Search Results (192)

Salinization represents a significant threat to freshwater resources worldwide, compromising water quality and security. In the Vieira de Leiria–Marinha Grande aquifer, salinization mechanisms are a complex interaction between seawater intrusion and evaporite dissolution. Near the coast, groundwater is mainly influenced by seawater, evidenced by Na-Cl hydrochemical facies, high electrical conductivity, and Na⁺/Cl⁻, Cl⁻/Br⁻ and SO₄^2−/Cl⁻ molar ratios consistent with marine signatures. In areas affected by diapiric dissolution, besides elevated electrical conductivity, groundwater is enriched in SO₄²⁻ and Ca²⁺ and in minor elements like K⁺, Li⁺, B³⁺, Ba²⁺ and Sr²⁺, and high SO₄²⁻/Cl⁻ and Ca²⁺/HCO₃⁻ molar ratios, indicative of gypsum/anhydrite dissolution. The relationship between δ¹⁸O and electrical conductivity further supports the identification of distinct salinity sources. This study integrates hydrogeochemical tracers to investigate hydrochemical evolution in the aquifer with increasing residence time and influence of water–rock interaction, as well as the accurate characterization of salinization mechanisms in multilayer aquifers. A comprehensive understanding of these processes is essential for identifying vulnerable zones and developing effective management strategies to ensure the protection and sustainable use of groundwater resources. Full article

Extensive research has addressed concrete deterioration and its countermeasures; however, studies on responsive repair methods and materials remain comparatively limited and less systematic. In this study, six mixtures of repair mortars (RMs) were formulated using aluminate-based binders, specifically calcium sulfoaluminate (CSA) and amorphous calcium aluminate (ACA) cements. The experiment evaluated the mechanical properties and freeze–thaw resistance of these mortars. To accelerate hydration, a controlled amount of anhydrite gypsum was incorporated into each mixture. The fluidity and setting time of fresh RMs were measured, whereas the compressive strength, flexural strength, and ultrasonic pulse velocity (UPV) of hardened RMs were evaluated at 1, 7, and 28 days. In addition, freeze–thaw resistance was assessed as per ASTM C666 by determining the relative dynamic modulus of elasticity. Additionally, the hydration products and microstructural characteristics of paste specimens were qualitatively analyzed. The mechanical performance, including strength and UPV, and freeze–thaw resistance of RMs containing ACA were superior to those of RMs containing CSA. In particular, compared to the CSA-containing specimens exposed to freeze–thaw action were significantly deteriorated, the ACA-containing specimens showed excellent resistance with relatively less cracking and spalling. This may imply that ACA is effective as rapid repair materials for concrete structures in cold regions. Microstructural observations revealed variations in hydration products depending on the aluminate binder employed, which significantly influenced the mechanical and durability properties of the RMs. These results may aid the selection of optimal repair materials for deteriorated concrete structures. Full article

This study focused on the dust in the ventilation of the underground coal mine of Ningwu Coalfield, Shanxi Province; the particle-size distribution and the mineralogical and geochemical characteristics of the vent dust were studied. The particle-size distribution of the vent dusts in the exhaust outlets of the four coal mines studied is similar and characterized by a single peak, which occurred at 3.5–4.0 μm. The minerals in the vent dusts are dominantly composed of kaolinite, followed by illite, quartz, calcite, dolomite, bassanite, and anhydrite. Except for the high content of bassanite, the vent dust discharged from the YS coal mine presents a similar mineral composition to the parent coal. Compared with the parent coal (and the Upper Continental Crust), the vent dust is enriched to varying degrees in the major element oxides Fe₂O₃, CaO, K₂O, Na₂O, and MgO, as well as trace elements Sb, Zn, Bi, Cd, Cu, As, W, and Pb, especially the contents of Sb, Zn, W, and As increased by 1177, 84, 15, and 12 times, respectively. The vent dusts emitted from these coal mines mainly come from the mining of coal seams; a small amount comes from the shotcrete and weathering products of the tunnel gallery, dust flame retardant, and the wear of coal cutters and coal transmission belts. Therefore, it is necessary to strengthen the management of coal mine vent dust emission to ensure that the mine vent emissions are pollution-free. Full article

Through this work, an experimental setup and pre-processing method for obtaining fluorescence and quasi-noise-free Raman spectra of minerals for in situ mineral identification in an underground environment is proposed. It uses a combination of methodologies like dual excitation wavelengths, Shifted Excitation Raman Difference Spectroscopy (SERDS), and deep learning-based U-Net model for background and noise correction. The dual excitation wavelengths technique employs a near-infrared SERDS laser for the fingerprint and a red laser for the large Raman shift region. The SERDS laser operates at two excitation wavelengths and is tuneable in the vicinity of 785 nm. The red laser uses 671 nm excitation wavelength. The obtained fingerprint and large Raman shift Raman spectra are then fed to a pre-processing method containing the trained U-Net model for obtaining a background-corrected and quasi-noise-free Raman spectrum. The proposed method addresses issues of existing handheld Raman systems in terms of spectrometer sensitivity, spectrum acquisition speed, pre-processing time, fluorescence effects, and other interferences due to surrounding light or vibration. The obtained final processed Raman spectrum is then deconstructed into pseudo-Voigt peaks. The identification of the minerals can be based on the number and the positions of the pseudo-Voigt peaks. Samples of gypsum (CaSO₄·2H₂O) and anhydrite (CaSO₄) were used for evaluating the performance of the proposed method. The influence of measurement time on the reproducibility and precision of the peak identification and, thus, mineral identification is also analyzed. Full article

Calcareous sandstones, acting as sealing layers, play a crucial role in hydrocarbon accumulation of formations with high sand content (sand content > 80%). However, the genetic mechanisms, sealing mechanisms, and effectiveness of calcareous sandstones remain unclear. This study takes the Zhuhai–Enping formations in the Panyu A Sag as an example. By comprehensively analyzing data from well logs, cores, cast thin sections, elemental geochemical analysis and carbon–oxygen isotopes, the genetic mechanisms, development patterns, and controlling effects on hydrocarbon accumulation of calcareous cement layers are investigated. The main findings are as follows: (1) The calcareous sandstone cements are mainly composed of dolomite, ankerite, and anhydrite. With increasing burial depth, dolomite transitions from micritic dolomite to silt-sized and fine-crystalline dolomite, and finally to coarse-crystalline dolomite. (2) The local transgression provided ions such as Ca²⁺ and Mg²⁺, forming the material basis for early dolomite formation. As burial depth increased, the diagenetic environment shifted from acidic to alkaline, leading to the dolomitization of early-formed calcite and the formation of ankerite. (3) The high source-reservoir displacement pressure difference effectively seals hydrocarbon accumulation. Vertically interbedded tight calcareous sandstones and thin marine transgressive mud-stones collectively control efficient hydrocarbon preservation and enrichment. This research addresses the current limits in the study of “self-sealing sandstone layers,” and provides new geological insights and predictive models for hydrocarbon exploration in sand-rich settings. Full article

Many small-size ore deposits occur in the Lower Paleozoic strata along the ENE-trending imbricate thrust fault in NW Tarim Basin. Based on field investigations and petrographic examinations, sulfur-related deposits mainly occur within the paleo-karst cavities and are composed of elemental sulfur and anhydrite. Elemental sulfur is extensively present, whereas anhydrite is limited to the Topulang area. The over-dispersed δ³⁴S values (−25.2 to +7.4‰ VCDT) suggest that elemental sulfur and anhydrite typically originate from a multi-phase process involving bacterial sulfate reduction (BSR) superimposed stepwise sulfur disproportionation. The source of sulfate most likely derived from the subsurface Cambrian evaporites. The lower δ¹³C (−6.43 to −3.10‰ VPDB) and δ¹⁸O values (−13.49 to −10.30‰ VPDB) and the higher ⁸⁷Sr/⁸⁶Sr ratios (>0.7105) further suggest that the calcite cements precipitated from near surface aquifer with significant meteoric water influx and were associated with southeastward propagation since the Cenozoic in response to the remote effects of the India–Eurasia collision. This regional tectonic uplift and meteoric water influx created favorable anoxic environments (“sulfur springs”) for subsequent BSR and sulfur disproportionation along the Kepingtage overthrust fault front, resulting in the mineralization of sulfur-bearing species. This study provides a useful example for understanding the repeated processes of BSR and sulfur disproportionation for deep-buried evaporites associated with tectonic-driven mineralization within the Tarim Basin and elsewhere. Full article

Africa hosts numerous emerald deposits, among which Sumbawanga, located at the junction of Tanzania, Zambia, Congo, and Malawi, stands out as one of the significant localities. This study presents a comprehensive analysis of the gemological, spectroscopic, and inclusion characteristics of Sumbawanga (Tanzania) emerald samples utilizing techniques such as gem microscopy, UV-Vis-NIR spectroscopy, Raman spectroscopy, GEM-3000, and EPMA, etc. These emerald crystals look like rolled pebbles and display a bluish-green coloration. They contain fingerprint-like fluid inclusions, which occasionally encompass a circular bubble (the gas phase is CO₂). Sumbawanga emeralds are characterized by abundant mineral inclusions, including quartz, apatite, anhydrite, diaspore, chrysoberyl, rutile, hematite, and magnetite. Particularly diagnostic are the mineral inclusion of chrysoberyl twins and the assemblages of quartz and diaspore. Full article

Fluid flow prediction in clastic heterogeneous reservoirs is a universal issue, especially when diagenetic development supplants structural and depositional controls. We consider this issue in the Middle Miocene Belayim Formation of the Gulf of Suez, a principal syn-rift reservoir where extreme, diagenetically induced pore system heterogeneity thwarts production. Although fault compartmentalization is understood as creating first-order traps, sub-seismic diagenetic controls on permeability anisotropy and reservoir within these traps are not restricted. This study uses a comprehensive set of petrophysical logs (ray gamma, resistivity, density, neutrons, sonic) of four key wells in the western field of Tawila (Tw-1, Tw-3, TW-4, TN-1). We apply an integrated workflow that explicitly derives permeability from petrophysical logs and populates it within a seismically defined structural framework. This study assesses diagenetic controls over reservoir permeability and fluid flow. It has the following primary objectives: (1) to characterize complicated diagenetic assemblage utilizing sophisticated petrophysical crossplots; (2) to quantify the role of shale distribution morphologies in affecting porosity effectiveness utilizing the Thomas–Stieber model; (3) to define hydraulic flow units (HFUs) based on pore throat geometry; and (4) to synthesize these observations within a predictive 3D reservoir model. This multiparadigm methodology, involving M-N crossplotting, Thomas–Stieber modeling, and saturation analysis, deconstructs Tawila West field reservoir complexity. Diagenesis that has the potential to destroy or create reservoir quality, namely the general occlusion of pore throats by dispersed, authigenic clays (e.g., illite) and anhydrite cement filling pores, is discovered to be the dominant control of fluid flow, defining seven unique hydraulic flow units (HFUs) bisecting the individual stratigraphic units. We show that reservoir units with comparable depositional porosity display order-of-magnitude permeability variation (e.g., >100 mD versus <1 mD) because of this diagenetic alteration, primarily via pore throat clogging resulting from widespread authigenic illite and pore occupation anhydrite cement, as quantitatively exemplified by our HFU characterization. A 3D model depicts a definitive NW-SE trend towards greater shale volume and degrading reservoir quality, explaining mysterious dry holes on structurally valid highs. Critically, these diagenetic superimpressions can replace the influence of structural geometry on reservoir performance. Therefore, we determine that a paradigm shift from a highly structured control model to an integrated petrophysical and mineralogical approach is needed. Sweet spot prediction relies upon predicting diagenetic facies distribution as a control over permeability anisotropy. Full article

As industry moves from fossil fuels to green energy, substituting hydrocarbons with hydrogen as an energy carrier seems promising. Hydrogen can be stored in salt caverns, depleted hydrocarbon fields, and saline aquifers. Among other criteria, these storage solutions must ensure storage safety and prevent leakage. The ability of a caprock to prevent fluid from flowing out of the reservoir is, thus, of utmost importance. In this review, the main factors influencing fluid flow are examined. These are the wettability of the caprock formation, the interfacial tension (IFT) between the rock and the gas or liquid phases, and the ability of gases to diffuse through it. To achieve effective sealing, the caprock formation should possess low porosity, a disconnected or highly complicated pore system, low permeability, and remain strongly water-wet regardless of pressure and temperature conditions. In addition, it must exhibit low rock–liquid IFT, while presenting high rock–gas and liquid–gas IFT. Finally, the effective diffusion coefficient should be the lowest possible. Among all of the currently reviewed formations and minerals, the evaporites, low-organic-content shales, mudstones, muscovite, clays, and anhydrite have been identified as highly effective caprocks, offering excellent sealing capabilities and preventing hydrogen leakages. Full article

Nanostructural optimization is key to enhancing the performance of low-carbon cements. Supersulfated cement (SSC) is an eco-friendly, low-carbon cement primarily composed of blast furnace slag and calcium sulfate. This study investigates the effects of two types of crystalline anhydrite on the hydration degree and strength of SSC. The experiment used III ${\mathrm{C}\mathrm{a}\mathrm{S}\mathrm{O}}_4$ (high solubility) and II-U ${\mathrm{C}\mathrm{a}\mathrm{S}\mathrm{O}}_4$ (low solubility) as sulfate activators, evaluating the mechanical properties of anhydrite produced at different calcination temperatures through an analysis of pore structure, phase composition, reaction degree of mineral powder, and hydration heat. The results indicate that II-U anhydrite enhances slag hydration, reduces pore size, and significantly improves the compressive strength of SSC. This improvement is attributed to its impact on slag hydration: it reduces gypsum consumption rate, delays ettringite formation, promotes gel product formation, decreases the volume ratio of ettringite to calcium silicate hydrate (C-S-H) gel, fills pores, and decreases porosity. This study reveals the influence of calcined dihydrate gypsum phase changes on the macroscopic properties of SSC and the microstructure of hydration, elucidating the hydration mechanism of anhydrite-based SSC. This work provides a nanomaterial-based strategy for SSC design via crystal phase engineering. Full article

For investigating and modeling the swelling potential of anhydrite rocks, it is important to define a fast but accurate, reliable, and repeatable procedure for mineral identification and quantification of anhydrite mineral in rock samples. We propose a quantitative evaluation of the applicability of two different SEM-based approaches (namely, image analysis and the use of the O/S atomic ratio) for the identification and quantification of anhydrite in polished slices of rock. We compare the results obtained with the bulk densities of the samples and with the outcomes of thermogravimetric analyses, demonstrating high convergence between the different data. We eventually propose a critical comparison between the proposed approaches and the existing methods, overall providing a practical guide for the selection of the best analytical procedure for the quantification of anhydrite content in rocks and, consequently, for the correct estimation of swelling potential. Full article

Soil salinization, particularly under irrigation in the arid regions of North Africa, represents a major constraint to sustainable agricultural development. This study investigates the Chott El Hodna region in Algeria, a Ramsar-classified wetland severely affected by salinization. Two representative soil profiles (P1 and P2) were initially characterized, revealing chemical properties dominated by calcium-chloride and calcium-sulfate types. Based on these findings, 26 additional profiles with moderate levels of gypsum, limestone, and soluble salts were analyzed. The limited number of profiles reflects the environmental homogeneity of the area, allowing the study site to be considered a pilot zone. Fuzzy logic was employed to classify soils, identify intergrade soils, and determine their degree of membership to Solonchaks within the Calcisol class, addressing the lack of precision in conventional classifications. Results indicate that 50% of soils are Solonchaks, 46.15% are Calcisols, and 3.85% are intergrades. Principal Component Analysis (PCA) revealed that soil solution chemistry is mainly governed by the dissolution of evaporite minerals (gypsum, halite, anhydrite) and the precipitation of carbonate phases (calcite, aragonite, dolomite). Statistical analyses using Artificial Neural Networks (ANN) and Multiple Linear Regression (MLR) demonstrated that ANN achieved superior predictive performance for the Solonchak index (Is), with R² = 0.70 and RMSE = 0.17, compared with R² = 0.41 for MLR. This study proposes a robust framework combining fuzzy logic and ANN to improve the classification of saline wetland soils, particularly by identifying intergrade soils, thus providing a more precise numerical classification than conventional approaches. Full article

Stone cleaning for cultural heritage monuments is a critical conservation intervention that must effectively eliminate harmful surface contaminants while preserving the material’s physical, chemical, and historical integrity. This study investigated the removal of tenacious black biofilms formed by Nocardia species previously isolated from deteriorated limestone from the Bastet tomb in Tell Basta, Zagazig City, Egypt, using a Q-switched 1064 nm Nd:YAG laser. Experimental limestone specimens were systematically inoculated with Nocardia sp. under controlled laboratory conditions to simulate biodeterioration processes. Comprehensive testing revealed that a laser fluence of 0.03 J/cm² with a 5 ns pulse duration, applied under wet conditions with 500 pulses, achieved the complete elimination of the biological black film without damaging the underlying stone substrate. The cleaning efficacy was evaluated through an integrated analytical framework combining stereomicroscopy, scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX), X-ray diffraction (XRD), and laser-induced plasma spectroscopy (LIPS). These analyses demonstrated a remarkable transformation from a compromised mineralogical composition dominated by gypsum (62%) and anhydrite (13%) to a restored state of 98% calcite, confirming the laser treatment’s effectiveness in reversing biodeterioration processes. SEM micrographs revealed the complete elimination of mycelial networks that had penetrated to depths between 984 μm and 1.66 mm, while LIPS analysis confirmed the restoration of elemental signatures to near-control levels. The successful application of LIPS for real-time monitoring during cleaning provides a valuable tool for preventing overcleaning, addressing a significant concern in laser conservation interventions. This research establishes evidence-based protocols for the non-invasive removal of Nocardia-induced black biofilms from limestone artifacts, offering conservation professionals a precise, effective, and environmentally sustainable alternative to traditional chemical treatments for preserving irreplaceable cultural heritage. Full article

The new mineral achyrophanite (K,Na)₃(Fe³⁺,Ti,Al,Mg)₅O₂(AsO₄)₅ was found in high-temperature sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aphthitalite-group sulfates, hematite, alluaudite-group arsenates (badalovite, calciojohillerite, johillerite, nickenichite, hatertite, and khrenovite), ozerovaite, pansnerite, arsenatrotitanite, yurmarinite, svabite, tilasite, katiarsite, yurgensonite, As-bearing sanidine, anhydrite, rutile, cassiterite, and pseudobrookite. Achyrophanite occurs as long-prismatic to acicular or, rarer, tabular crystals up to 0.02 × 0.2 × 1.5 mm, which form parallel, radiating, bush-like, or chaotic aggregates up to 3 mm across. It is transparent, straw-yellow to golden yellow, with strong vitreous luster. The mineral is brittle, with (001) perfect cleavage. D_calc is 3.814 g cm^–3. Achyrophanite is optically biaxial (+), α = 1.823(7), β = 1.840(7), γ = 1.895(7) (589 nm), 2V (meas.) = 60(10)°. Chemical composition (wt.%, electron microprobe) is: Na₂O 3.68, K₂O 9.32, CaO 0.38, MgO 1.37, MnO 0.08, CuO 0.82, ZnO 0.48, Al₂O₃ 2.09, Fe₂O₃ 20.42, SiO₂ 0.12, TiO₂ 7.35, P₂O₅ 0.14, V₂O₅ 0.33, As₂O₅ 51.88, SO₃ 1.04, and total 99.40. The empirical formula calculated based on 22 O apfu is Na_1.29K_2.15Ca_0.07Mg_0.34Mn_0.01Cu_0.11Zn_0.06Al_0.44Fe³⁺_2.77Ti_1.00Si_0.02P_0.02S_0.14V_0.04As_4.90O₂₂. Achyrophanite is orthorhombic, space group P222₁, a = 6.5824(2), b = 13.2488(4), c = 10.7613(3) Å, V = 938.48(5) ų and Z = 2. The strongest reflections of the PXRD pattern [d,Å(I)(hkl)] are 5.615(59)(101), 4.174(42)(022), 3.669(31)(130), 3.148(33)(103), 2.852(43)(141), 2.814(100)(042, 202), 2.689(29)(004), and 2.237(28)(152). The crystal structure of achyrophanite (solved from single-crystal XRD data, R = 4.47%) is unique. It is based on the octahedral-tetrahedral M-T-O pseudo-framework (M = Fe³⁺ with admixed Ti, Al, Mg, Na; T = As⁵⁺). Large-cation A sites (A = K, Na) are located in the channels of the pseudo-framework. The achyrophanite structure can be described as stuffed, with the defect heteropolyhedral pseudo-framework derivative of the orthorhombic Fe³⁺AsO₄ archetype. The mineral is named from the Greek άχυρον, straw, and φαίνομαι, to appear, in allusion to its typical straw-yellow color and long prismatic habit of crystals. Full article

Groundwater is the main source of water for both domestic and agricultural use in arid regions. This study assessed the hydrogeochemical characteristics and suitability of groundwater for drinking and irrigation in Kenya’s Ewaso Ng’iro–Lagh Dera Basin. A total of 129 borehole groundwater samples were collected and analyzed for pH, electrical conductivity (EC), total hardness, and major ions. The groundwater was found to be mostly neutral to slightly alkaline and ranged from marginal to brackish in salinity. The dominant water type is Na-HCO₃, with the ionic order Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ and HCO₃⁻ > Cl⁻ > SO₄²⁻ > NO₃⁻. Mineral saturation indices indicate that the water is undersaturated with gypsum and anhydrite but is saturated with calcite, dolomite, and aragonite. Groundwater chemistry is primarily influenced by ion exchange, the mixing of fresh and paleo-saline water, and rock weathering processes. The water quality index (WQI) reveals that 80.5% of groundwater is suitable for drinking. The rest have high levels of sodium, EC, and bicarbonate. Thus, they are not suitable. The irrigation water quality index (IWQI) places most samples in the moderate-to-severe restriction category due to high salinity and sodicity. These findings highlight the importance of properly treating groundwater before use. Full article