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

the development of volcanic hosted massive sulfide and barite gold orebodies on wetar island indonesia wetar island is composed of neogene volcanic rocks and minor oceanic sediments and forms part of the inner banda arc the island preserves precious metal rich volcanogenic massive sulfide and barite deposits which produced approximately 17 metric tonnes of gold the polymetallic massive sulfides are dominantly pyrite locally arsenian with minor chalcopyrite which are cut by late fractures infilled with covellite chalcocite tennantite tetrahedrite enargite bornite and fe poor sphalerite barite orebodies are developed on the flanks and locally overly the massive sulfides these orebodies comprise friable barite and minor sulfides cemented by a series of complex arsenates oxides hydroxides and sulfate with gold present as 10 m free grains linear and pipe like structures comprising barite and iron oxides beneath the barite deposits are interpreted as feeder structures to the barite mineralization hydrothermal alteration around the orebodies is zoned and dominated by illite kaolinite smectite assemblages however local alunite and pyrophyllite are indicative of late acidic oxidizing hydrothermal fluids proximal to mineralization altered footwall volcanic rocks give an illite k ar age of 4 7 0 16 ma and a 40ar 39ar age of 4 93 0 21 ma fluid inclusion data suggest that hydrothermal fluid temperatures were around 250 270 c showed no evidence of boiling with a mean salinity of 3 2 wt equivalent nacl the 34s composition of sulfides ranges between 3 3 and 11 7 and suggests a significant contribution of sulfur from the underlying volcanic edifice the 34s barite data vary between 22 4 and 31 0 close to miocene seawater sulfate whole rock 87sr 86sr analyses of unaltered volcanic rocks 0 70748 0 71106 reflect contributions from subducted continental material in their source region the 87sr 86sr barite data 0 7076 0 7088 indicate a dominant miocene seawater component to the hydrothermal system the mineral deposits formed on the flanks of a volcanic edifice at depths of 2 km spectacular sulfide mounds showing talus textures are localized onto faults which provided the main pathways for high temperature hydrothermal fluids and the development of associated stockworks the orebodies were covered and preserved by post mineralization chert gypsum globigerina bearing limestone lahars subaqueous debris flows and pyroclastics rocks

relative sea level rise and climate change over the last 1500 years we constructed a detailed relative sea level rise curve for the last 1500 years using a novel approach i e charting the rate of relative sea level rise using microfaunal and geochemical data from a coastal salt marsh sequence clinton ct usa the composition of benthic foraminiferal assemblages and the iron abundance in peats were used to describe shifts in marsh environment through time quantitatively the resulting sea level rise curve with age control from 14c dating and the onset of anthropogenic metal pollution shows strong increases in the rate of relative sea level rise during modern global warming since the late nineteenth century but not during the little climate optimum ad 1000 1300 there was virtually no rise in sea level during the little ice age ad 1400 1700 most of the relative sea level rise over the last 1200 years in clinton appears to have occurred during two warm episodes that jointly lasted less than 600 years changes from slow to fast rates of relative sea level rise apparently occurred over periods of only a few decades we suggest that changes in ocean circulation could contribute to the sudden increases in the rate of relative sea level rise along the northeastern usa seaboard relative sea level rise in that area is currently faster than the worldwide average which may result partially from an ocean surface effect caused by hydrodynamics our data show no unequivocal correlation between warm periods on a decaal to centennial time scale and accelerated sea level rise one period of acclerated sea level rise may have occurred between about ad 1200 and 1450 which was the transition for the little climate optimum to the little ice age i e a period of cooling at least in northwestern europe local changes in tidal range might also have contributed to this apparent increase in the rate of relative sea level however the second period of accelerated sea level rise occurred during the period of modern global warming that started at the end of the last century

sedimentological characteristics heavy metal distribution and magnetic properties in subtidal sediments ria de pontevedra nw spain the rias of nw spain are coastal ecosystems of high biological productivity and great economic importance they are intensively exploited by man for fish and shellfish there are a number of important centres of population and industrial activity along their margins which serve as sources of contamination in this context it is desirable to achieve the best possible understanding of the physico chemical processes that control spatial and temporal variations in the geochemical mineralogical and sedimentological characteristics of near surface sediments in the ria de pontevedra and in particular the distribution and mobility of heavy metal contaminants thus adequate environmental planning can be achieved for this site and understanding gained for comparable contexts core samples were examined from the inner middle and outer parts of the ria grain size distributions reflect the presence of two main populations one dominated by silt and clay derived mainly from terrestrial sources and the other by fine sand to coarse silt which is derived mainly from continental shelf and ria mouth sources mineralogical analysis shows an abundance of terrestrial intensive weathering products near the ria head a dominance of shelf derived sediment towards the mouth and the presence of several diagenetic minerals whose nature varies with location within the ria in the inner ria the near surface sediments are slightly enriched in pb cu and zn from anthropogenic sources these sediments are fine grained and have a high organic content hence they have a higher potential to sorb contaminants than the coarser grained less organic rich sediments of the mid and outer ria the estimated sedimentation rates for the fine grained organic rich sediments from the inner part of the ria are about 1 mm year 1 the dominant authigenic minerals in the inner ria are iron sulphides whereas in the mid and outer ria iron silicates and oxyhydroxides are more important these differences in authigenic iron mineralogy are clearly reflected by the magnetic properties of the sediments

s sr and pb isotopic systematics of hydrothermal chimney precipitates from the eastern manus basin western pacific evaluation of magmatic contribution to hydrothermal system 1 sulfur strontium and lead isotopic analyses were performed on chimneys from the hydrothermal vent fields the pacmanus and susu knolls in the eastern manus back arc basin lead isotope composition varies in a narrow range 206pb 204pb 18 75 18 78 207pb 204pb 15 51 15 54 and 208pb 204pb 38 31 38 40 strontium isotopic ratios 87sr 86sr of sulfate minerals vary from 0 7051 to 0 7077 falling between those of seawater 0 7090 and the hydrothermal fluid end member 0 7050 the 34s values of the chimneys are 8 0 to 3 9 for the susu knolls sulfide 1 0 to 4 3 for the pacmanus sulfides and 7 4 to 20 6 for sulfate the susu knolls sulfides have the lowest values so far reported for volcanic hosted massive sulfides from modern seafloor the low 34s values of sulfates and sulfides cannot be explained by a simple seawater circulation model without an additional source of light sulfur this is also supported by the presence of sulfate in hydrothermal end member fluid indicated by sulfur and strontium isotopic ratios in chimney sulfates biogenic sulfur and or oxidation of h2s after boiling are excluded from the possible sources of light sulfur because of the lack of sediment cover and nonequilibrium in isotopic fractionation by boiling at seafloor disproportionation of magmatic so2 introduced into hydrothermal system through preeruptive degassing is the most plausible mechanism for the observed low 34s values the lighter 34s values and more radiogenic lead isotope compositions of the susu knolls samples indicate that magmatic degassing was more vigorous at the susu knolls than pacmanus

fluid mixing and thermal regimes beneath the pacmanus hydrothermal field papua new guinea helium and oxygen isotope data abstract fluid mixing processes and thermal regimes within the snowcap and roman ruins vent sites of the pacmanus hydrothermal system papua new guinea were investigated using 3he 4he ratios from fluid inclusions within pyrite and anhydrite and the 18o signature of anhydrite depressed 3he 4he ratios of 0 2 6 91ra appear to be caused by significant atmospheric diffusive exchange whilst he ne diffusive fractionation precludes correction using 20ne 40ar 36ar ratios of 295 310 are elevated above seawater indicating the majority of argon is seawater derived but with a magmatic component 18o anhydrite ratios are 6 5 to 11 for snowcap and 6 4 to 11 9 for roman ruins using oxygen isotope fractionation factors for the anhydrite water system the temperatures calculated assuming isotopic equilibrium at depth are up to 100 c cooler than fluid inclusion trapping temperatures it is likely that anhydrite is precipitated rapidly preventing 18o equilibration by comparing new 18o values for anhydrite with corresponding published 87sr 86sr ratios seawater is inferred to penetrate deep into the snowcap system with little conductive heating a simple fluid mixing model has been constructed whereby the differing venting styles can be explained by a plumbing system at depth which favors delivery of end member hydrothermal fluid to the high temperature sites

the role of prokaryotes in supergene alteration of submarine hydrothermal sulfides we combine mineralogical stable isotope and organic biomarker data to understand the role of prokaryote activity in supergene reactions within submarine hydrothermal sulfidic sediments data are presented for two adjacent cores from the periphery of the inactive alvin hydrothermal mound the limit of oxygenated seawater penetration into the sulfidic sediments is expressed as a sharp peak in solid phase cu atacamite and secondary cu sulfides associated with supergene alteration of the sulfide pile total prokaryote numbers are low throughout the upper few metres of sediment relative to published data for deep sea sites however there is a statistically significant enrichment of prokaryote numbers at the redox front that coincides with abundant fe oxide filaments and a unique distribution of microbial biomarkers the dominance of quaternary branched alkanes in the oxidized transition zone immediately above the redox front and their absence below suggests a significant role of the source organisms in iron or sulfide oxidation under the more circumneutral conditions associated with the redox transition zone the morphology of the fe oxide filaments preserved within late stage silica and gypsum mineralization is consistent with a biogenic origin of the filaments gypsum sulfur isotopes are in equilibrium with fluids that are derived from quantitative sulfide oxidation and gypsum nucleation is inferred to be biologically induced these new data suggest that supergene alteration of sulfidic sediments generates sharp redox and ph gradients that stimulate prokaryotic activity in particular iron and sulfide oxidisers which in turn govern the distribution of secondary mineral phases and the abundance of redox sensitive trace metals

diagenesis in anoxic sediments from the california continental borderland and its influence on iron sulfur and magnetite behavior solid phase and pore water profiles of compounds containing iron and sulfur have been determined by wet chemical magnetic and x ray diffraction techniques in three california continental borderland basins the observed profiles have been fit by simple reaction diffusion models in order to determine reaction rates and constrain budgets for iron and sulfur more than 95 of the solid phase reduced sulfur is pyrite and down core profiles are well fit by a model in which net sulfate reduction rates decrease exponentially with depth net sulfate reduction rates determined from models fit to solid phase reduced sulfur measurements and pore water sulfate profiles yield results that are consistent depth integrated sulfate reduction rates for modern sediments in san pedro santa catalina and san nicolas basins are 11 4 6 3 and 6 3 8 8 mol cm 2yr 1 respectively measurements of solid phase iron species indicate that surficial sediments are enriched in easily reducible ferric oxyhydroxides the enrichment is maintained by a combination of oxidation of fe2 diffusing upward from underlying anoxic sediments as well as input of fresh sediment enriched in ferric oxyhydroxides the three primary sources for iron converted to pyrite and the sequence in which they are utilized are ferric oxyhydroxides magnetite and other crystalline oxides and exchangeable iron in phyllosilicates the majority 50 80 of the iron converted to pyrite is from the silicates and budgetary calculations indicate the amount of iron released from san pedro basin silicates agrees within 35 with the amount of magnesium removed from pore water to solid phases fe2 is enriched in near surface pore waters because rates of dissolved iron production by oxyhydroxide reduction exceed rates of sulfate reduction and pyrite formation at depth pore waters are sulfidic because rates of sulfate reduction exceed rates of iron release from silicates sulfide produced at depth diffuses upward until it reaches sediments with available iron causing a step like increase in solid phase sulfur concentration over 90 of the magnetite present in surficial sediments is dissolved at depth due to reaction with h2s a model is developed to predict the depth at which magnetite dissolution should occur based on sulfate reduction rates and the flux of ferric oxyhydroxides the results of this model predict the onset of dissolution at depths of 5 40 cm in different basins and agree well with the observed depths of magnetite dissolution

acidic and sulfate rich hydrothermal fluids from the manus back arc basin papua new guinea hot 88 120 c and acidic ph 2 1 hydrothermal fluids rich in sulfate were discovered venting in the desmos caldera depth 1926 m eastern manus back arc basin bismarck sea surrounded by papua new guinea the abundant sulfate 32 8 m m higher than the seawater value of 28 m m with elemental sulfur deposition around the vents and remarkably low d h 2 o and 34 s h 2 s values 8 1 and 5 6 respectively are suggestive of the incorporation of a magmatic fluid and the disproportionation of the exsolved so 2 from a magma body the desmos fluid may be similar in origin to the acidic sulfate chloride hot springs associated with subaerial volcanic activity in contrast to the typical hydrothermal end member mg concentration of 0 the desmos fluids are rich in mg 46 52 m m probably because of mg dissolution by acid attack upon magnesium silicate minerals

sulfur and strontium isotopic study of epithermal mineralization a case study from the se afar rift djibouti epithermal mineralization was recently described in synrift volcanic rocks from the se afar rift in djibouti to infer fluid sources in this system coupled sulfur and strontium isotopic analyses were performed on mineralized samples from hydrothermal veins and stockwork zones mineralization includes gypsum and chalcedony and or quartz carbonate containing gold and sulfides sulfur isotopic compositions of sulfides and sulfates were determined using multicollector inductively coupled plasma mass spectrometer mc icpms laser ablation mc icpms and continuous flow elemental analyzer isotope ratio mass spectrometry while strontium isotopes were determined by thermal ionisation mass spectrometry tims methods sulfur isotopic composition of sulfides mainly pyrite varies from 9 2 to 6 6 these values are classically reported for hydrothermal sulfides resulting from the mixing of variable s sources such as seawater sulfate and magmatic source in addition individual pyrite grains within the same sample show both positive and negative 34s values suggesting multi phase mineralization processes coupled sulfur and strontium isotopic compositions of seven sulfate samples hosted in i gypsum mound ii evaporites iii stockwork veins in sediments or in volcanic rocks were also investigated to characterize the sources of sr and s the 34s values of the sulfate ranged from 0 8 to 14 3 while the 87sr 86sr ranged from 0 70389 to 0 70639 consistent with variable mixing ratios of sr and s derived from volcanic sources and seawater derived sulfate this study shows that although precious metal deposition is related to low sulfidation epithermal environment both acidic fluid of magmatic and saline origins contributed to the hydrothermal system in the se afar rift

comment on the paper by sanchez espana et al source and evolution of ore forming hydrothermal fluids in the northern iberian pyrite belt massive sulphide deposits sw spain evidence from fluid inclusions and stable isotopes mineralium deposita 38 519 537 the recent paper by sanchez espana et al 2003 presents new fluid inclusion fi and stable isotope data on several massive sulphide deposits of the northern iberian pyrite belt ipb using these results together with previously published data on some large deposits of the southern ipb they concluded that the ore forming fluids in the ipb were a mixture of highly evolved seawater exchanged with the underlying sedimentary and magmatic rocks and a significant deep fluid component either of metamorphic or magmatic origin the latter is the favoured conclusion however this conclusion essentially depends on the fundamental assumption that neither fis nor stable isotope records were disturbed during the late variscantectono thermal event s yet according to the current knowledge on metamorphosed deposits e g marshall and spry 2000 marshall et al 2000 fis in such deposits generally do not preserve data pertinent to the pre metamorphic ore stage and the stable isotope data are usually difficult to interpret here we would like 1 to discuss the possibility of finding pristine fis in the ipb massive sulphide deposits that would have survived the late variscan low grade tectono thermal event 2 to present evidence for a significant gold depositing post kinematic hydrothermal stage in the ipb deposits with the concomitant development of pervasive lateto post kinematic fluid percolation through the ore bodies and 3 to discuss the real significance of the o h stable isotope data our discussion is mainly based on our study of the tharsisstockwork marignac et al 2003 with additional information from the la zarza and rio tintostockworks diagana2001 and from the nevescorvo deposit moura et al 1997a b we conclude that all fi data and many stable isotope data are in fact a record of the late variscan post kinematic hydrothermal overprint and that only few data may be of significance for the early syn sedimentary ore forming event in the ipb massive sulphide deposits

rare earth element abundances in hydrothermal fluids from the manus basin papua new guinea indicators of sub seafloor hydrothermal processes in back arc basins abstract rare earth element ree concentrations are reported for a large suite of seafloor vent fluids from four hydrothermal systems in the manus back arc basin vienna woods pacmanus desmos and susu knolls vent areas sampled vent fluids show a wide range of absolute ree concentrations and chondrite normalized reen distribution patterns lan smn 0 6 11 lan ybn 0 6 71 eu n eu n 1 55 reen distribution patterns in different vent fluids range from light ree enriched to mid and heavy ree enriched to flat and have a range of positive eu anomalies this heterogeneity contrasts markedly with relatively uniform reen distribution patterns of mid ocean ridge hydrothermal fluids in manus basin fluids aqueous ree compositions do not inherit directly or show a clear relationship with the ree compositions of primary crustal rocks with which hydrothermal fluids interact these results suggest that the rees are less sensitive indicators of primary crustal rock composition despite crustal rocks being the dominant source of rees in submarine hydrothermal fluids in contrast differences in aqueous ree compositions are consistently correlated with differences in fluid ph and ligand chloride fluoride and sulfate concentrations our results suggest that the rees can be used as an indicator of the type of magmatic acid volatile i e presence of hf so2 degassing in submarine hydrothermal systems additional fluid data suggest that near seafloor mixing between high temperature hydrothermal fluid and locally entrained seawater at many vent areas in the manus basin causes anhydrite precipitation anhydrite effectively incorporates ree and likely affects measured fluid ree concentrations but does not affect their relative distributions

extensional transform zones and oblique spreading centers extensional transform zones etzs are plate boundary segments of order 100 km long that strike at angles between 15 and 45 to the extension direction they are characterized by neovolcanic tectonic zones comprising overlapping en echelon volcanic systems and or faults that trend 30 75 to the extension direction sometimes accompanied by a riedel shear below these surficial en echelon structures the deformation is aseismic and ductile and the plate boundary is probably continuous etzs occur in fast and slow spreading and rifting environments and may persist in a stable configuration for several million years etzs link oblique spreading segments to transform faults in the manus and probably the lau backarc basins the reykjanes peninsula and tjornes fracture zone in iceland and the mak arrasou in afar are etzs that link subaerial to submarine spreading or rifting segments the brawley and cerro prieto seismic zones appear to be etzs in the imperial and mexicali valleys that link the san andreas imperial and cerro prieto transform faults experimental and analytical models of transtensional deformation in brittle ductile systems match many of the observed characteristics of etzs and oblique spreading centers including variably sigmoidal to straight en echelon faults that are not parallel to the extension direction the contrasting fault patterns reflect the rheology of the models and lithosphere they are more sigmoidal when the strain in the lower ductile layer is more focused causing the axial faults to curve as they propagate toward parallelism with the less ductile rift margins the angle o between the faults and the extension direction decreases with the angle between the strike of the zone and the extension direction etzs occur in the range 15 45 whereas oblique spreading centers have 45 90 and transform relay zones have 0 15 oblique fast spreading segments exhibit ridge parallel faults and volcanic systems o presumably reflecting locally rotated stress fields whereas at oblique slow spreading centers o is closer to orthogonal o 90

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

tracing the chemical evolution of fluids during hydrothermal recharge constraints from anhydrite recovered in odp hole 504b a unique record of the chemical evolution of seawater during hydrothermal recharge into oceanic crust is preserved by anhydrite from the volcanic sequences and sheeted dike complex in odp hole 504b chemical and isotopic analyses 87sr 86sr 18o 34s of anhydrite constrain the changing composition of fluids due to reaction with basalt there is a general trend of decreasing 87sr 86sr of anhydrite corresponding to the minor incorporation of basaltic strontium with depth in the volcanic rocks 87sr 86sr ratios decrease rapidly with depth in the dikes to values identical to host basalt 0 7029 sr ca ratios 0 1 mmol mol suggest that recharge fluids have very low sr concentrations and fluids evolve by first precipitating sr bearing phases before extensive exchange of sr with the host basalt there is a background trend of decreasing sulfate 18o with depth from 12 13 in the lower volcanics to 7 in the lower sheeted dikes recording an increase in recharge fluid temperature from 150 to 250 c and confirming the presence of sulfate in hydrothermal fluids at elevated temperatures from the amount of anhydrite recovered from hole 504b and the amount of seawater sulfur that has been reduced to sulfide a minimum seawater recharge flux can be calculated this value is 4 25 times lower than estimates of high temperature fluid fluxes based on either thermal constraints or global chemical budgets and suggests that there is significant deficit of seawater derived sulfur in the oceanic crust only a minor proportion of the seawater that percolates into the crust near the axis is heated to high temperatures and exits as black smoker type fluids a significant proportion of the axial heat loss must be advected at 200 250 c by sulfate bearing hydrothermal solutions that egress diffusely from the crust these fluids penetrate into the dikes and exchange both heat and chemical tracers without the extensive clogging of porosity by anhydrite precipitation which would halt hydrothermal circulation for any reasonable fluid flux the heating of the major proportion of hydrothermal fluids to only moderate temperatures 250 c reconciles estimates of hydrothermal fluxes derived from thermal models and global geochemical budgets the flux of hydrothermal sulfate would be of a magnitude similar to the riverine input and oxygen isotopic exchange at 200 250 c between dissolved sulfate and recharge fluids during hydrothermal circulation provides a mechanism to continuously buffer seawater sulfate oxygen to the light isotopic composition observed

geochemistry of hydrothermal fluids from the pacmanus northeast pual and vienna woods hydrothermal fields manus basin papua new guinea abstract processes controlling the composition of seafloor hydrothermal fluids in silicic back arc or near arc crustal settings remain poorly constrained despite growing evidence for extensive magmatic hydrothermal activity in such environments we conducted a survey of vent fluid compositions from two contrasting sites in the manus back arc basin papua new guinea to examine the influence of variations in host rock composition and magmatic inputs both a function of arc proximity on hydrothermal fluid chemistry fluid samples were collected from felsic hosted hydrothermal vent fields located on pual ridge pacmanus and northeast ne pual near the active new britain arc and a basalt hosted vent field vienna woods located farther from the arc on the manus spreading center vienna woods fluids were characterized by relatively uniform endmember temperatures 273 285 c and major element compositions low dissolved co 2 concentrations 4 4 mmol kg and high measured ph 4 2 4 9 at 25 c temperatures and compositions were highly variable at pacmanus ne pual and a large newly discovered vent area fenway was observed to be vigorously venting boiling 358 c fluid all pacmanus fluids are characterized by negative d h 2 o values in contrast to positive values at vienna woods suggesting substantial magmatic water input to circulating fluids at pual ridge low measured ph 25 c values 2 6 2 7 high endmember co 2 up to 274 mmol kg and negative 34 s h 2 s values down to 2 7 in some vent fluids are also consistent with degassing of acid volatile species from evolved magma dissolved co 2 at pacmanus is more enriched in 13 c 4 1 to 2 3 than vienna woods 5 2 to 5 7 suggesting a contribution of slab derived carbon the mobile elements e g li k rb cs and b are also greatly enriched in pacmanus fluids reflecting increased abundances in the crust there relative to the manus spreading center variations in alkali and dissolved gas abundances with cl at pacmanus and ne pual suggest that phase separation has affected fluid chemistry despite the low temperatures of many vents in further contrast to vienna woods substantial modification of pacmanus ne pual fluids has taken place as a result of seawater ingress into the upflow zone consistently high measured mg concentrations as well as trends of increasingly non conservative so 4 behavior decreasing endmember ca cl and sr cl ratios with increased mg indicate extensive subsurface anhydrite deposition is occurring as a result of subsurface seawater entrainment decreased ph and endmember fe mn ratios in higher mg fluids indicate that the associated mixing cooling gives rise to sulfide deposition and secondary acidity production several low temperature 80 c fluids at pacmanus ne pual also show evidence for anhydrite dissolution and water rock interaction fixation of b subsequent to seawater entrainment hence the evolution of fluid compositions at pual ridge reflects the cumulative effects of water rock interaction admixing and reaction of fluids exsolved from silicic magma phase separation segregation and seawater ingress into upflow zones

insights to magmatic hydrothermal processes in the manus back arc basin as recorded by anhydrite microchemical analyses of rare earth element ree concentrations and sr and s isotope ratios of anhydrite are used to identify sub seafloor processes governing the formation of hydrothermal fluids in the convergent margin manus basin papua new guinea samples comprise drill core vein anhydrite and seafloor massive anhydrite from the pacmanus roman ruins snowcap and fenway and susu knolls north su active hydrothermal fields chondrite normalized ree patterns in anhydrite show remarkable heterogeneity on the scale of individual grains different from the near uniform ree n patterns measured in anhydrite from mid ocean ridge deposits the ree n patterns in anhydrite are correlated with ree distributions measured in hydrothermal fluids venting at the seafloor at these vent fields and are interpreted to record episodes of hydrothermal fluid formation affected by magmatic volatile degassing 87 sr 86 sr ratios vary dramatically within individual grains between that of contemporary seawater and that of endmember hydrothermal fluid anhydrite was precipitated from a highly variable mixture of the two the intra grain heterogeneity implies that anhydrite preserves periods of contrasting hydrothermal versus seawater dominant near seafloor fluid circulation most sulfate 34 s values of anhydrite cluster around that of contemporary seawater consistent with anhydrite precipitating from hydrothermal fluid mixed with locally entrained seawater sulfate 34 s isotope ratios in some anhydrites are however lighter than that of seawater which are interpreted as recording a source of sulfate derived from magmatic so 2 degassed from underlying felsic magmas in the manus basin the range of elemental and isotopic signatures observed in anhydrite records a range of sub seafloor processes including high temperature hydrothermal fluid circulation varying extents of magmatic volatile degassing seawater entrainment and fluid mixing the chemical and isotopic heterogeneity recorded in anhydrite at the inter and intra grain scale captures the dynamics of hydrothermal fluid formation and sub seafloor circulation that is highly variable both spatially and temporally on timescales over which hydrothermal deposits are formed microchemical analysis of hydrothermal minerals can provide information about the temporal history of submarine hydrothermal systems that are variable over time and cannot necessarily be inferred only from the study of vent fluids

contrasting evolution of hydrothermal fluids in the pacmanus system manus basin the sr and s isotope evidence ocean drilling program odp leg 193 investigated two sites of hydrothermal activity along the crest of the pual ridge in the eastern manus basin a site of low temperature diffuse venting snowcap site 1188 and a high temperature black smoker site roman ruins site 1189 were drilled to depths of 386 and 206 m below seafloor mbsf respectively although the two sites are 1000 m apart the 87sr 86sr and 34s signatures of anhydrite recovered at both sites are very different the data suggest a complex interplay among hydrothermal fluid magmatic fluid and seawater during alteration and mineralization of the pacmanus papua new guinea australia canada manus system these new results significantly expand the subsurface data on seafloor hydrothermal systems and may begin to explain the earliest processes of multistage mineralization and alteration history that typify ancient massive sulfide systems

a simple three dimensional model of diffusion with precipitation applied to localised pyrite formation in framboids fossils and detrital iron minerals a three dimensional diffusion with precipitation model is constructed to estimate radial variations in the amounts of pyrite which precipitate where a spherical mass of organic matter producing h2s by sulphate reduction is enveloped in a dissolved iron bearing porewater the model indicates that higher rates of sulphate reduction more readily metabolisable organic matter and larger organic masses require increasingly high dissolved iron concentrations in order to confine pyrite or iron sulphide precipitation to the decay site the maximum size sphere of exceedingly metabolisable organic matter equivalent to fresh planktonic material which can be pyritised is about 50 m radius where decay occurs in porewaters with typical dissolved iron levels this radius is close to the maximum radius of framboidal pyrite the formation of which could involve model type processes fossil carcases although mainly composed of less readily metabolisable organic matter may be orders of magnitude larger and the model demonstrates that their pyritisation requires unusually high porewater dissolved iron concentrations these inferred chemical conditions are consistent with sedimentological observations of pyritisation in beecher s trilobite bed new york state at greater depths within the sediment pyritisation is controlled by the kinetics of iron mineral reactivity towards h2s sediments vary widely in their exposure times to h2s which can range at least from 50 to 106 years at low exposure times only iron oxides are pyritised whereas at high exposure times even the most refractory iron silicates can become pyritised

fluid inclusion evidence for subsurface phase separation and variable fluid mixing regimes beneath the deep sea pacmanus hydrothermal field manus basin back arc rift papua new guinea 1 altered volcanic rocks were cored from over 350 m below the seafloor at the papua new guinea australia canada manus basin hydrothermal field pacmanus deep sea hydrothermal field in the eastern manus back arc basin fluid inclusions in anhydrite veins reveal phase separation and fluid mixing beneath the seafloor the anhydrite precipitated from high temperature fluids 150 385 c at roman ruins a site of active high temperature venting 220 276 c measured by submersible the fluid inclusion thermal depth profile is uniform and high temperature 242 368 c at snowcap a site of warm water effusion 6 65 c the fluid inclusions indicate high temperatures at depth 270 385 c but both low and high temperatures in the shallower section this indicates a flow regime dominated by vertical advection and shallow entrainment and mixing with cool seawater inclusions at snowcap exhibit extreme salinity variations due to phase separation at temperatures above 350 c fluids contain na cl fe zn mg and ba and a minor gas component such as co2 or ch4 most inclusions at roman ruins exhibit salinities that fall within the range of those observed at modern active vent sites along the mid ocean ridge system fluid inclusion temperatures support a hypothesis developed previously from sr isotopic analysis that the subseafloor at snowcap is characterized by mixing between deep sourced hot hydrothermal fluids and cold seawater like fluid both heating of seawater and cooling of upwelling hydrothermal fluids can be recognized by combining isotopic and fluid inclusion data in contrast to snowcap the regime at roman ruins is less varied with uniformly high temperature upwelling fluids that have hydrothermally dominated sr isotopic ratios

s and sr isotopic compositions in barite silica chimney from the franklin seamount woodlark basin papua new guinea constraints on genesis and temporal variability of hydrothermal fluid isotopic ratios of strontium and sulfur in six layers across a horizontal section of a hydrothermal barite silica chimney from franklin seamount of western woodlark basin have been investigated sr isotopic ratios in barite samples 87sr 86sr 0 70478 0 70493 are less radiogenic than seawater 87sr 86sr 0 70917 indicating that substantial leaching of sub seafloor magma was involved in the genesis of hydrothermal fluid the so2 of magma likely contributed a considerable amount of lighter s isotope in fluid and responsible for the formation of barite which is isotopically lighter 34s 19 4 20 5 than modern seawater 34s 21 the systematic changes in isotopic compositions across the chimney wall suggest temporal changes in the mode of mineral formation during the growth of the chimney enrichment of heavy s and sr isotopes 34s 20 58 87sr 86sr 0 70493 in the outermost periphery of the chimney indicates that at the initial stage of chimney development there was a significant contribution of seawater sulfate during barite mineralization thereafter thickening of chimney wall occurred due to precipitation of fluid carrying more magmatic components relative to seawater this led to a gradual enrichment of lighter isotopes 34s 20 42 19 48 87sr 86sr 0 70491 0 704787 toward the inner portion of the chimney wall in contrast the innermost layer surrounding the fluid conduit is characterized by heavier and more radiogenic isotopes 34s 20 3 87sr 86sr 0 7049 this suggests there was increasing influence of percolating seawater on the mineral paragenesis at the waning phase of the chimney development

heating and freezing experiments on aqueous fluid inclusions in anhydrite recognition and effects of stretching and the low temperature formation of gypsum aqueous fluid inclusions in anhydrite that are frozen during microthermometry commonly develop new daughter crystals heating these inclusions induces the new daughter crystals to decompose repeated cycles of crystal growth and decomposition may result in morphological changes of the fluid inclusions this phenomenon of new mineral growth presumed to represent the low temperature hydrate gypsum has been recognized for over 20 years nevertheless its occurrence and its significance to the determination of inclusion salinities are not widely appreciated similarly the potential of inclusions in anhydrite to stretch when overheated is commonly assumed yet tests demonstrating the phenomenon have not been reported changes in the ice melting temperature of aqueous inclusions in anhydrite before and after gypsum formation were documented showing that hydration of the host anhydrite may significantly lower the ice melting temperature and increase the salinity of the residual inclusion fluid heating inclusions to induce gypsum to decompose results in the release of bound water restoring the inclusions to their original salinity the homogenization temperatures of inclusions that have undergone these phenomena are generally unchanged indicating that the inclusions specific volumes are unchanged however heating aqueous inclusions in anhydrite more than ten degrees or so above their homogenization temperature commonly results in stretching therefore those who study aqueous inclusions in anhydrite must avoid the determination of ice melting temperatures if new gypsum daughter crystals are present and must determine homogenization temperatures sequentially with rising temperature to avoid overheating and stretching

the range and unity of planetary circulations altering the rotation rate obliquity and diurnal period of an earth like model atmosphere produces a wide range of circulation forms some of which resemble those observed on venus mars jupiter saturn and perhaps on uranus and neptune these unified solutions suggest that jupiter and saturn resemble a larger faster spinning earth and possess a stress bearing or momentum exchanging sublayer that easterly winds prevail in uranus summer hemisphere and that venus resembles a slowly rotating earth if diurnal heating variations are included

geology fluid inclusion and sulphur isotope characteristics of the el cobre vhms deposit southern cuba the el cobre deposit is located in eastern cuba within the volcanosedimentary sequence of the sierra maestra paleogene arc the deposit is hosted by tholeiitic basalts andesites and tuffs and comprises thick stratiform barite and anhydrite bodies three stratabound disseminated up to massive sulphide bodies produced by silicification and sulphidation of limestones or sulphates an anhydrite stockwork and a siliceous stockwork grading downwards to quartz veins sulphides are mainly pyrite chalcopyrite and sphalerite gold occurs in the stratabound ores fluid inclusions measured in sphalerite quartz anhydrite and calcite show salinities between 2 3 and 5 7 wt nacl eq and homogenisation temperatures between 177 and 300 c sulphides from the stratabound mineralisation display 34s values of 0 to 6 0 whilst those from the feeder zone lie between 1 4 and 7 3 sulphides show an intra grain sulphur isotope zonation of about 2 usually 34s values increase towards the rims sulphate sulphur has 34s in the range of 17 to 21 except two samples with values of 5 9 and 7 7 sulphur isotope data indicate that the thermochemical reduction of sulphate from a hydrothermal fluid of seawater origin was the main source of sulphide sulphur and that most of the sulphates precipitated by heating of seawater the structure of the deposit mineralogy fluid inclusion and isotope data suggest that the deposit formed from seawater derived fluids with probably minor supply of magmatic fluids

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

enargite luzonite hydrothermal vents in manus back arc basin submarine analogues of high sulfidation epithermal mineralization abstract active and inactive hydrothermal chimneys composed almost entirely of enargite and luzonite rare minerals in seafloor hydrothermal deposits were found at the summits of two submarine volcanoes north su and kaia natai in the manus back arc basin detailed mineralogical and geochemical studies revealed that most probably these deposits precipitated at t 200 330 c and high fs2 the negative 34s values 8 58 to 3 70 of the enargite luzonite are best explained by disproportionation reactions of magmatic so2 and suggest that the high fs2 is likely provided by direct magmatic input of so2 into the hydrothermal system fractionation of cu stable isotopes during the precipitation of enargite luzonite 65cu ranges from 0 20 to 0 35 is inferred to be associated with either rayleigh type fractionation or redox processes cu oxidation to cu2 and the mass balance of dissolved cu and cu2 species in the hydrothermal fluid the trace element composition of enargite and luzonite indicates a temporal fluctuation of the chemistry of the ore forming fluid with an increase of fe ga tl au hg pb and ag and decrease of sb sn te ge and v concentrations with time and points out that this type of deposits is the richest in au average 11 9 ppm and te average 169 ppm among all other types of seafloor metal deposits in addition to the widespread inorganic precipitation of enargite and luzonite in this setting there is evidence that this mineralization may be biogenically mediated on the external surfaces of the active vents fungi like filaments mineralized by luzonite imply that the fungi dikarya subkingdom may be implicated in a mechanism of bio sequestration of as s and cu and provide the initial substrate for luzonite precipitation the studied enargite luzonite deposits have characteristics similar to those of subaerial high sulfidation epithermal mineralization back arc basin setting acid sulfate and boiling ore forming fluids altered advanced argillic stage dacitic host rocks major enargite luzonite and minor pyrite barite and s0 34s au mineralization at depth

mineralogical geochemical and isotopic characteristics of hydrothermal alteration processes in the active submarine felsic hosted pacmanus field manus basin papua new guinea during odp leg 193 4 sites were drilled in the active pacmanus hydrothermal field on the crest of the felsic pual ridge to examine the vertical and lateral variations in mineralization and alteration patterns we present new data on clay mineral assemblages clay and whole rock chemistry and clay mineral strontium and oxygen isotopic compositions of altered rocks from a site of diffuse low temperature venting snowcap site 1188 and a site of high temperature venting roman ruins site 1189 in order to investigate the water rock reactions and associated elemental exchanges the volcanic succession at snowcap has been hydrothermally altered producing five alteration zones 1 chlorite illite cristobalite plagioclase alteration apparently overprinted locally by pyrophyllite bleaching at temperatures of 260 310degreesc 2 chlorite mixed layer clay alteration at temperatures of 230degreesc 3 chlorite and illite alteration 4 illite and chlorite illite mixed layer alteration at temperatures of 250 260degreesc and 5 illite chlorite alteration at 290 300degreesc felsic rocks recovered from two holes 1189a and 1189b at roman ruins although very close together show differing alteration features hole 1189a is characterized by a uniform chlorite illite alteration formed at similar to250degreesc overprinted by quartz veining at 350degreesc in contrast four alteration zones occur in hole 1189b 1 illite chlorite alteration formed at similar to300degreesc 2 chlorite illite alteration at 235degreesc 3 chlorite illite and mixed layer clay alteration and 4 chlorite illite alteration at 220degreesc mass balance calculations indicate that the chloritization illitization and bleaching silica pyrophyllite assemblages alteration stages are accompanied by different chemical changes relative to a calculated pristine precursor lava the element cr appears to have a general enrichment in the altered samples from pacmanus the clay concentrate data show that cr and cu are predominantly present in the pyrophyllites illite shows a significant enrichment for cs and cu relative to the bulk altered samples considerations of mineral stability allow us to place some constraints on fluid chemistry hydrothermal fluid ph for the chloritization and illitization was neutral to slightly acidic and relatively acidic for the pyrophyllite alteration in general the fluids especially from roman ruins and at intermediate depths below snowcap show only a small proportion of seawater mixing 10 fluids in shallow and deep parts of the snowcap holes in contrast show stronger seawater influence copyright c 2004 elsevier ltd

rock magnetic evidence for the dissolution and authigenic growth of magnetic minerals within anoxic marine sediments of the california continental borderland the rock magnetic properties of marine sediments from the california continental borderland san pedro santa catalina and san nicolas basins have been studied in order to quantitatively assess the effects of sediment diagenesis on magnetic minerals previous studies have noted that the natural remanent magnetization in these sediments primarily carried by detrital magnetite decays to 10 or less of its surface value soon after deposition this decrease is caused by magnetite dissolution related to sediment diagenesis and is unrelated to paleoclimatic variations or changes in the regional influx of detrital magnetic material detailed rock magnetic measurements show that shifts to softer remanent coercivity and differences in the rate and degree of magnetic intensity loss with depth can be related to the dissolution process the shift to softer remanent coercivity is related to a coarsening of the magnetic mineral grain sizes with depth due to preferential dissolution of the finest grained magnetic material the intensity decreases which are linearly proportional to magnetite concentration decreases indicate that dissolution occurs with rate constants ranging from 0 3 to 1 6 kyr 1 the rate constants sulfide concentrations and magnetite grain size estimates from the borderland are consistant with previous studies of magnetite dissolution our results demonstrate the importance of both sulfide and magnetite surface area in the dissolution process anomalous peaks in viscous remanence within the sediments suggest the authigenic growth of greigite and its subsequent transformation to pyrite

mineralogy geochemistry and sr pb and in situ s isotopic compositions of hydrothermal precipitates from the tangyin hydrothermal field southern okinawa trough evaluation of the contribution of magmatic fluids and sediments to hydrothermal systems abstract the okinawa trough ot is a back arc basin where rifting is in its initial stages and where hydrothermal fields htfs have developed above terrigenous sediments and volcaniclastics layers of variable thickness the source of ore forming materials within the hydrothermal systems of the ot is complex and may include seawater magmatic rock magmatic fluid and sediments the contribution of magmatic fluids and sediments to the hydrothermal systems of the ot is still uncertain at least 10 modern seafloor htfs have been reported from the ot including the jade hakurei iheya north knoll clam tangyin yonaguni knoll iv hatoma and irabu here we report results of mineralogical geochemical and whole rock sr pb and in situ s isotopic analyses of hydrothermal precipitates from the tangyin htf in the southern ot this field was discovered during the hobab3 cruise in 2014 and contains four types of hydrothermal precipitates fe zn and zn pb rich massive sulfides silica rich precipitates and native sulfur rich samples sulfates in zn pb fe zn and silica rich samples have 87sr 86sr ratios of 0 71068 0 71750 which are higher than those of modern seawater and magmatic rocks and indicate that the sr is derived mainly from seawater and sediments the zn pb fe zn and silica rich samples have 206pb 204pb 18 5129 18 5307 207pb 204pb 15 6374 15 6489 and 208pb 204pb 38 8759 38 9113 ratios that are intermediate between sediments and magmatic rocks suggesting the pb is a mixture of sediment and magmatic rock derived pb the in situ s isotopic data indicate that the ore forming fluids associated with all sample types had low 34s values with the fe zn mean 34s 1 27 1 38 sd n 12 and zn pb rich mean 34s 0 93 0 32 n 36 massive sulfides and silica rich precipitates mean 34s 2 85 1 14 n 58 having lower 34s values than those of native sulfur rich samples mean 34s 4 23 0 72 n 5 the zn pb and fe zn rich massive sulfides and silica rich precipitates represent the medium high temperature 120 c early middle stages of mineralization formed under reducing conditions at low sulfur fugacity fs2 based on the occurrence of low fs2 mineral assemblages e g high fe sphalerite isocubanite pyrrhotite the low 34s values of these three types of samples and of the hakurei and clam htfs with low fs2 mineral assemblages and low concentrations of cu bi and au most likely reflect the incorporation of biological sulfur previously formed by msr within the sediments the native sulfur rich samples of the tangyin htf formed at low temperatures

a seeping sea floor in a ria environment ria de vigo nw spain the occurrence of gas accumulations in the ria de vigo nw spain have been characterized by the authors in previous research pockmarks frequently appear on seismic and sonar records covering ca 45 of the sea floor of the study area which indicates that gas expulsion is not an uncommon phenomena in the coastal ria environment here we report the occurrence of gas seepage for the first time along the coast of nw spain side scan sonar echo sounder and high resolution seismic techniques were used for mapping gas expulsion features some expulsion pockmarks sit over elongated features that represent bottom marks created by anthropogenic activity thus these anthropogenic sites may act as preferential venting zones for gas as well as being potential hazards on a muddy sea bed such as that of the ria where gas accumulates just below the surface of the sea floor

bulk geochemistry sulfur isotope characteristics of the yuhuang 1 hydrothermal field on the ultraslow spreading southwest indian ridge abstract the yuhuang 1 hydrothermal field hf was discovered recently on the ultraslow spreading southwest indian ridge segment 29 this field comprises two main sulfide deposition areas including the southwest sulfide area sws and the northeast sulfide area nes all of which are about 500 m in diameter sulfide rich samples collected on the seafloor consist of zinc rich iron rich and silicified samples the zn rich samples contain up to 60 sphalerite and 5 chalcopyrite while iron rich samples primarily contain pyrite and marcasite and silicified sulfide rich samples primarily consist of amorphous silicon 70 pyrite 15 20 and minor sphalerite sulfide rich samples generally show mound features with similar mineral assemblages except that the nes contains pyrrhotite indicating precipitation under relatively reduced conditions bulk geochemistry of the sws and nes massive sulfide samples display similar au co ni and si contents and ni co ratios similar to mafic related hfs while the sn content and the cd zn ratio are comparable to ultramafic related hfs which probably indicates a multi stage origin sulfides rich samples from the sws have 34s values ranging from 1 37 to 6 02 with a median value of 0 83 currently the 34s value of 1 37 is the lowest sulfur isotope composition observed in hfs on ultraslow spreading ridges bacteria derived sulfur which is calculated to be 10 25 of the total sulfur component is likely the cause of the negative sulfur isotope composition conversely the 34s values of the seafloor sulfides rich samples in the nes ranges from 3 75 to 8 73 with a median value of 4 74 which is distinctly heavier than that of the sws this study suggests that the sws and nes of the yuhuang 1 hf probably formed during different mineralization stages

mineralogy and composition of kuroko deposits from northeastern honshu and their possible modern analogues from the izu ogasawara bonin arc south of japan implications for mode of formation the kuroko deposits of ne honshu are a key type deposit for the study of volcanogenic massive sulfide deposits however these deposits have not been studied in detail since the early 1980 s and knowledge of their mode of formation is now dated in this study we present the analysis of 12 samples of the kuroko deposits 12 samples of submarine hydrothermal minerals from the sunrise deposit and 6 samples from suiyo seamount both of which are located on the izu ogasawara bonin arc for 27 elements for the kuroko deposit cd sb ag pb hg as zn cu are highly enriched au te bi ba mo are moderately enriched in tl are somewhat enriched and fe is not significantly enriched relative to the average continental crust within each of these deposits a similar pattern of element associations is apparent zn pb with as sb cd ag hg tl and au fe cu ba with as sb ag tl mo te and au si ba with ag and au caso4 the enrichment of the chalcophilic elements in these deposits is consistent with hydrothermal leaching of these elements from the host rocks which are dominantly rhyolite dacite in the case of the kuroko deposits rhyolite in the case of the sunrise deposit and dacite rhyolite in the case of the suiyo seamount deposit however this pattern of element enrichment is also similar to that observed in fumarolic gas condensates from andesitic volcanoes this suggests that there may be a significant magmatic contribution to the composition of the hydrothermal fluids responsible for the formation of the kuroko deposits although it is not yet possible to quantify the relative contributions of these two sources of elements the compositional data show that sunrise and suiyo seamount deposits are much closer compositionally to the kuroko deposits from ne honshu than are the submarine hydrothermal deposits from the jade site in the okinawa trough which contain on average significantly higher concentrations of pb zn sb as and ag than each of these deposits in spite of the greater similarity in tectonic setting of the hokuroku basin in which the kuroko deposits formed to the okinawa trough intracontinental rifted back arc basin compared to myojin knoll and suiyo seamount active arc volcanoes it appears that submarine hydrothermal deposits from myojin knoll and suiyo seamount are closer analogues of the kuroko deposit than are those from the okinawa trough the present data are consistent with the magmatic hydrothermal model for the formation of kuroko type deposits as formulated by urabe and marumo urabe t marumo k 1991 a new model for kuroko type deposits of japan episodes 14 246 251

phyllosilicate alteration mineral assemblages in the active subsea floor pacmanus hydrothermal system papua new guinea odp leg 193 pacmanus is an active submarine hydrothermal system in the manus back arc basin papua new guinea located at 1 600 to 1 700 m below sea level on the crest of a dacitic volcano it is inferred to represent a modern analogue of ancient mineralizing sea floor hydrothermal systems that produced volcanogenic polymetallic massive sulfide deposits ocean drilling program odp leg 193 drilled the subsea floor hydrothermal alteration zone of pacmanus in a high temperature discharge area roman ruins and a low temperature discharge area snowcap reaching a maximum depth of 380 m below the sea floor evidence from short wavelength infrared swir spectroscopy x ray diffraction xrd analyses calculated normative mineral abundances and electron microprobe data show that there are substantial variations in the hydrothermal phyllosilicate assemblages within the pacmanus hydrothermal system the altered dacite at roman ruins contains 10 to 25 wt percent normative chlorite smectite and up to 15 wt percent normative illite in contrast altered dacite below snowcap contains up to 50 wt percent combined normative illite paragonite chlorite smectite pyrophyllite swir data show that pyrophyllite is particularly abundant between 50 and 120 and between 220 and 270 m below sea floor indicating localized interaction of dacite with acidic hydrothermal fluids variations in the na k ratio of dioctahedral phyllosilicate determined by electron microprobe and spectral analyses confirm the presence of a paragonitic component at snowcap a model is suggested to explain the differences in the distribution of hydrothermal phyllosilicate assemblages in the two areas in terms of variations in fluid composition and changes to the subsea floor hydrology in a dynamically evolving volcanic hydrothermal environment

textural and mineralogical changes associated with the incipient hydrothermal alteration of glassy dacite at the submarine pacmanus hydrothermal system eastern manus basin variably altered dacite from the pacmanus vent field in the eastern manus back arc basin papua new guinea was studied to determine the textural and mineralogical characteristics of hydrothermal alteration taking place in the immediate subsurface of this modern seafloor hydrothermal system detailed textural investigations show that fluid flow through the glassy dacite has been strongly controlled by the primary volcanic textures quench fractures and networks of interconnected perlitic cracks linking vesicles provided pathways for hydrothermal fluids flowing up to the seafloor hydrothermal alteration along these pathways resulted in the formation of pseudoclastic textures textural evidence suggests that alteration of the glassy dacite has not been sustained the samples have been affected by incipient hydrothermal alteration that is typically not preserved in ancient volcanic rock hosted massive sulfide deposits interaction of the glassy dacite with hydrothermal fluids primarily resulted in the conversion of volcanic glass to dioctahedral smectite only minor amounts of trioctahedral smectite were formed destruction of the volcanic glass and the formation of smectite caused pronounced changes in the chemistry of the dacite samples in particular a decrease in the sio2 whole rock content and the na2o k2o ratio the two alkali elements behaved differently during hydrothermal alteration due to preferential incorporation of k into the interlayer position of the newly formed dioctahedral smectite smectite formation occurred under rock dominated conditions although the addition of mg was required to form trioctahedral smectite from the silicic volcanic glass primary plagioclase was resistant to hydrothermal alteration highlighting the fact that the destruction of volcanic glass and feldspar are not necessarily contemporaneous in massive sulfide forming hydrothermal systems incipient alteration of the glassy dacite close to the seafloor occurred at temperatures below 150 c in an environment that allowed the development of steep temperature gradients comparison of the new data to the findings of deep drilling during odp leg 193 suggests that the smectite rich alteration in the immediate subsurface of the pacmanus hydrothermal vent field represents the low temperature equivalent of illite and chlorite rich alteration associations forming in the upflow zones of the hydrothermal fluids in the deeper portion of the volcanic sequence

chemistry of hot springs along the eastern lau spreading center abstract the eastern lau spreading center elsc is the southernmost part of the back arc spreading axis in the lau basin west of the tonga trench and the active tofua volcanic arc over its 397 km length it exhibits large and systematic changes in spreading rate magmatic tectonic processes and proximity to the volcanic arc in 2005 we collected 81 samples of vent water from six hydrothermal fields along the elsc the chemistry of these waters varies both within and between vent fields in response to changes in substrate composition temperature and pressure ph water rock ratio and input from magmatic gases and subducted sediment hot spring temperatures range from 229 to 363 c at the five northernmost fields with a general decrease to the south that is reversed at the mariner field the southernmost field vai lili emitted water at up to 334 c in 1989 but had a maximum venting temperature of only 121 c in 2005 due to waning activity and admixture of bottom seawater into the subseafloor plumbing system chloride varies both within fields and from one field to another from a low of 528 mmol kg to a high of 656 mmol kg and may be enriched by phase separation and or leaching of cl from the rock concentrations of the soluble elements k rb cs and b likewise increase southward as the volcanic substrate becomes more silica rich especially on the valu fa ridge iodine and 7li increase southward and 11b decreases as b increases apparently in response to increased input from subducted sediment as the arc is approached species that decrease southward as temperature falls are si h2s li na cl fe mn and 87sr 86sr whereas ph alkalinity ca and sr increase oxygen isotopes indicate a higher water rock ratio in the three systems on valu fa ridge consistent with higher porosity in more felsic volcanic rocks vent waters at the mariner vent field on the valu fa ridge are significantly hotter more acid and metal rich less saline and richer in dissolved gases and other volatiles including h2s co2 and f than the other vent fields consistent with input of magmatic gases the large variations in geologic and geophysical parameters produced by back arc spreading along the elsc which exceed those along mid ocean ridge spreading axes produce similar large variations in the composition of vent waters and thus provide new insights into the processes that control the chemistry of submarine hot springs

geochemistry of hot springs at the susu knolls hydrothermal field eastern manus basin advanced argillic alteration and vent fluid acidity abstract susu knolls is an area of ongoing magmatic activity and recent volcanism located in the back arc spreading environment of the manus basin in the bismarck sea papua new guinea in 2006 hydrothermal fluids were collected from three areas of submarine hot spring venting and analyzed for the chemical and isotopic composition of major and trace species fluids were characterized by temperatures that varied from 226 325 c and formed grey to black smoke as they mixed with bottom seawater the compositions of seawater derived vent fluids are regulated by the relative contributions of fluid rock and fluid sediment interaction phase separation and the addition of volatiles from magmatic degassing in addition to phase separation leaching of cl from felsic rocks that compose the lithosphere in back arc environments may produce cl concentrations in excess of seawater values the measured ph25 c of susu knolls smoker fluids varied from 1 5 3 7 a range that includes values substantially more acidic than typically observed in fluids at mid ocean ridge spreading centers late stage addition of magmatic volatiles in the shallow seafloor is directly responsible for the most acidic fluids ph25 c values below 2 in contrast the acidity of vent fluids characterized by ph25 c values between 2 and 3 is not the direct result of the direct addition of magmatically derived acidic species instead the ph of these fluids likely reflects reaction with rocks that were previously altered by highly acidic magmatic fluids to an advanced argillic alteration assemblage containing quartz illite pyrophyllite anhydrite alunite in hydrothermal upflow zones fluids that do not react with advanced argillic alteration assemblages during upflow have measured ph25 c values between 3 and 4