釜石鉱山の高温交代銅鉄鉱床および周辺火成岩中の流体包有物に関する研究 Ｉ 火成岩中の流体包有物

Abstract

Fluid inclusions in quartz from several igneous rocks as well as from barren quartz veins were studied as a part of investigation for the origin of ore-forming fluids and mineralization of the pyrometasomatic iron-copper ore deposits in the Kamaishi mining district, Iwate prefecture, Japan. Igneous rocks are mainly composed of diorite-diorite porphyrite intruded before the mineralization, Ganidake granodiorite related to skarnization and mineralization, and Kurihashi granodiorite intruded after the mineralization. Polyphase, liquid and gaseous inclusions are observed in quartz of those igneous rocks. It is found that polyphase inclusions, which mainly contain halite, are abundant in quartz of the diorite-diorite porphyrite and Ganidake granodiorite, but remarkably poor in that of the Kurihashi granodiorite. This tendency is in good agreement with those of both chlorine and copper contents in the igneous rocks. The homogenization temperature of fluid inclusions in quartz from the Ganidake granodiorite ranges from 247 to over 380°C. On the basis of the data of disappearance temperature of halite in polyphase inclusions, it is deduced that the salinity of fluid would have been in a range between 30 to 50 weight percent NaCl equivalent concentration. From these results of investigation, it is inferred that the original ore-forming fluid was high in both temperature and salinity, and that highly saline fluid played an important role on the transportation of metal elements. It is also deduced from the distribution of polyphase inclusions in the rocks that highly saline fluid would have originated in some deeper parts of the Ganidake granodiorite, along which the ore deposits are distributed. But, the relation between the intrusion of the diorite-diorite porphyrite and mineralization has been left unsolved.