柴达木盆地大风山天青石矿床中低温流体成矿机理研究

As China's largest reserves of celestine deposits, Dafengshan celestine deposits in Qaidam basin are affected by both inland lake evaporation and hydrothermal fluid alteration. And it is also a good platform for Mid-Low temperature fluid mineralization research. The program will analyze some evaporite samples which collected from Dafengshan celestine deposits. Based on the C、O isotopic compositions for carbonate components of calc-mudstone and carbonate samples, Fluid inclusion analysis for vein-minerals such as quartz, calcite, celestine, Sr isotopic compositions for clastic sequences、sulphate samples and the surrounding water samples, S isotopic compositions for sulphate samples and the surrounding water samples, microphenomenon analysis of ore slides and Ca、Sr、Ba、Br and Cl values of the samples, as well as the micro-zone and in situ geochemical analysis on different phases of minerals caused by ore-forming fluid alteration. We try to obtain the following aims:(1) revealing the fluid source and its evolvement characteristics of the study area. (2)exploring the fluid transformation process of the evaporite sequcece and the ore belt. (3)identifying the regularities and differences of the fluid transformation in the several different evaporite sequences.(4)predicting the distribution and enrichment trend of strontium ore in the study area. The program will help to understand the ore-forming mechanisms of the large Sr-metallogenic belt of northwest area in Qaidam basin, and it could also contribute to the complement of ore-forming models of large celestine deposits.

柴达木盆地大风山天青石矿床是我国目前已知储量最大的内陆湖泊蒸发作用与热卤水成矿改造叠加的大型锶矿床，是研究中低温流体成矿作用的良好载体。本项目拟对大风山天青石矿床的蒸发岩样品进行矿物学与地球化学的分析，通过钙质泥岩中碳酸盐成分及碳酸盐岩C、O同位素；碳酸盐、石膏、天青石中的石英、方解石、天青石等脉体矿物的包裹体分析；碎屑岩、石膏、天青石及周边水样的Sr同位素及硫酸盐样品与周边水样的S同位素分析，结合岩矿样品的镜下鉴定特征与Ca、Sr、Ba、Br、Cl等元素的含量变化规律以及因流体改造作用导致的不同矿物相间的微区原位元素地球化学分析，揭示研究区内流体来源及其卤水演化特征，探讨蒸发岩层序与赋矿层位的后期流体改造作用过程，查明不同蒸发岩序列流体改造作用的规律性与差异性，进而对锶矿在区内的分布规律与富集趋势进行预测。本项目的进行将丰富对柴西北地区大型锶成矿带成矿机制的认识，完善锶矿的成矿理论模式。

柴达木盆地大风山地区发育有我国最大的内陆湖相沉积型天青石矿床，是进行中低温流体成矿作用研究的良好载体。以往的研究中针对矿区Sr的来源、高Sr/Ba比流体的形成及成矿元素迁移分布规律等方面的认识相对缺乏，而这对于内陆盆地大型锶矿的形成机理具有重要的理论意义。本项目对采自大风山矿区的6个地层剖面样品和矿区范围内及附近的油田水样品进行了沉积学、矿物学与地球化学方面的研究，揭示了成矿物质来源，阐明了成矿流体的形成与演化过程及成矿期和成矿后流体及后期构造作用对原生蒸发岩序列的影响和改造作用。研究表明，大风山天青石矿的Sr源应主要来自周围山系的风化剥蚀，而锶同位素证据表明油田卤水与天青石矿物的形成也存在一定的成因联系；研究区成矿期频繁的干湿波动促使原生天青石矿层品位的逐渐提高，而后期的区域构造作用则导致了高品位次生天青石矿的形成；成矿流体的高Sr/Ba特性是基于两种硫酸盐矿物显著的溶解度差异形成的，在稳定的蒸发环境下硫酸钡矿物先期伴随着粘土等碎屑物混杂沉积在矿层底部，导致了高Sr/Ba比成矿流体的形成。