On the Uraniferous Deposit of the Nodatamagawa Mine

with Special Reference to the Origin of Uranium

Abstract

The area surrounding the Nodatamagawa mine consists of Palaeozoic, Late Jurassic, and Pleistocene sediments, and granitic rock which intrudes and thermally metamorphoses the Palaeozoic sediments, and is overlain by the younger sediments.
Manganese ore deposits are distributed in a quartzite zone of the Palaeozoic sediments, and a schematic succession of phyllitic quartzite, manganese ore body, massive quartzite, and phyllitic quartzite is. apparent from the foot wall side to the hanging wall side. Many kinds of manganese minerals have been identified; hydroxides and oxides occur in the inner part and silicate minerals occur in the outer part of the ore body.
The uraniferous ore deposits develop in the Palaeozoic sediments and are classified into two types, a vein type and a bedded type. The vein type deposit occurs along faults and fractures which are concordant or discordant with the strata. The typical uraniferous veinlet includes molybdenite, pyrite, cobaltite, and gersdorffite, besides uraninite. The bedded type deposit is uraniferous hornfels that is. confined to a definite stratigraphic horizon. It is generally distributed between the massive and the phyllitic quartzite mentioned above. The hornfels is characterized by a remarkable abundance of sulphide and arsenide minerals, which occur generally as impregnations and/or streaks along the bedding plane. The uranium content of the entire hornfels body is estimated to be 0.01% or less, though uranium is locally concentrated in amounts up to 0.15%. Uraninite shows a close association with pyrite in the streaks, and the major part of the uranium occurs in biotite as very tiny uraninite with a diameter of 1-2μ. The ore minerals in the hornfels are pyrite, pyrrhotite, chalcopyrite, sphalerite, and nickel-cobalt minerals such as niccolite, gersdorffite, pentlandite, and cobaltite.
Analysis of several samples shows that arsenic, cobalt, molybdenum, nickel, and vanadium are abundant trace elements. The carbon content is less than 3.25%.
The writers conclude that a syngenetic origin of uranium in the hornfels is more likely than a magmatic origin related to the granitic rock. It is also conjectured that the uranium in the vein type deposit may have migrated, been redistributed, and concentrated from the uraniferous hornfels.