Moller P. and Timm F. "Electrochemical and electrokinetic aspects of porphyry copper systems: Experiments and field observations"

ABSTRACT - Experimental field and laboratory studies of porphyry copper systems indicate that recent electrochemical processes occur in the environment of large, vertically extended, semiconducting sulphide bodies. Vertical differences in oxygen fugacities cause specific electrochemical reactions around the sulphide mineralization, indicated by the dipole system with a negative self potential at the earth's surface near the deposits. As a result of electrochemical reactions, fluids with relatively high pH are formed at the cathode (top), while low pH fluids are formed at the anode (bottom) of sulphide bodies. Laboratory experiments show that high pH fluids move from the surroundings of the cathode towards the anode and being only partly neutralized by acidic fluids formed at the latter. The remaining acidic solution moves upwards for reasons of compensation wrapping the remaining high pH fluid. This onion-shell-like arrangement of the basic and acidic fluids around sulphide bodies is considered to maintain the potassic alteration zone and promotes sericitisation of the intermediate, quartz-sericite zone of porphyry copper systems, respectively. These two alteration zones, largely magmatic and transitional in origin, spatially coincide by and large with the presence of the two types of electrochemically altered fluids. At depth, sulphides are electrochemically oxidised to sulphates such as anhydrite. The released Cu ions (and other electropositive ions) are captured by the electric field and do not dissipate far into the country rocks.

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Lenaz D.* and Princivalle F."Detrital high pressure - low temperature minerals in Lower Eocene deep-sea turbidites of the Julian Alps (NE Italy) "

ABSTRACT - Detrital amphiboles (actinolite, Mg-hornblende, barroisite and glaucophane) associated with pyroxenes (omphacite) have been found in Lower Eocene (about 52Ma) deep-sea turbidite of the Julian Alps. The occurrences of these minerals are commonly related to the erosion of high pressure - low temperature metavolcanics in green - blue schist and eclogitic facies. It is suggested that these detrital minerals belong to limited metamorphic bodies exhumed at about 56Ma during a phase of Dinarides uplift.

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Bennio L.*, Brotzu P., Gomes C.B., D'Aantonio M., Lustrino M., Melluso L., Morbidelli L. and Ruberti E."Petrological, geochemical and Sr-Nd isotopic features of alkaline rocks from the Arraial do Cabo Frio peninsula (southeastern Brazil)"

ABSTRACT - The alkaline activity in the Cabo Frio region is made up mainly of intermediate and felsic differentiate rocks emplaced about 55 Ma ago into the crystalline basement as sills, plugs and dykes. Two magma suites can be distinguished: (a) a strongly silica-undersaturated tephriphonolite to phonolite serie; (b) a weakly silica-undersaturated to satured trachyandesite-trachyte series. Petrography, mineral chemistry, whole-rock chemistry trends and isotopic data strongly support a genetic link among the lithotypes of each suites consistent with fractional crystallization processes dominated by the observed phases. The same data, however appear to exclude a link between the two groups of rocks, supporting a petrogenesis by prolonged differentiation processes starting from two distinct parental magma with a slight difference in the SiO2 saturation. The scarce basanites and trachybasalts reported in the same area could represent the most probable compositions for the parental magmas of the two suites. The initial ⁸⁷Sr/⁸⁶Sr (0.70401-0.70458) and ¹⁴³Nd/¹⁴⁴Nd (0.51239-0.51247) isotopic ratios and the significant potassic component indicate derivation of these rocks from an enriched lithospheric mantle source.

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Di Grande A., Mazzoleni P., Lo Giudice A.*, Beccaluva L., Macciotta G. and Siena F. "Subaerial pro-pleistocene volcanism in the geo-petrographic and structural conxet of the north/central iblean region (Sicily)"

ABSTRACT - This paper deals with the petrographic, geological, stratigraphic and structural aspects of subaerial mid-Pliocene to Pleistocene volcanic rocks outcropping in the northern sector of the Iblean Plateau.
In the examined area, almost the entire Iblean sedimentary and eruptive sequence, from Late Cretaceous to Holocene, outcrops. Three main sedimentary cycles are identified.
A detailed field survey has revealed the link between magmatism and extensional-transtensional tectonics the latter principally connected to the structural NE-SW direction and characterised by both strike-slip and vertical movements. In particular, the late Miocene volcanic products (Lower Volcaniclastic Deposits) are connected with the mid-Miocene tectonic phase and represent a revival of basic eruptive activity after the late Cretaceous-early Tortonian hiatus. Similarly, the mid-late Pliocene/early Pleistocene volcanic activity is linked to the mid-Pliocene tectonic phase.
On the whole, the composition of the volcanic products ranges from nephelinite - ankaratrite to tholeiite, without any correlation with spatial distribution or age.
Subaerial Plio-Pleistocene volcanism emitted 10-15 km3 of products. Subalkaline products prevail over alkaline ones (tholeiite 62%; basanite 22%; alkali-basalt 8%; hawaiite 4%; transitional basalt 3%; nephelinite and ankaratrite 1%).
These products are the result of partial melting of different metasomatised spinel peridotite lithospheric sources. The partial melting fraction progressively increases and source depth decreases from strongly alkaline to tholeiitic magmas.
The alignment of eruptive centres with the tectonic features, together with the petrographic and geochemical features of the volcanites, indicate that the magma rose directly from the mantle along fault planes.

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Howari F.* "Spectroscopy of evaporites"

ABSTRACT - The presence of salt crusts can provide information on soil salinization. Spectroscopy and remote sensing of salt crusts are useful for assessing the distribution of salt crusts in barren landscapes of arid regions as well as to evaporite accumulation in playa basins. In this study are reported the results of spectral reflectance measurements in the visible and near infrared region of gypsum, halite, calcium carbonate, sodium bicarbonate, and their mixtures. Spectral analyses have shown that the studied samples have diagnostic absorption features between 1000 to 2500 nm which are consistent with the reported values in the libraries. The positions of the absorption bands were not affected significantly quantities of evaporites per unit area. However, reflectivites increased with increasing the weight fraction of evaporite present. The reflectivity of evaporite was related to the mixing ratios in a non-linear fashion. At certain mixing ratios, the spectral reflectance data from evaporites were similar to those of the endmembers. It is interpreted that this is due to crystals coating. The reflectivity of the mixed calcium carbonate and sodium bicarbonate decrease by increasing the sodium bicarbonate fraction, due to the coating of calcium carbonate by sodium bicarbonate. The data of this study point to a possibility that the presence of gypsum, halite, calcium carbonate, sodium bicarbonate, and their mixtures in salt crusts can be assessed quantitatively by examining the position and intensity of the absorption features. The presence of soil particles may affect these results, and this subject is currently being evaluated.

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