Argentina has the most advanced nuclear energy industry in South America, with three nuclear reactors and at least two more on the way in 2018. Argentine President Mauricio Macri, who is mandating a push toward clean energy, announced in May 2016 that the government is looking to increase the position of nuclear power in the country’s energy mix from 5 percent to 20 percent by 2025. But with no readily available domestic uranium supply and the high cost of imports, how can Argentina meet its mandate? One good answer to this dilemma can be found in sandstone and surficial-type uranium deposits, which offer the potential for near-surface, low-cost development and production along with economically important vanadium as a co-product.
Uranium occurs in a wide variety of geological environments worldwide, and the International Atomic Energy Agency (IAEA) has identified 15 major deposit types based on those differing environments. Sandstone uranium deposits contain uranium concentrated or “trapped” in permeable sandstones or conglomerates, in general confined between less permeable sedimentary sequences. Uranium is precipitated under reducing conditions (i.e. little or no oxygen present) created by varying types of agents within the sandstone, such as carbonaceous material, hydrocarbons, sulfides and interbedded volcanic ash. Common uranium minerals in sandstone deposits are uraninite, coffinite and brannerite. Sandstone deposits comprise 18 percent of world uranium resources and 41 percent of known deposits.
Surficial uranium deposits are near-surface uranium concentrations in sediments or soils. Calcrete-type (calcium and magnesium carbonates) are the largest subtype of surficial deposits, and usually form in regions where deeply weathered, uranium-rich granites or sandstones (as well as remobilization of previously formed uranium deposits) occur in a semi-arid to arid climate in valley-fill sediments along tertiary drainage channels and in playa lake sediments. The uranium mineralization is usually carnotite — hydrated potassium uranium vanadium oxide, according to the IAEA.
“Sandstone uranium deposits are generally found in continental or marginal marine sedimentary rocks, and in basins related to volcanism. Uranium can be associated to copper and vanadium in sandstone deposits, and in some cases close to oil– and gas-producing terrains,” said Guillermo Pensado, vice president of exploration and development at Blue Sky Uranium. He cited examples such as the Powder River Basin of Wyoming, US; the Coastal Plain of Texas, US; the Chu-Sarysu and Syrdarya basins of Kazakhstan; and the Neuquen basin in Argentina.
There are five subtypes of sandstone deposits. Sandstone deposits related to redox fronts, or fronts where the oxidation state of the minerals change by an agent, can be huge deposits if the redox front is related to regional or big-scale boundaries. Cameco’s Inkai deposit in Kazakhstan is a good example where the proven and probable reserves are about 270 million pounds of U3O8 at a grade of 0.03 percent or 300 ppm U3O8.
US Geological Survey (USGS) research has shown that calcrete-type surficial uranium deposits are usually found within arid climatic belts, which display high evaporation rates; hence why there is a strong concentration of such deposits in arid regions such as Australia, Namibia, Tanzania, Mauritania and Argentina. Western Australia is home to some of the most recognized calcrete uranium deposits, including Cameco’s Yeelirrie deposit, one of the world’s largest, as well as Lake Way, Centipede, Thatcher Soak and Lake Maitland. Namibia also hosts world-class surficial uranium deposits, the most well-known being Paladin Energy’s Langer Heinrich in the country’s Namib desert and AREVA’s Trekkopje.
“Calcrete uranium deposits are relatively low grade as compared with uranium deposits of all geologic types; however, they can be quite large,” Susan Hall, uranium resource specialist at the USGS, told INN. The USGS has published a database listing the grade and tonnage (not all NI 43-101 compliant) of all known world calcrete uranium deposits. “The Yeelirrie deposit in Australia is estimated to contain 128 million pounds U3O8, and the Langer Heinrich deposit in Namibia is estimated to contain in all (included mined uranium) 190 million pounds of U3O8. Deposits of this size are attractive targets,” added Hall.
Their large scale coupled with their near-surface occurrence make these deposits well suited to low-cost mining operations. “The deposits are found close to the surface and can be mined using shallow open pits,” explained Hall. “Ore is reached relatively early in the mining cycle, therefore returning on your investment sooner than if you were required to remove a great deal of rock before hitting ore.”
Large surficial deposits have also been identified in Argentina (which has similar geological characteristics to Namibia). “There are five known deposits in the country, ranging from <100,000 to more than 8 million pounds of U3O8 (not all NI 43-101 compliant),” said Hall. Her numbers are based on research data published in October 2017. “Exploration for calcrete uranium deposits in Argentina is in the early stages, no deposit has yet been mined. I am aware of one company, Blue Sky Uranium, who is exploring for calcrete uranium.”
Blue Sky Uranium’s wholly owned Amarillo Grande uranium-vanadium project is in the province of Rio Negro, in the Patagonia region of Argentina. Amarillo Grande presents district-scale potential with multiple uranium showings and three discovery targets across the 140-kilometer-long and 50-kilometer-wide property. The geology is similar to that of the Inkai deposit, where the mineralization is well preserved, with similarities to the Yeelirrie deposit, where mineralization is close to surface in sediments and soils which are likely dried up rivers and lake beds.
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Also see the newly recognized uranium mineral found in Texas (here).
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