Geological Characteristics And Genesis Of Dong Jielegele Ore Section In Bayun Obo,Inner Mongolia

The Dong Jielegele rare earth-niobium-iron ore section is one of the six major ore sections in Bayan Obo,located in Baotou City,Inner Mongolia,on the south side of Bayan Obo East Mine and Bo Luotou Section.It is very important to understand the orebody distribution and genesis of the Bayan Obo deposit,and is related to the deep resource exploration of the Bayan Obo deposit.At present,little work has been carried out and has not been put into production.With the decrease of ore output in the east mine year by year,it is very necessary to study the geological characteristics of the Dong Jielegele ore section as the main replacement resource base of the east mine in the future.Based on the observation and understanding of the geological characteristics of the Dong Jielegele ore section,combined with the existing geological data of the east ore,the main ore and the west mine,the genesis of the Dong Jielegele ore section is further discussed by using a variety of technical means.Some of the understandings and findings obtained in this paper are as follows:1.Dong Jielegele ore section is a dolomite rare earth-niobium-iron deposit related to mafic volcanic rocks and carbonate rocks in H8 strata.It is composed of four layers of ore,of which Ⅱ and Ⅳ are orebodies and Ⅰ and Ⅲ are mineralized bodies.TFe=24.92%and RE2O3=2.38%,Nb2O3=0.17%,incline steeply to the south.2.The ore minerals of Dong Jielegele ore section are mainly monazite,Bastnasite,rich in light rare earth elements,with contents of 70.60%and 61.61%,respectively.The contents of rich thorium,depleted uranium and thorium are 0.11%and 0.55%,respectively,and the contents of UO2 are 0.4%and 0.02%,respectively.The average content of REE2O3 in dolomite is 759.22ppm,which also reaches the industrial grade and is an important type of rare earth ore.3.Combined with field observation,zircon LA-MC-ICP-MS U-Pb dating and arfvedsonite Ar-Ar dating show that the superimposed metallogenic ages of the Dong Jielegele ore section are two stages.The first stage is the early Devonian(early Hercynian).The zircon U-Pb age is 402.8±4.8Ma,and the Ar/Ar plateau age of arfvedsonite is 418.08±4.02Ma.The second stage is the early Permian(late Hercynian):the zircon U-Pb age of siliceous slate is 271.5 ±3.OMa.4.The Dong Jielegele ore section is a hydrothermal deposit related to the carbonate rock-alkaline complex formed in the Mesoproterozoic Bayun Obo Rift(～1320Ma)on the basis of the Seertengshan group,the crystalline basement of the North China platform.The superimposed reformed igneous carbonate rare earth deposit formed by the superimposed reformed of the granite thermal event(～402.8-418.78Ma)at the end of Caledonian and the magmatic thermal event(～271.5-278.8Ma)at the end of Hercynian.It is a part of the rare earth-niobium-iron deposit related to the Bay an Obo igneous carbonate rock-alkaline complex.