NAKANISHI Tetsuya Kyushu Univ. Museum, Associate professor, 総合研究博物館, 助教授 (50315115)
ZENG Nanshi Kyushu Univ., Dept. of Earth Resources Eng., Research Assistance, 大学院・工学研究院, 助手 (20294887)
WATANABE Koichiro Kyushu Univ., Dept. of Earth Resources Eng., Associate Professor, 大学院・工学研究院, 助教授 (10182916)
TAGUCHI Sachihiro Fukuoka Univ., Dept. of Earth Science, Professor, 理学部, 教授 (00108771)
MOTOMURA Yoshinobu Kyushu Univ., Dept. of Earth and Planet. Sciences, Research Assistance, 大学院・理学研究院, 助手 (20037237)
To develop the evaluation procedure for the mineralization potential of magmatic hydrothermal systems the evolution of systems and factors controlling concentration of metals were examined on several important systems, emphasizing three dimensional structures, distribution of the boiling zone and information of the shallow part of systems. Major areas include Lepanto/FSE-Victoria, Kasuga, Hishikari, Kushikino, Fuke, Cibaliung, Iwami, Northern Queensland, Hoshino and Noya. Together with some experimental works the following important results were obtained.
1. Adakitic volcanic rocks were found in the areas of Kushikino, Hoshino and Iwami.
2. Age determination using fission track, K-Ar and ^<40>Ar/^<39>Ar methods for volcanic rocks and ores clearly showed that in a certain area the hydrothermal activity starts about 500,000 years after the commencement of the volcanic activity, and continues about 500,000 years with intermittent fracture formation.
3. If shallow part of a system is preserved, sinters may exist and the higher gold content of sinters indicates the possible gold mineralization.
4. The regional thermal structure of a hydrothermal system is constructed by hydrothermal alteration zoning. The area bounded by 150-200 C isotherms indicates the fracture system and extends for 3 km by 4 km.
5. Boiling zones are indicated by occurrence of bladed calcite/quartz, adularia and truscottite, and also by characteristics of fluid inclusions.
6. Flow-through type autoclave experiments indicate that concentrations of Si, Al and Ca in hydrothermal waters increase transiently during fracture formation.
7. Adsorption experiments of gold on Al and Fe(III) hydroxides suggest that deposition of gold is strongly controlled by adsorption process.