Abstract
Compositions of major dissolved components and of boron isotopes were investigated for hot spring waters in Ibusuki and adjacent areas (the Ibusuki region), Kyushu, Japan. The chemical compositions of the hot spring waters examined were consistent with the previous contention that major dissolved components of hot spring waters in the region are the resultant of the interaction of seawater with heated rocks underground. The δ11B values (relative to the isotopic ratio of NBS SRM 951) of the hot spring waters ranged from +2.1‰ to +39.4‰. A close inspection of the boron isotopic data identified two boron sources; one is seawater with a δ11B value of +39‰ and the other is volcanic gases with a δ11B value of ca. +6‰, which supply hot spring waters with boron with δ11B = ca. +2‰.
