drained and undrained anisotropic elastic stiffness parameters equations that map drained to undrained elastic stiffness parameters in a cross anisotropic material are presented graphs of various anisotropic stiffness ratios are used to illustrate the important trends a new 2 d graph showing the elastic bound enables measured elastic parameters to be plotted which all lie well within it the 2 d graph enables uncoupled and incompressible materials to be shown plus materials with particular initial effective stress path slopes in an undrained triaxial test bounds more restrictive than the elastic one are also discussed and the likely ranges of various anisotropic stiffness ratios are presented in general undrained anisotropy is much less than drained that is closer to isotropic in undrained plane strain conditions vertical and horizontal moduli are found to be the same in drained plane strain conditions the ratios of the moduli are almost the same as the young s moduli

effect of fabric on the behaviour of reservoir sandstones a laboratory investigation was undertaken on the mechanical behaviour of two sandstones that are commonly used as analogous hydrocarbon reservoir sandstones using triaxial apparatuses with a capacity of up to 70 mpa confining pressure both materials are lightly cemented but show a mechanical behaviour at large strains that is similar to that seen in rocks with much stronger cementation at small strains however these materials behave more like uncemented sands in that they show a strong stress dependency of the shear modulus and yield takes places at relatively small strains it is believed that fabric plays a fundamental role in the observed behaviour and this is supported by the experimental evidence so that the concept of strong fabric in sandstones is introduced

feldspar saturation state in natural waters the saturation state of feldspar minerals in natural waters ranging from 0 c to over 300 c was studied waters above 200 c have closely approached equilibrium with microcline and low albite this is consistent with the occurrence of these minerals as hydrothermal minerals in active geothermal systems with temperature in excess of some 200 c the na k activity ratio of geothermal waters with temperature as low as 50 c closely approaches that predicted from thermodynamic data for the reaction low albite k microcline na suggesting that na and k ion activities in these geothermal waters are controlled by simultaneous equilibrium with these two feldspars geothermal waters are undersaturated with primary disordered plagioclases and alkali feldspars of compositions typically found in volcanic rocks accordingly these feldspars tend to dissolve in such waters simultaneously with precipitation of ordered alkali feldspars surface and non thermal groundwaters are usually undersaturated with respect to igneous and metamorphic feldspars regardless of composition and al si ordering and tend therefore to dissolve under weathering conditions

transitional behaviors in well graded coarse granular soils abstractdrained triaxial compression tests were carried out for a well graded coarse granular soil cgs to investigate the effect of the initial specific volume on the location of the critical state line csl a family of parallel csls in the v logp plane was observed for the well graded cgs indicating that it exhibited transitional behavior the degree of transitional behavior was quantified from the relationship between the intercepts of the csls and the initial specific volumes giving a value of 0 59 which indicated a substantially transitional behavior the observations of the csl pattern in the cgs illustrated that transitional behavior could be extended to large sized granular soils beyond the usual transitional soils that have been observed so far which generally have gradings between those of clean sand and plastic clay

fayalite dissolution and siderite formation in water saturated supercritical co2 abstract olivines significant constituents of basaltic rocks have the potential to immobilize permanently co2 after it is injected in the deep subsurface due to carbonation reactions occurring between co2 and the host rock to investigate the reactions of fayalitic olivine with supercritical co2 scco2 and formation of mineral carbonates experiments were conducted at temperatures of 35 c to 80 c 90 atm pressure and anoxic conditions for every temperature the dissolution of fayalite was examined both in the presence of liquid water and h2o saturated scco2 the experiments were conducted in a high pressure batch reactor at reaction time extending up to 85 days the newly formed products were characterized using a comprehensive suite of bulk and surface characterization techniques x ray diffraction transmission emission mossbauer spectroscopy scanning electron microscopy coupled with focused ion beam and high resolution transmission electron microscopy siderite with rhombohedral morphology was formed at 35 c 50 c and 80 c in the presence of liquid water and scco2 in h2o saturated scco2 the formation of siderite was confirmed only at high temperature 80 c characterization of reacted samples in h2o saturated scco2 with high resolution tem indicated that siderite formation initiated inside voids created during the initial steps of fayalite dissolution later stages of fayalite dissolution result in formation of siderite in layered vertical structures columns or pyramids with a rhombus base morphology

peak shear strength and dilatancy of a pleistocene age sand abstractthis paper summarizes results of laboratory investigations performed to quantify the influence of diagenesis or aging processes on the peak shear strength and dilatancy of an uncemented pleistocene age sand sampled near charleston south carolina drained triaxial compression tests were performed on high quality intact specimens retrieved using the in situ freezing and sampling method and on remolded specimens prepared with matching densities the stress strain behavior of intact specimens is accompanied by dilation and a peak shear value whereas remolded specimens generally contracted throughout shearing an age dilatancy term is added to a dilatancy index equation to account for the difference between intact and remolded peak friction angles the resulting equation suggests that dilatancies due to age and density are suppressed with increasing confining pressure a profile of peak friction angle with depth is established from the results and compared with estimates from empirical relationships

the chemistry of geothermal waters in iceland ii mineral equilibria and independent variables controlling water compositions abstract the major element chemistry of icelandic geothermal waters is predictable provided two parameters are known this follows from an attainment of or a close approach to an overall chemical equilibrium in the geothermal systems at temperatures as low as 50 c it is considered that the geothermal system composition temperature and kinetic factors determine which alteration minerals form the system composition is not so much fixed by rock composition as by the rate of leaching of the various constituents from the fresh rock and the composition of inflowing water the water chemistry is determined by the system composition and the external variables acting on the system they include temperature and the mobility of chloride pressure which theoretically should be regarded as an external variable has insignificant effect on water compositions in the range 1 200 bars occurring in the geothermal systems

experimental determination of the stability constants of naso4 and nab oh 40 in hydrothermal solutions using a new high temperature sodium selective glass electrode implications for boron isotopic fractionation abstract a new sodium selective glass electrode was used to measure the association constants of the sodium sulfate naso 4 and sodium borate nab oh 4 0 ion pairs at temperatures from 50 to 200 c these data were used to generate within the framework of the revised hkf model naso 4 and nab oh 4 0 equation of state parameters calculation of nab oh 4 0 association constants at temperatures up to 500 c and pressures up to 5 kbar demonstrates that this ion pair dominates boron speciation in sodium rich hydrothermal fluids at ph 8 because it has been shown that boron isotopic fractionation in natural processes is strongly affected by its aqueous speciation the formation of nab oh 4 0 complexes cannot be neglected when using boron isotopes to estimate water rock interactions occurring in the continental and oceanic crust at moderate and high temperatures

geochemistry of thermal waters in the southern volcanic zone chile implications for structural controls on geothermal fluid composition abstract thermal waters in the southern volcanic zone svz of chile between 36 41 s were studied using major and selected trace element relationships to characterize their geochemistry formation mechanisms and to explore the influence of regional structural controls on fluid composition three sets of waters were identified based on physicochemical characteristics i nacl waters ii acid sulfate waters and iii bicarbonate hco3 waters nacl waters are the most abundant type in the studied region and their chemistry is controlled by significant water rock interaction they are characterized by an alkaline ph 7 2 9 3 generally lower temperatures avg 55 c and relatively high concentrations of cl na b as li and cs acid sulfate waters are typically associated with volcanoes and have a strong magmatic volcanic component due to the absorption of magmatic vapors they are acidic ph 892 ppm in the region and are similar in temperature 6 2 to nacl waters they have elevated concentrations of most cations ca k na mg ba sr as a result of intense shallow cation leaching due to the absorption of co2 rich volcanic vapors on the peripheries of geothermal systems the thermal waters were also characterized according to their spatial relation with the dominant fault systems of the region the nne striking intra arc liquine ofqui fault system lofs and the wnw striking andean transverse faults atf the inherent differences in fault nature between these fault systems constitutes the primary structural control influencing geothermal fluid development in the svz the chemistry of waters spatially associated with the lofs as a whole is defined by high vertical permeability networks and lack magmatic reservoir development therefore these waters tend to have higher cl b ratios and strong correlations between trace alkali metals and cl due to rapid efficient upflow pathways in contrast waters spatially associated with the atf have lower cl b ratios and show no correlation between trace alkali metals and cl due to degassing magma chambers and decreased vertical permeability the relationship between water type and structural domain in cl b ratios and trace metal behavior provides evidence that fault geometry and kinematics exert a fundamental control on geothermal fluid development in the svz of chile

the geochemistry of trace elements in geothermal fluids iceland abstract trace element geochemistry was studied in geothermal fluids in iceland the major and trace element compositions of hot springs sub boiling and two phase liquid and vapor wells from 10 geothermal areas were used to reconstruct the fluid composition in the aquifers at depth aquifer fluid temperatures ranged from 4 to 300 c ph values between 4 5 and 9 3 and fluids typically contained total dissolved solids

the effect of hydrothermal fluids on ordovician carbonate rocks southern ordos basin china abstract hydrothermal processes have an important influence on the spatial distribution and formation of carbonate reservoirs and play a critical role in certain deep reservoirs where hydrothermal fluid rock interaction may result in permeability creation due to carbonate dissolution or permeability destruction due to the deposition of cementing minerals this study analyzed certain hydrothermal indicator minerals quartz celestite multi stage calcareous fillings in carbonate rocks from the ordovician majiagou formation southern ordos basin china the petrological and geochemical characteristics of these indicator minerals imply that the majiagou formation was affected by two metasomatic events related to the hercynian indosinian and yanshanian orogenies and linked to magmatic hydrothermal fluids derived from basaltic melts most of the ce and eu values obtained from matrix dolomite samples were lower than one but u th and v c ratios showed positive anomalies the 13c and 18o values of the matrix dolomite were concentrated between 12 8 and 6 0 whereas 13c showed a bipolar distribution at the same depth elemental geochemistry results showed that the ordovician carbonate rocks were subjected to freshwater leaching followed by evaporation and widespread hydrothermal dissolution successively as a result of the multi episodic hydrothermal activity that affected the southern ordos basin and the path of migration channel a parental magmatic hydrothermal fluid fluid 1 that had been generated during the underplating of the southern north china craton by mesozoic alkaline basalt melts separated into two types of fluids with different chemical properties an acidic hydrocarbon bearing fluid fluid 2a mixed with cambrian oil and gas and a weakly to moderately alkaline brine fluid 2b not in contact with hydrocarbons both fluids 2a and 2b then interacted with the ordovician carbonate rocks with fluid 2a having undergone hydrothermal sulfate reduction with so42 in the layers in which gypsum was developed and convection of fluid 2a having resulted in brine formation the reaction products of h2s and co2 together with organic acid co dissolved carbonate minerals in the ordovician strata played a major role in the formation of a high porosity reservoir conversely owing to the progressive reduction of temperature and solubility during fluid ascent fluid 2b precipitated quartz calcite fillings in the residual pore spaces resulting in the localized destruction of the original reservoir permeability in summary this study analyzed the petrological and geochemical characteristics of 60 carbonate rock drill core samples established the likely formation mechanism of fluids 2a and 2b and determined the effects of these hydrothermal fluids on the ordovician majiagou formation carbonate reservoir

origin and timing of the metasomatic silicification of an early archean komatiite sequence barberton mountain land south africa abstract stratiform units of pervasively silicified early archean ultramafic rocks occur near the boundary between the onverwacht and fig tree groups in the barberton mountain land republic of south africa the origin of these units has been variously ascribed to early archean subaerial weathering or submarine alteration to cataclastic metamorphism and to the alteration of silicic tuffs an exceptionally well exposed example of such an alteration sequence along the skokohla river valley in the central barberton mountain land was studied to determine the nature of the precursor rocks and the timing and nature of the alteration processes well preserved ghosts of spinifex and culmulate textured olivines and pyroxenes establish the komatiitic ancestry of the skokohla rocks rock units of several distinctive lithofacies can be correlated over the entire 1 5 km strike of the sequence and were derived from the metasomatic conversion of a series of ultramafic flow units to rocks dominated by quartz dioctohedral mica and chlorite the original ultramafics have been strongly enriched in si k rb and ba and depleted in fe mg ca na mn sr zn and ni the elements al ti p cr zr y and nb were immobile alteration apparently occurred soon after extrusive activity and before any significant tectonic deformation it is most probable that alteration resulted from the dynamic hydrothermal upwelling of fluids through original fracture porosity in the ultramafic flows

thermo physical rock properties of greywacke basement rock and intrusive lavas from the taupo volcanic zone new zealand abstract greywacke of the waipapa and torlesse composite terrane form the basement of the taupo volcanic zone tvz new zealand together with inferred buried lavas domes and igneous complexes they are likely to be the dominant rock type prevailing at depths 4 km beneath the tvz a fundamental understanding of the rock properties of the deep formations is of utmost importance for the exploration of deep unconventional geothermal resources an outcrop analogue study was conducted to improve the understanding of the thermo physical rock properties of likely deep buried rock formations beneath the tvz a total of 145 core samples were taken at 10 locations inside and outside the tvz and their grain and bulk density porosity matrix permeability bulk thermal conductivity and specific heat capacity and the compressional and shear wave velocities measured on oven dry samples additional tests of the unconfined compressive strength were conducted for selected greywacke samples to quantify their mechanical rock strength the obtained data indicates that the thermo physical rock properties are mainly controlled by porosity and minor by mineralogy texture and grain size samples from waipapa type and torlesse type greywacke exhibit minor rheological differences with waipapa type greywacke having lowest porosity about 1 vs 3 and highest bulk thermal conductivity 2 5 w m 1 k 1 vs 1 7 w m 1 k 1 and specific heat capacity 0 8 kj kg 1 k 1 vs 0 7 kj kg 1 k 1 matrix permeability is 2 for all greywacke samples tested lavas exhibit heterogeneous rock properties due to their wide range of porosity the thermo physical rock properties were tested at laboratory conditions ambient temperature and pressure which do not reflect the in situ conditions at greater depth with depth thermal conductivity and acoustic wave velocity are likely to decrease caused by micro fractures resulting from thermal cracking of the rock while specific heat capacity increases the data presented in this paper are expected to improve the statistical confidence on input data to geophysical and thermo hydro mechanical numeric models and the ability to forecast rock properties at greater depths of the tvz

the measurement of local axial strains in triaxial tests using lvdts in this technical note the author describes an experiment in the use of linear variable differential transformer lvdt to allow accurate measurement of axial displacement over the complete range of strains of interest to geotechnical engineers

state dependent strength of sands from the perspective of unified modeling this paper discusses the state dependent strength of sands from the perspective of unified modeling in triaxial stress space the modeling accounts for the dependence of dilatancy on the material internal state during the deformation history and thus has the capability of describing the behavior of a sand with different densities and stress levels in a unified way analyses are made for the toyoura sand whose behavior has been well documented by laboratory tests and meanwhile comparisons with experimental observations on other sands are presented it is shown that the influence of density and stress level on the strength of sands can be combined through the state dependent dilatancy such that both the peak friction angle and maximum dilation angle are well correlated with a so called state parameter a unique linear relationship is suggested between the peak friction angle and the maximum dilation angle for a wide range of densities and stress levels the relationship which is found to be in good agreement with recent experimental findings on a different sand implies that the excess angle of shearing due to dilatancy in triaxial conditions is less than 40 of that in plane strain conditions a careful identification of the deficiency of the classical rowe s and cam clay s stress dilatancy relations reveals that the unique relationship between the stress ratio and dilatancy assumed in both relations does not exist and thereby obstructs unified modeling of the sand behavior over a full range of densities and stress levels

mixing hydrology and chemical equilibria in bakreswar geothermal area eastern india abstract a group of alkaline thermal springs of bakreswar having varying temperatures 45 71 c and identical compositions emerges through a nearly n s trending fault in the gneissic basement the thermal springs are of na cl so 4 type and are rich in sio 2 and f contrary to the local groundwaters which are mostly of ca hco 3 type the springs undergo mild to moderate dilution by local groundwater which does not significantly affect their original compositions agnikund the main spring with the highest temperature mild dilution consistent composition and negligible tritium discharges almost pure deep seated thermal water original thermal water is at equilibrium with quartz in the deep reservoir and attains surface temperature largely by conductive cooling with no significant loss of dissolved sio 2 certain ionic ratios coupled with very low tritium contents in the springs are indicative of prolonged subsurface circulation of the original water xrd results of the spring site sediments and the bore hole rocks fairly corroborate the predicted saturation state of thermal water with respect to quartz feldspar calcite fluorite etc which is believed to control the major chemical compositions of the springs a geothermal reservoir having probable temperature of about 100 5 c and possibly occurring at a depth of 1 km is the source of thermal water for the springs the present study is aimed at understanding the mixing trend between thermal springs and local groundwaters as well as the water rock equilibria

changes in seal capacity of fractured claystone caprocks induced by dissolved and gaseous co2 seepage 1 claystone caprocks are often the ultimate seal for co2 underground storage when residual co2 gas reaches the reservoir top due to buoyancy permeability changes of a fractured claystone due to seepage of co2 enriched brine and water vapor saturated co2 gas are investigated results show that brine flow induces a large porosity increase up to 50 in the vicinity of the fracture due to dissolution of calcite and quartz while permeability remains unchanged conversely cyclic flows of co2 brine and co2 gas increase the fracture aperture abruptly after each gas flow period producing a progressive decrease of the caprock seal capacity aperture increase is controlled by decohesion of the clay framework within a micrometer scale thick layer induced by co2 gas acidification results show that hydraulic aperture increases linearly with duration of the preceding co2 brine flow period emphasizing the kinetic control of the quartz grains dissolution during the brine flow periods

heat flux from magmatic hydrothermal systems related to availability of fluid recharge abstract magmatic hydrothermal systems are of increasing interest as a renewable energy source surface heat flux indicates system resource potential and can be inferred from soil co 2 flux measurements and fumarole gas chemistry here we compile and reanalyze results from previous co 2 flux surveys worldwide to compare heat flux from a variety of magma hydrothermal areas we infer that availability of water to recharge magmatic hydrothermal systems is correlated with heat flux recharge availability is in turn governed by permeability structure lithology rainfall topography and perhaps unsurprisingly proximity to a large supply of water such as the ocean the relationship between recharge and heat flux interpreted by this study is consistent with recent numerical modeling that relates hydrothermal system heat output to rainfall catchment area this result highlights the importance of recharge as a consideration when evaluating hydrothermal systems for electricity generation and the utility of co 2 flux as a resource evaluation tool

modeling the formation of advanced argillic lithocaps volcanic vapor condensation above porphyry intrusions hypogene advanced argillic alteration typically quartz alunite with halos of kaolinite dickite and roots of pyrophyllite diaspore forms in the epithermal environment from condensates of magmatic vapor that contain so2 and hcl which exsolved from an underlying intrusive source the most aggressive nearly isochemical leaching of the host rock by the most acidic condensate commonly ph 1 leaves residual silica that recrystallizes to quartz within the flow channel at a high condensate rock ratio forming the core of alteration the alteration characteristically flares upward along feeder structures and if a permeable lithologic unit is intersected the alteration zones mushroom to form a subhorizontal blanket due to lateral flow where subsequently mineralized the residual quartz commonly with a vuggy texture that reflects the texture of the original lithology has higher au and cu grades than the quartz alunite halo tonnage in these high sulfidation systems may develop within the subhorizontal lithocap although the highest grades are typically confined to the structurally controlled feeders we modeled a typical volcanic vapor condensate starting with the measured composition of 877 c fumaroles from satsuma iwojima rhyolite dome japan as it cooled and reacted with a host rhyolite the predicted hydrothermal mineralogy reproduces the alteration pattern observed in lithocaps that host high sulfidation deposits the modeling confirms that aluminum rich minerals pyrophyllite diaspore locally andalusite are stable at higher temperature at depth whereas at lower temperature and shallower depth na and k alunite become stable at the lowest temperature 10 1 and where so2 h2s in the original volcanic vapor this so2 dominant composition is typical of andesitic to rhyolitic volcanoes the reason for this mineral transition and the upward flare widening of the alteration zone along structures is related to the dissociation and increased reactivity of h2so4 and hcl as the temperature decreases below 200 c only quartz pyrite native s and anhydrite are stable hence the formation of the dominant quartz from the silica residue a further check on our modeling is the observation that the calculated composition of the condensate after reaction with fresh satsuma iwojima rhyolite and alteration minerals and cooling to 100 c is similar within a factor of two to that of acidic springs with ph 1 that discharge around satsuma iwojima and other active volcanoes the most extensive lithocap alteration residual quartz and or quartz alunite is commonly offset from the surface projection of the causative intrusion this observation can be explained by a combination of two factors hydrology and temperature due to hydraulic gradients at shallow depths in a volcanic edifice the acidic condensate tends to flow along permeable lithologic units away from the locus of the high temperature vapor plume which rises directly over the intrusion where lateral flow occurs the most intense leaching and widespread advanced argillic alteration which develops largely at temperatures of 200 to 250 c based on our modeling will form away from the near surface projection of the intrusion which is the area of highest surface temperature due to ascent of the vapor plume this potential for lithocap alteration to form on the shoulder of the underlying causative intrusion must be assessed when exploring for high sulfidation ore the highest ore grades are commonly related to structures that are proximal to the parent intrusion but they are unlikely to lie directly over the intrusion in addition identifying the most likely location of the source intrusion will help the explorer to efficiently assess any potential for deeper porphyry style mineralization

rock water interactions in hot dry rock geothermal systems field investigations of in situ geochemical behavior abstract two hot dry rock hdr geothermal energy reservoirs have been created by hydraulic fracturing of precambrian granitic rock between two wells on the west flank of the valles caldera in the jemez mountains of northern new mexico heat is extracted by injecting water into one well flowing it through the fractured region and recovering the heated water from the second well the produced fluid is cooled on the surface and reinjected into the system the first reservoir was formed by fracturing the injection well at a depth of 2 75 km where the initial rock temperature was 185 c a heat extraction experiment conducted in this reservoir was run from january 27 to april 13 1978 a second larger reservoir was created after cementing the fracture to wellbore connections at 2 75 km in the injection well and refracturing 180 m deeper this second reservoir was tested from october 23 to november 16 1979 during each of these experiments samples of the geothermal fluids and gases were collected at regular intervals from the injection wellhead the production wellhead and at the make up pump which provided the water from storage ponds to replace the water lost downhole by permeation into the reservoir walls changes in the composition of the produced fluid provide a means for studying the reservoir behaviour under normal recirculating operating conditions certain of the dissolved species appear to be derived by displacement of an indigenous pore fluid while others appear to be derived by dissolving minerals known to be present in the reservoir rock in this paper we describe the results of the chemical analysis of the geothermal fluids and relate the fluid and gas chemistry to geochemical processes that result from the heat extraction experiments in particular the implications of the silica and na k ca geothermometers and the pore fluid displacement theory are examined for insight about the long term effects of fluid geochemistry on heat extraction from hdr reservoirs

carbonate sulfide equilibria and stratabound disseminated epigenetic gold mineralization a proposal based on examples from alleghany california u s a abstract stratabound disseminated pyritic au ore bodies were produced by reactions between wall rocks and through flowing fluids in mesozoic epigenetic au quartz vein systems in the sierra nevada metamorphic belt equilibrium relations among fe bearing carbonate and sulfide minerals were critical in determining which rock types were likely to host disseminated mineralization along portions of discordant veins the compositions of metasomatic carbonates in hydrothermally altered wall rocks at alleghany california u s a were larely predetermined by the relative proportions of fe mg and ca in the unaltered wall rocks thus coexisting solid solutions in the magnesite siderite and dolomite ankerite series from a variety of different wall rocks yield an empirical phase diagram for a large part of the ca co 3 mgco 3 feco 3 system at the temperature of metasomatism 325 50 c because fe mg silicates were unstable in alteration zones adjacent to the veins wall rock fe was partitioned between carbonates and sulfides pyritization and disseminated au mineralization occur in a variety of igneous and metasedimentary wall rocks in which the initial molar fe fe mg 0 5 in altered wall rocks with initial molar fe fe mg 0 5 fe was incorporated almost entirely within mg rich carbonates x feco 3 0 6 in magnesite siderite solutions it is proposed that the co 2 rich vein fluid responsible for the alteration and mineralization was partially buffered with respect to h 2 s co 2 h 2 ratios by equilibrium between pyrite and mg 0 4 fe 0 6 co 3 graphite as it traversed and altered intermediate volcanic and sedimentary rocks this fluid then locally reacted with lower fe fe mg rocks to form fe bearing dolomite magnesite assemblages and reacted with higher fe fe mg rocks to form ankerite pyrite assemblages gold precipitated from saturated solutions of bisulfide complexes partly in response to fluid desulfidation and reduction caused by the pyritization reactions in terranes dominated by intermediate metavolcanic and metasedimentary rocks favorable host rocks for this type of mineralization need not have high fe contents but do require high fe fe mg ratios they may include felsic volcanic and plutonic rocks fe rich tholeiitic differentiates banded fe formations and a variety of siliceous and argillaceous sedimentary rocks rocks which tend not to be heavily sulfidized because they have low initial fe fe mg ratios include ultramafic and mafic igneous rocks and some argillaceous sedimentary rocks exploration guidelines based on these principles may be useful elsewhere in the sierra nevada and in other comparable heterogeneous metamorphic terranes if modified to reflect the dominant buffering rock types in a given fluid flow path carbonate sulfide equilibria are capable of approximately buffering the carbonate sulfide ratios of co 2 rich vein fluids f co 2 10 2 8 at 325 c 200mpa or 2000 bar the alleghany fluid f co 2 10 3 2 or 10 mol co 2 had a molar co 2 h 2 s ratio of approximately 10 3 assuming graphite saturation at lower co 2 fugacities fe bearing silicates entered the buffering assemblages carbonatization reactions could potentially de sulfidize some wall rocks releasing s and associated metals to the fluid this would be most likely to occur in pyrite bearing mafic and ultramafic rocks and some argillites

discrete element method simulations of analogue reservoir sandstones abstract the discrete element method was used to model the behaviour of two natural sandstones that are commonly used as analogues for oil reservoir sandstones with a relatively large number of parameters needed to define the model and few micro scale data on which to base them a parametric study was first carried out to identify how each parameter affects the overall macroscopic behaviour this study highlighted the importance of the load share between the particle contacts and the bonds the model for the more strongly cemented sandstone was calibrated against the response observed at a single stress level and predictions at other stress levels were then found to be good a second more weakly cemented sandstone was also modelled it was found that while this sandstone had a very much lower cement content by weight only minor modifications were needed to the bond strengths and the proportion of bonded contacts compared to the more strongly bonded material this may be because of the failure to model the natural fabric of the sandstones in general the post peak regime was not modelled well nor was the volumetric response the latter as a result of the failure to achieve the in situ porosities in the model

chemical and boron isotope compositions of tourmaline from the jaduguda u cu fe deposit singhbhum shear zone india implications for the sources and evolution of mineralizing fluids abstract the proterozoic jaduguda u cu fe deposit in the singhbhum shear zone eastern india hosts the oldest and most productive uranium mine in india the polymetallic ores in jaduguda are hosted in altered sheared and metamorphosed volcano sedimentary rocks and this complexity has lead to a confusion in ore genetic models for the deposit a characteristic of the mineralization is the presence of abundant tourmaline locally exceeding 50 vol which is spatially associated with u and cu mineralization in all rock types and its chemical and b isotopic variations provide important constraints on fluid source s and ore deposit affinity we examined tourmaline from the u cu ore zone and adjacent footwall and hanging wall meta sedimentary rocks tourmaline grew in three different stages pre kinematic tourmaline 1 represented by fractured and porphyroblastic grains is ubiquitous in the wall rocks and the u cu zone syn kinematic tourmaline 2 and post kinematic tourmaline 3 are found exclusively in the u cu zone where intense shear deformation has focussed fluid flow alteration and metamorphism all tourmalines belong to the alkalic group and most are dravitic systematic contrasts in major element compositions between tourmaline 1 and tourmaline 2 are attributed to the influence of high fluid rock ratios in the u cu ore zone tourmaline from the jaduguda deposit exhibits a wide overall range of 11b values from 6 8 to 17 2 positive values of tourmaline 1 are irrespective of host rock and ore association u or u cu and range between 2 3 to 17 2 n 44 the calculated 11b values of fluid in equilibrium with this tourmaline for mineralization temperatures of 300 450 c range from 4 to 20 the 11b values of syn kinematic tourmaline 2 are much lower than tourmaline 1 between 6 8 and 4 n 7 and the corresponding fluid 11b values are 4 8 6 the high values of 11b for tourmaline 1 and early fluid suggest a marine evaporite or basinal brine was the source of boron and this fits with abundant mineralogical and geochemical evidence for highly saline fluids during mineralization we propose that the isotopically lighter fluid associated with tourmaline 2 and related syn kinematic mineralization mobilization was derived from the metamorphic volcano sedimentary rocks at high fluid rock ratios in and around the shear zone post kinematic tourmaline 3 is compositionally and isotopically 11b 4 to 11 1 n 5 similar to tourmaline 1 in the same samples suggesting it formed by local recrystallization of the early tourmaline or from a renewed influx of saline fluids similar to those which formed the pre kinematic mineralization integrating the results of this tourmaline study with the geological and geochemical characteristics of the jaduguda u cu fe mineralization suggests that it is best regarded as a variant of the fe oxide cu u ree or iocg class of deposits

multistage strain localisation and fluid assisted cataclasis in carbonate rocks during the seismic cycle insights from the belluno thrust eastern southern alps italy abstract strain localisation in carbonate rocks impacts upon the nucleation and development of structures within the shallow seismogenic crust studying deformed carbonate rocks is thus a key to the refined understanding of the mechanical behaviour of rock successions with high potential to fail coseismically in response to stress accumulation we studied deformation structures and mechanisms of the miocene belluno thrust from the seismically active eastern southern alps italy the thrust contains several structural facies and features pressure soluted and veined lithons cataclasites s c fabrics principal slip surface which make it possible to define a sequence of deformation events in space and through time during thrusting image analysis of cataclasite particle size distribution and morphology supported by cathodoluminescence imaging indicates corrosive wearing as the main comminuting mechanism during cataclasis and repeated ingress of overpressured aqueous fluids promoting carbonate clast dissolution we propose an evolutionary scenario of multiple episodes of fabric formation and rejuvenation that localised and accommodated increasing shear strain into a progressively narrowing fault core we propose that strain localisation in carbonate rocks can be greatly facilitated by cyclic fluctuations between strain hardening and softening conditions punctuated by transient spikes of coseismic failure accommodated by cataclasis during the ingress of overpressured chemically reactive fluids that control carbonate precipitation and dissolution

undrained anisotropy and principal stress rotation in saturated sand this paper describes an investigation carried out in a new hollow cylinder apparatus into anisotropy and the effects of principal stress rotation in a medium loose sand tested under undrained conditions principal stresses have been rotated at a constant shear stress during both monotonie and cyclic loading the experimental observations are described and then explained within a framework based on the concept of state boundary surfaces the over riding importance of initial anisotropy in determining the response of the sand to rotations in principal stress directions is demonstrated pore pressures are shown to be generated by rotation of principal stress directions at constant shear stress and their accumulation during cyclic principal stress rotation can lead to failure l article presente une etude de l anisotropie effectuee dans un nouvel appareil creux cylindrique et decrit les effets de la rotation de la contrainte principale dans un sable moyennement l che teste dans des conditions non drainees l

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

multiple sulfur isotope systematics of icelandic geothermal fluids and the source and reactions of sulfur in volcanic geothermal systems at divergent plate boundaries abstract multiple sulfur isotope systematics of geothermal fluids at krafla northeast iceland were studied in order to determine the source and reactions of sulfur in this system as an example of a geothermal system hosted on a divergent plate boundary fluid temperatures ranged from 192 to 437 c and the fluids have low cl concentration between 10 and 150 ppm with liquid water and vapor being present in the reservoir dissolved sulfide s ii and sulfate svi predominated in the water phase with trace concentrations of thiosulfate s 2 o 3 2 whereas sulfide s ii was the only species observed in the vapor phase the reconstructed sulfur isotope ratios of the reservoir fluids based on samples collected at surface from two phase and vapor only well discharges indicated that 34s and 33s of sulfide in the reservoir fluid ranged from 1 5 to 1 1 and 0 001 to 0 017 respectively whereas 34s and 33s of sulfate were significantly different and ranged from 3 4 to 13 4 and 0 000 to 0 036 respectively depressurization boiling upon fluid ascent coupled with progressive fluid rock interaction and sulfide mineral pyrite formation results in the liquid phase becoming progressively isotopically lighter with respect to both 34s and 33s in contrast h2s in the vapor phase and pyrite become isotopically heavier the observed 33s and 34s systematics for geothermal fluids at krafla suggest that the source of sulfide in the reservoir fluids is the basaltic magma either through degassing or upon dissolution of unaltered basalts at high temperatures insignificant so4 was observed in the fluids but below 230 c significant concentrations of so4 were observed the source inferred to be h2s oxidation the two key factors controlling the multiple sulfur isotope systematics of geothermal fluids are 1 the isotopic composition of the source material and 2 the isotope fractionation associated with aqueous and vapor speciation and how these change as a function of processes occurring in the system including boiling oxidation and fluid rock interaction

reconstruction of a 200 ma multi stage five element bi co ni fe as s system in the penninic alps switzerland abstract hydrothermal five element veins ag co ni bi as are mineral successions of native metals encapsulated by fe co ni arsenides and carbonates recent studies focused on the evolution from ordinary base metal systems sulfide rich to five element veins sulfide poor and revealed the importance of hydrocarbon dominated fluids as essential redox agent in these systems although mineral successions reveal the natural subdivision into native as native ag bi or arsenide dominated vein types and suggested processes explain the mineralogical variation to a certain degree the ni co fe variations among the arsenides are not well understood yet this is the first case study explaining compositional mineralogical and textural features of five element veins by changing metal contents arsenic sulfur activities ph and temperatures applied to a multi stage vein mineralization in the penninic alps switzerland textural relationships mineral chemistry fluid inclusion compositions microthermometry and raman spectroscopy stable s isotopes and in situ u pb age dating of carbonates magnetite and multi mineral isochrons were investigated u pb ages of paragenetic mineral fractions constrain a primary formation of lollingite skutterudite dolomite dominated ores at 233 10 ma and niccolite gersdorffite skutterudite ankerite dominated ores at 188 32 ma which links their formation to crustal thinning caused by the breakup of the meliata ocean and alpine tethys as secondary processes during the alpine orogeny a in situ remobilization of the ores occurred as mostly ternary fe co ni sulfarsenides at 73 24 ma due to continent continent collision and neoformations of safflorite cobaltite skutterudite dominated ores at 29 16 ma due to transtensional strike slip tectonics ore textures indicate that the dissolution of primary siderite oxidation of ferrous iron and its precipitation as magnetite was the redox couple to precipitate native bi arsenides and sulfarsenides bi0 as3 and as 1 from their oxidized aqueous species bi3 cl4 and as3 oh 3 at temperatures between 200 and 300 c ni and co signatures of the arsenides sulfarsenides show increasing mobilization from the host rocks during the successive evolution of the hydrothermal system in the triassic jurassic and during the alpine orogeny stable s isotopes and as s signatures of the sulfarsenides indicate an increasing mobilization of host rock sulfides i e fahlbands from the primary to the secondary ores fluid inclusions and stable s isotopes suggest involvement of fluid modification by water rock interactions i e cover rocks carbonate sulfate and halite dissolution basement rocks albitisation of plagioclase during fluid descent

quantifying mixing boiling degassing oxidation and reactivity of thermal waters at vonarskard iceland abstract the chemical composition of geothermal fluids may be altered upon ascent from the reservoir to surface by processes including boiling degassing mixing oxidation and water rock interaction in an attempt to quantify these processes a three step model was developed that includes 1 defining the composition of the end member fluid types present in the system 2 quantifying mixing between the end members using non reactive elemental concentrations and enthalpy and 3 quantifying the changes of reactive elements including degassing oxidation and water rock interaction the model was applied to geothermal water at vonarskard iceland for demonstration having temperatures of 3 98 c ph of 2 15 9 95 and tds of 323 2250 ppm and was thought to be produced from boiled reservoir water condensed steam and non thermal water most geothermal water represented mixture of non thermal water and condensed steam whereas the boiled reservoir water was insignificantly mixed co2 and h2s degassing was found to be quantitative in steam heated water with oxidation of h2s to so4 also occurred in contrast major rock forming elements are enriched in steam heated water relative to their mixing ratios suggesting water rock interaction in the surface zone boiled reservoir water observed in alkaline hot springs have however undergone less geochemical changes upon ascent to surface and within the surface zone

forsterite dissolution and magnesite precipitation at conditions relevant for deep saline aquifer storage and sequestration of carbon dioxide the products of forsterite dissolution and the conditions favorable for magnesite precipitation have been investigated in experiments conducted at temperature and pressure conditions relevant to geologic carbon sequestration in deep saline aquifers although forsterite is not a common mineral in deep saline aquifers the experiments offer insights into the effects of relevant temperatures and pco2 levels on silicate mineral dissolution and subsequent carbonate precipitation mineral suspensions and aqueous solutions were reacted at 30 c and 95 c in batch reactors and at each temperature experiments were conducted with headspaces containing fixed pco2 values of 1 and 100 bar reaction products and progress were determined by elemental analysis of the dissolved phase geochemical modeling and analysis of the solid phase using scanning electron microscopy infrared spectroscopy and x ray diffraction the extent of forsterite dissolution increased with both increasing temperature and pco2 the release of mg and si from forsterite was stoichiometric but the si concentration was ultimately controlled by the solubility of amorphous silica during forsterite dissolution initiated in deionized water the aqueous solution reached supersaturated conditions with respect to magnesite however magnesite precipitation was not observed for reaction times of nearly four weeks magnesite precipitation was observed in a series of experiments with initial solution compositions that simulated extensive forsterite dissolution the precipitation of magnesite appears to be limited by the process of nucleation and nucleation requires a critical saturation index between 0 25 and 1 14 at 95 c and 100 bar pco2 magnesite precipitation is fastest in the presence of an initial magnesite seed although magnesite precipitates do form on the surfaces of forsterite particles the presence of the forsterite surface does not significantly accelerate magnesite precipitation relative to solid free systems

assessing the implications of tectonic compaction on pore pressure using a coupled geomechanical approach abstract overpressure prediction in tectonic environments is a challenging topic the available pore pressure prediction methods are designed to work in environments where compaction is mostly one dimensional and driven by the vertical effective stress applied by the overburden furthermore the impact of tectonic deformation on stresses porosity and overpressure is still poorly understood we use a novel methodology to capture the true compaction phenomena occurring in an evolving 3d stress regime by integrating a fully coupled geomechanical approach with a critical state constitutive model to this end numerical models consisting of 2d plane strain clay columns are developed to account for compaction and overpressure generation during sedimentation and tectonic activity we demonstrate that a high deviatoric stress is generated in compressional tectonic basins resulting in a substantial decrease in porosity with continuing overpressure increase the overpressure predictions from our numerical models are then compared to those estimated by the equivalent depth method edm in order to quantify the error induced when using classical approaches based on vertical effective stress in tectonic environments the stress paths presented here reveal that a deviation from the uniaxial burial trend can substantially reduce the accuracy of the edm overpressure predictions

the mechanics of cemented carbonate sands the behaviour of artificially cemented carbonate sand was investigated in triaxial tests at confining pressures of up to 9 mpa the results show that an important effect of cementing is a reduction in specific volume resulting from the increase in fines content this influences both the stress strain behaviour and the peak strength at strains beyond those required to fracture the cement bonding comparisons between the behaviour of cemented and uncemented soils should therefore be carried out on samples with the same gradings for cemented samples it is possible to identify a yield curve outside the state boundary surface of the uncemented soil a framework for the behaviour has been defined which depends on the relative magnitudes of the confining pressure and cement bond strength the behaviour of a natural cal carenite agreed well with this framework which is also likely to be applicable to other cemented soils le comportement d un sable carbonate artificiellement cimente a ete etudie a l aide d essa

on the mechanics of structured sands to date the effect of structure on the behaviour of natural sands has focused almost exclusively on the component of bonding and the effect of fabric has been largely overlooked the paper describes a detailed investigation of the behaviour of two natural sands by means of triaxial testing over a wide range of pressures one material had bonding as the principal element of its structure and the other fabric following on from a paper of cuccovillo and coop which examined the influence of the two structural elements on the small strain stiffness the current paper develops a new framework for the yielding and large strain behaviour it is suggested that structure should be considered as an element of the nature of a sand in addition to properties such as mineralogy particle shape and grading the resulting framework is then capable of encompassing the patterns of behaviour seen for both bonding and fabric dominated sands while bonding results in a cohesive mode of shearing it is demonstrated that when

the clumped isotope geochemistry of exhumed marbles from naxos greece exhumation and accompanying retrograde metamorphism alter the compositions and textures of metamorphic rocks through deformation mineral mineral reactions water rock reactions and diffusion controlled intra and inter mineral atomic mobility here we demonstrate that these processes are recorded in the clumped and single isotope 13 c and 18 o compositions of marbles which can be used to constrain retrograde metamorphic histories we collected 27 calcite and dolomite marbles along a transect from the rim to the center of the metamorphic core complex of naxos greece and analyzed their carbonate single and clumped isotope compositions the majority of 47 values of whole rock samples are consistent with exhumation controlled cooling of the metamorphic complex however the data also reveal that water rock interaction deformation driven recrystallization and thermal shock associated with hydrothermal alteration may considerably impact the overall distribution of 47 values we analyzed specific carbonate fabrics influenced by deformation and fluid rock reaction to study how these processes register in the carbonate clumped isotope system 47 values of domains drilled from a calcite marble show a bimodal distribution low 47 values correspond to an apparent temperature of 260 c and are common in static fabrics high 47 values correspond to an apparent temperature of 200 c and are common in dynamically recrystallized fabrics we suggest that the low 47 values reflect diffusion controlled isotopic reordering during cooling whereas high 47 values reflect isotopic reordering driven by dynamic recrystallization we further studied the mechanism by which dynamic recrystallization may alter 47 values by controlled heating experiments results show no significant difference between laboratory reactions rates in the static and dynamic fabrics consistent with a mineral extrinsic mechanism in which slip along crystal planes was associated with atomic scale isotopic reordering in the calcite lattice an intrinsic mechanism enhanced isotopic reordering rate in deformed minerals is contraindicated by these experiments we suggest that 47 values of dynamically recrystallized fabrics that form below the diffusion controlled blocking temperature for calcite constrain the temperature of deformation we find that 47 based temperatures of static fabrics from naxos marbles are 60 80 c higher than commonly observed in slowly cooled metamorphic rocks and would suggest cooling rates of 10 5 c myr 1 a similar thermal history is inferred for dolomite marbles from the core vicinity which preserve apparent temperatures up to 200 c higher than a typical blocking temperature 300 c this finding could be explained by a hydrothermal event driving a brief thermal pulse and locally resetting 47 values rapid cooling of the core complex region is consistent with a compilation of published cooling ages and a new apatite u th he age associating the thermal event with the emplacement of a granodiorite pluton at 12 ma

effect of cementation on the small strain parameters of sands natural cementation affects the properties of soils the interpretation of in situ and laboratory test results and the selection of criteria for geotechnical design in this paper published exper

dolomite effect on borosilicate glass alteration dolomite camg co3 2 is one of the common rock forming minerals in many geological media in particular in clayey layers that are currently considered as potential host formations for a deep radioactive waste disposal facility magnesium in solution is one of the elements known to potentially enhance the alteration of nuclear glasses the alteration of borosilicate glasses with dolomite as a mg bearing mineral source was investigated for 8 months in batch tests at 90 c glass composition effects were investigated through two compositions sibnaalcazro and sibnaalzro differing in their ca content the ca rich glass alteration is slightly enhanced in the presence of dolomite compared to the alteration observed in pure water this greater alteration is explained by the precipitation of mg silicate phases on the dolomite and glass surfaces in contrast the ca free glass alteration decreases in the presence of dolomite compared to the alteration observed in pure water this behavior is explained by ca incorporation in the amorphous layer formed during glass alteration coming from dolomite dissolution calcium acts as a layer reorganizer and limits glass alteration by reducing the diffusion of reactive species through the altered layer modeling was performed using the graal model implemented within the chess hytec geochemical code to discriminate and interpret the mechanisms involved in glass dolomite interactions magnesium released by dolomite dissolution reacts with silica provided by glass alteration to form mg silicates this reaction leads to a ph decrease the main mechanism controlling glass alteration is the ability of dolomite to dissolve during the experiment the quantities of secondary phases formed were very small but for longer time scales this mechanism could supply sufficient mg in solution to form large amounts of mg silicates and sustain glass alteration the ability of the graal model to reproduce the concentrations of elements in solution and solid phases regardless of the amount of dolomite and the glass composition strongly supports the basic modeling hypothesis

origins of calcite in a boiling geothermal system the formation of hydrothermal calcite relates to the movement of carbon dioxide in a geothermal system as governed by boiling dilution and condensation in this paper we show how these processes control the occurrence distribution and stable isotope composition of calcite based on a study at broadlands ohaaki the two principal calcite occurrences in the broadlands ohaaki geothermal system are 1 as replacement of rock forming minerals and volcanic glass and 2 as platy crystals infilling voids both are stable over a broad temperature range from 160 degrees c to 300 degrees c replacement calcite is widespread and forms through hydrolysis reactions involving calcium alumino silicates and sub boiling liquids that contain 0 3 to 0 75 m co 2 platy calcite in contrast forms over a restricted vertical interval of a few hundred meters within the upflow zone it precipitates from boiling fluids through exsolution of carbon dioxide as indicated by coeval liquid rich and vapor rich fluid inclusions and its formation in the two phase zone fluid inclusion data help to define the boiling paths of fluids from which platy calcite formed homogenization temperatures range from 160 degrees c to 310 degrees c and are consistent within the present geothermal regime ice melting temperatures range from 0 0 to 1 0 degrees c and indicate the presence of up to 0 5 m dissolved carbon dioxide model boiling curves calculated to match these data show how the concentration of dissolved carbon dioxide in the preboiled fluid dictates the depth of first boiling most fluid inclusion data lie along a model boiling path characteristic of the centre of the upflow zone in which the rising fluid initially containing 0 75 m co 2 begins to boil at approximately 320 degrees c and approximately 2000 m depth data from well br 18 instead matches a curve in which the rising fluid initially containing 0 53 m co 2 begins boiling at approximately 245 degrees c and approximately 900 m depth the shallowing of the depth of first boiling likely results from dilution of dissolved carbon dioxide in the parent chloride water as it rises and mixes with marginal waters calcite precipitates from both shallow formed steam headed groundwater and deeply derived chloride water and these waters are isotopically distinct at broadlands ohaaki the delta 18 0 values of calcite at 200 degrees c range from 0 5 to 7 5 per mil whereas delta 18 0 values of calcite at 200 degrees c range from 4 to 10 per mil taking appropriate temperature dependent fractionation factors into account these data indicate equilibration with chloride water delta 18 0 h2o 4 5 per mil and steam heated groundwater delta 18 o h2o 7 0 per mil respectively oxygen isotopes of hydrothermal calcites in the nearby wairakei and waiotapu geothermal systems show similar patterns consistent with the occurrence of both chloride and steam heated waters there calcite formation is explained by a model that describes the distribution of two phase conditions and aqueous carbon dioxide concentrations in a column of hydrothermal fluid rising through a rock matrix of isotropic permeability in this ideal situation platy calcite forms along the inner margin of the two phase zone having the shape of an inverted cone whereas replacement calcite mostly forms in the surrounding one phase liquid only zone the sparse occurrence of calcite at less than or equal to 800 m depth in the central upflow of the ohaaki sector at broadlands ohaaki is compatible with this model and appears related to the exsolution of dissolved carbon dioxide through boiling deeper in the system

physical and chemical characteristics of potential seal strata in regions considered for demonstrating geological saline co2 sequestration capture and geological sequestration of co2 from energy production is proposed to help mitigate climate change caused by anthropogenic emissions of co2 and other greenhouse gases performance goals set by the us department of energy for co2 storage permanence include retention of at least 99 of injected co2 which requires detailed assessments of each potential storage site s geologic system including reservoir s and seal s the objective of this study was to review relevant basin wide physical and chemical characteristics of geological seals considered for saline reservoir co2 sequestration in the united states results showed that the seal strata can exhibit substantial heterogeneity in the composition structural and fluid transport characteristics on a basin scale analysis of available field and wellbore core data reveal several common inter basin features of the seals including the occurrence of quartz dolomite illite calcite and glauconite minerals along with structural features containing fractures faults and salt structures in certain localities within the examined basins some seal strata also serve as source rock for oil and gas production and can be subject to salt intrusions the regional features identified in this study can help guide modeling laboratory and field studies needed to assess local seal performances within the examined basins

major and trace element and multiple sulfur isotope composition of sulfides from the paleoproterozoic surda copper deposit singhbhum shear zone india implications for the mineralization processes abstract the present study combines major and trace element composition and sulfur s isotope data of pyrite and chalcopyrite from the surda copper sulfide deposit in the singhbhum shear zone the most important copper and uranium producing belt singhbhum cu u belt in india three textural and compositional types of both pyrite and chalcopyrite were distinguished unzoned to partially zoned pyrite ia with high co up to 54900 ppm and low ni content is earliest followed by oscillatory zoned pyrite ib with high as up to 25600 ppm and co up to 46800 ppm both occurring in pyrite i chalcopyrite i pyrrhotite magnetite apatite vein cobaltite type substitution fe1 xcox s1 xasx 2 is suggested for pyrite ib gold occurs in pyrite i as minor invisible gold and as electrum inclusions it also occurs along with cu mn ni hg ag pb sb zn ce y u and th in micro fractures that transgress the primary zoning pattern defined by as co and ni in pyrite ib the early inclusion rich chalcopyrite generation chalcopyrite i contains high concentration of zn and se and minor to trace amounts of co ni hg pb sb te and bi appeared in between pyrite i and ii low co high ni up to 37700 ppm content pyrite ii and inclusion free chalcopyrite ii enriched in co ni hg bi mn ag sb v and pb are cogenetic and occurring in pyrite ii pyrrhotite pentlandite chalcopyrite ii violarite vein low co and ni containing pyrite iii chalcopyrite iii occur mainly as disseminated grains the relative timing of formation of pyrite ii chalcopyrite ii with pyrite iii chalcopyrite iii remains uncertain pyrite chalcopyrite textures indicate that all pyrite chalcopyrite formed at some time prior to the end of deformation and metamorphism both in situ and mineral separates of all pyrite types and associated chalcopyrite yield a narrow range of positive 34s values between 3 8 and 6 9 suggesting sulfur being derived from a similar source consistent positive 34s values and other circumstantial evidence indicate that most sulfur was derived from seawater sulfate or modified seawater brine evaporite 33s values revealed mass dependent fractionation mdf signature it is proposed that incorporation of mdf sulfur of the mineralization event in paleoproterozoic singhbhum cu u belt took place after the great oxidation event the high se concentrations 260 400 ppm and se s ratios for both pyrite i and ii from surda deposit 4 4 5 7 10 4 suggest a low temperature of the cu rich ores 250 350 c and precipitation from a metalliferous fluid with a high se s ratio 10 4 to 10 3 consistent with igneous input of these elements

description and interpretation of the composition of fluid and alteration mineralogy in the geothermal system at svartsengi iceland abstract the bulk composition and mineralogy of hydrothermally altered tholeiite along with the composition and speciation of fluid have been determined for a well defined alteration zone at 240 c and 110 bars at svartsengi iceland mass balances between the geothermal fluid and altered tholeiite relative to a seawater fresh water mixture and unaltered tholeiite indicate the overall reaction per 1000 cm 3 is 1325 gm plagioclase 1228 gm pyroxene 215 gm oxide minerals break down to form 685 gm chlorite 636 gm albite 441 gm quartz 249 gm epidote 266 gm calcite 201 gm oxide minerals 15 gm pyrite requiring an influx of 123 gm co 2 10 gm h 2 s and 4 gm na 2 o and a release of 57 gm sio 2 35 gm feo 21 gm cao 8 gm mgo and 4 gm k 2 o principal reactions deduced from textural evidence include na ca exchange in plagioclase precipitation of quartz calcite and anhydrite and formation of chlorite and epidote by reactions between groundmass minerals and fluid thermodynamic analyses of authigenic minerals and downhole fluid indicate that the fluid maintains a state close to equilibrium with the secondary mineral phases chlorite epidote albite quartz calcite prehnite anhydrite pyrite and magnetite whereas remnant primary labradorite and augite are out of equilibrium with the fluid water rock ratios for the system are determined under a variety of assumptions however the open nature of the system makes comparisons with experimental and theoretical closed system studies ambiguous

influence of amorphous silica layer formation on the dissolution rate of olivine at 90 c and elevated pco2 for mitigating against rising levels of atmospheric co2 carbonation of m2 bearing silicates has been proposed as a possible option for sequestering co2 over long time spans due to its rapid far from equilibrium dissolution rate and its widespread occurrence in mafic and ultramafic rocks olivine has been suggested as a potentially good candidate for achieving this goal although the efficacy of the carbonation reaction still needs to be assessed with this as a goal the present study aims at measuring the carbonation rate of san carlos olivine in batch experiments at 90 c and pco2 of 20 and 25 mpa when the reaction was initiated in pure water the kinetics of olivine dissolution was controlled by the degree of saturation of the bulk solution with respect to amorphous silica this yet unrecognized effect for olivine was responsible for a decrease of the dissolution rate by over two orders of magnitude in long term 45 days carbonation experiments with a high surface area to solution volume ratio sa v 24 600 m 1 the final composition of the solution was close to equilibrium with respect to sio2 am independent of the initial concentration of dissolved salts nacl and naclo4 ranging between 0 and 1 m and with an aqueous mg si ratio close to that of olivine no secondary phase other than a ubiquitous thin 40 nm si rich amorphous layer was observed these results are at odds with classic kinetic modeling of the process due to experimental uncertainties it was not possible to determine precisely the dissolution rate of olivine after 45 days but the long term alteration of olivine was indirectly estimated to be at least 4 orders of magnitude slower than predicted taken together these results suggest that the formation of amorphous silica layers plays an important role in controlling the rate of olivine dissolution by passivating the surface of olivine an effect which has yet to be quantified and incorporated into standard reactive transport codes

drained principal stress rotation in saturated sand an investigation into the effects of drained principal stress rotation on the behaviour of a saturated medium loose sand is described using a hollow cylinder apparatus the principal stress directions were rotated both at a constant shear stress and under an increasing shear stress during drained monotonic loading to failure the experimental results are presented the findings are used to support the notion that a bounding surface defined by tests with fixed principal stress orientations can be used to make a qualitative prediction of drained and undrained behaviour during monotonic loading to failure which includes rotation of principal stress directions the bounding surface conveys the importance of both anisotropy in determining strength and the direction of principal stress rotation in determining the magnitude of volumetric strains or pore pressures which develop the findings concerning the bounding surface apply to a medium loose sand which has a well defined con tractant region strains which

diffuse emission of co2 from the fossa crater vulcano island italy numerous measurements of co2 degassing from the soil carried out with the accumulation chamber method indicate that in the period april july 1995 the upper part of the fossa cone released a total output of 200 t d 1 of co2 which corresponds to approximately 1000 t d 1 of steam these large amounts of fluids are of the same order of magnitude as those released by the high temperature fumarolic field located inside the crater the spatial distribution of soil gas fluxes shows that the main structures releasing co2 are the inner slopes of the crater and a nw se line located ne of the crater rim which correspond to the main direction of vulcano island active faults the comparison of the co2 maps with the soil temperature distribution derived from both direct measurements and airborne infrared images indicates the occurrence of extensive condensation of fumarolic steam within the upper part of the fossa cone whose total amount is comparable to the rainfall budget part of the condensate which originates from this process contributes to the recharge of the phreatic aquifer of porto plain modifying the chemical and isotopic composition of the groundwater

geothermal mineral equilibria the dominant reaction determining the chemistry of fluids in a geothermal system of the new zealand type consists of the conversion of primary plagioclase by co2 to calcite and clays with log pco2 15 26 7850 t 273 2 temperature t in c subsequent reactions involving secondary minerals control relative co2 h2s contents the distribution of mineral phases throughout a geothermal system reflects the stepwise conversion of thermodynamically unstable primary phases through a series of intermediate metastable phases to a thermodynamically stable secondary assemblage the relative stabilities of these phases was evaluated on the basis of their solubilities the least soluble aluminiumsilicate representing the thermodynamically most stable phase under a given set of conditions observed assemblages of secondary minerals in geothermal systems represent indicators allowing mineral fluidinteraction conditions to be evaluated on the basis of multi component mineral stability diagrams

correlation of homogenization temperatures of accessory minerals from sphalerite bearing deposits and ga ge model temperatures abstract the ga ge ratio in sphalerite can be related to the temperature of the initial fluids from which the sphalerite grew after mixing with various amounts of fluids from different origins the extent of mixing of the two fluids can be qualitatively derived from the pressure corrected homogenization temperature which represents the temperature after mixing of the fluids and the ga ge temperatures of sphalerite which indicates the temperature of the hot metal bearing initial fluids different temperature information strongly indicate that mixing of fluids did occur prior to sulphide formation

mineral solubility and aqueous speciation under hydrothermal conditions to 300 c the carbonate system as an example carbon is a major element in the earth s system and plays an important role in many geochemical processes including metamorphism volcanism oceanic systems and atmospheric evolution knowledge and understanding of chemical speciation mineral solubility and reactivity involving carbon are very important in order to qualitatively and quantitatively understand these processes indeed dissolved inorganic carbon is among the major components of natural geothermal fluids it originates from various sources including magmatic degassing rock dissolution and organic matter degradation e g giggenbach 1992 giggenbach et al 1993 simmons and cristenson 1994 sanoa and marty 1995 dissolved co2 is the most common form of dissolved inorganic carbon in these systems though other forms exist like ch4 and co but usually in much lower concentrations than co2 e g chiodini and marini 1998 stefansson and arnorsson 2002 the concentrations of dissolved inorganic carbon dic in geothermal fluids from active geothermal systems throughout the world are shown in figure 1a together with the ph of the fluids in general the dic concentration increases in geothermal fluids with increasing temperature from a few mmol per kg up to half a mole per kg of fluid this increase is accompanied by a decrease in the fluid ph fig 1b higher concentrations not shown are observed in fumarole fluids discharging volcanic gases e g chiodini et al 1996 at earth s surface co2 also degasses through the soils in active geothermal systems e g chiodini et al 1998 the chemistry and transport of dic in natural geothermal systems is influenced by many processes including magma degassing water rock interaction and partitioning of co2 between liquid and vapor phases upon boiling and phase separation it has been concluded that the concentration of dic and all other major elements besides incompatible elements such as cl are

fluid evolution of the cantung tungsten skarn northwest territories canada differentiation and fluid rock interaction abstract the tombstone tungsten belt is the only plutonic belt with world class tungsten deposits in western north america the cantung deposit is a world class tungsten exoskarn and its mining has exposed a vertical section of hundreds of meters including spatially related plutons as well as skarns and orebodies in this study we sampled quartz veins with various mineralogical assemblages hosted in the granitic pluton and the overlying skarn host rocks the fluid inclusions fis in each sample show a range of gas and trace elements contents reflecting their origin and degree of fluid rock interaction we propose that high concentrations of b k rb and cs in the fis as well as the high salinity indicate the degree of fractionation of the magma when the fluid exsolved divalent cations ca sr ba and mn are almost exclusively detected in skarn hosted inclusions indicating the degree of fluid rock interaction with the metasedimentary cover the fluids located in the intrusion are co2 rich and indicate a less evolved magmatic source e g low cs rb while fluids that interacted with the limestone are ch4 rich and reflect a more differentiated source the ph neutralization of the acidic magmatic fluid and calcium addition during its interaction with the limestone may have triggered the ore precipitation

hydromechanical modeling of stress pore pressure and porosity evolution in fold and thrust belt systems we present coupled critical state geomechanical fluid flow simulations of the evolution of a fold and thrust belt in nw borneo our modelling is the first to include the effects of both syntectonic sedimentation and transient pore pressure on the development of a fold and thrust belt the present day structure predicted by the model contains the key first order structural features observed in the field in terms of thrust fault and anticline architectures stress predictions in the sediments show two compressive zones aligned with the shortening direction located at the thrust front and back limb between the compressive zones near to the axial plane of the anticline the modelled stress field represents an extensional regime the predicted overpressure distribution is strongly influenced by tectonic compaction with the maximum values located in the two laterally compressive regions we compared the results at three notional well locations with their corresponding uniaxial strain models the 2d thrust model predicted porosities which are as much as 7 5 lower at 2 5 km depth and overpressures which are up to 6 4 mpa higher at 3 km depth these results show that one dimensional methods are not sufficient to model the evolution of pore pressure and porosity in contractional settings finally we performed a drained simulation during which pore pressures were kept hydrostatic the predicted geological structures differ substantially from those of the coupled simulation with no thrust faulting these results demonstrate that pore pressure is a key control on structural development

on the behaviour of thanet sand an example of an uncemented natural sand an extensive laboratory investigation was made of the mechanics of thanet sand testing the soils from a number of locations and depths in the triaxial apparatus over a wide range of stress levels comparisons between tests on intact and reconstituted samples and between vertically and horizontally trimmed intact samples highlighted the effects of structure on the behaviour of this uncemented sand in particular a significant effect of anisotropy two distinct substrata have previously been identified with different fines contents and the key difference in their behaviour has been found here to be the location of their critical state line in the v lnp plane which has a significant effect on the engineering behaviour of the two substrata and can explain recent unusual observations of decreasing pile capacity with depth tests in which the glauconite content was removed from the sand showed that it did not affect its behaviour

mineralogical and fluid inclusion features of rock alterations in the seigoshi gold silver mining district western part of the izu peninsula japan abstract propylitic and advanced argillic alterations occur in the seigoshi gold silver mining district in the western part of the izu peninsula japan the propylitic alteration has the following zonal arrangement from the deeper portion to the shallower portion an epidote prehnite k feldspar chlorite zone a wairakite laumontite zone and a stilbite heulandite montmorillonite zone lateral and vertical zoning is conspicuous in the advanced argillic alteration the inner zone is silica rich and this grades laterally and vertically through alunite to clay rich zones fluid inclusions from the epidote prehnite k feldspar chlorite zone are liquid dominated and filling temperatures of this zone are in the range of 225 285 c filling temperatures for the zeolite zone are variable being in the range of 240 380 c this wide range suggests that boiling of the fluids was responsible for the zeolite zone filling temperatures of the advanced argillic alteration range widely from 210 to 430 c this wide range and the coexistence of liquid and vapor dominated fluid inclusions in a given sample suggest that liquid vapor separation simultaneously occurred during the advanced argillic alteration process it is deduced that the ranges of gaseous fugacity are quite different for each type of alteration for instance f s 2 and f o 2 of the advanced argillic alteration are estimated to be higher than those of the propylitic alteration based on the alteration mineral assemblage chemical composition and mode of occurrence of alteration minerals fluid inclusions estimated ranges of gaseous fugacities and comparison of these features with those of active geothermal systems it is concluded that the propylitic alteration minerals were probably precipitated due to the loss of gases such as co 2 and that the formation of advanced argillic alteration was caused by subsurface mixing of volcanic gas and or condensed hot water with groundwater these coexisting propylitic and advanced argillic alterations are commonly found in the other au ag mining districts in japan

induced and inherent anisotropy in sand data from an extensive series of drained tests on dense sand in a directional shear cell have been used to explore the interaction of inherent and induced anisotropy the essential link between previous strain and induced anisotropy has been demonstrated this link is shown to hold regardless of any inherent anisotropy or previous cyclic rotation of principal stress directions in dense sand a small permanent shear strain of the order of 0 5 leads to significant induced anisotropy induced anisotropy is shown as causing very large directional variations in stiffness of sand and associated capability for porewater pressure generation the underlying causes of inherent and induced anisotropy are discussed and related to the widely recognized persistence of inherent anisotropy which frequently controls peak shear resistance possible methods for predicting the effects of anisotropy are briefly discussed des donnees obtenues a partir d une serie grande d essais draines effectues sur du sable dense dans une

mineralogical and fluid inclusion studies of low sulfidation epithermal veins at osilo sardinia italy several precious metal bearing low sulfidation epithermal veins occur in the rolling topography of the osilo area northern sardinia the sa pala de sa fae and the sa pedra bianca veins were subject to intense diamond drilling exploration in the mid 1990 s the veins extend for 1 3 km dip steeply and range from 1 to 10 m in width high k calc alkaline volcanic deposits containing plagioclase phenocrysts along with lesser pyroxene amphibole magnetite olivine and sanidine form the main host rocks gold grades in drill intersections range from 50 m from the vein the assemblage albite fe chlorite illite pyrite montmorillonite calcite k feldspar prevails regionally and its formation is attributed to minor metasomatism of the country rock involving the addition of water carbon dioxide and hydrogen sulfide at distances 10 m from the vein the assemblage quartz k feldspar pyrite illite dominates forming an alteration envelope that cross cuts regional alteration quartz and k feldspar increase in abundance towards the vein quartz is the main vein mineral and it displays a range of morphologies and textures including crustiform colloform banding quartz pseudomorphs of platy calcite breccias and coarse euhedral crystals electrum and argentite which are the main gold and silver minerals deposited during the early stages of vein mineralization with rhomb shaped crystals of k feldspar adularia pyrite plus lesser marcasite arsenopyrite stibnite and sphalerite are the other sulfide phases in veins kaolinite halloysite jarosite form a late assemblage overprinting earlier hydrothermal alteration it is mostly restricted to shallow depths of a few meters except near veins most of this assemblage likely formed from weathering and oxidation of sulfides microthermometric measurements were made on quartz hosted two phase liquid vapor inclusions containing 75 liquid mean homogenization temperatures 750 measurements range from 220 to 250 c and ice melting temperatures 550 measurements range from 0 0 to 2 3 c the presence of co existing vapor rich and liquid rich inclusions with quartz pseudomorphs of platy calcite indicate that boiling conditions existed slight vapor bubble expansion of a few fluid inclusions subjected to crushing experiments indicates inclusion fluids contained variable but low concentrations of dissolved gas this study shows that gold silver mineralization formed in subvertical channels from ascending solutions at 250 c at around 300 to 450 m below the paleo water table in a typical low sulfidation epithermal environment hydrothermal solutions that produced vein mineralization and related alteration were dilute 4 1 equivalent wt nacl and 4 wt co2 near neutral ph reduced and at times boiling

quantifying the evolution of soil fabric during shearing using directional parameters over the past 50 years experimental studies have repeatedly demonstrated that the mechanical behaviour of sand is sensitive to the material fabric that is the arrangement of the grains up until now there have been relatively few attempts to describe this fabric quantitatively much of our understanding of the link between the particle movements and interactions and the macro scale response of granular materials including sand comes from discrete element modelling and experiments on analogue sands with simple idealised shapes this paper investigates methods of quantifying the directional fabric of a real sand and its evolution under loading statistical analyses of the distribution of fabric directional data in terms of particle contact normal branch vector and void orientations were carried out at different stages of shearing deformation the data show that the initial particle orientation fabric that develops during the deposition of the material tends to persist during shearing while in the