The Characteristics Of Ore-Controlling Structure And Structural Evolution In Penglai Gold Deposit, Eastern Shandong

The Jiaodong peninsula is the most important gold base in China,and it is distinguished from other typical gold mining systems in the world by the“Linglong-Jiaojia type”deposit.Penglai Gold Mine is located in the southeastern Penglai City of Jiaodong Peninsula,Developing crushing altered rock type and quartz vein type gold deposits,however,the research and study are relatively weak.Fault structure is the main ore-controlling factor in the area.So it is of great significance for the study of the mining area and the exploration of the deep periphery to card ore structure characteristics,summary the laws of ore-controlling structures,and establish a structural ore control model.The paper is based on field geological surveys and mine underground observations,combining with previous research data,by compiling the ore field construction maps and indoor studies in the study area,Analyzing the characteristics of the geological structure of the mining area and the occurrence and distribution of the ore body and the rock mass.We can determine the tectonic stress field during the mineralization period,analyze mineralization,discuss the ore-controlling patterns,and restore the history of tectonic evolution in the Penglai Goldfield.The research mainly achieved the following points:?1?The Penglai gold deposit mainly developes crushing altered rock type and quartz vein type gold deposits.The former is developed within the regional first-order pressure-torsion fracture zone,such as the Xiaogujia Fault,Xilin Fault,etc.The quartz vein veins develop in the tensile and shear secondary structures of the first-order fracture,both are spatially adjacent.?2?The Penglai gold deposit mainly develops NNE,NE,NEE and NW strike structures.Most NNE,NE,and NEE strike faults form during the mineralization period,controling the shape and distribution of veins;The NW strike structure was formed after the mineralization,destructiving to the ore body,but there are also individual NW strike structure develope mineralizations.?3?The NNE and NEE strikes quartzite veins in the mining area are longer extension,more stable,and mostly controlled by the extensional shear structure.The secondary structure of the two branches is developed,with the main vein constitutes appearing"Y"or"N"shape structure;NE strikes quartzite veins are shorter extension and shallower extension,showing the ore-controlling structures are extensional;The three have a unified metallogenic age and similar mineralization characteristics.The NNE structures of mineralization period are formed by right-lateral shearing,and the NEE structures of mineralization period are formed by left-wing shearing,they are a supporting structural system formed under the same tectonic stress field as the NE extensional ore-controlling structure.By analysising the structural stress field,it is believed that the mineralization period in this area was affected by the NE^SW zone compression.?4?The fault structure affects the migration and redistribution of elements in the mineralization process.The closer to the center of the tectonic belt,the stronger the degree of altered mineralization,the content of main elements SiO₂ and Fe₂O₃increase significantly,the contents of MgO,CaO,Na₂O+K₂O,Al₂O₃,FeO,P₂O₅ and TiO₂ show different degrees of reduction;The trace elements Sr,Ba,and Th show increasing changes in the degree of depletion;The total amount of rare earth elements show a downward trend.?5?Based on the early-late relationship between the mineralization period structure and the formation of other structural traces,the structural evolution of the Penglai gold ore district is divided into three stages:pre-mineralization,metallogenic period,and post-mineralization,including the crystal base deformation,multi-phase type of rock intrusion and the formation,preservation,destruction of ore body,etc.