mineralogy and chemistry of massive sulfide deposits from the juan de fuca ridge six hydrothermal vent sites and associated benthic communities were located in the axial valley of the southern juan de fuca ridge using transponder navigated bottom photography the hydrothermal deposits form ledges and shallow mounds within a central zone characterized by a linear bathymetric depression and numerous collapse features the flat valley floor adjacent to the central zone consists of ferrobasalt lobate flows and sheet flows sediment cover is minimal vent sites are characterized by concentrations of tube worms clams benthic siphonophores and several unidentified fauna two types of massive sulfide were dredged from one of the vent sites type a samples are angular slabs of dark gray zn rich sulfide with interlayers and a thin partly oxidized crust of fe sulfide these layered sulfide aggregates appear to be fragments of a sulfide wall enclosing an active hydrothermal vent the outer sulfide wall is composed mainly of colloform fe sulfide and fe poor sphalerite deposited under lower temperature conditions whereby sea water and hydrothermal fluid mix above the discharge point with continued sulfide deposition the wall inhibits mixing of sea water and hydrothermal fluid inside the wall the intensifying hydrothermal system deposits a higher temperature assemblage of granular fe rich sphalerite wurtzite pyrite and minor cu fe sulfide the zonation in wurtzite from fe rich cores to fe poor rims may result from a late stage cooling of the hydrothermal fluid and or a change in fluid chemistry the sulfide wall grows outward where a rupture in it permits the escape of high temperature fluid and then deposition of a secondary shell over the breakthrough point as temperature increases earlier formed minerals dissolve and zn fe and pb migrate toward the outer sulfide wall tube worms flourished in the outer wall of type a samples and abandoned tube structures served as conduits for the late stage hydrothermal fluids type b sulfide samples are subrounded spongy textured fragments composed almost entirely of dendritic aggregates of pale fe poor colloform sphalerite and opaline silica this type of sulfide is deposited in open space by moderate to low temperature fluid discharging at a slow but variable rate the fluid becomes increasingly oxidizing resulting in late stage deposition of hematite barite and sulfur type b samples show little evidence of burrowing animals this type of sulfide may be deposited in settings peripheral to sites of focused discharge

the juan de fuca ridge hot spot propagating rift system new tectonic geochemical and magnetic data underway geophysics deep tow camera work and preliminary geochemical and magnetic studies from a 1980 cruise to the juan de fuca ridge allow the following interpretations 1 the central third between 45 5 n and 46 5 n of the ridge is now actively spreading from a zone which is 10 to 20 km west of the axis bisecting the brunhes matuyama magnetic reversal boundary 2 the apparent terminus of surficial igneous activity at the northern tip of the active cobb propagator has been identified by dredging and camera work the tip appears curved or offset slightly to the west does not correspond to the northernmost tip of the central magnetic anomaly elvers et al 1974 and spreading has been initiated beneath sediments farther north and 3 iron and titanium in fresh glasses from the active volcanic zone exhibit a progressive enrichment northward then a pronounced reversal to more normal concentrations in the vicinity of the cobb offset

sulfate minerals control dissolved rare earth element flux and nd isotope signature of buoyant hydrothermal plume emso azores 37 n mid atlantic ridge abstract while hydrothermal vents are now thought to be a major source of dissolved iron to the oceans they have always been considered to be a sink for the dissolved rare earth elements drees however true dissolved ree observations in hydrothermal plumes are still lacking here we report for the first time the dree concentrations and neodymium isotopic compositions dend of buoyant hydrothermal fluids at lucky strike mid atlantic ridge we find that 27 to 62 of total hydrothermal drees are rapidly scavenged by anhydrite precipitation at the onset of buoyant plume formation after this initial loss all drees behave quasi conservatively within the buoyant plume dissolved phase end dend in the evolving plume are identical to black smoker dend of 9 0 and contrast radically with dend of the local deep water mass at 12 0 plume dend as low as 6 6 may be reconciled by dissolution of newly formed barite in the local environment and carrying seawater dend signature we find based on the first plume dree observations that hydrothermal plumes are in fact a source of dree to the north atlantic deep water precipitation dissolution processes of hydrothermally derived minerals i e sulfates in the buoyant plume and fe oxy hydroxide in the non buoyant plume will likely affect the fate of other trace metals and their isotopic composition

detailed geomorphology and neotectonics of the endeavour segment juan de fuca ridge new results from seabeam swath mapping a 36 km wide corridor of seabeam bathymetry was collected on the juan de fuca ridge north of 48 00 n in may 1983 these data merged with previous seabeam bathymetric compilations for the cobb offset as well as with sea marc i and sea marc ii side scan sonar seismic reflection magnetometer and deep tow photography data have been used to identify morphological variations along the spreading center of the endeavour segment of the juan de fuca ridge between the cobb offset and sovanco fracture zone the endeavour segment consists of two ridge sections separated by the 13 km wide endeavour offset which formed when spreading jumped from middle valley to west valley 200 000 yr ago the locus of spreading occurs along the entire endeavour segment as a narrow 1 2 km wide shallow 10 30 m deep inner rift which is superimposed upon larger structures that range from broad 5 10 km wide deep as much as 3 000 m median valleys to narrow 5 km wide shallow 2 100 m volcanic ridges an abrupt discontinuity in the tectonic fabric occurs at about 48 05 n south of this latitude spreading occurs within an axial high endeavour ridge which gradually deepens to the south south endeavour valley as it approaches the zone of overlap with the propagating rift at the cobb offset north of 48 05 n the axis is characterized by broad deep median valleys north endeavour valley and west valley these large scale morphological variations reflect a complex interplay of the spreading center with seamount volcanism waning magma supply at the distal ends of ridge axes thermal contrasts across ridge offsets propagating rifts and an unstable triple junction the pronounced axial deep of west valley is interpreted as reflecting the youth of the structure 200 000 yr and may be primarily due to collapse with little extension and magmatism the rift axis jump to west valley fortuitously isolated endeavour seamount the youngest edifice in the heck seamount chain from the pacific plate and trapped it between a pair of overlapping spreading centers at the newly formed endeavour offset development of a remarkably simple overlapping conjugate rift pair at endeavour offset has resulted in spite of the complex and highly variable crustal thickness magma supply and pre existing structural grain rifting in south west valley has caused pre existing topography generated at the endeavour ridge to be destroyed by subsidence and burial thereby creating the apparent discontinuity in morphology north of 48 05 n

rare earth element geochemistry of massive sulfides sulfates and gossans on the southern explorer ridge massive sulfide sulfate deposits on the southern explorer ridge were analyzed for 14 rare earth elements ree by a modified inductively coupled plasma mass spectrometric technique that included a correction for high ba content bulk samples of finely intermixed sulfides sulfate and amorphous silica contain ree concentrations of 6 ppm ree patterns range from 1 strongly enriched in light ree with positive eu anomalies to 2 relatively flat with positive eu anomalies and slightly negative ce anomalies to 3 slightly enriched in light ree with moderately negative ce anomalies pattern 1 is similar to that of 300 350 c solutions discharging at vents on the east pacific rise and the mid atlantic ridge whereas pattern 3 resembles ree distributions in normal oceanic bottom waters the sulfide sulfate patterns are interpreted to result from variable mixtures of hydrothermal and normal seawater barite in gossans capping the mounds has an ree pattern almost identical to patterns of high temperature vent solutions hydrothermal barite has lower ree contents and a different ree pattern relative to hydrogenous barite formed slowly on the sea floor

measurements of sound propagation in a littoral environment using a vertical synthetic array shallow water propagation experiments were carried out in st andrews bay florida these investigations used a vertical one dimensional synthetic array measurement system where two hydrophones incrementally mapped the acoustic pressure from 2m below through 2m above the sand water interface a broadband 1 to 12khz chirp was used to insonify the water channel the source to receiver distance was varied and included measurements at 20 30 50 70 and 90m these measurements quantified the acoustic pressure above and below a sandy bottom and the results are presented along with frequency analysis temporal impulse analysis and wave number analysis to obtain a better understanding of the results the measurements are compared to two numerical models the first model is a temporal ray path prediction of sound propagation in the water channel the second model range dependent acoustic model ram based on a parabolic equation predicts the sound propagating in a water channel with a sandy bottom the ex

geochemical behavior during mineralization and alteration events in the baiyinchang volcanic hosted massive sulfide deposits gansu province china abstract the zheyaoshan deposit is the largest within the baiyinchang byc volcanic hosted massive sulfide vhms district located in the northern qilian orogenic belt of north china the deposit is hosted by quartz keratophyre tuffs with wall rock alteration mainly comprising chlorite sericite quartz pyrite and epidote mineral assemblages within the altered host rocks can be divided into a sericite quartz dominant assemblage sericite silicified zone a chlorite dominant assemblage chlorite dominant zone and a pyrite dominant assemblage mineralized zone based on geochemical analysis and alteration characteristics we have conducted detailed processing and critical analysis of the geochemical data of both the altered and least altered host rocks in order to investigate the problem of closure in the geochemical dataset to eliminate the influence that each component has on the other in terms of mass change and have applied the standardized method of the mass change calculation to analyze this data the results show that 1 the sericite silicified zone formed along fissures due to the ingress of hydrothermal fluids with mno 2 na 2 o and cao being mobilized into the hydrothermal fluids leached and mgo fe 2 o 3 sio 2 k 2 o bao deposited additionally ag cu and chalcophile elements ag as and bi were enriched while pb zn and large ion lithophile elements liles cs sr eu be were mobilized into hydrothermal fluids 2 the physiochemical conditions and ph levels of the hydrothermal fluids changed during sericitization with mgo fe 2 o 3 bao being further enriched and mno na 2 o cao further depleted leading to formation of chlorite and the initial precipitation of metallogenic the cu zn pb and chalcophile elements ag as bi 3 the negative eu anomaly was mainly due to its strong activity when eu is mobilized into the hydrothermal fluids during since plagioclase break down during the sericite silicification process 4 ai and ccpi values gradually increase towards the orebody the chlorite dominant assemblage and sericite quartz dominant assemblage on the periphery of the chlorite dominant zone can all be used as vectors towards the volcanic massive sulfide orebody and for regional scale mineral exploration either leached elements or enriched elements can be considered as significant indicator elements and as prospective indicators for geochemical exploration within the byc district the eu anomaly may be especially useful as an indicator for distinguishing the least altered rocks which has great significance for exploration on the regional scale

parameter uncertainty analysis on acoustic response in fluid filled poroelastic media this paper examines the effect of input parameter uncertainty in the prediction of acoustic response in ocean sediment due to the relatively large number of physical parameters in the model and the difficulty of their direct measurement in the ocean environment uncertainty in the predicted acoustic response is expected utilizing a second order taylor series expansion this paper demonstrates a methodology for estimating the output uncertainty in terms of statistical moments from the input uncertainty the methodology is then tied to a practical procedure that uses engineering measurements and empirical relations to determine parameters such as shear modulus bulk modulus and permeability from porosity a related issue of pore size distribution and its effect on acoustic response is also investigated

mineralization of an intra oceanic arc in an accretionary orogen insights from the early silurian honghai volcanogenic massive sulfide cu zn deposit and associated adakites of the eastern tianshan nw china the honghai volcanogenic massive sulfide vms deposit occurs in the kalatage inlier of the dananhu haerlik arc eastern tianshan in the southern altaids the deformed deposit hosted in a suite of early paleozoic basic to intermediate volcanic volcaniclastic and sedimentary rocks consists of lenticular massive to semimassive and sulfide silicate stockwork orebodies the orebodies are characterized by zoning of metallogenic elements and sulfide minerals outward from a central stockwork zone as follows fe cu fe cu zn au ag cu zn fe zn cu au ag zn cu and fe cu zn a typical vms hydrothermal alteration zone that formed around the foot of the massive orebodies is several times larger than the lenticular massive orebody the hydrothermally altered rocks contain sericite chlorite and epidote zones from the core outward re os and argon dating of pyrite and sericite shows that the honghai vms deposit formed in the early silurian 436 2 ma and was deformed in the early devonian 410 4 ma this is the first documented early paleozoic vms deposit in the eastern tianshan our multidisciplinary data indicate that the honghai cu zn deposit formed in an immature nascent island arc where early tholeiitic lavas evolved into transitional basic andesitic volcanic rocks and calc alkaline intrusions with relatively high epsilon nd t values 6 2 8 4 and low sr 87 sr 86 i ratios 0 70412 0 70541 the sr nd pb s isotopic and geochemical data suggest that the ore forming melts started in mantle derived volcanic rocks and deep subvolcanic intrusions and some alteration was influenced by seawater the deposit formed in a high level subvolcanic intrusion driven by sub seafloor co2 rich nacl cacl2 h2o hydrothermal fluids temperatures 99 377 degrees c salinities 6 18 nacl equivalent circulating in active extensional faults in a submarine caldera extension of the immature nascent intra oceanic arc was one of the important factors that controlled the development and preservation of the vms deposit future work will benefit from this improved understanding of the vms deposits formed in immature nascent intra oceanic arcs especially in early paleozoic island arcs in the eastern tianshan in the southern altaids

the glacier creek cu zn vms deposit southeast alaska an addition to the alexander triassic metallogenic belt the glacier creek volcanogenic massive sulfide vms deposit alaska is hosted within late triassic oceanic back arc or intraarc rift related bimodal volcanic rocks of the allochthonous alexander terrane known as the alexander triassic metallogenic belt the alexander triassic metallogenic belt is host to the world class greens creek zn pb ag vms deposit near juneau in the south and the giant windy craggy cu co vms deposit in british columbia about 250 km to the north the glacier creek deposit located 80 km southeast of windy craggy consists of four tabular massive sulfide lenses within a bimodal mafic volcaniclastic and rhyolitic sequence the mineralization hosting stratigraphy is folded by a deposit scale anticline and offset by a thrust fault near the axial surface of the fold a resource of 8 13 mt has been inferred from drilling with grades of 1 41 cu 5 25 zn 0 15 pb 0 32 g t au and 31 7 g t ag six main mineralization types are recognized dominated by massive barite sphalerite pyrite which is replaced at the base and center of the main lenses by massive and semimassive chalcopyrite pyrite quartz the flanks and tops of the lenses are carbonate rich and consist of interbedded calcite dolomite barite and sulfide resedimented massive barite sulfide and mineralized massive carbonate rocks tuffaceous hydrothermal sediment with a distinct positive eu anomaly overlies the massive sulfide pyrrhotite and chalcopyrite in stringers constitute the main feeder zone stringer style sphalerite pyrite mineralization occurs above and below the lenses fe poor sphalerite is dominant throughout the lenses whereas fe rich sphalerite occurs at the stratigraphic top and bottom of the lenses in pyrrhotite rich zones galena tennantite tetrahedrite and arsenopyrite are the most important trace minerals within massive barite sphalerite pyrite mineralization which is generally enriched in sb hg and tl mineralization related gangue minerals include barite quartz barian muscovite calcite dolomite albite chlorite hyalophane and celsian four types of alteration are recognized in the dominantly basaltic host rocks pervasive muscovite rich alteration quartz pyrite alteration associated with sulfide stringers stratabound carbonate bearing alteration and background epidote bearing alteration mass balance calculations indicate gains of s fe si and k with coincident losses of ca na and mg in all of the alteration types trace elements tl sb hg ba zn cu and as were added to the rocks whereas sr was lost short wavelength infrared swir spectroscopy shows an increase in the wavelength of the aloh absorption feature toward mineralization at a scale of 30 to 50 m coincident with a general decrease in the na k and al and increase in the fe mg and ba content of muscovite the glacier creek deposit is transitional in character between greens creek which is more zn pb and precious metal rich and the windy craggy deposit which is more cu and co rich reflecting differences in the basement rocks and depositional settings within the alexander triassic metallogenic belt mineral chemical studies and sulfur isotope data suggest that the glacier creek deposit formed under initially oxidized and sulfate rich conditions that evolved to more reduced conditions in the latest stages of mineralization the abundant argillite and presence of hyalophane rather than barite in the immediate hanging wall of the deposit may be an indication of a deepening basin and development of local anoxia similar to greens creek

factors affecting the rare earth element compositions in massive sulfides from deep sea hydrothermal systems to reconstruct the evolution of ore forming fluids and determine the physicochemical conditions of deposition associated with seafloor massive sulfides we must better understand the sources of rare earth elements rees the factors that affect the ree abundance in the sulfides and the ree flux from hydrothermal fluids to the sulfides here we examine the ree profiles of 46 massive sulfide samples collected from seven seafloor hydrothermal systems these profiles feature variable total ree concentrations 37 2 4092 ppb and ree distribution patterns la cn lu cn ratios 2 00 73 8 eu eu cn ratios 0 34 7 60 the majority of the ree distribution patterns in the sulfides are similar to those of vent fluids with the sulfides also exhibiting light ree enrichment we demonstrate that the variable ree concentrations eu anomalies and fractionation between light rees and heavy rees in the sulfides exhibit a relationship with the ree properties of the sulfide forming fluids and the massive sulfide chemistry based on the sulfide ree data we estimate that modern seafloor sulfide deposits contain approximately 280 t of rees according to the flux of hydrothermal fluids at mid ocean ridges mors and an average ree concentration of 3 ng g in these fluids hydrothermal vents at mors alone transport more rees 360 t to the oceans over the course of just 2 years than the total quantity of rees in seafloor sulfides the excess rees i e the quantity not captured by massive sulfides may be transported away from the systems and become bound in sulfate deposits and metalliferous sediments

on the fate of sulfate during hydrothermal circulation at mid ocean ridges reliable sulfate data are reported for seafloor hydrothermal vents at the galapagos rift at 86 w and the east pacific rise at 21 n making use of sulfate 3he systematics a loss of sulfate comparable to the river input is estimated it is argued that the dominant chemical mechanism is reduction by iron a conclusion based on strontium systematics and indicators of the water rock ratios controls on the fate of sulfate in laboratory experiments are examined it is proposed that the mg ca ratio exerts a significant influence on the rate of sulfate reduction mixing of the hydrothermal endmember with seawater is considered with slow mixing alkaline earth sulfates should precipitate such precipitation accounts for the greater sulfate heat ratio in the galapagos fluids which are diluted extensively subsurface the particular sulfate mineral formed is not known because of questions concerning the control of alkalinity

growth history of hydrothermal black smoker chimneys hollow mineral spires known as black smoker chimneys precipitate around 350 c jets of hydrothermal fluid spouting from the sea floor on the east pacific rise epr at 21 n refs 1 2 i describe and discuss here the formation of mineral zoning across the walls of these structures throughout two major growth phases a sulphate dominated stage and a sulphide replacement stage during the sulphide replacement stage at least four distinct sulphide mineral zonation sequences develop across chimney walls from interior to exterior the apparently successive formation of these sulphide zonation sequences is attributed to evolution of radial thermal and chemical gradients accompanying the gradual thickening and sealing of black smoker chimney walls

seafloor massive sulfides from mid ocean ridges exploring the causes of their geochemical variability with multivariate analysis abstract the neovolcanic zones of mid ocean ridges are host to seawater derived hydrothermal systems forming seafloor massive sulfide sms deposits these deposits have high concentrations of base metals and potentially economic enrichment of a wide range of trace elements the factors controlling this enrichment are currently poorly understood we have investigated the main factors controlling sms compositional variability through robust principal component analysis and robust factor analysis of published and newly obtained bulk geochemical data for samples collected from sms deposits worldwide we found that a large part of the observed variability is produced by a combination of three independent factors which are interpreted to reflect in order of importance 1 the temperature of deposition 2 the ridge spreading rate and 3 zone refining the first and the third factors are mostly related to processes operating near the seafloor such as conductive cooling mixing of the hydrothermal fluids with seawater and metal remobilization and determine the relative proportions of the main minerals and thus of cu and zn co se sb pb the ridge spreading rate influences the structure of the oceanic lithosphere which exerts a major control on the length and depth of the hydrothermal convection cell and on the rock to water ratios in the reaction zone which in turn control the behavior of the precious metals au and ag and elements including ni mo se despite the obvious role of substrate rocks as metal sources their composition specifically mafic vs ultramafic does not emerge as a statistically significant independent factor

geochemistry of femn formations of the archaean sandur schist belt india mixing of clastic and chemical processes at a shallow shelf abstract the late archaean greenstone belts of karnataka are unique in having manganese formations with mineable ores an excellent example of these mn bearing greenstone belts is the sandur schist belt where fe mn formations are confined to the basin shelf clearly separated from the deeper water manganese free bif that accumulated at the basin margin and flanking the marine basin sedimentary textures and structures including stromatolites show that fe mn formations have been deposited on a shallow shelf within the photic zone and above wave base along with quartz fe mn minerals found in arenites argillites and carbonates include ripidolite mg chlorite sericite mn siderite kutnahorite dolomite ferroan dolomite psilomelane pyrolusite cryptomelane haematite and magnetite the manganese and iron contents of these rocks range up to 25 and 46 respectively al 2 o 3 tio 2 mgo cao mno 2 fe 2 o 3 t abundances and ratios show a wide variation ni cr co zr v sc rb sr u th ree lree hree la ce and eu anomalies and their binary relationships indicate that wherever the terrigenous component has increased the concentration of elements of felsic parentage such as zr and hf has gone up elevated concentrations of ni cr co and sc are contributed by chlorite and other components characteristic of basic volcanic debris the carbonates where clastic input is minimal are extremely depleted in ree and other trace elements it is proposed that feo mno and sio 2 probably were added to archaean ocean water at oceanic ridge vents the compositional data suggest that the fe mn formations of the sandur schist belt were generated by chemical and clastic sedimentary processes on a shallow shelf that led into a deeper basin open on one side in this environment chemical and clastic sediments and organic matter were mixed and buried during transgression chemical precipitation took place at the sediment water interface whereas at the time of regression these chemical sediments were buried by clastic sediments redox potential differences between the watermasses on the shallower and deeper shelf respectively fractionated fe and mn the fe mn formations were deposited within the photic zone and above wave base and in a setting where the water column was oxygenated but organic material accumulated by contrast bif was deposited below both wave base and photic zone in a relatively oxygen deficient setting where formation of stable mn oxides was not possible fe mn formation and bif provide an important constraint on greenstone tectonics a shorter distance between archaean oceanic ridge and shelf environments namely the smaller plates model appears to explain several features of fe mn formations bifs and greenstone belts

the development of seismic reflection sandbox modeling analog sandbox models provide cheap concise data and allow the evolution of geological structures to be observed under controlled laboratory conditions seismic physical modeling is used to study the effects of seismic wave propagation in isotropic and anisotropic media and to improve methods of data acquisition processing and interpretation by combining these two independent modeling techniques the potential exists to expand the benefits of each method for seismic physical modeling the main advantages are that the seismic data collected from these models contain natural variations that cannot be built into conventional solid models which are machined with predetermined structures in addition the cost and construction time to build these models is significantly reduced for sandbox modeling the ability to record three dimensional 3 d seismic images before the model is manually sectioned for conventional two dimensional 2 d structural interpretation allows far more detailed study of subtle 3 d structures than previously possible in the past other workers have attempted to use unconsolidated sands for seismic physical models but these attempts have been unsuccessful because of the lack of control or understanding of the natural variations that occur throughout the models the aim of our research has been to overcome such problems and to develop techniques to alter the acoustic impedance of sand layers thereby allowing the subsequent ultrasonic seismic recording of 3 d fault systems in sand analog geological models

microearthquakes on the endeavour segment of the juan de fuca ridge 1 we report the results of a 55 day microearthquake experiment on the endeavour segment of juan de fuca ridge the network covered a 5 km section of the ridge axis centered on the main vent field and extended 15 km off axis on the west flank the ridge axis and flanks were seismically active and 1750 earthquakes were located with a minimum of five travel time picks including at least one s wave over half the earthquakes occurred in swarms and a waveform cross correlation technique was used to obtain relative locations on the western flank the hypocenters for four swarms at midcrustal depths are compatible with steeply dipping fault planes that strike at 035 050 n and oblique to the abyssal hills focal mechanisms determined from p wave first motions and p s amplitude ratios are predominantly strike slip with north south compression and appear to be affected by the reorganization of the explorer plate earthquakes beneath the ridge axis are concentrated in a band of intense seismicity at 1 5 3 5 km depth to the north of high rise vent field the seismicity defines a plane striking parallel to the ridge axis and dipping east at 70 and the earthquakes appear to extend beneath an axial reflector previously imaged at 2 3 km depth farther south the hypocenters are not compatible with a single fault plane focal mechanisms are characterized by subhorizontal tension axes oriented in all directions except parallel to the ridge and suggest a stress field that is about equally influenced by ridge spreading and hydrothermal cooling

at sea measurements of sound penetration into sediments using a buried vertical synthetic array at sea measurements were conducted to understand the propagation of sound into sediments these investigations used a new buried vertical synthetic array system developed and built at the naval research laboratory the design of this at sea system is based on a system developed for laboratory experiments that utilized a two dimensional synthetic array technique j acoust soc am 107 2000 for the measurements reported here the hydrophone was water jetted into the sediment to a depth of 2 m once buried the hydrophone was mounted to a vertical robotics stage that pulled the hydrophone up in 1 cm increments a spherical source positioned 50 cm above the interface was used to ensonify the sediment the ensonification angle was varied by changing the horizontal distance of the source from the insertion point in this manner several measurements were made with ensonification angles above and below the critical angle in addition the enhancement of sound penetration due to interface roughness was investigated this new system along with the results of the measurements will be discussed work supported by onr

an assessment of the effect of chemical scavenging within submarine hydrothermal plumes upon ocean geochemistry profiles of 210pb over the endeavour and north cleft segments of the juan de fuca ridge are used to model a time scale for the scavenging by hydrothermal plumes of reactive elements in seawater the hydrothermal plumes above these ridge segments are sites of intense scavenging removal of 210pb at endeavour the total 210pb activities within the plume are as low as 8 dpm 100 l and dissolved activities are as low as 3 dpm 100 l at the north cleft which is characterized by higher particulate fe concentrations the total 210pb activities are 4 5 dpm 100 l the dissolved activities are 1 2 dpm 100 l and the 210pb activities are deficient with respect to the activity of the 210po daughter these are perhaps the lowest 210pb activities ever measured in the deep sea the large gradient of 210pb between the plume and surrounding deep water suggests that scavenging is focused into the plumes through horizontal transport the implication therefore is that this process might impact the ocean on a scale larger than that local to the ridge crest by coupling published measurements of particle flux from endeavour with 210pb activities on particles trapped at that site the total volume of seawater stripped of 210pb per year for that site was calculated to be 7 4 1012 l y globally the extrapolated volume flux of seawater stripped of reactive constituents is 5 7 1015 l y such that the entire ocean is processed in this manner in 2 4 105 y the geochemical cycle of elements with ocean residence times much shorter than this e g pb and th will not be greatly affected by hydrothermal scavenging on the other hand this process holds significance for the geochemistry of other elements scavenged by hydrothermal plumes such as p and v whose ocean residence times are 104 y

mobilization of ree during crustal aging in the troodos ophiolite cyprus ree data for secondary minerals from low and high temperature alteration environments in the troodos ophiolite have been determined using a combined mass spectrometry neutron activation technique smectite and analcime ree mimic fresh rock profiles and have concentrations ranging from 1 5 times chondritic values celadonite is depleted in lree and total ree relative to the rocks groundmass replacing chlorite and epidote are similar to or enriched in ree relative to fresh rocks in contrast fault related chlorite and void filling epidote are lree enriched with large positive eu anomalies and yield comparable ree profiles to those of hydrothermal fluids venting at mid ocean ridges the zeolites clinoptilolite and laumontite are also lree enriched with ree contents significantly lower than rock values carbonate is enriched in hree relative to lree and concentrations vary from 0 2 to 18 times chondritic values ree data for these minerals indicate that seawater ree contents are modified by seawater rock interaction in volcanic sequences and sheeted dykes in oceanic crust during axial hydrothermal alternation and subsequent crustal aging the absolute and relative abundances of ree in seawater derived solutions evolve in response to the precipitation of secondary minerals and the prevailing water rock ratios rocks altered at low temperatures will show no change or a decrease in ree content the lree hree ratio will reflect the proportion of smectite celadonite and carbonate in the groundmass assemblage in contrast rocks altered at high temperatures will show no change or an increase in ree the lree hree ratio will reflect the proportion of void filling and groundmass replacing chlorite and epidote in the rock

diffuse venting and background contributions to chemical anomalies in a neutrally buoyant ocean hydrothermal plume plumes originating in high temperature hydrothermal discharges entrain background water and often entrain diffuse source fluids during convective ascent the mixing of fluid from those three different sources determines the chemical composition of the ensuing neutrally buoyant plumes here convection models and aluminum data from the trans atlantic geotraverse tag site are used to examine relative contributions of focused diffuse and background sources to anomalies in the plume our analysis shows that anomalously high al values observed just above the seafloor at tag which we assume stem from diffuse flows can contribute as much as 50 to the al anomaly in the neutrally buoyant plume found 350 m above bottom background water contributes nearly an equal fraction of al to the anomaly more generally entrained contributions depend on gradients in profiles external to the rising plume entrainment also depends on effective source area distributed high temperature vents entrain more fluid than a single composite high temperature vent larger effective source area is particularly significant for entrainment of diffuse source or other tracers trapped within a few tens of meters of the seafloor downstream cross stream and temporal variabilities exhibited in the three dimensional model plume also underscore problems of sampling and interpreting actual plume data

a dual origin for the hydrothermal component in a metalliferous sediment core from the mid atlantic ridge a highly metalliferous sediment core collected from tag 26 n mid atlantic ridge has been analyzed for uranium series isotopes rare earth elements ree and radiogenic isotopes two types of deposition of hydrothermal material have been identified and characterized the first is sulfide material which has been rapidly deposited and is sometimes clearly turbiditic this material exhibits high u fe and eu sm ratios and low 230th fe and ree fe ratios it is proposed that u is incorporated into the sulfides by diffusion through the oxidized coating with reductive fixation near the sulfide oxide boundary the second hydrothermal component is particulate fallout from the neutrally buoyant plume which is diluted by the background pelagic sedimentation this component exhibits u fe ratios around 2 10 5 an order of magnitude greater than reported plume particulate levels but the 230th fe ree fe and eu sm ratios are similar to plume values nd and pb isotopes have been used to differentiate the hydrothermal and pelagic end members within this sediment core

biot model of sound propagation in water saturated sand elastic theory of wave propagation and the measured speed of sound in sandy ocean sediments indicate that such sediments are impenetrable to high frequency sound at shallow grazing angles the speed of sound in water saturated unconsolidated sand is in the region of 1700 m s which under the elastic theory of wave propagation gives it a critical grazing angle in the region of 28 at shallower grazing angles refraction is not permitted and total internal reflection is predicted recent experimental measurements contradict this view biot s theory of acoustic propagation in porous sediments is the most likely explanation biot s theory of acoustic propagation as it applies to water saturated sand is reviewed the speed of the slow wave is found to be higher than previously predicted new input parameter values are deduced

geological setting and mineralogical and geochemical investigations on sulfide deposits near 13 n on the east pacific rise geological mineralogical and geochemical investigations of hydrothermal deposits on one of the most studied segments of the east pacific rise near 13 n show that sulfides occur in four main tectonic settings these are 1 in the middle part of the central graben where active zones are located 2 at the top of the central graben where a second line of deposits is observed 3 on the marginal high which has sulfides both on its western tectonic side and at its top where a large deposit is located and 4 on the flank of the southeastern seamount which is the site of the most important deposit of the area the nature of the distribution of the samples through the area studied shows that hydrothermal activity has existed for more than 20 000 years mineral assemblages are dependent on the sample location the sulfide samples exhibit a wide range of mineralogical assemblages varying from high temperature hydrothermal cu fe rich chimneys black smokers which are characteristic structures of young edifices to mature cu fe rich massive sulfides similar to those found in the core of massive sulfide lenses mined on shore with respect to these observations a classification into nine types of sulfide assemblages is proposed hydrothermal activity at the axis is now increasing in intensity increase in temperature decrease in f s2 and f o2 the relative paucity of zn rich massive sulfides on the off axis structures is likely to be a consequence of the depletion of zn in the hydrothermal fluids r mode factor analysis applied to a population of nineteen representative bulk chemical analyses shows fractionation of the reduced sulfur fluid during the discharge into three main groups cu fe co se ca sr zn cd ag as pb and si ba displaying the principal types of sulfide samples collected in the 13 n area microprobe investigations conducted on sulfide minerals define the distribution of trace metal elements such as ag co se cd and as during the process of hydrothermal maturation of the deposits

archean seawater composition and depositional environment geochemical and isotopic signatures from the stromatolitic carbonates of dharwar craton india abstract the well preserved stromatolitic carbonates from neoarchean sandur chitradurga and shimoga greenstone belts of dharwar craton were studied to constrain the depositional conditions geochemical isotopic characteristics and the archean seawater temperatures these rocks display limited diversity in their morphological features such as columnar occasionally branched pseudo columnar domal crinkly laminated and oval elliptical shapes the stromatolites are associated with fe mn formations along with arenites argillites limestones and carbonaceous shales these stromatolites are cherty dolomites having variable sio2 mgo and cao contents the stromatolitic carbonates of the three greenstone belts possess low total rare earth elements plus ytterium rey along with positive la eu gd y anomalies and y ho ratios reflecting their deposition in marine conditions with variable hydrothermal and terrigenous inputs these stromatolites display predominantly negative 13c values ranging from 1 61 to 0 01 vpdb of sandur 2 53 to 1 35 vpdb of chitradurga and positive 13c of shimoga varying from 0 30 to 1 29 vpdb combined with the negative 18o values 20 95 to 7 72 vpdb our studies indicate fluctuating oxic to anoxic acidic to alkaline environment responsible for the deposition of these stromatolites with locally varying archean ocean temperatures from 25 to 75 c these conditions favoured the deposition of cherty dolomitic stromatolites in a shallow marine environment ranging from supra to subtidal zones with the minor influence of hydrothermal activity which is evident for the existence of archean smaller plate tectonics

evolution of a volcanogenic hydrothermal system recorded by the behavior of lree and eu case study of the key tuffite at bracemac mcleod deposits matagami canada abstract the distribution of rare earth elements ree in the alteration zones surrounding modern and ancient volcanogenic massive sulfide vms deposits is often characterized by a wide range of variations comprising both gains and losses of light ree lree la to sm and europium the evolution of the hydrothermal system is recorded by mineral assemblages and their chemical composition to address the behavior of the ree in such a context the bracemac mcleod archean vms deposits of the matagami district are used there mineralization was formed mainly by subsea floor replacement along a tuffaceous marker unit key tuffite of homogenous andesitic composition hence providing a single protolith to account for mineral and chemical variations in relation to ore position we combine whole rock and mineral ree data in both distal sericite and proximal chlorite alteration surrounding the mineralization a model integrating observed textural relationships geochemical data and current understanding of mineral stabilities is proposed to explain the redistribution of the ree during the evolution of the vms hydrothermal system the distal sericite zone represents the early low temperature alteration it is characterized by the destruction of volcanic glass and plagioclase leading to a negative eu anomaly in the whole rock analyses and the depletion of lree the proximal chlorite zone was formed during the thermal evolution of a fertile vms hydrothermal system it is generally characterized by gains of lree and eu although some chloritized samples are depleted in lree petrographic observations suggest that the coprecipitation of allanite with chlorite explains the increase of lree whereas a mass balance calculation indicates that the precipitation of apatite carbonates essentially controls the eu local silicification occurring as pulses during the hydrothermal system life is also of interest because it could preserve an intermediate alteration state and thus provide additional information on the evolution of the hydrothermal system the mobility of ree is indicative of specific hydrothermal conditions which may reflect the efficiency of a mineralizing hydrothermal system at matagami the mobility of lree and eu could be used for vectoring in exploration especially eu which has an anomalous behavior that extends far beyond the limit of the sulfide zone into the distal sericitic low temperature alteration up to 400 m from the ore zones

volcanism and metallogenesis of axial and off axial structures on the east pacific rise near 13 degrees n a fast spreading segment 12 cm yr super 1 of the east pacific rise near 12 degrees 50 n explored in detail by surface ship and manned submersible displays intense hydrothermal activity the rise crest about 1 500 m in width with a regional depth of 2 600 m is occupied at its center by an axial graben 1 3 titania alkali enriched olivine ti k basalts with high tio 2 1 4 and high alkali content na 2 o 3 0 k 2 o 0 3 occur on the southeastern seamount the fractionated tholeiites are believed to have been derived from primitive melts during differentiation which took place within a magma reservoir asymmetrical with respect to the axis of the graben which supplied both axial and off axial lava flows the ti k enriched basalts are believed to have been produced from an alkali enriched magmatic source

penetration of acoustic waves into rippled sandy seafloors the helmholtz kirchhoff integral and the kirchhoff approximation are applied to model the penetration of sound waves into rough sandy seafloors at grazing angles above and below the critical angle as the seafloor of interest is anisotropic emphasis is placed on simulating the response from a two dimensional interface the analytical development of the method is first presented followed by numerical examples simulations and data acquired at sea are in very good agreement in the 2 15 khz band maguer et al j acoust soc am 107 1215 1225 2000 the model predicts in agreement with the 2 15 khz acoustic data the contributions due to roughness effects that dominate the evanescent wave component over most of this frequency band secondary effects such as coherent bragg influence patterns and the loss of signal coherence with grazing angle or depth are correctly predicted the model simulations strongly suggest that roughness of the sediment interface is most likely the cause of anomalous sound penetration into the seabed

an example of a recent accretion on the mid atlantic ridge the snake pit neovolcanic ridge mark area 23 22 n abstract the inner rift vailey of the mark area mid atlantic ridge at the kane fracture zone was investigated with the submersible nautile at the latitude of the snake pit hydrothermal field 23 22 n a transect across the axial valley shows a stepwise increase in the sediment thickness away from the axis these steps probably reflect major magmatic and tectonic events in the evolution of the inner floor dives on the summit of the snake pit neovolcanic ridge constrain a generalized geological map and document relations between hydrothermal activity magmatism and faulting the neovolcanic ridge was constructed by the build up of several hundred metres of pillow lava flows its summit is intensely fissured and cut by an axial graben about 100 m wide three hydrothermal sites were recognized within the axial graben the eastern site the most active is structurally related to the eastern fault scarp the central site is located within the graben the western site associated with the western fault scarp is more complex and was constructed by two successive hydrothermal events the new data suggest a model of evolution for the inner floor of the rift valley involving alternating stages of magmatism and volcanism which produce ridges and troughs preserved outside of the axial domain these volcano tectonic cycles have an approximate duration of 100 000 years we discuss variations in the morphology of the mar along strike in the light of this model of evolution

plume dispersed hydrothermal particles a time series record of settling flux from the endeavour ridge using moored sensors abstract settling particles collected with moored sediment traps near an area of active hydrothermal venting in the northeast pacific ocean provide information about the deep sea distribution of hydrothermal material results of an 8 day near field single trap experiment and a 340 day multi instrument 5 trap deployment two kilometers from the endeavour ridge vent field show variability in the quantity and composition of the plume to sediment particle flux over time with depth and with distance from the vent field hydrothermal elemental fluxes vary by a factor of two among the four sampling intervals of the longer experiment a factor of three variation in fe s among these periods reflects temporal changes in phase composition changes in flux with depth for example a 200 fold increase in cu and zn between above and below plume traps are evidence of hydrothermal input comparison of fluxes determined in the near and far field experiments reveals the spatial influence of vent effluent near field particle flux exceeds that measured two kilometers away by a factor of 10 to 20 and is relatively enriched in fe cu and organic carbon but depleted in mn calculations of the residence time of the plume with respect to settling indicate that more than 90 percent of the particulate material is transported farther than two kilometers from the vent field interpretation of elemental mineralogical and grain size analyses suggest that chemical precipitation kinetics other physical and biological particle forming processes changes in vent output and lateral transport of hydrothermal material by abyssal currents are tenable explanations for our observations our findings suggest that these rate interdependent processes be included in realistic models of hydrothermal particle flux

oxidative dissolution of hydrothermal mixed sulphide ore an assessment of current knowledge in relation to seafloor massive sulphide mining highlights seafloor massive sulphides vary in mineralogy and oxidise at different rates galvanic cells play a role in increasing dissolution rates sms deposits that have been inactive for some time may have lost economic value the geochemistry of oxidation products has potential to be an exploration tool potential for anthropogenic release of heavy metals during seafloor mining any risk needs addressing by the isa prior to the formation of mining regulations the weathering process of seafloor massive sulphide sms deposits can be considered analogous to weathering of terrestrial volcanogenic massive sulphides vms deposits however in the context of sms deposits the process occurs in chemically buffered waters of near neutral ph resulting in the formation of insoluble fe oxy hydroxide minerals including goethite and hematite as well as sulphates such as jarosite as a result of this precipitation it is commonly assumed that any sms deposit is unlikely to exhibit a significant loss of metals dissolution and release of heavy metals into the water column however galvanic interactions have never been considered in this seafloor context whilst they have already been shown to have the ability to increase dissolution significantly in terrestrial deposits if heavy metal release is not temporally balanced by precipitation of oxide phases there is the potential that these metal occurrences lose economic value this is specifically significant if there is an industrial focus on exploiting deposits associated with hydrothermal vents that have been inactive for some time not only this but the geochemistry of weathering products gossans that are formed have the potential to be used as tools for exploration furthermore it is unknown what impact galvanic coupling may have with regards to anthropogenic release of heavy metals during seafloor mining of deposits associated with either active or inactive vents disturbance of sediment plume generation and dewatering process this environmental impact needs to be addressed prior to the formulation of regulations for deep sea mining by the international seabed authority the present review examines our current understanding of oxidation and dissolution of a mixed sulphide ore bringing together lines of evidence from a range of literature sources based on this review different seafloor sulphide ore deposits will dissolve by oxidation and release a variety of different metals economic and or toxic all at different rates with galvanic cells playing a role by increasing dissolution rates while precipitation of oxide and oxy hydroxide phases will occur it is unknown in both a natural weathering and anthropogenic mining context whether heavy metal release including economic and toxic metals is temporally balanced by this precipitation and any subsequent adsorption based on our current understanding certain sites will be more predisposed to oxidation as a result of their mineralogy those containing significant pyrrhotite marcasite galena and secondary copper sulphides and or environment higher temperatures and oxygen concentrations lower ph s furthermore certain sites pose more of an environmental risk in terms of toxicity than others with arc related sms deposits associated with higher concentrations of as pb sb cd and hg and ultra mafic hosted sms deposits associated with high concentrations of co and ni the review highlights the need for subsequent studies that investigate the natural weathering process of seafloor sulphide ore deposits including how this process impacts their economic value and consequent geochemical signature of oxides that are produced over time moreover this review underlines the necessity for experiments to elucidate the oxidative dissolution of ore throughout any mining process

discovery of the west 45 volcanic hosted massive sulfide deposit using oxygen isotopes and ree geochemistry a number of innovative geochemical techniques were tested around the thalanga volcanic hosted massive sulfide vhms deposit in north queensland with the objective of being able to recognize a near miss in the exploration drilling in and around the mine whole rock oxygen isotope analyses were used to determine temperature gradients in the footwall rocks just beneath the ore horizon by assuming a water 6180 value of 0 per mil consistent with a seawater dominated hydrothermal system an alteration temperature was calculated for each sample a quantitative determination of the mineralogy was used to work out a weighted fractionation factor for each sample so that the variance attributable to differences in mineralogy could be taken into account comparison of the temperatures to a sodium depletion index indicates that the 6180 halo is comparable in size to an alteration mineralogy halo but the distribution of na is somewhat unpredictable in the distal parts of the hydrothermal system this study identified a hot spot i km west of the limit of the mine workings the mount windsor volcanics which host the thalanga deposit contain a large number of stratiform quartz hematite lenses red jaspers rather than drill test all of these occurrences a geochemical index was determined to assist in ranking them elevated ba s and pb along with positive chondrite normalized europium anomalies were found to be characteristics of proximal jaspers as compared to barren jaspers a red jasper outcrop west of thalanga coincident with the 6180 hot spot was the most anomalous sample in this study subsequent drill testing of this target led to the discovery of the west 45 vhms deposit

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

rare earth element geochemistry of hydrothermal deposits from the active tag mound 26 n mid atlantic ridge the rare earth element ree geochemistry of various phases from the active tag hydrothermal mound has been examined and related to their mineralogy and fluid chemistry the mound deposits range from black and white smoker chimneys massive anhydrite sulphide mixtures oxides and ochres all phases except black smoker chimney anhydrite demonstrate a positive eu anomaly when normalised to chondrite ree values ree substitution into sulphide and sulphate phases appears to be strongly influenced by crystallographic control for all ree other than eu precipitation of anhydrite within the tag mound is the major mechanism for removal of ree during mound circulation and 0 15 0 35 g anhydrite is inferred to precipitate from every kg of fluid venting from the white smoker chimneys oxides from the mound fall into three different categories with distinct ree patterns oxide rims on sulphides atacamite bearing oxides and silica rich fe oxides and ochres the oxide rim phases contain sulphide and seawater derived rees whereas the atacamite bearing oxides and the ochreous material exhibit no seawater signature which suggests precipitation from or alteration by a modified hydrothermal fluid

geoacoustic inversion in range dependent ocean environments using a plane wave reflection coefficient approach a new efficient versatile ray based model is presented that performs geoacoustic inversions in range dependent ocean waveguides faster than alternative forward models for which the computation time becomes extremely long especially for broadband inversions the water propagation is approximately separated from the seabed interaction using predetermined bathymetry and a possibly range dependent water sound speed profile the geometrical optics approximation is used to calculate eigenrays between sources and receivers including bottom reflecting paths modeled broadband pressure fields are obtained by computing the plane wave reflection coefficient at specific angles and frequencies and by then linking this result with the bottom reflected eigenrays each perturbation of the seabed requires a recalculation of the plane wave reflection coefficient but not a recalculation of the eigenrays resulting in a highly efficient method range independent problems are treated as a limiting case of the approach the method is first described and then demonstrated with a few simple range independent theoretical models the versatility of addressing range dependence in the bottom seabed is demonstrated with a simulated data set finally the new model is applied to inversion from a measured data set taken with impulsive sources for both range independent and range dependent continental shelf environments

mineralogy bulk and rare earth element geochemistry of massive sulphide associated hydrothermal sediments of the brunswick horizon bathurst mining camp new brunswick massive sulphides are spatially and temporally associated with iron formation if and other hydrothermal sedimentary rocks in the vicinity of the brunswick no 12 brunswick no 6 and austin brook deposits bathurst mining camp sulphide carbonate oxide and silicate predominant if is present carbonate predominant if is best developed in and around the brunswick no 12 deposit whereas hematite bearing if is absent here but prominent in the austin brook brunswick no 6 area the if is composed dominantly of si co2 fe mn and ca minor constituents include mg p ti al and s statistically significant interelement correlations between eu fe mn pb zn cd au ca sr ba p co2 and s indicate that these elements were precipitated from hydrothermal fluids vented onto the seafloor positive interelement correlations between si ti al mg k zr rare earth elements ree s except eu se v y yb co ni and cr reflect the presence of detrital clastic mafic and aluminosilicate minerals and

evidence of dispersion in an artificial water saturated sand sediment a laboratory experiment was conducted to measure the speed of sound in an artificial water saturated granular sediment composed of cleaned and sorted medium grained sand and degassed distilled water the experiment was conducted within a range of frequencies where dispersion is predicted by a number of existing models between 2 and 4khz the sound speed was inferred from measurements of the resonance frequencies of a thin walled cylindrical container filled with the material an elastic waveguide model was used to account for the effect of the finite impedance of the walls although this effect was found to be small from 20 to 300khz the sound speed was obtained directly from time of flight measurements within the sediment dispersion in close agreement with the williams effective density fluid model k l williams j acoust soc am 110 2276 2281 2001 was observed

formation of massive sulfide deposits on oceanic ridge crests incremental reaction models for mixing between hydrothermal solutions and seawater equilibrium path calculations have been used to model mixing between hot 350 c hydrothermal solutions and ambient seawater in an attempt to simulate mineral precipitation at seafloor vents these calculations predict temperatures of precipitation paragenetic sequence of minerals and chemical composition of chimney deposits associated with vents on the seafloor at 21 n epr assuming sulfate sulfide disequilibrium during mixing the paragenetic sequence revealed is chalcopyrite anhydrite pyrrhotite pyrite sphalerite graphite and barite when sulfate sulfide equilibria is permitted during mixing however reduction of small amounts of sulfate results in early precipitation of pyrite and a sequence of cu rich sulfide minerals chalcopyrite bornite chalcocite covellite this sequence is analogous to that observed in thin chimney walls the calculations indicate that sulfide mineral precipitation occurs in response to both cooling and change in composition of the hydrothermal solutions as a result of mixing varying the amount of mixing with respect to temperature simulating conductive heating of seawater prior to mixing results in only minor variations in the sequence and abundance of precipitated phases anhydrite precipitation during mixing occurs early which is consistent with formation of an anhydrite leading edge of chimney structures similarly extrapolation of warm spring data from galapagos to zero so4 concentration suggests anhydrite formation due to mixing with seawater beneath the seafloor most likely below the level of reactive calcareous sediments subsequent interaction of the mixed hydrothermal solution with those sediments results in elevated and variable ca concentrations estimated for end member solutions from the galapagos precipitation of mg hydroxide sulfate hydrate in the walls of the vent chimneys at 21 n epr occurs as a result of conductive heating of ambient seawater with only very minor amounts of mixing in contrast precipitation of amorphous silica in the vents must be due to conductive cooling of the hydrothermal solutions thus incremental reaction calculations demonstrate that reactions occurring in and associated with venting ridge crest hydrothermal solutions can be effectively modeled using the thermodynamic data and reaction modeling codes available today departures from equilibrium required to accurately model the mixing process are easily accommodated and consistent with data from the vents and vent forming materials

phase relations involving pyrrhotite below 350 degrees c a hydrothermal recrystallization method was employed to determine the phase relations in the fe s system involving pyrrhotite between 350 degrees and 115 degrees c the superstructures of pyrrhotite as designated by nakazawa and morimoto 1970 1971 are considered to be thermodynamic phases the solvus between pyrite and hexagonal 1c 1 pyrrhotite continues below 325 degrees c along the slope established by toulmin and barton 1964 to 308 degrees c where a discontinuity marks the upper stability of the mc superstructure the solvus then continues along a similar slope to 262 degrees c where with the onset of the na superstructure there is a discontinuity and the curve reverses slope sharply at 254 degrees c monoclinic 4c pyrrhotite becomes stable in the peritectoid reaction hexagonal na pyrrhotite 47 30 at fe pyrite monoclinic 4c pyrrhotite 47 25 at fe monoclinic pyrrhotite exists over a range of compositions the maximum being 46 4 to 46 9 at percent fe at 115 degrees c hexagonal pyrrhotite is separated from monoclinic pyrrhotite by a narrow miscibility gap down to the upper stability limit of the nc superstructure at 209 degrees c below 209 degrees c the miscibility gap widens with hexagonal nc pyrrhotite of 47 3 at percent fe coexisting with monoclinic pyrrhotite of 46 9 at percent fe at the sulfur rich limit of the stability field monoclinic pyrrhotite coexists with pyrite the phases greigite smythite and marcasite were not encountered our results are in reasonable agreement with those obtained previously by hydrothermal synthesis methods but they are in disagreement with some results obtained in dry experiments which have produced metastable phase assemblages the phase diagram is compatible with natural pyrrhotite occurrences and in particular with those from geothermal boreholes at broadlands new zealand from which samples were recovered at known quench temperatures on the other hand our studies cast considerable doubt on the validity of the pyrrhotite geothermometer as applied to ores

three phase flow in porous media a review of experimental studies on relative permeability we present a detailed synthesized review of experimental studies on three phase relative permeability published since 1980 we provide comprehensive yet highly focused analysis of critical aspects of the field and their evolution over the last three decades in particular we review the effects of saturation history wettability spreading and layer drainage on the measured flow properties we also list all the processes rock types fluid systems and measurement techniques in order to provide a clear map for future studies behavior of the measured three phase relative permeabilities with respect to fluid saturations saturation histories wettability of rock samples spreading characteristics interfacial tensions and other pertinent properties are carefully discussed studies that use a diverse set of experimental techniques and data analysis to deduce relative permeability are included the experimental techniques that should be utilized to reduce uncertainty are also explored we interpret the measured properties and outcomes of different studies and compare them to substantiate distinct trends at various saturation ranges and provide ideas for new studies this is intended to distill a clear image of where the field stands and to allow composition of possible paths for future investigations the areas of critical relevance that have not been investigated or require further studies are highlighted

metalliferous sediments associated with presently forming volcanogenic massive sulfides the susu knolls hydrothermal field eastern manus basin papua new guinea short sediment cores were examined from the active susu knolls hydrothermal field in the eastern manus back arc basin papua new guinea in order to explain the origin of the currently accumulating metalliferous sediments the mineralogy and geochemistry of the sediments were studied by x ray diffraction scanning electron microscopy energy dispersive x ray fluorescence and instrumental neutron activation analysis sediments of the suzette site originated from the deposition of volcaniclastic material with the addition of a hydrothermal component from the mass wasting of old oxidized chimneys a strong mass wasting event was recognized at the base of the studied sedimentary succession from the occurrence of chalcopyrite pyrite and barite aggregates similar to those found in chimneys as well as the presence of atacamite the metalliferous component is characterized by high concentrations of cu up to 2 3 and au up to 3 5 ppm elevated concentrations of as ba zn and fe as well as a positive eu anomaly the material derived from eroded chimneys was deposited together with abundant glass fragments eroded from the volcanic edifice the mass wasting was succeeded by deposition of volcaniclastic sediment containing dacite fragments ca plagioclase pyroxene glass shards cristobalite si rich amorphous material alunite pyrite barite and magnetite the volcaniclastic sediment may have originated from hydrothermal eruptions at north su and south su the present day plume at suzette is a likely source of rare barite aggregates amorphous cu containing aggregates and cu fe sulfides creating geochemical anomalies of ba and cu in the uppermost sediments at suzette interbedded volcaniclastic and hemipelagic sediments were retrieved east and west of susu knolls the enrichment of mn in these sediments is considered to be a result of settling of mn oxides from a hydrothermal plume

controls of fluid chemistry and complexation on rare earth element contents of anhydrite from the pacmanus subseafloor hydrothermal system manus basin papua new guinea ocean drilling program odp leg 193 successfully drilled four deep holes 126 to 386 m into basement underlying the active dacite hosted pacmanus hydrothermal field in the eastern manus basin anhydrite is abundant in the drill core material filling veins and vesicles cementing breccias and occasionally replacing igneous material we report rare earth element ree contents of anhydrite from a site of diffuse venting site 1188 which show extreme variability in terms of both absolute concentrations e g 0 08 28 3 ppm nd and pattern shape lan smn 0 08 3 78 smn ybn 0 48 23 1 eu eu 0 59 6 1 the range of ree patterns in anhydrite includes enrichments in the middle and heavy rees and variable eu anomalies the patterns differ markedly from those of anhydrite recovered during odp leg 158 from the tag hydrothermal system at the mid atlantic ridge which display uniform lree enriched patterns with positive eu anomalies very similar to tag vent fluid patterns as the system is active the host rock composition is uniform and the anhydrite veins appear to relate to the same hydrothermal stage we can rule out predominant host rock and transport control instead we propose that the variation in ree content reflects waxing and waning input of magmatic volatiles hf so2 and variable complexation of rees in the fluids ree speciation calculations suggest that increased fluoride and possibly sulfate concentrations at pacmanus may affect ree complexation in fluids whereas at tag only chloride and hydroxide complexes play a significant role the majority of the anhydrites do not show positive eu anomalies suggesting that the fluids were more oxidizing than in typical mid ocean ridge hydrothermal systems we use other hydrothermal fluids from the manus basin vienna woods and desmos which bracket the pacmanus fluids in terms of acidity and ligand concentrations to examine the dependence of ree complexation on fluid composition geochemical modeling reveals that under the prevailing conditions at pacmanus ph 3 5 t 250 300 c eu oxidation state and the relative importance of fluoride versus chloride complexing are very sensitive to small variations in oxygen fugacity temperature and ph patterns with extreme mid ree enrichment may reflect speciation effects free ion abundance coupled with crystal chemical control we conclude that the great variability in ree concentrations and pattern shape is likely due to variable fluid composition and ree complexation in the fluids

mechanisms for subcritical penetration into a sandy bottom experimental and modeling results this paper presents preliminary results of a recent study whose overall objectives are to determine the mechanisms contributing significantly to subcritical acoustic penetration into ocean sediments and to quantify the results for use in sonar performance prediction for the detection of buried objects in situ acoustic measurements were performed on a sandy bottom whose geoacoustical and geomorphological properties were also measured a parametric array mounted on a tower moving on a rail was used to insonify hydrophones located above and below the sediment interface data covering grazing angles both above and below the nominal critical angle and in the frequency range 2 15 khz were acquired and processed the results are compared to two models that account for scattering of sound at the rough water sediment interface into the sediment although all possible mechanisms for subcritical penetration are not modeled the levels predicted by both models are consistent with the levels observed in the experime

paleo environmental variation and its control on organic matter enrichment of black shales from shallow shelf to slope regions on the upper yangtze platform during cambrian stage 3 abstract to understand the evolution of oceanic redox conditions and organic matter om accumulation in the shelf and slope regions of the upper yangtze platform during cambrian stage 3 high resolution geochemical data were obtained from two wells respectively representing shelf and slope environments based on redox proxies widespread anoxic euxinic waters with intermittent sulfidic water columns were formed from shallow shelf to deep water slope and basinal regions during stage 2 and early stage 3 then widespread anoxic waters were reduced and oxic waters expanded during the middle stage 3 after which fluctuating suboxic and oxic occasionally anoxic environments became predominant during late stage 3 the presence of hyalophane and positive eu anomalies suggest strong ba rich hydrothermal activities in the shelf and deep basin regions during early and middle stage 3 the ba rich hydrothermal fluids and upwelling events enhanced the primary productivity in surface waters and subsequently promoted organic matter enrichment during stage 2 and early stage 3 the high primary productivity driven by coastal upwelling and hydrothermal activity were the main factors controlling om enrichment during middle stage 3 the local anoxic water condition became responsible for om enrichment when oxic waters began to gradually expand during late stage 3 both primary productivity and redox conditions became the main control factors for om enrichment according to the analysis of primary productivity redox conditions hydrothermal activity and upwelling events an evolution model is proposed to account for the paleo environmental variation and the om enrichment from shallow shelf to slope regions during cambrian stage 3

low grazing angle bistatic sea floor scattering on the florida atlantic coastal shelf observations of bistatic scattering at moderate frequencies 3750 hz 7500 hz and 15 000 hz and low grazing angles 2 20 are presented with a geoacoustical description of the site given a source receiver separation of 80 7 m bistatic scattering strengths in the sandy sediments at the measurement site range from 70 to 15 db the observed bistatic scattering at low grazing angles depends primarily on the incident bearing angle bistatic scattering values are highest along the transect between the source and receiver maximum scattering strengths 20 to 15 db appear 30 m from the receiver regions of high scattering 30 db strength are centered along the direct path between the source and receiver the contribution of volume scattering to the observed scattering pattern is not very clear however given the sandy sediments found at the site roughness scattering is expected to be a major contributor to the observed bistatic scattering patterns

geo acoustic modelling of late and postglacial sedimentary units in the baltic sea and their acoustic visibility abstract acoustic profiling methods are commonly used in the geosciences to obtain knowledge about the sedimentary structures of marine deposits however their interpretation and the correlation of acoustic reflectors with sedimentological boundaries remain difficult the gradient in acoustic impedance determines the intensity of acoustic reflectors which are not necessarily sedimentary boundaries suitable geo acoustic models that cover a wide range of sediment types have not yet been developed for the baltic sea based on comprehensive investigations of sediment cores from mecklenburg bay and the arkona basin we developed geo acoustic models that enable the transfer of laboratory p wave velocity measurements to in situ conditions while considering changes in pressure salinity temperature and the frequency dependence of the p wave velocity i e acoustic dispersion this modelling allows the calculation of the wet bulk density and in situ p wave velocity from which the acoustic impedance is calculated from core logging and selected sedimentological data such as the water content loss on ignition and grain size precise plotting of core data into the acoustic profiles is now possible and represents a crucial step towards the interpretation of these profiles modelled p wave velocities are used to convert two way travel time to depth the average sedimentological parameters for the different development phases of the baltic sea are calculated using geo statistical methods and may allow for rough p wave estimations if core logging data are not available

transport and deposition of ree in h2s rich fluids evidence from accessory mineral assemblages abstract it is shown in four examples from geologically different environments that accessory or minor minerals rich in rare earth elements ree are often texturally associated with base metal sulfides the examples demonstrate that ree can migrate in hydrothermal fluids containing large amounts of reduced sulfur s ii species i e h 2 s hs and s 2 in certain fluids complexes of ree with s ii species may be important for the ree transport but most probably only in the absence of other strong ligands such as fluoride carbonate or possibly phosphate textural relationships and geochemical data suggest that the formation of ree bearing minerals in s ii rich environments is genetically related to the precipitation of basemetal sulfides

rare earth element geochemistry of standard sediments a study using inductively coupled plasma spectrometry the rare earth elements ree and y have been determined in 15 international standard sediments from france german democratic republic canada and the u s a samples were prepared using conventional rock dissolution techniques and the ree and y were separated from other constituents using cation exchange chromatography the ree la ce pr nd sm eu gd dy ho er yb lu and y were analysed simultaneously by inductively coupled plasma atomic emission spectrometry results indicate that u s g s standard shale sco 1 cody shale is a good reference material to use for the normalisation of the ree distributions of sediments data normalised to sco 1 are more readily interpreted than those normalised to existing estimates of average shale the ree patterns of standard sediments vary considerably in shape span an order of magnitude in absolute concentration and provide valuable reference values for the ree analysis of other sedimentary materials

europium redox equilibria in aqueous solution thermochemical data and recent advances in theoretical aqueous solution chemistry enable prediction of the relative stabilities of aqueous eu2 and eu3 over a wide range of temperatures and pressures at low temperatures near earth surface conditions the aqueous geochemistry of europium should be dominated by the trivalent state except possibly in the most reducing alkaline pore waters of anoxic marine sediments however at temperatures greater than about 250 c and elevated pressures divalent europium should predominate even with significant amounts of complexing trivalent europium is not stable at elevated temperatures and pressures consequently under most hydrothermal and metamorphic conditions europium in aqueous solution should be divalent at intermediate temperatures around 100 c significant activities of both eu2 and eu3 and related complexes can occur in aqueous solutions depending on the oxidation state and the ph of the solutions and the activities of potential ligands such as sulfate carbonate and chloride the predicted stability of divalent europium in aqueous solution at elevated temperatures is consistent with the large positive europium anomalies in rare earth element patterns of high temperature barites of hydrothermal and metamorphic origin reported by guichard et al 5 and with the observed depletion of europium as a result of high temperature sericitization of feldspar bearing assemblages discovered by alderton et al 1 it is suggested that significant fractionation of europium relative to the other rare earth elements may take place during high temperature hydrothermal alteration processes such as in the mid oceanic ridge systems because of the expected stability of divalent europium during these processes

footprints of spontaneous fluid redistribution on capillary pressure in porous rock pore scale imaging of two phase flow in porous media shows that pore filling occurs as cooperative events with accompanying spontaneous fluid redistribution in other parts of the pore space we present a level set method that controls saturation quasi statically to model experiments controlled by low constant flow rates and demonstrate that our method can describe the observed displacement mechanisms the level set approach determines states of capillary equilibrium which generally are different for displacement protocols constrained by saturation and pressure saturation controlled simulations of drainage in sandstone show spontaneous fluid redistributions with abrupt pressure jumps and cooperative behavior including snap off and interface retraction events consistent with experimental observations drainage capillary pressure curves are lower when saturation rather than pressure controls displacement remarkably these effects are less significant for imbibition processes where the development of hydraulically connected wetting phase moderates the cooperative behavior and associated pressure jumps

geological setting mineralogy geochemistry and genesis of the middle archaean kalyadi copper deposit western dharwar craton southern india the kalyadi polymetallic copper deposit occurs within the middle archaean 3 0 ga medium grade kalyadi schist belt which consists predominantly of ultramafic mafic schists interbedded with chemogenic chert detrital high al mg schists and siliceous schists this sedimentary exhalative type sedex type ore body is the only copper deposit hosted in cherts in the western dharwar craton the kalyadi supracrustal rocks are intruded by tonalite trondhjemitic gneisses ca 3 0 ga and granite ca 2 6 ga the kalyadi copper deposit is polygenetic in nature the primary ores represented by disseminations of pyrite linneite and chalcopyrite magnetite essentially along the bedding lamination of the metachert are referred to as the metamorphosed chert sulphide rhythmites of a primary stratiform type the ore is of low grade and records imprints of at least two events of deformation pyrite is characterised by high co values 262 4524 ppm and high co ni ratios 3 0 19 7 rare earth element patterns of the primary ores and the host metacherts are identical characterised by la enrichment absence of eu anomalies and flat to depleted hree patterns with 34 s 0 8 the secondary remobilised ores are structurally controlled occurring as veins and stringers discordant to the bedding lamination or schistosity the constituent ores are chalcopyrite pyrite pyrrhotite with minor pentlandite these sulphides with low co ni ratios 0 87 1 80 have either a strong positive or negative eu anomaly and show slight hree enrichment the 34 s value ranges from 2 64 to 4 29 it is interpreted that the primary stratiform ores and the cherts were derived from volcanogenic hydrothermal fluids as syngenetic chemical deposits in a deep sea environment the secondary epigenetic mineralisation is related to subsequent migmatisation deformational events and granitic activity

modeling of acoustic penetration into sandy sediments physical and geometrical aspects two different approaches to the problem of acoustic penetration into sandy marine sediments are considered application of the buckingham constitutive model for sediment with a plane surface and boundary element analysis of a rough surface of sediment represented as a homogeneous fluid by a careful modeling of the constitutive behavior for plane seafloors it is possible to partly reproduce some features of known experimental dependencies for acoustical pressure however accounting for roughness appears to be more important accordingly the authors present a detailed numerical analysis of penetration into rough sediments using the boundary element method the simulation results support conclusions reached by other investigators and demonstrate how local surface irregularities violate the evanescence condition that holds for a plane interface at subcritical incidence thus considerably increasing penetration the results apply to the frequency range 0 5 50 khz and grazing angles larger than approximately 6 8 at 10 50 khz for lower frequencies when diffraction becomes important the lowest possible grazing angle strongly depends on the range covered by the incident beam and is in general considerably larger the authors provide several characteristic examples with frequencies 5 and 15 khz and grazing angles 15 30 illustrating the impact of roughness on penetration

high element mobility in 1 9 1 86 ga hydrothermal alteration zones bergslagen central sweden relationships with exhalative fe ore mineralizations abstract the 1 9 1 86 ga ensialic belt of western bergslagen sweden comprizes a 12 km thick felsic volcano sedimentary sequence intruded by syn volcanic granitic plutons and mafic dykes and sheets developed in a rifted continental setting regional low temperature alteration of the supracrustal sequence produced greenschist to low amphibolite facies mineral assemblages localized cross cutting zones of intense alteration are developed in felsic volcanics which have been affected by the regional alteration producing drastic changes in both mineralogy and chemistry these zones are found close to the hjulsjo granite granophyre intrusive complex most probably the heat source for the hydrothermal system and related to the exhalative sirsjoberg osjoberg fe oxide deposits the hjulsjo zones are subdivided into inner and outer zones based on differences in mineralogy and chemistry resulting from the variable intensity of alteration while the degree to which most elements are leached increases from the outer into the inner zones mg increases with alteration intensity and si and al stay unchanged although they were mobilized during alteration initially k rb fe and mn increase in the outer zones but are depleted in the inner zones rare earth elements ree are depleted with the light ree being more depleted than the heavy ree a pronounced negative eu anomaly is generally present the hydrothermal fluid was enriched in ore forming metals during alteration and leaching ree patterns of exhalative minerals indicate that the fe oxide deposits were derived from these hydrothermal fluids

a discrete domain description of multiphase flow in porous media rugged energy landscapes and the origin of hysteresis we propose a discrete domain model to describe mesoscale many pore immiscible displacements in porous media we conceptualize the porous medium and fluid system as a set of weakly connected multistable compartments the overall properties of the system emerge from the small scale compartment dynamics our model aims at capturing the rugged energy landscape of multiphase porous media systems emphasizing the role of metastability and local equilibria in the origin of hysteresis under two phase displacements the system behaves hysteretically but our description does not rely on past saturations turning points or drainage imbibition labels we characterize the connection between micrometastability and overall system behavior and elucidate the different nature of pressure controlled and rate controlled immiscible displacements in porous media

hydrothermal discharge and alteration in near surface sediments from the guaymas basin gulf of california abstract in the guaymas basin gulf of california hydrothermal fluids discharge onto the seafloor via both direct emanation through hydrothermal spires and diffusely through the sediments the latter mode is the focus of this study short 20 cm sediment cores were taken in zones of diffuse hydrothermal flow for chemical investigation of interstitial fluids and bulk solids the hydrothermal component of the pore fluids was quite variable indicating the heterogenous nature of the near surface flow regimes the bulk solids chemistry indicates that the suite of cores has encountered different amounts of cumulative hydrothermal exposure dissolution of biogenic silica and deposition of large amorphous silica clasts in the sediment are related to the extent of hydrothermal exposure surface enrichments in ba are formed as barite precipitates when ba rich hydrothermal fluids mix with sulfate rich seawater at the seafloor formation of pyrite and removal of mg from the solid phases are also observed effects of hydrothermal flow through these sediments

ferruginous and manganiferous haloes around massive sulphide deposits of the urals proximal brecciform ferruginous and manganiferous rocks related to vms deposits of the urals are subdivided into jasperites gossanites and umbers in addition to thin bedded jaspers and cherts the coherence of host rock composition and mn fe fertility of the sediments have been established fe poor pink hematitic and gray sulphidic chert are typical of the felsic class of vms deposits in contrast the contents of fe vary from high to moderate in ferruginous rocks enclosed in basaltic units associate with vms deposits fe and mn rich ferruginous rocks and umbers occur in association with limestones and calcareous sedimentary rocks in both types of volcanic sequences a common feature of jasperites and umbers is the abundance of replacement textures of hyaloclastites and carbonates by hematite and silica in addition replacement of clastic sulphides by hematite and magnetite is a characteristic genetic feature of gossanites all of these sedimentary rocks are accompanied by pseudomorphs of hematite and quartz formed after bacterial filaments the abundance of replacement textures are supportive of the halmyrolysis model in addition to hydrothermal sedimentary and sub seafloor hydrothermal replacement theories study of chemical zonation of altered hyaloclasts shows depletion of their rims not only in mobile na k mg but also in immobile al ti and ree whereas si and fe are concentrated in situ the halmyrolysis model presented here involving organic rich calcareous hyaloclastic sediments resolves the problem of subtraction of al ti ree and other elements which are commonly immobile under hydrothermal conditions the evolution of the halmyrolysis process from acidic reducing to alkaline oxidized conditions infers a possible range in transformation from fe ii mg smectites to fe silicates and fe si oxides as precursors of brecciform jasperite and thin bedded jasper the higher acidic initial stage of gossanite formation seems to be required for oxidation of organic matter and or pyrite the acidic condition facilitates the temporal preservation of immobile elements al ti ree in immature chlorite hematite gossanites another peculiarity of the gossanite forming processes is the likely sorption of p u and v by iron hydroxides displacing sulphides the general evolution of all ferruginous sediments results in complete fe 2 oxidation and silicification accompanied by subtraction of other elements the vertical diagenetic differentiation leads to concentration of mn carbonates silicates and oxyhydroxides into the tops of jasperite and gossanite layers mn oxyhydroxides scavenge positively charged hydrated cations like co and ni near vent bacterial communities may activate the processes of volcanic glass and sulphide degradation the proposed processes of halmyrolysis followed by silicification in situ may resolve the enigma of silica rich sediment formation in a silica undersaturated ocean the discrimination between gossanite and jasperite is useful for elaboration of new criteria for local exploration of vms and mn deposits halo dispersion of gossanites covering an area about two to three times that of the massive sulphide deposit is a good vector for ore body discovery proximal gossanites can be differentiated from jasperites by presence of relic sulphide clasts or elevated contents of chalcophile elements cu fe zn pb bi te as sb ba noble metals au ag and distinct ree patterns with la and eu positive anomalies the development of halmyrolysis and biomineralization models merit further elaboration and testing in on going research in order to add or revise theories of iron and manganese deposit formation 2012 elsevier b v

the ree content of some hydrothermal fluids ree concentrations were determined in solutions from submarine hydrothermal vents on the east pacific rise and for the first time from continental geothermal fields in tibet and bulgaria they indicate that in hydrothermal systems ree are immobile at temperatures below 350 c and for water rock ratios of 105 nd values of submarine solutions and anhydrites 4 7 to 6 2 suggests recharge on the sedimentcovered flanks of the ridge carbonate anions as measured by alkalinity appear to increase the solubility of heavy ree somewhat but not to the extent that substantial amounts of ree could be driven out from rocks by hydrothermal activity

imaging of oil layers curvature and contact angle in a mixed wet and a water wet carbonate rock we have investigated the effect of wettability of carbonate rocks on the morphologies of remaining oil after sequential oil and brine injection in a capillary dominated flow regime at elevated pressure the wettability of ketton limestone was altered in situ using an oil phase doped with fatty acid which produced mixed wet conditions the contact angle where oil contacted the solid surface measured directly from the images 180 while brine filled regions remained water wet whereas the untreated rock without doped oil was weakly water wet 47 9 using x ray micro tomography we show that the brine displaces oil in larger pores during brine injection in the mixed wet system leaving oil layers in the pore corners or sandwiched between two brine interfaces these oil layers with an average thickness of 47 17 m may provide a conductive flow path for slow oil drainage in contrast the oil fragments into isolated oil clusters ganglia during brine injection under water wet conditions although the remaining oil saturation in a water wet system is about a factor of two larger than that obtained in the mixed wet rock the measured brine oil interfacial area of the disconnected ganglia is a factor of three smaller than that of oil layers

theory of compressional and shear waves in fluidlike marine sediments an unconsolidated saturated marine sediment consists of a more or less loose assemblage of mineral grains in contact with seawater in the interstices it is postulated that the two phase medium possesses no skeletal frame implying that the elastic rigidity modulus of the material is zero a theory of wave propagation in such a sediment is developed in which the medium is treated as a fluid that supports a specific form of intergranular dissipation two important equations emerge from the analysis one for compressional wave propagation and the second describing transverse disturbances for the type of dissipation considered which exhibits hysteresis or memory the shear equation admits a wavelike solution and is thus a genuine wave equation even though the sediment shows no elastic rigidity in effect the medium possesses a dissipative rigidity which is capable of supporting shear this behavior is distinct from that of a viscous fluid for which the shear equation is diffusionlike in character

from geology to geoacoustics evaluation of biot stoll sound speed and attenuation for shallow water acoustics a procedure for estimating acoustic wave velocity and attenuation in ocean sediment using a minimum amount of geological and geotechnical data is demonstrated first the biot stoll theory is presented next various asymptotic formulae for the attenuation coefficient are derived for high low and intermediate frequencies these expressions clearly isolate the effects of intergranular coulomb friction and fluid viscous dissipation on the attenuation of shear and compressional waves under the constraint of a minimum amount of geological and geotechnical information a sequence of empirical equations is compiled to convert basic data such as blow count number from a standard penetration test or shipboard density into sediment geoacoustic properties as a demonstration two well known field cases the atlantic generating station ags site and the atlantic margin coring amcor 6010 site are examined by incorporating the uncertainty involved in the data collection the estimated geoacoustical parameters are provided with a standard deviation

response to comments on biot model of sound propagation in water saturated sand j acoust soc am 103 2723 2725 1998 the approach advocated by prof stoll which lead to the parameter values marked historical has worked well for porous materials with cemented frames such as fused glass beads and sandstone but it does not work for sand the parameter values marked chotiros are uniquely able to match all four the main issue lies with the values of the frame and grain moduli