胶东黄铁矿显微构造变形与金富集关系：黄铁矿EBSD组构和地球化学约束

载金黄铁矿显微构造变形与金富集关系可以从显微-超显微尺度揭示金成矿作用和地质过程,探讨金的再活化或再聚集作用。在胶东焦家金矿带成矿期识别出4种类型的黄铁矿,文章应用光学显微镜、扫描电镜(SEM)、透射电镜(TEM)、电子背散射衍射(EBSD)和电子探针(EMPA)等技术方法,探讨黄铁矿显微构造特征、超微观结构与金的富集关系。结果显示:载金黄铁矿均不发育环带,其中w(Fe)为45.70%～46.85%,w(S)为52.57%～53.37%;显微构造变形既有脆性变形又有塑性变形;黄铁矿晶体优选方位(CPO)主要表现为平行于晶轴极密和复杂极密;黄铁矿晶格间距为0.58 nm,主要发育刃位错。焦家金矿带在金成矿作用过程中,可见金集合体经历了从复杂的纳米尺度到宏观尺度矿物载体富集的过程,包括成矿流体中金络合物、金-铋-硫族化合物富集等化学结构变化过程和纳米金、载金黄铁矿纳米颗粒、岩矿石显微-超显微构造微环境变化过程。因此,不同类型载金黄铁矿CPO受到化学结构变化和显微-超显微变形微环境变化的联合制约,间接反映出载金黄铁矿中金的富集与黄铁矿内部变形、表面形貌和结构缺陷有密切关系。

Genetic relationship between micro-deformation and gold enrichment of goldbearing pyrite in Jiaodong:Constraint from EBSD fabrics and geochemistry

The genetic relationship between the microstructural deformation of gold-bearing pyrite and gold enrichment could reveal gold mineralization and geological processes with microscopic-ultramicroscopic vision and constrain the remobilization or re-accumulation process of gold. The authors distinguished 4 types of gold-bearing pyrites in the large-superlarge Jiaojia gold ore belt in Jiaodong and, by applying optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), electron backscattered diffraction (EBSD) and electron probe micro-analyzer (EMPA) methods, investigated the characteristics of microstructures of pyrite and their relationship with gold enrichment. The result shows that gold bearing pyrite has no zonal texture with w(Fe) being 45.70%~46.85% and w(S) being 52.57%~53.37%. It suffered from both brittle deformation and plastic deformation for microstructure. The crystal preferred orientation (CPO) is mainly characterized by parallel arrangement of the crystal axes and extreme complex. The crystal lattice of pyrite is 0.58 nm, and edge dislocations are well developed. Gold mineralization features in the Jiaojia gold ore belt show that the visible gold cluster has experienced an enrichment process from nano-micron scale to macro scale mineral concentration, including chemical-structural variation from gold complex in ore-forming fluid to Au-Bi-chalcogenide enrichment, and micro-and ultral-microstructure of ore rock in local environment by nanogold and nanopartitcle of gold bearing pyrite. The gold enrichment can be divided into two types:one is the gold complex enrichment in the process of ore-forming fluid migration and the other is ultrastructural deformation enrichment of nano-gold and gold bearing nanoparticles of solid phase. Therefore, different types CPO of gold-bearing pyrite are controlled by chemical-structural variation combined with micro-and ultra-microstructure deformation variation in local environment, indicating that gold re-enrichment has an affinity to ultra-microstructures deformation and surface topography as well as structural defect of pyrite.