initial chronology of a recently discovered hydrothermal field at 14 45 n mid atlantic ridge two expeditions of the sevmorgeologija association 1991 1994 led to the discovery of two new hydrothermal sites on the mid atlantic ridge mar south of the 15 20 north fracture zone one around 14 45 n and the other around 14 42 n the northern one between 14 45 and 14 45 3 n has been studied in detail about 12 mounds have been mapped and 3 of them have been sampled using a large hydraulic grab sampler the largest one is about 200 m long and 200 m wide when progressively moving up on the slope of an uplifted block of the rift valley floor the sulphide samples have revealed ages ranging from about 10 ka to 60 ka the ages were obtained using the 230th 234u dating method used for chronological studies of diverse hydrothermal fields the general picture of this lateral location of the samples of different ages provides evidence of a shift in the focus of hydrothermal activity with time moreover there were rejuvenation stages of hydrothermal activity including black and white smokers

massive sulfides of mount jourdanne along the super slow spreading southwest indian ridge and their genesis abstract modern massive sulfide deposits are known to occur in diverse tectonic settings and it is generally expected that hydrothermal deposits of similar geological settings shall have more or less similar mineralogical and geochemical signatures however the mount jourdanne sulfide deposits along the super slow spreading southwest indian ridge deviate from this common concept these sulfide precipitates are zn rich up to 35 wt and are characterized by high concentrations of pb 3 5 wt as 1 1 wt ag 0 12 wt au 11 ppm sb 967 ppm and cd 0 2 wt which are unusual for a modern sediment free mid oceanic ridge system therefore we have reinvestigated the sulfide samples collected during the indoyo cruise in 1998 in order to explain their unusual mineralogy and geochemical composition the sulfide samples are polymetallic and are classified as a chimneys b mounds and c hydrothermal breccias the chimneys are small tube like symmetrical bodies 30 40 cm high 10 cm diameter and consist mainly of sphalerite and less chalcopyrite set in a matrix of late amorphous silica the inner wall shows a late stage colloform sphalerite containing co precipitates of galena and or pb as sulfosalts in contrast the mound samples are dominated either by fe sulfides pyrite or by a mixture of pyrite and chalcopyrite with less sphalerite pyrrhotite amorphous silica and barite both the chimney and mound samples are characterized by layering and mineral zonation the hydrothermal breccias are highly altered and mineralogically heterogeneous they consist of silicified basaltic material that are impregnated with sulfides and contain cm sized chimney fragments within a matrix of low temperature minerals such as sphalerite and pyrite the latter fragments mainly consist of chalcopyrite with isocubanite lamellae in addition these breccias contain late stage realgar boulangerite galena pb as sulfosalts and barite that are mostly confined to vugs or fractures at least five mineralogical associations are distinguished that indicate different thermal episodes ranging from black smoker mineralization conditions to cessation of the hydrothermal activity based on the mineralogical associations and established literature in this regard it is inferred that the mineralization at mt jourdanne occurred mainly in three temperature domains above 300 c the chalcopyrite with isocubanite pyrrhotite association formed whereas the sphalerite dominated assemblage with much less chalcopyrite and pyrite formed around and below 300 c the late stage mineralization below 200 c contains colloform sphalerite galena pb as sulfosalts realgar and barite the unusual mineralogy and trace element chemistry for this modern vhms deposit could be explained assuming hydrothermal leaching of some felsic differentiates underneath the basaltic cover and subsequent zone refining processes

the emergence of life from iron monosulphide bubbles at a submarine hydrothermal redox and ph front here we argue that life emerged on earth from a redox and ph front at c 4 2 ga this front occurred where hot c 150 c extremely reduced alkaline bisulphide bearing submarine seepage waters interfaced with the acid warm c 90 c iron bearing hadean ocean the low ph of the ocean was imparted by the ten bars of co 2 considered to dominate the hadean atmosphere hydrosphere disequilibrium between the two solutions was maintained by the spontaneous precipitation of a colloidal fes membrane iron monosulphide bubbles comprising this membrane were inflated by the hydrothermal solution upon sulphide mounds at the seepage sites our hypothesis is that the fes membrane laced with nickel acted as a semipermeable catalytic boundary between the two fluids encouraging synthesis of organic anions by hydrogenation and carboxylation of hydrothermal organic primers the ocean provided carbonate phosphate iron nickel and protons the hydrothermal solution was the source of ammonia acetate hs h 2 and tungsten as well as minor concentrations of organic sulphides and perhaps cyanide and acetaldehyde the mean redox potential eh across the membrane with the energy to drive synthesis would have approximated to 300 millivolts the generation of organic anions would have led to an increase in osmotic pressure within the fes bubbles thus osmotic pressure could take over from hydraulic pressure as the driving force for distension budding and reproduction of the bubbles condensation of the organic molecules to polymers particularly organic sulphides was driven by pyrophosphate hydrolysis regeneration of pyrophosphate from the monophosphate in the membrane was facilitated by protons contributed from the hadean ocean this was the first use by a metabolizing system of protonmotive force driven by natural aph which also would have amounted to c 300 millivolts protonmotive force is the universal energy transduction mechanism of life taken together with the redox potential across the membrane the total electrochemical and chemical energy available for protometabolism amounted to a continuous supply at more than half a volt the role of the iron sulphide membrane in keeping the two solutions separated was appropriated by the newly synthesized organic sulphide polymers this organic take over of the membrane material led to the miniaturization of the metabolizing system information systems to govern replication could have developed penecontemporaneously in this same milieu but iron sulphur and phosphate inorganic components of earliest life continued to be involved in metabolism

growth history of a diffusely venting sulfide structure from the juan de fuca ridge a petrological and geochemical study centimeter scale mineralogical and chemical analyses of a diffusely venting 280 c sulfide structure called roane from the mothra hydrothermal field on the juan de fuca ridge reveal a complex growth history these analyses document four well defined zones which from the exterior to the interior of the structure include a barite silica zone fossil worm tube zone a silica sulfide zone silica zone a sulfide silica zone outer sulfide zone and a sulfide gordaite silica zone inner sulfide zone these features are a product of a myriad of processes that include extensive mineral replacement ingress of seawater fracturing and breakout of hot hydrothermal fluids significant conductive cooling and the sustained broad scale outflow of warm fluids from the walls through a porous and permeable matrix roane lacks an open throughgoing chalcopyrite lined central conduit instead it hosts an anastomosing discontinuous network of tortuous channels within the interior of a sponge like matrix of amorphous silica sulfide sulfate and clay minerals megafaunal communities at the summit and sides of this mature diffusely venting chimney provide a constructional framework for new growth isolation of hydrothermal fluid from seawater during progressive fossilization of megafauna and the early formation of barite silica assemblages promote flow of higher temperature fluids within the interior continued isolation of interior higher temperature fluids through increased mineral precipitation and expansion of the structure leads to a zn sulfide pyrite dominated permeable matrix and a network of tortuous channels that form a central porous conduit this conduit is shielded by a weakly silicified metal sulfide inner wall and a strongly silicified outer wall the most outer portions of the walls are highly porous and sites of significant advection and mixing between hydrothermal fluids and seawater the mineralogy and chemistry of roane are strongly affected by ammonia ammonium buffering of the ph during cooling of the hydrothermal fluids the two major results of the buffering are 1 precipitation of zn sulfide at higher temperatures than are typical for bare rock systems leading to the correlation of cu zn cd and se and 2 increased deposition of amorphous silica and clay minerals

trace element distributions in the chalcopyrite wall of a black smoker chimney insights from laser ablation inductively coupled plasma mass spectrometry la icp ms abstract the thin walls of young black smoker chimneys experience steep physico chemical gradients during active venting of hydrothermal fluid and these gradients control trace element precipitation within those walls here we utilise a combination of high sensitivity icpms and uv laser ablation resolution of better than 30 m to demonstrate the existence of non random v ag in te ba au pb and u distributions within the chalcopyrite wall of an immature black smoker chimney the data are the first of their kind to be produced for black smoker chimney walls distributions of in and te are attributed to preferential incorporation into lattices at elevated temperature enrichments of u and v derived from seawater are the product of redox immobilisation on sulphide surfaces the distributions of au ag pb and ba may be related to interactions at the hydrothermal fluid seawater mixing front however comparison of distribution data with reaction transport models of chimney walls suggest a possible ph control on precipitation these data illustrate the power of the la icp ms method and such spatially resolved data have the potential to constrain models of element precipitation both in chimneys and in associated mounds

hydrothermal processes at mid ocean ridges submarine hydrothermal systems are an integral component of crustal construction along the global system of mid ocean ridges thermally induced circulation of seawater through the permeable parts of the crust and upper mantle has been estimated to account for 34 of the predicted global oceanic heat flux which in turn comprises close to 25 of the total heat flux of the earth stein and stein 1994 and references therein discharge of hydrothermal fluids is manifest along mid ocean ridges as high temperature 200 400 c focused and lower temperature 200 c diffuse fluid flow off axis fluid flow may extend out to the crustal sealing age of 65 10 million years and may be responsible for more than 70 of the hydrothermal heat flux stein and stein 1994

carbon isotopes and light element abundances in carbonaceous chondrites stepped combustions of whole rock samples of orgueil ci murchison cold bokkeveld and murray cm renazzo cr allende and mokoia c3v carbonaceous chondrites were carried out between 200 and 1200 c at each step co2 was collected for carbon isotope measurement and so2 and h2o yields were measured nitrogen was combined for several steps all samples released most of their carbon between 200 and 400 c due to combustion of the organic matter bulk carbon concentration and isotopic composition of each meteorite are therefore closely similar to those of this predominant reservoir between 400 and 700 c carbonates decomposed in all meteorites but the c3vs carbon isotopes in these carbonates matched previously published values in renazzo the carbonates have a 13c close to 42 pdb similar to those of cm meteorites above 700 c all meteorites but the c3vs show one or two occurrences of very13c rich carbon carbon concentration decreases from 350 to 30 ppb c as temperature increases between 700 and 885 c 13c reaches 240 4 in orgueil 73 9 in murchison 130 9 in cold bokkeveld and 125 5 in murray and then decreases between 950 and 1060 c 13c reaches 177 8 in renazzo 335 1 in cold bokkeveld and 384 6 in murchison finally murray yielded 3 ppm of carbon with a 13c of 1164 in the 1125 1210 c combustion step a qualitative inverse correlation among the c2 meteorites between the carbon concentration and 13c above 700 c suggests that these distinct heavy carbon releases could be actually due to a single heavy carbon component

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

fault and stratigraphic controls on volcanogenic massive sulphide deposits in the strelley belt pilbara craton western australia abstract early archaean fe zn cu volcanogenic massive sulphide deposits of the strelley belt pilbara craton occur at the top of a volcanic dominated sequence at the interface of felsic volcanic rocks and siliceous laminites beneath an unconformity overlain by clastic sedimentary rocks the structure of the sulphur springs and kangaroo caves vms deposits is relatively simple with the present morphology reflecting original deposition rather than significant structural modification the rocks have been tilted giving an oblique cross sectional view of discordant high angle deep penetrating faults in the footwall which splay close to the zones of volcanogenic massive sulphide mineralization faults do not extend far into the overlying sedimentary cover indicating their syn volcanic and syn mineralization timing both the sulphur springs and kangaroo caves sulphide deposits are located within elevated grabens in a setting similar to massive sulphide mineralization in modern back are environments mineralization at sulphur springs and kangaroo caves is located at the edge of the grabens at the site of intersecting syn volcanic extensional faults

mineralogy sulphur isotope geochemistry and the development of sulphide structures at the broken spur hydrothermal vent site 29 10 n mid atlantic ridge a large collection of hydrothermal sulphides from the broken spur hydrothermal vent site including representative samples of mound sulphide materials has been characterized using optical mineralogy and sulphur isotope analysis young mound sulphides from broken spur have a pyrrhotite dominated mineralogy unusual for bare ridge vent systems however pyrrhotite is metastable and is ultimately converted to iron disulphides mature sulphides are indurated recrystallized and contain abundant quartz sulphide mound materials are developed by three major processes i coalescing of chimney structures ii accumulation of talus from mass wasting and iii precipitation and growth in response to hydrothermal flow progressive maturation of mound materials is by modification of primary textures development of mineralogical zoning and replacement of metastable phases sulphur isotope analysis of 35 mineral separates returned 34 s values of 0 5 to 3 2 these values are similar to those previously measured for broken spur and snakepit but are distinctly 32 s enriched compared to the tag active mound and some pacific sites seawater entrainment and sulphate reduction within the subsurface feeder zone below broken spur mounds do not appear to be important processes at broken spur in contrast to the tag active mound

redox state of seafloor hydrothermal fluids and its effect on sulfide mineralization abstract the redox conditions f o 2 f s 2 of seafloor hydrothermal fluids were calculated from dissolved h 2 and h 2 s concentrations at conditions of 300 and 350 c 71 409 bars and seawater salinity the results were compared with f o 2 f s 2 conditions estimated from black smoker mineralogy as reported by previous studies and our own investigations for various geological settings including the okinawa trough sediment rich hakurei and sediment poor jade fields the manus back arc basin felsic hosted pacmanus and basalt hosted vienna woods fields and the central indian ridge mafic ultramafic hosted kairei and basalt hosted edmond fields in most cases the calculated fluid f o 2 f s 2 conditions agree well with estimates from primary mineral assemblages and fes contents in sphalerite wurtzite this correlation suggests that the redox states of sulfide mineralization in chimneys typically reflect dissolved h 2 and h 2 s concentrations in vent fluids it should be noted that variable h 2 concentrations in vent fluids 0 01 19 mmol kg dominantly control not only fluid f o 2 but also f s 2 whereas the more uniform h 2 s concentrations 1 20 mmol kg have less of an influence on fluid f s 2 fluid sediment interaction elevates h 2 concentrations to over 1 mmol kg which sufficiently lowers f o 2 f s 2 to the pyrrhotite stability field however low h 2 s concentrations do not necessarily account for low f s 2 calculations for the h 2 poor 0 1 mmol kg and h 2 s rich 10 mmol kg fluids in some felsic hosted arc backarc systems indicate relatively high f o 2 f s 2 states consistent with the bornite pyrite chalcopyrite assemblages these redox conditions result from a combination of fluid mineral equilibria at relatively oxidizing conditions elevated h 2 s concentrations from magmatic degassing redox calculations at 350 c indicate that neither pyrite nor pyrrhotite is stable in the initial hot fluids of the tag and ultramafic hosted mid atlantic ridge systems due to the low h 2 s concentrations with cooling of these fluids either conductively or by interacting with seawater higher f s 2 and f o 2 result and fe sulfides are stable in agreement with the higher f o 2 f s 2 mineral assemblages observed

bikpela a large siliceous chimney from the pacmanus hydrothermal field manus basin papua new guinea the 2 7 m bikpela chimney differs from sulfide rich chimneys at pacmanus eastern manus basin by virtue of high silica content a stromatolite like layered structure and the presence of a large internal collapse cavity its interior is dominated by 5 to 10 mm thick primary laminae of opal a dominated fronds clouded by submicroscopic sphalerite inclusions set between thin subhorizontal growth borders larger sphalerites with sulfosalt galena intergrowths at frond ends project into discoid cavities under the growth borders a steeper second order lamination reflects arrested expansion of the 50 cm high internal collapse cavity underlying the cavity floor an axial breccia pipe contains distorted fragments of laminated interior modified by dissolution and then redeposition of opal and further growth of pyrite and sphalerite beneath a thin mn oxide crust a hard outer sphalerite barite carapace 5 cm thick and devoid of opal is banded parallel to the chimney exterior at least three stages of chimney growth are evident beginning with repetitive deposition of opaline frond layers probably developed from microbial mat precursors by overgrowth of hydrothermal opal and fine sphalerite next with rising fluid temperatures hydrothermal fe poor sphalerite with pb sulfosalts and galena deposited at frond ends and under growth borders and via lateral diffusion and mixing with seawater formed abundantly in the outer carapace of the chimney passage of hot more acid fluids into the chimney axial zone then caused dissolution of primary opal and consequent formation of the collapse cavity and underlying breccia pipe together with deposition of fe rich sphalerite and pyrite in second order fractures and cavities related to the collapse finally conductive cooling during or after this latter stage produced films and spherules of clear opal coating pores and grain margins throughout the structure apart from in the carapace bikpela contains significant gold and silver avg 8 7 ppm au 250 ppm ag n 9 but it is low overall in cu up to 0 5 wt in the pipe and pb up to 0 7 wt in the carapace its carapace is relatively rich in zn up to 54 wt ag as and sb with one sample containing 0 12 wt silver

origin and distribution of terrestrial organic matter in the nw mediterranean gulf of lions exploring the newly developed bit index the branched and isoprenoid tetraether bit index is based on the relative abundance of nonisoprenoidal glycerol dialkyl glycerol tetraethers gdgts derived from organisms living in terrestrial environments versus a structurally related isoprenoid gdgt crenarchaeol produced by marine crenarchaeota the bit index varies between 0 and 1 representing marine and terrestrial organic matter om end members respectively hopmans et al earth planet sci lett 224 107 116 2004 in this study the applicability of the bit index to trace terrestrial om is tested in combination with other organic parameters toc c n ratio 13corg total lipid and n alkane in the gulf of lions a river dominated continental margin of the western mediterranean we analyzed a variety of soils and riverbed sediments from the continent as well as surface sediments from the shelf and canyons the bit index in soils and riverbed sediments shows high values 0 9 while it varies between 0 02 and 0 83 in marine sediments decreasing seaward from the inner shelf to the slope for marine surface sediments high bit values are associated with lower 13corg values as well as higher toc contents and higher n alkane concentrations our results confirm that the bit index can be applied in coastal marine environments in order to characterize terrestrial om as proposed by hopmans et al 2004 therefore the bit index is a useful addition to the proxies presently available for studying the origin and distribution of om in continental margins and especially valuable in multiproxy studies

microanalysis of nitrogen isotope abundances association of nitrogen with noble gas carriers in allende current research efforts to explore and account for the distribution of nitrogen isotope abundances in the ancient and present day solar wind and in meteorites often require measurement of nitrogen abundances and isotopic compositions in very small samples of rare extraterrestrial materials isotopic analysis of 1 g of n2 is possible with modern techniques of dynamic mass spectrometry but even this high sensitivity is a limiting factor for certain critical samples we have utilized a statistically operated mass spectrometer coupled to an ultrahigh vacuum gas extraction and processing system to lower this limit by approximately four orders of magnitude quantities of n2 ranging from 100 ng to 100 pg are measurable with permil to percent precision in isotope ratios nitrogen and all noble gases evolved during stepwise combustion of fine grained matrix material separated from the allende meteorite have been meausred simultaneously in a pilot experiment using this technique isotopically heavy h xe ccf xe and isotopically light n are co sited in a carbonaceous carrier phase supporting a nucleosynthetic origin for15n depleted nitrogen in allende the great isotopic uniformity of trapped ar in all carrier phases indicates that simple physical mass fractionation in gravitational escape of volatiles from the primitive nebula cannot have played a significant role in generating the nitrogen compositions observed in solar system matter

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

crustal fissuring and its relationship to magmatic and hydrothermal processes on the east pacific rise crest 9 12 to 54 n the deep towed argo i optical acoustical vehicle and a geographic information system gis have been used to establish the abundance widths and spatial distribution of fissures as well as the relative age distribution of lavas along the narrow 500 m wide axial zone of the east pacific rise epr from 9o12 to 9o54 n on a second order scale 78 km long wider but less numerous fissures are found in the northern portion of the survey area this changes to narrower more abundant fissures in the south a profile of the cumulative width added by fissures to the axial zone exhibits minima in three areas along strike near 9o49 9o35 and 9o15 n where the most recent eruptions have occurred above sites of magmatic injection from the upper mantle filling and covering older fissures on a fourth order scale 5 15 km long the mean density of fissuring on a given segment is greater where relative axial lava age is greater fissure density also correlates with hydrothermal vent abundance and type increased cracking toward segment tips is observed at the second order scale whereas fourth order segments tend to be more cracked in the middle cracking on a fourth order scale may be driven by the propagation of dikes rather than by the far field plate stresses the above relations constrain the model of haymon et al 1991 in which individual fourth order segments are in different phases of a volcanic hydrothermal tectonic cycle

active and relict sea floor hydrothermal mineralization at the tag hydrothermal field mid atlantic ridge the tag hydrothermal field is a site of major active and inactive volcanic hosted hydrothermal mineralization in the rift valley of the slow spreading mid atlantic ridge at 26 degree n the axial high is the principal locus of present magmatic intrusions the tag field contains three main areas of present and past hydrothermal activity 1 an actively venting high temperature sulfide mound 2 two former high temperature vent areas 3 a zone of low temperature venting and precipitation of fe and mn oxide deposits the volcanic centers occur at the intersections between ridge axis parallel normal faults and projected axis transverse transfer faults the intersections of these active fault systems may act as conduits both for magmatic intrusions from sources beneath the axial high that build the volcanic centers and for hydrothermal upwelling that taps the heat sources radiometric dating of sulfide samples and manganese crusts in the hydrothermal zones and dating of sediments intercalated with pillow lava flows in the volcanic center adjacent to the active sulfide mound indicate multiple episodes of hydrothermal activity throughout the field driven by heat supplied by episodic intrusions over a period of at least 140 times 10 sup 3 yr the sulfide deposits are built by juxtaposition and superposition during relatively long residence times near episodic axial heat sources counterbalanced by mass wasting in the tectonically active rift valley of the slow spreading oceanic ridge hydrothermal reworking of a relict hydrothermal zone by high temperature hydrothermal episodes has recrystallized sulfides and concentrated the first visible primary gold reported in a deposit at an oceanic ridge

environmental controls on branched tetraether lipid distributions in tropical east african lake sediments abstract quantifying past continental temperature changes is an important aspect of paleoclimate research as it allows us to constrain the amplitude of natural variability test predictive climate models and provide a proper context for changes that may arise in response to anthropogenically induced climate change the recently developed biomarker based methylation index of branched tetraethers cyclization ratio of branched tetraethers mbt cbt proxy shows potential as a new method for continental temperature reconstruction but thus far it has only been applied successfully in ocean margin sediments to assess whether this proxy is also applicable to the sedimentary record in tropical lacustrine systems we investigated the distribution of branched glycerol dialkyl glycerol tetraethers gdgts in recently deposited sediments from 46 lakes in tropical east africa these lakes span a substantial range in surface elevation 770 4500 m above sea level and thus also a wide gradient of mean annual temperature we find that saline lakes excepted branched gdgts are universally abundant in the lakes investigated and can be used to predict mean annual air temperature maat with a high degree of accuracy however the existing global mbt cbt calibration for maat based on soils predicts inaccurate temperatures when applied to our african lake dataset this observation together with the fact that surface water ph and to lesser extent lake depth appear to influence the distribution of branched gdgts among sites leads us to conclude that in situ production of branched gdgts in lakes is likely the robust relationship between branched gdgt distribution and the temperature and ph of african freshwater lakes makes these compounds suitable for paleoenvironmental reconstruction however we urge caution in using branched gdgts in lake sediments to infer past temperatures unless their exact origin can be determined

submarine gold mineralization near lihir island new ireland fore arc papua new guinea gold rich siliceous veins with disseminated polymetallic sulfides and pyritic stockwork mineralization have been recovered from the top of conical seamount a shallow 1 050 m water depth submarine volcano located about 10 km south of lihir island papua new guinea grab samples from the summit of conical seamount contain the highest concentration of gold yet reported from the modern sea floor max 230 ppm au avg 26 ppm n 40 the gold occurs in sulfide rich veins of black amorphous silica hosted by intensely altered high k calc alkaline basalts sulfides in the veins consist of sphalerite galena pyrite chalcopyrite marcasite and a variety of cu pb as sb sulfosalts the gold occurs as native gold and electrum in the amorphous silica and as inclusions in the sulfides the highest gold concentrations are associated with high ag as sb and hg zoned alteration adjacent to the veins consists of illite smectite amorphous silica k feldspar secondary plagioclase minor chlorite and trace carbonate the association of gold with illite smectite amorphous silica and k feldspar indicates deposition from near neutral ph hydrothermal fluids however the auriferous polymetallic sulfide veins and the associated alteration are overprinted on stockwork pyrite mineralization that is associated with earlier acid alteration containing alunite aluminum phosphate sulfates kaolinite and other clay minerals the platy habit of the alunite in this assemblage the presence of alumium posphate sulfate minerals and the sulfur isotope ratios of the crystalline pyrite 8 6 to 0 2 34 s n 28 and alunite 7 5 and 6 4 34 s are consistent with a contribution of magmatic volatiles in the earliest stages of the hydrothermal system framboidal pyrite within and at the margins of the mineralized zone has 34 s values suggesting involvement of biogenic activity 11 6 to 13 9 34 s the gold rich veins at conical seamount are distinct from sea floor massive sulfide deposits and represent a new style of mineralization on the modern sea floor the mineralogy alteration geochemistry and texture of the veins resemble those of some subaerial epithermal gold deposits and indicate that features long considered to define a subaerial setting can also form in a submarine environment the proximity of conical seamount to the giant ladolam epithermal gold deposit on nearby lihir island also raises the possibility that both subaerial and submarine gold mineralization in the region may be related to the same district scale magmatic events

mineralogical and geochemical features of sulfide chimneys from the meso zone central indian ridge hydrothermal activity is fairly well documented from most mid ocean ridges however despite various efforts there is only one hydrothermal field recognized so far in the indian ocean products of former hydrothermal activity were sampled in the fourth segment of the central indian ridge cir north of the rodriguez triple junction rtj near 23 s the mineralized area referred to as meso zone covers an area of about 0 6 km2 and is located at a water depth of 2850 m close to the height of a neovolcanic intrarift ridge hydrothermal mineralization is structurally controlled by fissures and cracks running both parallel and orthogonal to the general strike direction of the cir axis 152 n sulfides of the meso zone formed over a period of at least 30 000 years hydrothermal activity ceased 10 000 years ago detailed mineralogical and geochemical studies of sulfides establish the growth and decay of chimney structures which are mainly composed of pyrite marcasite and chalcopyrite chimneys show high concentrations of base metals particularly cu and fe more than 40 wt as well as high trace element contents like co up to 0 24 wt and as 1 wt in contrast sphalerite is rarely observed which is attributed to replacement and refining processes during the weathering and physical disintegration of the hydrothermal products the zn content is generally low 1 wt only selected samples show higher zn concentrations up to 7 9 wt remnants of chimney structures are characterized by the absence of sulfates but they contain minor amounts of amorphous silica

occurrences and distribution of invisible precious metals in sulfide deposits from the edmond hydrothermal field central indian ridge abstract here we report the first documented occurrences of invisible gold and silver in seafloor sulfide deposits from an active hydrothermal system on the central indian ridge a detailed mineralogical and geochemical study of polymetallic sulfides from the edmond vent field was conducted in order to identify controls on the distribution of precious metals bulk samples n 18 contain up to 18 7 ppm au and 1450 ppm ag with average concentrations of 2 3 ppm au and 218 9 ppm ag among them several zn rich chimney fragments and anhydrite dominated ore samples have higher contents of precious metals than fe cu rich massive sulfides and silica rich hydrothermal precipitates native gold grains are mainly associated with sphalerite anhydrite barite and fe oxyhydroxides abundant submicroscopic au ag alloys tend to occur along grain boundaries between cu fe sulfides and tennantite or close to the rims of fe poor sphalerite in contrast to primary electrum with high ag au ratios the absence of detectable silver in high purity gold indicates that secondary au enrichment has probably occurred after a direct co precipitation with zn rich mineral assemblages upon cooling and mixing of vent fluids with cold seawater a suite of late stage ag rich phases including argentotennantite pearceite and acanthite occur as crack filling veinlets and patches in low temperature fahlores or as tiny inclusions enclosed by pyrite chalcopyrite and colloform sphalerite by using hrtem combined with haadf stem imaging we have found out that silver is also present in significant quantities as discrete colloidal nanoparticles in tennantite minor native copper is closely associated with altered chalcopyrite sphalerite and covellite exhibiting signs of dissolution recrystallization and reprecipitation extensive hydrothermal reworking resulted from a long history of high temperature venting in this field together with post depositional supergene replacement processes involving oxidation leaching or coupled dissolution reprecipitation mechanisms facilitated by a permeable porosity generated in primary cu fe sulfides are considered to be important for the remobilization and local reconcentration of early formed precious metals and may have been responsible for the formation of relatively coarse grained native gold or silver within recrystallized massive sulfides and chimney debris

geology sulfide geochemistry and supercritical venting at the beebe hydrothermal vent field cayman trough the beebe vent field bvf is the world s deepest known hydrothermal system at 4960m below sea level located on the mid cayman spreading centre caribbean the bvf hosts high temperature 401 c black smoker vents that build cu zn and au rich sulphide mounds and chimneys the bvf is highly gold rich with au values up to 93 ppm and an average au ag ratio of 0 15 gold precipitation is directly associated with diffuse flow through beehive chimneys significant mass wasting of sulphide material at the bvf accompanied by changes in metal content results in metaliferous talus and sediment deposits situated on very thin 2 3km thick oceanic crust at an ultraslow spreading centre the hydrothermal system circulates fluids to a depth of 1 8km in a basement that is likely to include a mixture of both mafic and ultramafic lithologies we suggest hydrothermal interaction with chalcophile bearing sulphides in the mantle rocks together with precipitation of au in beehive chimney structures has resulted in the formation of a au rich volcanogenic massive sulphide vms deposit with its spatial distribution of deposit materials and metal contents the bvf represents a modern day analogue for basalt hosted au rich vms systems this article is protected by copyright all rights reserved

coupled thermal and hydrological evolution of tropical africa over the last deglaciation we analyzed the distribution of branched tetraether membrane lipids derived from soil bacteria in a marine sediment record that was recovered close to the congo river outflow and the results enabled us to reconstruct large scale continental temperature changes in tropical africa that span the past 25 000 years tropical african temperatures gradually increased from 21 to 25 c over the last deglaciation which is a larger warming than estimated for the tropical atlantic ocean a direct comparison with sea surface temperature estimates from the same core revealed that the land sea temperature difference was through the thermal pressure gradient an important control on central african precipitation patterns

crenarchaeotal membrane lipids in lake sediments a new paleotemperature proxy for continental paleoclimate reconstruction paleoclimate studies of continental environments have been hampered by the lack of an independent paleotemperature proxy a novel sea surface temperature proxy has been proposed for marine systems based on membrane lipids of marine crenarchaeota this proxy will provide an independent continental paleotemperature tool that will allow paleoclimatologists to address fundamental questions about temperature variability in continental environments and its relationship to climate change

sulfide mineralization in an ultramafic rock hosted seafloor hydrothermal system from serpentinization to the formation of cu zn co rich massive sulfides abstract the rainbow vent field is an ultramafic rock hosted seafloor hydrothermal system located on the mid atlantic ridge issuing high temperature acidic metal rich fluids hydrothermal products include cu zn co rich massive sulfides with characteristics comparable to those found in mafic volcanic hosted massive sulfide deposits petrography mineralogy and geochemistry of nonmineralized and mineralized rocks sampled in the rainbow vent field indicate that serpentinized peridotites host the hydrothermal vent system but serpentinization reactions occurred prior to and independently of the sulfide mineralization event the onset of sulfide mineralization is reflected by extensive textural and chemical transformations in the serpentine group minerals that show clear signs of hydrothermal corrosion element remobilization is a recurrent process in the rainbow vent field rocks and during simple peridotite serpentinization ni and cr present in olivine and pyroxene are incorporated in the pseudomorphic serpentine mesh and bastite respectively ni is later remobilized from pseudomorphic serpentine into the newly formed sulfides as a result of extensive hydrothermal alteration bulk rock geochemistry and correlation coefficients discriminate the different processes serpentinization sulfide mineralization and superficial seafloor low temperature processes related to the circulation of seawater e g carbonatization sulfide oxidation and b and u uptake

insights into tide related variability at seafloor hydrothermal vents from time series temperature measurements abstract thermocouple thermistor array packages and an in situ gamma detector were deployed in 1994 at two vent sites on the northern cleft segment of the juan de fuca ridge continuous records of fluid temperatures were obtained in four separate locations over a period of 5 5 months and these data were supplemented by current meter observations made 2 5 km to the south within the axial valley temperatures measured at a location of focused high temperature flow showed that 1 the maximum temperature in the chimney was stable and did not exhibit tide related variability 2 temperatures within the chimney wall were variable on time scales of minutes indicating rapid shifts in amounts of cold seawater or hot vent fluid flowing across chimney walls and 3 the stable maximum temperature within the chimney conduit was 9 c less than the maximum fluid temperature recorded at the vent site during the same time interval and thus stable high temperatures within chimneys are not necessarily indicative of the maximum temperature within the vent structure or the hydrothermal system time series records from areas of diffuse flow indicate modulation of temperature and total radioactivity by tidally induced changes in bottom currents spectra of the current meter record and temperature records are similar with spectral peaks observed at 12 4 h 16 17 h inertial peak and 4 5 days phases between maxima in current tide and temperature records are consistent with temperature changes resulting from periodic shifts in currents from north to south and the subsequent northward or southward advection of warm fluids venting from multiple local sources periodic 12 4 h variability of temperature was also recorded by a thermocouple buried 1 cm within one of the deposits and is likely a result of periodic variations in the temperature at the boundary of the highly conductive sulfide deposit the time series results presented demonstrate the need for measuring and considering the effects of local currents when investigating causes of temporal variability within seafloor hydrothermal systems

relict hydrothermal events along the super slow southwest indian spreading ridge near 63 56 e mineralogy chemistry and chronology of sulfide samples abstract during the indoyo cruise in 1998 with shinkai 6500 a massive sulfide field was located in a water depth of about 2940 m near 27 51 s 63 56 e east of the melville fracture zone the newly discovered hydrothermal field is situated at the summit of an axial volcanic ridge informally called mount jourdanne within the field inactive chimneys as well as hydrothermal mounds were observed on the ocean floor but no indications such as shimmering water chemical anomalies in the water column or faunal relicts which might point to an active vent site were observed our discovery proves for the first time that high temperature massive sulfide chimneys can also develop at a super slow spreading ridge such as the southwest indian ridge this discovery of massive sulfides will possibly open new aspects in the understanding of hydrothermal processes along super slow spreading ridges since the sulfide samples from mt jourdanne show interesting differences in their mineralogical as well as chemical compositions when compared to sulfide samples from faster opening ridge environments to reconstruct the history of the evolution of this field age dating studies were carried out on the recovered sulfide samples these indicate activity between 70 000 and 13 000 years ago

resource assessment of undiscovered seafloor massive sulfide deposits on an arctic mid ocean ridge application of grade and tonnage models abstract norway has started ongoing initiatives related to deep sea mining these include the evaluation of mineral resources within its sovereign territorial waters on the deep ocean floor of the arctic region i e the mohns ridge 71 73 n among the variety of possible seabed resources seafloor massive sulfides sms attract particular interest owing to the significant development potential and the general lack of knowledge of the sms deposits the present study aims at assessing mineral resources i e cu zn au and ag from a number of undiscovered sulfide deposits with the help of a revised model for mafic hosted volcanogenic massive sulfide vms deposits that adequately corresponds to geological settings of slow spreading ridges application of the model requires a priori knowledge of the seafloor terrain to depict favorable geologic environments for the occurrence of sms deposits in such context estimates are conducted for the easily accessible volcanically active parts of the ridge where 11 undiscovered deposits are expected in these areas total metal endowments are calculated to be on average 447 000 tonnes using a monte carlo simulation that combines the probabilistic estimates of number of undiscovered deposits with the grade and tonnage models estimates of in place metal resources are generated in cumulative distribution form to present expected amount of undiscovered metals at 90 confidence intervals

the effects of training set selection on the relationship between pollen assemblages and climate parameters implications for reconstructing past climate abstract 494 surface soil pollen samples were collected from forests steppes deserts shrubs and meadows in the northern china and compared with modern climate data two approaches for estimating climate parameters from pollen data were tested independently wa pls weighted averaging regression and calibration partial least squares and mat the modern analogues technique methods the results of cross validation showed that pollen data could effectively estimate annual average precipitation pann wa pls rjack2 0 84 rmsepjack 78 mm mat r 0 91 std dev 79 mm but were only moderately successful at estimating either mean annual temperature wa pls rjack2 0 48 rmsepjack 2 5 c mat r 0 68 std dev 2 5 c or the mean temperature of the warmest month wa pls rjack2 0 50 rmsepjack 2 6 c mat r 0 72 std dev 2 6 c one of the reasons for errors in estimating thermal parameters is the presence of some troublesome samples in the dataset samples from communities with severe human disturbance or from small patches of vegetation close to an ecotone removing 104 samples affected by these factors gave a best pollen dataset which was able to estimate thermal parameters with a greater degree of accuracy r 0 8 or rjack2 0 64 all these methods were applied to a published paleo record the anyang chadianpo section covering the period about 10 000 cal b p present mat and wa pls methods reconstructed similar pann records but thermal parameters showed more severe and abrupt changes when reconstructed using the mat approach rather than the wa pls method using the different pollen data sets all 494 or 390 best samples for each method led to similar paleoclimate reconstructions in most periods apart from periods of climate transition e g 6200 6800 cal b p 3000 4000 cal b p or intensive human activity after 1000 cal b p suggesting that the influence of human activities and small patches on the composition of the pollen record are more significant in these periods

a model for growth of steep sided vent structures on the endeavour segment of the juan de fuca ridge results of a petrologic and geochemical study petrologic and geochemical studies of vent solids from the main endeavour field mef and the high rise field hrf juan de fuca ridge demonstrate that the steep sided vent structures characteristic of these sites form dominantly by flange growth combined with diffuse flow through sealed portions of structures and incorporation of flanges into structures geochemical calculations suggest that the prevalence of amorphous silica and flanges in endeavour deposits is the result of conductive cooling of vent fluids that have high concentrations of ammonia at endeavour as the temperature of vent fluid decreases ammonia ammonium equilibrium buffers ph and allows more efficient deposition of sulfide minerals and silica from fluids that have a higher ph than conductively cooled ammonia poor fluids present at most other unsedimented mid ocean ridge vent sites deposition of silica stabilizes flanges and allows structures to attain large size it also leads to diffuse flow and further conductive cooling by reducing the permeability and porosity of the structures and of feeder zones thus decreasing entrainment of seawater most inactive vent samples recovered from areas peripheral to the hrf and mef are similar to barite silica rich samples from the explorer ridge and axial seamount and likely formed from precipitation of silica and barite on a biological substrate active white smoker chimneys from the clam bed field located south of the hrf are pyrrhotite rich and likely formed from vent fluids that are depleted in zn and cd and enriched in pb and ba relative to fluids exiting trans atlantic geotraverse tag and cleft segment white smoker chimneys

constraints on the application of the mbt cbt palaeothermometer at high latitude environments svalbard norway abstract branched glycerol dialkyl glycerol tetraethers gdgts are membrane lipids of unknown bacteria that are ubiquitous in soil and peat two indices based on the distribution of these lipids in soils the cyclization of branched tetraethers cbt and the methylation of branched tetraethers mbt indices have been shown to correlate with soil ph and mean annual air temperature mat and soil ph respectively and can be used to reconstruct mat in palaeoenvironments to verify the extent to which branched gdgts in marine sediments reflect the distribution pattern on land and whether these proxies are applicable for palaeoclimate reconstruction in high latitude environments with a mat of

gold enrichment in hydrothermal sulfides from the okinawa trough an in situ la icp ms study abstract we assess the distribution of gold and investigate the physicochemical controls on gold enrichment in the okinawa trough an immature back arc basin we conducted a systematic study of gold and other trace element concentrations using in situ laser ablation inductively coupled plasma mass spectrometry la icp ms for various minerals in hydrothermal sulfide samples from the iheya north knoll and the yonaguni knoll iv hydrothermal fields orpiment colloform pyrite and colloform sphalerite are relatively enriched in au mean contents of 30 60 17 48 and 8 68 ppm respectively compared with gold poor massive chalcopyrite sphalerite and pyrite based on gold budget estimation colloform pyrite is the most important au host followed by colloform sphalerite and orpiment with these three minerals containing the majority of gold in hydrothermal sulfides gold occurs as invisible in host minerals as lattice bound and submicron inclusions in colloform pyrite as homogeneously distributed lattice bound or nano inclusions in colloform sphalerite and generally as lattice bound in orpiment and tetrahedrite three sets of gold host minerals are identified with distinct ore formation temperatures colloform sulfides and orpiment incorporate the majority of gold at low temperatures whereas tetrahedrite and massive sulfides incorporate only minor or trace amounts of gold at medium and high temperatures respectively our results show that gold enrichment in si ba fe rich hydrothermal sulfides at low temperatures is a significant contributor to gold enrichment in hydrothermal sulfide deposits in the okinawa trough along with the more common zn and cu rich hydrothermal sulfides thermodynamic modeling calculations suggest that the near neutral ph of hydrothermal fluids and the dominant transport species namely au hs complexes rather than au cl complexes are likely responsible for gold enrichment in low temperature mineral assemblages in hydrothermal precipitates from the okinawa trough

the influence of hydrothermal fluid composition and advection rates on black smoker chimney mineralogy insights from modeling transport and reaction abstract a detailed study of black smoker chimneys was carried out by drawing together mineralogical observations and measured fluid compositions the modeling technique which establishes a link between vent fluid chemistry and vent deposit mineralogy is used to examine the influence of the physical environment on transport across short length scales centimeters which are subject to steep thermal 350 c and chemical gradients and to predict saturation states of minerals as functions of position within chimney walls owing to short length scales steep gradients and constancy of bounding fluid compositions concentration profiles are controlled by transport the effect of reaction rates on profiles is assumed to be negligible precipitation at points within the chimney wall is thus kinetically controlled local equilibrium does not apply and precipitation must be suppressed when calculating distributions of species and saturation states of minerals model calculations are performed in a series of four steps the first is speciation of measured fluid compositions at in situ temperature and pressure conditions results of calculations are plotted on stability diagrams of log fo2 log f s2 and log fo2 log a fe 2 a cu 2 to examine how closely the predicted saturation states fit with observations of minerals coexisting with the hydrothermal fluid at the vent sites the second step is calculation of heat and mass transport across the chimney wall the third is speciation of the pore fluid compositions calculated to exist in the wall subsequent to transport and the fourth is comparison of calculated mineral saturation states to observations of naturally occurring chimney samples application of the modeling technique to five vent sites which exhibit distinct fluid compositions allows reproduction of observed mineralogy model results demonstrate the sensitivity of geochemical processes to the physical environment porosity tortuosity permeability mineral composition to rates of advection of seawater inward or hydrothermal fluid outward across chimney walls and to endmember fluid composition

the changing vision of marine minerals abstract non fuel marine minerals are reviewed from the perspective of resources and their value as active analogs that can advance understanding of types of ancient ore deposits that formed in marine settings the theory of plate tectonics is the largest influence in expanding our vision of marine minerals and in developing our understanding of geologic controls of mineralization in space and time prior to the advent of plate tectonics we viewed the ocean basins as passive sinks that served as containers for particulate and dissolved material eroded from land this view adequately explained marine placer deposits heavy minerals and gems aggregates sand and gravel and precipitates phosphorites and manganese nodules although numerous sites of placer mineral deposits are known on continental shelves worldwide current activity pertains to diamond mining off southwestern africa tin mining off southeastern asia and intermittent gold mining off northwestern north america which are all surpassed economically by worldwide recovery of marine sand and gravel in turn dwarfed by offshore oil and gas with the advent of plate tectonics plate boundaries in ocean basins are recognized as active sources of mineralization in the form of hydrothermal massive sulfide deposits and proximal lower temperature deposits hosted in oceanic crust mafic at ocean ridges and felsic at volcanic island arcs and of magmatic ni cu sulfide chromite and pge deposits inferred to be present in the oceanic upper mantle lower crust based on their occurrence in ophiolites some 300 sites of hydrothermal active and relict mineralization most of them minor are known at this early stage of seafloor exploration on ocean ridges in fore arc volcanoes at back arc spreading axes and in arc rifts deposits formed at spreading axes and transported off axis by spreading are present in oceanic lithosphere but are virtually unknown the tag trans atlantic geotraverse hydrothermal field in the axial valley of the mid atlantic ridge latitude 26 n is considered to exemplify a major volcanogenic massive sulfide vms deposit forming at a spreading axis the most prospective of these occurrences lie within the 200 nautical mile 370 km wide exclusive economic zone eez of the nations of the volcanic island arcs of the western pacific where metal content of massive sulfides ag au ba cu pb sb zn exceeds that at ocean ridges plate tectonics early provided a framework for mineralization on the scale of global plate boundaries and is providing guidance to gradually converge on sites of mineralization through regional scales of plate reorganization with the potential to elucidate the occurrence of individual deposits e g eocene carlin type gold deposits investigation of the spectrum of marine minerals as active analogs of types of ancient mineral deposits is contributing to this convergence consideration of questions posed by brian skinner 1997 of what we do and do not know about ancient hydrothermal mineral deposits demonstrates the ongoing advances in understanding driven by investigation of marine minerals

the influence of spreading rate basement composition fluid chemistry and chimney morphology on the formation of gold rich sms deposits at slow and ultraslow mid ocean ridges seafloor massive sulphide sms deposits are variably enriched in precious metals including gold however the processes invoked to explain the formation of auriferous deposits do not typically apply to mid ocean ridge settings here we show a statistically significant negative correlation between the average gold concentration of sms deposits with spreading rate at non sedimented mid ocean ridges deposits located at slow spreading ridges 20 40 mm a have average gold concentrations of between 850 and 1600 ppb however with increasing spreading rate up to 140 mm a gold concentrations gradually decrease to between 50 and 150 ppb this correlation of gold content with spreading rate may be controlled by the degree and duration of fluid rock interaction which is a function of the heat flux crustal structure faulting and the permeability of the source rocks deposits at ultraslow ridges including ultramafic hosted deposits are particularly enriched in gold this is attributed to the higher permeability of the ultramafic source rocks achieved by serpentinisation and the inherent porosity of serpentine minerals combined with relatively high gold concentrations in peridotite compared with mid ocean ridge basalt variations in fluid chemistry such as reducing conditions and the potential for increased sulphur availability at ultramafic hosted sites may also contribute to the high concentrations observed beehive chimneys which offer more favourable conditions for gold precipitation may be more prevalent at ultramafic hosted sites due to diffuse low velocity venting compared with more focussed venting at basalt hosted sites

seamount formation and associated caldera complex and hydrothermal mineralization in ancient oceanic crust troodos ophiolite cyprus abstract the inter graben zone between the solea and mitsero grabens in the northern part of the troodos ophiolite cyprus displays igneous tectonic and physiographic features that are characteristic of seamount volcanism at modern oceanic spreading centers in this zone the 200 m high alestos hill volcanic edifice consisting of pillow lavas with preserved lava tubes and cone sheet intrusions is interpreted to have developed as a seamount fed by a late stage off axis shallow level gabbroic pluton that was intrusive into young oceanic crust concentric cone sheet intrusions and associated faults and shear zones in and around the alestos hill seamount collectively form a seafloor caldera complex which probably formed during the extrusion of lavas and subsequent cauldron subsidence over the gabbroic pluton the ene trending elongated massive sulfide ore deposit formation in the alestos memi area represents a focused upflow zone for hydrothermal fluids driven by the same off axis gabbroic intrusion responsible for formation of the alestos hill seamount the ene trending and up to 150 m wide alestos memi fault zone dissects the elongated ore body in a dextral sense and might have provided a high permeability conduit in the upper crust for upwelling hydrothermal flow at the time of magmatism the geometry of this fault zone and its kinematic relations with a n s striking alestos forest normal fault in the west are suggestive of its transfer fault origin reminiscent of mineralized transfer faults found at the mid atlantic ridge the active tag hydrothermal mound with massive sulfide deposits that is located on a small volcanic dome 3 km off axis and along a transfer fault in the trans atlantic geotraverse tag area at 26 n provides a modern analogue for the alestos hill seamount and associated faulting and mineralization in the ancient oceanic crust of the troodos ophiolite these findings indicate that off axis magmatism played a major role in crustal accretion hydrothermal alteration and ore mineralization during the late stage evolution of the troodos ophiolite

divining gold in seafloor polymetallic massive sulfide systems hydrothermal fluids on the modern seafloor are important carriers of base and precious metals in a wide range of volcanic and tectonic settings the concentrations and distribution especially of gold and silver in associated seafloor massive sulfide sms deposits are strongly influenced by variable source rocks fluid chemistry and precipitation mechanisms compositional data of 130 sms deposits around the world show a large range of gold and silver grades in part reflecting strong buffering of the hydrothermal fluids by their host rocks geochemical reaction path modeling shows that in most cases the investigated hydrothermal fluids are undersaturated with gold and silver and solubilities can be orders of magnitude higher than the au and ag concentrations measured in the corresponding fluids precipitation of gold during conductive cooling of mid ocean ridge black smoker mor fluids occurs at low temperatures but can be very rapid with 90 of the gold deposited in the first 25 c of cooling below 150 c the result is a zn au polymetallic assemblage with au and ag deposited at the same time together with pb and sulfosalts in ultramafic dominated um systems the strongly reduced hydrothermal fluids promote the deposition of gold at higher temperatures and explain the correlation between gold and copper in these deposits in this case the lower stability of the auhs complex at low o2 buffered by fayalite magnetite and quartz results in gold deposition at 250 c with early bornite and chalcopyrite and before sphalerite and silver producing a high temperature cu au assemblage in sediment hosted sed systems the much higher ph stabilizes au hs 2 and keeps gold in solution to very low temperatures after the precipitation of chalcopyrite sphalerite and galena resulting in au poor polymetallic sulfides and very late stage deposition of gold commonly with amorphous silica in arc related arc systems gold deposition occurs at somewhat higher temperatures than in the mor case in part because the fluids start with higher gold concentrations this can be explained by probable direct magmatic contributions and the high o2 of the fluids which promotes the solubility of gold at the source during cooling gold precipitates at about 160 c with sphalerite tennantite silver and galena resulting in an au rich polymetallic sulfide assemblage the mixing of hydrothermal fluids with seawater generally causes oxidation and eventually a decrease in the ph at a mixing ratio of 1 1 causing an initial increase in the solubility of gold and silver this can delay gold deposition from aqueous species to very low temperatures these complex systematics make prediction of au and ag grades difficult however important new data are coming to light on the actual concentrations of the precious metals in hydrothermal fluids in particular the input of magmatic volatiles and leaching of pre existing gold can lead to significant increases in the au and ag concentrations of the venting fluids and earlier deposition in several cases it appears that at least part of the gold load is present as nanoparticles in suspension allowing bulk gold concentrations that may be far in excess of liquid saturation boiling at the seafloor is now widely observed even at great water depths close to the critical point of seawater model calculations of phase separation during boiling show the competing effects on gold solubility of h2 h2s and co2 partitioning into the vapor which can result in highly variable gold to base metal ratios in the deposits flashing of the vent fluids into steam at high temperatures is also commonly observed and can lead to spectacular au grades with a strong cu au association in the deepest and hottest vents

application of bacterial glycerol dialkyl glycerol tetraethers gdgts to develop modern and past temperature estimates from new zealand lakes abstract branched isoalkyl glycerol dialkyl glycerol tetraethers gdgts of bacterial origin have been found in high abundance in both modern and glacial sediments of new zealand south island freshwater lakes covering a wide range of altitude 101 2000 m like isoprenoid gdgts of archaeal origin they provide excellent potential for temperature assessment for this study their distribution patterns mbt methylation ratio and cbt cyclisation ratio of branched gdgts have been successfully used to develop an initial temperature calibration for the study area and to provide preliminary palaeo environmental interpretations mbt data from modern lake sediments correlate well with measured annual air temperature r2 0 74 enabling a regional calibration for reconstructing palaeotemperatures for fossil samples mbt derived palaeotemperatures for alpine lake calibrated against mean annual temperature were determined for the last glacial during an early cold phase between 29 000 and 26 000 years bp and for later less cold phases between 23 000 and 18 000 years bp compared with the modern temperature regime the mbt data indicate a decrease of ca 5 6 and 2 8 c respectively during this time modern and past mbt derived temperatures correlate with chironomid based temperature reconstructions in the area archaeal gdgts commonly used for the tex86 index are abundant in fossil sediments alpine lake but scarce in modern sediments hindering a new local calibration for this palaeotemperature proxy

applicability and calibration of the tex86 paleothermometer in lakes abstract we have conducted a global survey of archaeal glycerol dialkyl glycerol tetraether gdgt lipids in lake sediments in order to develop the tex86 paleotemperature proxy for application in continental systems surface sediments of 46 globally distributed lakes were analyzed for gdgt but isoprenoid gdgt derived from aquatic crenarchaeota were only unambiguously detected in 20 of the 46 lakes analyzed aquatic crenarchaeotal gdgt were detected mainly in sediments from large lakes 4000 km2 and hydrothermal or volcanic lakes suggesting that in some mostly smaller lakes either aquatic crenarchaeota are present at low abundance resulting in sedimentary lipids below levels of detection or they are absent branched gdgt thought to be derived primarily from soil bacteria were identified in all lake sediments analyzed correlation of the tex86 in those lakes with sufficient amounts of putative crenarchaeotal gdgt with annual mean lake temperature is reasonably good r2 0 68 n 20 in order to reduce the influence of soil derived isoprenoid gdgt on the tex86 lake temperatures we have applied a filter based on relative soil derived inputs as determined by the bit branched and isoprenoid tetraether index which results in a calibration relationship with r2 0 86 n 12 and an estimated temperature error of 3 6 c our results suggest that the tex86 should be applied only in lakes with sufficient production of gdgt by aquatic crenarchaeota relative to isoprenoid gdgt derived from soil in the watershed or other aquatic sources

native gold and gold rich sulfide deposits in a submarine basaltic caldera higashi aogashima hydrothermal field izu ogasawara frontal arc japan sulfide deposits with extremely high au concentrations up to 275 ppm avg 102 ppm n 15 high au ag ratios 0 24 n 15 and low cu cu zn ratios 0 03 n 15 were discovered in 2015 in active hydrothermal fields at a water depth of 760 m in a basalt dominated submarine caldera in the izu ogasawara frontal arc japan native gold grains occur in massive sulfide fragments concretions and metalliferous sediments from a sulfide mound 40 m across and 20 m high with up to 30 m high black smoker chimneys tiny native gold grains up to 14 m in diameter are mainly present in sulfide fallouts from chimney orifices and plumes larger native gold grains up to 150 m long occur mostly as discrete particles and or with amorphous silica and sulfides the larger gold grains are interpreted to represent direct precipitation from au bearing hydrothermal fluids circulating in and or beneath the unconsolidated sulfide mound deposits sulfur isotope compositions from a limited number of sulfide separates n 4 range from 4 3 to 5 8 34s similar to the quaternary volcanic rocks of the arc barite separates have values of 22 2 and 23 1 close to modern seawater values and indicate probable seawater sulfate origin the cu zn and pb concentrations in bulk samples of sulfide rich rocks are similar to those of volcanogenic massive sulfides formed in continental crustal environments the gold is interpreted to have formed by low temperature hydrothermal activity perhaps genetically different from systems with documented magmatic contributions or from seafloor hydrothermal systems in other island arc settings its presence suggests that basalt dominated submarine calderas situated on relatively thick continental crust in an intraoceanic arc setting such as the higashi aogashima knoll caldera may be perspective for gold mineralization

hydrothermal vents near a mantle hot spot the lucky strike vent field at 37 n on the mid atlantic ridge the lucky strike hydrothermal field occurs in the summit basin of a large seamount that forms the shallow center of a 65 km long ridge segment near 37 n on the mid atlantic ridge the depth and chemistry of the ridge segment are influenced by the azores hot spot and this hydrothermal field is the first atlantic site found on crust that is dominated by a hot spot signature multiple hydrothermal vents occur over an area of at least 300 m by 700 m vent morphologies range from flanges and chimneys with temperatures of 200 212 c to black smoker chimneys with temperatures up to 333 c cooler fluids from northern vents have higher chlorinities and lower gas volumes while hotter southern fluids have chlorinities 20 below seawater with higher gas volumes suggesting phase separation has influenced their compositions all gas volumes in fluids are higher than those at tag and snake pit hydrothermal fields black smokers exhibit their typical mineralogy except that barite is a major mineral particularly at lower temperature sites which contrasts with previously investigated atlantic sites the fluid chemistry distribution of the relict sulfide deposits on the seamount summit in the areas investigated using dsv alvin and contact relationships between active vent sites and surrounding basaltic and sulfide substrate suggest that the hydrothermal system has a long history and may have recently been rejuvenated fauna at the lucky strike vent sites are dominated by a new species of mussel and include the first reported sea urchins the lucky strike biological community differs considerably from other vent fauna at the species level and appears to be a new biogeographic province the lucky strike field helps to constrain how variations in the basaltic substrate influence the composition of hydrothermal fluids and solids because basalt compositions at lucky strike are 10 30 times enriched in incompatible elements compared to other atlantic hydrothermal sites such as tag snake pit and broken spur the incompatible element

distributions of branched gdgts in a tropical lake system implications for lacustrine application of the mbt cbt paleoproxy branched glycerol dialkyl glycerol tetraether gdgt lipids are abundant and ubiquitous in lake sediments potentially allowing for a paleolimnological application of the so called mbt cbt proxy methylation index of branched tetraethers cyclization ratio of branched tetraethers to investigate the origin and characteristics of these compounds in lacustrine environments we examined the distributions of gdgts in soils river sediments and lake sediments from lake towuti on the island of sulawesi indonesia we found significant differences in the degree of methylation and cyclization expressed by way of the mbt and cbt indices between the soil samples and the aquatic samples suggesting that there may be in situ production of gdgts in the aquatic environment based on these findings we urge caution in the application of the mbt cbt paleoproxy to lake sediments and encourage more rigorous study of these compounds in freshwater environments

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

chemical microenvironments within sulfide structures from the mothra hydrothermal field evidence from high resolution zoning of trace elements abstract massive portions of a 300 c black smoker finn and a diffusely venting intermediate temperature 200 c chimney roane recovered from the mothra hydrothermal field on the juan de fuca ridge have been analyzed in detail for bulk chemistry the size of the recovered pieces of chimney enabled physical segregation and analysis of distinct chemical zonation within the structures in particular large variations in the concentrations of minor and trace elements in the different mineralogical zones provide new insight into the processes involved in chimney growth that are not evident from the bulk mineralogy systematic zonation of trace and minor elements is strongly influenced by redox conditions multiple host phases single or dual fluid source and the mixing cooling history of the fluids even within an individual mineralogical zone distinct chemical microenvironments within the chimneys are recognized that provide a basis for detailed reconstruction of the changing conditions in the interiors of the chimneys during their growth in finn 14 discrete chemical microenvironments are recognized in 80 of 90 samples based on high resolution zoning of major and trace elements four of the microenvironments are cu rich three are zn rich one is fe rich with low cu two are ca rich three are sio2 rich and one is ba and sio2 rich in roane 24 discrete chemical microenvironments are recognized six of the microenvironments are sio2 poor

microstructural characterization and in situ sulfur isotopic analysis of silver bearing sphalerite from the edmond hydrothermal field central indian ridge abstract a close zn ag association has been noted recently in several polymetallic sulfide ore deposits from the indian ocean however the role of nanotextural controls on invisible silver distribution within sphalerite a significant ag carrier is still not well understood in this study typical zn sulfide samples from the edmond vent field central indian ridge can be roughly classified into three different groups based on their chemical compositions and mineral textures among them sulfosalt bearing fe poor zinc sulfides in sulfate dominant outer chimney walls usually contain higher contents of ag cu and pb up to wt levels than fe rich massive to disseminated sphalerite in zn fe rich chimney fragments coated by silicified crusts such sphalerite is represented by colloform botryoidal aggregates of optically anisotropic zns with a strongly disordered structure or hexagonal habit which are actually formed by coalescence and agglomeration of colloidal nanocrystalline particles using high resolution transmission electron microscopy hrtem and in situ micro xrd techniques we have investigated the ultrastructure and crystal chemistry of the 1 1 1 twin boundaries and wurtzite type stacking faults that occur in ag rich colloform or porous dendritic sphalerite submicroscopic electrum and ag nanoparticles appear to nucleate on the micro nano pore walls as cavity fillings or occur along grain boundaries between chalcopyrite tennantite inclusions and the host sphalerite interestingly the inhomogeneous distribution of precious metals and other chalcophile elements is generally concordant with the extent of recrystallization intragranular porosity as well as various degrees of structural disordering imperfectness i e bulk defect density in zns domains lattice defects and interfaces may play a limited role in promoting the simultaneous introduction of exotic impurities into colloform sphalerite during rapid growth even though certain morphological traits and aggregation state at the nanoscale seem to support a biogenic origin of these zns particles characterized by admixed polytypic intergrowth structures the mineralogical and geochemical features of highly defective sphalerite crystals in addition to their microscale s isotope signatures with relatively high 34 s values exhibit signs of abiologically mediated rapid precipitation caused by extensive mixing and cooling at edmond the physicochemical conditions and seafloor disequilibrium processes indicated by zns formation mechanism might facilitate the incorporation and enrichment of ag or other trace elements in hydrothermal sphalerite

geotectonic setting of hydrothermal activity on the summit of lucky strike seamount 37 17 n mid atlantic ridge we have investigated the relations between volcanic tectonic and hydrothermal activity on lucky strike seamount 37 17 n mid atlantic ridge using a nested survey strategy involving collection of data from different deep sea mapping systems the highly tectonized seamount summit consists of three volcanic cones surrounding a relatively flat depression with a young lava lake in its center hydrothermal activity is focused mainly within the summit depression with most of the vents located proximal to the lava lake isolated active and inactive chimneys and mounds are widespread throughout the summit depression and occur on both volcanic pillow lava and hydrothermal sulfide rubble and hydrothermally cemented breccias substrates the large volume of sulfide rubble together with the nature of the sulfide structures indicates that hydrothermal activity has been episodic but ongoing for a long period of time hundreds to thousands of years on the basis of the distribution of hydrothermal deposits we propose a model of alternation between tectonic and volcanic control on hydrothermalism at lucky strike seamount midsegment melt focusing produces a spatially and temporally stable heat source that sustains focused high temperature hydrothermal activity over long time periods during periods of amagmatic extension active faulting within the summit depression provides multiple near surface fluid flow pathways for discharge of high temperature fluids and widespread deposition of massive sulfides during eruptive events rapid effusion of very hot lava creates a lava lake and hyaloclastite deposits the new sheet flows form a cap on the hydrothermal system and fluid upflow is reorganized discharge of high temperature fluids is restricted to isolated sites with relatively high permeability for example the edges of the lava lake much of the upwelling hydrothermal fluid pools in the subsurface conductively cools and mixes with entrained seawater before discharging as widespread low temperature diffuse flow hyaloclastites become cemented further augmenting the sealing of the system present day activity at lucky strike seamount represents this locally volcanically controlled phase of activity despite the segment as a whole being dominantly amagmatic

fossil evidence for serpentinization fluids fueling chemosynthetic assemblages among the deep sea hydrothermal vent sites discovered in the past 30 years lost city on the mid atlantic ridge mar is remarkable both for its alkaline fluids derived from mantle rock serpentinization and the spectacular seafloor carbonate chimneys precipitated from these fluids despite high concentrations of reduced chemicals in the fluids this unique example of a serpentinite hosted hydrothermal system currently lacks chemosynthetic assemblages dominated by large animals typical of high temperature vent sites here we report abundant specimens of chemosymbiotic mussels associated with gastropods and chemosymbiotic clams in approximately 100 kyr old lost city like carbonates from the mar close to the rainbow site 36 n our finding shows that serpentinization related fluids unaffected by high temperature hydrothermal circulation can occur on axis and are able to sustain high biomass communities the widespread occurrence of seafloor ultramafic rocks linked to likely long range dispersion of vent species therefore offers considerably more ecospace for chemosynthetic fauna in the oceans than previously supposed

selective preservation of soil organic matter in oxidized marine sediments madeira abyssal plain in ocean margin sediments both marine and terrestrial organic matter om are buried but the factors governing their relative preservation and degradation are not well understood in this study we analysed the degree of preservation of marine isoprenoidal and soil derived branched glycerol dialkyl glycerol tetraethers gdgts upon long term oxygen exposure in om rich turbidites from the madeira abyssal plain by analyzing gdgt concentrations across oxidation fronts relative to the anoxic part of the turbidites ca 7 20 of the soil derived branched gdgts were preserved in the oxidized part while only 0 2 3 of the marine isoprenoid gdgt crenarchaeol was preserved due to these different preservation factors the branched isoprenoid tetraether bit index a ratio between crenarchaeol and the major branched gdgts that is used as a tracer for soil derived organic matter substantially increases from 0 02 to 0 4 split flow thin cell splitt separation of turbidite sediments showed that the enhanced preservation of soil derived carbon was a general phenomenon across the fine particle size ranges 38 m calculations reveal that despite their relatively similar chemical structures degradation rates of crenarchaeol are 2 fold higher than those of soil derived branched gdgts suggesting preferential soil om preservation possibly due to matrix protection

pge fractionation in seafloor hydrothermal systems examples from mafic and ultramafic hosted hydrothermal fields at the slow spreading mid atlantic ridge the distribution of platinum group elements pges in massive sulfides and hematite magnetite pyrite assemblages from the recently discovered basalt hosted turtle pits hydrothermal field and in massive sulfides from the ultramafic hosted logatchev vent field both on the mid atlantic ridge was studied and compared to that from selected ancient volcanic hosted massive sulfide vhms deposits cu rich samples from black smoker chimneys of both vent fields are enriched in pd and rh pd up to 227 ppb and rh up to 149 ppb when compared to hematite magnetite rich samples from turtle pits pd up to 10 ppb rh up to 1 9 ppb a significant positive correlation was established between cu and rh in sulfide samples from turtle pits pge chondrite normalized patterns with a positive rh anomaly and pd and au enrichment pd pt and pd au ratios close to global morb and high values of pd ir and pt ir ratios indicate mafic source rock and seawater involvement in the hydrothermal system at turtle pits similarly shaped pge chondrite normalized patterns and high values of pd pt and pd ir ratios in cu rich sulfides at logatchev likely reflect a similar mechanism of pge enrichment but with involvement of ultramafic source rocks

the filon norte orebody tharsis iberian pyrite belt a proximal low temperature shale hosted massive sulphide in a thin skinned tectonic belt the filon norte orebody tharsis iberian pyrite belt is one of the largest pyrite rich massive sulphide deposits of the world the present structure of the mineralization consists of an internally complex low angle north dipping thrust system of variscan age there are three major tectonic units separated by thick fault zones each unit with its own lithologic and hydrothermal features they are internally organized in a hinterland dipping duplex sequence with high angle horses of competent rocks igneous and detritic rocks and massive sulphides bounded by phyllonites the mineralization is within the lower unit and is composed of several stacked sheets of massive sulphides and shales hosting a stockwork zone with no obvious zonation the intermediate unit is made up of pervasively ankeritized shales and basalts spilites here hydrothermal breccias are abundant the upper unit is the less hydrothermally altered one and consists of silicified dacites and a diabase sill the tectonic reconstruction suggests that the sequence is inverted and the altered igneous rocks were originally below the orebody carbon oxygen and sulphur isotopes in the massive sulphides and hydrothermal rocks as well as the mineral assemblage and the paragenetic succession suggest that the sulphide precipitation in the sea floor took place at a low temperature 150 c without indication at least in the exposed section of a high temperature copper rich event sporadic deep subsea floor boiling is probably responsible for the formation of hydrothermal breccias and the wide extension of the stockwork its co au enrichment is interpreted as being related with the superposition of some critical factors such as the relationship with black shales the low temperature of formation and the boiling of hydrothermal fluids the present configuration and thickness of the orebody is due to the tectonic stacking of a thin and extensive blanket 2 4 km2 of massive sulphides with low aspect ratio they were formed by poorly focused venting of hot modified seawater equilibrated with underlying rocks into the seafloor massive sulphide precipitation took place by hydrothermal fluid quenching bacteriogenic activity and particle settling in an unusual restricted euxinic and shallow basin brine pool with a low detritic input but with important hydrothermal activity related to synsedimentary extensional faulting resedimentation of sulphides seems to be of major importance and responsible for the observed well mixed proximal and distal facies the tectonic deformation is largely heterogeneous and has been mostly channelled along the phyllonitic tectonized shales deformation bands thus sedimentary and diagenetic textures are relatively well preserved outside the deformation bands in the massive sulphides superimposed variscan recrystallization is not very important and only some early textures are replaced by metamorphic tectonic ones the stockwork is much more deformed than the massive sulphides the deformation has a critical effect on the present morphology of the orebody and the distribution of the ore minerals this deposit is a typical example of the sheet like shale hosted anoxic low temperature and zn rich massive sulphides developed in a ensialic extensional basin

copper isotope systematics of the lucky strike rainbow and logatchev sea floor hydrothermal fields on the mid atlantic ridge in this paper we present the copper isotope signatures of black smoker sulfides massive sulfides and their alteration products and provide new insights into mineralization processes and applications of copper isotope geochemistry to sea floor hydrothermal systems on the mid atlantic ridge the hydrothermal systems studied include the lucky strike field at 37 17 n on a basaltic substrate and the rainbow and logatchev fields situated on ultramafic rock copper isotope variation in the hydrothermal precipitates was examined in conjunction with s isotopes and se and co concentrations the comparison between 65cu and se contents shows that subsurface precipitation of cu rich sulfides does not control significantly the 65cu values of the hydrothermal chimneys it appears that the major cause of copper isotope fractionation in hydrothermal systems up to 3 is the sea floor oxidation of primary copper sulfides enrichment in the heavy copper isotope can be explained by processes occurring at the sea floor such as hydrothermal reworking of previously altered sulfides by high temperature fluid massive sulfides characterized by negative 65cu values have undergone extensive recrystallization in these mineralogical assemblages isotopically heavy copper typical of altered sulfides has been leached and redeposited in the external zones or incorporated in hydrothermal fluids copper isotopes are therefore a promising tool for the study of supergene processes and the recycling of previously oxidized sulfides as well as a means of characterizing the degree of hydrothermal reworking of large sulfide deposits further studies of copper isotope fractionation under controlled laboratory experimental conditions are required to identify copper isotope fractionation during sulfide alteration in particular the possible biological mediation of copper isotope fractionation during sulfide oxidation may be an important direction for further studies

chemical and mineralogical influences on concentrations of trace metals in hydrothermal fluids abstract concentrations of trace metals in hydrothermal solutions from the southern juan de fuca ridge sjfr and the tag hydrothermal field on the mid atlantic ridge are influenced by the combined effects of source rock composition brine seawater mixing and complex interplay among various metals and minerals deposited and remineralized in vent mounds and chimneys copper mo and co show predicted sharp decreases in concentration for vent fluids as temperatures decrease below 350 c however concentrations of cu in 363 c fluids at the tag site are well above values determined from seawater basalt interactions due to subseafloor refining processes and remineralization of chalcopyrite concentrations of zn cd pb as and ga do not show any temperature dependence between 214 to 363 c however zn values do correlate well with cl on an area by area basis due to subseafloor mixing of brine with altered seawater zinc levels also correlate well with concentrations of cd pb and as for all vent fluid samples as well as with basalt and zn rich sulfides implying some continuity in behavior from source rock to vent fluid to sulfide minerals gallium values correlate with zn and cl levels for the sjfr but are high relative to zn at the tag site due to subseafloor refining processes concentrations of tl follow cl k and rb consistent with the behavior predicted for tl overall the cl and zn rich fluids from the sjfr are characteristic of a brine dominated system formed during recent volcanism in contrast high temperature fluids from the tag area are representative of a system that has evolved over the past 100 000 yr with high concentrations of cu co and ga that result from higher temperatures and complex refining processes within a large vent mound

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

influences of the tonga subduction zone on seafloor massive sulfide deposits along the eastern lau spreading center and valu fa ridge abstract this study investigates the morphology mineralogy and geochemistry of seafloor massive sulfide sms deposits from six back arc hydrothermal vent fields along the eastern lau spreading center elsc and valu fa ridge vfr in the context of endmember vent fluid chemistry and proximity to the tonga subduction zone to complement deposit geochemistry vent fluid analyses of cu zn ba pb and h 2 aq were completed to supplement existing data and enable thermodynamic calculations of mineral saturation states at in situ conditions results document southward increases in the abundance of mantle incompatible elements in hydrothermal fluids ba and pb and sms deposits ba pb as and sb which is also expressed in the abundance of barite baso 4 and galena pbs in sms deposits these increases correspond to a decrease in distance between the elsc vfr and the tonga subduction zone that correlates with a change in crustal lithology from back arc basin basalt in the north to mixed andesite rhyolite and dacite in the south barite influences deposit morphology contributing to the formation of horizontal flanges and squat terraces results are also consistent with a regional scale lowering of hydrothermal reaction zone temperatures from north to south except at the southernmost mariner vent field that leads to lower temperature higher ph vent fluids relative to mid ocean ridges of similar spreading rates mottl et al 2011 these fluids are cu and zn poor and the deposits formed from these fluids are cu poor but zn rich in contrast at the mariner vent field higher temperature and lower ph vent fluids are hypothesized to result from higher reaction zone temperatures and the localized addition of acidic magmatic volatiles mottl et al 2011 the mariner fluids are cu and zn rich and vent from sms deposits that are rich in cu but poor in zn with moderate amounts of pb thermodynamic calculations indicate that the contrasting metal contents of vent fluids and sms deposits can be accounted for by vent fluid ph wurtzite sphalerite zn fe s and galena pbs are saturated at higher temperatures in higher ph zn cu and pb poor elsc vfr vent fluids but are undersaturated at similar temperatures in low ph zn cu and pb rich vent fluids from the mariner vent field indicators of ph in the elsc and vfr sms deposits include the presence of co precipitated wurtzite and chalcopyrite along conduit linings in deposits formed from higher ph fluids and different correlations between concentrations of zn and ag in bulk geochemical analyses significant positive bulk geochemical zn ag correlations occur for deposits at vent fields where hydrothermal fluids have a minimum ph at 25 c 3 6 data show that the compositions of the mineral linings of open conduit chimneys minerals present mol fes in zn fe s that precipitate directly from hydrothermal fluids closely reflect the temperature and sulfur fugacity of sampled hydrothermal fluids these mineral lining compositions thus can be used as indicators of hydrothermal fluid temperature and composition ph metal content sulfur fugacity

sulfide geochronology along the northern equatorial mid atlantic ridge abstract hydrothermal processes and seafloor massive sulfide sms deposits have different characteristics at fast and slow spreading mid ocean ridges one such parameter is the age of a sms deposit which differs by 1 2 orders of magnitude between the fast spreading east pacific rise epr and the slow spreading mid atlantic ridge mar the large collection of sms samples dated from the 18 hydrothermal fields of the northern equatorial part of the mid atlantic ridge 194 samples demonstrates a relatively old average age of hydrothermal fields here 66 ka with the oldest one estimated as ca 223 ka peterburgskoye field based on geochronological data it was confirmed that hydrothermal discharge has an episodic character active and inactive periods of the sms formation alternate the distribution of events at all hydrothermal fields demonstrates that maximum activity occurred at 38 35 30 20 and 8 2 ka and increased with time based on statistical analyses dating variations can be explained as a superposition of several periods of activity with the duration of 15 10 and 5 ka relationship between the age and distance from the axial rift zone as well as between the age and aerial distribution is different for sms deposits hosted by basalts and by gabbro peridotites depending on their geological setting on the particular mar segment this difference can be explained by a variety of hydrothermal processes determined by tectonic or magmatic segment evolution and symmetrical or asymmetrical mode of accretion escartin et al 2008

twentieth century proxy records of temperature and soil organic matter input in the drammensfjord southern norway abstract the drammensfjord in southern norway is an enclosed anoxic basin with a laminated sedimentary record the fjord is a transition area between the marine and terrestrial environments and thus its sedimentary archive contains information on both environments in order to reconstruct recent environmental changes in southern norway two sediment cores covering the last 90 years were analyzed we used the branched versus isoprenoid tetraether bit index as an indicator of terrestrial organic mater input and compared it to the stable carbon isotopic composition of total organic carbon 13 c toc the 13 c toc and bit index show opposing trends with 13 c toc indicating an increase in terrestrial input while the bit index suggests a decrease towards the present this contradiction is probably due to the different sources reflected by 13 c toc vegetation soil and anthropogenic input and the bit index only soil organic matter input in addition an increase in the recycling of respired co 2 within the fjord s water column could have depleted the 13 c toc of the marine component towards more negative values thus seemingly indicating an increase in terrestrial input whilst the bit index could have been affected by a reduction of riverine input and or an increase in archaeal biomass production the tetraether index of lipids with 86 carbons tex 86 was determined as a proxy for past water surface temperatures while some of the signal could be coming from the chemocline our results suggest that tex 86 indicates surface upper 25 m temperatures moreover tex 86 temperature patterns seem to follow variations in the historical record of averaged spring to fall oslo air temperature relatively closely suggesting the signal is produced during this period therefore tex 86 temperature records of fjord sediment cores can potentially be a useful tool in reconstructing past variations of coastal climates

pinguino in bearing polymetallic vein deposit deseado massif patagonia argentina characteristics of mineralization and ore forming fluids the pinguino deposit located in the low sulfidation epithermal metallogenetical province of the deseado massif patagonia argentina represents a distinct deposit type in the region it evolved through two different mineralization events an early in bearing polymetallic event that introduced in zn pb ag cd au as cu sn w and bi represented by complex sulfide mineralogy and a late ag au quartz rich vein type that crosscut and overprints the early polymetallic mineralization the indium bearing polymetallic mineralization developed in three stages an early cu au in as sn w bi stage ps1 a zn pb ag in cd sb stage ps2 and a late zn in cd ps3 indium concentrations in the polymetallic veins show a wide range 3 4 to 1 184 ppm in the highest indium values up to 1 184 ppm relate to the ps2 mineralization stage and are associated with fe rich sphalerites although significant in enrichment up to 159 ppm is also present in the ps1 paragenesis associated with sn minerals ferrokesterite and cassiterite the hydrothermal alteration associated with the polymetallic mineralization is characterized by advanced argillic alteration within the immediate vein zone and sericitic alteration enveloping the vein zone fluid inclusion studies indicate homogenisation temperatures of 308 2 327 c for ps1 and 255 312 4 c for ps2 and low to moderate salinities 2 to 5 eq wt nacl and 4 to 9 eq wt nacl respectively 34s values of sulfide minerals 0 76 to 3 61 indicate a possible magmatic source for the sulfur in the polymetallic mineralization while pb isotope ratios for the sulfides and magmatic rocks 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 17 379 to 18 502 15 588 to 15 730 and 38 234 to 38 756 respectively are consistent with the possibility that the pb reservoirs for both had the same crustal source spatial relationships hydrothermal alteration styles s and pb isotopic data suggest a probable genetic relation between the polymetallic mineralization and dioritic intrusions that could have been the source of metals and hydrothermal fluids mineralization paragenesis alteration mineralogy geochemical signatures fluid inclusion data and isotopic data confirm that the in bearing polymetallic mineralization from pinguino deposit is a distinct type in comparison with the well known epithermal low sulfidation mineralization from the deseado massif

an unusual isoprenoid tetraether lipid in marine and lacustrine sediments abstract recent studies have shown that glycerol dialkyl glycerol tetraether gdgt lipids thought be unique for hyper thermophilic archaea are also present in non thermophilic archaea and environments in this study an unusual h shaped isoprenoid gdgt in which the two biphytanyl carbon skeletons are covalently bound by a carbon carbon bond was unambiguously identified in a number of sediments from marine and lacustrine environments its abundance varies from 0 2 to 6 of isoprenoid gdgts the h shaped isoprenoid gdgt was originally identified in hyperthermophilic archaea and its presence in marine and lacustrine sediments suggests it is also synthesized by certain non thermophilic relatives possibly euryarchaeota

detailed geological mapping of two contrasting second order segments of the mid atlantic ridge between oceanographer and hayes fracture zones 33 30 n 35 n we present detailed geological mapping of the axial valley floor and ridge flanks of two neighboring but contrasting spreading segments oh1 and oh3 of the mid atlantic ridge between oceanographer and hayes fracture zones new in situ observations from the submersible nautile correlated with swath bathymetry and acoustic backscattering data from these segments reveal that the along and across axis volcanic tectonic variability within second order segments is larger than commonly acknowledged segment oh1 is a long and robust segment with a narrow and shallow axial valley the most intense magmatic activity is found at the segment center where the thickest crust has been imaged suggesting focused magma supply away from this part of the segment faulting and sedimentary cover predominate in contrast the center of segment oh3 is dominated by extensive sedimentary cover fissuring and faulting furthermore the most recent constructional volcanism is located away from the segment center in a region of greater depth and thinner crust this relocation of volcanism suggests either a recent shift in the magmatic source or the last vestige of a centrally located source fed by lateral dike injection segment tip magmatic oscillations are suggested by the distribution of rock types at both segment ends serpentinized peridotites and associated dolerites are exposed at the massifs located at the intersection with nontransform offsets ntos whereas only basaltic rocks crop out on the nodal basin floors we suggest that the combination of low magmatic budget and extension taking place at the ntos during a segment retreat favors the uplift and exposure of ultramafic massifs

mineralogy and geochemistry of hydrothermal sediments from the serpentinite hosted saldanha hydrothermal field 36 34 n 33 26 w at mar abstract the saldanha hydrothermal field is located at the top of a serpentinized massif mount saldanha ms at a non transform offset nto5 along the mid atlantic ridge mar south of the azores it is one of the rare known sites on a worldwide basis where direct evidence of low temperature 7 9 c hydrothermal activity has been provided by direct observation of hydrothermal fluid venting through small orifices in the ocean floor sedimentary cover this study focuses on the mineralogy and geochemistry of 14 sediment cores collected at ms for comparison four samples collected at the rainbow site nto6 were also studied mount saldanha hydrothermal sediments are highly diluted within a dominant foraminiferal nanofossiliferous ooze with small fragments of underlying rocks the mineral assemblage of the hydrothermal component is characterized by sulphides nontronite smectites poorly crystallized mn oxyhydroxides and amorphous material cu zn and fe sulphides mn mg oxy hydroxides and putative manganobrucite were also identified in one sample collected at an orifice vent in this sample micro chimneys conduits composed of isocubanite and sphalerite were also identified mount saldanha sediments show a clear enrichment in elements such as mn mg fe cu p and v derived from hydrothermal fluids and ni cr and co derived from ultramafic rocks the geochemical data together with the observed mineral assemblage suggest that the hydrothermal fluids are at a higher temperature than those measured at the escape orifices 7 9 c and a strong enrichment in mg mainly at the top of the mount agrees with extensive mixing of the hydrothermal fluid with unmodified seawater nevertheless the mineral assemblage of ms sediments is consistent with the precipitation from hydrothermal fluids at much lower temperatures than at rainbow the presence of serpentinized and steatitized talcshist ultramafic rocks and the occurrence of a strong methane anomaly within the overlying water column collectively suggest that the hydrothermal circulation at ms is driven by exothermic reactions closely associated with the serpentinization process rainbow sediments have a higher concentration in transition metals and consequently an enrichment in sulphides these differences are likely to be a consequence of the higher temperature of hydrothermal fluids reflected in the composition of hydrothermal solutions and of a stronger hydrothermal flux at the rainbow site

redox changes in a seafloor hydrothermal system recorded in hematite chalcopyrite chimneys abstract hydrothermal chimneys composed of hematite and chalcopyrite grow at the irina ii vent site logatchev hydrothermal field mid atlantic ridge hematite and chalcopyrite form layers that repeatedly alternate within the chimney wall the repeating alternation of hematite and chalcopyrite implies for repeating changes in the physico chemical parameters of the vent fluid the modeled stability diagrams of hematite and chalcopyrite at the physico chemical conditions of the irina ii hydrothermal site showed that the precipitation of these two fe minerals is primarily governed by the activity of h2s and ph fe isotope studies suggest that the successive deposition of chalcopyrite 56 54fe 0 20 and hematite 56 54fe 0 60 layers in the irina ii chimneys is a result of redox changes in the hydrothermal fluid the replacement of hematite by either magnetite or chalcopyrite at some places also suggests for a redox inversion in the hydrothermal system from oxic to reduced chondrite normalized rare earth element distribution patterns of the hematite layers show a strong negative eu anomaly which is interpreted to be a result of crystal chemical control on the rare earth element fractionation during hematite precipitation sr isotope systematics indicate significant and variable incorporation of seawater from 40 to 80 in the hydrothermal system nd pb isotope studies show that nd and pb in chalcopyrite and hematite layers are derived mainly from the underlying mafic and ultramafic rocks the chimneys are young 5 13 1 28 kyrs b p and their wall thickened inward the duration of redox cycles oxic and reducing within the scale of a single chimney is about several hundred years the hematite layers are enriched in w in sn and u indicating that primary hematite hydrothermal deposits at the seafloor may be a potential source for these strategic trace elements high concentrations of these elements in the studied hematite layers can be explained by their easy ion substitution for fe3 in the hematite crystal lattice whereas the most plausible source of the elevated w in and sn contents are the hydrothermal fluids the seawater is the possible major source of u

effects of long term oxic degradation on the u37k tex86 and bit organic proxies abstract one of the primary prerequisites for the application of organic proxies is that they should not be substantially affected by diagenesis however studies have shown that oxic degradation of biomarker lipids can affect their relative distribution we tested the diagenetic stability of the u 37 k and tex86 palaeothermometers upon long term oxygen exposure for this purpose we studied the distributions of alkenones and glycerol dialkyl glycerol tetraethers gdgts in different sections of turbidites at the madeira abyssal plain map that experienced different degrees of oxygen exposure sediments were deposited anoxically on the shelf and then transported by turbidity currents to the map which has oxic bottom water this resulted in partial degradation of the turbidite organic matter as a result of long term exposure to oxic bottom water concentrations of gdgts and alkenones were reduced by one to two orders of magnitude in the oxidized parts of the turbidites compared to the unoxidized parts indicating substantial degradation high resolution analysis of the pleistocene f turbidite showed that the u 37 k index of long chain alkenones increased only slightly 0 01 corresponding to u 37 k while for other pliocene miocene turbidites it either remained unchanged or decreased substantially up to 0 06 corresponding to 6 c previous observations showed that the bit index a proxy for the contribution of soil organic matter to total organic carbon was always substantially higher in the oxidized part in all the turbidites as a result of preferential degradation of marine derived gdgts this relative increase in soil derived gdgts affects tex86 as the isoprenoid gdgt distribution on the continent can be quite different from that in the marine environment our results indicate that the organic proxies are affected by long term oxic degradation to different extents this should be taken into account when applying these proxies in palaeoceanographic studies of sediments which have been exposed to prolonged oxic degradation

distributions and temperature dependence of branched glycerol dialkyl glycerol tetraethers in recent lacustrine sediments from china and nepal 1 glycerol dialkyl glycerol tetraether gdgt membrane lipids in surface sediments from 24 lakes in china and nepal were analyzed the result shows that branched gdgt lipids occur widely in the studied lake sediments the different distribution of branched gdgts between the chinese soils from weijers et al 2007b and the chinese lake sediments indicates that the branched gdgts in the lacustrine sediment are the mixture of allochthonous and autochthonous branched gdgts our result supports the suggestion that temperature is the principal factor affecting the distribution of gdgts seasonality sources and precipitation increase the uncertainty of the correlation between the methylation index of branched tetraethers mbt cyclization ratio of branched tetraethers cbt proxy and the temperature the correlations of the mbt cbt index with mean annual air temperature t for the global lakes are t 6 803 7 062 cbt 37 090 mbt n 139 p 0 0001 r2 0 62 and rmse 5 24 c for the global lakes with ph 8 5 t 3 949 5 593 cbt 38 213 mbt n 100 p 0 0001 r2 0 73 and rmse 4 27 c the significant correlation suggests that the mbt cbt proxy might be used as a potential paleotemperature proxy in the limnic environment the mbt cbt proxy provides an independent way to evaluate and verify the sensitivities of the different proxies for paleotemperature reconstruction from lacustrine sediments

nitrogen isotopes in lunar highlands breccias abstract some breccias from the lunar highlands have probably trapped solar wind gases at a very early epoch in the history of the moon as implied by their high contents of parentless fissiogenic xenon and sometimes of parentless radiogenic129xe four samples of this type on which noble gas data already exist have been selected for analysis of nitrogen contents and isotopic composition by using step wise heating techniques 14047 14055 14307 60255 since uncertainties in the evolution of the solar wind15n 14n ratio with time are due in part to uncertainties in the measurement of the epoch of exposure those samples provided the opportunity to measure the isotopic composition of nitrogen which has been trapped in the remote past avoiding the problems inherent in the use of spallogenic nuclides results show that in the samples studied from the apollo 14 landing site nitrogen is not particularly light and has not been acquired as a whole in very ancient times the conflicting presence of both parentless xenon and nitrogen of relatively recent isotopic signature can be explained if the hypothetical light nitrogen is diluted by more abundant heavier nitrogen accordingly the very ancient soil components which are implied in these objects by the presence of excess fission xenon have been re exposed at a much later epoch or mixed with some younger soil components before the compaction event the present data do not question the hypothesis of a secular isotopic variation of lunar trapped nitrogen but cannot prove that very light nitrogen was trapped together with parentless fission xenon in the soil components of the highlands soil breccias the very unusual release pattern of nitrogen in breccia 60255 can result from nitrogen isotopic homogenization with gas loss

recent tectonic magmatic and hydrothermal activity on the east pacific rise between 17 s and 19 s submersible observations the objective of the naudur cruise december 1993 of the submersible nautile was to study the interaction among magmatic tectonic and hydrothermal processes at a very fast spreading mid ocean ridge axis twenty three dives were completed both along and across the axis in four areas located between 17 10 and 18 45 s on the east pacific rise rock sulfides water and biological samples have been collected along each of the segments two main types of segments have been distinguished characterized either by the predominance of present day volcanic activity or by predominant tectonic activity linked to both types of activity 69 hydrothermal sites have been discovered and sampled they comprise four types interpreted as successive evolutionary stages the first are shimmering water sites which occur immediately after the formation of lava lakes and are characterized by large surface area and poorly developed associated fauna the second in areas dominated by recent volcanic activity have waters venting directly from lava fissures and more focused discharge areas through black smoker chimneys the third stage is represented by more mature hydrothermal vents and deposits along the faults bounding the eastern side of the axial graben in tectonic dominated areas the associated fauna is well developed the fourth stage corresponds to the reactivation of volcanic activity with lava flows young black smokers and diffuse venting associated with the faults bounding the axial graben fluids collected range from 200 to 340 c and show a wide variability in chemical and gas composition within each of the explored areas evidence of recent volcanic activity has been observed

mineralogy and geochemistry of hydrothermal precipitates from kairei hydrothermal field central indian ridge the kairei hydrothermal field was the first confirmed active submarine hydrothermal system on the central indian ridge it has been suggested to be related to mafic as well as ultramafic host rocks based on vent fluid composition and the presence of ultramafic rocks in its vicinity in this study detailed geochemical and mineralogical analyses have been carried out on the hydrothermal precipitates from the kairei vent field in order to investigate the possible presence of indications for an ultramafic substrate at this vent site the studied samples included fragments of sulfide chimneys massive sulfides and talc bearing and silicified breccias three mineralization stages were identified 1 a high temperature stage consisting largely of chalcopyrite isocubanite and pyrite 2 a medium to low temperature stage characterized by the mineral assemblages of sphalerite and pyrite and 3 a weathering stage characterized by secondary cu sulfides bornite digenite covellite and idaite fe oxihydroxides opal a and cu chloride paratacamite and atacamite the sulfide geochemistry is characterized by high concentrations of cu and zn cu zn up to 29 3 wt n 17 and au mean 5 28 ppm n 17 which is comparable to results from seafloor massive sulfides collected from ultramafic hosted sites in the atlantic ocean but differs from those of typical mafic hosted deposits the high concentrations of cu and au at the kairei hydrothermal field could be an indication for the involvement of ultramafic rocks in the subseafloor ultramafic hosted au rich sulfide deposits may not be restricted to the atlantic ocean and may be common along all slow and intermediate spreading ridges

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