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

low temperature silica rich gold mineralization in mafic vms systems evidence from the troodos ophiolite cyprus the troodos ophiolite cyprus hosts the on land analogue for actively forming mafic cu rich or cyprus type vms deposits in addition to high temperature 350 c sulfide mound related mineralization other fossil seafloor mineralizing systems are known to operate including those characterized by an enrichment in au and abundant silicification in this study the mineralogy and geochemistry of four au and silica rich localities in troodos are considered and these include kokkinovounaros mathiatis south touronjia and alpen rose we present whole rock geochemical and mineralogical data characterizing the distribution of au in the hydrothermal systems of troodos samples from silica rich localities have two distinct sample mineralogies supergene samples that contain predominantly goethite hematite and jarosite and hypogene samples that contain quartz amorphous silica and minor hematite hypogene samples from mathiatis south and kokkinovounaros are enriched in au with a median concentration of 1 5 ppm relative to supergene samples that contain 0 1 ppm n 107 this indicates that au enrichment occurred on the seafloor and is not solely related to supergene weathering of silica rich mineralization we suggest that silica rich au mineralization in troodos formed during the migration of newly formed crust off axis or as white smokers proximal to known vms deposits in silica rich mineralization that is located distally from known massive sulfide deposits au was probably remobilized from shallow crustal reservoirs during the low temperature fluid flow 100 300 c in the lower extrusive sequence as the crust cooled and migrated off axis based on modern seafloor analogues we propose a revised model for the troodos hydrothermal system that explains the distribution of au in silica rich mineralization that formed off axis and postdates vms formation and in zones proximal to vms deposits that formed simultaneously as white smoker type vents we suggest that silica rich mineralized zones formed an intermediary between high temperature 350 c on axis vms deposits and the low temperature silicification of umbers 100 c

formation of large sulfide mineral deposits along fast spreading ridges example from off axial deposits at 12 43 n on the east pacific rise abstract submersible investigations with nautile near the 13 n hydrothermal field on the epr were made in 1992 we selected diving areas based on deep towed side scan sonar imaging close to a pit crater at the top of a young seamount 2 km east of the axial ridge we discovered one of the largest 70 m high and 200 m in diameter sulfide mounds formed at a fast spreading ridge 12 cm yr despite an overlap in composition between axial and off axial deposits the general trend reflects real differences in compositions off axis deposit differs from axial deposits by the scarcity of zinc sulfides and cobalt and selenium enrichment sulfur isotope variation is minimal for the off axis seamounts and suggests that sulfides precipitated from unmodifed end member hydrothermal solutions axial sulfides have a broader range due to reduction of seawater sulfate at mixing fronts between hydrothermal and seawater solutions along the axial graben fault system lead isotopic compositions of sulfides are in two overlapping but distinct fields indicating different pb sources and separate convective systems for the seamount and the axial deposits our observations suggest that the plumbing system is stable and centred on a shallow localised magma chamber under the seamount this configuration is by far more efficient than unstable axial processes to create during several hydrothermal episodes major sulfide deposits near a fast spreading ridge off axis seamounts are localised areas with high magmatic budget able to drive and focus hydrothermal systems at the same place for a long time other known occurrences of sulfides related to seamounts are at less than 11 km from the ridge axis thus we suggest that off axial volcanoes close to the ridge are first order targets to discover active or inactive large deposits along fast to medium spreading ridges

reconstructing past seawater mg ca and sr ca from mid ocean ridge flank calcium carbonate veins proxies for past seawater chemistry such as mg ca and sr ca ratios provide a record of the dynamic exchanges of elements between the solid earth the atmosphere and the hydrosphere and the evolving influence of life we estimated past oceanic mg ca and sr ca ratios from suites of 1 6 to 170 million year old calcium carbonate veins that had precipitated from seawater derived fluids in ocean ridge flank basalts our data indicate that before the neogene oceanic mg ca and sr ca ratios were lower than in the modern ocean decreased ocean spreading since the cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early tertiary may explain the recent rise in these ratios

computation of wind wave spectra in coastal waters with swan on unstructured grids abstract an unstructured grid procedure for swan is presented it is a vertex based fully implicit finite difference method which can accommodate unstructured meshes with a high variability in geographic resolution suitable for representing complicated bottom topography in shallow areas and irregular shoreline the numerical solution is found by means of a point to point multi directional gauss seidel iteration method requiring a number of sweeps through the grid the approach is stable for any time step while permitting local mesh refinements in areas of interest a number of applications are shown to verify the correctness and numerical accuracy of the unstructured version of swan

hydrothermal mounds and young ocean crust of the galapagos preliminary deep sea drilling results leg 70 a total of 32 holes at 5 sites near 1 n 86 w drilled on deep sea drilling project dsdp leg 70 november december 1979 provide unique data on the origin of the hydrothermal mounds on the south flank of the galapagos spreading center hydrothermal sediments primarily mn oxide and nontronite are restricted to the immediate vicinity of the mounds 100 m and are probably formed by the interaction of upward percolating hydrothermal solutions with sea water and pelagic sediments above locally permeable zones of ocean crust mounds as much as 25 m in height form in less than a few 10 5 yrs and geothermal and geochemical gradients indicate that they are actively forming today the lack of alteration of upper basement rocks directly below the mounds and throughout the galapagos region indicates that the source of the hydrothermal solutions is deeper in the crust

a coupled hydrodynamic modeling system for phailin cyclone in the bay of bengal abstract east coast of india is characterized by low to medium topography and an extensive network of major estuaries bays mangrove creeks rivers and tidal inlets that permit inland flooding during tropical cyclones a coupled wave surge hydrodynamic modeling system adcirc swan is implemented to simulate storm surge still water level elevation and wave induced setup associated with phailin a very severe cyclonic storm that made landfall in the odisha state east coast of india during october 2013 the coupled model provides a realistic description on the dynamic interaction of tides wind waves and currents which is critical for operational needs the study assesses the role of wave induced setup on the net water level elevation using time varying wave radiation stress that is dynamically updated in the coupled model run numerical experiments are carried out for both storm surge alone and coupled mode versions dependent upon complex bathymetry and coastal geometry inclusion of wave induced setup in coupled runs results in an additional 23 36 increase of peak surge relative to an uncoupled surge tide simulation the significant wave height from coupled model also shows an excellent match with observed wave heights from a wave rider buoy located off the odisha coast the comparison of surge residuals between model and observation also exhibits a good match the study highlights the importance of having a coupled wave hydrodynamic model for operational needs in the north indian ocean

gold speciation and transport in geological fluids insights from experiments and physical chemical modelling this contribution provides an overview of available experimental thermodynamic and molecular data on au aqueous speciation solubility and partitioning in major types of geological fluids in the earth s crust from low temperature aqueous solution to supercritical hydrothermal magmatic fluids vapours and silicate melts critical revisions of these data allow generation of a set of thermodynamic properties of the auoh aucl 2 auhs and au hs 2 complexes dominant in aqueous hydrothermal solutions however other complexes involving different sulphur forms chloride and alkali metals may operate in high temperature sulphur rich fluids vapours and melts the large affinity of au for reduced sulphur is responsible for au enrichment in s rich vapours and sulphide melts which are important gold sources for hydrothermal deposits thermo dynamic speciation and partitioning data and their comparison with au and s contents in natural fluid inclusions from magmatic hydrothermal gold deposits provide new constraints on the major physical chemical parameters temperature pressure salinity acidity redox and ubiquitous fluid components sulphur carbon dioxide arsenic affecting au concentration transport precipitation and fractionation from other metals in the crust the availability and speciation of sulphur and their changes with the fluid and melt evolution are the key factors controlling gold behaviour in most geological situations

constraints on the energy and chemical balances of the modern tag and ancient cyprus seafloor sulfide deposits the size chemical composition energy flux and fluid composition of the tag hydrothermal sulfide deposit at the mid atlantic ridge and the size chemical composition and reaction zone characteristics of the skouriotissa volcanogenic massive sulfide deposit of the troodos ophiolite in cyprus are used to examine the energy requirements and chemical balances associated with the generation of a large volcanogenic massive sulfide deposit we conclude that formation of large sulfide deposits from oceanic hydrothermal systems is a geologically rapid process and occurs on timescales of hundreds of years with episodes of activity as short as a few tens of years separated by thousands of years of inactivity about 2 1019 j of energy supplied at high temperature is required to form a deposit the size of the tag mound metals up to 4 times the mass of any element present in the sulfide deposit are leached out of relatively small reaction zones most likely at the base of the sheeted dikes chemical balance can be struck for all elements except sulfur with a reaction zone 1 2 km3 in volume from which a small proportion of iron and large proportions of copper zinc and manganese are removed a sulfur balance requires that a significant fraction of sulfur be derived from reduction of seawater sulfate as suggested by stable isotope analyses we argue that the principal source of energy that drives hydrothermal circulation is latent heat of crystallization of magma close to the top of the plutonic section furthermore we speculate that activity of the tag hydrothermal system is related to periods of more rapid magma supply from the mantle at magma supply rates similar to those observed in volcanoes in hawaii and iceland

metal fluxes during magmatic degassing in the oceanic crust sulfide mineralisation at odp site 786b izu bonin forearc volcanogenic massive sulfide deposits are enriched in metals that are either derived from hydrothermal alteration of the basement rocks or supplied by exsolution of metal rich volatiles during magmatic differentiation the extent to which each process contributes to metal enrichment in these deposits varies between different tectonic settings ocean drilling program hole 786b recovered 800 m of upper oceanic crust from a supra subduction zone setting and includes a 30 m thick mineralised zone in situ s isotopic compositions of pyrite decrease from 5 9 2 9 in the upper mineralised zone down to 3 3 2 1 in the extensively altered central mineralisation zone potentially indicating strong magmatic fluid input in this area whole rock data and in situ trace element analyses in sulfide minerals show enrichment of ag as au bi mo s se sb and te in the mineralised zone evaluation of metal behaviour during magmatic differentiation and primary metal fertility of basement rocks suggests that degassing melt is the main source for the high au se and s enrichment observed in the mineralised zone magmatic volatile exsolution occurred late during the magmatic differentiation 2 wt mgo concomitant with oxide crystallisation and metal depletion in the melt comparison of ocean drilling program hole 786b with volcanogenic massive sulfide deposits hosted by boninitic volcanic successions such as in the semail ophiolite the newfoundland appalachians and the flin flon belt suggests that magmatic fluid exsolution could be a common mechanism for au enrichment in bimodal mafic volcanogenic massive sulfide deposits

the abundance of seafloor massive sulfide deposits the possibility of mining seafl oor massive sulfide deposits has stirred debate about the sustainable use of this new resource and whether commercial development is worth the risk among the outstanding questions is how many deposits might be accessible to deep sea mining more than 300 sites of high temperature hydrothermal venting have been identifi ed since the discovery of black smokers but signifi cant massive sulfide accumulation has been found at only 165 of these sites estimates of the total number of vent fields and associated mineral deposits based on plume studies and deposit occurrence models range from 500 to 5000 we have used new deposit occurrence data from 10 000 km of ridge arc and backarc spreading centers to estimate the amount of massive sulfide in the easily accessible neovolcanic zones of the global oceans the total accumulation in these areas is estimated to be on the order of 6 108 tonnes containing 3 107 tonnes of copper and zinc this is similar to the total discovered copper and zinc in cenozoic massive sulfi de deposits mined on land but is insuffi cient to satisfy a growing global demand for these metals

seismicity and seismic hazard parameters evaluation in the island of crete and the surrounding area inferred from mixed data files abstract a study of the spatial distribution of seismicity and seismic hazard is undertaken for crete and the surrounding area cisa for the estimation of seismicity parameters cisa is divided in rectangular subregions by applying the centroid of strain energy technique we obtain seismicity parameter maps closely related to the tectonics of the area the b value from the magnitude frequency distribution is calculated by a maximum likelihood technique page 1968 bull seism soc am 58 1131 1168 as well as by gumbel s first asymptotic distribution of extreme values technique the b value shows consistent spatial variation along cisa for both techniques low b values are dominant in the western part of cisa while higher b values are present to the east side forming a pattern like a sleeping letter s this pattern may be attributed to the variation of the regional velocity of deformation finally we performed seismic hazard analysis for shallow and intermediate events from mixed historical and instrumental data files we estimated the regional maximum magnitude mmax as well as the other parameters like the activity rate of seismic events and the well known b parameter kijko and sellevoll 1989 bull seismol soc am 79 645 654

chalcophile and platinum group element pge concentrations in the sulfide minerals from the mccreedy east deposit sudbury canada and the origin of pge in pyrite magmatic sulfide deposits consist of pyrrhotite pentlandite chalcopyrite pyrite and platinum group minerals pgm understanding the distribution of the chalcophile and platinum group element pge concentrations among the base metal sulfide phases and pgm is important both for the petrogenetic models of the ores and for the efficient extraction of the pge typically pyrrhotite and pentlandite host much of the pge except pt which forms pt minerals chalcopyrite does not host pge and the role of pyrite has not been closely investigated the ni cu pge ores from the south range of sudbury are unusual in that sulfarsenide pgm rather than pyrrhotite and pentlandite are the main carrier of pge probably as the result of arsenic contribution to the sulfide liquid by the as bearing metasedimentary footwall rocks in comparison the north range deposits of sudbury such as the mccreedy east deposit have as poor granites in the footwall and the ores commonly contain pyrite our results show that in the pyrrhotite rich ores of the mccreedy east deposit os ir ru rh ipge and re are concentrated in pyrrhotite pentlandite and surprisingly in pyrite this indicates that sulfarsenides which are not present in the ores were not important in concentrating pge in the north range of sudbury palladium is present in pentlandite and together with pt form pgm such as ptpd tebi 2 platinum is also found in pyrite two generations of pyrite are present one pyrite is primary and locally exsolved from monosulfide solid solution mss in small amounts 2 wt together with pyrrhotite and pentlandite this pyrite is unexpectedly enriched in ipge as pt and the concentrations of these elements are oscillatory zoned the other pyrite is secondary and formed by alteration of the mss cumulates by late magmatic hydrothermal fluids this pyrite is unzoned and has inherited the low concentrations of ipge and re from the pyrrhotite and pentlandite that it has replaced

sulfidation equilibria as guides to gold mineralization in volcanogenic massive sulfides evidence from sulfide mineralogy and the composition of sphalerite hydrothermal fluids responsible for the formation of volcanogenic massive sulfides may transport gold in solution as au hs 2 super at low temperatures or 350 degrees c low ph and elevated salinities or 1 m nacl the documented fluid chemistry of active hydrothermal vents on the modern seafloor confirms that gold transport is mainly due to au hs 2 super and the calculated solubility of gold as au hs 2 super is highest in low temperature 150 degrees 250 degrees c vent fluids at elevated oxygen and sulfur activities sulfides which coprecipitate with gold commonly have properties which can be related to the temperature and sulfidation state of the hydrothermal fluids and therefore reflect conditions which were favorable for the transport or deposition of gold as au hs 2 super a comparison of gold grades with sulfide mineral equilibria and the fes contents in sphalerite from a variety of deposits indicates that gold enrichment is closely related to the temperature a sub s 2 conditions in the ore forming fluids sea floor sulfides range from sulfur rich pyrite marcasite assemblages to relatively sulfur deficient pyrrhotite isocubanite assemblages with coexisting sphalerite containing 0 to 55 mole percent fes significant gold enrichment occurs exclusively in low temperature 300 degrees c contain ferich sphalerite 1 5 mole fes and gold grades 1 ppm au archean cu zn deposits at noranda quebec consist mainly ofpyrite pyrrhotite ores containing 0 5 to 1 ppm au together with fe rich sphalerite 10 12 mole fes however pyritic ores which occur stratigraphically up section commonly contain 1 to 3 ppm au and relatively fe poor sphalerite 5 mole fes different sulfide mineral equilibria and fes contents in sphalerite are interpreted to reflect the same physical and chemical conditions which influence gold grades and suggest that petrologic indicators of the sulfidation state may be useful guides to gold mineralization in volcanogenic massive sulfides

a high resolution coupled riverine flow tide wind wind wave and storm surge model for southern louisiana and mississippi part ii synoptic description and analysis of hurricanes katrina and rita abstract hurricanes katrina and rita were powerful storms that impacted southern louisiana and mississippi during the 2005 hurricane season in part i the authors describe and validate a high resolution coupled riverine flow tide wind wave and storm surge model for this region herein the model is used to examine the evolution of these hurricanes in more detail synoptic histories show how storm tracks winds and waves interacted with the topography the protruding mississippi river delta east west shorelines manmade structures and low lying marshes to develop and propagate storm surge perturbations of the model in which the waves are not included show the proportional importance of the wave radiation stress gradient induced setup

prediction of potentially damaging earthquakes in the cretan segment of the hellenic arc abstract based on a regularity in the occurrence of potentially damaging shocks in the cretan segment of the hellenic arc a prediction experiment is conducted which indicates that the next event of m s 6 7 must be expected within the second half of 1989 the most likely earthquake source is the seismic fracture zone between the hellenic trench and crete

zinc copper and lead in mid ocean ridge basalts and the source rock control on zn pb in ocean ridge hydrothermal deposits the contents of zn cu and pb in mid ocean ridge basalts morb and the morb source rock control on zn pb in ocean ridge hydrothermal deposits are examined the values of zn cu and pb for submarine mid ocean ridge basalts morb are respectively in ppm average morb 75 75 and 0 7 west valley juan de fuca ridge jfr 87 64 and 0 5 southern jfr 120 and 0 5 and 21 n east pacific rise epr 73 78 and 0 5 values of zn pb range from about 100 240 and cu pb from 100 156 in this study zn is found to correlate positively with tio2 feo mean square of weighted deviates mswd of 1 6 for jfr basalt and inversely with mg number mswd of 3 5 therefore contrary to statements in the literature that zn should be compatible in morb zn is a mildly incompatible element and must be enriched in the glass phase relative to olivine as zn does not fit into the other major phenocryst phase plagioclase in the source of morb zn likely is most enriched in oxides spinel magnetite and titanomagnetite copper generally does not correlate well with other elements in most morb data examined when differentiation is dominated by olivine cu has a tendency to behave incompatibly e g at mg numbers 70 but overall cu shows some tendency towards being a compatible element particularly along the mid atlantic ridge a behavior presumably due to separation of sulfides in which cu but not zn is markedly enriched copper thus may be in dispersed sulfides in the source of morb ocean ridges provide important data on source rock controls for sulfide deposits because in sediment starved ridges much is known about the possible source rocks and mineralization is presently occurring in contrast to zn pb 5 in continental hot cl rich brines zn pb in the hottest sediment starved ridge black smoker hydrothermal fluids at 21 n epr is about 110 similar to local morb 145 but cu pb is closer to 30 possibly due to subsurface deposition of cu at the jfr the best value of zn pb in the hydrothermal fluids is about 175 again similar to local morb 240 but cu is very low in the fluids that are at temperatures less than 300 c the large morb like zn pb in the hottest black smoker fluids suggests a source rock control for the metals that prohibits significant galena in the black smoker deposits of sediment starved ridges in contrast exhalative deposits on sediment swamped ridges have significant galena its presence is suggestive of pb derivation from sediments an origin supported by pb isotope studies of lehuray and colleagues in 1988

trace element systematics and ore forming processes in mafic vms deposits evidence from the troodos ophiolite cyprus abstract the volcanogenic massive sulfide vms deposits in the troodos ophiolite cyprus are ancient analogues for modern day seafloor massive sulfide mineralisation formed in a supra subduction zone environment in this study we present the first detailed in situ study of trace elements in sulfides from twenty vms deposits hosted in the troodos ophiolite to better understand factors that influence the distribution enrichment and incorporation of trace elements in different sulfide minerals on a mineral scale trace elements exhibit systematic variations between pyrite chalcopyrite and sphalerite pyrite preferentially incorporates as sb au and te whilst chalcopyrite is enriched in co and se sphalerite is trace element poor with the exception of ag and cd selenium averages 278 ppm n 150 in chalcopyrite but only 42 ppm n 1322 in pyrite bismuth and te in pyrite show a weak positive correlation r2 0 35 in some vms deposits possibly linked with the occurrence of bi telluride inclusions trace element concentrations also vary between colloform and euhedral pyrite with an enrichment of au as sb cu and zn in colloform compared to euhedral pyrite time resolved laser ablation profiles reveal that the trace element distribution on a mineral scale is not uniform and varies with crystallographic effects fluctuating physicochemical fluid conditions such as temperature ph fs2 fo2 and ligand availability during sulfide precipitation incorporation mechanisms in sulfides differ between elements in pyrite ag as se and pb are hosted in solid solution or as nanoscale inclusions whilst au sb and te may form micro scale inclusions on a regional scale 20 km the distribution of trace elements exhibits systematic variations between three major structural domains namely the solea mitsero and larnaca grabens the vms deposits of the magmatic tectonic solea graben are enriched in se co te au and cu relative to mitsero which is a purely extensional feature therefore we hypothesise that a variable magmatic volatile influx related to a magma volume b migration of the magmatic hydrothermal crack front and associated brine liberation or c a variation in protolith metal concentration are responsible for regional scale variations in vms geochemistry this is suggested to be intrinsically linked to the spreading architecture of troodos

spreading structure of the troodos ophiolite cyprus orientations of dikes within the sheeted dike complex of the troodos ophiolite reveal primary spreading structure produced at a complex ridge transform intersection three structural grabens are defined by listric and planar normal faults and rotated dikes that dip symmetrically toward graben axes faults flatten at depth into a detachment within the upper parts of the plutonic complex large exhalative massive sulfide deposits occur within the pillow sections of two of the grabens and appear to be associated with underlying altered and mineralized normal fault zones that channeled hydrothermal fluids we suggest that the grabens are fossil axial valleys produced by successive eastward jumps of an approximately north trending present coordinates slow spreading ridge crest a simple model for ridge migration indicates eastward jumps of 8 13 km changes in ridge orientation are suggested by changes in trends of dikes and graben axes comparison of the pattern of dikes near the arakapas fault zone with the structure of active ridge transform intersections suggests that the fault is a right offset sinistral transform in contrast to earlier models in which a ridge to the west of the exposed troodos complex was proposed

petrology and oxygen isotope geochemistry of a fossil seawater hydrothermal system within the solea graben northern troodos ophiolite cyprus hydrothermal mineral zonations and o isotope patterns of the northern troodos complex do not parallel the ophiolite pseudostratigraphy but reflect the convective geometry of an upper cretaceous seawater hydrothermal system large areas of the sheeted intrusive complex sic including the subaxial region of the solea graben are composed of 18o rich subgreenschist mineral assemblages and may represent regions of diffuse seawater recharge other areas of the sic are recrystallized to distinctive epidosite rocks granular high variance assemblages of epidote quartz chlorite that are depleted in 18o al2o3 na2o k2o zr cu and zn and are enriched in cao and sr compared with other mafic volcanic and dike rocks of the solea graben epidosite alteration occurred at temperatures of 310 370 c and involved fluids with 18o values and salinities similar to those of upper cretaceous seawater the epidosite zones are discordant with earlier mineral o isotope zonations and with the axis of spreading in the solea graben suggesting a postspreading off axis origin the seawater hydrothermal system responsible for solea graben massive sulfide deposits was probably driven by hypabyssal intrusions not exposed emplaced in a terminal failed spreading episode the geometries of o isotope surfaces within the solea graben imply that the epidosites formed in fossil upflow and deep recharge conduits depletions in base metals show that epidosite alteration liberated cu and zn to mineralizing fluids within the fossil upflow zone

systematic variations of trace element and sulfur isotope compositions in pyrite with stratigraphic depth in the skouriotissa volcanic hosted massive sulfide deposit troodos ophiolite cyprus the troodos ophiolite represents one of the best preserved fossil analogs of modern oceanic crust and includes numerous volcanic hosted massive sulfide deposits the skouriotissa deposit can be separated into a stockwork ore zone and an overlying massive sulfide lens that is covered by metalliferous sediments representing the former sulfide seawater interface pyrite is the dominant sulfide mineral within these ores the trace element composition of pyrite varies systematically with stratigraphic depth down to 150 mbsf probably reflecting fluid temperature variations and effects of phase separation co ni se te bi and cu metal remobilization due to hydrothermal zone refining zn sb and pb and fluid seawater mixing at the seafloor mo represent further important processes controlling the pyrite chemistry massive sulfide hosted sphalerite and euhedral pyrite probably formed from hot fluids 400 c while the occurrence of colloform pyrite indicates lower precipitation temperatures 400 c similar 18o quartz fluid equilibration temperatures 400 c in the stockwork zone suggest that the skouriotissa fluids did not cool significantly during the final 150 m of fluid ascent to the seafloor the 34s composition of deep stockwork pyrite 1 4 suggests that an isotopically light magmatic volatile phase 0 was added to the hydrothermal system of skouriotissa during further fluid ascent about 38 of cretaceous seawater 34s 18 19 was added leading to the precipitation of stockwork pyrite with positive 34s values 6 1 in addition the chemical and textural similarities between skouriotissa and modern seafloor vent systems and massive sulfide deposits suggest that the skouriotissa hydrothermal system has a modern analog

the distribution of gold in sub seafloor stockwork mineralization from dsdp hole 504b and the agrokipia b deposit cyprus the distribution of gold has been examined in sub seafloor stockworks from two sections of hydrothermally altered oceanic crust beneath the axial zones of fossil spreading centers deep sea drilling project hole 504b leg 83 contains a narrow zone of stockwork like sulfides in 6 ma old basalt from the transition zone between sheeted dikes and overlying pillow lavas 910 928 m mineralization occurred as a result of local mixing between ascending hydrothermal fluids 350 c and seawater that penetrated the top of the dike section previous studies indicate that a significant amount of gold was leached from the sheeted dikes during high temperature greenschist facies alteration but mineralized wall rock in the transition zone is not substantially enriched in gold sulfide concentrates from the narrow stockwork average 26 ppb au and one sample of as rich pyrite from a quartz epidote breccia contains 100 ppb au cyprus custal study project hole cy 2a contains an equivalent section of altered cretaceous p

hydrothermal sulfides from a submarine caldera in the shichito iwojima ridge northwestern pacific abstract a large mineralized block of two pyroxene andesite was dredged from a 913 m deep wall of a submarine caldera of the kaikata seamount about 180 km north of iwojima island the kaikata caldera 26 42 n 141 05 e is a seamount in active volcanic front schichito iwojima ridge to the west of ogasawara bonin trench sulfide minerals observed in the sample are dominantly pyrite with minor amount of sphalerite and cu fe sulfide chalcopyrite they occur in 5 mm thick veinlets together with euhedral quartz and chlorite the high filling temperatures 290 c of fluid inclusions in the quartz crystals and enrichment of gold max 142 ppb in vein materials both indicate a hydrothermal origin of the sulfides this is to our knowledge the first discovery of hydrothermal precious and base metal mineralizations associated with front volcanism in the marine environment

a multiple sulfur isotope study through the volcanic section of the troodos ophiolite abstract multiple s isotope systematics 34s and 33s and high resolution in situ s isotope measurements offer new perspectives on the study of biological and abiotic cycling of sulfur in hydrothermal systems we applied these techniques to the tethyian troodos ophiolite 91 ma from cyprus one of the best preserved remnants of oceanic crust in the world using materials from deep drill cores and surface sampling we focused on the volcanic section of the ophiolite including the hydrothermal massive sulfide deposit at agrokipia which represents a fossil zone of high temperature fluid upwelling and the akaki river section which displays a range of lower temperature alteration types the 34s and 33s values of bulk and sims secondary ion mass spectrometry analyses from the agrokipia sulfide deposits show that the sulfide minerals are largely derived from thermochemical reduction of entrained seawater sulfate and leached h2s from the root zone of hydrothermal upwelling the contributions of these two sources can vary substantially within individual sulfide grains indicating a very dynamic mixing between these sulfur sources microbial reworking of the sulfide mound is recorded in a sample with very elevated 33s values 0 22 the akaki and agrokipia volcanics experienced low temperature sulfur loss and removal of heavier sulfur isotopes due to partial oxidation by microbes while some intervals gained sulfur and have 34s and 33s values indicative of microbial sulfate reduction ree data of vein quartz containing pyrite with 34s 21 implies local ephemeral hydrothermal upwelling in the lower akaki volcanics possibly associated with the late stage boninitic magmatic activity in the troodos ophiolite suggesting that microbial sulfate reduction in oceanic crust may continue for 10 15 ma in crustal sections with prolonged igneous activity such as troodos

a mid ocean ridge thermal model constraints on the volume of axial hydrothermal heat flux the depth to the axial magma chamber at three oceanic spreading centers as indicated by seismic reflection surveys is greater than that predicted by conductive cooling thermal models of ridge crests the additional cooling at the ridge axis is owed to the circulation of seawater through the shallow crust a theoretical model for the temperature distribution at spreading centers which includes distributed heat sources and sinks is presented by representing the hydrothermal heat loss as a series of heat sinks the depths to the axial magma chamber at the east pacific rise at latitude 9 n the southern juan de fuca ridge and the lau basin spreading center are modeled heat sinks are added to the input model to increase the solidus depth until the computed magma chamber depth matches the magma chamber depth determined by seismic reflection surveys the thermal modeling indicates that the axial hydrothermal heat flux is between 7 1 106 and 13 8 106 mj m2 or 10 to 20 of the total missing heat at the ridge axis requiring extensive low temperature circulation off axis high temperature vents that are spaced 1 km apart and are active between 4 and 10 of the time would account for the axial hydrothermal heat loss

a sulfur isotopic profile through the troodos ophiolite cyprus primary composition and the effects of seawater hydrothermal alteration the sulfide mineralogy sulfur contents and sulfur isotopic compositions were determined for a section through the troodos ophiolite as represented by drillcore from holes cy1a cy2a and cy4 plus selected outcrops with the goals of understanding the geochemistry of s during hydrothermal alteration of the crust and obtaining a mass balance for sulfur in altered ophiolitic crust primary 34s values of the ophiolite are 0 1 consistent with a morb or bab like sulfur source the volcanic rocks have low sulfur contents mean 40 ppm and generally negative 34s values to 26 1 these are the results of sulfur loss through oxidation by seawater at low temperatures 100 c and isotopic fractionation during partial oxidation of igneous sulfides the sheeted dike complex is uniformly enriched in 34s 34s 5 4 as the result of mixing of reduced cretaceous seawater sulfate 17 with primary crustal sulfide sulfate was reduced through oxidation of ferrous iron in the dikes and conversion of igneous pyrrhotite to secondary pyrite decreasing water rock ratios with depth in the plutonic section led to a general decrease in 34s values downward to igneous values in the lower gabbros seawater effects are present locally to the base of the section however cooling of diffuse upwelling hydrothermal fluids t 250 c produced s and metal enrichments in the upper dikes 1 26 wt s whereas sulfur was lost from the lower dikes and upper plutonic rocks which contain 200 ppm and 10 1640 ppm s respectively through higher temperature 350 c alteration reactions epidosites at the dikes gabbro transition contain 30 ppm s with 34s 5 2 6 5 these rocks lost sulfur and metals during reaction with 34s enriched deep hydrothermal fluids at high temperatures 350 400 c and high water rock ratios in basal hydrothermal upflow zones the ultimate effect of alteration of ophiolitic crust is redistribution of igneous sulfur within the crust and exchange of crustal sulfur for seawater sulfur with little net change in the sulfur content of the crust overall the bulk altered troodos crust is enriched in 34s having 34s 3 6 fluxes of sulfur between seawater and ophiolitic crust are an order of magnitude smaller than modern riverine input to and sedimentary sulfide output from the oceans the amount of seawater sulfur that reacted with troodos ophiolite crust is approximately twice that for a composite section of oceanic crust consistent with the generally greater intensity of alteration of ophiolitic crust compared to modern oceanic crust

systematic variations in magmatic sulphide chemistry from mid ocean ridges back arc basins and island arcs abstract immiscible sulphide liquids preserved as magmatic sulphide globules are hosted in igneous rocks of highly variable composition formed during magmatic processes at different tectonic settings here we report on compositional in situ data of magmatic sulphides from mid ocean ridge back arc and island arc magmatic systems iron ni rich monosulphide solid solutions mss that mainly consist of pyrrhotite and pentlandite are the dominant phases in magmatic sulphide globules in subduction related magmas mss are most abundant in relatively evolved melts and characterised by low ni and high fe contents as well as low ni cu ratios 1 thus mss chemistry varies systematically in lavas from the different tectonic settings in terms of their fe ni distribution and ni cu ratio the observed mineralogical and chemical variations between mss from the different settings reflect early s saturation accompanied by olivine fractionation along mid ocean ridges compared to later stage s saturation in arc systems associated with fe ti oxide fractionation these systematics are probably related to the relatively oxidised character of subduction zone magmas opposed to more reduced mid ocean ridge melts large ni cu variations in mss from the same locality and in individual samples suggest that s saturation is a multistage or continuous process leading to inclusions of magmatic sulphides that represent different fractionation stages in the ascending magma

formation of volcanogenic massive sulfide deposits the kuroko perspective abstract the main objective of this paper is to identify the geochemical hydrological igneous and tectonic processes that led to the variations in the physical size geometry and chemical mineralogy metal ratios and zoning characteristics of volcanogenic massive sulfide deposits with respect to space from a scale of mining district size area to a global scale and time from a all volcanogenic massive sulfide deposits vmsds appear to have formed in extensional tectonic settings such as at mid ocean spreading centers backarc spreading centers and intracontinental rifts and failed rifts all vmsds appear to have formed in submarine depressions by seawater that became ore forming fluids through interactions with the heated upper crustal rocks submarine depressions especially those created by submarine caldera formation and or by large scale tectonic activities e g rifting become most favorable sites for the formation of large vmsds because of hydrological physical and chemical reasons the fundamental processes leading to the formation of vmsds include the following six processes 1 1 intrusion of a heat source typically a 10 3 km size pluton into an oceanic crust or a submarine continental crust causes deep convective circulation of seawater around the pluton the radius of a circulation cell is typically 5 km the temperature of fluids that discharge on the seafloor increases with time from the ambient temperature to a typical maximum of 350 c and then decreases gradually to the ambient temperatures in a time scale of 100 to 10 000 years the majority of sulfide and sulfate mineralization occurs during the waxing stage of hydrothermal activity 2 2 reactions between low temperature t 2 4 as disseminated gypsum and anhydrite in the country rocks 3 3 reactions of the modified seawater with higher temperature rocks at depths during the waxing stage cause the transformation of the seawater to metal and h 2 s rich ore forming fluids the metals and sulfide sulfur are leached from the county rocks the previously formed gypsum and anhydrite are reduced by fe 2 bearing minerals and organic matter providing additional h 2 s the mass of high temperature rocks that provide the metals and reduced sulfur is typically 10 11 tons 40 km 3 in volume the roles of magmatic fluids or gases are minor in most massive sulfide systems except for so 2 to produce acid type alteration in some systems 4 4 reactions between the ore forming fluids and cooler rocks in the discharge zone cause alteration of rocks and precipitation of some ore minerals in the stockwork ores 5 5 mixing of the ore forming fluids with local seawater within unconsolidated sediments and or on the seafloor causes precipitation of primitive ores with the black ore mineralogy sphalerite galena pyrite barite anhydrite 6 6 reactions between the primitive ores with later and hotter hydrothermal fluids cause transformation of primitive ores to matured ores that are enriched in chalcopyrite and pyrite variations in the mineralogical and elemental characteristics the geometry and the size of submarine hydrothermal deposits are controlled by the following four parameters 1 a the chemical and physical characteristics of seawater composition temperature density which depend largely on the geographical settings e g equatorial evaporating basins 2 b the chemical and physical characteristics of the plumbing system lithology fractures 3 c the thermal structure of the plumbing system which is determined largely by the ambient geothermal gradient and the size and temperature of the intrusive and 4 d the physical characteristics of the seafloor depth basin topography for example the submarine hydrothermal deposits developed in basaltic plumbing systems are generally poor in pb and ba compared to those developed in felsic plumbing systems the lower temperature systems are generally poorer in sulfides but richer in iron oxides and sulfates the higher temperature and larger hydrothermal systems tend to produce chalcopyrite and pyrite rich ores contrasts in the metal ratios between the noranda type archean vmsds and the younger vmsds reflect the differences in the geothermal gradient of the plumbing systems the submarine hydrothermal deposits developed in the near equatorial regions tend to form large continuous bedded type ores because of the likeliness of creating large stratified basins the basic processes of submarine hydrothermal mineralization have remained essentially the same throughout the geologic history from at least 3 5 billion year ago to the present

comparative mineralogy and geochemistry of gold bearing sulfide deposits on the mid ocean ridges a comparative study of the mineralogy and geochemistry of sulfide deposits on mid ocean ridges in the northeast pacific and the mid atlantic reveals common characteristics associated with primary gold enrichment average gold contents of 0 8 to 5 ppm au occur in sulfides from southern explorer ridge and axial seamount northeast pacific and from the tag hydrothermal field and snakepit vent field mid atlantic ridge the enrichment of gold in these deposits is consistently related to a phase of late stage low temperature 1 ppm au occur exclusively in pyritic assemblages and commonly with abundant fe poor sphalerite and a suite of complex pb sb as sulfosalts amorphous silica and locally barite or carbonate are important constituents of the gold rich precipitates but do not contain gold themselves high temperature 350 c black smoker assemblages consisting dominantly of pyrite chalcopyrite pyrrhotite isocubanite and abundant anhydrite are uniformly gold poor 0 2 ppm au to the extent that individual sulfides can be mechanically separated chemical analyses by neutron activation indicate that gold is most abundant in sphalerite up to 5 7 ppm au but also occurs in pyrite and marcasite samples of sphalerite with abundant inclusions of fine grained sulfosalts locally contain up to 18 ppm au suggesting that sulfosalts may be repositories for gold no free gold has been observed at 4000 magnification of polished specimens indicating that the gold is present only as submicroscopic inclusions or as a chemical constituent within the sulfides samples from gold rich deposits in the northeast pacific and mid atlantic are compared with similar but relatively gold poor sulfides from the galapagos rift and 13 n on the east pacific rise epr and with barren sulfides from 11 n epr 21 n epr the endeavour ridge and the southern juan de fuca ridge trace element analyses of more than 170 samples show that gold enrichment in almost all of the deposits is associated with high concentrations of ag as sb pb and zn and locally with high cd hg tl and ga in contrast gold is typically depleted in samples with high co se and mo the close association of au with ag as sb and pb may reflect the common behavior of these metals as aqueous sulfur complexes e g au hs 2 at low temperatures similar mineralogical and geochemical associations are observed in sulfide deposits from modern back arc settings and in the ancient geologic record

chemical characteristics of hydrothermal fluids from the tag mound of the mid atlantic ridge in august 1994 implications for spatial and temporal variability of hydrothermal activity the tag hydrothermal mound on the mid atlantic ridge 26 08 n 44 50 w was revisited in august 1994 with the submersible shinkai 6500 in order to characterize time series fluid chemistry prior to the odp drilling fluid samples were taken from both black smokers and white smokers si ph alkalinity h 2 s major cations na k ca 2 mg 2 major anions cl so 4 2 and minor elements li sr b fe mn cu zn br as well as sr isotope ratios were measured we report the first br ci ratios for the tag hydrothermal fluids showing no fractionation between br and cl during the fluid rock interaction this study shows small changes in composition of the black smoker fluids from the 1990 data edmond et al 1995 changes of ph alkalinity fe k and 87 sr 86 sr values are suggestive of subsurface fes precipitation and a decrease of water rock ratio at a deeper reaction zone differences in chemical characteristics between the black and white smoker fluids were similarly observed as in 1990

the gold content of volcanogenic massive sulfide deposits volcanogenic massive sulfide deposits contain variable amounts of gold both in terms of average grade and total gold content with some vms deposits hosting world class gold mines with more than 100 t au previous studies have identified gold rich vms as having an average gold grade expressed in g t exceeding the total abundance of base metals expressed in wt however statistically meaningful criteria for the identification of truly anomalous deposits have not been established this paper presents a more extensive analysis of gold grades and tonnages of 513 vms deposits worldwide revealing a number of important features in the distribution of the data a large proportion of deposits are characterized by a relatively low gold grade 2 g t with a gradual decrease in frequency towards maximum gold grades defining a log normal distribution in the analysis presented in this paper the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of vms deposits based on gold grade especially when comparing deposits within individual belts and districts the geometric mean gold grade of 513 vms deposits worldwide is 0 76 g t the geometric standard deviation is 2 70 g t au in this analysis deposits with more than 3 46 g t au geometric mean plus one geometric standard deviation are considered auriferous the geometric mean gold content is 4 7 t au with a geometric standard deviation of 26 3 t au deposits containing 31 t au or more geometric mean plus one geometric standard deviation are also considered to be anomalous in terms of gold content irrespective of the gold grade deposits with more than 3 46 g t au and 31 t au are considered gold rich vms a large proportion of the total gold hosted in vms worldwide is found in a relatively small number of such deposits the identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in vms at the district scale the gold rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes the gold rich vms are commonly associated with transitional to calc alkaline intermediate to felsic volcanic rocks which may reflect a particularly fertile geodynamic setting and or timing e g early arc rifting or rifting front at the deposit scale uncommon alteration assemblages e g advanced argillic aluminous strongly siliceous or potassium feldspar alteration and trace element signatures may be recognized e g au ag as sb bi hg te suggesting a direct magmatic input in some systems

dissolved and particulate trace metals in hydrothermal plumes at the mid atlantic ridge seawater samples from the non buoyant plume have been collected at the tag 26 n and snakepit 23 n hydrothermal sites on the mid atlantic ridge mar and analysed for dissolved 0 4 m trace metals up to 50 of vent fluid fe is present in the 0 4 m fraction in the non buoyant plume increases in particulate concentrations of cd are accompanied by a reduction in dissolved cd to levels below ambient seawater we show that dissolved cd is scavenged from seawater in the buoyant section of the plume while cd re dissolves from the particles in the non buoyant plume up to 43 of hydrothermally injected cu is found in the 0 4 m fraction in the non buoyant plume

the internal structure of an active sea floor massive sulphide deposit the hydrothermal circulation of sea water through permeable ocean crust results in rock water interactions that lead to the formation of massive sulphide deposits these are the modern analogues of many ancient ophiolite hosted deposits1 4 such as those exposed in cyprus here we report results obtained from drilling a series of holes into an actively forming sulphide deposit on the mid atlantic ridge a complex assemblage of sulphide anhydrite silica breccias provides striking evidence that such hydrothermal mounds do not grow simply by the accumulation of sulphides on the sea floor indeed the deposit grows largely as an in situ breccia pile as successive episodes of hydrothermal activity each form new hydrothermal precipitates and cement earlier deposits during inactive periods the collapse of sulphide chimneys dissolution of anhydrite and disruption by faulting cause brecciation of the deposit the abundance of anhydrite beneath the present region of focused hydrothermal venting reflects the high temperatures 150 c currently maintained within the mound and implies substantial entrainment of cold sea water into the interior of the deposit these observations demonstrate the important role of anhydrite in the growth of massive sulphide deposits despite its absence in those preserved on land

drilling to gabbro in intact ocean crust sampling an intact sequence of oceanic crust through lavas dikes and gabbros is necessary to advance the understanding of the formation and evolution of crust formed at mid ocean ridges but it has been an elusive goal of scientific ocean drilling for decades recent drilling in the eastern pacific ocean in hole 1256d reached gabbro within seismic layer 2 1157 meters into crust formed at a superfast spreading rate the gabbros are the crystallized melt lenses that formed beneath a mid ocean ridge the depth at which gabbro was reached confirms predictions extrapolated from seismic experiments at modern mid ocean ridges melt lenses occur at shallower depths at faster spreading rates the gabbros intrude metamorphosed sheeted dikes and have compositions similar to the overlying lavas precluding formation of the cumulate lower oceanic crust from melt lenses so far penetrated by hole 1256d

a synchronously coupled tide wave surge model of the yellow sea abstract a coupled wave tide surge model has been established in this study in order to investigate the effect of tides storm surges and wind waves interactions during a winter monsoon on november 1983 in the yellow sea the coupled model is based on the synchronous dynamic coupling of a third generation wave model wam cycle 4 and the two dimensional tide surge model the surface stress generated by interactions between wind and waves is calculated using the wam cycle 4 directly based on an analytical approximation of the results obtained from the quasi linear theory of wave generation the changes of bottom friction factor generated by waves and current interactions are calculated by using simplified bottom boundary layer model the model simulations showed that bottom velocity and effective bottom drag coefficient induced by combination of wave and current were increased in shallow waters of up to 50 m in the yellow sea during the wintertime strong storm conditions

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

strontium and oxygen isotopic constraints on fluid mixing alteration and mineralization in the tag hydrothermal deposit abstract strontium and oxygen isotopic measurements of samples recovered from the trans atlantic geotraverse tag hydrothermal mound during leg 158 of the ocean drilling program provide important constraints on the nature of fluid rock interactions during basalt alteration and mineralization within an active hydrothermal deposit fresh mid ocean ridge basalt morb with a 87 sr 86 sr of 0 7026 from the basement beneath the tag mound was altered at both low and high temperatures by seawater and altered at high temperature by near end member black smoker fluids pillow breccias occurring beneath the margins of the mound are locally recrystallized to chlorite by interaction with large volumes of conductively heated seawater 200 c the development of a silicified sulfide mineralized stockwork within the basaltic basement follows a simple paragenetic sequence of chloritization followed by mineralization and the development of a quartz pyrite paragonite stockwork cut by quartz pyrite veins initial alteration involved the development of chloritic alteration halos around basalt clasts by reaction with a mg bearing mixture of upwelling high temperature 300 c black smoker type fluid with a minor 300 c interaction between the wallrock and these mg bearing fluids results in the complete recrystallization of the wallrock to chlorite quartz pyrite the quartz pyrite paragonite assemblage replaces the chloritized basalts and developed by reaction at 250 360 c with end member hydrothermal fluids having 87 sr 86 sr 0 7038 similar to present day vent fluids the uniformity of the 87 sr 86 sr ratios of hydrothermal assemblages throughout the mound and stockwork requires that the 87 sr 86 sr ratio of end member hydrothermal fluids has remained relatively constant for a time period longer than that required to change the interior thermal structure and plumbing network of the mound and underlying stockwork precipitation of anhydrite in breccias and as late stage veins throughout most of the mound and stockwork down to at least 125 mbsf records extensive entrainment of seawater into the hydrothermal deposit 87 sr 86 sr ratios indicate that most of the anhydrite formed from 2 1 mixture of seawater and black smoker fluids 65 15 seawater oxygen isotopic compositions imply that anhydrite precipitated at temperatures between 147 c and 270 c and require that seawater was conductively heated to between 100 c and 180 c before mixing and precipitation occurred anhydrite from the tag mound has a sr ca partition coefficient kd 0 60 0 28 2 this value is in agreement with the range of experimentally determined partition coefficients kd 0 27 0 73 and is similar to those calculated for anhydrite from active black smoker chimneys from 21 n on the east pacific rise the 18 o so 4 of tag anhydrite brackets the value of seawater sulfate oxygen 9 5 dissolution of anhydrite back into the oceans during episodes of hydrothermal quiescence provides a mechanism of buffering seawater sulfate oxygen to an isotopically light composition in addition to the precipitation and dissolution of anhydrite within the oceanic basement during hydrothermal recharge at the mid ocean ridges

recharge flux to ocean ridge black smoker systems a geochemical estimate from odp hole 504b we use the sr isotopic composition of rock and anhydrite as a monitor of fluid composition in dsdp odp hole 504b to calculate the recharge flux to the axial high temperature hydrothermal circulation the fluid and rock sr isotope profiles are well fit by a tracer transport mass balance model that approximates fluid solid exchange by linear kinetics the calculated time integrated flux of 1 7 0 2 x 106 kg m 2 is significantly less than the 5 x 106 kg m 2 calculated from thermal models that assume all magma is intruded into a high level magma chamber at the base of the sheeted dykes our low flux is consistent with the observed thermal structure as recorded by secondary alteration minerals in hole 504b and the intrusion of magma as lenses distributed through the lower oceanic crust it leaves open the questions as to how the lower oceanic crust cools and how seawater geochemical budgets balance

forecasting large intermediate depth earthquakes in the south aegean abstract statistical considerations and periodic patterns of seismicity supply evidence that hazardous shock s of m s 6 8 8 0 must be expected in the next few years at depths of 80 100 km of the south aegean benioff zone space time characteristics indicate that the most likely location of the next event is one of the two earthquake nests at the central and eastern earthquake sections of the zone from the history and a lithospheric model of the region the most probable locations of maximum intensity are along the convex arc side

a note on the prediction of the september 13 1986 strong earthquake in kalamata southwest peloponnesus greece abstract a comparison between the observed focal parameters of the september 13 1986 kalamata greece strong shock and the predicted ones shows that the prediction was quite successful as far as time of occurrence location and focal depth are concerned the discrepancy between the observed m s 6 2 and predicted m s 6 5 7 6 magnitude is attributed to the use of old seismological information and the lack of systematic observation of non seismic earthquake precursors precursors of this type observed by local people before some recent greek shocks including the kalamata earthquake indicate that their systematic monitoring could substantially contribute toward earthquake prediction in greece assuming the random model the probability that the kalamata earthquake occurred in the specified target area by chance is 0 65

effects of magmatic volatile influx in mafic vms hydrothermal systems evidence from the troodos ophiolite cyprus abstract the troodos ophiolite cyprus is the principal on land analogue for mafic hosted volcanogenic massive sulfide vms deposits this study for the first time presents sulfur isotope 34s data on a regional scale from vms deposits and other mineralised zones across the troodos ophiolite in combination 34s se s ratios and trace element chemistry e g se cu and au of different hydrothermal sulfides are used to assess variations in magmatic volatile influx and the source of metals and sulfur in ancient hydrothermal systems sulfur isotope analyses n 180 across 19 mineral deposits indicate a variable source of sulfur in the troodos vms hydrothermal system this in turn allows a variable source of metals to be inferred pyrite 34s range from 5 5 to 13 2 with an average of 4 6 n 160 for all deposits investigated these 34s variations cannot only be explained by variable proportions of thermochemical seawater sulfate reduction 34s 18 to 19 and leaching of primary magmatic sulfur from igneous rocks 34s 0 1 consequently two processes are proposed explaining the trace metal and 34s variation across the troodos ore forming systems including i a variable source of metals in the sheeted dyke complex and ii the addition of a magmatic volatile rich phase to the vms hydrothermal systems two distinct lava units exist in the troodos stratigraphy namely the upper and lower pillow lavas upl and lpl the more primitive upl are enriched in au se and cu relative to as sb and zn that are concentrated in the lpl some vms deposits pre date the formation of the upl e g agrokipia a suggesting se cu and au depleted source rocks hence the stratigraphic position of vms deposits and the ratio of upl lpl affinity elements e g as zn sb vs cu se au imply a systematic relationship between trace element distribution and stratigraphic depth this relates to the relative proportion of upl and lpl affinity lavas within the metal source region 34s values 106 ratios 500 in pyrite suggest the contribution of a magmatic volatile component e g apliki and skouriotissa we demonstrate that the source of metals and sulfur in the troodos vms hydrothermal system is affected by regional scale processes related to i variable source lithologies and ii the contribution of a magmatic volatile phase to some troodos vms hydrothermal systems

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

chimneys in paleozoic massive sulfide mounds of the urals vms deposits mineral and trace element comparison with modern black grey white and clear smokers in the urals a wide range of well preserved chimneys are found in vms deposits which are associated with ultramafic atlantic type dergamysh mafic cyprus type buribay bimodal mafic uralian type yubileynoye sultanovskoye yaman kasy molodezhnoye uzelga 4 valentorskoye and bimodal felsic kuroko or baymak type oktyabrskoye tash tau uselga 1 talgan alexandrinskoye sequences chimneys have also been found in the safyanovskoye deposit altay type that is hosted by intercalated felsic lavas and carbonaceous shales a combination of geological mineralogical and trace element data provide a general outline for comparison between chimneys from the urals deposits and modern vent sites the chimneys from the dergamysh deposit show a broad affinity with those from the rainbow and other vent sites associated with serpentinites of the mid atlantic ridge the chimneys from the buribay deposit are similar to the black smokers of the epr vent sites including the scarcity of rare minerals the chimneys from the urals type of the vms deposits show some similarities with grey smokers from the brother volcano and pacmanus sites the chimneys from the baymak type of the vms deposits resemble grey and white smokers of the pacmanus and grey smokers of the suiyo vent sites the chimneys from the safyanovskoye deposit are similar to the black and clear smokers from the okinawa trough mineral assemblages are controlled by the combination of host rock composition and physico chemical conditions of the ore forming processes amount of colloform pyrite isocubanite and pseudomorphic pyrite and marcasite after pyrrhotite decreases in the chimneys across the range from ultramafic and mafic to felsic hosted deposits and is concomitant with increase in the contents of sphalerite galena bornite fahlores native gold and barite across this range the chimneys from the urals type contain abundant tellurides and sulfoarsenides while these minerals are rare except for hessite in the baymak type deposits in the same range the buffering capacity of host rocks decreases in contrast to the increase in s2 and o2 with the exception of the safyanovskoye deposit trace element assemblages in chalcopyrite vary to reflect the host rock ultramafic high se sn co ni ag and au mafic high co se mo and low bi au and pb bimodal mafic high te au ag bi pb co moderate se and variable as and sb bimodal felsic high as sb mo pb moderate bi and low co te and se in sphalerite of the same range the contents of bi pb ag au and sb increase versus fe se and o the variations in trace elements in colloform pyrite coincide with these changes the specific mineral changes in the local ranges from cu to zn rich chimneys in each vms deposit are similar to the general changes in the range of host rock classes of the deposits however the local t s2 and o2 changes can broadly be interpreted in terms of contribution of variable oxygenated cold seawater to the subseafloor and seafloor hydrothermal processes

official earthquake prediction procedure in greece abstract since jan 19 1983 the authors have been operating a telemetric network of electrotelluric stations in greece the real time observation of specific pre seismic variations in the electric field of the earth seismic electric signals ses allows us to predict the time epicenter and magnitude of an impending earthquake eq initially the predictions were announced by expediting telegrams prior to the event after the ministry of public works established the earthquake prediction council epc in september 1985 predictions were dealt with in special sessions of the council prior to the occurrence of an earthquake it was decided to announce only eq s with an expected magnitude ms 4 8 for epicenters predicted within or near the perimeter surrounding the network of measuring stations and ms 5 for eq s predicted outside the perimeter this procedure was followed from september 1985 to march 18 1986 with the following results 1 1 within the network only one eq with ms 4 9 occurred during the period mentioned the prediction of the magnitude was accurate to within a few tenths of a magnitude unit while the epicenter was predetermined to within some tens of kilometers no predictions were made that were not followed by earthquakes 2 2 outside the network three eq s with ms 5 4 5 2 and 5 3 occurred on nov 9 dec 18 and dec 23 1985 respectively the first was missed the magnitudes of the other two were predicted to be ms 5 2 and 5 5 respectively the corresponding epicentral coordinates were forecast with an accuracy of 150 and 160 km respectively the sessions were discontinued on march 18 1986 on march 24 1986 a ms 6 1 eq was predicted and directly announced to the ministry of public works the event occurred on march 29 with the predicted magnitude and less than 50 km from the predicted epicenter

hydrothermal circulation within the endeavour segment juan de fuca ridge areas of the seafloor at mid ocean ridges where hydrothermal vents discharge are easily recognized by the dramatic biological physical and chemical processes that characterize such sites locations where seawater flows into the seafloor to recharge hydrothermal cells within the crustal reservoir are by contrast almost invisible but can be indirectly identified by a systematic grid of conductive heat flow measurements an array of conductive heat flow stations in the endeavour axial valley of the juan de fuca ridge has identified recharge zones that appear to represent a nested system of fluid circulation paths at the scale of an axial rift valley conductive heat flow data indicate a general cross valley fluid flow where seawater enters the shallow subsurface crustal reservoir at the eastern wall of the endeavour axial valley and undergoes a kilometer of horizontal transit beneath the valley floor finally exiting as warm hydrothermal fluid discharge on the western valley bounding wall recharge zones also have been identified as located within an annular ring of very cold seafloor around the large main endeavour hydrothermal field with seawater inflow occurring within faults that surround the fluid discharge sites these conductive heat flow data are consistent with previous models where high temperature fluid circulation cells beneath large hydrothermal vent fields may be composed of narrow vertical cylinders subsurface fluid circulation on the endeavour segment occurs at various crustal depths in three distinct modes 1 general east to west flow across the entire valley floor 2 in narrow cylinders that penetrate deeply to high temperature heat sources and 3 supplying low temperature diffuse vents where seawater is entrained into the shallow uppermost crust by the adjacent high temperature cylindrical systems the systematic array of conductive heat flow measurements over the axial valley floor averaged 150 mw m2 suggesting that only about 3 of the total energy flux of ocean crustal formation is removed by conductive heat transfer with the remainder being dissipated to overlying seawater by fluid advection

a chemical model for the concentration of gold in volcanogenic massive sulphide deposits abstract study and review of the gold distribution in selected volcanogenic massive sulphide deposits rosebery and hellyer in tasmania mt chalmers in queensland and millenbach in quebec indicates that gold has two distinct occurrences in these deposits 1 a gold zinc lead silver association which is commonly found in the upper part of zinc rich massive sulphide lenses e g rosebery and hellyer and 2 a gold copper association which is commonly present in the stringers and lower portions of copper rich deposits e g mt chalmers and millenbach in each deposit one of these occurrence dominates almost to the exclusion of the other thermodynamic modelling of the volcanogenic fluid which is based on previous work by large 1977 eldridge et al 1983 and pisutha arnond and ohmoto 1983 indicates that gold in the upper part of the zinc rich massive sulphide lenses was transported as au hs 2 while gold in the stringers and bases of copper rich massive sulphide deposits was transported as aucl 2 the ph and o 2 of the ore forming fluid have an important control on gold deposition and therefore gold grades high gold grades in zinc rich massive sulphide are promoted by near neutral oxidised and low temperature 150 c to 275 c fluids as indicated by the presence of barite carbonate feldspar gangue high gold grades in the copper rich stringers and base of the massive sulphide are promoted by higher temperatures 275 c to 350 c relatively oxidised fluids as indicated by bornite or by barite or hematite gangue and relatively acid fluids as indicated by kaolinite gangue in o 2 t space significant gold transport by au hs 2 occurs only in the pyrite stability field at relatively low temperatures 2 is not restricted by iron mineral equilibria but is greatest in the hematite magnetite and pyrite fields at high temperatures 300 c and high o 2 10 30 under conditions of au hs 2 transport bonanza type gold deposition may be found in areas where the hydrothermal fluids passed from the field of pyrite stability to that of hematite stability oxidation of hydrothermal fluids by seawater mixing and the rapid precipitation of sulphide minerals at the top of the massive sulphide lens may cause the precipitation of gold via the mechanisms of either h 2 s oxidation or sulphide gold coprecipitation other types of gold deposits may be classified into either the gold zinc or gold copper association the gold copper bismuth association is developed in higher temperature systems of moderate to high salinity where aucl 2 is the dominant complex e g porphyry cu au deposits and au rich skarns whereas the gold zinc lead silver association is developed in systems of low salinity and high h 2 s where au hs 2 is the dominant complex e g epithermal au ag and archean greenstone hosted au quartz

long term accelerating foreshock activity may indicate the occurrence time of a strong shock in the western hellenic arc abstract in the decades prior to the occurrence of the 1899 ms 6 6 and 1947 ms 7 0 main shocks in the western hellenic arc wha the rate of occurrence of foreshocks ms 5 2 within a radius of 100 km around the epicenters can generally be said to have accelerated after a long period of very low foreshock activity stage i the process culminates in a final rapid acceleration of foreshocks some months before the main shocks stage ii while the last two months are quiescent stage iii these three stages are in good correspondence with the three stages of crustal deformation and several precursors to the main shock as predicted by the dilatancy model the data fit very well power law equations similar to those found for short term foreshocks of ordinary earthquakes and those associated with the creation of artificial lakes the position of the rupture zones of past wha strong shocks implies that the eastern part of the segment is the most probable location for the next strong shock in the arc a process of accelerating seismic activity similar to that which preceded the 1899 and 1947 shocks has been under way since 1966 around this part of the segment a comparison between changes in the power law curves for the earlier earthquakes and the one now expected indicates that the latter is now 3 8 months overdue assuming that the long term accelerating foreshock activity is a seismotectonic peculiarity of the wha segment i suggest that the preparation of the next rupture in the wha has entered a highly mature stage and that there will very probably be an earthquake in this area within the next few months

mobility of au and related elements during the hydrothermal alteration of the oceanic crust implications for the sources of metals in vms deposits volcanogenic massive sulphide vms deposits are commonly enriched in cu zn and pb and can also be variably enriched in au as sb se and te the behaviour of these elements during hydrothermal alteration of the oceanic crust is not well known ocean drilling program odp hole 1256d penetrates a complete in situ section of the upper oceanic crust providing a unique sample suite to investigate the behaviour of metals during hydrothermal alteration a representative suite of samples was analysed for au as sb se and te using low detection limit methods and a mass balance of metal mobility has been carried out through comparison with a fresh mid oceanic ridge basalt morb glass database the mass balance shows that au as se sb s cu zn and pb are depleted in the sheeted dyke and plutonic complexes by 46 12 27 5 2 5 0 5 27 6 8 4 0 7 9 6 1 6 7 9 0 5 and 44 6 respectively arsenic and sb are enriched in the volcanic section due to seawater derived fluid circulation calculations suggest that large quantities of metal are mobilised from the oceanic crust but only a small proportion is eventually trapped as vms mineralisation the quantity of au mobilised and the ratio of au to base metals are similar to those of mafic vms and ten times enrichment of au would be needed to form a au rich vms the cu rich affinity of mafic vms deposits could be explained by base metal fractionation both in the upper sheeted dykes and during vms deposit formation

dyke domains in the mitsero graben troodos ophiolite cyprus an off axis model for graben formation at a spreading centre abstract graben at oceanic spreading centres may form at on axis or off axis positions their formation is dependent on the tectonic processes active in the oceanic crust evidence for the position of formation of graben in oceanic analogues ophiolites can be obtained from the orientation of dykes within sheeted dyke complexes dyke orientation data and dyke relations from the mitsero graben and environs troodos ophiolite cyprus have been used to determine the tectonic setting of graben formation five major dyke domains were delineated on the basis of orientation of dykes in the sheeted dyke complex in the mitsero graben between domains the mean strike rotates counter clockwise by 25 in the easternmost domain dyke strikes are roughly 070 and progressively westward the mean strikes of dykes within domains are roughly 045 026 000 and 324 within domains the dyke trends show no systematic changes in strike toward the domain edges dyke cross cutting relations the degree of their rotation and relations to other features such as hydrothermal alteration leads to the suggestion that the mitsero graben formed late in the history of the area possibly in an off axis position

sulfide impregnated and pure silica precipitates of hydrothermal origin from the central indian ocean abstract this is the first report about silica rich hydrothermal precipitates which were sampled together with hydrothermal sulfides chimney fragments in an extinct vent field in the central indian ocean there are two kinds of silica rich rocks a jasper which is impregnated and replaced to various degrees mainly by sphalerite and to a lesser extent by barite pyrite and traces of chalcopyrite and an opalite which is an almost pure silica phase without any sulfide or sulfate impregnations but which is sometimes covered by manganese crusts no internal concentric zoning indicating typical chimney structures can be recognized in the jasper and or opalite samples the textures rather suggest a sedimentary silica and or iron deposition from diffuse low temperature 60 c vent fluids partly with still visible indications of former bacterial mats and synsedimentary deformation structures the sphalerite and barite impregnations within the jasper however are considered to have precipitated from white smoker type fluids since they were deposited under intermediate temperatures between 155 and 265 c according to fluid inclusion studies the sulfur isotopic composition 34 s of our sulfide samples has mean values of 6 1 for sphalerite and 5 7 for pyrite indicating a mixture of predominantly basaltic sulfur with subordinate amounts of reduced seawater sulfur the oxygen isotope signals of some pure jasper concentrate samples indicate that the mean formation temperature calculated from these values lies at 63 2 c the relationship between the massive pyrite and chalcopyrite ores from the extinct chimney structures and the silica rich precipitates can be explained by different cycles of hydrothermal activity one high temperature above 300 c cycle dominated by pyrite and chalcopyrite formation and one later epithermal below 300 c cycle which resulted in sphalerite and silica dominated precipitates furthermore zonation and zone refining processes are part of the evolution of the mineralized field

the formation of gold rich seafloor sulfide deposits evidence from the beebe hydrothermal vent field cayman trough the beebe vent field bvf in the cayman trough has built an auriferous massive sulfide deposit on the ultra slow spreading mid cayman spreading centre the genesis of auriferous sulfide deposits at mid ocean ridges is not fully understood although there is a growing recognition that slow and ultra slow spreading centres are conducive to gold mineralization analysis of hydrothermal precipitates from the bvf indicates that the highest gold contents are present within beehive diffusers which have developed a highly porous pyrrhotite framework the beehive structure allows vent fluids to effuse slowly while allowing ingress of seawater to cool the fluid the prevalence of pyrrhotite in the beehive samples lack of sulfates association between pyrrhotite and gold grains and results of thermodynamic modelling suggests gold precipitation occurred under highly reduced conditions even during mixing with seawater in contrast high temperature chimneys with a single orifice maintain high temperatures to the primary vent orifice and much of the gold is lost to seawater despite this both chimney types are relatively gold enriched which points to a further underlying cause for high gold at the bvf such as interaction of hydrothermal fluids with ultramafic lithologies in the basement the final gold composition of the deposit is partially controlled by loss of gold during mass wasting of the material with gold depletion most prevalent in blocks formed at beehive type chimneys the bvf demonstrates that the overall gold content of a massive sulfide deposit is the sum of basement precipitation and surface processes

distribution of gold in altered basalts of dsdp hole 504b deep sea drilling project dsdp hole 504b is the only hole drilled in the dsdp program that intersected both pillow and dike basaltic units and greenschist facies alteration zones pillowed basaltic units constitute the upper portion of the basaltic pile lower in the section a pillow dike unit is transitional to a sheeted dike unit that constitutes the lowest unit of the hole hydrothermal alteration of the basaltic units consists of from top to bottom a low temperature oxidized alteration zone a low temperature reduced alteration zone a transition stockwork zone and a greenschist facies alteration zone samples of the altered basaltic units were analyzed for gold content and 18o the initial primary gold content of basalts of the core is believed to have been relatively uniform and between 0 5 and 1 0 ppb average results for the various alteration zones are 0 44 0 07 for the low temperature oxidized zone 0 40 0 08 for the low temperature reduced zone 0 66 0 21 for the transition stockwo

effects of temperature sulfur and oxygen fugacity on the composition of sphalerite from submarine hydrothermal vents experimental studies have shown that temperature pressure sulfur fugacity fs2 and oxygen fugacity fo2 influence the fe content of sphalerite we present compositional in situ data on sphalerite from submarine volcanic hosted massive sulfide vhms ores of hydrothermal vents from different plate tectonic settings and with variable host rock compositions sphalerite from sediment hosted vents has systematically higher s contents and fe zn ratios than those of the sediment starved vents reflecting an influence of fs2 and fo2 on fe partitioning between fluid and sphalerite the fe zn ratios of sphalerite from sediment starved vent systems apparently increase systematically with the fluid temperatures of the corresponding vents we conclude that the composition of sphalerite can be used to 1 distinguish between sediment hosted and sediment starved hydrothermal processes and 2 estimate minimum fluid temperatures of sphalerite precipitation from inactive sediment starved hydrothermal vent sites and fossil vhms deposits

coupling of surge and waves for an ivan like hurricane impacting the tampa bay florida region 1 the interactions between waves and storm surge are investigated using an unstructured grid coupled wave surge model forced by a hypothetical ivan like hurricane impacting the tampa bay florida region the waves derived from the unstructured version of the third generation wave model simulating waves nearshore the surge derives from the unstructured finite volume coastal ocean model to which wave induced forces based on radiation stress theory are added to the traditional forces by winds and atmospheric pressure dependent upon complex bathymetry and geometry the wave induced forces result in an additional 0 3 0 5 m of surge relative to an uncoupled surge only simulation and the increase in coastal sea level by the storm surge adds some 1 0 1 5 m to the significant wave heights nearshore such strong interactions through coupling suggest that waves should not be omitted in hurricane storm surge simulations especially because the forces by waves on coastal structures are perhaps the most damaging of the hurricane related forces

mineral deposits of canada a synthesis of major deposit types district metallogeny the evolution of geological provinces and exploration methods wayne d goodfellow editor 1 068 pp geological association of canada mineral deposits division special publication no 5 2007 hardcover isbn 13 978 1 897095 24 9 price members cdn 60 00 non members cdn 80 00 following in the footsteps of other landmark reviews of major ore producing countries such as australia hughes 1990 solomon and groves 1994 and south africa anhaeusser and maske 1986 this substantial 1 000 pages monograph is a great achievement that should be in every geologic research library in the world in many ways it sets a new standard most notably in that all figures and photographs are in color and that the entire volume is available in electronic form both as an included dvd and mostly on the gac website it is common in such compendia to have a spectacular cover photo or frontispiece to catch the reader s attention and this book does not disappoint the frontispiece photo is of a 61 8 kg sample from the dome mine timmins ontario and is stated to contain 20 wt percent gold at today s prices the gold alone would be worth 1 5 million dollars

resolving the relative timing of au enrichment in volcanogenic massive sulfide deposits using scanning electron microscopy mineral liberation analyzer empirical evidence from the ming deposit newfoundland canada the metamorphosed cambro ordovician ming volcanogenic massive sulfide deposit in northern newfoundland canada is locally overlain by a unit consisting of mafic to intermediate medium to coarse grained volcaniclastic breccia with up to 10 vol sulfide clasts analysis via mineral liberation analyzer of two sulfide clasts completed using scanning electron microscope observations allowed the identification of a number of microscopic and submicroscopic electrum grains these electrum grains occur in three types of textural settings 1 free electrum grains with tellurides within gangue minerals 2 inclusions of electrum with tellurides in pyrrhotite grains and 3 free electrum grains with base metals and tellurides interstitial between base metals and along cataclastic fractures in pyrite these three textural settings are similar to those in the underlying massive sulfide orebodies that represent very likely sources to the sulfide clasts the polylithic nature and angularity of the volcaniclastic fragments in the breccia suggest a postmineralization gravity controlled debris flow proximal to its source the mineral assemblage and textures of electrum in the sulfide clasts implies evidence in support of syngenetic and predeformation au introduction in the volcanogenic massive sulfide deposit and argues against an orogenic overprint as the cause for au enrichment

sulfur isotopic profile through the oceanic crust sulfur mobility and seawater crustal sulfur exchange during hydrothermal alteration measurements of the abundance of anhydrite and pyrite veins and the distribution of alteration types in oceanic basement enable estimates of global mass and isotopic fluxes of sulfur during hydrothermal alteration of oceanic crust fluxes of 2 5 10 12 g yr s 34 s 2 7 from the volcanic section to seawater and 2 1 10 12 g yr of seawater s 21 into the crust result in an insignificant change in the s content of altered ocean crust these are clearly second order fluxes compared to the riverine input of s to the oceans and the output of sedimentary pyrite most of the anhydrite that forms in the high temperature axial convection cell must later be dissolved at lower temperatures during off axis circulation the mean 34 s of altered oceanic basement is 0 9 only slightly changed from the primary value of 0 1 unless s is preferentially mobilized from 34 s rich sulfide deposits or mineralized zones subduction of altered basaltic crust is unlikely to be the source of high 34 s values of arc volcanic rocks 4 but could contribute to isotopic heterogeneities of s in the mantle

petrography of the dike gabbro transition at iodp site 1256 equatorial pacific the evolution of the granoblastic dikes 1 the ocean drilling program odp integrated ocean drilling program iodp three leg campaign at site 1256 leg 206 expeditions 309 and 312 provides the first continuous in situ sampling of fast spread ocean crust from the extrusive lavas through the sheeted dikes and down into the uppermost gabbros cocos plate east pacific rise eastern equatorial pacific the lowest 60 m of the dikes above the gabbros were transformed to granoblastic dikes through a metamorphic overprint characterized by two pyroxene domains formed under granulite facies conditions equilibrium temperatures estimated by the two pyroxene thermometer range between 930 c and 1050 c implying that conditions within the granoblastic zone were appropriate for hydrous anatexis with the potential to generate partial melts of trondhjemitic composition the downhole evolution of the granoblastic overprint is expressed by systematic changes in texture phase composition and calculated equilibrium temperature consistent with thermal metamorphism by a deeper heat source thermal modeling implies a long lasting heat source located beneath the granoblastic dikes providing thermal energy over several thousands of years the most likely such source is a steady state high level axial magma chamber amc located at the base of the sheeted dike section we interpret the interval of granoblastic dikes as part of a dynamic conductive boundary overlying the amc

gold in sea floor polymetallic sulfide deposits bulk chemical analyses of 48 samples of hydrothermal precipitates from seven polymstallic sulfide deposits at sea floor spreading centers in the eastern pacific reveal distinct patterns of gold enrichment high gold contents are found in samples from two sulfide deposits the axial seamount 45057 n 130002 w and the southern explorer ridge 49045 6 n 130016 2 w a large 160 kg sample composed of silica barite and sphalerite from the top of the axial seamount deposit gives analyses up to 6 700 ppb au averaging 4 900 ppb au similar material from the southern explorer ridge gives analyses up to 1 500 ppb au averaging 660 ppb au detailed mineralogical studies together with bulk chemical analyses of a wide range of samples from these two sites reveal strong elemental associations and paragenetic controls on gold deposition gold at concentrations of about 200 ppb is associated with high cu 1 wt and mo up to 470 ppm at concentrations 800 ppb with high zn 10 wt ba 3 wt and sio 20 wt and at concentrations 1 200 ppb with high pb 0 1 wt ag 100 ppm as 300 ppm and sb 50 100 ppm samples with the highest gold values from both locations contain late sinterlike low temperature sulfosalts of pb as sb ag and s in a matrix of amorphous silica these sulfosalts are the probable repositories of the gold published analyses of au poor 300oc cu fe rich sulfides and subsequently remobilized by late sustained low temperature 250oc fluids and concentrated in sio ba zn rich precipitates near the surface suitable fluid chemistry is required to mobilize the gold and a favorable precipitation mechanism is needed to concentrate it these observations could explain the occurrence of high gold concentrations in selected ore types of some ancient massive sulfide deposits on land

structural and geophysical expression of the solea graben troodos ophiolite cyprus field studies show that extensional structures in the north central part of the troodos ophiolite including steep normal faults grabens dikes and low angle detachment faults are related to e w present coordinates spreading the solea graben directly north of the mafic ultramafic rock outcrops around mount olympus consists of a 10 to 15 km wide western portion that is underlain by a low angle detachment fault between the sheeted dike complex and the plutonic section structural and paleomagnetic evidence indicates that the sheeted dikes above this detachment have been rotated 40 or more about subhorizontal axes the eastern portion of the graben contains sheeted dike blocks with varying axes of rotation and significantly different style of intrusive activity most structural features in the graben formed simultaneously with or shortly after cessation of spreading at the graben axis based on cross cutting ophiolitic dikes and hydrothermal mineralization timing of the uplift of the central part of the troodos ophiolite is uncertain but is probably related to the tectonic thinning of the upper crust by low angle normal faulting the solea graben spreading center provides a model for the structure of modern mid ocean ridges that are spreading amagmatically

channelling of hydrothermal fluids during the accretion and evolution of the upper oceanic crust sr isotope evidence from odp hole 1256d abstract odp hole 1256d in the eastern equatorial pacific is the first penetration of a complete section of fast spread ocean crust down to the dike gabbro transition and only the second borehole to sample in situ sheeted dikes after dsdp hole 504b here a high spatial resolution record of whole rock and mineral strontium isotopic compositions from site 1256 is combined with core observations and downhole wireline geophysical measurements to determine the extent of basalt hydrothermal fluid reaction and to identify fluid pathways at different levels in the upper ocean crust the volcanic sequence at site 1256 is dominated by sheet and massive lava flows but the sr isotope profile shows only limited exchange with seawater however the upper margins of two anomalously thick 25 m massive flow sequences are strongly hydrothermally altered with elevated sr isotope ratios and appear to be conduits of lateral low temperature off axis fluid flow elsewhere in the lavas high 87 sr 86 sr are restricted to breccia horizons mineralised hyaloclastic breccias in the lava dike transition are strongly altered to mg saponite silica and pyrite indicating alteration by mixed seawater and cooled hydrothermal fluids in the sheeted dike complex 87 sr 86 sr ratios are pervasively shifted towards hydrothermal fluid values 0 705 dike chilled margins display secondary mineral assemblages formed during both axial recharge and discharge and have higher 87 sr 86 sr than dike cores indicating preferential fluid flow along dike margins localised increases in 87 sr 86 sr in the dike gabbro transition indicates the channelling of fluids along the sub horizontal intrusive boundaries of the 25 to 50 m thick gabbroic intrusions with only minor increases in 87 sr 86 sr within the cores of the gabbro bodies when compared to the pillow lava dominated section from hole 504b the sr isotope measurements from site 1256 suggest that the extent of hydrothermal circulation in the upper ocean crust may be strongly dependent on the eruption style sheet and massive flow dominated lava sequences typical of fast spreading ridges may experience relatively restricted circulation but there may be much more widespread circulation through pillow lava dominated sections in addition the hole 1256d sheeted dikes display a much greater extent of sr isotopic exchange compared to dikes from hole 504b because seawater derived hydrothermal fluids must transit the dikes during their evolution to black smoker type fluids the different sr isotope profiles for holes 504b and 1256d suggest there are significant variations in mid ocean ridge hydrothermal systems at fast and intermediate spreading ridges which may impact geochemical cycles of elements mobilised by fluid rock exchange at different temperatures

the seismology of greece abstract a review and a bibliography are given of the seismological literature for the area of greece in the period from 1950 up to the present time the aim is to incorporate all aspects of seismology starting with instrumental installations passing on to earthquake catalogues statistics and effects and ending up with structural properties and seismotectonics the purpose is to provide a service to every geophysicist who has an interest in this tectonically complex area and particularly to the numerous researchers engaged in geophysical expeditions to greece

uranium lead isotopic ages of plagiogranites from the troodos ophiolite cyprus and their tectonic significance zircon populations from two plagiogranites in the plutonic section of the troodos ophiolite yield u pb dates between 90 3 0 7 and 92 4 0 7 ma zircons from one of the two samples yield u pb dates of 90 3 0 7 and 92 1 0 7 ma this difference is greater than our analytical error and the zircons are therefore considered to be slightly discordant two fractions from another sample are internally and externally concordant and have an average date of 91 6 1 4 ma this date is adopted as the age of plagiogranite crystallization the plutonic section of the troodos ophiolite is complex in that several generations of intrusion can be identified the plagiogranites occur at the top of the intrusive section and represent fractionated residua of magma chambers related to the lower pillow lavas they are possibly slightly older than small ultramafic layered complexes that represent the final intrusive episode within the troodos ophiolite there is good agreement between our results and the ages of radiolaria which occur in umbers intercalated with the upper pillow lavas of troodos blome and irwin 1985 this shows that the 75 to 85 ma k ar dates on the lavas and sheeted dikes desmet et al 1978 delaloye and desmet 1979 delaloye et al 1980 staudigel et al 1986 represent age resetting unrelated to ophiolite formation the troodos u pb zircon ages are slightly lower than u pb zircon ages from the samail ophiolite in oman which vary between 93 5 and 97 9 ma and average 95 ma tilton et al 1981 the small difference in age between the troodos and the samail ophiolites and the geochemical similarities of basalts from both complexes to island arc volcanic rocks imply that a 3000 km axis of rift related island arcs formed between 91 and 98 ma emplacement of the ophiolites followed during the early maastrichtian

geochemistry of hydrothermal fluids from axial seamount hydrothermal emissions study vent field juan de fuca ridge subseafloor boiling and subsequent fluid rock interaction hydrothermal fluids collected from the ashes vent field in 1986 1987 and 1988 exhibit a very wide range of chemical composition over a small area 60 m in diameter compositions range from a 300 c gas enriched 285 mmol kg co2 low chlorinity 33 of seawater fluid to a 328 c relatively gas depleted 50 mmol kg co2 high chlorinity 116 of seawater fluid the entire range of measured compositions at ashes is best explained by a single hydrothermal fluid undergoing phase separation while rising through the ocean crust followed by partial segregation of the vapor and brine phases other mechanisms proposed to produce chlorinity variations in hydrothermal fluids precipitation dissolution of a chloride bearing mineral or crustal hydration cannot produce the covariation of chlorinity and gas content observed at ashes there is good agreement of the measured fluid compositions with compositions generated by a simple model of phase separation in which gases are partitioned according to henry s law and all salt remains in the liquid phase significant enrichments in silica lithium and boron in the low chlorinity fluids over levels predicted by the model are attributed to fluid rock interaction in the upflow zone depletions in iron and calcium suggest that these elements have been removed by iron sulfide and anhydrite precipitation at some time in the history of the low chlorinity fluids the distribution of low and high chlorinity venting is consistent with mechanisms of phase segregation based on differential buoyancy or relative permeability the relatively shallow depth of the seafloor 1540 m and the observed chemistry of ashes fluids are consistent with phase separation in the sub critical or near critical region

metal depleted root zones of the troodos ore forming hydrothermal systems cyprus the cupriferous pyrite deposits of cyprus were precipitated from hydrothermal solutions derived by interaction of contemporaneous seawater with hot mafic rock at the ancient troodos spreading centre here we identify the zones in which this interaction took place the zones occur in the lower part of the sheeted dyke complex and within them 30 50 of the rock is made up of epidosite an epidote quartz rock replacing the dykes as sheets and pipes the epidosites contain abundant fluid inclusions which give trapping temperatures of 350 400 c or even higher and contain water normally near seawater in salinity zones of epidosite are elongate parallel to the strike of the sheeted dykes and are up to 1 km wide the rocks throughout these zones are strongly depleted in cu and zn and the metals removed are sufficient to supply the ore deposits in fact several large ore deposits lie along strike from zones of epidosite all of these features support the identification of the epidosites as the hydrothermal reaction zones the location of the epidosite zones immediately above the gabbros of the plutonic complex supports the hypothesis that the heat to drive the ore forming systems came from the underlying magma as is also likely for modern black smoker springs

hydrothermal mobilisation of au and other metals in supra subduction oceanic crust insights from the troodos ophiolite the troodos ophiolite is an ideal location to investigate the relationships between the mobilisation of metals by hydrothermal fluids from the lower oceanic crust and the formation of volcanogenic massive sulphide vms deposits the ophiolite hosts the classic cyprus type cu rich vms deposits as well as abundant zones of epidosite alteration in the lower sheeted dyke section that are significantly depleted in base metals including cu and zn and are considered to be the source of the metals enriched in the overlying deposits previous research indicates that the troodos vms deposits are irregularly enriched in au and related elements as sb and se but the behaviour of these elements during the hydrothermal alteration of the troodos ophiolite hitherto has been poorly investigated low detection limit whole rock analyses of fresh glass samples reveal that the troodos primitive crust has a similar metal content and distribution to modern day arc related environments such as the manus basin compared to mid oceanic ridge basalt morb the troodos primitive crust is enriched in as sb and pb most likely due to addition from a subducting slab during crustal formation during early stages of magmatic differentiation 9 3 5 wt mgo au as sb se cu zn and pb behave as incompatible elements due to the sulphide undersaturated nature of the melt the onset of magnetite crystallisation however at 3 5 wt mgo leads to sulphide segregation and depletion of strongly chalcophile elements au cu and se during continued differentiation 3 5 wt mgo whereas poorly chalcophile elements as sb zn and pb remain incompatible these differences in metal behaviour can account for the cu rich zn pb poor of the cyprus type vms deposits as the source area rocks show high cu fertility compared to zn and pb mobilisation of metals during hydrothermal alteration of the troodos ophiolite is more extensive than observed in hydrothermally altered morb mass balance calculations show that the epidosite zones are significantly depleted in au 88 16 as 89 23 sb 60 12 se 91 20 cu 84 18 zn 63 9 and pb 60 8 background altered diabase from outside epidosite zones shows similar metal depletions which suggests that the source areas of vms are not restricted to epidosite zones but are extended to the lower sheeted dyke section the masses of metals mobilised from a source area of 10 9 km3 composed of a 5 km3 epidosite zone and 5 9 km3 of background altered diabase in the solea graben are 47 t au 21 kt as 1200 t sb 3100 t se 2 4 mt cu 1 8 mt zn and 27 kt pb comparison of metal quantities mobilised from lower sheeted dike section in the solea graben with those hosted in vms deposits shows trapping efficiencies ranging from 4 to 37 indicating that most of the metals is lost by other processes

an experiment in earthquake prediction and the 7 may 1986 andreanof islands earthquake abstract the occurrence of the 7 may 1986 andreanof islands earthquake provides the opportunity to evaluate the earthquake forecast and specific prediction that had been formulated and promulgated starting more than 2 yr before the prediction experiment was based on the observation of seismic quiescence in the part of the aleutian subduction zone monitored by the central aleutians adak seismic network the magnitude estimate m s 7 to 7 5 was based on the size of the quiescent zone and the seismic history of the adak region since 1900 the time of occurrence was predicted as a test of the discovery by habermann of a quiescence lasting about 3 yr prior to the 2 may 1971 adak canyon event and the hypothesis that a characteristic precursor time is a valid concept the place was originally forecast as near adak island then specified with epicenter at the eastern margin of adak canyon rupturing to the west under the canyon the 7 may 1986 earthquake had magnitude m s 7 7 m w 8 0 with epicenter 140 km east of the predicted place rupturing east of adak canyon and stopping in the area predicted as the nucleation point the time of this event was 6 months later than predicted thus the specifically predicted event has not happened the largest part of the rupture did go through the segment that had been most active before the onset of quiescence and which experienced the sharpest and most persistent quiescence a cause and effect relation between preparation for this earthquake and the quiescence is still to be firmly established but the distribution of the pattern of quiescence relative to the epicentral location and the site of the greatest moment release suggest a physical connection between earthquake and seismicity patterns the predictions of location and time were acknowledged throughout as highly speculative no firm basis exists for quantitative estimation of the uncertainties to be assigned to the elements of an intermediate term prediction this experiment lends support to the validity of quiescence as a precursor at least for some earthquakes and demonstrates the need for local network data to provide the high resolution of seismicity required for prediction efforts based on seismicity patterns

influence of the galapagos hotspot on the east pacific rise during miocene superfast spreading at the present the geochemical influence of the galapagos hotspot offshore south america can be seen only along the galapagos spreading center north of the hotspot it is possible however that galapagos plume material also reached the east pacific rise in the past detecting such influence would be of particular importance for the interpretation of geochemical data from oceanic crust at ocean drilling program odp site 1256 which formed 15 m y ago at the east pacific rise during a miocene period of superfast spreading and is considered to be a reference site for oceanic crust produced at fast spreading ridges here we present geochemical data from miocene basaltic crust 23 7 ma drilled at several deep sea drilling project dsdp odp and integrated ocean drilling program iodp sites that formed along the east pacific rise between 3 s and 7 n lavas formed between ca 22 5 and ca 11 ma show enriched galapagos plume like pb and nd isotope ratios with a peak in enrichment between 18 and 12 ma compared to lavas created shortly before or after this time interval despite their enriched isotope composition these samples generally show depletion in more incompatible relative to less incompatible trace elements derivation from an enriched galapagos plume source that had experienced recent melt extraction before it melted further beneath the east pacific rise can explain the combined incompatible trace element depletion and isotopic enrichment of the 22 5 11 ma lavas the influence of plume material correlates with the interval of superfast spreading along the equatorial east pacific rise suggesting a causal relationship enhanced ridge plume interaction ridge suction due to superfast spreading could have facilitated the flow of galapagos plume material to the ridge on the other hand the arrival of galapagos type signatures took place immediately after formation of the galapagos spreading center which could have provided a pathway for hot plume material to spread into the main ridge network

gold mineralization associated with low temperature off axis fluid activity in the troodos ophiolite cyprus silicification of umbers in the troodos ophiolite complex in cyprus provides evidence for low temperature hydrothermal activity occurring late in the process of ocean crust formation after the crust had moved away from the oceanic spreading centre umbers which are mn fe rich sediments precipitate some distance away from oceanic spreading axes the movement of the fluids partially silicifying the umbers must post date umber formation and therefore also occurs off axis these fluids may form part of low temperature hydrothermal circulation similar to those identified by off axis heat anomalies in the modern oceans in cyprus the silicified umbers often are located away from volcanogenic massive sulphide vms deposits and are aligned along sea floor faults they are characterized by quartz veins as well as pervasive silicification recent analyses have revealed unexpectedly anomalous 1 5 ppm concentrations of au in these silicified umbers gold mineralization is known to occur in ophiolite complexes as part of the metal concentrations in vms deposits these deposits are thought to be formed by ancient hydrothermal circulation similar to that associated with black smokers observed at modern mid ocean ridges the research presented in this paper provides evidence for a second phase of au mineralization in cyprus caused by low temperature silicifying fluids resulting from oceanic hydrothermal activity which occurred away from the spreading centre the mineralizing fluids which silicified the umbers may have been more widespread impregnating other lithologies and may have overprinted the first phase of au mineralization in some vms deposits after they had become inactive and had been moved away from the spreading centre the mineralizing fluids passing through these vms may have used the same structural pathways as the original base metal rich hydrothermal solutions which formed the vms

a coupling module for tides surges and waves a generic module in which tides surges and waves are incorporated has been developed tested and prepared for dissemination within the framework of the mast iii promise pre operational modelling in the seas of europe project two existing pre operational numerical models a wave model and a hydrodynamic model were incorporated into a coupling framework that allows an efficient exchange of information between them minimal adaptation of the models was needed the module has then been implemented and applied to the north sea then a series of experiments were performed to investigate the sensitivity of waves and surges to coupling these experiments show that the sensitivity of waves to coupling increases from deep to shallow water the sensitivity of surges is more uniformly distributed the sensitivity of surges to coupling along the spanish coast was also studied the model results were less sensitive than in the north sea this is explained by the relative importance of the two forcing components the atmospheric pressure and the wind stress in both areas c 2000 elsevier science b v all rights reserved

sulphide mineral evolution and metal mobility during alteration of the oceanic crust insights from odp hole 1256d fluxes of metals during the hydrothermal alteration of the oceanic crust have far reaching effects including buffering of the compositions of the ocean and lithosphere supporting microbial life an

role of continental shelf on non linear interaction of storm surges tides and wind waves an idealized study representing the west coast of india abstract the study reports role and dependence of continental shelf geometry on the non linear interaction of storm surges tides and wind waves as a case study the shelf geometry representing the west coast of india is considered and numerical simulations are executed using the standard representation of a tropical cyclone the idealized experiments assume the west coast of india as a straight coastline with varying continental shelf width ranging from 35 km in the south to 330 km in the north for the experiments adcirc model in standalone mode and coupled adcirc swan are used by considering 13 idealized cyclone tracks covering the study domain it is noticed that an amplification of peak storm surge of 12 cm for every 10 km increase in the shelf width during different phases of the tide the surge wave interaction modifies the water level elevation and its occurrence as the tidal range increases towards north the interaction of tides on surges and wind waves is observed maximum at low tide and minimum at flood tide over the wide shelf regions in general the non linear interaction is found to be 15 20 for any cyclone track or tidal phase the wave setup caused by wind waves is marginally varies with change of amplitude and phase of the tide however its profile is significantly modified particularly over the wider shelf widths

oceanic detachment faults focus very large volumes of black smoker fluids it is generally assumed that the seawater derived fluids that feed black smoker vent fields on the seafloor are discharged vertically from depths of 1 3 km we present new oxygen and strontium isotope data that show that fluids at black smoker temperatures of 300 400 c were focused along a low angle detachment fault at 15 45 n near the mid atlantic ridge isotopic alteration is the most extreme ever reported from oceanic rocks altered at similar temperatures indicating intensely focused fluid flow both in recharge and discharge parts of the hydrothermal system rare earth element mobility in the fault rocks demonstrates isotopic alteration by evolved hydrothermal fluids not conductively heated seawater the fault zone protolith was predominantly ultramafic but also included mafic rocks with metasomatic alteration to talc tremolite chlorite schists resulting mainly from chemical exchange between these lithologies during fluid flow fluids in equilibrium with this assemblage would be similar to ultramafic hosted black smoker fluids we present a new model in which hydrothermal circulation around detachment faults evolves from basalt hosted tag type to footwall ultramafic hosted rainbow type to low temperature ultramafic hosted lost city type key features of our model are the intrusion of gabbro bodies immediately below the detachment to provide a heat source for circulation and focusing of fluid flow into the detachment fault to allow venting away from the neovolcanic axis