Study On The Process Of The Element Migration And Its Mechanism During Weathering Of The Zhuopan Alkaline Complex In Yunnan Province

The area of Zhuopan which is an important component of alkali-rich intrusive rock zone in Jinshajiang-Ailaoshan.is located between the fault zones of Ailaoshan-Jinshajiang and Lancangjiang,in the southwest of Lanping Basin,Although magma-mineralization has not been found in the interior of Lanping Basin,the weathering of surface in Zhuopan area is extremely developed,and reserves the complete weathering crust,and its parent rocks are rich in rare earth elements.Further study of weathering profile in this area can provide geological basis for whether it really has the metallogenic potential of rare earth deposits with the weathering crust.Two weathering profiles are systematically sampled in this paper.One is alkaline gabbro weathering profile with a height of about 10 m and the other is alkaline syenite weathering profile with a height of about 5 m.In this paper,the migration law and mechanism of elements in weathering profile are discussed from petrographic of rock mass,geochemical behavior of elements in weathering profile and elements geochemistry of single mineral,and the main enrichment forms of rare earth elements in weathering profile are analyzed.The study of the weathering profile of alkaline gabbro is about the relationship between major oxides,trace elements and depth,furthermore,exploring its the variation law.The profile is stratified according to the weathering degree,the weathering behavior and migration rule of elements are analyzed with the relationship between main oxides,trace elements and weathering index.The content of REE is during the990×10^-62034×10^-6,which indicates it has the metallogenic potential of rare earth element?REE?deposits about weathering crust.The approximate distribution curve of the rare earth with the bedrock indicates that the source is similar,which may be a residual weathering crust.By introducing the mass transfer coefficient of elements,the migration process of rare earth elements is further discussed.It can be seen that the light rare earth will take precedence over the heavy rare earth enrichment in the surface layer,which indicates that the hydrolysis ability of light rare earth is stronger than that of heavy rare earth,leading to the weakening of the activity of light rare earth in the surface layer and the priority of heavy rare earth enrichment.Heavy rare earths are more likely to form organic complexes and carbonates than light rare earths in the acidic environment of the surface soil,which preferentially dissolve and gradually migrate downward.Based on the single mineral study of weathered gabbro,pyroxene and gabbro protolith in this area,it is indicated that the enrichment of rare earth elements should be mainly in the form of isomorphism in apatite,an independent mineral.The weathering degree of alkaline syenite is very high.The total amount of rare earth elements of the profile samples are ranged from 88.0×10^-6 to 287×10^-6 with strong positive Ce anomaly.According to XRD diffraction patterns,the main evolution process of clay minerals might be feldspar?montmorillonite?kaolinite?gibbsite.The results show that it is formed into an open oxidizing environment on the surface,and judged that the collected profile should be located in the surface soil layer to the weathered layer.The surrounding strata are Quaternary and Cretaceous sandstones,which are low-lying areas transiting to hills,and are conducive to shallow groundwater and surface water flow,thus leaching aluminosilicate cations in permeable parent rocks,thus providing a good ore-hosting site.