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

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

world s largest known precambrian fossil black smoker chimneys and associated microbial vent communities north china implications for early life abstract black smoker chimneys and biological vent communities have been identified at many sites on the deep seafloor particularly along oceanic spreading centers we report the largest and oldest known microbe rich sub meter sized black smoker chimneys and mounds from a 1 43 billion year old sulfide deposit in a continental graben in northern china these chimneys are especially well preserved with characteristic morphology internal textures and internal cylindrical mineralogical zonation four main types of chimneys are distinguished on textural and mineralogical criteria exhibiting either zn fe sulfide or pb zn fe sulfide internal cylindrical mineralogical zones the chimneys mark vent sites in submarine grabens indicating focused flow venting processes the fossil chimneys have mineralogical and geological evolutionary features similar to their counterparts on the modern seafloor and other submarine hydrothermal vents black smoker vent fluids and seafloor tectonism played important roles for formation of the massive sulfide deposits in the mesoproterozoic we also report the first known remarkably diverse assemblage of fossil microbialites from around and inside precambrian vent chimneys demonstrating that proterozoic life flourished around submarine hot vents and deep within the chimney vent passages filamentous spherical rod and coccus shaped fossil microbes are preserved preferentially on sulfide precipitates based on the depth and setting of the fossil biota the organisms that produced the microbialites were likely sulfate reducing chemosynthetic and thermophyllic microbes textural and mineralogical evidence shows that biomineralization processes enhanced chimney growth and sulfide precipitation close association of microorganisms with sulfide chimneys in modern deep sea hydrothermal vents and younger ophiolites has sparked speculation about whether life may have originated at similar vents however little is known about fossil equivalents of vent microfossils and black smoker chimneys from earth s early evolution the fossilized microorganisms from the gaobanhe black smoker chimney sulfide deposits include thread like filaments with branching and twisted forms and preserved organic carbon representing fossilized remnants of microbial mats metabolized at high temperatures characteristic of venting fluids the preservation of fossil microorganisms provides evidence that microbial populations were closely associated with black smoker chimneys in earth s early history the microbial population clearly constitutes the site for mediating mineral formation these ancient microbial fossils lead to a much better understanding of early life on the deep seafloor the discovery of the mesoproterozoic microfossils within black smoker hydrothermal chimneys indicates that hydrothermal activity around sea floor vents supported dense microbial communities and supports speculation that vent sites may have hosted the origin of life

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

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

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

origin of fe mn si layers associated with the permian volcanic hosted massive sulphide deposits in the tasik chini district peninsular malaysia abstract the volcanic hosted massive sulphide vhms deposits in the tasik chini district peninsular malaysia are hosted in permian volcano sedimentary rocks and are composed of fe mn si layers which occur stratigraphically above the ore bodies the oxide layers are 1 cm to 2 m thick and occur discontinuously throughout the bukit botol deposit whereas layer of oxides up to 10 m thick occurs continuously over a strike length of over 50 m at the bukit ketaya deposit their mineralogy is dominated by hematite quartz barite magnetite pyrite clastic components and commonly exhibit massive iron silica banding to microbreccia like textures the fe mn si layers from the bukit botol and bukit ketaya deposits generally have high si fe mn and base metals contents various proportions of al zr and ti and high levels of ba as u and v such mineralogical and geochemical concentrations and other geological suggest that the associated fe mn si layers were deposited by the mixing of mainly chemical components and to a smaller degree detrital components in a local submarine environment due to hydrothermal activity on the seafloor

radiochronological investigation of hydrothermal deposits from the meso zone central indian ridge abstract hydrothermal activity in the indian ocean has hitherto only been poorly documented first indications of hydrothermal mineralization were observed in 1987 during the gemino cruise over the 4th ridge segment of the central indian ridge 270 km north of the rodriguez triple junction subsequent cruises in 1993 hydrotrunc and in 1995 hydrock were carried out in order to obtain detailed information about the geological setting and the extent and mineral distribution of the field but primarily to sample the first massive sulfides of the indian ocean floor this hydrothermal field which was called the meso zone was studied by detailed mapping and by ocean bottom photography hydrothermal precipitates were recovered with a tv grab sampler at four sampling locations two in the northern part of the mineralized field called the talus tips site and two in the central part called the sonne field the sulfide samples were age dated using the 230 th 234 u method they show different periods of activity at each site 52 5 22 7 3 and 16 2 ka for the main events at the talus tips site and 18 2 and 12 5 1 5 ka for the sonne field we conclude from these data that the two sites were not active at the same time if it is assumed that there is a complete cessation of activity between 52 and 23 ka for more recent periods from 23 to 10 ka it may be postulated that the deep seated hydrothermal circulation is continuous but that the discharge of hot fluid occurs alternately at the sonne field or at the talus tips site comparing our results with those obtained previously at the different hydrothermal sites we favor the conclusion of episodic activity moreover in the sonne field jasper formation resulting from a low temperature hydrothermal event dated at around 11 ka is presently the youngest hydrothermal formation in the entire meso zone

life on the edge microbial biomineralization in an arsenic and lead rich deep sea hydrothermal vent abstract unravelling complex microbial activity in modern hydrothermal vents can provide crucial insights into the evolution of ancient life on earth it is well established that microorganisms in hydrothermal vents have a significant impact on the cycling of metals and mineral formation however the detailed roles played by microorganisms in driving sulfide deposition and cycling of toxic metals like arsenic as and lead pb in high temperature deep sea hydrothermal vents remain unknown the understanding of these mechanisms in extreme environments is of particular importance as as has been postulated as a driver of microbial activities on the early earth here we present the first geologic evidence of pb as rich microbial filamentous clusters observed in a modern high temperature black smoker from the manus back arc basin papua new guinea the clusters occur as net like structures on the surface of barite and sulfides and are composed of multiple filaments and fine grained pb as sulfosalt each of the filaments includes an as pb rich sulfosalt core and organic rich shell structure with elevated carbon nitrogen and phosphorus further synchrotron x ray absorption near edge structure analysis shows that the clusters contain a mixture of as ii and as iii additionally those filaments show a close association with realgar as4s4 by penetrating and dissolving this as sulfide mineral we interpret the filaments to be a result of as related microbial activity in as and pb enriched hydrothermal environments the findings show possible processes through which extremophiles live in pb and as rich environments during chimney growth in addition as hydrothermal vents are regarded as modern analogs of ancient volcanogenic massive sulfide deposits the observed biominerals present the potential to be used as proxies to trace the signatures of early life in ancient geological systems

do marine moulds influence hg and si precipitation in the hydrothermal jade field okinawa trough abstract several massive sulfide smoker fragments from the jade field okinawa trough japan yielded filamentous aggregates of both cinnabar hgs and amorphous silica si02 resembling fungal hyphens for this similarity polished and thin sections of filaments were compared with recent moulds that had formed on sulfide samples since the influence of marine moulds on mineral precipitation is poorly known studies on bacterial and algal mineralization mechanisms were reviewed to generally identify microbial metabolism processes that could lead to the formation of the observed filaments the development of hgs pseudomorphs is likely to have occurred through methylation reactions while the filament replacement by silica probably happened via an intermediate formation of silica carbon compounds followed by a successive breakdown of these phases under changing geochemical conditions

tube fossils from gossanites of the urals vhms deposits russia authigenic mineral assemblages and trace element distributions abstract the occurrence types morphology and mineralogical characteristics of tube microfossils were studied in gossanites from twelve vhms deposits of the urals several types of tube microfossils were recognized including siboglinids polychaetes and calcerous serpulids replaced by a variety of minerals e g hematite quartz hematite chlorite carbonate hematite depending on the nature of the substrate prior to the formation of the gossanites colonial hematite tube microfossils 150 m across 1 2 mm long are composed of hematitic outer and inner walls and may exhibit a cellular structure within their cavities spherical forms are saturated with fe oxidizing bacteria inside the tubes probably analogues of trophosomes colloform stromatolitic outer wall surfaces are characterized by the presence of numerous interlaced filaments of hematite 2 3 m diameter up to 1 2 mm long between tube microfossils the hematitized cement contains bundles of hematitized filaments with structures similar to the hyphae of fungi hematite chlorite tube microfossils are scattered in gossanites mostly as biological debris they are typically 30 to 300 m in diameter and 1 to 5 mm long the layered structure of their tube walls is characterized by hematite quartz and chlorite layers abundant filamentous bacteria coated by glycocalix and chlorite stromatolite are associated with hematite chlorite tubes the carbonate hematite tube microfossils up to 300 m across 2 3 mm long occur in carbonate rich gossanites the tubes are characterized by fine 10 m thick walls of hematite and cavities dominated by relatively dark carbonate or hematite carbonates may be present both in walls and cavities stromatolite like leucoxene or hematite carbonate aggregates were also found in association with tubes randomly oriented filaments are composed of ankerite single filaments are composed of individual cells typically smaller than 100 nm across similar to that of magnetotactic bacteria three dimensional tomographic images of all types of tube microfossils demonstrate a clear wavy microlayering from outer and inner walls which may reflect segmentation of the tube worms the traces of burrowing or fragments of glycocalix with relict spheres are typical of tube microfossils from gossanites the carbon isotopic composition of carbonates associated with tube microfossils from hematite quartz hematite carbonate and hematite chlorite gossanites average 7 2 6 8 22 8 pdb respectively these values are indicative of a biogenic origin for the carbonates the oxygen isotopic composition of these carbonates is similar in all three gossanite types averaging 13 5 14 2 13 0 relative to smow and indicative of active sulfate reduction during the diagenetic and anadiagenetic stages of the sediments evolution the trace element characteristics of hematite from tube microfossils are characterized by high contents of following trace elements average ppm mn 1529 as 714 v 540 w 537 mo 35 and u 5 such high contents are most likely the result of metal and metalloid sorption by fine particles of precursor iron hydroxides during the oxidation of sulfides and decomposition of hyaloclasts via microbially mediated reactions

hydrothermal silica chimney fields in the galapagos spreading center at 86 w silica chimneys were discovered in 1985 at 86 w in the rift valley of the galapagos spreading center at 2600 m depth cauliflower garden the inactive chimneys lack any sulfides and consist almost entirely of amorphous silica up to 96 wt sio2 opal a fe and mn oxides are minor constituents oxygen isotope data show that formation of the silica chimneys took place at temperatures between 32 c 29 9 18o and 42 c 27 8 18o th udating reveals a maximum age of 1440 300y amorphous silica solubility relations indicate that the silica chimneys were formed by conductive cooling of pure hydrothermal fluids or by conductive cooling of a fluid seawater mixture assuming equilibrium with quartz at 500 bars initial fluid temperatures of more than 175 c i e a concentration of 182 ppm sio2 were required to achieve sufficient supersaturation for the deposition of amorphous silica at 40 c and 260 bars if the silica chimneys originate from the same or a similar fluid as higher temperature 300 c sulfide silica precipitates found nearby i e 2 5 km away then subsurface deposition of sulfides may have occurred

geochemical studies on permian manganese deposits in guichi eastern china implications for their origin and formative environments abstract permian manganese ore deposits are widely distributed in southwestern and eastern china guichi permian manganese district in southern anhui province central eastern china is currently the most important manganese metal producers in eastern china manganese ores mno 18 2 45 4 wt in guichi region occur in calcareous argillaceous and siliceous mn bearing sequence of the permian gufeng formation in contrast to mn bearing rocks the ores have higher mn fe p sr more than 1500 ppm and ni contents 480 ppm higher mn fe 5 and lan cen 2 values and lower co ni

bedded jaspers of the ordovician lokken ophiolite norway seafloor deposition and diagenetic maturation of hydrothermal plume derived silica iron gels sedimentary beds of jasper red hematitic chert in the ordovician lokken ophiolite of norway are closely associated with volcanogenic massive sulphide vms deposits the jaspers occur in the immediate hangingwall and laterally peripheral to the large lokken 25 30 mt and small hoydal 0 1 mt vms deposits and are exposed discontinuously for several kilometres along strike massive or laminated types predominate jasper sulphide debris flow deposits are also abundant near vms deposits the jaspers contain hematite rich laminae showing soft sediment deformation structures and microtextural evidence that record the presence of a colloidal precursor and an origin as gels early textures include 1 straight or curved chains of hematitic filaments 3 10 m in diameter and 20 100 m long 2 branching networks of 15 25 m thick tubular structures surrounded by cryptocrystalline hematite and filled with quartz and euhedral hematite 3 small up to 10 m spherules composed of cryptocrystalline hematite and silica and 4 up to 50 m silica spherules with hematitic cores the small filaments seem to have been deposited in varying proportions in the primary laminae possibly together with hematitic and siliceous microspheroids diagenetic changes are represented by polygonal syneresis cracks and the presence of cryptocrystalline originally opaline silica chalcedony quartz carbonate and cryptocrystalline hematite and or goethite forming botryoidal masses and spheroids 10 m to 5 mm in diameter coarser euhedral grains of quartz carbonate and hematite are integral parts of these textures bleached silica rich jaspers preserve only small relics of fine grained hematite rich domains and locally contain sparse pockets composed of coarse euhedral hematite epidote

paleozoic and mesozoic silica rich seawater evidence from hematitic chert jasper deposits laterally extensive beds of highly siliceous hematitic chert jasper are associated with many volcanogenic massive sulfide vms deposits of late cambrian to early cretaceous age yet are unknown in analogous younger including modern settings textural studies suggest that vms related jaspers in the ordovician lokken ophiolite of norway were originally deposited as si and fe rich gels that precipitated from hydrothermal plumes as colloidal silica and iron oxyhydroxide particles rare earth element patterns and ge si ratios of the jaspers reflect precipitation from plumes having seawater dilution factors of 10 3 to 10 4 similar to modern examples we propose that silica in the ancient jaspers is not derived from submarine hydrothermal fluids as suggested by previous workers but instead was deposited from silica rich seawater flocculation and precipitation of the silica were triggered inorganically by the bridging effect of positively charged iron oxyhydroxides in the hydrothermal plume a model involving amorphous silica opal a precursors to the jaspers suggests that silica contents of cambrian early cretaceous oceans were at least 110 mg l sio 2 compared to values of 40 60 mg l sio 2 estimated in other studies the evolution of ancient silica rich to modern fe rich precipitates in submarine hydrothermal plumes reflects a changeover from silica saturated to silica depleted seawater through phanerozoic time due mainly to ocean wide emergence of diatoms in the cretaceous

mineralized microbes from giggenbach submarine volcano 1 the giggenbach submarine volcano which forms part of the kermadec active arc front is located 780 km nne of the north island of new zealand samples collected from chimneys associated with seafloor hydrothermal vents on this volcano at a depth of 160 180 m contain silicified microbes and microbes entombed in reticular fe rich precipitates the mineralized biota includes filamentous rod shaped and rare coccoid microbes in the absence of organic carbon for rdna analysis or preserved cells the taxonomic affinity of these microbes in terms of extant taxa remains questionable because of their architectural simplicity and the paucity of taxonomically significant features the three dimensional preservation of the microbes indicates rapid mineralization with a steady supply of supersaturated fluids to the nucleation sites present on the surfaces of the microbes the mineralization styles evident in the microbes from the giggenbach submarine volcano are similar to those associated with mineralized microbes found in terrestrial hot spring deposits in new zealand iceland yellowstone and kenya these similarities exist even though the microbes are probably different and the fluids become supersaturated with respect to opal a by different mechanisms for ancient rocks it means that interpretations of the depositional settings cannot be based solely on the silicified microbes or their style of silicification

siliceous sublacustrine spring deposits around hydrothermal vents in lake taupo new zealand chimneys around hydrothermal vents at a depth of c 140 m in the horomatangi reefs area in lake taupo new zealand are composed of amorphous silica opal a with lesser amounts of mn fe and hg rich precipitates detrital quartz and feldspar grains are found in the surrounding sediments the associated biota includes fish bacteria sponges crayfish amphipods copepods ostracodes annelids and other unidentified organisms much of this biota however is not preserved in the opal a deposits instead the silicified biota includes filamentous microbes and diatoms scattered coccoid microbes fungal hyphae and spores rare sponge spicules and rare worm tubes the diatoms coccoid microbes and fungi were brought into the area with the detrital sediment in ancient successions distinction between sublacustrine terrestrial and some marine hot spring deposits may be difficult because the precipitates share many similarities distinction based on the biota is viable only if palaeoecological information can be inferred from accurately identified organisms unfortunately silicification commonly disguises microbes and precludes their accurate identification diagenetic transformation of opal a to its more stable polymorphs also destroys many original depositional fabrics and silicified microbes distinction between the different types of spring deposit may therefore depend on the interpretation of their overall sedimentological and stratigraphic setting

native aluminium spherules and particles in the central indian basin sediments implications on the occurrence of hydrothermal events abstract we have sampled particles of native aluminium al in two sediment cores from the central indian basin cib the cores are geographically separated but are located at the base of two seamounts the native al particles occurring as grains and spherules have an average al content of 95 and are associated with volcanogenic hydrothermal material morphologically and compositionally the specimens are similar to those reported from the east pacific rise after ruling out several processes for the presence of the native al we hypothesize that during progressive melting of magma a basaltic magma is produced which has high contents of reductants such as methane and hydrogen and a low oxygen fugacity during the upward migration of such magma reduction to metallic aluminium and the formation of native al particles takes place

compositions growth mechanisms and temporal relations of hydrothermal sulfide sulfate silica chimneys at the northern cleft segment juan de fuca ridge three active hydrothermal vents forming sulfide mounds and chimneys monolith fountain and pipe organ and more widely distributed inactive chimneys are spatially related to a system of discontinuous fissures and young sheet flow lavas at the northern cleft segment juan de fuca ridge the formation of zoned tubular curich chimneys type i on the monolith sulfide mound is related to focused flow of high temperature to 328 c fluid bulbous chimneys type ii or beehives at the monolith and fountain vents are products of diffuse high temperature to 315 c discharge a broader zone of vigorous mixing between the hydrothermal fluid and seawater results in quench crystallization of anhydrite rich shells columnar zn sulfide rich chimneys with narrow channelways type iii are constructed where focused and relatively low temperature 261 c fluid vents directly from the basalt substrate the bulk chemistry low cu high pb ag and sio2 contents mineralogy pyrite marcasite wurtzite amorphous silica anglesite colloform and filamentous textures and oxygen isotope characteristics of inactive type iv chimneys indicate a low temperature 250 c origin involving diffuse and sluggish flow patterns and conductive cooling seafloor observations and 210pb data indicate that 1 type iv chimneys are products of an earlier period of hydrothermal activity that ended no more than 60 years ago but prior to the sheet flow eruption 2 the high temperature monolith and fountain vents are manifestations of the same heating event shallow emplacement of magma that led to the sheet flow eruption and recent megaplumes and 3 the pipe organ vent is in a very youthful stage of development and chimney deposition postdates the sheet flow eruption

formation and decay of a modern massive sulfide deposit in the indian ocean in december 1993 the first massive sulfides were recovered from the indian ocean floor north of the rodrigues triple junction the polymetallic deposit is situated in the fourth central indian ridge segment close to the rift axis it is hydrothermally no longer active the deposit appears to be typical of mid ocean ridge massive sulfide occurrences but is in a phase of disintegration and about to be buried by sediment the chimney structures were formed by multiple hydrothermal events and are now degraded by mass wasting showing various stages of weathering later stage low temperature hydrothermal mineralization processes led to copper and gold enrichment here we report on the geological setting mineral zonation different sulfide types and stages of formation of the sonne sulfide field which is part of a larger mineralized zone

diversity of biogenic minerals in low temperature si rich deposits from a newly discovered hydrothermal field on the ultraslow spreading southwest indian ridge 1 a newly discovered hydrothermal field on the ultraslow spreading southwest indian ridge expands the known ranges of biogenic minerals microbes and hydrothermal deposits the deposits from this vent site show typical characteristics of low temperature hydrothermal deposits rare earth element fractionation might be partly influenced by bacterial activity a physicochemical gradient is present across the layer of deposits providing suitable microhabitats for various microbes molecular phylogenetic analysis demonstrates a diverse range of bacteria some of which are involved in sulfur iron and nitrogen metabolism a high diversity of biogenic fe and si minerals are present in the deposits biogenic silica fe sulfides and fe oxides with distinctive morphologies are closely related to microbes several novel fe oxide structures are found and attributed to new types of biogenic minerals the precipitation of porous silica spherules and fe sulfides can be strongly promoted by extracellular polymer saccharides biomineralization features indicate that these deposits evolved through four stages these results help us to better understand the formation of biogenic minerals and low temperature deposits associated with microbes in the earth s modern and ancient seafloor hydrothermal vent fields

mn ba hg mineralization at shallow submarine hydrothermal vents in bahia concepcion baja california sur mexico coastal submarine hydrothermal venting occurs on the west shore of the fault bounded bay of bahia concepcion along a stretch of about 700 m of rocky shoreline diffuse hydrothermal seepage of water and continuous gas bubbling mainly co2 and n2 take place through the sediment covered seafloor at shallow depth 5 to 15 m in addition at about 500 m se a cluster of hot springs occurs within the intertidal zone the temperature and ph of the hydrothermal fluids varies from 72 to 87 c and 5 95 to 6 02 in the submarine diffuse venting area and reaches 62 c and ph of 6 68 in the intertidal hot springs mn ba hg mineralization is presently forming as a result of the hydrothermal venting at the intertidal hot springs moss like crusts of manganese oxides and structureless detrital aggregates cemented by opal a barite and calcite occur around the main discharge conduits these aggregates are overlaid by silica carbonate fine layered stromatolitic aggregates that extend some meters from the hot springs forming crusts and coalescing rims over volcanic pebbles and boulders manganese crusts are made up of barium rich x ray amorphous todorokite like and romanechite phases and represent a rare example of a manganese deposit formed in a shallow submarine hydrothermal environment in the submarine diffuse venting area the hydrothermal precipitates are less conspicuous and consist in millimeter thick iron oxyhydroxide coatings on volcanic cobbles and boulders these coatings are composed of poorly crystallized six line ferrihydrite accompanied by minor cinnabar and fine grained colloform pyrite textures and fabrics of the mineral assemblages suggest microbial mediation for mineral deposition the vent precipitates display a significant enrichment of hg as and sb arsenic is probably adsorbed onto mn and fe oxide substrates the nasc north american shale composite normalized ree patterns of the vent precipitates show a pronounced positive eu anomaly that is probably inherited from the hydrothermal fluid

first cosmic ray exposure dating in situ produced 10be of the late pleistocene and holocene glaciation in the nanhutashan mountains taiwan in taiwan efficient climate driven strong erosion processes are the leading cause for low preservation of geomorphic landforms despite the absence of present day glaciers glacial relicts have been reported in high altitude areas these scarce landforms provide opportunities for reconstructing the timing of the last deglaciation in a region where glacial history is poorly documented we have collected boulders and striated bedrocks in the nanhutashan area and calculated surface exposure ages based on in situ produced 10be concentrations the oldest glacial remains dated at 11 1 3 3 ka correspond to the last glacial advance the holocene is characterized by a continuous retreat of the ice cap until at least 7 2 1 0 ka our results are in agreement with a scenario where changes of monsoon regimes lead to a strong reduction of the winter monsoon during the early holocene causing a decrease of snow supply and disequilibrium of the hydrological budget

time dependent factors of soil and weathering mantle diversity in the humid tropics and subtropics a concept of soil self development and denudation abstract time dependent processes are the most important factor contributing to diversity of the soil and weathering mantle swm in the humid tropics and subtropics two models of swm self development in time are proposed and exemplified by soil chronosequences on tropical volcanic islands in the pacific ocean and in the humid subtropics on the east coast of the black sea the first derived from basic ash parent material lacking phyllosilicates is an eutric regosol vitric andosol mollic andosol chromic luvisol humic ferralsol sequence the second formed on basic material rich in phyllosilicates is a leptosol regosol ferrallic cambisol haplic nitisol stagnic acrisol sequence each component of these chronosequences contributes to swm diversity in time and space and to the complexity of the soil cover patterns the swm denudation model is exemplified by a stagnic acrisol haplic nitisol eutric cambisol lithic leptosol chronosequence on eroded hills and terraces of the east coast of the black sea temporal and spatial changes in soil properties texture chemistry mineralogy are examined in all three swm chronosequences

first results regarding the influence of mineralogy on the mechanical properties of seafloor massive sulfide samples abstract seafloor massive sulfides sms are increasingly accepted as important marine raw material resources for the future in particular because of their polymetallic character many industrial nations are researching not only on the scientific importance of these deposits but also on their economic value regarding the current state of the international exploration mainly two dimensional surface close observations are accessible whereas only some core data and measurements are publicly available to date in fact there are few successful drilling campaigns containing information about the size and shape which also give information on the structure and content of modern massive sulfide ore bodies in their third dimension regarding the mechanical properties of sms samples only few data are available geotechnical data of these deposits are important in order to develop an efficient mining technology for exploitation in this research 12 sms samples from two different locations were investigated based on the mineralogical characterization of the studied samples the geotechnical properties were preliminary correlated with the mineralogical results the comparative study indicates how far the geotechnical data are controlled by mineral type and composition including the porosity a regression relation between compressive strength and the porosity based on the mineralogy shows a distinct relation between these parameters therefore the geomechanical and mineralogical features have a strong importance for deep sea mining applications and this should be kept in mind considering the hyperbaric effects on the rock cutting

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

petrological geochemical and hydrothermal characteristics of ordovician cherts in the southeastern tarim basin nw china and constraints on the origin of cherts and permian tectonic evolution abstract cherts occur extensively as stratal wedges embedded in the middle lower ordovician carbonate successions in the circum tangguzibasi areas south east tarim basin where thick up to 2 km dark grey well stratified limestones deposited in shelf and platform environments are prominent based on detailed core and thin section observations with petrographic microthermometric and geochemical data for the middle lower ordovician cherts in some key wells two lithotypes of chert are identified across the marginal zone in the western tangguzibasi areas replacement and filled cherts replacement chert is characterized by granular microcrystalline quartz or radially fibrous chalcedony and commonly retains the pre existing dolomite rhombs and elliptical ooids floating in these cherts filled chert the most common type is generally rimmed by fine gained euhedral quartz that grades abruptly into vein cavity fill mega quartz compositionally these chert deposits are strongly enriched in cr zn ba and u and generally show apparent right convex ree patterns with low ree values avg 4 24 ppm weak negative ce anomalies ce ce avg 0 93 and low to intermediate positive eu anomalies eu eu avg 1 19 particularly the replacement cherts microthermometry of fluid inclusions from coarse quartz reveals high homogenization temperatures from 135 to 195 c for trapped primary fluids with high salinities 11 0 18 9 wt these siliceous deposits also have low la ho and th u relatively high y ho and ba sr high ce ce 1 06 intermediate to high lu la n 0 5 1 0 and low la ce n mostly 1 31 1 45 all these data suggest that the cherts formed under the strong influence of hydrothermal fluids originating from detritus poor hydrogenetic fe mn crusts at deep continental margins extensive silicification occurred after intense dolomitization and calcitization while fracturing faulting were greatly intensified in the host carbonates induced by intense extension because of the uplift force of the magma cushion under oblique collision during the early permian most silica could have directly precipitated from hydrothermal fluids to chalcedony fibres around voids and vein cherts along fracture conduits these petrological and geochemical data also provide a useful clue to better understand the extensive silica precipitation intense tectono hydrothermal activity and significant lithospheric fracturing events as a result of the closure of the south tienshan and palaeo tethys oceans during the early middle permian

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

three dimensional visualization of the archean horne and quemont au bearing volcanogenic massive sulfide hydrothermal systems blake river group quebec the hydrothermal system architecture related to the formation of the contemporaneous au bearing horne and quemont volcanogenic massive sulfide vms deposits was visualized by employing kriging methods to map whole rock oxygen isotope compositions zones of silica addition and loss and water contents in two and three dimension zones of alteration were mapped in three dimensions in the vicinity of the steeply dipping horne deposit to depths of as much as 2 km in all nearly 300 samples were analyzed for oxygen isotopes and supplemented by previously published whole rock analyses contents of sio2 h2o mgo al2o3 and s from chemical analyses of nearly 5 000 samples within the two and three dimensional study regions were used separately and in combination with the oxygen isotope data for modeling and hydrothermal mapping purposes the horne and quemont deposits formed within a similar time frame but in different magmatic hydrothermal systems distinguished by their mapped hydrothermal architecture the quemont deposit appears to be centered on the powell pluton which intruded late into an apparent volcanic filled rift graben structure although structural complexities are apparent we infer mineralizing high temperature upflow in the footwall of the quemont deposit to have emanated from a reaction zone above the powell pluton and its precursors beneath a zone of extensive silicification faulting on the andesite fault and horne creek faults plus erosion has removed evidence of the upflow zone in the hydrothermal system of the horne deposit areas of silicification correspond in general with isotopic evidence of lower temperature alteration such alteration east of the quemont deposit signaled the waning of hydrothermal activity the suggested cooling for the most part promoted the precipitation of silica in the case of the horne deposit mixing of metalliferous hydrothermal fluid with cold seawater in the permeable footwall rocks in an apparently relatively stratigraphically stable and long lived hydrothermal system evidently led to marked footwall silicification the silicified footwall may have contributed to an increased efficiency of sulfide precipitation in the horne deposit continued intrusion and some post vms hydrothermal activity is recorded in the hanging wall section to the horne deposit our data suggest that deposition of the 10 million ounces moz of au within the horne deposit was syngenetic and not the product of subsequent hydrothermal activity

petrology and geochemistry of chert on the marginal zone of yangtze platform western hunan south china during the ediacaran cambrian transition the ediacaran cambrian transition was one of the most critical intervals in earth history during this interval widespread chert was precipitated commonly as a stratal wedge in carbonates along the southern margin of the yangtze platform south china the chert wedge passes into a full chert succession further basinward to the south east four lithotypes of chert are identified across the marginal zone in western hunan mounded vein brecciated and bedded chert the mounded chert is characterized by irregular to digitiform internal fabrics generally with abundant original vesicles and or channels that mostly are lined by botryoidal chalcedony cements with minor quartz and barite crystals the host chert or matrix of these mounds is dominated by amorphous cryptocrystalline silica commonly disseminated with pyrite the vein chert with minor quartz locally generally cross cuts the overlying dolostone and chert horizons and terminates under the mounded and or bedded chert bodies the brecciated chert commonly occurs as splayed intrusions or funnel shaped wedges and cross cuts the topmost dolostones the bedded chert the most common type generally is thin to medium bedded and laminated locally it is composed of amorphous silica with minor amounts of black lumps microthermometry of fluid inclusions from vein and void lining minerals mainly quartz and barite revealed homogenization temperatures from 120 to 180 c for the trapped primary fluids compositionally these chert deposits generally are pure with sio2 92 wt and only minor fe2o3 and al2o3 contents most of which show positive europium anomalies in rare earth element patterns especially for the mounded chert all these data suggest that the marginal zone chert deposits resulted from a low temperature silica rich hydrothermal system in which the mounded chert was precipitated around the releasing vents i e as silica chimneys the vein and splayed brecciated chert however was formed along the syndepositional fault fracture conduits that linked downward while the bedded chert was precipitated in the quieter water column from the fallout of hydrothermal plumes onto the sea floor these petrological and geochemical data provide compelling evidence and a new clue to the understanding of the extensive silica precipitation rapid tectonodepositional and oceanic changes during the ediacaran cambrian transition in south china

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

growth history of a hydrothermal silica chimney from the mariana backarc spreading center southwest pacific 18 13 n abstract a hydrothermal field consisting of inactive silica chimneys was investigated in 1988 at 18 13 n in the median rift valley of the mariana trough backarc spreading centre topless tower that was reported to be active 3 years previously a detailed mineralogical and geochemical study of a 0 75 m long and 0 61 m wide silica chimney revealed its growth history the inactive chimney consists almost entirely of amorphous silica up to 86 wt opal a and barite a cross section indicates two ancient fluid channels infilled by pyrite barite and marcasite the outer rim of the chimney shows alteration oxidation features of up to 30 fe2o3 the distribution patterns of fe mn ba cu and zn reveal the structure of the chimney the alteration effects in the outer rim by mn and fe enrichments and the two fluid channels by ba cu and zn enrichments oxygen isotope data indicate that the formation of the silica chimney occurred at temperatures ranging between 41 and 50 c although the occurrence of pyrite barite marcasite and quartz in the fluid channels suggests a higher growth temperature for the inner part 230 c 230 th 234 u dating indicates an age of 7500 yr for the chimney in agreement with 226ra and 210pb results amorphous silica solubility relationships suggest that the silica chimney was formed by conductive cooling as well as by mixing of hydrothermal fluids and seawater a second stage of high temperature 230 280 c hydrothermal discharge occurred that resulted in the formation of 226ra rich sr and ba bearing silica with quartz and pyrite