ABSTRACT

A siliceous sublimate, collected from an active fumarole of Kuju Volcano, was analyzed for major constituents. The water soluble fraction of the sublimate contains large quantities of halogen acids and silicon, and the insoluble fraction consists of hydrated silica with a trace amount of native sulfur. In order to ascertain the presence of gaseous silicon compounds in fumarolic gases, condensate samples were collected from high temperature fumaroles of Kuju and Nasudake Volcanoes with a silica-free sampling device. The silicon and fluorine contents of fumarolic gases range from 1 to 52 mg Si/kg H₂O and 1 to 320 mg F/kg H₂O, respectively. Silicon is transported probably as fluoride in fumarolic gases, and the sublimate is formed by hydrolysis of silicon fluoride when the gas temperature falls to the boiling point of water.