锡石振动光谱特征与矿物成因类型

Vibration Spectra and Genetic Type of Cassiterites

以芙蓉矿田个别矿床为例,研究了锡石的振动光谱和成因之间的关系。芙蓉矿田锡石中含有一定量的Fe,Mn,Ti,Nb和Ta等元素。X光粉晶衍射分析得出锡石晶胞体积平均为nm3量级,明显比其他成因类型的锡石晶胞体积大,主要为锡石—硫化物型。锡石样品红外光谱中4个本征峰的相对强度表明矿田中锡石的红外光谱主要为变形谱,进一步表明芙蓉矿田锡石成因以锡石—硫化物型为主。锡石拉曼光谱中A1g峰频率为632cm-1左右,与锡石—硫化物型接近,并且锡石中的Nb和Ta含量越高,A1g峰向低频方向的频移越大。A1g作为全对称伸缩振动模式是锡石以及同结构类型的AO2氧化物的特征峰,锡石中的杂质元素将会影响它的拉曼频率。结合前人的研究结果认为锡石样品激光拉曼光谱中A1g峰的拉曼频率对其成因有指示意义。拉曼光谱的测试结果与锡石晶胞参数和红外光谱分析的结果一致。结合锡石晶体化学特征和振动光谱特征对矿物成因研究有一定的参考意义。

Trace elements determination of cassiterites from Furong ore field indicates that there is a certain amount of Fe, Mn and Ti elements in cassiterite. The mean of unit-cell parameters for cassiterite is 7. 165（nm^3 ） by the method of XRD analysis and the unit-cell parameter which also indicates that the genetic type of the ore field belongs to cassiterite-sulfide type, is bigger than that of other genetic type. Four IR active vibration frequencies in cassiterite samples also suggest that the IR spectra of cassiterites from Furong ore field belongs to deformed spectra suggesting that the genetic type of cassiterite from Furong ore field is mainly of cassiteriate-sulfur type. The Raman frequency of A1g peak has typomorphic significance to study its genetic type. A1g is a characteristic peak of cassiterite and AO2 oxide of the same structure style. Impure elements of cassiterite remarkably affect its Raman frequency which will move to low frequency if the contents of Nb and Ta reach a certain amount. In Furong ore field, A1g frequency of casstiterite is about 632 cm^-1 which is bigger than other cassiterites of various genetic types and the implication and character of Raman spectra are consistent with the cell parameters and IR analysis of these samples. Combined with the study of chemical composition and crystal structure, the IR spectra and Raman spectra can mean a lot for the analysis of genetic type of the cassiterite.