全岩样品碳酸盐矿物选择性溶解方法改进及其锶同位素比值测定

Method improvement of selective dissolution of carbonate minerals in whole rock samples and determination of strontium isotopic ratio

研究岩石和矿物中87Sr/86Sr值具有重要的意义。采用0.2 mol·L-1盐酸溶液及5%醋酸溶液对两个全岩样品中碳酸盐矿物进行分步溶解实验,用电感耦合等离子质谱仪(ICP-MS)分析溶解过程中各元素含量及热电离质谱仪(TIMS)测定87Sr/86Sr值。结果显示采用0.2 mol·L-1盐酸溶液溶解,随着盐酸用量增加,方解石、白云石、绿泥石及其他矿物成分相继溶出,与X射线衍射(XRD)矿物成分分析一致,可通过控制盐酸的浓度和加入量选择性溶解全岩样品中碳酸盐组份,但进一步区分碳酸盐中不同矿物的溶解顺序则需采用酸性较盐酸溶液更弱的5%醋酸溶液。对溶解过程中的87Sr/86Sr值进行测定,结果显示其变化趋势与不同矿物组份溶出顺序一致。实际应用过程中可通过控制溶解条件实现全岩样品中目标碳酸盐矿物的选择性溶解,使锶同位素比值测定结果更加准确。

The study on87Sr/86 Sr ratio of rocks and minerals is significant. In the case, carbonate minerals of two whole rock samples are sequentially leached in 0.2 mol·L-1hydrochloric acid solution and 5% acetic acid solution, followed by the measurement of target elements content with Inductively Coupled Plasma Mass Spectrometry（ICP-MS） and87Sr/86 Sr ratio with Thermal Ionization Mass Spectrometer（TIMS）. In 0.2 mol·L-1hydrochloric acid solution, calcite, dolomite and chlorite are dissolved successively by increasing hydrochloric acid. The results show that dissolved mineral composition is same as that determined by X-ray diffraction（XRD）. Carbonate minerals in whole rock samples can be selectively dissolved by controlling the concentration and amount of hydrochloric acid,but for the selective dissolution of different carbonate minerals, only 5% acetic acid solution is effective, which is of weaker in acidity than hydrochloric acid solution, and dissolve calcite first and dolomite the second.87Sr/86 Sr ratio of solution has also been determined, the results show that the changing trends is consistent with the order of dissolution. In practical application, target minerals can be selectively dissolved through controlling the dissolving conditions, so we can determinate strontium isotopic ratio more accurately.