Sulfate Melts Research Articles

Experimental Equilibrium and Fractional Crystallization of a H2O, CO2, Cl and S-Bearing Potassic Mafic Magma at 1.0 GPa, With Implications for the Origin of Porphyry Cu (Au, Mo)-Forming Potassic Magmas

ABSTRACT The origin of intermediate to felsic potassic magmas is debated, and not much is known about the volatile content of potassic magmas associated with porphyry Cu (Au, Mo) deposits. To better understand the liquid line of decent of mafic potassic magmas and the behavior of volatiles during magma differentiation, we performed 19 experiments at 1.0 GPa and 1150 °C to 850 °C using piston cylinder presses. We developed a new experimental technique that involves a capsule liner made of single-crystal zircon to prevent the loss of Fe and S in the starting material to the noble metal capsule. The starting material is a high-Mg, basaltic trachyandesite (52 wt% SiO2, 12 wt% MgO, 1.9 wt% Na2O and 5.3 wt% K2O) from the Sanjiang region in southwestern China, doped with geologically realistic amounts of volatiles (i.e. 4.0 wt% H2O, 0.34 wt% CO2, 0.27 wt% Cl and 0.25 wt% S). The addition of 0.25 wt% S in the form of anhydrite internally buffered the experiments at an oxygen fugacity of 2.0 ± 0.5 log units above the fayalite–magnetite–quartz buffer, which is similar to the redox state of the Sanjiang variously evolved potassic magmas. The experimentally produced silicate melts match well with the Sanjiang intermediate to felsic magmas in terms of major, minor and trace element compositions, and also with regard to the S and Cl contents. The sequence of crystallizing minerals (olivine + clinopyroxene –> biotite ± orthopyroxene –> apatite –> K-feldspar) also fits with the one observed in the Sanjiang mafic to intermediate magmas. These results suggest that the Sanjiang intermediate to felsic magmas, including the porphyry Cu (Au, Mo)-forming magmas, can form solely by differentiation of potassic mafic magmas without any involvement of old crustal material. During experimental differentiation at 1.0 GPa, the S content of the evolving silicate melt first increased until ~57 wt% melt SiO2, and then decreased in response to precipitation of sulfides, sulfate melt and/or anhydrite, whereas the H2O and Cl contents of the evolving silicate melt increased exponentially until saturation in a CO2-rich fluid was reached at 60 to 65 wt% melt SiO2 and ~ 8 wt% melt H2O. During further magma differentiation the H2O and Cl contents of the evolving silicate melt remained constant until ~70 wt% melt SiO2, after which point the Cl content of the silicate melt decreased due to increased partitioning of Cl into the fluid phase ± increased fluid/melt ratio. Based on these experimental results and petrographic and geochemical evidence from natural samples, the Sanjiang porphyry Cu (Au, Mo)-forming magmas (65–70 wt% SiO2) are interpreted to have formed through differentiation of primitive, mantle-derived, potassic magmas in the lower crust (≥1.0 GPa), and to have ascended ±directly from the lower crust to shallow crustal levels. They likely contained 8 to 13 wt% H2O, 0.37 to 0.90 wt% Cl and 0.07–0.29 wt% S. This case study on the magma evolution in the Sanjiang region may have implications for the origin and nature of intermediate to felsic potassic magmas in various tectonic settings.

Influence of compound additive on concrete in hot and dry climate

In the conditions of hot and dry climate, the concrete mixture quickly loses its mobility and workability. In this regard, it is necessary to plasticize it by introducing various surfactants; at the same time, the surfactant additive should not slow down the process of hydration and hardening. To ensure salt resistance, it is necessary to increase the density and strength of concrete. The proposed complex additive is obtained by joint grinding in a ball mill of soda sulfate melt and gossypol resin to a specific surface of 2800 cm2/g at the rate of 0.5-1.5% and 0.1-0.3% by weight of cement. From the obtained results, it can be seen that with an increase in the content of gossypol resin from 0.1 to 0.3%, the normal density decreases by 1.4-4 points, and the setting time due to the accelerating action of the soda sulfate melt is reduced at the beginning by 20-50 minutes and the end by 60 - 240 min. Reference cement for 28 days gained a strength of 56 MPa, with a complex additive of 60-68 MPa. The coefficient of salt resistance of the reference 0.55-0.65 and with a complex additive of 0.80-0.86 is observed due to the strength and density of the samples. Increasing the strength makes it possible to save 17-21% of cement.

Isothermal oxidation and hot corrosion behavior of HVOF sprayed 80Ni-20Cr coatings at 750 °C

NiCr thermal spray coatings are widely used in many different industrial areas, especially in aviation, automotive, and thermal power plants, in order to obtain abrasion resistance. The determination of high-temperature properties is of great importance in terms of determining the limits to which the coating can operate without being damaged and its structural stability. In this study, 80Ni-20Cr alloy powder was deposited onto 316L stainless steel substrates using a high velocity oxygen fuel (HVOF) spraying technique, and the coatings' oxidation and corrosion behaviors at high temperatures were assessed. In this context, while isothermal oxidation tests were conducted at 750 °C for 5, 25, 50 and 75 h, the hot corrosion behavior of the coatings was investigated for 1, 3 and 5 h at 750 °C in an environment consisting of a 55 wt% V2O5–45 wt% Na2SO4 corrosive salt mixture. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to evaluate powder feedstock and as-deposited, oxidized, and corroded coating samples' phase formation and microstructural changes. In all cases, the coated samples showed good resistance to isothermal oxidation, with no damage such as flaking and peeling. No oxide formation was observed on the coating surfaces. The oxidation started from the coating and substrate interface and proceeded towards the coating surface. Following the hot corrosion experiments, it was observed that the 80Ni-20Cr coating's reaction with the vanadate-sodium sulfate melt resulted in the formation of the corrosion product Ni3V2O8 in all time periods. As a result, under high temperature oxidation and hot corrosion environmental conditions, 80Ni-20Cr coatings have been observed to retain their durability without major damage.

Trace element partitioning between anhydrite, sulfate melt, and silicate melt

AbstractAnhydrite has become increasingly recognized as a primary igneous phase since its discovery in pumices from the 1982 eruption of El Chichón, Mexico. Recent work has provided evidence that immiscible sulfate melts may also be present in high-temperature, sulfur-rich, arc magmas. In this study we present partition coefficients for 37 trace elements between anhydrite, sulfate melt and silicate melt based on experiments at 0.2–1 GPa, 800–1200 °C, and fO2 > NNO+2.5.Sulfate melt–silicate melt partition coefficients are shown to vary consistently with ionic potential (the ratio of nominal charge to ionic radius, Z/r) and show peaks in compatibility close to the ionic potential of Ca and S. Partition coefficients for many elements, particularly REE, are more than an order of magnitude lower than previously published data, likely related to differences in silicate melt composition between the studies. Several highly charged cations, including V, W, and Mo are somewhat compatible in sulfate melt but are strongly incompatible in anhydrite. Their concentrations in quench material from natural samples may help to fingerprint the original presence of sulfate melt.Partition coefficients for 2+ and 3+ cations between anhydrite and silicate melt vary primarily as a function of the calcium partition coefficients (DCaAnh−Sil) and can be described in terms of exchange reactions involving the Ca2+ site in anhydrite. Trivalent cations are dominantly charge-balanced by Na1+. Most data are well fit using a simple lattice-strain model, although some features of the partitioning data, including DLaAnh−Sil>DCeAnh−Sil, suggest the occurrence of two distinct anhydrite Ca-sites with slightly different optimum radii at the experimental conditions.The ratio DSrAnh−Sil>DCaAnh−Sil is shown to be relatively insensitive to silicate melt composition and should vary from 0.63–0.53 between 1200–800 °C, based on a simple, “one-site” lattice strain model. Comparison to DSrAnh−Sil and DCaAnh−Sil calculated for natural anhydrite suggests that in most cases, including the S-rich eruptions of Pinatubo and El Chichón, the composition of anhydrite is consistent with early crystallization of anhydrite close to the liquidus of silicate melt with a composition approximately that of the bulk erupted material. This illustrates how anhydrite (and perhaps sulfate melt) provides a mechanism to transport large quantities of sulfur from significant depth to the eruptive environment.

Melt–Fluid and Fluid–Fluid Immiscibility in a Na2SO4–SiO2–H2O System and Implications for the Formation of Rare Earth Deposits

AbstractLiquid–liquid immiscibility has crucial influences on geological processes, such as magma degassing and formation of ore deposits. Sulfate, as an important component, associates with many kinds of deposits. Two types of immiscibility, including (i) fluid–melt immiscibility between an aqueous solution and a sulfate melt, and (ii) fluid–fluid immiscibility between two aqueous fluids with different sulfate concentrations, have been identified for sulfate–water systems. In this study, we investigated the immiscibility behaviors of a sulfate‐ and quartz‐saturated Na2SO4–SiO2–H2O system at elevated temperature, to explore the phase relationships involving both types of immiscibility. The fluid–melt immiscibility appeared first when the Na2SO4–SiO2–H2O sample was heated to ∼270°C, and then fluid–fluid immiscibility emerged while the sample was further heated to ∼450°C. At this stage, the coexistence of one water‐saturated sulfate melt and two aqueous fluids with distinct sulfate concentrations was observed. The three immiscible phases remain stable over a wide pressure–temperature range, and the appearance temperature of the fluid–fluid immiscibility increases with the increased pressure. Considering that sulfate components occur extensively in carbonatite‐related deposits, the fluid–fluid immiscibility can result in significant sulfate fractionation and provides implications for understanding the formation of carbonatite‐related rare earth deposits.

Solubility of K2SO4 in silica-saturated solutions and applications to determine the composition of ore-forming fluids

Sulfate-bearing geofluids are widespread in many geological environments and play important roles in ore-forming processes. Recent experiments provide evidences that in silica-rich fluids, Na2SO4 solubility exhibits a complex temperature dependence, first decreasing from 25 to 313 °C and then increasing from 313 to 425 °C. The fluid-borne silica have critical implications for sulfate-bearing hydrothermal systems and formations of rare earth element deposits. However, whether other sulfate salts share the same characteristics remains unknown.In this study, fused silica capillary capsules (FSCCs) containing K2SO4-saturated solutions and K2SO4 crystals are used to quantitatively investigate the solubility of K2SO4 at different temperatures in the K2SO4-SiO2-H2O system. In the K2SO4-SiO2-H2O system, K2SO4 shows prograde solubility from 50 to 400 °C, and does not melt through the whole investigated temperature range. The relationship between temperature and the solubility of K2SO4 can be described by a simple linear function with R2 = 0.991: Csulfate = 4.1307 × 10−3 × T + 0.5532, where Csulfate and T represent the solubility of K2SO4 in m (mol/kg H2O) and temperature in °C, respectively. These results show that the solubility of K2SO4 can be enhanced by 3 to 5 times at 300–400 °C by the presence of silica, compared with that in silica-absent system, even without the formation of sulfate melt. Considering that quartz is ubiquitous in the Earth's crust, the solubility of sulfate in natural geofluids may reach a much higher level than previously expected.The temperature dependences of the solubilities of K2SO4 and Na2SO4 in silica-saturated fluids were used to constrain the compositions of the mineralizing fluids of the synmetamorphic hematite-quartz veins at Ouro Fino (SE Brazil) and the Maoniuping REE deposit (SW China), based on the previously reported microthermometric results of fluid inclusions that contain sulfate daughter minerals. For the hematite-quartz vein at Ouro Fino, the sulfate concentration was calculated to be 8.9–19.2 wt%, which is in line with previous laser ablation measurements (~15.3 wt%). For the Maoniuping REE deposit, the total sulfate concentration was determined to be 16.3–27.4 wt%, and the REE concentration of the ore-fluid was further estimated to be 0.30–0.44 wt%.

Micro‐Raman study of cesanite (Ca2Na3 (OH)(SO4)3) in chloride segregations from Udachnaya‐East kimberlites

AbstractCesanite (Ca2Na3(OH)(SO4)3), a rare mineral, has been found in a few places restricted to a geothermal field and caves. We report the new occurrence of cesanite in quite different geological site—within sulfate‐rich melt inclusions in chloride segregations from kimberlites of Udachnaya‐East pipe (Siberia). Two halite generations: сesanite free and сesanite‐bearing, were distinguished in concentrically zonal segregations according to the results of the mineral and sulfate melt inclusion study by micro‐Raman spectroscopy and SEM‐EDS. We have applied the Raman spectroscopy and first principles calculations to understand structural and vibrational properties of cesanite daughter mineral in polyphase sulfate inclusions. Polarized spectra provided additional information on the overlapped components of the spectral profile. The Raman spectra of cesanite in the range of OH stretching vibrations are reported for the first time. The study aims to clarify the source of the NaSCl‐enrichment in the Udachnaya‐East pipe, which is highly discussed.

Evidence for iron-rich sulfate melt during magnetite(-apatite) mineralization at El Laco, Chile

Abstract The origins of Kiruna-type magnetite(-apatite) [Mt(-Ap)] deposits are contentious, with existing models ranging from purely hydrothermal to orthomagmatic end members. Here, we evaluate the compositions of fluids that formed the classic yet enigmatic Mt(-Ap) deposit at El Laco, northern Chile. We report evidence that ore-stage minerals crystallized from an Fe-rich (6–17 wt% Fe) sulfate melt. We suggest that a major component of the liquid was derived from assimilation of evaporite-bearing sedimentary rocks during emplacement of andesitic magma at depth. Hence, we argue that assimilation of evaporite-bearing sedimentary strata played a key role in the formation of El Laco and likely Mt(-Ap) deposits elsewhere.

Solubility of Na2SO4 in silica-saturated solutions: Implications for REE mineralization

Abstract Sulfate is traditionally considered to have retrograde solubility in aqueous solutions. However, our recent hydrothermal diamond-anvil cell (HDAC) experiments have shown that the solubility of Na2SO4 changes from retrograde to prograde in the presence of silica, leading to the formation of sulfate-rich solutions at high temperatures, in line with observations on natural geofluids. In this study, we use synthetic inclusions of fused silica capillary capsules containing saturated Na2SO4 solutions and Na2SO4 crystals to quantitatively investigate the solubility of Na2SO4 at different temperatures in the Na2SO4-SiO2-H2O system. Sulfate concentrations were measured using Raman spectroscopy and calibrated using Cs2SO4 solutions with known concentrations. The solubility of crystalline Na2SO4 dropped slightly when heated from 50 to 225 °C and dramatically from 225 to 313 °C. At 313 °C, the Na2SO4 crystals began to melt, forming immiscible sulfate melt coexisting with the aqueous solution, with or without solid Na2SO4. With the formation of sulfate melt, the solubility of Na2SO4 was reversed to prograde (i.e., solubility increased considerably with increasing temperatures). The solubility of Na2SO4 in the measured solution was significantly higher than that predicted in the absence of SiO2 over the entire temperature range (except for temperatures around 313 °C). This indicates that the presence of SiO2 greatly changes the dissolution behavior of Na2SO4, which may be caused by the formation of a sulfate–silicate intermediates such as Si(OH)4SO42−. Considering that most crustal fluids are silica-saturated, the solubility curve of Na2SO4 obtained in this study can better reflect the characteristics of geofluids when compared to that of Na2SO4-H2O binary system. At temperatures of 313–425 °C, the solubility of Na2SO4 increases with temperature following the function Csulfate = –3173.7/T + 5.9301, where Csulfate and T represent the solubility of Na2SO4 in mol/kg H2O and temperature in Kelvin, respectively. As an application, this temperature-solubility relationship can be used to evaluate the sulfate contents in fluid inclusions that contain sulfate daughter minerals, based on the temperature of sulfate disappearance obtained from microthermometric analysis. The sulfate concentrations of the ore-forming fluids of the giant Maoniuping carbonatite-related rare earth element (REE) deposit (southwest China) were calculated to be 4.67–4.81 m (mol/kg H2O). These sulfate concentrations were then used as internal standards to calibrate the previously reported semi-quantitative results of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis of REE-forming stage fluid inclusions at this deposit. The calculated Ce concentrations in the REE-mineralizing fluid range from 0.42 to 0.49 wt%. The high fluid REE contents suggest that the sulfate-rich fluids are ideal solvents for REE transport. A mass-balance calculation was carried out to evaluate the minimal volume of carbonatite melt that was required for the formation of the giant Maoniuping REE deposit. The result indicates that the carbonatite dikes in the mining area are enough to provide the required fluids and metals, and thus a deep-seated magma chamber is not necessary for ore formation.

Rare earth elements deposits in China: Spatio-temporal distribution and ore-forming processes

<p indent=0mm>China dominates the world REE (rare earth elements) resources, 98% of which are from carbonatite-related REE deposits. Extensive studies of this type of REE deposits are available, but it is still poorly understood how carbonatite magmas were generated and how REEs were transported and precipitated in such magmas. On the basis of previous studies, this paper synthesizes the spatio-temporal distribution of this type of REEs deposits in China and their major features, including characteristics of ore-forming fluids, and discusses existing genetic models regarding the origin of causative magma, and mechanics of REE enrichment, transportation and precipitation. In China, carbonatite-related REE deposits occur in the craton margin environments with four major REE metallogenic belts: the Mesoproterozoic Bayan Obo-Langshan belt (e.g., the Bayan Obo deposit), the early Mesozoic eastern Qinling-Dabie belt (e.g., the Miaoya deposit), the late Mesozoic Zibo-Laiwu-Weishan belt (e.g., the Chishan deposit), and the Cenozoic Mianning-Dechang belt (e.g., the Maoniuping deposit). In these belts, REE-hosting carbonatites were emplaced in continental rift zones or along large-scale strike-slip faults at the Precambrian craton margins. The causative magmas were originated from partial melting of enriched lithospheric mantle sources, which may have undergone metasomatism by subducted slab-related fluids/melts, and may have also asthenospheric material involvement. These magmas may have formed through melt immiscibility and fractional crystallization from primary carbonated silicate melt. The melt immiscibility may include unmixing between alkaline silicate and carbonate melts, or multi-phase melt immiscibility of carbonate melt, mafic or ultramafic melt, phosphomagnesite melt, and alkaline silicate melt. The immiscibility and/or crystal fractionation of mafic mineral can lead to the formation of carbonate melts rich in REEs. The newly discovered lithofacies zonation at Bayan Obo, with a biotitite outer zone, implies a magmatic evolution of a silica-rich parent magma. The low REE concentrations and LREE/HREE ratios of biotitite indicate possible LREE enrichment in the evolved carbonatite magma by biotite fractional crystallization. The crystallization of carbonate minerals during the upwelling and emplacement of carbonatite magmas, may further enrich late-stage carbonatite melts and carbonatite fluids in LREE. This process can better explain the REE mineralization dominantly in the late-stage of carbonatite magmatism or post-magmatic fluid stage. The melt, melt-fluid and fluid inclusion results for Bayan Obo, Maoniuping and Chishan indicate SO₄²⁻ and CO₂-rich carbonatite fluids. The microthermometry and SEM/EDS results for primary melt-fluid inclusions hosted in fluorite from Maoniuping indicate that carbonatite fluids were extremely rich in SO₄²⁻, and underwent an unmixing process between sulfate melt and aqueous fluid. Both inclusion and experimental results indicate that the sulfate has a very high solubility in SiO₂-bearing aqueous fluids, inconsistent with the SiO₂-free system. The geochemical thermodynamic results also confirm the SO₄²⁻ -dominated agent for REE transportation. The unmixing process between sulfate melts and aqueous fluids would lead to extensive decrease of SO₄²⁻ in the fluid, and bulk REE precipitation. The rapid evolution of carbonatite fluids prevents long distance migration of carbonatite fluids, resulting in all REE mineralization within, or proximal to the carbonatite bodies. The strong mineralization would occur in the central zone or the shallow level and then would become weaker outwards and downwards of carbonatite bodies.

A fundamental role of carbonate–sulfate melts in the formation of iron oxide–apatite deposits

Genetic models for iron oxide–apatite deposits are controversial and span a spectrum from orthomagmatic to hydrothermal endmembers. This lack of consensus is rooted in uncertainties as to the nature and origin of ore-forming fluids in these systems. Here, we present a fluid-inclusion study of mineralizing fluids at two iron oxide–apatite deposits (Buena Vista, Nevada and Iron Springs, Utah). We found that the inclusions in both systems comprise both aqueous brine and ubiquitous iron-rich carbonate–sulfate melts. These melts were found throughout the paragenesis of both deposits and show a tremendous capacity to transport ferric iron. Hence, we argue that orthomagmatic fluids played a role in mineralization at both Buena Vista and Iron Springs, and that the main ore-forming fluid was an iron-rich carbonate–sulfate melt formed by the assimilation and anatexis of evaporite-bearing carbonate rocks. The geological conditions that give rise to carbonate–sulfate melts are also a common feature of other classic iron oxide–apatite systems worldwide. Hence, we argue that the process of assimilation, anatexis and immiscibility of carbonate–sulfate melts is fundamental to iron oxide–apatite formation and provides a common link between iron oxide–apatite systems in different geological settings. Iron-rich carbonate–sulfate melts are fundamental to the formation of iron oxide–apatite ore deposits, according to a detailed fluid-inclusion study that characterized the mineralizing fluids for two mineralizing systems in the United States.

The stability and composition of sulfate melts in arc magmas

The stability field and composition of immiscible sulfate melts in equilibrium with silicate magmas has been determined using experiments over a range of crustal pressures, allowing an assessment of their possible role in transporting sulfur into the sub-volcanic arc and porphyry copper deposit systems. Experimental starting materials were based on natural trachyandesite and trachydacite compositions, with 3.5–7 wt% H2O and 3.5–5.5 wt% sulfur added to produce large, analyzable amounts of sulfate phases. Conditions ranged over 800–1200 °C, 0.2-1GPa and ƒO2 > NNO + 2.5. Sulfate melts formed at temperatures above 1000 °C at 0.75 and 1 GPa and above 900 °C at 0.2 GPa, suggesting some pressure dependence on their stability. At temperatures below 1100 °C sulfate melts and anhydrite crystals commonly coexist. Sulfate melts quenched to an intergrowth that was difficult to prepare for analysis. However, the composition was approximated by EPMA and further constrained by mass balance calculations. Sulfate melts were dominated by CaO and SO3, but also contained, in order of decreasing abundance, Na2O, K2O, MgO, FeO, Cl and P2O5. Chlorine showed a particular preference for the sulfate melt relative to the coexisting silicate melt, and calculated partition coefficients for sulfate/silicate melts were 5–13 at 1200 °C, 0.75–1 GPa. Experimental data show that, in the absence of an exsolved, hydrous fluid phase, sulfate melts can form in natural arc magmas at near-liquidus temperatures ≥ 1000 °C, assuming that magmas are oxidized and contain sufficient sulfur (> 2000–3000 ppm S). These results suggest that sulfate melt could be an important component in transporting sulfur as well as chlorine to shallow levels in the crust for hydrous magmas under a specific range of conditions. Both the non-quenchable and water-soluble nature of sulfate melts (and anhydrite) make them difficult to identify, unless trapped as mineral inclusions similar to the “wormy anhydrite” trapped in high-temperature amphiboles from Yanacocha, Peru.

Forming sulfate- and REE-rich fluids in the presence of quartz

Abstract The presence of sulfate-rich fluids in natural magmatic hydrothermal systems and some carbonatite-related rare earth element (REE) deposits is paradoxical, because sulfate salts are known for their retrograde solubility, implying that they should be insoluble in high-temperature geofluids. Here, we show that the presence of quartz can significantly change the dissolution behavior of Na2SO4, leading to the formation of extremely sulfate-rich fluids (at least 42.8 wt% Na2SO4) at temperatures &amp;gt;∼330 °C. The elevated Na2SO4 solubility results from prograde dissolution of immiscible sulfate melt, the water-saturated solidus of which decreases from ≥∼450 °C in the binary Na2SO4-H2O system to ∼270 °C in the presence of silica. This implies that sulfate-rich fluids should be common in quartz-saturated crustal environments. Furthermore, we found that the sulfate-rich fluid is a highly effective medium for Nd mobilization. Thermodynamic modeling predicts that sulfate ions are more effective in complexing REE(III) than chloride ions. This reinforces the idea that REEs can be transported as sulfate complexes in sulfate-rich fluids, providing an alternative to the current REE transport paradigm, wherein chloride complexing accounts for REE solubility in ore fluids.

Experimental Study of REEs, Ba, and Sr Interphase Partitioning in Fluid–Magmatic Silicate Systems at T = 1250°C and P = 2 kbar

The results of study of the alkaline silicate melt–hydrous saline (carbonate, sulfate, and fluoride) fluid system, as well as partitioning of ore metals (Ba, Sr, and REEs) between coexisting phases at T = 1250°C and P = 2 kbar are reported. It is shown that aqueous solutions with the compositions studied cannot be effective concentrators and transporters of ore elements such as REEs, Sr, and Ba. The sulfate melt accumulates Sr and Ba in the alkaline silicate melt–hydrous sulfate fluid system, which provides evidence for the efficiency of sulfate ore extraction of Sr and Ba from the melt. The results obtained support the important oregenerating role of dense saline phases formed upon the development of liquid heterogeneity in fluid–magmatic systems.

The pressure–temperature stability and composition of sulphate melts

"The pressure–temperature stability and composition of sulphate melts." Applied Earth Science, 126(2), pp. 67–68

A model for carbonatite hosted REE mineralisation — the Mianning–Dechang REE belt, Western Sichuan Province, China

The Mianning–Dechang (MD) REE belt of Sichuan, China is one of the most important REE belt in China, which includes Maoniuping, the third largest REE deposit in the world and a series of large to small REE deposits. Mineralization styles varied across the belt, as well as within different parts of the same deposit. Styles include vein-stockworks, pegmatites, breccias and disseminated REE mineralization. Based on geological, geochemical and inclusion studies, this paper proposes a new model for carbonatite hosted REE mineralization. The results show that ore-forming fluid is derived from carbonatite magma, which has high temperature, pressure and density, and is characterized by high K, Na, Ca, Sr, Ba, REE and SO4 contents. The supercritical ore fluid underwent a distinctive evolution path including phase separation, exolution of sulfate melt and unmixing between aqueous fluid and liquid CO2. Rapid geochemical evolution of a dense carbonatite fluid causes REE mineralization and associated alteration to occur within or proximal to the source carbonatite. Veins, pegmatites and carbonatite comprise a continuum of mineralization styles. Veins occur in the outer zone of the upper levels of the deposit. Pegmatites occur in the inner zone of upper levels, whereas disseminated REE ore occurs at the base of the carbonatite. High water solubility in the carbonatite magma and low water, high REE in the exsolved ore-forming fluids, imply that a giant carbonatite body and deep magma chamber are not necessary for the formation of giant REE deposits.

Harmunite CaFe2O4: A new mineral from the Jabel Harmun, West Bank, Palestinian Autonomy, Israel

Harmunite, naturally occurring calcium ferrite CaFe2O4, was discovered in the Hatrurim Complex of pyrometamorphic larnite rocks close to the Jabel Harmun, the Judean Desert, West Bank, Palestinian Autonomy, Israel. The new mineral occurs in larnite pebbles of the pseudo-conglomerate, the cement of which consists of intensely altered larnite-bearing rocks. Srebrodolskite, magnesioferrite, and harmunite are intergrown forming black porous aggregates to the central part of the pebbles. Larnite, fluorellestadite, ye’elimite, fluormayenite, gehlenite, ternesite, and calciolangbeinite are the main associated minerals. Empirical crystal chemical formula of harmunite from type specimen is as follows Ca1.013(Fe3+1.957Al0.015Cr3+0.011Ti4+0.004 Mg0.003)∑1.993O4. Calculated density is 4.404 g/cm3, microhardness VHN50 is 655 kg/mm2. The Raman spectrum of harmunite is similar to that of the synthetic analog. Harmunite in hand specimen is black and under reflected plane-polarized light is light gray with red internal reflections. Reflectance data for the COM wavelengths vary from ~22% (400 nm) to ~18% (700 nm). The crystal structure of harmunite [ Pnma; a = 9.2183(3), b = 3.0175(1), c = 10.6934(4) A; Z = 4, V = 297.45(2) A3], analogous to the synthetic counterpart, was refined from X-ray single-crystal data to R 1 = 0.0262. The structure of CaFe2O4 consist of two symmetrically independent FeO6 octahedra connected over common edges, forming double rutile-type ∞1[Fe2O6] chains. Four such double chains are further linked by common oxygen corners creating a tunnel-structure with large trigonal prismatic cavities occupied by Ca along [001]. The strongest diffraction lines are as follows [ d hkl , ( I )]: 2.6632 (100), 2.5244 (60), 2.6697 (52), 1.8335 (40), 2.5225 (35), 2.2318 (34), 1.8307 (27), 1.5098 (19). Crystallization of harmunite takes place in the presence of sulfate melt.

Fluidized Bed Selective Oxidation-Sulfation Roasting of Nickel Sulfide Concentrate: Part II. Sulfation Roasting

The fluidized bed sulfation roasting process followed by water leaching was investigated as an alternative process to treat nickel sulfide concentrate for nickel production. The effects of several roasting parameters, such as the sulfation gas flow rate, roasting temperature, the addition of Na2SO4, and the roasting time, were studied. 79 pct Ni, 91 pct Cu, and 95 pct Co could be recovered with minimal dissolution of Fe of 4 pct by water leaching after two-stage oxidation-sulfation roasting under optimized conditions. The sulfation roasting mechanism was investigated, showing that the outermost layer of sulfate melt and the porous iron oxide layer create a favorable sulfation environment with high partial pressure of SO3. Sulfation of the sulfide core was accompanied by the conversion of the sulfide from Ni1−x S to Ni7S6 as well as inward diffusion of the sulfation gas.

Ampandrandava and similar phlogopite deposits in southern Madagascar: Derivation from a silicocarbonatitic melt of crustal origin

The Ampandrandava phlogopite deposit, located near Beraketa in southern Madagascar, and others like it in the region, in both the Androyen and Anosyen domains, were created by the crystallization of pods and dikes of crustally derived silicocarbonatitic melt. The anatectic reaction seems to have involved regional marble with C and O isotopes shifted toward mantle values and, at Ampandrandava, in particular, input from an evaporitic sequence. This hypothesis accounts for the importance of magmatic anhydrite in the pegmatitic pods and the presence of chlorine in the fluorapatite and phlogopite. The pods and dikes were emplaced in phlogopite-bearing clinopyroxenite; the aggressive carbonate–sulfate melt digested the host locally, and the diopside, phlogopite and fluorapatite crystallized quickly owing to a vapor pressure quench rather than a thermal quench. The high-temperature anatectic event occurred after the final episode of regional metamorphism, at a time of exhumation of deep crust, tectonic quiescence accompanying post-orogenic collapse, and anorogenic magmatism once collision and deformation had ceased.

A method for investigation of hot corrosion by gaseous Na2SO4

A novel in situ exposure method for investigating hot corrosion of aluminde coatings in the absence of an alkali sulphate melt is presented. The samples are exposed to Na2SO4(g) at a temperature above the dew point of the gas. Results from 100 and 500h exposures at 900°C of Ni-based In792 covered with SIF232 aluminide coating are presented. Already after 100h of testing, attack characteristic for Type I hot corrosion is observed. The reactions taking place during the testing are discussed and the results are compared with those from the well-known ex situ salt hot corrosion test.