Ca Cl Brines Research Articles

Application of hierarchical cluster analysis and principal component analysis to identify compositional trends of brine in crystalline basements and sedimentary basins

The present study identifies distinct geochemical signatures of deep brines originating from crystalline basements and sedimentary basins. A corresponding conceptual hydrogeochemical model is developed outlining the evolution of crystalline and sedimentary brines. The combined application of Hierarchical Cluster Analysis and Principal Component Analysis allowed the identification of evolutionary trends of groundwater towards crystalline and sedimentary brines. Using 308 brine samples from the existing literature, eight chemical species were considered in the analysis: sodium, magnesium, potassium, calcium, strontium, chlorine, sulfate, and bromine, from which two salinity evolution pathways towards common Ca–Cl brines were derived: (1) the evolution of crystalline brines, which evolved from recharge water to brine through hydration of silicates, is described by the linear equation Ca = −1610 + 0.4*Cl; and (2) the evolution of sedimentary brines, which evolved from recharge water to brine through dissolution and precipitation of halite, is described by the linear equation Cl/Br = 103 + Na/Br. We also discuss differences in water isotopes, and in lithium and boron concentrations which directly reflect various temperature-dependent processes that control the evolution of sedimentary and crystalline brines. This leads to development of a discriminatory graphical tool using B/Br and Li/Br ratios, with crystalline brines having B/Br and Li/Br ratios below 0.01 and sedimentary brines above 0.01. Our results improve our understanding of deep crustal brine evolution through brine-rock interaction.

Brine formation in cold desert, shallow groundwater systems: Antarctic Ca-Cl brine chemistry controlled by cation exchange, microclimate, and organic matter

Groundwater in the McMurdo Dry Valleys of Antarctica is commonly enriched in calcium and chloride, in contrast to surface and groundwater in temperate regions, where calcium chemistry is largely controlled by the dissolution of carbonates and sulfates. These Antarctic Ca-Cl brines have extremely low freezing points, which leads to moist soil conditions that persist unfrozen and resist evaporation, even in cold, arid conditions. Several hypotheses exist to explain these unusual excess-calcium solutions, including salt deliquescence and differential salt mobility and cation exchange. Although the cation exchange mechanism was shown to explain the chemistry of pore waters in permafrost cores from several meters depth, it has not been evaluated for near-surface groundwater and wetland features (water tracks) in which excess-calcium pore-water solutions are common. Here, we use soluble salt and exchangeable cation concentrations to determine whether excess calcium is present in water-track brines and if cation exchange could be responsible for calcium enrichment in these cold desert groundwaters. We show that calcium enrichment by cation exchange is not occurring universally across the McMurdo Dry Valleys. Instead, evidence of the present-day formation of Ca-Cl−rich brines by cation exchange is focused in a geographically specific location in Taylor Valley, with hydrological position, microclimate, soil depth, and organic matter influencing the spatial extent of cation exchange reactions. Up-valley sites may be too cold and dry for widespread exchange, and warm and wet coastal sites are interpreted to host sediments whose exchange reactions have already gone to completion. We argue that exchangeable cation ratios can be used as a signature of past freeze-concentration of brines and exchange reactions, and thus could be considered a geochemical proxy for past groundwater presence in planetary permafrost settings. Correlations between water-track organic matter, fine sediment concentration, and cation exchange capacity suggest that water tracks may be sites of enhanced biogeochemical cycling in cold desert soils and serve as a model for predicting how active layers in the Antarctic will participate in biogeochemical cycling during periods of future thaw.

Source and genesis of Ca-Cl type brines in Qaidam Basin, Qinghai-Tibetan Plateau: evidence from hydrochemistry as well as B and Li isotopes

Ca-Cl brine is a highly mineralized special water body occurring in oceanic ridges or basins. The deep part of the western Qaidam Basin is rich in Ca-Cl brine, which is essential for the formation of (MgSO4-deficient) potash deposits. Previous studies on this type of brine in the Qaidam Basin focused on its source tracing, but different carriers led to different conclusions. Moreover, the genesis of Ca-Cl brines in inland basins still remains unclear. In essence, a solid understanding of the relatively abundant Ca sources for the formation of Ca-Cl brines in inland basins has not been reached. In addition, a metallogenic model for this type of brine has not yet been established. Through hydrochemical analysis as well as Band Li isotope tracing, this study clarified that the main elements (Na and Cl) in these Ca-Cl brines mainly originated from the dissolution of existing evaporites in the inner basin. Further, trace elements in Ca-Cl brines (such as Band Li) mainly originated from lixiviation; atmospheric rainfall infiltrated and interacted with ore-rich mother rocks along the basin-margin fracture system under suitable temperature-pressure conditions; alternatively, they may have originated from mixing with magmatic hydrothermal fluids. This study showed that Ca-Cl brines in the western part of the Qaidam Basin have a typical “binary structure” in terms of their sources. In addition, the sources of Ca in Ca-Cl brines were further discussed based on B and Li isotope data, thus exploring a new genesis of Ca-Cl brines in inland basins. Finally, by integrating the above findings, an ore-forming model of this type of water body in the western part of the Qaidam Basin is proposed. This study is valuable for understanding the genesis mechanism of Ca-Cl brines in inland basins, and also has practical significance for the prediction, exploration, and evaluation of this type of brine resource.

Lithium Prospectivity in the Northeast German and Thuringian Ba-sins

Over the years many boreholes have been drilled into the Northeast German Basin (NEGB) in pursuit of the exploration of hydrocarbons. As well as gaining important information regarding petrophysical and geophysical data, legacy boreholes also provide information regarding total dissolved solids in formation water, which sometimes includes lithium concentrations. With the rapid increase in demand for electric vehicles in combination with EU net-zero targets, lithium is a vital component of the future of the energy industry as it transitions away from fossil fuel dependence.
 So, where can we find lithium, how much of it is there, and where does it come from? After extracting lithium content data from formation water trace element data, we can answer two of these questions. The data gathered [1] is from boreholes drilled in the NEGB (in the states of Brandenburg, Mecklenburg-Vorpommern, and Sachsen-Anhalt) and the Thuringian Basin. The Northeast German Basin makes up the eastern part of the North German Basin, which, in turn, is part of the Southern Permian Basin. It is located between the Baltic Shield to the north and the Variscan belt to the south [2]. The basin contains up to 12km of Phanerozoic strata [2], the evolution of which began with Late Carboniferous/Early Permian (Stephanian/Autunian) volcanism [3, 4, 5, 6]. In the NEGB increased concentrations of lithium can be found within the Zechstein Staßfurt Carbonate (Ca2) and the Rotliegend. In Brandenburg the highest values of 230 mg/L can be found in the geothermal well doublet Groß Schönebeck which was drilled into sedimentary Rotliegend and Permo-Carboniferous volcanics. Comparable values (190 mg/L) can be found in formation water samples of the Ca2 in the well Lübben 103. In Mecklenburg-Vorpommern, lithium contents of 600 mg/L were encountered in the Rotliegend of the well Gristow 7, with lithium contents in the Ca2 of the nearby well Gristow 6h2 reaching 300 mg/L. The Reinkenhagen field (which targeted the hydrocarbons of the Ca2) has several wells which exhibit lithium contents in the Ca2 of up to 140 mg/L. In Sachsen-Anhalt elevated lithium values are limited to the Ca2. The Fallstein field, originally drilled for the exploration of hydrocarbons, encountered lithium contents of up to 189 mg/L. Spatial distribution of the lithium data can be seen in Figure 1 along with current geothermal projects. Also displayed are areas of proven and suspected geothermal potential.
 The Thuringian Basin is located between the Harz Mountains and the Thuringian Forest Mountains, the formation of which was part of the intramontane sudsidence zone of the Variscan mountains [7]. The trough shaped sedimentation area of the basin was formed in the early Mesozoic [8]. In Thuringia, as in Sachsen-Anhalt, elevated lithium values are limited to the Ca2. The fields of Kirchheilingen, Langensalza, and Mühlhausen all have multiple wells which show lithium contents of up to 200 mg/L.
 The source of lithium in formation water is not well understood and therefore cannot be clearly defined. A case study in Thurinigia focusing on Zechstein salts in Gorleben and Morlseben made the assumption that lithium content in the salt brines were leached from phyllosilicate bearing units (T4, A3, Ca3, T3) in the Zechstein [9]. Other sources discussed include relict metamorphic brines and organic compounds. A different study focusing on Rotliegend Ca-Cl brines in the
 North German Basin found that brines rich in lithium originated from the leaching of lithium rich mica in the Lower Rotliegend (volcanics) [10]. If lithium accumulation in formation waters is related to Permo/Carboniferous rocks, it is possible that deep faults may have acted as conduits for lithium rich brines to migrate into overlying formations [11]. This may be a plausible theory as this dataset shows that elevated lithium contents in the Ca2 can be found within the carbonate margin facies in areas through which major faults run. This is especially evident on the northern basin margin.
 Ultimately the data compiled from both basins will be used to perform a lithium in place analysis.

Sr isotope and major ion compositional evidence for formation of Qarhan Salt Lake, western China

Qarhan Salt Lake (QSL) is the largest potash brine deposit in the continental Qaidam Basin (QB) of western China. The origins of the Qarhan brines, whether from migration of Qaidam mega-paleolakes, paleoriver capture, or mixing of modern river water and Ca-Cl spring water, are controversial. Details about the origin (hydrothermal, diagenetic or both) of the Ca-Cl inflow waters entering QSL in the QB are unclear. Here we show from the strontium (Sr) isotope ratios of river waters, intercrystalline brines, spring waters, halite, gypsum, and Corbicula shells from Qarhan playa, that 87Sr/86Sr increases from Bieletan (western QSL) to Huobuxun (eastern QSL). This trend verifies that river water-spring water mixing has been operating at QSL for the past 50,000 years. Contributions of Ca-Cl inflow waters to the QB have profoundly influenced the brine evolution and mineralogy of salt deposits. Mixing between low Sr2+ concentration, low 87Sr/86Sr value of river waters and high Sr2+ concentration, high 87Sr/86Sr value of Ca-Cl spring inflow waters has produced various intercrystalline brines and salt deposits at QSL. Ca-Cl inflow waters and brines are enriched in Sr2+ and Ca2+ and depleted in Mg2+ and SO42−. These characteristics suggest brine-sedimentary rock (silicate) interactions at burial diagenetic or hydrothermal conditions. Ca-Cl inflow waters and brines have a similar Sr isotopic range as oilfield brines and celestite deposits in the QB, which also suggests a diagenetic-hydrothermal origin. Ca-Cl brines discharge as springs or seeps along fault zones in the QB. They are interpreted to reach the surface of the northern margin of Qarhan playa by topographically driven circulation.

Formation of Rotliegend Ca-Cl brines in the North German Basin compared to analogues in the geological record

The formation of terrestrial Ca-Cl brines is controlled by two major processes: chemical reactions between halite brines and igneous and metamorphic rocks and/or their debris in sedimentary basins, and the abstraction of H2O by evaporation, freezing or formation of hydrous minerals. Albitization dominates in environments of low H2O activity, i.e., halite saturated systems. Chloritization, serpentinization and formation of smectites seems to be related to less saline systems, i.e., enhanced water activity.The Rotliegend brines of the North German Basin evolved by interaction of infiltrating halite brines with volcanic debris of the Permian acid volcanic rocks by albitization and chloritization of plagioclase. At present their temperatures are between 130 and 150°C at 3000–4000m depth. Although they developed in a different environment they chemically and isotopically resemble the basinal brines from the Mississippi Salt Dome basin or even the deep brines from the Red Sea. All these brines have in common that halite brines interacted with plagioclase (An+SiO2+2Na+⇔2Alb+Ca2+) or possibly with clay minerals (Ca-clay+2Na+⇔Na2-clay+Ca2+) at enhanced temperatures. The trends of stable isotopes show slopes in the δD-δ18O diagram which are typical for hydrothermal reactions of evaporation brines with rock or sediments. The genesis of Rotliegend brines differ from Ca-Cl brines in the Canadian Shield, Siberian Platform, the Dry Valleys in Antarctica and even the local brines from the Chilean salars and the Californian Bristol Dry Lake. The Antarctic Dry Valley brines seem to be dominated by melting of ice-cements of their permafrost sections. The Ca-Cl brines of springs in the Chilean salars and the Bristol Dry Lake ascend due to thermal convection along tectonic faults. Although the Canadian Shield brines chemically resemble those of the Siberian Platform their stable isotope fractionation suggest that they developed by different processes of water abstraction. Exotic stable isotope values in brines are gained by freezing or ultrafiltration processes in the precursor sediments of the present crystalline rocks of the Canadian Shield and by small volume ratios of liquids and metamorphic rocks such as of KTB/VB.

The effect of Na–Ca–Cl brines on the dissolution of arsenic from arsenopyrite under geologic carbon dioxide storage conditions

Arsenopyrite (FeAsS) is one of the most common mineral sources of arsenic in rocks, sediments, and ores. The dissolution of arsenopyrite releases arsenic, which has potential implications for human and environmental health. With carbon dioxide storage in saline, sedimentary geologic formations being an important component of mitigation strategies for global warming, the effect of injected CO2 mixed with anoxic brines on dissolution of arsenic from arsenopyrite merits examination. Arsenopyrite dissolution was studied using anoxic Na–Ca–Cl brines in the presence and absence of CO2, at both ambient and high temperature and pressure conditions. Results revealed that the dissolution rate of arsenic ranged from 10−10 to 10−12mol/m2s, with an average dissolution rate of 10–10.7±0.2mol/m2s in the absence of CO2. Understanding effects of particular brine constituents on arsenopyrite dissolution requires further investigation, however. The observed arsenopyrite dissolution rates under anoxic conditions are about two orders of magnitude lower than those observed under oxidizing conditions. The presence of dissolved CO2 in brines resulted in dissolution rates marginally lower than those observed in the absence of CO2, with an average dissolution rate of 10–11.2±0.5mol/m2s, even though a reduction in pH to approximately 3.5 was observed. Increase in temperature and pressure from 25°C to 60°C, and 1bar to 100bars respectively, increased As dissolution rate from arsenopyrite by 1logunit.

Paragenesis of fluids under evaporates in the Volga-Ural Basin

To unravel the mystery of the relationship between evaporates, Ca–Cl brines and accumulations of oil and N2 in the basins of ancient cratons, their N2, CH4 and He concentration ratios, as well as the isotopic composition (δ15N, δ13C and 3He/4He) were compared within the Volga-Ural basin. The study allowed subsalt fluids from Volga-Ural Basin to divide into two genetic groups. The first one is found within the basin's platform area. It includes Ca–Cl brines, high-viscosity heavy oil, bitumen and N2, which has concentrations higher than that of CH4 and positive values of δ15N. The second one is tied to the edge of the platform, the Ural Foredeep and Peri-Caspian Depression. In this group, only the oil and gas reservoirs, which have more CH4 than N2, and possibly negative values of δ15N, were discovered. Interaction of gas components in compared fluids indicates great role of degassing in the formation of their composition. It is suggested that the fluids of the first group (N2 > CH4) is what remains, and the second group (N2 < CH4) is what is disappears from the rocks during their metamorphism and degassing.

Hydrochemical characteristics and controlling factors for waters’ chemical composition in the Tarim Basin, Western China

This paper covers the chemical and isotopic composition of river water, groundwater from wells (15–25m), saline spring water and stagnant surface water providing evidence for controlling factors of water composition and water evolution process in the Tarim Basin, Xinjiang, western China. Analytical data for major and minor ions of totaling 537 water samples were obtained from both years of teamwork and old reference materials. It is found that the ion background value ratio SO4/Cl for river water (2.75) of the Tarim Basin is two times higher than that of the Qaidam Basin (0.88) and 18 times higher than seawater (0.14); K/Cl of these two basins (0.06 and 0.07) are all two times higher than seawater (0.02). This reveals that material sources of Lop Nur are relatively richer in potassium and sulfate, while poorer in chloride. Gradual changes of stable isotopic compositions in waters clearly indicate the effect of evaporation on water evolution of the basin. Besides evaporation and weathering of surrounding rocks, wide distribution of chloride type water, which commonly exist in saline springs/brines and seldom exist in other waters, indicates that hydrothermal Ca–Cl brines discharged from deep within the earth join water evolution of the basin.

Messinian Ca–Cl Brines from Mediterranean Basins: Tracing Diagenetic Effects by Ca/Mg Versus Ca/Sr Diagram

In natural resource exploration, Ca–Cl basinal brines are important for understanding the origin and spatial and temporal distribution of hydrocarbons and sedimentary ore deposits. Little attention has been paid to the possible connection between fossil basinal brines and paleo-seawaters and to the implications for reconstructing paleo-seawater compositions. Secular variations of Ca/Mg and Ca/Sr ratios in seawater have been documented mainly using fluid inclusions in halite, calcareous fossils and mineral analyses. However, brines and other sedimentary records connected to paleo-seawater or its evaporated residues may be chemically affected by burial diagenesis or the effects of continental waters of meteoric origin, thus complicating interpretations of the analytical results. To investigate these effects on fluids and minerals related to the Messinian salinity crisis of the Mediterranean basin, we re-evaluate published data from: (1) brackish-to-brine waters from onshore (Northern Apennine foredeep; Levantine basin) and offshore (porewaters from the Deep Sea Drilling Project); (2) Messinian parental seawater deduced from calcareous fossils, fluid inclusions and sulfate minerals; (3) meteoric waters dissolving evaporites. The compositional trends related to seawater evaporation, diagenesis and mixing that affect the Ca/Mg and Ca/Sr molar ratios of the basinal brines are effectively discriminated on a binary plot depicting the proper fields for seawater and meteoric-derived fluids. Brines showing stronger dolomitization start from Ca/Mg and Ca/Sr molar ratios of Messinian seawater deduced from the published analysis of fluid inclusions and open ocean fossils, that are therefore here validated ex post.

Don Juan Pond, Antarctica: Near-surface CaCl2-brine feeding Earth's most saline lake and implications for Mars

The discovery on Mars of recurring slope lineae (RSL), thought to represent seasonal brines, has sparked interest in analogous environments on Earth. We report on new studies of Don Juan Pond (DJP), which exists at the upper limit of ephemeral water in the McMurdo Dry Valleys (MDV) of Antarctica, and is adjacent to several steep-sloped water tracks, the closest analog for RSL. The source of DJP has been interpreted to be deep groundwater. We present time-lapse data and meteorological measurements that confirm deliquescence within the DJP watershed and show that this, together with small amounts of meltwater, are capable of generating brines that control summertime water levels. Groundwater input was not observed. In addition to providing an analog for RSL formation, CaCl2 brines and chloride deposits in basins may provide clues to the origin of ancient chloride deposits on Mars dating from the transition period from “warm/wet” to “cold/dry” climates.

Closed Basin Brine Evolution and the Influence of Ca–Cl Inflow Waters: Death Valley and Bristol Dry Lake California, Qaidam Basin, China, and Salar de Atacama, Chile

Diagenetic-hydrothermal brines, here called “hydrothermal Ca–Cl brines,” have compositions that reflect interactions between groundwaters and rocks or sediments at elevated temperatures. Hydrothermal Ca–Cl brines reach the surface by convection-driven or topographically driven circulation, and discharge as springs or seeps along fault zones to become important inflow waters in many tectonically active closed basins. Case studies from (1) Qaidam Basin, China, (2) Death Valley, California, (3) Salar de Atacama, Chile, and (4) Bristol Dry Lake, California illustrate that hydrothermal Ca–Cl inflow waters have influenced brine evolution in terms of major ion chemistries and mineral precipitation sequences. All four basins are tectonically active; three (Death Valley, Salar de Atacama, and Qaidam Basin) have well-documented Ca–Cl spring inflow and Holocene faulting. Bristol Dry Lake has young volcanic deposits and Salar de Atacama has an active stratovolcano on its eastern margin, indicating subsurface magma bodies. A midcrustal magma chamber has been identified in southern Death Valley. Volcanism and faulting in these closed basins provides the heat source for hydrothermal-diagenetic processes and the energy and pathways to deliver these waters to the surface.

Deep reaching fluid flow in the North East German Basin: origin and processes of groundwater salinisation

Major element chemistry, rare-earth element distribution, and H and O isotopes are conjointly used to study the sources of salinisation and interaquifer flow of saline groundwater in the North East German Basin. Chemical analyses from hydrocarbon exploration campaigns showed evidence of the existence of two different groups of brines: halite and halite Ca–Cl brines. Residual brines and leachates are identified by Br−/Cl− ratios. Most of the brines are dissolution brines of Permian evaporites. New analyses show that the pattern of rare-earth elements and yttrium (REY) are closely linked to H and O isotope distribution. Thermal brines from deep wells and artesian wells indicate isotopically evaporated brines, which chemically interacted with their aquifer environment. Isotopes and rare-earth element patterns prove that cross flow exists, especially in the post-Rupelian aquifer. However, even at depths exceeding 2,000 m, interaquifer flow takes place. The rare-earth element pattern and H and O isotopes identify locally ascending brines. A large-scale lateral groundwater flow has to be assumed because all pre-Rupelian aquifer systems to a depth of at least 500 m are isotopically characterised by Recent or Pleistocene recharge conditions.

Geochemistry and stable isotopic signatures, including chlorine and bromine isotopes, of the deep groundwaters of the Siberian Platform, Russia

The chemical composition and the isotopic characteristics of formation waters from the Siberian Platform are presented. The study involved samples of formation brines from depths ranging from 100 to ∼4000 m at five different sites covering a large area of the Siberian Platform. Four water types were identified. The two main water types that were found are: (1) Ca–Cl brines that are believed to be the residual of an evaporated paleoseawater; and (2) Na–Cl brines that are derived mainly from halite dissolution. The origin of a third group of highly saline samples was not determined. However, the chemical and isotopic characteristics of this group of samples suggest that they were produced by various complex scenarios such as metamorphism, water–rock interaction, permafrost freezing and mixing. The last group of samples represents fresh and brackish waters across the area. A wide range for the natural variation of Br stable isotopes (between −0.80‰ and +3.35‰) was found. The δ 81Br results obtained during this study indicate that Br stable isotopes can have large natural variations and that different evolutionary processes affecting water chemistry may cause significant fractionation.

Chemical evolution of saline waters in the Jordan-Dead Sea transform and in adjoining areas

The Ca–Mg relationship in groundwaters strongly points to the overall dolomitization and local albitization. The Mg/Ca ratios reveal two trends by which saline waters develop: increase of Mg/Ca ratio by evaporation and decreasing Mg/Ca ratios due to dolomitization and albitization. Br/Cl vs. Na/Cl ratios demonstrate that albitization does not play a major role which leaves dolomitization to be the main source for decreasing Mg/Ca ratios in saline waters. In the eastern and southern Region of Lake Kinneret, salinization occurs by mixing with a Ca/Mg molar ratio 1 dominates, which developed by the albitization of plagioclase in abundant mafic volcanics and the dolomitization of limestones. The most saline groundwater of the Tabgha-, Fuliya-, and Tiberias clusters could be regional derivatives of at least two mother brines: in diluted form one is represented by Ha’On water, the other is a Na-rich brine of the Zemah type. Additionally, a deep-seated Ca-dominant brine may ascend along the fractures on the western side of Lake Kinneret, which is absent on the eastern side. Groundwaters of the Lower Jordan Valley are chemically different on both sides of the Jordan River, indicating that the exchange of water is insignificant. All saline waters from the Dead Sea and its surroundings represent a complex mixture of brines, and precipitation and local dissolution of halite and gypsum. Many wells of the Arava/Araba Valley pump groundwater from the Upper Cretaceous limestone aquifer, the origin of the water is actually from the Lower Cretaceous Kurnub Group sandstones. Groundwater drawn from the Quaternary alluvial fill either originates from Kurnub Group sandstones (Eilat 108, Yaalon 117) or from altered limestones of the Judea Group. The origin of these waters is from floods flowing through wadis incised into calcareous formations of the Judea Group. On the other hand, as a result of step-faulting, hydraulic contact is locally established between the Kurnub- and the Judea Groups aquifers facilitating the inter-aquifer flow of the confined Kurnub paleowater into the karstic formations of the Judea Group. Two periods of Neogene brine formation are considered: the post-Messinan inland lagoon resulting in drying up of the Sdom Sea and the evaporation of the Pleistocene Samra Lake, which went further through the stage of Lake Lisan to the present Dead Sea. For the first period, major element hydrochemistry suggests that the saline waters and brines in the Jordan-Dead Sea–Arava Valley transform evolved from the gradual evaporation of an accumulating mixture of sea-, ground-, and surface water. Due to the precipitation of carbonates, gypsum, and halite, such an evaporating primary water body was strongly enriched in Mg, Br, and B and shows high molar ratios of Br/Cl, B/Cl, and Mg/Ca but low Na/Cl ratios. The development of the Br/Cl ratio is chemically modelled, showing that indeed brine development is explicable that way. Along with the evaporation brine, evaporites formed which are leached by infiltrating fresh water yielding secondary brines with Na/Cl ratios of 1. When primary brines infiltrated the sub-surface, they were subjected to Mg–Ca exchange in limestones (dolomitization) and to chloritization and albitization in basic igneous rocks turning them into Ca-Cl brines. These tertiary brines are omnipresent in the Rift. The brines of the late Lisan and Dead Sea were generated by evaporating drainage waters, which leached halite, gypsum, and carbonates from the soil and from the sub-surface. All these brines are still being flushed out by meteoric water, resulting in saline groundwaters. This flushing is regionally enhanced by intensive groundwater exploitation. In variable proportions, the Neogene and late Lisan Lake and Recent Dead Sea brines have to be considered as the most serious sources of salinization of groundwaters in the Rift. Deep-seated pre-Sdom brines cannot strictly be excluded, but if active they play a negligible role only.

Brittle tectonics and pore-fluid conditions in the evolution of the Great Boundary Fault around Chittaurgarh, Northwestern India

This paper aims at reconstructing paleostress history and deciphering the pore-fluid pressure conditions during the reactivation of a regional-scale fault. Paleostress analyses of the mesoscopic structures suggest that three successive events of reactivation on the Great Boundary Fault occurred in thrust-type, strike-slip type and thrust-type tectonic-settings, respectively. Whereas the pore-fluid pressure was supralithostatic during the first and third events of reactivation, it was sublithostatic during the second event. Each event of reactivation induced a fluid pressure gradient, which resulted in the focused and enhanced flow of syntectonic fluids within the high permeability locales, primarily fractures and faults. Fluid inclusion study on strike-slip veins reveals that the syntectonic fluids were highly dense, Na–Ca–Cl brines of formational water origin. Stratigraphic evidence in favour of a 2-km-thick column of overburden above Kaimur sandstone beds implies that the strike-slip faulting occurred at 160–202 °C temperature and 53 MPa pressure. Variation in homogenization temperature reflects fluctuation in pore-fluid pressure during entrapment of syntectonic fluids and points to seismic pumping as a possible mechanism of fluid flow during faulting. High paleogeothermal gradient, obtained by fluid inclusion data, is ascribed to the high heat flow due to crustal stretching during the Proterozoic rifting, the basal and intermittent volcanism in the basin, and occurrence of Berach granite as the basement.

Hydrothermal fluid flow models of stratiform ore genesis in the McArthur Basin, Northern Territory, Australia

AbstractThis paper explores the role of basin‐scale fluid migration in stratiform Pb–Zn ore formation in the southern McArthur Basin, Australia. Mathematical models are presented for coupled brine migration and heat transport in the basin. The models account for: (i) topographically driven flow (forced convection) during periods when parts of the McArthur Basin were subaerial and elevated above the central Batten Fault Zone; (ii) density‐driven flow (free convection) during periods when the basin was mostly submarine; and (iii) transient flows associated with fault rupture during periods of transpression. These hydrologic models help to compare and contrast a variety of hypotheses concerning deep fluid migration and the origin of base metal ores in the McArthur Basin. The numerical results exhibit a strong structural control on fluid flow caused by the north‐trending fault systems that characterize the Batten Fault Zone. As a result, fluids descend to depths of a few kilometers along the western side, migrate laterally to the east through the clastic and volcanic aquifers of the upper Tawallah and lowest McArthur Groups, and then ascend along the eastern side of the fault zone. This recharge–discharge pattern dominates all of the hydrogeologic models. The basin‐wide flow pattern suggests that Na–Ca–Cl brines acquired base metals in the deepest levels of the basin stratigraphy as the fluids migrated eastwards through the aquifer system. Upward flow was relatively rapid along the Emu Fault Zone, so much so that fluid temperatures likely approached 130°C in the muddy sediments near the sea floor due to upward flow and venting at the HYC (‘Here’s Your Chance'). Transient pulses of flow characterized periods of transpressional stress and subsequent faulting may have punctuated the basin history. Large‐scale free convection, however, characterized notably long periods of diagenesis and ore mineralization during the Proterozoic in the McArthur Basin.

Brines in the Carboniferous Sydney Coalfield, Atlantic Canada

Formation waters within Upper Carboniferous sandstones in the sub-sea Prince and Phalen coal mines, Nova Scotia, originated as residual evaporative fluids, probably during the precipitation of Windsor Group (Lower Carboniferous) salts which underlie the coal measures. Salinity varies from 7800 to 176,000 mg/l, and the waters are Na–Ca–Cl brines enriched in Ca, Sr and Br and depleted in Na, K, Mg and SO 4 relative to the seawater evaporation curve. Br:Cl and Na:Cl ratios suggest that the brine composition corresponds to an evaporation ratio of as much as 30. The brines lie close to the meteoric line on H/O isotopic plots but with a compositional range of δ 18O from −4.18 to −6.99 and of δD from −42.4 to −23.5, distant from modern meteoric or ocean water. Mine water composition contrasts with that of nearby salt-spring brines, which are inferred to have originated through dissolution of Windsor Group evaporites by modern meteoric waters. However, a contribution to the mine waters from halite dissolution and from Br in organic matter cannot be ruled out. Present concentrations of several elements in the brines can be explained by water–rock interaction. The original Windsor brines probably moved up into the overlying coal-measure sandstones along faults, prior to the Late Triassic. The high salinity and irregular salinity distribution in the Phalen sandstones suggests that the brines have undergone only modest dilution and are virtually immobile. In contrast, Prince waters show a progressive increase in salinity with depth and are inferred to have mixed with surface waters. Basinal brines from which these modern formation fluids were derived may have been important agents in base-metal and Ba mineralisation from the mid-Carboniferous onwards, as saline fluid inclusions are common in Zn–Pb sulphide deposits in the region.

Geochemical processes affecting meltwater chemistry and the formation of saline ponds in the Victoria Valley and Bull Pass region, Antarctica

Major ion, trace element and nutrient concentrations have been determined in meltwater streams, frozen lakes and isolated saline ponds of the Victoria Valley and Bull Pass regions in Victoria Land, Antarctica. Geochemical processes affecting glacial meltwater composition with time and distance from the source glaciers include solute acquisition by soil salt leaching and solute concentrations by evaporation. Evaporation in the marginal lake melt and in isolated saline ponds appears to increase the Mg/Ca ratio of these meltwaters relative to that of meltwater streams. With progressive evaporation gypsum and calcite may precipitate, leading to the development of Na-Cl and Na-HCO3 brine ponds. These ponds may be vertically stratified with respect to temperature and salinity if they experience partial or complete freezing over the winter season. The chemical characteristics and nutrient concentrations of meltwaters in the Victoria Valley are similar to those of other drainage systems in the region, although the Ca-Cl brines reported from the Wright Valley immediately to the south were not observed. Trace element (Cu, Pb, Zn, Cd, Mn and Fe) concentrations measured in the lakes and large ponds do not show any evidence of unusual enrichment in the drainage.

Trace-metal behaviour in oxic and anoxic CaCl brines of the Wright Valley drainage, Antarctica

Geochemical speciation and reaction path models have been used to identify the major factors controlling Mn, Fe, Cu, Pb, Zn, Ni and Co concentrations in meltwaters and CaCl brines of the closed-basin Wright Valley drainage system in Antarctica. The major aqueous features of this drainage system are: (a) the Onyx River, a meltwater stream; (b) Lake Vanda, an ice-covered stratified lake in which CaCl brines become more concentrated and ultimately anoxic with depth; and (c) Don Juan Pond, a small, highly saline CaCl brine pond. Trace-metal concentrations in the groundwater have been estimated and used to derive hypothetical concentrations for trace metals in the ancient brine pool from which Lake Vanda was formed. The results of this calculation support the premise that the trace-metal distribution profiles observed in Lake Vanda are attributable to the influx of trace metals from the Onyx River and to modern, ongoing lake processes. In the Onyx River and in the oxic CaCl brines of Lake Vanda and Don Juan Pond, trace-metal concentrations appear to be consistently controlled by adsorption and desorption from the surface of particulate Fe-oxides or Fe-hydroxides. Variations in the trace-metal concentrations measured in the oxic brines can be directly related to the effect of changes in pH and major-ion chemistry on the adsorption of each metal at the Fe-oxide surface. For the Onyx River and Lake Vanda, this hypothesis is presented as modification to the currently accepted model (Green et al., 1989) which postulates Cu and Ni adsorption onto particulate Mn-oxide. In the anoxic, H 2S-bearing CaCl brines at the base of Lake Vanda, Cu, Pb, Zn, Ni, Co and Fe concentrations appear to be limited by precipitation of metal-sulphide mineral phases and by the stability of metal-bisulphide and -polysulphide complex species. Mn is relatively mobile in the anoxic brine, but Mn concentrations may be limited by precipitation of a Mn-carbonate phase.