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Negev Desert Uranium and Phosphate Mineralisation |
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Israel |
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U P V
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Uranium mineralisation in the Negev Desert of Israel occurs in part as secondary, yellow uranium minerals formed by weathering, soil formation or sedimentary processes which are widespread in the arid areas of the northern Negev and the Judean Desert.
This mineralisation occurs as scattered exposures covering areas of as much as several hundred square metres in extent, distributed over a district of 700 square kilometres. Uranium values of from 200 to 3900 ppm are found in hand specimens of this material.
It has been suggested (Ilani and Strull, 1988) that the uranium has been leached out of the Cretaceous Senonian phosphorites, exposed over much of the area, and from the metamorphosed phosphorites of the Senonian to Palaeocene Hatrurim formation which has then migrated towards the local low elevations, principally towards the Dead Sea Rift Valley. The Hatrurim Formation, or Mottled Zone, outcrops all around the Dead Sea Basin in the Negev Desert in Israel, in the Judaean Desert on the West Bank, and in western Jordan. It includes late Cretaceous to Eocene aged impure limestone along with coal bearing chalk, marl and phosphorite.
Uranyl ions, together with ions of vanadate, phosphate and carbonate form a range of uranium minerals (meta-autunite, meta-tyuyamunite and carnotite). Secondary uranium minerals are associated with gypsum, occurring as thin veins and as matrix in pedogenic layers that range from 0.2 to 1.5 m in thickness. This gypsum-rich pedogenic layer, like calcrete, appears to be a lithological marker and trap, especially under reducing conditions.
This mineralisation is found on the opposite side of the Dead Sea to similar mineralisation described in more detail as 'surficial mineralisation' in the Central Jordan Uranium Project record. See that record for more details of the occurrence of phosphorite and uranium in the region.
Israel has also apparently extracted uranium from the phosphate deposits in the Negev desert, where there is an estimated thirty to sixty thousand tonnes of uranium oxide contained at low grades within phosphate ores (Wisconsin Project on Nuclear Arms Control, 2023). Phosphorites are actively mined from a number of operations in the Negev Desert east of Beersheba where, e.g., at the Zohar deposit, there was a resource of the order of 200 Mt @ 31.1 to 33.9% P2O5. The ore from the Rotem deposit (130 Mt @ 20 to 30% P2O5) in the same area of Israel has been sampled and assayed to contain 120 ppm U (Schnug, 2014). Uranium from Rotem is believed to supply the nearby Dimona nuclear plant. The other key phosphate mines are Zafir (Oron-Zin) and Eilat Quarry. Israel lies within the Middle East-North Africa phosphate belt. Deposition of the P-rich sequence in Israel generally occurred between 80 and 72 Ma, during the Upper Campanian of the Cretaceous, and mostly in the Negev area, where it is known as the Mishash Formation (equivalent to the phosphorite hosting Amman Formation of the Belqa Group in Jordan). An important influence on the development of phosphorites in the Negev is the ~90 Ma Late Turonian tectonics which deformed the area to form a series of gentle highs, the Negev 'anticlines', and semi-confined lows, the Negev 'synclines'/'basins'. This resulted in restricted marine circulation and contributed to the trapping of abundant organic-rich detritus in the Negev 'basins'. Degradation of the organic detritus together with the activity of microbial mats on the seafloor and suitable redox conditions led to the formation of discrete apatite bodies in bottom sediments. These, were subsequently, mechanically concentrated by bioturbation and bottom currents, and redeposited as granular phosphorite strata. The economic phosphate section of the Negev sequence, mostly a few to 10 m thick, is generally composed of alternating P-rich granular phosphorite beds and 'sterile' P-poor interlayers, which are mostly carbonates. The phosphate fraction mainly comprises sub-millimetric ovoid grains/peloids, some bone fragments, phosphatised foraminiferid shells, and many rounded fragments of phosphate-coated remnants of mat-forming microorganisms (fungi, bacteria and cyanobacteria). As in other sedimentary phosphorites elsewhere, the phosphate mineral of the Negev phosphorites is carbonate-fluorapatite. Phosphate concentration of the economic phosphorite beds mostly varies from 23 to 30 % P2O5.
See also the Al Jalamid, Umm Wu al, Al Khabra record for an outline of the Middle East-North Africa phosphate belt of which these deposits are part and a description of similar, but possibly a little younger phosphorite occurrences.
The most recent source geological information used to prepare this decription was dated: 2020.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Ilani S, Strull A, 1988 - Uranium mineralization in the Judean Desert and in the northern Negev, Israel : in Ore Geology Reviews v4 pp 305-314
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