Evaporite Salt Research Articles

Syndepositional architecture of the northern Athabasca Oil Sands Deposit, northeastern Alberta

Salt dissolution collapse-subsidence is proposed as the dominant tectono-stratigraphic control on the deposition of major sand trends across the northern Athabasca Oil Sands Deposit. Salt removal along linear dissolution trends 200 m below in the Prairie Evaporite (Middle Devonian) halite beds resulted in the collapse of the overlying Upper Devonian strata. The collapse-induced differential subsidence of the fault blocks formed the floor underlying the McMurray deposits in the 50 km long V-shaped Bitumount Trough extending across the northern area of the Athabasca Oil Sands Deposit. The lower and middle-upper McMurray sand trends filled the accommodation created by collapses of a linear chain of Upper Devonian fault blocks along the northern margin of the western Trough. A pair of tens-of-metres thick and 20–30 km long sand trends developed parallel in overlying accumulations of the lower and middle-upper McMurray Formation (Aptian). This half-graben tilted northward as the dissolution trend in the underlying Prairie Evaporite salt scarp widened, and the scarp margin was deeply embayed. Salt dissolution-induced structures were the principal control that located the large sand complexes exploited by bitumen mining projects. Earlier models of McMurray architecture interpreted the underlying karst collapse to have been largely pre-Cretaceous. This new architectural model reinterprets the spatio-temporal balance between erosion at the pre-Cretaceous surface and within the buried salt beds. Extensive salt removal resulted in collapse of the underlying hypogene karst during the late Aptian age. This resulted in the over-thickened multi-kilometres long McMurray sand trends. The underlying karst collapse resulted in unstable deposition surfaces along the sub-Cretaceous trough floors. This tectono-stratigraphic architecture, called the syndepositional model in this study, is proposed as an alternative to two other models, one of which proposes that deeply incised channel valleys and fills resulted from multiple significant sea-level fluctuations, while the other proposes that stacked parasequences accumulated along overlying shallow channels that meandered across a stable fluvio-estuarine coast.

Changes in the electrical resistivity of arid soils during oedometer testing

Electrical methods used in geotechnical engineering are considered to be potentially useful for characterising soil settlement. In this study, a standard American Society for Testing and Materials oedometer was specifically designed for measuring the electrical resistivity of soils during oedometer testing. Relationships between the electrical resistivity and soil settlement were established for three remolded samples of saturated soils collected from the Yazd University (Iran) test site. The low resistivity values (less than 3 Ω m) measured during the oedometer tests were correlated with the high-salinity solutions in the pores (i.e. interstitial brine) that are typically observed in arid soils. In contrast to similar studies conducted in silty and clayey soils collected from areas with a moderate climate, our results have shown for the first time that the resistivity of the soil increases with increasing soil settlement and for loadings greater than 24.43 kPa. This increase was more pronounced for the soil with the highest evaporite minerals content, which reveals the strong effect of chemical reactions between the percolating brine and the solid skeleton. The increase in resistivity during settlement was interpreted as resulting from the crystallisation of evaporite salts from the interstitial brine that was induced by the decrease in brine solubility during drainage.

Draft Genome Sequence of the Extremely Halophilic Archaeon Halogranum salarium B-1 T

Halogranum salarium is an extremely halophilic archaeon isolated from evaporitic salt crystals and belongs to the family Halobacteriaceae. Here, we present the 4.5-Mb draft genome sequence of the type strain (B-1(T)) of H. salarium. This is the first report of the draft genome sequence of a haloarchaeon in the genus Halogranum.

Plutonium in the WIPP environment: its detection, distribution and behavior

The Waste Isolation Pilot Plant (WIPP) is the only operating deep underground geologic nuclear repository in the United States. It is located in southeastern New Mexico, approximately 655 m (2150 ft) below the surface of the Earth in a bedded Permian evaporite salt formation. This mined geologic repository is designed for the safe disposal of transuranic (TRU) wastes generated from the US defense program. Aerosol and soil samples have been collected near the WIPP site to investigate the sources of plutonium in the WIPP environment since the late 1990s, well before WIPP received its first shipment. Activities of (238)Pu, (239+240)Pu and (241)Am were determined by alpha spectrometry following a series of chemical separations. The concentrations of Al and U were determined in a separate set of samples by inductively coupled plasma mass spectrometry. The annual airborne concentrations of (239+240)Pu during the period from 1998 to 2010 show no systematic interannual variations. However, monthly (239+240)Pu particulate concentrations show a typical seasonal variation with a maximum in spring, the time when strong and gusty winds frequently give rise to blowing dust. Resuspension of soil particles containing weapons fallout is considered to be the predominant source of plutonium in the WIPP area. Further, this work characterizes the source, temporal variation and its distribution with depth in a soil profile to evaluate the importance of transport mechanisms affecting the fate of these radionuclides in the WIPP environment. The mean (137)Cs/(239+240)Pu, (241)Am/(239+240)Pu activity ratio and (240)Pu/(239)Pu atom ratio observed in the WIPP samples are consistent with the source being largely global fallout. There is no evidence of any release from the WIPP contributing to radionuclide concentrations in the environment.

Using 87Sr/86Sr, δ18O and δ2H isotopes along with major chemical composition to assess groundwater salinization in lower Shire valley, Malawi

Groundwater resources in some parts of the lower section of Shire River valley, Malawi, are not useable for rural domestic water supply due to high salinity. In this study, a combined assessment of isotopic (87Sr/86Sr, δ18O and δ2H) and major ion composition was conducted in order to identify the hydro-geochemical evolution of the groundwater and thereby the causes of salinity. Three major end-members (representing fresh- and saline groundwater, and evaporated recharge) were identified based on major ion and isotopic composition. The saline groundwater is inferred to result from dissolution of evaporitic salts (halite) and the fresh groundwater shows influence of silicate weathering. Conservative mixing models show that brackish groundwater samples result from a three component mixture comprising the identified end-members. Hence their salinity is interpreted to result from mixing of fresh groundwater with evaporated recharge and saline groundwater. On the other hand, the groundwater with low TDS, found at some distance from areas of high salinity, is influenced by mixing of evaporated recharge and fresh groundwater only. Close to the Shire marshes, where there is shallow groundwater, composition of stable isotopes of water indicates that evaporation may also be an important factor.

Halogranum salarium sp. nov., a halophilic archaeon isolated from sea salt

Three halophilic archaea, strains B-1 T, B-3 and B-4, were isolated from evaporitic salt crystals from Namhae, Korea. Cells of the strains were Gram-stain-negative, motile and pleomorphic, and colonies were red-pigmented. The three isolates had identical 16S rRNA gene sequences and formed a tight phylogenetic clade with Halogranum rubrum RO2-11 T in the genus Halogranum, showing 99.5% sequence similarity. The next most closely related species were Halogranum amylolyticum and Halogranum gelatinilyticum (97.4 and 96.3% similarity to the respective type strains). The phylogeny based on the full-length RNA polymerase subunit B′ gene ( rpoB′) was in agreement with the 16S rRNA gene sequence analysis, but allowed better discrimination. DNA–DNA hybridization between a representative strain (B-1 T) and the type strains of Hgn. rubrum, Hgn. amylolyticum and Hgn. gelatinilyticum revealed less than 40% relatedness. Polar lipid analysis showed that the three isolates contained phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and three glycolipids. Combined genotypic and phenotypic data supported the conclusion that strains B-1 T, B-3 and B-4 represent a novel species of the genus Halogranum, for which the name Halogranum salarium sp. nov. is proposed. The type strain is B-1 T (=KCTC 4066 T = DSM 23171 T).

Laboratory simulations of Mars evaporite geochemistry

Evaporite‐rich sedimentary deposits on Mars were formed under chemical conditions quite different from those on the Earth. Their unique chemistries record the chemical and aqueous conditions under which they were formed and possibly subsequent conditions to which they were subjected. We have produced evaporite salt mineral suites in the laboratory under two simulated Martian atmospheres: (1) present‐day and (2) a model of an ancient Martian atmosphere rich in volcanic gases. The composition of these synthetic Mars evaporites depends on the atmospheres under which they were desiccated as well as the chemistries of their precursor brines. In this report, we describe a Mars analog evaporite laboratory apparatus and the experimental methods we used to produce and analyze the evaporite mineral suites. The acidic, “paleo‐Mars” gas mixture was CO2 with trace amounts of SO2, N2O, and HCl to simulate an atmosphere influenced by volcanic emissions. Brines formed by the interaction of water with an SNC‐derived synthetic Mars mineral mix were produced under the acidic Mars atmospheric gas mixture. The brines were then desiccated under the two different simulated Mars conditions in the evaporite apparatus. Infrared reflectance spectroscopy and SEM microprobe analyses reveal that salts precipitated from the brine evaporated under simulated present Mars conditions were chemically different from those formed under the acidic Mars atmosphere conditions. The primary salt precipitated from the brine evaporated under present‐day Mars conditions was a hydrated calcium sulfate, with lesser amounts of a magnesium sulfate and aluminum sulfate. Salts precipitated from the brine evaporated under an acidic atmosphere were dominated by magnesium sulfates, with lesser amounts of Na2SO4. These experiments suggest ways that relative cation abundances in Martian sulfate‐bearing sediments can indicate the atmospheric and aqueous conditions under which they were formed. We conclude that the salts that make up the Meridiani sediments were probably formed by the interaction of water and igneous rocks at a high water‐to‐rock ratio, followed by desiccation under an atmosphere rich in acidic volcanic volatiles. The formation of Ca sulfates on Mars has most likely been due to the evaporation or freezing and sublimation of waters in equilibrium with an atmosphere much like the present.

Wash-out processes of evaporitic sulfate salts in the Tinto river: Hydrogeochemical evolution and environmental impact

Abstract This work deals with the wash-out processes of evaporitic salts in the Tinto river in October 2005, with the arrival of the first rainfall after the summer. In order to monitor water levels and electrical conductivity, a datalogger was set up in the river, while sampling was performed by a portable autosampler. Thirty-two samples were selected for analysis for a wide range of elements by ICP-AES. Three different flood events, with a maximum discharge of 8.1 m3/s, were monitored. River waters suffered from a dilution effect at the beginning of the first event, recording a concentration decrease of most elements, just before the wash-out of soluble salts precipitated during the summer took place. Wash-out processes provoked a sharp increase in most element concentrations coinciding with an intense decrease in Na and Sr. After the first event, there was strong enrichment of As, and to a lesser extent in Fe, Cr and Pb, due probably to the redissolution/transformation of Fe oxyhydroxysulfates. During the third event, evaporitic sulfate salts were depleted from riverbanks ending wash-out processes, and a decrease in most element concentrations was observed. Barium exhibited different behaviour to the rest of elements owing to the solubility control exerted by barite. Lead also showed a different pattern throughout the study period, its concentration decreasing due probably to its great affinity for coprecipitate on jarosite-group minerals, and increasing when schwertmannite precipitation is thermodynamically favoured. In October 2005, the Tinto river carried around 8100 t SO4, 1300 t Fe, 400 t Al, 100 t Zn and Cu, etc., highlighting the importance of wash-out processes of soluble salts in the Ria de Huelva ecosystem and metal fluxes into the Atlantic Ocean.

Halorubrum chaoviator sp. nov., a haloarchaeon isolated from sea salt in Baja California, Mexico, Western Australia and Naxos, Greece

Three halophilic isolates, strains Halo-G*T, AUS-1 and Naxos II, were compared. Halo-G* was isolated from an evaporitic salt crystal from Baja California, Mexico, whereas AUS-1 and Naxos II were isolated from salt pools in Western Australia and the Greek island of Naxos, respectively. Halo-G*T had been exposed previously to conditions of outer space and survived 2 weeks on the Biopan facility. Chemotaxonomic and molecular comparisons suggested high similarity between the three strains. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that the strains clustered with Halorubrum species, showing sequence similarities of 99.2-97.1%. The DNA-DNA hybridization values of strain Halo-G*T and strains AUS-1 and Naxos II are 73 and 75%, respectively, indicating that they constitute a single species. The DNA relatedness between strain Halo-G*T and the type strains of 13 closely related species of the genus Halorubrum ranged from 39 to 2%, suggesting that the three isolates constitute a different genospecies. The G+C content of the DNA of the three strains was 65.5-66.5 mol%. All three strains contained C20C20 derivatives of diethers of phosphatidylglycerol, phosphatidylglyceromethylphosphate and phosphatidylglycerolsulfate, together with a sulfated glycolipid. On the basis of these results, a novel species that includes the three strains is proposed, with the name Halorubrum chaoviator sp. nov. The type strain is strain Halo-G*T (=DSM 19316T=NCIMB 14426T=ATCC BAA-1602T).

Rates of drainage-water evaporite salt dissolution in water

Solar evaporators are an important component of systems for managing salts in agricultural drainage water. In California, solar evaporators have been integrated into on-farm drainage management (IFDM) systems as the final stage concentration process following sequential use of drainage water on increasingly salt tolerant crops. In most cases, salts are accumulated in the evaporator basins over a number of years. During months of high precipitation, dry salts redissolve in collected rainwater. Rates of dissolution are important to the design and management of the evaporator to avoid excessive salt concentrations in water displaced from the basin during storm events. The rate at which a solid, dehydrated evaporite salt redissolves in water was simulated and also tested experimentally to validate model predictions. Both model and experimental results show that rain water collecting in an evaporator basin can become saturated within 60 min at 24°C and within 90 min at 10°C with a 0.01 m water depth over solid salt. The thickness of the diffusion layer above the solid surface was calculated in the range of 8.3 × 10 − 5 and 1.25 × 10 − 4 m. For a mostly sodium sulfate evaporite salt, pH increased up to 9 from 5.5 in 5 min, and then decreased slowly converging to about 8.7 due to likely absorption of CO 2 from the atmosphere.

Hydrochemical variations and contaminant load in the Río Tinto (Spain) during flood events

The aim of this work is to study the hydrochemical variations during flood events in the Rio Tinto, SW Spain. Three separate rainfall/flood events were monitored in October 2004 following the dry season. In general, concentrations markedly increased following the first event (Fe from 99 to 1130 mg/L; Q(max) = 0.78 m(3)/s) while dissolved loads peaked in the second event (Fe = 7.5 kg/s, Cu = 0.83 kg/s, Zn = 0.82 kg/s; Q(max) = 77 m(3)/s) and discharge in the third event (Q(max) = 127 m(3)/s). This pattern reflects a progressive depletion of metals and sulphate stored in the dry summer as soluble evaporitic salt minerals and concentrated pore fluids, with dilution by freshwater becoming increasingly dominant as the month progressed. Variations in relative concentrations were attributed to oxyhydroxysulphate Fe precipitation, to relative changes in the sources of acid mine drainage (e.g. salt minerals, mine tunnels, spoil heaps etc.) and to differences in the rainfall distributions along the catchment. The contaminant load carried by the river during October 2004 was enormous, totalling some 770 t of Fe, 420 t of Al, 100 t of Cu, 100 t of Zn and 71 t of Mn. This represents the largest recorded example of this flush-out process in an acid mine drainage setting. Approximately 1000 times more water and 1408 200 times more dissolved elements were carried by the river during October 2004 than during the dry, low-flow conditions of September 2004, highlighting the key role of flood Events in the annual pollutant transport budget of semi-arid and and systems and the need to monitor these events in detail in order to accurately quantify pollutant transport. (c) 2007 Elsevier B.V. All rights reserved.

Hydrogeochemical characteristics of the Tinto and Odiel Rivers (SW Spain). Factors controlling metal contents

The Tinto and Odiel Rivers are strongly affected by acid mine drainage (AMD) due to the intense sulphide mining developed in their basins over the past 5000 years. In this study the results obtained from a weekly sampling in both rivers, before their mouth in the Ría of Huelva, over three and a half years of control are analysed. In the Tinto River, the concentrations of sulphates, Al, Cd, Co, Li and Zn are double to those of the Odiel as a consequence of lower dilution. However, the concentration of Fe in the Odiel River is 20 times lower, since the precipitation of Fe oxyhydroxysulphates caused by neutralisation processes is more intense. Lower As, Cr, Cu and Pb concentrations are also found in the Odiel River as, to a greater or lesser extent, they are sorbed and/or coprecipitated with Fe. Other elements such as Be, Mn, Ni and Mg show similar values in both systems, which is ascribed to lithological factors. The seasonal evolution of contaminants is typical of rivers affected by AMD, reaching a maximum in autumn due to the dissolution of evaporitic salts precipitated during the summer. Nevertheless, in the Tinto River, Ca, Na and Sr show a strong increase during the summer, probably due to a greater water interaction with marly materials, through which the last reach of the river flows. Barium has a different behaviour from the rest of the metals and its concentration seems to be controlled by the solubility of barite. Iron, As and Pb show different behaviours in both rivers, those for Fe and As possibly linked to the prevalence of different dissolved species of Fe. The different Pb pattern is probably due to the control of Pb solubility by anglesite or other minerals rich in Pb in the Tinto River.

Numerical modelling of the ore forming fluid migration in the sediment-hosted stratiform copper deposit, Zambian Copperbelt

As an aid to better understanding fluid flow processes and potential source rocks for the Zambian Copper Belt, preliminary numerical fluid flow modelling has been undertaken, coupled to salinity and heat transfer. The computer code used for the modelling is from Yang and Large (2001), and has been previously used to successfully model fluid flow-salinity-heat transfer in the McArthur Basin related to Stratiform Zn-Pb-Ag ore genesis (Large, et al., 2002). A 43.5km ´ 17km theoretical geological section was constructed, based on our current understanding of the structure, stratigraphy and basin architecture in the ZCB. The geological model section incorporates elements of basement, footwall succession, Ore Shale, hangingwall lower Roan siltstones and carbonates, upper Roan siltstones, carbonates and a layer of salt, Mwashia and overlying Kundelungu shales. Porosity and permeability parameters have been assigned based on our understanding of the sedimentary facies, alteration zones, petrographic evidence and local to regional structures. The most permeable elements assigned in the model are; the Mindola Clastics in the immediate footwall to the Ore Shale; crosscutting breccias in the hangingwall (below salt layer) and fault zones. The least permeable elements assigned are the Ore Shale, hangingwall carbonates and siltstones, the Mwashia shales and the basement. A one km thick salt layer in the Upper Roan has been assigned a salinity of 30 wt% (the maximum allowable by the computer code). Other sedimentary units have been given lesser initial salinities depending on the interpreted sedimentary environment (evaporitic, marine or lacustrine). A normal geothermal gradient through the basin of 30°C per km has been assumed. The model has been designed to test fluid flow and temperature gradients associated with the downward flow and convective circulation of saline fluid, from the hanging wall evaporitic salt layer into the Lower Roan stratigraphy and basement. A number of scenarios have been tested by varying the permeability of certain basin elements and fault structures. The results indicate that the most likely scenario to account for the stratiform Cu deposits involves penetration of high salinity brines from the Upper Roan salt layer down into the basement along a series on normal master faults, with brine circulation and leaching of Cu from the basement terrain. The oxidised metalliferous fluids more upwards along second order faults and are channelled into the Mindola Clastics below the organic-bearing shale cap rocks where potassic alteration and Cu-mineralisation occurs.

Iodine and Bromine: Geochemical Indicators of Deep Ore Deposits by N.N. Trofimov & A.I. Rychkov , 2004 translated by Dr Edward Erlich & Mrs Mary-Margaret Coates. Colorado Mountain Publishing House, Denver, Colorado, 205 pp, US$43, ISBN 0-9759087-0-7.

This publication is an English translation of a Russian text on the geochemistry of iodine and bromine and application in the assessment of hydrothermal ore deposits. The volume was first published in 1994 as a summary of more than 30 years of research by the authors. The book is virtually unique in the exploration geochemistry literature in that it focuses on two elements not often examined in exploration studies, except perhaps some hot spring, uranium and evaporite salt deposits. Yet the authors demonstrate in a comprehensive study of geochemical halos of the application of both elements to 75 different deposits ranging from granitoid-hosted pegmatites and associated hydrothermal ore deposits, such as those of porphyry copper and tin to those of vein and replacement gold, lead-zinc, copper, and skarn style deposits; to volcanogenic-hosted sulphide mineralization; and to epithermal mineralization …

Geochemical variations in aeolian mineral particles from the Sahara–Sahel Dust Corridor

The Sahara–Sahel Dust Corridor runs from Chad to Mauritania and expels huge amounts of mineral aerosols into the Atlantic Ocean. Data on samples collected from Algeria, Chad, Niger, and Western Sahara illustrate how corridor dust mineralogy and chemistry relate to geological source and weathering/transport history. Dusts sourced directly from igneous and metamorphic massifs are geochemically immature, retaining soluble cations (e.g., K, Na, Rb, Sr) and accessory minerals containing HFSE (e.g., Zr, Hf, U, Th) and REE. In contrast, silicate dust chemistry in desert basins (e.g., Bodélé Depression) is influenced by a longer history of transport, physical winnowing (e.g., loss of Zr, Hf, Th), chemical leaching (e.g., loss of Na, K, Rb), and mixing with intrabasinal materials such as diatoms and evaporitic salts. Mineral aerosols blown along the corridor by the winter Harmattan winds mix these basinal and basement materials. Dusts blown into the corridor from sub-Saharan Africa during the summer monsoon source from deeply chemically weathered terrains and are therefore likely to be more kaolinitic and stripped of mobile elements (e.g., Na, K, Mg, Ca, LILE), but retain immobile and resistant elements (e.g., Zr, Hf, REE). Finally, dusts blown southwestwards into the corridor from along the Atlantic Coastal Basin will be enriched in carbonate from Mesozoic–Cenozoic marine limestones, depleted in Th, Nb, and Ta, and locally contaminated by uranium-bearing phosphate deposits.

The Mineralogy and Distribution of Zeolitic Tuffs in the Maramures Basin, Romania

AbstractThe Maramures Basin, in the Carpathian mountain belt of northern Romania on the border with the Ukraine, belongs to the eastern part of the Pannonian Basin. In the study area, extensional tectonic movements during the Miocene were coeval with silicic and intermediate volcanism in the inner part of the Eastern Carpathians. Throughout this region, explosive events have resulted in the deposition of pyroclastic flows and ash-fall deposits interbedded with marine sediments.Several tuff units of Badenian (15–13.6 Ma) age occurring throughout the area are extensively zeolitized. These rocks occur as massive homogeneous beds, white to pale greenish-blue, and are commonly extensively jointed. In the Bârsana-Calinesti area and along the Morii Valley, two conspicuous tuff units that can be traced over many km are separated by a calcareous sandstone bed. Most tuffs have a vitroclastic texture in which former glass shards are pseudomorphed by clay minerals and clinoptilolite. Opal-CT commonly occurs as clumps of radiating rods that produce a spherical morphology. Also, rare celadonite is found in the lower greenish tuffs. Pyrogenic crystal fragments are quartz, plagioclase and biotite. Folded muscovite plates and fragments of basement rocks are dominant among the lithic clasts. Above the Bârsana Formation, a second series of white zeolitized tuff, the Ocna Sugatag Formation, is represented by at least two different units overlying an evaporite salt deposit. A large outcrop of a massive white tuff at this locality contains abundant fine-grained clinoptilolite and cation-exchange capacity values of >160 meq/100 g. Clinoptilolite-Ca is also present in the Sighetu tuff unit in the northern part of the Maramures Basin where a distinctive horizon contains plant remains preserved in spherical concretions. Plant material and algal limestones in the same succession strongly suggest that the marine depositional environment was close inshore, and shallow-rather than deep-water conditions are inferred. A mineralogically similar, unaltered, volcanic tuff found in the Coas area suggests that the precursor glass was rhyolitic (72–74% SiO2) with a high-K calc-alkaline affinity. We conclude that pervasive zeolitization is due to the interaction between seawater and vitroclasts at an early stage after deposition.

The lithium isotopic composition of waters of the Mono Basin, California

Mono Lake, a major closed-basin alkaline salt lake in eastern California, derives its water from a mixture of creeks and springs, with the former providing in excess of 75% of the total. The Li isotopic composition of lake water has not varied significantly over a 4 year meromictic period (δ 7Li ∼ +19.5). Springs are isotopically distinct: groundwater springs and seeps carry water enriched in isotopically heavy Li whereas thermal springs supply isotopically light (δ 7Li < lake), but 10 times more Li-rich, water. Isotopic fractionation during crystallization of carbonate tufa and evaporitic salt appears to be insignificant, and thus cannot be called on as a principal control of the isotopic balance of Li of the lake. Isotopic differences between the end-member source components permit a water budget to be calculated, suggesting (1) springs provide > 50% of the Li to the lake; (2) the Li budget is sensitively balanced on small thermal spring contributions, < 3% of the total spring inflow; and (3) the residence time of Li in the lake is 28 ka. Other Great Basin closed lakes have variable Li isotopic compositions (δ 7Li from +16.7 to +23.7), all of which differ significantly from those of several major lakes and seawater (homogeneously ∼ +32).

Mineralogic controls on the composition of natural waters dominated by silicate hydrolysis

A detailed mineral-solute mass-balance spreadsheet model has been developed to improve understanding of mineralogic controls on water composition in surface waters and groundwater systems dominated by silicate lithologies. The spreadsheet-based approach is used to investigate mass-balance solutions over a range of mineral compositions for predominant, multi-element phases such as plagioclase, biotite, chlorite, amphibole, and dioctahedral smectite. The mass-balance technique has been applied to a variety of hydrogeologic environments including calibrated watersheds, springs and groundwater systems. Lithologic settings include plutonic, metamorphic, minor volcanic, and sedimentary (alluvial and glacial deposits) materials. Sites investigated, most of which allowed comparison with earlier work, include ephemeral and perennial springs of the central Sierra Nevada Mountains, California; the Loch Vale, Colorado high-altitude watershed; four catchments in the Inyo Mountains, California and Nevada; watersheds in the Catoctin Mountain, Maryland area; and ground-water flow systems in Vekol Valley, Arizona and in the Trout Lake area, Wisconsin. Analytical mass balances were derived with a novel approach that permits graphic analysis of the functional dependency of mineral mass-transfer coefficients on variations in major silicate composition. A 10 x 10 matrix of mineral-solute reaction equations was used to solve for the best mass balances. Alternative methods were developed to investigate cases where the number of mineral phases exceeds the number of solute constraints (10) that are commonly found in clastic, silicate-dominated systems with diverse sources and/or phase mixtures of variable chemistry (such as an assortment of plagioclase compositions). Techniques were also developed to allow for important structurally controlled compositional variation in clay minerals. Final mass-balance choices were tempered by thermodynamic stability calculations for various minerals under near-surface weathering conditions. Mineral mass-transfer ratios were also found to be useful in restricting mass balances. Additional constraints were provided by establishing consistent sets of similar mineral assemblages and mineral compositions for a series of wells along a ground-water flow path, or through comparison of multiple nearby watersheds subject to similar climatic and vegetative conditions. Whereas unique analytical solutions from spreadsheet mass balances were not always possible, a surprisingly limited range was obtained for mineral assemblages and compositions satisfying observed mineral occurrences and thermodynamic stability conditions. Our results demonstrate the importance of having well-characterized mineral compositions for both reactant and product phases. The mass-balance results are particularly sensitive to the compositions of plagioclase, dioctahedral smectite, and a few primary mafic mineral groups (trioctahedral mica, amphibole, and pyroxene). In addition to mineral controls, the specific examples studied demonstrate effects of dolomite and calcite overprints on silicate weathering, biomass fluctuations, road salt contamination, and on buried evaporite salts. A comparison of the mass-balance results from surface- and groundwater systems indicates strong similarities, suggesting that similar processes dominate the mineral controls in both settings, and that, under soil weathering conditions ion exchange might have been overemphasized, except under conditions where pre-existing waters are displaced by solutions of significantly different composition.

Selenium stable isotope ratios in California agricultural drainage water management systems.

Selenium stable isotope ratios are known to shift in predictable ways during various microbial, chemical, and biological processes, and can be used to better understand Se cycling in contaminated environments. In this study we used Se stable isotopes to discern the mechanisms controlling the transformation of oxidized, aqueous forms of Se to reduced, insoluble forms in sediments of Se-affected environments. We measured 80Se/76Se in surface waters, shallow ground waters, evaporites, digested plants and sediments, and sequential extracts from several sites where agricultural drainage water is processed in the San Joaquin Valley of California. Selenium isotope analyses of samples obtained from the Tulare Lake Drainage District flow-through wetland reveal small isotopic contrasts (mean difference 0.7%) between surface water and reduced Se species in the underlying sediments. Selenium in aquatic macrophytes was very similar isotopically to the NaOH and Na2SO3 sediment extracts designed to recover soluble organic Se and Se(0), respectively. For the integrated on-farm drainage management sites, evaporite salts were slightly (approximately 0.6%) enriched in the heavier isotope relative to the inferred parent waters, whereas surface soils were slightly (approximately 1.4%) depleted. Bacterial or chemical reduction of Se(VI) or Se(IV) may be occurring at these sites, but the small isotopic contrasts suggest that other, less isotopically fractionating mechanisms are responsible for accumulation of reduced forms in the sediments. These findings provide evidence that Se assimilation by plants and algae followed by deposition and mineralization is the dominant transformation pathway responsible for accumulation of reduced forms of Se in the wetland sediments.

Measurements of the suitability of large rock salt formations for radio detection of high-energy neutrinos

We have investigated the possibility that large rock salt formations might be suitable as target masses for detection of neutrinos of energies about 10 PeV and above. In neutrino interactions at these energies, the secondary electromagnetic cascade produces a coherent radio pulse well above ambient thermal noise via the Askaryan effect. We describe measurements of radio-frequency attenuation lengths and ambient thermal noise in two salt formations. Measurements in the Waste Isolation Pilot Plant, located in an evaporite salt bed in Carlsbad, NM yielded short attenuation lengths, 3– 7 m over 150– 300 MHz . However, measurements at United Salt's Hockley mine, located in a salt dome near Houston, Texas yielded attenuation lengths in excess of 250 m at similar frequencies. We have also analyzed early ground-penetrating radar data at Hockley mine and have found additional evidence for attenuation lengths in excess of several hundred meters at 440 MHz . We conclude that salt domes, which may individually contain several hundred cubic kilometer water-equivalent mass, provide attractive sites for next-generation high-energy neutrino detectors.