Alteration Zoning And Geochemical Characteristics Of Altered Rocks In The Hongdoushan Copper,Yunxian,Western

The Hongdoushan copper deposit is one of the newly discovered deposits in the north part of Lancangjiang metallogenic belt in recent years.Previous studies on the tectonic geochemistry and zircon U-Pb age of the deep buried granitic porphyry of the deposit have accumulated some research results,but there are few studies on the alteration and geochemical characteristics of altered rocks.On the basis of previous studies,this paper studies on alteration and geochemical characteristics of altered rocks of the deposit through the large scale structure-alteration precise measuring in 1272 and 1220 level in the mining area,systematic lithofacies and mineragraphy analyses.The main knowledge obtained in the paper are as follows:1)The altered types of Hongdoushan deposit are mainly silicification,potassic feldspathization,chloritization,epidotization;the alteration zones are mainly controlled by the NE trending F₁fault and the NWW-EW trending F₃fault.According to the characteristics of altered rocks in the area,from the fault zone to the hanging wall rock,there are four typical alteration zones,which are felsic lithification–silicification zone?I??felsic lithification–carbonate–sericite zone?II??silicification–chlorite–epidote zone?III??weakly felsic lithificatic zone?IV?.The concentric alteration zones from the inner outward of the porphyry veins are successively the potassic zone?sericite zone?propylitic zone.2)The feature of major elements shows that the migration regularity of major elements is obvious,The major elementsexperienced losses from?IV?to?III?,where as major elements experienced gains from?III???II?and?II???I?,In general,SiO₂,CuO,K₂O and Fe₂O₃have larger migration and are closely associated with Cu element enrichment.3)The feature of trace elements shows that the content of Cu in different alteration zones is different,which is characterized by:???and???>???>???,that is,Cu is enriched in the areas with strong alteration.In the process of alteration and mineralization,the trace elements Cu,Zn,Mo,Ag,U,K,P,Th are always in the state of immigration in the alteration process of Hongdoushan copper deposit,indicating that the metallogenic hydrothermal fluid forming the alteration belt is rich in these components,which is beneficial to the precipitation of copper.4)The feature of rare elements shows that?REE quantity is higher.The REE curves assume a rightly dipping REE pattern,The abnormal characteristics of Eu and Ce in each alteration zone indicate that the crystallization of Hongdoushan granite porphyry should occur in a lower oxygen fugacity environment.5)Carbon and oxygen isotope compositions range from-7.02‰?-6.13‰and8.56‰?10.92‰,with an average of-6.67‰and 9.66‰,suggesting that the carbon was mainly derived from magmatism.