硼同位素对鞍本地区富铁矿成因的制约

The genesis of the high-grade magnetite ores related to banded iron formations (BIFs) in the Anshan-Benxi area, Liaoning Province in China, have long been widely debated. The newest findings indicated that the metallogenesis of the high-grade iron deposit in this area is associated with the intrusion of non orogenic-magmatic intrusion which caused by crustal uplift after the ancient Proterozoic orogenic movement in Liaodong area (1.85Ga). The ore-forming hydrothermal fluid is evolved from meteoric water, which leached the ore-forming material of evaporites in Liaohe Group. This new understanding is of great significance，but still need to be verified by further research. Evaporation salt of Liaohe Group has special boron isotopic composition, meanwhile a large number of tourmaline crystallized in the altered wallrocks of high-grade iron ore, which has great significance for revealing the origin of ore fluids. In our study, we will use LA-MC-ICP-MS system to analyze B isotopic composition of tourmaline in the altered wallrocks.The B isotope characteristics, combained with the age of high-grade iron ore, geochemical compositions (major, trace and rare earth elements) and isotopic compositions (C, O, S) of high-grade iron ore, the lean iron ore and the altered wallrocks, will rebuild the composition and properties of the ore-forming fluids, With these, the metallogenic conditions and forming mechanism of the high-grade iron deposit in the Anshan-Benxi area will be revealed.

辽宁鞍本地区大型磁铁富矿的成因长期以来存在争论，最新研究结果表明鞍本地区富铁矿的成矿作用与辽东地区古元古代造山运动结束后（1.85Ga）地壳抬升引发的非造山岩浆侵入和热液活动有关，成矿热液由大气降水演化形成，成矿热液淋滤了辽河群蒸发盐地层中的成矿物质。这一新认识具有重要意义，但尚需通过进一步深入研究证实。辽河群蒸发盐具有独特的硼同位素组成，富铁矿蚀变围岩中发育有大量电气石，其B同位素组成对揭示富矿成矿热液来源具有重要指示意义。本项目拟以富铁矿蚀变围岩中的电气石为研究对象，采用LA-MC-ICP-MS硼同位素分析技术开展B同位素地球化学研究，并结合鞍本地区富铁矿的形成时代和富铁矿、贫铁矿、蚀变围岩的主微量、稀土元素、C、S、O等同位素特征，恢复重建成矿流体的成分和性质，揭示鞍本地区富铁矿的成矿条件和形成机制。