硅铍石的包裹体及其形成条件研究

A study of the inclusions in phenakite and the formation conditions of phenakite

对硅铍石样品进行放大观察,可见大量杂乱分布的黄色透明针状固态包裹体、少量红色不透明粒状固态包裹体,气液包裹体和愈合裂隙普遍存在。通过激光拉曼光谱分析,测得硅铍石样品中气液包裹体的液态部分为含有CO2等气体的NaCl盐水溶液,气态部分的化学成分为CO2、水蒸气等。对硅铍石样品中气液包裹体的气体比和充填度进行估测,利用冷热台测出其均一温度和冰点分别为378.9～425.5℃和-12.1～-6.3℃。经过计算,得出硅铍石的近似形成温度为378.9～425.5℃,近似形成压力为234.44～428.56MPa。

The formation conditions of phenakite were studied through investigating its gas-liquid inclusions by means of Laser Raman spectrum analysis and microscopic heating/cooling stage. The observation of phenakite samples revealed numerous randomly-distributed yellow acicular transparent solid inclusions, a few red granular opaque solid inclusions, lots of gas-liquid inclusions and healed cracks. The gas-liquid inclusions in phenakite were divided into two types according to their forms and substances. Type included rich liquid two-phase H20-NaCl inclusions （ I a） and pure liquid H20-NaC1 inclusions （ I b）, whereas Type 11 could be further divid- ed into three-phase H20-NaC1-CO2 inclusions containing liquid COe （ 11 a） and two-phase H2O-NaC1-CO2 inclu- sions without liquid CO2 （ 11 b）. Then some gas-liquid inclusions of different types with clear demarcated gas part and liquid part were chosen to do further test. Using Laser Raman spectrum analysis, the authors affirmed that phenakite is a kind of silicate which contains Be as the matrix for inclusions, and that the gas part of the gas- liquid inclusions contain such components as CO2 and water vapor, whereas the liquid part is NaCl aqueous solu- tion with the dissolution of a little CO2. Two different gas-liquid inclusions were chosen for microscopic heating/ cooling stage test, and the results show that the homogenization temperatures of the inclusions are from 378.9℃ to 425.5℃; by homogenization method, and their freezing points are about - 12.1- - 6.3℃ by freezing method. These data were used to figure out the salinities of these inclusions, which are 9.60 % - 16.14 %. Cal- culations show that the homogenization pressures range from 234.44 MPa to 428.56 MPa. The formation tem- perature and the formation pressure of phenakite estimated from homogenization temperature and homogeniza- tion pressure are about 378.9-425.5℃ and 234.44-428.56 MPa respectively.