稳定氯同位素分馏机理及其应用的研究

DEVELOPMENT OF FRACTIONATION AND APPLICATION OF STABLE CHLORINE ISOTOPE

过去一直认为稳定氯同位素比值(^(37)Cl/^(35)Cl)几乎不变。80年代以来利用高精度质谱法成功地发现了自然界氯同位素分馏作用。单纯的溶解和对流迁移作用不能引起同位素组分变化,而扩散作用、离子渗透作用和对流混合作用却可导致同位素分馏。各地不同深度海水的氯同位素成分极为一致,故以标准平均海水氯(SMOC)作为对比标准。得克萨斯—路易斯安那海湾油田水的δ^(37)Cl大致为+0.5‰^-1.25‰,且与氯浓度大致呈正相关。热液成矿系统中,氯同位素可作为研究矿床成因的示踪剂,如美国田纳西州密西西比河谷型矿床(MVD)的δ^(37)Cl在+0.2‰^-1.1‰之间,几个斑岩铜矿床(PVD)的早期脉岩与晚期脉岩中不同δ^(37)Cl的存在,都表明在成矿过程中有不同氯源的参与。

It was believed previously that there is almost no variation in the stable isotope ratio of chlorine 37C1/35C1. The isotope fractionation in natural chlorides was found by using high precision mass spectrometry in 1980s. Dissolution and advective transport alone do not produce a change in isotope composition, while the diffusion, ion filtration and advective mixing could result in fractionation of chlorine isotope. The chlorine isotope composition of ocean water from a variety of locations and depths is remarkably consistent, so the standard mean ocean chloride ( SMOC ) can be used as a standard (δ 37Cl=0) or comparison . The δ37 Cl of oil field formation water a long the Texas-Louisiana Gulf Coast ranges from + 0 . 5‰to - 1. 25‰and shows a general trend of 37C1 enrichment with increasing chloride concentration. In ore-forming hydrothermal systems 37C1 is a trace to study the origin of ore-deposit. For exampfe the δ37C1 of Mississippi valley-type deposits (MVD) in Tennessee ranges from + 0. 2‰ to-1. 1‰ and the different δ37Cl between early and late veins exists in some porphyry copper deposits. All these cases indicate the involvement of different sources for chloride in ore-forming process.