Due to the toxicity of selenium it is quite essential to analyze theconditions under which selenites and selenates replace selenides in the oxidation zones of sulfide ore deposits and upon weathering of technologic waste. This purpose is performed by summarizing in Eh-pH diagrams the results of calculations of equilibrium, and considering geologic occurrences. It is the purpose of this work to consider the manner of occurrence and the behavior of selenium during crystallization and dilution of selenites (chalcomenite, ahlfeldite, and cobaltomenite) and sulpates (chalcanthite, bieberite, and morenosite) in order to interpret conditions of formation of these minerals and to compare their geologic stabilities in low-temperature conditions. The interpretations are summarized on the diagrams, synthesized from equilibrium calculations of the mineral solubility in the systems Cu2*, Ni2*, Co2* // SeO,2, SO42 - H2O (including five subsystems: Ni2+, Co2* // SeO,2, SO42 - H2O; Cu2*, Co2+ // SeO,2, SO42 - H2O; Cu2*, Ni2* // SeO,2, SO42 - H20; Cu2+, NP, Co2+ // SeO,2 - H20, and Cu2*, Ni2+, Co2* // SO,2 - H2O), and reported geologic occurrences. The most recent thermodynamic data available were used for the construction of diagrams from reactions which are balanced equations among species which are thermodynamically stable within the ranges of conditions considered for each reaction.