Microprobe research was performed on transparent polished plates (thin sections) of samples of fluorite and uranium ore from the Argun deposit in Zabaikal'skii Krai, Russia. The composition of minerals was determined at the Center for Isotopic Study of the Russian Geological Research Institute using a Cam-Scan MX 2500 scanning electron microscope equipped with a Link Pentaflet energy-dispersion spectrometer. Certified natural and synthetic samples were used as the standards.