Zircon U–Pb,molybdenite Re–Os and muscovite Ar–Ar isotopic dating of the Xitian W–Sn polymetallic deposit,eastern Hunan Province,South China and its geological significance

The Xitian tungsten–tin (W–Sn) polymetallic deposit, located in eastern Hunan Province, South China, is a recently explored region containing one of the largest W–Sn deposits in the Nanling W–Sn metallogenic province. The mineral zones in this deposit comprise skarn, greisen, structurally altered rock and quartz-vein types. The deposit is mainly hosted by Devonian dolomitic limestone at the contact with the Xitian granite complex. The Xitian granite complex consists of Indosinian (Late Triassic, 230–215 Ma) and Yanshanian (Late Jurassic–Early Cretaceous, 165–141 Ma) granites. Zircons from two samples of the Xitian granite dated using laser ablation-inductively coupled mass spectrometer (LA-ICPMS) U–Pb analysis yielded two ages of 225.6 ± 1.3 Ma and 151.8 ± 1.4 Ma, representing the emplacement ages of two episodic intrusions of the Xitian granite complex. Molybdenites separated from ore-bearing quartz-veins yielded a Re–Os isochron age of 149.7 ± 0.9 Ma, in excellent agreement with a weighted mean age of 150.3 ± 0.5 Ma. Two samples of muscovites from ore-bearing greisens yielded ⁴⁰Ar/³⁹Ar plateau ages of 149.5 ± 1.5 Ma and 149.4 ± 1.5 Ma, respectively. These isotopic ages obtained from hydrothermal minerals are slightly younger than the zircon U–Pb age of 151.8 ± 1.4 Ma of the Yanshanian granite in the Xitian area, indicating that the W–Sn mineralization is genetically related to the Late Jurassic magmatism. The Xitian deposit is a good example of the Early Yanshanian regional W–Sn ore-forming event (160–150 Ma) in the Nanling region. The relatively high Re contents (8.7 to 44.0 ppm, average of 30.5 ppm) in molybdenites suggest a mixture of mantle and crustal sources in the genesis of the ore-forming fluids and melts. Based upon previous geochemical studies of Early Yanshanian granite and regional geology, we argue that the Xitian W–Sn polymetallic deposit can be attributed to back-arc lithosphere extension in the region, which was probably triggered by the break-off of the flat-slab of the Palae-Pacific plate beneath the lithosphere.     

Pyrite Re–Os and muscovite 40Ar/39Ar dating of the Beizhan iron deposit in the Chinese Tianshan Orogen and its geological significance

The Awulale iron metallogenic belt (AIMB) hosts the majority of rich iron ores in Tianshan Orogen and has attracted much attention. However, a hot debate exists about the genesis of these iron deposits. Geochronological data are among the few critical evidences to solve the dispute. This study chooses the Beizhan iron deposit to carry out a geochronological research. The Beizhan magnetite deposit, with total iron ore reserves of 468 Mt at an average grade of 41% TFe, is the largest iron deposit in the AIMB. The orebodies of the Beizhan deposit are hosted in Carboniferous dacite and crystal tuff. Four stages of mineral formation can be recognized: an early skarn mineral stage, followed by the magnetite stage, the sulphide stage, and the carbonate stage in order. Pyrite separated from pyrite-rich ore samples yields an isochron age of 302.5 ± 8.2 Ma. Muscovite separated from muscovite-rich ore samples yields ⁴⁰Ar/³⁹Ar plateau ages of 304.7 ± 1.8 Ma, 304.5 ± 1.9 Ma, 308.1 ± 1.9 Ma, and 307.2 ± 1.8 Ma, and isochron ages of 306.1 ± 3.5Ma, 304.0 ± 3.0Ma, 308.2 ± 3.1Ma, and 308.7 ± 3.1Ma, respectively. These ages are consistent within the error range and are interpreted as the age of the Beizhan iron deposit. The results, combined with the other latest precise dating and geologically inferred ages, demonstrate that the iron deposits in the AIMB were formed in the Late Carboniferous. These iron deposits are considered to be iron skarn or medium–low -temperature hydrothermal origin and have genetic linkages between each other. They may be different mineralizing manifestations proximal to or distal from a pluton. The Late Carboniferous iron ores and the related magmatic rocks in the AIMB were produced when upwelling of the asthenosphere causes the partial melting of various sources and the formation of a narrow linear extension in the upper crust. The upwelling of the asthenosphere may be triggered by the detachment of an orogenic root zone.     

Re–Os dating of sulphides from the Yushui Cu-polymetallic deposit in eastern Guangdong Province,South China

The Yushui Cu-polymetallic deposit, which is associated with Ag, Pb, and Zn, is located in the middle part of the Yongan–Meixian Late Paleozoic Hercynian depression. It was discovered in eastern Guangdong Province in the late 1980s and is one of the richest copper deposits in China with high-grade copper averaging 3.25% and locally reaching 50–60%. The main ore body is located along the unconformity between the Upper Carboniferous Hutian Group limestone and the Lower Carboniferous Zhongxin Formation quartz sandstone with a bedded and lenticular morphology. The ores exhibit massive textures dominated by chalcopyrite, bornite, chalcocite, pyrite, sphalerite, galena, and a trace amount of argentite. Although researchers began studying the Yushui deposit in the early 1990s, the ore genesis remains controversial because of the lack of precise mineralisation age constraints. In this study, direct Re–Os dating of Cu sulphides aided in facilitating a better understanding of the timing of formation of the Yushui deposit. This study is the first attempt to use the Re–Os isotopic system for directly dating chalcopyrite and bornite ores for the Yushui deposit. The contents of Re, common Os, ¹⁸⁷Re and ¹⁸⁷Os in nine sulphides are 1.68–219.35 ppb, 0.003–0.427 ppb, 1.05–137.31 ppb, and 0.045–0.734 ppb, respectively. The isotope data yielded an isochron age of 308 ± 15 Ma (mean square weighted deviates = 2.4) using the ⁸⁷Re/¹⁸⁸Os–¹⁸⁷Os/¹⁸⁸Os plot, which is interpreted to represent the age of formation for these sulphides, suggesting that the mineralisation age of the Yushui deposit is close to the age of the host rocks. The ¹⁸⁷Os/¹⁸⁸Os initial value obtained from the Re–Os isochron is 1.81 ± 0.34, which corresponds to the γOs value of + 1349. This value indicates that the ore-forming materials were derived from the crust without mixing with materials from the mantle, and that the Yushui massive sulphide deposit may be of sedimentary exhalative origin.     

SHRIMP U–Pb (zircon), Ar–Ar (muscovite) and Re–Os (molybdenite) isotopic dating of the Taoxikeng tungsten deposit,South China Block

The Taoxikeng tungsten deposit is located in the Jiangxi Province in the southern part of China, and is one of the largest wolframite quartz-vein type tungsten deposits in the country. The deposit is situated in Sinian (Neoproterozoic) to Permian strata at the contact with the buried Taoxikeng Granite. Sensitive High Mass Resolution Ion Microprobe (SHRIMP) zircon U–Pb analysis of the granite has yielded dates of 158.7 ± 3.9 and 157.6 ± 3.5 Ma, which are interpreted as the emplacement age of the granite. Molybdenite separated from ore-bearing quartz-veins yields a Re–Os isochron age of 154.4 ± 3.8 Ma, and muscovite separated from greisen between the granite and country rocks yields ⁴⁰Ar/³⁹Ar plateau ages of 153.4 ± 1.3 and 152.7 ± 1.5 Ma. These dates obtained from three independent geochronological techniques constrain the ore-forming age of the Taoxikeng deposit and link the ore genesis to that of the underlying granite. The Taoxikeng deposit is an example of a Jurassic regional-scale tungsten–tin ore-forming event between 160 and 150 Ma in the Nanling region of the South China Block. The deposit's strikingly low rhenium contents (4.9 to 13.0 × 10^? 3 μg/g) in molybdenite suggests that the ore was derived from a crustal source. This conclusion is consistent with previously published constraints from S, D and O stable isotopes, Sr–Nd systematics, and petrogenetic interpretations of spatially related granites.     

Dating the giant Zhuxi W–Cu deposit (Taqian–Fuchun Ore Belt) in South China using molybdenite Re–Os and muscovite Ar–Ar system

The recently discovered Zhuxi W–Cu ore deposit is located within the Taqian–Fuchun Ore Belt in the southeastern edge of the Yangtze Block, South China. Its inferred tungsten resources, based on new exploration data, are more than 280 Mt by 2016. At least three paragenetic stages of skarn formation and ore deposition have been recognized: prograde skarn stage; retrograde stage; and hydrothermal sulfide stage. Secondly, greisenization, marmorization and hornfels formation are also observed. Scheelite and chalcopyrite are the dominant metal minerals in the Zhuxi deposit and their formation was associated with the emplacement of granite stocks and porphyry dykes intruded into the surrounding Carboniferous carbonate sediments (Huanglong and Chuanshan formations) and the Neoproterozoic slate and phyllites. The scheelite was mostly precipitated during the retrograde stage, whereas the chalcopyrite was widely precipitated during the hydrothermal sulfide stage. A muscovite ⁴⁰Ar/³⁹Ar plateau age of about 150 Ma is interpreted as the time of tungsten mineralization and molybdenite Re–Os model ages ranging from 145.9 ± 2.0 Ma to 148.7 ± 2.2 Ma (for the subsequent hydrothermal sulfide stage of activity) as the time of the copper mineralization. Our new molybdenite Re–Os and muscovite ⁴⁰Ar/³⁹Ar dating results, along with previous zircon U–Pb age data, indicate that the hydrothermal activity from the retrograde stage to the last hydrothermal sulfide stage lasted up to 5 Myr, from 150.6 ± 1.5 to 145.9 ± 1 Ma, and is approximately coeval or slightly later than the emplacement of the associated granite porphyry and biotite granite. The new ages reported here confirm that the Zhuxi tungsten deposit represents one of the Mesozoic magmatic–hydrothermal mineralization events that took place in South China in a setting of lithospheric extension during the Late Jurassic (160–150 Ma). It is suggested that mantle material played a role in producing the Zhuxi W–Cu mineralization and associated magmatism.     

LA-ICPMS Zircon U–Pb and Molybdenite Re–Os Isotopic Dating of the Tungsten Deposits in the Dengfuxian W–Sn Orefield, Eastern Hunan Province, South China, and Their Geological Implications

Please refer to the attachment(s) for more details.     

Ages of sediment-hosted Himalayan Pb–Zn–Cu–Ag polymetallic deposits in the Lanping basin,China: Re–Os geochronology of molybdenite and Sm–Nd dating of calcite

The Lanping basin is a significant Pb–Zn–Cu–Ag mineralization belt of the Sanjiang Tethyan metallogenic province in China. Over 100 thrust-controlled, sediment-hosted, Himalayan base metal deposits have been discovered in this basin, including the largest sandstone-hosted Pb–Zn deposit in the world (Jinding), and several Cu ± Ag ± Co deposits (Baiyangping, Baiyangchang and Jinman). These deposits, with total reserves of over 16.0 Mt Pb + Zn, 0.6 Mt Cu, and 7000 t Ag, are mainly hosted in Meso-Cenozoic mottled clastic rocks, and strictly controlled by two Cenozoic thrust systems developed in the western and eastern segments of the Lanping basin.To define the metallogenic history of the study area, we dated nine calcite samples associated with copper sulfides from the Jinman Cu deposit by the Sm–Nd method and five molybdenite samples from the Liancheng Cu–Mo deposit by the Re–Os method. The calcite Sm–Nd age for the Jinman deposit (58 ± 5 Ma) and the molybdenite Re–Os age for the Liancheng deposit (48 ± 2 Ma), together with previously published chronological data, demonstrate (1) the Cu–Ag mineralization in the western Lanping basin mainly occurred in three episodes (i.e., ∼56–54, 51–48, and 31–29 Ma), corresponding to the main- and late-collisional stages of the Indo–Asian orogeny; and (2) the Pb–Zn–Ag (±Cu) mineralization in the eastern Lanping basin lacked precise and direct dating, however, the apatite fission track ages of several representative deposits (21 ± 4 Ma to 32 ± 5 Ma) may offer some constraints on the mineralization age.     

Re–Os dating of chalcopyrite from selected mineral deposits in the Kalatag district in the eastern Tianshan Orogen,China

The Kalatag Cu–Zn–Au district contains a number of economically important Cu deposits in eastern Tianshan in Xinjiang, NW China. Due to the lack of precise mineralization ages, the metallogenesis of this area has long been a matter of debate. In this study, chalcopyrite Re–Os isotope methods are used to date the South Meiling Cu–Zn and Hongshi Cu deposits in the eastern part of Kalatag area.The South Meiling Cu–Zn deposit is hosted in volcanic-sedimentary rocks of the Late Ordovician to Early Silurian Daliugou Formation. The deposit consists of two parts: a concordant massive sulfide ores and discordant vein-type ores located in the footwall strata. The principal ore minerals are pyrite, chalcopyrite, sphalerite, minor tetrahedrite, galena and pyrrhotite. Gangue minerals include quartz, sericite and barite, and minor chlorite, plagioclase and carbonate minerals. The Hongshi Cu deposit represents a hydrothermal vein system hosted in the mafic volcanic rocks of Daliugou Formation. The orebodies are associated with quartz veins and controlled by subsidiary faults of the Kalatag fault. The ore-forming process can be divided into the early, middle and late stages and is characterized by quartz–pyrite, quartz–chalcopyrite–pyrite and quartz–carbonate–gypsum veins, respectively.Re–Os analyses of chalcopyrite from the South Meiling Cu–Zn deposit yield an isochron age of 434.2 ± 3.9 Ma and initial ¹⁸⁷Os/¹⁸⁸Os ratio of 0.647 ± 0.098 (MSWD = 0.59). Re–Os analyses of chalcopyrite from the Hongshi Cu deposit yield an isochron age of 431.8 ± 2.7 Ma and initial ¹⁸⁷Os/¹⁸⁸Os ratio of − 0.165 ± 0.075 (MSWD = 0.77). Since chalcopyrite is the primary copper mineral, we interpret these isochron ages as the timing of Cu mineralization, based on field geology and petrographic evidence. These results suggest that the Re–Os ages presented here provide, for the first time, a direct constraint on an early Paleozoic Cu mineralization event of the eastern Tianshan Orogen. The high initial ¹⁸⁷Os/¹⁸⁸Os ratios (0.647 ± 0.098) ratio of ~ 434 Ma chalcopyrite from the South Meiling deposit suggest that the metal was sourced from a two end-member mixing of crust and mantle materials. Moreover, we propose that the VMS mineral system and hydrothermal vein system of the Kalatag district were related to the south-dipping subduction of the Kalamaili oceanic plate during the Late Ordovician–Silurian.     

Molybdenite Re–Os and U–Pb zircon dating and genesis of the Dayana W-Mo deposit in eastern Ujumchin,Inner Mongolia

The Dayana W-Mo deposit in eastern Ujumchin of Inner Mongolia is a quartz-vein type deposit in the mid-western part of the Central Asian Orogenic Belt (CAOB). Biotite monzogranite, quartz porphyry and hornfels host W-Mo in quartz veins. Based on spatial relationships, molybdenite was deposited first followed by wolframite. This contribution presents precise laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) U–Pb zircon dating and geochemical analysis of the biotite monzogranite. The U–Pb dating shows that the monzogranite is 134 ± 1 Ma. Major and trace element geochemistry shows that the monzogranite is characterized by high SiO₂ and K₂O contents, a “Right-inclined” shape of the chondrite normalized REE patterns, enrichment of large ion lithophile elements (LILEs), and depletion of high field strength elements (HFSEs) such as Nb, P, Ba. The monzogranite is high-K calc-alkaline, has a strong negative Eu anomaly (Eu/Eu* = 0.04–0.45), low P₂O₅ content, high A/CNK of > 1.2, enriched in large-ion lithophile elements (LILEs; such as Rb, Th, U, Nd, and Hf), and notably depleted in Ba, Sr, P, Ti, and Nb. These characteristics define the Dayana monzogranite as a highly fractionated peraluminous granite. Re–Os isotopic analysis of seven molybdenite samples from the deposit yield an isochron age of 133 ± 3 Ma (MSWD = 2.2), which indicates that the monzogranite and ore have the same age within error, are probably genetically related, and related to a major Early Cretaceous mineralizing event in China known as the Yanshanian.     

Temporal consistency between granite evolution and tungsten mineralization in Huamei'ao,southern Jiangxi Province,China: Evidence from precise zircon U–Pb,molybdenite Re–Os,and muscovite 40Ar–39Ar isotope geochronology

The large Huamei'ao tungsten deposit, with total WO₃ reserves of 67,400 tons at an average grade of 1.334% WO₃, is located in the convergent zone of the eastern Nanling E–W-trending tectono-magmatic belt and the western Wuyishan NNE–SSW-trending tectono-magmatic belt in southern Jiangxi Province, China. The tungsten mineralization in this deposit is mainly found in quartz–wolframite veins, with most orebodies distributed at the outer contact zone between concealed Late Jurassic granitic stocks and Sinian weakly metamorphosed sandstones and phyllites. Zircons collected from medium- to fine-grained biotite granite in a diamond drill hole at a sea level of ca. − 10 m yield a crystallization age of 159.9 (± 1.2) Ma through laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA–MC–ICP–MS) U–Pb dating. Molybdenite and muscovite that were both separated from quartz–wolframite veins yield a Re–Os isochron age of 158.5 (± 3.3) Ma and an ⁴⁰Ar–³⁹Ar weighted plateau age of 157.9 (± 1.1) Ma, respectively. These dates, obtained via three independent geochronological techniques, constrain the ore-forming age of the Huamei'ao deposit and link the genesis of the ore and the underlying granite. Analyses of available high-precision zircon U–Pb, molybdenite Re–Os and muscovite ⁴⁰Ar–³⁹Ar radiometric ages of major W–Sn deposits in southern Jiangxi Province indicate that there is no significant time interval between W–Sn mineralization and its intimately associated parent granite emplacement (interval of 0–6 Ma). These deposits formed over three intervals during the Mesozoic (240–210, 170–150, and 130–90 Ma), with large-scale W–Sn mineralization occurring mainly between 160 and 150 Ma. The majority of W–Sn deposits in this region are located in southern Jiangxi and southern Hunan provinces.     

Zircon U–Pb and molybdenite Re–Os geochronology of copper–molybdenum deposits in southeast Liaoning Province,China

ABSTRACT

Liaoning Province in China is an area known for the occurrence of numerous copper and/or molybdenum deposits of variable size. However, the age of mineralization and tectonic setting in this region are still a subject of debate. In this study we describe the geology of these deposits and apply zircon U–Pb and molybdenite Re–Os isotopic dating to constrain their ages and define the metallogenic epochs of this province. The Huatong Cu–Mo deposit yields molybdenite Re–Os model ages of 127.6–126.3 Ma and an isochron age of 127.4 ± 0.7 Ma. The Dongbeigou Mo deposit yields molybdenite Re–Os model ages of 132.6–127.1 Ma, an isochron age of 128.1 ± 5.1 Ma, and a zircon U–Pb age of 129.4 ± 0.3 Ma for the associated monzogranite. The granodiorite associated with the Wanbaoyuan Cu–Mo deposit yields a zircon U–Pb age of 128.4 ± 1.1 Ma; the plagiogranite associated with the Yaojiagou Mo deposit yields an age of 167.5 ± 0.9 Ma; and the biotite–plagioclase gneiss from the Shujigou Cu deposit yields an age of 2549.4 ± 5.6 Ma. These results, together with previous geochronology data, show that intense Cu–Mo porphyry and skarn mineralization were coeval with Early–Middle Jurassic and Early Cretaceous granitic magmatism. The former was associated with the orogeny that followed the collision of the Siberian and North China plates and the resulting closure of the palaeo-Asian Ocean, and the latter with rifting that followed the subduction of the palaeo-Pacific Plate and associated lithospheric thinning. Volcanogenic massive sulfide Cu deposit. mineralization took place much earlier, in the late Archaean, and was related to continent–continent collision, palaeo-ocean closure, the formation of a united continental landmass, bimodal volcanism, magma emplacement, and subsequent metamorphism and deformation of syn-collisional granites.     

Re–Os isotopic dating of molybdenite and pyrite in the Baishan Mo–Re deposit, eastern Tianshan, NW China, and its geological significance

The Baishan Mo–Re deposit is located in the eastern section of the eastern Tianshan orogenic belt, NW China. The deposit has a grade of 0.06% Mo and a high content of rhenium of 1.4 g/t. Rhenium and osmium isotopes in sulfide minerals from the Baishan deposit are used to determine the age of mineralization. Rhenium concentrations in molybdenite samples are between 74 and 250 g/g. Analysis of eight molybdenite samples yields an isochron age of 224.8±4.5 Ma (2). Pyrite samples have rhenium and osmium concentrations varying in the range 33.4–330.6 ng/g and 0.08–0.81 ng/g, respectively. Isotope data on seven pyrite samples yield an isochron age of 225±12 Ma (2) on the ¹⁸⁷Re/¹⁸⁸Os versus ¹⁸⁷Os/¹⁸⁸Os plot and an age of 233±14 Ma (2) on the ¹⁸⁷Os versus ¹⁸⁷Re correlation diagram. The ages of molybdenite and pyrite are consistent within the analytical errors. Combined with field observations, the data indicate that Mo–Re mineralization in the Baishan deposit is produced by a magmatic-hydrothermal event in an intracontinental extensional setting after late Paleozoic orogeny. The initial ¹⁸⁷Os/¹⁸⁸Os ratio of pyrite is 0.3±0.07. The ³⁴S values of molybdenite vary from +0.5 to +3.6. Both data indicate that mineralization is derived mainly from a mantle source.Editorial handling: J. Richards     

Re–Os geochronology of Cu and W–Mo deposits in the Balkhash metallogenic belt, Kazakhstan and its geological significance

The Central Asian metallogenic domain (CAMD) is a multi-core metallogenic system controlled by boundary strike-slip fault systems. The Balkhash metallogenic belt in Kazakhstan, in which occur many large and super-large porphyritic Cu–Mo deposits and some quartz vein- and greisen-type W–Mo deposits, is a well-known porphyritic Cu–Mo metallogenic belt in the CAMD. In this paper 11 molybdenite samples from the western segment of the Balkhash metallogenic belt are selected for Re–Os compositional analyses and Re–Os isotopic dating. Molybdenites from the Borly porphyry Cu deposit and the three quartz vein-greisen W–Mo deposits—East Kounrad, Akshatau and Zhanet—all have relatively high Re contents (2712–2772 μg/g for Borly and 2.267–31.50 μg/g for the other three W–Mo deposits), and lower common Os contents (0.670–2.696 ng/g for Borly and 0.0051–0.056 ng/g for the other three). The molybdenites from the Borly porphyry Cu–Mo deposit and the East Kounrad, Zhanet, and Akshatau quartz vein- and greisen-type W–Mo deposits give average model Re–Os ages of 315.9 Ma, 298.0 Ma, 295.0 Ma, and 289.3 Ma respectively. Meanwhile, molybdenites from the East Kounrad, Zhanet, and Akshatau W–Mo deposits give a Re–Os isochron age of 297.9 Ma, with an MSWD value of 0.97. Re–Os dating of the molybdenites indicates that Cu–W–Mo metallogenesis in the western Balkhash metallogenic belt occurred during Late Carboniferous to Early Permian (315.9–289.3 Ma), while the porphyry Cu–Mo deposits formed at 316 Ma, and the quartz vein-greisen W–Mo deposits formed at 298 Ma. The Re–Os model and isochron ages thus suggest that Late Carboniferous porphyry granitoid and pegmatite magmatism took place during the late Hercynian movement. Compared to the Junggar-East Tianshan porphyry Cu metallogenic belt in northwestern China, the formation of the Cu–Mo metallogenesis in the Balkhash metallogenic belt occurred between that of the Tuwu-Yandong in East Tianshan and the Baogutu porphyry Cu deposits in West Junggar. Collectively, the large-scale Late Carboniferous porphyry Cu–Mo metallogenesis in the Central Asian metallogenic domain is related to Hercynian tectono-magmatic activities.     

Re–Os pseudo-isochron of disseminated ore from the Kalatongke Cu–Ni sulfide deposit,Xinjiang, Northwest China: Implications for Re–Os dating of magmatic Cu–Ni sulfide deposits

Re–Os dating of disseminated ore from the Kalatongke Cu–Ni sulfide mineral deposit, Xinjiang, Northwest (NW) China, yields an apparent isochron age of 433 ± 31 Ma with an apparent initial ¹⁸⁷Os/¹⁸⁸Os (433 Ma) ratio of 0.197 ± 0.027. This apparent age is older than not only the zircon U–Pb age of the host intrusion (287 ± 5 Ma, Han et al., 2004) but also the stratigraphic age of the intruded country rock. Thus, the regression line is a pseudo-isochron. However, previous Re–Os dating of massive ores of the same deposit yielded an age that is consistent, within analytical uncertainty, with the zircon U–Pb age (Zhang et al., 2008). This relationship is similar to that observed in the Jinchuan deposit, NW China. Therefore, we suggested that the same mechanism, post-segregation diffusion of Os (Yang et al., 2008), is applicable to the Kalatongke deposit.Re–Os isotopic studies of Kalatongke, Jinchuan and representative magmatic Cu–Ni sulfide deposits suggest that the massive ores of mafic–ultramafic-rock-associated Cu–Ni sulfide deposits would yield geologically meaningful Re–Os age, whereas a pseudo-isochron would be obtained for the disseminated ores. Therefore, to obtain a geologically meaningful Re–Os age, the type of the deposit, the type of the ore and the ore-forming process should be taken into account.     

Zircon U–Pb and Molybdenite Re–Os Dating of the Dongleiwan Skarn Cu Polymetallic Deposit in Jiangxi Province, Eastern China

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Re–Os dating and sulfur isotope composition of molybdenite from tungsten deposits in western Namaqualand, South Africa: implications for ore genesis and the timing of metamorphism

Both stratiform/stratabound and granite-related models have been used to explain the genesis of W(Mo) deposits in the Okiep copper district in western Namaqualand, South Africa. Apparently, stratabound mineralization (Fe-rich wolframite with accessory molybdenite) occurs in foliation-parallel quartz veins in high-grade (∼750 °C, 5–6 kbar) metapelites of the Wolfram Formation, and less commonly in small bodies of silicified leucogranites and pegmatites. Six Re–Os ages for molybdenites from four deposits (Nababeep Tungsten Far West, Kliphoog, Narrap, Tweedam) range between 1000 ± 4 and 1026 ± 5 Ma. These molybdenites define a well-constrained ¹⁸⁷Re–¹⁸⁷Os isochron with an age of 1019 ± 6 Ma, which is interpreted as the age of W(Mo) mineralization. This age is significantly younger than Proterozoic protolith ages for supracrustal rocks and the emplacement ages for the main intrusive suites, but geologic evidence requires overlap with a period of high-grade metamorphism. We suggest that W(Mo) mineralization is genetically linked to intra-crustal magmatic processes at ∼1020 Ma, thereby precluding the ∼1060 Ma Concordia granite as the source for mineralizing fluids. A narrow range of positive δ³⁴S compositions (+3.6 to +4.5‰) for eight molybdenites from five W(Mo) mines is consistent with a SO₂-rich fluid and a granite-related genetic model. Post-peak metamorphic deformation and metamorphism of W(Mo) ores is most likely related to the retrograde stage of the Namaquan orogeny, which overlaps emplacement of late-orogenic, evolved granites and pegmatites, and the formation of W(Mo) deposits in western Namaqualand. Therefore, the effects of retrograde Namaquan metamorphism extend at least to ∼1020 Ma or, alternatively, these W(Mo) veins were affected by a poorly constrained later event (e.g. early Pan-African). Received: 12 September 1999 / Accepted: 20 April 2000     

The 40Ar/39Ar and Rb–Sr chronology of the Precambrian Aksu blueschists in western China

Three metapelite samples from the Aksu blueschist terrane, Xinjiang, China, were dated by the ⁴⁰Ar/³⁹Ar method on separated phengite grains, obtaining plateau ages in the range of 741−757 Ma. In contrast, the measured Rb and Sr isotope data for the three samples yielded isochron ages ranging from 630 Ma to 900 Ma, suggesting large heterogeneity in the blueschist protolith and suppression of diffusional exchange owing to the low-temperature metamorphic conditions. Because the protolith of Aksu blueschist is composed of oceanic materials that formed ⁴⁰Ar-free phengite during HP and UHP metamorphism and the apparent ⁴⁰Ar/³⁹Ar plateaus ages in this study are similar to previous K–Ar and Rb–Sr ages, the existence of excess argon in these rocks is considered to be insignificant. As a result, the ⁴⁰Ar/³⁹Ar plateau ages in this study (ca. 750 Ma) likely represent the approximate time for peak metamorphism, given the low peak metamorphic temperatures for the Aksu blueschist terrane (300−400 °C). This strongly implies that modern style, cold subduction tectonics operated along the margin of the Aksu terrane no later than 750 Ma, in Neoproterozoic time.     

Late Palaeozoic mineralization and tectonic evolution of the West Junggar metallogenic belt,Central Asia: constraints from Re–Os and 40Ar/39Ar geochronology

ABSTRACT

The West Junggar Metallogenic Belt (WJMB) is located between the Tianshan fault system and the Ertix fault system in the western part of the Central Asian Metallogenic Domain (CAMD). The belt features widespread late Palaeozoic granitic plutons, strike-slip faults, and porphyry copper and orogenic gold deposits. We collected nine molybdenite samples from the Baogutu III–IV Cu–Mo deposit and the Suyunhe Mo–W deposit, and 12 granitoid samples from the Jiaman, Kangde, Kulumusu, Bieluagaxi, Hatu, Akbastau, Miaoergou, Baogutu, Karamay, and Hongshan plutons in the WJMB. Molybdenite Re–Os dating gives metallogenesis ages of 312.7 and 299.7 Ma for the Baogutu III–IV and Suyunhe deposits, respectively. ⁴⁰Ar/³⁹Ar thermochronology yields biotite ages ranging from 326 to 302 Ma and K-feldspar ages from 297 to 264 Ma, indicating a regional medium-temperature cooling history in the WJMB during the late Carboniferous to middle Permian. By integrating these data with previous zircon U–Pb, amphibole ⁴⁰Ar/³⁹Ar, and zircon and apatite fission-track ages, we reconstruct the whole thermal history of the WJMB, which includes late Palaeozoic intrusive magmatism, porphyry Cu and W–Mo mineralization, and late Mesozoic tectonic uplift and exhumation of the WJMB. The regional ⁴⁰Ar/³⁹Ar cooling ages are consistent with the timing of regional sinistral strike-slip faulting, thereby indicating the tectonic significance of the cooling ages. We suggest that the biotite ⁴⁰Ar/³⁹Ar ages represent the static cooling of the granitic plutons after emplacement, since the ages are consistent with the U–Pb ages of the plutons. Thereafter, the oldest K-feldspar ⁴⁰Ar/³⁹Ar age may record the initiation of sinistral strike-slip movement on the Darabut, Mayile, and Baerluke faults. The regional faulting resulted in significant uplift of the WJMB during the early and middle Permian.     

Re–Os Isotopic Dating of the Molybdenite from the Tongshan Porphyry Cu–MoDeposit in Heilongjiang Province, NE China

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Late Permian–Triassic metallogeny in the Chinese Altay Orogen: Constraints from mica 40Ar/39Ar dating on ore deposits

The Central Asian Orogenic Belt (CAOB) constitutes the largest Phanerozoic accretionary orogen on Earth. It extends over 5000 km and hosting numerous metal deposits. The Chinese Altay Orogen, an important element of the CAOB, hosts abundant Devonian (ca. 410–370 Ma) deposits. The ⁴⁰Ar/³⁹Ar dating of seven mica separates from the representative samples syngenetic with orogenic-type mineralization is summarized to record a poorly studied Permian to Triassic metallogenic episode in the Chinese Altay Orogen. The Kelan and Maizi basins in the Chinese Altay Orogen, which likely represent an arc accretionary complex, contain a series of polymetallic lode deposits hosted in low-grade metamorphic volcano–sedimentary rocks. Two muscovite and five biotite separates were obtained from the ore-forming veins paragenetically associated with Au-bearing polymetallic sulfides in the Keketale Pb–Zn, Wulasigou Cu, Tiemurt Pb–Zn, Dadonggou Pb–Zn and Sarekuobu Au deposits. These separates yielded ⁴⁰Ar/³⁹Ar plateau ages ranging from 260 Ma to 205 Ma. Integration of these results with other published geological and geochronological data indicates that the Au–Cu–Pb–Zn mineralization post-dated the final CAOB assembly, with fluid movement and mineralization possibly driven by regional metamorphism and deformation. It is herein proposed for a metallogenic model that the metamorphic fluid migration following final assembly of the CAOB results into the formation of the deposits.