著者

浜辺 修二 野納 敏展

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.26, no.136, pp.93-104, 1976-05-31 (Released:2009-06-12)

参考文献数

17

被引用文献数

2

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The Kamaishi Mine is one of the major producers of copper-iron ores of skarn type in Japan. In this paper the geological structure of the Kamaishi mining district is described.The Kamaishi mining district is located in the Southern Kitakami terrain with abundant limestone near the boundary to the Northern Kitakami terrain with abundant chert. The district is covered by Paleozoic and Mesozoic formations intruded by igneous rocks of Early Cretaceous.The geological structure of the Paleozoic formations is characterized by a large anticlinolium trending N-S. The deformed Paleozoic formations are covered unconformably by Mesozoic Maginouchi Formation and Ganidake igneous complex is emplaced into the axial part of the anticlinolium. At a stage between the deposition of Maginouchi Formation and the intrusion of Ganidake igneous complex, fault movement occurred resulting in the separation of the area into several geological blocks. Eastern wing of the anticlinolium was displaced downward several hundred meters from the western wing by Nakanosawa fault.The ore deposits are formed at the neighborhood of the contact of Paleozoic limestone and Ganidake igneous complex. The igneous complex consists of Ganidake granodiorite, diorite, diorite porphyry, gabbro and monzonite. The diorite porphyry is intruded along thrusts and faults providing with favourable condition for skarnization and metallic mineralization of the western orebodies of the Kamaishi deposits. "Sennin porphyrite" which has been considered as a member of Ganidake igneous complex was ascertained to be pyroclastics of Carboniferous Tsuchikura Formation. After the intrusion of the Ganidake igneous complex Kurihashi granodiorite was emplaced. Ganidake granodiorite body swells downward while Kurihashi granodiorite body pinches in the depth. This suggests that the former is exposed in its upper level while the latter is deeply eroded.