Abstract
In an attempt to improve the interpretation of the geophysical results of an exploration programme in Norrbotten country, northern Sweden, a systematic investigation has been made of the magnetization and densities of the main rock and ore types. The rocks have low porosities and their densities vary predictably according to their composition between 2.6 and 3.1 g cm −3 with an average of 2.73 g cm −3 for the Precambrian bedrock of the area. The high grade magnetite ores have susceptibilities in the 0.5 –1.2 emu cm −3 range but for the normal rock types there is a well defined upper limit at about 2·10−2 emu cm −3 and there is no general systematic variation with the composition. The remanent magnetization in both the rocks and magnetite ores is generally weak with Q-values between 0.1 and 1.0 and shows many features characteristic of viscous remanent magnetization (VRM) including a coincidence of the directions of magnetization with that of the geomagnetic field. In the rocks the field direction is undisturbed but due to the strong demagnetization fields within the magnetite ores the direction of the incucing field is determined by the form and position of the ore deposit. The remanent magnetization generally influences only the amplitudes of the magnetic anomalies observed but not their forms. There is some evidence from the results of this survey that there is a significant difference between the remanence of samples collected from outcrops and from drillcores, suggesting that the weak VRM can be disturbed by drilling processes.
Published Version
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