Re-Os dating of auriferous pyrite from the Zhenyuan super-large gold deposit in Ailaoshan gold belt, Yunnan Province, Southwestern China

Zhenyuan gold deposit is the largest super large gold deposit in the Ailaoshan gold belt,but its precise mineralization age is still lack.Re-Os isotopic age of the auriferous pyrite from the Zhenyuan gold deposit was determined by using a high-resolution inductively coupled plasma mass spectrometry(HR-ICP-MS).The pyrite samples were decomposed in carius tubes,Os was separated by distillation and Re was extracted by acetone,respectively.The results show that the Re-Os isochron age is 229±38 Ma(MSWD=2.0,confidence level is 95%),with an initial 187 Os/188 Os value of 0.68±0.24 and a corresponding Os value of 442±91.The Re/Os ratios of the pyrite vary from 40.8 to 100.5.The data suggest that at least one important ore-forming event was occurred during Indosinian epoch,and the ore-forming materials probably derived from mixed sources of crustal and mantle,while the later dominated.The Ailaoshan composite orogen experienced complicated evolutional processes,including formation of Precambrian-Early Paleozoic basement,subduction and orogenesis of Late Paleozoic era,collisional orogenesis of Late Hercynian-Indosinain epoch,and extensional or striking orogenesis of Yanshainan-Cenozoic epoch.The polycycle tectonic evolution and magmatism in this area caused multi-stage and superposition metallization characteristics of the Zhenyuan gold deposit:the mineralization probably occur mainly during the Indosinian collisional orogeny,while the minor gold ores of altered granite-porphyry and altered lamprophyre may be formed in the late superposition metallization.     

Re-Os dating of gold-bearing arsenopyrite of the Maoling gold deposit,Liaoning Province,Northeast China and its geological significance

The Maoling gold deposit, one of the large gold deposits in eastern Liaoning Province, NE China, is an arsenopyrite-disseminated gold deposit with a resource of approximately 25 t Au and an average Au grade of 3.2 g/t. Six arsenopyrites closely related to Au mineralization of the Maoling gold deposit are dated by Re-Os technique and define a Re-Os isochron with an age of 2316±140 Ma, which suggests that the deposit was formed in the Paleoproterozoic era rather than in the Indosinian period as some early researchers suggested. High initial ^187Os/^188Os ratio of 1.32±0.48 indicates a crustal derivation of the ore-forming material of the deposit, which may be derived from rocks of the Gaixian formation of the Liaohe Group. Furthermore,the result also implies that the age of the Gaixian Formation in the Maoling district is older than 2316±140 Ma.     

Re-Os isotopes and PGE geochemistry of black shales and intercalated Ni-Mo polymetallic sulfide bed from the Lower Cambrian Niutitang Formation, South China

The paleo oceanenvironmentalchangeduringthePrecambrian Cambriantransitionisakeyissuere latedtothecausesforanexplosiveradiationofdiffer entmetazoanphyladuringtheEarlyCambrianera .Thechemicalandisotopiccompositionsofmarinesed iments (carbonates ,phosphorites ,siliceousrocks ,andblackshales)recordthechangingcompositionandphysicalconditionsoftheseawaterinwhichtheserocksaccumulated .Organiccarbon richblackshalesfrommarineenvironmentsarecommonlyenrichedinanumberoftraceelementssuchasNi,Mo ,V ,Co ,…     

Re-Os dating of pyrite from Giant Bayan Obo REE-Nb-Fe deposit

The giant Bayan Obo REE-Nb-Fe deposit is locatedat the northern margin of the North China Block, i.e. atlatitude 41.7° north and longitude 110.0° east. The depositis very special in the world because it is the largest LREEdeposit and the second largest Nb deposit in the world,and also a large iron deposit. Geological features, mineralassemblage and geochronology of the deposit have beenreported[1—6]. However, various dating methods gave dif-ferent mineralization ages, and discrepancie…     

In situ Re-Os isotope ages of sulfides in Hannuoba peridotitic xenoliths： Significance for the frequently-occurring mantle events beneath the North China Block

In situ Re-Os isotopes of sulfides in peridotitic xenoliths from Cenozoic Hannuoba basalts were analyzed by LAM-MC-ICPMS. The suifides developed two types of occurrences including silicate-enclosed and interstitial. In the enclosed sulfides, 187Os/188Os vary from 0.1124 to 0.1362 and 187Re/188Os from 0.0026 to 1.8027. In the interstitial ones, 187Os/188Os have a range from 0.1174 to 0.1354 and 187Re/188Os from 0.0365 to 1.4469. The oldest age, calculated by TRD for the enclosed sulfides, is 2.1 Ga. An isochron age of 2.3±1.2 Ga is obtained by five grains of enclosed sulfides and primitive mantle. The sulfides used have lower Re-Os isotopic ratio than primitive mantle. Meanwhile, an isochron age of 645±225 Ma is given by all in- terstitial sulfides and the enclosed sulfides with higher Re-Os isotopic ratio due to Re addition after man- tle formation. In addition, the model age of 1.3 Ga recorded by one interstitial sulfide, having similar TDM and TRD, should be meaningful to deep thermal event. The coexistence of different ages, revealed by in situ Re-Os isotope, indicates frequently-occurring mantle events beneath Hannuoba area.     

Re-Os dating of the Raobazhai ultra mafic massif in North Dabie

The ultramafic massif at Raobazhai in North Dabie is located in the suture zone between the Yangtze craton and North China eraton. The Re-Os isotope compositions of the massif are used to decipher the origin and tectonics of the ultramafic rocks involved in continental subduction and exhumation. Fifteen samples were collected from five drill holes along the main SE-NW axis of the Raobazhai massif. Major and trace element compositions of the samples show linear correlations between MgO, Yb and Al_2O_3. This suggests that the massif experienced partial melting with variable degrees and is from fertile to deplete in basaltic compositions. Nine selected samples were analyzed for Re-Os isotope compositions. Re contents range from 0.004 to 0.376 rig/g, Os contents from 0.695 to 3.761 ng/g, ~(187)Re/~(188)Os ratios from 0.022 to 2.564 and ~(187)Os/~(188)Os ratios from 0.1165 to 0.1306. These indicate that the massif is a piece of continental lithospheric mantle with variable depletion. Using the positive corre     

Sm-Nd and Rb-Sr isotopical ages of magnetite-chlorite formation gold deposit in the volcanic rock area of Late Paleozoic Era, East Tianshan

Through studying geo-geochemical characteristics and determining Sm-Nd and Rb-Sr isotopical ages in the Kanggur magnetite-chlorite formation gold deposit, some conclusions can be achieved: Sm-Nd isochron age is (290.4 ± 7)Ma, Rb-Sr isochron age is (282.3 ± 5)Ma, mineralization is Late Hercynian and the formation of this gold deposit is related to the macroscopic Huangshan-Qiugemingtashi ductile shear zone which is produced as a result of collision between the Tarim plate and the Junggar plate.     

Ore-forming event and geodynamic setting of molybdenum deposit at Wenquan in Gansu Province, Western Qinling

The Wenquan molybdenum deposit is associated with a Triassic granite in this area. The Wenquan granite is enriched in LILE and LREE, poor in HFSE, and has significantly higher contents of alkali （K2O＋Na2O） and Sr, Ba than those of the island arc volcanic rocks. These geochemical characteristics are similar to post-collisional granites in high K calc-alkaline series. Studies of major elements, trace elements, REEs and chronology of the Wenquan pluton show that, in the geodynamic transition stage of continent-continent convergence to extension, the partial melting of the enriched lithospheric mantle generated the basaltic magma and triggered the partial melting of the thickened lower crust which produceded the acidic magma, and the Wenquan pluton was formed by mixing of the two magmas. Molybdenite Re-Os isotopic dating gave Os model ages of 212.7±2.6 Ma to 215.1±2.6 Ma with a weighted mean of 214.1±1.1 Ma, and an Re-Os isochron age of 214.4±7.1 Ma. These ages are close to K-Ar ages （223 to 226 Ma） and a SHRIMP zircon U-Pb age （223±7 Ma） for the Wenquan granite within the error range, but relatively younger. This implies that the Mo mineralization occurred in a late stage of the magmatic intrusion, and the metallogenesis took place in the transition stage from syn-collision to post-collision in the tectonic setting of the Qinling Orogenic Belt （QOB） after continental collision between the North China Block （NCB） and the South China Block （SCB）. This process is also corresponding to the geological events of metamorphism and deformation in South Qinling, closure of the Mian-Lue oceanic basin, and exhumation of the Dabie-Sulu ultrahigh-pressure metamorphic rocks. The large-scale continent-continent collision between NCB and SCB in the middle Triassic triggered significant crustal thickening and exhumation of subducted slab. In the late Triassic, the tectonic setting was transformed to the transition stage from collision to extension. Materials from the asthenospheric mantle would ascend into the root of the lower crust, which could induce partial melting of the lower crust and generate Mo-enriched granitic magma. The ore-forming elements enriched in the fluid derived from the condensation and fraction of the magma resulted in the Mo mineralization. The Mo deposits in the QOB are mainly formed in two episodes, namely 220± Ma and 140± Ma. The two episodes of metallogenesis were developed in the tectonic transition settings from compression to extension, but they were in the different stages of the tectonic evolution. The occurrence of the Wenquan Mo-bearing pluton indicates that the Triassic tectonic-magmatic belt of Western Qinling is another favorable region for Mo mineralization in the QOB. Therefore, it is significant to pay more attention to evaluation of the ore-forming potentiality in the Triassic granites in Western Qinling.     

塔里木盆地晚古生代古盐度与古环境探讨

目的利用古盐度数据为有争议的塔里木盆地上古生界地层的沉积环境研究提供判定依据。方法对盆地巴楚、塔中、塔北地区的上古生界泥岩样品进行B,Ba,Sr,Ga等微量元素及K2O含量测试,开展古盐度地球化学分析,使用多指标恢复出研究区晚古生代水体的古盐度。结果本研究测试的古盐度数据分布于4.7‰～55.2‰,变化范围较大,涵盖了淡水、半咸水、咸水、超咸水各种类型。其中,以半咸水—咸水样品多见,超咸水样品集中出现于巴楚地区二叠系南闸组及库普库兹曼组,淡水样品出现于塔中地区砂泥岩段。结论古盐度测试显示,塔河地区"东河塘组"具半咸水特征,这一结果与该区钻、测井揭示的三角洲沉积吻合;石炭系巴楚组—卡拉沙依组各泥岩段的古盐度具半咸水特点,反映了该时期为有河流注入的淡化泻湖环境;砂泥岩段沉积期,淡水河流注入对古盐度控制作用较为明显。巴楚地区二叠系南闸组—库普库兹曼组泥岩为咸水浅海陆棚—半咸水泻湖与潮坪沉积,个别样品的古盐度偏高可能与样品含火山凝灰质有关。     

湘中拗陷海相页岩层系岩相古地理特征

湘中拗陷是一个以下古生界浅变质岩系为基底发展起来的晚古生代沉积拗陷区,发育有机质丰度高的海相页岩层系,具有形成页岩气藏的基本地质条件。以现代沉积学和层序地层学理论为指导,结合湘中拗陷区域构造背景,分析页岩层系沉积环境,恢复页岩层系的岩相古地理,确定富有机质页岩层系发育层段。湘中拗陷的泥页岩主要发育于下石炭统及中上泥盆统和上二叠统,分布在海侵体系域上部和高水位体系域下部,平面上多与凹槽台地相的发育和分布有关。最有利于泥页岩发育的主要沉积相带是台地海盆相和滨海(海湾)沼泽相。     

Indosinian isotope ages of plutons and deposits in southwestern Miaoershan-Yuechengling,northeastern Guangxi and implications on Indosinian mineralization in South China

The Miaoershan-Yuechengling complex pluton is the largest granitoid complex in the western Nanling metallogenic belt with a surface exposure of >3000 km2.The complex pluton is composed of an early stage granitoid batholith and late stage small intrusions.The early stage batholith contains mainly medium-grained porphyritic mica granite and porphyritic monzonite granite,whereas the late stage intrusions are composed of muscovite granite porphyry and muscovite monzonitic granite.There are many W-Sn-Mo-Pb-Zn-Cu ores in the contact zone between the batholith and strata,forming an ore-rich belt around the batholith.Based on zircon LA-ICP-MS U-Pb ages,the southwestern part of the early stage batholith formed at 228.7 ± 4.1 Ma(MSWD = 2.49),with slightly earlier magmatic activity at 243.0 ± 5.8 Ma(MSWD = 2.62).The Yuntoujie muscovite granite was associated with W-Mo mineralization and has a zircon LA-ICP-MS U-Pb age of 216.8 ± 4.9 Ma(MSWD = 1.44).The Re-Os isochron age of molybdenite from the Yuntoujie W-Mo ore was 216.8 ± 7.5 Ma(MSWD = 11.3).Our new isotope data suggest that the late stage intrusive stocks from the southwestern Miaoershan-Yuechengling batholith were closely associated with W-Mo mineralization from the Indosinian period.These new results together with previous isotope data,suggest that South China underwent not only the well-known Yanshanian mineralization event,but also a widespread Indosinian metallogenic event during the Mesozoic period.Therefore,South China has a greater potential for Indosinian mineralization than previously thought such that more attention should be given to the Indosinian ore prospecting in South China.     

东北地区晚二叠世岩相古地理研究

利用野外地质剖面、钻井剖面和区域地质资料,在地层划分对比和构造格局研究基础上,运用沉积相分析的方法,系统分析了东北地区晚二叠世岩相古地理特征,将晚二叠世分为吴家坪期、长兴期两个编图单元进行岩相古地理编图,恢复了东北地区晚二叠世的岩相古地理面貌。研究表明,晚二叠世经历了卡匹敦期的快速海退后,到吴家坪期晚期古亚洲洋完全闭合,随后全区进入了陆相碎屑岩沉积阶段,主要发育湖泊沉积体系和河流沉积体系,其次为扇三角洲沉积体系。长兴期延续了吴家坪期的特征,整体演化为陆相沉积,主要发育湖泊沉积体系,漠河陆及佳木斯古陆仍然存在。     

Geochronolosic constraints on masmatic intrusions and mineralization of the Zhunuo porphyry copper deposit in Gansdese, Tibet

In situ zircon U-Pb ages for the recently discovered Zhunuo porphyry copper deposit in the western part of the Gangdese metallogenic belt in Tibet were determined by sensitive high-resolution ion microprobe （SHRIMP）. The ages can be divided into two separate groups, reflecting more than four major tectono-magmatic events in the area. The 62.5±2.5 Ma age of inherited zircons may be related to the volcanic eruption of the Linzizong Group formed shortly after the India-Asia continental collision. The 50.1±3.6 Ma age most likely corresponds to the time of underplating of mantle-derived mafic magma in Gangdese. The 15.6±0.6 Ma age obtained from magmatic zircons is interpreted as the age of crystallization of the Zhunuo ore-forming porphyry. Finally, a molybdenite Re-Os isochron age of 13.72±0.62 Ma is consistent with another zircon U-Pb age of 13.3±0.2 Ma, representing the time of copper mineralization. These ages, in combination with available literature data, indicate that magmatic crystallization and copper mineralization in the Gangdese metallogenic belt became gradually younger westward, and further suggest that the Zhunuo porphyry copper deposit was formed in the same tectonic stage as other porphyry copper deposits in the eastern and central Gangdese belt. This conclusion provides critical information for future exploration of porphyry copper deposits in western Gangdese.     

On emplacement ages of lamproites in Zhenyuan County, Guizhou Province, China

Emplacement ages of lamproites that comprise lamproite and olivine lamproite in Zhenyuan County, Guizhou Province, China, have been constrained by the whole-rock Sm-Nd and Rb-Sr isochron methods and the whole rock K-Ar method. Intrusive activities of lamproites in the Sinantang area of Zhenyuan County, Guizhou Province, took place during the Late Cambrian, as indicated by the Sm-Nd isochron ages ( t ) = (503 ± 17) (2σ) Ma and by the Rb-Sr isochron ages ( t ) = (501.2 ± 4.6) (2σ) Ma. Intrusive activities of olivine lamproites at the Maping with Ⅱ-type diamond and Xitou in Zhenyuan County, Guizhou Province, took place from the Late Cambrian to the Early Ordovician, as evidenced by the Sm-Nd isochron ages ( t ) = (502 ± 27) (2σ) Ma and by the Rb-Sr isochron age ( t ) = (502 ± 27) (2σ) Ma. This suggests that the upwelling hot materials derived from the deep mantle were emplaced from the Late Cambrian to the Early Ordovician (503-497 Ma), while the time terminal of cooling of the geothermal event of magmatism-tectonism probably was at 442.64-435.54 Ma, as dated by the whole rock K-Ar method.     

下寒武统黑色页岩金属富集机理与小行星撞击

扬子地台寒武系下统存在富含V、Ni、Mo和铂族元素(platinum group element, PGE)等的黑色页岩,局部地区有U或者Ba、Hg、As等的富集,研究这些元素富集机理有利于寻找相关矿产或者探究地质事件。6 500万年前的小行星撞击地球产生了高PGE含量的地层或者化石,依据这一事实和陨石的特征及其他地质地球化学证据,推断下寒武统黑色页岩中Ni-Mo-PGE富集是陨石撞击结果,PGE中的Ir、Os富集最明显是因为二者最抗淋滤。U在康滇地轴东侧黑色页岩中最高可达480×10^-6,因康滇地轴本身就存在混合型铀矿,推测黑色页岩中U来自它的风化。据V和Ba-Hg-As等的地化特性,认为V富集是受生物活动影响,但因V易于在热泉水中富集,故寒武纪早期泛非运动的构造-热事件可导致V富集成矿,Ba、Hg、As也因该事件产生构造裂隙后,它们优先随热液沿裂隙上升富集,并在海底局部成矿。此外,5.65亿年前的埃迪卡拉动物群发生地基本上就是5.8亿年前小行星撞击地点,提出此次行星撞击可能与埃迪卡拉生物群出现存在因果关系。由于在中国存在寒武纪澄江生物群大爆发事件,推测该次生物...     

New chronological evidence for Yanshanian diagenetic mineralization in China’s Altay orogenic belt

Granitoids and related pegmatitic rare-metal deposits are widespread in China’s Altay region, they used to be considered as Hercynian rocks and mineral deposits. Reported here are the⁴⁰Ar-³⁹Ar ages of potassium-rich minerals (muscovite and microcline) in the Koktokay pegmatitic rare-metal orefield and whole-rock as well as quartz fluid-inclusion Rb-Sr isochron ages of granite and ores in the Shangkelan pegmatite rare-metal orefield. The ages indicate that there are Yanshanian Diagenetic Mineralization events happening in China’s Altay orogenic belt and that formation of the famous Koktokay No.3 pegmatitic rare-metal deposit endured about 30 Ma of magmatic crystallization differentiation.     

内蒙古扎鲁特旗林西组页岩沉积环境的地球化学表征

探讨内蒙古扎鲁特旗地区上二叠统林西组对应地质时期的沉积环境特点。在对该区及周缘的区域地质进行野外调查和资料调研的基础上,通过对页岩中生物标志化合物与微量元素的研究,饱和烃生物标志化合物和微量元素特征所揭示的相应地质信息展现出较好的一致性和互补性,认为林西组暗色富有机质泥页岩为陆壳贴合背景下的残余海盆沉积,展布应具有稳定性;该区具有成为泥页岩油气有利勘探区的潜力,但较高的有机母质成熟度可能为泥页岩油气勘探开发中的风险因素。     

准苏吉花斑岩型钼铜矿床岩体特征及成矿机制研究

通过对辉钼矿的Re-Os及锆石U-Pb同位素年代学研究, 得到辉钼矿的Re-Os等时线年龄为297.2±4.3 Ma, 赋矿花岗斑岩的锆石U-Pb年龄为 301.1±4.0 Ma, 确定准苏吉花斑岩型钼铜(Mo-Cu)矿床的成岩成矿时代为晚石炭世至早二叠世。准苏吉花矿区不含矿花岗闪长岩的锆石U-Pb 年龄为301.2±2.2 Ma, 与花岗斑岩成岩时代一致。发育角闪石和黑云母的矿物学特征以及高Rb, Th和Ba, 低P和Ti的岩石地球化学特征表明, 花岗斑岩和花岗闪长岩同属于I型花岗岩。较低的Re含量、Mg#值、Nb/Ta值和Zr/Hf值以及低ISr值和正ε_Nd(t)值的全岩Sr-Nd同位素特征表明, 准苏吉花花岗岩的源区为新生下地壳的部分熔融, 岩浆演化过程中, 花岗斑岩和花岗闪长岩均经历较强烈的分离结晶作用, 有利于Mo进一步在残余熔体中富集。通过锆石的Ce⁴⁺/Ce³⁺值计算获得岩浆结晶分异时的氧逸度, 发现花岗斑岩岩浆的氧逸度相对较高(ΔFMQ平均值为+4.8), 花岗闪长岩岩浆氧逸度相对较低(ΔFMQ平均值为+2.2), 表明高氧逸度的岩浆更有利于Mo和Cu富集成矿。     

排山楼金矿床~(40)Ar-~(39)Ar年龄及其地质意义

采用Ar-Ar同位素测年法对辽宁排山楼金矿床矿化阶段形成的钾长石和似斑状花岗岩中的钾长石进行了测试,获得矿化阶段形成钾长石40Ar-39Ar坪年龄为(116.69±1.15)Ma,等时线年龄为(116.97±1.39)Ma,以及似斑状花岗岩中原生钾长石40Ar-39Ar坪年龄为(126.71±2.03)Ma,等时线年龄为(124.00±4.32)Ma的数据.前者代表了该矿床的形成年龄,即该矿床形成于早白垩世,后者表明金矿化不早于(126.71±2.03)Ma.这一成矿年龄与华北陆块北缘大部分金矿床的成矿年龄一致,表明华北陆块北缘绝大多数金矿床形成于中国东部中生代动力学体制发生转折的时期.     

The Rb-Sr isochron of ore and pyrite sub-samples from Linglong gold deposit, Jiaodong Peninsula, eastern China and their geological significance

Here we report the first direct Rb-Sr dating of pyrites and ores using sub-sampling from lode gold deposits in Linglong, Jiaodong Peninsula, which is a supra-large lode gold deposit and propose this as a useful geochronological technique for gold mineralization with poor age constraint. The Rb-Sr data of pyrites yield an isochron age of (121.6±8.1) Ma, whereas those of ore and ore-pyrite spread in two ranges from 120.0 to 121.8 Ma and from 110.0 to 111.7 Ma. Studies of characteristic of gold deposit and microscopy of pyrite and quartz indicate that the apparent ages of ore and ore-pyrite are not isochron ages, only mixed by two end members, i.e. the primitive hydrothermal fluids and wall rocks, whereas the isochron age of pyrite sub-samples constrains the age of gold mineralization (121.6±8.1) Ma, i.e. early Cretaceous, which is in good agreement with the published SHRIMP zircon U-Pb ages.