Quartz Grains Research Articles

МИКРОСТРУКТУРЫ НА ПОВЕРХНОСТИ ЗЕРЕН КВАРЦА И ПРОИСХОЖДЕНИЕ ПАЛЕОГЕНОВЫХ ПЕСКОВ УЛЬЯНОВСКО-СЫЗРАНСКОГО ПОВОЛЖЬЯ

Quartz grains were separated by standard sieving of the Paleogene sands from the Sosnovka Formation of the Ulyanovsk-Syzran Volga region, which are a scarce and valuable raw material for glass making and construction. In order to establish the origin of the sands and restore the facies conditions of their formation, the surface microtextures of the separated quartz grains were examined by optical and electron microscopy. It was shown that the clastic grains of the Sosnovka sands bear the signs of a multi-stage formation process under the conditions of subaquatic (beach zone), eolian, mixed subaquatic-eolian (coastal dunes), injective, and continental pedological settings. For the first time, a complex of microtextures characteristic of the extrusion of grains from deep horizons under pressure and inherent in the injection mechanism of sand formation was described. The diagnostic complex of injectites includes rotational microtextures, notched microtroughs, and deformed fluid inclusions. The rather fresh appearance of the listed microtextures suggests that they were superimposed on the coastal-marine and eolian stages of the evolution with the subsequent formation of sand intrusions. At the final stage of the geological history of the Sosnovka sands, the grains were shaped by the continental pedological conditions, when secondary silica in the form of globules and their clusters cemented the quartz grains, the surface of which concatenated the features of the previous stages. Based on the results of the study, an interpretation scheme summarizing various microtextural features of the reconstructed paleoenvironments and the stages of formation the Sosnovka sands was developed. The finding that the Sosnovka sands are sand intrusions is of great practical importance, as it necessitates new approaches to the discovery and prediction of glass and quartz sand deposits confined to the Paleogene Sosnovka Formation of the Ulyanovsk-Syzran Volga region.

Hematization of Quartz Grains: Study of the Surface of Quartz Grains (M.E.B) and Semi-Quantitative Mineralization

Hematization of Quartz Grains: Study of the Surface of Quartz Grains (M.E.B) and Semi-Quantitative Mineralization

Micromechanical characterisation of overburden shales in the Horn River Basin through nanoindentation

The paper presents a micromechanical characterisation of Fort Simpson shale, which overlies unconventional gas-producing lithologies in the Horn River Basin, NW Canada. The Fort Simpson formation is clay-rich and microseismic data recorded during hydraulic fracturing events in the underlying reservoir has shown the formation acts as a barrier to fracture development, with a notably anisotropic seismic response. Samples were prepared from core fragments and the composition and texture of the shale was characterised using X-ray diffraction, mercury injection porosimetry and scanning electron microscopy (SEM). Nanoindentation testing was used to obtain the mechanical response of the shale microstructure, at grain-scale. The indentation was conducted on a grid pattern and samples were oriented both parallel and perpendicular to the bedding plane to assess the inherent mechanical anisotropy. Chemical analysis of the grids was also undertaken through SEM/EDS (energy dispersive X-ray spectroscopy) and the coupled chemo-mechanical data was used to characterise the material phases of the shale through a statistical clustering procedure. The results show that Fort Simpson shale broadly consists of a soft clay phase, with strongly anisotropic elastic stiffness, and stiffer but effectively isotropic grains of quartz and feldspar. A simple upscaling scheme was also applied to link the grain-scale elastic stiffness to the field-scale microseismic data.

Characterization the dynamics of transport of quartz grains in the Amizmiz watershed (Western High Atlas): Exoscopic approach

Characterization the dynamics of transport of quartz grains in the Amizmiz watershed (Western High Atlas): Exoscopic approach

Electron Spin Resonance Dating of the Quaternary Fluvial Terrace System of the Upper Han River, Central China

The geomorphology of the upper Han River, which is located in the southern Qinling Mountains (central China) and within the northern subtropical monsoon climate zone, contains abundant information on tectonic and climatic changes. Many Paleolithic sites are preserved in the Quaternary terraces in this region, making it an ideal area for studying both geomorphology and ancient human activity. However, owing to limitations in dating methods, the formation ages of the higher terraces T3–T5 of the upper Han River remain unclear. We collected 11 samples of sediment from the higher Quaternary terraces of Wufeng, Qingqu and the Yunyang Basin for electron spin resonance (ESR) dating of quartz grains. Results show that the formation ages of terraces T3, T4 and T5 are 422–401 ka, 627–621 ka and 1129–1099 ka, respectively. Integrating this information with the timings of documented climatic transitions and the history of regional uplift, we propose that the upper Han River terraces formed in response to the combined effects of climatic transition and tectonic uplift.

ФРИКЦІЙНІ ЯВИЩА У ВУГІЛЬНИХ ШАХТАХ: ПРИЧИНИ, НАСЛІДКИ ТА ВПЛИВ НА ГАЗОДИНАМІЧНІ ЯВИЩА

Coal mines are objects of increased danger, since dynamic, gas-dynamic and thermal phenomena occur in them. These phenomena lead to violations of the operating regime, the failure of mining equipment, the death of miners, an increase in the cost of coal mining and other consequences. The purpose of the article is to present the results of studies of the conditions for the formation of thermal effects in coal mines and the reasons for their occurrence, which has both scientific and applied relevance. The conducted studies made it clear that sparking can occur under the influence of both man-made and natural factors. Friction phenomena leading to thermodynamic effects have been recorded in many mines and countries of the world. The main part of explosions and fires of methane occurs during frictional sparking of rocks containing sulfides. The latter produce sparks of a sufficiently high temperature, which can lead to the ignition of combustible gases, as well as the release of hydrogen sulfide, which has a low ignition temperature. In world practice, cases of ignition of combustible materials during the landing of the roof in the absence of coal have been described. British researchers concluded that the methane-air mixture can be ignited by a spark generated by the friction of sandstone against sandstone or mudstone against sandstone. According to the literature data, the ignition of combustible materials and coals can occur as a result of: emissions and explosions, rock collapse during landing, when a spark discharge occurs in quartz during a tribo- or piezoelectric effect; the presence of sulfides in coals or rocks, pyroelectric effect; electrification of coals. At the micro level, in quartz grains of sandstones, the formation of static charges by dislocations, which are decorated with dust, has been established. A particularly strong effect can occur if, in addition to methane, carbon monoxide, hydrogen, hydrogen sulfide, and acetylene are present in the air. An increase in sparking during frictional friction of quartz in the presence of coal dust has been established. The presence of gas inclusions in sandstone minerals during shear deformations leads to the appearance of additional concentrations of hydrocarbons. As a result of contact of such a mixture with a heated area, a short-term small flash occurs, which is a spark.

Paleoenvironmental reconstruction of the Aptian-Albian deposits in the Western High Atlas (Morocco) by the geochemical study of carbonates and the exoscopy of quartz grains

Paleoenvironmental reconstruction of the Aptian-Albian deposits in the Western High Atlas (Morocco) by the geochemical study of carbonates and the exoscopy of quartz grains

Heavy rare earth element and crustal-derived silicon enrichment in Huayangchuan carbonatites, Qinling orogenic belt

The Huayangchuan carbonatite is found in the North Qinling orogenic belt. It is distinguished from most carbonatites worldwide by its abundance of quartz and high heavy rare earth element (HREE) content. The origin of Si supersaturation and HREE enrichment in carbonatite is still unknown. Here, we conducted a detailed mineralogical investigation and in situ geochemical analyses on a suite of drill-core samples obtained from Huayangchuan carbonatite. In situ titanite and monazite UPb dating yielded ages of 212.3 ± 6.4 Ma and 211.8 ± 5.0 Ma, respectively, corresponding to the post-collision stage of the Qinling orogeny. Clinopyroxene and amphibole in the carbonatite are commonly intergrowth with quartz grains and trapped by quartz as mineral inclusions. The mineralogical textures and compositions indicate that quartz crystallized simultaneously with the mafic minerals from a Si supersaturation magma. The high Si activity during clinopyroxene formation may be related to Si assimilation from the wall-rocks. In situ Nd isotopic compositions of apatite and titanite show consistent εNd(t) ranging from −4.8 to −9.0, similar to the values of the whole-rocks and calcites. This indicates that the REE were derived from carbonatite magma without an external source. Two types of calcites were identified based on their cathodoluminescence characteristics, and they have variable chondrite-normalized REE patterns (La/Yb(CN) ranging from <0.01 to 19) but similar HREE contents. This implies that the carbonatite underwent strong crystal fractionation of early LREE-rich minerals, which may be essential for HREE enrichment. Therefore, we proposed that Si supersaturation in the carbonatite was probably caused by wall-rock assimilation, and fractional crystallization yielded primary HREE enrichment in the residual melts. Moreover, HREE enrichment in highly evolved carbonatites is further aided by high Si and alkaline activities.

Abu Hureyra, Syria, Part 2: Additional evidence supporting the catastrophic destruction of this prehistoric village by a cosmic airburst ~12,800 years ago

At Abu Hureyra, a well-studied archeological site in Syria, the onset boundary of the Younger Dryas climatic episode ~12,800 years ago has previously been proposed to contain evidence supporting a near-surface cosmic airburst impact that generated temperatures &gt;2000°C. Here, we present a wide range of potential impact-related proxies representing the catastrophic effects of this cosmic impact that destroyed the village. These proxies include nanodiamonds (cubic diamonds,n-diamonds,i-carbon, and lonsdaleite-like crystals); silica-rich and iron-rich micro-spherules; and melted chromite, quartz, and zircon grains. Another proxy, meltglass, at a concentration of 1.6 wt% of bulk sediment, appears to have formed from terrestrial sediments and was found to partially coat toolmaking debitage, bones, and clay building plaster, suggesting that village life was adversely affected. Abundant meltglass fragments examined display remarkably detailed imprints of plant structures, including those of reeds. The nanodiamonds are proposed to have formed under anoxic conditions from the incineration of plant materials during high-temperature, impact-related fires, while geochemical evidence indicates that the micro-spherules formed from the melting of terrestrial sediments. Broad archeological and geochemical evidence supports the hypothesis that Abu Hureyra is the oldest known archeological site catastrophically destroyed by cosmic impact, thus revealing the potential dangers of such events.

Microtextures on quartz grains in the Estuary sediments of Gurupura River, Dakshina Kannada district, Karnataka State, West coast, India.

The present study focuses on the surface textures of the quartz grains derived from the granitic rocks in a fluvial regime on the west coast of India. The surface microtextures formed during transport due to their stable physical and chemical properties. The surface textures include information about source rock types, transporting force, sedimentary environment and evolution history of the sediment. For this purpose, eight samples were collected and investigated from the Gurupura River estuary of Dakshina Kannada District of Karnataka state west coast in India. The quartz grains show distinct surface textures with unique mechanical, chemical and morphological features. The mechanical features such as conchoidal fractures with arcuate steps indicate that the sand grains were derived from crystalline source rock (i.e., granite) and transported in a high-energy condition. The silica globule, overgrowth, and precipitation marks on the grain surfaces suggest action of chemical processes in a saturated silica environment, which is evident in the upper reaches of the Gurupura River. Surface textures of the quartz grains along the lower reaches of the Gurupura River display an array of mechanical features like a conchoidal fracture, V-shaped marks and impact pits, indicating the impact of mechanical processes. The overall pattern of the surface textures present on the quartz grains suggests moderate to high energy conditions in the Gurupura River.

Thin-section Petrography and Heavy Mineral Study of sandstones of the Barail Group of rocks occuring around Sonapur area of Jaintia Hills, Meghalaya, India

The study area represents a part of the South Shillong Shelf, Meghalaya, where sandstones belonging to the Barail Group (Eocene-Oligocene) are well exposed. Thin section petrography and heavy mineral investigations have been undertaken to assess the geological significance of the sandstones. Framework grains of the Barail sediments comprise of quartz (56.98 to 71.91%), feldspar (1.87 to 7.35%), mica (1.07 to 9.72%), lithic fragments (2.20 to 8.41%) and matrix (9.20 to 20.43%). The detrital composition of the sandstones comprises primarily of quartz grains, angular to sub-rounded, fine to medium grained and moderately sorted in nature. The sandstones are classified as subarkose, feldspathic graywacke and lithic graywacke. Provenance discrimination triangular plots of QFL and QmFLt reflect that the detritus were mostly derived from cratonic interior sources. The Diamond diagram indicates that the Barail sandstones were derived from middle and upper rank metamorphic source. Heavy mineral study of these sandstones indicates the presence of zircon, tourmaline, rutile, sillimanite, kyanite, staurolite, garnet, epidote, sphene, hypersthene, hornblende, chlorite, chloritoid, andalusite, apatite and opaque minerals. The percentages of most stable heavy minerals zircon, tourmaline and rutile vary from 6.11to 21.61, 2.60 to 6.56 and 2.42 to 7.57 respectively. The ZTR maturity index varies from 15.15 to 34.37, which reflects that the sandstones are mineralogically immature. The petrographic and heavy mineral study of the sandstones suggest that the detritus was probably derived from Shillong Massif where Precambrian metamorphic rocks of pelitic and arenaceous composition with plutonic bodies were exposed around the shelf margin. As the Shillong Massif comprises of Precambrian metamorphic rocks of pelitic and semitic (arenaceous) composition with intrusive plutonic bodies.

Characterizing a weathering profile over quartz-mica schists in undulating terrain in Peninsular Malaysia

The weathering profile can be differentiated into an upper, 4.8 m thick, pedological soil (zone I) and a lower, &gt;16.2 m thick, saprock (zone II). Zone I comprises thin IA and IB soil horizons of firm, clayey sand with lateritic concretions, and a IC soil horizon of stiff, clayey silt with quartz clasts and lateritized core-stones. Zone II comprises steeply dipping to vertical, bands of pinkish to grey, stiff silt with distinct relict foliation (highly weathered schist) inter-fingering with bands of reddish yellow, firm clayey silt with indistinct foliation (completely weathered schist) towards its top, and bands of white to light grey, hard silt with distinct foliation (moderately weathered schist) towards its bottom. Lateral variations in abundance of differently weathered schist and preservation of fracture planes allow zone II to be separated into IIA, IIB and IIC sub-zones. The pedological soil (zone I) can be correlated with Class VI of standard rock mass weathering classifications, whilst the saprock sub-zones IIA, IIB and IIC are correlated with Classes V, IV and III, respectively. Silt fractions in the profile consist predominantly of sericite flakes, whilst the sand fractions are mostly of quartz grains and the clay fractions of mainly illite and kaolinite. Decreasing densities, unit weights and silt contents up the profile, but increasing porosities and clay contents, indicate increasing in situ alteration of the schist bedrock. Lowering of an unconfined groundwater table as a result of down-cutting by rivers in adjacent valleys is considered responsible for development of the weathering profile.

РЕМОНТНЫЕ СТРОИТЕЛЬНЫЕ РАСТВОРЫ, ПОЛУЧЕННЫЕ ПЛАЗМЕННОЙ МОДИФИКАЦИЕЙ И ВИХРЕВОЙ АКТИВАЦИЕЙ

Introduction: The service life of reinforced-concrete structures can be increased with the use of effective repair compositions obtained by activating the original components. Purpose of the study: We aimed to develop effective repair compounds obtained by activating the original components. Methods: To process the original components, low-temperature non-equilibrium plasma (LTNP) and electromagnetic activation in a vortex layer device were used. In the course of the study, we used polypropylene, steel, glass, and basalt fiber and fiber made of structured ferromagnetic microwire. Electron microscopy and X-ray diffraction analysis were applied. Results: It was established that the combined use of the above methods for the modification of raw components makes it possible to improve the strength of these materials by more than 50%, which is due to the characteristics of structure formation in the developed compositions. For instance, LTNP increases the amount of portlandite and reduces the main phases of cement stone— C3S and β-C2S, and vortex activation contributes to an increase in the total number of crystalline phases. Quartz powder particles processed in an electromagnetic mill are characterized by layered structure, high surface roughness, large developed cracking, as well as inclusions as a result of impact action. All that improves the physical and mechanical properties of the resulting repair compositions by an average of 20%. Repair compositions additionally treated with plasma modification feature new hydrated formations on quartz grains.

Insights into the Weathering Crust Reservoirs of Granitoids: A Case Study from Qinghai Oilfield of Qaidam Basin, Northwest China

With proven reserves of 9.836 × 1010 m3, the largest known natural gas reservoir among terrigenous basement rocks has been discovered within the granitoids of the northern Qaidam Basin. Due to their high heterogeneity, the genesis of basement reservoirs remains unknown. Herein, the structure of the weathering crust in granitoids and their potential controlling factors on the reservoir development mechanism are discussed using a multidisciplinary approach based on data from cores, thin sections, scanning electron microscopy (SEM), conventional and imaging logs, and physical property and major elements analyses. Moreover, the classification standard of the weathering crust structure is established. The dissolution belt holding diverse reservoir spaces accounts for more than 50% of the total porosity, while the disintegration belt is the main context for the development of cleavage fractures and crack fractures. The original pores exist mainly among the crystal grains of quartz and mica, while the secondary pores and fractures were generated by the alteration of aluminosilicate minerals as well as biotite or hornblende. The quality of these reservoirs is controlled by their mineral composition, tectonic uplift, faulting, and paleogeomorphology. The femic granitoid is the main reservoir-forming lithology in the case of dissolution, while the felsic granitoid is more likely to develop cracks. The formation of the disintegration belt is significantly linked to the presence of faulting. These belts were mostly induced by tectonic deformation along the Altyn fault belt from the late Oligocene to the early Miocene. The diversity in paleogeomorphology influences the extent of the weathering. The exhumation in the Altyn terrane from the late Jurassic to the Cenozoic corresponds to the weathering and hypergene leaching period of the weathering crust within granitoids. Three types of reservoirs are present in the rocks: fractured-porous (Type Ⅰ); porous (Type Ⅱ); and fractured (Type Ⅲ). The fractured-porous and fractured reservoirs were developed mainly in the granitic gneiss and granite, while the porous reservoir was formed in granitic diorite and granitic gneiss. The reservoirs that developed in the weathering crust of granitoids are dominated by Type Ⅰ and Type Ⅱ. The highest quality reservoir, which is the fractured-porous type, developed mainly in the dissolution belt of the weathering crust, and has a porosity ranging from 1.56% to 8.48% and a permeability ranging from 0.03 mD to 14.48 mD. The mechanisms of the development of weathering crust reservoirs provide further information for the hydrocarbon exploration of basement rocks worldwide.

Evaluation of provenance and weathering of beach sediments in the lower part of the Cameroonian coast

The hinterland of Campo is marked by Archean, Paleoproterozoic, and Cretaceous geological formations. Petrographic, mineralogical and geochemical analyzes of beach sediment samples were performed to determine the origin, alteration, and paleoclimate of the various coastal sediment layers and to reconstruct the structural context of the source region. The beach sediments are fine to medium-grained in size. Morphoscopic examination showed a predominance of very angular and shiny quartz grains. These data reflect a relatively close source with transport in a fluvial environment. The Chemical Index of Alteration (CIA: average = 79.94%), Plagioclase Index of Alteration (PIA: average = 85.31%), as well as the A–CN–K and (A-K)-C-N triangular diagram, show that the weathering affected the source area rocks. The ratios of SiO2/Al2O3, K2O/Na2O, and the chemical composition variation index (ICV ∼ 1.32) show that the sediment samples are immature to mature in terms of texture and chemical composition. Al2O3/TiO2 ratio values ranged from 3.04 to 33.44, indicating an intermediate to felsic rock signature, confirmed by Zr vs TiO2, La/Sc, and Th/Co binary diagrams. Geochemical results reveal a passive marginal continental environment. The passive margin emerged during the opening of the South Atlantic Ocean, which is compatible with the overall geology and structural setting of the studied area.

Geochronology (U-Pb and Re-Os) and H[sbnd]O[sbnd]S isotopes reveal ore fluid origin and crucial role of meteoric water for Laozuoshan quartz-vein-hosted gold metallogeny in Jiamusi, NE China

The Laozuoshan auriferous sulfide-quartz veins, which are hosted in the granodiorite, monzogranite, and quartz diorite, are the only Early Cretaceous gold deposit discovered in the central Jiamusi Massif, but its origin and ore-forming processes remain unclear. Here, we integrate mineralogy, HOS isotopes, and U-Pb and Re-Os geochronology to unravel the formation of the Laozuoshan quartz-vein gold mineralization. Zircon and molybdenite from the monzogranite wallrock and gold ores yield weighted mean U-Pb and isochron Re-Os dates of 259.9 ± 2.1 Ma and 103.3 ± 2.3 Ma, respectively. Our radiometric dating suggests that the Laozuoshan quartz-vein gold mineralization was coeval with the quartz diorite (105–103 Ma) but after the monzogranite emplacement. Quartz grains from the auriferous veins of different stages yielded scattered δ18O values (5.4 to 13.0 ‰), with the δD values (fluid inclusions) ranging from –99.9 to –74.9 ‰. The δ18O values of quartz (10.9–13.3 ‰) and feldspar (9.4–11.0 ‰) from the unaltered wallrocks are similar to those (δ18Oquartz = 11.2–13.2 ‰ and δ18Ofeldspar = 10.0–10.4 ‰) from the potassic alteration halos. Meanwhile, the sericite-altered rocks have δ18O values of 12.4–12.9 ‰ (quartz) and 3.4–5.2 ‰ (sericite). Sulfides from the gold ores yielded decreasing δ34S values from 5.3 to 6.9 ‰ (early stage), through 1.0–3.5 ‰ (intermediate stage), to –4.9 to –4.4 % (late stage). The isotope data reflect a largely magmatic source for the early ore fluids, whilst the sulfur was possibly derived from the Mashan Group migmatite. The results, in combination with geologic evidence, indicate that the Laozuoshan quartz-vein gold mineralization was spatially, temporally, and genetically related to the Early Cretaceous quartz diorite, and thus can be classified as intrusion-related, magmatic-hydrothermal-vein type. In the ore-forming processes, the ascending Early Cretaceous magma may have acquired most of their sulfur and gold through assimilation of the Mashan Group migmatite. The early ore fluids derived from the quartz diorite magma may have initially focused into narrow cracks/fractures in the quartz diorite margin and then flow along the fracture system. Subsequently, meteoric water incursion led to temperature drop, boiling, oxygen fugacity increase, and chemical exchange of the resultant fluids, which facilitated gold scavenging by bismuth-rich melts and rapid precipitation as arsenopyrite-hosted electrum and gold-bismuth mineral eutectic assemblage. This study highlights the crucial role of meteoric water in formation of the magmatic-hydrothermal-vein type gold deposit.

Mineral textures, mineral chemistry and S isotopes of sulphides from the Tianbaoshan Pb–Zn–Cu deposit in the Sichuan–Yunnan–Guizhou triangle: implications for mineralization process

AbstractThe carbonate-hosted Pb–Zn deposits in the Sichuan–Yunnan–Guizhou (SYG) triangle region are important Indosinian deposits in South China. The Tianbaoshan deposit is a typical large Pb–Zn deposit in the SYG area and occurs as pipe-like type, hosted by Sinian dolostone. It contains ∼26 Mt Zn–Pb ore (7.76–10.09 % Zn, 1.28–1.50 % Pb and 93.6 g t−1 Ag) and &gt;0.1 Mt Cu ore (2.55 % Cu). In this study, the detailed mineral textures, mineral chemical and sulphur isotopic compositions of the various sulphides have been analysed to constrain the abnormal enrichment mechanism and mineralization relationship. Four mineralization stages have been recognized: Stage 1, minor early pyrite (Py1) with relics and infill of intergranular dolomite or quartz grains; Stage 2, Cu mineralization with coarse-grained, elliptical crystal chalcopyrite (Cp1); (3) Stage 3, Zn mineralization with dark fine-grained sphalerite (Sph1) and light coarse-grained sphalerite (Sph2); and (4) Stage 4, as represented by a quartz–calcite assemblage with galena, minor pyrite (Py2) and chalcopyrite (Cp2). The petrography of the sulphide minerals (Py1, Cp1, Sph1 and Sph2) demonstrates a mutual inclusion relationship. The nature of this relationship from core to rim and their similar sulphur isotope values (5.5–8.3 ‰) indicates a single sulphur source, suggesting that the different mineralization types are the result of different stages of a continuous hydrothermal system. Sphalerite geothermometer study suggests that sphalerite in the Tianbaoshan deposit formed in a low-temperature (&lt;200 °C) hydrothermal system. The low concentrations of Mn and In, low In/Ge ratios and high Fe/Cd ratios in the sphalerite are consistent with those of Mississippi Valley-type (MVT) deposits, but different from those of magmatism-related deposits (e.g. epithermal, skarn and VMS deposits). The positive δ34S values for Py1 (5.1–7.9 ‰), Cp1 (5.1–7.2 ‰), Sph1 (4.7–7.4 ‰), Sph2 (3.9–8.7 ‰), Py2 (4.4–9.3 ‰) and Cp2 (5.0–6.8 ‰) indicate a sulphur source from thermochemical reduction of coeval seawater sulphate. Widely developed dissolved textures (caverns and breccias) with massive sulphide infillings and deformed host rock remnants suggest that replacement of host dolostones by ore fluids was volumetrically significant and the ore formed nearly simultaneously with the cavities. The Tianbaoshan deposit is a typical MVT deposit, which resulted from mixing of a H2S-rich fluid and a metal-rich fluid, with thermochemical sulphate reduction occurring before ore precipitation rather than during ore precipitation.

Protracted melt-present deformation during the Rigolet phase of the Grenvillian Orogeny. Insights from geochronology along the highway 117 transect through the Grenville Province in western Quebec, Canada

In this contribution we use U-Pb zircon geochronology to investigate the age of melt-present deformation within the various structural levels of the Mesoproterozoic Grenville Orogen that are exposed along the Highway 117 transect in western Quebec, Canada. Samples include six syn- to late-deformational felsic leucosomes and injected veins. Four of them are physically linked with hornblende-bearing leucosome in their host gneiss and all six contain undeformed quartz grains, implying they were deformed while still partially molten. Zircon from all samples reveal complex morphologies defined by inherited cores and successions of texturally distinct zones, that mostly share trace element characteristics and yield overlapping Grenvillian 207Pb/206Pb weighted mean ages between ca. 1020–968 Ma. A crustal panel charactered by pervasive migmatites that present evidence for protracted suprasolidus deformation, are key characteristics of channel flow during the youngest phase (Rigolet) of the Grenville Orogen. Field data also indicate that, coeval to deformation in the lower structural level, felsic dykes brecciated mafic components within the upper level; these components were subsequently incorporated into the ductile channel as decametre-sized mafic boudins. Our findings are comparable to recent models advocating Rigolet ductile flow within the Parautochthonous Belt in eastern Quebec but differ from the current conceptual models viewing proposed for the evolution of the orogen during this phase.

Luminescence dosimetry for evaluation of the external exposure in Metlino, upper Techa River valley, Southern Urals, Russia: Analysis of new results

Luminescence dosimetry was applied in the former settlement of Metlino, Southern Urals, Russia as part of a full-scale study to validate the Techa River Dosimetry System (TRDS) 2016 for the upper Techa River region. The village, which was evacuated in 1956, was located 7 km downstream of the release point of liquid radioactive waste by the Mayak plutonium facility. Several brick samples were taken from north-eastern and south-eastern walls of the granary, facing the former Techa river shoreline and floodplain. Samples were all taken at the same height and measured at different depths into the brick. For the majority of brick samples, good Optically Stimulated Luminescence properties of the quartz grains were observed. In some cases, however, strong levels of sensitization and/or signal recuperation were encountered which necessitated adjustment in the measurement protocols. Anthropogenic doses in bricks varied from 1.5 to 6.6 Gy and the horizontal profiles along both walls showed significant variation, which is explained on a qualitative basis. A dose depth profile is observed for selected samples, which is different from the dose depth profile measured and simulated for samples from the north-western wall of the granary in previous studies. This is qualitatively explained by the differences in source configuration.

Breakdown and Modification of Microplastic Beads by Aeolian Abrasion.

Saltation is an important wind erosion process that can cause the modification and breakdown of particles by aeolian abrasion. It is recognized that microplastic particles can be transported by wind, but the effect of saltation on microplastic properties is unknown. This study examined the impact of simulated saltation alongside quartz grains on the size, shape, and surface properties of spherical microplastic beads. The diameter of the microplastics was reduced by 30-50% over 240-300 h of abrasion with a mass loss of c. 80%. For abrasion periods up to 200 h, the microplastic beads remained spherical with minimal change to overall shape. Over 95% of the fragments of plastic removed from the surface of the microbeads during the abrasion process had a diameter of ≤10 μm. In addition, during the abrasion process, fine particles derived from breakdown of the quartz grains became attached to the surfaces of the microbeads resulting in a reduction in carbon and an increase in silicon detected on the particle surface. The results suggest that microplastics may be mechanically broken down during aeolian saltation and small fragments produced have the potential for long distance transport as well as being within the size range for human respiration.