evolution of the south central segment of the archean abitibi belt quebec part iii plutonic and metamorphic evolution and geotectonic model textural criteria permit distinction between the pre kenoran and kenoran phases of plutonism and metamorphism the pre kenoran plutons and pre kenoran metamorphic phases are directly related to the volcanic evolution synvolcanic tonalite trondhjemite plutons and swarms of mafic and felsic dykes core central volcanic complexes the volcanic rocks underwent three types of pre kenoran metamorphism namely a pervasive alteration a thermal contact metamorphism that affected narrow aureoles around synvolcanic plutons and a high intensity hydrothermal alteration that affected cross cutting pipes in central volcanic complexes synkinematic kenoran metamorphism resulted in the growth of minerals chlorite actinolite etc parallel to schistosities synkinematic metamorphic grade ranges form the pumpellyite prehnite facies to the amphibolite facies late to post kinematic metamorphic phases resulted in the growth of minerals across schistosities syn to post kinematic plutons are not voluminous in the part o

calibration of the ion microprobe for quantitative trace precious metal analyses of ore minerals quantitative ion microprobe analysis because of its sensitivity and low minimum detection limits is uniquely suited for the determination of precious metals in common sulfide and sulfosalt mineral particles since the early work of biirg 1930 1935 the presence of trace amounts of precious metals in common ore minerals like pyrite arsenopyrite sphalerite etc has been debated by many mineralogists in s udies of synthetic gold bearing sulfides kurauti 1941 clark 1960 bulk analyses of ore sulfides and sulfarsenides boyle 1965 badalov and badalova 1967 korobushkin 1970 and in radioisotopic studies of synthetic sulfides mironov and geletiy 1979 mironov et al 1986 the term invisible gold was used by boyle 1979 to denote differences between colloidal and solid solution gold in ore minerals of course one of the major problems in determining the role of invisible gold in sulfides is ascertaining the absence of gold mineral inclusions gold silver and palladium have been determined irectly in sulfides in only a few cases where concentrations exceeded the minimum detection limits of the electron microprobe aubert et al 1964 or proton microprobe cabri et al 1984 1985 data on the invisible precious metal content of common sulfides and sulfosalts are essential for precious metal geochemistry and exploration and for determining the mineralogical distribution of precious metals in samples from processing circuits silver and gold in major sulfide minerals can account for substantial fractions of the total silver cabri 1988 chryssoulis and surges 1988 and gold chryssoulis 1989 in some ores thus affecting the precious metal distribution between flotation products or causing refractoriness in some metallurgical processes the ion microprobe has been used for qualitative determinations oftrace elements in geologic materials andersen 1973 lovering 1975 shimizu et al 1978 however because of difficulties inherent in the technique slodzian 1975 leta and morrison 1980 zinner 1980 metson et al 1983 quantitative determination was hampered for several years mcintyre et al 1984 first attempted to calibrate the ion microprobe on ore minerals in order to quantify the silver and indium content of sphalerite synthetic standards of sphalerite doped with variable amounts of silver and indium were used for calibration because of factors not well understood at the time e g the effect of fe substitution for zn on the ion yields charging effects reprodueibility was not as good as expected nevertheless the results confirmed the proportionality between the secondary ion signal and concentration chryssoulis et al 1986 used quantitative ion implantation to determine the silver concentration in sphalerite pyrite and ehaleopyrite from the brunswick massive sulfide base metal ore luff 1986 quantitative gold ion implantation was developed to determine the gold concentration in common sulfide and sulfarsenide minerals from refractory ores chryssoulis et al 1987 the gold concentration in copper anodes was determined with the ion microprobe using synthetic standards of gold in copper in the current study synthetic sulfides were employed to calibrate the ion microprobe for the platinumgroup elements this study discusses comparatively the methods available to calibrate the ion microprobe for quantitative in situ analysis of precious metals in ore minerals and metallurgieal products

solute transport in rivers with multiple storage zones the stir model solute transport in rivers is controlled by surface hydrodynamics and by mass exchanges between the surface stream and distinct retention zones this paper presents a residence time model for strea

thermobarometry in a subgreenschist to greenschist transition in metabasites of the abitibi greenstone belt superior province canada mineral equilibria in the system cao mgo al2o3 sio2 h2o provide a basis for mapping of four reaction isograds and one bathograd in the low pressure transition from subgreenschist to greenschist facies most of the matachewan area of the abitibi greenstone belt is in the lower pressure bathozone as indicated by the widespread occurrences of the subassemblage prh chl the higher pressure bathozone is indicated by two occurrences of pmp act ep qtz but in these samples the bathograd is displaced to anomalously low pressure by the high fe content of the coexisting minerals this illustrates the need to analyse coexisting minerals calculate activities of end member species and compute p t curves for individual samples before interpreting the isograd bathograd pattern petrographic and microprobe analysis indicates that great care must be taken in the selection of equilibrium assemblages pyroxene phenocrysts in one sample are replaced by the assemblage pmp act ep chl qtz whereas prh act ep chl qtz occurs in the groundmass compositional variation may be more cryptic as in a sample of metabasaltic hyaloclastite that contains two spatially distinct univariant assemblages prh pmp ep chl qtz and prh act ep chl qtz within the devitrified matrix whereas chlorite compositions are similar in both assemblages prehnite and epidote in the latter assemblage are significantly richer in fe and poorer in al accordingly the rock is interpreted to contain two distinct univariant assemblages rather than one invariant assemblage prh pmp act ep chl qtz the displaced univariant curves for this sample intersect at 2 2 kbar and 250 c taking account of all thermobarometric implications the low grade limit of the greenschist facies is at 250 270 c and 2 2 5 kbar corresponding to depths of 7 8 km comparison of apparent p t conditions on both sides of the larder lake cadillac break a regional co2 metasomatized fault zone that is spatially associated with many archaean gold deposits provides an upper limit of not more than c 1 km for post metamorphic south side up dip slip displacement

the hydraulics of a straight bedrock channel insights from solute dispersion studies bedrock channels represent a hydraulic environment quite different from that of alluvial channels but currently little is known about bedrock channel hydraulics and whether they differ in any fundamental sense from those of alluvial channels a series of dye dilution experiments was carried out over a range of discharges in a straight reach of a bedrock channel birk beck u k and an aggregated dead zone adz model for longitudinal solute transport and dispersion applied to the resulting time concentration curves the results of the experiments indicate the existence of two significant threshold discharges q1 and q2 the dispersive fraction parameter of the adz model is found to decrease with increasing discharge levelling off at a value close to zero for moderate to high discharges in excess of q1 at these discharges the flow behaves almost as plug flow with very little dispersion taking place at high discharges greater than q2 the stage discharge relationship deviates from a power law and discharge increases more slowly with increasing stage in addition area weighted and momentum weighted mean velocity values diverge strongly as do estimates of reach volume derived from survey and from discharge and mean travel times celerity estimated from the slope of the stage discharge relationship is found to peak at moderate discharges and to fall below momentum weighted mean velocity estimates at a discharge equal to q2 two hypotheses the macroturbulent mixing hypothesis and the decoupled dead zone hypothesis are advanced to account for these observations the fall in dispersive fraction to near zero at discharges above q1 is best explained as the result of a combination of increasing flow uniformity and effective lateral mixing across the whole channel cross section due to high turbulence intensities and large turbulent length scales this means that potential dead zones in the bed and margins of the channel become well flushed and do not act as temporary storage zones for solute the changes in bulk flow parameters observed at discharges in excess of q2 indicate that a significant portion of the channel cross section is acting only as storage and is not contributing to the discharge of the channel this can be explained by the presence of a central core flow decoupled from marginal slack water and from dead zones in the margins the results show that the study reach behaves differently from channels from which dispersive fraction values have previously been reported for a range of discharges

archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec part i geologic relations and formation of the vein system the sigma deposit consists of an archean gold bearing vein system in metavolcanic rocks intruded by an irregular body of porphyritic diorite both affected by regional deformation and in turn cut by younger undeformed feldspar porphyry dikes the veins cut all rock types and are composed chiefly of quartz and tourmaline with minor amounts of carbonates pyrite chlorite scheelite and free gold they were emplaced during or after a greenschist facies metamorphism postdating the intrusion of feldspar porphyry dikes the veins were not significantly affected by any subsequent metamorphism or tectonism two principal types of veins occur in the mine subvertical veins and subhorizontal veins they are contemporaneous and cogenetic subvertical veins occur within steeply dipping east west trending ductile shear zones along which reverse subvertical displacements have taken place the veins occupy openings created by overriding of undulations and irregularities of foliation and slip planes during progressive shearing movements within the shears subhorizontal veins occupy extensional fractures which developed between ductile shear zones preferentially in the more competent host rocks these veins were formed by one or several episodes of open space filling geologic relations indicate that the mineralized veins were emplaced progressively in a dynamic tectonic environment during and shortly after the formation of ductile shear zones a structural analysis has shown that the ductile shear zones and the two vein types can be related to a single strain ellipsoid of the following orientation the z axis trending north south and horizontal the y axis plunging 10 degrees west and the x axis plunging 80 degrees east the deformation responsible for the generation of ductile shear zones and emplacement of the veins is ascribed to a late north south trending compression postdating regional deformation

the experimental ductile deformation of polycrystalline and single crystal pyrite polycrystalline pyrite deformed in triaxial compression tests at a confining pressure of 300 mpa strain rates of 10 super 4 sec super 1 to 10 super 5 sec super 1 and temperatures above about 450 degrees c shortens by dislocation flow mechanisms above 500 degrees c dynamic recovery and recrystallization are important and steady state flow is attained after 10 to 20 percent shortening the dynamically recrystallized grain size d in mu m is related to the flow stress sigma by the relationsigma g k d b super 0 9 where k 16 2 g 7 8 x 10 4 mpa and b 5 42 x 10 super 4 mu m below about 450 degrees c polycrystalline pyrite deforms by brittle mechanisms after less than a few percent strain by dislocation flow the strength of polycrystalline pyrite decreases significantly with increasing temperature and decreasing strain rate over the temperature interval 500 degrees to 700 degrees c at strain rates of 2 x 10 super 5 sec super 1 the steady state flow stress drops from about 500 to 70 mpa pyrite single crystals shortened in the and orientations at 600 degrees c about 10 super 5 sec super 1 and 300 mpa confining pressure exhibit three stage work hardening behavior in which the stage 2 work hardening rates are nearly as high as the elastic modulus for shortening the yield stress 280 mpa and the differential stress at the commencement of stage 3 800 mpa are several times larger than for shortening the strength during shortening is comparable to that of the polycrystalline pyrite tested the single crystal strength data structural considerations and transmission electron microscopy suggest that 100 and possibly 100 are major slip systems the 110 dislocation glide may also be important but has a critical resolved shear stress several times higher than 100 glide the present data indicate that pyrite can be considerably weaker and more ductile than indicated by previous studies and that pyrite is likely to be deformed by dislocation flow mechanisms under a range of geologically realistic conditions

surface subsurface water interactions in an alluviated mountain stream channel data from an instream tracer experiment performed in north fork dry run shenandoah national park virginia illustrate that the transport of water and conservative solute in the stream is greatly influenced by interaction with water present in both the relatively shallow gravel bed and in the relatively deeper alluvial infill material the shape of concentration time curves from the field tracer experiment exhibit storage of tracer in the subsurface short term storage imposed by exchange with the gravel bed and long term storage by exchange with the deeper alluvial infill time series models fit the observed concentration data very well estimates of mixing volumes generated by the time series analysis indicate that a large volume of the gravel bed participates in rapid mixing with the surface stream at one point along the study reach a second order time series model is supported by the data suggesting two independent parallel flow paths observations of tracer in wells more than 10 m from the stream and the very extended recession of the tracer in the stream where it flows over a bedrock ledge support the contention that the deeper alluvium plays an important role in transient storage of solute in north fork dry run the work implies that physically based models to predict transport and storage in alluviated mountain catchments may have to account for interactions between the stream and large portions of its floodplain

deformation of stratiform znpb barite deposits in the northern canadian cordillera abstract the major stratiform sediment hosted zn pb barite deposits of the northern canadian cordillera occur in the palaeozoic selwyn basin kechika trough they formed in euxinic fine grained clastic dominated extensional basins that developed within the carbonate platform of the passive margin of ancestral north america during the late jurassic to mid cretaceous these basins and the stratiform ore deposits were subjected to low greenschist facies regional metamorphism and fold and thrust deformation as they were incorporated into the western part of the rocky mountains mackenzie mountains foreland fold and thrust belt this paper summarises the results of detailed field and microscopic studies on four of these deposits the tom deposit the howards pass deposit the cirque deposit and the driftpile creek deposit the dominant mineralogy of these deposits is sphalerite galena pyrite and in some cases significant barite is present low greenschist grade metamorphism and deformation is characterised by cataclastic flow and brecciation in coarse grained massive pyritic sulphides and by folding recrystallisation and cleavage development in fine grained sulphides and barite relict primary depositional diagenetic structures are found within the orebodies deformation is characterised by strong pressure solution fabrics in barite in fine grained laminated pyrite layers and in mixed sulphide carbonate beds marked local transposition is found with significant remobilisation of galena barite and pyrite the deformation mechanics of these sulphide barite deposits are illustrated using schematic deformation mechanism maps

observing lingering hyporheic storage using electrical resistivity variations around stream restoration structures crabby creek pa time lapse geophysical surveys can map lingering hyporheic storage by detecting changes in response to saline tracer tracer tests were conducted in crabby creek an urban stream outside philadelphia to examine the influence of stream restoration structures and variable sediment thickness we compared electrical resistivity surveys with extensive well sampling 57 wells in two 13 5 m long reaches each with a step drop created by a j hook the two step drops varied in tracer behaviour based on both the well data and the geophysical data the well data showed more variation in arrival time where the streambed sediment was thick and was more uniform where sediment was thin the resistivity in the reach with thin sediment showed lingering tracer in the hyporheic zone both upstream and downstream from the j hook in the second reach where the sediment was thicker the lingering tracer in the hyporheic zone was more extensive downstream from the j hook the contrasting results between the two reaches from both methods suggested that sediments influenced hyporheic exchange more than the step at this location resistivity inversion differed from well data in both reaches in that it showed evidence for tracer after well samples had returned to background mapping lingering tracer either upstream or downstream of a step we conclude that resistivity surveys may become an important tool for hyporheic zone characterization because they provide information on the extent of slow moving fluids in the hyporheic zone which have the potential to enhance chemical reactions copyright 2012 john wiley sons ltd

an introduction to remobilization information from ore body geometry and experimental considerations abstract mobilization involves the translocation and concentration of originally dispersed metallic constituents remobilization is the translocation resulting in modified concentration and distribution of pre existing metalliferous concentrations mobilization and remobilization proceed by chemical liquid state mechanical solid state and mixed processes the paradox of remobilization is that the more complete the process the more difficult becomes substantiation regional metamorphic remobilization is commonly invoked to explain the morphology of supposedly once stratiform massive sulphides and their feeder and alteration systems analysis of the principal dimensions of stratiform massive sulphides in non metamorphic and regionally metamorphosed deposits shows that whereas comparative morphology may be a guide to remobilization it does not constitute proof similarly feeder and alteration morphology suggests that geometric analysis may be of value in establishing mechanical remobilization but the more complex alteration distributions which exist could well lead to misinterpretation in highly deformed terranes ore composition internal structure and zonation influence the ore s capacity to be remobilized mechanical remobilization requires rheological divergence between sulphides and their host rocks experimental deformation of dry sulphides shows that most common sulphides pass through the brittle ductile transition before entering the field of regional metamorphism but that the strength order of sulphides silicates and carbonates remains dynamic until all are undergoing steady state flow within this context experimental strength orders support galena weakest experimental considerations indicate that during diagenesis and early prograde metamorphism the brittle ductile transition will result in widely distributed micro and mesoscale mechanical remobilization nevertheless there is usually insufficient gross behavioural contrast to engender discordant macroscale remobilization possible exceptions particularly in relation to thrusting are outlined but we conclude that macroscale mechanical remobilization during the brittle ductile transition is an uncommon occurrence experimental data were also examined relative to subsequent prograde to peak metamorphism and strength contrasts during decaying and retrogressive metamorphism because the largest strength difference between sulphides and the host sequence is in the lower part of the 350 650 c metamorphic range we contend that macroscale mechanical remobilization is more probable during prograde metamorphism in the 350 500 c interval we similarly believe that macroscale mechanical remobilization is more likely during deformation accompanying retrogressive cooling in the range 500 350 c and we note that it may also result from deformation exploiting the brittle ductile contrasts between silicate and sulphide rocks during the water deficient non retrogressive metamorphic decay cycle chemical mobilization and remobilization require the dissolution of base metals by metamorphic fluids the compositions of hydrothermal low grade metamorphic fluids and their precipitates in active geothermal systems show that the fluids can dissolve transport and form concentrations of base and precious metals similarly fluid inclusion compositions from low to medium grade metamorphic rocks show that such fluids can dissolve a few ppm of base metals in both cases low salinities and low dissolved base metal contents raise doubts over whether such metamorphic fluids can form ore grade base metal concentrations we submit that they can metamorphogenesis is favoured by high initial base metal concentrations preferential dissolution of sulphides over silicates and fluid dominated metamorphism as found in a multiple pass fluid system preferential dissolution of sulphides and the need for high water rock ratios are supported by theoretical considerations experimental work on mafic felsic and sedimentary source rocks and field based studies in the context of mobilization the work strongly implies that prograde metamorphic devolatilization and a mobile fluid phase have substantial ore forming capability retrograde revolatilization does not remobilization is more complex although favoured by high initial metal concentrations dissolution is inhibited by the low permeability of homogeneous low silicate massive sulphides and the consequent peripheral fluid channeling it is conversely enhanced by fine grainsize in discordant fluid focussing retro grade shear zones in all cases for remobilization to form a new ore body both fluid flow and the precipitation process must be focussed and efficient

the effect of streambed topography on surface subsurface water exchange in mountain catchments a numerical hydrological simulation suggested that water exchange between stream channels and adjacent aquifers is enhanced by convexities and concavities in streambed topography at st kevin gulch an effluent stream in the rocky mountains of colorado subsurface hydraulic gradients and movement of ionic tracers indicated that stream water was locally recharged into well defined flow paths through the alluvium stream water filled flow paths in the alluvium referred to as substream flow paths returned to the stream a short distance downstream 1 to 10 m recharge to the substream flow paths occurred where stream water slope increased at the transition from pools 1 to steeper channel units 5 20 return of substream flow paths to the stream occurred where stream water slope decreased at the transition from steeper channel units to pools a net water flux calculation is typically used to characterize water and solute fluxes between surface and subsurface zones of catchments along our study reach at st kevin gulch the net inflow of water from subsurface to stream 1 6 ml s 1 m 1 underestimated the gross inflow 2 7 ml s 1 m 1 by 40 the influence of streambed topography is to enhance hydrological fluxes between stream water and subsurface zones and to prolong water sediment contact times these effects could have important consequences for solute transport retention and transformation in catchments

archean wrench fault tectonics and structural evolution of the blake river group abitibi belt quebec structural analysis of the blake river group volcanic rocks in the rouyn noranda region shows the formations to be distributed largely in z shapes resulting from the interference of two early fold systems oriented west northwest east southeast and east west respectively the first of these two fold systems is probably related to the shortening associated with left lateral movement along the two major fractures in the region namely the porcupine destor and larder lake cadillac faults the second system appears to be the result of north south compression perpendicular to the two major fractures the two major faults the first system of early folding the normal and reverse faults and the minor dextral and sinistral strike slip faults that have been observed in the blake river group rocks can all be integrated into one tectonic system that of wrench fault tectonics the orientations of the principal structures recognized in the abitibi belt major shear zones folding and faulting suggest that the d

gold distribution in the mobrun volcanic associated massive sulfide deposit noranda quebec a preliminary evaluation of the role of metamorphic remobilization the mobrun zn cu au ag orebodies show metal zonation typical of volcanic associated massive sulfide deposits although some metamorphic remobilization of metals has occurred the nature and distribution of primary facies are the result of synvolcanic deposition and reworking of sulfides by hydrothermal fluids secondary facies resulting from metamorphism and deformation locally overprint primary facies and include transgressive veins which contain remobilized au as electrum the distribution of secondary facies was controlled by the mechanical properties of the mineralization as well as of the surrounding rocks the mechanical response of different facies to deformation influenced the development and distribution of zones containing easily recoverable gold preservation of primary textures is best in the main and satellite lenses the 1100 lens also shows significant preservation of primary facies however development of secondary facies is pronounced textural structural and chemical evidence indicates that the 1100 lens was subjected to more extreme metamorphic recrystallization and deformation than the other lenses metamorphic remobilization was important in releasing refractory au from sulfides and locally concentrating it in a recoverable form electrum

integrated overview of the vertebrate fossil record of the ladrunan anticline spain evidence of a barremian alluvial lacustrine system in ne iberia frequented by dinosaurs abstract the barremian mirambel formation maestrazgo basin iberian chain ne spain preserves different types of dinosaur and other vertebrate fossils skeletal eggshell and ichnological remains a total of 31 vertebrate fossil sites and tracksites have been recognized within this unit in the ladrunan area teruel province detailed stratigraphic sedimentological and micropalaeontological analyses have also been performed in the unit a vertical sedimentary trend from alluvial dominated facies meandering river and related overbank areas to palustrine lacustrine facies and back has been defined for the mirambel formation in this area the depositional system was located close to the coastline as indicated by sporadic marine input in the lower part of the unit most fossil remains were recovered by surface collection as well as by the usual techniques used for macrovertebrate excavations the dinosaur record identified comprises ornithopods theropods and sauropods four distinct track bearing horizons have been identified the heterolithic nature and aggradation characteristic of the mirambel formation are favourable factors for track formation and preservation the dinosaur tracks consist of convex hyporeliefs or concave epireliefs that record the trackmakers as they frequented lakeshores alluvial floodplains and fluvial courses macrovertebrate bonebeds occur in alluvial settings poorly drained floodplains and ponds microvertebrate concentrations are located in shallow lacustrine deposits isolated skeletal elements can be found in a great variety of deposits attritional accumulation in a low energy depositional context is the general pattern of origin for the bone bearing fossil sites of the mirambel formation as regards the genetic framework the resulting skeletal assemblages are predominantly the result of physical factors with sedimentology as a key factor rather than biological phenomena eggshell fragments are frequent throughout the unit but are clearly more common in palustrine lacustrine deposits these can be taken to be parautochthonous bioclasts from nearby areas and might be indicative of the preferential affinity of the egg layers for wetlands and lakeshores

shape free inference of hyporheic traveltime distributions from synthetic conservative and smart tracer tests in streams 1 the hyporheic zone has been identified as important for river ecology natural biogeochemical turnover filtration of particles degradation of dissolved pollutants and thus for the self cleaning capacity of streams and for groundwater quality good estimation of the traveltime distribution in the hyporheic zone is required to achieve a better understanding of transport in the river system the transient storage model has been accepted as an appropriate tool for reach scale transport in rivers undergoing hyporheic exchange but the choice of the best parametric function for the hyporheic traveltime distribution has remained unclear we present an approach to obtaining hyporheic traveltime distributions from synchronous conservative and smart tracer experiments that does not rely on a particular functional form of the hyporheic traveltime distribution but treats the latter as a continuous function nonnegativity of the hyporheic traveltime distribution is enforced by the application of lagrange multipliers a smoothness parameter needed for regularization and uncertainty bounds are obtained by the expectation maximization method relying on conditional realizations the shape free inference provides the opportunity for capturing unconventional shapes e g multiple peaks in the estimation we test the approach by applying it to a virtual test case with a bimodal hyporheic traveltime distribution which is recaptured in the inversion of noisy data

retracted and replaced a modelling study of hyporheic exchange pattern and the sequence size and spacing of stream bedforms in mountain stream networks oregon usa this article has been retracted and replaced see retraction and replacement notice doi 10 1002 hyp 6350 studies of hyporheic exchange flows have identified physical features of channels that control exchange flow at the channel unit scale namely slope breaks in the longitudinal profile of streams that generate subsurface head distributions we recently completed a field study that suggested channel unit spacing in stream longitudinal profiles can be used to predict the spacing between zones of upwelling flux of hyporheic water into the stream and downwelling flux of stream water into the hyporheic zone in the beds of mountain streams here we use two dimensional groundwater flow and particle tracking models to simulate vertical and longitudinal hyporheic exchange along the longitudinal axis of stream flow in second third and fourth order mountain stream reaches modelling allowed us to 1 represent visually the effect that the shape of the longitudinal profile has on the flow net beneath streambeds 2 isolate channel unit sequence and spacing as individual factors controlling the depth that stream water penetrates the hyporheic zone and the length of upwelling and downwelling zones 3 evaluate the degree to which the effects of regular patterns in bedform size and sequence are masked by irregularities in real streams we simulated hyporheic exchange in two sets of idealized stream reaches and one set of observed stream reaches idealized profiles were constructed using regression equations relating channel form to basin area the size and length of channel units step size pool length etc increased with increasing stream order simulations of hyporheic exchange flows in these reaches suggested that upwelling lengths increased from 2 7 m to 7 6 m and downwelling lengths increased from 2 9 m to 6 0 m with increase in stream order from second to fourth order step spacing in the idealized reaches increased from 5 3 m to 13 7 m as stream size increased from second to fourth order simulated upwelling lengths increased from 4 3 m in second order streams to 9 7 m in fourth order streams with a pool riffle step channel unit sequence and increased from 2 5 m to 6 1 m from second to fourth order streams with a pool step riffle channel unit sequence downwelling lengths also increased with stream order in these idealized channels our results suggest that channel unit spacing size and sequence are all important in determining hyporheic exchange patterns of upwelling and downwelling though irregularities in the size and spacing of bedforms caused flow nets to be much more complex in surveyed stream reaches than in idealized stream reaches similar trends emerged relating the average geomorphic wavelength to the average hyporheic wavelength in both surveyed and idealized reaches copyright 2005 john wiley sons ltd

in stream geomorphic structures as drivers of hyporheic exchange 1 common in stream geomorphic structures such as debris dams and steps can drive hyporheic exchange in streams exchange is important for ecological stream function and restoring function is a goal of many stream restoration projects yet the connection between in stream geomorphic form hydrogeologic setting and hyporheic exchange remains inadequately characterized we used the models hec ras modflow and modpath to simulate coupled surface and subsurface hydraulics in a gaining stream containing a single in stream geomorphic structure and to systematically evaluate the impact of fundamental characteristics of the structure and its hydrogeologic setting on induced exchange we also conducted a field study to support model results model results indicated that structure size background groundwater discharge rate and sediment hydraulic conductivity are the most important factors determining the magnitude of induced hyporheic exchange followed by geomorphic structure type depth to bedrock and channel slope model results indicated channel spanning structures were more effective at driving hyporheic flow than were partially spanning structures and weirs were more effective than were steps across most structure types downwelling flux rate increased linearly with structure size yet hyporheic residence time exhibited nonlinear behavior increasing quickly with size at low structure sizes and declining thereafter important trends in model results were observed at the field site and also interpreted using simple hydraulic theory thereby supporting the modeling approach and clarifying underlying processes

textural evidence for remobilization in metamorphic environments remobilization of stratabound massive sulphide deposits involves both dislocation flow mechanical remobilization and fluid state processes chemical remobilization textural support for such remobilization is presented at micro meso and macroscales microscale evidence establishes the degree the amount of a deposit affected of remobilization likewise mesoscale textures establish the degree and may provide mesoscale models of macroscale remobilization processes but still do not establish the extent the distance over which translocation may have occurred of remobilization where macrotexture indicates a departure from an original conformable relationship gross remobilization is suggested and may be the consequence of mechanical and or chemical processes the case for gross mechanical and or chemical remobilization is often difficult to sustain because alternative hypotheses e g hydrothermal replacement may be compatible with the observed relationships remobilization of a conformable ore layer may involve internal redistribution during which sulphides have been modified by dislocation flow and or fluid state processes within the layer constraints or external where the layer constraints have been substantially transgressed during dislocation flow and or fluid phase remobilization if mesoscale textures indicate remobilization of the external type then macroscale gross remobilization remains a possibility subject to substantiation

convective transport within stable river sediments local pressure variations of the order of 100 1000 n m2 can be observed between the upstream and downstream faces of the typically triangular shaped dunelike sediment structures that form at the sediment water interface of rivers laboratory experiments were conducted examining the influence of this localized pressure variation on contaminant transport processes within the sediment numerical modeling of the in bed flow via boundary element methods was also undertaken in order to predict convective transport under typical field conditions the laboratory experiments and numerical simulation of the in bed flow in several rivers verified that the pressure distribution observed on the sediment surface and the resulting interstitial fluid convection can control transport of chemically inert nonsorbed contaminants in stable sediments in bed peclet numbers were of the order of 100 1000 indicating the negligible influence of diffusion under the conditions examined

effects of greenschist facies metamorphism and related deformation on the mobrun massive sulfide deposit quebec canada the mobrun zn cu ag au deposit in the noranda mining camp is hosted by archean mafic and felsic submarine volcanic rocks the deposit comprises three massive sulfide complexes the main and satellite lenses near surface and the 1100 orebody at depth the rocks have been subjected to lower greenschist facies metamorphism and related deformation which resulted in changes in ore textures development of shear zones and veins systems remobilization of gold and formation of a new mineral electrum within the orebodies both mechanical and chemical processes operated to produce secondary textures and structures resulting from brittle deformation ductile deformation and annealing the specific deformation mechanisms include brittle failure and cataclastic flow dislocation glide dislocation creep and solution precipitation creep the main and satellite lenses are characterized by excellent preservation of primary sulfides deposited from and reworked by synvolcanic hydrothermal fluids these orebodies were affected to a limited degree by mechanical processes of deformation in contrast the 1100 orebody is characterized by a higher degree of development of textures and structures related to metamorphism and deformation especially those formed by chemical processes the differences may be due to the greater depth of the 1100 orebody relative to the other lenses as regional metamorphic isograds are subhorizontal and more extensive interaction between metamorphic fluids and the 1100 lens

pyrite deformation in stratiform lead zinc deposits of the canadian cordillera pyrite textures in five stratiform lead zinc deposits from lower to upper greenschist facies environment of the canadian cordillera are described and discussed in terms of deposition early diagenesis deformation metamorphism and hydrothermal alteration processes overgrowth is an important process during both diagenesis and deformation diagenetic and deformational overgrowths can be distinguished diffusive mass transfer involving pressure solution and oriented overgrowth of pyrite is the main deformation mechanism in pyrite deposits at low metamorphic grades although diffusive mass transfer favours fine grained mineral aggregates its effect on coarse pyrite grains has also been identified ore minerals dissolved by pressure solution may be transported with the assistance of pore fluids within fractures and grain boundaries over distances significantly greater than the scale of individual grains to give a range of pressure solution overgrowth textures the textural modification of pyritic ores from the early stages of diagnesis through metamorphism and deformation to post deformation thermal annealing has important implications for the distribution of trace elements and isotopic compositions in pyritic ores

evolution of the south central segment of the archean abitibi belt quebec part ii tectonic evolution and geomechanical model in this paper we describe the relations between the paleogeographic and tectonic evolution of the southwestern part of the archean abitibi and bellecombe belts volcanism in the abitibi belt created a very thick anisotropic plate composed of competent volcanic rocks and broken by the duparquet destor break the depocenters of the upper division of diverse volcanic rocks subsided about 10 km relative to their surroundings and some central volcanic complexes within this division were consolidated by synvolcanic plutons and their thermal metamorphic aureole the cadillac break a normal fault separated the abitibi and bellecombe belts the latter consisted of comparatively incompetent sedimentary rocks on top of a basement composed of ultramafic mafic flows north south compression of the volcanic terrain during the kenoran orogeny produced a set of flexure folds f1 that curve around the consolidated cores of central volcanic complexes generally in an easterly direction synclinoria nucleated at the dee

dense nonaqueous phase liquid dnapl source zone characterization influence of hydraulic property correlation on predictions of dnapl infiltration and entrapment 1 the influence of aquifer property correlation on multiphase fluid migration and entrapment was explored through the use of correlated and uncorrelated porosity permeability and capillary pressure saturation pc sat parameter fields in a cross sectional numerical multiphase flow model data collected from core samples in a nonuniform sandy aquifer were used to generate three dimensional aquifer parameter fields porosity was assumed to be uniform or simulated using sequential gaussian simulation sgs permeability k was modeled independently of porosity using sgs as well as simulated geostatistical indicator classes derived from measured grain size distribution curves retention characteristics were assigned employing leverett scaling of a representative pc sat curve to the geostatistical k fields or alternatively on the basis of simulated indicator classes and porosity values ensemble dense nonaqueous phase liquid dnapl infiltration and entrapment behavior for a hypothetical tetrachloroethylene pce spill was simulated in four sets of two dimensional profiles extracted from these realizations comparisons of saturation profiles and spatial moments from point source dnapl infiltration simulations suggest that choices involving the geostatistical algorithm used to model k and the incorporation of variable versus uniform porosity have a smaller influence than choices involving the scaling of capillary retention properties to k from these simulations it is apparent that the degree of spatial correlation in pc sat parameters exerts a controlling influence on predicted dnapl spreading and redistribution in saturated aquifers the resultant distribution of mass within a dnapl source zone will have implications for dnapl recovery and subsequent mass fluxes in remediation operations

massive sulfide deposits of the noranda area quebec iv the mobrun mine the corbet deposit is located in the upper part of the flavrian andesite the lowest volcanic formation within cycle iii of the noranda central mine sequence the deposit consisted of one main lens of massive sulfides and several smaller lenses and contained 2 7 106 t of mineable ore at 2 92 cu 1 98 zn 20 6 g t ag and 1 0 g t au the orebody had a massive pyrrhotite chalcopyrite core which passed laterally into massive pyrite sphalerite the northwestern part of the ore body is overlain by 50 100 m of flavrian andesite whereas the southeastern portion is overlain by northwest rhyolite lavas within the flavrian andesite and the lower northwest rhyolite are low in k2o 0 5 and are partly of tholeiitic affinity and partly of transitional affinity the tholeiitic volcanic series has zr y ratios of 2 8 to 4 5 whereas the transitional series has zr y ratios of 4 5 to 7 1 the two series are also distinct in plots of nb zr yb zr nb y and the rare earth elements these data indicate that two s

ore mineralogy of the applachian caledonian stratabound sulfide deposits abstract the diverse ore mineralogies of more than 100 stratabound sulfide deposits that occur along the length of the appalachian caledonian orogen have been tabulated the minerals reflect the varying cu zn pb ratios that have been used as a means to separate the ore deposits into six distinct types following the igcp project 60 guidelines the ore deposits each containing at least one million metric tons of ore are typical of massive sulfide deposits throughout the world and provide a basis for contrasting and comparing this orogen with others differing grades of metamorphism have significantly modified the ore mineral grain sizes and textures but do not seem to have effectively influenced the number or variety of mineral species present

spatially distributed characterization of hyporheic solute transport during baseflow recession in a headwater mountain stream using electrical geophysical imaging summary the transport of solutes along hyporheic flowpaths is recognized as central to numerous biogeochemical cycles yet our understanding of how this transport changes with baseflow recession particularly in a spatially distributed manner is limited we conducted four steady state solute tracer injections and collected electrical resistivity data to characterize hyporheic transport during seasonal baseflow recession in the h j andrews experimental forest oregon usa we used temporal moment analysis of pixels generated from inversion of electrical resistivity data to compress time lapse data into descriptive statistics mean arrival time temporal variance and temporal skewness for each pixel a spatial visualization of these temporal moments in the subsurface at each of five 2 d transects perpendicular to the stream was interpreted to inform transport processes as baseflow recession progressed we found increasing first arrival times persistence mean arrival time temporal variance and coefficient of variation and decreasing skewness these trends suggest that changes in hydrologic forcing alter the relative influence of transport phenomena e g advection vs other transport processes such as dispersion along flowpaths spatial coverage obtained from electrical resistivity images allowed for qualitative comparison of spatial patterns in temporal moments both at an individual cross section as well as between cross sections we found that geomorphologic controls e g bedrock confinement vs gravel wedge deposits resulted in different distributions and metrics of hyporheic transport results of this study provide further evidence that hyporheic transport is highly variable both in space and through the baseflow recession period geophysical images differentiate advection dominated flowpaths from those that are more affected by other transport processes e g dispersion mobile immobile exchange

hyporheic zone hydrologic science a historical account of its emergence and a prospectus the hyporheic zone defined by shallow subsurface pathways through river beds and banks beginning and ending at the river is an integral and unique component of fluvial systems it hosts myriad hydrologically controlled processes that are potentially coupled in complex ways understanding these processes and the connections between them is critical since these processes are not only important locally but integrate to impact increasingly larger scale biogeochemical functioning of the river corridor up to the river network scale thus the hyporheic zone continues to be a growing research focus for many hydrologists for more than half the history of water resources research this manuscript partly summarizes the historical development of hyporheic zone hydrologic science as gleaned from papers published in water resources research from the birth of the concept of the hyporheic zone as a hydrologic black box sometimes referred to as transient storage zone to its adolescent years of being torn between occasionally competing research perspectives of interrogating the hyporheic zone from a surface or subsurface view to its mature emergence as an interdisciplinary research field that employs the wide array of state of the art tools available to the modern hydrologist the field is vibrant and moving in the right direction of addressing critical fundamental and applied questions with no clear end in sight in its growth there are exciting opportunities for scientists that are able to tightly link the allied fields of geology geomorphology hydrology geochemistry and ecology to tackle the many open problems in hyporheic zone science

prolonged river water pollution due to variable density flow and solute transport in the riverbed a laboratory experiment and numerical modeling were used to examine effects of density gradients on hyporheic flow and solute transport under the condition of a solute pulse input to a river with regular bed forms relatively low density gradients due to an initial salt pulse concentration of 1 55 kg m23 applied in the experiment were found to modulate significantly the pore water flow and solute transport in the riverbed such density gradients increased downward flow and solute transport in the riverbed by factors up to 1 6 this resulted in a 12 2 increase in the total salt transfer from the water column to the riverbed over the salt pulse period as the solute pulse passed the effect of the density gradients reversed slowing down the release of the solute back to the river water by a factor of 3 7 numerical modeling indicated that these density effects intensified as salt concentrations in the water column increased simulations further showed that the density gradients might even lead to unstable flow and result in solute fingers in the bed of large bed forms the slow release of solute from the bed back to the river led to a long tail of solute concentration in the river water these findings have implications for assessment of impact of pollution events on river systems in particular long term effects on both the river water and riverbed due to the hyporheic exchange

parameterization of mean residence times in idealized rectangular dead zones representative of natural streams abstractthree dimensional reynolds averaged navier stokes modeling validated against experimental data is used to parameterize the flow features and time scales in idealized rectangular cavities for a wide range of width to length ratios 0 4 w l 1 1 and reynolds number based on the depth 5 000 rd 20 300 representative of isolated dead zones in small natural streams the flow features for this parameter range are similar to open cavity flows and consist of a mixing layer spanning the entire length of the dead zone together with a single main recirculation region the langmuir time scale ratio of dead zone volume to discharge based on the assumption of a well mixed dead zone is found to be a function of the mean rotation time scale inverse of average rotation rate within the dead zone the momentum thickness of the upstream boundary layer and the dead zone width the entrainment coefficient used to relate the exchange velocity to the average free stream velocity is shown to be directly related

substrate size and heterogeneity control anomalous transport in small streams in alluvial systems substrate characteristics play a critical role in slowing downstream transport of both water and solutes we present results from solute injection experiments testing the influence of sediment size pea gravel versus coarse gravel and heterogeneity alternating sections versus well mixed reaches on solute transport dynamics in four experimental streams at the notre dame linked experimental ecosystem facility the stream with pea gravel resulted in more long term retention than the stream with coarse gravel whereas both streams with heterogeneous substrate alternated and mixed fell between with similar late time scaling inverse modeling of solute breakthrough curves suggested that residence times were distributed according to a truncated power law while conservative solute transport in all four streams was anomalous truncation times were influenced by sediment size with the smaller pea gravel exhibiting a later truncation time than the coarse gravel and the two streams with heterogeneous substrate having an intermediate cutoff these results uniquely associate transport scaling with substrate characteristics in fluvial systems revealing truncation time scales that had been previously predicted but not observed and quantified in field conditions because both benthic i e substrate water interface and subsurface hyporheic regions are known biogeochemical hot spots relating physical characteristics to the macroscopic transport behavior could be crucial to improve our estimates of solute export from fluvial systems

determining in channel dead zone transient storage by comparing solute transport in a bedrock channel alluvial channel sequence oregon 1 current stream tracer techniques do not allow separation of in channel dead zone e g eddies and out of channel hyporheic transient storage yet this separation is important to understanding stream biogeochemical processes we characterize in channel transient storage with a rhodamine wt solute tracer experiment in a 304 m cascade pool type bedrock reach with no hyporheic zone we compare the solute breakthrough curve btc from this reach to that of an adjacent 367 m alluvial reach with significant hyporheic exchange in the bedrock reach transient storage has an exponential residence time distribution with a mean residence time of 3 0 hours and a ratio of transient storage to stream volume of 0 14 demonstrating that at moderate discharge bedrock in channel storage zones provide a small volume of transient storage with substantial residence time in the alluvial reach though pools are similar in size to those in the bedrock reach transient storage has a power law residence time distribution with a mean residence time of 100 hours estimated at nearly 1200 hours and a ratio of storage to stream volume of 105 because the in channel hydraulics of bedrock reaches are simpler than alluvial step pool reaches the bedrock results are probably a lower end member with respect to volume and residence time though they demonstrate that in channel storage may be appreciable in some reaches these results suggest that in stream dead zone transient storage may be accurately simulated by exponential rtds but that hyporheic exchange is better simulated with a power law rtd as a consequence of more complicated flow path and exchange dynamics