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Wide areas of the Southern sector of Ecuador are characterized by Cretaceous mafic volcanic rocks, pervasively altered by a propylitic mineralogical assemblage with epidote, chlorite, and quartz with minor titanite, illite and prehnite. These propylitically altered rocks host significant gold mineralization in veins, deeply exploited in the last decades. Porphyry Au-Cu deposits also occur in the area. This work focuses on the study of this propylitic alteration to assess the genetic conditions and the relation with the distance from the porphyry system, through the chemical composition of the secondary minerals (particularly trace elements in epidote and chlorite) and fluid inclusion data. The aim is to improve knowledge of the trace element geochemistry of secondary minerals in propylitic alteration and their relationship to the causative porphyry systems. The results of this work indicate that alteration affecting the rocks of the Pallatanga Fm. can be related to the propylitic hydrothermal alteration halo of porphyry copper deposits. Fluid inclusion investigation in quartz veins associated with epidote and chlorite evidenced at least two pulses of hydrothermal fluids characterized by temperature around 345°C for the first one and around 305°C for the second one. The salinity of the fluids is always low (around 1.5 wt% NaClequiv.) suggesting a dominantly meteoric component. Evidence of boiling processes have not been observed. We hypothesize that the hydrothermally altered “green rocks” of the Ponce Enriquez Mining District could be envisaged as the propylitic halo of the Miocene hornblende-bearing Au-Cu porphyry deposits of Gaby-Papa Grande, and discuss the epidote and chlorite trace element composition in this scenario. The results help improving the general knowledge of the propylitically altered rocks in southern Ecuador and add new data for the use of trace element chemistry of epidote and chlorite in mineral exploration elsewhere.

The Mn-oxide mineralizations from Sardinia (Italy) represent examples of Mn deposits in a continental environment and, as such, their investigation can shed light on the genesis and characteristics of this deposit type, less studied than their more common oceanic counterpart. In this paper, the genetic mechanisms, the physical-chemical conditions and the origin of the mineralizing fluids are discussed for the volcanic-hosted Mn ores of the San Pietro Island (SW Sardinia), through an integrated geochemical, mineralogical and radiogenic isotope approach. New and published data are here examined on the basis of recent trace element discrimination schemes for Mn ores and a model for the genesis is proposed. The mineralogy of the alteration paragenesis (argillic facies) and the type of observed fluid inclusions (very small monophase liquid inclusions) suggest a circulation of mineralizing fluids characterized by weak acidic conditions (pH indicatively around 5) and relatively low temperature (<100–120 °C). Geochemical features such as the contents of transition metals (Mn, Fe, Cu, Co, Ni, Zn), and contents and ratios of rare-earth elements and yttrium (REY), suggest that the San Pietro Island Mn metallogenesis is the result of combined hydrothermal and hydrogenetic mechanisms of formation. The Pb isotope compositions of different Mn veins exhibit a significant spread that suggests the contribution of distinct mineralizing fluids, deriving their isotopic signature from both seawater and water-rock interaction processes. The possible model of formation of the San Pietro Mn mineralization can be viewed as a complex process, in which Mn-bearing fluids originated from remobilization of Mn oxides sequestered in shelf and slope sediments and/or from leaching of the older Cenozoic volcanic rocks that form the basement of the island. Fluid rise was due to hydrothermal convection, possibly related to the general thermal anomaly active in the area from 15 to 12 Ma, during the final stage of the intense Cenozoic volcanic activity of the Sulcis area (San Pietro, Sant'Antioco, Isola del Toro volcanic activity). The fluids were probably dominated by seawater, characterized by relatively low temperatures and acidic conditions, due to the input of H 2 S of hydrothermal origin. The Mn ore deposition occurred in relatively shallow water and oxidizing environment, following the pH neutralization induced by water-rock interaction processes. • We studied volcanic-hosted Mn-oxide ores of San Pietro Island (Italy) • An integrated geochemical, mineralogical and isotopic study was undertaken • We discuss San Pietro ores based on trace element discrimination schemes for Mn ores • The physical and chemical conditions of Mn transport and precipitation are assessed • A mixed low-T hydrothermal‑hydrogenetic model is proposed [ABSTRACT FROM AUTHOR]

The quartz-monzonitic intrusion of 'Botro ai Marmi' in Tuscany, Italy, can be considered to be a typical example of an intrusion-centred 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 post-magmatic 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 vapour aqueous phase, at a temperature ranging from ~500 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. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the development of an exhumed Sb-ore deposit associated with Neogene–Quaternary magmatism of southern Tuscany. This epithermal mineralization represents a fossil hydrothermal system that was probably active during the volcanic activity that produced rhyolitic lava flows (~2.3Ma), presently exposed close to the study area (Roccastrada volcanic complex). Volcanism was coeval with strike-/oblique-slip and normal faults that controlled the hydrothermal circulation. Faults were active until the Pleistocene. Our study, based on fluid inclusion and structural data, demonstrates that fluids were channeled in damage zones of the Pliocene–Quaternary strike-/oblique-slip and normal faults and permeated within damage zones of Middle–Late Miocene extensional detachments, consisting of fractured carbonate rock masses sandwiched between successions with very low permeability. Fluids produced a diffuse hydrothermal alteration both in the cataclasite and in carbonate damage zones where jasperoid strata bounds developed. Fluid inclusion investigation allowed tracing the evolution of the hydrothermal fluids that is interpreted in terms of a progressive cooling of the hydrothermal system. Such evolution could be related to large infiltration of shallow waters from the early mineralizing stage (fluids at about 200–225°C, salinity around 3wt.% NaClequiv.) down to the later post-ore stages, characterized by more diluted fluids (salinity of about 2.1wt.% NaClequiv) having lower temperatures (Th around 155°C). The latest hydrothermal activity in the area is indicated by fluid inclusions hosted in late calcite veins that are characterized by Th values of about 125°C. This fossil hydrothermal system may provide a close analog to the active geothermal systems occurring in southern Tuscany, thus the results are useful for better understanding the relationships between brittle structures and fluids migration. [Copyright &y& Elsevier]

Abstract: Fluid inclusions hosted in sanidine from xenoliths, representing the crystallization front of the AD 79 magma chamber of Vesuvius, offer a rare opportunity to track the composition of magmatic fluids exsolving at the peripheral part of a growing K-alkaline magma chamber disrupted by an explosive eruption. This work demonstrates that the exsolving magmatic fluids have a complex composition taking in evidence the great capability of metal transport by means of these solutions. Inclusions are particularly enriched in Zn, Mo, W, Sb, Bi, Tl and Pb. Metals display two different positive correlations: 1) Pb–Zn–Tl–Bi; 2) Mo–W. The different trends may reflect the different complexing agent for these elements (probably chloride for Pb–Zn–Tl–Bi and probably hydroxy for Mo–W). The occurrence of a “silicothermal” component in these fluids may furthermore favor the metal transport of these solutions. This is probably a major, previously underestimated process in the enrichment of some metals in magmatic–hydrothermal systems. This hypothesis may challenge conventional ideas on fluid-phase mass transport of components by means of magmatic–hydrothermal fluids, and should be taken into account in future works on these topics. [Copyright &y& Elsevier]

The thermal and compositional conditions of magma chambers constrain the type and complexity of their metasomatic aureoles. Fragments of these aureoles, disrupted during explosive eruptions of Vesuvius, provide quenched snapshots of interactions between potassic magmas and carbonate country rocks. Near the highly crystallized peripheral portions of the chambers, represented by magmatic xenoliths (fergusites, syenites and pyroxenites), skarn aureoles form. Open conduit reservoirs and the lower portions of plinian and subplinian eruption magma chambers develop aureoles controlled by diffusive metasomatism by high-T-modified silicate melts, generating magmatic skarn. In contrast, infiltrative metasomatism by magmatic fluids exsolved from crystallizing margins is responsible for endoskarn (magmatic protolith) and exoskarn (carbonate protolith) formation in the upper portions of plinian and subplinian eruption magma chambers. [ABSTRACT FROM AUTHOR]

This work is focused on juvenile components and some cognate xenoliths of the Breccia Museo (BM) unit. The BM is a coarse-grained proximal unit of the caldera-forming phase of the Ignimbrite Campana (IC) eruption, southern Italy. The BM products show some peculiar characteristics that distinguish them from the other IC deposits. In particular, different types of pumice fragments constitute the juvenile fraction and their crystal contents are remarkably higher than the other IC units. Slightly porphyritic and highly porphyritic trachytic to phonolitic pumices were distinguished in each sample and investigated separately for mineralogy, matrix glass composition, melt and fluid inclusion studies. Most feldspar crystals may have formed at the margins of the magma chamber and the crystal content of both types of pumice fragments can be ascribed to variable entrainment of these crystals (from the solidification front) by the melt. Variably porphyritic (<5 to 30 vol% phenocrysts) pumice and completely crystallized nodules may represent samples of progressively crystallized magma at the chamber walls. Crystallization temperatures of magmas and xenoliths were estimated using two independent methods: a two-feldspar geothermometer and the homogenization temperatures of melt and fluid inclusions in clinopyroxene and K-feldspar. The decrease in the estimated crystallization temperatures from the melt (980–850°C) to the nodules (840–820°C) is consistent with a model of decreasing temperature at a magma chamber solidification front. The study of xenoliths revealed that exsolution of a hypersaline aqueous fluid phase occurred at the peripheral parts of the magma chamber. [Copyright &y& Elsevier]

A shallow (∼2 km) granite body has been intersected by the MONT-4 well in new producing areas of the Larderello geothermal field. The granite at 2.2–2.5 km and below 3 km underwent pervasive propylitic alteration that is dominated by the assemblage chlorite+adularia+quartz+illite+calcite+albite±epidote±sphene. Fluid inclusion studies indicate two stages of alteration. The first one is characterised by high-temperature fluids that, at 2218 m, were trapped under boiling conditions at about 340°C and 15 MPa, whereas at 3520 m evidence of boiling is not revealed and the temperature of the fluid was calculated to be about 350°C. The second alteration stage shows a cooling of the system, particularly evident in the shallower portion of the intrusion (∼235°C at 2218 m and ∼315°C at 3520 m). The temperature of homogenisation for subsequent cooler inclusions approximates present-day down-hole temperatures, and may be considered as representative of the fluid actually circulating in the granite in recent times. Calculated δ18O values of 0±1‰, for fluids in equilibrium at 340°C (2218 m) and 350°C (3520 m) with feldspar, epidote and chlorite, and δD values of −51 to −61‰, for fluids in equilibrium with chlorite, together with directly measured δD values of −33 to −61‰ for fluid inclusions in quartz, indicate derivation from meteoric waters. The original meteoric signature of the fluids has been altered through water–rock interaction, but remains clearly distinguished from a primary magmatic signature, for which no isotopic evidence was found. Active fracturing and the high structural relief of granite emplacement promoted hydrothermal circulation in the granitic body drilled by MONT-4 well, suggesting that such characteristics may be a pre-requisite for such circulation at Larderello. [Copyright &y& Elsevier]

The mineralization potential of arc magmas depends, among other factors, on the timing of sulfide melt saturation relative to magma differentiation and to exsolution of a magmatic fluid phase. In fossil mineralized or barren systems, understanding the evolution of metals along the magma differentiation path is often hindered by late magmatic processes and hydrothermal alteration. To better understand the process of metal evolution "caught in the act" in crustal reservoirs, we analyzed magmatic sulfides and melt inclusions found within eruptive products from the active arc volcano, La Fossa (Vulcano Island, Italy), for the basalt to rhyolite compositional spectrum. We found that, in case of sulfide-undersaturated and volatile-rich arc basalts, metals are scarcely subtracted by degassing during ascent to shallow crustal reservoirs and reach the highest abundances in intermediate magmas (250 ppm Cu). At sulfide saturation the sulfide melt has 34–66 wt% Cu, leading to a dramatic decrease in chalcophile metals dissolved in the silicate melt. After fractionation of only 0.2–0.3 wt% of sulfide in the solid assemblage, the exsolved sulfide is a monosulfide solid solution (pyrrhotite) containing <3 wt% Cu. Metals that do not partition in sulfides (Pb, Zn) increase their concentrations during magmatic evolution until they are sequestered by a Cl-rich aqueous fluid phase exsolved at the rhyolitic stage. The absolute and Cu-normalized concentrations of metals in sulfide inclusions are similar to sulfide accessories in magmatic rocks associated with world-class porphyry Cu systems. Our results demonstrate that the mechanisms governing metal evolution inferred for the magmatic stage in porphyry Cu environments can be also tracked at an active arc volcano, using eruptive products as snapshots of the magmatic evolution. Arc volcanoes can thus be viewed as ideal active analogues when studying these crucial processes for the formation of porphyry Cu deposits. • We tracked metal evolution in the plumbing system of La Fossa active volcano. • Sulfide saturation is achieved in intermediate composition magmas. • Two types of Cu-bearing magmatic sulfides were identified. • Cu and Pb evolution during magmatic differentiation is modeled. • Metal evolution gives insights into the mineralizing potential of arc magmas. [ABSTRACT FROM AUTHOR]

• Trails of polyphase sulfosalt inclusions have been observed in quartz and baryte. • Sulfosalts are enriched in Low-Melting point Chalcophile Elements (LMCE). • Coexisting fluid inclusions gave homogenization temperature between 265 °C and 296 °C. • Textures and microthermometric data agree with the occurrence of sulfide melts. • Pyrite ore enriched in LMCE may be another kind capable of producing sulfide melts. Sulfide melting is increasingly recognized as an efficient ore remobilization process in several ore bodies deformed and metamorphosed under amphibolite to granulite facies conditions. Actually, sulfide melts may also occur at lower metamorphic conditions, provided the abundance of the so-called Low-Melting point Chalcophile Elements (LMCE). The Monte Arsiccio ore body (Apuan Alps, northern Tuscany, Italy) is strongly enriched in several LMCE, i. e., Ag, As, Hg, Pb, Sb, and Tl, and experienced greenschist facies metamorphism (T = 350–450 °C; P = 0.3–0.4 GPa) during the Alpine orogeny. Trails of polyphase sulfosalt inclusions (up to five phases), coexisting with fluid inclusions, were observed within quartz and baryte crystals found in late-stage veins. Sulfosalt assemblages are formed by LMCE-rich phases, the main being ferdowsiite, Ag 8 As 3 Sb 5 S 16 , chabournéite, Tl 2 Pb(Sb,As) 10 S 17 , and intermediate members of the arsiccioite/routhierite isotypic pair, (Ag 1 − x Cu x)Hg 2 TlAs 2 S 6 , along with minor realgar. Sulfosalt inclusions range between 200 nm and more than 100 µm in size, whereas larger inclusions, likely formed through the coalescence of smaller melt droplets, are up to 500 µm. Sulfosalt inclusions are associated with primary two-phase liquid-rich fluid inclusions (Type 1a), containing CO 2 and N 2 , as revealed by microthermometric investigations and micro-Raman spectroscopy. Secondary two-phase liquid-rich fluid inclusions (Type 1b) were also identified. Microthermometric measurements carried out on Type 1a fluid inclusions gave homogenization temperatures (T h) in the range 265–296 °C, whereas Type 1b fluid inclusions showed lower T h , between 222 and 246 °C. As microthermometric heating experiments on sulfosalt inclusions revealed homogenization temperatures around 270 °C, it is very likely that sulfosalt inclusions were in the liquid state during their entrapment, in agreement with many Tl-bearing systems. These results are fully consistent with the occurrence of LMCE-rich sulfide melt during the formation of the sulfosalt assemblages observed at the Monte Arsiccio mine. In addition, the polyphase nature of most of the observed sulfosalt inclusions may be related to the unquenchable nature of sulfide melts. The formation of LMCE-rich sulfosalt assemblages could be related to the release of these elements from pyrite during its metamorphic recrystallization. Consequently, pyrite ores may produce sulfide melts, with potential implications in the change of speciation of LMCE, from trace to major elements. [ABSTRACT FROM AUTHOR]