The late Cretaceous Tanakami Granite is composed of well fractionated biotite granite of the ilmenite-series having high silica and alkali contents (73.3-76.7% SiO2; 8.0-8.9% Na2O+K2O),and high Rb/Sr ratios. The core of the pluton is coarse grained, containing high F and Li contents, but low at the margin, implying these volatile components were diffused out during the crystallization. The Granite is rich in rare-earth elements (REE), especially of HREE, and radioactive components. The magma is considered to have originated in reduced felsic materials, then fractionated and emplaced. The radioactive decay heat may have provided enough heat to generate hydrothermal fluid system and resulting the mica-clay mineralizations within the granitic body.