ABSTRACT LXXVIII, December 2009 n. 3:

Abstract - In general, vesuvianite occurs in lowpressure environments such as contact aureoles, rodingite/metarodingites, and skarns. We describe a new occurrence of vesuvianite in a high-pressure metamorphic jadeitite. The composition of this phase is characterized by up to 1.5 wt.% Na₂O. This content is higher than those of vesuviani te from elsewhere. Sodium is introduced into vesuvianite mainly by the substitution Ca + Al = Na + Ti. Electron microprobe measurements demonstrate an oscillatory growth zoning with Na and Ti showing the largest variation. The formation of vesuvianite and its zonation are explained by an interaction with a hydrous fluid phase that is characterized by a continuous increase of the chemical potentials of Ti and Ca. This fluid phase accounts for the simultaneous crystallization of vesuvianite + jadeite and the subsequent replacement of jadeite by vesuvianite.

Maria Boni, Giuseppina Balassone, Luca Fedele, Nicola Mondillo - Post-Variscan hydrothermal activity and ore deposits in southern Sardinia (Italy): selected examples from Gerrei (Silius Vein System) and the Iglesiente district.

Abstract - The current understanding of post-Variscan hydrothermal activity and mineralization in southern Sardinia (italy) is reviewed in the framework of the geological evolution of Western Europe. The structural and geochemical data are discussed for both the Southwestern Iglesiente-Arburese-Sulcis district, and for the Southeastern Sarrabus-Gerrei one (Silius mine). In the Southwest part the majority of the deposits, aligned coaxially to crustal extension, can be classified as vein- and palaeokarst-types (sphalerite, Ag-galena and barite). The prevalent mineralizing fluid across the whole mining district is a H₂O-NaClCaCl₂ fluid with a salinity above 20 wt. % NaCl eq. and T_h <=140 °C. A similar fluid (T_h mean ˜ 100 °C) also caused the precipitation of the widespread hydrothermal dolomites (Geodic Dolomite). Another type of fluid, with much lower salinities and T_h up to 200 °C, has been recorded locally near magmatic intrusions and at the periphery of skarn bodies. In the Southwest area, Pb isotopes of related minerals bear the imprint of a radiogenic “Variscan” component, and of another component derived from the Paleozoic/prePaleozoic basement. One of the most impressive vein systems cropping in the Southeast district, exploited in the Silius mine (Gerrei), consists of an association of fluorite, galena and barite. Here most ore minerals were precipitated at temperatures in the range of 120 - 180 °C from a dominant fluid consisting also of an Nacl ± CaCl₂ rich brine. The origin of the fluids in both areas is mainly from evaporated seawater, bearing a small contribution from halite dissolution. Ore Pb in the Silius veins could have been derived from a mixture of Pb from the Ordovician metarhyolites and metasediments as well as from the late-Variscan granites. The suggested timing for the hydrothermal events in southern Sardinia are: 1) Middle Permian (270 Ma); 2) Triassic-Jurassic. It has been hypothesized that the Mesozoic events were related to the onset of Tethys spreading.

Anna Maria De Francesco, Maria Teresa Iannelli, Eugenio Barrese, Eliana Andaloro, Vincenzo G. Imperitura and Marco Bocci - Provenance and technology of bricks from the Greek colony of Kaulon (Calabria, Italy).

Abstract - This paper presents the first results from a study of 26 bricks used in two buildings (called Casa Matta and San Marco) of the ancient city of Kaulon of Magna Graecia, in Calabria, Southern Italy. Archaeological research dates the beginning of Greek occupation of the area around the end of the VII century B.C.. Several methods were used to study the bricks of ancient Kaulon: petrographical analyses by optical microscopy, mineralogical analysis by XRD, and chemical analysis by XRF. Petrographical analysis distinguished the bricks into two groups: the first composed of some of the bricks of Casa Matta, in which non-plastic inclusions are mainly represented by granitic rocks, and the second, which includes all the San Marco bricks and the remaining ones of Casa Matta, in which non-plastic inclusions contain metamorphic and granitic rocks. XRF chemical analyses of all brick samples confirmed optical microscopy observations. Clay and silty clay, potential raw materials for producing bricks, were taken from Pliocene deposits near the present-day town of Monasterace Marina, and subjected to XRF analyses for major and trace elements, in order to compare them with the chemical composition of the bricks. Results show that the raw materials for all bricks were probably quarried locally. Clay samples were also experimentally fired in an oxidising atmosphere, in order to compare the developed mineral phases of the studied bricks. On the basis of these results, a furnace temperature of at least 900°C is inferred for most of the bricks.

Angela Baldanza, Giuseppe Sabatino, Maurizio Triscari, M.C. De Angelis- The Dunarobba Fossil Forest (Umbria, Italy): mineralogical transformations evidences as possible decay effects.

Abstract - The Dunarobba Fossil Forest, close to Avigliano Umbro (Tr) in central italy, is world registered as one of the very few locations where is documented a Middle Pliocene (about 2.5 My B.P.) forest. Lacustrine clay sediments preserved about 70 specimens, in life position, of “palaeo-sequoias” belonging to genus Taxodioxylon. Since its discovery, the Dunarobba site pointed out preservation problems. Natural weathering effects, of the “once buriednow exposed” mummified trunks, are responsible for significant decay effects on the exposed trees. SEM-EDX, FT-IR and XRD investigations have been carried on tree fossil samples, affected by peculiar mineralogical transformations. Reducing environmental condition transforms sulphides into Fe-oxides and prevailing hydroxides with sulphuric acid production. This diffused alteration process is responsible for these new mineralogical phases, and related volume increasing effects, probable “addon” cause, of the exfoliating effects locally observed on the exposed trunks.