Structural key features of bismuth and Sb-As sulfosalts from hydrothermal deposits-micro-Raman spectrometry

The sulfosalt minerals are of great importance for a better understanding of ore forming conditions and mineralization distribution, especially in the case of hydrothermal deposits. So far, few Raman studies were conducted on this type of minerals. In the present work, were studied several samples from Baia Sprie ore deposit, Romania-a worldwide classic example for hydrothermal mineralizations. Bismuthinite, lillianite-gustavite, heyrovskyite, cosalite, tetrahedrite-tennantite, bournonite and semseyite have been analyzed using electron microprobe and Raman spectrometry. The Raman spectra of bismuth sulfosalts, Ag-rich tetrahedrite and semseyite are discussed for the first time. The Bi sulfosalts show typical ν1 symmetric stretching modes of the MS6 octahedra at 286-279 cm−1, ν2 stretching at 216-207 cm−1 and ν5 bending modes at 140-112 cm−1. The transition from tetrahedrite to tennantite is very clearly observed in the Raman spectra. Several changes are marked through the solid solution, as the Sb-As isomorphic substitution takes place. Therefore, as the composition changes from As-member (tennantite) to the Sb-member (tetrahedrite), a shifting trend is observed in the Raman spectra, especially for the fundamental modes. The spectra of bournonite are dominated by two very strong lines at 325 and 296 cm−1. The Raman band at 331 cm−1 in semseyite is assigned to ν1 symmetric stretching modes of the octahedra. The ν2 stretching is observed at 212 cm−1, while the bending mode ν5 appears at 148-143 cm−1.