Geological, geochronological, pyrite geochemical and stable isotope studies of the Tantou gold deposit in central China

Journal Pre-proofs Geological, geochronological, pyrite geochemical and stable isotope studies of the Tantou gold deposit in central China Weiwei Chao, Huishou Ye, Kenichiro Hayashi, Jingwen Mao, Yang Gao PII: DOI: Reference:

S0169-1368(19)30019-8 https://doi.org/10.1016/j.oregeorev.2019.103222 OREGEO 103222

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Ore Geology Reviews

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6 January 2019 29 October 2019 9 November 2019

Please cite this article as: W. Chao, H. Ye, K. Hayashi, J. Mao, Y. Gao, Geological, geochronological, pyrite geochemical and stable isotope studies of the Tantou gold deposit in central China, Ore Geology Reviews (2019), doi: https://doi.org/10.1016/j.oregeorev.2019.103222

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Geological, geochronological, pyrite geochemical and stable isotope studies of the Tantou gold deposit in central China Weiwei Chaoa,b, Huishou Yec*, Kenichiro Hayashib, Jingwen Maoc, Yang Gaod a

State Key Laboratory of Nuclear Resources and Environment, East China University of

Technology, Nanchang, 330013, Jiangxi, China b

Graduate School of Life and Environmental Sciences (Earth Evolution Sciences), University of

Tsukuba, Ibaraki 305-8572, Japan c

MLR Key laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources,

Chinese Academy of Geological Sciences, Beijing 100037, China d

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

Abstract: The Tantou Au deposit is a large-scale gold deposit in the Xiong’ershan area. A geochemical study of pyrite was conducted using laser ablation inductively coupled plasma mass spectrometry. Two types of hydrothermal pyrite were identified in the ores and wall rocks, i.e., the fine euhedral pyrite in brecciated ores (Py1) and coarse grains disseminated in the quartz-sulfide veins (Py2). The trace elements of the two pyrite types exhibit different concentrations, associations and rim-core zoning, implying different geneses and crystallization processes. Both pyrites of the two mineralization stages were hydrothermal pyrite. However, the Au, As, Co, Ni, and Zn were more rich in Py1, while Ag, Cu, Mo, Sb, and Pb were favored in Py2. The growth rims of Py1 suggest several pulses of fluid activities. Hydrothermal sulfides from the main ore-forming stage have a Rb-Sr isochron age of 124.2 ± 3.1 Ma, placing the gold mineralization in the Early Cretaceous. The initial 87Sr/86Sr value of the sulfides is 0.71124 ± 0.00010, suggesting an ancient crust source (the Paleoproterozoic Xiong’er Group). In situ S isotope data acquired from the main sulfides suggest that the ore-forming materials underwent isotopic fractionation because of oxidation of the ore-forming fluids during the hydrothermal process. The C-O isotope values of calcite from the postore stage indicate that magmatic fluids were likely the principle sources of carbon and that low temperature alteration has had a significant effect on the levels of CO2 and carbonate ions. Together, these results suggest that the Tantou Au deposit is genetically

related to the destruction of the North China Craton as a result of lithospheric thinning during the Early Cretaceous. Keywords: Tantou gold deposit; Xiong’ershan region; Rb-Sr isotopic dating; S-C-O isotope; trace elements

1. Introduction The southern margin of the North China Craton (NCC) hosts large-scale Mo-Au-Ag-Pb-Zn ore deposits (e.g., Mao et al., 2011a, 2011b; Deng et al., 2014; Bao et al., 2017; Li and Pirajno, 2017), especially Au deposits (Chen et al., 2009; Mao et al., 2002). The Xiong’ershan-Waifangshan region, which forms part of the middle segment of the southern margin of the NCC, contains more than 20 gold deposits. These deposits are considered to be closely related to Mesozoic granites, which are typically found 1-10 km away from granite plutons (Chen and Fu, 1992; Mao et al., 2002). The majority of these Au deposits are located in volcanic rocks of the Xiong’er Group and metamorphic rocks of the Taihua Complex. As major constituents in a variety of gold deposits, including Carlin-type, epithermal-porphyry and orogenic Au deposits, pyrite host metals and metalloids, such as Au, Ag, Cu, Pb, Zn, Co, Ni, and As (Tardani et al., 2017), can be used to reflect ore-forming processes and trace the sources of ore-forming fluids (Keith et al., 2016a, 2016b, 2017). The texture and geochemistry of pyrite have been used extensively in unraveling the genesis of many ore deposits. For example, the texture, habit and morphology of pyrite can record replacement or dissolution and can also be used to distinguish between supersaturation events, near-equilibrium crystallization or recrystallization (Tanner et al., 2016). The sulfur isotope composition of pyrite can be used to evaluate the physiochemical conditions during deposition and provides an alternative technique with which to identify fluid sources or fluid mixing. Recent advances in in situ microanalytical techniques permit us to probe the geochemistry of individual bands in minerals and thus record geochemical variations between the core and rim of a crystal. This ability to track temporal changes within the crystallization histories of individual minerals provides us with a chronological framework that we can link with geochemical data to ascertain the genetic evolution of the ore fluids (Tanner et al., 2016).

The Tantou gold deposit, located in the Xiong’ershan-Waifangshan region at the southern margin of the NCC, is hosted in Paleoproterozoic volcanic rock (the Xiong’er Group) and is one of the largest gold deposits in the Xiaoqinling-Xiong’ershan region (Mao et al., 2002). Research regarding the deposit has focused on its geological characteristics, mineralization, wallrock alteration and fluid inclusions (Ren and Li, 1996; Mao et al., 2002; Meng et al., 2011). Nevertheless, the metallogenic epoch and source of the ore-forming fluids and materials in the deposit are not well understood, which limits our knowledge of the genesis and ore-forming mechanisms of the deposit. Herein, we present the results of a detailed survey of the temporal and geological characteristics of the Tantou deposit based on Rb-Sr geochronology as well as new C -O-S isotope data and trace element analysis of gold-bearing pyrite. Combined with previous data, this work gives a better understanding of the ore genesis and provides information that will assist in prospecting.

2. Geological setting 2.1. Regional geology Tectonically, the Xiong’ershan-Waifangshan region lies in the southern margin of the NCC, which is part of the Qinling-Dabie Orogenic Belt. The region is bounded by the Machaoying and Luoning Faults to the south and the northwest, respectively (Fig. 1). In this region, the Archean Taihua Group is the metamorphic basement, which is consist of biotite-plagioclase gneiss, amphibolites, granulite, graphite gneiss and tonalite-trondhjemite-granite (TTG) gneiss (Huang et al., 2012). The amphibolites and TTG gneiss have a zircon U-Pb age of 2.5-2.3 Ga (Kröner et al. 1988; Xu et al., 2009). The overlying Paleoproterozoic Xiong’er Group consists of basaltic andesite and andesite, with minor amounts of dacite and rhyolite (Zhao et al., 2002). These rocks have sensitive high-resolution ion microprobe (SHRIMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb ages of 1.78-1.75 Ga (Peng et al., 2008; He et al., 2009; Zhao et al., 2009). Additionally, the minor Mesoproterozoic Guandaokou Group, which is composed of clastic and carbonate rocks (Fig. 1). The Machaoying Fault is 200 km long, 5 km wide, and deep-seated and dips at a 50–80° NNE angle (Yan et al., 2005). Several NE-trending secondary or higher order faults occur north of the

Machaoying Fault, including the Tieluping, Kangshan–Shanggong, Hongzhuang–Qinggangping, and Taocun–Mayuan Faults running from west to east. The Mesozoic granitic suite includes the Huashan (132.0 ± 1.6 Ma; Mao et al., 2010), Wuzhangshan (156.8 ± 1.2 Ma; Mao et al., 2010), Heyu (148.2–127.2 Ma; Mao et al., 2010; Gao et al., 2010) and Taishanmiao (115 ± 2 Ma; Ye et al., 2008) plutons, which have intruded into the Taihua and Xiong’er Groups (Fig. 1). In addition, porphyritic granite dikes, including the Haopinggou (130.5 ± 1.1 Ma; Liang et al., 2015), Dianfang (142.6 ± 2.1 Ma; Tian et al., 2016), Leimengou (136.2 ± 1.5 Ma; Li et al., 2006a) and Donggou (118.0-117.0 Ma; Yang et al., 2013) occur in this region.

2.2. Geology of the Tantou deposit The Tantou gold deposit (111°43′56″ to 111°45′38″E, 34°03′15″ to 34°04′11″N) is located in the vicinity of Tantou village in Luanchun County, Henan Province. The deposit was first discovered in 1988 and has estimated reserves of 44 t Au (Mao et al., 2002). The local geology of the mining area is dominated by the andesite and basaltic andesite of the Paleoproterozoic Majiahe Formation (Xiong’er Group). The deposit is situated north of the WNW-trending Machaoying Fault system in the Xiong’ershan region, and the study area is structurally controlled by NW, EW and NE-trending faults. There are no alkaline nor felsic dikes in the mine area. The orebodies are hosted in andesite, volcaniclastic rocks and tuff within the Xiong’er Group and structurally controlled by the NW-striking fault (Fig. 2a). The mineralization features within the deposit are represented by the largest orebody (no. 881), which is approximately 1300 m long and 0.58 to 13.29 m thick and dips 22-52° to the SW. This body continues to a subsurface depth of at least 288 m. Some ore veins have several branches at various depths (Fig. 2b), and the ores contain gold grades ranging from 3.05 to 20.34 g/t, with an average value of 8 g/t. The primary ores are presented as altered tectonic breccias with lesser amounts of quartz sulfide veins (Fig. 3). The mineralogy of the veins is composed of quartz plus variable amounts of carbonate. Metallic minerals occur as disseminations and thin veinlets (Fig. 3) and are dominated by pyrite, followed by chalcopyrite, galena, sphalerite, bornite, argentite,

hessite and native gold (Fig. 4). Gangue minerals include quartz, feldspar, epidote and calcite as altered relicts. Silicification and carbonation are common in the Tantou deposit (Fig. 3). Based on a) the nature of the host-veins, b) mineral assemblages, and c) intersecting relationships of the veins, the ore-forming process can by subdivided into the K-feldspar-quartz stage (stage Ⅰ), the quartz-pyrite stage (stage Ⅱ), the quartz-sulfide stage (stage Ⅲ), and the calcite-quartz vein stage, respectively (stage Ⅳ) (Fig. 5). Stage Ⅰ is characterized by a barren quartz vein, which has massive amounts of K-feldspar and epidote disseminated in it. Stage Ⅱ is dominated by disseminated fine-grained pyrite and minor galena, chalcopyrite, bornite and native gold. The quartz occurs as smoky thin veins in brecciated ores. Some pyrite grains show distinct cyclic characteristics. Anhedral chalcopyrite was replaced by bornite along the individual margins prior to the galena filling in the fissures of the chalcopyrite. Native gold occurs in the microcracks of pyrite. Stage Ⅲ is mainly composed of galena and argentite. Native gold mainly occurs as intergranular grains together with sphalerite and hessite. The quartz in this stage is white in color and is more transparent then that in stage Ⅱ. The widespread calcite occurs in the last stage (stage Ⅳ) and is banded with lesser amounts of quartz.

3. Sampling and analytical methods 3.1. Sulfide Rb-Sr dating A total of seven ore samples (six pyrites from a quartz-pyrite vein and one galena from a quartz-sulfide vein) were collected from underground outcrops in orebodies no. 881, no. 971, and no. 976 at various elevations. These samples were rinsed several times with distilled water then dried and crushed to a 40 mesh particle size. Pyrite and galena components of the ore samples were manually extracted for analysis under a binocular microscope, with purity levels of >98%. The sulfide grains were crushed to a particle size of less than 200 mesh, and then washed in an ultrasonic bath and dried. Crushing the mineral grains to <200 mesh and cleaning using ultrasonication may have eliminated interference by primary and secondary inclusions. In

preparation for Rb-Sr isotope analyses, each sulfide sample (having a mass of 0.2-0.3 g) was dissolved in a mixture of HF and HNO3 in a Teflon beaker. The Rb and Sr were separated for isotopic analysis using AG50W×8 resin in conjunction with various eluents. The isotopic analyses were performed using a VG 354 mass spectrometer with five collectors at the Center of Modern Analysis, Nanjing University. Details of the chemical separation and mass spectrometric procedures have been previously reported by Wang et al. (2007). The ratios were normalized to

86Sr/88Sr

87Sr/86Sr

= 0.1194 to correct for instrument fractionation. During the

time span covered by this study, measurements of a National Bureau of Standards NBS 987 Sr standard gave a 87Sr/86Sr value of 0.710236 ± 7 (2σ).

3.2. Analysis of trace elements in pyrite In this study, 20 samples were collected from the ores and wall rocks of different orebodies and polished into polished sections for petrographic study. From these, nine samples (Fig. 2) were selected for pyrite trace element analysis using the LA-ICP-MS technique. Elemental analysis of the minerals in the thin sections was conducted by LA-ICP-MS at Nanjing FocuMS Technology Co., Ltd. by using the Teledyne Cetac Technologies Analyte Excite laser-ablation system (Bozeman, Montana, USA) and the Agilent Technologies 7700x quadrupole ICP-MS (Hachioji, Tokyo, Japan) in combination. The 193 nm ArF excimer laser, homogenized by a set of beam delivery systems, was focused on the mineral surface with fluence of 6.06 J/cm2. The ablation protocol employed a spot diameter of 40 μm at a 7 Hz repetition rate for 40 seconds. Raw

data

reduction

was

performed

off-line

by

ICPMSDataCal

software

using

a

100%-normalization strategy without applying an internal standard (Liu et al., 2008). A 15 seconds gas background was collected prior to each ablation. Helium carrier gas efficiently transports aerosol and was mixed with Argon via a T-connector before entering the ICP-MS. The USGS polymetal sulfide pressed pellet MASS-1 and synthetic basaltic glasses GSE-1G were utilized as a combined calibration for sulfides.

3.3. In situ LA-ICP-MS sulfur isotope analysis and EMPA mapping Sulfur isotope analyses of six standard polished sulfide sections collected from the orebodies (no. 912 and no. 913) were performed in situ using a Nu Plasma Ⅱ MC-ICP-MS, equipped with a Resonetics-S155 excimer ArF laser ablation system at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan. The laser beam diameter was 40-50 μm with a laser repetition rate of 10 Hz and the ablation time span was 40 s. Standard-sample bracketing (SSB) was used to determine the δ34S values of samples throughout the MC-ICP-MS analyses. The true sulfur isotope ratios were calculated by correcting for instrumental mass bias via linear interpolation between the biases calculated from two neighboring standard analyses. Isotope ratio data were reported in delta notation (‰) relative to Vienna-Canyon Diablo Troilite (V-CDT). The analytical precision (1σ) was determined to be approximately ± 0.1 ‰. Details of the analytical conditions and procedures have been previously reported by Zhu et al. (2016, 2017). Wavelength-dispersive spectrometry (WDS) X-ray maps were collected using a Jeol JXA-8530F at the University of Tsukuba, Japan, in conjunction with an accelerating voltage of 20 kV, beam current of 300 nA and counting time of 20 ms/step.

3.4. C and O isotopes in calcite Calcite specimens were manually extracted mainly from orebody no. 971 under a stereomicroscope and washed with distilled water. Carbon and oxygen isotopic measurements were performed at the Stable Isotope Laboratory of the Mineral Resources Institute, Chinese Academy of Geological Sciences. Prior to each analysis, each dry powdered calcite specimen was reacted with 100% H3PO4 at 25 °C for approximately 3 h. The resulting CO2 was analyzed to determine the carbon and oxygen isotope ratios using a MAT-253 isotopic ratio mass spectrometer, and the δ13C and δ18O values are reported herein relative to Pee Dee Belemnite (PDB). The δ18OPDB values were converted to δ18OSMOW (SMOW = Standard Mean Ocean Water) using the equation δ18OSMOW = 1.03091 × δ18OPDB + 30.91 (Coplen et al., 1983).

4. Results 4.1. Rb-Sr isotope compositions and isochron ages The six pyrite grains and one galena grain from the main ore-forming stage quartz vein yielded an Rb-Sr isochron age of 124.2 ± 3.1 Ma (n = 7, MSWD = 1.6, Fig. 6 and Table 1) (MSWD = mean squared weighted deviation). The Rb and Sr concentrations in the rocks were found to range from 0.0837 to 1.9820 ppm and from 0.4438 to 0.6270 ppm, respectively. The

87Rb/86Sr

ratios

ranged from 0.1012 to 4.8030, while the 87Sr/86Sr values were much more consistent, varying only between 0.711454 and 0.719763. The initial

87Sr/86Sr

ratio was determined to be 0.71124 ±

0.00010 while a standard NIST-NBS987 solution gave a mean

87Sr/86Sr

value of 0.710236 ±

0.000007.

4.2. Pyrite types and textures Hydrothermal pyrite is widely distributed in the quartz-sulfide disseminated, breccia-type and vein-type ores, which can be divided into two subtypes according to the host ore, as follows: (1) Py1: distributed in breccia-type ores and occurs as euhedral crystals of 10-400 μm. Some of the Py1 grains show zoning characteristics (Fig. 4a). Fig. 7 displays an example of complex (Cu, As)-growth zoning in Py1 in sample B711-2-1 from the Tantou deposit, consisting of three Asand/or Cu-rich growth zones; (2) Py2: found in quartz-sulfide veins, comprising coarse-grained anhedral pyrite with size range of 100-500 μm, with some showing a core with a smooth, flat surface and a rim with irregular dissolution holes (Fig. 4d); occasionally, visible sulfide inclusions occur in the rim.

4.3. LA-ICP-MS profile characteristics of pyrite A total of 62 LA-ICP-MS spot analyses were completed on pyrite selected from different samples at Tantou deposit (Table 2), including 47 spots from Py1 and 15 spots from Py2. In addition to spot analyses, trace element distribution within one pyrite sample of Py1 was imaged by EMPA. In this study, no attempt was made to remove the effects of the micron-sized

inclusions on the pyrite. However, inspection of the LA-ICP-MS output traces from each laser spot analysis enables an estimation of whether a particular trace element occurs within a homogeneous invisible or nanosized inclusion or as larger, isolated microsized inclusions in the pyrite (Maslennikov et al., 2009). Representative time-resolved depth profiles for pyrites are illustrated in Fig. 8. A total of 62 hydrothermal pyrite spots contain measurable quantities of gold. A feature of the dataset for Au is that Au concentration can vary several by orders of magnitude in Py1 and Py2. Au distribution patterns for the Py1 pyrite with Au contents between 10 and 1000 ppm are relatively smooth (Figs. 8a, b) with no spikes, indicating that gold occurs primarily as solid solution or as nanoparticles within the pyrite lattice. However, the Au distribution patterns for the Py1 with Au content less than 10 ppm and Py2 are spiky, suggesting that gold occurs as microsized inclusions in them (Figs. 8c, d). Time-resolved depth profiles for arsenic are flat, and arsenic is abundant in most samples, suggesting that the pyrites at the Tantou are As-bearing. The parallel trends of smooth patterns between Au and As in the Py1 pyrite with Au contents between 10 and 1000 ppm (Figs. 8a, b) support the close correlation of their concentration in the Au-rich pyrite. Measured values for Pb vary over several orders of magnitude. The majority of the higher concentrations (numerous spikes in Figs. 8b, d) can be readily attributed to inclusions of galena. However, for samples B711-2-1 and B712-2-1, the consistent concentrations and flat time-resolved depth profile (Fig. 8a, c) indicate incorporation of Pb in solid solution up to dozens of ppm. All pyrites contain measurable quantities of Ag (Table 2). Fig. 8(d) shows that the trend of Ag is parallel to those of Cu, Sb and Zn in Py2, which indicates that Ag may occur as Ag-Sb sulfosalt inclusions (e.g., Ag-rich tetrahedrite and/or polybasite) in Py2. Co and Ni are the common trace elements in pyrites (Table 2) and are usually incorporated within the pyrite lattice. The flat and similar time-resolved depth profiles (Fig. 8) for Co, Ni and Fe prove the occurrence state of Co and Ni in pyrites. Spikes of Zn occur in time-revolved depth profiles (Fig. 8), indicating the probability of sphalerite inclusions.

4.4. Data trends among different pyrite types Element contents and their variation within the pyrites of different types derived from quartz-pyrite veins and quartz-sulfide veins are shown in Fig. 9. From Py1 to Py2, the Au contents gradually decrease (Table 2, Fig. 9). Au contents in Py1 range from 0.937 to 688.162 ppm (n = 47), greater than those in Py2 that range from 0.095 to 9.126 ppm (n = 15). Arsenic is the most abundant trace element from pyrite in the Tantou deposit, with As concentrations ranging from 9.413 to 44899.082 ppm, spanning four orders of magnitude (Table 2). Fig. 9 shows the Py1 with higher (48.604 - 44899.082 ppm) and the Py2 with lower (9.413 4819 ppm) As distributions, respectively. A positive correlation exists between Au and As in both Py1 and Py2 (Fig. 10a), which is similar to that known for pyrite in Calin, an orogenic and epithermal gold deposit (Li et al., 2004; Reich et al., 2005; Large et al., 2009; Sung et al., 2009). The Ag contents for Py1 and Py2 were 2.725 - 1453.545 ppm and 0.155 - 1833.137 ppm, respectively (Table 2, Figs. 9, 10b). The good correlation between Ag and Sb, Ag and Cu, and Cu and Sb (Figs. 10c, d, e) are likely linked to inclusions of Ag-Sb sulfosalt (e.g., Ag-rich tetrahedrite and/or polybasite), thus confirming silver occurrence in Py2. The plot (Fig. 10f) reveals a positive correlation between Co and Ni. The Co/Ni ratios in Py1 and Py2 are 0.77-2.77 and 1.06-3.17, respectively. On the Co/Ni vs. Au/Ag plot, the Py1 spots are primarily in the first and second quadrants with high Co/Ni values and widely variable Au/Ag ratios; almost all Py2 spots are located in the second quardrant with Co/Ni > 1 and Au/Ag < 1 (Fig. 10g). Concerning other measured elements, Py1 and Py2 contain similar amounts of trace elements, while Py2 is more enriched in Cu, Mo, Sb, Te, and Pb and relatively depleted in Zn (Fig. 9). The rims of Py1 and Py2 are too small to carry laser ablations.

4.5. In situ S isotope analyses Eleven in situ LA-ICP-MS sulfur isotope analyses were performed (eight in pyrite, two in galena, one in argentite) from a total of six ore samples covering both the quartz-pyrite stage and the quartz-sulfide stage. The sulfur isotope results for the main ore stage sulfide phases are

summarized in Fig. 11. In the main ore stage, the δ34S values for the galena were slightly lighter than those of the pyrite. The values ranged between -14.7 and -13.1‰ (avg. -13.8‰) for pyrite and from -17.6‰ to -17.1‰ (avg. -16.6‰) for galena, while a value of -15.9‰ was obtained for argentite. These data demonstrate that all three materials had relatively homogeneous, negative sulfur signatures (with δ34S values ranging from -14.7 to -17.1‰). Ren and Li (1996) also reported negative δ34S values for pyrite from a bulk sample of the main stage of between -13.5 and -2.2‰ (avg. -10.3‰).

4.6. C and O isotopic compositions The δ13C and δ18O values of three calcite samples collected from the quartz-calcite vein are provided in Table 3 and plotted in Fig. 12. The data fall between the box of continental carbonates and magma-mantle carbonates (Fig. 12). The δ13CV-PDB‰ value in the calcite varied between -3.8‰ and -1.7‰ (average of -2.7‰), while the δ18OV-SMOW‰ value ranged from 12.8‰ to 17.3‰ (average of 15.6‰). The ranges in δ13C values of different sampling localities are similar, but the δ18O values vary significantly. The δ13CV-PDB‰ value in the calcite collected from other gold deposits in the Xiong’ershan region shows a range between -5.8‰ and 0.0‰.

5. Discussion 5.1. Timing of mineralization Isotopic dating using ore minerals have been proven to be the most useful means of determining the age of a hydrothermal mineralization. In addition, Rb-Sr isotopic dating of sulfides is a reliable approach to constraining the timing of mineralization (e.g., Han et al., 2007a; Tian et al., 2017). Rb and Sr, as trace elements in pyrite generally occur in K-bearing mineral inclusions such as sericite or feldspar (Li et al., 2008), although the microprobe observation in this work eliminated the possibility of such inclusions in the pyrite. Therefore, the age obtained during this study had a small associated error and a relatively low MSWD of 1.6 (Fig. 7). The Rb-Sr isochron age of the pyrite and galena reported in our study is therefore reliable and fixes the timing of the gold mineralization event at 124.2 ± 3.1 Ma.

This age corresponds to mineralization in the Early Cretaceous, which is consistent with results obtained for other Au deposits in the Xiong’ershan-Waifangshan region (e.g., Dianfang (121.5 ± 1.7 Ma), Tian et al., 2016; Qianhe (134.5 ± 0.6 Ma), Tang et al., 2013; Miaoling (121.6 ± 1.2 Ma), Zhai et al., 2012; Qiyugou (135.6 ± 5.6 Ma), Yao et al., 2009; Gongyu (129.8 ± 0.9 Ma), Tang, 2014; Jijiawa (118 ± 2.4 Ma), Zhang et al., 2018). These ages were determined by several different methods, including through the use of Re-Os, 40Ar-39Ar and Rb-Sr isotopes.

5.2. Trace element distribution in pyrite Trace metals in pyrite may occur in several ways: (1) as an invisible solid solution within the crystal lattice, (2) within invisible nanoparticles of sulfides (Ciobanu et al., 2012), (3) within visible microsized inclusions of sulfides, or (4) within visible microsized inclusions of silicate or oxide minerals (Thomas et al., 2011). According to the analytical results, pyrites of different types have shown certain similarities and differences in element compositions as addressed below. Siderophile and chalcophile elements, including Co, Ni, As, Se and Te, are commonly distributed in pyrite; Ni and Co enter the lattice via isomorphous replacement of Fe, and As, Se and Te enter the lattice via the replacement of S. The LA-ICP-MS time-resolved depth profiles for Co, Ni and As are generally smooth and consistent with Fe (Fig. 8), indicating that these elements occur in different pyrite types via isomorphism. The metallogenic elements are dominated by Au, Ag, Sb, Cu, and Pb, with minor Zn in the Tantou deposit. The Au distribution in most samples illustrates a relatively smooth pattern similar to As in Py1 grains with Au concentration > 10 ppm (Figs. 8a, b), indicating that gold occurs primarily as invisible solid solution or as nanoparticles in these pyrite grains. The occurrence of Au is further confirmed by the EMPA mapping result (Fig. 7d). Zn and Pb are primarily distributed in pyrite as invisible or visible sphalerite or galena inclusions (Fig. 8). The relatively uniform distribution of Cu in Py1 indicates that the Cu may occur as solid solution in the pyrite lattice (Fig. 7c), with only minor enrichment at the margin of each pyrite generation. The positive correlation between Ag, Cu, and Sb indicates the existence of Ag-Sb sulfosalt (e.g., Ag-rich tetrahedrite and/or polybasite) in Py2 (Figs. 8d, 10c, d, e).

5.3. Pyrite genesis As introduced in Section 4, two subtype hydrothermal pyrites present contrasting crystal forms and textures. Furthermore, the LA-ICP-MS analyses proved their differences in trace-element concentrations and occurrences. Factors that caused these differences are discussed below. The Co and Ni contents in pyrite can reflect the origin of the pyrite and the geological setting (Bralia et al., 1979; Cook et al., 2009). The Co/Ni ratios of Py1 range from 0.77 – 2.77 (Table 2), with an average of 1.41, which is characteristic of hydrothermal pyrite. The majority of Co/Ni ratios of Py2 range from 1.06 – 3.17 (av. 1.56), which is also attributed to hydrothermal pyrite. The Py1 hosted in the quartz-pyrite vein has the highest contents of Au, As (Table 2, Fig. 8a), indicating that the initial hydrothermal fluids were enriched in these ore-forming elements. The Au contents of Py1 vary by three orders of magnitude. The zoning of Py1 shows several pulses of fluids activities, which cause the enrichment of arsenic at the contact surface of each generation of pyrite (Fig. 7b); this result demonstrates that the fluids overprinting with the same compositions may cause the enrichment of arsenic. In terms of the Py2, the fluids of this stage contain more Ag, Cu, Sb, and Pb as microsized inclusions in Py2 grains (Figs. 8d, 9), contrasting with their occurrence as either solid solution or nanoparticles in Py1. According to the texture characteristics and trace-element geochemistry discussed above, the hydrothermal pyrites in the Tatou deposit belong to different stages, i.e., the Py1 formed by hydrothermal fluids contains more As and Au, and the Py2 formed by hydrothermal fluids contains more Ag, Cu, Sb, Pb, Zn and Tl microsized inclusions.

5.4. Sources of the ore-forming materials and fluids The

87Sr/86Sr

values of the sulfides range from 0.711454 to 0.719763 with an initial value of

0.71124. These values are higher than that of basalt (<0.7037), and lower than that of terrigenous silicate (>0.720) (Faure, 1986). In addition, the Heyu, Huashan and Leimengou intrusions yield initial 87Sr/86Sr values of 0.706878-0.706984 (Wang et al., 2015), 0.7078 (Bi and Luo, 1995) and 0.709319-0.709326 (Cao et al., 2016), respectively, and are considered to be formed by the mixing of crustal and mantle materials (Han et al., 2007b; Wang et al., 2011). Their values are much lower than that of the sulfides from Tantou deposit. However, after recalculating the result of Peng

et al. (2008), the initial 87Sr/86Sr values of the wall rock (Xiong’er Group) calculated at t = 124 Ma range from 0.71135 to 0.73161. The 87Sr/86Sr values of the sulfides from Tantou deposit are close to that of the Xiong’er Group. Hence, the ore-forming materials were possibly derived from the upper crust, possibly the Xiong’er Group. The Late Mesozoic gold deposits in the Xiong’ershan-Waifangshan area have δ34S values of -16.8 to +5.3‰ (-1.9‰ on average) and are primarily in the range of -3 to +1‰ (Fig. 13). The δ34S values of these gold deposits are similar to those of typical magmatic-hydrothermal deposits (± 5‰, Ohmoto and Rye, 1997; Hoefs, 2009) as well as to those of the stratum of the Taihua Complex (δ34S values of -5.3 to +5.7‰, Fan et al., 1994b; Nie et al., 2001; Zhao et al., 2011) and the Xiong’er Group rocks (δ34S values of 2.5-5.4‰, Fan et al., 1994a, 1994b). Therefore, the gold deposits in this region are in a close relationship with Mesozoic granitic intrusions and surrounding rocks. We suggest that the negative δ34S compositions found in this work are likely related to the oxidation of the ore fluid system, since no organic sulfur has been found in the Xiong’ershan area. The presence of barite can confirm the oxidation of the fluids (Mao et al., 2002). The brecciation and influx of meteoric water can result in oxidation of the fluids. Therefore, the sulfur in this deposit, similar to that in other Late Mesozoic Au deposits in the same general area, is derived from the ancient crystalline basement (e.g., the Taihua and Xiong’er Groups). The carbon and oxygen isotopes of carbonates can assist in tracing the source of carbon in the ore-forming fluids due to the widespread nature of the calcite veins. Generally, carbon in hydrothermal fluids may have come from the mantle, marine carbonate rocks or sedimentary organic matter (Demény et al., 1998; Demény and Harangi, 1996; Liu and Liu, 1997; Taylor et al., 1967; Veizer and Hoefs, 1976). The variation in carbon and oxygen isotopic composition of the Tantou hydrothermal carbonates is similar to those of carbonatites (-4.0 ‰ ~ -7.5‰), diamond (-3.2‰ ~ -8.8‰), and carbonate in kimberlite (-4.7‰ ± 1.2‰) (Wei et al., 1988), indicating a deep source of the carbon in the ore-forming fluids. In the δ13CPDB versus δ18OSMOW diagram, the δ13C values of the calcite from the Tantou deposit imply that magmatic fluids were likely the principle carbon source. The δ18OSMOW versus δ13CPDB plot (Fig. 12) also indicates that low temperature alteration had a significant effect on the CO2 and carbonate ion levels.

5.5. Ore-forming process In the brecciated zones, the primary Py1 grains were formed and occur as euhedral shapes (Fig. 4a). Fracturing caused by tectonic activities could result in the phase separation and partitioning of reduced H2S into the vapor phase to produce residual fluids enriched in more oxidized sulfur species (Ohmoto, 1972; Drummond and Ohmoto, 1985). With the cyclic fluctuations of the hydrothermal fluids and addition of ore-forming materials from the fluids infiltrating the wall rock, As-rich and As-poor Py1 precipitated successively (Fig. 7b). Whereas some metals transferred from Py1 into Py2, others transferred into minor Cu-, Pb-, Ag-, or Sb- bearing inclusions. Further brecciation and influx meteoric water resulted in oxidation and/or immediate reduction in threshold supersaturation (Putnis et al., 1995). Next, the subsequent fluids that were enriched in Pb, Cu, Ag, and Sb overprinted the Py1 grains, which extracted ore-forming metals from the Py1 grains and formed coarser-grained Py2, which allowed the trace elements to be partitioned into separate mineral phases rather than incorporated into pyrite in solid solution or as tiny inclusions. Thermodynamic modeling reveals that removal of H2S from ore fluids into vapor phase during boiling lowers the total activity of sulfur in ore fluids, which destabilizes the gold-bisulfide complexes and leads to gold precipitation (Williams-Jones, et al., 2009).

5.6. Regional synthesis and geodynamic setting To the west of the Xiong’ershan-Waifangshan area, the Xiaoqinling region hosts more than 40 Au deposits with ore-forming ages in the range of 154-119 Ma (Li et al., 2012a, b). This finding shows that the gold deposits in the Xiong’ershan and Xiaoqinling regions were emplaced during the same approximate time span. In addition, the occurrence of A-type and/or highly fractionated I-type granites (150-114 Ma; Ye et al., 2006; Dai et al., 2009; Li and Bao, 2010; Yang et al., 2013; Gao et al., 2014a, 2014b; Wang et al., 2018) combined with the emplacement of the Xiaoqinling metamorphic core complexes (135-123 Ma; Zhang and Zheng, 1999) demonstrates that the gold deposits in the southern margin of the NCC were formed in an extensional setting. The westward subduction of the Paleo-Pacific Plate occurring at the same time may have played a critical role in the destruction of the NCC (Xu et al., 2011; Zhu et al., 2011). The growth rate and significant change in the subduction direction of the Paleo-Pacific Plate possibly modified the

upper mantle of the NCC, triggering a loss of the lithospheric mantle and a rising of the hot asthenosphere (Bartolini and Larson, 2001; Sun et al., 2008). Consequently, widespread felsic and mafic intrusions were produced along the major rupture zones at the margins of the NCC. The front edge of the subducting slab may have reached as far as the Xiaoqinling-Xiong’ershan area (Huang and Zhao, 2006; Xu et al., 2011). Volatile exsolution of the crustal and mantle melts could have provided sufficient fluids, sulfur and other components necessary to form the gold province at the southern margin of the NCC (Fig. 14). The geological, geochronological and geochemical data demonstrate that the Tantou gold deposit is possibly related to the destruction of the NCC as a result of lithospheric thinning.

6. Conclusions (1)

Gold mineralization in this region took place during the Early Cretaceous era (124.2 ± 3.1 Ma).

(2)

Hydrothermal pyrite is the dominant Au-bearing mineral, and two types are distinguishable: fine euhedral grains in breccia-type ores (Py1) and coarse grains in quartz-sulfide veins (Py2). Type Py1 shows clear rim-core structures.

(3)

Analysis using laser ablation inductively coupled plasma mass spectrometry shows that gold in Py1 at the Tantou deposit occurs mainly at lattice, as invisible solid solution and as nanoparticles. Gold in Py2 mainly precipitated as microsized inclusions or native gold grains. Co, Ni and As occur in pyrite as isomorphism. Ag, Cu, Sb, Pb and Zn are distributed primarily as invisible or sulfide inclusions. The ore metals (Ag, Cu, Mo, Sb, and Pb) show enrichment in Py2, while other metals (Au, As, Co, Ni, and Zn) are more enriched in Py1.

(4)

The Sr-C-O isotopic data and Co/Ni ratios for the pyrite suggest that the hydrothermal fluids extract metals from the wall rock (the Xiong’er Group), and magmatic fluids were likely the principle carbon source. The depleted δ34S values of sulfides are attribute to the fractionation between barite and sulfide minerals.

(5)

The Tantou gold deposit was formed under conditions of lithospheric extension from the Late Jurassic to Early Cretaceous and resulted from the thinning or destruction of the lithosphere due to westward subduction of the Pacific Plate.

Acknowledgments This research was supported by a fund from the National Key R&D Program of China (grant no. 2017YFC0601403), by the Basal Research Fund of the Chinese Academy of Geological Sciences (grant no. YYWT-201713), by the National Natural Science Foundation of China (grant no. 41272104) and by Open Fund of MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS (grant no. ZS1704). The authors are also grateful to the Luanling Gold Group Co., Ltd. for providing assistance during field work in the Luanling gold deposit. Appendix A. Supplementary material

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Figure captions Fig. 1 Geological map of the Xiong’ershan-Waifangshan region showing the distribution of gold deposits (modified from Guo et al. 2005). Major porphyry Mo and Ag-Pb-Zn vein-type deposits are also shown. Mineralized porphyry stocks are not included due to their minimal exposure (generally 0.5 km2). The insert shows tectonic divisions in the eastern China continental margin and the location of the Xiong’ershan-Waifangshan area.

Fig. 2 (a) Simplified geological map of the Luanling gold deposit and (b) Representative cross-section showing the occurrence, morphology and geometry of the largest ore body (no. 881) in the Tantou gold deposit.

Fig. 3 Photographs of orebody and rocks at Tantou deposit. (a) Thin quartz-pyrite vein cut by calcite vein; (b) stockwork quartz-pyrite vein cut by calcite vein; (c) mineralized cataclastic rock with disseminated pyrite cut by calcite vein; (d) brecciated rock with disseminated pyrite; (e) quartz-sulfide vein associated with calcite; and (f) Milky barren quartz vein before the ore-forming stage, associated with K-feldspar and epidote. The white stars indicate sample locations. Abbreviations: Q = quartz, Ep = epidote, Kfs = K-feldspar, and Cal = calcite.

Fig. 4 Reflected-light photomicrographic images showing the mineral paragenesis of the Tantou deposit. (a) Fine grained euhedral pyrite in quartz-pyrite veins (Py1); (b) irregular galena intergrown with pyrite; (c) coarse-grained chalcopyrite with a bornite rim cut by fine-grained galena; (d) coarse grained pyrite with porous rim in quartz-sulfide veins (Py2); (e) native gold

coexisting with hessite, galena, sphalerite and pyrite; and (f) galena replaced by argentite. The white stars indicate sample locations. Abbreviations: Py = pyrite, Gn = galena, Bn = bornite, Ccp = chalcopyrite, Au = native gold, Hes = hessite, Sp = sphalerite, and Arg = argentite.

Fig. 5 Paragenetic sequence for major minerals of the Tantou deposit. For more details see text.

Fig. 6 Rb-Sr isochron ages of sulfides from the Tantou gold deposit.

Fig. 7 (a) Backscattered electron image of the zoned pyrite, and the corresponding electron microprobe elemental maps for (b) As, (c) Cu and (d) Au.

Fig. 8 Representative time-resolved depth profiles for pyrite analyzed in this study indicating the occurrences of gold and other major metal elements. Fe exhibits a relative flat response typical of major elements in homogeneous pyrite. See text for detailed explanation.

Fig. 9 Comparative box plot of trace elements concentration in two types of pyrite with different characteristics. Boxes represent interquartile range (data between 35th and 75th percentiles). Py1 = pyrite from stage Ⅱ; and Py2 = pyrite from stage Ⅲ.

Fig. 10 Binary plots of (a) Au vs. As, (b) Au vs. Ag, (c) Sb vs. Ag, (d) Cu vs. Ag, (e) Cu vs. Sb, (f) Co vs. Ni, and (g) Co/Ni vs. Au/Ag in different pyrite types. The trace element concentrations are from Table 2.

Fig. 11 Photomicrographic images of representative pyrite, galena and argentite, showing the δ34S values of various spots analyzed by LA-ICP-MS.

Fig. 12 Plot of δ13CPDB values against δ18OSMOW values for carbonates from the Tantou deposit (modified from Wang et al., 2015).

Fig. 13 Histogram of δ34S (‰) data for sulfides in the late Mesozoic Au deposits in the Xiong’ershan region (See Table S1 for sources).

Fig. 14 Schematic showing the geodynamic setting of the southern margin of the NCC (modified from Li et al., 2012a; Mao et al., 2002).

Table captions

Table 1 Rb-Sr isotope ratios and Rb-Sr contents of sulfide samples from the Tantou deposit, western Henan Province.

Table 2 LA-ICPMS analyses of selected pyrite types from the Tantou gold deposit.

Table 3 C-O isotopic compositions of calcite separates from the Tantou gold deposit.

Table 1 Sample no.

Mineral

Rb (ppm)

Sr (ppm)

87Rb/86Sr

87Sr/86Sr

TI-12

Pyrite

0.8047

1.3450

1.7620

0.714271±9

0.00005

TI-41

Pyrite

1.4630

1.3870

3.1240

0.716748±8

0.00005

TI-36

Pyrite

1.9820

1.2180

4.8030

0.719763±6

0.00005

B7303

Pyrite

0.9141

5.6270

0.4792

0.712077±9

0.00005

TI-40

Pyrite

0.3156

0.9476

0.9817

0.713067±9

0.00005

TI-25

Pyrite

0.2809

0.4438

1.8630

0.714462±8

0.00005

B7319

Galena

0.0837

2.4410

0.1012

0.711454±9

0.00005

(±2σ)

Error

Sample no.

Au (ppm)

As (ppm)

Ag

Co

Ni

Cu

(ppm)

(ppm)

(ppm)

(ppm)

Zn

Mo

(ppm)

(ppm)

Sn (ppm)

Sb (ppm)

Te (ppm)

Pb (ppm)

Py1 B711-4-1

27.595

4824.510

19.447

148.017

63.051

581.947

72.191

2.913

0.222

B711-4-2

28.894

B711-1-1

389.235

B711-1-2

14.066

169.622

14.443

11227.329

6.697

169.377

76.742

422.048

61.855

1.389

0.556

45.535

82.569

43.744

37585.925

292.930

76.148

41.172

722.438

13.112

2.983

0.236

697.203

713.210

1033.589

542.653

44899.082

71.076

102.851

55.146

238.071

8.091

1.738

0.129

1824.847

477.142

180.157

B711-3-1

46.080

9999.491

194.290

148.310

67.129

638.719

20.436

0.428

0.108

77.115

317.845

171.494

B711-3-2

44.053

10789.823

107.692

144.286

65.884

545.645

14.975

0.533

0.085

73.237

266.795

443.005

B711-2-1

279.907

32928.647

123.477

144.340

89.760

429.016

16.917

4.016

0.067

739.340

821.167

91.404

B711-2-2

230.133

23887.737

29.251

304.388

109.996

890.438

44.707

2.460

0.000

235.052

647.714

5.080

B7325-4-1

33.392

8506.916

79.227

33.779

23.904

384.757

91.525

56.036

0.070

238.209

265.863

103.289

B7325-4-2

14.951

3555.654

69.903

72.384

77.284

320.969

52.931

388.395

0.000

135.601

221.187

287.070

B7325-2-1

0.937

486.191

8.288

110.994

83.159

1179.388

136.209

12.637

0.169

343.752

4.347

98.630

B7325-2-2

11.081

3346.000

22.743

37.547

38.841

201.773

24.665

7.407

0.586

288.250

20.226

105.623

B7325-1-2

50.883

4299.973

45.297

20.676

21.204

452.640

217.751

27.540

0.673

732.786

122.942

59.986

B7325-1-3

537.080

15971.950

554.963

14.752

19.248

733.743

267.912

12.376

0.151

5860.580

1824.986

231.092

B7325-1-4

572.391

12879.624

967.393

10.135

6.219

791.729

47.912

12.813

0.000

4972.652

2256.596

241.910

B7325-5-1

25.748

5346.793

60.999

70.530

82.271

475.567

20.890

9.174

0.665

405.460

142.937

63.479

B7325-3-1

41.285

8958.429

45.602

74.300

83.755

279.444

38.104

9.780

0.963

414.861

108.363

411.854

B7306-1-1

25.088

5393.412

168.462

94.353

92.044

254.475

25.559

0.340

0.502

280.238

158.511

103.240

B7306-1-2

2.855

201.016

57.955

144.130

162.931

139.258

11.691

0.259

0.356

54.497

55.091

33.520

B7306-2-1

101.442

23677.020

43.138

38.968

23.641

375.842

45.639

7.179

0.221

729.825

49.405

41.723

B7306-3-1

267.052

19603.555

178.892

127.265

69.228

1376.699

15.157

2.121

0.000

67.104

565.907

141.629

B7306-3-2

190.084

27719.032

30.846

53.420

41.953

649.115

115.308

0.159

0.315

628.844

167.541

18.290

B7306-4-1

24.301

4577.787

143.401

201.893

182.397

282.852

36.557

40.871

2.029

203.411

189.066

345.365

B7306-4-2

37.555

9539.362

146.667

97.590

77.827

460.709

77.084

17.635

0.153

399.427

119.848

149.642

B7306-5-1

23.470

7381.703

68.273

694.196

318.168

196.000

108.475

1.640

0.897

615.077

39.857

133.458

B7306-5-2

66.203

14119.995

90.809

347.265

195.316

183.450

1745.057

0.000

0.628

863.414

53.435

68.337

B7308-7-1

3.976

1722.145

33.438

337.485

237.793

740.059

729.261

8.939

0.313

28.055

18.754

62.013

B7308-7-2

3.041

2277.363

7.551

316.183

252.726

785.439

394.390

1.796

0.444

17.533

3.866

19.767

B7308-5-1

2.535

981.969

145.238

312.723

139.295

308.352

281.596

0.312

0.563

56.367

81.838

43.557

B7308-5-2

5.171

799.865

753.458

35.889

15.683

567.241

666.873

0.388

0.400

69.523

554.737

52.784

B7308-6-1

13.691

13165.751

14.997

138.456

100.758

658.311

307.033

0.870

0.287

4.637

9.939

18.371

B7308-8-1

87.720

18952.076

475.459

16.358

14.237

350.145

168.567

4.411

0.000

39.425

346.123

29.051

B7308-1-1

5.328

1532.065

851.842

240.583

215.268

1930.659

2149.842

219.708

1.676

208.078

659.978

701.702

B7308-2-1

42.418

17136.746

1453.545

67.628

66.361

1342.214

411.002

1162.014

5.112

511.555

1302.069

3018.773

B7308-3-1

24.801

10292.220

1347.280

29.631

24.341

2177.812

315.620

149.508

5.812

169.416

1406.411

567.136

B7305-2-1

3.563

71.110

3.831

46.454

55.390

1597.758

1342.304

35.910

0.096

7.667

32.856

788.720

B7305-2-2

1.360

48.604

2.725

209.029

208.171

451.187

267.493

2.473

0.517

9.813

28.891

1453.522

B712-4-1

15.518

3371.450

243.933

250.073

300.044

690.063

204.828

1.674

0.754

239.126

409.486

387.176

B712-3-1

8.057

3365.421

102.283

322.481

325.391

716.605

319.295

0.479

0.541

151.822

243.574

166.337

B712-2-1

5.011

2374.960

21.714

154.146

114.770

313.154

45.216

0.568

1.901

42.079

37.489

40.401

B712-2-2

15.966

4939.261

77.466

239.566

216.432

305.212

783.592

98.244

1.123

57.086

122.971

52.819

B712-1-1

688.162

17592.626

523.536

140.801

97.573

832.228

42.669

6.552

1.011

5520.645

3228.825

232.802

B7303-1-1

22.592

11507.577

20.716

174.877

135.785

324.751

294.029

0.538

0.782

22.740

17.836

62.173

B7303-1-2

16.745

5555.753

9.816

180.664

154.857

424.613

1248.492

0.436

3.127

17.281

219.080

16.826

B7303-3-1

9.968

5527.609

15.557

256.137

201.714

406.567

185.074

2.023

2.479

76.508

14.231

144.982

B7303-3-2

113.204

37565.891

14.347

117.380

105.882

432.820

560.428

1.688

3.582

41.445

51.712

379.386

B7303-2-1

1.986

959.079

19.924

153.035

126.517

916.819

143.547

2.747

1.437

182.506

9.119

260.251

Py2 B7312-1-1

3.955

1057.571

26.493

60.367

48.872

378.901

35.998

2.909

0.958

633.484

2.714

28.884

B7312-2-1

2.512

2422.137

51.058

53.310

36.045

811.731

429.636

62.219

1.013

227.874

16.633

1493.232

B7312-4-1

0.331

12.928

7.283

43.561

32.950

87.930

34.933

0.125

6.120

4.747

6.001

20.760

B7312-4-2

0.095

9.413

0.155

14.360

13.520

37.521

66.098

0.219

4.224

7.729

0.130

19.619

B7312-3-1

1.228

2088.785

12.484

59.034

47.563

1068.376

16.182

0.264

0.253

330.316

7.793

28.582

B7312-3-2

2.954

3573.734

1.802

53.086

41.867

595.017

23.125

0.048

0.137

310.148

8.034

3.583

B7311-1-1

5.551

3468.681

354.246

235.477

151.868

1253.263

143.706

20.940

2.520

2177.707

64.346

3743.746

B7311-2-1

2.489

2663.089

1833.137

167.623

109.079

5632.184

1554.943

618.001

3.107

6156.393

277.504

19275.691

B7311-7-2

2.284

2055.061

48.706

50.311

41.920

660.994

25.830

2.237

0.307

184.929

21.562

6082.316

B7311-8-1

0.570

2820.367

41.614

41.214

25.361

309.739

38.666

8.726

1.970

220.450

6.418

12230.481

B7311-8-2

1.641

3329.448

473.101

143.657

45.340

1388.893

25.421

11.144

3.600

67.723

151.093

60227.838

B7311-6-1

8.645

4819.297

109.329

158.140

128.249

806.688

148.069

23.034

1.026

823.831

23.369

20313.744

B7311-6-2

9.126

4066.264

94.212

43.318

32.495

613.862

95.267

8.479

0.000

294.691

25.434

12608.332

B7311-5-1

2.992

1963.637

462.870

146.706

55.811

898.799

75.631

154.651

0.460

1115.804

86.415

147931.918

B7311-5-2

1.167

834.563

241.818

66.004

41.867

906.357

152.293

43.215

1.788

2464.950

42.724

12512.078

Table 3 Sample no.

mineral

δ13CV-PDB‰

δ18OV-SMOW‰

LL-7

Calcite

-2.7

12.8

LL-11

Calcite

-3.8

17.3

B7307

Calcite

-1.7

16.8

1 2

3 4 5 6 7 8

Fig. 1

9 10 11 12

Fig. 2

13 14 15 16

Fig. 3

17 18 19 20

Fig. 4

21 22 23 24

Fig. 5

25 26 27 28

Fig. 6

29 30 31 32

Fig. 7

33 34 35 36

Fig. 8

37 38 39 40 41

Fig. 9

42 43 44 45

Fig. 10

46 47 48 49

Fig. 11

50 51 52 53

Fig. 12

54 55 56 57

Fig. 13

58 59 60 61

Fig. 14

62

Highlights:

63 64



the Early Cretaceous era.

65 66

The sulfides Rb-Sr isochron age indicates that gold mineralization occurred during



Two types of pyrite are distinguishable: Py1 and Py2. Gold in Py1 at the Tantou

67

deposit occurs mainly at lattice, as invisible solid solution and as nanoparticles,

68

while in Py2 mainly precipitated as microsized inclusions or native gold grains.

69



metals (Au, As, Co, Ni, and Zn) are more enriched in Py1.

70 71



74

Multiple stable isotopes indicating the ore-forming material are from the wall rock (the Xiong’er Group), and magmatic fluids is likely the principle carbon source.

72 73

The ore metals (Ag, Cu, Mo, Sb, and Pb) show enrichment in Py2, while other



Formed in an lithospheric thinning geodynamic setting

75 76 77 78 79 80

Comparative box plot of trace elements concentration in two types of pyrite with different characteristics. Boxes represent interquartile range (data between 35th and 75th percentiles). Py1 = pyrite from quartz-pyrite stage (stage Ⅱ); Py2 = pyrite from quartz-sulfide stage (stage Ⅲ)