Geochronology and geochemistry of the Wunugetushan porphyry Cu–Mo deposit in NE china, and their geological significance

Ore Geology Reviews 43 (2011) 92–105

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Geochronology and geochemistry of the Wunugetushan porphyry Cu–Mo deposit in NE china, and their geological significance Zhiguang Chen a, b, Lianchang Zhang a,⁎, Bo Wan c, Huaying Wu a, b, Nathan Cleven d a

Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, P. O. Box 9825, Beijing, China Graduate University of Chinese Academy of Sciences, P. O. Box 3908, Beijing, China State Key Laboratory of Lithosphere Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, P. O. Box 9825, Beijing, China d University of Waterloo, Ontario, Canada b c

a r t i c l e

i n f o

Article history: Received 15 November 2009 Received in revised form 11 August 2011 Accepted 13 August 2011 Available online 18 August 2011 Keywords: Porphyry Cu–Mo deposit Concentric alteration and mineralization Isotope geochronology Geochemistry Mixing magma source Mongol–Okhotsk Orogen

a b s t r a c t The Wunugetushan porphyry Cu–Mo deposit is located in the Manzhouli district of NE China, on the southern margin of the Mesozoic Mongol–Okhotsk Orogenic Belt. Concentric rings of hydrothermal alteration and Cu– Mo mineralization surround an Early–Middle Jurassic monzogranitic porphyry. The Cu–Mo mineralization is clearly related to the quartz–potassic and quartz–sericite alteration. Molybdenite Re–Os and groundmass 40 Ar/39Ar of the host porphyry dates indicate that the ore-formation and porphyry-emplacement occurred at 177.6 ± 4.5 Ma and 179.0 ± 1.9 Ma, respectively. Geochemically, the host porphyry of the deposit is characterized by strong LREE/HREE fractionation, enrichment in LILE, Ba, Rb, U, Th and Pb, and depletion of HFSE, Nb, Ta, Ti and HREE. The Sr–Nd–Pb isotopic compositions of the porphyry display an varied initial (87Sr/86Sr)i ratio, a positive εNd(t) values and high 206Pb/204Pbt, 207Pb/204Pbt and 208Pb/ 204Pbt ratios. These data indicate that the magmatic source of the host porphyry comprised two end-members: lithospheric mantle metasomatized by fluids derived from the subducted slab; and continental crust. We infer that the primitive magma of the host porphyry was derived from crust–mantle transition zone. Based on regional geology and geochemistry of the host porphyry, the Wunugetushan deposit is suggested to form in a continental collision environment after closure of the Mongol–Okhotsk Ocean. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.

1. Introduction The Wunugetushan porphyry Cu–Mo deposit is located approximately 22 km SW of Manzhouli City, northeastern China (Fig. 1). The deposit was first discovered by the Inner Mongolia Geological Survey Bureau in 1960, but it was considered as a minor occurrence with insignificant Cu–Mo mineralization. Subsequently, the Metallurgical and Geological Prospecting Company of Heilongjiang Province carried out geological prospecting in the area of mineralization between 1977 and 1992. More recent exploration by the China National Gold Group Corporation (CNGGC) shows that the deposit is a large porphyry Cu–Mo deposit with an explored metal reserve of 849.7 Mt of Cu–Mo-ore at an average grade of 0.46% Cu and 0.053% Mo (CNGGC, 2006). The age of mineralization has previously been inferred from whole rock Rb–Sr dating of the intrusion related to mineralization as 130 to 140 Ma (Wang and Qin, 1988) and from U–Pb zircon ages for host

⁎ Corresponding author. Tel.: + 86 10 8299 8185; fax: + 86 10 6201 0846. E-mail address: [email protected] (L. Zhang).

rock and K–Ar ages of hydrothermal sericite (180 to 190 Ma; Qin et al., 1999). More recently, Li et al. (2007a) argued that the Wunugetushan Cu–Mo deposit was formed at 170 to 180 Ma based on Re–Os isotope dating of molybdenite. The deposit was considered to relate to a volcanic–magmatic event induced by subduction of the Paleo-Asian ocean slab (Qin et al., 1999; Wang and Qin, 1988; Zhang et al., 2001; Zhao and Zhang, 1997). Limited major and trace element data indicated that the rock hosting the mineralization was derived from lower crust (Wang and Qin, 1988). However, other geologists argued that the deposit was associated with magmatic activity in a continental rift environment (Lϋ et al., 2001; Xu et al., 1998). Mao et al. (2005) have presented a synthesis of large-scale Mesozoic metallogeny in North China in a geodynamic context and have suggested that the host porphyry of the Wunugetushan Cu–Mo deposit is an I-type granite formed in a continent–continent collisional setting between the Siberian and North China Cratons. Li et al. (2007a) studied fluid inclusion systematics in the Wunugetushan deposit and also suggested that the deposit was a typical example of a porphyry ore system and was generated in a continental collisional regime. The fluid inclusion study showed that the mineralizing fluids were mainly magmatic in origin and that early stage CO2-rich fluids were characterized by high temperature (N510 °C), high salinity (75.8 wt.% NaCl equiv.) and high fO2 (Li et al., 2007b).

0169-1368/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.oregeorev.2011.08.007

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Fig. 1. (A) Tectonic scheme of Northeastern Asian showing the location of the Mongol–Okhotsk Orogen Belt (modified from Safonova, 2009). (B) Regional geological map showing the position of the Mongol–Okhotsk suture, the Onon island arc terrane, and the extensive magmatic arcs on both sides of the suture. The location of the study area is indicated in this map (modified from Tomurtogoo et al., 2005). (C) Simplified geological map of Manzhouli area showing major lithological units and faults. The location of the Wunugetushan mine is indicated (modified from Zhang, 2006).

Although a number of studies have been carried out on the deposit by local geologists, the timing of ore formation and geodynamic setting are still disputed. Moreover, the metal source and mechanism of deposit formation have not been adequately constrained until now, largely due to a lack of detailed geochemical data for the deposit. In this paper we provide new geological and geochemical evidence that can contribute to the debate and help resolve genetic aspects of the Wunugetushan deposit. The study of this paper focuses on the mine's geology, Re–Os and 40Ar/ 39Ar geochronology and the geochemistry of the host rock. Based on isotope geochronological and geochemical data we discuss the timing of ore formation and the magma source of the host rock. Taking known regional geology and relevant previous studies into consideration, we further discuss the geodynamic setting of ore formation and present a new geodynamic model. This new model has important implications for understanding the regional tectonic evolution and for exploration of mineral resources related to Mesozoic tectonomagmatic events in the region.

2. Regional geology 2.1. Mongol–Okhotsk Orogen belt The Mongol–Okhotsk Orogenic belt stretches along the southwestern boundary of the Siberian plate for over 3000 km, extending from the present Udsky gulf of the Okhotsk Sea to Khangay mountain range in Central Mongolia. The orogenic belt was formed along with the closure of the Mongol–Okhotsk Ocean which separated the Siberian Craton from the amalgamated Mongolia–North China Plate (e.g., Kuzmin and Fillipova, 1979; Sorokin, 1992; Zonenshain et al., 1976). Geochronological studies of granitoids along the suture show progressively younger ages from west to east, with ages ranging from Late Carboniferous-Permian to Cretaceous. This suggests that the ocean closed in a scissor-like movement. Although the closing model of the Mongol–Okhotsk Ocean has been recognized, the final time of ocean closure is still controversial (Chen et al., 2006; Cogne et al., 2005; Halim et al., 1998; Kravchinsky et al., 2002; Metelkin et

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al., 2007; Ruzhentsev and Nekrasov, 2009; Sorokin et al., 2007; Tomurtogoo et al., 2005). In the Mongol–Okhotsk Orogen, both Early and Late Mesozoic tectonic and magmatic events are observed (Koval et al., 1989, 1999). As shown in Fig. 1B, the orogen is bordered on both sides by extensive late Paleozoic–Mesozoic calc-alkaline to peralkaline volcanic–plutonic belts (Litvinovsky et al., 1999; Wickham et al., 1995; Zanvilevich et al., 1995). A number of mineralized belts have been found in the Mongol–Okhotsk Orogen, and the metallic mineralization related to the orogen is marked by both a wide diversity and large-scale (Koval et al., 1999). Ores include rare metals (Ta, Li, Nb, Zr), uranium, precious metals (Au, Ag), and base metals (Cu, Mo, Pb, Zn, W, Sn). The dominant mineralization processes are closely related to Mesozoic syn-orogenic magmatic activity. 2.2. Manzhouli area The Manzhouli area is located on the southern side of Mongol– Okhotsk Orogen. Magmatism in this region took place during two main stages (Permian and late Triassic to Jurassic; Fig. 1C). The Permian plutons mainly comprise granite and granodiorite, and most are covered by thick volumes of Mesozoic volcanic rocks. The second generation of magmatic rocks, including both intrusives and volcanics, are represented by monzogranitic porphyry, biotite granite and syenogranite. Trachyandesite, trachyte and rhyolite, with ages of 150 to 164 Ma. These ages imply that the volcanic rocks must have formed during the post-orogenic stage of the Mongol–Okhotsk Orogen (Chen et al., 2006; Ying et al., 2008). The main regional fault in the Manzhouli area is NE–SW-trending Ergun fault (Fig. 1C). The spatial distribution of Mesozoic intrusive rocks and mineralization was controlled by NW–SE- and NE–SWtrending secondary faults of the Ergun regional fault. Discovery of the large Wunugetushan porphyry Cu–Mo deposit triggered extensive regional exploration in areas around the deposit. As a result, a number of additional deposits have been found in the past few years. These new discoveries include the small Changling porphyry Mo deposit and Halasheng epithermal Pb–Zn deposit, the Longling skarn Cu–Zn–Sn and the Toudaojingzi skarn Cu–Mo ore prospects (Fig. 1C). 3. Geology of the Wunugetushan porphyry Cu–Mo deposit

magmatic activity (Fig. 2A) and displays a sharp boundary with the biotite granite. The rhyolite porphyry is one of the wall rocks of the mine, emplaced in the NW part of the volcanic conduit with an outcrop area of about 0.48 km 2. The monzogranitic porphyry, the host rock of the mineralization, intruded into the wall rocks as a central stock and adjacent apophyses after formation of the rhyolite porphyry (Figs. 2A, 3 and 4A). The porphyry stock (outcrop area 0.42 km 2) is located in the center of the volcanic conduit north of F7 (Fig. 2A). The numerous porphyry apophyses ranging from 5 m to 100 m in width surround the porphyry stock and often intrude biotite granite along the concentric fracture system of the volcanic edifice. As shown in Fig. 4B, the porphyritic texture of the monzogranitic porphyry is well developed. Phenocryst abundance in the porphyry ranges from 40 to 45 vol.% of the whole rock, and consists mainly of plagioclase (~20 to 25 vol.%), quartz (~ 15 to 20 vol.%), and lesser amounts of biotite (b2 vol.%) and K-feldspar (b1 vol.%). The groundmass is composed of quartz, plagioclase and K-feldspar, together accounting for 55 to 60 vol.% of the whole rock. Some fine-grain quartz displays equant bipyramidal and hexagonal growth forms, characteristics of high-temperature β-quartz as described by Harris et al. (2004). The dacitic breccia lava, quartz porphyry and diorite porphyry were formed during the late stages of volcanic activity (Fig. 2A). The dacitic breccia lava is more common in the southern mine and shows vertical explosive breccia pipe. The quartz porphyry and the diorite porphyry, occurring as generally NE-striking dikes, are clearly controlled by volcanic ring fractures and late faults, representing the latest expression of magmatic activity in the mine area. 3.2. Fault and fracture systems Throughout the Wunugetushan mine area, NE–SW- and NW–SEtrending faults and ring fractures are dominant (Fig. 2A). These faults and fractures can be subdivided into two groups according to their crosscutting relationship: (1) NE–SW trending faults and volcanic ring fractures formed earlier than or simultaneous with mineralization; (2) The NW–SE-trending faults are post-mineralization faults. The strike-slip normal faults F7 and F8 cut the continuity of the Cu– Mo orebody (Fig. 2A).

3.1. Magmatic rocks

4. Alteration and mineralization

As shown in Fig. 2A, there are two main episodes of magmatism in the Wunugetushan area: (1) Late Triassic biotite granite, granophyre and granite porphyry, which together account for N60% of the surface outcrop across the whole mine area; and (2) Jurassic magmatism including intrusive and volcanic rocks, with an outcrop area of about 2.7 km 2. The Late Triassic intrusive rocks include biotite granite, granophyres and granitic porphyry. The biotite granite strikes NE and its surface outcrop area is up to 110 km 2. These granophyres and granitic porphyry are considered to represent shallow emplacement of biotite granite magma. The Late Triassic biotite granite, constituting the main wall rock of the mineralization, is characterized by coarse grain texture (3–6 mm grain size) and a weak superimposed schistosity. Previous geochemistry and K–Ar and Rb–Sr isotopic geochronological data (Qin et al., 1998; Wang and Qin, 1988) suggested the biotite granite was derived from remelting of upper crustal materials at 190 to 211 Ma. The Jurassic volcanic–magmatic rocks represent a complex volcanic edifice. Lithologies consist, from older to younger, of rhyolite porphyry, monzogranitic porphyry, dacitic breccia lava, quartz porphyry and diorite porphyry. The rhyolite porphyry intruded into the biotite granite through a vertical volcanic conduit during an early stage of

4.1. Hydrothermal alteration In the Wunugetushan mine, hydrothermal alteration is centered on the monzogranitic porphyry stock. The alteration of the mine shows NE–SW trending with about 4 km in length and 2 km in width (Fig. 2B). Depending on the assemblage of alteration minerals, three distinct hydrothermal alteration haloes are recognized from the center of the porphyry stock outwards: (1) quartz–potassic alteration; (2) quartz–sericite alteration; and (3) illite–hydromuscovite alteration (Fig. 2B). Quartz–potassic alteration occurs mainly in the exocontact zone of the host monzogranitic porphyry and the wall rocks. This zone is elongated 2 km in the NE direction and is 0.8 km wide, located in the central part of the alteration belt (Fig. 2B). The quartz–potassic alteration is characterized by an early, high-temperature assemblage of K-feldspar + quartz ± biotite with rare sericite and anhydrite. The hydrothermal quartz (N15 vol.%) and K-feldspar (5–10 vol.%) usually occur as micro-veinlet (b2 mm) and large vein (N1 cm) fillings and also replace original quartz and feldspar along twin planes or rims (Fig. 4C). Rare hydrothermal biotite (b2 vol.%) is scattered mainly in the side of quartz–K-feldspar veinlets. The pervasive quartz–potassic alteration completely destroyed the primary minerals

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Fig. 2. (A) Geological map of the Wunugetushan mine showing the main lithologies and faults with a volcanic edifice (modified map of CNGGC, 2006). (B) and (C) Simplified maps of hydrothermal alteration and Cu–Mo mineralization showing their location and relationship with major lithological units respectively.

in the monzogranitic porphyry and their mutual textures and makes the altered rocks distinctly flesh-colored. The Quartz–sericite alteration zone is observed in biotite granite, rhyolite porphyry and some monzogranitic porphyry apophyses outside the K-silicate core (Fig. 2B). The alteration surrounds the K-sillicate core as an elliptical ribbon zone and its outcrop width ranges from 0.1 to 0.6 km. It is characterized by the appearance of abundant sericite and hydromuscovite. The alteration assemblage consists of quartz (15–20 vol.%), sericite (25–35 vol.%) and hydromuscovite (20–30 vol.%) with lesser illite, kaolinite and calcite (Fig. 4D). The quartz–sericite alteration occurs mainly as veins and pervasive replacement of primary minerals. The veins are

irregular to planar consisting mainly of quartz with lesser sericite. Pervasive replacement is characterized by strong replacement and fracturing of plagioclase, K-feldspar and biotite phenocrysts and by the quartz–sericite–hydromuscovite–kaolinite assemblage. Illite–hydromuscovite alteration, the outermost effects of hydrothermal alteration in the Wunugetushan mine, is very well developed in the biotite granite and rhyolite porphyry. It also overprints the early alteration types at all scales (Fig. 2B). Alteration minerals are dominated by illite (2–10 vol.%), hydromuscovite (15–25 vol.%), sericite (1 to 10 vol.%) with lesser calcite and kaolinite (Fig. 4E). The illite–hydromuscovite alteration can be characterized by complete replacement of all silicates except quartz. In the alteration, feldspar

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Fig. 3. Northwest–southeast section through the Wunugetushan deposit showing the relationship of host monzogranitic porphyry, alteration and mineralization. a–b (620 line) and c–d (660 line) cross section based on unpublished exploration data (modified map of CNGGC, 2006, see locations of these sections in Fig. 2). The altered zones and ore bodies lie around the center of porphyry. The early alteration and mineralization were broken by a late, vertical breccia pipe.

minerals are pervasively replaced by illite, hydromuscovite, sericite, kaolinite and calcite, and biotite is replaced by hydromuscovite, sericite and quartz.

4.2. Mineralization types Ore mineralization can be subdivided into two mineralized types based on the various metal sulfides assemblages: (1) Mo–Cu mineralization; and (2) Cu mineralization.

Mo–Cu mineralization is closely associated with quartz–potassic alteration and occurs mainly in the marginal zone of the altered center and the transitional zone to quartz–sericite alteration (Fig. 2C and 3). Ore minerals are molybdenite, chalcopyrite and pyrite with molybdine, covellite, malachite and limonite in surface oxidation zones. The sulfides occur generally as disseminated (Figs. 4F and 5A) to veinlets fillings (Figs. 4G and 5B) in coarse veins. These veins mainly include discontinuous quartz+K-feldspar+molybdenite±pyrite±chalcopyrite, planar quartz+molybdenite±K-feldspar±pyrite±chalcopyrite and quartz+ molybdenite. The Mo–Cu orebody is characterized by a straight pipe-

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Fig. 4. Photographs of main lithologies and photomicrographs of altered rocks and Cu–Mo ore in the Wunugetushan mine area. (A) Intrusive contact relationship of biotite granite and monzogranitic porphyry. (B) Monzogranitic porphyry showing clear porphyritic texture and phenocrysts consisting mainly of plagioclase and quartz. (C) Monzogranitic porphyry with quartz–potassic alteration showing the original texture destroyed by quartz–K feldspar veins. (D) Altered biotite granite with the quartz–sericite alteration zone, showing complete alteration of plagioclase and biotite to quartz and sericite. (E) Biotite granite with illite–hydromuscovite alteration, showing complete replacement of feldspar and biotite, and some feldspar and biotite are still preserved the original crystal form. (F) and (G) Mo–Cu mineralization in the quartz–potassic alteration zone showing disseminated molybdenite and chalcopyrite and molybdenite + pyrite veinlet respectively. (H) and (I) Cu mineralization in the quartz–sericite alteration zone showing disseminated chalcopyrite + pyrite, chalcopyrite + molybdenite and chalcopyrite + pyrite veinlet respectively. Qtz = quartz, Kf = K-feldspar, Ser = sericite, Anh = anhydrite, Hmu = hydromuscovite, Kao = kaolinite, Mo = molybdenite, Py = pyrite, Cpy = chalcopyrite, Cv = covellite.

Fig. 5. Photographs of mineralized rocks in the Wunugetushan mine area. (A) Scattered-disseminated molybdenite in the Mo–Cu mineralization zone. (B) A molybdenite vein. (C) and (D) Malachite and covellite occur in the fracture surfaces of the oxidation zone and Cu mineralization belt, respectively. (E) Disseminated chalcopyrite and pyrite in the Cu mineralization belt. (F) Chalcopyrite + pyrite veins in the Cu mineralization belt.

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Table 1 Re–Os isotope data for analyzed molybdenite as determined by ICP-MS. Sample

W W W W W W W

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

Weight (mg) 50.26 20.06 50.16 50.48 2.46 7.18 46.55

Re (μg/g)

Common Os (ng/g)

187

187

Re (μg/g)

Os (ng/g)

Model age (Ma)

Measured

2σ

Measured

2σ

Measured

2σ

Measured

2σ

Measured

2σ

188.87 175.76 182.48 185.26 141.98 148.15 368.79

1.40 1.37 1.46 1.94 1.30 1.12 2.78

0.05 0.05 0.05 0.11 0.08 1.38 0.06

0.23 0.11 0.17 0.52 0.19 0.94 0.25

118.71 110.47 114.69 116.44 89.23 93.12 231.79

0.88 0.86 0.92 1.22 0.82 0.71 1.75

353.0 327.5 338.5 344.0 264.1 280.3 687.3

4.3 3.0 3.8 3.0 14.3 10.9 7.5

178.2 177.7 176.9 177.1 177.4 180.4 177.7

2.9 2.6 2.8 2.8 9.8 7.3 2.8

Decay constant: λ (187Re) = 1.666 × 10−11 year− 1 (Smoliar et al., 1996). Uncertainties include absolute at 2σ with error on Re and 187Os concentrations and the uncertainty in the 187 Re decay constant.

like shape with 120 to 300 m thickness (Fig. 3). It contains approximately 90% of the Mo reserves and 60% of the Cu reserves of the Wunugetushan mine. Copper mineralization in the Wunugetushan mine is related to quartz–sericite alteration and appears to be slightly later than Mo–Cu mineralization. This mineralization surrounds the Mo–Cu mineralized zone with a transitional relationship (Figs. 2C and 3). The most obvious characteristic of the Cu mineralized zone is the increase of Cu-sulfides and corresponding decrease in the proportion of molybdenite. The Cubearing minerals are chalcopyrite, bornite, chalcocite and tetrahedrite. Malachite and covellite often occur in the fracture surfaces of altered rocks in the oxidation zone (Fig. 5C, D). The sulfides generally occur as disseminated mineralization (Figs. 4H and 5E) to veinlet fillings in various veins (Figs. 4I and 5F). These veins mainly include discontinuous quartz + pyrite±sericite±chalcopyrite±molybdenite veinlets and planar quartz + pyrite ±chalcopyrite veins. The Cu orebody has similar occurrence to the Mo–Cu orebody and is characterized by a gradual decrease of thickness (Fig. 3). The Cu orebody extends downwards to about 450 m with a width from 10 to 180 m. The Cu mineralization zone accounts for almost 40% of the total Cu reserve and 10% of the total Mo reserve in the mine.

core. In the mine itself, the host rock, especially around the orebody, is always altered to some degree. In order to correctly characterize the chemical composition of the host porphyry, less altered drill core samples were chosen to perform systematic major and trace element and Sr–Nd–Pb isotope analyses. 5.2. Analytical methods 5.2.1. Re–Os analyses Seven molybdenite samples were picked from the different ore types, including disseminated and stockwork veinlet molybdenite ore, and prepared for Re–Os analyses. The ore samples were crushed, split and ground to b100-mesh. Sample preparation and mineral separation followed techniques outlined by Du et al. (1994), Shirey and Walker (1995) and Mao et al. (1999). Analysis was carried out in the Re–Os Laboratory, National Research Center of Geoanalysis, Chinese Academy of Geological Sciences (CAGS). Re–Os isotopic data were obtained by isotope dilution ICP-MS (TJA PQ-EXCELL). The uncertainty in each individual age determination is about 1.5%, including the uncertainty of the decay constant of 187Re, uncertainty of the isotope ratio measurement, and the spike calibration.

5. Sample preparation and analytical methods 5.1. Sample preparation We collected samples comprising stockwork veinlets and disseminated ores of the quartz–potassic alteration zone from drill core and separated molybdenite from these for Re–Os isotopic analysis. The groundmass of a fresh monzogranitic porphyry sample was analyzed using the 40Ar/ 39Ar dating method. All geochemical samples of the host porphyry in the Wunugetushan mine were collected from drill

5.2.2. 40Ar/ 39Ar analyses Sample preparation and analytical methodology are described in detail by Wang et al. (2006). Samples of groundmass material from a fresh monzogranitic porphyry were collected for 40Ar/39Ar dating. The samples were crushed to 40–60 mesh and 0.2 g of the groundmass was handpicked under a binocular microscope. The groundmass sample was dated by using the step-heating 40Ar/39Ar method. Step-heating 40 Ar/39Ar analyses were carried out at the Ar–Ar laboratory in the Institute of Geology and Geophysics, Chinese Academy of Sciences.

Table 2 40 Ar/39Ar incremental heating data for groundmass sample of the host porphyry. Temp (°C)

40

Ar/39Ar

37

Ar/39Ar

36

Ar/39Ar

Sample WS05-2: groundmass, J = 0.00513955, ±0.5%; wt = 14.81 mg 700 26.74675 0.00252 0.02067 760 21.86951 0.00065 0.00296 820 20.97885 0.00031 0.00197 860 20.91350 0.00028 0.00184 890 20.55037 0.00016 0.00038 920 20.55565 0.00014 0.00040 950 20.58416 0.00019 0.00055 980 20.40991 0.00016 0.00079 1020 20.41073 0.00015 0.00084 1060 20.40972 0.00021 0.00092 1100 20.42775 0.00061 0.00357 1150 20.47651 0.00058 0.00387 1220 20.98109 0.00129 0.00746 1300 22.48553 0.00293 0.01267 1400 22.57014 0.00369 0.01390 40

Ar⁎ = radiogenic

40

Ar. Errors are 2σm and refer to the last digits.

Ar⁎/39Ark

Ar⁎ (%)

40

40

21.175347 21.015148 20.377328 20.348198 20.413191 20.409186 20.402896 20.155007 20.136002 20.124864 19.397601 19.340351 18.815826 18.826974 18.722050

79.46 96.29 97.30 97.47 99.50 99.46 99.30 98.92 98.82 98.83 95.28 94.73 89.91 83.97 83.34

%

39

Ark (released)

0.23 2.57 10.40 19.48 31.78 50.71 58.67 69.27 84.52 90.88 93.31 96.72 98.48 99.56 100.00

Age (Ma)

Error (Ma 2σ)

186.4 185.1 179.7 179.5 180.0 180.0 179.9 177.8 177.7 177.6 171.5 171.0 166.6 166.6 165.8

± 4.2 ± 1.2 ± 0.8 ± 0.8 ± 0.8 ± 0.8 ± 0.9 ± 0.8 ± 0.8 ± 0.8 ± 1.1 ± 0.9 ± 1.0 ± 1.2 ± 4.2

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Fig. 6. Re–Os isochron diagram for seven molybdenite samples (A) and 40Ar/39Ar age spectra of groundmass collected from a monzogranitic porphyry sample (B) in the Wunugetushan deposit. ISOPLOT software of Ludwig (1999) was used to calculate the isochron age, decay constant: λ (187Re) = 1.666 × 10− 11 year− 1 (Smoliar et al., 1996). Uncertainties including A and B are absolutely at 2σ.

5.2.3. Whole rock major and trace element composition Samples were collected from less altered monzogranitic porphyry in drill core. All whole-rock analysis was carried out at the Geochemical

Analysis Center of IGGCAS. Sample preparation and analysis followed procedures described by Zhang et al. (2008). For major element analyses, mixtures of whole-rock powder (0.5 g) and Li2B4O7 +LiBO2 (5 g) were

Table 3 Major (wt.%) and trace element (ppm) compositions of the host porphyry intrusion. Sample no.

05WS-1

05WS-2

05WS-3

05WS-4

05WS-5

WS07-9

W-X(1)

W-X(2)

W-X(3)

W-X-87

SiO2 TiO2 Al2O3 Fe2O3 FeO MnO MgO CaO Na2O K2O P2O5 LOI Total Mg# Rb Sr Y Zr Nb Ba Ga Pb La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Th U Eu/Eu* La/Yb Nb/Y Th/Ce Y + Nb Yb + Ta

71.57 0.24 14.82 0.52 1.15 0.02 0.25 0.92 4.43 3.93 0.09 2.03 99.97 0.22 114 43.7 3.92 135 4.98 760 14.8 4.73 16.1 30.2 3.46 11.6 1.85 0.46 1.23 0.15 0.62 0.11 0.31 0.05 0.39 0.07 3.85 0.31 2.27 0.80 0.91 42 1.27 0.08 8.90 0.70

70.31 0.22 14.82 0.56 1.31 0.03 0.31 1.06 4.85 4.06 0.08 1.44 99.05 0.33 157 46.9 3.60 132 4.99 720 18.7 12.3 16.6 30.6 3.47 11.4 1.87 0.43 1.23 0.14 0.61 0.11 0.30 0.05 0.39 0.07 3.85 0.31 3.12 1.22 0.81 43 1.39 0.10 8.59 0.70

70.92 0.18 14.83 0.21 1.46 0.03 0.34 1.55 4.26 3.70 0.05 2.09 99.62 0.24 102 26.8 5.75 101 5.55 770 16.2 7.13 16.4 33.9 4.23 15.5 2.82 0.62 1.85 0.23 1.04 0.17 0.47 0.07 0.51 0.08 3.28 0.38 2.43 1.34 0.69 32 0.97 0.07 11.30 0.89

69.20 0.37 16.05 1.13 1.14 0.01 0.10 1.29 4.50 3.36 0.12 2.64 99.91 0.20 135 26.7 3.96 111 5.21 660 23.1 6.45 16.3 30.5 3.52 11.6 1.85 0.44 1.19 0.14 0.65 0.11 0.32 0.05 0.40 0.07 3.45 0.35 2.39 1.10 0.75 41 1.32 0.08 9.17 0.76

70.46 0.39 14.86 0.83 1.45 0.00 0.34 1.35 4.73 3.65 0.03 1.36 99.45 0.29 113 95.6 4.45 138 5.40 720 17.1 11.4 19.1 36.6 4.18 14.3 2.25 0.56 1.43 0.17 0.80 0.14 0.40 0.06 0.47 0.09 4.28 0.38 3.38 1.36 0.86 41 1.21 0.09 9.85 0.85

70.09 0.41 14.70 0.47 1.44 0.01 0.52 1.58 4.98 3.63 0.03 2.06 99.92 0.31 96 143.2 5.94 122 4.52 730 12.0 23.7 15.8 31.6 3.57 13.0 2.34 0.61 1.82 0.26 1.27 0.22 0.55 0.08 0.53 0.09 3.45 0.29 2.85 1.73 0.82 30 0.76 0.09 10.45 0.82

70.03 0.31 15.42 0.50 1.70 0.00 0.37 1.42 4.69 3.92 0.03 1.87 100.3 0.22

71.70 0.22 14.65 0.40 1.39 0.00 0.24 1.52 4.62 3.74 0.02 1.64 100.1 0.24

70.13 0.26 14.67 0.49 1.53 0.00 0.44 1.45 4.82 3.53 0.03 2.08 99.4 0.27

70.10 0.42 14.79 0.51 1.41 0.01 0.47 1.56 4.67 3.61 0.03 1.93 99.5 0.08

Notes: Major elements were analyzed by XRF and trace elements by ICPMS; LOI = loss on ignition; Mg# = Mg/(Mg + Fe+ 2); Eu/Eu⁎ = EuN/(SmN × GdN)1/2; N = chondritenormalized concentrations from Boynton (1984). Data for the W-X-50-(1), W-X-50-(2), W-X-50-(3) and W-X-87 from Wang and Qin (1988).

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heated and fused into glass disks and analyzed by X-ray fluorescence spectroscopy (XRF). The precision and accuracy of the major element data as determined on the Chinese whole-rock granite standard GSR-1 (Xie et al., 1985) are ≤5% and 5% (2σ), respectively. Trace-element abundances were determined with a Finnigan Element ICP-MS at IGGCAS. Precision and accuracy of the data are better than 5% as determined on standard sample GSR-1. 5.2.4. Sr–Nd–Pb isotope analysis The isotopic compositions of these elements were measured on a Finnigan MAT-262 mass spectrometer at IGGCAS. Thermal mass fractionation of Sr and Nd isotopes was corrected with a power law and 86 Sr/ 88Sr = 0.1194 and 146Nd/ 144Nd = 0.7219, respectively. Pb isotopic ratios were corrected using 0.1% per a.m.u. The total procedure blanks are 1 ng for Sr, Nd and Pb not significant for the whole-rock compositions. 6. Results 6.1. Isotopic ages The Re–Os isotopic data for the molybdenite samples and 40Ar/ Ar analytical results are listed in Tables 1 and 2 respectively, and are plotted in an isochron diagram in Fig. 6. Seven samples yielded a Re–Os isochron age of 177.6 ± 4.5 Ma, as calculated by ISOPLOT software (Ludwig, 1999) with an initial Os ratio of − 0.1 ± 9.3 (MSWD = 0.28, Fig. 6A). The 40Ar- 39Ar plateau ages were determined from 15-step incremental heating experiments. Groundmass samples of the host porphyry yielded a well-defined plateau age of 179.0 ± 1.9 Ma (Fig. 6B) calculated by 8-step incremental heating experiments data from 820 °C to 1060 °C, comprising N80% of the total 39Ar released. 39

Fig. 7. Major-element characteristics of the Cu–Mo hosting porphyry from the Wunugetushan mine. (A) Q` vs. ANOR diagram (Streckeisen and Le Maitre, 1979) showing rock types according to their normative mineral proportions. (B) Molar ratios of Al/ Ca, Na, K (Shand, 1947) in samples of this study revealing transitional I- to S-type compositions. The stippled line delineates I-type from S-type granite.

6.2. Major- and trace-element compositions of the host porphyry The chemical compositions of the host porphyry in the Wunugetushan mine are listed in Table 3 and plotted in Figs. 7 and 8. The normative quartz and feldspar proportions derived from the CIPW-norm show the host rock type is mainly monzogranite (Fig. 7A). The analytic results from 19 samples show that the Wunugetushan monzogranitic porphyry is characterized by high SiO2 (69.20–71.70 wt.%), high Al2O3 (14.65– 16.05 wt.%) and low MgO (0.10–0.52 wt.%) and CaO (0.92–1.58 wt.%). The K2O (3.36–4.06 wt.%) and Na2O (4.26–4.98 wt.%) contents show that the host porphyry can be characterized as high-K calc-alkaline. According to the molar ratios of Al/Ca, Na, and K the monzogranitic porphyry has transitional I- to S-type affinity with a sedimentary component of crust reflected in its peraluminous composition (Fig. 7B). Fig. 8A shows the chondrite-normalized (Boynton, 1984) rare earth elements (REE) pattern of the host porphyry. The REE patterns are very consistent with strong fractionation between light rare earth elements (LREE) and heavy rare earth elements (HREE) (La/Yb N 30) and slightly negative Eu anomalies (Eu/Eu⁎ = 0.69–0.91). Chondritenormalized patterns characteristically slope smoothly down to the right, suggesting that the porphyry is related to mantle magmatism and different from upper crustal magmatism (Wilson, 1989). Like REE, the trace elements of the host porphyry also show regular variation. Large ion lithophile elements (LILE), Rb, U, K and Pb are enriched, whereas high field strength elements (HFSE), Nb, Ta, Ti and HREE Yb are strongly depleted (Fig. 8B). This feature clearly suggests typical characteristics of arc magmatism related to a subduction zone (Wilson, 1989). 6.3. Sr–Nd–Pb isotopes The Sr, Nd and Pb isotopic compositions are listed in Table 4 and plotted in Fig. 9. Initial isotopic ratios were calculated for a host

Fig. 8. Chondrite-normalized rare earth element distribution pattern (A), and primitive mantle-normalized trace element spider diagram (B) for the host porphyry. Normalizing data from Boynton (1984) and Sun and McDonough (1989) respectively. Patterns shown for comparison include typical intraplate granite of NE China and late orogeny-related host porphyry in Gangdese (Qu et al., 2004; Wu et al., 2002).

Sr and Nd: Initial 87Sr/86Sr and εNd(t) values were calculated for an age of 179 Ma. Other parameters: 143Nd/144NdCHUR(0) = 0.512638, 147Sm/144NdCHUR( 0) = 0.1967, λ87Rb = 1.42 × 10− 11 a− 1, λ147Sm = 6.54 × 10− 12 a− 1; the 2σm error refers to the last digits. Pbm = measured ratios, t = initial ratios for an age of 179 Ma; Errors are 2σm and refer to the last digits.

38.21 38.09 38.10 38.18 38.23 38.28 15.58 15.56 15.55 15.57 15.58 15.60 18.58 18.36 18.28 18.45 18.67 18.34 38.529 ± 18 38.255 ± 13 38.319 ± 12 38.419 ± 13 38.428 ± 16 38.361 ± 16 15.598 ± 19 15.568 ± 13 15.572 ± 11 15.592 ± 12 15.596 ± 13 15.605 ± 15 18.926 ± 18 18.563 ± 12 18.664 ± 11 18.799 ± 11 18.913 ± 10 18.490 ± 14 722 739 792 715 775 793 0.9 0.8 1.0 1.0 0.3 1.1 0.512559 ± 12 0.512552 ± 14 0.512577 ± 13 0.512561 ± 10 0.512531 ± 12 0.512586 ± 12 0.0885 0.0900 0.1032 0.0878 0.0917 0.1050 12.33 11.22 16.99 12.71 14.50 13.65 1.805 1.669 2.900 1.846 2.200 2.370 0.70603 0.70698 0.70538 0.70579 0.70695 0.70627 7.27 9.75 11.1 15.8 3.49 1.87 106 136 94.8 124 109 99.1 WS-1 WS-2 WS-3 WS-4 WS-5 WS-9

42.2 40.3 24.7 22.8 90.1 154

0.724529 ± 14 0.731797 ± 13 0.733657 ± 11 0.746010 ± 13 0.715840 ± 14 0.711027 ± 13

Sr/86Sr ± 2σm 87

Rb/86Sr 87

Sr (ppm) Rb (ppm) Sample

Table 4 Sr, Nd and Pb isotopic compositions of the host porphyry.

87

Sr/86Sr(i)

Sm (ppm)

Nd (ppm)

147

Sm/144Nd

143

Nd/144Nd ± 2σm

εNd(t)

tDM (Ma)

206

Pb/204Pbm.

207

Pb/204Pbm

208

Pb/204Pbm.

206

Pb/204Pbt

207

Pb/204Pbt

208

Pb/204Pbt

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porphyry forming at 179 Ma. The host porphyry samples have a relatively wide variation range of ( 87Sr/ 86Sr)i from 0.70538 to 0.70698 and small positive εNd(t) values of +0.3 to + 1.1, suggesting that the host porphyry may derive from a mixed magma source and that the end-member components include mantle and continental crust (Fig. 9A). The initial 206Pb/ 204Pbt, 207Pb/ 204Pbt and 208Pb/ 204Pbt ratios of the host porphyry are 18.28 to 18.67, 15.55 to 15.60 and 38.10 to 38.28, respectively. In the 206Pb/ 204Pbt vs. ( 87Sr/ 86Sr)i and 206Pb/ 204 Pbt vs. εNd(t) diagrams (Fig. 9B), the host porphyry also shows features that are best interpreted as a mixed rock with both mantle and continental crust character. 7. Discussion 7.1. Ages of Cu–Mo mineralization and host porphyry Previous studies summarized the character of mineralization and the metallogenic association of the Wunugetushan porphyry Cu–Mo deposit and suggested that lithogenesis and mineralization were related to Yanshanian magmatism (Wang and Qin, 1988; Zhao and Zhang, 1997; Zhang et al., 2001; Qi et al., 2005). Qin et al. (1999) obtained single grain zircon U–Pb data by the evaporation method, Rb–Sr ages of whole rock samples and a K–Ar age for alteration sericite. The results of zircon U–Pb (188.3±0.6 Ma) and Rb–Sr method (183.9±1.0 Ma) were considered to represent an intrusion age of the porphyry magma, and the age of alteration sericite (183.5±1.7 Ma) was interpreted as the time of mineralization, even though a younger age (130–140 Ma; whole rock Rb–Sr age) had been long regarded as the ore-formation age for Wunugetushan (Wang and Qin, 1988; Zhao and Zhang, 1997; Zhang et al., 2001). More recently, Li et al. (2007a, 2007b) demonstrated that the Wunugetushan deposit was formed at 178±10 Ma using the Re–Os molybdenite geochronometer and considered that the deposit was associated with a continental collision environment. Unfortunately the Re–Os age given by Li et al. (2007a) is constrained by five data points and has a relatively large error. Recent studies have shown that the molybdenite Re–Os chronometer is a robust, accurate and precise method for age determinations (e.g., Stein et al., 2001). The Re–Os molybdenite chronometer appears to be reliable, even in situations where superimposed metamorphism and deformation are recognized (e.g., Bingen and Stein, 2003; Stein et al., 2004; Stein and Bingen, 2002). We also adopt this dating method to constrain the time of mineralization in this study and obtained a robust isochron age based on 7 data points of 177.6 ± 4.5 Ma. Furthermore, the initial Os ratio of −0.1 ± 9.3 indicates that there is almost no common Os involved in the isotopic system during mineralization, therefore almost all Os is of radiogenic origin. The Re–Os isochron age of 177.6 Ma is concordant, within error limits, with the results obtained by Li et al. (2007a, 2007b). The 40Ar/ 39Ar dating method was developed from the K–Ar method and has been widely used to determine the age of rock and minerals or the timing of their latest tectonothermal event. The fresh porphyry groundmass sample studied here yielded well-defined age spectra with a plateau age of 179.0 ± 1.9 Ma. The groundmass 40Ar/ 39 Ar age represents the cooling time after intrusion of the porphyry magma and suggests emplacement was not much earlier than 179 Ma. Our study suggests that the age of the major Cu–Mo mineralization is 179–178 Ma, and not the ~ 184 Ma or 140–130 Ma given in some earlier studies. 7.2. Sources and petrogenesis of the host porphyry In the εNd(t) vs. ( 87Sr/ 86Sr)i diagram (Fig. 9A), the host porphyry samples plot in the transitional zone of MORB and continental crust with a positive εNd(t) value and varied ( 87Sr/ 86Sr)i. This feature of the Sr–Nd isotope data implies that the primitive magma of the host

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Fig. 10. Tectonic discrimination diagrams for the host porphyry of the Wunugetushan mine show the collision environment of the monzogranitic porphyry. (A) R1 vs. R2 diagram (after Batchelor and Bowden, 1985). Late orogeny-related host porphyry in Gangdese is from Qu et al. (2004). (B) Rb vs. (Y + Nb) and Rb vs. (Yb + Ta) diagrams (after Pearce et al., 1984). R1 = 4Si − 11(Na + K) − 2(Fe + Ti) (mol), R2 = 6Ca + 2 Mg + Al (mol); ORG, oceanic ridge granite; VAG, volcanic arc granite; syn-COLG, syn-collision granite.

87

86

Fig. 9. (A) ( Sr/ Sr)i vs. εNd(t) diagram for the host porphyry of the Wunugetushan mine assuming an age of 179 Ma (modified from Civetta et al., 1998). (B) (206Pb/204Pb)t vs. (87Sr/86Sr)i and (206Pb/204Pb)t vs. εNd(t) diagrams of the host porphyry identified by Zindler and Hart (1986).

porphyry is derived from a mixed source comprising both mantle and continental crust. As is shown in the 206Pb/ 204Pbt vs. ( 87Sr/ 86Sr)i and 206Pb/ 204Pbt vs. εNd(t) diagrams (Fig. 9B), the host porphyry has a trend from MORB to EMII, emphasizing the important contribution from upper crustal material during ascent of the primitive porphyry magma. Rare earth element data show a strong LREE/HREE fractionation without an obvious negative Eu anomaly (Fig. 8A) and trace elements patterns (Fig. 8B) which are typical of arc magmatism in a subduction setting (Tatsumi et al., 1986; Wilson, 1989), where the suprasubduction lithospheric mantle is refertilized by an influx of a slabderived component (Arculus, 1994; Hawkesworth et al., 1993; Iwamori, 1998). It should be pointed out that depletion of Th relative to Ba among the enriched elements suggests that the enrichment was induced by the fluids released by the subducted slab in arc magma (Bédard, 1999; Seghedi et al., 2001). We consider that the metasomatism of slabderived fluids may relate to the subduction of the Mongol–Okhotsk Ocean under the Siberian Craton and the combined Mongolia–North China in Permian time (Fig. 11A; Li, 2006; Maruyama et al., 1997; Shi, 2006). The geochemical characteristics of the host porphyry show that lithospheric mantle metasomatized by fluids derived from a subducted slab plays an important role in magma generation.

In summary, the primitive magma of the host porphyry was derived from the crust–mantle transition zone. Some crustal material was added to the ascending magma under the collisional and compressional orogenic setting (see below). The mixing magma was emplaced into the shallow crust and formed the monzogranite porphyry. Later, the hydrothermal fluids of enriched sulfides induced the formation of the Wunugetushan porphyry Cu–Mo deposit (Fig. 11B). 7.3. Geodynamic setting of the host porphyry and its implications Mesozoic volcanic rocks are widely distributed on the southern side of the eastern Mongol–Okhotsk Orogen. U–Pb and 40Ar/ 39Ar geochronological data show that these volcanic rocks were formed between 163 and 113 Ma (Chen et al., 2006; Ying et al., 2008; Zhang et al., 2007). The geochemical data indicate that the extensive alkaline and sub-alkaline volcanism, including trachybasalt, basaltic trachyandesite, trachyandesite, trachydacite and rhyolite, can be attributed to post-orogenic extension of the Mongol–Okhotsk Orogen (Chen et al., 2006; Fan et al., 2003). Moreover, Wu et al. (2008) and Zorin et al. (2001) suggest that collision of the Siberian Craton with the combined Mongolia–North China Plate took place in the Middle to Late Jurassic in the eastern Mongol–Okhotsk Orogen. From this evidence, we infer that the tectonic setting of the Manzhouli area is collisional, that a compressional environment prevailed in the Middle Jurassic, and that the Wunugetushan deposit is related to a continental collision regime. The geochemistry of the host porphyry also supports a collisional setting for the Wunugetushan deposit. Features of the trace element and REE data clearly display comparable characters with the host porphyry of late orogenic setting in the Gangdese metallogenic belt (Qu

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Fig. 11. Regional tectonic evolutionary model of eastern Mongolia–Okhotsk Orogen shows pre-collisional and collisional settings. (A) Pre-collisional setting model showing the Mongol–Okhotsk Ocean slab subducted under the Siberia craton northward and Amalgamated Mongolia–North China plate southward, and the supra-subduction lithospheric mantle was metasomatized by fluids of subducted slab in Permian. (B) Collisional setting model showing the primitive magma derived from crust–mantle transition zone mixed abundant crustal substances during its ascent along the regional fault. The mixed magma emplaced into the shallow crust differentiating enriched-sulfides fluids which induced the formation of the Wunugetushan porphyry Cu–Mo deposit.

et al., 2004) and distinct differences, when compared to intraplate granites from NE China (Wu et al., 2002) (Fig. 8A, B). In the R1 vs. R2 diagram (Batchelor and Bowden, 1985), the host porphyry samples trend from a syn-collisional to late-orogenic environment, like the late orogeny-related host porphyries in Gangdese (Fig. 10A). These features imply that the host porphyry was formed in a collisional setting. In addition, the host porphyry has relatively lower Y, Yb, Nb and Ta concentrations and higher Rb concentrations, reflecting the syn-collisional orogenic signature (Fig. 10B; Pearce et al., 1984). Based on the geochemical characteristics we suggest that the host porphyry was formed during the continental collision between the Siberian Craton and combined Mongolia–North China plate after closure of the Mongol–Okhotsk Ocean (Fig. 11B; Li et al., 2007a, 2007b; Mao et al., 2005. Regarding the final time of closure of the eastern side of the Mongol–Okhotsk Ocean, this is still controversial and there are three principal different perspectives: (1) Early–Middle Jurassic (Chen et al., 2006; Sorokin et al., 2007; Tomurtogoo et al., 2005); (2) Middle–Late Jurassic (Ruzhentsev and Nekrasov, 2009; Ying et al., 2008); and (3) Early Cretaceous (Cogne et al., 2005; Halim et al., 1998; Kravchinsky et al., 2002; Metelkin et al., 2007). Formation of the Wunugetushan porphyry Cu–Mo deposit in the Early–Middle Jurassic may provide evidence for solving this controversial problem in the Manzhouli area. Considering the collisional geodynamic setting of the deposit we agree that the final closure of Mongol–Okhotsk Ocean in Manzhouli area may have occurred before 180 Ma, and possibly during the Early Jurassic.

(2)

(3)

(4)

(5)

porphyry intrusion. The characteristics of the host rocks suggest that the deposit is a typical porphyry-type deposit. 40 Ar/ 39Ar dating on groundmass of the host porphyry and Re– Os chronometric techniques on molybdenite allowed the emplacement age of the porphyry and the timing of mineralization to be constrained. Isotopic geochronology suggests that the Wunugetushan deposit was formed at around 179– 178 Ma. The host porphyry is geochemically characterized by enrichment of the LILE Ba, Rb, U, Th and Pb, and depletion of the HSFE Nb, Ta, Ti and HREE. The geochemical characteristics of the host porphyry show that lithospheric mantle metasomatized by fluids derived from a subducted slab plays an important role in magma generation. The Sr–Nd–Pb isotope data show that the host porphyry is characterized by widely varying ( 87Sr/ 86Sr)i (0.70538 to 0.70698), positive εNd(t) values (0.3 to 1.1) and relatively higher radiogenic Pb. All of these isotopic characteristics suggest that the magmatic source of the host porphyry contained two end-members - mantle and continental crust. Based on regional geology and geochemical evidence, the Wunugetushan porphyry deposit is considered to have formed during the continental collision period when the Siberian Craton and combined Mongolia–North China Plate collided after closure of the Mongol–Okhotsk Ocean. We further deduce that closure of the eastern Mongol–Okhotsk Ocean in the Manzhouli area may have occurred in the Early Jurassic.

8. Conclusions

Acknowledgments

The Wunugetushan Cu–Mo deposit is the second largest porphyrytype deposits in NE China. Our study on the geology, geochronology and geochemistry allows us to reach the following conclusions:

This work was financially supported by the National Natural Science Foundation (NSFC grant 41073037) and the National Basic Research Program of China (grant 2006CB403506). We thank all the technicians from Geochemical Analyses Center of IGGCAS, 40Ar/39Ar Laboratory of IGGCAS and Re–Os Laboratory, National Research Center of Geoanalysis of CSA for their kind support and help during experiment and data

(1) The Wunugetushan Cu–Mo deposit was formed within a complicated volcanic edifice and is related to the monzogranitic

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