Characterising Magnetic Susceptibility and Remanent Magnetisation of Magnetite and Hematite Rich Drill-Core Samples at Blötberget

Summary

Petrophysics prove powerful as a complement to geological and mineral exploration geophysical studies. Statistical relationships between magnetic properties and thin section analysis can be used in a methodology to characterise iron oxide ore deposits. In this study drill core samples are studied and reveal noticeable changes in susceptibility across the Verwey transition temperature (153°C), Curie temperature (580°C) and Néel temperature (680°C). High temperature measurements allow for the contribution of magnetic susceptibility to be separated out, and directly related to ore content in drill core samples. This study shows that a mere 20 samples were enough to delineate a linear relationship susceptibility and magnetite content at Blötberget, Sweden with R²=0.73. In 6 out of the 20 measurements a similar relationship with R²=0.81 was indicated for hematite. Low temperature measurements also found that samples within this lower-amphibolite facies setting held a Morin transition suppressed to -60 °C, or missing. It has been suggested that the temperature discrepancy is likely an effect of elevated traces of Vanadium and Titanium. It is also possible that suppression is caused during the formation of martite and/or Fe(III) replacement by Fe(II).

• Iron-ore
• magnetism
• susceptibility
• Curie
• anisotropy