察尔汗盐湖北缘CaCl2卤水成因及与盆地中西部相似卤水物源联系

The deeper parts of most sedimentary basins or ocean ridges are saturated with large volumes of CaCl2 brines. These brines with salinities ranging from 100 to 300 g/L are crucial to form (MgSO4-deficient) potash deposits in the marine, non-marine and rift valley basins in the world. Previous studies indicate that there are beaded CaCl2 brine lakes in western (Jiahu), middle (Niulangzhinv and Balunmahai lakes) and eastern (Qarhan Salt Lake) Qaidam Basin (QB). Qarhan is a typically MgSO4-deficient terrestrial potash-bearing salt lake in the world. However, the origin of CaCl2 brines in the northern margin of Qarhan Salt Lake (QSL) and their hydrological connection among similar brines in western and middle QB are still unclear. No direct evidence from petrography of sediment core and isotopic geochemistry of different waters were reported. In order to improve our understanding on these special brines in this evaporitic basin, micro-morphology of thin section, mineral assemblages and leaching experiment of water-clastic rock based on a sediment core (ISL1) in the QSL carry firstly out for obtaining diagenesis evidence; Secondly, trace and heavy metal elements of CaCl2 brines and fluid inclusions in halite from sediment cores (DL1, XZ1 and NHBX1) are compared each other for obtaining hydrothermal fluid evidence; Thirdly, detailed investigations on elemental and isotopic (Mg, Sr, O, H) compositions of CaCl2 brines among fault zone in western, middle and eastern QB, and leaching results of clastic sediments from outcrops among anticlines in western and middle QB; Finally, we will compare all data (elements, isotopes and other data) and discuss origin of CaCl2 brines in QSL and their hydrological connection among CaCl2 brines in western, middle and eastern QB. This project will offer important data for understanding forming mechanism of potash deposits and exploiting these useful components from QB in the future works.

CaCl2卤水是赋存于洋脊或盆地内高矿化度、富含多种有益组分（钾硼锂锶）或重金属元素特殊卤水，对形成贫MgSO4盐钾盐矿床起到重要作用。以往研究表明，柴达木盆地西部（钾湖）、中部（牛郎织女和巴伦马海）和东部（察尔汗盐湖）串珠状分布CaCl2卤水。察尔汗是世界上最大的陆相成钾盐湖，其北缘CaCl2卤水成因及与盆地中西部卤水物源联系，目前缺乏岩芯岩相特征和不同水体同位素证据。本项目拟以盆地CaCl2卤水和察尔汗岩芯为研究对象，开展岩芯薄片形貌、矿物及水岩溶滤分析，查明成岩作用岩相证据；验证察尔汗北缘CaCl2卤水与石盐包体微量和重金属元素含量关系，判定热液流体证据；揭示盆地西-中-东部CaCl2卤水元素和同位素（镁锶氢氧）及背斜露头碎屑溶滤地球化学特征；多指标对比，探讨察尔汗北缘CaCl2卤水成因及与盆地相似卤水空间物源联系。项目的实施，对盆地有益组分开采与成钾机理认识具有重要理论和现实意义。

CaCl2卤水是一种特殊的水型，已在中国塔里木盆地、柴达木盆地、四川盆地、江汉盆地等多个盆地内发现这种水体。CaCl2卤水的水化学组成很难用地球表层大气降水（河水）与围岩风化、蒸发浓缩来解释，但它对古代大型海相、裂谷和陆相盆地（卤水）钾盐矿床的形成起到至关重要的作用。青海柴达木盆地是一个典型的陆相成盐成钾盆地，盆地内没有古海水残留或补给，CaCl2卤水到底是怎样形成的？通过盆地西部大浪滩盐湖第三系油田卤水（埋深500-1500 m）化学组成和氢氧锶硫硼同位素比值分析，学者们提出CaCl2油田卤水是大气降水沿断裂埋藏的“深循环”水，富含有益组份可能发生白云石化、钠长石化、SO42-的还原作用及深源岩浆流体的参与形成的，断层裂隙提供了卤水储水空间。该卤水是水岩改造成因还是热液流体成因？它对钾盐矿床的形成具有怎样的贡献？另外，总结前人的研究成果，发现柴达木盆地西部昆特依钾湖和大浪滩油田卤水、中部牛郎织女湖和巴伦马海湖、东部察尔汗盐湖东陵湖、协作湖和北霍布逊湖串珠状分布有CaCl2卤水，它们之间是否存在着一定的物源联系？.针对上述科学问题，项目系统总结柴达木盆地CaCl2卤水分布、储层及化学组成；基于2016年察尔汗盐湖千米钻探岩芯样品，开展第四系（中更新世以来）湖相沉积矿物组合、微量元素（锶）含量和锶同位素比值及晶间卤水镁同位素比值，结合上覆盐层和卤水的地球化学特征，对比研究查明察尔汗盐湖北部CaCl2卤水成因；通过盐湖钻探盐层石盐包裹体化学组成、晶间卤水化学组成和重金属元素含量、同位素比值分析，阐明了柴达木盆地西-中-东沿断裂带分布CaCl2卤水的水力联系；采集断裂带周边背斜构造深部卤水样品，完成了深部CaCl2卤水储存时代和成因联系。发表论文12篇，其中SCI论文8篇，EI论文1篇，中文核心论文3篇；申请发明专利5件，其中2件已授权，3件已进入实质性审查阶段；培养学生6名，其中毕业博士和硕士生3名，在读博士和硕士生3名；参加国内国际会议共8次，其中国际会议2次，国内会议6次；邀请专家开展学术报告4次；完成成果鉴定1项，达到国内领先水平。