ABSTRACT LXXVI, April 2007 n.1:

Abstract - A glass from a rhyolite belonging to the calc-alkaline magmatism of the island of Capraia, in the Neogene-Quaternary Tuscan Magmatic Province of Central Italy, has been examined by ¹¹B solid-state nuclear magnetic resonance spectroscopy, secondary electron imaging for surface morphology and electron microprobe analysis for glass chemistry. The glass is chemically homogeneous and does not show evidence of significant alteration processes, with a boron content of 126 ppm. The deconvolution of the ¹¹B MAS NMR spectrum reveals the occurrence of boron in both tetrahedral BO_4/2 - and trigonal BO_3/2 structural units in which all the oxygens are bridging, even if, according to the glass chemistry and following the “aluminium priority model”, all the available charge balancing cations would be requested to form tetrahedrally coordinated aluminum. A possible explanation involves the role of residual H⁺ ions in the glass/melt which could behave as charge balancing cations for B in tetrahedral coordination or the occurrence of Al “triclusters” in the glass, making alkali ions available to charge balance. The lack of a significant amount of boron in trigonal BO_2/2O^- sites, characterized by nonbridging oxygen, might be interpreted as evidence of copolymerization of the boron structural units with the glass network, occurring when boron is at trace element concentration such as in natural magmas of this composition.

M. HASSAN AND H. BAIOUMY - Characterization and origin of alunite in the El-Gideda iron mine (Egypt)

Abstract -Alunite in El-Gideda iron mine, Bahria Oasis, occurs as very soft and light white to pinkish beds and pockets ranging in thickness from few cm to 0.5 m intercalated with glauconites of the Hamra Formation. The fine scale mineralogy was determined using XRD, SEM, DTA, TG, IR and XRF. Alunite is the main constituent, and jarosite was detected as a minor mineral. Hydrated halloysite is the main aluminum silicate mineral associated with alunite in varying proportions. Gibbsite and trace of quartz are also detected. Iron oxides are represented by iron-oxyhydroxide (goethite) in size and shape similar to that of bacterial iron mineralization. Amorphous silica was recorded in SEM image and IR spectra. Morphology of alunite ranged from tubular or flatten rhombohedral to well crystallized cubes. This is very characteristic for supergene alunite formed by oxidation of sulfides in a K-rich environment. Due to acid alteration of sulfate, glauconites of the overlying Hamra Formation were altered and released K, Al, Si, and Fe. The former three elements form alunite and halloysite. Iron forms at least a part of the iron ore in the El-Gideda mine. Glauconite intercalated by alunite is highly destabilized with fractured pellets and iron rims as well as low potassium content. Therefore, alunite and halloysite can be considered as byproducts of weathering of the intercalated glauconites in an environment of sulfide oxidation (i.e., high Eh, low pH together with biological activities).

L. DE CAPITANI, M. CARNEVALE AND M. FUMAGALLI - Gamma-ray spectroscopy determination of radioactive elements in late-Hercynian plutonic rocks of Val Biandino and Val Trompia (Lombardy, Italy)

Abstract - The results from natural gamma radiation measurements in main plutonic rocks outcropping in Val Biandino (VB) and Val Trompia (VT), pertaining to the central sector of the South Alpine domain, are presented and compared with data on Valle del Cervo pluton. The measurements were performed with the aid of a high-resolution gammaray spectroscopic system using HPGe detector. The aim is to contribute to the establishing of a baseline map of environmental radioactivity levels. In the VB samples the granite activities of ²³⁵U and ²³⁸U are only slightly higher than ²³²Th specific activity, while the opposite occurs in more basic rocks; moreover, U and Th contents are in agreement with the levels of rocks of calc-alkaline affinity and Hercynian age. In VT rock types the activities of ²³⁸U are in the range 48-74 Bq kg_-1 and the granite shows the lowest value of activity. The ²³²Th activities are quite similar for granite and granodiorite. Samples coming from Torgola fluorite mine, hosted in the graniticgranodioritic rocks, show U and Th activities that do not exceed 80 and 70 Bq kg_-1 respectively. The U and Th specific activities of VT rocks are not completely explained by the magmatic character of the pluton; in fact, in the granite the U activity is lower than the Th one. This opposite trend could be due to the effects of a large-scale hydrothermal system coeval with upper Palaeozoic plutono-volcanic activity and tectonism.

R. CIDU, R. BIDDAU, F. MANCA AND M. PIRAS- Hydrogeochemical features of the Sardinian rivers

Abstract - The physical-chemical parameters and contents of the main dissolved components, together with some minor elements, were determined in 35 waters from rivers flowing in Sardinia (Italy). Dominant Na-Cl, low salinity (<0.5 g/L) and high SiO₂ concentrations are observed in waters draining silicate environments, and dominant Na-Ca-Cl- HCO₃ and higher salinity (0.6 to 1.2 g/L) occur in waters from sedimentary environments. Waters draining areas that host Pb-Zn ores show higher SO₄ due to the oxidation of sulphide minerals. The main chemical composition does not change when waters are sampled at different climatic conditions; however, salinity and concentrations of the main ions increase at low-flow condition in the summer season. At high-flow condition, i.e. when the rivers have a high rainwater component, a decrease in many chemical species is observed due to dilution processes, but at the same time, an increase in the concentration of soluble species, such as nitrate, may occur.

P. TUCCI, P. MORBIDELLI, C. IMPERATORI AND G. DE CASA- Study for restoration purposes about the obelisk located in “Piazza della Libertà” at Ostuni (Brindisi, Southern Italy)

Abstract - Oronzo Rococò (local Baroque) obelisk, dedicated to patron saint of Ostuni in 1771 AD, were characterised. The monument is located in “Piazza della Libertà” at Ostuni (Brindisi, Southern Italy). The obelisk is composed of two different lithotypes, more or less pure Cretaceous limestone, with a variable porosity and biogenous component. Mineralogical, petrographical, geochemical and palaeontological and ⁸⁷Sr/⁸⁶Sr datation comparisons between finding lithotypes and Cretaceous limestones cropping out in four quarries already studied from some authors in the Ostuni sector, allow to ascribe obelisk samples to megabreccia quarry of Melpignano close to the ancient city wall of Ostuni. On the most used lithotype, recognised and sampled in the quarry, physical, mechanical and ageing tests have been carried out. These tests have evidenced the high porosity of the materials and have furnished some indications about utilisation and restoration methods.