Mineralogy,Geochemistry And Metallogenic Mechanism Of Rare Earth Mine In Fengshan Area,Southern Jiangxi Province

The Dabu composite granite body is located in the hinterland of southern Jiangxi and is an important component of the Yudu Ganxian polymetallic ore concentration area.In this paper,rare earth minerals in the Fengshan area in the west of Dabu rock mass are taken as the research object,and the representative samples of bedrock and weathering crust are systematically analyzed by petrography,mineralogy,and major,trace and rare earth element geochemistry.The characteristics of rare earth minerals in bedrock and weathering crust are identified,and the migration and enrichment rules of rare earth elements in the weathering process are discussed,and the following new understandings are obtained:(1)Through the study of petrology,mineralogy and geochemistry of the ion-adsorbed rare-earth ore bedrock in Fengshan area,it is confirmed that the ore-forming parent rock of the rare-earth ore belongs to late Jurassic granite of Dabu rock mass,whose lithology is biotite monzogranite.The rare earth minerals(or rare earth minerals)in the rocks mainly include apatite,monazite,bastnaesite,fergusonite,polycrase,yttrium-rich thorianite and xenotime,which are characterized by heavy rare earth,and the rocks have the characteristics of high differentiation,thus controlling the weathering crust to form heavy rare earth and heavy rare earth symbiosis type rare earth ore.(2)Rare earth elements in weathering crust mainly exist in ion adsorbed state and independent mineral form,among which ion adsorbed state is the main form.Weathering results in the dissolution of rare earth minerals,such as apatite and bastnaesite,which are easily weathered,and rare earth minerals,which release a large number of rare earth ions and adsorb on the surface of clay minerals formed by weathering of bedrock.At the same time,rare earth independent minerals such as cerianite and xenotime are found in the weathering profile.Xenotime is the residual of rare earth minerals in the bedrock,and cerianite is the secondary rare earth minerals co-precipitated with Fe-Mn oxides during the weathering process.(3)The distribution of rare earth elements in the weathering crust is "bowed",and the ore body is located in 2~9m of the weathering crust.The average content of rare earth is516.8×10-6,and the leaching rate of ionic phase rare earth is 51%~84%.The distribution characteristics of ionic phase are consistent with the total rare earth in the whole term.The enrichment of rare earth elements in the profile is mainly controlled by weathering degree and clay minerals.(4)The differentiation of rare earth elements in weathering crust is mainly due to the selective adsorption of clay minerals.The upper part of ore body is relatively enriched with light rare earth,while the lower part is relatively enriched with heavy rare earth.The increase in the ratio of light and rare earth in the lower part of weathering crust relative to the bedrock may be caused by the incomplete weathering of bastnaesite and the large amount of secondary cerianite.(5)The development of light and heavy rare earth symbiosis rare earth minerals in Fengshan area may be caused by the difference in the properties of light and heavy rare earth minerals.During weathering,the migration ability of heavy rare earth minerals is stronger than that of light rare earth minerals,so that the light rare earth mineral layer is formed first in the weathering profile.With the enhancement of weathering degree,the weathering layer level gradually moves down.Finally form light and heavy rare earth symbiosis rare earth ore.