対州陶石・対州白土中の粘土鉱物

抄録

Mineralogical descriptions are made for the Taishu hakudo and Taishu toseki which have been mined as refractory clay and a raw material for sanitary ware at Azu in the Tsushima Shimoshima Island, Nagasaki Prefecture, Japan. These ores were formed by hydrothermal alteration of quartz porphyry of Miocene age. X-ray powder diffraction, electron probe microanalysis and polarizing microscopy have revealed that the Taishu hakudo (white clay) is composed mainly of halloysite and the Taishu toseki (altered quartz porphyry) is composed of 2M₁ sericite, Ca-beidellite, albite, quartz, etc. with residual quartz and oligoclase.
The toseki is well jointed in the same direction with a vertical dip, and the alteration products are abundant along the fissures. Three types of alteration can be recognized at this deposit. The first alteration is characterized by the assemblage of albite, sericite and beidellite which crystallized in this order. This alteration is considered to have transformed quartz porphyry into toseki by pervasive alteration around the fissures subsequent to the igneous activity of the original quartz porphyry. The second alteration is characterized by the assemblage of FeMg-chlorite, sericite, calcite and galena and the assemblage of interstratified chlorite/vermiculite, sericite and quartz which were formed filling the fissures and disseminated in the toseki. The hydrothermal solution of this alteration may have a genetical relation to a granitic pluton near this deposit. The last alteration is intense halloysitization which affected the toseki pervasively around the fissures and formed the hakudo.