个旧锡矿锡石的矿物学研究

Mineralogical Study of Cassiterite Grains from the Gejiu Tin Deposit

对个旧锡矿床的块状硫化物型、电气石细脉带型、含锡白云岩型、层间氧化矿型矿床中的锡石晶体运用扫描电镜、阴极发光成像技术、X-射线粉晶衍射、电子探针等试验开展了矿物学的系统研究。结果表明从块状硫化物型→电气石细脉带型→含锡白云岩型→层间氧化矿型矿床中的锡石有如下特征或变化规律:1颗粒体积依次变小。2深色的锡石到浅色锡石晶胞参数变大,c∶a值变小。3锡石晶体单型组合共有7种,单型从{111}锥面发育逐渐向{110}柱面发育。4锡石内部环带从均匀发育到不发育。以上特征均指示了4种矿床类型中锡石的形成温度依次降低。根据CL阴极发光下锡石亮度的差异,判断块状硫化物型、电气石细脉带型、含锡白云岩型矿床中锡石存在2个形成期次,认为此3类矿床在早阶段高温热液流体活动与早期锡石结晶作用有关,晚阶段低温热液流体活动与晚期锡石结晶作用有关。而层间氧化矿型矿床中的锡石具备悬浮在流体中生成的特征,可能为被流体搬运沉积形成,认为此矿床为重泥质沉积成因。

Through using scanning electron microscope, cathodoluminescence imaging, X-ray powder diffraction and electronic probe test, the mineralogy characteristics of various cassiterite crystals from the Gejiu tin deposit have been studies systematically in this paper, and their ore types include massive sulfide type, tourmaline veinlet belt type, tin dolomite, interlayer oxidized ore. The following conclusions have been drawn： ①the cassiterite particles from these four types of ore are progressively smaller.②The cell parameters become larger from brunet cassiterite to light-colored ones, and their c. a value change smaller. ③There are seven types of monotype combination for cassiterite crystal, and their monotype are developed from { 111 } cone to { 110} cylinder gradually. ④The internal bands of Cassiterite are changed from uniform development to nonuniform ones. The features mentioned above show that the temperatures for the formation of these cassiterites with four types are reducing successively. According to the luminance differenceof cassiterite under CL cathodoluminescence, it＇s found that two forming periods existed in the cassiterite ore of massive sulfide type, tourmaline veinlet belt and tin dolomite. Thus, it＇s be- lieved that the high temperature hydrothermal fluid activity of the cassiterite deposits with these three types is associated with early cassiterite crystallization in the early stage, but the low tem- perature hydrothermal fluid activity is associated with late cassiterite crystallization in the late stage. It＇s thought that the genesis of ore deposit is oriented argillaceous sedimentary origin, such as interlayer oxidized cassiterite deposit was generated in the suspended in a fluid and might be formed by fluid transportation and deposition.