Magnetic properties of natural pyrrhotite Part I: Behaviour

Abstract

The grain-size dependence of the initial susceptibility (X 1~),saturation magnetization (.1,), saturation remanence (J~),coercive force (He), remanent coercive force (Hcr) and remanent acquisition coercive force (Hcr’), is reported for four natural pyrrhotites in a grain-size range from 250 ~zmdown to <5 ~im. X1~,decreases with decreasing grain size (range 7 x 10 ~—iX 10~ m 3 kg1); H~,Hcr and Hc,’ all increase with decreasing grain size (ranges respectively 7—80, 8—85 and 14—80 kAm1). The magnitudes of .J~(8.9—16.7 Am2 kg~)and ~ (2.0—6.0 Am2 kg1) correspond with the trend indicated by the microprobe analysis (47.8 down to 46.9 at.% equivalent Fe). -Trs shows a maximum in the pseudo-single domain region (range 2.0—6.0 A m2 kg 1)~ J~shows a marked decrease for the finest grain-size fractions. Typical for pyrrhotite are a large Hc/Hcr ratio and a .Jrs/Xin ratio which is larger than Her. When the presence of pyrrhotite has been established in a sample, its grain size is preferable determined by the ~ trend because pyrrhotite compositional differences hardly showup in this trend.