Electromagnetic Modelling and Inversion of Seafloor Massive Sulphide Deposits - Imaging of SMS Deposits and the Asthenosphere at the Atlantic Mid-Ocean Ridge
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Seafloor massive sulphides (SMS) are seen as an increasingly important mineral resource for the future. Fewer mineral discoveries are being made in the shallow subsurface onshore, and therefore a more petroleum related approach will be used in order to explore for mineral ores at greater depths. With electromagnetics (EM) being frequently used for decades in subsurface imaging, and recent years with controlled source electromagnetics (CSEM) for hydrocarbon exploration, marine CSEM could be used to detect conductive anomalies in the mineral deposits at the ocean floor. In this thesis, the objective was to investigate if it is possible to image SMS with marine CSEM through synthetic forward modelling and inversion with structured and unstructured grids in MARE2DEM. It was also tested how well marine magnetotelluric (MT) and marine CSEM was able to image a mantle structure beneath the mid-ocean ridge through modelling and inversion. Survey geometry and parameters were set up before creating a start model in order to generate synthetic data through forward modelling. Noise was added to the data before a simple inversion model with refined rectangular and triangular grids was created. Through inversion, a resistivity model as close to the start model as possible was generated in MARE2DEM. From changing parameters, such as frequency, receiver spacing, and mineral mound sizes, in the modelled CSEM survey and inversion it was found that buried SMS deposits must be of a significant size in order to be detected and that high frequencies and shorter receiver spacing enhance the geophysical response of the deposits. For mineral mounds found on the seabed, smaller geometries could be detected.