Li Isotopic Composition and Its Constrains on Rare Metal Mineralization of Jiajika Two-Mica Granite,Sichuan Province

Hou Jianglong; Li Jiankang; Zhang Yujie; Li Chao

Abstract：Jiajika superlarge hard rock type lithium deposit is one of the most abundant lithium mineral resouces in China.The two-mica granite outcropped in the southern Jiajika orefield is generally regarded as source rocks of the ore-bearing pegmatites. Li isotopic composition is a useful tool to explore the origin and evolution of rare metal.Based on the detailed field work,the lithium isotopic composition of granite was tested by MC-ICP-MS in this study.The results show that the lithium content of the granite is from 192×10—6to 470×10—6,and the mean value is 309×10—6;the value ofδ7Li ranges from —1.56‰ to 0.90‰, and the mean value is —0.24‰,which is closed to the average value of upper crust.Jiajika two-mica granite apparently has higher content of lithium and lower value ofδ7Li,and theδ7Li and Li,Rb,Ga,SiO2andεNd(t)have no obvious correlation. Lithium isotopic composition of granite reflects its characteristics of source rock,and it has not been influenced by crystalliza-tion differentiation of magma and alteration.The geochemical and isotope geochemistry data indicate that the source of magma is mainly composed of partial melting of Triassic Xikang sand-mudstone,which may have been mixed with materials from deep source.In addition,variations of lithium content and Li isotopic composition show that the fluid of magma migrated from cen-ter to the north and south,and the metallogenic fluid of pegmatite is derived from Jiajika two-mica granite.The content of lithi-um and Li isotopic composition can not only be used to classify the types of lithium deposits,but also can facilitate the prospec-ting of rare metals.