Electron microscope images and FEG-SEM–EDS analyses of pyrrhotite grains on particles A0226 and C0242. (a) Backscattered electron (BSE) image of a relict pyrrhotite grain on the surface of particle A0226, with corresponding Fe-K ((c)) and S-K ((e)) EDS elemental maps. (b) BSE image of a pristine pyrrhotite grain on the surface of particle C0242, with corresponding Fe-K ((d)) and S-K ((f)) EDS elemental maps.