Study On Geochemical Characteristics And Genesis Of The Bayan Obo REE-Nb-Fe Ore Deposit,Inner Mongolia

Bayan Obo REE-Nb-Fe ore deposit is the world's super large deposit and world important producing area for rear earth elements.Since it was discovered by Prof.Ding Daoheng in 1927,many geologists have carried out a great sum of research works.Although great achievement has been made,its genesis is still unknown owning to mixture of minerals,combination of multiple-stage geologic structures and superposition of various metallogenesis and so on.Combined with published data,this thesis engage in the Bayan Obo deposit:genesis of ore-bearing dolomitite and slate,metallogenic environment and mineralization stages.The slate in the mining area presents broken and metasomatism characteristics,and showing multiple-stage geologic structures.The field geologicaworks and the microscope observation show metasomatism features,the later minerals interplaced the early dolomite rock.The EPMA analysis of pyrite indicate the ore was of metamorphic hydrothermal and volcanic hydrothermal characteristics.The dolostone and slate all are riched in Ba,Th,Nb and REE,and depleting U?K?Zr and Ti.REE type all belong to light rare earth enrichment type,and as the increase of the content of REE,the content of trace elements corresponding increased.Rare earth and metamorphic slate riched Nb element,show the hydrothermal ore-forming with strong riched Nb and depleted Ta characteristic.Our results of element analysis also indicates that the mining dolomite possess characteristics of both carbonatite and sedimentary carbonate.Show the genesis of the dolomite in Bayan Obo is:it was a product of sedimentary carbonates metasomatism by carbonatite magma and its derived fluid.This is also supported by the result of the C13?O18,sulfur and Sr isotopic composition.The synchronized radiation device is used in our study of dolostone inclusion,results show that the fluid inclusions contained Ca?Mn?Fe,indicating that fluid inclusions are influenced by later hydrothermal events and the Later hydrothermal activity had a stack enrichment role in the form of Bayan Obo ore deposits.XRF can be used as a reliable tool in the study of fluid inclusion.The measured AFT ages is 180Ma?170Ma and 99Ma,indicting the cooling process after the granite fromation.Based on the statistic of Bayan Obe deposist ages and tectonic analysises,we concluded the deposist suffered massive thermal events and metasomatism in local fault zone area,the Sr isotopes system also replaced.