Rare Earth Elements and The Moon: KREEP Basalts
Mining the Moon for Rare Earth
Elements - Is It Really Possible?
By Robert Beauford, 13 Feb. 2011
Recent international excitement over the development of new rare earth element resources has caused an uncommon burst of speculation about the possibility of mining rare earths off planet. Apollo explorers, 40 years ago, brought back rocks that proved to be anomalously high in a variety of what are geologically termed ‘incompatible elements.’ The region from which these rocks originated is called the Procellarum KREEP Terrane. The REE in KREEP stands for rare earth elements.
The rare earth elements are a series of 16 metals with names most people have never heard of, such as dysprosium, lanthanum, and yttrium. Ores of these metals are comparatively scarce. They are found in mineable concentrations only in limited number of unusual rock outcrops on earth. Their value to society, however, far outweighs their availability or pronouncability. The reason behind the excitement about rare earths is their importance to green technologies and to high tech products. Energy efficient technologies ranging from solar cells and hybrid cars to compact fluorescent and LED light bulbs and wind power turbines are critically dependent on these resources. High tech computing and communications devices are similarly dependent. Without the rare earth elements, society would not have CDs, any of the compact computer memory devices, satellite communications, iPods, full color monitors, or even the fiber optic cables and lasers that make the internet possible.
Figure 1: Rare Earth Elements - Image from USGS Fact Sheet 087-02. http://pubs.usgs.gov/fs/2002/fs087-02/
Recent dramatic growth in demand for rare earths has presented the world with a challenge. In 2010, China exported between 95 and 97 percent of the global supply of rare earth elements, but demand within China is growing as fast as everywhere else. The Chinese government and industry leaders have expressed that China is not interested in selling these products to other countries in unlimited amounts on an indefinite basis, and has been moving towards larger and larger export limitations. In essence, China has started telling the rest of the world that Chinese industry wants the raw metals for manufacturing, and that the rest of the world should start seeing to their own needs. With global demand for rare earths growing by 10 to 12 percent per year, and with China expected to consume their own annual metal production in the first half of the present decade, world governments are listening. The U.S., Canada, and other countries that have mineable rare earth resources have been taking rapid and necessary steps to encourage domestic mining. Interest in rare earth exploration is at an all time high.
For some, all of this attention on the rare earths has brought to mind the moon and its famous rare earth rich KREEP basalts. Recent articles exploring the possibility of mining the moon have been abundant both in print and on the web, but few, if any have looked at any real numbers.
[Place Holder for Thorium Proxy Map]
So what are the facts?
The moon is a very different place form the earth in a lot of ways. The moons gravity is about 1/6th of earth, the temperature can reach below negative 200° Celsius during the two week lunar night, there is no significant available water, the surface atmospheric pressure approaches that of the near absolute vacuum of space, the radiation environment is extreme due to the suns direct intense rays, and could be lethal in a solar storm, and micrometeorites bombard the surface at 15 kilometers per second or more at unpredictable intervals. The moon is not a hospitable place.
In addition to the extreme physical differences in potential mining environments on the moon’s surface compared to the surface of earth, there are also important geological differences to consider.
Ores are concentrations of minerals that contain profitably mineable quantities of desirable elements. Whether on Earth or on the Moon, ores form by the sorting of elements through geological processes. These typically include surface weathering, the action of hot (hydrothermal) subsurface water, or sorting by igneous processes called partial melting and fractional crystallization. ‘Igneous processes’ means any natural process that results from the melting and cooling of rocks. On the moon, the first two of these mechanisms can be eliminated. There is no water and no atmosphere, so there is no weathering. The only significant ongoing processes that are currently affecting the Moon’s surface are irradiation by the sun and bombardment by meteorites. And though there may have been small scale changes in the Moon’s rocks due to the action of subsurface water in the Moon’s early history, such action was never appreciable, due to the lack of surface water and of any continents or continental motion. Without going into too much detail, this means that any ores found on the moon must be formed by only one of the three primary mechanisms: igneous sorting processes.
The moon is about 4.5 billion years old, and for much of that time, it has been a relatively static and unchanging environment. Its igneous history is brief and limited. We thought, until very recently, that the moon’s outer layers had been frozen in a solid state for almost 4 billion years. We now suspect that limited volcanism continued on the moon until about two billion years ago. This is a brief time when compared against the geological environment of the earth, which still has pervasive volcanism and constant ongoing motion within the crust, mantle and core of the planet.
Not only were the duration of the igneous processes that affected the moon shorter than the equivalent processes on earth, they were also different in character. Earth’s surface and interior have been constantly stirred and recycled, like a big pot of boiling soup, by large scale slow motion turbulence. This process is still going on today, and earthquakes and volcanoes are two of the results. The Moon shared a very similar early history with the earth, but while both started as giant spheres covered in an ocean of molten rock, the much smaller moon cooled quicker. With the cooling of the Moon’s surface, and later it’s interior, igneous geological processes stopped.
The Procellarum KREEP Terrane represents a deep area of the Moon’s outer surface that became enriched in rare earth elements, along with various low temperature melting minerals and incompatible radioactive elements such as uranium and thorium, during the initial cooling of the moon. These minerals essentially floated or were forced to the top of a magma ocean as it cooled and crystallized. Because the crust of the moon cooled before its interior, the KREEP should have been trapped deep beneath the surface. Radioactive elements, which were much more numerous in the early solar system, however, migrated outward with the KREEP, providing the heat necessary for the material to climb to the surface of the planet in large scale regional upwelling of hot rock and localized magma surges.
Related processes happened in the early earth, and continue to happen today. On Earth, however, these large scale generalized concentrations of elements are lost in the complex cycling of the crust and mantle of a planet that is orders of magnitude more geologically active than the moon. Essentially, the igneous processes that sort out enriched bodies of ore bearing rock on earth started on the moon, but then froze. The result is a single large scale concentration of very low grade ore that represents something like 18% of the moon’s surface. This means that the baseline concentrations of rare earth elements in the Lunar KREEP are only a few times higher than background levels in the Earth’s crust, and that even its most dense known concentrations are still only a fraction of REE concentrations on Earth.
So, in answer to the question: Can we profitably mine the moon for REEs and ship them back to the earth to sell? No. Rare earth oxide concentrations in known lunar ores do not support it, even at the level of conjecture, and our current understanding of lunar geology does not predict the existence of substantially more enriched ore deposits. Lack of sufficiently enriched ore, however, is not the only challenge to lunar mining for export to earth. (This is an understatement of epic proportions.) Keeping the analysis, for the moment, focused on basic mining issues rather than on the challenges facing planetary colonization, it must also be observed that competitively economical transport of marketable quantities of either ore or refined metals across planetary distances is neither available with current technology, nor on the mid-term technological horizon. Imagine transporting thousands of tons of ore output from a remote mine in Canada to a processing facility in Brazil in the small passenger seat of a fighter jet, one of the least fuel efficient aircraft ever invented, while trying to maintain profitability in the mine. Now multiply that by a factor of 100,000.
Figure 3: Lunar KREEP basalts are enriched by the standards of moon rocks, but the geological processes are very different. Compared to terrestrial concentrations of rare earths sorted and emplaced by multiple phases of geological sorting and weathering in earth’s continental crust, there is just no comparison. The above graph compares the presence of rare earth elements in typical Lunar KREEP basalts and Lunar ultra-KREEP basalts with the average presence of these elements, expressed in parts per million, in two rare earth element mines located on Earth. The first mine is Mountain Pass, owned by Molycorp, in California. The second is Mount Weld, which is being developed by Lynas Corporation, in Australia. These are, admittedly, two of the best rare earth mines on the planet, but they represent only two of many very good mines with which a hypothetical Lunar export process would have to compete. The Mount Weld Mine, in particular, stands beside the South African Steenkampskraal Mine, which is owned by the Canadian company Great Western Minerals Group, as one of the highest quality ore bodies ever discovered on earth.
But, that’s not the end of the story. In space science, the first answer is almost never the only answer.
The factor that makes many rare earth element locations profitably mineable, on earth, is co-products. Co-products are things like iron, thorium, gold, or other valuable commodities recoverable from the same ores from which rare earth elements are extracted. China’s Bayan Obo mines, for instance, which provide a significant percentage of the world’s annual rare earth production, are first and foremost iron mines, holding 470 million tonnes of iron ore reserves. The same multiple product approach will almost certainly be necessary in space. Rocks and sunlight are, essentially, the only resources available on the moon. This means that mining will be fundamental and central to any sustained lunar presence, and that mining will need to provide far more than a single product.
When humanity makes the leap outward to the moon, and decides to put down roots and stay there, colonists are going to need far more than rare earth elements. They will need shaped rock for construction and for defense against space dust, radiation, cold temperatures, and against the ever present empty vacuum of airless space. They will also need oxygen, nitrogen and other gasses to produce a supply of breathable air, along with hydrogen to produce water. Igneous rocks such as the KREEP basalts, along with surface breccia, the lunar equivalent of sterile soil (crushed rock and dust) will need to be mined for metals, gasses, silica, water, and everything else necessary to support life, buildings, and food production. All of this means digging holes and refining what comes out of them. There is no more geologically diverse region on the moon’s surface than the KREEP terrane. Because it contains the most ‘evolved’ volcanic rocks on the planet, there is also no other region more geologically likely to produce low temperature igneous rocks such as carbonates and phosphates, from which oxygen and other gasses can be recovered at relatively low energy expense.
The moon is the gateway to the solar system and one of only two logical next steps for humanity, alongside Mars. Mining the moon for rare earths may not be economically viable today, but building mines in the KREEP Terrane will almost certainly be one of humanity’s future steps as we reach for the outer solar system and for the stars.