Quartz Grains Research Articles

Effect of binary raw materials replacement (quartz and feldspar) for porcelain chamotte on the electro-technical siliceous porcelain properties

The hurry for ecological practices and waste control has emerged as an obligation in modern times, demanding precise strategies to restrain waste accumulation and to stimulate recycling and reuse actions to lower the climate effect. The replacement of binary raw materials for porcelain chamotte waste in siliceous porcelain was studied to obtain eco-friendly high-voltage porcelain. Quartz and feldspar were progressively replaced by 5, 10, and 15 wt.% of porcelain chamotte in a conventional siliceous electro-technical porcelain composition. The replacement effect on sintered samples at 1250°C under industrial heat treatment was evaluated by measuring the linear shrinkage, bulk density, porosity, flexural strength, and microhardness technological properties. Phase analysis was carried out by X-ray diffraction. Microstructural characteristics were studied using a scanning electron microscope. The results showed that chamotte-containing samples reached bulk densities of about 2.36 g/cm3 and a porosity percentage near zero. The maximum flexural strength value at glazed states was 87.8 MPa, for 15 wt.% scrap-containing samples. X-ray diffraction studies revealed a higher mullite phase content in chamotte-containing samples. Scanning electronic microscopy images of the polished and etched specimens show the presence of quartz grains and secondary mullite needles embedded in a feldspathic vitreous matrix. The properties reached by the chamotte-containing samples are attractive since the values obtained in terms of flexural strength, density, and porosity are compared to those reported for conventional siliceous porcelain were obtained. The most noticeable result was observed in flexural resistance. The glazed porcelain bodies showed a flexural strength improvement of about 15%. Then, these porcelain compositions suggest an alternative to produce a more sustainable, affordable, and environmentally-friendly porcelain insulator product.

Intraparticle sorption and desorption of antibiotics

Intraparticle domains are the critical locations for storing contaminants and retarding contaminant transport in subsurface environments. While the kinetics and extent of antibiotics sorption and desorption in subsurface materials have been extensively studied, their behaviors in intraparticle domains have not been well understood. This study investigated the sorption and desorption of antibiotics (ATs) in the intraparticle domains using quartz grains and clay, and antibiotic tetracycline (TC) and levofloxacin (LEV) as examples that are commonly present in groundwater systems. Batch experiments coupled with the analyses using various microscopic and spectroscopic techniques were performed to investigate the sorption and desorption kinetics, and to provide insights into the intraparticle sorption and desorption of TC and LEV. Results indicated that both TC and LEV with different physiochemical properties can migrate into intraparticle domains that were consistent with sorptive diffusion. The rate and extent of the sorption are a function of intraparticle surface area and properties, pore volume and connectivity, and ionic properties of the ATs. The sorptive diffusion led to the slow desorption of both TC and LEV after their sorption, apparently showing an irreversible desorption behavior (with desorption percentage about 1.86–20.51%). These results implied that intraparticle domains can be important locations for storing ATs, retarding ATs transport, and may serve as a long-term secondary source for groundwater contamination.

Soil organic matter and biogenic-abiogenic interactions in soils of Larsemann Hills and Bunger Hills, East Antarctica

Although Antarctic soils are usually described as weakly developed, recent studies indicated the significant variability in soil forming conditions across the sixth continent as well as considerable diversity of soils. The identification of pedogenetic processes in Antarctica is crucial for understanding not only the current state of its environment, but also for better understanding of soil development on Earth through time. Our study provides a detailed investigation of micromorphological features and molecular composition of organic matter of soil and soil-like bodies of remote areas of East Antarctica - Larsemann Hills and Bunger Hills, which are characterized by harsh environmental conditions. Studied soils showed predominantly coarse structure and low organic carbon content, alkaline to almost neutral pH range. Thin sections of studied soils were characterized by predominance of grains of quartz, feldspars, and other primary minerals with angular shapes indicating relatively weak degree of their alteration. All studied humic substances are characterized by the predominance of aliphatic structures. Moreover, it was observed that studied humic acids contains significant amounts of carbohydrates, polysaccharides, esters and amino acids and hydrophilic fragments predominate. Organo-mineral interactions were mostly connected with development of biofilms in the topsoil horizons with the maximal biological activity among studied soils.

Quartz Grain Microtextures in the Paleogene Sosnov Formation: Implications for Sediment Provenance in the Eastern Russian Platform

The purpose of the research. The chief task of the research is to examine the microtextures of quartz grains in the Paleogene Sosnov Formation, which is a sedimentary unit located in the Ulyanovsk-Syzran Volga Region of the Russian Platform. By examining the microtextures, which include mechanical, chemical and mechanical/chemical features, it becomes possible to find out the mechanisms by which grains were transported and subsequently modified. The relevance of the research. The relevance of this research lies in the fact that the analysis of quartz grain microtextures provides valuable insights into sediment provenance of sedimentary deposits is crucial for reconstructing past geological environments and unraveling depositional histories. Research methodology. Twenty quartz grains were collected from sands of the Paleogene Sosnovka Formation, exposed by the Eastern-Tashlinsky and the Kuchurovsky quarries to a depth of 5 and 7.5 m, respectively. The research methodology involved scanning electron microscopy (SEM) to investigate the microtextures of quartz grains. Results and conclusions. The study reveals 19 microtextures types, which were categorized into mechanical, chemical, and combined mechanical/chemical microtextures. An analysis of SEM indicated that chemical microtextures are present in the Paleogene Sosnov Formation, which made it possible to suggest that the sands passed through a low-energy phase during their transition. The data obtained enables us to reconstruct the diverse depositional paleoenvironments, including eolian, subaqueous, mixed subaqueous-eolian, and pedological settings.

A New Type of White Nephrite from Limestone Replacement along the Kunlun–Altyn Tagh Mountains: A Case from the Mida Deposit, Qiemo County, Xinjiang, China

The recently discovered Mida nephrite deposit, located in the East Kunlun Mountains, Qiemo County, Xinjiang, Northwest China, contains new types of white and greenish white nephrite formed by limestone replacement, which shows microstructures, macroscopic features and country rocks typologies that are quite different from those of the other deposits along the Kunlun–Altyn Tagh Mountains. The gemological and mineralogical characteristics of Mida nephrite are presented here. These nephrites show an ivory white color and a porcelain-like appearance, with semitranslucent-to-opaque transparency and a porcelain-to-greasy luster. Petrographic study, electron probe microanalysis (EPMA) data and scanning electron microscopy (SEM) images have indicated that the nephrite is composed of tremolite, accompanied by minor quartz, calcite and diopside. Tremolite aggregates have shown different textures, like flaky, granular, fibrous–felted, bundle, radial and metasomatic relict textures. Quartz has appeared in granular or disseminated form, dispersed in the tremolite matrix. Calcite has shown a metasomatic relict texture in the white nephrite samples. Diopside has shown euhedral grains, with some distributed with a certain geometric appearance. Based on our observations, it is suggested that the quartz in the nephrite originated from Si-rich hydrothermal fluids. We propose that the substantial size difference of mineral grains, together with uncompacted grains with inter-particle pores, are the main reasons for the internal reflection and refraction under transmitted light, which allow less transmitted light to pass through the nephrite body and generate the appearance of a semitranslucent-to-opaque transparency, ivory white color and porcelain luster. Our study has unveiled that the Mida nephrite is not typical of the two known types (D-type: dolomite-related; S-type: serpentinite-related) and is overlapped by quartz grains dispersed throughout the less compact tremolite matrix. These observations would help set it apart from the majority of nephrite jades found in the Kunlun Mountains region and provide valuable insights for enhancing comprehension of the diversity of the nephrite deposits.

Melting Processes of Pelitic Rocks in Combustion Metamorphic Complexes of Mongolia: Mineral Chemistry, Raman Spectroscopy, Formation Conditions of Mullite, Silicate Spinel, Silica Polymorphs, and Cordierite-Group Minerals

Melted rocks (clinkers and paralavas) of the Mongolian combustion metamorphic (CM) complexes were formed during modern and ancient (since the Quaternary) wild-fires of brown coal layers in the sedimentary strata of the Early Cretaceous Dzunbain Formation. According to XRD, Raman spectroscopy, and SEM-EDS data, cordierite, sekaninaite, indialite, ferroindialite, silica polymorphs, mullite, Fe-mullite, anhydrous Al-Fe-Mg silicate spinel (presumably new mineral), and other phases were identified. It has been established that isomorphic impurity of potassium in the cordierite-group minerals does not correlate with their crystal structure (hexagonal or orthorhombic). Indialite and ferroindialite retained their hexagonal structure in some fragments of the CM rocks, possibly due to the very fast cooling of local zones of sedimentary strata and the quenching of high-temperature K-rich peraluminous melt. Clinkers, tridymite–sekaninaite, and cristobalite–fayalite ferroan paralavas were produced by partial melting of Fe-enriched pelitic rocks (mudstone, siltstone, and silty sandstone) in a wide temperature range. The formation of mullite, Fe-mullite, and Al-Fe-Mg silicate spinel in clinkers developed from dehydration–dehydroxylation and incongruent partial melting of Fe-enriched pelitic matter (Al-Mg-Fe-rich phyllosilicates, ‘meta-kaolinite’, and ‘meta-illite’). Large-scale crystallization of these minerals in the K-rich peraluminous melts occurred, presumably, in the range of T > 850–900 °C. The subsurface combustion of coal layers heated the overburden pelitic rocks from sedimentary strata to T > 1050 °C (judging by the formation of cordierite-group minerals) or locally till the melting point of detrital quartz grains at T > 1300 °C and, possibly, till the stability field of stable β-cristobalite at T > 1470 °C. Ferroan paralavas were formed during the rapid crystallization of Fe-rich silicate melts under various redox conditions. From the analysis of the liquidus surface in the Al2O3–FeO–Fe2O3–SiO2 major-oxide system, it follows that the least high-temperature (<1250 °C) and the most oxidizing conditions occurred during the crystallization of mineral assemblages in the most-enriched iron silicate melts parental for cristobalite–fayalite paralava.

Evolution of H2O content in deforming quartz aggregates: An experimental study

Deformation experiments were carried out on pure quartzite samples (>99% quartz) with a grain size of ∼200 μm from Tana, Northern Norway. Deformation conditions were 900 °C, 0.1 wt% H2O added, strain rate ∼1 × 10−6 s−1 at variable confining pressures from 600 to 2000 MPa. Detailed FTIR measurements of H2O indicate that the H2O content in the grain boundary region is higher than that inside quartz grains. Hydrostatic treatment and deformation at the chosen temperature and pressure conditions lead to further H2O loss from grain interiors and H2O increase in the grain boundary region. Varying the confining pressure does not have an observable effect on the H2O transfer from grains to the grain boundary region. The 3585 cm−1 absorption band increases systematically with increasing confining pressure. As this band is associated with OH in dislocations, the increase may indicate an increased dislocation density with increasing pressure. The triplet of 3317, 3375 and 3438 cm−1 associated with Al-content in quartz increases in the grain boundary region indicating an exchange of H+ together with Al3+ for Si4+. The Al and H exchange suggest dissolution-precipitation processes in the grain boundary region facilitating the movement of the quartz grain boundaries (grain boundary migration). The H2O in the grain boundary region will be important for enhancing grain boundary migration and thus recrystallization processes during deformation.

The sensitisation of quartz extracted from andesite

Low quartz sensitivities have been reported in several studies in Iran, and in part this is presumed to be a result of the volcanic provenance of many of the sediments in the study areas. In this study we test experimentally whether a quartz sample, extracted from an andesitic rock and showing an insensitive fast component in the Optically Stimulated Luminescence (OSL) signal, can be sensitised using optical and thermal methods.The luminescence characteristics of quartz extracted from a rock sample from a landslide in Iran (Rudbar-Manjil) are compared to those of a well-characterised quartz sample. We find that very few of aliquots prepared from extracted quartz grains show any sensitivity of the most easily stimulated part of the OSL signal, but that ∼23% of aliquots give detectable initial signals after repeated dosing and bleaching. Surprisingly, a large fraction of the most easily stimulated quartz OSL is removed by infra-red stimulation, even though there is no significant IRSL signal in the UV. However thermal annealing at 700 °C gives rise to a test-dose response that is unaffected by IR. This annealing sensitises all aliquots to some degree and induces a signal which is stable up to 260 °C, in contrast to that following optical sensitisation, which begins to decrease when heated to 140 °C. The implications of these observations are discussed, both in terms of luminescence process and potential for dating.

Record of aeolian processes in Pleistocene deposits in the foreland of the European sand belt

Abstract This article presents the degree of aeolization of Pleistocene deposits in the foreground of the European sand belt in southern Poland. Ten of the 13 sites were established in the Oświęcim Basin and three in the south part of the Silesian Upland. Attention was focused on four types of deposits formed during three glaciations (Sanian, Odranian, Vistulian): boulder clay, fluvioglacial sands and gravels, end moraine deposits, and aeolian sands. Quartz grain abrasion (for the 0.8–1.0 mm fraction) was examined by mechanical graniformametry and the morphoscopic method. The record of aeolian processes in analyzed deposits is the presence of quartz grains RM (very well-rounded and mat) and EM/RM (moderately rounded and mat). They were found in deposits of various origins and ages but in variable proportions. Considering only the average percentage of grains RM, it should be regarded that abrasion of deposits is low in the case of fluvioglacial deposits, moderate in the case of glacial deposits, and good in the case of aeolian deposits. However, the key factor in determining the degree of abrasion is the share of EM/RM grains, which in the abovementioned deposits are seven, three, and twice as many as RM grains. Therefore, the most noteworthy research result is the very high total share of grains with aeolian abrasion (RM + EM/RM), amounting on average to 84.1% for Odranian fluvioglacial deposits, 86.7% for Sanian glacial deposits and 92.6% for Late Glacial aeolian deposits. It means that in the study area, glacial and fluvioglacial transport included deposits with good aeolian abrasion obtained in the periglacial environment before the transgression of the ice sheets. Probably due to the longer persistence of periglacial conditions in southern Poland, compared to its central and northern parts, the degree of aeolization of fluvioglacial and glacial deposits is better. At the same time, there is a significant differentiation in the aeolization of fluvioglacial deposits within the outwash plain in the foreland of the maximum extent of the Odranian ice sheet. In its proximal part, near the front of the ice sheet, fluvioglacial deposits are characterized by much worse abrasion of quartz grains than in the distal part.

Sequential extractions versus alpha autoradiography: Mutually complementary for the identification of U- and Ra-bearing minerals in mine tailings

To assess the long-term stability of uranium in mill tailings, the identification of radionuclide (238U and daughters)-bearing minerals is the first step. A combination of sequential extractions and alpha autoradiography (coupled to scanning electron microscopy) seems powerful for this purpose. Tailings coming from uranium mine sites in Gabon are composed mainly of quartz, feldspars, mica/illite, chlorite and kaolinite and many accessory minerals (siderite, Fe and Ti oxides, sulfate- or sulfide-bearing minerals, uraninite, zircon, etc.).Uranium was detected in minerals inherited from the ore, such as uraninite enclosed in quartz or bitumen and zircons (up to 18 wt% of U), and in newly formed minerals, such as siderite (up to 1.7 wt% of U) and Ti and Fe oxides (up to 3.5 wt% U). Sequential extractions indicate that 40 % of U is unextractable, which indicates U is trapped in an efficient way in the tailings, probably in zircon and in uraninite enclosed in quartz grains. U was mainly released during the acetate extraction step targeting the Ti and Fe oxides and siderite and during the H2O2 step that attacked the bitumen, allowing the dissolution of enclosed uraninite.Ba/Pb sulfates, which are well known to incorporate 226Ra through solid solution mechanisms, are identified as the main trap of 226Ra in the studied tailings. Barite, the predominant sulfate, occurs in two populations: an inherited one under grain form and a newly formed one under fibrous habits. Some fibrous habits are sometimes observed at the inherited barite grain surface, corresponding to barite recrystallization. Using alpha autoradiography, amounts of 226Ra ranging from 2 to 30 ppm were estimated in these sulfate minerals (corresponding to specific activities from 70 kBq to 1 MBq per gram of sulfate grain). Barite, the predominant and 226Ra richest sulfate mineral (30 ppm), is quite insoluble. Only the strongest leaching steps partially dissolved it; 40 % of 226Ra remained unextractable, highlighting its low mobility in environmental conditions.

Rock - soil transition during weathering of rhyolite

Concentric layers of weathered materials around core-stones show the rhyolite to experience sequential, but gradational, changes in visible features, textures and mineralogy as it transforms from ‘rock’ into ‘soil’. The changes start with the opening-up of grain boundaries and micro-cracks (stage 1) followed by their dark brown staining (stage 2) and the subsequent alteration (to sericite and clay minerals) of plagioclase feldspar groundmass grains and phenocrysts (stage 3). Biotite flakes are then bleached and altered (to chlorite and clay minerals) (stage 4) before there starts alteration (to sericite and clay minerals) of groundmass alkali feldspar grains (stage 5) and finally alteration of alkali feldspar phenocrysts (stage 6). Quartz grains are not altered during these stages of weathering but disaggregate and reduce in size due to continual opening-up of grain boundaries and micro-cracks. Increasing stages of weathering are marked by decreasing dry unit weights, dry densities and uniaxial compressive strengths, but increasing apparent porosities. The transition between ‘rock’ and ‘soil’ occurs during weathering stage 6 when all plagioclase groundmass grains and phenocrysts have been altered as have been all alkali feldspar groundmass grains and most phenocrysts. Stage 6 is marked by large apparent porosities (>14%) but low values of dry unit weight (<21.90 kN/m3) and dry density (<2,232 kg/m3).

Shocked quartz in sandstone from the buried Ilkurlka impact structure, Officer Basin, Western Australia

AbstractThe Ilkurlka structure is an ~12 km diameter buried circular aeromagnetic anomaly within the Officer Basin in Western Australia. Prior studies postulated a range of origins, including meteorite impact. We report the presence of pervasive deformation in the first drill cores from the structure. Brecciated sandstone and siltstone contain arrays of quartz grains with concussion fractures and rare shocked quartz grains with planar deformation features (PDF). Universal stage measurements of two quartz grains reveal one grain with PDF parallel to (0001) orientation and three PDF sets parallel to . A second grain contains three PDF sets parallel to and one set parallel to . The shocked grains are interpreted to have formed in situ, rather than representing transported detrital shocked grains. These results suggest local shock compression of at least 10 GPa; however, preservation of primary porosity and overall paucity of shocked grains may indicate lower mean shock pressures. (U‐Th)/He dating of 58 apatite grains from four samples across both cores shows a dominant age population at ~265 Ma and a minor age population at ~135 Ma. These dates overlap with regional events and thus do not provide an unambiguous impact age. An upper Carboniferous to lower Permian maximum impact age is provisionally proposed based on inferred missing target rock stratigraphy.

Characteristics of quartz grains in the middle and lower reaches of the Hutubi River, NW China, and its paleo-environmental significance

Quartz sand characteristics in the downstream floodplain of the Hutubi River, located near the oasis–desert transition zone at the southern edge of the Gurbantunggut Desert, were examined to understand the sedimentary dynamics and processes. By analyzing three fluvial–lacustrine–eolian profiles and collecting surface sediment samples from different reaches of the Hutubi River, the characteristics of quartz sand were examined using optically stimulated luminescence (OSL) dating and scanning electron microscopy (SEM). The qualitative and quantitative results reveal spatial variations in surface sedimentary quartz sand, reflecting a transition from glacial–hydraulic interaction to alluvial dominance, followed by a balance between eolian and alluvial processes, and ultimately eolian dominance. The quartz sand within the profiles exhibits sub-rounded and rounded shapes, with significant alluvial-pluvial characteristics, indicating a predominance of fluvial processes within the lower sections of the profiles, while the upper sections exhibit a higher occurrence of eolian microstructures. Overall, the study area experienced a shift from a relatively high-energy and stable depositional environment during the mid-Holocene to a relatively low-energy and unstable condition in the Late Holocene. This was evidenced by stable fluvial–lacustrine deposition between 8 and 6ka and subsequent transitions between high and low-energy hydraulic processes, accompanied by wind erosion and frequent changes in sedimentary environments since 4.2ka.

Identification of quartz cement in sandstone through deep learning segmentation of electron microscopy images

Quartz cementation is a crucial factor in controlling the petrophysical properties of sandstone reservoirs. However, reliable identification of sandstone cementation often requires petrographic analysis of rock thin sections using a combination of optical light microscopy, backscattered electron (BSE), and cathodoluminescence (CL) images. This process is currently carried out manually and is both costly and time consuming. In this study, we present the first attempt to automate this process by identifying sandstone cement through convolutional neural networks (CNNs). We used a combination of BSE and CL images acquired from sandstone thin sections sourced from formations in the US, Israel, and the Netherlands. For each image pair we created a labeled mask with 4 classes: (i) quartz grains; (ii) quartz cement; (iii) porosity; and (iv) Other phases. We developed a U-Net with a total of 10 layers: 5 layers for the contracting path and 5 layers for the expansive path. The model is trained to predict the segmentation mask for a given input of paired BSE and CL images. A high level of accuracy is achieved for quartz grains (91%), quartz cement (78%), and porosity (95%). By contrast, the Other phase class was poorly predicted due to a combination of mineral heterogeneity and low representation. Our results indicate that Deep Learning algorithms provide a promising avenue for the automation of quartz cement detection in sandstone images.

Testing new kinetic models and calibration methods for Rock Surface Luminescence Exposure dating using controlled experiments

Rock surface luminescence exposure dating (RSLED) is an evolving tool in dating prehistoric rock surfaces. In this study, we explore and compare current and new models and calibration methods using optically stimulated luminescence (OSL) depth profiles from quartz grains and Infrared Stimulated Luminescence (IRSL; IR50, pIRIR225, and MET290) from feldspar grains found in granite and sandstone samples.This study shows that, although correct model assumptions improve the quality of exposure age estimates, significant discrepancies between observed and expected fitting parameter values remain, and these discrepancies leads to inaccurate age estimation. This is particularly the case when post-IR signals from feldspar are used. Here, the spectral dependency of luminescence signals is examined to better understand these problems. The demonstrated depth dependency of fitting parameters, previously assumed to be constant with depth, also gives rise to discrepancies in parameter values. The surprising observation that, in rocks, the IR50 signal is apparently more easily bleached than the quartz fast-component OSL signal is explained in terms of the wavelength dependence of light attenuation increasing the effective path length for shorter wavelengths, and so changing the shape of the light spectrum with penetration depth. This complicates parameter estimates in exposure dating even more.Alternative approaches (rather than parameter estimation) for estimating how long a rock surface has been exposed to light are considered, based on modelling the shape and position of the measured luminescence-depth profile. It is concluded that the most accurate exposure age is derived by interpolating the depth of an unknown profile onto a curve of profile depths from known age profiles (the Exposure Response Curve, or ERC, approach).

Swiss deep drilling campaign 2019–2022: Geological overview and rock properties with focus on porosity and pore-space architecture

A recently completed deep drilling campaign, comprising 9 deep boreholes penetrating the Mesozoic sedimentary sequence of northern Switzerland, yielded >6 km of drillcore. One of the main objectives was to characterise the low-permeability sequence with the lower Jurassic Opalinus Clay in its centre, motivated by the site selection for a deep geological repository for radioactive waste. In this context, the chemical and isotopic composition of the porewater, as well as the mineralogical and petrophysical properties of the rocks, were among the main study targets. In this paper, the main objective was the characterisation of the lithologically diverse Jurassic rock sequence with focus on mineralogy, porosity and pore-space architecture. Given the large amount of data, a well constrained relationship between clay content (relating to fine-grained sheet-silicate minerals) and porosity could be established. Porosity increases with clay content along a concave curve, but in detail minor formation-specific differences of the positions relative to the best-fit curve were identified. These are attributed to the highly variable deposition rates that resulted in different times available for early diagenesis to alter the rock fabric by mineral dissolution and cementation, thereby affecting the compaction behaviour. Pore-size distributions were obtained from N2 ad-/desorption isotherms. A distinct peak at a radius of 3 nm can be clearly correlated with clay minerals, whereas limestones are dominated by pore sizes in the range of 40–100 nm, and marls show intermediate distributions. A conceptual framework is proposed distinguishing a nanometric porosity that is proportional to the clay content and a contribution of larger pores that are related to the geometric incompatibility between platy clay minerals and isometric calcite or quartz. The contribution of these larger pore is thought to explain the curvature of the clay content-porosity relationship and the more limited compaction of the clay in pressure shadows adjacent to the larger grains. A number of outliers towards high porosity at a given clay content were identified in oolites (most strongly in Fe-rich oolites), sandstones and a unit containing coral-reef material. All these units have in common the presence of competent calcite or quartz grains at the time of deposition, leading to grain-supported fabrics and therefore to a more limited compaction in the interstitial pore space.

New insights into sedimentological and geochemical conditions of marine Pleistocene sediments in the Tangier region (Morocco): First implications for paleoenvironmental and paleoclimatic reconstructions

The Pleistocene period is characterized by important periodic climatic variations, marked by alternating arid and humid phases. This work aims to reconstruct the prevailing Pleistocene paleoenvironment and paleoclimate in the Tangier area based on a multidisciplinary study of a marine formation dating from 125 ka. Field investigations and sedimentological, micropaleontological, mineralogical, and geochemical analyses were carried out on samples from the Pleistocene Achakkar formation. The granulometric study, combined with a morphoscopic, exoscopic analysis of quartz grains and evidence for diverse benthic foraminifera, suggests a low-energy marine depositional environment, most likely foreshore to shoreface. Moreover, analysis of clay minerals and major elements suggests mineralogical evolution, indicating an arid climate. The sedimentary successions of the Pleistocene Achakkar littoral are progressively more and more coarse; emplacement was subject to several interactive factors, such as climatic and eustatic responsible for reconstituting the geological history of the Tangier Peninsula.

Petrographic analysis of Oligocene carbonates of Kachchh basin

The Kachchh basin is located on the northwestern margin of India. The basin consists of a relatively continuous sequence of sediments from the Mesozoic, followed by the Deccan Traps and finally a complete sequence of the Cenozoic sediments. The Cenozoic sediments of Kachchh basin are mainly shallow marine deposits characterised by five formations viz. Matanomadh, Naredi, Harudi, Fulra Limestone and Maniyara Fort Formation. The Maniyara Fort Formation belongs to the Oligocene age. The field and petrographic characteristics of the Oligocene limestones from the Golay river section were studied in order to understand the depositional environment. The petrographic investigation of the carbonate rocks of three members of the Maniyara Fort Formation, namely Lumpy Clay Member, Coral Limestone Member and Bermoti Member provides important information for understanding the depositional facies and diagenetic signatures. The Lumpy Clay Member has shale-siltstones with interbedded limestones, characteristically composed of a significant proportion of detrital grains of quartz and some lithic fragments. The lithic fragments are sub-angular to rounded, which indicates substantial transport. They are also worn down and broken, bear small cracks which are filled by micritic matrix or mud. The presence of stylolitic seams within the limestone (though not significant) along with mud filling is also noticed. The dissolution is not prominent, pointing towards shallow burial of the sediments. Paucity of marine fossils as well as the rarity of foraminifera in the Lumpy Clay Member indicate a restricted to semi-restricted shallow marine environment. The limestones of the Coral Limestone Member are petrographically classified as packstone, wackestone and mudstone. Thus, the environment of deposition seems to have varied from restricted lagoonal to shallow marine environment. The Bermoti Member is characterised by a lens of claystone, which consists of both greyish to yellow coloured claystones interbedded with limestones. The Bermoti limestones are petrographically classified as packstone, wackestone and mudstone assemblage. The limestones were observed to be highly micritised, which indicates open, shallow marine settings. The Maniyara Fort Formation, thus characterised by wackestone-packstone-mudstone facies of carbonates, is interpreted to be part of a carbonate ramp system. The limestones from Maniyara Fort Formation exhibit signatures of marine as well as meteoric diagenesis.

Nature, origin, and evolution of carbon-rich fluids in orogenic gold deposits: Insights from fluid inclusion and C-H-O isotope studies of the Tokuzbay gold deposit, Chinese Altai

Carbon-rich or carbonic fluids are identified in some orogenic-type gold deposits worldwide. Their nature, origin, evolution, and relations with gold mineralization are still poorly understood. The Tokuzbay large-size orogenic-type gold deposit in Chinese Altai is characterized by enormous CO2-rich fluid inclusions (FIs), providing an ideal case to investigate the genetic relationship between carbon-rich hydrothermal systems and orogenic-type gold mineralization. The mineralization process in the Tokuzbay includes four stages: (1) stage I quartz-magnetite veins; (2) stage II quartz-pyrite veins; (3) stage III quartz-polymetallic sulfide veins; and (4) stage IV quartz-carbonate veins. Based on the microscopic investigation, cathodoluminescence (CL) imaging, Raman spectrum analysis, and mircothermometric measurements, three types of FIs are identified in the veins, including the N2-bearing carbonic or CO2-rich inclusions (PC-type), the CO2-H2O inclusions (C-type), and the H2O-dominated or aqueous inclusions (W-type). The FIs in the stage I minerals are dominated by PC- and C-types, with minor amount of W-type, and occur as primary and pseudosecondary within quartz grains. These inclusions show a salinity of 5.0—9.5 wt% NaCl eqv. and homogenize to liquid phase during 272℃ to 399℃, indicating their entrapment from an initially homogeneous carbon-rich CO2-H2O-NaCl metamorphic fluid system. From early to late stages, the PC- and C-type FIs are getting infertile, while the W-type FIs become more abundant, indicating the escapes of CO2 and compositional transition from CO2-rich to H2O-rich system. Moreover, the decreasing in temperature (272–399 ℃, 238—326 ℃, 173—267 ℃ and 135—182 ℃ from stages I to IV, respectively) and salinity (5.0—9.5, 2.6—9.2, 2.3—7.8 and 1.4—4.3 wt% NaCl eqv. from stages I to IV, respectively), together with the decrease of the δ18O values, suggests an input of meteoric water during mineralization. In the main mineralization stages (II and III), some FIs show divergent homogenization direction (liquid vs vapor) at similar homogeneous temperatures, yielding quite different salinities. For example, the coexisting W-type and C-type FIs yield similar homogenization temperatures, and the liquid-rich and vapor-rich FIs divergently homogenize to liquid and vapor at similar temperatures with different salinities. This indicates that the fluid effervescence drove phase separation and caused the CO2 escape from the fluid system which promoted the gold precipitation at the ductile-to-brittle transition zone that revealed by the depth (8—11 km) calculated by the C-type FIs of the immiscible inclusion assemblages.The δ13C values of the CO2 extracted from fluid inclusions range from –7.6 to –22.8‰, suggesting that the CO2 might be derived from the hydrolysis of organic matter in the source sediments during metamorphism, rather than simply sourced from magma or the mantle. This understanding is supported by the widespread observation of the low δ13C values from most of orogenic-type gold deposits hosted in sedimentary rocks worldwide.

Deformation and paleopiezometry of auriferous quartz veins in Archean orogenic gold deposits of the Abitibi greenstone belt

Most Archean orogenic gold deposits are associated with major faults such as the Larder Lake-Cadillac fault zone (LLCFZ) in the Superior craton and are hosted in or adjacent to second-order structures as quartz vein systems. Microstructures induced by quartz deformation in these faults or shear zones, such as typical textures of recovery and dynamic recrystallization, give indication of the P-T conditions during deformation. Electron backscatter diffraction (EBSD) analysis of grain lattice orientation and grain size determination, for flow stress calculation, are commonly performed on mylonite or quartzite samples from shear zones. This study tests the validity of such methods on hydrothermal auriferous quartz veins to better constrain the conditions of quartz vein deformation in the vicinity of the LLCFZ and evaluate the effect of depth and local variations on the microstructures and flow stress. Samples were collected in 24 gold deposits and showings along the LLCFZ. The microstructural observations and EBSD analysis allowed the distinction of six microstructural types within the studied samples. Samples analyzed with EBSD display a log-normal distribution of recrystallized grain sizes that is consistent with data for natural samples. The calculated flow stress is highly variable between samples and ranges from 38.2 + 5.1/-6.1 to 74.5 + 2.2/-3.0 MPa in surface samples only. Quartz recrystallization overprints primary textures in all but one samples, which indicates that recrystallization and its associated deformation occurred after the complete crystallization of the veins. Samples with bimodal distribution of recrystallized quartz grain sizes highlight the potential of quartz veins to record several deformation events. Samples are recrystallized at higher temperature and lower stress in the east than in the west of the LLCFZ, which could indicate the exposure of a deeper crust in the east. These data underline the potential of quartz vein microstructures to contribute to the evaluation and evolution of deformation conditions of auriferous quartz vein in an orogenic context.