Geological And Geochemical Characteristics And Genesis Of The Zhujiaba Copper Deposit,Yunnan Province

The Zhujiaba copper deposit is located in the polymetallic metallogenic belt in Central Yunnan,which belongs to the Proterozoic rift zone.The ore bodies mainly occured in the Luoxue and the Yinmin Formation,in the Kunyang Group of the Proterozoic.Based on the study of geological and geochemical characteristics of the Zhujiaba copper deposit,the following conclusions are listed below:?1?The ore bodies of the Zhujiaba copper deposit occured mostly in stratiform structure or stratoid structure,and in veined structure.Field observation and mineragraphy research shows that the major mineralization is divided into sedimentary diagenesis period,hydrothermal mineralization period?including early disseminated pyrite stage,quartz-carbonate vein copper mineralization stage and late quartz vein stage?and epigenetic oxidation period.The metallic minerals in the deposit are chalcopyrite,bornite,pyrite,tennatite,digenite,chloanthite,malachite,azurite magnetite and ilmenite.The gangue minerals are quartz,calcite and dolomite.These ores generally show automorphic granular texture,xenomorphic granular texture,metasomatic texture,and separation of solid solution texture.The ore structures mainly include vein filling structure,disseminated structure,laminar structure and the horsetail filaments of banded structure.?2?Fluid inclusions are mainly liquid aqueous or two phase fluid inclusions?W type?and halitic fluid inclusions?H type?,and coexist a small amount of gas-rich inclusions.The H type inclusions in the main stage of the mineralization are medium to high temperature?207⁴45°C?and high salinity?33.5⁴8.6%NaCleqv?,the W type inclusions are medium to low temperature?120³69°C?and medium low salinity?5.9²3.1%NaCleqv?,and inclusions of the late stage are low temperature?123²25°C?and medium low salinity?3.9²3.2%NaCleqv?.The fluid compositions are dominated by H₂O-NaCl,and the subminerals are halite and hematite,etc.?3?The study of S and Pb isotopes indicates that the metallogenic process has superposition and transformation of hydrothermal fluids.The sulfur is derived from the strata and magma.The lead originates from the sedimentary rocks in the upper crust,and has undergone hydrothermal transformation.Carbon,hydrogen and oxygen isotopic studies show that the ore-forming fluid has a mixed source of magmatic water and atmospheric precipitation,and carbon mainly comes from the dissolution of marine sedimentary carbonates,and may be exchanged with the hydrothermal fluids from the intrusive rocks.The geochemical data of the rocks and ores shows that the distribution of the rare earth elements in the ore is similar to the host rocks.The variation of trace element contents indicates that the main ore-forming elements have been exchanged during the metallogenic process.Thus,the ore-forming materials originated from the deep source and the formation.?4?Comprehensive research shows the existence of boiling effect in the ore-forming fluid,during the process of migration.Fluid evolution and isotopic tracing show the characteristics of fluid mixing.The boiling of the hot brine containing ore and the continuous mixing from the shallow surface fluid lead to the mass enrichment and precipitation of the minerals,forming the existing lamellar and vein orebodies.