Kayelekera open pit mine
| Kayelekera | |||
|---|---|---|---|
| General information about the mine | |||
| Mining technology | Open pit mine on 55.2 km² | ||
| Funding / total | ≈4200 t uranium | ||
| Information about the mining company | |||
| Operating company | Paladin Limited (Africa) | ||
| Start of operation | April 17, 2009 | ||
| End of operation | April 2014 | ||
| Funded raw materials | |||
| Degradation of | uranium | ||
| uranium | |||
| Raw material content | 0.1% | ||
| Greatest depth | 160 m | ||
| Geographical location | |||
| Coordinates | 9 ° 59 '34 " S , 33 ° 41' 53" E | ||
|
|||
| region | Northern region | ||
| Country | Malawi | ||
The Kayelekera open pit mine is a uranium mine in the north of the East African Republic of Malawi . It is the largest such mining project in Malawi to date. The corresponding uranium deposit is one of the largest known to date in the sedimentary rocks of the Karoo supergroup . From 2009 to 2014 around 4200 t of uranium were mined here.
geography
Kayelekera is located about 25 km (as the crow flies) west of Karonga and 575 km from Lilongwe in the valley of the Northern Rukuru in the northern province of Malawi. The area around Kayelekera is drained by two rivers: the Sere and its tributaries in the north and the Muswanga and its tributaries in the south. Both are tributaries of the Northern Rukuru.
geology
General
The uranium deposit Kayelekera in the northern part of the Northern-Rukuru Basin ( North Rukuru Basin ). The basin filling represents one of several erosion remains of an extensive late Paleozoic-early Mesozoic sedimentation area in the region. The Northern Rukuru Basin is a half-ditch bounded by faults . It extends almost parallel to Lake Malawi and is around 50 km long and up to 6.5 km wide. Its formation takes place after the sediment filling that is currently still being deposited and well before the onset of the rift fracture tectonics of the East African Rift system (earliest date: Upper Jurassic ). Beyond the basin rim faults there are metamorphic and igneous rocks of the Precambrian basement , which are regionally assigned to the Misuku Belt , a southeastern branch of the Ubendian Mobile Belt .
The sedimentary rocks preserved in the basin belong to the Karoo supergroup and are of the Late Carboniferous to Middle Permian ages. The sequence of layers, which has the younger and at the same time the largest part of the 1500 m thick basin filling, is called the North Rukuru Formation ( North Rukuru Sandstone and Shale Formation ). It generally represents lacustrine - fluvial sedimentation conditions. The uranium deposit is located in the youngest layer member of the Northern Rukuru Formation, the " Kayelekera Member ". The "Kayelekera member" has been dated to Middle Permian ("Kasanium") with the help of fossil pollen ( palynostratigraphy ) and therefore correlates with the strata of the Ecca group of the Karoo main basin in South Africa .
Deposit
Stratigraphy and Lithologies
The Kayelekera uranium deposit is located entirely within the "Kayelekera member", which is 150 m thick on site. It consists of eight powerful (around 10 m) arkotischen sandstone packages in alternation with powerful, partially silt leading mudstone packets ( "intermediate means"). The sandstone parcels have the designations X 3 , X 2 , W, V, U, T, S and R from the lying to the hanging wall. Some of the sandstone parcels are internally structured by thinner claystone layers. The mudstone-sandstone ratio within the "Kayelekera member" is about 1: 1. The sediments of the Kayelekera sequence are partly deposited in an oxidizing, partly in a reducing environment, which can be read from the color of the rock: oxic layers are red to brown (" red beds "), the layers deposited under reducing conditions are dark green, some mudstone horizons are gray to black in color, and some are even referred to as "coal" or " coal shale ".
The arkose sandstones were all deposited in a reducing environment. They are typically characterized by a low grain sorting and have a high proportion of unweathered feldspars (approx. 25% albite / oligoclase and a maximum of 25% potassium feldspar ). Some sandstone packages sometimes show several “ fining upward cycles” , in which the mica content increases upwards. In the coarser-grained layers, the flesh-colored potassium feldspar clasts contrast with the greenish, carbon- and pyrite-rich matrix .
Structural geology
The basin filling was slightly folded during the sinking of the half-ditch. The "Kayelekera Members" is therefore in the core of a synclines whose fold axis parallel to the east edge of the bowl sweeps . The syncline is also divided into individual clods by a system of steeply dipping faults that either run parallel to or across the eastern basin rim fault. Layers of the “Kayelekera member” are only preserved on the deepest floes. The Kayelekera uranium deposit is located on such a floe.
Mineralization and Formation
The mineralization is lenticular and mostly bound to the arkose sandstone. The ore lenses in the individual sandstone packages are all more or less in the same place in relation to the terrain surface - they are, so to speak, "stacked" on top of one another. Three “redox facies” can be distinguished within an ore lens: reduced facies (uranium-rich), oxidized facies (uranium-poor) and transition facies. The proportion of the respective facies in an ore lens varies relatively strongly between the individual sandstone packages. In sandstones W and V, for example, the proportion of reduced facies is particularly high, whereas in sandstone package T there is only a little ore of the reduced facies. The stratigraphically highest sandstone package R is largely free of ore.
The most important uranium mineral of the reduced facies is coffinite , U [SiO 4 , (OH) 4 ]. It occurs, particularly often in areas rich in carbon and pyrite, finely grown with chlorite and clay minerals in the interstitial space of the sandstones. Uranium ore minerals occurring in smaller quantities in the reduced facies and in the transition facies have not yet been precisely identified. It probably is uraninite , UO 2 , and a uranium-titanium mineral, probably Betafit , (CAU) 2 (Ti, Nb, Ta) 2 O 6 (OH) or Tanteuxenit , (Y, Ce, Ca) ( Ta, Nb, Ti) 2 (O, OH) 6 . The oxidative facies show several greenish-yellowish secondary minerals, especially meta-autunite , Ca (UO 2 ) 2 [PO4] 2 · 6–8H 2 O (a slightly dehydrated variant of autunite ) and boltwoodite , (K 0.56 Na 0.44 ) [(UO 2 ) (SiO 3 OH)] · 1.5H 2 O, in smaller quantities also uranophane , CaH 2 (SiO4) 2 (UO 2 ) · 5H 2 O.
From a genetic point of view, Kayelekera is a sedimentary- hydrothermal uranium deposit of the sandstone or roll front type or a special variant of this type. What is special about Kayelekera is the enrichment of uranium minerals in the core of a syncline and the resulting “stacking” of ore lenses, which does not occur in North America, the type region of roll front deposits. The uranium originally comes from the erosion of granitic rocks of the Precambrian basement and was initially deposited in a reducing chemical environment as part of the arkoses. The arkoses are thus the "proto-ore" containing small amounts of uranium. After the northern Rukuru half-ditch had subsided and the synclines had formed, oxidizing hydrothermal waters circulated in the permeable sandstone packages and mobilized (dissolved) the uranium salts, which were poorly soluble under reducing conditions. On the one hand, the oxidation front propagated further and further in the direction of flow of the hydrothermal water and, on the other hand, the continual reprecipitation of uranium salts in the not yet oxidized zone immediately in front of the oxidation front increasingly enriched that zone with uranium. Since the clay-rich intermediates are relatively impermeable to aqueous solutions, they are largely excluded from mineralization. Sandstones containing feldspar that have been enriched with uranium, such as those in the Kayelekera deposit, are also known in German as Aktivarkosen .
history
In 1957 handpieces of radioactive arcoses were found for the first time at Mwankimene in the valley of Northern Rukuru. However, subsequent prospecting initially did not produce any positive results. In 1977 the Italian Agip carried out radiometric reconnaissance flights over the region and discovered a number of radiation anomalies. The subsequent exploration work on the ground led to the discovery of secondary uranium minerals in outcrops near the village of Kaleyekera. After further, more intensive prospecting measures on site, the Agip did not renew its exploration license.
As early as the late 1970s, the British Central Electricity Generating Board (CEGB) evaluated Malawi's uranium potential. a. the Northern Rukuru Basin became the focus of interest. In 1989, after a feasibility study had confirmed the economic potential of the deposit, the CEGB entered into negotiations with the state of Malawi with the intention of building a uranium mine. For various reasons, including a. the privatization of the CEGB and a collapse in the world market price for uranium, this project fell asleep in the early 1990s.
In 1997, Balmain Resources Pty Ltd, Australia, acquired a prospecting license for the Kayelekera area. In March 1998, Paladin Energy, also from Australia, took over 90% of the shares in the exploration project as part of a joint venture (“farm-in agreement”) with Balmain Resources. In 2005, Paladin and its African subsidiary, Paladin (Africa) Ltd (PAL), finally took over the remaining 10%. In July 2009, 15% of the shares in PAL were transferred to the state of Malawi as part of a development agreement. The open-cast mine was officially opened on April 17, 2009 in the presence of the then Malawian President Bingu wa Mutharika . The ramp-up phase ended in 2010 and triuranium octoxide (U 3 O 8 ) was extracted for the first time from the ore that had meanwhile been mined in the connected processing plants .
Kayelekera was designed for an annual production of 3.3 million pounds (approx. 1495 tons) of U 3 O 8 , which corresponds to around 1268 tons of pure uranium. However, this goal has not yet been achieved in any year. The best result so far came from 2013 with just under 3 million pounds (approx. 1344 tons) of U 3 O 8 . In February 2014, ore mining was temporarily stopped again. The main reason given was the currently too low world market price for uranium, which does not even enable the mine to cover its costs. After a shutdown phase ( rundown ), during which at least the facilities for processing the ore still in stock were still running, the entire mine was put into a temporary sleep state ( care and maintenance ) on May 6, 2014 . Production is slated to resume when the uranium price is sustained above $ 75 a pound.
The table below contains a list of the ore mining quantities and the uranium production quantities for the years 2009 to 2014.
| Fiscal year | Mined ore (average concentration> 1000 ppm; in t ) | Uranium production (in lbs U 3 O 8 ) |
Uranium production (in t U 3 O 8 ) |
Uranium production (in tU) |
Production target of 3.3 million lbs / year reached too |
|---|---|---|---|---|---|
| 2009 | Start-up phase | k. A. | k. A. | k. A. | ? % |
| 2010 | 948,536 | 963,000 | 437 | 370 | 29.2% |
| 2011 | 946.410 | 2,196,000 | 996 | 845 | 66.5% |
| 2012 | 1,993,651 | 2,478,000 | 1,124 | 953 | 75.1% |
| 2013 | 1,072,225 | 2,963,000 | 1,344 | 1,140 | 89.8% |
| 2014 | k. A. | 2,350,000 | 1,066 | 904 | 71.2% |
| total | 4,960,822 | 10,950,000 | 4,967 | 4.212 | 66.4% |
literature
- RA Bowden, RP Shaw: The Kayelekera uranium deposit, Northern Malawi: past exploration activities, economic geology and decay series disequilibrium. Applied Earth Science. Vol. 116, No. 2, 2007, pp. 55-67, doi : 10.1179 / 174327507X167082 (alternative full-text access : CORE , unedited manuscript).
Web links
Individual evidence
- ↑ a b c Paladin Energy Ltd Annual Report 2009 ( PDF 10.73 MB)
- ^ Bowden, Shaw: The Kayelekera Uranium Deposit. 2007 (see literature )
- ↑ a b Kayelekera production suspended. Article on world nuclear news on February 7, 2014. Retrieved December 10, 2014
- ↑ a b Paladin Energy Ltd Annual Report 2014 ( PDF 7.63 MB)
- ^ Paladin Energy: Project Update Kayelekera Mine (on care & maintenance). September 2014 ( PDF ( Memento of the original from December 10, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this note. 1.69 MB)
- ↑ Paladin Energy Ltd Annual Report 2010 ( PDF 10.98 MB)
- ↑ Paladin Energy Ltd Annual Report 2011 ( PDF 4.56 MB)
- ↑ Paladin Energy Ltd Annual Report 2012 ( PDF 9.47 MB)
- ↑ Paladin Energy Ltd Annual Report 2013 ( PDF 5.00 MB)
