July 2012

          The primary uranium minerals in commercial ores are uraninite (UO₂), pitchblende (U₃O₈), coffinite (U(SiO₄), brannerite (UTi₂O₆), davidite ((REE)(Y,U)(Ti,Fe³)₂₀O₃₈) and thucholite (Uranium-bearing pyrobitumen). There are a number of other common uranium minerals which form hydrated crystals incorporating water molecules.

          The mineralogy of the host minerals, the reduction-oxidation potential of the uranium mineral and the porosity which determines water infiltration are important factors in the formation of uranium deposits. Since uranium is highly soluble, it can be easily moved around by the flow of water underground. This contributed to the variety of places and manners in which uranium may accumulate. The way in which uranium interacts with other elements and compounds in melted rock also influences its distribution.

          Combinations of surface weathering, sedimentation, diagenetic, magmatic and hydropthermal geological processes mentioned in a previous post produce fifteen general types of uranium deposits.

         The richest uranium ore deposits are found near unconformities. An unconformity is a break in between two layers of rock that have been laid down at different times. In the case of uranium deposits, the two layers are a quartz rich sedimentary layer and a metamorphic layer has been altered by heat and pressure. These deposits were formed between two billion five hundred million years ago and five hundred million years ago.

         The second best uranium ore deposits form in sedimentary deposits on continental shelves and freshwater areas such as river deltas, lakes, etc. In an oxygen rich environment, the uranium dissolves and then moves with the water. When it encounters an oxygen poor or reducing environment, it precipitates out of solution.

         Tabular deposits occur parallel to groundwater flow in sandstone. The ores are rich but the deposits are small.

         Roll front uranium deposits form when ground water dissolves the uranium in sandstone and, after flowing underground, collides with some sort of organic matter rich in carbon. The uranium precipitates out at the “front” when the water encounters the organic material.

         Basal channel deposits form from moving ground water like the tabular and roll front deposits, but the deposition occurs along channels of moving surface water such are rivers. When the water evaporates along desert margins or in shallow saline ponds, the uranium is deposited.

         Quartz-pebble conglomerate deposits are created by the separation and movement of particles of uranium in flows of surface water and their deposit in river beds, river deltas and lakes. These deposits generally contain large quantities of low grade ore

          Breccia complex deposits contain uranium along with iron oxide, copper, gold, silver and rare earth elements. Hydrothermal processes enriched the uranium content of  the quartz-hematite breccias.

          Vein deposits are uranium minerals filling in cracks, veins, fractures and breccias in steeply dipping fault systems. Magmatic processes in molten rock create the veins and later hydrothermal activity can concentrate the uranium. Some veins contain a variety of other metals in combination with the uranium.

          Intrusive uranium deposits form when magma is forced into older rocks deep within the Earth’s crust.

          Marine sedimentary deposits of phosphorite (which contain large amounts of phosphorus) sometimes contain uranium.

          Collapsed breccia pipe deposits are created when vertical cylindrical cavities formed by groundwater dissolving limestone are filled with fragments of rock when they collapse. Uranium fills cavities and coats other rocks.

          Volcanic deposits of uranium may be formed by magmatic processes in the molten rock or later mineralization by groundwater and chemical processes. Such deposits are usually small with low grade ore.

          Surface deposits can form in peat bogs, karst caverns and in soil from the weathering of shallow sedimentary deposits of uranium.

          Metasomite deposits are the result of uranium minerals being distributed in rocks that have been subjected to sodium metasomatism which is chemical alteration by hot subsurface solutions of sodium.

          Metamorphic deposits were laid down by sedimentary or magmatic processes and then remained unaltered by any other processes.

          Lignite is a soft brown young coal derived from wood. Some deposits contain significant amounts of uranium minerals.

          Black shale deposits form in oxygen-free submarine sedimentation processes. The uranium is not mineralized by organic materials due to the lack of oxygen. These deposits are considered very low grade ores.

          There are many other types of uranium minerals but these fifteen types constitute the pool from which uranium ores are chosen for extraction.

Sedimentary layers:

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          Uranium is a naturally occurring radioactive chemical element. It was formed in super novae explosions about 6.6 billion years ago. In its pure form it is a silvery colored heavy metal. It is 70% denser than lead but not quite as dense as gold and will burn in a powdered form. A little softer than steel, it is malleable, ductile, paramagnetic, weakly electropositive and a poor conductor of electricity. It will oxidize in air and can be dissolved by acids.

          The main location for testing nuclear bombs in the United States between 1951 and 1962 was the Nevada Test Site. Eighty six nuclear bombs were exploded either at ground level or above and fourteen nuclear devices were exploded underground. Radioactive materials were injected into the atmosphere from all the tests. The government told people to sit outside and watch the mushroom clouds caused by the explosions.

          The United States government began construction at Hanford in south central Washington State in 1943. Three nuclear reactors and two chemical processing plants were built and operated at Hanford during the Manhattan Project to develop nuclear weapons for use in World War II. The U.S. government retained private contractors including DuPont and General Electric to oversee the production of materials for nuclear weapons.

          Shortly after the discovery of X rays in 1895, papers began appearing in scientific publications about the negative effects of high levels of exposure to such radiation. In the first year, suggestions about how to protect against ionizing radiation were made including the three main measures that are still emphasized today, limit the exposure to the shortest possible time, maintain as great a distance from the source as possible and employ shielding of some sort.

           In 1988 the Radiation and Public Health Project (RPHP) was created by the United Church of Christ Commission for Racial Justice. Jay M. Gould and Benjamin A Goldman started the project as a spinoff of their work at Public Data Access, Inc. In 1995 RPHP became an independent non-profit 501(c)3 organization. The mission of the organization includes research, education and raising public awareness.

            Back in the 1950s at the height of the cold war, there was a great deal of talk about fallout shelters. When people were very serious about the prospect of nuclear war with the Russians and the Chinese, shelters were built that were intended to allow people to survive if their city was hit by a nuclear blast and they were outside the radius of immediate destruction.

            Radioresistance is defined as the ability of some organisms to survive in environments where there is a high level of radioactivity. There may be naturally occurring radiation from uranium ores or man-made radiation from nuclear bombs or nuclear accidents. After the Chernobyl accident in Ukraine, scientists were surprised to find that many species survived when the assumption was that the high level of radiation should have killed most of them.

          There is a type of bacteria named Deinococcus radiodurans (Latin for “terrific berry that withstands radiation”) that is very resistant to damage by ionizing radiation. It is known as an extremophilic bacterium meaning that it is very tough. In addition to being able to withstand radiation it can also survive dehydration, extremely low temperatures, some acids and even vacuum.