pyrite mineralization in microbial mats from the mid proterozoic newland formation belt supergroup montana u s a abstract the mid proterozoic newland formation a shale dominated unit of the belt supergroup was deposited in an eastern extension of the belt basin the helena embayment a variety of different shale facies types can be distinguished of particular interest for this study is a shale facies that has been interpreted to be the result of microbial mat growth resulting in carbonaceous shale beds interrupted by storm deposition causing deposition of graded silt mud couplets alternation of carbonaceous beds with silt mud couplets gives these shales a characteristic striped appearance along the basin margins a pyrite rich sub facies of these striped shales is found locally consisting of laminated pyrite beds that alternate with non pyritic silt mud couplets laminated pyrite beds in pyritic striped shales are interpreted as mineralized microbial mats because of wavy crinkly internal laminae and because of the direct association with unmineralized striped shales that contain microbial mat deposits excess iron in pyritic shale horizons was probably supplied by terrestrial runoff in colloidal form iron hydroxides introduced by rivers into basin marginal lagoons flocculated and were then incorporated into microbial mats and reduced to pyrite upon burial

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

sulfur geochemical constraints on mesoproterozoic restricted marine deposition lower belt supergroup northwestern united states abstract despite nearly a century of study by a diverse group of precambrian workers competing interpretations have persisted that favor both marine and nonmarine depositional settings for the mesoproterozoic belt supergroup of the northwestern united states our data for sedimentary pyrite formation in unmetamorphosed organic rich shales of the newland formation of the lower belt supergroup western montana argue that at least a portion of the belt basin during its early history was characterized by restricted marine conditions with only episodic incursions of seawater this model is supported by ratios of organic carbon corg to pyrite sulfur that once corrected for selective diagenetic and thermal loss of corg and the inferred high reactivity of the corg reservoir in the absence of vascular land plant remains suggest degrees of sulfate limitation consistent with a restricted marine setting the isotopically heavy disseminated pyrite that dominates the black shales shows a broad range of 34s values of bacterial origin 34s ranges from 8 7 to 36 3 mean 7 6 n 41 the pyrite data overlap with the 34s range of coeval barite sulfate within the basin and are similar to independent estimates for the sulfate of mesoproterozoic seawater these relationships have allowed us to delineate a record of bacteriogenic pyrite that formed in a modified marine reservoir where the supply of sulfate was limited a bacterial mechanism is further suggested by the morphological character of this early formed pyrite including the ubiquitous framboids after comparing our results with those from present day localities such as the black sea and sites of lacustrine deposition we conclude that the abundant 34s enriched bacteriogenic disseminated pyrite observed in black shales of the newland formation must record a style of sulfate limitation possible only within an isolated marine basin receiving an intermittent flux of seawater although the entire belt basin likely remained a restricted marine setting throughout deposition of the lower belt supergroup sulfur isotope data from the newland formation at two localities separated by more than 150 km in the eastern belt basin reveal stratigraphic trends in the strength of the marine connection specifically the connection evolved such that inputs of seawater sulfate increased progressively in frequency and possibly strength during deposition of the newland formation overall the hypothesized restricted marine setting when viewed in light of independent tectonic sedimentologic and geochronologic evidence suggests syndepositional and likely episodic continental rifting which helps constrain the proterozoic paleotectonic history of western laurentia

twin lake tracer tests transverse dispersion two natural gradient dispersion tests were performed at the chalk river nuclear laboratories in ontario in 1982 and 1983 during the field tests 131i was used to label the groundwater and its activity was measured in situ collecting continuous records of activity versus depth at selected times and of activity versus time at selected locations curves generated by a three dimensional analytical solution to the advection dispersion equation were fit to activity versus depth scans recorded at various locations in the test aquifer within the individual velocity regions the vertical dispersivities were 0 0006 and 0 0008 m with the arithmetic average 0 0007 m as calculated from the 1982 data the vertical dispersivity values calculated from 1983 data were 0 0014 and 0 0010 m for the high and intermediate velocity regions respectively with an arithmetic average 0 0012 m the increase in dispersivity was attributed to the error associated with the sampling and fitting procedures the average vertical dispersivity of the tracer test aquifer was an order of magnitude less than the average longitudinal dispersivity 0 0010 m versus 0 010 m for the intermediate velocity region within individual velocity regions the vertical dispersivity of the porous medium was independent of the travel distance of the tracer and was proportional to the velocity

geochemistry of molybdenum in the chao phraya river estuary thailand role of suboxic diagenesis and porewater transport abstract the concentration of dissolved molybdenum mo was measured in the chao phraya river estuary thailand to examine the sources and geochemical behavior of mo water samples in the salinity range of 0 02 24 5 collected during periods of contrasting river discharge have mo concentrations of 3 2 117 nm in the estuary mo and salinity show strong linear correlations suggestive of conservative mixing however at salinity 5 mo concentrations are much higher than that can be achieved from mixing of river water and average seawater desorption from river borne and estuarine sedimentary particles contribute mo that is significantly less than the observed excess mo in the chao phraya estuary groundwater discharge is unlikely to be an important source of mo in the estuary reductive mobilization of mo in the sediments of the gulf of thailand its transport to the overlying water and finally to the estuary is likely to be the dominant mechanism that is responsible for the observed excess mo this inference is drawn from higher salinity and excess mo in deepwater of the gulf of thailand strong correlation between dissolved mo and 228 ra and the observation of suboxic diagenesis in the gulf sediments contribution of mo to the estuary via porewater transport is likely to be enhanced by higher water temperature tidal currents sediment re working and bottom water upwelling which are all documented in the northern gulf of thailand porewater flux of mo estimated using 228 ra flux is much higher than the average riverine mo flux temporal changes in redox condition and circulation pattern in the gulf seem to be responsible for the observed seasonal variation of mo abundances in the estuary

migration of contaminants in groundwater at a landfill a case study 3 tritium as an indicator of dispersion and recharge abstract since the beginning of the era of major atmospheric tests of nuclear weapons in 1953 rain and snow has contained concentrations of 3 h that have been above the natural levels that existed prior to 1953 as a consequence 3 h now serves as an identifier or tracer of post 1952 water in groundwater flow systems in this study the distribution of 3 h in and near the contaminant plume at the borden landfill was determined by analysis of samples from multilevel point samplers and from bundle piezometers the contaminant plume which was delineated using cl and so 2 4 patterns was found to contain a large zone of tritiated water and a smaller zone with no detectable 3 h much of the zone of untritiated water exists in the frontal segment of the plume this is consistent with the fact that landfilling operations at the site began in 1940 and that as the plume developed in the period from 1940 to 1952 any natural 3 h that may have existed in the plume during this period is now below the detection level an estimate of the 3 h concentrations in water that has recharged the aquifer beneath the landfill was developed using the nearly continuous record for 3 h in precipitation at ottawa ontario with comparisons to less frequent data from other sampling stations the ottawa record indicates that during the years in the 1960 s in which peak 3 h concentrations occurred values of thousands of tu in precipitation were common and levels of many hundreds of tu or higher existed almost continuously in the zone of tritiated water in the plume and in the tritiated zone in the natural groundwater up and downgradient of the plume all of the sample points except three in the plume had concentrations below 150 tu two of these three have concentrations below 290 tu the general occurrence in the aquifer of 3 h levels that are much below the high levels that existed in precipitation prior to the 1970 s is attributed to radioactive decay and to the effect of longitudinal hydrodynamic dispersion that has caused mixing of the tritiated groundwater with older untritiated water an analytical solution to the one dimensional form of the advection dispersion equation was used with the method of superposition to simulate the distribution of 3 h along the central flow path in the contaminant plume simulated 3 h distributions using longitudinal dispersivity values in the range of 30 60 m gave 3 h distributions similar to the field values although the longitudinal dispersivity range of 30 60 m is far above the range reported from laboratory experiments on sand and although it is much above the range obtained in a small scale tracer test at the borden site it is within the range reported in the literature based on the calibration of models to regional contaminant migration patterns in glaciofluvial or alluvial aquifers the strong longitudinal dispersion is believed to be caused by mixing between the ubiquitous layers of fine and medium grained sand and silty sand that comprise the aquifer an estimate of the average annual rate of recharge that has contributed to the groundwater zone beneath the landfill during the bomb tritium period was obtained by comparing the input of 3 h to an area segment of the landfill with the 3 h contained within a groundwater flow tube leading from the specified area along the centerline of the contaminant plume this approach yielded a minimum average annual recharge rate of 50 with the main cause of uncertainty being the extent of the area in which recharge occurs

twin lake tracer tests setting methodology and hydraulic conductivity distribution following evaluation of three potential sites a fluvial sand aquifer with high 0 7 1 6 m d 1 linear average groundwater flow velocities was instrumented with a fully penetrating injection well and 82 monitoring installations over a 40 m flow path length two natural gradient tracer migration experiments have employed pulse injections of a nonreactive radioisotope 131i in a study of hydraulic conductivity structure and dispersive characteristics of the flow system the use of a gamma emitting radionuclide in these experiments allowed measurement of tracer distribution by scanning fully penetrating boreholes with a scintillation detector this technique provided many advantages in data collection over conventional tracers including unprecedented resolution of the vertical distribution of tracer measurements without pumping and the attendant concerns for flow system perturbation and minimal manpower for sample analysis tracer breakthroughs at monitors along the axis of flow revealed the presence of heterogeneities in aquifer hydraulic conductivity at two scales over the 40 m path length six regions with hydraulic conductivities substantially different from adjacent strata were identified thicknesses of these regions varied from 0 2 to more than 3 m their lateral extents in the direction of groundwater flow ranged from 15 m to more than 40 m smaller strata with an average thickness of 0 34 m and lengths of less than 10 m were detected within all six of the hydraulic conductivity regions but there was no evidence of increases in local dispersivity with increased transport distance as a result of these variations the six hydraulic conductivity regions do however have measurable effects on whole aquifer dispersion stratification characteristics of the tested aquifer believed to have been deposited in a sandy braided river are consistent with those observed in similar modern environments estimation of the magnitude and spatial structure of hydraulic conductivity variations in aquifers of concern would be greatly aided by studies of the stratification characteristics in well exposed modern or lithified sedimentary analogues

rise of atmospheric oxygen and the upside down archean mantle 1 the establishment of an oxygen rich atmosphere dramatically altered the evolution of life on earth most of the recent discussion of the topic has been focused on the timing of the event rather than on its mechanism here we draw upon recent developments in the understanding of earth s interior to propose that the rise of oxygen followed a geologically abrupt period of mantle overturn and or intense plume activity near the archean proterozoic transition 2470 2450 million years ago the magmatic event has already been linked to the widespread deposition of oxide facies banded iron formation and the rise of oxygen has been implicated as the trigger for iron deposition and earth s first major glaciation we argue that these events are all related to a change in redox state of volcanic gases brought about by deep seated late archean and earliest paleoproterozoic magmatism

tritium as an indicator of recharge and dispersion in a groundwater system in central ontario the detailed distribution of tritium 3h in the recharge area of a shallow unconfined sand aquifer near sturgeon falls ontario is described at this forested shallow water table site bomb tritium has penetrated uniformly to a depth of 8 12 m indicating recharge of 15 cm year which is 16 of precipitation the zone of bomb tritium contains 3h concentrations of from 16 to 269 tritium unit tu whereas much lower values 1 tu are observed in groundwaters recharged only a few years prior to 1953 the year when significant fallout of bomb tritium began tritium distribution is accurately simulated using one and two dimensional models when the ottawa record is used for the post 1953 tritium input function when dispersion is low and when a prebomb tritium input value of 3 tu is used this prebomb value is slightly lower than that suggested by kaufman and libby 1954 based on precipitation and surface water samples from the early 1950s the simulations indicate and field data corroborate that in 1986 3h levels of more than 100 tu occur only in groundwaters recharged between 1957 and 1971 while levels in excess of 200 tu occur only in groundwaters recharged during 1961 1967 the 1960s tritium peak is observed within a narrow distinct depth zone at all locations along the flow section investigated

early proterozoic metasediments from north central colorado metamorphism provenance and tectonic setting early proterozoic metasediments from the big thompson canyon area in north central colorado increase in metamorphic grade from the biotite zone to the sillimanite zone representing a low pressure facies series that probably developed in response to a steep geotherm over a thermal high high grade rocks are enriched in k 2 o al 2 o 3 fe 2 o 3 mgo tio 2 cr sc cs rb ba and light ree and are depleted in sio 2 cao and zr relative to low grade rocks these differences chiefly reflect differences in the original sandstone shale ratio detrital grains in medium and coarse metasediments are quartz quartzite and feldspar and they suggest a recycled orogen provenance in which granitic rocks and quartzites dominate in the source the abundance of shale in the original succession also attests to the importance of granite in the source major and trace element contents of the rocks constrain the input of mafic to dacitic detritus to less than a few percent ree patterns in all rocks are similar to phanerozoic shales and cratonic sandstones the big thompson canyon metasediments may have been derived from an uplifted collisional orogen in southern wyoming in which unroofed proterozoic granitic rocks and quartzites of the snowy pass supergroup served as the principal sources

the possible role of benthic microbial mats during the formation of carbonaceous shales in shallow mid proterozoic basins a considerable portion of the upper member of the mid proterozoic newland formation meagher county montana consists of carbonaceous silty shales striped shale facies this type of shale facies is common in proterozoic basins and is host to several major base metal deposits the striped shales were deposited in a subtidal setting basinward of carbonates characterized by cryptalgal laminites mudcracks and flat pebble conglomerates the carbonaceous silty shales are considered remnants of benthic microbial mats irregular internal laminae patterns of particle trapping mechanical deformation during penecontemporaneous soft sediment deformation and filamentous microbiota provide evidence for this interpretation the dolomitic clayey shale contains graded silt clay couplets and these are interpreted as storm layers modern subtidal microbial mats can only survive under special conditions but in the proterozoic it is suggested that benthic microbial mats colonized the shallow seafloor during periods of low sediment input leading to the formation of carbonaceous shales

hydrochemical and isotopic investigation of groundwater of al batin alluvial fan aquifer southern iraq major ions and important trace elements in addition to 18o and 2h were analysed for 43 groundwater samples sampled from the al batin alluvial fan aquifer south iraq the most dominant ions with respect to molarity were na cl so4 2 ca2 mg2 no3 hco3 with total dissolved solids tds averaging 7855 mg l high concentrations were found for the trace elements u mo v b sr and cr this study suggests a hydraulic connection exists near the fan apex between the uppermost part of the al batin aquifer and the underlying dammam aquifer by means of the abu jir fault system except for the effects of extensive irrigation fertilizer use and poorly maintained sewers the groundwater chemistry is mainly controlled by geological processes such as dissolution of evaporites and the enrichment of dissolved ions as a result of the high evaporation and low recharge rate furthermore it is shown that the kuwaiti fuel oil burning during gulf war in 1991 contributed to the enrichment of v and mo in the studied aquifer the spatial distribution of most ions appears to generally increase from the south west towards the north east in the direction of groundwater flow the stable isotopes show heavier values in groundwater with a gradually increasing trend in the direction of groundwater flow due to the decreasing depth to groundwater and thus increasing of evaporation from both groundwater or irrigation return water additionally the stable isotope signature suggests that rainfall from sources in the arabian gulf and the arabian sea is the major source of recharge for the al batin aquifer except for two samples of groundwater all samples were not suitable for potable use according to the who standards most of the groundwater is suitable for some agricultural purpose and for livestock water supply apart from the high salinity boron represents the most critical element in the groundwater with respect to agricultural purposes

nitrate reduction in an unconfined sandy aquifer water chemistry reduction processes and geochemical modeling nitrate distribution and reduction processes were investigated in an unconfined sandy aquifer of quaternary age ground water chemistry was studied in a series of eight multilevel samplers along a flow line deriving water from both arable and forested land results show that plumes of nitrate contaminated groundwater emanate from the agricultural areas and spread through the aquifer the aquifer can be subdivided into an upper 10 to 15 m thick oxic zone that contains o2 and no3 and a lower anoxic zone characterized by fe2 rich waters the redox boundary is very sharp which suggests that reduction processes of o2 and no3 occur at rates that are fast compared to the rate of downward water transport nitrate contaminated groundwater contains total contents of dissolved ions that are two to four times higher than in groundwater derived from the forested area the persistence of the high content of total dissolved ions in the no3 free anoxic zone indicates the downward migration of contaminants and that active nitrate reduction is taking place nitrate is apparently reduced to n2 because both nitrite and ammonia are absent or found at very low concentrations possible electron donors in the reduced zone of the aquifer are organic matter present as reworked brown coal fragments from the underlying miocene and small amounts of pyrite at an average concentration of 3 6 mmol kg electron balances across the redoxcline based on concentrations of o2 no3 so42 and total inorganic carbon tic indicate that pyrite is by far the dominant electron donor even though organic matter is much more abundant groundwater transport and chemical reactions were modeled using the code phreeqm which combines a chemical equilibrium model with a one dimensional mixing cell transport model only the vertical component of the water transport was modeled since in contrast to rates along flow lines the vertical rates are close to constant as required by the one dimensional model average vertical transport rates of water in the saturated zone were obtained by tritium dating the modeling process is a two step procedure first the sediment column is initialized with natural water containing only oxygen as electron acceptor and subsequently agricultural waters containing both oxygen and nitrate are fed into the column the nitrate concentration of agricultural waters entering the saturated zone varies with time and an input function was therefore constructed by linear mixing of natural waters and agricultural waters this input function was fed into the column initialized with natural water and the model run forward in time to the year 1988 where field data are available comparison with field data shows that the variation in groundwater chemistry is well described by the model when reduction of oxygen and reduction of nitrate by pyrite oxidation are the only redox reactions occurring finally predictions are made for the distribution of water chemistry in the year 2003 downward progression of the redoxcline is accelerated by a factor of five due to nitrate pollution of the aquifer but absolute rates remain small of the order of a few centimeters per year the controlling factor for nitrate migration through the aquifer once it has reached the anoxic zone is the concentration and distribution of pyrite in the sediments

facies and origin of shales from the mid proterozoic newland formation belt basin montana usa shales constitute more than 60 of the world s sediments yet while facies models for sandstones and carbonates are at a high level of sophistication the study of shales has clearly lagged behind in the mid proterozoic newland formation six major shale facies types deposited in nearshore to basinal environments are distinguished on the basis of bedding characteristics textural features and the proportions of silt clay and carbonate textural features of these shale types are related to sedimentary environments as deduced from associated lithologies the shales are undisturbed by bioturbation and their textural and sedimentary characteristics reflect subaqueous growth of microbial mats erosion and deposition by storms deposition of flocculated vs dispersed clays continuous slow background sedimentation winnowing by waves or currents and subaerial exposure

residence time indicators in groundwater the east midlands triassic sandstone aquifer the east midlands triassic sherwood sandstone aquifer which has been the subject of detailed radiometric age studies is used to investigate both inert and reactive constituents of groundwater as indicators of residence time detailed resampling of the aquifer in 1992 has provided a considerable body of new inorganic geochemistry data though without radiocarbon several inert indicators are defined including the isotopic ratios 18o 2h 36cl noble gas ratios as well as the halogen elements cl br f i and their element ratios these form a group of essentially unreactive tracers primarily reflecting changing rainfall inputs and palaeoclimatic conditions except at outcrop where human impacts are also seen clearly the concentrations of cl mainly from atmospheric sources remain below 25 mg l 1 cl over a distance of some 30 km from outcrop reactive indicators the result of time dependent water rock interactions include 13c mg ca sr ca na cl and show diagnostic trends along the flow lines however the concentrations of certain trace elements li rb cs mn and mo which are not limited by solubility constraints show linear trends along the present day flow gradient this water rock interaction is taking place in groundwaters with low total mineralisation and it can be demonstrated that reactions involving these elements and isotopes are occurring entirely within the aquifer since high salinity groundwaters are found below the sherwood sandstone there is good correlation between some of the elements and 14c activities in the 1977 data set and this has been used to derive a concentration age relationship for the 1992 set of data a chemical timescale for the aquifer is then established using a li and b a combination of five trace elements the age of the fresh groundwater is thus shown to be up to 100 ka bp indicating the likelihood of semi continuous recharge during the devensian glacial period preceding the glacial maximum when no recharge occurred 10 20 ka bp this approach may be of value in extending groundwater dating beyond the radiocarbon timescale as well as interpreting sites where no radiocarbon data are available the scatter from the mean age line indicates those groundwaters which are derived from either rapid or slower than average flow zones within the aquifer as well as age stratification this stratification is borne out by a depth profile of groundwater from a new borehole near to outcrop which is shown by a combination of chemical and isotopic tracers to contain holocene overlying late pleistocene water

pyritic shales and microbial mats significant factors in the genesis of stratiform pb zn deposits of the proterozoic extensive horizons of pyritic shale occur in mid proterozoic sediments of the eastern belt basin montana u s a these pyritic shales are of striped appearance laminated pyrite beds alternate with nonpyritic shale beds laminated pyrite beds have wavycrinkly internal laminae and are interpreted as mineralized microbial mats pyrite is essentially the only sulfide mineral in these shales pyritic shale horizons occur along the basin margins and it is feasible that colloidal iron was introduced by rivers into basin marginal lagoons and then incorporated into microbial mats and reduced to pyrite the pyritic shales in the newland formation show great similarity to those that host the pb zn deposits of mt isa and mcarthur river it is suggested that pyritic shales of this kind are relatively common in mid proterozoic shales and that the processes that led to the occasional formation of pb zn ore bodies in these shales are not related to those that formed the pyritic shales themselves

comparative behavior of authigenic re u and mo during reoxidation and subsequent long term burial in marine sediments the trace element re is enriched in mildly reducing suboxic sediments close to or slightly later in the redox sequence than u and before reduction of mo in more reducing sulfidic sediments this work investigates the behavior of authigenic re during oxidation and long term burial in the sediments of several turbidites from the madeira abyssal plain exposure to bottom water o2 clearly remobilizes authigenic re as found in previous work but reimmobilization occurs in reducing sediments below the oxidation front over a depth range of 0 5 3 m the large spread of the re burndown peak must be kinetically controlled perhaps influenced by the corg content once reimmobilized however the authigenic re signal remains immobile for at least 3 4 myr authigenic u in contrast consistently forms peaks 0 5 m broad whereas authigenic mo is lost on oxidation and does not appear to be refixed unless authigenic pyrite is formed these results imply that any paleoenvironmental significance of authigenic re will be compromised in low sedimentation rate environments 10 cm kyr where there is significant exposure of authigenic re to bottom water o2 however authigenic re records from rapidly accumulating continental margin sediments with much less exposure to bottom water o2 still offer considerable potential as high fidelity recorders of past reducing conditions

source transport and fate of rhenium selenium molybdenum arsenic and copper in groundwater associated with porphyry cu deposits atacama desert chile we collected groundwaters in and around a large 313 mt at 1 08 cu and 0 3 cutoff undisturbed porphyry copper deposit spence in the hyperarid atacama desert of northern chile which is buried beneath 30 180 m of miocene piedmont gravels groundwaters within and down flow of the spence deposit have elevated se up to 800 g l re up to 31 g l mo up to 475 g l and as up to 278 g l concentrations compared to up flow waters interpreted to represent regional groundwater flow in contrast cu is only elevated up to 2036 g l in groundwaters recovered from within the deposit cu concentrations are low down gradient of the deposit the differential behavior of the metals metalloids occurs because the former group dissolves as anions enhancing their mobility whereas the base metals dissolve as cations and are lost from solution most likely through adsorption to clay surface exchange sites and through formation of secondary copper chlorides carbonates and oxides most groundwaters within and down flow of the deposit have eh ph values around the feii feiii phase boundary limiting the impact of fe oxyhydroxides on oxyanions mobility se re mo and as are all mobile with filtered unfiltered samples 1 to the limit of sampling 2 km down gradient from the deposit the increase in ore related metals metalloids and sulfate and decrease in sulfate s isotope ratios from values similar to regional salars 4 to 8 34scdt to lower values closer to hypogene sulfides 1 to 4 34scdt is consistent with active water rock reactions between saline groundwaters and the spence deposit it is likely that hypogene and or supergene sulfides are being oxidized under the present groundwater conditions and mineral saturation calculations suggest that secondary copper minerals antlerite atacamite malachite may also be actively forming suggesting that supergene and exotic copper mineralization is possible even under the present hyperarid climate of the atacama desert

the origin and economic potential of sandstone hosted disseminated pb zn mineralization in pyritic shale horizons of the mid proterozoic newland formation montana usa pyritic shale horizons of the newland formation belt series mid proterozoic show striking similarities to proterozoic pyritic shales elsewhere that are host to major lead zinc deposits such as mt isa and mcarthur river however in contrast to these deposits the pyritic shales of the newland formation contain only minute quantities of lead and zinc elevated concentrations of lead and zinc are only found in pore spaces of intercalated sandstone beds petrographic and geochemical data indicate that pyritic shale deposition and elevated lead zinc concentrations in sandstone beds are unrelated that base metal mineralization is controlled by initial porosity and that iron and base metals were derived from different sources

distribution and mobility of geogenic molybdenum and arsenic in a limestone aquifer matrix abstract to investigate the potential of mo and as as possible geogenic contaminants three sediment cores were examined to evaluate their mineralogical association distribution and mobility the cores were described and analyzed for total organic carbon toc ca mg si al p sr as mo fe and s content except in the uppermost segment limestone was the main lithology with the occasional presence of dolomite and clay that change in lithology was also observed in the bulk chemical composition where ca mg and sr concentrations increased with depth while si al and p concentrations decreased with depth minor minerals included pyrite fes 2 powellite camoo 4 and ferrihydrite the minimum maximum median and standard deviations for all analyzed elements including as and mo were comparable for all three cores molybdenum and as however varied significantly with depth and median as and mo values were above their respective crustal averages of approximately 1 1 mg kg and 1 5 mg kg the median values for as were 1 9 mg kg in core dep 1 3 3 mg kg in dep 2 and 1 mg kg in dep 5 the median values for mo were 2 3 mg kg in core dep 1 2 5 mg kg in dep 2 and 2 5 mg kg in dep 5 maximum concentrations for as were 101 9 mg kg 47 5 mg kg and 56 2 mg kg in cores dep 1 dep 2 and dep 5 respectively maximum concentrations for mo were 880 mg kg 123 mg kg and 225 mg kg in cores dep 1 dep 2 and dep 5 respectively electron microprobe analyses of individual minerals revealed variable concentrations of as ranging from approximately 300 to 9000 mg kg in pyrite and up to 17 600 mg kg in powellite camoo 4 the mo concentration in pyrite was consistently below the detection limit of approximately 100 mg kg in powellite the mo concentration was up to 42 wt a subset of 10 samples from different stratigraphic sections and with different as and mo concentrations was further investigated to assess as and mo mobility under changing physicochemical conditions leaching the aquifer matrix with a 1 m naoac solution at a ph of 8 1 removed more than 70 mo in 8 of the 10 samples the maximum value was 97 in contrast to mo as was mobilized to a lesser degree in 8 of the samples less than 30 were removed and the maximum was only 50 molybdenum which seemed to be loosely bound to mineral and organic matter surfaces thus could easily be removed from the aquifer matrix while as on the other hand should be much less mobile because it occurred either tightly adsorbed by hydrous ferric oxide or as an impurity in pyrite thus it is advisable to include mo in the analytical program whenever elevated as concentrations are encountered in groundwater

hydrochemical effects of saltwater intrusion in a limestone and dolomitic limestone aquifer in lebanon this study demonstrates groundwater quality differences between a limestone and a dolomitic limestone sub oxic coastal aquifer in the eastern mediterranean lebanon with and without ongoing moderate salinization since the last decades for this purpose 8 major and 50 trace elements tes were analyzed in 80 water and 65 rock samples and interpreted with a quad fold approach utilizing 1 nonparametric statistical tests 2 concentration deviations from ideal conservative freshwater seawater mixing lines 3 a new parameter called mixing enrichment factor to assess the mobility of chemical constituents under salinizing conditions and 4 1 d dual porosity flow path modeling with phreeqc dissolution precipitation of caxmgysrzco3 and cation exchange were the main disclosed hydrogeochemical processes besides minor signs of organic matter oxidation in the dolomitic limestone aquifer less carbonate dissolved as compared to the limestone aquifer partly because of lower pco2 in addition to seawater inflow triggering mg calcite precipitation by cation exchange saltwater intrusion led to mobilization of as ba cu ni rb sr and u in both aquifers sometimes likely by cation exchange e g ba and sr some of these tes notably cu and ni recorded higher concentrations in the dolomitic limestone regardless of salinization other elements like al be ce cr nb pb v y and zr revealed no or a low mobilization tendency the concentration of all tes in groundwater remained below drinking water limits notwithstanding moderate salinization this classifies carbonate rocks as a weak geogenic source of tes whereas encroaching seawater appears to be a more important source

twin lake tracer tests longitudinal dispersion two natural gradient dispersion tests were conducted at the chalk river nuclear laboratories ontario in 1982 and 1983 in order to quantify field scale dispersion processes over a 20 and 40 m distance of a radiotracer migration the patterns of dispersion that were observed in the field using a dry access tube monitoring technique were compared with patterns predicted by the advection dispersion model with constant parameters analysis of the time concentration profiles of the tracer at observation wells located along the mean direction of the longitudinal spreading showed that the dispersion model adequately describes the dispersion patterns actually observed and averaged over the aquifer depth the values of longitudinal dispersivity determined from continuous time concentration profiles were virtually equal to those obtained from laboratory scale columns the dispersive properties of the aquifer were characterized at the local scale by a constant independent of travel distance dispersivity value of 0 0045 m averaging the test data over the aquifer depth analogous to the information provided by a fully penetrating pumping well yielded a full aquifer dispersivity varying in an irregular fashion from 0 16 to 0 06 m the scale effect observed between local scale and full aquifer dispersivities is the result of inhomogeneity of the aquifer and the concentration averaging produced by the sampling instrumentation the results of two tracer tests also showed that the use of the dry access tube monitoring technique for field experimentation provides detailed representation of spatial and temporal distribution of a radiotracer s activity and consequently provides a practical means to determine the groundwater velocity field and dispersive properties of porous materials

banded iron formations through much of precambrian time similarities between proterozoic 1 8 2 5 gyr and archean 2 5 gyr banded iron formations are probably more significant than their differences the contrasts largely reflect differences in the tectonic settings of proterozoic and archean terrains archean banded iron formations are not as thick nor laterally as extensive as the major proterozoic iron formations nevertheless some archean iron formations have strike lengths of over 150 200 km and may have been quite extensive prior to the deformation that has affected most archean terrains stratigraphic sequences in which iron formations occur are highly variable and indicate that iron formations formed in many depositional environments sedimentary textures in the iron formations are dominated either by granules and oolites or laminations including microbanding reflecting differences in their physical conditions of deposition granular and oolitic textures are abundant in only three proterozoic depositional basins and most precambrian iron forma

century long record of mo isotopic composition in sediments of a seasonally anoxic estuary chesapeake bay abstract a double spike method was used to obtain mo isotope data for sediments and waters of the seasonally anoxic chesapeake bay and its primary tributary the susquehanna river the dissolved mo distribution in the estuary is non conservative reflecting minor mo loss to the sediments although removal of mo to the sediments does not have a large influence on the isotopic composition of the water column the 98mo of dissolved mo in most of the estuary is dominated by seawater six samples with salinity 15 have an average 98mo 2 17 0 12 which agrees well with a 98mo value for the cass 4 seawater standard of 2 23 a single sample of susquehanna river water has a 98mo of 1 02 consistent with recent findings of positive 98mo in rivers worldwide susquehanna river sediments in contrast have 98mo 0 1 the difference between the river water and sediment values implies that isotopic fractionation occurs within the river basin the 98mo values for estuarine sediments are offset from values in the overlying water most samples deposited before 1925 have 98mo less than 0 similar to the susquehanna sediments subsequently there is an increase in the variability of 98mo with values ranging up to 0 8 the transition to increased variability coincides with the onset of authigenic mo deposition which was previously attributed to escalating summertime anoxia authigenic mo concentrations correlate poorly with 98mo in core samples suggesting that independent mechanisms influence the two parameters authigenic mo concentrations may be controlled by shifting pore water h2s levels while 98mo may be primarily affected by annual variations in mn refluxing

hydrogeochemistry of arsenic and other inorganic constituents in groundwaters from la pampa argentina groundwaters from quaternary loess aquifers in northern la pampa province of central argentina have significant quality problems due to high concentrations of potentially harmful elements such as as f no3 n b mo se and u and high salinity the extent of the problems is not well defined but is believed to cover large parts of the argentine chaco pampean plain over an area of perhaps 106 km2 groundwaters from la pampa have a very large range of chemical compositions and spatial variability is considerable over distances of a few km dissolved as spans over 4 orders of magnitude 4 5300 g l 1 and concentrations of f have a range of 0 03 29 mg l 1 b of 0 5 14 mg l l v of 0 02 5 4 mg l 1 no3 n of 0 2 140 mg l 1 mo of 2 7 990 g l 1 and u of 6 2 250 g l 1 of the groundwaters investigated 95 exceed 10 g as l 1 the who guideline value and 73 exceed 50 g as l 1 the argentine national standard in addition 83 exceed the who guideline value for f 1 5 mg l 1 99 for b 0 5 mg l 1 47 for no3 n 11 3 mg l 1 39 for mo 70 g l 1 32 for se 10 g l 1 and 100 for u 2 g l 1 total dissolved solids range between 730 and 11400 mg l 1 the high values resulting mainly from evaporation under ambient semi arid climatic conditions the groundwaters are universally oxidising with high dissolved o2 concentrations groundwater phs are neutral to alkaline 7 0 8 7 arsenic is present in solution predominantly as as v groundwater as correlates positively with ph alkalinity hco3 f and v weaker correlations are also observed with b mo u and be desorption of these elements from metal oxides especially fe and mn oxides under the high ph conditions is considered an important control on their mobilisation mutual competition between these elements for sorption sites on oxide minerals may also have enhanced their mobility weathering of primary silicate minerals and accessory minerals such as apatite in the loess and incorporated volcanic ash may also have contributed a proportion of the dissolved as and other trace elements concentrations of as and other anions and oxyanions appear to be particularly high in groundwaters close to low lying depressions which act as localised groundwater discharge zones concentrations up to 7500 g l 1 were found in saturated zone porewaters extracted from a cored borehole adjacent to one such depression concentrations are also relatively high where groundwater is abstracted from close to the water table presumably because this zone is a location of more active weathering reactions the development of groundwaters with high ph and alkalinity results from silicate and carbonate reactions facilitated by the arid climatic conditions these factors together with the young age of the loess sediments and slow groundwater flow have enabled the accumulation of the high concentrations of as and other elements in solution without significant opportunity for flushing of the aquifer to enable their removal

redistribution of rare earth elements during diagenesis of carbonate rocks from the mid proterozoic newland formation montana u s a abstract ree data for carbonate rocks from the mid proterozoic newland formation belt supergroup show variable degrees of relative ree enrichment when normalized to a composite shale of the newland formation most conspicuous are relative enrichments in lree s and positive eu anomalies possible coprecipitation of ree s in carbonates from seawater is much too small to account for the ree enrichment thus only diagenetic ree enrichment has to be considered by far the strongest lree enrichment is observed in carbonates with interbedded shales during diagenesis ree apparently moved from the shale partings to the adjacent limestone beds massive limestone units have considerably smaller ree enrichments except in proximity to shales suggesting that ree addition from formation waters is less efficient for supplying ree s than is local redistribution between shale and limestone beds early precipitation of diagenetic silica in pore spaces reduces ree enrichment in limestone beds by reducing their permeability dolostones are cemented by pervasive early diagenetic silica and lack significant ree enrichment except for eu probably because silica cement prohibited access of ree bearing pore waters positive eu anomalies indicate reduction of eu to the divalent state during diagenesis and relatively large mobility of divalent eu

large scale dispersion experiments in a sandy aquifer in denmark observed tracer movements and numerical analyses a large scale natural gradient dispersion experiment was carried out in a sandy aquifer in the western part of denmark using tritium and chloride as tracers for both plumes a marked spreading was observed in the longitudinal direction while the spreading in the transverse horizontal and transverse vertical directions was very small the horizontal transport parameters of the advection dispersion equation were investigated by applying an optimization model to observed breakthrough curves of tritium representing depth averaged concentrations no clear trend in dispersion parameters with travel distance for distances between 50 and 200 m could be found suggesting that the asymptotic stage was reached within a short distance from the point of injection a three dimensional numerical model for flow and transport was applied to the aquifer in order to quantify the dispersivity parameters more closely the following best fit dispersivity parameters were identified longitudinal horizontal 0 45 m transverse horizontal 0 001 m and transverse vertical 0 0005 m

determination of molybdenum isotope fractionation by double spike multicollector inductively coupled plasma mass spectrometry 1 molybdenum isotopic compositions are precisely determined by mc icp ms measurements using a mo double spike the double spike is added prior to chemical purification so that laboratory and instrumental mass fractionations are separated from natural mass dependent fractionation fractionation is determined on four mo mass ratios providing an internal consistency check the external standard reproducibility is at 0 06 per mil on the 98mo 95mo ratio 2 standard deviation using a normal microconcentric nebuliser with a cyclonic spray chamber the minimum quantity of mo is 1 g for high precision results a hydrothermal molybdenite shows fractionation of 0 3 per mil on the 98mo 95mo ratio relative to our standard johnson matthey 1000 g ml 0 3 icp standard solution lot 602332b fine grained sediments show fractionation of 0 1 and 0 3 per mil on the 98mo 95mo ratio the observed mo isotope fractionation is small but resolvable with the presented high resolution technique

environmental geochemistry 40years research at imperial college london uk abstract this paper reviews the development of multi purpose geochemical mapping and the progress of research in applied environmental geochemistry and health at imperial college over the past 40 years with funding from the research councils uk government eu industry and ngos research has provided the basis for postgraduate training in areas ranging from the applications of geochemistry to plant agricultural livestock and wildlife nutrition to evaluating contamination from metalliferous mining and smelting understanding the chemical nature of the urban environment and relationships between geochemistry and human health and disease examples include 1 the influence of mo in marine black shales on the cu nutrition of grazing cattle and sheep 2 the importance of soil ingestion on trace element intake and metabolism and metal exposure in farm livestock 3 the impacts of soil contamination from historical metalliferous mining and smelting on agriculture and human exposure to metals including potential health problems from cd at shipham and from as in sw england 4 the growth of urban geochemistry and the importance of pb in the urban environment 5 the health impacts due to hg losses from the informal sector au mining in brazil and 6 health issues relating to f excess and se deficiency in china

the molybdenum isotopic composition in river water constraints from small catchments we report molybdenum isotope compositions and concentrations in water samples from a variety of river catchment profiles in order to investigate the influence of anthropogenic contamination catchment geology within river precipitation and seasonal river flow variations on riverine molybdenum our results show that the observed variations in 98 95mo from 0 to 1 9 are primarily controlled by catchment lithology particularly by weathering of sulfates and sulfides erosion in catchments dominated by wet based glaciers leads to very high dissolved molybdenum concentrations in contrast anthropogenic inputs affect neither the concentration nor the isotopic composition of dissolved molybdenum in the rivers studied here seasonal variations are also quite muted the finding that catchment geology exerts the primary control on the delivery of molybdenum to seawater indicates that the flux and isotope composition of molybdenum to seawater has likely varied in the geologic past

is unique scaling of aquifer macrodispersivity supported by field data spreading of conservative solutes in groundwater due to aquifer heterogeneity is quantified by the macrodispersivity which was found to be scale dependent it increases with travel distance stabilizing eventually at a constant value however the question of its asymptotic behavior at very large scale is still a matter of debate it was surmised in the literature that macrodispersivity scales up following a unique scaling law attempts to define such a law were made by fitting a regression line in the log log representation of an ensemble of macrodispersivities from multiple experiments the functional relationships differ among the authors based on the choice of data our study revisits the data basis used for inferring unique scaling through a detailed analysis of literature marcodispersivities in addition values were collected from the most recent tracer tests reported in the literature we specified a system of criteria for reliability and reevaluated the reliability of the reported values the final collection of reliable estimates of macrodispersivity does not support a unique scaling law relationship on the contrary our results indicate that the field data can be explained as a collection of macrodispersivities of aquifers with varying degree of heterogeneity where each exhibits its own constant asymptotic value our investigation concludes that transport and particularly the macrodispersivity is formation specific and that modeling of transport cannot be relegated to a unique scaling law instead transport requires characterization of aquifer properties e g spatial distribution of hydraulic conductivity and the use of adequate models

trace element patterns in dutch coastal dunes after 50 years of artificial recharge with rhine river water trace elements tes are important in water quality monitoring of managed aquifer recharge mar systems because they need to be tested against maximum permissible concentrations mpcs and some can be used as a tracer of either infiltration water pollution or geochemical processes the behavior of 55 dissolved trace elements and 20 major constituents is shown for an 800 m long 35 m deep transect with slow groundwater flow 0 01 0 1 m day and a nearby 100 m long 20 m deep transect with fast groundwater flow 0 3 2 m day both between a recharge and recovery canal in the coastal dune aquifer system of the netherlands this study demonstrates how tes behaved in a ph 7 8 artificial recharge system in coastal sediments where pretreated rhine river water has been infiltrated in the period 1957 2007 the spatial and age distribution of the infiltrated rhine water was mapped using a combination of environmental tracers cl br 18o 3h cl and so4 allowing the comparison between young and old rhine water and between rhine and dune groundwater it is revealed which tes can be used in specific cases as additional tracers b f mo which tes showed clear redox dependent behavior as mo u or clear sorptive behavior b ba co cs cu f li mo ni rb sb sr u w which tes received significant geogenic inputs as sr u w which classical tes need much less monitoring compared to the 1970s and 1980s b ba be cd co ni hg pb zn and which tes can normally be neglected rare earth elements precious metals

unsaturated zone tritium and chlorine 36 profiles from southern australia their use as tracers of soil water movement in this paper we present seven unsaturated zone profiles of 36cl and three 3h profiles from southern australia all profiles show single peaks corresponding to high radionuclide fallout from nuclear testing in the 1950s and 1960s the profiles are used to estimate rates of water movement leading to recharge of the groundwater among these profiles is the first profile on which high concentrations of 36cl have been found below a 2 m depth in this profile 3h and 36cl peaks coincide in six of the seven profiles total 36cl fallout was found to be between 1 2 and 2 4 1012 atoms m 2 and is of similar magnitude to that found at similar latitudes in the northern hemisphere comparisons of soil water fluxes estimated with 3h 36cl and chloride are briefly discussed

a combined petrographical geochemical provenance study of the newland formation mid proterozoic of montana a provenance study was conducted on the mid proterozoic newland formation in which petrographical features of sandstones and geochemical characteristics of shales were integrated to arrive at an internally consistent interpretation sandstones of the newland formation are typically arkosic sands and arkoses with very well rounded quartz and feldspar grains and only minor amounts of extrabasinal rock fragments the predominant feldspar types are k spar and microcline feldspar grains are smaller than quartz grains and feldspars show little alteration due to weathering detrital modes of newland sandstones qfl diagrams indicate that they were derived from a stable cratonic source these petrographical features imply a source area dominated by granites and granitoid gneisses semi arid to arid climate tectonic quiescence and overall peneplain conditions shales of the newland formation are dominated by illite quartz silt and fine crystalline dolomite they have small la th rations relatively large hf contents and small contents of cr co and ni all indicative of derivation from crust of granitic composition small tio 2 al 2 o 3 ratios also suggest source rocks of granitic composition the average chemical index of alteration cia for newland shales is 71 8 which in light of the probable granitoid source indicates modest amounts of chemical weathering relatively large sio 2 contents and large k 2 o na 2 o ratios reflect derivation from stable cratonic areas and tectonic quiescence thus in general the petrography of sandstones and geochemistry of shales provides the same provenance clues for the newland formation one notable discrepancy between the two approaches is that the sandstones indicate an arid to semi arid climate with very minor chemical weathering whereas the cia of the shales indicates at least modest amounts of chemical weathering this indicates on one hand the need to better calibrate the cia with a large variety of muds from modern climatic settings and on the other hand the possibility that this discrepancy is due to transport segregation

release of selected chemical elements from shale drill cuttings to aqueous solutions of different ph abstract the effect of ph changes on leachability of light and heavy metals from shale drill cuttings generated from unconventional shale gas production was investigated cuttings being the primary byproduct generated from drilling operations belong to the potentially hazardous type of wastes due to presence of heavy and radioactive elements and remains of drilling fluid in this regard assessment of potentially dangerous components pdcs from rock waste materials was performed by application of batch leaching tests which has provided information on the sensitivity of leaching under externally imposed changes in ph natural or caused by treatment in specific scenarios the description of shale rocks mineralogical and chemical properties was performed by means of x ray fluorescence spectroscopy diffractometry as well as scintillation spectrometry the concentrations of released constituents due to the leaching tests were measured by atomic absorption spectrophotometry results were compared and discussed accordingly with the waste acceptable criteria of elution limits analysis of the substrate revealed that the elemental composition was dominated by light elements whereas heavy metals were present in trace amounts however noticeable release of barium 2 0 4 6 was also recorded which has originated from not only rock material but also drill mud minor mobility was observed for transition elements such as cr co fe mn ni zn cu and pb results revealed that drill cuttings follow the requirements for other than hazardous and municipal type of deposition with exception for barium moreover content of radioactive isotopes fulfill the requirements range of acceptable concentrations

groundwater age distributions at a public drinking water supply well field derived from multiple age tracers 85kr 3h 3he and 39ar 1 groundwater age is a key aspect of production well vulnerability public drinking water supply wells typically have long screens and are expected to produce a mixture of groundwater ages the groundwater age distributions of seven production wells of the holten well field netherlands were estimated from tritium helium 3h 3he krypton 85 85kr and argon 39 39ar using a new application of a discrete age distribution model and existing mathematical models by minimizing the uncertainty weighted squared differences of modeled and measured tracer concentrations the observed tracer concentrations fitted well to a 4 bin discrete age distribution model or a dispersion model with a fraction of old groundwater our results show that more than 75 of the water pumped by four shallow production wells has a groundwater age of less than 20 years and these wells are very vulnerable to recent surface contamination more than 50 of the water pumped by three deep production wells is older than 60 years 3h 3he samples from short screened monitoring wells surrounding the well field constrained the age stratification in the aquifer the discrepancy between the age stratification with depth and the groundwater age distribution of the production wells showed that the well field preferentially pumps from the shallow part of the aquifer the discrete groundwater age distribution model appears to be a suitable approach in settings where the shape of the age distribution cannot be assumed to follow a simple mathematical model such as a production well field where wells compete for capture area

rhenium in the black sea comparison with molybdenum and uranium rhenium concentrations were measured in the black sea to determine the behavior of this redox sensitive element in an anoxic basin under reducing conditions re is removed from solution leading to its depletion from black sea deep waters compared with uranium water column re and mo profiles show evidence of removal from mid depths suggesting that these elements are scavenged either in the water column or slope sediments to a greater degree than u black sea surface waters are enriched in re reflecting re in rivers draining into the northern black sea that are enhanced up to 80 fold over other large world rivers this enrichment is most likely anthropogenic and may be due to coal burning in the region a simple two box model is used to demonstrate that re concentrations in the black sea are not in steady state with respect to current riverine inputs and authigenic fluxes riverine inputs of u and mo are not as significant perhaps reflecting the fractionation of re from the other elements during a high temperature combustion process re2o7 is volatile above 270 c

molybdenum isotope fractionation during adsorption by manganese oxides the isotopic composition of mo 97 95mo in seawater is 2 heavier than mo in marine ferromanganese crusts and nodules barling et al earth planet sci lett 193 2001 447 457 siebert et al earth planet sci lett 211 2003 159 171 to explore this phenomenon we have conducted an experimental investigation into the mass dependent fractionation of mo isotopes during adsorption onto mn oxyhydroxide two series of experiments were carried out a time series in which adsorption proceeded for 2 96 h and a ph series in which ph varied from 6 5 to 8 5 the extent of mo adsorption by mn oxyhydroxides decreases with increasing ph a trend typical of anion adsorption and takes 48 h to reach steady state lighter mo isotopes are preferentially adsorbed experimentally determined fractionation factors soln mnox exhibit no systematic variation with either time or experimental ph the mean soln mnox for all experiments is 1 0018 0 0005 2 s d comparison of the mo isotopic data for experimental solutions and mo adsorbed to mn oxyhydroxide with predictions for closed system equilibrium and rayleigh fractionation models indicates that isotope fractionation occurs as a result of closed system equilibrium exchange between dissolved and adsorbed mo the isotopic offset between dissolved and adsorbed mo is comparable to that observed between mo in seawater and mo in ferromanganese nodules and crusts it is therefore likely that adsorption of mo to mn oxyhydroxides is a significant factor in the fractionation of mo isotopes in the oceans

anomalous iron distribution in shales as a manifestation of non clastic iron supply to sedimentary basins relevance for pyritic shales base metal mineralization and oolitic ironstone deposits in previous investigations nearshore pyritic shale horizons in the mid proterozoic newland formation were interpreted to be due to non clastic colloidal iron supply by streams new data on the chemical composition of shales in the newland formation support this interpretation in these shales fe and al show a positively correlated trend that intercepts the fe axis above the origin these relationships suggest control of fe by clays via iron oxide coatings on clay minerals and the presence of an additional non clastic iron component shales from stratigraphic intervals during which pyritic shale horizons were deposited plot above the fe al trend typical for the remainder of the newland formation

transport and degradation of chlorofluorocarbons cfcs in the pyritic rabis creek aquifer denmark 1 vertical profiles of the chlorofluorocarbons cfc 11 cfc 12 and cfc 113 penetrating aerobic and anaerobic parts of a shallow sandy aquifer show that the cfc gases are degraded in the 1 m thick transition zone from aerobic to anaerobic groundwater in a pyritic sand aquifer at rabis creek denmark two dimensional solute transport simulations with either zero order or first order degradation in the anaerobic zone corroborate this interpretation the transport model was previously calibrated against detailed tritium profiles in the same wells first order degradation is found to best match the observed cfc profiles yielding an approximate half life of a few months for cfc 11 degradation is not as clearly recognized for cfc 12 and cfc 113 but it may occur with rates corresponding to a half life of a few years or more data indicate a geochemical control of the cfc concentration gradient at the redox front and that denitrification and denitrifiers are not of major importance for the observed cfc degradation the responsible mechanism behind the observed degradation is not known but we suggest that reductive dehalogenation by surface bound fe ii on pyrite possibly enhanced by the presence of fe iii bearing weathering products green rust may be a plausible mechanism the observed data and the performed simulations confirm the potential application of the cfc gases as age dating tools in the aerobic part of the investigated aquifer but also that cfc data must be analyzed carefully before it is used as a dating tool in reducing aquifers because degradation may have occurred the use of multiple or alternative tracers should be considered in anaerobic environments

trace element geochemistry and sedimentary provinces a study from the tasman geosyncline australia abstract the abundances of la th u and hf have been determined in flysch sequences of the tasman geosyncline australia the arc derived graywackes differ from those of rifted continental margins and marginal basins in containing low abundances of la th u and hf la 9 2 1 7 ppm th 1 4 0 6 ppm u 0 52 0 2 ppm hf 2 1 0 6 ppm reflecting similar low abundances in the andesitic source rocks graywackes of rifted continental margins and marginal basins in contrast are mature and characterised by high abundances of la th u and hf la 39 9 9 ppm th 16 0 6 ppm u 3 40 0 5 ppm hf 7 9 ppm mirroring increased abundances in the granitic and sedimentary source rocks sedimentary rocks deposited in inter arc basins show wide dispersion but have characteristics intermediate between these two types the th u ratio for magmatic arc sediments is 2 7 for most other sedimentary rocks it remains uniform at 4 5 0 3 for sediments having andesitic and dacitic rocks as provenance the la th ratios are 6 7 and 4 5 respectively this ratio remains constant at 2 6 for most quartzose sedimentary rocks

field study of dispersion in a heterogeneous aquifer 1 overview and site description results are presented for a large scale natural gradient tracer experiment conducted in a heterogeneous alluvial aquifer at a site near columbus mississippi the study was initiated with a 48 hour pulse injection of 10 m3 of groundwater containing bromide and three organic tracers pentaflourobenzoic acid o trifluoromethylbenzoic acid and 2 6 diflourobenzoic acid over a 20 month period seven comprehensive samplings of the tracer plume were performed at approximately 1 to 4 month intervals using an extensive three dimensional sampling well network the dominant feature of the tracer plume that evolved during the study was the highly asymmetric concentration distribution in the longitudinal direction this asymmetry was produced by accelerating groundwater flow along the plume travel path that in turn resulted from an approximate 2 order of magnitude increase in the mean hydraulic conductivity between the near field and far field regions of the site the columbus study is distinct from previous natural gradient experiments because of the extreme heterogeneity of the aquifer the large scale spatial variations in groundwater velocity and the extensive set of hydraulic conductivity measurements for the aquifer

stratigraphic control of rare earth pattern types in mid proterozoic sediments of the belt supergroup montana u s a implications for basin analysis abstract within sediments of the helena embayment an eastern extension of the mid proterozoic belt basin montana u s a three different types of ree patterns were identified the lower part of the investigated sequence chamberlain shale and lower newland formation is a uniform shale interval which accumulated during a period of tectonic quiescence the ree patterns of these shales normalized to nasc are either flat or lree enriched lacking eu deficiencies the superjacent unit newland transition zone contains variable amounts of feldspathic sandstone it indicates rejuvenation of the hinterland and regression the uppermost unit upper newland formation consists of alternating packages of carbonates and shales ree patterns in shales of the newland transition zone and upper newland formation have negative eu anomalies this drastic change of ree patterns was observed in all stratigraphic sections the source rocks of the beltian sequence were probably dominated by granitoid gneisses and migmatites and rocks of this composition show negative eu anomalies against nasc in many other places the observed negative eu anomalies in the shales were probably inherited from the source rocks however the patterns of the chamberlain shale and the lower newland formation are not as easy to explain because the source rocks seem not to have changed during deposition of the beltian sequence perhaps more intense chemical weathering during chamberlain shale lower newland time obscured the negative eu anomalies in the residual clays adsorption of lree s on clays during transport may have caused the lree enriched patterns a change in tectonic regime and weathering intensity coincides with the stratigraphic distribution of the different ree pattern types thus stratigraphically controlled ree pattern distribution in a sedimentary basin may help to establish quasi time lines and may allow monitoring of tectonic pulses and of weathering conditions in the hinterland

hydrochemical evolution of the east midlands triassic sandstone aquifer england a detailed hydrogeochemical interpretation has been made of the red bed sherwood sandstone triassic aquifer of the east midlands of england on which a radiocarbon model has been used to establish a chronology of groundwaters along the flow line groundwater evolution is dominated by carbonate and sulphate mineral solution and precipitation and by redox reactions cation exchange reactions are negligible and the hydrogeochemistry has evolved in the absence of residual saline water three distinct zones are recognised 1 i recent groundwater mainly 100 y oxidising dominated by congruent dissolution of dolomite and by inputs from atmospheric and anthropogenic sources 2 ii groundwater age 103 104 y predominantly reducing dominated by incongruent dissolution of dolomite 3 iii groundwater age 104 y reducing conditions approach to isotopic and chemical equilibrium in the carbonate system dominance of gypsum dissolution the minor and trace element variation can be interpreted in relation to the principal geochemical reactions and recharge history na cl f and b are controlled by atmospheric inputs sr2 and mn2 trends can be explained by carbonate and sulphate mineral dissolution ba2 is derived from carbonates but controlled by barite equilibrium fe so42 no3 and u are strongly influenced by redox reactions the concentrations of transition metals and other elements remain very low only li and k are considered to represent additions by reaction of silicate minerals the extent of direct anthropogenic influence is probably limited to enhanced so4 no32 and possibly cu zn and pb in zone i

ultimate removal mechanisms of elements from the ocean abstract the surface complex formation model can adequately explain the observed partitioning of most of the elements between seawater and pelagic clays and between river water and river suspended particles the adsorption of elements on the hydrous oxide surface of iron oxide manganese oxide and clay minerals is the most important ultimate removal mechanism of most of the elements from the ocean

occurrence of molybdenum in british surface water and groundwater distributions controls and implications for water supply data for mo in british surface water and groundwater collated from a number of databases show that concentrations are in most cases low of the order of 2 g l or less however variability is large and sporadic high values are found in both streamwaters and groundwaters data for some 11 600 british streamwater samples indicate a 10 90th percentile range of 0 08 2 44 g l with a median of 0 57 g l and maximum observation of 230 g l high values tend to be from streams on clay rich formations and sulphide mineralised bedrock and streams affected by localised urban and industrial contamination monitored lowland river waters also typically have median concentrations 1 g l although higher values are present in a number of urban industrialised english rivers highest observed concentrations median 20 g l occur under low flow conditions in a river system from an urban industrial area of ne england and are likely the products of industrial contamination and mine drainage concentrations in 96 upland lakewater samples from nw england are universally 0 1 g l or less data for 1735 groundwater samples from across britain have a 10 90th percentile range for mo of 0 035 1 80 g l with a median of 0 20 g l and maximum observation of 89 g l relatively high values derive from some lower cretaceous greensand carboniferous limestone and mudstone coal measures aquifers particularly under anaerobic conditions release from fe oxides and possibly mn oxides by reductive dissolution is a likely mechanism for the concentrations under more rarely observed sulphate reducing conditions in british aquifers concentrations of mo diminish likely due to sequestration by precipitating sulphide minerals the observed ranges in aqueous samples indicate that most water sources in britain have mo concentrations more than an order of magnitude below the who health based value for mo in drinking water 70 g l such sources are unlikely to pose a risk to drinking water from the current who guidance provided those impacted locally by mining or other industrial contamination are avoided

2000 years of sediment borne heavy metal storage in the yorkshire ouse basin ne england uk floodplain overbank sediments are often used to evaluate the influence of environmental change on sediment and chemical fluxes within river basins this paper presents the results of an investigation of heavy metal storage in seven floodplain reaches in the yorkshire ouse basin in north east england floodplain heavy metal storage has been greatest since c 1750 and many of the post 1750 sedimentary units exhibit heavy metal values that exceed recommended trigger and guideline values for contaminated land relatively high heavy metal storage occurs from ad 1250 1750 in most of the reaches these patterns are related to 2000 years of pb and zn mining in the yorkshire dales and c 250 300 years of industrial and urbanization activity around leeds and bradford and increased delivery of fine grained sediment during the last millennium possibly owing to factors such as population growth and agricultural expansion during the middle ages and climate change during the little ice age copyright 1999 john wiley sons ltd

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 sulfur isotope study of pyrite genesis the mid proterozoic newland formation belt supergroup montana abstract different generations of sedimentary pyrite from the mid proterozoic newland formation usa have been analysed for their sulfur isotopic compositions the results indicate bacterial sulfate reduction as the pyrite forming process the 34 s values for early diagenetic pyrite around 14 are in contrast to dominantly more positive values for many other middle proterozoic units a progressive reduction of sulfate availability during diagenesis can be recognized by an increase in 34 s content rayleigh distillation as well as through detailed petrographic observations contemporaneous seawater had a sulfur isotopic ratio between 14 and 18 as measured from sedimentary barite within the unit

large scale dispersion in a sandy aquifer simulation of subsurface transport of environmental tritium large scale dispersion in a sandy unconfined aquifer in denmark was studied by simulating subsurface transport of environmental tritium subsurface transport included transport in a moderately deep unsaturated zone and in a relatively long cross section of the aquifer the tritium data from the site enabled a four step modeling analysis comprising 1 estimation of tritium content in the infiltration water 2 transport in the unsaturated zone 3 estimation of flux averaged tritium concentration in the recharge water and 4 transport in the groundwater zone the groundwater model simulations were sensitive to the longitudinal and transverse dispersivity parameters l and r as a set of parameters but a model sensitivity analysis showed that it was not possible to identify a unique set of parameter values a likely range of variation for the two parameters could be identified l t 1 m 0 005 m 10 m 0 0 m the two parameters being interdependent in that an increase in l results in a decrease in t and vice versa the reported dispersivities represent a scale of 1000 m the approximate travel distance from the water table to the observation wells if the estimated l can be regarded as being of intermediate reliability following earlier defined criteria the range or the representative set of values then represent the largest scale of earlier reported values including our range of l in the set of reported dispersivities suggests that l does not increase indefinitely with scale