Uranium ore
[2] The challenge for commercial uranium extraction is to find those areas where the concentrations are adequate to form an economically viable deposit.
Uranium has the highest atomic weight of the naturally occurring elements and is approximately 70% denser than lead, but it is not as dense as tungsten, gold, platinum, iridium, or osmium.
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.
The IAEA classification scheme works well but is far from ideal, as it does not consider that similar processes may form many deposit types, yet in a different geological setting.
When the fluids change redox state, generally in contact with carbon-rich organic matter, uranium precipitates to form a 'front'.
Probably more significant than their larger size, roll front deposits have the advantage of being amenable to low cost in situ leach recovery.
[16][17][18] These deposits are hosted in palaeochannels filled with Cenozoic sediments and sourced their uranium from uranium-rich Paleoproterozoic to Mesoproterozoic rocks of the Mount Painter Inlier and the Olary Domain of the Curnamona Province.
Tectonic-lithologic controlled uranium deposits occur in sandstones adjacent to a permeable fault zone[13] which cuts the sandstone/mudstone sequence.
[11] Quartz pebble conglomerate hosted uranium deposits are of historical significance as the major source of primary production for several decades after World War II.
Host rocks are typically submature to supermature, polymictic conglomerates and sandstones deposited in alluvial fan and braided stream environments.
The host conglomerates of the Huronian deposits are situated at the base of the sequence, whereas the mineralized horizons at Witwatersand are arguably along tectonized intraformational unconformities.
[19] Quartz pebble conglomerate uranium deposits are typically low grade but characterized by high tonnages.
Textural evidence indicates that the uranium and gold have been remobilized to their current sites; however the debate continues if the original deposition was detrital or was entirely hydrothermal, or alternatively related to high grade diagenesis.
Strong regional scale alteration consists of pyrophyllite, chloritoid, muscovite, chlorite, quartz, rutile, and pyrite.
Only one iron oxide copper gold ore deposit is known to contain economically significant quantities of uranium.
[13] Uranium occurs with copper, gold, silver, and rare-earth elements in a large hematite-rich granite breccia complex in the Gawler Craton overlain by approximately 300 metres of flat-lying sedimentary rocks of the Stuart Shelf geological province.
Hydrothermal processes at about 300 million years ago remobilised uranium from these granites and enriched them in the quartz-hematite breccias.
Franz Ernst Brückmann made the first mineralogical description of the mineral in 1727, and the vein deposit Jachymov in the Czech Republic became the type locality for uraninite.
[21] In 1789 German chemist Martin Heinrich Klaproth discovered the element uranium in a sample of pitchblende from the Johanngeorgenstadt vein deposit.
The first industrial production of uranium was made from the Jachymov deposit, and Marie and Pierre Curie used the tailings of the mine for their discovery of polonium and radium.
Remobilisation of uranium occurred at later stages producing polymetal veins containing silver, cobalt, nickel, arsenic and other elements.
However, only 5 to 12% of the vein areas carry mineralization and although massive lenses of pitchblende can occur, the overall ore grade is only about 0.1% uranium.
[22][23] The Bohemian Massif contains shear zone hosted uranium deposits with the most important one being Rozna-Olsi in Moravia northwest of Brno.
After the Variscan orogeny, extension took place and hydrothermal fluids overprinted fine grained materials in shear zones with a sulfide-chlorite alteration.
Major world deposits include Rossing (Namibia), Ilimaussaq intrusive complex (Greenland) and Palabora (South Africa).
[13] Marine sedimentary phosphorite deposits can contain low grade concentrations of uranium, up to 0.01–0.015% U3O8, within fluorite or apatite.
[11][13] Primary ore minerals are uraninite and pitchblende, which occur as cavity fills and coatings on quartz grains within permeable sandstone breccias within the pipe.
[11] Metasomatite deposits consist of disseminated uranium minerals within structurally deformed rocks that have been affected by intense sodium metasomatism.
Organic matter in clay-rich sediments will not be converted to CO2 by biological processes in this environment and it can reduce and immobilise uranium dissolved in seawater.
Chattanooga Shale in the southeastern United States is estimated to contain 4 to 5 million tonnes at an average grade of 54 ppm.
