短報
北海道樽前山溶岩ドーム中の硫化鉱物
2010 年 39 巻 3 号 p. 104-109
詳細
2010 年 39 巻 3 号 p. 104-109
Sulfide blebs composing of bornite solid-solution, mooihoekite, isocubanite and pyrrhotite occur in andesite from the lava dome, Tarumai volcano, Hokkaido, Japan. The lava dome consists of two-pyroxene andesite. Some bornite solid-solutions are found as exsolution lamellae in mooihoekite which is originally crystallized as intermediate solid-solution (iss) in the Cu-Fe-S system at high-temperature, included in magnetite phenocrysts of the andesite. Isocubanite occurs closely associating with pyrrhotite included in orthopyroxene phenocrysts of the andesite, and is exsolved from the Cu-bearing pyrrhotite. Some bornite solid-solutions and mooihoekite are found in a ground mass as micro-crystals. The magnetite including mooihoekite and bornite solid-solution, and the orthopyroxene including pyrrhotite and isocubanite may be crystallized at different conditions. The crystallization temperatures are about 950 °C for the silicate melt including magnetite phenocrysts, and about 1150 °C for the orthopyroxene bearing silicate melt. Therefore, this andesite magma is thought to be formed by the magma mixing.
