ion probe determinations of the rare earth concentrations of individual meteoritic phosphate grains abstract a new ion probe method for quantitative measurements of the concentrations of all the ree down to the ppm level in 5 20 m spots is presented the first application of the method is the determination of ree abundances in meteoritic phosphates results are shown to be in good agreement with previous inaa and ion probe determinations the merrillites in the st severin amphoterite are richer in ree than the apatites the enrichment factors for various ree range from 2 3 to 14 2 in contradiction with the results of ebihara and honda 1 provided good standards for other mineral phases are found or implanted marker ion techniques are used the method should find a wide range of applications for the study of both terrestrial and extraterrestrial crystals at the microscopic level

varves of the dead sea sedimentary record abstract the sedimentary record of the dead sea provides an exceptional high resolution archive of past climate changes in the drought sensitive eastern mediterranean levant a key region for the development of humankind at the boundary of global climate belts moreover it is the only deep hypersaline lake known to have deposited long sequences of finely laminated annually deposited sediments i e varves of varied compositions including aragonite gypsum halite and clastic sediments vast efforts have been made over the years to decipher the environmental information stored in these evaporitic clastic sequences spanning from the pleistocene lake amora to the holocene dead sea a general characterisation of sediment facies has been derived from exposed sediment sections as well as from shallow and deep water sediment cores during high lake stands and episodes of positive water budget mostly during glacial times alternating aragonite and detritus laminae aad facies were accumulated whereas during low lake stands and droughts prevailing during interglacials laminated detritus ld facies and laminated halite lh facies dominate the sequence in this paper we i review the three types of laminated sediments of the dead sea sedimentary record aad ld and lh facies ii discuss their modes of formation deposition and accumulation and their interpretation as varves and iii illustrate how dead sea varves are utilized for palaeoclimate reconstructions and for establishing floating chronologies

first measurements of neutral wind and turbulence in the mesosphere and lower thermosphere over taiwan with a chemical release experiment 1 neutral winds and turbulence structure in the mesosphere and lower thermosphere were measured with a sounding rocket chemical release experiment carried out in taiwan trimethyl aluminum tma was used as a tracer of the drift of the background atmosphere the results show that the measured neutral wind had a maximum speed of 154 m s at a height around 105 km the wind vectors were found to rotate clockwise with height in the altitude range from about 98 to 121 km on the basis of the hodograph analysis of the measured neutral wind vectors an upward propagating inertio gravity wave with intrinsic period of 11 2 hours and vertical wavelength of 19 5 km was believed to be primarily responsible for the height variations of the neutral wind and the richardson number large vertical wind shears were observed near 100 km and 106 km turbulent structures were observed in much of the trail below 110 km but there were enhanced structures in the altitude range between the two large shears i e at and near the altitude of the maximum wind speed comparing the positions of the turbulent features with expected atmospheric stability zones induced by an upward propagating gravity wave indicates that the turbulence structures were primarily located within the wave induced convectively unstable zone the structures are therefore interpreted as counterrotating vortices within the convective instability zone of a breaking gravity wave moreover the relation between the horizontal separations l about 1 8 km of the turbulent structures and the vertical extent h about 0 7 and 1 5 km of the wind shear zones with richardson numbers less than 0 25 did not conform to the predicted l h ratio of a factor of approximately 8 predicted by simple linear kelvin helmholtz instability theory for the primary billow structures associated with the instability these results suggest that the observed structures were not the primary billows but were more likely associated with a secondary instability such as the counterrotating vortices that develop later in the evolution of the instability in general the observations reported here support the interpretation that the turbulence evident in the trail was very likely generated in the convectively unstable zone induced by the inertio gravity wave propagating through the region with large temperature gradients 32 k km produced by wave breaking processes

high resolution sims analysis of common lead an evaluation of the sims technique for precise analysis of common lead in natural materials has been undertaken the instrument used is a new generation of high resolution high transmission ion probe the isolab 120 two glass standards nbs 610 and waterford have been characterised for their pb isotope composition by tims repeated sims analyses of these materials have failed to reveal any resolvable mass discrimination of pb isotopes the mass discrimination is shown to be 0 2 amu 1 in all cases comparison of sims pb analyses of natural ferromanganese samples with tims pb isotope analyses on adjacent portions are in good agreement and support the conclusion that mass discrimination is minimal the basic performance characteristics of the instrument operated at high mass resolving power are detailed in terms of transmission extraction efficiency pb ion yield from different materials and repeatability of measurements the precision and accuracy of common pb isotope ratio measurement by sims approaches that of tims to the point where application to palaeo oceanographic problems for example become entirely feasible

high spatial resolution u pb geochronology and pb isotope geochemistry of magnetite apatite ore from the pea ridge iron oxide apatite deposit st francois mountains southeast missouri usa the pea ridge iron oxide apatite ioa deposit is one of the major rhyolite hosted magnetite deposits of the st francois mountains terrane which is located within the mesoproterozoic 1 5 1 3 ga granite rhyolite province in the u s midcontinent precise and accurate determination of the timing and duration of oreforming processes in this deposit is crucial for understanding its origin and placing it within a deposit scale and regional geologic context apatite and monazite well established u pb mineral geochronometers are abundant in the pea ridge orebody however the potential presence of multiple generations of dateable minerals processes of dissolution reprecipitation and occurrence of micrometer sized intergrowths and inclusions complicate measurements and interpretations of the geochronological results here we employ a combination of several techniques including id tims and high spatial resolution geochronology of apatite and monazite using la sc icpms and shrimp and pb isotope geochemistry of pyrite and magnetite to obtain the first direct age constraints on the formation and alteration history of the pea ridge ioa deposit the oldest apatite tims 207 pb 206 pb dates are 1471 1 and 1468 1 ma slightly younger than but within error of the 1474 to 1473 ma u pb zircon ages of the host rhyolites dating of apatite and monazite inclusions within apatite provides evidence for at least one younger metasomatic event at 1 44 ga and possibly multiple superimposed metasomatic events between 1 47 and 1 44 ga lead isotop analyses of pyrite show extremely radiogenic 206 pb 204 pb ratios up to 80 unsupported by in situ u decay this excess radiogenic pb in pyrite may have been derived from the spatially associated apatite as apatite recrystallized several tens of million years after its formation the low initial 206 pb 204 pb ratio of 16 5 and 207 pb 204 pb ratio of 15 4 for individual magnetite grains indicate closed u pb system behavior in this mineral and are consistent with derivation of the pb from a mantle like source

rare earth element geochemistry of dolomites in the middle devonian presqu ile barrier western canada sedimentary basin implications for fluid rock ratios during dolomitization rare earth elements ree were determined in fine medium and coarse crystalline replacement dolomites and for saddle dolomite cements from the middle devonian presqu ile barrier from pine point and the subsurface of the northwest territories and north eastern british columbia ree patterns of the fine crystalline dolomite are similar to those of middle devonian limestones from the presqu ile barrier fine crystalline dolomite occurs in the back barrier facies and may represent penecontemporaneous dolomitization at or just below the sea floor medium crystalline dolomite is widespread in the lower southern and lower central barrier medium crystalline dolomite is slightly depleted in heavy ree compared with devonian marine limestones and fine crystalline dolomite and has negative ce and eu anomalies medium crystalline dolomites replaced pre existing limestones or were recrystallized from earlier fine crystalline dolomites during these processes the ree patterns of their precursors were modified late stage coarse crystalline replacement dolomite and saddle dolomite cements occur together in the upper barrier and have similar geochemical signatures coarse crystalline dolomites have negative eu anomalies and those from the pine point area also have positive la anomalies saddle dolomites are enriched in light ree and have positive la anomalies the ree patterns of coarse crystalline dolomite and saddle dolomite differ from those of marine limestones and fine and medium crystalline dolomites suggesting that different diagenetic fluids were responsible for these later dolomites although massive dolomitization requires relatively large volumes of fluids in order to provide the necessary amounts of mg2 dolomitization and subsequent recrystallization may not necessarily modify the ree signatures of the precursor limestones because of the low concentrations of ree in most natural fluids thus relative fluid rock ratios during diagenesis may be estimated from ree patterns in the diagenetic and precursor minerals fine crystalline dolomites retain the ree patterns of their limestone precursors in the medium and coarse crystalline dolomites the precursor ree patterns were apparently altered by large volumes of fluids involved during dolomitization this study suggests that ree compositions of dolomites and their limestone precursors may provide important information about the relative amounts of fluids involved during diagenetic processes such as dolomitization

recent developments in dating ancient crustal fluid flow several isotopic techniques have recently been developed or substantially improved allowing the accurate determination of the timing of fluid related processes these include k ar rb sr and sm nd dating of diagenetic minerals in clastic rocks u pb dating of carbonates sm nd dating of fluorite and uraninite re os and rb sr dating of sulfides 40ar 39ar and rb sr dating of fluid inclusions and u pb dating of ilmenite magnetite sphene and rutile while many of these techniques require further evaluation some have already resulted in new constraints on a variety of crustal fluid flow models

evaluation and application of the ion microprobe in the strontium isotope geochemistry of carbonates abstract a modified aei im20 ion microprobe has been used to measure 87 sr 86 sr ratios in carbonates a suite of carbonates with varying major elements ca mg fe mn was studied at low and high m m 3000 mass resolution to determine the types and intensities of molecular species isobaric with sr peaks sr data collected at low mass resolution must be corrected for ca 2 and camgo species rb sr ratios are extremely low and correction for 87 rb is not required 87 sr usable sr isotopic data may be obtained from calcite given sr 400ppm and for sr 5000 ppm a precision of 1 0 0007 in 87 sr 86 sr 2 mean can be achieved under optimum conditions the corrections for ca 2 and camgo are smaller than the within run precision in calcite but in dolomite the correction for camgo is 1 5 mass fractionation corrections to 87 sr 86 sr based on 86 sr 88 sr 0 1194 are typically 8 to 10 good agreement between ion probe and solid source mass spectrometer results was found for calcites of known sr isotopic composition st4a 400ppm sr average ion probe 87 sr 86 sr 0 7267 0 0015 solid source 87 sr 86 sr 0 72680 0 00008 14 jcg36 6000ppm sr average ion probe 87 sr 86 sr 0 7056 0 0009 solid source 87 sr 86 sr 0 70588 0 00009 16 jcg44 6000ppm sr average ion probe 87 sr 86 sr 0 7057 0 0006 solid source 87 sr 86 sr 0 70540 0 00008 16 the ability of the ion microprobe to measure 87 sr 86 sr for 10 m spots in calcite was used 1 to measure variation in 87 sr 86 sr of 0 01 on a centimetre scale in a hydrothermally altered basalt from the isle of skye northwestern scotland and 2 to determine the sr isotopic composition of tiny 87 sr 86 sr

stability and meromixis in a water filled mine pit a field experiment examined stability and stratification in a disused mine fit filled with 1 75 x lo7 m3 of water vertical profiles of conductivity and temperature indicated that due to substantial chemical stratification spring and autumn overturn did not penetrate to the base of the pit although parameterization indicated that double diffusion should be expected we found only circumstantial evidence of associated step structure the available data suggest that groundwater inflow created a warm salty pool of water at the base of the water column giving the appearance of a meromictic structure with a monimolimnion however this pool was noi a consistent feature suggesting both a variable inflow and significant diffusion rates from the temperature data estimates indicated that hypolimnetic vertical eddy diffusivity varied between 1 x 10e7 and 5 x lo m s l the observations identify short term relatively energetic internal wave events that may have a significant impact on this value the present study is useful in two ways first it shows how pit lakes form a natural laboratory fcr a range of processes and second it illustrates how these processes relate to diffusion paranieterization it is clear that reliable parameterization is vital for long term modeling required for prediction of water quality over decadal timescales with the closure of an open cut mining operation come the dual problems of rehabilitation of the mine pit and containment of deleterious material generated by the mine during its life in many cases the pit fills with water either naturally or through mine activities thus an artificial lake of moderate volume is created davis and ashenberg 1989 characterization of the transport processes within the water column is important for two reasons first the pit is likely to contain hazardous levels of dissolved metals and second if vertical transport rates are low then the pit may prove suitable as a storage location for hazardous material water filled mine pit lakes pit lakes have received consideration in the literature but with a biological or geochemical emphasis e g klapper and schultz 1995 crater lakes are the natural system most similar to these artificial water bodies martin 1985 macintyre and melack 1985 pit lakes are unique for several reasons they are often deep relative to natural lakes of similar surface area they have high surrounding walls that often generate a microclimate different to that outside the pit they typically have very thin sediment layers they may undergo substantial and rapid changes in water level and they are likely to contain significant concentrations of dissolved material the final point is important if the dissolved material is environmentally harmful or if it leads to meromixis with these departures from what might be associated with typical natural lakes

rare earth element geochemistry of clastic and chemical metasedimentary rocks associated with hydrothermal sulphide mineralisation in the olary block south australia abstract analysis of a variety of rock types from the south australian portion of the lower to middle proterozoic willyama inliers by icp ms demonstrate that primary rare earth element ree distributions remained essentially unchanged despite multiphase deformation and amphibolite grade metamorphism variable trends of preferential ree mobilisation are observed only where large amounts of fluid caused the rock to undergo strong retrogression and or hydrothermal alteration except for these conditions ree can be considered immobile and their distribution is generally independent of mineralogy thus providing a powerful tool for the characterisation of provenance of protoliths in a high grade metamorphic terrain ree signatures and other geochemical constraints of some volcanogenic sediments for example point to an andesitic parentage suggesting bimodal and gradually changing volcanism occurring in a developing intracontinental rift zone ree distributions in metasediments associated with sulphide mineralisation reflect both physico chemical characteristics of the ore bearing fluids and rock compositions comparison of their ree profiles allows discrimination between a strata bound redox controlled deposits b exhalative mineralisation and c epigenetic vein type mineralisation ree distributions in the analysed rocks are in agreement with other lines of textural and geochemical evidence for that limited syn tectonic remobilisation low fluid rock ratios unchanged primary ree signatures but widespread late stage mobilisation of sulphides high fluid rock ratios selective mobilisation of ree occurred in the olary block ree signatures of exhalative precipitates associated with sulphide mineralisation do not show a systematic stratigraphic variation but are indicative of fluctuating f o 2 conditions over short distances and display only moderately positive eu anomalies this contrasts with findings for the adjacent broken hill block and highlights the dissimilarities of ore formation processes that were active in the olary and the broken hill block as well as the depositional differences between the two blocks

rare earth element distribution in lake tyrrell groundwaters victoria australia abstract the rare earth element ree geochemistry of the saline to hypersaline acidic brines of lake tyrrell victoria australia were analyzed in order to determine the relative importance of concentration and modification processes in the lake system several types of brines were identified on the basis of different ree patterns and concentrations regional groundwater flowing into lake tyrrell yields the highest concentrations of ree while a transitional water group is identified on the basis of lower ree concentrations a third water group the reflux brine is characterized by extremely low ree concentrations the ree patterns suggest that ree are introduced to the lake tyrrell system by the regional groundwater which has concentrated ree from the aquifer material in its acidic waters eventually ree are removed from the evolving water mass as higher levels of ph are reached the data of the study strongly suggest that ree are scavenged from solution by fe oxyhydroxide phases which precipitate as the ph of the system rises water rock interactions probably control ph in the lake system and therefore ultimately control the concentration of ree in solution in this system our results are directly correlated with studies of hydrothermal vents and geothermal solutions which have shown the concentration of ree in solution to be dominantly controlled by ph

high latitude e and f region coupling signature a case study results from rapid run ionosonde rapid run ionosonde installed in the high latitude sodankyla geophysical observatory enables us to observe for the first time extraordinary details of e f region coupling process in high latitude ionosphere during geomagnetically quiet period we present an example on 15 august 2009 when a dense patchy sporadic e layer was detected associated with this unstable sporadic e layer exhibiting in addition an unusual enhancement with a vertical extent of about 10 km the highly structured f layer plasma was observed with apparent plasma depletions we examine this event taking into account the presence of mesoscale traveling ionospheric disturbances which can initiate coupling between these two regions and compare the data with current theories

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

origins of nd sr pb isotopic variations in single scheelite grains from archaean gold deposits western australia accessory gangue scheelite cawo4 from the archaean mt charlotte lode au deposit can be divided into two types with different rare earth element ree signatures in some scheelite grains specific ree signatures are reflected by different cathodoluminescence colours which can be used to map their often complex oscillatory intergrowths domains with specific ree contents from two grains were sampled for sm nd rb sr and pb isotopic analyses using a micro drilling technique type i scheelite is strongly enriched in middle ree mree and eu anomalies are either absent or slightly positive four fragments collected from type i regions of two crystals have initial 87sr 86sr and end values ranging from 0 70141 to 0 70163 and 2 5 to 3 5 respectively and pb isotope ratios reflecting the composition of greenstone sequence this may indicate that nd and pb have their source either locally or regionally in the greenstones basic greenstone lithologies have 87sr 86sr 0 7015 and the radiogenic sr signatures indicate that part of the sr originated from felsic lithologies located either within or beneath the host greenstone pile alternatively the sr signature may have evolved from preferential leaching of a rb rich mineral during hydrothermal alteration of the greenstone the ree patterns of type ii scheelite are either flat or mree depleted and have strong positive eu anomalies three fragments collected from type ii regions of the same two crystals have initial 87sr 86sr ratios and end values between 0 70130 and 0 70146 and 1 1 to 2 6 respectively and pb isotope signatures that are once again similar to that of the greenstone this implies that 87sr 86sr ratios in type ii fluids were closer to those of the host dolerite 0 7008 0 7013 due to more extensive fluid interaction with the dolerite a positive correlation between na and ree suggests that ree3 are accommodated by the coupled substitution ree3 na 2 ca2 into both type i and type ii scheelite this is consistent with a fractional crystallisation model to explain the change in ree patterns from type i to type ii but not with a model involving different coupled substitutions and fluids from different origins we propose that the complex ree and isotopic signatures of scheelite at mt charlotte are related to small m to medium km scale processes involving mixing between fresh batches of hydrothermal fluid with fluids that had already been involved in extensive wall rock alteration the very high end values measured in some scheelites have been previously used to link gold mineralisation with komatiites containing unusually high sm nd ratios however tiny 20 m grains of secondary hydroxyl bastnasite were found within micro fractures of one scheelite grain containing an extremely high end signature the hydroxyl bastnasite probably formed during recent ree redistribution within the scheelite as a result of meteoric fluid circulation the scale of this cryptic low temperature alteration is sufficient to explain the anomalously high endi values observed in scheelite from western australia

18th century lead smelting in central north america evidence from lead isotope and inaa measurements archaeological and historical studies suggest that metallic lead artefacts from early 18th century historic sites in the central united states were smelted from local ores direct confirmation of this can be obtained from lead isotope ratio measurements the isotopic composition of leads from galena pbs deposits in south east and central missouri sem cm are different from those of ores from the upper mississippi valley umv in iowa illinois wisconsin and also from leads originating in north western europe there is no evidence that smelting alters the isotopic ratios so that the sources of metallic artefacts can also be determined samples of galena and lead recovered from four sites in illinois kolmer 11r50 guebert 11r1 fox encampment mi 6 newell fort near starved rock were analysed the isotopic data show that smelting of galena from the missouri deposits began prior to 1730 umv ores were being smelted prior to 1722 at least two sources of galena in sem cm were exploited as distinguished by a combination of lead isotope and neutron activation analysis only one source in umv appears to have been utilized metallic lead rich artefacts of european origin such as bale seals musket balls and pewter form a small fraction 15 of the artefact set this is consistent with historic records which suggest that smelting of local galena began soon after the arrival of european colonists

effects of mississippi valley type mineralization on ree patterns of carbonate rocks and minerals viburnum trend southeast missouri the lead zinc ores of the viburnum trend were deposited as replacements and open space fillings within the cambrian bonneterre formation the shapes of rare earth element ree patterns of unmineralized limestones and dolostones of the bonneterre formation host rocks are similar to each other and to shale ree patterns regardless of facies or of insoluble residue content in mineralized zones recrystallized and mineralized dolostones mean la sm 2 6 vug dolomites mean la sm 1 6 and vug calcites mean la sm 0 9 have la sm ratios that are significantly lower than those of host rocks mean la sm 5 7 vug calcites have lower sm lu mean 6 7 and vug dolomites have higher sm lu mean 22 5 than host rocks mean sm lu 11 5 preliminary partitioning experiments and estimates of the effects of complexing suggest that the observed ree patterns of carbonate minerals could not have developed from a solution with a ree distribution like that of host rocks or by dissolution and reprecipitation

archaeological reconstruction of medieval lead production implications for ancient metal provenance studies and paleopollution tracing by pb isotopes abstract the identification of metal provenance is often based on chemical and pb isotope analyses of materials from the operating chain mainly ores and metallic artefacts such analyses however have their limits some studies are unable to trace metallic artefacts or ingots to their ore sources even in well constrained archaeological contexts possible reasons for this difficulty are to be found among a variety of limiting factors i problems of ore signatures ii mixing of different ores alloys iii the use of additives during the metallurgical process iv metal recycling and v possible pb isotopic fractionation during metal production this paper focuses on the issue of pb isotope fractionation during smelting to address the issue of metal provenance through an experimental reconstruction of argentiferous pb production in the medieval period an attempt was made to better understand and interpret the pb isotopic composition of ore smelting products it is shown that the measured differences outside the total external uncertainties of 0 005 2 sd for 206 pb 204 pb ratios in pb signatures measured between ores slag and smoke are not due to pb mass fractionation processes but to 1 ore heterogeneity 206 pb 204 pb slag ores 0 066 and 2 the use of additives during the metallurgical process 206 pb 204 pb slag ores 0 083 even if these differences are due to causes 1 and or 2 smoke from the ore reduction appears to reflect the ore mining area without a significant disturbance of its pb signature for all the isotopic ratios 206 pb 204 pb smokes ores 0 026 thus because the isotopic heterogeneity of the mining district and additives is averaged in slags slag appears as the most relevant product to identify ancient metal provenance whereas aiming at identifying a given mine seems beyond the possibilities provided by the method searching for the mining district through analysis of the smelting workshop materials should provide a more appropriate approach in cases where no archaeological evidence of ancient mining is available furthermore smoke pb isotopic composition does not seem to be significantly affected by the metallurgical process paleopollution recorded in peat deposits could help to detect ancient mining production and workshops integrated collaboration between mining archaeologists and geochemists appears crucial to achieve this goal

the nature of groundwater flow in fractured rock evidence from the isotopic and chemical evolution of recrystallized fracture calcites from the canadian precambrian shield abstract the isotope geochemistry of fracture calcites in three precambrian plutons on the canadian shield has been investigated in order to understand the paleohydrogeological conditions in fractured crystalline rock fracture calcites of ancient hydrothermal origins in the chalk river and east bull lake plutons exhibit 18o enrichment and 13c depletion trends resulting from recent low temperature calcite recrystallization under open system conditions for oxygen but semiclosed for carbon and under extremely variable time integrated water rock calcite ratios this process causes recycling of elements with calcite distribution coefficients 1 rare earths manganese and possibly iron from the precursor calcite to younger calcites as well as calcite control over the 87 sr 86 sr ratio of the groundwater within the chalk river pluton the large but variable water rock calcite mole ratios calculated from the shifts in the stable isotopic compositions of fracture calcites are compatible with fracture flow models that invoke flow channeling within single fractures that also contain regions of immobile porosity quantification of isotopic shifts resulting from recrystallization requires that the initial isotopic composition of the precursor hydrothermal calcite be well constrained unlike the chalk river and east bull lake plutons hydrothermal fracture calcites in the white lake pluton which intrudes marble rich country rocks of the grenville supergroup have highly variable 13c and 18o values this is attributed to mixing of carbon from magmatic and sedimentary reservoirs and to oxygen isotopic exchange between hydrothermal fluids and carbonate country rocks at the time of intrusion convective circulation of meteoric groundwater from the surrounding 13c rich carbonate rocks up to 6 6 resulted in 13c values as heavy as 3 0 for the fracture calcites in the pluton

a review of oceanic salt fingering theory salt fingering is a potentially important mechanism for mixing different water masses in those parts of the ocean where warm salty waters overlie cooler fresher this review surveys advances in salt fingering theory as they pertain to ocean mixing basic equations are presented along with steady maximum buoyancy flux and fastest growing finger solutions attempts to quantify theoretically finger induced fluxes of heat salt and buoyancy and to understand staircase formation and maintenance are described also considered are the confounding influences of internal wave shear and strain and intermittent internal wave shear driven turbulence which are present in the ocean but in few theories finally outstanding theoretical questions about the role of salt fingers in the ocean are raised

a review of gravity wave saturation processes effects and variability in the middle atmosphere this paper provides a review of our current understanding of the processes responsible for gravity wave saturation as well as the principal effects and variability of saturation in the lower and middle atmosphere we discuss the theoretical and observational evidence for linear and nonlinear saturation processes and examine the consequences of saturation for wave amplitude limits momentum and energy fluxes the diffusion of heat and constituents and the establishment of a near universal vertical wavenumber spectrum recent studies of gravity wave variability are reviewed and are seen to provide insights into the significant causes of wave variability throughout the atmosphere

changes in the thermo haline structure of the dead sea 1979 1984 abstract from 1979 to 1984 the overall water balance of the dead sea was characterized by a water deficit however an excess of freshwater inflow during the 1979 80 rainy season resulted in a 3 year long meromictic phase this was followed by three consecutive overturns of the water column in december 1982 1983 and 1984 the buildup and dissipation of the seasonal thermocline and halocline is followed throughout this period which covers a wide range of water balance situations the gravitational stabilities of the summer pycnoclines measured in terms of n 2 3 10 2 s 2 are at least one order of magnitude greater than the values reported in freshwater lakes and oceans the contributions of temperature and salinity to n 2 and to the integrated stability w are examined separately and their interdependence is pointed out two irreversible effects in the evolution of the properties of the water masses are identified 1 a monotonic increase in the density of the deep waters and 2 a monotonic shift of the nacl saturation curve towards higher salinities

lead isotope zoning in galena an ion microprobe study of a galena crystal from the buick mine southeast missouri ion microprobe techniques have been used to determine the variations of pb isotope ratios within a single octahedral crystal of galena from the buick mine southeast missouri the crystal shows uniform concentric zonation of pb isotope ratios with a total variation of approximately 3 percent in 208 pb 206 pb and approximately 4 percent in 207 pb 206 pb and with the crystal margin being less radiogenic lower 206 204 than the core the range in the observed 208 pb 206 pb ratio is larger than that observed previously for bulk galena analyses from throughout the mine and is almost as large as the total variation reported for the whole southeast missouri ore district the ion probe results are demonstrated to be accurate to 0 1 0 2 percent by comparison with conventional mass spectrometric analyses performed on microsamples of the same crystal the ion probe technique holds promise for establishing a pb isotope chronostratigraphy for the ore bearing solutions which will be useful in delineating temporal and spatial aspects of the fluid circulation patterns

sulfur isotope evidence for penetration of mvt fluids into igneous basement rocks southeast missouri usa previous studies of galena and sphalerite from paleozoic mvt deposits in the viburnum trend southeast missouri documented large variations in 34s values throughout the ore forming event the present study of cu fe sulfides reveals a similar 34s variation that reflects two end member sulfur reservoirs whose relative importance varied both temporally and spatially more 34s enriched sulfides 34s approaching 25 indicate introduction of sulfur from basinal sedimentary sources whereas more 32s enriched sulfides 34s 600 m vertically through underlying precambrian igneous rocks such basement involvement has been suggested for other carbonate hosted base metal districts e g irish base metal deposits and should be considered an integral part of the ore forming process in southeast missouri

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

direct dating of mississippi valley type mineralization use of sm nd in fluorite suggested that the technique may be applicable to mississippi valley type deposits in the present study an sm nd age and ree contents in fluorite from the illinois kentucky fluorite district are used to constrain the timing and genesis of mississippi valley type ore deposition

seasonal variations of halite saturation in the dead sea hypersaline lakes and seas were common in the past precipitating thick evaporitic salt deposits the only modern analogue for the paleo limnology of deep salt saturated aquatic environments exists in the dead sea in this study we present new insights from the dead sea on the role of seasonal thermohaline stratification and water balance on the seasonal and depth variations of the degree of saturation of halite salt and the rate of halite growth along the water column we developed methodologies to accurately determine the empirical degree of halite saturation of the lake based on high accuracy densitometry and to quantify halite growth rate along the water column during summer the epilimnion is undersaturated and halite is dissolved whereas during winter the entire water column is supersaturated and crystallizes halite this result is not trivial because the variations in the water balance suggest the opposite summer is associated with higher loss of water by evaporation from the lake compared to the winter hence the thermal effect overcomes the hydrological balance effect and thus governs the seasonal saturation cycle the hypolimnion is supersaturated with respect to halite and crystallizes throughout the year with higher super saturation and higher crystallization rates during winter during summer simultaneous opposing environments coexist an under saturated epilimnion that dissolves halite and a supersaturated hypolimnion that crystallizes halite which results in focusing of halite deposits in the deep hypolimnetic parts of the evaporitic basins and thinning the shallow epilimnetic deposits this article is protected by copyright all rights reserved

pb isotope evidence for the role of mesozoic basins in the genesis of mississippi valley type mineralization in somerset uk the mendip bristol veinfield is one of a number of british mississippi valley type deposits the genesis of which has never been fully explained the mendip bristol pb zn ba vein mineralization is hosted in carboniferous permo triassic and jurassic sediments the metal sources involved during mineralization were investigated using pb isotope analysis of vein galenas 206 pb 206 pb values range from 18 311 to 18 594 207 pb 204 pb values from 15 601 to 15 688 and 208 pb 204 pb values from 38 257 to 38 565 the data show three isotopically different mineralizing fluids which it is suggested reflect fluid expulsion from adjacent mesozoic sedimentary basins as a result of overpressuring due to rapid subsidence in the triassic jurassic

uraninite recrystallization and pb loss in the oklo and bangombe natural fission reactors gabon abstract the oklo and bangombe natural fossil fission reactors formed ca 2 ga ago in the franceville basin gabon the response of uraninite in the natural reactors to different geological conditions has implications for the disposal of the uo 2 in spent nuclear fuel uraninite and galena from two reactor zones rz16 at oklo and rzb at bangombe were studied to clarify the chronology and effect of alteration events on the reactor zones in addition ion microprobe u pb analysis of zircons from a dolerite dyke in the oklo deposit were completed to better constrain the age of the dyke and thereby testing the link between the dyke and an important alteration event in the reactor zones the analyzed uraninite from rz16 and rzb contains ca 6 wt pbo indicating a substantial loss of radiogenic pb transmission electron microscopy showed that microscopic uraninite grains in the reactor zones consist of mainly defect free nanocrystalline to microcrystalline aggregates however the nanocrystalline regions have elevated si contents and lower pb contents than coarser uraninite crystallites single stage model ages of large millimeter sized galena grains at both rz16 and rzb correlate well with the age of the oklo dolerite dyke 860 39 ma 2 thus the first major pb loss from uraninite occurred at both oklo and bangombe during regional extension and the intrusion of a dyke swarm in the franceville basin 860 890 ma ago uraninite pb isotopes from rz16 and rzb give lower ages of ca 500 ma these ages agree with the chemical ages of the uraninite and show that an ancient pb loss occurred after the intrusion of the dolerite dykes the presence of nanocrystallites in the reactor uraninite indicates internal recrystallization which may have occurred around 500 ma resulting in the 6wt pbo uraninite it is suggested that leaching by fluid interaction triggered by the pan african orogeny was important during this second pb loss event thus there are indications that uraninite at both the oklo and bangombe natural reactors has experienced at least two ancient episodes of pb loss associated with internal recrystallization these recrystallization events have occurred without significantly depleting the 2 ga fission products compatible with the uraninite structure

ore fluid geochemistry of the hehuashan pb zn deposit in the tongling ore district anhui province china evidence from ree and c h o isotopes of calcite abstract calcite is the main gangue mineral of the hehuashan lead zinc deposit which is located in the tongling ore district anhui province east china the ore bodies of the hehuashan deposit are hosted by dissolution breccia of the lower triassic carbonate sediments we report petrography rare earth elements ree and c h o isotope data of four generations of calcite recognized in the hehuashan deposit namely the pre ore stage calcite cal 1 early ore forming stage calcite cal 2 late ore forming stage calcite cal 3 and post ore stage calcite cal 4 in addition we also report c h o isotopes data of dolostone from the lower triassic carbonate sediments all four calcite generations show a low ree content 13 50 ppm on average indicating that the related ore forming fluids may not have been derived a magmatic fluid but rather be derived from the carbonate sediments or basinal brines low lree hree ratio 1 1 6 1 on average of all four calcite generations implies that no significant ree fractionation happened during the mineralizing processes the wide distribution of y ho ratios 17 70 of calcite indicates a result of fluids mixing the 13c values of calcite 1 4 to 4 2 are comparable to marine carbonates but the 18o values are lower indicating possibly a result of carbonates dissolution calculated 18o of the fluid in equilibrium with calcite vary from 3 1 to 0 1 combining the dv smow 100 to 81 implying a fluid mixing of a brine fluid and meteoric water or diagenetic pore water for the mineralization of the hehuashan deposit

u pb systematics and alteration trends of pennsylvanian aged aragonite and calcite abstract carbonate allochems from the mid pennsylvanian buckhorn fauna of the boggy formation oklahoma usa consist of primary aragonite preserved in nautiloids and of secondary low mg calcite present in crinoids and corals unaltered nautiloids contain 11 38 ppb u and 23 422 ppb pb and have low 238 u 204 pb values from 4 1 14 8 they give a 238u 206pb isochron age of 311 48 ma 2 which is in agreement with the assigned stratigraphic age mid desmoinsian 305 ma of the boggy formation sediments their initial lead isotope ratios are 206 pb 204 pb 19 11 0 08 207 pb 204 pb 15 70 0 04 and 208 pb 204 pb 38 7 and reflect an upper crustal source for pb in mid pennsylvanian seawater these values are similar to those of coals of this age the contents of both u and pb in the buckhorn nautiloids are significantly higher than those found in the modern nautilus nautilus pompilius these enrichments are attributed to bitumen which was added to the carbonates during diagenesis the diagenetic transformation of aragonite to low mg calcite in the buckhorn nautiloids was apparently associated with a net loss of pb thereby increasing their values the secondary carbonates of crinoids contain 265 352 ppb u 136 262 ppb pb and their values range from 68 111 consequently their present day uranogenic lead isotopic ratios are higher than those of the buckhorn nautiloids the u pb data for some diagenetic low mg components indicate an age of 280 ma suggesting an early timing for the post depositional alteration process the apparent initial lead isotope ratios of crinoids are variable and some are significantly higher than the coexisting aragonite 206 pb 204 pb 20 50 207 pb 204 pb 15 73 this very radiogenic signature is similar to those of mississippi valley type ore deposits and both types may share a similar genesis

the demise of a salt giant driven by uplift and thermal dissolution abstract the development of giant salt basins and eventual cessation of rapid salt deposition is founded on a delicate balance of salinity and heat fluxes within the water body governed by tectonic climatic and eustatic change the onset of salt deposition in such basins is widely accepted to be initiated by basin restriction however the processes that lead to the termination of salt deposition are comparatively unclear here we use an array of 2d and 3d seismic surveys to reveal that the truncation surface at the top of a thick salt sequence in the eastern mediterranean is far more extensive than previously thought we show that uplift of the salt driven by deformation and thermal dissolution initiated the demise of the salt giant even prior to the final dilution and emplacement of brackish lago mare and fluvial deposits progressive uplift of the salt through the thermocline and into the under saturated epilimnion led to dissolution we argue that dissolved salt was recycled and re precipitation from the hypolimnion in the deepest sections of the basin contemporaneous with dissolution of halite from the shallower epilimnion these findings explain how rapid basinwide salt deposition was brought to an end in the eastern mediterranean and present a novel process for sculpting the final architecture of a salt giant

determination of the rare earth element abundances in 29 international rock standards by instrumental neutron activation analysis a critical appraisal of calibration errors abstract a standard additions method has been used to calibrate an in house multi element rock standard for the analysis of the rare earth elements ree and th ta hf and co by instrumental neutron activation analysis this preliminary calibration with a precision of typically better than 7 1 has been refined by comparing our analyses of the four u s g s standard rocks agv 1 bcr 1 g 2 and gsp 1 with compiled analyses obtained by a critical survey of over 70 published references our standard calibration was adjusted by the average discrepancy between our analyses and published analyses for each element for all four u s g s standards the accuracy of this final calibration is estimated to be better than 5 absolute and it has been used to determine the above elemental abundances in 29 international rock standards five of the ree have been determined by interpolation from chondrite normalised plots

isotope systematics in vein gold from brusson val d ayas nw italy 1 pb pb evidence for a piemonte metaophiolite au source the monte rosa gold district nw italian alps comprises hundreds of late alpine epigenetic gold bearing quartz veins we report a lead isotope study on an important one of these veins fenilia brusson val d ayas which reveals a complex isotope geochemistry of petrographically cogenetic vein minerals petrographic observations allow to distinguish a quartz dominated main stage and a quartz poor final stage mineral assemblage most of the free gold crystallized in the beginning of the final stage whereas sulphides were deposited during its waning three distinct lead isotope fields result for the paragenetic sequence of vein minerals the variable lead isotope signature 15 517 15 706 as well as from the uniform radiogenic lead 15 649 207pb 204pb 15 691 characteristic of the waning final stage we favour a model where the deeply circulating final stage fluid the ultimate source of which remains obscure acquired lead and thus possibly its gold in piemonte metaophiolitic rocks beneath the monte rosa nappe during ascent the primitive gold bearing fluid was variably contaminated by an evolved crustal lead 15 706 207pb 204pb 15 743 compatible with derivation from monte rosa nappe rocks during deposition of final stage minerals the pb isotope composition of the fluid changed to a constant signature becoming again dominated by a radiogenic lead source thus within an assemblage defined as cogenetic on petrographic grounds the pb isotopic signature is not necessarily uniform and source modelling based on lead isotopes of associated minerals may be inappropriate it remains open at present whether the inferred piemonte metaophiolite gold source is confined to the fenilia vein in val d ayas only or whether it might be more widespread in the monte rosa gold district

trace element and isotopic zoning in minerals models of compositional fractionation by mineral separation procedures abstract data on compositional zoning of minerals are required to apply thermodynamic models to mineral chemistry and to constrain kinetic models of diffusion and grain growth trace elements and isotopes have not been utilized fully in these applications because in situ methods of analysis e g sims and pixe have not become routine trace element and isotopic compositions of minerals are usually determined from mineral separates however routine mineral separation procedures are not designed to detect and characterize zoning mineral separates are formed by segregating simple monomineralic particles of a mineral from other minerals and compound particles models of the formation of simple and compound particles during rock comminution show how the size and shape of mineral grains and the size of the particles formed affect the constitution of the separates the interior portions of minerals are strongly over represented in mineral separates while the margins of the grains are preferentially included in compound particles the particle size grain size ratio is the dominant factor in the segregation of the rims of minerals from the cores the particle size grain size ratio can be controlled through regulation of rock comminution and sieving procedures separation protocols are suggested to gain information about the nature of chemical and isotopic heterogeneities in minerals in particular chemical and isotopic effects associated with thin zones near grain boundaries can be investigated effectively

chronology with a pinch of salt integrated stratigraphy of messinian evaporites in the deep eastern mediterranean reveals long lasting halite deposition during atlantic connectivity abstract the messinian salinity crisis msc 5 97 5 33 ma is considered an extreme environmental event driven by changes in climate and tectonics which affected global ocean salinity and shaped the biogeochemical composition of the mediterranean sea yet after more than 50 years of research msc stratigraphy remains controversial recent studies agree that the transition from the underlying pre evaporite sediments to thick halite deposits is conformal in the deep eastern mediterranean basin however the age of the base and the duration of halite deposition are still unclear also disputed is the nature of the intermediate and upper msc units which are characterized as periods of increased clastic deposition into the eastern mediterranean based on marginal outcrops and seismic data we provide a multidisciplinary study of sedimentary geochemical and geophysical data from industrial offshore wells in the levant basin which recovered a sedimentary record of deep basin mediterranean evaporites deposited during the msc in combination with previous observations of the msc throughout the mediterranean basin our results promote the need for a new chronological model remarkably the one kilometer thick lower part of the evaporitic unit is composed of essentially pure halite except for a thin transitional anhydrite layer at its base the halite is undisturbed and homogeneous lacking diverse features apparent in more proximal sections indicating a deep sea depositional environment we find that distinct meters thick non evaporitic intervals interbedded with the halite previously thought to be clastic layers are diatomites while xrd analysis confirms an increase in clastic components in these sediments they are composed primarily of well preserved marine and freshwater planktonic diatoms the occurrence of marine planktonic diatoms in these intervals indicates the input of atlantic waters into the mediterranean basin during the deposition of the massive halite unit seismic stratigraphy and well log cyclostratigraphy further support deep basin halite deposition which started about 300 kyr earlier than widely assumed 5 97 ma we propose that halite deposition in the deep mediterranean took place during stage 1 of the msc rather than being limited to the short 50 kyr msc acme when sea level was presumably at its lowest thus brine formation salt precipitation and faunal extinction occurred at least in part in a deep non desiccated basin with a restricted yet open mediterranean atlantic connection that allowed inflow of oceanic water we observe an increase in heavy minerals and reworked fauna within the clastic evaporitic interbedded evaporites of the basinal msc section and argue that these settings correspond in the deep basins with a significant sea level drawdown during stage 2 of the msc as observed in the marginal sections this correlation is corroborated by astrochronology and chemostratigraphic markers such as the distribution of n alkanes and biomarker based thermal maturity indices the levant deposits indicate that high sea level and partial connectivity with global oceans promoted the deposition of deep basin deep water halite while sea level drawdown promoted deposition of reworked and transported material from the margins into deep mediterranean basins this study modifies the current understanding of the mechanisms governing salt deposition throughout the msc with implications for other evaporitic events in the geologic record

petroleum migration fluid mixing and halokinesis as the main ore forming processes at the peridiapiric jbel tirremi fluorite barite hydrothermal deposit northeastern morocco the jbel tirremi fluorite barite sulfide deposit in northeastern morocco is hosted in a jurassic aged structurally high carbonate platform known as the jbel tirremi dome the host rocks consist of unmetamorphosed flat lying early jurassic dolomitized limestones locally intruded by eocene lamprophyre dikes the orebodies consist mostly of fluorite and barite and occur as open space fillings and partial to massive replacement of the enclosing medium to coarse grained dolomitized limestones the ore mineralogy is dominated by fluorite of different colors and habits barite and to a lesser extent sulfides rare earth element compositions along with fluid inclusion halogen and isotopic data suggest that the fluorite barite mineralization and the spatially associated eocene alkaline magmatism are petrogenetically unrelated pointing instead to the regional circulation of hydrothermal basinal brines mixed to various degrees with meteoric water in a dominantly closed rock buffered system at progressively higher temperatures and fluid rock ratios in this respect fluid inclusion microthermometric measurements show that the ore bearing hydrothermal system developed in two separate stages of fluorite barite mineralization as also revealed by isotopic data both stages precipitated from saline fluids at shallow crustal levels i e 82 degrees c and possibly up to 218 degrees c whereas in the second stage the mineralizing fluid had a similar temperature range but lower salinities similar to 20 10 wt nacl equiv the recorded high salinities are interpreted to represent the involvement of a mixture of halite dissolution water and evaporated seawater component oxygen delta o 18 21 7 to 29 6 0 v smow and carbon delta c 13 7 9 to 0 2 0 v pdb isotope data along with strontium sr 87 sr 86 0 70300 070789 and lead pb 206 pb 204 17 961 20 96 pb 207 pb 204 15 511 15 697 pb 208 pb 204 37 784 39 993 isotope ratios suggest the involvement of a mixture of oil bearing fluids basinal brines and meteoric fluids that interacted extensively with the early jurassic host carbonates the underlying triassic salt bearing diapir associated siliciclastic rocks and the highly fractionated and greisenized hercynian granitic crystalline basement resulting in the release of fluoride metals and other constituents to form the jbel tirremi deposit petroleum bearing fluid released from overpressured portions of the guercif basin at lithostatic pressures and bittern brines dominated the first stage of mineralization mixing of saline oxidized cacl2 and sulfate rich bittern brine with oil bearing fluid resulted in fluorite precipitation of stage i conversely during the second stage of mineralization the hydrothermal system was open to the influx of oxidized meteoric water as a consequence of the upward migration of the triassic salt bearing diapir and associated pressure decrease the shift from stage i to stage ii is associated with the evolution of the system from lithostatic to mostly hydrostatic pressure conditions stage i mineralization is thought to have occurred during the late miocene in response to rapid sedimentation and high subsidence rates and subsequent hydrocarbon migration associated with the outward migration of the rif thrust front conversely stage ii mineralization occurred coevally with the uplift phase during tortonian time

observations of overturning in the upper mesosphere and lower thermosphere 1 a number of observations of the sodium density primarily in the mesosphere and lower thermosphere but also of the electron density structure have shown what appears to be overturning or convective roll cells near the transition from the mesosphere to the lower thermosphere the cells are found in the region between 95 and 105 km and occur near the boundary between the region of lower stability in the mesosphere and the region of higher stability in the lower thermosphere the vertical scale for the rolls is 5 6 km and the timescale is 1 3 hours the rolls occur in a region characterized by large shear in the neutral winds but the timescales are too long to be explained by simple kelvin helmholtz instability we present observations from the university of illinois lidar facility located at the starfire optical range near albuquerque new mexico from the arecibo observatory in puerto rico and from the maui malt lidar facility located on maui in hawaii that show the overturning structure possible mechanisms for generating the convective rolls are discussed including the relationship of the observed features to the characteristics expected for an inflection point instability

stable lead isotopes contaminant metals and radionuclides in upper hudson river sediment cores implications for improved time stratigraphy and transport processes radionuclide stable lead isotope and trace metal analyses on fine grained sediment cores collected along a 24 mile reach of the upper hudson river were used to establish temporal trends of contaminant loadings to establish stable lead isotopes as an additional stratigraphic tool and as tracers for resolving particle transport fluxes over periods of decades very large contaminant inputs of cd sb pb and cr were evident in the sediment record one potential large source for these metals was from a pigment manufacturing facility in glens falls ny the total range in stable lead isotope ratios observed in well dated cores from about 15 miles downstream of the potential metal inputs was large e g maximum difference in 206 pb 207 pb is 10 and characterized by four major shifts occurring in the 1950s 1960s 1970s and 1980s the temporal trend in 206 pb 207 pb has been used to establish precise dating of a sediment core from 24 miles further downstream the large magnitude and abrupt shifts in stable lead isotope ratios preserved in upper hudson sediment cores provide a way to significantly improve dating models based only on radionuclide analyses cadmium lead and antimony were identified as quite sensitive tracers of upper hudson sediments due to the magnitude of contamination and the lack of significant additional downstream sources of these contaminant metals metal measurements in a pair of sediment cores located 24 miles apart were used to constrain relative fluxes of sediment entering the river between the two coring locations with sediment sections deposited between the early 1960s and the late 1970s in these two cores suggesting that 3 4 times more sediment entered the river between the two coring sites than was transported from upstream these dilution factors agree very well with estimates based on suspended sediment measurements during a flood event in april 1994 and with estimates based on mechanistic model of suspended sediment transport between 1977 and 1992 d 2003 elsevier science b v all rights reserved

metallogenesis of the abitibi greenstone belt of canada a contribution from the analysis of trace lead in sulfide minerals pb isotopic compositions are reported for 12 ore localities within the late archean abitibi greenstone belt the studied samples carry massive or disseminated sulfides hosted in a variety of materials including mafic ultramafic igneous rocks felsic lavas porphyries and sedimentary iron formations repeated leaching experiments on these sulfides frequently revealed the presence of a radiogenic pb component which is attributed to in situ decay of u and th the leaching experiments make it possible in some cases to separate the radiogenic pb from the initial pb included in the minerals six pb pb isochrons formed by the analyses on leachates and residues show little evidence of secondary perturbations and yield ages that are within error similar to those determined for the supracrustal assemblage this implies that the ores were concentrated synchronously with the main phases of magmatic activity close to 2 7 ga the initial isotopic compositions of the sulfide specimens point to the existence of two different sources of metals i juvenile mantle derived igneous rocks and ii older recycled supracrustal series ore formation frequently involves mixing of metals from these two sources in variable proportions the initial isotopic composition of these two reservoirs is best evaluated by examining the composition of sulfides associated with komatiitic lava flows and with sedimentary iron formations respectively la composition isotopique du plomb a ctc dctermin6e pour 12 indices mctallifkres situcs dans la ceinture mctavolcanique de i abitibi les cchantillons ctudics ctaient porteurs de sulfures massifs ou disscminks dans diffkrents types de matkriaux cornme des roches ignces ultramafiques des laves felsiques des porphyres et des formations de fer sdimentaires l extraction du plomb contenu dans ces sulfures par des attaques mcnagces et rkpktitives met en kvidence la prksence de plomb radiogcnique provenant de la dkroissance radioactive in situ d uranium et de thorium la pratique des attaques mcnagces permet dans un certain nombre de cas de scparer le plomb radiogknique du plomb initial des mincraux six isochrones pb pb ont ctc ainsi obtenues celles ci montrent peu d kvidence d ouverture du systkme u pb et livrent des bges qui sont aux erreurs prks semblables 2 ceux obtenus dans leur encaissant ceci montre que la formation des concentrations mctallifkres est voisine de 2 7 ga et synchrone des principales phases d activitk magmatique les compositions isotopiques initiales obtenues sur ces cchantillons mettent en cvidence l existence de deux sources pour les mctaux i des roches ignces juvcniles directement dcrivces du manteau et ii des roches issues du recyclage d une crotite continentale plus bgce la plupart des minkralisations sulfurces resultent d un mclange de mctaux issus de ces deux sources la composition isotopique de ces deux rcservoirs est bien dcfinie par l analyse de sulfures assocics d une part aux cpanchements komatiitiques et d autre part aux formations de fer sdimentaires

temperature seasonality control on modern halite layers in the dead sea in situ observations layered halite sequences are found in deep basins throughout the geological record however analogs for such sequences are commonly studied in shallow environments here we studied active precipitation of halite layers from the only modern analog for deep halite precipitating basins the hypersaline dead sea in situ observations in the dead sea link seasonal thermohaline stratification halite saturation and the characteristics of the actively forming halite layers the spatiotemporal evolution of halite precipitation in the dead sea was characterized by means of monthly observations of 1 lake thermohaline stratification temperature salinity and density 2 degree of halite saturation and 3 textural evolution of the active halite deposits we present the observed relationships between the textural characteristics of layered halite deposits i e grain size consolidation and roughness and the degree of saturation which in turn reflects the limnology and hydroclimatology the lake floor is divided into two principal environments a deep hypolimnetic lake floor and a shallow epilimnetic lake floor in the deeper hypolimnetic lake floor halite continuously precipitates with seasonal variations 1 during summer consolidated coarse halite crystals form rough surfaces under slight supersaturation 2 during winter unconsolidated fine halite crystals form smooth lake floor deposits under high supersaturation these observations support interpretations of the seasonal alternation of halite crystallization mechanisms the shallow epilimnetic lake floor is highly influenced by the seasonal temperature variations and by intensive summer dissolution of part of the previous year s halite deposit which results in thin sequences with annual unconformities this emphasizes the control of temperature seasonality on the characteristics of the precipitated halite layers in addition precipitation of halite on the hypolimnetic floor at the expense of the dissolution of the epilimnetic floor results in lateral focusing and thickening of halite deposits in the deeper part of the basin and thinning of the deposits in shallow marginal basins

pb isotope evidence on the origin of the west shropsh orefield england pb isotope data on ore galenas from the west shropshire orefield show a significant spread of 20 pb 204 pb values with minor variation in 207pb 204 pb and 208pb 204 pb ratios these indicate that lead was derived from multiple sources some of them uranium enriched and incompletely mixed prior to ore deposition four possible mineralizing agents are considered circulating sea water metamorphic waters basinal brines and convecting formation waters pb isotope data exclude a circulating sea water origin for the mineralization and best support a convecting formation water mineralizing agent a model involving a single fluid tapping multiple lead sources is proposed to explain the observed pb isotope variation

carbonatite associated with ultramafic diatremes in the avon volcanic district missouri usa field petrographic and geochemical constraints abstract here we report field petrographic and geochemical analyses of the southeast missouri avon volcanic district intrusive rocks and present the first combined textural and geochemical evidence for the presence of a primary magmatic carbonatite phase among ultramafic dikes pipes and diatremes of olivine melilitite alnoite and calciocarbonatite the 13 c vpdb values measured for primary calciocarbonatite as well as carbonates in olivine melilitite and alnoite rocks range from 3 8 to 8 2 which are within the typical range of mantle values and are distinct from values of the carbonate country rocks 0 0 to 1 3 the carbonate oxygen isotope compositions for the intrusive lithologies are in the range of 21 5 to 26 2 vsmow consistent with post emplacement low temperature hydrothermal alteration or kinetic fractionation effects associated with decompression and devolatilization metasomatized country rock and breccia contaminated igneous lithologies have carbonate 13 c vpdb values gradational between primary carbonatite values and country rock values unaltered sedimentary dolomite breccia and mafic spheroids entrained by calciocarbonatite and the lack of microstratigraphic crystal growth typical of carbonate replacement also exclude the possibility of hydrothermal replacement as the cause of the magmatic textured carbonates rare earth element ree patterns for the alnoite olivine melilitite and carbonatite are similar to each other with strong light ree enrichment and heavy ree depletion relative to morb these patterns are distinct from those of country rock rhyolite and sedimentary carbonate these data suggest that rocks of the avon volcanic district represent a single ultramafic carbonatite intrusive complex possibly derived from a single mantle source

heat flow in the dead sea from the icdp boreholes and its implication for the structure of the basin abstract numerical simulations emulating the formation of the dead sea basin dsb infer that it could not have been formed as a pull apart basin with a surface heat flow lower than 50 m w m 2 however previous measurements determined values of 32 40 m w m 2 this contradiction is known as the dead sea heat flow paradox here we set to re examine the paradox by analyzing heat flow data in boreholes drilled by the icdp international continental drilling program in the northern dsb the boreholes and the extracted sediment cores offer a unique opportunity to re measure the heat flow in the dsb and assess the paradox heat flow was determined by obtaining in situ temperature profiles from the boreholes and conducting 469 thermal conductivity measurements on the cores the newly computed values are in agreement with those previously obtained for the dsb and fall below the threshold of 50 m w m 2 different explanations proposed to justify higher heat flow seem to fail leaving the dead sea heat flow paradox unresolved heat flow values and the sedimentation corrections determined in this research are consistent with the ginzburg and ben avraham subsurface model for the dsb suggesting deeper sediment filling in the southern part of the basin

lead isotope systematics of vein type antimony mineralization rheinisches schiefergebirge germany a case history of complex reaction and remobilization processes mesothermal vein type sb mineralization in the rheinisches schiefergebirge germany is characterized by two different mineralization styles which are 1 extensional quartz stibnite vein systems and 2 cu pb sb sulphosalt assemblages in overprinted pre existing pb zn veins a detailed pb isotope study of 52 representative samples from both mineralization types indicates distinct compositional patterns cu pb sb sulphosalts meneghinite boulangerite bournonite formed by reaction remobilization are characterized by pb isotope compositions 206pb 204pb 18 179 18 223 which are identical to the precursor galena 206pb 204pb 18 168 18 223 the pb isotope composition of sulphosalt minerals in these vein systems was controlled by lead inherited from pre existing galena stibnite and pb sulphosalts zinkenite semseyite plagionite formed in quartz stibnite vein systems display pb isotope ratios 206pb 204pb 18 250 18 354 which are more radiogenic than galenas from variscan pb zn ore veins 206pb 204pb 18 162 18 303 detailed small scale investigation of thrust zones hosting pb zn ores and crosscutting quartz ankerite fissure veins ramsbeck deposit indicates that the pb isotope compositions of recrystallized galena and remobilized phases boulangerite semseyite bournonite are arranged along a linear trend this is interpreted as mixing between primary galena with 206pb 204pb 18 206 and overprinting hydrothermal fluids with a more radiogenic composition 206pb 204pb 18 354 expressed by intermediate compositions 206pb 204pb 18 256 18 334 of newly formed sulphosalts the pb isotope systematics of the vein type sb mineralization is in accordance with a model of pb extraction from similar crustal sources palaeozoic sedimentary sequences at different times

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism

isotopic composition of lead in moss and soil of the european arctic moss o and c horizons of podzols mainly forming complementary sample triplets as well as filter residues of molten snow from northern norway northern finland and nw russia have been analyzed by tims for their pb isotopic composition in order to study the impacts of local geogenic anthropogenic sources and long range atmospheric transport on the pb balance in the european arctic samples were taken along two n s transects covering an area of 188 000 km2 including both pristine environments in the w and certain regions towards the e severely contaminated by heavy metal emissions originating from large nickel smelters and processing plants in nw russia the lead in moss and o horizon samples clearly reflects atmospheric deposition as it displays overall uniform isotope ratios and is decoupled from the geogenic background i e the underlying mineral soils in the c horizon moss and o horizon samples from the eastern n s transect are isotopically indistinguishable from those taken along the western transect but their pb concentrations tend to be 2 times higher this points to considerable contamination originating from the nearby russian industrial and urban centers however isotopic signals of emissions from individual industrial point sources cannot be unambiguously identified because they lack characteristic isotope signatures pb derived from gasoline additives is swamped by pb from other sources and can also be excluded as a major contributor to the environmental pb in the european arctic overall the pb isotopic signatures of moss and o horizon overlap values recorded in atmospheric lead all over central and southern europe more than 2000 km south of the study area this may be taken as indicating continent wide mixing of pb derived from similar sources in the atmosphere or as reflecting economic globalization or both o horizon samples which accumulate lead over 20 30 yr conform to a distinct pb isotope reference line in 207pb 206pb vs 208pb 206pb space european standard pollution esp defined by atmospheric pb considered to be representative for the technical civilization in europe conversely the arctic moss samples with a lifetime of 3 yr display a deviating linear trend reflecting a recent change of atmospheric input towards significantly more radiogenic pb derived from mississippi valley type ores in the u s fully compatible with signatures found in epiphytic lichens from canada but also in pb from urban waste incinerators in central europe considering the elevated pb concentrations in moss collected along the eastern n s transect this congruence indicates that the pb in moss of the european arctic most probably originates from the nearby russian centers of urbanization and not from transatlantic transport we therefore suspect imported industrial goods and their subsequent attrition to be a more plausible explanation for the appearance of mvt lead in europe

petrography and geochemistry of early stage fine and medium crystalline dolomites in the middle devonian presqu ile barrier at pine point canada the petrography and geochemistry of fine and medium crystalline dolomites of the middle devonian presqu ile barrier at pine point western canada sedimentary basin are different from those of previously published coarse crystalline and saddle dolomites that are associated with late stage hydrothermal fluids fine crystalline dolomite consists of subhedral to euhedral crystals ranging from 5 to 25 m mean 8 m the dolomite interbedded with evaporitic anhydrites that occur in the back barrier facies in the elk point basin fine crystalline dolomite has 18 values between 1 6 to 3 8 pdb and 87sr 86sr ratios from 0 7079 0 7081 consistent with derivation from middle devonian seawater its sr concentrations 55 225 p p m mean 105 p p m follow a similar trend to modern little bahama seawater dolomites its rare earth element ree patterns are similar to those of the limestone precursors these data suggest that this fine crystalline dolomite formed from middle devonian seawater at or just below the sea floor medium crystalline dolomite in the presqu ile barrier is composed of anhedral to subhedral crystals 150 250 m mean 200 m some of which have clear rims toward the pore centres this dolomite occurs mostly in the southern lower part of the barrier medium crystalline dolomite has 18o values between 3 7 to 9 4 pdb mean 5 9 pdb and 87sr 86sr ratios from 0 7081 0 7087 mean 0 7084 sr concentrations from 30 to 79 p p m mean 50 p p m and mn content from 50 to 253 p p m mean 161 p p m and negative ce anomalies compared with those of marine limestones the medium crystalline dolomite may have formed either 1 during shallow burial at slightly elevated temperatures 35 40 c from fluids derived from burial compaction or more likely 2 soon after deposition of the precursor sediments by middle devonian seawater derived from the elk point basin these results indicate that dolomitization in the middle devonian presqu ile barrier occurred in at least two stages during evolution of the western canada sedimentary basin the geochemistry of earlier formed dolomites may have been modified if the earlier formed dolomites were porous and permeable and water rock ratios were large during neomorphism