Role of pH changes in primary uraninite mineralization

Uranyl minerals form a distinct series based on their solubilities in environments of different pH, beginning with the molybdenates, and proceeding through the arsenates, phosphates, vanadates, and silicates of the soddyite groups. Unlike exogenetic-epigenetic uranium deposits with pitchblende, infiltrational deposits with uranyl mineralization are primarily the result of changes in the pH of the environment. The model presented gives the precipitation of uranyl vanadates at an acidic geochemical barrier, and it can be used to explain the genesis of carnotite deposits in calcretes. A geochemically opposite model for the formation of uranyl minerals as the result of the neutralization of interstitial waters that have been strongly acidified (to pH 2) in conjunction with the oxidation of sulfide-bearing rocks must be adopted to explain the distribution and conditions of the formation of the uraninite deposits in black shales