Changes In Fluid Chemistry Research Articles

Fluid-rock reaction path modeling of uranium mobility in granite-related mineralization: A case study from the Variscan South Armorican Domain

The mobilization of uranium in granite-related systems presents a complex interplay of chemical and hydrodynamic factors. This is particularly obvious within syn-orogenic detachment zones where per descensum surface-derived fluids interact with per ascensum deeply sourced hydrothermal fluids. In this study, we employ a thermo-hydro-chemical (TH-C) modeling approach to explore the multifaceted processes that govern uranium transport and deposition in such environments. Our findings indicate that uranium mobility is not solely determined by the oxidizing nature of the percolating surface-derived fluids. Actually, the oxidation-reduction potential of these fluids varies as they flow in the crust, ultimately adjusting towards more neutral or mildly reducing conditions conducive to uranium dissolution and precipitation. Even in the presence of magnetite, which enhances the reductive potential of the fluids, uranium continues to dissolve, albeit in much smaller quantities, with U(IV) being the predominant species in the aqueous phase. The study highlights the crucial roles of temperature, pH, and fluid/rock interaction ratios in influencing uranium leaching efficacy. High fluid/rock ratios enhance uranium extraction from source rocks. A fluid/rock ratio around 1 is optimal, maximizing the dissolution of uranium-bearing minerals in the source rock and promoting the precipitation of uranium minerals in different locations along the fluid pathway due to changes in fluid chemistry. The TH-C modeling has the potential to be applied to a variety of other uranium deposits, developed below 300°C.

Polyphased gold enrichment as a key process for high-grade gold formation: Insights from the 10 Moz Jundee-Bogada camp (Yilgarn Craton, Western Australia)

High-grade (> 10 g/t) gold mineralization in orogenic gold deposits is of significant economic importance. Understanding the formation of such enriched ore zones is critical for gold exploration success. The world-class Jundee-Bogada gold camp in the Yilgarn Craton of Western Australia comprises both high-grade (avg. > 10 g/t, Jundee deposit) and low-grade (avg. < 3 g/t, Bogada prospect) lodes, despite shared host stratigraphy. The paragenetic framework established for the Jundee gold deposit suggests that the overall gold endowment developed over three deformation events. An early episode of low-grade gold mineralization is associated with colloform-crustiform veins that formed during extensional deformation (DJB2A). A switch to transtensional deformation (DJB2B) resulted in brecciation of the colloform-crustiform veins and coeval deposition of native gold. Late reverse faults record evidence for a third mineralization stage resulting from a NE-SW-directed shortening (DJB3). Mineralization during this late stage was dominantly low-grade, with local occurrences of ultra-high-grade ore zones (> 100 g/t). Each event records transient changes in fluid chemistry during continued hydrothermal activity that spanned local deformation histories. We argue that at the Jundee gold deposit, protracted gold enrichment during three polyphased mineralization episodes resulted in the formation of high-grade gold ores. Whereas the complete metallogenic history is recorded at the Jundee deposit, gold within the Bogada prospect was introduced solely during the late contractional stage (DJB3), resulting in a bulk low-grade endowment. We hypothesize that gold enrichment in high-grade orogenic gold deposits is a direct consequence of the spatial superimposition of protracted ore-forming events.

A geochemically informed leak detection (GILD) model for CO2 injection sites

Early detection of CO2 leakage through monitoring is important to ensure long-term safety for geologic carbon storage (GCS). A geochemically informed leak detection (GILD) model has been developed for groundwater chemistry monitoring at CO2 injection sites. The GILD model integrates a geochemical model that simulates fluid chemistry changes in CO2 leakage events and a Bayesian belief network (BBN) model that evaluates monitoring observations to identify leakages. The geochemical model is implemented using Geochemists’ Workbench to assess fluid chemistry changes as a result of small CO2 leakage in an above-zone monitoring interval (AZMI) formation with varying mineral assemblages and background fluids. Response functions are fitted to the output of the geochemical model and are translated to conditional probabilities in the BBN model. The BBN model gives operational prediction of the leak probability given a set of groundwater monitoring measurements and the probability of detecting a leak at a given magnitude. The detection capabilities of multiple monitoring parameters are compared. For aquifers that contain calcite, it is valuable to incorporate other monitoring parameters with pH to increase the sensitivity of detection. For aquifers with no calcite, pH alone is a sensitive parameter. This research illustrates a method of identifying CO2 leakage into aquifers with both geochemical and statistical tools.

Effects of different types of fractures on shale gas preservation in Lower Cambrian shale of northern Sichuan Basin: Evidence from macro-fracture characteristics and microchemical analysis

The Lower Cambrian Qiongzhusi shale is the main producing layer of shale gas in the northern Sichuan Basin. Natural fractures are considered an important factor that influences the exploration and development of shale gas. In this study, outcrops, drill cores, thin sections, fluid inclusions and rare earth element (REE) were analyzed to determine the characteristics, changes in fluid chemistry, and fluid source of different types of fractures and then reveal their effects on the accumulation and preservation of shale gas. Natural fractures of Qiongzhusi shale are mainly composed of non-strata-bounded fractures (NSBFs), strata-bounded fractures (SBFs), and bed-parallel fractures (BPFs). NSBFs span multiple layers, which can significantly enhance the vertical connectivity of shale reservoirs. There are three dominant orientations of NSBFs, as N-S, NNE-SSW, and E-W trends. The E-W trending fractures, which intersect with the maximum principal stress (NWW-SEE) at a small angle, have larger permeability and control the vertical leakage of shale gas. SBFs are confined to individual layers. Homogenization temperatures of aqueous inclusions in SBF veins vary from 149.7 to 172.3 °C. Calcite veins exhibit positive Eu anomalies (δEu = 11.71, 27.9). Analysis of fluid inclusions and rare earth elements indicated that SBF vein-precipitating fluids were derived from the surrounding wall rock. The development of SBFs contributes to shale gas enrichment. BPFs are parallel to bedding planes or intersect at a low angle (<20°). Microstructural analysis suggests that cemented BPFs form from the multiple crack-seal processes. The temperature of fluid during mineral precipitation exceeds 200 °C. REE concentrations vary significantly across the BPF veins (δEu = 2.31–119.37), donating that fluid characteristics episodically changed during vein growth. The methane inclusions trapped in cements and mixing externally sourced fluids indicate that BPFs are the preferential fluid-flow pathway of shale gas and controls the lateral migration of shale gas.

Rare Time Series of Hydrothermal Fluids for a Submarine Volcano: 14 Years of Vent Fluid Compositions for Brothers Volcano, Kermadec Arc, New Zealand

AbstractHydrothermal vent fluids from Brothers submarine arc volcano were previously collected in 2004, 2005, and 2017. We present new data from 2018 along with a unique time series of a submarine volcano hosting two distinct types of hydrothermal venting to better understand subsurface processes and how they evolve over time. Samples were collected from known venting locations along the NW Caldera, the Upper and Lower Cone sites, and the newly sampled Upper Caldera site. The NW Caldera wall and Upper Caldera vent fluid compositions are controlled by high-temperature water-rock interactions and phase separation between 2004 and 2018. Fe/Mn molar values suggest that the magmatic impact on all fields has been increasing over time. The Upper Cone has varying influences, including short-term pulses of magmatic degassing, as revealed in K-Mg-SO4 ternary diagrams, Fe/Mn values, and δD and δ18O data. The Lower Cone is dominated by low temperatures and CO2 degassing and shows a pulse in magmatic influence in 2017, followed by a decrease toward earlier conditions in 2018. The 2017 pulse was accompanied by the increase of an enigmatic, soluble MgSO4 phase, potentially due to the “mining” of a magmatic brine sequestered inside the cone. Stable isotope data across the sites indicate pulses of magmatic waters in 2004 and 2017, immediately followed by episodes of more seawater-dominated fluids in 2005 and 2018. Magmatic degassing, phase separation, permeability, and mineral solubility all strongly influence changes in vent fluid composition. This study highlights the dynamic nature of the Brothers volcano hydrothermal system and the changes in fluid chemistry that may affect resultant mineralization.

Response of Mg isotopes to dolomitization during fluctuations in sea level: Constraints on the hydrological conditions of massive dolomitization systems

Marine dolomitization processes are characterized by complex variations in hydrological conditions and pore-fluid chemistry. Deposition of massive dolomitized carbonates on the Comanche Platform of south Texas, USA, during the Albian coincided with multiple fluctuations in sea level, thereby providing an ideal setting to study the response of magnesium isotopes to dolomitization during eustatic sea-level change. In this study, we conducted Mg, C, and O isotope analyses and complimentary mineralogical and petrographic investigations of dolomitized massive carbonates of the Albian Edwards Group in the Comanche Platform. Petrographic observations indicate that the carbonate rocks in the studied units were not altered by deep burial diagenesis or hydrothermal fluids. Based on our petrographic observations and the trace element and C–O isotope data, we infer the dolomites were formed via syn-depositional dolomitization during a period of low sea level. The δ26Mg values of the dolomites increase rapidly from −2.5‰ to −1.8‰ in the basal part of the unit, reflecting a change in fluid chemistry caused by dolomitization in a restricted marine environment. Subsequently, δ26Mgdolomite values gradually decrease back to their initial value of approximately −2.5‰ due to seawater replenishment during transgression. The observed variability in dolomite δ26Mg values reflects changes in the connectivity of the platform with the open ocean during marine transgressions. However, the δ26Mgdolomite values do not vary with the high-frequency eustatic sea-level change recorded in the lithological variations, indicating uniform hydrologic conditions of the massive dolomitization system despite the hydrodynamic variations in the sedimentary environment. Therefore, we propose that massive dolomitization systems are mostly fluid-buffered and, as a result, Mg isotopes of dolomites can be used to trace changes in the paleo-marine environment, such as basin connectivity.

Comparación de los alcances de terapia manual, agentes electrofísicos o combinados para el abordaje del dolor lumbar crónico en adultos

Introducción: el objetivo de esta revisión fue comparar los alcances de la terapia manual, los agentes electrofísicos o combinados para el abordaje del dolor lumbar crónico en personas de 20 a 60 años. &#x0D; Materiales y métodos: estudio descriptivo de revisión narrativa de artículos ubicados en PubMed y EBSCOhost publicados en inglés y español durante el periodo 2015-2020, utilizando como estrategia la combinación de descriptores relacionados a modalidades de terapia manual y agentes electrofísicos. Además, se consultó por medio de una encuesta de criterio de expertos a 30 terapeutas físicos, 7 del sector público y 23 del sector privado, de los cuales respondieron 16. Se incluyeron 29 artículos, clasificados según el nivel de evidencia de Sackett como sigue: 19 artículos de nivel 1 (66%), 5 de nivel 2 (17%), 3 de nivel 3 (10%) y 2 de nivel 5 (7%). &#x0D; Resultados: las modalidades de terapia manual y agentes electrofísicos reportaron reducir el dolor y mejorar la capacidad funcional. Otros alcances de la terapia manual son la reducción de la compresión nerviosa por la herniación de disco, mejora en los parámetros respiratorios, una reducción del grado de deslizamiento vertebral en espondilolistesis, cambios en la química del líquido intersticial y mejora en la amplitud del movimiento. &#x0D; Conclusiones: la terapia manual y los agentes electrofísicos son efectivos en el abordaje de pacientes con dolor crónico lumbar reduciendo el dolor y mejorando la capacidad funcional. Son complemento a otros tratamientos conservadores antes de progresar a manejos más costosos. Debe haber una intervención multimodal que incluya educación y ejercicios en un enfoque bio psicosocial. &#x0D;

The interaction of tectonics, climate and eustasy in controlling dolomitization: A case study of Cenomanian–Turonian, shallow marine carbonates of the Iberian Basin

abstractDuring the Cretaceous, high global sea‐level and low latitudinal temperature variations led to the growth of epeiric carbonate platforms. Platform‐scale dolomitization of these platforms is not common, reflecting the low Mg/Ca ratio of seawater and a humid climate. This study describes the processes governing pervasive dolomitization of a land‐attached carbonate platform within the Iberian Basin. Dolomite is planar to sub‐planar with a geochemical signature consistent with dolomitization from penesaline seawater. Dolomitization was most pervasive during a 1 Myr period in the middle Cenomanian, by repeated reflux of seawater from brine pools formed on the top of a southward‐prograding carbonate platform. Tilting and structural reorganization in the Upper Cenomanian led to a reversal in polarity of the platform, and dolomitization was restarted by the northward reflux of seawater. Rising relative sea‐level and oceanic acidification led to back‐stepping of the platform such that the supply of dolomitizing fluids was cut off. In the Lower Turonian, pervasively dolomitized rudist rudstone facies in the south of the study area indicate that dolomitization restarted, either penecontemporaneously or later, from highly evaporated Campanian–Maastrichtian seawater. A systematic increase in dolomite crystal size up‐section ties broadly, but not entirely, to stratigraphy. It is possible that these textural differences reflect changes in fluid chemistry, limestone permeability or precursor rock texture. However, the lack of stratigraphic conformance, and the preservation of the earliest‐formed dolomite only in the oldest sediments, could indicate a progressive recrystallization of early‐formed dolomite through repeated reflux of brines. As such, the succession appears to preserve a fossilized record of dolomite recrystallization through time during the Cenomanian–Turonian. The results of this study therefore provide a record of the progressive dolomitization of a carbonate platform and demonstrate the important interplay of climate and basin‐scale tectonics on dolomite distribution and crystallinity.

Evaporite-bearing orogenic belts produce ligand-rich and diverse metamorphic fluids

Detailed petrologic and chemical investigation of mid-amphibolite facies calcareous, scapolite-rich metasedimentary rocks from the Mount Isa region in northern Australia is used to explore changing fluid chemistry with prograde metamorphism. The presence of widespread scapolite with Cl- and variably SO4-rich compositions in upper amphibolite facies rocks makes it unavoidable that the regional metamorphic fluids were locally highly saline and oxidised, and that high salinities persisted throughout metamorphism. Electron microprobe analyses and chemical maps of individual scapolite grains show zoning in Cl and S, likely to reflect buffering of the metamorphic fluid by scapolite during progressive metamorphism. The zoning in Cl and S demonstrates that scapolite has the potential to record changes in fluid chemistry during metamorphism. The variation in scapolite composition between samples, in combination with whole rock geochemistry, shows that different layers within this heterogenous rock package generated fluids of different chemistries. Interaction between scapolite-bearing rocks and externally-derived magmatic or metamorphic fluids that are out of equilibrium drives scapolite breakdown, releasing Cl to the fluid. In the Mount Isa region, metamorphic fluid production was enhanced by periods of magmatism, which promoted development of a regionally extensive and unusually saline fluid system that was active at multiple stages over a 250 million-year period. The highly saline and oxidised fluids formed through interaction with scapolite are well suited to transporting a broad range of metals, and may explain the diverse range of syn-orogenic mineral deposits in the Mount Isa Inlier. Metamorphic belts with large volumes of evaporitic material are ideal for generating a broad spectrum of syn-orogenic hydrothermal ore deposit types - including Fe oxide Cu-Au, Fe sulphide Cu-Au, Mo-Re and U-REE, but lacking the Au-only deposits found in typical orogenic belts. Unlike regions hosting traditional orogenic gold deposits, belts containing evaporitic sequences can preserve Cl-rich minerals such as scapolite in the metamorphosed source region, allowing them to remain active as ore forming systems through relatively high-grade metamorphism and multiple stages of tectonism. Periods of supercontinent breakup, such as the Mesoproterozoic, may have resulted in the formation of large, intracontinental basins well suited to the development of widespread evaporitic sequences. This, in combination with overprinting orogenesis and high temperature magmatism, may have provided the ingredients for widespread ore deposit formation at a global scale.

New insights into application of nanoparticles for water-based enhanced oil recovery in carbonate reservoirs

Crude oil, water and rock (CWR) surface chemistry is a key parameter in oil and gas recovery from hydrocarbon reservoirs. This paper presents the chemistry of CWR interaction in presence of two water soluble nanoparticles for carbonate rocks. Two most common nanoparticles of aluminium oxide (Al2O3) and silica (SiO2) were selected and utilised for this study. Calcite was first modified to an oil-wet system to resemble the reservoir wetting condition then treated with nano-fluids containing under study nanoparticles at different concentrations. Alteration of wettability was then quantified using contact angle measurements, and zeta potential analysis. The change in fluid chemistry of the water due to presence of nanoparticles was also monitored before and after treatment of carbonate rock. The results show that after treatment of the oil-wet samples with nano-fluids, the solution’s pH decreased for SiO2 while it increased slightly for Al2O3. The contact angle results show a decrease trend for both nanoparticles but more pronounced for Al2O3. These results are in line with zeta potential results in which very negative surface charge for an oil-wet rock was converted to less negative or even positive for certain concentrations of nano-particles. Floating phenomenon also applied to calculate the level of water percentage between floated and sank powder for the modified calcite where amount of water level increased significantly when nanoparticles added to water solutions. Comparison of all tests show that silica nano-fluid with concentration between 0.1 and 2 wt % can be efficient EOR agent. High salinity is definitely not a good option to formulate nano-fluids such as alumina and silica at high concentrations showing inverse effects.

Enhanced hydrothermal processes at the new-born Lusi eruptive system, Indonesia

Little is known about the processes taking place in new-born hydrothermal systems. We investigate the eruptive activity of Lusi, a sediment-hosted hydrothermal system active since 2006 in East Java, Indonesia. We show that superimposed on the regular geysering activity, Lusi features periods of enhanced hydrothermal processes during which boiling mud breccia is violently discharged from the eruptive vents. This results in sudden flooding lasting from several minutes to several hours and featuring almost instantaneous temperature peaks (i.e. from 35 °C to more than 65 °C in less than 2 min). Such activity (here named hydrothermal waves) is marked by high-frequency seismic radiations and is distinguished by sharp peaks of CH4 and CO2 concentrations in the erupted fluids. This suggests fluids upwelling from at least tents of meters below the near-surface. The injection into the shallow plumbing system of CH4- and CO2-rich batches of fluids may promote instabilities in the mud-breccia column leading to the hydrothermal waves. Our findings provide key insights into the deep charging dynamics of a new-born hydrothermal system and highlight the effects imposed by subtle variations in fluid-chemistry changes at depth.

Impact of Pore Fluid Chemistry on Fine‐Grained Sediment Fabric and Compressibility

AbstractFines, defined here as grains or particles, less than 75 μm in diameter, exist nearly ubiquitously in natural sediment, even those classified as coarse. Macroscopic sediment properties, such as compressibility, which relates applied effective stress to the resulting sediment deformation, depend on the fabric of fines. Unlike coarse grains, fines have sizes and masses small enough to be more strongly influenced by electrical interparticle forces than by gravity. These electrical forces acting through pore fluids are influenced by pore fluid chemistry changes. Macroscopic property dependence on pore fluid chemistry must be accounted for in sediment studies involving subsurface flow and sediment stability analyses, as well as in engineered flow situations such as groundwater pollutant remediation, hydrocarbon migration, or other energy resource extraction applications. This study demonstrates how the liquid limit‐based electrical sensitivity index can be used to predict sediment compressibility changes due to pore fluid chemistry changes. Laboratory tests of electrical sensitivity, sedimentation, and compressibility illustrate mechanisms linking microscale and macroscale processes for selected pure, end‐member fines. A specific application considered here is methane extraction via depressurization of gas hydrate‐bearing sediment, which causes a dramatic pore water salinity drop concurrent with sediment being compressed by the imposed effective stress increase.

The formation of geyser eggs at Old Faithful Geyser, Yellowstone National Park, U.S.A.

One geyser egg (a smooth, oval, siliceous pebble found in alkali chloride hot pools) from the siliceous sinter slope surrounding Old Faithful Geyser was examined to determine its genesis, sinter architecture and elemental composition. The multi-technique approach included Scanning Electron Microscopy (SEM), petrographic microscopy, X-Ray Diffraction, Energy Dispersive Spectroscopy, iTRAX Core Scanner and Computerised Tomography (CT) scans. The geyser egg architecture consists of alternating smooth and porous concentric bands of opal-A silica around a nucleus. These alternating bands are signatures of changes in the degree of silica oversaturation of the discharging fluid. CT scans mapped changes in density throughout the sample and also showed concentric banding of varying density around a core. SEM observations showed the geyser egg has an abiotic origin with subsequent microbial filamentous void infill creating an abiotic-biotic sinter structure. iTRAX scans revealed the geyser egg preserved signatures of changes in fluid chemistry with time, and that the core is rich in arsenic and calcium. iTRAX scans also documented significantly higher concentrations of gallium in the geyser egg compared to those documented in rhyolites and tuffs from the same area. Unravelling geyser egg formation mechanisms and their microbial content provide useful insights on fluid chemistry, water temperature, and flow conditions in these unique hot spring environments.

A chemo-mechanical insight into the failure mechanism of frequently occurred landslides in the Loess Plateau, Gansu Province, China

Thick loess deposits are considered problematic soils due to their susceptibility to collapse suddenly and in large volumes upon increase of water content. In the past decades, a large number of landslides occurred in the Loess Plateau in Gansu Province, north-western China, triggered by the extensive irrigation. The increase of water content has been identified as a key factor controlling the loess strength. However, the role of long-term saturation and pore fluid chemistry changes has not been investigated systematically. This paper reports on an experimental study on loess samples from Heitai loess terrace (Yongjing, Gansu) carried out through chemical analyses, oedometer and ring shear tests. The natural pore fluid was found to be a concentrated saline solution in unsaturated soil condition. Upon saturation, the pore ion concentration drop can contribute to shear strength loss in the clay component and volume decrease. A prolonged exposure to the irrigation water might facilitate cement dissolution, which could result in further weakening.

Rapid reactions between CO2, brine and silicate minerals during geological carbon storage: Modelling based on a field CO2 injection experiment

The dissolution of CO2 into formation brines and the subsequent reactions of the CO2-charged brines with reservoir minerals are two key processes likely to increase the security of geological carbon-dioxide storage. These processes will be dependent on the permeability structure and mineral compositions of the reservoirs, but there is limited observational data on their rates. In this paper we report the cation and anion concentrations and Sr, oxygen and carbon isotopic compositions of formation waters from four extraction wells sampled at surface, over ~6months after commencement of CO2 injection in a five spot pattern for enhanced oil recovery at the Salt Creek field, Wyoming. Sampled fluids, separated from the minor oil component, exhibit near-monotonic increases in alkalinity and concentrations of cations but little change in Cl and Br concentrations and oxygen and deuterium isotope ratios. The increases in alkalinity are modelled in terms of reaction with reservoir calcite and silicate minerals as the changes in fluid chemistry and Sr-isotopic compositions are inconsistent with simple addition of injected fluids sampled over the course of the experiment. The reservoir mineral chemical and isotopic compositions are characterised by sampling core as well as surface exposures of the Frontier Formation elsewhere in Wyoming. The evolution of the fluid chemistries reflects extensive dissolution of both carbonate and silicate minerals over the course of the six months sampling implying rapid dissolution of CO2 in the formation waters and reaction of CO2-bearing brines with formation minerals. Rates of CO2 diffusion into the brines and advection of CO2 charged brines in the reservoir are sufficiently slow that, if present, calcite should react to be close to equilibrium with the fluids. This allows estimation of the CO2 partial pressures in the sampled fluids and comparison with the thermodynamic driving force for the relatively rapid average plagioclase dissolution rates of ~10−12mol·m−2·s−1.

Impact of CO2-induced Geochemical Reactions on the Mechanical Integrity of Carbonate Rocks

In a CO2 storage site, carbonate rocks might be good reservoir rocks or good seals depending on their porosity and permeability. However, these properties may change in time due to deformation processes related to CO2 injections and/or withdraws. In this pilot study, we investigate at the laboratory scale the influence of CO2-induced geochemical reactions on the mechanical integrity of carbonate rocks. To achieve this target, we have performed an experimental HP-HT test on brine saturated oolitic limestone samples that were exposed to 230 bar CO2 pressure and 37.5oC reaction temperature (supercritical conditions) for a period of 2 weeks. Although changes in fluid chemistry have been identified via ICP-OES analysis, we have observed no particular differences in terms of ooids and cement deformation and/or calcite dissolution when comparing ESEM images of pre- and post-treatment samples. We are currently performing more experiments under different conditions (particularly longer exposure and higher brine-rock ratios that can be linked to higher dissolution of calcite) in order to better understand the dominant CO2 sequestration mechanisms in oolitic limestone-containing reservoirs.

Evolution of fault permeability during episodic fluid circulation: Evidence for the effects of fluid–rock interactions from travertine studies (Utah–USA)

Faults are known to be important pathways for fluid circulation within the crust. The transfer properties along faults can evolve over time and space. The Little Grand Wash and Salt Wash normal faults, located on the Colorado Plateau, are well known examples of natural CO2 leakage systems from depth to surface. Previous studies dated and established a chronology of CO2-enriched fluid source migration along the fault traces and linked the aragonite veins observed close to Crystal Geyser to CO2-pulses. However, multiple circulation events recorded along a given fault segment deserve to be studied in minute detail in order to unravel the chronology of these events, precipitation processes and associated mechanisms. A combination of structural geology, petrography, U/Th dating, oxygen and carbon isotope analysis were used to study the fault related CO2-enriched paleo-circulations in order to build a conceptual model of CO2-circulation along the faults. This study resulted in the precise descriptions of the features attesting CO2-enriched fluid circulation by a characterization of their relationship and architecture at the outcrop scale. These features are witnesses of a large range of circulation/sealing mechanisms, as well as changes in fluid chemistry and thermodynamic state of the system, providing evidence for (i) the evolution of the fluid through a pathway from depth to the surface and (ii) different cycles of fault opening and sealing. Large circulation events linked with fault opening/sealing are observed and calibrated in nature with millennial circulation and sealing time-lapses. Numerical modelling indicates that such sealing timescale can be explained by the introduction of a fault sealing factor that allows modifying permeability with time and that is calibrated by the natural observations.

Experimental constraints on fluid-rock reactions during incipient serpentinization of harzburgite

The exposure of mantle peridotite to water at crustal levels leads to a cascade of interconnected dissolution-precipitation and reduction-oxidation reactions-a process referred to as serpentinization. These reactions have major implications for microbial life through the provision of hydrogen (H 2 ). To simulate incipient serpentinization under well-constrained conditions, we reacted centimeter-sized pieces of uncrushed harzburgite with chemically modified seawater at 300 °C and 35 MPa for ca. 1.5 yr (13 441 h), monitored changes in fluid chemistry over time, and examined the secondary mineralogy at the termination of the experiment. Approximately 4 mol% of the protolith underwent alteration forming serpentine, accessory magnetite, chlorite, and traces of calcite and heazlewoodite. Alteration textures bear remarkable similarities to those found in partially serpentinized abyssal peridotites. Neither brucite nor talc precipitated during the experiment. Given that the starting material contained ~4 times more olivine than orthopyroxene on a molar basis, mass balance requires that dissolution of orthopyroxene was significantly faster than dissolution of olivine. Coupled mass transfer of dissolved Si, Mg, and H + between olivine and orthopyroxene reaction fronts was driven by steep activity gradients and facilitated the precipitation of serpentine. Hydrogen was released in significant amounts throughout the entire experiment; however, the H 2 release rate decreased with time. Serpentinization consumed water but did not release significant amounts of dissolved species (other than H 2 ) suggesting that incipient hydration reactions involved a volume increase of ~40%. The reduced access of water to fresh olivine surfaces due to filling of fractures and coating of primary minerals with alteration products led to decreased rates of serpentinization and H 2 release. While this concept might seem at odds with completely serpentinized seafloor peridotites, reaction-driven fracturing offers an intriguing solution to the seemingly self-limiting nature of serpentinization. Indeed, the reacted sample revealed several textural features diagnostic of incipient reaction-driven fracturing. We conclude that fracturing must have far reaching impacts on the rates of serpentinization and H 2 release in peridotite-hosted hydrothermal systems.

The case for reprecipitation of human bone as an event in a Bronze Age cist burial, Scotland

A hard whitish precipitate was observed on the lower part of the sandstone sidewalls and as pebble coatings in a Bronze Age cist burial near Forteviot, Strathearn, Scotland. The cist was discovered on excavation of a Neolithic henge in August 2009 during the joint Glasgow and Aberdeen Universities [Strathearn and Environs Royal Forteviot (SERF)] archaeological landscape research project and summer field school. Similar cists have not been found in this area. Scrapings of the precipitate proved on examination by powder X-ray diffraction to be hydroxyapatite. The mamillary material proved on examination by scanning electron microscopy to be calcium carbonate, calcite which had grown as groups of mm-size spheroids consisting of bundles of acicular crystals. Both components of the precipitate were also identified using oil immersion microscopy. Much organic material was preserved in the cist but neither (inorganic) bone nor teeth has been located to date (November 2010). The phosphatic mineral-precipitates provided the first confirmation that there had been bone and therefore an inhumation. Computational aqueous geochemistry using Geochemist’s Workbench confirms that the inorganic calcium phosphate component of human bone is soluble in acidic fluid and demonstrates how it can reprecipitate with change in fluid chemistry. Bone dissolution should be anticipated as being an expected early process when a human body produces an acidic fluid rich in organic molecules as it decays in an essentially closed, but wet, anoxic environment. Any precipitates on grave stonework should be identified as such material could represent human remains and could also provide evidence of environmental processes in the archaeological setting of a burial.

Magmatic eruptions and iron volatility in deep-sea hydrothermal fluids

Author(s): Pester, NJ; Ding, K; Seyfried, WE | Abstract: During periods of volcanic activity, hydrothermal fluid chemistry changes drastically, becoming unusually dilute due to enhanced degrees of phase separation. Despite decreases in nearly all other metals, these dilute fluids maintain surprisingly high dissolved Fe concentrations. This is demonstrated by a 17 yr time series from 9°50'N on the East Pacific Rise, where two eruption cycles are separated by a decade of steady-state chemical and physical conditions. We report experimental data confi rming a sharp increase in Fe solubility in low-salinity and low-density vapors that constitutes a reversal in behavior exhibited in near-critical vapors characteristic of the steady-state condition. In accordance with field observations during the eruptions, a fundamental divergence between the otherwise similar behaviors of Fe and Mn also results. This helps explain how Fe fluxes are maintained during magmatic events, which may have important implications for the succession and temporal evolution of vent-related fauna. Calibrated geochemical proxies for subseafl oor reaction conditions (pressure-temperature) now allow us to elucidate hydrothermal processes from steady state through eruptive and recovery stages at the 9°50'N system. © 2014 Geological Society of America.