柴达木盆地盐湖钾锂硼分布规律及成矿化学研究

Salt lakes in the Qaidam Basin reserve nearly 80% of brine lithium found in China, and provide about 67% of total annual K-fertilizer production of the country. Qarhan salt lake holds the largest potassic brine deposits in China, which was relatively well investigated over the past 60 years. However, lacking of the in-depth understanding of constraints on the distribution of K, Li and B in the salt-lake ore deposits led to the loss of large amounts of lithium resource via improper disposal of after-K-production brines rich in Li from Bieletan and unsustainable consumption of K-bearing brines for K-fertilizer production. In addition, improved knowledge on physical chemistry of the ore-forming brines is required because of the desperate need of effectively extracting potassium from poor-grade solid-phase deposits containing K as low as 0.5% in KCl. The proposed project sets to investigate the mineral assemblages and permeability of the evaporite deposits for inverse modelling of the brine chemistry useful for finding out the composition of the mixed brine suitable for lixiviation of low-grade potassium ore deposit. Investigation of monthly runoff and chemical composition of H-N river waters, as well as Li concentration is used to find the relationship with variations in water level and chemical composition of the saline lake brines, which help to better understand the water cycle of the watershed and best management of the water resource to keep an ordered potassic-salt production. A survey of the underground brine level and K composition will be carried out for assessing the present reserve of the K-brine deposits of the Bieletan. Most importantly, a field investigation is set to test the sufficiency of the potassium lixiviation from low-grade K-ore deposits using the brines stored in Senie. This will help to evaluate whether the maximum amounts of K-bearing brines produced in this way is enough to meet the need of annual K-fertilizer production of 3000 thousand tonnes. Another aim of the project is to investigate the constraints on the distribution of solid boron ore deposit in the Da Qaidam salt lake, which may provide important implication for finding new sites of the boron deposit.

我国已查明卤水锂资源总量的80%左右和将近67%的钾肥年生产量源自柴达木盆地盐湖。钾、锂规模化开采后含钾卤水快速耗竭、早期锂资源量丢失等问题，以及高效溶采低品位固相钾矿的迫切需求，凸显矿床地球化学特征和成矿化学的认知亟待加深。研究高质量蒸发盐地层盐类矿物组合及孔隙特征，反演盐湖水化学及其演化特征，为选择天然混合卤水溶采剂最佳配方提供基础依据。开展洪－那水系河流及其4个终端盐湖以及关联地下卤水水位和水化学的月变化规律调查，建模研究水系出山流量与东台、西台、一里坪盐湖水面积变化及其与表卤和地下卤水化学特征变化的关联，摸清流域水循环特征和规律，为合理调配水资源和盐田生产服务。开展别勒滩地下卤水水位和钾含量，估算钾锂资源的现存量。开展涩聂湖混和溶采剂渗透实验摸清别勒滩最大产钾出卤量。探究大柴旦盐湖硼的分布规律，丰富硼酸盐成矿理论，指导盐湖富硼矿体的找寻。

我国已查明卤水锂资源总量的80%和近67%的钾肥年生产总量源自柴达木盆地盐湖。近十年大规模抽卤生产钾肥的开发实践造成含钾卤水快速耗竭、锂资源丢失，凸显对矿床特征和成矿地球化学的认知亟待加深。本项目对察尔汗干盐湖地下卤矿水位埋深、水化学参数进行了跟踪取样和检测，获得了评估锂、钾卤水资源现存量的关键数据。结果显示，别勒滩锂矿资源量流失近半。摸清了柴达木盆地沉积系统成盐成矿机制：晚晚更新世以来区域气温升高造成高山区降水增加及入湖水量增多以及盐湖区蒸发加剧，是石盐为主含钾矿物蒸发盐地层形成的基本必要条件；山区降水量增加还改变了火山岩浆岩区水热循环，引发大量含锂硼热水输入盐湖、蒸发形成我国最大的卤水锂矿床。研究查明了察尔汗转变成干盐滩后地下卤水继续富集钾锂的作用过程以及钾矿物组合分区的制约因素。提出了既能保护锂矿资源又能可持续开采卤水钾矿资源还能自然溶采S4主矿层中分散钾矿物三方面兼顾和并举的工程措施和现场实验方案。根据大柴旦湖底盐类地层岩性、沉积构造、矿物组合特征，得出柱硼镁石矿体的成矿化学条件、其后不同时间尺度上湖水化学动态变化特征。摸清了不同地带形成的各类硼矿体成矿过程和成因联系，可用于指导湖滨地带富集硼矿物现场实验。柴达木盆地盐湖沉积系统及其钾锂硼矿床在全球独具特色，本项目从区域地质背景、水热循环与深大活动断裂、新生代火山喷发岩、地形地貌效应、水文气候变化等诸多方面深入解析，厘清了它们与盐湖钾锂硼矿床的成因关联，建立的成矿模型丰富和发展了盐类矿床成因理论。