Ore-controlling Model Of The Jiaojia Gold Belt,Shandong Province,China

Jiaodong has been not only world's important gold producer area,but also China's top gold resource district,especially the Jiaojia gold belt has been proven more than 1000 t gold resources.Those gold deposits(ore bodies)are strictly controlled by the second-order faults(fractures)in the footwall of the Jiaojia fault zone,therefore orecontrolling structural model became the key point to study in depth for the gold mineralization.This paper focus on the typical cross section of these gold deposits,mapping the detailed of their structural-alteration-mineralization networks,analyzing the architecture of the Jiaojia fault zone by outcrop scale,using in-situ microanalytical testing techniques for gold bearing pyrite and 3D finite element simulations method.We systematically analyzes the relationship between the distribution of gold deposits(orebodies)and those different orders,sequences and types of the ore-controlling structures in the diversity scale varying from regional scale,outcrop scale to mineral scale.In order to reveal the rule of ore controlling structures and the mechanism of structural control on the massive gold activation and enrichment.Thus establishing the ore-controlling structural model that could provide the theoretical basis for the new arrangement of prospecting in the Jiaojia gold belt.The results and highlights of this paper are listed as below(1)The detailed architecture of the Jiaojia fault zone can be divided into fault core(fault plane,fault gouge,schistositized and mylonitized zone),damage zone(cataclastic rock,Tectonic hydrothermal vein,concentrated joints and cleavages zone)and weak deformation zone(sparse joints zone).(2)Jiaojia fault zone went through five deformation stages.D1 is NE trending ductile shear zone before mineralization by compression.D2 is ductile to brittle deformation by activation of preexisting structures before mineralization.D3 is ductile to brittle deformation during gold mineralization(accompanying intensive fluid rock interaction and large scale gold metallogenic events).D4 is brittle deformation during gold mineralization,which is presenting as brittle fractures and tectonic hydrothermal veins(such as sulfide veins and few calcite veins).D5 is brittle deformation after mineralization.(3)It has been recognized four types of pyrite in the Jiaojia gold belt.These pyrites often occurred with visible gold which is mainly filled in the fractures across the pyrite crystal or between two crystals,and few visible gold occur as inclusion in the pyrite,even some nanoparticle gold among dislocation of pyrite probability formed by the gold mobilization during the deformation.(4)The striation of slickenside indicates that the complicated kinematic and dynamic features of the Jiaojia fault,which could be a nomal fault or a reverse fault even having a bit strike-slip component.It is showing that the ore-controlling structural model is mainly transtension during the mineralization(NW extension and with sinistral strike-slip component),resulting from the reactivation of the pre-existing deformation traces by the stress field during gold mineralization.The 3D finite element simulation of the Jiaojia gold belt showing that the high value areas of main stress and shear stress before mineralization are the potential position for the concentration of gold bearing fluid and precipitation of ore,accompanying the structural reactivation and strain energy release.