Environmental implications of developing porphyry-type mineralizations in the Siliqua area, Sardinia, Italy

The development of studies concerning volcanism-related deposits renewed the interest in porphyry-type and epithermal bodies in Sardinia. Calc-alkaline volcanics of Oligo-Miocene age widely outcrop in the western half of this island where a series of field surveys showed that metal - bearing hydrothermal alterations are widespread in the Tertiary subvolcanic rocks. A Cu-Au-Mo-bearing porphyry-system, of "diorite model" type, has been discovered in the area of Siliqua (southern Sardinia) and an exploration programme is going to be developed. In ore outcrops, characterized by abundant sulphide minerals, weathering-related reactions cause acid mine and rock drainage (AMD/ARD) having the potential to produce large volumes of low-pH sulphate-bearing waters during oxidation and leaching of mineralized materials. These solutions may generate many different geochemical phenomena especially concerning metal mobility and subseguent precipitation outside mining environments. Environmental concerns, associated with the starring of open-pit operations, ore removal activities and waste accumulation, in the local warm and semiarid climate, are largely related to possible contamination of the surrounding soils and freshwater bodies. Other risks are related to some possible exploration works, especially exploratory trenches and excavations. Furthermore some controls on the surrounding water bodies and soils have already shown high heavy metal contents.