群馬県大戸のCa・Na-Cl型塩水について [in Japanese] On a Ca•Na-Cl-type saline water from Ohodo, Gunma Prefecture [in Japanese]
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Chemical and isotopic compositions of the saline water from Ohodo were continuously observed from 1982 to 1986. In 1985, it happened that hydrogen and oxygen isotopic ratios and also concentrations of most of dissolved components sharply decreased, while Ca<sup>2+</sup>, Sr<sup>2+</sup>, SO<sub>4</sub><sup>2-</sup> and F<sup>-</sup> concentrations increased. The relationships of δD vs. Cl<sup>-</sup> and δD vs. δ<sup>18</sup>O showed that the saline water before 1985 was a mixture of a fossil sea water and a saline water of meteoric origin of which Cl content is 13.5 g/l, and the mixing ratio of sea water drastically decreased in 1985. Then, the fossil sea water component completely disappeared early in 1986. The chemical composition, especially Br/Cl, Sr/Ca and Li/Na ratios of the saline water of meteoric origin suggest that its dissolved salts originated from sea salts, and the cation composition was changed through some interaction with rocks at low temperature, in which cation exchange reaction with montmorillonite may play a principal role.
Chikyukagaku 23(1), 45-52, 1989
The Geochemical Society of Japan