现代内陆盐湖杂卤石沉积成矿流体演化与成矿作用研究

Polyhalite is an important potassium-containing mineral and polyhalite deposits will be a replaceable potash resource for development of potash industry in China. Although there exist voluminously polyhalite deposits in Kunteyi Playa of north Qaidam Basin, the utilization of this mineral has been seriously subject to constraint of the low-level or poor study in this area. Choosing the polyhalite in Dayantan mining area of Kunteyi Playa as the main research object, the study will be carried out with comprehensive methods. Through mienralogical and lithological analyses of drillcore samples, the mineral component of polyhalite deposit and the ocuurence feature of polyhalite will be made sure, and the polyhalites with different origins will be identificated. By studying on primary fluid inclusions in halites, the information of environmental temperature and main components of original ore-forming fluids will be obtained and the natures of main components and their variation rule will be revealed. Through the hydrogeochemical simulation by EQL/EVP and PHREEQC computer program, combining analysis of boron isotope composition of natural waters, the main contributors for formation of ore-forming fluids will be confirmed, the salting-out sequences of various water bodies during evaporation and the evolution of ore-forming fluids will be discussed. Based on those study results mentioned above, the evolution of ore-forming fluids will be deciphered and the intrinsic connection relationship between ore-forming evolution and formation of polyhalite deposits will be systematically elucidated. The execution of this project will enrich the ore-forming theory of polyhalite deposit in inland salt lake and be able to provide the theoretical support for exploiting the polyhalite deposits in study area. At same time, these study results will play a significant reference role when studying the analogous deposits.

杂卤石是一种重要的含钾矿物，杂卤石矿是我国钾盐工业发展的重要接替钾资源。柴达木盆地北部昆特依盐湖中赋存大量杂卤石，但较低的研究水平已经制约了对该矿物的进一步利用。本项目拟在昆特依盐湖大盐滩矿区以杂卤石沉积为对象，利用综合方法开展研究。通过对钻孔岩芯的矿物学和岩相学分析，查明杂卤石矿的矿物组成和杂卤石的赋存特征，区分不同成因的杂卤石；通过原生石盐包裹体研究，揭示原始成盐母液的组分特征及其变化规律；利用EQL/EVP和PHREEQC程序对获取的各类水体水化学数据进行地球化学模拟，结合硼同位素组成分析，确定对成矿流体形成有重要贡献的水体，讨论水体蒸发过程中的析盐序列及成矿流体的演化过程。在上述研究的基础上，系统阐释研究区成矿流体演化过程及其与杂卤石形成之间的内在联系。本项目的实施将丰富内陆盐湖杂卤石成矿理论，为该地区杂卤石矿的开发提供理论支持，对类似矿床的研究也具有借鉴意义。

钾盐是我国紧缺的大宗矿产。然而，一方面我国找钾工作至今仍没有重大进展，另外一方面现代盐湖钾资源因过度开发也渐趋枯竭。充分研究和利用尚未开发的续接钾盐矿床对于保障我国钾肥工业可持续发展和我国农业安全具有重要战略意义。昆特依盐湖是柴达木盆地杂卤石资源最为丰富的盐湖，但较低的研究水平制约了该资源的开发利用。本项目以该昆特依盐湖杂卤石矿床为主要研究对象开展系统研究，最终为该矿床的开发利用提供科技支撑依据。详细的沉积学和矿物学分析表明，杂卤石赋存形式可分为碎屑层杂卤石和石盐层杂卤石两种，两种类型交替出现，具有旋回特征。EQL/EVP水文地球化学模拟显示，地表水或深部油田卤水独自演化都难以解释当前杂卤石的产出形式；在盐湖卤水浓缩到一定程度后，深部富钙油田水与之混合掺杂才能形成杂卤石高度富集层位。石盐流体包裹体均一温度结果显示，最大均一温度范围为17.1-35.5℃，平均值为22.1℃，表明成盐卤水温度较低；氯同位素组成分析表明，数值整体逐渐偏负，代表了气候环境日趋变干和卤水逐渐浓缩的趋势。石盐流体包裹体成分分析表明，化学组分自下而上逐渐升高，也指示了卤水逐渐浓缩的过程；主要化学组分与杂卤石含量对比显示，石盐层杂卤石的形成不需要额外的钙源，而碎屑层杂卤石的形成在需要外源钙的补给。昆特依盐湖卤水观测和分析表明，卤水水化学组成与储集层的渗透性及卤水温度具有明显的相关性，该研究对固-液转化机理的深刻认识具有重要作用。杂卤石静态和动态溶浸实验表明，选用含5% MgCl2的饱和NaCl溶液作为溶浸剂，可以在对储层结构较小破坏的情况下实现最大程度溶钾的效果。综合上述研究结果，构建了构造活动脉冲式驱动深部卤水与盐湖浓缩卤水混合掺杂的杂卤石形成新模式。该模式的提出，是对现代盐湖杂卤石成矿理论的一个发展，具有重要科学意义。此外，对储卤层性质与卤水组成关系的研究以及杂卤石溶浸实验，对于杂卤石资源的开发利用具有实际价值。