Characteristics Of Tectonic Lithofacies And Relationship Of Diagenesis And Metallogenesis Of Iron-Basic Rocks In Yinmin Of Dongchuan,Yunnan Province

There was multi-period tectonic-magmatic-thermal event on the western margin of the Yangtze massif,which formed the Proterozoic IOCG deposit metallogenic domain.But the mineralization relationship between iron-base rocks and the mechanism of iron-copper deposit was unclear.The iron-based rocks were chosen as the research object,in the Yinmin iron-copper area of Dongchuan,Yunnan Province.It focused on research and exploration on magmatic evolution dynamics mechanism and mineralization of iron-copper deposits,based on the study of the types and characteristics of the tectonic-lithology facies of the iron-base rocks,by measuring tectonic-lithology facies,lithology facies,mineralogy facies,geochemistry,chronology,and other means of comprehensive study.Main findings in this paper are as follows.1.Iron-riching rocks form a complex volcanic-subvolcanic complex in the Yinmin iron-copper area,and their tectonic facies zonation is obvious and characterized by the same phase of heterogeneous structure and the different time at the same time superposition.Early diabase gabbro invaded Late Archean-Early Proterozoic Rock Formation,which was divided into center facies,transitional facies,and marginal facies.At the same time,diabase-gabbro was accompanied by volcanic overflow facies.Subsequently,subvolcanic rocks invaded early iron-based lava.Late volcanic blasting breccia facies,which belonged to volcanic channel facies,inserted into early diabasic gabbro and subsequent diabase-diabasic gabbro.There were facies of magmatic hydrothermal breccia near the volcanic blasting breccia facies.Combined with volcanic hydrothermal-related volcanic eruption sedimentary facies,facies of volcanic hot-water-jet channels,and the recovery study of tectonic facies restoration,it shows that volcanic rocks and subvolcanic rocks are metallogenic system root facies and mineralization material supply center of iron-copper deposits in this area.2.Iron-based rocks in Yinmin iron-copper area are characterized by low SiO2(45.96%?50.71%),high FeO(10.38%?20.51%),high alkaline(high Na and low K,Na2O+K20=1.07%?8.31%),high LILE,REE and HFSE.Rare earth distribution pattern and trace element content and ratios of incompatible elements are similar to OIB mantle component.Their magma source of iron bedrock could come from OIB,and is formed from continental rift extensional environment.The evolution level of basic magma is high.The magmatic evolution has the trend of evolution from pecritic basalt to trachybasalt to phonolitic tephrite.3.The diagenetic and mineralization has multiple stages of superposition in Yinmin iron-copper area.Early(Yinmin Period),the age of magma activity is 1800±3 7Ma,which represents the boundary age of the Dongchuan group.Late glacial gabbro invaded age is 1720+31/-32Ma,and the magma activity of the gabbro have been extended to 1667±13 Ma.They formed volcanic rock-subvolcanic complex together.The magmatic-hydrothermal activity associated with diagenetic mineralization can be divided into four periods.(1)Crystallization differentiation of late magma,is mainly calcium and sodium silicate alteration phase,in a high temperature and strong oxidizing environment(T=662?1684?,ANNO=+0.78?+2.11).Fe appeared in the form of magnetite.(2)Magmatic hydrothermal equilibrium stage,is mainly hydrolysis of potassium silicate alteration phase,in a high temperature and strong oxidizing environment(T=505?590?,lgfO2=-12.4?-5.25,P=1.16?2.26kbar).Fe is primarily in the form of hematite ore.It is the main stage of enrichment and mineralization of Xikuangshan-type iron-copper deposits in this area.(3)Volcanic hydrothermal leaching stage,is mainly hydrolytic silicate alteration phase,formed a convection circulation system with magmatic hydrothermal fluids,precipitation and basin fluid,belonging to the low temperature and strong reducing fluid(T=170?235?,lgfO2=-51.93?-43.70,1gfS2=-13.34?-2.50).The leaching Fe and Cu in the iron-based formed ore-forming fluids,migrating and unloading mineralization along the tectonic development zone.It is the main stage of enrichment and mineralization of Xikuangshan-type and Dongchuan-type iron-copper deposits in this area.(4)Hydrothermal superimposition transformation enrichment stage.The multiphase tectonic-magmatic-thermal events(1800Ma?1000Ma)and iron-based rock magma not only bring new ore-forming materials from upper mantle and lower crust,but also provide a new thermal anormalous area and re-activate the circulation of hydrothermal fluid convection system of ore-forming hydrothermal fluid.At the same time,iron-based rock as the object of leaching,has become a stable and continuous mineralization element supply system for iron-copper deposits in this area.