Early Precambrian Tectonic Evolution And Uranium Mineralization In Lianshanguan Area,Eastern Liaoning Province

The Lianshanguan area locates in the eastern Liaoning uranium metallogenic belt,belonging to the uranium metallogenetic province in the North China Craton,and it therefore become an important window to reveal the Precambrian tectonic evolution and mineralization.The previously discovered uranium deposits(or points)are well developed along the Lianshanguan ductile shear zone.Recently,the studies on the genesis of uranium deposits in the Lianshanguan area are still controversial.Particularly,there is a lack of in-depth and detailed study on the ore control of shear zone,as well as the relationship between basic rocks and uranium deposits is unclear.In order to solve the above problems,this study focuses on the typical uranium deposits,peripheral ductile shear zones and basic rocks,to carry out the petrography,geochemistry,zircon U-Pb isotopic chronology,etc.,and to discusses the control of the main geological units of the early Precambrian on uranium deposits,to improve the uranium metallogenic model in this area and enrich the metallogenic mechanism of orogenic belt.The study puts forward a new idea for the uranium prospecting in the future.Main conclusions of our study are listed below:1.The Lianshanguan granitic body underwent three stages of structural deformation.The first stage deformation was characterized by uplift of the Lianshanguan granitic rocks and bedding detachment of the overlying the Liaohe Group.The second stage deformation was represented by north-south compression,resulting in strong ductile shearing deformation along the southern edge of the granitic body between the contact zone of the Liaohe Group.The third stage was NW trending compression deformation,forming NE to NEE trending brittle faults.The strain type of dextral ductile shear zone in the southern margin of the Lianshanguan granitic body is characterized by flattened strain,which belongs to the general compression plane strain.The K value of Flinn index is between 0.19 and 0.69,indicating that the rock is S/SL type taconite.The uranium ore bodies in the study area are all concealed blind ore bodies,which mainly occurs in the core of anticline fold formed by dextral ductile shear along the contact zone between the Lianshanguan granitic body and the Liaohe Group,and are closely related to NEE trending faults.2.The Lianshanguan granite complex is dominated by potassic migmatite,with a small amount of early sodic granite gneiss residues,Anshan Group residues,and gray white re-melting migmatite at the edge.The spectrum of zircon U-Pb ages show that the peak ages are 1760?1940Ma,?2275Ma,2500Ma.Among them,?2500Ma age represents the main formation age of the Lianshanguan pluton,which indicates an important event of continental cratonization and crustal differentiation;?2275Ma peak age represents the first stage re-melting event of basement rocks in the Lianshanguan area;1780?1990Ma peak age represents the strong re-melting of basement rocks under the action of Luliang movement,which may be beneficial to uranium enrichment,consistent with the formation age of the Lianshanguan uranium deposit.3.In the study area,the alteration of country rocks are strong with obvious hydrothermal activity.There are many types of the rock alterations in the investigated rocks,for example,hydromicazation,pyritization,chloritization,hematitization,zoisitization,carbonatation and silication.Uranium mineralization is closely related to chloritization and hematization,and brown hematization after chlorite alteration is significantly related to uranium mineralization.4.There are four type anatexites of the ore-hosting rock,which are characterized by the high silica content and the various content of chlorite.Moreover,there is a negative correlativity relationship between quartz and chlorite contents.The major element characteristics show that it contains high Si O₂,Na₂O and K₂O,with slightly high Al₂O₃and low Mg O and Ca O;meanwhile,the trace element show the enrichment of Be,Mo,Pb,Y,Ba,La,Cu and depletion of Co,Ni,Zn,Cr,Ti,V.The studies significantly demonstrate that Pb,Mo,V,Be as the paragenetic elements are also closely related to Uranium resources.The samples of rare-earth elements with remarkable Eu negative anomaly are enriched in LREE(light rare earth elements)and depleted in HREE(heavy rare earth elements).5.The basic rocks in the deep part of the borehole are mainly metadiabase and sillite,furthermore,the major element characteristics show that they are peraluminous,with equivalent content of Na₂O and K₂O,and belong to alkaline peralkaline series.The basic rocks are characterized by enriched in LREE(light rare earth elements)and depleted in HREE(heavy rare earth elements)with negative Eu anomaly and weak negative Ce anomaly,meanwhile,they also have enrichment of Ba,La,Zr,Hf and depletion of U,K,P,Ti.According to the geochemical characters,the basic rocks investigated belong to intraplate alkaline basalts,formed in the tectonic environment of extension environment after continental collision.There is crustal contamination in the process of magma upwelling,and the source area of the basic rocks is transitional mantle.Significantly,the ductile shear zone developed in the southern margin of the Lianshanguan granitic body and the associated tensile fracture provide space for the emplacement of basic rock.Moreover,the basic rocks provide heat source,mineralizer and some ore-forming fluids for uranium mineralization.6.The comprehensive analysis shows that the NW dextral ductile shear zone in the south margin of the Lianshanguan granitic body is a first-order ore controlling structure,which is the channel of hydrothermal migration of uranium deposits in the area,while the late NEE trending faults at the edge of the shear zone are the storage space of uranium deposits.Meanwhile,the uranium may be derived from Archean weathering crust and migrated and enriched under the comprehensive factors of large-scale ductile shear(providing hydrothermal migration pathway)and basic rocks intrusion(providing heat source and reducing agent).Combined with the uranium metallogenic model,it indicates that the intersection of the uplift and the NE trending fault in the Liaohe Group coverage area in the south of the Lianshanguan pluton can be used as the next key prospecting targets.