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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 5. (May)

First Page: 575

Last Page: 575

Title: Sedimentary and Structural Setting, Kuroko Ore Formation, Hokuroku District, Japan: ABSTRACT

Author(s): Albert L. Guber, Hiroshi Ohmoto

Article Type: Meeting abstract

Abstract:

The Kuroko massive sulfides are thought to have formed on the sea bottom during middle Miocene time. The deposits are interstratified with a highly variable sequence of volcaniclastic and detrital sediments, some of the latter bearing foraminifera. Our studies of the paleontological and sedimentological characteristics of the sediments place the following constraints on models of the sedimentologic-tectonic setting before, during, and after ore genesis. (1) Contrary to previously accepted ideas, ore genesis in the Hokuroku district (a 30 by 30 km area) was not contemporaneous and may have spanned as much as 6 million years as is suggested by the planktonic foraminifera. (2) Most previous ideas embodied a shallow-sea origin for the ores, but benthic foraminifera indicate t at the ores formed at great depths (about 3,500 m). (3) The district subsided from subaerial to deep submarine during the early Miocene, when the late Paleozoic metamorphic basement was lowered along high Previous HitangleNext Hit faults. Rapid subsidence is suggested by thick-bedded, poorly sorted sedimentary breccias and sandstones on the downfaulted blocks. (4) Middle Miocene detrital turbidite muds are Previous HitcommonNext Hit in the district, and a mixing ratio of benthic foraminifera from different depths is used to determine turbidite source areas. (5) Further high Previous HitangleTop faulting during the middle Miocene produced a large scale submarine topography which limited the distribution of the muddy turbidites. These fault-generated submarine highs are relatively free from turbidite influence and contain most of the ores.

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