Numerical Simulation For Structural Geometry Controls On Mineralization

The Sanshandao gold deposit is a supergiant deposit with gold resources of more than 1200 t which is located on the western side of the Jiaodong gold ore concentration area on the southeastern margin of the North China Craton.With gold reserves of more than 5000 t,the Jiaodong gold ore concentration area is china’s largest and the world’s third-largest gold concentration area.The morphology,amounts,and location of orebodies in the Sanshandao gold belt,Jiaodong Peninsula are closely related to the fault.The orebodies are mostly hosted by the fault parts with the characteristics of gentle and/or dip changing from gentle to steep.Previous researchers have conducted many studies on structural features of Sanshandao gold belt and its ore-controlling rules,but it remains unclear the stress regimes,nature and deformation of the Sanshandao fault during the mineralization period,and there is lack of quantitative understanding of the relationship between the tectonic geometry of the fault and the heterogeneous distribution of the orebodies.In this study we combined systematic data collection,tectonic production statistics,fault geometry concept modeling,three-dimensional modeling of faults and ore bodies,and numerical simulation analysis based on the fault geometry concept model and the geological model of Sanshandao gold belt to(1)identify the mechanical nature and stress regimes of the Sanshandao fault zone during the metallogenic period;(2)quantify the relationships between fault structural features and the formation and distribution of mineralization(3)discuss how the sanshandao fault geometry features controll gold metallogenesis and localization.Major results and findings of this thesis are as follows:(1)11(strike)+ 8(tendency)sets of typical geometric conceptual models on the combination of fault strike dip,bend length,tendency ducted section and bend section dip were designed and simulated under two stress backgrounds of extrusion and tension,and the simulation results show that the fault and its nearby surrounding rocks are the parts with concentrated stress and large strain,indicating that they are prone to destabilization and developmental expansion,which provide favorable space for ore-forming fluid activity and ore body filling The simulation results show that the fault and its surrounding rocks are the areas with high stress concentration and strain,indicating that they are prone to destabilization and expansion,which provide favorable space for mineralizing fluid activity and ore body filling.At the same time,the nature of tectonic stress and fault geometry jointly control the development and distribution of positive volume strain(tensional dilation)within the fault,revealing that the geometry of the structure may influence the strain development and thus control the location of the ore body.Numerical simulation results also show that abrupt changes in fault geometry(dramatic changes in strike and dip)cause abrupt changes in strain distribution,which may explain the predominant distribution of ore bodies in steeply shifting transitions.(2)A three-dimensional geological structure model of Sanshandao was constructed based on geological research data,and two stress backgrounds of NNW–SSE–oriented tectonic extrusion/extension were set for simulation.The results show that the dilation space indicated by the positive volume strain in the NNW–SSE oriented tectonic extrusion background of the Sanshandao fault zone corresponds to the actual distribution of the ore bodies,while the dilation space developed in the NNW-SSE oriented tectonic extension background corresponds to the orefree section,suggesting that the stress state of the Sanshandao gold belt during the metallogenic period may be NNW–SSE oriented extrusion.The distribution of mineralized enrichment zones in the Sanshandao Fault is controlled by the tensional dilation of the gently dipping parts caused by the recoil activity of the fault in the context of the extrusive tectonic stress.(3)Through the numerical simulation study,some new understanding of the gold mineralization law of Sanshandao gold belt has been obtained.For example,the formation and distribution of ore bodies in the Sanshandao gold belt may be mainly influenced by the morphology of the fault and the tectonic activity during the main metallogenic period,and the transformation of the regional stress field after mineralization does not significantly modify the Sanshandao fault zone and the overall distribution of gold ore;fluids in the Sanshandao fault surface mostly transport from the deep NE to the shallow SW,and in the Xinli area fluids transport from the deep SE to the shallow NW;within the Sanshandao ore belt,the SE direction in the Xinli area,the The SE direction,Sanshandao,Xiling,and the deep NE direction in the northern sea area are favorable mineralization sites,which can be the key areas for future deep exploration.Therefore,this study not only elucidates the general mineral control law of typical tectonic geometrical features and the control role of the geometrical features of the Sanshandao fault on the spatial location of ore bodies in different tectonic stress contexts,but also emphasizes the application prospects of the integrated research method of tectonic analysis+ 3D modeling + numerical simulation in the fields of mineralization process,deposit investigation,mineral control mechanism and mineralization prediction.