Structural Hydrodynamics Of Metallogenesis Of Gold Deposits In Northwestern Jiaodong,Eastern China

Jiaodong is not only the largest gold producing area in China,but also the research hotspot of global gold mineralization.Northwestern Jiaodong owns about 80%of gold reserves in Jiaodong gold province,its formation is strictly controlled by the structural hydrodynamics of fault system,and gold deposits cluster in space and time.However,there is a lack of research on the mechanism of structure-fluid coupling on mineralization.Focus on the scientific problem of the cluster mechanism,this paper uses multi-disciplinary methods and technologies to carry out systematic research on the structure-fluid coupling mineralization dynamics,finally access the following conclusions:1.Through systematic regional-deposit scale investigation and comprehensive analysis,the framework of ore controling fault zone is identified,and its evolution history are determined,and it is found that the formation and evolution of is identified,is related to the late Mesozoic extension and the tectonic regime in Jiaodong area,which has a typical three-layer structure of metamorphic core complex.Linglong granite was emplaced at about 166?149Ma,then rapidly cooled and exhaled along the detachment fault.Early gold mineralization occurred in the brittle-ductile transition zone of the detachment fault at about 130Ma.The main gold mineralization event at about 120Ma developed in the superposition of brittle deformation and hydrothermal alteration overprinting the brittle-ductile structural transition zone of the detachment fault.Large-super large gold deposits are controlled by regional fault zones,middle-small old deposits are controlled by scendary fault zones.The gold deposits share similar mineralization characteristics and are controlled by the same tectonic regime.Large scale gold mineralization is controlled by the process of the switchover from a compressional to extensional tectonic regime.2.On the basis of clarifying the framework and kinematic properties of the ore controlling fault zone,a three-dimensional finite element model of the fault zone is established to conduct structural stress transfer modelling,it is figured that the area of high permeability caused by structural activity in the fault zone is distributed in the specific part of the fault zone,which leads to the rule of spatial clustering of gold deposits.There are 28 areas of increasing Coulomb Failure Stress in Jiaojia gold field,and they are coupling with the spatial distribution of explored gold deposits.The empirical formula of gold metal amount(Q)and Coulomb fracture stress(? CFS)is obtained:Q=4.526 x?CFS-83.27.The basement structure in Jiaojia gold field had dextral strike slip activity during mineralization period,and had an effect on the change of regional Coulomb Failure Stress3.In the mineralization system of northwestern Jiaodong,alternation rock type gold ore bodies develop in the footwall of the main fault and quartz vein type gold ore bodies develop in secondary structures away from the main fault.Through the digital analysis and simulation of the gold ore body shape by the structural wireframe,the different geometric characteristics of the two kinds of gold ore bodies are obtained:the alternation rock type gold ore body has a larger U/V value,which can reach 17.54198,the migration of ore-forming fluid has the characteristics of tube flow;the quartz vein type gold ore body has a lower W value,which can as low as 0.718787,and the permeability of surrounding rock is lower.The ore body in the same deposit has the trend of evolution from No.1 alternation rock type oblate ore body to No.3 quartz vein type more flat ore body.According to the combination of geostatistics semi-variogram analysis and ore controlling structure analysis,No.1 ore bodies in Sizhuang gold deposit is generally plunge to SW 200°,No.3 ore body group and high-grade ore shoot plunge to NE 48°;the migration mode and orientation of ore-forming fluid between different ore bodies have changed,and No.1 ore bodies plunging to SW is formed during the sinistral-reverse fault movement in the early stage of mineralization in Jiaojia fault zone;the dextral-normal fault movement during the late stage of mineralization,lead to the formation of No.? ore bodies,which resulted in the superposition of mineralization in ore body I and the formation of NE plunging ore shoots.4.The parameter indicting permeability and microporosity of different parts of the fault zone in the footwall of Jiaojia fault were obtained by the recognition and analysis of micro image pore(particle)and fracture image and the statistics of macro network vein density.It is revealed that the alteration rock type gold ore bodies have the characteristics of high permeability(1×10-16m2?4×10-16m2),high porosity(46%?69%),while quartz-vein type gold ore bodies have the characteristics of high permeability(2x 10-16m2?4.2×10-15m2),low porosity(19%?21%).The differences of permeability and microporosity of different mineralized types lead to different pathway of fluid migration in different ore bodies.Fluid migration in alternation rock type ore bodies is highly efficient in the form of tube flow.5.By analysing of the process of structure-fluid coupling mineralization process,we figured out that after the Linglong granite emplaced and before it cooled to the surrounding rock temperature,the ductile tectonic activity and temperature gradient drove the fluid directional migration,and early gold mineralization developed in the brittle-ductile transition zone of the detachment fault in about 130Ma.while the main driving force of ore-forming fluid migration comes from regional tectonic stress field and fluid potential difference caused by brittle activity of fault zone during the large-scale gold mineralization event in about 120Ma.Sanshandao,Jiaojia and Zhaoping fault zone provides the channel and driving force for the migration of ore-forming fluid.In the damage zone in the footwall of the main fault zone,the ore-forming fluid reacts with the surrounding rock to form the alternation rock type ore body.In the high angle extensional fracture in the footwall far away from the main fault,the hydrothermal fluid filled and precipitated to form the quartz vein type ore body.