The Ghorveh-Seranjic (GS) skarn is located in the northern part of the Sanandaj-Sirjan zone, NW Iran, which is part of Alpine-Himalaya orogenic belt. The GS metamorphic complex is the oldest unit in the GS area composed of marble, dolomitic marble, greenschist, and amphibolite of Early Jurassic age. The complex is intruded by NW-SE trending Late Jurassic peraluminous granitoids, which caused contact metamorphism and resulted in the development of skarn, hornfels and crystallization of marble. The skarn is showing distinct textural, mineralogical and geochemical zonation. At least four stages of skarn development have been recognized; stage I, clinopyroxene+garnet±vesuvianite±quartz±calcite±scheelite± pyrrhotite; stage II, garnet+clinopyroxene +vesuvianite+scheelite±apatite+calcite±pyrrhotite; stage III, amphibole+vesuvianite+epidote+chlorite±quartz±calcite±pyrrhotite±pyrite±chalcopyrite and stage IV, quartz+calcite±amphibole±epidote±chlorite±pyrite±chalcopyrite. Scheelite occurs in stages 1 and 2 together with garnet and clinopyroxene, and its abundance slightly increases with vesuvianite growth. In general, mineral chemistry of the GS skarn shows enrichment in Ca, Al and Mg. Two types of garnet, clinopyroxene and vesuvianite are identified in the prograde stage within the GS skarn. Variable Mg:Mn:Fe proportions in clinopyroxene of the early prograde stage suggest formation from a relatively homogeneous F-rich volatile phase. Mineralogical documentation of the GS skarn indicates that presence of the F-rich volatile phase affected zoning patterns and mineral abundances. Addition of fluorine increases the solubility of Al in the hydrothermal fluid by forming strong Al-F complexes, causing an increase in vesuvianite instead of clinopyroxene during the late prograde substage, resulting in high garnet/clinopyroxene ratios. The presence of granditic (grossular-andradite) and subcalcic (grossular-almandine-spessartine) garnet during the skarn evolution suggests variable Fe/Mn and Fe2+/Fe3+ ratios during the prograde stage of the skarn formation. Subcalcic garnet formed in a relatively reduced environment compared to the granditic garnet. Paragenetic reconstructions indicate that clinopyroxene, garnet and scheelite grew together during the prograde stage. These minerals were stable and coexisted at temperatures between 580 °C and 400 °C and at a logfO2 = −18 to −28.

The Siah-Kamar Mo deposit (SKMD) is located at the northwestern termination of the Urumieh-Dokhtar magmatic zone and it is the only porphyry Mo ore reserve in Iran. The exploration program documented 39.2 Mt proved reserves @ 539 ppm Mo and 66.4 Mt probable reserves @ 266 ppm Mo. In this study, field and petrographic investigations, integrated with geochemical (fluid inclusion and quartz chemistry) and geochronological (U-Pb zircon, Re-Os molybdenite, and Rb-Sr multimineral isochron) studies are used to propose a metallogenic model for the Mo mineralisation in the SKMD. The geology of the SKMD is characterized by the emplacement of a multiphase Oligocene basic/intermediate (at ca. 33-30 Ma) to acidic (29-28 Ma) magmatic suite, which intruded the Eocene volcanic country rocks. The alteration zone, about 4 x 3 km in size and with a general NW-SE trend, is centered within the main basic porphyry stock, grading from an inner potassic-sodic zone to peripheral phyllic/propylitic halos. The late acidic magmatic products (stocks and dykes) intruded and post-dated the main alteration zone. Two-stage Mo mineralisation is recognised, including: (i) stage-1, disseminated molybdenite, coeval with the formation of potassic-sodic alteration and minor, microscale Fsp, Bt, Qz + Po veinlets; and (ii) stage-2, high-grade molybdenite + carbonate (sericite), structurally-controlled stockwork veining. Fluid inclusion systematics combined with TitaniQ thermometry documents a mineralising fluid system compatible with a transition from high-temperature (up to ca. 600 degrees C) magmatic to epithermal (250 degrees C) conditions during progressive cooling, exhumation and mixing with meteoric sources at shallow crustal conditions (ca. 7-3 km). The Re-Os molybdenite dating constrains the high-grade Mo ore formation at ca. 29-28 Ma, attesting for the intimate linkage between the main Mo mineralisation and the acidic magmatic phase in the area. The Rb-Sr geochronology of the potassic-sodic alteration zones confirms the two-stage magmatic/mineralisation scenarios, overlapping within errors with the results obtained from the U-Pb zircon geochronology and constraining the formation of the potassic-sodic and phyllic alteration at ca. 33 and 28 Ma, respectively. Our results document an uncommon scenario of two-stage porphyry Mo mineralisation associated with intensive late stage carbonate precipitation and achieved during a long-lasting and multiphase magmatic pulses of Oligocene age. We highlight the dominant role of acidic fluid neutralisation for further ore enrichment during polyphase magma intrusion as the dominant factor controlling the Mo mineralisation in the SKMD. Comparison at a regional-scale indicates that parameters such as longevity of magma supply, progressive magma crystallization/differentiation, and the presence of a possible pre-enriched crustal material should be considered responsible for the Mo endowment in the UDMZ.

The characterisation of the late Variscan intrusion of Monte Linas (southern Sardinia) allowed to firstly study some Sn-bearing ores of this area and their relationships with the surrounding intrusives. The Monte Linas pluton was emplaced at ca. 290 Ma at a shallow crustal level between allochthonous units and the foreland of the Sardinian Variscan belt. The pluton emplaced in a post-collisional regime into a previously exhumed low-grade basement, forming a coarse-grained monzogranite that is capped by an almost continuous sub-horizontal sheet of fine-grained rocks. The rocks within the pluton are ferroan F-bearing granites, belonging to the ilmenite-series. They have alumina saturation index values indicative of sub-aluminous to slightly peraluminous granitoids, as also indicated by the chemical composition of biotite within the pluton. The new data of this study indicate that the Monte Linas pluton formed from water-undersaturated magmas under low-fO(2) conditions at temperatures >850 degrees C. The later stages of magmatism were characterised by boiling and fluid expulsion at confining pressures of <1 kbar, producing fayalite-bearing pegmatites, miarolitic facies and greisening.A wide variety of mineral deposits are associated with the Monte Linas pluton, including different types of Sn-bearing and Mo-bearing ores. Sn-bearing ores are represented by 1) Sn-As and Sn-Pb-Zn-Cu veins, and 2) "wrigglite" skarn Fe-Zn-Sn ores. Field and analytical studies, including fluid inclusion analyses, EMPA and SEM-EDS, allow to refer these deposits to the evolution of initial highly saline, hypothermal magmatic fluids, as confirmed by parageneses and fluid inclusion analyses of cassiterite in veins, which provide evidence of polyphase processes that started at temperatures close to 400 degrees C. The hydrothermal systems were initially characterised by low-fO(2) and high-chlorine solutions that mobilised Sn and underwent rapid changes in physicochemical conditions that led to the deposition of cassiterite. In the "wrigglite" F-rich genetic environment, a role of fluoride as complexing agent for Sn can be inferred. The Monte Linas pluton is also characterised by Mo deposits, not typical in ilmenite series granites; they occur both as greisens and veins. Mo was mobilized as a result of rapid increases in 102 within the magmatic system, and precipitated in a fS(2)-rich environment nearby the contact between the intrusion and the surrounding country rocks.The variety of Sn mineralising events around the Monte Linas pluton confirms the role of physicochemical characters of magmas and of magmatic processes in the genesis of tin deposits. The occurrence in southern Sardinia of a wide suite of ilmenite-series ferroan granites emplaced in similar geological contexts allows to consider the idea of a low-grade tin province and opens the way to further explorations. (C) 2016 Elsevier B.V. All rights reserved.

A giant carbonate vein (≥ 50 m thick; fissure ridge travertines) and nearby travertine plateaus in the Semproniano area (Mt. Amiata geothermal field, southern Tuscany, Italy) are investigated through a multidisciplinary approach, including field and laboratory geochemical analyses (U/Th geochronology, C, Nd, O and Sr isotope systematics, REE abundances, and fluid inclusion microthermometry). The main aim of this work is to understand: (1) modes and rates for the growth of the giant vein and nearby travertine deposits within a Quaternary volcano-tectonic domain; (2) implications in terms of the CO2 leakage; and (3) possible relationships with Quaternary paleoclimate and hydrological oscillations. Results show that the giant vein was the inner portion of a large fissure ridge travertine and grew asymmetrically and ataxially through repeated shallow fluid injections between > 650 and 85 ka, with growth rates in the 10− 2–10− 3 mm/a order. The giant vein developed mainly during warm humid (interglacial) periods, partially overlapping with the growth of nearby travertine plateaus. Estimated values of CO2 leakage connected with the vein precipitation are between about 5 × 106 and 3 × 107 mol a− 1 km− 2, approximately representing one millionth of the present global CO2 leakage from volcanic areas. Temperature estimates obtained from O-isotopes and fluid inclusion microthermometry indicate epithermal conditions (90–50 °C) for the circulating fluid during the giant vein growth, with only slight evidence of cooling with time. Geochemical and isotope data document that the travertine deposits formed mainly during Pleistocene warm humid periods, within a tectonically-controlled convective fluid circuit fed by meteoric infiltration and maintained by the regional geothermal anomaly hosted by the carbonate reservoir of the Mt. Amiata field.

In the Arburese region (SW Sardinia, Italy) several vein-type ore deposits, including small Sn minerali-zations, are arranged, with different trends, around two contrasting late-to post-collisional shallow plutons: the Arbus and the Monte Linas plutons, dated at 304 +/- 1Ma, and 289 +/- 1Ma respectively. These intrusions belong to two different ilmenite suites: an earlier high-K rock-series (Arbus Pluton), and a later F-bearing rock-series (Monte Linas Pluton). In the apical portion, close to the host rocks, they suffered greisen type alteration testified by secondary muscovite, B-rich and F-bearing phases. Preliminary fluid inclusion analyses in cassiterite veins, documented polyphase mineralizations and temperature close to 400 degrees C. The petrochemical features and the emplacement history of the Linas pluton meet high favourability for tin accumulation. Despite of their limited extent, the Sn ores of SW Sardinia have a metallogenic relevance as they document a long lasting metallogenic epoch all over the South Variscan Realm.

Data constraining the paleoenvironmental conditions during the Messinian evaporative drawdown of the Mediterranean basin are still conflicting. Here we present a comprehensive paleoclimatic reconstruction during Messinian halite deposition from several Italian sites. We performed fluid inclusion analyses to define better both the composition of the Mediterranean water body and the paleotemperatures of the Messinian brine during halite crystallization. We measured homogenization temperatures on 218 primary all‐liquid fluid inclusions in Messinian halite from the Volterra, Crotone, and Caltanissetta evaporite basins. These measurements provided mean homogenization temperatures of 17–18°C, with a range between 10–11°C and 28–29°C, which should be close to the SST of the Mediterranean Sea during halite deposition. The occurrence of major elements such as Cl, Na, Mg, S, Ca, and K within the halite fluid inclusions, together with the presence of minerals such as pentahydrite, polyhalite, and Ca‐, K‐, and Mg‐sulfates, indicates that these salt bodies originated from mainly marine water. Taking into account both the present‐day annual SST of the Mediterranean Sea around the sampling sites, which ranges between 18 and 20°C, and the lower latitude of the Mediterranean Basin during the Messinian Salinity Crisis, our homogenization temperatures point to a colder climate during the Messinian halite deposition compared to the present interglacial climate stage. This conclusion is consistent with halite deposition during a Late Miocene glacial interval (TG12).

Raman spectroscopy is a versatile non-destructive technique for fluid inclusion analysis, with a wide field of applications ranging from qualitative detection of solid, liquid and gaseous components to identification of polyatomic ions in solution. Raman technique is commonly used to calculate the density of CO2 fluids, the chemistry of aqueous fluids, and the molar proportions of gaseous mixtures present as inclusions. Raman spectroscopy has been applied to measure the pH range and oxidation state of fluids. The main advantages of this technique are the minimal sample preparation and the high versatility. Present review summarizes the recent developments of Raman spectroscopy in fluid inclusions research to provide support for laboratory analyses.

This study discusses new and published data on the composition of fluid inclusions contained in mantle minerals of spinel and garnet peridotite xenoliths, in samples from geodynamically distinct settings (Ethiopian plateau, Hawaii, Canary Islands, and western Mediterranean region). Based on spectroscopic Raman and FTIR analyses we show that, contrary to a commonly held view, fluid inclusions either contain relevant amounts of unsuspected H2O, or represent a “dehydrated” composition from multicomponent aqueo-carbonic fluids. We identify water loss from fluid inclusions through decrepitation, stretching and hydrogen diffusion. We also show that talc, magnesite, chlorides, and sulfates represent common phases in fluid inclusions. Talc and magnesite form through reactions of fluids with the surrounding minerals. Thermodynamic modeling in the MFSHC system of observed reactions between fluid inclusions and surrounding mantle minerals provides the basis for predicting water amounts in shallow-mantle fluids, and suggests XH2O in the range of 10–50mol%. Model hydrous fluids are relatively enriched solutions, dominated by Si, Cl, and alkalies, with significant amounts of Ca, and S, and low levels of Mg and Fe. This study argues that multicomponent hydrous fluids may be widespread in the shallow mantle, not only in subduction zones but also in intraplate and extensional settings.

Compositions of biotite from three different rock types of Mashhad granitoids, i.e., granodiorite, monzogranite and leucogranite in NE of Iran have been documented by electron microprobe and wet chemistry for Fe3+ and Fe2+. Mashhad granitoids have been geochronologically and petrologically grouped into G1 and G2 phases. Microprobe data show that the total Fe contents in biotite from G2 leucogranite are higher than those in biotite from G1 granites. In addition, the oxidation state of iron determined by wet chemistry shows that Fe3+/(Fe2+ + Fe3+) ratio in biotite from G2 leucogranite is 0.10 indicating relatively reducing whereas, in G1 ones is 0.18 and 0.23 suggesting more oxidizing conditions. The most outstanding compositional characteristics of Mashhad biotite are differences in total Al contents and Fe/(Fe+Mg) ratios. In the annite-siderophylite-phlogopite-eastonite (ASPE) quadrilateral, represented based on the above parameters, biotite samples from G1 and G2 granites define two distinct and non-overlapping trends. Each trend is characterized by a pronounced trend of increasing total Al at relatively narrow Fe/(Fe+Mg) values. The total Al contents of G1 biotite are in the range of 2.8 to 3.1, whereas, in G2, 3.3 to 3.6 (apfu). Fe/(Fe+Mg) values of G1 biotite are in the range of 0.52 to 0.59 which is considerably lower than those from G2 biotite, 0.67 to 0.72. The trend of increasing Al contents at constant Fe/(Fe+Mg) is relatively common and observed in biotite from several locations worldwide and attributed to considerable contributions from aluminous supracrustal material, either by assimilation or anatexis.

Petrological and geochemical study of volatile bearing phases (fluid inclusions, amphibole, and nominally anhydrous minerals) in a spinel lherzolite xenolith suite from Quaternary lavas at Injibara (Lake Tana region, Ethiopian plateau) shows compelling evidence for metasomatism in the lithospheric mantle in a region of mantle upwelling and continental flood basalts. The xenolith suite consists of deformed (i.e., protogranular to porphyroclastic texture) Cl-rich pargasite lherzolites, metasomatized (LILE and Pb enrichment in clinopyroxene and amphibole) at T⩽1000°C. Lherzolites contain chlorine-rich H2O–CO2 fluid inclusions, but no melt inclusions. Fluid inclusions are preserved only in orthopyroxene, while in olivine, they underwent extensive interaction with the host mineral. The metasomatic fluid composition is estimated: XCO2=0.64, XH2O=0.33, XNa=0.006, XMg=0.006, XCl=0.018, (salinity=14–10 NaCl eq. wt.%, aH2O=0.2, Cl=4–5mol.%). Fluid isochores correspond to trapping pressures of 1.4–1.5GPa or 50–54km depth (at T=950°C). Synchrotron sourced micro-infrared mapping (ELECTRA, Trieste) shows gradients for H2O-distribution in nominally anhydrous minerals, with considerable enrichment at grain boundaries, along intragranular microfractures, and around fluid inclusions. Total water amounts in lherzolites are variable from about 150 up to 400ppm. Calculated trace-element pattern of metasomatic fluid phases, combined with distribution and amount of H2O in nominally anhydrous minerals, delineate a metasomatic Cl- and LILE-rich fluid phase heterogeneously distributed in the continental lithosphere. Present data suggest that Cl-rich aqueous fluids were important metasomatic agents beneath the Ethiopian plateau, locally forming a source of high water content in the peridotite, which may be easily melted. High Cl, LILE, and Pb in metasomatic fluid phases suggest the contribution of recycled altered oceanic lithosphere component in their source.

Abstract The Neogene extensional province of southern Tuscany in central Italy provides an outstanding example of fossil and active structurally controlled fluid flow and epithermal ore mineralization associated with post-orogenic silicic magmatism. Characterization of the hydrodynamic regime leading to the genesis of the polysulphide deposit (known as Filone di Boccheggiano) hosted within the damage zone of the Boccheggiano Fault is a key target to assess modes of fossil hydrothermal fluid circulation in the region and, more generally, to provide inferences on fault-controlled hydrothermal fluid flow in extensional settings. We provide a detailed description of the fault zone architecture and alteration/mineralization associated with the Boccheggiano ore deposit and report the results of fluid inclusion and stable oxygen isotope studies. This investigation shows that the Boccheggiano ore consists of an adularia/illite-type epithermal deposit and that sulphide ore deposition was controlled by channelling of hydrothermal fluids of dominantly meteoric origin within the highly anisotropic permeability structure of the Boccheggiano Fault. The low permeability structure of the fault core compartmentalized the fluid outflow preventing substantial cross-fault flow, with focused fluid flow occurring at the hangingwall of the fault controlled by fracture permeability. Fluid inclusion characteristics indicate that ore minerals were deposited between 280° and 350°C in the upper levels of the brittle extending crust (lithostatic pressure in the order of 0.1 GPa). Abundant vapour-rich inclusions in ore-stage quartz are consistent with fluid immiscibility and boiling, and quartz ore vein textures suggest that mineralization in the Boccheggiano ore deposit occurred during cyclic fluid flow in a deformation regime regulated by transient and fluctuating fluid pressure conditions. Results from this study (i) predict a strongly anisotropic permeability structure of the fault damage zone during crustal extension, and (ii) indicate the rate of secondary (structural) permeability creation and maintenance by active deformation in the hangingwall of extensional faults as the major factor leading to effective hydraulic transmissivity in extensional terranes. These features intimately link ore-grade mineralization in extensional settings to telescoping of hydrothermal flow along the hangingwall block(s) of major extensional fault zones.

We describe the chemistry of the fluids circulating during skarn formation by focusing on fluids trapped in calcsilicate minerals of the inner thermal aureole of the Late Miocene Monte Capanne intrusion of western Elba Island (central Italy). Primary, CH4-dominant, C-O-H-S-salt fluid inclusions formed during prograde growth of the main skarn-forming mineral phases: grossular/andradite and vesuvianite. The variable phase ratios attest to heterogeneous entrapment of fluid, with co-entrapment of an immiscible hydrocarbon-brine mixture. Chemical elements driving skarn metasomatism such as Na, K, Ca, S and Cl, Fe and Mn were dominantly partitioned into the circulating fluid phase. The high salinity (apparent salinity between 58 and 70 wt% NaCl eq.) and the C-component of the fluids are interpreted as evidence for a composite origin of the skarn-forming fluids that involves both fluids derived from the crystallizing intrusion and contributions from metamorphic devolatilization. Oxidation of a Fe-rich brine in an environment dominated by fluctuation in pressure from lithostatic to hydrostatic conditions (maintained by active crack-sealing) contributed to skarn development. Fluid infiltration conformed to a geothermal gradient of about 100 degrees C km(-1), embracing the transition from high-temperature contact metamorphism and fluid-assisted skarn formation (at ca 600 degrees C) to a barren hydrothermal stage (at ca 200 degrees C).

Fluid–rock interaction was investigated in the inner aureole of the Late Miocene Monte Capanne pluton on Elba Island (Tuscany, central Italy) by integrating structural, petrological, fluid inclusion, and stable isotope analyses. In the north-western sector of the aureole (Procchio–Spartaia area), calc–silicates alternate with nearly pure carbonate layers at the metre scale. Close to the pluton, the prograde metamorphic sequence includes calc–silicates that transition within a few metres to overlying nearly pure calcite marbles. The calc–silicates are extensively metasomatised to form massive wollastonite-grossular-bearing exoskarn. The mineralogical assemblage found in the marbles and the unshifted carbon and oxygen isotopic ratios in calcite attest that the fluid phase was internally buffered. On the other hand, the calc–silicates constituted channels for infiltration of disequilibrium fluids of magmatic origin. Fluid infiltration was enhanced by hydrofracturing and structurally-controlled by existing planar anisotropies in calc–silicates (layering and lithological boundaries). At the metamorphic peak (∼600°C and 1.5–2 kbar), the marble–calc–silicate interface acted as a barrier to fluids exsolved from the crystallising intrusions, separating two different flow patterns in the inner aureole: a high fluid–flux region on its higher grade side (Wol-zone) and a low fluid–flux region on the lower-grade side (Cpx zone). Results of this study: (1) documented that fluid pathways in the aureole rocks at the top of the pluton were largely horizontal, controlled by the lithological layering and the pluton–host rock contact; and (2) elucidated the primary control exerted by the structural and rheological properties of the host rocks on the geometry of fluid flow during pluton emplacement.