The Ore Genesis And Geodynamic Setting Of The Fe-Cu-Au-U-REE Deposits In The Wuding Region, Yunnan Province, SW China

The iron-copper polymetallic metallogenic belt of the Wuding,Yunnan,is located in the southwestern margin of the Yangtze block and the south-central part of the Kangdian axis.Precambrian iron-copper minerals are abundant in this region.Its Paleoproterozoic to Mesoproterozoic strata are composed of metamorphic volcanic rocks and metamorphic sedimentary rocks.It is now considered that the deposits in the Kangdian area belonging to iron oxide-copper-gold type?IOCG?deposits.We take the deposits of Yinachang,Shaojiapo and E'touchang in Yunnan province as examples,the main achievements are as follows:1.It is the first time to observe the CL image of apatite has zonal texture in Yinachang deposit,and the brighter part of the core is rich in La,Ce,Nd and other rare earth elements.It shows two stages of rare earth enrichment process,with strong rare earth enrichment in the early stage and gradually weakening in the late stage,which coincides with the rule that rare earth mineral particles from the core to the edge of apatite in back scattered electron imaging changes from large to small until to none.2.It is concluded that the Yinachang deposit,E'touchang deposit and Shaojiapo deposit have similar mineral assemblages by analyzing the mineralogy of different types of ores.They all contain a certain amount of rare earth minerals and uranium minerals,but in different quantities.The ore of Shaojiapo deposit is mainly chalcopyrite.It is the first time to report the ore in Shaojiapo copper deposit contains the rare earth minerals and uranium minerals.The rare earth minerals mainly include bastnaesite,parasite,monazite and so on.Uranium minerals are distributed as inclusions in chalcopyrite.Rare earth minerals such as monazite and bastnaesite and uranium minerals are also found in E'touchang iron deposit.Uranium minerals are mainly distributed in pyrite and quartz.3.In-situ sulfur isotopes of sulfides in Yinachang deposit shows the value of?³⁴S_V-CDT ranges from+1‰to+3‰,indicating that sulfur originates from magmatic sulfur,while sulfer in the E'touchang deposit and Shaojiapo deposit originates from seawater sulfate In-situ lead isotopes indicate that lead originates from mantle and mantle magmatic upwelling.Hydrogen and oxygen isotope analysis shows that the value of?¹⁸O_H2O changes from 2.7‰to 10.7‰and the value of?D_V-SMOW varies from-98.2‰to-47.7‰,suggesting ore-forming fluids are derived from magmatism in the early stage and have the addition of metamorphic water in the late stage.Carbon and oxygen isotope analysis shows the value of?¹³C_V-PDB varies from-2.4‰to 1.00‰and the value of?¹⁸O_V-SMOW changes from 6.9‰to 18.4‰,stating a small amount of carbon comes from the deep mantle xenoliths in the early stage of mineralization and the carbon is mainly from the dissolution of marine carbonate during the mineralization process.The biotite in ore sample of ⁴⁰Ar-³⁹Ar isotope age is 897±14Ma and 886±72 Ma,respectively,which is the time of regional metamorphism.The regional metamorphism has related to the enrichment and mineralization of rare earth minerals.4.Zircon U-Pb isotope studies of intermediate-mafic magmatic intrusions and sandstone indicate that there were magmatic activities in the Paleo-Mesoproterozoic region,and a large number of Archean-Paleoproterozoic zircons were found in clastic zircons,of which the oldest zircon age is 2948±13 Ma.By the Hf-O isotope diagrams of zircons from intermediate-mafic magmatic rocks,it can be concluded that they mainly originate from depleted mantle.The mineralization in the study area is related to magmatism derived from the depleted mantle.