Identification of ferromagnetic minerals in a rock by coercivity and unblocking temperature properties

TLDR

Common ferromagnetic minerals exhibit distinct coercivities and thermomagnetic properties, yet IRM acquisition curves alone are often ambiguous, requiring combination with thermal demagnetization for clearer interpretation. The study proposes a modified method to enhance the analysis of ferromagnetic minerals. The method remagnetizes IRM fractions in decreasing fields along three orthogonal axes and then thermally demagnetizes each component separately, producing distinct plots. The technique yields clearer interpretations of ferromagnetic mineral content, as demonstrated on limestone and sandstone samples.

Abstract

The common ferromagnetic minerals have distinctive, characteristic coercivities and thermomagnetic properties. The analysis of the acquisition curve of isothermal remanent magnetization (IRM) is a useful but often ambiguous diagnostic technique. For a more conclusive interpretation, IRM acquisition must be combined with subsequent thermal demagnetization of the IRM. A modification of this method is proposed as a more powerful analytical technique. Different coercivity fractions of IRM are remagnetized in successively smaller fields along three orthogonal directions. The thermal demagnetization of each orthogonal component of the composite IRM is then plotted separately. This method often gives a clearer interpretation of the ferromagnetic mineral content of a rock. Examples are described for limestone and sandstone samples.