Carbonatite ore deposits attract much attention as resources of Nb and rare earth elements. Analytical method of uranium in weathered carbonatite ore deposit in Brazil was studied. The KOH fusion, which is used for the determination of U in rock samples, is proved to be applicable to the decomposition of such samples. The gamma-spectrometry is non-destructive and suitable for samples containing insoluble minerals. The ICP analysis combined with acid decomposition might produce low results owing to the insufficient decomposition of samples. The KOH fusion–fluorimetry method was applied to the weathered carbonatite samples taken from Brazil and good results were obtained. U contents ranged from 10 to 1200ppm, which are higher than the average contents of rocks and soils. U seemed to be concentrated during the weathering process.
Opal boulders taken from the Shikaribetsu area, central Hokkaido, were preliminarily studied on their occurrences, properties and chemical compositions. They suggested hydrothermal activities in the past. Opals showed fluorescence of red, green, orange, yellow and blue colors. Some of them were enriched in gold, silver, mercury, arsenic, antimony and tellurium compared with the crustal abundance of elements.