geology of a vigorous hydrothermal system on the endeavour segment juan de fuca ridge a high precision high resolution geologic map explicitly documents relationships between tectonic features and large steep sided sulfide sulfate silica deposits in the vigorously venting endeavour hydrothermal field near the northern end of the juan de fuca ridge water depth in the vent field varies from 2220 to 2200 m location of the most massive sulfide structures appears to be controlled by intersections of ridge parallel normal faults and other fracture fissure sets that trend oblique to and perpendicular to the overall structural fabric of the axial valley the fractured basaltic substrate is primarily composed of well weathered pillow and lobate flows as presently mapped the field is about 200 by 400 m on a side and contains at least 15 large 1000 m3 sulfide edifices and many tens of smaller commonly inactive sulfide structures the larger sulfide structures are also the most vigorously venting features in the field they are commonly more than 30 m in diameter and up to 20 m in height actively venting sulfide structures in the northern portion of the field stand higher and are more massive than active structures in the southern portion of the field which tend to be slightly to distinctly smaller maximum venting temperatures of 375 c are associated with the smaller structures in the southeastern portion of the field highest temperature venting fluids from the more massive structures in the northern portion of the field are consistently 20 30 c lower hydrothermal output from individual active sulfide features varies from no flow in the lower third of the edifice to vigorous output from fracture controlled black smoker activity near the top of the structures a different type of high temperature venting takes place from the upper sides of the structures in the form of overflow from fully exposed quiescent pools of buoyant 350 c vent water trapped beneath overhanging sulfide sulfate silica ledges or flanges these flanges are attached to the upper outer walls of the large sulfide edifices two types of diffuse venting in the endeavour field include a lower temperature 8 15 c output through colonies of large tubeworms and 25 50 c vent fluid that seems to percolate through the tops of overhanging flanges the large size and steep walled nature of the these structures evidently results from sustained venting in a mature hydrothermal system coupled with dual mineral depositional mechanisms involving vertical growth by accumulation of chimney sulfide debris and lateral growth by means of flange development

the distribution of geothermal fields on the juan de fuca ridge near bottom water temperatures were mapped along 400 km of the strike of the juan de fuca ridge as part of a combined sea marc seabeam experiment to image the variability of morphology and structure along a spreading center segment the water temperature data collected by a continuously towed thermistor chain in addition to salinity data indicate that there are four geothermal areas spaced at distances of 100 km from each other south of the cobb propagator and one field just to the north of the propagator on the endeavor ridge segment each thermal region is located above a morphological dome on the spreading center these domes are an average of 100 200 m shallower than the rest of the axis the structure of bottom water suggests that the geothermal regions are on average 20 km long and that the heat from these fields raises the temperature in the water column by a minimum of 0 06 sup 0 c up to 300 m above the bottom two simple models are used to estimate the heat flux associated with these features

morphological characterization of cluster microforms a field study was conducted on two mountain streams in the cascade mountains of washington state on the morphological characterization of cluster microforms morphological characterization of clusters is presented in terms of i cluster shape ii cluster geometric properties and iii the spatial arrangement of clusters in the horizontal plane clusters were differentiated from other microtopography features such as reticulate structures and transverse ribs and identified clusters were categorized by shape as being of pebble line comet heap or ring type the complex spatial arrangement of clusters at the sites was characterized by using a two dimensional correlation function which allowed for measurement of the average cluster spacing properties for the rivers examined pebble shaped clusters were the most frequently observed cluster shape cluster geometric properties were found to be controlled by particles of the largest size fraction in the bed and the projected frontal width of the cluster with cluster length being linearly related to cluster width for cluster width to height ratios 3 5 results of the cluster spacing analysis suggest that cluster spacing increases with cluster size and decreases with local slope application of this principle to the available spacing data shows that cluster spacing scales with the ratio of s d0 such that s d0 constant where s is the local slope and d0 the diameter of the largest particle in the cluster

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

pb zn deposits and salt bearing diapirs in southern europe and north africa many diapirs with triassic evaporite successions in southern europe and north africa are accompanied by strata bound pb zn mineral deposits these are of two types 1 epigenetic mineralization filling cavities exhibiting analogies with mississippi valley type deposits and 2 syndiagenetic mineralization in sediments rich in organic materials this second type is very similar to the so called volcanic exhalative type in most of these ore deposits diapirism seems to be a determining factor in the development of base metal concentrations diapir growth can be divided into four distinct stages initiation ascent piercement and subsequent deformation study of north african and southern european deposits has led to a genetic model of diapir emplacement and associated pb zn mineralization the source of these metals is unknown the transport of the metals is provided or facilitated by the brine from adjacent triassic evaporites deposition of sulfides occurs where the deep fluids meet the upper beds these deposits can be remobilized with each new phase of diapir growth

paleohydrogeology of the canadian rockies and origins of brines pb zn deposits and dolomitization in the western canada sedimentary basin results of stable isotopic and fluid inclusion studies of cambrian carbonate units in the southern canadian rockies indicate that during the late devonian or early mississippian a warm brine migrated from miogeoclinal shales in the western part of the western canada sedimentary basin into the eastern carbonate sequences this fluid had a temperature of 150 25 c salinity values of 20 to 25 equivalent wt nacl and isotopic values of 18 o 7 to 0 13 c 1 2 d 70 19 and 87 sr 86 sr 0 710 the fluids formed large bodies of coarse sparry dolomite as well as pb zn magnesite and talc mineralizations in the cambrian units it is probable that this event was also responsible for the development of pb zn mineralization specifically pine point in the devonian units as well as a component of the present day basinal brines in the basin

sediment supply limited bedforms in sand gravel bed rivers the stability of bedforms in mixtures of gravel and sand is not well understood two bedform types are characteristic flow parallel sand ribbons and flow transverse barchans flume experi ments and field data presented here show that gradual transitions exist from sand ribbons to barchans and from barchans to fully de veloped dunes barchans and sand ribbons occur when not enough transportable sediment is available for the formation of fully devel oped ripples or dunes the reason is that a part of the bed sediment is immobile e g with an armor layer which limits the sediment sup ply and thus the volume of sediment available for the formation of bedforms bedform stability diagrams are shown to be extendable to sedi ment supply limited bedforms in sand gravel sediment if the par ticle parameters of the diagrams are derived from the transported sediment instead of the bed sediment barchans and forms transi tional to fully developed dunes plot in the dune stability fields sand ribbons on the other hand plot in the ripple lower plane bed and dune fields in the case of sediment supply limitation bedforms are partly or completely related to the characteristics of the sediment supply from upstream the sediment underlying the bedforms may be a stable armor and the exchange of sediment between this armor and the bedforms may be small or non existent consequently bedform char acteristics in sand gravel mixtures in supply limited conditions often are not predictable from the local hydraulics and sediment charac teristics

variations in ambient light emission from black smokers and flange pools on the juan de fuca ridge ambient light emitted by high temperature black smokers and flange pools on the juan de fuca ridge was imaged using a new spectral imaging camera most of the light is emitted at long wavelengths 700 1000 nm and corresponds well to thermal radiation from a body at the same temperature as the vents flanges however black smokers also emit time varying radiation in the visible region 400 650 nm which cannot be explained by a thermal source this visible radiation is 1 2 orders of magnitude greater than would be expected for purely thermal radiation it exhibits variation with time despite relatively constant vent temperatures and it is not associated with the hottest part of the plume i e the orifice flange pools do not exhibit excess visible light over that for a thermal source suggesting that the light at smokers is caused by mechanisms related to turbulence mixing or precipitation

erosion of sand from a gravel bed abstractcleaning of fine sediment out of gravel streambeds has become an important method to restore affected stream habitats introducing the increased flows needed to entrain fine sediments without eroding the coarser fractions of the bed and potentially destroying its usefulness as a habitat requires careful selection of flow strength toward this end a series of flume experiments was conducted on the entrainment of sand from immobile gravel beds to determine the depth to which the sand could be eroded without the gravel being mobilized a series of steady flows was imposed on three gravel beds filled with sand with median sizes of 0 2 0 3 and 0 9 mm the shear stress of the series of flows ranged from just above the critical shear stress for initiation of motion of the sand up to 0 9 times the critical stress of the 36 1 mm gravel the experiments continued until the rate of fine sediment exiting the channel was very small it was found that the cleanout depth of the sand was reasonably predicted b

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

the significance of rb sr glauconite ages bonneterre formation missouri late devonian early mississippian brine migration in the midcontinent rb sr mean model ages of 370 plus minus 10 ma for glauconites from the cambrian lower bonneterre formation in southern and central missouri are in excellent agreement with a rb sr isochron age of 359 plus minus 22 ma for glauconites from the magmont mine viburnum trend in the southeast missouri lead district the lower bonneterre and magmont mines ages probably reflect isotopic resetting most likely associated with dolomitization and or mississippi valley type ore formation in the southeast missouri lead district the temporal relation between widespread dolomitization and ore formation in missouri is unclear but mounting evidence for two devonian disturbances permits the following interpretation 1 a devonian timing 380 400 ma for widespread dolomitization and 2 a late devonian early mississippian timing 360 370 ma for ore formation in southeast missouri late devonian early mississippian fluids associated with the earliest stages of collisional tectonics and metamorphism to the south and southeast may have been important in the formation of southeast missouri ore deposits these tectonically driven waters may themselves have been the mississippi valley type ore fluids entering missouri by way of the black warrior basin and reelfoot rift and or the arkoma basin alternatively the movement of orogenic fluids hundreds of kilometers distant may have initiatedmore and distally influenced the migration of more locally derived mississippi valley type ore fluids broad regions of missouri and adjacent areas experienced heating and crustal flexing in the late devonian and consequently preservation of elevated temperatures in mississippi valley type fluids as they move great lateral distances may not be necessary for ore formation in southeast missouri less

tectonic evolution of the northern african margin in tunisia from paleostress data and sedimentary record abstract a reconstruction of the tectonic evolution of the northern african margin in tunisia since the late permian combining paleostress tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns the extension lasting from the late permian to the middle triassic is contemporaneous of the rifting related to the break up of pangea during liassic times regional extensional tectonics originated the dislocation of the initial continental platform in northern tunisia the evolution of the liassic ne sw rifting led during dogger times to the north african passive continental margin whereas in southern tunisia a n s extension associated with e w trending subsiding basins lasted from the jurassic until the early cretaceous after an upper aptian early albian transpressional event ne sw to ene wsw trending extensions prevailed during late cretaceous in relationship with the general tectonic evolution of the northeastern african plate the inversions started in the late maastrichtian paleocene in northern tunisia probably as a consequence of the africa eurasia convergence two major nw se trending compressions occurred in the late eocene and in the middle late miocene alternating with extensional periods in the eocene oligocene early middle miocene and pliocene the latter compressional event led to the complete inversion of the basins of the northwestern african plate originating the maghrebide chain such a study supported by a high density of paleostress data and including complementary structural and stratigraphic approaches provides a reliable way of determining the regional tectonic evolution

bedload model for nonuniform sediment abstractin this study a bedload model for nonuniform sediment is developed considering the density function of sediment entrainment with no active layer the model is formulated based on physical considerations dimensional reasoning regression analysis and laboratory data four parameters are incorporated in the model formulation namely the shields stress g the critical shields stress cg the kramer coefficient of uniformity cu and the relative grain size size of the jth grain fraction to the geometric mean size dj dg the model collectively accounts for the hiding effects and the variation of the transported bedload material fractions from the surface and subsurface material the findings of the study show that at low values of g cg fractions within the range of 0 3 dj dg 3 0 are present with larger amounts in the transported bedload material than in the substrate whereas fractions finer or coarser than that range are present with larger amounts in the surface layer than in the subst

spatially averaged flows over mobile rough beds definitions averaging theorems and conservation equations abstractthis paper reports the double averaged in space and in time hydrodynamic equations for mobile boundary conditions that are derived based on the refined double averaging theorems modified reynolds decomposition and improved definitions of the spatial and time bed porosities the obtained double averaged conservation equations provide a mathematical framework for studying mobile boundary flows such as gravel bed rivers during flood events or flows over vegetated beds these equations will help in designing measurement campaigns for obtaining mobile bed data and their interpretation and parameterization eventually leading to improved and more robust predictive models

sources of light in the deep ocean studies during recent decades have shown that the deep ocean depths below where solar luminance plays a direct environmental role is far from a dark cold lifeless region evidence obtained by utilizing a variety of photo optical devices providing spatial temporal and spectral information has demonstrated that this portion of the earth is a region rich in life and light findings to date have provided challenges for geologists physicists biologists chemists and oceanographers and the sharing of techniques and expertise among these disciplines has demonstrated the rewards to be gained from interdisciplinary research bioluminescence has been found far below the depths at which it has received most attention historically the study of this phenomenon is complicated by the fact that the measuring apparatus itself causes a stimulation of the luminescence so that a true background will be difficult to determine nuclear physics has played a role in that the electron resulting from the decay of an isotope of potassium k40 provides an ubiquitous background of light through a process known as cerenkov radiation the possibility of light generated by cosmic rays must also be taken into account an intriguing source of light at the very bottom of the sea is found at hydrothermal vents here are found not only light but also abundant life at the vent orifice temperatures are found to be as high as 250 400 c a large component of the light is due to thermal radiation however the light in the wavelengths 450 600 nm is significantly greater than the thermal flux at those wavelengths identifying the physical mechanisms that may account for this excess is important in providing insight into the processes occurring in the vents and plumes and in the accompanying ecosystem

pbzn mineralization associated with diapirism fluid inclusion and stable isotope h c o evidence for the origin and evolution of the fluids at fedj el adoum tunisia pb zn mineralizations occur in the contact zone to a saliferous diapir and its surrounding cretaceous limestonerich sediments the diapir of triassic formations was initially intruded hot from a depth of 3 7 km during the cretaceous three principal types of mineralization occur bedded vein and massive combined microthermometric and stable isotope h c o studies have characterized three principal thermal events before cool meteoric waters entered the system 1 1 hot 170 250 c saline 22 33 eq wt nacl fluids of probable deep formation water origin with d 43 and 18o 20 precipitated calcite with 13c 8 and celestite in the inner part of the contact zone with the diapir 2 2 hot 100 130 c saline 18 23 eq wt nacl fluids with d 60 and 18o 13 containing co2 n2 and hydrocarbons precipitated sphalerite calcite 13c 9 quartz and minor galena as banded mineralization in the outer part of the contact zone more galena rich vein mineralizations in the contact zone were deposited at similar temperatures from comparable fluids mineralizing solutions are interpreted to be formation waters with the carbonate carbon being derived from organic carbon the colloform textures in the banded mineralization suggest that the nearby sedimentary basin underwent episodic dewatering 3 3 warm 70 90 c saline 16 22 eq wt nacl fluids with d 110 and 18o 10 precipitated calcite with 13c 16 galena rich ore in the massive mineralizations and vein mineralizations in the cenomanian turonian limestones and essentially sulphide free calcite in the banded and contact vein mineralizations a locally derived organic water origin is proposed where both hydrogen and carbon were derived from organic constituents such as petroleum during bacterial sulphate reduction reactions variable d and salinity values suggest mixing processes between the d depleted organic water and a more d rich formation or meteoric water 4 4 low temperature 50 c meteoric waters with d 15 to 25 introduced a second generation of calcite with the carbonate largely coming from the sedimentary carbonates in the massive and turonian vein mineralizations anhydrite was probably converted to gypsum at about this time and before fedj el adoum arrived at its present altitude

carbonate hosted zinc lead deposits in the lower cambrian of hunan south china a radiogenic pb sr isotope study zinc lead deposits hosted by lower cambrian carbonate rocks near huayuan in the hunan guizhou orogenic belt southern china have been studied by means of pb and sr isotopes the deposits are characterized by two mineralization stages 1 a main economic stage comprising cockade style sphalerite galena pyrite marcasite fluorite barite and calcite and 2 a subsequent noneconomic stage with nodular rosette sphalerite saddle dolomite and bitumen both ore stages are postdated by a generation of late calcite main stage sulfides 206pb 204pb 18 162 18 225 display a steep linear trend on conventional pb pb diagrams which indicates binary mixing of lead components bearing the imprint of ancient 207pb dominated crustal rocks and reservoirs with elevated th u ratios possibly located in the lower crust nodular rosette sphalerites fall outside this line but reflect a second mixing trend between mineralizing fluids characterized by 206pb 204pb 18 3 and lead isotopically similar to specific main stage cockade sphalerites suggesting either remobilization of pb from main stage ores or contemporaneous mixing of three distinct lead components in the course of an evolving hydrothermal event the 87sr 86sr ratios of diagenetic and hydrothermal carbonate cements and barites range from 0 70905 to 0 71006 and increase systematically with the paragenetic sequence indicating progressive mixing of marine sr derived from the lower cambrian carbonate host rocks with radiogenic sr supplied by external mineralizing fluids in order to identify possible local metal sources u pb and rb sr analyses were performed on six whole rock samples from the lower cambrian sequence and their time integrated pb and sr isotope evolution was compared to the isotopic signature of the mineralization whereas shales and black shales of the cambrian balang and niutitang formations underlying the ore bearing qingxudong carbonate unit appear to be possible external sources for the radiogenic sr found in hydrothermal carbonates the u pb data do not permit these shales to be considered as primary source rocks for the ore lead both the pb and the sr isotopes indicate mineralizing fluids that had interacted with various external metal sources some of them most probably being located in sedimentary or crystalline basement rocks this refutes prevailing genetic models favoring the hydrocarbon and metal rich lower cambrian niutitang black shales as the most likely source reservoir for the zn and pb in the deposits of the huayuan district the pb and sr isotope mixing trends observed for the ore and gangue preciptates reflect small scale heterogeneous fluid systems that were not capable of producing large deposits this may indicate that the huayuan district is not a favorable target for future exploration of economic ore deposits it also limits the prospects of successful radiometric dating of the mineralization since conventional geochronologic models require initial isotopic homogeneity

turbulent flows within random arrays of rigid and emergent cylinders with varying distribution abstractthe spatial distribution of emergent vegetation in rivers is frequently nonuniform here spatial nonuniformity is simulated in the laboratory by varying longitudinally the stem areal number density m time and space averaged flow variables corresponding to different values and gradients of m and different stem reynolds numbers are calculated from instantaneous velocity maps obtained with particle image velocimetry piv results show that reynolds stresses are completely determined by the local spatially averaged number of stems per unit area they are not sensitive to local spatial gradients of m these variables seem to adjust locally to the spatial variations of the stem distribution contrarily the spatial distribution of the time averaged flow is influenced not only by the local value of m but also by its spatial gradients form induced stresses express this influence they reveal a subsistence of flow complexity generated by the upstream stem distribution as a form of spatial memory

gradients in the composition of hydrothermal fluids from the endeavour segment vent field phase separation and brine loss hydrothermal fluid samples collected in 1984 1987 and 1988 from a large vent field near 47 57 n on the endeavour segment of the juan de fuca ridge jfr have been analyzed for major and minor elements and gases there are of the order of 100 individual smoker vents on 10 large sulfide structures which are localized along faults and fault intersections across the vent field each sulfide structure has a characteristic fluid composition which varies very little from one vent orifice to the next or from year to year on a given structure however there are large gradients in fluid composition across the vent field with endmember chlorinity increasing from 255 mmol kg in the sw to 505 mmol kg in the ne end member concentrations of major elements are well correlated with chlorinity and endmember volatile concentrations in the lowest chlorinity fluids are approximately twice as high as in the highest chlorinity fluids the gradients in composition across the vent field and measured vent fluid temperatures 400 c are consistent with supercritical phase separation and loss of brine phase below the seafloor the factor of 2 variation in co2 and h2s is larger than expected for loss of a very high chlorinity brine concentrations of iron and manganese are not positively correlated with chlorinity suggesting that temperature and ph are more important in controlling metal solubility elevated ammonia and bromide chloride ratios indicate that there has been subseafloor interaction between the hydrothermal fluids and organic matter and high boron concentrations point to a sedimentary source

the pb sr nd isotope geochemistry of some recent circum mediterranean granites pb sr and nd isotopic compositions have been analyzed in recent granites from northern africa northern italy and greece lead isotope compositions of k feldspars are rather homogeneous and cluster close to the modern lead of stacey and kramers 1975 but with slightly higher207pb 204pb and208pb 204pb ratios the cyclades samples however have higher206pb 204pb ratios addition of mantle derived lead was probably very limited which supports a quasi closed system evolution of this element in the continental crust the sr nd data fall in the enriched part of the143nd 144nd vs 87sr 86sr diagram and define a smooth hyperbolic mixing curve over a wide area straddling different orogens most granites may be accounted for by a binary mixture between a recycled crustal component and a depleted mantle like component no correlation is observed between either pb and sr or nd isotopic ratios or any isotopic ratio and major element contents quantitative modelling suggests that two cases fit the sr and nd characteristics of these granites they both require anatexis of the crust on a scale large enough to average the isotopic properties of heterogeneous terranes in the first case the mantle derived component may be represented by differentiated island arc type magmas and the granites result from mixing these magmas with anatectic melts in the second case mantle derived igneous rocks such as obducted ophiolites are part of the crustal source and their variable involvement in the anatectic process causes isotopic variations

les mineralisations stratiformes a f ba de hammam zriba jebel guebli tunisie nord orientale l apport des etudes d inclusions fluides a la modelisation genetique le gite de h zriba j guebli reserves 5 millions de tonnes a 15 35 caf2 est constitue pour l essentiel d amas stratoides encaisses dans des formations phosphatiferes argileuses et carbonatees d ge campanien inferieur quatre formations mineralisees mo fr f2 et f3 ont ete distinguees la plus ancienne formation mo ne contient pas de fluorine elle est a dominante quartzeuse ou barytique avec quelques sulfures le minerai a fluorine rubanee formation f1 est le plus important sous l angle economique trois types d inclusions fluides ont ete observes dans la fluorine 1 d abondantes inclusions aqueuses 2 de rares inclusions gazeuses et 3 de frequentes inclusions a hydrocarbures liquides jaunes fluorescentes en eclairage u v les etudes microthermometriques montrent une augmentation des temperatures d homogeneisation 100 a 130 c dans la fluorine f1 150 185 c dans la fluorine f3 avec augmentation parallele de la salinite des solutions piegees on propose un modele de mise en place de la fluorine par voie epigenetique a partir de solutions semblables aux eaux de formation des champs petroliferes suivi par des remaniements lies a des circulations hydrothermales recentes

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

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

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

large scale particle image velocimetry for low velocity and shallow water flows large scale particle image velocimetry lspiv is an extension of quantitative imaging techniques for measurements of water surface velocities using inexpensive standard video equipment the present technical note describes capabilities and limitations of lspiv for low velocity shallow flows measurements in low velocity shallow flume flows were performed to investigate the lspiv sensitivity to seeding density and time interval between successive images the results show that the accuracy of the lspiv technique does not deteriorate as the flow velocity is reduced to as low as 0 015 m s provided an adequate seeding and suitable time difference between images are selected the results suggest that lspiv is well suited for flow fields with small velocities that are often below the limit of detection of most conventional devices

bedload transport in the instrumented catchment of the rio cordon part ii analysis of the bedload rate abstract sediment transport is monitored by a specially designed instrumentation installed on a steep mountain streams the rio cordon the variability of bedload rate and yield reflects the variability in flow discharge bedload and flow data for ordinary low peak flow floods and exceptional sediment transport events are used to test the range of application of the bedload equations proposed for high gradient streams such equations overestimate bedload rate for ordinary events while their reliability increases when used to predict high bedload transport rates like those recorded during the exceptional flood that affected rio cordon on september 14 1994 the best agreement between computed and measured values of cumulated bedload volumes is found by using the bagnold bagnold r a 1956 the flow of cohesionless grains in fluids philos trans r soc london 249a 235 297 smart and jaeggi smart j m jaeggi m n r 1983 sediment transport on steep slopes mitteil 64 versuchsanstalt fur wasserbau hydrologie und glaziologie eth zurich switzerland 191 pp and rickenmann rickenmann d 1991 hyperconcentrated flow and sediment transport at steep slopes j hydraul eng zurig 117 11 1419 1439 formulas the schoklitsch equation schoklitsch a 1962 handbuch des wasserbaues 3rd edn springer wien also provides good estimations for instantaneous bedload rates at high sediment transport intensity and unlimited sediment supply conditions the formal type of the last equation is still valid and can be calibrated for low intensity bedload rates

field mapping and digital elevation modelling of submerged and unsubmerged hydraulic jump regions in a bedrock step pool channel high resolution tacheometric field surveying was integrated with computer assisted drafting to visualize and contrast three dimensional bed and water surface digital elevation models dems for submerged and unsubmerged hydraulic jump regions in a bedrock step pool channel measurements were conducted for two discharge conditions since previous applica tions of three dimensional field mapping and digital elevation modelling of stream channels have been limited to smoothly contiguous gravel bedded systems surveying was optimized by topographic setting and scaled to localized bed and water surface discontinuities traces and visualizations of the jump regions indicated that dichotomous decimetre shifts in water surface topography occurred for both jump regions from lower to higher discharges systematic removal of the survey points and dem differencing indicated that point densities of ten points per square metre in conjunction with a survey structure targeting grade breaks of 0 3 0 5 m were required to capture decimetre form variations of the natural jump regions the dems highlight the importance of recognizing the relationship between transcritical flow structures and localized topographic heterogeneities in bedrock channels copyright 2006 john wiley sons ltd

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

growth of large sulfide structures on the endeavour segment of the juan de fuca ridge abstract mapping and sampling with dsrv alvin has established that sulfide blocks 0 5 m across dredged from the axial valley of the endeavour segment at 47 57 n are samples of unusually large sulfide structures the steep sided structures up to 30 m in length 20 m in height and 10 15 m across are localized by venting along normal faults at the base of the western axial valley wall and are distributed for about 200 m along strike paralleling the 020 trend of the ridge crest high temperature fluids 350 to more than 400 c pass through the massive sulfide structures and enter seawater through small concentric nozzle like features projecting from the top or the sides of the larger vent structures diffuse low temperature flow is pervasive in the vicinity of the active sulfide structures exiting from basalt and sulfide surfaces alike evidence of recent volcanic activity is sparse the two largest samples taken with the dredge would not have been recoverable using the submersible these samples represent massive complex portions of the sulfide structures which were not closely associated with rapid high temperature fluid flow at the time of sampling they contain textural evidence of sealed hydrothermal fluid exit channels mineralogy is dominated by fe sulfides nnd amorphous silica pyrite marcasite wurtzite chalcopyrite and iss are the most common sulfide phases pyrrhotite galena and sphalerite are present in trace amounts barite amorphous silica and chalcedony are the only non sulfide phases anhydrite is not observed in any of the dredge samples although it is common in the chimney like samples recovered by alvin specific mineralogical textural zones within the dredge samples are anaoogous to individual layers in east pacific rise at 21 n and southern juan de fuca ridge samples with two exceptions a coarse grained highly porous fe sulfide rich interior containing sulfidized tubeworm casts and a 2 5 cm thick zone near the outer margin of the samples dominated by late stage amorphous silica the porous interior may have formed by dendritic crystal growth from a slowly circulating fluid within a large enclosed chamber the amorphous silica deposited from a seawater hydrothermal fluid mixture percolating slowly through the walls of the enclosed chamber conductive cooling of the fluid as it traversed the walls allowed amorphous silica to precipitate these silica rich zones are the densest most durable portions of the structures and may be responsible for the lasting stability of the large sulfide features observations in these samples are consistent with two distinct phases of development phase 1 is analogous to chimney growth and construction at 21 n and ends when flow channels become sealed to rapid flow of through going fluid the flow is evidently redirected within the structure phase 2 includes dissolution of anhydrite and precipitation of amorphous silica during conductive cooling of sluggishly circulating hydrothermal fluid or seawater hydrothermal fluid mixtures evolution of vent structures through phase 2 allows lateral and vertical growth of unusually large structures

sand transport over an immobile gravel substrate abstractexperiments were conducted in a laboratory flume channel to evaluate the effects of increasing amounts of sand on its transport over and through an immobile coarse gravel bed detailed measurements of sand transport rate bed texture and bed topography were collected for four different discharges at approximately the same flow depth of 0 2 m for 11 different elevations of sand in the gravel bed sand transport was measured using both physical samples and a density cell for a given flow rate increases in the elevation of sand relative to gravel resulted in decreases of bed shear stress from 32 44 and increases in sand transport by three orders of magnitude for the highest two discharges the sand merged into a small number of long and low bed forms that translated through and over the gravel bed a collapse of the transport data was accomplished by relating the sand transport rate to the bed shear stress scaled by the cumulative probability distribution function of the gravel surface evaluated

investigating the role of clasts on the movement of sand in gravel bed rivers the bed morphology of mountain rivers is characterized primarily by the presence of distinguishable isolated roughness elements such boulders or clasts the objective of this experimental study was to provide a unique insight into the role of an array of clasts in regulating sand movement over gravel beds for low relative submergence conditions h dc 1 and flow depth h to the diameter of the clast dc a process that has not been studied thoroughly to assess the role of clasts in controlling incoming sand movement detailed flume experiments were conducted by placing 40 equally spaced clasts atop a well packed glass bead bed for replicating the isolated roughness flow regime the experiments were performed for moderate 2 50 cr where cr is the critical dimensionless bed shear stress and high 5 50 cr applied bed shear stress conditions representative of gravel bed rivers for comparison purposes experiments were also repeated for nearly identical flow conditions but without the presence of

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

unobstructed and obstructed turbulent flow in gravel bed rivers an acoustic doppler velocimeter was used to characterize turbulence in two gravel bed rivers data were collected in unobstructed flow and compared to recent investigations additional data collected in the wake of emergent boulders indicate that mean flow velocity turbulent kinetic energy gradients in the streamwise velocity and reynolds stress downstream from large rocks deviate from unobstructed flow results but similar turbulence patterns are found behind each boulder results of this study are discussed with regard to natural channel design and fish habitat

calculating bed load transport in steep boulder bed channels 1 steep rough channels occupy a large fraction of the total channel length in mountainous regions most sediment mobilized on hillslopes must pass through these streams before reaching lower gradient channels steep channels have wide grain size distributions that are composed of finer more mobile sediment and large rarely mobile grains the large grains can bear a significant portion of the total shear stress and thereby reduce the stress available to move the finer sediment conventional bed load transport equations often overpredict the sediment flux in steep channels by several orders of magnitude we hypothesize that sediment transport equations overpredict the sediment flux because they do not 1 account for the stress borne by rarely mobile grains 2 differentiate between highly and rarely mobile sediment and 3 account for the limited availability of mobile sediment here we modify a conventional bed load transport equation to include these three effects we use measurements of the flow bed properties and sediment flux in a small steep flume to test this equation we supply gravel at a constant rate through fields of regularly spaced immobile spheres and measure the bed coverage by gravel and sphere protrusion the percent of the sphere that protrudes above the gravel deposit for a given sphere spacing the proportion of the bed covered by gravel increases and the sphere protrusion decreases with greater sediment supply thus bed coverage and immobile grain protrusion may serve as proxies for sediment availability in steep rough streams unlike most transport equations that we tested our modified bed load equation predicts sediment fluxes to within an order of magnitude of the measured values our results demonstrate that accurately predicting bed load transport in steep rough streams may require accounting for the effects of local sediment availability coverage by mobile sediment and drag due to rarely mobile particles

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

diapirism in northern tunisia abstract the diapirs of northern tunisia composed mainly of evaporitic triassic material are the result of a complex evolution initiated by local basement movements of nne ssw faults which at the end of the early cretaceous this first uplift occurring during a period without any folding of the sedimentary series is purely halokinetic such diapiric activity remained in active progress throughout the cretaceous and early tertiary causing local disturbance in the related series and then during the alpine atlas orogeny the diapiric structures underwent deformation according to their position in the orogenic area

effect of bed sand content on the turbulent flows associated with clusters on an armored gravel bed surface abstractas a gravel bed river armors a bed surface often develops clusters as part of its structure the influence of sand on armoring and the impact of clusters on the surrounding flow processes were investigated through flume experiments armored beds were created from four different sediments which progressively increased from 1 38 sand in the bed sediment extending from gravel framework to sand matrix beds turbulent kinetic energy tke and xz direction reynolds stress calculated from velocity profiles showed the clusters increased turbulence and induced formation of recirculation cells similar recirculation cells formed downstream of every cluster but the strength and orientation of these cells varied with bed condition the increase in sediment sand content and change in bed condition from gravel framework to sand matrix correlated to an increase in the energy and momentum in the recirculation cell but a reduction in cluster influence across the flow profile results show that the sand conten

a novel eye in eyeless shrimp from hydrothermal vents of the mid atlantic ridge rimicaris exoculata1 is a shrimp that swarms over high temperature 350 c sulphide chimneys at mid atlantic ridge hydrothermal fields 3 600 m 1 7 this shrimp lacks an externally differentiated eye1 having instead a pair of large organs within the cephalothorax immediately beneath the dorsal surface of the transparent carapace connected by large nerve tracts to the supraesophageal ganglion these organs contain a visual pigment with an absorption spectrum characteristic of rhodopsin ultra structural evidence for degraded rhabdomeral material suggests the presence of photoreceptors no image forming optics are associated with the organs we interpret these organs as being eyes adapted for detection of low level illumination and suggest that they evolved in response to a source of radiation associated with the environment of hydrothermal vents

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

hydrothermal fluid origins in mississippi valley type ore districts combined noble gas he ar kr and halogen cl br i analysis of fluid inclusions from the illinois kentucky fluorspar district viburnum trend and tri state districts midcontinent united states samples were selected from three of the classic mississippi valley type districts in the midcontinent area of north america the illinois kentucky fluorspar district belongs to the fluoritic subtype of mississippi valleytype districts and the ozark districts of the viburnum trend and tri state are representative of the pb rich and more typical zn rich subtypes of mississippi valley type mineralization respectively noble gas ar kr and halogen cl br i data have been obtained simultaneously by noble gas mass spectrometry of inclusion fluids released by in vacuo crushing of irradiated fluorite quartz carbonate and sphalerite samples additionally he analyses have been obtained from nonirradiated fluorite from the illinois kentucky fluorspar district fluorite from the illinois kentucky fluorspar district has a maximum 3 he 4 he ratio of 0 35 ra where ra atmospheric 3 he 4 he ratio of 1 4 10 6 higher than values typical of crustal fluids and confirming the presence of a minor mantle component equal to less than 6 percent of the total he in the fluids of the illinois kentucky fluorspar district the br cl mol ratios of all the deposits are with one exception higher than the value of seawater 1 54 10 3 ranging from 1 69 to 3 70 10 3 and indicating acquisition of salinity by the evaporation of seawater beyond the point of halite saturation late quartz from the tri state district contains a very minor component of halite dissolution water and has a br cl mol ratio of 1 46 10 3 the i cl mol ratios are typical of oil field brines and are ubiquitously higher than what is attainable by the evaporation of seawater alone i cl mol ratios are in the range of 6 to 270 10 6 indicating that the fluids have interacted with i rich organic matter present in sedimentary rocks in the ozark districts 40 ar 36 ar ratios vary between 320 and 345 in the tri state and between 350 and 420 in the viburnum trend in the illinois kentucky fluorspar district 40 ar 36 ar ratios reach values of 1 200 the corresponding concentrations of 40 arexcess 40 ar not attributable to radiogenic decay of 40 k or an atmospheric source are similarly elevated in the main stage fluorite mineralization of the illinois kentucky fluorspar district 6 8 18 2 10 4 cm 3 cm 3 h2o relative to the viburnum trend and tri state districts mostly 1 3 3 3 10 4 cm 3 cm 3 h2o and 0 3 1 4 10 4 cm 3 cm 3 h2o respectively together the noble gas and halogen data indicate the existence of three brine provinces 1 a regional tristate brine present throughout the ozark region 2 a viburnum trend brine and 3 an illinois kentucky brine furthermore in the viburnum trend the halogen composition of main stage dolomite is distinct from that of the main stage sphalerite but identical to the regional hydrothermal dolomite seen in the tri state district the data imply that mixing relationships in the viburnum trend are highly complex but are compatible with regional models in which the tri state brine present throughout the ozark region was sourced in the arkoma basin

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

influence of rock fragment coverage on soil erosion and hydrological response laboratory flume experiments and modeling two laboratory flume experiments on the effect of surface rock fragments on precipitation driven soil erosion yields were carried out the total sediment concentration the concentration of seven individual size classes and the flow discharge were measured digital terrain models dtms were generated before and after one of the experiments the results revealed that the rock fragments protected the soils from raindrop detachment and retarded the overland flow therefore decreasing its sediment transport capacity rock fragments were found to affect selectively the different size classes in a manner that changed according to the time scale for short times the rock fragment coverage reduced erosion of the finer particles 100 m was unaffected at long times the rock fragment cover decreased the concentration of the individual size classes in proportion to effective rainfall intensity and the area exposed to raindrops an area based modification of the hairsine and rose h r soil erosion model was employed to analyze the experimental data the h r model predictions agreed well with the measured sediment concentrations when high rainfall intensity and low rock fragment cover were used predictions were instead less accurate with low rainfall intensity and high rock fragment cover the dtm results showed that the presence of rock fragments on the soil surface led to increased soil compaction perhaps due to higher soil moisture content from greater infiltration within the rock fragment covered flumes

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

stochastic incipient motion criterion for spheres under various bed packing conditions incipient motion criteria based solely on time averaged bed shear stress may underpredict sediment transport the focus of this study is on the stochastic aspect of the problem of incipient motion specifically the role of near bed turbulent structures and bed packing density on the commencement of sediment motion is investigated the cornerstone of the proposed model is based on the concept that the particle motion is governed by the intermittent nature of near bed turbulence based on this mechanism in this article we provide a quantitative model for predicting the commencement of sediment entrainment for the first time under three representative bed packing densities corresponding to the isolated wake interference and skimming flow regimes the performance of the proposed model is compared to published experimental data and the conventional approach that is based on the consideration that flow parameters are statistically well represented by a normal distribution

emerald mineralisation in colombia fluid chemistry and the role of brine mixing emerald mineralisation in colombia is located in two distinct zones along the borders of the eastern cordillera some 80 km apart mineralisation in the western zone has been dated at ca 35 ma whereas in the eastern zone it is 30 ma older crush leach analysis of the electrolyte chemistry of fluid inclusions contained in emerald quartz calcite dolomite and fluorite from both zones demonstrates that in each region brines associated with emerald mineralisation range between two extremes with many samples yielding intermediate compositions fluid 1 found mainly in emerald hosted fluid inclusions is dominated by nacl with high cl br ratios indicating that the salinity was derived by dissolution of halite most probably from the local salt beds fluid 2 found notably in quartz hosted fluid inclusions is of similar salinity but contains less na and significant concentrations of ca k fe cl and other cations it has lower cl br ratios more comparable with formation waters but is inferred to have obtained part of its salinity by halite dissolution bivariate plots of almost all cations have linear or sublinear trends regardless of the mineral hosting the inclusions or the locality from which the samples originated demonstrating that mixing of the two saline fluids has occurred because the same two fluids occur in both eastern and western zones despite the difference in space and time it is inferred that fluid compositions were rock controlled by similar interactions with evaporites and black shales in both instances it is proposed that beryllium was transported as be f complexes in the nacl fluid and was precipitated as emerald after mixing with the calcic brine caused precipitation of fluorite and parisite

bed load transport of coarse nonuniform sediment experiments involving measurements of the bed load transport rates of different fractions in a mixture are reported a conceptual model for the effect of a particular size of sediment on the transport rates of other sizes of sediment is proposed the experimental data are analyzed with the dual objectives of assessing the accuracy of existing methods of computation of bed load transport and of proposing a new method of computation

transport of fine sediment over a coarse immobile riverbed sediment transport in cobble boulder rivers consists mostly of fine sediment moving over a coarse immobile bed transport rate depends on several interrelated factors boundary shear stress the grain size and volume of fine sediment and the configuration of fine sediment into interstitial deposits and bed forms existing models do not incorporate all of these factors approaches that partition stress face a daunting challenge because most of the boundary shear is exerted on immobile grains we present an alternative approach that divides the bed into sand patches and interstitial deposits and is well constrained by two clear end member cases full sand cover and absence of sand entrainment from sand patches is a function of their aerial coverage entrainment from interstices among immobile grains is a function of sand elevation relative to the size of the immobile grains the bed sand coverage function is used to predict the ratio of the rate of entrainment from a partially covered bed to the rate of entrainment from a completely sand covered bed which is determined using a standard sand transport model we implement the bed sand coverage function in a morphodynamic routing model and test it against observations of sand bed elevation and suspended sand concentration for conditions of nonuniform fine sediment transport in a large flume with steady uniform flow over immobile hemispheres the results suggest that this approach may provide a simple and robust method for predicting the transport and migration of fine sediment through rivers with coarse immobile beds

strontium and sulphur isotope geochemistry of low temperature barite fluorite veins of the catalonian coastal ranges ne spain a fluid mixing model and age constraints sulphur and strontium isotope analyses from the low temperature barite fluorite veins of the catalonian coastal ranges ne spain reveal the nature and source of the ore forming fluids and constrain the ages of the mineralizations sulphur isotope values in the barite 34s 15 to 20 are similar to those of sulphates in nearly triassic jurassic evaporites 34s 11 to 19 87sr86sr isotopic composition ratios of barites and fluorites are 0 7094 0 7167 the variation of 87sr86sr within individual veins suggests that the sr had two different sources granites rocks in the hercynian basement and seawater or evaporites of triassic early jurassic age vein formation is modelled as a two component mixing process in which the s and sr isotopic composition of the end members change with time the observed difference in mean s and sr isotopic compositions among the veins is interpreted to reflect differences in mineralization age ore deposition occurred between 225 and 195 ma triassic to early jurassic in all cases except the berta mine which may be as young as miocene

flow heterogeneity over 3d cluster microform laboratory and numerical investigation the present study examines the flow around a self occurring cluster bed form and the use of general computation fluid dynamics methods for hydraulic and geophysical flow applications this is accomplished through a comprehensive experimental numerical investigation in the laboratory cluster bed forms are first formed from movable sediment and laser doppler velocimeter measurements of two dimensional fluid velocity are then taken around a formed cluster a three dimensional 3d reynolds averaged navier stokes simulation of the physical cluster and flow conditions is then conducted using near wall shear stress transport sst turbulence modeling with the inclusion of hydraulic roughness ks r 31 150 ks h 0 1 ks 274 i e in the fully rough regime sst near wall modeling is advantageous compared to the more widely used wall functions approach for flows with significant roughness and flow separation because the model equations can be integrated down to the wall therefore sst near wall model

fluid rock interactions in the salt dome environment an introduction and review abstract the salt dome environment in the gulf of mexico coast u s a provides one of the most diverse and long lived records of fluid rock interactions in an active sedimentary basin dominated by saline formation waters the geochemical record most of which is isotopic appears to span a temperature range between earth surface temperatures and lower greenschist facies most mineral forming processes in the salt dome cap rocks appear to involve mixtures of warm saline formation fluids from deep basin sources and cool dilute meteoric waters papers in this issue of chemical geology document some of the current research on fluid rock interactions in the salt dome environment these papers highlight the diversity of opinion about salt dome processes offering clues for further research the present paper reviews some of the key and more current literature on salt dome geochemistry fluid convection around salt domes and fluid rock interactions within salt and within the salt dome environment

the age and origin of the barite fluorite pbzn veins of the sierra del guadarrama spanish central system spain a radiogenic nd sr and stable isotope study fluorite and barite rich veins sulphides of the sierra del guadarrama spanish central system are usually hosted by hercynian granitoids zoned fluorites from one of these veins have a sm nd age of 145 18 ma this age is similar to the k ar ages obtained in other hydrothermal rocks of the spanish central system 156 152 ma and confirms the existence of an important hydrothermal event during the late jurassic probably related to extensional fracturing accompanying the opening of the north atlantic ocean the 87sr 86sr ratio found in fluorite and barite 0 7154 0 7207 is in most cases lower than that found in the host granitoids 0 7194 and 0 7209 suggesting more than one source of strontium this in turn supports previous models that involve mixing of two fluids during mineralization an ascending hot 300 c and low salinity fluid and a shallow cooler 100 c and more saline brine the ascending fluid probably reacted to a variable extent with the host granitoids and the most likely source for the shallow fluid derived from a marine evaporitic environment with a low 87sr 86sr ratio 0 7069 in the late jurassic the calculated end composition of the fluorites 8 8 to 7 6 as well as the 147sm 144nd variation found in this mineral 0 153 0 405 do not conflict with the mixing model although they can be largely explained by interaction of the ascending fluid with the host granitoids sulphur isotopic compositions of sulphides range between 3 4 and 0 8 and those of barites from 15 5 to 15 8 the near 34s value of the sulphides suggests that their sulphur was derived from the hydrothermal leaching of the granitoids by the ascending fluid the 34s value of barite is consistent with upper jurassic marine sulphate as the source of sulphate in the shallow fluid the absence of equilibrium between reduced and oxidized sulphur species can be easily interpreted as a consequence of the short residence time of the mixed fluid in the open fractures at temperatures between 250 and loo c although no pre cretaceous sediments are found on this part of the iberian hercynian basement the data presented here support the existence of a shallow platform joining central spain with the iberian or the subbetic realm in late jurassic times

carbon and oxygen isotope study of hydrothermal carbonates in the zinc lead deposits of the san vicente district central peru a quantitative modeling on mixing processes and co2 degassing abstract carbon and oxygen isotope studies of the host and gangue carbonates of mississippi valley type zinc lead deposits in the san vicente district hosted in the upper triassic to lower jurassic dolostones of the pucara basin central peru were used to constrain maiels of the ore formation a mixing model between an incoming hot saline slightly acidic radiogenic pb sr fluid and the native formation water explains the overall isotopic variation 13 c 11 5 to 2 5 relative to pdb and 18 o 18 0 to 24 3 relative to smow of the carbonate generations the dolomites formed during the main ore stage show a narrower range 13 c 0 1 to 1 7 and 18 o 18 7 to 23 4 which is explained by exchange between the mineralizing fluids and the host carbonates combined with changes in temperature and pressure this model of fluid rock interaction explains the pervasive alteration of the host dolomite i and precipitation of sphalerite i the open space filling hydrothermal white sparry dolomite and the coexisting sphalerite ii formed by prolonged fluid host dolomite interaction and limited co 2 degassing late void filling dolomite iii or calcite and the associated sphalerite iii formed as the consequence of co 2 degassing and concomitant ph increase of a slightly acidic ore fluid widespread brecciation is associated to co 2 outgassing consequently pressure variability plays a major role in the ore precipitation during the late hydrothermal events in san vicente the presence of native sulfur associated with extremely carbon light calcites replacing evaporitic sulfates e g 13 c 11 5 altered native organic matter and heavier hydrothermal bitumen from 27 0 to 23 0 13 c points to thermochemical reduction of sulfate and or thiosulfate the 13 c and 18 o values of the altered host dolostone and hydrothermal carbonates and the carbon isotope composition of the associated organic matter show a strong regional homogeneity these results coupled with the strong mineralogical and petrographic similarities of the different mvt occurrences perhaps reflects the fact that the mineralizing processes were similar in the whole san vicente belt suggesting the existence of a common regional mineralizing hydrothermal system with interconnected plumbing

mechanisms driving groundwater flow near salt domes groundwater flow near salt domes is complex because groundwater is subject to a variety of driving forces including the release of geopressured fluids large lateral density gradients and regional hydraulic head gradients the complexity of this environment is born out by recent geochemical and geophysical observations that indicate the occurrence of upward groundwater flow near some salt domes in order to evaluate the relative importance of different mechanisms driving groundwater flow near salt domes the authors have developed a numerical model that couples groundwater flow heat transport and transport of dissolved salt and accounts for salt diapirism the calculations indicate that upward groundwater flow can occur as the result of thermal convection when the regional background salinity is greater than 15 weight percent a value typical of many areas of the south louisiana salt dome province for lower background salinities dissolution causes salt laden groundwater near the dome to sink leading to depressed isotherms while the release of geopressured fluids is difficult to quantify it remains a likely mechanism for driving upward groundwater flow near some salt domes

the impact of biological bedforms on near bed and subsurface flow a laboratory evaluated numerical study of flow in the vicinity of pits and mounds the complex surface topography of river substrates controls near bed hydraulics and drives the exchange of subsurface and surface flow in rivers the topographic structures that are studied are usually formed by the flow but it is known that many animals also create biogenic bedforms such as pits and mounds here a large eddy simulation les model of flow over a pit and a mound is evaluated with flume experiments the model includes actual bedform topography and the topographic complexity of the surrounding bed surface subsurface grains are organized in a body centered cubic packing arrangement model evaluation showed strong agreement between experimental and modelling results for velocity r2 0 8 and good agreement for reynolds stresses r2 0 7 which is comparable to other similar studies simulation of the pit shows that the length of the downwelling region is smaller than the upwelling region and that the velocity magnitude is higher in the downwelling region simulation of the mound reveals that the flow is forced into the bed upstream of the mound and re emerges near the top of the mound the recirculation zone is limited at the leeside of the mound with increasing reynolds number the depth of the upwelling region at the leeside of the mound increases the analysis of shear stress indicates that sediments on the upstream edge of the pit and on the downstream face of the mound are relatively unstable these results demonstrate the effect of biogenic structures on the near bed flow field hyporheic exchange and sediment stability

a salt diapir related mississippi valley type deposit the bou jaber pb zn ba f deposit tunisia fluid inclusion and isotope study the bou jaber ba f pb zn deposit is located at the edge of the bou jaber triassic salt diapir in the tunisia salt diapir province the ores are unconformity and fault controlled and occur as subvertical column shaped bodies developed in dissolution collapse breccias and in cavities within the late aptian platform carbonate rocks which are covered unconformably by impermeable shales and marls of the fahdene formation late albian cenomanian age the host rock is hydrothermally altered to ankerite proximal to and within the ore bodies quartz as fine grained bipyramidal crystals formed during hydrothermal alteration of the host rocks the ore mineral assemblage is composed of barite fluorite sphalerite and galena in decreasing abundance the ore zones outline distinct depositional events sphalerite galena barite ankerite and fluorite fluid inclusions commonly oil rich have distinct fluid salinities and homogenization temperatures for each of these events sphalerite galena 17 to 24 wt nacl eq and th from 112 to 136 c ankerite barite 11 to 17 wt nacl eq and th from 100 to 130 c fluorite 19 to 21 wt nacl eq th from 140 to 165 c the mean temperature of the ore fluids decreased from sphalerite 125 c to barite 115 c and increased during fluorite deposition 152 c then decreased to 110 c during late calcite precipitation laser ablation inductively coupled plasma mass spectrometry la icp ms analyses of fluid inclusions in fluorite are metal rich hundreds to thousands ppm pb zn cu fe but the inclusions in barite are deficient in pb zn cu fe inclusions in fluorite have cl br and na br ratios of several thousand consistent with dissolution of halite while the inclusions analysed in barite have values lower than seawater which are indicative of a br enriched brine derived from evaporation plus a component of halite dissolution the salinity of the barite hosted fluid inclusions is less than obtained simply by the evaporation of seawater to halite saturation and requires a dilution of more than two times by meteoric water the higher k na values in fluid inclusions from barite suggest that the brines interacted with k rich rocks in the basement or siliciclastic sediments in the basin carbonate gangue minerals ankerite and calcite have 13c and 18o values that are close to the carbonate host rock and indicate fluid equilibrium between carbonate host rocks and hydrothermal brines the 34s values for sphalerite and galena fall within a narrow range 1 to 10 with a bulk value of 7 5 indicating a homogeneous source of sulfur the 34s values of barite are also relatively homogeneous 22 with 6 higher than the 34s of local and regional triassic evaporites 15 the latter are believed to be the source of sulfate temperature of deposition together with sulfur isotope data indicate that the reduced sulfur in sulfides was derived through thermochemical sulfate reduction of triassic sulfate via hydrocarbons produced probably from late cretaceous source rocks the 87sr 86sr ratio in the bou jaber barite 0 709821 to 0 711408 together with the lead isotope values of bou jaber galena 206pb 204pb 18 699 to 18 737 207pb 204pb 15 635 to 15 708 and 208pb 204pb 38 321 to 38 947 show that metals were extracted from homogeneous crustal source s the tectonic setting of the bou jaber ore deposit the carbonate nature of the host rocks the epigenetic style of the mineralization and the mineral associations together with sulfur and oxygen isotope data and fluid inclusion data show that the bou jaber lead zinc mineralization has the major characteristics of a salt diapir related mississippi valley type mvt deposit with superimposed events of fluorite and of barite deposition field relations are consistent with mineral deposition during the eocene miocene alpine orogeny from multiple hydrothermal events 1 zn pb sulfides formed by mixing of two fluids one fluid metal rich but reduced sulfur poor and a second fluid reduced sulfur rich 2 barite precipitation involved the influx of a meteoric water component that mixed with a barium rich fluid and 3 fluorite precipitated from a highly saline fluid with higher temperatures

strontium isotopic evidence for the origin of barites and sulfides from the mississippi valley type ore deposits in southeast missouri several barites from the lead barite district contain between 1 170 and 1 633 ppm sr their 87 sr 86 sr ratios range from 0 7098 to 0 7118 in contrast to the values of 0 7082 to 0 7089 for the host carbonate rocks four galenas from the viburnum mine in southeast missouri provide a rb sr age of 392 or 21 m y and an initial isotopic composition of 0 7104 or 0 0004 indicating the period of mineralization to be early devonian modified journal abstract

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

an experimental study into the geometry of supply limited dunes the relationship between dune geometry and the volume of mobile sediment was studied in flume experiments in these flume experiments the volume of mobile sediment on top of an immobile coarse sediment layer was increased stepwise and the bedform characteristics were observed a strong relationship was found between the volume that is mobile and therefore available for bedform formation and the dune dimensions and regularity if the sediment supply is limited dunes are smaller and more regular series of experiments with a decreasing supply limitation were conducted for different flow velocities and water depths the relationship between the dune dimensions and the available volume is different for each series the observed relationships between dune dimensions and layer thickness collapse to one relationship for height and one for length if scaling parameters are introduced current models for bedform dimensions under alluvial conditions can be extended to partial transport conditions using this relationship

variation in the reference shields stress for bed load transport in gravel bed streams and rivers 1 the present study examines variations in the reference shear stress for bed load transport r using coupled measurements of flow and bed load transport in 45 gravel bed streams and rivers the study streams encompass a wide range in bank full discharge 1 2600 m3 s average channel gradient 0 0003 0 05 and median surface grain size 0 027 0 21 m a bed load transport relation was formed for each site by plotting individual values of the dimensionless transport rate w versus the reach average dimensionless shear stress the reference dimensionless shear stress r was then estimated by selecting the value of corresponding to a reference transport rate of w 0 002 the results indicate that the discharge corresponding to r averages 67 of the bank full discharge with the variation independent of reach scale morphologic and sediment properties however values of r increase systematically with average channel gradient ranging from 0 025 0 035 at sites with slopes of 0 001 0 006 to values greater than 0 10 at sites with slopes greater than 0 02 a corresponding relation for the bank full dimensionless shear stress bf formulated with data from 159 sites in north america and england mirrors the relation between r and channel gradient suggesting that the bank full channel geometry of gravel and cobble bedded streams is adjusted to a relatively constant excess shear stress bf r across a wide range of slopes

effects of rock fragment covers on erosion and transport of noncohesive sediment by shallow overland flow rock fragments on soil surfaces can have a variety of contrasting effects on the hydraulics of overland flow and soil erosion this makes modeling soil erosion difficult systematic studies are needed to assess the effects of rock fragments on the hydraulics of overland flow and to specifically relate these hydraulics to sediment yield therefore flume experiments were conducted in which overland flow was applied to a highly erodible sediment surface covered by various percentages of rock fragments high local turbulence was caused by horseshoe vortex erosion around individual rock fragments for a given discharge and slope the dimension of the scour was affected by the space between the rock fragments for low cover percentages the scour can develop undisturbed and sediment yield increases with percent of rock fragment cover up to about 20 sediment yield then declines as percent cover increases above 20 beyond a cover threshold value of 20 the larger opportunity for scour hole development is counteracted by limited inter rock fragment space that does not allow scour holes to develop to their full extent as sediment yield varies nonmonotonically with rock fragment cover percent sediment yield cannot be predicted by spatially averaged flow hydraulics

light at deep sea hydrothermal vents ambient light spectral data were acquired at two deep sea hydrothermal vents with a temperature of 350 c the hole to hell site on the east pacific rise at 9 n and the snake pit site on the mid atlantic ridge measurements were made with a simple multi channel photometer which simultaneously detected light in four 100 nm wide bands over the wavelength range of 650 1050 nm most of the light detected is near infrared 750 1050 nm but there is a 19x greater photon flux than expected from thermal radiation alone at shorter wavelengths 650 750 nm at the hole to hell vent at snake pit more light in the 750 850 nm band was observed 10 cm above the orifice where the temperature was 50 100 c than at the 351 c vent opening these data suggest the presence of non thermal light sources in the vent environment some possible non thermal mechanisms are identified but further data will be required to resolve them

geology and geochemistry of the reocin zinc lead deposit basque cantabrian basin northern spain the reocin zn pb deposit 30 km southwest of santander spain occurs within lower cretaceous dolomitized urgonian limestones on the southern flank of the santillana syncline the reocin deposit is one of the largest known strata bound carbonate hosted zinc lead deposits in europe the total metal endowment of the deposit including past production and remaining reserves is 62 mt of ore grading 8 7 percent zn and 1 0 percent pb the epigenetic mineralization consists of sphalerite and galena with lesser marcasite and trace pyrite with dolomite as gangue microprobe analyses of different generations of dolomite revealed nonstoichiometric compositions with various amounts of iron up to 14 mol of feco3 replacement of host dolomite open space filling of fractures and cementation of breccias derived from dissolution collapse are the principal types of ore occurrence detailed cross section mapping indicates a stratigraphic and structural control on the deposit a stratiform morphology is present in the western part of the orebody capa sur whereas mineralization in the eastern part is highly discordant but strata bound barrendera stratigraphic studies demonstrate that synsedimentary tectonic activity related to the rifting of the north atlantic bay of biscay was responsible for variation in sedimentation presence of unconformities including paleokarsts local platform emergence and dolomitization along the n60 fault trend in the reocin area two stages of dolomitization are recognized the first stage is a pervasive dolomitization of the limestone country rocks that was controlled by faulting and locally affected the upper part of the aptian and the complete albian sequence the second dolomitization event occurred after erosion and was controlled by karstic cavities this later dolomitization was accompanied by ore deposition and locally filling of dolomite sands and clastic sediments in karstic cavities the circulation of hydrothermal fluids responsible for sulfide deposition and the infilling of karst cavities were broadly contemporaneous indicating a post albian age vitrinite reflectance data are consistent with previously measured fluid inclusion temperatures and indicate temperatures of ore deposition that were less than 100 c carbon and oxygen isotopic data from samples of regional limestone host rock dolostone and ore stage dolomite suggest an early hydrothermal alteration of limestone to dolostone this initial dolomitization was followed by a second period of dolomite formation produced by the mixing of basinal metal rich fluids with local modified seawater both dolomitization events occurred under similar conditions from fluids exhibiting characteristics of basinal brines the 34s values of sulfides are between 1 8 and 8 5 per mil which is consistent with thermochemical sulfate reduction involving organic matter as the main source of reduced sulfur galena lead isotope compositions are among the most radiogenic values reported for zn pb occurrences in europe and they are distinct from values reported for galena from other basque cantabrian deposits this suggests that a significant part of the lead was scavenged from the local underlying asturian sediments the stratigraphic and structural setting timing of epigenetic mineralization mineralogy and isotopic geochemistry of sulfide and gangue minerals of the reocin deposit are consistent with the features of most of mississippi valley type ore deposits

ambient light emission from hydrothermal vents on the mid atlantic ridge 1 a spectral imaging camera was used to observe light emission from high temperature deep sea vents at three hydrothermal sites on the mid atlantic ridge mar logatchev snake pit and lucky strike ambient light measured at these sites is similar to that observed at sites along the east pacific rise and the juan de fuca ridge with components from both thermal and non thermal sources the shrimp species rimicaris exoculata which is found on the mar but not in the eastern pacific possesses a unique photoreceptor capable of detecting low light levels it is not yet known if r exoculata sees vent light however since the characteristics of vent light appear to be unrelated to geographical location the exclusion of r exoculata from the eastern pacific is probably unrelated to differences in ambient light conditions

petrographic and geochemical arguments for hydrothermal formation of the ouenza siderite deposit ne algeria the ouenza siderite deposit is located proximal to evaporitic diapirs of triassic age mineralization occurs mainly in aptian neritic limestones which host important iron concentrations 120 150 mt and minor pb zn cu ba and f occurrences the iron ore consists of iron carbonate minerals which have been oxidized partially to hematite fine grained ankerite and siderite replace limestones whereas sparry ankerite and siderite were emplaced in veins limited variation in the chemical and isotopic compositions of ankerite and siderite were observed which indicate that they precipitated from the same fluid stable isotope compositions 18o and 13c of iron carbonates and limestones allow estimation of the isotopic composition of the mineralizing fluid and precipitation temperature 18o 7 5 smow t 100 120 c later deposition of pb zn cu ba and f minerals is controlled by fractures oriented ne sw and se nw fluid inclusion studies of quartz yield salinities of 18 22 wt equivalent nacl and homogenization temperatures between 150 and 180 c these values are similar to those of mississippi valley type deposits which are associated with basinal brines