| The tin-polymetallic ore field of Dachang in Guangxi is located in the central part of the Danchi metallogenic belt,in the complex area of Pacific Ocean the Himalayan tectonic field of Paleo-Tethys,on the southwest margin of the Jiangnan old land,in the fault depression basin of the Hercynian-Indosinian passive continental margin Basin.Previous studies have been carried out on ore deposits,ore-controlling factors and metallogenic models of the ore field,but the research on the structure of ore field is weak.Based on the detailed investigation of structure traces distributed in the surface and the roadways in the Dachang mine field,this paper learns from the collected borehole datas and the previous research results,uses the structural analysis software and Win-tensor software to analyze the folds,faults and the conjugate joints in the Devonian sedimentary stratum and reveals its tectonic deformation characteristic.The Devonian strata is the first platform sedimentary covering after the return of the Caledonian Geosyncline.This paper summarizes the tectonic evolution of the area from the deposition base and the Devonian cap layer respectively,and uses the recovering technique of the balanced section to operate the inversion of the Devonian tectonic profiles in Dachang ore field,analyze the tectonic movement characteristics and evolution process of ore field quantitatively.The main results and cognitions are as follows:1.The strata exposed are Devonian,Carboniferous,Permian and Triassic in the ore field,and the Devonian strata distributes the most widely.The basic tectonic pattern is chess-board structure divided by NNW complex fold-fault zone consisting of thrusting faults and compact folds,NE fractures,SN fractures and EW folds.2.After analyzing structural features of the folds,faults and conjugate joints in the study area,it can be drawed that the ore field was squeezed from NE,NNW,near SN,NWW,NNE direction in the geological history.According to this result,two different periods of deformation are divided.Among them,the NW linear folds,thrust faults,shear joints were produced in the crushing environment of the Indosinian period;The interbedded tectonic zone,the stone sausage structure,the north-east and north-south tension joints and the near-east-west folds are produced in Regional stretch environment of Yanshan period.3.Through the balance profile restoration of the four structural sections in Dachang orefield,the evolution process of Dachang ore field is obtained during the deposition of the Nabiao group to the Tongchejiang group in the Devonian.That is,the entire field where the ore field lied in is subjected to the north-east squeezing force,so that it is in a state of contraction for a long time.This stage and stretching stage during the deposition of the Lianhuashan group to the Tangding group,the smooth deposition stage of Nabiao group were called the three steps of the Devonian strata evolution in Dachang Ore.It were called three-step step of the evolution of the Devonian strata in Dachang orefield.In other words,the study area undergoes a spiraling process from motion to stability to movement. |
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