Deep in the Australian desert, an expedition in search of rare earth elements
As a teacher-researcher and geologist for over 20 years, I have had the opportunity to go on numerous field missions during my career. The expedition I am going to tell you about was my last field mission, back in the pre-pandemic days, during the southern winter of 2019.
Bénédicte Cenki, University of Montpellier
As a teacher-researcher and geologist for over 20 years, I have had the opportunity to undertake numerous field missions during my career. Each time, I have been driven by the same passion for discovering new territories, from the Peruvian Altiplano for my master's thesis in 1997 (I traveled in a truck bed filled with potatoes), to all those years spent exploring active quarries in South India for my dissertation in the early 2000s, to all those field missions in the mountains (even on a Via Ferrata at an altitude of over 3,000 m on Mont Emilius in the Aosta Valley in 2007) or on idyllic Greek islands where metamorphic rocks (rocks transformed during tectonic processes such as the formation of mountain ranges) plunge into crystal-clear, Bahamas-green water.
The expedition I am about to tell you about was my last field mission, back in the pre-pandemic days, during the southern winter of 2019.
The objective of this mission was to study rocks in an area near Nolans Bore, which in the coming years will become one of Australia's largest rare earth mines in the Northern Territory.
Rare earth elements such as lanthanum, cerium, praseodymium, neodymium, thulium, and ytterbium are chemical elements that are essential to new technologies (wind turbines, solar panels, electric vehicles).
These metals are considered critical because, in addition to their economic importance, their supply is heavily dependent on China.
Why go looking for rare earth elements in Central Australia?
In order to prevent future economic, geopolitical, and environmental problems, Western countries have been embarking on major research projects for the past decade with a view to diversifying their sources of supply in the long term and ensuring that extraction is carried out in a responsible manner that respects people and the environment.
See also:
The shortage of these metals: a challenge for tomorrow's societies
As the winner of a European Marie Curie Horizon 2020 project, I had the opportunity to spend 18 months on secondment at the University of Sydney to acquire additional skills in digital modeling. I took advantage of this opportunity to organize a mission to the Australian desert, known as the bush, to assess the rare earth potential of the pegmatites of the Entia metamorphic dome (a circular outcrop of partially melted rocks from the deep Earth's crust formed during the formation of ancient mountain ranges) in Central Australia. Pegmatites are products of the melting of the continental crust, which is rich in quartz, feldspars, and micas, but also in rare metals.
To this end, I invited two colleagues: Patrice Rey, a tectonicist and modeler from the University of Sydney, and Fleurice Parat, a petrologist specializing in magmatism from the University of Montpellier.
Organize a mission with complete autonomy in the Australian bush
This meticulous organization begins several months in advance, because nothing can be left to chance (there will be enough uncertainties when the time comes). For this mission to be a success, I absolutely must find the GPS coordinates of the rare earth deposits listed in the 1990s archives of the Northern Territory Geological Survey. After being intensively explored for uranium at the end ofthe 20th century, this territory has shown considerable interest in rare earths since the beginning ofthe 21st century (rare earth minerals are often radioactive, which also complicates their extraction).
Since we won't have Internet access, I absolutely must prepare for this mission "the old-fashioned way": selecting targets from reports that are over 30 years old, printing all the satellite images, topographical or geological maps that may be necessary, buying a solar charger for the GPS and iPad that will allow us to navigate through the bush to reach the geological targets, and of course remembering the Geosciences Montpellier satellite phone and emergency GPS beacon that would allow us to be found in case of a serious problem (and making sure to register it before leaving civilization!).
I arrive in Alice Springs from Sydney on the morning of July 11, almost at the same time as my colleague Fleurice arrives from France after a 24-hour flight. Our colleague Patrice will join us two days later. So the two of us are planning the logistics and essential shopping. We are leaving with only one 4×4, so we will have to stay on the tracks visible from the satellite images without risking leaving them.
Source, Author provided
Alice Springs is a small town of around 20,000 inhabitants in central Australia, lost thousands of kilometers from civilization (1,500 km north of Darwin and south of Adelaide). The local supermarket is nothing like the extravagant European hypermarkets or those found on the upscale Pacific coast! But it has the essentials: water for 15 days (there are no sources where we are going), pasta, canned vegetables, freeze-dried soups, tea, muesli, spreads, vitamin powder (such as spirulina), tables, folding chairs and crockery (which we will leave to the locals after the mission), shovels (to dig daily individual toilets), sun cream, large hats and... fly nets! We are setting off completely independently, but with light and minimalist equipment (I am reassured by the fact that my colleague Patrice has many bush missions behind him): cooking over a fire (a hearth dug into the sand of the creek), no generator, no refrigerator, so we are only taking food that can be stored at room temperature and, of course, a first aid kit.
The Entia metamorphic dome is located on the private land of Ambalindum Station, a huge cattle farm covering several thousandsquare kilometers. My requests for permission to access the site sent to the head office in Brisbane have gone unanswered, so we will have to negotiate access with the farmers on site when the time comes. This means a 300 km detour, without even being sure that they will welcome us!
So we spend our first three nights acclimatizing at the Hale River Homestead campground in Old Ambalindum (150 km east of Alice Springs). After a quick phone call to the farmer on the second evening, she tells me to come by the next day at 7 a.m. after their morning debriefing. The sun rises through a veil of dry red dust, and I spot the farmers' helicopter, its rotating blades breaking the icy morning silence. We park in front of the small single-story hut where the morning meeting is being held. We are not invited inside, despite the temperature being only a few degrees above freezing. We wait for the farmer to arrive with maps, which we unroll on the hood of the car. She hesitates to give us access, and we repeat that we are not a mining company, but academics. Finally, the key to getting in is the name of a colleague from the University of Adelaide who came the previous year and made a good impression. Phew, mission accomplished. We set off on a six-hour drive to enter the Entia dome via a passable and secure track with a single vehicle. Last stop to fill up with diesel before leaving civilization behind: the remote Aboriginal community of Atitjere, so far removed from our Western view of the world.
Our daily life for 10 days in the heart of the Entia dome
We arrive at our campsite in the late afternoon, in the heart of the dome, which will allow us to explore the area every day. It is located in a dry creek bed that Patrice recognizes from having been there several times before: this rocky area is the kitchen area (magnificent migmatites!), there the sand is the most comfortable for tents, and over there are the toilets. Once our camp is set up, we cook our first dinner (pasta with ratatouille!) under the stars on a campfire dug into the sand. With a bowl of tea warming our hands, as it is only a few degrees, we enjoy our first evening under the immensity of a magnificent starry sky and in an enveloping, reassuring silence. The second day begins like the following ones, with the morning ritual at sunrise around 6:30 a.m.: Patrice and Fleurice rekindle the fire and prepare tea and breakfast while I check that the electronic devices are charged and plan our itinerary for the day and the order in which we will visit geological targets. Very quickly, everyone finds their natural place in this type of mission and everything works perfectly and simply.
Source, Author provided
The days pass and are all much the same: we drive as close as possible to our targets in a 4×4, following the tracks visible on Google Earth. Then we set off on foot with water, our hammers, field notebooks, and GPS devices to reach the selected outcrop. Fortunately, the vegetation is sparse and sparse, and the elevation gain is low, allowing us to navigate in a straight line and by sight: pegmatites are very light-colored rocks and therefore clearly visible in the monotonous brown-ochre landscape. Once we reach the outcrop, Fleurice and I take out our magnifying glasses to try to spot rare minerals with strange names such as samarskite, fergussonite, and monazite, while Patrice takes out his compass to take measurements and compare the direction of the pegmatites with that of the surrounding rocks. A well-oiled and efficient team! These minerals contain heavy rare earth elements such as thulium and ytterbium (used in superconductors, radiotherapy, and infrared lasers), as well as niobium and tantalum (used mainly in alloys for aeronautics).
One evening, on his way back to camp, Patrice stops the 4×4 near a cattle trough, climbs up the few rungs of the ladder and discovers that the hatch covering it is open: from now on, we will be able to collect a jerry can of water every evening for washing up (and the occasional cup shower—what luxury!).
Every evening, we return shortly before nightfall at around 6 p.m. to make the most of the ten or so hours of daylight in the southern winter. Our evening ritual is therefore often carried out by headlamp: gathering some dry grass to relight the fire, cooking, washing up with a trickle of water, sorting the day's samples, and updating our field notebooks while trying to synthesize all the information and formulate and debate scientific hypotheses to be tested later. A last glance at the Milky Way and the Southern Cross while sipping tea, before we each retire to our tents around 9 p.m.
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The days pass peacefully and are all much the same. Only the last afternoon holds a surprise for us: our first (and last) encounter with the dingo, that famous wild dog that is an icon of the Australian bush. We are at the last outcrop, in the heart of the Inkamulla sub-dome. We discuss the significance of the folded structures and carefully sample rock slabs with chisels and hammers, looking for folds that are important for understanding the formation of this geological structure. The evening light intensifies the red-ochre color of the rock, with its rounded, welcoming, and timeless contours.
In fact, it looks like an Aboriginal cave, protected from wild animals, a few meters up and easy to climb. A few Aboriginal artifacts found in the dust bear witness to this. The shadows of the eucalyptus trees, with their white-speckled trunks and light green leaves, grow longer by the minute. It is in this peaceful and surreal moment that a dingo nonchalantly approaches our group, who are engaged in a lively geological discussion about our technique for sampling these small shear bands that we need to date. Curious, the dingo circles around us a few meters away and sits down on a rock to continue watching us.
What now?
Before flying back to civilization, we stop at the post office in Alice Springs to send the four barrels of samples to France, which we carefully cataloged and packed the night before in the parking lot of the Alice Springs motel.
Since returning to France in August 2020, I have carefully sawn each sample to produce thin sections 30 micrometers thick, which can be studied under an optical microscope and then under a scanning electron microscope, an electron microprobe, and a laser ablation mass spectrometer in order to quantify the mineral content of major chemical elements and rare earth elements.
Jonas Nollo, a Master's student in the "exploration and reservoir geology" program, is providing us with invaluable assistance on the analytical side of the study. If the borders reopen, I sincerely hope that he will be awarded a thesis scholarship in Australia so that he can continue his work exploring critical metals, which include rare earth elements: this is a profession with a bright future, because the ecological transition must be carried out with the help of geologists! The initial results of our study will be presented in early July 2021 at the annual Goldschmidt international conference, scheduled to take place (virtually) in Lyon. Through meticulous study, Jonas has identified four families of pegmatites with different mineralogical compositions that could have very distinct depths and ages of formation, and therefore varying rare earth potential. He will quantify the chemical composition of the major and critical elements using an electron microprobe and mass spectrometer in early May.
Unfortunately, microscopic analysis has not yet enabled us to find the rare minerals we were hoping for, but we have found a lot of garnet pegmatites (which contain heavy rare earth elements, but in lower concentrations). However, Jonas has confirmed the presence of allanite pegmatites containing light rare earth elements to the southwest of the Entia dome (lanthanum, cerium, neodymium, praseodymium). Science often advances in small steps. Major discoveries are always preceded and driven by a multitude of fundamental studies conducted by numerous researchers collaborating around the world. To be continued...
Bénédicte Cenki, Associate Professor at Montpellier University, EU H2020 MSCA visiting researcher at Sydney University, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.