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Uranium ore

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Sample of uranium ore

Uranium ore depositsare economically recoverable concentrations ofuraniumwithinEarth's crust.Uranium is one of the most commonelementsin Earth's crust, being 40 times more common thansilverand 500 times more common thangold.[1]It can be found almost everywhere in rock, soil, rivers, and oceans.[2]The challenge for commercial uranium extraction is to find those areas where the concentrations are adequate to form an economically viable deposit. The primary use for uranium obtained from mining is in fuel fornuclear 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 theAthabasca Basinregion 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 theInternational Atomic Energy Agencyand subdivides deposits into 15 categories.

Uranium[edit]

Uraniumis a silvery-graymetallicweaklyradioactivechemical element.It has thechemical symbolUandatomic number92. The most commonisotopesinnatural uraniumare238U(99.274%) and235U(0.711%). Alluranium isotopespresent in natural uranium areradioactiveandfissionable,and235U isfissile(will support aneutron-mediated chain reaction). Uranium,thorium,and one radioactive isotope ofpotassium(40
K) as well as their decay products are the main elements contributing to natural terrestrial radioactivity.[3]Cosmogenic radionuclidesare of less importance, but unlike the aforementionedprimordial radionuclides,which date back to the formation of the planet and have since slowly decayed away, they are replenished at roughly the same rate they decay by the bombardment of Earth withcosmic rays.

Uranium has the highestatomic weightof the naturally occurring elements and is approximately 70% denser thanlead,but it is not as dense astungsten,gold,platinum,iridium,orosmium.It is always found combined with other elements.[4]Along with all elements having atomic weights higher than that ofiron,it is only naturally formed insupernovaexplosions.[5]

Uranium minerals[edit]

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

The primary uranium oremineralisuraninite(UO2) (previously known as pitchblende). A range of other uranium minerals can be found in various deposits. These includecarnotite,tyuyamunite,torberniteandautunite.[6]Thedavidite-brannerite-absitetype uranium titanates, and theeuxenite-fergusonite-samarskitegroup are other uranium minerals.

A large variety of secondary uranium minerals are known, many of which are brilliantly coloured and fluorescent. The most common aregummite(a mixture of minerals),[7]autunite(withcalcium),saleeite(magnesium) andtorbernite(withcopper); and hydrated uranium silicates such ascoffinite,uranophane(with calcium) andsklodowskite(magnesium).

Uranium Minerals[8][9]
Primary uranium minerals
Name Chemical Formula
uraniniteor 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)2x 8–12 H2O
carnotite K2(UO2)2(VO4)2x 1–3 H2O
gummite gum like mixture of various uranium minerals
saleeite Mg(UO2)2(PO4)2x 10 H2O
torbernite Cu(UO2)2(PO4)2x 12 H2O
tyuyamunite Ca(UO2)2(VO4)2x 5–8 H2O
uranocircite Ba(UO2)2(PO4)2x 8–10 H2O
uranophane Ca(UO2)2(HSiO4)2x 5 H2O
zeunerite Cu(UO2)2(AsO4)2x 8–10 H2O

Ore genesis[edit]

Wood fragment in a conglomerate fromUtah,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 uraniumore genesisare host mineralogy,reduction-oxidation potential,andporosity.

Uranium is a highly soluble and radioactiveheavy metal.It can be easily dissolved, transported and precipitated withingroundwaterby subtle changes in oxidation conditions. Uranium 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 withinmagmas,and as such it tends to become accumulated within highlyfractionatedand evolvedgranitemelts, particularly alkaline examples. These melts tend to become highly enriched in uranium, thorium and potassium, and may in turn create internalpegmatitesor hydrothermal systems into which uranium may dissolve.

Classification schemes[edit]

IAEA Classification (1996)[edit]

TheInternational 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[edit]

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)[edit]

Unconformity-related deposits[edit]

Ranger 3open pit,Northern Territory,Australia: Uranium mineralised Cahill Formation as visible in the pit is unconformably overlain by Kombolgiesandstoneforming 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 unconformities between relativelyquartz-richsandstonescomprising the basal portion of relatively undeformedsedimentary basinsand deformedmetamorphicbasement rocks.These sedimentary basins are typically ofProterozoicage, however somePhanerozoicexamples exist.

Phanerozoic unconformity-related deposits occur in Proterozoicmetasedimentsbelow an unconformity at the base of overlying Phanerozoic sandstone. These deposits are small and low-grade (e.g.,BertholeneandAveyrondeposits in France).[11]

Athabasca Basin[edit]

The highest grade uranium deposits are found in theAthabasca Basinin Canada, including the two largest high grade uranium deposits in the world,Cigar Lakewith 217 million pounds (99,000 t) U3O8at an average grade of 18% andMcArthur Riverwith 324 million pounds (147,000 t) U3O8at 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% U3O8containing 79,610,000 pounds of U3O8."Inferred Mineral Resources" are estimated to total 901,000 tons at an average grade of 1.30% U3O8containing 25,884,000 pounds of U3O8.[12]

McArthur Basin[edit]

The deposits of theMcArthur River basinin the EastAlligator Riversregion of theNorthern Territoryof Australia (includingJabiluka,Ranger,andNabarlek) 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 Landarea.[13]

Sandstone deposits[edit]

A uranium mine, nearMoab, Utah.Note alternating red and white/greensandstone.This corresponds tooxidizedandreducedconditions in groundwaterredoxchemistry. The rock forms in oxidizing conditions, and is then "bleached" to the white/green state when a reducing fluid passes through the rock. The reduced fluid can also carry uranium-bearingminerals.

Sandstone deposits are contained within medium to coarse-grained sandstones deposited in a continental fluvial or marginal marinesedimentary environment.Impermeableshaleormudstoneunits 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, withweatheringproducing 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. Wyoming basins
  2. Grants Districtof New Mexico
  3. Central Europe
  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[edit]

Tabular deposits consist of irregular tabular or elongatelenticularzones 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 contain many of the highest grades of the sandstone class, however the average deposit size is very small.

Roll front[edit]

Structures interpreted as Palaeo-rollfronts in South Australia

Roll-front uranium deposits are generally hosted withinpermeableandporoussandstones orconglomerates.The mechanism for deposit formation is dissolution of uranium from the formation or nearbystrataand the transport of this soluble uranium into the host unit. When the fluids changeredoxstate, generally in contact withcarbon-rich organic matter, uranium precipitates to form a 'front'.

The roll front 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 theInkaideposit in Kazakhstan and theSmith Ranchdeposit in Wyoming. Probably more significant than their larger size, roll front deposits have the advantage of being amenable to low costin situ leachrecovery.

Typical characteristics:

  • roll-front deposits are crescent-shaped bodies that transect the hostlithology
  • typically the convex side points down thehydraulic gradient.
  • the limbs or tails tend to be peneconcordant with the lithology.
  • most ore-bodies consist of several interconnected rolls.
  • individual roll-front deposits are quite small but collectively can extend for considerable distances.

Basal channel (palaeochannel)[edit]

Basal channel deposits are often grouped with tabular or roll front deposits, depending on their unique characteristics. The model for formation ofpalaeochanneldeposits is similar to that for roll front deposits except that the source of uranium may be in the watershed leading into a stream or in thebed loadof the palaeochannel. This uranium is transported through groundwater 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 incalcretisedevaporation sites or even insaline lakesas the water evaporates.

Some particularly rich uranium deposits are formed in palaeochannels which are filled in the lower parts byligniteor browncoal,which acts as a particularly efficient reductive trap for uranium. Sometimes, elements such asscandium,gold and silver may be concentrated within these lignite-hosted uranium deposits.[14]

TheFrome EmbaymentinSouth Australiahosts several deposits of this type includingHoneymoon,Oban,Beverleyand Four-Mile[15](which is the largest deposit of this class).[16][17][18]These deposits are hosted in palaeochannels filled withCenozoicsediments and sourced their uranium from uranium-richPaleoproterozoictoMesoproterozoicrocks of theMount PainterInlier and the Olary Domain of the Curnamona Province.

Structurally related[edit]

Westmoreland uranium deposit, Queensland, Australia: most of the orebodies (the positions of two of them marked) are hosted along the Redtreedoleritedyke (broken line) within the Paleoproterozoic Westmoreland conglomerate

Tectonic-lithologic controlled uranium deposits occur in sandstones adjacent to a permeablefault 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 mineralised zones 'stacked' vertically on top of each other within sandstone units adjacent to the fault zone.[11]

Quartz conglomerate deposits[edit]

Quartz pebble conglomerate hosted uranium deposits are of historical significance as the major source of primary production for several decades afterWorld War II.This type of deposit has been identified in eight localities around the world. The most significant deposits are in theHuronian SupergroupinElliot Lake,Ontario,Canada and in theWitwatersrand SupergroupofSouth Africa.These deposits make up approximately 13% of the world's uranium resources.[13]

Quartz pebble conglomerate hosted uranium deposits formed from the transport and deposition of uraninite in a fluvial sedimentary environment[10]and are defined as stratiform and strataboundplacer deposits.Host rocks are typically submature to supermature, polymictic conglomerates and sandstones deposited inalluvial fanandbraided streamenvironments. 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.

Uranium minerals were derived from uraniferous pegmatites in the sediment source areas. These deposits are restricted to theArcheanand early Paleoproterozoic and do not occur in sediments younger than about 2,200 million years whenoxygen levels in the atmospherereached a critical level, making simpleuranium oxidesno longer stable in near-surface environments.[19]

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

Witwatersrand[edit]

In the Witwatersrand deposits, ores are found along unconformities, shale and siltstone beds, and carbonaceous seams. The West Rand Group of sediments tend to host the most uranium within 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 gradediagenesis.

Uranium minerals 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 ofpyrophyllite,chloritoid,muscovite,chlorite,quartz,rutile,andpyrite.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[edit]

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

Ore consists of uraninite with lesser brannerite and thucholite. These occur in thin beds exhibitinggraded beddingreminiscent of placer sorting. Alteration is nonexistent to very weak at best, and the weak chlorite andsericiteare believed to be mainly post-ore effects. Other post-depositional alteration includespyritization,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 thePenokean orogenyaround 1.9 billion years. The main regional structure is the Quirkesynclinealong the margins of which the majority of the known deposits are situated. Ore bodies range from subhorizontal to steeplydipping.

Breccia complex deposits[edit]

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 oneiron oxide copper gold ore depositis known to contain economically significant quantities of uranium.Olympic Damin 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, andrare-earth elementsin a largehematite-rich granitebrecciacomplex in theGawler Cratonoverlain by approximately 300 metres of flat-lying sedimentary rocks of theStuart Shelfgeological 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 U3O8at 615 ppm in average.[20]

Vein deposits[edit]

Uranium ore (pitchblende in dolomite) from the vein-type depositNiederschlema-Alberoda
Polymetallic uranium ore,Marienberg,Erzgebirge Mountains, Germany

Veindeposits 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.Franz Ernst Brückmannmade the first mineralogical description of the mineral in 1727, and the vein deposit Jachymov in theCzech Republicbecame the type locality for uraninite.[21]In 1789 German chemistMartin Heinrich Klaprothdiscovered 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, andMarieandPierre Curieused thetailingsof the mine for their discovery ofpoloniumandradium.

Vein deposits consist of uranium minerals filling in cavities such as cracks, veins, fractures, breccias, andstockworksassociated 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
  • mineralised fault and shear zones (Central Africa; Bohemian Massif)

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 depositsSchneeberg-Schlema-Alberodain Germany (96,000 t uranium content) as well as Pribram (50,000 t uranium content) and Jachymov (~10,000 t uranium content) in the Czech Republic. Also they are closely related to the granites, the mineralization is much younger with a time gap between granite formation and mineralisation of 20 million years. The initial uranium mineralisation consists of quartz,carbonate,fluoriteand pitchblende. Remobilisation of uranium occurred at later stages producing polymetal veins containing silver,cobalt,nickel,arsenicand 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 Bohemian Massif contains shear zone hosted uranium deposits with the most important one being Rozna-Olsi in Moravia northwest ofBrno.Rozna is currently the only operating uranium mine in central Europe with a total uranium content of 23,000 t and an average grade of 0.24%. The formation of this mineralisation occurred in several stages. After theVariscan 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 theShinkolobwedeposit in Congo containing about 30,000 t of uranium.[25]

Intrusive associated deposits[edit]

Intrusive deposits make up a large proportion of the world's uranium resources. Included in this type are those associated with intrusive rocks includingalaskite,granite,pegmatiteandmonzonites.Major world deposits includeRossing(Namibia),Ilimaussaq intrusive complex(Greenland) andPalabora(South Africa).[13]

Phosphorite deposits[edit]

Marine sedimentaryphosphoritedeposits can contain low grade concentrations of uranium, up to 0.01–0.015% U3O8,withinfluoriteorapatite.[10]These deposits can have a significant tonnage. Very large phosphorite deposits occur inFlorida,Idaho,Morocco,and some middle eastern countries.[11][13]

Collapse breccia pipe deposits[edit]

Collapsebreccia pipedeposits occur within vertical, circular solution collapse structures, formed by thedissolutionoflimestoneby 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 areuraniniteandpitchblende,which occur as cavity fills and coatings onquartzgrains within permeable sandstone breccias within the pipe. Resources within individual pipes can range up to 2500tonnesU3O8at an average grade of between 0.3 and 1.0% U3O8.[10][11]The best known examples of this deposit type are in theArizona breccia pipe uranium mineralizationin the US, where several of these deposits have been mined.

Volcanic deposits[edit]

Volcanic deposits occur infelsicto intermediatevolcanicto volcaniclastic rocks and associatedcalderasubsidence structures, comagmatic intrusions, ringdykesanddiatremes.[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 permeablesedimentary 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 withmolybdeniteand minor amounts of lead,tinand 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 areStreltsovskoye, Russia;Dornod, Mongolia;andMcDermitt, 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 easternSiberia.This is in fact not a single stand-alone deposit, but 18 individual deposits occurring within theStreltsovsk calderacomplex. Nevertheless, the average size of these deposits is far greater than the average volcanic type.

Surficial deposits (calcretes)[edit]

Surficial deposits are broadly defined asTertiarytoHolocenenear-surface uranium concentrations in sediments or soils.[13]Mineralization in calcrete (calciumandmagnesium carbonates) are the largest of the surficial deposits. They are interbedded with Tertiary sand and clay, which are usually cemented by calcium and magnesium carbonates.[11]Surficial deposits also occur inpeat bogs,karstcaverns and soils. Surficial deposits account for approximately 4% of world uranium resources.[13]TheYeelirrie depositis by far the world's largest surficial deposit, averaging 0.15% U3O8.Langer Heinrich[26]inNamibiais another significant surficial deposit.[11]

Metasomatite deposits[edit]

Metasomatite deposits consist of disseminated uranium minerals within structurally deformed rocks that have been affected by intensesodiummetasomatism.[10][11]Ore minerals are uraninite andbrannerite.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 inCentral Ukraineand Brazil.[citation needed]

Two subtypes are defined based on host lithologies:

Metamorphic deposits[edit]

Abandoned open pit of Mary Kathleen uranium mine; the orebody is askarnmineralisation 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 areMary Kathleen, Queensland,Australia, andForstau,Austria.

Lignite[edit]

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 beenadsorbedonto carbonaceous matter and as a result no discrete uranium minerals have formed. Deposits of this type are known from theSerres Basin,inGreece,and inNorthandSouth Dakota.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[edit]

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 CO2by 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 isRanstadin 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.Chattanooga Shalein thesoutheastern United Statesis estimated to contain 4 to 5 million tonnes at an average grade of 54 ppm.[25]

Only theRonneburgdeposit in eastern Thuringia, Germany, has produced significant amounts of uranium. TheOrdovicianandSilurianblack shales have a background uranium content of 40 to 60 ppm. However, hydrothermal andsupergeneprocesses 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[edit]

See also[edit]

References[edit]

  1. ^"Cameco – Uranium 101".RetrievedFebruary 1,2009.
  2. ^"Cameco – Uranium 101, Where is uranium found?".Retrieved2009-01-28.
  3. ^Plant, J., Simpson, P.R., Smith, B., and Windley, B.F. (1999), "Uranium Ore Deposits: Products of the Radioactive Earth", in Burns, P.C.; Finch, R. (eds.),Reviews in Mineralogy,vol. 38: Uranium: Mineralogy, Geochemistry and the Environment., Washington D.C., U.S.A.: Mineralogical Society of America, pp. 255–320,ISBN0-939950-50-2{{citation}}:CS1 maint: multiple names: authors list (link)
  4. ^"Uranium".Los Alamos National Laboratory.Retrieved2009-02-11.
  5. ^"WorldBook@NASA: Supernova".NASA. Archived fromthe originalon 2006-09-30.Retrieved2009-02-11.
  6. ^Klein, Cornelis and Cornelius S. Hurlbut, Jr.,Manual of Mineralogy,Wiley, 1985, 20th ed. pp. 307–308ISBN0-471-80580-7
  7. ^"Gummite".
  8. ^Merkel, B., und Sperling, B. (1998), "Hydrogeochemische Soffsysteme Teil II",Schriftenreihe des Deutschen Verbandes für Wasserwirtschaft und Kulturbau (DVWK),Schriften 117, DVWK,ISSN0170-8147{{citation}}:CS1 maint: multiple names: authors list (link)
  9. ^"Mineralogy Database".RetrievedMarch 25,2009.
  10. ^abcdefghijkLally, J. & Bajwah, Z. (2006),Uranium Deposits of the NT,vol. Report 20, Northern Territory Geological Survey,ISBN0-7245-7107-8
  11. ^abcdefghijklmnopqMcKay, A.D. & Meiitis, Y. (2001),Australia's uranium resources, geology and development of deposits.(PDF),AGSO-Geoscience Australia, Mineral Resources Report 1,ISBN0-642-46716-1,archived fromthe original(PDF)on October 2, 2012,retrievedFebruary 12,2009
  12. ^RPA Fission U Patterson Lake South Technical Report
  13. ^abcdefghijklm"Geology of Uranium Deposits".world-nuclear.org.Retrieved15 April2023– via World Nuclear Association.
  14. ^Douglas, G., Butt, C., and Gray, D. (2003)."Mulga Rock Uranium and Multielement Deposits, Officer Basin, WA"(PDF).RetrievedFebruary 13,2009.{{cite web}}:CS1 maint: multiple names: authors list (link)
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Further reading[edit]

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