Formation conditions of oxidation zones of uranium deposits and uranium mineral accumulations in the gipergenesis zone

The diversity of oxidation zones of uranium deposits and other accumulation s of uranium hypergene minerals is defined by the greater case of primary u ranium minerals to be transformed during oxidation as compared with that of most sulfides and sulfarsenides. The interaction of solutions with sulfide s and uranium minerals during oxidation proceeds in, three stages, namely: (1) oxidation of primary uranium minerals, (2) simultaneous oxidation of su lfides and uranium minerals, and (3) transformation of previously formed mi nerals after complete sulfide oxidation. The first stage occurs in neutral or alkaline environments favorable for hydration and the replacement of pri mary minerals by uranium hydroxides and silicates in the form of gummite wi thin contours of primary ores, without significant uranium removal. The sec ond stage proceeds under increasing acidity and the simultaneous oxidation of sulfides and uranium minerals with formation of uranium phosphates and a rsenates. During this process, minerals of the first stage unstable in acid ic environments are partly or completely decomposed. The preponderance of s ulfides 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 com pletely missing. The performed study made it possible to establish regulari ties in the formation of secondary zoning. The horizontal zoning observed i n the oxidation zone of sulfide-free and sulfide-poor uranium deposits in t he form of "gummite" fringes develops after primary minerals, while vertica l zoning is manifested in sulfide-uranium deposits. The upper part of the l atter is marked by the formation of hydroxides, uranium silicates, and uran ium-containing hyalites, which are replaced by uranite when they go deeper. The deeper horizon located at the level of ground water oscillations corre sponds to the zone of a secondary enrichment with regenerated uranium oxide s. The proposed classification includes three types of exogenic uranium acc umulations in the hypergenesis zone: (1) the oxidation zone of uranium depo sits, (2) the oxidation zone of sulfide and sulfide-uranium deposits, and ( 3) accumulations of uranium minerals in the hypergenesis zone not related t o uranium and other deposits. Characteristics of these zones and practical recommendations are discussed. For instance, in sulfide-free deposits, uran ium is virtually not removed beyond ore bodies, a fact that allows us to qu antitatively estimate the primary ore mineralization potential. In oxidatio n zones of sulfide-uranium deposits, a decisive role belongs to a total sul fide amount and their relationships with uranium, as well as to the presenc e of neutralizing minerals in host rocks and veins. The considered material s can be used for the assessment of the mineral composition of primary ores and ore mineralization scales (using exposures) and for solving problems o f ore mineralization distribution with the depth, formation of secondary en richments zones, etc. This approach to the study and classification of uran ium deposits can also be applied to other mineral deposits.