| After contains diamond“Dongfeng 1”rock was firstly found in Zhenyuan area,Guizhou Province,a new upsurge of searching for primary diamond deposits in lamproites in Southeastern Guizhou Province has been aroused.However,in the past,the research on petrology,mineralogy and chronology of lamproites Southeastern Guizhou was mainly focused on Diamond Prospecting,the enrichment of critical metal elements and even metallogenic theory in lamproites in Southeastern Guizhou Province have not been studied.Therefore,this paper selects 7representative rock bodies in Zhenyuan and Majiang,which are representative areas of lamproites in Southeast Guizhou Province,as the research objects,and studies on geological characteristics,occurrence and mechanism of REE and Nb enrichment of critical metal elements in the weathering crust of lamproites by means of electron microscope,electron probe,LA-ICP-MS and element geochemical research methods Set.According to the study of element geochemistry,REE and Nb are generally enriched in lamproites weathering crust in Southeast Guizhou.The content of?REE is 558.87?2409.94×10-6(average 1442×10-6),and Nb is 101?404×10-6(average 264.8×10-6)in olive lamproites weathering.The content of?REE is 666.33?1551.02×10-6(average 973.17×10-6),Nb is120?477×10-6(average 222.1×10-6)in weathering crust of mica lamproites,and there are many large-scale lamproites weathering crust in Zhenyuan Baifen,Majiang Longchang and other places in Southeast Guizhou,which has the geological conditions and metallogenic potential to form lamproites weathering crust REE and Nb deposits.Through comparative analysis,it is found that the enrichment degree of REE and Nb in the weathering crust of olive lamproites is much higher than that of mica lamproites,which may be different from the magma source depth,resulting in the enrichment difference of REE and Nb.In the lamproites weathering crust,the enrichment of light and thin is related to the weathering degree of the rock mass,and the content of?REE is positively related to the weathering intensity as a whole,and it is characterized by enrichment of LREE,mainly enrichment of La,Ce,Nd,Pr,and has the change characteristics of Ce>La>Nd>Pr.In addition,by analyzing the Nb in the lamproites weathering crust,it is found that the the content of Nb are the most abundant in the weathering olivine lamproites in Majiang area and the weathering mica lamproites in Maping?MP2?,and the Nb content in the weathering mica lamproites rocks in Baifen,sinantang and other places is relatively low,often lower than 200×10-6.In the same rock mass,the content of Nb in the highly weathered crust is high,and Nb tends to be enriched gradually in the process of supergene lamproites weathering.The occurrence of REE and Nb in lamproites weathering crust is studied.It is found that REE mainly occurs in the form of rare earth independent minerals such as monazite and calcium cerium titanite,and a certain proportion of REE may exist in clay minerals in the form of ion-adsorption.There may be a variety of Nb rich minerals in the weathering crust of lamproites,rare Nb rich phlogopite and Nb rich rutile are found in the weakly weathered mica lamproites,Nb in the strongly weathered lamproites weathering crust mostly occurs as rich Nb rutile,and some Nb may coexist with clay minerals in the form of oxidized minerals in the weathering process.The rare earth and niobium elements in the weathered crust of the lamproites in southeastern Guizhou may be derived from the partial metamorphic magma enriched in the deep metasomatic mantle.The metasomatic mantle itself is rich in REE,and Nb-rich minerals such as garnet or rutile may occur in the source partially melted to form REE and Nb-rich magma.Under the background of the ancient craton structure,it rises along deep deep faults and undergoes crystalline differentiation to form REE and Nb-rich lamproites parent rocks.During the crystallization process,REE mainly enters monazite,Ce-perovskite and other accessory minerals in a homogenous manner.These minerals are difficult to be weathered and decomposed in the form of independent minerals in the weathered crust during the superficial weathering stage.In addition,some rare earth elements are released by surface weathering,which releases REE3+from the rare earth-containing minerals that are easily weathered and decomposed,which is attached to the clay minerals formed by weathering.Research on the enrichment mechanism of Nb believes that the high-temperature and high-pressure tectonic environment of the ancient craton is conducive to rutile formation,and enriches Nb to form a large amount of Nb-rich rutile,and it is difficult to decompose during the weathering process,and the rutile mineral remains the weathered crust.In addition,under the constraints of high temperature and high pressure environment,under the magma system rich in Ca and Ti,the Nb may have been highly dissolved into pyroxene,mica and other minerals,and it is easy to dissociate and form niobium oxide during the weathering process.Coexist with clay minerals. |
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