Low-density Vapor Research Articles

The transport of bismuth in HCl-bearing aqueous vapour and low-density aqueous supercritical fluids: Implications for natural systems

Hydration by H2O clusters has been shown to be an important means of transporting metal complexes in hydrothermal vapours and low-density supercritical aqueous fluids. However, the effect of hydration on the transport of relatively volatile metal complexes such as those involving bismuth and chloride has not been evaluated. This effect is important to evaluate because bismuth is a key pathfinder element for gold in many intrusion-related gold ore-forming systems, where low-density supercritical aqueous fluids and vapour may play an important role in metal transport. Here, we present the results of experiments investigating the solubility of BiOCl(s) and the speciation of bismuth in HCl-bearing aqueous vapour and low-density supercritical aqueous fluids at temperatures between 250 and 400 °C and pressures of 5 to 296 bar. Two gaseous bismuth species formed in the HCl-bearing fluids (X(HCl) > 0.0005), namely BiCl3(g) and BiCl3(H2O)n(g). Our data clearly show that BiCl3(g) is highly volatile at low water fugacity (between 30 and 110 bar) and acts as an unhydrated gas molecule. At higher water fugacity, the gaseous BiCl3(g) reacts with water to form hydrated BiCl3(H2O)n(g) species. Significantly, the stability of hydrated bismuth chloride species, BiCl3(H2O)n(g), with low hydration numbers is lower than that of the unhydrated species, BiCl3(g), resulting in a decrease in bismuth solubility with increasing f(H2O). However, at a water fugacity great than 30–110 bar, that increases with increasing temperature, the hydration number and the solubility of hydrated species BiCl3(H2O)n(g) increase with increasing water fugacity or the density of the fluid. Consequently, unhydrated gaseous bismuth species increase in importance with increasing temperature and become dominant at temperatures > 450 °C in fluids that have low density (<0.10 g/cm3). Hydrated bismuth chloride species are dominant in fluids having higher density (0.10–0.34 g/cm3). The overarching conclusion of this study is that aqueous low-density supercritical fluids, which exsolve from magmas to form intrusion-related gold deposits, can transport bismuth in concentrations (up to hundreds ppm) sufficient to form economic deposits.

Platinum-group elements (PGE) in the New Afton alkalic Cu-Au porphyry deposit, Canadian Cordillera, II: PGE distribution and models for the hydrothermal coprecipitation of Co-Ni-Pd-Pt in pyrite

The first part of this article can be found here: 10.3389/feart.2023.819129 (DOI). Occurrences of significant concentrations of platinum-group elements (PGE) in porphyry deposits have seen limited attention and the geochemical controls on their deposition are poorly understood. New Afton is a late Triassic alkalic Cu-Au porphyry deposit situated 10 km west of Kamloops, British Columbia with Pt and Pd enrichments locally exceeding 30 ppm. Primary PGE deposition accompanied hypogene Cu-Au mineralization linked to potassic alteration, with Pt and Pd deportment dominated by their inclusion in early Ni- and Co-rich pyrite with secondary amounts of platinum-group minerals (PGM) mertieite-II, isomertieite &amp;gt; temagamite, and kotulskite. Secondary hydrothermal alteration of hypogene PGE-rich pyrite promoted remobilization of PGE, creating vein-controlled PGE enrichment where essentially all Pt and Pd are hosted by PGM dominated by temagamite &amp;gt; mertieite-II, and sperrylite, leaving behind complementary PGE-depleted domains. Thermodynamic modelling shows that primary co-precipitation of Pt with Co and Pd with Ni can be explained solely through the cooling of a hydrothermal system, regardless of whether the mineralizing fluid was a brine or a low-density vapour. Pd and Pt were transported from an underlying magma reservoir into the porphyry system by a magmatic-hydrothermal fluid as Cl− complexes. Pt-rich cobaltian pyrite formed at the highest temperatures, whereas Pd-rich nickeliferous pyrite formed at somewhat lower temperatures. Zonation of metals in pyrite suggests that PGE were incorporated in pyrite under conditions of fluctuating fluid temperatures during transport and cooling of orthomagmatic fluids during the main Cu-Au mineralization stage. There exists a hitherto overlooked potential for significant Pt and Pd mineralization in early hypogene pyrite that may be spatially separated from visible Cu mineralization, especially in potassic or ultrapotassic systems.

Numerical simulation of flow boiling heat transfer characteristics of R134a/Ethane binary mixture in horizontal micro-tube

The cryogenic organic Rankine cycle (ORC) is appropriate for recovering the cold energy of liquefied natural gas (LNG) for power generation. However, pure working fluids in ORC are challenging to match the evaporation curve of LNG appropriately, which causes a large amount of exergy loss. Thus, adopting mixture working fluid is a good option due to their temperature-varying evaporation and condensation process. This study investigates the heat transfer characteristic of R134a/ethane (widely adopted in cryogenic ORC as pure working fluid) binary mixture in the horizontal micro-tube through numerical simulation. The law of boiling heat transfer characteristics with vapor quality, heat flux, mass flow, ethane mole fraction, and other factors are obtained. The simulation illustrated that the boiling heat transfer coefficient increases with the heat flux and mass flow. Furthermore, compared with R134a, ethane has higher thermal conductivity, lower vapor density, and latent heat of vaporization. Hence, the heat transfer coefficient of the R134a/ethane mixture increases with the ethane’s mole fraction. The fluid disturbance mainly influences the pressure drop and the turbulence intensity significantly when the fluid is transformed into a gas–liquid flow. This study could provide insights into boiling heat transfer improvement of binary mixtures for ORC power generation applications.

Fluid Evolution at the Batu Hijau Porphyry Cu-Au Deposit, Indonesia: Hypogene Sulfide Precipitation from a Single-Phase Aqueous Magmatic Fluid During Chlorite–White-Mica Alteration

Abstract Mineralization at the Cu-Au porphyry deposit of Batu Hijau, Indonesia, was previously reported to be associated mainly within stockwork quartz veins accompanied by pervasive biotite-magnetite alteration. We use cathodoluminescence imaging of vein textures followed by microthermometry and laser ablation-inductively coupled plasma-mass spectrometry microanalysis of fluid inclusions to decipher the spatial-temporal evolution of the hydrothermal system. Our results indicate that sulfide precipitation largely postdated the main stockwork quartz veining. Chalcopyrite and bornite were found in three textural positions: (1) within conspicuous quartzpoor veinlets (“paint veins”) that postdate quartz stockwork veins and that also appear to account for the bulk of seemingly disseminated sulfides, (2) as centerlines in B-type veins, and (3) as interstitial grains in A-type veins. In all three textural positions, the sulfides occur together with a volumetrically minor, dull-luminescent quartz generation after local dissolution of the granular quartz dominating the stockwork veins. All three positions are associated with chlorite ± variable phengitic white mica with 3–6 wt % FeO + MgO. In the barren core of the deposit, quartz veins host, almost exclusively, fluid inclusions of intermediate density (~0.6 g/cm3) and near-constant salinity of ~3.7 wt % NaCl equiv, representing the input magmatic fluid. This fluid subsequently separated into a highly saline brine1 and low-density vapor during quartz vein formation in the mineralized parts of the deposit, but we found no textural or fluid-chemical evidence that brine + vapor already reached saturation in sulfides. Within the studied samples, Cu-Fe sulfides are invariably associated with the dull-luminescent quartz hosting only low-salinity (~2–8 wt % NaCl equiv) aqueous fluid inclusions with a density of ~0.8 g/cm3 and minimum formation temperatures of 300°–360°C, in agreement with Ti-inquartz and chlorite thermometry indicating trapping conditions only slightly above the boiling pressure of these liquids. On average, this mineralizing aqueous fluid is compositionally similar to the initial magmatic fluid, suggesting a common source, but some inclusion assemblages deviate to significantly lower or higher salinities (0.5–25 wt % NaCl equiv). We propose a formation model for the Batu Hijau porphyry Cu-Au deposit in which mostly barren quartz veins formed at high temperature (&amp;gt;400°C) in the central part of the system, while sulfide mineralization commences to form peripheral to this zone. The economic ore shell was growing inward and downward as a zone of active sulfide precipitation at 300°–360°C shifted in response to progressive retraction of isotherms, while barren quartz vein formation continued in the system’s core at higher temperature. The aqueous ore-forming liquid is interpreted to have formed by rehomogenization of magmatic brine and vapor that previously formed by phase separation and later became miscible again after cooling over a narrow temperature interval. Vapor condensation into the highly saline brine phase at low pressure and subcritical temperature led to partial dissolution of earlier formed quartz veins and created secondary porosity for subsequent sulfide deposition. We propose that Cu-Fe sulfide precipitation by the low-temperature aqueous fluid was driven by the rehomogenization of S-rich vapor with Cu-rich brine originating from the same input fluid. The selective dissolution of earlier quartz veins in an inward- and downward-growing ore shell explains the positive correlation of ore grades with the density of earlier quartz veining in the ore shell, even though copper mineralization postdates quartz vein formation at any location in the deposit. Late-stage sulfide deposition in paint veins has been noted at other porphyry Cu-(Au-Mo) deposits worldwide, indicating that the proposed fluid evolution model may be applicable to many other porphyry systems.

Falling film evaporation and pool boiling heat transfer of R1233zd(E) on thermal spray coated tube

• Falling film evaporation heat transfer of R1233zd(E) was experimentally investigated. • Up to 4.2-fold heat transfer enhancement could be obtained by thermal spray coating. • R1233zd(E) achieved a lower heat transfer coefficient than R134a at 20 °C. Falling film evaporators have been expected as an alternative to flooded evaporators for reducing the refrigerant usage. It is important for the enhancement of the film evaporation heat transfer to keep a liquid film and promote nucleate boiling in the liquid film. This study focused on nucleate boiling heat transfer in the liquid film by thermal spray coating that can be applied regardless of the material of heat transfer tubes. The heat transfer performance of falling film evaporation on a horizontal copper tube was experimentally evaluated. Since nucleate boiling phenomena, such as activation of nucleation sites and bubble behaviors in the liquid film, strongly depend on the physical properties of the refrigerant, the experimental results for R1233zd(E), one of the alternative refrigerants with low GWP, were compared with those for R134a. Two types of tubes were used: the smooth tube and the thermal spray coated tube fabricated by an arc wire spraying method, with the outer diameter of 19.05 mm and the heating length of 50 mm. Pool boiling experiments were also conducted to confirm the wall superheat for nucleate boiling. The heat transfer coefficients were evaluated with a film mass flow rate range of 8.5 × 10 −3 to 6.3 × 10 −2 kg/(m·s), a heat flux range of 10 to 85 kW/m 2 , and a saturation temperature at 20 °C. The effects of the structure of the heating surface, heat flux, and thermophysical properties of the refrigerant on the heat transfer performance are discussed. Results show that the heat transfer of the falling film became the nucleate boiling dominant with a sufficient heat flux and liquid film flow rate. The thermal spray coated surface enhanced not only the nucleate boiling but also the liquid spreading by the vapor bubbles in the liquid film, and thus the coated tube produced higher heat transfer coefficients of 2.1 to 4.8 times those for the smooth tube. The wall superheat at the onset of nucleate boiling was higher for R1233zd(E) than for R134a, because R1233zd(E) has a higher surface tension and lower vapor density. Thus, the pool boiling and falling film evaporation heat transfer coefficients were lower for R1233zd(E) than for R134a.

Experimental measurement of H2(aq) solubility in hydrothermal fluids: Application to the Piccard hydrothermal field, Mid-Cayman Rise

In mid-ocean ridge hydrothermal systems the fluid redox state is controlled by oxidation of ferrous iron in the host rock and generation of aqueous hydrogen, H2(aq). A quantitative interpretation of redox state requires conversion of H2(aq) concentrations to H2 fugacity, f H2. Here we present the results of hydrothermal experiments that calibrate the f H2-concentration relationship in saline hydrothermal fluids, YH2-Cl. H2(aq) concentrations were measured between 400 and 500 °C, 210 and 510 bar, in both single-phase fluids and low-density vapors in the KCl-H2O system. The assemblage hematite-magnetite was used to buffer f H2. Values of YH2-Cl are well above unity and decrease as temperature increases. Along isotherms YH2-Cl decreases as the fluid density decreases. At 400 °C, 330 bar and 1000 mmol/kg KCl YH2-Cl is 316 bar/molal and decreases to 4 bar/molal at 500 °C, 400 bar and 33 mmol/kg KCl. In combination with previous determination of H2S(aq) solubility at hydrothermal conditions, the data presented here permit calculation of the redox conditions of natural vent systems. Redox conditions calculated for the basalt-hosted Piccard hydrothermal field suggest amphibolite facies mineral assemblages are present at depth, consistent with the extremely hot temperatures (>500 °C) inferred from analysis of other aspects of vent fluid chemistry (e.g., Cl and SiO2). Piccard may be the first location of active venting that records, through its composition, evidence for an alteration assemblage that had been previously observed only in fossilized submarine hydrothermal systems.

Long-wavelength density fluctuations as nucleation precursors.

Recent theories of nucleation that go beyond classical nucleation theory predict that diffusion-limited nucleation of both liquid droplets and of crystals from a low-density vapor (or weak solution) begins with long-wavelength density fluctuations. This means that in the early stages of nucleation, "clusters" can have low density but large spatial extent, which is at odds with the classical picture of arbitrarily small clusters of the condensed phase. We present the results of kinetic Monte Carlo simulations using forward flux sampling to show that these predictions are confirmed, namely, that on average, nucleation begins in the presence of low-amplitude, but spatially extended density fluctuations thus confirming a significant prediction of the nonclassical theory.

Flotation mechanism of sulphide melt on vapour bubbles in partially molten magmatic systems

The motion of dense Fe-rich immiscible sulphide liquids is generally supposed to be dominated by gravitational settling in crustal magma chambers, however they may become buoyant by attachment to low-density vapour bubbles to form compound drops, possibly contributing to the upward transfer of sulphur and transition metals in degassing magma bodies. Here, using numerical models, we consider constraints on the flotation of compound drops, and find a wide range of morphologies that would be expected to be capable of migrating through magmatic systems, including both melt- and mush-dominated domains, but also some situations where the compound drops will spontaneously separate to allow the vapour to rise while the sulphide phase is sequestered in the mush. The stability of compound drops is empirically related to a function f(Bo)=|σMV−σMS|σMS⋅1/BoS+|σVS−σMS|σMS⋅1/BoV, where M, V, and S denote silicate melt, vapour, and sulphide liquid, σ is surface tension (N⋅m−1), and Bo is the Bond number. Over a range of plausible conditions in magmas, f(Bo) must exceed values of 3 to 4 for capillary forces to overcome buoyancy forces tending to pull them apart. Using published thermodynamic models for vapour and sulphide solubility in silicate melts, we show that in many magmas the second boiling of vapour occurs synchronously with the saturation of sulphide liquid, increasing the potential for coupling of vapour and sulphide droplets. Diffusive coarsening produces mm-sized bubbles within 100-500 years, generating enough buoyancy to trigger the migration of compound drops. During compaction-driven expulsion of interstitial melt, compound drops can pass through constrictions between crystals in mush. The flotation of sulphide-vapour aggregates is likely to occur in crustal magma reservoirs and provides a feasible mechanism for the removal of sulphide liquid from crystal mushes, promoting its ability to participate in the generation of magmatic sulphide and porphyry copper deposits, emissions of the metals during volcanic eruptions, and even the remobilization of chalcophile metals sequestered in deep arc cumulates to generate porphyry Cu-(Au) deposits.

A comprehensive study of the second virial coefficient of low-density 84krypton vapor in the temperature range 0.01–700 K

The second virial coefficient B for 84krypton (84Kr) vapor is evaluated over the broad temperature range 0.01–700 K. The classical expression for B, Bcl, as well as the first quantum correction Bqc and the Beth–Uhlenbeck formula for the quantum coefficient Bq, is used. The deviation from Bcl with decreasing temperature is marked out clearly. It turns out that B is a powerful indicator of the demarcation boundary between the classical and quantum regimes. The dependence of B on the input Kr–Kr potential is examined. In the high-T limit, it is found that B is weakly dependent on the type of potential. At lower T, the behavior of Bq reflects a remarkable degree the intimate details of the respective regions of the interatomic potential itself. The compressibility of the system is examined in both classical and quantum regimes.

The classical and quantum second virial coefficient of low-density 132Xe vapor in the temperature-range 0.1 mK–30 000 K

The second virial coefficient B for 132xenon (132Xe) vapor is evaluated over the broad temperature-range 0.1 mK–30 000 K. The classical expression for B, Bcl, is used, as well as the first quantum correction Bqc, and the quantum second virial coefficient, Bq. The borderline interfacing the classical and quantum regimes is explored. It turns out that B is a powerful indicator of the demarcation boundary between the classical and quantum regimes. Equally important is that a very large negative Bq is symptomatic of conditions favoring clustering. Small 132Xe clusters are predicted at low temperatures ~10−2 K. Our results are compared to previous results whenever possible. The agreement is very good.

Long range dipole-dipole interaction in low-density atomic vapors probed by double-quantum two-dimensional coherent spectroscopy.

Optical double-quantum two-dimensional coherent spectroscopy (2DCS) was implemented to probe interatomic dipole-dipole interactions in both potassium and rubidium atomic vapors. The dipole-dipole interaction was detected at densities of 4.81×108 cm -3 and 8.40×109 cm -3 for potassium and rubidium, respectively, corresponding to a mean interatomic separation of 15.8 μm or 3.0×105 a 0 for potassium and 6.1 μm or 1.2×105 a 0 for rubidium, where a 0 is the Bohr radius. The experimental results confirm the long range nature of the dipole-dipole interaction, which is critical for understanding many-body physics in atoms/molecules. The long range interaction also has implications in atom-based applications involving many-body interactions. Additionally, we demonstrated that double-quantum 2DCS is sufficiently sensitive to probe dipole-dipole interaction at densities that can be achieved with cold atom in a magneto-optical trap, paving the way for double-quantum 2DCS studies of cold atoms and molecules. The method can also open a new avenue to study long-range interactions in solid state systems such as quantum dots and color centers in diamonds.

The origin of CH4-rich fluids in reduced porphyry–skarn Cu–Mo–Au systems

Although most of the methane on Earth is of biogenic origin, significant abiogenic methane has been identified in a variety of geological environments. Moreover, the presence of methane has been reported recently in fluid inclusions from a number of reduced porphyry deposits. The genesis of this methane, however, remains poorly understood. Here, we present results of a study of magma-exsolved CH4-rich aqueous fluid inclusions in the Seleteguole reduced porphyry–skarn Cu–Mo–Au deposit, NW China. Four types of fluid inclusions, namely intermediate-density two-phase aqueous inclusions, low-density vapor inclusions, brine inclusions and aqueous liquid inclusions, have been distinguished on the basis of the phases present at room temperature. The intermediate-density inclusions were trapped as a single phase and contain 3.8–10.4 mol/kg CH4, corresponding to an oxygen fugacity between ΔFMQ − 1 and ΔFMQ − 0.5. This attests to the remarkably reduced nature of the fluid. The δ13C value of the CH4-hosted fluid inclusions ranges from –29.4‰ to –19.1‰ (PDB), which distinguishes this methane from biogenic methane. Indeed, the high homogenization temperature of the CH4-rich inclusions (~400 °C) implies that the CH4 was exsolved directly from the magma. Given the environment in which the magma was likely generated, i.e., at or immediately above a subducting plate, we propose that the methane was produced by reactions involving organic matter-bearing carbonate rocks in the subduction zone. Although Cu, Mo and Au in most porphyry systems are interpreted to have been transported under oxidizing conditions, our results indicate that reduced aqueous liquids and vapors are also capable of transporting appreciable concentrations of these metals.

Badzhal Tin Magmatic-Fluid System, Far East, Russia: Transition from Granite Crystallization to Hydrothermal Ore Deposition

The Badzhal tin magmatic-fluid system of the eponymous volcanoplutonic zone in the Middle Amur Region has been studied to reveal special characteristics of the transition from granite crystallization to rare-metal deposition. Therefore, the authors have conducted an in-depth study of melt, fluid-melt, and fluid inclusions and oxygen isotope composition of minerals from granitic rocks of the Verkhneurmiisky pluton within the Badzhal volcanoplutonic zone and minerals of the Pravourmiisky and Blizhnee Sn-W deposits. Greisen alteration and hydrothermal veins at the Pravourmiisky and Blizhnee deposits resulted from a single magmatic-fluid system related to the Verkhneurmiisky granite pluton, which is one of domes of the Badzhal batholith. The transition has been traced from magmatic crystallization of granite to hydrothermal ore formation and evolution of magmatic fluid from its separation to Sn and W deposition. Mixed fluid-melt inclusions directly support tin-bearing fluid separation during melt crystallization. The glass compositions indicate that granite and porphyry granite crystallized from felsic metaluminous to peraluminous melts with an ASI index and alkali content ranging from 0.95 to 1.33 and from 6.02 to 9.02 wt %, respectively. The Cl and F concentrations in glasses are 0.03–0.14 and 0.14–0.44 wt %, respectively, and are higher than those in the bulk rock compositions, 0.02 and 0.05–0.13 wt %, respectively. These differences indicate that Cl and F could have been removed from a granitic melt during its crystallization and degassing. The H2O concentration estimated based on the electron deficiency of summed microprobe analyses is 8–11 wt %. This was estimated taking into account the possible effect of “sodium loss” (Nielsen and Sigurdson, 1981) when analyzing hydrated glasses. Taking into account the high uncertainty of such estimation (Devine et al., 1995), this value is extremely uncertain and the studied melts should be considered as containing 9.5–10.0 wt % H2O. The melt inclusion study shows that some of the magmatic rocks of the Badzhal ore-magmatic system formed at approximately 650°C. The melt from which these rocks crystallized was felsic, moderate in fluorine, and meta- and peraluminous. Low-temperature crystallization is probably caused by high water pressure and elevated fluorine content. These inclusions most likely characterize the final stage of the pluton, at which crystals, residual melt, and magmatic fluid phase coexist. Fluid responsible for the formation of greisens at the Pravourmiisky deposit has features very close to those of supercritical fluid trapped by magmatic minerals. Its salinity, ranging from ∼9 to 12 wt % NaCl equiv., and maximal temperature of 550°C (taking into account pressure correction for ∼1 kbar) are close to those of magmatic fluid. This makes it possible to relate the origin of the fluid to cooling of the pluton. Greisen and quartz-cassiterite-topaz veins of the Pravourmiisky deposit formed from magmatic fluid at a decreased temperature from 550–450 to 480–380°C. The fluid responsible for the formation of quartz-cassiterite veins at the Blizhnee deposit also separated from magma as indicated by the oxygen isotope composition ( $${\delta^{18}}{{\rm{O}}_{{{\rm{H}}_2}{\rm{O}}}}\sim8.5{\%\circ}$$ ), which evolved in a shallower environment under much lower pressure. This resulted in fluid with a salinity of ∼13 wt % NaCl equiv. at 420–340°C being separated into a low-density low-saline vapor and brine with a salinity of 33.5–37.4 wt % NaCl equiv. The oxygen isotope composition of the mineralizing fluid was governed by equilibrium with granite within a wide temperature range (from ∼700°C to the onset of greisen crystallization). The agreement between the measured data and those calculated based on the suggested model indicates that a significant volume of external fluid having different isotopic features and not in equilibrium with the Verkhneurmiisky granite did not enter the magmatic-fluid system. The revealed differences in the physicochemical formation conditions of the two studied deposits are not critical and support their formation within a single magmatic-fluid system.

Water delivery in the inner solar nebula

Context.Endogenous or exogenous, dry or wet, various scenarios have been depicted for the origin of water on the rocky bodies in our solar system. Hydrated silicates found in meteorites and in interplanetary dust particles, together with observations of abundant water reservoirs in the habitable zone of protoplanetary disks, are evidence that support aqueous alteration of silicate dust grains by water vapor condensation in a nebular setting.Aims.We investigate the thermodynamics (temperature and pressure dependencies) and kinetics (adsorption rates and energies, surface diffusion and cluster formation) of water adsorption on surfaces of forsterite grains, constraining the location in the solar nebula where aqueous alteration of silicates by water vapor adsorption can occur efficiently and leads to the formation of phyllosilicates. We analyze the astrophysical conditions favorable for such hydration mechanism and the implications for water on solid bodies.Methods.The protoplanetary disk model (ProDiMo) code is tuned to simulate the thermochemical disk structure of the early solar nebula at three evolutionary stages. Pressure, temperature, and water vapor abundance within 1 au of the protosun were extracted and used as input for a Monte Carlo code to model water associative adsorption using adsorption energies that resemble the forsterite [1 0 0] crystal lattice.Results.Hydration of forsterite surfaces by water vapor adsorption could have occurred within the nebula lifetime already at a density of 108cm−3, with increasing surface coverage for higher water vapor densities. Full surface coverage is attained for temperatures lower than 500 K, while for hotter grain surfaces water cluster formation plays a crucial role. Between 0.5 and 10 Earth oceans can arise from the agglomeration of hydrated 0.1μm grains into an Earth-sized planet. However, if grain growth occurs dry and water vapor processes the grains afterward, this value can decrease by two orders of magnitude.Conclusions.This work shows that water cluster formation enhances the water surface coverage and enables a stable water layer to form at high temperature and low water vapor density conditions. Finally, surface diffusion of physisorbed water molecules shortens the timescale for reaching steady state, enabling phyllosilicate formation within the solar nebula timescale.

Linear and nonlinear coherent coupling in a Bell-Bloom magnetometer

Spin-exchange collisions in hot vapours are generally regarded as a decoherence mechanism. In contrast, we show that linear and non-linear spin-exchange coupling can lead to the generation of atomic coherence in a Bell-Bloom magnetometer. In particular, we theoretically and experimentally demonstrate that non-linear spin exchange coupling, acting in an analogous way to a wave-mixing mechanism, can create new modes of coherent excitation which inherit the magnetic properties of the natural Larmor coherence. The generated coherences further couple via linear spin-exchange interaction, leading to an increase of the natural coherence lifetime of the system. Notably, the measurements are performed in a low-density caesium vapour and for non-zero magnetic field, outside the standard conditions for collisional coherence transfer. The strategies discussed are important for the development of spin-exchange coupling into a resource for an improved measurement platform based on room-temperature alkali-metal vapours.

An experimental study of R410A condensation heat transfer and pressure drops characteristics in microfin and smooth tubes with 5 mm OD

Heat transfer and pressure drop characteristics of R410A condensing flow in horizontal small microfin and smooth tubes with outer diameter of 5.0 mm were studied experimentally at relatively high mass fluxes ranging from 390 to 1583 kg/m2 s with different saturation temperatures of 309.15 K, 316.15 K, and 323.15 K. The results indicate that heat transfer coefficients and pressure gradients increase with increasing mass flux and with decreasing saturation temperature for both microfin and smooth tubes. The lower vapor density, higher liquid thermal conductivity, and higher surface tension effect all contribute to the higher heat transfer coefficients at a lower saturation temperature. The experimental heat transfer coefficients and frictional pressure gradients fit well with the empirical correlations. The heat transfer coefficient ratios between microfin and smooth tube range from 1.65 to 1.28 which means that microfin tubes can enhance heat transfer coefficients efficiently. Both heat transfer enhancement ratio and pressure drop penalty ration decrease with increasing mass flux and saturation temperature. Compared with other refrigerant properties, the liquid-vapor density contributes more to the heat transfer enhancement ratio at high mass flux.

Nature and evolution of fluid inclusions in the Cenozoic Beiya gold deposit, SW China

The Beiya Au deposit in the Sanjiang metallogenic belt, SW China, is a porphyry-skarn deposit that formed in an intracontinental setting. Three stages of hydrothermal veins, namely quartz veins (Stage 1), quartz-pyrite veins (Stage 2), and Au-rich sulfide-quartz veins (Stage 3) were identified on the basis of field relationship and petrography under scanning electron microscopy cathodoluminescence (SEM-CL). Intermediate density aqueous fluid inclusions (ID1, ID2), high density brine inclusions (B1, B2), and low density vapor inclusions (V1, V2) have been identified in both Stage 1 and Stage 2 veins. Only liquid-rich fluid inclusions (L3) were found in Stage 3 veins. Raman spectroscopy revealed that all the inclusions contain abundant CO2. H2S was identified in ID2 and V2 inclusions. Salinities and homogenization temperatures of the intermediate density aqueous fluid inclusions (ID1, ID2), high density brine inclusions (B1, B2), and low density vapor inclusions (V1, V2) are 7.4 ± 1.1–11.9 ± 2.2, 33.6 ± 0.5–39.2 ± 1, and 1.6 ± 0.7–5.8 ± 0.8 (wt% NaCl equiv.) and 400 ± 35–440 ± 37, 395 ± 20–414 ± 6, and 386 ± 5–416 ± 4 °C, respectively. Salinities and homogenization temperatures of the L3 inclusions range from 4.9 ± 1.6 to 9.8 ± 0.7 (wt% NaCl equiv) and from 301 ± 28 to 398 ± 4 °C, respectively. Initial intermediate density aqueous fluid inclusions contain 2000–10,000 ppm Fe, 2000–4000 ppm Cu, 200–600 ppm Zn, 200–500 ppm Pb, 17–89 ppm Mo, 1–8 ppm Ag, and 0.9–5.9 ppm Au, comparable to that of intermediate density inclusions in subduction-related porphyry deposits. Brine inclusions are rich in metals and have 9000–24600 ppm Fe, 3400–11,000 ppm Cu, 1200–5200 ppm Pb, 500–3000 ppm Zn, hundreds of ppm Mo, and tens of ppm Ag. The corresponding vapor inclusions contain lower metal concentrations: 400–6000 ppm Fe, 1700–4700 ppm Cu, 50–270 ppm Pb, 100–500 ppm Zn, and minor Mo and Ag. Low to intermediate density fluids are abundant and are inferred to have been the main metal transporting medium. A temperature decrease to approximately 350 °C during Stage 3 triggered metal precipitation.

Distribution and composition of gold in porphyry gold systems: example from the Biely Vrch deposit, Slovakia

The Biely Vrch deposit in the Western Carpathians is assigned to the shallow, sulfide-poor porphyry gold deposit type and has an exceptionally low Cu/Au ratio. According to 3-D geochemical models, there is a limited spatial correlation between Au and Cu due to the primary introduction of gold by a salt melt and Cu by low-density vapor. Despite a rough spatial correlation of gold grades with quartz stockwork intensity, gold is hosted mostly by altered rock, exclusively in native form. Three main gold mineral assemblages were recognized here. In the deepest parts of the system, the K- and Ca-Na silicate gold assemblage is associated with minerals of high-temperature alteration (plagioclase, K-feldspar, actinolite), with gold grades and fineness depending on depth and potassium content of the host rock: K-silicate alteration hosts the lowest fineness gold (~ 914), whereas Ca–Na silicate alteration has the highest (~ 983). The intermediate argillic gold assemblage is the most widespread, with gold hosted mainly by chlorite, illite, smectite, and interstratified illite–chlorite–smectite minerals. The gold fineness is mostly variable (875–990) and inherited from the former gold mineral assemblages. The latest advanced argillic gold assemblage has its gold mostly in kaolinite. The extremely high fineness (~ 994) results from gold remobilization by late-stage aqueous magmatic-hydrothermal fluids. Uncommon bonanza-grade appears where the earlier gold mineral assemblages were further enriched by this remobilized gold. Primary precipitation of gold occurred during ascent and cooling of salt melts at 450 to 309 °C, mostly during retrograde quartz solubility.

CuCl Complexation in the Vapor Phase: Insights from Ab Initio Molecular Dynamics Simulations

We investigated the hydration of the CuCl0 complex in HCl-bearing water vapor at 350°C and a vapor-like fluid density between 0.02 and 0.09 g/cm3 using ab initio molecular dynamics (MD) simulations. The simulations reveal that one water molecule is strongly bonded to Cu(I) (first coordination shell), forming a linear [H2O-Cu-Cl]0 moiety. The second hydration shell is highly dynamic in nature, and individual configurations have short life-spans in such low-density vapors, resulting in large fluctuations in instantaneous hydration numbers over a timescale of picoseconds. The average hydration number in the second shell (m) increased from ~0.5 to ~3.5 and the calculated number of hydrogen bonds per water molecule increased from 0.09 to 0.25 when fluid density (which is correlated to water activity) increased from 0.02 to 0.09 g/cm3 (fH2O 1.72 to 2.05). These changes of hydration number are qualitatively consistent with previous solubility studies under similar conditions, although the absolute hydration numbers from MD were much lower than the values inferred by correlating experimental Cu fugacity with water fugacity. This could be due to the uncertainties in the MD simulations and uncertainty in the estimation of the fugacity coefficients for these highly nonideal “vapors” in the experiments. Our study provides the first theoretical confirmation that beyond-first-shell hydrated metal complexes play an important role in metal transport in low-density hydrothermal fluids, even if it is highly disordered and dynamic in nature.

The Magmatic to Magmatic-Hydrothermal Evolution of the El Laco Deposit (Chile) and Its Implications for the Genesis of Magnetite-Apatite Deposits

Abstract The geology and geochemistry of the El Laco iron oxide deposit (Central Andes, Chile) support a genesis related to the ascent, degassing, and subvolcanic emplacement of an unusual oxidized silica-poor but water-and iron-rich melt that took place during the growth of the host Pliocene-Holocene andesitic volcano. The model proposed in this paper for the evolution of the deposit involves the formation of a shallow telescoped magmatichydrothermal system with complex melt-fluid unmixing in a vertical column of less than 1 km. The dominant mineralization occurs as large stratabound apatite-poor magnetite bodies interfingered with an andesite host and rooted in vertical dikes of magnetite with minor apatite. The stratabound mineralization is crosscut by abundant coeval diatreme-like structures indicative of vigorous degassing. The andesite underlying the mineralization is pervasively replaced by a high-temperature alkali-calcic alteration assemblage (K feldspar-diopside-magnetite-scapolite) that includes coarse-grained diopside-magnetite-anhydrite veins and large subvertical bodies of magmatic-hydrothermal breccias. The host andesite also shows a large strata-bound steam-heated acid alteration that is devoid of any magnetite but has produced the replacement of a significant proportion of the early magnetite by hematite. The El Laco system is rich in anhydrite but poor in sulfides, suggesting that there were persistent oxidizing conditions that inhibited the formation of a sulfide-bearing mineralization. Field evidence, oxygen isotope geothermometry, and thermodynamic constraints suggest that the magnetite mineralization formed close to the surface at temperatures above 800°C. The magnetite textures, similar to those of subaerial low-viscosity basalts, and the presence of melt inclusions in the host andesite recording the presence of immiscible Fe-Mg-Ca-(Si-Ti-P-S) and Si-K-Na-Al melts, suggest that the magnetite ore formed by direct crystallization from an iron-rich melt; its chemistry inhibited the formation of most other magmatic phases except minor apatite, anhydrite, and diopside. The crystallization of the iron-rich melt at shallow depths promoted the separation of large amounts of two immiscible aqueous fluids: a dominant low-density vapor phase and a small volume of hypersaline fluid. Diopside-magnetite-anhydrite veins are interpreted as the product of the crystallization of the residual melts, whereas the interaction of the brine with the host andesite formed the deep alkali-calcic hydrothermal assemblage. The condensation and mixing of the low-density magmatic vapor with meteoric water produced the steam-heated alteration. Isotope data from the host andesite (87Sr/86Sr: 0.7066–0.7074; εNd: −5.5 to −4.1; δ18Owhole rock: 7.2–9.6‰; δ18Omagnetite: 5.1–6.2‰) and an underlying andesite porphyry (87Sr/86Sr: 0.7075–0.7082; εNd: −5.9 to −4.6) reflect the interaction of a primitive mantle melt with Andean crustal rocks. The isotope geochemistry of the magnetite ore (87Sr/86Sr: 0.7083; εNd: −5.4 to −5.1; δ18O 3.5–5.5‰) and the alkali-calcic alteration and related diopside-magnetite-anhydrite veins (87Sr/86Sr: 0.7080–0.7083; εNd: −5.1 to −4.6; δ18Odiopside: 7.2–8.2%c; δ18Omagnetite 4.4–6.3‰) show that the mineralization has a more crustal signature than the host andesite and all the volcanic rocks of the Central Andes. Therefore, ore-forming fluids/melts were not equilibrated with the host volcanic rocks and are interpreted as related to a deep yet undiscovered batch of highly contaminated igneous rocks. Crustal contamination is interpreted as due to major interaction of a juvenile melt with the underlying Late Mesozoic-Tertiary Salta Group, located 1 to 6 km beneath the volcano and which has high 87Sr/86Sr values (0.7140–0.7141).