New high-resolution aeromagnetic and radiometric surveys in Finnmark and North Troms: linking anomaly patterns to bedrock geology and structure

Abstract

New high-resolution aeromagnetic data from the Caledonides and Archaean-Palaeoproterozoic crystalline basement of Finnmark and North Troms derived from surveys conducted as part of NGU's MINN programme provide spectacular and confirmatory evidence for the continuation of diverse, Precambrian greenstone belts and granulite terranes beneath the magnetically transparent Caledonian nappes. Complementary airborne radiometric data collected in the same survey contribute to the analytical process and to an evaluation of the mineral potential in the area. Some parts of existing data have also been reprocessed using new techniques and software to reach the same level as the newly acquired data. The new compiled data provide images of the magnetic field at sufficiently high resolution to allow us to examine finer details of the bedrock geology. One of the principal outcomes of the analysis is a picture of the detailed structural fabric of the region provided by images of tilt derivatives of the magnetic field that enhance anomalies. This fabric is an important framework for developing exploration strategies. Patterns and other characteristics of the magnetic field have been used to revise positions of some geological boundaries, especially in poorly exposed areas, and delineate specific domains within northern Norway. Radiometric data have been used to supplement the magnetic interpretations in some cases. In general, there is a good correlation between the radiometric data and magnetic anomaly maps which can be utilised to re-evaluate the geological boundaries. Several such features of interest are discussed. As an example, NW-SE-trending, fault-bounded terranes or belts which extend from Finnmark and Troms through northern Finland, Sweden and Russia can be easily followed on the high-resolution data. In this contribution, all the main geological terranes from the Archaean-Palaeoproterozoic belt to the Caledonian nappes in northern Norway will be discussed in relation to their magnetic patterns and radiometric anomalies.

Late Devonian–Carboniferous faulting and controlling structures and fabrics in NW Finnmark

“…Aeromagnetic data in this area (Nasuti et al, 2015b) also show a c. 15 km-wide NNE-SSW-trending positive anomaly below the Ryggefjorden trough and the extension of the trough to the south onto the Porsanger Peninsula (Fig. 12E).…”

“…We applied supplementary onshore-nearshore aeromagnetic data from the Geological Survey of Norway (Nasuti et al, 2015b) including aeromagnetic data (Fig. 5A) and a tilt-derivative function (Fig.…”

Revisiting Austfonna, Svalbard, with potential field methods – a new characterization of the bed topography and its physical properties

“…The correctness of the resulting topography depends on several glacier parameters, including density, porosity and the water content fraction, which determine the permittivity and, therefore, the radio wave velocity used to derive the thickness (Lapazaran et al, 2016). These parameters cannot be directly measured and are highly influenced by temporal and spatial variations of the water content fraction distribution through the glacier (Barrett et al, 2007;Navarro et al, 2009;Jania et al, 2005).…”

Prospectivity Mapping of Mineral Deposits in Northern Norway Using Radial Basis Function Neural Networks

“…For predictive mapping of favorable Cu mineralization, the present study involves an analysis of GIS data of Finnmark, which was acquired and distributed by the Geological Survey of Norway (NGU) (Datasets available online: http://www.ngu.no/en/topic/datasets). These data include (1) a geological map of the subject area at a scale of 1:250,000 (see [16] for details), (2) a compilation of airborne magnetic and radiometric data (U, K and Th) acquired between 1979 and 2015 (see [41][42][43] and references therein) ( Figure 3) with diverse line spacing and flight altitudes (mostly 200 m spacing and 60 m altitude; see Figure A1), (3) the regional gravity field acquired based on measurements at gravity stations established by NGU with a minimum spacing of 800 m (Figure 4) (see [44]) and (4) the coordinates of known mineral deposits (Table 1; Figure 2), notably several sulfidic Cu-rich occurrences, which are mainly hosted by mafic rocks. These occurrences were used to train the classifier, although no distinction was made among the different types of ore deposits (such as, e.g., porphyry or volcanogenic massive sulfide deposits) possibly associated with mafic host-rocks.…”