Ore-controlling Structural Model Of The Pinglidian Gold Deposit,Northwest Jiaodong Peninsula,China

Jiaodong gold concentration area is a very important gold producing area in the world.It is also the area with the largest proven gold reserves in China.Jiaojia fault is a very important ore-controlling fault in Northwest Jiaodong.The Pinglidian gold deposit studied in this paper is a quartz vein type gold deposit which is considered to be located in the southern margin of Jiaojia fault.However,it is obviously different from most of the deposits affected by Jiaojia fault control because it mainly occurs in Jiaodong metamorphic group,and its ore-controlling structure has little correlation with Jiaojia fault.The spatial framework of Pinglidian gold deposit is constructed by means of in-situ attitude measurement,profile mapping,outcrop and microscopic structural observation and structural analysis combined with 3D finite element numerical simulation.The spatial relationship of ore-controlling structures at different scales is analyzed to explore the structural ore-controlling model of Pinglidian gold deposit.The main conclusions are as follows:Pinglidian gold deposit is located in the South extension of Jiaojia fault and occurs in metamorphic rocks of Jiaodong Group.The surrounding rocks are single.The orebodies are stratified and nearly parallel in layers.The ore-bearing quartz veins are filled along both sides of the earlier quartz veins without ore.The north and south ends of the orebody are affected by tectonic superposition and the occurrence changes greatly.Tectonic activities in the mineralization process can be divided into four stages:D1 stage is formed by regional metamorphism and deformation in the mining area,basement folds dominated by ductile deformation and weak interlayer zones such as biotite and Muscovite?vein?zones in the stratum,with obvious mineral orientation.The structural weak zone formed before mineralization is the main controlling factor of the shape and occurrence position of Pinglidian quartz vein orebody.In the early stage of mineralization,the compressive shear changed into tensional shear.The brittle-ductile structural deformation caused by underground uplift resulted in gentle folds,and the normal fault slip occurred between strata,forming a series of ore-hosting structures in the structural weak zone.D3 stage is the late stage of mineralization,which is influenced by NNW-NW compressive force.Structural superimposition of the previous folds resulted in strong structural deformation of the northern and southern margins of the orebody,deformation of the flanks of the folds to the outer end and reverse fault activity at the junction end,which resulted in the superimposition and thickening of the veins.D4 stage is NW-oriented,NE-oriented right-lateral tensional normal fault activity,obviously dislocated quartz vein orebody,fault spacing ranging from 10 cm to several meters.Pinglidian gold deposit occurs in Jiaodong Group,and its spatial distribution is obviously affected by folding tectonics.The Pinglidian gold deposit was affected by uplift and NNW-NW compression before and after the metallogenic period.Fold superimposition occurred in the region,and fault activity occurred in the area with strong activity.Finite element numerical simulation shows that the stress concentration of ?₃??₃ on both flanks of folds and ?₁??₁ on both ends of folds in the stress-strain field of the deposit.It shows that tensional space is easier to be generated in the middle of both ends of fold,which is beneficial to enrichment of ore-forming fluids.In the deformation field,the north and south ends of the fold are deformed greatly.During the two-stage fold superimposition,reverse faults are easy to occur and vein superimposition is formed.Through the Z and Y sections in the simulation,it can be seen that the orebody is on the wing of the fold,and the simulation results are similar to the actual situation of the vein body.It is easy to mineralize in the middle of the vein body,and the north and south ends are farther away from the axis.