Effects of redox conditions on the mineral form of uranium in hydrothermal deposits

Mineral formation at a hydrothermal uranium deposit almost always occurs in several stages. The minerals produced in the uranium-ore stage are usually localized in aureoles of altered rocks along fault lines produced in the preceding stage. The minerals of the ore stage are also exposed to later solutions, which are often not in equilibrium with the minerals. As a result, the uranium minerals partly dissolve and new mineral species are produced. Data on the composition, formation sequence, and location of the various parageneses of uranium minerals sometimes make it possible to judge the chemistry of the process, particularly the variations in redox conditions. In this paper, the mineral form of uranium is related to the redox conditions of deposition for mineral associations in three ore fields. (JMT)