MAGMATIC VERSUS HYDROTHERMAL PROCESSES IN THE FORMATION OF RAW CERAMIC MATERIAL DEPOSITS IN SOUTHERN TUSCANY

Ceramic raw material in Tuscany is currently mined in four main deposits (Marciana and La Crocetta in Elba Island, Botro ai Marmi near Campiglia Marittima, and Piloni di Torniella near Roccastrada). The deposits are associated with magmatic rocks of the so-called “Tuscan Magmatic Province”, and reflect various degrees of modification of original magmatic features by interaction with hydrothermal fluids. At Marciana, the mined material is an essentially unaltered K- and Na- rich porphyritic aplite; at Botro ai Marmi, a sienogranite intrusion (possibly already K-rich because of phenomena developed at the magmatic stage) was enriched in K through deposition of a second generation of K-feldspar by high-temperature, highly saline flu-ids, of dominantly magmatic nature; at La Crocetta, a porphyritic aplite similar to that mined at Marciana was transformed into a sericitized, K-rich Na-poor rock by moderate temperature, moderate salinity fluids of magmatic(?)-meteoric origin; at Piloni, rhyolitic lavas were kaolinitized in a shallow epithermal environment, perhaps by steam-heated meteoric waters.