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

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

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

engineering geological mapping of tropical soils for land use planning and geotechnical purposes a case study from jamaica west indies abstract an area of a tertiary and cretaceous deposits 100 310 m above sea level and on predominant 20 45 highly dissected concave slopes was investigated to assess its geotechnical characteristics and land use planning implications lithologies include turbidites fluvial conglomerates breccias sandstones mudrocks carbonates granodiorite acid dykes chloritized and epidotized volcanics andesite and holocene fluvial deposits bedrock is highly fractured and sheared hydrothermally altered and highly weathered soils are quite variable with a strong geological control on soil properties soils are generally sandy to gravely with local silts and clays in mudrocks within holocene alluvium or in hydrothermally altered and sheared granodiorites the soils are composed of 0 14 80 00 gravel 5 36 62 50 sand 2 33 50 55 silt 0 17 51 50 clay and total fine content between 2 50 and 94 50 with natural moisture between 4 and 44 during the dry season plastic limit between 6 and 35 liquid limit between 19 and 83 and plasticity index between 1 and 59 sandy soils have residual friction angles between 19 and 39 pi values less than 35 with cohesion between 1 00 and 5 27 kn m 2 for cohesive samples astm classification of soils include soil groups gc gm gw gp sp sm sc sm sc ml cl and ch based on the characteristics of the terrain the geotechnical and land use planning problems include high landslide frequency and susceptibility soil erosion fluvial and reservoir sedimentation high debris flow hazard cut slope failures potentially expansive clays and silts seepage erosion and soil piping differential settlement in interlayered competent and incompetent lithologies high solution erosion and potential subsidence over limestones waste water disposal problems and groundwater pollution and seismic induced settlement and ground failures these phenomena suggest that systematic site investigations should be conducted prior to the utilization of these areas for construction and development in order to minimize the deleterious effects resulting from ground failure

assessing landslide potential using gis soil wetness modeling and topographic attributes payette river idaho this study utilizes gis modeling to determine if the location of 559 landslides in the 875 km2 catchment of the middle fork of the payette river idaho can be predicted based on topographic attributes and a wetness index generated by the dynwet model slope and elevation were significantly related to landslide occurrence at this landscape scale aspect was also retained as a variable for further analysis because despite a non significant chi square relation to landslide occurrence graphical analysis suggested a relation between aspect and mass wasting chi square analysis indicated that plan and profile curvature flow path length upslope contributing area and the dynwet based moisture index were not significantly related to landsliding a bayesian probability model based on combinations of elevation slope aspect and wetness indicates that elevation exhibits the closest relation to landsliding followed by slope but that neither aspect nor wetness index values help in prediction the bayesian probability model using elevation and slope generates a map of relative landslide risk that can be used to direct activities away from mass wasting prone areas the association between elevation and landslides is perplexing but is perhaps due to the location of logging road at specific elevations roads could not be included in the input data for analysis because they have not been adequately mapped the lack of explanation provided by the dynwet wetness index was also surprising and may be due to the 30 m digital elevation model dem and the soils data having resolutions too coarse to adequately portray local variations key to mass wasting we believe the inadequacy of data to drive the models is typical of the majority of catchment scale setting for now the ability of researchers to effectively model landscape scale landsliding is more limited by the type resolution and quality of available data than by the quality of the landslide models

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

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

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

the 17 march 2005 kuzulu landslide sivas turkey and landslide susceptibility map of its near vicinity landslides are common natural hazards in the seismically active north anatolian fault zone of turkey although seismic activity heavy rainfall channel incisions and anthropogenic effects are commonly the main triggers of landslides on march 17 2005 a catastrophic large landslide in sivas northeastern of turkey the kuzulu landslide was triggered by snowmelt without any other precursor the initial failure of the kuzulu landslide was rotational following the rotational failure the earth material in the zone of accumulation exhibited an extremely rapid flow caused by steep gradient and high water content the agnus creek valley where kuzulu village is located was filled by the earth flow material and a landslide dam was formed on the upper part of agnus creek the distance from the toe of the rotational failure down to the toe of the earth flow measured more than 1800 m with about 12 5 million m3 of displaced earth material the velocity of the kuzulu landslide was extremely fast approximately 6 m s the main purposes of this study are to describe the mechanism and the factors conditioning the kuzulu landslide to present its environmental impacts and to produce landslide susceptibility maps of the kuzulu landslide area and its near vicinity for this purpose a detailed landslide inventory map was prepared and geology slope aspect elevation topographic wetness index and stream power index were considered as conditioning factors during the susceptibility analyses the conditional probability approach was used and a landslide susceptibility map was produced the landslide susceptibility map will help decision makers in site selection and the site planning process the map may also be accepted as a basis for landslide risk management studies to be applied in the study area

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

assessing susceptibility to landslides using models to understand observed changes in slopes abstract a map of landslide susceptibility is a necessary tool for proper planning and selection of sites for agriculture infrastructure and other human developments the paonia mcclure pass area of colorado usa is well known for active mass movements large losses of property and risks to people highlight the need to accurately map susceptibility to shallow landslides and to identify safe locations for infrastructure and residential development we mapped 735 active mass movements and 17 factors about each one the weights of evidence frequency ratio of landslides and fuzzy logic method were used to create an optimum map of landslide susceptibility weights of the evidence were used to categorize continuous factor data frequency ratios of shallow landslides were used to assign the membership values for the categories of the factors and the fuzzy logic method was used to integrate the membership values four models from the fuzzy inference network of mapping susceptibility to shallow landslides were developed based on the combination of factors using five types of fuzzy operators the first inference network model was comprised of the combination of factors which are independent of each other the second third and the fourth inference network models were developed such that factors are not necessarily independent of each other these models combine all dependent and independent factors based on the expert s knowledge intermediate steps in the second third and fourth models were developed by combining the fuzzy factors in the first step by fuzzy or fuzzy and and fuzzy or plus fuzzy and operations respectively all models predicted similar percentages of observed shallow landslides with the fuzzy gamma operation although the prediction capabilities of all the models are not significantly different the fourth model is the best because it is the only model that accommodates the under sampled and missed landslide data and the effect of increasing and decreasing gamma values the first and third models create a problem if a category of a factor has a 0 membership value because of the absence or under sampling of shallow landslides the second model incurs the highest increasing effect of gamma values and the third model incurs the highest decreasing effect of gamma values the approaches described in this paper reduce the uncertainties associated with the categorization of continuous data determination of fuzzy membership values and the combination of factors that causes shallow landslides

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

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

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

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

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

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

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

landslide hazard assessment of the 2008 wenchuan earthquake a case study in beichuan area the wenchuan earthquake magnitude ms 8 0 of 12 may 2008 triggered widespread and large scale landslides over an area of about 50 000 km2 a study was undertaken to determine the primary factors associated with seismic landslide occurrence an index based approach used to assess earthquake triggered landslide hazard in the central part of the wenchuan earthquake area affected is described slope gradient relief amplitude lithology bedding slope relations fault proximity stream proximity and antecedent rainfall are recognized as factors that may have had an important influence on landslide occurrence the assessment of the influence of each of these factors is presented through use of a series of maps showing areas of low moderate high and very high landslide hazard areas identified as having very high and high landslide hazard were located along the earthquake source fault and along both banks of the jian river the role of rainfall is very significant for future landslide occurrence in the

how wide is a road the association of roads and mass wasting in a forested montane environment a spatial data base of 1609 landslides was analysed using a geographic information system to determine landslide frequency in relation to highways a 126 km long transportation network in a 201km 2 area of humid tropical mountainous forested terrain in puerto rico was used in conjunction with a series of 20 buffer disturbance zones varying from 5 to 400 m in length measured perpendicular to the highways average landslide frequency in the study area at distances greater than 85 m from roads was about six landslides per square kilometre at distances of 85 m or less on either side of a highway landslide frequency was about 30 landslides per square kilometre on average this elevated disturbance rate affected 330 m 2 km 2 a 1 within the 170 m swath the mass wasting rate outside of the disturbance zone affected 40 m 2 km 2 a 1 these results indicate that the rate of mass wasting disturbance is increased from five to eight times in a 170 m wide swath along road corridors the lateral extent of the environmental impact of roads in the study area is greater than is commonly perceived the approach described herein demonstrates a simple method to assess the spatial association of mass wasting with highways 1997 by john wiley sons ltd

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

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

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

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

gis based landslide susceptibility mapping for a problematic segment of the natural gas pipeline hendek turkey a segment of natural gas pipeline was damaged due to landsliding near hendek re routing of the pipeline is planned but it requires the preparation of a landslide susceptibility map in this study the statistical index wi and weighting factor wf methods have been used with gis to prepare a landslide susceptibility map of the problematic segment of the pipeline for this purpose thematic layers including landslide inventory lithology slope aspect elevation land use land cover distance to stream and drainage density were used in the study area landslides occur in the unconsolidated to semi consolidated clayey unit and regolith the wf method gives better results than the wi method lithology is found to be the most important aspect in the study area based on the findings obtained in this study the unconsolidated to semi consolidated clayey unit and alluvium should be avoided during re routing agricultural activities should not be allowed in the close vicinity of the pipeline

trace metal distributions in sulfide scales of the seawater dominated reykjanes geothermal system constraints on sub seafloor hydrothermal mineralizing processes and metal fluxes abstract mineral precipitation in the seawater dominated reykjanes geothermal system on the mid atlantic ridge iceland is caused by abrupt artificially induced pressure and temperature changes as deep high temperature liquids are drawn from reservoir rocks up through the geothermal wells sulfide scales within these wells represent a complete profile of mineral precipitation through a seafloor hydrothermal system from the deep reservoir to the low temperature silica rich surface discharge mineral scales have formed under a range of conditions from high pressures and temperatures at depth 2 km to boiling conditions in the upflow zone and at the surface consistent trace element enrichments similar to those in black smoker chimneys are documented cu zn cd co te v ni mo w sn fe and s are enriched at higher pressures and temperatures in the deepest scales zn and cu bi pb ag as sb ga hg tl u and th are enriched at lower temperatures and pressures nearer to the surface a number of elements e g co se cd zn cu and au are deposited in both high and low pressure scales but are hosted by distinctly different minerals other trace elements such as pb ag and ga are strongly partitioned into low temperature minerals such as galena pb ag and clays ga boiling and destabilization of metal bearing aqueous complexes are the dominant control on the deposition of most metals particularly au other metals e g cu and se may also have been transported in the vapor phase very large enrichments of au ag and pb in the scales e g 948 ppm au 23 200 ppm ag and 18 8 wt pb versus average concentrations in black smoker chimneys likely reflect that some elements are preferentially deposited in boiling systems a mass accumulation of 5 7 t yr of massive sulfide was calculated for one high temperature production well equating to metal fluxes of 1 7 t yr zn 0 3 t yr cu 23 kg yr pb 4 1 kg yr ag and 0 5 kg yr au at least three quarters of the major and trace element load is precipitated within the well before reaching the surface we suggest that a similar proportion of metals may be deposited below the seafloor in submarine hydrothermal systems where significant boiling has occurred mass accumulation estimations over the lifetime of the reykjanes system may indicate significant enrichment of zn pb au and ag relative to both modern and ancient mafic dominated seafloor massive sulfide deposits and highlights the potential for metal enrichment and accumulation in the deep parts of geothermal systems

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

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

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

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

source of gold in neoarchean orogenic type deposits in the north atlantic craton greenland insights for a proto source of gold in sub seafloor hydrothermal arsenopyrite in the mesoarchean abstract given that gold au mostly remained in the incipient earth mantle until ca 3 9 3 8 ga a proto source of gold may have been present in the dominantly mafic crust precursor born through first stage melting of the early earth mantle in south westernmost greenland a fragment of the north atlantic craton is characterised by greenstone belts comprising mafic volcanic and magmatic rocks and harzburgite cumulates that were emplaced at ca 3 0 ga prograde amphibolite facies metamorphic assemblages and caused local dissolution of arsenopyrite during this retrograde tectono metamorphic stage in gold rich shear zones the re os geochronometer in arsenopyrite was reset to a neoarchean age while invisible gold was liberated and deposited as free gold with 2 66 ga pyrite re os isochron ages the initial os isotope ratios of neoarchean arsenopyrite 187os 188osi 0 13 0 02 and gold bearing pyrite 0 12 0 02 overlap with the estimated 187os 188os ratio of the mesoarchean mantle 0 11 0 01 and preclude contribution of radiogenic crustal os from evolved lithologies in the accretionary arc complex but instead favour a local contribution in os from basaltic rocks and serpentinised harzburgite protoliths by metamorphic fluids thus the ca 2 66 ga lode gold mineralisation identified in the north atlantic craton may illustrate a gold endowment in shear zones in earth s stabilizing continental crust at the time of the 2 75 2 55 ga global gold event through metamorphic upgrading of bulk gold which had originally been extracted from the mesoarchean mantle and concentrated in hydrothermal arsenopyrite deposits in oceanic crust beneath the overall reduced mesoarchean ocean

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

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

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

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

geomorphology and the urban tropics building an interface between research and usage abstract the developing countries located almost entirely within the tropics are currently undergoing urbanization at a rapid pace many of these cities are not more than a few centuries old having been established to function as regional trading posts or administrative centers by either colonial or regional powers it is doubtful that the site conditions were taken into consideration and consequently many of these cities were established in hazardous or environmentally sensitive areas as these cities developed over time they spread across a wide range of terrain conditions much of which are unsuitable such as floodplains coastal swamps steep slopes or sand dunes for a number of these cities which are located near active plate margins and tropical cyclone belts such problems are magnified increased demand for water has required subsurface extraction leading to problems of subsidence and quality we examine the range of these cities with reference to 1 their site related problems 2 the nature of geomorphological information required for specific ameliorating actions and 3 the level of management required for city maintenance management requires interfacing geomorphology with engineering practices and urban planning we present case studies of cities ranging from those with limited problems and possible engineering and land zoning solutions singapore to cities where the hazards either natural or anthropogenic are so acute and widespread that a practical solution is difficult to achieve kingston bangkok precise geomorphological and geological information and long term data sets are not available for most of the cities furthermore it is necessary to present the information in formats appreciated by the engineering and planning communities often a set of specialized maps are extremely useful we complete the discussion with several examples and suggestions for collection of geomorphological information and inventory preparation for communicating geomorphological data to city engineers and planners

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

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

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

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

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

use of fuzzy relations to produce landslide susceptibility map of a landslide prone area west black sea region turkey abstract preparation of landslide susceptibility maps is important for engineering geologists and geomorphologists however due to complex nature of landslides producing a reliable susceptibility map is not easy for this reason many procedures have been used to produce such maps in this study a new attempt is tried to produce landslide susceptibility map of a part of west black sea region of turkey to obtain the fuzzy relations for producing the susceptibility map a landslide inventory database is compiled by both field surveys and airphoto studies a total of 266 landslides are identified in the study area and dominant mode of failure is rotational slide while the other mode of failures are soil flow and shallow translational slide the landslide inventory and the parameter maps are analyzed together using a computer program fullsa developed in this study the computer program utilizes the fuzzy relations and produces the landslide susceptibility map automatically according to this map 9 6 of the study area is classified as very high susceptibility 10 3 as high susceptibility 8 9 as moderate susceptibility 27 5 as low susceptibility and 43 8 as very low susceptibility or nonsusceptible areas the prediction performance of the susceptibility map is checked by considering actual landslides in the study area for this purpose strength of the relation rij and the root mean square error rmse values are calculated as 0 867 and 0 284 respectively these values show that the produced landslide susceptibility map in the present study has a sufficient reliability it is believed that the approach employed in this study mainly prevents the subjectivity sourced from the parameter selection and provides a support to improve the landslide susceptibility mapping studies

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

landslides triggered by the 20 april 2013 lushan earthquake sichuan province china abstract the 20 april 2013 lushan earthquake with a magnitude of m s 7 0 induced widespread landsliding along the southern segment of the longmen shan fault zone this paper presents a preliminary analysis of the characteristics of these co seismic landslides triggered in an area of 13 323 km 2 a total of 3810 individual landslide points were identified through an intensive field investigation and from digital aerial photographs taken after the lushan earthquake to facilitate the more detailed analysis on the areal frequency of co seismic landslides as polygons we selected an area of 732 km 2 around the epicenter that had the highest density of co seismic landslides the sizes of the landslides are in general much smaller than those that were triggered by the 2008 wenchuan earthquake the most common types of landslides in the study area were rock falls and shallow disrupted landslides from steep slopes which typically involved the top few meters of weathered bedrock and colluvium in this study the relation between the landslide distribution and five main factors was analyzed fault proximity epicenter proximity peak ground acceleration pga slope angle and lithology our study results show that the landslide concentration tends to decrease with distance from the seismogenic fault and the highest landslide concentration is located within a distance of 5 km regarding the distance to the epicenter the largest landslide density is found at a distance between 5 and 10 km the landslide concentration also increases with increasing slope angle until a maximum for the slope class 45 55 in addition results show that slopes consisting of deeply weathered and fractured sandstones and mudstones were the most susceptible to co seismic landslides in this study we found that the location of the hanging wall and the footwall of the fault did not seem to have an important effect on the landslide distribution this is in contradiction to what has been reported in other earthquake areas such as the wenchuan area

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

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

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

volatiles co2 s f cl br in the dike gabbro transition zone at iodp hole 1256d magmatic imprint versus hydrothermal influence at fast spreading mid ocean ridge abstract the dike gabbro transition zone of mid ocean ridges mors is a critical site for the accretion of oceanic crusts as it is the main zone of interactions between the hydrothermal and magmatic systems in this study volatiles contents of co 2 s f cl and br for a variety of lithologies from the dike gabbro transition zone of an intact oceanic crust were investigated in order to examine the magmatic imprint versus hydrothermal influence the studied samples include plutonic rocks gabbros diorites and tonalites hornfelses i e granoblastic dikes an amphibole rich vein and albitites these rocks were recently sampled by the iodp integrated ocean drilling program at site 1256 representing parts of an oceanic crust that formed at the fast spreading ridge of the east pacific rise the bulk co 2 contents 500 10 000 ppm show no lithological dependence and are similar to those of fresh lavas highly variable bulk s concentrations 3 900 ppm show significant depletions compared to undegassed morb melts which might be caused by exsolution of magmatic fluids during crystallization the plutonic samples have cl concentrations of 500 1000 ppm remarkably higher than the hornfelses 200 600 ppm cl and erupted lavas average 200 ppm cl except for the albitites that contain very low f 20 30 ppm and the hydrothermal amphibole rich vein that contains extremely high f 1000 ppm the other lithologies have similar f concentrations within 100 350 ppm the br concentrations of different lithologies are largely overlapping within 0 5 3 5 ppm petrological and mineralogical evidence indicates that bulk f concentrations are dominated by the presence of amphibole and apatite whereas cl and br are mainly hosted in fluid inclusions rather than in hydrous minerals the variation of f cl and br cl ratios may trace the mixing between morb magmas and seawater derived fluids crystallization of apatite and amphibole and or extraction of magmatic fluids our data support the current s budget of oceanic crust but indicate that the budgets of c and cl may have been underestimated

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

structure and variability of the alboran sea frontal system physical characteristics of the alboran sea in the western mediterranean were examined in october 1977 during a survey by ship and aircraft the main features observed were a distinct oceanic front coinciding with the jet of incoming north atlantic water and an associated anticyclonic gyre in the western half of the basin the front was confined to the upper 200 m and was a continuous feature extending from the strait of gibraltar 500 km eastward to the prime meridian of particular interest was the observed variability of the anticyclonic gyre in 10 days between two surveys the center of the gyre shifted 50 km westward this shift may correspond to changes in strength of the north atlantic inflow as inferred by local wind and the average atmospheric pressure over the western mediterranean

assessment of landslide susceptibility for a landslide prone area north of yenice nw turkey by fuzzy approach regional landslide susceptibility assessments pose complex problems to solve these problems numerous approaches such as statistical analysis geotechnical engineering approach geomorphologic approach and fuzzy logic have been employed however all the available methods for regional landslide susceptibility assessments have some uncertainties due to a lack of knowledge and variability minimizing these uncertainties provides realistic approaches use of the fuzzy logic approach to produce a landslide susceptibility map of a landslide prone area in nw turkey is the main purpose of the present study for this purpose the study includes five main stages these being the preparation of a landslide inventory of the study area the application of factor analysis the extraction of fuzzy if then rules the use of a geographical information system and the control of the reliability of the resulting landslide susceptibility map slope angle slope aspect land use weathering depth water conditions and topographical elevation were considered as landslide conditioning factors for the study area a total of 23 if then rules was extracted from the field data employing these rules fuzzified index maps representing each parameter were obtained finally combining these maps the landslide susceptibility map of the area was prepared when compared with the landslide susceptibility map the landslides identified in the area were found to be located in the very high and high susceptibility zones as far as the performance of the fuzzy approach for processing is concerned the images appear to be quite satisfactory the zones determined on the map being zones of relative susceptibility

landslide processes and landslide susceptibility analysis from an upland watershed a case study from st andrew jamaica west indies abstract rainfall induced landslides are common geomorphic events on the steeper slopes of upper st andrew and cause severe environmental engineering social and economic repercussions in the area a geotechnical study was initiated to identify a past present and potential landslide types and sites for landslides b to examine the nature of geological geomorphological and geotechnical conditions under which failures can take place and c the potential landslide hazard in the area 886 failures were mapped more than 80 of which were located in soils a total of 1 55 km2 9 80 of the total area had failed approximately 59 failures per km2 were mapped with the highest density within elastic sedimentary units and weathered granodiorite 789 failure were mapped on slopes between 20 45 with no failure on slope less than 10 481 failures were mapped along twelve major roadways 46 6 km of road with approximately 10 failures km of road analysis of eighteen geotechnical units within nine geological formations revealed that the highest susceptibility for failure was within old landslide deposits with granular nonplastic to low plasticity soils and on slopes between 20 and 30 the lowest susceptibility was found within white limestones and recent alluvium and terrace deposits granular nonplastic to low plasticity soils are generally more susceptible than fine soils especially on slopes between 30 and 45 while granular and expansive clay soils demonstrate similar susceptibilities but on slopes between 30 and 45 and 20 and 45 respectively clastic sedimentary rocks are more susceptible that igneous lithologies an increase in slope angle increases the susceptibility to failures but only on slopes up to 45 an increase in the degree of weathering of soils and bedrock and fracturing of bedrock as well as road construction increases the landslide susceptibility in the area

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

gold mobility during palaeoarchaean submarine alteration abstract seafloor alteration provides large amounts of solutes to the hydrosphere in order to investigate gold mobility during water rock interaction prior to 3 billion years ago low detection limit analysis of au concentrations was carried out on rocks from marine alteration zones stratiform zones recording low temperature 150 c seafloor alteration are a characteristic feature of greenstone belts older than 3 0 ga hydrothermal processes were operating on and immediately below the seafloor giving rise to extensive silicification of sub seafloor volcanic rocks and silicification of seafloor sediments in order to investigate gold mobility during silicification unaltered and variably silicified volcanic rocks and associated cherts from palaeoarchaean greenstone successions c 3 4 ga of south africa were analyzed results show mobility of gold during silicification of mafic ultramafic rocks and transfer to the archaean ocean some gold was incorporated into carbonaceous marine sediments overlying the alteration zones a combination of pervasive silicification rarity of black shales and low gold content in komatiites can explain the low mineralization potential of palaeoarchaean greenstone belts for orogenic gold deposits

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

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