Pyrochlores as Indicators of the Uranium-Bearing Potential of Magmatic Melts

摘要

The interaction of columbite and uraninite with a fluid-magma system consisting of a melt of Li-F-granite and fluoride fluid at 750℃ and P= 2300 bar causes the formation of zonal pyrochlores being considerably different in uranium and fluorine contents. Fluorine-rich pyrochlores (to 7-12 at %) preserve the Nb/U ratio of the initial columbite (15-30). Uranium-bearing pyrochlores contain 2-4 times less amounts of fluorine, above 2 at % of uranium, and the Nb/U molar ratio decreases to 5-15. The analysis of Ca, U, and F variation trends points to the influence of temperature on the reactions of Ca~(2+) to U~(4+) cation exchange. The statistical analysis (250 measurements) showed that the maximum uranium content in pyrochlores amounted to 16 ± 5 wt % for the magmatic system saturated with uraninite.