Study On Enrichment Mechanism Of Rare Earth Elements In Posphorus Dposits In Dfferent Sedimentary Evironments Of Early Cambrian In Guizhou

Phosphorite type rare earth deposits are one of the important sources of rare earth.Aiming at the problem of rare earth enrichment mechanism of rare earth rich phosphate deposits in different sedimentary environments of the Early Cambrian in Guizhou,this paper focuses on the Xinhua platform facies rare earth rich phosphate deposits in Zhijin County and the Bahuang slope facies rare earth rich phosphate deposits in Tongren city,and based on detailed field geological work,conducts major,trace,and rare earth element analysis of the entire rock,rock mineral identification,and TOC analysis of total organic carbon In situ microanalysis（LA-ICP-MS）has identified differences in sedimentary environments,explored the source of metallogenic materials,geological factors controlling ore formation,and established a rare earth enrichment model.The main findings are as follows:（1）The Mineral-bearing rock series of the Gezhongwu Formation of xinhua in Zhijin,country is rich in rare earth phosphorus ore.The ore minerals are mainly microcrystalline apatite,and the gangue minerals are mainly dolomite,quartz,and so on;Develop bioclastic structure,sand debris structure,oolitic structure,banded structure,lenticular bedding,trough cross bedding,herringbone cross bedding,etc.The rare earth rich phosphorus ore minerals of the Niutitang Formation of Bahuang in Tongren,are mainly cryptocrystalline apatite,and the gangue minerals are mainly clay minerals,quartz,and organic matter;It develops gel structure,silty structure,recrystallization structure,horizontal bedding,laminar structure,vein structure,etc.（2）The mineral-bearing rock series of the Gezhongwu Formation in Zhijin and the mineral-bearing rock series of the Niutitang Formation in Bahuang are both highly concentrated in rare earth elements,especially in the heavy rare earth element yttrium（Y）,and the total average content of the latter∑REY is slightly lower.It is assumed that the rare earth elements may be mainly endomorphic in apatite lattice defects or adsorbed by colloidal phosphorites,and a few rare earth elements may be adsorbed by clay minerals and organic matter in Bahuang rare earth rich phosphorites.（3）LA-ICP-MS analysis shows that the rare earth elements of rare earth-rich phosphate ores in Zhijin are mainly concentrated in the biological shell and shell wall,followed by the sand flakes,edges and phosphate clumps and phosphate cement.It indicates that the cavities of the small shell organisms in the terrace phase area after death provide the best space for enrichment of rare earth elements,and the living organisms also enrich rare earths in the process of absorbing phosphate mass to build shell walls,in addition to the sand debris and some late pore water produced by wave tides are also important carriers of rare earths;The rare earth elements in the rare earth-rich phosphate ores in Bahuang are mainly found in colloidal phosphate,organic matter and veins,indicating that rare earth enrichment may be related to bio-organic matter and that later hydrothermal activity contributed to the enrichment of rare earth elements.（4）The depositional characteristics,Ni/Co ratio,authigenic uranium（AU）,Sr/Ba ratio and Al₂O₃/Mg O ratio all indicate that the overall oxidized and sometimes oxygen-poor water bodies and the overall arid climate of the mineral-bearing rock series of the Gezhongwu Formation in Zhijinat the time of deposition,with its flourishing biology,shallow water bodies and strong hydrodynamic environment,may have been the key to the enrichment of rare earths.When the ore-bearing rock series of Niutitang Formation in Bahuang was deposited,the water body was generally reduced and sometimes oxidized,and the paleoclimate was generally humid.The role of microorganisms and organic matter in the reduced environment with relatively deep water body and weak hydrodynamics may be conducive to the enrichment of rare earths.（5）Rare earth distribution curves,Eu anomalies,relative enrichment of Sb and As elements,U/Th ratio,Si O₂/Al₂O₃ ratio and LA-ICP-MS analysis results indicate that phosphorus and rare earths should be of the same source,hot water activity and normal seawater provide the main mineralized material,terrestrial sources provide part of the mineralized material,and later hydrothermal fluids brought a small amount of mineralized material to the Bahuang ore-bearing rock system while contributing to the improvement of ore grade.（6）The enrichment of phosphorus and rare earths is controlled by paleogeographic conditions,redox conditions and bio-organic conditions,mainly through four stages:seafloor jet seawater mixing,phosphorus-rare earth-rich water mass formation stage;Sea level rise,phosphorus-rare earth migration stage;Environmental changes,phosphorus-rare earth co-precipitation stage;Rock formation,phosphorus-rare earth co-precipitation stage.In addition,the phosphorus-rare earth enrichment in the slope phase area of the terrace margin has also gone through hydrothermal activation and phosphorus-rare earth re-enrichment stage.