| The central Yunnan Province region,located in the southwestern margin of the Yangtze Block,is a well-known Precambrian Fe-Cu metallogenic belt in China.Beside Fe and Cu,there contains large amounts of REEs?mainly La,Ce?,Nb,Au,U,Ti,Sc,and other strategic metal elements in the Precambrian Fe-Cu-?REE?deposits in central Yunnan Province?e.g.,the Yinachang Fe-Cu-REE deposit,Etouchang Fe-Cu-?REE?deposit and Dahongshan Fe-Cu-?Au-Ag?deposit?.In order to explore the occurrence characteristics of REEs and rare elements of the Precambrian Fe-Cu-?REE?deposits in central Yunnan,this paper took the Yinachang deposit,Etouchang deposit and Dahongshan deposit as examples,used the Automated Mineral Identification and Characterization System?AMICS?,which is the most up-to-date mineral automatic analysis system in mineralogy and geology in the world,combined with the Scanning Electron Microscope and X-ray Energy Dispersive Spectrometer?SEM-EDS?microstructure in-situ analysis technique,to investigate the rare earth minerals and rare minerals characteristics of ores from the deposits.The quantitative mineral identification,which was difficult to achieve by conventional means of rock mineral identification,have been completed.This study obtained the following points new discoveries and understandings:?1?There is an unbalance in space distribution for the rare and rare earth elements in the central Yunnan Province,showed that the north area was more than the south area.Rare earth elements are relatively high both in the banded ores and vein ores,rare elements?mainly Nb?are enriched in banded ores in the Yinachang Fe-Cu-REE deposit.The?REE content reaches up to 1446.83×10-611259.23×10-6and 2020.92×10-63415.51×10-6 in the banded ores and vein ores,respectively,especially enrich in the LREE?e.g.,La,Ce?.The content of Nb reaches up to278.8×10-6529×10-6 in the banded ores in the Yinachang Fe-Cu-REE deposit.Rare earth elements and rare elements?mainly Nb?are enriched to some extent in the Etouchang Fe-Cu deposit,but the content is far less than that of the Yinachang Fe-Cu-REE deposit.There is almost no enrichment of rare earth elements and rare elements in the Dahongshan Fe-Cu-?Au-Ag?polymetallic deposit.?2?The Yinachang Fe-Cu-REE deposit contains a large number of rare earth minerals?e.g.,parasite,bastnaesite,monazite,allanite,fergusonite,and yttrialite?and a small number of rare minerals?e.g.,columbite,fergusonite,and Nb-bearing rutile?.Bastnaesites,monazites,columbite and fergusonite are mainly concentrated in the banded ore,closely associated with iron oxide minerals?magnetites?,siderites,apatites,flourite and early sulfides such as chalcopyrite,pyrite,etc.Parasites,allanite,yttrialite and Nb-bearing rutile are enriched in the vein ores,mainly coexisted with chlorites,calcite,quartz and late sulfides such as chalcopyrite,pyrite,etc.The Etouchang Fe-Cu-?REE?deposit contains a small number of independent rare earth minerals and rare minerals such as parasite,bastnaesite and fergusonites.Rare and rare earth minerals are seldom found in the Dahongshan Fe-Cu polymetallic deposit,but there contains considerable titanium minerals such as rutile and ilmenite.?3?Both of the Fe oxides-REE and Cu sulfides-?Au?mineralization stages are associated with REE mineralization in the Yinachang Fe-Cu-REE deposit.Two main mineralization stages are identified,i.e.,the Fe oxides-apatites-REE mineralization stage??-1?and Cu sulfides-?Au?-REE mineralization stage??-2?.The bastnaesites,monazites,columbite and fergusonite are mainly formed in the Fe oxides-apatites-REE mineralization stage??-1?,while the parasites,allanite,yttrialite and Nb-bearing rutile are mainly formed in the Cu sulfides-?Au?-REE mineralization stage??-2?.?4?Summarize the research results of this study and the previous research data,the mineralization of Precambrian Fe-Cu-?REE?deposits in the central Yunnan Province area can be summarized as follows:Early bimodal magmatism and mineralization?1.701.50Ga?,formed iron oxide-apatite type Fe-?Cu-Nb?-REE polymetallic ore body;Late hydrothermal events superimposition and transformation ore-forming processes?1.100.90Ga?and metamorphic hydrothermal remobilization and enrichment?0.850.75Ga?,formed quartz-calcite vein type Cu-?Au-U?-REE polymetallic ore body.The superposition of mineralization at different stages eventually formed the Precambrian Fe-Cu-?Au-U-Nb?-REE polymetallic deposits in the Central Yunnan Province. |
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