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1.
Sanidine grains (100–600 μm in diameter) were subjected to dissolution at 82°C in aqueous electrolyte solutions of pH ranging from 4 to 8 for 293 or 377 hr. Dissolution equivalent to the removal of silica from the outer 300–900 A of these grains was accomplished. The shallow subsurfaces of feldspar grains were then analyzed for K, Al, and Si by X-ray photoelectron spectroscopy. The results rule out any continuous precipitate layer; if an alkali-depleted subsurface zone (leached layer) was present in the feldspar, the thickness of such a zone approximated by linear increase of alkali concentration with depth was not more than about 17 Å.It is concluded that in the absence of a compact precipitate layer, dissolution of feldspars in the temperature range corresponding to deep diagenesis is controlled by the processes at the feldspar-solution interface and a leached layer more than one feldspar unit cell thick does not form. Whether the same applies at the temperatures of shallow diagenesis and weathering cannot be judged with certainty, but parallels with leached layers on alkali silicate glasses suggest that it does.  相似文献   

2.
合川地区须二段砂岩储层成岩作用及其对储层的影响   总被引：1，自引：0，他引：1  
依据普通薄片、铸体薄片、扫描电镜、X衍射等实验分析手段,对合川地区须家河组二段砂岩储层的岩石学特征、成岩作用及孔隙演化进行了研究。结果表明,该区须二段砂岩储层主要由长石岩屑砂岩和岩屑长石砂岩组成。主要成岩作用类型有压实作用、胶结作用、溶蚀作用和交代作用,成岩演化阶段已达到中成岩B期。早成岩A期—B期,压实作用强烈,原生孔隙迅速减少;中成岩A期,压实作用及硅质胶结作用是原生孔隙继续降低,有机质热演化过程中产生的有机酸及无机酸,使长石及富长石的岩屑颗粒发生强烈溶蚀,形成大量次生孔隙;中成岩B期,含铁方解石及铁白云石交代充填,使储层致密。压实作用及胶结作用是原生孔隙遭受破坏的主要成岩作用类型,而溶蚀作用是形成次生孔隙的主要成岩作用类型。受成岩作用及成岩演化阶段的控制,研究区须二段储集空间类型多样,粒内溶孔、粒间溶孔及残余粒间孔发育,特别是长石及富长石岩屑颗粒的溶蚀,使须二段储层出现孔隙度、渗透率异常发育带。  相似文献   

3.
Examination of the surface morphology (via scanning electron microscopy) and surface composition (via X-ray photoelectron spectroscopy) of sodic plagioclase and potash feldspar grains taken from four different soils, provides little or no evidence for the existence of a tightly adhering protective surface layer of altered composition on the feldspar surface. Grains, from which all adhering clay has been removed by ultrasonic cleaning, exhibit the same chemical composition in the outermost few tens of angstroms as the underlying feldspar. Aluminum-rich ‘clay’ coatings which continue to adhere to the grains after ultrasonic treatment are patchy, highly hydrous, and unlikely to act as major diffusion-limiting, and thus protective, barriers. Attack by dissolution of the feldspar surface is non-uniform and follows a definite etching sequence characterized by the development and growth of distinctive etch pits. This dissolution sequence can be reproduced by treating fresh feldspars in the laboratory with strong HF-H2SO4? solutions and, thus, the sequence is unaffected by the composition of the attacking solution. All of our results suggest that the dissolution of feldspar during weathering is controlled by selective chemical reaction at the feldspar-solution interface and not by uniform diffusion through a protective surface layer.  相似文献   

4.
Fayalite, hypersthene, basalt, and obsidian were dissolved in buffered solutions (25°C; pH 4.5 and 5.5) under air, N2 or O2 atmospheres, in order to follow the kinetics of dissolution. Each dissolved more rapidly at lower pH values, dissolving most rapidly in the initial few days, followed by slower dissolution for periods up to six months. Dissolution was more rapid when air was excluded. In oxygen atmospheres an Fe(OH)3 precipitate armors mineral surfaces, thus inhibiting further dissolution, and further affects the solution by scavenging dissolved silica and cations. Dissolution reactions include initial exchange between cations and H+, incongruent dissolution of silicate structures, oxidation of Fe2+ in solution, precipitation of Fe(OH)3, and scavenging of dissolved silica and cations by Fe(OH)3. Dissolution kinetics may explain weathering of mafic rocks and minerals at the Earth's surface, the formation of Fe-oxide coatings on mineral grains, weathering of submarine mafic rocks and intrastratal solution of mafic minerals in buried sandstones. Early Precambrian weathering would have been more rapid before the appearance of large amounts of oxygen in the atmosphere, and continental denudation rates may have been higher than at present because of this effect and the predominance of mafic igneous rocks at an early stage of continent formation and growth.  相似文献   

5.
It has been widely accepted that a chemically altered, protective surface layer regulates the dissolution, and hence the weathering, of plagioclase feldspars under Earth's surface conditions. In this study, we examine this hypothesis in detail with the aid of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Using these techniques, we have been unable to find any direct evidence suggesting the presence of a chemically altered coating on feldspar surfaces which have been weathered in the lab. Instead, our results suggest that the mechanism controlling feldspar weathering is a surface controlled reaction.Based on SEM observations and measurements of rate of release of silica, we postulate that the process of feldspar dissolution proceeds in two stages in the lab. Initially, one observes the dissolution of ultrafine (? 1 μm diameter) particles which are produced during grinding of the sample, and which adhere tenaciously to the surfaces of larger grains. This is the stage which results in the non-linear rates of dissolution which are commonly observed in the lab (parabolic kinetics). Secondly, the dissolution occurs at sites of excess surface energy such as at dislocations or similar crystal defects. This process yields linear rates of dissolution, and it dominates the weathering of feldspars in the field.  相似文献   

6.
山东省牛庄洼陷古近系沙河街组沙三中亚段储集层岩石类型以长石岩屑砂岩和岩屑长石砂岩为主,岩石结构成熟度和成分成熟度均较低。砂岩成岩作用包括压实作用、胶结作用、交代作用、溶解作用等。压实作用主要有刚性颗粒发生脆性破裂、颗粒之间呈线接触和凹凸接触、岩石碎屑颗粒呈明显的定向排列、塑性颗粒挤压变形或刚性颗粒嵌入变形颗粒中、粘土质碎屑被挤压变形发生假杂基化等五种表现形式。胶结物主要有泥质胶结物、碳酸盐胶结物、自生粘土矿物和自生石英、长石。交代作用主要有石英交代长石颗粒、碳酸盐胶结物交代石英、长石及岩屑颗粒、碳酸盐胶结物之间的相互交代。发生溶解作用的主要是石英、长石和岩屑颗粒,胶结物中主要是碳酸盐矿物。目前研究区沙三中亚段储集层成岩演化处于晚成岩A期。影响成岩作用的主要因素为岩石成分、沉积环境、孔隙流体性质等。成岩作用对储集物性的影响主要表现在孔隙度和渗透率的变化,其中压实作用和胶结作用使储层原生孔隙迅速减少、渗透率降低,使得储集物性变差;而溶解作用是次生孔隙发育的主要因素,从而改善砂岩的储集性能。  相似文献   

7.
The enhancement of dissolution of quartz under the influence of clays has been recognized in sandstones for many years. It is well known that a grain of quartz in contact with a clay flake dissolves faster than when in contact with another grain of quartz. This phenomenon promotes silica transfer during the diagenesis of sandstones and is responsible of deformation and porosity variations. Here we make an attempt to explain the process of this rock deformation using a pressure solution mechanism.

The model of water film diffusion assumes that matter is dissolved inside the contact between two grains. The resulting solutes are transported to the pore fluid through diffusion along an adsorbed water film. Between two micas, this trapped film is thicker than between two grains of quartz. As a consequence diffusion is easier and the rate of pressure solution faster.

Experiments on pressure solution show that diffusion controls the mechanism at great depth whereas a model based on natural mica indentation indicates that kinetics is the limiting process through the precipitation rate of quartz at low depth, thus temperature is a crucial parameter. There should be a transition between thermally controlled rate and diffusion limited evolution.  相似文献   


8.
《Sedimentology》2018,65(4):1277-1300
Fluvially derived tuffaceous Chinle sandstones from Petrified Forest National Park provide a well‐preserved Late Triassic archive of climate information. Petrographic analysis of 38 Chinle sandstones provides new insight into the depositional history and evolution of palaeoclimate during Chinle deposition. This study focuses on the relationship between climate and meteoric diagenesis as a guide for constraining climate change in western equatorial Pangea during the Late Triassic. Petrographic analysis of Chinle sandstones reveals their wide range of textural attributes, as well as pedogenic and shallow burial diagenetic features that occurred during the Late Triassic. These diverse petrological characteristics are indicative of the evolving Late Triassic climate, when placed into a well‐constrained stratigraphic and geochronological framework. The stratigraphic succession is characterized by variations in the abundance of framework grains, detrital matrix, weathering intensity of feldspar and volcanic rock fragments, and the mineralogy of clay cements. Climate records from Chinle palaeosol geochemistry indicate a progression from wet to dry conditions. This trend is also reflected in the meteoric diagenetic features of Chinle sandstones. During deposition of the lower Chinle, elevated rainfall promoted the weathering of labile volcanic detritus to kaolinite, whereas feldspars (especially plagioclase) were partially or completely dissolved. In the upper Chinle, a trend towards drier conditions favoured the formation of smectite and less feldspar dissolution resulting in a higher abundance of well‐preserved plagioclase grains. Shallow burial meteoric weathering reactions in Chinle sandstones reflect the evolving climate during the Late Triassic.  相似文献   

9.
综合运用岩心观察、薄片鉴定、物性分析等技术方法,系统分析了文安斜坡沙三段储层岩石学特征、成岩作用特征及储集特征。研究表明,文安斜坡沙三段储层岩石类型以岩屑长石砂岩为主,杂基含量低,成分成熟度和结构成熟度中等;储集空间以原生孔隙为主,占总孔隙的72.81%,储集物性较差,属中低孔-低渗特低渗储层;储层主要经历了压实作用/早期碳酸盐胶结→长石、岩屑溶解/石英次生加大/高岭石充填→石英溶解/碳酸盐胶结→黄铁矿胶结。在有效储层物性下限计算的基础上,选取孔隙度差值作为参数,系统分析了有效储层控制因素。有效储层的形成主要受沉积微相、粒度、分选、成岩作用以及地层压力控制。水下分流河道和河口坝微相中碎屑颗粒越粗,分选越好,杂基含量越少,有效储层越发育;胶结作用对储层物性的控制较明显,是影响中深层储层物性的主要因素;溶蚀作用主要表现为长石等硅酸盐矿物的溶蚀,平均增孔量3.42%;早期地层超压抑制压实作用,保护孔隙,是有效储层发育的有利因素。  相似文献   

10.
鄂尔多斯盆地延长组物源与成岩耦合关系研究   总被引：4，自引：0，他引：4  
丁晓琪 《地质与勘探》2013,49(2):384-392
随着油气勘探的逐渐深入,致密低渗油气藏所占比例越来越高,将是今后油气勘探的一个重要领域。颗粒成分不同导致的成岩差别对致密低渗储层的储集物性具有明显的控制作用。本文以鄂尔多斯盆地上三叠统延长组长8-长6段致密砂岩为例,研究砂岩骨架颗粒、孔隙类型与成岩作用之间的关系。在此基础上,分析由不同类型母岩形成的砂岩成岩作用差别。结果表明,鄂尔多斯盆地长8-长6段物源对砂岩成岩作用具有非常明显的控制作用:(1)石英、长石等刚性颗粒的含量直接影响着压实作用的强度;(2)火山岩屑可以导致绿泥石环边和浊沸石胶结物的形成,火山岩屑和浊沸石胶结物的溶蚀较强,易形成次生孔隙;(3)黑云母可以导致强压实形成致密层,但黑云母水解可以提供大量的铁和镁,利于绿泥石环边的形成;(4)碳酸盐岩岩屑的溶解可以为碳酸盐胶结物的形成提供额外的物质来源。所以,物源研究可以有效地预测深层致密碎屑储层的成岩作用及成岩强度,进而对高效储层的发育作出预测。  相似文献   

11.
Chemical analyses of 300 solutions produced by the artificial weathering of eight different feldspars in fourteen experiments of up to 1200hr duration were used to study the evolution of water during weathering. The range of pH was between 4 and 5·5. Within 4 hr of dissolution, the activity of Al was controlled by the pH and the solubility of microcrystalline gibbsite. After 100 hr of dissolution, the pH and microcrystalline halloysite controlled the activities of Al and silicic acid in all of the solutions.Microcrystalline halloysite was the only phase identified in the weathering of plagioclases in distilled water and 1 atm CO2 partial pressure. Montmorillonites, halloysite and other clay minerals were produced from oligoclase in aqueous solutions containing high initial concentrations of Ca. Mg, K and SiO2.The experimentally determined log solubility product of microcrystalline gibbsite was ?32·78 ± 0·04 and log K for the hydrolysis of microcrystalline halloysite was 11.58 ± 0·05. The results suggest that very poorly crystalline metastable phases may control the initial compositions of some waters in contact with rocks containing feldspar minerals.  相似文献   

12.
This work examines the different effects meteoric versus marine diagenesis had on Cambro-Ordovician tidal sandstones during episodes of fluctuating sea level. The distribution of diagenetic fabrics was compared to a sequence stratigraphic framework. Initially, a rise in relative sea level (RSL) resulted in deposition of transgressive systems tract sands directly onto crystalline basement. These sandstones display evidence of limited cementation by marine, grain-fringing dogtooth-like and fibrous calcite. A fall in RSL resulted in the progradation of a tidal flat complex and deposition of highstand systems tract (HST) and lowstand systems tract (braided fluvial) sandstones. Contemporaneous meteoric-water flux into sands of all the systems tracts occurred. Sequence boundaries (SB) are marked by fluvial incision of tidal sands and by the development of palaeosols. Meteoric incursion during sea-level lowstands resulted in the dissolution and kaolinitization of feldspars, micas and mud intraclasts in all systems tracts, but is most extensive in HST sandstones below the SB. The effect of meteoric-water flux on the dissolution of marine calcite cements is poorly known. Mesogenetic alterations include intergranular pressure dissolution and formation of variable amounts of syntaxial quartz overgrowths in all systems tracts. Telogenetic alteration (i.e. weathering) in the sandstones includes the formation of goethite and calcite. Thus, the integration of diagenesis with sequence stratigraphy provides a useful tool with which to understand reservoir-quality distribution in sand-dominated, tidal sediments.  相似文献   

13.
Jarosite [KFe3(SO4)2(OH)6] is a mineral that is common in acidic, sulphate-rich environments, such as acid sulphate soils derived from pyrite-bearing sediments, weathering zones of sulphide ore deposits and acid mine or acid rock drainage (ARD/AMD) sites. The structure of jarosite is based on linear tetrahedral-octahedral-tetrahedral (T-O-T) sheets, made up from slightly distorted FeO6 octahedra and SO4 tetrahedra. Batch dissolution experiments carried out on synthetic jarosite at pH 2, to mimic environments affected by ARD/AMD, and at pH 8, to simulate ARD/AMD environments recently remediated with slaked lime (Ca(OH)2), suggest first order dissolution kinetics. Both dissolution reactions are incongruent, as revealed by non-ideal dissolution of the parent solids and, in the case of the pH 8 dissolution, because a secondary goethite precipitate forms on the surface of the dissolving jarosite grains. The pH 2 dissolution yields only aqueous K, Fe, and SO4. Aqueous, residual solid, and computational modelling of the jarosite structure and surfaces using the GULP and MARVIN codes, respectively, show for the first time that there is selective dissolution of the A- and T-sites, which contain K and SO4, respectively, relative to Fe, which is located deep within the T-O-T jarosite structure. These results have implications for the chemistry of ARD/AMD waters, and for understanding reaction pathways of ARD/AMD mineral dissolution.  相似文献   

14.
During diagenesis quartz grains undergo selective dissolution, controlled in location by the surface energy characteristics of the individual grains. Experimental etching in HF of isolated quartz grains reproduces comparable textures to those of natural occurrences. Some experimental results illustrate the specific effects of surface textures on their initial dissolution rates, so demonstrating the control surface energy variation has over dissolution. A hierarchy of grain surface characteristics, according to surface energies, provides a useful guide to the relative rates of dissolution during decomposition.  相似文献   

15.
Quaternary alkaline basalts of Middle Atlas, are weathered into spheroidal volumes organized into weathering cover. In the profile studied, the study of transformations from a fresh core basalt to the most weathered rinds, has been analysed using BESI images (backscattred electron image analysis). A part from the microscopic analysis of each weatherted basalt, proportions of primary minerals, clays and pore space has been quantified in different stages of weathering. Indeed, in fresh core basalt, weathering is characterized by a first dissolution of the glass, followed by feldspar transformations in twinning plans, cleavages and in micropores inherited from the magmatic and cristallographic history of the rock.

In most basaltic weathered rinds, pore spaces given by the dissolution of the glass, were filled by a mixture of clays and iron products. In these samples, feldspars are completely dissolved giving important porosity occupied by small quantity of halloysite and kaolinite. The olivine and pyroxene transformations are accompanied by weak pore space formation. At the bottom of the soil, this porosity decreases in response to filling by later secondary products which come from the upper part of the soil by weathering solutions.  相似文献   


16.
Sedimentary basins containing igneous intrusions within sedimentary reservoir units represent an important risk in petroleum exploration. The Upper Triassic to Lower Jurassic sediments at Wilhelm?ya(Svalbard) contains reservoir heterogeneity as a result of sill emplacement and represent a unique case study to better understand the effect of magmatic intrusions on the general burial diagenesis of siliciclastic sediments. Sills develop contact metamorphic aureoles by conduction as presented in many earlier studies. However, there is significant impact of localized hydrothermal circulation systems affecting reservoir sediments at considerable distance from the sill intrusions. Dolerite sill intrusions in the studied area are of limited vertical extent(～12 m thick), but created localized hydrothermal convection cells affecting sediments at considerable distance(more than five times the thickness of the sill)from the intrusions. We present evidence that the sedimentary sequence can be divided into two units:(1) the bulk poorly lithified sediment with a maximum burial temperature much lower than 60-70 ℃,and(2) thinner intervals outside the contact zone that have experienced hydrothermal temperatures(around 140 ℃). The main diagenetic alteration associated with normal burial diagenesis is minor mechanical plastic deformation of ductile grains such as mica. Mineral grain contacts show no evidence of pressure dissolution and the vitrinite reflectance suggests a maximum temperature of ～40 ℃. Contrary to this, part of the sediment, preferentially along calcite cemented flow baffles, show evidence of hydrothermal alteration. These hydrothermally altered sediment sections are characterized by recrystallized carbonate cemented intervals. Further, the hydrothermal solutions have resulted in localized sericitization(illitization) of feldspars, albitization of both K-feldspar and plagioclase and the formation of fibrous illite nucleated on kaolinite. These observations suggest hydrothermal alteration at T 120-140 ℃ at distances considerably further away than expected from sill heat dissipation by conduction only, which commonly affect sediments about twice the thickness of the sill intrusion. We propose that carbonate-cemented sections acted as flow baffles already during the hydrothermal fluid mobility and controlled the migration pathways of the buoyant hot fluids. Significant hydrothermally induced diagenetic alterations affecting the porosity and hence reservoir quality was not noted in the noncarbonate-cemented reservoir intervals.  相似文献   

17.
Geochemistry of soil, soil water, and soil gas was characterized in representative soil profiles of three Michigan watersheds. Because of differences in source regions, parent materials in the Upper Peninsula of Michigan (the Tahquamenon watershed) contain only silicates, while those in the Lower Peninsula (the Cheboygan and the Huron watersheds) have significant mixtures of silicate and carbonate minerals. These differences in soil mineralogy and climate conditions permit us to examine controls on carbonate and silicate mineral weathering rates and to better define the importance of silicate versus carbonate dissolution in the early stage of soil-water cation acquisition.Soil waters of the Tahquamenon watershed are the most dilute; solutes reflect amphibole and plagioclase dissolution along with significant contributions from atmospheric precipitation sources. Soil waters in the Cheboygan and the Huron watersheds begin their evolution as relatively dilute solutions dominated by silicate weathering in shallow carbonate-free soil horizons. Here, silicate dissolution is rapid and reaction rates dominantly are controlled by mineral abundances. In the deeper soil horizons, silicate dissolution slows down and soil-water chemistry is dominated by calcite and dolomite weathering, where solutions reach equilibrium with carbonate minerals within the soil profile. Thus, carbonate weathering intensities are dominantly controlled by annual precipitation, temperature and soil pCO2. Results of a conceptual model support these field observations, implying that dolomite and calcite are dissolving at a similar rate, and further dissolution of more soluble dolomite after calcite equilibrium produces higher dissolved inorganic carbon concentrations and a Mg2+/Ca2+ ratio of 0.4.Mass balance calculations show that overall, silicate minerals and atmospheric inputs generally contribute <10% of Ca2+ and Mg2+ in natural waters. Dolomite dissolution appears to be a major process, rivaling calcite dissolution as a control on divalent cation and inorganic carbon contents of soil waters. Furthermore, the fraction of Mg2+ derived from silicate mineral weathering is much smaller than most of the values previously estimated from riverine chemistry.  相似文献   

18.
Highly insoluble Ce-bearing phosphate minerals form by weathering of apatite [Ca5(PO4)3.(OH,F,Cl)], and are important phosphorous repositories in soils. Although these phases can be dissolved via biologically-mediated pathways, the dissolution mechanisms are poorly understood. In this paper we report spectroscopic evidence to support coupling of redox transformations of organic carbon and cerium during the reaction of rhabdophane (CePO4·H2O) and catechol, a ubiquitous biogenic compound, at pH 5. Results show that the oxic–anoxic conditions influence the mineral dissolution behavior. Under anoxic conditions, the release of P and Ce occurs stoichiometrically. In contrast, under oxic conditions, the mineral dissolution behavior is incongruent, with dissolving Ce3+ ions oxidizing to CeO2. Reaction product analysis shows the formation of CO2, polymeric C, and oxalate and malate. The presence of more complex forms of organic carbon was also confirmed. Near edge X-ray absorption fine structure spectroscopy measurements at Ce-M4,5 and C-K absorption edges on reacted CePO4·H2O samples in the absence or presence of catechol and dissolved oxygen confirm that (1) the mineral surface converts to the oxide during this reaction, while full oxidation is limited to the near-surface region only; (2) the Ce valence remains unchanged when the reaction between CePO4·H2O and O2 but in the absence of catechol. Carbon K-edge spectra acquired from rhabdophane reacted with catechol under oxic conditions show spectral features before and after reaction that are considerably different from catechol, indicating the formation of more complex organic molecules. Decreases in intensity of characteristic catechol peaks are accompanied by the appearance of new π* resonances due to carbon in carboxyl (ca. 288.5 eV) and carbonyl (ca. 289.3 eV) groups, and the development of broad structure in the σ* region characteristic of aliphatic carbon. Evolution of the C K-edge spectra is consistent with aromatic-ring cleavage and polymerization. These results further substantiate that the presence of catechol, O2 (aq) causes both the oxidation of structural Ce3+ and the transformation of catechol to more complex organic molecules. Scanning Transmission X-Ray Microscopy measurements at the C K and Ce M4,5 edges indicate three dominant organic species, varying in complexity and association with the inorganic phase. Untransformed catechol is loosely associated with CeO2, whereas more complex organic molecules that exhibit lower aromaticity and stronger CO π* resonances of carboxyl-C and carbonyl-C groups are only found in association with the grains. These results further serve as basis to postulate that, in the presence of O2, CeO2 can mediate the oxidative polymerization of catechol to form higher molecular weight polymers. The present work provides evidence for a pathway of biologically-induced, non-enzymatic oxidation of cerium and formation of small CeO2 particles at room temperature. These findings may have implications for carbon cycling in natural and cerium-contaminated soils and aqueous environments.  相似文献   

19.
Scanning electron microscope (SEM) photographs of olivine grains shown that dissolution of olivine may occur more rapidly on some surfaces than on others and that initial dissolution of freshly crushed grains occurs primarily along lattice imperfections such as dislocations or cleavage planes. The SEM photographs generally do not show the presence of thick or continuous residual or precipitated layers which might render the dissolution reaction diffusion controlled. The specific surface area of olivine grains increased greatly during initial dissolution due to formation of etch features. However, despite the increased surface area the rate of dissolution decreased during the experiments. These observations suggest that some assumptions underlying derivation of the diffusion controlled models are invalid for olivine dissolution and suggest that dissolution is controlled by rates of surface reactions.  相似文献   

20.
Previous experiments to determine the aqueous solubility of lead-rich orthoclase in the presence of the ethanoic acid anion (acetate) at 150°C and 50 MPa have shown that the observed fluid compositions are essentially controlled by the presence of secondary mineral precipitates, which buffer dissolved species apart from lead. Data for lead suggest that dissolution increased with increasing fluid ethanoic acid anion content, but the ethanoic acid anion was unstable under the experimental conditions. Additional experiment have now been carried out using pure natural albite and ethanoic acid anion solutions at 150°C and 50 MPa, in which the ethanoic acid anion remains stable. The results for albite again demonstrate the influence on fluid composition of secondary mineral precipitates, but data for silica allow the rates of dissolution to be estimated. Values obtained for the dissolution rate constant increase from 1.8 × 10−7 to 5.3 × 10−7 s−1 with increasing fluid ethanoic acid anion content (0.1–2.5 molal) and approximate to values for quartz and orthoclase dissolution rates for similar PT conditions, reflecting similarity in the mechanisms of dissolution of the minerals' three dimensional (alumino)silicate frameworks. However, these experiments provide no other evidence that the ethanoic acid anion enhances equilibrium solubilities of feldspars or quartz. In contrast to the results for the ethanoic acid anion, data for albite dissolution experiments in the presence of the ethanedioic acid anion (oxalate) at 150°C and 50 MPa show an inhibitionn of solubility (apart from aluminium), while data for the 2-hydroxy-1,2,3-propanetricarboxylic acid trivalent anion (citrate) show considerable enhancement of solubility for aluminium and silicon, and titanium derived from the reaction vessel. The 2-hydroxy-1,2,3-propanetricarboxylic acid trivalent anion is unstable, decaying according to first order kinetics (half life = 1.5 days). In their application to problems of diagenesis in the presence of organic acid anions, these results suggest that the ethanoic acid anion may influence feldspar dissolution by accelerating diagenetic reactions, while geologically short-lived species such as the 2-hydroxy-1,2,3-propanetricarboxylic acid trivalent anion and its decay products may dramatically enhance aluminosilicate solubility.  相似文献   

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