盐湖硼酸盐沉积对于辽东硼矿床形成的指示意义

辽东古元古代变质硼矿床是我国最重要的硼矿资源,然而由于该区物质组成多样,构造演化复杂的特点,导致对于硼矿的物质来源、构造环境及成矿过程的认识存在很大差异。目前多数学者认为辽东硼矿床经历了早期的盐湖硼酸盐沉积阶段及晚期构造热事件引起的变质作用阶段。当前的研究认为古元古代辽东地区处于活动大陆边缘,且发育大量的钙碱性岩浆活动,这与第三纪以来的大型硼酸盐沉积矿床形成的构造环境及岩浆活动相似。结合现代盐湖体系下的硼酸盐沉淀物理化学条件讨论辽东地区古元古代沉积硼酸盐特征,根据硼同位素组成探讨物质来源及构造环境,发现辽东地区的硼矿床存在钠硼解石、硬硼钙石两种硼酸盐的沉积,硼同位素组成显示其硼源应来源于俯冲板块下蛇纹石及海相沉积物的脱水作用释放的硼,这种硼随钙碱性岩浆活动及热液活动在局限海盆中蒸发形成含水硼酸盐。

Indicative Significance of Salt Lake Borate Deposits for the Formation of Boron Deposits in Eastern Liaoning Province

The boron deposits in Liaoning province are the most important boron resources in China.Because of the late metamorphism,there are cognitive differences in the sources of metallogenic materials,tectonic evolution and mineralization process.Most scholars believe that the boron deposits in eastern Liaoning have undergone the salt lake borate deposition in early stage and the metamorphism stage caused by late tectonic thermal events.Current studies suggest that the Paleoproterozoic Liaodong area was located on the active continental margin,and experienced a large number of calc-alkaline magmatic activities.This tectonic environment and magmatic activities are consistent with the large borate deposits since the Tertiary.Based on the physical and chemical conditions of borate precipitation in modern salt lake system,the characteristics of Paleoproterozoic sedimentary borate in eastern Liaoning Province are discussed,and the material source and tectonic environment are also discussed according to the boron isotopes.It is found that there are two kinds of borate minerals in eastern Liaoning.The boron isotope composition shows that the boron was originated from the dehydration of serpentine and marine sediments under subduction plate,and converged to restricted basin with calc-alkaline magmatic and hydrothermal activities to evaporate into water-bearing borates.