|11/21/2014 by mdc|
|Although there are between 12 and 15 different typestyles of uranium deposits, almost all economic uranium deposits come from just two types -|
unconformity-related deposits, and
sandstone uranium deposits.
Unconformity-related deposits account for around on third of the uranium production, while sandstone uranium deposits account for another third. The remaining third of production comes from a variety of the remaining 10 or so deposit types.
The most common uranium mineral is uraninite or pitchblende. There are a range of other uranium minerals including carnotite, brannerite and euxenite. Uranium is reactive and forms a large number of colorful secondary minerals including autunite - with calcium, saleeite - magnesium, and torbernite -copper. Uranium is only weakly radioactive, but is highly soluable, which is used to advantage with some mining methods.
An unconformity is a boundary between two rock units that reflects a time gap. Uranium unconformity deposits are generally associated with structures in sedimentary rocks that reflect the erosion surface rocks, and then the later subsequent deposition of younger sedimentary rocks above. Uranium deposits occur in sedimentary basins deposited on top of very old basement metamorphic rocks. The source of uranium is either from the basin or the basement rocks. Groundwater circulating in the basin results in the concentration and deposition of the mineralization.
Uranium deposits occurring at or near an unconformity between basin sedimentary rocks and basement metamorphic rocks. Uranium is highly reactive and will deposit and accumulate in response to the changing chemical environment particularly when moved from an oxidizing environment to a reducing one. As the fluids move through the basin and basement rocks, they convert uranium to a highly oxidized state. Eventually this fluid reaches an area which is less oxidative such as graphitic or volcanic rocks, etc.