古钾盐中的水不溶物及其对化学沉积分异的制约

The marine potash deposits on Khorat Plateau are good carriers to study the evolution of ancient seawater and the ore-forming process. The Vientiane Basin of Laos is a part of Khorat Plateau and a set of abnormal chemical sedimentary rocks was deposited in this basin. In this study, the Nongdao mining area which is located in northeast Vientiane Basin was selected as the study area. .As the study objects, some typical cores in this mining area were chosen to carry out systematical works. Through studies of elemental geochemistry characteristics of saline minerals in bearing-potassium layers, the basal evolution information of ancient seawater were acquired. By the mineralogical, elemental and isotopic geochemical analyses of insoluble minerals in bearing-potassium seams, the indication of insoluble mineral to palaeohydrological environment was systematically discussed and the hydraulic condition and sedimentary environment of ancient brine during ore-forming were revealed. Comprehensively analyzing above research results, the constraint of insoluble mineral on chemical sedimentation will be concluded during the formation of potash deposits in study area and the genesis of chemical sedimentary differentiation will be discussed. This project will enrich the non-typical marine forming-potash theory and have a good reference for studying the ancient potash deposits in Yunnan of China.

呵叻高原海相钾盐沉积是研究白垩纪古海水演化和成矿作用的良好载体。老挝万象盆地属于呵叻高原的一部分，沉积了一套异常化学沉积岩。本研究以老挝万象盆地东北部的农刀矿区为研究区，以该矿区钻孔中的钾盐矿层为对象开展系统研究工作。通过赋矿层盐类矿物元素地球化学特征研究，获取基本的古卤水演化信息；通过赋矿层中的水不溶矿物的矿物学、元素及同位素地球化学分析，系统探讨水不溶矿物对古水文环境的指示作用，揭示成矿期古卤水的水动力条件和沉积环境；集成分析上述研究成果，揭示研究区钾盐成矿过程中水不溶物对化学沉积的制约作用并探讨化学沉积分异成因。本项目的开展将丰富非典型海相成钾理论，对于我国云南古钾盐的研究也具有借鉴意义。

呵叻高原海相钾盐沉积是研究白垩纪古海水演化和成矿作用的良好载体。以往的研究中主要针对古钾盐的沉积特征及资源分布，对于古钾盐的物质来源、沉积环境及后期改造的响应过程尚不清楚。为此，通过赋矿层盐类矿物元素地球化学特征；赋矿层中的水不溶矿物的矿物学、元素及同位素地球化学分析研究；并结合对比分析、集成分析、系统总结和制约因素研究。结果表明：研究区古钾盐矿床的的物质来源应该主要来自海水。而古钾盐形成的沉积环境可分为5个阶段：钾盐沉积前的石盐时期（卤水浓缩程度很高，较深水体，稳定沉积）—钾盐沉积开始（卤水高度浓缩，水体变浅，陆源水体参与卤水演化，水体具有波动性）—钾盐沉积高峰期（卤水进一步浓缩，水体进一步变浅，水体基本处于稳定期，）—钾盐沉积晚期（卤水逐渐变淡，水体较浅，陆源水体强烈影响，水体环境为浅水，后期有一定的改造）—盐湖强烈萎缩阶段（仍为水下环境，盐湖区局部可能无地表水（干盐湖阶段），晶间卤水浓度依然较高）。