成矿流体运移与就位及其构造控制机理:以胶东焦家金矿带为例

Migration and Emplacement of Ore-forming Fluids and Their Structural Controlling Mechanisms:An Example from Jiaojia Gold Belt in Jiaodong Peninsula

热液成矿系统的形成受控于构造运动引发的成矿流体运移和就位,构造是一级控矿因素,成矿流体的运移与就位则为构造控矿理论的核心。以流体压力差为主导、综合水力梯度和热传导等多种或单一主导因素驱动流体在围岩中由断层、裂隙和孔隙组成的输运通道中运移。流体在构造裂隙或孔隙中发生化学反应、流体混合和不混溶作用、流体沸腾都会导致流体物理化学性质发生变化,导致成矿物质沉淀;流体运移形式影响着矿化形式的表达,以管道流形式在宏观断层和裂隙中运移的流体以形成规模较大且矿化程度高的脉状矿体为主,而在围岩微米级裂隙和孔隙中广泛发育的渗透流多形成矿化品位稳定、规模中等的细脉-浸染状矿体。构造变形与流体压力、应力状态之间的动态耦合导致矿体的时空定位,断层阀-泵吸机制是解释造山型金成矿作用最具代表性的构造-流体耦合成矿动力学模型。胶东焦家金矿带中矿床的形成与分布受到焦家断裂带上一、二、三级断裂构造的联合控制:压剪性的焦家断裂为一级控矿构造,控制了广泛的以绢英岩化为主的热液蚀变作用和破碎带蚀变岩型金矿体的形成与就位;在其下盘张剪性的望儿山断裂为二级控矿构造,热液蚀变相对较弱,发育过渡型金矿体;三级控矿构造为以鲍李断裂为主的数十条张剪性断裂和节理系,蚀变-矿化程度最弱,主要控制石英脉型金矿体的产出。寺庄金矿床矿体三维几何学结构研究表明从I号到Ⅲ号矿体群的形态扁平程度增加,说明成矿流体输运方式由渗透流向管道流的空间演变,矿体产状差异则反映成矿流体运移方向也发生了变化。进一步研究需融合多学科方法和成果,特别是深入剖析显微-超显微变形组构与成矿流体行为耦合关系,构建逼近实际的多尺度构造-流体耦合成矿模型,揭示热液成矿系统形成的精细过程和机理。

Hydrothermal ore-forming system can be controlled by the migration and placement of ore-forming fluids induced by tectonic movement.Structure is the primary ore-controlling factor,and the migration and placement of ore-forming fluids are the core theory of tectonic ore-controlling.Multiple or single dominant fac-tors,such as fluid pressure differences,integrated hydraulic gradients,and heat conduction,drive fluid migra-tion within transport channels formed by faults,cracks,and pores in the surrounding rocks.Chemical reactions of fluids in structural cracks or pores,fluid mixing and immiscibility,and fluid boiling lead to changes in the physical and chemical properties of the fluids,resulting in the precipitation of ore-forming materials.Fluid mi-gration patterns affect the form of mineralization.Fluid migrating through macroscopic faults and fractures,re-sembling pipeline flow,primarily forms large vein ore bodies with high mineralization.However,permeation flow,which widely develops in micron-scale cracks and pores of surrounding rock,mostly forms fine veins and disseminated ore bodies with stable mineralization grade and medium scale.The dynamic coupling between tec-tonic deformation,fluid pressure,and stress state leads to the temporal and spatial occurrence of the ore body.The fault valve-pumping mechanism is the most representative tectonic-fluid coupling model to explain orogenic gold mineralization.The formation and distribution of deposits in the Jiaojia gold belt are controlled by three-or-der fault structures.The compression-shear Jiaojia fault is a first-order ore-controlling structure,which governs the extensive hydrothermal alteration dominated by sericitization and the placement of altered rock type gold ore bodies within fracture zones.The Wangershan fault,a tensile shear structure in its footwall,serves as a second-ary ore-controlling structure,where hydrothermal alteration is relatively weaker,resulting in the development transitional gold orebody.The third-order ore-controlling structure consists of dozens of tensile-shear faults and joint systems dominated by the Baoli fault,which exhibits the weakest degree of alteration and mineralization.This structure mainly controls the occurrence of quartz vein-type gold orebodies.The study of the three-dimen-sional geometry of the orebody in Sizhuang gold deposit shows that the morphological flatness of the ore-body group increase from No.I ore body to No.Ⅲore body.This indicates the spatial evolution of ore-forming fluid transport from infiltration to pipeline flow,and the differences in ore-body occurrence reflect changes in ore-forming fluid migration directions.Further research needs to integrate results from multidisciplinary studies,es-pecially conducting in-depth analysis of the coupling relationship between micro-ultra-microscopic deformation fabric and ore-forming fluid behaviors.This includes constructing a multi-scale structure-fluid coupling ore-forming model that closely mimics reality and reveals the intricate processes and mechanisms of hydrothermal ore-forming system.