Geological Characteristics And Metallogenic Model Of Iron And Copper Deposits In Wuding-Yimen Region

Yunnan,Guizhou and Sichuan iron-copper polymetallic metallogenic belt locates in Kunyang rift,southwestern margin of Yangtze Block,where there are well tectonic-developed areas with great mineralization conditions.As one of the most important iron and copper region,the research for metallogenic model in Wudind-Yimen will be of great value to better understanding the whole mineralization mechanism in Yunnan,Guizhou and Sichuan iron-copper polymetallic metallogenic belt.Based on a large number of datas from previous scholars,by doing field investigation,sampling,microscopic mineral identification,geochemical analysis,we get the region's geological background,ores structure,texture,geochemical characteristics,diagenesis and mineralization epoch and thus make the following conclusions:The ore-hosting strata in Wuding-Yimen region is mainly from Kunyang Group in Middle Proterozoic,partly from Kunyang Group in Early Proterozoic.,The metamorphic intensity of strata gradually weakened from Wuding to Yimen area,corresponding to the transition from iron-copper deposits to copper deposits.Compositions,structures and textures of ores from Wuding-Yimen region(Yinachang iron-copper deposit,Luoci iron deposit,Yiduchang copper deposit,Shangchang iron deposit)were detailed identified.The trace elements of iron ores such as Ba,U,La,Ce,Nd,Sm show enrichment,Zr,Y,Yb show weak loss,which indicate the formation of iron ores may be related to the emplacement of mafic magma;Most trace elements of copper ores except for Y and Yb show enrichment,especially Rb,Th,U,La and Ce show strong enrichment,indicating fluid affection on copper mineralization.The fractionation between LREE and HREE is obvious in both iron and copper ores: LREE enrichment,HREE loss.?Eu of iron ores shows positive anomaly,indicating mineralization may be related to mantle fluid;?Eu of copper ores shows weak negative anomaly,indicating copper mineralization fluid may be contaminated by crustal materials,and the hydrothermal mineralization may contain both hydrothermal from mantel and epithermal from surrounding formations.The content of Cu in copper ores shows positive correlation to Ag,S,negative correlation to Fe,and no correlation to Au,Co,Ni,Ti,V,indicating that copper mineralization is not a simple process.The content of Fe in iron ores shows positive correlation to Ag,Co,negative correlation to Cu,S,Ni,and no correlation to Au,Ti,V,indicating the process of iron mineralization is consisted of several times work.The evolution process of iron and copper deposits in Wuding-Yimen region can be expressed as follow: In Mesoproterozoic,Columbia supercontinent started cracking globally,accompanying with Kunyang rift expanding in southweste of Yangtze Block.The Expansion of rift thinned the crust,magma from the upper mantle brought a wealth of minerals,forming iron-copper deposits in Wuding area and source beds in Yimen area.Afterward,the Rodinia supercontinent cracked,hydrothermal from upper mantle and epithermal from surrounding rocks reforming the former deposits and source beds,stratiform and stratoid ore bodies were formed in Yimen area,veined ore bodies were formed in Yimen area.In Himalayan stage,precipitation and groundwater activities led the oxidation of some ore bodies,formating a large number of malachite,hematite in Yimen area.