钼及钼同位素地球化学--同位素体系、测试技术及在地质中的应用  

Mo and Mo stable isotope geochemistry:Isotope system,analytical technique and applications to geology

作　　者：徐林刚[1,2] Bernd Lehmann 

机构地区：[1]克劳斯塔尔工业大学,德国克劳斯塔尔-采勒菲尔德38678 [2]中国地质科学院矿产资源研究所,北京100037

出　　处：《矿床地质》2011年第1期103-124,共22页Mineral Deposits

基　　金：国家留学基金;中国地质大调查项目(No.1212010634001);国家973基础研究项目(2007CB411302)的联合资助

摘　　要：多接收电感耦合等离子体质谱(MC-ICP-MS)的广泛应用使过渡金属元素同位素地球化学的研究近年来获得蓬勃发展。利用元素双稀释剂法对钼同位素值进行校正,目前可以获得±0.1‰(2σ)的测试精度。自然界中钼同位素分馏δ98/95Mo可达～3‰,其分馏机制与环境的氧化-还原状态有关。在氧化环境下钼以MoO24-的形式与锰的氧化物和氢氧化物共存,并以富集轻钼同位素为特征。在还原环境下由于水体中H2S的存在使MoO24-转换为MoOxS42--x的形式,钼同位素在这一化学过程中分馏作用明显,静水还原环境沉积物(比如黑色页岩)富集重钼同位素。由于具有对氧化-还原环境敏感的特性,钼同位素被认为是反演全球范围内古海洋及古大气氧化环境变化最有效的手段之一。基于最近几年的研究成果,文章对钼同位素体系做了详细论述,包括钼及钼同位素地球化学行为、钼同位素分析测试技术、同位素分馏机理、钼同位素在各种储库中的特征以及应用钼同位素反演古海洋氧化-还原环境和约束矿床成因等,以推动过渡金属元素同位素特别是钼同位素在地球科学领域的研究和应用。Recently a number of transitional metal isotope systems have been investigated thanks to the advent of multi-collector inductively coupled plasma mass spectrometry（MC-ICP-MS）.For example,the analytical uncertainty for Mo isotope measurement is less than±0.1‰（2σ）using the element double spike method to calibrate mass fractionation during Mo purification and mass spectrometric analysis.Natural materials have maximum～3‰ δ98/95Mo fractionation,which is related to redox processes.Under oxic conditions Mo coexists with Mn-oxyhydroxides as the stable oxyanion molybdate（MoO2-4）,resulting in Mo-enriched Mn-Fe sediments characterized by light δ98/95Mo values.In contrast,in reducing H2S-rich environments,Mo is efficiently removed from seawater.Dissolved molybdate（MoO2-4）is quantitatively transferred to thiomolybdate（MoS2-4）without isotopic fractionation.The isotopic composition in euxinic depositional settings therefore records δ98/95Mo values of contemporaneous seawater.Due to the redox-sensitive property,Mo isotope fractionation is a promising proxy for paleo-redox conditions of the Earth＇s oceanic system and atmosphere.The authors here provide an overview of the current state,including a review of the Mo geochemistry and its isotopic behavior,analytical technique,fractionation mechanism,natural reservoirs,and applications both as redox proxy and indicator of ore genesis.

关 键 词：地球化学 钼同位素 同位素分馏 测试技术 氧化-还原环境 黑色页岩 

分 类 号：P597[天文地球—地球化学]