It is more useful to consider the time-bound character of uranium mineralising processes than the time-bound character of uranium deposits. This is because present uranium deposits are the result of a series of mineralising steps which occurred over hundreds of millions of years. We have identified five periods which are characterised by moderately distinct mineralising processes. 1.(1) Before 2800 Ma. Uranium was fractionated into the upper crust during late Archaean—Early Proterozoic cratonisation by magmatic and metamorphic processes. The granitic terranes were an important source of uranium for subsequent mineralising events.2.(2) 2800-2200 Ma. Although the atmosphere was probably not reducing at this time, the level of oxygen was sufficiently low for uraninite to be transported and concentrated in sedimentary basins. Cratonisation was a prerequisite for the formation and preservation of long-lived basins. Rapid burial and reducing conditions during diagenesis were important for preserving the uranitite. The uranium was mobilised during diagenesis and metamorphism.3.(3) 2200-1200 Ma. After ∼ 2000 Ma, when the oxygen level in the atmosphere increased markedly, the movement of uranium in solution as uranyl ions became more important. The first marine shelf sequences containing chemical and organic sediments to be deposited on the cratons formed excellent sites for the syn-sedimentary, diagenetic or metamorphic concentration of uranium. In some cases this mineralisation was economic; in other cases it may have been just a step in a succession of mineralising events. Continental clastic sediments which overlie these shelf sediments were excellent hosts for large hydrothermal circulation systems which could remobilise the uranium from either granites or sediments. The lack of organic and argillaceous material in these continental sequences resulted in the precipitation of uranium near the basal unconformity, where there were reducing sediments.4.(4) 1200-400 Ma. With the start of modern plate tectonics there was greater potential for the thermally activated remobilisation of uranium. The period 1200-900 Ma marked the final mineralisation in some important deposits. The Pan-African and Brazilian events (700-400 Ma) mobilised uranium of uncertain origin and concentrated it in previously deposited marginal marine sediments.5.(5) 400-0 Ma. The incorporation of organic material into continental clastic sediments allowed uranyl ions to be precipitated before they reached the sea, to form the important sandstone-type of deposits.Any time-bound mineralising process may be either the final or an intermediate step in forming an economic uranium deposit. Which of these it is depends on the subsequent history of the area; on whether the uranium is preserved, dispersed or reconcentrated. That many major uranium deposits occur on late Archaean—Early Proterozoic cratons emphasises the importance of the long-term preservation of sedimentary sequences, even though the uranium may be remobilised several times within the sediments.

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{{Explor lien
   |wiki=    Wicri/Terre
   |area=    CobaltMaghrebV1
   |flux=    Main
   |étape=   Exploration
   |type=    RBID
   |clé=     ISTEX:7106C6EF1C94A8A48FE7D75DB3DC95A1E354E882
   |texte=   The time-bound character of uranium mineralising processes, with special reference to the Proterozoic of Gondwana
}}