2. Formation of Uranium ore deposits

3. Due to its solubility in oxidising conditions, any uranium mineral exposed at the Earth’s surface will undergo chemical weathering, be dissolved and taken into solution in the surface and groundwater.

4. We know that groundwater flows through aquifers. Buried fossil river channels containing porous and permeable sandstones and conglomerates make good aquifers. Buried fossil river channels

5. When the groundwater meets a change in conditions from oxidising to reducing, uranium ore minerals are reprecipitated in the palaeo- channel sediments.

6. Roll-front deposits cut across bedding planes. Uranium-bearing ground waters precipitate uranium oxide minerals when they come into contact with reducing conditions in porous and permeable rocks. Curved ‘roll-type’ uranium ore deposits form at the oxidation-reduction (redox) boundary. Often the redox boundary is at the water table.

7. In many sandstone hosted uranium ore deposits there is a close association between the uranium ore and organic matter. It is highly likely that sulphur- reducing bacteria present in decaying vegetation are involved in the ore forming process. There are examples of individual fossil logs that have been entirely replaced by uranium minerals, making small but high grade ore deposits. Uranium ore deposits of this type are found in the Colorado Plateau areas of the western USA.

8. To Sum Up: