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Geologic Characteristics and Formation Environments of the Furutobe and Matsuki Kuroko Deposits, Akita Prefecture, Northeast Japan

By
Hideo Kuroda
Hideo Kuroda
Hosokura Mine, Mitsubishi Metal Company, Uguisuzawa-cho, Kurihara-gun, Miyagi Prefecture, Japan
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Published:
January 01, 1983

Abstract

Among Kuroko deposits in the Hokuroku district, some differences are observed in the modes of occurrence and the characteristics of ore which are due mainly to the different environments of ore formations. The Furutobe deposit, a typical Kuroko deposit, is composed of the siliceous ore zone and the stratiform ore zone and occurs in and on dacitic lavas and pyroclastics. The Furutobe deposit may have formed in the area where active volcanic action occurred before ore formation. The sea bottom consisted mainly of unconsolidated dacitic pyroclastics and well-fissured dacitic lavas which gave a favorable condition for upwelling of hydrothermal solutions and circulation of seawater. The siliceous ore zone is composed of fissure and interstice-filling ore which formed in dacitic lavas and pyroclastics. The stratiform ore zone is divided into two types by modes of occurrence: (1) the primary ore deposits which seem to have been formed on the sea floor and in the unconsolidated tuffs; (1) ore deposits which are believed to have been transported and redeposited in a trough by slumping from the primary ore deposits.

The Matsuki ore deposit, a somewhat peculiar Kuroko deposit, contains a group of unit orebodies consisting mainly of high-grade yellow ore and occurs in mudstone and dacitic pyroclastics. The Matsuki ore deposit may have formed in the area where the preceding volcanism was minimal and the sea bottom consisted mainly of mudstone. The mudstone, overlying the permeable dacitic pyroclastics, behaved as an aquiclude layer against the rising hydrothermal solution and circulating seawater. The ore deposit is considered to have been formed in unconsolidated mudstone and dacitic pyroclastics from the modes of occurrence of the deposits and the existence of benthonic foraminifera in the mineralized zone.

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Contents

Economic Geology Monograph Series

The Kuroko and Related Volcanogenic Massive Sulfide Deposits

Hiroshi Ohmoto
Hiroshi Ohmoto
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Brian J. Skinner
Brian J. Skinner
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Society of Economic Geologists
Volume
5
ISBN electronic:
9781629490007
Publication date:
January 01, 1983

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