热液矿床矿物微形貌与晶体生长环境研究

应用高分辨率扫描隧道显微镜(STM)和场效应扫描电镜(FEG SEM),对取自山西义兴寨金矿等4处热液矿床的黄铁矿、方铅矿、赤铁矿等矿物的表面生长微形貌进行了观察研究,并与实验合成的黄铁矿、方铅矿等矿物的微形貌特征进行对比。发现了自然矿物结晶三维成核成因的黄铁矿微球状晶,在合成和自然矿物的晶面观察到漏斗状晶和胞状结构等生长形貌。合成黄铁矿表面发育平整光滑的生长台阶,反映静态无扰动、接近平衡的晶体生长环境;而大量产于热液矿床的黄铁矿、方铅矿等晶体普遍发育胞状或拉长的胞状结构表面,并总体呈台阶状排列的表面结构,证明自然成矿热液体系的高过饱和度和流动生长环境。研究表明,热液成矿过程中矿物结晶作用有从成核、台阶状晶体生长、到形成“平衡”多面体生长的一个演化过程;形成于复杂条件的矿物晶体表面微观结构,包含丰富的成矿环境信息。

The surface micromorphology of minerals in hydrothermal ore deposits and growth environments of crystal

The surface growth micromorphology of some sulfide minerals in hydrothermal deposits has been observed by means of STM and SEM at nano-scale resolution. For comparison, the surface structures of a set of artificial pyrite and galena crystals have also been studied. It was discovered that on the surface of some natural pyrite pisolitic hillock micromorphology was developed, which shows a natural 3-dimensional nucleation. In addition, on the crystal surface of both natural and artificial minerals, funnel-shaped crystals and pustular-shaped (cellular) growth hillocks were observed. The level and smooth growth steps on the artificial pyrite surface imply a static crystallization environment, without disturbance and nearly in equilibrium. At the same time, a great number of pustular-shaped structures and stretched pustular-shaped growth hillocks developed on the crystal surface of hydrothermal sulfide minerals indicate the high super-saturation of the ore-formation system. The present study reveals that mineral crystallization during the hydrothermal ore-formation characteristically evolved in three stages: (1) 3-dimensional nucleation, (2)step growth, and (3)equilibrium polyhedron; correspondingly the surface micromorphology evolved from pisolitic hillock, to pustular and finally to the growth steps with smooth surface. Therefore, the mineral surface microstructures formed in complex geological environments bear rich information on the thermodynamic and dynamic conditions of the ore-formation.