花崗岩地帯湧水の化学組成に関する一考察 A study on the chemical composition of ground waters from granitic areas
Powdered granitic rocks were allowed to react with distilled water under various conditions to estimate the formation mechanism of natural waters from granitic area and to discuss on the factors influencing the chemical composition of the waters. The experimental results indicate that the chemical composition and pH of the waters are influenced by the kind of granitic rocks, the water/rock ratio and P<sub>CO<sub>2</sub></sub>. The alkaline ground waters may result from the reactions of granitic rocks with the waters having low P<sub>CO<sub>2</sub></sub>. The ground waters from granitic areas where CO<sub>2</sub> from underground occurs abundantly are neutral or weak acidic, and their major species are Na<sup>+</sup>, Ca<sup>2+</sup>, HCO<sub>3</sub><sup>-</sup>. The proportion of the components is nearly equal to that of the surface waters. The percolation time of ground waters in granitic areas was inferred to be relatively short because of the high permeability of water into granitic rocks and low content of dissolved species. Accordingly, the metastable alminosilicates produced during the incongruent dissolution of granitic rocks, may control the chemical composition and pH of the ground waters.
地球化学 14(2), 69-76, 1981