湖北江陵凹陷古近系富钾卤水物质来源研究-锂同位素约束

Potash salt is one of strategic mineral sources which are in great shortage in China. Making a domestic breakthrough in potash exploration is a primary way to relieve the pressure that most potash resources have been importing for a long time. Jiangling Depression, lies on the west of the Jianghan Basin, was discovered high temperature and high pressure brines which contain K, Li, Rb, and Cs exceed economic grade. The potassium-rich brines have long been received less attention, and thus the source of solutes in the bines, e.g. K, Li, was uncertain. Previous study speculated that volcanism mainly account for the sources. This research mainly focus on the brines newly discovered in well GJ1, oilfield water, thermal springs, country rocks (volcanic rocks, sandstones and mudstones) and salt rocks in drilling cores. High precise measurements will be applied to multidisciplinary research mainly composed of Li isotope geochemistry,aiming to reveal the relationship between high concentration of Li in the potassium-rich brines and thermal springs, and trace the contribution of volcanism source to concentration of Li in the brines, which provides scientific basis to trace the sources of Li and accompanying elements in the brines. The results are not only significant to potash exploration in Jiangling Depression, but also of importance to understand the potash-forming conditions, and potash resource prospects of rift basins in Eastern China.

钾盐是我国紧缺的战略性矿产资源，取得国内找钾突破是缓解我国钾盐资源主要长期依赖进口的首要途径。江汉盆地西侧江陵凹陷内的高温高压卤水，富含钾、锂、铷、铯等超过综合利用品位的元素，长期以来其成因一直未查清，对卤水中钾、锂等物质的来源还没有取得可靠认识，前人推测物质来源主要与火山活动有关。本研究以新钻探的江陵凹陷岗钾一井富钾卤水和地层水、热泉水，以及围岩（火山岩、砂岩和泥岩）和盐岩岩心为研究对象，运用高精度的现代测试分析手段，开展以锂同位素地球化学为主要手段的多学科研究，揭示富钾卤水中锂元素富集与温热泉水的关系，探讨火山活动对富钾卤水中锂富集的贡献，进而为约束江陵凹陷富钾卤水锂及伴生元素的物质来源提供科学依据。研究成果不仅对江陵凹陷富钾卤水找矿调查具有重要的实际意义，而且对于中国东部裂谷盆地成钾条件、找钾前景具有重要的科学意义。

江陵凹陷内的高温高压卤水，富含钾、锂、铷、铯等超过综合利用品位的元素，长期以来其成因一直未查清，对卤水中钾、锂等物质的来源还没有取得可靠认识。本次研究开展了三方面的研究工作，一是通过多口钻井岩心编录，沉积学和地球化学分析，系统厘定了古新世以来的盐湖演化，表明从沙市组到新沟嘴组沉积时期，盐湖逐渐消亡；二是开展了火山岩地球化学和氩-氩年代学工作，结果表明八岭山玄武岩年龄在53.19~60.78Ma之间，是岩石圈地幔的部分熔融结果，为高温高压卤水与玄武岩间的相互作用提供了约束；三是开展了富钾卤水的元素地球化学以及硼，锶和锂多同位素综合分析，结果表明水-岩反应使得卤水的硼和锂同位素组成增大，富钾卤水中富集的硼和锂系高温热液与玄武岩的水-岩反应导致玄武岩淋滤的结果。因此综合分析，我们推断江陵凹陷富钾卤水是沙市组沉积时期，由于玄武岩岩浆的大量上涌、喷发途中与热流体发生高温下的水-岩作用，使得热流体富集钾、锂和硼等元素，同时随着同沉积期的断裂到地表盐湖或直接水下喷发，经强烈蒸发浓缩而成。该成果基本解决了富钾卤水的成因，对该区进一步的富钾卤水勘查工作具有非常重要的指导意义。