GOLD METALLOGENY IN SARDINIA: A SYNTHESIS OF ITS EVOLUTION AND MINERALISING PROCESSES, AND A STRESS ON THE TERTIARY EPOCH

The recently developed exploration of gold in Sardinia has stressed the occurrence of gold indications related with different metallogenetic phases from the Palaeozoic to the Tertiary. For several years, researchers of the IGAG-CNR together with University researchers have carried out a set of studies on the ore-forming processes that developed from the Palaeozoic to the Tertiary in order to detect gold-bearing ore bodies. Previous data on gold occurrence in Palaeozoic ore bodies led to re-consider the real importance of gold occurrence all along the metallogenic history of Sardinia; the occurrence of important gold concentrations has been stressed and the potentiality for economically relevant findings has been confirmed. In the Monte Ollasteddu prospect the geological estimation of the outcropping recognised mineralisation would give a figure in excess of 50 t of recoverable gold. These occurrences should be referred to as shear-zone-related, and Carlin-type. Since the eighties, field observations on mineralisations related to Tertiary volcanics have led the above research team to the conviction that it was possible to find precious-metal ore bodies (“young gold”) related to the Tertiary calc-alkaline cycle, whose ore potentialities had not yet been realised in the long mining history of Sardinia, which lasted at least since the Bronze Age, possibly because these potentialities were hardly “visible”. In particular, economic gold occurrences were discovered at Furtei (high-sulphidation system; active mine) and Osilo (low-sulphidation vein swarm; ready to start). In 2001 an acid-sulphate epithermal system was discovered in the Siliqua area, where the team had already detected a porphyry copper-gold-molybdenum system. A geophysical study would confirm that the ore bodies are deeply rooted. Though it is premature to talk of industrial interest, the fact that this ore field extends over several square kilometres gives us reasons to be optimistic.