Pierfranco Lattanzi

The campi flegrei (Italy) geothermal system: A fluid inclusion study of the mofete and San Vito fields

Abstract A fluid inclusion study of core from the Mofete 1, Mofete 2, Mofete 5, San Vito 1, and San Vito 3 geothermal wells (Campi Flegrei, Campania, Italy) indicates that the hydrothermal minerals were precipitated from aqueous fluids ( ±CO 2 ) that were moderately saline (3–4 wt.% NaCl equiv.) to hypersaline (> 26 wt.% NaCl equiv.) and at least in part, boiling. Three types of primary fluid inclusions were found in authigenic K-feldspar, quartz, calcite, and epidote: (A) two-phase [ liquid (L) + vapor (V) ], liquid-rich inclusions with a range of salinity; (B) two-phase ( L + V ), vaporrich inclusions with low salinity; and (C) three-phase [ L + V + crystals (NaCL) ], liquid-rich inclusions with hypersalinity. Results of microthermometric and crushing studies are reported for twenty drill core samples taken from the lower portions of the five vertical wells. Data presented for selected core samples reveal a general decrease in porosity and increase in bulk density with increasing depth and temperature. Hydrothermal minerals commonly fill fractures and pore-spaces and define a zonation pattern, similar in all five wells studied, in response to increasing depth (pressure) and temperature. A greenschist facies assemblage, defined by albite + actinolite , gives way to an amphibolite facies, defined by plagioclase (andesine) + hornblende , in the San Vito 1 well at about 380°C. The fluid inclusion salinity values mimic the saline and hypersaline fluids found by drilling. Fluid inclusion V/L homogenization temperatures increase with depth and generally correspond to the extrapolated down-hole temperatures. However, fluid inclusion data for Mofete 5 and mineral assemblage data for San Vito 3, indicate fossil, higher-temperature regimes. A limited 87 Sr/ 86 Sr study of leachate (carbonate) and the leached cores shows that for most samples (except San Vito 3) the carbonate deposition has been from slightly 87 Sr-enriched fluids and that Sr isotopic exchange has been incomplete. However, San Vito 3 cores show an approach to fluid/rock Sr equilibrium with a fluid similar to modern ocean water in 87 Sr/ 86 Sr ratio. The Campi Flegrei volcanic system has evolved undersaturated products, mostly trachyte, and defines a large ( ≈ 12 km ) caldera. The hydrothermal system developed in this location can be used as an analog for fossil systems in similar trachytic environments. The potential for ore mineralization is expressed by the recognition, from fluid inclusion and drilling data, of ore-forming environments such as boiling and brine stratification.

Concentration, distribution, and translocation of mercury and methylmercury in mine-waste, sediment, soil, water, and fish collected near the Abbadia San Salvatore mercury mine, Monte Amiata district, Italy

The distribution and translocation of mercury (Hg) was studied in the Paglia River ecosystem, located downstream from the inactive Abbadia San Salvatore mine (ASSM). The ASSM is part of the Monte Amiata Hg district, Southern Tuscany, Italy, which was one of the worlds largest Hg districts. Concentrations of Hg and methyl-Hg were determined in mine-waste calcine (retorted ore), sediment, water, soil, and freshwater fish collected from the ASSM and the downstream Paglia River. Concentrations of Hg in calcine samples ranged from 25 to 1500 μg/g, all of which exceeded the industrial soil contamination level for Hg of 5 μg/g used in Italy. Stream and lake sediment samples collected downstream from the ASSM ranged in Hg concentration from 0.26 to 15 μg/g, of which more than 50% exceeded the probable effect concentration for Hg of 1.06 μg/g, the concentration above which harmful effects are likely to be observed in sediment-dwelling organisms. Stream and lake sediment methyl-Hg concentrations showed a significant correlation with TOC indicating considerable methylation and potential bioavailability of Hg. Stream water contained Hg as high as 1400 ng/L, but only one water sample exceeded the 1000 ng/L drinking water Hg standard used in Italy. Concentrations of Hg were elevated in freshwater fish muscle samples and ranged from 0.16 to 1.2 μg/g (wet weight), averaged 0.84 μg/g, and 96% of these exceeded the 0.3 μg/g (methyl-Hg, wet weight) USEPA fish muscle standard recommended to protect human health. Analysis of fish muscle for methyl-Hg confirmed that >90% of the Hg in these fish is methyl-Hg. Such highly elevated Hg concentrations in fish indicated active methylation, significant bioavailability, and uptake of Hg by fish in the Paglia River ecosystem. Methyl-Hg is highly toxic and the high Hg concentrations in these fish represent a potential pathway of Hg to the human food chain.

Fluid inclusions in minerals from the geothermal fields of Tuscany, Italy

Abstract A reconnaissance study on fluid inclusions from the geothermal fields of Tuscany indicates that the hydrothermal minerals were formed by fluids which were, at least in part, boiling. Four types of aqueous inclusions were recognized: (A) two-phase (liquid + vapor) liquid rich, (B) two-phase (vapor + liquid) vapor rich, (C) polyphase hypersaline liquid rich and (D) three phase—H2O liquid + CO2 liquid + CO2-rich vapor. Freezing and heating microthermometric determinations are reported for 230 inclusions from samples from six wells. It is suggested that boiling of an originally homogeneous, moderately saline, CO2-bearing liquid phase produced a residual hypersaline brine and a CO2-rich vapor phase. There are indications of a temperature decrease in the geothermal field of Larderello, especially in its peripheral zones.

Mercury deposits in metamorphic settings: the example of Levigliani and Ripa mines, Apuane Alps (Tuscany, Italy)

In addition to the world-class epithermal deposits in the Monte Amiata area (Southern Tuscany), mercury production in Tuscany is recorded from the Levigliani and Ripa deposits in Apuane Alps. Both deposits are hosted by sedimentary and subordinate volcanic rock sequences, belonging to the Apuane Metamorphic Complex (AMC), metamorphosed in the greenschist facies during the Apenninic orogeny (ca. 27–8 Ma). At Ripa, mineralization is very simple, consisting of cinnabar with minor pyrite in quartz gangue. Its emplacement is obviously controlled by shear structures produced during the second Apenninic deformation event (D2). At Levigliani, both the setting and the mineral assemblage are more complex. Mineralization is confined to a lithologic horizon comprised of carbonatic chloritic phyllites and calc-alkaline metabasites. The mineralizing process spanned the entire tectono-metamorphic Apenninic event. A first mineral assemblage (cinnabar I+zincian metacinnabar+pyrite) was formed under conditions presumably not far from the metamorphic thermal peak, whereas a second assemblage (cinnabar II+mercurian sphalerite+pyrite±native mercury±chalcopyrite±galena±pyrrhotite±grumiplucite) was formed in a retrograde stage. In both deposits, the overall P–T–X features of fluid inclusions in quartz are similar to those previously established for syn-metamorphic hydrothermal circulation in AMC. At Ripa, the syn-D2 shear structures provided a hydrologic trap for mercury mobilized from an unknown source. At Levigliani, the strict lithological control, the protracted nature of the mineralizing process, and the similarities to the setting of Palaeozoic peri-Mediterranean mercury deposits, suggest a small scale remobilization from a pre-existing anomaly.

The cassiterite-polymetallic sulfide deposits of Dachang (Guangxi, People's Republic of China)

The Dachang mining district is the second largest producer of Sn in China and an important source of other metals. The known mineralizations can be divided into four groups: (1) cassiterite + Cu-Fe-Pb-Zn sulfides and sulfosalts, (2) Zn-Cu skarn, (3) Sb-W veins and (4) residual and placer concentrations of Sn and Fe oxides.Most orebodies are hosted by Upper Devonian calcareous, marly and quartzitic formations in spatial association with Cretaceous Yanshanian magmatites. A characteristic feature is the occurrence of stratiform, lens-shaped orebodies which appear to represent the root zone of overlying stockwork mineralizations.The metallogeny of the district may be interpreted in terms of an Upper Devonian Sn and polymetallic concentration with subsequent remobilization and, possibly, the introduction of additional elements during the late stages of the Yanshanian magmatism.

Chemical speciation of Ag in galena by EPR spectroscopy

Abstract Electron paramagnetic resonance (EPR) spectroscopy has been used to study the valence state of silver in “argentiferous” galena samples from the Apuane Alps (Tuscany, Italy) mining district. This method was used to reveal primary metallic silver (Ag0) in galena. Both thermodynamic data and experimental studies suggest that galena and native silver can stably coexist, but have not been reported as a primary (hypogene) assemblage in natural samples. EPR spectroscopy proved to be a suitable tool to solve this problem, because this technique is capable of detecting paramagnetic species down to the ppb level, even in a highly absorbent matrix such as galena. A detailed SEM-EDS investigation could not detect metallic silver (or gold) in galena samples, but did reveal small (few micrometers) inclusions of Ag-bearing phases, in which silver has a formal valence of +1. On the other hand, EPR spectra indicated the presence in galena of pairs and clusters of elemental silver atoms, which may be associated with pairs of metallic gold, or with silver-gold hetero-atomic pairs. Therefore, SEM/EDS and EPR are complementary techniques, revealing the presence of both Ag+ and Ag0. The Ag(Au) metallic species were apparently deposited on the galena surface during its growth from mineralizing fluids. Their scarcity, and the presence of larger amounts of Ag1+ phases, suggest that the assemblage galena-metallic silver was stable only under peculiar physical and chemical conditions. The formation of Ag0 was presumably linked to local and rare chemical fluctuations of the hydrothermal environment, characterized by low activities of S, Sb, Bi (Cu…) and high activity of Ag in the fluids. The occurrence of both homo- and hetero-atomic pairs suggests either different kinetics of pair formation, or possible fluctuations in the composition of the hydrothermal fluids, which alternatively carried Ag or Au species, or both

Metamorphogenic barite-pyrite (Pb-Zn-Ag) veins at pollone, apuane alps, tuscany: vein geometry, geothermobarometry, fluid inclusions and geochemistry

SummaryThe barite-pyrite-(Pb-Zn-Ag) deposit of Pollone is located in the southernmost tip of the Apuane Alps metamorphic core complex, and is hosted by a siliciclastic formation of pre-Norian age. The southern sector of the deposit mainly consists of stratiform, supposedly syngenetic, barite-pyrite orebodies, whereas the northern area is characterized by a barite-pyrite-(Pb-Zn-Ag) vein system. Vein geometry in the northern area is controlled by a shear zone, developed during the greenschist facies metamorphism which affected the Apuane Alps core complex between 27 and 8 Ma, that was responsible for fluid focusing and vein emplacement. At Pollone, arsenopyrite and chlorite geothermometers show broadly comparable results, and suggest local metamorphic peak temperatures between 320 and 350°C. Phengite geobarometry indicates minimum pressures of about 3.5 kbar. Fluid inclusion data and mineral equilibria suggest that the mineralizing fluids were initially hotter than the country rocks (about 450°C at 3.5–4.0 kbar). Rocks in direct contact with the orebodies are depleted in Rb and enriched in Sr in comparison to similar rocks elsewhere in the area. This is attributed to the presence of Rb-poor muscovite and Sr-rich barite. Rb-depleted muscovites suggest mineral-fluid interaction in a rock reservoir characterized by a different (modal) mineralogical composition than the Pollone host rocks. The progressive decrease of Sr in barite with increasing distance from the orebodies may be explained with a temperature decrease along the infiltration paths of mineralizing fluids (i.e., from the vein into the wall rocks). The similar O-isotope composition of quartz from veins and host rocks is explained with the overall homogeneous O-isotope composition of the Alpi Apuane basement rocks. This indicates a limited interaction between mineralizing fluids and the rocks exposed at Pollone. Remobilization of syngenetic orebodies was conceivably of minor importance in the production of metamorphogenec veins. Fluid cooling along a major tectonic lineament is thought to be responsible for barite deposition.ZusammenfassungDie Baryt-Pyrit (Pb-Zn-Ag) Lagerstätte von Pollone liegt im südlichsten Ende des metamorphen Kern-Komplexes der Apuanischen Alpen, und sitzt in einer siliziklastischen Formation prä-Norischen Alters auf. Der südliche Sektor der Lagerstätte besteht hauptsächlich aus stratiformen, wahrscheinlich syngenetischen Baryt-Pyrit-Erzkörpern, während der nördliche Teil des Gebietes durch ein Baryt-Pyrit (Pb-Zn-Ag) Gangsystem charakterisiert wird. Die Geometrie der Gänge im Nordteil wird durch eine Scherzone kontrolliert, die während einer grünschieferfaziellen Metamorphose entstanden ist, die den Kernkomplex der Apuanischen Alpen zwischen 27 und 8 Ma betroffen hat. Diese Scherzone war auch für die Zufuhr der Fluide und die Platznahme der Gänge verantwortlich. In Pollone zeigen Arsenopyrit- und Chlorit-Geothermometrie weithin vergleichbare Ergebnisse und weisen auf lokale Maximaltemperaturen der Metamorphose zwischen 320 und 350°C hin. Phengit-Geobarometrie läßt Minimal-Drucke von ungefähr 3,5 kbar erkennen. Fluidflüssigkeitseinschluß-Daten und Mineral-Gleichgewichte zeigen, daß die erzbringenden Fluide ursprünglich heißer als die Wirtsgesteine waren (ca. 450 °C für P von 3,5 bis 4 kbar). Gesteine, die im direkten Kontakt mit den Erzkörpern sind, zeigen eine Anreicherung an Rb und eine Anreicherung an Sr, im Vergleich mit ähnlichen Gesteinen, die im Gebiet anzutreffen sind. Dies wird auf das Vorkommen von Rb-armen Muscovit und Sr-reichen Baryt zurückgeführt. An Rbabgereicherte Muscovite legen Mineral-Fluid-Reaktionen nahe, die in einem Gesteinsreservoir abliefen, das durch eine andere mineralogische Zusammensetzung als die Wirtsgesteine von Pollone charakterisiert war. Der zunehmende Verlust von Sr im Baryt mit zunehmender Entfernung von den Erzkörpern, kann durch einen Temperaturabfall entlang der Infitrations-Pfade der erzführenden Lösungen erklärt werden (d.h. von Gang in die Nebengeseine). Die ähnliche Sauerstoff-Isotopen-Zusammensetzung für Quarz aus den Gängen und den Nebengesteinen läßt sich auf die allgemein homogene Sauerstoffisotopen-Signatur des Basements der Apuanischen Alpen zurückführen. Dies weist auf beschränkte Wechselwirkung zwischen erzführenden Lösungen und den in Pollone anstehenden Gesteinen hin. Die Remobilisation von syngenetischen Erzkörpern in Pollone war nur von geringer Bedeutung für die Entstehung der metamorphogenen Gänge. Abkühlung der Fluide an einem wichtigen tektonischen Lineament gilt als Ursache für den Absatz von Baryt.

Source of metals in metamorphic ore-forming processes in the Apuane Alps (NW Tuscany, Italy): Constraints by Pb-isotope data

SummaryA total of 19 samples of sulfides, barite and country rocks from three important deposits of the Apuane Alps district (Bottino, Pollone and Monte Arsiccio) were analyzed for Pb-isotopic compositions. Ore lead shows a fairly homogeneous isotopic signature (206/204: 18.2-18.4; 207/204 ≈ 15.7; 208/204: 38.5-38.6), defining a high μ, high W province suggestive of an evolution in a crustal environment since at least the Middle Proterozoic. Pb-Pb model age of the ores is in the order of ≈ 350 Ma, in gross agreement with the Lower-Middle Paleozoic age assigned to most country rocks. The present-day Pb-isotope ratios of presumed exhalative tourmalinites associated with the Bottino deposit and of other country rocks from mineralized areas are also similar. Moreover, most of these rocks show relatively high total Pb contents (> 70 ppm). HCl-soluble lead in these samples also has a roughly similar isotopic signature. In contrast, rock samples collected at greater distances from mineralized bodies have lower Pb concentrations (< 10 ppm) and more radiogenic 206/204 and 208/204 ratios (18.6 to 18.9 and 38.9 to 39.3 respectively). HCl-soluble lead in these samples has distinctly lower 208/204, and to a lesser extent 206/204 ratios (38.6 to 38.9 and 18.5 to 18.9 respectively). In agreement with previously established genetic models, these results may be interpreted in terms of a major episode of lead extraction in the Paleozoic, possibly in association with exhalative tourmalinites, followed by remobilization and reconcentration in vein mineralization during the Apenninic orogeny. The isotopic signature of country rocks in mineralized areas may be ascribed to a “Pb-isotope halo effect” induced by metamorphism. When compared with Pb-isotope data from deposits of the southern Tuscany mining district, the ore lead in Apuane Alps exhibits similar isotopic patterns, but with lower 208/204 and 206/204 ratios. This fact suggests for the two districts source(s) with similar evolutions of their U/Pb and Th/Pb ratios, but distinctly different times of Pb extraction.ZusammenfassungIn den Apuanischen Alpen (NW Toskana) treten prämetamorphe, schichtförmige Fe-Ba Erzlagerstätten in grünschieferfaziell metamorphen Serien sedimentären und vulkanosedimentären Ursprungs auf (e.g. Pollone und Monte Arsiccio), die von syn- bis spätkinematisch gebildeten, diskordanten Vererzungen begleitet werden. Ein Gangsystem mit Quarz, Karbonat und Pb-Zn-Ag (Bottino) wird von einem stratiformen Turmalinithorizont mit erhöhten Metallgehalten begleitet.Um die Frage eines metamorphogenen Ursprungs der gangförmigen Vererzungen im Gefolge der Appenninischen Metamorphose (Oligozän-Miozän) und die vermutete Herkunft der Metalle aus den schichtförmigen Lagerstätten und Metallanreicherungen zu überprüfen, wurden Pb-Isotopenuntersuchungen an Sulfiden, Bariten, Turmaliniten und Nebengesteinen durchgeführt. Das Erzblei aus stratiformen wie auch gangförmigen Lagerstätten zeigt nur geringe Variationen der Pb-isotopenverhältnisse und ist innerhalb eines Vorkommens homogen (206/204: 18.2-18.4; 207/204: 15.68; 208/204: 38.538.6). Seine relativ hohen μ- and W-Werte weisen auf eine Bleientwicklung in kontinentalem Krustenmilieu, spätestens seit dem mittleren Proterozoikum hin. Die 207/206 Modellalter von ca. 350 Ma stimmen größenordnungmäßig mit dem vermuteten paläozoischen Alter des Nebengesteins überein, sind aber für die gangförmigen tertiären Vorkommen zu hoch. Baryt-, Turmalinit- und Gesamtgesteinsproben aus der Nähe der Lagerstätten zeigen alle ähnliche Pb-Isotopenverhältnisse wie die Sulfide. Die Gesteine weisen hohe Pb-Gehalte von > 70 ppm auf. In größerer Entfernung zu den Lagerstätten sind die Pb-Gehalte mit < 10 ppm deutlich niedriger und die Pb-Isotopenverhältnisse sind radiogener (206/204: 18.8-18.9; 208/204: 38.9-39.3). Ihr HCl-1ösliches Blei ist hingegen weniger radiogen.Die Resultate stützen die neueren Ansichten, daß es im Paläozoikum zur Bildung von exbalativen Turmaliniten verbunden mit einer Metallanreicherung und von stratiformen Fe-Ba-Lagerstätten kam. Während der appenninischen Metamorphose wurden die Metalle remobilisiert, und es kam zur Bildung von gangförmigen Vorkommen und Lagerstätten. Die hohen Pb-Gehalte der Nebengesteine und die Isotopensignatur des HC1-löslichen Bleis deuten auf eine metamorphogene Halo-Bildung. Die Bleiisotopen von jungtertiären Erzen aus der südlichen Toskana sind im Vergleich mit dem apuanischen Erzblei radiogener. Sie weisen aber dieselben hohen μ- und W-Werte auf. Das heißt, das Blei stammt aus Gesteinen, die eine qualitativ wie auch quantitativ ähnliche Entwicklung bezüglich der U/Pb und Th/Pb Verhältnisse durchlaufen haben wie jene, die das Blei der apuanischen Lagerstätten geliefert haben.

Environmental mineralogy and geochemistry of waste dumps at the Pb(Zn)-Ag Bottino mine, Apuane Alps, Italy

The Bottino mine (Apuane Alps, Tuscany) had been exploited for silver and lead since at least Renaissance times. Detailed field work has led to the recognition of several mine dumps which differ in size, age, and types (rock waste dumps; jigging and handpicking wastes). In the dumps, the primary sulfides are sphalerite, galena, and pyrite ± variable amounts of chalcopyrite, pyrrhotite, arsenopyrite, and a wealth of other sulfides and sulfosalts. These mine- rals are associated with gangue quartz, white micas, chlorite, and carbonates, mostly of the siderite-magnesite and dolomite-ankerite series, whereas calcite is scarce. Supergene alteration led to the development of secondary mine- rals such as goethite, lepidocrocite, pyrolusite, cerussite, and clay minerals (kaolinite, montmorillonite, and vermi- culite). Two main types of supergene effects have been observed: (a) development in situ of pseudomorphic replacement of primary minerals, and (b) leaching and dissolution. Acid generation and metal release are mainly pro- duced by the replacement of pyrrhotite by iron hydroxides, the partial dissolution of siderite-magnesite carbonates, and the extensive dissolution/replacement of galena and sphalerite. Given the scarcity of calcite in the primary assem- blage, the most effective attenuators of acidity seem to have been dolomite-ankerite and siderite-magnesite. The mainly unpolluted character of the Bottino waters may be explained by a number of concurring factors, including the moderate volume of wastes, their overall coarse grain size, the low abundance of acid-producing phases (pyrite and pyrrhotite) relative to acid-consuming phases such as dolomite-ankerite, and the steep topography.

Arsenic-bearing calcite in natural travertines: evidence from sequential extraction, μXAS, and μXRF.

Recent studies demonstrated that synthetic calcite may host considerable amounts of arsenic (As). In this paper, the concentration of As in natural calcite was determined using two novel, specifically designed, sequential extraction procedures. In addition, the oxidation state of As and its distribution between calcite and coexisting Fe-oxyhydroxides was unravelled by μXRF elemental mapping and As K-edge μXAS spectroscopy. Our results conclusively demonstrate that arsenic can be found in natural calcite up to 2 orders of magnitude over the normal crustal As abundances. Because of the large diffusion of calcite in the environment, this phase may exert an important control on As geochemistry, mobility, and bioavailability.