Boron contents of condensed water samples from fumaroles (orifice temperature : 90～850℃) at Satsuma-iwo-jima Volcano were determined by using a spectrophotometric method based on the extraction of methylene blue-tetrafluoroborate ion pair. Condensed water samples were collected with special caution to avoid the contamination of boron from the sampling apparatus and from volcanic incrustations deposited around fumaroles. Boron contents of the high temperature fumarolic gases (＞700℃) were rather constants as shown in Table 1. On the other hand, those of low temperature fumaroles vary considerably. The F/B atomic ratios in condensates increase almost linearly with the orifice temperatures of fumaroles above 200℃. However, they show considerable scattering around 100℃. The B/Cl ratios are almost constant above 200℃. But, they also vary very widely around 100℃. These results indicate that boron in the volcanic gas behaves similarly to chlorine above 200℃. Below 200℃, fractionation of boron is very much complicated, because of the partial condensation of water in the gas and of the deposition of sassolite as volcanic sublimate.
