Uranium ore

Source: Wikipedia, the free encyclopedia.
Sample of uranium ore

Uranium ore deposits are economically recoverable concentrations of

nuclear reactors
.

Globally, the distribution of uranium ore deposits is widespread on all continents, with the largest deposits found in Australia, Kazakhstan, and Canada. To date, high-grade deposits are only found in the Athabasca Basin region of Canada.

Uranium deposits are generally classified based on host rocks, structural setting, and mineralogy of the deposit. The most widely used classification scheme was developed by the International Atomic Energy Agency (IAEA) and subdivides deposits into 15 categories.

Uranium

Uranium is a silvery-gray

cosmic rays
.

Uranium has the highest atomic weight of the naturally occurring elements and is approximately 70%

atomic weights higher than that of iron, it is only naturally formed in supernova explosions.[5]

Uranium minerals

Uraninite, also known as pitchblende
Autunite, a secondary uranium mineral named after Autun in France
Torbernite, an important secondary uranium mineral

The primary uranium ore mineral is

samarskite
group are other uranium minerals.

A large variety of secondary uranium minerals are known, many of which are brilliantly coloured and fluorescent. The most common are gummite (a mixture of minerals),[7] autunite (with calcium), saleeite (magnesium) and torbernite (with copper); and hydrated uranium silicates such as coffinite, uranophane (with calcium) and sklodowskite (magnesium).

Uranium Minerals[8][9]
Primary uranium minerals
Name Chemical Formula
uraninite or pitchblende UO2
coffinite U(SiO4)1–x(OH)4x
brannerite UTi2O6
davidite (REE)(Y,U)(Ti,Fe3+)20O38
thucholite Uranium-bearing pyrobitumen
Secondary uranium minerals
Name Chemical Formula
autunite Ca(UO2)2(PO4)2 x 8–12 H2O
carnotite K2(UO2)2(VO4)2 x 1–3 H2O
gummite gum like mixture of various uranium minerals
saleeite Mg(UO2)2(PO4)2 x 10 H2O
torbernite Cu(UO2)2(PO4)2 x 12 H2O
tyuyamunite Ca(UO2)2(VO4)2 x 5–8 H2O
uranocircite Ba(UO2)2(PO4)2 x 8–10 H2O
uranophane Ca(UO2)2(HSiO4)2 x 5 H2O
zeunerite Cu(UO2)2(AsO4)2 x 8–10 H2O

Ore genesis

Wood fragment in a conglomerate from Utah, which has been partially replaced by pitchblende (black) and surrounded by carnotite (yellow)

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, as well as a radioactive, heavy metal. It can be easily dissolved, transported and precipitated within

ground waters
by 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

hydrothermal
systems into which uranium may dissolve.

Classification schemes

IAEA Classification (1996)

The International Atomic Energy Agency (IAEA) assigns uranium deposits to 15 main categories of deposit types, according to their geological setting and genesis of mineralization, arranged according to their approximate economic significance.

  1. Unconformity-related deposits
  2. Sandstone deposits
  3. Quartz-pebble conglomerate deposits
  4. Breccia complex deposits
  5. Vein deposits
  6. Intrusive deposits (Alaskites)
  7. Phosphorite deposits
  8. Collapse breccia pipe deposits
  9. Volcanic deposits
  10. Surficial deposits
  11. Metasomatite deposits
  12. Metamorphic deposits
  13. Lignite
  14. Black shale deposits
  15. Other types of deposits

Alternate scheme

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. The following table groups the above deposit types based on their environment of deposition.

Uranium Deposit Classification[10]
Uranium Transport /
Precipitation Conditions
Deposit Type
Surface Processes / synsedimentary Surficial deposits
Quartz-pebble conglomerate deposits
Phosphorite deposits
Lignite
Black shales
Diagenetic
Sandstone deposits
Diagenetic – Hydrothermal? Unconformity-related deposits
Vein deposits
Collapse breccia pipe deposits
Magmatic – Hydrothermal? Breccia complex deposits
Volcanic deposits
Metasomatite deposits
Vein deposits
Intrusive deposits
Metamorphic – Hydrothermal? Metamorphic deposits

Deposit types (IAEA Classification)

Unconformity-related deposits

open pit, Northern Territory, Australia: Uranium mineralised Cahill Formation as visible in the pit is unconformably overlain by Kombolgie sandstone
forming the mountains in the background

Unconformity-type uranium deposits host high grades relative to other uranium deposits and include some of the largest and richest deposits known. They occur in close proximity to

basement rocks. These sedimentary basins are typically of Proterozoic age, however some Phanerozoic
examples exist.

Phanerozoic unconformity-related deposits occur in Proterozoic metasediments below an unconformity at the base of overlying Phanerozoic sandstone. These deposits are small and low-grade (

Bertholene and Aveyron deposits, in France).[11]

The two most significant areas for this style of deposit are currently the Athabasca Basin in Saskatchewan, Canada, and the McArthur Basin in the Northern Territory, Australia.

Athabasca Basin

The highest grade uranium deposits are found in the

Cigar Lake with 217 million pounds (99,000 t) U3O8 at an average grade of 18% and McArthur River with 324 million pounds (147,000 t) U3O8 at an average grade of 17%. These deposits occur below, across and immediately above the unconformity. Additionally, another high grade discovery is in the development stage at Patterson Lake (Triple R deposit) with an estimated mineral resource identified as; "Indicated Mineral Resources" estimated to total 2,291,000 tons at an average grade of 1.58% U3O8 containing 79,610,000 pounds of U3O8. "Inferred Mineral Resources" are estimated to total 901,000 tons at an average grade of 1.30% U3O8 containing 25,884,000 pounds of U3O8.[12]

McArthur Basin

The deposits of the McArthur River basin in the East Alligator Rivers region of the Northern Territory of Australia (including Jabiluka, Ranger, and Nabarlek) are below the unconformity and are at the low-grade end of the unconformity deposit range but are still high grade compared to most uranium deposit types. There has been very little exploration in Australia to locate deeply concealed deposits lying above the unconformity similar to those in Canada. It is possible that very high grade deposits occur in the sandstones above the unconformity in the Alligator Rivers/Arnhem Land area.[13]

Sandstone deposits

minerals
.

Sandstone deposits are contained within medium to coarse-grained sandstones deposited in a continental fluvial or marginal marine sedimentary environment. Impermeable shale or mudstone units are interbedded in the sedimentary sequence and often occur immediately above and below the mineralised horizon.[13] Uranium is mobile under oxidising conditions and precipitates under reducing conditions, and thus the presence of a reducing environment is essential for the formation of uranium deposits in sandstone.[11]

Primary mineralization consists of pitchblende and coffinite, with weathering producing secondary mineralization. Sandstone deposits constitute about 18% of world uranium resources. Orebodies of this type are commonly low to medium grade (0.05–0.4% U3O8) and individual orebodies are small to medium in size (ranging up to a maximum of 50,000 t U3O8).[13]

Sandstone hosted uranium deposits are widespread globally and span a broad range of host rock ages. Some of the major provinces and production centers include:

  1. the Wyoming basins
  2. the Grants District of New Mexico
  3. deposits in Central Europe and
  4. Kazakhstan

Significant potential remains in most of these centers as well as in Australia, Mongolia, South America, and Africa.

This model type can be further subdivided into the following sub-types:

  • tabular
  • roll front
  • basal channel
  • structurally related

Many deposits represent combinations of these types.

Tabular

Tabular deposits consist of irregular tabular or elongate

lenticular zones of uranium mineralisation within selectively reduced sediments. The mineralised zones are oriented parallel to the direction of groundwater flow, but on a small scale the ore zones may cut across sedimentary features of the host sandstone.[11][13]
Deposits of this nature commonly occur within palaeochannels cut in the underlying basement rocks.

Tabular sandstone uranium deposits contains many of the highest grades of the sandstone class, however the average deposit size is very small.

Roll front

Structures interpreted as Palaeo-rollfronts in South Australia

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 Rollfront subtype deposits typically represent the largest of the sandstone-hosted uranium deposits and one of the largest uranium deposit types with an average of 21 million lb (9,500 t) U3O8. Included in this class are the

in-situ leach
recovery.

Typical characteristics:

Basal channel (palaeochannel)

Basal channel deposits are often grouped with tabular or rollfront deposits, depending on their unique characteristics. The model for formation of

saline 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.[14]

The Frome Embayment in South Australia hosts several deposits of this type including Honeymoon, Oban, Beverley and [Four-Mile][15] (which is the largest deposit of this class).[16][17][18] These deposits are hosted in palaeochannels filled with Cainozoic sediments and sourced their uranium from uranium-rich Palaeo- to Mesoproterozoic rocks of the Mount Painter Inlier and the Olary Domain of the Curnamona Province.

Structurally related

dolerite
dyke (broken line) within the Paleoproterozoic Westmoreland conglomerate

Tectonic-lithologic controlled uranium deposits occur in sandstones adjacent to a permeable fault zone[13] which cuts the sandstone/mudstone sequence. Mineralisation forms tongue-shaped ore zones along the permeable sandstone layers adjacent to the fault. Often there are a number of mineralised zones 'stacked' vertically on top of each other within sandstone units adjacent to the fault zone.[11]

Quartz-pebble conglomerate deposits

Quartz pebble conglomerate hosted uranium deposits are of historical significance as the major source of primary production for several decades after

Witwatersrand Supergroup of South Africa. These deposits make up approximately 13% of the world's uranium resources.[13]

Two main sub-types have been identified:

Quartz pebble conglomerate hosted uranium deposits formed from the transport and deposition of uraninite in a fluvial sedimentary environment

braided stream
environments. The host conglomerates of the Huronian deposits in Canada are situated at the base of the sequence, whereas the mineralized horizons in the Witwatersand are arguably along tectonized intraformational unconformities.

Uranium minerals were derived from uraniferous pegmatites in the sediment source areas. These deposits are restricted to the

oxygen levels in the atmosphere reached a critical level, making simple uranium oxides no longer stable in near-surface environments.[19]

Quartz pebble conglomerate uranium deposits are typically low grade but characterized by high tonnages. The Huronian deposits in Canada generally contain higher grades (0.15% U3O8)[10] and greater resources (as shown by the Denison and Quirke mines), however some of the South African gold deposits also contain sizeable low grade (0.01% U3O8)[10] uranium resources.

Witwatersrand sub-type

In the

Witwatersrand Supergroup. The uranium rich Dominion Reef is located at the base of the West Rand Supergroup. The Vaal Reef is the most uranium rich reef of the Central Rand Group of sediments. Structural controls on the regional scale are normal faults while on the deposit scale are bedding parallel shears and thrusts. 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
.

Uranium minerals in the Witwatersrand deposits are typically uraninite with lesser uranothorite, brannerite, and coffinite. The uranium is especially concentrated along thin carbonaceous seams or carbon leaders. Strong regional scale alteration consists of pyrophyllite, chloritoid, muscovite, chlorite, quartz, rutile, and pyrite. The main elements associated with the uranium are gold and silver. Gold contents are much higher than in the Elliot Lake type with U:Au ranging between 5:1 and 500:1, which indicates that these gold-rich ores are essentially very low grade uranium deposits with gold.

Elliot Lake sub-type

Sedimentological controls on the Huronian deposits of the Elliot Lake district appear to be much stronger than in the Witwatersrand deposits. Ores grade from uranium through thorium to titanium-rich with decreasing pebble size and increasing distance from their source. While evidence of post-diagenetic remobilization has been identified, these effects appear far subordinate to the sedimentological controls.

Ore consists of

pyritization, silicification
, and alteration of titanium minerals. The most prominent geochemical associations with the uranium are thorium and titanium.

This schematic model represents the original depositional setting. The

Huronian underwent mild post-depositional folding during the Penokean orogeny around 1.9 billion years. The main regional structure is the Quirke syncline along the margins of which the majority of the known deposits are situated. Due to this structural overprint ore bodies range from subhorizontal to steeply dipping
.

Breccia complex deposits (IOCG-U)

Chalcopyrite-rich ore specimen from Olympic Dam: copper-rich sections of the deposits are usually also rich in uranium
Uranium-rich breccia at Mount Gee, Mount Painter Inlier, South Australia

Only one

Olympic Dam in South Australia is the world's largest resource of low-grade uranium[11] and accounts for about 66% of Australia's reserves plus resources.[13]

Uranium occurs with copper, gold, silver, and

rare earth elements (REE) 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.

Another example for the Breccia type is the Mount Gee area in the Mount Painter Inlier, South Australia. Uranium mineralised quartz-hematite breccia is related to Palaeoproterozoic granites with uranium contents of up to 100 ppm. Hydrothermal processes at about 300 million years ago remobilised uranium from these granites and enriched them in the quartz-hematite breccias. The breccias in the area host a low grade resource of about 31,400 t U3O8 at 615 ppm in average.[20]

Vein deposits

Niederschlema-Alberoda
Polymetallic uranium ore, Marienberg, Erzgebirge Mts, Germany

Vein deposits play a special role in the history of uranium: the term "pitchblende" ("Pechblende") originates from German vein deposits when they were mined for silver in the 16th century. F.E. 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 the German chemist M. H. Klaproth discovered the element of 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.

Vein deposits consist of uranium minerals filling in cavities such as cracks, veins, fractures, breccias, and stockworks associated with steeply dipping fault systems. There are three major subtypes of vein style uranium mineralisation:

  • intragranitic veins (Central Massif, France)
  • veins in metasedimentary rocks in exocontacts of granites
    • quartz-carbonate uranium veins (Erzgebirge Mts, Germany/Czech Republic; Bohemian Massif, Czech Republic)
    • uranium-polymetal veins (Erzgebirge Mts, Germany/Czech Republic; Saskatchewan, Canada)
  • mineralised fault and shear zones (central Africa; Bohemian Massif, Czech Republic)

Intragranitic veins form in the late phase of magmatic activity when hot fluids derived from the magma precipitate uranium on cracks within the newly formed granite. Such mineralisation contributed much to the uranium production of France. Veins hosted by metasedimentary units in the exocontact of granites are the most important sources of uranium mineralisation in central Europe including the world class deposits

pitchblende. Remobilisation of uranium occurred at later stages producing polymetal veins containing silver, cobalt, nickel, arsenic and other elements. Large deposits of this type can contain more than 1,000 individual mineralized veins. 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

Variscan Orogeny, extension took place and hydrothermal fluids overprinted fine grained materials in shear zones with a sulfide-chlorite alteration. Fluids from the overlying sediments entered the basement mobilising uranium and while uprising on the shear zone, the chlorite-pyrite material caused precipitation of uranium minerals in form of coffinite, pitchblende and U-Zr-silicates. This initial mineralisation event took place at about 277 million to 264 million years. During the Triassic a further mineralisation event took place relocating uranium into quartz-carbonate-uranium veins.[24] Another example of this mineralisation style is the Shinkolobwe deposit in Congo, Africa, containing about 30,000 t of uranium.[25]

Intrusive associated deposits

Intrusive deposits make up a large proportion of the world's uranium resources. Included in this type are those associated with intrusive rocks including

Phosphorite deposits

Marine sedimentary phosphorite deposits can contain low grade concentrations of uranium, up to 0.01–0.015% U3O8, within fluorite or apatite.[10] These deposits can have a significant tonnage. Very large phosphorite deposits occur in Florida and Idaho in the United States, Morocco, and some middle eastern countries.[11][13]

Collapse breccia pipe deposits

Collapse

dissolution of limestone by groundwater.[10] Pipes are typically filled with down-dropped coarse fragments of limestone and overlying sediments and can be from 30 to 200 metres (100 to 660 ft) wide and up to 1,000 metres (3,300 ft) deep.[11][13]

Primary ore minerals are

tonnes U3O8 at an average grade of between 0.3 and 1.0% U3O8.[10][11]

The best known examples of this deposit type are in the Arizona breccia pipe uranium mineralization in the US, where several of these deposits have been mined.

Volcanic deposits

Volcanic deposits occur in

volcanic to volcaniclastic rocks and associated caldera subsidence structures, comagmatic intrusions, ring dykes and diatremes.[10]

Mineralization occurs either as structurally controlled veins and breccias discordant to the stratigraphy and less commonly as stratabound mineralization either in extrusive rocks or permeable

sedimentary facies. Mineralization may be primary, that is magmatic-related or as secondary mineralization due to leaching, remobilization and re-precipitation. The principal uranium mineral in volcanic deposits is pitchblende, which is usually associated with molybdenite and minor amounts of lead, tin and tungsten mineralization.[11]

Volcanic hosted uranium deposits occur in host rocks spanning the Precambrian to the Cenozoic but because of the shallow levels at which they form, preservation favors younger age deposits. Some of the more important deposits or districts are

McDermitt, Nevada
.

The average deposit size is rather small with grades of 0.02% to 0.2% U3O8.[11] These deposits make up only a small proportion of the world's uranium resources.[13] The only volcanic hosted deposits currently being exploited are those of the Streltsovkoye district of eastern Siberia. This is in fact not a single stand-alone deposit, but 18 individual deposits occurring within the Streltsovsk caldera complex. Nevertheless, the average size of these deposits is far greater than the average volcanic type.

Surficial deposits (calcretes)

Surficial deposits are broadly defined as

peat bogs, karst
caverns and soils.

Surficial deposits account for approximately 4% of world uranium resources.[13] The Yeelirrie deposit is by far the world's largest surficial deposit, averaging 0.15% U3O8. Langer Heinrich[26] in Namibia is another significant surficial deposit.[11]

Metasomatite deposits

Metasomatite deposits consist of disseminated uranium minerals within structurally deformed rocks that have been affected by intense sodium metasomatism.[10][11] Ore minerals are uraninite and brannerite. Th/U ratio in the ores is mostly less than 0.1. Metasomatites are typically small in size and generally contain less than 1000 t U3O8.[11] Giant (up to 100 thousands t U) U deposits in sodium metasomatites (albitites) are known in Central Ukraine and Brazil.[citation needed]

Two subtypes are defined based on host lithologies:

Metamorphic deposits

Abandoned open pit of Mary Kathleen uranium mine; the orebody is a skarn mineralisation enriched in U, Cu, Th and REE

Metamorphic deposits those that occur in metasediments or metavolcanic rocks where there is no direct evidence for mineralization post-dating metamorphism.[10][11] These deposits were formed during regional metamorphism of uranium bearing or mineralized sediments or volcanic precursors.

The most prominent deposits of this type are Mary Kathleen, Queensland, Australia, and Forstau, Austria.

Lignite

Lignite deposits (soft brown coal) can contain significant uranium mineralization. Mineralization can also be found in clay and sandstone immediately adjacent to lignite deposits. Uranium has been adsorbed onto carbonaceous matter and as a result no discrete uranium minerals have formed. Deposits of this type are known from the Serres Basin, in Greece, and in North and South Dakota in the USA. The uranium content in these deposits is very low, on average less than 0.005% U3O8, and does not currently warrant commercial extraction.[10][11]

Black shale deposits

Black shale mineralisations are large low-grade resources of uranium. They form in submarine environments under oxygen-free conditions. 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. Average uranium grades of black shales are 50 to 250 ppm. The largest explored resource is Ranstad in Sweden containing 254,000 t of uranium. However, there are estimates for black shales in the US and Brazil assuming a uranium content of over 1 million tonnes, but at grades below 100 ppm uranium. The Chattanooga Shale in the southeastern USA for example is estimated to contain 4 to 5 million tonnes at an average grade of 54 ppm.[25]

Because of their low grades, no black shale deposit ever produced significant amounts of uranium with one exception: the

Ronneburg deposit in eastern Thuringia, Germany. The Ordovician and Silurian black shales at Ronneburg have a background uranium content of 40 to 60 ppm. However, hydrothermal and supergene processes caused remobilsation and enrichment of the uranium. The production between 1950 and 1990 was about 100,000 t of uranium at average grades of 700 to 1,000 ppm. Measured and inferred resources containing 87,000 t uranium at grades between 200 and 900 ppm are left.[23]

Other types of deposits

See also

References

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  2. ^ "Cameco – Uranium 101, Where is uranium found?". Retrieved 2009-01-28.
  3. ISBN 0-939950-50-2{{citation}}: CS1 maint: multiple names: authors list (link
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  6. ^ "Gummite".
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  8. ^ "Mineralogy Database". Retrieved March 25, 2009.
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  10. ^ (PDF) on October 2, 2012, retrieved February 12, 2009
  11. ^ RPA Fission U Patterson Lake South Technical Report
  12. ^ a b c d e f g h i j k l m "Geology of Uranium Deposits". world-nuclear.org. Retrieved 15 April 2023 – via World Nuclear Association.
  13. ^ Douglas, G., Butt, C., and Gray, D. (2003). "Mulga Rock Uranium and Multielement Deposits, Officer Basin, WA" (PDF). Retrieved February 13, 2009.{{cite web}}: CS1 maint: multiple names: authors list (link)
  14. ^ "Alliance Resources Limited – Uranium and gold producer – Projects : Four Mile Uranium Project, SA". www.allianceresources.com.au. Archived from the original on 13 March 2017. Retrieved 18 April 2018.
  15. ^ "AGM Presentation by MD Mr Patrick Mutz". allianceresources.com.au. Retrieved 18 April 2018.
  16. ^ "Australia' s Uranium Deposits and Prospective Mines". www.world-nuclear.org. Archived from the original on 2011-06-04.
  17. ^ "Geoscience Australia: Australia's uranium resources, geology and development of deposits". Archived from the original on 2009-12-25. Retrieved 2010-01-26.
  18. .
  19. ^ "Marathon Resources Ltd – Paralana Mineral System (Mt Gee)". Archived from the original on 2009-04-10. Retrieved 2009-04-22.
  20. ^ Veselovsky, F., Ondrus, P., Gabsová, A., Hlousek, J., Vlasimsky, P., Chernyshew, I.V. (2003). "Who was who in Jáchymov mineralogy II".
    Journal of the Czech Geological Society. 48 (3–4 ed.): 93–205.{{cite journal}}: CS1 maint: multiple names: authors list (link
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  21. ^ Ruzicka, V. (1993). "Vein uranium deposits". Ore Geology Reviews. 8 (3–4): 247–276. .
  22. ^ a b c various... (1999), Chronik der Wismut, Chemnitz: Wismut GmbH
  23. S2CID 128402163.{{cite journal}}: CS1 maint: multiple names: authors list (link
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  24. ^ a b unknown (2001), Analysis of uranium supply to 2050, Vienna: International Atomic Energy Agency
  25. ^ "Langer Heinrich Uranium Mine – Mining Technology | Mining News and Views Updated Daily". Mining Technology.
  26. ^ Winning, David (22 February 2010). "Out of the Ashes". Wall Street Journal.

Additional sources