Bentonite occurrences in Tertiary volcanic rocks of central Sardinia, Italy

Studies made over the last decade suggest that the main Italian reserves of bentonite are in these rocks. Several of the most important occurrences are in the Sarcidano-Barigadu area where the mineralized bodies occur either as interlayered beds in the Tertiary ignimbrite sequence or as originally cineritic single lenses overlying Jurassic limestones. The petrology and mineralogy of the volcanic rocks and their associated mineralization permit the potential exploitation of the deposits to be evaluated. Two types of deposit, distinguished on the basis of geology and petrology, were found. Those of type I occur in the upper part of an ignimbritic body, often along faults and/or joints, while those of type II are developed in the cineritic lenses, interbedded within fluvial-deltaic Miocene sedimentary rocks. Economically, the most important deposits occur in the Neoneli area. Physicochemical properties also confirm the economic importance of Busachi, Su Lau and Neoneli deposits. The others are less important because of their low reserves, argillization, or excess of sand and low c.e.c.