|Fig. 1: Global reasonably assured resources of Uranium by Deposit type. |
The World Nuclear Association, an international organization that promotes and supports companies that make up the global nuclear industry, organizes deposits of uranium in fourteen categories based on geologic setting. Unlike petroleum and mining deposits, uranium deposits exist in igneous, hydrothermal, and sedimentary geological environments.  Uranium resources are classified from geological certainty and costs of production to combine resource estimates from a number of different countries into global figures. Identified resources (which include RAR and inferred) refer to uranium deposits delineated by sufficient direct measurement to conduct pre-feasibility and sometimes feasibility studies. For reasonably assured resources (RAR), high confidence in estimates of grade and tonnage are generally compatible with mining decision-making standards. Inferred resources are not defined with such a high a degree of confidence and generally require further direct measurement prior to making a decision to mine (Fig. 1). 
Sandstone hosted uranium deposits account for around 18% of world resources. The formation of these deposits is nearly always caused by the interaction of uranium, being transported by oxygen-rich groundwater, with a reduced host rock. In this geological environment it is possible to use this native groundwater in the ore body, once fortified with a complexing agent and likely an oxidant, to be pumped through the ore body in order to leach the minerals present. Once the pregnant solution is returned to the surface it is recovered similarly to any other uranium plant.  This technique is know as in situ leaching and was first attempted in Wyoming in the 1960s.  The world's leaders at in situ leaching of uranium deposits are the United States of America and Kazakhstan. There are two operating regimes for in situ leaching, determined by the chemistry of the geology and groundwater. If the ore body has significant amounts of calcium (limestone), alkaline (carbonate) leaching must be used, otherwise acid (sulfate) leaching is usually best. The techniques involved with in situ leaching have evolved to where it can be done in a safe, controllable way that is environmentally benign and can exist in a regulatory climate that is very similar to oil and gas exploration. Many of the technologies and techniques used are directly related to the oil and gas industry as well. The actual process of recovering uranium begins with use of a submersible pump to remove the native groundwater in order to add the uranium complexing reagents.  The techniques for optimization economic value of the deposit also are in line with industry practice in oil and gas.  The merits of in situ leaching have been looked into by many countries as a way to either find enough resource for their demand or to help minimize their need to import. In either sandstone or limestone in situ leaching (ISL) of uranium can be done successfully, but as of now none of the other uranium deposit-types are candidates for ISL.
Much of what determines the significance of in situ leaching techniques worldwide is demand for nuclear power. In 2011, globally we consumed 4.39 million barrels oil equivalent of nuclear power.  The OECD Nuclear Energy Agency foresees continued growth in demand for nuclear power. While incidents have occurred in the nuclear power industry recently (Fukushima) and skepticism has been seen about these types of issues, there is going to be a future for nuclear energy.  One of the primary benefits of nuclear energy is that it is one of the only virtually carbon free primary energy sources we have that is economic with current technologies. As more questions about the safety of nuclear power plants and the waste they produce are mentioned we will have to resolve them. If resolved the potential for nuclear power demand could be significant to the point that its share of total primary energy consumption globally could become a plurality.
As our society progresses we will continue to demand electricity in greater amounts and in greater percentages across all industries. If we are serious about a commitment to stabilizing or reducing concentrations of CO2 in our atmosphere we must be serious about considering nuclear power as a keystone to that process. When discussing renewables (Wind, Solar) the question is always about the variability and the lack of necessary base load power.  With nuclear energy we are capable of eliminating this problem by providing a reliable, economic, base load electric power output that is essentially carbon-free. This would allow to use all of the great things individuals like Elon Musk are inventing today and in the future. [7,8] When this happens the practice of in situ leach mining for uranium deposits capable of meeting demand for nuclear power will become a sound investment for all sizes of investors. Currently in the United States of America we have nearly 100 publicly traded oil and gas exploration and/or production companies whose market capitalization can range from tens of millions to hundreds of billions in US Dollars. Unlike the mining industry, oil and gas economics is usually calculated on a per well basis. The compartmentalization of the economics in a single unit that can be scaled to any size big or small is the primary reason why we see such a range of values for the market capitalization of the companies and such a large number of companies in the industry. In mining, you must find a deposit that is large enough to justify the capital-intensive investment that is open-pit or underground mining. If in situ techniques continue to become more efficient and more successful we could see the same type of companies large and small be attracted to this industry. As our primary energy mix continues to become more diversified with renewables (wind, solar) that take space on our earth's surface it is important to note the benefits that nuclear energy provides. Nuclear energy has the potential to deliver nearly equivalent loads of power in ways that provide the benefit of essentially zero-emissions like renewables but also low land intensity similar to oil and natural gas production.
So while many tend to look to the surface and the sky for the future of upstream energy resource production, a betting man would look down. The past, present and future of our energy landscape will be shaped by economically significant accumulations of minerals and organic matter that reside in the subsurface of our earth.
© Tyler Scott. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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