Mineral Replacement Reactions Research Articles

Hydrothermal alteration associated with Mesozoic granite-hosted gold mineralization at the Sanshandao deposit, Jiaodong Gold Province, China

The Sanshandao gold deposit (reserves of more than 200t Au and average grade of 3.96g/t), located at northwestern edge of the Jiaodong Peninsula, eastern North China Craton, is one of the largest gold deposits in the Jiaodong gold province. In this deposit, disseminated- and stockwork-style ores are hosted in Mesozoic granitoids; mineralization and alteration are largely controlled by the regional Sanshandao–Cangshang fault. Host granitic rocks for the deposit display a complex paragenetic sequence of alteration and mineralization. Activities of the Sanshandao–Cangshang fault created structurally controlled permeability allowing for infiltration of hydrothermal fluids, leading to diffusive K-feldspar alteration on the two fault planes. Later, large scale diffusive sericitization symmetrically developed across the main fault, and partially overprinted the earlier K-feldspar alteration. Following the sericitization, relatively small scale silicification occurred, but now it is only retained in the hanging wall of the main fault. Subsequently, the fault gouge formed as a “barrier layer”, which is impermeable for later fluids to move upward. After that, strong pyrite–sericite–quartz alteration occurred only in the footwall of the main fault, and was accompanied by gold precipitation. The last stage carbonation and quartz-carbonate veins marked the waning of gold-related hydrothermal activity. Mass-balance calculations indicate complex behaviors of different types of elements during fluid–rock interaction. Most major elements were affected by intensive mineral replacement reactions. As expected, the fluid-mobile elements, LILE and LREE, generally show moderate to high mobility. It is notable that even the commonly assumed fluid-immobile elements, such as HREE and HFSE, tend to be changed to various degrees. In addition, Y–Ho, Zr–Hf and Nb–Ta fractionations are observed in altered domains. Studies on alteration assemblages and fluid inclusions suggest that the ore-forming fluids were characterized by low salinity (≤8.4wt.% NaCl equiv.), moderate temperature (300–400°C), weakly acidic (pH: 3–5), and relatively reducing (log fO2: ~–28) characteristics. In this type of fluids, gold was most likely transported as Au(HS)2− complex. With alteration going on, log (aK+/aH+) of fluids generally decreased due to significant formation of secondary K-bearing minerals. In addition, there might be a decrease of fO2 from pre-gold alteration stage to the main gold mineralization stage, and decrease of fO2 was probably one of the factors controlling gold precipitation. The Sr and Nd isotopic compositions of hydrothermal minerals, combined with previous H–O and He–Ar isotopic studies, indicate that the hydrothermal fluids were mainly derived from crustal sources (e.g., degassing of felsic magmas and meteoric water), but with involvement of mantle derived components. The gold mineralization event just coincided with reactivation of the North China Craton, as marked by asthenosphere upwelling, voluminous igneous rocks, and high crustal heat flow, which may have provided sufficient heat energy and fluid input required for the formation of the gold deposits.

Hydrothermal replacement of Aragonite by Calcite: interplay between replacement, fracturing and growth

The hydrothermal transformation of single aragonite crystals into polycrystalline calcite has been studied under hydrothermal conditions. The transformation involves a fluid-mediated replacement reaction, associated with fracturing of the initial aragonite crystal and growth of calcite throughout various parts of the reacted aragonite. The observed overall preservation of the crystal morphology is typical of an interface-coupled dissolution-reprecipitation mechanism. Analysis of the crystallographic orientation of the product calcite using electron backscatter diffraction (EBSD) showed little to no link between the two phases under the studied conditions, with calcite crystallites exhibiting dominantly different crystallographic orientations compared to those of the aragonite and of neighbouring calcite domains. The complexity of the observed textures is mainly a result of the combination of fracturing of the crystal and initiation of nucleation and growth at different points of the exposed aragonite surface. Experiments performed with solutions enriched in 18O as a tracer for oxygen exchange and monitored by Raman spectroscopy, showed that carbonate ions in the starting solution are mixed with carbonate from the dissolving aragonite, resulting in an 18O concentration in the product calcite which depended on the local fluid transport through the fractures. As replacement processes among the CaCO3 phases are relevant to a wide range of applications, understanding the mechanisms is essential for the interpretation of observations of natural and/or experimental samples. This study describes the interplay between the replacement process, the fracturing of the crystal and growth of the new phase, calcite, and provides new insights into the mechanism of the aragonite to calcite transition. The combination of the two methods, EBSD and Raman spectroscopy, demonstrates the importance of local fluid composition and transport pathways in determining the isotope and element exchange in mineral replacement reactions.

Mineral replacement reactions in naturally occurring hydrated uranyl phosphates from the Tarabau deposit: Examples in the Cu–Ba uranyl phosphate system

Uranyl phosphates are a mineral group which include a wide range of different species, each containing specific cations within the hydrated interlayer, and often display a geochemical/mineralogical relationship with Fe(III) oxy-hydroxides. The environmental relevance of these U-phases arises from their low solubility at most surface and groundwater conditions, where they can ultimately control aqueous U levels.In the present work, samples of naturally occurring uranyl phosphates from the Tarabau site, included in the Nisa deposit, located in central-eastern Portugal, are studied with X-ray diffraction (XRD), Electron Microprobe (EMP) and Scanning Electron Microscopy, with the purpose of i) identifying uranyl phosphate mineral paragenesis, ii) assessing chemical homogeneity and stoichiometry of the most relevant phases and iii) unraveling possible textural features of mineral reequilibration processes. XRD studies revealed that the analyzed samples comprehend metatorbernite-like structures, consistent with Cu(UO2)2(PO4)2·8H2O formula. Further EMP determinations allowed the definition of nearly stoichiometric Cu and Ba hydrated uranyl phosphates; CuxBa1−x(UO2)2(PO4)2·nH2O intermediate compositions and interlayer cation-depleted phases. The obtained results, combined with textural observations, allowed us to decipher mineral reequilibration reactions affecting the studied samples. Thus, reactive paths involving the replacement of Cu-bearing by Ba-bearing uranyl phosphates, cation-bearing uranyl phosphate by cation-depleted uranyl phosphate and cation-bearing uranyl phosphate by Fe, Al oxy-hydroxides have been defined. However, the studied textural features point toward two different mechanisms of mineral replacement, with superimposed expressions. On one hand, the replacement of Cu by Ba uranyl phosphate phases, and these last by oxy-hydroxides, takes place by coupled dissolution–precipitation reactions. On the other hand, cation depletion affecting uranyl phosphates occurs by a cation exchange process, possibly giving rise to increasing mineral porosity.

Mineral replacement rate of olivine by chrysotile and brucite under high alkaline conditions

Olivine mineral replacement by serpentine is one major alteration reaction of oceanic hydrothermalism. In the present experimental study, olivine grains were replaced by chrysotile and brucite under high alkaline conditions. In our study, olivine replacement implied a spatial and temporal coupling of dissolution and precipitation reactions at the interface between olivine and chrysotile–brucite minerals. Coupled dissolution–precipitation led to the alteration of starting olivine grains (so-called primary or parent mineral) to a porous mineral assemblage of chrysotile and brucite with preservation of the initial olivine morphology. This mineral replacement reaction of olivine (serpentinization) has been characterized using XRD, FESEM and FTIR measurements. Moreover, a simple and novel method is here proposed to quantify the mineral replacement rate (or serpentinization rate) of olivine using thermogravimetric (TG) and differential TG (DTG) analyses. Serpentinization extent depends on the grain size: it is complete after 30 days of reaction for the smallest olivine grains (<30μm), after 90 days of reaction for the intermediate olivine grains (30μm–56μm). For the largest fraction (56–150μm), 55% of serpentinization extent was reached after 90 days. Based on the fitting of the serpentinization extent (ξt) versus time (t) using a kinetic pseudo-second-order model, the serpentinization rates vary from 3.6×10−6s−1 to 1.4×10−7s−1 depending on the olivine grain size. An additional correlation between FTIR spectra analysis and TG measurements is proposed. The mineral replacement reactions frequently observed in natural alteration processes could be a powerful synthesis route to design new porous and/or nanostructured materials.

Posner's cluster revisited: direct imaging of nucleation and growth of nanoscale calcium phosphate clusters at the calcite-water interface

Although many in vitro studies have looked at calcium phosphate (Ca–P) mineralization, they have not emphasized the earliest events and the pathway of crystallization from solvated ions to the final apatitic mineral phase. Only recently has it become possible to unravel experimentally the processes of Ca–P formation through a cluster-growth model. Here we use mineral replacement reactions by the interaction of phosphate-bearing solutions with calcite surfaces in a fluid cell of an atomic force microscope (AFM) and reveal that the mineral surface-induced formation of an apatitic phase proceeds through the nucleation and aggregation of nanosized clusters with dimensions similar to those of Posner's clusters, which subsequently form stable amorphous calcium phosphate (ACP) plates prior to the transformation to the final crystalline phase. Our direct AFM observations provide evidence for the existence of stable Posner's clusters even though no organic template is applied.

Unifying natural and laboratory chemical weathering with interfacial dissolution–reprecipitation: A study based on the nanometer-scale chemistry of fluid–silicate interfaces

Chemical weathering reactions of rocks at Earth's surface play a major role in the chemical cycle of elements, and represent one of the major abiotic sinks for atmospheric CO2. Because natural chemical weathering reactions occur at different and more complex chemical conditions than laboratory-based weathering experiments, it has long been thought that the underlying fluid–mineral interaction mechanisms are different. In contrast to most previous studies that have relied on ion, electron, and X-ray beam techniques (characterized by μm to mm lateral spatial resolution) to obtain chemical depth profiles of altered mineral surfaces, we have used high resolution and energy filtered transmission electron microscopy (HRTEM, EFTEM) to study mineral–fluid interfaces using TEM foils cut directly across the reaction boundaries. This allowed measurements to be made directly in cross section at nanometer to sub-nanometer-resolution. Our measurements of the surface chemistry and structure of a large suite of laboratory-altered and field-weathered silicate minerals indicate the general presence of surface layers composed of amorphous, hydrated silica. In each case, the boundary between the parent mineral and the corresponding silica layer is characterized by sharp, nanometer-scale chemical concentration jumps that are spatially coincident with a very sharp crystalline-amorphous interfacial boundary. TEM, atomic force microscopy (AFM), and aqueous chemistry data suggest that the surface layers are permeable to fluids. Taken together, our measurements are not in agreement with currently accepted models for chemical weathering, in particular the leached layer theory. Most importantly, our data provide critical evidence for a single mechanism based on interfacial dissolution–reprecipitation. This concept not only unifies weathering processes for the first time, but we also suggest that nanoscale-surface processes can have a potentially negative impact on CO2 uptake associated with chemical weathering. The results in this study, when combined with recently published research on fluid-assisted mineral replacement reactions, supports the idea that dissolution–reprecipitation is a universal mechanism controlling fluid–mineral interactions (Putnis and Putnis, 2007). Based on this we propose the existence of a chemical weathering continuum based solely on the interfacial dissolution–reprecipitation mechanism.

ChemInform Abstract: A Novel Route for the Synthesis of Mesoporous and Low‐Thermal Stability Materials by Coupled Dissolution‐Reprecipitation Reactions. Mimicking Hydrothermal Mineral Formation

AbstractReview: 55 refs.

Mineral replacement reactions in solid solution-aqueous solution systems: Volume changes, reactions paths and end-points using the example of model salt systems

The published evidence on whether workplace health and well-being interventions are as effective in male-dominated industries compared with mixed-gender environments has not been synthesised. We performed a systematic review of workplace interventions aimed at improving employee health and well-being in male-dominated industries. We searched Web of Knowledge, PubMed, Medline, Cochrane Database and Web of Science for articles describing workplace interventions in male-dominated industries that address employee health and well-being. The primary outcome was to determine the effectiveness of the intervention and the process evaluation (intervention delivery and adherence). To assess the quality of evidence, Cochrane Collaboration’s Risk of Bias Tool was used. Due to the heterogeneity of reported outcomes, meta-analysis was performed for only some outcomes and a narrative synthesis with albatross plots was presented. After full-text screening, 35 studies met the eligibility criteria. Thirty-two studies delivered the intervention face-to-face, while two were delivered via internet and one using postal mail. Intervention adherence ranged from 50% to 97%, dependent on mode of delivery and industry. 17 studies were considered low risk of bias. Albatross plots indicated some evidence of positive associations, particularly for interventions focusing on musculoskeletal disorders. There was little evidence of intervention effect on body mass index and systolic or diastolic blood pressure. Limited to moderate evidence of beneficial effects was found for workplace health and well-being interventions conducted within male-dominated industries. Such interventions in the workplace can be effective, despite a different culture in male-dominated compared with mixed industries, but are dependent on delivery, industry and outcome. CRD42019161283.

Crystallographic Control of the Hydrothermal Conversion of Calcitic Sea Urchin Spine (Paracentrotus lividus) into Apatite

We analyzed the crystallographic relationships during hydrothermal conversion of a calcitic sea urchin spine into apatite. We identified a pseudomorphic mineral replacement mechanism involving a superficial dissolution of calcite and a subsequent overgrowth of oriented carbonated hydroxylapatite (HA) nanocrystals. Cross-section images of these converted spines show that the dimensions of the HA crystals increase the further they are from the outer surface. This replacement process is favored by an increase in porosity, which enables both fluid and mass to be transported by diffusion, thereby allowing the replacement reaction to progress toward the interior of the spine. These recrystallization reactions take place on the surface of the calcite single crystal, which acts as a substrate for the epitaxial nucleation of HA crystals. The epitaxial relationship observed between the parent calcite crystal and the newly formed apatite crystals can be defined as (0001) apatite//(011̅8) calcite and [10.0] apatite//[4̅4.1] calcite. The apatite crystals are related by the 3-fold axis arising from the trigonal symmetry of the parent calcite crystal. There is therefore a strong structural control which favors the conversion of calcite into apatite. This process coexists with the formation of apatite crystals which are not structurally related to the calcite crystal and which may precipitate within the porosity of the material. The analysis of crystallographic relationships is a fundamental step toward understanding mineral replacement reactions, which can be used for the synthesis of artificial materials with predefined shapes and microstructural characteristics, a technique that may have interesting technological applications.

A Novel Route for the Synthesis of Mesoporous and Low-Thermal Stability Materials by Coupled Dissolution-Reprecipitation Reactions: Mimicking Hydrothermal Mineral Formation

Replacement reactions ('pseudomorphism') commonly occur in Nature under a large range of conditions (T 25 to >600 degrees C; P 1 to >5 kbar). Whilst mineral replacement reactions are often assumed to proceed by solid-state diffusion of the metal ions through the mineral, many actually proceed via a coupled dissolution and reprecipitation (CDR) mechanism. In such cases, a starting mineral is dissolved into a fluid and this dissolution is coupled with the precipitation of a replacement phase across the reaction front. In cases where there are close relationships between the crystal structures of the parent and newly formed minerals, the replacement can be topotactic (interface-coupled dissolution and reprecipitation). The kinetics and chemistry of the CDR route are fundamentally different from solid-state diffusion and can be exploited i) for the synthesis of materials that are often difficult to synthesise via traditional methods and ii) to obtain materials with unique properties. This review highlights recent research into the use of CDR for such synthetic challenges. Emphasis has been given to i) the use of CDR to synthesise compounds with relatively low thermal stability such as the thiospinel mineral violarite ((Ni,Fe)(3)S(4)), ii) preliminary work into use of CDR for the production of roquesite (CulnS(2)), a potentially important photovoltaic component and, iii) examples where the textures resulting from CDR reactions are controlled by the nature and texture of the parent phase and the reaction conditions; these being the formation of micro-porous gold and three-dimensional ordered arrays of nanozeolite of uniform size and crystallographic orientation.

Comparison of numerical codes for geochemical modelling of CO 2 storage in target sandstone reservoirs

Long-term containment of CO 2 and storage security depends mainly on physical and geochemical trapping mechanisms. Injected CO 2 dissolves in the formation fluid and causes a sharp decrease in pH which in turn drives the dissolution and precipitation of minerals. Geochemical modelling is an important tool to understand and predict the behaviour of CO 2 reactivity. In this paper three numerical codes, PHREEQC, GEM and TOUGHREACT, are compared with respect to brine – CO 2 – rock reactions. Formation water compositions and mineralogies of three sandstone core samples from target CO 2-storage formations were used as input for kinetic models. Mineral replacement reactions were observed when CO 2 injection was initiated in all scenarios. While PHREEQC and GEM were generally in good agreement, TOUGHREACT gave diverging predictions on two models. It is considered that the discrepancies are caused primarily by the differences in the thermodynamic databases and activity models. The uncertainties in these calculations suggest that appropriate experimental tests should be performed to validate the models, so that they can be used to make predictions at the field scale.

A novel pre-treatment of calaverite by hydrothermal mineral replacement reactions

We report a new method for pre-treatment of refractory gold-bearing tellurides employing the hydrothermal mineral replacement reactions. The method is illustrated by the replacement of calaverite by metallic gold at 150–250 °C under vapor saturated pressures. The influences of temperature, pH, and additional salts (NaCl and Na2SO4) on the conversion rate were investigated using the orthogonal array design method. The results indicate that temperature is the most significant factor, followed by pH, and then additional salts. The optimal condition for fast and low cost conversion is 200 °C, pH 6.0, 0.01 M NaCl, and <38 μm particle size. Under this condition, the conversion can be completed within 15 h. These preliminary results indicate that the hydrothermal mineral replacement reaction is a promising pre-treating step for gold-bearing tellurides processing.

High-temperature amphibolization synchronous with enderbite migmatization of mafic granulites in granulite-enderbite-charnockite complexes in Karelia

Detailed data on the area of lakes Notozero-Kovdozero and Lake Kerchug are used to analyze petrological aspects (mineral replacement reactions Opx + Cpx + Pl → Hbl with plagioclase of various composition, mineral compositions, and P-T parameters) of the high-temperature amphibolization of mafic granulites in the Archean granulite-enderbite-charnockite (GECH) complexes of Karelia. It was concluded that the amphibolization of the mafic crystalline schists in GECH complexes occurs at the peripheral zones of enderbite migmatization. In the course of pyroxene replacement by hornblende, the primary two pyroxene-plagioclase granulites are transformed into two pyroxene-amphibole-plagioclase crystalline schists with more sodic plagioclase and, if the process is more intense, into amphibolites. Our results testify that equilibrium in mafic crystalline schists at the peak of granulite metamorphic and the inflow of Na-rich fluids begins to shift toward an increase in the content of Na-bearing mafic minerals (amphiboles) instead of pyroxenes. At the same time, more sodic plagioclase is formed in place of labradorite-bytownite. The process of amphibolization in these rocks differs from that related to either retrograde metamorphism or younger diaphthoresis under amphibolite-facies conditions in geochemical regime, P-T parameters, and the type of hornblendes.

Mechanism and kinetics of pseudomorphic mineral replacement reactions: A case study of the replacement of pentlandite by violarite

Although pseudomorphic mineral replacement reactions are common in all geological environments, and have long been considered important to many geological processes such as metamorphism, metasomatism, diagenesis, and chemical weathering, their mechanisms are still not well known. We present a combined textural and kinetic study of the replacement of pentlandite, (Fe,Ni) 9S 8, by violarite (NiFe) 3S 4, and describe the mechanisms and kinetic behavior of this reaction by considering the role of the fluid phase, the causes of coupling between pentlandite dissolution and violarite precipitation, the rate-limiting steps controlling the kinetic behavior, and the origin of the length scale of the features preserved during pseudomorphism. The experiments were conducted under mild hydrothermal conditions (80–210 °C, vapor saturated pressures). Reaction kinetics shows a complex behavior depending on various physical and chemical parameters including temperature, pH, concentrations of various reaction species, solid-weight-to-fluid-volume-ratio and specific surface area. The rate of replacement (i) increases with temperature from 80 to 125 °C, then decreases as temperature further increases to 210 °C, (ii) first increases then decreases with decreasing pH from pH 6 to 1, (iii) increases with increasing concentration of oxidants such as O 2(aq), H 2O 2, and KMnO 4, but decreases with increasing concentration of Ni 2+ and Fe 3+, and with increasing solid-weight-to-fluid-volume ratio, (iv) increases linearly with the specific surface area. This kinetic behavior as well as the resulting textures revealed a coupled dissolution–reprecipitation reaction mechanism. Nanometer-scale pseudomorphic replacement, through which the crystallographic orientation of pentlandite is inherited by violarite, occurs only between 1 < pH < 6, and spatial coupling between dissolution and reprecipitation is controlled by the local solution chemistry as well as by epitaxial nucleation mediated by the pentlandite substrate. The kinetic results show that pentlandite dissolution is rate-limiting under mild acidic to neutral conditions (1 < pH < 6), while violarite precipitation is rate-limiting under strong acidic conditions (pH 1). The difference in rate-limiting steps influences the coupling mechanism and causes the different degrees of preservation (length scale of pseudomorphism) and different morphologies observed at high and low pHs: pentlandite dissolution being rate-limiting results in nanoscale coupling between dissolution and precipitation and thus nanoscale pseudomorphism (length scale <20 nm), in which the replacement precisely preserves the morphology and internal details, resembling remarkably the natural pentlandite/violarite assemblages. In contrast, violarite precipitation being rate-limiting results in microscale pseudomorphism (length scale ∼10 μm): the morphology of the pentlandite grains is only roughly preserved and internal details are not preserved. This case study illustrates some general principles of replacement reactions proceeding via the coupled dissolution–reprecipitation mechanism: (i) primary mineral dissolution needs to be rate-limiting compared to the secondary mineral precipitation in order to achieve a high degree pseudomorphic replacement; (ii) the effects of solution composition on reaction kinetics can be qualitatively rationalized by considering the rate-limiting step reaction.

Mineral Replacement Reactions

Research Article| January 01, 2009 Mineral Replacement Reactions Andrew Putnis Andrew Putnis Institut für Mineralogie, University of Münster, Münster, 48149 Germany, putnis@uni-muenster.de Search for other works by this author on: GSW Google Scholar Author and Article Information Andrew Putnis Institut für Mineralogie, University of Münster, Münster, 48149 Germany, putnis@uni-muenster.de Publisher: Mineralogical Society of America First Online: 09 Mar 2017 © The Mineralogical Society Of America Reviews in Mineralogy and Geochemistry (2009) 70 (1): 87–124. https://doi.org/10.2138/rmg.2009.70.3 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Andrew Putnis; Mineral Replacement Reactions. Reviews in Mineralogy and Geochemistry 2009;; 70 (1): 87–124. doi: https://doi.org/10.2138/rmg.2009.70.3 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Whenever a mineral or mineral assemblage comes into contact with a fluid with which it is out of equilibrium, reequilibration will tend to take place to reduce the free energy of the whole system (i.e., of the solid + fluid). Such fluid-solid interactions span a very wide range of possible reactions, and are responsible for most of the mineral assemblages we see in the Earth’s crust. However, before discussing mineral replacement reactions, we will put them into the broader context of fluid-solid interactions by considering some examples of such reequilibration. In the simplest case, we could consider the situation where... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Mechanism of pseudomorphic mineral replacement reactions revealed by a combined textural and kinetic study

Mechanism of pseudomorphic mineral replacement reactions revealed by a combined textural and kinetic study

In situ AFM observations of mineral replacement reactions on sulphate and carbonate surfaces

In situ AFM observations of mineral replacement reactions on sulphate and carbonate surfaces

Oxygen isotope zoning profiles in hydrothermally altered feldspars: Estimating the duration of water-rock interaction

Research Article| January 01, 2004 Oxygen isotope zoning profiles in hydrothermally altered feldspars: Estimating the duration of water-rock interaction David R. Cole; David R. Cole 1Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Search for other works by this author on: GSW Google Scholar Peter B. Larson; Peter B. Larson 2Department of Geology, Washington State University, Pullman, Washington 99164-2812, USA Search for other works by this author on: GSW Google Scholar Lee R. Riciputi; Lee R. Riciputi 3Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Search for other works by this author on: GSW Google Scholar Claudia I. Mora Claudia I. Mora 4Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37996-1410, USA Search for other works by this author on: GSW Google Scholar Author and Article Information David R. Cole 1Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Peter B. Larson 2Department of Geology, Washington State University, Pullman, Washington 99164-2812, USA Lee R. Riciputi 3Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Claudia I. Mora 4Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37996-1410, USA Publisher: Geological Society of America Received: 03 Jun 2003 Revision Received: 24 Sep 2003 Accepted: 29 Sep 2003 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2004) 32 (1): 29–32. https://doi.org/10.1130/G19881.1 Article history Received: 03 Jun 2003 Revision Received: 24 Sep 2003 Accepted: 29 Sep 2003 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David R. Cole, Peter B. Larson, Lee R. Riciputi, Claudia I. Mora; Oxygen isotope zoning profiles in hydrothermally altered feldspars: Estimating the duration of water-rock interaction. Geology 2004;; 32 (1): 29–32. doi: https://doi.org/10.1130/G19881.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The characterization of intragrain mineralogical and isotopic zoning patterns provides the basis for estimating the duration of fluid-rock interaction associated with mineral replacement reactions. In the Rico, Colorado, hydrothermal system, oxygen isotope ratios in reaction rims on partially reacted plagioclase feldspar exhibit some of the largest gradients yet reported for individual grains (to 15‰). The extent of rim formation and accompanying isotopic exchange vary across the system as a function of temperature, fluid isotope composition, and the local fluid/rock ratio. Distal feldspars show narrow rims with 18O enrichments relative to pristine feldspars. Feldspars intermediate or proximal to the system's center have wide reaction rims or are completely exchanged and show 18O depletions. Formation times of reaction rims and associated isotopic patterns have been estimated with a coupled reaction-diffusion model that suggests that hotter (∼250–350 °C) hydrothermal circulation was active for ∼100–300 k.y. in the center part of the system, perhaps only while the igneous heat engine was still magma. Cooler (∼150–200 °C) circulation was widespread, lasting for >1000 k.y. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Mineral replacement reactions: from macroscopic observations to microscopic mechanisms

AbstractMineral replacement reactions take place primarily by dissolution-reprecipitation processes. Processes such as cation exchange, chemical weathering, deuteric alteration, leaching, pseudomorphism, metasomatism, diagenesis and metamorphism are all linked by common features in which one mineral or mineral assemblage is replaced by a more stable assemblage. The aim of this paper is to review some of these aspects of mineral replacement and to demonstrate the textural features they have in common, in order to emphasize the similarities in the underlying microscopic mechanisms. The role of volume change and evolution of porosity is explored both from natural microtextures and new experiments on model replacement reactions in simple salts. It is shown that the development of porosity is often a consequence of mineral replacement processes, irrespective of the relative molar volumes of parent and product solid phases. The key issue is the relative solubility of the phases in the fluid phase. Concepts such as coupled dissolution-precipitation, and autocatalysis are important in understanding these processes. Some consequences of porosity generation for metamorphic fluid flow as well as subsequent crystal growth are also discussed.

The role of biomineralization in microbiologically influenced corrosion.

Synthetic iron oxides (goethite, alpha-FeO.OH; hematite, Fe2O3; and ferrihydrite, Fe(OH)3) were used as model compounds to simulate the mineralogy of surface films on carbon steel. Dissolution of these oxides exposed to pure cultures of the metal-reducing bacterium, Shewanella putrefaciens, was followed by direct atomic absorption spectroscopy measurement of ferrous iron coupled with microscopic analyses using confocal laser scanning and environmental scanning electron microscopies. During an 8-day exposure the organism colonized mineral surfaces and reduced solid ferric oxides to soluble ferrous ions. Elemental composition, as monitored by energy dispersive x-ray spectroscopy, indicated mineral replacement reactions with both ferrihydrite and goethite as iron reduction occurred. When carbon steel electrodes were exposed to S. putrefaciens, microbiologically influenced corrosion was demonstrated electrochemically and microscopically.