The Tectonic Stress Field Numerical Simulation Study Of Dachang Ore Field Tongkeng Mining Area In Guangxi

Nandan-Hechi metallogenic belt is an important non-ferrous metal metallogenic belt of China,it is located in the Nandan-Hechi metallogenic belt of Jiangnan ancient land swell southwestern margin and the edge of Youjiang regenerated geosyncline,it belongs to the composite part of Paleo-Tethy structural and the Pacific tectonic domain,the Tongkeng deposit is located in the western ore belt of Dachang tin polymetallic ore field in the middle of metallogenic belt.This paper through the field geological survey and indoor comprehensive analysis and research,use analytic method of regional tectonic geology and conjugate shear joint method and so on,to analysis stress field evolution of Tongkeng tin deposit,establish the time series of structural deformation,and use finite element method and elastic mechanics calculation to try to numerical simulation of tectonic stress field, exploring the relationship between tectonic stress field and regional structure.Through this study we achieved the following understanding:(1)Through the fold data analysis and research in Dachang Tongkeng deposit, prove that the orefield has experienced NE,NEE,NNW direction and near SN direction compressive stress.(2)Through the point stress state of each observation point reflected by the joint occurrence data in the mining area,Then according to the joint cutting relationship、the joints and the relevant structural features and regional tectonic background to divide tectonic stress field of this area into two phases:the first phase of the study area tectonic stress field is Indosinian period,σ1 direction between about 49°～64° and 229°～244°; The second phase of the study area tectonic stress field is Yanshan period,σ1 direction between about 162°～178° and 342°～358°.(3)Through summarizing the tectonic development history of the mining area,the tetonic evolution experienced NEE-SWW direction compressional effect in Indosinian period,under the stress field emerge a large number of NW oriented extrusion liner fold,reverse fault,NW direction cleavage and NE direction faults occurrence of. compression and torsion;Then under the NNW-SSE direction compression effect and nearly EW direction tension effect in Yanshan period,the early NW trending reverse faults and NE trending compression torsion faults occurrence of tension torsion,in some sections of the early faults superpose the later stage fault mud and tensile breccia,formation of near SN trending tension(torsion) faults and near EW trending folds and interlayer sliding fracture zones;besides,the nearly SN direction faults occur tension activity in the late mineralization period.(4)Tectonic stress field numerical simulation results shows that:The Indosinian stress field characteristics mainly as nearly north-south distribution.Because of in this period develop many faults in the middle of the study area and the lithology is complex,the maximum principal stress high value region is more appears in this region,at the fault or the fault occurrence change region,the minimum principal stress value is the lowest and the shear stress value is generally low;The stress field distribution in Yanshan period is more complicated than the previous period,The nearly SN direction,NNW direction and NE direction faults control the maximum,high,low stress and minimum principle stress shear stress distribution in this periods of the study area.In the fault zone,the fault occurrence change region and near the fault on both sides appear the maximum stress high value and the minimum principle stress low value area,stress high value(low value) often distributed along the fault,at the intersection of the fault corresponding to the local stress extreme value area,the shear stress features of this period more performance as relatively low value area and high value area accompanied output,and generally occur stress value gradient change along the fault trend.