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Liancheng is an important Cu–Mo deposit hosted by red-beds in the Mesozoic to Cenozoic Lanping Basin located in the Sanjiang Tethyan Orogen of SW China. The deposit is fault controlled where it has been affected and enriched by four hydrothermal events indicated by four distinct sets of veins and their cross-cutting relationships. A detailed Cu–S–H–O isotopic study is reported here on the mineralization focusing on the source of the metals and fluid, and on the mineralizing processes. The first two hydrothermal events are characterised by CO 2 and fluid-rich inclusions with homogenisation temperatures of 124–446 °C and salinities ranging from 0.4 to 24.6 wt% NaCl equiv. The next two hydrothermal events are characterised by liquid–rich fluid inclusions that homogenise at 145–256 °C, with salinities ranging from 1.4 to 22.9 wt% NaCl equiv. The H–O isotope values obtain from the fluid inclusions indicate that the first three hydrothermal events relate to mineralizing fluids derived from a metamorphic source, but the last event includes a mixed metamorphic and meteoric source. Chalcopyrite, tennantite, and bornite from the deposit have δ 34 S values between  −11.5 and 3‰. The δ 65 Cu values for quartz-Cu sulfide mineralization associated with the second hydrothermal event range from −0.31 to 0.2‰, but carbonate-Cu sulfide mineralization associated with the third hydrothermal event ranges from −1.01 to −1.08‰. The combination of the Cu and S isotopic values and field observations indicate that the controlling factors include structures, the temperature of regional metamorphism, and the pH of the mineralizing fluid. The zation is, therefore, characteristic of an orogenic-type deposit. [ABSTRACT FROM AUTHOR]

The chemical evolution of fluids in Alpine fissure veins (open cavities with large free-standing crystals) has been studied by combination of fluid inclusion petrography, microthermometry, LA- ICPMS microanalysis, and thermodynamic modeling. The quartz vein systems cover a metamorphic cross section through the Central Alps (Switzerland), ranging from subgreenschist- to amphibolite-facies conditions. Fluid compositions change from aqueous inclusions in subgreenschist- and greenschist-facies rocks to aqueous-carbonic inclusions in amphibolite-facies rocks. The fluid composition is constant for each vein, across several fluid inclusion generations that record the growth history of the quartz crystals. Chemical solute geothermometry, fluid inclusion isochores, and constraints from fluid-mineral equilibria modeling were used to reconstruct the pressure-temperature conditions of the Alpine fissure veins and to compare them with the metamorphic path of their host rocks. The data demonstrate that fluids in the Aar massif were trapped close to the metamorphic peak whereas the fluids in the Penninic nappes record early cooling, consistent with retrograde alteration. The good agreement between the fluid-mineral equilibria modeling and observed fluid compositions and host-rock mineralogy suggests that the fluid inclusions were entrapped under rock-buffered conditions. The molar Cl/Br ratios of the fluid inclusions are below the seawater value and would require unrealistically high degrees of evaporation and subsequent dilution if they were derived from seawater. The halogen data may thus be better explained by interaction between metamorphic fluids and organic matter or graphite in metasedimentary rocks. The volatile content ( CO2, sulfur) in the fluid inclusions increases systematically as function of the metamorphic grade, suggesting that the fluids have been produced by prograde devolatilization reactions. Only the fluids in the highest grade rocks were partly modified by retrograde fluid-rock interactions, and all major element compositions reflect equilibration with the local host rocks during the earliest stages of postmetamorphic uplift. [ABSTRACT FROM AUTHOR]

The Wulasigou Cu-Pb-Zn deposit, located 15km northwest of Altay city in Xinjiang, is one of many Cu-Pb-Zn polymetallic deposits in the Devonian Kelan volcanic-sedimentary basin in southern Altaids. Two mineralizing periods can be distinguished: the marine volcanic sedimentary Pb-Zn mineralization period, and the metamorphic hydrothermal Cu mineralization period, which is further divided into an early bedded foliated quartz vein stage (Q1) and a late sulfide-quartz vein stage (Q2) crosscutting the foliation. Four types of fluid inclusions were recognized in the Q1 and Q2 quartz from the east orebodies of the Wulasigou deposit: H2O-CO2 inclusions, carbonic fluid inclusions, aqueous fluid inclusions, and daughter mineral-bearing fluid inclusions. Microthermometric studies show that solid CO2 melting temperatures ( Tm,co2) of H2O-CO2 inclusions in Q1 are from −62.3°C to −58.5°C, clathrate melting temperatures ( Tm,clath) are from 0.5°C to 7.5°C, partial homogenization temperatures ( Th,co2) vary from 3.3°C to 25.9°C (to liquid), and the total homogenization temperatures ( Th,tot) vary from 285°C to 378°C, with the salinities being 4.9%-15.1% NaCl eqv. and the CO2-phase densities being 0.50-0.86 g/cm3. H2O-CO2 inclusions in Q2 have Tm,c02 from −61.9°C to −56.9°C, Tm,clath from 1.3°C to 9.5°C, Th,co2 from 3.4°C to 28.7°C (to liquid), and Th,tot from 242°C to 388°C, with the salinities being 1.0%-15.5% NaCl eqv. and the CO2-phase densities being 0.48-0.89 g/cm3. The minimum trapping pressures of fluid inclusions in Q1 and Q2 are estimated to be 260-360 MPa and 180-370 MPa, respectively. The δ34S values of pyrite from the volcanic sedimentary period vary from 2.3‰ to 2.8‰ (CDT), and those from the sulfide-quartz veins fall in a narrow range of −1.9‰ to 2.6‰ (CDT). The δD values of fluid inclusions in Q2 range from −121.0‰ to −100.8‰ (SMOW), and the δ18OH2O values calculated from δ18O of quartz range from −0.2‰ to 8.3‰ (SMOW). The δD- δ18OH2O data are close to the magmatic and metamorphic fields. The fluid inclusion and stable isotope data documented in this study indicate that the vein-type copper mineralization in the Wulasigou Pb-Zn-Cu deposit took place in an orogenic-metamorphic enviroment. [ABSTRACT FROM AUTHOR]

The Lamego orogenic gold deposit (440,742 oz gold measured reserves and 2.4 million t measured resources, with an average grade of 5.71 g/t Au and a cut-off grade of 2.15 g/t Au; AngloGold Ashanti Córrego do Sítio Mineração S/A (AGA) personal communication, 2014) is located in the 5 km-long trend that includes the world-class Cuiabá deposit. It is hosted in the Neoarchean metavolcano–sedimentary rocks of the Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Brazil. Mineralization is associated mainly with metachert–banded iron formation (BIF) and carbonaceous phyllites in the reclined Lamego fold, in which the Cabeça de Pedra orebody represents the hinge zone. Mineralization is concentrated in silicification zones and their quartz veins, as well as in sulfide minerals, product of BIF sulfidation. Hydrothermal alteration varies according to host rock, with abundant sulfide–carbonate in BIF, and sericite–chlorite in carbonaceous phyllite. Quartz vein classification according to structural relationships and host rocks identified three vein systems. The V1 system, mainly composed of smoky quartz (Qtz I) and pyrite, is extensional, crosscuts the bedding plane S 0 of BIF, and is parallel to the fold axis. The V2 system, of the same composition, is represented by veins that are parallel to the S 1–2 foliation and S 0 . This system is also characterized by silicification zones in the BIF–carbonaceous phyllite contact that has its maximum expression in the hinge zone of folds. The V3 system has milky quartz (Qtz II) veins, which result from the recrystallization of smoky quartz, located mainly in shear zones and faults; these veins form structures en echelon and vein arrays. The most common ore minerals are pyrite, As-pyrite and arsenopyrite. Fluid inclusion-FI trapped in all quartz veins present composition in the H 2 O–CO 2 ± CH 4 –NaCl system. Fluid evolution can be interpreted in two stages: i) aqueous–carbonic fluid trapped in Qtz I, of low salinity (~ 2% equiv. wt.% NaCl), and ii) carbonic–aqueous fluid, of moderate salinity (average 9 eq. wt.% NaCl) hosted in Qtz II. Both stages are characterized by decrepitation temperatures in the range of 200 to > 300 °C, and suggest a fluid of metamorphic origin. Applying an arsenopyrite geothermometer, the calculated formation temperature for the Cabeça de Pedra orebody is 300 to 375 °C. The vertical intersection of the isochors allows a minimum pressure calculation of 2.6 kbar. The composition of individual FIs of this orebody, obtained by LA-ICP-MS analyses, compared with results of FIs for the Carvoaria Velha deposit, Córrego do Sítio lineament, highlights a standard composition typical of metamorphic fluids with Na > K > Ca > Mg, which increase or decrease in concentration as a function of salinity in both deposits. Trace elements vary according to fluid–rock reactions, and are directly related to the host rock composition. The comparison of data sets of the two deposits shows that the Cabeça de Pedra FIs have a higher enrichment in Zn, while Cu, As and Sb are richer in Carvoaria Velha, suggesting influence of the host rock geochemistry. The suggested mechanisms for gold precipitation at the Cabeça de Pedra orebody, Lamego gold deposit are: i) hydrolysis of the carbonaceous matter of phyllite and BIF, affecting f O 2 , destabilizing sulfur complexes and enhancing gold precipitation; ii) replacement of BIF iron carbonates by sulfides; and iii) continuous pressure changes that lead to silica precipitation and free gold. Other than playing the long-recognized role of the carbonaceous phyllites as a fluid barrier, the data highlight their importance as a source of metals. [ABSTRACT FROM AUTHOR]

Available fluid inclusion data on hydrothermal deposits, deep-seated xenoliths, magmatic and metamorphic rocks were used to generalize the determinations of physicochemical parameters (temperature, pressure, and compositions) of natural fluids. It was established that fluid pressures during formation of hydrothermal deposits often exceeded lithostatic loading (250-270 bar/km) of the overlying rocks. Fluids from deep-seated xenoliths, magmatic and metamorphic objects are considered as the possible sources of high-pressure fluids. Data on temperatures, pressures, and fluid composition are generalized for each object. [ABSTRACT FROM AUTHOR]

Vein and shear-zone hosted gold deposits in orogenic terrains of Archean to Phanerozoic age are formed from dominantly metamorphic fluids. It is debated, however, whether normal crustal source rocks are adequate to generate economic deposits, or whether selectively gold-enriched sources such as mafic to ultramafic lavas, black shales or an input of magmatic fluid make a decisive difference between the formation of high-grade deposits and barren vein systems. As an essential baseline study in this debate, we have analyzed the metal and sulfur content of fluid inclusions in barren veins across a prograde sequence from greenschist to amphibolite facies in the Central Alpine metamorphic belt. Comparison of the analyzed fluid compositions with thermodynamic solubility calculations shows that the fluids record metamorphic dehydration, decarbonation and desulfidation of the continental crust. However, gold with concentrations of 0.003 to 0.03 ppm is increasingly undersaturated in the highest-temperature aqueous–carbonic fluids, which otherwise resemble those forming major gold deposits elsewhere. Our results show that the regional-metamorphic fluids could carry 10–1000 times higher gold concentrations, implying that pre-enriched source rocks or hydrous magmas may play an essential role in generating highly gold-endowed orogenic belts. [ABSTRACT FROM AUTHOR]

The fluid evolution of late-metamorphic quartz vein systems in the fold-and-thrust belt of the Rhenish Massif has been studied by microthermometry and LA-ICPMS microanalysis. The quartz veins are hosted by very low-grade organic-matter-rich metasiltstones and metapelites of the Hunsrück nappe complex. The veins record two major stages of textural evolution, a massive vein filling assemblage with elongate-blocky quartz, chlorite, albite and apatite, and a later open space filling assemblage with euhedral crystals of quartz, ankerite/dolomite and minor calcite and sulfides. The euhedral quartz crystals host well-preserved fluid inclusion assemblages, which made it possible to reconstruct the chemical evolution of the fluid system with time. The fluid inclusions are all aqueous two-phase with low salinity, and three successive fluid generations record a systematic decrease in salinity from 4.7–5.3 to 3.1–3.9 and then to 1.4–1.7wt.% eqv. NaCl. The salinity decrease is paralleled by a decrease in homogenization temperatures from 210–225°C to 148–164°C and 124–139°C. Using LA-ICPMS microanalysis of individual fluid inclusions, reproducible elemental concentrations of Li, Na, K, Rb, Cs, Mg, Ca, Ba, Sr, B, Al, As, Sb, S, Cl and Br could be determined. The concentrations of the alkali metals and of boron, arsenic and antimony are correlated with the fluid salinity. Element concentrations are highest in the early fluid generation and decrease systematically in the latter two generations. The systematic changes in fluid composition (salinity, homogenization temperature and elemental concentrations) are best explained by fluid mixing between a hot metamorphic fluid of moderate salinity (that carried elevated concentrations of B, As and Sb) and a cooler dilute fluid that was of meteoric origin. The fluid evolution therefore signals deep ingression of meteoric water during late-metamorphic exhumation and uplift. The molar Cl/Br ratios of the fluid inclusions lie on a linear array that extends from close to seawater to values that are substantially below seawater. Because evaporitic sources are conspicuously absent in the shallow-water marine sequence of the Rhenish Massif, the elevated Br concentrations (and Cl/Br ratios below seawater) are best explained by fluid–rock interaction and liberation of Br from the organic matter in the metasediments. [ABSTRACT FROM AUTHOR]

The Tharsis massive sulphide deposit, one of the major VMS-type deposits in the Iberian pyrite belt (IPB) was severely deformed by the Variscan tectono-thermal events. The question of whether or not these events affected the metal distribution in the deposit has been addressed by simultaneously studying the mineral parageneses (Tharsis stockwork) and the fluid circulation (at local and regional scales). The results are:(1)The early paragenesis in the stockwork (Q1 quartz–pyrite–chlorite–phengite±cobaltite±ankerite) was strongly overprinted by a late post-kinematic mineral deposition, including new quartz veins (Q3 quartz) and base metal sulphides (chalcopyrite, sphalerite, Bi and Te minerals, pyrite and galena) and gold.(2)At a regional scale, fluids accompanying the peak metamorphism conditions (ca. 300 MPa, ca. 300 °C) were of C–O–H–N–NaCl type, CO2-dominated with CH4 and N2, and are considered to be “metamorphic” on the basis of microthermometry and geochemistry. The late- to post-kinematic evolution (“retrograde” stage) was characterised by a pressure drop, down to 40 MPa (lithostatic to hydrostatic transition), and a heat input leading to temperatures ≥430 °C, then decreasing to temperature around 170 °C. Fluids of the “retrograde” type exhibit both dilution of the C–O–H–N–NaCl fluid by a low salinity “meteoric” water and progressive loss of volatile components.(3)Fluids of the retrograde type pervasively percolated through the Tharsis stockwork and were responsible for the strong mineral overprint on the early (deformed) paragenesis. All the measurable fluid inclusions (f.i.) record these late fluids. There are primary fluid inclusions in Q1, but they are systematically imploded due to the external overpressure generated by the Variscan tectonic events. Although base metal distribution in the stockwork is basically the result of the “retrograde” fluid circulation, it remains unclear whether these metals were newly introduced into the stockwork from elsewhere or simply redistributed from the existing primary assemblages in the massive sulphide bodies. [Copyright &y& Elsevier]

Fluid inclusion salinities from quartz veins in the Otago Schist, New Zealand, range from 1.0 to 7.3 wt% NaCl eq. in the Torlesse terrane, and from 0.4 to 3.1 wt% NaCl eq. in the Caples terrane. Homogenization temperatures from these inclusions range from 124 to 350 °C, with modal values for individual samples ranging from 163 to 229 °C, but coexisting, low-salinity inclusions exhibiting metastable ice melting show a narrower range of T h from 86 to 170 °C with modes from 116 to 141 °C. These data have been used in conjunction with chlorite chemistry to suggest trapping conditions of ≈350–400 °C and 4.1–6.0 kbar for inclusions showing metastable melting from lower greenschist facies rocks, with the densities of many other inclusions reset at lower pressures during exhumation of the schist. The fluid inclusion salinities and Br/Cl ratios from veins from the Torlesse terrane are comparable to those of modern sea-water, and this suggests direct derivation of the vein fluid from the original sedimentary pore fluid. Some modification of the fluid may have taken place as a result of interaction with halogen-bearing minerals and dehydration and hydration reactions. The salinity of fluids in the Caples terrane is uniformly lower than that of modern sea-water, and this is interpreted as a result of the dilution of the pore fluid by dehydration of clays and zeolites. The contrast between the two terranes may be a result of the original sedimentary provenance, as the Torlesse terrane consists mainly of quartzofeldspathic sediments, whilst the Caples terrane consists of andesitic volcanogenic sediments and metabasites which are more prone to hydration during diagenesis, and hence may provide more fluid via dehydration at higher grades. [ABSTRACT FROM AUTHOR]

[Display omitted] • The metamorphic fluids in Ailaoshan orogenic belt belong to medium temperature, low salinity and low density NaCl-CO 2 -H 2 O system with high CO 2 , Ca2+ and Mg2+ content. • The ore forming fluids of orogenic gold deposits belong to lower temperature, medium salinity and medium density NaCl-H 2 O-CO 2 system with low CO 2 content and high K+. • Combined with the distinct distributions of δ34S and δ18O H2O values between the two kinds of fluids, the ore forming fluids in Ailaoshan orogenic belt cannot be evolved from regional metamorphism. The source of ore-forming fluids for orogenic gold deposits is still disputed with models ranging from derivation from metamorphism of continental crust to derivation from metasomatized mantle lithosphere. This dispute is addressed by this study of the Ailaoshan orogenic gold belt, southeastern Tibet, whose evolution involved intense metamorphism on the eastern side of the Ailaoshan shear zone. Both the regional metamorphic barren quartz veins and gold-related quartz veins in this belt are genetically related to movement on the Ailaoshan shear zone and thus formed over the same limited age span. Microthermometry, fluid compositions and stable isotope analyses conducted on both metamorphic fluids extracted from regional metamorphic quartz veins and ore-forming fluids collected from auriferous quartz veins at Zhenyuan and Jinchang gold deposits reveal significant differences. These include: (1) regional metamorphic quartz veins contain three types of fluid inclusions, including CO 2 -rich, aqueous-CO 2 and aqueous types. The CO 2 -bearing inclusion types are more abundant than those in auriferous quartz veins; (2) those fluids from barren metamorphic veins with high CO 2 content (up to 45 mol%) are typified by low-medium temperature (217–418 °C), low salinity (2–8 wt% NaCl) and variable pressure (28–440 MPa), and belong to the NaCl-CO 2 -H 2 O system. In contrast, the ore-forming fluids, which exhibit lower temperature (mainly 170–270 °C), higher salinity (mainly 5–13 wt% NaCl), and lower pressure (20–282 MPa and 14–44 MPa for Zhenyuan and Jinchang, respectively), belong to the NaCl-H 2 O-CO 2 system; (3) the metamorphic fluids contain high Ca2+ and Mg2+ in liquids and CO 2 , N 2 and CO in gases, whereas the ore-forming fluids are enriched in K+ in liquid and H 2 O, CO 2 , CH 4 in gases; (4) the pyrites from regional metamorphic quartz veins have δ34S values ranging from 2.08 to 2.86‰ (mean = 2.50‰), indicating a single sulfur source of metamorphic fluids, thus contrasting with the broad range of δ34S values of ore sulfides. These distinctions negate a genetic relationship between crustal metamorphism and gold mineralization and demonstrate that ore-fluids that deposit orogenic gold deposits, at least in the Ailaoshan belt cannot be derived or evolved from crustally-derived regional metamorphic fluids. This provides a new line of evidence for the derivation of ore-forming fluids from a sub-crustal, metasomatized mantle lithosphere source for at least some orogenic gold deposits. [ABSTRACT FROM AUTHOR]

• Earliest W-stage Fluid inclusions (FI) at Panasqueira are deformed and destroyed. • Preserved fluids found in the topaz are dense H 2 O-CO 2 FI and dense CO 2 FI. • P-T pair is 500 ± 20 °C and 250 ± 20 MPa, consistent with deep levels at 8–10 km depth. • Genesis of volatile-rich fluids is linked to deep-seated fluid-graphite interaction. • High gradients (60 °C/km−1) are related either to magma pulse or migmatitic levels. The Variscan vein-type Panasqueira W-Sn(Cu) deposit, one of the main tungsten deposits in Western Europe, has a long and complicated geological history. The first vein infillings, which consist of the quartz-wolframite association as well as the first generation of topaz, underwent significant deformation. As a consequence, most fluid inclusions of the earliest hydrothermal event are deformed and destroyed. Two preserved fluid inclusion assemblages are, however, found in the topaz overgrowth band and are dense aqueous-carbonic inclusions as well as dense CO 2 dominated fluid inclusions. The P-T conditions of fluid trapping are constrained by using the intersection between isochores, as well as graphite-water equilibrium data and yield the following trapping conditions: 500 ± 20 °C and 250 ± 20 MPa. These P-T conditions are incompatible with fluid unmixing. Fluid chemistry results from water-graphite equilibrium, probably in metapelites, at two distinct temperatures: around 450–500 °C for the predominant aqueous-carbonic fluid, and higher temperatures of maximal 550 °C for the CO 2 -rich fluid enriched in N 2. These P-T estimates are consistent with deep crustal levels around 8–10 km depth and a high geothermal gradient around c. 60 °C/km−1. The ascending non-magmatic fluids, enriched in volatiles, are essential in the ore genesis. The high thermal gradients may be related either to new magma pulse after the formation of the Panasqueira granite intrusion or to anomalous heat flux produced by the hot fluids ascending from migmatitic levels present at greater depth. This hypothesis necessitates to consider the role of a crustal weakness, which is attested both by the successive intrusions of several granitic magmas at the same place, and the presence of inherited quartz filled structures so-called Seixo-Bravo found only in the Panasqueira area. [ABSTRACT FROM AUTHOR]