硼及硼同位素地球化学在地质研究中的应用

总结了硼及硼同位素的地球化学特征：（１）硼是易溶元素，主要赋存在地球表层，尤其是海水、海相沉积物及海水交代岩石中。其同位素组成δ１１Ｂ值按顺序变化，封闭盐湖卤水（＞４０‰）＞海水（３９５‰）＞海相硼矿物（１８２‰～３１７３‰）＞海相沉积物（１３９‰～２５２‰）＞海水交代岩石（４５１‰～１０８５‰）。大陆水及陆相沉积物硼含量及硼同位素组成变化极大，并多以负值为主。海陆过渡构造带则具有过渡的硼丰度值和硼同位素组成。（２）１１Ｂ较１０Ｂ具有更活跃的地球化学性质，因此在水岩作用中具有明显的同位素交换。硅化交代作用中，岩石被硅化交代，释放硼，并优先释放重硼，同位素组成变轻；在脱硅反应中，岩石释放硅吸收硼，并优先吸收重硼，同位素组成变重。在封闭体系中，水溶液淋滤岩石中部分的硼，即可大量富集，并富集１１Ｂ；在开放体系中，岩石硼被大量淋滤流失，δ１１Ｂ值明显降低。由于水岩作用的结果，从新鲜海底玄武岩到正常海水，硼同位素值从－２９５‰到３９５‰逐渐升高。（３）变质脱水反应中硼被大量排出，并优先排出重硼同位素，进入流体相，因此随着变质程度由低到高，岩石中硼含量及同位素组成δ１１Ｂ值由高变低。（４）在成矿研究中?

硼及硼同位素地球化学在地质研究中的应用

This paper summarizes the geochemical characteristics displayed by boron and its isotopic composition in nature: (1) Boron can be easily dissolved in water, mainly presents in the upper part of the Earth′s crust, particularly in seawater, marine sediment and rocks replaced by seawater. The boron isotopic compositions ( δ 11 B) may vary sequentially, showing as brine (>40‰)> seawater (39.5‰)> marine boron minerals (18.2‰～31.73‰)> marine sediment (13.9‰～25.2‰)> rocks replaced by seawater (4.51‰～10.85‰). Boron content and boron isotopic composition in continental water and sediment may change greatly, but δ 11 B of isotopic composition is mainly <0. In the transitional belt between marine facies and continental facies, the abundance of boron content and isotopic composition vary also transitionally. (2) Owing to 11 B being more reactive than 10 B in geological process, boron isotopic fraction occurs during water rock reaction. During silicification, boron, i.e. 11 B is firstly released from rock into water and δ 11 B of rock drops. During desilicification, 11 B is firstly absorbed from water into rock. In confining reaction system, a little boron is released from rock, and water solution may get a lot of boron, i.e. 11 B firstly. In the open reaction system, a lot of boron is released from rock into water, and δ 11 B of rock is dropped. From basalt to cold seawater in the base of sea, δ 11 B increases from -2.95‰ to 39.5‰ owing to water rock reaction. (3) During dehydrating reaction, a lot of boron is released from rock into fluid. Boron content varies from high to low along with the change of metamorphic grade from low to high. (4) Boron isotopic composition of tourmalines, which may be used as a criterion for distinguishing ore source and mineralization stage, is determined and utilized to compare with the boron isotopic composition of known environment. The geochemical characteristics of boron and its isotope may be used to distinguish sediment environment, nature of water rock reaction and character of metamorphism, and to study the genesis of mineral deposits and origin of metallogenic element.