Uranium deposit

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Uranium deposits are natural enrichments of uranium from which the element can be extracted economically.

Basics

Uranium geochemistry

Uranium is a so-called lithophilic element, which means that it accumulates preferentially in silicate-rich melts. This is caused on the one hand by the relatively large ion diameter and on the other hand by the high oxidation states with which uranium occurs in nature, namely tetravalent and hexavalent. Uranium is neither enriched in the metallic core of the earth nor in the earth's mantle, but rather accumulates in magmas in the later differentials. This is why acidic magmatites are the most widely differentiated rocks and have the highest uranium content on earth. The average uranium content of the continental crust is 2 to 4  ppm . In addition to the lithophilic character of uranium, the different mobility of the two natural oxidation states of uranium is of paramount importance for the formation of uranium deposits: While uranium (IV) is practically insoluble in aqueous solutions, uranium (VI) forms more than 40 stable uranyl complexes in aqueous solutions and is very mobile. In practice, this means that uranium is immobile under reducing conditions and very mobile under oxidizing conditions. The most important complex that uranium forms is UO 2 [CO 3 ] 3 4− . If these complexes come under reducing conditions, they break down and uranium minerals precipitate. The following reactions are examples of the formation of uranium minerals from hydrothermal solutions:

 
 

As shown, the presence of reducing material plays an important role in the precipitation of uranium minerals. As in the example equation, this can be reduced iron (e.g. in magnetite ), reduced sulfur (e.g. in sulfides) or reduced (organic) carbon in solid fossil plant material, but also crude oil and natural gas. Organic carbon plays an important role in the formation of many uranium deposits. Mixing of oxidizing uranium-bearing fluids with reducing fluids can also lead to the precipitation of uranium (so-called “fluid mixing”).

Therefore, the following basic genesis can be described for many uranium deposits (but not for all): A uranium-rich, acidic igneous rock serves as a uranium source. An oxidizing aqueous solution flows through it, which mobilizes uranium from the igneous rock. The uranium-bearing solution is channeled on certain paths and releases its uranium load when it flows through a reducing horizon.

However, there are also processes that can lead to the formation of uranium ore bodies under oxidizing conditions. For example, uranyl vanadates have only a very low solubility in normal aqueous solutions. So z. B. the mixing of oxidizing uranium-bearing with oxidizing vanadium-bearing solutions lead to the formation of uranium ore bodies.

mineralogy

In normal rocks, uranium is mostly incorporated into the accessory minerals zircon (ZrSiO 4 ) and monazite ((Ce, Y, La, Th) PO 4 ). These are among the few minerals that uranium can build into their structure as a secondary component. If there is not enough space in these minerals or if geochemical conditions prevail which do not lead to the formation of these minerals, uranium forms its own minerals. Today more than 200 uranium minerals are known. Since uranium (VI) can form complexes with a wide variety of elements, there are a large number of uranium carbonates, hydroxides, phosphates, arsenates, niobates, titanates and other complex compounds. The two most important uranium minerals, however, are pitchblende U 3 O 8 (in their crystallized form as uraninite UO 2 ) and coffinite U (SiO 4 ) 1 – x (OH) 4x . There are also organic uranium compounds such as tucholite. The following uranium minerals are the most economically important:

Pitchblende from the Saxon Erzgebirge
Autunit, a secondary uranium mineral named after Autun in France
Torbernite, an important secondary uranium mineral
Uranium minerals
Primary uranium minerals
Surname chemical formula
Uraninite UO 2
Pitchblende U 3 O 8 , rarely U 3 O 7
Coffinite U (SiO 4 ) 1-x (OH) 4x
Brannerite UTi 2 O 6
Davidite (REE) (Y, U) (Ti, Fe 3+ ) 20 O 38
Thucholite Uranium-containing pyrobitumen
Secondary uranium minerals
Surname chemical formula
Autunit Ca (UO 2 ) 2 (PO 4 ) 2 x 8-12 H 2 O
Carnotite K 2 (UO 2 ) 2 (VO 4 ) 2 x 1-3 H 2 O
Rubber rubbery mixture of different amorphous uranium compounds
Seleeit Mg (UO 2 ) 2 (PO 4 ) 2 x 10 H 2 O
Torbernite Cu (UO 2 ) 2 (PO 4 ) 2 x 12 H 2 O
Tyuyamunit Ca (UO 2 ) 2 (VO 4 ) 2 x 5-8 H 2 O
Uranocircit Ba (UO 2 ) 2 (PO 4 ) 2 × 8-10 H 2 O
Uranophane Ca (UO 2 ) 2 (HSiO 4 ) 2 x 5 H 2 O
Zeunerite Cu (UO 2 ) 2 (AsO 4 ) 2 x 8-10 H 2 O

Deposit types

Uranium deposits can be divided into igneous, hydrothermal , metamorphic and sedimentary types. This classification can be further subdivided according to various aspects. The IAEA currently has 14 uranium deposit types with various sub-variants. The classification and naming is not entirely in accordance with modern deposit theory ; there are also deposits that combine characteristics of several types. Nevertheless, the IAEA classification is to be used below to introduce the various types.

By definition, the term “deposit” includes the criterion of the economic recoverability of a raw material deposit. In the following descriptions, however, the term will also be used in a broader sense for the sake of simplicity for potential, currently non-economic types and occurrences. The IAEA has around 1,260 uranium deposits with a uranium content of more than 300 t.

Discordance-related deposits (Unconformity-related)

Ranger 3 open pit mine, Northern Territory, Australia: In the discordance-bound deposit, the ore is located in the Cahill Formation (basement, in open pit), which is discordantly overlaid by the Kombolgie Formation (overburden, table mountains in the background).

Discordance-bound deposits are currently the most important source of uranium and, in addition to sandstone-bound deposits, also harbor the greatest potential for economically significant new discoveries. Two major deposit provinces are currently known for this type: the Athabasca Basin in Saskatchewan (Canada) and the Alligator River Basin in the Northern Territory (Australia). In both provinces, the metamorphic, archaic to paleoproterozoic basement is discordantly overlaid by little stressed Meso- to Neoproterozoic sediments. In the area of ​​this discordance between the two rock units, irregularly shaped, rich uranium ore bodies have formed in fault and shear zones. The uranium grades are abnormally high and are not matched by any other type of uranium deposit. In the Northern Territory this is between 0.3 wt.% And 2 wt.% Uranium, in the Athabasca Basin between 0.5 wt.% And 20 wt.% Uranium on average, whereby rich zones with up to 50 wt.% Uranium are also known are.

Zones rich in graphite in the basement near the discordance area play a major role in the formation of the deposits . The deposits were created by acidic hydrothermal solutions with moderate temperatures between 160 ° C and 220 ° C, which were formed during the diagenesis (compaction) of the cover sediments and subsequent reactions with the rock. The uranium-bearing solutions were focused in fault zones of the basement and unloaded their uranium load in the reducing area close to the discordance. The source for the uranium is currently still under discussion. There are works that see the overburden as well as the basement as a uranium source. Investigations on the basement in the Athabasca Basin showed that oxidizing solutions could mobilize large amounts of uranium from monazite and other uranium-bearing minerals of the metamorphic rocks and are therefore a likely source of the uranium bound in the deposits. The main uranium mineral in the deposits is pitchblende. Some deposits such as Key Lake in Canada have high grades of nickel, while Jabiluka in Australia has high gold grades.

  • Origin: hydrothermal
  • Age: Proterozoic
  • Uranium content (order of magnitude): 1,000 t to 200,000 t
  • Average ore grades: 0.3 wt.% to 20 wt.% uranium
  • possible further winnable contents: nickel, gold
  • Notable examples: Ranger, Northern Territory, Australia; MacArthur River, Saskatchewan, Canada

Corridor deposits (Vein-type)

Typical polymetallic uranium ore from the Ore Mountains
Uranium ore of the dolomite uranium formation from Niederschlema-Alberoda

Ore veins are narrow, elongated ore bodies of hydrothermal origin. They represent the oldest source for the element uranium. The type locality for uraninite is the St. Joachimsthal deposit (today Jáchymov), from where it was described by F. E. Brückmann in 1727. In 1789, Martin Heinrich Klaproth discovered the element uranium in a sample from a vein deposit in the Ore Mountains . In this region, uranium has been extracted as a by-product since the first half of the 19th century and for the first time since the second half on an industrial scale from the corridors of St. Joachimsthal in the Bohemian Ore Mountains. In 1898 , Marie Curie discovered the elements polonium and radium in waste products from the Joachimsthal uranium dye factory . After the discovery of radium, it was industrially produced in St. Joachimsthal, and the world's first radium spa was created using circulating water from the reservoirs for healing purposes. After the Second World War , the German and Czech Ore Mountains were the most important sources of uranium for the Soviet nuclear weapons program in its initial phase. This type of deposit played an outstanding role in the scientific and political history of uranium. The largest deposit province for this type are the variscides of Central Europe with the world's largest deposits of this type; Schneeberg - Schlema - Alberoda (≈ 80,000 t uranium production) in Germany and Příbram (≈ 45,000 t uranium production) in the Czech Republic . There are other important corridor deposits in Central Africa such as B. Shinkolobwe in the Congo (≈ 30,000 t production + resources) and in Saskatchewan , Canada, north of Lake Athabasca near Uranium City .

There are different types of vein deposits with uranium mineralization:

  • intragranitic corridors (e.g. Massif Central, France)
  • Dikes in metasediments in the exocontact of granite bodies
    • Uranium-quartz-carbonate veins (Ore Mountains; Bohemian Massif)
    • uranium-bearing polymetallic veins (Ore Mountains; Saskatchewan, Canada)
  • vein-shaped mineralized fault and shear zones (e.g. Bohemian Massif; Democratic Republic of the Congo).

The formation of the dikes is due to diverse geochemical processes. Intragranitic veins like those in the French Massif Central emerged in the late phase of the granite ascent, when hot fluids differentiated from the solidifying granite body and intruded into the host rock or into the granite itself . These late differentials were enriched with uranium, which then crystallized in existing rock fissures as pitchblende or in the form of other uranium-containing minerals.

The uranium deposits of the Ore Mountains and Příbram in the Bohemian Massif are located in the outer contact area of granite plutons . The veins are, however, much younger than the granites themselves, which essentially served as a source for the uranium. These dikes formed about 280 million years ago during an extension phase; a system of fissures opened up in the granite, uranium was mobilized from the rock by hydrothermal solutions and then excreted in larger fissures. In the Erzgebirge, after the formation of the monometallic uranium veins, further stages of mineralization followed, in which magnesium (formation of dolomite ) and selenium , later cobalt , nickel , bismuth , arsenic and silver were introduced into the mineralization of the veins. In these processes, uranium was rearranged on a large scale from old vein structures , but no new uranium was added.

Uranium-mineralized fault and shear zones exist in the Bohemian Massif such as B. Hohensteinweg and Wäldel in Germany or Rožná - Olší in Moravia. Rožná contains 23,000 t of uranium with an average ore content of 0.24 wt.% Uranium. The formation of the deposit is divided into three phases. After the Variscan mountain formation, there was an extension phase in the Bohemian massif. Mylonites and cataclasites were overprinted in shear zones with a pyrite- chlorite alteration. Subsequently, solutions from the overlying sediments penetrated the basement and mobilized uranium from the metamorphic rock bodies. When the solutions rose along shear zones, the zones previously enriched with pyrite and carbon acted as reduction horizons and precipitated uranium in the form of coffinite, pitchblende and U- Zr silicates. The age of uranium mineralization is between 277 million years and 264 million years. The temperatures during the mineralization phase ranged from 150 ° C to 180 ° C. During the Triassic , another hydrothermal phase followed, during which uranium was partially redistributed in quartz-carbonate-uranium veins. While coffinite is the main uranium mineral in Rožná, pitchblende is predominant in other deposits of this origin. These deposits can also have a polymetallic design.

What is interesting about the deposits in the Ore Mountains and the Bohemian Massif is their connection to supra-regional fault zones. The Příbram and Jáchymov deposits are located on the Czech side and Johanngeorgenstadt , Pöhla , Schneeberg-Schlema-Alberoda, Neumark - Hauptmannsgrün and Ronneburg on the German side are all located on the Gera- Jáchymov fault zone, although the latter two deposits are hydrothermal black slate deposits . The Rožná-Olší, Stráž pod Ralskem , Königstein and Delitzsch deposits , on the other hand, sit on the Elbe - Lineament , but only the first-mentioned deposit is of the dike type.

Despite their historical importance and a historical production of several 100,000 tons of uranium worldwide, these deposits hardly play a role today. On the one hand, the known deposits have largely been mined and, on the other hand, there are hardly any exploration measures for these deposits. This is due to the difficult economic and technological conditions for mining, as the narrow ore bodies leave no space for large-scale efficient mining. The dikes in the Schneeberg-Schlema-Alberoda deposit are usually only 5 cm to 30 cm thick, and thicknesses of more than one meter have rarely been observed. The distribution of the ore is also very irregular, rich zones with an ore content of up to a few percent alternate with large uranium-free areas. In Schneeberg-Schlema-Alberoda uranium-bearing veins were only 5% of the vein area mineralized with uranium, in Jáchymov it was 8% and in Příbram 12% of the area.

  • Origin: hydrothermal
  • Age: Mesoproterozoic to Mesozoic
  • Uranium content: <100 t to 100,000 t
  • Average ore grades: 0.05 wt.% to 1 wt.% uranium
  • other possible extractable raw materials: silver, cobalt, nickel, copper , selenium , fluorite , barite
  • important examples: Schneeberg-Schlema-Alberoda, Erzgebirge, Germany; Příbram, Czech Republic.

Breccia-type

Chalcopyrite-rich ore from Olympic Dam: Copper-rich portions of the deposit usually contain high grades of uranium
Uranium-rich breccia at Mt. Gee in South Australia

The type of mineralization referred to by the IAEA as breccia type includes the deposits referred to by geologists as Iron-Oxide-Copper-Gold (IOCG, English: Iron Oxide-Copper-Gold ). With uranium, there is only one economic example: Olympic Dam in South Australia . This is why there is also the name Olympic Dam type. This deposit was discovered in 1975 and until the mid-1980s it was interpreted as a sedimentary brecciated trench filling, hence the IAEA designation. However, after the Olympic Dam Mine was excavated and commissioned , this assessment changed fundamentally: The modern deposit models assume a magmatic-hydrothermal formation. The deposit is bound to the approximately 1.58 billion year old Roxby Downs granite. It is assumed that when the granite solidified, hot hydrothermal fluids degassed from the magma, which brecciated the newly formed granite. The fluids brought large amounts of iron, copper, gold and other elements with them and impregnated the breccia with these elements (hence the IOCG name). The core of the deposit consists of a massive hematite body with no significant copper content. The iron content decreases towards the outside into an unmineralized breccia and finally into unchanged granite. The significant copper-gold mineralization is located in the intermediate area between the hematite core and the hematite-free breccia. Furthermore, in the upper area of ​​the deposit there are intercalations of acidic volcanic rocks, which indicates a very shallow formation of the deposit under a volcanic complex. The uranium of the deposit was likely brought in by oxidizing meteoric (surface coming) waters. These dissolved uranium from the overlying volcanic rocks and the uranium-rich Roxby Downs granite, mixed with the fluids from the magma and deposited their uranium in the form of pitchblende, coffinite and brannerite . The deposit's proven resource is currently 8.3 billion tons. The uranium content is stated by BHP Billiton to be over 2 million tons. The average ore grade for the total resource is 0.8% copper and 280 ppm U 3 O 8 . It is by far the largest conventional uranium deposit and the fourth largest copper deposit in the world.

In the meantime, further IOCG deposits have been found which are also being commercially mined, e.g. B. Earnest Henry in Queensland , Australia, or Prominent Hill 200 km northeast of Olympic Dam. The latter also leads to significantly higher uranium contents, but only around 50 ppm to 100 ppm, which makes extraction uneconomical. The Hillside iron oxide-copper-gold mineralization currently being explored on the Yorke Peninsula , South Australia, shows up to 800 ppm U 3 O 8 in places .

The Mt. Gee deposit in the Mt. Painter area of ​​the Flinders Ranges , South Australia, is also brecciated, albeit without significant copper and gold grades. The quartz hematite breccias are bound to an A-type granite about 1.5 billion years old, but are only about 300 million years old themselves. They contain a uranium resource of 31,400 t with a content of 615 ppm U 3 O 8 .

  • Origin: magmatic-hydrothermal
  • Age: Mesoproterozoic
  • Uranium content: up to more than 2 million tons
  • Average ore grades: 0.02 wt.% to 0.05 wt.% uranium
  • possible other winnable content: copper, gold, silver, rare earth elements
  • Notable examples: Olympic Dam, Australia; Mt. Painter area, Australia

Volcanic (Volcanic-type)

Volcanic deposits are almost exclusively bound to caldera structures, which are filled with mafic and felsic volcanic rocks, pyroclastics and clastic sediments. By far the largest resource of this type is the Strelzowska Caldera in Russia , which contains around 20 individual deposits. This ore field is currently the most important Russian uranium supplier and until 2007 produced 120,000 t uranium with resources of a further 127,000 t uranium with an average ore content of 0.18% by weight. The caldera has a diameter of about 20 km and contains basalt, andesite, trachydacite, rhyolite and sediments embedded in it. The filling was made in the late Jurassic period. The rhyolites are part of one of the last volcanic events and have been dated to about 142 million years. The caldera is underlain by a granite. The mineralization in the individual deposits is in the form of tunnels and floors, locally also disseminated in the volcanic rocks and inserted sandstones. There are also mineralizations of fluorite and molybdenum . The main uranium minerals are zirconium- rich pitchblende and subordinate to coffinite and brannerite. The mineralization arose immediately after the volcanic activity in five phases, with the pitchblende molybdenite mineralization occurring in the fourth phase and the fluorite mineralization in the fifth phase. Calculations show that around 900,000 t of uranium and 1.6 billion t of fluorine as well as a further 750,000 t of uranium from the granitic basement were provided by leaching the rhyolites. The overlaying of two such large potential uranium sources is probably an explanation for the large uranium resource in the caldera. The mobilization and relocation of the uranium was done by meteoric fluids, which were heated by the underlying magma chamber.

The second largest volcanic uranium resource Mardai in Dornod is around ten times smaller than the Strelsovska caldera in Russia with a uranium content of around 33,000 t and is located in Mongolia . Another important deposit is Xiangshan in Chongren County in China with around 26,000 t of uranium. All other known deposits of this type have uranium contents of less than 10,000 t. The largest volcanic-bound uranium deposits in the United States are located in the tertiary volcanics of the McDermitt Caldera and the Virgin Valley Caldera in Nevada and Oregon and contain a resource of approximately 10,000 t U 3 O 8 . In Germany there is a uranium province of this type in northern Saxony near Delitzsch . The mineralization occurs here in carbonic sediments, in direct contact with a plagiogranite porphyry. Felsic sub-volcanic dykes from the Carboniferous and Permian as well as Alpidic carbonatite intrusions also occur . The assumed total resource is 6,660 t of uranium, with mineralization of tungsten , molybdenum, REE, niobium , tantalum and phosphate in the wider area.

  • Origin: hydrothermal
  • Age: Paleo to Cenozoic
  • Uranium content: <1,000 t to 300,000 t
  • Average uranium content: 0.01 wt.% to 0.2 wt.%
  • possible further extractable content: molybdenum
  • Notable examples: Strelzowska Caldera (Russia); Mardai in Dornod (Mongolia)

Intrusive Type

Some types of intrusive bodies (acidic plutonites , carbonatites, pegmatites ) can contain uranium in recoverable amounts. The most important deposit of this group is Rössing in Namibia. The uranium is bound in an alaskite body , a sodium-rich acidic plutonite. Rössing was created either as a highly differentiated part of a granite body or through the partial melting of uranium-rich sediments. The contents are low with about 0.02 wt.% To 0.03 wt.% Uranium, but the deposit is very large and close to the surface, so that it can be extracted in open-cast mining . Uranium-containing pegmatites represent smaller uranium deposits. These coarse-grained rocks arise as the last phase of the crystallization of a magma body. Examples are Radium Hill in South Australia or Beaverlodge, Canada. The mineralogy is usually complex and therefore unfavorable for the extraction of uranium. Radium Hill produced around 850 tons of uranium oxide from davidite- containing pegmatites with an average uranium content of 0.1 wt.%. The carbonatite of Phalaborwa in South Africa contains elevated concentrations of uranium. Depending on the uranium price, the element is extracted as a by-product of copper production. Copper-porphyry deposits such as Chuquicamata in Chile or Bingham in the USA also produce uranium as a by-product, depending on the world market price. The uranium content in the rocks of these deposits is around 10  ppm . Deposits that are bound to fractional crystallization have not yet been dismantled. In these deposits, the uranium is bound to complex minerals such as steenstrupine , which form in the magma, sink in it and accumulate at the edges of the magma chamber. The most important example is the Kvanefjeld deposit in Ilimaussaq, Greenland .

  • Origin: magmatic
  • Age: Proterozoic to Mesozoic
  • Uranium content: <1,000 t to 200,000 t
  • Average uranium content: 0.01 wt.% to 0.1 wt.%
  • possible further extractable contents: copper, phosphate, REE, thorium (carbonatite, pegmatite)
  • Significant examples: Rössing, Namibia; Phalaborwa, South Africa

Metasomatic (Metasomatic)

Metasomatic deposits arise from the chemical change in rocks through alteration. Most often, deposits of this type are bound to sodium-calcium-altered rock units. There are significant deposits of this type in the Ukraine (including Michurinskoje), Brazil (Lagoa Real; Espinharas), Sweden (Skuppesavon), Guyana (Kurupung batholith in the Cuyuni-Mazaruni region ) and Queensland, Australia (Valhalla; Skal). The sodium-calcium alteration precedes the mineralization phase. The mineralization itself usually consists of brannerite or pitchblende, accompanied by uranium titanates, apatite , zirconium , xenotime and carbonate. This is usually followed by a weaker mineralization phase, which can contain hematite, carbonate, quartz, chlorite , non-ferrous metal sulphides , pitchblende and coffinite. The Valhalla and Skal deposits near Mount Isa in Queensland are also very rich in zirconium and rare earth metals (REE) . They were likely formed during the peak of the Isan mountain range 1.5 billion years ago. Valhalla contains inferred resources of 29,900 tons of uranium oxide grading 0.077% by weight uranium oxide. The currently most important deposit region for deposits of sodium metasomatism is located in Ukraine with the deposits Watutinskoje , Mitschurinskoje and Sewerinskoje. The deposits contain between 10,000 t and 50,000 t of uranium with a maximum content of 0.2 wt.% And they make up the largest part of Ukraine's uranium resources of 131,000 t.

  • Origin: metasomatic-hydrothermal
  • Age: Proterozoic
  • Uranium content: 1,000 t to 50,000 t
  • Average uranium content: 0.01 wt.% to 0.1 wt.%
  • possible further extractable contents: zirconium, SEE, thorium
  • Notable examples: Michurinskoye, Ukraine; Lagoa Real, Brazil

Metamorphic

Open pit mine of the skarn-bound metamorphic deposit Mary Kathleen, Queensland, Australia

Uranium deposits that form under metamorphic conditions are relatively rare. The most significant example is the Mary Kathleen deposit in Queensland, Australia. It is located in approximately 1.7 billion year old skarns, which were mineralized around 1.5 billion years ago during orogenesis with uranium, thorium and rare earth elements. Mary Kathleen produced around 8,500 tons of uranium oxide from ores grading 0.1 wt% to 0.15 wt% uranium. A European example is the Forstau deposit in Austria .

  • Origin: metamorphic-hydrothermal
  • Age:
  • Uranium content: some 1000 t
  • average uranium content: k. A.
  • possible further winnable content: none
  • Notable examples: Mary Kathleen, Queensland, Australia; Forstau, Austria

Collapse Breccia

  • Formation: sedimentary (hydrothermal)
  • Age: Mesozoic
  • Uranium content: some 1000 t
  • Average ore grades: 0.05 wt.% to 0.6 wt.% uranium
  • possible further extractable contents: vanadium , copper
  • Notable examples: Arizona Strip, USA; Sanbaqi, Lanshan County , China

Quartz pebble conglomerates (quartz pebble conglomerates)

Uranium-bearing conglomerates represent two of the largest uranium resources on earth, the Witwatersrand gold uranium field and the deposits around Elliot Lake in Ontario , Canada. They only formed in the Archean and Paleoproterozoic, as the formation of these deposits was only possible during this period. Uranium was transported as heavy mineral in rivers from these deposits and deposited as a conglomerate in shallow basins with quartz rubble and in the Witwatersrand together with solid gold and pyrite. The source for the pitchblende in Elliot Lake is possibly in an igneous uranium deposit similar to that of Rössing in Namibia, which was eroded. Cyanobacterial lawns sometimes acted as a kind of mechanical filter in which pitchblende and gold clogs got caught and contributed to their accumulation. Furthermore, after the formation of the deposits, the organic matter formed a reducing zone, which could have prevented the remobilization of uranium in later processes. The presence of pitchblende and pyrite in the conglomerates shows that the atmosphere at that time did not have high concentrations of oxygen. Otherwise, the minerals would have been oxidized, i.e. in the case of uranium dissolved and pyrite converted into iron hydroxides. The resources of the deposits are very large and contain more than 200,000 t of uranium in both Canada and South Africa. However, the contents are low, especially in the Witwatersrand, with only around 350 ppm on average and the extraction stages are very large. This means that extraction is only economical together with gold and depends on the market price for gold and uranium. In Canada, the grades are higher at around 0.1 wt.% Uranium, but mining in the Elliot Lake area is on hold for economic reasons.

  • Origin: sedimentary
  • Age: archaic-paleoproterozoic
  • Uranium content: over 200,000 t
  • Average uranium content: 0.02 wt.% to 0.1 wt.%
  • possible further winnable content: gold
  • notable examples: Witwatersrand, South Africa; Elliot Lake, Canada

Sandstone bound (sandstone)

Tabular deposits

Palaeo roll front in the Lake Frome Basin at the foot of the Mt. Painter area in South Australia
Westmoreland uranium deposit, Queensland, Australia: the position of two ore bodies in the Westmoreland conglomerate along the Redtree Dolerite Ganges is marked.
  • Formation: sedimentary (hydrothermal)
  • Age: Paleo to Cenozoic
  • Uranium content: <100 t to 100,000 t
  • Average ore grades: 0.01 wt.% to 0.5 wt.% uranium
  • possible further extractable contents: vanadium, copper
  • Notable examples: Henry Mountains District, Colorado Plateau , USA; Culmitzsch , Thuringia, Germany

Roll front storage facilities

  • Formation: sedimentary (hydrothermal)
  • Age: Paleo to Cenozoic
  • Uranium content: <100 t to 100,000 t
  • Average ore grades: 0.01 wt.% to 0.5 wt.% uranium
  • possible further extractable content: vanadium
  • notable examples: Powder River Basin , Arizona, USA; Koenigstein, Saxony, Germany; Kayelekera , Malawi (see there for a more detailed description of the genesis of this type of deposit)

Tectono-lithological deposits

  • Formation: sedimentary (hydrothermal)
  • Age: Archaic to Cenozoic
  • Uranium content: a few 100 t to 100,000 t
  • Average ore grades: 0.01 wt.% to 0.5 wt.% uranium
  • possible further winnable content: none
  • Significant examples: Arlit , Niger; Oklo * , Gabon
* Note: The natural reactors of Oklo as well as a neighboring uranium deposit represent a special feature: it is known that chain reactions occurred there in a natural environment about 1.5 to 2 billion years ago for thousands of years .

Surface type (Surficial)

  • Origin: sedimentary
  • Age: Mesozoic to Neogene
  • Uranium content: <1,000 t to 50,000 t
  • Average uranium content: 0.05 wt.% to 0.1 wt.%
  • possible further extractable content: vanadium
  • important examples: Langer Heinrich , Namibia; Yeelirrie , Western Australia , Australia

Black Shale ( Blackshale )

Uranium deposits in black schist represent large uranium enrichments with low grades. The known deposits are therefore to be seen as potential future uranium resources, as their mining is only worthwhile when uranium prices are high. These deposits arise on the sea floor under Euxinian (oxygen-free) conditions. Clayey sediments with high contents of organic material are deposited, which cannot be converted to CO 2 due to the lack of oxygen . This carbon-rich material can reduce dissolved uranium from seawater and bind it to itself. The average uranium content is between 50 ppm and 250 ppm. The largest resource is Ranstad in Sweden with a uranium content of 254,000 t. However, there are estimates for black shale deposits in the USA and Brazil, which assume more than one million tons of uranium, but with contents of less than 100 ppm uranium. For example, a uranium content of four to five million tons at a content of 54 ppm has been estimated for the Chattanooga Shale in the southeastern USA.

The Ronneburg deposit in Thuringia is a special form of this type of mineralization and the only significant black shale uranium deposit in the world that has been mined to date. Like the large vein deposits in the Western Ore Mountains, it lies on the Gera-Jáchymov fault zone. Hydrothermal and supergenic processes led to a rearrangement of uranium in the Ordovician and Silurian black schists, which were already rich in uranium, and enriched them further. The uranium is not only found finely distributed in the slates, but also in small passages and in brecciated zones. The upcoming diabase are also mineralized. The production between 1950 and 1990 was around 100,000 t of uranium with an average uranium content of the ores between 0.07 wt.% And 0.1 wt.%. A further 87,243.3 t of uranium were identified as explored and presumed resources in 1990, with contents between 0.02% by weight and 0.09% by weight, making it one of the largest uranium deposits on earth. There are also smaller occurrences of this type in Vogtland and in the Thuringian Forest .

  • Formation: sedimentary (hydrothermal)
  • Age: Paleozoic
  • Uranium content: <100 t to 300,000 t uranium
  • Average ore content: 0.005 wt.% to 0.02 wt.% uranium (purely sedimentary); 0.05 wt.% To 0.11 wt.% Uranium (sedimentary-hydrothermal)
  • possible further winnable content: none
  • notable examples: Randstad, Sweden (sedimentary); Ronneburg, Thuringia, Germany (sedimentary-hydrothermal)

phosphate

Phosphate deposits like black shale can be enriched with uranium. The deposits originated in the marine area on flat continental shelves in areas of limited water circulation. Uranium from sea water was mainly incorporated into apatite (CaPO 4 ). The uranium levels are between 50 ppm and 100 ppm. Supergene enrichment can sometimes lead to higher levels, as they are known from Brazil. Due to the low uranium content, uranium will only be obtained from these deposits as a by-product in the future and uranium production from them will therefore depend , in addition to the uranium price, primarily on the need for phosphate fertilizers . The world's uranium inventories of phosphates are estimated at around 9 million tons, of which Jordan with 6.9 million and the USA with 1.2 million tons have the largest share. In Brandenburg and Mecklenburg-Western Pomerania, the SDAG Wismut also investigated phosphate uranium mineralization with levels between 40 ppm and 200 ppm, but assessed it as unworthy of construction. A deposit in the Santa Quitéria area, Brazil, is a special variant. Phosphate contents are relatively low with 11% P 2 O 5 on average, whereas the uranium oxide contents are relatively high with 0.0998% by weight. It also contains a large amount of uranium-free marble. The deposit contains around 79,300 t of uranium oxide and is currently being examined for its profitability.

  • Origin: sedimentary
  • Age: Meso-Cenocian
  • Uranium content: 1,000 t to over 1,000,000 t
  • Average uranium content: 0.005 wt.% to 0.09 wt.%
  • possible further extractable content: phosphate (main product)
  • notable examples: Florida, USA; Morocco; Jordan; Brazil

(Brown) coal (lignite)

Coal deposits often contain high levels of uranium. The organic material could e.g. Sometimes bind uranium from solutions during the peat stage . A later entry during the diagenesis is also possible. The resources of some deposits can e.g. Sometimes considerable and contain several 10,000 tons of uranium. The coal used annually for power generation worldwide contains around 10,000 t of uranium and 25,000 t of thorium . However, the contents are usually low with a few tens of ppm and extraction from coal is difficult. Therefore, the possibility of extracting uranium from lignite filter ash is currently being investigated in China and Hungary. A direct uranium extraction from coal took place at the Freital / Dresden-Gittersee deposit in Saxony. The uranium content of the hard coal and surrounding Rotliegend sediments was around 0.1% and 3,500 t of uranium were produced.

  • Origin: sedimentary
  • Age: Paleo to Cenozoic
  • Uranium content: 1,000 t to a few 10,000 t
  • Average uranium content: 0.005 wt.% to 0.1 wt.%
  • possible further winnable content: coal (main product)
  • Significant examples: Freital, Saxony, Germany; Yili Basin , China / Kazakhstan ; Lignite filter ash

Sea water and salt lakes

Both seawater and salt lakes contain increased concentrations of dissolved uranium. In the sea this is 3 µg / L or three tons of uranium per cubic kilometer. This corresponds to a uranium content of more than four billion tons. Studies on the extraction of uranium from seawater have been carried out in Japan, among others, and have shown the basic technical possibility of uranium extraction. However, the cost is estimated at around USD 300 per kg of uranium and is therefore not currently competitive. Salt lakes can contain much higher concentrations than seawater, but extraction does not take place here either.

Table of the largest uranium deposits

rank Country Occurrence
or District 		Uranium content in 1000 t Base rock Type Age status
1 Morocco Oulad Abdoun Basin 3200 Phosphorites synsedimentary Cretaceous - Eocene potential resource
2 Morocco Meskala Basin 2000 Phosphorites synsedimentary Cretaceous - Eocene potential resource
3 Australia Olympic Dam 1900 Breccias IOCG Mesoproterozoic in production (by-product)
4th Morocco Gantour basin 1200 Phosphorites synsedimentary Cretaceous - Eocene potential resource
5 United States East Florida 270 Phosphorites synsedimentary Miocene - Pliocene historical production (by-product), potential resource
6th Sweden Ranstad 250 Black pelite synsedimentary Cambrian historical production, potential resource
7th Namibia Rössing mine 250 intrusive - partial melt Cambrian in production
8th United States Central Florida 225 Phosphorites synsedimentary Miocene - Pliocene historical production ( by-product ), potential resource
9 Canada Denison Mine 185 Quartz rubble - conglomerates synsedimentary Archean historical production
10 United States Northeast Florida 180 Phosphorites synsedimentary Miocene - Pliocene historical production (by-product), potential resource
11 Canada McArthur River 180 Discordance bound diagenetically hydrothermal Mesoproterozoic in production
12 Australia Jabiluka 2 170 Discordance bound diagenetically hydrothermal Mesoproterozoic potential resource
13 Germany Ronneburg (Thuringia) 160 (200) Black pelite synsedimentary / hydrothermal Devonian - Permian historical production
14th Kazakhstan Inkai 150 Sandstone Roll front Chalk - Tertiary in production
15th Niger Open pit Imouraren 150 Sandstone Tabular chalk in production
16 Australia Ranger 3 135 Discordance bound diagenetically hydrothermal Mesoproterozoic in production
17th Kazakhstan Mynkuduk 125 Sandstone Roll front Chalk - Tertiary in production
18th Brazil Santa Quiteria 120 Metasomatic Cambrian in preparation for extraction
19th Canada Cigar Lake 110 Discordance bound diagenetically hydrothermal Mesoproterozoic in preparation for extraction
20th Brazil Lagoa Real 100 Metasomatic Mesoproterozoic in production

See also

Commons : Geology of Uranium  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d V. Ruzicka: Vein uranium deposits. In: Ore Geology Reviews. 8, 1993, pp. 247-276.
  2. ↑ M. Min, D. Zheng, B. Shen, G. Wen, X. Wang, SS Gandhi: Genesis of the Sanbaqi deposit: a paleokarst-hosted uranium deposit in China. In: Mineralium Deposita. 32, 1997, pp. 505-519.
  3. ↑ B. Merkel, B. Sperling: Schriften 117: Hydrogeochemical Soffsysteme Part II. ISSN  0170-8147 , 1998.
  4. ^ Mineralogy Database. Retrieved March 25, 2009 .
  5. ↑ a b M. Cuney: Giant Uranium Deposits. In: Giant Ore Deposits Down Under: Symposium Proceedings, 13th Quadrennial IAGOD Symposium 2010 Adelaide, South Australia 6-9 April
  6. ↑ a b c d Geology of Uranium deposits .
  7. ↑ a b c d e f g M. Cuney: The extreme diversity of uranium deposits. In: Miner Deposita. 44, 2009, pp. 3-9 ( doi: 10.1007 / s00126-008-0223-1 ).
  8. ↑ L. Hecht, M. Cuney: Hydrothermal alteration of monazite in the Precambrian crystaline basement of the Athabasca Basin (Saskatchewan, Canada): implication for the formation of unconformity-related uranium deposits. In: Mineralium Deposita. 35, 2000, pp. 791-795 ( doi: 10.1007 / s001260050280 ).
  9. ↑ F. Veselovsky, P. Ondrus, A. Gabsová, J. Hlousek, P. Vlasimsky, IV Chernyshew: . Who was who in Jáchymov mineralogy II In: Journal of the Czech Geological Society. 48, No. 3-4, 2003, pp. 193-205.
  10. ↑ a b c d e f g h M. Hagen, R. Scheid, W. Runge: Chronik der Wismut . Ed .: WISMUT GmbH, Chemnitz. 1999 (CD-Rom).
  11. ^ A b c d Douglas H. Underhill: Analysis of uranium supply to 2050. In: International Atomic Energy Agency. Vienna 2001.
  12. ↑ B. Kribek, K. Zák, P. Dobes, J. Leichmann, M. Pudilová, M. René, B. Scharm, M. Scharmova, A. Hájek, D., Holeczy, UF Hein, B. Lehmann: The Rožná uranium deposit (Bohemian Massif, Czech Republic): shear zone-hosted, late Variscan and post-Variscan hydrothermal mineralization. In: Miner. Deposit. 44, 2009, pp. 99-128.
  13. ↑ K. Ehrig, BHP Billiton SA Explorers Conference 2008 , Adelaide, Nov. 28, 2008 (talk)
  14. ↑ Marathon Resources Ltd - Paralana Mineral System (Mt Gee). In: Official website. Retrieved April 23, 2009 .
  15. ↑ a b A. Chabiron, M. Cuney, B. Poty: Possible uranium sources for the largest uranium district associated with volcanism: the Streltsovka caldera (Transbaikalia, Russia). in Mineralium Deposita 38, 2003, pp. 127-140.
  16. ^ S. Castor, C. Henry: Geology, geochemistry, and origin of volcanic rock-hosted uranium deposits in northwestern Nevada and southeastern Oregon, USA. In: Ore Geology Reviews. 16, 2000, pp. 1-40.
  17. ↑ a b Australian Uranium Association Former Australian Uranium Mines. (No longer available online.) Archived from the original on January 24, 2009 ; accessed on April 23, 2009 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / aua.org.au
  18. ↑ PA Polito, TK Kyser, C. Stanley: The Proterozoic, albitite-hosted, Valhalla uranium deposit, Queensland, Australia: a description of the alteration assemblage associated with uranium mineralization in diamond drill hole V39. In: Miner. Deposit. 44, 2009, pp. 11-40 ( doi: 10.1007 / s00126-007-0162-2 ).
  19. ^ Uranium Production Plans and Developments in the Nuclear Fuel Industries of Ukraine 1998. ( Memento from May 17, 2013 in the Internet Archive )
  20. ^ World Nuclear Association Nuclear Power in Ukraine 2009. Retrieved April 23, 2009 .
  21. ↑ M. Min, D. Zheng, B. Shen, G. Wen, X. Wang, SS Gandhi: Genesis of the Sanbaqi deposit: a paaelokarst-hosted uranium deposit in China. In: Mineralium Deposita . 32, 1997, pp. 505-519 ( doi: 10.1007 / s001260050118 ).
  22. ^ A b A. Robinson, ETC Spooner: Source of the detrital components of uraniferous conglomerats, Quirke ore zone, Elliot Lake, Ontario, Canada. In: Nature . 299, 1982, pp. 622-624 ( doi: 10.1038 / 299622a0 ).
  23. ↑ CS Spirakis: The roles of organic matter in the formation of uranium deposits in sedimentary rocks. In: Ore Geology Reviews. 11, 1996, pp. 53-69.
  24. ^ A b Warren I. Finch: Uranium Provinces of North America - Their Definitions, Distribution, and Models. (= US Geological Survey Bulletin. 2141). United States Government Printing Office , Washington 1996; (PDF)
  25. ↑ F. Password: URANIUM: Namibia. In: Africa Research Bulletin: Economic, Financial and Technical Series . 43, No. 10, 2006, pp. 17164C-17165C ( doi: 10.1111 / j.1467-6346.2006.00586.x ).
  26. ^ Galvani to work on Brazil's largest uranium reserve. In: World Nuclear News. Retrieved April 23, 2009 .
  27. ↑ a b world-nuclear.org
  28. ^ Turning ash into cash. In: Nuclear Engineering International. April 2009, pp. 14-15.

Web links

Commons : Uranium  - album with pictures, videos and audio files
Wiktionary: uranium deposit  - explanations of meanings, word origins, synonyms, translations