Abstract
The technical evolution of unmanned aerial systems (UAS) for mineral exploration advances rapidly. Recent sensor developments and improved UAS performance open new fields for research and applications in geological and geophysical exploration among others. In this study, we introduce an integrated acquisition and processing strategy for drone-borne multi-sensor surveys combining optical remote sensing and magnetic data. We deploy both fixed-wing and multicopter UAS to characterize an outcrop of the Otanmäki Fe-Ti-V deposit in central Finland. The lithology consists mainly of gabbro intrusions hosting ore bodies of magnetite-ilmenite. Large areas of the outcrop are covered by lichen and low vegetation. We use two drone-borne multi- and hyperspectral cameras operating in the visible to near-infrared parts of the electromagnetic spectrum to identify dominant geological features and the extents of ore bodies via iron-indicating proxy minerals. We apply band ratios and unsupervised and supervised image classifications on the spectral data, from which we can map surficial iron-bearing zones. We use two setups with three-axis fluxgate magnetometers deployed both by a fixed-wing and a multi-copter UAS to measure the magnetic field at various flight altitudes (15 m, 40 m, 65 m). The total magnetic intensity (TMI) computed from the individual components is used for further interpretation of ore distribution. We compare to traditional magnetic ground-based survey data to evaluate the UAS-based results. The measured anomalies and spectral data are validated and assigned to the outcropping geology and ore mineralization by performing surface spectroscopy, portable X-ray fluorescence (pXRF), magnetic susceptibility, and traditional geologic mapping. Locations of mineral zones and magnetic anomalies correlate with the established geologic map. The integrated survey strategy allowed a straightforward mapping of ore occurrences. We highlight the efficiency, spatial resolution, and reliability of UAS surveys. Acquisition time of magnetic UAS surveying surpassed ground surveying by a factor of 20 with a comparable resolution. The proposed workflow possibly facilitates surveying, particularly in areas with complicated terrain and of limited accessibility, but highlights the remaining challenges in UAS mapping.
Highlights
The demand for raw materials is steadily growing in our technology driven societies
We introduce an integrated acquisition and processing strategy for drone-borne multi-sensor surveys combining optical remote sensing and magnetic data
We use two setups with three-axis fluxgate magnetometers deployed both by a fixed-wing and a multi-copter unmanned aerial systems (UAS) to measure the magnetic field at various flight altitudes (15 m, 40 m, 65 m)
Summary
The demand for raw materials is steadily growing in our technology driven societies. In Europe, industry and businesses depend heavily on direct and indirect raw material imports (metal ores, fossil energy carriers) [1]. The difficulty of providing selected critical raw materials by European producers is increasing—e.g., for rare earth elements [2]—and innovative technologies in exploration and recycling are needed to decrease dependencies on non-domestic imports of raw materials In this context, we see a high demand for the exploration of new deposits and/or small or less profitable prospects to sustain the need for metallic and raw materials [3,4,5] and inaccessible or formerly non-lucrative mineral deposits are needed [6]. Mineral exploration in Europe has to fit to our present societal and economic standards, meaning that sustainable, non-invasive, and efficient exploration strategies are required Following these requirements, exploration in little explored regions can be started with regional survey approaches, e.g., large-scale satellite and regional airborne mapping. Ground based surveying that includes geophysics, drilling, and extensive sampling are applied to obtain detailed knowledge from identified deposits
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