Mineralogy of the scheelite-bearing ores of Monte Tamara, SW Sardinia: insights for the evolution of a Late Variscan W-Sn skarn system

Southwestern Sardinia, Italy, hosts several skarn, W-Sn-Mo greisen and hydrothermal deposits related to a 289 +/- 1 Ma Late Variscan granite suite. Among them, the most representative scheelite-bearing skarns belong to the San Pietro and Sinibidraxiu localities, in the Monte Tamara area, Sulcis region. The San Pietro deposit is a typical calc-silicate skarn whereas Sinibidraxiu is a sharply bounded orebody hosted in a marble unit. Optical petrographic observations and compositional data of major and trace elements were obtained for samples from both localities. San Pietro data suggests evolution from an oxidising prograde skarn stage (andradite-diopside, hematite and scheelite), to progressively more reducing conditions from the early retrograde (magnetite-cassiterite) to the late sulfide stage (arsenopyrite, stannite, molybdenite, Bi sulfosalts and Zn-Cu-Pb-Fe sulfides); Sinibidraxiu has diffuse carbonate-quartz intergrowths pseudomorphic over an early mineral assemblage with fibrous habit, followed by abundant ore mineral precipitation under reducing conditions (scheelite, arsenopyrite and Pb-Zn-Cu-Fe sulfides). Geothermometers indicate a comprehensive temperature range of 460-270 degrees C for the sulfide stages of both deposits. The differences between the two deposits might be controlled by the distance from the source intrusion coupled with the different reactivity of the host rocks. The San Pietro mineralogy represents a more proximal skarn, contrasting with more distal mineralogical and chemical features characterising the Sinibidraxiu orebody (lack of Mo-Sn-Bi phases; LREE-MREE-HREE signature of scheelite). This investigation contributes for the first time to the identification of a W-Sn skarn system in SW Sardinia, thereby suggesting the Monte Tamara area and its surroundings as favourable for further exploration.