| 講演要旨(和文) | | 石見鉱床（島根県大田市五十猛）は，第三紀中新世のグリーン・タフ地域に胚胎する黒鉱型鉱床である．かつては鉛，亜鉛，銅などを産出する鉱山であったが，現在は流紋岩質凝灰岩中のゼオライトが主に採掘されている．ゼオライトの品質を計るパラメータの一つに塩基置換容量があるが，比抵抗との有意な関連性を明らかになれば，試錐によらずに電気探査や電磁探査による探鉱が可能になる．本研究では，石見鉱床エリアを北北西-南南東に横断する測線（長さ約700m）でAMT法探査を実施した．2次元比抵抗構造を推定したところ，地質構造の特徴と一致しており，�々�鉱鉱床や石膏鉱床，網状鉱染鉱体の分布する領域では数Ohm-m程度の低比抵抗値を示すこと，�⇔�紋岩質凝灰岩の比抵抗は約10Ωmだが，熱水変質の影響が大きな領域では約20Ωm程度とわずかに違いが見られ，その領域がゼオライト鉱床の開発領域とよく一致すること，などの知見が得られた． |
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| | 講演要旨(英文) | | The Iwami mine is known as the kuroko-type deposit in the "green tuff region" of the Southwest Japan, where the zinc-lead-copper ore had been produced during the period of 1966 to 1984. Presently, the development of zeolite deposit has been conducted. To investigate the relationship between the resistivity structure and the distribution and its grade of zeolite deposit, electromagnetic studies have been carried out in the Iwami mine area. In this study, an audio-frequency MT investigation was conducted in the kuroko and zeolite deposits. The estimated resistivity distributions by two-dimensional inversion show good correlation with the geological features obtained by the drillings. The location of extremely conductive zone (around a few Ohm-m) is consistent with the kuroko deposit and the border of rhyolitic rocks, indicating the existence of zinc-lead-copper ore and gypsum deposit. The resistivity of rhyolitic tuff layer is about 10 Ohm-m, however, slightly resistive (about 20 Ohm-m) around the border of kuroko deposit, where is overlapping to the zeolite mining zone. The hydrothermal alteration might cause the resistivity change in the rhyolitic tuff layer. |
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