| 白云鄂博矿区H_9变质岩的Sm-Nd年龄、成因及与成矿关系 |
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| 关键词:Sm Nd age overling metamorphic rock Bayan Obo ore deposit |
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| Sm Nd Ages and Origins of Metamorphic Rocks for the H 9 Formation in the Bayan Obo Ore District,and Relationship with the Ore Forming Event |
| The Bayan Obo ore deposit in Inner Mongolia ,China is the largest REE deposit in the world.Many Words on this deposit have been made and vast amount of scientifil data have been accumulated.However,the origin ,especially ore_forming age have been ubder dispute for a long time. The geochronology of potassium_rich slates,dard slates and metabasic volcanitesfor the overling H 9 formation of the main ore body in the Bayan Obo ore deposit has been studied.Their Sm Nd ages have been obtained.The samples of the pottasium_rich slates present a Sm Nd isochron age of 1 096±56(2σ) Ma,with I Nd =0.51100±4(2σ),ε Nd (t) =-4.4±0.7.The Sm Nd isotopic analytical results of the 5 dark slate samples define a very good isochron of t =1 208±123(2σ) Ma with I Nd =0.51102±10(2σ),ε Nd ( t )=-1.1±1.9.The calculated isochron age of the 8 metabasic volcanic samples is 1 337±86(2σ) Ma,corresponding to I Nd =0.51091±6(2σ),ε Nd ( t )=-0.06±1.13. The Sm Nd isochron ages of the metamorphic rocks of the H 9 formation in the Bayan Obo ore district shows that the forming time for the ore deposit should be>1 000 Ma ,it implies ,the ore forming events chiefly took place in the middly Porterozoic. The Opinions that this ore deposit forms in the Calednian time of～400 Ma and the REE mineralization have two forming stages have not been demonstrated.The potassium rich slates,the dark slates and the metabasic volcanites have the variational ε Nd ( t ) values and ε Nd ( t )<0.But calculated ε Nd values are each other very close on condition of the same time and are in range of -0.4～-1.7 when t =1 286 Ma.It indicates that the metamorphic rocks of the H 9 formation in the Bayan Obo ore district, as this ore deposit which Sm Nd age of whole ore samples is 1 286±91(2σ) Ma ,with I Nd =0.51098±4(2σ),ε Nd ( t )=-0.06±0.78,have been derived from the mantle of LREE slight enrichment. |
| ZHANG Zong-qing,TANG Suo-han,CHEN Qi-tong,WANG Jin-hui,YUAN Zhong-xin,BAI Ge.1997.Sm Nd Ages and Origins of Metamorphic Rocks for the H 9 Formation in the Bayan Obo Ore District,and Relationship with the Ore Forming Event[J].Acta Geoscientica Sinica,18(3):267-274. |
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