Selenium is an essential trace element in sulfide ores. The selenium minerals (clausthalite, PbSe, tiemannite, HgSe, and naumannite, Ag 2 Se) have been found with goethite and siderite as newly formed phases in the oxidation zone of the Jubileynoe copper-sulfide ore deposit at the Urals, in Russia. Thermodynamic modeling was used to assess physical-chemical parameters of selenide stability, and estimate the possibility of the Pb, Hg and Ag selenites formation while the oxidation of sulfide ores. Eh-pH diagrams of Fe-S-CO 2 -H 2 O, Fe-Se-CO 2 -H 2 O systems were calculated for physi- cal-chemical formation conditions of the oxidation zone of the Jubileynoe deposit, as well as for systems M-Se-H 2 O and M-S-H 2 O (M = Hg, Pb, Ag). Exchange reactions between sulfides and selenides have allowed estimating the ratio of selenium and sulfur activities in the mineral-forming media. It is shown that among selenites of lead, silver and mercury only PbSeO 3 compound may be formed theoretically in the oxidation zone of the Jubileynoe deposit.