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Uranium ore deposits
Uranium ore deposits are ore deposits which constitute economically recoverable concentrations of uranium within the Earth's crust.
Additional recommended knowledge
The distribution of uranium ore deposits is widespread, with sizeable deposits and mines in Australia (40% of EDR), Canada, former Soviet republics, Africa and South America.
Uranium ore deposits can be divided into several broad classes:
There are several themes of uranium ore deposit formation which are caused by geological and chemical features of rocks and the element uranium. The basic themes of uranium ore genesis are host mineralogy, reduction-oxidation potential, and porosity.
Uranium is a highly soluble heavy metal, as well as a radioactive heavy metal. Uranium can be easily dissolved, transported and reprecipitated within ground waters by very subtle changes in oxidation conditions. Uranium also does not usually form very insoluble mineral species, which is a further factor in the wide variety of geological conditions and places in which uranium mineralization may accumulate.
Uranium is an incompatible element within magmas, and as such it tends to become accumulated within highly fractionated and evolved granite melts, particularly alkaline examples. These melts tend to become highly enriched in uranium, thorium and potassium, and may in turn create internal pegmatites or hydrothermal systems into which uranium may dissolve.
Roll front uranium deposits
Roll-front uranium deposits are generally hosted within permeable and porous sandstones or conglomerates. The mechanism for deposit formation is dissolution of uranium from the formation or nearby strata and the transport of this soluble uranium into the host unit. When the fluids change redox state, generally in contact with carbon-rich organic matter, uranium precipitates to form a 'front'.
The model for formation of palaeochannel deposits is similar to that for roll-front deposits, above, except that the source of uranium may be in the watershed leading into a stream, or the bed load of the palaeochannel itself. This uranium is transported through the groundwaters and is deposited either at a reduced boundary, or in ephemeral drainage systems such as those in deserts of Namibia and Australia, it is deposited in calcretised evaporation sites or even in salt lakes as the ground water evaporates.
Some particularly rich uranium deposits are formed in palaeochannels which are filled in the lower parts by lignite or brown coal, which acts as a particularly efficient reductive trap for uranium. Sometimes, elements such as scandium, gold and silver may be concentrated within these lignite-hosted uranium deposits .
Pegmatite hosted deposits
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Uranium_ore_deposits". A list of authors is available in Wikipedia.|