The diversity of oxidation zones of uranium deposits and other accumulations of uranium hypergene minerals is defined by the greater case of primary uranium minerals to be transformed during oxidation as compared with that of most sulfides and sulfarsenides. The interaction of solutions with sulfides and uranium minerals during oxidation proceeds in, three stages, namely: (1) oxidation of primary uranium minerals, (2) simultaneous oxidation of sulfides and uranium minerals, and (3) transformation of previously formed minerals after complete sulfide oxidation. The first stage occurs in neutral or alkaline environments favorable for hydration and the replacement of primary minerals by uranium hydroxides and silicates in the form of gummite within contours of primary ores, without significant uranium removal. The second stage proceeds under increasing acidity and the simultaneous oxidation of sulfides and uranium minerals with formation of uranium phosphates and arsenates. During this process, minerals of the first stage unstable in acidic environments are partly or completely decomposed. The preponderance of sulfides results in the uranium removal from oxidation zones, whereas under their lower amount, uranium hydroxides of the schoepite-paraschoepite type are formed. Under an insignificant sulfide content, the second stage is completely missing. The performed study made it possible to establish regularities in the formation of secondary zoning. The horizontal zoning observed in the oxidation zone of sulfide-free and sulfide-poor uranium deposits in the form of "gummite" fringes develops after primary minerals, while vertical zoning is manifested in sulfide-uranium deposits. The upper part of the latter is marked by the formation of hydroxides, uranium silicates, and uranium-containing hyalites, which are replaced by uranite when they go deeper. The deeper horizon located at the level of ground water oscillations corresponds to the zone of a secondary enrichment with regenerated uranium oxides. The proposed classification includes three types of exogenic uranium accumulations in the hypergenesis zone: (1) the oxidation zone of uranium deposits, (2) the oxidation zone of sulfide and sulfide-uranium deposits, and (3) accumulations of uranium minerals in the hypergenesis zone not related to uranium and other deposits. Characteristics of these zones and practical recommendations are discussed. For instance, in sulfide-free deposits, uranium is virtually not removed beyond ore bodies, a fact that allows us to quantitatively estimate the primary ore mineralization potential. In oxidation zones of sulfide-uranium deposits, a decisive role belongs to a total sulfide amount and their relationships with uranium, as well as to the presence of neutralizing minerals in host rocks and veins. The considered materials can be used for the assessment of the mineral composition of primary ores and ore mineralization scales (using exposures) and for solving problems of ore mineralization distribution with the depth, formation of secondary enrichments zones, etc. This approach to the study and classification of uranium deposits can also be applied to other mineral deposits.
