The Beiminghe Skarn Iron Deposit, Eastern China: Geochronology, Isotope Geochemistry and Implications for the Destruction of the North China Craton

Lithos 156–159 (2013) 218–229

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The Beiminghe skarn iron deposit, eastern China: Geochronology, isotope geochemistry and implications for the destruction of the North China Craton

Jun-Feng Shen a,⁎, M. Santosh a,b, Sheng-Rong Li a, Hua-Feng Zhang a, Na Yin a, Guo-Cheng Dong a, Yan-Juan Wang a, Guang-Gang Ma a, Hong-Jun Yu a a School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China b Division of Interdisciplinary Science, Faculty of Science, Kochi University, Kochi 780-8520, Japan article info abstract

Article history: The Beiminghe (BMH) iron ore in the southern part of the Taihang Mountain (TM), Hebei province, is one of the Received 29 May 2012 largest skarn iron deposits in China. Here we report phlogopite 40Ar–39Ar and zircon U–Pb age data, as well as Accepted 6 November 2012 sulfur, lead, and He–Ar isotope geochemistry of pyrite from the ores and skarnitized rocks in the deposit in an Available online 13 November 2012 attempt to constrain the timing and mechanism of formation of the mineralization. The phlogopite 40Ar–39Ar and LA-ICP-MS zircon U–Pb data show markedly consistent ages constraining the timing of ore formation as Keywords: 136–137 Ma. The presence of several inherited zircons with late Archean or Paleoproterozoic ages indicates Skarn iron deposit δ34 Geochronology the participation of the basement rocks during the ore-forming process. The Svaluesofpyritefromthe 206 204 207 204 208 204 Isotope geochemistry ores range from 12.2 to 16.5‰, with Pb/ Pb=17.84–18.79, Pb/ Pb=15.46–15.62, and Pb/ Pb= South Taihang Mountain 37.93–39.75, suggesting that continental crust is the major contributor. This is further confirmed by the He–Ar North China Craton isotope data (3He/4He=0.0648–0.1886 Ra, mean 0.1237Ra; 40Ar/36Ar=311.7–22909.4; and 40Ar⁎/4He= 0.036–0.421). The Mesozoic magmatism and metallogeny in the BMH correlate well with the peak event of lithospheric thinning and destruction of the North China Craton during this process, the early Precambrian lower crustal rocks in the region were re-melted through underplating of mantle magmas, leading to the formation of the Beiminghe monzodioritic pluton. Minor mantle input occurred during the evolution of the monzodiorite magma, which scavenged the ore-forming materials from the lower crust. Interaction of the magmas and fluids with the surrounding rocks resulted in the formation of the Beiminghe skarn iron deposits. The magmatism and metallogeny in the Taihang Mountain are signatures of the extensive craton destruction and lithospheric thinning in the eastern part of the North China Craton during Mesozoic, probably associated with Pacific slab subduction. © 2012 Elsevier B.V. All rights reserved.

1. Introduction In this study, we present new geochronological data and mineral isotopic compositions of pyrites from ores and country rocks from the The Beiminghe (BMH) iron deposit is located at the southern part of BMH iron deposit. Based on the results, we evaluate the age of ore the Taihang Mountain (TM), ca. 10 km from northwest of the Wu'an formation, the source of ore-forming materials, and the geodynamic City in the Hebei province of China. Nearly one hundred skarn-type setting of ore genesis. iron deposits termed as “mineralizing districts” with comparable features have been recognized, which are described in Chinese literature 2. Geological setting as the Handan–Xingtai or Han-Xing skarn iron deposits (Feng, 1998; Zheng et al., 2007a, 2007b, 2007c). The Han-Xing skarn iron deposits 2.1. Regional geology have been widely accepted as products of contact metamorphism between the Mesozoic pluton and the surrounding Ordovician carbon- The major lithological units of the TM are composed of early Pre- ate sedimentary strata (Feng, 1998; Niu et al., 1995; Zhang et al., cambrian metamorphic rocks, Phanerozoic sedimentary units and 2009; Zheng et al., 2007a, 2007b, 2007c). Although some previous stud- Mesozoic magmatic intrusions (Li et al., 2012). The basement mainly ies (Chen et al., 2005a; Zheng et al., 2007a) have attempted to propose consists of TTG (tonalite–trondhjemite–granodiorite) gneisses and am- the ore-forming model, no detailed information is available on the phibolites, the protoliths of which formed during Meso-Neoarchean, timing and mechanism of ore formation in this area. and were later metamorphosed during late Paleoproterozoic, associated with the ﬁnal cratonization of the NCC (Geng et al., 2012; Li et al., 2012; ⁎ Corresponding author. Tel.: +86 10 8232 1732. Liu et al., 2011; Zhai and Santosh, 2011; Zhao et al., 2000). The skarn E-mail address: [email protected] (J.-F. Shen). iron deposits of MBH are located within the eastern periphery of the

Central Orogenic Belt, also termed as the Trans-North China Orogen features of the ore bodies are visible near their edges, with both inward (TNCO) adjacent to the western margin of the Eastern Block of the and outward contact zones. Field studies reveal a close relationship be- NCC (Fig. 1A,B, Xu et al., 2009b, 2009c; Zhai and Santosh, 2011; Zhao tween the diorite, which at some places grades to diorite porphyrite or et al., 2001; Zhu et al., 2011). Regionally, the sedimentary rocks in this monzodiorite, and the formation of the skarn and ores. We show in area are dominated by Cambrian–Ordovician carbonates in the western Fig. 3 a horizontal level cross section at 110 m below the surface. part, and Carboniferous–Permian clastic rocks in the eastern part Alteration zones are clearly developed at the contact of the intrusive (Fig. 2). with the surrounding limestone, and these zones can be divided into al- The Mesozoic magmatic rocks intruding the Precambrian basement tered diorite zone, the endoskarn zone, the sulfide–magnetite zone, the as well as the younger sedimentary cover belong to a major NNE- exoskarn zone and the marble zone. In general, the endoskarn zone trending magmatic belt (Li et al., 2012). Several batholiths, stocks and shows a wider distribution as compared to the exoskarn zone which sills mainly composed of intermediate calc-alkaline rocks have been is narrow. The diopside-type skarn dominates the BMH iron deposit, identified (Chen et al., 2006; Li et al., 2012; Liu et al., 2009; Peng et al., with occasional garnet-type. The skarn mineral compositions basically 2004; Zheng et al., 2007a, 2007b; Zhou and Chen, 2005). include diopside, tremolite, actinolite, phlogopite, humite, serpentine, garnet, and epidote. The marble at the external contact zone often has 2.2. Ore geology been brecciated or altered by chlorite. The main metallic minerals are magnetite, pyrite, and a small amount of hematite, chalcopyrite, The BMH skarn iron deposit belongs to the Wu'an iron cluster pyrrhotine, and nickeliferous magnetite. The content of magnetite in region, composed of several iron deposits to the west of the Wu'an the ores varies from 50 to 80%. The subhedral to anhedral coarse mag- city, surrounding the major pluton (Fig. 2). The dominant basement netite grains range from 0.15 to 0.4 mm in size. Under the influence of rocks in this region are the Archean Zanhuang Complex, intruded by late hydrothermal alteration, the magnetite grains are replaced by py- Mesozoic intermediate plutons comprising mostly of monzonite, rite, calcite, and hematite, with the relict texture preserved in many monzodiorite, diorite, and quartz–diorite (Chen et al., 2009). The gene- cases. The pyrite is subhedral to idiomorphic and generally ranges in sis of these intrusions has been linked to the subduction of the Paleo- content from 1 to 10%, and sometimes up to 25–50% in some domains. Pacificplate(Zheng et al., 2007c). The major sedimentary unit in the mine is the Majiagou limestone, deposited during Middle Ordovician. 3. Sampling and analytical methods The main ore-controlling structure in the mine is an anticline trending NW. The ore bodies typically occur at the contact zones of 3.1. Sampling the dioritic intrusion and the Majiagou limestone. From the contact zone profile, the shape of the ore bodies is reconstructed as complex The phlogopite-bearing sample for 40Ar–39Ar dating was collected lenses with end-to-end discontinuity. The serrated and interspersed from the exoskarn zone at a depth of −230 m in the mine. Here,

Fig. 1. The location of Beiminghe iron skarn deposit at the eastern periphery of the Trans-North China Orogen. The inset ﬁgure shows the major tectonic units of the North China Craton. WB — Western Block. EB — Eastern lock. TNCO — Trans-North China Orogen. Modiﬁed after Xu et al. (2009a), Zhai and Santosh (2011) and Zhao et al. (2001). 220 J.-F. Shen et al. / Lithos 156–159 (2013) 218–229

Fig. 2. Geological map and distribution of iron deposits in Handan district, Hebei province. After Zheng et al. (2007a). grey-green phlogopite-rich vein occurs in the skarn (Fig. 4a), and the assemblage can be divided into two stages: stage 1 where diopside mineral shows intergrowth with magnetite (Fig. 4b). occurs as small grains and stage 2 where it occurs as euhedral coarse Two representative samples of the magmatic intrusive were select- grains (Fig. 5d). Calcite veins are partly developed, occasionally in ed for zircon separation and U–Pb dating: one from 110 m depth (sam- association with disseminated pyrite and chalcopyrite. ple B110-9-2), and the other from 245 m depth (sample B245-1). Sample B110-9-2 was collected from weakly altered diorite 3.2. Analytical methods porphyrite, away from the ore body in the main tunnel. The sample exhibits porphyritic texture with phenocrysts of euhedral plagioclase 3.2.1. 40Ar/39Ar dating (Fig. 5a) and minor hornblende. Taxitic and striped texture are also The skarn containing phlogopite grains were crushed and sieved, visible at places. The plagioclase shows marginal albitization and and purified phlogopite sample was obtained using the conventional sericitic alteration. Albite also occurs as coarse tabular and columnar techniques of magnetic separators and heavy liquids. The phlogopite crystals. The major mineral assemblage in this sample is plagioclase for 40Ar/39Ar analysis was purified to 99%, and then ultrasonically (ca. 90%) and hornblende (ca. 10%), with occasional quartz and calcite cleaned in distilled water and ethanol. veins (Fig. 5b). The 40Ar/39Ar dating of phlogopite was carried out using stepwise Sample B245-1 was taken from the skarnitized diorite close to the incremental heating method at the Institute of Geology, Chinese Acade- ore body (Fig. 5c). The sample is intensely altered, with hydrothermal my of Geological Sciences (CAGS). Instrumental conditions and analyti- calcite veins visible in the hand specimens, and some of the domains cal details are as described by Chen et al. (2002). The purified samples are cracked and brecciated. The breccias are grey to black with grains were wrapped in aluminum foil and loaded into a tube of aluminum 6–8 mm across set within ferruginous cement. Under the microscope, foil. Each tube contains 2–3 monitors (an internal standard: Fangshan the intense alteration zone shows abundant diopside. The alternation biotite, 132.7±1.2 Ma, Chen et al., 2002) in between the minerals. A

Fig. 3. The horizontal level cross section geological map at height of −110 m. J.-F. Shen et al. / Lithos 156–159 (2013) 218–229 221

Fig. 4. Field and thin section photographs of phlogopite and associated rocks and minerals from the Beiminghe ore deposit. a. Phlogopite in the exoskarn zone, from the mine tunnel. b. Phlogopite associated with diopside and magnetite. The phlogopites were collected for 40Ar–39Ar dating.

number of such tubes were sealed into quartz vial and irradiated for analyze Ar isotopic ratios. Measured isotopic ratios were corrected for 2941 min in the nuclear reactor at the Chinese Academy of Atomic En- mass discrimination, atmospheric Ar component, procedural blanks ergy. The reactor delivers a neutron flux of about 6.0×1012 ncm−2 s−1; and mass interference induced by irradiation. The blanks of m/e of the integrated neutron flux is about 1.15×1018 ncm−2. The irradiated 40Ar, 39Ar, 37Ar and 36Ar are less than 6×10−15,4×10−16,8×10−17 samples and monitors were loaded into the vacuum extraction system and 2×10−17 mol, respectively. The correction factors of interfering and baked for 48 h at 120–150 °C. The Ar extraction system comprises isotopes produced during irradiation were determined by the analysis 40 39 an electron bombardment heated furnace in which the samples are of irradiated K2SO4 and CaF4 pure salts. The values are: ( Ar/ Ar)k = 36 37 39 37 heated under vacuum. The duration is 30 min for heating–extraction 0.004782; ( Ar/ Ar)Ca=0.000240; and ( Ar/ Ar)Ca =0.000806. at each temperature increment, and 30 min for purification. The puri- Ages were calculated using the ISOPLOT program (version 2.49, fied Ar was trapped in activated charcoal finger at liquid–nitrogen tem- Ludwig, 2001). The K decay constant used was 0.5543 Ga−1.All37Ar perature, and then released into the MM-1200B Mass Spectrometer to were corrected for radiogenic decay (half-life 35.1 days). Uncertainties

Fig. 5. Field photograph and photomicrographs of the samples collected for zircon U–Pb dating. a. Location of diorite porphyrite sample B 110-9-2 inside mine tunnel. b. Photomicrograph (crossed nicols) of the sample. c. Location of skarnitized diorite sample B245-1 inside mine tunnel. d. Photomicrograph (parallel nicols) of the sample. Abbreviations. Hbl — hornblende; Pl — plagioclase; Di — diopside; Cal — calcite. 222 J.-F. Shen et al. / Lithos 156–159 (2013) 218–229 on the apparent ages on each step are quoted at the 1σ level, but 4. Results weighted mean plateau ages and isochron ages are given at the 2σ level. 4.1. 39Ar–40Ar age

3.2.2. Zircon U–Pb dating The stepwise incremental heating method depends on the apparent Separation of zircon grains was performed using the conventional age to derive credible data (Chen et al., 2005b). If the 39Ar release is over techniques including heavy liquids, magnetic separator and hand- 50% during more than three heating steps, and the plateau age of each picking under a binocular microscope fitted with a UV light. Zircon step is less than 2σ, the corresponding plateau age is considered as grains were mounted in epoxy disks, polished to expose the authentic (Dalrymple and Lanphere, 1974). Due to argon loss induced half-sections of grains, and then coated with gold. by mineral margin or lattice defects, abnormal values could result in Prior to the U–Th–Pb dating, the internal textures of the zircons either low or high temperature step. Therefore, the medium–high tem- were studied by transmitted and reflected lights microscope, and perature step most likely represents the real age (Chen et al., 2005b). cathodoluminescence (CL) technique using a CAMECA SX51 at the As shown in Table 1 and Fig. 6, the sample heating procedure is Key Laboratory of Metallogeny and Mineral Assessment, Institute of divided into 10 steps (700–1400 °C). An unstable plateau appears at Mineral Resources, CAGS. The procedures are the same as those de- the initial low temperature (700–940 °C), with apparent age ranging scribed by Hou et al. (2009). from 27.8 to 153.6 Ma. However, the deviation of plateau data calculat- LA-ICP-MS isotope U–Pb dating was performed by the conventional ed from 700 °C to 860 °C is over 2σ,withlow39Ar 22.86%. These could isotope dilution technique of single zircons after air abrasion. Fraction be initiated by little argon loss of mineral margin (Chen et al., 2005b), size varied somewhat depending on U content and grain size of zircon. and may have no relation with the actual ore-forming age. Zircon digestion, separation of U and Pb, and isotope dilution mass spec- Over 1100 °C, the 39Ar release clearly decreases. Although there is a trometry using a 205Pb–235U enriched tracer solution were made fluctuation from 1220 to 1400 °C, considering the deviation of plateau following the procedure described by Krogh (1982). The total proce- data to be over 2σ, the data might not represent the true crystallization dure blanks for Pb and U are less than 0.05 and 0.002 ng, respectively. age of phlogopite. Only plateau data calculated from the 980 to 1060 °C Isotope ratios are measured by single collector peak jumping VG-354 step tends to be continuous and steady, and represents 53% of the 39Ar mass spectrometer equipped with a Daly-type detector operating in released. The plateau age data calculated from this thermal step shows ion-counting mode at Tianjin Institute of Geology and Mineral 137±2 Ma, which we consider to represent the crystallization age of Resources. Errors to the atomic and isotopic ratios are quoted at the phlogopite in this ore deposit. 2σ confidence level. Common Pb corrections are made by using the Furthermore, ignoring the two abnormal values (27.8 Ma at 700 °C model Pb composition of Stacey and Kramers (1975). The age calcula- and 257.4 Ma at 1400 °C, respectively), the correlation of other 9 data tions were performed by means of the ISOPLOT program of Ludwig is R2 =0.997, with a mean age of 137.5 Ma, which is close to the plateau (1994). age 137±2 Ma obtained from the 980 to 1060 °C step. From the correlation of 40Ar/36Ar and 39Ar/36Ar, we obtain the initial value of 40Ar/36Ar for sample at 298.6, which is similar to the standard value of atmo- 3.2.3. S/Pb/He–Ar isotopic composition spheric argon 295.5. This further confirms that the age of 137 Ma reli- The sample preparation for sulfur isotope analyses followed the pro- ably represents the crystallization age of phlogopite. cedures outlined by Glesemann et al. (1994) and the measurement was Since the field studies and petrography clearly indicate a cogenetic performed on a MAT-251EM mass spectrometer at the Stable Isotope nature of the phlogopite and magnetite, the age obtained from phlogo- Laboratory of CAGS. Data are reported with an accuracy of ±0.2‰ (2σ). pite can be taken as the timing of mineralization in the BMH iron The Pb isotope analysis was performed at the CAGS, and the proce- deposit. dure adopted is as follows. The whole-rock Pb was separated by anion – exchange on HCl Br columns. Within the analytical period, 30 measure- Table 1 206 204 ments of NBS981 gave average values of Pb/ Pb=16.937±1 (1σ), Ar isotopic data for phlogopite in BMH iron deposit. 207Pb/204Pb=15.491±1, and 208Pb/204Pb=36.696±1. The BCR-2 T (°C) (40Ar/39Ar) (36Ar/39Ar) (37Ar/39Ar) (38Ar/39Ar) 40Ar(%) standard gave 206Pb/204Pb=18.742±1 (1σ), 207Pb/204Pb=15.620± m m m m 1, and 208Pb/204Pb=38.705±1. Total procedural Pb blanks were in 700 57.0512 0.1848 0.459 0.1766 4.35 the range of 0.1–0.3 ng. 800 117.0246 0.3551 0.0957 0.1247 10.33 – 860 53.1192 0.1331 0 0.0504 25.97 He Ar gas isotope analyses were performed with a MM5400 gases 940 46.1235 0.1081 0.0501 0.0451 30.77 mass spectrometer (Micromass, GB) at Lanzhou Center for Oil and Gas 980 16.4144 0.0123 0 0.0023 77.83 Resources, Institute of Geology and Geophysics, China Academy of 1020 16.1043 0.0121 0.0156 0.023 77.76 1060 16.0667 0.0119 0 0.0232 78.08 Sciences. Experiment was done at electric current It4 =800 μA, It40 = μ 1100 15.4623 0.0112 0 0.0222 78.58 200 A, and high voltage 9.000 kV. All weighed samples of pyrite for 1160 16.3979 0.0147 0.0082 0.0223 73.48 analysis were packed into aluminum foil and shifted to the crucible 1220 18.4316 0.0225 0 0.0242 63.84 for gas extraction under high vacuum conditions. When a pressure 1400 49.714 0.0853 0 0.0554 49.26 lower than 1×10−5 Pa was attained, the samples were heated at F 39Ar (×10−14 mol) 39Ar (Cum.) (%) Age (Ma) ±1 Ma 130 °C for at least 10 h to eliminate secondary fluid inclusions and trace gases occurring in cleavages or fractures in the crusts. The samples 2.4817 0.42 2.52 27.8 2 12.0907 0.32 4.43 131.7 5 were then fused at high temperatures of up to 1600 °C, and the released 13.794 0.43 6.99 149.5 2.4 fi gases were puri ed through activated charcoal traps at the liquid nitro- 14.1919 2.65 22.87 153.6 1.5 gen temperature to separate He and Ar from Ne+Kr+Xe for He and Ar 12.7754 2.69 39.05 138.9 1.4 analyses on the mass spectrometer, respectively. The minimum heat 12.5229 3.91 62.51 136.2 1.3 blanks for the MM5400 mass spectrometer at 1600 °C are: 4He= 12.5442 2.35 76.61 136.4 1.3 −14 20 −14 40 −13 12.1501 1.85 87.75 132.3 1.3 1.10×10 mol; Ne=1.82×10 mol; Ar=6.21×10 mol; 12.0489 1.68 97.83 131.2 1.3 84 −16 132 −18 Kr=1.37×10 mol; and Xe=5.65×10 mol. The standard 11.7674 0.3 99.62 128.3 2.6 for normalizing the analytical results is air in Lanzhou (AIRLZ2003). De- 24.4915 0.06 100 257.4 7.7 40 ⁎ 39 tailed sample preparation and measurement procedures followed those Note: W=30.56 mg, J=0.006263, F= Ar / Ar, is the ratio of radiogenic Argon40 in He et al. (2011) and Ye et al. (2001, 2007). and Argon39. J.-F. Shen et al. / Lithos 156–159 (2013) 218–229 223

The second group consists of 5 data with ages ranging from 2500 to 2786 Ma. These belong to the inherited zircons with clear dissolution features and blurred growth edges. We consider these ages to represent the inherited zircons, derived from a Neoarchean magmatic protolith in the basement. The third group is defined by 5 data, with ages ranging from 2216 to 2408 Ma. This group is identical to the previous group in morphology and internal structure, and represents inherited zircons from a Paleoproterozoic magmatic source. The fourth group, represented by only 2 results, defines ages of 1553 and 1898 Ma. These spots are from structureless inherited domains and therefore represent Paleo- to Mesoproterozoic metamorphic zircons. The analytical data from sample B245-1 shown in Table 3 spread along the Concordia, with only few deviations. The data define a concor- Fig. 6. Plateau age plot of phlogopite in BMH iron deposit. dant age at 2482±20 Ma (Fig. 8b). The majority of data define Neoarchean and Paleoproterozoic ages, clearly indicating closely comparable with those from sample B110-9-2. 4.2. Zircon U–Pb age 4.3. Mineral isotopic compositions 4.2.1. Zircon CL image Most zircon grains from the diorite porphyrite are short columnar or 4.3.1. Sulfur isotope anhedral ellipsoidal grains. Some grains show anhedral morphology, Previous studies (Liu and Shi, 1998) have reported δ34Sfromthe whereas few others are well-formed idiomorphic crystals. As seen skarn iron ore in Han-Xing which shows a range of 7.27 to 16.36‰, from Fig. 7 many of the zircons display clear core–rim structure. Some values that are higher than the range of meteorite S. In the present of the grains are cracked and contain fractures. study, the δ34S values of pyrite from the BMH iron deposit show a Zircon grains in our sample can be divided into two types in terms of range of 12.2 to 16.5‰ (Table 4). Although the range is relatively morphology and internal structure. The first type is inherited zircons, narrow, the values do not correspond with that of meteorite S isotope mostly forming the core domains and is white or grayish under the (Fig. 9, where the data from Beiminghe iron are plotted together with CL. Some of these grains show clear zoning. Based on the presence or those reported by Zhang et al., 2009 and Zheng, 2007d). Thus, the absence of zoning, the inherited zircons can be further divided into δ34S values of the BMH iron deposit do not provide any clear mantle S magmatic zircons with bands and structure metamorphic zircons. signature, and instead indicate the involvement of crustal materials in Among these, some grains show intense etching and inhomogeneous the metallogenic process. optical characteristics. The second type is neo-formed zircons, mostly developed in the rim 4.3.2. Lead isotopic composition of grains, with various core–rim structures, indicating crystallization Five pyrite samples analyzed in this study (Fig. 10), show 206Pb/ from magma. 204Pb values of 17.84–18.79 (average 18.42); 207Pb/204Pb values of 15.46–15.62 (average 15.56) and 208Pb/204Pb values of 37.93–39.75 4.2.2. Zircon U–Pb age (average 38.73). In the evolution models of 207Pb/204Pb with 206Pb/ The zircon U–Pb analytic data and computed ages are reported in 204Pb (Fig. 10a), five analyses fall between the orogenic belt and the Tables 2 and 3. mantle evolution lines, mainly clustering near the orogenic belt line. The data for sample B110-9-2 (Table 2) show considerable spread 207Pb/204Pb and 206Pb/204Pb values of intrusive rocks in southern and the 17 analyses can be divided into 4 groups as described below. TM plot near the lower crust and mantle evolution lines (colored The first group includes 4 analyses with ages ranging from 134 to region in Fig. 10b; additional data from Cai et al., 2004a and Zhang 137 Ma, and defines a concordant age of 136±2 Ma (Fig. 8a). Among et al., 2009). these, points 14 and 19 are from domains showing magmatic texture. In the evolution model of 208Pb/204Pb and 206Pb/204Pb, the analytical In particular, point 19 represents newly formed magmatic zircon. data also plot near the orogenic belt line trending towards the field of lower crust; this is further supported by similar values from the intrusive rocks in southern TM (colored region Fig. 10b; additional data from Zhang et al., 2009).

4.3.3. He–Ar isotopic compositions Numerous studies reveal that the He and Ar gases trace the characteristics of differentiation along with the degassing in the Earth's evolution (Baptiste and Fougute, 1996; Barnard et al., 1994a, 1994b; Dunai and Touret, 1995; Hu, 1997; Hu et al., 1999; Li et al., 2004; Marty et al., 1989; Matthews et al., 1987; Simmons et al., 1987; Stuart et al., 1995; Wu et al., 2003). Thus, the He and Ar isotopes are distinct for the mantle, crust and surface atmosphere. Among these, the mantle retains higher original He and Ar (such as 3He and 36Ar), but lower radiogenic 4He and 40Ar. Therefore, it is generally considered that the value of 3He/4He in the continental mantle is 6–9Ra(Ra=3He/4He= 1.400×10−6), the value of 40Ar/36Ar is greater than 20,000, and the value of 40Ar/4He is about 0.33–0.56 (Cai et al., 2004b; Hu et al., 1999; Simmons et al., 1987). However, the value of 3He/4He in the typical – Fig. 7. CL images of zircons from the diorite porphyrite. The analytical spots and age crust is usually less than 0.1 Ra, in most cases even only 0.01 0.05 Ra. 40 data are also shown. As there is abundant radiogenic Ar in the crust, the concentration of 224 J.-F. Shen et al. / Lithos 156–159 (2013) 218–229

Table 2 Results of zircon LA-ICP-MS dating on sample B110-9-2.

Spot U Th 232Th/ Error 206Pb/ Error 207Pb/ Error 207Pb/ Error 206Pb/238U Error 207Pb/235U Error 207Pb/206Pb Error (ppm) (ppm) 238U 238U 235U 206Pb (age) (age) (age)

1 73 14 1.4384 ±0.0152 0.5229 ±0.0043 13.3658 ±1.0474 0.1854 ±0.0126 2711 ±22 2706 ±212 2702 ±183 2 47 8 0.5441 ±0.0052 0.5096 ±0.0102 11.3609 ±2.0362 0.1617 ±0.0302 2655 ±53 2553 ±458 2474 ±463 5 234 36 0.547 ±0.0034 0.4437 ±0.0030 9.5144 ±0.4078 0.1555 ±0.0066 2367 ±16 2389 ±102 2407 ±103 6 206 46 0.2144 ±0.0019 0.0274 ±0.0004 0.8476 ±0.1354 0.2245 ±0.0471 174 ±2 623 ±100 3013 ±632 7 83 14 0.6095 ±0.0039 0.4777 ±0.0040 10.7462 ±0.7235 0.1631 ±0.0107 2517 ±21 2501 ±168 2489 ±164 8 480 23 0.4535 ±0.0017 0.0214 ±0.0002 0.1436 ±0.0091 0.0486 ±0.0031 137 ±1 136 ±9 128 ±8 10 75 12 0.2739 ±0.0009 0.4497 ±0.0035 9.7175 ±0.6120 0.1567 ±0.0098 2394 ±19 2408 ±152 2421 ±151 11 126 19 0.4744 ±0.0053 0.2685 ±0.0021 5.5489 ±0.2307 0.1499 ±0.0056 1533 ±12 1908 ±79 2345 ±87 12 113 16 0.7359 ±0.0048 0.4103 ±0.0030 7.9015 ±0.2560 0.1397 ±0.0045 2216 ±16 2220 ±72 2223 ±72 13 23 4 0.6957 ±0.0221 0.5405 ±0.0039 14.3612 ±0.8254 0.1927 ±0.0115 2786 ±20 2774 ±159 2765 ±165 14 49 3 0.6108 ±0.0023 0.021 ±0.0002 0.1723 ±0.0096 0.0594 ±0.0032 134 ±1 161 ±9 583 ±32 17 39 5 1.6465 ±0.0146 0.3424 ±0.0033 5.4493 ±0.6628 0.1154 ±0.0143 1898 ±18 1893 ±230 1887 ±235 18 110 16 0.5712 ±0.0053 0.4109 ±0.0031 8.2348 ±0.2830 0.1453 ±0.0050 2219 ±17 2257 ±78 2292 ±78 19 511 27 0.4994 ±0.0092 0.0215 ±0.0002 0.1544 ±0.0009 0.052 ±0.0003 137 ±1 146 ±1 287 ±2 20 90 15 0.4619 ±0.0020 0.4452 ±0.0034 10.2039 ±0.3503 0.1662 ±0.0056 2374 ±18 2453 ±84 2520 ±84 22 269 13 0.2707 ±0.0017 0.0214 ±0.0006 0.1453 ±0.0073 0.0491 ±0.0014 137 ±4 138 ±7 155 ±4 24 42 7 0.6048 ±0.0059 0.4738 ±0.0037 10.983 ±0.6249 0.1681 ±0.0095 2500 ±20 2522 ±143 2539 ±144

40Ar/36Ar often exceeds 45,000, and that of 40Ar/4He is generally within Where the lower limit of 3He/4He of the crust end-member is the range of 0.16–0.25 (Feng et al., 2006; Hu et al., 1999; Simmons et al., 2×10−8 and that of the mantle is 1.1×10−8 (Stuart et al., 1995). 1987; Stuart et al., 1995). Thus, the He–Ar isotopic composition in the The results show that the percentage of the mantle derived He in crust and mantle is significantly different. Furthermore, it is usually the pyrite from the BMH deposit ranges from 0.17 to 2.98. In general, considered that the He–Ar isotopic composition in the atmospheric the 3He/4He ratios of ore fluids in the BMH are close to the crustal saturated water is the same as that in the surface atmosphere, with value, reflecting that the ore fluids mainly came from the crust and 3He/4He=1Ra, 40Ar/36Ar=295.5, and 40Ar/4He approximately 0.001 were mixed with a small amount of the mantle component in the (Hu et al., 1999; Simmons et al., 1987; Stuart et al., 1995). Thus, the metallogenic process. significant differences between the crust and mantle reservoirs allow In addition, the 40Ar/36Ar ratios mostly range from 311.7 to 673.5, 3He/4He, 40Ar/36Ar and 40Ar/4He to be used as potential traces in iden- except for one sample which gives 22,909.4 (Table 5 and Fig. 12). The tifying the source characteristics of ore-forming fluids. results are higher than that of the atmosphere (40Ar/36Ar=295.5), The pyrites from BMH iron deposit possess 3He/4He ratios of 0.0648– indicating the presence of excess argon produced probably by higher 0.1886Ra, with a mean value of 0.1237Ra (Table 5), which are a slightly radiogenic 40Ar. higher than that of the crust (0.01–0.1 R/Ra), but markedly lower than But as we know, the 40Ar/4He ratios of mantle fluids are in the that of the mantle (6–9R/Ra).Onthe3He versus 4He diagram range of 0.33–0.56 (Dunai and Touret, 1995) and the average value (Fig. 11), all of the data points from pyrites plot between the crust and of the crust is ~0.2 (Hu, 1997; Stuart et al., 1995). The 40Ar/4He ratios mantle, but closer to crustal domain. The percentage of mantle-derived of ore fluids in the BMH iron deposit are 0.362–0.716 (see Table 5), He can be calculated according to the crust–mantle mixing model, close to the value of the mantle. 3 4 3 4 3 4 40 36 which is expressed as: He=[( He/ He)(sample) −( He/ He)(Crust)]/ However, the plots of He/ He (R/Ra) vs. Ar/ Ar of fluids in py- 3 4 3 4 [( He/ He)(Mantle)−( He/ He)(Crust)]×100(Xu et al., 1995). rite from the BMH iron deposit (Fig. 13) fall close to the field of the

Table 3 Results of zircon LA-ICP-MS dating on sample B245-1.

Spot U Th 232Th/ Error 206Pb/ Error 207Pb/ Error 207Pb/ Error 206Pb/238U Error 207Pb/235U Error 207Pb/206Pb Error (ppm) (ppm) 238U 238U 235U 206Pb (age) (age) (age)

1 59 91 1.5413 ±0.1380 0.3109 ±0.0074 4.5998 ±0.1122 0.1073 ±0.0009 1745 ±41 1749 ±43 1754 ±15 2 33 64 1.9301 ±0.0187 0.3272 ±0.0029 5.0344 ±0.0479 0.1116 ±0.0009 1825 ±16 1825 ±17 1826 ±14 3 251 244 0.9734 ±0.0049 0.4716 ±0.0034 10.6336 ±0.0542 0.1635 ±0.0009 2491 ±18 2492 ±13 2493 ±14 4 491 265 0.5399 ±0.0075 0.4761 ±0.0034 10.8433 ±0.0573 0.1652 ±0.0009 2510 ±18 2510 ±13 2509 ±14 5 230 71 0.3086 ±0.0046 0.4765 ±0.0032 10.8165 ±0.0488 0.1646 ±0.0009 2512 ±17 2507 ±11 2504 ±14 6 135 156 1.1519 ±0.0107 0.4704 ±0.0034 10.377 ±0.0572 0.16 ±0.0009 2485 ±18 2469 ±14 2456 ±13 8 126 72 0.5688 ±0.0037 0.4927 ±0.0029 11.8569 ±0.0417 0.1745 ±0.0010 2582 ±15 2593 ±9 2602 ±15 10 321 215 0.6686 ±0.0040 0.4735 ±0.0037 10.868 ±0.1411 0.1665 ±0.0017 2499 ±19 2512 ±33 2522 ±26 11 6 5 0.814 ±0.0064 0.3439 ±0.0028 5.6294 ±0.1901 0.1187 ±0.0039 1905 ±16 1921 ±65 1937 ±63 13 99 85 0.858 ±0.0044 0.4698 ±0.0034 10.4637 ±0.0585 0.1615 ±0.0009 2483 ±18 2477 ±14 2472 ±14 14 196 101 0.5152 ±0.0047 0.5026 ±0.0038 12.2847 ±0.0795 0.1773 ±0.0010 2625 ±20 2626 ±17 2628 ±14 15 88 92 1.0451 ±0.0078 0.4627 ±0.0034 10.1976 ±0.0672 0.1598 ±0.0009 2452 ±18 2453 ±16 2454 ±14 16 19 49 2.5815 ±0.0407 0.4886 ±0.0032 11.8199 ±0.1001 0.1754 ±0.0018 2565 ±17 2590 ±22 2610 ±26 17 257 299 1.1623 ±0.0216 0.4658 ±0.0035 10.3631 ±0.0601 0.1614 ±0.0009 2465 ±19 2468 ±14 2470 ±13 18 266 142 0.5325 ±0.0075 0.3334 ±0.0049 7.3404 ±0.1011 0.1597 ±0.0009 1855 ±27 2154 ±30 2452 ±13 22 158 58 0.3662 ±0.0177 0.2607 ±0.0076 4.9464 ±0.1328 0.1376 ±0.0027 1494 ±44 1810 ±49 2197 ±43 23 635 294 0.4627 ±0.0042 0.0241 ±0.0003 ±0.2002 0.0042 0.0603 ±0.0007 153 ±2 185 ±4 613 ±8 24 734 140 0.191 ±0.0057 0.4653 ±0.0031 10.3334 ±0.0514 0.1611 ±0.0009 2463 ±17 2465 ±12 2467 ±13 25 46 19 0.4188 ±0.0039 0.4608 ±0.0085 9.9622 ±0.1700 0.1568 ±0.0010 2443 ±45 2431 ±41 2421 ±16 27 673 101 0.1496 ±0.0031 0.3876 ±0.0026 8.441 ±0.0401 0.158 ±0.0009 2111 ±14 2280 ±11 2434 ±13 28 450 95 0.211 ±0.0063 0.3331 ±0.0027 5.2205 ±0.0318 0.1137 ±0.0006 1853 ±15 1856 ±11 1859 ±10 29 234 134 0.5742 ±0.0100 0.4726 ±0.0029 10.7701 ±0.0403 0.1653 ±0.0009 2495 ±15 2503 ±9 2510 ±14 30 205 110 0.5373 ±0.0204 0.0431 ±0.0003 0.8334 ±0.0107 0.1401 ±0.0017 272 ±2 615 ±8 2229 ±27 J.-F. Shen et al. / Lithos 156–159 (2013) 218–229 225

Fig. 9. The distribution of pyrite δ34S‰ in the Beiminghe iron ore deposit compared with those from other localities.

associated with the mineralization. Therefore, we conclude that timing of both magmatism and mineralization in the Beiminghe iron deposit took place at round of 136–137 Ma.

5.2. Sources of ore-forming materials

The sulfur isotope data obtained in our study indicate that the ore-forming materials were mainly tapped from crustal sources by the Mesozoic pluton. In the evolution models of 207Pb/204Pb with 206Pb/ 204Pb, the data fall in between the orogenic belt and mantle evolution lines, mostly tending towards the orogenic belt line. The 208Pb/204Pb and 206Pb/204Pb relationship shows a lower crustal origin. Thus, we infer a mixed source, with most of the Pb derived from the lower crust with limited input from mantle sources. The 3He/4He and 40Ar/4He values indicate that the ore-forming fluids had a dominantly crustal origin, mixed with minor amounts of Fig. 8. U–Pb concordia diagram of zircons in weakly altered diorite porphyrite mantle-derived fluids. The He–Ar isotopic composition, however points (a. B110-9-2) and in skarnization diorite (b. B245-1). to an ultimate mantle origin for the fluids. However, in the evolved and homogenized fluids system, the mantle-derived component is comput- crustal fluid component, indicating that the ore fluids were mainly ed to be less than 3%. The ore fluids preserve a complex evolutionary derived from crust. history, including the involvement of minor meteoric water. In summary, it is inferred that the ore-forming fluids of BMH iron The summary of zircon U–Pb geochronology in our study indicates deposit are mainly derived from crust with small volume of mantle the following main age groups: (1) inherited Neoarchean and component during the metallogenic processes. Paleoproterozoic magmatic zircons with ages ranging from 2500 to 2786 and 2216 to 2408 Ma; (2) few Paleo-Mesoproterozoic metamor- 5. Discussion phic zircons with ages of 1553 Ma; and (3) magmatic zircons with crystallization age of ca. 136 Ma. Obviously, the type (1) and (2) zircons 5.1. Timing of mineralization and magmatism in the Beiminghe iron above were captured from the country rocks during magma ascent deposit and emplacement and confirms the varying degrees of incorporation of the Neoarchean and Paleo-Mesoproterozoic basement lithologies In skarn-type ore deposits, the timing of mineralization is broadly during magma tectonics. The Neoarchean and Paleoproterozoic coincident with the time of magma emplacement. The 40Ar/39Ar age inherited magmatic zircons in our samples from the Mesozoic ore of 137±2 Ma obtained from phlogopite in the skarn iron ores of deposit correlate well with similar ages widely reported from the base- present study is markedly consistent with the U–Pb age of 136±2 Ma ment rocks of the NCC (Wang and Liu, 2012; Wang et al., 2012; Zhai and obtained from zircons in the weakly altered diorite porphyrite Santosh, 2011). The Paleo-Mesoproterozoic metamorphic zircons captured by the magma are also in accordance with similar aged zircons widely reported from the high grade metamorphic rocks of the NCC. Table 4 Thus, it is clear that the ore-forming magma had interacted with the δ34 S values of pyrite in Beiminghe Fe-ore deposit. ancient lower crust of the NCC. Sample no. Tested mineral δ34S‰ In summary the primary fluids appear to have been derived from

B-110-6-3 Pyrite 13.5 mantle sources, which subsequently underwent a complex evolution- B-230-2-5 Pyrite 12.2 ary history. The high temperature magma, as it migrated through B-230-2-3 Pyrite 13.7 the lower crust, caused partial melting of the ancient lower crust, B-245-3 Pyrite 14.4 and older zircons were captured from the surrounding rocks. When B-245-5 Pyrite 16.5 the hot magma was emplaced into the carbonate rocks, skarn 226 J.-F. Shen et al. / Lithos 156–159 (2013) 218–229

Fig. 10. Pb isotope composition of pyrite and host magmatic rock from the BMH iron deposit. mineralization occurred, generating the BMH iron deposit, as well mantle lithosphere beneath some of the old cratons of the world are as similar occurrences in the Han-Xing region through contact more than 200–250 km in thickness, and some of these have survived metamorphism. for periods more than 3 billion years in spite of later tectonic disturbance (Carlson, 2005; Gao et al., 2009; Pearson, 1999; Sleep, 2005; Zhu et al., 2011). The cratonic root of the NCC, since its formation in the 5.3. Geodynamic implications Paleoproterozoic remained largely stable until the late Paleozoic (Xu et al., 2009a; Zhai and Bian, 2001; Zhao et al., 2001; Zheng and Wu, 2009), Santosh (2010) presented a synthesis of geological and geophysical with an estimated thickness of over 200 km (Deng et al., 1994; Fan and features of the NCC including a re-interpretation of the deep seismic Menzies, 1992). Active magmatism in the Eastern Block of the NCC started data from various traverses across the crustal blocks and suture zones in during early Paleozoic triggering decratonization and refertilization, this Craton. The results brought out a multiple subduction history in the particularly beneath the Eastern Block of the NCC (Zhang, 2009, 2012; Paleoproterozoic with the Western and Eastern Blocks amalgamated Zhang et al., 2012). The late Mesozoic witnessed extensive and along the Trans-North China Orogen (Central Orogenic Belt) and the craton-wide magmatism resulting in the widespread destruction of the Yinshan and Ordos blocks assembled along the Inner Mongolia Suture sub-continental lithospheric mantle, with a thin and fertile lithosphere fi Zone, marking the nal cratonization of the NCC. The sub-continental replacing the older thick and refractory sub-continental mantle (e.g., Gao et al., 2002; Menzies et al., 1993; Santosh, 2010; Zhai et al., 2004). Thus, Mesozoic magmatism is a hallmark of craton destruction in the NCC, and is therefore significant in understanding the geological history and geodynamic processes associated with decratonization. A number of studies have addressed the process of destruction of the NCC. Delamination (Gao et al., 2009) or erosion (Xu, 2006; Xu et al., 2009a) is among the principal mechanism suggested. Thermal and chemical erosion occurs through the upwelling of the hot as- thenosphere, which rises up and infiltrates the lithospheric mantle and lower crust (Zhang et al., 2005; Zhu et al., 2008). The heat and volatile input would also lead to upper crustal remelting, thereby generating magmas at various levels of the crust, with partial input from the mantle (Luo et al., 1997). Extensive magma migration from depth to shallower crustal levels has been considered as one of the hallmarks of lithospheric destruction (Xu et al., 2009b). Subduction–erosion is also one of the important mechanisms by which extensive erosion of the ‘tectosphere’ (sub-continental mantle Fig. 11. He isotope composition of BMH iron deposit. lithosphere) occurs (Santosh, 2010). Fluids released from downgoing J.-F. Shen et al. / Lithos 156–159 (2013) 218–229 227

Table 5 Helium and argon isotope data of pyrite from Beiminghe iron deposit.

Sample no. B110-6-3 B230-2-3 B230-2-5 B245-3 B245-5

Lithology Ore Skarn Ore Skarn Ore

4He (10−7) 2.37±0.16 4.97±0.34 10.87±0.73 3.87±0.26 15.30±1.0 3He/4He 0.1405 0.0907 0.2429 0.1280 0.2640 3He (10−7) 0.3327 0.4508 2.6403 0.4954 4.0392 R/Ra 0.10034±0.00057 0.06479±0.00074 0.17350±0.0024 0.09140±0.0031 0.18860±0.0016 40Ar (10−7) 1.194±0.097 1.800±0.13 4.630±0.34 2.770±0.21 5.980±0.44 40Ar/36Ar 359.2±13.7 673.5±041.4 22909.4±181.0 311.7±15.7 638.8±29.1 36Ar (10−7) 0.0033 0.0027 0.0002 0.0089 0.0094 40 ⁎ −7 Ar (10 ) 0.2188 1.0021 4.5709 0.1400 3.2023 40 ⁎ 4 Ar / He 0.092 0.202 0.421 0.036 0.209 F4He 4339.4 11122.3 328398.8 2627.4 9834.8

4 4 36 4 36 4 36 40 40 40 40 36 F He=ratios of He/ Ar sample and He/ Ar atmosphere ( He/ Ar atmosphere =0.1655); Ar* is the excess argon without Ar atmosphere; Ar*=( Ar)sample −295.5×( Ar)sample. slabs hydrate and weaken the large mantle wedge, and magmas The ore formation at BMH not only coincides with the time of generated by slab melting rise up and invade the lithospheric mantle. magmatic activity in southern TMs, but also relates to the peak of The prolonged subduction of the Pacific slab from the east is consid- 110–140 Ma identified for the large-scale lithospheric destruction of ered to have hydrated the mantle beneath East Asia and extensively the eastern block of NCC (Lin et al., 2008; Peng et al., 2004; Xu, destroyed the eastern part of the NCC. 2006; Zhu and Zheng, 2009; Zhu et al., 2011). The geodynamic setting The TM Belt records strong and widespread magmatic activity during for magma generation and lithospheric destruction can be correlated Mesozoic, covering the whole “Yanshanian” event, with a peak at 124– with the tectonic processes associated with the deep and prolonged 153 Ma (Luo et al., 1996, 2006). Among these, the magmatic rocks of subduction of the Pacific plate, and resulting tectonic, thermal and southern TM were formed mainly during 125–136 Ma (Chen et al., chemical erosion as well as refertilization through magma injection 2005a; Dong et al., 2003; Peng et al., 2004; Wang et al., 2006; Zheng et (Deng et al., 2000; Santosh, 2010; Tang et al., 2012; Xu et al., 2009a, al., 2007c). Their REE characteristics including lack of obvious Eu anoma- 2009b; Zhang, 2012). lies and the Sr–Nd–Pb isotopic features have been interpreted as the sig- A recent study on the zircons in granulite xenoliths entrained in nature of deep magma sources (Cai et al., 2004a, 2006; Niu et al., 1995). Cenozoic basalts from within the Trans-North China Orogen that

Furthermore, their low initial strontium ratio (w (87Sr)I/w (86Sr)I= amalgamates the Western and Eastern Blocks of the NCC showed a 0.7050–0.7069) has provided conclusive evidence for the involvement large spread of Phanerozoic concordant ages ranging from 470 Ma of mantle-derived materials mixing during formation in this area (Luo to 40 Ma with peaks at 315 Ma, 220–230 Ma, 120 Ma and 46 Ma, et al., 1997). suggesting episodic magmatic underplating in the ancient lower The time of formation of the BMH iron deposit was at ca. 136 Ma is crust of the NCC, lasting continuously throughout Phanerozoic, pro- consistent with the peak of 125–136 Ma for the magmatic activity in ducing zircons from the underplated magmas or providing the heat southern TM. Our study of the BMH iron ore deposit reveals mixed source for the recrystallization of zircons from the ancient crust (Liu source characteristics and complex evolution of the ore-forming et al., 2012; Zhang, 2012; Zhang et al., 2012). In another recent fluids. The S, Pb, He and Ar isotopic tracers indicate that the work, Tang et al. (2006, 2012) investigated the high Mg peridotite xe- ore-forming materials were mainly sourced from the lower crust, noliths in the Cenozoic Hebi basalts and the results indicate that the with input from mantle-derived fluids. It is possible that the 136 Ma lithospheric mantle beneath the TNCO formed during the Archean and age marks the initiation of the destruction of the NCC, as also was refertilized by multiple additions of fluids and melts. The critical lo- supported the higher degree of crustal contamination. This feature cation of the MBH iron ore deposit at the eastern margin of the TNCO, is comparable with the processes associated with several major along the western periphery of the Eastern Block, and its genetic link metallogenic provinces of the world where mantle material transmit- with the Mesozoic magmatism in this region suggest that the mineral- ted to the crust involves multiple contaminations at various crustal ization is a response to the processes associated with lithospheric levels (e.g., Mao et al., 2005; Zhao et al., 2000). Importantly, the thinning in the NCC. It has been noted in some of the previous studies metallogenic process of BMH iron deposit is also a significant marker that the large-scale lithosphere thinning process in eastern China was for the lithospheric destruction in this region.

Fig. 12. He–Ar isotope composition of BMH iron deposit. Fig. 13. 40Ar/4He vs. Rc/Ra plots for BMH iron deposit. 228 J.-F. Shen et al. / Lithos 156–159 (2013) 218–229 accompanied by large-scale mineralization events (Yang et al., 2003; Deng, J.F., Zhao, G.C., Zhao, H.L., Luo, Z.H., Dai, S.Q., Li, K.M., 2000. Mesozoic igneous petrotectonic assemblage and orogene — deep processes in East China. Geological Zheng et al., 2007b), and the formation of BMH iron deposit is an obvi- Review 46 (1), 41–48 (in Chinese with English abstract). ous manifestation of the NCC lithosphere thinning in southern TM. Dong, J.H., Chen, B., Zhou, L., 2003. Genesis of Fushan intrusive in Southern Taihang Mountains: the evidences from petrology and geochemistry. Progress in Natural Science 13 (7), 767–774 (in Chinese with English abstract). 6. Conclusion Dunai, T., Touret, J.L.R., 1995. Helium, neon and argon isotope systematics of European lithospheric mantle xenoliths: implications for its geochemical evolution. Geochimical et Cosmochimica Acta 59 (13), 2767–2783. 39 40 1. Based on phlogopite Ar– Ar dating and zircon U–Pb dating, it can Fan, W.M., Menzies, M.A., 1992. Destruction of aged lower lithosphere accretion of be determined that BMH iron deposit was formed in 136–137 Ma. asthenospheric mantle beneath eastern China. Geotectonica et Metallogenia 16, – 2. The ore-formation of BMH iron deposit mainly involved contribu- 171 180 (in Chinese with English abstract). Feng, Z.Y., 1998. Comparison of iron skarn generating intrusions with barren intrusions tions from the Late Archean and Early Proterozoic basement rocks. in Southern Taihang Mountain, China. 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