HYDROTHERMAL ALTERATION OF MIOCENE TUFFS IN NAOH•KOH SOLUTIONS, WITH SPECIAL REFERENCE TO CHEMICAL BEHAVIOR (HYDROTHERMAL STUDIES ON THE WALL-ROCK ALTERATION-3-)

Abstract

Natural green tuff and rhyolitic tuff (Miocene age) were subjected to alter in sodium hydroxide and potassium hydroxide solutions under 200°C and 200kg/cm². Various chemical behaviors were shown under the influence of running times and chemical conditions. Al₂O₃ content in the alteration product shows an apparent increase. However, Al₂O₃ is absent from the present hydrothermal solutions. It is assumed that during hydrothermal alteration, fresh rock has decreased in weight so that Al₂O₃ has apparently increased. Column A in Table 5 shows the culculated weight in grams of each oxide remaining from the alteration of 100g of fresh rock, on the assumption of constant Al₂O₃. It may be concluded from the present experiments that the amount of analcime in the alteration product depends upon mineral mineral association of starting material and contents of SiO₂ in alteration products.