diversity of iron and silica precipitation by microbial mats in hydrothermal waters iceland implications for precambrian iron formations direct examination of microbial mats from icelandic hot springs with transmission electron microscopy and energy dispersive x ray spectroscopy revealed a consortium of bacterial cells in varying stages of mineralization differences in observed mineralogy largelyreflectdifferencesinthechemistryofthehydrothermalwaters silica richspheroids formedepicellularlyoncellwallsandsurroundingsheathsandcapsulesofmicroorganisms and insomecases intracellularlywhenpresumablythecell s hadlysed commonly these precipitateswereobservedcoalescingtoformamatrixofamorphoussilicathatcompletely encapsulated the cells and or replaced their cytoplasmic material however in other cells the precipitates were composed of amorphous granules made exclusively of iron and silica inapproximatelyequalproportions atonelocality thebacteriaformedseveralepicellular iron minerals ranging from iron mineralized capsules tofine grained spheroids of amorphous ferric hydroxide and acicular aggregates of goethite the complete encrustation of bacterial cells by silica iron or a combination of both may greatly enhance their preservation potential such that these mineralized microorganisms may conceivably represent future microfossils thus we may be witnessing contemporaneous biomineralization processes that are similar to those of the geologic past particularly with regard to the origin of some precambrian banded iron formations

carbonate control of h2 and ch4 production in serpentinization systems at elevated p ts 1 serpentinization of forsteritic olivine results in the inorganic synthesis of molecular hydrogen h 2 in ultramafic hydrothermal systems e g mid ocean ridge and forearc environments inorganic carbon in those hydrothermal systems may react with h 2 to produce methane ch 4 and other hydrocarbons or react with dissolved metal ions to form carbonate minerals here we report serpentinization experiments at 200 c and 300 bar demonstrating fe 2 being incorporated into carbonates more rapidly than fe 2 oxidation and concomitant h 2 formation leading to diminished yields of h 2 and h 2 dependent ch 4 in addition carbonate formation is temporally fast in carbonate oversaturated fluids our results demonstrate that carbonate chemistry ultimately modulates the abiotic synthesis of both h 2 and ch 4 in hydrothermal ultramafic systems and that ultramafic systems present great potential for co 2 mineral sequestration

hydrochemistry to delineate groundwater flow conditions in the mogher al mer area damascus basin southwestern syria the hydrochemistry of groundwater from the mogher al mer area located in southwestern syria has been used as a tool to identify and assess the hydrogeological systems and associated conditions in this arid region of syria groundwater is considered as the main source of water supply for both drinking and irrigation purposes the detailed description of hydrogeochemical conditions including major ions physico chemical and in situ field parameters has underlined the very complex variability of the stratigraphic sequences and hence the numerous hydrogeological units within the study area on the one hand groundwater chemical signature is found to be mainly controlled by the water rock interaction processes in the mountainous western part of the study area on the other hand anthropogenic influences are observed in the eastern plain in terms of recharge mechanisms the region can be considered as a part of a main intermediate or even regional flow system instead of a local one

kinetics of biotite dissolution and fe behavior under low o2 conditions and their implications for precambrian weathering abstract biotite dissolution experiments were carried out to better understand the dissolution kinetics and fe behavior under low o 2 conditions and to give an insight into the precambrian weathering mineral dissolution with a continuous flow through reactor was employed at 25 c for up to 65 days varying partial pressure of atmospheric oxygen p o 2 ph 6 86 and 3 01 and fe content in mineral 1 06 and 0 11 mol of fe per o 10 oh f 2 for biotite and phlogopite respectively independently for the examination of their effects on biotite dissolution low p o 2 conditions were achieved in a newly developed glove box p o 2 6 10 4 atm referred to as anoxic conditions which was compared to the present ambient air conditions 0 2 atm of p o 2 oxic conditions the biotite dissolution rate was slightly faster under anoxic conditions at ph 6 86 while it was not affected by p o 2 at ph 3 01 there was no direct effect of fe content on dissolution rate at ph 6 86 while there was a small difference in dissolution rate between biotite and phlogopite at ph 3 01 the 1 5 order of magnitude faster release rate of fe under anoxic conditions for biotite dissolution at ph 6 86 resulted from the difference in ratio of fe 3 precipitates remaining in the reactor to fe dissolved about 60 and 100 under anoxic and oxic conditions respectively which is caused mainly by the difference in p o 2 the results infer that the fe 2 and fe 3 contents in the paleoproterozoic paleosols fossil weathering profiles are reflected by atmospheric oxygen levels at the time of weathering

experimental evaluation of in situ co2 water rock reactions during co2 injection in basaltic rocks implications for geological co2 sequestration 1 deep aquifers are potential long term storage sites for anthropogenic co2 emissions the retention time and environmental safety of the injected co2 depend on geologic and physical factors and on the chemical reactions between the co2 the aquifer water and the host rocks the ph buffer capacity of the aquifer water and the acid neutralization potential of the host rocks are important factors for the permanent stabilization of the injected co2 mafic rocks such as basalt which primarily consists of ca mg silicate minerals have a high acid neutralization capacity by providing alkaline earth elements that form stable carbonate minerals the carbonate minerals formed thus sequester co2 in a chemically stable and environmentally benign form in this study we present results from a small scale co2 injection test in mafic and metasedimentary rocks the injection test was conducted using a single well push pull test strategy co2 saturated water ph 3 5 was injected into a hydraulically isolated and permeable aquifer interval to study the acid neutralization capacity of ca mg silicate rocks and to estimate in situ cation release rates release rates for ca mg and na were calculated by use of solute compositions of water samples retrieved after the co2 injection the incubation time of the injected solution within the aquifer and geometric estimates of the reactive surface area of the host rocks our results confirm rapid acid neutralization rates and water rock reactions sufficient for safe and permanent storage of co2 carbonic acid was neutralized within hours of injection into a permeable mafic aquifer by two processes mixing between the injected solution and the aquifer water and water rock reactions calculated cation release rates decrease with increasing ph that is confirmed by laboratory based experiments large differences between release rates obtained from the field and laboratory experiments may be mainly due to uncertainties in the estimation of the reactive surface area in the field experiment and in hydrological and geological factors our results underscore the importance of defining bulk rock dissolution rates under in situ conditions in order to evaluate target formations for permanent mineral sequestration of carbon dioxide

thermodynamic constraints on mineral carbonation of serpentinized peridotite abstract carbonation of serpentinite appears to be a promising process to mitigate rising concentrations of atmospheric co2 however given that chemical affinities of mineral carbonation reactions in serpentinized peridotite change drastically with temperature protolith and the activities of dissolved constituents this process is incompletely understood in this report numerical models are used to investigate the heterogeneous phase equilibria and the speciation of intergranular fluids during mineral carbonation of serpentinite dunite at 100 200 300 and 400 c the results suggest that temperature dependent activity gradients of both aqueous carbon dioxide aco2 aq and aqueous silica asio2 aq determine the carbonation potential of serpentinite at low to moderate temperatures there is ample thermodynamic driving force for the carbonation of serpentinite as the gradients in asio2 aq and aco2 aq set between talc quartz magnesite and serpentine brucite equilibria are steepest with increasing temperature these activity gradients become smaller because the stability fields of brucite serpentine and talc expand toward higher aco2 aq and asio2 aq while the stability field of magnesite contracts in addition the enhanced solubility of quartz toward higher temperatures shifts the talc quartz magnesite equilibrium to very high aco2 aq field observations of carbonated serpentinite reveal a rather simple sequence of arrested carbonation reactions which is typically fossilized as spatially distinct metasomatic zones a zone of serpentinized peridotite is followed by a zone of serpentine carbonate then talc carbonate and finally quartz carbonate our modeling results not only reproduce these observations they also suggest that complete carbonation is favored at low to moderate temperatures since complete carbonation of serpentinite is achieved at relatively small fluid to rock ratios at temperatures 200 c prolonged fluid influx at low temperatures can result in decarbonation and silicification of the altered rock in contrast at temperatures 200 c decarbonation and silicification reactions are unlikely even at very high fluid to rock ratios since serpentinized peridotite is highly reactive in the presence of co2 aq its widespread exposure at slow and ultraslow spreading mid ocean ridges may represent a significant sink for co2 in the global carbon cycle our modeling results can be used to evaluate fluid rock interactions in active or fossil mineral carbonation systems if the mineralogy is known and the temperature of formation can be constrained independently the asio2 aq aco2aq oxygen fugacity fo2 g and ph can be estimated in turn if the alteration temperature asio2 aq and aco2 aq are known governing phase equilibria can be approximated the latter is a promising tool to monitor the reaction progress during co2 sequestration into serpentinized peridotite

the dissolution of high feo olivine rock from the lovasjarvi intrusion se finland at 25 c as a function of ph the high feo olivine rich rock from the lovasjarvi intrusion 65 olivine 20 plagioclase 8 magnetite 4 pyroxene and 3 serpentine has been proposed as a potential redox active backfill additive in deep high level nuclear waste repositories in this work the authors report on kinetic dissolution studies of this solid under different ph and redox conditions performed by using a flow through methodology assuming that silicon is mainly released to solution from the olivine contained in the solid the experimental results have been adjusted to an empirical rate law as a function of proton concentration the proton concentration reaction orders agree with results found in the literature for both acidic and alkaline ph ranges the calculations conducted with the reactive transport code retraso show that at alkaline ph the olivine rock might have a lower redox buffer capacity than expected

carbonation of ca bearing silicates the case of wollastonite experimental investigations and kinetic modeling abstract carbonation reactions of wollastonite have been investigated in experiments conducted at conditions relevant to geologic co 2 sequestration in subsurface environments t 90 c and pco 2 25 mpa experiments were performed in batch reactors on single mineral powders of selected grain size either in supercritical co 2 or in aqueous solutions with different alkalinities the main reaction products were calcite and amorphous silica calcite occurred either as a compact continuous coating of small crystals in the case of supercritical co 2 and in circum neutral ph aqueous solutions or as isolated larger crystals in acidic aqueous solutions measured extents of carbonation were faster in aqueous solutions than in supercritical co 2 extents of carbonation in aqueous acidic solutions were modelled using a geochemical code incorporating kinetic parameters for wollastonite dissolution and calcite precipitation taken from the literature comparison with experimental results shows that in aqueous solutions wollastonite dissolution is the rate limiting step of the carbonation reaction and that silica layers have only a minor passivation effect on the overall reaction rate in acidic solutions secondary calcite coating has only a minor effect on carbonation extent whereas the experimental data in circum neutral ph aqueous solutions are consistent with dissolution rates inhibited by the observed dense calcite coating a geochemical code incorporating a modified reactive surface model successfully accounted for this passivation effect the more efficient carbonation in acidic than in circum neutral ph solutions is thus ascribed to differences in microstructures of the secondary calcite layers due to differences in supersaturation states of calcite when its precipitation begins inhibitory effects of dense calcite coating are also invoked for limiting carbonation extents of wollastonite in supercritical co 2 secondary calcite precipitations are thus shown to play a major role both as coatings of reactive surfaces and by maintaining large undersaturation with respect to wollastonite dissolution

isotopic and geochemical evolution of ground and surface waters in a karst dominated geological setting a case study from belize central america abstract analysis of stable isotopes and major ions in groundwater and surface waters in belize central america was carried out to identify processes that may affect drinking water quality belize has a subtropical rainforest savannah climate with a varied landscape composed predominantly of carbonate rocks and clastic sediments stable oxygen 18 o and hydrogen d isotope ratios for surface and groundwater have a similar range and show high d excess 10 40 8 the high d excess in water samples suggest secondary continental vapor flux mixing with incoming vapor from the caribbean sea model calculations indicate that moisture derived from continental evaporation contributes 13 to overhead vapor load in surface and groundwater concentrations of dissolved inorganic carbon dic ranged from 5 4 to 112 9 mg c l and 13 c dic ranged from 7 4 to 17 4 so 4 2 ca 2 and mg 2 in the water samples ranged from 2 163 2 6593 and 2 90 mg l respectively the dic and 13 c dic indicate both open and closed system carbonate evolution combined 13 c dic and ca 2 mg 2 and so 4 2 suggest additional groundwater evolution by gypsum dissolution and calcite precipitation the high so 4 2 content of some water samples indicates regional geologic control on water quality similarity in the range of 18 o d and 13 c dic for surface waters and groundwater used for drinking water supply is probably due to high hydraulic conductivities of the karstic aquifers the results of this study indicate rapid recharge of groundwater aquifers groundwater influence on surface water chemistry and the potential of surface water to impact groundwater quality and vise versa

hydrochemical indications of human impact on karst groundwater in a subtropical karst area chongqing china the application of combined isotopic and hydrochemical compositions may be useful for evaluating water quality problems in karst aquifers in which it is difficult to distinguish the sources of solutes from the natural background of those due to human activities multiple isotopes 13c dic 34s so4 2 and chemical parameters were measured in rainwater groundwater and sewage in order to elucidate the solute sources and impacts from human activities and natural background in the laolongdong karst catchment in chongqing municipality sw china overall the dissolution of carbonate rock controls ca2 mg2 and hco3 content in rainwater and karst groundwater so4 2 originated mainly from gypsum dissolution in karst groundwater carbonate rocks in the studied site could be dissolved jointly by h2co3 from the natural co2 h2o reaction and other acids organic acids and hno3 from sewage and soils sewage discharge from urban areas and agriculture activities lead to the increase of no3 po4 3 and cl in karst groundwater to protect and sustainably utilize the karst aquifer sewage originating from urban areas must be controlled and treated and the use of fertilizer should be limited

geochemical and isotopic characterization of groundwater from shallow and deep limestone aquifers system of aleppo basin north syria stable isotopes 18o 2h and 13c and radioactivity 3h 14c have been used in conjunction with chemical data to evaluate the processes generating the chemical composition reconstruct the origin of the water and groundwater residence time the aleppo basin is comprised of two main limestone aquifers the first one is unconfined of paleogene age and the second is confined of upper cretaceous age the chemical data indicate that the dissolution of minerals and evaporation are the main processes controlling groundwater mineralization the groundwater from the two aquifers is characterized by distinctive stable isotope signatures this difference in water isotopes is interpreted in terms of difference origin and recharge period fresh and brackish shallow groundwater were mostly recharged during the holocene period the presence of 3h in several groundwater samples of this aquifer gives evidence that groundwater recharge is going on brackish water of the deep confined aquifer has depleted stable isotope composition and very low 14c activity that indicates recharge during the late pleistocene cold period

use of hydrochemistry and environmental isotopes for evaluation of groundwater in the paleogene limestone aquifer of the ras al ain area syrian jezireh atmospheric precipitation and groundwaters from the paleogene aquifer system in northeastern syria jezireh have been investigated using major ions and environmental isotope methods to interpret the hydrogeological features characterizing this system based on the chemical ratios and isotopic compositions the groundwater bodies are differentiated into three main groups 1 fresh cold and shallow groundwater 2 brackish thermal and deep groundwater and 3 an admixed groundwater the fractions of deep thermal water in the total discharge of admixed groundwaters were estimated and the elevations of recharge zones for the paleogene aquifer were determined based on tritium content in atmospheric precipitation and by adopting a model with exponential time distribution function the mean residence time of groundwater is evaluated radiocarbon groundwater ages were calculated and corrected according to the most commonly used models the extensive declining of major karst springs discharge in the ras al ain area is the consequence of a severe groundwater pumping from the paleogene aquifer the remaining groundwater resources in this aquifer are subject to be exhausted in the future years in the absence of any real rational treatment and suitable management strategies

styles of volcanism on venus new arecibo high resolution radar data arecibo high resolution 1 5 to 2 km radar data of venus for the area extending from beta regio to western eisila regio provide strong evidence that the mountains in beta and eisila regiones and plains in and adjacent to guinevere planitia are of volcanic origin recognized styles of volcanism include large volcanic edifices on the beta and eisila rises related to regional structural trends plains with multiple source vents and a mottled appearance due to the ponding of volcanic flows and plains with bright features surrounded by extensive quasi circular radar dark halos the high density of volcanic vents in the plains suggests that heat loss by abundant and widely distributed plains volcanism may be more significant than previously recognized the low density of impact craters greater than 15 km in diameter in this region compared to the average density for the higher northern latitudes suggests that the plains have a younger age

recharge mechanisms and geochemical processes in a semi arid sedimentary basin eastern cape south africa abstract stable isotope 18 o and 2 h and geochemical signatures are used to gain some insight into recharge processes and groundwater salinization mechanisms in a semi arid rangeland catchment the 665 km 2 catchment is underlain by fractured lower beaufort sandstones and mudstones and is intruded by several dolerite dykes chloride and isotopic relationships suggest that chloride ions in ground water are of meteoric origin the hypothesized recharge and salinization mechanism is that large storm events periodically dissolve accumulated surficial meteoric salts and after a period of evaporative enrichment at or near the soil surface leach them into the ground water geochemical variations imply that spatial differences exist in recharge volumes in evaporative enrichment or in the extent of leaching of surficial salts meteoric sodium chloride contributes greater than 90 of the dissolved sodium except at low salinities where cation exchange processes yield additional sodium inputs in exchange for dissolved calcium and magnesium at high salinities this process reverses and sodium is adsorbed releasing calcium and magnesium this process accounts for up to 40 of the dissolved calcium and magnesium contributions from geochemical weathering are relatively uniform in spite of highly variable salinities which implies that residence times are also relatively uniform

origin of ultramafic hosted vein magnesite deposits abstract large deposits of magnesite mgco3 occur either as carbonated ultramafic rocks or as sedimentary beds the origins of both sedimentary and ultramafic hosted deposits remain controversial as does the relationship between them ultramafic hosted deposits are reviewed herein with an emphasis on veins rather than massive bodies magnesium apparently has been supplied to magnesite veins by their ultramafic host uncertainties concerning ultramafic hosted deposits include the source state and mode of transportation of carbon the cause of its precipitation and the mineralogy of the initial precipitate genetic questions about ultramafic hosted vein deposits are summarized with the aid of flow charts the preferred route through these charts attributes most vein magnesite to an influx of metamorphic degassing co2 and ch4 into groundwater which flows through serpentinite or peridotite the source of co2 ch4 is considered to be deeper than 10 km because metamorphism 300 c is required to release carbonaceous volatiles of the type which apparently induced observed magnesite mineralization however vein magnesite precipitation generally has occurred within just a few hundred meters of the earth s surface vein deposits are considered to be genetically related to massive bodies but the massive bodies typically contain less 12c the 12c rich co2 which has produced vein deposits is attributed to a fluid phase variably mixed ch4 co co2 which rose until it reached upper crustal groundwater the hypothetical water poor fluid presumably became slightly oxidized hence richer in soluble co2 as it encountered near surface sulfate bearing water co2 enriched water is envisioned to have been expelled regionally due to tectonic processes leaving little mineralogical evidence of its expulsion through non ultramafic rock co2 rich water which happened to encounter either serpentinite or peridotite presumably has produced magnesite vein deposits and a common silicate byproduct nontronite according to the following reaction 12 mg3si2o5 oh 4 serpentine 36 hco3 4 fe3o4 o2 12 fesi2o5 oh nontronite 36 mgco3 magnesite 36 oh 18h2o

dissolution of olivine during natural weathering abstract naturally weathered olivine occurring as phenocrysts in hawai ian volcanic rocks from several volcanic centers and regolith outcrop settings and as tectonized olivines from several metadunite bodies in the southern appalachian blue ridge are all similarly corroded by natural weathering conical funnel shaped etch pits occur as individual pits base to base pairs of cone shaped pits or en echelon arrays etch pit shapes and orientations in the smallest etch pit arrays visible in conventional scanning electron microscopy resemble even smaller features previously reported from transmission electron microscope investigations of olivine weathering etch pits occur in samples with chemical and or mineralogical evidence of weathering and or are associated with or proximal or directly connected to fractures or exposed outcrop surface and therefore are formed by weathering and not inherited from pre weathering aqueous alteration e g serpentinization iddingsitization of these parent rocks many etch pits are devoid of weathering products natural weathering of olivine is surface reaction limited similarity of corrosion forms from naturally weathered olivine from multiple igneous and metamorphic parent rock bodies suggests that olivine weathers in the same manner regardless of its specific crystallization recrystallization history eruption weathering exposure ages of the olivine s host rock and the local regolith history

groundwater residence time and palaeohydrology in the otway basin south australia 2h 18o and 14c data stable isotopes 2h 18o and 13c and radiocarbon 14c have been used in conjunction with chemical data to evaluate recharge mechanisms groundwater residence time and palaeohydrology within the confined dilwyn sand aquifer in the gambier embayment of the otway basin this aquifer does not receive recharge down gradient of the hydraulic hinge line and data have been interpreted along two discrete flow lines the mean residence time of groundwater determined by 14c in the confined aquifer from the hydraulic hinge position to the sea a distance of about 50 km along an inferred flow path is approximately 12 800 years the corresponding hydraulic travel time calculated from darcy s law is approximately 49 000 years the apparent discrepancy may be a result of eustatic sea level lowering during the last glacial because the groundwater system is hydraulically connected to the sea lower sea level would result in increased gradients and a decrease in groundwater residence time variations in stable isotopic composition along flow lines suggest a number of recharge mechanisms stable isotope data indicate progressive depletion of 2h and 18o in the groundwaters over the past 30 000 years groundwaters older than about 10 000 years b p were recharged either during a cooler climate climatic regime lower precipitation evapotranspiration and temperature and or the vapour source s had travelled over greater continental mass than those recharged over the past 10 000 years lower chloride concentrations in some of the older groundwaters indicate lower evapotranspiration rates in the recharge areas before 10 000 years ago

geochemical and isotopic characterization of groundwater from the paleogene limestone aquifer of the upper jezireh syria this research aims to evaluate the groundwater resources of paleogene aquifer in the upper jazireh area syria in terms of chemical water type recharge zones and water ages the results show that the main recharge zones for the paleogene aquifer range between 650 and 900 m a s l which coincide with the outcrop of the karstified limestone in the mardin uplift the chemical and isotopic behaviors of groundwater together with radiometric 14c reflect the existence of three different groundwater groups 1 the fresh and cold water percolating in short and shallow flow paths for which the main replenishment processes are recent 2 the brackish and thermal water containing certain amounts of h2s gas that percolate in longer and deeper flow paths for which the main replenishment processes occurred during the palaeoclimatic humid conditions of pleistocene time placed at 10 18 ka bp 3 the brackish and admixed thermal groundwater with intermediate 14c age which seems to be formed as a result of mixing between the previous two groups

isotopic evidence to characterize the sources of sulfate ions in the carbonate aquifer system in aleppo basin north syria sulfur and oxygen isotopic compositions of sulfate 34sso4 18oso4 and 18oh2o 13cdic have been used in conjunction with chemical data to constrain sulfate sources and geochemical processes in carbonate aquifers of the aleppo basin in north syria the aleppo basin comprises two limestone aquifers the first one is shallow unconfined of paleogene age and the second is deep confined of upper cretaceous age the chemical data indicate that dissolution of carbonate and evaporites is the main process controlling groundwater quality in the mainly unconfined modern groundwater the wide range of 34sso4 values 10 39 17 6 indicates a variety of input sources the likely sources of sulfur include meteoric precipitation and sewage waters which recharge the aquifer through qweik river crossing the area these waters have low so4 2 concentration 20 mg l sulfate increases in deep confined groundwater in some of which gypsum saturation is reached the 34sso4 and 18oso4 are relatively constant with mean values of 18 5 and 13 5 respectively this indicates that gypsum and anhydrite dissolution are the primary sources of sulfate this water is associated with higher depleted value of 18oh2o the heavier 13cdic with mean value 1 8 and high mg2 concentration 100 mg l in the high sulfate deep groundwater indicates that the de dolomitization reactions dominate along flow paths where sulfate concentrations increase

the role of fe and redox conditions in olivine carbonation rates an experimental study of the rate limiting reactions at 90 and 150 c in open and closed systems abstract the mechanisms and rates of olivine carbonation reactions have been the object of a number of studies but the thermodynamic limitations and the kinetics of the elementary processes that control the overall reaction are still poorly understood and characterized the main objective of this study is to probe the effect of fe on the measured rates of olivine carbonation and its role in the formation of si rich surface layers which can significantly inhibit olivine dissolution and limit the extent of the carbonation reaction a series of batch and flow through reactor experiments was conducted in pure water at 90 and 150 c and under a co 2 partial pressure of 100 and 200 bar using both a natural sample of fe bearing olivine fo 88 and a synthetic sample of pure forsterite fo 100 experimental results show that fe plays an ambivalent role in the carbonation rates of olivine on one hand the presence of fe favors the formation of fe si rich protective layers at the interface between olivine and aqueous solution slowing down the dissolution reaction and limiting the extent of carbonation whereas pure silica coatings have little to no inhibiting effect on measured carbonation rates on the other hand fe enhances olivine to carbonate conversion rates at low degrees of supersaturation by promoting the formation of fast precipitating mg fe carbonate solid solutions the passivating properties of fe si rich layers originate from the strong fe iii si interaction and are linked to the permanence of oxidizing conditions in the aqueous fluid as a consequence under reducing conditions olivine carbonation rates can be significantly increased by higher extents of dissolution and by the formation of ferroan magnesites mg fe co 3 which nucleate faster than the pure mg end member forsterite and olivine carbonation reactions can be hindered by the formation of secondary mg sheet silicates but at the conditions studied the formation of such silicate phases was observed to be transitional and not affecting significantly the rates of carbonation at the end of one month long experimental runs this work presents new measurements of olivine carbonation rates and delivers relevant information that suggest new reference criteria for the assessment of the sequestration potential of co 2 repositories and the optimization of the mineral carbonation process in mafic and ultramafic rocks

the use of na cl ratios to trace solute sources in a semiarid zone rainwater interaction with soils is a major source of dissolved salts in groundwater the transition zone between the humid and the arid area is characterized by a specific combination of reactions which do not exist elsewhere this combination of caco3 dissolution and base exchange reactions affects the na cl ratio which is the quantitatively most important parameter used for tracing salinity sources of groundwater the increase in the na cl ratio in the coastal plain aquifer of israel from north to south is related to local recharge of na rich water after interaction with soils of loessial origin

baseline geochemical conditions in the chalk aquifer berkshire u k a basis for groundwater quality management the chalk aquifer is the most important british aquifer and is also important over much of northern europe aquifer protection requires a sound knowledge of the baseline conditions and how these might vary or have varied with time this detailed geochemical study of a representative area of chalk in berkshire u k includes a consideration of several components 1 the inputs from the atmosphere 2 the interstitial water of the soil and the unsaturated zone 3 the interstitial water in the confined and unconfined sections of the aquifer and 4 the saturated mainly fissure flow along the hydraulic gradient which forms an important water supply of the thames valley region atmospheric inputs form an important source of some elements but the dominant chemical characteristics of the chalk groundwater are acquired during percolation through the soil and the upper unsaturated zone during saturated flow downgradient the chemistry is modified mainly by incongruent reactions of the carbonate matrix and by redox reactions and only to a minor extent by exchange reactions and mixing with residual saline connate water the incongruent reaction of carbonate results in a marked increase in the mg ca ratio and the sr and 13c contents of the groundwater with increased residence time oxygen concentrations are reduced mainly by oxidation of fe2 and the onset of reducing conditions allows dissolved fe2 to increase and rapid denitrification to occur the salinity profile through the confined chalk confirms that residual connate water up to one fifth sea water concentration still remains at depth and this accounts for some salinity increase in the confined groundwater resulting from fissure water pore water diffusional exchange timescales for groundwater movement have been established using tritium radiocarbon and indirectly using inert gas ratios and stable isotope ratios on balance it is concluded that all abstracted water is of holocene age although inert gas temperatures indicate cooler climatic conditions for recharge for some of the confined groundwater the implications for development and aquifer protection are discussed especially the prospect of natural in situ denitrification problems of fe solubility and the recognition of groundwater of different maturities