[en] The authors identified varieties of pyrites in infiltration deposits of uranium in the Bukinaysk ore field (the Central Kyzylkums), within which there is evidence of hydrothermal activity, and investigated these pyrites for admixture elements (Se, As, and Co). The abundance of admixture elements, both in pyrites from unaltered rock (slands) and in pyrites from ore bodies at pinch-outs of layered-oxidized rock, are similar to the background values. Low abundances of admixture elements are typical of the groundmass of neogenic pyrites in epigenetically altered (silicified, kaolinized, carbonatized) sandstones. Specific arsenic- (>3) and selenium-bearing (>8%) pyrites were found in zones of montmorillonitization and weak kaolinization. 16 refs., 4 figs., 1 tab