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本文对淘锡坑锡矿床的含矿石英脉中的锡石晶体开展了晶体形态学和地球化学的系统研究。按晶面组合特征,淘锡坑锡矿床中的锡石可分为三种类型:由{111}锥面+{110}柱面共2个单形构成的A型锡石、由{111}锥面+{110}柱面+{100}柱面共3个单形构成的B型锡石和由{111}锥面+{101}锥面+{110}柱面+{100}柱面共4个单形构成的C型锡石。综合各种锡石晶型与结晶条件的资料分析,本文推测A型、B型锡石的结晶温度高于C型锡石的。本文首次利用电子探针分析仪对锡石进行阴极发光(CL)成像观测,发现淘锡坑锡矿床中的锡石经历了两期结晶作用:早期锡石以CL荧光亮度较小(黑色——暗灰色)为特征,边缘有明显的溶蚀痕迹,常见典型的韵律振荡构造和砂钟构造,其晶面组合特征显示了早期锡石属于A型或B型锡石;晚期锡石以CL荧光亮度较大(白色——浅灰色)为特征,往往沿着早期锡石的溶蚀边界面充填生长,一般不显示韵律振荡构造和砂钟构造,其晶面组合特征显示了晚期锡石属于C型锡石。电子探针分析显示,淘锡坑锡矿床中锡石的FeO、Ta_2O_5含量较高,指示其形成于高温热液环境;HfO_2含量较高,Zr/Hf比值较低,说明成矿热液来源于高度分异的花岗质岩浆。两期锡石的FeO含量和In_2O_3含量的对比结果显示,早期锡石相对富FeO而贫In_2O_3,反映了早期锡石的结晶温度和压力均高于晚期锡石的,故两期锡石的结晶作用分别与淘锡坑矿床的两期岩浆热液成矿作用相关。
In this paper, we systematically studied the crystal morphology and geochemistry of cassiterite in the ore-bearing quartz veins of the Taoxikeng tin deposit. According to the characteristics of crystal plane assemblage, cassiterite in the Taoxikeng tin deposit can be divided into three types: type A cassiterite composed of 2 simplex forms consisting of {111} cones and {110} B-type cassiterite which is composed of three simplex cones, {110} cylinders and {100} cylinders, and B type cassiterite which is composed of {111} cones and {101} cones and {110} cylinders and {100} Four single-shaped C-type cassiterite. Based on the data analysis of various cassiterite and crystallization conditions, this paper speculates that the crystallization temperature of cassiterite type A and B is higher than that of C-type cassiterite. For the first time, the electron probe analyzer was used for cathodoluminescence (CL) imaging of cassiterite and found that cassiterite in the Taoxikeng-tin deposit experienced two phases of crystallization: the early cassiterite has a lower CL fluorescence brightness (black- Dark gray), with obvious corrosion marks on the edges, common typical rhythmic oscillation structures and sand clock structures, and their crystal face assemblages show that early cassiterite belonged to type A or B cassiterites. Late cassiterites were characterized by CL fluorescence brightness Larger (white-light gray) features are often filled along the dissolutional boundaries of early cassiterites, generally showing no rhythmic oscillation and sand-bell structure, and the combination of their facets shows that later cassiterite is C-type tin stone. Electron probe analysis showed that the CaO in Taoxikeng-Sn deposits is high in FeO and Ta_2O_5, indicating that it was formed in high temperature hydrothermal environment. The higher HfO_2 content and the lower Zr / Hf ratio indicate that the hydrothermal fluids originated from Highly differentiated granitic magma. The comparison of FeO content and In_2O_3 content of two cassiterite shows that the early cassiterite is relatively rich in FeO and poor in Fe_2O_3, reflecting that the crystallization temperature and pressure of early cassiterite are higher than that of late Cassiterite, so the crystallization of two cassiterite Respectively, related to the two stages of magmatic hydrothermal mineralization in the Amoy Pit.