R7: Petrology, Mineralogy and Economic geology (Joint Session with Society of Resource Geology)

[R7-05] The mechanism of bipyramidal quartz formation in Kuroko deposits

[Presentation award entry]

*Jumpei Sugioka¹, Ryoichi Yamada¹, Atsushi Okamoto¹ (1. Tohoku Univ. Env.)

Keywords:Quartz, Silica, Kuroko deposits, Submarine hydrothermal deposits, Hydrothermal experiments

We analyzed Kuroko ore specimens and conducted hydrothermal experiments to discuss the mechanism of bipyramidal quartz formation in Kuroko deposits. Fluid inclusion microthermometry revealed that the bipyramidal quartz in Kuroko formed in fluid at about 300℃. Hydrothermal experiments revealed that the bipyramidal quartz formed by phase transition from amorphous silica. The bipyramidal quartz is thought to have formed by supersaturation of silica in a fluid maintained at high temperature in the stockworks in the subsurface of the Kuroko deposits.