Abstract
Natural rhyolitic tuff and green tuff (Miocene age) were subjected to alter in sodium hydroxide solution under 200°C and 20kg/cm2. When these were treated at 200°C for 50 hours, analcime (NaAISi2O6•H2O) was formed as an alteration product, whose X-ray reflections were gradually intensified with the duration of treatment. From the diffraction intensities, it was found that the alteration products of green tuff contained about 3 times more analcime than in the case of rhyolitic tuff. A comparison of chemical compositions between the original green tuff and its alteration products showed that SiO2 was much dissolved out in the process of analcimization. On the basis of the present result, it is considered that the analcime zone surrounding Kuroko deposits is formed by the reaction between highly saline alkaline solution and tuffaceous sediments of middle Miocene age. The solutions are considered to have been heated by submarine volcanism and/or exhalative activities, thus accelerated the alteration.
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Schedule a callMore From: The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists
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