铅同位素在矿床研究和找矿勘探中的应用综述

铅同位素用于示踪成矿物质来源已得到广泛应用,其方法主要有：模式年龄法、PbSL等时年龄法、构造模式法、Δβ-Δγ图解法以及直接对比法。其中单用模式年龄来示踪成矿物质来源已逐步淘汰,只能用通过合理模式计算的模式年龄来进行检验或佐证;铅构造模式因提出时没有考虑中国的地质问题而遭质疑;Δβ-Δγ图解法虽然考虑到中国的地质问题但仍需接受检验;而直接对比法是示踪成矿物质来源最有效、最直观的方法。此外,矿石全岩Pb-Pb等时线定年在一些矿床中应用获得成功,通过剔除系统样品中的后期干扰样品,可以使矿石全岩Pb-Pb等时线定年变得更加精确。铅同位素地球化学研究开始走向应用于化探与找矿评价,特别是运用铅同位素三维空间拓扑投影特征值V1和V2进行隐伏矿深度预测和资源量评价的铅同位素系统剖面化探方法,使铅同位素化探方法得到了新的发展。     

Re-Os同位素定年方法进展及ICP-MS精确定年测试关键技术

本文介绍了Re-Os同位素定年的基本原理、技术发展及应用现状;综述了样品分解和Re-Os分离富集的主要方法,重点对ICP-MS法进行Re-Os同位素定年做了较详尽的介绍,包括质量分馏校正、干扰校正、含量初测、取样量的确定、稀释剂的稀释比及稀释剂加入量等,以确保高精度测试;评述了ICP-MS最常见的测定对象-辉钼矿中Re-Os的失耦现象及降低其对Re-Os同位素定年影响的对策,文中描述了由测定同位素比值计算含量时的误差传递公式并重申了最佳稀释比。最后,指出了Re-Os同位素定年方法研究中应该关注的工作方向。     

铅同位素研究新进展—“双稀释剂”测定方法和“AGSO—CSIRO”模式年龄

适当的仪器质量分馏校正是提高同位素分析数据精度的关键。重新“复活”了的铅同位素“双稀释剂”测定方法可实现严格的仪器质量分别校正,以区域锆石Ｕ－Ｐｂ年龄为控制点的“ＡＧＳＯ－ＣＳＩＲＯ”铅同位素模式年龄方法可获得精度很高的定年结果,铅同位素研究的应用必将因此而得到更大的发展。     

用双稀释法测定地质样品中的铅同位素组成

随着超净化实验室条件的完善以及多接收同位素质谱技术的成熟，铅同位素双稀释法倍受关注。用双稀释法测定铅同位素比值的方法原理，以及^204Pb—^207Pb双稀释剂的配制和标定方法。通过对标准物质NBS981和地质样品的分析测定，表明用双稀释法测定铅同位素比值，可以有效校正由质谱分析造成的同位素分馏效应，从而提高分析结果的精度和准确度。     

一种新的 K-Ar定年方法：峰值比较法

K-Ar法定年技术经历了体积法和稀释法等不断趋于成熟，但对于年轻火山岩进行定年时，由于同位素质量分馏的影响，上述方法都具有不可克服的缺陷。随着质谱仪稳定度和精度的提高，直接建立氩同位素含量与峰强度之间的定量关系，从而不再使用稀释剂（ 38 Ar）成为可能，这就是 K-Ar定年的新方法：峰值比较法（或无稀释剂法）。该方法可以消除质量分馏作用带来的误差，对年轻火山岩定年具有重要意义。近代火山物质都含有初始氩，且有不同程度的质量分馏，其同位素比值落在质量分馏线上，这表明质量分馏作用影响 K-Ar定年的准确性，尤其是非常年轻的样品。通过精确测定样品的 38 Ar／ 36 Ar比值，可以准确扣除样品中的初始 40 Ar，从而得到放射成因 40 Ar含量。这种测量方法可以用于较老岩石、矿物样品的年龄测定，其结果与 K-Ar稀释法以及 40 Ar－ 39 Ar法相一致；更重要的是可以用于年轻样品的年龄测定，可以测 2～5ka的岩矿样品，对富钾矿物的测量误差小于 1ka；对老于 0．1Ma的样品，相对误差不大于 1．5％。介绍了峰值比较法的基本原理和测试过程，同时还讨论它的使用条件和定年范围。     

铅同位素数据的应用及若干问题探讨

一、普通铅同位素年龄的地质意义目前,在多金属矿床成矿年龄测定中,普通铅同位素年龄仍具有重要的意义。这不仅因为普通铅同位素年龄测定用的矿石铅或岩石铅样品比较容易获得,测试方法也相对简单,而且通过一个样品的铅同位素数据同时获得几组年龄值,可以相互检验。虽然也可采用 K—Ar法和R b—Sr 等时线法及 U、Tn—Pb 法等放射性同位素测定成矿年龄,但因为对样品要求比     

基性岩斜锆石U-Pb同位素定年3种方法之比较

根据新的研究成果,结合近年来文献报道的资料,对利用3种方法,即同位素稀释-热电离质谱(ID-TIMS)法、高灵敏度高分辨率离子探针质谱(SHRIMP)法、激光烧蚀电感耦合等离子体质谱(LA-ICPMS)法做基性岩斜锆石U-Pb同位素定年的优点和局限性进行比较,并讨论了针对具体样品选择定年方法的基本原则。新的研究成果表明,基性岩斜锆石U-Pb同位素年龄测定的3种方法各有不同的特点及局限性。在实际工作中,根据从具体样品中分选得到的斜锆石的数量、粒度大小、年龄范围、U-Pb含量、测年精度要求等因素,灵活地选择测年方法,对于获得比较理想的测年结果是非常重要的。     

同位素双稀释剂法的原理与应用Ⅰ:原理部分

随着MC-ICP-MS的推广使用,同位素双稀释剂法在国际上已被广泛用于非传统稳定同位素领域中低浓度元素同位素组成的高精度分析,其可有效校正化学纯化和质谱测定过程中的同位素质量分馏,但该方法在国内还未得到全面应用。制约该方法使用的关键在于难以掌握两单稀释剂间(λ)以及双稀释剂与样品之间(p)的最优配比值。本文以Siebert等(2001)的几何迭代算法为例,详细说明了双稀释剂法的计算流程,提出了定性和定量双稀释剂的选择原则,并以硒同位素为例,说明了两单稀释剂间和双稀释剂与样品间最佳配比值的优化步骤,最后简要说明了双稀释剂组成的标定方法、双稀释剂法的优缺点,以及可用于同位素非质量分馏研究的发展趋势。     

同位素双稀释剂技术的数值模拟与应用

近年来,非传统稳定同位素地球化学已成为新兴发展的研究领域,同位素双稀释剂技术是该领域的主流分析方法之一,但始终存在的困扰问题是如何进行同位素双稀释剂间以及稀释剂与样品间的最优混合。这两种混合比严重制约着同位素比值测试的准确度、精度和重现性。本文从同位素双稀释剂技术的数学原理出发,以Cr、Mo同位素为例,结合MonteCarlo误差模型,深入讨论和分析了两单稀释剂间比值(λ)及双稀释剂与自然样品间比值(p)的最优化数值模拟,得到了以双稀释剂~50(Cr)-~54(Cr)、~97(Mo)-~(100)Mo为例的λ、p值的最优取值范围。该数值模拟可适用于所有能够利用同位素双稀释剂技术的元素。在此基础上,就数值模拟结果如何应用于同位素双稀释剂的选择和组成标定也给予了详细说明,这为我国开展和使用同位素双稀释剂技术提供了基本思路和需要注意的关键问题,有助于推动同位素双稀释剂技术在我国地学界的广泛应用和发展。     

同位素稀释热电离质谱法测定锡石U-Pb年龄探索

针对我国锡多金属矿床的定年问题,建立一种采用同位素稀释热电离质谱(ID-TIMS)法进行锡石U-Pb同位素定年的方法,并与激光烧蚀电感耦合等离子体质谱(LA-ICP-MS)法进行对比验证。由于采用化学处理技术分别纯化了U和Pb,减少了普通铅的影响,大大提高了分析测定精度。将该方法应用于某地区石英-锡石-黑钨矿脉的锡石样品分析,获得了精确的U-Pb年龄值。     

The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures,South Wales,UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)

Pant-y-ffynnon Quarry in South Wales yielded a rich cache of fossils in the early 1950s, including articulated specimens of new species (the small sauropodomorph dinosaur Pantydraco caducus and the crocodylomorph Terrestrisuchus gracilis), but no substantial study of the wider fauna of the Pant-y-ffynnon fissure systems has been published. Here, our overview of existing specimens, a few described but mostly undescribed, as well as freshly processed material, provides a comprehensive picture of the Pant-y-ffynnon palaeo-island of the Late Triassic. This was an island with a relatively impoverished fauna dominated by small clevosaurs (rhynchocephalians), including a new species, Clevosaurus cambrica, described here from a partially articulated specimen and isolated bones. The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago. The larger reptiles on the palaeo-island do not exceed 1.5?m in length, including a small carnivorous crocodylomorph, Terrestrisuchus, and a possible example of insular dwarfism in the basal dinosaur Pantydraco.     

The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts

The solubilities of columbite, tantalite, wolframite, rutile, zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts. All experiments were conducted at 1035 °C and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt.% H₂O. Accessory phase solubilities are not affected by the water content of the peralkaline melt. By contrast, solubilities are affected by the water content of the subaluminous melt, where the solubilities of all the accessory phases examined increase with the water content of the melt, up to 2 wt.% H₂O. At higher water contents, solubilities are nearly constant. It can be concluded that water is not an important control of accessory phase solubility, although the water content will affect diffusivities of components in the melt, thus whether or not accessory phases will be present as restite material. The solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies, which have observed differences in the coordination of high field strength elements in dry vs. wet subaluminous granitic glasses, but not for peralkaline granitic glasses. Lastly, the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species.     

Quaternary stresses revealed by calcite twinning inversion: insights from observations in the Savonnières underground quarry (eastern France)

Calcite samples were extracted both from the rock matrix and the superficial coating of a karstified fault plane of an underground quarry, located in the eastern border of the Paris basin. The karstification is dated as Quaternary. Analysis of mechanical calcite twinning reveals that only the calcite matrix has also undergone a compression trending WNW that can be attributed to the Mio-Pliocene alpine collision. Both coating and matrix have undergone a strike-slip regime with σ₁ roughly trending north–south, that could correspond to the regional present-day state of stress, a strike-slip compression rather trending NNW, modified by local phenomena. To cite this article: M. Rocher et al., C. R. Geoscience 335 (2003).     

HYDROGEOLOGY

正20141756 Chen Ruige(Mathematical College,China University of Geosciences,Beijing100083,China);Zhou Xun Numerical Simulation of Groundwater Level Fluctuation in a Coastal Confined Aquifer with Sloping Initial Groundwater Level Induced by the Tide(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(7),2013,p.1099-1104,6 illus.,16 refs.) Key words:confined water,groundwater level     

METAMORPHIC PETROLOGY

正20141408 Cai Jia(Institute of Geology,Chinese Academy of Geological Sciences,Beijing100037,China);Liu Fulai Petrogenesis and Metamorphic P-T Conditions of Garnet-Spinel-Biotitebearing Paragneiss in Danangou Area,Daqingshan-Wulashan Metamorphic Complex Belt(Acta Petrologica Sinica,ISSN1000-0569,CN11-1922/P,29(7),     

SERIALS

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GEOPHYSICAL EXPLORATION

正20142386An Guoying(China Aero Geophysical Survey and Remote Sensing Center for Land and Resources,Beijing 100083,China)Application of Satellite Remote Sensing in Regional Hydrogeological Investigation:Taking Cenozoic Strata in Wenquan Sheet(1∶250 000)of Karakoram Range as an Example(Geosci-     

QUATERNARY GEOLOGY & GEOMORPHOLOGY

正20141016An Chengbang(Key Laboratory of Western China’s Environmental Systems,Ministry of Education,Lanzhou University,Lanzhou 730000,China);Zhao Yongtao Lake Records during the Last Glacial Maximum from Xinjiang,NW China and Their Climatic Impli-     

PETROLEUM GEOLOGY

正20141538 Cao Qing(School of Earth Sciences and Engineering,Xi’an Petroleum University,Xi’an 710065,China);Zhao Jingzhou Characteristics and Significance of Fluid Inclusions from Majiagou Formation,Yichuan Huangling Area,Ordos Basin(Advances in Earth Science,ISSN1001-8166,CN62-1091/P,28(7),2013,p.819-828,7 illus.,3 tables,43 refs.)     

GEOCHEMISTRY

正20142002 Wei Hualing(Institute of Geophysical and Geochemical Exploration,Chinese Academy of Geological Sciences,Langfang065000,China);Zhou Guohua Element Content and Mineral Compositions in Different Sizes of Soil in Tongling Area,Anhui Province(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(11),2013,p.1861