Drone-based magnetic and multispectral surveys to develop a 3D model for mineral exploration at Qullissat, Disko Island, Greenland
Authors: Jackisch Robert , Heincke Björn H. , Zimmermann Robert , Sørensen Erik V. , Pirttijärvi Markku , Kirsch Moritz , Salmirinne Heikki , Lode Stefanie , Kuronen Urpo , Gloaguen Richard 
Published: April 2022

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.