Halite Dissolution Research Articles

Vertical mixing with return irrigation water the cause of arsenic enrichment in groundwater of district Larkana Sindh, Pakistan

Stable isotopes ratios (‰) of Hydrogen (δ2H) and Oxygen (δ1⁸O) were used to trace the groundwater recharge mechanism and geochemistry of arsenic (As) contamination in groundwater from four selected sites (Larkana, Naudero, Ghari Khuda Buksh and Dokri) of Larkana district. The stable isotope values of δ2H and δ1⁸O range from 70.78‰ to −56.01‰ and from −10.92‰ to −7.35‰, relative to Vienna Standard for Mean Ocean Water (VSMOW) respectively, in all groundwater samples, thus indicating the recharge source of groundwater from high-salinity older water. The concentrations of As in all groundwater samples were ranged from 2 μg/L to 318 μg/L, with 67% of samples exhibited As levels exceeding than that of World Health Organization (WHO) permissible limit 10 μg/L and 42% of samples expressed the As level exceeding than that of the National Environmental Quality Standard (NEQS) 50 μg/L. The leaching and vertical mixing with return irrigation water are probably the main processes controlling the enrichment of As in groundwater of Larkana, Naudero, Ghari Khuda Buksh and Dokri. The weathering of minerals mostly controlled the overall groundwater chemistry; rock-water interactions and silicate weathering generated yielded solutions that were saturated in calcite and dolomite in two areas while halite dissolution is prominent with high As area.

Hydrogeochemistry and groundwater quality assessment of high fluoride levels in the Yanchi endorheic region, northwest China

Groundwater is the primary source of water for irrigation and domestic purposes in the Yanchi endorheic region, an arid area in northwest China. A comprehensive understanding of the hydrogeochemical characteristics and groundwater quality is indispensable for the sustainable utilization of the groundwater sources. For this reason, twenty-seven groundwater samples were collected in three seasons. A hydrogeochemical assessment and entropy-weighted water quality index (EWQI) were used to investigate the sources of high sodium, sulfate and fluoride concentrations, to evaluate the groundwater quality and to ascertain the factors controlling the groundwater quality, the spatial distribution and the seasonal variation. The dissolution of halite and gypsum supplies most of the Na+ and SO42−, respectively, in the groundwater, and cation exchange further enhances the Na+ content. The main sources of the high F− concentrations are the dissolution of fluorite and desorption of exchangeable F−. This groundwater environment, which is Na-rich and Ca-poor, has high pH values, and the precipitation of calcite and dolomite provides favorable conditions for the enrichment of fluoride. In the three sampling seasons, 48%, 52% and 48% of the groundwater was categorized as poor- or extremely poor-quality water, which is not suitable for drinking purposes, according to the self-defined classifications of EWQI. The high EWQI values are mainly observed in the mountain front and discharge area of the groundwater runoff. The high concentrations of Na+, SO42−, F−, and TDS are the greatest contributing parameters to the low groundwater quality, and the assessed impacts decrease in the following order: Na+ > TDS > SO42− > F−. The spatial distribution of the EWQI versus four hydrochemical parameters reveals that the groundwater quality improves but the influential factors do not change with the seasonal variation.

Hydrochemical classification and multivariate statistical analysis of groundwater from Wadi Sahba area in central Saudi Arabia

The central region of Saudi Arabia is underlain by thick sedimentary formations belonging to the Mesozoic and Cenozoic era. These sedimentary formations form a prolific aquifer supplying groundwater for agricultural and domestic usage in and around Riyadh. The region south of Riyadh City is well known for agricultural activities. Wadi Sahba, which is an eastward extension of Wadi Nisah, has readily available groundwater resources in the Cretaceous Biyadh sandstone aquifer to sustain agricultural activities. The objective of the present study was the hydrochemical assessment of groundwater in the area to understand the main hydrological processes which influence groundwater chemistry. To achieve this objective, 20 groundwater samples were collected from agricultural farms in the Wadi Sahba in central Saudi Arabia, and the major physiochemical constituents were analyzed and interpreted. The average TDS value of the analyzed samples is 1578.05 mg/l, whereas the average EC concentration is 3220.05 μS/cm. Groundwater facies classification inferred from the Piper plot shows that groundwater in the study area belongs to the Ca-SO4-Cl type and Ca-Na-SO4-Cl type. The Ca-SO4-Cl type of groundwater facies is influenced mainly by gypsum dissolution and base ion exchange, whereas the Ca-Na-SO4-Cl type is influenced by gypsum and halite dissolution. All the groundwater samples are undersaturated with respect to these two principal mineral phases. The Q-mode cluster analysis results in two main groups of groundwater samples, mainly based on the TDS content. Cluster 1 has an average TDS value of 1980 mg/l, whereas cluster 2 has an average TDS of 1176 mg/l. The groundwater facies identified through the Piper plot reflects the major hydrological processes controlling groundwater chemistry in the area and was found to be more useful in this study as compared to cluster analysis.

Salt dissolution and permeability in the Western Canada Sedimentary Basin

Extensive dissolution of evaporites has occurred in the Williston Basin, Canada, but it is unclear what effect this has had on bulk permeability. The bulk of this dissolution has occurred from the Prairie Evaporite Formation, which is predominantly halite and potash. However, minor evaporite beds and porosity infilling have also been removed from the overlying Dawson Bay and Souris River formations, which are predominantly carbonates. This study examines whether permeability values in the Dawson Bay and Souris River formations have been affected by dissolution, by analyzing 142 drillstem tests from those formations. For both the Dawson Bay and Souris River formations, the highest permeabilities were found in areas where halite dissolution had occurred. However, the mean permeabilities were not statistically different in areas of halite dissolution compared to those containing connate water. Subsequent precipitation of anhydrite is known to have clogged pore spaces and fractures in some instances. Geochemical relationships found here support this idea but there is no statistically significant relationship between anhydrite saturation and permeability. Geomechanical effects, notably closure of fractures due to collapse, could be a mitigating factor. The results indicate that coupling dissolution and precipitation to changes in permeability in regional flow models remains a significant challenge.

Physicochemical characterization of El Ouldja valley waters, in the province of Khenchela, eastern Algeria

This work has been carried out at the southern side of the Tabouant anticlinal in El Ouldja valley in the Aures, east of Algeria. The different water tables exploited belong to many lithological entities (evaporitic and carbonated). The combination of geology and statistics has allowed to study the chemistry origin of these waters. This is water of evaporitic and secondarily carbonates origin. The phenomena causing this class are numerous and are essentially linked to the aquifers chemical composition. The chemical analysis of all samples of the area confirms this. Waters salinity is very variable and generally high. Waters electrical conductivity ranges between 1504 and 6150 μS cm− 1. The extreme chemical facies are chloride–sulfate and calcium–sulfate, with a predominance of this latter. Sulfate and chloride contents can locally reach the respective values of 1100 mg/l− 1and 650 mg/l− 1. Thermodynamic analysis indicated the waters saturation with carbonates, calcite and dolomite, because of the degassing and the CO2 dissolution of evolutive formations, gypsum and halite. The crossed binary diagrams suggest that water salination might be attributed to water–rock interaction through the geochemical process of mineral dissolution, precipitation and ions exchange.

Hydrogeochemical Characterization and Quality Assessment of Groundwater in a Long-Term Reclaimed Water Irrigation Area, North China Plain

Water scarcity has led to wide use of reclaimed water for irrigation worldwide, which may threaten groundwater quality. To understand the status of groundwater in the reclaimed water irrigation area in Beijing, 87 samples from both shallow and deep aquifers were collected to determine the factors affecting groundwater chemistry and to assess groundwater quality for drinking and irrigation purposes. The results show that groundwater in both shallow and deep aquifers in the study area is weakly alkaline freshwater with hydrogeochemical faces dominated by HCO3-Na·Mg·Ca, HCO3-Mg·Ca·Na, HCO3-Ca·Na, and HCO3-Na. The chemical composition of groundwater in both shallow and deep aquifers is dominantly controlled by the dissolution of halite, gypsum, anhydrite, and silicates weathering, as well as ion exchange. Geogenic processes (rock weathering and ion exchange) are the only mechanisms controlling groundwater chemistry in deep aquifers. Besides geogenic processes, evaporation and anthropogenic activities also affect the chemistry of shallow groundwater. Quality assessment reveals that both shallow and deep groundwater are generally suitable for drinking and irrigation purposes. The quality of deep groundwater is more excellent for drinking than shallow groundwater. However, long-term use of deep groundwater for irrigation exhibits higher potential risks to deteriorate soil property due to the relative higher permeability indexes (PI). Therefore, it is recommended that deep groundwater is preferentially used for drinking and domestic purpose, and shallow groundwater for agricultural irrigation.

Hydrogeochemical evolution of groundwater in a Quaternary sediment and Cretaceous sandstone unconfined aquifer in Northwestern China

A better understanding of the hydrogeochemical evolution of groundwater in vulnerable aquifers is important for the protection of water resources. To assess groundwater chemistry, groundwater sampling was performed from different representative aquifers in 2012–2013. A Piper trilinear diagram showed that the groundwater types can be classified into Na–SO4 and Na–Cl types. Only one groundwater sample was Na–HCO3 type. The dominant cations for all samples were Na+. However, the dominant anions varied from HCO3− to SO42−, and as well Cl−. The mean total dissolved solid (TDS) content of groundwater in the region was 1889 mg/L. Thus, only 20% of groundwater samples meet Chinese drinking water standards (< 1000 mg/L). Principal component analysis (PCA) combined with hierarchical cluster analysis (HCA) and self-organizing maps (SOM) were applied for the classification of the groundwater geochemistry. The three first principal components explained 58, 20, and 16% of the variance, respectively. The first component reflects sulfate minerals (gypsum, anhydrite) and halite dissolution, and/or evaporation in the shallow aquifer. The second and third components are interpreted as carbonate rock dissolution. The reason for two factors is that the different aquifers give rise to different degree of hydrogeochemical evolution (different travel distances and travel times). Identified clusters for evolution characteristic and influencing factors were confirmed by the PCA–HCA methods. Using information from eight ion components and SOM, formation mechanisms and influencing factors for the present groundwater quality were determined.

Study on the dynamic characteristics of groundwater in the valley plain of Lhasa City

The valley plain of Lhasa City is located on the Qinghai-Tibetan Plateau, which is one of the most developed and densely populated areas in Tibet. Groundwater is an important water supply source and plays an irreplaceable role in the social and economic development of Lhasa City. This study has investigated the dynamic characteristics of groundwater in the valley plain of Lhasa City through the methods of mathematical statistics and hydrochemical analysis. The results showed that local topography, climate, and urbanization substantially influenced the groundwater dynamics. Under the combined influences from urbanization and climate, the groundwater level decreased over three time periods, but the groundwater-level configuration has not shown significant changes in over 15 years. From 1997 to 2015, the hydrochemical type of groundwater has changed from HCO3–Ca to HCO3·SO4–Ca·Mg and HCO3·SO4–Ca. The concentrations of Cl−, Mg2+, and SO42− in groundwater increased, but the concentrations of other ions were relatively stable. Water–rock interaction was the main mechanism controlling the groundwater chemistry in the study area, and it was mainly associated with the dissolution of silicate, carbonate, and halite.

Genesis of formation water in the northern sedimentary basin of South China Sea: Clues from hydrochemistry and stable isotopes (D, 18O, 37Cl and 81Br)

Formation water is an important fluid in sedimentary basins, hydrogeochemical characteristics of which has important instructions to oil and gas generation and preservation. The South China Sea (SCS) oilfield is a large oil field in China, but research on origin and evolution of formation waters in SCS oilfield has been poorly documented. In this study, major ions, as well as δ2H, δ18O, δ37Cl and δ81Br in formation waters of two basins (BBWB and ZJKB) of SCS were analyzed to fill the gap. The results showed that the chemical types of formation waters in both basins are ClNa. The relationship between Br vs major ions and 2H/18O compositions showed the origin of formation water are mainly ancient seawater. The formation waters are enriched in Ca and Sr, and depleted of Na and Mg compared with seawater mainly owing to albitization of plagioclase, whereas the dolomitization is minor. Comparing to the BBWB, the formation waters in ZJKB were more enriched in 2H and 81Br, and more depleted in 37Cl. The formation waters in ZJKB were stored in a relatively more closed environment and might have been affected more by evaporation, whereas those in BBWB might experience more influence from halite dissolution by ancient precipitation through open fracture structures.

The connection between hydrothermal fluids, mineralization, tectonics and magmatism in a continental rift setting: Fluorite Sm-Nd and hematite and carbonates U-Pb geochronology from the Rhinegraben in SW Germany

Understanding the physical basics of tectonic events, related fluid flow and ore deposition represents one of the great challenges in modern geosciences. In this contribution, Sm-Nd ages of hydrothermal fluorites and U-Pb ages of carbonates and iron oxides from unconformity-related vein type deposits in the Schwarzwald next to the Upper Rhinegraben rift in SW Germany are used to distinguish different pulses of hydrothermal fluid activity and to understand their relation to large-scale tectonics and magmatism. While the fluorites are of Early Jurassic to Oligocene age, carbonate (calcite, dolomite, siderite) and hematite dated by U-Pb small-scale isochrons records formation from Permian to Quaternary with a clear culmination in the Neogene.These new age-data in combination with microthermometry data of primary fluid inclusions from growth zones in the fluorites and carbonates are used to constrain the timing of fluid signatures. This contribution shows that the ages are correlated with changes in fluid properties and/or tectonic events in the evolving continental crust. Comparison with published thermochronological data, apparent ages of URG-related volcanic rocks and the tectono-sedimentary evolution of the Upper Rhinegraben rift show clear correlations between the intensity of hydrothermal mineralization (and, hence, the intensity of fracture-bound fluid flow) with the U-Pb carbonate ages. This method accordingly provides an excellent tool to date rift-related processes like fluid flow, ore deposition and tectonic activation or reactivation of fractures.Fluid properties changed after the deposition of Middle Triassic Muschelkalk evaporites from low salinity, high temperature (1–6 wt.% NaCleq, 200–270 °C, cooling late-metamorphic basement fluids) to high salinity, moderate temperature (20–26 wt.% (NaCl + CaCl2), 50–170 °C, mixture of a modified bittern brine (“basement brine”) with halite dissolution brine). This change led to large scale ore deposition (fluorite-barite-quartz with Pb-Zn-Cu, Bi-Co-Ni-Ag-U, Fe-Mn ores). During the Paleogene and Neogene, previously separated aquifers from various sedimentary units were connected by juxtaposition of the fluid source rocks during Rhinegraben rifting, which resulted in variable salinity and temperature fluids (1–26 wt. % (NaCl + CaCl2), 50–350 °C) by a multi-component fluid mixing process. Typical mineralization related to this shows barren or Pb-Zn-Cu veins with large amounts of barite.

Numerical Simulation of Groundwater Flow and Vulnerability in Wadi El-Natrun Depression and Vicinities, West Nile Delta, Egypt

ABSTRACT During the last 25 years, rapid and unplanned land reclamation activity has been carried out in the areas located in both south and east of Wadi El - Natrun Depression of Egypt. Accordingly, negative effects on groundwater levels and vulnerability are frequently caused by localized high levels of abstraction and the return-flow of polluted irrigation water respectively. A groundwater model is a computational method that presents an approximation of an underground water system. In this study the groundwater system is simulated both in quantity and quality by using Mass Balance Transfer Model (NETPATH), Groundwater Modeling System (GMS) and DRASTIC Model to investigate the water - rock interactions, groundwater levels drawdown and vulnerability respectively. Three main geochemical processes namely dedolomitisation, dissolution of halite and silicate weathering were estimated during the flow path. The present over-abstraction of groundwater (105.84 million m3/year) has induced a general head drawdown from 3 to 40 m in years 2015 and 2050 respectively. Best estimate using a 3D GMS hydraulic model was (157000 m3/day) a strategy proposed for the management of groundwater without critical depletion (second scenario). The results document the extent to which a high drawdown can greatly reach 4 m by the end of simulation year 2050. The vulnerability maps of groundwater were constructed using the DRASTIC index method. The results indicated that, the southeastern and central portions of the study area are having high vulnerability rate (&amp;gt; 110). Modified DRASTIC map showed many more dominant high risk areas in the eastern parts of the study area that were low risk, which may be attributed to return flow of polluted irrigation water.

A Study of Hydrogeochemical Processes on Karst Groundwater Using a Mass Balance Model in the Liulin Spring Area, North China

Exploring the hydrogeochemical processes of karst groundwater has significant meaning for protecting local groundwater systems in semi-arid areas. Taking a typical semi-arid karst groundwater system—the Liulin spring area—as the research region, hydrogeochemical processes from rainfall infiltration to formation of higher total dissolved solids (TDS) water were studied, applying a mass balance model and the prediction of water chemical components in the focus area was explored. The results showed that hydrogeochemical processes dominating chemical components of karst groundwater included lixiviation, cation exchange and mixture. Calcite dissolved during rainfall infiltration processes in recharge area and saturated, then precipitated along the whole flow path. CO2 dissolved significantly along with rainfall infiltration process and outgassed in discharge area and stagnant area. The dissolution of dolomite, gypsum and halite accompanied entire flow path and maximum dissolution load occurred in stagnant area. Mg-Na or Ca-Na exchange prevailed along flow path but exchange types depended on ionic concentration. The mixture between surface water and karst groundwater took place in surface water leakage belt in recharge and discharge area and mixture ratio for surface water ranged from 40% to 70%. TDS of the Liulin springs will increase with decreasing surface water leakage. Conversely, TDS of karst groundwater near Henggou area will decrease accompanied by the continuous discharge of the Henggou artesian well.

Sedimentology and diagenetic evolution of the Neogene ‘Intermediate Sandstone Unit’ in the halite deposits of the Granada Basin (SE Spain): the turning point in the change from marine to continental sedimentation

The Granada Basin is a small (50 × 50 km) Neogene intramontane basin located in the central part of the Betic Cordillera (Spain). In the latest Tortonian, the Granada Basin desiccated and a thick salt succession formed, encompassing three halite-bearing units: the ‘Lower Halite Unit’, the ‘Intermediate Sandstone Unit’ (ISU), and the ‘Upper Halite Unit’ (UHU). ISU deposits record the onset of marine to non-marine conditions in the Granada Basin. The main purpose of this paper is to study the environment of formation and the diagenetic evolution of the ISU salt-bearing unit, in order to assess the events leading to and resulting from the continentalization of this basin in the late Miocene. This study includes visual core descriptions, petrographic (conventional petrography and scanning electron microscopy), and geochemical (δ34S and δ18O and 87Sr/86Sr) analyses. ISU deposition took place in a coastal lake, isolated from the open sea by a sand barrier. Lake evolution was from a very shallow, hypersaline lacustrine environment to a deeper, perennial lake undergoing frequent storm-induced marine flooding and, finally, to a shallower, perennial saline lake. Isotope analyses point to a mixture of different inflow waters, including marine- and underground (hydrothermal)-water inputs for the origin of the brines. Halite dissolution occurred after flooding events and clear-halite cement was precipitated inside primary-halite dissolution cavities. Early diagenesis involves halite re-crystallisation during repetitive, dissolution–precipitation cycles, gypsum replacement by halite, halite replacement by nodular anhydrite, and framboid pyrite formation. Intermediate- to late-diagenetic processes are silica (megaquartz, chalcedony, and lutecite) replacement of halite and anhydrite, and celestine replacement. Megaquartz formation relates to sulfate-depleted, UHU percolating brines. Chalcedony and lutecite crystallization took place sometime later from sulfate-rich percolating brines, during deposition of the gypsum sequence occurring on top of the salt. Celestine, replacing lutecite, resulted from the interaction with Sr-rich underground waters (via dissolution of previously formed celestine).

Assessment of groundwater salinity using GIS and multivariate statistics in a coastal Mediterranean aquifer

The integration of the statistical approaches and GIS tools with the hydrogeological and geological contexts allowed the assessment of the processes that cause groundwater quality deterioration in the great important deltaic aquifer in the northeastern Tunisia (Medjerda Lower Valley Aquifer). The spatial variation of the groundwater parameters and the molar ratio (Cl−/Br−) were also used to determine the possible impacts from seawater intrusion and from the septic tank leachate. Sixty shallow groundwater samples were collected in 2014 and analyzed for major and trace ions over an area of about 1090 km2 to determine the suitability for drinking or agricultural purposes. The total dissolved solids (TDS) content ranges from 1005 to 19,254 mgl−1 with a mean value of 3477.18 mgl−1. The chemistry is dominated by the sodium–chloride waters (55%). Mapping of TDS, Cl−, Na+, SO42− and NO3− using kriging method shows a clear increase in salinity toward the coastline accompanied by Na+ and Cl− increase which may be related to seawater intrusion and halite dissolution. Locally, higher nitrate concentration is related to the agricultural activities inducing contribution of chemical fertilizers and irrigation with treated wastewater. The saturation indices indicate that all carbonate minerals tend to reach saturation equilibrium confirming water–rock interactions, while evaporitic minerals are still in sub-saturation state and may increase the salinity of the groundwater. The principal component analysis proves the occurrence of groundwater contamination principally by seawater intrusion in the factor I (74.15%) and secondary by an anthropogenic source in the factor II (10.35%).

Hydrogeochemical controls on brackish groundwater and its suitability for use in hydraulic fracturing: The Dockum Aquifer, Midland Basin, Texas

To better understand controls on the origin and evolution of brackish groundwater, the hydrogeochemistry of brackish groundwaters was studied within the Triassic Dockum Group across the Midland Basin in Texas. The suitability of Dockum Aquifer water for use in hydraulic fracturing fluid was examined because the area overlies the largest and most productive tight oil province in the United States. Groundwater generally flows southward and eastward across the basin. Transmissivities indicate that water yield from the Dockum Aquifer is mixed. Higher salinity (up to ∼100 g/L), group I water is found mainly in the center and western parts of the basin; chemistry of these meteoric waters is controlled by water–rock interaction with salinity increasing along its flow path via dissolution of halite and anhydrite, followed by salinity-enhanced carbonate dissolution and/or cation release from clays. Along the down-gradient basin margins, lower salinity (<7.5 g/L), group II waters of various ion compositions are more commonly found. Group II waters are also meteoric but from local recharge including downward flow from the Edwards–Trinity or other aquifers. Despite having lower salinity, the water in the down-gradient southern and eastern margins of the basin can exceed acceptable SO4 limits for cross-linked gel fluids. Generally, the majority of the water in the basin is suitable for use with slick-water hydraulic fracturing. Findings from this research provide important information on the complex controls on the chemistry of brackish groundwater and their potential beneficial uses in the oil and gas industry.

Reconstruction of a >200 Ma multi-stage “five element” Bi-Co-Ni-Fe-As-S system in the Penninic Alps, Switzerland

Hydrothermal five-element veins (Ag-Co-Ni-Bi-As) are mineral successions of native metals, encapsulated by Fe-Co-Ni arsenides and carbonates. Recent studies focused on the evolution from ordinary base-metal systems (sulfide-rich) to five-element veins (sulfide-poor) and revealed the importance of hydrocarbon-dominated fluids as essential redox agent in these systems. Although mineral successions reveal the natural subdivision into native As-, native Ag/Bi- or arsenide-dominated vein types and suggested processes explain the mineralogical variation to a certain degree, the Ni-Co-Fe-variations among the arsenides are not well understood yet.This is the first case study explaining compositional, mineralogical, and textural features of five-element veins by changing metal contents, arsenic/sulfur activities, pH and temperatures, applied to a multi-stage vein mineralization in the Penninic Alps, Switzerland. Textural relationships, mineral chemistry, fluid inclusion compositions (microthermometry and Raman spectroscopy), stable S-isotopes and in-situ U-Pb age dating of carbonates, magnetite and multi-mineral isochrons were investigated.U-Pb ages of paragenetic mineral fractions constrain a primary formation of löllingite-skutterudite-dolomite-dominated ores at 233 ± 10 Ma and niccolite-gersdorffite-skutterudite-ankerite-dominated ores at 188 ± 32 Ma, which links their formation to crustal thinning caused by the breakup of the Meliata ocean and Alpine Tethys. As secondary processes during the Alpine Orogeny, a in-situ remobilization of the ores occurred as mostly ternary Fe-Co-Ni sulfarsenides at ∼73–24 Ma due to continent-continent collision and neoformations of safflorite-cobaltite-skutterudite-dominated ores at ∼29–16 Ma due to transtensional strike-slip tectonics.Ore textures indicate that the dissolution of primary siderite, oxidation of ferrous iron and its precipitation as magnetite was the redox couple to precipitate native Bi, arsenides and sulfarsenides (Bi0, As3− and As−1) from their oxidized aqueous species Bi3+Cl4−, and As3+(OH)3 at temperatures between 200 and 300 °C. Ni and Co signatures of the arsenides/sulfarsenides show increasing mobilization from the host rocks during the successive evolution of the hydrothermal system in the Triassic, Jurassic and during the Alpine Orogeny. Stable S-isotopes and As/S signatures of the sulfarsenides indicate an increasing mobilization of host rock sulfides (i.e. fahlbands) from the primary to the secondary ores. Fluid inclusions and stable S-isotopes suggest involvement of fluid modification by water-rock interactions (i.e. cover rocks: carbonate, sulfate and halite dissolution; basement rocks: albitisation of plagioclase) during fluid descent.

Salt precipitation and dissolution in the late Quaternary Dead Sea: Evidence from chemical and δ37Cl composition of pore fluids and halites

The chemical composition and δ37Cl of pore fluids from the ICDP core drilled in the deepest floor of the terminal and hypersaline Dead Sea, and halites from the adjacent Mount Sedom salt diapir, are used to establish the dynamics of halite precipitation and dissolution during the last interglacial and glacial periods. Between ∼132 and 116 thousand years ago (ka) halites precipitated in the lake resulting in the expulsion of Na+ and Cl− from the residual solution. Over 50% of the Cl− reservoir was removed, resulting in a decrease in the Na/Cl ratio from 0.57 to 0.19. This process was accompanied by a decrease in δ37Cl values in the precipitating halites and the associated residual Cl− in the lake. The observed decrease fits a Rayleigh distillation curve with a fractionation factor of Δ(NaCl–Dead Sea solution) = +0.32‰ (±0.12) determined in the present study. This behavior implies negligible contribution of external sources of Cl− to the lake during the main peak of the last interglacial, MIS5e. Subsequently, during the last glacial (ca. 117 to 17 ka) dissolution of halite took place, the Na+ and Cl− inventory were replenished, accompanied by an increase in Na/Cl from 0.21 to 0.55 and in the δ37Cl values from −0.46‰ to −0.12‰. While the lake underwent significant dilution during that time, the decrease in salinity was somewhat suppressed by the dissolution of the halite which was mostly derived from Mount Sedom salt diapir.

Sedimentological and stratigraphic characterization of Cretaceous upper McMurray deposits in the southern Athabasca oil sands, Alberta, Canada

The Lower Cretaceous McMurray Formation located in northeastern Alberta, Canada, is host to one of the largest bitumen resources in the world. In this paper, we provide an integrated sedimentological and stratigraphic analysis of the upper McMurray member located in the Pike and Jackfish project areas (Townships 73–76 and Ranges 4–7 W4M) of the southern Athabasca oil sands. Using core data, geophysical well logs, and seismic data, two main facies associations (embayment and fluvial) are evident. The embayment deposits were likely sourced by up-dip distributary channels and are commonly expressed in the subsurface as a series of coarsening-upward parasequences. The facies expressions in core range from bioturbated mudstones to wave-rippled sandstones. Noticeable, however, is the fact that there are areas where strata within the parasequences are instead substituted with sand, inclined heterolithic stratification, and mud. These deposits, in the form of fluvial channels with brackish-water overprint, occur at three different parasequence horizons within the study area. The removal of these embayment deposits is believed to be initiated, in part, by halite dissolution of the Middle Devonian Prairie Evaporite Formation deposits during upper McMurray deposition. Notably, the halite dissolution edge on the eastern half of the study area is believed to have created a subregional shelf–slope break during upper McMurray deposition. As such, the distributary channels likely re-equilibrated themselves to the slope created by the salt dissolution edge and thus proceeded to incise into previously deposited upper McMurray parasequence and underlying middle McMurray deposits.

Formation of the chemical composition of brackish and brine groundwater in the Tuva depression and surrounding areas

Groundwater with high salinity is widespread in different climatic and geologic environments of the world. The formation of its chemical composition, however, is still debatable. The chemical composition of groundwater has been studied in 19 springs of the Tuva depression. In this area, hydrocarbonate, sulfate, and chloride waters with different cation compositions discharge. Their TDS value varies mainly from 1 to 6 g/L, reaching 315 g/L at only one locality. The chemical composition of the studied waters is reflective of the geostructural, hydrogeologic, landscape, and geochemical conditions. The main processes determining the chemical composition of the waters are their interaction with aluminosilicate minerals, dissolution of gypsum and halite, evaporation, and oxidation of sulfide minerals.

Hydrochemistry and water quality of Rewalsar Lake of Lesser Himalaya, Himachal Pradesh, India.

The present research is to study hydrochemistry and water quality of Rewalsar Lake during pre-monsoon, monsoon, and post-monsoon seasons. The Ca2+ and Na+ are observed as the dominant cations from pre- to post-monsoon season. On the other hand, HCO3- and Cl- are observed dominant anions during pre-monsoon and monsoon seasons, whereas HCO3- and SO42- during post-monsoon season. The comparison of alkaline earth metals with alkali metals and total cations (Tz+) has specified that the carbonate weathering is the dominant source of major ions in the water of lake. The HCO3- is noticed to be mainly originated from carbonate/calcareous minerals during monsoon and post-monsoon, but through silicate minerals during pre-monsoon. The SO42- in Rewalsar Lake is produced by the dissolution of calcite and dolomite etc. The alkali metals and Cl- in the lake can be attributed to the silicate weathering as well as halite dissolution and anthropogenic activities. Certain other parameters like NO3-, NH4+, F-, and Br- are mainly a result of anthropogenic activities. The alkaline earth metals are found to surpass over alkali metals, whereas weak acid (HCO3-) exceed to strong acid (SO42-). The Piper diagram has shown Ca2+-HCO3- type of water during all the seasons. The water quality index has indicated that the water quality of the lake is unsuitable for drinking from pre- to post-monsoon. Several parameters like salinity index, sodium adsorption ratio, sodium percent, residual sodium carbonate, magnesium hazard etc. have revealed the water of Rewalsar Lake as suitable for irrigation.