Rock Salt Samples Research Articles

Fracturing behavior of feather salt rock samples under compression

The paper presents the compression test results for salt rock samples and the study into the stress-strain state of cylindrical samples with different height-diameter ratios. Based on the analysis of a representative structural element of the sample material with a spherical pore, a variant of the fracture mechanism in the salt rock samples under compression is offered, that explains the abnormal response of the limit compression stress value to the geometry of samples in the conditions of dry friction and sliding due to lubrication.

Contact metamorphism, halocarbons, and environmental crises of the past

Environmental context. What caused the biggest known mass extinction on Earth ~252 million years ago? A possible killer mechanism was the release of specific gases into the atmosphere, which eventually led to destruction of the ozone layer. This is now supported by new laboratory experiments in which ozone-destructing gases were generated when heating rocks from East Siberia (Russia) – reconstructing what happened naturally in Siberia during explosive gas eruptions 252 million years ago. Abstract. What triggered the largest know mass extinction at the Permian–Triassic boundary 252 million years ago, when 95% of the species in the oceans disappeared? New geological data suggest that eruptions of carbon (CH4, CO2) and halocarbon (CH3Cl and CH3Br) gases from the vast sedimentary basins of east Siberia could have triggered a period with global warming (5°–10°C) and terrestrial mass extinction. The gases were generated during contact metamorphism of sedimentary rocks around 1200°C hot igneous intrusions. One of the suggested end-Permian extinction mechanisms is the extreme ultraviolet radiation (UV-B) caused by a prolonged destruction of stratospheric ozone induced by the emitted halocarbons. This hypothesis is supported by a new set of experiments, where natural rock salt samples from Siberia were heated to 275°C. Among the gases generated during heating are methyl chloride (CH3Cl) and methyl bromide (CH3Br). These findings open up new possibilities for investigating ancient environmental crises.

Percolation model for dilatancy-induced permeability of the excavation damaged zone in rock salt

A new percolation model is presented that predicts the dilatancy-induced permeability increase in the excavation damaged zone (EDZ) of rocks salt. The micro-fracture geometry and network properties of the rock salt samples are determined by visualisation and evaluated by using statistical and stereological methods. The permeability at full connectivity is modelled using the cubic law with a semi-empirical estimation of the micro-fracture aperture. This model is coupled with a percolation model to incorporate the connectivity behaviour. The percolation threshold is related to the dilatancy boundary, which is defined as the starting point for the energy release that causes the grain boundaries to dislocate. The shift between the dilatancy boundary and the percolation threshold is further applied to complete the modelling approach. The model is calibrated and validated by the stress-permeability results of the triaxial measurements. The matches vary from satisfactory to excellent.

CLAY MINERALS IN THE ROCK SALT OF MIOCENE EVAPORATES OF THE CARPATHIAN REGION, UKRAINE

Clay mineral association in water insoluble residue of 33 rock salt samples from Miocene evaporites of the Carpathian Foredeep were investigated by means of X-ray diffraction (XRD). The clay minerals of halite facies of the Carpathian Region of Ukraine in both Eger-Eggenburgian (Vorotyshcha suite) and Badenian (Tyras and Tereblya suites) rock salt deposits contain illite, chlorite and mixed-layer illite/smectite, while the smectite, mixed-layer chlorite/smectite and corrensite is revealed only in Badenian rock salt and is caused by volcanic activity in Badenian

GEOCHEMICAL AUREOLES AROUND OIL AND GAS ACCUMULATIONS IN THE ZECHSTEIN (UPPER PERMIAN) OF POLAND: ANALYSIS OF FLUID INCLUSIONS IN HALITE AND BITUMENS IN ROCK SALT

Fluid inclusions in halite and bitumens in rock salt in Upper Permian Zechstein evaporites in West Poland were studied in locations where the evaporites lie above oil and gas reservoir rocks. The samples were taken from halite intercalated within the Basal Anhydrite; this unit lies above the Main Dolomite which serves as both source rock and reservoir. Samples came from a depth of 2.3–3.2 km. A characteristic feature of the fluid (gas‐brine) inclusions was their high methane content together with the occasional presence of bitumen globules of near‐spherical form. Geochemical analyses of the bitumen in bulk samples of rock salt (including content and distribution of n‐alkanes and isoprenoids, and carbon isotope ratios) suggest an algal origin, similar to that of the oil in the underlying source rocks. For comparison, we studied fluid inclusions in halite from Zechstein evaporites in northern Poland, where hydrocarbon accumulations do not occur in underlying strata and where mostly single‐phase (brine) inclusions with a low methane content have been recorded. However, published data indicate that similar inclusions to those occurring in the Zechstein of West Poland (comprising brine with a high methane content, bitumen films and/or oil droplets) are present in other salt‐bearing sequences, where their origin is related to the thermal degradation of organic material dispersed within the salt itself. Accordingly, such fluid inclusions in an evaporite succession can only be considered to form a geochemical aureole where the bitumens in the rock salt (including those in the fluid inclusions in halite) can be compositionally linked to those in the associated oil accumulation.

Determination of natural radioactivity in rock salt and radiation doses due to its ingestion

The Khewera Mines located in Pakistan contain the world’s second largest reserves ofrock salt. Rock salt is used in Pakistan in food recipes. It was decided toinvestigate the concentrations of naturally occurring radionuclides in rock saltfrom the Khewera Mines. Samples of rock salt were collected from 10 differentlocations and analysed by gamma spectrometry. The mean activity concentrations of226Ra,232Th and 40K were 790 ± 262, 640 ± 162 and 23 000 ± 6000 mBq kg−1, respectively. The mean annual effective dose due to the intake ofnatural radionuclides from rock salt for adults was estimated to be0.0638 ± 0.015 mSv, which is lower than the average annual effective dose of 0.29 mSv received percaput worldwide due to the ingestion of natural radionuclides, as reported bythe United Nations Scientific Committee on the Effects of Atomic Radiation in2000.

Cryogenic vitrification and 3D serial sectioning using high resolution cryo‐FIB SEM technology for brine‐filled grain boundaries in halite: first results

AbstractThe structure of brine films in grain boundaries of halite has been the subject of much controversy over the past 20 years; although a number of innovative methods have been developed to study these structures, much is still unknown and fundamental information is missing. In this study, we investigated different methods of plunge‐freezing to vitrify the brine fill of grain boundaries for natural salt polycrystal. This was followed by a preliminary study of the 3D morphology of a vitrified grain boundary in a natural rock salt sample with a focused ion beam (FIB) excavation system. We have shown that brine‐filled grain boundaries in rock salt can be efficiently well frozen when dimensions are less than about 1 mm. Coupled with an ion beam tool, cryo‐SEM allows 3D observation of the well‐frozen grain boundaries in large volumes and high resolution. Initial results of brine‐filled natural halite grain boundaries show non‐faceted crystal–brine interfaces and unexpectedly low dihedral angles at room temperature and pressure.

Characterization of ultra‐heavily damaged NaCl

AbstractIn this paper we present the progress made to (i) characterize the defect state of ultra‐heavily damaged rock salt samples with up to more than 20 at% Na colloids, which had been irradiated with 0.5 MeV electrons at 100 ºC up to 104 MGy (1000 GRad), and (ii) understand their physical properties. The explanation of the observations, made by means of a variety of experimental techniques, is not trivial and often the results obtained with different experimental techniques lead to conflicting interpretations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Trace elements in rock salt and their bioavailability estimated from solubility in acid

In this study, 18 partly commercially available samples of rock salt from Austria, Germany, Pakistan, Poland, Switzerland, and Ukraine were investigated with respect to their content of trace elements using instrumental neutron activation analysis. Elements detected were Al, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Eu, Fe, Hf, La, Mn, Na, Rb, Sb, Sc, Sm, Sr, Ta, Tb, Th, and Zn, some of them only in individual cases. An estimation of the bioavailability of these trace elements was performed by dissolving an equivalent of the sodium chloride samples in diluted hydrochloric acid (simulating stomach acid), filtering off the insoluble components, and analyzing the evaporated filtrate. It could be shown that in most cases bioactive trace elements like Fe can be found in rock salt in the form of almost insoluble compounds and are therefore not significantly bioavailable, whereas thorium, for example, was partly bioavailable in two cases. A significant contribution to the recommended daily intake of metal trace elements by using rock salt for nutrition can be excluded.

Rock salt dilatancy boundary from combined acoustic emission and triaxial compression tests

This paper presents an experimental investigation of rock salt dilatancy boundary based on combined acoustic emission and triaxial compression tests carried out on the rock salt samples from the Asse Salt Mine, Germany. The experimental results were evaluated to determine the dilatancy boundary under specified stress, stress loading rate and pore pressure. Pore volume changes caused by deviatoric stresses were measured during triaxial compression tests. The dilatancy boundary was then determined from the maximum compression on a stress–strain curve which separates the compression and dilatancy regions. Variations in acoustic emissions that occur during microcrack development under triaxial compression were recorded with ten sensors mounted on the outer surface of the cylindrical samples. A spontaneous increase observed in the cumulative number of acoustic events is consistent with the dilatancy boundary determined from the minimum pore volume. It is confirmed that the dilatancy boundary depends on both stress loading rate and pore pressure. The dilatancy boundary slightly decreases with increasing the loading rate, but increases with increasing the minor normal stress. High pore pressures accelerate the dilatancy. A Biot coefficient of 0.25 for Asse rock salt was determined from the dilatancy boundary. An analysis of two-dimensional (2D) fractal dimensions determined for several samples shows that the samples with smaller dimensions have slightly higher dilatancy boundaries. The dilatancy boundary values of Asse rock salt are lower than those reported for crystalline rocks, although both rock types show similar dilatancy behaviour.

MEASUREMENT OF ATTENUATION LENGTH FOR RADIO WAVE IN NATURAL ROCK SALT SAMPLES CONCERNING ULTRA HIGH ENERGY NEUTRINO DETECTION

Ultra high energy (UHE) neutrinos with the energy larger than 1015 eV, surely arrive at the earth with Greisen, Zatsepin, Kuz'min (GZK) effect, though the rate is very few. The rare call requires us to utilize a large mass (>10 Gton) of detection medium. UHE neutrino generates a huge number of unpaired electrons in rock salt. They would emit sensible radio wave by coherent Cherenkov (Askar'yan) effect. The longer attenuation length of radio wave in rock salt reduces the number of antennas required. Several rock salt samples including synthesized one are measured in attenuation length for radio wave transmission at 0.3 and 1.0 GHz. Some show attenuation length larger than 300 m, which indicate a possibility for constructing a salt neutrino detector.

Radiolysis of NaCl at high and low temperatures: development of size distribution ofbubbles and colloids

New experimental results are presented on low temperature irradiation(18 °C) of rock-salt samples which had been exposed to initial doses up to 320 GRad at100 °C. Differential scanning calorimetry (DSC) shows that the latent heat of melting (LHM) ofsodium colloids decreases during subsequent low-temperature irradiation, whereas thestored energy (SE) increases slowly, indicating that the process of radiolysis continues. Thedecrease of the LHM is due to dissolution of large colloids, because the intensities of themelting peaks decrease during the second stage irradiation at low temperature. The modelis formulated to describe the nucleation kinetics and the evolution of the sizedistribution of chlorine precipitates and sodium colloids in NaCl under high doseirradiation. It is shown that the mechanism of dissolution of large Na colloidsduring low temperature irradiation can be related to melting of sodium colloids.

Characteristics of chlorine isotope distribution and analysis on sylvinite deposit formation based on ancient salt rock in the western Tarim Basin

During formation of the Tarim Basin, there repetitively happened seawater invasion for it was ever connected with wide Paleo-mediterranean Sea. At the same time, for the application of tectonic and paleoenvironmental condition, the basin deposits many sequences of thick strata of evaporites, especially in its two largest subbasins of Kuqa in the north and Shaqa in the southwest. Therefore, the western Tarim Basin has been considered to be a favorable location to prospect ancient sylvinite deposit. But it is unfortunate that the Br×103/Cl ratio, as a common geochemical index to uncover clues of sylvinite deposit, is almost invalid to indicate the stage of ancient brine condensation for very low content of bromine in salt rock samples (less than 10−6 commonly) in the western Tarim Basin evaporites. Fortunately, we noticed recently that the values of chlorine isotope (δ 37Cl value) for salt rock samples follow some clear laws from place to place, which in the Shaqa subbasin, all δ 37Cl values of salt rock samples behaved negatively and on the contrary, they all surprisingly showed positive values in the Kuqa subbasin. Based on conclusions of previous research and referring to the ratios of Br×103/Cl for salt rock or brine samples, we proved that the chlorine isotope (δ 37Cl) could be used as an effective index to find ancient sylvinite deposit in those evaporites rock basin with low content of Br element background, such as the Tarim Basin. Thus according to the new index of chlorine isotope, we conclude that the concentration of ancient brines formed ancient salt rocks is much more concentrated in the Shaqa subbasin than that in the Kuqa subbasin. Particularly, the δ 37Cl value of salt rock in Kashi depression of the western Shaqa subbasin is greatly negative (<-1.00‰), which may predicate that the ancient brine has been concentrated to the terminal stage of salt deposit or even the later stage of sylvinite deposit. Then it is possible to find sylvinite-bearing deposits around the western region (periphery of Kashi depression) of the Shaqa subbasin if we carry out more careful exploration in later works.

Influence of Stress Rate on Rheology – An Experimental Study on Rocksalt of Simla Himalaya, India

The stress-strain behaviour and mechanical properties were investigated on rocksalt samples collected from Guma rocksalt Mine, District Mandi, Himachal Pradesh, India. Cylindrical samples cored perpendicular to the bedding planes, were compressed using an automated closed loop servo-controlled testing machine at stress rates ranging from 9.12×10−3 MPa/minute to 9.12 MPa/minute. The effects of stress rate on stress-strain behaviour as well as on mechanical properties were investigated by controlling the time of deformation. The stress-strain behaviour of rocksalts were verified by theoretical analysis with the help of the derivation of equations for Maxwell and Kelvin-Voigt Models connected in series.

Rheological behaviour of synthetic rocksalt: the interplay between water, dynamic recrystallization and deformation mechanisms

The ductile deformation of rocks in nature can be greatly enhanced by the presence of water. Part of the water-induced weakening of rocks at depth may come from fluid-assisted deformation or recrystallization mechanisms that are absent in dry rocks. In this study, we investigate the effect of water on the rheological behaviour of rocksalt. We focus on quantification of the contribution of individual deformation and recrystallization mechanisms to deformation. We also aim to calibrate a flow law that incorporates the effect of all the relevant microphysical processes and hence more accurately describes the flow of rocksalt in nature. For this purpose, the mechanical behaviour and microstructural evolution of synthetic rocksalt samples that are similar, except for differences in water content (determined using FTIR analysis), are investigated. The samples are deformed to natural strains of 0.07–0.46 at 50 MPa confining pressure, strain rates of 5×10 −7–1×10 −4 s −1 and temperatures of 75–240 °C, resulting in flow stresses of 7–22 MPa. The flow stress of samples with a water content below ∼5 ppm (‘dry’) is higher than that of samples with a water content of ∼9–46 ppm (‘wet’) at all strains under the investigated conditions. The difference in flow stress can be explained as due to the operation of only work hardening dislocation creep without dynamic recrystallization in the dry material versus combined dislocation and solution-precipitation creep plus fluid-assisted grain boundary migration in the wet material. The results allow us to calibrate a flow law for wet rocksalt that incorporates the effects of solution-precipitation creep and fluid-assisted grain boundary migration. The results also suggest that strain localization in natural rocksalt is more likely to be localized due to fluid infiltration and associated rheological weakening, than due to progressive removal of strain hardening substructure by grain boundary migration.

Laboratory investigations for the evaluation of in situ geophysical measurements in a salt mine

Abstract Problem zones in a sylvinite mine were explored by underground measurements using a set of geophysical methods (geosonar, seismics, georadar, EM methods and geoelectrics), which yield parameter sets for disturbed and undisturbed rock. Underground geo-electrical methods are most suitable for examining humidity content and structures for the transport of brines, although they have to be constrained by wave-propagation methods. Additional laboratory experiments on rock salt samples were carried out in order to provide quantitative evaluation methods. A titration method was used to determine the amount of water. This was applied simultaneously with a four-electrode resistivity measuring system for samples with very high resistivity. These measurements were made on samples at different scales, yielding relationships between water content and resistivity, as well as information about the parameter distribution in larger core samples. Together, the field and laboratory results show that geo-electrics is a suitable method for the detection and evaluation of problem zones of the geological barrier of hazardous waste repositories, and a criterion for the risk assessment based upon resistivity measurements is defined.

Systematic UHV‐AFM experiments on Na nano‐particles and nano‐structures in NaCl

Results of systematic AFM (atomic force microscopy) experiments on heavily and moderatly irradiated NaCl samples are presented. The sodium nanoparticles and structures of nanoparticles are poduced in sodium chloride during irradiation. The AFM images of the nanoparticles have been obtained in ultra high vacuum (UHV) in the non-contact mode with an Omicron UHV AFM/STM system. The sizes and arrangements of the observed particles depend on the irradiation conditions. The melting behaviour of the sodium nanoclusters has been studied for these samples by differential scanning calorimetry (DSC). A phenomenological model has been proposed which explains the observed behaviour by the existence of two different structural states in the population of sodium colloids. AFM measurements of heavily irradiated natural rock salt samples have revealed ring- and chain-like clusters (or agglomerates) of Na colloid particles. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Salt neutrino detector for ultrahigh-energy neutrinos

Rock salt and limestone are studied to determine their suitability for use as a radio-wave transmission medium in an ultrahigh energy (UHE) cosmic neutrino detector. A sensible radio wave would be emitted by the coherent Cherenkov radiation from negative excess charges inside an electromagnetic shower upon interaction of a UHE neutrino in a high-density medium (Askar’yan effect). If the attenuation length for the radio wave in the material is large, a relatively small number of radio-wave sensors could detect the interaction occurring in the massive material. We measured the complex permittivity of the rock salt and limestone by the perturbed cavity resonator method at 9.4 and 1 GHz to good precision. We obtained new results of measurements at the frequency at 1.0 GHz. The measured value of the radio-wave attenuation length of synthetic rock salt samples is 1080 m. The samples from the Hockley salt mine in the United States show attenuation length of 180 m at 1 GHz, and then we estimate it by extrapolation to be as long as 900 m at 200 MHz. The results show that there is a possibility of utilizing natural massive deposits of rock salt for a UHE neutrino detector. A salt neutrino detector with a size of 2×2×2 km would detect 10 UHE neutrino/yr generated through the GZK process.

Kaiser Effect in Rock Salt

Using the results of experiments with rock salt samples under various loading regimes as an example, the regularities of the Kaiser effect formation and manifestation in rocks with plastic properties are investigated.

Observation of Post-failure Kaiser Effect in a Plastic Rock

— Cyclic uniaxial and triaxial tests of rock salt samples were carried out in pre- and post-failure regimes. In all tests, a distinct Kaiser effect was observed in the post-failure region. The slope of the curve “cumulative AE counts versus axial strain” increased dramatically (several times to an order) when the strain attained its peak value achieved previously. Neither preliminary hydrostatic compression nor preliminary uniaxial cyclic pre-failure loading influence the post-failure Kaiser effect. The results for the plastic rock are opposite to the familiar absence of the Kaiser effect in brittle rocks at stress values approaching the ultimate strength. The results obtained during laboratory tests of a plastic rock are of importance for the proof of a connection between the Kaiser effect and foreshocks preceding earthquakes.