PYRRHOTITE-INDUCED AEROMAGNETIC ANOMALIES IN WESTERN GERMANY

Magnetic anomalies from four sites in Germany are described together w ith their interpretation based on magnetic modelling. The tops of the source bodies are situated several hundred meters below the surface. B oreholes at all the sites enabled the identification of pyrrhotite as the carrier of magnetization. In all four sites the pyrrhotite was fou nd in metamorphic rocks of Palaeozoic age. Peak values of the remanent magnetization are as high as 13 A/m. The ratio of remanent to induced magnetization ranges between 3 and 70. The occurrence of pyrrhotite a t the surface is rare due to oxidation. In three of the four sites the shapes of the anomalies correspond to magnetization directions clearl y deviating from the present geomagnetic field direction. Computations of the magnetic field of rhombohedric model bodies with inverse direc tions of magnetization showed that, with increasing depths, the minimu m of their anomalies decreases quicker than the maximum. That means th at some positive anomalies (indicating a ''normal'' direction of magne tization) of deep-seated bodies may turn into an anomaly with maximum and minimum at smaller depths (indicating rather ''inverse'' direction of magnetization).