Fluid Composition, δD of Channel H2O,and δ18O of Lattice Oxygen in Beryls: Genetic Implications for Brazilian,Colombian, and Afghanistani Emerald Deposits

The fluid composition, δD of channel H₂O, and δ₁₈O of lattice oxygen have been determined in beryl and emerald from a variety of geological environments and used to constrain the origin of the parental fluids from which beryl has grown. Step-heating analyses performed by quadrupolar mass spectrometry were used to quantify the composition of the fluid phases in beryl from granitic pegmatites and greisens and emerald from Brazil, Colombia, and Afghanistan. An important conclusion is that beryl and emerald have a similar fluid composition, with concentrations of H₂O being greater than 90% of the total water in the mineral irrespective of the age of formation (2.0 Ga to 32 Ma) and tectonic settings. However, the Brazilian Santa Terezinha shear-zone emerald deposit contains abundant CO₂, up to 13 wt% of the total fluid. A second conclusion is that the channel H₂O content for some Brazilian emeralds is higher than the range defined for beryl in the literature, especially for those related to the shear-zone type (2.99 lt; H₂O < 3.16 wt%) and the pegmatite type from the Pombos, Pela Ema, and Pirenopolis deposits (2.78 < H₂O < 3.01 wt%). Colombian emeralds have very low H₂O contents (1.30 < H₂O < 1.96 wt%), among the lowest in the world.

Brazilian, Colombian, and Afghanistani emeralds have contrasting and restricted ranges of δ¹⁸O values. In Brazil, emeralds related to pegmatites have a systematic δ¹⁸O inter-deposit variability (+6.3 < δ¹⁸O < +12.4‰). The calculated δ¹⁸O of the fluid was buffered by the host ultrabasic rocks during fluid-rock interaction. Emerald and cogenetic phlogopite related to shear-zone-type deposits have a quite restricted δ¹⁸O range (+12.0 < δ¹⁸O 7lt; +12.4‰); the calculated is interpreted to represent the original isotopic composition of the hydrothermal fluid. Relative to Brazil, the δ¹⁸O of Colombian and Afghanistani emeralds shows strong enrichment in ¹⁸O (+13.4 < δ¹⁸O < +23.6‰), and the high calculated δ¹⁸O of the fluid suggests extensive reaction with 18O-rich sedimentary or metasedimentary rocks.

In Brazil, the δD composition of channels in emerald and the calculated δ¹⁸O^H₂O for phlogopite are compatible with both magmatic and metamorphic origins. A magmatic origin is supported for emeralds associated with the pegmatitic Socotó and Carnaiba deposits (mean δD = ?37.8 ± 8‰) and a metamorphic origin is suggested for the Santa Terezinha shear-zone type (mean δD = ?32.4 ± 3‰). A metamorphic origin is proposed for Colombian emeralds. Afghanistani emeralds have a δD composition of channels (mean δD = ?46.3 ± 1.3‰) that is compatible with both magmatic and metamorphic origins.     

Formation of tonalite in island arcs by seawater-induced anatexis of mafic rocks; evidence from the Lyngen Magmatic Complex, North Norwegian Caledonides

The Lyngen Magmatic Complex (LMC) of North Norway, consists of a western suite of layered gabbros of normal-mid oceanic ridge basalt (N-MORB) affinity and an eastern suite of layered gabbronorites, quartz-bearing gabbros and diorites/quartz-diorites of IAT (island-arc tholeiitte) to boninitic affinity. The boundary between the suites is defined by a large-scale ductile shear zone, the Rypdalen shear zone (RSZ). In this shear zone anatectic tonalites were generated by partial melting of the gabbro in the presence of an H₂O bearing fluid phase.Quartz from the tonalites contains early secondary and secondary liquid-dominated inclusions (88-99 wt.% H₂O), with an average salinity of 18 wt.% (calculated as NaCl_eq). Combined gas and ion chromatography shows that the major ions in the fluid are Cl⁻, Ca²⁺, Na⁺ with smaller amounts of K⁺, Mg²⁺, Sr²⁺, Br⁻ and NO₃⁻. The dominant non-H₂O volatile species is N₂ (0.5-10%), and small amounts of CO₂, CH₄ and other hydrocarbons are also present.The cation concentrations in the fluid are variable, due to element exchange during interaction of the fluids with the tonalites, amphibolites and metagabbros of the RSZ. The fluid contributed Na⁺ and K⁺ to the melt and gained Ca²⁺ in exchange, explaining the variable Na⁺/Ca²⁺ ratio of the fluid. The Br⁻ and Cl⁻ contents of the fluid inclusions plot on the same line as evaporating sea water, which strongly suggests a seawater origin for the fluid phase, and a seawater source fits well with other geochemical signatures and the tectonic setting of the LMC.It is suggested that seawater escaped from a subducting slab and was channelled along the Rypdalen shear zone. This caused anatexis of the gabbro, generating tonalitic melts at 0.5-0.9 GPa and 680-800°C.     

Microthermometrical and chemical studies of fluid inclusions in minerals from Alpine veins from the penninic rocks of the central and western Tauern Window (Austria/Italy)

The fluid inclusions in samples of quartz, apatite, epidote, diopside, beryl and phenakite from Alpine veins in gneisses, amphibolites and mica schists from the western Tauern Window were analysed by microthermometrical, chemical and neutron activation methods. The inclusions of the eclogites contain a high density CO₂ phase without optically detectable H₂. In the Greiner Schieferserie the fluid inclusions show high CO₂/H₂O ratios and low salt contents. In the Zentralgneis area inclusions with low CO₂/H₂O ratios and high salt contents are typical. In the calcareous mica schists of the lower Schieferhülle, in the eastern part of the investigated area, generally no CO₂ could be detected in the inclusions. These inclusions contain aqueous solutions showing a low salt content. The only CO₂ bearing inclusions observed here were in the graphite-rich rocks of the so-called Habachzungen and in the eclogites from south of the Großvenediger. Trapping pressures estimated from the fluid inclusions are up to 7.5 kbar in the eclogites, but in general the pressures are between 2 and 4 kbar. These pressure data are in good agreement with the pressure data of mineral equilibria. The chemically analysed elements in the fluid inclusions are Na, K, Cs, Mg, Ca, Mn, As, Cl and Br. From the K/Na ratios temperatures between 435 and 490°C can be deduced. The very low Cl/Br ratios (<110) suggest that the dissolved elements came from the country rocks. The alkali/chlorine ratios (～1) indicate that the positive loadings of the cations are balanced by Cl.     

Geochemistry and fluid inclusions study of highly fractionated garnet-bearing granite of Gabal Abu Diab, central Eastern Desert of Egypt

The Neoproterozoic granite of Gabal Abu Diab, central Eastern Desert of Egypt, comprises mainly garnet-bearing granite and alkali feldspar granite intruded into calc-alkaline granodiorite–tonalite and metagabbro–diorite complexes. The garnet-bearing granite is composed mainly of plagioclase, K-feldspar, quartz, garnet and primary muscovite ± biotite. The presence of garnet and primary muscovite of Abu-Diab granite suggests its highly fractionated character. Geochemically, the garnet-bearing granite is highly fractionated as indicated from the high contents of SiO₂ (74.85–77.5%), alkalis (8.27 to 9.2%, Na₂O+K₂O) and the trace elements association: Ga, Zn, Zr, Nb and Y. This granite is depleted in CaO, MgO, P₂O₅, Sr and Ba. The alumina saturation (Shand Index, molar ratio A/CNK) of 1.0 to 1.1 indicates the weak peraluminous nature of this garnet-bearing granite. The geochemical characteristics of the Abu Diab garnet-bearing granite are consistent with either the average I-type or A-type granite and also suggest post-orogenic or anorogenic setting. A fluid inclusions study reveals the presence of three fluid generations trapped into the studied granite. The earlier is a complex CO₂–H₂O fluid trapped in primary fluid inclusions with CO₂ contents >?60 vol.%. These inclusions were probably trapped at minimum temperature >?400°C and minimum pressure >?2 kb. The second is immiscible water–CO₂ fluid trapped in secondary and/or pseudo-secondary inclusions. The trapping conditions were estimated at temperature between 400°C and 170°C and pressure between 900 and 2000 bar. The latest fluid is low-salinity aqueous fluid trapped in secondary two-phase and mono-phase inclusions. The trapping conditions were estimated at temperature between 90°C and 160°C and pressure <?900 bar. The origin of the early fluid generation is magmatic fluid while the second and third fluids are of hydrothermal and meteoric origin, respectively.     

Compositions of magmatic melts and evolution of mineral-forming fluids in the banska Stiavnica epithermal Au-Ag-Pb-Zn deposit, Slovakia: A study of inclusions in minerals

Melt and fluid inclusions were investigated in minerals from igneous rocks and ore (Au-Ag-Pb-Zn) veins of the Stiavnica ore field in Central Slovakia. High H₂O (7.1–12.0 wt %) and Cl (0.32–0.46 wt %) contents were found in silicate melt inclusions (65–69 wt % SiO₂ and 5.2–5.6 wt % K₂O) in plagioclase phenocrysts (An 68–36) from biotite-homblende andesites of the eastern part of the caldera. Similar high water contents are characteristic of magmatic melts (71–76 wt % SiO₂ and 3.7–5.1 wt % K₂O) forming the sanidine rhyolites of the Vyhne extrusive dome in the northwestern part of the Stiavnica caldera (up to 7.1 wt %) and the rhyolites of the Klotilda dike in the eastern part of the ore field (up to 11.5 wt %). The examination of primary inclusions in quartz and sanidine from the Vyhne rhyolites revealed high concentrations of N₂ and CO₂ in magmatic fluid (8.6 g/kg H₂O and 59 g/kg H₂O, respectively). Fluid pressure was estimated as 5.0 kbar on the basis of primary CO₂ fluid inclusions in plagioclase phenocrysts from the Kalvari basanites. This value corresponds to a depth of 18 km and may be indicative of a deep CO₂ source. Quartz from the granodiorites of the central part of the Stiavnica-Hodrusa complex crystallized from a melt with 4.2–6.1 wt % H₂O and 0.24–0.80 wt % Cl. Magmatic fluid cogenetic with this silicate melt was represented by a chloride brine with a salinity of no less than 77–80 wt % NaCl equiv. Secondary inclusions in quartz of the igneous rocks recorded a continuous trend of temperature, pressure, and solution salinity, from the parameters of magmatic fluids to the conditions of formation of ore veins. The gold mineralization of the Svyatozar vein system was formed from boiling low-salinity fluids (0.3–8.0 wt % NaCl equv.) at temperatures of 365–160°C and pressures of 160–60 bar. The Terezia, Bieber, Viliam, Spitaler, and Rozalia epithermal gold-silver-base metal veins were also formed from heterogeneous low-salinity fluids (0.3–12.1 wt %) at temperatures of 380–58°C and pressures of 240–10 bar. It was found that the salt components of the solutions were dominated by chlorides (high content of fluorine, up to 0.45 mol/kg H₂O, was also detected), and sulfate solutions appeared in the upper levels. The dissolved gas of ore-forming solutions was dominated by CO₂ (0.1–8.4 mol %, averaging 1.3 wt %) and contained minor nitrogen (0.00–0.85 mol %, averaging 0.05 mol %) and negligible methane admixtures (0.00–0.05 mol %, averaging 0.004 mol %). These data allowed us to conclude that the magmatic melts could be sources of H₂O, Cl, CO₂, and N₂. The formation of the epithermal mineralization of the Stiavnica ore field was associated with the mixing of magmatic fluid with low-concentration meteoric waters, and the fluid was in a heterogeneous state.     

Fluid inclusion and stable isotope evidence for the genesis of quartz-scheelite veins, Metaggitsi area, central Chalkidiki Peninsula, N. Greece

Scheelite mineralization accompanied by muscovite and albite, and traces of Mo-stolzite and stolzite occurs in epigenetic quartz vein systems hosted by two-mica gneissic schists, and locally amphibolites, of the Paleozoic or older Vertiskos Formation, in the Metaggitsi area, central Chalkidiki, N Greece. Three types of primary fluid inclusions coexist in quartz and scheelite: type 1, the most abundant, consists of mixed H₂O-CO₂ inclusions with highly variable (20–90 vol.%) CO₂ contents and salinities between 0.2 and 8.3 equivalent weight % NaCl. Densities range from 0.79 to 0.99 g/cc; type 1 inclusions contain also traces (<2 mol%) of CH₄. Type 2 inclusions are nearly 100 vol.% liquid CO_2, with traces of CH₄, and densities between 0.75 and 0.88 g/cc. Type 3 inclusions, the least abundant, contain an aqueous liquid of low salinity (0.5 to 8.5 equivalent weight% NaCl) with 10–30 vol.% H₂O gas infrequently containing also small amounts of CO₂ (<2 mol%); densities range from 0.72 to 0.99 g/cc. The wide range of coexisting fluid inclusion compositions is interpreted as a result of fluid immiscibility during entrapment. Immiscibility is documented by the partitioning of CH₄ and CO₂, into gas-rich (CO₂-rich) type 1 inclusions, and the conformity of end-member compositions trapped in type 1 inclusions to chemical equilibrium fractionation at the minimum measured homogenization temperatures, and calculated homogenization pressures. Minimum measured homogenization temperatures of aqueous and gas-rich type 1 inclusions of 220°–250 °C, either to the H₂O, or to the CO₂ phase, is considered the best estimate of temperature of formation of the veins, and temperature of scheelite deposition. Corresponding fluid pressures were between 1.2 and 2.6 kbar. Oxygen fugacities during mineralization varied from 10⁻³⁵ to 10⁻³¹ bar and were slightly above the synthetic Ni-NiO buffer values. The fluid inclusion data combined with δ¹⁸O water values of 3 to 6 per mil (SMOW) and δ¹³C CO₂₋ fluid of −1.2 to +4.3 per mil (PDB), together with geologic data, indicate generation of mineralizing fluids primarily by late- to post-metamorphic devolatilization reactions. Received: 8 April 1997 / Accepted: 8 July 1997     

Genesis of massive sulfide deposits in the Verkhneural’sk ore district, the South Urals, Russia: Evidence for magmatic contribution of metals and fluids

Melt inclusions and aqueous fluid inclusions in quartz phenocrysts from host felsic volcanics, as well as fluid inclusions in minerals of ores and wall rocks were studied at the Cu-Zn massive sulfide deposits in the Verkhneural’sk ore district, the South Urals. The high-temperature (850–1210°C) magmatic melts of volcanic rocks are normal in alkalinity and correspond to rhyolites of the tholeiitic series. The groups of predominant K-Na-type (K₂O/Na₂O = 0.3–1.0), less abundant Na-type (K₂O/Na₂O = 0.15–0.3), and K-type (K₂O/Na₂O = 1.9–9.3) rhyolites are distinguished. The average concentrations (wt %) of volatile components in the melts are as follows: 2.9 H₂O (up to 6.5), 0.13 Cl (up to 0.28), and 0.09 F (up to 0.42). When quartz was crystallizing, the melt was heterogeneous, contained magnetite crystals and sulfide globules (pyrrhotite, pentlandite, chalcopyrite, bornite). High-density aqueous fluid inclusions, which were identified for the first time in quartz phenocrysts from felsic volcanics of the South Urals, provide evidence for real participation of magmatic water in hydrothermal ore formation. The fluids were homogenized at 124–245°C in the liquid phase; the salinity of the aqueous solution is 1.2–6.2 wt % NaCl equiv. The calculated fluid pressure is very high: 7.0–8.7 kbar at 850°C and 5.1–6.8 kbar at 700°C. The LA-ICP-MS analysis of melt and aqueous fluid inclusions in quartz phenocrysts shows a high saturation of primary magmatic fluid and melt with metals. This indicates ore potential of island-arc volcanic complexes spatially associated with massive sulfide deposits. The systematic study of fluid inclusions in minerals of ores and wall rocks at five massive sulfide deposits of the Verkhneural’sk district furnished evidence that ore-forming fluids had temperature of 375–115°C, pressure up to 1.0–0.5 kbar, chloride composition, and salinity of 0.8–11.2 (occasionally up to 22.8) wt % NaCl equiv. The H and O isotopic compositions of sericite from host metasomatic rocks suggest a substantial contribution of seawater to the composition of mineral-forming fluids. The role of magmatic water increases in the central zones of the feeding conduit and with depth. The dual nature of fluids with the prevalence of their magmatic source is supported by S, C, O, and Sr isotopic compositions. The TC parameters of the formation of massive sulfide deposits are consistent with the data on fluid inclusions from contemporary sulfide mounds on the oceanic bottom.     

Genesis of tin and tantalum mineralization in pegmatites from the Bynoe area,Pine Creek Geosyncline,Northern Territory

The tin‐ and tantalum‐bearing pegmatites of the Bynoe area are located in the western Pine Creek Geosyncline. They are emplaced within psammopelitic rocks in the contact aureole of the Two Sisters Granite. The latter is a Palaeoproterozoic, fractionated, granite with S‐type characteristics and comprises a syn‐ to late‐orogenic, variably foliated, medium‐grained biotite granite and a post‐orogenic, coarse‐grained biotite‐muscovite granite. The pegmatites comprise a border zone of fine grained muscovite + quartz followed inward by a wall zone of coarse grained muscovite + quartz which is in turn followed by an intermediate zone of quartz + feldspar + muscovite. A core zone of massive quartz is present in some occurrences. Feldspars in the intermediate zone are almost completely altered to kaolinite. This zone contains the bulk of cassiterite, tantalite and columbite mineralization. Fluid inclusions in pegmatitic quartz indicate that early Type A (CO₂ + H₂O ± CH₄) inclusions were trapped at the H₂O‐CO₂ solvus at P～100 MPa, T～300°C (range 240–328°C) and salinity ～6 wt% eq NaCl. Pressure‐salinity corrected temperatures on Type B (H₂O + ～20% vapour), C (H₂O + < 15% vapour) and D (H₂O + halite + vapour) inclusions also fall within the range of Type A inclusions. Oxygen and hydrogen isotope data show that kaolin was either formed in isotopic equilibrium with meteoric waters or subsequent to its formation, from hydrothermal fluid, underwent isotopic exchange with meteoric waters. Fluid inclusion waters from core zone quartz show enrichment in deuterium suggesting metamorphic influence. Isotope values on muscovite are consistent with a magmatic origin. It is suggested that the pegmatites were derived from the post‐orogenic phase of the Two Sisters Granite. Precipitation of cassiterite took place at about 300°C from an aqueous fluid largely as a result of increase in pH due to feldspar alteration.     

Geology and fluid evolution of the Wangfeng orogenic-type gold deposit,Western Tian Shan,China

The Wangfeng gold deposit is located in Western Tian Shan and the central section of the Central Asian Orogenic Belt (CAOB). The deposit is mainly hosted in Precambrian metamorphic rocks and Caledonian granites and is structurally controlled by the Shenglidaban ductile shear zone. The gold orebodies consist of gold-bearing quartz veins and altered mylonite. The mineralization can be divided into three stages: quartz–pyrite veins in the early stage, sulfide–quartz veins in the middle stage, and quartz–carbonate veins or veinlets in the late stage. Ore minerals and native gold mainly formed in the middle stage. Four types of fluid inclusions were identified based on petrography and laser Raman spectroscopy: CO₂–H₂O inclusions (C-type), pure CO₂ inclusions (PC-type), NaCl–H₂O inclusions (W-type), and daughter mineral-bearing inclusions (S-type). The early-stage quartz contains only primary CO₂–H₂O fluid inclusions with salinities of 1.62 to 8.03 wt.% NaCl equivalent, bulk densities of 0.73 to 0.89 g/cm³, and homogenization temperatures of 256 °C–390 °C. Vapor bubbles are composed of CO₂. The middle-stage quartz contains all four types of fluid inclusions, of which the CO₂–H₂O and NaCl–H₂O types yield homogenization temperatures of 210 °C–340 °C and 230 °C–300 °C, respectively. The CO₂–H₂O fluid inclusions have salinities of 0.83 to 9.59 wt.% NaCl equivalent and bulk densities of 0.77 to 0.95 g/cm³, with vapor bubbles composed of CO₂, CH₄, and N₂. Fluid inclusions in the late-stage quartz are NaCl–H₂O solution with low salinities (0.35–3.87 wt.% NaCl equivalent) and low homogenization temperatures (122 °C–214 °C). The coexistence of inclusions of these four types in middle-stage quartz suggests that fluid boiling occurred in the middle-stage mineralization. Trapping pressures estimated from CO₂–H₂O inclusions are 110–300 MPa and 90–250 MPa for the early and middle stages, respectively, suggesting that gold mineralization mainly occurred at depths of about 10 km. In general, the Wangfeng gold deposit originated from a metamorphic fluid system characterized by low salinity, low density, and enrichment of CO₂. Depressurized fluid boiling caused gold precipitation. Given the regional geology, ore geology, fluid-inclusion features, and ore-forming age, the Wangfeng gold deposit can be classified as a hypozonal orogenic gold deposit.     

Chemical composition,volatile components,and trace elements in the magmatic melt of the Kurama mining district,Middle Tien Shan: Evidence from the investigation of inclusions in quartz

Melt and fluid inclusions were investigated in six quartz phenocryst samples from the igneous rocks of the extrusive (ignimbrites and rhyolites) and subvolcanic (granite porphyries) facies of the Lashkerek Depression in the Kurama mining district, Middle Tien Shan. The method of inclusion homogenization was used, and glasses from more than 40 inclusions were analyzed on electron and ion microprobes. The chemical characteristics of these inclusions are typical of silicic magmatic melts. The average composition is the following (wt %): 72.4 SiO₂, 0.06 TiO₂, 13.3 Al₂O₃, 0.95 FeO, 0.03 MnO, 0.01 MgO, 0.46 CaO, 3.33 Na₂O, 5.16K₂O, 0.32 F, and 0.21 Cl. Potassium strongly prevails over sodium in all of the inclusions (K₂O/Na₂O averages 1.60). The average total of components in melt inclusions from five samples is 95.3 wt %, which indicates a possible average water content in the melt of no less than 3–4 wt %. Water contents of 2.0 wt % and 6.6 wt % were determined in melt inclusions from two samples using an ion microprobe. The analyses of ore elements in the melt inclusions revealed high contents of Sn (up to 970 ppm), Th (19–62 ppm, 47 ppm on average), and U (9–26 ppm, 18 ppm on average), but very low Eu contents (0.01 ppm). Melt inclusions of two different compositions were detected in quartz from a granite porphyry sample: silicate and chloride, the latter being more abundant. In addition to Na and K chlorides, the salt inclusions usually contain one or several anisotropic crystals and an opaque phase. The homogenization temperatures of the salt inclusions are rather high, from 680 to 820°C. In addition to silicate inclusions with homogenization temperatures of 820–850°C, a primary fluid inclusion of aqueous solution with a concentration of 3.7 wt % NaCl eq. and a very high density of 0.93 g/cm³ was found in quartz from the ignimbrite. High fluid pressure values of 6.5–8.3 kbar were calculated for the temperature of quartz formation. These estimates are comparable with values obtained by us previously for other regions of the world: 2.6–4.3 kbar for Italy, 3.7 kbar for Mongolia, 3.3–8.7 kbar for central Slovakia, and 3.3–9.6 kbar for eastern Slovakia. Unusual melt inclusions were investigated in quartz from another ignimbrite sample. In addition to a gas phase and transparent glass, they contain spherical Feoxide globules (81.2 wt % FeO) with high content of SiO₂ (9.9 wt %). The globules were dissolved in the silicate melt within a narrow temperature range of 1050–1100°C, and the complete homogenization of the inclusions was observed at temperatures of 1140°C or higher. The combined analysis of the results of the investigation of these inclusions allowed us to conclude that immiscible liquids were formed in the high-temperature silicic magma with the separation of iron oxide-dominated droplets.     

Fluid inclusion,rare earth element geochemistry,and isotopic characteristics of the eastern ore zone of the Baiyangping polymetallic Ore district,northwestern Yunnan Province,China

The Baiyangping Cu–Ag polymetallic ore district is located in the northern part of the Lanping–Simao foreland fold belt, which lies between the Jinshajiang–Ailaoshan and Lancangjiang faults in western Yunnan Province, China. The source of ore-forming fluids and materials within the eastern ore zone were investigated using fluid inclusion, rare earth element (REE), and isotopic (C, O, and S) analyses undertaken on sulfides, gangue minerals, wall rocks, and ores formed during the hydrothermal stage of mineralization. These analyses indicate: (1) The presence of five types of fluid inclusion, which contain various combinations of liquid (l) and vapor (v) phases at room temperature: (a) H₂O (l), (b) H₂O (l) + H₂O (v), (c) H₂O (v), (d) C_mH_n (v), and (e) H₂O (l) + CO₂ (l), sometimes with CO₂ (v). These inclusions have salinities of 1.4–19.9 wt.% NaCl equivalents, with two modes at approximately 5–10 and 16–21 wt.% NaCl equivalent, and homogenization temperatures between 101 °C and 295 °C. Five components were identified in fluid inclusions using Raman microspectrometry: H₂O, dolomite, calcite, CH₄, and N₂. (2) Calcite, dolomitized limestone, and dolomite contain total REE concentrations of 3.10–38.93 ppm, whereas wall rocks and ores contain REE concentrations of 1.21–196 ppm. Dolomitized limestone, dolomite, wall rock, and ore samples have similar chondrite-normalized REE patterns, with ores in the Huachangshan, Xiaquwu, and Dongzhiyan ore blocks having large negative δCe and δEu anomalies, which may be indicative of a change in redox conditions during fluid ascent, migration, and/or cooling. (3) δ³⁴S values for sphalerite, galena, pyrite, and tetrahedrite sulfide samples range from −7.3‰ to 2.1‰, a wide range that indicates multiple sulfur sources. The basin contains numerous sources of S, and deriving S from a mixture of these sources could have yielded these near-zero values, either by mixing of S from different sources, or by changes in the geological conditions of seawater sulfate reduction to sulfur. (4) The C–O isotopic analyses yield δ¹³C values from ca. zero to −10‰, and a wider range of δ¹⁸O values from ca. +6 to +24‰, suggestive of mixing between mantle-derived magma and marine carbonate sources during the evolution of ore-forming fluids, although potential contributions from organic carbon and basinal brine sources should also be considered. These data indicate that ore-forming fluids were derived from a mixture of organism, basinal brine, and mantle-derived magma sources, and as such, the eastern ore zone of the Baiyangping polymetallic ore deposit should be classified as a “Lanping-type” ore deposit.     

Origin of carbonatite magma during the evolution of ultrapotassic basite magma

Clinopyroxene phenocrysts in fergusite from a diatreme in the Dunkel’dyk potassic alkaline complex in the southeastern Pamirs, Tajikistan, and from carbonate veinlets cutting across this rock contain syngenetic carbonate, silicate, and complex melt inclusions. The homogenization of the silicate and carbonate material of the inclusions with the complete dissolution of daughter crystalline phases and fluid in each of them occur simultaneously at 1150?1180°C. The pressures estimated using fluid inclusions and mineral geobarometers were 0.5–0.7 GPa. The behavior of the inclusions during their heating and their geochemistry are in good agreement with the origin of carbonate melts via liquid immiscibility. Carbonatite magma was segregated at the preservation of volatile components (H₂O, CO₂, F, Cl, and S) in the melt, and this resulted in the crystallization of H₂O-rich minerals and carbonates and testifies that the magma was not intensely degassed during its ascent to the surface. The silicate melts are rich in alkalis (up to 4 wt % Na₂O and 12 wt % K₂O), H₂O, F, Cl, and REE (up to 1000 ppm), LREE, Ba, Th, U, Li, B, and Be. The diagrams of the concentrations of incompatible elements of these rocks typically show deep Nb, Ta, and Ti minima, a fact making them similar to the unusual type of ultrapotassic magmas: lamproites of the Mediterranean type. These magmas are thought to be generated in relation to subduction processes, first of all, the fluid transport of various components from a down-going continental crustal slab into overlying levels of the mantle wedge, from which ultrapotassic magmas are presumably derived.     

Phase equilibria constraints on melting of stromatic migmatites from Ronda (S. Spain): insights on the formation of peritectic garnet

Stromatic metatexites occurring structurally below the contact with the Ronda peridotite (Ojén nappe, Betic Cordillera, S Spain) are characterized by the mineral assemblage Qtz+Pl+Kfs+Bt+Sil+Grt+Ap+Gr+Ilm. Garnet occurs in low modal amount (2–5 vol.%). Very rare muscovite is present as armoured inclusions, indicating prograde exhaustion. Microstructural evidence of melting in the migmatites includes pseudomorphs after melt films and nanogranite and glassy inclusions hosted in garnet cores. The latter microstructure demonstrates that garnet crystallized in the presence of melt. Re‐melted nanogranites and preserved glassy inclusions show leucogranitic compositions. Phase equilibria modelling of the stromatic migmatite in the MnO–Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂–O₂–C (MnNCaKFMASHOC) system with graphite‐saturated fluid shows P–T conditions of equilibration of 4.5–5 kbar, 660–700 °C. These results are consistent with the complete experimental re‐melting of nanogranites at 700 °C and indicate that nanogranites represent the anatectic melt generated immediately after entering supersolidus conditions. The P–T estimate for garnet and melt development does not, however, overlap with the low‐temperature tip of the pure melt field in the phase diagram calculated for the composition of preserved glassy inclusions in garnet in the Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O (NCKFMASH) system. A comparison of measured melt compositions formed immediately beyond the solidus with results of phase equilibria modelling points to the systematic underestimation of FeO, MgO and CaO in the calculated melt. These discrepancies are present also when calculated melts are compared with low‐T natural and experimental melts from the literature. Under such conditions, the available melt model does not perform well. Given the presence of melt inclusions in garnet cores and the P–T estimates for their formation, we argue that small amounts (<5 vol.%) of peritectic garnet may grow at low temperatures (≤700 °C), as a result of continuous melting reactions consuming biotite.     

Chemical composition and crystallization conditions of trachybasalts from the Dzhida field, Southern Baikal volcanic area: Evidence from melt and fluid inclusions

Melt and fluid inclusions have been studied in olivine phenocrysts (Fo 81–79) from trachybasalts of the Southern Baikal volcanic area, Dzhida field. The melt inclusions were homogenized, quenched, and analyzed on an electron and ion microprobe. The study of homogenized glasses of nine inclusions showed that basaltic melts (SiO₂ = 47.1–50.3 wt %, MgO = 5.0–7.7 wt %, CaO = 7.1–11.1 wt %) have high contents of Al₂O₃ (17.1–19.6 wt %), Na₂O (4.1–6.2 wt %), K₂O (2.2–3.3 wt %), and P₂O₅ (0.6–1.1 wt %). The volatile contents are low (in wt %): 0.24–0.31 H₂O, 0.08 F, 0.03 Cl, and 0.02 S. Primary fluid inclusions in olivines from four trachybasalt samples contain high-density CO₂ (0.73–0.87 g/cm³), indicating a CO₂ fluid pressure of 4.3–6.6 kbar at 1200–1300°C and olivine crystallization depths of 16–24 km. Ion microprobe analyses of 20 glasses from melt inclusions for trace elements showed that the magmas of the Baikal rift were enriched in incompatible elements, thus differing from oceanic rift basalts and resembling oceanic island basalts. A comparison of our data on melt and fluid inclusions in olivine from trachybasalts of the Dzhida field with preexisting data on the Eastern Tuva volcanic highland in the Southern Baikal volcanic area showed that they had similar contents of volatiles, major, and trace elements.     

Fluid inclusions in granulite-facies metapelites of the Hercynian ancient lower crust of the Serre,Calabria, Southern Italy

Investigations of fluid inclusions in granulitefacies metapelites of southern Calabria enable characterization of the fluid composition of these lower crustal rocks, and constrain the petrologically deduced retrograde P-T path characterized by isothermal uplift prior to isobaric cooling in middle crustal levels. Fluid inclusions in cordierite, garnet and sillimanite have a CO₂-rich composition. Inclusions in cordierite rarely contain minor amounts of N₂ and H₂O, and in garnets some CO₂–CH₄–N₂ inclusions have been analyzed by Raman microprobe. Quartz reveals the most complex fluid melusion compositions (1) CO₂-rich, (2) CO₂–CH₄–N₂, (3) CH₄–N₂, (4) H₂O–MgCl₂–CaCl₂–NaCl, (5) H₂O–NaCl and (6) H₂O–CO₂. The earliest fluid inclusions after peak metamorphism are rich in CO₂ with minor amounts of N₂ and H₂O. An early CO₂–(H₂O–N₂) fluid composition has been confirmed by detection of CO₂, H₂O and N₂ in the channels of the cordierite structure. Most of the early CO₂-rich fluid inclusions were modified during the uplift from the lower to the middle crustal level, resulting in a density decrease with CO₂ still dominant. The subsequent isobaric cooling led to further modifications of the fluid inclusions. High-density inclusions around implosion textures or scattered amongst lower-density ones must have formed during this cooling episode. Aqueous inclusions in quartz are mostly formed late and are consistent with trapping during retrograde rehydration.This project has been supported by the DFG as contribution to the special program Continental Lower Crust     

Fluid geochemistry in the Ivigtut cryolite deposit, South Greenland

The 1.27 Ga old Ivigtut (Ivittuut) intrusion in South Greenland is world-famous for its hydrothermal cryolite deposit [Na₃AlF₆] situated within a strongly metasomatised A-type granite stock. This detailed fluid inclusion study characterises the fluid present during the formation of the cryolite deposit and thermodynamic modelling allows to constrain its formation conditions.Microthermometry revealed three different types of inclusions: (1) pure CO₂, (2) aqueous-carbonic and (3) saline-aqueous inclusions. Melting temperatures range between − 23 and − 15 °C for type 2 and from − 15 to − 10 °C for type 3 inclusions. Most inclusions homogenise between 110 and 150 °C into the liquid.Stable isotope compositions of CO₂ and H₂O were measured from crushed inclusions in quartz, cryolite, fluorite and siderite. The δ¹³C values of about − 5‰ PDB are typical of mantle-derived magmas. The differences between δ¹⁸O of CO₂ (+ 21 to + 42‰ VSMOW) and δ¹⁸O of H₂O (− 1 to − 21.7‰ VSMOW) suggest low-temperature isotope exchange. δD (H₂O) ranges from − 19 to − 144‰ VSMOW. The isotopic composition of inclusion water closely follows the meteoric water line and is comparable to Canadian Shield brines. Ion chromatography revealed the fluid's predominance in Na, Cl and F. Cl/Br ratios range between 56 and 110 and may imply intensive fluid–rock interaction with the host granite.Isochores deduced from microthermometry in conjunction with estimates for the solidification of the Ivigtut granite suggest a formation pressure of approximately 1–1.5 kbar for the fluid inclusions. Formation temperatures of different types of fluid inclusions vary between 100 and 400 °C. Thermodynamic modelling of phase assemblages and the extraordinary high concentration in F (and Na) may indicate that the cryolite body and its associated fluid inclusions could have formed during the continuous transition from a volatile-rich melt to a solute-rich fluid.     

Fluid evolution in the Pote Shear Zone Harare-Shamva-Bindura greenstone belt (northeast Zimbabwe)

A fluid inclusion study was completed on syn-deformational quartz veins of the Pote River Shear Zone, which is situated on the border between the Harare-Bindura greenstone belt and the granitoids of the Chinamora Batholith. The fluid inclusions were studied by means of microthermometry and Laser-Raman microspectrometry. The fluid inclusions consist of three major compositional types: (1) H₂OCO₂±N₂±halite inclusions in clusters and trails; (2) H₂OCO₂ inclusions (H₂O = 30–60 vol. %) in trails; and (3) H₂O-halite inclusions in trails. These fluid generations are explained by trapping at different P-T conditions of two different fluids: a high salinity aqueous fluid and a low salinity H₂OCO₂ fluid with XH₂O around 0.8. High salinity aqueous fluid inclusions are characteristic for the granite-greenstone contact and are absent within the Harare-Shamva-Bindura greenstone belt. The high salinity aqueous fluid has, therefore, been interpreted as magmatic in origin. The low salinity H₂OCO₂ fluid is most likely metamorphic in origin.     

The origin and evolution of the parental magmas of frontal volcanoes in Kamchatka: Evidence from magmatic inclusions in olivine from Zhupanovsky volcano

The paper presents data on naturally quenched melt inclusions in olivine (Fo 69–84) from Late Pleistocene pyroclastic rocks of Zhupanovsky volcano in the frontal zone of the Eastern Volcanic Belt of Kamchatka. The composition of the melt inclusions provides insight into the latest crystallization stages (∼70% crystallization) of the parental melt (∼46.4 wt % SiO₂, ∼2.5 wt % H₂O, ∼0.3 wt % S), which proceeded at decompression and started at a depth of approximately 10 km from the surface. The crystallization temperature was estimated at 1100 ± 20°C at an oxygen fugacity of ΔFMQ = 0.9–1.7. The melts evolved due to the simultaneous crystallization of olivine, plagioclase, pyroxene, chromite, and magnetite (Ol: Pl: Cpx: (Crt-Mt) ∼ 13: 54: 24: 4) along the tholeiite evolutionary trend and became progressively enriched in FeO, SiO₂, Na₂O, and K₂O and depleted in MgO, CaO, and Al₂O₃. Melt crystallization was associated with the segregation of fluid rich in S-bearing compounds and, to a lesser extent, in H₂O and Cl. The primary melt of Zhupanovsky volcano (whose composition was estimated from data on the most primitive melt inclusions) had a composition of low-Si (∼45 wt % SiO₂) picrobasalt (∼14 wt % MgO), as is typical of parental melts in Kamchatka and other island arcs, and was different from MORB. This primary melt could be derived by ∼8% melting of mantle peridotite of composition close to the MORB source, under pressures of 1.5 ± 0.2 GPa and temperatures 20–30°C lower than the solidus temperature of “dry” peridotite (1230–1240°C). Melting was induced by the interaction of the hot peridotite with a hydrous component that was brought to the mantle from the subducted slab and was also responsible for the enrichment of the Zhupanovsky magmas in LREE, LILE, B, Cl, Th, U, and Pb. The hydrous component in the magma source of Zhupanovsky volcano was produced by the partial slab melting under water-saturated conditions at temperatures of 760–810°C and pressures of ∼3.5 GPa. As the depth of the subducted slab beneath Kamchatkan volcanoes varies from 100 to 125 km, the composition of the hydrous component drastically changes from relatively low-temperature H₂O-rich fluid to higher temperature H₂O-bearing melt. The geothermal gradient at the surface of the slab within the depth range of 100–125 km beneath Kamchatka was estimated at 4°C/km.     

The geochemistry of volatile species in melt inclusions and sulfide minerals from Izu-Oshima volcano, Japan

Olivine-hosted melt inclusions in the O95 pyroclastic layer of Izu-Oshima volcano, Japan are basaltic to basaltic-andesitic in composition. The negative correlation between SiO₂ and H₂O in melt inclusions and reverse compositional zoning observed in olivine and other mineral phenocrysts is inferred to arise from mixing between a highly evolved and a less evolved magma. The latter is characterized by the highest S (0.15 wt.%) and H₂O (3.4 wt.%) concentrations among those described in reports of previous studies. The S⁶⁺/S_total ratios in melt inclusions were 0.64?–?0.73, suggesting a relatively high oxidation state (NNO + 0.87 at 1150°C). The presence of pyrrhotites, which are found only in titanomagnetite microlites, suggests that sulfide saturation occurred during microlite growth under at a sulfur fugacity (log fS₂) value of around + 0.5 for T = 1060°C. The groundmass glass compositions are more evolved (andesitic composition) than any melt inclusions containing high amounts of Cl (0.13 wt.%) but negligible H₂O (0.20 wt.%) and S (< 70 ppm), suggesting that Cl was retained in the magma, in contrast to S and H₂O, which degassed strongly during magma effusion.     

Carbonic metamorphism of charnockites in the southwestern Indian Shield: A fluid inclusion study

Forming the southwestern segment of the Precambrian granulite facies terrain of the Indian shield, the Kerala region largely comprises charnockites, khondalites and migmatitic gneisses. Fluid inclusions in quartz from the charnockites show distinct distribution patterns consistent with three generations of inclusions. The early monophase type records entrapment of high-density CO₂-rich fluid (0.95–1.0 g cm⁻³). A subsequent monophase type with lower-density CO₂-rich fluid (0.65–0.75 g cm⁻³) coexists with CO₂H₂O inclusions having an average degree of filling of 0.2 (H₂O = 20%; CO₂ = 80%). Late aqueous biphase inclusions show coexistence with a second category of CO₂H₂O inclusions showing a degree of filling of 0.6 (H₂O = 60%; CO₂ = 40%). The CO₂-isochores for early carbonic inclusions yield a pressure range of 4.6–6.1 kbar at granulite facies temperatures of 650–800°C, depicting the entrapment of fluids present during or close to the peak metamorphic stage. A definite sequence of fluid evolution is traceable for the subsequent stages. Thus, the coexisting CO₂ and CO₂H₂O inclusions were entrapped at 510°C and 2.2 kbar, marking the waning of carbonic regime and the beginning of aqueous regime. At 330°C and 0.4 kbar, fluid unmixing occurred, leading to the simultaneous entrapment of mixed CO₂H₂O and H₂O inclusions along rehealed microfractures. The data presented indicate that the metamorphic fluids evolved from early high-density carbonic through mixed carbonic-aqueous to late aqueous types. The dry granulite mineral assemblage of charnockites is a result of metamorphic equilibration under water-deficient and high-P_CO2 conditions.