Processing and interpretation of Magnetic and Gravity data from Brattbakken, Verdal municipality, Trøndelag county

Abstract

This report describes data processing and interpretation of magnetic and gravity data acquired in Brattbakken area, Verdal, Trøndelag county. The survey was carried out in September 2020. This work is part of the project named NIKKEL I TRØNDELAG, a project aiming at understanding the lateral and vertical extents of the nickel deposits in Trøndelag region.The interpretation was carried out by incorporating 3D VOXI inversion of magnetic data and 2D forward modelling of the magnetic and gravity data. The areal geology indicates the presence of Gula group dominating the survey area. The group is comprised of Gula schist intercalated with Gula amphibolite and banded iron formation (BIF). The Gula group, namely the amphibolite is intruded by gabbro and pyroxenite. The south-eastern part of the survey area is covered by Funnsjø greenstone.The results from 3D inversion and 2D modelling suggest the intrusions to be about 215 - 260 m wide and 90 -270 m thick.The ore zone within the pyroxenite intrusion was further examined. An inversion with denser grid cell size was carried out. The interpreted result suggests the identified ore prospect to be between 20 - 30 m thick with susceptibility of 0.12 SI. However, there is a potential for significant larger thickness and up to 145 m with varying susceptibility from 0.06 SI to 0.12 SI across the prospect area. The variation of susceptibility values could indicate varying ore grades or that some anomalies are caused by other high magnetic sources.