Geochronology, isotopic chemistry, and gold mineralization of the black slate-hosted Haoyaoerhudong gold deposit, northern North China Craton

Journal Pre-proofs Geochronology, isotopic chemistry, and gold mineralization of the black slatehosted Haoyaoerhudong gold deposit, northern North China Craton Hai-Ddong Zhang, Jian-Chao Liu, Qian Xu, Jin-Ya Wang PII: DOI: Reference:

S0169-1368(19)30715-2 https://doi.org/10.1016/j.oregeorev.2020.103315 OREGEO 103315

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Ore Geology Reviews

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Please cite this article as: H-D. Zhang, J-C. Liu, Q. Xu, J-Y. Wang, Geochronology, isotopic chemistry, and gold mineralization of the black slate-hosted Haoyaoerhudong gold deposit, northern North China Craton, Ore Geology Reviews (2020), doi: https://doi.org/10.1016/j.oregeorev.2020.103315

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Geochronology, isotopic chemistry, and gold mineralization of the black slate-hosted Haoyaoerhudong gold deposit, northern North China Craton Hai-Ddong Zhang1, 2, Jian-Chao Liu1, Qian Xu3, Jin-Ya Wang1 1

School of Earth Science and Resource, Chang’an University, Xi’an, Shaanxi 710056, China

2

Department of Geology，Northwest University, Xi’an 710069, China

3

Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

ABSTRACT The Haoyaoerhudong gold deposit is the largest gold deposit in the north margin of the North China Craton gold province, and contains over 7 Moz of gold at an average grade of 0.62 g/t. The deposit is hosted in the carbonaceous and pyritic slate, phyllite, and schist and is controlled by a tight syncline and shear zones. The high-grade orebodies contains abundant pyrite veins and pyrite-quartz veins. Three stages of pyrite have been identified, including the diagenetic disseminated pyrite, pyrite veins caused by peak matamorphism, and pyrite-quartz veins forming during post-peak metamorphism. Native gold has been observed in pyrite veins and pyrite-quartz veins. The 40Ar/39Ar plateau age of a biotite separate from a tails of boudinaged pyritequartz veins is 260.1±2.9 Ma. Combined with previously published 40Ar/39Ar mica age data and low closure temperature of mica, these results suggest that pyrite veins and pyrite-quartz veins were formed during the peak, to post-peak metamorphism during 1

285‒260 Ma, respectively. The lower limit of the formation age of sedimentary disseminated pyrites has constrained to 1670-1560 Ma by the intruded mafic-ultramafic dikes. Disseminated pyrite separates have δ34S values ranging from -39.40 ‰ to +17.85 ‰, 206Pb/204Pb

of 19.144‒21.892, 207Pb/204Pb of 15.681‒15.864, and 208Pb/204Pb of

37.502‒38.925, suggesting they were formed from seawater sulfate and has experienced strong sulfur isotopic fractionation. In contrast, hydrothermal pyrites from pyrite veins and pyrite-quartz veins have δ34S values ranging from +6.8 ‰ to +16.47 ‰, 206Pb/204Pb

of 18.566‒18.922, 207Pb/204Pb of 15.645‒15.684, and 208Pb/204Pb of

38.924‒38.983, which may reflect dissolution-reprecipitation of disseminated sulfides from the pre-existing organic-rich sediments. The mineral paragenetic, geometric, and cross-cutting relationships of pyrite veins and pyrite-quartz veins at Haoyaoerhudong suggest that gold was most likely introduced into pyrite, accompanying sedimentation of the organic-rich shales, and then became enriched during diagenesis. Subsequently, the hydrothermal fluids following metamorphism and shear zone activity make dissolution of the gold in the diagenetic pyrite and precipitated in the intersection of shear zone and tight syncline. Keywords Black slate-hosted gold deposit · Mineral paragenesis · 40Ar/39Ar age · SPb isotope · Mineralization processes

1. Introduction The Central Asian Orogenic Belt (CAOB) is one of the world’s largest economic gold belts (Fig 1a; Goldfarb et al., 2014; Chen et al., 2000) since the discovery of the 2

Muruntau (>175 Moz Au; Graupner et al., 2005, 2006) in Uzbekistan, as well as the Sukhoi Log (105 Moz Au; Yudovskaya et al., 2011) and Olimpiada (46 Moz Au; Afanaseva et al., 1995) in Russia. Many other large gold deposits, such as Kokpatas (5 Moz Au), Daugytau (6 Moz Au), Zarmitan (11 Moz Au), Kumtor (19 Moz Au), Sawayaerdun (10 Moz Au), Haoyaoerhudong (7 Moz Au) and Zhulazhaga (6 Moz Au), were also discovered in four gold provinces (Fig 1a). These deposits share many similarities, including (i) hosted in greenschist facies black shales/slates, (ii) control by shear zones and tight folds, and (iii) close spatial and temporal relationship with postcollisional intrusions (Ding et al., 2016; Kempe et al., 2016; Wang et al., 2014; Yakubchuk et al., 2014; Chen et al., 2012; Wilde et al., 2001; Alekseyev, 1979). The gold deposits in the CAOB had a long and protracted fluid history, which includes fluid events associated sedimentary-diagenetic processes, metamorphism, deformation, and magmatic-hydrothermal events (Kempe et al., 2016; Nozhkin et al., 2011; Zhang et al., 2017; Large et al., 2007). The stages and origins of the sulfides and gold are difficult to be identified because of parallel of auriferous sulfide veins to stratiform layers or plane axial of folding and faulting (Kempe et al., 2016; Ding et al., 2006). However, multistage sulfides were described by Large et al., (2007) in Sukhoi Log and Zhang et al., (2017) in Sawayaerdun gold deposits. These new discoveries stimulate more studies to assess gold mineralization in the CAOB. The Haoyaoerhudong gold deposit is the largest gold deposit in the north margin of the North China Craton (NCC) gold province (Fig. 1a, b) and contains over 7 Moz of gold (Zhang et al., 2014; Liu et al., 2016). Gold mineralization of Haoyaoerhudong deposit is mainly associated with disseminated pyrite, pyrite veins, and pyrite-quartz 3

veins. Geometry of orebodies is mainly controlled by the bedding-parallel brittle-ductile shear zones and an NNE-striking tight syncline (Fig. 2a, b; Zhang et al., 2014). Wang et al. (2014) and Zhang et al. (2014) proposed that gold was initially enriched in the Mesoproterozoic black shales, and was then remobilized and locally concentrated by magmatic-hydrothermal fluid flow at the intersection of the shear faults and the tight syncline. However, poor identification of different types of pyrites leads to debates regarding the timing of gold mineralization and ore-forming sources (Wang et al., 2014; Cao et al., 2014). In this paper, we identify different stages of pyrite based on the intergrowth relationship of pyrite and metamorphic garnet grains and crosscutting relationship between pyrite veins and pyrite-quartz veins. Textures of pyrite, biotite 40Ar-39Ar dates, and S and Pb isotopes were carried out to (1) constrain the age of main-stage gold mineralization; (2) reveal a source of ore-forming gold, and (3) reconstruct the model of gold mineralization.

2. Regional geology Many large gold depoists are hosted in the Mesoproterozoic passive margin sequences termed Bayan Obo and Zhaertai Groups that formed at passive margin (eg., Haoyaoerhudong and Zhulazhaga gold deposit; Zhang et al., 2014; Ding et al., 2016). The Bayan Obo and Zhaertai Groups contain clastic organic-rich, pyritic black phyllite and slate that is up to 6 km thick on the north margin of the NCC (Zhao and Zhai, 2013; Zhai et al., 2001; Fig. 1b). Subsequently, arc and post-collision magmatism related to the subduction of the Paleo-Asian oceanic plate beneath the NCC and collision of the 4

Siberian craton and NCC took place along the north margin of the NCC during the Paleozoic, respectively (Xiao et al., 2003; Xu et al., 2013). Large-scale magmatism was formed during the post-collision setting and widespread in Haoyaoerhudong area (Fig. 1b, 2a). The major lithological units in the north margin of the NCC consist of the Precambrian metamorphic basement and a Phanerozoic cover sequence (Fig. 2a; Zhang et al., 2047). The Precambrian metamorphic basement comprises the Archean Wulashan, Mesoproterozoic Bayan Obo, and Zhaertaishan Groups (Fig. 2a). The Bayan Obo Group consists of five formations termed from the bottom to top as Dulahala, Jianshan, Halahuogete, Bilute, Baiyinbaolage, and Huji’ertu Formations. The former four formations are widely distributed in the Haoyaoerhudong area (Fig. 2a, b; BGMRIM, 1991). The Dulahala Formation (>1081 m) consists of coarse quartz sandstone, and quartzite with some interlayers of black slate, with the youngest detrital zircon age of 1809 ± 36 Ma (Hu, 2016). The Jianshan Formation (>1757 m) consists of black carbonbearing and silty slate, siltite, and sandstone with few interlayers of mafic tuff with a magmatic zircon isotope age of 1728 Ma (Liu and Liu, 2015). The Halahuogete Formation of carbonae, slate, and sandstone (>1507 m) can be divided into three units: (1) grey to black calcareous phyllite, slate, and shist (h1), (2) interbedded limestone, quartzite, and phyllite (h2), and (3) grey limestone (h3). These rocks were intruded by ca. 1670 Ma and 1560 Ma mafic to ultramafic dikes (Hu, 2016).The Bilute Formation (>1193 m) mainly comprises black carbonaceous slate and phyllite and is divided into four units: (1) carbonaceous siltstone with few interlayers of silty slate (b1), (2) carbonaceous slate, phyllite, and two-mica schist with few interlayers of siltstone (b2), (3) siltstone and 5

sandstone with few interlayers of sedimentary breccia (b3), (4) and upper unit of limestone (b4). Hu (2016) obtained the youngest detrital zircon with U-Pb age of 1583 ± 60 Ma from the Bilute Formation that is in agreement with the magmatic zircon isotope age of 1342 ± 9 Ma for the gabbro dyke intruded into the Bilute Formation (Zhou et al., 2016). The metamorphic grade of the Bayan Obo Group surrounding the Haoyaoerhudong gold deposit is greenschist facies, locally up to lower amphibolite facies. The Sm-Nd dating of metamorphic garnet from the Bilute Formation in Haoyaoerhudong indicates that the peak metamorphism occurred at ~285 Ma (Wang, 2016). The Phanerozoic volcanic-sedimentary cover sequence is composed dominantly of the Upper to Middle Jurassic rhyolite, tuff, and carbonate. Large-scale late Paleozoic magmatism along the north margin of the NCC (Fig., 1b, 2a) contains monzonite (with zircon U-Pb age of 287.5 ± 1.9 Ma), granite porphyry (with zircon U-Pb age of 290.9 ± 2.8 Ma), granodiorite (with zircon U-Pb age of 280 ± 1.2 Ma; unpublished data), biotite adamellite (with zircon U-Pb age of 267.9 - 274.0 Ma; Xiao et al., 2012) and less gabbro with a zircon U-Pb age of 279 ± 2 Ma (Wang, 2016; Liu et al., 2019). Multistage dykes are widespread in the Bayan Obo Group (Liu et al., 2016), and include amphibole olivine gabbro (with zircon age of 282 ± 1 Ma), porphyritic diorite (with zircon U-Pb age of 288 ± 3 Ma), diabase, lamprophyre and post-mineralization pegmatite dikes (zircon age of 182 ± 1 Ma) (Fig. 2b). Lack of dykes in the Late Paleozoic intrusions compared with the Bayan Obo Group suggests that dykes formed prior to, or during emplacement of the Late Paleozoic intrusions (Fig. 2b). The Bayan Obo group was intruded by numerous Late Paleozoic intrusions and dykes, and strongly modified by the NW- and -WE-treading Gaoletu and Shibeng fault 6

systems into a series of NE- and NEE-treading folds (Fig. 2). The Gaoletu fault system consists of a series of subsidiary sinistral ductile-brittle sub-faults (F1-F7; Fig. 2). The faults control the morphology of Bayan Obo Group, and locally crosscut the late Paleozoic granitoid (Fig. 2a). The Gaoletu fault system strikes NW-NEE and dips NE-N 50-80°, and generally follows the contacts between Late Paleozoic granitoid as the hanging wall and the Bayan Obo Group as the footwall.

3. Deposit geology The deformed Bayan Obo Group occur as boat-shaped and was intruded by the late Protezoic granitoids and dykes (Fig. 2). The Haoyaoerhudong gold deposit occurs at the intersection of a tight syncline and a shear fault. The gold orebodies do not occur in the core, but occur along the southeast limb of the tight syncline (Fig. 2b, c). The syncline plunges northeast and its axial surface dips northwest at 70 ～ 85°. The NE-treading shear zone is 4.5 km long and 200 m width, dips 70 - 88° NW, and is concordant with both bedding and cleavage (Fig. 2b). The Haoyaoerhudong gold deposit extends in excess of 50-200 m wide, 3000 m long and is separated by F6 into two ore blocks termed the northeast and southwest ore block(Fig. 2; BJJYFW, 2012). The northeast ore block is generally 1900 m long, 200 m width, and 700 m deep, accounting for 86% of the gold reserve in the Haoyaoerhudong deposit (BJJYFW, 2012). The deposit develops disseminated (Fig. 3a) and vein-type pyrite (Fig. 3b-d). A total of 44 economic ore bodies was defined, of which 7 largest ore bodies are larger than 500 kg Au occurring as laminar lenses (BJJYGE, 2012). The ore minerals are predominantly pyrite and pyrrhotite with minor chalcopyrite, arsenopyrite, 7

and ilmenite. The gangue minerals are mainly quartz, calcite, garnet, sericite and biotite with minor hornblende. Based on the mineral paragenesis, the content of pyrite, and geometry and distribution of the veins, three types of veins were defined in the Haoyaoerhudong gold deposit as: (1) pyrite veins (Fig.3c), (2) pyrite-quartz veins ( Fig.3b-d), and (3) barren quartz and calcite veins (Fig.3e). The fine-grained stratiform disseminated pyrite is abundant in the carbonaceous and pyritic slate and phyllite and occurred as anhedral to subhedral crystals with size ranging from 0.5 μm to 5 μm, which is interpreted to be of diagenetic origin (Fig. 3a; Wagner and Boyce, 2006). Pyrite veins are commonly 1 to 3 cm thick and consist of euhedral or subhedral coarse-grained pyrite (>90 vol.%), garnet (～5 vol.%), and anhedral quartz (～3 vol.%), as well as minor chalcopyrite (～1 vol.%).

Abundance of oriented metamorphic garnet inclusions in the vein-type pyrite (Fig. 3c, f-h) indicates that formation of pyrite veins is most likely related to peak-metamorphism and activity of the shear zone. Pyrite-quartz veins are less than 3 cm in thickness and contain quartz and pyrite, with little chalcopyrite (Fig. 3b-c, i-k). The barren quartz veins are 0.5‒5 cm in thickness, and extend for several centimeters (Fig. 3e). The boundaries of gold orebodies of the Haoyaoerhudong deposit are defined by an Au cut-off grade, rather than by any lithologic change. The higher gold grades (>1.2 g/t) and larger gold ore bodies occur within the shear zone of the northeast ore block and are characterized by widespread occurrence of pyrite veins and pyrite-quartz veins. However, carbonaceous slate and phyllite without pyrite veins and pyrite-quartz veins contain

8

disseminated pyrites and have 0.1‒0.2 g/t Au, suggesting that disseminated pyrite contains gold (BJJYFW, 2012). Intergrowth of pyrite (with some garnet inclusions) with metamorphic garnet in pyrite veins (Fig. 3f-h) shows these veins were formed during post-peak metamorphism. Furthermore, the pyrite veins were cut by low-angle pyrite-quartz veins (Fig. 4i), suggesting that pyrite-quartz veins postdated pyrite veins and were most likely formed during post-peak metamorphism. Some native gold grains occur garnet fractures, along boundaries of pyrite and quartz, and within quartz as inclusions (Fig. 3l). Few unmodified quartz veins (Fig. 3e) are barren and postdated the deformation and gold mineralization. Therefore, the paragenetic succession of sulfides can be divided into four main stages (Fig. 4): (1) diseminated fine-grained diagenetic pyrite; (2) peak metamorphic pyrite veinS; and (3) post-peak metamorphic of pyrite-quartz veins; and (4) post-mineralization quartz veins.

4. Sampling and analytical methods 4.1 Biotite 40Ar-39Ar dating Sample 16HY02-2 of pyrite-quartz vein with Au grade of 0.45 g/t (based on assay data from the Taiping mining company) was collected from the northeast open pit (Fig. 3d). The ～10 cm thick pyrite-quartz veins, which contain 85 to 90 vol.% quartz, 8 vol.% pyrite, and 5 vol.% biotite, were modified by the shear fault into lens-like boudins (Fig. 3d). Biotite grains mainly occur at the tails of the boudinaged pyrite-quartz veins,

9

indicating that crystallization of biotite is related to deformation. The biotite grains were handpicked under a binocular microscope. Isotopic measurements were made with a Noblesse mass spectrometer at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS). Ca and K correction factors were [36Ar/37Ar]Ca=0.000261±0.0000142, [39Ar/37Ar]Ca=0.000724±0.0000281, [40Ar/39Ar]K=0.00088±0.000023. The experimental temperature varies from 300 to 1350 °C. Isotope ages were calculated using the decay constant (5.54310-10yr-1) according to Steiger and Jäger (1977) and all errors are quoted at the 2σ level. Plateau ages were determined from three or more contiguous steps that comprise >50% of the 39Ar released, revealing concordant ages at the 95% confidence level. Because no assumption was made regarding the trapped component, the preferred ages are isochron age, calculated from the results of plateau steps using the York regression algorithm (York, 1969). Uncertainties on all data reported herein are at the 95% confidence level (2σ). The data were processed using ArArCALC (Koppers, 2002).

4.2 S-Pb isotope Eight samples (6 disseminated and 2 vein-type pyrite samples) were collected from the open pit for S and Pb isotope analysis. Pyrite grains with more than 99% purity were handpicked using a binocular microscope. Sulfur isotopes were determined at the Geological Analysis and Research Centre of Nuclear Industry of China (GARCNIC). The pyrite samples were first treated with a carbonate-zinc oxide semi-dissolved technique to separate pure BaSO4, and then final 10

SO2 samples were prepared with a V2O5 oxidation technique. The samples were conducted using a MAT-253 EM mass-spectrometer and the results are expressed relative to the international standard CDT with an analysis accuracy better than ±0.2‰. Lead isotopic compositions were also determined at the GARCNIC. The samples were first dissolved by acids. Lead was separated from the treated samples using a resin exchange technique. The evaporated-dry samples were analyzed using a MAT261 mass spectrometer, for which 1 μg Pb yields an accuracy of <0.05% and 0.005% for 204Pb/206Pb and 208Pb/206Pb, respectively.

5. Results 5.1 40Ar-39Ar dating of biotite Ten step-heating experiments were conducted at a varible temperature of 400-1350 °C for the 16HY01-2 sample of pyrite-quartz veins from the Haoyaoerhudong gold deposit (Table 1, Fig. 5). During the heating, few 39Ar (0.29%) was released below 400 °C, subsequently 3.00% 39Ar was released during the temperature increasing from 400 to 600 °C, and finally 96.71% 39Ar was released at the temperature of 600-1350 °C with a resulting narrow range of apparent ages from 262.09 to 258.32 Ma. The biotite 16HY02-2 yielded a well-defined plateau age of 260.1 ± 2.9 Ma (2σ, MSWD = 1.3) corresponding to 96.71% released 39Ar. It is consistent with the isochron age of 260.9 ± 3.4 Ma (MSWD = 1.29). 5.2 S-Pb isotope composition of sulfides

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Five samples of disseminated pyrite yielded δ34S values in a narrow range of +15.02 to +17.85 ‰ with an average of +16.98 ‰, but δ34S values of other two disseminated pyrite samples (16HR01-6, -6-2) are -39.40 ‰ and -39.26 ‰, respectively. δ34S values of two pyrite samples from the pyrite-quartz veins are +14.3‰ and +12.2‰. Combined with the published δ34S data on pyrite/pyrrhotite veins and pyrite-quartz veins from references of Wang et al. (2014) and Liu et al. (2016) (Table 2, Fig. 6), these data can be used to confirm different S isotope signatures of disseminated pyrite, pyrite veins, pyrite-quartz veins, and quartz veins that is useful for reconstructing of process of gold mineralization. The lead isotopic composition for the six disseminated pyrite samples in the Haoyaoerhudong deposit yielded large variations in 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb,

ranging from 19.144‒21.892, 15.681‒15.864, and 37.502‒38.925,

respectively. Hydrothermal vein-type pyrite samples have 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb

values of 18.794‒18.790, 15.674‒15.684, and 38.924‒38.983, respectively.

Sedimentary disseminated pyrite displays scattered Pb isotope values and relatively radiogenic compositions (Fig. 7) in comparison to the vein-type pyrite (Zhao et al., 2011).

6. Discussions 6.1 Age of gold mineralization It is clear that disseminated pyrite contains gold content up to 0.1‒0.3 ppm, suggesting that gold was initially introduced into pyrite during sedimentation of the Bayan Obo Group (BJJYFW, 2012), but it cannot exclude the possibility of gold introduction by alteration of disseminated pyrite and later auriferous fluids. The major 12

stage of gold mineralization in the Haoyaoerhudong deposit is closely associated with development of pyrite veins and pyrite-quartz veins, which contains visible native gold. Gold mineralization at the Haoyaoerhudong gold deposit was previously dated to ca. 267.4 ± 2 Ma and 256‒246 Ma based on 40Ar/39Ar data for biotite and muscovite separates from pyrite-quartz veins (Wang et al., 2014; Cao et al., 2014; Fig. 8). Our biotite 40Ar/39Ar plateau age of ~260 Ma for pyrite-quartz veins (16HY02-2) is comparable to the published biotite 40Ar/39Ar age of ~267 Ma (Wang et al., 2014). The closure temperatures of Ar in biotite and muscovite are 630 K and 580 K, respectively (Hodges, et al., 1994), so the mica 40Ar/39Ar age of 267-243 Ma (Wang et al., 2014; Cao et al., 2014) is most likely interpreted to record a long period of deformation at the Haoyaoerhudong area. Distribution of biotite along the tails of boudinaged pyrite-quartz veins also support that growth of biotite is associated with activity of shear zones (Fig. 3d). Metamorphic garnet separates yielded Rb-Sr age of 286 Ma (Wang, 2016) and metamorphosed porphyritic diorite yielded zircon U-Pb age of 288 Ma (Liu et al., 2016), indicating that the regional metamorphism reached peak metamorphism most likely at ~286 Ma. Therefore, the regional magmatic events at 290-268 Ma in the Haoyaoerhudong area (Liu et al., 2016; Xiao et al., 2012; Wang, 2016) postdate postpeak metamorphism (Fig. 9). On the basis of the intergrowth of pyrite with metamorphic garnet (Fig. 3h) in pyrite veins and the crosscutting relationship between pyrite veins and pyrite-quartz veins (Fig. 3i), we argue that hydrothermal gold mineralization mainly occurred during peak, to post-peak metamorphism 285-260 m.y. ago and would have been overprinted by the contemporaneous magmatic-hydrothermal events. Additionally, the age of diagenetic disseminated pyrite may be generally constrained by a U-Pb 13

isotope age of 1670-1560 Ma for mafic-ultramafic dikes intruded into the Bilute Formation (Hu, 2016).

6.2 Sources of ore-forming metals and gold The disseminated pyrite samples from the Bilute Formation, except for samples of 16HR01-6 and 16Hr01-7 (with δ34S values ranging from -39.40 ‰ to -39.26 ‰), exhibit a narrow range of δ34S values ranging from +15.02 ‰ to +17.85 ‰, which characteristics are similar to those of pyrite from euxinic black shales in the MidProterozoic marine Roper basin, Australia (Fig. 9; Shen et al., 2003). The wide range of around +55‰ to +58‰ δ34S values for disseminated pyrite indicates that significant fractionations (> +50‰) occurred during the formation of disseminated pyrite with strongly negative δ34S values (～-40‰; Canfield and Raiswell, 1999). Canfield and Raiswell (1999) and Shen et al. (2003) suggested that sulfate-reducing bacteria are capable to fractionate sulfur isotopes up to +45‰ in an open sulfate system with unlimited sulfate supply. Thus, the 34S-depleted isotope composition of disseminated pyrite is consistent with sulfide deposition from seawater sulfate with δ34S values range from +15 to +18‰ that is accompanied by sulfur isotopic fractionation. Walker et al. (1983) and Shen et al. (2003) proposed that bacterial sulfate reduction decreases supplies of sulfate under the low diffusion rates in the aquifer systems that results in enrichment in 34S of sulfate and solution. Thus, the lowest δ34S values (～+15‰) of disseminated pyrite should be closest to the initial value of sulfate deposited in the Bilute Formation.

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Sulfur isotope compositions of sulfides precipitated from the hydrothermal fluid is mainly controlled by the isotope composition of the sulfur source, as well as temperature, Eh, and pH at the site of precipitation of sulfides (Ohmoto, 1986; Ohmoto and Rye, 1979). An occurrence of a pyrite-chalcopyrite assemblage, absence of magnetite and sulfate (Fig. 4), and microthermometry of fluid inclusions (Wang et al., 2015) in the Haoyaoerhudong deposit show that gold mineralization was taken place at the temperature of 250-350 °C, with fluid oxygen fugacity of 10-32 to 10-28 bars (Mikucki and Ridley, 1993), and under relatively reduced condition (Kerrich et al., 2000). Ohmoto and Rye (1979) showed that equilibrium isotopic fractionation of H2S and most sulfides is less than ± 2 ‰ at a temperature above 250 °C. The δ34S values of hydrothermal sulfides from pyrite veins and pyrite-quartz veins range from +6.8 ‰ to +16.5 ‰ (Fig. 6, Table 2). These relatively inhomogeneous sulfur values are higher than those of majority of lode gold deposits, such as the Bendigo, Kumtor, and Sawayaerdun (Fig. 9). Based on results of sulfur values, hydrothermal sulfides can be divided into two groups. Sulfur values (+13.1 ‰ to +16.5 ‰) of fist group is relative lower than disseminated pyrite, which is within error of sulfur derived from the dissolution-reprecipitation of disseminated pyrites with δ34S values of +15.02 to +17.85 ‰. While, the second group has distinctive lower δ34S values than disseminated pyrite, which cannot be introduced that the second hydrothermal sulfides derived from sedimentary pyrites. The possibility scheme is that the second hydrothermal sulfides represent a mixture of sedimentary and hydrothermal sulfur. Therefore, these data suggest that the hydrothermal sulfides most likely derived their gold and sulfur from sedimentary sulfides by the dissolutionreprecipitation process and hydrothermal system. 15

Compared with the data of strata-hosted gold deposits (Fig. 7; Chiaradia et al., 2006; Chen et al., 2012; Chugaev et al., 2014; Groves et al., 1998), disseminated pyrites form Haoyaoerhudong deposit have higher radiogenic 207Pb and 206Pb, and lower radiogenic 208Pb,

while lead isotope composition of hydrothermal pyrites from pyrite veins and

pyrite-quartz veins is consistent with those of the Verninskoe, Sawayaerdun, and Bendigo gold deposits. On the basis of the sedimentary-diagenetic origin of disseminated pyrite (Fig. 3a), the relatively high 207Pb/204Pb and 206Pb/204Pb , low 208Pb/204Pb

ratios of disseminated pyrite exhibits the feature of Pb isotopic composition

of the Bilute Formation as far as the Bayan Obo Group. The 16HR01-5 sample of disseminated pyrite from the Haoyaoerhudong deposit shares a similar Pb isotopic composition to the hydrothermal pyrites form the Haoyaoerhudong (Fig. 7a), supporting that the host rocks are likely the source of ore-forming materials, which is also suggested by the S isotopic tracer (Fig. 7, 9) and occurrence of depyritization (Andrews, 1991). Compared with the disseminated pyrite, the changing of Pb isotope composition of hydrothermal pyrites cannot be explained by an accumulation of radiogenic Pb for these hydrothermal pyrites, because these young hydrothermal pyrites have lower radiogenic Pb than disseminate pyrites. An alternative explanation for this shifting is the fluid-rock interaction between host rocks (high 207Pb/204Pb and 206Pb/204Pb, low 208Pb/204Pb) 208Pb/204Pb

and ore-forming fluids with a low 207Pb/204Pb, 206Pb/204Pb, and high

signature. A sample of 16HR01-5 has low δ34S values and lead isotope

composition, showing this type of disseminated pyrites were formed by dissolutionrecrystallization of sedimentary-diagenetic pyrite with additional hydrothermal sulfides during main-stage gold mineralization. 16

6.3 Does magmatism facilitate gold mineralization? Although isotope age data do not provide the precise age of the formation of the Bayan Obo Group, peak metamorphism, deformation, and magmatism, as well as the hydrothermal events, the relative chronological order of the principal geological events in the area can be identified (Fig. 4). Firstly, youngest detrital zircon from the Bilute Formation with the age of 1583 Ma (Hu, 2016) and 1342 Ma-old magmatic zircon from mafic tuff and dykes (Zhou et al., 2016) constraint the age range of 1583‒1342 Ma both for the Bilute Formation and contemporaneous diagenetic disseminated pyrite. Secondly, peak metamorphism in the Haoyaoerhudong area was dated to 285 Ma based on the Sm-Nd isotope age of metamorphic garnet (Wang, 2016). The U-Pb dating of magmatic zircon shows that the large-scale late Paleozoic magmatism lasted from 290 to 268 Ma in the region (Xiao et al., 2012; Wang, 2016; Liu et al., 2019). Finally, according to the 40Ar/39Ar data of biotite from pyrite-quartz veins (Fig. 3d, 5) and the occurrence of undeformed metamorphic garnet with the age of 285 Ma, the peak deformations took place between 285 to 260 Ma. Chloritization is limited developed in dykes, while biotitization is wide developed in dykes and tails of pyrite-quartz veins, which most likely shows that the main gold mineralization occurred during post-peak metamorphism at 285-260 Ma and was subsequently overprinted by magmatismhydrothermal and deformation events. Medium-temperature and -salinity of fluid inclusions (231~333 °C, 7.04%~21.26 wt. % NaCl equiv.; Wang et al., 2015) in quartz and H-O isotopic composition (δHH2O = -96.2 ‰ ~ -82.8 ‰, δ18OH2O = 3.97‰ ~ 7.93 ‰; Wang et al., 2014) of quartz from pyrite-quartz and pyrite veins cannot play critical role 17

for identification whether the Paleozoic magmatism was a crucial factor for the gold mineralization. Relative high gold content of disseminated pyrite shows that gold was likely initially introduced during sedimentation of the organic-rich shale. The S and Pb data of pyrite from auriferous veins (pyrite veins and pyrite-quartz veins) also support that gold was likely liberated from disseminated pyrite to form Au-bearing pyrite veins and pyrite-veins during peak to post-peak metamorphism. Therefore, there is no direct evidence supporting that magmatism played a significant role in gold mineralization, which may not be necessary.

6.4 Model of gold mineralization Based on the S-Pb isotope data, Au contents of different pyrites, and Ar-Ar age of biotite, we present a genetic model for Haoyaoerhudong deposit (Fig. 10) that suggest a process similar to those described by Huston et al. (1992) and Large et al. (2007). We argue that gold was liberated from diagenetic pyrite of the stratiform sulfide bodies during deformation and metamorphism as it is documented for the similar-style gold deposits in the CAOB, Australia, and Canada. At the reduced condition, gold and other trace elements (eg., As, Pb, Zn, Se, Te) were carried by deep basinal H2S-rich fluids and were exhaled with organic-rich muds along EW-trending rift fault during the Mesoproterozoic (Fig. 10a). Gold and other trace elements were concentrated in pyrite (disseminated pyrite) being enriched during diagenesis (Fig. 10b). During metamorphism, the sedimentary rocks of Bayan Obo Group were deformed into a series of EW-treading folds and brittle fractures by the stress of subduction of the Paleo-Asian oceanic plate beneath the NCC These 18

deformations createdchannels and network for effective fluid transportation. During peak metamorphism triggered by the post-collision of the Siberian craton and NCC (Xiao et al., 2003; Xu et al., 2013), the original feeder fault was reactivated as a thrust fault (eg., Gaoletu fault; Buryak and Khmelevskaya, 1997) that deformed the Bayan Obo Group layers into the series of the NE- and NEE-treading tight folds and associated sub-faults (Fig. 2). A huge volume magma chamber was formed in? the low crust (Fig. 2 – why this reference is here?) that provided specific heat and fluid to accelerate fluid flow and depyritization, causing remobilization of gold from organic-rich host rocks into the pyrite-bearing veins. At post-peak metamorphism, Au-bearing fluid activity within the Bayan Obo Group sedimentary host may lead to further precipitation of sulfides and quartz within the ductile-brittle faults at the limb of the tight syncline.

7. Conclusions The Haoyaoerhudong gold deposit shares some similarities with other black shalehosted gold deposits in the CAOB. Based on the mineral paragenesis, crosscutting relationship between pyrite veins and pyrite-quartz veins, content of pyrite, geometry of veins, three types of pyrite were distinguished. Disseminated pyrites commonly developed in stratiform layers and are interpreted to be of diagenetic origin. Pyrite veins and pyrite-quartz veins commonly developed in the economic orebodies and are interpreted to form at the peak and post-peak metamorphism, respectively. Whereas barren quartz veins formed after the main-stage gold mineralization. The 40Ar/39Ar age of biotite from the boudinaged pyrite-bearing quartz veins is 260.1 ± 2.9 Ma, combined with other published age data and low closure temperature of mica, 19

the extensive deformation occurred at age of 267-243, while the main-stage gold mineralization took place at peak and post-peak metamorphism at the age of 285-260 Ma. The disseminated pyrite with large range of δ34S values and high radiogenic Pb isotope suggest it was formed from seawater sulfate and suffered strongly sulfur isotopic fractionation. Hydrothermal pyrites with consistent S-Pb isotopes formed by dissolution-reprecipitation of sedimentary disseminated pyrites. The mineral paragenetic, geometric, and cross-cutting relationships of different veins at Haoyaoerhudong suggest that gold was most likely introduced into pyrite, accompanying sedimentation of the organic-rich shales. Subsequently, accompanying metamorphism and deformation, gold was liberated by heat and fluids from the metamorphism, from organic-rich sediments to form Au-bearing hydrothermal fluids, which may have led to precipitation of Au-bearing sulfides in Haoyaoerhudong. Acknowledgements We greatefully acknowledge the the staff in the Institute of Geology and Geophysics, Laboratory of Mineralization and Dynamics and Nuclear Industry of China for analyses. We also thank J. P. Richards, X. Y. Meng, and J. J. Zhu for their constructive comments on the initial version. This work was supported by the Nature Science Foundation of China (41402042, 41002064); Fundamental Research Funds for the Central Universities (310827172006; 300102278402); Geological investigation work project of China Geological Survey (12120115069701).

References

20

Afanaseva, Z, Ivanova, G., Raimbault, L., 1995. Scheelite as an indicator of formation-conditions of goldsulphide mineralization: The Olimpiada Au-(Sb-W) contact metamorphic deposit, Russia. Mineral deposits: From their origin to their environmental impacts. AA Balkema, Rotterdam 835-838. Alekseyev, V.B., 1979 Succession of deformations in the Besopan suite (Paleozoic?), Kyzylkum. Geotectonics 13, 375-381. Andrews, G., 1991. A model for coal depyritization. Resources, Conservation and Recycling 5, 285-295. Beijing Jinyou geological exploration Ltd. (BJJYGE)., 2012. Detailed geological report between #6800E – #11000E exploration line and below 1436 m elevation of the Haoyaoerhudong gold deposit. Beijing 194 (in Chinese). Bureau of Geology and Mineral Resources of Inner Mongolia (BGMRIM), 1991. Regional geology of Nei Mongol (Inner Mongolia) Autonomous Region. Geol. Publ. House, Beijing 725 (in Chinese with English summary). Buryak, V.A., Khmelevskaya, N.M., 1997. Sukhoy Log, one of the greatest gold deposits in the world: Genesis, distribution patterns, prospecting criteria Vladivostok: Dalnauka 156 (in Russian). Canfield, D.E., Raiswell. R., 1999. The evolution of the sulfur cycle. American Journal of Science 299, 697-723. Cao, Y, Nie. F.J., Xiao, W, Liu, Y.F., Zhang, W.B., Wang, F.X., 2014. Metallogenic age of the Changshanhao gold deposit in Inner Mongolia, China. Acta Petrologica Sinica 30, 2092–2210 (in Chinese with English summary). Chen, H.Y., Chen, Y.J., Baker, M., 2012. Isotopic geochemistry of the Sawayaerdun orogenic-type gold deposit, Tianshan, northwest China: Implications for ore genesis and mineral exploration. Chemical Geology 310-311, 1-11. Chen, Y.J., 2000. Progress in the study of Central Asian type orogenesis-metallogenesis in Northwest China. Geological Journal of China Universities 6, 16-23 (in Chinese with English abstract). Chiaradia, M., Konopelko, D., Seltmann, R., Cliff, R.A., 2006. Lead isotope variations across terrane boundaries of the Tien Shan and Chinese Altay. Mineralium Deposita 41, 411-428.

21

Chugaev, A.V, Plotinskaya, O.Y., Chernyshev, I.V., Kotov, A.A., 2014. Lead isotope heterogeneity in sulfides from different assemblages at the Verninskoe gold deposit (Baikal-Patom Highland, Russia). Doklady Earth Sciences 457, 887-892. Goldfarb, R.J., Taylor, R.D., Collins, G.S., Goryachev, N.A., Orlandini, O.F., 2014. Phanerozoic continental growth and gold metallogeny of Asia. Gondwana Research 25, 48-102. Graupner, T, Kempe, U., Klemd, R., Schüssler, U., Spooner, E.T.C., Götze, J., Wolf, D., 2005. Two stage model for the Muruntau (Uzbekistan) high grade ore structures based on characteristics of gold, host quartz and related fluids. Neues Jahrbuch für Mineralogie - Abhandlungen, 181, 67-80. Graupner, T., Niedermann, S., Kempe, U., Klemd, R., Bechtel, A., 2006. Origin of ore fl uids in the Muruntau gold system: Constraints from noble gas, carbon isotope and halogen data: Geochimica et Cosmochimica Acta 70, 5356–5370 Groves, D.I., Goldfarb, R.J., Gebre-Mariam, M., Hagemann, S.G., Robert, F., 1998. Orogenic gold deposits: a proposed classification in the context of their crustal distribution and relationship to other gold deposit types. Ore geology reviews 13, 7-27. Hodges, K.V., Harries, W.E., Bowring, S.A., 1994. 40Ar/39Ar age gradients in micas from a hightemperature-low-pressure metamorphic terrain: Evidence for very slow cooling and implications for the interpretation of age spectra. Geology 22, 55-58. Hu, M.M., 2016. Chronology and significance of Bayan Obo Group in Siziwangqi, Inner Monglia. China University of Geosciences (Beijing), Master thesis 24-47 (in Chinese with English abstract). Huston, D.L., Bottrill, R.S., Creelman, R.A., Khin, Z., Ramsden, T.R., Rand, S.W., Gemmell, J.B., Jablonski, W., Sie, S.H., Large, R.R., 1992. Geologic and geochemical controls on the mineralogy and grain size of goldbearing phases, eastern Australian volcanic-hosted massive sulfide deposits: Economic Geology 87, 542–586. Kempe, U., Graupner, T., Seltmann, R., Boorder, H., Dolgopolova, A., Zeylmans van Emmichoven, M., 2016. The Muruntau gold deposit (Uzbekistan) – A unique ancient hydrothermal system in the southern Tien Shan. Geoscience Frontiers 7, 495-528. Kerrich, R., Goldfarb, R.J., Groves, D.I., Gorwin, S., 2000. The geodynamics of world class gold deposits: Characteristics, space-time distribution, and origins. Reviews in Economic Geology 13, 501-551. 22

Koppers, A.A.P., 2002. ArArCALC—software for 40Ar/39 Ar age calculations. Computers & Geosciences 28, 605-619. Large, R.R., Maslennikov, V.V., Robert, F., Danyushevsky, L.V., Chang, Z., 2007. Multistage sedimentary and metamorphic origin of pyrite and gold in the giant Sukhoi Log deposit, Lena gold province, Russia. Economic Geology 102, 1233-1267. Liu, C.H., Liu, F.L., 2015. The Mesoproterozoic rifting in the North China Craton: A case study for magmatism and sedimentation of the Zhaertai-Bayan Obo-Huade rift zone. Acta Petrologica Sinica 31, 3107-3128 (in Chinese with English abstract). Liu, J., Wang, C., Liu, Y., Zhang, H., Ge, J., 2019. Middle Permian Wuhaolai mafic complex in the northern North China Craton: Constraints on the subduction‐related metasomatic mantle and tectonic implication. Geological Journal, 54(4), 1834-1852. Liu, Y.F., Nie, F.J., Jiang, S., Bagas, L., Xiao, W., Cao, Y., 2016. Geology, geochronology and sulfur isotope geochemistry of the black schist-hosted Haoyaoerhudong gold deposit of Inner Mongolia, China: Implications for ore genesis. Ore Geology Reviews 73, 253-269. Mikucki, E.J., Ridley, J.R., 1993. The hydrothermal fluid of Archean lode-gold deposits at different metamorphic grades: Compositional constraints from ore and wallrock alteration assemblages. Mineralium Deposita 28, 469-481. Nozhkin, AD, Borisenko, AS, Nevol’ko, P.A., 2011. Stages of Late Proterozoic magmatism and periods of Au mineralization in the Yenisei Ridge. Russian Geology and Geophysics 52(1), 124-143. Ohmoto, H., 1986. Stable isotope geochemistry of ore deposits. Reviews in Mineralogy 16, 491–560. Ohmoto, H., Rye, R.O., 1979. Isotopes of sulfur and carbon, in Barnes, HL, ed., Geochemistry of hydrothermal ore deposits: New York, Wiley Interscience, 509-567. Shen, Y.A., Knoll, A.H., Walter, M.R., 2003. Evidence for low sulphate and anoxia in a mid-Proterozoic marine basin. Nature 423, 632. Steiger, R.H., Jäger, E., 1977. Subcommission on geochronology: convention on the use of decay constants in geo-and cosmochronology. Earth and Planetary Science Letters 36, 359-362. Walker, R.N., Gulson, B., Smith, J., 1983. The Coxco Deposit; a Proterozoic mississippi valley-type deposit in the McArthur River District, Northern Territory, Australia. Economic Geology 78, 214-249. 23

Wang D.Q., Wang, J.G., Wang Y.Z., Liu J.C., Zhang H.D., 2015. Study on fluid inclusions and genetic type of Haoyaoerhudong gold deposit, Inner Mongolia. Journal of Geomechanics, 21, 517-526 (in Chinese with English abstract). Wang, J.P., Liu, J.J., Peng, R.M., Liu, Z.J., Zhao, B.S., Li, Z., Wang, Y.F., Liu, C.H., 2014. Gold mineralization in Proterozoic black shales: example from the Haoyaoerhudong gold deposit, northern margin of the North China Craton Ore Geology Reviews 63, 150-159 Wang, X., 2016. Geological, geochemical characteristics and geochronology of gabbro rocks in the Haoyaoerhudong gold deposit, Inner Mongolia, China. China University of Geosciences (Beijing), Master thesis, 22-41 (in Chinese with English abstract). Wilde, A.R., Layer, P., Mernagh, T., Foster, J., 2001. The giant Muruntau gold deposit: Geologic, geochronologic, and fl uid inclusion constraints on ore genesis: Economic Geology and the Bulletin of the Society of Economic Geologists 96, 633-644. Xiao, W.J., Nie, F.J., Liu, Y.F., Liu, Y., 2012. Isotope geochronology study of the granitoid intrusions in the Changshanhao gold deposit and its geological implications. Acta Petrol. Sin. 28, 535-543 (In Chinese with English abstract). Xiao, W.J., Windley, B.F., Hao, J., Zhai, M.G., 2003. Accretion leading to collision and the Permian Solonker suture, Inner Mongolia, China: termination of the central Asian orogenic belt. Tectonics 22, 1069. Xiao, W.J., Windley, B.F., Sun, S., Li, J.L., Huang, B., Han, C.M., Yuan, C., Sun, M., Chen, H., 2015. A tale of amalgamation of three Permo-Triassic collage systems in Central Asia: oroclines, sutures, and terminal accretion. Annual review of earth and planetary sciences, 43, 477-507. Xu, B., Charvet, J., Chen, Y., Zhao, P., Shi, G.Z., 2013. Middle Paleozoic convergent orogenic belts in western Inner Mongolia (China): framework, kinematics, geochronology and implications for tectonic evolution of the Central Asian Orogenic Belt. Gondwana Res. 23, 1342-1364. Yakubchuk, A., Stein, H., Wilde, A., 2014. Results of pilot Re-Os dating of sulfides from the Sukhoi Log and Olympiada orogenic gold deposits, Russia. Ore Geology Reviews 59, 21-28. York, D., 1969. Least squares fitting of a straight line with correlated errors. Earth Planet. Sci. Lett. 5, 320-324. 24

Yudovskaya, M.A., Distler, V.V., Rodionov, N.V., Mokhov, A.V., Antonov, A.V., Sergeev, S.A., 2011. Relationship between metamorphism and ore formation at the Sukhoi Log gold deposit hosted in black slates from the data of U-Th-Pb isotopic SHRIMP-dating of accessory minerals. Geology of Ore Deposits 53, 27-57. Zhai, M.G., Guo, J.H., Zhao, T.P., 2001. Study advances of Neoarchaean–Paleoproterozoic tectonic evolution in the North China Plate. Prog. Precambrian Res. 24.17-27 (In Chinese with English abstract). Zhang, G.Z., Xue, C.J., Chi, G.X., Liu, J.Y., Zhao, X.B., Zu, B., Zhao, Y., 2017. Multiple-stage mineralization in the Sawayaerdun orogenic gold deposit, western Tianshan, Xinjiang: Constraints from paragenesis, EMPA analyses, Re-Os dating of pyrite (arsenopyrite) and U–Pb dating of zircon from the host rocks. Ore Geology Reviews 81, 326-341. Zhang, H.D., Liu, J.C., Santosh, M., Tao, N., Zhou, Q.J., Hu, B., 2017. Ultra-depleted peridotite xenoliths in the Northern Taihang Mountains: Implications for the nature of the lithospheric mantle beneath the North China Craton. Gondwana Research, 48, 72-85. Zhang, H.D., Zhao, Z.Q., Li, Q., Gao, H.L., Wang, D.Q., Liu, J.C., Xue, C.J., Wu, D., Yuan, K.J., 2014. The geological characteristics and metalallogenic ore-controlling tectonic of Haoyaoerhudong gold deposit in Inner Mongolian. Earth Science Frontiers 24, 122-130 (in Chinese with English abstract). Zhao, B.S., Liu, J.J., Wang, J.P., ZHAI, Y.S., Peng, R.M., Wang, S.G., Shen, C.L., 2011. Geologicalgeochemical characteristics and genesis of Changshanhao gold deposit in Inner Mongolia, China. Geoscience 25(6), 1077-1087 (in Chinese with English abstract). Zhao, G.C., Zhai, M.G., 2013. Lithotectonic elements of Precambrian basement in the North China Plate: review and tectonic implications. Gondwana Researcg. 23, 1207-1240. Zhou, Z.G., Wang, G.S., Zhang, D., Gu, Y.C., Zhu, W.P., Liu, C.F., Zhao, X.Q., Hu, M.M., 2016. Zircon ages of gabbros in the Siziwangqi, Inner Mongolia and its constrain on the formation time of the Bayan Obo Group. Acta Petrologica Sinnica 32, 1809-1822 (in Chinese with English abstract).

25

Table 1 40Ar/39Ar data of biotite 16HR1-1 sample of the pyrite-quartz veins from the Haoyaoerhudong gold deposit Stage

T (°C)

1

400

193.3

121.20

0.5612

27.50

14.22

0.29

190.85± 55.4

2

500

47.9

19.33

0.0419

35.54

74.15

2.07

243.04± 6.6

3

600

50.8

29.32

0.0476

36.70

72.31

3.29

250.48± 9.3

4

700

44.9

2.039

0.0221

38.36

85.47

19.50

261.01± 11.2

5

800

41.8

2.696

0.0132

37.93

90.66

32.72

258.32± 2.9

6

900

55.3

11.85

0.0582

38.06

68.88

35.57

259.12± 6.6

7

1000

40.1

1.709

0.0060

38.34

95.55

55.95

260.90± 3.1

8

1100

42.3

6.586

0.0154

37.71

89.21

61.10

256.90± 3.6

9

1200

40.5

0.905

0.0068

38.53

95.03

97.32

262.09± 2.6

10

1350

40.2

13.32

0.0059

38.47

95.68

100.00

261.74± 4.8

40

Ar/39Ar

37

Ar/39Ar

36

Ar/39Ar

40

Ar*/39Ark

40

Ar* (%)

26

39

Ar (%)

Age (Ma)

Table 2 Sulfur and lead isotopic ratios of sulfides from the Haoyaoerhudong gold deposit Sample No.

Type of ores

Minerals

δ34S

206

Pb/204Pb

207

Pb/204Pb

208

Pb/204Pb

Reference This study

Sedimentary-diagenesis: 16HR01-1

15.02

20.371

15.825

37.964

16HR01-2

DS

Py

17.54

20.408

15.772

37.813

16HR01-3

17.53

20.43

15.778

37.862

16HR01-4

17.85

20.470

15.864

38.222

16HR01-5

16.95

19.144

15.681

37.502

16HR01-6

-39.40

21.892

15.705

38.925

16HR01-7

-39.26

Post-peak metamorphism: E14

PoVs

Po

ZK13

10.55

ZK21

13.5

ZK23

14.15

ZK25

14.25

ZK27

14.17

ZK29

14.71

ZK31

13.9

ZK33

13.41

E42

Wang et al., (2014)

12.38

PQVs

Py

12.06

Wang et al., (2014)

W7

11.65

16HR02-2

14.3

18.790

15.684

38.983

16HR02-3

12.2

18.794

15.674

38.924

18.566

15.645

38.961

18.922

15.674

38.979

06SCH-1 06SCH-2

Asp

E12

Py

10.53

W12

13.4

ZK5

12.49

ZK7

14.08

ZK15

14.26

ZK17

14.45

ZK19

14.77

ZK35

13.83

SCH-B3

6.8

SCH-B5

13.2

SCH-B7

13.4

SCH-B8 W23

This study Zhao et al., (2011) Wang et al., (2014)

Liu et al., (2016)

11.5 PVs

16.47

W25

10.15

ZK9

13.48

ZK11

12.66

SCH-A1

12.4

SCH-A2

13.1

SCH-A4

10.8

Wang et al., (2014)

Liu et al., (2016)

DS-Disseminated pyrite; PoVs-Pyrrhotite veins; PVs-Pyrite veins; PQVs=Pyrite-quartz veins

27

Figures

Fig. 1 Fig. 1 (a) Simplified tectonic map of the Central Asian Orogenic Belt (modified after Jahn et al., 2000), in which the position of gold deposits hosted in the black shales after Chen et al., 2012, Yudovskaya et al., 2016 and Liu et al., 2016. (b) Regional geological map of the north of North China Craton, in which the position of Phanerozoic intrusions after Sheng et al., 2004 and, 1:250,000 geologic maps, respectively. Gold deposits: 1-Kokpatas; 2-Muruntau; 3-Daugytau; 4-Zarmitan; 5-Taror; 6-Taldybulak; 7Kumtor; 8-Sawayaerdun; 9-Olimpiada; 10-Sovetskoe; 11-Eldorado; 12-Veduga; 13Vasievskoe; 14-Samsonovskoe; 15-Zun-Kholba; 16-Mukodek; 17-Sukhoi Log; 18Vysochaishee, 19-Verninskoe; 20-Uryakh; 21-Irokinda; 22-Nazarovskoe; 23-Saiwusu; 24-Bilute; 25-Haoraoerhudong; 26-Zhulazhaga. Abbreviation: CAOB-Central Asian Orogenic Belt; NSGL-North-South gravity Lineament; NCC-North China Craton.

Fig. 2 (a) Sketch geological map of the margin of North China Craton gold province; (b) simplified geological map of the Haoyaoerhudong gold deposit (modified after BGMRIM, 1991).

Fig. 3 Main styles of sulfide mineralization in the Haoyaoerhudong gold deposit. adisseminated pyrite in the oganic-rich black slate; b-pyrite-quartz veins; c-bedding28

parallel pyrite veins and pyrite-quartz veins; d-16HR-02-2 sample of pyrite-quartz veins, some biotite grains occur at the trail of boudinaged vein; e-the latest barren quartz veins; f-pyrite from pyrite veins; g-pyrite with some originated garnet inclusions; h-intergrowth of pyrite and garnet in pyrite veins; i-pyrite veins were cut by low-angle pyrite-quartz veins; j-metamorphic garnet was cut by pyrite-quartz veins; k-cataclastic garnet inclusions within pyrite-quartz veins; l-native gold occurred at garnet fracture fills, boundary of pyrite and quartz, and as inclusions within quartz. Abbreviation: Py-pyrite; Grt-garnet; Q-quartz; Au-gold.

Fig. 4 Paragenetic chart illustrating relative timing of different types of pyrite, arsenopyrite, pyrrhotite and chalcopyrite.

Fig. 5 40Ar-39Ar stage heating spectra (a) and 39Ar-40Ar vs. 36Ar-40Ar isochron diagram of biotite from 16HR02-2 sample of pyrite-quartz veins.

Fig. 6 Histogram of δ34S values for pyrite and pyrrhotite from the disseminated pyrite, pyrrhotite veins, pyrite veins, and pyrite-quartz veins.

29

Fig. 7 Pb isotopic compositions of pyrite from the disseminated pyrite and pyrite-quartz veins. The evoluviton lines for major geological unites are from Zartman and Haines (1988). Ranges of Pb isotopes of the major deposits in the southern Tianshan are from Chiaradia et al. (2006). Lead data of Verninskoe, Sawayaerdun and Bendigo gold deposits are from Chugaev et al. (2014), Chen et al. (2012) and Bierlein and McNaughton (1998), respectively.

Fig. 8 Comparison of 39Ar-40Ar biotite age of biotite from sample of 16HR02-2 to existing ages for the Haoyaoerhudong gold deposit. The references for age data are given in the figure.

Fig. 9 Comparison of δ34S values of sulfides from Haoyaoerhudong to existing data of other gold deposits and black shales. References for data are shown in the figure.

Fig. 10 Genetic model for the evolution of the Haoyaoerhudong gold deposit. a. gold and arsenic, as part of the fluvial detrital input, initially concentrated in organic muds on the sea floor; b. gold and arsenic were liberated from the organometallic complexes, into the reprecipitated pyrite during diagenesis; c. during metamorphism, the sedimentary rocks of Bayan Obo

Group were deformed into a series of EW-treading folds and brittle fractures. A huge volume magma chamber was formed and provided specific heat and fluid to accelerate 30

fluid flow, causing remobilization of gold from disseminated pyrite into the pyrite-bearing veins at intersection of shear zone and tight cyncline.

31

Highlights  Three types of auriferous pyrites have been defined;  Major gold mineralization occurred at 285-260 Ma;  Gold was liberated from carbonaceous sediments, and enriched during metamorphism.

32

33

34

35

36

37

38

39

40

41

42

43