Lithium Enrichment Mechanism Of The Lithium Deposit In Jiajika,Sichuan:Zinc Isotope Restriction

Lithium,as a high starting point"green metal","energy metal"and"key metal",is widely used in aerospace and other high-tech and national defense industry,and has extremely important strategic significance for national economic development and national defense security.Hard rock lithium mine has the characteristics of high value of easy mining and comprehensive utilization,is the main type of lithium mine in our country at present,and the key to crack our lithium resource"tight neck"problem.However,the origin of pegmatite,which is the main host rock of lithium deposits,is still controversial,which limits the study of metallogenic theory and prospecting method of hard rock lithium deposits to a certain extent.Therefore,the representative Jiajika pegmatite type lithium deposit is selected as the research object,and zinc isotope analysis is carried out to explore the genetic relationship between two mica granite,ore bearing pegmatite and ore free pegmatite,which will restrict the lithium enrichment mechanism of Jiajika pegmatite deposit and provide theoretical guidance for the ore prospecting of hard rock type lithium deposit.The zinc isotopic compositions of two-mica granites(δ⁶⁶Zn=0.47～0.85‰),Li-rich pegmatites(δ⁶⁶Zn=0.59～1.21‰)and Li-poor pegmatites(δ⁶⁶Zn=0.33～0.99‰)in Jiajika pegmatite type lithium,have obvious heavy zinc isotope characteristics and exceed that of igneous rocks reported so far.The zinc content and isotopic composition of pegmatite are higher than that of two-mica granite with the increase of magmatic evolution,which indicates that pegmatite may be the product of the high differentiation of two-mica granite.Through Rayleigh fractionation simulation of zinc isotopes,it was found that fluid exsolution（15～25%）occurred in the late stage of magma differentiation and evolution,resulting in magma separation into H₂O-rich silicate-poor melt（supercritical fluid）system and H₂O-poor silicate-rich melt system,and then evolved into Li-rich pegmatites and Li-poor pegmatites.Fluid exsolution is a key role in the enrichment of rare metals such as lithium in Li-rich pegmatites.Our results also prove that zinc isotope can be used as a powerful indicator of magmatic hydrothermal evolution.The metallogenic mechanism of methyl carmine lithium deposit can be summarized into three stages:the first enrichment is sedimentary and metamorphic process（metamorphism,deep burial and remelting）,the second enrichment is granitic process（partial melting and separation crystallization）,and the third enrichment is pegmatite process（separation crystallization and fluid dissolution）.