珠峰地区热曲锂辉石伟晶岩的发现及对喜马拉雅稀有金属成矿作用研究的启示

Discovery of spodumene-bearing pegmatites from Ra Chu in the Mount Qomolangma region and its implications for studying rare-metal mineralization in the Himalayan orogen

目前研究已经显示,喜马拉雅淡色花岗岩具有良好的铍-铌钽-锂等稀有金属成矿潜力。其中珠穆朗玛峰(后文简称珠峰)西侧的普士拉一带,是喜马拉雅地区锂辉石伟晶岩集中的区域。本文报道在普士拉东北的珠峰北侧热曲地区,发现有含锂辉石伟晶岩脉,这些伟晶岩呈透镜体状集中赋存于肉切村群“黄带层”大理岩与北坳组钙质硅酸岩的接触界线部位,同围岩一起经历了强烈的变形,且未出现明显内部分带结构,矿物组成中包含锂辉石、透锂长石、绿柱石、铌钽铁矿、锡石等锂-铍-铌钽-锡稀有金属矿物,其Li_(2)O含量达1.30%~2.15%,显示经历过高程度分异演化的岩浆结晶特征。热曲含锂辉石伟晶岩的发现表明珠峰地区具有锂成矿的良好前景,是未来锂矿产勘查的重点靶区,而藏南拆离系韧性剪切带中的肉切村群“黄带层”下部与北坳组顶部位置,是锂辉石伟晶岩的重要富集层位,值得今后在锂资源寻找过程中予以充分关注。

Present studies have revealed the leucogranites from Himalayan orogen are vital potential for Be-Nb-Ta-Li rare-metal mineralization,and spodumene-bearing pegmatites dominantly concentrated in the Pusi La of the Mount Qomolangma region.In this study,the first spodumene-bearing pegmatite is discovered in the Ra Chu transect,north of the Pusi La.The foliated pegmatites present as lenses concordant with the prominent mylonitic fabric and mainly concentrated in the contact boundary between the calc-silicate of the North Col Formation and the marble in the“Yellow Band”of the Rouqiecun Group.Internal zonation is not observed from the pegmatites.The mineral assemblages of the pegmatite contain Li-Be-Nb(Ta)-Sn minerals including spodumene,petalite,beryl,columbite and cassiterite.Li_(2)O concentrations of the pegmatite samples from the transect are 1.30%~2.15%.Mineralogy and geochemistry results suggest the pegmatites have experienced a high degree of crystal fractionation,which indicates that there is a sufficient prospect for lithium mineralization in the Mount Qomolangma region.The bottom of the“Yellow Band”and top of the North Col Formation corresponding to the high-strain shear zone of the South Tibetan Detachment System is probably the enrichment layer of spodumene-bearing pegmatites and it is an important target zone for lithium mineral exploration in the future.