Relationship Between Ductile Shear Zone And Tin Mineralization In Jiuwandashan Area,Northern Guangxi

The Jiuwandashan area in the north of Guangxi is located in the hinterland of the South China continent.The geotectonic position belongs to the southwestern section of the Yangtze and Huaxia block collage belt(Jiangnan orogenic belt).The geological structure of this area is complex and the tectonic movement is frequent.It is an important tin-polymetallic ore-forming area in the southern margin of the Yangtze platform in the South China continent.Based on the previous research results and the measured field geological profile,this paper takes the Jiufeng tin mine in the Jiuwan Dashan area of northern Guangxi as the research object,using magnetic fabric,electron backscatter diffraction(EBSD),hydrothermal zircon geochronology,The ore elemental analysis and elemental correlation analysis to study the geometry,kinematics,dynamics and chronological characteristics of the ductile shear zone in the Jiufeng tin area of the Jiuwanshan area,northern Guangxi,and to explore the mineralization relationship between the ductile shear structure and tin deposits.The main achievements are as follows:Jiufeng ductile shear zone is mainly distributed in the Wentong Formation,the Yuxi Formation and the mafic-ultramafic rocks in the Sibao Group.The ductile shear structure generally follows NNE and tends to SEE.The overall width is about 500 m,and the length is about 1000 m,extending beyond the mine from south to north.According to the magnetic anisotropy,the ductile shear zone of the whole mine can be divided into eight ductile deformation zones and nine weak ductile deformation zones.The kinematics and dynamics of the ductile shear zone in Jiufeng mining area indicated that the ductile shear structure activities occurred at least twice.In the early stage,the activity is affected by the compressive stress of NE-SW and the right-lateral shear sliding occurs;in the late stage,it is subjected to the SEE-NWW direction of the compressive stress,and the left-lateral thrust shear sliding occurs.It is shown that the ductile shear deformation age of Jiufeng ductile shear zone of Guibei is Caledonian period(440 Ma),and then it was reformed by tectonic activities of Hercynian,Indosinian and Yanshanian periods.The U-Pb dating of the ore samples from the Jiufeng mining area indicating that the metallogenic age of the Jiufeng tin mine was 834.5±5.3 Ma.The age of cassiterite mineralization is inconsistent with the age of tectonic deformation,indicating that the ductile shear structure is a post-metallogenic structure of the Jiufeng tin deposit,not a mineralization period structure.The Jiufeng ductile shear zone and the Jiufeng tin mine are in the same spatial position,but the extension directions are not exactly the same.The tin ore extends in the SN direction,while the ductile shear zone extends in the NNE direction.The correlation between the P value of the magnetic anisotropy and the Sn element in the mining area is analyzed.The results show that the correlation between the enrichment of Sn element and the ductile deformation is weak(correlation coefficient is 0.08?0.48).The study on the mineralization relationship between the Jiufeng ductile shear zone and the tin deposit shows that the Jiufeng tin deposit was formed in the Sibao period(834.5±5.3Ma).and then in the ductile shear deformation process during Caledonian period(440 Ma±),the early cassiterite mineral particles are ground and refined,and later tectonic activities further enrich the fine granulated cassiterite along the early structural fractures.