Numerical Simulation Of Tectonic Stress Field In Guanfang Copper Mine In Western Yunna

The Yunxian-Jinggu volcanic arc belt is located in the closed position of the Paleo-Tethys Ocean.With the eruption of magma,a large number of ore-forming elements are brought from the deep,and many deposits(points)are formed in the arc volcanic rocks.Guanfang copper deposit in western Yunnan is located in the northern section of Yunxian-Jinggu volcanic arc belt.It is the largest and most representative basalt copper deposit in the copper polymetallic deposits(spots)in the area.Through field geological survey and indoor comprehensive research,this paper uses regional tectonic analysis method,fault structure analysis method,joint analysis method,conjugate shear joint method,etc.,to determine the principal stress direction of tectonic activity in different periods of Guanfang copper mining area.Combined with structural deformation characteristics,cutting relationship evidence and magmatic activity,the evolution process of tectonic stress field in the study area is analyzed.The finite element method is used to simulate the tectonic stress field,and the relationship between tectonic activity and stress field in the area is explored according to the simulation results.This study mainly achieved the following understanding :(1)According to the structural deformation characteristics of the fault and the conjugate relationship of the joints,it is judged that the Guanfang copper mine area has been subjected to principal compressive stress in at least four directions since the Indosinian period : near EW direction(82° ～ 109°),near SN direction(353° ～ 0 ～12°),NE-SW direction(30 ° ～ 70 °)and NW-SE direction(305° ～ 345°).Combined with the evidence of regional tectonic background,fault dislocation relationship and magmatic activity,the order of variation of the maximum principal compressive stress σ1 direction is determined : the first stage is near EW direction → the second stage is near EW direction → the third stage is NE-SW direction → the fourth stage is NW-SE direction,which corresponds to the period before Indosinian period(>250Ma)→ Indosinian period(250 ～ 222Ma)→ early Yanshanian period(222 ～208Ma)→ middle and late Yanshanian period(208 ～ 65Ma).(2)Through the division of the direction and period of the maximum principal compressive stress in the study area,the tectonic stress field and the history of tectonic development in the area are restored and inverted.It is judged that the tectonic evolution of the Guanfang copper mine area has experienced four periods and four stages :(1)Before the Indosinian period(> 250Ma),the Lancang River plate and the Simao block collided and closed before the stage;(2)Indosinian period(250 ～ 222Ma),the collision closure stage of Lancangjiang oceanic plate and Simao block;(3)Early Yanshanian(222 ～ 208Ma),stage I after the collision and closure of Cangjiang oceanic plate and Simao block;(4)In the middle and late Yanshan period(208 ～ 65Ma),after the collision and closure of Lancangjiang oceanic plate and Simao block,stage II.(3)The results of numerical simulation of stress field show that before the Indosinian period,the high value area of the maximum principal stress is generally distributed along the fault strike in the EW direction.The high value area of minimum principal stress is distributed at the intersection of near EW fault and western boundary and the turning point of fault strike change.During the Indosinian period,the high value areas of the maximum and minimum principal stresses were distributed at the intersection of near EW-trending faults and near SN-trending faults and the turning points where the fault strike changed.In the early Yanshan period,the high value areas of the maximum and minimum principal stresses are mainly distributed near the faults and the intersection of faults.In the middle and late Yanshan period,the high value area of the maximum principal stress is concentrated in the intersection of near NE faults and NW,EW and SN faults.The high value area of minimum principal stress is concentrated in the NE fault and the intersection of NE and NW faults.The distribution characteristics of the maximum and minimum principal compressive stress in the area show that the intersection of the four groups of faults(near EW,near SN,NW and NE faults)is a concentrated area with high stress values.Combined with the evolution process of tectonic stress field in the area,it is found that the distribution characteristics of tectonic stress in each period are obviously correlated with the development of faults.The tectonic activity is very strong in the location where the fault strike changes and the intersection of the four groups of faults.The earlier the fault is formed,the more times the stress superposition effect is,and the greater the influence of stress on its development characteristics.(4)According to the results of the numerical simulation of the stress field,the parts with strong tectonic activity in the area can be determined.The strong tectonic activity provides a favorable space for the migration and precipitation of hydrothermal fluid.Based on this,10 positions with better metallogenic potential are delineated in the Guanfang copper deposit.