Ore deposits study and prospecting of kaolin deposits in Western-Central Sardinia. Mineral- petrographic and ore deposits characteristics of kaolin and its relationship with Tertiary acid volcanism.

In the western-central area of Sardinia (Tresnuraghes) were founds outcrops of kaolin in volcanic rocks, mainly of rhyolitic type, of Oligocenic age. The mineral-petrographic study of the volcanics show that they include two facies, the former characterized by a marked like-fluid texture and matrix more or less kaoiinized, the latter by spherulitic structure ("piromeridi") cristobalitic-kaolinitic in composition. Kaolin principally occurs in the lower rhyolites. A systematic sampling was carried out by a square grid on area of 5 Km2. In addition, a detailed sampling was carried out on the quarry-faces by a grid of 3 m per 2 m vertically. Samples were submitted to XRD, TA and XRF and EPMA analyses. Studies allowed to: - classify the volcanic rocks according to their chemical composition, by De La Roche's diagram (1980), into rhyolites and dacites; - determine the variation of grades in AL2O3; - suggest a pcssible genetic model for the kaolin mineralization in this area; - determine the correlation between the volcanic facies, the structural characteristic of rocks and mineralization.