High CaO Concentrations Research Articles

Water-Rock Interactions in the Metamorphic Complex of Geothermal Field: Case Study in Wahlua Complex, Buru Island

In Indonesia, surface thermal manifestation is commonly found in a volcanic geological setting. However, hot springs and alteration minerals in study area occur on metamorphic rock. In order to study its correlation with the emergence of the thermal fluid, the objective of this study is to characterize each metamorphic zone based on rock chemistry and the appearance of index minerals. Consequently, the correlation with thermal fluid chemistry can be observed. Data for this study are surface rock samples and thermal manifestation data. Metamorphic zones were determined by integrating geomorphology, petrography, and X-Ray Fluorescence (XRF) analyses. Three metamorphic zones were identified, namely, Garnet Zone, Biotite Zone, and Chlorite Zone. Garnet Zone is characterized by high concentrations of CaO and Al2O3 due to the presence of garnet. The abundance of biotite and muscovite in Biotite Zone may contribute to the highest concentration of K2O than the other two zones. Meanwhile, Chlorite Zone is characterized by the concentrations of SiO2, Fe2O3, and MgO. However, the composition of MgO might be influenced by mineral-fluid reaction. There are two clusters of thermal manifestation, which are western and eastern cluster manifestations. Western cluster manifestations are in the Biotite Zone. Meanwhile, the eastern cluster manifestation is in the Chlorite Zone. However, both clusters’ fluid chemistry shows significant differences in some elements such as SiO2, Na, K, Fe, and Mg concentration. It might suggest that the enrichment and depletion of these constituents in thermal fluid might correlate with each metamorphic zone’s characteristics. An inconsistent pattern between thermal fluid composition and rock chemistry was found in Mg concentration. It is most likely that the Mg concentration was influenced by groundwater dilution rather than the mineral-fluid interaction. The study concludes that the appearance of index minerals shows consistencies with composition variation of some elements in the manifestation fluid, such as SiO2, Na, K, and Fe.

Geochemical Criteria for Discriminating Shallow and Deep Environments in Oligocene-Miocene Succession, Western Iraq

The geochemical study of the Oligocene-Miocene succession Anah, Euphrates, and Fatha formations, western Iraq, was carried out to discriminate their depositional environments. Different major and trace patterns were observed between these formations. The major elements (Ca, Mg, Fe, Mn, K, and Na) and trace elements (Li, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Cs, Ba, Hf, W, Pb, Th, and U) are a function of the setting of the depositional environments. The reefal facies have lower concentrations of MgO, Li, Cr, Co, Ni, Ga, Rb, Zr, and Ba than marine and lagoonal facies but have higher concentrations of CaO, V, and Sr than it. Whereas dolomitic limestone facies are enriched V, and U while depletion in Li, Cr, Ni, Ga, Rb, Sr, Zr, Ba, and Pb Conversely, the lagoonal facies are rich in clay minerals and associated trace elements Li, V, Cr, Co, Ni, Cu, Ga, Rb, Zr, Ba, and Pb.

CO2‐Rich Rejuvenated Stage Lavas on Hawaiian Islands

AbstractSedimentary carbonates are sent to the deep mantle if they are not completely destroyed at subduction zones, and subducted carbonates may contribute to plume volcanism. To better constrain the role of recycled carbonates in Hawaiian volcanism, we report high‐precision olivine and whole‐rock geochemical compositions of shield and rejuvenated stage lavas from Kauai, Oahu and Maui Islands. The studied rejuvenated stage whole‐rocks have low SiO2 and high CaO concentrations, and are depleted in high field strength elements, such as, Nb and Zr, consistent with a role of carbonated melt. Rejuvenated stage olivines have Ni abundance lower than and CaO and MnO contents similar to those of shield stage at a given Fo. The calculated partition coefficients of Ca () and Mn () between olivine and shield melts are consistent with those of a dry melt system. However, the low and for rejuvenated lavas can only be explained by a volatile‐rich melt system. Based on the observed and in rejuvenated lavas, and considering the effect of H2O, our modeling calculation shows that rejuvenated primary magmas contain up to ∼10 wt% CO2, indicating a CO2‐rich mantle source. Using olivine‐spinel aluminum exchange thermometry, we show that the rejuvenated primary magma temperatures are similar to those of shield stage. We posit that the CO2‐rich rejuvenated stage lavas with lower olivine Ni than those of shield stage lavas were originated from melting of carbonated peridotites in the plume. The carbonated melts that metasomatized the peridotites were likely derived from subducted ancient carbonate‐bearing lithospheric mantle.

Chemical and statistical characterization of beach sand sediments: implication for natural and anthropogenic origin and paleo-environment

This study investigates chemical properties, the statistical variation in elements, paleo-environmental properties and accumulation, density maps, degree of weathering and the classification of the beach sand. Forty-seven samples were collected along the sampled beach sand. Chemical analysis was done on fine grains of all 47 beach sand samples and coarse grains of 19 selected rock samples by X-ray fluorescence analysis. CaO, SiO2 and MgO were the most abundant major elements in the samples. CaO and MgO show high concentrations in the northern section of the study area, while SiO2 is more prevalent in the southern section of the study area. Relatively higher concentrations of CaO, Al2O3, Fe2O3, TiO2, K2O, P2O5 and SO3 were observed in the fine grains, due to their susceptibility to weathering, while relatively higher SiO2 and MgO were observed in the coarse grains due to their resistance to weathering. Calcite and dolomite are major sources for the high concentrations of Ca and Mg, especially in the northern sections of the study area, while augite, clinoenstatite, ankerite, clinopyroxene, cordierite, magnetite are likely sources of Si, Mg and Fe. The beach sand indicated a mixture of high-CaO source type and high-SiO2 source type, with the high-CaO type dominating. Investigations revealed the sand as marine carbonaceous to carbonaceous ferrites with magnesium association, deposited in an oxic environment where the marine skeleton could not be preserved due to high aerobic activity, and not far from their carbonate (neritic) parent source. The high-SiO2 resulted from the Tekirova ophiolite in the region.

Influence of ashes in the use of forest biomass as source of energy

One of the main challenges using biofuels, such as pellets or wood chips in domestic boilers, is the slagging and fouling risks associated to the process, which could damage the boiler and limit its efficiency. The prediction of sintering and slagging in biomass combustion is essential to establish biofuel quality standards, and minimize their harmful effects. In this work, we analysed the chemical composition of 40 woodchips samples from different genera and origins in order to predict slagging. We studied two indexes of deposition (%B and the NaK/B) in order to limit sintering of biomass ashes. In addition, a new threshold classification was proposed for ratio-slag viscosity index. These indexes were validated with two different tests: a qualitative test, and a quantitative test (Bioslag). Our results showed that the species chosen did not have an impact in slagging and sintering. However, biomass with high concentrations of SiO2 and tree bark showed high risk of slagging. On the other hand, high CaO concentrations showed a low slagging risk. The results obtained from the validation tests showed similar results to the ones obtained from the indexes. It can be concluded that the %B and NaK/B indexes show good potential and should be considered as tools for predicting slagging in woody and herbaceous biomass.

Distribution of Lanthanides, Yttrium, and Scandium in the Pilot-Scale Beneficiation of Fly Ashes Derived from Eastern Kentucky Coals

In this study, Central Appalachian coal-derived fly ashes from two power plants were beneficiated in a pilot-scale facility in order to produce a product with a relatively consistent concentration of rare earth elements (REE). The <200-mesh final fly ash product was produced by removing the carbon- and Fe-rich particles prior to screening at 200 mesh (75 µm). The Plant D fly ash had high concentrations of CaO and SO3, which were diminished through the two months when the ash was being beneficiated, representing a consequence of the heat, humidity, and excessive rainfall in the Kentucky summer. The high CaO and SO3 concentrations through the early runs likely contributed to the lower REE in the <200-mesh products of those runs. Of the non-REE minor elements, Ba, V, Mn, Zn, and As showed the greatest between-run variations within the runs for each plant. The overall REE concentrations proved to be similar, both on a between-run basis for the individual fly ash sources and on a between-plant basis. Variations in fly ash quality will occur in larger-scale operations, so on-going attention to the fly ash quality and the response of the fly ash to beneficiation is necessary. Changes in the Plant D fly ash with time imply that both the freshness of the original ash and the length and conditions of its storage at the site of beneficiation could be factors in the quality and consistency of the processed fly ash.

High-Temperature thermochemical interactions of molten silicates with Yb2Si2O7 and Y2Si2O7 environmental barrier coating materials

The thermochemical behavior of EBC candidate materials yttrium disilicate (Y2Si2O7) and ytterbium disilicate (Yb2Si2O7) was evaluated with three calcium-magnesium-aluminosilicate (CMAS) glasses possessing CaO:SiO2 ratios relevant to gas turbine systems. Pellet mixtures of 50 mol% EBC powder to 50 mol% CMAS glass powder were heat treated at 1200°C, 1300°C, and 1400°C. The products of these interactions were evaluated using X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Above glass melting temperatures, exposure of the disilicates primarily resulted in dissolution into the molten glass followed by precipitation of a Ca2RE8(SiO4)6O2 (RE = Yb3+, Y3+) apatite-type silicate and/or rare earth disilicate. In glasses with high CaO concentrations, apatite readily forms while the disilicate material is consumed by the reaction. As CaO content decreases, the disilicate phase becomes the main reaction product. Overall, reactions with yttrium disilicate favored more apatite crystallization than ytterbium disilicate. The viability of using these disilicates in various operating environments is discussed.

Immiscibility of Fluoride–Calcium and Silicate Melts in Trachyrhyolitic Magma: Data on Acidic Volcanic Rocks from the Nyalga Basin, Central Mongolia

An Early Cretaceous (120 ± 5 Ma) trachyrhyolite lava sheet in the Nyalga basin, Central Mongolia, includes a domain (∼0.5 km2) of unusual fluorite-enriched rocks with anomalously high concentrations of CaO (1.2–25.7 wt %) and F (0.6–15 wt %). The textures and structures of the rocks suggest that they were produced by two immiscible melts: fluoride–calcium (F–Ca) and trachyrhyolitic. Data on mineral-hosted inclusions and SEM EDS studies of the matrixes of the rocks indicate that a F–Ca melt occurred in the trachyrhyolitic magmas during its various evolutionary episodes, starting from the growth of minerals in a magmatic chamber and ending with eruptions on the surface. Elevated fluorine concentrations (up to 1.5–2 wt %) in local domains of the trachyrhyolitic melt may have resulted in the onset of its liquid immiscibility and the exsolution of a F–Ca liquid phase. This was associated with the redistribution of trace elements: REE, Y, Sr, and P were preferably concentrated in the F–Ca melt, while Zr, Hf, Ta, and Nb were mostly redistributed into the immiscible silicate liquid. The F–Ca melt contained oxygen and aqueous fluid and remained mobile until vitrification of the trachyrhyolitic magma. The oxygen-enriched F–Ca phase was transformed into fluorite at 570–780°? and a high oxygen fugacity Δlog fO2 (0.9–1.7) relative to the NNO buffer. Ferrian ilmenite, monazite-group As-bearing minerals, and cerianite crystallized under oxidizing conditions, and the titanomagnetite was replaced by hematite. The Ca- and F-enriched rocks were affected by low-density (0.05–0.1 g/cm3) aqueous fluid, which was released from the crystallizing trachyrhyolitic melt, and this led to the partial removal of REE from the F–Ca phase. The chondrite-normalized REE and Y patterns of the fluidmodified rocks show positive Y anomalies and W-shaped minima from Gd to Ho. A composition of the F–Ca phase close to the original one is conserved in mineral-hosted inclusions and in relict isolations in the rocks matrix. It is so far unclear why fluorite did not crystallize from the F–Ca melt contained in the trachyrhyolitic magma. Conceivably, this was favored by high-temperature oxidizing conditions under which the melt accommodated oxygen and aqueous fluid. The possible origin of mobile oxygen-bearing fluorite–calcic melt at subsolidus temperature should be taken into account when magmatic rocks and ores are studied. Fluorite and accompanying ore mineralization might have been formed in certain instances not by hydrothermal–metasomatic processes but during the fluid–magmatic stage as a result of the transformation of F–Ca melt enriched in REE, Y, and other trace elements.

Elemental Chemical Analysis by X-ray Fluorescence of Calcarenite Stones Used in Historical Monuments Building of Rabat (Morocco)

A good knowledge of chemical properties, thermophysical and petrophysical parameters, makes it possible to understand the mechanisms of alteration of historical monuments, and to predict solutions limiting their evolution. The main objective of this work is chemical analysis by X-ray fluorescence spectrometry on calcarenite stones, often used as a building material for historical monuments of Rabat (Morocco), in order to identify the nature of the rock. The elemental chemical composition shows high concentrations of CaO and SiO2, which confirms that the main phases of the calcarenite rock studied are calcite and quartz. These are the characteristic minerals of calcareous rocks.

Fake age hiatus in a loess section revealed by OSL dating of calcrete nodules

Optically stimulated luminescence (OSL) dating on potassium feldspar has been performed with high resolution in the Luochuan section in the Chinese Loess Plateau. An age hiatus of ∼ 15 ka is found at the top of L2 layer within the loess/paleosol sequences. The age of the potassium feldspar from the calcrete nodules along the S1/L2 boundary is significantly older than those of the paleosol and loess samples lying above and below the boundary. The age overestimation of the potassium feldspar from calcrete nodules is caused by the underestimation of the dose rate, because accretion of carbonates could dilute the radioactivity. The age hiatus at the top of L2 also resulted from the underestimation of the dose rates of four loess samples beneath this hiatus. These four loess samples have high CaO concentrations. Ages of these samples are overestimated in the similar way as the nodules, but with smaller degrees. All results suggest that the accretion of carbonates happened after the loess deposition.The carbonate accretion process of the calcrete nodules has been simulated with accumulation models. The accretion can be as young as 46 ka, assuming the calcrete nodules formed rapidly at a certain time point. For slow and gradual accretion models, the carbonate started to accumulate slowly since the dust deposition and the accumulation became faster afterwards. The transition of the accretion rate may relate to the climate change or a change in the carbonate leaching and re-precipitation system.

Influence of structure and temperature on the thermal conductivity of molten CaO–B2O3

AbstractThe effect of the temperature and borate structure on the thermal conductivity of the molten CaO–B2O3 binary system was investigated. The thermal conductivity was measured from 1573 K to approximately the liquidus temperature using a transient hot‐wire method, and was found to decrease with increasing temperature. The temperature dependence of the thermal conductivity in the molten oxide system was interpreted in terms of the lifetime of phonon‐like excitations and Maxwell relaxation times. The short‐range order borate structure was investigated through magic angle spinning (MAS) and triple‐quantum MAS (3Q‐MAS) NMR. Although the content of 4‐coordinated boron was not significantly affected by the addition of CaO, structural changes associated with the fraction of 3‐coordinated boron in ring and non‐ring sites were observed. The Raman spectra showed that the intermediate range order borate structure was changed from boroxyl rings to chain‐type metaborate units at higher CaO concentrations. The thermal conductivity decreased with decreasing BO1.5/CaO ratio, owing to the depolymerization of the borate network.

(Im)mobilization of soil heavy metals using CaO, FA, sulfur, and Na2S: a 1-year incubation study

The immobilization of heavy metals (HMs)-contaminated soils using amendments is a cost-effective remediation technique. Therefore, the aim of this study was to evaluate the effectiveness and aging factor of CaO, fly ash (FA), sulfur, and Na2S on the immobilization of Cd, Cu, and Pb in three different contaminated soils under 1-year incubation. The study sites (S) and amendments treatments (T) are termed as S1, S2, and S3 and T1, T2, T3, and T4, respectively. The TCLP-extractable HMs were analyzed in treated soils after 2, 6, and 12 months. The higher concentrations of CaO, FA, and Na2S (T3 and T4) efficiently immobilized the Cd. However, a moderate Cd decrease was noted in sulfur-treated samples with no significant difference in ratios as compared to control in used soils. Likewise, CaO decreased moderately Cu content in used soils with gradual increase in Cu mobility. Similarly, FA, sulfur, and Na2S showed effective immobilization of Cu content with no difference in treatment ratios as compared to control. In addition, CaO, sulfur, and Na2S decreased the significant content of Pb as compared to control. However, FA treatments showed moderate reduction in Pb content with no difference in ratios. The higher concentrations of alkaline amendments should be avoided in the farmland soils as they increase the soil pH and EC of soil ecosystem. The higher ratios of alkaline amendments would be suitable to remediate the abandoned lands/brownfields. The sulfur amendment would be suitable for immobilization of metals in alkaline soils rather than in acidic soils.

Revisiting the importance of residual source material (restite) in granite petrogenesis: The Cardigan Pluton, New Hampshire

The Cardigan Pluton of New Hampshire exhibits a positive correlation between peraluminosity with maficity, with as much as 8% normative corundum in rocks with 53 wt.% SiO2. No mafic magmas of these compositions exist; the whole-rock compositions reflect high concentrations of garnet. The mafic rocks have higher CaO concentrations than garnet and require high concentrations of plagioclase as well. The presence of melt depleted, restitic garnetites in the pluton that are in isotopic equilibrium with the host rocks provides evidence for the textures and compositions of restitic plagioclase and peritectic garnet that can be compared to plagioclase and garnet in the host rocks. Some restitic grains of plagioclase in the garnetites contain needles of rutile and ilmenite. Plagioclase crystals with these same inclusions are also present in the host rocks. Inclusion-bearing plagioclase in both settings has identical Sr, Ba, Eu, Pb, and Ga concentrations, indicating that these crystals in the host rock are also restite. Most host rock plagioclase crystals that lack inclusions have higher Ba concentrations resulting from the fractionation of Ba which was an incompatible element until K-feldspar crystallized; these are phenocrysts. Peritectic garnet is inclusion-rich and has flat chondrite-normalized HREE patterns. The HREE elements incorporated into peritectic garnet were continuously supplied by zircon during the melting process. Once the melt separated from the source, fractionation of zircon and garnet depleted the melt in the HREE and phenocrystic garnet shows a progressive depletion in HREE from cores to rims. Peritectic garnet entrained in the host rocks show the same textural and chemical characteristics as garnet in the garnetites, but is mantled by inclusion-poor, HREE depleted, phenocrystic garnet. The Cardigan Pluton thus contains both peritectic garnet and restitic plagioclase, the retention of which in variable amounts can account for the range of whole-rock compositions of the pluton. If retention of relatively high density peritectic garnet occurs in other granitic plutons, then retention of lower density restitic phases such as plagioclase should occur as well, lending legitimacy to the peritectic/restitic phase entrainment/unmixing model in peraluminous plutons.

Modification of the lithospheric mantle by melt derived from recycled continental crust evidenced by wehrlite xenoliths in Early Cretaceous high-Mg diorites from western Shandong, China

This paper reports petrographic, mineral chemical, olivine oxygen isotopic, and whole-rock geochemical data for wehrlite xenoliths from the Early Cretaceous Tietonggou high-Mg diorites in western Shandong Province, in the eastern part of the North China Craton (NCC), and describes the origin of these wehrlites and the processes that affected the deep lithospheric mantle in this area. Wehrlite xenoliths are rounded and vary in size between 3 cm × 4 cm × 5 cm and 3 cm × 2 cm × 1 cm. Olivine within these xenoliths occurs as an isolated residual phase within clinopyroxene, has Fo contents between 89 and 91, and contains between 1414 and 3629 ppm Ni, similar to the values of olivine from peridotite xenoliths in the Cenozoic basalts of eastern China, but lower than the values of olivine from harzburgite xenoliths in the Early Cretaceous high-Mg diorites in western Shandong. In situ oxygen isotope analysis yielded δ 18O values of olivine from (6.03±0.33)‰ to (6.82±0.35)‰, averaging (6.5±0.4)‰; this is higher than typical mantle-derived olivine ((5.2±0.3)‰). Compared with clinopyroxenes from peridotite xenoliths in the Late Cretaceous and Cenozoic basalts, clinopyroxenes in the wehrlites contain relatively low concentrations of Na2O, TiO2, and Al2O3, high concentrations of CaO, and higher Mg# (91.2–94.1) and Ti/Eu ratios (2082–2845), being similar in composition to clinopyroxenes within harzburgite xenoliths in the Early Cretaceous high-Mg diorites. Clinopyroxenes from wehrlite xenoliths are characterized by low total REE abundance, enrichment in light REEs, and depletion in high field strength elements such as Nb, Ta, Zr, and Hf. Moreover, the 87Sr/86Sr, 143Nd/144Nd, and 187Os/188Os (125 Ma) ratios of these wehrlites vary from 0.70596 to 0.70737, 0.512181 to 0.512416, and 0.12661 to 0.57650, respectively. These data suggest that these wehrlite xenoliths were formed by modification of the lithospheric mantle by melts derived from recycled continental crust.

Experimental effects of pressure and fluorine on apatite saturation in mafic magmas, with reference to layered intrusions and massif anorthosites

Apatite is a cumulate phase in the upper parts of some mafic layered intrusions and anorthositic complexes. We investigated the effect of pressure and fluorine on apatite saturation in mafic magmas to better understand under which conditions this mineral crystallizes. Apatite saturation gives information about the formation of silicate rocks, and is of interest in explaining the formation of apatite–oxide-rich rocks (e.g. nelsonites comprising approximately, one-third apatite and two-third Fe–Ti oxide). Two models of formation are proposed for this rock type: crystal fractionation followed by accumulation of apatite and Fe–Ti oxides and liquid immiscibility. New experiments carried out with mafic compositions at 500 MPa confirm that the most important variables on phosphate saturation are SiO2 and CaO. Fluorine addition leads to apatite saturation at lower SiO2 and higher CaO concentrations. Comparison of our results with those of previous experimental studies on liquid–liquid immiscibility at upper-to-mid-crustal conditions allows us to investigate the relative importance of apatite saturation versus liquid–liquid immiscibility in the petrogenesis of nelsonites and similar rocks. The liquid line of descent of three natural examples studied (the Sept-Iles intrusive suite, the anorthositic Complex of the Lac-St-Jean and the Skaergaard layered intrusion) do not cross the liquid–liquid immiscibility field before they reach apatite saturation. Thus, the apatite–oxide-rich rock associated with these three intrusive suites are best explained by crystal fractionation followed by accumulation of apatite and Fe–Ti oxides.

Degradation processes in colourless Roman glass: cases from the Bocholtz burial

A group of Roman glass objects from the Bocholtz burial in the SW of Limburg (The Netherlands) was found to have been subject to varying degrees of degradation. Many of the 25 colourless glass objects were fragmented to pieces <0.1 cm (“sugared”), whereas the three transparent blue-green glass objects were in near-pristine state. Analyses using SEM, XRF and EDS revealed that the fragmentation was the direct result of the intense leaching of Na 2O from the glass structure and its replacement with water. The resulting gel layers with low-Na 2O contents and large amounts of water are sensitive to cracking when they dry out. Thin-walled glass appears to be less sensitive to cracking from the resulting stress than thick-walled glass. Local differences in the moisture regime during burial also influence the severity of the glass degradation. Glass with low concentrations of CaO seems to be the most sensitive to this form of degradation. The typical blue-green Roman glass is less sensitive as it generally has considerably higher concentrations of CaO. “Sugared” glass has – until now – only been reported in a small number of high-status burials. However, glass fragments that are degraded as strongly as some of the objects in the Bocholtz burial may have been overlooked in other archaeological settings (e.g. settlements), especially in coarse-grained soils or soils containing debris or rock fragments. As a result, the archaeological record for Roman glass may be biased towards the “typical” blue-green transparent glass objects.

Reductive dechlorination of polychlorinated dibenzo- p-dioxins and dibenzofurans in MSWI fly ash by sodium hypophosphite

Reductive dechlorination of polychlorinated dibenzo- p-dioxins and dibenzofurans (PCDD/Fs) in fly ash from municipal solid waste incinerator (MSWI) by sodium hypophosphite was carried out in a lab scale experiment. The MSWI fly ash with high concentrations of CaO and Fe 2O 3 and also trace metals such as Cu, Pb and Zn has the catalytic potential in dechlorinating PCDD/Fs at about 250–450 °C under oxygen deficient conditions. Sodium hypophosphite generates reducing agents (PH 3 and H 2) at about 300 °C, which can increase the detoxification efficiency and accelerate the dechlorination reaction. The reductive dechlorination with 10% (w/w) sodium hypophosphite has shown high detoxification efficiencies of 99.4% and 99.3% at 350 °C and 450 °C, respectively, and as well as the dechlorination efficiencies about 98.7%. The reductive dechlorination is about the same efficiency as the melting process. In this study it is also shown that the bioassay method combined with HRGC/MS method as a reference is a feasible and low-cost technology for determining PCDD/Fs in environmental matrices.

Fluorite solubility in hydrous haplogranitic melts at 100 MPa

Fluorite is the most common fluoride mineral in magmatic silicic systems and its crystallization can moderate or buffer fluorine concentrations in these settings. We have experimentally determined fluorite solubility and speciation mechanisms in haplogranitic melts at 800–950 °C, 100 MPa and aqueous-fluid saturation. The starting haplogranite compositions: peraluminous (alumina saturation index, ASI = 1.2), subaluminous (ASI = 1.0) and peralkaline (ASI = 0.8) were variably doped with CaO or F 2O −1 in the form of stoichiometric mineral or glass mixtures. The solubility of fluorite along the fluorite–hydrous haplogranite binaries is low: 1.054 ± 0.085 wt.% CaF 2 (peralkaline), 0.822 ± 0.076 wt.% (subaluminous) and 1.92 ± 0.15 wt.% (peraluminous) at 800 °C, 100 MPa and 10 wt.% H 2O, and exhibits a minimum at ASI ∼ 1. Fluorite saturation isotherms are strongly hyperbolic in the CaO–F 2O −1 space, suggesting that fluorite saturation is controlled by the activity product of CaO and F 2O −1, i.e., these components are partially decoupled in the melt structure. The form of fluorite liquidus isotherms implies distinct roles of fluorite crystallization: in Ca-dominant systems, fluorite crystallization is controlled by the fluorine concentration in the melt only and remains nearly independent of calcium contents; in F-rich systems, the crystallization of fluorite is determined by CaO contents and it does not buffer fluorine concentration in the melt. The apparent equilibrium constant, K, for the equilibrium CaO + cF 2O −1 = CaF 2 (+ associates) is log K= − (2.449 ± 0.085)·Al 2O 3 exc + (4.902 ± 0.066); the reaction-stoichiometry parameter varies as follows: c= − (0.92 ± 0.11)·Al 2O 3 exc + (1.042 ± 0.084) at 800 °C, 100 MPa and fluid saturation where Al 2O 3 exc are molar percent alumina in excess over alkali oxides. The reaction stoichiometry, c, changes at subaluminous composition: in peralkaline melts, competition of other network modifiers for excess fluorine anions leads to the preferential alkali–F short-range order, whereas in peraluminous compositions, excess alumina associates with calcium cations to form calcioaluminate tetrahedra. The temperature dependence of fluorite solubility is described by the binary symmetric Margules parameter, W = 36.0 ± 1.4 kJ (peralkaline), 39.7 ± 0.5 kJ (subaluminous) and 32.8 ± 0.7 kJ (peraluminous). The strong positive deviations from ideal mixing imply the occurrence of CaF 2–granite liquid–liquid immiscibility at temperatures above 1258 °C, which is consistent with previous experimental data. These experimental results suggest very low solubilities of fluorite in Ca-rich melts, consistent with the lack of fluorine enrichment in peralkaline rhyolites and calc-alkaline batholiths. On the other hand, high CaO concentrations necessary to crystallize fluorite in F-rich peraluminous melts are not observed in nature and thus magmatic crystallization of fluorite in topaz-bearing silicic suites is suppressed. A procedure for calculating fluorite solubility and the liquidus isotherms for a whole-rock composition and temperature of interest is provided.

Magmatic evolution of the Heiðarsporður ridge, NE-Iceland

The Heiðarsporður ridge, located just south of the Krafla central volcano in the northern rift-zone of Iceland, was formed in several small eruptions in the early Holocene. The rock suite of Heiðarsporður is quite different from that of Krafla and other central volcanoes in the northern rift zone. It consists of an almost continuous series of olivine tholeiites, basaltic icelandites, icelandites and a dacite in addition to small amounts of Fe-rich tholeiites which are similar to rocks from Krafla. The occurrence of silicic rocks in the Heiðarsporður ridge is rather anomalous because usually silicic rocks in Iceland are associated with central volcanoes. This paper presents the petrography and mineral chemistry of the Heiðarsporður rock suite together with major and trace element geochemistry and oxygen isotope ratios. The intermediate and silicic rocks of Heiðarsporður are characterized by relatively high concentrations of CaO and Al 2O 3 coupled with relatively low concentrations of FeO, compared with evolved rocks elsewhere in the rift zones of Iceland. Furthermore, ∂ 18O values are higher in the evolved rocks of Heiðarsporður. The olivine tholeiites are of a very common regional type and represent mantle-derived magma. The Fe-rich tholeiites which only occur in the northern end of Heiðarsporður are derived from the Krafla central volcano. The basaltic icelandites represent hybrids of olivine tholeiites and icelandites. The icelandites and the dacite are proposed to have formed by near-solidus differentiation at a deeper level in the crust than silicic rocks in the nearby Krafla central volcano. This interpretation is supported by petrogenetic modelling using the MELTS software. The melts were extracted from the source by crustal deformation, most likely related to concurrent activity in the Krafla volcanic system.

Volatilisation of trace elements for coal–sewage sludge blends during their combustion ☆

The influence of sewage sludge addition on the volatility of 37 trace elements (Ag, As, Au, B, Ba, Bi, Cd, Ce, Co, Cr, Cs, Cu, Ga, Hf, Hg, La, Li, Mn, Mo, Nb, Ni, Pb, Rb, Sb, Sc, Se, Sn, Sr, Ta, Te, Th, Tl, U, V, Y, Zn, Zr) during coal combustion was studied. For this purpose, a bituminous coal from the Asturian Central Basin and sewage sludge treated with Ca(OH) 2 and FeCl 3, as well as 10 and 50 wt% sludge–coal blends were used. Combustion experiments were performed in a laboratory electric furnace at 800, 900, 1000 and 1100 °C. The results have confirmed that the high Cl contents of the sludge can produce a pronounced effect on the volatilisation of some trace elements (Ag, Cd, Cs, Cu, Li, Pb, Rb and Tl) due to the probable formation of volatile chlorides, while the high CaO concentrations increase the retention of some elements in ash as As, Se and Te. The above opposite effects of Cl and CaO on trace element volatilisation were generally inappreciable for the 10 wt% blend, while they were more significant, but not as noticeable as expected, for the 50 wt% blend.