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1.
The dominant process limiting CO2-contents of fluids in high temperature (>240°), liquid-dominated systems consists of the conversion of primary plagioclase by CO2 to calcite and clay according to log PCO2 = 15.26 ? 7850/(t + 273.2), temperature t in °C, with a likely error in log PCO2 due to variations in the activities of the anorthite and kaolinite components of the mineral phases involved of around ± 1 log unit. Secondary processes such as adiabatic expansion, conductive cooling and mixing with cooler groundwaters are largely responsible for subsequent variations in PCO2 at lower temperatures (>240°).  相似文献   

2.
《Applied Geochemistry》1998,13(5):543-552
The accumulation chamber methodology allows one to obtain reliable values of the soil CO2 flux, ϕsoil CO2, in the range 0.2 to over 10 000 g m−2 d−1, as proven by both laboratory tests and field surveys in geothermal and volcanic areas. A strong negative correlation is observed between Δϕsoil CO2/Δt and ΔPatm/Δt. Maps of classes of log ϕsoil CO2 for the northern sector of Vulcano Island, Solfatara of Pozzuoli, Nea Kameni Islet and Yanbajain geothermal field evidence that active faults and fractures act as uprising channels of deep, CO2-rich geothermal or magmatic gases. The total diffuse CO2 output was evaluated for each surveyed area.  相似文献   

3.
A sedimentary formation perturbated by supercritical CO2 reacts by dissolving primary minerals and forming new secondary phases. In this process CO2 may be trapped in stable carbonate minerals and may thereby be immobilized for long time spans. The potential for mineral trapping can be estimated by solving kinetic expressions for the reservoir minerals and possible secondary phases. This is, however, not trivial as kinetic data are uncertain or even lacking for the minerals of interest. Here, the rate equations most commonly used for CO2 storage simulations have been solved, and the rate parameters varied, to obtain sensitivity on the total amount of CO2 stored as mineral carbonate. As various expressions are in use to estimate growth rates of secondary carbonates, three formulations were compared, including one taking into account mineral nucleation preceding growth. The sensitivity studies were done on two systems, the Utsira Sand being representative for a cold quartz-rich sand (37 °C, 100 bar CO2), and the Gulf Coast Sediment, being representative for a medium temperature quartz–plagioclase-rich system (75 °C, 300 bar CO2).The simulations showed that the total predicted CO2 mineral storage is especially sensitive to the choice of growth rate model and the reactive surface area. The largest sensitivity was found on α, fraction of total surface area available for reactions, with a reduction of one order of magnitude for all reacting phases leading to 3–4 times lower predicted CO2 mineral storage. Because the reactive surface area is highly uncertain for natural systems, the range in predicted results may be even larger. The short-term predictions (<100–1000 a), such as the onset of carbonate growth, were highly sensitive to nucleation and growth rates. Moreover, the type of carbonate minerals formed was shown to be model dependent, with the simplest model predicting an unlikely carbonate assemblage at low temperature (i.e., formation of dolomite at 37 °C). Therefore, to use kinetic models to upscale short-term (<months) laboratory experiments in time, to identify the past reactions and physical conditions of natural CO2 storage analogues, and finally to predict the potential for CO2 trapping in existing and future storage projects, more knowledge has to be collected, especially on the reactive surface area of CO2 storage reservoirs, and on the rate of secondary carbonate nucleation and growth.  相似文献   

4.
The dissolution kinetics of shallow water marine carbonates (low-Mg calcite, aragonite and Mg-calcites) were investigated in seawater (S = 35) at 25°C and a PCO2 of 10?2.5 atm. using the pH-stat method. Carbonate dissoluton rates (μmoles g?1 hr?1) fit the empirical kinetic expression, R = k(1 - Ω)n, where R = dissolution rate, k = rate constant, Ω = saturation state, and n = order of reaction. Reaction orders were near 2.9 for low-Mg calcites, 2.5 for aragonites and 3.4 for Mg-calcites.The rate constant, k, expressed as μmoles g?1 hr?1, varied by nearly a factor of ten for the different samples, reflecting differences in amount of reactive surface area. Reactive surface area of the biogenic phases ranged from 0.3% to 66% of the total surface area determined by the BET gas adsorption method. The discrepancy between reactive and total surface area was greatest for samples with high BET surface areas (> 1 m2 g?1) and delicate microstructures.Relative dissolution rates of the various biogenic carbonates as a function of seawater calcium carbonate ion molal product (IMP) were related to both mineral stability and grain microstructure. In seawater undersaturated with respect to aragonite, finely crystalline aragonites dissolved more rapidly than thermodynamically less stable high Mg-calcites (15–18 mole% MgCO3) with lower reactive surface areas. Therefore, under certain conditions, differences in grain microstructural complexity can override thermodynamic constraints and lead to selective dissolution of a thermodynamically more stable mineral phase.  相似文献   

5.
Heating and freezing studies on fluid inclusions in quartz from mineralized quartzfeldspar reef reveal the presence of type A CO2-H2O (H2O>50% by volume), type B CO2-H2O (H2O<50% by volume), type C pure CO2 and type D pure aqueous inclusions. Types A, B and C are primary and/or psuedo-secondary inclusions while type D are secondary. Types A and B homogenize on heating into different phases at similar temperatures ranging between 307 and 476°C, indicating entrapment from boiling hydrothermal solutions. Type D inclusions homogenize into a liquid phase at temperatures between 88 and 196°C. Boiling of hydrothermal solutions led to the formation of a CO2-rich phase of low density and salinity that coexisted with another dense and saline aqueous phase with very little CO2 dissolved in it. Ore and gangue mineral assemblage of primary ores indicate that ore deposition was characterized by logf O 2=?34.4 to ?30.2 atm, logf S 2=?11.6 to ?8.8 atm and pH=4.5 to 6.5.  相似文献   

6.
The bulk composition and mineralogy of hydrothermally altered tholeiite, along with the composition and speciation of fluid, have been determined for a well-defined alteration zone at 240°C and 110 bars at Svartsengi, Iceland. Mass balances between the geothermal fluid and altered tholeiite, relative to a seawater/fresh water mixture and unaltered tholeiite, indicate the overall reaction per 1000 cm3 is: 1325 gm plagioclase + 1228 gm pyroxene + 215 gm oxide-minerals break down to form 685 gm chlorite + 636 gm albite + 441 gm quartz + 249 gm epidote + 266 gm calcite + 201 gm oxide-minerals + 15 gm pyrite, requiring an influx of 123 gm CO2, 10 gm H2S and 4 gm Na2O and a release of 57 gm SiO2, 35 gm FeO, 21 gm CaO, 8 gm MgO and 4 gm K2O.Principal reactions, deduced from textural evidence, include Na-Ca exchange in plagioclase, precipitation of quartz, calcite and anhydrite, and formation of chlorite and epidote by reactions between groundmass minerals and fluid.Thermodynamic analyses of authigenic minerals and downhole fluid indicate that the fluid maintains a state close to equilibrium with the secondary mineral phases chlorite, epidote, albite, quartz, calcite, prehnite, anhydrite, pyrite and magnetite, whereas remnant primary labradorite and augite are out of equilibrium with the fluid.Water/rock ratios for the system are determined under a variety of assumptions. However, the open nature of the system makes comparisons with experimental and theoretical closed system studies ambiguous.  相似文献   

7.
A microthermometric study of inclusions in granites and pegmatites in the Proterozoic Harney Peak Granite system identified four types of inclusions. Type 1 inclusions are mixtures of CO2 and H2O and have low salinities, on average 3.5 wt.% NaCleq; type 2 inclusions are aqueous solutions of variable salinities, from 0 to 40% wt.% NaCleq; type 3 inclusions are carbonic, dominated by CO2, with no detectable water; and type 4 inclusions consist of 20 to 100% solids, with the remaining volume occupied by a CO2-H2O fluid. Many inclusions have a secondary character; however, a primary character can be unambiguously established in several occurrences of the type 1 inclusions. These inclusions were trapped above the solidus and represent the exsolved magmatic fluid. The secondary populations of types 1, 2, and 3 probably formed as a result of reequilibration and unmixing of the type 1 fluid that progressively changed composition and density with decreasing temperature and pressure and was finally trapped along healed microfractures under subsolidus conditions. Type 4 inclusions are primary and are interpreted to be trapped, fluid-bearing, complex silicate melts that subsequently solidified or underwent other posttrapping changes.It is demonstrated that primary type 1 fluid inclusions that coexist with crystallized melt inclusions in the complex, Li-bearing Tin Mountain pegmatite were trapped along the two-fluid phase boundary in the system CO2-H2O-NaCleq. Consequently, the temperature and pressure conditions of trapping are identical to the bulk homogenization conditions—on average 340°C and 2.7 kbar. These conditions indicate that this Li-, Cs-, Rb-, P-, and B-rich pegmatite crystallized at some of the lowest known temperatures for a silicate melt in the crust. An internally consistent, empirical solvus surface in P-T-XCO2 coordinates was generated for the pseudobinary CO2-(H2O-4.3 wt.% NaCleq) pegmatite fluid system. Distribution coefficients for the major species CO2, H2O, NaCl, and CH4 between the immiscible CO2-rich and H2O-rich fluid phases as a function of pressure and temperature were extracted from data for the two cogenetic fluid inclusions types.  相似文献   

8.
Giggenbach (1981) has proposed a relation of van't Hoff form, log10PCO2 = A ? B/(t + 273), between temperature and CO2 partial pressure in deep liquid in geothermal systems. The proposed values for the coefficients are A = 15.26, B = 7850.The proposal is not supported by pressure-temperature data used by Giggenbach, and a survey of different fields indicates that the proposal is not valid.  相似文献   

9.
Using the method of Schreinemakers, along with other thermodynamic considerations, a phase diagram for the system CaO-MgO-Al2O3-SiO2-CO2-H2O was constructed. The phases prehnite, pumpellyite, calcite, chlorite, dolomite, quartz, tremolite, talc, zoisite, grossularite and vapor were considered in this construction. The results indicate that prehnite-pumpellyite facies mineral assemblages will only exist in equilibrium with a vapor phase in which the mole fraction of CO2 is less than 0.2 at 1 kb, and less than 0.15 at 2 kb. Although talc could theoretically be a stable phase under these conditions, its common absence from rocks of this facies probably results from the existence of an enantiomorphic point which makes tremolite-calcite-CO2 the stable assemblage at low X CO 2, and the compositionally equivalent talc-calcite-CO2 assemblage stable at moderate X CO 2.  相似文献   

10.
In order to evaluate the extent of CO2–water–rock interactions in geological formations for C sequestration, three batch experiments were conducted on alkali feldspars–CO2–brine interactions at 150–200 °C and 300 bars. The elevated temperatures were necessary to accelerate the reactions to facilitate attainable laboratory measurements. Temporal evolution of fluid chemistry was monitored by major element analysis of in situ fluid samples. SEM, TEM and XRD analysis of reaction products showed extensive dissolution features (etch pits, channels, kinks and steps) on feldspars and precipitation of secondary minerals (boehmite, kaolinite, muscovite and paragonite) on feldspar surfaces. Therefore, these experiments have generated both solution chemistry and secondary mineral identity. The experimental results show that partial equilibrium was not attained between secondary minerals and aqueous solutions for the feldspar hydrolysis batch systems. Evidence came from both solution chemistry (supersaturation of the secondary minerals during the entire experimental duration) and metastable co-existence of secondary minerals. The slow precipitation of secondary minerals results in a negative feedback in the dissolution–precipitation loop, reducing the overall feldspar dissolution rates by orders of magnitude. Furthermore, the experimental data indicate the form of rate laws greatly influence the steady state rates under which feldspar dissolution took place. Negligence of both the mitigating effects of secondary mineral precipitation and the sigmoidal shape of rate–ΔGr relationship can overestimate the extent of feldspar dissolution during CO2 storage. Finally, the literature on feldspar dissolution in CO2-charged systems has been reviewed. The data available are insufficient and new experiments are urgently needed to establish a database on feldspar dissolution mechanism, rates and rate laws, as well as secondary mineral information at CO2 storage conditions.  相似文献   

11.
Fluid inclusions in quartz veins within Proterozoic metamorphic rocks in the Black Hills, South Dakota, were examined by microthermometry and Raman spectroscopy to assess the evolution of fluid compositions during regional metamorphism of organic-rich shales and late-orogenic magmatism, both of which were related to the collision of the Wyoming and Superior crustal blocks. Fluid inclusions occur in veins that began to be generated before or during regional compression and metamorphism that reached at least garnet-grade conditions, and in veins within the aureole of the Harney Peak Granite (HPG), where temperatures reached second-sillimanite grade conditions. Early veins in the schists have undergone recrystallization during heating and deformation that modified the composition of early CH4 or CO2 and N2-dominated inclusions. These fluids were apparently trapped under conditions of immiscibility with a saline aqueous fluid phase. They are interpreted to represent components generated during maturation of organic matter and dehydration of phyllosilicates during incipient metamorphism at reducing fO2 conditions. Most inclusions in the quartz veins are, however, secondary CO2-bearing. They imply a transition to higher fO2 conditions with increasing temperature of regional metamorphism. The fO2 conditions may have been controlled by the mineral assemblage in the host metapelites. The prevalence of bimodal distributions of trapped CO2-N2 and aqueous endmembers in the biotite and garnet zones also suggests that two immiscible fluid phases existed during the regional metamorphism.In the aureole of the HPG, graphite was evidently consumed by influx of magmatic fluids. CO2-H2O fluid inclusions dominate, but they have significantly less N2 than inclusions at lower metamorphic grades. All inclusions define secondary trails in mostly unstrained quartz. The bimodality of inclusion compositions is not as well defined as at lower grades, with many inclusions containing intermediate CO2-H2O compositions. This suggests that a single fluid phase existed at the high temperatures in the granite aureole, but then unmixed during cooling. A set of late quartz veins with graphitized and tourmalinized selvages in the granite aureole contains CH4-bearing inclusions with little N2. The existence of CH4 in these inclusions is attributed to complexing of magmatic B with hydroxyl anions taken from the CO2-H2O fluid phase, effectively causing reduction in fO2 and promoting precipitation of graphite.  相似文献   

12.
Comparison of theoretical and analytical equilibrium constants based on the reactions CH4 + 2H2O = CO2 + 4H2, 2NH3 = N2 + 3H2 and iron(II)-aluminium-silicate + 2H2S = FeS2 + H2 + aluminium-silicate, shows that the composition of fluids discharged from geothermal areas in New Zealand (Wairakei, Kawerau, Broadlands) reflects close to complete attainment of chemical equilibrium within the system H2O, CO2, H2S, NH3, H2, N2 and CH4. Under conditions prevailing in explored geothermal systems in New Zealand, the minerals graphite (elemental carbon), anhydrite, pyrrhotite, magnetite do not appear to take part in the overall equilibrium system. The three physical parameters required to evaluate geothermal gas reactions are temperature, pressure and vapor-liquid ratios within the gas equilibration zone.  相似文献   

13.
《Applied Geochemistry》2004,19(6):917-936
Carbon dioxide disposal into deep aquifers is a potential means whereby atmospheric emissions of greenhouse gases may be reduced. However, our knowledge of the geohydrology, geochemistry, geophysics, and geomechanics of CO2 disposal must be refined if this technology is to be implemented safely, efficiently, and predictably. As a prelude to a fully coupled treatment of physical and chemical effects of CO2 injection, the authors have analyzed the impact of CO2 immobilization through carbonate mineral precipitation. Batch reaction modeling of the geochemical evolution of 3 different aquifer mineral compositions in the presence of CO2 at high pressure were performed. The modeling considered the following important factors affecting CO2 sequestration: (1) the kinetics of chemical interactions between the host rock minerals and the aqueous phase, (2) CO2 solubility dependence on pressure, temperature and salinity of the system, and (3) redox processes that could be important in deep subsurface environments. The geochemical evolution under CO2 injection conditions was evaluated. In addition, changes in porosity were monitored during the simulations. Results indicate that CO2 sequestration by matrix minerals varies considerably with rock type. Under favorable conditions the amount of CO2 that may be sequestered by precipitation of secondary carbonates is comparable with and can be larger than the effect of CO2 dissolution in pore waters. The precipitation of ankerite and siderite is sensitive to the rate of reduction of Fe(III) mineral precursors such as goethite or glauconite. The accumulation of carbonates in the rock matrix leads to a considerable decrease in porosity. This in turn adversely affects permeability and fluid flow in the aquifer. The numerical experiments described here provide useful insight into sequestration mechanisms, and their controlling geochemical conditions and parameters.  相似文献   

14.
The interaction between CO2-rich waters and basaltic glass was studied using reaction path modeling in order to get insight into the water-rock reaction process including secondary mineral composition, water chemistry and mass transfer as a function of CO2 concentration and reaction progress (ξ). The calculations were carried out at 25-90 °C and pCO2 to 30 bars and the results were compared to recent experimental observations and natural systems. A thermodynamic dataset was compiled from 25 to 300 °C in order to simulate mineral saturations relevant to basalt alteration in CO2-rich environment including revised key aqueous species for mineral dissolution reactions and apparent Gibbs energies for clay and carbonate solid solutions observed to form in nature. The dissolution of basaltic glass in CO2-rich waters was found to be incongruent with the overall water composition and secondary mineral formation depending on reaction progress and pH. Under mildly acid conditions in CO2 enriched waters (pH <6.5), SiO2 and simple Al-Si minerals, Ca-Mg-Fe smectites and Ca-Mg-Fe carbonates predominated. Iron, Al and Si were immobile whereas the Mg and Ca mobility depended on the mass of carbonate formed and water pH. Upon quantitative CO2 mineralization, the pH increased to >8 resulting in Ca-Mg-Fe smectite, zeolites and calcite formation, reducing the mobility of most dissolved elements. The dominant factor determining the reaction path of basalt alteration and the associated element mobility was the pH of the water. In turn, the pH value was determined by the concentration of CO2 and extent of reaction. The composition of the carbonates depended on the mobility of Ca, Mg and Fe. At pH <6.5, Fe was in the ferrous oxidation state resulting in the formation of Fe-rich carbonates with the incorporation of Ca and Mg. At pH >8, the mobility of Fe and Mg was limited due to the formation of clays whereas Ca was incorporated into calcite, zeolites and clays. Competing reactions between clays (Ca-Fe smectites) and carbonates at low pH, and zeolites and clays (Mg-Fe smectites) and carbonates at high pH, controlled the availability of Ca, Mg and Fe, playing a key role for low temperature CO2 mineralization and sequestration into basalts. Several problems of the present model point to the need of improvement in future work. The determinant factors linking time to low temperature reaction path modeling may not only be controlled by the primary dissolving phase, which presents challenges concerning non-stoichiometric dissolution, the leached layer model and reactive surface area, but may include secondary mineral precipitation kinetics as rate limiting step for specific reactions such as retrieved from the present reaction path study.  相似文献   

15.
《地学前缘(英文版)》2020,11(6):2183-2196
The stability of titanite is sensitive to temperature and partial pressure of CO2. The finding of authigenic titanite grains in weathering regolith formed on Paraná basalts, Brazil, under tropical climatic conditions, reveals the thermodynamically-driven conversion from calcite to titanite at elevated ambient temperatures. Being unusual nowadays, this phase transition provides important implications for the understanding of silicate weathering in earlier geological epochs.Two types of secondary titanites were identified in the weathering profile of the study area. The tiny grains of 10 ​μm are forming in the microscopic voids in the rock. Also, large fractures filled with Fe-rich clay minerals contain bigger specimens of up to 170 ​μm. The titanites of second type often coexist with chalcedony and barite. No carbonate minerals were found in the weathering profile. Weathering sphene can be discriminated from other titanite types by its strong positive Eu anomaly, increased Al2O3 content and low content of trace elements. Its specific chemical composition and reactive transport modeling link this secondary mineral with dissolution of plagioclase. The titanite precipitation is controlled by slow diffusion in poorly-aerated, highly-alkaline pore fluids.The subaerial weathering of basaltic rocks provides a significant reservoir for atmospheric CO2. However, the deposition of carbonate minerals is thermodynamically avoided at the stability field of titanite. We demonstrate a complex feedback between CO2 and soil carbonates. The rise in pCO2 triggers the precipitation of calcite in the weathering regolith, but the greenhouse effect increasing the temperature can cease carbonate deposition. Secondary titanites were found in several paleosols and at least a part of them can be of weathering origin.  相似文献   

16.
The evaluation of the feasibility of ex situ carbonation in landfills utilizing raw natural substances (namely serpentinites as Mg-source and the CO2-rich fraction of biogas as C-source) was tested through a laboratory procedure comprising three steps. The first step is the acid attack of a serpentinite at 70 °C, by means of HCl 2 M, to get MgCl2-rich solutions. Attacks of different durations were performed to evaluate the time needed. The second step is the neutralization of the MgCl2-rich solution by addition of concentrated ammonia. The third (carbonation) step is mixing of the neutralized MgCl2-rich solution with a solution of ammonium carbonate. This was produced in a landfill by absorption of CO2 contained in biogas in a solution of ammonia. The neutralization of acid MgCl2-rich solutions caused the precipitation of ferrihydrite with secondary ammonium carnallite and salammoniac, whereas abundant precipitation of Amorphous Hydrated Impure Magnesium Carbonate (AHIMC), sometimes with minor nesquehonite, occurred in the third step. This solid carbonate acts as a stable CO2 sink up to 380 °C. The geochemical behavior of some minor elements was also investigated during the experimental processes revealing that Al, Cr and Ni were removed during neutralization (second step), in contrast to Ca which remained in the circumneutral MgCl2-rich solution and entered into the structure of AHIMC. During the carbonation step, precipitation of artinite, hydromagnesite, lansfordite, magnesite and nesquehonite was thermodynamically impossible as the aqueous phase was undersaturated with respect to these solid phases upon separation of AHIMC.  相似文献   

17.
The understanding of the evolution of microstructures in a metamorphic rock requires insights into the nucleation and growth history of individual grains, as well as the coarsening processes of the entire aggregate. These two processes are compared in impure carbonates from the contact metamorphic aureole of the Adamello pluton (N‐Italy). As a function of increasing distance from the pluton contact, the investigated samples have peak metamorphic temperatures ranging from the stability field of diopside/tremolite down to diagenetic conditions. All samples consist of calcite as the dominant matrix phase, but additionally contain variable amounts of other minerals, the so‐called second phases. These second phases are mostly silicate minerals and can be described in a KCMASHC system (K2O, CaO, MgO, Al2O3, SiO2, H2O, CO2), but with variable K/Mg ratios. The modelled and observed metamorphic evolution of these samples are combined with the quantification of the microstructures, i.e. mean grain sizes and crystal size distributions. Growth of the matrix phase and second phases strongly depends on each other owing to coupled grain coarsening. The matrix phase is controlled by the interparticle distances between the second phases, while the second phases need the matrix grain boundary network for mass transfer processes during both grain coarsening and mineral reactions. Interestingly, similar final mean grain sizes of primary second phase and second phases newly formed by nucleation are observed, although the latter formed later but at higher temperatures. Moreover, different kinetic processes, attributed to different driving forces for growth of the newly nucleated grains in comparison with coarsening processes of the pre‐existing phases, must have been involved. Chemically induced driving forces of grain growth during reactions are orders of magnitudes larger compared to surface energy, allowing new reaction products subjected to fast growth rates to attain similar grain sizes as phases which underwent long‐term grain coarsening. In contrast, observed variations in grain size of the same mineral in samples with a similar T–t history indicate that transport properties depend not only on the growth and coarsening kinetics of the second phases but also on the microstructure of the dominant matrix phase during coupled grain coarsening. Resulting microstructural phenomena such as overgrowth and therefore preservation of former stable minerals by the matrix phase may provide new constraints on the temporal variation of microstructures and provide a unique source for the interpretation of the evolution of metamorphic microstructures.  相似文献   

18.
Mn-rich members of the pyrosmalite-family [(Mn, Fe)8Si6O15(OH, Cl)10], friedelite and schallerite have been identified as rock-forming minerals together with caryopilite, in several metamorphosed carbonate Mn-deposits. The phase assemblages and mineral compositions are described for eight of these localities each of which represents a distinct geologic situation. Friedelite is always Cl-bearing and occurs both as a prograde phase in low-grade metamorphic rocks (Pyrenees, Haute-Maurienne) and as a secondary phase formed by retrogressive replacement of primary anhydrous phases in higher-grade rocks. Schallerite, an Asbearing relative of friedelite, occurs in the greenschist metamorphic deposit of the Ködnitztal (Austria) together with other As-minerals. In these deposits, caryopilite is typically formed during retrograde metamorphism by alteration of, generally anhydrous, Mn-silicates. Based upon these occurrences, a qualitative petrogenetic grid for the system MnO-SiO2-CO2-H2O with the phases friedelite, caryopilite, pyroxmangite/rhodonite, tephroite, rhodochrosite, quartz, CO2, and H2O is proposed. The phase relations imply that Cl- (or As-) free friedelite is not stable in hydrous systems with respect to caryopilite. From the mineral assemblages containing hydrous Mn silicates, waterrich fluids are inferred during the retrograde metamorphic evolution of the investigated deposits. Chemical data for Mn-rich chlorites, which are basically members of the clinochlore-pennantite series which coexist with the pyrosmalite minerals, show the absence of intermediate Mn/Mg ratios. This supports the existence of a miscibility gap as previously hypothesized by other authors.  相似文献   

19.
Continental flood basalts (CFB) are considered as potential CO2 storage sites because of their high reactivity and abundant divalent metal ions that can potentially trap carbon for geological timescales. Moreover, laterally extensive CFB are found in many place in the world within reasonable distances from major CO2 point emission sources. Based on the mineral and glass composition of the Columbia River Basalt (CRB) we estimated the potential of CFB to store CO2 in secondary carbonates. We simulated the system using kinetic dependent dissolution of primary basalt-minerals (pyroxene, feldspar and glass) and the local equilibrium assumption for secondary phases (weathering products). The simulations were divided into closed-system batch simulations at a constant CO2 pressure of 100?bar with sensitivity studies of temperature and reactive surface area, an evaluation of the reactivity of H2O in scCO2, and finally 1D reactive diffusion simulations giving reactivity at CO2 pressures varying from 0 to 100?bar. Although the uncertainty in reactive surface area and corresponding reaction rates are large, we have estimated the potential for CO2 mineral storage and identified factors that control the maximum extent of carbonation. The simulations showed that formation of carbonates from basalt at 40?C may be limited to the formation of siderite and possibly FeMg carbonates. Calcium was largely consumed by zeolite and oxide instead of forming carbonates. At higher temperatures (60 ?C 100?C), magnesite is suggested to form together with siderite and ankerite. The maximum potential of CO2 stored as solid carbonates, if CO2 is supplied to the reactions unlimited, is shown to depend on the availability of pore space as the hydration and carbonation reactions increase the solid volume and clog the pore space. For systems such as in the scCO2 phase with limited amount of water, the total carbonation potential is limited by the amount of water present for hydration of basalt.  相似文献   

20.
The mineral water deposits in Kiseljak are located in the central Dinarids, Bosnia and Herzegovina, in the southwestern edge of Sarajevo–Zenica basin that was formed in the zone of Busova?a fault. Busova?a fault reaches deep into the Earth’s crust and is characterised by the presence of mineral and thermomineral water enriched with CO2 and CO2 springs (mofetes) in the direction of Ilid?a–Kiseljak–Busova?a. Deposits are constructed of layers of Palaeozoic to Cretaceous age. Primary aquifer of mineral waters is Permian clastites and evaporites and secondary Anisian carbonates. Mineral water and CO2 are of different origin. The water is of atmospheric origin. Due to slow circulation, water descends in the primary aquifer where it becomes enriched with CO2 and minerals. Due to high pressure in the primary aquifer mineral water ascends along Busova?a fault, mounts into the secondary aquifer and rises at spring sources. Water is a mixture of two or more waters of different mineralization. Mixing of water occurs in the zone of secondary aquifer even at greater depths without the influence of contemporary climatic factors. Intensive water mixing is indicated by the high ratio of Ca/Sr, Na/Cl and Ca/SO4 and the mixing diagram. CO2 is thermometamorphic, arising from the catalytic activity of SiO2 on carbonates in the deeper layers of the Earth’s crust, where quartz porphyry broke through Palaeozoic formations.  相似文献   

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