The limestone and dolomite deposit at Kuzuu-machi, Tochigi prefecture is very famous as one of those largest deposits in Japan. It is Permian in age and consists of the Nabeyama formation, which is divided into the lower limestone, the middle dolostone and the upper limestone. The Nabe-yama formation overlies conformably the Aizawa formation, which consists of sandstone, alternation of sandstone and shale, and schalstein in ascending order, and is covered unconformably by the Ado-yama formation, which consists of mainly chert and shale.
Because of minor phosphor contents and small grain sizes of the phosphor-bearing mineral, it has long been impossible to confirm the mode of occurrences of phosphor and the phosphor mineral.
It is concluded, however, from the results of X-ray powder diffraction, chemical analyses and electron microscopic analyses, that the phosphor mineral occurs as cryptocrystalline fluor-apatite.
The mode of occurrences of apatite is classified as follows:
1) Apatite is disseminated within the definite horizons in limestone and dolostone.
2) Apatite forms a lamina intercalated in the alternation zone of shale and calcitic dolostone in the middle dolostone.
3) Apatite occurs in the lowermost part of the Adoyama formation as gravels with maximum dimensions of 10cm×5cm×3cm in the calcareous breccia and as tiny grains with diameter of0.2-0.5cm in the calcarenite.
4) Apatite occurs in the fillings of cracks in limestone and dolostone as grains with diameter of0.5-1.5cm.
5) Apatite occurs in the fault clay in limestone and dolostone as clay fraction.
It is considered that apatite in the first two cases is syngenetic with limestone and dolostone deposits and apatite in the other three cases is derived from the syngenetic apatite.
抄録全体を表示