群馬県星尾鉱泉の流下による組成変化と石灰華の生成について

概要

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The Hoshio Mineral Spring is characterized by CO_2-rich Na・Ca-HCO_3・Cl waters. During streaming down of spring water on a slope for about 120 m, pH, and CO_2, HCO_3^-, Ca^<2+> and Fe^<2+> concentrations of the water change largely, caused by release of dissolved CO_2 and consequent precipitation of ferruginous and calcareous deposits. The changes of the other major components are due to dilution by shallow ground water. The precipitation of CaCO_3 starts when the degree of supersaturation reaches 14〜22. It occurs actively at the places where a travertine terrace is forming. Therefore, the precipitation of CaCO_3 seems to be controlled not only by the degree of supersaturation but by other factors such as the turbulence of stream. At one of the places where the dilution by ground water occurred, the increases of Ca^<2+> and HCO_3^- were observed, and it is estimated that the spring water should be undersaturated with CaCO_3, thus resulting in dissolution of CaCO_3. Although the degree of supersaturation is 3.3 at that place, the apparent supersaturation may be due to amorphous character of CaCO_3 freshly precipitated and/or over estimation of Ca^<2+> and HCO_3^- concentrations caused by dissolution of suspended fine CaCO_3 particles.
日本地球化学会の論文
1983-12-25