Geological Characteristics And Ore-controlling Factors Of Yanmen Pyrite Deposit In Jiangyou City, Sichuan Province

The Yanmen pyrite deposit is located at the northwest wing of Yangtianwo overturned/reversed syncline on the north section of Longmenshan Mountain.The NE-SW trending Longmenshan structural belt is located on the east side of the Qinghai-Tibet Plateau(or Qiangtang plate).It is located in the intersection of the Yangtze,North China,and Qiangtang plates with complicated structures.This belt is separated from the Songpan-Ganzi fold belt in the northwestern side by the Wenchuan-Maoxian-Qingchuan fault,and from the Sichuan Basin in the southeastern side by the Shuangshi-Pengguan-Majiao fault zone,forming a basin-ridge.In addition,the Longmenshan structural belt is also seperated from the nearly EW-trending Qinling orogenic belt in its northeastern side by the Mianlue suture zone and the Dabashan tectonic belt.In the southwestern side,it is connected with the Xianshuihe fissure zone,showing a Y-shaped tectonic pattern in general.Through the comprehensive collection of regional and mining geological data,the typical ore-bearing construction,pyrite,ore body rock and altered rock in the mining area were selected for macroscopic research and microscopic identification and analysis,and different types of yellow were selected.Fully chemical analysis of iron ore,in-depth study of the geological characteristics of the deposit,draw the following understanding: 1)Yanmen pyrite deposit is located in the northern section of Longmenshan Yangtian inverted diversion northwest wing,the main ore body MS1 by the lateral thrust fault Controlled by F18,in addition,the distribution direction of the 126 ore/ore deposits in the Yangtianwo Pyrite belt is almost the same as that of the Yangtianwo inverted-steering axis,and the extension direction of the ancient continental margin is the same;2)The ore-bearing surrounding rock is viewed as The thick to massive dolomitization dolomite in the second section of the second sub-group(D2gw2)of the Wushan Formation belongs to the tidal flat-lagoon environment sedimentary product mainly in the lagoon environment;3)the ore of the mining area is in massive and disseminated structures.The main ore veins,veins,breccia,strips and other ore structures are secondary;the ore structures are mainly gel-like,it is granular,followed by semi-self-shaped granular structures;4)there are three distributions in the mining area.Orebody,MS1,MS2,MS3,mainly as a layered,lenticular output,controlled by the strata.In addition,through the study of the spatial distribution and variation law of the main ore body(MS1),it was found that the MS1 ore body has reduced extension stability from the northeast to the southwest,and the thickness gradually decreases or even tapers out.MS1 ore body thickness The overall extension is more stable in the longitudinal direction.5)Metal minerals in ore are mainly pyrite.Occasionally,a small amount of white iron ore and sphalerite are found.The gangue minerals are mainly dolomite,followed by a small amount of shaly,organic carbon and quartz;6)the mining area The wall rock alterations are generally weaker,mainly including dolomitization,serpentinization,and a small amount of silicification.7)The deposits are multistage mineralization products and can be initially divided into three metallogenic phases,which are diagenesis and mineralization periods and post-generation heat.Liquid superposition transformation into mineralization and epigenetic period.According to the deposits and characteristics of the ore body in the mining area,some information on the genesis of the deposits obtained from the structure and structure of the pyrite ore,combined with the sulfur/ isotope ratio and the Co/Ni ratio of the pyrite,and the typical sulfur at home and abroad The comparative study of iron ore deposits preliminarily believed that the origin of the Yanmen pyrite deposit is a sedimentary-hydrothermal modified type deposit.The rough formation process is the initial enrichment of minerals formed in the diagenetic process,the formation of a poor ore-bearing strata,and later hydrothermal fluids.Extracting and transporting to favorable lithology and structural sites for metasomatism or filling methods to form minerals,such as stratum or structural weaknesses,and traps or baffles are dominated by filling methods,followed by metasomatism;and where fractures are not developed The main method of metasomatism is that the minerals are enriched in the surrounding rock that formed first,resulting in mineralization of the whole rock.Combined with the comprehensive analysis of ore controlling factors such as rock lithology,lithofacies palaeogeography and structure in mining area,it is clear that ore prospecting marks in mining area are mineralized outcrop and wall rock alteration in mining area.The prospecting direction is the lithofacies palaeogeographic condition,the second subgroup of the Wan Shan formation and the ore controlling structure,which is of certain guiding significance for the next step of the pyrite prospecting in this area.