Gravity and Magnetic Survey, Modelling and Interpretation in the Blötberget Iron-Oxide Mining Area, Bergslagen, Sweden Ezra YehuwalashetThe Blötberget mining area, the focus of this MSc project, is located about 230 km northwest of Stockholm and 12 km southwest of the city of Ludvika (central Sweden). The mining area has been known since 1600 for its various types of mineralization particularly iron-oxide deposits (magnetite and hematite) with the mining commenced in 1944. Previous geoscientific research in the area provides detailed information about lithological variations and structure of the bedrock near the surface. However, knowledge of the depth extent of the mineral deposits and their host rocks is limited. To shed lights on these issues and support deep mineral exploration potential in the study area, within the recently launched StartGeoDelineation project, new ground gravity data, 180 data points on average 150 m apart, were collected during two field campaigns in 2015 and 2016. Aeromagnetic data were obtained from the Geological Survey of Sweden (SGU) to complement the ground gravity measurement interpretations and modelling. After a careful inspection of the field gravity data, they were reduced to complete Bouguer anomaly with a maximum error estimate of about 0.6 mGal due to uncertainty in the instrumental drift, slab density, geodetic surveying, diurnal variations and terrain (or topography) correction. The Bouguer gravity data after separation of regional field (second order polynomial at the end was used) were used (~ 8 mGal range) for interpretation and 3D inverse modelling. Clear anomalous zones are noticeable in the gravity data particularly due to mineralization and a major boundary separating a gravity low from gravity high in the southern part of the study area likely representing a fault boundary separating two different lithological units. In my study, both forward and inverse modelling using rudimentary objects/shapes and voxel-type (mesh) approach were carried out. Effect of initial and reference models were tested on both gravity and magnetic datasets. While the constrained models have still significant ambiguity, they help to suggest structural control on the location of mineralization and may allow estimating an excess tonnage due to the presence of mineralization in the study area. Due to access limitations (e.g., unable to measure on the water-filled pit) the gravity model is sensitive to the measuring positions and constraints using known shape of mineralization was not at the end successful to overcome this. Collecting more gravity data on the target area and repeated test of 3D inversion by adjusting the inversion parameters might help to improve the final result.