Papers by Yuri Dublyansky
Geoscientific Model Development Discussion
A unique conceptual model envisaging conductive heating of rocks in the thick unsaturated zone of... more A unique conceptual model envisaging conductive heating of rocks in the thick unsaturated zone of Yucca Mountain, Nevada by a silicic pluton emplaced several kilometers away is accepted by the US Department of Energy (DOE) as an explanation of the elevated depositional temperatures measured in fluid inclusions in secondary fluorite and calcite. Acceptance of this model allowed the DOE not to consider hydrothermal activity in the performance assessment of the proposed high-level nuclear waste disposal facility. Evaluation shows that validation of the model by computational modeling and by observations at a natural analog site was unsuccessful. Due to the lack of validation, the reliance on this model must be discontinued and the scientific defensibility of decisions which rely on this model must be re-evaluated.
Secondary calcite residing in open cavities in the unsaturated zone of Yucca Mountain has long be... more Secondary calcite residing in open cavities in the unsaturated zone of Yucca Mountain has long been interpreted as the result of downward infiltration ofmeteoric water through open fractures. In order to obtain information on the isotopic composition (δD and δ18O) of the mineral-forming water we studied fluid inclusions from this calcite. Water was extracted from inclusions by heated crushing and the δD values were measured using a continuous-flow isotope-ratio mass spectrometry method. The δ18O values were calculated from the δ18O values of the host calcite assuming isotopic equilibrium at the temperature of formation determined by fluid-inclusion microthermometry. The δD values measured in all samples range between −110 and −90‰, similar to Holocene meteoric water. Coupled δ18O–δD values plot significantly, 2 to 8‰, to the right of the meteoric water line. Among the various processes operating at the topographic surface and/or in the unsaturated zone only two processes, evaporation and water–rock exchange, could alter the isotope composition of percolatingwater. Our analysis indicates, however, that none of these processes could produce the observed large positive δ18O-shifts. The latter require isotopic interaction between mineral-forming fluid and host rock at elevated temperature (>100°C), which is only possible in the deepseated hydrothermal environment. The stable isotope data are difficult to reconcile with a meteoric origin of the water from which the secondary minerals at Yucca Mountain precipitated; instead they point to the deep-seated provenance of the mineral-forming waters and their introduction into the unsaturated zone from below, i.e. a hypogene origin.
Elevated temperatures of waters that circulated through the thick unsaturated zone of Yucca Mount... more Elevated temperatures of waters that circulated through the thick unsaturated zone of Yucca Mountain and deposited secondary minerals have been explained by conductive heating of the rock mass by a magma body emplaced in association with the activity of the Timber Mountain silicic volcanic center (the ‘‘conductive heating’’ conceptual model). The model was evaluated by means of numerical modeling. Two- and three-dimensional simulations of the conductive heat transfer, as well as three-dimensional simulations considering convective flow of water, did not match the target temperature-time ‘‘trajectory’’ established from fluid inclusion studies and
radiometric dating of secondary minerals at Yucca Mountain. This result was obtained despite the fact that the modeling was nonconservative in that the initial conditions, boundary conditions, and parameters of the models were selected so that they would return higher temperatures and longer cooling times. We conclude that the ‘‘conductive heating’’ conceptual model does not appear to constitute a plausible explanation for
the circulation in the past of thermal waters (up to 70–90oC, according to fluid inclusion data) in the vadose zone of Yucca Mountain. The finding has important implications for the safety and expected performance of the proposed high-level nuclear
waste disposal facility at Yucca Mountain.
The U.S. Code of Federal Regulations, 10 CFR Part 63, stipulates that the expected performance of... more The U.S. Code of Federal Regulations, 10 CFR Part 63, stipulates that the expected performance of the geological high-level nuclear waste repository must be demonstrated through a total system performance assessment (TSPA). The TSPArepresents an analysis that identifies all features, events, and processes (FEPs) that might affect the disposal system and examines the effects of the identified FEPs upon the performance of the system. Secondary minerals from the thick unsaturated zone of Yucca Mountain were deposited from waters with temperatures up to 70–90◦C. U-Pb dating constrained the ages of the elevated temperatures to the period between 10 and 5–6 million years ago. Relatively youthful circulation of thermal waters (hydrothermal activity) would be of concern for the safety of the disposal facility. A phenomenological model was advanced by the U.S. Department of Energy (DOE), which proposed that the minerals were deposited by infiltrating meteoric waters that were heated upon contact with the bedrock; it was hypothesized that the latter was conductively heated by a shallow silicic magma body. The model rendered processes responsible for elevated water temperatures inconsequential for the safety of the proposed nuclear waste facility. However, attempts by DOE at validating the model by means of numeric thermal simulations and analogue system observations were unsuccessful. Regulations specify two criteria for exclusion of a FEP from consideration in the TSPA: low probability and low consequence. The lack of a plausible phenomenological model makes it impossible to apply either of these two criteria to the FEP Hydrothermal Activity. Despite the lack of a valid criterion for exclusion, it was excluded from the TSPA. Both the development of DOE’s thermal model and the formal FEP analysis were associated with deviations from DOE’s quality assurance regulations.
A semi-empirical model is presented, which describes the processes of formation, migration, and a... more A semi-empirical model is presented, which describes the processes of formation, migration, and accumulation of radiogenic lead (PbRn) in opals deposited in open cavities. In contrast to lead that forms in situ through radioactive decay of uranium trapped by opal, PbRn is produced from uranium disseminated in the rock enclosing the cavities. Its incorporation into the opal is described by the following chain of processes: decay of parental uranium to yield radon — emanation and diffusion migration of radon from the rock into the cavity — decay of radon to yield lead — diffusion migration of lead in the cavity — adsorption of lead on colloidal silica particles — coagulation and settling of the colloidal particles — formation of opal. Besides the colloidal adsorption, PbRn can also be incorporated into the growing opal through direct diffusion flow onto its surface. The latter mechanism is also relevant to minerals crystallizing from ionic solutions; it is less efficient than the mechanism of colloidal adsorption. Distribution of PbRn isotopes throughout a cavity depends on the cavity geometry and the half-life of the parental Rn isotope. In cavity filled with stagnant water, the concentration profiles of PbRn show maxima at some distance from the cavity wall. The movement of water through a cavity leads to a more complex distribution of PbRn isotopes. The model describes accumulation of PbRn on silica micelles during their growth until the critical size of coagulation (5–10 nm) is reached and during the subsequent coagulation. For micelles 5–50 nm in size, the calculated concentrations of PbRn agree with those in young (Miocene and younger) natural opals. Opals formed in open cavities in acid volcanic rocks (with U = 4–5 ppm) can trap significant amounts of PbRn. Applying standard U-Pb dating equations, which ignore PbRn, will yield an overestimated age of such opals. This is true for young opals (younger than ∼30 Ma). As the age of opal increases, the share of radiogenic Pb formed in situ also grows, and the PbRn correction becomes negligible.
Chemical Geology, 2001
Samples of opal–quartz–calcite crusts from the 7.8-km-long tunnel excavated under Yucca Mountain ... more Samples of opal–quartz–calcite crusts from the 7.8-km-long tunnel excavated under Yucca Mountain were studied to determine their origin. Calcite in these crusts commonly forms relatively large (up to 1.5 cm), euhedral crystal terminations. In some crusts, layers of chalcedony and patches of opal alternate with calcite layers. Chalcedony commonly grades into euhedral quartz crystals. Quartz also forms microdruses of individual crystals up to 8 mm in size. Fluorite was identified in four samples.Fluid inclusion studies on calcite revealed formation temperatures of 35–85°C. Gas-filled inclusions are apparently of low-density (P<1 bar at room temperature) and contain aromatic hydrocarbons. In four studied calcite samples, values of δ18O remain virtually constant across crusts (−10.6‰ to −12.1‰ V-PDB). In one sample, the earliest part of calcite had δ18O of −19‰; in this part of the sample, the highest fluid inclusion temperatures, 70–85°C, were measured.The secondary calcite found at Yucca Mountain is commonly interpreted as being formed through a “pedogenic” process from rain waters percolating in the vadose zone and carrying dissolved carbonate from overlying soils [e.g., Stuckless, J.S., Peterman, Z.E., Muchs, D.R., 1991. U and Sr isotopes in ground water and calcite, Yucca Mountain, Nevada: evidence against upwelling water. Science 254, 551–554; NAS/NRC, 1992. Ground Water at Yucca Mountain: How High Can It Rise? National Academy Press, Washington, DC; Roedder, E., Whelan, J.F., Vaniman, D.T., 1994. Fluid inclusion studies of calcite veins from Yucca Mountain, Nevada, tuffs: environment of formation. High-Level Radioactive Waste Management. Proc. Int. Conf., Am. Nucl. Soc. La Grande Park, IL, pp. 1854–1860]. Our data indicate that the calcite–opal–quartz (with minor fluorite) crusts from the presently unsaturated (vadose) zone of Yucca Mountain were formed from low-temperature hydrothermal aqueous fluids in the saturated (phreatic) environment.The issue has direct bearing on the suitability of Yucca Mountain as a site for permanent geological disposal of the high-level nuclear waste.
Quaternary Science Reviews, 2011
The Vil-car-1 flowstone core from Villars cave (SW France) provides one of the first European spe... more The Vil-car-1 flowstone core from Villars cave (SW France) provides one of the first European speleothem records extending back to 180 ka, based on UeTh TIMS and MC-ICP-MS measurements. The core offers a continuous record of Termination II and the Last Interglacial. The penultimate deglaciation is characterized by a prominent 5& depletion in calcite d 18 O. Determining which specific environmental factors controlled such a large oxygen isotopic shift offers the opportunity to assess the impact of various factors influencing d 18 O variations in speleothem calcite. Oxygen isotope analyses of fluid inclusions indicate that drip water d 18 O remained within a very narrow range of AE1& from Late MIS6 to the MIS5 d 18 O optimum. The possibility of such a stable behaviour is supported by simple calculations of various effects influencing seepage water d 18 O.
International Journal of Earth Sciences, 2009
The area south of the prominent east-west trending Salzach Valley at the northern rim of the Cent... more The area south of the prominent east-west trending Salzach Valley at the northern rim of the Central Alps of Austria has long been known to host anomalously warm springs emerging from a highly deformed calcite marble (Klammkalk). This unit also hosts cavities whose shapes suggest a hydrothermal karst origin and which are lined by calcite spar. We report here petrographic and isotopic evidence suggesting that dissolution by ascending low-temperature thermal waters also played an important role in the origin of a large cave in this region, Entrische Kirche. A paleo cave wall, preserved behind a thick flowstone in the interior of this cave, revealed a brownish bleaching zone which contrasts to the medium grey colour of the unaltered marble beneath. Across this zone the C and O isotope values gradually decrease by 3 and 11%, respectively. These compositions are very different from those of the speleothem above but are similar to phreatic calcite spar from hydrothermal karst cavities in other outcrops in the area, where the absence of two-phase fluid inclusions suggests a low-temperature (less than ca. 50°C) hydrothermal origin. U/Th dating of the flowstone capping the alteration zone yielded a minimum age of the thermal water invasion in Entrische Kirche of ca. 240 kyr. There is no evidence in Entrische Kirche that these palaeowaters reached the point of calcite precipitation, but it is physically conceivable that higher and as yet unexplored parts of this deep (ca. 900 m) cave contain cavities lined by phreatic cave spar.
Investigations into the genesis and dynamical properties of cave ice are essential for assessing ... more Investigations into the genesis and dynamical properties of cave ice are essential for assessing the climate significance of these underground glaciers. We drilled an ice core through a 7.1 m-thick ice body filling a large cavern of the dynamic ice cave Eisenriesenwelt (Austria). In addition to visual core inspections, quasi-continuous measurements at 2 cm resolution comprised particulate matter, stable water isotope (δ 18 O, δD) and electrolytic conductivity profiles supplemented by specifically selected samples analyzed for tritium and radiocarbon. We found that recent ablation led to an almost complete loss of bomb-derived tritium removing any ice accumulated since, at least, the early fifties leaving the actual ice surface even below the natural tritium level. The small particulate organic masses rendered radiocarbon dating inconclusive, though a crude estimate gave a basal ice age in the order of several thousand years. The visual stratigraphy and all investigated parameters showed a clear dichotomy between the upper 2 m and the bottom 3 m of the core, which points to a substantial change in the ice formation process. Main features of the core comprise the changing appearance and composition of distinct cryocalcite layers, extremely low total ion content and a surprisingly high variability of the isotope signature. Co-isotope evaluation (δD versus δ 18 O) of the core in comparison with data from precipitation and karst spring water clearly indicate that ice formation is governed by (slow) freezing of dripping water.
Two main types of karst formation are commonly known: the surficial meteoric one and the subsurfa... more Two main types of karst formation are commonly known: the surficial meteoric one and the subsurface (hypogenic) karst, which can be related to both carbonic (H 2 CO 3 ) and sulfuric (H 2 S) acids. This paper documents evidence for a third, CO 2 -regime related, type of karst that is less commonly described. Petrographic and geochemical properties of exhumed Pleistocene phreatic cave deposits from the diapiric Jabal Madar dome in northern Oman are documented and discussed in a process-oriented context. These calcites form at the interface between two fundamentally different diagenetic and hydrogeological domains: the deep-seated, hydrothermal and the near-surficial, meteoric-vadose one.
Some problems in theoretical karst science ('karstology') are considered. An attempt is made to m... more Some problems in theoretical karst science ('karstology') are considered. An attempt is made to match the fundamentals of karstology with recent ideas on the structure of the lithosphere and the vertical zonation of the hydrosphere. Boundary conditions of karstogenesis and karst zoning are discussed. The boundaries and the structure of the karstosphere, as well as the place of karst among other geological processes are defined. The book will be of interest for karstologists, hydrogeologists, geologists and geographers.
Insights into the origin of secondary calcite at Yucca Mountain (Nevada) from high-resolution sta... more Insights into the origin of secondary calcite at Yucca Mountain (Nevada) from high-resolution stable isotope data coupled with fluid-inclusion microthermometry and δD analyses
An analytical line for stable isotope analyses of water recovered from fluid inclusions in minera... more An analytical line for stable isotope analyses of water recovered from fluid inclusions in minerals was built and successfully tested. The line is based on the principle of continuous-flow analysis of water via high-temperature reduction on glassy carbon. It includes a custom-designed set of high-efficiency crushers and a cryo-focusing cell. This paper provides details of the line design and discusses strategies for line conditioning and mitigation of memory effects. The line allows measurements of hydrogen and oxygen isotopes during a single acquisition. The precision of the analyses depends on
the amount of water released from the inclusions. The best results are obtained for samples containing at least 0.1–0.2 uL (0.06–0.11 umol) H2O. For such samples precision is better than 1.5% for dD and 0.5% for d18O (1 sigma). Smaller amounts of water can be measured but at lower precision. Analyses of modern calcite formed under stable conditions in a deep cave allowed assessment of the accuracy of the analyses. The dD values measured in fluid inclusions of this working standard match the dD value of the parent water, and the oxygen isotope values agree within ca. 0.5%. This indicates that fluid inclusions trapped in calcite at near-ambient temperatures (e.g. speleothems and low-temperatures phreatic calcite) faithfully preserve the original isotopic composition of the parent waters.
Cent. Eur. J. Geosci.
Two crushing cells have been described for the release of volatiles from fluid inclusions in mine... more Two crushing cells have been described for the release of volatiles from fluid inclusions in minerals in vacuum, static gas, and gas-flow applications. To minimize the adsorption of released volatiles on the freshly created mineral surfaces, both devices employed heated crushing. In the MTSN (Museo Tridentine di Scienze Naturali) crusher, samples were disintegrated by a piston driven by an induction coil. For efficient crushing, the lectromagnet operated in dynamic impulse mode. In the LFU (Leopold-Franzens-Universität) crusher, the sample was disintegrated through the combined action of compression (manually operated hydraulic ram) and attrition. Crushers are able to be used in off-line and on-line modes, in gas chromatographic and mass spectrometric analyses.
Journal of Contaminant Hydrology, 2005
Two papers recently published in the Journal of Contaminant Hydrology by Marshall et al. [Marshal... more Two papers recently published in the Journal of Contaminant Hydrology by Marshall et al. [Marshall, B.D., Neymark, L.A., Peterman, Z.E., 2003. Estimation of past seepage volumes from calcite distribution in the Topopah Spring Tuff, Yucca Mountain, Nevada. J. Contam. Hydrol. 62–63, 237–247] and Xu et al. [Xu, T., Sonnenthal, E., Bodvarsson, G., 2003. A reaction–transport model for calcite precipitation and evaluation of infiltration fluxes in unsaturated fractured rock. J. Contam. Hydrol. 64, 113–127] attempt to assess past volumes of seepage and infiltration fluxes through the vadose zone of Yucca Mountain, Nevada, on the basis of the modeling of the spatial distribution of secondary calcite. In this commentary, we argue that the employed methodology is not viable. In addition, the thermal boundary conditions used in simulations do not correspond to the temperatures of the mineral forming fluids established on the basis of the fluid inclusion studies.
Overview of calcite/opal deposits at or near the proposed high-level nuclear waste site, Yucca Mountain, Nevada, USA: Pedogenic, hypogene, or both?
Environmental Earth Sciences, 1995
Calcite/opal deposits (COD) at Yucca Mountain were studied with respect to their regional and fie... more Calcite/opal deposits (COD) at Yucca Mountain were studied with respect to their regional and field geology, petrology and petrography, chemistry and isotopic geochemistry, and fluid inclusions. They were also compared with true pedogenic deposits (TPD), groundwater spring deposits (GSD), and calcite vein deposits (CVD) in the subsurface. Some of the data are equivocal and can support either a hypogene or pedogenic origin for these deposits. However, Sr-, C-, and O-isotope, fluid inclusion, and other data favor a hypogene interpretation. A hypothesis that may account for all currently available data is that the COD precipitated from warm, CO2-rich water that episodically upwelled along faults during the Pleistocene, and which, upon reaching the surface, flowed downslope within existing alluvial, colluvial, eluvial, or soil deposits. Being formed near, or on, the topographic surface, the COD acquired characteristics of pedogenic deposits. This subject relates to the suitability of Yucca Mountain as a high-level nuclear waste site.
Geochimica Et Cosmochimica Acta, 2005
Yucca Mountain in southern Nevada is being evaluated as a potential site for the geological dispo... more Yucca Mountain in southern Nevada is being evaluated as a potential site for the geological disposal of high-level nuclear waste. A reliable assessment of the future performance of the repository will require detailed paleohydrogeological information. Hydrogenic secondary minerals from the vadose zone of Yucca Mountain are being studied as paleohydrogeological indicators. A phenomenological model envisaging the deposition of secondary minerals by meteoric fluids infiltrating downward though the vadose zone was proposed in the reviewed paper. Our evaluation reveals that the model is not supported by empiric evidence reported in the paper.
Open-system alpine speleothems: implications for U-series dating and paleoclimate reconstructions... more Open-system alpine speleothems: implications for U-series dating and paleoclimate reconstructions -The present work is a critical review of 130 alpha-spectrometric U/Th analyses of speleothems from north-eastern Italy. About 33% of measurements display activity ratios ( 230 Th/ 234 U)>1 while maintaining ( 234 U/ 238 U) close to unity, thus falling outside the closed system U-series disequilibrium fi eld. The open-system behaviour was mostly observed in speleothems that, based on geological data and petrographic observations, have experienced dramatic environmental changes, such as fl ooding of caves by glacial meltwater or dissolution by undersaturated waters. The paper discusses possible causes of the open-system behaviour in the U-Th system, and evaluates evidence for the U leaching vs. 230 Th introduction. By considering only samples which do not show the open-system behaviour and are not contaminated by detrital thorium, fi ve periods of active speleothem deposition have been identifi ed for north-eastern Italy: 0 to 10 ka, 40 to 63 ka, 88 to 100 ka, 140 to 160 ka, and 190 to 250 ka. Even in these, apparently good, data set, the ages of 140 to 160 ka might be affected by undetected 230 Th introduction, since they appear to be 20 to 40 ka older than the data obtained for the same paleoclimate period from European speleothems.
Environmental Earth Sciences, 1995
The hydrothermal karst of Hungary displays at least two principal stages of development in two di... more The hydrothermal karst of Hungary displays at least two principal stages of development in two differing environments. Caves of an early stage were formed within a deep zone of low thermal gradient. These caves (vugs) are small (tens of centimeters) and lined with scalenohedral crystals of calcite that are often in association with barite. Calcite yields fluid inclusion temperatures of 55-95~ and is depleted in a80 (-11.2 to -17.6 per mil PDB). The caves were formed by ascending thermal waters charged with CO2. Solubility of CaCO3 in such a system gradually increases with the ascent of the fluid (solutional zone) but drops sharply at a depth of -250 m to -500 m below the water surface (depositional zone). Caves formed in the solutional zone may be shifted into the depositional zone due to tectonic uplift, and calcite lines their walls. Large caves (tens to thousands of cubic meters) of a late stage were formed within a shallow zone of high thermal gradient immediately below and above the thermal water table. The calcite of the phreatic crusts has a rhombohedral habit, displays lower fluid inclusion temperatures (35-55~ and less), and a depletion in 1so of -9.5 to -14.6 per mil PDB. Several powerful cave-forming processes may operate there including convection, mixing/cooling corrosion, and condensation corrosion. Due to differences in the rate of tectonic uplift, rate of hydrothermal system decay, and hydrogeologic pattern, these caves were either filled with water for a long period of time (phreatic calcite crusts are formed) or partly dewatered early in their history (waterline and subaerial speleothems are formed). The zones of thermal cave formation recognized in Hungary may have a universal character. Very similar features are found in other hydrothermal karst areas of the world (Kirghizia, Algeria, South Dakota). Key words Paleohydrogeology 9 Hydrothermal karst 9 Calcite" Fluid inclusions'Hungary Y. V. Dublyansky ([~<])
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Papers by Yuri Dublyansky
radiometric dating of secondary minerals at Yucca Mountain. This result was obtained despite the fact that the modeling was nonconservative in that the initial conditions, boundary conditions, and parameters of the models were selected so that they would return higher temperatures and longer cooling times. We conclude that the ‘‘conductive heating’’ conceptual model does not appear to constitute a plausible explanation for
the circulation in the past of thermal waters (up to 70–90oC, according to fluid inclusion data) in the vadose zone of Yucca Mountain. The finding has important implications for the safety and expected performance of the proposed high-level nuclear
waste disposal facility at Yucca Mountain.
the amount of water released from the inclusions. The best results are obtained for samples containing at least 0.1–0.2 uL (0.06–0.11 umol) H2O. For such samples precision is better than 1.5% for dD and 0.5% for d18O (1 sigma). Smaller amounts of water can be measured but at lower precision. Analyses of modern calcite formed under stable conditions in a deep cave allowed assessment of the accuracy of the analyses. The dD values measured in fluid inclusions of this working standard match the dD value of the parent water, and the oxygen isotope values agree within ca. 0.5%. This indicates that fluid inclusions trapped in calcite at near-ambient temperatures (e.g. speleothems and low-temperatures phreatic calcite) faithfully preserve the original isotopic composition of the parent waters.