Coarse Crystalline Research Articles

The Niederschlag fluorite-(barite) deposit, Erzgebirge/Germany\u2014a fluid inclusion and trace element study

The Niederschlag fluorite-barite vein deposit in the Western Erzgebirge, Germany, has been actively mined since 2013. We present the results of a first comprehensive study of the mineralogy, petrography, fluid inclusions, and trace element geochemistry of fluorite related to the Niederschlag deposit. Two different stages of fluorite mineralization are recognized. Stage I fluorite is older, fine-grained, associated with quartz, and forms complex breccia and replacement textures. Conversely, the younger Stage II fluorite is accompanied by barite and often occurs as banded and coarse crystalline open-space infill. Fluid inclusion and REY systematics are distinctly different for these two fluorite stages. Fluid inclusions in fluorite I reveal the presence of a low to medium saline (7–20% eq. w (NaCl+CaCl2)) fluid with homogenization temperatures of 140–180 °C, whereas fluorite II inclusions yield distinctly lower (80–120 °C) homogenization temperatures with at least two high salinity fluids involved (18–27% eq. w (NaCl+CaCl2)). In the absence of geochronological data, the genesis of the earlier generation of fluorite-quartz mineralization remains enigmatic but is tentatively related to Permian magmatism in the Erzgebirge. The younger fluorite-barite mineralization, on the other hand, has similarities to many fluorite-barite-Pb-Zn-Cu vein deposits in Europe that are widely accepted to be related to the Mesozoic opening of the northern Atlantic Ocean.

Origin of Middle-Upper Cambrian dolomites in eastern Laurentia: A case study from Belle Isle strait, western Newfoundland

The Middle and Upper Cambrian Port au Port Group of western Newfoundland consists mainly of mixed carbonates and siliciclastics and is composed of the March Point, Petit Jardin, and Berry Head formations. Samples were collected from the core NF-02 that spans the uppermost Hawke Bay (40 m), the March Point (~83 m thick) and the lowermost Petit Jardin (~47 m). Petrographic examination of carbonates of the March Point and Petit Jardin carbonates reveals three generations of dolomite: (i) micritic to near-micritic (D1, 4 μm −35 μm) fabric-retentive dolomite, (ii) coarse crystalline sucrosic (D2, 60 μm−150 μm) fabric-destructive dolomite (sub-to euhedral zoned rhombs with clear rim and cloudy core), and (iii) coarse anhedral (D3, >0.5 mm) fracture-filling saddle dolomite. The microthermometric measurements of primary two-phased fluid inclusions retained in D2, and D3 samples yielded homogenization temperatures (Th) showing a general increase with burial. The mean values of Th and salinity are 89.1 ± 6.4 °C vs 21.2 ± 2.2 eq. wt% NaCl, and 110 ± 8.2 °C vs 21.1 ± 4.7 eq. wt% NaCl, respectively. The investigated dolomites show a decrease of Sr from D1 (102 ± 49 ppm) to D3 (47 ± 15 ppm) which reflects the influence of progressive burial. The mean δ18O values decrease from D1 (−6.3 ± −1.1‰ VPDB), to D3 (−9.7 ± 1.7‰ VPDB) where D2 (−7.6 ± 1.2‰ VPDB) is in the middle. The estimated δ18O values of the D1 parent fluid (−5 to −10‰ VSMOW) are bracketed by those suggested for the Middle Cambrian meteoric and seawaters. The fluid-inclusion gas analyses provided CO2/CH4 and N2/Ar ratios coherent with the conclusions from the petrographic examination and geochemical compositions.

Thermal Evolution of Natural Layered Double Hydroxides: Insight from Quintinite, Hydrotalcite, Stichtite, and Iowaite as Reference Samples for CO3- and Cl-Members of the Hydrotalcite Supergroup

In Situ high-temperature powder X-ray diffraction experiments were undertaken for the coarse crystalline natural layered double hydroxides (LDHs) quintinite, hydrotalcite, stichtite, and iowaite in the temperature range 25–1000 °C, with thermal analyses of these minerals and their annealed forms carried out in parallel. In the temperature range from 25 °C to 170–210 °C quintinite, hydrotalcite, and stichtite (carbonate members of the LDH family) demonstrated contraction of the basal d00n-value of 0.1–0.3 Å, followed by a sharp contraction of 1.0–1.1 Å at T > 170–210 °C. The high-temperature modified states were stable up to 380–420 °C, before decomposing to an amorphous phase. Iowaite (chloride member of the family) was stable up to 320 °C and transformed to an amorphous phase at higher temperature. Iowaite experiences continuous contraction of the d00n-value of up to 0.5 Å in the temperature range 25–200 °C, reaching a plateau at a temperature range of 200–320 °C. Assessing the reversibility of thermal transformation shows complete reconstruction of the crystal structure of the hydrotalcite and iowaite heated to 300 °C. Solid-state nuclear magnetic resonance analysis shows that some Al changes coordination from 6- to 4-fold, synchronously with quintinite transformation to the amorphous phase. All phases transform to periclase and a spinel-type compound upon further heating. Thermal analysis of samples annealed at 125 °C shows that carbonate members do not have a tendency to form dehydrated phases, whereas for iowaite, a dehydrated phase having 0.9 apfu lesser water content as in the initial sample has been obtained. Thermal evolution of LDHs is found to depend on the nature of the interaction of interlayer species and water molecules to H atoms of the metal-hydroxide layer.

The nature, type, and origin of diagenetic fluids and their control on the evolving porosity of the Lower Cambrian Xiaoerbulak Formation dolostone, northwestern Tarim Basin, China

The study on Lower Cambrian dolostones in Tarim Basin can improve our understanding of ancient and deeply buried carbonate reservoirs. In this research, diagenetic fluid characteristics and their control on porosity evolution have been revealed by studying the petrography and in situ geochemistry of different dolomites. Three types of diagenetic fluids were identified: (1) Replacive dolomites were deviated from shallow burial dolomitizing fluids, which might probably be concentrated ancient seawater at early stage. (2) Fine-to-medium crystalline, planar-e diamond pore-filling dolomites (Fd1) were likely slowly and sufficiently crystallized from deep-circulating crustal hydrothermal fluids during Devonian. (3) Coarse crystalline, non-planar-a saddle pore-filling dolomites (Fd2) might rapidly and insufficiently crystallize from magmatic hydrothermal fluids during Permian. Early dolomitizing fluids did not increase the porosity, but transformed the primary pores to dissolution pores through dolomitization. Deep-circulating crustal hydrothermal fluids significantly increased porosity in the early stages by dissolving and then slightly decreased the porosity in the late stage due to Fd1 precipitation. Magmatic hydrothermal fluids only precipitated the Fd2 dolomites and slightly decreased the porosity. In summary, Devonian deep-circulating crustal hydrothermal fluids dominated the porosity evolution of the Lower Cambrian dolostone reservoir in the Tarim Basin.

Hereditary effect of the charge structure on Al-Si-Cu alloy density, gas content and solidification processes

The paper provides the results obtained when studying the initial charge structure effect on the density, gas content and temperature-time parameters of AK6M2 (Al-6%Si-2%Cu) alloy solidification. Coarse crystalline charge billets ( C -charge) were obtained when pouring the melt into ceramic molds with sand filling providing a cooling rate υ охл ~0.5÷ 1.0 °C/s. Finely crystalline charge billets ( F -charge) were prepared by pouring the melt to cold cast iron molds ( υ охл ~ 5÷ 10 °C/s). Charge billets obtained were separately remelted with the same temperature-time conditions, rerefined and degassed with samples taken to determine hydrogen content as well as density values in liquid and solid states. It is established that structural information inherited from the initial charge billets is stable in the solid-liquid-solid system. It was found using direct thermal analysis that the melt obtained from C -charge solidifies with a reduction in liquidus temperature by 3 °С and in the temperatures of the beginning and end of eutectic solidification by 10 °C and 3 °С, respectively, as compared to the melt obtained from C -charge. At the same time, α-Al and eutectic dendrites form in the C -charge melt 0.4 and 0.6 min faster, respectively. The results obtained at the Paraboloid-4 unit showed that the F -charge melt has higher density as compared to the C -charge alloy due to a smaller number of pulses passing through it in the studied temperature range of 750 — 450 °C. Temperature values of aluminum and eutectic dendrite formation determined by J—t temperature relationships (where J is the number of γ pulses, t is the temperature) correlate with the results of direct thermal analysis. General practical recommendations on the purposeful conservation of positive structural information in aluminum alloys are formulated in terms of the structural heredity phenomenon.

Unconformity-controlled dissolution contributes to reservoirs in the carbonate-rich Permian Fengcheng Formation, northwestern Junggar Basin, China

The Permian Fengcheng Formation is a set of complex sedimentary strata in the Mahu Sag, northwestern Junggar Basin, where various types of carbonate minerals occur. Coarse crystalline calcite assemblages and other carbonate minerals, such as dolomite, shortite and sodium carbonates, are also common in the Fengcheng Formation. Their dissolution by meteoric freshwater leaching at tectonic high positions, which was controlled by an unconformity, developed uncommonly high-quality secondary porosity and contributed to unconventional oil and gas exploration. Based on core analyses, thin section studies under optical and cathodoluminescence (CL) microscopes, geological interpretations of seismic profiles, and carbon and oxygen isotope composition analyses from coarse crystalline calcite assemblages and comparisons to other carbonate minerals, this study focuses on the origin of coarse crystalline calcite assemblages and the mechanism of unconformity-related dissolution to form hydrocarbon reservoir spaces. Coarse crystalline calcite assemblages are the products of multiple stages of recrystallization of other carbonate minerals in nearby host rocks. Hydrolysis of feldspar and volcanic sediments provided additional Ca2+ for calcite precipitation. The dissolution and reprecipitation of carbonate minerals were associated with organic maturation and hydrocarbon expulsion and migration. The crystallization process was slow, which allowed the crystal assemblages to grow to large sizes. Organic carbon was involved in the formation of the coarse crystalline calcite assemblages, which resulted in much more negative carbon isotope compositions than those of other carbonate minerals via diluting the carbon isotope compositions of preexisting carbonate minerals. Later tectonic uplift caused a regional unconformity and formed dissolution reservoirs in tectonically high positions. Furthermore, faults and fractures provided paths for the solutes to transfer to lower positions and reprecipitate when they became saturated.

Diagenetic Pore Fluid Evolution and Dolomitization of the Silurian and Devonian Carbonates, Huron Domain of Southwestern Ontario: Petrographic, Geochemical and Fluid Inclusion Evidence

Core samples from two deep boreholes were analyzed for petrographic, stable and Sr isotopes, fluid inclusion microthermometry and major, minor, trace and rare-earth elements (REE) of different types of dolomite in the Silurian and Devonian carbonates of the eastern side of the Michigan Basin provided useful insights into the nature of dolomitization, and the evolution of diagenetic pore fluids in this part of the basin. Petrographic features show that both age groups are characterized by the presence of a pervasive replacive fine-crystalline (<50 µm) dolomite matrix (RD1) and pervasive and selective replacive medium crystalline (>50–100 µm) dolomite matrix (RD2 and RD3, respectively). In addition to these types, a coarse crystalline (>500 µm) saddle dolomite cement (SD) filling fractures and vugs is observed only in the Silurian rocks. Results from geochemical and fluid inclusion analyses indicate that the diagenesis of Silurian and Devonian formations show variations in terms of the evolution of the diagenetic fluid composition. These fluid systems are: (1) a diagenetic fluid system that affected Silurian carbonates and was altered by salt dissolution post-Silurian time. These carbonates show a negative shift in δ18O values (dolomite δ18O average: −6.72‰ VPDB), Sr isotopic composition slightly more radiogenic than coeval seawater (0.7078–0.7087), high temperatures (RD2 and SD dolomite Th average: 110 °C) and hypersaline signature (RD2 and SD dolomite average salinity: 26.8 wt.% NaCl eq.); and (2) a diagenetic fluid system that affected Devonian carbonates, possibly occurred during the Alleghenian orogeny in Carboniferous time and characterized by a less pronounced negative shift in δ18O values (dolomite δ18O average: −5.74‰ VPDB), Sr isotopic composition in range with the postulated values for coeval seawater (0.7078–0.7080), lower temperatures (RD2 dolomite Th average: 83 °C) and less saline signature (RD2 dolomite average salinity: 20.8 wt.% NaCl eq.).

Pore-fillings of dolomite reservoirs in Sinian Dengying Formation in Sichuan basin

Abstract The Sinian Dengying Formation in the Sichuan basin is an important potential reservoir for oil and gas exploration in the periphery of the Sichuan basin. Its reservoirs were well developed. And many kinds of fillings which lead to the decrease of pores can be seen in reservoir pores and caves. In this paper, the pore fillings of the Dengying Formation reservoir in Sichuan basin are the object of study. The types and characteristics of the fillings are studied in detail by means of rock slices analysis, cathode luminescence, trace elements and inclusion temperature measurement. The study shows that the fillings include dolomite fillings and siliceous quartz fillings and bitumen fillings. Among them, dolomite fillings can be divided into botryoidal dolomite fillings, foliated dolomite fillings, finely-medium crystalline dolomite fillings and coarse crystalline dolomite fillings. 50%–80% of the pores are filled by the dolomite fillings with botryoidal structure, and the pores can be partially full filled; 0%–20% of pores are filled by foliated dolomite fillings; 20–80% of the pores are filled by finely-medium dolomite fillings; 20–80% of the pores are filled by coarse crystalline dolomite fillings. 1%–5% of secondary pores are often filled by siliceous quartzs, and the pores can be partially full filled. Bitumen fillings often occur after the above-mentioned fillings, and the residual pores are often semi-filled by bitumens, which makes the original pores and throat smaller and reduces the effective porosity and permeability of the reservoir. So, it is a destructive diagenesis. The pore fillings make the secondary porosity in the reservoir significantly lower, which is not conducive to the formation and preservation of the Dengying Formation reservoir.

Fluid system and pressure evolution study based on isotope and fluid inclusion geochemistry: a case study on the Sinian Dengying and the Cambrian Longwangmiao Formation in the Gaoshiti-Moxi structure, Central Sichuan Basin

Systematic microscopic observation and analysis reveal multi-stage mineral fillings and fluid charging in the Sinian (Ediacaran) Dengying and the Cambrian Longwangmiao Formation in the Gaoshiti-Moxi structure, Central Sichuan Basin. Reservoir pore space is filled with five different stages of minerals from the edge to the center: fine crystalline dolomite, rimmed bitumen, coarse crystalline dolomite, stripped or oil droplet-like bitumen, and calcite or quartz, respectively. Sr, C, and O isotopic analysis for fine crystalline dolomite and the late stage calcite and quartz filled in reservoir pore space indicate that, prior to oil-generating window of the Cambrian Qiongzhusi Formation, the Sinian Dengying and the Cambrian Longwangmiao Formation were within the same connected and open fluid system. But after the gas-generating window, the Cambrian Longwangmiao Formation evolves gradually into a relatively independent and closed fluid system. By restoring the paleo fluid pressure, it is found that the paleo fluid pressure coefficient of the Sinian Dengying Formation has gone from 1.0, 1.1 to 1.2, 1.2, 1.2 to 1.3, and 1.0 to 1.1 at different evolution stages of source rock (at corresponding Ro value of 0.5, 1.3, 1.7, 2.0, and over 2.8, respectively), and the paleo fluid pressure coefficient of the Cambrian Longwangmiao Formation has varied from 1.0, 2.1 to 2.2, 1.8 to 1.9, 1.6 to 1.8, and 1.55 to 1.75. The pressure restoration result reveals that overpressure has never occurred in the Sinian Dengying Formation during the geological history, but overpressure commonly occurred in the Cambrian Longwangmiao Formation, and the values varied at different evolution stages of source rock. This pressure evolution process also demonstrates that the Sinian Dengying and the Cambrian Longwangmiao Formation, prior to the oil-generating window, were within an identical normal pressure fluid system. Meanwhile, it also matches well with the present exploration discoveries: the overpressured gas pools of the Cambrian Longwangmiao Formation are preserved up to now and hold hundreds of billions cubic meters of gas reserves, while the Sinian Dengying Formation contains residual normal pressure gas pools that formed after the adjustment of natural gas over a large area.

Crystallization of Amorphous Germanium Films and Multilayer a-Ge/a-Si Structures upon Exposure to Nanosecond Laser Radiation

The processes of the crystallization of amorphous germanium films and multilayer germanium/silicon structures upon exposure to nanosecond (70 ns) ruby laser radiation (λ = 694 nm) are studied. The samples are grown on silicon and glassy substrates by plasma-enhanced chemical vapor deposition. Pulsed laser annealing of the samples is conducted in the range of pulse energy densities Ep from 0.07 to 0.8 J cm–2. The structure of the films after annealing is determined by analyzing the scanning electron microscopy data and Raman spectra. It is established that, after annealing, the films are completely crystallized and, in this case, contain regions of coarse crystalline grains (>100 nm), whose fraction increases, as Ep is increased, and reaches 40% of the area. From analysis of the position of the Raman peaks, it is conceived that the crystalline grains, whose dimensions exceed 100 nm, either contain structural defects or stretching strains. The correlation length of optical vibrations is determined from the phonon confinement model and found to increase from 5 to 8 nm, as Ep is increased. Pulsed laser annealing of multilayer Ge(10 nm)/Si(5 nm) structures induces partial intermixing of the layers with the formation of Ge–Si alloys.

Emplacement origins of coarsely-crystalline mafic rocks hosted in greenstone belts: Examples from the 2.7 Ga Yilgarn Craton, Western Australia

Coarsely crystalline mafic rocks, commonly referred to as dolerite and diabase, make up a substantial proportion of Archean greenstone belts and are hosts to major orogenic gold deposits, yet their internal architecture and contact relationships remain poorly documented and their emplacement origins are assumed rather than supported with evidence. We present results from drill core logging of several late Archean coarsely crystalline packages from the Eastern Goldfields Superterrane of the Yilgarn Craton, Western Australia, including the Golden Mile Dolerite. These large mafic bodies comprise mostly medium- to coarsely crystalline mafic rocks, but also include a variety of other products of differentiation. The bodies range from ∼75 to 460 m thick and extend for tens of kilometers, are primarily hosted in mudstones and basalt and appear to be concordant to stratigraphy. As such, this study excludes mafic dykes and extremely thick and internally complex bodies such as the Bushveld Complex. From base to top, the internal stratigraphy generally consists of a lower unit of aphyric basalt, dolerite/gabbro and peridotite ± pyroxenite, then a voluminous middle dolerite/gabbro, and an upper quartz dolerite/gabbro, and a topmost aphyric basalt. Granophyric veins and domains are common in the upper third of the mafic body. Contacts are gradational between all lithofacies, with the exception of granophric veins, which have sharp contacts. Within this overall stratigraphic framework there is variability in the relative thickness of lithofacies, number of lithofacies, as well as repetition of some lithofacies (several examples also include basalt in the interior). In well exposed examples, the key evidence for distinguishing intrusions from extrusions is provided by the top contact. However, the top contact from these examples is ambiguous. To overcome this gap, we review the character of well-studied thick ponded lavas from the literature. Most aspects of the internal character are not unique to intrusions, although the maximum groundmass grain size (excluding granophyric veins) of the Archean examples (>3 mm) is significantly coarser than that for any known ponded lavas (≪1 mm). The ability to distinguish intrusions from extrusions has important implications for reconstructing Archean greenstone stratigraphy and mineral exploration.

Multiphase dolomitization in the Jutana Formation (Cambrian), Salt Range (Pakistan): evidences from field observations, microscopic studies and isotopic analysis

Excellent dolomite exposures are observed in the eastern Salt Range (Pakistan), where the Cambrian Jutana Formation consists of two distinct units (i.e. oolitic – pisolitic unit and massive dolomite unit). Field observations revealed that the lower, oolitic-pisolitic unit mostly comprises medium to thick bedded, interlayered brown yellowish dolostone containing ooids/pisoids and faunal assemblages, and grey whitish sandstone with distinct depositional sedimentary features (i.e. trough-, herringbone- and hhummocky crossbedding). The upper massive dolostone unit consists of thick bedded to massive dolostone. These two units are separated by shale. Petrographic studies identified three dolomite types, which include: fine crystalline dolomite (Dol. I), medium-coarse crystalline dolomite (Dol. II) and fracture associated, coarse crystalline dolomite (Dol. III). Stable isotope studies indicate less depleted δ 18 O values for Dol. I (-6.44 to -3.76‰V-PDB), slightly depleted δ18O values for Dol. II (-7.73 to -5.24‰V-PDB) and more depleted δ 18 O values for Dol. III (-7.29 to -7.20‰V-PDB). The δ 13 C values of the three dolomite phases are well within the range of Cambrian sea-water signatures. Furthermore, δ 26 Mg-δ 25 Mg signatures (Dol. I; δ 26 Mg=-1.19 to -1.67, δ 25 Mg=-0.61 to -0.86 and Dol. II; δ 26 Mg=-1.34 to -1.59, δ 25 Mg=-0.70 to -0.83) indicate three phases of dolomitization in different diagenetic settings. First, an initial stage of dolomitization during the early Cambrian resulted from altered marine, Mg-rich fluids associated with the mixing zone mechanism. Second, a late stage of dolomitization was associated with burial during late Permian. A third dolomitization phase was related to post-Eocene times.

Кристаллизация плeнок аморфного германия и многослойных структур a-Ge/a-Si под действием наносекундного лазерного излучения

AbstractThe processes of the crystallization of amorphous germanium films and multilayer germanium/silicon structures upon exposure to nanosecond (70 ns) ruby laser radiation (λ = 694 nm) are studied. The samples are grown on silicon and glassy substrates by plasma-enhanced chemical vapor deposition. Pulsed laser annealing of the samples is conducted in the range of pulse energy densities E _ p from 0.07 to 0.8 J cm^–2. The structure of the films after annealing is determined by analyzing the scanning electron microscopy data and Raman spectra. It is established that, after annealing, the films are completely crystallized and, in this case, contain regions of coarse crystalline grains (>100 nm), whose fraction increases, as E _ p is increased, and reaches 40% of the area. From analysis of the position of the Raman peaks, it is conceived that the crystalline grains, whose dimensions exceed 100 nm, either contain structural defects or stretching strains. The correlation length of optical vibrations is determined from the phonon confinement model and found to increase from 5 to 8 nm, as E _ p is increased. Pulsed laser annealing of multilayer Ge(10 nm)/Si(5 nm) structures induces partial intermixing of the layers with the formation of Ge–Si alloys.

Ceramic binder jetting additive manufacturing: Particle coating for increasing powder sinterability and part strength

The objective of this research is to test a hypothesis that particle coating increases the sinterability of ceramic powder. This method is developed for binder jetting additive manufacturing but tested using a pressing and sintering route for the simplicity. Binder jetting additive manufacturing has demonstrated its considerable capability in manufacturing ceramic parts with a complex shape and/or a customized design. Currently, the density of the ceramic parts made by binder jetting is low and their mechanical properties are inferior. The main reason is the low sinterability of the powder feedstock. A new powder surface modification method, i.e., particle coating, was applied to increase the powder sinterability and the part strength. Specifically, coarse crystalline alumina particles (70 and 10 µm in average) were coated with amorphous alumina, in which the microsized core was designed to provide the high flowability and the amorphous shell to promote sintering due to its high activity. The coated powder was pressed into disk samples and sintered. The samples from the coated powder showed significantly higher shrinkage and compressive strength than those from the raw powder, which proved the feasibility of the particle coating method to increase the powder sinterability and part strength.

Structure of crystallized particles in sputter-deposited amorphous germanium films

Pristine thin films of amorphous Ge prepared by sputtering are unstable and form coarse crystalline particles of 100 nm in size upon crystallization by electron irradiation. These crystalline particles exhibit unusual diffraction patterns that cannot be understood from the diamond cubic structure. The structure has previously been assumed to be a metastable hexagonal form. In the present work, the structure of the coarse crystalline particles has been analysed in detail by transmission electron microscopy, considering the possibility that those diffraction patterns might occur with the diamond cubic structure if the particle consists of thin twin layers. By high-resolution lattice imaging the particles have been shown to be of the diamond cubic structure containing a high density of twins and stacking faults parallel to {111}. With such defects, diffraction patterns can be complex because of the following effects: superposition of two or more diffraction patterns of the same structure but of different orientations, double diffraction through twin crystals, and streaks parallel to the thin crystal which give rise to extra diffraction spots. It is found that diffraction patterns taken from various orientations can be explained in terms of these effects.

Formation mechanism of carbonates in the lacustrine muddy shale and it implication for shale oil and gas: A case study of source rocks in Member 4 and Member 3 of Shahejie Formation, Dongying sag

Through analysis of microscopic characteristics, mineral components, elements and isotopes, the genetic mechanism of carbonates in the deep lacustrine source rocks in the upper submember of Member 4 and lower submember of Member 3 of Shahejie Formation in Dongying sag, is well investigated. The results show that four types of carbonates in the deep lake, i.e., lenticular coarse crystalline carbonate, lamellar micro-fine crystalline carbonate, lamellar cryptocrystalline carbonate and massive cryptocrystalline carbonate. Of which, the lenticular coarse crystalline carbonate is formed by diagenetic recrystallization. For the lamellar micro-fine crystalline carbonate and the lamellar cryptocrystalline carbonate, through the alga photosynthesis, the carbon dioxide (CO2) is constantly extracted from water, thus the concentration of CO3−2 ion in water increases, and then the CO3−2 ion reacts with Ca2+ ion in lake water surface to form the carbonates; the saline water environment is favorable for preservation of carbonate particles which mostly occur in lamellar micro-fine crystalline; in the brackish water environment, the water is deep, and the carbonate crystalline beneath the carbonate compensation depth surface is usually is dissolved, and most of lamellar cryptocrystalline are preserved. The massive cryptocrystalline carbonate is formed by the sedimentary carbonate which transport from shallow water to deep water by gravity flow. To some extent, the carbonates control reservoir property and compressibility of muddy shale in the upper submember of Member 4 and lower submember of Member 3 of Shahejie Formation in Dongying sag, and provide important information for reconstruction of sedimentary environment of the ancient lake.

Sedimentology and geochemistry of a human‐induced tufa deposit: Implications for palaeoclimatic research

AbstractGeochemical variations across laminated tufas and travertines may reflect the growth style of the carbonate build‐up and not just climate‐related changes. This work presents the study of a carbonate deposit, formed on a ravine wall in Gran Canaria Island (Spain), from a broken pipe system used for irrigation of banana plantations. The deposit is a few tens of metres long and has a stepped morphology formed by successive cascade‐barriers and pools. The main facies are framestones of coated stems, laminated bindstones, phytoclastic wackestones and silty mudstones, all of which display micritic or coarse crystalline textures. Lamination from a framestone with coarse crystalline texture was studied from a petrological–sedimentological and geochemical perspective, and water palaeotemperatures were calculated. Lamination displaying five orders of magnitude, from daily to annual or higher, was controlled by the discontinuous supply of water. Lamination consists of crystalline laminae–discontinuity couplets at all observed scales. Estimated mean precipitation rates are 0·7 mm year−1, but discontinuity of sedimentation at all lamination orders may have involved greater precipitation rates. Whereas elemental geochemistry suggests variable conditions not far from chemical equilibrium, stable isotopes suggest that calcite precipitated under disequilibrium conditions. However, the small dimensions of the deposit and the relatively high flow velocities allowed lack of δ13C and δ18O isotope fractionation in CO2‐ nor in ‐calcite, leading to independent temperature calculations, both with mean values of 25°C. Isotopic trends found throughout lamination cannot be explained by strong changes in water temperature nor in δ13CDIC or δ18Ow. The correction made to eliminate these isotopic trends yielded narrower temperature ranges. This paper discusses the accuracy of temperature estimations despite the difficulties coming from disequilibrium and how isotopic trends through time could be explained by the growth of the deposit and not by climate‐related changes.

Integrated process for potassium sulfate and a mixture Of ammonium chloride/potassium sulfate salts production

Relatively pure and coarse crystalline potassium sulfate of about 52 wt % K2O content and almost chlorine free has been obtained by reacting commercial potassium chloride and commercial ammonium sulfate in a stirred tank reactor at moderately low temperature. To increase the yield of potassium sulfate to a reasonable value, an evaporation stage located between the reactor and the crystallizer is used. The main steps of the production process include dissolution, reaction, evaporation, crystallization, centrifuging, drying, and then cooling. It is found that the best operating parameters to produce potassium sulfate of good quality, quantity, and crystal size are 1:1 as KCl/ (NH4)2SO4 mole ratio, 60 ºC reaction temperature, 1 hour reaction time, about one third of the total water used in the dissolution step is to be evaporated, 10 ºC crystallization temperature, 1 hour crystallization time, and 160 and 60 rpm agitation speeds in the reactor and the crystallizer respectively. Applying these operating conditions, a potassium sulfate yield of about 78 % can be achieved. Also, a fully soluble complex salt as a mixture of ammonium chloride and potassium sulfate is obtained by further treatment of the mother liquor. Further concentration of the mother liquor by further water evaporation of about 40 wt % and then crystallization of the slurry at 25 oC can recover up to about 60 wt % of the remaining solid in the mother liquor as a complex salt. The total yield of potassium sulfate is found to be about 95 wt % and the whole value of the solid product obtained is about 79 wt %.

Microstructure and hardness of Ti6Al4V/NiAl/Ti6Al4V joints obtained through resistive heating

Resistive heating of Ti6Al4V/NiAl/Ti6Al4V stack resulted in formation of two strips of new phases at the filler/Ti6Al4V interface. The thinner one, growing into filler material, consists of the NiAl(Ti) phase. Parts of thicker strip, being in a contact with α-Ti grains, are filled with the coarse crystalline α2-Ti3Al phase, while those adjacent to β-Ti grains consist of α2-Ti3Al matrix with separate Ti2Ni crystallites. The hardness of Ti6Al4V plates and NiAl filler material after 6 min of processing time were measured to be ∼390HV0.05 and ∼840HV0.05, respectively, what matched the hardness of the base elements. All above indicates that the exothermic reaction of Ni/Al multilayers backed with resistive heating allowed to obtain practically defect free connection for Ti6Al4V parts.

Combining satellite image data and field observations to characterize fresh-water carbonates in Kurkur Oasis, Southern Egypt

Several fresh-water carbonate deposits (tufa and travertine) were formed at different elevations within the Kurkur paleolake, 50 km west of Aswan, Egypt. Such paleolake was unique and confined in sag between the cuesta and the capping platform of Sin El-Kaddabaa Plateau. This work aims at integrating the remote sensing data together with the chemical and petrographic analyses to map and characterize these tufa and travertine deposits to define their paleo-depositional environment. A DEM with 2.5 m spatial resolution was generated from two ALOS/PRISM images to show geomorphological and hydrological parameters. In addition, full-polarimetric SAR data were used to investigate the scattering response of these tufa and travertine deposits. These deposits show a volume scattering response, with an increase in the pedestal height of the co- and cross-polarized signatures. The tufa and travertine deposits range from Pleistocene (older upper level) to Recent (younger lower level). The young tufa is hard, light brown porous and thinly-laminated, while the old tufa is generally coarse crystalline and consists of columnar pseudo denderitic calcite crystals. The travertine displays a stromatolitic fabric, where thin dark micritic algal laminae alternate with relatively thick calcitic bands (∼1 cm). Conducted XRD and chemical analyses reveal that these tufa and travertine are entirely composed of low magnesium calcite, with traces of quartz (<2%). Moreover, the δ13C and δ18O values suggest that the old tufa have been developed during warm pluvial periods, while the younger ones were precipitated in drier periods. Two hypotheses were introduced to explain the changes in the hydrological regime of Kurkur paleolake; the first proposes a hydrological breaching due to water overflow on the lake's low periphery areas that led to their desiccation (where the tufa and travertine were deposited) and the second is the possible integration into the regional drainage networks of the area presently occupied by Lake Nasser.