Search Results (144)

The microbial reduction of Fe(III) is a major component of Fe cycling in terrestrial and aquatic environments and is affected by the Fe(III) mineralogy of the system. The majority of the research examining the bioreduction of Fe(III) oxides by Fe(III)-reducing bacteria (IRB) has focused on the reduction of poorly crystalline Fe(III) phases, primarily ferrihydrite; however, crystalline Fe(III) oxides like goethite (α-FeOOH) and hematite (α-Fe₂O₃) comprise the majority of Fe(III) oxides in soils. This study examined the bioreduction of goethite and hematite of geogenic and synthetic origin by Shewanella putrefaciens CN2, a well-studied model IRB, in laboratory incubations. Overall, the rate and extent of Fe(II) production were greater for goethite than for hematite, and for geogenic Fe(III) oxides relative to their synthetic analogs. Although there was substantial production of Fe(II) (i.e., >5 mM Fe(II)) in many of the systems, X-ray diffraction analysis of the solids at the end of the incubation did not indicate the formation of any Fe(II)-bearing secondary minerals (e.g., magnetite, siderite, green rust, etc.). The results of this study demonstrate the variability in the extent of bioreduction of geogenic goethite and hematite, and furthermore, that synthetic goethite and hematite may not be good analogs for the biogeochemical behavior of Fe(III) oxides in aquatic and terrestrial environments. Full article

Rare earth elements (REEs) have been identified as valuable and critical raw materials, vital for numerous technologies and applications. With the increasing demand for and supply gap in REEs, many research studies have focused on alternative sources of REEs. This study involved an elemental and mineralogical characterisation of discarded coal from a coal plant and coal fly ash (CFA) from a power station in South Africa for REE presence. XRD results revealed that the discard coal sample consisted mainly of kaolinite, pyrite, siderite, quartz, calcite, gypsum, and muscovite, whereas CFA contained abundant glassy amorphous phases, alumina silicates, quartz, gypsum, calcite, and minute levels of muscovite and hematite. SEM-EDAX showed REE-carrying grains containing phosphorus in both discard coal and CFA samples. This was followed by investigating the leaching potential of REEs using hydrochloric acid from discard coal and CFA. This research’s potential impact is possibly providing a new and sustainable source of REEs. For that purpose, multiple batch leaching tests were performed to investigate the effects of temperature and acid concentration on the leaching efficiencies of REEs from discard coal and CFA. The experimental results indicated that temperature strongly influences REE leaching efficiency, while acid concentration has a lesser impact. This study identifies the best leaching conditions for the total REE recovery as 1 M HCl and 80 °C for discard coal and CFA. Full article

This study aims to investigate the depositional environment, sediment sources, and elemental occurrence of Upper Paleozoic coal in the Renjiazhuang Mining District, Western Ordos Basin. Furthermore, SEM-EDX, optical microscope (OM), ICP-AES, ICP-MS, and AAS were used. Compared with hard coal of the world, M3 coals were enriched in Ga, Li, Zr, Be, Ta, Hf, Nb, Pb, and Th, M5 coals were enriched in Li (CC = 10.21), Ta (CC = 6.96), Nb (CC = 6.95), Be, Sc, Ga, Hf, Th, Pb, Zr, In, and REY, while M9 coals were enriched in Li (CC = 14.79), Ta (CC = 5.41), Ga, W, Hf, Nb, Zr, Pb, and Th. In addition, minerals were mainly composed of kaolinite, dolomite, pyrite, feldspar, calcite, and quartz, locally visible minor amounts of monazite, zircon, clausthalite, chalcopyrite, iron dolomite, albite, fluorite, siderite, galena, barite, boehmite, and rutile. In addition, maceral compositions of M3 coals and M9 coals were dominated by vitrinite (up to 78.50%), while M5 coals were the main inertite (up to 76.26%), and minor amounts of liptinite. REY distribution patterns of all samples exhibited light REY enrichment and negative Eu anomalies. The geochemistry of samples (TiO₂ and Al₂O₃, Nb/Y and Zr × 0.0001/TiO₂ ratios, and REY enrichment types) indicates that the sediment sources of samples originated from felsic igneous rocks. Indicator parameters (TPI, GI, VI, GWI, V/I, Sr/Ba, Th/U, and Ce_N/Ce_N*) suggest that these coals were formed in different paleopeat swamp environments: M3 coal was formed in a lower delta plain and terrestrial (lacustrine) facies with weak oxidation and reduction, and M5 coal was formed in a terrestrial and dry forest swamp environment with weak oxidation–oxidation, while M9 coal was formed in a seawater environment of humid forest swamps and the transition from the lower delta plain to continental sedimentation with weak oxidation and reduction. Statistical methods were used to study the elemental occurrence. Moreover, Li, Ta, Hf, Nb, Zr, Pb, and Th elements were associated with aluminosilicates, and Ga occurred as silicate. Full article

The Huangjindong gold deposit in northeastern Hunan is one of the most representative gold deposits in the Jiangnan Orogenic Belt. The orebodies are mainly hosted in the Neoproterozoic Lengjiaxi Group, which comprises carbonaceous slates. Abundant carbonaceous material (CM) can be found in the host rocks and ore-bearing quartz veins, but its geological characteristics and genesis, as well as its association with gold mineralization, are still unclear. Systematic petrographic observation demonstrated two types of CM in host rocks and ores, i.e., CM1 and CM2. Among them, CM1 is the predominant type and mainly occurs in the layered carbonaceous slates, while CM2 is mostly present in quartz veins and mineralized host rocks. Laser Raman spectroscopic analyses of CM1 were performed at higher temperatures (376–504 °C), and CM2 was generated at similar temperatures (255–435 °C) to gold mineralization. Combined with previous studies, we can conclude that CM1 was produced by Neoproterozoic to early Paleozoic metamorphism before gold mineralization, while CM2 is of hydrothermal origin. Geochemical modeling indicates that CM1 could promote gold precipitation through reduction, as well as facilitate structure deformation and metal absorption as previously proposed. However, hydrothermal CM2 is favorable for gold mineralization because it triggers sulfidation, similar to other Fe-bearing minerals (such as siderite) in the host rocks. Consequently, both types of CM in the Huangjindong deposit are favorable for gold mineralization and carbonaceous slates could be important gold-bearing units for future ore prospecting in the Jiangnan Orogen as well as other places in South China. Full article

The Václav vein (Březové Hory deposit, Příbram ore area, Czech Republic) is a base–metal vein containing minor Cu-Zn-Pb-Ag-Sb sulfidic mineralization in a usually hematitized gangue. A detailed mineralogical study using an electron microprobe revealed a complicated multistage evolution of the vein. Early siderite and Fe-rich dolomite were strongly replaced by assemblages of hematite+rhodochrosite and hematite+kutnohorite/Mn-rich dolomite, respectively. In addition, siderite also experienced strong silicification. These changes were associated with the dissolution of associated sulfides (sphalerite, galena). The following portion of the vein contains low-Mn dolomite and calcite gangue with Zn-rich chlorite, wittichenite, tetrahedrite-group minerals, chalcopyrite, bornite, and djurleite, again showing common replacement textures in case of sulfides. The latest stage was characterized by the input of Ag and Hg, giving rise to Ag-Cu sulfides, native silver (partly Hg-rich), balkanite, and (meta)cinnabar. We explain the formation of hematite-bearing oxidized assemblages at the expense of pre-existing “normal” Příbram mineralization due to repeated episodic infiltration of oxygenated surface waters during the vein evolution. Episodic mixing of ore fluids with surface waters was suggested from previous stable isotope and fluid inclusion studies in the Příbram ore area. Our mineralogical study thus strengthens this genetic scenario, illustrates the dynamics of fluid movement during the evolution of a distinct ore vein structure, and shows that the low content of ore minerals cannot be necessarily a primary feature of a vein. Full article

The main goal of this paper is to determine the order of the paragenetic sequence and phase transitions of the Ni–Fe sulfide association hosted in listvenites. Listvenites are hydrothermally altered mafic and ultramafic rocks that are often associated with active tectonic settings, such as transform faults, suture zones, and regional extensional faults, usually in contact with volcanic or carbonate rocks. Listvenitization is displayed by a carbonation process when the original olivine, pyroxene, and serpentine group minerals are altered to Mg–Fe–Ca carbonates (magnesite, calcite, dolomite, and siderite), talc, quartz, and accessory Cr spinel, fuchsite, and Ni–Fe sulfides. The formed rocks are highly reactive; therefore, very often, younger hydrothermal processes are observed, overprinting the mineralogy and geochemistry of the original listvenitization products, including accessory Ni–Fe sulfide paragenesis. The studied samples of listvenites were collected from two locations in Kosovo (Vardar Zone): Janjevo and Melenica. The Ni–Fe sulfide textures and relationships with the surrounding listvenite-hosted minerals were obtained using reflected and transmitted light microscopy, while their chemical composition was determined using an electron microprobe. They form accessory mono-or polymetallic aggregates that usually do not exceed 100 μm in size disseminated in the studied listvenites. Generally, the paragenetic sequence of Ni–Fe sulfides is divided into three stages. The first pre-listvenite magmatic phase is represented by pentlandite and millerite. The second listvenite stage consists of Ni–Co bearing pyrite I (Ni content up to 11.57 wt.% [0.24 apfu], and Co content up to 6.54 wt.% [0.14 apfu]) and differentiated thiospinels (violarite + siegenite ± polydymite). The last, late listvenite stage is represented by younger gersdorffite−ullmannite and base metal mineralization: pyrite + marcasite + sphalerite + galena ± chalcopyrite ± sulfosalts. The findings obtained should help in the interpretation of many disseminated accessory Ni–Fe–Co mineralizations associated with mafic and ultramafic rocks worldwide. Full article

Tight oil reservoirs are considered important exploration targets in lacustrine basins. High-quality reservoir prediction is difficult as the reservoirs have complex distributions of depositional facies and diagenesis processes. Previous research has found that the diagenesis process of tight oil sandstones varies greatly in different depositional facies. However, diagenesis variation in different depositional facies is still poorly studied, especially in distributary channels of shallow water delta deposits in lacustrine basins. Based on the description of core samples, the observation of rock slices, the interpretation of well logging data, and the analysis of porosity and permeability data, the differences in the lithofacies types, diagenesis processes, and pore structures of different distributary channels have been clarified. Ultimately, a model of diagenesis and reservoir heterogeneity distribution in the shallow-water delta of Chang 8 Member of the Yanchang Formation in the Caijiamiao area of the Ordos Basin has been established. This research indicates that the main distributary channels in the study area are dominated by massive bedding sandstone lithofacies, while the secondary distributary channels are primarily characterized by cross-bedding sandstone lithofacies. There are significant differences in the compaction, dissolution, and cementation of authigenic chlorite and carbonate among different parts of the distributary channels. Plastic mineral components, such as clay and mica, are abundant in sheet sands, and are more influenced by mechanical and chemical compaction. Influenced by the infiltration of meteoric water and hydrocarbon generation, dissolution pores are relatively well-developed in the underwater distributary channel reservoirs. A large amount of carbonate cementation, such as calcite and siderite, is found within the sandstone at the interface between sand and mud. The occurrence of authigenic chlorite exhibits a clear sedimentary microfacies zonation, but there is little difference in the kaolinite and siliceous cementation among different microfacies reservoirs. Finally, a model of diagenetic differences and reservoir quality distribution within dense sand bodies has been established. This model suggests that high-quality reservoirs are primarily developed in the middle of distributary channels, providing a theoretical basis for the further fine exploration and development of oil and gas in the study area. Full article

Low-maturity shale oil predominates in shale oil resources. China’s onshore shale oil, particularly the Cretaceous Nenjiang Formation in the Songliao Basin, holds significant potential for low-maturity shale oil, presenting promising exploration and development prospects. This study delves into the hydrocarbon generation conditions, reservoir characteristics, and oil-bearing property analysis of the mud shale from the Nen-1 and Nen-2 sub-formations of the Nenjiang Formation to pinpoint favorable intervals for shale oil exploration. Through the integration of lithology, pressure, and fracture distribution data in the study area, favorable zones were delineated. The Nen-1 sub-formation is widely distributed in the Changling Depression, with mud shale thickness ranging from 30 to 100 m and a total organic content exceeding 2.0%. Type I kerogen predominated as the source rock, while some samples contained type II kerogen. Organic microcomponents primarily comprised algal bodies, with vitrinite reflectance (R_o) ranging from 0.5% to 0.8%. Compared to Nen-1 shale, Nen-2 shale exhibited less total organic content, kerogen type, and thermal evolution degree, albeit both are conducive to low-maturity shale oil generation. The Nen-1 and Nen-2 sub-formations predominantly consist of clay, quartz, feldspar, calcite, and pyrite minerals, with minor dolomite, siderite, and anhydrite. Hydrocarbons primarily reside in microfractures and micropores, including interlayer micropores, organic matter micropores, intra-cuticle micropores, and intercrystalline microporosity, with interlayer and intra-cuticle micropores being dominant. The free oil content (S₁) in Nen-1 shale ranged from 0.01 mg/g to 5.04 mg/g (average: 1.13 mg/g), while in Nen-2 shale, it ranged from 0.01 mg/g to 3.28 mg/g (average: 0.75 mg/g). The Nen-1 and Nen-2 sub-formations are identified as potential intervals for shale oil exploration. Considering total organic content, oil saturation, vitrinite reflectance, and shale formation thickness in the study area, the favorable zone for low-maturity shale oil generation is primarily situated in the Heidimiao Sub-Depression and its vicinity. The Nen-2 shale-oil-enriched zone is concentrated in the northwest part of the Heidimiao Sub-Depression, while the Nen-1 shale-oil-enriched zone lies in the northeast part. Full article

Uruguayan ammonoids are preserved in phosphate and siderite nodules found at the basalmost tillite-like conglomerates of the San Gregorio Formation. This lithostratigraphic unit was deposited under glacial conditions and its age (as well as that of the nodules) has been highly debated because glaciations were intermittent in Gondwana during the Late Paleozoic. Reef-builder organisms (e.g., Rugosa and Tabulata), goniatite and orthoceratid cephalopods, brachiopods, sponges, actinopterygians and other indeterminate gnatostomes, as well as fragmentary stems and roots of cf. Lycopsida are the most frequent fossils in the nodules. According to new biostratigraphic and paleoclimatic evidence, these taxa are representative of a reefal environment of a preliminary Devonian age including species that are common in the underlying Early Devonian (Emsian) Durazno Group. Among the ammonoid remains, more than 40 clusters of hatchling goniatites were found in the nodules. Each cluster contains a variable number of shells similar in shape to some of the adults also preserved within the nodules, representing a single species preserved at the same developmental stage (3 mm on size average). The strongly packed shells are enveloped by a substance with a different chemical composition and microstructure with respect to that of the nodule matrix, possibly indicating the presence of a gelatinous-like substance reminiscent of that secreted by the females of some extant cuttlefish and octopuses at the time of the egg spawn. Differing from previously described ammonoid accumulations, our clusters are unique in containing individuals of just a single species preserved in the same ontogenetic stage. That allows us to suggest that they represent a mode of reproduction in which hatchlings were morphologically similar to their parents and occupied the same habitat. Our results are thus one of the oldest known records of reproductive strategies in Paleozoic ammonoids and the phosphate and siderite nodules from the San Gregorio Formation are here classified as a new Konservat-Lagerstätte, which is the oldest known for South America. Full article

The Carboniferous-Permian coal measure strata in the Qinshui Basin exhibit highly lithium (Li) enrichment, with substantial exploitation potential. To further explore the enrichment mechanism of lithium in coal measure strata, the No. 15 coal of the Taiyuan Formation from the Gaoping mine is taken as the research object, and its mineralogical and geochemistry characteristics are evaluated using optical microscopy, X-ray diffraction, scanning electron microscopy, inductively coupled plasma mass spectrometry, X-ray fluorescence, and infrared spectral. The results show that the No. 15 coal is semi-anthracite coal with low moisture, low ash, low volatility, and high sulfur. Organic macerals are primarily vitrinite, followed by inertinite, and liptinite is rare; the inorganic macerals (ash) are dominated by clay minerals (predominantly kaolinite, cookeite, illite, and NH₄-illite), calcite, pyrite, quartz, siderite, gypsum, and zircon. The average Li content in the coal is 66.59 μg/g, with higher content in the coal parting (566.00 μg/g) and floor (396.00 μg/g). Lithium in coal occurs primarily in kaolinite, illite, cookeite, and is closely related to titanium-bearing minerals. In addition, Li in organic maceral may occur in liptinite. The No. 15 coal was formed in the coastal depositional system, and the deposition palaeoenvironment is primarily a wet–shallow water covered environment in open swamp facies; the plant tissue preservation index is poor, and aquatic or herbaceous plants dominate the plant type. The reducing environment with more terrestrial detritus, an arid climate, and strong hydrodynamic effects is favorable for Li enrichment in coal. The results have important theoretical significance for exploring the enrichment and metallogenic mechanisms of Li in coal. Full article

Large-scale subsurface hydrogen storage is critical for transitioning towards renewable, economically viable, and emission-free energy technologies. Although preliminary studies on geochemical interactions between different minerals, aqueous ions, and other dissolved gasses with H₂ have helped partially quantify the degree of hydrogen loss in the subsurface, the long-term changes in abiotic hydrogen–brine–rock interactions are still not well understood due to variable rates of mineral dissolution/precipitation and redox transformations under different conditions of reservoirs. One of the potentially understudied aspects of these complex geochemical interactions is the role of iron on the redox interactions and subsequent impact on long-term (100 years) hydrogen cycling. The theoretical modeling conducted in this study indicates that the evolution of secondary iron-bearing minerals, such as siderite and magnetite, produced after H₂-induced reductive dissolution of primary Fe³⁺-bearing phases can result in different degrees of hydrogen loss. Low dissolved Fe²⁺ activity (<10⁻⁴) in the formation water can govern the transformation of secondary siderite to magnetite within 100 years, eventually accelerating the H₂ consumption through reductive dissolution. Quantitative modeling demonstrates that such secondary iron mineral transformations need to be studied to understand the long-term behavior of hydrogen in storage sites. Full article

This study’s aim is to fully characterize ferronickel slag from New Caledonia, considered a multiphase mineral containing amorphous material. The methodology consisted of combining chemical, mineral, and morphological characterization techniques, such as ICP-AES, TGA, Q-XRD, microscopy, spectroscopy, etc. The ferronickel slag consisted of 44 wt. % forsterite, with the inclusion of iron as a substitution for magnesium (Mg_1.8Fe_0.2SiO₄), 1.7 wt. % chromite and 54 wt. % amorphous phase containing iron, magnesium, aluminum, and silica (Mg/Si = 0.4; Fe/Si = 0.2; Al/Si = 0.1). This material was slightly reactive in a cementitious medium, thus limiting its use as an SCM in the construction sector. The ferronickel slag was then subjected to an attrition-leaching carbonation process at 180 °C and a partial pressure of CO₂ of 20 bar. The obtained product, carbonated at 80% of its capacity, was also characterized. It was composed of carbonates (37% of magnesite and 4% of siderite), remaining forsterite (7 wt. %), chromite (1 wt. %), and 50% of an amorphous phase, mainly composed of silica and aluminum. The complete characterization of those products helped in understanding the chemistry of the carbonation process and finding valorization paths for the carbonated products in the construction sector. The carbonated product may be used either as an SCM in blended cement or as a precursor of magnesium–silicate binders. Full article

The Malysheva emerald mine (Urals, Russia) boasts a long history and extraordinary emerald output. However, recent studies indicate that Malysheva emeralds share highly similar inclusion varieties, UV-visible-near infrared (UV-Vis-NIR) spectra, and compositional characteristics with other tectonic-magmatic-related (type I) emeralds from Zambia, Brazil, and Ethiopia. This similarity poses challenges for determination of the emeralds’ origin. This paper systematically investigates the microscopy, spectroscopy, and trace element chemistry of Malysheva emerald samples and compiles previously reported compositional data for the aforementioned Type I emeralds. Based on this dataset, principal component analysis (PCA) and machine learning methods are employed to construct models for emerald provenance discrimination. The results have updated the provenance characteristics of Malysheva emeralds, confirming the solid phase component of their three-phase inclusions as siderite and revealing two UV-Vis-NIR spectral patterns. Furthermore, the unique infrared absorptions related to HDO and D₂O molecules within the 2600–2830 cm⁻¹ range were discovered, which can be indicative of the origin of Malysheva. The prediction results of the machine learning model demonstrate an accuracy rate of 98.7%, and for an independent validation set of Malysheva emeralds, the prediction accuracy reached 100%. The feature importance ranking of the model highlights trace elements and parameters strongly correlated with the emeralds’ origin. These results illustrate the enormous potential of machine learning in the field of emerald origin determination, offering new insights into the traceability of precious gemstones. Full article

The aim of this study was to characterize the influence of CO₂ in geological structures on mineralogical changes in rocks and assess the sequestration capacity in mineral form and solution of a potential pilot storage site in the Czech Republic. Rock samples from a dolomite reservoir and the overburden level, as well as the corresponding pore water, were used. The most important chemical process occurring in the reservoir rock is the dissolution of carbonate minerals and feldspars during the injection of CO₂ into the structure, which increases the porosity of the structure by approximately 0.25 percentage points and affects the sequestration capacity of the reservoir rock. According to the results of geochemical modeling, the secondary carbonate minerals (dolomite, siderite, and ephemeral dawsonite) were present only during the first 50 years of storage, and the porosity at this stage decreased by 1.20 pp. In the caprocks, the decomposition of K-feldspar and calcite resulted in an increase in porosity by 0.15 percentage points at the injection stage only, while no changes in porosity were noted during storage. This suggests that their insulation efficiency can be maintained during the injection and post-injection periods. However, further experimental research is needed to support this observation. The results of this study indicate that the analyzed formation has a low potential for CO₂ sequestration in mineral form and solution over 10,000 years of storage, amounting to 5.50 kg CO₂/m³ for reservoir rocks (4.37 kg CO₂/m³ in mineral form and 1.13 kg CO₂/m³ in dissolved form) and 3.22 kg CO₂/m³ for caprock rocks (3.01 kg CO₂/m³ in mineral form and 0.21 kg CO₂/m³ in dissolved form). These values are lower than in the case of the depleted Brodské oil field, which is a porous reservoir located in the Moravian part of the Vienna Basin. Full article