The aluminian clay minerals, “sudoite and tosudite, ” sericite, interstratified sericite-montmorillonite, kaolinite and montmorillonite occur in the core samples from the altered zone of the Kuroko-type deposit at Niida, Akita Prefecture, northeast Japan. In drill-hole #445, the di. trioctahedral chlorite, sudoite, occurs dominantly in the black-ore zone (baritepyrite). On the other hand, in drill-hole #457, the magnesium-bearing aluminian interstratified chlorite-montmorillonite, “tosudite, ” was found in the gypsum zone (gypsum-anhydrite-pyrite). In the drill-hole #445, sericite occurs only in the brecciated rhyolite under the black-ore whereas interstratified sericite-montmorillonite was found in the fine tuff above the black-ore. Kaolinite was found locally in the tuff above the gypsum zone of the drill-hole #457. Mineralogical properties of these clay minerals, especially of sudoite and tosudite, are discussed in this paper.
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Kimbara et al. (1974) studied this question.