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Geochemical Journal
Geochemical Journal An open access journal for geochemistry
Published for geochemistry community from Geochemical Society of Japan.

Variation in the chemical composition of Obuki Spring, Tamagawa Hot Springs (1951–2000)

Yuzo Yoshiike
Geochemical Journal, Vol. 37, No. , P. 649-662, 2003


A change in the chemical composition of Obuki Spring, a typical chloride-sulfate acid hot spring in Japan, has been revealed by continuous observation for more than 40 years. The concentration of SO42- increased markedly from 1972 (∼1 g/l) to 1978 (∼3 g/l), then decreased gradually from 1978 to 1990 (∼1 g/l). Variations in the Cl- concentration were apparently within a smaller range than those of the SO42- concentration. The concentrations of numerous cations increased during 1972–1990, as did the SO42- concentrations. This variation is thought to be the result of a mechanism involving a second source, namely, volcanic emanations of a sulfur-rich composition, which were temporarily added to emanations from the first source; the first source has continuously supplied volcanic emanations to the original acid hydrothermal solution at Obuki Spring, and the second source is responsible for the increase in SO42-, Cl-, and acidity. Variations in the concentrations of most other components can be explained as the result of changes in the interaction between the acid hydrothermal solution and the surrounding rocks; the latter changes were themselves the consequence of increases in acidity.

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