Drone-Borne Hyperspectral and Magnetic Data Integration: Otanmäki Fe-Ti-V Deposit in Finland

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 droneborne multisensor surveys combining optical remote sensing and magnetic data. We deploy both fixedwing and multicopter UAS to characterize an outcrop of the Otanmäki FeTiV deposit in central Finland. The lithology consists mainly of gabbro intrusions hosting ore bodies of magnetiteilmenite. Large areas of the outcrop are covered by lichen and low vegetation. We use two droneborne multi and hyperspectral cameras operating in the visible to nearinfrared parts of the electromagnetic spectrum to identify dominant geological features and the extents of ore bodies via ironindicating proxy minerals. We apply band ratios and unsupervised and supervised image classifications on the spectral data, from which we can map surficial ironbearing zones. We use two setups with threeaxis fluxgate magnetometers deployed both by a fixedwing and a multicopter 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 groundbased survey data to evaluate the UASbased results. The measured anomalies and spectral data are validated and assigned to the outcropping geology and ore mineralization by performing surface spectroscopy, portable Xray 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.

Detection of REEs with lightweight UAV-based hyperspectral imaging

“…UAVs can also serve as platforms for a large amount of other sensors such as LIDAR 32 , 33 , magnetometers 34 or radiometers 35 . The value of HSI can thus greatly be enhanced with the integration of additional remote sensing and geophysical data 13 . We expect drone-borne HSI to become standard in exploration schemes.…”

“…Difficult terrain or outcrops unreachable on foot or by vehicles can be rapidly surveyed with UAVs from a safe distance with minimal personnel on site, ensuring safety, efficiency and speed 16 , 17 . A few studies have shown the potential of using UAV-based HSI for geological mapping (e.g., Jackisch et al 13 ). In the context of carbonate geology, Madjid et al 18 and Dujoncquoy et al 19 used UAV-based photogrammetry in order to map sedimentary carbonate lithologies.…”

“…Drones have been increasingly used in mineral exploration (e.g., Booysen et al 3 ; Jackisch et al 13 ; Malehmir et al 14 ; Sayab et al 15 ). Difficult terrain or outcrops unreachable on foot or by vehicles can be rapidly surveyed with UAVs from a safe distance with minimal personnel on site, ensuring safety, efficiency and speed 16,17 .…”

Integrated Geological and Geophysical Mapping of a Carbonatite-Hosting Outcrop in Siilinjärvi, Finland, Using Unmanned Aerial Systems

“…We summarize the main characteristics of used sensors here (Table 1) and for specific technical details of our UAS workflow and data acquisition, we refer to Appendix A and [24]. We used the senseFly eBee Plus fixed-wing (www.sensefly.com, senseFly, Cheseaux-sur-Lausanne, Switzerland) equipped with either a high-resolution RGB camera (www.parrot.com, Parrot S.O.D.A., Parrot SA, Paris, France), or a multispectral camera (Parrot Sequoia).…”

“…UAS-based hyperspectral imaging and magnetics were identified as a promising sensor combination for direct targeting of iron ores [24], using surficial proxy iron-bearing minerals and high magnetic susceptibility. While there is ample scientific literature on using UAS for geological investigations, UAS are not established in the mineral exploration and mining industry.…”