It can be said that our present knowledge of geology and mineralogy of domestic uranium deposits, acquired as a result of the active search in the last five years, is quite a renewed one, because, until 1954, only several kinds of uranium-thorium bearing minerals in radioactive pegmatites were known in Japan.
More than 40 localities of vein-type deposits and about 30 of sedimentary type have been newly found. Although the genetical classification of these deposits is not easy at present, the known uraniferous deposits may be tentatively classified as follows :
(A) Pegmatite
(B) Contact-metasomatic
(C) Pneumatolytic to hypothermal
(D) Hydrothermal
(E) Sedimentary 1-Syngenetic deposit in Palaeozoic black slate, usually accompanied by bedded manganese deposit
2-Ningyo-toge type, epigenetic deposit, chemical process of concentration by ground water in Tertiary conglomerate or arkose sandstone
(F) Placer
These deposits of all kinds except (1) are distributed in the area of so-called "Massif" which consists of granitic intrusion masses and pre-granite formations, more or less metamorphosed by the granite. Of them economically most important is (2), Ningyo-toge type, of sedimentary origin.
It should be noted that "Massif" areas are favourable for formation of both vein- and sedimentary type deposits. Discovery of new deposits of Ningyo-toge type can be expected hereafter, because vast areas of "Massif" in Japan still remain unprospected for uranium.
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