Mineral Grain Size Research Articles

Express determination of the grain size of nickel-containing minerals in ore material

Timely operational information about the quality of ore material that is supplied to the processing plant is one of the most important issues in the field of mineral processing. Such a factor as the grain size of a useful mineral today requires a lot of labor and time for its study. At the same time, a change in this property of the ore material has a great impact on the recovery rate of the useful component. Prompt determination of the size of grains of recoverable minerals will allow for a more efficient homogenization of technological ore material supplied to the processing plant. This article is devoted to the express determination of the grain size of nickel-containing ore materials based on a comprehensive measurement of the magnetic characteristics of the ore flow. It is especially noted that the research was carried out with the involvement of young professionals and students.

Particle-size dependent magnetic properties of Scotia Sea sediments since the Last Glacial Maximum: Glacial ice-sheet discharge controlling magnetic proxies

The strong glacial–interglacial similarity between the magnetic susceptibility (MS) of Southern Ocean sediments and Antarctic ice core dust records has often been used to reconstruct Southern Hemisphere atmospheric variability. Although evaluation of various magnetic properties is essential for identifying the magnetic carriers linked to sedimentological variation, detailed magnetic studies are not sufficient in the Scotia Sea. Here we investigate the bulk and particle-size dependent magnetic properties of Scotia Sea sediments over the past ~22 kyr, to determine the main sediment transport mechanism driving bulk magnetic proxies including MS. In bulk sediments, MS is highest during the last glacial period and is accompanied by an increase in the concentration and grain size of ferrimagnetic and antiferromagnetic minerals. For magnetic mineral assemblages, coarse detrital magnetite is dominant. Of three particle-size fractions (>63, 16–63, and <16 μm), the coarse silt fraction (16–63 μm) is responsible for the magnetic properties of bulk glacial sediments. Such dominant contribution of coarse silts rules out a major input of dust, which is expected as finer silt and clay. The silt fraction exhibits a co-varying magnetic mineral concentration with that of the sand fraction (>63 μm) throughout the last deglaciation, indicating a close linkage between their input mechanisms. Thus, the sediment particles ranging from sand to coarse silt, which control the bulk glacial magnetic proxies, are most plausibly transported by iceberg-rafted debris (IRD). As hematite is relatively concentrated in the sand fraction, the hematite contribution in the bulk sediment can highlight IRD-related magnetic signals rather than magnetite. The bulk hematite contribution simultaneously varies with the deglacial influx of coarse IRD particles (>1 mm) in Scotia Sea sediments, although their glacial inconsistency possibly suggests a different IRD input mechanism during the advancement and retreat of the ice sheet. Consequently, the glacial increase in the bulk magnetic concentration indicates vigorous iceberg calving activity in the Scotia Sea and further suggests the coupled cryosphere–atmosphere system.

An insight into pore-network models of high-temperature heat-treated sandstones using computed tomography

The pore network attributes help assess the fluid-flow behaviour in various reservoir rocks. As, in the cases of various unconventional energy exploration, the reservoir rocks are being exposed to different sets of temperatures that result in microstructural alteration in the pore and throat scale. Since the last decade, X-ray computed tomography (XCT) has been proved to be a useful tool in determining the micro-scale pore structures. However, such results are greatly influenced by the structure of the rocks, pore spaces, grain size, and nature of minerals. Here in this study, an attempt has been made to investigate the microstructural alteration and pore-network configuration of thermally-treated three Indian sandstones (Dholpur sandstone, Jodhpur sandstone and Gondwana sandstone) of varying mineralogy using the high-resolution micro-CT techniques. Microstructural modifications, the evolution of pores spaces, pore-size distribution, pore-network attributes such as nature of connectivity, pore radius, pore-volume, pore coordination number, throat radius and throat channel lengths of the three sandstones were investigated in a temperature range from 25 °C to 800 °C. The microstructural responses of these sandstones in terms of pore-space evolution and pore network models were found to be dependent on the presence of clay minerals. The overall trend of porosity for Dholpur and Gondwana sandstone was found to increase as a function of temperature. For Jodhpur sandstone, the maximum porosity was achieved at 600 °C and thereafter a decreasing trend up to 800 °C. Gondwana sandstone, most clay-rich, was found to be most vulnerable to elevated temperatures compared to the other two sandstones. The maximum average pore coordination number for Dholpur and Jodhpur sandstone was observed at 600 °C (7.097) and 800 °C (6.953), respectively.

Anisotropy of Full and Partial Anhysteretic Remanence Across Different Rock Types: 1—Are Partial Anhysteretic Remanence Anisotropy Tensors Additive?

AbstractSeveral types or grain sizes of ferromagnetic minerals can contribute to a rock's remanence and anisotropy of remanence. Each subpopulation may have a different fabric. Measuring anisotropy of partial anhysteretic remanent magnetization (ApARM) allows one to determine the anisotropy contribution of subpopulations with different coercivity distributions. Separating these contributions to remanence anisotropy can provide information about early versus late stages of deformation in fabric studies and is the basis for improved anisotropy corrections in paleomagnetic studies. Unfortunately, collecting multiple ApARM tensors on each specimen is time‐consuming and not often done. Measuring a smaller number of carefully chosen ApARM tensors and obtaining the remaining tensors of interest by tensor calculation would be more efficient. This can only be done, however, when ApARM tensors are additive. Here we investigate the additivity of ApARM tensors in a range of lithologies, by measuring a total of seven ApARM and anisotropy of anhysteretic remanent magnetization (AARM) tensors for each specimen, and comparing the tensors calculated from a combination of ApARM tensors to the corresponding measured AARM. Differences in principal directions between measured and calculated tensors are often smaller than the confidence angles of the measurements. Mean anhysteretic remanences are additive to within ±5%. The anisotropy degree varies by ±30% (k′) or ±0.15 (P), and the shape parameter U by ±0.4. These error limits will help to determine whether or not it is necessary to measure each ApARM tensor in future fabric or paleomagnetic studies, or if these tensors can be calculated from a smaller set of measurements.

Influence of Thermal and Mechanical Loading on Development of Microcracks in Granite

Fire safety is one of the most important concerns in underground engineering projects. Exposure to high temperature can weaken rocks and potentially cause catastrophic failure of the rock mass, either during the fire, or after the fire. In this study, Brazilian tensile tests were conducted on unheated and heat-treated Bukit Timah Granite. The microcrack length distribution and orientation were then recorded and analyzed through the fluorescent dye impregnation technique. The amount of microcracks generated was found to be proportional to the heating temperature. However, other factors such as the mineralogy and the texture of the rock were also found to influence the length and orientation of the microcracks. The modal microcrack lengths of the specimens were found to be similar despite different thermal and mechanical treatments of the specimens, while the orientation of the microcracks was found to be influenced by the type of minerals. Besides the average grain size, another factor which played a key role in determining the microcrack characteristics is the size and shape of the individual mineral grains.

Weathering behaviour of road aggregate of andesitic composition in a New Zealand quarry

The process of weathering progressively affects the characteristics of geomaterials. Despite prior assertions, this process may happen in a relatively short time and can cause ageing and deterioration of the structure of aggregates. This study investigates the effect of natural weathering processes on characteristics of road materials, exposed within a quarry that produces road materials compliant with New Zealand specifications for premium base course material. While not an exact replica of in-use weathering conditions, this case study serves as an observable analogue, recording the chemical and mineralogical degradation of andesite aggregate materials. The variations in chemical and physical properties of roading materials of andesitic composition were investigated using image processing and a variety of analytical methods, including thin section petrography, X-Ray Fluorescence (XRF), and X-ray Diffraction (XRD). Whilst initially there was almost no obvious sign of weathering in fresh materials, within a short time-frame (less than 15 years) intense weathering was evident. The immediate loss of bases (notably alkalies) is the primary chemical trend in the natural weathering, although the rate of loss appears to decrease with time. It is consistent with the results of chemical indices of weathering, including Chemical Index of Weathering and Alteration (CIW and CIA), Weathering Index of Parker (WIP), Plagioclase Index of alteration (PIA), and A-CN-K diagram. Furthermore, XRD analysis revealed the presence of clay minerals in the weathered materials, with kaolinite and smectites the product of relatively short-term of weathering. Thin-section petrography indicates that the original textural features of the andesites were significantly changed during weathering. The results suggested that the grain size and zonation of primary minerals are critical controls in the weathering process and glass and plagioclase phenocryst are the least stable mineral phases in the examined andesitic aggregate materials.

Linearno toplotno širenje građevinskog kamena poreklom iz plutonskih magmatskih kompleksa Eksterne vardarske zone Srbije

Thermal properties of the building stone used for cladding and flooring, especially in exteriors, are significant for durability and lifespan of buildings' surfaces covered with it, but also their aesthetic properties in the sense of integrity. Linear thermal expansion of natural stone units is determined in laboratory examinations, aiming to provide the value of yield between the units as free space for their dilatation and contraction upon temperature oscillations. Where this space is not provided, diurnal changes, especially temperature increase, create stone expansion and tension which can lead to deformations of stone units and mar units' and covered surfaces' integrity and aesthetics. Data on linear thermal expansion values of natural stone, especially from Serbia, are very rare in the literature, so our aim is to contribute to this type of knowledge. Examination of thermal dilatation of stone originating from eight plutonic massifs in External Vardar zone of Serbia has shown that the values are very small, parts of millimetres, and lower than those of the similar rock types originating from China, Brazil and Eastern Serbia. A clear grouping of the values of thermal expansion of the stone according to the genetic groups to which the plutons belong to can be observed. Mineral composition, grain size and presence of metallic minerals in samples have shown no clear influence on thermal dilatation values, but fabric inhomogeneity appears to cause the increase of these values.

Mineralogical and morphometric aspects of the rock analysis as the basis for choosing a scheme for ore preparation

The complexity of deep processing of fine-grained and refractory mineral raw materials is determined by the difficulty of disclosing aggregates of ore components during disintegration and extracting them into commercial products of standard quality. The main task of the disintegration of such ores is to destroy the object along the phase boundaries without overgrinding while minimizing energy costs. To implement selective disintegration, a precise study of the properties of the mineral components of the ore is necessary. However, there are no systematic data on the effect and relationship of the mineralogical-technological, structural-textural and physical-technical properties of minerals, rocks and ores with the processes of selective disintegration. The article presents the results of computer microtomographic and optical-microscopic studies of the structural and textural characteristics of typical sulfide copper-nickel ores using a SkyScan-1173 microtomograph from Bruker (Belgium), as well as a specialized, accredited as a measuring tool, Thixomet Pro software (Russia). The studies made it possible to identify automatically 19 morphometric parameters of ore grains in three mutually perpendicular sections, the most informative of which were the grain size of individual ore minerals, their perimeter, distance between grains and grain shape (sphericity, edge roughness, and others). The obtained quantitative characteristics of the structural and textural parameters, the analysis of the granulometric composition of the grains of ore minerals make it possible to assess the possibility of using selective grinding at various stages of ore preparation.

Grain-size mineral analysis of verdete rock coarse and fine aggregates and adjustment to two granulometric distribution models

The supremacy of the mineral industry added to the necessity to supply the world market demand justifies the continuous research efforts for optimizing of the activities of mineral resource utilization. In an approach of mineral characterization, a grain-size analysis study of coarse and fine aggregates of verdete rock was presented in this work. The particle size distribution (PSD) of two samples of aggregates with granulometry &lt; 2.36 mm was experimentally obtained using sieving techniques and adjustment to Rosin-Rammler-Bennet (RRB) and Gates-Gaudin-Schuhmann (GGS) granulometric distribution models. Both RRB and GGS models regressed well to the experimental data, presenting correlation coefficient values were extremely close between them approximately 0.99. The PSD’s results indicated that 65.97% dry aggregates and 67.68% wet aggregates had a particle size with mean diameter &gt; 0.0050 mm; a similar behavior of the grain-size distributions presented by dry and wet aggregates; and a tiny presence of fine particles natural in the analyzed ore sample. The results suggested the suitability of the methodology to predict the grain-size performance the verdete ore beyond to show itself as a contribution to the enriching of the mineral characterization of the studied rock, as a potassium potential source for the mineral processing Brazilian industry.

The Generation of Plate Tectonics From Grains to Global Scales: A Brief Review

AbstractThe physics of rock deformation in the lithosphere governs the formation of tectonic plates, which are characterized by strong, broad plate interiors, separated by weak, localized plate boundaries. The size of mineral grains in particular controls rock strength and grain reduction can lead to shear localization and weakening in the strong ductile portion of the lithosphere. Grain damage theory describes the competition between grain growth and grain size reduction as a result of deformation, and the effect of grain size evolution on the rheology of lithospheric rocks. The self‐weakening feedback predicted by grain damage theory can explain the formation of mylonites, typically found in deep ductile lithospheric shear zones, which are characteristic of localized tectonic plate boundaries. The amplification of damage is most effective when minerallic phases, like olivine and pyroxene, are well mixed on the grain scale. Grain mixing theory predicts two coexisting deformation states of unmixed materials undergoing slow strain rate, and well‐mixed materials with large strain rate; this is in agreement with recent laboratory experiments, and is analogous to Earth's plate‐like state. A new theory for the role of dislocations in grain size evolution resolves the rapid timescale of dynamic recrystallization. In particular, a toy model for the competition between normal grain growth and dynamic recrystallization predicts oscillations in grain size with periods comparable to earthquake cycles and postseismic recovery, thus connecting plate boundary formation processes to the human timescale.

Mineral associations and Mo-W ore types of the Slepaya Zalezh' orebody at Tyrnyauz deposit

Slepaya Zalezh is the largest ore body of the Tyrnyauz Mo-W deposit. It is the priority object on the renewal of its operation. A dissemination of molibdoscheelite, scheelite and molibdenite, controling ore concentrations, is confined to metasomatic rocks of the productive stage, laid on skarns, near-skarn rocks, hornfelses and marbles. The types of the ores are divided accordingly of ratio in them of different facies of ore-bearing metasomatic and initial rocks, which is a working out mass of ore. 7 types of the ores are divided and maped on the ore body vertical projection. Aposkarn ores predominate clearly in the I and II types, accordingly laid over endo- (substituting hornfelses) or exo- (apomarble) skarns. In the III type there are ores laid over endo-skarns and near-skarn rocks in equal parts. Relative to it the type IV contain less of of near-skarn rocks, but more of hornfelses. Ores replacing exo-skarns and to a lesser degree (up to 25%) – marbles dominate in the V type. The type VI is an intermediate one between the types III and IV. In the type VII all initial rocks are presented. Every of the types has a stable mineral and chemical composition inherited from the initial rocks. The ores of the specific type have convenient simple distinguishing features for a hand sorting of specimens, samples, and a preliminary ore separation. The types of ores have narrow change limits in size and form of ore mineral grains and their intergrowthes, percentage of minerals harmful for the flotation. Minor differences in contents of the useful components of each ore type offer possibilities of their selective working off and burdening. Mapping results contain data of the distribution of accompany sorts of mineral resources: garnet and wollastonite in the skarns and productive metasomatic rocks, pyroxene-plagioclase near-skarn rocks and hydrothermal alterated rocks with Cu, Au and other mineralization.

Effect of aluminum content on reduction of silico-ferrite of calcium and aluminum (SFCA)

Silico-ferrite of calcium and aluminum (SFCA) is a key bonding phase in high basicity sinter and its reducibility affects the reducibility of sinter. In this work, the reduction process of the Ca5Si2(Fe18−xAlx)O36 with change of aluminum content had been investigated using the thermogravimetric method at 1073 K, 1173 K and 1273 K in reducing atmosphere respectively. X-ray diffraction was used to characterize the mineral composition of the samples. Jade software was used to calculate the grain size of minerals and micro stain in samples. The results show that the reduction process of the SFCA to FeO could be divided into two steps, SFCA to Fe3O4 and Fe3O4 to FeO. Ca2Al2SiO7 as a by-product appeared in the stage of SFCA to Fe3O4. The increase of aluminum content in SFCA decreased the formation of Ca2Fe2O5 to promote the reducibility of SFCA at 1273 K. By calculation it was also found that the addition of aluminum resulted in more micro strain in the SFCA, which could deduced that the release of stress in the reduction process is also conducive to promote the reduction of SFCA.

Binding of metals in dacryoliths by means of biomineralization

Dacryoliths are organomineral aggregates released from human lacrimal ducts, and are known to include a 1 to 3 % (by volume) of a mineral (inorganic) component This study was based on a collection of approximately 800 dacryoliths collected from a patient in Siberia. The shapes and sizes of mineral grains, their composition and their distribution in the organic matrix are very diverse; our detailed investigation identifies a number of inorganic phases that were not previously recognized. These were imaged on a scanning electron microscope (Tescan VEGA II LMU), and the chemical composition of the inorganic component was determined by energy dispersive X-Ray spectroscopy (INCA Energy350, Oxford Instrument), and X-ray analysis (X-ray diffractometer XPert PRO (PANalytical). For the first time, we identified the following minerals which can be divided into three groups: 1) oxide Si, pyrite, calcium oxalate, barite, which are often present in the tissues of the living organism and are also known in geological processes; 2) abundant complex mineral phases, consisting of Al, Si, K and Ti or Fe (titanium and iron aluminosilicates), which are also present in organism but have no analogues in the abiogenic environment; and 3) oxygen-containing compounds of Ni and Pb-Cr (possibly nickel oxide and lead chromate, respectively) which are only found in the abiogenic environment. Those mineral phases of biogenic origin are due to an endogenous (pathological) process in the body caused by internal factors (hypoergosis and metabolic disorders). This biomineralization may have a role in the removal of toxic and / or excess ions of Fe, Ti, Cr, Pb, Ni, Al, and Si from tissues.

Sorption of Eu(III) on Eibenstock granite studied by \xb5TRLFS: A novel spatially-resolved luminescence-spectroscopic technique

In this study a novel technique, micro-focus time-resolved laser-induced luminescence spectroscopy (µTRLFS) is presented to investigate heterogeneous systems like granite (mainly consisting of quartz, feldspar, and mica), regarding their sorption behavior. µTRLFS is a spatially-resolved upgrade of conventional TRLFS, which allows point-by-point analysis of single minerals by reducing the beam size of the analytic laser beam to below the size of mineral grains. This provides visualization of sorption capacity as well as speciation of a luminescent probe, here Eu3+. A thin-section of granitic rock from Eibenstock, Saxony, Germany was analyzed regarding its mineralogy with microprobe X-ray fluorescence (µXRF) and electron probe microanalysis (EPMA). Afterwards, it was reacted with 5.0 × 10−5 mol/L Eu3+ at pH 8.0 and uptake was quantified by autoradiography. Finally, the µTRLFS studies were conducted. The results clearly show that the materials interact differently with Eu3+, and often even on one mineral grain different speciations can be found. Alkali-feldspar shows very high uptake, with an inhomogeneous distribution, and intermediate sorption strength. On quartz uptake is almost 10-fold lower, while the complexation strength is higher than on feldspar. This may be indicative of adsorption only at surface defect sites, in accordance with low hydration of the observed species.

Compositional variation in modern estuarine sands: Predicting major controls on sandstone reservoir quality

Primary depositional mineralogy has a major impact on sandstone reservoir quality. The spatial distribution of primary depositional mineralogy in sandstones is poorly-understood and consequently empirical models typically fail to accurately predict reservoir quality. To address this challenge, we have determined the spatial distribution of detrital minerals (quartz, feldspar, carbonates and clay minerals) in surface sediment throughout the Ravenglass Estuary, UK. We have produced, for the first time, high resolution maps of detrital mineral quantities over an area that is similar to many oil and gas reservoirs. Spatial mineralogy patterns (based on x-ray diffraction data) and statistical analyses revealed that estuarine sediment composition is primarily controlled by provenance, i.e. the character of bedrock and sediment drift in the source area. The distributions of quartz, feldspar, carbonates and clay minerals are primarily controlled by the grain size of specific minerals (e.g. rigid versus brittle grains) and estuarine hydrodynamics. The abundance of quartz, feldspar, carbonates and clay minerals is predictable as a function of depositional environment and critical grain-size thresholds. This study may be used, by analogy, to better predict the spatial distribution of sandstone composition, and thus reservoir quality in ancient and deeply-buried estuarine sandstones.

Quaternary tephra from the Valles caldera in the volcanic field of the Jemez Mountains of New Mexico identified in western Canada

AbstractA fine-grained, up to 3-m-thick tephra bed in southwestern Saskatchewan, herein named Duncairn tephra (Dt), is derived from an early Pleistocene eruption in the Jemez Mountains volcanic field of New Mexico, requiring a trajectory of northward tephra dispersal of ~1500 km. An unusually low CaO content in its glass shards denies a source in the closer Yellowstone and Heise volcanic fields, whereas a Pleistocene tephra bed (LSMt) in the La Sal Mountains of Utah has a very similar glass chemistry to that of the Dt, supporting a more southerly source. Comprehensive characterization of these two distal tephra beds along with samples collected near the Valles caldera in New Mexico, including grain size, mineral assemblage, major- and trace-element composition of glass and minerals, paleomagnetism, and fission-track dating, justify this correlation. Two glass populations each exist in the Dt and LSMt. The proximal correlative of Dt1 is the plinian Tsankawi Pumice and co-ignimbritic ash of the first ignimbrite (Qbt1g) of the 1.24 Ma Tshirege Member of the Bandelier Tuff. The correlative of Dt2 and LSMt is the co-ignimbritic ash of Qbt2. Mixing of Dt1 and Dt2 probably occurred during northward transport in a jet stream.

Magma ascent in planetesimals: Control by grain size

Rocky planetesimals in the early solar system melted internally and evolved chemically due to radiogenic heating from 26Al. Here we quantify the parametric controls on magma genesis and transport using a coupled petrological and fluid mechanical model of reactive two-phase flow. We find the mean grain size of silicate minerals to be a key control on magma ascent. For grain sizes ≳1 mm, melt segregation produces distinct radial structure and chemical stratification. This stratification is most pronounced for bodies formed at around 1 Myr after formation of Ca,Al-rich inclusions. These findings suggest a link between the time and orbital location of planetesimal formation and their subsequent structural and chemical evolution. According to our models, the evolution of partially molten planetesimal interiors falls into two categories. In the magma ocean scenario, the whole interior of a planetesimal experiences nearly complete melting, which would result in turbulent convection and core–mantle differentiation by the rainfall mechanism. In the magma sill scenario, segregating melts gradually deplete the deep interior of the radiogenic heat source. In this case, magma may form melt-rich layers beneath a cool and stable lid, while core formation would proceed by percolation. Our findings suggest that grain sizes prevalent during the internal heating stage governed magma ascent in planetesimals. Regardless of whether evolution progresses toward a magma ocean or magma sill structure, our models predict that temperature inversions due to rapid 26Al redistribution are limited to bodies formed earlier than ≈1 Myr after CAIs. We find that if grain size was ≲1 mm during peak internal melting, only elevated solid–melt density contrasts (such as found for the reducing conditions in enstatite chondrite compositions) would allow substantial melt segregation to occur.

Magnetic Properties of Deep‐Sea Sediments From the North Pacific: A Proxy of Glacial Deep‐Water Ventilation

AbstractThe magnetic properties of deep‐sea sediments in the North Pacific vary in sync with glacial‐interglacial climatic changes and have thus been considered as a paleoclimate indicator. However, the causes of these variations in magnetic properties, including the concentration, grain size, and mineralogy of magnetic minerals, remain poorly understood. Here we investigate the magnetic properties of deep‐sea sediments recovered from the Shatsky Rise in the North Pacific to investigate the cause of the variability associated with glacial‐interglacial cycles. Compared to the potential sediment provenances, the interglacial‐stage and more than half of the glacial‐stage sediments reveal magnetic mineralogical properties (S ratio and L ratio) of the Gobi and Taklimakan deserts, probably indicating dust from the both sources. During glacials, an abrupt decrease in the concentration of magnetic minerals is associated with increases in the average grain size and in the proportion of hematite relative to magnetite. The changes during glacials are mostly a result of dissolutions of magnetite by exposure to ambient ocean environments after deposition. Both magnetic and geochemical proxies validate that poor ventilation of the glacial deep waters in the North Pacific possibly induced iron‐reducing conditions. With comprehensive compilation with the S‐ratio data in the North Pacific sediments, our result indicates that the poorly ventilated deep waters reached up to water depths of ~2,500 m during glacials.

Application of Tip-Enhanced Raman Spectroscopy for the nanoscale characterization of flooded chalk

One of the most challenging goals of flooded chalk analyses used in Enhanced Oil Recovery (EOR) is to reach high-resolution mineralogical data, in order to detect the composition of new crystals grown after brine injections, with ≤1 μm grain size. Understanding how flooding affects chemical induced compaction, mechanical strength permeability, and porosity is paramount in EOR related investigations. Magnesite formation is the most pervasive process when MgCl2 is injected into chalk, and the submicrometric grain size of the new minerals requires a high performing imaging technique and a new methodological approach: in our study, we present the first attempt of applying Tip-Enhanced Raman Spectroscopy (TERS) to rock and mineral samples. It is a new frontier technique that couples Raman Spectroscopy with Atomic Force Microscopy, allowing impressively high-resolution topography and mineralogical maps. Two long term experiments have been analyzed, where chalk cores were flooded for 718 days and 1072 days, at reservoir conditions comparable to hydrocarbon reservoirs in chalk at the Norwegian continental shelf. Few microns squared areas have been imaged by Atomic Force Microscopy using ultra-polished thin sections. First analyses identified a less pervasive secondary growth of magnesite in the 718 days test and an almost pure magnesite composition in the 1072 days test. Transmission Electron Microscopy (TEM) has been employed to confirm the results of TERS and add dark and bright field grain imaging to the investigations. This confirms the need for high-resolution methodologies such as TERS and TEM to fully understand the EOR effects at submicron-scale.

A continuum theory for phase mixing and grain-damage relevant to tectonic plate boundary evolution

The unique occurrence of plate tectonics on Earth is rooted in the intricate physics of weakening and shear-localization in the cold ductile lithosphere. The pervasiveness of mylonites at lithospheric shear zones is a key piece of evidence that localization is correlated with reduction in mineral grain-size. The positive feedback leading to such localization, however, is often thought to be paradoxical because grain-size reduction by deformation-induced damage, and grain-size sensitive weakening do not necessarily co-exist in monomineralic materials. However, most lithospheric mylonites are polymineralic and the interaction between mineral phases, such as olivine and pyroxene, especially through Zener pinning, impedes normal grain growth while possibly enhancing grain-reduction via damage, even down to grain-sizes in which grain-size sensitive weakening is active. The efficacy of pinning, however, relies on the mineral phases being mixed and dispersed at the grain scale. Indeed, recent models and experiments imply that enhanced mixing between phases leads to greater grain-size reduction and weakening, whereas unmixed regions remain large-grained and strong. This duality of mixed states leads to a hysteresis effect, wherein slowly deforming states with large grains coexist with mylonitic-like states with rapid deformation, akin to the tectonic state of the Earth, with stiff plates coexisting with rapidly deforming plate boundaries. However, the different deformation states necessarily correspond to heterogeneity in mineral phase volume fractions, where the strong states correspond to monomineralic units of large-grained tectonites, while weaker mylonitic states occur in well-mixed polymineralic units. To model grain mixing between different phases at the continuum scale, we develop a new theory treating grain-scale processes as diffusion between phases, but driven by imposed stresses acting on the interface between phases. Simple one-dimensional (1-D) applications of the theory, and concomitant scaling laws show that diffusive grain mixing enhances grain-reduction by amplifying the influence of Zener pinning. The coupling between inter-phase diffusion and grain-damage promotes a positive mixing-localization feedback, which leads to narrow, weak, well-mixed polymineralic zones at the boundary between monomineralic units, as expected for bands of mylonites and ultramylonites. Flanking these narrow mixed zones are poorly mixed regions that have weaker pinning and grain-reduction, leading to large grains typical of tectonites and protomylonites. Thus, the continuum model for grain mixing and damage also predicts that weak, mylonitized plate boundaries can coexist with strong plate interiors for the same lithospheric temperature and driving stresses.