G. Aversa, G. Balassone, M. Boni* and C. Amalfitano The mineralogy of the «Calamine» Ores in SW Sardinia (Italy): preliminary results

ABSTRACT - Recently, due to new extraction technologies, there has been a marked revival of interest in the geology and exploration for non-sulfide zinc deposits in the world. The Iglesiente area (SW Sardinia, Italy) is one of the oldest mining districts in the world. Significant occurrences of secondary non-sulfide Zinc ores, were exploited from the Iglesiente district until the 1960’s. Although this is one of the oldest mining districts in the world, there are very limited published data.
The most economically important non-sulfide zinc minerals (Zn-and minor Pb-carbonates and silicates) found at seven historical mining areas were characterized by combined XRD, SEM, EPM and FTIR investigations. Mineralogically the studied ores are composed mainly of smithsonite, which occurs in predominant microcrystalline, as well as concretionary and stalactitic forms. SEM analyses of the Zn carbonate have revealed interesting features, including six distinct habits (called I- to V-type and M-Type). Ongoing studies on C-isotopes ratios suggest that these are very variable, and may relate to the distinct crystal morphologies. Chemically the smithsonites are nearly pure Zn-carbonates, with traces of Fe, Mg, Mn and Cd and occasionally slightly higher Ca contents (up to 0.09 apfu Ca). Monheimite (M-type) shows a composition nearly intermediate between smithsonite and siderite, with up to 0.74 apfu Fe. Microcrystalline to earthy hydrozincite, as well as hemimorphite and cerussite, represent the other common phases found in the secondary mineral assemblage. Hydrozincite is more abundant in the samples found in the higher levels of the mines and decreases with depth relative to the smithsonite concentrations. Their chemical compositions are also quite homogeneous, except for minor amounts of Ca and Zn in cerussite and of Cu in hemimorphite from the Sa Duchessa mine. XRD and FTIR analyses of the studied mineral phases are in agreement with the literature data.

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M. L. Fiorentini, G. Grieco, A. Ferrario and A. Tunesi Petrological and metallogenic outlines of the Valmaggia ultramafic pipe (Ivrea zone), NW Alps, Italy

ABSTRACT - The Valmaggia pipe intrudes the uppermost part of the Main gabbro (Basic Complex, Ivrea-Verbano Zone, Italy). The ore body associated with the pipe consists of a stockwork and disseminated Fe-Ni-Cu sulphide mineralisation, with accessory Platinum Group Elements (PGE). The pipe consists of a roughly ellipsoidal main body, shortened along a WNW-ESE axis and elongated along a NNE-SSW axis, dipping steeply (70°-90°) towards WNW. Fe-Ni-Cu sulphide mineralisation is hosted in the internal margins of the pipe, from the contact with the host gabbro to a distance of 4-5 metres inside the pipe. The ore mineral paragenesis comprises sulfides (pyrrhotite, pentlandite, chalcopyrite, cubanite), tellurides (altaite, wehrlite, hessite) and PGM (merenskyte).
Cross-sections of the pipe mapped from the drives, together with petrographic and metallogenic observations, show that the pipe is concentrically zoned, with a homogeneous core and a heterogeneous rim.
On the basis of textural evidences and mineral chemistry we suggest that the pipe is primarily composed of a crystal mush comprising relatively low Fo olivine including buck-shot textured Fe-Ni sulphides and hercynite, which is cemented by products of the residual liquid. Crystallisation proceeded from the rim to the core, where residual melt was no more in equilibrium with cumulus phases, that were replaced extensively by late hydrous phases. PGE-sulphide mineralisation formed in the early stages of crystallisation and is limited to the rim portions of the pipe. It is possible, mainly on the basis of age relationships, to envisage a correlation between the restitisation process that occured in Finero ultramafic body and production of melt that formed Valmaggia and other pipes of Ivrea Verbano Zone. PGE chondritic profiles of sulphide-poor and sulphide-rich portions are generally similar and reflect the primary PGE content of the magma.

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M. Lustrino, A. Marturano, V. Morra* and G. Ricci Volcanological and geochemical features of young pyroclastic levels (< 12 ka) in the urban area of Naples (S. Italy)

ABSTRACT - Two stratigraphic sections (Palazzo Reale and Castel Nuovo), found in Naples during archaeological excavations, were investigated from the geochemical and volcanological points of view. These sections consist of Phlegrean and Vesuvian pyroclastic rocks, emitted after the emplacement of the Neapolitan Yellow Tuff (NYT; 12 ka).
Pyroclastic products belonging to Pomici Principali (trachyphonolitic), Soccavo 4 (trachytic) and Minopoli 2 (shoshonitic) levels were identified in the Palazzo Reale section. These eruptions belong to the first epoch of post-NYT magmatic activity. The Pomici Principali deposit, more than 2 m thick, shows no appreciable change in chemical composition upwards, due to the tapping of a chemically homogeneous magma chamber. The other two pyroclastic layers reach a total thickness of about 30 cm.
Trachytic rocks with higher contents of incompatible elements (Nb 52-67 ppm, Zr 374-500 ppm), correlated to the last epoch of the Phlegrean magmatic activity (4.8-3.8 ka BP), are found in the Castel Nuovo section. The correlation between trachytic rocks at Castel Nuovo and the last-epoch products of the Phlegrean magmatic activity is confirmed by the lack of the Pomici Principali deposit and by their chemical affinity; these rocks generally display contents of incompatible elements higher than the products of the first and second post-NYT epochs. This is related to the long quiescence period between the two last phases of magmatic activity (about 3.5 ka), during which the Phlegrean magmatic system mainly evolved by fractional crystallization processes.

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P. Censi*, S. Mazzola, G. Alonzo, F. Saiano, B. Patti, M. Sprovieri, A. Bonanno and S.E. Spoto Trace element distributions in the Strait of Sicily (Central Mediterranean Sea). I. Evidence of rock-water interactions and pollution

ABSTRACT - Distributions of V, Cr, Fe, Co, Ni, Cu, Zn, Y, Cd, Ba, La, Ce, Nd, Eu, Pb were determined in seawater samples collected at different depths in the Strait of Sicily (Central Mediterranean) during the oceanographic cruise BANSIC 98. Sampling sites were selected in order to study mechanisms of water-rock interactions and anthropic inputs.
Application of Principal Component Analysis (PCA) carried out on the whole dataset allowed us to recognize different behaviours of the studied elements along the water column. In particular:
– Water-rock interactions probably take place at the bottom of the stations around Pantelleria Island and can be invoked as responsible of some observed elemental distributions. Distribution patterns of Ce and Nd behaviours reflect recycling phenomena at the presence of iron oxyhydroxides. Barium and Eu distributions could be related to the effects of alteration of feldspar bearing rocks similar to those outcropping in the Pantelleria area.
– Distribution patterns of V, Cr, Ni, Cu, Zn and Cd are probably of atmospheric origin and their concentration are also driven by biological cycling processes mediated by organic particulate. Distribution of Co and Pb could be explained as result of surface absorption processes on calcite particulate. Vanadium and Ni contents in seawater seem also strongly related to petroleum pollution mainly present in the Strait of Sicily close to the Gulf of Gela.

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G. Barone * Preliminary archaeometric analysis on amphorae, in VI and V centuries B.C., from excavations at Gela (Sicily)

ABSTRACT - This work is part of a joint research project between the Department of Geological Sciences of the University of Catania and the Department of Antiquities, Archeology Section, of Messina. It aims at characterizing ceramics coming from several Greek colonies in Sicily and Calabria (Gela, Agrigento, Segesta, Selinunte, Naxos, Sibari, Locri).
Current scientific documentation regarding the archaeometric study of these ceramics is very limited. In particular, the present work focuses on amphorae found in the acropolis of Gela.
These amphorae, used for transport and table purposes, are either «massaliote» (VI-V centuries B.C.) or «pseudo-chiota» (V century B.C.) in shape, or imitations of Corinthian ware (V century B.C.).
Samples were analysed by X-ray diffractometry (XRD), optical analysis under a polarized-light microscope (OM), X-ray fluorescence (XRF) and plasma emission spectrometry (ICP-MS).
Data processing revealed that most of the amphorae were made in Gela itself, with the exception of one sample which had a chemical composition remarkably similar to that of samples found at Agrigento. The Gela samples were subdivided into three groups according to the grain size of the aggregate. It is interesting to note that the oldest ceramic products (VI century B. C.) are made of a mainly coarse mixture
whereas the more recent products (V century B. C.) are made of an increasingly finer original material.

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V. Ferrini*, S. Mignardi and A. Colangelo Provenance of stones employed in building the Badia Morronese (L'Aquila, Italy)

ABSTRACT - Mineralogical, petrographic, paleontological and geochemical studies were carried out to characterize the limestone used as the building stone of the Badia Morronese (XIII century A.D.) near Sulmona (L’Aquila, Italy). Comparison between 19 samples from the monument and 63 samples of formations outcropping around the Valle Peligna, collected from documented, recognizable or suspected quarries and natural outcrops, revealed that the building stone show petrographic characters and fossil content similar to those of the Calcari Cristallini Fm (Upper Cretaceous-Paleocene). The provenance of the stone for the monument from quite small areas is supported by the homogeneity of determined trace element contents and carbon and oxygen isotopic compositions, which are substantially close to those of samples collected at Colle Mitra (Sulmona).

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