内蒙古红花尔基白钨矿矿床赋矿花岗岩Sr-Nd-Pb-Hf同位素特征

对内蒙古红花尔基白钨矿矿床的赋矿花岗岩进行了全岩Sr、Nd同位素、钾长石Pb同位素以及LA-MC-ICPMS锆石Hf同位素特征研究。结果表明,从肉红色二长花岗岩、灰白色二长花岗岩到石英二长岩,它们的(~(87)Sr/~(86)Sr)_i值依次降低,均值分别为0.70525、0.70517和0.70482,_(εNd)(t)值则依次增加,均值分别为+2.2、+2.3和+3.1。2种二长花岗岩的钾长石Pb同位素值较均一,其中~(206)Pb/~(204)Pzb为18.258~18.276,~(207)Pb/~(204)Pb为15.507~15.512;~(208)Pb/~(204)Pb为37.994~38.018。3种花岗岩的锆石Hf同位素特征显示~(εHf)(t)值分别为+5.2~+10.4(均值+8.1)、+3.1~+9.8(均值+7.5)、+5.8~+14.4(均值+9.2)。赋矿花岗岩的Sr-Nd-Pb-Hf同位素特征指示其源岩物质很可能是以新元古代起源于亏损地幔的下地壳物质为主,石英二长岩可能是岩浆混合了少量地幔物质形成的包体。区域构造分析表明,红花尔基白钨矿矿床赋矿花岗岩岩浆源区的形成可能与新元古代古亚洲洋演化过程中俯冲大洋板块与上地幔的相互作用有关;早侏罗世,蒙古—鄂霍次克洋盆在本区闭合后,板块碰撞隆起的挤压环境触发了源岩物质的部分熔融,从而形成了赋矿花岗岩。     

Reconstruction of the ore-forming system in the Mnogovershinnoe gold-silver deposit (Lower Amur River Region) based on the structure of ore-bearing zones and isotopic studies

The hydrothermal ore-forming paleosystem of the Mnogovershinnoe deposit is reconstructed by defining lithothectonic elements constituting ore-bearing zones with account for their formation mechanisms and positions in the conditional geochronological scale of the hydrothermal activity and isotopic data. The use of lithotectonic elements for deciphering ore genesis events made it possible to take into account both synchronously and successively formed parts of ore bodies, which substantially improved the quality of the reference data for developing a dynamic model of the deposit. The approach proposed for reconstructing the hydrothermal paleosystem of the Mnogovershinnoe deposit may be used for developing models of other ore objects.     

湖南黄沙坪多金属矿床成矿斑岩锆石U-Pb年代学及Hf同位素制约

湖南黄沙坪铅锌钨钼多金属矿床位于南岭花岗岩带中段的北缘,是区内的典型矿床之一.该矿床与成矿关系密切的岩体为花岗斑岩、花斑岩和石英斑岩.LA-ICP-MS锆石U-Pb年代学显示,花岗斑岩的成岩年龄为(150.1±0.4) Ma,花斑岩的年龄为(150.2±0.4) Ma,石英斑岩的年龄为(155.3±0.7) Ma,表明岩体形成于晚侏罗世.锆石原位Hf同位素数据分析结果表明,含矿斑岩可能来源于中元古代古老基底的重熔,其中石英斑岩主要来源于地壳,花岗斑岩与花斑岩的形成伴有少量地幔物质的加入,是壳幔相互作用的产物.另外,由于花岗斑岩与花斑岩成岩年龄相近,Hf同位素组成相似,进一步印证了花斑岩和花岗斑岩是同源同期岩浆的产物.结合该矿床所处的区域大地构造背景以及成矿年龄,认为该矿床形成的动力学机制主要为中-晚侏罗世活动的Farallon-Izanagi洋岭和转换断层俯冲,导致华南内陆岩石圈全面伸展-减薄-地幔物质上涌,从而使得地壳物质部分熔融.     

The first results of U-Pb dating of zircons from gneissic granites of the Kharbei Complex (Polar Urals)

Data on the age of gneissic granites from the Precambrian Kharbei Complex (Polar Urals) have been obtained for the first time. Local U-Pb dating was carried out using a SHRIMP-II ion microprobe. Zircons were taken from three granitic bodies close in petrographic and petrochemical parameters. The formation of gneissic granites was implemented in two stages: during the Late Ediacarian (556 ± 2.2 Ma) and in the Late Cambrian (497 ± 3 and 487.1 ± 2.1 Ma). The rocks formed owing to rheomorphic flow of granitic material, caused by tectonic events related to Timanian (Baikalian) tectogenesis and epicontinental riftogenesis, which occurred prior to the appearance of the Paleouralian Ocean.     

First results of the U-Pb isotopic (LA-ICP-MS) dating of detrital zircons from the Lower Paleozoic of Spitsbergen

This work presents the first results of dating of detrital zircons (dZr _s) from the Lower Paleozoic terrigenous-carbonate rocks of the Cambrian Blåstertoppen (samples 08-137 and 08-142, south of the Wedel Jarlsberg Land) and Ordovician Wiederfjellet (sample K06-17, north of the Land) sequences, which are widespread to the north and south of the Hornsund Fjord, on the southwestern coast of Spitsbergen Island. Against the background of sporadic values of 1–3 Ga, samples K06-17 and 08-142 showed similar spectra of the age distribution of dZr _s with dominant compact numerous age groups of ～1.8–1.9 Ga and peaks of the maximum of the probability density of 1850 and 1862 Ma, respectively. The only noticeable difference in these spectra is the presence of a young grain of 541 Ma in sample 08-142 (with a very good value of concordance), which is close to the suggested Cambrian age of formation of the Blåstertoppen sequence. The distribution of the dZr ages in sample 08-137 is significantly distinct. First, the general age range is narrower: 1.15–1.95 Ga (no Archean ages). Second, the age of 1.8–2.0 Ga dominant in the other two samples corresponds to only one grain. Thus, although samples 08-137 and 08-142 were taken from closely located levels of the section of the Cambrian Blåstertoppen sequence (in the same interception), the age spectra of dZr _s from these samples differ cardinally. The statistical Kolmogorov-Smirnov test quantitatively supports the visual similarity of age spectra of dZr _s from samples K06-17 and 08-142 (p = 0.913) and the distinction of those from samples 08-142 and 08-137 (p = 0). Thus, the provenance areas, which supplied the clastic material to the sedimentary basin, whose remnants are presently located in the southwestern part of Spitsbergen, abruptly changed in the Cambrian. The basal levels of the Cambrian section of this basin (sample 08-137) were mostly formed due to accumulation of the erosion products of the local (Spitsbergen) sources: metarocks of the Eimfjellet Group located in the south of the Wedel Jarlsberg Land and of the Smerenburgfjord Group abundant on the Albert I Land. The dZr _s age spectrum is a print of the ages of the Late Paleoproterozoic-Mesoproterozoic (pre-Grenville) basement unaffected by assemblage of Rodinia. Then the conditions changed and the basin became to accumulate the material from the remote regions, significant parts of which were the areas of ancient cratons, including Archean blocks. The general sedimentation conditions did not change considerably, because the rock type remained the same.     

Mineral composition of gold-bearing veins and typomorphic features of their minerals in the Kirovskoe deposit (Upper Amur region)

A collection of quartz veinlets with ore mineralization sampled from the dumps of the abandoned pit of the Kirov mine was analyzed with defining the mineral assemblages productive for gold mineralization and determining the composition of the main ore minerals and their typomorphic features, which are used for interpreting the genesis of the mineral associations and the deposit as a whole.     

Petrogenesis of ore-bearing porphyry from the Tangjiaping porphyry Mo deposit,Dabie orogen: Zircon U-Pb geochronology,geochemistry and Sr-Nd-Hf isotopic constraints

Extensive Early Cretaceous post-collisional igneous rocks, especially the large volume of granitoids developed in the Dabie orogen. Some of these granitic rocks are spatially, temporally, and genetically associated with economically important molybdenum deposits. The Tangjiaping large-scale (> 0.1 million ton) porphyry Mo deposit is located in the northwest of the Northern Dabie Complex unit. The Mo mineralization is mainly hosted in molybdenite-bearing quartz veinlets and stockworks in the Tangjiaping granite porphyry, which intruded into Proterozoic biotite-plagioclase gneiss and amphibole-plagioclase gneiss. Two alteration zones from the porphyry centre outwards and downwards can be recognized: (1) K-silicate alteration-silicification zone; (2) silicification-phyllic alteration zone. The Tangjiaping ore-bearing granite porphyry occurs as an individual stock with an outcrop of 0.4 km². LA-ICP-MS zircon U-Pb dating of the Tangjiaping granite porphyry yields crystallization age of 115 ± 1 Ma, which is consistent with the molybdenite Re-Os age of the deposit given by previous studies. The Tangjiaping granitic rocks are metaluminous and belong to high-K calc-alkaline and shoshonitic series. They are relatively enriched in light rare earth elements and have moderately negative Eu anomalies. Geochemical and mineralogical characteristics indicate that the Tangjiaping granite is an A-type granite and was generated by partial melting of intermediate-felsic rocks at pressures of ca. 0.4–0.8 GPa. There are high initial ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.707367 to 0.709410 and negative ε_Nd(t) values varying from − 15.0 to − 14.2 for the Tangjiaping granite. In situ zircon Hf isotopic analyses show that the ε_Hf(t) values of zircons from the Tangjiaping granite porphyry vary from − 17.0 to − 6.0. The geochemical data and Sr-Nd-Hf isotopes, coupled with the Neoproterozoic inherited zircon age (652 ± 21 Ma), indicate that the Tangjiaping granite porphyry was most likely derived from partial melting of the Northern Dabie gneiss with some relatively enriched mantle materials involved. The Tangjiaping Mo ore-forming granite porphyry was formed in an extensional setting. The Early Cretaceous asthenospheric upwelling might have played an important role in the formation of the approximately coeval Mo-bearing magmas in the Dabie orogen.     

First U-Pb dates for detrital zircons from deposits of Serebryanka Group (Upper Proterozoic,Middle Urals)

The results of application of the LA-ICP-MS method for analysis of U-Pb ages of detrital zircons from Serebryanka Group (Middle Urals) has been presented for the first time. It has been found that the detrital zircon population in tillite-like conglomerates of the Tany Formation is represented nearly in equal shares by grains with Neoarchean and Paleoproterozoic U-Pb ages. This allows the basement crystalline rocks from the eastern part of the East European Craton to be considered as the principal source of aluminosilicate clastic material in the beginning of the Serebryanka. The population of detrival zircons in sandstones from the Kernos Formation consists of Meso- and Neoarchean (approximately 15%), Paleoproterozoic (∼60%), and Mesoproterozoic (∼26%) zircon grains. Comparison of the obtained data with the materials on detrital zircons from Tonian and Ediacarian sandstones in the southern Urals has shown that the principal role in formation of Tonian and Ediacaran sedimentary sequences was played by the products of Mid- and Late Paleoproterozoic crystalline rock erosion in the craton socle. In addition to this, accumulation of the Serebryanka Group took place with visible participation of more ancient—Early Paleoproterozoic, Neo- and Mesoarchean—rock associations on the paleo-water catchment areas. The end of the Serebryanka period differed from its beginning by the additional appearance of Mesoproterozoic complexes in alimentation zones; for comparison, the role played by these complexes in formation of Ectasian-Ediacarian deposits of the adjacent southern Urals segment is insufficient, judging by the currently available data. All these facts may indicate that there are significant differences in the spatiotemporal distribution of clastic material sources for Upper Precambrian deposits in the West Megazone of the southern and middle Urals.     

Patterns of ore localization and the mineral composition of ores and ore-bearing rocks of the Koretkonde uranium deposit (Vitim ore-bearing region)

This work presents the geological structure of the Neogen uranium-bearing ore sedimentary strata that filled the paleovalleys of the Koretkonde deposit. As a result of work we carried out, productive deposits were stratigraphically divided, the patterns of the localization of uranium mineralization were studied, and lithological and mineralogical ore-controlling factors were revealed. The main mineral phases of uranium were identified with scanning-electron microscopy and microprobe studies. In the future, a more detailed study of the deposits is planned in order to reveal methods for improving the efficiency of their exploration and organize the search for uranium deposits of such a type within the Vitim uranium-bearing ore region to expand the mineral resource base of Russia.     

U-Pb dating and provenance of detrital zircons from the Upper Precambrian deposits of North Timan

Timan comprises the southwest edge of the Pechora Plate. The plate basement is composed of variably metamorphosed sedimentary, mainly terrigenous, and igneous rocks of the Late Precambrian age that are generally overlain by Ordovician-Cenozoic platform cover. Poor exposition and discontinuous distribution of the Upper Precambrian outcrops of dominantly fossil-free sedimentary rocks cause considerable disagreements in stratigraphic correlation. This applies equally to North Timan, which represents an uplifted block of basement, in which sedimentary-metamorphic rocks form the Barminskaya Group (～5000 m thick), previously dated as Early Riphean to Vendian. Earlier Rb-Sr and Sm-Nd isotope dating of schist and cross-cutting gabbro-dolerite and dolerite established the timing of greenschist facies metamorphism at 700 Ma. Thus, Late Riphean age of the Barminskaya Group has been suggested. Results of local U-Pb dating of detrital zircon from silty sandstones of the Malochernoretskaya Formation, which constitutes the middle part of the outcropping section of the Barminskaya Group, confirm this conclusion. Age data for 95 zircon grains cover the range of 1035–2883 Ma with age peaks at 1150, 1350, 1550, 1780, and 1885 Ma. The minimum age of zircons, considered as the lower age constraint on sediment deposition, provides grounds to date the Barminskaya Group as Late Riphean and indicates eroded rock complexes of the Fennoscandian Shield as the possible provenance areas.     

德兴矿集区花岗闪长斑岩锆石U-Pb年龄、Hf同位素特征及其意义

德兴矿集区位于赣东北地区,是中国东部中生代钦杭成矿带中的大型铜金铅锌矿集区之一,集中了铜厂、富家坞和朱砂红斑岩铜钼(金)矿、银山银铜铅锌多金属矿和金山金矿等大型、超大型矿床。本文在系统的野外地质调查与样品采集的基础上,对铜厂、富家坞、朱砂红及银山花岗闪长斑岩进行了LA-MC-ICP-MS锆石U-Pb定年和原位Hf同位素分析。德兴矿集区花岗闪长斑岩的LA-MC-ICP-MS锆石U-Pb的4组年龄分别为:(171±1.2)Ma(铜厂)、(172±0.68)Ma(富家坞)、(173±1.3)Ma(朱砂红)、(176±1.5)Ma(银山),表明这些岩体均为中侏罗世的产物。样品Hf两阶段模式年龄平均值分别为861 Ma、876 Ma、904 Ma和941 Ma,正的εHf(t)平均值在4.34-5.54,Zr/Hf比值接近于上地幔的Zr/Hf比值。锆石Hf同位素组成显示,岩浆源区主要来源于亏损地幔组分,但在岩浆演化中遭受了古老地壳物质的混染,幔源物质在德兴矿集区花岗闪长斑岩的形成过程中发挥了重要作用。德兴矿集区4个矿床成岩成矿的最重要时期在170-175 Ma,该矿集区岩浆热液系统持续活动可能是该大型矿集区形成的重要原因。     

云南德钦羊拉大型铜矿区花岗闪长岩的锆石U-Pb年龄、Hf同位素特征及其地质意义

云南德钦羊拉大型铜矿隶属我国著名的羊拉-鲁春铜多金属矿化集中区,其铜矿产与区内印支期侵入岩有着密切的时空、成因联系。云南德钦羊拉大型铜矿区与花岗闪长岩岩体密切共生,花岗闪长岩由南往北依次出露路农、里农、江边、贝吾岩体,其中里农花岗闪长岩可见辉绿岩墙侵入。锆石原位U-Pb定年和Lu-Hf同位素分析结果表明,4组年龄分别为238～239Ma(里农和路农岩体),228Ma(江边岩体),222Ma(辉绿岩墙),214Ma(贝吾岩体)。这些年龄代表锆石的结晶年龄,对应路农、里农、江边、辉绿岩墙、贝吾花岗闪长岩岩体的形成年龄,同时显示该岩带由南往北年龄由老到新的侵位序列。显示羊拉大型铜矿区花岗闪长岩体是三叠纪时期的花岗质岩浆多次涌动侵入形成的,其中伴随辉绿岩墙的侵入,岩浆活动持续时间约15Ma。里农铜矿体辉钼矿成矿(Re-Os)年龄为228～230Ma,显然羊拉铜矿床的成矿作用也在该时期完成。羊拉大型铜矿区花岗闪长岩体的全岩εNd(t)值为-5.0～-5.5,中元古代(1.24～1.39Ga)的亏损地幔模式年龄,锆石εHf(t)值为-4.3～+2.4,锆石Hf同位素地壳模式年龄(1.1～1.5Ga),εHf(t)值主要为负值揭示其源区可能主要为陆壳物质,部分锆石的εHf(t)值为正值,说明在其形成过程中有一定比例的亏损地幔物质的加入,源区同位素的不均一,是壳幔相互作用的结果,中元古代模式年龄说明其源区主要以扬子克拉通下地壳物质为主。这些新资料为理解滇西古特提斯构造演化提供了重要的地球化学制约。     

Al-Si order and degree of disturbance of perthites from the Upper Amur region

Doklady Earth Sciences -     

闽中梅仙铅锌多金属矿区花岗岩锆石U-Pb年龄、Sr-Nd同位素组成特征及其地质意义

为探讨闽中梅仙矿区花岗岩的成因,对小焦、寨头、根竹园花岗岩体的岩相学、年代学和Sr-Nd同位素特征进行研究。LA-ICP-MS锆石U-Pb测年结果显示,小焦花岗岩体的结晶年龄为158±3Ma,形成于燕山中期晚侏罗世。同位素分析显示,样品具有高I_(Sr)(0.707099～0.710082)和低ε_(Nd)(t)(-9.79～-10.92)的特点,显示明显的壳源特征,其岩石成因类型属高分异的Ⅰ型花岗岩。结合前人最新的研究成果表明,梅仙矿区燕山中期花岗岩形成于古太平洋板块向欧亚板块的俯冲-消减的伸展拉张环境,是板内伸展造山阶段的产物。     

激光探针等离子体质谱法（LAM—ICPMS）用于年龄锆石U—Pb定年

利用激光探针等离子体普（ＬＡＭ－ＩＣＰＭＳ）技术对中生代锆石进行了详细的２０６Ｐｂ／＾２３８定年研究。采用线扫描（Ｌｉｎｅ ｓｃａｎ）进样法减小了传统的剥深（Ｄｅｐｔｈ ｐｒｏｆｉｌｅ）进样法所引起的激光熔蚀分异效应;优化仪器参数可三ＩＣＰ－ＭＳ对Ｐｂ和Ｕ的质量歧视效应。测得了精确的＾２０６Ｐｂ／＾２３８Ｕ比值及年龄。研究结果表明,均匀颗粒锆石的＾２０６Ｐｂ／＾２３８Ｕ比值测量精度为２％～１０％,     

The U-Pb age dating of detrital zircons from Upper Jurassic-Lower Cretaceous deposits of Stolbovoy Island (New Siberian Islands)

The results of the U-Pb (SIMS and LA-ICPMS) age dating of detrital zircons from Upper Jurassic-Lower Cretaceous sandstones of Stolbovoy Island show that these deposits contain zircons of a wide age range, from Archean to Lower Cretaceous. Precambrian gneisses and granites, as well as Late Paleozoic and Mesozoic plutonic and volcanic complexes, are considered to be the main source areas of clastic material of Upper Jurassic-Lower Cretaceous formations of Stolbovoy Island. The U-Pb age dating of detrital zircons from sandstones without making a selection on any basis yields the most complete information about source areas of clastic material in a sedimentary basin. In some cases the data on euhedral (idiomorphic) and transparent zircon crystals can be useful to clarify the lower age boundary of sedimentation.     

二连盆地巴彦乌拉铀矿区花岗岩锆石U-Pb年龄和Hf同位素特征及地质意义

二连盆地中部巴彦乌拉地区位于中亚造山带东段,发育有多个砂岩型铀矿床（点）。利用LA-ICP-MS锆石U-Pb同位素和Hf同位素分析对巴彦乌拉地区巴音宝力格隆起东部花岗岩开展了年代学研究。结果显示,2个样品的锆石U-Pb年龄在292±3~288±2 Ma之间,与巴彦乌拉地区巴音宝力格隆起中西部发育的早二叠世花岗岩及流纹岩的年龄范围基本一致。结合区域成岩年代学数据可知,巴彦乌拉地区巴音宝力格隆起发育一条主要由晚石炭世—早二叠世花岗岩及火山岩组成的岩浆岩带。锆石Hf同位素数据显示,2个花岗岩样品的εHf（t）值为+10.6~+18.2,表明其源区为新生下地壳物质。综合区域地质特征可知,中亚造山带东段显生宙的构造-岩浆活动与二连盆地中部及巴彦乌拉地区赛汉组上段砂岩型铀成矿作用关系密切,为砂岩型铀矿床的形成提供了一系列有利条件。