Abstract
The Koujyaku granite, which intrudes the Mesozoic formations of the Mino-Tanba Belt, occupies the Nosaka Mountain range to the north of Lake Biwa, southwest Japan. It consists mainly of three major rock types, coarse-grained biotite granite, medium-grained biotite granite and hornblende-bearing fine-grained porphyritic biotite granite. The coarse-grained biotite granite is a deep-seated faces of the pluton, and grades into the medium-grained biotite granite. The fine-grained porphy-ritic biotite granite intrudes other two rock types. Small dikes such as aplite, granite-porphyry, finegrained biotite granite and porphyrite, intrude into the major three rock types. Comparing with the granite plutons around Lake Biwa, the Koujyaku granite is characterized by lower plagioclase content in modal composition, and by higher SiO2 content and Fe2O3/FeO ratio. Similarly to the granites of the San'yo Belt, the greater part of the Koujyaku granite shows lower-magnetic susceptibility than 2.6×10-3 SIunit, but some parts show higher values which correspond to the magnetite series granites.
