HYDROTHERMAL ALTERATION AT THE DENBEKOBA DEPOSIT OF AMAKUSA POTTERY STONE

概要

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Mineral parageneses and high-low inversion temperature of quartz at the Denbekoba deposit of the Amakusa pottery stone have been investigated by X-ray powder diffraction, differential thermal analysis and polarizing microscopy. The main constituent minerals of the pottery ores are quartz and sericite. Kaolinite, dickite, tosudite, rectorite, calcite, siderite and residual feldspar are also contained in some ores. The deposit is considered to have been formed by hydrothermal alteration subsequent to the intrusion of rhyolitic magma. The central zone of the alteration is rich in sericite, kaolinite and rectorite. Tosudite is abundant in the intermediate zone between the central zone and the weakly altered zone. The central zone appears to have been subjected to conspicuous alteration at a late stage. The high-low inversion peak in the DTA curve for the quartz is broad and the peak temperature is 4-23℃ lower than that of standard quartz. Quartz samples in the central zone have higher inversion temperature as compared with those in the outer alteration zones. Moreover, the quartz samples in the central zone also show another low-temperature broad peak which may be due to the quartz having formed in the late stage of the alteration.
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