geochemical constraints on the origin of calcite veins and associated limestone alteration ordovician viola group arbuckle mountains oklahoma u s a abstract isotopic and elemental analyses constrain the origins of two types of calcite veins and associated limestone alteration in the ordovician viola group arbuckle mountains oklahoma u s a calcite from small millimeter wide veins has similar 87 sr 86 sr ratios 0 70781 0 70792 and 13c values 1 4 to 1 6 pdb to host viola limestone 87 sr 86 sr 0 70779 0 70794 13c 2 2 to 1 7 pdb indicating that the fluids from which the vein calcite precipitated were chemically buffered by the host limestone the low 18o values 8 2 to 5 5 pdb of the vein calcite relative to the host limestone 5 0 to 3 1 pdb suggest that the vein calcite probably precipitated from 18o depleted meteoric water calcite from large veins 5 50 cm wide is characterized by radiogenic 87 sr 86 sr ratios 0 70887 0 70915 and low 13c values 8 0 to 2 5 pdb relative to host viola limestone such isotopic compositions demonstrate that the fluids responsible for the formation of the large veins were enriched in 87sr and depleted in 13c relative to the host limestone the 18o values 4 8 to 3 7 pdb of calcite from the large veins coupled with the presence of hot 50 90 c and saline fluid inclusions constrain the formation of the vein calcite to 18o enriched 18 o 2 smow fluids on this basis calcite from the large veins is believed to have precipitated from basin derived fluids adjacent to the large veins alteration zones up to 0 5 m wide have developed in host limestone relative to other limestones the altered limestones display radiogenic 87 sr 86 sr ratios 0 70792 0 70880 low 13c values 8 2 to 2 0 pdb and low sr concentrations the similar isotopic compositions of the altered limestone to those of the large veins suggest that alteration of limestones was also caused by basinal fluids

the role of eddies in solute transport and recovery in rock fractures implication for groundwater remediation a better understanding of solute transport and retention mechanism in rock fractures has been challenging due to difficulty in their direct observations in microscale rough walled fractures six representative troughs in a rough walled fracture were selected for microscale observations of eddy formation with increasing flow velocity and its effect on spatiotemporal changes of solute concentration this experimental study was enabled by a microscale visualization technique of micro particle image velocimetry with increasing flow velocity re 2 86 no eddies were generated and solutes along the main streamlines transported rapidly whereas those near the wall moved slowly a larger amount of solutes remained trapped at all troughs at re 2 86 than re 10 and this flow range could be favourable for efficient remediation

effects of grand cycle cessation on the diagenesis of upper cambrian carbonate deposits in the southern appalachians u s a abstract the vertical transition from the mainly subtidal alternating shale and carbonate units or grand cycles of the conasauga group middle to upper cambrian to the peritidal dolostone of the knox group upper cambrian to lower ordovician marks a major change in the early paleozoic passive margin sedimentation of the southern appalachians the grand cycles represent an interplay between intrashelf shale basin and carbonate platform deposition the end of grand cycle deposition occurred in response to carbonate platform progradation over the infilled intrashelf basin and is associated with a prominent change in diagenetic patterns observed in the uppermost conasauga group strata the maynardville formation the maynardville records upward shallowing from subtidal shale and limestone into peritidal dolostone this change from a subtidal into a peritidal depositional regime influenced the early diagenesis of the maynardville and in conjunction with the changes in the regional facies distribution at the end of grand cycle deposition extended its influence upon the burial diagenesis of these deposits the subtidal deposits of the maynardville contain a variety of calcite cements dolomite is not abundant in these deposits where it occurs mainly as a fine crystalline ferroan phase associated with argillaceous layers and pressure dissolution features the local source for this dolomite during burial was provided by expulsion of pore fluids from interbedded shale deposits diagenesis of clay minerals and pressure dissolution of carbonates ferruginous coatings on hardgrounds in the subtidal deposits provided an additional local source of iron for the formation of replacement saddle dolomite the subtidal deposits also contain saddle dolomite cement associated with mississippi valley type mvt minerals which indicate the involvement of externally derived fluids during late burial diagenesis of these strata the peritidal deposits on the other hand are extensively dolomitized fine crystalline dolomite most likely represents early diagenetic replacement of tidal flat carbonate sediment coarse crystalline replacement dolomite formed during burial by recrystallization of early dolomite and dolomitization by warm burial brines fenestrae desiccation cracks and evaporite dissolution voids are occluded with dolomite cement which is commonly complexly zoned zoned dolomite precipitated during shallow to intermediate burial and is postdated by saddle dolomite cement saddle dolomite in pore centers dissolutional voids and tectonic fractures formed during late burial from warm fluids associated with the migration of mvt brines the effects of changes in the depositional setting on diagenesis are reflected in similar early diagenesis between the subtidal maynardville and the underlying conasauga group carbonate deposits and between the peritidal deposits of the upper maynardville and the rest of the overlying knox group the depositional environments and early diagenesis also affected the burial diagenesis the changes in regional facies distribution caused by carbonate platform progradation at the end of grand cycle deposition resulted in a decrease in the proportion of siliciclastic components this decrease was accompanied by a decline in the amount of ferroan carbonate in the peritidal deposits the maynardville is conformably overlain by carbonate deposits of the knox group this allowed the maynardville knox succession to behave as a single hydrologic unit for the migration of burial fluids in response to the formation of the ordovician foreland sevier basin to the southeast during the conversion from a passive into a convergent continental margin the nolichucky shale separates the maynardville knox succession from the carbonate deposits of the underlying conasauga group which were in contrast affected by the migration of burial fluids from the cambrian intrashelf shale basin to the west

advection and dispersion of contaminant in a permeable medium embedding fractures in which advection velocity is comparatively slow abstract this paper concerns the advective migration of an aqueous contaminant in a fractured permeable formation calculation and analysis refer to fractures in which advection velocity is comparatively small the slow advective velocity is created by some local cavities or almost vertical orientation of the fractures it is shown that the advective contaminant transport is characterized by two dimensionless parameters 1 the ratio between the permeable block and fracture flow rates termed the mobility number 2 the ratio between the longitudinal advection velocity of the permeable block flow and that of the fracture flow termed the advection velocity ratio for a sufficiently large domain continuum parameters can be applied to characterization of the fractured permeable formation then the mixing between the permeable block flow and the fracture flow is a mechanism leading to contaminant dispersion for very small values of the advection velocity ratio the effective dispersivity is fully determined by the mobility number its value decreases with increase of the mobility number under such conditions the equivalent porosity is constant and its value is identical to that of the permeable blocks a significant value of the advection velocity ratio increases the equivalent porosity of the fractured permeable formation with regard to the effective dispersivity of the domain if the advection velocity ratio is equal to unity then the effective dispersivity vanishes the larger the deviation of the advection velocity from unity the larger is the effective dispersivity of the fractured permeable medium

state of the art of modelling two phase flow in fractured rock two phase flow in fractured rock is an important phenomenon for a range of practical problems not the least of which is non aqueous phase liquid napl contamination of groundwater although multiphase systems have long been studied in the petroleum field in the hydrogeological field progress has only just reaches the point where models are being developed scale effect is one of the main issues of concern although models presented in this paper have the potential to provide useful predictions they can only be used to investigate a variety of possible scenarios with parameters being specified in the form of distribution of values the calibration and validation of all but the simplest of these models poses a formidable task with great demands on hydrogeologists and geophysicists to provide adequate data

preliminary interpretation of tracer experiments conducted in a discrete rock fracture under conditions of natural flow the authors present a preliminary analysis of tracer experiments conducted on a natural horizontal fracture system in shale and limestone at a depth of roughly 10 m an array of 27 boreholes on 5 m spacings was placed into this fracture system and apertures of the fractures were determined hydraulically at each hole a conservative tracer was injected into one borehole and monitored in the array the tracer transport process was modeled by a one dimensional model and indicates that transverse dispersion and diffusion in the matrix are the predominant processes which inhibit tracer migration and result in spreading

interpretation of field tracer tests of a single fracture using a transient solute storage model the results and interpretation of five induced gradient tracer tests performed at five different average interborehole fluid velocities in a single fracture in monzonitic gneiss are described the experiments were conducted using radioactive 82br and a fluorescent dye as conservative tracers where the tracers were pulse injected into radial convergent and injection withdrawal flow fields the flow fields were established between straddle packers isolating the fracture in three boreholes over distances of 12 7 29 8 m the tracer breakthrough curves were determined from samples of the withdrawn groundwater and were interpreted using residence time distribution rtd theory and two deterministic simulation models the rtd curves of the tracer experiments were interpreted by fitting to the field data a simple advection dispersion model and an advection dispersion model with transient solute storage in immobile fluid zones both models consider the different flow field geometries associated with injection withdrawal and radial convergent tests comparison of the fits obtained by the simulation models suggest that the initial period of solute transport in single fractures is advection dominated and with increasing tracer residence time or decreasing fluid velocity transport progresses toward more fickian like behavior during the advective dominated period the transient solute storage model is shown to adequately describe the asymmetries and long tails characteristic of the fracture rtds interpretation of the tracer experiments using both simulation models further suggests that induced gradient tracer experiments are likely to underestimate the dispersive characteristics of single fractures under natural flow conditions

acoustic multipole logging in transversely isotropic poroelastic formations the properties of the modes generated by multipole sources in a fluid filled borehole embedded in radially layered formations that include transversely isotropic poroelastic layers are investigated these layers are modeled following biot s and homogenization theories under the assumption that the principal axes of symmetry of both the transversely isotropic skeleton and the complex permeability tensor are parallel to the vertical axis of the borehole a general formulation based on the thomson haskell method accounts for any combination of fluid elastic and poroelastic layers either isotropic or transversely isotropic the investigation is achieved through the computation of dispersion and attenuation curves and frequency dependent sensitivity coefficients with respect to the parameters in the presence of a fast or slow radially semi infinite transversely isotropic poroelastic formation with an impermeable borehole wall the shear wave transverse isotropy of the skeleton can be determined using t

modelling of contaminant migration in a chalk aquifer abstract a numerical model is formulated and used to investigate chloride migration in the chalk aquifer beneath effluent lagoons to the north of royston hertfordshire uk the aquifer is characterised as a dual porosity medium in which lateral advection and hydrodynamic dispersion are dominant in the fissure system whereas molecular diffusion is dominant in the chalk matrix the galerkin finite element method is used to solve the equations of flow and transport in the fissure system a recurrence relationship is found which permits the coupling to the fissure model of a truncated series approximation to the analytical solution for one dimensional diffusion in the surrounding porous matrix the combined model has been calibrated using data collected between 1975 and 1979 and predictive simulations have been performed for the period from 1979 to 1986 the results are compared with data collected in 1986 the model is found to produce acceptable estimates of the spread of the chloride plume the value of the model and the causes and potential implications of the observed model errors are discussed

analysis of hydrodynamic dispersion in discrete fracture networks using the method of moments recent field investigations in crystalline rock give strong indications that water flows in largely isolated channels in fissured rock the channels are located in fracture planes and may or may not connect to other channels in the same plane or at fracture intersections in the present paper hydrodynamic dispersion in such fracture networks is investigated using the concepts of residence time distribution theory it is shown that from a set of simple relations at least the first four statistical moments for the system response are easily obtained even for complicated networks in particular an equivalent dispersion coefficient may be calculated from the second central moment variance the effect of channeling generally decreases in systems with many mixing steps a criterion based on the coefficients of skewness and kurtosis is derived for when the response of the system is in accordance with the diffusion dispersion model examples show that this limit may not be obtained under realistic repository conditions in fissured rock

sr isotope study of vein and cave calcites from southern israel abstract the strontium isotope compositions of secondary calcites from the negev southern israel were compared to those of the marine carbonate host rocks which range in age from triassic to eocene in order to understand fluid source and migration through fracture systems in dominantly carbonate strata the sr isotopes of these calcite clusters are divided into two groups 1 calcites with 87 sr 86 sr values greater than those of the host carbonates and 2 calcites with 87 sr 86 sr values close to the values of the host carbonate 1 1 these secondary calcites were found on the main tectonic lines of the negev faults and fold axes and are enriched in 87sr 87 sr 86 sr 0 707709 0 709151 relative to the marine carbonate country rocks 87 sr 86 sr 0 707251 0 70755 with one exception these calcites are associated or crossed by thin veins filled by fe and mn oxides 2 2 secondary calcites with 87 sr 86 sr values close to those of the marine carbonate country rocks 0 7073 0 7077 are found in karstic caves and veins and are located in sites which are not on the major faults and fold axes these calcites are not crossed by fe and mn oxides the isotopic results indicate that the solutions from which the secondary minerals of the first group precipitated were not in isotopic equilibrium with the marine host rocks the possible source of the precipitating solutions can be either surface rain descending through the fault system or ascending groundwaters from the deep nubian aquifer paleozoic to early cretaceous in age in both cases there would be a limited interaction with the host sandstone rock which usually is depleted in sr the similarity of the 87 sr 86 sr values to those of the host rocks in the second group suggests that the main source of sr in these calcite crystals was from the dissolution of the marine carbonate country rocks by rain and flood waters

strontium isotopic evidence for the origin of siderite ankerite and magnesite mineralizations in the eastern alps metasomatic magnesite siderite and ankerite mineralizations within paleozoic sediments of the northern greywacke zone and its metamorphic counterpart in the crystalline basement upper austroalpine unit were investigated with respect to their strontium isotopic composition the results support a sedimentary s l model for the magnesites within visean platform carbonates of the veitsch nappe and an epigenetic hydrothermal model for the siderites and ankerites in devonian platform carbonates of the noric nappe and from huttenberg the fe transporting fluids can be characterized either as magmatogene or more probably as metamorphogene by increasing the stage of recrystallization and or remobilization due to at least two later metamorphic overprints sr in the various ore minerals beame enriched in radiogenic 87sr

laboratory assessment of the equivalent apertures of a rock fracture hydraulic electrical and tracer test results are presented for a natural fracture in granite the hydraulic and electrical apertures of the fracture are similar and suggest minimal fracture surface to surface contact tracer aperture exceeds hydraulic aperture indicating transport at a rate less than that predicted on the basis of hydraulic aperture numerical simulation of tracer transport reveals that transport within the fracture is not explicable in terms of parallel plate flow and that transport occurs locally at rates in excess of the overall rate defined by tracer aperture

field measurement of radial solute transport in fractured rock the results of a tracer experiment conducted in a single fracture are interpreted using a semianalytical model which accounts for advective dispersion matrix diffusion mixing in the test zones and for tortuosity the experiment was conducted using a conservative tracer which was injected into a steady divergent flow field arrival of tracer was monitored in an array of 13 boreholes intersecting the fracture over a square area of approximately 30 m on a side the arrival of tracer was detected in 11 of the 13 boreholes simulation of the transport process suggests that matrix diffusion may play a significant role in the migration of solutes contrary to previously published results the relative influence of advective dispersion was found to be increasingly diminished with increasing scale fracture apertures determined from the results of the tracer experiment were found to be in general agreement with apertures calculated from independent hydraulic tests the individual advective processes that contribute to advective dispersion remain unresolved on the basis of this experiment

strontium isotopic constraints on the origin of ore forming fluids of the viburnum trend southeast missouri abstract we have measured 87 sr 86 sr and rb and sr concentrations in several minerals primarily sulfides spanning the paragenesis of hydrothermal mineralization in the viburnum trend in southeast missouri separate measurements were made for fluid inclusions opened by crushing or thermal decrepitation and for the solids for comparison measurements were also made on samples of probable local aquifers the bonneterre formation and the lamotte sandstone for some of the samples concentrations of k ca cl na and mg are also reported in several cases 87 sr 86 sr ratios are different higher in the solids than in the fluid inclusions we have investigated the possibility that either type of sample gives spurious results e g that the fluid inclusions are secondary or contaminated by host dolomite or that sr in the solids reflects a detrital rather than an authigenic source consideration of mass balance overall solute chemistry and examination of non sulfide dissolution residue however suggests that both types of sample reflect primary fluid sr composition we thus adopt the working hypothesis that sr isotopic composition in fluids at the time of hydrothermal mineralization was highly variable the observed results for the viburnum trend do not conform well to expected trends for mississippi valley type mvt mineralization based primarily on analyses of gangue carbonates barite and fluorite fluid inclusion sr in some of the viburnum trend samples is more radiogenic than in the host dolomite but only moderately so in other samples notably main stage octahedral galena fluid inclusion sr composition is within the range observed for the host dolomite in contrast sr in some of the sulfides is very radiogenic much more so than previously reported for mvt minerals and is very radiogenic early in the paragenesis pyrite chalcopyrite sphalerite less radiogenic during main stage ore deposition and again more radiogenic in later paragenetic stages

gangue mineral 87 sr 86 sr ratios and the origin of mississippi valley type mineralization the 87 sr 86 sr ratio measurements in mississippi valley type gangue minerals and host marine carbonates ranging in age from upper cambrian to mississippian show that in northwestern ohio where the mineralization is sparse the minerals precipitated from fluids in local isotopic equilibrium with the host carbonates in which the minerals were emplaced in contrast most gangue minerals from districts of major mineralization in illinois kentucky virginia and tennessee contain strontium with higher 87 sr 86 sr ratios than the carbonate hosts and appear to have crystallized from fluids containing strontium from silicate minerals in the sedimentary succession no evidence has been found for a magmatie component in the ore fluid strontium data from elmwood tennessee show that the early ore fluids like those of northwestern ohio were in isotopic equilibrium with the host carbonates but that they were mixed with and displaced by introduced fluids containing more radiogenic strontium these findings are consistent with the two fluid mixing model for the mississippi valley mineralization where a fluid indigenous to the host carbonates and containing reduced sulfur was mixed with introduced fluids analogous to metal bearing and low sulfide oil field brines with an extensive history of chemical exchange with clays and other silicate minerals in the sedimentary succession

inferring transport characteristics in a fractured rock aquifer by combining single hole ground penetrating radar reflection monitoring and tracer test data 1 investigations of solute transport in fractured rock aquifers often rely on tracer test data acquired at a limited number of observation points such data do not by themselves allow detailed assessments of the spreading of the injected tracer plume to better understand the transport behavior in a granitic aquifer we combine tracer test data with single hole ground penetrating radar gpr reflection monitoring data five successful tracer tests were performed under various experimental conditions between two boreholes 6 m apart for each experiment saline tracer was injected into a previously identified packed off transmissive fracture while repeatedly acquiring single hole gpr reflection profiles together with electrical conductivity logs in the pumping borehole by analyzing depth migrated gpr difference images together with tracer breakthrough curves and associated simplified flow and transport modeling we estimate 1 the number the connectivity and the geometry of fractures that contribute to tracer transport 2 the velocity and the mass of tracer that was carried along each flow path and 3 the effective transport parameters of the identified flow paths we find a qualitative agreement when comparing the time evolution of gpr reflectivity strengths at strategic locations in the formation with those arising from simulated transport the discrepancies are on the same order as those between observed and simulated breakthrough curves at the outflow locations the rather subtle and repeatable gpr signals provide useful and complementary information to tracer test data acquired at the outflow locations and may help us to characterize transport phenomena in fractured rock aquifers

tail shortening with developing eddies in a rough walled rock fracture understanding fluid flow and solute transport in rough walled fractures is important in many problems such as geological storage of co2 and siting of radioactive waste repositories the first microscopic observation of fluid flow and solute transport through a rough walled fracture was made to assess the evolution of eddies and their effect on non fickian tailing a noteworthy phenomenon was observed that as the eddy grew the particles were initially caught in and swirled around within eddies and then cast back into main flow channel which reduced tailing this differs from the conventional conceptual model which presumes a distinct separation between mobile and immobile zones fluid flow and solute transport modeling within the 3 d fracture confirmed tail shortening due to mass transfer by advective paths between the eddies and the main flow channel as opposed to previous 2 d numerical studies that showed increased tailing with growing eddies

controls of mass recovery rates in single well injection withdrawal tracer tests with a single porosity heterogeneous conceptualization 1 a single well injection withdrawal swiw test is evaluated as a tool to assess a single porosity conceptualization for a transport system we have shown that there are cases in which matrix diffusion cannot be proven definitively from the results of swiw tests owing to uncertainties of aquifer properties drift during the resting phase of the test can carry a plume to areas where the flux is lower during the withdrawal phase leading to decreased mass recovery rates results of sensitivity studies on multiple stochastically generated heterogeneous transmissivity fields indicate that variance in transmissivity has a strong effect on drift and consequently mass recovery rates in addition to impacting drift directly the regional gradient has the potential to influence mass recovery rates by interfering with the pumping induced fluxes toward the well during withdrawal the kolmogorov smirnov test is used to evaluate whether simulated data using a single porosity conceptualization with plume drift significantly differ from swiw tracer test data from a fractured dolomite unit at the waste isolation pilot plant given the uncertainty in the variance of transmissivity it is unlikely that a single porosity conceptualization can match the field data matrix diffusion is a likely explanation for the observed gradual mass recovery rates

brine history indicated by argon krypton chlorine bromine and iodine analyses of fluid inclusions from the mississippi valley type lead fluorite barite deposits at hansonburg new mexico argon krypton chlorine bromine and iodine were measured in a homogeneous population of high salinity hydrothermal fluid inclusions from the tertiary age mississippi valley type mvt lead fluorite barite deposits at hansonburg new mexico to establish new types of evidence for the history of both the fluid and the major dissolved salts noble gases and halogens in fluid inclusions containing 10 10 10 9 l of brine cl 3 molal were analyzed by laser microprobe noble gas mass spectrometry lmngms on neutron irradiated samples the concentrations of36ar 4 7 10 8 molal and84kr1 8 10 9 molal in the fluid inclusions are equal to those of fresh surface waters in equilibrium with air at approximately20 5 the mole ratios ofbr cl 1 2 10 4 andi cl 1 2 10 6 are among the lowest measured in any natural waters similar to those of modern brines formed by dissolution of permian nacl bearing evaporites in southeast new mexico 40ar 36ar ratios 600 are twice that of air and indicate that the fluid inclusions had excess radiogenic40ar 1 4 10 5 molal when trapped the amount of excess40ar appears to be too large to have been acquired with cl by congruent dissolution of halite bearing evaporites and possibly too small to have been acquired with pb by congruent dissolution of granitic basement rocks with proterozoic kar ages from thelmngms data combined with published pb and s isotope data we infer the following sequence of events in the history of the hansonburg mvt hydrothermal brine 1 the brine originated as relatively dilute meteoric water and it did not gain or lose atmospheric ar or kr after recharge 2 the originally dilute fluid acquired the bulk of its cl and sulfate in the subsurface after recharge by dissolving halite bearing permian marine evaporites 3 the high salinity brine then acquired most of its pb and excess radiogenic40ar from interactions with aquifer rocks other than evaporites possibly clastic sedimentary rocks or basement rocks with phanerozoic kar ages and 4 the brine deposited fluorite without having boiled or degassed

the interpretation of a tracer experiment conducted in a single fracture under conditions of natural groundwater flow the development of conceptual models to describe the hydrogeology of sparsely fractured media requires the characterization of the properties of discrete fractures at the field scale in this study a tracer experiment conducted under conditions of natural groundwater flow in a discrete fracture in an interbedded shale and limestone sequence is interpreted this experiment which was initiated by injecting a small quantity of tracer into the fracture plane involved monitoring tracer movement using 27 boreholes within a 35 40 m area test data revealed a tracer plume which spread both longitudinally and transversely in the direction of mean groundwater flow the field breakthrough curves were interpreted using a two dimensional finite element transport model that incorporated longitudinal and transverse dispersion diffusion into the rock matrix and constant fracture aperture additional simulations which incorporated the effects of aperture variability were conducted in a monte carlo format by varying the spatial correlation and variance of the aperture field the constant aperture analysis found that the mean aperture determined from the tracer experiment was approximately 20 greater than the mean aperture measured by hydraulic methods values of matrix porosity ranging between 1 and 3 a constant longitudinal dispersivity of 0 1 m and a large range in transverse dispersivity from 0 01 to 0 22 m were required to simulate the data trends of increasing aperture and matrix porosity with distance were observed suggesting that tracer transport followed increasingly tortuous pathways although the variable aperture simulations were not fitted to the field data the aperture field having an isotropic spatial correlation length of 0 5 m and variance of 10 000 m2 provided simulated plumes that appeared to be most similar to the shape and concentration of the field plume evidence from the hydraulic measurement of the aperture distribution suggests that this is a reasonable estimate of the natural aperture field

fast inversion of formation permeability from stoneley wave logs using a simplified biot rosenbaum model this paper describes a fast algorithm for estimating formation permeability from stoneley wave logs the procedure uses a simplified biot rosenbaum model formulation the input to the inversion is the stoneley wave spectral amplitudes at each receiver position the bore hole fluid properties velocity and density the borehole caliper log the formation density and porosity from log data and the compressional and shear velocities for the interval of interest the model uses the borehole caliper and elastic properties to compute the stoneley wave excitation that is predicted amplitude without permeability effects as a function of frequency and the porosity and permeability to compute the fluid flow amplitude reduction this method also uses a reference depth of known permeability and compares amplitude variations at other depths relative to the reference depth the permeability value obtained from the inversion represents the best fit over all receivers and all relevant frequencies a processing example is shown to demonstrate the ability of this technique to extract formation permeability from stoneley wave logs

strontium boron oxygen and hydrogen isotope geochemistry of brines from basal strata of the gulf coast sedimentary basin usa abstract significant spatial heterogeneities exist in the stable isotopic composition of saline formation waters from reservoirs of the smackover formation upper jurassic we focused on the southwest arkansas shelf a structurally simple portion of one of the interior basins of the northern gulf coast sedimentary basin here faulting and facies changes juxtapose dominantly oolitic carbonate strata against basal evaporites red beds and siliciclastics as well as metamorphosed basement rocks brines from this area have exceptionally high br and alkali element concentrations and have spatially heterogeneous hydrogen sulfide concentrations strontium boron oxygen and hydrogen isotope compositions exhibit coherent relations with other aspects of brine geochemistry sr isotope compositions range from those expected for carbonates and evaporites deposited from jurassic seawater 0 7071 to radiogenic ratios as high as 0 7107 generally most radiogenic sr isotope values are associated with h 2 s rich waters which also have elevated alkali element li b k rb concentrations these alkali element rich waters are associated with portions of the south arkansas fault system which reach basement boron isotope compositions are similarly heterogeneous ranging from values of 26 to 50 brines with highest b contents are most depleted in 11 b consistent with boron input from brines generated from high temperature siliciclastic diagenetic reactions normalizing b contents to br in the brines reveals a reasonable mixing trend between a dead sea type composition and texas gulf coast type shale sand reservoir waters oxygen and hydrogen isotope data exhibit regional variations which are controlled by meteoric water invasion along the northern limb of the southwest arkansas fault which has surface expression although oxygen isotope compositions are often near equilibrium with respect to reservoir carbonate it is more difficult to ascribe trends in d values to local water rock interaction the stable isotope trends can be explained either in terms of an evolved marine evaporite brine or a water evolved via water rock interaction and mixing with meteoric water in the vicinity of the southwest arkansas fault spatial heterogeneity in isotopic composition of formation waters from this relatively restricted study area suggests that assumptions of a homogeneous sr reservoir in dating regional mineralization events require careful assessment in ancient systems

reconstruction and geostatistical analysis of multiscale fracture apertures in a large block of welded tuff reconstruction of fracture apertures in a block of welded tuff has revealed two scales of autocorrelation one on the order of millimeters the other on the order of tens of centimeters the spatial and frequency distributions of apertures changed drastically as a result of minor nondestructive shear

rb sr dating of sphalerites from tennessee and the genesis of mississippi valley type ore deposits mississippi valley type mvt ore deposits commonly consist of some combination of lead zinc and iron sulphides accompanied by barite fluorite dolomite and calcite they are thought to form by fluid expulsion from sedimentary successions1 3 but their exact origin has remained controversial because of the scarcity of reliable geochronological data in a recent and widely quoted model the mvt deposits of the central and eastern united states formed as a result of large scale lateral fluid flow driven by the tectonic squeezing of sedimentary successions during the late palaeozoic alleghenian orogeny 330 250 myr 4 here we report the first direct rb sr dating of sphalerites from an mvt deposit and propose this as a useful geochronological technique for sulphide mineralization with poor age control rb sr data for sphalerites from coy mine east tennessee define an isochron age of 377 29 myr ruling out any genetic connection with the alleghenian orogeny instead mvt mineralization in the eastern united states was apparently generated from fluids expelled during thrusting associated with the older acadian orogeny 380 350 myr

strontium isotopic composition of devonian dolomites western canada sedimentary basin significance of sources of dolomitizing fluids abstract dolomites from the middle and upper devonian of five regions in the western canada sedimentary basin wwere studied middle devonian winnipegosis formation outcrop keg river formation reefs in the rainbow field and presqu ile barrier and the upper devonian miette buildup and the wabamun group of northern alberta data from the upper middle devonian swan hills formation in the rosevear field and nisku formation reefs were also included in these areas of western canada there are at least three dolomitizing events 1 early dolomites in winnipegosis reefs and the subsurface part of the presqu ile barrier have 87sr 86sr values near 0 7080 wabamun sabkha dolomites have 87sr 86sr values near 0 7083 and all fall on their respective parts of the seawater curve thus the sources of dolomitizing fluids were devonian seawaters 2 secondary matrix dolomites from the presqu ile barrier rainbow rosevear miette nisku and wabamun all have slightly higher 87sr 86sr values 0 7081 0 7094 than the correspnding devonian seawater dolomitizing fluids were probably modified from devonian seawater with small amounts of radiogenic 87sr being added during early compaction from adjacent or underlying clastics or older carbonates 3 late stage saddle dolomites from presqu ile rainbow rosevear miette nisku and wabamum are all highly radiogenic 0 7100 up to 0 7151 except for most pine point saddle dolomites indicating significant input of radiogenic 87sr with likely sources from the underlying cambrian and precambrian clastics and or the precambrian basement at pine point some presqu ile saddle dolomites have sr isotopic values similar to matrix dolomites suggesting a different fluid source possibly from subsurface brines that may have evolved from pressure solution of devonian strata alternatively formation waters derived from the deeper part of the basin may have been progressively diluted with low 87sr 86sr shallow formation waters as they moved updip along the presu ile barrier the 87sr 86sr values support and refine earlier conclusions based on textual evidence c and o isotopes geochemistry and fluid inclusions they considerably limit the sources of the dolomitizing fluids in open diagenetic systems however the timing of the widespread secondary matrix dolomites can only be broadly constrained to sometime during the late paleozoic the similarity of the o and sr isotopes in the replacement dolomites from widely separated locations geographically and stratigraphically tentatively suggests that these dolomites may have precipitated from similar formation waters on a basin wide scale the late stage saddle dolomites and probably the coarsely crystalline dolomites could only have formed near maximum burial conditions in the late cretaceous to early tertiary from warm hydrothermal brines that moved updip from more deeply buried portions of the basin later coarse crystalline calcites precipitated from highly saline brines and are generally more radiogenic than saddle dolomites they apparently formed from more radiogenic formation waters than have curretly been reported from the basin

strontium isotope trends during diagenesis in ore bearing carbonate basins strontium isotope studies 120 analyses were carried out on ore and gangue minerals from five ore districts in different carbonate basins most of the samples were separated from consecutive diagenetic generations even for diverse stratigraphic positions and mineralogies very consistent trends are recognized in all cases87sr 86sr ratios increase with advancing diagenetic stage however each district shows a different behaviour in the magnitude of increase over the first diagenetic generation which ideally is close to contemporaneous seawater the increase of the strontium ratios in the subsequent diagenetic generations is explained by equilibration during crystallization with fluids evolving towards more radiogenic compositions this is interpreted as a consequence of the reaction of the fluids with rb bearing phases mainly detrital clay minerals variation ranges of87sr 86sr ratios can constitute a sensitive tool for determining the stage of basin evolution in a similar way as vitrinite reflectance or illite crystallinity this method has the disadvantage that the increase of radiogenic strontium depends not only on the evolution stage i e temperature pressure and time but also on the amount of rb bearing minerals present in the basin on the other hand this method has the important advantage that within a given basin this last parameter can be modelled each evolution stage is recorded in the cements or crystallization generations by its strontium isotope signatures which tend towards increased radiogenic values with advancing diagenesis

ree and isotope sr s and pb geochemistry to constrain the genesis and timing of the f ba pb zn ores of the zaghouan district ne tunisia abstract the f ba pb zn ore deposits of the zaghouan district located in ne tunisia occur as open space fillings or stratabound orebodies hosted in jurassic cretaceous and tertiary layers the chondrite normalized rare earth element ree patterns may be split into three groups i normal marine patterns characterizing the wallrock carbonates ii light ree lree enriched slide shaped patterns with respect to heavy ree hree with small negative ce and eu anomalies characteristic of the early ore stages iii bell shaped ree patterns displaying lree depletion as well as weak negative ce and eu anomalies characterizing residual fluids of subsequent stages the 87 sr 86 sr ratios 0 707654 0 708127 8 show that the sr of the epigenetic carbonates dolomite calcite and ore minerals fluorite celestite are more radiogenic than those of the country triassic jurassic cretaceous lower miocene sedimentary rocks the uniformity of this ratio throughout the district provides evidence for the isotopic homogeneity and consequently the identity of the source of the mineralizing fluids this signature strongly suggests that the radiogenic sr is carried by upper paleozoic basinal fluids the 34 s values of barite associated to mineralizations are close to those of the triassic sea water 17 the 34 s values of sulfide minerals range from 13 6 to 11 4 suggesting two sulfur reduced end members bsr tsr with a dominant bsr process taking account of the homogeneity in the pb isotope composition of galenas 18 833 18 954 0 001 15 679 15 700 0 001 and 38 690 38 880 0 004 for the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios respectively a single upper crustal source for base metals is accepted the late paleozoic basement seems to be the more plausible source for f pb zn concentrated in the deposits the genesis of the zaghouan district ore deposits is considered as the result of the zaghouan fault reactivation during the late miocene period

a field example of measuring hydrodynamic dispersion in a single fracture a field example of measuring the dispersive properties of a single fracture in fractured plutonic rock is presented the experimental technique involves injecting a slug of conservative tracer into a steady groundwater flow field established between a pumping and recharging borehole and monitoring the tracer breakthrough by sampling the withdrawal water directly the breakthrough curves from two experiments were analyzed with a model which describes the flow field geometry either analytically or numerically and solves for hydrodynamic dispersion analytically a longitudinal dispersivity of 1 40 m was estimated by fitting the model to each set of field data the magnitude of the dispersion was determined to be independent of dispersive effects created by flow through the borehole instrumentation and thought to be purely hydrodynamic in nature

nd sr pb isotopic constraints on metal and fluid sources in w sb au mineralization at woxi and liaojiaping western hunan china this paper presents nd sr pb isotope data on scheelite inclusion fluids and residues of gangue quartz and sulfides from the w sb au ore deposits at woxi and liaojiaping ljp in the xuefeng uplift belt xub western hunan china sm and nd concentrations in scheelite from woxi are much lower than in scheelite from ljp and can be distinguished by their high 147sm 144nd ratios of 1 25 from the much lower ratios around 0 26 in scheelites from the ljp end values compared to values at 200 ma which is the average timing of granitoid emplacement during the indosinian yanshanian periods in the xub are around 10 for the ljp and compare well with the range of 5 to 11 defined by the granitoids whereas they are around 27 for scheelite from woxi this might indicate that rees in the mineralizing fluids at ljp originated from granitoids that are concentrated along the southern border of the xub whereas in the case of woxi the original fluids might have been masked by rees released during intense high temperature wall rock alteration of unexposed precambrian basement rocks at depth sr isotopes of scheelite from these two deposits show similar relations to host nearby rocks in that 87sr 86sr t 200 ma ratios of 0 721 for ljp scheelite agree with values ranging between 0 718 0 726 for granitoids whereas these ratios are much higher i e 0 745 for scheelite from woxi and correspond to the 87sr 86sr t 200 ma ratio range of 0 743 0 749 for precambrian host slates crushing experiments to release inclusion fluids from gangue quartz and sulfides deposited during later stages of ore deposition in both deposits failed to provide accurate and geologically meaningful two point fluid residue tie lines in rb sr isochron diagrams however sr released from fluid inclusions generally reveals lower initial 87sr 86sr ratios than the respective residues and shows affinities to 87sr 86sr t 200 ma values of indosinian yanshanian granitoids both at woxi and ljp pb stepwise leaching of scheelite and sulfides did not result in sufficient spreads in pb isotope diagrams and therefore no information regarding exact mineralization ages in the two deposits could be deduced overall ore pb isotopes reveal upper crustal signatures and are compatible with pb isotope signatures of the predominant precambrian slates in the woxi area steep trajectories through late stage quartz sulfide mineralization in pb isotope diagrams may hint at mixing scenarios involving pb from the host rocks and a component with lower 207pb 204pb and 208pb 204pb ratios relative to 206pb 204pb ratios which cannot be linked to any known reservoir in the xub mining district sr isotopes of four out of seven residual sulfide samples from woxi plot along a paleomixing line at an age of 199 8 ma supporting a mixing scenario for the fluids indicated by the pb isotopes and pointing to a possible genetic relationship with the emplacement of indosinian yanshanian granitoids the budgets of rees rb sr and pb in the original fluids were severely affected by contamination of these elements apparently during intense wall rock alteration but after sealing of the major pathways the mineralizing fluids tend to have better preserved their original signatures these attest a genetic relationship between the metallogeny in the xub w sb au province and the emplacement of indosinian yanshanian granitoids during mesozoic intracontinental tectonic uplift and thrusting

the mississippi valley type fluorite ore at jebel stah zaghouan district north eastern tunisia contribution of ree and sr isotope geochemistries to the genetic model abstract the fluorite district of zaghouan north eastern tunisia is characterized by f ba pb zn ore deposits mineralization occurs within stratabound to stratiform bodies either within jurassic back reef limestone uplifted blocks or along unconformity surfaces that separate them from the overlying sequence fluorite mineralization also occurs within fractures crosscutting the uplifted limestone blocks and their overburden despite the similarity of the liassic series throughout the major part of the district stratabound fluorite deposits formed subsequent to a strong epigenetic dolomitization souissi et al 1998 and occurring along the lower middle liassic unconformity are known only at jebel stah and at the adjacent jebel kohol four petrographic types of fluorite are recognized the finely laminated karst deposits fl1a the macrogranular fluorite fl1b resulting from the recrystallization of fl1a and the megacrystalline fluorite fl2 associated to calcite in lodes and fluorite in geodes fl3 this study gives new arguments in terms of the genetic model of the fluorite ore of jebel stah and by using trace metal elements mte rare earth elements ree and sr isotope geochemistry the mte geochemistry shows that the epigenetic dolomites and the fluorite fl1a bear higher concentrations in mn and zn with respect to the fluorites fl1b fl2 and fl3 while the latter are depleted in all mte but enriched in co the similarity of their ree patterns indicates that the latter are coeval and that fl1a fluorite may be considered as the early ore generation the same argument confirms that this geochemical imprint has been inherited from a hydrothermal fluid that had remained in equilibrium with shales at depth fluorite deposition appears related to an oxidized fluid derived from a sedimentary basin fluid circulation may have been triggered in response to hydraulic fracturing within a high geothermal gradient setting especially along the major structural trends fl1b fl2 and fl3 fluorites have been generated from the residual fraction of the ore fluid at later stages of mineralization and in a closed system both mineralization and the epigenetic dolomites are characterized by sr isotope ratios that are higher than the barren lower middle liassic rocks indicating that the sr cannot be derived from the wallrocks however these ratios are higher than the triassic seawater yet consistent with those of the paleozoic period thus the fluorite ore of jebel stah is believed to be remobilized from primary ore deposits which are suspected to be hosted in the late series within this period

major element compositions of fluid inclusions from hydrothermal vein type deposits record eroded sedimentary units in the schwarzwald district sw germany mixing of sedimentary formation fluids with basement derived brines is an important mechanism for the formation of hydrothermal veins we focus on the sources of the sediment derived fluid component in ore forming processes and present a comprehensive fluid inclusion study on 84 jurassic hydrothermal veins from the schwarzwald mining district sw germany our data derive from about 2300 fluid inclusions and reveal differences in the average fluid composition between the northern central and southern schwarzwald fluids from the northern and southern schwarzwald are characterised by high salinities 18 26 wt nacl cacl2 low ca ca na mole ratios 0 1 0 4 and variable cl br mass ratios 30 1140 in contrast fluids from the central schwarzwald show even higher salinities 23 27 wt nacl cacl2 higher ca ca na mole ratios 0 2 0 9 and less variable cl br mass ratios 40 130 these fluid compositions correlate with the nature and thickness of the now eroded sedimentary cover rocks compared to the northern and the southern schwarzwald where halite precipitation occurred during the middle triassic the sedimentary basin in the central schwarzwald was relatively shallow at this time and no halite was precipitated accordingly cl br ratios of fluids from the central schwarzwald provide no evidence for the reaction of a sedimentary brine with halite whereas those from the northern and southern schwarzwald do instead elevated ca ca na high so4 contents and relatively low cl br imply the presence of a gypsum dissolution brine during vein formation in the central schwarzwald which agrees with the reconstructed regional triassic geology hence the information archived in fluid inclusions from hydrothermal veins in the crystalline basement has the potential for reconstructing sedimentary rocks in the former overburden

isotopic fronts in hydrothermally mineralized carbonate rocks advective dispersive fluid flow through permeable and porous rock causes systematic alteration of the infiltrated rock o and sr isotopes can be used as tracers to monitor exchange processes between mineralizing hydrothermal solutions and carbonate host rocks fluid infiltration into rock of initially uniform isotopic composition leads to characteristic changes in 18o and 87sr in the rock that depend on infiltration distance fluid velocity diffusivity and reaction kinetics for fast fluid solid equilibrium during advective flow the shape of such alteration profiles can be described by the dimensionless peclet number p e which expresses the fluid flux infiltration distance and diffusivity in the case of mineralization from low to moderate temperature solutions isotope exchange is not instantaneous but kinetically controlled and a similar parameter the damkohler number n d expressing fluid flux isotope exchange rate and infiltration distance becomes more useful n d and p e values have been estimated for various examples of carbonatehosted hydrothermal mineralization in the eastern alps austria and the benue trough nigeria by modelling o and sr isotope data from ore or gangue minerals and host rock the values obtained enable a rough differentiation between pervasive and channelled fluid flow as the prevailing transport mechanism to be made results indicate that both highly channelled fluid flow through fractures without significant interaction with the wall rock and pervasive fluid flow with infiltration distances into the percolated host rock of the order of 100 m occur near mineral deposits in the latter case the extent of o and sr isotopic alteration of the host rock can be used as an effective exploration tool

a large scale flow and tracer experiment in granite 2 results and interpretation water and tracer flow has been monitored in a specially excavated drift in the stripa mine several new experimental techniques and equipment were developed and used the whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift the flow rate and tracer monitoring was kept up for more than 2 years the tracer breakthrough curves and flow rate distributions were used to study the flow paths velocities hydraulic conductivities dispersivities and channeling effects in the rock in a companion paper the experimental design and performed experiments are described the present paper describes the interpretation of flow and tracer movement in the rock outside the drift the tracer movement was measured by the more than 160 individual tracer curves the tracer experiments have permitted the flow porosity and dispersion to be studied the possible effects of channeling and the diffusion of tracers into stagnant waters in the rock matrix and in stagnant waters in the fractures have also been addressed

estimating slowness dispersion from arrays of sonic logging waveforms acoustic wave propagation in a fluid filled borehole is affected by the type of rock which surrounds the hole more specifically the slowness dispersion of the various body wave and borehole modes depends to some extent on the properties of the rock we have developed a technique for estimating the dispersion relations from data acquired by full waveform digital sonic array well logging tools the technique is an extension of earlier work and is based on a variation of the well known prony method of exponential modeling to estimate the spatial wavenumbers at each temporal frequency this variation known as the forward backward method of linear prediction models the spatial propagation by purely real valued wavenumbers the prony exponential model is derived from the physics of borehole acoustics under the assumption that the formation does not vary in the axial or azimuthal dimensions across the aperture of the receiver array but can vary arbitrarily in the radial dimension the exponential model fits

assessing the validity of the channel model of fracture aperture under field conditions in recent investigations of fluid and solute movement in discrete fractures spatial heterogeneity of the fracture aperture has been conceptualized as a series of noninterconnecting constant aperture flow paths or channels two methods of estimating the distribution of the aperture sizes are presented using information from a single hole pumping test and a radially converging tracer test the first method uses the transmissivity of the fracture and mean arrival time of the tracer while the second method uses the mean and variance of the solute arrival time if the fracture can be conceptualized as a series of nonintersecting flow paths of constant aperture the two methods should yield identical estimates for the parameters of the distribution the validity of the channel model can be assessed by comparing the parameters of the distribution that are estimated by the two methods this technique was demonstrated using hydraulic and tracer tests conducted in a discrete areally extensive horizontal fracture in the silurian dolomite in the northeastern illinois a lognormal and a truncated gamma distribution were used to describe the distribution of constant aperture flow paths the lognormal distribution could not reproduce the abrupt rising limb and maximum rate of mass arrival that characterized the tracer tests the gamma distribution more accurately predicted the shape of the breakthrough curves however the two methods of estimating the parameters of the distribution provided significantly different estimates of the variances of the aperture sizes the mean aperture as estimated by the two methods was similar the difference in the variance of the aperture as estimated by the two methods indicates that alternative conceptual models of aperture heterogeneity are required to more accurately describe both fluid and solute movement in this field situation

new constraints on carbonate diagenesis from integrated sr and s isotopic and rare earth element data jurassic smackover formation u s gulf coast a reply isotopic sr s o c and trace element including rare earth element ree compositions of calcite cements metal sulfides and sulfate minerals from oolitic carbonate grainstones of the smackover formation jurassic southwest arkansas shelf constrain the mechanism of sulfate reduction and establish temporal relations between sulfur and carbonate diagenesis strontium isotopic values of calcite cements range from near jurassic age sea water values 0 7068 up to values of 0 7096 this evidence coupled with variation in o and c isotopic compositions and in cement zoning under cathodoluminescence suggests that calcite cement precipitated over the course of burial diagenesis strontium isotopic compositions of pyrite marcasite and native s range up to maximum values observed for calcite cements but galena and sphalerite are less radiogenic the sr contents of sulfides and native s are 30ppm but the rb content is sufficiently low that in situ growth of87sr would not dramatically alter the initial sr isotope ratio diagenetic sulfate minerals also exhibit a range of sr isotopic compositions anhydrites range from 0 7071 to 0 7081 while celestites are more radiogenic 0 7096 the ree patterns of early and late calcite cements and framework grains differ using sm yb ratios as an indicator of heavy vs light ree enrichment early calcites have sm yb ratios 1 whereas late calcite cements have ratios of 1 8 3 2 importantly both cement signatures differ from framework grain ratios 1 3 1 7 indicating lack of rock buffering in fluids from which the cements precipitated furthermore the sympathetic increase in sm yb and sr isotopic ratios from early to late calcites is consistent with input of light ree from siliciclastic sources sulfur isotopic compositions of metal sulfide minerals range from 32 to 8 cdt native s and anhydrite values 18 are near jurassic age sulfate values while celestites are heavier 28 although thermochemical sulfate reduction has been proposed to explain h2s in deeply buried carbonate units associated with evaporite s lack of s isotopic homogenization between sulfate and sulfide minerals lack of s isotopic equilibration of oil with reservoir so4 and the limited distribution of h2s rich brines in southwest arkansas demand a more complex origin

tracer transport in fractured crystalline rock evidence of nondiffusive breakthrough tailing extended tailing of tracer breakthrough is often observed in pulse injection tracer tests conducted in fractured geologic media this behavior has been attributed to diffusive exchange of tracer between mobile fluids traveling through channels in fractures and relatively stagnant fluid between fluid channels along fracture walls or within the bulk matrix we present a field example where tracer breakthrough tailing apparently results from nondiffusive transport tracer tests were conducted in a fractured crystalline rock using both a convergent and weak dipole injection and pumping scheme deuterated water bromide and pentafluorobenzoic acid were selected as tracers for their wide range in molecular diffusivity the late time behavior of the normalized breakthrough curves were consistent for all tracers even when the pumping rate was changed the lack of separation between tracers of varying diffusivity indicates that strong breakthrough tailing in fractured geologic media may be caused by advective transport processes this finding has implications for the interpretation of tracer tests designed to measure matrix diffusion in situ and the prediction of contaminant transport in fractured rock

the strontium isotopic composition of ordovician and silurian brachiopods and conodonts relationships to geological events and implications for coeval seawater utilized for strontium isotope measurements the results document a gradual decrease in 87 sr 86 sr from 0 7091 to 0 7087 from tremadoc to llandeilo a sharp decline to 0 7078 during the late llandeilo early caradoc little change during caradoc and the ashgil and a steady rise to 0 7087 through the silurian these long term 10 7 yr variations with magnitudes in the range of 10 23 are interpreted to be controlled primarily by continental collisional tectonics and its associated erosion and weathering the gradual decrease in 87 sr 86 sr ratio during the early ordovician may record the reduction in uplift and weathering rates due to waning of the pan african orogenies the rapid decline near the llandeilo caradoc boundary suggests a strong hydrothermal flux likely due to increased sea floor spreading and a possible superplume event the latter may have caused the prominent transgressive phase the largest in the phanerozoic which would have muted continental flux input although the caradoc was the main interval for the taconic orogeny its impact on the sr continental flux may have been delayed until the early llandovery this effect complemented by reworking of glacial deposits near the ordovician silurian boundary and enhanced by phases of the silurian salinic orogeny may have combined to give the progressive increase in the strontium isotope ratio through the silurian the scale and directionality of these changes makes the strontium isotope curve valuable for dating and correlation purposes copyright 1998 elsevier science ltd

chalcopyrite bornite and chalcopyrite bornite barite in the acton vale limestone southeastern quebec mineralized shelf margin slivers in a taconian nappe the acton vale limestone units of probable early ordovician age in the external nappe zone of the appalachian foldbelt in southeastern quebec host numerous occurrences of vein and breccia type cop

radionuclide transport in fast channels in crystalline rock recent field investigations in crystalline rock give strong indications that water flows in largely isolated channels in fissured rock the present paper sets out to investigate radionuclide transport in such channels including diffusion into the rock matrix it is shown that the uptake from a cylindrical hole in a matrix is much more effective per unit contact area than a flat surface semi infinite solid comparison of diffusion from cylindrical and slit formed channels shows that the differences in interfacial flux are minor a slit formed channel may therefore be approximated by a cylindrical one diffusional transport in the matrix is then treated as one dimensional instead of two dimensional which gives a considerable numerical simplification a simple estimate of the penetration depth into the cylindrical region i e the location of the diffusional front is proposed by using the integrated finite difference method a number of radionuclide transport calculations are performed for the case of flow and dispersion in a cylindrical channel coupled to diffusion and sorption in the matrix

constraints from fluid inclusion compositions on the origin of mississippi valley type mineralization in the illinois kentucky district fluid inclusions hosted by mississippi valley type mvt ores in the illinois kentucky district were analyzed using microthermometry laser ablation inductively coupled plasma mass spectrometry la icp ms and raman spectroscopy to characterize the composition and temperature of mineralizing fluids in order to seek insights into the process of ore formation results from the present study support the interpretation of previous microthermometry studies that relate mineralization to mixing of two higher temperature brines and a cooler dilute meteoric fluid fluid inclusions in the illinois kentucky district have overall higher atomic ratios of ba na ca mg k na sr na and lower atomic ratios of mg na compared to inclusions in the ozark mvt districts and are thus compositionally distinct these differences may indicate that the illinois kentucky and ozark mvt ore fluids were derived largely from different source basins or may reflect input from igneous rocks in the illinois kentucky district low ca mg ratios of illinois kentucky fluid inclusions indicate that mineralizing fluids were dolomitizing and therefore could not have traveled far through the limestone ore host formations but instead traveled through deeper nonlimestone units before rising along faults and fractures in the district some fluid inclusions in illinois kentucky mvt mineralization yielded strong la icp ms responses for ore metals a single sphalerite hosted fluid inclusion out of 18 analyzed contained detectable pb corresponding to a concentration of 420 ppm whereas numerous fluorite hosted fluid inclusions contained detectable pb zn and cu corresponding to maximum concentrations on the order of 1 000s of ppm the high and similar concentrations of cu pb and zn in some fluorite hosted fluid inclusions in the illinois kentucky district are problematic because cu sulfide mineralization should be much more abundant than pb and zn sulfide mineralization owing to the lower solubility of cu relative to pb and zn in the presence of reduced sulfur which is not observed in the field this raises the possibility that ore metals may exist as solid phases in suspension or adhering to fluid inclusion walls in some inclusions rather than as dissolved species in aqueous solution raman microprobe analyses of fluid inclusions hosted by minerals occurring throughout the paragenetic sequence detected methane concentrations ranging from about 40 to 1 200 ppm with most on the order of 100s ppm even for the lowest methane concentration determined redox conditions would have been reducing at a log of 55 4 at a temperature of 100 c at such reducing conditions sulfide would predominate over sulfate this is supported by high concentrations of ba in the fluid inclusions the overall reducing conditions throughout the paragenetic sequence and the possible presence of both metal poor and rich fluid inclusions would suggest that mixing between a metal rich sulfide poor fluid and a metal poor sulfide rich fluid were an important mechanism for sulfide mineral precipitation minimum depths of mineralization estimated from methane concentrations in fluid inclusions range to about 1 500 m and possibly 2 500 m which would not have been reached until late pennsylvanian to permian time i e during the alleghanian orogeny

oil shales evaporites and ore deposits abstract the relationships between oil shales evaporites and sedimentary ore deposits can be classified in terms of stratigraphic and geochemical coherence oil shale and black shale deposition commonly follows continental red beds and is in turn followed by evaporite deposition this transgressive regressive sequence represents an orderly succession of depositional environments in space and time and results in stratigraphic coherence the amount of organic carbon of a sediment depends on productivity and preservation both of which are enhanced by saline environments work on great salt lake utah allows us to estimate that only 5 of toc originally deposited is preserved inorganic carbonate production is similar to toc production but preservation is much higher oil shales and black shales commonly are enriched in heavy metals through scavenging by biogenic particles and complexation by organic matter ore deposits are formed from such rocks through secondary enrichment processes establishing a geochemical coherence between oil shales and ore deposits the permian kupferschiefer of n europe is used as an example to define a kupferschiefer type kst deposit here oxygenated brines in contact with red beds become acidified through mineral precipitation and acquire metals by dissolving oxide coatings oxidation of the black shale leads to further acid production and metal acquisition and eventually to sulfide deposition along a reducing front in order to form ore bodies the stratigraphic coherence of the red bed black shale evaporite succession must be joined by the geochemical coherence of the ore body evaporite black shale association the cretaceous cu zn deposits of angola the zambian copperbelt as well as the creta oklahoma deposits are other kst examples in the zambian copperbelt evaporites are indicated by the carbonate lenticles thought to be pseudomorphs after gypsum anhydrite nodules mvt deposits are also deposited by acid brines but at more elevated temperatures and with carbonates as principal host rocks the pine point deposits are cited for their close association with evaporites alkaline metal rich brines are postulated for the hyc deposit of mcarthur river australia such brines are known from the green river formation and deposits formed from such brines constitute the grt class they can be recognized by the presence of magadi type cherts and zeolite analcime k spar tuffs the cu co ore bodies of outokumpu finland might also belong to this type a new classification of sedimentary ore deposits is proposed based on their geochemical environment kst and mvt are formed from acid ore fluids while grt and ct creede type are derived from basic ore fluids ph of the fluids is best evaluated not from the ores themselves but from their effect on the host rocks

chemical evolution of ore forming brines basement leaching metal provenance and the redox link between barren and ore bearing hydrothermal veins a case study from the schwarzwald mining district in sw germany abstract six mineralogically exemplary barren and mineralized hydrothermal veins with pb and zn ores of jurassic cretaceous and cenozoic age in the schwarzwald mining district sw germany were chosen to shed light on the origin of their mineralogical diversity the selection of the veins was guided by the fact that they represent the largest number of veins in the region are very well known mineralogically and geochemically and they provide nice examples of barren and mineralized veins of similar age fluid inclusion data from the individual veins overlap implying their diverse mineralogy is not caused by different fluid compositions participating during fluid mixing la icpms data of single fluid inclusions indicate no systematic variations in major elements but significant changes in fluid mixing ratios which caused variable trace element concentrations of different fluid inclusion assemblages in one sample we suggest that different ore gangue assemblages can be produced by mixing of identical fluid endmembers but variable mixing ratios la icpms analyses of single fluid inclusions in barren and mineralized veins record similar base metal and sulfur concentrations hence sulfide mineralization in the veins appears not to be controlled by metal solubility thermodynamic modeling based on the fluid data indicates that the presence of a reducing phase during fluid mixing is required for sulfide mineralization to precipitate la icpms trace element analyses of feldspars biotites chlorites and clay minerals in granites and paragneisses which are the source of the metal content in the ore forming fluids demonstrate that the dominant provenance for pb zn as sb ba tl mo fe and mn are probably paragneisses while co cu and ni are probably sourced from s type granite a rough quantification indicates that

multipole acoustic waveforms in fluid filled boreholes in biaxially stressed formations a finite difference method a finite difference method is developed to simulate elastic wave propagation in a borehole surrounded by a biaxially stressed solid formation the linear elastic formation is altered by such tectonic stresses that cause significant changes in the characteristics of wave propagation in a borehole the 2 5 dimensional problem addressed in this work concerns the three dimensional wave propagation in a medium inhomogeneous in two spatial coordinates transverse to the borehole axis a second order finite difference method is developed to solve the partial differential equations arising from a published acoustoelastic model for borehole acoustic wave propagation in prestressed formations the algorithm is validated and applied to model both the borehole flexural and axisymmetric stoneley waves the computed waveforms are processed by a variation of prony s algorithm that yields dispersion curves for flexural waves polarized both parallel and perpendicular to the stress direction the flexural dispersion crossover in a uniaxially stressed formation is quantitatively confirmed the stoneley dispersion in the presence of such stresses exhibits approximately a uniform shift toward lower slownesses over the entire bandwidth of interest this implies that azimuthal averaging of formation stiffnesses approximately yields the same effective stoneley stiffness at different radial positions

the analysis of tracer experiments conducted in divergent radial flow fields analytical models are developed to interpret tracer experiments conducted in divergent flow fields the models account for the mixing of tracer in both the source and observation wells and for the diffusion of tracer into adjacent aquitards a solution for the particular case of an observation well of infinitesimally small volume is also presented solutions are derived for both resident and flux concentrations and for macroscopically discontinuous conditions at both the inlet and outlet boundaries the solutions for resident and flux concentration are identical when the mixing volume in the observation well is of finite volume two tracer experiments were conducted in a horizontally fractured shale to demonstrate the application of the new analytical models experiments were conducted with observation wells of finite volume and using a new sampling packer which eliminates the volume of the observation well the results show that for experiments conducted in fractured media the analytical model developed in this paper provides an improved fit to the shape of the concentration curve relative to models which do not account for mixing in the source and observation wells alternatively by modifying the field method such that the volume of the observation well is eliminated using the sampling packer either conventional models or the new model for concentration in the formation will provide equally suitable fits to the concentration data

borehole flexural modes in transversely isotropic formations low frequency asymptotic velocity dipoleacousticloggingiswidelyusedforinsitumeasurement of formation shear velocity this technique is based on the theoretical result in isotropic formations that the velocity ofthedispersiveflexuralmodeapproachestheshearvelocity at the low frequency limit transversely isotropic ti formations frequently are encountered in petroleum engineering so it is necessary to determine if shear velocity along the borehole can be determined from the low frequency flexural wave in ti cases the flexural wave in a borehole parallel to thesymmetryaxisofatiformationisinvestigated theborehole acoustic field is formulated in the frequency wavenumber domain as the sum of a direct field from the source and a reflected field from the borehole wall poles and branch points of the reflection coefficient are analyzed and component waves contributed by those singularities are calculated thedispersionfeatureoftheflexuralmodeinsometiformationsdiffersfromisotropiccases thelow frequencylimitof flexural mode velocity trends to a value lower than the shear velocity when parameters of the formation satisfy c44 2c33 where and arethomsenparametersandc33 and c44 are the elastic moduli that asymptotic value corresponds to a newly found branch point of the reflection function numerical results show that the low frequency flexural wave travels slower than the shear wave in the synthetic full waveforms in mesaverde clayshale 5501 extracting the shearvelocityfromtheflexuralarrivalleadstoinaccuracyon theorderof10 inthisformation

permeability and borehole stoneley waves comparison between experiment and theory we performed laboratory experiments to evaluate theoretical models of borehole stoneley wave propagation in permeable materials a berea sandstone and synthetic samples made of cemented glass beads were saturated with silicone oils we measured both velocity and attenuation over a frequency band from 10 khz to 90 khz our theoretical modeling incorporated biot theory and deresiewicz skalak boundary conditions into a cylindrical geometry and included frequency dependent permeability by varying the viscosity of the saturating pore fluid we were able to study both low frequency and high frequency regions of biot theory as well as the intermediate transition zone in both low frequency and high frequency regions of the theory we obtained excellent agreement between experimental observations and theoretical predictions velocity and attenuation 1 q are frequency dependent especially at low frequencies also at low frequencies velocity decreases and attenuation increases with increasing fluid mobility permeability viscosity more complicated behavior is observed at high frequencies these results support recent observations from the oil field suggesting that stoneley wave velocity and attenuation may be indicative of formation permeability

fast and slow flexural waves in a deviated borehole in homogeneous and layered anisotropic formations summary dipole acoustic fields in an arbitrarily deviated well penetrating a homogeneous as well as a stratified transversely isotropic formation are simulated using a 3 d finite difference timedomain algorithm in cylindrical coordinates the modelling results show that a dipole source can excite a fast and a slow flexural mode due to the shear wave anisotropy when the borehole is inclined with respect to the symmetry axis of transverse isotropy both flexural slownesses change with the wellbore deviation angle the splitting of flexural modes is prominent in full wave arrays when the shear anisotropy is strong enough it is revealed that the dipole orientation influences the relative amplitudes of the fast and slow flexural waves but it has no effect on their slownesses or phases in a vertical well parallel to the symmetry axis the two flexural waves degenerate and propagate at the same speed the degenerated flexural wave travels approximately at the shear speed along the borehole wall except in a few formations our study shows for example that it is about 10 per cent slower than the shear wave in mesaverde clayshale 5501 even in that kind of formations however extraction of the fastand slow shear velocities from the flexural modes is still possible if the borehole deviation is large enough to examine the effect of layering we modelled the full waves in a formation with a sandwich when the well is perpendicular to the layer interfaces reflection is obvious and can be recognized it becomes weaker or even invisible as the deviation angle increases so it is difficult to detect a thin layer embedded in a formation directly from reflected waves the sandwich can instead be recognized from the irregularity in the spectra of the full waveforms displayed versus depth

modeling of borehole stoneley waves in the presence of skin effects an important aspect of oil production from a geological formation is the process of flow into a well penetrating the formation recent laboratory experiments indicate that well inflow can be significantly reduced by a skin effect caused by the presence of a thin layer of low permeability around the wellbore this impairment layer is drilling induced and differs from the mudcake that is usually encountered when logging a well whereas a mudcake may have built up on the borehole wall during drilling the drawdown pressure often removes it when oil is produced from the well in contrast with such a temporary mudcake the impairment layer is believed to form a permanent flow impedance throughout the lifetime of a well unless extensive cleaning measures are taken a simple poro elastic model is constructed to investigate the propagation of stoneley waves in a borehole with a thin impairment layer if the impairment layer affects stoneley wave propagation it may be possible to acoustically detect this layer with sonic logging tools using realistic values for the impairment flow impedance model calculations for a typical sandstone reservoir of 20 porosity indicate that the impairment layer changes the dispersion characteristics of borehole stoneley waves the magnitude of these changes increases with increasing mobility of the reservoir pore fluid

strontium isotope systematics of hydrothermal vein minerals in deposits of west germany vein minerals in west germany hosted by crystalline basement rocks and paleozoic and mesozoic sedimentary rocks are characterized by87sr 86sr ratios which indicate continental derivation of sr incorporated into the minerals neither mantle derived sr nor prominent contribution of this element from sea water except for the strontianites of munsterland can be substantiated by the data presented

theoretical study on inversing the anisotropic permeability of vti two phase media by flexural waves in a fluid filled borehole abstractwe developed a theoretical method of estimating the vertical and horizontal permeability of a transversely isotropic two phase formation with a vertical symmetry principle axis vti by using the attenuation characteristic of the dipole flexural waves in a fluid filled borehole the attenuation value of flexural waves was extracted from synthetic data the inversion was operated by the least squares method two main conclusions were obtained based on the analysis of the results of inversion implemented on multiple sets of synthetic waveform data first the simultaneous estimation of vertical and horizontal permeability was feasible for the slow vti formation which means its shear wave velocity is slower than the acoustic velocity of fluid in a borehole that is different from the previous understanding in some studies second the fast formation corresponded to the opposite case from the slow formation the precision of the estimated horizontal permeability relates to the accuracy of the vertical

simple mathematical model of a rough fracture a simple mathematical model of rough walled fractures in rock is described which requires the specification of only three main parameters the fractal dimension the rms roughness at a reference length scale and a length scale describing the degree of mismatch between the two fracture surfaces fractured samples collected from natural joints and laboratory specimens have been profiled to determine the range of these three parameters in nature it is shown how this surface roughness model can be implemented on a computer allowing future detailed study of the mechanical and transport properties of single fractures and the scale dependence of these properties

large scale natural gradient tracer test in sand and gravel cape cod massachusetts 1 experimental design and observed tracer movement a large scale natural gradient tracer experiment was conducted on cape cod massachusetts to examine the transport and dispersion of solutes in a sand and gravel aquifer the nonreactive tracer bromide and the reactive tracers lithium and molybdate were injected as a pulse in july 1985 and monitored in three dimensions as they moved as far as 280 m down gradient through an array of multilevel samplers the bromide cloud moved horizontally at a rate of 0 42 m per day it also moved downward about 4 m because of density induced sinking early in the test and accretion of areal recharge from precipitation after 200 m of transport the bromide cloud had spread more than 80 m in the direction of flow but was only 14 m wide and 4 6 m thick the lithium and molybdate clouds followed the same path as the bromide cloud but their rates of movement were retarded about 50 relative to bromide movement because of sorption onto the sediments

a large scale flow and tracer experiment in granite 1 experimental design and flow distribution this paper describes the stripa three dimensional experiment where water and tracer flow has been monitored in a specially excavated drift in the stripa mine several new experimental techniques and equipment were developed and used the experiment was performed in a specially excavated drift 100 m long at the 360 m level in granite the whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift the flow rate and tracer monitoring was kept up for more than 2 years the tracer breakthrough curves and flow rate distributions were used to study the flow paths velocities hydraulic conductivities dispersivities and channeling effects in the rock this paper describes the experimental techniques the fracture mapping the tracer and flow rate measurements and the results of the flow rate measurements the detailed observations made possible by the plastic sheeting technique have given some qualitative as well as quantitative information on flow rate distribution in fractured rock which previously has not been available these observations may be of importance for assessing the transport of dissolved species such as radionuclides through fractured rock

strontium isotopic geochemistry of fluorite mineralization coahuila mexico abstract the widespread fluorite deposits of coahuila mexico include limestone replacement deposits formed at the contact with tertiary rhyolites and microsyenites as well as mantos and veins that are not clearly associated with any known igneous body in recent studies it was concluded that most of the calcium in these deposits came from the limestone whereas the fluorine was derived largely from the tertiary igneous rocks we have tested this model using strontium isotopic data and simultaneously placed constraints on the mechanisms of fluorite deposition our results indicate that the 87sr 86sr ratio of the host limestones ranges from 0 7075 to 0 7078 whereas that of the tertiary rocks at the time of mineralization was 0 7074 0 7118 the 87sr 86sr ratios of the fluorite range from 0 7076 to 0 7083 the fluorites fall on two distinct mixing lines between cretaceous limestone and tertiary igneous rock between 70 and 98 of the sr in the fluorite came from limestones relative abundances of sr and f in the limestone and the igneous rocks suggest that between 70 and 96 of the fluorine came from the igneous rocks

rb sr k ar and stable isotope evidence for the ages and sources of fluid components of gold bearing quartz veins in the northern sierra nevada foothills metamorphic belt california gold bearing quartz veins occur in and near major fault zones in deformed oceanic and island arc rocks west of the main outcrop of the sierra nevada composite batholith veins typically occupy minor reverse faults that crosscut blueschist to amphibolite grade metamorphic rocks whose metamorphic ages range from early paleozoic to jurassic vein micas and carbonate quartz mica assemblages that formed by hydrothermal metasomatism of ultramafic wall rocks in the alleghany grass valley washington and mother lode districts yield concordant k ar and rb sr ages the dated veins are significantly younger than prograde metamorphism penetrative deformation and accretion of their host rocks to the continental margin new and previously published mineralization ages from 13 localities in the sierra foothills range from about 140 to 110 m y ago with mean and median between 120 and 115 m y the age relations suggest that mineralizing fluids were set in motion by deep magmatic activity related to the resumption of east dipping subduction along the western margin of north america following the late jurassic nevadan collision event co 2 bearing fluids responsible for metasomatism and much of the vein mica carbonate albite and quartz deposition in several northern mines were isotopically heavy delta 18 o asymp 8 14ppm delta d between about 10 and 50ppm and do not resemble seawater magmatic or meteoric waters metasomatic and vein filling mica dolomite magnesite and quartz in altered ultramafic rocks generally formed from fluids with similar sr and o isotope ratios at a given locality consistent quartz mica delta 18 o fractionations delta 18 o sub q m 4 5 4 9ppm from various localities imply uniform equilibration temperatures probably between 300 degrees and 350 degrees c on a local mine scale fluids responsible for both carbonate alteration of mafic and ultramafic wall rocks and albitic alteration of felsic and pelitic rocks had similar sr isotope ratios samples from three veins in the central alleghany district fit a 115 7 or 3 m y rb sr isochron with a 87 sr 86 sr i value of approximately 0 7119 inferred 87 sr 86 sr ratios of metasomatic fluids from mines in different parts of the foothills region vary considerably 0 704 0 718 suggesting that sr was derived from sources ranging from western assemblage mesozoic ophiolitic or arc volcanic rocks to early paleozoic continent derived clastic rocks of the shoo fly complex systematic geographic variations in both sr and o isotopes can be rationalized by assuming extensive fluid interaction with rocks similar to the ones that are exposed within a few kilometers of the veins but the ultimate sources of the fluids and of au and other constituents may be independent of these isotopically lighter meteoric fluids deposited some late quartz overgrowths and occupied secondary fluid inclusions in earlier vein quartz