O–S–Pb isotopes; Zircon U–Pb geochronology; Whole-rock geochemistry; Budunhua Cu deposit; Southern Great Xing’an Range. 1. Introduction The Central Asian Orogenic Belt (CAOB) is the world’s largest Phanerozoic accretionary collage and continental metallogenic domain and lies between the East European, Siberian, North China, and Tarim cratons (Fig. 1A; Sengör et al., 1993; Windley et al., 2007; Xiao et al., 2009; Wilhem et al., 2012). Renowned for the occurrence

of

various

ore

deposits

closely

related

to

Phanerozoic

magmatic–hydrothermal activity, the CAOB is an ideal site for economic geology and mineral exploration research (Seltmann et al., 2014; Lv et al., 2017; Xiao et al., 2017; Gao et al., 2018). The Great Xing’an Range (GXR) of China constitutes the eastern segment of the CAOB and is an important metallogenic province with more than 100 ore deposits, including the Wunugetushan, Badaguan, Chaobuleng, Bairendaba, Dajing, Baerzhe, Budunhua, and Aolunhua deposits (Fig. 1B; Liu et al., 2004; Zeng et al., 2011; Chen et al., 2017). The Budunhua Cu deposit is located in the southern part of the GXR (Fig. 1B–C). This deposit differs from other Cu deposits in southern GXR (i.e., Lianhuashan and Naoniushan) because of its two distinctive mineralization types: the Jinjiling ore block with porphyry-type mineralization in the south, and the Kongqueshan ore block with vein-type mineralization in the north. These two ore blocks are separated by the Budunhua composite intrusion (Fig. 2A–C), which is spatio-temporally associated with the Cu mineralization. Since the Budunhua deposit was discovered in the 1960s, few studies of the Jinjiling ore block have been undertaken regarding its general geology, characteristics of ore-forming fluids, and isotopic composition (Wang, 1995; Xiao, 2008; Wu et al., 2012, 2014; Chen et al., 2013), and limited research has been conducted on the Kongqueshan ore block because of its relatively small reserves (Ouyang et al., 2014). This lack of systematic research has limited our understanding of the genesis of the Budunhua deposit, and the ore-forming mechanisms remain controversial. Some studies have regarded Budunhua as a low-sulfidation epithermal 3

deposit (Jin and Pang, 1983), whereas others consider that the mineralization in the Jinjiling ore block is of porphyry type (Wang, 1995; Sheng and Fu, 1999; Xiao, 2008; Wu et al., 2012, 2014), and yet others have proposed an atypical porphyry deposit model (Ouyang et al., 2014). In this paper we give a detailed description of geology and mineralization, then we present systematic fluid inclusion microthermometry and C–H–O–S–Pb isotope studies to provide insights into the nature and sources of ore fluids and ore-forming materials of the Jinjiling and Kongqueshan ore blocks. Precise laser ablation ICP-MS zircon U–Pb ages and whole-rock geochemical data for ore-forming tonalite porphyry and post-ore dioritic porphyrite are reported to elucidate the age, origin, and metallogenic setting of the Budunhua Cu deposit. Based on the data generated, together with the results of previous studies, we classify the deposit type and propose a metallogenic model for the Budunhua Cu deposit. 2. Geological setting 2.1. Regional geology Tectonically, the GXR is part of the eastern CAOB, which is thought to have evolved during the late Mesoproterozoic–late Palaeozoic through the accretion of ophiolites, arc/back-arc systems, and microcontinental fragments (Kovalenko et al., 2004; Windley et al., 2007; Yarmolyuk et al., 2012; Kröner et al., 2014). The GXR is characterized by immense volumes of Phanerozoic granitoids with low Sr and high Nd contents, which record significant continental growth (Guo et al., 2010; Wu et al., 2011). The GXR is divided, from north to south, into the Erguna fold belt (EB), the Hercynian fold belt of the northern GXR (HBNGXR), and the Hercynian fold belt of the southern GXR (HBSGXR), separated by the Derbugan, Erlian–Hegenshan, and Xar Moron–Changchun faults, respectively (Fig. 1B; Zeng et al., 2011). The E-trending Xar Moron–Changchun fault is generally considered as the final suture zone between the North China platform and the Siberian Plate (Xiao et al., 2003; Chen et al., 2009; Wu et al., 2011). The regional stratigraphy of the GXR includes Precambrian

metamorphic

basement,

Palaeozoic

metamorphosed 4

volcano-sedimentary assemblages, and Mesozoic intermediate–acidic continental volcanic–volcaniclastic rocks (Fig. 1B). The GXR has great potential for ore prospecting because of its complex and protracted tectonic evolution, which includes closure of the Paleo-Asian Ocean during the late Palaeozoic, closure of the Mongol–Okhotsk Ocean, and oblique subduction of the Pacific Plate beneath the Eurasian continent during the Mesozoic (Meng, 2003; Xiao et al., 2003; Ying et al., 2010; Wu et al., 2011; Wang et al., 2015; Chen et al., 2017). 2.2. Tuquan ore-concentrated area Four Cu deposits (the Lianhuashan, Naoniushan, Budunhua, and Chentaitun deposits) and two Pb–Zn–Ag polymetallic deposits (the Meng’entaolegai and Changchunling deposits) have so far been discovered in the Tuquan District, in the eastern segment of the HBSGXR (Fig. 1B–C). Porphyry and vein types are the principal deposits. Geological characteristics of these deposits are given in Supplementary Table 1. Lithostratigraphic units in the Tuquan District are mainly Jurassic with minor Permian and Cretaceous contributions (Fig. 1C). Permian strata comprise a series of submarine clastic rocks considered to be the local source bed for metal mineralization (Sheng and Fu, 1999; Liu et al., 2004; Wang et al., 2006). The overlying Mesozoic sequence (J–K) is dominated by extensive intermediate to felsic continental volcanic and pyroclastic rocks. Regional tectonostratigraphic units and faults in the area strike NNE to NE (e.g., the Nenjiang deep fault) and are crosscut by a series of NW-striking faults, resulting in a latticed fault system that provided conduits for volcanism, magmatism, and ore deposition (Fig. 1C). Magmatic activity in the Tuquan District was frequent and intensive. Intrusions include widely exposed Yanshanian granitoids and minor Hercynian granitoids. The former occur mainly as batholiths and stocks comprising granodiorite and monzonite granite, which are considered to have originated from the same sources as contemporaneous volcanic rocks and to be closely related to mineralization. In comparison, Hercynian granitoids are relatively rare and crop out only locally as batholiths in the Changchunling and Meng'entaolegai areas (Fig. 1C). 5

2.3. Geology of Budunhua Cu deposit The Budunhua Cu deposit is located in the southern end of the Tuquan ore-concentrated area, 50 km south of Tuquan County and to the west of the Nenjiang fault (Fig. 1C). The deposit includes the southern Jinjiling and northern Kongqueshan ore blocks separated by the Budunhua granitic intrusion (Fig. 2A). Recent exploration indicates Cu reserves of >0.16 Mt, with an average grade of 0.7 wt.% (XLJM, 2015). Strata exposed in the mining area are of the lower Permian Dashizhai, Middle Jurassic Wanbao, and Upper Jurassic Manketou'ebo formations (Fig. 2A). The metasandstone of the Dashizhai Formation is the dominant host rock of the Cu orebodies and has the widest distribution (Fig. 2A–C). The Jurassic unit unconformably overlies the Dashizhai Formation, cropping out in the southeastern part of the area. The Wanbao Formation consists of sandy conglomerate intercalated with tuffs, whereas the Manketou'ebo Formation comprises mainly rhyolite, rhyolitic tuff, and dacitic tuff (Fig. 2A). Intrusions in the deposit (referred to as the Budunhua complex) comprise predominantly concealed tonalite porphyry and exposed biotite granodiorite and granite porphyry (Fig. 2A–B). These rocks have similar mineralogical compositions in the form of stocks and intrude the Dashizhai Formation. The intrusions are inferred by some researchers to have been derived from a single magma chamber (Wang, 1997), and the tonalite porphyry is considered to be the intrusion that caused the mineralization (Wang, 1995; Ouyang et al., 2014). In addition, numerous dioritic porphyrite dykes occur in the mine district, especially in the Kongqueshan Block where the dykes accompany Cu lodes filling N-trending fissures (Fig. 2A). Some ore veins are locally crosscut by dioritic porphyrite dykes (Fig. 2A and C), indicating that the dykes post-date mineralization. Structurally, the ore district includes at least two phases: in the first (Palaeozoic) phase, the Dashizhai Formation underwent N-directed compression, resulting in the Kongqueshan anticline and an N-oriented fracture zone; the second (Mesozoic) phase involved the development of numerous NE-trending faults and some younger NW-trending faults (Fig. 2A). About 30 stratiform-like and lenticular Cu orebodies have been delineated in the Jinjiling ore block. These concealed orebodies occur mainly in the outer contact zone 6

between the tonalite porphyry and Dashizhai Formation (Fig. 2B), with no distinct boundaries between orebodies and country rocks. The orebodies strike NW and dip to the NE at 45°–60° and have lengths of 100–580 m, thicknesses of 2–15 m, and slope depths of 45–300 m. In the Kongqueshan ore block, 12 ore veins have been identified, spatially confined to N-trending fracture zones (Fig. 2A and C). The ore veins are 350–1100 m long, 160–350 m deep, and 1–3 m thick, with eastward dips of 65°–85°. Stockworks and disseminations are the predominant ore styles in the Budunhua deposit, with mainly granular and metasomatic–relict textures (Figs. 3 and 4). The principal metallic minerals are chalcopyrite, pyrite, and pyrrhotite, with lesser amounts of arsenopyrite, sphalerite, galena, molybdenite, magnetite, hematite, supergene malachite, and limonite (Fig. 4). Gangue minerals include mainly quartz, calcite, biotite, K-feldspar, sericite, chlorite, and tourmaline. Rocks within the Budunhua deposit record intense hydrothermal alteration, including silicification, K-feldspathization, biotitization, phyllic alteration, tourmalization, propylitization, argillization, and carbonatization (Fig. 2E–K). During exploration of the Jinjiling ore block, Wang (1995) recognized obvious alteration zoning, i.e. from the center of tonalite porphyry outward, potassic alteration and tourmalition, phyllic alteration to chloritization and carbonatization. There are no clear boundaries between the alteration zones, with most exhibiting gradational relationships. Most Cu orebodies are confined to the phyllic alteration zone (Fig. 2D–E). Alteration in the Kongqueshan ore block is controlled by faults and is dominated by silicification, biotitization, chloritization, and phyllic alteration with silicification and biotitization displaying close spatial relationships with mineralization (Fig. 2J–K). Based on mineral assemblages, ore fabrics, and vein crosscutting relationships, we conclude that the Jinjiling and Kongqueshan ore blocks shared similar ore-forming processes, which involved a supergene period and a hydrothermal period. Malachite and limonite, at surfaces formed by the weathering of sulfides, represent a supergene oxidation period, whereas the hydrothermal period is the predominant and include four stages from early to late, as follows. Stage I is a quartz–K-feldspar stage (Fig. 3A–C, J–K), with pyrite and arsenopyrite in quartz–K-feldspar veins occurring mostly 7

as euhedral–subhedral crystals (Fig. 4A, E–F) and with minor disseminated molybdenite and magnetite scattered in the porphyry (Fig. 4G). Coeval alteration includes silicification, tourmalization, and potassic alteration. Stage II is characterized by a stockwork of quartz + pyrite + chalcopyrite + pyrrhotite veins or veinlets (Fig. 3D–G, L–N). In stage III, quartz–polymetallic sulfide veins are characterized by abundant polymetallic sulfides (Fig. 3H, O) such as pyrite, chalcopyrite, sphalerite, galena, and pyrrhotite (Fig. 4C, I). Stages II and III are the principal Cu mineralization stages associated with local phyllic alteration. Stage IV marks the end of hydrothermal activity and is defined by veinlets of quartz and calcite (Fig. 3I, P), with minor pyrite, chalcopyrite, and siderite (Fig. 4D, J), that typically cut earlier-formed veins or veinlets. Carbonation and argillization are also developed in stage IV. The paragenetic sequence of the Budunhua deposit is summarized in Fig. 5.

3. Sampling and analytical methods 3.1. Zircon LA-ICP-MS U–Pb dating Samples of tonalite porphyry (BDHA) and diorite porphyrite (BDH), collected from outcrops and drill cores in the Budunhua ore district (Fig. 2B–C), were selected for zircon LA–ICP–MS U–Pb dating. The tonalite porphyry contains phenocrysts of quartz, plagioclase, and amphibole in a felsic groundmass, with pervasive silicification, sericitization, argillization, and potassic alteration (Fig. 6A–C). The main constituents of diorite porphyrite are plagioclase (~55 vol.%) and amphibole (~45 vol.%), with minor chloritization and carbonation (Fig. 6D–F). Zircon crystals were extracted using conventional heavy-liquid and magnetic separation techniques and further purified by handpicking under a binocular microscope at the Langfang Honesty Geological Service Co., Ltd, China. Representative zircon grains were mounted in epoxy resin and polished to expose grain

centres.

Reflected-

and

transmitted-light

photomicrographs

and

cathodoluminescence (CL) images were obtained at the Wuhan Sample Solution Analytical Technology Co., Ltd, China, to reveal the morphology and internal structures of individual zircon grains and to select the least-fractured and 8

inclusion-free zones for U–Pb analyses. Zircon U–Pb isotope analyses were performed using LA–ICP–MS at the MNR Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Jilin University, China, using an Agilient 7900 ICP–MS instrument connected to a Geolaspro 193 nm ArF Excimer laser. The laser spot diameter was 32 µm, and He was used as carrier gas. International standard zircon 91500 was used as an external standard to normalize isotopic fractionation during analysis. Analytical procedures followed those described by Yuan et al. (2004), and raw data were processed using the GLITTER program. Concordia diagrams and weighted-mean ages were obtained using Isoplot (v.3.0; Ludwig, 2003). Uncertainties of individual analyses are reported at the 1σ level, and weighted-mean ages were calculated at the 1σ confidence level. The zircon U–Pb isotope data are given in Table 1. 3.2. Major- and trace-element analyses Five minimally altered tonalite porphyry samples (GBDH-1 to GBDH-5) were collected for whole-rock geochemical analyses at the ALS Chemex (Guangzhou) Co., Ltd, China. Rock samples were crushed and powdered to 200 mesh in an agate mill. Major-element concentrations were determined by XRF with analytical uncertainties of <5%. The samples were melted at high temperature after being fully mixed with lithium nitrate-lithium borate containing lithium nitrate melting flux. The melt was poured into a platinum mould to form a flat glass, which was analysed using PANalytical PW2424. The loss on ignition (LOI) was acquired by heating samples in a muffle furnace at 1000 °C for an hour and recording the percentage weight loss. Trace-element compositions were determined by ICP–AES and ICP–MS with analytical precisions better than 10%. The samples were digested with perchloric acid, nitric acid and hydrofluoric acid. Samples steamed to near-dry were dissolved in dilute hydrochloric acid and volumetrized, then were analysed using Agilent VISTA and Agilent 7700x. Rare-earth-element (REE) compositions were determined by ICP–MS with analytical precisions better than 10%. The samples were added to the lithium metaborate or lithium tetraborate flux. The mixture was melted in the furnace above 1025 °C. After 9

cooling, it was volumetrized with nitric acid, hydrochloric acid and hydrofluoric acid, and then analyzed by Perkin Elmer Elan 9000. 3.3. Fluid inclusion analysis Fluid inclusion studies were conducted on mineralised quartz and calcite. Twenty-one samples from outcrops and diamond drill holes, covering all hydrothermal veins from different stages, were doubly polished into thin-sections (<0.30 mm thick) for fluid inclusion petrographic and microthermometric analyses. Of these samples, 12 were from the Jinjiling ore block and 9 from the Kongqueshan ore block. Following detailed petrographic examination, microthermometric measurements were performed on a Linkam THMS-600 heating–freezing stage with a temperature range of −195 to +600 °C in the Key Laboratory of Geological Fluid, Jilin University, China. The equipment was calibrated by the freezing point of pure-water inclusions (0 °C) and the triple point of pure CO2 inclusions (−56.6 °C). Measurement precisions are estimated as ±0.2 °C at <30 °C, ±1 °C at 30–300 °C, and ±2 °C at >300 °C. Ice-melting temperatures (Tm,ice), halite dissolution temperatures (Tm,d), and total homogenization temperatures (Th) were measured. Heating and freezing rates were usually 1–5 °C

min−1, reducing to 0.1–0.5 °C min−1 as phase transitions were

approached. Salinities are expressed as wt% NaCl equivalent (NaCl eqv.) and were estimated from the melting temperatures of ice in aqueous (NaCl–H2O) inclusions (Bodnar, 1993), using the data and methodology of Bodnar and Vityk (1994) for halite daughter mineral-bearing inclusions. 3.4. Isotope analysis Representative ores from both the Jinjiling and Kongqueshan ore blocks that precipitated during the different stages of mineralization were collected for isotope analysis. Separated quartz, calcite, and sulfide grains were crushed to 40–60 mesh before samples were handpicked under a binocular microscope to achieve >99% purity. All the isotope analyses were performed at the Analytical Laboratory, Beijing Research Institute of Uranium Geology, Beijing, China. Oxygen isotopic compositions of quartz and hydrogen isotopic compositions of fluid inclusions (FIs) in quartz were determined using a Finnigan MAT 253 mass 10

spectrometer. The conventional BrF5 method was used to determine oxygen isotopic compositions (Clayton and Mayeda, 1963), and hydrogen isotopic compositions were determined using the Zn-reduction method (Coleman et al., 1982). The O and H isotopic values are reported in per mil relative to V-SMOW with analytical precisions of ± 0.2‰ for δ18Oquartz and ± 2‰ for δDH2O. For C–O isotope analyses, CO2 was produced by reacting calcite samples with phosphoric acid at 25 °C and analyzed using a Finnigan MAT 253 mass spectrometer. C and O isotopic compositions are reported relative to PDB and SMOW, respectively, with accuracies better than ± 0.2‰. Sulfur isotopic compositions were determined using a Delta v plus mass spectrometer using the conventional combustion method (Robinson and Kusakabe, 1975). Results are reported as δ34S relative to V-CDT with reproducibilities of ± 0.2‰. Lead isotope analyses were conducted using a Phoenix thermal-ionization mass spectrometer. All Pb ratios were corrected according to the values of NBS SRM 981. Pb isotope analytical errors are reported as ±2σ, and analytical precision was better than 0.005% for 208Pb/206Pb ratios.

4. Results 4.1. Zircon U–Pb ages Zircon grains from sample BDHA are euhedral–subhedral, display fine-scale oscillatory growth zoning, and have Th/U ratios of 0.30–0.57, indicative of a magmatic origin. Twenty analyses formed a coherent cluster and yielded a weighted-mean 206Pb/238U age of 151.1 ± 1.1 Ma (MSWD=0.27; Fig. 7A, B), taken as the crystallization age of the tonalite porphyry. Zircons from sample BDH are mostly subhedral, display oscillatory growth zoning, and have Th/U ratios of 0.18–1.26, suggesting an igneous origin. Twenty analyses yielded concordant

206

Pb/238U ages between 125 Ma and 2322 Ma (Fig. 7C). The

youngest group (129.9 ± 1.9 Ma, MSWD=0.16, n=9; Fig. 7D) is interpreted as the emplacement age of the diorite porphyrite, and the older ages are inferred to represent the crystallization age of inherited zircons. 11

4.2. Major and trace elements Major- and trace-element compositions of the tonalite porphyry samples are presented in Table 2. The analyzed samples have high SiO2 (70.43–71.43 wt.%), total alkali (Na2O + K2O = 7.88–8.09 wt.%), and Al2O3 contents (14.01–14.40 wt.%), and low P2O5 (0.06–0.07 wt.%), TiO2 (0.27–0.33 wt.%), MgO (0.66–0.91 wt.%), and CaO contents (1.39–1.98 wt.%). K2O/Na2O ratios, Mg# values, and A/CNK ratios are 1.04–1.08, 37.17–41.74, and 1.01–1.06, respectively. All samples plot in the high-K calc-alkaline field in a K2O–SiO2 diagram (Fig. 8A) and are classified as weakly peraluminous in a A/NK–A/CNK diagram (Fig. 8B). Chondrite-normalized REE patterns for the tonalite porphyry samples are characterized by enrichment in light REEs (LREEs) relative to heavy REEs (HREEs) (Fig. 8C), with LREE/HREE and (La/Yb)N ratios of 8.63–9.46 and 8.72–10.55, respectively, and moderately negative Eu anomalies (Eu/Eu* = 0.47–0.54). In primitive-mantle-normalized spider diagrams (Fig. 8D), the tonalite porphyry samples are enriched in large-ion lithophile elements (LILEs; e.g., Rb, Th, U, and K) and relatively depleted of high-field-strength elements (HFSEs; e.g., Nb, Ta, and Ti). 4.3. Fluid inclusion studies 4.3.1. Fluid inclusion petrography All samples contained abundant primary (isolated or as random groups in intragranular crystals) and secondary (aligned along micro-fractures in transgranular trails) inclusions. Only primary FIs (criteria of Roedder, 1984) were analyzed in this study. Based on phase relationships at room temperature and phase transitions during heating and cooling, three types of primary FIs were recognized in the studied samples from the Budunhua deposit, as shown in Fig. 9 and described below. Liquid-rich two-phase aqueous FIs (L-type; Fig. 9A, E, I, M–N, T) contain a liquid phase and a vapour bubble at room temperature with a gas/liquid ratio of 15%–40% and display total homogenization to the liquid phase upon heating. These inclusions are oval, elongate, or irregular in shape, with a size range of 4–25 µm. They are commonly distributed in groups or isolated in veins of all stages and account for ~75% of the total FIs. 12

Vapour-rich aqueous FIs (V-type; Fig. 9B, F, J, O) are generally biphase inclusions with high vapour-phase volumetric proportions (>60%) and are rarely present as monophase vapour inclusions. These inclusions typically display negative-crystal or elliptical shapes with a size range of 5–25 µm. They generally occur in clusters or are distributed randomly in the veins of stages I–III but are absent in the late mineralization stage. These inclusions account for ~20% of the total FIs and homogenized to the vapour phase when heated. Daughter mineral-bearing multi-phase FIs (S-type; Fig. 9C, G, K, P) consist of one or more daughter minerals, a brine liquid, and a vapour bubble. These FIs generally have a size range of 4–18 µm with negative-crystal or irregular forms, and account for ~5% of the total FIs. S-type FIs occur throughout quartz crystals of stages I–III, either isolated or in groups, and can coexist with V-type FIs in the same crystal, indicating boiling features (Fig. 9D, H, L, Q–S). The most common daughter minerals are transparent and include cubic halite and round sylvite crystals as well as unidentified minerals. Minor amounts of opaque metallic minerals were also observed. During heating, halite in most S-type FIs dissolves before homogenization of the vapour bubble into the liquid, with a few being homogenized by final halite dissolution. The populations of V- and S-type FIs gradually decrease and L-type populations increase from the early to late stages. Abundant L-, V-, and S-type FIs were observed in stage I quartz veins. Inclusions from stages II–III quartz are mainly L-type, with subordinate V- and S-types. Only L-type FIs were recognized in stage IV veins. 4.3.2. Fluid inclusion microthermometry Microthermometric studies were conducted on various types of inclusions in stages I–IV from both ore blocks. As the phase transition was difficult to observe, the ice-melting

temperatures

of

V-type

FIs

are

not

particularly

precise.

Microthermometric results and calculated parameters are summarized in Table 3 and illustrated in Fig. 10. Results for the two ore blocks are described in detail below. 4.3.2.1. Jinjiling ore block Stage I: The L-type FIs have ice-melting temperatures of −16 to −5 °C, corresponding to salinities of 7.9–19.6 wt.% NaCl eqv. These FIs homogenize to the liquid phase at 13

temperatures of 320–396 °C. The V-type FIs have homogenization temperatures of 300–360 °C, ice-melting temperatures of −6.2 to −2 °C, and calculated salinities of 3.4–9.5 wt.% NaCl eqv. The S-type FIs homogenize to the liquid phase at temperatures of 315–378 °C, with halite dissolution occurring at 300–370 °C, corresponding to salinities of 38.2–44.3 wt.% NaCl eqv. Stage II: The L-type FIs have ice-melting temperatures of −12.1 to −3.2 °C, with salinities of 5.3–16.1 wt.% NaCl eqv. The homogenization temperatures of these FIs are in the range 245–330 °C. The ice-melting temperatures of V-type FIs are −5 to −2.6 °C, with salinities of 4.3–7.9 wt.% NaCl eqv. and homogenization temperatures of 275–320 °C. The S-type FIs have total homogenization temperatures of 310–330 °C, halite dissolution temperatures of 295–325 °C, and salinities of 37.8–40.2 wt.% NaCl eqv. Stage III: The L-type FIs have homogenization temperatures of 220–300 °C and ice-melting temperatures of −6 to −1.2 °C, corresponding to salinities of 2.1–9.2 wt.% NaCl eqv. The V-type FIs homogenize to the vapour phase at 250–290 °C, with ice-melting temperatures of −4 to −0.9 °C and salinities of 1.6–6.4 wt.% NaCl eqv. For S-type FIs, the disappearance temperature of halite daughter minerals is 254–300 °C, with total homogenization temperatures of 260–300 °C and salinities of 34.9–38.2 wt.% NaCl eqv. Stage IV: Only L-type FIs were observed in the late-stage calcite crystals. These FIs have homogenization temperatures of 140–228 °C and ice-melting temperatures of −4 to −0.6 °C, corresponding to salinities of 1.0–6.4 wt.% NaCl eqv. 4.3.2.2. Kongqueshan ore block As noted above, quartz veins of stages I–III in the Kongqueshan ore block contain abundant L-, V-, and S-type FIs, with only L-type FIs being recognized in stage IV quartz veins. Homogenization temperatures of FIs in stage I are 265–360 °C, with salinities of 3.7–41.5 wt.% NaCl eqv. Stage II FIs have homogenization temperatures of 249–350 °C and salinities of 2.9–38.9 wt.% NaCl eqv. For stage III, the homogenization temperatures of FIs are in the range 200–272 °C, with calculated salinities of 1.4–36.0 wt.% NaCl eqv. The FIs of stage IV homogenize to the liquid 14

phase at temperatures of 90–208 °C, with salinities of 0.9–9.2 wt.% NaCl eqv. 4.4. Isotope systematics Oxygen and Hydrogen isotope data for 16 quartz samples (8 from each ore block) from the different stages are presented in Table 4 and plotted in Fig. 11. No systematic variations in the isotope data occur between the two ore blocks, although there are significant variations between mineralization stages. The measured δ18Oquartz values of quartz samples from different stages range from 5‰ to 10.6‰. The O isotopic compositions of hydrothermal fluids (δ18OH2O) in equilibrium with quartz were calculated from δ18Oquartz values and the mean Th of each stage using the quartz–water isotopic equilibrium function (Clayton et al., 1972). The calculated δ18OH2O values of stage I quartz veins are between 2.3‰ and 3.8‰, with measured δDH2O values varying from −114‰ to −112.1‰. Stage II quartz samples have δ18OH2O values ranging from 0.6‰ to 2.6‰ and δDH2O values ranging from −123.6‰ to −115.5‰. The δ18OH2O values of stage III quartz veins are from −2.3‰ to 1.6‰, with measured δDH2O values varying between −128.5‰ and −125.9‰. Stage IV quartz samples have δ18OH2O values of −6.6‰ to −2.5‰, with δDH2O values of −136‰ to −128.6‰. Carbon and O isotopic compositions of two late-stage calcite samples from the Jinjiling ore block are presented in Table 5, together with previously published data (Sheng and Fu, 1999). The δ13CPDB values are between −9.6‰ and −6.4‰, with δ18OSMOW varying from −4.8‰ to 15.0‰, respectively. Sulfur isotopic results are summarized in Supplementary Table 2 and Fig. 12A and include data from previous studies (IMGMB, 1994; Sheng and Fu, 1999; Wu, 2012). A total of 73 sulfide samples, including pyrite, chalcopyrite, and pyrrhotite, display a limited range of δ34S values of −4.90‰ to 4.93‰, with a mean of −0.16‰, suggesting a homogeneous sulfur source. Table 6 lists the lead isotope data from our study and previously published studies (Wu, 2012; Gu, 2016). Eighteen sulfide samples yielded uniform 207

Pb/204Pb,

208

and

Pb/204Pb

ratios

of

18.274–18.366,

206

Pb/204Pb,

15.509–15.579,

and

38.015–38.252, respectively. Two tonalite porphyry samples have 206Pb/204Pb ratios of 18.298–18.303,

207

Pb/204Pb ratios of 15.540–15.541, and

208

Pb/204Pb ratios of 15

38.092–38.100 (Gu, 2016). All of these data at Budunhua show analogous lead isotope compositions.

5. Discussion 5.1. Nature of ore-forming fluid and metal source Petrographic observations and microthermometric studies indicate that there are no obvious distinctions between the characteristic of FIs of the Jinjiling and Kongqueshan ore blocks, implying a common origin. Fluid inclusions provide a record of ancient fluid systems, and primary FIs in earliest-stage minerals can indicate the

nature

of

the

original

fluids

(Chen

et

al.,

2007).

The

peak

homogenization-temperature interval of FIs of stage I is 320–340 °C, with a salinity range of 12–42 wt.% NaCl eqv., indicating characteristics of a medium–high temperature and high-salinity fluid. In addition, observations of magnetite and hematite in the mineral assemblage of the early stage, and the absence of pyrrhotite, suggest that the initial ore-forming fluid was relatively oxidized. Furthermore, fluid inclusion petrographic studies indicate that no aqueous–carbonic FIs were observed, and CO2 was not detected in the inclusions by Raman spectroscopy. The initial ore-forming solutions of the Budunhua deposit are thus characterized by medium–high temperature, high salinity, and relative oxidation, and represent an H2O–NaCl fluid system indicative of a magmatic origin. The H–O isotopic compositions provide further evidence of fluid evolution from a magmatic–hydrothermal system. In a bivariate δD–δ18OH2O plot (Fig. 11), samples from stage I plot adjacent to the primary magmatic water field, suggesting that initial ore-forming fluids were dominated by magmatic water. Samples from the main ore stages (II and III) display lower δD and δ18OH2O values than those from stage I. These values plot between the magmatic water field and the meteoric water line but closer to the former, suggesting that ore-forming fluids in the main ore-forming stages had a mixed magmatic–meteoric origin, although they were still dominated by magmatic fluids. Stage IV samples plot near Mesozoic meteoric water in the southern GXR (Sheng and Fu, 1999), indicating a significant input of meteoric water into the fluid 16

system. Similar evolutionary paths of H–O isotopic compositions are observed in typical porphyry Cu–Mo deposits in the GXR (e.g., the Duobaoshan, Wunugetushan, and Aolunhua deposits) (Ma and Chen, 2011; Tan et al., 2013; Wu, 2014) and worldwide (e.g., El Salvador, Oyu Tolgoi, and Toromocho) (Sheppard and Gustafson, 1976; Khashgerel et al., 2009; Catchpole et al., 2015). The δ13CPDB values of calcite samples in the Budunhua deposit lie in a narrow range of −9.6‰ to −6.4‰, lower than those of marine carbonate values (~0‰; Hoefs, 2009), higher than those of organic materials in sedimentary rocks (−30‰ to −15‰; Hoefs, 2009), and within the range of magmatic carbon (−9‰ to −3‰; Taylor, 1986), suggesting a predominantly magmatic origin for the carbon. The lack of sulfate minerals in the Budunhua deposit means that the δ34S values of sulfide minerals represent bulk-fluid values (Ohmoto and Rye, 1979). The sulfides have well-defined δ34S values of −4.9‰ to 4.93‰ (mean −0.16‰; n = 73), within the overall range of sulfides in most porphyry Cu deposits (Fig. 12B; −5‰ to 5‰; Cooke et al., 2011), indicating that S and perhaps the metals were derived mainly from a magmatic system. In comparison with the Jinjiling ore block (−2‰ to 4.93‰; mean 1.55‰; n = 32), the more negative values of the Kongqueshan ore-block sulfides (−4.9‰ to 0.7‰; mean −1.5‰; n = 41) may reflect more violent boiling processes during mineralization. Moreover, the S isotopic compositions of the Budunhua deposit are comparable with those of other Cu deposits in the SGXR, including the Lianhuashan (−1.4‰ to 5‰), Naoniushan (2.0‰−3.5‰), Aonaodaba (−6.2‰ to 3‰), and Daolundaba (−3.6‰ to 4.6‰) deposits, all of which are commonly considered to be of magmatic origin ( Sheng and Fu, 1999; Ma and Chen, 2011; Zhang, 2011; Li et al., 2016; He et al., 2017). The Pb isotopic compositions of sulfides in the Budunhua deposit have narrow variations, suggesting that Pb sources were relatively homogeneous. In Pb isotope evolution diagrams (Fig. 13), all sulfide samples plot between the orogen and mantle evolution curves but are closer to the former, indicating that the Pb was derived mostly from the crust with the addition of mantle compositions and that it was related to the orogenic Pb reservoir. Lead isotopic compositions of the Budunhua sulfides 17

overlap those of other Cu deposits in the SGXR (Zhang, 2011) and are consistent with those of the tonalite porphyry (Gu, 2016), indicating that the tonalite porphyry contributed to ore-forming materials. Based on the above characteristics of FIs and H–O–C–S–Pb isotopic compositions, we

conclude

that

the

Budunhua

deposit

formed

in

an

H2O–NaCl

magmatic–hydrothermal system with high temperature and high salinity; the ore-forming fluids and materials show evidence of a magmatic origin linked to the tonalite porphyry. 5.2. Evolution of fluid system and mineralization process 5.2.1. Fluid boiling and depth estimation Fluid inclusion studies have been widely used to constrain ore fluid trapping pressures and to estimate formation depths. Trapping pressure can be estimated only when the actual trapping temperature is known or if the FIs were trapped under immiscible or boiling conditions (Roedder and Bodnar, 1980; Brown and Hagemann, 1995). Fluid boiling can be inferred from the coexistence of S- and V-types FIs as clusters in individual mineral grains that are divergently homogenized at similar temperatures and yield contrasting salinities (Roedder, 1984; Lu et al., 2004). These phenomena are suggested by the measurement of FIs in quartz grains of stages I–III (Fig. 9D, H, L, Q–S and Fig. 10), indicating that the ore-forming fluids underwent multiple stages of fluid boiling in the Budunhua deposit. Microthermometric data for end-members of boiling inclusion assemblages from stages I–III were used to estimate trapping pressures by applying Flincor software (Brown and Hagemann, 1995) and the equation of Brown and Lamb (1989), and assuming that the ore fluids constituted an H2O–NaCl system. The estimated pressures of stages I, II, and III are approximately 80–150 bar, 50–80 bar, and 30–50 bar, respectively, corresponding to depths of 0.8–1.5 km, 0.5–0.8 km, and 0.3–0.5 km, respectively, assuming a hydrostatic environment. These depths are consistent with the estimated mineralization depths of porphyry deposits worldwide (Pirajno, 2009). 5.2.2. Fluid evolution and ore precipitation The fluids of stage I are of an H2O–NaCl system characterized by medium–high 18

temperatures (265–396 °C), high salinity (3.4–44.3 wt.% NaCl eqv.), and oxidizing conditions, which are unfavourable for sulfide deposition and Cu mineralization, as supported by the precipitation of abundant magnetite. Such fluids filtered through and reacted with cooling porphyry rocks and host metasandstone, causing extensive silicification and potassic alteration. Due to the intense fluid boiling and K-feldspar alteration during stage I, consuming heat energy, releasing H2O and CO2, and consequently, the homogenization temperatures (245–350 °C) and salinities (2.9–40.2 wt.% NaCl eqv.) of FIs of stage II are lower than stage I, the fO2 of the ore fluids decreased, whereas S2- activity increased. These changes of ore fluids facilitated the deposition of sulfides including chalcopyrite, pyrite, and pyrrhotite with phyllic alteration, forming the stage II quartz + pyrite + chalcopyrite + pyrrhotite veins or veinlets. Further boiling and cooling of the ore-fluid system and the addition of meteoric

water

caused

deposition

of

abundant

sulfides,

forming

the

quartz–polymetallic sulfide veins of stage III in which the fluids were diluted (1.4–38.2 wt.% NaCl eqv.), resulting in most stage III FIs being L-type inclusions, with minor V

and S types. The subsequent ascent of hydrothermal fluids to

shallower depths precipitated barren carbonate–quartz veinlets containing only small L-type FIs. This stage represented the termination of the ore-forming hydrothermal process and resulted from low-temperature (90–228 °C) and dilute (0.9–9.2 wt.% NaCl eqv.) hydrothermal fluids being sourced mainly from meteoric water, as indicated by their H–O isotopic compositions. Fluid boiling is recognized as a very important ore-forming mechanism for porphyry systems such as the Bingham Cu–Mo deposit, USA (Roedder, 1971); the EI Teniente deposit (Klemm et al., 2007); the Grasberg Cu–Au deposit, Indonesia (Lu, 2000); and the Dexing Cu deposit, Jiangxi, China (Yao et al., 2012). As described above, fluid boiling assemblages have been observed for stage I−III at Budunhua, the intensive multistage boiling reflects repeated pressure fluctuation during mineralization processes and it is believed to be a great promoter for rapid, large scale metal precipitation in a short time (Roedder, 1971; Yao et al., 2012). Fluid boiling can cause the release of volatile components (e.g., H2O and CO2) with condensation of fluid, 19

increases in pH, and decreases in oxygen fugacity, leading to extensive precipitation of chalcopyrite and other ore minerals. Hydrogen and O isotopic compositions indicate that the mixing of fluids with external meteoric water occurred through the whole fluid-evolution process (Fig. 11). This not only reduced fluid temperatures and therefore metal solubilities but also caused dilution, which changed fluid salinity, acidity, and redox properties, promoting metal deposition. Fluid boiling and mixing could thus be the main mechanism of ore precipitation in the Budunhua deposit. 5.3. Petrogenesis and magma source The absence of aluminous primary minerals with A/CNK values of <1.1 (Fig. 8B) suggests that the tonalite porphyry are mainly A- or I-type granites, but not S-type. The Zr– and Nb–(10000 × Ga/Al) discrimination diagrams indicating that most of them are I-type granites (Fig. 8E, F). The Nb, Ta, P, Ti, Eu, and Ba anomalies of the tonalite porphyry imply various degrees of fractional crystallization during magma evolution. In addition, the significant LILE and LREE enrichments and HFSE depletion in the primitive-mantle-normalized spidergram (Fig. 8D), as well as the high SiO2 contents (70.43–71.43 wt.%), suggest that the primary magma was derived from partial melting of crustal material. The tonalite porphyry has relatively high initial 176

Hf/177Hf ratios of 0.282786–0.282882 and positive εHf(t) values of +0.48 to +3.89

with young Hf two-stage model ages of 828–647 Ma (Gu, 2016), indicating that the primary magma could have originated from partial melting of a thickened lower crust. Such isotopic characteristics are typical of Phanerozoic granitoids in the CAOB (Guo et al., 2010; Wu et al., 2011; Wang et al., 2015, 2017). In summary, we conclude that the parental magma of the tonalite porphyry was derived from partial melting of Neoproterozoic lower crust and underwent fractional crystallization during its evolution. Melts finally ascended to a shallow level, leading to the formation of tonalite porphyry. 5.4. Timing and geodynamic setting 5.4.1. Age of the Budunhua deposit Multiple intrusive activities have been recorded in the Budunhua district, referred to as the Budunhua complex, which consist of biotite granodiorite, tonalite porphyry, 20

and granite porphyry, from early to late estimated by the occurrences and crosscuting relationships of intrusions (Fig. 2A). Copper mineralization is spatially related to the tonalite porphyry. The orebodies occur primarily in the outer contact zone between the tonalite porphyry and Permian metasandstone in the Jinjiling ore block (Fig. 2B) and are confined to N-trending fracture zones (in the periphery of the tonalite porphyry) in the Kongqueshan ore block (Fig. 2A, C). The tonalite porphyry exhibits concentric alteration zones, from an inner potassic zone through a phyllic zone to an outer propylitic zone, with orebodies occurring mainly in the phyllic zone (Fig. 2D, E). The tonalite porphyry is therefore considered as the intrusion that led to the mineralization. However, the emplacement age of the tonalite porphyry has not yet been well constrained. A Rb–Sr isochron age of 166 ± 2 Ma was obtained for five tonalite porphyry whole-rock samples (Sheng and Fu, 1999), and Feng (2010) reported a SHRIMP zircon U–Pb age of 154.1 ± 1.6 Ma. In the present study, a new LA–ICP–MS zircon U–Pb age of 151.1 ± 1.1 Ma was obtained for the tonalite porphyry, consistent within error with a previous molybdenite Re–Os single-point model age of 150.0 ± 2.2 Ma (Ouyang et al., 2014), suggesting that a Late Jurassic magmatic–hydrothermal event was responsible for the generation of the Budunhua Cu deposit. The U–Pb age of the diorite porphyrite dykes is 129.9 ± 1.9 Ma, much younger than the mineralization. This age accords with field observations of diorite porphyrite dykes cutting Cu veins and is considered to represent the end of magmatic activity in this deposit. 5.4.2. Geodynamic setting Geodynamic models of Late Jurassic magmatism and mineralization in the SGXR remain poorly defined but include westward subduction of the Paleo-Pacific Plate (Wu et al., 2005; Zhou et al., 2009; Wang et al., 2013; Dong et al., 2015) as well as post-orogenic lithospheric extension related to closure of the Mongol–Okhotsk Ocean (Meng, 2003; Ying et al., 2010; Ouyang et al., 2015). The SGXR lies too far from the Paleo-Pacific margin. Furthermore, seismological constraints indicate that the back-arc extension of the Paleo-Pacific Plate did not reach the SGXR during the Mesozoic (Zheng et al., 2015). In addition, Late Jurassic 21

igneous rocks of NE China occur mainly in the GXR and adjacent areas (limited to the west of the Songliao Basin) (Xu et al., 2013). Therefore, Late Jurassic magmatic activity in the SGXR cannot be ascribed to subduction of the Paleo-Pacific Plate. However, GXR Jurassic igneous rocks display an ENE-aligned distribution parallel to the Mongol–Okhotsk suture zone, with a broad southward-younging trend (Xu et al., 2013). Furthermore, a regional unconformity exists beneath the Haifanggou Formation in northern Hebei and western Liaoning provinces, related to southward thrusting (Meng et al. 2011). We therefore conclude that Late Jurassic magmatism and mineralization in the SGXR were controlled predominantly by the Mongol–Okhotsk tectonic regime. There is a growing consensus that the Mongol–Okhotsk Ocean closed in a scissor-like manner from west (Late Triassic) to east (Late Jurassic–Early Cretaceous). Li et al. (2015) reported a Middle Jurassic (ca. 168 Ma) muscovite granite from the Sunwu area in NE China. This granite, together with contemporaneous C-type adakites (e.g., the Xinghua and Heihuashan plutons) in the northeastern part of the GXR (Sui et al., 2007), indicates that the Mongol–Okhotsk Ocean to the northwest of the Erguna Massif was closed during the Middle Jurassic. All the Late Jurassic tonalite porphyry samples of the present study, as well as contemporaneous granites in the Tuquan area from previous studies, plot in the post-collisional granite field in tectonic discrimination diagrams (Fig. 8G, H). Taken together, we propose that Late Jurassic magmatism and associated Cu mineralization in the Budunhua district formed in response to post-collisional extensional collapse following closure of the Mongol–Okhotsk Ocean. 5.5. Genetic model During the Late Jurassic, the Tuquan area was under a post-collisional extensional setting following closure of the Mongol–Okhotsk Ocean, resulting in asthenospheric upwelling that led to partial melting of the thickened lower crust. The primary magmas that produced the ore-forming tonalite porphyry in the Budunhua deposit were generated during partial melting of Neoproterozoic lower crust and subsequently underwent extensive fractional crystallization. Ore fluids released from the porphyry magma were characterized by medium–high temperatures, high salinities, and 22

relatively oxidizing conditions, and were Cu-rich. Such fluids reacted with the cooling porphyry rocks and host metasandstone, causing extensive alteration and fine-vein-disseminated mineralization in the Jinjiling ore block. When the fluids migrated through the N-trending fracture zones, the peripheral Cu ore veins of the Kongqueshan ore block formed. Ore precipitation during mineralization may have been enhanced by fluid boiling, fluid–rock interactions, and mixing with meteoric water. In summary, the combined evidence of geological, isotopic, fluid inclusion, and geochronological investigations consistently supports a porphyry ore system for the Budunhua deposit that is spatially, genetically, and temporally associated with the tonalite porphyry.

6. Conclusions (1) Zircon LA–ICP–MS U–Pb dating reveals that the ore-causative tonalite porphyry and post-ore dioritic porphyrite of the Budunhua deposit were emplaced at 151.1 ± 1.1 Ma and 129.9 ± 1.9 Ma, respectively. The Late Jurassic tonalite porphyry and associated Cu mineralization formed in response to a post-collisional extensional setting following closure of the Mongol–Okhotsk Ocean. (2) Geochemical data indicate that the tonalite porphyry exhibit a I-type characteristic and were derived from partial melting of Neoproterozoic lower crust. (3) The Budunhua deposit formed in an H2O–NaCl magmatic–hydrothermal system with high temperature, high salinity, and relatively oxidizing conditions, at mineralization depths of 0.3–1.5 km. Ore-forming fluids and materials show evidence of a magmatic origin. Fluid boiling and mixing were the likely main mechanisms for ore precipitation. (4) The Budunhua deposit is a porphyry ore system that is spatially, genetically, and temporally associated with tonalite porphyry. Acknowledgements The authors are grateful to Associate Editor Christopher Spencer and two anonymous 23

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Table captions Table 1. LA-ICP-MS zircon U–Pb dating results for tonalite porphyry and dioritic porphyrite samples in the Budunhua Cu deposit.

Table 2. Major (wt.%) and trace elements (ppm) data for the tonalite porphyry samples in the Budunhua Cu deposit. Table 3. Microthermometric data of fluid inclusions. Table 4. The hydrogen and oxygen isotope data of quartz from the Budunhua Cu deposit. Table 5. The carbon and oxygen isotope data of calcite from the Budunhua Cu deposit. Table 6. The lead isotope data of sulfide and tonalite porphyry from the Budunhua Cu deposit. Figure captions Fig. 1. (A) Schematic map showing the location of the Central Asian Orogenic Belt (CAOB, modified from Jahn et al., 2000). (B) Simplified geological map of the Great Xing’an Range (modified after Chen et al. 2017), showing the representative deposits and the location of Tuquan area. (C) Geological map of the Tuquan area in southern 35

Great Xing'an Range. Fig. 2. (A) Local geology of the Budunhua Cu deposit (modified from XLJM, 2015). (B) Cross section along the exploration line 11–11’ in the Jinjiling ore block (modified from XLJM, 2015), showing the location of tonalite porphyry samples. (C) Cross section along the exploration line 29–29’ in the Kongqueshan ore block (modified from XLJM, 2015), showing the location of dioritic porphyrite samples. Lithologic column (D) and alteration assemblages (E) of drill hole ZK1117. Alteration types developed in the Jinjiling ore block (F–I) and the Kongqueshan ore block (J–K). Abbreviations: Kfs–K-feldspar; Qz–quartz; Chl–chlorite; Ser–sericite; Cal–calcite. Fig. 3. Photographs showing vein types and mineral assemblages in various ore stages of the Jinjiling ore block (A–I) and Kongqueshan ore block (J–P). (A) Stage I disseminated pyrite in porphyry with intense K-feldspathization. (B–C) Stage I quartz–arsenopyrite–pyrite vein, showing that euhedral–subhedral arsenopyrite and pyrite

occurred

as

disseminations

within

quartz.

(D)

Stage

II

quartz–pyrite–chalcopyrite vein cutting stage I quartz–pyrite vein. (E) Stage II quartz–chalcopyrite–pyrite–pyrrhotite

stockworks.

(F–G)

Stage

II

quartz–chalcopyrite–pyrrhotite vein. (H) Stage II quartz–chalcopyrite–pyrite vein cut by Stage III quartz–sphalerite–galena vein. (I) Stage IV barren calcite vein. (J) Stage I quartz–arsenopyrite

vein.

(K)

Stage

I

quartz–pyrite

vein,

showing

that

euhedral–subhedral pyrite occurred as disseminations within quartz. (L–N) Stage II quartz–chalcopyrite ± pyrite ± pyrrhotite vein. (O) Stage III quartz–sphalerite–galena vein cutting Stage II quartz–chalcopyrite–pyrite vein. (P) Stage IV quartz –calcite–chlorite vein. Abbreviations: Kfs–K-feldspar; Qz–quartz; Cal–calcite; Chl–chlorite;

Py–pyrite;

Apy–arsenopyrite;

Ccp–chalcopyrite;

Po–pyrrhotite;

Sp–sphalerite; Gn–galena. Fig. 4. Photomicrographs showing representative mineral assemblages in various ore stages of the Jinjiling ore block (A–D) and Kongqueshan ore block (E–J). (A) Stage I euhedral–subhedral

arsenopyrite.

(B)

Stage

II

chalcopyrite–pyrite–pyrrhotite 36

assemblage. (C) Pyrrhotite replaced by chalcopyrite and sphalerite of Stage III, forming metasomatic-relict textures. (D) Stage IV anhedral–subhedral chalcopyrite. (E–F) Stage I euhedral–subhedral arsenopyrite and pyrite. (G) Molybdenite occurring as scaly aggregates in stage I. (H) Stage II chalcopyrite–pyrite–pyrrhotite–sphalerite assemblage. (I) Stage III quartz–sphalerite–galena assemblage, with two different types of chalcopyrite. (J) Stage IV anhedral–subhedral pyrite.

Fig. 5. Mineral paragenesis of the Budunhua Cu deposit.

Fig. 6. Representative photographs and photomicrographs of tonalite porphyry (A–C) and dioritic porphyrite (D–F) samples from the Budunhua Cu deposit. Abbreviations: Pl–plagioclase; Qz–quartz.

Fig. 7. Zircon U–Pb concordia diagram and weighted mean age for the tonalite porphyry and dioritic porphyrite at Budunhua.

Fig. 8. (A) K2O vs. SiO2 diagram (after Peccerillo and Taylor, 1976). (B) A/NK [molar ratio Al2O3/(Na2O + K2O)] vs. A/CNK [molar ratio Al2O3/(CaO + Na2O + K2O)] diagram (after Maniar and Piccoli, 1989). (C) Chondrite-normalized REE patterns, chondrite values are from Boynton (1984). (D) Primitive-mantle-normalized trace element spidergram, primitive-mantle values are from Sun and McDonough (1989). (E–F) Classification diagrams for granitoids (after Whalen et al., 1987). (G–H) Trace element-tectonic setting discrimination diagrams for granitoids (after Pearce et al., 1984). VAG = volcanic arc granites; Syn-COLG = syn-collisional granites; WPG = within-plate granites; ORG = oceanic ridge granites; Post-COLG = Post-collisional granites. Contemporaneous granitoid data within Tuquan area are from Gao (2018), Jiang et al. (2011), and Tian et al. (2017).

Fig. 9. Photomicrographs showing the types and distribution of fluid inclusions observed in the Jinjiling ore block (A–M) and Kongqueshan ore block (N–T). (A–L) 37

L–type inclusions, V–type inclusions, S–type inclusions and V– and S–type fluid inclusions assemblage in stage I-III quartz. (M) L–type inclusions from stage IV calcite. (N–S) L–type inclusions, V–type inclusions, S–type inclusions and V– and S–type fluid inclusions assemblage in stage I–III quartz. (T) L–type inclusions from stage IV quartz. Abbreviations: L–liquid; V–vapor; S–halite daughter mineral.

Fig. 10. Histograms of homogenization temperatures and salinities of fluid inclusions in different stages for the Budunhua Cu deposit.

Fig. 11. Hydrogen and oxygen isotopic compositions of the ore-forming fluids for the Budunhua Cu deposit. Base diagram is from Taylor (1974); meteoric water in Southern GXR is from Sheng and Fu (1999).

Fig. 12. (A) Sulfur isotopic compositions of sulfide from the Budunhua Cu deposit. (B) Comparison of the Budunhua deposit with other typical porphyry Cu deposits worldwide (Field , 1966; Field and Gustafson, 1976; Eastoe, 1983; Kusakabe et al., 1984; Sheng and Fu, 1999; Field et al., 2005; Meng et al., 2006; Wang et al., 2007; Zhang, 2011; Tan et al., 2013; Wu, 2014; Yang et al., 2016; Li et al., 2016; He et al., 2017; Yuan et al., 2018).

Fig. 13. Lead isotopic compositions of sulfide and tonalite porphyry from the Budunhua Cu deposit. Base map is from Zartman and Doe (1981); the tonalite porphyry data are from Gu et al. (2016); shaded area of Cu deposits in the SGXR are modified from Zhang (2011).

38

Table 1. LA-ICP-MS zircon U–Pb dating results for tonalite porphyry and dioritic porphyrite samples in the Budunhua Cu deposit. Isotopic ratios 207

206

Pb/ Pb

Simple No.

Th (ppm)

U (ppm )

Pb (ppm)

Ages (Ma) 207

235

Pb/ U

206

238

Pb/ U

207

Pb/206Pb

207

Pb/235U

206

Pb/238U

Th/ U

Ratios

1σ

Ratios

1σ

Ratios

1σ

Ratios

1σ

Ratios

1σ

Ratios

1σ

0.42 0.43 0.47 0.41 0.52 0.43 0.48 0.50 0.44 0.42 0.42 0.47 0.57 0.30 0.42 0.41 0.44 0.52

0.0490 0.0468 0.0491 0.0534 0.0501 0.0511 0.0495 0.0484 0.0472 0.0495 0.0492 0.0485 0.0507 0.0491 0.0482 0.0498 0.0511 0.0493

0.0030 0.0028 0.0028 0.0034 0.0028 0.0027 0.0032 0.0037 0.0081 0.0026 0.0028 0.0036 0.0048 0.0025 0.0031 0.0033 0.0060 0.0029

0.1559 0.1499 0.1575 0.1753 0.1629 0.1637 0.1628 0.1568 0.1590 0.1604 0.1579 0.1622 0.1657 0.1642 0.1636 0.1637 0.1655 0.1641

0.0097 0.0092 0.0087 0.0111 0.0088 0.0082 0.0102 0.0117 0.0296 0.0085 0.0081 0.0122 0.0158 0.0083 0.0121 0.0104 0.0189 0.0094

0.0237 0.0237 0.0236 0.0238 0.0236 0.0236 0.0238 0.0235 0.0240 0.0236 0.0236 0.0241 0.0236 0.0240 0.0239 0.0236 0.0235 0.0237

0.0004 0.0004 0.0004 0.0004 0.0004 0.0004 0.0005 0.0004 0.0006 0.0004 0.0004 0.0005 0.0006 0.0004 0.0005 0.0005 0.0006 0.0004

146 37 153 344 201 246 169 117 60 169 156 123 228 153 108 186 244 164

111 100 97 115 93 87 106 171 302 92 86 129 171 88 125 108 264 102

147 142 149 164 153 154 153 148 150 151 149 153 156 154 154 154 156 154

9 8 8 10 8 7 9 10 26 7 7 11 14 7 11 9 17 8

151 151 150 152 150 150 152 150 153 150 150 154 150 153 152 151 150 151

2 3 2 2 3 2 3 2 3 2 3 3 4 2 3 3 4 2

Tonalite porphyry (BDHA) BDHA-01 BDHA-02 BDHA-03 BDHA-04 BDHA-05 BDHA-06 BDHA-07 BDHA-08 BDHA-09 BDHA-10 BDHA-11 BDHA-12 BDHA-13 BDHA-14 BDHA-15 BDHA-16 BDHA-17 BDHA-18

242 298 356 288 337 294 319 424 308 310 322 406 220 272 194 327 291 459

578 700 753 694 646 676 659 856 696 731 776 860 386 893 456 790 664 889

23.50 25.88 27.23 24.42 23.02 22.85 23.58 28.72 25.33 23.58 24.93 28.69 15.02 28.64 15.31 25.56 22.85 29.36

BDHA-19 BDHA-20

279 359

653 786

21.19 27.29

0.43 0.46

0.0466 0.0488

0.0033 0.0027

0.1506 0.1643

0.0104 0.0087

0.0234 0.0241

0.0004 0.0004

30 137

157 90

142 154

9 8

149 153

3 3

0.27 1.26 0.63 0.49 0.79 0.66 0.47 0.44 0.39 0.58 0.59 0.54 0.40 0.57 0.59 0.57 0.34 0.18 0.57 0.71

0.0497 0.0674 0.0531 0.0520 0.0497 0.0488 0.0508 0.0493 0.0485 0.0518 0.0497 0.1523 0.0479 0.1097 0.0518 0.0499 0.0484 0.0515 0.0519 0.0479

0.0029 0.0031 0.0111 0.0027 0.0072 0.0025 0.0036 0.0030 0.0025 0.0263 0.0062 0.0037 0.0056 0.0026 0.0078 0.0086 0.0041 0.0021 0.0058 0.0051

0.2405 1.3747 0.1460 0.2753 0.1812 0.1384 0.1822 0.1368 0.1366 0.1371 0.1356 9.1909 0.1365 4.8225 0.1383 0.1628 0.1579 0.2623 0.1677 0.1363

0.0151 0.0607 0.0313 0.0189 0.0261 0.0071 0.0129 0.0083 0.0069 0.0631 0.0160 0.2483 0.0167 0.1142 0.0197 0.0284 0.0130 0.0106 0.0171 0.0139

0.0346 0.1470 0.0200 0.0379 0.0266 0.0205 0.0260 0.0202 0.0203 0.0196 0.0204 0.4336 0.0204 0.3167 0.0201 0.0235 0.0236 0.0367 0.0234 0.0205

0.0008 0.0019 0.0012 0.0010 0.0007 0.0003 0.0008 0.0003 0.0003 0.0015 0.0006 0.0068 0.0007 0.0039 0.0006 0.0013 0.0006 0.0005 0.0005 0.0004

183 850 334 284 181 139 231 164 124 278 179 2372 93 1795 275 192 117 262 282 93

101 71 337 111 261 91 108 112 90 697 215 26 202 25 262 266 139 69 191 187

219 878 138 247 169 132 170 130 130 130 129 2357 130 1789 132 153 149 237 157 130

12 26 28 15 22 6 11 7 6 56 14 25 15 20 18 25 11 8 15 12

219 884 127 240 169 131 166 129 130 125 130 2322 130 1774 128 150 150 232 149 131

5 10 8 6 5 2 5 2 2 10 3 30 5 19 4 8 4 3 3 3

Dioritic porphyrite (BDH) BDH-01 BDH-02 BDH-03 BDH-04 BDH-05 BDH-06 BDH-07 BDH-08 BDH-09 BDH-10 BDH-11 BDH-12 BDH-13 BDH-14 BDH-15 BDH-16 BDH-17 BDH-18 BDH-19 BDH-20

621 357 349 1999 316 782 503 391 549 233 268 728 134 300 164 78 470 541 434 1161

2265 283 553 4044 399 1193 1065 889 1406 400 455 1356 333 530 280 138 1400 3036 764 1634

105.2 73.73 22.60 209.0 19.40 36.66 38.27 25.69 38.51 15.29 15.87 810.6 10.89 226.5 9.071 5.741 43.29 134.5 25.35 46.17

Table 2. Major (wt.%) and trace elements (ppm) data for the tonalite porphyry samples in the Budunhua Cu deposit. Simple No. SiO2 TiO2 Al2O3 TFe2O3 MnO MgO CaO Na2O K2O P2O5 LOI Total A/CNK K2O/ Na2O Mg# Rb Sr Y Zr Nb V Cr Ni Ga Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf

GBDH-1

GBDH-2

GBDH-3

GBDH-4

GBDH-5

71.16 0.27 14.01 2.60 0.08 0.66 1.63 3.87 4.19 0.06 0.58 99.20 1.01 1.08 37.17 147.0 206 20.5 159 8.1 27 17 2.8 18.35 4.98 480 30.9 58.6 6.54 22.3 4.37 0.63 3.77 0.58 3.44 0.69 2.06 0.33 2.05 0.32 4.6

71.34 0.30 14.14 2.88 0.09 0.78 1.65 3.90 4.16 0.07 0.73 100.14 1.02 1.07 38.69 149.5 209 20.3 179 8.1 31 17 3.3 18.25 5.95 550 32 61.4 6.99 22.9 4.66 0.68 3.94 0.62 3.48 0.71 2.07 0.35 2.04 0.35 5.1

70.43 0.33 14.27 2.96 0.11 0.91 1.39 3.93 4.16 0.07 0.88 99.52 1.06 1.06 41.74 151.5 189.5 20.6 155 8.0 37 20 3.9 18.45 5.77 450 31.4 58.6 6.75 21.7 4.46 0.7 3.79 0.58 3.54 0.71 2.04 0.32 2.03 0.33 4.7

71.4 0.3 14.2 2.8 0.1 0.8 1.6 3.9 4.1 0.1 0.7 100.0 1.02 1.05 39.00 145.0 198.5 20.0 175 7.9 31 18 3.3 18.05 5.41 480 30 57.3 6.68 23.1 4.48 0.67 3.89 0.62 3.48 0.73 2.17 0.35 2.23 0.35 5.2

70.8 0.3 14.4 2.9 0.1 0.8 2.0 3.9 4.0 0.1 0.6 99.9 1.01 1.04 38.78 146.5 217 19.3 160 7.7 32 17 3.5 18.35 4.64 500 29.7 55.1 5.96 19.8 3.93 0.64 3.36 0.53 2.97 0.63 1.85 0.29 1.88 0.3 4.4

Ta Th U δEu ∆LREE/∆HREE (La/Yb)N

0.87 17.85 3.5 0.47 9.20 10.29

0.86 17.70 3.2 0.49 9.34 10.55

0.90 17.80 3.6 0.52 9.06 10.11

0.87 16.90 3.6 0.49 8.63 8.72

0.83 16.70 3.3 0.54 9.46 10.03

Table 3. Microthermometric data of fluid inclusions. Stage

Mineral

Jinjiling ore block I quartz

II

III

IV

quartz

quartz

calcite

Kongqueshan ore block I quartz

II

III

IV

quartz

quartz

quartz

Type (number)

Size (µm)

Tm,ice (℃)

Th (℃)

L (26) V (8) S (13) L (30) V (8) S (8) L (20) V (9) S (10) L (18)

10–25 10–20 8–18 5–20 5–20 5–15 5–15 5–15 5–10 5–12

–16 to –5 –6.2 to –2

320–396 300–360 315–378 245–330 275–320 310–330 220–300 250–290 260–300 140–228

L (26) V (7) S (10) L (21) V (8) S (9) L (14) V (6) S (8) L (21)

8–25 8–20 8–18 5–18 5–18 5–15 5–12 5–12 5–10 5–12

–12.1 to –3.2 –5 to –2.6 –6 to –1.2 –4 to –0.9 –4 to –0.6 –13.3 to –2.2 –6.2 to –2.2 –7.2 to –1.7 –4 to –2 –5.1 to –0.9 –2.6 to –0.8 –6 to –0.5

265–350 305–333 300–360 249–350 275–330 249–310 200–260 228–260 240–270 90–208

Tm,d (℃)

300–370

295–325

254–300

290–340

260–310

248–272

Salinity (%NaCl eqv.) 7.9–19.6 3.4–9.5 38.2–44.3 5.3–16.1 4.3–7.9 37.8–40.2 2.1–9.2 1.6–6.4 34.9–38.2 1.0–6.4 3.7–17.3 9.5–3.7 37.4–41.5 2.9–10.7 3.4–6.4 35.3–38.9 1.6–8 1.4–4.3 34.1–36.0 0.9–9.2

Table 4. The hydrogen and oxygen isotope data of quartz from the Budunhua Cu deposit. T (℃)

δDH2O (‰)

δ18Oquartz (‰)

δ18OH2O (‰)

JJL-1 JJL-2 JJL-3 JJL-4 JJL-5 JJL-6 JJL-7 JJL-8

340 240 300 300 260 260 220 220

–112.7 –114 –118.3 –123.6 –128.4 –125.9 –128.6 –131

8.7 9 9.1 10 10.6 9.9 8.5 8

2.6 2.9 1.7 2.6 1.6 0.9 –2.5 –3.0

Kongqueshan ore block I KQS-1 I KQS-2 II KQS-3 II KQS-4 III KQS-5 III KQS-6 IV KQS-7 IV KQS-8

320 320 280 280 250 250 210 210

–112.1 –113 –119.2 –115.5 –126.6 –128.5 –136 –135

10.5 9 9.6 8.7 8 7.2 5 6

3.8 2.3 1.45 0.55 –1.46 –2.26 –6.6 –5.6

Stage

Sample No.

Jinjiling ore block I

I II II III III IV IV

Table 6. The lead isotope data of sulfide and tonalite porphyry from the Budunhua Cu deposit. Simple No.

Mineral

206

Pb/204Pb

207

Pb/204Pb

208

Pb/204Pb

Source

Jinjiling ore block jjl-1 jjl-2 jjl-5 BJS205 BJX210 BJX215 BJS205 BJX215 BJS209 BJS205

chalcopyrite chalcopyrite pyrrhotite chalcopyrite chalcopyrite chalcopyrite pyrite pyrite galena galena tonalite porphyry tonalite porphyry

Kongqueshan ore block kqs-1 kqs-2 kqs-3 kqs-4 BKS107 BKS109 BKX301 BKX309

pyrite pyrite pyrite pyrite chalcopyrite chalcopyrite chalcopyrite chalcopyrite

18.276 18.315 18.366 18.315 18.287 18.333 18.301 18.274 18.307 18.282 18.298 18.303

15.521 15.517 15.531 15.571 15.517 15.579 15.556 15.510 15.560 15.528 15.540 15.541

38.04 38.15 38.191 38.217 38.044 38.247 38.166 38.022 38.180 38.079 38.092 38.100

This paper

18.322 18.304 18.339 18.331 18.344 18.294 18.292 18.308

15.577 15.535 15.578 15.568 15.511 15.518 15.509 15.509

38.252 38.115 38.249 38.211 38.097 38.045 38.015 38.022

This paper

Wu, 2012

Gu, 2016

Wu, 2012

Table 5. The carbon and oxygen isotope data of calcite from the Budunhua Cu deposit. Sample No.

δ13CPDB (‰)

δ18OPDB (‰)

δ18OSMOW (‰)

Source

Jinjiling ore block JJL-9 JJL-10 BTC13-1

–7.7 –9.6 –6.4

–26.4 –19.7

3.7 10.6 15.0

This paper This paper Sheng and Fu, 1999

Kongqueshan ore block C-23

–8.2

–4.8

Sheng and Fu, 1999

Highlights Tonalite porphyry associated with mineralisation and post-ore dioritic porphyrite were emplaced at 151.1 ± 1.1 Ma and 129.9 ± 1.9 Ma, respectively. Primary magmas of tonalite porphyry originated from partial melting of lower crustal material. Mineralisation fluids and materials were derived principally from a magma source. The Budunhua Cu deposit is a porphyry ore system closely related to the emplacement of Late Jurassic tonalite porphyry and was formed in a post-collisional extensional setting following closure of the Mongol–Okhotsk Ocean.

Declaration of Interest Statement