Searching for traces with drones: Novel approach for the exploration of Rare Earth Elements
Rare Earth Elements (REE) are essential resources to ensure the energy transition, e-mobility and future technologies. The use of lightweight unmanned aerial vehicles (UAV) provides a unique opportunity to conduct rapid and non-invasive exploration for REE even in ecologically sensitive areas and in relatively inaccessible locations. For the first time scientists from the Helmholtz Institute Freiberg for Resource Technology (HIF) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have directly identified and mapped REEs in both arid and subarctic environments using UAV-based hyperspectral data. They have now published their novel detection method in Scientific Reports.
Mineral resources are becoming increasingly scarce and harder to find. However, at the same time, we need raw materials, especially Rare Earth Elements (REE), to achieve our goals towards a greener society. Conventional exploration methods especially in remote areas are costly, time-consuming and often not environmentally friendly. Most methods rely on substantial geological fieldwork including dense in-situ sampling with long delays until provision of analytical results.
That is why scientists from Freiberg developed a novel approach to detect and assess REE deposits. “We employ drones with hyperspectral sensors to detect REEs at the Earth’s surface and thus contribute to a rapidly evolving field at the cutting edge of exploration technologies,” says René Booysen, scientist at HIF and first author of the publication. “With innovation we can render exploration more efficient and, more importantly, socially and environmentally more acceptable,” says Dr. Richard Gloaguen, leader of the exploration department at HIF.
How to find REE deposits?
Booysen and her colleagues demonstrate how UAV-based hyperspectral data can be used in a multi-scale remote sensing exploration approach to map the abundance of REEs directly. In this context, the characteristics of REE deposits play a significant role. The scientists use reflective spectroscopy (laboratory- or ground-based hyperspectral imaging - HSI) to identify the chemical element Neodymium. Neodymium has characteristic absorption features in the visible to near infrared (VNIR) range of the electromagnetic spectrum. This element can thus be used as a key pathfinder element for REEs.
To enable sensor-based exploration in difficult terrain where outcrops are unreachable on foot or by vehicles, the team used drones. The flexibility of UAV-based hyperspectral imaging can ensure personal safety as well as efficiency and speed during the exploration process. “We use two types of unmanned aerial systems: a fixed-wing system for the rapid acquisition of photogrammetric data as basis for digital surface models and a multi-copter for HSI collection. Using a fixed-wing system, we capture nadir stereo-imagery meaning the direction pointing directly below a particular location with a portable snapshot camera. That is also referred to as RGB camera as it acquires three bands in the visible part of the electromagnetic spectrum for Structure-from-Motion Multi-Vision-Stereo photogrammetry, which provides hyperscale landform models using images acquired from a range of digital cameras and optionally a network of ground control point,” explains René Booysen.
Test area of 10.000 square meters
To test their remote sensor techniques the researchers chose two representative sites to highlight the diversity of environments in which REEs can be found. On the one hand, the Marinkas Quellen alkaline-carbonatite intrusive complex located in southern Namibia. Most of the complex is not accessible by car and demands long hikes to access the target areas. Carbonatite is a unique igneous rock type, in that it formed predominantly of carbonate minerals of which it must contain more than 50 percent along with lesser silicates, phosphate minerals, and oxides. On the other hand, the researchers tested the techniques on the Archean Siilinjärvi carbonatite complex in central Finland. It is one of the oldest known carbonatites. In both regions, they selected areas of interest of approximately 10,000 square meters.
There they captured hyperspectral data with a frame-based sensor, mounted on a multi-rotor platform. Additionally, they took in-situ spectral measurements with a portable VNIR-shortwave infrared field spectrometer and samples for petrological and geochemical validation. With these techniques, they rapidly produced with high spatial resolution digital surface models and orthomosaics by stitching UAV-produced images together into a single scene. “Our solution has the advantage of quick turn-around times, low detection limits and is ideally suited to support exploration campaigns. This strategy should invigorate the use of drones in exploration and for the monitoring of mining activities,” resumes René Booysen.
Dr. Richard Gloaguen | René Booysen
Helmholtz Institute Freiberg for Resource Technology at HZDR
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