Geochemical applications of quantitative ion-microprobe analysis

Abstract

A method for quantitative analysis of silicates with an ion-microprobe has been developed by suppressing the intensities of interfering molecular ion species based on the difference in the kinetic energy distributions between molecular and single-atom ions. Molecular ions drop their intensities rapidly with increasing energy and are virtually eliminated at the energy level 150eV higher than the energy acquired by acceleration. Outlines of geochemical applications of the technique are given for: 1. (a) analysis of isotopic composition of Pb in galena 2. (b) analysis of isotopic composition of Mg in anorthite and hibonite in inclusions in the Leoville meteorite 3. (c) quantitative analysis of major and trace elements in Ca-rich pyroxene, garnet and plagioclase 4. (d) determination of REE pattern in hornblende; and 5. (e) in-depth profiling of 18O 16O ratios to determine oxygen self-diffusion in silicates in hydrothermal conditions. Although the potential capabilities of an ion-microprobe are not well-realized at the present stage, due in part to the lack of well-documented standards for trace elements and a relatively large beam spot size, it is concluded, considering the technical development foreseeable in the near future, that the ion-microprobe should prove extremely useful in geochemistry.