An Fe-57 Mossbauer spectral study of vermiculitization in the Palabora Complex, Republic of South Africa

Two phlogopite, two mixed-layer. phlogopite-vermiculite, and two vermiculit e samples collected from the Palabora Complex of South Africa have been inv estigated at 295 K by X-ray diffraction, chemical analysis, and Mossbauer s pectroscopy. In addition the temperature dependence of the Mossbauer spectr a has been measured between 95 and 295 K for one phlogopite and one mixed-l ayer sample. The results of the chemical analyses and the Mossbauer spectra improve our knowledge of the vermiculitization process in the Palabora Com plex. Both techniques indicate oxidation of the Fe ions during the sequence : phlogopite --> mixed-layer --> vermiculite. Further, the Mossbauer spectr a indicate that Fe oxidation occurs mainly in the octahedral sites and sugg est that migration and oxidation of the Fe2+ ions From the octahedral sites to the tetrahedral sites may occur during the transformation of phlogopite into a mixed-layer phase. Finally, the vermiculitization process involves both Fe oxidation and loss of K with a concomitant increase in the Mg conte nt.