Drone-based magnetic and multispectral surveys to develop a 3D model for mineral exploration at Qullissat, Disko Island, Greenland

Abstract

Mineral exploration in the West Greenland flood basalt province is attractive because of its resemblance to the magmatic sulfide-rich deposit in the Russian Norilsk region, but it is challenged by rugged topography and partly poor exposure for relevant geologic formations. On northern Disko Island, previous exploration efforts have identified rare native iron occurrences and a high potential for Ni–Cu–Co–PGE–Au mineralization. However, Quaternary landslide activity has obliterated rock exposure in many places at lower elevations. To augment prospecting field work under these challenging conditions, we acquire high-resolution magnetic and multispectral remote sensing data using drones in the Qullissat area. From the data, we generate a detailed 3D model of a mineralized basalt unit, belonging to the Asuk Member of the Palaeocene Vaigat Formation. Different types of legacy data and newly acquired geo- and petrophysical as well as geochemical-mineralogical measurements form the basis of an integrated geological interpretation of the unoccupied aerial system (UAS) surveys. In this context, magnetic data aim to define the location and the shape of the buried magmatic body, and to estimate if its magnetic properties are indicative for mineralization. UAS-based multispectral orthomosaics are used to identify surficial iron staining, which serves as a proxy for outcropping sulfide mineralization. In addition, UAS-based digital surface models are created for geomorphological characterization of the landscape to accurately reveal landslide features. UAS-based magnetic data suggest that the targeted magmatic unit is characterized by a pattern of distinct positive and negative magnetic anomalies. We apply a 3D magnetization vector inversion (MVI) model to the UAS-based magnetic data to estimate the magnetic properties and shape of the magmatic body. By means of introducing constraints in the inversion, (1) UAS-based multispectral data and legacy drill cores are used to assign significant magnetic properties to areas that are associated with the mineralized Asuk Member, and (2) the Earth's magnetic and the palaeomagnetic field directions are used to evaluate the general magnetization direction in the magmatic units. Our results suggest that the geometry of the mineralized target can be estimated as a horizontal sheet of constant thickness, and that the magnetization of the unit has a strong remanent component formed during a period of Earth's magnetic field reversal. The magnetization values obtained in the MVI are in a similar range to the measured ones from a drillcore intersecting the targeted unit. Both the magnetics and topography confirm that parts of the target unit were displaced by landslides. We identified several fully detached and presumably rotated blocks in the obtained model. The model highlights magnetic anomalies that correspond to zones of mineralization and is used to identify outcrops for sampling. Our study demonstrates the potential and efficiency of using high-resolution UAS-based multi-sensor data to constrain the geometry of partially exposed geological units and assist exploration targeting in difficult or poorly exposed terrain.