Bismuth Minerals in the Molibdenum Showings from Salto di Quirra District, SE Sardinia, Italy

The mineralizations related to the Hercynian magmatism of Sardinia are represented by interesting ore-associations. Molybdenum is scattered in several part of the island and many Mo prospects are Known in the Ogliastra region, SE Sardinia where the molybdenite-wolframite vein of Perda Majori displays mineralogical peculiarities of extreme rareness. A member of the lillianite-gustavite series has been detected and the samples compared with data collected from the literature. In the system PbS-Ag2S-Bi2S3 most of our samples spread between the line lollianite-gustavite join. The possible occurrence of solid solutions having compositions along both these joins is suggested in litterature but there is a miscibility gap in the series at temperatures above 500°C. High-temperature natural phases belonging to the lillianite-like structures situated in the compositional gaps should commonly exibit exsolution phenomena. The exsolved textures of Pb-Ag-Bi sulphosalts from Perda Majori let the mineralization under study be referred to pneumatholitic-hydrothermal stages of deposition.