新第三紀熱水活動によって形成された愛媛県西条市・市之川角礫岩における砥素およびアンチモンの挙動

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In this paper, formation process of Ichinokawa breccia and antimony-arsenic mineralization in the breccia in the Ichinokawa area of Saijyo City, Ehime Prefecture, Japan, has been studied on the basis of geological, petrological and geochemical data. We have focussed on "hydraulic fracturing" process for the genesis of the Ichinokawa conglomerate. Ichinokawa conglomerate can be divided mainly into Ichinokawa breccia and Myojin Group. Carbonate-rich breccia and sandstone filling fractures are also found in the Sanbagawa schists adjacent to the Ichinokawa breccia. High-angle breccia zones, the Ichinokawa breccia, cut across the Sanbagawa schistocity. The Ichinokawa breccia consist principally of breccias which have been partly altered and veined by quartz, carbonate minerals and pyrite, and matrix of carbonate-rich sandstone. Schist clasts (up to 10 m across) in the breccia are angular but not variably rotated. Breccias are both clast- and matrix-supported and show evidence for single fracturing and healing by hydrothermally precipitated minerals such as carbonate minerals, pyrite, stibnite, pyrite and quartz. Two Sb and As-rich zones in the Ichinokawa breccia along the Ichinokawa River are about 10-30 m wide adjacent to the Sanbagawa schists. As and Sb values of carbonate matrix in the breccia are extremely high. These observations suggest that the the Ichinokawa breccia formed through a hydrofracturing process associated with hydrothermal fluid infiltrated into Sanbagawa metamorphic as precursor of the antimony ore forming. Hydrothernal fluid seems to have caused mineralization of carbonate minerals and sulfide minerals. Afterwards, the Myojin Group was accumulated above on the Ichinokawa breccia.
2005-03-25

新第三紀熱水活動によって形成された愛媛県西条市・市之川角礫岩における砥素およびアンチモンの挙動

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