Discussion Of Bayan Obo Fe、REE Deposite Mineralization:New Evidences In Geochemistry

Bayan Obo REE-Fe-Nb deposit is famous for its large percentage of REE(60%) in the world,it is not only a super-large REE deposit,but also a large Fe deposit,and the reserves of Nb is the largest in China(second largest in world).In addition,the deposit contains a lot of metallogenic element,such as F,P,S,K,Th,Sc.The research on the genesis of Bayan Obo deposit has a long history of half a century,many models of the genesis of the deposit are proposed. Most reserchers tend to believe that the deposit is formed by the intrusion of carbonate magma;The view of volcanic eruption is also proposed by some reserchers;In addition, hydrothermal origin, metamorphosed sedimentary hydrothermally-reworked origin and impact origin are supported by different reserchers. Complexity of the genesis is showed by two different views:’sedimentary’ or ’magmatic’.Many geologists studied the deposit on different aspects,made a contribution for research and production.But,most researches commonly focus on one aspect of the genesis of Fe and REE,or the characteristic and genesis of dolomite. The relationship of distribution regularity of Fe and REE is unclear.Did the Fe and REE form by the same geological event or not?This question is significant not only for explaining the genesis of deposit,but also for guiding Mineral exploration.Our research showing,the spatial enrichment regulation of Fe and REE is different, the grade of Fe is stable in whole ore body,with the characteristics of element distribution of "sedimentarydeposit".The content of Fe barely changed in the trend,in the dip,the variation is obvious.However,the grade of REE is not homogeneous in whole deposit,the phenomenon of local concentration is normal, showing the characteristic of extending to the depth,the grade of REE decrese sharply in the trend of ore body.On the whole,the stable variation of Fe content along the trend,and the characteristic of ’intrusion’ of REE content in vertical showing Fe and REE is not formed by the same geological process.So this article foucus on the Eastern deposit and Major deposit,aiming at the enrichment regulation of Fe and REE,and the relation of individual mineralizing events of Fe and REE.Field work,microscopic petrography,geophysical analysis,ICP-MSanalysis, fluid inclusion research are used in this study,to analyse the geological connotation of mineralizing events.On the basis of above,we proposed a metallogenic model of Bayan Obo deposit.On the basis of many field works,geochemistry,fluid inclusion researches,this article proposed that Fe and REE of Bayan Obo is a result of two different geological events, with the characteristic of ’Fe early,REE later, multistage’.This kind of model barely discovered in the world,during the formation of H8dolomite of Bayan Obo group(1200Ma),Fe-formation similar to BIF deposited,the later dolomitization enrich the Fe element.The carbonate magma containd REE replacemented the Fe ore deposit and dolomite,forming the REE deposit.The occlusion of Paleo-Asian Ocean resulting the formation of fold in the region,the former trail of the mineralization is disappeared.By this model,a advise for exploration of ore deposit is proposed,and it is significant for ore exploration to the depth ofBayan Obo region.