Clay Minerals in Hydrothermal Systems

The study of active and fossil hydrothermal systems shows clay minerals to be a fundamental tool for the identification and characterization of hydrothermal alteration facies. The occurrence and composition of hydrothermal alteration facies could provide useful information on the physicochemical conditions of the hydrothermal activity affecting a rock volume. In particular, clay minerals (i.e., smectite group, chlorite, illite, kaoline group, pyrophyllite, biotite) are pivotal for extrapolating important parameters that strongly affect the development of water/rock interaction processes such as the temperature and pH of the hydrothermal environment. This work aims to give a general reference scheme concerning the occurrence of clay minerals in hydrothermal alteration paragenesis, their significance, and the information that can be deduced by their presence and chemical composition, with some examples from active and fossil hydrothermal systems around the world. The main mineralogical geothermometers based on chlorite and illite composition are presented, together with the use of hydrogen and oxygen isotope investigation of clay minerals in hydrothermal systems. These techniques provide a useful tool for the reconstruction of the origin and evolution of fluids involved in hydrothermal alteration. Finally, a list of oxygen and hydrogen fractionation factor equations between the main clay minerals and water is also provided

Fluid inclusion evidence on the direct exsolution of magmatic brines from a granite intrusion beneath the eastern sector of Larderello geothermal field (Italy)

This work is based on a fluid inclusion investigation on two core samples (sampled at 3017m and 4150m of depth) of a granite intrusion drilled by the Travale 1 sud geothermal well, in the eastern sector of Larderello geothermal field. Fluid inclusion data demonstrate that the earliest fluids circulating in the intrusion were high-temperature brines exsolved directly from the crystallizing magma during its ascent in the shallow crust. The progressive release of magmatic fluids from the crystallizing granitic magma probably occurred under confining lithostatic pressure of about 200 MPa. Two phase fluid inclusions represent the hydrothermal meteoric water-dominated fluids that penetrated in the granite after opening of the system, induced by cooling and consequent transition from ductile behaviour to brittle fracturing. Type 1b two phase fluid inclusions, having temperature of homogenization that agree well with down-hole measured temperatures, may be considered to approximate the fluid that is actually circulating in the granite in recent times

Hydrothermal fluid evolution in the "Botro ai Marmi" quartz-monzonitic intrusion (Campiglia Marittima, Tuscany, Italy). Evidence from a fluid inclusion investigation

Abstract: The quartz-monzonitic intrusion of "Botro ai Marmi" (Tuscany, Italy) can be considered to be a typical example of an intrusion-centered magmatic hydrothermal system. The evolution of hydrothermal fluids in the "Botro ai Marmi" intrusion was investigated using fluid inclusion analyses to provide suitable physico-chemical constraints on the fluids involved in the late- to postmagmatic hydrothermal activity that affected the intrusion, providing inferences on their origin and variations of temperature and pressure with time. This work demonstrates that the earliest fluids circulating in the "Botro ai Marmi" intrusion were high-temperature brines exsolved directly from the crystallizing magma. This fluid circulated in the intrusion under lithostatic conditions (P > 90 MPa, T > 540°C). A second evolutionary stage of the magmatic hydrothermal system is marked by the transition from lithostatic (>90 MPa) to hydrostatic dominated conditions (50 to 10 MPa). In this stage the fluids are also interpreted to be mainly orthomagmatic in origin but unmixed in a high-salinity brine and in a low-salinity vapor aqueous phase, at a temperature ranging from about 500°C to 300°C. These fluids were responsible for the potassic alteration facies. At a later stage of hydrothermal evolution, abundant meteoric dominated fluids entered the system and are associated with propylitic alteration. This event marks the transition from a magmatic-hydrothermal system to a typical hydrothermal (“geothermal”) system, which can be assumed to be similar to some extent to the nearby active high-enthalpy geothermal system of Larderello. Low-temperature and low-salinity meteoric water-dominated fluids characterize the latest stage of the "Botro ai Marmi" hydrothermal system

L'adeguatezza patrimoniale del sistema bancario tra crisi e Basilea III

Il presente lavoro si propone di far emergere sia il ruolo essenziale della banca all’interno della società moderna, come strumento universalmente riconosciuto di mobilitazione del risparmio e di supporto alla crescita dell’economia, sia la sua caratteristica di intrinseca fragilità.In Basilea III la dotazione di mezzi patrimoniali e la verifica dell’adeguatezza rispetto all’operatività bancaria, assieme con un adeguato sistema di controllo finalizzato al fronteggiamento dei rischi, si confermano quali elementi fondanti del processo di controllo prudenziale, già posto in risalto dal Secondo Pilastro di Basilea II. L'attenzione viene inoltre centrata sulle tematiche maggiormente critiche rispetto alla situazione attuale e prospettica, considerando le potenzialità non ancora sfruttate appieno e le nuove sfide. Lo stato dell’arte attuale e le lacune di Basilea II, la nuova architettura di vigilanza in fieri per il 1 gennaio 2013, la “qualità” del capitale, le possibilità di convergenza tra gestione del capitale in ottica strategica e regole di vigilanza, in definitiva come potrà cambiare il modo di fare banca

Evidence of Na-metasomatism of phyllite rocks from the Verrucano of Monti Pisani (Tuscany, Italy

We report here for the first time the occurrence of albitite rocks in the Middle Triassic "Verruca" Formation (Monti Pisani, Northern Apennine, northern Tuscany, Italy). The albitite is the result of a pervasive Na-metasomatism of phyllites (originally formed by potassic white mica + quartz + chlorite + hematite + albite). The albitisation process took place after the Miocene main phases of Apenninic deformation and was followed by the formation of a system of veins made of Fe-carbonate ± quartz. Hydrothermal alteration continued with the ingression, possibly favored by the increase of permeability due to albitization, of a slightly acidic, oxidizing, aqueous fluid that led to the kaolinization of the albitite and to the complete replacement of the Fe-carbonate of the veins by Fe-hydroxides. This stage was followed by a supergene alteration that led to the formation of a pervasive network of tiny veins of halloysite and colloform (P-Al-Si)-bearing Fe-hydroxides. Finally, the hydrothermally altered rock underwent a localized brittle fracturing without new minerals formed. The most important chemical changes occurred during the whole hydrothermal process were the inversion of the Na2O/K2O ratio of the whole rocks (from 0.07 in the pristine phyllite to up to 200 for the kaolinized albitite), the loss of Fe and Mg, and the enrichment of Sb. Light REE and HREE behaved conservatively, whereas MREE were partially lost. The occurrences of hydrothermal alteration are common in central-southern Tuscany, and generally related to the post-collisional extensional regime, lithospheric thinnning, and emplacement of magmatic bodies in the crust. The Monti Pisani kaolinized albitite, altough occurring far from potential magmatic sources, can be considered related to this post-collisional extensional tectonic setting, thus stretching out northward the occurrence of post-Miocene hydrothermal activity in Tuscany

PIXE mapping on multiphase fluid inclusions in endoskarn xenoliths of AD 472 eruption of Vesuvius (Italy)

In this work we report a microthermometric and proton-induced X-ray emission (PIXE) mapping investigation on multiphase fluid inclusions hosted within nepheline and clinopyroxene of endoskarn xenoliths present in the deposits of the AD 472 eruption of Vesuvius. PIXE mapping on magmatic fluid inclusions repesents a useful tool for the characterization of the composition of magma derived fluids, exsolved from active magma chambers. In fluid inclusions we observed the occurrence of widespread solid phases formed by Fe, Pb, Zn, As ± Cu ± Mn, suggesting the good metal transport capability of Vesuvius magmatic fluids, which interacted with carbonate country rocks leading to the formation of endoskarn

3D geothermal modelling of the Mount Amiata hydrothermal system in Italy

In this paper we build a subsurface model that helps in visualizing and understanding the structural framework, geology and their interactions with the Mt. Amiata geothermal system. Modelling in 3D provides the possibility to interpolate the geometry of structures and is an effective way of understanding geological features. The 3D modelling approach appears to be crucial for further progress in the reconstruction of the assessment of the geothermal model of Mt. Amiata. Furthermore, this model is used as the basis of a 3D numerical thermo-fluid-dynamic model of the existing reservoir(s). The integration between borehole data and numerical modelling results allows reconstructing the temperature distribution in the subsoil of the Mt. Amiata area. Keywords