Geological-geochemical Characteristics And Ore-bearing Potential Of Granites In The Jiajika Mining Area,Sichuan

With the rise of global development upsurge of lithium ore,the Jiajika rare metal deposit in Sichuan become a popular star of the domestic lithium deposits.It is the largest spodumene deposit in China and a research hotspot in lithium deposits of hard-rock type,which has attracted much attention from the academic circles.Most of the former studies have regarded the Jiajika deposit as an ideal pegmatite type object.However,geological exploration in recent years pointed out that the fine-grained crystalline rock is also an important prospecting target.The Jiajika deposit is not suitable as a typical pegmatite type,and its ideas for next prospecting work need to be further deepened and explored.Therefore,this thesis starts from the perspective of petrology,takes the contemporary metallogenic theory as a guide,and combines the previous data to explore the geological background,petrological characteristics and lithogeochemical characteristics of the Jiajika deposit.The main understandings and conclusions are as follows:1.The lithology of the Majingzi granite mass in the Jiajika mining area is mainly fine grained tourmaline-bearing two-mica monzonitic granite,which can be partially transformed into moyite or granodiorite.The mineral assemblages of the Majingzi granite mass are different from that of the granite veins.The former generally contains tourmaline,the plagioclases which are oligoclase and albite?An=8-18?,and the microclines which are richer in potassium?Or=94?,there are biotite and relatively rich magnesium muscovite;the latter contains plagioclase which is albite?An<2?,only muscovite,and the lithology is mostly albite granite?plagioclase granite?.2.The veins the Jiajika mining area are not completely composed of pegmatite veins,collectively referred to as granitic veins.According to the rock structure,mineral assemblage and mineralization characteristics,it can be divided into 7 rock types:?muscovite?microcline pegmatite,muscovite granitic pegmatite,muscovite albite spodumene pegmatite,fine-grained?inequigranular?muscovite spodumene granite,fine-grained?inequigranular?Be industrial mineralized muscovite granite,fine-grained?inequigranular?Nb-Ta industrial mineralized muscovite granite,fine-grained?inequigranular?muscovite granite.3.There is almost no distribution of lepidolite in the granitic veins of the Jiajika mining area,and the zoning of rock types is not obvious.There are differences in the intrusion time,the content of rare earth elements and Rb,Ta,and the indicator of genesis study of lithium isotope between the Majingzi granite mass and the granite veins which are not the same set of rocks.4.The granitic rocks in the Jiajika mining area belong to calc-alkali series.Compared with the granitic veins,the Majingzi granite mass has higher CaO,MgO,TiO₂,P₂O₅,total rare earth,and lower Rb/Ba.Li mineralized granitic veins are characterized by low Na;Be or Nb-Ta mineralized granitic veins are characterized by high Na;Rb mineralized veins are characterized by high K and medium Na.The better the mineralization,the smaller the K/Rb ratio in rocks.5.The mineralized rare metal elements in the Jiajika mining area are mainly Li,Rb,Be,Nb,Ta and so on.Because the fine-grained spodumene in fine-grained granitic rocks is characterized by uniform distribution and stable content,Li mineralization is relatively good.And the fine-grained spodumene is crystallized under conditions in which the concentration of lithium in the magma is saturated and the volatile components in the magma are relatively small.6.The study proposes that the Jiajika deposit is a granite vein type rare metal deposit associated with the Triassic granite dome,which is a crystalline product of a rare metal-rich granitic magma when the volatile components are dispersed.