| Mengjiagang iron ore is located in Jiamisi massif,the north of Huanan uplift.The study area have a complex geological background with old Paleoproterozoic crystalline basement,experienced Jinning movement and Caledonian movement,after which the continental crust transformation have begun to take its present size.Obvious activity of magma and fault in indosinian deformation.During the period of Yanshan,the movement of magma ang fault was further strengthened,and the strong formation of the fault was formed.To form a rift basin because of Dunmi fault strong activity.There are abundant sediment sources,active faults and magmatic activities in the region,so the region has a good metallogenic background.In this paper,through the analysis of geological background of Mengjiagang iron ore,combined with the analysis of the main trace elements and zircon U-Pb dating,to further determine the sources of iron and the formation age of Mengjiagang iron ore.As a whole,the main achievements are listed as following:1.Large area of the early Paleozoic granite and the Xingdong group,the formation of the Jiantang Formationthe exposed in the study area.The ore body is layered,and the stratum is produced in the strata of Dapandao Formation.The mineralization type is in banded magnetite quartzite,part of the ore experienced later transformation.Metallic minerals are mainly magnetite,followed by pyrite,pyrrhotite,chalcopyrite,hematite,etc.;the gangue minerals are mainly quartz,often bundles,strip-like aggregates.The ore is semi-self-shaped granular texture,banded structure.2.According to the results of field investigation and microscopic observation,the metallogenic period of the deposit is divided into four stages: sedimentary period,metamorphic period,hydrothermal superimposition period and oxidation period.The formation of the first phase of the magnetite,is also the formation of the main period of magnetite;metamorphic period to form a special strip of magnetite and quartz intertwined;hydrothermal stacking period by the hydrothermal secondary superposition,the formation of The second phase of the magnetite and quartz,and also the formation of some pyrite,chalcopyrite and other original magnetite;oxidation period of orebody is tectonic uplift,subjected to weathering,magnetite is oxidized to hematite.3.Marble samples in Mengjiagang iron ore show delepe LREE with(La/Yb)SN=0.56~2.03,relative to HREE.Eu positive anomaly,with Eu=1.25~1.43,Ce has no obvious abnormality,with Ce=0.88~1.03.REE marble figure is similar to seawater,illustrate that iron ore deposits in marine environment.The ore and marble samples in Mengjiagang ore with Y/Ho=35.54,whichbetween seawater(Y/Ho=44~65)and hydrothermal fluid(Y/Ho=28),indicating that Mengjiagang iron ore is the interaction of seawater and hydrothermal results.Gneiss formation related to volcano arc,suggesting that Mengjiagang iron ore formed in the tectonic environment of back-arc basin.4.The zircon U-Pb dating of the fine grained hornblende biotite feldspar gneiss in mining area,the weighted average age is 286 ±7Ma,illurstrate the crystallization age of magma is in the Early Permian,the same forming age with Meizuo ganite(259±3.6Ma)in Huanan uplift,southern Jiamusi block the Chaihe(254±5Ma),Qingshan(270±4Ma)and Chushan(256±5Ma)in Jiamusi massif.Combined with the research results and the previous chronology research in Dapandao layer,Xingdong group,suggest that iron ore deposition time for Mengjiagang is in the Neoproterozoic,in Cambrian(500Ma)metamorphism time is in the Cambrian(500Ma),and in the Permian(285±7Ma)the second time of hydrothermal superimposition is in the Permian(285±7Ma). |
PDF Full Text Request