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 (Xmax
= 13.25%, Isola Santa; Xmin = 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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