Mixing Of Brines Research Articles

Chemical and isotopic constraints on evolution of groundwater salinization in the coastal plain aquifer of Laizhou Bay, China

A hydrochemical-isotopic investigation of the Laizhou Bay Quaternary aquifer in north China provides new insights into the hydrodynamic and geochemical relationships between freshwater, seawater and brine at different depths in coastal sediments. Saltwater intrusion mainly occurs due to two cones of depression caused by concentrated exploitation of fresh groundwater in the south, and brine water for salt production in the north. Groundwater is characterized by hydrochemical zonation of water types (ranging from Ca-HCO3 to Na-Cl) from south to north, controlled by migration and mixing of saline water bodies with the regional groundwater. The strong adherence of the majority of ion/Cl ratios to mixing lines between freshwater and saline water end-members (brine or seawater) indicates the importance of mixing under natural and/or anthropogenic influences. Examination of the groundwater stable isotope delta O-18 and delta H-2 values (between -9.5 parts per thousand and -3.0 parts per thousand and -75 parts per thousand and -40 parts per thousand, respectively) and chloride contents (similar to 2 to 1000 meq/L) of the groundwater indicate that the saline end-member is brine rather than seawater, and most groundwater samples plot on mixing trajectories between fresh groundwater (delta O-18 of between -6.0 parts per thousand and -9.0 parts per thousand; Cl 1000 meq/L). Locally elevated Na/Cl ratios likely result from ion exchange in areas of long-term freshening. The brines, with radiocarbon activities of similar to 30 to 60 pMC likely formed during the Holocene as a result of the sequence of transgression-regression and evaporation: while deep, fresh groundwater with depleted stable isotopic values (delta O-18 = -9.7 parts per thousand and delta H-2 = -71 parts per thousand) and low radiocarbon activity (<20 pMC) was probably recharged during a cooler period in the late Pleistocene, as is common throughout northern China. An increase in the salinity and tritium concentration in some shallow groundwater sampled in the 1990s and re-sampled here indicates that intensive brine extraction has locally resulted in rapid mixing of young, fresh groundwater and saline brine. The 6180 and delta H-2 values of brines (similar to-3.0 parts per thousand and -35 parts per thousand) are much lower than that of modern seawater, which could be explained by 1) mixing of original (5180 enriched) brine that was more saline than presently observed, with fresh groundwater recharged by precipitation and/or 2) dilution of the palaeo-seawater with continental runoff prior to and/or during brine formation. The first mechanism is supported by relatively high Br/Cl molar ratios (1.7 x 10(-3)-2.5 x 10(-3)) in brine water compared with similar to 1.5 x 10(-3) in seawater, which could indicate that the brines originally reached halite saturation and were subsequently diluted with fresher groundwater over the long-term. Decreasing C-14 activities with increasing sampling depth and increasing proximity to the coastline indicate that the south coastal aquifer in Laizhou Bay is dominated by regional lateral flow, on millennial timescales. (C) 2013 Elsevier B.V. All rights reserved.

Fluid mixing forms basement-hosted Pb-Zn deposits: Insight from metal and halogen geochemistry of individual fluid inclusions

Fluid mixing across unconformities between crystalline basement and overlying sedimentary basins is commonly invoked as an efficient chemical mechanism for ore deposition, but the origin of basement brines and the process of ore formation have rarely been linked by direct evidence. Using laser ablation–inductively coupled plasma–mass spectrometry microanalysis of individual fluid inclusions with an improved detection approach for anion components, we determined simultaneously the ore metal concentrations and the Cl/Br ratio in texturally well constrained inclusion assemblages from a basement-hosted quartz-fluorite-barite-Pb-Zn vein system. An inverse correlation between the Pb + Zn concentrations and the Cl/Br mass ratios in the fluid inclusions provides clear evidence for mixing of a basement-derived metal-rich brine and a metal-poor formation water that acquired its salinity from halite dissolution in Triassic evaporites of the sedimentary cover. This mixing of two distinct brines with comparable salinity is recorded during the growth of individual quartz crystals containing small galena inclusions, demonstrating the transient and episodic nature of fluid mixing during mineral deposition.

Physicochemical and biological dynamics in a coastal Antarctic lake as it transitions from frozen to open water

AbstractPony Lake, at Cape Royds, Antarctica, is a shallow, eutrophic, coastal lake that freezes solid in the winter. Changes in Pony Lake's physicochemical parameters and microbial community were studied during the transition from ice to open water. Due to rising water temperatures, the progressive melt of the ice column and the gradual mixing of basal brines into the remaining water column, Pony Lake evolved physically and chemically over the course of the summer, thereby affecting the microbial community composition. Temperature, pH, conductivity, nutrients and major ion concentrations reached their maximum in January. Pony Lake was colonized by bacteria, viruses, phytoflagellates, ciliates, and a small number of rotifers. Primary and bacterial production were highest in mid-December (2.66 mg C l-1d-1and 30.5 μg C l-1d-1, respectively). A 16S rRNA gene analysis of the bacterioplankton revealed 34 unique sequences dominated by members of theβ- andγ-proteobacterialineages. Cluster analyses on denaturing gradient gel electrophoresis (DGGE) banding patterns and community structure indicated a shift in the dominant members of the microbial community during the transition from winter ice, to early, and late summer lakewater. Our data demonstrate that temporal changes in physicochemical parameters during the summer months determine community dynamics and mediate changes in microbial species composition.

Syndepositional Deformation Features In High-Relief Carbonate Platforms: Long-Lived Conduits for Diagenetic Fluids

Abstract Syndepositional faults and fractures are known to affect early fluid flow in carbonate platforms. Less clear is whether they are active fluid conduits throughout the entire history of the platform strata. Syndeformational fractures in Permian (late Guadalupian) carbonates exposed in Dark Canyon, Guadalupe Mountains, New Mexico, U.S.A., address this question. Transmitted-light and cathodoluminescent petrography, stable-isotope and fluid-inclusion analyses, and clumped-isotope thermometry show that there were multiple episodes of fracturing, dissolution, cementation, and replacement in the fractures. Dolomite cement or dolomitized marine cements line the walls of some fractures and indicate the syndepositional reflux of evaporated Permian seawaters through the fractures. Fine- to medium-crystalline, luminescently zoned calcite may overlie the dolomite and marine cements, line fracture walls where those phases are absent, or cement karst breccia on fracture walls. The δ18O values of this calcite (−8.8 to −14.0‰ VPDB) and clumped-isotope temperatures (16° to 32°C) indicate precipitation from meteoric fluids (δ18OSMOW of −6.2 to −10.5‰) associated with episodic sea-level lowstands during the development of high-frequency depositional sequences. The early calcites can themselves be fractured, rotated, and recemented, indicating recurrent deformation and meteoric influx. Evaporite cements were once the dominant pore-filling phase in the fractures, forming both before and after the early meteoric cements. The earliest evaporites formed during deposition of Tansill limestone, probably from the same brines that formed dolomites. Evaporites that postdate the early calcite probably did not form until Permo-Triassic burial, when geomechanical analysis indicates that the syndepositional fractures were likely reactivated and brines could have been sourced from overlying bedded evaporite. All evaporite cements subsequently were calcitized, mainly by coarse-crystalline, inclusion-rich calcites that formed from warm (59° to 96°C) fluids. Calculated fluid isotopic compositions (δ18OSMOW of −0.5 to −4.7‰) imply mixing of meteoric and oil-field brines. Carbon isotope values (+2 to −17‰) indicate microbial degradation of hydrocarbons in some of those fluids, but not all. Geomechanical analysis indicates the potential for syndepositional fractures to have failed (reactivated) during Basin and Range extension, and the warm basinal fluids are interpreted to have migrated upward through the fractures during that event. Platform-margin fractures (unassociated with faults) witnessed cooler fluids (59° to 65°C) than outer-shelf fractures (70° to 96°C) because outer-shelf faults tapped waters from greater depths. The most recent fluid flow through the fractures generated dissolution features and laminated speleogenetic calcites, which are interpreted to result from intrastratal karsting associated with exhumation and weathering. Diagenetic features in the syndepositional fractures are equivalent to those observed in the adjacent limestones, suggesting active fluid communication between matrix and fractures throughout the diagenetic history of the rocks. The complex fracture paragenesis also indicates that syndepositional fractures are not only conduits for early fluid-flow networks, but they can also impact a rock's entire diagenetic history if reactivated by changing stress fields.

The origin of sulfate mineralization and the nature of the BaSO4–SrSO4 solid-solution series in the Ain Allega and El Aguiba ore deposits, Northern Tunisia

Ain Allega and El Aguiba are among the largest barite–celestite deposits attributed to the Triassic period in Tunisia. They are located in the flysch zone on the eastern edge of the Triassic diapir of Jebel Hamra. The ore body consists of dolomite intensely brecciated and surrounded by marls, clay, gypsum and dolomite which forms the hanging wall of the deposit, and rimmed by Paleocene marls. The ore minerals show a cap-rock type mineralization with various forms and types, in particular impregnation in dolomite, breccia cement, replacement of carbonate cap-rock and open space-filling in the dissolution cavities and fractures. Ore minerals include sphalerite, galena, marcasite and pyrite. Principal gangue minerals are barite, celestite, calcite, dolomite and quartz. The ore minerals are hosted by the Triassic carbonate rocks, which show hydrothermal alteration, dissolution and brecciation.The study of barite–celestite solid-solution shows a bimodal distribution in which the composition is not continuous. Some intermediate compositions are missing; 20–80% SrSO4 for the El Aguiba ore deposit and 50–70% SrSO4 for the Ain Allega ore deposit.X-ray diffraction peaks in the BaSO4–SrSO4 series display considerable broadening at intermediate compositions. The unit cell volume varies from 346.97Å3 in barite (100% BaSO4) to 308.29Å3 in celestite (100% SrSO4). This variation in cell parameters is attributed to the degree of substitution of barium by strontium since there is less variation between ionic radii of these elements. Consequently, these substitutions caused variation in morphologies, position and d-spacing of peaks (200, 011, 113, 312,122, 112, and 111). Some barite crystals have small-scale, strontium compositional banding which suggests that the crystals responded to regular fluctuations in physiochemical conditions during deposition. The degree of supersaturation in Ba2+ and Sr2+ controls the growth mechanism and consequently the surface structure, which in turn controls the mechanism of adsorption and incorporation of minor and trace elements into the growing crystal. For a solid solution, the transitional supersaturation for different growth mechanisms can be significantly different for the two end members. One of the most interesting and intriguing phenomena observed in natural crystals of the (Ba,Sr)SO4 solid solution from this study area is the development of compositional oscillatory zoning, consisting of alternating Ba-rich and Sr-rich layers.The sulfur isotope analyses show significant variability for barite and celestite (from 16.2 to 23‰). These values are interpreted as the result of the mixing of two sulfur end-members in the mineralizing fluids, corresponding to thermochemical sulfate reduction of Messinian seawater, together with Triassic sulfate, as sulfur sources.Fluid inclusion studies of celestite show that the BaSO4–SrSO4 solid-solution in both deposits was precipitated from hot saline solution (Th=190±20°C; 16.37wt.% NaCl equivalent in Ain Allega and 8.2wt.% NaCl equivalent in El Aguiba). Consequently, the precipitation could be from mixing of basinal brines with magmatic–meteoric fluid.

Longitudinal dispersion in spiral wound RO modules and its effect on the performance of batch mode RO operations

Operation of reverse osmosis (RO) in cyclic batch mode can in principle provide both high energy efficiency and high recovery. However, one factor that causes the performance to be less than ideal is longitudinal dispersion in the RO module. At the end of the batch pressurisation phase it is necessary to purge and then refill the module. During the purge and refill phases, dispersion causes undesirable mixing of concentrated brine with less concentrated feed water, therefore increasing the salt concentration and energy usage in the subsequent pressurisation phase of the cycle. In this study, we quantify the significance of dispersion through theory and experiment. We provide an analysis that relates the energy efficiency of the batch operation to the amount of dispersion. With the help of a model based on the analysis by Taylor, dispersion is quantified according to flow rate. The model is confirmed by experiments with two types of proprietary spiral wound RO modules, using sodium chloride (NaCl) solutions of concentration 1000 to 20,000ppm. In practice the typical energy usage increases by 4% to 5.5% compared to the ideal case of zero dispersion.

Genesis of celestite – bearing cap rock formation from the Ain Allega ore deposit (northern Tunisia): contributions from microthermometric studies

Abstract The Ain Allega ore deposit represents one of the most significant Pb-Zn Sr-Ba deposits of the flysch zone in northern Tunisia. The total quantity of sulphide produced is 22,700 metric tons, with 13,300 t of galena and 9,400 t of sphalerite. It is located on the eastern edge of the Triassic diapir of the Jebel Hamra. The main ore minerals include sphalerite, galena, pyrite and marcasite, and gangue minerals including dolomite, calcite, celestite, quartz and barite. The mineralization hosted by carbonate rocks, shows some evidence of dissolution and brecciation characteristic of cap-rock formation. The fluid inclusion study from the celestite suggests that the primary and secondary monophase liquid (L) inclusions are most abundant compared to the other types. The microthermometric analyses of two-phase primary inclusions display homogenization temperatures ranging from 136 to 208°C (average of 180°C) and salinities ranging from 11.34 to 24.38 equivalent weight % NaCl (average of 16.4). The calculated density, pressure and depth are 0.965 g/cm3, 18 bars and 80 m, respectively. The hydrothermal fluid resulted from mixing of basinal brines and magmatic-meteoric solutions. Geological, mineralogical and thermometric data indicate that the Ain Allega ore deposit results of a mixing of basinal fluids (Mississippi valley type deposit) and hydrothermal fluids related to a shallow intrusion.

Halogens and noble gases in sedimentary formation waters and Zn–Pb deposits: A case study from the Lennard Shelf, Australia

Halogen ratios (Br/Cl and I/Cl) and concentrations provide important information about how sedimentary formation waters acquire their salinity, but the possible influence of organic Br derived from sedimentary wall-rocks is rarely quantified. Here, it is demonstrated that Br/Cl versus I/Cl mixing diagrams can be used to deconvolve organic Br contributions; that organic matter has a limited range of Br/I ratios; and that organic Br is a more significant component in Zn–Pb deposit ore fluids than previously recognised. The significance of these findings is illustrated for the Lennard Shelf Zn–Pb deposits of Western Australia. Fluid inclusions related to Lennard Shelf Zn–Pb mineralisation have variable salinity and hydrocarbon contents. The halogen data from these fluid inclusions require mixing of three fluid end-members: (1) an evaporated seawater bittern brine (30 wt.% NaCl equiv.) with greater than seawater Br/Cl ratio; (2) a lower salinity pore fluid (⩽5 wt.% NaCl equiv.) with moderately elevated Br/Cl and I/Cl; and (3) fluids with Br/Cl ratios of ∼5 times seawater and extremely elevated I/Cl ratios of ∼11,500 times seawater. The first two fluids have 40Ar/36Ar of 300–400 and greater than air saturated water 36Ar concentrations that are typical of fluid inclusions related to Zn–Pb mineralisation. The third ‘organic-rich’ fluid has the highest 40Ar/36Ar ratio of up to 1500 and a depleted 36Ar concentration. Mineralisation is interpreted to have resulted from mixing of Zn-rich evaporitic brines and H2S present in hydrocarbons. It is suggested that aqueous fluids acquired organic Br and I from hydrocarbons, and that hydrocarbons exsolving from the aqueous fluid removed noble gases from solution. Interaction of variably saline brines and hydrocarbons could account for the variable Br/Cl and I/Cl composition, and 36Ar concentrations, recorded by Lennard Shelf fluid inclusions. The distinct 40Ar/36Ar signature of the fluid with the highest I/Cl ratio suggests the hydrocarbons and brines were sourced independently from different parts of the sedimentary basin. These data indicate the complementary nature of halogen and noble gas analysis and provide new constraints on important mixing processes during sediment-hosted Zn–Pb mineralisation.

Multi stage flash desalination plant with brine–feed mixing and cooling

Improving the performance of Multi Stage Flash (MSF) desalination plants is a major objective in the seawater desalination industry. Fresh water production rates from MSF plants depend on the evaporation range defined as the difference between the top brine temperature (TBT) and the bottom stage temperature. Lowering the temperature of the plant bottom stage elongates the evaporation range and increases the yield. A modified multi stage flash plant with brine mixing and cooling (MSF-MC) is presented in this paper. Part of the brine leaving the plant is mixed with fresh seawater feed then cooled to low temperature before it enters the bottom stage feed heater. This MSF-MC features several advantages such as expanded evaporation range at the conventional TBT levels, reduced feed pumping power, moderate levels of chemical treatment requirements and fixed fresh water production rates independent of seasonal seawater conditions. Operating with low feed mass fraction minimizes the cooling load and reduces the cooler size. An improvement in the yield by 1.18%–1.4% for every 1 °C reduction in the plant bottom temperature can be achieved with MSF-MC compared to conventional MSF systems.

Environmental research on brine discharge optimization: A case study approach

Desalination plants constitute a new way of solving the shortage and degradation of Mediterranean hydric resources by providing a new source of water supply according to local demand, and, at the same time, being climatically independent. Since all desalination plants are located on the shoreline, environmental constraints have to do with water intake and sea outfall discharges. As for brine discharging, a wide range of case-study research is being carried out in order to solve technical uncertainties and provide our projects with preventive measures. The first of these case studies regards the prediction of brine discharge behaviour by using a reduced scale model to simulate the way it is likely to perform in a harbour. The second case-study deals with mixing brine with a thermal effluent in a pipeline to obtain a better dilution that might then minimize its impact on the area. The third case-study is aimed at protecting marine biodiversity by studying into the effects of salinity increase on the growth and survival of the seagrass Cymodocea nodosa.

Downward penetration and mixing of sedimentary brines and dilute hot waters at 5 km depth in the granite basement at Soultz-sous-Forêts (Rhine graben, France)

Fluids trapped in granite microfissures around 5 km depth in the GPK2 drilling from the European Hot Dry Rock (HDR) Energy program at Soultz-sous-Forêts, can be related to the rather recent (post-Oligocene) fluid flow due to the rifting of the Rhine graben. Most of fluid inclusions planes were healed by fluids similar to those trapped in hydrothermal quartz veins from the shallower levels of the granite. The fluid inclusion dataset indicates a model of mixing between a sedimentary brine rich in divalent cations (around 20 wt.% eq. NaCl) and a dilute fluid slightly hotter than the brine, and characterized by a temperature close to the present-day measured temperature. The penetration of brines down to 5 km is significant, as well as the lack of homogenization of the reservoir fluids, i.e., each fluid is characterized by a specific salinity in between the two fluid end-members.

Helium isotopic ratios in fluid inclusions from fluorite-rich Mississippi Valley-Type district of Asturias, northern Spain

Helium isotopes have been measured in fluorite and sulphides from fluorite-rich Mississippi Valley-type (MVT) deposits from Asturias, Spain, in order to assess the involvement of mantle and crust-derived volatiles in the genesis of the deposits. The 3He/4He of the ore fluids are ≤0.1 Ra ruling out a contribution of mantle-derived magmatic helium in the inclusion fluids. Data support a crustal source for the volatiles and is consistent with the existing basinal model for the genesis of the Asturias MVT mineralization by mixing of sedimentary brines with infiltrating superficial fluids.

Application of salinity gradient power for brines disposal and energy utilisation

Disposal of high saline brines is a common and important problem in many industrial plants. These waste streams may be generated in large volumes in many different industries. It is well known that these concentrated brines cannot be desalted by using the conventional desalination technologies due to two crucial factors which are; cost and reliability. Moreover, these factors have limited the scope of choice of other desalination processes for such applications. Hence this paper is aimed at providing an ideal disposal method that is economically and technically capable of producing energy by mixing and then disposing of high saline brines into a large body of water, with least harm to the environment. In this paper, various concepts in the utilisation of salinity gradient power are discussed to highlight what kind of methods are being proposed around the world for the energy exploitation, and also several novel ideas were addressed in this study to present the possibilities of implementing the osmotic power plants as a dual purpose plant (power plus disposal). In addition, the paper shows the results of the mathematical calculations for the amount of energy that can be generated by mixing high saline brines (with a TDS of 100,000 ppm up to 250,000 ppm) and different sources of water. These calculations have been performed for mixing of high saline brines with: river water (with an average TDS of 300 ppm), Normal Ocean seawater (35,000 ppm), Arabian Gulf seawater (46,000 ppm) and municipal wastewater (10,000 ppm). When mixing 1 km3 of concentrated brine (100,000 ppm) with 1 km3 of river water at 25°C, 1.6 kWh of energy can be generated, whilst for 1 km3 of concentrated brine (250,000 ppm) with 1 km3 of river water, 4.03 kWh is generated. This amount of energy becomes greater by increasing the volume ratio. For Normal Ocean seawater the results show that the maximum and minimum energies available (at a volume ratio of 1) are 2.15 and 0.38 kWh, respectively, for the mixing of seawater with concentrated brines of 250,000 and 100,000 ppm. While the maximum and minimum energy available decreased to 1.82 and 0.24 kWh, respectively if the concentrated brines of 250,000 and 100,000 ppm are mixed with the Arabian Gulf seawater. The amount of energy available when mixing the concentrated brines and municipal wastewater have also been determined, and the results show that the maximum and minimum amount of energy available (at a volume ratio of 1) are 3.24 and 1.01 kWh, respectively at brine concentrations of 250,000 and 100,000 ppm. Hence the advantages and also the theoretical results proved that the osmotic power plant might be competitive with other brine disposal processes, because the outcome would render several benefits including; utilisation of alternative energy, a significant amount of energy available can be generated, safe disposal, and the energy produced is completely renewable and sustainable, clean, and green since it does not produce CO2 or other significant effluents that may interfere with the natural climate.

Fault/fracture controlled hydrothermal dolomitization and associated diagenesis of the Upper Devonian Jean Marie Member (Redknife Formation) in the July Lake area of northeastern British Columbia

Abstract The Jean Marie in the July Lake area of northeastern British Columbia consists of mainly limestones and partially dolomitized limestones, with variable dolomite content and porosity of dissolutional origin. Pure dolostones occur as metre-thick bodies, at the very top of the Jean Marie in only a few wells. Dolomite also occurs as a selective replacement of internal sediment infilling fractures. This mode of occurrence, as well as the patchy distribution of pure dolostones at the very top of the Jean Marie, suggests that matrix replacement dolomites formed from fluids that were delivered from flow through a vertical, or near-vertical, fault-conduit system, rather than from fluids that were delivered from flow laterally through matrix pores in a stratal-controlled system. Later mineral phases, including (in paragenetic order) saddle dolomite cement, sphalerite, dickite and barite, are also interpreted as part of the fault/fracture controlled system of diagenesis. The homogenization temperatures of saddle dolomite range from 80°C to 163°C and those of sphalerite and barite, collectively, from 55°C to 126°C, with a broad range of calculated salinities for all these phases ranging from approximately 9.0 to 27.0 wt.% NaCl + CaCl2 equivalent. The wide range of salinities for these phases is interpreted to be from the mixing of evaporative brines with less saline formation waters away from the fault/fracture conduits. The δ13C and δ18O values for a combined set of matrix replacement dolomites and saddle dolomites fall along a covariant linear trend, suggesting both phases formed from fluids with similar isotopic compositions. Using the oxygen isotopic composition calculated for fluids from which saddle dolomite formed (+0.7‰L SMOW), crystallization temperatures for matrix replacement dolomites of approximately 80°C to 100°C were calculated from the range of δ18O values. The range of crystallization temperatures for both matrix replacement dolomites and saddle dolomites far exceeds the ambient formation temperature at the time of dolomitization or dolomite cementation, estimated to be no higher than 50°C to 60°C. Thus, the formation of both matrix replacement dolomites and saddle dolomite cements conforms to the standard for inferring a hydrothermal origin. The estimated range of ambient formation temperatures suggests an interval of hydrothermal diagenesis possibly starting as early as latest Devonian and continuing into the early Mississippian, at burial depths no deeper than approximately 900 m. The parent fluids for the hydrothermal phase are interpreted to be residual evaporitic brines. During latest Devonian to early Mississippian time, heated brines flowed up through fault-controlled conduits, bypassing approximately 850 m of overlying shale and basinal limestone, into the Jean Marie Member until the flow was impeded by the overlying impermeable shales of the informal upper member of the Redknife Formation. The brines then moved laterally into permeable limestones with grain-support matrices of the upper transgressive-regressive (T-R) cycle of the Jean Marie. This resulted in the formation of scattered metre-thick dolostones at the top of the Jean Marie, and the partial dolomitization of limestones away from the faults.

Geochemical characteristics of the fluids and muds from two southern Taiwan mud volcanoes: Implications for water–sediment interaction and groundwater arsenic enrichment

Abstract Mud volcanoes distributed in the southern part of Taiwan are believed to be sourced from an accretionary prism located along the collision boundary between the Philippine Sea plate and the Asian Continental plate. Fluid and mud samples have been collected from Wushanting and Hsiaokunshui mud volcanoes during October 2004, March and June 2005, and analyzed for major ions, trace elements, and stable isotopes. The results show that the mud volcano fluids are enriched in Na + and Cl − but are depleted in Ca 2+ and Mg 2+ . The chemical composition and oxidation state of the fluids fluctuate seasonally, with ionic contents being notably higher during the dry pre-monsoon period. The enriched ionic (e.g., Na + , NH 4 + , K + , Mg 2+ and Cl − ) compositions of the exchangeable fractions indicate that the muds were sourced from a marine depositional environment. δD and δ 18 O values indicate that the mud volcano fluids may have been modified by chemical exchange with 18 O-rich crustal rocks and possibly originated from mixing of deep brines with circulating meteoric water. The spatial and temporal distribution of ions in the muds suggests a varied mixing regime within the mud volcanoes. Incubation study of the muds shows the leaching of soluble salts under aerobic conditions, which is generally consistent with the fluid geochemical characteristics. Moreover, elevated trace element (e.g., As, Zn, Cu and Mn) concentrations are also observed in the fluids and muds. Geochemical correlations between As, Zn and Cu in the muds suggest prevailing SO 4 -reducing conditions at depth. The relatively low Eh values (range: −50 to −30 mV) of the fluids near the surface would favor bacterial Fe reduction and mobilization of As. The dewatering of mud volcanoes may represent a significant source of groundwater As in the nearby Chianan plain.

Hydrogeochemical Modeling for Natural Analogue Study of CO2 Leakage due to Matsushiro Earthquake Swarm

Abstract For natural analogue study of CO2 leakage, the Matsushiro field in central Japan was selected to investigate hydrogeochemical behavior due to CO2 leakage from a fault zone during the period of the Matsushiro Earthquake Swarm between 1965 and 1967. One of the main objectives of the modeling study is to understand effects of hydrogeological characteristics of shallow aquifers and seal mechanism due to mineral precipitation in a fault zone. Reactive geochemical transport simulations were carried out using TOUGHREACT. Based on the historical data including discharge rate, chemical composition of water and seismic activity, we developed a numerical model to reproduce the geochemical behavior during and after the swarm earthquakes. A two-dimensional model (2000 m×1800 m) for the fault zone using the Multiple Interacting Continua (MINC) method was set up to evaluate geochemical effects during degassing and mixing of brine upwelling along the fault zone. The simulation results can capture the observed trend at the Matsushiro field. Supercritical and gaseous CO2 occur in the deep and the shallow fracture zones, respectively. During the earthquake swarm, CO2 saturated brine moves up along the fracture zone and CO2 degassing occurs in the shallow zone. Subsequently, water pH increases and a small amount of calcite precipitates. Lateral groundwater flow in shallow aquifers, which transports the CO2 away from the fault zone, makes CO2 surface discharge small. At the same time, calcite dissolves after the swarm due to lateral fresh water recharge. The result is consistent with the fact that no calcite observed in the core from the 80 m borehole drilled during the course of this study, indicating that CO2 discharge is likely affected by lateral shallow groundwater flow. Measurements of surface CO2 flux and soil gas δ 13 C indicated that little seepage of CO2 occurs in the area of the fan deposits at present, 40 years after the earthquake swarm. Using the same model, long term leakage simulations (if supercritical CO2 leaked along fault zone from the storage reservoir) were carried out to test whether CO2 surface leakage occurs or not. Two simulations were performed, with CO2 upflow rates of 50,000 and 100,000 kg/year in an area of 25 m×25 m. CO2 surface leakage does not occur in the first case, while CO2 leakage occurs in the second case. CO2 surface leakage is reduced because CO2 dissolves in groundwater flowing laterally in shallow aquifer. These simulations indicate that it is important to understand hydrogeological characteristics of aquifers underlain by reservoir as well as cap rocks.

Post-Early Cretaceous Mississippi Valley-type Zn-Pb Mineralization in the Bongara Area, Northern Peru: Fluid Evolution and Paleo Flow from Fluid Inclusion Evidence

The Bongara area, northern Peru, contains Zn-Pb mineralization with characteristics typical of Mississippi Valley-type (MVT) systems. The northwest–southeast-trending late Triassic–Jurassic carbonate host rocks of the Pucara Group were locally replaced by early (D1) and late (D2) dolomite. Fluid inclusion microthermometric data from dolomite and sphalerite are typical of MVT ore fluids (78° to 187°C; ~15–23 wt.% CaCl 2 equivalent), and do not show apparent covariation between temperature and salinity. Homogenization temperature data from D1 and D2 dolomite show a decrease from northern (mean Th = 138°C) to central (mean Th = 126°C) to southern areas (mean Th = 102°C), suggesting fluid flow from north to south. Assuming a geothermal gradient of ~30°C/km and an average surface temperature of ~20°C, the lower temperature limits might approximate the ambient host-rock temperatures, whereas the upper temperature limits may represent minimum temperatures of a deeper aquifer, probably at a maximum depth of ~6000 m. The lower temperature limits are also similar to the estimated temperatures if dolomitization and mineralization took place in the Late Cretaceous at ~2000–3000 m depth, probably during the formation of the Peruvian fold and thrust belt near the present day Peru–Ecuador border. Fluid inclusion data show that the fluids in each studied location had relatively uniform temperatures and salinities during dolomitization and mineralization. A significant salinity drop and a slight temperature decrease are observed during late calcite precipitation, suggesting mixing of brines with dilute, cooler fluids.

Post-Early Cretaceous Mississippi Valley-type Zn-Pb Mineralization in the Bongara Area, Northern Peru: Fluid Evolution and Paleo Flow from Fluid Inclusion Evidence

Research Article| January 01, 2009 Post-Early Cretaceous Mississippi Valley-type Zn-Pb Mineralization in the Bongara Area, Northern Peru: Fluid Evolution and Paleo Flow from Fluid Inclusion Evidence N.I. Basuki; N.I. Basuki † 1F. Gordon Smith Fluid Inclusion Lab., Department of Geology, University of Toronto, 22 Russell St., Toronto, Ontario M5S 3B1. *Present address: Department of Geology, Institut Teknologi Bandung (ITB), Ganesha 10, Bandung 40132, Jawa Barat, Indonesia. †Corresponding Author: E-mail: basuki@gc.itb.ac.id Search for other works by this author on: GSW Google Scholar E.T.C. Spooner E.T.C. Spooner 1F. Gordon Smith Fluid Inclusion Lab., Department of Geology, University of Toronto, 22 Russell St., Toronto, Ontario M5S 3B1. Search for other works by this author on: GSW Google Scholar Exploration and Mining Geology (2009) 18 (1-4): 25–39. https://doi.org/10.2113/gsemg.18.1-4.25 Article history received: 05 Nov 2007 accepted: 19 Apr 2009 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation N.I. Basuki, E.T.C. Spooner; Post-Early Cretaceous Mississippi Valley-type Zn-Pb Mineralization in the Bongara Area, Northern Peru: Fluid Evolution and Paleo Flow from Fluid Inclusion Evidence. Exploration and Mining Geology 2009;; 18 (1-4): 25–39. doi: https://doi.org/10.2113/gsemg.18.1-4.25 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyExploration and Mining Geology Search Advanced Search Abstract The Bongara area, northern Peru, contains Zn-Pb mineralization with characteristics typical of Mississippi Valley-type (MVT) systems. The northwest–southeast-trending late Triassic–Jurassic carbonate host rocks of the Pucará Group were locally replaced by early (D1) and late (D2) dolomite. Fluid inclusion microthermometric data from dolomite and sphalerite are typical of MVT ore fluids (78° to 187°C; ~15–23 wt.% CaCl2 equivalent), and do not show apparent covariation between temperature and salinity.Homogenization temperature data from D1 and D2 dolomite show a decrease from northern (mean Th = 138°C) to central (mean Th = 126°C) to southern areas (mean Th = 102°C), suggesting fluid flow from north to south. Assuming a geothermal gradient of ~30°C/km and an average surface temperature of ~20°C, the lower temperature limits might approximate the ambient host-rock temperatures, whereas the upper temperature limits may represent minimum temperatures of a deeper aquifer, probably at a maximum depth of ~6000 m. The lower temperature limits are also similar to the estimated temperatures if dolomitization and mineralization took place in the Late Cretaceous at ~2000–3000 m depth, probably during the formation of the Peruvian fold and thrust belt near the present day Peru–Ecuador border.Fluid inclusion data show that the fluids in each studied location had relatively uniform temperatures and salinities during dolomitization and mineralization. A significant salinity drop and a slight temperature decrease are observed during late calcite precipitation, suggesting mixing of brines with dilute, cooler fluids. You do not currently have access to this article.

Dedolomitization and calcite cementation in the Middle Devonian Winnipegosis Formation in Central Saskatchewan, Canada

AbstractLimestone consisting of finely to medium crystalline calcite mosaics is present in the upper part of the Winnipegosis Formation on the east‐central margin of the Elk Point Basin where the overlying Prairie Evaporite deposits have been removed. This type of crystalline limestone is interpreted as dedolomite, based on petrographic observations. The δ18O and δ13C values of the Winnipegosis dedolomite vary from −12·8‰ to −11·9‰ VPDB (Vienna Pee Dee Belemnite) and from −0·5‰ to +1·7‰ VPDB, respectively; both values are significantly lower than those for the corresponding dolomite. The 87Sr/86Sr ratios of the dedolomite are significantly higher, between 0·7082 and 0·7087. The spatial distribution and geochemical data of the Winnipegosis dedolomite suggest that dedolomitization was related to an influx of fresh groundwater and dissolution of the Prairie Evaporite anhydrite during the latest Mississippian to the Early Cretaceous when the basin was subjected to uplift and erosion. The Winnipegosis dedolomite displays a series of replacement fabrics showing progressive calcitization of dolomite, including the occurrence of dedolomite restricted along fractures and adjacent areas, dolomite patches ‘floating’ in the dedolomite masses and massive dedolomite with sparsely scattered dolomite relicts. However, the characteristic fabrics resulting from dedolomitization documented in the literature have not been observed in the Winnipegosis dedolomite. Coarsely to very coarsely crystalline, subhedral to euhedral calcite cement is restricted in the dedolomite. The petrographic features, isotopic compositions and homogenization temperatures, coupled with the burial history of the Winnipegosis Formation, constrain the precipitation of the calcite cement from a mixing of basinal brines and fresh groundwater during Late Cretaceous to Neogene time. The more negative C‐isotopic signatures of the calcite cement (−5·3‰ to −2·3‰ VPDB) probably reflect a hydrocarbon‐derived carbon.

Regional stratigraphy and distribution of epigenetic stratabound celestine, fluorite, barite and Pb–Zn deposits in the MVT province of northeastern Mexico

Northeastern Mexico hosts numerous epigenetic stratabound carbonate-hosted low-temperature hydrothermal deposits of celestine, fluorite, barite and zinc-lead, which formed by replacement of Mesozoic evaporites or carbonate rocks. Such deposits can be permissively catalogued as Mississippi Valley-type (MVT) deposits. The deposits studied in the state of Coahuila are associated with granitic and metasedimentary basement highs (horsts) marginal or central to the Mesozoic Sabinas Basin. These horsts controlled the stratigraphy of the Mesozoic basins and subsequently influenced the Laramide structural pattern. The Sabinas Basin consists of ~6,000-m-thick Jurassic to Cretaceous siliciclastic, carbonate and evaporitic series. The MVT deposits are mostly in Barremian and in Aptian-Albian to Cenomanian formations and likely formed from basinal brines that were mobilized during the Laramide orogeny, although earlier diagenetic replacement of evaporite layers (barite and celestine deposits) and lining of paleokarstic cavities in reef carbonates (Zn–Pb deposits) is observed. Fluid inclusion microthermometry and isotopic studies suggest ore formation due to mixing of basinal brines and meteoric water. Homogenization temperatures of fluid inclusions range from 45°C to 210°C; salinities range from 0 to 26 wt.% NaCl equiv., and some inclusions contain hydrocarbons or bitumen. Sulfur isotope data suggest that most of the sulfur in barite and celestine is derived from Barremian to Cenomanian evaporites. Regional geology and a compilation of metallogenic features define the new MVT province of northeastern Mexico, which comprises most of the state of Coahuila and portions of the neighboring states of Nuevo Leon, Durango and, perhaps extends into Zacatecas and southern Texas. This province exhibits a regional metal zonation, with celestine deposits to the south, fluorite deposits to the north and barite and Zn–Pb deposits mostly in the central part.