Metallogenic Mechanism Of Zhawulong Granitic Pegmatite-type Lithium Deposit In Western Sichuan

Zhawulong rare metal deposit is located in Songpan-Ganzi orogenic belt.It belongs to the granite pegmatite type spodumene deposit,accompanied by beryllium and niobium-tantalum deposits.It is a comprehensive large-scale rare metal deposit dominated by lithium and an ideal target for studying the Granite-pegmatite type rare metal deposit.On the basis of field geological observation,the main and trace elements,zircon U-Pb dating,niobium-tantalum U-Pb dating,Sr-Nd-Hf isotope analysis of granite,pegmatite dike and wall rocks have been carried out,and the genetic relationship among muscovite granite,No.14 pegmatite dike and Triassic Xikang Group in mining area have been systematically studied.This paper mainly obtains the following understandings:Spatially,the pegmatite dikes are mainly distributed in the internal and external contact zones of the Zawulong rock pluton,and the distance between different types of pegmatite dikes and the parent rock pluton is approximately zonal distribution.No.14 pegmatite dike can be divided into mica quartz belt,plagioclase belt,albite spodumene belt and quartz spodumene belt from the edge to the core.No.14 pegmatite dike is a peraluminous rock,which is rich in silicon,aluminium and potassium.From the edge to the core zone,the content of aluminum saturation index and rare metals such as Li,Rb and Cs gradually increased,while the content of total alkali(Na2O+K2O),CaO,MgO and Sr,Ba,Zr,Hf,etc.generally become lower,the ratios of K/Rb,Zr/Hf and Nb/Ta also decrease.The above characteristics reflect the characteristics of continuous differentiation of pegmatite.From granite to pegmatite,the ratios of K/Rb,Zr/Hf and Nb/Ta decreased significantly,while the contents of rare metals such as Li,Be,Rb and Cs and volatile F increased significantly;Zircon U-Pb age of Zawulong muscovite granite is 212 Ma,and Nb-Ta U-Pb age of No.14 pegmatite dikes is 205 Ma.The above characteristics reflect the Zhawulong muscovite granite and pegmatite dikes are products of different stages of homogeneous magmatic differentiation and evolution,and the muscovite granite is the ore-forming parent rock of Zhawulong deposit.Zhawulong muscovite granite belongs to high potassium calc-alkaline strong peraluminous granite with Sr-Nd-Hf isotopic composition close to the crust.The rock has a high Rb/Sr and a high Rb/Ba and a low CaO/Na2O.The above geochemical compositions are similar to the surrounding rocks in the mining area,indicating that they originated from the dehydration and melting of deep metamorphic argillaceous rocks.Many LCT pegmatites occur in meta-argillaceous rocks in the world.Orogenic movement leads to deep remelting of meta-argillaceous rocks,and the differentiation and evolution of magma are the fundamental reasons for the formation of such deposits.In short,the Zawulong rare metal deposit was formed in the residual melt of crystallization differentiation of muscovite granite magma.The ore-forming magma is formed in the orogenic process of the Songpan-Ganzi area,after the closure of the Paleo-Tethys Ocean,and The ore-forming source rocks are the sedimentary rocks of the Triassic Xikang Group.During orogenesis,the deep flysch deposits are partially melted due to the dehydration reaction of water-bearing minerals such as biotite,which results in the enrichment of rare metal elements in melted granite magma.After granite magma is emplaced at a certain depth,rare metal pegmatite melts are separated,and large-scale rare metal mineralization takes place.