Mössbauer spectroscopy of Pb-bearing minerals from the jarosite group

Abstract

The minerals of the jarosite group, including the jarosite-beudantite-segnitite and jarosite-beaverite-osarizawaite isomorphic series, were studied with Mossbauer spectroscopy. All the samples were collected from the oxidation zones of the South Urals sulfide deposits. In contrast to the jarosite containing one Fe3+ doublet in the Mossbauer spectrum, the Pb-bearing members of the jarosite group—beudantite and beaverite—have two doublets in their spectra. Fe3+ is distributed at two sites with similar isomer shifts and different quadrupole splitting. The quantitative ratio of those doublets in the structure is roughly equal. The Mossbauer spectra of the intermediate jarosite-beudantite and beaverite-osarizawaite members are superpositions of the jarosite and beudantite spectrum types with a prevalent jarosite doublet and larger quadrupole splitting. An admixture of antimony increases the Fe3+ content in the doublet with smaller quadrupole splitting. The unequal Fe3+ distribution in those two sites may be related to the ordering of cations in octahedrons. The appearance of two different Fe3+ sites probably resulted from the local coordinating role of Pb rather than from isomorphic replacement in anion groups.