Astorri F., Lombardi S. and Paoloni F. Soil gas investigations over sulphide ore-bearing fractures - the Fontalcinaldo case study (Boccheggiano and Niccioleta mining district - southern Tuscany, Italy) 93-108

ABSTRACT - The application of soil-gas analysis to sulphide exploration has been evaluated at Fontalcinaldo (southern Tuscany, Boccheggiano-Niccioleta mining district). Samples were collected for He, Rn and CO₂ analysis and compared with deep sulphide-bearing fractures identified using borehole and geophysical data. The selected gases were chosen because they are proven fault tracers. In addition CO₂ has the added benefit that it can also give indirect information on the presence of buried sulphide deposits, as sulphide mineral oxidation produces sulphuric acid which, in turn, react with host-rock carbonate minerals to form carbon dioxide. Elevated He, ²²²Rn and CO₂ concentrations have been found over fault and fracture systems defined on the basis of geological and geophysical mapping; further N-S trending lineations have also been highlighted, including a possible northward extention of the Boccheggiano Fault. The surveys also indicated systematic soil-gas anomalies related to mineral occurrences, with the most consistent patterns (i.e. elevated CO₂ values) occurring other the main sulphide orebodies present in the area. The present research indicates that soil-gas techniques can provide useful information on the presence of ore-bearing fractures, especially during initial reconnaissance exploration or where other geochemical data are scarce because of unfavourable geological conditions (i.e. impermeable covers).
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ABSTRACT - Over the past fifteen years many scientific papers have been published on the nature and origin of diamonds. Modern analytical techniques show that diamonds’ solid inclusions are sometimes as small as 150.200 microns. They have also shown that diamonds invariably derive from peridotitic and eclogitic rocks; kimberlites and lamproites are generally more recent than the diamonds themselves indicating that kimberlites and lamproites are not necessarily directly linked to the origin of these precious crystals, but constitute instead the means by which diamonds reach the surface of our planet. It has also been shown that diamonds associated with peridotitic rocks are about 3.3 billion years old, whereas those associated with eclogitic rocks vary in age between 1.6 and 1.0 billion years. In light of their considerable age difference we can safely surmise that, as diamonds generally precede their including volcanic rocks, their genetic connections to kimberlites and lamproites are rare; that they have been intermittently generated over long periods of the planet’s geological history, and that kimberlites and lamproites are mixed volcanic rocks derived from deeper magmatic source than previously hypothesized. Although kimberlitic rocks are present in all continents, important diamond-bearing deposits can be located not only in the continental cratonic masses, but also in adjacent regions, particularly in the associated "mobile belts". Even if the kimberlitic and lamproitic rocks belong to intrusive phases of different ages, they can still crop out in the same geological sectors; therefore some diamantiferous diatremes may contain diamonds of different ages. As the majority of kimberlitic and lamproitic rocks belong to relatively recent intrusive phases (the last 200 million years), some significant intrusions reveal ages of about 1.6 billion years (Low Proterozoic) as well as ages preceding 2.6 billion years.
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ABSTRACT - Six pyroclastic formations from volcanic districts of northern Latium have been investigated. These formations were subjected to post-depositional diagenetic processes which gave rise to the crystallization of chabazite and subordinate phillipsite. Zeolite grades are greater tha 50 wt% for most of the analysed samples. Generally, the phillipsite content does not exceed 20 wt%. The chemical composition of chabazite is quite variable as far as the different formations are considered, but Ca and K generally prevail over the other extraframework cations. A very high Ca content is responsible for incomplete cation exchange process, both due to the preferential selectivity of the zeolite towards cations of higher valence and to the steric hindrance of the "ingoing" cation. The cation exchange capacity of the bulk rock is not influenced by the joint presence of the two zeolites. The large available tonnages of these materials and the well known selectivity of chabazite towards many polluting cations offer good potential for applications in several technological fields.
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Negri Arnoldi C., Azzaro E., Barbieri M. and Tucci P. Petrographic and geochemical features of the "Cipollino Verde" marble from the Apuan Alps (northern Tuscany, Italy) and archeometric implications 145-162

ABSTRACT - Petrographic and geochemical (major and trace element contents and C, O and Sr isotopic ratios) features of 23 samples of "Cipollino Verde" marbles from the Apuan Alps sectors od Arni, Isola Santa and Monte Corchia (northern Tuscany, Italy) are defined. The results are compared with the "Cipollino Verde" samples quarried, since ancient time, in Euboea (Greece) in order to individualize some discriminating parameters between the Italian and Greek marbles. These would allow to assign archaeological artifacts to their own provenance areas.
The Apuan sectors can be distinguished each other by: the presence of five different lithotypes; the different weight per cent of insoluble residue contents (X_max = 13.25%, Isola Santa; X_min = 6.09, Arni); the presence of dolomite. Chemical compositions are homogeneous but Sr and P₂O₅ contents are higher in the Isola Santa and Monte Corchia samples, respectively. Finally, while carbonium (¹³C-PDB= 2.16-2.80‰) and oxygen (¹⁸O-PDB = 1.6-4.23‰) isotopic ratios do not allow any discrimination, strontium isotopic ratio (⁸⁷Sr/⁸⁶Sr = 0.70764-0.71062) make possible to distinguish Arni sector from the others. From the obtained results, the following discriminating parameters can be used: 1) possible presence of dolomite; 2) normalized (5% of insoluble residue) Al₂O₃ vs Y; 3) C isotopic ratios only for central and western Euboea; 4) Sr isotopic ratios only for Arni.
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ABSTRACT - Phenocryst assemblages, chemical features and magmatic inclusions in Fo-rich olivine crystals were investigated in members from the earliest alkaline succcessions of Mt. Etna: the "Ancient Alkaline Centres" Unit (AAC) and the "Trifoglietto" Unit (TU). The study confirm the occurrence of two distinct group in the AAC sequence according to their P₂O₅ contents, namely the "high P" and "low P" lavas, and supports the idea of genetic links between the "hight P" and the TU series.
Apatite occurs as micro-phenocryst and even enclosed in the most Mg-rich olivine crystals in the "high P" AAC and TU hawaiites. Alkali basalts were found among "low P" lavas with Cr-spinel, either as isolated micro-phenocryst or enclosed in Cr-diopside and Fo-rich (Fo₈₇) olivine, more magnesian than in "high P" hawaiite (Fo₈₂). Clinopyroxene mg# value in these rocks are strictly related to those olivine, suggesting their co-crystallization.
The density of olivine-trapped CO₂ fluid inclusions, found in "low P" alkali basalts, indicates their crystallization at pressures up to around 0.55 GPa, which are consistent with the coexisting Cr-diopside compositions.
Melt inclusions (mg# 69) in the Mg-rich olivines (Fo₈₇) of the "low P" alkali basalts are widely scattered (from the "high P" to "low P") in their compositions, whereas they are more homogeneous, with lower incompatible elements concentrations, in less magnesian olivines.
In the most magnesian olivines of "high P" hawaiites, from AAC (Fo₈₂) and TU (Fo₇₃), only "high P" tephritic and phonotephritic melt inclusions (mg# 60%) occur respectively, suggesting that they could have derived by differentiation of a common parent magma.
Furthermore, it is possible that "high P" and "low P" magmas may be originated by different degrees of partial melting of a heterogeneous mantle. Magma mixing and fractional crystallization processes may then account for all the varieties of both the two groups.
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De Capitani L., Moroni M. and Rodeghiero F. Geological and geochemical characteristics of Permian Tourmalinization at Val Trompia (southern Alps, northern Italy) and relationship with the Orobic tourmalinites 185-212

ABSTRACT - Tourmaline breccias in the pre-Alpine basament in Val Trompia (Southern Alps, Northern Italy) are related to late Palaeozoic granites and are associated with Sn-W-bearing ore deposits. The breccias are rich in acicular tourmaline with variable textural and compositional characteristics. At least four stages of tourmaline crystallization are distinguished, mainly by Mg/Fe ratios. All tourmaline can be classified as "alkali group" varieties using recent nomenclature schemes. Compositions vary from schrol-dravite for earlier, main-stage type I and II coarse crystals, to highly Fe-enriched tourmalines, probably approaching the povondraite endmember (typical of oxidize hydrothermal environments), for type III and IV fine-grained tourmalines within late veinlets. Whole-rock REE geochemical data show variable, locally remarkable enrichments in LREE related to the action of hydrothermal fluids. Coarse tourmalines occurring in the crypto-crystalline groundmass of the Orobic tourmalinites, which are hosted in cataclastic zones along the tectonic contact between basament and Permian volcano-sedimentary cover rocks in the Lake Diavolo area (southern Alps), have schrol-dravite compositions similar to type I and II, main-stage Val Trompia tourmalines. The Orobic tourmalinites were considered of metasomatic origin by previous studies.
The Val Trompia tourmalinites can be interpreted as having formed by magmatic-hydrothermal fluids that produced metasomatic tourmalines with different compositions at different distances from the fluid source (magma). Compositional analogies between tourmalinites of the two areas may therefore reflect similarities between the tourmalinization processes that developed in relation to large-scale Permian magmatic-tectonic activity. The Val Trompia tourmalinites thus may represent deeper metasomatic products, closer to the magma chamber, whereas the Orobic tourmalinites would have formed hydrothermal fluids injected along shallower faults during coeval volcanic activity.
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