There are several igneous rocks in the Kamaishi mining district. Ganidake igneous complex, which is mainly composed of Ganidake granodiorite, diorite-diorite porphyry and monzonite, plays an important role on skarnization and mineralization. The complex was studied in detail and compared with Kurihashi granodiorite and so-called Sennin porphyrite, which are unrelated to mineralization. The results of this study are summarized as follows.
1) Ganidake granodiorite body swells downward, especially at the northern part, while Kurihashi granodiorite body pinches out in the depth.
2) On the fissure pattern study, two different directions are observed. The N-S trend fissures which were formed at the same stage as mineralzation are predominant in the northern part of the granodiorite, and the post ore E-W trend fissures are predominant in the southern part.
3) Ganidake igneous complex has been suffered from remarkable hydrothermal alteration along the fissure zone of N-S trend, and Ganidake granodiorite gives relative addition of Na2O and K2O to the surrouding diorite and so-called Sennin porphyrite.
4) It is revealed that magnetic susceptibility depends on the magnetite content and that it becomes low near the alteration zone and ore deposits.
5) Chlorine and copper contents of Ganidake granodiorite which are considered to have genetical relation to the skarnization and mineralization, are higher than those of the Kurihashi granodiorite.
