Geology And Geochemistry Of Doubi Granite-hosted Rare Metal Deposit And Its Metallogenesis In Zhengxiangbai Banner,inner Mogonia

With the rapid economic growth and the continuous emergence of new technologies,the demands of rare metals(Nb,Ta,Zr,Hf,U,Th,REE,Y,Rb,Cs,Li,Be,etc.)as raw materials for some special materials and functional materials have been increased very rapidly,those which are widely used in machinery industry,defense industry,aerospace industry,information industry,etc.Based on the unique position and extremely important strategic value of rare metals in economic construction and development,some countries regard rare metal mineral resources as strategic mineral resources,some countries regard rare metal mineral resources as strategic mineral resources.At present,the prospecting methods of strategic key metal deposits,the supernormal enrichment mechanism of key metals and their speciations,and the cost-effective and green separation technology of the metals have become hot and difficult issues in the geological and mineral exploration sectors.Granite-type rare metal deposits are an important one of rare metal deposits,and they are also the important or potential source of strategic key minerals such as Nb,Ta,Li,Rb,Cs,and REE.The main feature of this type of deposits is that the mineralization of rare and rare earth metals is mostly located in the marginal facies of the late strongly differentiated granite intrusions,or in the late high-differentiated granitic stocks or veins such as granite pegmatites,with obvious alterations such as albiteization and dalimitization,or without alterations such as albiteization and dalimitization in late period.At the same time,granite,granite pegmatite,and altered rocks are themselves also as a part of rare earth mineralization.The boundary of the deposit is mainly delineated by the grade of rare metals.Therefore,to study the metallogenesis of granite-hosted rare metal deposits,their enriched mechanism and speciations has a significance for improving the understanding of granite-type rare metal deposits and their mineralizations,as well as the deployment of regional geological prospecting.The Dubi granite-hosted rare metal deposit is the first rare metal one discovered in Zhengxiangbai Banner,which occurs in a hidden granite stock.Prevous researches were mainly focused on the general geological and geochemical characteristics of the stock,while the metallogenic age of the stock,its mineralization characteristics,the speciations of key rare metals,and the metallogenesis of the deposit have not been extensively involved by others.Based on the given data of geology and petrogeochemistry,the mineralizing age of the Dubi granite stock were determined,the geololical and geochemical characteristics of the Dubi granite-hosted rare metal deposit were studied,then the metallogenesis of the deposit was discussed.Main considerations of the thesis are as follows:(1)Niobium,tantalum,and rare earth mineralization are mainly produced on the edges and tops of concealed granite bodies,while Rb mineralization is distributed throughout the granite bodies.The main minerals containing Nb and Ta are columbite,ferro-niobium rutile,columbium yttrium,tantalite,complex rare gold ore,etc.The rare earth-containing minerals mainly include bastnaite,bastnaesite,bastnasite,fluorite,etc.Minerals containing U and Th are mainly zircon,thorium,uranium ore,etc.The minerals containing Rb and Cs are mainly biotite,streak feldspar,and plagioclase.(2)The average grades of Nb₂O₅and Ta₂O₅in the ore are 0.016%and 0.0016%,respectively,with Nb₂O₅>Ta₂O₅.The average grades of Rb₂O and Cs₂O in the ore are0.083%,respectively,with Rb₂O>Cs₂O.The Dubi rare metal deposits are mainly Nb and Rb,but also rare metal deposits such as rare earth,U,Th,Cs,Li and so on.(3)The biotite in the Dubi rare metal granite body is iron mica;the rock is rich in Si,high in alkali,and rich in iron,but poor in Ca and Mg;the aluminum saturation index(A/CNK)is 0.93-1.02,which is quasi-aluminum-weaker than Aluminium,high potassium calcium alkaline series of rocks.The Rb,U,Th,Ta,Nd,Sm and other elements in the rock are enriched,while Ba,Sr,Eu,Ti,and P are strongly depleted;the distribution mode of rare earth elements presents a right-leaning"V"shape with relatively enriched light rare earths.There is an obvious negative Eu anomaly.(4)The zircon U-Pb age of the flesh-red porphyritic medium-fine alkaline feldspar granite in the rare metal granite body is 131±2 Ma,which indicates that the diagenesis and mineralization age of the Dubi rare metal granite stock is the early Cretaceous.The rock mass is A1 type granite,formed in the non-orogenic extensional structure of the intraplate,and its source rock is mainly clay-rich argillaceous rock or metasedimentary rock.The highly differentiated evolution and crystal differentiation of fluorine-rich,rare metal granitic magma during the ascent process promotes the gradual enrichment of rare metals into ore in the residual magma.(5)The Dubi granite-hosted rare metal deposits is mainly formed by magma cryatallization and fractionation processes.