The analysis of fluid inclusions in the microgram range with an ion microanalyzer

This paper deals with the development of a method of microanalysis of inclusions by means of the ion microanalyzer. In this method, the ion beam works not only to analyze the inclusion fluid, but also to sputter the host mineral which encloses an inclusion. The fluid inclusions are kept frozen to avoid rapid evaporation into vacuum. The ionization properties of aqueous solution in the frozen state were investigated, since such a study had never been done. Semi-quantitative analysis is possible, using the relative ion intensities and the molarity of inclusion. Results are reported on the samples from hydrothermal deposits in Japan. It was found that the compositions of mineralizing fluid varied with time especially in Mg and Al, even in the same minerals from the same deposit. As an example of application to prospecting, a new copper deposit was found based on the analysis of fluid inclusions under the so called barren zone of Pb˗Zn vein type deposit.