Discrimination of remmanence carrying inerals using IRM curves.
Авторы: Robertson D., France D.
It is found that, in general, the isothennal remanent magnetisation (IRM) acquired by natural mineral assemblages closely conforms to a cumulative log gaussian (CLG) function of the magnetising field. The experimentally determined area, mean and standard deviation of the underlying log gaussian function are useful for identifying the type, grain-size and concentration of the magnetic minerals present and for correlating samples containing a common magnetic mineral but derived from different sources. If more than one magnetic mineral is present their IRM acquisition curves combine linearly, and may therefore be resolved by a technique of curve fitting so that the type, grain-size and concentration of each magnetic mineral may be estimated separately, provided that the apparent coercivity spectrum of each phase present approximates to a log gaussian function. Mathematical models of the IRM acquisition process appropriate to single-domain, multi-domain and interacting single-domain grain assemblages have been investigated. It is found that the dispersion parameter (DP) of 0.3 which is usually found experimentally in magnetite assemblages is approximated in the multi-domain model, whereas smaller DP values, corresponding to the value of 0.1 sometimes observed in haematite and goethite, are predicted for single-domain assemblages. Modelling demonstrates that the DP would be affected by grain interactions in an assemblage of single-domain grains, but for magnetite the effect is expected to be minimal unless grains are nearly touching each other.