Mineral Volume Fraction Research Articles

Nano-scale modeling of energy dissipation in a single lamella reveals the significant contribution of collagen-mineral sliding to intrinsic bone toughness

Although collagen-mineral sliding is recognized as one of the intrinsic mechanisms that contribute to the bone toughness, its precise role in energy release at the nano-scale, as well as its relationship to other intrinsic toughness mechanisms, remains unclear. This lack of understanding stems from the challenges associated with quantifying the specific nature of contact at the mineral-collagen interface, and the energy dissipation capacity resulting from plastic deformation at this scale. To address this issue, we developed a three-dimensional model of mineralized collagen fibril using ABAQUS, incorporating hyperelastic isotropic collagen, elastic isotropic mineral, and a cohesive contact formulation to represent the collagen-mineral interface. Knowing the properties of collagen and mineral and using a parametric modeling approach, we estimated the properties of contact based on experimental measurements of the stress-strain behavior in a single bone lamella, considering the angle of the collagen fibril in relation to the loading axis. By comparing the experimental elastic modulus with the model predictions, we determined that the cohesive contact exhibited a maximum strength of 9 MPa and a fracture energy of 50 mJ/m2 within the bone. Further analysis indicated that fracture energy at the collagen-mineral interface is potentially closer to 5 mJ/m2. Using these findings, we concluded that the interfaces were responsible for 52% to 98% of the energy release in mineralized collagen fibrils, depending on collagen angle, both directly and indirectly by influencing stress and strain in adjacent collagen fibril. The results of this study demonstrated that plastic deformation at the collagen-mineral interface is the primary mechanism underlying bone toughness at the nano-scale. Importantly, we found that these conclusions held true regardless of the angle of the collagen fibril relative to the loading axis. The modeling framework presented in this study provides a valuable tool for investigating the elastic and post-yield behavior of bone across different mineral volume fractions at the nano-scale, and at the lamellar level.

Analysis of influence mechanism of CO2-water coupling fracturing sandstone

The existence of hard rock layers has a serious impact on coal seam mining, in order to explore the acidification and crushing mechanism of hard sandstone rock layers, this paper adopts the self-developed CO2-water-rock coupling test device to carry out the testing of mechanical properties and internal structural characteristics of rock samples before and after the coupling action of the three sandstones, and analyzes the influencing factors of sandstone CO2 coupling crushing. The study shows that: the lower the temperature of CO2-water-rock coupling, the higher the pore pressure, the higher the volume fraction of CO2 in the coupling fracturing fluid, and the longer the coupling time, the greater the decrease in the mechanical strength of the rock samples, and the more complicated the splitting damage pattern is, and the CO2-water-rock coupling makes the pore and fracture volume fraction and fractal dimension of three kinds of sandstone samples increase to varying degrees, whereas the volume fraction of minerals and the fractal dimension decrease, and the CO2-water-rock coupling results in a decrease in the volume fraction of minerals and fractal dimension, and a decrease in the volume fraction of minerals and fractal dimension. The pore volume fraction and fractal dimension of the three sandstone samples increased to different degrees, while the mineral volume fraction and fractal dimension decreased, and the pore volume fraction and fractal dimension of the three sandstone samples decreased. The damage pattern of sandstone samples after coupling is affected by both chemical and mechanical damages. When using coupling fracturing fluid with 8 % CO2, the degree of mineral dissolution and dissolution is the largest, and the dissolution effect is larger than the precipitation effect, which has the most significant effect on the morphology type and connectivity of microscopic pore cracks, and the study in this paper has certain theoretical and practical value for the chemical softening of sandstone.

Geochemical evaluation of Washita-Fredericksburg formation as a carbon storage reservoir

Geological carbon sequestration is a promising technique to reduce atmospheric greenhouse gas emissions. The Washita-Fredericksburg formation in the southeastern United States is being considered as a prospective storage formation. This requires understanding the geochemical impact of CO2 injection on the formation, which is the focus of this work. Here, sandstone samples from the Washita-Fredericksburg formation are analyzed to understand their overall mineralogical composition and the potential geochemical processes that might occur following CO2 injection. Powder X-ray diffraction (XRD) analysis, Scanning Electron Microscopy (SEM) imaging, and image analysis were used to identify mineral phases. SEM images were processed to create a segmented mineral map, which was then used to calculate mineral volume fractions and porosity. Results show that the sample has a porosity of 20% and is mainly composed of quartz, K-feldspar, muscovite, and clays. Accessory minerals such as titanite were also found. Reactive transport models were constructed to assess potential CO2-brine-mineral interactions following CO2 injection. Simulation results suggest that the overall extent of mineral dissolution and precipitation reactions over 10,000 days is limited, with muscovite dissolution increasing porosity to 22%. Limited mineral reactions suggest more injected CO2 will exist in free and dissolved forms, which may require more extensive long-term monitoring.

Formation integrity evaluation for geosequestration of CO2 in depleted petroleum reservoirs under cyclic stress conditions

The geological storage of carbon dioxide (CO2), also referred to as CO2 geosequestration, represents one of the most promising options for reducing greenhouse gases in the atmosphere. However, most of the time, CO2 is captured with small amounts of other industrial gases such as sulphur dioxide (SO2) and hydrogen sulphide (H2S), which might be compressed together and stored in depleted petroleum reservoirs or aquifers. Moreover, during CO2 geosequestration in reservoirs, pressure variations during injection could force some amount of CO2 (with or without other acid gas impurities) into the caprock; thereby, altering the petrophysical, geochemical, and geomechanical properties of the caprock. Thus, the brittleness index of the reservoir and caprock might be impacted during CO2 geosequestration due to the chemical reactions between the rock minerals and the formation fluid. Furthermore, to meet the world net-zero carbon target, the promotion of CO2 utilization is paramount. This could be possible by developing an effective technology for cyclic CO2 geosequestration (with or without gas impurities). Therefore, studies on the co-injection of CO2 with other acid gases from industrial emissions, their withdrawal from the porous medium, and their impact on reservoir and caprock integrity are paramount. In this study, a dual-tubing string well completion technology was designed for cyclic injection and withdrawal of CO2 (with or without another acid gas), and numerical simulations were performed using TOUGHREACT codes, to model the cyclic process and investigate the co-injection of SO2 and H2S (separately) with CO2 in sandstone formations overlain by shale caprock. A novel technique of converting the volume fraction of minerals to their weight fraction was developed in this study, to evaluate the brittleness index of the sandstone reservoir and shale caprock during CO2 geosequestration. The findings of the study indicate that the porosity and permeability increase for the CO2 only and CO2–H2S injection cases, in the shale caprock; while for the CO2–SO2 injection case, porosity and permeability only decreased in the layers of the shale caprock contacted by SO2 and due to anhydrite precipitation. In all the injection cases, the porosity and permeability of the sandstone reservoir decreased in a few layers directly below the perforation interval of the production zone. However, in other regions in the sandstone reservoir, the porosity and permeability increased for the CO2 only and CO2–H2S injection cases. In contrast, for the CO2–SO2 co-injection case, porosity and permeability decreased in the layers of the sandstone rock contacted by SO2. In all the CO2 geosequestration cases, the brittleness of the shale and sandstone rocks investigated decreased slightly, except in the CO2–SO2 co-injection case where the brittleness of the sandstone rock decreased significantly. Based on the mineralogical composition of the formations in this study, co-injection of SO2 gas with CO2 gas, only decreased the brittleness index of the shale caprock slightly, but significantly decreased the brittleness of the sandstone reservoir.

Correlation between induced polarization and sulfide content of rock samples obtained from seafloor hydrothermal mounds in the Okinawa Trough, Japan

AbstractThe physical properties of seafloor massive sulfides are crucial for interpreting sub-seafloor images from geophysical surveys, shedding light on the evolution of seafloor mineral deposits. While some studies have explored the relationship between electrical properties and the volume of conductive minerals in rocks from seafloor massive sulfide deposits, they primarily focused on artificial samples, leaving the characteristics of natural samples less understood. Moreover, there has been no comprehensive study detailing the general characteristics of electrical properties, particularly chargeability and relaxation time, in relation to the volumetric fraction of sulfides in rocks from massive sulfide mounds in typical hydrothermal areas. In this study, we employed complex conductivity measurements, elemental concentration analysis, and mineral content identification on to rock samples from the active hydrothermal zones of the Okinawa Trough in Japan. The complex conductivity observed was remarkably high, with a pronounced imaginary component and a broad frequency range. This is attributed to induced polarization extending beyond our measurement range. The rock samples were rich in conductive sulfide minerals such as pyrite, chalcopyrite, and galena. Using the Cole–Cole rock physics model, we established a correlation between rock chargeability and relaxation time coefficient with the volume fraction of conductive sulfide minerals, which deviated from previous findings. The intensity of induced polarization was notably higher than anticipated in earlier studies using artificial samples. Furthermore, we observed a distinct positive correlation between the coefficient of relaxation time and the increase in sulfide volume, likely due to the geometric characteristics of the sulfide minerals. Our findings suggest that rocks in massive sulfide mounds may generally construct sulfide clusters that lengthen the conductive path of the electrical carrier. Graphical Abstract

The effect of microfabric heterogeneity on shear wave properties in fine-grained sediments

The water-sediment interface is highly susceptible to physical, biological, and chemical processes, which can create significant levels of heterogeneity in sediment biogeoacoustic properties at various spatial scales that affect transmission and scattering of elastic waves. Using a suite of microscopy, spectroscopy, and medical sonoelastography techniques, relationships between heterogeneity in the sediment microfabric and shear wave speed can be investigated at spatial scales ranging from centimeters to micrometers. Here, we study fine-grained sediments extracted from two unique intertidal mudflats in the Great Bay Estuary, New Hampshire, USA. Shear waves were excited via acoustic radiation force and external vibration in the 50–200 Hz frequency band, and particle velocity was sensed in the top 2 centimeters of sediment at approximately 0.5-micrometer spatial resolution using a research-grade medical imaging array. By directly imaging the propagating shear wave, spatial heterogeneity of shear wave speed was directly measured. Next, subsamples were extracted and prepared for microscopy, where volume fraction and orientation of organic, mineral, and aqueous components were studied at various spatial scales. A comparison of between shear wave speed and microfabric parameters will be presented. [Work sponsored by ONR.]

Microstructure evolution law and dissolution time effect of bituminous coal under acetic acid acidification: Based on Micro-CT image analysis

Undeveloped pores and fractures in coal seams constrain coalbed methane mining and dust disaster prevention significantly. The existing hydraulic fracturing technology has achieved some effects in coal seam modification. Still, there are hidden dangers in inducing microseismicity and other aspects. Applying acidification technology for pore and fracture modification improves the efficiency of coalbed methane mining and dust suppression. In this paper, 75% concentration of acetic acid was utilized to treat columnar coal samples, and the experimental method of X-ray computed tomography was applied to study the role of dissolution time on the microcomponents and structure of samples. The experimental results showed that the porosity increased with the dissolution time; the effect of acetic acid on the pore expansion and mineral dissolution showed three periods, i.e., the beginning of the reaction period (0 ∼ 12 h), the full reaction period (12 ∼ 48 h), and the reaction slowing down period (>48 h). The mineral volume fraction showed an overall decreasing trend; before 36 h, the dissolution of acetic acid on the mineral structure within the coal was faster, making it loose, which in turn accelerated the dissolution of coal, and after 36 h, the dissolution effect of acetic acid weakened, and the mineral was gradually stabilized. Acetic acid first reacts with minerals in large quantities. With the increase of products, the solution's ionic complexity increases, so acetic acid accelerates the ionization of more H+ ions, and the solution's acidity increases. After a while of dissolution, the content of acetic acid decreases, the ionized H+ ions are not enough to continue to react with the minerals, and the rate of the mineral's crystal particle size reduction slows down gradually. In conclusion, acetic acid has the potential for pore and fracture modification of coal reservoirs. It can affect the mineral through dissolution, at the same time, improve the porosity. The research results provide an essential reference for using acidification technology to modify the pores and fractures in coal seams.

PRRX1+MSCs Enhance Mandibular Regeneration during Distraction Osteogenesis

Bone defect (BD) caused by trauma, infection, congenital defects, or neoplasia is a major cause of physical limitation. Distraction osteogenesis (DO) is a highly effective procedure for bone regeneration, while the concrete mechanism remains unknown. In this study, canine DO and BD models of the mandible were established. The results of micro–computed tomography and histological staining revealed that DO led to an increased mineralized volume fraction and robust new bone formation; in contrast, BD demonstrated incomplete bone union. Mesenchymal stem cells (MSCs) from DO and BD calluses were isolated and identified. Compared with BD-MSCs, DO-MSCs were found to have a stronger osteogenic capability. Single-cell RNA sequencing analysis was further performed to comprehensively define cell differences between mandibular DO and BD calluses. Twenty-six clusters of cells representing 6 major cell populations were identified, including paired related homeobox 1–expressing MSCs (PRRX1+MSCs), endothelial cells (ECs), T cells, B cells, neutrophils, and macrophages. Interestingly, 2 subpopulations in PRRX1+MSCs in the DO group were found to express the marker of neural crest cells (NCCs) and were associated with the process of epithelial–mesenchymal transition. The immunofluorescence assay was performed to further corroborate these results in vivo and in vitro, experimentally validating that continuous distraction maintained the PRRX1+MSCs in an embryonic-like state. Finally, we used CRISPR/Cas9 to knock out (KO) PRRX1 in the context of DO, which significantly blunted the capability of jawbone regeneration, resulting in a diminished NCC-like program and reduction of new bone volume. In addition, the ability of osteogenesis, cell migration, and proliferation in cultured PRRX1KO MSCs was inhibited. Taken together, this study provides a novel, comprehensive atlas of the cell fates in the context of DO regeneration, and PRRX1+MSCs act essential roles.

Unfolding the role of topology-driven toughening mechanisms in nacre-like composite design through XFEM

Biological materials have evolved through thousands of years, adapting, morphing, and optimizing to their particular function. One of the many natural materials that are widely studied is nacre, an elegant merge of stiff (mineral) and soft (biopolymer) components with extremely high mechanical properties, which are highly desired for structural applications. Naturally, nacre has been a source of inspiration for developing artificial composites with different levels of intrinsic designs. Some of these designs exploit the microstructures of the materials, such as the connection between the composite stiffer parts, known as mineral bridges. To develop an eXtended Finite Element Method (XFEM)-based model of a biphasic composite inspired by the nacreous brick-and-mortar morphology, initially, we evaluate the use of XFEM on single materials models, including a hyperelastic material. Then, simulation of complex bioinspired materials shows that structures mimicking mineral bridges considerably improve composites’ mechanical properties such as strength and toughness. The influence of the biomimetic mineral volume fraction on the overall toughening mechanisms, particularly crack arresting, is demonstrated. Our results provide a numerical approach to simulating biphasic materials with hyperelastic components and contrasting material properties (e.g., stiff and ductile) that have potential applications in complex composite structural designs.

Rock physics modeling and quantitative seismic interpretation workflow for organic-rich mudrocks

A quantitative seismic interpretation workflow based on rock physics was developed for an organic-rich mudrock formation in order to estimate porosity, and organic matter and clay contents from seismically-derived acoustic and shear impedances. This deterministic workflow consists of: developing a rock physics model that accurately estimates the elastic properties of the formation; finding inter-relationships between the formation's petrophysical properties; and validating the model after upscaling and applying it to seismically-derived acoustic and shear impedances. By analyzing wireline data from this organic-rich mudrock formation, we find that the P-wave velocity at fixed porosity may vary by as much as 1.0 km/s, while the respective variation in the S-wave velocity reaches 0.5 km/s. A robust discriminator for velocity appears to be, in addition to the total porosity, the volumetric fraction of the soft components of the solid matrix where the kerogen is included, namely the sum of the clay and kerogen. The ensuing velocity-porosity-mineralogy relations are accurately described by the soft-sand rock physics model. Thus, an attempt to interpret seismically-derived impedance volumes based on rock physics modeling is performed after simplifying the rock's petrophysical variables by building site-specific internal relations between mineral's volume fractions that comprise the rock's solid matrix. This workflow helps in hydrocarbon exploration by identifying favorable areas with relatively high porosities and organic matter content.

Rock physics based velocity-porosity correlations developed for estimation of the elastic properties of the Bakken formations of the Williston Basin, North Dakota

Rock physics models are predictive tools used to estimate the velocity, or elastic properties of formations, based on strong theoretical foundations, as opposed to some of the simple empirical correlations that have been developed for specific regional formations. While the basic rock physics models use simplified assumptions and involve less input, more complex models, such as inclusion-based models, estimate velocity-porosity relation as function of different parameters including pore's fluid saturation and type, cementation, confining pressure and diagenesis. The downside is that these models require performing tedious calculations and in some cases solving complex differential equations. These models may also differ depending on the type of formation, for example, separate models may be used for shales compared to the siliciclastic or carbonate formations.In this paper, we present newly developed correlations that can substitute the rock physics modeling. The developed velocity-porosity correlationsare based on the mineralogical data from the Bakken formation in the Williston Basin, North Dakota, however, they can be used with good accuracy for other formations too. These models were developed based on large volumes of data from simulation of many cases using the differential effective medium (DEM) theory, a commonly used rock physics model. DEM models were developed for composite rock, but assuming single mineral type constituting the rock. The inclusion phase was incrementally added to the matrix phase. The pores were then modeled with three phase fluid (water, oil, and gas) at different saturation levels and finally, different pore's aspects ratios (AR) were assumed to simulate pores heterogeneity (i.e., crack, intraparticle, intergranular and moldic type pore geometries). The correlations constants were extracted for different key minerals in the Bakken, including quartz, calcite, dolomite, anhydrite, illite and kerogen. Having the volume fraction of minerals from lab-based XRD or Elemental Capture Spectroscopy (ECS) logs, linear averaging was applied to estimate the equivalent velocity and elastic properties of the formations.The correlations were applied to several case studies in the Bakken and also compared with the existing lab data, which showed a good agreement with the DEM model. The simplicity of using the correlations consists of simply entering the input values in an excel template that accounts for the constant parameters, using a single approach for different type of formations. This offers a great advantage for their applications. The workflow of developing the correlations and its applications in one case stduy using data from a Well in the Mountrail County will be presented.

An Inexpensive 3D Printed Mouse Model of Successful, Complication-free Long Bone Distraction Osteogenesis.

A lightweight tibial distractor was developed using CAD and 3D printing. The device was fixed to the tibia of C57Bl/6J mice prior to osteotomy. Postoperatively, mice underwent 5 days latency, 10 days distraction (0.15 mm every 12 hours), and 28 days consolidation. Bone regeneration was examined on postoperative day 43 using micro-computed tomography (μCT) and Movat's modified pentachrome staining on histology (mineralized volume fraction and pixels, respectively). Costs were recorded. We compared cohorts of 11 mice undergoing sham, DO, or acute lengthening (distractor acutely lengthened 3.0 mm). The histological bone regenerate was significantly increased in DO (1,879,257 ± 155,415 pixels) compared to acute lengthening (32847 ± 1589 pixels) (P < 0.0001). The mineralized volume fraction (bone/total tissue volume) of the regenerate was significantly increased in DO (0.9 ± 0.1) compared to acute lengthening (0.7 ± 0.1) (P < 0.001). There was no significant difference in bone regenerate between DO and sham. The distractor was relatively low cost ($11), with no complications. Histology and µCT analysis confirmed that the proposed tibial DO model resulted in successful bone formation. Our model is cost-effective and reproducible, enabling implementation in genetically dissectible transgenic mice.

Automatic Bulk Composition Analysis of Lunar Basalts: Novel Big-Data Algorithm for Energy-Dispersive X-ray Spectroscopy

The bulk composition of lunar basaltic meteorites and clasts provides crucial information for understanding their petrogenesis and thus lunar thermal evolution. Meanwhile, the basalt type of Chang’E-5 based on the bulk TiO2 contents remains debatable. Modal recombination based on mineral volume fraction, densities, and average compositions is currently the most popular method to determine the bulk composition of lunar samples. Yet, the latter two parameters can be biased markedly by ubiquitous compositional variations in pyroxene, olivine, and plagioclase. To rectify these issues and provide more accurate classifications, this study devises a novel big-data algorithm that analyzes maps of energy-dispersive X-ray spectroscopy (EDS) data of lunar basalts. The algorithm starts by labeling each point through a newly devised mineral classifier, then uses the mean of all points per mineral to represent average composition, and finally recalculates the true density per mineral to replace standard density. The accuracy of this mineral classifier is demonstrated by tests on a database of lunar minerals. The accuracy and precision of EDS mapping were verified by test analysis on certified reference minerals. Measurements on a lunar meteorite sample with a known composition, NWA 4734, are comparable to those measured using inductively coupled plasma optical emission spectrometry and confirm the reliability of the bulk composition algorithm. To demonstrate its utility for comprehensive understanding of petrographic features, the high-efficiency algorithm was applied to Chang’E-5 basalts. The results reveal that these basalts are characterized by low-Ti and low-Mg features, thus distinct from previous Apollo and Luna samples.

Estimation of Mineral Accessible Surface Area from Mineral Abundance and Clay Content

The mineral reactive surface area is often quantified through a wide range of approaches (e.g., Brunauer–Emmett–Teller adsorption, geometry approximation, and imaging techniques). As such, values vary 1–5 orders of magnitude which can result in large discrepancies when used in reactive transport models to simulate geochemical reaction rates. Simulations carried out using mineral accessible surface areas (ASAs) determined from a coupled 2D and 3D imaging approach have shown better match with reaction rates measured in core-flood experiments. However, such image processing requires large amounts of time and resources. In this work, the possibility of estimating mineral ASAs from easily measured properties like mineral abundance and porosity is explored. Six sandstone samples of varying compositions were studied along with data from three additional samples from the previous literature. Mineral ASAs were quantified using a combined 2D scanning electron microscopy and 3D X-ray nano-computed tomography imaging approach. Sample properties like mineral accessibility, mineral ASAs, connected porosity, and clay content were compared to explore potential correlations between properties. Overall, it was observed that mineral accessibility can be predicted where feldspar mineral accessibility generally increases with increasing abundance and quartz accessibility decreases with increasing clay content. Mineral ASAs vary between samples, depending on the relative abundance of minerals and overall pore connectivity. While the ASA of quartz decreases with abundance, albite and carbonate mineral ASAs increase with abundance. Quantitative observations, including predictive relationships for ASAs from porosity and mineral volume fraction, are developed. Estimations of ASAs and mineral accessibility from more easily quantifiable properties can largely reduce the required extent of image analysis.

Effect of geometrical structure variations on strength and damage onset of cortical bone using multi-scale cohesive zone based finite element method

Three-dimensional multi-scale finite element models were designed to examine the effects of geometrical structure variations on the damage onset in cortical bone at multiple structural scales. A cohesive zone finite element approach, together with anisotropic damage initiation criteria, is used to predict the onset of damage. The finite element models are developed to account for the onset of microdamage from the microscopic length scales consisting of collagen fibres, to the macroscopic level consisting of osteons and the Haversian canals. Numerical results indicated that the yield strain at the initiation of microcracks is independent of variations in the local mineral volume fraction at each structural scale. Further, the yield strain and strength properties of cortical bone are dependent on its structural anisotropy and hierarchical structure. A positive correlation is observed between bone strength and mineral content at each length scale.

Reactive transport investigations of the long-term geochemical evolution of a multibarrier system including bentonite, low-alkali concrete and host rock

The Canadian concept for a deep geological repository for used nuclear fuel includes highly-compacted and homogenized bentonite (HB) and low-alkali concrete such as Low-Heat High-Performance Concrete (LHHPC) as engineered barrier materials. The initial mineralogy and pore water compositions are different for bentonite, LHHPC and potential host rocks, such as granite and limestone. Consequently, chemical alterations are expected at the interfaces between these materials. Two scenarios were simulated to investigate the alterations at the material interfaces: 1) HB/LHHPC/host rock; 2) HB/host rock. For both scenarios, excavation damage zones (EDZs) were taken into consideration. Because of the low reactivity of bentonite compared to LHHPC, for the second scenario, only relatively minor mineral volume fraction and porosity changes were predicted for the HB/granite and HB/limestone host rock cases, with limited impact on radionuclide migration. For the first scenario; however, due to the relatively high pH of pore water in LHHPC, substantial mineral dissolution and precipitation were predicted to occur at the HB/LHHPC and/or LHHPC/host rock interfaces, leading to porosity reduction or even pore clogging in close proximity (<1 cm) of the interfaces. The predicted geochemical evolution depends mainly on the mineralogy and pore water chemical composition of the host rock. In the case of granitic host rock, Calcium Silicate Hydrate (C–S–H) phases initially present in LHHPC are predicted to transform into tobermorite, phillipsite, saponite and gypsum within 1,000 years. The simulations indicate a complex evolution of porosity, with an initial reduction, followed by a slight increase, and subsequent pore clogging. In the case of limestone host rock, saponite and sepiolite are the dominant minerals formed in the LHHPC. A sensitivity analysis shows that higher initial effective diffusion coefficients in the LHHPC enhance the diffusive fluxes of ions and result in earlier pore clogging in the host rock. The simulations illustrate that reactive transport modelling accounting for barrier reactivity and pore clogging provides a useful tool for assessing the migration of radionuclides across material interfaces for various canister failure scenarios.

Impact of Pore Connectivity on Quantification of Mineral Accessibility in Sandstone Samples

Characterization of microscale features and mineral distributions in rock samples can be facilitated non-destructively with imaging analysis. Scanning electron microscopy combined with backscattered electron and energy-dispersive spectroscopy is particularly valuable and can be utilized to identify minerals. Mineral segmentation coupled with quantitative image processing can yield mineral volume fractions and accessibility from these images. Prior estimates of mineral accessibility from images have improved the simulations of mineral reaction rates, but it is unclear how pore connectivity should be accounted for. This is further complex in samples with clay minerals where nanopores in clays need to be considered. Here, the impacts of different approaches to assess pore connectivity on quantification of mineral accessibility are considered for seven sandstone samples with varying composition. Mineral accessibilities are calculated by counting the interfacial pixels between the associated minerals and the adjacent pores from the 2D mineral segmented maps. Three types of accessibilities are considered: the first approach accounts for all the macropore space, the second approach considers only the 2D connected macropores, and the third approach includes the 2D connected porosity considering nanopores in clays. The observed variations in accessibility for most mineral phases are within 1 order of magnitude when nanopore connectivity is considered and thus not anticipated to largely impact the simulated reactivity of samples. However, greater variations were observed for clay minerals, which may impact long-term simulations (years). Larger variations in accessibility were also noted for carbonate minerals, but only some samples contained carbonate phases, and additional data is needed to assess the trends.

Quantification of the volume fraction of fat, water and bone mineral in spongiosa for red marrow dosimetry in molecular radiotherapy by using a dual-energy (SPECT/)CT

A patient-specific absorbed dose calculation for red marrow dosimetry requires quantifying patient-specific volume fractions of the red marrow, yellow marrow, and trabecular bone in the spongiosa of several skeletal sites. This quantification allows selecting appropriate S values calculated from the parameterized radiation transport models for bone and bone marrow dosimetry. Currently, no comprehensive, individualized, and non-invasive procedure is available for quantifying the volume fractions of red marrow, yellow marrow, and trabecular bone in the spongiosa. This study aims to provide a new quantitative method based on dual-energy computed tomography to fill this gap in red marrow dosimetry using a (SPECT/)CT system. MethodsFirst, a method for parametrizing the photon attenuation coefficients relative to water was implemented. Next, a method to calculate the effective atomic number (Zeff) and effective mass density (ρeff) using dual-energy CT (DECT) was employed. Lastly, two- and three-material decomposition using a dual-energy quantitative CT method (DEQCT) was performed in an anthropomorphic spine phantom and two bone samples of a boar, respectively.The measurements of Zeff and ρeff were compared with the syngo.CT DE Rho/Z tool (Siemens Healthineers). Furthermore, the DEQCT method implemented in this study (DEQCT-I) was compared with a second DEQCT method based on the use of external material standards (DEQCT-II). DEQCT-II was used as reference method for calculating relative errors. ResultsThe two-material decomposition in the anthropomorphic spine phantom presented a maximum relative error of −10% for the bone mineral density quantification. Furthermore, Zeff and ρeff calculated by DEQCT-I differed from syngo.CT DE Rho/Z tool by less than 4.4% and 1.9%, respectively. The three-material decomposition in the two bone samples showed a maximum relative error of 21%, −17%, and 15% for the quantification of the volume fractions of fat, water, and bone mineral equivalent materials. Lastly, Zeff and ρeff calculated by DEQCT-I differed from syngo.CT DE Rho/Z tool by less than 8.2% and 7.0%, respectively. ConclusionThis study shows that quantifying the volume fraction of fat, water, and bone mineral using a phantom-independent and post-reconstruction DEQCT method is feasible. DEQCT-I has the advantage of not requiring prior information about the X-ray spectra or the detector sensitivity function, as is the case with spectral-based DEQCT methods. Instead, DEQCT-I, similar to other DEQCT methods depends on the chemical description of reference materials and a beam hardening correction function.DEQCT-I method provides an individualized and non-invasive procedure using a (SPECT/)CT system to apply S values based on the patient-specific volume fractions of yellow marrow, red marrow, and bone mineral in red marrow dosimetry.

Magmatic and hydrothermal evolution of mafic pegmatites and their host basalts, Paraná Large Igneous Province, Brazil

The high-Ti Paranapanema sequence in the Paraná Large Igneous Province consists of a succession of pahoehoe lava flows. Some of these flows host mafic segregation structures, such as horizontal pegmatitic sheet layers and vesicular cylinders. Geochronology, whole-rock and mineral chemistry of two pegmatite occurrences and their host basalts permit characterizing crystal-melt segregation processes that occur during magmatic differentiation after lava flow emplacement. The mineralogy of the pegmatites is similar to that of the host basalts, and it includes plagioclase, pyroxene and titanomagnetite-ilmenite crystals; the only observable difference is the coarser grain size of primary phases and an increase in the volume fraction of clay minerals derived from glass devitrification and vesicle infilling in the pegmatites (~15 vol% clay in the pegmatites vs. ~6 vol% clay in the basalts). The pegmatites from both sites are more fractionated than the enclosing lavas and are enriched in TiO2, FeOtotal, K2O, P2O5 and incompatible trace elements (e.g., Ba, Rb, Nb, Hf, Y, Zr, La, Ce, Yb). Thermodynamic modeling of whole-rock compositional data suggests that the Barracão pegmatites were formed after ~8–27 wt% fractional crystallization of the host basalt, whereas the Capanema pegmatites formed after ~38–43 wt% fractional crystallization of the host basalt. 40Ar/39Ar geochronology indicates slight yet significant age differences between plagioclase phenocrysts from the pegmatites and whole-rock fragments from the enclosing lavas (Capanema: 133.56 ± 0.52 pegmatite vs. 134.30 ± 0.46 Ma enclosing lava; Barracão: 133.23 ± 0.88 pegmatite vs. 134.49 ± 0.31 Ma enclosing lava). These age differences likely result from hydrothermal alteration of the plagioclase phenocrysts (e.g., secondary albite and K-feldspar), and they are not due to resolvable differences in crystallization age. Smectite-celadonite aggregates recovered from the Capanema basalt suggest that hydrothermalism occurred at 123.18 ± 0.61 Ma, approximately ten million years after rock crystallization.

Elastic anisotropies of deformed upper crustal rocks in the Alps

Abstract. The crust within collisional orogens is very heterogeneous both in composition and grade of deformation, leading to highly variable physical properties at small scales. This causes difficulties for seismic investigations of tectonic structures at depth since the diverse and partially strong upper crustal anisotropy might overprint the signal of deeper anisotropic structures in the mantle. In this study, we characterize the range of elastic anisotropies of deformed crustal rocks in the Alps. Furthermore, we model average elastic anisotropies of these rocks and their changes with increasing depth due to the closure of microcracks. For that, pre-Alpine upper crustal rocks of the Adula Nappe in the central Alps, which were intensely deformed during the Alpine orogeny, were sampled. The two major rock types found are orthogneisses and paragneisses; however, small lenses of metabasites and marbles also occur. Crystallographic preferred orientations (CPOs) and volume fractions of minerals in the samples were measured using time-of-flight neutron diffraction. Combined with single crystal elastic anisotropies these were used to model seismic properties of the rocks. The sample set shows a wide range of different seismic velocity patterns even within the same lithology, due to the microstructural heterogeneity of the deformed crustal rocks. To approximate an average for these crustal units, we picked common CPO types of rock forming minerals within gneiss samples representing the most common lithology. These data were used to determine an average elastic anisotropy of a typical crustal rock within the Alps. Average mineral volume percentages within the gneiss samples were used for the calculation. In addition, ultrasonic anisotropy measurements of the samples at increasing confining pressures were performed. These measurements as well as the microcrack patterns determined in thin sections were used to model the closure of microcracks in the average sample at increasing depth. Microcracks are closed at approximately 740 MPa yielding average elastic anisotropies of 4 % for the average gneiss. This value is an approximation, which can be used for seismic models at a lithospheric scale. At a crustal or smaller scale, however, local variations in lithology and deformation as displayed by the range of elastic anisotropies within the sample set need to be considered. In addition, larger-scale structural anisotropies such as layering, intrusions and brittle faults have to be included in any crustal-scale seismic model.