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... Heishan Meng et al. (2015) Orthogneiss 485 link between the mineralization and granites. Previous studies on the Baiganhu mineral field reported regional metallogenesis Song et al., 2010), geological features of the deposits (Li et al., 2005), geochronological and geochemical studies of granites (e.g., Gao and Li, 2011;Li et al., 2012;Wang et al., 2014b), and the nature of ore-forming fluids and the genesis of Sn-W mineralization (Gao et al., 2014;Zheng et al., 2016). Previous researchers described these granites (Gao and Li, 2011;Li et al., 2012;Wang et al., 2014b) and some consider that it belongs to S-type (Wang et al., 2014). ...
... Previous studies on the Baiganhu mineral field reported regional metallogenesis Song et al., 2010), geological features of the deposits (Li et al., 2005), geochronological and geochemical studies of granites (e.g., Gao and Li, 2011;Li et al., 2012;Wang et al., 2014b), and the nature of ore-forming fluids and the genesis of Sn-W mineralization (Gao et al., 2014;Zheng et al., 2016). Previous researchers described these granites (Gao and Li, 2011;Li et al., 2012;Wang et al., 2014b) and some consider that it belongs to S-type (Wang et al., 2014). Since no systematic research has been conducted on the origin and the tectonic setting for the Sn-W mineralization, this contribution documents the petrology, whole-rock geochemistry, and whole-rock Nd and zircon Hf isotope compositions of granites genetically linked with the Sn-W mineralization to discuss the geological and tectonic setting for the mineralization. ...
... This regional extensional regime is accompanied by the intrusion of voluminous ca. 432-421 Ma A-type granites (Li et al., 2012;Li et al., 2013a;Gao et al., 2014;Zhang et al., 2014). Minor mafic and ultramafic intrusions also emplaced during this period ( Li et al., 2015). ...
... Bao et al. (2008) reported a TIMS U-Pb zircon age of 432 ± 1 Ma for the monzogranite suggesting a Middle Silurian age for the intrusion and associated mineralization. Other ages obtained for these rocks include (i) a SIMS U -Pb zircon ages of 421 ± 4 Ma and 422 ± 3 Ma for the monzogranite and potassic granite, respectively (Li et al., 2012), (ii) a LA-ICP-MS U -Pb zircon age of 430.5 ± 1.2 Ma for the monzogranite (Gao et al., 2014), and (iii) ID-TIMS and LA-MC-ICP-MS ages of 416 ± 1 Ma and 426 ± 13 Ma, respectively, for cassiterite (Deng et al., 2017). ...
... Our cassiterite U-Pb age is older than the earlier reported ID-TIMS and LA-ICP-MS cassiterite ages (416 ± 1 Ma and 426 ± 13 Ma) for the same deposit (Deng et al., 2017). Our LA-SF-ICP-MS age, however, is consistent with earlier reported SHRIMP and LA-ICP-MS zircon ages (430-420 Ma, Bao et al., 2008;Li et al., 2012;Gao et al., 2014). W -Sn mineralization in the Kekekaerde deposit is associated with the 430 Ma monzogranite (Gao et al., 2014). ...
Cassiterite, the economically most important tin mineral, typically has moderate U and variable common Pb contents, making it amenable for UPb dating. Cassiterite has extremely low Th/U ratios (Th/U < 0.01) and its ²⁰⁸Pb is dominantly common Pb. This is particularly helpful as there is significant interference of tungsten oxides on ²⁰²Hg and ²⁰⁴Pb. The feasibility of the ²⁰⁸Pb correction procedure is discussed in detail. The ²⁰⁸Pb corrected LA-SF-ICP-MS data are in good agreement with intercept ages in the Tera-Wasserburg diagram and ²⁰⁷Pb corrected ages.
Twelve cassiterite samples were investigated using the ID-TIMS and LA-SF-ICP-MS methods. The ID-TIMS results of Pit-AB, Rond-A, RG-114, BB#7 and 19GX cassiterite are reported for the first time in this study. RG-114, BB#7 and 19GX cassiterite have very low common Pb contents and are recommended for use as primary reference materials for in situ cassiterite. Pit-AB, Rond-A and Yankee cassiterite contain a small amount of common Pb, produce reliable and consistent ages and are suitable as primary reference materials. The remaining five cassiterite samples (Kard, Zinnwald, Els, XBD-W and Y724) were only investigated using the LA-SF-ICP-MS method and produce ages consistent with published age data from the host rocks associated with the tin deposits and with published UPb ages of cassiterite from the same deposits. We present an ID-TIMS UPb of 154.3 ± 0.7 Ma for the commonly used cassiterite reference material AY-4. This age differs from previously reported ID-TIMS ages. This age discrepancy is caused by different initial common Pb compositions rather than age heterogeneity.
... Ma (Feng et al., 2013). LA-ICP-MS and SIMS U\ \Pb zircon dating of the spatially associated monzogranite yield the ages of 430.5 ± 1.2 Ma (Gao et al., 2014) and 421 ± 3.7 Ma (Li et al., 2012a), respectively. Two wolframite samples (KA-18 and KA-19, Fig. 3M-O) as well as one cassiterite sample (BGH) are all chosen from quartz-vein type ores for dating and comparing with each other. ...
... Cassiterite (BGH) U\ \Pb dating in our analysis yields a lower intercept 206 Pb/ 238 U ages of 425.6 ± 5.7 Ma and a weighted mean 206 Pb/ 238 U age of 427.6 ± 5.1 Ma (Fig. 5d). These ages agree well with each other and fall in the age range of 412-427 Ma for W\ \Sn mineralization from previous studies (cassiterite U\ \Pb and muscovite 40 Ar/ 39 Ar dating, Feng et al., 2013;Gao et al., 2014;Zheng et al., 2016) and are also confirmed by the age of 421 ± 3.7 Ma (Li et al., 2012a) and 430.5 ± 1.2 Ma (Gao et al., 2014) from the spatially associated monzogranite. ...
Direct dating of W and WSn deposits by wolframite is more reliable relatively to gangue mineral and important for understanding their timing and genesis. However, such analysis still lacks of homogeneous wolframite standard recently. Due to containing considerable and variable common lead, and inhomogeneous in different grains, the wolframite sample of MTM, which is a promising candidate reference material proposed by previous studies, is not suitable as a primary standard for wolframite UPb dating by LA-ICP-MS using the normal normalization method as zircons. In this contribution, a modified normalization method is established for wolframite UPb dating, in which NIST612 or 614 and MTM are used for correction of PbPb and UPb ratios, respectively. Wolframite UPb dating are performed on the Langcun, Xihuashan, Piaotang, Shamai W or WSn deposits and the Baiganhu ore district, the obtained lower intercept ²⁰⁶Pb/²³⁸U ages are comparable with the ages from syngenetic molybdenite, cassiterite, muscovite and the genetically related granites, as well as wolframite by water vapor-assisted ns-LA-ICP-MS UPb dating method. The results of this analysis demonstrate that the robust age for W mineralization can be determined by LA-ICP-MS UPb dating of wolframite using this modified calibration method. Mineralization ages of 125–130 Ma by directly dating of metal minerals for the Langcun W, Jianfengpo Sn and large-size Xianglushan W deposits confirm that there exists an important WSn mineralization event in this period. The close temporal and spatial correlation indicates the granites and W-Cu-Mo-Pb-Zn-Sn mineralization have a genetic relationship with each other and are resulted from the same tectonic-magmatic-hydrothermal events during 140 to 120 Ma in South China.
... Volcanic -magma arc belt including different kinds of basic-acid magmatic rocks related to the early Paleozoic subduction of oceanic crust formed in Qiman Tagh area, such as the Yaziquan gabbro and diorite (480 ± 3 Ma; Cui Meihui et al., 2011), Kuangou-Xiaolangyashan basalt and rhyolite (440 ± 2 Ma and 450 ± 1.2 Ma; Wang Bingzhang et al., 2012) and Bashierxi granite (458 ± 9 Ma; Gao Xiaofeng et al., 2010). Consequently, the Baiganhu flysch basin formed due to the back-arc extension in Silurian (Li Guochen et al., 2012). Moreover, gabbro from Qingshuiquan area (452 ± 5 Ma;Sang Jizhen et al., 2016), meta-lava near Dulan County (448 ± 4 Ma;Chen Nengsong et al., 2002) and granodiorite from Gouli area (454 ± 2 Ma; Chen Jiajie et al., 2016) were the responsive product of the subduction northward of the Proto-Tethys Oceanic plate in the eastern part. ...
... Meanwhile, Wang Xiaoxia et al. (2012) and Wang Tao et al. (2016) suggested that the Wanbaogou rapakivi granite (441 ± 5 Ma) and Wulonggou granite (438 ± 3 Ma) formed in the syn-collisional/conversion of syn-collision and postcollision setting. A series of granites in Baiganhu Wu-Sn orefield (430-414 Ma;Gao Yongbao and Li Wenyuan, 2011;Li Guochen et al., 2012;Wang Zengzhen et al., 2014;Zhou Jianhou et al., 2015;Zheng Zhen et al., 2016), including a strongly peraluminous S-type granite, a high-K calc-alkaline I-type granite and a post-orogenic A 2 -type granite, were considered forming in the tectonic setting of post-collision and within-plate. The late Ordovician lava located near Dulan County yielded a 40 Ar-39 Ar plateau age of hornblende with metamorphic origin of 427 ± 4 Ma and represent the metamorphic peak timing of orogenic process (Chen Nengsong et al., 2002). ...
The Shitoukengde Ni-Cu deposit, located in the Eastern Kunlun Orogen, comprises three mafic–ultramafic complexes, with the No. I complex hosting six Ni-Cu orebodies found recently. The deposit is hosted in the small ultramafic bodies intruding Proterozoic metamorphic rocks. Complexes at Shitoukengde contain all kinds of mafic-ultramafic rocks, and olivine websterite and pyroxene peridotite are the most important Ni-Cu-hosted rocks. Zircon U-Pb dating suggests that the Shitoukengde Ni-Cu deposit formed in late Silurian (426–422 Ma), and their zircons have εHf(t) values of −9.4 to 5.9 with the older TDM1 ages (0.80–1.42 Ga). Mafic-ultramafic rocks from the No. I complex show the similar rare earth and trace element patterns, which are enriched in light rare earth elements and large ion lithophile elements (e.g., K, Rb, Th) and depleted in heavy rare earth elements and high field strength elements (e.g., Ta, Nb, Zr, Ti). Sulfides from the deposit have the slightly higher δ³⁴S values of 1.9–4.3± than the mantle (0 ± 2±). The major and trace element characteristics, and Sr-Nd-Pb and Hf, S isotopes indicate that their parental magmas originated from a metasomatised, asthenospheric mantle source which had previously been modified by subduction-related fluids, and experienced significant crustal contamination both in the magma chamber and during ascent triggering S oversaturation by addition of S and Si, that resulted in the deposition and enrichment of sulfides. Combined with the tectonic evolution, we suggest that the Shitoukengde Ni-Cu deposit formed in the post-collisional, extensional regime related to the subducted oceanic slab break-off after the Wanbaogou oceanic basalt plateau collaged northward to the Qaidam Block in late Silurian.
... The nature and origin of hydrothermal fluids forming the Baiganhu W-Sn deposit have been the subject of many mineralogical and fluid inclusion studies (Liu et al., 2007;Cao and Lai, 2012;Li et al., 2012;Li et al., 2013;Gao et al., 2014). The source and behavior of the ore-forming elements and whether they were sourced from crustal rocks or magmas, are still poorly understood. ...
... The Baiganhu W-Sn metallogenic belt is located in the western of Qiman Tagh (Fig. 1b), including three deposits at Bashierxi, Baiganhu, and Kekekaerde ( Fig. 2; Li et al., 2006Li et al., , 2012Li et al., , 2013Cao and Lai, 2012;Gao et al., 2014). All the orebodies are hosted in the Mesoproterozoic Xiaomiao Formation of the Jinshuikou Group, and occur on the northwest side of the NE-trending Baiganhua Fault. ...
... U-Pb ages for early Paleozoic magmatic rocks are indicated in the map. Data sources are superscripted as follows: (a) Cowgill et al. (2003); (b) Wu et al. (2007); (c) Yang et al. (2012); (d) Cao et al. (2010); (e) Li et al. (2009); (f) Ma et al. (2011); (g) Sun et al. (2012); (h) Dong et al. (2011); (i) this study; (j) Li et al. (2013); (k) Gao and Li (2011); (l) Guo et al. (2011); (m) Li et al. (2012); (n) Wang et al. (2010); (o) Cui et al. (2011). HKCA-high-K calc-alkaline. ...
... Qi et al. (2013) and Bao et al. (2013) also documented a suite of 380 ± 2 Ma (U-Pb zircon) basic dyke swarms in the Qimantagh. New geochemical and geochronological studies suggest that the granitoid rocks show the characteristics of I-type granites at 485-462 Ma (Cui, 2011;Li et al., (Watson and Harrison, 1983). ...
Voluminous and discrete early Paleozoic bimodal magmatic suites are thought to be the result of post-collisional extension following the amalgamation of East Kunlun and Altyn Tagh. In this paper, four representative magmatic units were studied for their geochemical fingerprint in conjunction with geochronological studies. The 467–445 Ma Mangya mafic suite shows E-MORB type rare earth element (REE) patterns that are as the result of asthenospheric interaction with a metasomatized subcontinental lithosphere. High-K calc-alkaline granodiorites, intruded at ca. 450 Ma, are characterized by high Mg#, the least fractionated REE pattern without an Eu anomaly, as well as high Sr and low Rb/Sr ratio. We interpret these geochemical signals to result from lower crustal melting of garnet amphibolite at pressures between 16–22 kbar. A 430–420 Ma A-type granite is interpreted to result from the melting of metaigneous rocks at middle to lower crustal depths. Lastly, a late magmatic pulse occurs between 400–380 Ma and is represented by the Alk granite. The Alk granite is interpreted to be a product of metapelite melts and is associated with a smaller volume of mafic melts. U–Pb zircon geochronology of Paleozoic igneous rocks of the Qimantagh–South Altyn reveals that most of the magmatic episodes are either coeval with, or post, extensional deformation. This phase of extension is supported by the exhumation of HP/UHP metamorphic rocks and crustal anatexis. Collectively, the evolutionary stages documented in this study correspond to a succession of post-collisional, postorogenic and, ultimately, within plate magmatic episodes. The overall features support orogenic collapse via removal of a thickened lithospheric root beneath the East Kunlun–Alty Tagh collisional orogen during early Paleozoic.
... A large W-Sn mineralisation occurred in the Baiganhu area during the post-collisional extension. Various intrusions related to the mineralisation also formed under post-collisional extensional regime at ca. 432-412 Ma between the Middle Altyn and Eastern Kunlun terranes (Supplementary Table S1, Fig. 1, Fig. 12) (Dong et al., 2018;Gao et al., 2010, Li et al., 2012, 2013aWang et al., 2014;Zhang et al., 2014;Zhou et al., 2015). ...
... The closure time of Qimantagh back-arc basin is constrained by the syn-collisional plutons with ages of ca. 425-420 Ma Li et al., 2012;Gao et al., 2014;Zhou et al., 2015;Zheng et al., 2016), and can also be limited by the post-collisional plutons with ages of 420-390 Ma. For instance, the gabbronorite and pyroxenite with ages of ca. ...
The Central China Orogenic Belt (CCOB) comprises, from the east to the west, the Tongbai-Dabie, Qinling, Qilian and Kunlun Orogens, and preserves abundant and important amalgamation records of the North China, South China, Qaidam, Tarim and Qiangtang Blocks. The CCOB offers an excellent window to the tectonic evolution from Proto-Tethys to Paleo-Tethys domains and the formation of East Asian continent. In this Centennial Review of Gondwana Research, we assemble comprehensive and multidisciplinary information of geological, geochemical, geophysical and high-precision geochronological dataset from individual orogens of the CCOB, together with a synthesis of Paleomagnetic data, to gain insights on the tectonic framework and evolutionary history of CCOB. The detailed and highly-integrated analysis leads to the following major conclusions. (1) Prior to ca. 550 Ma, break-up of the Rodinia supercontinent led to the formation of Proto-Tethys Ocean, wherein the above crustal blocks were isolated discrete units. (2) During ca. 541–485 Ma, spreading of all the embranchments of the Proto-Tethys Ocean at the early stage and the onset of subduction at the late stage. (3) Up to ca. 485–444 Ma, continued subduction of the Proto-Tethys Oceans resulted in opening and closing of the back-arc basin in the Qinling area. (4) During ca. 444–420 Ma, the Proto-Tethys Oceans along the Qilian and Shangdan were closing. (5) During ca. 420–300 Ma, the Paleo-Tethys Ocean in the Kunlun area inherited the Proto-Tethys Ocean, while the Paleo-Tethyan Mianlue Ocean experienced spreading. (6) At ca. 300–250 Ma, subduction retreat of the Kunlun Ocean occurred from the Aqikekulehu-Kunzhong suture to the Muztagh-Buqingshan-Anemaqen suture. (7) The Paleo-Tethys Ocean underwent eastward diachronous closing processes throughout the Kunlun to Qinling and Dabie areas during ca. 250–200 Ma; (8) The entire CCOB range has evolved into intracontinental deformation since 200 Ma.
... Some of the mafic-ultramafic complexes and A-type granitoids in the EKOB have similar ages, as exemplified by the Xiarihamu I mafic-ultramafic complex (423 ± 1 Ma; Wang et al. [63]), the Xiarihamu II mafic-ultramafic complex (424 ± 1 Ma; Peng et al. [7]), and the Baiganhu A-type moyite and monzonitic granites (ages of 422 ± 3 and 421 ± 3.7 Ma, respectively; Li et al. [64]). The Wulonggou A2-type granite, which formed at 426-424 Ma, represents the earliest evidence for a post-orogenic tectonic setting in this area (Xin et al. [9]). ...
The Akechukesai Ⅳ mafic–ultramafic complex, located in the western segment of the eastern Kunlun orogenic belt (EKOB), represents a newly-discovered complex, containing Ni ores at grades of up to 0.98% Ni. It is dominated by olivine pyroxenite, pyroxenite, and gabbro units. The gabbros are enriched in lithophile elements (e.g., Rb, U, and K) and light rare-earth elements (LREE), with negative anomalies in high field-strength elements, except Zr, Ta. Nb/Ta(∼5) and Zr/Hf (∼10) ratios lower than the primitive mantle and chondrites, respectively, indicate the influence of the mantle metasomatic process or fractionation of accessory mineral phases. Zircon U–Pb dating of the gabbro yielded an age of 423.9 ± 2.6 Ma, indicating that the complex formed contemporaneously with the Xiarihamu Ni deposit (423 ± 1 Ma). The gabbro has negative Hf(t) values (–11.3 to –1.2) with corresponding TDM1 ages of 1535–1092 Ma. The vein-like and disseminated mineralization (i.e. pyrite and pyrrhotite) have 34S values of 13.1‰–13.4‰ and 5.0‰–8.5‰, respectively, suggesting that the magmas that formed the complex assimilated crustal sulfur. They yield 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 17.323–18.472, 15.422–15.626, and 37.610–38.327, respectively, indicating Pb derived from multiple sources (i.e. mantle crustal sources). Geochemical and Hf–S–Pb isotopic characteristics suggest that the complex formed from a primitive magma derived by partial melting of a spinel- and garnet-bearing lherzolite mantle at variable degree of 5%–10%. This source region was geochemically enriched by previous interaction with slab-related fluids. Tectonic reconstruction suggests that the Akechukesai Ⅳ complex was generated in a post-collisional extensional environment.
... Bao et al. (2008) report a TIMS U-Pb zircon age of 432 ± 1 Ma for the same monzogranite suggesting a Middle Sil-urian age for the intrusion and mineralization. In addition, the monzogranite and potassic granite from the Kekekaerde area yield a SIMS U-Pb zircon age of 421 ± 4 Ma and 422 ± 3 Ma, respectively (Li et al., 2012b), demonstrating the presence of Late Silurian magmatism in the area. Feng et al. (2013), however, muscovite 40 Ar/ 39 Ar dating from a quartz-wolframite vein and greisenized granite give plateau ages of 412 ± 2 Ma and 412 ± 3 Ma, respectively, suggesting that the W-Sn mineralization is Early Devonian in age. ...
... XYGX -Xiang Yang Gou Xi; SXN -Shui Xian Nan; DTG -De Tan Gou. Li et al. 2012). These granitoids belong to the high-K calcalkaline series, and these rocks, together with the coeval mafic-ultramafic igneous complexes, indicate that the tectonic regime in the EKOB changed from a syn-to postcollisional setting in the late Silurian. ...
The East Kunlun Orogenic Belt (EKOB) in northern Tibet provides an important record of the amalgamation of the Wanbaogou oceanic basalt plateau and the Qaidam Block. Here we report geochemical, geochronological, and Hf isotopic data for newly identified late Silurian–Early Devonian mafic–ultramafic igneous complexes from the EKOB at the northern margin of the Tibetan Plateau. These complexes are dominantly composed of gabbro and pyroxenite rocks. Three complexes yield zircon U–Pb ages of 398.8 ± 1.8, 420.2 ± 1.2, and 413.4 ± 0.78 Ma. The εHf(t) values of zircons range from +0.8 to +3.3 with TDM1 ages of 897 to 998 Ma. Modelling of the geochemical data indicates that these igneous complexes have a hybrid origin, involving depleted mantle fluids derived from a previous subduction event and crustal materials. The geochemical and geochronological data suggest that these complexes formed in a post-collisional setting linked to break-off of a subducted oceanic slab, which occurred after the Wanbaogou oceanic basalt plateau amalgamated with the Qaidam Block in the late Silurian–Early Devonian.
... The syn-collisional plutons are represented by the monzogranite and syenogranite in the Baiganhu area. They belong to metaluminous to peraluminous and high K calcalkaline series, and exhibit enrichment of LREE with clear Eu anomaly, and depletion of Ba, Nb, Ta, Sr, P and Ti Li et al., 2012;Zhou et al., 2015). Zircons from granitoids display ε Hf (t) values of − 2.17-5.57 ...
The Kunlun Orogen is generally divided into the East Kunlun Orogenic Belt (E-KOB) and the West Kunlun Orogenic Belt (W-KOB) by the Altyn Tagh fault. The E-KOB forms part of the western segment of the Central China Orogenic System (CCOS), and is considered to have formed by the collision between the Qaidam Block and Qiangtang or Bayanhar Terrane as a consequence of the closure of the Kunlun Ocean (branch of the Paleo-Tethyan Ocean). Based on a compilation recently published high-quality data, this contribution provides an overview of the composition, nature and ages of the principal tectonic elements, including ophiolitic mélanges and related volcanic rocks, intrusive plutons and sedimentary cover sequences in the E-KOB. According to multiple lines of evidence from these tectonic elements, we proposed herewith a Paleozoic-Triassic subduction and accretionary tectonic model to interpret the spatiotemporal tectonic framework, plate subduction polarity, and tectonic processes from accretion to collision of the E-KOB. Three main ophiolitic mélange zones are identified in the E-KOB, from north to south, they are the Qimantagh-Xiangride ophiolitic mélange zone (QXM), the Aqikekulehu-Kunzhong ophiolitic mélange zone (AKM) and the Muztagh-Buqingshan-Anemaqen ophiolitic mélange zone (MBAM). According to these ophiolitic mélange zones, the E-KOB is divided into four major tectonic units: the North Qimantagh belt, the Central Kunlun belt, the South Kunlun belt and the Bayanhar Terrane. Based on several lines of evidence from geology, geochemistry and geochronology, the South Kunlun belt is interpreted as a Paleozoic to Triassic fore-arc and accretionary complex related to northward subduction of the Kunlun Ocean during the Ordovician-Triassic time. The AKM, MABM and the South Kunlun belt constitute a wide accretionary complex along the Kunlun Suture zone that marks final closure of the major Paleo-Tethyan Ocean, while the QXM represents the best expression of another suture that records final closure of the Qimantagh back-arc basin. The Central Kunlun Belt, as a long-lived island-arc terrane from Ordovician to Triassic times, rifted from the Qaidam Block due to the spreading of the Qimantagh back-arc basin during the period of ca. 485-425. Ma. Taken into all the geological, geochemical and geochronological lines of evidence together, a trench / arc / back-arc basin tectonic system in the E-KOB was built up, and evolved into a protracted and long-lived northward-subduction and accretion along the Kunlun Suture during Paleozoic and Triassic time.
... A range of zircon U-Pb ages of ca. 240-204 Ma for intermediate-felsic intrusions within these deposits indicate a close relationship between Triassic intrusive activity and skarn (-porphyry) mineralization ( Liu et al., 2006;Wang et al., 2009;Feng et al., 2011a;Li et al., 2012Li et al., , 2015Qu et al., 2015). Published molybdenite Re-Os and muscovite 40 Ar/ 39 Ar dates within these skarn and porphyry deposits gave a similar, narrow time span ranging from 239 to 224 Ma ( Li et al., 2008;Feng et al., 2009Feng et al., , 2011aGao, 2013;Tian et al., 2013;Qu et al., 2015;Yu et al., 2015), further indicating that hydrothermal events in the QMB mainly resulted from Triassic magmatic activity. ...
The Weibao Cu-Pb-Zn deposit is typical of skarn deposits in the Qimantagh metallogenic belt (QMB), East Kunlun Mountains, northern Tibetan Plateau. It comprises three ore blocks from west to east, known as Weixi, Main and Weidong. Mineralization in the Weibao deposit is intimately related to Late Triassic intrusions occurring at Weixi and Weidong, and orebodies are predominantly hosted by the Langyashan Formaton (marine carbonate rocks), and to a lesser extent the Devonian volcanic rocks. Skarns from Weixi and Weidong are characterized by a high garnet/pyroxene ratio and diopside- and andradite-rich composition of pyroxenes and garnets, indicating a proximal, oxidized type. In contrast, skarn mineralogy of Main indicates a slightly reduced condition, typical of Pb-Zn skarn deposits. At least five hydrothermal mineralization stages can be identified and the microthermometric study indicates a general trend of cooling and dilution of the magmatic-hydrothermal fluids. Significant precipitation of Cu-Fe sulfides commenced from the fluid with the temperature of 340-448°C and the salinity of 2.1-15.0 wt.%. NaCl equiv. Pb-Zn sulfides however mainly precipitated when the temperatures declined to < 370°C and the salinity declined to < 7.6 wt.% NaCl equiv. Carbone, hydrogen and oxygen isotopic composition of the fluids suggests a predominantly igneous source for the initial fluids, which were modified outward by fluid-rock interaction and mixing with meteoric waters. Both sulfur and lead isotope composition of sulfides supports a mixed sulfur and metal reservoir consisting of Triassic intrusive rocks and wall rocks. Compared to early skarn-forming stages and late quartz-carbonate stages, two ore-forming stages show clear evidence of fluid boiling and fluid-rock interaction. Combined with microthermometric data of ore-forming stages, it can be deduced that fluid cooling, boiling and fluid-rock interaction were responsible for the significant metal precipitation. The Weibao deposit shows many similarities with skarn deposits in the QMB, and its genetic model therefore can be extrapolated to other skarn deposits in this region.
... The Early Paleozoic granitoids, which are restricted to the North Qiman Tagh Mountains, are largely distibuted in the northern part of the Baiganhu and Adatan thrust fault (Gao and Li, 2011;Li et al., 2012;Li et al., 2013;Liu et al., 2014;Lu et al., 2005a;Wang, 2011;Wang et al., 2014b). The rocks are preferentially aligned along NE and NWW trends (Fig. 1). ...
... Bao et al. (2008) report a TIMS U-Pb zircon age of 432 ± 1 Ma for the same monzogranite suggesting a Middle Sil-urian age for the intrusion and mineralization. In addition, the monzogranite and potassic granite from the Kekekaerde area yield a SIMS U-Pb zircon age of 421 ± 4 Ma and 422 ± 3 Ma, respectively (Li et al., 2012b), demonstrating the presence of Late Silurian magmatism in the area. Feng et al. (2013), however, muscovite 40 Ar/ 39 Ar dating from a quartz-wolframite vein and greisenized granite give plateau ages of 412 ± 2 Ma and 412 ± 3 Ma, respectively, suggesting that the W-Sn mineralization is Early Devonian in age. ...
The Baiganhu W-Sn ore field in the northwestern area of the East Kunlun Orogen, NW China, contains three economically important W-Sn deposits, namely Kekekaerde, Baiganhu and Bashierxi. Timing of the W-Sn mineralization remains under debates due to lack of precise isotope dating directly conducted on ore minerals.We herewith report LA-MC-ICP-MS (laser ablation (multi-collector) inductively coupled plasma mass spectrometry) and ID-TIMS (isotope dilution thermal ionization mass spectrometry) cassiterite U-Pb ages for the Kekekaerde W-Sn deposit in the Baiganhu W-Sn ore field. The ID-TIMS cassiterite ²⁰⁶Pb/²³⁸U results yield a weighted mean age of 416±1Ma (95% confidence, MSWD=0.8), and the LA-MC-ICP-MS analytical data give a ²⁰⁶Pb/²⁰⁷Pb-²³⁸U/²⁰⁷Pb isochron age of 426±13Ma (95% confidence, MSWD=0.1). These two ages are same within errors, suggesting that the mineralization in the Baiganhu W-Sn ore field occurred at ca. 416Ma. These new ages and understandings are consistent with the previously reported zircon U-Pb ages of 430-420Ma for the ore-bearing granites in the ore-field, and with the ⁴⁰Ar/³⁹Ar plateau ages of ca. 412Ma for the hydrothermal muscovite from ore-bearing quartz veins and greinsenized granite. It shows that the granite magmatism and its associated hydrothermal mineralization resulted from the Caledonian Orogeny that accommodated the closure of the Proto-Tethys, followed by the continental collision between the Central Kunlun, Northern Kunlun terranes and the Qaidam Block.
... Abundant intrusions of different ages are preserved in the Qimantagh area (Fig. 1b). Both of the Paleozoic and Triassic granitoids are volumetrically widespread Feng et al., 2010Feng et al., , 2012Gao and Li, 2011;Gao et al., 2012aGao et al., , 2012bGao et al., , 2014aGao et al., , 2014bLi et al., 2012;Xiao et al., 2013), whereas economic Cu-Pb-Zn-Fe mineralization is mainly related to Triassic granitoids (e.g., Feng et al., 2009Feng et al., , 2010Feng et al., , 2011aFeng et al., , 2012. Other igneous rocks, such as mafic dykes, are mainly post-skarn and post-mineralization (e.g., Luo et al., 2002). ...
The Weibao copper–lead–zinc deposit, located in the eastern part of the Qimantagh area, East Kunlun Orogenic Belt (EKOB), consists of three skarn ore blocks known as Weixi, Main and Weidong from west to east. The mineralization within the Weibao Cu–Pb–Zn deposit is hosted by the Mesoproterozoic Langyashan Formation. In this study, we describe for the first time basaltic lavas that intruded into this host sequence and chronological, isotopic, major and trace element data of these volcanic rocks are presented here to constrain their eruption age as well as the tectonic setting. Two basaltic lava samples yield sensitive, high-resolution ion-microprobe (SHRIMP) U–Pb zircon ages of 393.0±5.5 Ma–392.0±5.0 Ma, indicating that volcanic rocks in the Weibao deposit erupted in Middle Devonian. The majority of the volcanic rocks have compositions characterized by high potassium, light rare earth element (LREE)-enriched patterns in chondrite-normalized rare earth elements (REE) diagrams, and evident enrichment of Rb, Ba and K and depletion of Th, U, Nb and Ta contents in primitive mantle-normalized patterns, although the degrees of enrichment and depletion are variable. These characteristics of major and trace element data highlight a hornblende-dominated fractionation during ascent of magmas. The εHf(T) values of zircons are relatively scattered and slightly enriched, ranging from -2.6 to +7.5. Modelling the features of the major, trace and isotopic element data indicates a hybrid origin involving combined depleted mantle (and hence asthenospheric mantle) and melts and/or fluids inherited from an early subduction event. Besides, these geochronological and geochemical data, together with previously published data in the EKOB, suggest that the Weibao basaltic lavas formed in a post-collisional setting, and that the Qimantagh area underwent strong interactions between mantle and crust in Early Paleozoic–Middle Devonian.
... The new world-class Jiangnan W ore belt was defined , located to the south of and parallel to the Middle-Lower Yangtze River porphyry-skarn Cu-Au-Mo-Fe ore belt (Mao et al., 2011d;Chang et al., 2019), and W ores were explored and studied (Mao, Z.H., et al., 2013. Exploration at Baiganhu at the remote western end of the eastern Kunlun orogen, Xinjiang Uygur Autonomous Region (Gao and Li, 2011;Li, G.C., et al., 2012;Zhou et al., 2016;Zheng, Z., et al., 2016), has indicated large potential reserves of W. ...
This study focuses on quartz monzonite and diorite plutons in Dachaigou, East Kunlun, examining their formation, age, petrogenesis, magmatic source, and tectonic setting. Through comprehensive field observations, zircon geochronology, geochemistry, and Hf isotope analysis, new insights into the Paleozoic tectonic evolution of the proto-Tethys Ocean in the East Kunlun orogenic belt are provided. Zircon U–Pb dating reveals that quartz monzonite and diorite formed at 417.4 ± 2.1 and 404.6 ± 1.8 Ma, respectively. Geochemical analysis shows that the A/CNK value of quartz monzonite ranges from 0.98 to 1.07, with the Pb content proportional to SiO2, which aligns with the characteristics of I-type granite. The εHf(t) values for quartz monzonite and diorite are −0.84 to 2.2 and −13.22 to 2.04, respectively. Considering the formation age, geochemical characteristics, and regional tectonic evolution, it is concluded that quartz monzonite has a crust-derived origin, whereas diorite has a crust–mantle mixing origin. Both were formed in a post-collision extensional tectonic setting resulting from slab break-off, implying the Proto-Tethys Ocean East Kunlun entered a post-collisional extension stage in the Late Silurian–Early Devonian.
Tungsten and Sn deposits in China are widely distributed in the South China block (i.e., Yangtze craton-Cathaysian block), Himalaya, Tibetan, Sanjiang, Kunlun, Qilian, Qinling, Dabie, and Sulu orogens, and Central Asian orogenic belt. Among these, the South China block hosts the majority of the mineralization with about 73% (9.943 million tonnes WO3) and 85% (6.561 million tonnes Sn) of the country’s total W and Sn resources, respectively. The W resource mainly occurs as skarn (63%), quartz-vein (17%), porphyry (17%), and greisen (3%) Sulu deposits, whereas Sn is present in skarn (81%), quartz veins that are typically tourmaline-bearing (6%), sulfide-rich veins or mantos (5%), greisen (5%), and porphyry (3%) Sulu deposits.
The W and Sn mineralization formed during numerous events from Neoproterozoic to Paleocene with a peak in the period from the Middle Jurassic to Early Cretaceous, and with an uneven spatial and temporal distribution pattern. The Neoproterozoic Sn (W) deposits (850–790 Ma) occur on the southern and western margins of the Yangtze craton, the early Paleozoic W(Sn) deposits (450–410 Ma) are mainly distributed in the northern Qilian and the westernmost part of the eastern Kunlun orogens, the late Paleozoic Sn and W deposits (310–280 Ma) are mainly developed in the western part of the Central Asian orogenic belt, the Triassic W and Sn deposits (250–210 Ma) are widely scattered over the whole country, the Early Jurassic to Cretaceous W and Sn deposits (198–80 Ma) mainly occur in eastern China, and the late Early Cretaceous to Cenozoic Sn and W deposits (121–56 Ma) are exposed in the Himalaya-Tibetan-Sanjiang orogen.
The petrologic characteristics of W- and Sn-related granitoids in China vary with the associated ore elements and can be divided into the Sn-dominant, W-dominant, W-Cu, and Mo-W (or W-Mo) groups. The granitoids associated with the Sn- and W-dominant magmatic-hydrothermal systems are highly fractionated S- and I-type, high-K calc-alkaline and (or) shoshonitic intrusions that show a metaluminous to peraluminous nature. They exhibit enrichments in F, B, Be, Rb, Nb, and Ta, depletions in Ti, Ca, Sr, Eu, Ba, and Zr, and strongly negative Eu anomalies. The granitoids associated with W-Cu and W-Mo deposits are of a high-K calc-alkaline to shoshonitic nature, metaluminous, depleted in Nb and Ta, and display weakly negative Eu anomalies. Granitoids associated with Sn- and W-dominant deposits are reduced, whereas those linked to W-Cu and Mo-W deposits are relatively more oxidized. The magma sources of W-dominant granitoids are ancient crust, whereas those connected with Sn, Mo-W, and W-Cu deposits are from variable mixing of ancient and juvenile crustal components.
The spatial and temporal distribution pattern of W and Sn deposits in China is intimately related to the regional geodynamic evolution. The Neoproterozoic Sn deposits are associated with peraluminous, highly fractionated, and volatile-enriched (boron and fluorine) S-type granites sourced from the melting of an ancient crust in a postcollisional setting related to the assembly of the Rodinia supercontinent. The early Paleozoic W deposits are genetically associated with highly fractionated S-type granites formed during postcollisional events and were derived from the partial melting of a thickened continental crust in the context of Proto-Tethyan assembly. Granitoids associated with late Paleozoic Sn and W deposits were derived from the melting of an ancient and juvenile crust with I-type affinity associated with the closure of the Paleo-Asian Ocean. Although the Triassic W and Sn deposits are related to the assembly of Asian blocks within the Pangea supercontinent, their geologic settings are variable. Those in the South China block and the Himalaya-Tibetan-Sanjiang belt are associated with collision and magma derivation through the partial melting of a thickened continental crust, whereas in the Kunlun-Qilian-Qinling-Dabie-Sulu orogen and the Central Asian orogenic belt, a postcollisional extensional setting dominates. The Early Jurassic (198–176 Ma) W deposits, located in the northern part of northeast China, are associated with highly fractionated I-type granites derived from melting of juvenile crust and emplaced during the subduction of the Mongol-Okhotsk oceanic plate. The extensive group of Middle Jurassic to Cretaceous W and Sn deposits formed at two stages at 170 to 135 and 135 to 80 Ma. The former stage is associated with highly fractionated S- and I-type granites that are the products of partial melting of thickened crust with heat input possibly derived from a slab window associated with the Paleo-Pacific oceanic plate subduction beneath the Eurasian continent. The later stage is closely associated with NNE-trending strike-slip faults along the Eurasian continental margin and is coeval with the formation of rift basins, metamorphic core complexes, and porphyry-epithermal Cu-Au-Ag deposits. These processes, which were instrumental for the formation of a wide range of mineral deposits, can be ascribed to the regional lithospheric thinning and delamination of a thickened lithosphere and thermal erosion in a postsubduction extensional setting. The 121 to 56 Ma Sn deposits in the Himalaya-Tibetan-Sanjiang orogen are associated with S-type granite or I-type granodiorite emplacement in a back-arc extensional setting during Neo-Tethys plate subduction.
The tectonic evolution of the Proto‑Tethys in the East Kunlun Orogenic Belt (EKOB) is controversial. Herein, new petrological, whole-rock geochemical, zircon U–Pb geochronological and zircon Lu–Hf isotopic data for early Paleozoic intrusive rocks in the Delite region are reported. LA-ICP-MS zircon U–Pb isotopic data show that the Delite monzogranite and quartz syenite were formed at 437.0 ± 2.9 Ma and 424.8 ± 2.2 Ma, respectively. The Delite monzogranite contains high SiO2, Al2O3 and K2O and A/CNK ratios, but low MgO and Mg# values (33–38). This study considers that the monzogranite is a typical S-type granite and originated from partial melting of ancient crustal clastic material (metagreywacke) in a syn-collision setting. The quartz syenite is K-rich and Mg-poor, with low Mg# values (36–41), exhibiting geochemical signatures of an alkalic syenite derived from partial melting of basaltic lower crust in a post-collision setting. Combining with the previous work, we suggest that in the middle part of the EKOB the Proto-Tethys closed at ca 437 Ma with a post-collisional setting after ca 427 Ma.
• KEY POINTS
• Zircons LA-ICP-MS U–Pb isotopic data indicate that the Delite monzogranite and quartz syenite were formed at 437.0 ± 2.9 Ma and 424.8 ± 2.2 Ma, respectively.
• The Delite monzogranite was formed in a syn-collision setting. The Delite quartz syenite was related to the post-collision setting.
• It is suggested that the Proto-Tethys closed at ca 437 Ma in the middle part of the EKOB, and the post-collisional setting was after ca 427 Ma in the EKOB.
The East Kunlun Orogen (EKO) is located in the western part of the Central Asian Orogenic Belt, and it records the Neoproterozoic–Early Devonian tectonic evolution involving the subduction and extinction of the Proto-Tethys Ocean. The Heihaibei granite is located in the South Kunlun belt within EKO. In this study, geochronology, geochemistry, and Hf isotope analysis of Heihaibei monzogranite and granodiorite were carried out. Their LA-ICP-MS zircon U-Pb results yielded ages of 414.1 ± 2.0 and 417.8 ± 2.0 Ma. The Heihaibei granite is peraluminous (A/CNK = 0.99–1.30), with high alkali contents (7.76–9.14 wt.%) and 10 000 Ga/Al (2.60–3.38), FeOT/MgO (27.6–49.5), and Y/Nb ratios (1.93–2.93), suggesting that the Heihaibei granite is an A2-type granite. The Heihaibei granite samples have zircon εHf(t) values ranging from −6.3 to −0.3, which suggests that the Early Devonian granite was derived from partial melting of Mesoproterozoic (TDM2 = 1797–1415 Ma) crust. When considering data on contemporaneous granites, geochronological and geochemical data for the Heihaibei granite indicate that it was emplaced in a post-collisional extension environment following the closure of the Proto-Tethys Ocean. The Heihaibei granite was formed by extension of the southern subduction accretionary complex as part of the post-collisional setting during the closure of the Proto-Tethys Ocean.
The East Asian continent records a complex geologic and tectonic history that involved the amalgamation of several small- to medium-sized blocks from Laurasia or Gondwana. The China continent is located at the core of East Asia, and is the key to understanding the formation and evolution of the East Asian Continent. The most important tectonic framework controlling the formation and evolution of the main China continent is the EW-trending Central China Orogenic Belt and the NS-trending Helan-Chuandian Orogenic Belt, defined as the ‘Cross Orogenic Belts’. The former includes, from east to west, the Qinling, Qilian and Kunlun Orogens, which were formed by the subduction-collision between the southern and northern continental blocks during the Early Paleozoic–Triassic and constitute the mainland of China Continent. Following this, the Central China Orogenic Belt was overprinted by the Mesozoic to Cenozoic intracontinental orogenic events, resulting in a prominent north and south division of geology, geography, ecology, environment, economy and culture. The latter inherited the Paleoproterozoic and the Neoproterozoic plate tectonic frameworks in its north and south, respectively, and was gradually transformed into the continental margin of the Paleo-Asian Ocean or Paleo-Tethys tectonic domain. Associated with the Neo-Tethys tectonic evolution, it evolved into the eastern boundary of the uplift and expansion of the Tibetan Plateau, controlling the Late Mesozoic–Cenozoic reverse evolution of the western and eastern China Continent. The Cross Orogenic Belts experienced multiple phases of uplift, which were dominated by deep geological process together with surface geomorphologic influence. The uplift of the Cross Orogenic Belts resulted in differential evolution of the climate, environment, as well as economy and culture in four quadrants of the China Continent.
The Qaidam Basin is the largest intermountain basin within the northeastern Tibetan Plateau, which is a key area to understand the tectonic evolution of the Tibetan Plateau. The evolution history and provenances of the western Qaidam Basin were influenced by the surrounding ranges and recorded the history of the topographic changes. To ascertain the relationship between the sediments in the western Qaidam Basin and surrounding source regions is important to understand the tectonic evolution of the Qaidam Basin and the northern Tibetan Plateau. In this study, the 745 detrital zircon LA-ICP-MS U-Pb ages of 14 samples collected from the Heishuigou and Mangya sections were used to trace the provenances of the Jurassic sediments in the western Qaidam Basin and to further constrain the tectonic evolution of the Qaidam Basin in the Meso-Cenozoic. The detrital zircon ages show three age peaks at ∼450 Ma, ∼380 Ma, and ∼260 Ma. Two dated granitoids from the Mangya area have weighted mean ages of 451±3 Ma and 384±3 Ma, respectively. Compared with published zircon U-Pb ages from the relevant basement and magmatic and metamorphic rocks, our results indicate that the South Altyn Tagh Range and the South Qilian Range were main sources of the early-middle Jurassic sediments in the western Qaidam Basin. Together with published stratigraphic, paleocurrent, and seismic profile data, the Jurassic proto-basin was reconstructed. The original Jurassic basin was developed along the southwestern margin of the Paleo-South Qilian Range and displaced sinistrally by the Altyn Tagh Fault during the Cenozoic.
The Proterozoic–Phanerozoic tectonic evolution of the Qilian Shan, Qaidam Basin, and Eastern Kunlun Range was key to the construction of the Asian continent, and understanding the paleogeography of these regions is critical to reconstructing the ancient oceanic domains of central Asia. This issue is particularly important regarding the paleogeography of the North China-Tarim continent and South China craton, which have experienced significant late Neoproterozoic rifting and Phanerozoic deformation. In this study, we integrated new and existing geologic field observations and geochronology across northern Tibet to examine the tectonic evolution of the Qilian-Qaidam-Kunlun
continent and its relationships with the North China-Tarim continent to the north and
South China craton to the south. Our results show that subduction and subsequent
collision between the Tarim-North China, Qilian-Qaidam-Kunlun, and South China continents occurred in the early Neoproterozoic. Late Neoproterozoic rifting opened
the North Qilian, South Qilian, and Paleo-Kunlun oceans. Opening of the South Qilian
and Paleo-Kunlun oceans followed the trace of an early Neoproterozoic suture. The opening of the Paleo-Kunlun Ocean (ca. 600 Ma) occurred later than the opening of the North and South Qilian oceans (ca. 740–730 Ma). Closure of the North Qilian and South Qilian oceans occurred in the Early Silurian (ca. 440 Ma), whereas the final consumption
of the Paleo-Kunlun Ocean occurred in the Devonian (ca. 360 Ma). Northward subduction
of the Neo-Kunlun oceanic lithosphere initiated at ca. 270 Ma, followed by slab rollback beginning at ca. 225 Ma evidenced in the South Qilian Shan and at ca. 194 Ma evidenced in the Eastern Kunlun Range. This tectonic evolution is supported by spatial trends in the timing of magmatism and paleo-crustal thickness across the Qilian-Qaidam-Kunlun continent. Lastly, we suggest that two Greater North China and South China continents, located along the southern margin of Laurasia, were separated in the early Neoproterozoic along the future Kunlun-Qinling-Dabie suture.
High-Mg andesites (HMAs) and their cognate intrusive rocks constitute volumetrically very small proportions of the total earth, and are mainly distributed along the edges of convergent plates. Petrogenetic studies can provide possible solutions for discrepancies in the geodynamics and subduction zone evolution. This paper presents the first ever reports of the newly discovered high-Mg diorite in Akechukesai area, the western part of the East Kunlun Orogenic Belt, and provides a reference for the evolutionary history and subduction mechanism of the Proto-Tethys Ocean. Akechukesai high-Mg diorites yielded a weighted mean zircon U-Pb dating age of 427.3 ± 2.3 Ma (Middle Silurian). Results of the geochemical analyses show that the high-Mg diorites were high-K calc-alkaline series with the SiO2 content ranging 50.40 to 55.41 wt%. They are characterized by high values of Mg# (67–77), high MgO (6.92–10.58 wt%), TiO2 (0.53–0.87 wt%), Cr (286–615 ppm), Ni (61–124 ppm), Ba (570–927 ppm) contents, and low FeOtotal/MgO ratios (0.54–0.89). Furthermore, they exhibit nearly flat right-declined rare-earth element (REE) patterns with slight LREE enrichment. The samples are enriched in large ion lithophile elements (e.g., Ba, Rb, and Th) and depleted in high field strength elements (e.g., Ta, Nb, and Ti). These geochemical features are analogous to the sanukitic high-Mg andesites. The mean value of the initial εHf(t) is −1.3, indicating that the source is enriched mantle. The values of Rb/Cs, Ba/La, and La/Sm ratios suggest that subducting sediments formed an important component of the magmatic source. The presence of water-bearing minerals such as amphibole and biotite indicate a water-rich and oxygen-rich primitive magma system. Petrogenetic analysis indicates that the Akechukesai high-Mg diorites probably formed by melts and aqueous fluids produced from partial melting of the subducting sediments interacting with mantle peridotites. We hypothesize that, after the closure of the Proto-Tethys Ocean Basin in the Middle Silurian, the deep subducted slab broke-off and formed a slab window, asthenospheric material upwelled heating the subducting sediments and causing them to melt. Thus, we suggest that the emplacement of the Akechukesai high-Mg diorites mark the commencement of post-collisional magmatism.
The Jingren deposit, which contains a large amount of late Triassic intrusive rocks, is part of the Qimantage metallogenic belt of the eastern Kunlun orogenic belt, which is the largest metallogenic belt in Qinghai Province, northwestern China. Exploration data show that the metal resources of the Jingren deposit are greater than 93000 t in a mining area of 76.15 km2, which indicates significant exploration potential in the near future. Three west‐east‐trending faults, F1, F2, and F3, dominate the extension of the mineralization zone, which consists of chalcopyrite, pyrite, magnetite, galena, sphalerite, and molybdenite as well as bismuth‐bearing minerals. However, previous research does not show a unified opinion on the timing or the origin of the mineralization owing to a lack of geochronological data and poor exposure conditions. In the present study, Re‐Os isotopic dating is conducted on six molybdenite samples collected from a borehole of the granodiorite in the Jingren deposit using negative thermal ionization mass spectrometry (NTIMS). The 187Re and 187Os concentrations are shown to be 0.26–4.40 ppm and 1.03–16.46 ppb, respectively, with an initial 187Os/188Os value of 0.06±0.19. This proves that the Jingren deposit has a metallogenic age of (225±4) Ma and is the product of unitive mineralization of the Qimantage metallogenic belt. Re‐Os dating shows that the Jingren deposit might be an Indosinian metallogeny. In addition, the Re content of these samples, at 0.42×10−6 to 7.00×10−6 shows that the mineralization was derived mainly from crustal source. Furthermore, electron probe microanalysis (EPMA) was conducted on chalcopyrite obtained from 22 metallic mineral samples. The results revealed (Fe + Cu)/S ratios of 1.801–1.947 with an average of 1.852, which is lower than 1.875 and the main ore body formed in a relatively higher temperature environment than the surrounding rocks. These data indicate that the Jingren deposit formed in a metallogenic environment at lower temperature. Moreover, according to the TiO2–Al2O3–(MgO + MnO) and TiO2–Al2O3–MgO genetic classification diagram of the magnetite, the Jingren deposit most likely belongs to the skarn family. Further, the Co–Ni–As genetic classification diagram of the pyrite indicates sedimentary and skarn genetic characteristics.
The Qiman Tagh W-Sn ore belt is located in the westernmost sector of the East Kunlun Orogen, NW China. It has been recognized as a unique W-Sn belt that formed in the early Paleozoic and related to closure of the Proto-Tethys. To understand the evolution of ore-forming fluids and its relationship with the tectonic setting of East Kunlun Orogen, we report the results obtained from fluid inclusion and H-O isotopic studies of ores and quartz veins for the Qiman Tagh W-Sn ore belt. Mineralization in Qiman Tagh includes four stages characterized by quartz-cassiterite-wolframite assemblage stage 1, quartz ± scheelite assemblage stage 2, quartz-polymetallic sulfides stage 3, and ore-barren veins stage 4. The former two stages are conducive to mineralization, while the latter two stages are less important. The fluid inclusions are distinguished between CO 2-H 2 O (C-type) and NaCl-H 2 O (W-type) in composition, containing a trace of CH 4 , N 2 , C 2 H 6 , SO 2 , and CO 3 2-. Cassiterite and quartz in stage 1, instead of wolframite, contain a great deal of C-type inclusions. All inclusions in minerals of stage 1 yield homogenization temperatures of 230.1-384.1°C (peaking at 310-320°C), with salinities lower than 14.76 wt% NaCl equiv. and bulk densities of 0.63-0.89 g/cm 3. The stage 2 minerals contain both two types of inclusions, yielding homogenization temperatures of 183.4-335.9°C (peaking at 280-290°C), with salinities lower than 14.53 wt% NaCl equiv. and bulk densities of 0.66-0.97 g/cm 3. Fluid inclusions in minerals of stages 3 and 4 are mainly W-type and homogenized at temperatures of 140.6-277.6°C (peaking 210-220°C), and 116.9-255.1°C (peaking 160-170°C), respectively. The H-O isotopic systematics shows that the fluids were dominated by magmatic water in stages 1 and 2, but by meteoric water in stages 3 and 4. Integrating all the geological and geochemical data, we conclude that the fluids forming the Qiman Tagh W-Sn ore belt evolved from granite-derived, CO 2-rich and reducing, to meteoric water-dominated, CO 2-poor and oxidizing. Fluid immiscibility, cooling and interaction with rocks are main mechanisms for metallic deposition.
The recently discovered Akechukesai mafic–ultramafic complex is located in the East Kunlun Orogenic Belt, northern Tibet Plateau, China. Two mafic–ultramafic complexes (Akechukesai I and Ⅱ) intrude marble of the Cambrian–Ordovician Tanjianshan Group. Cu–Ni sulfide mineralization occurs in these complexes. Pyroxenite in the Akechukesai-I complex has an age of 422 ± 10 Ma(1σ), similar to that of the Xiarihamu and Shitoukengde Cu–Ni deposits of the East Kunlun area. The positive εHf(t) values (1.7–4.9) and SiO2, TiO2, and Al2O3 contents of clinopyroxene from pyroxenite suggest that the parental magma of the Akechukesai-I complex was derived from depleted mantle composed of garnet lherzolite and spinel lherzolite in varying proportions. Pyroxenite of the Akechukesai-I complex has (⁸⁷Sr/⁸⁶Sr)i ratios of 0.70993–0.71405, εNd(t) values of −1.97 to −6.64, (²⁰⁶Pb/²⁰⁴Pb)i ratios of 17.113–18.994, (²⁰⁷Pb/²⁰⁴Pb)i ratios of 15.548–15.673, and (²⁰⁸Pb/²⁰⁴Pb)i ratios of 37.066–38.650, which together indicate a depleted mantle source with 18–35 wt.% upper-crustal contamination. δ³⁴S values of sulfide minerals are 5‰–11.5‰ with S/Se ratios of ore-bearing pyroxenite being in the range 3738–15,501, both being higher than mantle values (−2‰ to +2‰ and 2850–4350, respectively) and indicating the addition of crustal S. The incorporation of primitive magma into the marble host during ascent caused a reduction in sulfide solubility owing to increased oxygen fugacity of the magma, leading to S saturation. These observations and the geodynamic setting indicate that the complex is a favorable environment for mineralization.
Subduction-related basaltic rocks in active continental margins should record information about the lithospheric mantle. Mafic rocks from the Qimantag region of the East Kunlun Orogenic Belt (EKOB), NW China, can be used to constrain the evolution of mantle sources. The Heishan basalts (445 Ma) and Xiarihamu gabbros (427 Ma) display distinct geochemical and isotopic features, with basalts yielding relatively lower Na2O+K2O (1.48–4.16 wt.%) and Mg# (0.50–0.57) than gabbros (Na2O+K2O = 2.96–4.07 wt.%, Mg# = 0.65–0.81). Although the basalts and gabbros show similar enrichment of LILE and depletion of HFSE, the gabbros have higher Th/Y and lower Sm/Th and Nb/U ratios than the basalts, indicative of derivation from a more enriched mantle source. The Heishan basalts have relatively positive εNd(t) values (+4.7 to +5.8) whereas the Xiarihamu gabbros have negative εNd(t) values ranging from −5.5 to −3.8. Crustal contamination played an insignificant role in the formation of the basalts and gabbros. Our data suggest that the basalts originated from a depleted mantle source, slightly enriched by subduction-related fluids, whereas the gabbros originated from an enriched mantle source. These findings support a subduction-related progressive lithospheric mantle enrichment model over ~20 Ma beneath the Qimantag region in the Early Palaeozoic.
The Qiman Tagh Orogenic Belt (QTOB), located along the northern part of the Qinghai-Tibet plateau, was constructed through protracted accretion and collision of a collage of terranes during subduction and closure of the Qiman Tagh Ocean, a branch of Paleo-Tethys Ocean from the Neoproterozoic to Early Mesozoic. The orogen is located between the Qaidam Basin and Kumukuri Basin, and cut by the Altun Fault to the west. The early Neoproterozoic (ca. 1000–820 Ma) ages from this orogen suggest a link with the formation of the supercontinent Rodinia. The QTOB is tectonically divided into the North Qiman Tagh Terrane (NQT) and the South Qiman Tagh Terrane (SQT). The NQT developed as an active continental margin, and preserves abundant Early Paleozoic granitoids, which possibly formed through the melting of old basement, and a series of mafic–ultramafic rocks considered as VA (volcanic arc) type ophiolites. In contrast, the SQT witnessed intra-oceanic subduction, where SSZ (supra-subduction zone) type ophiolites are documented together with island arc tholeiite (IAT) and calc-alkaline lavas, in a primary oceanic island arc environment during the Early Paleozoic. With continued subduction, the young island arc was transformed into a mature island arc with thickened crust. This region preserves typical evidence for sedimentation and volcanism in the initial stages of volcanic arc development. The collision between the SQT and NQT occurred probably in the Late Silurian (ca. 422 Ma) and continued until ca. 398 Ma, as evidenced from the ages of the abundant within-plate granitic magmatism in the NQT that formed after 398 Ma. In the SQT, voluminous oceanic island arc granitoids formed during the Early-Middle Devonian (ca. 418–389 Ma), with contrasting geochemical features as to those in the NQT. The SQT is interpreted as an exotic terrane that has been incorporated into the continental margin and contributed significantly to the continental growth in this orogenic belt. A trench jam might explain the large gap (ca. 357–251 Ma) of granitoid magmatism. The final closure of the Paleo Tethyan Qiman Tagh Ocean might have occurred in the Late Permian, and resulted in the accretion of the Kumukuri microcontinent; which formed in response to the orocline formation of western Qiman Tagh Orogen and the rotation of the western South Qiman Tagh Terranes. A series of Y-depleted granitoids formed during Early-Middle Triassic (before 237 Ma), which might be associated to the partial melting of thickened lower crust induced by the oceanic lithosphere delamination. Subsequently, a series of calc-alkaline and alkaline granitoids generated through melting of older crustal material which were emplaced in the SQT, and their formation is interpreted to be linked with the transition from post-collision to within-plate settings. Our model is not only suitable to trace the tectonic evolution of the Qiman Tagh orogen, but also valid for the plate tectonic setting orogens in the modern earth.
In the Qiman Tagh metallogenic belt, Fe, Zn, Pb, Cu and Au skarns and epithermal Cu and Mo deposits are spatially and temporally associated with Triassic granitoid rocks including granodiorite, monzogranite and syenogranite which are only occurred in the South Qiman Tagh Terrane as a result of completely different geotectonic setting between the SQT and NQT. The plutonic associations related to mineralization have various ages between middle-Triassic (237 Ma–226 Ma) and late-Triassic (226 Ma–204 Ma). The abundant volatile components evolved from magma are responsible for the significant transportation of metals. The initial oxygen fugacity of magma will affect the different mineralization types.
The Wulonggou area in the Eastern Kunlun Orogen (EKO) in Northwest China is characterized by extensive granitic magmatism, ductile faulting, and orogenic gold mineralizations. The Shidonggou granite is located in the central part of the Wulonggou area. This study investigated the major as well as trace-element compositions, zircon U–Pb dates, and zircon Hf isotopic compositions of the Shidonggou granite. Three Shidonggou granite samples yielded an average U–Pb zircon age of 416 Ma (Late Silurian). The Late Silurian Shidonggou granite is peraluminous, with high alkali contents, high Ga/Al ratios, high (K2O + Na2O)/CaO ratios, and high Fe2O3T/MgO ratios, suggesting an A-type granite. The Shidonggou granite samples have zircon εHf(t) values ranging from −7.1 to +4.4. The Hf isotopic data suggest that the Late Silurian granite was derived from the partial melting of Palaeo- to Mesoproterozoic juvenile mantle-derived mafic lower crust. Detailed geochronological and geochemical data suggest that the Late Silurian granite was emplaced in a post-collisional environment following the closure of the Proto-Tethys Ocean. Combining data of other A-type granitic rocks with ages of Late Early Silurian to Middle Devonian, such post-collisional setting related to the Proto-Tethys Ocean commenced at least as early as ~430 Ma (Late Early Silurian), and sustained up to ~389 Ma (Middle Devonian) in the EKO.
The Wulonggou Pluton is located in Wulonggou area, eastern segment of the Eastern Kunlun Orogenic Belt, NW China, and consists of mainly alkali-feldspar granites covering an area of about 150 km². Petrogenesis of these granitoids has been investigated through an integrated study of petrography, zircon U–Pb ages, whole-rock geochemistry, and Hf–Nd isotopic compositions. U–Pb dating of magmatic zircons indicated these granites crystallized during 426–424 Ma in the middle Silurian. The granites display high SiO2 (75.26–77.55 wt%), K2O + Na2O (7.98–9.03 wt%), extremely low MgO (0.04–0.19 wt%), CaO (0.28–0.61 wt%), and TiO2 (0.05–0.09 wt%) contents showing metaluminous, calcic-alkali and ferroan features; enrichment in Rb and some HFSEs (Zr, U, Nb, Ta, and Y), depletion in Sr, Ba, P, and Ti, mostly right-inclined REE curve, flat HREE patterns, high 10,000 ∗ Ga/Al and intensively negative Eu anomalies, exhibiting an A2-type granite affinity with Y/Nb > 1.2 mostly. The primitive magma of these large quantities of granites was generated under a high temperature, low pressure, reduced and anhydrous environment indicating intense upwelling of asthenosphere. Combining with the positive uniform zircon εHf(t) values of −0.2 to +3.8 and decoupled εNd(t) values of −4.9 to −2.1 at t = 424 Ma, it can be concluded that subduction-related juvenile materials, probably calc-alkaline granitoids, are the source of these A-type granites. Geochemical studies of Wulonggou granites, spatial and temporal distributions of regional magmatism, metamorphism, and sedimentary records throughout the Eastern Kunlun Orogen Belt jointly indicate that the whole orogenic belt was in a typical post-collision extension setting and experienced an isostatic uplift during the middle Silurian triggered by delamination after the convergence of the northeastern margin of Gondwana.
The Baiganhu W–Sn orefield in the southeastern Xinjiang Uygur Autonomous Region is associated with Caledonian S-type syenogranites and metasediments of the Paleoproterozoic Jinshuikou Group. Four types of garnets have been identified in the orefield using petrographic and major and trace element data. Grt-I garnets are generally present as inclusions within magmatic quartz in the syenogranites, with end-member formulas of Sps45–53Alm46–53Adr0–1Grs0–1Prp0–1 and rare earth element (REE) patterns that are enriched in heavy REE (HREE) and contain strong negative Eu anomalies. Grt-II garnets are associated with tourmaline and quartz and occur in interstices between feldspars within the syenogranites. In general, the Grt-II garnets have end-member formulae (Sps64–70Alm29–34Adr0–1Grs0–2Prp0) and REE patterns that are similar to the Grt-I garnets although they are more spessartine-rich and contain higher concentrations of HREE. Grt-III garnets coexist with clinopyroxenes and Mo-rich scheelites within skarns developed along the syenogranite and marble contact. Their compositions are Adr62–88Grs1–18Sps3–12Alm0–8Pyr0 and they have relatively flat REE patterns with no negative Eu anomalies. Grt-IV garnets are present as massive aggregates that are often cross-cut by Mo-poor scheelite-bearing calcite veins. Their end-member formulas are Adr4–22Grs62–73Sps5–16Alm2–10Pyr0 and they have slightly domed REE patterns without negative Eu anomalies. Both Grt-III and Grt-IV garnets contain lower concentrations of the HREE (2–3 and 4–32 ppm, respectively) than Grt-I and Grt-II garnets (682–1352 ppm with Y = 1558–2159 ppm, and 6051–12831 ppm with Y =9663–13333 ppm, respectively).
The newly discovered large-scale Baiganhu W–Sn orefield, consisting of the Kekekaerde, Baiganhu, Bashierxi, and Awaer deposits, is located in Ruoqiang County, southeastern Xinjiang, China. These deposits comprise mainly three types of W–Sn mineralization: early-stage skarn-type, middle-stage greisen-type, and late-stage quartz-vein-type. In this study, we classified seven major vertical zones on the basis of petrographic characteristics, roughly from the bottom of the parental granitic intrusions upward, as (A) fresh syenogranite, (B) argillic alteration, (C) muscovite-dominated greisenization, (D) tourmaline-dominated greisenization, (E) marginal facies (including K-feldspar pegmatite and fine-grained granite), (F) aplitic apophysis, and (G1) skarn or (G2) infilled silification zones. According to the alteration–mineralization assemblages and cross-cutting relationships, five stages of mineralization are recognized in the orefield (I, skarn stage; II, greisen stage; III, quartz vein stage; IV, argillic alteration stage; and V, supergene stage), and reverse alteration zonation in the altered intrusion is also observed.
Late Paleozoic post-collisional granitoids are widespread in West Junggar and even in the whole northern Xinjiang. As a representative of these intrusions, the Jietebutiao granite occurs in the southwestern margin of West Junggar, mainly comprises middle-coarse-grained monzogranite and syenogranite, and provides important clues for petrogenesis of granites and evolution of tecton-ic-magmatism in West Junggar. This paper reports the results of high-precision zircon LA-ICP-MS U-Pb dating of the Jietebutiao granite, which yields weighted mean 206Pb/238U ages of (287±9) Ma (n=10, MSWD=0.92) and (278±3) Ma (n=14, MSWD=0.43) for monzogranite and syenogranite, respectively, corresponding to the Early Permian and implying that the granite is the product of post-collisional magmatic activity around the Junggar area approximately at 300 Ma. Petrogeochemical analyses suggest that the Jietebutiao pluton which has long been thought to be of I-type granite actually belongs to A-type. The syenogranite is characterized by high silica (SiO2: 76.11%~76.82%), alkali (Na2O+K2O: 8.47%~8.49%), and low titanium and calcium (TiO2: 0.04%~0.05%, CaO: 0.36%~0.42%). Moreover, the monzogranite is similar to the syenogranite in such aspects as high silica (SiO2: 68.35%~71.80%) and alkali (Na2O+K2O: 6.80%~7.86%) as well as low titanium and calcium (TiO2: 0.29%~0.82%, CaO: 1.76%~2.87%); nevertheless, they both belong to metaluminous or peraluminous (ACNK: 0.98~1.09) high-K calc-alkaline series. Compared with the monzogranite, the syenogranite has relatively low REE content (ΣREE: 23.8×10-6~49.3×10-6, 95.23×10-6~222.2×10-6) with significant negative Eu anomalies (Eu/Eu*: 0.01~0.02, 0.57~0.72). They are also enriched with large ion lithophile elements such as Rb, Th and K and high strength field elements such as Zr, Hf and Nb and strongly depleted in Ba, Sr, Eu and Ti, with high 10000Ga/Al ratios (>2.44). These characteristics are more clearly in syenogranite than in monzogranite. Based on trace element ratios and related discrimination diagrams, the Jietebutiao pluton can be further subdivided into A1 and A2 type granites, which are usually believed to have been formed in an post-collisional tectonic setting and derived from the lower crust composed of juvenile mantle-origin substance. In the early post-collisional magmatism, A2-type monzogranite magma characterized by island arc features was derived from partial melting of the lower crust and, with the further extension of the lithos-phere, probably formed a rift-like environment in local area, producing the A1-type syenogranite magma.
The East Gurenggesala granitic intrusion in Gulungou area on the northern margin of Middle Tianshan Mountains consist of granodiorite-porphyry with porphyry copper mineralization. The intrusion is characterized by enrichment of alkali, with Na2O/K2O ratio changing from 1.95 to 19.00, and depletion of Fe and Mg, accompanied by sub-alkaline (mainly tholeiitic and calc-alkaline series) and weakly peraluminous features (A/CNK=0.98~1.11). REE concentrations are low (∑REE=61.28×10-6~99.50×10-6) and show obvious differentiation between LREE and HREE (LaN/YbN=7.82~22.80), with weak Eu negative anomalies (δEu=0.72~0.97). In addition, the rock mass is relatively rich in such elements as Rb, Ba, Th, U and K, and poor in Nb, Ta, P, Ti etc., suggesting characteristics of volcanic-arc granite (VAG). Zircon LA-ICP-MS U-Pb dating results show that the crystallization of the intrusion took place from (488.9±1.7) Ma to (470.5±3.1) Ma, i.e., in Early Ordovician. Sr-Nd isotopic compositions of East Gurenggesala granitic intrusion are fairly uniform: (87Sr/86Sr)i=0.70677~0.70685, εSr(t)=40.10~41.21, (143Nd/144Nd)i=0.51190~0.51191, εNd(t)=-2.62 ~ -2.30, tDM=1.31~1.38 Ga, implying that magma originated from partial melting of Meso-Proterozoic mantle-derived basic lower crust. Based on both previous and present research results, the authors have reached the conslusion that East Gurenggesala granitic intrusion was formed in the epicontinental arc relevant to the subduction of the paleo-Junggar ocean towards Yili-Central Tianshan plate in Early Ordovician together with porphyry copper mineralization. In general, the emplacement of East Gurenggesala granitic intrusion marked the epoch when the northern margin of Middle Tianshan entered into the stage of active epicontinental arc in connection with subduction in Early Ordovician.
The Huxiaoqin mafic rocks which distribute in the Central Kunlun Suture Zone, are mainly composed of hornblende diabases. LA-ICP-MS zircon U-Pb analyses gave 438 ±2Ma (MSWD = 1. 06, n = 15) of the crystallization age, suggesting Huxiaoqin mafic rocks are the products of the Early Silurian magmatism. All the rock samples are characterized by relatively low TiO 2 (0. 43% ∼ 1. 58%), variable MgO (2. 83% ∼8. 22%) and Mg#(45-74), slight enriched Hf isotopic composition (εHf(t) =3. 68 ∼8. 20, tDM2 = 0. 90 ∼ 1. 19Ga), enrichment of large ion lithophile elements (LILE: eg. Rb, Ba, Th, U and LREE) and marked depletion of high field strength elements (HFSE: eg. Nb, Ta, Ti). Various binary diagrams taking Mg as the abscissa, and a diagram plotting (2 CaO + Na2O)/TiO2 vs. Al2O 3/TiO2 reveal fractional crystallization of clinopyroxene, olivine, and plagioclase. Crustal contamination was insignificant, as reflected by whole-rock relatively low Nb/La and Nb/Ce ratios, high Nb/Ta and Zr/Hf ratios. Based on our geochemical and Lu-Hf isotopic studies, we suggest the mafic dykes likely were generated by partial melting of the spinel peridotites metasomatised by slab-derived fluids. Huxiaoqin mafic rocks have similar chemical composition to island arc basalts, and they formed earlier than metamorphic peaks of eclogite and epidote-amphibolite facies (428Ma and 427Ma, respectively), indicating their formation were closely related to the subduction of Early Paleozoic Eastern Kunlun Oceanic lithosphere. Combining with regional studies, we suggest that Huxiaoqin mafic rocks may represent the latest magmatism which related to Early Paleozoic ocean subduction. Finally, we infer the tectonic transition from ocean subduction to collisional orogeny commenced at Early Silurian, the duration of ocean subduction is more than 79Myr and that of collisional orogeny is more than 8Myr.
Baiganhu tungsten-tin ore field is located in Ruoqiang County, Xinjiang. It is in the west of Qimantage mountain, East Kunlun and consists of four deposits of Baiganhu, Kekekaerde, Bashierxi and Awaer. These deposits are spatially associated with the Caledonian Bashierxi Magmatic Series. With particular focus on the Baiganhu deposit, we conducted detailed studies on the petrology, geochronology and geochemistry of the causative granite and discuss its characteristics, genetic type and the relationship with W-Sn mineralization. The causative granite is syenogranite based on slice identification. LA-MC-ICP-MS zircon U-Pb dating reveals that the syenogranite was emplaced at 413.6 ± 2.4Ma (MSWD = 0.36, n = 30). Our and previously published ages and geochemical data of the plutons in the Baiganhu area together show that the S-type granites and A-type granites are coexisting in Bashierxi Magmatic Series and they were formed in a post-collisional setting during the Middle Silurian-Early Devonian (433∼413Ma). Baiganhu syenogranite contains magmatic garnets and muscovites and the values of A/CNK and A/NK are in the range of 1.07 ∼ 1.11 and 1.45 ∼ 1.49, respectively, with a relatively low zircon saturated temperature and high field strength elements (HFSEs) content. Thus this plu ton is peraluminous and high-K calc-alkaline S-type granite. It formed during the late stage of Bashierxi Magmatic Series and has a closely genetic connection with the tungsten-tin mineralization. We suggest that more attention should be payed to the buried or apophysis-like syenogranite during the further exploration for tungsten-tin in this area. Whereas the monzogranite and alkali feldspar granite contain hornblendes and biotites which penetrate in the interstices between magmatic feldspar and quartz or even enclave magmatic quartz. They have relatively high K2O content (5.25% ∼6.29%), with A/CNK ranging from 0.92 to 1.02, thus belong to metaluminous or weakly peraluminous shoshonite series. Their zircon saturated temperature (866 ∼ 917°C), all alkali content (8.30% ∼ 9.69%), Σ REE content (200×10-6-413×10-6) and HFSEs content such as Zr, Nb, Ce and Y (Zr + Nb + Ce + Y =556 × 10-6 -1006 × 10-6) all are obviously high thus belong to the shoshonite series A-type granites. It is inferred that rare and rare earth element mineralization related to A-type granite may be found in the Baiganhu and adjacent region.
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