Geology and properties of the Kawasaki and Dobuyama bentonite deposits of Zao region in northeastern Japan
Authors: Takagi, T.; Koh, S. M.; Song, M. S.; Itoh, M.; Mogi, K.
Source: Clay Minerals, Volume 40, Number 3, September 2005 , pp. 333-350(18)
Publisher: Mineralogical Society
Abstract:The Kawasaki and Dobuyama bentonite deposits in northeastern Japan show contrasting properties even though they are only 5 km apart in a sequence of Neogene sedimentary and pyroclastic rocks. The Kawasaki deposit consists of stratiform bentonite layers up to >50 m thick, and its wall rocks are unaltered shallow marine sedimentary rocks. In contrast, the Dobuyama deposit consists of a funnel-shaped ore body 200 m across, and its wall rocks are hydrothermally altered terrestrial rhyolitic pyroclastic rocks. The Kawasaki and Dobuyama bentonites mainly consist of Na-Ca smectite and Ca smectite, respectively, with subordinate opal-CT, quartz and zeolite. The geological occurrences of the deposits and wall-rock properties suggest that the Kawasaki and Dobuyama deposits were probably formed by diagenesis and low-temperature hydrothermal alteration, respectively. The difference in exchangeable cation ratios of the smectite between the two deposits is attributable to the difference in their sedimentary environments and/or burial depth.
Document Type: Research Article
Publication date: September 2005