Rock magnetic properties and their anisotropy from the Outokumpu assemblage in the Outokumpu deep drilling, Finland

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The aim of this project is to provide rock and paleomagnetic data under consideration of paleomagnetic field vectors (inclination) and of the directional dependence of magnetic susceptibility and magnetic remanence for the interpretation of the magnetic logging data (see proposal by Hördt and Leuven). We focus in our study on the Outokumpu assemblage between 1314 and 1515 m of the Outokumpu deep drilling. This assemblage is characterized by several geophysical anomalies including both very high magnetic susceptibilities and remanent magnetizations and is the host rock of the Outokumpu-type Cu-Co-Zn-Ni(-Ag-Au) deposits. The remanent magnetization in the serpentinites is carried by magnetite and pyrrhotite. Different degrees of silica-carbonate alteration of serpentinite caused a decomposition of magnetite and a transformation of ferrimagnetic into antiferromagnetic pyrrhotite along with Ni-sulfide formation, which is seen in strong susceptibility variation in the serpentinite unit. Although we found no correlation between rock magnetic properties and chemical composition, we observed a clear relationship between mineralogy and magnetic properties in relation to the silica-carbonate alteration. This finding also explains the strong magnetic field variation within the investigated Outokumpu assemblage measured by Hördt and co-workers.