PARAGENESES OF THE MINERALS OF THE NINGYÔ-TÔGÉ MINE

Abstract

In the Ningyô-tôgé area, uranium is emplaced in the Neogene basal conglomerate deposited on the eroded surface of the Mesozoic granite. The geological environment of the uranium ores is similar to the general sandstone type uranium deposits, but the mineralogy is peculiar in some respects. three uranium minerals, ningyoite, autunite and uraninite have been identified in the mine, and besides them humic acid, limonite and biotite were found to be uraniferous. Most of the uranium in the ores is contained principally in ningyoite in the unoxidized zone, and in autunite in the oxidized zone. Uranium of the other forms occurs rather locally or less abundantly.
The ores are mostly composed of allogenic rock forming minerals and their altered products. authigenic minerals, though they are less in the amounts than the allogenic minerals, occur commonly coating pebbles or mineral grains, filling cavities, and replacing allogenic minerals. These are kaolinite, chlorite, montmorillonite, carbonaceous matter, marcasite, pyrite, sphalerite, gypsum, melanterite, uranous minerals, sericite, calcite, siderite, limonite and uranyl minerals, roughly in the order of the formation. the last four minerals are found only in the oxydized zone. Part of the authigenic minerals appears to have been formed during the diagenesis and the others were precipitated from or altered by the extrinsic solution. The correlation analysis revealed that uranium is associated with P, S, Ca, Zn and As, and the exceedingly good correlation of phosphorus with uranium has been demonstrated. The correlation analysis was applied also for some minerals, which were analyzed quantitatively with X-ray diffractometer. Remarkably good correlation was found between uranium and sericite, and between uranium and gypsum, while the strongly negative correlation was shown between uranium and kaolinite.
These statistical consideration of uranium with some authigenic minerals and elements, together with the paragenetic study of the ores by microscopic observation indicated that uranium was precipitated mostly as ningyoite with gypsum from uranium containing ore solution, which transformed kaolinite partly into sericite during the uranium mineralization.