Relations between chemical composition of granitic rocks and metallization in the Outer Zone of southwest Japan

In the outer zone of southwest Japan, Tertiary granitic rocks of the Southwestern Outer Zone-type are genetically related to the associated metallic ore deposits represented by the Obira-type, which are characterized by a wide range of complex metallization, such as, pneumatolytic, hypothermal and xenothermal types, with most of the ores having extremely variable mineral assemblages. The physical conditions of formation suggested by mineral assemblage, type of metallization and mode of occurrence, show that the ore deposits formed at high temperatures and shallow depths, and harmonize with those of the Southwestern Outer Zone-type granitic rocks. Throughout that region, granitic rocks of high silica-content are commonly accompanied by many ore depositsbut, in contrast, those of low silica-content by little or no ore deposits. Plots on AKF diagram representing granitic rocks accompanied by many ore deposits suggest concentration in alkali and aluminium during the differentiation and contamination-assimilation of magmas