Natural Analogue study on the Long-Term Durability of Bentonite –Time-temperature condition and water chemistry on illitization at the Murakami deposit, Japan.–

Abstract

ABSTRACTTime-temperature conditions and water chemistry on illitization at the Murakami deposit in central Japan were determined. The extent of the illitization and timetemperature condition estimated were as follows: the duration for conversion from 0 to 80%illite (volumetric ratio) was approximately 3.5Ma in the temperature range from 340 to 100°C. Conversion from 0 to 40% requires approximately 3.0Ma in the temperature range from 240 to 100°C. During 2.0Ma in the temperature range from 160 to 100°C, however, illite was scarcely observed. Water chemistry is estimated from two approaches, namely laboratory experiment and numerical analysis. The former is an interactive experiment between seawater and the tuff of the deposit. The latter is a calculation based on the difference of bulk composition between illitized and non-illitized tuff. The extent of each ionic concentration is inferred to be as follows: K+; 560 to 6400, Mg2+; 800 to 1700, Ca2+; 360 to 2900, Na+; 9400 to 15000 (mg/l).