Hydrothermal syenite in the Hira Granite pluton, west of Lake Biwa, central Japan

Abstract

We identified subsolvus syenite (episyenite) veins formed by hydrothermal metasomatism in the Hira granite pluton, west of Lake Biwa, central Japan. The veins comprise four facies with different mineral assemblages and bulk chemical compositions. Feldspars in the syenite include K-and Na-feldspars that are close to end-member compositions. Other silicate minerals include holmquistite, green mica, and chlorite, which are variably associated with sphalerite and Fe-bearing material (magnetite, hematite, and amorphous Fe oxides). The subsolvus syenite in the Hira granite pluton underwent K-feldspathization, albitization, and Zn mineralization. We present petrographic and mineralogical data for the syenite.