Mica Content Research Articles

Polycarbonate/mica extrusion using mixing elements: Improvement of transparency and thermal, mechanical and water and gas barrier properties

Polycarbonate (PC) was loaded with mica fillers by melt mixing process using a twin-screw extruder. The influence of the mica content on the PC properties was analyzed. Also, the presence of mixing elements of grid shape on the mica distribution during the PC extrusion was discussed. These elements allowed us to significantly improve the fillers dispersion in the polymer matrix. As a consequence, the transparency of the PC films was maintained up to 5 wt% of mica due to reducing the aggregates formation and the homogeneous mica dispersion. Despite a slight decrease of the polymer molar mass, a strong improvement of the PC thermal stability, mechanical resistance as well as barrier properties towards water and gases (N2, O2 and CO2) was obtained due to the reinforce and tortuosity effects induced by mica fillers in the PC matrix. The gas and water transport properties of the PC/mica films were well-fitted using a predictive empirical model, that took into account the double tortuosity and immobility effect of mica particles. In addition, mica fillers were found to have specific interactions with water molecules, that led to enhancement of the moisture resistance of PC, thus improving its performance.

Heavy mineral record from the east China sea inner shelf: Implications for provenance and climate changes over the past 1500 years

The heavy mineral composition and sensitive grain size changes from core SS4 retrieved from the mud wedge on the East China Sea inner shelf have been studied for better understanding provenance variations in the sediment and climate changes during the last ~1500 yr. High dolomite content and occurrence of ubiquitous polysynthetic mica indicate that the sediments in core SS4 were mainly derived from the Yangtze River, while the relatively high epidote content represent the contribution of small local rivers from Zhejiang and Fujian provinces. The substantial decrease in the epidote/hornblende ratio since ~730 yr BP manifests a decline in the relative contribution of sediment from the small local rivers to the core. We propose that the changes in drought/flood conditions in response to the East Asian winter monsoon (EAWM) and human activities might have been mainly responsible for changes in sedimentary characteristics. During 1400–730 yr BP, the core sediments were characterized by relatively finer sensitive grain size and high epidote/hornblende ratio, due to a possibly weaker EAWM (i.e., less Yangtze River-derived sediment transported by the southward coast current). This time interval coincides with the Sui-Tang Warm Period (1400–1130 yr BP) in China and the Medieval Warm Period (1000–730 yr BP) on a broader regional scale. The prolonged warm periods were, however, interrupted by three short cold phases at 1350–1280 yr BP, 1130–1000 yr BP and 870–750 yr BP, characterized by coarse sensitive grain size and decreased epidote/hornblende ratio. Between 360 and 150 yr BP, the sensitive grain size significantly coarsened, which corresponded to the Little Ice Age. Our new findings suggest that sedimentation processes of mud wedge formation are responsive to natural environmental change and human activity.

Study on the Tensile Strength and Crack Development of Granite Crystal Models with Different Fabrics

According to the relationship between the development of hydraulic fracture and the distribution of different rock and mineral fabrics, digital image technology was used in this study based on the discrete element particle flow method. An SCGM numerical model, which can control fabric and refine mesoscopic crystal defects, was constructed. The tensile strength test of granite specimens with different component contents and polymerization conditions was conducted, with the monitorization of damaged cracks. The test results showed that (1) the SCGM model could construct a model of a crystal structure containing variable components and polymerization, to achieve numerical experiments of different parameters; (2) compared with previous models, the SCGM model can reflect internal stress change of a specimen with the variation of the structure. At the same time, the contained crystal structure can characterize different failure modes such as intergranular cracks of different components, grain boundary cracks of the same component, and transgranular cracks, which were in good agreement with the actual failure state of granite; (3) the mica content of the specimen and its strength presented a linear relationship of y = − 14.723 x + 12.642 . The degree of polymerization of the components and the strength of the specimens were both affected by the accumulation of microcracks and stress concentration, which appeared to increase first and then decrease. When the specimen was broken, the number of microcracks and the degree of polymerization of the components also increased first and then decreased. The SCGM model can construct a numerical model of granite with arbitrary fabric and crystal structure and provide a hydraulic fracturing analysis method.

Barium-calcium aluminosilicate glass/mica composite seals for intermediate solid oxide fuel cells

In this paper, the effects of phlogopite mica addition on the properties of barium-calcium-aluminosilicate (BCAS) glass seals are studied. Accordingly, BCAS glass powder is mixed with up to 30 wt% of phlogopite mica; the resulting mixture is formed and sintered at different temperatures. The microstructure and phase content of the samples are then analyzed by scanning electron microscope (SEM) and X-ray diffraction method. Mechanical properties including, hardness, compression strength, fracture toughness and Young's modulus are investigated. The coefficient of thermal expansion (CTE) and softening temperature of the seals are measured. The electrical conductivity of the selected specimens is studied by applying the electrochemical impedance spectroscopy method. The performance of the composite seals is analyzed under fuel cell working conditions by the leak test. It is found that the samples with the mica content of more than 10 wt% cannot be sintered to near full relative density. The sintering temperature above 750°C raises the risk of unfavorable reactions between mica and the BCAS glass matrix. It is also revealed that the addition of 5 wt% phlogopite increases Young's modulus and fracture toughness of the BCAS glass seals by 13% and ~633%, respectively, without impairing other mechanical and thermal properties. The composites seals with more than 10 wt% of mica content don't meet the required mechanical properties demands for SOFC seals. It is found that the composite seal with 5 wt% of phlogopite mica has very low electrical conductivity and leak rate of less than 1.2×10−4sccm/cm. This composite seal shows high thermal stability with ~5% reduction in CTE after 10 cycles under SOFC working conditions and consequently can be considered as a promising seal for SOFCs.

Tungsten mineralization during the evolution of a magmatic-hydrothermal system: Mineralogical evidence from the Xihuashan rare-metal granite in South China

Abstract Tungsten deposits are usually associated with granitic intrusions that record a long and complex evolution of the magmatic-hydrothermal system. However, the genetic link between magmatic-hydrothermal evolution and tungsten mineralization remains unclear. The Xihuashan tungsten deposit in South China, an important vein-type wolframite deposit, is closely associated with greisen and multi-phase intrusive activity that produced biotite granite, two-mica granite, and muscovite granite. From the biotite granite to the two-mica granite to the muscovite granite, micas vary from siderophyllite to lithian siderophyllite, with decreasing K/Rb and Nb/Ta ratios and increasing Rb and Cs contents. The zoned micas in the muscovite granite and greisen display fluorine-depleted rims, reflecting subsolidus replacement by external aqueous fluids. The presence of siderite indicates a Fe-, Mn-, and CO2-rich fluid under reducing conditions. The micas in the greisen have higher-F contents and lower Fe3+/Fe2+ ratios than those in the muscovite granite, suggesting that the fluids contributing to greisen formation had a relatively high-fluorine content and were reduced. The increase of CO2 in the fluid enhanced its ability to unlock W from melts/rocks into fluids. The reducing environment also facilitated the tungsten mineralization. During greisenization, the pH value of the fluid increased, which destabilized the polymeric tungstates to form WO42–. The mixture of W-rich solution and Fe-, Mn-rich external fluid eventually precipitated as vein-type wolframite in favorable locations. An empirical equation (Li2O = 0.0748 × F2 + 0.0893 × F) was introduced for estimating the Li2O contents of hydrothermal micas using the F contents determined by EPMA.

Позднепалеолитический комплекс культурного горизонта 2Г стоянки Коврижка IV на р. Витим (Байкало-Патомское нагорье)

In 2016—2018 a living complex dated to ca. 18,6 kyr cal BP was excavated at Kovrizhka IV site, level 2G. This is an ocher colored area of 5.0 m in diameter, with a semi-circular hearth lined by four slabs, and a massive slab surrounded with large boulders and gneiss fragments. Slabs and boulders forming an arc were recorded on the periphery of the complex, and two pits (post-holes?) of 20 cm in diameter were found on the northern and southern outskirts. Based on use-wear analysis, 17 tools were identified as meat knives, scrapers and carvers for bone, antler and skins. Their number and composition indicate a short-term occupation. About 60% of artifacts in the collection are of quartz, hence it is assumed that access to pebble raw materials was seasonally limited. The three central stones in the hearth were heated to the temperature ranging from 250 to 380—440 °C. The source of ocher is hematite of two types: quartz-hematite association and rock with a significant content of calcite, chlorite, feldspar and mica. A comparison with the ore compositions of the known iron locations and archaeological sites showed that ocher was delivered from the north of Western and Eastern Baikal regions, situated more than 500 km away from Kovrizhka. The available evidence points to the existence of a winter dwelling. The closest analogies are known at the Transbaikalian sites of Studenoye–1 and 2, Ust-Menza–1 and 2, Sukhotino–4, etc.

Mineralogical and geochemical constraints on the origin of the Sohland-Rožany Ni-Cu-(PGE) sulfide mineralization (Lausitz Block, Bohemian Massif, Germany/Czech Republic)

The Sohland-Rožany Ni-Cu-(PGE) sulfide mineralization is hosted by a small gabbroic dike that is one of several Ni-Cu sulfide-bearing gabbroic intrusions in the northern Bohemian Massif. The intrusions are associated with a Middle Devonian to Early Carboniferous mafic–ultramafic plumbing system that emplaced within Cadomian granodiorites of the Lausitz Block. The Sohland-Rožany dike comprises varitextured olivine- and hornblende-bearing gabbro and hornblende gabbro which originated from differently fractionated magma batches. Fractionation likely took place in deeper parts of the magmatic systems, e.g. within staging magma chambers. Mineralogical features like Ti-rich primary brown hornblende and diopsidic clinopyroxene as well as overall enriched incompatible element contents suggest moderate alkaline basaltic parental magmas with relatively high volatile contents.The magmatic sulfide mineralization is exclusively hosted by the olivine- and hornblende-bearing gabbro and include disseminated, net-textured and massive sulfides. The ore types are predominated by pyrrhotite-pentlandite-chalcopyrite assemblages accompanied by secondary violarite and pyrite as well as by accessory Pt, Pd, Au and Ag phases. The disseminated and net-textured sulfides have highly variable modal proportions of base-metal sulfides with pyrrhotite-dominated beside chalcopyrite-dominated aggregates on the hand specimen scale. The platinum-group mineral (PGM) assemblage includes Pd-Pt-Ni-bearing bismuthotellurides of the melonite–merenskyite and michenerite–testibiopalladite solid solution series as well as sperrylite. The sulfide ores feature predominantly elevated Ni and highly variable Cu and Pt, Pd and Au tenors (3.5–6.4 wt.% Ni, 0.1–16.6 wt.% Cu, 80–3080 ppb Pt, 50–5320 ppb Pd and 20–3770 ppb Au). The magmatic sulfides are locally characterized by a late-stage hydrothermal overprint where sulfides were replaced by hydrous secondary phases (e.g. actinolite–tremolite and chlorite). A significant redistribution of the PGE due to hydrothermal alteration is unlikely as the majority of PGM show a close spatial association to the base-metal sulfides.Textures and chemical compositions of the sulfides suggest that repeated magma batches eroded already fractionated sulfide pools and entrained early crystalized cumulates of monosulfide solid solution (MSS) together with variable fractionated sulfide melts. Sulfide saturation in the Sohland-Rožany magmas was locally controlled by assimilation of the granodioritic wall-rock in the course of thermomechanical erosion. This process was amplified by high mica contents of the granodiorites. Sulfur isotope signatures (–2.0 to –1.2‰ VCDT) and the S-poor nature of the hosting granodiorites exclude a significant contribution of S from the country rocks.

K–Ar geochronology of orogenic gold mineralization in the Vangtat gold belt, southeastern Laos: Effect of excess argon in hydrothermal quartz

AbstractThe Thongkai‐Ok gold deposit is one of several actively mined deposits in a newly discovered orogenic gold belt in southeastern Laos. At a district scale, gold mineralization occurs within the Vangtat shear zone, one of the tectonic structures of the Poko suture zone that marks the collision between the Indochina Terrane and the Kontum Massif in southern Laos‐central Vietnam. High grade gold mineralization is associated with quartz–pyrite–white mica veins and silicified zones up to 10 m thick, hosted by strongly deformed and sheared pelitic schist. Lower‐grade gold mineralization occurs in a graphite–carbonate–quartz–sulfide hydrothermal alteration envelope that grades into sub‐economic/barren altered pelitic schist. The objective of this study is to establish the age of mineralization in the Vangtat orogenic gold belt by K–Ar dating of hydrothermal white mica in the gold‐bearing quartz‐sulfide veins in order to better understand its spatial and temporal relation to other gold deposits in Southeast Asia and to regional tectonic events. Three‐white mica bearing quartz–pyrite samples were collected from the open pit at Thongkai‐Ok. The dominant white mica phase in the samples is 2M1 muscovite and the K2O content measured by electron microprobe techniques in individual white mica crystals ranged between 8.61 and 9.79 wt%. Two of the three vein samples were separated by gravity settling into four size fractions, <2, 2–4, 4–10, and 10–40 μm, respectively. The results of potassium measurements by flame photometry in the K–Ar sample aliquots show a range in potassium content which reflects the amount of quartz present in each sample as an impurity. With one exception, a correlation was observed between potassium concentration in the samples, including the size fraction separates, and the calculated K–Ar age. The large range of calculated ages, from 348 to 206 Ma, is interpreted to reflect excess argon contained in fluid inclusions in the hydrothermal quartz present in the analyzed samples. We interpret the youngest age of the quartz‐free samples, 206 ± 4 Ma, as closest to the age of mineralization in the Vangtat gold belt. The age could be as young as ~170 Ma if the age versus potassium content relation is extrapolated to the average potassium content of white mica in the samples analyzed.

Key patterns of S‐type granitic gneiss to define the baric (low‐ to high‐pressure) nature of Phanerozoic basement terranes

AbstractS‐type granitic gneiss is a major rock type in exposed Phanerozoic basement areas. However, it is hardly used to decipher the metamorphic evolution of such areas formed by the collision of tectonic plates. It is demonstrated by thermodynamic modelling of the metamorphism of common to evolved S‐type granite that mineralogical key patterns can elucidate the baric nature of granitic gneiss. Low‐ to medium‐grade granitic gneiss shows increasing and decreasing contents of potassic white mica and biotite, respectively, with rising pressure. Pressures above c. 12 kbar (500°C) result in considerable amounts of Na‐rich clinopyroxene. A relatively precise peak‐pressure estimate can be obtained by the determination of the Si content in potassic white mica but only for water pressures below 13–15 kbar. Thus, eclogite facies granitic gneiss can only be recognized by the presence of Na‐rich clinopyroxene. Silicon contents in biotite might have a geobarometric potential as potassic white mica. Titanium minerals in S‐type granitic gneiss are of limited baric potential.

The Influence of Fresh and Weathered Rock Foliation on the Stability of the Monte Seco Tunnel

The Monte Seco tunnel (MST) is one of several old unlined tunnels constructed for Brazilian railways in the 1950s, and the MST still receives intense train traffic (primarily for iron ore transportation). The MST was constructed in a fractured gneissic rock mass, which has potential instability problems associated with gravity-driven block falls (at low stress confinements) defined by three fracture sets and the metamorphic foliation. Previous geological and geotechnical surveys at the MST site have included basic geomechanical classifications from outcrops and drill core specimens, detailed terrestrial laser scanning (TLS) mapping of foliation and fracture planes, geoelectrical imaging and laboratory tests. These surveys discovered two sections of the tunnel (referred to herein as MS1 and MS2) with major potential for instability problems (i.e., poor rock mass qualities). In this paper, the 3D discrete element method (DEM) was used to assess the potential stability problems in these sections with particular interest on the role of the rock foliation strength on the current stability state of these sections. Three instability indicators were developed and monitored during and after the DEM simulations: the total failed block volume (FBV), the average displacement of the tunnel face (AD), and the percentage of slipping contacts near the tunnel face (SC). The weathering effects were considered in two different scenarios: the occurrence of isolated weathered foliation planes (WFPs) and the general weathering advance through potentially weathered regions. In the latter scenario, the percentage of weathered contacts (WC) increased progressively. The overall results indicated that fresh foliation planes ensured the current tunnel stability due to the moderate mica content (Ma) in such geological structures. Thus, underestimating the strength of foliation planes causes unrealistic instability conditions in the tunnel. However, the weathering advance on fractures and foliation planes can trigger important instability problems over time.

Petrography, diagenesis and geochemistry of the Cambro-Ordovician Khabour sandstones, western Iraq: Implications for reservoir quality and the impact of the Hirnantian glaciation

Deeply buried (2.3–3.5 km) sandstones of the Cambro-Ordovician Khabour Formation are important hydrocarbon reservoirs in western Iraq. An integrated approach incorporating petrography, scanning electron microscope (SEM) and X-ray diffraction (XRD) was applied to investigate diagenesis and diagenetic minerals and their impacts on reservoir quality. Major and trace element distribution using X-Ray Fluorescence (XRF) analysis also was carried out to identify sandstones deposition during or after the Hirnantian glaciation. The sandstones of the Khabour Formation are dominated by sublitharenites and subarkoses. Several diagenetic processes have affected the sandstones of the Khabour Formation. These include early diagenetic porosity occluding events, such as common formation of illite and sericite coatings, along with rare quartz overgrowths, and calcite cementation. This was followed by secondary porosity forming events which include calcite dissolution, leaching of feldspar, alteration of micas and fracturing. The pore systems are dominated by secondary pores, vuggy and fractured porosity, intergranular and intragranular pores and poorly-connected macropores. A decrease in heavy minerals in sandstones from the upper part of the Khabour Formation and an associated decrease in both Zr and Hf concentration, which are typically associated with zircon, supported by a decrease in mica content and low API gamma ray unit values are considered to be a signature of sandstones affected by the Hirnantian glaciation.

Clay mineralogical composition and chemical properties of Haplic Luvisol developed on loess in the protected landscape area Litovelské Pomoraví

AbstractThe character of parent material, organic matter and climatic conditions are the crucial factors of pedogenesis. They directly influence the intensity of weathering, transformation processes, elements release and geochemical cycles. The mineral transformation in a profile of the recent soil developed on loess (Haplic Luvisols, Siltic, Epidystric, Ochric) was studied. The land area Litovelské Pomoraví was chosen because of the stability of soil‐forming factors such as topography, relief, vegetation and climate. X‐ray diffraction (XRD) quantitative analysis of the fine earth (<2 mm) and XRD analysis of clay (<2 μm) and the fine clay fraction (<0.2 μm) were applied. The obtained results showed the most significant differences between the argic horizons (Bt1 and Bt2) and other soil horizons. The lower content of quartz and feldspars and higher content of dioctahedral micas and phyllosilicates in both Bt horizons was observed. It was assumed the clay illuviation/lessivage process was preceded by long‐term leaching of carbonate in humid continental conditions during almost the whole Holocene. The distribution of the clay fraction correlates with the distribution of phyllosilicates through the profile. Major clay minerals in the clay fraction (<2 μm) were illite and kaolinite, smectite, chlorite, vermiculite and several types of mixed‐layered phases. The analysis of the finer clay fraction (<0.2 μm) identified the new phase hydroxy‐interlayered minerals as the product of illite (vermiculite) weathering in humid continental conditions.Highlights Clay mineralogy of Haplic Luvisols on loess was studied. XRD analysis identified the new phase of hydroxy‐interlayered minerals. Increasing of smectites, dioctahedral micas, and goethite as a result of clay illuviation/lessivage process was observed.

Evaluation of two nano-silane-modified emulsion stabilised pavements using accelerated pavement testing

ABSTRACT Upgrading, maintenance and rehabilitation of road infrastructure is expensive, especially in view of the growing scarcity and cost of suitable road building materials. In areas with high mica content and secondary minerals such as smectite in the natural materials, stabilisation with cement is not viable. The Council for Scientific and Industrial Research of South Africa has embarked on a research programme to evaluate the performance of substandard materials improved with anionic nano-silane modified bitumen emulsions for use in base and subbase layers. This work comprises laboratory testing as well as Accelerated Pavement Testing using the Heavy Vehicle Simulator (HVS). The results of a full-scale HVS test on a light pavement as well as initial analysis on a medium traffic road are discussed. It has been shown that stabilisation of available substandard materials using an anionic nano-silane modified bitumen emulsion compared with the standard approach of importing high quality crushed aggregate can lead to savings as high as 40%–50% for equivalent performance. In addition, there was also a significant reduction in construction effort and time.

A laboratory approach for the calibration of seismic data in the western part of the Swiss Molasse Basin: the case history of well Humilly-2 (France) in the Geneva area

A collection of 81 plugs were obtained from the Humilly-2 borehole (France), that reached the Permo-Carboniferous sediments at a depth of 3051 m. Experimental measurements of physical parameters and mineralogical analysis were performed to explore the links between sedimentary facies and seismic characteristics and provide a key tool in the interpretation of seismic field data in terms of geological formations. The plugs, cylinders of 22.5 mm in diameter and sim30 mm in length were collected parallel and perpendicular to the bedding in order to explore their anisotropy. Ultrasound wave propagation was measured at increasing confining pressure conditions up to 260 MPa, a pressure where all micro-fractures are considered closed. The derivatives of velocities with pressure were established, allowing the simulation of lithological transitions at in-situ conditions. At room conditions, measured grain densities (kg/m3) range from 2630 to 2948 and velocities vary from 4339 to 6771 and 2460 to 3975 {text {m/s}} for P- and S-waves propagation modes, respectively. The largest seismic-reflections coefficients were calculated for the interface between the evaporitic facies of the Keuper (Lettenkohle) and the underlying Muschelkalk carbonates (R_{text {c}}= 0.3). The effective porosity has the range of 0.23% to 16.65%, while the maximum fluid permeability left( text {m}^{text {2}}right) is 9.1 times text {10}^{-{text {16}}}. A positive correlation between porosity and ultrasound velocity has been observed for P- and S-waves. The link between velocities and modal content of quartz, dolomite, calcite, and micas has been explored. This paper presents a unique set of seismic parameters potentially useful for the calibration of seismic data in the Geneva Molasse Basin.

Influence of mineralogical and chemical compositions on alkali-silica-reaction of Tennessee limestones

The paper aims to identify potential correlations between mineralogical and chemical compositions of AAR reactive dolomitic limestone aggregates from Tennessee and their expansion on ASTM C1293 for quick evaluation of reactivity. The chemical compositions of 26 limestones, namely the silica content (SiO2), showed a strong correlation with the expansion in the concrete prism test. The early and highly expansive limestones are characterized by a high clay/ mica content (>5%). The reactivity of Tennessee limestones is mainly caused by crypto/microcrystalline quartz, chert, and finely disseminated silica in carbonate and clay/mica matrices, and it can be reasonably evaluated using X-ray diffraction and chemical analysis coupled with petrographic examinations.

A Middle Crustal Channel of Radial Anisotropy Beneath the Northeastern Basin and Range

AbstractA challenge in interpreting the origins of seismic anisotropy in deformed continental crust is that composition and rheology vary with depth. We investigated anisotropy in the northeastern Basin and Range where prior studies found prevalent depth‐averaged positive radial anisotropy (VSH > VSV). This study focuses on depth‐dependence of anisotropy and potentially distinct structures beneath three metamorphic core complexes (MCCs). Rayleigh and Love wave dispersion were measured using ambient noise interferometry, and Bayesian Markov chain Monte Carlo inversions for VS structure were tested with several (an)isotropic parameterizations. Acceptable data fits with minimal introduction of anisotropy are achieved by models with anisotropy concentrated in the middle crust. The peak magnitude of anisotropy from the mean of the posterior distributions ranges from 3.5–5% and is concentrated at 8–20 km depth. Synthetic tests with one uniform layer of anisotropy best reproduce the regional mean results with 9% anisotropy at 6–22 km depth. Both magnitudes are plausible based on exhumed middle crustal rocks. The three MCCs exhibit ~5% higher isotropic upper crustal VS, likely due to their anomalous levels of exhumation, but no distinctive (an)isotropic structures at deeper depths. Regionally pervasive middle crustal positive radial anisotropy is interpreted as a result of subhorizontal foliation of mica‐bearing rocks deformed near the top of the ductile deformation regime. Decreasing mica content with depth and more broadly distributed deformation at lower stress levels may explain diminished lower crustal anisotropy. Absence of distinctive deep crustal VS beneath the MCCs suggests overprinting by ductile deformation since the middle Miocene.

Evaluation of mechanical properties of mica-mixed sand considering inherent anisotropy

This paper presents the effects of inherent anisotropy on the shear strength and shear modulus of both saturated and unsaturated sands. Several triaxial compression tests were performed using Toyoura sand with different contents of mica: 0%, 1%, 2.5%, 5%, and 10%. Specimens with various deposition angles α were prepared using the air pluviation (AP) and dry vibration (DV) methods. The shear strength properties were measured by conventional triaxial tests, whereas the small strain stiffness was measured by both local small strain (LSS) tests and bender element (BE) tests. The orientation of the sand particles was assessed based on two-dimensional optical microscopic measurements and mathematical estimation. The results showed that an increase in the mica content brought about a decrease in the degree of anisotropy of the shear strength because of mica particle breakage. However, the degree of anisotropy of the shear modulus became higher with a 0%–10% increase in the mica content. The shear modulus of the unsaturated sand had a slightly higher degree of anisotropy than that of the saturated sand. In addition, the degree of anisotropy of the shear modulus was assessed based on the average orientation angle θ of the sand particles.

Key factors controlling radiocesium sorption and fixation in river sediments around the Fukushima Daiichi Nuclear Power Plant. Part 2: Sorption and fixation behaviors and their relationship to sediment properties

We systematically investigated the sorption and fixation behaviors of radiocesium (137Cs) for sediments taken from the rivers of Ukedo and Odaka around the Fukushima Daiichi Nuclear Power Plant. By comparing the Cs sorption and sequential desorption results at various Cs concentrations, across a range of sediment properties, we were able to understand the different contributions at frayed edge sites (FESs) and regular exchange sites (RESs) of the clay minerals, and their relationships with the Cs concentrations and the contents of organic matter (OM). The Cs sorption and fixation were dominated by FESs at trace Cs concentrations, and by ion exchange at RES and the collapse of interlayers at higher Cs concentrations. The Cs sorption at lower Cs concentration was strongly related to radiocesium interception potential (RIP); however, Cs fixation was more related to clay mineralogy (i.e. contents of mica, vermiculite and hydroxy-interlayered vermiculite) rather than the RIP. The first-order kinetic constants for time-dependent Cs sorption at low Cs concentrations were correlated negatively to the ratio between the total organic carbon and RIP values. This implies that Cs access to FESs requires a relatively long duration that is dependent on the contents of the OM. From these results, the sorption and fixation mechanisms were confirmed to be significantly different at different Cs concentrations. Then, the prediction of Cs transport should be based on the key mechanisms that are dominant at the actual trace levels of Cs. A significant difference between the Cs fixation behaviors at the Ukedo River and Odaka River may be understood by considering the differences in their clay mineralogy, due to the different geological settings and weathering stages of both catchments.

A geochemical and biostratigraphic approach to investigating regional changes in sandstone composition through time; an example from Paleocene–Eocene strata, Taranaki Basin, New Zealand

AbstractA geochemical and biostratigraphic approach has been applied to investigate the spatial and stratigraphic variability of Palaeogene sandstones from key wells in Taranaki Basin, New Zealand. Chronostratigraphic control is predominantly based on miospore zonation, while differences in the composition of Paleocene and Eocene sandstones are supported by geochemical evidence. Stratigraphic changes are manifested by a significant decrease in Na2O across the New Zealand miospore PM3b/MH1 early Eocene zonal boundary, at approximately 53.5 Ma. The change in Na2O is associated with a decrease in baseline concentrations of many other major (MnO, CaO, TiO2) and trace elements, and is interpreted to reflect a significant change in sandstone maturity. Paleocene sandstones are characterized by abundant plagioclase (albite and locally Na–Ca plagioclase), significant biotite and a range of heavy minerals, while Eocene sandstones are typically quartzose, with K-feldspar dominant over plagioclase, low mica contents and rare heavy minerals comprising a resistant suite. This change could reflect a change in provenance from local plutonic basement during the Paleocene Epoch to relatively quartz- and K-feldspar-rich granitic sources during Eocene time. However, significant quartz enrichment of Eocene sediment was also likely due to transportation reworking/winnowing along the palaeoshoreface and enhanced chemical weathering, driven in part by long-term global warming associated with the Early Eocene Climatic Optimum. The broad-ranging changes in major-element composition overprint local variations in sediment provenance, which are only detectable from the immobile trace-element geochemistry.

Effects of grain shape on the standard penetration test and particle packing

Coarse soils can contain flaky grains in addition to rounded or angular grains, along with a varying fines content. Depending on the regional geology, however, the mica grain content can be remarkable, reaching 30 % or higher. Therefore, it is reasonable to expect that mica grains would affect the soil behaviour. In this study, soils of a delta deposit that are known to involve mica grains were examined. The river sand was considered as the host material and the mica grain contents were determined by means of the flotation technique. A correlation between the mica content as found using the flotation technique and XRD count numbers obtained using an X-ray diffraction test method for each soil sample was established. The standard penetration test (SPT) blow counts from various boreholes were interpreted from the mica content’s influence point of view. The results showed that the mica grains would reduce the SPT resistance at certain fines-content, host-sand, mica-grain combinations. The reduction in the SPT resistance as a result of the presence of mica grains might reach eight units at depths close to the ground surface. This influence is expressed by means of a dimensionless parameter (MCef); however, it diminished with an increasing effective stress and fines content. The findings of the present study show that the influence of particle shape on the overall soil behaviour deserves further study.