柴达木盆地大柴旦硼矿床地质特征及成矿机理  

Geological Characteristics and Minerogenetic Mechanism of the Borate Deposit of Da Qaidam Salt Lake in Qaidam Basin

作　　者：高春亮[1] 余俊清[1] 闵秀云[1] 成艾颖[1] 何先虎 辛首臻 洪荣昌[1,3] 刘永 张丽莎[1] 

机构地区：[1]中国科学院青海盐湖研究所,西宁810008 [2]青海省能源局,西宁810008 [3]中国科学院大学,北京100049 [4]中化地质矿山总局浙江地质勘查院,杭州310002

出　　处：《地质学报》2015年第3期659-670,共12页Acta Geologica Sinica

基　　金：国家自然科学基金-青海联合基金(编号U1407206);国家自然科学基金面上项目(编号41171171));中国科学院青海盐湖研究所青年引导基金项目;中国科学院"西部之光"西部博士资助项目自主的成果

摘　　要：大柴旦盐湖因蕴藏固体和液体硼矿资源成为柴达木盆地诸多盐湖中最早被关注和开发的盐湖之一。不仅如此,大柴旦盐湖还沉积有全球少有分布的特色柱硼镁石矿床。此种特色硼矿床的成矿环境和形成机理目前尚未得到应有的关注和研究。本研究基于大柴旦盐湖因开采硼矿而揭露出来的湖中高分辨率的天然沉积剖面DCD-2和DCD03,利用岩性地层学、沉积学、矿物学、地球化学以及AMS 14 C年代学等多指标研究方法,深入探讨了更具特色的湖底柱硼镁石矿层以及其他硼矿层的成矿环境和成矿机理,丰富和完善了盐湖硼矿床成因理论。研究结果显示,大柴旦湖底柱硼镁石矿层（第一硼矿层）形成年代始于BC 1790a左右。湖底柱硼镁石含量为35%,B2O3含量约为3%~16%,属于中低品位硼矿层;而湖滨钠硼解石和水方硼石含量分别为82%和35%,B2O3平均含量约为3%~9%,属于低品位硼矿层。硼矿形成前的较长时期内,大柴旦盐湖是以碎屑沉积为主的非盐湖相沉积环境,此后快速进入硫酸盐型盐湖阶段和湖底柱硼镁石矿层形成阶段。湖底柱硼镁石以及湖滨钠硼解石和水方硼石是在特定水文地球化学条件和湖泊环境下形成,在湖区的不同地带,由于不同的成矿作用和成矿机理形成了不同的硼酸盐矿物或硼矿床。大柴旦盐湖硼酸盐矿床的形成受控于硼自身内在地球化学特性及其外在控制条件,是内外条件耦合的结果。在固体硼酸盐整个形成过程中,盐湖卤水都呈现弱碱性—碱性,这是盐湖硼酸盐沉积形成的先决条件。文章提出了盐湖固体硼酸盐的具体形成机理并确定大柴旦盐湖硼矿床为高山-深盆-浅水成矿模式。Da Qaidam Salt Lake,northern Qaidam Basin,is known for its liquid and solid boron resource.More than that,pinnoite bearing sediments,occurring in this lake,are rare in the world.However,little attention has been paid to the ore-forming environment and minerogenetic mechanism of this special borate deposit.The study analyzes high resolution subbottom sediment profile DCD-2and DCD03 from Da Qaidam Salt Lake,through multi-index methods including lithostratigraphy,sedimentology,mineralogy,geochemistry and radiocarbon chronology,which aims to demonstrate the minerogenetic mechanism of pinnoite and other borate mineral deposits,and to provide contribution to the ore-forming theory of borate deposits in salt lake systems.The results show that subbottom pinnoite deposition commenced from 1790 a BC with the content is 35 percent,and the content of boron oxide is approximately 3percent to 16 percent which belongs to middle and low grade borate deposit.The content of ulexite and hydroboracite in lakeside is 82 percent and 35 percent respectively,and the content of boron oxide is approximately 3percent to 9percent which belongs to low grade borate deposit.The results indicate that Da Qaidam was not a salt lake before the pinnoite formed,and that the salinity and calcite began to increase with occurrence of gypsum,which represent a rapid transition into a sulfate type salt lake.The pinnoite deposit was formed in a salt lake environment.Pinnoite in subbottom as well as ulexite and hydroboracite in lakeside formed in the lake environment with specific hydrogeochemical conditions,and a set of borate mineral deposits finally formed due to different mineralizations and minerogenetic mechanisms in different zones.The forming of borate deposit was controlled by the inherent geochemical characteristics of boron and the external conditions,which is a coupling mechanism.The salt lake brine is weak alkaline to alkaline in the whole forming process of borate deposit.At last,we propose the specific minerogenetic mechanism of borate deposi

关 键 词：柴达木盆地 大柴旦盐湖 硼酸盐矿床 柱硼镁石 地质特征 成矿机理 

分 类 号：P619.2[天文地球—矿床学]